JP2014010357A - Image forming apparatus - Google Patents

Abstract

A conveyor such as a belt is driven to rotate only to obtain the amount of reflected light received by an optical sensor.
When a conveyance area 13A that has conveyed a sheet at the time of formation of a printed image on the surface of a belt 13 reaches a mark detection position X2, the printer 1 uses reflected light from the conveyance area as sensor sensitivity information. A transfer area acquisition process to be acquired, a determination process for determining an adjustment value of the sensor sensitivity of the mark sensor 15 based on PWM values for a plurality of transfer areas acquired by executing the transfer area acquisition process a plurality of times, and a mark 60 on the forming unit And a mark detection process for detecting a mark with the sensor sensitivity after adjustment with the determined adjustment value.
[Selection] Figure 5

Description

  The present invention relates to a technique for adjusting the light receiving sensitivity of a mark sensor that emits light toward a rotationally driven carrier and receives reflected light from the carrier.

  Some image forming apparatuses have a function of correcting a shift of an image forming position on a sheet, for example. Specifically, in this image forming apparatus, a pattern composed of a plurality of marks such as a registration pattern is formed on the belt, light is emitted toward the belt by a mark sensor, and the reflected light is received. Based on the amount of reflected light received by the mark sensor, the mark position is determined by reading the difference in reflectance or amount of reflected light between the belt surface and the mark surface, and image formation is performed based on the determination result. Misalignment is corrected.

  Here, for example, the surface of the belt may be scratched or dirty, and light is irregularly reflected by the scratch or dirt, so that the reflectivity of the belt surface is lowered and the mark determination may not be performed normally. Therefore, conventionally, there is a technique in which the surface of a belt on which no mark is formed by a mark sensor is irradiated with light, and the light receiving sensitivity of the mark sensor is adjusted according to the amount of light received by the reflected light (see Patent Document 1).

JP 2008-134333 A

  However, since the conventional image forming apparatus is configured to rotate the belt only to obtain the amount of reflected light received, there is a problem of wasting time and apparatus life.

  In the present specification, a technique for suppressing the rotational driving of a carrier such as the belt is disclosed only for obtaining the amount of light received by the optical sensor.

  An image forming apparatus disclosed in this specification includes a conveyance body that conveys a sheet by rotational driving, a light emitting unit that emits light toward a mark detection position through which the surface of the conveyance body passes, and reflection from the mark detection position. A mark sensor having a light receiving part for receiving light, an adjustment part for adjusting sensor sensitivity of the mark sensor, a print image is formed on a sheet conveyed to the conveyance body, and a correction mark is formed on the conveyance body. A forming unit formed on the surface; and a control unit, wherein the control unit conveys a sheet on the surface of the conveyance body when the sheet is conveyed when the print image is formed, when the mark detection position is reached. The transfer area acquisition process for acquiring the sensor sensitivity information related to the sensor sensitivity by causing the light receiving unit to receive the reflected light from the transfer area and the transfer area acquisition process are executed a plurality of times. Determination processing for determining an adjustment value of the sensor sensitivity of the mark sensor based on the acquired sensor sensitivity information for the plurality of transport areas, and after adjustment by the adjustment value determined in the determination processing by forming the mark in the forming unit And a mark detection process for detecting the mark with the sensor sensitivity.

  According to this image forming apparatus, when the conveyance area where the sheet was conveyed at the time of forming the print image reaches the mark detection position, the sensor sensitivity information is acquired by causing the light receiving unit to receive the reflected light from the conveyance area. A transfer area acquisition process is executed. Thereby, it can suppress that a conveyance body is rotationally driven only in order to acquire the sensor sensitivity information in a mark sensor. In addition, since the sensor sensitivity information for the conveyance area where the colorant or the like hardly adheres to the surface due to the presence of the sheet at the time of forming the print image is used, only the sensor sensitivity information for the non-conveyance area where the sheet was not conveyed is used. Compared with the configuration for determining the adjustment value, sensor sensitivity information that is less influenced by the colorant or the like is acquired, so that the sensor sensitivity can be adjusted with high accuracy. Moreover, in order to determine the sensor sensitivity adjustment value based on the sensor sensitivity information for a plurality of transfer areas acquired by executing the transfer area acquisition process a plurality of times, the sensor sensitivity adjustment value based on the sensor sensitivity information for only one transfer area As compared with the configuration for determining the sensor sensitivity, it is possible to acquire a lot of sensor sensitivity information and adjust the sensor sensitivity with high accuracy.

  In the image forming apparatus, a plurality of unit acquisition processes for acquiring sensor sensitivity information by causing the light receiving unit to receive reflected light from the mark detection position are determined in advance, and the control unit includes a plurality of unit acquisition processes. , Having a configuration for executing a designation process for designating one or more of the unit acquisition processes to be executed in each conveyance area acquisition process, and in each of the conveyance area acquisition processes, the one or more designated in the designation process The unit acquisition process may be executed, and in the determination process, the adjustment value may be determined based on sensor sensitivity information acquired by executing all of the plurality of unit acquisition processes.

  According to this image forming apparatus, one or more unit acquisition processes to be executed in each transfer area acquisition process are specified, and the specified unit acquisition process is executed in each transfer area acquisition process. Thereby, a plurality of predetermined unit acquisition processes can be executed in the transport area acquisition process.

  In the image forming apparatus, the control unit stores one or more unit acquisition processes among the plurality of unit acquisition processes as a comparison acquisition process, and stores sensor sensitivity information acquired by executing the comparison acquisition process. A difference between the current sensor sensitivity information acquired by executing the comparison acquisition process in the transport area acquisition process and the previous sensor sensitivity information stored in the storage process. Is configured to execute a sensitivity difference determination process for determining whether or not the difference is equal to or less than a sensitivity difference threshold, and when the affirmative determination is made in the sensitivity difference determination process, execution of the determination process is prohibited and a negative determination is made In this case, the execution of the determination process may be continued.

  The difference between the current sensor sensitivity information acquired by executing the comparison acquisition process, which is one or more unit acquisition processes among a plurality of unit acquisition processes, and the previous sensor sensitivity information stored in the storage process is the sensitivity. When the difference is less than or equal to the difference threshold, there is a high possibility that the deviation of sensor sensitivity from the previous acquisition of sensor sensitivity information is small, and the necessity for sensitivity adjustment is low. Therefore, according to this image forming apparatus, when the difference is equal to or smaller than the sensitivity difference threshold value, execution of the determination process is prohibited, so that the determination process is performed wastefully when the necessity for sensitivity adjustment is low. Can be suppressed.

  In the image forming apparatus, when the control unit first executes the comparison acquisition process among the plurality of unit acquisition processes and makes an affirmative determination in the sensitivity difference determination process, the control unit performs a process other than the comparison acquisition process. If the unit acquisition process is prohibited and a negative determination is made, execution of the other unit acquisition process may be continued.

  According to this image forming apparatus, the difference between the current sensor sensitivity information acquired by the first acquisition processing for comparison among the plurality of unit acquisition processing and the sensor sensitivity information before the previous time is greater than the sensitivity difference threshold. If it is smaller, execution of unit acquisition processing other than the comparison acquisition processing is prohibited. Thereby, it is possible to prevent the unit acquisition process from being performed wastefully when the necessity for sensitivity adjustment is low.

  In the image forming apparatus, the comparison acquisition process may be a unit acquisition process having the largest number of acquisition times of sensor sensitivity information or a unit acquisition process having the longest acquisition period of sensor sensitivity information among the plurality of unit acquisition processes. Good.

  According to this image forming apparatus, the comparison acquisition process is a unit acquisition process with the largest number of acquisitions of sensor sensitivity information or a unit acquisition process with the longest acquisition period of sensor sensitivity information. Thereby, compared with the case where the acquisition process for comparison is a unit acquisition process etc. whose acquisition frequency is comparatively few, for example, the necessity of a sensitivity adjustment can be determined more accurately.

  In the image forming apparatus, the control unit has a configuration for executing a detection process for detecting a state change of at least one of the transport body and the mark sensor, and before the execution of all of the plurality of unit acquisition processes is completed. In addition, when the state change is detected in the detection process, the plurality of unit acquisition processes may be executed again from the beginning.

  According to this image forming apparatus, when the state of at least one of the carrier and the mark sensor changes before the execution of all of the plurality of unit acquisition processes is completed, the plurality of unit acquisition processes are re-executed from the beginning. . Thereby, it is possible to prevent the accuracy of sensitivity adjustment from being reduced by using sensor sensitivity information acquired before the state changes, even though the state has changed, for sensitivity adjustment.

  In the image forming apparatus, in the transport area acquisition process of each time, the unit acquires more unit acquisition processes with respect to the transport area as the transit time for the transport area to pass the mark detection position is longer. Alternatively, a unit acquisition process with a long processing time may be executed.

  According to this image forming apparatus, as the transit time for the transport area to pass the mark detection position is longer, a larger number of unit acquisition processes or unit acquisition processes are performed on the transport area. This makes it possible to effectively use the transport area, compared to a configuration in which unit acquisition processing is always executed for the same number or the same processing time regardless of whether the transport area passes through the mark detection position for a long time. Can do.

  The image forming apparatus includes: a conveyance path that conveys a sheet onto the conveyance body; and a sheet sensor that detects the presence or absence of a sheet at a sheet detection position on the conveyance path, and the control unit acquires the conveyance area. In the processing, the passage time of the sheet conveyance area may be detected from the time during which the sheet sensor detects the sheet.

  According to this image forming apparatus, from the time when the sheet sensor detects the sheet, the passing time during which the conveyance area of the sheet passes the mark detection position is detected. Thereby, the passage time of a conveyance area can be indirectly detected using the sheet sensor which detects the presence or absence of a sheet.

  In the image forming apparatus, the control unit has a configuration for executing a condition determination process for determining whether or not an execution condition for the mark detection process is satisfied, and in the transfer area acquisition process, all of the plurality of unit acquisition processes are performed. If the affirmative determination is made in the condition determination process before the execution of is completed, at least an unexecuted unit acquisition process is performed on the surface of the transport body without waiting for the transport area to reach the mark detection position. May be executed.

  According to this image forming apparatus, when the execution condition of the mark detection process is satisfied before the execution of all of the plurality of unit acquisition processes is completed, at least without waiting for the transport area to reach the mark detection position. An unexecuted unit acquisition process is executed on the surface of the carrier. As a result, it is possible to prevent the sensitivity adjustment from being performed even though the execution condition is satisfied.

  The image forming apparatus includes: a conveyance path that conveys a sheet onto the conveyance body; and a sheet sensor that detects the presence or absence of a sheet at a sheet detection position on the conveyance path, and the control unit acquires the conveyance area. In processing, based on the timing at which the sheet sensor detects the sheet, it is determined whether the conveyance area has reached the mark detection position. The sheet detection position is the mark detection position in the width direction of the conveyance path. Or a position outside the mark detection position with respect to the center position of the transport path.

  For example, in a configuration in which the sheet detection position is located inside the mark detection position with respect to the center position of the conveyance path in the width direction of the conveyance path, the sheet conveyance area detected at the sheet detection position is mark detection. Since the position is not passed, there is a possibility that the transfer area acquisition process is not normally executed. On the other hand, according to this image forming apparatus, the sheet detection position is the same position as the mark detection position in the width direction of the conveyance path or a position outside the mark detection position with respect to the center position of the conveyance path. is there. Thereby, it can suppress that a conveyance area acquisition process is not performed normally.

  In the image forming apparatus, when the non-conveying area that does not convey the sheet at the time of forming the print image on the surface of the conveying member reaches the mark detection position, the control unit starts from the non-conveying area. The non-conveyance area acquisition process is performed in which reflected light is received by the light receiving unit and sensor sensitivity information is acquired. In the determination process, the sensor sensitivity for the plurality of conveyance areas acquired in the conveyance area acquisition process The adjustment value may be determined based on information and sensor sensitivity information acquired in the non-transport area acquisition process.

  According to this image forming apparatus, the adjustment value is determined based on the sensor sensitivity information for the plurality of transport areas acquired in the transport area acquisition process and the sensor sensitivity information acquired in the non-transport area acquisition process. Thereby, compared with the structure which determines an adjustment value, without using the sensor sensitivity information acquired by the conveyance area acquisition process at all, the influence of a coloring agent etc. can be suppressed. In addition, it is possible to determine an adjustment value suitable for a situation where there is no transfer area in the mark detection process, compared to a configuration in which the adjustment value is determined using only the sensor sensitivity information acquired in the transfer area acquisition process.

  The present invention can be realized in various modes such as an image forming apparatus, a sensitivity adjustment method, a computer program for realizing the functions of these methods or apparatuses, and a recording medium on which the computer program is recorded.

  According to the invention disclosed in this specification, it is possible to suppress the rotational driving of a transport body such as the belt just to acquire the amount of reflected light received by the optical sensor.

1 is a side sectional view showing a schematic configuration of a printer according to a first embodiment. Block diagram schematically showing the electrical configuration of the printer Top view of mark sensor, sheet sensor and belt Diagram showing circuit configuration of mark sensor Flow chart showing printing / sensitivity adjustment processing Schematic diagram of belt unit etc. showing a state where the non-transport area passes the mark detection position Schematic diagram of the belt unit etc. showing the state where the transport area passes the mark detection position Flow chart showing first and third sensitivity adjustment steps Flow chart showing second and fourth sensitivity adjustment steps Flow chart showing the fifth sensitivity adjustment step Flow chart showing ratio adjustment process Graph showing the comparison result between the received light signal and the high threshold Graph showing correlation between received light signal and PWM value Flow chart showing the sixth sensitivity adjustment step Flow chart showing the seventh sensitivity adjustment step Time chart showing the execution order of unit acquisition processing

<Embodiment 1>
The printer 1 according to the first embodiment will be described with reference to FIGS. In the following description, the left side of FIG. 1 is the front side (F) of the printer 1, the front side of the paper is the right side (R) of the printer 1, and the upper side of the paper is the upper side (U) of the printer 1. In addition, a thick solid line in FIG.

  The printer 1 is an example of an image forming apparatus. For example, the printer 1 is a multi-transfer tandem color printer that forms a color image using four color toners of black K, yellow Y, magenta M, and cyan C. In order to distinguish each component or term of the printer 1 for each color, K (black), C (cyan), M (magenta), Y (yellow) meaning each color at the end of the code of the component. ).

(Entire printer configuration)
As shown in FIG. 1, the printer 1 includes a casing 2, and a cover 2 </ b> A is provided on the upper surface portion of the casing 2 so as to be opened and closed. By opening the cover 2A, it is possible to replace the belt unit 11 and the process units 19K to 19C described later. The casing 2 is provided with a cover sensor 8. The cover sensor 8 detects opening / closing of the cover 2A and outputs the detection result to the control unit 40 described later.

  A tray 4 on which a plurality of sheets 3 (specifically, sheets, OHP sheets, etc.) can be stacked is provided at the bottom of the casing 2. A pickup roller 5 is provided above the front end of the tray 4, and this pickup roller 5 is rotationally driven to send out the sheet 3 stacked on the top of the tray 4 to the registration roller 6. The registration roller 6 corrects the skew of the sheet 3 and then conveys the sheet 3 onto the belt unit 11.

  Further, in the vicinity of the registration roller 6, for example, a pair of sheet sensors 7 are provided side by side in the left-right direction. The pair of sheet sensors 7 detects the presence or absence of the sheet 3 at the sheet position X1 on the conveyance path Z, and outputs the detection result to the control unit 40 described later. Note that the sheet detection position X1 is not limited to the position illustrated in FIG. 1, and may be in the section between the tray 4 and the belt unit 11.

  The belt unit 11 is an example of a conveyance body, and has a configuration in which an annular belt 13 is stretched between a pair of support rollers 12A and 12B. The belt 13 is made of a resin material such as polycarbonate, and the surface thereof is mirror-finished. The belt 13 circulates and moves in the clockwise direction on the paper surface when the rear support roller 12B is driven to rotate, and conveys the sheet 3 placed on the upper surface thereof to the rear. Four transfer rollers 14 are provided inside the belt 13, and each transfer roller 14 is opposed to a photosensitive member 28 of each of the process units 19 </ b> K to 19 </ b> C described later with the belt 13 interposed therebetween.

  A mark sensor 15 is provided on the rear end side of the belt 13 for detecting the position of a mark M (an example of a correction mark) formed on the surface of the belt 13 when a correction process described later is executed. Yes. Further, a cleaning device 16 that collects toner (including a correction pattern P described later), paper dust, and the like attached to the surface of the belt 13 is provided below the belt unit 11.

  Above the belt unit 11, four exposure units 17K, 17Y, 17M, and 17C and four process units 19K, 19Y, 19M, and 19C are provided side by side in the front-rear direction. A set of image forming units 20 (an example of a forming unit) is configured to include each of the exposure units 17K to 17C, the process units 19K to 19C, and the transfer roller 14 described above. Four sets of image forming units 20K, 20Y, 20M, and 20C corresponding to the respective colors of black, yellow, magenta, and cyan are provided.

  Each exposure unit 17 </ b> K to 17 </ b> C includes an LED head 18, and a plurality of LEDs (not shown) are arranged in a line in the left-right direction of the printer 1. Therefore, in the printer 1, the left-right direction is the main scanning direction, and the front-rear direction is the sub-scanning direction. Each of the exposure units 17K to 17C is controlled to emit light based on image data to be formed, and performs exposure by irradiating light from the LED head 18 to the surface of the opposing photoconductor 28 line by line.

  Each of the process units 19K to 19C includes a toner storage chamber 23 that stores toner of each color that is a colorant. The toner in the toner storage chamber 23 is supplied onto the supply roller 24, and the toner on the supply roller 24 is positively frictionally charged with the development roller 25 while being supplied to the development roller 25. The toner on the developing roller 25 is further frictionally charged with the layer thickness regulating blade 26 to be a thin layer having a constant thickness.

  Each of the process units 19K to 19C includes a photoreceptor 28 whose surface is covered with a positively chargeable photosensitive layer, and a scorotron charger 29. At the time of mark detection and printing, the photosensitive member 28 is rotationally driven, and accordingly, the surface of the photosensitive member 28 is uniformly positively charged by the charger 29. The positively charged portion is exposed by the exposure units 17K to 17C, and an electrostatic latent image is formed on the surface of the photoreceptor 28.

  Next, the toner on the developing roller 25 is supplied to the electrostatic latent image, whereby the electrostatic latent image is visualized to form a toner image. Thereafter, the toner image carried on the surface of each photoconductor 28 is negatively applied to the transfer roller 14 while the sheet 3 passes through each transfer position between the photoconductor 28 and the transfer roller 14. The images are sequentially transferred onto the sheet 3 by the transfer voltage. The sheet 3 on which the toner image has been transferred is then conveyed to the fixing device 31 where the toner image is thermally fixed, and then the sheet 3 is conveyed upward and discharged onto the upper surface of the casing 2.

(Electrical configuration of printer)
As shown in FIG. 2, the printer 1 includes a control unit 40, the above-described image forming units 20K to 20C, a sheet sensor 7, a cover sensor 8, a mark sensor 15, a communication unit 41, a display unit 42, an operation unit 43, A drive mechanism 44 is provided. The control unit 40 includes a CPU (central processing unit) 41A and a memory 40B. The memory 40B includes, for example, a ROM, a RAM, and the like, and the ROM executes a program (an example of a sensitivity adjustment program) for executing print / sensitivity adjustment processing described later and various operations of the printer 1. Is stored. The CPU 41A controls each unit of the printer 1 according to a program read from the ROM. In addition to the ROM 12 and the RAM 13, the medium for storing the various programs may be a non-volatile memory such as a CD-ROM, a hard disk device, or a flash memory (registered trademark).

  The communication unit 41 is connected to an external computer (not shown) or the like via a communication line by wire or wireless, and can perform data communication with each other between the external computers and the like. The display unit 42 includes a liquid crystal display, a lamp, and the like, and can display various setting screens and operation states of the apparatus. The operation unit 43 includes a plurality of buttons, and various input operations can be performed by the user. The drive mechanism 44 includes a drive motor (not shown) and the like, and rotationally drives the belt 13 and the like.

(Configuration of mark sensor)
As shown in FIG. 3, one or a plurality of mark sensors 15 (for example, two in this embodiment) are provided on the lower rear side of the belt 13, and these two mark sensors 15 are arranged side by side in the left-right direction. ing. Each mark sensor 15 is a reflective optical sensor having a light emitting element 51 (for example, an example of an LED light emitting unit) and a light receiving element 52 (for example, an example of a phototransistor light receiving unit).

  Specifically, the light emitting element 51 irradiates light on the surface of the belt 13 from an oblique direction, and the light receiving element 52 receives reflected light from the surface of the belt 13. The spot position where the light from the light emitting element 51 forms on the belt 13 is the mark detection position X2 of the mark sensor 15. Each mark detection position X2 is the same position as the sheet detection position X1 of each sheet sensor 7 in the left-right direction (the width direction of the transport path Z). Here, for example, in a configuration in which the sheet detection position X1 is located on the inner side of the mark detection position X2 with respect to the center position of the transport path Z in the left-right direction, the sheet 3 detected at the sheet detection position X1 is detected. Since the conveyance area 13A does not pass the mark detection position X2, there is a possibility that the conveyance area acquisition process described later will not be executed normally. On the other hand, if it is the structure of this embodiment, it can suppress that a conveyance area acquisition process is not performed normally.

  As shown in FIG. 4, the light emitting element 51 has an anode side connected to the power supply line Vcc and a cathode side grounded via a resistor 53, a switch element 54, and a resistor 55. The controller 40 changes the light emission amount of the light emitting element 51 when executing a printing / sensitivity adjustment process or a deviation correction process described later. Specifically, for example, the control unit 40 increases a PWM value (an example of duty ratio adjustment value and sensor sensitivity information) of the PWM signal while giving a PWM (Pulse Width Modulation) signal to the switch element 54 to turn it on / off. By doing so, the amount of light emission is increased. By changing the light emission amount, it is possible to adjust the light reception signal level (hereinafter referred to as “sensor sensitivity”) when the reflectance of the belt 13 is the same condition. The switch element 54 and the like are an example of the adjustment unit.

  The light receiving element 52 has a collector side connected to the power supply line Vcc and an emitter side grounded via a variable resistor 56. Therefore, the level of the light reception signal SA output from the light receiving element 52 increases as the received light level of the reflected light received by the light receiving element 52 increases. The comparator 57 compares the light reception signal SA level with a threshold value, and gives a binarized signal SB whose level is inverted according to the comparison result to the control unit 40. Hereinafter, it is assumed that the binarized signal S2 becomes a high level when the light reception signal SA level is equal to or lower than the threshold. The controller 40 can change the threshold value by changing the voltage level applied to the input terminal of the comparator 57. The control unit 40 can acquire not only the binarized signal SB but also a digital signal SC obtained by A / D converting the received light signal SA by the A / D converter 58.

(Image formation position deviation correction processing and correction pattern)
For example, the printer 1 performs a shift correction process for correcting a shift in the sub-scanning direction for the formation positions on the sheet 3 between different color images. In this embodiment, black is used as a reference color, yellow, magenta, and cyan are used as adjustment colors, and the image formation position of each adjustment color is adjusted based on the image formation position of the reference color.

  In the shift correction process, for example, a correction pattern P shown in FIG. 3 is used. The correction pattern P has marks 60 (an example of correction marks) of each color elongated in the main scanning direction. The correction pattern P is a set of four marks 60K to 60C arranged in the order of black, yellow, magenta, and cyan, and the mark detection position on the belt 13 with a plurality of sets of marks 60 spaced apart in the sub-scanning direction. It is formed at a position corresponding to each of X2. Then, the control unit 40 executes mark detection processing for detecting the position of each mark 60 based on the level inversion of the binarized signal SB from the mark sensor 15.

  When the adjustment color image formation position deviates in the sub-scanning direction with respect to the reference color image formation position, the relative distance between the adjustment color marks 60Y to 60C and the reference color mark 60K position changes. Therefore, the control unit 40 calculates the relative distance between the position of each of the adjustment color marks 60Y to 60C and the position of the reference color mark 60K for each group based on the detection result of the mark detection process, and in all the groups. Based on the calculation result, the average value of the relative distance is calculated for each adjustment color. Then, the difference between the average value and a predetermined ideal value is used as the sub-scanning deviation amount of the image forming position with respect to the reference color, and the sub-scanning deviation amount is stored in the memory 40B. For example, during a normal image forming process based on an image forming command from an external computer, the exposure units 17Y to 17C corresponding to the respective adjustment colors expose the photosensitive member 28 so as to cancel out the sub-scanning deviation amount. adjust.

(Printing / sensitivity adjustment processing)
For example, when the print data is received from an external computer via the communication unit 41 or a print command is input from the operation unit 43, the control unit 40 executes the print / sensitivity adjustment process illustrated in FIG. The controller 40 executes a determination process for determining an adjustment value (PWM value) of the sensor sensitivity of the mark sensor 15 while forming a print image on the sheet 3 by the printing / sensitivity adjustment process.

  The control unit 40 first activates the drive mechanism 44 and starts to rotate the belt 13 for printing (S1). Next, the control unit 40 determines whether or not the sensitivity adjustment execution condition is satisfied (S2). As an example of the sensitivity adjustment execution condition, the number of sheets 3 printed since the previous execution of sensitivity adjustment, the number of rotations of the belt 13 and the photosensitive member 28, and the like have reached a predetermined value or more. When it is determined that the sensitivity adjustment execution condition is not satisfied (S2: NO), the control unit 40 executes printing for forming a print image on the sheet 3 based on the print data or the like (S3), and performs the main printing / sensitivity adjustment processing. Exit.

  On the other hand, when it is determined that the sensitivity adjustment execution condition is satisfied (S2: YES), the control unit 40 sets a sensitivity adjustment flag in the memory 40B (S4), and determines whether the deviation correction execution condition is satisfied. Is executed (S5). An example of the deviation correction execution condition is that the opening / closing of the cover 2 </ b> A is detected based on the detection result of the cover sensor 8. When it is determined that the deviation correction execution condition is not satisfied (S5: NO), the control unit 40 starts printing to form a print image based on the print data or the like on the sheet 3 (S6).

  Next, the control unit 40 determines whether or not the designated number N is 6 (S7). Here, in the printer 1, first to seventh sensitivity adjustment steps necessary for determining an adjustment value of the sensor sensitivity of the mark sensor 15 are predetermined. Each sensitivity adjustment process is a process including a unit acquisition process for causing the mark sensor 15 to perform a light projecting / receiving operation and acquiring the binarized signal SB once or more, and the specific processing content will be described later. The designation number N (= 0 to 6) is a number for designating these first to seventh sensitivity adjustment steps. If the designated number N is 1, the control unit 40 is a first sensitivity adjustment step, if it is 2, a second sensitivity adjustment step, if it is 3, a third sensitivity adjustment step, if it is 4, a fourth sensitivity adjustment step, If it is 5, the fifth sensitivity adjustment step is designated, if it is 6, the sixth sensitivity adjustment step is designated, and if it is 0, the seventh sensitivity adjustment step is designated. The designation number N is stored in the memory 40B, and is set to 1, for example, when the printer 1 is shipped. The designation number N is changed at any time when the above sensitivity adjustment steps are executed.

  When the control unit 40 determines that the designated number N is other than 6 (S7: NO), the sensitivity adjustment process (first to fifth and seventh) designated by the current designated number N in the transport area acquisition process. Execute any one of the sensitivity adjustment steps). In the conveyance area acquisition process, the binarization signal SB is sent once by causing the mark sensor 15 to perform a light projecting / receiving operation within the transit time in which the conveyance area 13A of one sheet 3 passes the mark detection position X2. This is the process to acquire. Further, the conveyance area 13A is an area on the surface of the belt 13 where the sheet 3 to be printed is currently conveyed (placed).

  First, the control unit 40 determines whether or not the total length (hereinafter simply referred to as sheet length) in the transport direction of the sheet 3 to be printed is greater than or equal to a reference length (S8). Specifically, the control unit 40 measures the detection time during which the sheet sensor 7 detects the sheet 3 based on the detection result from the sheet sensor 7, for example, and the detection time and the conveyance speed of the sheet 3. From this, the sheet length is specified. The control unit 40 may specify the sheet length from the sheet size information included in the print command, the sheet size information stored in the memory 40B, and the like. The reference length is a length corresponding to the amount of movement of the belt 13 during a period in which the binarized signal SB from the mark sensor 15 is acquired by an amount necessary for the conveyance area acquisition process, particularly the ratio adjustment process. Letter size.

  When the control unit 40 determines that the sheet length is less than the reference length (S8: NO), it is determined that the conveyance area acquisition process may not be performed normally, and the conveyance area acquisition is performed for the sheet 3 to be currently printed. Without executing the process, the printing process of S3 is executed and the process proceeds to S17.

  On the other hand, when the control unit 40 determines that the sheet length is equal to or longer than the reference length (S8: YES), the control unit 40 determines whether the transport area 13A has reached the mark detection position X2 (S9). For example, the control unit 40 determines whether the transport area 13A has reached the mark detection position X2 from the elapsed time from the time when the sheet sensor 7 detects the sheet 3 and the transport speed of the belt 13. The control unit 40 determines whether or not the conveyance area 13A has reached the mark detection position X2 from the elapsed time from the feeding timing by the registration roller 6, the detection timing of the leading edge of the sheet 3 near the fixing device 31, and the like. May be.

  FIG. 6 shows a state in which the non-conveyance area 13B where the sheet 3 to be printed is not conveyed is passing through the mark detection position X2 on the surface of the belt 13. FIG. 7 shows a state where the transport area 13A passes the mark detection position X2. When it is determined that the transport area 13A has reached the mark detection position X2 (S9: YES), the control unit 40 determines the first to fifth designated by the current designation number N in one transport area acquisition process. One of the seventh sensitivity adjustment steps is executed (S10), and the process proceeds to S17. That is, the control unit 40 designates the sensitivity adjustment step one by one in a predetermined order from the first to fifth and seventh sensitivity adjustment steps in each transfer area acquisition process, and the designated sensitivity adjustment step. Execute. And the control part 40 performs a conveyance area acquisition process in multiple times until it performs all the 1st to 5th, 7th sensitivity adjustment process. The first to fifth and seventh sensitivity adjustment steps are as follows.

(First and third sensitivity adjustment steps)
In the first sensitivity adjustment process, the control unit 40 performs the light extinction level check and the low threshold adjustment process, and in the third sensitivity adjustment process, the low threshold adjustment process is performed without executing the light extinction level check. The low threshold adjustment process is an example of a unit acquisition process, and is a process of searching for a low PWM value that is a PWM value when the light reception signal SA level becomes the low threshold TH1.

  When determining that the current designated number N is 1 or 3 in the transfer area acquisition process of S10, the control unit 40 executes the first and third sensitivity adjustment steps shown in FIG. When it is determined that the designated number N is 1 (S21: YES), the control unit 40 performs a turn-off level check. First, the control unit 40 sets the threshold value of the comparator 57 to a startup threshold value TH0 (for example, 0.6 [V]) (S22), and determines whether or not an abnormal turn-off level has occurred in the mark sensor 15. (S23).

  Specifically, the control unit 40 determines whether or not the binarized signal S2 is at a high level. At this time, since the mark sensor 15 is not activated, if the light is normal, the light emitting element 51 is turned off, the light reception signal SA level is lower than the activation threshold TH0, and the binarization signal SB is high level. become. At this time, the control unit 40 determines that no extinction level abnormality has occurred (S23: YES), and proceeds to S24.

  On the other hand, if the binarization signal S2 is at a low level, the control unit 40 determines that a light extinction level abnormality has occurred in the mark sensor 15 (S23: NO), and executes error processing in S29. . In this error processing, for example, an error message or the like is displayed on the display unit 42, or a predetermined pattern is turned on, or an error signal is output to an external device. When executing the error processing, the control unit 40 stops the first and third sensitivity adjustment steps, and proceeds to S17 of FIG. Note that the control unit 40 may forcibly terminate the print / sensitivity adjustment process without executing the error process after executing the error process.

  In S24, the control unit 40 activates the mark sensor 15, sets the threshold value to a low threshold value TH1 (eg, 0.89 [V]) that is higher than the activation threshold value, and determines whether or not an activation abnormality has occurred. Is determined (S25). Specifically, the control unit 40 determines whether or not the binarized signal SB is at a high level. At this time, although the mark sensor 15 is activated, the light emission amount is extremely low. Therefore, if it is normal, the light reception signal SA level falls below the low threshold TH1, and the binarization signal SB becomes high level. At this time, the control unit 40 determines that no startup abnormality has occurred (S25: YES), and proceeds to S26. On the other hand, if the binarized signal SB is at a low level, the control unit 40 determines that a start abnormality has occurred in the mark sensor 15 (S25: NO), and executes error processing in S29.

  In S26, the control unit 40 increases the light emission amount by increasing the PWM value of the PWM signal applied to the mark sensor 15 by a predetermined unit amount, and executes a low threshold adjustment process for bringing the light reception signal SA level closer to the low threshold TH1. To do. If the binarized signal SB is at the high level, the control unit 40 determines that the light reception signal SA level is less than the low threshold value TH1 (S27: NO), and returns to S26.

  On the other hand, if the binarized signal SB is at the low level, the control unit 40 determines that the light reception signal SA level is equal to or higher than the low threshold value TH1 (S27: YES), and sets the current PWM value as the low PWM value D1. Store in memory 40B. Note that the low PWM value D1 is individually stored when the first sensitivity adjustment step is executed and when the third sensitivity adjustment step is executed. Next, the control unit 40 adds 1 to the designated number N (S28), ends the first and third sensitivity adjustment steps, and proceeds to S17 in FIG. Thereby, if the control part 40 is after execution of a 1st sensitivity adjustment process, in the next conveyance area acquisition process, since the designation | designated number N is 2, it designates and performs a 2nd sensitivity adjustment process, After the execution of the third sensitivity adjustment step, in the next transfer area acquisition process, since the designation number N is 4, the fourth sensitivity adjustment step is designated and executed.

(Second and fourth sensitivity adjustment steps)
When determining that the current designation number N is 2 or 4 in the transfer area acquisition process of S10, the control unit 40 executes the second and fourth sensitivity adjustment steps, and the second and fourth sensitivity. In the adjustment step, the high threshold adjustment process shown in FIG. 9 is executed. The high threshold adjustment process is an example of a unit acquisition process, and is a process of searching for a high PWM value that is a PWM value when the light reception signal SA level becomes the high threshold TH2.

  First, the control unit 40 sets the threshold value to a threshold value TH2 higher than the low threshold value TH1 (eg, 3.0 [V]) (S31), and determines whether or not a light emission abnormality has occurred (S32). . Specifically, the control unit 40 determines whether or not the binarized signal SB is at a high level. At this time, although the mark sensor 15 emits light, but the light emission amount is low, if it is normal, the light reception signal SA level falls below the high threshold TH2, and the binarization signal SB becomes high level. At this time, the control unit 40 determines that a light emission abnormality has not occurred (S32: YES), and proceeds to S33. On the other hand, if the binarized signal SB is at a low level, the control unit 40 determines that a light emission abnormality has occurred in the mark sensor 15 (S32: NO), and performs error processing similar to S29 above. This is executed (S36), the second and fourth sensitivity adjustment steps are stopped, and the process proceeds to S17 in FIG. Note that the control unit 40 may forcibly terminate the print / sensitivity adjustment process without executing the error process after executing the error process.

  In S33, the control unit 40 increases the light emission amount by increasing the PWM value of the PWM signal applied to the mark sensor 15 by a predetermined unit amount, thereby bringing the light reception signal SA level closer to the high threshold value TH2. If the binarized signal SB is at the high level, the control unit 40 determines that the light reception signal SA level is less than the high threshold value TH2 (S34: NO), and returns to S33.

  On the other hand, if the binarized signal SB is at the low level, the control unit 40 determines that the light reception signal SA level is equal to or higher than the high threshold value TH2 (S34: YES), and sets the current PWM value as the high PWM value D2. Store in memory 40B. Note that the high PWM value D2 is stored separately when the second sensitivity adjustment step is executed and when the fourth sensitivity adjustment step is executed. Next, the control unit 40 adds 1 to the designated number N (S35), ends the second and fourth sensitivity adjustment steps, and proceeds to S17 in FIG. Thereby, if the control part 40 is after execution of a 2nd sensitivity adjustment process, in the next conveyance area acquisition process, since the designation | designated number N is 3, it designates and performs a 3rd sensitivity adjustment process, After the execution of the fourth sensitivity adjustment step, in the next transfer area acquisition process, since the designation number N is 5, the fifth sensitivity adjustment step is designated and executed.

(Fifth sensitivity adjustment step)
When determining that the current designation number N is 5 in the transfer area acquisition process of S10, the control unit 40 executes the fifth sensitivity adjustment step shown in FIG. 10, and in the fifth sensitivity adjustment step, A ratio adjustment process and a calculation process of sensor output characteristics when the transfer area is used are executed. The ratio adjustment process is an example of the unit acquisition process, and the binarized signal SB is acquired from the mark sensor 15 a plurality of times, and the ratio of the number of times the binarized signal SB is at the high level or the low level is within the reference range. This is a process of searching for a high-precision PWM value D3. The sensor output characteristic when the transport area is used is a correlation between the PWM value when the mark sensor 15 performs the light projecting / receiving operation with respect to the transport area 13A, and the slope shown in FIG. α1.

  The controller 40 executes the ratio adjustment process shown in FIG. 11 (S41). In the ratio adjustment process, the control unit 40 sets the PWM value for controlling the light emission amount of the mark sensor 15 to the initial PWM value, and initializes the decrease count C1 and the increase count C2 to zero (S51). The initial PWM value is preferably an average value of the high PWM value D2 searched in the second and fourth sensitivity adjustment steps. In this way, compared to the configuration in which the initial PWM value is a fixed value, the ratio of the number of times of high level or low level is greatly deviated from the reference range at the beginning of the ratio adjustment process, and the high precision PWM value is set. It can be suppressed that the time required for the search becomes long or varies.

  Next, as shown in FIG. 12, the control unit 40 acquires the binarized signal SB from the mark sensor 15 a plurality of times at a certain cycle (S52). In addition, this period (for example, 10 [ms], 5 [ms]) and the number of acquisitions (for example, 100 times and 200 times) can be changed by, for example, an operation on the operation unit 43. In S53 and S54, the number of high levels, which is the number of times when the binarized signal SB is high (“H” in the figure) during the acquisition period of the binarized signal SB, and the low level. The degree of approach between the average level of the light reception signal SA during belt irradiation and the high threshold value TH2 is evaluated based on at least one of the low level counts (“L” in the figure).

  Specifically, the approach level is considered to be higher as the low level ratio, which is the ratio of the low level count to the total acquisition count, approaches 50%. Therefore, the control unit 40 determines whether the low level ratio is within a reference range (for example, 40% to 60%). If the low level ratio is within the reference range (S53: NO and S54: NO), the average level of the received light signal SA during belt irradiation and the high threshold TH2 are set so as not to hinder the mark detection accuracy. The success flag is set in the memory 40B (S55), the ratio adjustment process is terminated, and the process proceeds to S42 in FIG.

  When the low level ratio is outside the reference range, the current PWM value is changed in a direction in which the low level ratio is within the reference range, that is, in a direction in which the average level of the light reception signal SA approaches the high threshold value TH2. Specifically, when it is determined that the low level ratio exceeds the reference range (S53: YES), the control unit 40 decreases the current PWM value by a predetermined unit amount in S56, and adds 1 to the decrease count C1. Then, the process proceeds to S58. When it is determined that the low level ratio falls below the reference range (S54: YES), the current PWM value is increased by a predetermined unit amount in S57, and 1 is added to the increase number C2, and the process proceeds to S58.

  In S58, the control unit 40 determines whether the magnitude relationship between the low level ratio and the high level ratio is reversed during the ratio adjustment process. Specifically, the control unit 40 determines whether both the decrease count C1 and the increase count C2 are not zero. For example, when the low level ratio exceeds the reference range (S53: YES), the PWM value is decreased in S56, and as a result, the low level ratio falls below the reference range (S54: YES). In such a case, it is determined that the magnitude relationship has been reversed (S58: YES), and the flow proceeds to S55 in order to prevent the low-level ratio from being in the reference range indefinitely and repeatedly repeating the magnitude relationship. .

  On the other hand, when the magnitude relationship is not reversed (S58: NO), the control unit 40 determines that the decrease count C1 or the increase count C1 is equal to or less than a predetermined count X (for example, X = 7) ( (S59: NO), returning to S52, the acquisition of the binarized signal SB is repeated. On the other hand, if the control unit 40 determines that the predetermined number of times X has been exceeded (S59: YES), it is unlikely that the low level ratio can be within the reference range even if the ratio adjustment process is further advanced. The failure flag is set in the memory 40B (S60), the ratio adjustment process is terminated, and the process proceeds to S42 in FIG.

In S42, when it is determined that the success flag is set (S42: YES), the control unit 40 performs a storage process of storing the PWM value at the end of the ratio adjustment process in the memory 40B as the high-precision PWM value D3. Execute (S43). Next, the control unit 40 adds 1 to the designated number N (S44), calculates the sensor output characteristic (inclination α1) when using the transport area by the following equation, and stores it in the memory 40B (S45, see FIG. 13). ), The fifth sensitivity adjustment step is terminated, and the process proceeds to S17 in FIG. Thereby, in the next conveyance area acquisition process, since the designation number N is 6, the control unit 40 designates and executes the sixth sensitivity adjustment step.
Inclination α1 = {(TH2-TH1) / (D3-D1A)}
D1A: Average value of the low PWM values D1 searched in the first and third sensitivity adjustment steps

  On the other hand, when determining that the failure flag is set (S42: NO), the control unit 40 does not store the current PWM value in the memory 40B, but resets the designated number N to 1 (S46). The fifth sensitivity adjustment step is terminated, and the process proceeds to S17 in FIG. As a result, in the next transfer area acquisition process, the control unit 40 starts over from the first sensitivity adjustment step because the designated number N is 1.

(Seventh sensitivity adjustment step)
In the transfer area acquisition process of S10, the control unit 40 determines that the sensitivity adjustment execution condition is newly satisfied after executing the fifth sensitivity adjustment step at least once (S2: YES), and the current designation If it is determined that the number N is 0, the seventh sensitivity adjustment step is executed. In the seventh sensitivity adjustment step, the control unit 40 determines whether or not the first to sixth sensitivity adjustment steps are necessary.

  As illustrated in FIG. 15, the control unit 40 performs the ratio adjustment process (an example of the acquisition process for comparison) illustrated in FIG. 11 described above during the period in which the transport area 13A passes the mark detection position X2 as illustrated in FIG. 7. ) Is executed (S81). Next, when the control unit 40 determines that the success flag is set (S82: YES), the current PWM value at the end of the ratio adjustment process of S81 and the already executed fifth sensitivity adjustment step A sensitivity difference determination process is performed to determine whether or not the difference from the previous high-accuracy PWM value D3 acquired in the ratio adjustment process of S41 is equal to or less than the PWM threshold (S83). The PWM threshold value is an example of a sensitivity difference threshold value, and is a PWM value difference that does not substantially affect the mark detection accuracy. For example, the PWM threshold value can be obtained from experiments.

  If the control unit 40 determines that the difference between the previous PWM value and the current PWM value is equal to or less than the PWM threshold (S83: YES), the sensor sensitivity deviation is likely to be small since the previous sensitivity adjustment is performed. Since the necessity for adjustment is low, the sensitivity adjustment flag is cleared, the designated number N is reset to 0 (S85), the seventh sensitivity adjustment step is terminated, and the process proceeds to S17 in FIG. Thereby, the control unit 40 prohibits execution of the first to sixth sensitivity adjustment steps until it is determined that the sensitivity adjustment execution condition is newly satisfied next time. When the necessity for sensitivity adjustment is low, the first to sixth sensitivity adjustment steps can be prevented from being performed wastefully.

  On the other hand, when the control unit 40 determines that the difference between the previous PWM value and the current PWM value exceeds the PWM threshold (S83: NO), the sensor sensitivity deviation from the previous sensitivity adjustment is relatively large. Since the necessity of sensitivity adjustment is high, the designated number N is added to 1 (S84), the seventh sensitivity adjustment step is terminated, and the process proceeds to S17 in FIG. Thereby, the control part 40 performs a sensitivity adjustment by performing the 1st-6th sensitivity adjustment process in the conveyance area acquisition process and non-transport area acquisition process after the next time. Even when it is determined that the failure flag is set (S82: NO), the control unit 40 cannot determine whether the sensitivity adjustment is necessary, and thus proceeds to S84 to execute the sensitivity adjustment.

  In S7 of FIG. 5, when it is determined that the designation number N is 6 (S7: YES), the control unit 40 executes a sixth sensitivity adjustment step in the non-transport area acquisition process. The non-transport area acquisition process is a process in which the mark sensor 15 performs a light projecting / receiving operation within the transit time during which the non-transport area 13B passes the mark detection position X2, and the binary signal SB is acquired one or more times. It is. As an example of the non-transport area 13B, if there is an area in front of or behind the one transport area 13A on the surface of the belt 13 or a plurality of transport areas 13A, there are areas between the plurality of transport areas 13A. Can be mentioned.

  The control unit 40 determines whether or not the non-transport area 13B whose total length in the transport direction is equal to or greater than the reference length has reached the mark detection position X2 (S15). The reference length in S15 may be the same as or different from the reference length in S8 described above. The control unit 40 can make the determination in S15 based on, for example, a time difference in timing when each of the plurality of sheets 3 is sent out by the registration roller 6.

  When it is determined that the non-transport area 13B has reached the mark detection position X2 (S15: YES), the controller 40 executes the sixth sensitivity adjustment step shown in FIG. 14 in one non-transport area acquisition process. (S16), the process proceeds to S17.

(Sixth sensitivity adjustment step)
The controller 40 executes a ratio adjustment process for the non-transport area 13B, a sensor output characteristic calculation process when the non-transport area is used, and a sensor sensitivity adjustment value determination process. The sensor output characteristic when the non-transport area is used is a correlation between the PWM value when the mark sensor 15 performs a light projecting / receiving operation with respect to the non-transport area 13B. For example, FIG. The slope α2 is shown.

  As shown in FIG. 14, when the control unit 40 first determines that color printing is designated by the print command or the like (S71: YES), as shown in FIG. 6, the non-transport area 13B is located at the mark detection position. The ratio adjustment process shown in FIG. 11 described above is executed during the period of passing through X2 (S72).

Next, the control unit 40 calculates the rising PWM value D0 (S73). As shown in FIG. 13, the rising PWM value D0 is a PWM value at the start of light reception when the light emission amount of the mark sensor 15, in other words, the light reception signal SA level rises from substantially zero. The rising PWM value D0 is a value unique to the mark sensor 15, and its fluctuation due to the surrounding environment and deterioration is relatively small. The control unit 40 calculates the rising PWM value D0 by the following equation and stores it in the memory 40B.
Rising PWM value D0 = D1A- (TH1 / α1)

When calculating the rising PWM value D0, the control unit 40 calculates the sensor output characteristic (inclination α2) when using the non-transport area by the following equation and stores it in the memory 40B (see FIG. 13 in S74).
Inclination α2 = TH2 / (D4-D0)
D4: PWM value at the end of the ratio adjustment process of S72 As shown in FIG. 13, the difference between the high-accuracy PWM value D3 and the PWM value D4, or the difference between the inclination α1 and the inclination α2 is the transfer area 13A. It fluctuates in accordance with the difference in the degree of toner adhesion between the non-transport area 1B, in other words, the difference in the so-called fogging degree.

When calculating the inclination α2, the control unit 40 calculates the saturation PWM value D5 (S75). As shown in FIG. 13, the saturation PWM value D5 is a PWM value when the light reception signal SA of the mark sensor 15 reaches the saturation level VS (eg, 3.3 [V]) of the light receiving unit of the mark sensor 15. is there. The control unit 40 calculates the saturation PWM value D5 by the following formula and stores it in the memory 40B.
Saturation PWM value D5 = D0 + (VS / α2)
In this way, if the saturation PWM value D5 is determined as an adjustment value of sensor sensitivity at the time of mark detection (hereinafter referred to as an adjustment value at the time of mark detection), for example, the PWM value D4 is determined as an adjustment value at the time of mark detection. Compared to the configuration, it is possible to reduce the influence of noise components mixed in the light reception signal SA due to scratches on the surface of the belt 13 or the like.

  In addition to the low PWM value D1, the high PWM value D2, and the high-precision PWM value D3 acquired in the first to fifth sensitivity adjustment steps in the transfer area acquisition process, the sixth sensitivity adjustment step in the non-transfer area acquisition process The mark detection adjustment value is determined based on the rising PWM value D0, PWM value D4, etc. As a result, the influence of toner or the like attached to the belt 13 can be suppressed as compared with the configuration in which the adjustment value at the time of mark detection is determined without using the result acquired in the conveyance area acquisition process. In addition, the mark detection adjustment value suitable for the situation in which the conveyance area 13A does not exist is determined in the mark detection process as compared with the configuration in which the mark detection adjustment value is determined using only the result acquired in the transfer area acquisition process. can do.

  Next, the control unit 40 determines whether or not the difference in sensor output characteristics is within a specified range based on the inclination α1 and the inclination α2 (S76). For example, if the ratio of the inclination α1 to the inclination α2 (α1 / α2) is less than a predetermined value (for example, less than 1.5), the control unit 40 determines that the difference in sensor output characteristics is within a specified range. (S76: YES). Then, the control unit 40 resets the designated number N to zero, clears the sensitivity adjustment flag (S77), ends the sixth sensitivity adjustment step, and proceeds to S17 in FIG. Thereby, in the next conveyance area acquisition process, since the designation number N is 0, the control unit 40 designates and executes the seventh sensitivity adjustment step. Only when it is determined that the difference in sensor output characteristics is within the specified range (S76: YES), the control unit 40 may execute the process of S75 thereafter.

  On the other hand, when it is determined that the difference in sensor output characteristics is outside the specified range (S76: NO), the control unit 40 can adjust the sensor sensitivity with high accuracy because the difference in the degree of toner adhesion is large. If not, error processing similar to S29 is executed (S78), the sixth sensitivity adjustment process is terminated without adjusting the sensor sensitivity, and the process proceeds to S17 in FIG. Note that the control unit 40 may forcibly terminate the print / sensitivity adjustment process without executing the error process after executing the error process.

  In S71, when the control unit 40 determines that monochrome printing is designated by the print command (S71: NO), the sixth sensitivity adjustment step ends. As described above, the shift correction processing is executed by forming the correction pattern P by color printing using all color toners. For this reason, it is preferable to use the non-transport area 13B at the time of color printing in the ratio adjustment process of S72 as well as the deviation correction process. For this reason, the controller 40 does not execute the sixth sensitivity adjustment step during monochrome printing in which the environment is different from that during the deviation correction process.

  In S <b> 17 of FIG. 5, the control unit 40 determines whether or not there is a next transport area 13 </ b> A in which the print target sheet 3 is transported based on the reception of the current print data or the print command. For example, the control unit 40 can specify the number of sheets 3 to be printed based on print data or a print command, and make the determination in S <b> 17 from the number of printed sheets and the number of printed sheets 3. Further, the control unit 40 may make the determination in S <b> 17 based on the detection result of the sheet sensor 7. If the control unit 40 determines that there is the next transport area 13A (S17: YES), it returns to S2, and if it determines that there is no next transport area 13A (S17: NO), it performs this printing / sensitivity adjustment processing. Ends and waits for reception of next print data or print command.

  With the above configuration, the control unit 40 performs the designation process for designating the seventh, first to fifth sensitivity adjustment processes one by one in this order each time the process proceeds to the transfer area acquisition process of S10 in FIG. The designated sensitivity adjustment process (unit acquisition process) is sequentially executed (see FIG. 16). Then, in the fifth sensitivity adjustment step, the control unit 40 determines the adjustment value at the time of mark detection based on the PWM value acquired by executing the transfer area acquisition process a plurality of times.

  However, the control unit 40 repeatedly executes the cover detection process at a predetermined time interval in parallel with the printing / sensitivity adjustment process. Specifically, based on the detection result from the cover sensor 8, the control unit 40 determines whether the open state of the cover 2A has continued for a predetermined time or more. If the determination is affirmative, the control unit 40 forcibly resets the designated number N to 0 or 1 and sets the sensitivity adjustment flag, assuming that there is a high possibility that the belt 13 has been replaced. As a result, if the control unit 40 makes an affirmative determination before the execution of all the first to seventh sensitivity adjustment steps is completed, the execution order starts again from the first sensitivity adjustment step. Thereby, it can suppress that the precision of sensitivity adjustment falls by using the result of the unit acquisition process before the belt 13 replacement | exchange for sensitivity adjustment.

  Further, when the control unit 40 determines that the deviation correction execution condition is satisfied in S5 of FIG. 5 and that the entire sensitivity adjustment process is completed (S5: YES and S11: YES), the sensitivity adjustment process is performed in these sensitivity adjustment processes. The above-described deviation correction processing is executed with the sensor sensitivity adjusted by the determined adjustment value at the time of mark detection (S13), and printing for forming a print image based on the print data or the like on the sheet 3 is executed (S14).・ End sensitivity adjustment processing.

  On the other hand, if the control unit 40 determines that the deviation correction execution condition is satisfied in S5 of FIG. 5 and that the entire sensitivity adjustment process has not been completed (S5: YES and S11: NO), the sensor sensitivity is urgent. Therefore, the continuous sensitivity adjustment process is executed (S12), and the process proceeds to S13. The continuous sensitivity adjustment process is a process for continuously executing the entire sensitivity adjustment process regardless of whether or not the transfer area 13A is the transfer area 13A without waiting for the transfer area 13A to reach the mark detection position X2. Thereby, it is possible to prevent the adjustment of the sensor sensitivity from being executed even when the deviation correction execution condition is satisfied. In S12, the control unit 40 may continuously execute only the unadjusted sensitivity adjustment step among all sensitivity adjustment steps.

(Effect of this embodiment)
According to the present embodiment, when the conveyance area 13A that has conveyed the sheet 3 when the print image is formed reaches the mark detection position X2, the mark sensor 15 performs a light projecting / receiving operation on the conveyance area 13A to receive light. The transfer area acquisition process for acquiring the signal SA is executed a plurality of times. Thereby, it is possible to prevent the belt 13 from being driven to rotate only to acquire the PWM value at the mark sensor 15.

  Further, since the light reception signal SA for the transport area 13A in which toner or the like hardly adheres to the surface due to the presence of the sheet 3 is formed at the time of forming the print image, the adjustment value at the time of mark detection using only the light reception signal SA for the non-transport area 13B As compared with the configuration for determining the sensor sensitivity, it is possible to acquire a large number of light reception signals SA that are less affected by toner or the like and adjust the sensor sensitivity with high accuracy. In addition, since a plurality of transfer areas 13A are used, it is possible to obtain more light reception signals SA and adjust the sensor sensitivity with higher accuracy than in a configuration using only one transfer area 13A.

<Embodiment 2>
Embodiment 2 will be described. The difference between the second embodiment and the first embodiment lies in the designation process of the sensitivity adjustment step, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are given and the redundant description is omitted, and only different points will be described next.

  In each transfer area acquisition process (S10 in FIG. 5), the control unit 40 increases the sensitivity adjustment process with respect to the transfer area 13A as the transit time for the transfer area 13A to pass the mark detection position X2 is increased. The sensitivity adjustment process with a long processing time is executed. For example, the control unit 40 can count the detection time based on the detection result from the sheet sensor 7. The detection time changes depending on the sheet length, the conveyance speed of the belt 13, and the like.

Here, the execution time of each sensitivity adjustment step is as follows.
First sensitivity adjustment step, third sensitivity adjustment step: 1 second each Second sensitivity adjustment step, fourth sensitivity adjustment step: 1.5 seconds each Fifth sensitivity adjustment step, third sensitivity adjustment step: 2 seconds

Further, the total execution time and priority for the combination pattern of the sensitivity adjustment process are as follows.
Combination 1: first sensitivity adjustment step + third sensitivity adjustment step (2.0 seconds, priority 1)
Combination 2: first sensitivity adjustment step + second sensitivity adjustment step (2.5 seconds, priority 1)
Combination 3: first sensitivity adjustment step + fourth sensitivity adjustment step (2.5 seconds, priority 2)
Combination 4: second sensitivity adjustment step + third sensitivity adjustment step (2.5 seconds, priority 3)
Combination 5: third sensitivity adjustment step + fourth sensitivity adjustment step (2.5 seconds, priority 4)
Combination 6: second sensitivity adjustment step + fourth sensitivity adjustment step (3.0 seconds, priority 1)

  In each transfer area acquisition process, the control unit 40 measures the passing time of the transfer area 13A, and includes the unexecuted sensitivity adjustment step from among the combinations 1 to 6, and the total execution time is closest to the passing time. The combination having the highest priority is designated. Instead of the passage time, a time obtained by subtracting a predetermined buffer time from the passage time may be used. If it is this structure, it can suppress that the situation where the said combination cannot be completed within the one conveyance area 13A.

  According to the present embodiment, the transport area 13A is more effective than the configuration in which the same number of sensitivity adjustment steps are always executed regardless of whether the time during which the transport area 13A passes the mark detection position X2 is long. Can be used.

<Other disclosed technologies>
From the above embodiments, it can be said that the following configuration is also disclosed. The numbers and alphabets in parentheses indicate the reference numerals of the components in the above embodiment corresponding to the respective components.

[Configuration 1]
A conveyance body (13) for conveying the sheet (3) by rotational driving;
A mark sensor (15) having a light emitting part (51) that emits light toward the mark detection position (X2) through which the surface of the carrier passes, and a light receiving part (52) that receives reflected light from the mark detection position; ,
An adjustment unit (54) for adjusting the sensor sensitivity of the mark sensor;
Forming a print image on a sheet conveyed to the conveyance body, and forming a correction mark (60) on the surface of the conveyance body (20);
A control unit (40),
The controller is
A plurality of unit acquisition processes (S26 to S28, S33 to S35, S41, S72, and S81) for causing the light emitting unit to emit light and causing the light receiving unit to receive light to acquire sensor sensitivity information (D1, D3) related to the sensor sensitivity. When,
A determination process (S75) for determining an adjustment value of the sensor sensitivity of the mark sensor based on sensor sensitivity information acquired by executing all of the plurality of unit acquisition processes;
A storage process (S43) for storing sensor sensitivity information acquired by executing one or more unit acquisition processes among the plurality of unit acquisition processes as a comparison acquisition process and executing the comparison acquisition process;
Sensitivity difference determination process for determining whether the difference between the current sensor sensitivity information acquired by executing the comparison acquisition process and the previous sensor sensitivity information stored in the storage process is equal to or less than a sensitivity difference threshold value. (S76), and
An image forming apparatus (1) that prohibits execution of the determination process when an affirmative determination is made in the sensitivity difference determination process and continues the determination process when a negative determination is made.
The configuration 1 includes a configuration in which a plurality of unit acquisition processes are executed regardless of whether or not the transport area 13A reaches the mark detection position X2.

[Configuration 2]
A conveyance body (13) for conveying the sheet (3) by rotational driving;
A mark sensor (15) having a light emitting part (51) that emits light toward the mark detection position (X2) through which the surface of the carrier passes, and a light receiving part (52) that receives reflected light from the mark detection position; ,
An adjustment unit (54) for adjusting the sensor sensitivity of the mark sensor;
Forming a print image on a sheet conveyed to the conveyance body, and forming a correction mark (60) on the surface of the conveyance body (20);
A control unit (40),
The controller is
A condition determination process (S5) for determining whether or not a mark detection execution condition is satisfied;
When the transport area (13A) that transported the sheet when forming the print image before reaching the execution condition reaches the mark detection position, the reflected light from the transport area is reflected. A transport area acquisition process (S10) for causing the light receiving unit to receive light and acquiring sensor sensitivity information related to the sensor sensitivity;
If the execution area satisfies the execution condition before the transport area reaches the mark detection position, the reflected light from the surface of the transport body is received without waiting for the transport area to reach the mark detection position. A transport area unquestioning process (S12) in which the sensor sensitivity information is acquired by receiving light in the unit;
A determination process (S75) for determining an adjustment value of the sensor sensitivity of the mark sensor based on the sensor sensitivity information acquired in the transport area acquisition process or the non-transport area unquestioned process;
An image forming apparatus comprising: a mark detection process (S13) for forming the mark on the forming unit and detecting the mark with a sensor sensitivity after adjustment based on the adjustment value determined in the determination process.
Note that the configuration 2 includes a configuration in which the adjustment value is determined based on the sensor sensitivity information acquired in one transfer area acquisition process.

[Configuration 3]
A conveyance body (13) for conveying the sheet (3) by rotational driving;
A mark sensor (15) having a light emitting part (51) that emits light toward the mark detection position (X2) through which the surface of the carrier passes, and a light receiving part (52) that receives reflected light from the mark detection position; ,
An adjustment unit (54) for adjusting the sensor sensitivity of the mark sensor;
Forming a print image on a sheet conveyed to the conveyance body, and forming a correction mark (60) on the surface of the conveyance body (20);
A transport path (26) for transporting the sheet onto the transport body;
A sheet sensor (7) for detecting the presence or absence of a sheet at a sheet detection position (X1) on the conveyance path;
A control unit (40),
The controller is
Based on the detection of the sheet by the sheet sensor, it is assumed that the conveyance area (13A) that has conveyed the sheet at the time of formation of the print image on the surface of the conveyance body has reached the mark detection position, from the conveyance area. A transfer area acquisition process (S10) in which reflected light of the light is received by the light receiving unit and sensor sensitivity information related to the sensor sensitivity is acquired;
A determination process (S75) for determining an adjustment value of the sensor sensitivity of the mark sensor based on sensor sensitivity information for the transfer area acquired in the transfer area acquisition process;
The image forming apparatus, wherein the sheet detection position is the same position as the mark detection position in the width direction of the transport path, or a position outside the mark detection position with respect to a center position of the transport path.
Note that the configuration 3 includes a configuration in which the adjustment value is determined based on the sensor sensitivity information acquired in one transfer area acquisition process.

[Configuration 4]
A conveyance body (13) for conveying the sheet (3) by rotational driving;
A mark sensor (15) having a light emitting part (51) that emits light toward the mark detection position (X2) through which the surface of the carrier passes, and a light receiving part (52) that receives reflected light from the mark detection position; ,
An adjustment unit (54) for adjusting the sensor sensitivity of the mark sensor;
Forming a print image on a sheet conveyed to the conveyance body, and forming a correction mark (60) on the surface of the conveyance body (20);
A control unit (40),
The controller is
Assuming that the transport area (13A) that transported the sheet at the time of forming the print image on the surface of the transport body has reached the mark detection position, the light receiving unit receives reflected light from the transport area and A transfer area acquisition process (S10) for acquiring sensor sensitivity information related to sensor sensitivity;
When a non-transport area (13B) that is not transporting a sheet when the printed image is formed on the surface of the transport body reaches the mark detection position, reflected light from the non-transport area is received by the light receiving unit. Non-transport area acquisition processing for acquiring sensor sensitivity information,
A determination process (S75) for determining an adjustment value of the sensor sensitivity of the mark sensor based on the sensor sensitivity information for the plurality of transport areas acquired in the transport area acquisition process and the sensor sensitivity information acquired in the non-transport area acquisition process. And an image forming apparatus.
Note that the configuration 4 includes a configuration in which the adjustment value is determined based on the sensor sensitivity information acquired in one transfer area acquisition process.

<Other embodiments>
The technology disclosed in the present specification is not limited to the embodiments described with reference to the above description and drawings, and includes, for example, the following various aspects.

  In the above embodiment, the tandem printer of the multiple transfer system is taken as an example, but the image forming apparatus is not limited to this. A multi-transfer type transfer body type or a multiple development type (multi-rotation type, single-pass type) printer may be used. In this case, the photoconductor conveys an electrostatic latent image and a toner image. The developing device and the charger are examples of the image forming unit.

  In addition, a printer of a multiple transfer / intermediate transfer method (intermediate transfer member method / tandem method) may be used. In this case, the intermediate transfer member or the photosensitive member conveys an electrostatic latent image and a toner image. The developing device and the charger are examples of the image forming unit. Further, other electrophotographic printers such as a polygon scanning method may be used, and an ink jet printer may be used.

  In the above embodiment, the control unit 40 is configured to change the sensor sensitivity by changing the light emission amount of the mark sensor 15. However, the configuration is not limited to this, and the control unit 40 may be configured to change the light reception sensitivity (the conversion rate between the light reception amount and the light reception signal SA level) in the mark sensor 15. For example, the amplification degree of an amplification circuit (not shown) on the light receiving side of the mark sensor 15 may be changed, or the photoelectric conversion rate in the light receiving element 52 may be changed.

  In the above-described embodiment, the control unit 40 is configured to execute the printing / sensitivity adjustment processing by the single CPU 40A and the memory 40B. However, the present invention is not limited to this, and the control unit 40 is configured to execute print / sensitivity adjustment processing by a plurality of CPUs, to execute print / sensitivity adjustment processing only by hardware circuits such as ASIC (Application Specific Integrated Circuit), A configuration in which the print / sensitivity adjustment processing is executed by the CPU and the hardware circuit may be employed. For example, a configuration in which a hardware circuit executes the above ratio adjustment processing or the like may be used.

  In the above embodiment, the control unit 40 performs each unit acquisition process based on the binarized signal SB from the comparator 57. However, the configuration is not limited thereto, and the control unit 40 may be configured to execute each unit acquisition process based on the light reception signal SA level from the light receiving element 52.

  In the above embodiment, the control unit 40 may be configured to execute one unit acquisition process over a plurality of transport areas 13A. For example, the control unit 40 may execute the acquisition process of S52 in the ratio adjustment process by dividing each of the plurality of transport areas 13A through the mark detection position X2.

  In the above embodiment, the sheet detection position X1 of each sheet sensor 7 is the same position as each mark detection position X2 in the left-right direction. However, the present invention is not limited to this, and the sheet detection position X1 may be positioned outside the mark detection position X2 with respect to the center position of the transport path Z in the left-right direction.

  In the above embodiment, the control unit 40 is configured to perform the ratio adjustment process only for the high threshold TH2 and search for the high-accuracy PWM value D3. However, the control unit 40 is not limited to this, and may be configured to execute the ratio adjustment process for the low threshold. However, in general, the optical sensor tends to lose linearity between the PWM value and the light emission amount as the light emission amount increases. On the contrary, when the light emission amount is relatively small as in the case of setting the low threshold TH1, the linearity tends to be maintained. Therefore, even if the ratio adjustment process is not executed, the accuracy is low. It is possible to retrieve the PWM value D1. For this reason, the structure of the said embodiment is preferable also considering the processing burden of the control part 40. FIG.

  In the above embodiment, the PWM value is given as an example of the sensor sensitivity information. However, the sensor sensitivity information is not limited to this, and may be the amount of light received by the mark sensor 15, the sensor output characteristics, or the like. In short, it may be information that has a correlation with the sensor sensitivity. For example, the control unit 40 may be configured to acquire, as sensor sensitivity information, the amount of received light when the mark sensor 15 performs a light projecting / receiving operation with a predetermined PWM value.

  In the above embodiment, the control unit 40 is configured to determine whether or not the difference in the sensor output characteristics is within the specified range based on the ratio of the inclination α2 and the inclination α1 in S76 of FIG. However, the control unit 40 is not limited to this, and may be configured to make the above determination based on the difference between the inclination α1 and the inclination α2 or the difference between the high-accuracy PWM value D3 and the PWM value D4. When using the difference between the high-precision PWM value D3 and the PWM value D4, the control unit 40 determines whether or not the difference in sensor output characteristics is within a specified range after S72 and makes an affirmative determination. Only in cases, the processing from S73 to S75 may be executed. With this configuration, it is not necessary to execute the processing from S73 to S75 when the difference in sensor output characteristics is outside the specified range.

  In the embodiment described above, the ratio adjustment process is given as an example of the comparison acquisition process. However, the present invention is not limited to this, and the comparison acquisition process may be a low threshold adjustment process, a high threshold adjustment process, or the like, and may not be a unit acquisition process that is executed first. Further, two or more unit acquisition processes among the low threshold adjustment process, the high threshold adjustment process, the ratio adjustment process, and the like may be included. However, as in the above-described embodiment, if the ratio adjustment process to be executed first is the comparison acquisition process, the control unit 40, when making a negative determination in the sensitivity difference determination process, performs the first to sixth sensitivities. It is not necessary to execute the adjustment process without permission.

  Further, as an example of the acquisition process for comparison, the ratio adjustment process in which the number of acquisition times of the received light signal SA is the largest or the acquisition period is the longest. However, the comparison acquisition process may be a unit acquisition process with the smallest number of acquisitions of the received light signal SA or the shortest acquisition period, such as a low threshold adjustment process. If it is this structure, the control part 40 can perform a sensitivity difference determination process simply and early. On the other hand, according to the above embodiment, the necessity for sensitivity adjustment can be determined with higher accuracy than when the comparison acquisition process is, for example, a unit acquisition process with a relatively small number of acquisitions.

  In the first embodiment, the control unit 40 may execute the low threshold adjustment process and the high threshold adjustment process in an order different from that in FIG. Further, the control unit 40 may be configured to execute the low threshold adjustment process and the high threshold adjustment process one or more times. The control unit 40 may be configured not to execute at least one of the first to seventh sensitivity adjustment steps.

  In the above embodiment, the control unit 40 is configured to detect whether or not the belt 13 has been replaced based on the open state of the cover 2A. However, the present invention is not limited to this, and the printer 1 is provided with, for example, a belt sensor that detects whether or not the belt 13 is replaced. The control unit 40 directly detects whether or not the belt 13 is replaced based on the detection result of the belt sensor. The structure to do may be sufficient. Further, the printer 1 may be provided with a temperature sensor, and the control unit 40 may be configured to detect a state change (change in output characteristics) of the mark sensor 15 based on a detection result of the temperature sensor. Further, the control unit 40 may be configured to detect a change in the state of the surface of the belt 13 (change in reflectance) based on the rotation amount of the belt 13, the driving time, the number of sheets 3 printed, and the like. In short, the control part 40 should just be the structure which detects the state change of at least one of a conveyance body and a mark sensor.

In the above embodiment, the control unit 40 may be configured to determine the saturation PWM value D6 as the adjustment value at the time of mark detection by the following equation without executing the sixth sensitivity adjustment step.
Saturation PWM value D6 = D0 + (VS / α1)
Further, the controller 40 may be configured to determine the mark detection adjustment value based on at least one of the low PWM value D1 and the high PWM value D2 without executing the fifth sensitivity adjustment step.

  1: Printer 3: Sheet 7: Sheet sensor 13A: Transport area 15: Mark sensor 40: Control unit 51: Light emitting element 52: Light receiving element X1: Sheet detection position X2: Mark detection position Z: Transport path

Claims (12)

A conveying body that conveys the sheet by rotational driving; and
A light emitting unit that emits light toward a mark detection position through which the surface of the carrier passes, and a mark sensor that includes a light receiving unit that receives reflected light from the mark detection position;
An adjustment unit for adjusting the sensor sensitivity of the mark sensor;
Forming a print image on a sheet conveyed to the conveyance body, and forming a correction mark on the surface of the conveyance body;
A control unit,
The controller is
When the conveyance area that has conveyed the sheet at the time of formation of the print image on the surface of the conveyance body reaches the mark detection position, the light receiving unit receives reflected light from the conveyance area and relates to the sensor sensitivity. A transport area acquisition process for acquiring sensor sensitivity information;
A determination process for determining an adjustment value of the sensor sensitivity of the mark sensor based on sensor sensitivity information for the plurality of transfer areas acquired by executing the transfer area acquisition process a plurality of times;
An image forming apparatus comprising: a mark detection process for forming the mark on the forming unit and detecting the mark with a sensor sensitivity after adjustment based on the adjustment value determined in the determination process. The image forming apparatus according to claim 1,
A plurality of unit acquisition processes for obtaining sensor sensitivity information by causing the light emitting unit to emit light and causing the light receiving unit to receive light are predetermined,
The controller is
From the plurality of unit acquisition processes, it has a configuration to execute a designation process that designates one or more unit acquisition processes to be executed in the transport area acquisition process of each time,
In each transfer area acquisition process, the one or more unit acquisition processes specified in the specification process are executed,
In the determination process, the adjustment value is determined based on sensor sensitivity information acquired by executing all of the plurality of unit acquisition processes. The image forming apparatus according to claim 2,
The controller is
One or more unit acquisition processes among the plurality of unit acquisition processes are set as a comparison acquisition process, and a storage process for storing sensor sensitivity information acquired by executing the comparison acquisition process is executed.
Whether the difference between the current sensor sensitivity information acquired by executing the comparison acquisition process in the transport area acquisition process and the previous sensor sensitivity information stored in the storage process is equal to or less than a sensitivity difference threshold value. And a sensitivity difference determination process for determining
An image forming apparatus that prohibits execution of the determination process when an affirmative determination is made in the sensitivity difference determination process and continues the determination process when a negative determination is made. The image forming apparatus according to claim 3, wherein
The controller is
Of the plurality of unit acquisition processes, the comparison acquisition process is first executed,
When an affirmative determination is made in the sensitivity difference determination process, execution of another unit acquisition process other than the comparison acquisition process is prohibited, and when a negative determination is made, execution of the other unit acquisition process is continued. The image forming apparatus according to claim 3, wherein:
The comparison acquisition process is an image forming apparatus that is a unit acquisition process having the largest number of acquisition times of sensor sensitivity information or a unit acquisition process having the longest acquisition period of sensor sensitivity information among the plurality of unit acquisition processes. An image forming apparatus according to any one of claims 2 to 5,
The controller is
It has a configuration for executing a detection process for detecting a state change of at least one of the transport body and the mark sensor,
An image forming apparatus that re-executes the plurality of unit acquisition processes from the beginning when the state change is detected by the detection process before the execution of all of the plurality of unit acquisition processes is completed. The image forming apparatus according to any one of claims 2 to 6,
The controller is
In each transfer area acquisition process, the longer the transit time for which the transfer area passes through the mark detection position, the more the unit acquisition process or the unit acquisition process with a longer processing time for the transfer area. An image forming apparatus to be executed. The image forming apparatus according to claim 7,
A transport path for transporting the sheet onto the transport body;
A sheet sensor that detects the presence or absence of a sheet at a sheet detection position on the conveyance path,
The controller is
In the conveyance area acquisition process, the image forming apparatus detects the passage time of the conveyance area of the sheet from the time when the sheet sensor detects the sheet. The image forming apparatus according to any one of claims 2 to 8,
The controller is
It has a configuration for executing a condition determination process for determining whether or not an execution condition for the mark detection process is satisfied,
In the transfer area acquisition process, if the determination in the condition determination process is affirmative before the execution of all of the plurality of unit acquisition processes is completed, without waiting for the transfer area to reach the mark detection position, An image forming apparatus that executes at least an unexecuted unit acquisition process on the surface of the conveyance body. An image forming apparatus according to any one of claims 1 to 9,
A transport path for transporting the sheet onto the transport body;
A sheet sensor that detects the presence or absence of a sheet at a sheet detection position on the conveyance path,
The control unit determines whether the transport area has reached the mark detection position based on the timing at which the sheet sensor detects a sheet in the transport area acquisition process,
The image forming apparatus, wherein the sheet detection position is the same position as the mark detection position in the width direction of the transport path, or a position outside the mark detection position with respect to a center position of the transport path. The image forming apparatus according to any one of claims 1 to 10,
The controller is
When a non-conveying area that does not convey a sheet during the formation of the print image on the surface of the conveying body reaches the mark detection position, reflected light from the non-conveying area is received by the light receiving unit. It has a configuration for executing non-transport area acquisition processing for acquiring sensitivity information,
In the determination process, the adjustment value is determined based on sensor sensitivity information for the plurality of transport areas acquired in the transport area acquisition process and sensor sensitivity information acquired in the non-transport area acquisition process. A conveying body that conveys the sheet by rotational driving; and
A light emitting unit that emits light toward a mark detection position through which the surface of the carrier passes, and a mark sensor that includes a light receiving unit that receives reflected light from the mark detection position;
An adjustment unit for adjusting the sensor sensitivity of the mark sensor;
Forming an image on a sheet conveyed to the conveyance body, and forming a correction mark on the surface of the conveyance body.
When the conveyance area that has conveyed the sheet at the time of formation of the print image on the surface of the conveyance body reaches the mark detection position, the light receiving unit receives reflected light from the conveyance area and relates to the sensor sensitivity. A transport area acquisition process for acquiring sensor sensitivity information;
A determination process for determining an adjustment value of the sensor sensitivity of the mark sensor based on sensor sensitivity information for the plurality of transfer areas acquired by executing the transfer area acquisition process a plurality of times;
A sensitivity adjustment program for forming the mark in the forming unit and executing a mark detection process for detecting the mark with a sensor sensitivity after adjustment based on the adjustment value determined in the determination process.

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