JP2014213986A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device in which presence or absence of a gap between sheets conveyed in the image formation device can be accurately determined.SOLUTION: An image formation device 1A comprises pick-up means 22, paper feed means 24, gap detection means 40 and control means 4. The pick-up means 22 picks up a paper from a paper feed cassette 6. The paper feed means 24 feeds the paper picked up by the pick-up means 22. The gap detection means 40 is provided in the paper feed section F1 from the pick-up means 22 to the paper feed means 24 and includes a luminous element 42 and light receiving elements 48. The control means 4 determines presence or absence of a gap between the rear end of a preceding paper P1 and the front end of a subsequent paper P2, based on a changing rate of the output from the light receiving elements 48 which receive light by the luminous element 42.

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus provided with means for determining a gap between sheets conveyed through the image forming apparatus.

  For example, an image forming apparatus described in Patent Document 1 is known as an image forming apparatus provided with a unit that detects the position of a sheet conveyed in the image forming apparatus. The image forming apparatus described in Patent Document 1 will be described below.

  The image forming apparatus described in Patent Document 1 includes an image forming unit that forms a toner image by a known electrophotographic process, and transfers the toner image on a sheet fed from the sheet feeding unit one by one at the transfer unit. An apparatus for forming an image on a sheet. In addition, the image forming apparatus described in Patent Document 1 includes a sheet position detecting unit 515 (see FIG. 23) for specifying the position of the sheet in order to transfer the image onto the sheet with high accuracy.

  The paper position detection unit 515 is provided between the paper feeding unit and the transfer unit. Further, as shown in FIG. 23, the paper position detecting means 515 includes a light emitting element 518-1, a light guide 518-2 for irradiating light from the light emitting element toward the paper P, and a light guide 518 across the paper. -2 and a light receiving element 519 arranged in parallel to the transport direction.

  The paper position detection unit 515 specifies the position of the paper when the light receiving element 519 receives the light from the light emitting element 518-1. Specifically, the light emitted from the light emitting element 518-1 is converted by the light guide 518-1 into light that is parallel to the direction perpendicular to the paper surface of the paper P and directed toward the light receiving element 519. Here, when the paper P exists between the light guide 518-2 and the light receiving element 519, the light from the light emitting element 518-1 is blocked by the paper. Accordingly, the amount of light received by the light receiving element 519 is small, and the output from the light receiving element 519 is small. When the paper P that has blocked the light from the light emitting element 518-1 moves downstream in the transport direction, the light from the light emitting element 518-1 reaches the light receiving element 519 without being blocked by the paper. At this time, the amount of light received increases sequentially from the light receiving element 519 located upstream in the transport direction, and accordingly, the output from the light receiving element 519 also increases. Then, when the output from each light receiving element exceeds a predetermined threshold, the paper position detecting means 515 specifies the position of the edge of the paper.

  By the way, the paper position detection method by the paper position detection means 515 can be used to determine the presence or absence of a gap between the conveyed paper. For example, as shown in FIG. 24, when the leading end of the sheet P1 transported in advance and the leading end of the sheet P2 transported next overlap each other, the sheet P1 and the sheet P2 are not transported. Since there is no gap, the light from the light emitting element 518-1 does not reach the light receiving element 519. On the other hand, as shown in FIG. 25, when there is a gap between the paper P1 and the paper P2, the light passes through the gap and the light reaches the light receiving element 519. As a result, the output from the light receiving element 519 exceeds a predetermined threshold value. Thereby, it can be determined that a gap is generated between the paper P1 and the paper P2.

  However, when the output from the light receiving element 519 exceeds the threshold value, the method of determining the presence or absence of a gap between the paper P1 and the paper P2 has a problem of erroneously determining the presence or absence of a gap when the paper is thin. There is. Specifically, when the paper is thin, the light from the light emitting element 518-1 passes through the paper even if there is no gap between the paper P1 and the paper P2. The output of the light receiving element 519 that has received the light is larger than the threshold value. As a result, although there is no gap between the paper P1 and the paper P2, it is erroneously determined that there is a gap.

JP 2007-3736 A

  An object of the present invention is to provide an image forming apparatus that can accurately determine the presence or absence of a gap between sheets conveyed in the image forming apparatus.

An image forming apparatus according to a first aspect of the present invention includes:
Pick-up means for picking up the paper from the paper placement section;
Paper feeding means for feeding paper picked up by the pick-up means;
A gap detecting means provided in a paper feed section from the pickup means to the paper feed means, including a light emitting element and a light receiving element;
Based on the rate of change of the output from the light receiving element that has received light from the light emitting element, the gap between the trailing edge of the first sheet and the leading edge of the second sheet fed next to the first sheet is determined. Control means for determining presence or absence;
It is characterized by providing.

  The control unit of the image forming apparatus determines the presence or absence of a gap between sheets based on the rate of change in output from the light receiving element that has received light from the light emitting element. Thereby, the control means does not determine that a gap is generated between the sheets only by the large output from the light receiving element. That is, the control means does not erroneously determine that there is a gap between the sheets even when light is transmitted through the sheet and the output from the light receiving element is large. On the other hand, when a gap is generated between the sheets, the output from the light receiving element is changed, so that it is possible to determine that a gap is generated between the sheets.

  According to the present invention, it is possible to accurately determine the presence or absence of a gap between sheets conveyed in the image forming apparatus.

1 is a schematic diagram illustrating an internal structure of an image forming apparatus according to an embodiment. It is explanatory drawing which shows a conveyance part. It is explanatory drawing which shows a clearance gap detection means. It is explanatory drawing when a gap | interval detection means is seen from the arrow v direction of FIG. FIG. 6 is a diagram illustrating a position of a sheet that passes through a conveyance path. FIG. 6 is a diagram illustrating a position of a sheet passing through a conveyance path and a light receiving state. It is a figure explaining the relationship between time passage and the output from a light receiving element. It is a figure explaining the relationship between time passage and the change rate of the output from a light receiving element. FIG. 6 is a diagram illustrating a position of a sheet that passes through a conveyance path. FIG. 6 is a diagram illustrating a position of a sheet passing through a conveyance path and a light receiving state. It is a figure explaining the relationship between time passage and the output from a light receiving element. It is a figure explaining the relationship between time passage and the change rate of the output from a light receiving element. It is a figure explaining the relationship between time passage and the output from a light receiving element. It is a graph which shows the time-dependent change of the light quantity of a light emitting element. It is a block diagram which shows the relationship between a control means and a conveyance part. It is a flowchart regarding operation | movement of the conveyance part relevant to a clearance gap detection means and a clearance gap detection means. 6 is a flowchart relating to light amount correction of a gap detection unit when a paper feed cassette is opened and closed. It is the figure which expanded the most downstream part in the paper feed area of a clearance gap detection means. It is explanatory drawing which shows the clearance gap detection means which concerns on a 1st modification. It is explanatory drawing which shows the clearance gap detection means which concerns on a 2nd modification. It is explanatory drawing when the clearance gap detection means which concerns on a 2nd modification is seen from the arrow v direction of FIG. It is a figure explaining the relationship between time passage and the output from a light receiving element. FIG. 10 is an explanatory diagram showing a paper position detection unit of the same type as the paper position detection unit described in Patent Document 1. FIG. 10 is an explanatory diagram showing a paper position detection unit of the same type as the paper position detection unit described in Patent Document 1. FIG. 10 is an explanatory diagram showing a paper position detection unit of the same type as the paper position detection unit described in Patent Document 1.

(Schematic configuration of image forming apparatus)
Hereinafter, an image forming apparatus 1 as an embodiment will be described with reference to the drawings.

  As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 5 that forms a toner image by a well-known electrophotographic process, and the sheets fed one by one from a sheet feeding cassette 6 via a conveying unit 7. A toner image is transferred onto P by the transfer unit 8. The image forming unit 5 may be a unit that forms a full-color toner image or a unit that forms a monochrome toner image. The full-color toner image may be formed by any of a tandem method, a four-cycle method, and the like. The paper P onto which the toner image has been transferred by the transfer unit 8 is heated and fixed by the fixing unit 9, cooled by the cooling fan 10, and then discharged from the discharge roller pair 11 one by one. Each unit of the image forming apparatus 1 is controlled by the control unit 4.

(Conveyor configuration)
As shown in FIG. 2, the transport unit 7 includes a pickup roller 22 (pickup unit) that picks up the paper from the paper feed cassette 6 (paper mounting unit) on which the paper is placed, and picks up the paper in the transport direction Y. The sheet feeding unit 24 that feeds downstream, the vertical conveyance roller 26 that feeds the sheet fed from the sheet feeding unit 24 toward the transfer unit 8, and the sheet fed from the vertical conveyance roller 26 are stopped immediately before the transfer unit 8. In addition, a timing roller 28 is provided for feeding the paper so that the transfer of the toner image by the transfer unit 8 and the paper passage timing are matched. The paper feeding unit 24 includes a paper feeding roller 30 and a separating roller 32. The paper feeding roller 30 and the separating roller 32 sandwich the paper conveyed from the pickup roller 22 from above and below, so that a plurality of papers overlap. In this state, it is prevented from being conveyed downstream in the conveyance direction Y. Further, the vertical conveying roller 26 is driven independently with respect to the pickup roller 22, the paper feeding roller 30, and the separating roller 32.

  The transport unit 7 further includes a gap detection unit 40, a vertical transport sensor 50, and a timing sensor 52. The gap detection means 40 is a gap between the trailing edge of the preceding sheet P1 (first sheet) picked up by the pickup roller 22 and the leading edge of the succeeding sheet P2 (second sheet) picked up next to the preceding sheet P1. Used to determine the presence or absence of The vertical conveyance sensor 50 is provided on the downstream side in the conveyance direction Y around the vertical conveyance roller 26 and detects the arrival of the sheet at the vertical conveyance roller 26. The timing sensor 52 is provided on the upstream side in the transport direction Y around the timing roller 28 and detects the arrival of the sheet at the timing roller 28.

(Configuration of gap detection means)
As shown in FIG. 3, the gap detection means 40 is provided in a paper feed section F1 from the pickup roller 22 to the paper feed means 24 and an additional section F2 extending from the paper feed section F1 to the downstream side in the transport direction Y by a predetermined distance. It has been. The gap detection means 40 includes a light emitting element 42, a diffusion plate 44, and a plurality of light receiving elements 48 that are arranged in parallel with the transport direction Y. As shown in FIG. 4, the gap detection unit 40 is arranged so that the light from the light emitting element 42 is not blocked by the pickup roller 22 and the sheet feeding unit 24.

  As shown in FIG. 3, the light emitting element 42 is provided above the transport path R of the transported paper in the paper feed section F1. And between the light emitting element 42 and the conveyance path | route R, the diffusion plate 44 which diffuses the light from the light emitting element 42, and irradiates light to the whole area of the paper feeding area F1 and the additional area F2 from the upper direction is conveyed. It is provided substantially parallel to the direction Y. Further, a light receiving element 48 that receives the diffused light is provided below the transport path R.

(Gap discrimination method)
The control means 4 determines whether or not there is a gap between the trailing edge of the preceding paper P1 (first paper) and the leading edge of the following paper P2 (second paper) based on the rate of change in the output of the light receiving element 48. ing. Below, the clearance discrimination method by the control means 4 will be described in detail.

  As shown in FIG. 5, when the trailing edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2 are positioned at the most upstream side of the sheet feeding section F1, that is, at the nip portion U of the pickup roller 22, the rotation of the vertical conveying roller 26 is performed. When the preceding sheet P1 is conveyed downstream in the conveying direction Y, a gap is generated between the trailing edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2, as shown in FIG. At this time, light from the light emitting element 42 enters the light receiving element 48 through the gap via the diffusion plate 44. Thereby, the output from the light receiving element 48 increases. The output from the light receiving element 48 continues to increase until the trailing edge of the preceding paper P1 reaches the most downstream portion D of the additional section F2.

  Here, assuming that the time when the trailing edge of the preceding paper P1 is located at the nip portion U is time T1, and the time when it is located at the most downstream portion D is T2, as shown in FIG. From time T1 to time T2, the output from the light receiving element 48 increases, and then the output becomes constant. Here, in the gap discriminating method by the control means 4, as shown in FIG. 8, a threshold value α is provided for the change of output with respect to time, that is, the rate of change of output. When the output change rate exceeds the threshold value α, the control unit 4 determines that a gap is formed between the trailing edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2. As shown in FIG. 8, the rate of change in output from the light receiving element 48 when the paper type is thick is larger than the rate of change in output when the paper type is thin.

  Next, as shown in FIG. 9, the trailing edge of the preceding sheet P1 and the leading edge of the trailing sheet P2 are located at the most downstream side of the sheet feeding section F1, that is, at the nip portion N of the sheet feeding roller 30 and the separating roller 32. In this case, when the preceding paper P1 is transported downstream in the transport direction Y by the rotation of the vertical transport roller 26, as shown in FIG. 10, in the additional section F2, between the rear end of the paper P1 and the front end of the paper P2. A gap is created. At this time, light from the light emitting element 42 is inserted into the light receiving element 48 through the gap through the diffusion plate 44. Thereby, the output from the light receiving element 48 increases. The output from the light receiving element 48 continues to increase until the trailing edge of the preceding paper P1 reaches the most downstream portion D of the additional section F2.

  Here, the time when the trailing edge of the preceding paper P1 is located at the nip portion U of the pickup roller 22 is defined as time T3, and the time when the trailing edge of the preceding paper P1 is located at the nip portion N of the paper feed roller 30 and the separating roller 32 Assuming that time is time T4 and further that the time when it is located in the most downstream portion D is T5, the output from the light receiving element 48 increases rapidly from time T4 to time T5 as shown in FIG. After that, the output becomes constant. At this time, the rate of change in the output from the light receiving element 48 exceeds the threshold value α from time T4 to time T5, as shown in FIG. Thus, the control unit 4 determines that a gap has occurred between the rear end of the paper P1 and the front end of the paper P2. From time T3 to time T4, although the preceding paper P1 and the succeeding paper P2 are overlapped, the light from the light receiving element 48 slightly increases because the light slightly passes through the paper.

(Calculation method of threshold value α)
The threshold value α is determined in advance as a reference threshold value αs by experiments. For example, as shown in FIG. 13, the output of the light receiving element 48 is 0 before and after a gap is formed between the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2 in the paper feeding section F1 or the additional section F2. Suppose the change from .01A to 0.05A. When the time difference (detection cycle) t1 between the time T6 when 0.01A is recorded and the time T7 when 0.05A is recorded is 0.002 seconds, the threshold value αs can be obtained by the following equation.
αs = (output at time T7−output at time T6) / detection period t1
αs = (0.05−0.01) /0.002
= 20

Further, when the threshold value αs is obtained by experiment, it is assumed that the rotational speed of the drive motor of the vertical conveyance roller 26 that determines the conveyance speed of the paper P1 is 3200 rpm. When the rotational speed of the motor is the reference rotational speed Rs and the rotational speed of the drive motor of the vertical conveying roller 26 is a rotational speed Rx other than 3200 rpm, for example, Rx = 800 rpm, the threshold value α is obtained by the following equation. be able to.
α = rotation speed Rx / reference rotation speed Rs × reference threshold value αs
= 800/3200 × 20
= 5

Furthermore, when determining the threshold value α, it is necessary to correct the threshold value α in consideration of the temporal deterioration of the light emitting element 42. Specifically, as the light emitting element 42 is used repeatedly, the amount of light emission decreases as shown in FIG. Accordingly, when the ratio of the light amount A2 at the usage time T8 to the light amount A1 at the start of use of the light emitting element 42 is a light amount reduction ratio β, the corrected threshold value αc is expressed as follows.
Threshold value αc after correction = light amount A2 / light amount A1 × threshold α
= Light intensity reduction ratio β x threshold value α

(Operation of gap detection means)
As shown in FIG. 15, output data d <b> 1 from the light receiving element 48 of the gap detection unit 40 is transmitted to the CPU 60 in the control unit 4 that controls each part of the image forming apparatus 1. In response to this, the CPU 60 refers to the threshold value α stored in the data storage unit M in the control means 4 to determine whether or not a gap has occurred between the rear end of the paper P1 and the front end of the paper P2. . Based on the determination result, a drive signal d2 to the vertical conveyance motor 62 that drives the vertical conveyance roller 26, and a drive signal d3 to the paper feed motor 64 that drives the pickup roller 22, the paper feed roller 30, and the separating roller 32 are provided. Send. Below, operation | movement of the clearance gap detection means 40 is demonstrated in detail, referring drawings.

  As shown in FIG. 16, in step S <b> 1, the control unit 4 receives a job that uses paper such as a print job or a copy job, and drives the vertical conveyance roller 26. At the same time, the vertical conveyance sensor 50 and the gap detection means 40 are operated.

  In step S2, the control unit 4 drives the pickup roller 22, the paper feed roller 30, and the separating roller 32, and starts conveying the preceding paper P1.

  In step S <b> 3, when the vertical conveyance sensor 50 detects the arrival of the preceding paper P <b> 1, the control unit 4 stops the pickup roller 22, the paper feeding roller 30, and the separating roller 32. Since the vertical conveyance roller 26 continues to be driven, the conveyance of the preceding paper P1 is continued.

  In step S4, the control unit 4 receives the output data d1 sequentially sent from the gap detection unit 40, refers to the threshold value α stored in the data storage unit M, and the trailing edge and the trailing sheet of the preceding sheet P1. It is determined whether or not there is a gap between the tip of P2. If it is determined that a gap has occurred, the process proceeds to step S5.

  In step S5, the control means 4 starts a timer for measuring time t2. The time t2 is based on the time when a gap is generated between the trailing edge of the paper P1 and the leading edge of the paper P2, and the control unit 4 resumes driving of the pickup roller 22, the paper feeding roller 30, and the roller 32. This is the time until determining whether or not to do.

  In step S6, the control means 4 determines whether or not the time t2 has elapsed. If the time t2 has elapsed, the process proceeds to step S7. If the time t2 has not elapsed, the process returns to step S6. In this case, the control means 4 stands by until the time t2 elapses.

  In step S <b> 7, the control unit 4 determines whether or not the preceding paper P <b> 1 that has passed through the vertical conveyance roller 26 is the last paper in the print or copy job. If the preceding paper P1 is not the final paper, the process returns to step 2 to resume driving the pickup roller 22, the paper feed roller 30, and the separating roller 32, and the conveyance of the subsequent paper P2 is started. On the other hand, when the preceding paper P1 is the last paper, the process is finished.

(Identification processing of correlation between light of light emitting element and output from light receiving element)
In the gap detection means 40, processing for identifying the correlation between the light from the light emitting element 42 and the output from the light receiving element 48 is appropriately performed in consideration of the usage status of the light amount from the light emitting element 42. (Hereinafter referred to as light quantity correction). This light quantity correction will be described in detail with reference to the drawings.

  As shown in FIG. 17, when the paper feed cassette 6 is opened, the light quantity correction interruption process starts.

  In step S11, the control unit 4 determines whether or not the paper feed cassette 6 is closed. When the paper feed cassette 6 is closed, the process proceeds to step S12. When the paper feed cassette 6 is closed, no paper is present in the paper feed section F1 and the additional section F2.

  In step S12, the control means 4 commands the operation of the gap detection means 40.

  In step S <b> 13, the control unit 4 acquires output information of the light receiving element 48 that has received the light from the light emitting element 42.

  In step S <b> 14, the control unit 4 performs light amount correction based on the output information of the light receiving element 48. Thus, the process ends.

(effect)
According to the image forming apparatus 1, it is possible to accurately determine the presence or absence of a gap between sheets conveyed in the image forming apparatus 1. Specifically, in the control unit 4 of the image forming apparatus 1, the leading edge of the preceding paper P1 and the leading edge of the succeeding paper P2 based on the rate of change of the output from the light receiving element 48 that has received the light from the light emitting element 42. Whether or not there is a gap is determined. Therefore, in the control means, there is a gap between the preceding paper P1 and the succeeding paper P2 even when light passes through the preceding paper P1 and the following paper P2 and the output from the light receiving element 48 is large. Is not mistakenly identified. On the other hand, when a gap is generated between the preceding paper P1 and the succeeding paper P2, the output from the light receiving element 48 changes. Then, the control means 4 can determine that a gap has occurred between the preceding paper P1 and the succeeding paper P2 when the output change rate exceeds the threshold value α. That is, according to the image forming apparatus 1, it is possible to accurately determine the presence or absence of a gap between the preceding paper P1 and the following paper P2. Based on this determination result, the image forming apparatus 1 can appropriately adjust the conveyance timing of the succeeding sheet P2, and can accurately maintain the sheet interval between the preceding sheet P1 and the following sheet P2. .

  Further, the gap detection means 40 is provided in the additional section F2 in addition to the sheet feeding section F1. As a result, even if there is no gap between the preceding paper P1 and the succeeding paper P2 in the paper feeding section F1, if there is a gap in the additional section F2, the control means 4 The presence or absence of a gap between P1 and the succeeding paper P2 can be determined.

  Further, since the gap detection means 40 is provided in the sheet feeding section F1 and the additional section F2, the interval L1 in which the light receiving element 48 is provided can be widened. Specifically, as shown in FIG. 18, the light receiving elements 48 are provided in parallel to the transport direction Y with a certain interval L1. If the distance L1 is larger than the distance L2 between the position where the gap is generated between the preceding sheet P1 and the succeeding sheet P2 and the most downstream portion of the sheet feeding section F1, it is near the most downstream side of the sheet feeding section F1. When a gap is generated between the preceding paper P1 and the succeeding paper P2, the light receiving element 48 may not be able to receive light incident through the gap. As a result, the control unit 4 may not be able to determine the gap. However, the gap detection means 40 is also provided in the additional section F2 in addition to the sheet feeding section F1. Thus, the light receiving element 48 provided in the additional section F2 can receive the light inserted from the gap between the preceding paper P1 and the succeeding paper P2, and the gap detecting means 40 is the interval at which the light receiving element 48 is provided. Even if L1 is widened, the gap can be detected.

  By the way, the control means 4 of the image forming apparatus 1 corrects the threshold value α for gap determination in consideration of a decrease in the light amount of the light emitting element 42 due to deterioration over time. Therefore, the image forming apparatus 1 can more accurately determine whether there is a gap between the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2.

  Further, the gap detection means 40 performs light amount correction when the paper feed cassette is opened and closed. At this time, there is no sheet in the sheet feeding section F1 and the additional section F2. Therefore, the light from the light emitting element 42 can reach the light receiving element 48 without being blocked by the paper. Thereby, the gap detection means 40 can correct the light amount accurately.

(First modification)
The difference between the image forming apparatus 1 </ b> A as the first modification and the image forming apparatus 1 is the installation angle of the diffusion plate 44 of the gap detection means 40. As shown in FIG. 19, the diffusion plate 44 in the gap detection means 40A of the image forming apparatus 1A is inclined with respect to the paper transport path R. Accordingly, the light from the light emitting element 42 is incident on the sheet passing through the transport path R at an angle. As a result, the path length L3 of the light passing through the paper P becomes longer than when light enters the paper perpendicularly. Accordingly, the diffusion plate 44 is provided to be inclined with respect to the transport path R, so that the amount of light transmitted through the paper P is reduced when the paper P passes through the transport path R. On the other hand, when the sheet is not in the transport path R, the light from the light emitting element 42 reaches the light receiving element 48 without being blocked by the sheet. That is, in the gap detection unit 40A of the image forming apparatus 1A, compared with the gap detection unit 40 of the image forming apparatus 1, the amount of light received by the light receiving element 48 when the light is blocked by the paper is reduced and blocked. The amount of light received in the case of no change does not change. As a result, the rate of change of the output from the light receiving element 48 in the gap detecting unit 40A is larger than the rate of change of the output from the light receiving element 48 in the gap detecting unit 40, and the presence / absence of a gap between sheets is more accurately determined. be able to. The configuration of the image forming apparatus 1A other than the diffusion plate 44 is the same as that of the image forming apparatus 1. FIG. 1 is used as a schematic diagram illustrating the internal structure of the image forming apparatus 1A.

(Second modification)
The difference between the image forming apparatus 1 </ b> B and the image forming apparatus 1, which is the second modification, is the light receiving method of the gap detection unit 40. The light receiving method in the gap detecting means 40 of the image forming apparatus 1 is a so-called transmission type, whereas the light receiving method of the gap detecting means 40B in the image forming apparatus 1B is a so-called reflection as shown in FIGS. It is a type. Therefore, the light receiving element 48 in the gap detection means 40B is provided on the upper side of the transport path R similarly to the light emitting element 42. Here, as shown in FIG. 22, the light output from the light receiving element 48 is all reflected from the light emitting element 42 when there is no gap between the preceding paper P1 and the succeeding paper P2. , Showing a large value. On the other hand, when a gap is generated between the preceding paper P1 and the succeeding paper P2, light leaks from the gap, and the output of the light receiving element 48 decreases. By this change in output, the control means 4 can determine the presence or absence of a gap generated between the preceding paper P1 and the succeeding paper P2. In other words, the image forming apparatus 1B does not erroneously determine that a gap has occurred between the preceding sheet P1 and the succeeding sheet P2 due to the magnitude of the output due to the reflectance of the sheet, and accurately determines the preceding sheet P1 and the following sheet P2. Whether or not there is a gap between them can be determined. The configuration other than the gap detection unit 40 in the image forming apparatus 1B is the same as that of the image forming apparatus 1. In addition, FIG. 1 is used as a schematic diagram illustrating the internal structure of the image forming apparatus 1B.

(Other examples)
The image forming apparatus according to the present invention is not limited to the above embodiment, and can be variously modified within the scope of the gist. For example, the light emitting element 42 and the diffusion plate 44 may be provided below the transport path R, and the light receiving element 48 may be provided above the transport path R. Further, the light receiving element 48 need not be provided in parallel to the diffusion plate 44. That is, it is only necessary that the diffusion plate 44 that receives the light from the light emitting element 42 and the light receiving element 48 face each other across the transport path R. If the gap detection means 40 is also provided in a part of the paper feed section F1, the control means 4 determines the presence or absence of a gap generated between the preceding paper P1 and the succeeding paper P2 in the part. can do.

  As described above, the present invention is useful for an image forming apparatus, and is particularly excellent in that it can accurately determine the presence or absence of a gap between sheets conveyed in the image forming apparatus.

F1 paper feeding section F2 additional section P1 preceding paper (first paper)
P2 trailing paper (second paper)
1, 1A, 1B Image forming apparatus 4 Control means 6 Paper feed cassette (paper placement section)
22 Pickup roller (Pickup means)
24 Paper feed means 40, 40A, 40B Gap detection means 42 Light emitting element 48 Light receiving element

Claims (5)

Pick-up means for picking up the paper from the paper placement section;
Paper feeding means for feeding paper picked up by the pick-up means;
A gap detecting means provided in a paper feed section from the pickup means to the paper feed means, including a light emitting element and a light receiving element;
Based on the rate of change of the output from the light receiving element that has received light from the light emitting element, the gap between the trailing edge of the first sheet and the leading edge of the second sheet fed next to the first sheet is determined. Control means for determining presence or absence;
An image forming apparatus comprising: The gap detecting means is provided in an additional section from the paper feeding means to a predetermined position on the downstream side in the transport direction in addition to the paper feeding section.
The image forming apparatus according to claim 1. In determining the rate of change, using the conveyance speed of the paper and the detection period of the light receiving element as parameters,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. For the determination of the rate of change, using a temporal change in the amount of light emitted from the light emitting element as a parameter,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The process of identifying the correlation between the light from the light emitting element and the output from the light receiving element that has received the light is performed after the paper feed cassette is opened and closed,
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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