JP2009135730A - Image reading device - Google Patents

Abstract

An image reading apparatus capable of appropriately moving an image sensor to a home position is provided.
A scanner unit 3 measures a dark signal level Vd for each chip constituting an image sensor 14 and stores the result in an NVRAM 34 in advance. Prior to the movement to the home position P, the scanner unit 3 acquires the dark signal level Vd. The image sensor 14 performs black and white discrimination based on a voltage value obtained by subtracting the dark signal level Vd as an offset value from the output voltage value.
[Selection] Figure 6

Description

  The present invention relates to an image reading apparatus that reads an image of a document with an image sensor. More specifically, the present invention relates to an image reading device that positions a home position of the image sensor by reading a predetermined mark.

  Conventionally, as an image reading apparatus that reads an image of an original, the image of the original is read by an image sensor equipped with a plurality of reading elements and converted into an electrical image signal, and the analog image signal is further converted by an A / D converter. What converts into a digital signal is known. In such an image reading apparatus, it is necessary to move the image sensor to a predetermined image reading start position (home position) before starting a document reading operation. Therefore, in such an image reading apparatus, a home position sensor such as a photodiode is provided for detecting the home position.

In recent years, an image reading apparatus that moves an image sensor to a home position without the above-described home position sensor has been disclosed in response to a request for cost reduction. As such an image reading apparatus, for example, in Patent Document 1, a specific mark (origin identification mark) is arranged in the moving range of the image sensor, and the reference position is determined by reading the origin identification mark. It is disclosed. As the origin identification mark, a pattern in which a white area and a black area are arranged adjacent to each other in the sub-scanning direction is used.
JP 2000-113162 A

  However, the image reading apparatus that reads the origin identification mark has the following problems. That is, when the origin identification mark is detected, the accuracy of black and white discrimination is not sufficient, and there are cases where the home position cannot be appropriately moved.

  Specifically, an image reading apparatus that reads an origin identification mark performs a reading operation with an image sensor, and searches for an origin identification mark based on acquired data (mainly a voltage value corresponding to optical density). When searching for the origin identification mark, the following discrimination is performed.

First, the output (= black output) when reading the highest density is given by the following equation.
Black output = Vd + Vb
On the other hand, the output (= white output) when the one with the lowest density is read is as follows.
White output = Vd + Vw
Here, Vd is a dark signal level (= output when the light source of the image sensor is off), Vb is a black dynamic range (= output when reading black with reference to Vd), and Vw is a white dynamic range (= Vd. This means the output when reading white as a reference).

A reading operation is performed by the image sensor, and the obtained data V (= output at the time of reading based on Vd) is compared with a black and white determination threshold value Vs prepared in advance to perform black and white discrimination. That is, it is as follows.
If (Vd + V) <Vs, the output data is determined to be black. If (Vd + V) ≧ Vs, the output data is determined to be white.

Here, each reading element constituting the image sensor normally satisfies black output (= Vd + Vb) <white output (= Vd + Vw). However, when adverse conditions such as external light and aging (light source deterioration) overlap, the black output may be larger than the white output between different elements as shown in the following equation.
Vdmax + Vbmax> Vdmin + (y × Vwmin)
Vdmax: The maximum value of Vd variation.
Vbmax: the maximum value of Vb.
Vdmin: the minimum value of Vd variation.
Vwmin: The minimum value of Vw.
y: The maximum of the aging coefficient “%” of Vw corresponding to the aging of the light source.

  Thus, depending on the element, the black reading may result higher than the white reading. For example, as shown in FIG. 10, assuming that Vd of chip # 1 is Vdmin and Vd of chip # 3 is Vdmax, the white output after aging of chip # 1 is smaller than the black output of chip # 3. Sometimes. Therefore, an appropriate black and white determination threshold value Vs cannot be selected. As a result, the origin identification mark to be detected could not be detected correctly, and the image sensor could not be properly moved to the home position.

  The present invention has been made to solve the problems of the conventional image reading apparatus. That is, the problem is to provide an image reading apparatus capable of appropriately moving the image sensor to the home position.

  An image reading apparatus designed to solve this problem moves in the sub-scanning direction, acquires a reading unit that reads an image of a document, a mark used to detect the home position of the reading unit, and an acquisition of an offset voltage value And a moving means for detecting a mark based on a detection value obtained from the offset voltage value and the reading voltage value output from the reading means and moving the reading means to the home position.

  The image reading apparatus of the present invention reads a predetermined mark by the reading means and moves the reading means to the home position. That is, it is an image reading device without a home position sensor. As the home position detection mark, for example, a mark in which a white area and a black area are adjacent in the sub-scanning direction can be applied.

  The image reading apparatus of the present invention acquires the offset voltage value by the acquisition unit prior to the movement to the home position. The moving means detects the mark in consideration of the offset voltage value. Specifically, black and white discrimination is performed based on the voltage value obtained by subtracting the offset voltage value from the reading voltage value of the reading means. That is, the black and white discrimination is performed by the accurate voltage value necessary for the black and white discrimination. As a result, the influence of variations in offset voltage values can be avoided, and as a result, the reading means can be moved to the home position with high accuracy.

  In addition, the image reading apparatus of the present invention preferably includes a non-volatile storage unit that stores an offset voltage value corresponding to each reading unit, and the acquisition unit acquires the offset voltage value from the storage unit. That is, the offset voltage value corresponding to each reading unit is stored in advance in the storage unit. Thereby, the acquisition unit can acquire the offset voltage value unique to the reading unit, and can detect the mark more accurately.

  Further, the reading means of the image reading apparatus includes a reading element group in which a plurality of reading elements are arranged in the main scanning direction, and the storage means has a position in the main scanning direction among the reading elements of the reading element group. It is better to store the offset voltage value applied to the reading element included in the range of the mark in the main scanning direction. That is, by storing the minimum offset voltage value necessary for mark detection, the capacity of the storage means can be reduced.

  Further, the acquisition means of the image reading apparatus of the present invention acquires a reading voltage value when the light source of the reading means is turned off, and when the reading voltage value is within a predetermined range, the acquisition voltage value is set as an offset voltage value, In other cases, an arbitrary voltage value stored in advance may be used as the offset voltage value. That is, every time the home position is detected, the read voltage value when the light source is turned off is obtained, and the offset voltage value is obtained according to the result. As a result, it is not necessary to store the offset voltage value in advance, and the effort at the pre-shipment stage is reduced.

  In the image reading apparatus of the present invention, it is better that the position of the mark in the main scanning direction is outside the document reading range. That is, since the mark detection position is outside the document reading range, the reading means is not easily affected by external light. Therefore, the mark detection becomes more accurate.

  Further, the mark of the image reading device is arranged at least to one end of the moving range of the reading means in the sub-scanning direction, and the moving means moves the reading means in the sub-scanning direction based on the detected value. It is better to switch between moving to one end side or moving to the other end side. That is, by arranging the mark up to the end on one end side of the moving range of the reading means in the sub-scanning direction, the moving range of the reading means in the sub-scanning direction The area can be divided into two. Then, before the reading means is moved, the moving direction of the reading means is switched according to which region the current reading means is located. As a result, there is no movement of the reading means to the end of the moving range when the home position is detected, so that failure can be avoided and the product life can be extended.

  The image reading apparatus according to the present invention further includes a measuring means for measuring an offset voltage value within the original reading range, and the moving means moves the reading means to a position where the offset voltage value is measured by the measuring means after the mark is detected. It is better if it is. That is, obtaining the actual offset voltage value contributes to high accuracy of the correction process.

  Further, it is better that the measuring means measures an offset voltage value for each of a plurality of reading elements constituting the reading means. That is, by measuring the offset voltage value for each reading element, it is possible to avoid the influence due to individual differences of the reading elements.

  According to the present invention, an image reading apparatus capable of appropriately moving the image sensor to the home position is realized.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying an image reading apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the present invention is applied to a multi-function machine having a scanner function, a printer function, a copy function, a facsimile function, and the like.

[Configuration of MFP]
As shown in FIG. 1, the MFP 100 according to the present embodiment includes a main body unit 2 including an image forming unit that prints an image on a sheet, and a scanner unit 3 (an example of an image reading device) that reads an image of a document. ing. The image forming method may be an electrophotographic method or an ink jet method. Further, even if a color image can be formed, it may be dedicated to a monochrome image.

  Further, the scanner unit 3 is provided with an operation panel 4 provided with various buttons, a liquid crystal display, and the like on the front side, and the operation panel 4 can display an operation status and input a user's operation. .

  As shown in FIG. 2, the scanner unit 3 includes an image reading unit 6 that reads an image of a document, and a document cover unit 7 that covers the upper part of the scanner unit 3 so as to be openable and closable. The image reading unit 6 includes two transparent platen glasses 8 and 9 positioned on the upper surface thereof, and an image sensor 14 (an example of a reading unit) positioned therein.

  The image sensor 14 is of a CIS (Contact Image Sensor) type, and includes a CMOS image sensor 15, an optical element 16 made of a lens, and a light source 17 made of RGB light emitting diodes. The CMOS image sensor 15 is composed of a plurality of photodiodes arranged in a line in the main scanning direction (a direction orthogonal to the paper conveyance direction, the depth direction in FIG. 2). The reflected light is received by each photodiode via the optical element 16, and the light intensity (brightness) of the reflected light is converted into an electrical signal for each pixel and output.

  The document cover unit 7 includes an ADF (Auto Document Feeder) 11 that automatically transports a document, a document tray 12, and a discharge tray 13. The ADF 11 takes out the originals placed on the original tray 12 one by one and conveys the originals to a position facing the platen glass 9 (hereinafter referred to as “ADF glass 9”). Thereafter, the document is discharged onto the discharge tray 13.

  As a document reading method, there are a flat bed (document fixed scanning) method and an ADF (document moving scanning) method. In the case of the flat bed system, documents are placed one by one on a platen glass 8 (hereinafter referred to as “FB glass 8”). In this state, the image sensor 14 moves in the sub-scanning direction (a direction orthogonal to the main scanning direction, the direction of arrow A in FIG. 2), and at that time, an image of the document is read line by line in the main scanning direction. On the other hand, in the case of the ADF method, documents are collectively placed on the document tray 12. Then, the image sensor 14 moves to a position facing the ADF glass 9 and is fixed. In this state, the document is conveyed to a position facing the ADF glass 9, and the image of the document is read line by line in the main scanning direction.

  In the flat bed method, the image sensor 14 reads an image when moving from the end portion of the FB glass 8 on the ADF glass 9 side in the sub-scanning direction toward the opposite end portion. Therefore, in the movement of the image sensor 14 in the sub-scanning direction, the ADF glass 9 side is upstream and the FB glass 8 side is downstream.

  Further, the document reading unit 6 has a reference member 20 in a region adjacent to the ADF glass 9 on the inner surface of the housing. As shown in FIG. 3, the reference member 20 has a rectangular plate shape. The length in the main scanning direction is longer than the length of the FB glass 8 or ADF glass 9 in the main scanning direction. More specifically, as shown in FIG. 4, the length of the reference member 20 in the main scanning direction is slightly longer than the one-line reading area of the image sensor 14 (in this embodiment, constituted by chips # 1 to # 12). About big.

  Further, the reference member 20 is divided into two in the sub-scanning direction, and a white reference portion 21 on the upstream side and a resolution measurement reference portion 22 on the downstream side. The white reference portion 21 is white with a uniform density throughout. On the other hand, in the resolution measurement reference unit 22, one end in the main scanning direction is a black region 22A, the remaining part is a white region 22B, and the black region 22A and the white region 22B are adjacent to each other in the main scanning direction. Further, the black area 22A is adjacent to the white reference area 21 in the sub-scanning direction.

  Further, a part of the black area 22A is located outside the range of the original reading surface (range X in FIG. 4: equivalent to the width of the FB glass 8 in the main scanning direction) in the main scanning direction. The black area 22A is mainly read by chips (chips # 1 and # 2 in FIG. 4 in this embodiment) located outside the range of the original reading surface and in the reading range (range Y in FIG. 4).

  Further, the position of the upstream end portion in the sub-scanning direction of the white reference portion 21 is equivalent to the position of the upstream end portion of the moving range of the image sensor 14 in the sub-scanning direction. As a result, the moving range of the image sensor 14 in the sub-scanning direction has an output voltage value higher than the monochrome determination threshold Vs across the boundary between the white reference portion 21 and the black region 22A as shown in the graph of FIG. An area (white area) and another area (black or resin color area) are divided into two.

  The reference member 20 is used for detecting the home position P and measuring the resolution. In the detection of the home position P, the image sensor 14 is moved to the upstream side or the downstream side in the sub-scanning direction, and based on the output of the image sensor 14, the white reference region 21 that is a white level region and the black region that is a black level region. The boundary with 22A is detected. That is, in the present embodiment, the white reference area 21 and the black area 22A are “origin identification marks”. Then, the image sensor 14 is moved to the home position P with the detected boundary as a reference. Note that the position of the white reference portion 21 may be the home position, or the detected boundary position may be the home position. Description of the resolution measurement is omitted.

[Electric configuration of MFP]
Next, the electrical configuration of the multifunction machine 100 will be described. As shown in FIG. 5, the multi-function device 100 includes a control device 30 including a CPU 31, a ROM 32, a RAM 33, an NVRAM 34 (an example of a storage unit), an ASIC 35, a network interface 36, and a facsimile interface 37. is doing.

  The ROM 32 stores various control programs for controlling the multifunction peripheral 100, various settings, initial values, and the like. The RAM 33 is used as a work area from which various control programs are read or as a storage area for temporarily storing image data. The ASIC 35 is electrically connected to the image forming unit 38, the document reading unit 3, the operation panel 4, and the like. The CPU 31 controls each component of the multifunction peripheral 100 via the ASIC 35 while storing the processing result in the RAM 33 or NVRAM 34 according to the control program read from the ROM 32.

  Information equipment is connected to the network interface 36, and mutual data communication is possible via the network interface 36. The facsimile interface 37 is connected to a telephone line, and data communication with an external facsimile apparatus or the like is enabled via the facsimile interface 37.

[Scanner Document Reading Operation (First Embodiment)]
Next, the document reading operation of the scanner unit 3 will be described. The dark signal level Vd (offset voltage value) in units of chips constituting the image sensor 14 is measured in advance for each scanner unit 3, and the result is stored in the NVRAM 34.

  That is, the dark signal level Vd is a unique value for each chip. Therefore, before the factory shipment, the light source 17 of the image sensor 14 is turned off, and the average value of the dark signal level Vd of the prescribed pixel is calculated for each chip. The result is stored in the NVRAM 34 as the dark signal level Vd of the chip. Since it is an average value for each chip, the data amount is smaller than storing all the pixels. Also, it is more accurate for each pixel than storing the average value of all pixels.

  Further, the stored dark signal level Vd is not necessarily required for all chips (chips # 1 to # 12 in this embodiment). That is, it is only necessary to store the dark signal level Vd only for a chip that is likely to pass under the origin identification mark used for detecting the home position P. Therefore, in this embodiment, only the dark signal level Vd for the chips # 1 and # 2 is stored.

  Hereinafter, the procedure of the document reading operation will be described with reference to the flowchart of FIG. When the start of document reading is instructed, the dark signal level Vd is first acquired from the NVRAM 34 (S101). At this time, the NVRAM 34 stores only the dark signal levels Vd of the chips # 1 and # 2 that are the detection targets of the origin identification mark, and the dark signal levels of the other chips are not acquired.

  Next, the image sensor 14 is moved to the home position P (S102). In the processing of S102, the image sensor 14 is moved upstream or downstream in the sub-scanning direction, and black and white are determined depending on whether or not the outputs of the chips # 1 and # 2 exceed a predetermined black and white determination threshold Vs. In this monochrome determination, a voltage based on the dark signal level Vd corresponding to each chip is output. That is, the difference between the actual output voltage and the dark signal level is used as an output value, and the output value is compared with the monochrome determination threshold value Vs. Thus, by subtracting the dark signal level Vd from the actual output voltage, it is possible to avoid the influence of variations in the dark signal level Vd. Therefore, as shown in FIG. 7, the white output value and the black output value are stabilized, and the black and white discrimination threshold Vs for black and white discrimination is easily set. After the origin identification mark is detected, the image sensor 14 is moved to the home position P with reference to the position of the origin detection mark.

  Next, the dark signal level Vd is acquired again (S103). In the process of S103, the image sensor 14 is moved to the white reference unit 21, the light source 17 is turned off, and the dark signal level Vd is acquired by actually measuring the output of the image sensor 14. In the process of S103, the dark signal level Vd is obtained for the chips # 3 to # 12 that are not stored in the NVRAM 34. As a result, the dark signal level Vd for the entire region in the main scanning direction is acquired again. For the dark signal level Vd, an average value of the dark signal levels Vd of the prescribed pixels is calculated for each chip.

  This reacquisition of the dark signal level Vd is preferably performed even if the dark signal levels Vd for the chips # 3 to # 12 are stored in the NVRAM 34 in advance. That is, when acquiring the dark signal level Vd before the factory shipment, the image sensor 14 is not necessarily in the same position. For example, it may be located at the home position P or may be located under the FB glass 8. That is, in a strict sense, the dark signal level Vd is not always accurate. Therefore, by re-acquiring the dark signal level Vd under the white reference portion 21, a correction process described later can be performed with higher accuracy.

  Thereafter, various correction processes are performed based on the newly acquired dark signal level Vd (S104). Examples of correction processing include black level correction, shading correction, and gamma correction.

  Next, conveyance of the image sensor 14 for image reading is started (S105). Then, the image of the original is read (S106). That is, in the case of the ADF method, the image sensor 14 is moved to below the ADF glass 9 and fixed. Then, the image of the document conveyed by the ADF 11 is read. On the other hand, in the case of the FB method, the image sensor 14 is moved to below the FB glass 8 and further moved at a predetermined speed toward the downstream side. Then, the image of the document placed on the FB glass 8 is read while moving.

  Thereafter, it is determined whether or not the image reading is completed (S107). If the image reading is completed (S107: YES), the image sensor 14 is moved to the home position P again (S108). After the process of S108 ends, the image reading process ends.

  As described above in detail, the scanner unit 3 according to the present embodiment acquires the dark signal level Vd unique to the image sensor 14 from the NVRAM 34 before moving to the home position P. The image sensor 14 performs black and white discrimination based on a voltage value obtained by subtracting the dark signal level Vd as an offset value from the output voltage value. That is, the black and white discrimination is performed based on the accurate voltage value necessary for the black and white discrimination. As a result, the influence of variations in the dark signal level Vd can be avoided, and the image sensor 14 can be moved to the home position P with high accuracy. Therefore, an image reading apparatus that can appropriately move the image sensor to the home position P is realized.

  The scanner unit 3 stores only the dark signal level Vd of the chips # 1 and # 2 among the chips # 1 to # 12. That is, the minimum dark signal level Vd necessary for detecting the origin identification mark is stored, and the capacity of the NVRAM 34 can be reduced.

  Further, after detecting the home position P, the scanner unit 3 acquires the actual dark signal level Vd for each of the chips # 3 to # 12 in the document reading surface. Thus, the image correction process can be performed more appropriately based on the actual dark signal level Vd at the current time. Further, since the dark signal level Vd is acquired for each chip, it is possible to perform correction in consideration of the variation for each chip. Therefore, it contributes to high accuracy of the correction process.

  The origin identification mark is located outside the original reading surface, that is, outside the FB glass 8 or ADF glass 9. Therefore, it is not easily affected by outside light. As a result, the origin identification mark can be detected with high accuracy.

[Scanning operation of scanner unit (second embodiment)]
Next, a procedure different from the first embodiment described above for the document reading operation of the scanner unit 3 will be described with reference to the flowchart of FIG. In this embodiment, an arbitrary dark signal level Vd is set in advance. This is different from the first embodiment in which the dark signal level Vd based on the actual measurement value is stored for each chip of the image sensor 14.

  When an instruction to start document reading is given, first, the light source 17 of the image sensor 14 is turned off, and the output Vd of the image sensor 14 is measured (S201). At this time, the chips to be measured are not necessarily required for all chips (in this embodiment, chips # 1 to # 12). That is, it is only necessary to measure at least a chip that may pass under the origin identification mark used for detecting the home position P. Therefore, in this embodiment, the output is actually measured only for the chips # 1 and # 2.

  Next, it is determined whether or not the acquired actual measurement value Vd is smaller than the maximum specification value Vdmax of the image sensor 14 (S202). If Vd is smaller than Vdmax (S202: YES), the acquired Vd value is set as the dark signal level Vd (S203). On the other hand, if Vd is not smaller than Vdmax (S202: NO), a predetermined arbitrary Vd value is set as the dark signal level Vd (S204).

  That is, if the image sensor 14 is positioned below the FB glass 8 at the start of the document reading operation, it is easily affected by external light irradiation. And, under the influence of external light irradiation, accurate dark signal level measurement becomes difficult. Therefore, when the actual measurement value Vd becomes equal to or greater than the maximum specification value Vdmax, an arbitrary Vd value is set to the dark signal level. As a result, an outline operation is possible, and erroneous determination of black and white determination can be avoided.

  Thereafter, the image sensor 14 is moved to the home position P (S205). Then, the dark signal level Vd is obtained again (S206), and various correction processes are performed based on the dark signal level Vd (S207). Thereafter, conveyance of the image sensor 14 is started (S208), and an image of the document is read (S209). When the reading of the document is completed (S210: NO), the image sensor 14 is moved to the home position P and this process is terminated (S211). The processing from S205 to S211 is the same as the processing from S102 to S108 in the first embodiment.

  In the document reading operation of the second mode, compared to the first mode, there is no step of acquiring the dark signal level Vd for each image sensor 14 at the stage before shipment. For this reason, there is little labor at the time of factory shipment. On the other hand, in the first embodiment, since the accurate dark signal level Vd, which is an actual measurement value, is stored for each chip, it is hardly affected by the environment during actual use. In addition, the number of actual measurements of the dark signal level Vd is smaller than that in the second embodiment. Therefore, the operation is simple.

[Image sensor home position detection]
Next, details of the operation of the image sensor 14 when the home position is detected (details of the processing of S102 to S205) will be described with reference to the flowchart of FIG.

  First, the light source 17 of the image sensor 14 is turned off, and the output voltage of the image sensor 14 at the current position is measured (S301). Specifically, in this embodiment, output voltages are actually measured for chips # 1 and # 2. Next, it is determined whether or not the output voltage value is greater than a threshold value (S302). The threshold value is set to a value higher than the resin color level on the inner surface of the housing. Thus, the process of S302 is a determination as to whether or not the image sensor 14 is in the white level region, that is, the white reference portion 21.

  When the output voltage value is equal to or lower than the threshold value (S302: NO), that is, when it is determined that the image sensor 14 is in an area other than the white reference portion 21, the image sensor 14 is roughly moved toward the upstream side in the sub-scanning direction. Move (S303). Then, the output voltage is measured at predetermined time intervals, and the white reference portion 21 is detected (S304). The approximate movement here means movement with a high moving speed and a large output voltage measurement pitch.

  When the white reference portion 21 is detected during the rough movement (S304: YES), or when the output voltage value is smaller than the threshold value in the processing of S302 (S302: YES), that is, the image sensor 14 is in the white reference portion 21. If it is determined, the image sensor 14 is moved in detail toward the downstream side in the sub-scanning direction (S305). Then, the output voltage is measured at predetermined time intervals to detect the black area 22A (S306). The detailed movement here means a movement with a slow moving speed and a small output voltage measurement pitch.

  If the black area 22A is detected during the detailed movement (S306: YES), it can be determined that the position at the time of detection is a white / black boundary. Thereafter, the image sensor 14 is moved to the home position P with reference to the boundary position (S307).

  On the other hand, if the black area 22A is not detected during the detailed movement (S306: NO), or if the white reference portion 21 is not detected during the approximate movement (S304: NO), the boundary cannot be detected. Determination is made and a warning message is displayed on the operation panel 4 (S308). As a warning method, in addition to displaying a message, for example, an error lamp may be turned on, a warning sound may be generated, or data may be transmitted to another information device. After the processing of S308 to S307 is finished, the home position detection processing is finished.

  As described above, by moving the moving direction toward the home position P before the movement of the image sensor 14 is started, there are the following advantages. That is, as in the present embodiment, in the scanner unit 3 not equipped with the home position sensor, it is not possible to know where the current position of the image sensor 14 is relative to the home position P when the home position detection is started. For this reason, there is a method of moving in one direction of the sub-scanning direction and turning back if it cannot be detected. However, with this method, the image sensor 14 hits the end wall in the sub-scanning direction, causing a failure.

  Therefore, before moving the image sensor 14, it is determined in which region the current image sensor 14 is located, and the moving direction of the image sensor 14 is switched according to the result. That is, the moving range of the image sensor 14 in the sub-scanning direction is divided into two parts, the white level region and the other region with the origin identification mark interposed therebetween. Therefore, the direction toward the origin identification mark is determined by the current position. As a result, there is no movement of the image sensor 14 toward the end of the moving range when the home position is detected, and a collision with the side wall of the image sensor 14 can be avoided. As a result, failure can be avoided and product life can be extended.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention is not limited to a multi-function device, and can be applied to any device having a scanner function, such as a copying machine, a scanner, and a FAX.

  In the embodiment, the dark signal level Vd is actually measured before shipment from the factory, but it may be after shipment. If the measurement result is an abnormal value, an arbitrary dark signal level Vd may be set.

1 is a diagram illustrating an appearance of a multifunction machine according to an embodiment. 3 is a cross-sectional view illustrating a configuration of a scanner unit of the multifunction machine. FIG. FIG. 3 is a schematic diagram illustrating a configuration of an upper surface side of a document reading unit. It is the schematic which shows the relationship between an image sensor and an origin identification mark. 1 is a block diagram showing an electrical configuration of a multifunction machine according to an embodiment. 6 is a flowchart illustrating a procedure (first embodiment) of a document reading operation of the scanner unit. It is a graph which shows the image of the black-and-white discrimination threshold concerning an embodiment. 10 is a flowchart illustrating a procedure (second embodiment) of a document reading operation of the scanner unit. It is a flowchart which shows the home position detection procedure of an image sensor. It is a graph which shows the image of the black-and-white discrimination threshold concerning the conventional form.

Explanation of symbols

2 Main unit 3 Scanner unit 8 Platen glass (FB glass)
9 Platen glass (ADF glass)
14 Image sensor 20 Origin identification part 21 White reference part (origin identification mark)
22A Black area (origin identification mark)
34 NVRAM
100 MFP

Claims (8)

Reading means that moves in the sub-scanning direction and reads an image of the document;
A mark used to detect the home position of the reading means;
An acquisition means for acquiring an offset voltage value;
An image comprising: a moving unit that detects the mark based on a detection value obtained from the offset voltage value and a reading voltage value output from the reading unit, and moves the reading unit to a home position. Reader. The image reading apparatus according to claim 1,
Non-volatile storage means for storing an offset voltage value corresponding to each of the reading means,
The image reading apparatus, wherein the acquisition unit acquires an offset voltage value from the storage unit. The image reading apparatus according to claim 2,
The reading means includes a reading element group in which a plurality of reading elements are arranged in the main scanning direction,
The storage means stores an offset voltage value applied to a reading element whose position in the main scanning direction is included in a range of the mark in the main scanning direction among the reading elements of the reading element group. . The image reading apparatus according to claim 1,
The acquisition unit acquires a reading voltage value when the light source of the reading unit is turned off. When the reading voltage value is within a predetermined range, the acquisition voltage value is set as an offset voltage value; An image reading apparatus characterized in that a stored arbitrary voltage value is used as an offset voltage value. In the image reading device according to any one of claims 1 to 4,
The position of the mark in the main scanning direction is outside the original reading range. The image reading apparatus according to claim 5,
The mark is disposed at least up to an end portion on one end side of the moving range in the sub-scanning direction of the reading unit,
The image reading apparatus characterized in that the moving means switches between moving the reading means to one end side or the other end side in the sub-scanning direction based on the detection value. In the image reading device according to any one of claims 1 to 6,
Measuring means for measuring the offset voltage value within the document reading range;
The moving means moves the reading means to a measurement position of an offset voltage value by the measuring means after detecting the mark. The image reading apparatus according to claim 7,
The image reading apparatus, wherein the measuring means measures an offset voltage value for each of a plurality of reading elements constituting the reading means.

Images