JP2021035018A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that increases the possibility to be able to detect a leading end of a sheet.SOLUTION: An image forming apparatus 100 comprises: a line sensor 12 that is provided on a conveyance path X1 of a sheet P; and a control unit 16. The control unit 16 detects a leading end E1 of the sheet P in a conveyance direction of the sheet P based on output from the line sensor 12. The line sensor 12 has a first pixel group including pixels in a number (Na) corresponding to a reading width La larger than a sheet size L in a main scanning direction intersecting with the conveyance direction of the sheet P, and the pixels in the first pixel group are arranged side by side to form one line in the main scanning direction. The control unit 12 detects the leading end E1 based on output of a second pixel group including the pixels in the first pixel group in a number (N) corresponding to the sheet size L.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus.

The image forming apparatus described in Patent Document 1 detects the leading edge of paper by using a line sensor having a reading width shorter than the paper size in the main scanning direction intersecting the paper transport direction.

Japanese Unexamined Patent Publication No. 2003-248410

In the image forming apparatus described in Patent Document 1, a line sensor having a short reading width is used. Therefore, when a part of the line sensor is contaminated with a foreign substance such as paper dust, the tip of the paper can be accurately read. The possibility of being undetectable increases. The same applies when the paper is fed diagonally or when a tab is provided at the tip of the paper.

In view of the above problems, an object of the present invention is to provide an image forming apparatus having an increased possibility of detecting the tip of a paper.

The image forming apparatus according to the present invention includes a line sensor provided on a paper transport path and a control unit. The control unit detects the tip of the paper in the transport direction of the paper based on the output of the line sensor. The line sensor has a first pixel group including a number of pixels corresponding to a reading width larger than the paper size in the main scanning direction intersecting the conveying direction of the paper, and the first pixel group is the main scanning. They are lined up so as to form one line in the direction. The control unit detects the tip based on the output of the second pixel group including the number of pixels corresponding to the paper size in the first pixel group.

According to the present invention, it is possible to provide an image forming apparatus having an increased possibility of detecting the tip of a paper.

It is a figure which shows an example of the structure of the image forming apparatus which concerns on embodiment of this invention. It is a top view which shows an example of a line sensor. It is a side view which shows an example of a line sensor. It is a block diagram which shows an example of the control part which a main body part has. It is a flowchart which shows an example of the tip detection processing of a control part. It is a flowchart which shows an example of the both side end detection processing of a control part. It is a flowchart which shows an example of the rear end detection processing of a control part. It is a flowchart which shows an example of the paper presence / absence determination processing of a control part. It is a flowchart which shows an example of the threshold value setting process of a control part.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 9. In the drawings, the same or corresponding parts are designated by the same reference numerals and the description is not repeated. Further, in the figure, X-axis, Y-axis and Z-axis which are orthogonal to each other are shown. The X-axis and Y-axis are parallel to the horizontal plane, and the Z-axis is parallel to the vertical line. The Z-axis positive side may be described as the upper side, the Z-axis negative side as the lower side, the X-axis positive side as the left side, the X-axis negative side as the right side, the Y-axis positive side as the front side, and the Y-axis negative side as the rear side.

The configuration of the image forming apparatus 100 according to the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing an example of the configuration of the image forming apparatus 100. In the present embodiment, the image forming apparatus 100 is a color inkjet recording apparatus.

As shown in FIG. 1, the image forming apparatus 100 includes a main body portion 1, an intermediate portion 3, and a post-processing unit 5. The main body 1 forms an image on the paper P. The intermediate unit 3 relays the paper P from the main body unit 1 to the post-processing unit 5. The post-processing unit 5 performs post-processing on the paper P on which the image is formed, and discharges the paper P.

First, the configuration of the main body 1 will be described. The housing 1a of the main body 1 is provided with a plurality of paper feeding units 11 and an inkjet image forming unit 13. The plurality of paper feeding units 11 are arranged side by side in the vertical direction under the housing 1a, and each has a paper cassette 15 and a feeding device 17. The paper cassette 15 accommodates the paper P. The feeding device 17 feeds the paper P from the paper cassette 15. The image forming unit 13 is arranged above the paper feeding unit 11, and includes a transport belt 19 and four line heads 21. The transport belt 19 circulates so as to transport the paper P. The four line heads 21 are arranged along the traveling direction of the transport belt 19. A paper P carry-out port 23 is formed on the upper part of the side surface of the housing 1a on the side (left side) of the intermediate portion 3.

The housing 1a is formed with a paper P transport path X1 from the feeding device 17 of the paper feeding unit 11 to the carry-out port 23 through the image forming unit 13. The transport path X1 has an inversion path X2 that reverses the front and back of the paper P. The reversing path X2 branches from the transport path X1 on the downstream side of the image forming section 13 in the transport direction, and joins the transport path X1 on the upstream side of the image forming section 13.

A resist roller pair 10 is arranged in the transport path X1 on the upstream side of the image forming unit 13 in the transport direction. The resist roller pair 10 corrects the inclination of the paper P that has come into contact with the resist roller pair 10 and stopped. Then, the resist roller pair 10 temporarily waits for the paper P in order to synchronize the image formation timing with the transfer of the paper P, and then sends the paper P to the image forming unit 13 in accordance with the image forming timing.

The line sensor 12 is arranged on the transport path X1 of the paper P on the downstream side of the resist roller pair 10 and on the upstream side of the image forming unit 13. The line sensor 12 has a plurality of pixels arranged so as to form one line. Each of the plurality of pixels undergoes photoelectric conversion. The line sensor 12 executes imaging for one line in order to acquire the position information of the paper P sent out from the resist roller pair 10. The line sensor 12 is a CIS (Contact Image Sensor) or a CCD (Charge Coupled Device).

Next, the operation of the main body 1 will be described. First, in the paper feeding unit 11, the feeding device 17 feeds the paper P from the paper cassette 15 to the transport path X1. The fed paper P is conveyed along the transfer path X1 and is attracted to the upper surface of the transfer belt 19 at the image forming unit 13. Then, an image is formed on the paper P by the ink discharged from each line head 21 while being conveyed along with the rotation of the conveying belt 19. The line sensor 12 executes front edge detection, both side edge detection, and rear edge detection of the paper P prior to image formation. The image forming unit 13 refers to the output of the line sensor 12 and executes image forming so as not to eject ink to the outside of the paper P and contaminate the transport belt 19.

The paper P on which the image is formed is conveyed by the transfer belt 19 and then discharged from the carry-out port 23. The paper P is discharged from the carry-out port 23 in a posture in which the surface on which the image is formed faces upward. When double-sided printing is performed, the paper P on which an image is formed on one side is conveyed to the reversing path X2, the front and back sides are inverted, and then transported to the transport path X1 and attracted to the upper surface of the transport belt 19. To. Then, an image is formed on the other surface while being transported as the transport belt 19 rotates. The paper P is ejected from the carry-out port 23 with the last printed surface facing upward.

Next, the configuration of the post-processing unit 5 will be described. The post-processing unit 5 selectively performs a perforation process, a staple process, and a center folding process on the paper P. The housing 5a of the post-processing unit 5 is provided with a punching device 25, a staple device 27, and a center folding device 29. The punching device 25 is arranged above the housing 5a, the staple device 27 is arranged below the punching device 25, and the center folding device 29 is arranged below the housing 5a. Of the side surfaces of the housing 5a, a carry-in inlet 31 for receiving the paper P from the intermediate portion 3 is formed on the side surface on the side (right side) of the intermediate portion 3. A first discharge port 33a, a second discharge port 33b, and a third discharge port 33c are formed on the side surface of the housing 5a on the side opposite to the intermediate portion 3 (left side). The first discharge port 33a is formed on the side of the punching device 25, the second discharge port 33b is formed on the side of the staple device 27, and the third discharge port 33c is formed on the side of the center folding device 29. A first discharge tray 35a is provided below the first discharge port 33a, a second discharge tray 35b is provided below the second discharge port 33b, and a third discharge tray 35c is provided below the third discharge port 33c.

The housing 5a is formed with a first transport path Y1, a second transport path Y2, and a third transport path Y3. The first transport path Y1 goes from the carry-in port 31 to the first discharge port 33a through the punching device 25. The second transport path Y2 branches off from the first transport path Y1 on the downstream side of the punching device 25, passes through the staple device 27, and heads for the second discharge port 33b. The third transport path Y3 branches from the second transport path Y2, passes through the center folding device 29, and heads for the third discharge port 33c.

Next, the operation of the post-processing unit 5 will be described. The paper P on which the image is formed by the main body portion 1 is received from the carry-in entrance 31 into the first transport path Y1 via the intermediate portion 3. When the paper P is punched, the paper P is conveyed to the punching device 25 through the first transfer path Y1. The transported paper P is punched by the punching device 25, then discharged from the first discharge port 33a through the first transport path Y1 and loaded on the first discharge tray 35a. When the paper P is stapled, the paper P is transported from the first transport path Y1 to the staple device 27 along the second transport path Y2. The conveyed paper P is stapled by the staple device 27, then discharged from the second discharge port 33b and loaded on the second discharge tray 35b. When the paper P is subjected to the center folding process, the paper P is transported from the first transport path Y1 to the center folding device 29 through the second transport path Y2 and the third transport path Y3. The conveyed paper P is center-folded by the center-folding device 29, then discharged from the third discharge port 33c and loaded on the third discharge tray 35c.

Next, the configuration of the intermediate portion 3 will be described. The intermediate portion 3 is provided separately from the main body portion 1 and the post-processing unit 5, and is connected to each of the main body unit 1 and the post-processing unit 5. While the paper P is relayed from the main body 1 to the post-processing unit 5, the intermediate portion 3 reverses the front and back of the paper P, corrects the position of the paper P in the width direction orthogonal to the transport direction, and decals the paper P. It can be performed.

Of the side surfaces of the housing 3a of the intermediate portion 3, a receiving port 41 for paper P from the main body portion 1 is formed on the side surface (right side) of the main body portion 1. The receiving port 41 is formed at the same height as the carry-out port 23 of the main body 1. Of the side surfaces of the housing 3a, a paper P delivery port 43 is formed on the side surface (left side) of the post-processing unit 5. The delivery port 43 is formed at the same height as the carry-in port 31 of the post-processing unit 5. Further, a discharge tray 47 is formed on the upper surface of the housing 3a.

The housing 3a is formed with a transport path in which the paper P is transported along the transport direction from the receiving port 41 to the delivery port 43. The transport paths include a common path M on which all the paper P is transported, a first reversal path N1 and a second reversal path N2 as parallel paths, and a first correction path C1 and a second correction path as other parallel paths. It has C2. The first reversing path N1 and the second reversing path N2 are parallel paths provided so as to merge with the common path M after branching from the common path M, and the paper P is alternately conveyed. The first correction path C1 and the second correction path C2 are also parallel paths provided so as to join the common path M after branching from the common path M, and the paper P is alternately conveyed.

The common road M is provided with a first branch point D1 and a first confluence point J1 at predetermined intervals along the transport direction. The first reversal path N1 and the second reversal path N2 branch at the first branch point D1 and merge at the first confluence point J1. Further, the common path M is provided with a second branch point D2 and a second confluence J2 on the downstream side of the first confluence J1 in the transport direction with a predetermined interval along the transport direction. The first correction path C1 and the second correction path C2 are branched at the second branch point D2 and merge at the second junction point J2.

Of the common road M, the part from the receiving port 41 to the first branch point D1 is the first common road M1, and the part from the first confluence J1 to the second branch point D2 is the second common road M2 and the second confluence. The portion from J2 to the delivery port 43 is designated as the third common road M3. The first reversing path N1 and the second reversing path N2 are reversing portions that reverse the front and back of the paper P. The first correction path C1 and the second correction path C2 are correction units for correcting the position of the paper P in the width direction.

The first common road M1 extends substantially horizontally to the left from the receiving port 41 and branches into a first reversing road N1 and a second reversing road N2 at the first branch point D1.

The first reversal path N1 has a switchback path N11, an outward path N12, and a return path N13. The outward path N12 conveys the paper P to the switchback path N11. The switchback path N11 reverses the direction in which the paper P is conveyed. The return path N13 conveys the switched back paper P. The outward route N12 extends substantially horizontally to the left from the first branch point D1. Two sets of transport roller pairs 51 are provided on the outward route N12 at predetermined intervals. The switchback path N11 extends horizontally to the left from the exit of the outward path N12, and then slopes diagonally downward to the left. Two sets of transport roller pairs 53 are provided on the switchback path N11 at predetermined intervals. Each of the transport roller pairs 53 can rotate in the forward and reverse directions. The return path N13 extends downward from the entrance / exit P1 of the switchback path N11. A set of transport roller pairs 55 is provided on the return route N13.

The second reversal path N2 has a switchback path N21, an outward path N22, and a return path N23. The outward path N22 conveys the paper P to the switchback path N21. The switchback path N21 reverses the direction in which the paper P is conveyed. The return path N23 carries the switched back paper P. The outward route N22 extends downward from the first branch point D1. A set of transport roller pairs 59 is provided on the outbound route N22. The switchback path N21 extends downward from the entrance / exit P2 of the outward path N22. Two sets of transport roller pairs 57 are provided on the switchback path N21 at predetermined intervals. Each of the transport roller pairs 57 can rotate in the forward and reverse directions. The return route N23 extends to the left from the entrance / exit P2 of the switchback road N21. Two sets of transport roller pairs 61 are provided on the return route N23 at predetermined intervals.

The first reversing path N1 and the second reversing path N2 have the same length. That is, the total length of the switchback path N11, the outward path N12, and the return path N13 of the first reverse path N1 is the same as the total length of the switchback path N21, the outward path N22, and the return path N23 of the second reverse path N2.

Further, the length of the outward path N12 of the first reversal path N1 is longer than the length of the outward path N22 of the second reversal path N2, and the length of the return path N13 of the first reversal path N1 is the return path N23 of the second reversal path N2. It is formed shorter than the length of. As a result, the time when the first sheet P is conveyed to the switchback path N11 of the first reversing path N1 and the time when the second sheet P is conveyed to the switchback path N21 of the second reversing path N2. Will be the same. Further, the time when the first sheet P is conveyed from the first reversing path N1 to the second common path M2 is the time when the second sheet P is conveyed from the second reversing path N2 to the second common path M2. This is earlier than the transfer interval of the paper P from the main body 1 to the first common path M1 by the same time.

The return path N13 of the first reversal path N1 and the return path N23 of the second reversal path N2 meet at the first confluence point J1. The second common road M2 extends downward from the first confluence J1 and then turns back while curving in the upper left direction. The second common road M2 is branched into the first correction road C1 and the second correction road C2 at the second branch point D2.

The first correction path C1 and the second correction path C2 are formed side by side in the vertical direction and extend substantially horizontally. In the first correction path C1 and the second correction path C2, three sets of switching roller pairs 63 and correction roller pairs 65 are provided in order from the upstream side, respectively. The three sets of switching roller pairs 63 and the one set of correction roller pairs 65 are arranged at predetermined intervals along the transport direction. The roller 63a on the upper side of the switching roller pair 63 can move in the vertical direction between the nip position and the nip release position. At the nip position shown by the solid line in FIG. 1, the upper roller 63a sandwiches the paper P together with the lower roller 63b. At the nip release position shown by the broken line in FIG. 1, the upper roller 63a is separated upward from the paper P. The correction roller pair 65 is provided so as to be movable in the width direction intersecting the conveying direction of the paper P.

The first correction path C1 and the second correction path C2 have the same length. Further, the distance between the second branch point D2 and the correction roller pair 65 of the first correction path C1 is formed to be longer than the distance between the second branch point D2 and the correction roller pair 65 of the second correction path C2. Has been done. On the other hand, the distance between the correction roller pair 65 of the first correction path C1 and the second confluence point J2 is formed to be shorter than the distance between the correction roller pair 65 of the second correction path C2 and the second confluence point J2. Has been done. As a result, the time when the tip of the first sheet of paper P conveyed to the first correction path C1 reaches the correction roller pair 65 and the tip of the second sheet of paper P conveyed to the second correction path C2 reach the correction roller. The time to reach vs. 65 is the same. Further, the time when the first sheet P is conveyed from the first correction path C1 to the third common path M3 is the time when the second sheet P is conveyed from the second correction path C2 to the third common path M3. This is earlier than the transfer interval of the paper P from the main body 1 to the first common path M1 by the same time.

The first correction path C1 and the second correction path C2 merge with the third common path M3 at the second confluence point J2. The third common road M3 extends upward from the second confluence J2 and curves to the left toward the delivery port 43.

Further, a first sub-path S1 and a second sub-path S2 are formed in the housing 3a of the intermediate portion 3. Paper P, which does not require inversion, position correction, and post-processing, is conveyed to the first sub-path S1. Paper P, which does not require inversion and position correction and is only post-processed, is conveyed to the second secondary path S2.

The first sub-path S1 branches upward at a third branch point D3 in the middle of the outward path N12 of the first reversal path N1 and extends toward the discharge tray 47. The second sub-path S2 branches at the fourth branch point D4 in the middle of the switchback path N11 of the first reversal path N1 and joins the third common path M3 at the third confluence J3.

Further, warm air type decal portions 71 are provided at seven locations in the intermediate portion 3.

Next, the operation of the intermediate portion 3 will be described. The paper P discharged from the carry-out port 23 of the main body 1 is conveyed to the first common road M1 through the receiving port 41 of the intermediate portion 3. It is assumed that the paper P is continuously conveyed from the main body 1 to the first common road M1 at a predetermined interval.

The first sheet P is conveyed from the first common path M1 to the first reversal path N1 at the first branch point D1. In the first reversing path N1, the transport roller pair 51 of the outward path N12 and the transport roller pair 53 of the switchback path N11 rotate in one direction to transport the paper P from the outward path N12 to the switchback path N11. After that, the transport roller pair 53 of the switchback path N11 rotates in the opposite direction to switch back the paper P. As a result, the front and back sides of the paper P are reversed. The paper P whose front and back sides are reversed is conveyed to the return path N13, and is conveyed from the first reverse path N1 to the second common path M2 at the first confluence point J1 by rotating the transfer roller pair 55 of the return path N13.

The second sheet P branches to the second reversal path N2 at the first branch point D1. In the second reversing path N2, the transport roller pair 59 of the outward path N22 and the transport roller pair 57 of the switchback path N21 rotate in one direction to transport the paper P from the outward path N22 to the switchback path N21. After that, the transport roller pair 57 of the switchback path N21 rotates in the opposite direction to switch back the paper P. As a result, the front and back sides of the paper P are reversed. The paper P whose front and back sides are reversed is conveyed to the return path N23, and is conveyed from the second reverse path N2 to the second common path M2 at the first confluence point J1 by rotating the transfer roller pair 61 of the return path N23.

As described above, the first sheet of paper P conveyed to the first reversing path N1 and the second sheet of paper P conveyed to the second reversing path N2 are the switchback path N11 and the switchback path N21, respectively. Is switched back at the same time. That is, the first reversing path N1 and the second reversing path N2 are formed so as to enable parallel processing in which the switchback operation of the paper P is performed at the same time. Further, the time when the first sheet P is conveyed from the first reversing path N1 to the second common path M2 is the time when the second sheet P is conveyed from the second reversing path N2 to the second common path M2. This is earlier than the transfer interval of the paper P from the main body 1 to the first common path M1 by the same time.

That is, the first sheet P and the second sheet P conveyed from the first common path M1 at a predetermined transfer interval are switched back at the same timing, and then the second common path M2 is conveyed at a predetermined transfer interval. It is designed to be transported to.

The first sheet P is conveyed along the second common path M2, and is conveyed from the second common path M2 to the first correction path C1 at the second branch point D2. In the first correction path C1, first, the rotation is temporarily stopped with the switching roller pair 63 and the correction roller pair 65 sandwiching the paper P. Next, the roller 63a on the upper side of the switching roller pair 63 moves from the nip position to the nip release position. After that, the correction roller pair 65 moves in the width direction based on the result of detecting both ends of the paper P by the line sensor 12 while sandwiching the paper P. For example, when the line sensor 12 detects that the paper P is displaced 1 mm from the reference position to the front side in the width direction, the correction roller pair 65 moves 1 mm to the rear side in the width direction. As a result, the position of the paper P in the width direction is corrected.

After the position of the paper P in the width direction is corrected, the upper roller 63a of the switching roller pair 63 moves from the nip release position to the nip position. After that, the rotation of the switching roller pair 63 and the correction roller pair 65 is restarted, and the position-corrected paper P is conveyed from the first correction path C1 to the third common path M3 at the second confluence point J2.

The second sheet P is conveyed along the second common path M2, and is conveyed from the second common path M2 to the second correction path C2 at the second branch point D2. In the second correction path C2, similarly to the first correction path C1, the correction roller pair 65 sandwiches the paper P and moves in the width direction to correct the position of the paper P in the width direction, and then the switching roller pair 63. The upper roller 63a moves from the nip release position to the nip position. After that, the rotation of the switching roller pair 63 and the correction roller pair 65 is restarted, and the position-corrected paper P is conveyed from the second correction path C2 to the third common path M3 at the second confluence point J2.

The positions of the first sheet P conveyed to the first correction path C1 and the second sheet P conveyed to the second correction path C2 in the width direction of the sheets P are corrected at the same time. That is, the first correction path C1 and the second correction path C2 are formed so as to enable parallel processing in which the position correction in the width direction of the paper P is performed at the same time. The time when the first sheet P is conveyed from the first correction path C1 to the third common path M3 is the time when the second sheet P is conveyed from the second correction path C2 to the third common path M3. This is earlier than the transfer interval of the paper P from the main body 1 to the first common path M1 by the same time.

That is, the first sheet P and the second sheet P conveyed from the second common road M2 at a predetermined transfer interval are corrected in the width direction at the same timing, and then at a predetermined transfer interval. It is designed to be transported to the third common road M3.

The first sheet P is discharged from the delivery port 43 of the housing 3a through the third common road M3 and is received by the carry-in port 31 of the post-processing unit 5. Similarly, the second sheet P is also received from the delivery port 43 to the carry-in port 31 of the post-processing unit 5 through the third common road M3.

The paper P, which does not require any of the reversing process, the correction process, and the post-processing, is conveyed from the first common path M1 to the outward path N12 of the first reversing path N1 at the first branch point D1. The paper P conveyed to the outward path N12 is conveyed from the outward path N12 to the first sub-path S1 at the third branch point D3, and is conveyed along the first sub-path S1. After that, the paper P is discharged from the outlet of the first sub-path S1 and loaded on the discharge tray 47. Further, the paper P which does not require the reversing process and the correction process and only requires the post-processing is conveyed from the first common path M1 to the outward path N12 of the first reversing path N1 at the first branch point D1, and then is a switchback path. It is transported along N11. The paper P conveyed along the switchback path N11 is conveyed from the switchback path N11 to the second sub-path S2 at the fourth branch point D4, and is conveyed to the third common path M3 at the third confluence J3. After that, the paper P is discharged from the delivery port 43 of the housing 3a through the third common road M3 and is received by the carry-in inlet 31 of the post-processing unit 5.

Next, the line sensor 12 will be described in detail with reference to FIGS. 1 to 3. FIG. 2 is a plan view showing an example of the line sensor 12. FIG. 3 is a side view showing an example of the line sensor 12.

As shown in FIGS. 2 and 3, the line sensor 12 includes a light emitting unit 12a and a light receiving unit 12b. The light emitting unit 12a is a light source. The light receiving unit 12b is arranged to face the light emitting unit 12a so as to sandwich the transport path X1 of the paper P.

The transport direction (X-axis direction) of the paper P is the sub-scanning direction, and the direction intersecting the sub-scanning direction (Y-axis direction) is the main scanning direction. The paper P has a rectangular outer shape, and usually the front end E1 and the rear end E4 extend along the main scanning direction, and one side end E2 and the other side end E3 extend along the sub-scanning direction. In the posture, it passes between the light emitting unit 12a and the light receiving unit 12b.

Paper P has a paper size L in the main scanning direction. The line sensor 12 has a reading width La larger than the paper size L, and has a first pixel group including a number (Na) of pixels corresponding to the reading width La. The first pixel group is arranged so as to form one line in the main scanning direction. For the detection of the front end E1 and the rear end E4, the output of the second pixel group including the number (N) of pixels corresponding to the paper size L in the first pixel group is used. The entire output of the first pixel group is used for detecting the side end E2 and the side end E3.

Next, the control unit 16 included in the main body 1 of the image forming apparatus 100 will be described with reference to FIGS. 1 to 4. FIG. 4 is a block diagram showing an example of the control unit 16.

As shown in FIG. 4, the main body unit 1 includes a transfer motor 14, a control unit 16, and a storage unit 18 in addition to the line sensor 12 and the image forming unit 13.

The control unit 16 includes a processor such as a CPU (Central Processing Unit). The storage unit 18 includes a main storage device such as a semiconductor memory and an auxiliary storage device such as a hard disk drive, and stores data and computer programs. The processor of the control unit 16 controls each configuration of the main body unit 1 by executing a computer program stored in the storage unit 18. For example, the control unit 16 controls the rotation of the resist roller pair 10 by driving the transfer motor 14. The line sensor 12 is connected to the control unit 16. The image forming unit 13 is also connected to the control unit 16.

The control unit 16 determines the presence / absence of the paper P according to the result of size comparison between the pixel value obtained from the light receiving unit 12b and the predetermined threshold value TH. The threshold value TH is variable according to the characteristics (thickness and paper quality) of the paper P. The storage unit 18 stores a table 18a showing the correspondence between the characteristics of the paper P and the threshold value TH.

Next, the tip detection process of the control unit 16 will be described with reference to FIGS. 2, 3, 4, and 5. FIG. 5 is a flowchart showing an example of the tip detection process of the control unit 16.

Step S101: The control unit 16 reads out one line data (N pixels) from the second pixel group of the line sensor 12. The control unit 16 has received information indicating the paper size L (for example, “A4 portrait”) in advance. Therefore, the control unit 16 can calculate the number N of pixels constituting the second pixel group. The position of the second pixel group is fixed to, for example, the center position of the first pixel group.

Step S103: The control unit 16 determines whether or not “paper is available” with a predetermined number or more of pixels in the second pixel group. When the number of pixels is a predetermined number or more and the number of pixels is not "paper available" (No in step S103), the process of the control unit 16 returns to step S101. When the number of pixels is a predetermined number or more and "paper is available" (Yes in step S103), the process of the control unit 16 proceeds to step S105.

Step S105: The control unit 16 detects the tip E1 of the paper P in the sub-scanning direction. After that, the control unit 16 ends the tip detection process.

Next, the bilateral end detection processing of the control unit 16 will be described with reference to FIGS. 2, 3, 4, and 6. FIG. 6 is a flowchart showing an example of both side edge detection processing of the control unit 16. The bilateral end detection process starts after the tip detection process is completed.

Step S201: The control unit 16 determines whether or not a predetermined number of lines have been skipped from the line sensor 12. If a predetermined number of lines have not been skipped (No in step S201), the process of the control unit 16 returns to step S201. When a predetermined number of lines are skipped (Yes in step S201), the process of the control unit 16 proceeds to step S203.

Step S203: The control unit 16 reads out one line data (Na pixel) from the first pixel group of the line sensor 12. After that, the process of the control unit 16 proceeds to step S205.

Step S205: The control unit 16 detects one side edge E2 and the other side edge E3 of the paper P in the main scanning direction based on the output of the first pixel group. After that, the control unit 16 ends the bilateral end detection process.

Next, the rear end detection process of the control unit 16 will be described with reference to FIGS. 2, 3, 4, and 7. FIG. 7 is a flowchart showing an example of the rear end detection process of the control unit 16. The rear end detection process starts after the end of both side end detection processes.

Step S301: The control unit 16 reads out one line data (N pixels) from the second pixel group of the line sensor 12.

Step S303: The control unit 16 determines whether or not there is “no paper” in the predetermined number or more of the pixels in the second pixel group. When the number of pixels is a predetermined number or more and the number of pixels is not "no paper" (No in step S303), the process of the control unit 16 returns to step S301. When the number of pixels is a predetermined number or more and there is no paper (Yes in step S303), the process of the control unit 16 proceeds to step S305.

Step S305: The control unit 16 detects the rear end E4 of the paper P in the sub-scanning direction. After that, the control unit 16 ends the rear end detection process.

Next, the paper presence / absence determination process of the control unit 16 will be described with reference to FIGS. 2, 3, 4, and 8. FIG. 8 is a flowchart showing an example of the paper presence / absence determination process of the control unit 16.

Step S401: The control unit 16 determines whether or not the pixel value of the next pixel is larger than the threshold value TH. When the pixel value is larger than the threshold value TH (Yes in step S401), the process of the control unit 16 proceeds to step S403. When the pixel value is not larger than the threshold value TH (No in step S401), the process of the control unit 16 proceeds to step S405.

Step S403: The control unit 16 determines that there is no paper. After that, the process of the control unit 16 proceeds to step S407.

Step S405: The control unit 16 determines that "paper is available". After that, the process of the control unit 16 proceeds to step S407.

Step S407: The control unit 16 checks whether or not the presence or absence of paper has been determined for all the pixels constituting the one-line data. When the target pixel for the paper presence / absence determination remains (No in step S407), the process of the control unit 16 returns to step S401. When the target pixel for the paper presence / absence determination does not remain (Yes in step S407), the paper presence / absence determination process of the control unit 16 ends.

The threshold value TH can be determined from the correspondence of the table 18a according to the characteristics of the paper P. As a result, for example, since the paper P is thin paper, an appropriate threshold value TH can be determined even when a part of the light from the light emitting unit 12a passes through the paper P.

Finally, the threshold value setting process of the control unit 16 will be described with reference to FIGS. 2, 3, 4, and 9. FIG. 9 is a flowchart showing an example of the threshold value setting process of the control unit 16.

Step S501: The control unit 16 acquires the pixel value W1 in the case of “no paper” from the line sensor 12. After that, the process of the control unit 16 proceeds to step S503.

Step S503: The control unit 16 acquires the pixel value W2 in the case of “with paper” from the line sensor 12. After that, the process of the control unit 16 proceeds to step S505.

Step S505: The control unit 16 sets the average value of the pixel value W1 and the pixel value W2 as the threshold value TH in real time. After that, the threshold value setting process of the control unit 16 ends.

According to the embodiment, it is possible to provide an image forming apparatus 100 having an increased possibility of detecting the tip E1 of the paper P. That is, since the tip detection of the paper P is executed based on the output of the second pixel group including the number (N) of pixels corresponding to the paper size L in the main scanning direction, a part of the line sensor 12 is made of paper dust. Even when the paper P is contaminated with such foreign matter, the possibility that the tip E1 of the paper P can be accurately detected increases. The same applies when the paper P is fed diagonally or when a tab is provided at the tip E1 of the paper P.

Further, according to the embodiment, the positional deviation of the paper P in the main scanning direction can be accurately detected by detecting both side edges of the paper P.

Further, according to the embodiment, since the information indicating the accurate supply timing of the paper P to the image forming unit 13 in the case of double-sided printing can be obtained by detecting the front end and the rear end of the paper P, the paper in the reversing path X2 can be obtained. Accurate front-to-back alignment of P can be achieved.

The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to the above-described embodiment, and can be implemented in various aspects without departing from the gist thereof. The drawings are schematically shown mainly for each component for easy understanding, and the thickness, length, number, etc. of each component shown are different from the actual ones for the convenience of drawing creation. In some cases. Further, the shape, dimensions, and the like of each component shown in the above embodiment are merely examples, and are not particularly limited, and various changes can be made without substantially deviating from the configuration of the present invention.

For example, in the embodiment, the image forming apparatus 100 is an inkjet method, but the present invention is not limited to this. The image forming apparatus 100 may be an electrophotographic system.

The present invention can be used in the field of image forming apparatus.

1 Main body 3 Intermediate 5 Post-processing unit 12 Line sensor 12a Light emitting unit 12b Light receiving unit 13 Image forming unit 14 Conveying motor 16 Control unit 18 Storage unit 100 Image forming device E1 Tip E2 Side end E3 Side end E4 Rear end L Paper size La Reading width P Paper TH Threshold X1 Transport path

Claims (7)

A line sensor installed on the paper transport path and
A control unit that detects the tip of the paper in the paper transport direction based on the output of the line sensor is provided.
The line sensor has a first pixel group including a number of pixels corresponding to a reading width larger than the paper size in the main scanning direction intersecting the conveying direction of the paper, and the first pixel group is the main scanning. Arranged so as to form one line in the direction,
The control unit is an image forming apparatus that detects the tip of the first pixel group based on the output of the second pixel group including a number of pixels corresponding to the paper size. The image forming apparatus according to claim 1, wherein the control unit detects the tip when it is determined that paper is present in a predetermined number or more of the pixels in the second pixel group. After the tip is detected, the control unit detects the rear edge of the paper in the transport direction when it is determined that there is no paper in a predetermined number or more of the second pixel group. The image forming apparatus according to claim 1 or 2. The control unit detects both edges of the paper in the main scanning direction based on the output of the first pixel group after the tip is detected, according to any one of claims 1 to 3. The image forming apparatus described. The line sensor is
The light emitting part as a light source and
A light receiving unit is provided so as to face the light emitting unit so as to sandwich the transport path.
The control unit determines whether or not paper is present according to the result of magnitude comparison between the pixel value obtained from the light receiving unit and a predetermined threshold value.
The image forming apparatus according to any one of claims 1 to 4, wherein the threshold value is variable according to the characteristics of the paper. The image forming apparatus according to claim 5, further comprising a storage unit for storing the correspondence between the characteristics of the paper and the threshold value. The image forming apparatus according to claim 5 or 6, wherein the control unit sets an average value of the pixel value when there is no paper and the pixel value when there is paper as the threshold value.

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