JP2015148662A - Image forming apparatus and image forming control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect an image failure without using a large-scale density sensor, which has high resolution equal to or higher than an exposure section and is as large as the exposure section, in forming an image by use of the exposure section formed by combining a plurality of light-emitting element arrays.SOLUTION: An image forming apparatus includes: the exposure section formed by combining the plurality of light-emitting element arrays in a main scanning direction; an image carrier which is scanned in a sub-scanning direction orthogonal to the main scanning direction, relatively with respect to the exposure section, and exposed by the exposure section to carry an image according to image data; a sensor which reads the image formed on the image carrier; and a control section which controls exposure on the image carrier by the exposure section. The control section controls some light-emitting elements in the light-emitting element arrays to emit light, and controls a plurality of patches for changing light emission of the light-emitting elements to be formed on the image carrier. The patches are read by the sensor. When there is a predetermined difference or more in density between the patches, a failure is determined.

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet based on image data, and in particular, includes a line-shaped light emitting element array as an exposure unit, performs relative scanning between the exposure unit and the image carrier, and The present invention relates to various image forming apparatuses that form an image by performing exposure according to image data from an exposure unit to the image carrier.

  In the image forming apparatus, exposure is performed from the exposure unit based on the image data, and an electrostatic latent image is formed on the image carrier. The electrostatic latent image is developed with toner as a developer to generate a toner image. The generated toner image is transferred from the image carrier to a sheet. Further, the sheet on which the toner image is placed is fixed by heat and pressure, whereby the sheet on which the image is formed is output from the image forming apparatus. Such image forming apparatuses exist in copiers, facsimile machines, printers, and the like.

  In this type of image forming apparatus, the first direction is the longitudinal direction, and a plurality of light emitting element arrays each including a plurality of light emitting elements are combined to form an exposure unit. Furthermore, an image carrier that carries an image (electrostatic latent image) corresponding to image data that is exposed by the exposure unit while being scanned in a second direction orthogonal to the first direction relative to the exposure unit. Is provided.

  In this way, an image having a desired size can be formed with a desired resolution. In addition, a device using LEDs as light emitting elements in this exposure unit is called an LED printer head.

  An image forming apparatus using this type of LED printer head as an exposure unit is required to form an image without causing a density change even at a joint where a plurality of light emitting element arrays are combined. In addition, a technique for forming a good image even at the joint of the light emitting element arrays has been proposed in the following patent documents.

JP 2006-192772 A

  In the above-mentioned Patent Document 1, when a long exposure unit is formed by combining a plurality of light emitting element arrays in the main scanning direction, the density of the seam of the light emitting element array is detected by the sensor so that the density becomes uniform. Correction techniques have been proposed.

  In this case, in order to accurately detect the density difference of the seam of the light emitting element array, a high resolution and large sensor having a resolution equal to or higher than the resolution of the light emitting element array and the same size as the length of the exposure unit in the main scanning direction. Is required. Such a high resolution and large sensor is expensive and impractical.

  The exposure unit that combines a plurality of light emitting element arrays includes a light amount correcting unit that corrects a light amount difference between the light emitting elements included in the light emitting element array, and a memory that stores light amount correction data for the light amount correcting unit. Things exist. Such light quantity correction makes it possible to form a good image even when a plurality of light emitting element arrays are used.

  By the way, in the image forming apparatus, a high voltage of several hundred volts or more is handled in a charging unit and a transfer / separation unit in an electrophotographic process. Noise may be generated by this high-pressure leak or the like. Noise caused by such leaks is mixed into the control signal and reset signal, or the noise caused by leaks deviates the ground reference potential, so that the operation of the light quantity correction unit described above is stopped or the light quantity correction data is reset. There is also a possibility.

  Since the above exposure unit is a terminal part of image formation control, there is no mechanism for error detection or error correction. Therefore, considering the occurrence of image abnormality due to the abnormal operation of the light quantity correction unit, the high-resolution and large-sized expensive density sensor described in Patent Document 1 is required.

  The present invention has been made in view of such a problem, and in an image forming apparatus having an exposure unit in which a plurality of light emitting element arrays are combined, a large-sized image having a resolution equal to or higher than that of the exposure unit and the same size as the exposure unit. An object of the present invention is to provide an image forming apparatus and an image forming control method capable of detecting an image abnormality without using a density sensor.

In order to achieve at least one of the above objects, an image forming apparatus and an image forming control method reflecting one aspect of the present invention are configured as follows.
(1) An exposure unit configured by combining a plurality of light emitting element arrays with the first direction as a longitudinal direction, and being scanned in a second direction orthogonal to the first direction relative to the exposure unit. An image carrier that carries an image according to image data exposed by the exposure unit, a sensor that reads an image formed on the image carrier, and controls exposure of the image carrier by the exposure unit. In an image forming apparatus having a control unit, or in an image forming control method for controlling the image forming apparatus, the control unit causes a part of the light emitting elements to emit light and emit light in the light emitting element array. A plurality of patches with different values are controlled to be formed on the image carrier, and the plurality of patches are controlled to be read by the sensor, and a difference of a certain level or more is detected in the density of the plurality of patches. It is determined to be abnormal when, characterized in that.

  (2) In the above (1), when the control unit causes some of the light emitting elements to emit light in the light emitting element array, at least one of the number of light emitting elements to emit light or the position of the light emitting element to emit light is arbitrarily selected. It is possible to change to.

  (3) In the above (2), the control unit causes the light emitting element to emit light at intervals of a unit common to an anode or a cathode of the light emitting element in the different light emitting element arrays.

  (4) In the above (1) to (3), a light amount correction function for correcting a light amount difference of each light emitting element included in the light emitting element array is provided, and the control unit has a certain density or more in the density of the plurality of patches. If a difference is detected, it is determined that the correction is abnormal.

  (5) In the above (1) to (4), the control unit has a function of forming a toner image on the image carrier for a predetermined operation time or for a predetermined number of sheets. The difference in density is detected using the patch.

  (6) In the above (1) to (5), during execution of a printing operation for forming an image on the paper, the control unit performs the patch between a printing operation on a certain paper and a printing operation on the next paper. It controls to form.

  (7) In the above (1) to (6), the control unit stops a printing operation for forming an image on the paper when a certain difference is detected in the densities of the plurality of patches. It is characterized by controlling.

  (8) In the above (1) to (7), a display unit for displaying various information is provided, and the control unit is configured to display the display unit when a certain difference is detected in the densities of the plurality of patches. An abnormality occurrence is displayed on the screen.

In the image forming apparatus and the image forming control method reflecting one aspect of the present invention, the following effects can be obtained.
(1) The control unit controls the light emitting element array to emit a part of the light emitting elements and to form a plurality of patches with different light emitting elements to be emitted on the image carrier, and to read the plurality of patches by the sensor. If a difference of a certain level or more is detected in the density of a plurality of patches, it is determined that there is an abnormality.

  That is, by reading a plurality of patches with different light emitting elements to emit light in the light emitting element array, even if a sensor with a resolution lower than the arrangement density of the light emitting elements is used, the light amount of the light emitting elements in the light emitting element array The difference is detected as a patch density difference. As a result, in an image forming apparatus having an exposure unit in which a plurality of light emitting element arrays are combined, an image abnormality can be detected without using a large density sensor having a resolution equal to or higher than that of the exposure unit and the same size as the exposure unit. Is possible.

  (2) In the above (1), when some of the light emitting elements are caused to emit light in the light emitting element array, by arbitrarily changing at least one of the number of light emitting elements to emit light or the position of the light emitting element to emit light, Even when a sensor having a resolution lower than the arrangement density of the light emitting elements is used, the light amount difference of the light emitting elements in the light emitting element array is reliably detected as the patch density difference.

  (3) In the above (2), the control unit causes the light emitting elements to emit light at intervals of a unit common to the anodes or cathodes of the light emitting elements in different light emitting element arrays, thereby lowering the resolution than the arrangement density of the light emitting elements. Even when the sensor is used, the light amount difference of the light emitting elements in the light emitting element array is reliably detected as the patch density difference.

  (4) In the above (1) to (3), a light amount correction function for correcting a light amount difference of each light emitting element included in the light emitting element array is provided, and the control unit detects a certain difference or more in the density of a plurality of patches. In such a case, it is possible to reliably detect an image abnormality in the image forming apparatus having the light quantity correction function by determining that the correction is abnormal.

  (5) In the above (1) to (4), the control unit has a function of forming a toner image on the image carrier every predetermined operation time or every predetermined number of sheets, and the toner image is patched as the toner image. By using this to detect the difference in density, it is possible to reliably detect an image abnormality using conventional operations without newly executing dedicated processing.

  (6) In the above (1) to (5), the control unit forms a patch between the printing operation for a certain sheet and the printing operation for the next sheet during execution of the printing operation for forming an image on the sheet. By controlling in such a manner, it is possible to reliably detect an image abnormality without disturbing the printing operation.

  (7) In the above (1) to (6), the control unit controls to stop the printing operation for forming an image on the sheet when a difference of a certain level or more is detected in the density of the plurality of patches. Thus, it is possible to reliably detect the image abnormality without outputting the paper in which the image abnormality has occurred.

  (8) In the above (1) to (7), a display unit for displaying various information is provided, and the control unit generates an abnormality in the display unit when a difference of a certain level or more is detected in the density of a plurality of patches. By displaying, it is possible to reliably detect an image abnormality and notify the user with certainty.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention. 1 is a configuration diagram illustrating a configuration of an image forming apparatus according to an exemplary embodiment of the present invention. 1 is a configuration diagram illustrating a configuration of a main part of an image forming apparatus according to an exemplary embodiment of the present invention. 1 is a configuration diagram illustrating a configuration of a main part of an image forming apparatus according to an exemplary embodiment of the present invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of the conventional apparatus. It is explanatory drawing which shows the operation state of the conventional apparatus. It is explanatory drawing which shows the operation state of the conventional apparatus. It is explanatory drawing which shows the operation state of the conventional apparatus. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. It is explanatory drawing which shows the operation state of embodiment of this invention. 6 is a flowchart illustrating a printing operation according to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.
〔Constitution〕
The configuration of the image forming apparatus according to the present embodiment will be described with reference to the block diagram of FIG. 1 and the configuration diagram of FIG.

  The image forming apparatus 100 includes a control unit 101, a communication unit 102, an operation display unit 103, a storage unit 104, a paper feeding unit 105, a transport unit 110, an image data storage unit 130, an image processing unit 140, an image forming unit 150, and a density sensor. 160 is comprised.

  The control unit 101 controls each unit in the image forming apparatus 100. The communication unit 102 communicates with other devices. The operation display unit 103 notifies the control unit 101 of an operation input signal corresponding to the operation input by the user and displays the status of the image forming apparatus 100. The storage unit 104 stores a control program and various setting data and is used as a work area for the control program. The paper feeding unit 105 feeds the stored paper. The transport unit 110 transports paper that is fed and printed at a predetermined speed. The image data storage unit 130 stores image data and various data for printing. The image processing unit 140 executes various image processes necessary for printing. The image forming unit 150 executes image formation (which means a series of operations such as image formation, transfer, and fixing, and is collectively referred to as “print”) based on a print command and image data after image processing. The density sensor 160 detects the density of the patch formed on the image carrier of the image forming unit 150.

  Further, as shown in FIG. 2, the image forming unit 150 includes an image carrier 151, a charging unit 152, an exposure unit 153, a developing unit 154, a transfer separation unit 155, a fixing unit 156, and a cleaning unit 157. And a static elimination unit 158. Here, an electrostatic latent image and a toner image are formed on the image carrier 151. The charging unit 152 charges the image carrier 151 with a predetermined potential. The exposure unit 153 forms an electrostatic latent image by exposing the charged image carrier 151 according to image data. The developing unit 154 develops the electrostatic latent image into a toner image. The transfer separation unit 155 transfers the toner image on the image carrier 151 to a sheet and separates the sheet from the image carrier 151. The fixing unit 156 fixes the toner image on the paper with heat and pressure. The cleaning unit 157 removes toner remaining on the image carrier. The neutralization unit 158 removes the potential of the image carrier 151.

The density sensor 160 is arranged so as to detect the density of the patch formed on the image carrier 151.
In FIG. 2, the direction perpendicular to the paper surface of the cylindrical image carrier 151 is defined as the first direction (main scanning direction), and the rotation direction about the central axis of the cylindrical image carrier 151 is the second direction. Direction (sub-scanning direction). The exposure unit 153 and the density sensor 160 are configured with the main scanning direction as the longitudinal direction.

The exposure unit 153 includes a light emission control unit 153a and a print head 153b, as shown in FIG.
Here, the print head 153b receives demultiplexer 1531 that distributes the image data from the light emission control unit 153a to a plurality of light emitting element arrays, which will be described later, and correction data that corrects the light amount difference between the light emitting elements included in the light emitting element array. The memory 1532 to be accumulated, drivers 1533_1 to 1533_n for driving the respective light emitting element arrays, and a plurality of light emitting element arrays 1534_1 to 1534_n that are driven by the drivers 1533_1 to 1533_n to expose the image carrier 151. ing.

  Here, the plurality of light-emitting element arrays 1534_1 to 1534_n constituting the exposure unit 153 are configured by combining a plurality of light-emitting element arrays with the first direction (main scanning direction) as the longitudinal direction in FIG. Has been. In FIG. 3, eight light emitting elements are provided per light emitting element array.

When the light emitting elements included in the light emitting element array are light emitting diodes (LEDs), the light emitting elements are configured by matrix wiring as shown in FIG.
For example, the cathodes of the light emitting diodes included in the light emitting element array are commonly connected. That is, the cathode wiring C1 of the light emitting element array 1534_1, the cathode wiring C2 of the light emitting element array 1534_2, the cathode wiring C3 of the light emitting element array 1534_3, the cathode wiring C4 of the light emitting element array 1534_4,. The demultiplexer 1531 is connected.

  The anodes of the light emitting diodes included in each light emitting element array are connected to the same numbered anodes in each light emitting element array. That is, the first anode wiring A1 of the light emitting element arrays 1534_1 to 153n_, the second anode wiring A2 of the light emitting element arrays 1534_1 to 153n_, the third anode wiring A3 of the light emitting element arrays 1534_1 to 153n_, The fourth anode wiring A4 of the light emitting element arrays 1534_1 to 153n_,..., And the nth anode wiring An of the light emitting element arrays 1534_1 to 153n_ are connected to the demultiplexer 1531.

  In such a different light emitting element array, by emitting light from the light emitting element with a unit common to the anode or cathode of each light emitting element as described later, a sensor having a resolution lower than the arrangement density of the light emitting elements can be obtained. Even when it is used, the light amount difference of the light emitting elements in the light emitting element array is reliably detected as the patch density difference.

[Light emission state of light emitting element array and density difference of image]
FIG. 5A is a characteristic diagram showing a light amount distribution in the main scanning direction of the exposure unit 153 using a printer head in which eight light emitting element arrays each having eight light emitting elements are combined. Here, each light emitting element array has the same characteristics. Therefore, dots formed on the image carrier 151 when the same current is supplied to each light emitting element are as shown in FIG. In addition, although the difference in the light quantity of each light emitting element appears as a difference in dot size, since each dot is a minute size, it is visually recognized as a difference in density.

  FIG. 6A is a characteristic diagram showing a corrected light quantity distribution in the main scanning direction of the exposure unit 153 using a printer head in which eight light emitting element arrays each having eight light emitting elements are combined. Here, although each light emitting element array has the same characteristics as those in FIG. 6A, the drivers 1533_1 to 1533_n are controlled by the light emission control unit 153a using the correction data stored in the memory 1532. Adjusts the drive current to correct the light amount. Thereby, the light quantity difference of each light emitting element is corrected so as to be uniform. For this reason, when the same current is supplied to each light emitting element, the dots formed on the image carrier 151 are uniform as shown in FIG.

  However, in the image forming apparatus 100, a high voltage of several hundred volts or more is handled by the charging unit 152 and the transfer separation unit 155 in the electrophotographic process. Noise may be generated by this high-pressure leak or the like. Noise due to such leaks may be mixed into the control signal or reset signal, or noise due to leaks may disrupt the ground reference potential, thereby stopping the above-described light amount correction operation or resetting the correction data. obtain. Since the above exposure unit 153 is a terminal part of image formation control, there is no mechanism such as a return signal for error detection or error correction. Therefore, it is necessary to depend on the confirmation of the output image by a high-resolution and large-sized density sensor higher than that of the light-emitting element array and the occurrence of image abnormality due to abnormal operation or non-operation of light amount correction.

[Various patch formation during printing]
The image forming apparatus 100 has a function of forming a toner image on the image carrier 151 every predetermined operation time or every predetermined number of sheets. Here, FIG. 7 shows a state in which the surface of the image carrier 151 that is a cylindrical surface is developed, and shows a state of a toner image formed on the surface of the image carrier 151.

Here, Pr # 1, Pr # 2, and Pr # 3 are images formed based on the image data, and should be transferred to a sheet and output.
Here, Pt # 1 and Pt # 2 are toner images formed on the surface of the image carrier 151 in a region (non-image region or inter-paper region) between images to be output. When enlarged, a halftone pattern as shown in FIG. 8 is obtained. The toner image reaches the cleaning unit 157 while remaining on the surface of the image carrier 151 without being transferred by the transfer separation unit 155.

  Since the cleaning blade provided in the cleaning unit 157 is in contact with the surface of the image carrier 151, the cleaning blade may be in a drowned state when the lubricity is lowered. Therefore, in order to prevent such blurring, a toner image is intentionally supplied to the cleaning unit 157 so that the lubricating state is maintained with the oil and fat component contained in the toner. For this reason, the toner image shown here is sometimes called a cleaning patch.

  Note that the cleaning patches shown in FIGS. 7 and 8 show the case where the state of the light emitting element array of the exposure unit 153 is in a normal state as shown in FIG. As already described, even if the light amount correction of the light emitting element array is executed due to various causes, there is a possibility of falling into a light emitting state with a light amount difference as shown in FIG.

  FIG. 9 shows a state of the cleaning patch in the case where the light emitting element array in a state where there is a light amount difference as shown in FIG. 5 is used. Since the arrangement density of the light emitting elements included in the light emitting element array is very fine, even if there is a light amount difference as shown in FIG.

  FIG. 10 is an enlarged view of the toner images Pt # 1 and Pt # 2 as the cleaning patches in FIG. When the magnification is enlarged as shown in FIG. 10, the light amount difference of each light emitting element can be confirmed, but if there is no resolution higher than the resolution of the light emitting element array, the light amount difference is averaged with surrounding pixels and cannot be detected. .

[Patch formation during printing operation according to this embodiment]
11 to 13 show a state in which the patch of this embodiment is applied to a cleaning patch. Here, FIG. 11 shows a state where the surface of the image carrier 151 that is a cylindrical surface is developed, and shows a state of a toner image formed on the surface of the image carrier 151.

FIG. 12 shows an example of a patch that makes it possible to detect a light amount difference as shown in FIG. 5 when a light-emitting element array composed of eight light-emitting elements is used.
Here, for each light emitting element array, the cleaning patch Pt # 1 causes the first light emitting element of each light emitting element array to emit light (FIG. 12A). Similarly, for each light emitting element array, the cleaning patch Pt # 2 causes the second light emitting element of each light emitting element array to emit light (FIG. 12B). Similarly, for each light emitting element array, the cleaning patch Pt # 3 causes the third light emitting element of each light emitting element array to emit light (FIG. 12C). Similarly, for each light emitting element array, the cleaning patch Pt # 4 causes the fourth light emitting element of each light emitting element array to emit light (FIG. 12D). Similarly, for each light emitting element array, the cleaning patch Pt # 5 causes the fifth light emitting element of each light emitting element array to emit light (FIG. 12E). Similarly, for each light emitting element array, the cleaning patch Pt # 6 causes the sixth light emitting element of each light emitting element array to emit light (FIG. 12F). Similarly, for each light emitting element array, the cleaning patch Pt # 7 causes the seventh light emitting element of each light emitting element array to emit light (FIG. 12G). Similarly, for each light emitting element array, the cleaning patch Pt # 8 causes the eighth light emitting element of each light emitting element array to emit light (FIG. 12 (h)).

  That is, when the print head 153b including a plurality of light emitting element arrays having M light emitting elements is used, m = 1 to M, and the mth light emitting element in each light emitting element array for the mth cleaning patch Pt # m. Control to turn on.

Then, the electrostatic latent image formed by exposure on the image carrier 151 in this way is developed to form a toner image, and the density is detected by the density sensor 160.
Thus, even when the density sensor 160 having a resolution lower than that of the light emitting element array is used, an image abnormality caused by a light amount difference between the light emitting elements in the light emitting element array can be detected. It becomes possible.

  Further, as shown in FIG. 13, for each light emitting element array, the cleaning patch Pt # 1 causes the first and fourth light emitting elements of each light emitting element array to emit light (FIG. 13A). Similarly, for each light emitting element array, the cleaning patch Pt # 2 causes the second and fifth light emitting elements of each light emitting element array to emit light (FIG. 13B). Similarly, for each light emitting element array, the cleaning patch Pt # 3 causes the third and sixth light emitting elements of each light emitting element array to emit light (FIG. 13C). Similarly, for each light emitting element array, the cleaning patch Pt # 4 causes the fourth and seventh light emitting elements of each light emitting element array to emit light (FIG. 12D).

  That is, when the print head 153b including a plurality of light emitting element arrays having M light emitting elements is used, m = 1 to M, and the mth light emitting element in each light emitting element array for the mth cleaning patch Pt # m. And (M / 2 + (m−1)) light emitting elements are controlled to light up.

Then, the electrostatic latent image formed by exposure on the image carrier 151 in this way is developed to form a toner image, and the density is detected by the density sensor 160.
In this way, even when the density sensor 160 having a resolution lower than that of the light emitting element array is used, it is possible to detect an image abnormality caused by a light amount difference between the light emitting elements in the light emitting element array. It becomes possible.

  When the number of light emitting elements in the light emitting element array is small, a patch for emitting light one by one as shown in FIG. 12 is formed. When the number of light emitting elements in the light emitting element array is large, a plurality of patches are formed as shown in FIG. It is desirable to form a patch that emits light from each light emitting element.

[Operation of Embodiment]
Hereinafter, the image forming apparatus and the image forming control method of the present embodiment will be described with reference to the flowchart shown in FIG.

  When the image forming apparatus 100 is powered on, the control unit 101 initializes each unit in the image forming apparatus 100. Further, based on an instruction from the control unit 101, the light emission control unit 153a reads the correction data stored in the memory 1532 and sets the correction data in the drivers 1533_1 to 1533_n (step S101 in FIG. 14).

Here, the control unit 101 waits for an instruction to execute printing from the operation display unit 103 or the external PC (step S102 in FIG. 14).
Upon receiving the print execution instruction, the control unit 101 sets the initial value of the variable m to 1 (step S103 in FIG. 14), and in the image forming unit 150 based on the image data of the m (= 1) page. An image is printed on the paper (step S104 in FIG. 14).

  Here, the control unit 101 forms the m (= 1) -th cleaning patch on the surface of the image carrier 151 in the image forming unit 150, detects the density of the cleaning patch with the density sensor 160, and stores the detection result. 104 or the like (step S105 in FIG. 14).

  The cleaning patch after density detection is processed by the cleaning unit 157 as originally intended. In addition, the m-th cleaning patch is a patch by exposure that has a function as a cleaning patch and has a light emitting element driving characteristic of the present embodiment as described in FIG. 12 or FIG. The density sensor 160 may detect the density of a certain area of the patch with a resolution lower than that of the light emitting element array.

  Then, the control unit 101 increments the variable m = m + 1 (step S106 in FIG. 14), and checks whether image data of the mth page exists (step S107 in FIG. 14).

If there is no image data for the m-th page (NO in step S107 in FIG. 14), the control unit 101 ends the printing process (end in FIG. 14).
On the other hand, if the mth page of image data exists (YES in step S107 in FIG. 14), the control unit 101 prints an image on the sheet in the image forming unit 150 based on the mth page of image data. (Step S108 in FIG. 14).

  If the m-th cleaning patch exists (YES in step S109 in FIG. 14), the control unit 101 forms the m-th cleaning patch on the surface of the image carrier 151 in the image forming unit 150. The density of the cleaning patch is detected by the density sensor 160, and the detection result is stored in the storage unit 104 or the like (step S110 in FIG. 14). The cleaning patch after density detection is processed by the cleaning unit 157 as originally intended.

  Then, the control unit 101 compares the density of the first patch to the density of the mth patch (step S111 in FIG. 14). Here, if m is 2, the density of the first patch is compared with the density of the second patch. If m is 3 or more, the density of the first patch, the density of the second patch,..., The density of the mth patch are compared with each other. Note that the density difference equal to or greater than a certain level means a predetermined level at which a difference equal to or greater than a detection error has occurred and is considered to cause a problem in image quality.

  The predetermined level is stored in the storage unit 104 or the like. However, the user can change the image quality and productivity desired by the user (such as preventing the print operation from being stopped by a slight change in image quality). It is also possible to change.

  Even if such a comparison is made, if the density of one of the patches does not differ from the density of the other patch by a certain level or more (NO in step S112 in FIG. 14), the control unit 101 determines that m Increment (step S106 in FIG. 14), m-th page print existence confirmation (step S107 in FIG. 14), m-th page print (step S108 in FIG. 14), m-th patch existence confirmation (step S109 in FIG. 14) ), M-th patch formation / density detection / density storage (step S110 in FIG. 14), and density difference detection of the 1st to m-th patches (step S111 in FIG. 14) are repeated.

  If such a comparison is made and the density of any one of the patches is different from the density of the other patches by more than a certain level (YES in step S112 in FIG. 14), the control unit 101 performs the image forming unit. Control is performed to stop the printing operation at 150, and a message indicating that an abnormality has occurred in the print head 153b is displayed on the operation display unit 103 (step S113 in FIG. 14).

[Effect obtained by the embodiment]
As described above, the control unit 101 controls the plurality of patches to be formed on the image carrier 151 by causing some of the light emitting elements to emit light and changing the light emitting elements to emit light in the light emitting element array. Even if a sensor with a resolution lower than the arrangement density of the light emitting elements is used by controlling the reading by the sensor and judging that it is abnormal when a difference of a certain level or more is detected in the density of the plurality of patches, A light amount difference between the light emitting elements in the light emitting element array is detected as a patch density difference. That is, in the image forming apparatus 100 having the exposure unit 153 in which a plurality of light emitting element arrays are combined, image abnormality can be detected without using a large density sensor having a resolution equal to or higher than that of the exposure unit 153 and the same size as the exposure unit 153. It becomes possible to detect.

  In the above case, when some of the light emitting elements emit light in the light emitting element array, the arrangement of the light emitting elements can be changed by arbitrarily changing at least one of the number of light emitting elements to emit light or the position of the light emitting elements to emit light. Even when a sensor with a resolution lower than the density is used, the light quantity difference of the light emitting elements in the light emitting element array is reliably detected as the patch density difference.

  Further, in the above case, the control unit 101 causes the light emitting elements to emit light at intervals of a unit common to the anodes or cathodes of the light emitting elements in different light emitting element arrays, so that the sensor has a lower resolution than the arrangement density of the light emitting elements. Even when the light source is used, the light amount difference of the light emitting elements in the light emitting element array is reliably detected as the patch density difference.

  Further, in the above case, a light amount correction function for correcting the light amount difference of each light emitting element included in the light emitting element array is provided, and the control unit 101 detects a difference of a certain level or more in the density of a plurality of patches. By determining that the correction is abnormal, it is possible to reliably detect the image abnormality in the image forming apparatus having the light amount correction function.

  In the above case, the control unit 101 has a function of forming a toner image on the image carrier for a predetermined operation time or for a predetermined number of sheets. By detecting the difference, it is possible to reliably detect an image abnormality using a conventional operation without newly executing a dedicated process.

  In the above case, the control unit 101 performs control so as to form a patch between the printing operation for a certain sheet and the printing operation for the next sheet during the execution of the printing operation for forming an image on the sheet. Thus, it is possible to reliably detect an image abnormality without disturbing the printing operation.

  In the above case, the control unit 101 controls to stop the printing operation for forming an image on the paper when a difference of a certain level or more is detected in the density of the plurality of patches. Image abnormality can be reliably detected without outputting the generated paper.

  Further, in the above case, a display unit that displays various information is provided, and the control unit 101 displays an abnormality occurrence on the operation display unit 103 when a certain difference is detected in the density of the plurality of patches. As a result, it is possible to reliably detect the image abnormality and notify the user with certainty.

[Other Embodiments]
In the above embodiment, correction data is stored in the memory 1532, and the driver 1533_1 to 1533_n corrects the light amount difference of each light emitting element. However, the present invention is not limited to this. That is, there are various methods such as the presence / absence of correction and the difference in correction method.

  For example, when starting to use a light emitting element array in a state where there is no light amount difference between the light emitting elements, even when a light amount difference occurs due to deterioration of the light emitting element, the present embodiment is applied to detect an abnormality. Can do.

  In the above embodiment, the image abnormality is detected using the cleaning patch. However, the present invention is not limited to this. For example, various toner images such as a density adjusting patch can be used. Further, it is possible to perform the operation of the present embodiment during a period when printing is not executed.

  In the above density comparison (step S112 in FIG. 14), it is possible to provide a plurality of types of determination criteria for density differences. In this case, if the print density can be continued with little influence on the image quality, but a slight density difference that should be communicated to the service person, only the display on the operation display unit 103 is performed without stopping printing. Further, in the case where the influence on the image quality is not negligible and the density difference is severe enough that printing should not be continued, step-by-step control such as displaying on the operation display unit 103 at the same time as stopping printing is possible.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 Control part 102 Communication part 103 Operation display part 104 Storage part 105 Paper feed part 110 Conveyance part 120 Document reading part 130 Image data storage part 140 Image processing part 150 Image forming part 160 Density sensor

Claims (16)

An exposure unit configured by combining a plurality of light emitting element arrays with the first direction as a longitudinal direction;
An image carrier that carries an image according to image data that is exposed by the exposure unit while being scanned in a second direction orthogonal to the first direction relative to the exposure unit;
A sensor for reading an image formed on the image carrier;
A control unit for controlling exposure of the image carrier by the exposure unit,
The control unit controls to form a plurality of patches in the light emitting element array so that some light emitting elements emit light and change the light emitting elements to emit light on the image carrier, and the plurality of patches are formed by the sensor. Control to read, and if a difference of a certain level or more is detected in the density of the plurality of patches, it is determined to be abnormal,
An image forming apparatus. The control unit can arbitrarily change at least one of the number of light emitting elements to emit light or the position of the light emitting element to emit light when emitting some of the light emitting elements in the light emitting element array.
The image forming apparatus according to claim 1. The control unit causes the light emitting elements to emit light at intervals of units common to the anodes or cathodes of the light emitting elements in the different light emitting element arrays.
The image forming apparatus according to claim 2. A light amount correction function for correcting a light amount difference of each light emitting element included in the light emitting element array,
The control unit determines that the correction is abnormal when a certain difference is detected in the density of the plurality of patches.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control unit has a function of forming a toner image on the image carrier for each predetermined operation time or every predetermined number of sheets, and detects the difference in density using the patch as the toner image. ,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control unit controls to form the patch between a printing operation for a certain sheet and a printing operation for the next sheet during execution of a printing operation for forming an image on the sheet.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The control unit controls to stop a printing operation for forming an image on the paper when a certain difference or more is detected in the density of the plurality of patches;
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. It has a display unit that displays various information,
The control unit displays an abnormality occurrence on the display unit when a certain difference or more is detected in the density of the plurality of patches.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An image formation control method for controlling image formation in an image forming apparatus,
The image forming apparatus includes:
An exposure unit configured by combining a plurality of light emitting element arrays with the first direction as a longitudinal direction;
An image carrier that carries an image according to image data that is exposed by the exposure unit while being scanned in a second direction orthogonal to the first direction relative to the exposure unit;
A sensor for reading an image formed on the image carrier;
A control unit that controls exposure of the image carrier by the exposure unit,
The controller is
Controlling to form a plurality of patches in the light-emitting element array, and a plurality of patches in which the light-emitting elements that emit light are changed on the image carrier,
Controlling the plurality of patches to be read by the sensor;
When a difference of a certain level or more is detected in the density of the plurality of patches, it is determined to be abnormal.
An image formation control method characterized by this. The control unit can control to arbitrarily change at least one of the number of light emitting elements to emit light or the position of the light emitting element to emit light when emitting some of the light emitting elements in the light emitting element array. Is,
The image formation control method according to claim 9. The control unit causes the light emitting elements to emit light at intervals of units common to the anodes or cathodes of the light emitting elements in the different light emitting element arrays.
The image formation control method according to claim 10. A light amount correction function for correcting a light amount difference of each light emitting element included in the light emitting element array,
The control unit determines that the correction is abnormal when a certain difference is detected in the density of the plurality of patches.
12. The image formation control method according to claim 9, wherein the image formation control method is any one of claims 9 to 11. The control unit has a function of forming a toner image on the image carrier for each predetermined operation time or every predetermined number of sheets, and detects the difference in density using the patch as the toner image. ,
13. The image formation control method according to claim 9, wherein the image formation control method is any one of claims 9 to 12. The control unit controls to form the patch between a printing operation for a certain sheet and a printing operation for the next sheet during execution of a printing operation for forming an image on the sheet.
14. The image formation control method according to claim 9, wherein the image formation control method is any one of claims 9 to 13. The control unit controls to stop a printing operation for forming an image on the paper when a certain difference or more is detected in the density of the plurality of patches;
15. The image formation control method according to claim 9, wherein the image formation control method is any one of the above. It has a display unit that displays various information,
The control unit displays an abnormality occurrence on the display unit when a certain difference or more is detected in the density of the plurality of patches.
16. The image formation control method according to claim 9, wherein the image formation control method is any one of the above.