WO2022202097A1 - Image formation device - Google Patents

Abstract

An image formation device (100) includes a sheet conveying unit (5b), an image formation unit (5c), a sheet reading unit (6), a binarization circuit (92), and a control circuit (9). The sheet reading unit (6) includes a lamp (6c) and a line sensor (8). The line sensor (8) reads a conveying sheet and outputs an analog image signal. The binarization circuit (92) receives inputs of a reference voltage and the analog image signal. When a translucent film is conveyed as the conveying sheet, the control circuit inputs, as the reference voltage, a first reference voltage into the binarization circuit (92). The first reference voltage is at a level at which edges of the translucent film can be read.

Description

image forming device

The present invention relates to an image forming apparatus that conveys a sheet to be printed and reads the conveyed sheet.

An image forming apparatus may be provided with an image sensor and a lamp for reading the conveyed sheet. The image sensor performs reading based on the light emitted from the lamp and reflected from the sheet. In some cases, a translucent sheet such as an OHP sheet is conveyed by the image forming apparatus. Since a translucent sheet transmits light, the image sensor may not be able to read the sheet properly. As a result, printing errors may occur. Japanese Patent Application Laid-Open No. 2002-200000 describes an example of an image forming apparatus that determines whether a sheet is a translucent sheet or plain paper in order to prevent printing errors.

Specifically, Japanese Patent Application Laid-Open No. 2002-200000 discloses a first detection unit provided in a recording material conveying path for detecting a conveyed recording material of a first paper type, and a second detection unit provided on the downstream side in the conveying direction for detecting a recording material of a second paper type different from the first paper type; According to the detection result, the paper type of the recording material to be conveyed and whether or not there is an abnormality in the conveyance of the recording material are determined. and the recording material of the second paper type is the other of the transparent recording material and the opaque recording material.

JP 2015-124046 A

A lamp and an image sensor (line sensor) may be installed in the sheet conveying path of the image forming apparatus. The lamp irradiates the sheet being conveyed with light. The image sensor reads the conveyed sheet. The image sensor performs reading based on the light reflected by the sheet. The edge (peripheral edge) of the sheet can be detected from the image data obtained by reading the image sensor. For example, based on the image data, it is possible to recognize the arrival of the leading edge of the sheet to the image sensor.

Here, the image forming apparatus may print on a sheet such as an OHP sheet that allows the light of the lamp to pass through well. Therefore, the edge of the sheet may not be read. In other words, image data may not be generated such that the edges of the sheet are known. When conveying a highly translucent sheet, there is a problem that the edge of the sheet may not be detected based on the image data read by the image sensor.

The device described in Patent Document 1 uses three sensors, a registration sensor, a line sensor, and a transport sensor, to determine whether the sheet is a translucent sheet or plain paper. A large number of sensors is required. Higher manufacturing costs. Furthermore, Patent Document 1 describes a lateral edge detection mode as a mode for detecting the edge of a sheet. However, there is a description of lateral edge detection only for plain paper. Regarding the OHP sheet, there is no description of lateral edge detection. Japanese Patent Application Laid-Open No. 2002-200002 does not describe detecting the edge of a sheet with high translucency using only the image data of the image sensor.

In view of the above problems, the present invention uses a line sensor to generate image data so that the position of the edge of the sheet can be detected when reading the transported translucent film.

An image forming apparatus according to the present invention includes a sheet conveying section, an image forming section, a sheet reading unit, a binarization circuit, and a control circuit. The sheet conveying section conveys the sheet. The image forming section forms an image on a conveying sheet. The sheet reading unit includes lamps and line sensors. The lamp irradiates the conveying sheet with light. The line sensor has a light receiving element, reads the conveying sheet based on the light of the lamp, and outputs an analog image signal. The binarization circuit receives the reference voltage and the analog image signal. Based on the reference voltage and the analog image signal, the binarization circuit binarizes the analog image signal. Based on the conveying sheet image data obtained by binarization, the control circuit obtains the position of the edge of the conveying sheet. The sheet reading unit is provided upstream of the image forming unit in the sheet conveying direction. When conveying a translucent film as the conveying sheet, the control circuit inputs a first reference voltage as the reference voltage to the binarization circuit. The first reference voltage is a level at which the edge of the translucent film is read.

According to the present invention, image data can be generated so that the position of the edge of the sheet can be detected when reading the transported translucent film using the line sensor. Sheet arrival and edge position can be accurately detected.

1 is a diagram illustrating an example of a multifunction device according to an embodiment; FIG. 1 is a diagram illustrating an example of a multifunction device according to an embodiment; FIG. 3 is a diagram showing an example of an image forming section according to the embodiment; FIG. 1 is a diagram illustrating an example of a multifunction device according to an embodiment; FIG. 1 is a diagram showing an example of a sheet reading unit according to an embodiment; FIG. FIG. 4 is a diagram showing an example of a registrationless unit according to the embodiment; FIG. 4 is a diagram showing an example of a registrationless unit according to the embodiment; 1 is a diagram illustrating an example of a multifunction device according to an embodiment; FIG. It is a figure explaining an example of the signal processing part which concerns on embodiment. It is a figure explaining an example of the signal processing part which concerns on embodiment. FIG. 10 is a diagram illustrating an example of preparation processing of the sheet reading unit according to the embodiment;

An image forming apparatus according to an embodiment will be described below with reference to FIGS. 1 to 11. FIG. In the following, the image forming apparatus will be described by taking the multifunction machine 100 as an example. The MFP 100 can print and transmit based on image data. Note that the image forming apparatus is not limited to the MFP 100, and may be, for example, a printer. Each element such as configuration and arrangement described in the description of the present embodiment does not limit the scope of the invention and is merely an example of description.

(MFP 100)
A multifunction device 100 according to an embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 and 2 are diagrams showing an example of a multifunction machine 100 according to an embodiment. FIG. 3 is a diagram showing an example of the image forming section 5c according to the embodiment.

As shown in FIG. 1, the MFP 100 includes a control section 1, a storage section 2, an image reading section 3, an operation panel 4, and a printer section 5.

The control unit 1 controls the operation of the MFP 100 . The control unit 1 controls the operation of each unit of the multifunction machine 100 in a job (copying or transmission). The control unit 1 includes a main control circuit 11 , an image data generation circuit 12 , an image processing circuit 13 and a communication circuit 14 . For example, the main control circuit 11 is a CPU. The main control circuit 11 performs job-related processing and calculations. The image data generation circuit 12 includes an A/D conversion circuit. The image data generation circuit 12 processes the analog image signal output by the image reading section 3 after reading the document to generate document image data. The image processing circuit 13 is an integrated circuit (for example, ASIC) for image processing. The image processing circuit 13 performs image processing of document image data.

The communication circuit 14 includes a communication control circuit and a communication memory. The communication memory stores communication software. The communication control circuit controls communication based on communication software. Communication circuitry 14 communicates with computer 200 . For example, computer 200 is a PC or server. Communication circuit 14 receives print data from computer 200 . The control unit 1 causes the printer unit 5 to print based on the received print data (print job). Further, the operation panel 4 accepts destination settings. The control unit 1 causes the communication circuit 14 to transmit the image data based on the reading of the document to the set destination (scan transmission).

The storage unit 2 includes RAM, ROM, and storage. For example, the storage is one or both of HDD and SSD. Based on the programs and data stored in the storage unit 2, the control unit 1 controls each unit. The image reading unit 3 includes a light source and an image sensor. The image reading section 3 reads an original.

The operation panel 4 includes a display panel 41, a touch panel 42, and hard keys 43. The operation panel 4 accepts user settings. The control unit 1 causes the display panel 41 to display a message, a screen for setting, and an image for operation. For example, the operation images are buttons, keys, and tabs. Based on the output of the touch panel 42, the control unit 1 recognizes the operated image for operation. Hard keys 43 include a start key and numeric keys. The touch panel 42 and hard keys 43 accept user's setting operations (job-related operations). For example, it accepts the type of job to be executed and the setting of job setting values. Based on the output of the operation panel 4, the control section 1 recognizes the setting contents.

The printer section 5 includes an engine control section 50, a sheet supply section 5a, a sheet conveying section 5b, an image forming section 5c, an intermediate transfer section 5d, and a fixing section 5e. Based on the print instruction from the control section 1, the engine control section 50 controls the operations of the sheet feeding section 5a, the sheet conveying section 5b, the image forming section 5c, the intermediate transfer section 5d, and the fixing section 5e.

For example, the sheet supply unit 5a includes a sheet cassette 51 that stores the set sheets, and a pickup roller 52 that feeds the sheets. During printing, the engine control unit 50 causes the sheet supply unit 5a to supply sheets. For example, the sheet conveying section 5b includes a motor, a pair of conveying rollers 53, and a conveying guide 54. FIG. A space defined by the transport guide 54 is a path (sheet transport path 54a, space) for transporting the sheet. The engine control section 50 causes the sheet conveying section 5b to convey the sheet fed from the sheet feeding section 5a. A sheet used for printing passes through the sheet conveying path 54a.

The image forming unit 5c forms an image (toner image). As shown in FIGS. 2 and 3, the image forming section 5c includes image forming units for four colors and an exposure device . The MFP 100 includes an image forming unit 55B for forming a black image, an image forming unit 55Y for forming a yellow image, an image forming unit 55C for forming a cyan image, and an image forming unit 55M for forming a magenta image. including. The image forming units 55B to 55M form different colors of toner images. However, the configuration of each image forming unit 55B to 55M is basically the same. Therefore, in the following description, the symbols Bk, Y, C, and M representing colors will be omitted unless otherwise specified.

Each image forming unit includes a photosensitive drum 57, a charging device 58 (charging roller), and a developing device 59 (developing roller). During printing, the engine control unit 50 rotates a drum motor (not shown) to rotate the photosensitive drum 57 . Also, the engine control unit 50 causes the charging device 58 to charge the photosensitive drum 57 . Further, the engine control unit 50 causes the exposure device 56 to expose the photosensitive drum 57 based on the image data. The developing device 59 contains developer including toner. The engine control unit 50 causes the developing device 59 to develop the electrostatic latent image on the photosensitive drum 57 with toner.

The intermediate transfer portion 5d includes an intermediate transfer belt 510, a secondary transfer roller 511, a driving roller 512, primary transfer rollers 513B, 513Y, 513C and 513M, and driven rollers 514 and 515. The axial directions of the rollers of the intermediate transfer portion 5d are parallel. The intermediate transfer belt 510 is endless. The intermediate transfer belt 510 is looped around each roller of the intermediate transfer portion 5d. The intermediate transfer portion 5 d (intermediate transfer belt 510 ) receives the primary transfer of the toner image from the photosensitive drum 57 . Further, the intermediate transfer portion 5d secondarily transfers the toner image onto the sheet.

The fixing section 5e includes a heater 516 and fixing rotary members 517 and 518. The engine control unit 50 causes the fixing rotary members 517 and 518 to heat and press the sheet onto which the toner image has been transferred. The engine control unit 50 causes the fixing unit 5e to fix the toner image. The sheet conveying portion 5b discharges the sheet after fixing to the outside of the machine (discharge tray 519).

(Sheet reading unit 66 and registrationless unit 7)
Next, an example of the sheet reading unit 66 and the registrationless unit 7 according to the embodiment will be described with reference to FIGS. 4 to 8. FIG. FIG. 4 is a diagram showing an example of the multifunction machine 100 according to the embodiment. FIG. 5 is a diagram showing an example of the sheet reading unit 66 according to the embodiment. 6 and 7 are diagrams showing an example of the registrationless unit 7 according to the embodiment. FIG. 8 is a diagram showing an example of the multifunction machine 100 according to the embodiment.

The MFP 100 includes a sheet reading unit 66 and a registrationless unit 7. The sheet reading unit 66 and the registrationless unit 7 are provided in a sheet conveying path (sheet conveying path 54a). The sheet reading unit 66 reads the conveyed sheet. In the following description, the conveyed sheet will be referred to as a conveyed sheet. The sheet reading unit 66 is provided upstream of the image forming section 5c (secondary transfer roller 511) in the sheet conveying direction (see FIG. 2). As shown in FIG. 5, on one surface of the sheet reading unit 66, a transparent plate 6b is attached. The transparent plate 6b is a glass plate or a transparent resin plate. A lamp 6c, a lens 6d, and a line sensor 8 are accommodated in a sealed space formed by the housing 6a and the transparent plate 6b. The sheet reading unit 66 is a CIS scanner unit.

The engine control unit 50 includes an engine control circuit 50a, an engine memory 50b, and a unit control circuit 9. The engine memory 50b stores programs and data for print control. For example, the engine control circuit 50a and the unit control circuit 9 are CPUs. The unit control circuit 9 receives instructions from the engine control circuit 50a and performs predetermined processing. In the MFP 100 , the unit control circuit 9 controls operations of the sheet reading unit 66 and the registrationless unit 7 . Note that the engine control circuit 50a may control the operation of either one of the sheet reading unit 66 and the registrationless unit 7, or both. Further, the main control circuit 11 may control the operation of either one of the sheet reading unit 66 and the registrationless unit 7, or both.

FIG. 5 is a diagram of the sheet conveying path 54a viewed from the main scanning direction (the direction perpendicular to the sheet conveying direction). The main scanning direction is the direction in which the line sensor 8 scans (reads). The main scanning direction is also the direction in which the light receiving elements (pixels, photoelectric conversion elements) of the line sensor 8 are arranged. During a print job, the unit control circuit 9 turns on the lamp 6c. FIG. 5 shows an example in which the sheet reading unit 66 includes two lamps 6c. The lamp 6c emits light along the main scanning direction. For example, lamp 6c includes an LED.

The line sensor 8 includes a plurality of light receiving elements. Pixels are arranged in the main scanning direction. Light emitted from the lamp 6c and reflected by the document enters each pixel of the line sensor 8 through the lens 6d. When conveying a sheet (during a print job), the unit control circuit 9 causes the line sensor 8 to read. The reading width of the line sensor 8 is narrower than that of a standard printable sheet having a maximum width in the main scanning direction.

The line sensor 8 may be divided into multiple blocks. In other words, the line sensor 8 may comprise multiple split line sensors 80 . FIG. 4 shows a line sensor 8 with three blocks (divided line sensor 80). A combination of three read sensors can be used as the line sensor 8 . Note that the number of divided line sensors 80 is not limited to three.

Each divided line sensor 80 includes a plurality of light receiving elements. For convenience, they are referred to as a first divided line sensor 81, a second divided line sensor 82, and a third divided line sensor 83 in order from one side in the main scanning direction (the right side in FIG. 4, the fulcrum shaft 76 side). Each divided line sensor 80 is arranged in a row (one row). As a result, the light receiving elements (pixels) of the divided line sensors 80 are arranged along the main scanning direction.

Here, in the MFP 100, the sheet is conveyed by the central sheet feeding method. The sheet cassette 51 regulates the position of the sheet so that the center of the sheet conveying path 54a in the main scanning direction coincides with the center of the sheet to be conveyed in the main scanning direction. As a result, the sheet conveying portion 5b conveys the sheet so that the center of the sheet conveying path 54a in the main scanning direction coincides with the center of the conveyed sheet in the main scanning direction. A dashed line in FIG. 4 indicates the center of the sheet and the sheet conveying path 54a in the main scanning direction. The third split line sensor 83 is provided at a position for reading the center in the main scanning direction. When a sheet having a maximum width in the main scanning direction is used, the first divided line sensor 81 is provided at a position for reading one edge in the main scanning direction. The second segmented line sensor 82 is arranged between the first segmented line sensor 81 and the third segmented line sensor 83 .

The unit control circuit 9 inputs the trigger signal TR to each divided line sensor 80 . Each split line sensor 80 includes a charge transfer circuit (shift register, transfer CCD). The charge stored in each pixel is transferred to the charge transfer circuit in accordance with the trigger signal TR. A charge transfer circuit converts the charge into a voltage. The cycle of the trigger signal TR is the cycle of one scan.

The multi-function device 100 includes a clock signal generation circuit 90. A clock signal generation circuit 90 generates a read clock signal CLK. The clock signal generation circuit 90 inputs the read clock signal CLK to each divided line sensor 80 . Each divided line sensor 80 outputs an analog image signal A1 for one pixel per read clock signal CLK. The read clock signal CLK has a frequency that allows one divided line sensor 80 to send out all the pixel analog image signals A1 during one period of the trigger signal TR.

A registrationless unit 7 is provided at a position where a pair of registration rollers is provided in a conventional image forming apparatus (see FIG. 2). A conventional registration roller pair stops when the sheet reaches the leading edge. The skew of the sheet is corrected by abutting the sheet against the stopped pair of registration rollers. However, using a pair of registration rollers causes the sheet to pause. Therefore, the registrationless unit 7 conveys the sheet downstream without stopping the sheet. Moreover, the registrationless unit 7 can correct the skew. The registrationless unit 7 is provided upstream in the sheet conveying direction from the image forming section 5c (secondary transfer nip 5n, secondary transfer roller 511) (see FIG. 2). The registrationless unit 7 is provided downstream of the sheet reading unit 66 in the sheet conveying direction.

6 and 7 show an example of the registrationless unit 7. FIG. As shown in FIGS. 6 and 7, the registrationless unit 7 includes a case 71 and a moving plate 7a. A space is provided between the case 71 and the moving plate 7a. In the examples of FIGS. 6 and 7, the case 71 is box-shaped. The moving plate 7a is plate-shaped. Both the case 71 and the moving plate 7a have the main scanning direction as their longitudinal direction. The plane of the moving plate 7a and the bottom surface of the case 71 (the surface on the side of the moving plate 7a) are parallel. FIG. 6 is an example of a diagram of the registrationless unit 7 viewed from the upstream side in the sheet conveying direction in FIG. FIG. 7 is a diagram showing an example of the surface of the case 71 facing the moving plate 7a (illustration of the moving plate 7a is omitted).

The case 71 accommodates the resistless roller pair 72 and the resistless motor 73 . Registrationless roller pair 72 includes a driving roller 74 and a driven roller 75 . The rotation axis of the drive roller 74 and the rotation axis of the driven roller 75 are parallel. The peripheral surface of the driving roller 74 and the peripheral surface of the driven roller 75 are in contact with each other. As shown in FIG. 2, the sheet is conveyed from bottom to top. A conveying sheet enters the nip between the drive roller 74 and the driven roller 75 . Drive of the registrationless motor 73 is transmitted to the drive roller 74 by a plurality of gears. When the registrationless motor 73 is rotated, the registrationless roller pair 72 is rotated. As a result, the conveyed sheet that has entered passes through the nip of the registrationless unit 7 .

A fulcrum shaft 76 (fulcrum, rotating shaft) is provided on the moving plate 7a. One end of the fulcrum shaft 76 is fixed to the moving plate 7a. The fulcrum shaft 76 stands perpendicular to the plane of the moving plate 7a. The fulcrum shaft 76 is inserted into one end of the case 71 in the main scanning direction (the direction perpendicular to the sheet conveying direction). The fulcrum shaft 76 allows the other end of the case 71 (a part of the registrationless unit 7) to swing. The case 71 (part of the registrationless unit 7) can be rotated. That is, as indicated by the solid line arrow in FIG. 4, the other end of the case 71 can be swung downstream or upstream in the sheet conveying direction.

The registrationless unit 7 includes a skew correction mechanism 7b and a misregistration correction mechanism 7c. The skew correcting mechanism 7b moves the other side (moving side) of the case 71 in order to correct the skew of the conveyed sheet. The skew correction mechanism 7b includes a correction motor 7d, a correction belt 7e, and a correction tooth surface member 7f.

For example, the correction motor 7d is a stepping motor. The correction motor 7d is attached to the moving plate 7a. The correction motor 7d can rotate both forward and backward. A first correction gear 7g is provided on the shaft of the correction motor 7d. A corrective tooth surface member 7f (rack teeth) is attached to the surface of the case 71 facing the moving plate 7a. The teeth of the corrective tooth surface member 7f are arranged along the sheet conveying direction. The second correction gear 7h meshes with the correction tooth surface member 7f. The correction belt 7e is wound around the first correction gear 7g and the second correction gear 7h. When the correction motor 7d is rotated, the first correction gear 7g, the correction belt 7e, and the second correction gear 7h are rotated. As a result, the case 71 to which the corrective tooth surface member 7f is attached rotates about the fulcrum shaft 76. As shown in FIG.

The other side of the registrationless unit 7 (case 71, registrationless roller pair 72) can be moved in a direction (sheet conveying direction) perpendicular to the main scanning direction. The amount of movement of the other end of the registrationless unit 7 (case 71) by the skew correction mechanism 7b is about several mm to 5 mm upstream in the transport direction and about 5 mm downstream, centering on the first home position (first reference position). It may be several mm to 5 mm on the side. Details of the first home position will be described later.

The positional deviation correction mechanism 7c includes a deviation correction motor 7i. For example, the deviation correction motor 7i is a stepping motor. The displacement correction motor 7i is attached to the moving plate 7a. The deviation correction motor 7i can rotate both forward and backward. A shift correction gear 7j is provided on the shaft of the shift correction motor 7i. The shift correction gear 7j meshes with a correction tooth surface member 7k (rack teeth) formed on the edge of the moving plate 7a. When the deviation correction motor 7i is rotated, the deviation correction motor 7i and the deviation correction gear 7j are rotated.

As a result, the registrationless unit 7 (moving plate 7a and case 71) moves in the main scanning direction. The displacement amount of the conveying sheet in the main scanning direction is about several millimeters at maximum. The movement range of the registrationless unit 7 in the main scanning direction by the positional deviation correction mechanism 7c is about several mm to 5 mm on one side in the main scanning direction and about 5 mm on the other side around the second home position (second reference position). It may be several mm to 5 mm. For example, the positional deviation correction mechanism 7c can move the registrationless unit 7 by 2 mm to each of the one side and the other side around the second home position.

Next, the first home position will be explained. The first home position is the position (angle) of the case 71 at which the axial direction of the registrationless roller pair 72 and the main scanning direction are parallel. At the first home position, the conveyed sheet is fed in a direction parallel to the sheet conveying direction and perpendicular to the main scanning direction. A first home sensor 9a is provided. The first home sensor 9a is a sensor for adjusting the position of the case 71 (registrationless unit 7) in the rotational direction to the first home position.

For example, a transmissive optical sensor can be used as the first home sensor 9a. In this case, the first home sensor 9a includes a light emitting element and a light receiving element. A gap is provided between the light emitting surface of the light emitting element and the light receiving surface of the light receiving element. The output level (output voltage value) of the light receiving element changes depending on the amount of light received from the light emitting element. The registrationless unit 7 (case 71) is provided with a detection projection 71a. 6 and 7 show an example in which a detection protrusion 71a is provided at the end of the case 71 on the other side (moving side) in the main scanning direction. A first home sensor 9a is provided at a position facing the detection protrusion 71a. When the registrationless unit 7 (case 71) is rotated, the detection protrusion 71a passes through the gap of the first home sensor 9a. The detection protrusion 71a that has entered the gap blocks the optical path from the light emitting element to the light receiving element.

The output of the first home sensor 9a (light receiving element) is input to the unit control circuit 9. The unit control circuit 9 recognizes the output level of the first home sensor 9a (light receiving element). When the correction motor 7d is operated and the output level of the first home sensor 9a reaches the level when the detection protrusion 71a is detected, the unit control circuit 9 causes the registrationless unit 7 (case 71) to move to the first position. 1 home position.

Here, as shown in FIG. 2, the registrationless unit 7 is installed so that the sheet can be removed from the bottom to the top. Therefore, when the correction motor 7d is not excited, the case 71 is lowered by its own weight on the other side in the main scanning direction. When maintaining the case 71 at the first home position, the unit control circuit 9 excites the correction motor 7d. Thereby, the position of the registrationless unit 7 (case 71) is maintained. For example, when the MFP 100 is activated by turning on the main power supply, or when the power saving mode is canceled and the active mode (normal mode) is restored, the unit control circuit 9 causes the registrationless unit 7 (case 71) to move to the first home state. position.

For example, when adjusting to the first home position, the unit control circuit 9 reversely rotates the correction motor 7d from the hanging state of the case 71 to lift the case 71 up. When the output level of the first home sensor 9a reaches the level when the detection protrusion 71a is detected, the unit control circuit 9 stops the rotation of the correction motor 7d, and then rotates it forward. After forward rotation of the correction motor 7d for a predetermined number of pulses, the unit control circuit 9 stops the correction motor 7d. When stopped, the registrationless unit 7 (case 71) becomes the first home position.

The registrationless unit 7 can also be moved in the main scanning direction. Therefore, the second home position is also predetermined. The second home position is the home position of the moving plate 7a (registrationless unit 7) in the main scanning direction. For example, the center position of the moving range of the registrationless unit 7 (moving plate 7a) in the main scanning direction can be set as the second home position. The second home position is a position where the registrationless unit 7 (moving plate 7a) can be moved to one side in the main scanning direction and also to the other side.

A second home sensor 9b is provided to set the registrationless unit 7 (moving plate 7a) to the second home position. A second home sensor 9b can be provided at the other end of the moving plate 7a in the main scanning direction (it may be at one end).

For example, a transmissive optical sensor can be used as the second home sensor 9b. In this case, the second home sensor 9b includes a light emitting element and a light receiving element. A gap is provided between the light emitting surface of the light emitting element and the light receiving surface of the light receiving element. The output level (output voltage value) of the light receiving element changes depending on the amount of light received from the light emitting element.

The second home sensor 9b is provided at a position where the other end of the moving plate 7a enters the gap when the registrationless unit 7 moves to the othermost side. The second home sensor 9b is a sensor for detecting that the registrationless unit 7 (moving plate 7a) has moved to the othermost side in the main scanning direction.

The output of the second home sensor 9b (light receiving element) is input to the unit control circuit 9. The unit control circuit 9 recognizes the output level of the second home sensor 9b (light receiving element). When the registrationless unit 7 (moving plate 7a) is set to the second home position, the unit control circuit 9 operates the displacement correction motor 7i to move the moving plate 7a to the other side in the main scanning direction. When the output level of the second home sensor 9b reaches the level when the end of the moving plate 7a in the main scanning direction is detected, the unit control circuit 9 moves the registrationless unit 7 (moving plate 7a) to the main position by a predetermined distance. It is moved to one side in the main scanning direction toward the central position of the moving range in the scanning direction.

(Signal processing unit 91)
Next, an example of the signal processing unit 91 according to the embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 and 10 are diagrams illustrating an example of the signal processing unit 91 according to the embodiment.

The multi-function device 100 includes a signal processing section 91. The signal processing unit 91 processes the analog image signal A1 output by the line sensor 8 (each divided line sensor 80). Specifically, the signal processing section 91 processes and converts the analog image signal A1 output from each division line sensor 80 to generate the conveying sheet image data B1. The value of each pixel of the conveyed sheet image data B1 indicates whether or not the conveyed sheet facing the sheet reading unit 6 has been read. Also, the signal processing unit 91 counts each pixel of the image data for each line.

The signal processing unit 91 includes a binarization circuit 92 and a count circuit 93 . A binarization circuit 92 receives the reference voltage and the analog image signal A1. Based on the reference voltage and the analog image signal A1, the binarization circuit 92 binarizes the analog image signal A1. The conveyed sheet image data B1 is data obtained by converting each pixel analog image signal A1 into a binary signal by a binarization circuit. A binarization circuit 92 generates conveying sheet image data B1. For example, the binarization circuit 92 is a comparator (comparison circuit). For example, the analog image signal A1 is input to the plus input terminal of the comparator. A reference voltage is input to the negative input terminal of the comparator.

Note that the signal processing unit 91 is provided for each divided line sensor 80 . FIG. 10 shows one of a plurality of signal processing units. The circuit configuration of each signal processing unit 91 may be the same. Each pixel analog image signal A1 of the first divided line sensor 81 is input to the first binarization circuit 92 . Each pixel analog image signal A1 of the second split line sensor 82 is input to the second binarization circuit 92 . Each pixel analog image signal A1 of the third divided line sensor 83 is input to the third binarization circuit 92. As shown in FIG. As a result, conveyed sheet image data B1 is generated for each divided line sensor 80 . In the MFP 100 according to this description, three signal processing units 91 are provided.

The voltage value of the analog image signal A1 of the light receiving element (pixel) that read the conveying sheet increases. The larger the voltage value of the analog image signal A1, the brighter the read (whiter, lighter color). On the contrary, the voltage value of the analog image signal A1 becomes small in the portion where there is no conveying sheet or the reflected light of the received sheet is small. The voltage value of the pixel analog image signal A1 that has read the conveying sheet is higher than the voltage value of the pixel analog image signal A1 that has not read the conveying sheet.

When the voltage value of the analog image signal A1 is higher than the reference voltage, the binarization circuit 92 (binarization circuit) outputs first level conveyed sheet image data B1. The first level indicates that the sheet has been read. When the voltage value of the analog image signal A1 is equal to or lower than the reference voltage, the binarization circuit 92 (binarization circuit) outputs conveyed sheet image data B1 of the second level. The second level indicates that the sheet has not been read. The conveying sheet image data B1 is monochrome image data of 1 bit per pixel.

As shown in FIG. 10, the signal processing section 91 also includes a reference voltage generation circuit 94. The reference voltage generation circuit 94 includes a first resistor R1, a capacitor C, and a second resistor R2. One end of the first resistor R1 is connected to the unit control circuit 9 . The other end of the first resistor R1 is connected to one end of the capacitor C and one end of the second resistor R2. The other end of capacitor C is connected to ground. The other end of the second resistor R2 is connected to the negative input terminal of the binarization circuit 92. For example, the unit control circuit 9 inputs a PWM signal. The voltage smoothed by the capacitor C is input to the negative input terminal of the binarization circuit 92 as a reference voltage.

The binarization circuit 92 (comparator) binarizes the analog image signal A1. When the voltage value of the analog image signal A1 is higher than the reference voltage, the binarization circuit 92 outputs first level conveyed sheet image data B1. In this case, the first level is High level. The analog image signal A1 of the light-receiving element that has received a large amount of reflected light from the paper becomes High level. On the other hand, when the voltage value of the analog image signal A1 is equal to or lower than the reference voltage, the binarization circuit 92 outputs conveyed sheet image data B1 of the second level. In this case, the second level is the Low level. The analog image signal A1 of the light-receiving element that has not received the reflected light from the paper becomes Low level.

The output of each binarization circuit 92 is input to the unit control circuit 9. Binary image data (monochrome image data, conveying sheet image data B1) generated by each binarization circuit 92 is input to the unit control circuit 9 . The unit control circuit 9 can recognize which pixel of each divided line sensor 80 is at the first level and which pixel of each divided line sensor 80 is at the second level. The unit control circuit 9 determines the boundary between the pixels of the first level and the pixels of the second level as the position of the edge. Further, based on the conveyed sheet image data B1, for example, the unit control circuit 9 can also recognize (determine) the tilt direction and tilt angle of the conveyed sheet (details will be described later).

In addition, the conveyed sheet image data B1 is input to the count circuit 93 . For example, the count circuit 93 is a circuit (logic filter circuit) using a plurality of logic circuits. The unit control circuit 9 inputs a signal (threshold setting signal E1) indicating a threshold. A threshold setting signal E1 is a signal for setting a threshold.

The count circuit 93 outputs the detection result signal C1. In addition, the count circuit 93 counts the number of continuous first level pixels (continuous number) during one scanning period. When the count value becomes equal to or greater than the threshold (when the number of consecutive sheets becomes equal to or greater than the threshold), the count circuit 93 sets the detection result signal C1 to a level indicating presence of a sheet (for example, High level). While the number of continuations is less than the threshold, the count circuit 93 keeps the detection result signal C1 at a level indicating no sheet (for example, Low level). Note that the count circuit 93 may reset the count value when a pixel of the second level appears during one scanning period.

The detection result signal C1 is input to the unit control circuit 9. The unit control circuit 9 monitors the level of the detection result signal C1. For example, the unit control circuit 9 determines (recognizes) that the leading edge of the sheet has reached the line sensor 8 when the level of the detection result signal C1 reaches a level indicating that there is a sheet. A trigger signal TR is also input to the count circuit 93 . When the trigger signal TR rises or falls, the count circuit 93 resets the count value to zero.

The noise may temporarily increase the analog image signal A1. By making a determination based on the detection result signal C1, even if the voltage value of the analog image signal A1 of some of the light receiving elements temporarily increases due to noise, the unit control circuit 9 determines that the sheet has arrived. Don't misjudge.

(Recognition of Inclination Angle of Conveying Sheet)
Next, an example of recognizing the inclination angle of the conveying sheet based on the conveying sheet image data B1 will be described. First, the signal processing section 91 (counting circuit 93 ) is provided for each divided line sensor 80 . After the level of the detection result signal C1 of a certain count circuit 93 reaches the level indicating that there is a sheet, the unit control circuit 9 sets the level of the detection result signal C1 of another count circuit 93 to the level indicating that there is a sheet. measure the time until For example, the unit control circuit 9 monitors the detection result signals C1 of the two count circuits 93 connected to the split line sensors 80 adjacent in the main scanning direction. Hereinafter, this time measured by the unit control circuit 9 is referred to as measurement time.

(1) The unit control circuit 9 determines that the tilt angle is zero when a plurality of detection result signals C1 simultaneously reach a level indicating that there is a sheet.
(2) The unit control circuit 9 determines that the tilt angle is not zero when the two detection result signals C1 reach a level indicating that there is a sheet at different times.
(a) Direction of Inclination The level of the detection result signal C1 of the count circuit 93 connected to a given divisional line sensor 80 becomes the level indicating the presence of a sheet, and then the divisional line sensor 80 on the other side in the main scanning direction When the detection result signal C1 of the connected count circuit 93 reaches the level indicating the presence of a sheet, the unit control circuit 9 tilts the conveyed sheet so that one corner in the main scanning direction protrudes downstream. recognize that The level of the detection result signal C1 of the count circuit 93 connected to a certain division line sensor 80 becomes the level indicating the existence of the sheet, and then the count circuit 93 connected to the division line sensor 80 on one side in the main scanning direction is turned on. When the detection result signal C1 reaches a level indicating that there is a sheet, the unit control circuit 9 recognizes that the corner of the conveyed sheet on the other side in the main scanning direction is tilted in a direction protruding downstream.
(b) Inclination Angle When the conveying sheet is inclined, the unit control circuit 9 may calculate the arc tangent (tan ⁻¹ ) to obtain the inclination angle. Specifically, the unit control circuit 9 may perform the following calculations.
Inclination angle = tan ^-1 (a/b)
Here, a is the conveying distance of the sheet during the measurement time. For example, the unit control circuit 9 multiplies the measured time by the sheet conveying speed per unit time to obtain a. b is the distance between the two split line sensors 80 in the main scanning direction. The length of the divided line sensor 801 may be set to b. Also, the distance between the center points in the main scanning direction of the two divided line sensors 80 used to measure the measurement time may be set to b.

(c) Correction of Skew During a print job, before the sheet enters the registrationless unit 7 (registrationless roller pair 72), the unit control circuit 9 completes movement from the home position to the correction position. good.

When the corner of the sheet on one side in the main scanning direction (on the fulcrum shaft 76 side) protrudes downstream in the conveying direction, the unit control circuit 9 controls the registrationless unit 7 (case 71) before the leading edge of the conveyed sheet reaches. is moved to the upstream side in the sheet conveying direction. The correction position is the position where the registrationless unit 7 is moved (rotated) by the same angle as the tilt angle from the first home position.

When the corner on the other side (moving side) in the main scanning direction protrudes downstream in the conveying direction, the unit control circuit 9 controls the other side of the registrationless unit 7 (case 71) before the leading edge of the conveyed sheet reaches. The end portion is moved downstream in the sheet conveying direction. The correction position is the position where the registrationless unit 7 is moved (rotated) by the same angle as the tilt angle from the first home position.

When the conveyed sheet enters the registrationless roller pair 72, the unit control circuit 9 moves (returns) the registrationless unit 7 (case 71) from the correction position to the first home position. The unit control circuit 9 completes the movement to the first home position before the conveying sheet reaches the secondary transfer nip 5n. By returning to each home position, it is possible to correct the skew of the conveyed sheet while continuing to convey the sheet.

(Recognition of Positional Deviation Amount of Conveying Sheet in Main Scanning Direction)
Next, an example of recognizing the positional deviation amount of the conveying sheet in the main scanning direction based on the conveying sheet image data B1 will be described. Since central feeding is performed, the ideal position through which the edge of the sheet (the edge in the main scanning direction) passes is determined for each sheet size. In other words, when the position of the conveying sheet is not shifted in the main scanning direction, the positions of the pixels for reading the edge of the sheet are determined. The storage unit 2 stores data (misalignment amount recognition data D1) defining the positions of pixels at the sheet edges when there is no misalignment in the main scanning direction for each sheet size (see FIG. 1).

The unit control circuit 9 obtains the position of the pixel at the end (most side) in the main scanning direction among the first level pixels in the conveying sheet image data B1 as the actual edge position. The actual edge position is the position of the actual edge of the conveying sheet in the main scanning direction. In other words, the actual edge position is the position of the low-density pixel (the pixel whose analog image signal A1 is equal to or lower than the reference voltage) at the edge of the conveying sheet. The unit control circuit 9 recognizes in which direction and by how many pixels the actual edge position is shifted from the position defined by the shift amount recognition data D1. The unit control circuit 9 can recognize the deviation direction (either one side or the other side in the main scanning direction). Also. The unit control circuit 9 multiplies the number of pixels of deviation by the pitch of one pixel of the conveyed sheet image data B1 to obtain the amount of deviation in the main scanning direction.

(1) When the position of the sheet is shifted to one side (fulcrum shaft 76 side) in the main scanning direction Before the conveyed sheet reaches the leading edge, the unit control circuit 9 moves the registrationless unit 7 (moving plate 7a) to the main scanning direction. Move to one side of the direction by the recognized displacement amount.

(2) When the position of the sheet is shifted to the other side (moving side) in the main scanning direction Before the leading edge of the conveyed sheet reaches, the unit control circuit 9 moves the registrationless unit 7 (moving plate 7a) in the main scanning direction. It is moved to the other side by the recognized deviation amount.

After the movement of the moving plate 7a, when the transport sheet enters the registrationless roller pair 72, the unit control circuit 9 moves the registrationless unit 7 (case 71) from the correction position to the second home position. The unit control circuit 9 completes the movement to the second home position before the conveying sheet reaches the secondary transfer nip 5n. By returning to the second home position, it is possible to correct the misalignment in the main scanning direction while continuing to convey the sheet.

(Preparation processing for sheet reading)
Next, an example of preparation processing of the sheet reading unit 6 according to the embodiment will be described with reference to FIG. 11 . FIG. 11 is a diagram showing an example of preparation processing of the sheet reading unit 6 according to the embodiment.

Sometimes printed on a sheet that allows light to pass through. For example, light-transmitting sheets include OHP sheets, silk screen sheets, and backlight films. Such a translucent resin sheet that transmits light is hereinafter referred to as a translucent film. When conveying a translucent film, it may be difficult to detect the edge of the sheet. Therefore, it may not be possible to correctly recognize the tilt angle and the amount of deviation in the main scanning direction. As a result, there is a possibility that the registrationless unit 7 cannot operate correctly when transporting a translucent film. Tilt and misalignment may not be properly corrected. Depending on the case, either one or both of the tilt and deviation may become strong.

If the reference voltage of the binarization circuit 92 is made small, the edge of the translucent film may be detected. However, if the reference voltage is reduced and the range (voltage range) for determining whether there is a sheet is widened, it becomes susceptible to noise. For example, there may be more false edge detections. As a result, inappropriate correction or correction may occur due to erroneous detection of noise.

Also, the toner image is transferred to the sheet based on the detection of sheet arrival based on the line sensor 8 . For example, the transfer to the sheet is started after a predetermined time has passed since the detection result signal C1 reaches a level indicating that the sheet is present. For example, the predetermined time is the time obtained by dividing the distance from the line sensor 8 to the secondary transfer nip 5n by the conveying speed. In other words, the conveyed sheet reading unit 6 also functions as a sensor for detecting arrival of the sheet. If an erroneous detection occurs, it may become difficult to adjust the transfer timing.

Therefore, the unit control circuit 9 adjusts the magnitude of the reference voltage input to the binarization circuit 92 according to the type of conveyed sheet. An example of adjustment of the magnitude of the reference voltage according to the type of conveying sheet will be described below.

The start in FIG. 5 is the time to start the print job. Note that the print job is, for example, a copy job or a print job. First, the unit control circuit 9 determines whether or not the sheet used in the print job is a transparent film (step #1).

Here, the operation panel 4 accepts selection (setting) of the sheet cassette 51 to be used in the print job. Further, the operation panel 4 accepts setting of sheets contained in the sheet cassette 51 to be used. For example, the operation panel 4 accepts setting of sheet type and size. Selectable sheet types include permeable film and paper. That is, the operation panel 4 accepts selection (setting) of the sheet type and size used in the print job. For example, when using a permeable film, the user selects the permeable film as the sheet to be used. When using paper (paper) rather than transmissive film, the user selects the paper. When selecting paper, the operation panel 4 also accepts selection of paper color. That is, the operation panel 4 accepts selection of whether to use a transparent film or paper, and, if paper is used, selection of the color of the paper.

Based on the output of the operation panel 4, the control section 1 recognizes the sheet cassette 51 used in the print job. Further, the control unit 1 recognizes the type and size of sheets used in the print job. The control section 1 notifies the unit control circuit 9 of the recognized sheet type, color, and size. At the time of notification using a transparent film, the unit control circuit 9 determines that the sheet used in the print job is a transparent film. Upon notification of the paper and its color, the unit control circuit 9 determines that the sheet used in the print job is paper, not transmissive film, and its color.

When the sheet used in the print job is a transparent film (Yes in step #1), the unit control circuit 9 inputs the first reference voltage Vref1 as a reference voltage to the binarization circuit 92 (step #2). In other words, the unit control circuit 9 outputs a PWM signal with a duty ratio that makes the reference voltage equal to the first reference voltage Vref1.

The magnitude of the first reference voltage Vref1 is predetermined. The first reference voltage Vref1 is at a level capable of detecting the edge of the translucent film. For example, experiments are performed to determine the magnitude of the first reference voltage Vref1. The analog image signal A1 of the light-receiving element that reads the edge is smaller for the transmissive film than for the paper. Therefore, the first reference voltage Vref1 when conveying a transparent film is smaller than the reference voltage when conveying paper.

When the transparent film is conveyed, the voltage of the analog image signal A1 of the light receiving element that reads the transparent film and its edge is not as large as when it is paper. Also, the potential difference between the analog image signal A1 of the light receiving element that has read the sheet and the analog image signal A1 of the light receiving element that has not read the sheet is not large. When transporting the transparent film, the unit control circuit 9 reduces the reference voltage. As a result, the analog image signal A1 of the light receiving element that has read the edge is binarized to the first level. Specifically, the conveyed sheet image data B1 in which the High level and Low level are switched at the edge portion is generated. It is possible to generate conveying sheet image data B1 in which the edge of the translucent film is known.

When the sheet used in the print job is not a transparent film (No in step #1 when paper), the unit control circuit 9 recognizes the color of the paper (sheet) to be conveyed (step #3). Based on the notification from the controller 1 to the unit control circuit 9, the unit control circuit 9 can recognize the color of the paper. Then, the unit control circuit 9 inputs the second reference voltage Vref2 having a magnitude corresponding to the paper color to the binarization circuit 92 (step #4).

First, the second reference voltage Vref2 is higher than the first reference voltage Vref1. The magnitude of the second reference voltage Vref2 may be fixed regardless of the sheet color. However, in the MFP 100, the unit control circuit 9 changes the magnitude of the second reference voltage Vref2 according to the color of the sheet (paper).

Even if the light intensity of the lamp 6c is the same, the voltage value of the analog image signal A1 obtained by reading the sheet may differ depending on the color of the paper. For example, in a specific color, the voltage value of the analog image signal A1 may become small on average. For example, red paper may have a lower average voltage value of the analog image signal A1 than white, green, blue, or yellow paper. Further, the voltage value of the analog image signal A1 of the light receiving element that has read the gray paper may be even smaller than that for the red paper.

Depending on the magnitude of the second reference voltage Vref2, when reading a red or gray sheet, the pixel value of the light receiving element that has read the sheet may become a value (second level) indicating that the sheet has not been read. be. As a result, there is a possibility that the arrival of the sheet and the actual edge position cannot be detected accurately. Therefore, the unit control circuit 9 changes the magnitude of the second reference voltage Vref2 according to the color of the sheet.

The magnitude of the second reference voltage Vref2 for each color is determined in advance. The magnitude relationship of the second reference voltage Vref2 for each color is also determined in advance. For example, the unit control circuit 9 may set the second reference voltage Vref2 when the color of the paper is white higher than the second reference voltage Vref2 when the color of the paper is gray. For example, the second reference voltage Vref2 for white office paper (plain paper) may be higher than the second reference voltage Vref2 for gray rough paper (straw paper).

In addition, colored (chromatic) paper may be printed. For example, colored paper includes paper for partitions, thick paper for construction, and the like. Colored paper often reflects less light than white paper. Therefore, the unit control circuit 9 may set the second reference voltage Vref2 for white higher than the second reference voltage Vref2 for chromatic paper. For example, the magnitude relationship of the second reference voltage Vref2 may be gray<red<blue=green=yellow<white.

For example, the engine memory 50b stores the second reference voltage value data D2 (see FIG. 8). The second reference voltage value data D2 is data defining the magnitude of the second reference voltage Vref2 for each color and the duty ratio of the PWM signal corresponding to the magnitude. The unit control circuit 9 refers to the second reference voltage value data D2 and generates a second reference voltage Vref2 having a magnitude corresponding to the color.

After step #2 or step #4, the unit control circuit 9 sets the threshold of each count circuit 93 (step #5). In other words, the unit control circuit 9 inputs the threshold setting signal E<b>1 to each count circuit 93 . Specifically, the unit control circuit 9 sets the threshold when the conveying sheet is a translucent film to be higher than the threshold when the conveying sheet is paper. For example, the unit control circuit 9 sets the threshold value for translucent film to a value larger than the threshold value for paper by a predetermined ratio. The predetermined ratio is any value within the range of 10% to 100%.

By step #5, the sheet reading preparation process is completed (end). Subsequently, the engine control unit 50 causes the printer unit 5 to start printing. For example, the engine control unit 50 causes the sheet supply unit 5a to start feeding sheets. Further, the engine control section 50 causes the sheet conveying section 5b to convey the sheet. Further, the engine control section 50 causes the image forming section 5c to form a toner image and transfer the toner image to the conveying sheet. Further, the engine control section 50 causes the fixing section 5e to perform a fixing operation.

Furthermore, the unit control circuit 9 causes the sheet reading unit 6 to read the conveyed sheet. Further, the unit control circuit 9 recognizes the arrival of the leading edge of the sheet to the sheet reading unit 6 and the position of the edge based on the conveyed sheet image data B1. Using the recognition result, the unit control circuit 9 corrects the skew of the sheet and corrects the position in the main scanning direction.

Thus, the image forming apparatus (multifunction machine 100) according to the embodiment includes the sheet conveying section 5b, the image forming section 5c, the sheet reading unit 6, the binarization circuit 92, and the control circuit (unit control circuit 9). Prepare. The sheet conveying portion 5b conveys sheets. The image forming section 5c forms an image on the conveying sheet. The sheet reading unit 6 includes a lamp 6c and a line sensor 8. FIG. The lamp 6c irradiates the conveying sheet with light. The line sensor 8 has a light receiving element, reads the conveyed sheet based on the light from the lamp 6c, and outputs an analog image signal A1. A binarization circuit 92 receives the reference voltage and the analog image signal A1. Based on the reference voltage and the analog image signal A1, the binarization circuit 92 binarizes the analog image signal A1. Based on the conveying sheet image data B1 obtained by binarization, the control circuit obtains the position of the edge of the conveying sheet. The sheet reading unit 6 is provided on the upstream side in the sheet conveying direction of the image forming section 5c. When conveying a translucent film as a conveying sheet, the control circuit inputs the first reference voltage Vref1 to the binarization circuit 92 as a reference voltage. The first reference voltage Vref1 is the level at which the edge of the translucent film is read.

Conveying sheet image data B1 can be obtained by binarizing the analog image signal A1. Then, when the translucent film is transported, the reference voltage can be automatically adjusted to a magnitude suitable for reading the translucent film. As a result, the edge of the translucent film can be read. In other words, it is possible to generate the conveying sheet image data B1 including pixels for which edge positions can be determined. When conveying the translucent film, the edge position can be detected without using a sensor other than the line sensor 8 .

When conveying paper instead of a translucent film as a conveying sheet, the control circuit (unit control circuit 9) inputs the second reference voltage Vref2 to the binarization circuit 92 as a reference voltage. The first reference voltage Vref1 is lower than the second reference voltage Vref2. Paper transmits less light than translucent film. A difference can be provided between the reference voltage for reading the translucent film and the reference voltage for reading the paper. In addition, the edge of the sheet can be read regardless of whether the translucent film or paper is used. Conveying sheet image data B1 can be generated in which the position of the edge of any sheet can be known.

When conveying paper as a conveying sheet, the control circuit changes the magnitude of the second reference voltage Vref2 according to the color of the paper. Depending on the color of the conveyed sheet, the magnitude of the output of the line sensor 8 (analog image signal A1) may differ. The second reference voltage Vref2 can be changed according to the color of the sheet. It is possible to generate conveying sheet image data B1 in which the position of the edge of the conveying sheet can be known regardless of the color of the paper.

The line sensor 8 receives light reflected by the conveying sheet. The control circuit makes the second reference voltage Vref2 when the color of the paper as the conveying sheet is white higher than the second reference voltage Vref2 when the color of the paper as the conveying sheet is gray. In general, white paper reflects light better than gray paper. The magnitude of the analog image signal A1 from the light-receiving element that has read the white paper is on average larger than the magnitude of the analog image signal A1 from the light-receiving element that has read the gray paper. Then, the second reference voltage Vref2 has a magnitude that matches the color of the paper. In other words, the second reference voltage Vref2 can be appropriately set according to the color of the paper.

The line sensor 8 receives light reflected by the conveying sheet. The control circuit makes the second reference voltage Vref2 when the color of the paper as the conveying sheet is white higher than the second reference voltage Vref2 when the color of the paper as the conveying sheet is chromatic. In the case of chromatic paper, even if the amount of light and the distance from the line sensor 8 are the same, the magnitude of the analog image signal A1 from the light receiving element that reads the paper may differ depending on the color. For example, when red paper is read, the average voltage value of the analog image signal A1 may be smaller than when the paper color is green. The second reference voltage Vref2 has a magnitude that matches the color of the paper. In other words, the second reference voltage Vref2 can be appropriately set according to the color of the paper.

The image forming apparatus (multifunction machine 100) is provided with a count circuit 93 to which conveyed sheet image data B1 is input and which outputs a detection result signal C1. When the analog image signal A1 exceeds the reference voltage, the binarization circuit 92 outputs a first level indicating that the sheet has been read. When the analog image signal A1 is below the reference voltage, the binarization circuit 92 outputs a second level indicating that the sheet is not read. The counting circuit 93 counts the number of continuous pixels of the first level for the conveying sheet image data B1. When the number of continuations reaches or exceeds a predetermined threshold value, the count circuit 93 sets the level of the detection result signal C1 to a level indicating presence of a sheet. When the number of continuations is less than the threshold, the count circuit 93 sets the level of the detection result signal C1 to a level indicating no sheet. The control circuit (unit control circuit 9) determines whether the conveyed sheet has reached the sheet reading unit 6 based on the level of the detection result signal C1. Arrival of the sheet to the line sensor 8 (sheet reading unit 6) can be detected. Here, due to noise, some pixels of the conveyed sheet image data B1 may have a value (level) indicating that the sheet has been read even though the sheet has not been read. If it is determined that the sheet has arrived in response to this noise, the timing of the sheet arrival is erroneously detected. When printing based on erroneous detection, the print position of the image is shifted. Since the number of continuous pixels of the first level indicating that the sheet has been read is counted, it is possible to prevent erroneous detection of paper arrival due to noise. It is possible to prevent the occurrence of print position deviation due to noise.

The control circuit makes the threshold when the conveying sheet is a translucent film larger than the threshold when the conveying sheet is paper. If the first reference voltage Vref1 is set so that the translucent film can be read, it may become susceptible to noise. In other words, the pixel values of the pixels of the conveyed sheet image data B1 are likely to be at the first level even though the sheet is not read. Therefore, when transporting the translucent film, the unit control circuit 9 automatically increases the threshold value. This makes it possible to increase the number of continuous pixels of the first level until it is determined that the sheet has reached the sheet. It is possible to prevent erroneous detection of sheet arrival.

Although the embodiment of the present invention has been described above, the scope of the present invention is not limited to this, and various modifications can be made without departing from the gist of the invention. For example, an example in which the line sensor 8 includes three divided line sensors 80 has been described. However, the number of divisions may be two or may be four or more.

The present invention can be used in an image forming apparatus including a sheet reading unit.

Claims (7)

1. a sheet conveying unit that conveys the sheet;
   an image forming unit that forms an image on a conveying sheet;
   a sheet reading unit including: a lamp for irradiating the conveying sheet with light; and a line sensor including a light-receiving element for reading the conveying sheet based on the light of the lamp and outputting an analog image signal;
   a binarization circuit that receives a reference voltage and the analog image signal and binarizes the analog image signal based on the reference voltage and the analog image signal;
   a control circuit for determining the position of the edge of the conveying sheet based on the conveying sheet image data obtained by binarization;
   The sheet reading unit is provided upstream in the sheet conveying direction from the image forming unit,
   When conveying a translucent film as the conveying sheet, the control circuit inputs a first reference voltage to the binarization circuit as the reference voltage,
   The image forming apparatus, wherein the first reference voltage is a level at which an edge of the translucent film is read.
2. When conveying a sheet of paper instead of the translucent film as the conveying sheet, the control circuit inputs a second reference voltage as the reference voltage to the binarization circuit,
   The image forming apparatus according to claim 1, wherein the first reference voltage is lower than the second reference voltage.
3. 3. The image forming apparatus according to claim 2, wherein when paper is conveyed as the conveying sheet, the control circuit changes the magnitude of the second reference voltage according to the color of the paper.
4. The line sensor receives light reflected by the conveying sheet,
   3. The image formation according to claim 2, wherein the control circuit makes the second reference voltage when the color of the paper as the conveying sheet is white higher than the second reference voltage when the color of the paper as the conveying sheet is gray. Device.
5. The line sensor receives light reflected by the conveying sheet,
   3. The image formation according to claim 2, wherein the control circuit makes the second reference voltage when the color of the paper as the conveying sheet is white higher than the second reference voltage when the color of the paper as the conveying sheet is a chromatic color. Device.
6. a counting circuit that receives the conveying sheet image data and outputs a detection result signal;
   The binarization circuit is
   outputting a first level indicating that the sheet has been read when the analog image signal exceeds the reference voltage;
   outputting a second level indicating that the sheet is not read when the analog image signal is equal to or lower than the reference voltage;
   The count circuit
   counting the number of consecutive pixels of the first level for the conveying sheet image data;
   setting the level of the detection result signal to a level indicating presence of a sheet when the number of continuations reaches or exceeds a predetermined threshold;
   when the number of continuations is less than the threshold, the level of the detection result signal is set to a level indicating no sheet;
   2. The image forming apparatus according to claim 1, wherein the control circuit determines whether the conveyed sheet has reached the sheet reading unit based on the level of the detection result signal.
7. The image forming apparatus according to claim 6, wherein the control circuit makes the threshold when the conveying sheet is the translucent film larger than the threshold when the conveying sheet is paper.

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