JP2010254456A - Paper conveying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate the erroneous determination of a paper jam caused by non-detection of a transparent sheet such as an OHP sheet with a resist sensor. <P>SOLUTION: There is a case where, when the OHP sheet is in a deflected state at a resist roller pair, the resist sensor cannot detect the OHP sheet and a detection signal is not output. Then, when a detection signal is output from the resist sensor, a paper jam determining operation is turned off and paper jam is not determined. In order that a paper jam determination section recognizes that the front end to the rear end of a paper sheet surely passes the resist sensor, the paper jam determining operation is started again at earlier timing than that at which a detection signal is turned off after the rear end of the paper sheet passes the resist sensor. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a sheet conveying apparatus that conveys a recording medium using an intermediate roller and a registration roller, and an image forming apparatus including the sheet conveying apparatus.

  In a sheet conveying apparatus that conveys a sheet stored in a sheet tray toward an image forming unit, a case in which a registration roller that adjusts timing for conveying the sheet to the image forming unit is provided on the upstream side of the image forming unit is generally used. . Further, a registration sensor is disposed on the upstream side of the registration roller, and the registration roller driving unit drives the registration roller in accordance with detection of the sheet by the registration sensor and image formation timing, and feeds the sheet to the image forming unit.

  Here, in order to correct the skew in the main scanning direction orthogonal to the conveyance direction of the sheet conveyed to the registration roller (skew correction), the registration roller driving unit performs predetermined processing after the sheet is detected by the registration sensor. Time does not drive the registration rollers. As a result, the sheet is bent in the conveying direction with its leading edge reaching the registration roller, and skew correction is performed. As the registration roller is driven, the deflection is eliminated and sent to the image forming unit.

  This resist sensor often uses a reflection type photosensor, and has a drawback that it is difficult to detect an OHP sheet when a transparent OHP sheet or the like is conveyed as paper. Therefore, Patent Documents 1 to 4 describe techniques related to this problem.

JP 2006-151564 A JP 2002-068528 A JP 2002-347983 A Japanese Patent No. 395136

  When the OHP sheet reaches the registration roller, deflection occurs due to skew correction. However, when the OHP sheet is bent, a sufficient amount of light emitted from the registration sensor is not reflected due to the transparent material and is detected. Sometimes became unstable. Furthermore, since the range of the detectable angle of the resist sensor with respect to the OHP sheet (the angle of the surface of the OHP sheet intersecting the optical axis of the light emitted from the resist sensor) is very narrow, there is an OHP sheet in front of the resist sensor. Regardless, a situation occurs in which the reflective photosensor cannot detect the OHP sheet.

  The paper detection by the registration sensor may be used for paper jam detection. In this case, there is a possibility that the control unit erroneously determines that the paper jam has occurred due to the deflection of the OHP sheet. The misjudgment of a paper jam has hindered stable continuous paper feeding and reduced productivity.

  The present invention has been made in order to solve the above-described problem, and a paper transport device and an image forming apparatus that eliminate the misjudgment of paper jam due to the fact that the registration sensor cannot detect the presence of the recording medium depending on the type of the transport medium. The object is to provide an apparatus.

  The sheet conveying device according to the first aspect of the present invention includes an intermediate roller that conveys a recording medium, a registration sensor that is disposed downstream of the intermediate roller and that outputs a detection signal while detecting the recording medium, A registration roller disposed on the downstream side of the registration sensor; and a determination unit configured to determine whether the recording medium is jammed based on the presence or absence of a detection signal output from the registration sensor, the determination unit including: A paper jam non-detection period from when the registration sensor outputs the detection signal with the passage of the leading edge of the recording medium until the timing at which the detection signal is not output with the passage of the trailing edge of the recording medium. As described above, during the paper jam non-detection period, the judgment of the paper jam of the recording medium is stopped.

  Conventionally, the detection result of the registration sensor is often used for detecting a paper jam. However, there are cases where the registration sensor cannot detect the recording medium that has been transported accurately. For example, when the recording medium is a transparent sheet and the registration sensor is a sensor that optically detects the presence of the recording medium, such as a reflective photosensor, the transparent sheet has been conveyed and has been bent by the registration roller. Sometimes, the resist sensor cannot detect the transparent sheet because the detectable angle of the resist sensor with respect to the transparent sheet is narrow. If the detection signal is not output from the registration sensor, it may be erroneously determined that a paper jam has occurred even though there is a transparent sheet in front of the registration sensor.

  Therefore, when the registration sensor outputs a detection signal as the leading edge of the recording medium passes (that is, when the registration sensor detects the leading edge of the recording medium), the judging means determines a paper jam non-detection period during which the paper jam is not judged. Thus, when the transparent sheet is bent by the registration roller, the registration sensor cannot detect the transparent sheet and does not output a detection signal, thereby preventing misjudgment of a paper jam. Various types of recording media can be stably and continuously fed.

  According to a second aspect of the present invention, in the paper conveyance device according to the first aspect, the paper jam non-detection period is set in advance according to a length in the conveyance direction of the recording medium and a conveyance speed of the recording medium. The determination means has a measurement means for measuring the time after the registration sensor outputs the detection signal, and immediately after the measurement result by the measurement means reaches the preset time. From this, the judgment of the paper jam of the recording medium is resumed.

  According to this configuration, the paper jam non-detection period is set to a timing earlier than the timing at which the detection signal is not output as the trailing edge of the recording medium passes in front of the registration sensor. Is determined in advance according to the length in the conveyance direction of the recording medium and the conveyance speed of the recording medium. It is possible to recognize that it has passed in front of.

  The invention according to claim 3 is the paper conveying apparatus according to claim 1, wherein the paper jam non-detection period is a time until the registration sensor continues to output the detection signal for a preset time. And the determination unit includes a measurement unit that measures a time during which the detection signal is continuously output, and immediately after the measurement result by the measurement unit reaches the preset time, The judgment of paper jam is resumed.

  According to this configuration, the paper jam non-detection period is set to a timing earlier than the timing at which the detection signal is not output as the trailing edge of the recording medium passes in front of the registration sensor. Is the time until the detection signal continues to be output for a preset time, and when the paper jam non-detection period has passed, the judgment means restarts the paper jam judgment operation, so that the judgment means has the registration sensor from the leading edge to the trailing edge of the recording sensor. It is possible to recognize that the vehicle has passed in front.

  Invention of Claim 4 is a paper conveying apparatus as described in any one of Claims 1-3, Comprising: A transparent sheet is included as the said recording medium made into conveyance object, The said registration sensor is optically said The presence of the recording medium is detected.

  When the registration sensor is a sensor that optically detects a recording medium, the transparent sheet may not be stably detected when the transparent sheet is conveyed as the recording medium. Therefore, when a detection signal is output from the registration sensor, a paper jam detection period in which paper jam is not judged is set to be a non-paper jam detection period, so that the registration sensor cannot detect a transparent sheet and does not output a detection signal. And the transparent sheet can be passed continuously and stably.

  An image forming apparatus according to a fifth aspect of the present invention is an image forming apparatus for forming an image on the paper conveying apparatus according to any one of the first to fourth aspects and a recording medium conveyed by the paper conveying apparatus. Means.

  According to this structure, there exists an effect similar to the invention of Claims 1-3.

  According to the present invention, when the registration sensor outputs a detection signal along with the passage of the leading edge of the recording medium, the judging means sets the paper jam non-detection period during which the paper jam is not judged, so that the transparent sheet is bent by the registration roller. This prevents mis-judgment of a paper jam caused by the registration sensor not detecting a transparent sheet and outputting a detection signal when it enters a state. Various types of recording media can be stably and continuously fed.

  In addition, a paper jam detection period is set to a timing earlier than the timing at which the detection signal is not output as the trailing edge of the recording medium passes in front of the registration sensor, and thereafter, the paper jam determination operation is resumed. The judging means can recognize that the trailing edge from the leading edge of the recording medium has surely passed in front of the registration sensor.

FIG. 3 is a cross-sectional view showing an internal structure of the image forming apparatus. The graph which showed the detection distance and angle characteristic of a resist sensor. The figure shown about the state of a registration roller pair and an OHP sheet. The figure which showed the detection signal from a registration sensor in case an OHP sheet was conveyed. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus. FIG. 4 is a diagram illustrating detection signals output from a registration sensor when an OHP sheet is conveyed and ON / OFF of a paper jam determination operation by a paper jam determination unit. 6 is a flowchart illustrating a flow of a paper jam determination process performed by a paper jam determination unit according to the first exemplary embodiment. 9 is a flowchart illustrating a flow of a paper jam determination process of a paper jam determination unit according to the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 1 according to the present embodiment. In the present embodiment, a color printer provided with a paper transport device according to the present invention will be described as an example of the image forming apparatus 1, but the present invention can be applied to a copying machine, a facsimile machine, a multifunction machine having these functions, and the like. is there.

  The image forming apparatus 1 includes an apparatus main body 200 connected to a personal computer (not shown) or the like directly or via a LAN, and a paper supply unit 130 provided below the apparatus main body 200 and configured to supply paper. including. A front cover 23 is attached to the front side of the apparatus main body 200, and an unillustrated input operation unit for performing an input operation of the output conditions of the paper P is provided on the upper surface of the front cover 23. . The input operation unit is provided with a power key, a start button (not shown), various keys for inputting output conditions, and the like. In addition, a manual feed tray 40 for manually feeding paper is attached to the front surface of the front cover 23 so that the paper can be pulled forward.

  The apparatus main body 200 includes toner containers 900Y, 900M, 900C and 900K, an intermediate transfer unit 92, an image forming unit 93, an exposure unit 94, a fixing unit 97, a casing 90 (main body frame) of the apparatus main body 200, and a top cover 911. And a front cover 23.

  The image forming unit 93 includes a yellow toner container 900Y, a magenta toner container 900M, a cyan toner container 900C, and a black toner container 900K, and developing devices 10Y, 10M, and 10C corresponding to each color of YMCK. 10K.

  The image forming unit 93 is provided with a photosensitive drum 17 that carries toner images of the respective colors. Each photosensitive drum 17 is supplied with yellow, magenta, cyan and black toner from the corresponding toner containers 900Y, 900M, 900C and 900K, respectively. Note that the image forming unit 93 of the present embodiment has a configuration capable of forming a full-color image as described above, but is not limited to this, and forms a monochrome image or a color image that is not full-color. It may be configured.

  Around the photosensitive drum 17, a charger 16, a developing device 10 (10Y, 10M, 10C, and 10K), a transfer roller 19, a cleaning device 18, and the like are disposed. The charger 16 uniformly charges the surface of the photosensitive drum 17. The surface of the photosensitive drum 17 after charging is exposed by the exposure unit 94 to form an electrostatic latent image. The developing devices 10Y, 10M, 10C, and 10K develop the electrostatic latent images formed on the respective photosensitive drums 17 using the toners of the respective colors supplied from the toner containers 900Y, 900M, 900C, and 900K, respectively ( Visualization). The transfer roller 19 forms a nip portion with the photosensitive drum 17 across the intermediate transfer belt 921, and primarily transfers the toner image on the photosensitive drum 17 onto the intermediate transfer belt 921. The cleaning device 18 cleans the peripheral surface of the photosensitive drum 17 after the toner image is transferred.

  The exposure unit 94 includes various optical system devices such as a light source, a polygon mirror, a reflection mirror, and a deflection mirror, and light based on image data is provided on the peripheral surface of the photosensitive drum 17 provided in each of the image forming units 93. To form an electrostatic latent image. The intermediate transfer unit 92 includes an intermediate transfer belt 921, a driving roller 922, a driven roller 923, and a transfer roller 924. On the intermediate transfer belt 921, toner images are primarily transferred from the plurality of photosensitive drums 17 in an overcoated state. The driving roller 922 and the driven roller 923 drive the intermediate transfer belt 921 to rotate. The transfer roller 924 is disposed at a position facing the driving roller 922 and in contact with the surface of the intermediate transfer belt 921. When the paper supplied from the paper supply unit 130 passes through the nip portion between the intermediate transfer belt 921 and the transfer roller 924, the toner image on the intermediate transfer belt 921 is secondarily transferred.

  The fixing unit 97 performs a fixing process on the toner image on the sheet onto which the toner image has been secondarily transferred, and includes a fixing roller 97a having a built-in heat source, and a pressure forming a nip portion with the fixing roller 97a. And a roller 97b. The sheet on which the fixing process has been completed is conveyed toward a discharge roller pair 96 formed on the upper part of the apparatus main body 200. The discharge roller pair 96 discharges the paper conveyed from the fixing unit 97 onto a top cover 911 as a paper discharge tray.

  The paper supply unit 130 is detachably attached to the housing 90 of the apparatus main body 200 and is detachably attached to the front cover 23 of the apparatus main body 200 in the front (rightward in the drawing). And a manual feed tray 40. Between the paper supply unit 130 and the intermediate transfer unit 92, a paper feed conveyance path 24 through which the paper from the paper supply unit 130 is conveyed is provided. The sheet supply unit 130 further includes a sheet feeding device 30 for feeding sheets to the sheet feeding conveyance path 24. The paper feeding device 30 feeds and conveys the paper stored in the paper cassette 41 and the manual paper feeding device 30 </ b> A for feeding the paper placed on the manual tray 40 by the user to the paper feeding and conveying path 24. It comprises a cassette paper feeding device 30B for feeding to the path 24.

  The papers placed on the paper placement surface 42 of the manual feed tray 40 are picked up one by one by the paper feed roller 32 constituting the manual paper feed device 30A and are fed through the intermediate roller pair 29 to the paper feed conveyance path. It goes out to 24. On the other hand, the paper placed on the paper placement surface 43 of the paper cassette 41 is picked up one by one by driving the pickup roller 35 or the like constituting the cassette paper feeding device 30B and passes through the intermediate roller pair 29. The sheet is fed out to the sheet feeding path 24.

  When images are formed on both sides of a sheet, the toner image transferred to one side of the sheet is fixed by the intermediate transfer unit 92 and then the sheet is nipped between the discharge roller pair 96. To do. In this state, the discharge roller pair 96 is reversed to switch back the paper, and the paper is sent to the paper feed path 25 to be transported again to the upstream area of the intermediate transfer unit 92. The intermediate transfer unit 92 has a toner image on the other surface. Form. After the fixing process, the discharge roller pair 96 discharges the paper onto the top cover 911.

  A registration roller pair 27 is disposed on the upstream side of the intermediate transfer unit 92 on the paper feed conveyance path 24, and a registration sensor 28 is disposed on the upstream side of the registration roller pair 27. The registration roller pair 27 is for adjusting the timing at which the sheet is conveyed to the intermediate transfer unit 92. The registration roller pair 27 is rotationally driven by a driving unit (not shown). The driving unit drives the registration roller pair 27 in accordance with the detection of the sheet by the registration sensor 28 and the secondary transfer timing, and feeds the sheet to the intermediate transfer unit 92. . The registration sensor 28 uses a sensor (for example, a reflective photosensor) that optically detects the presence of a sheet, and outputs a detection signal to a control unit described later while the sheet is being detected.

  Here, in order to correct (skew correction) the inclination in the main scanning direction orthogonal to the conveyance direction of the sheet conveyed to the registration roller pair 27, the driving unit of the registration roller pair 27 detects the sheet by the registration sensor 28. Then, the registration roller pair 27 is not driven for a predetermined time. As a result, the paper is bent in the transport direction with the leading edge of the registration roller pair 27 reaching the skew, and skew correction is performed. As the registration roller pair 27 is driven, the deflection is eliminated and the registration roller pair 27 is sent to the intermediate transfer unit 92. During this time, since the sheet exists in front of the registration sensor 28, the registration sensor 28 continues to output a detection signal indicating that the sheet is detected.

  However, in the case of a transparent OHP sheet, there are cases in which it is difficult for the registration sensor 28 to detect the OHP sheet when the OHP sheet is bent by skew correction. FIG. 2 is a graph showing the detection distance and angle characteristics of the registration sensor 28. In FIG. 2, G1 is a black sheet, G2 is a white sheet, and G3 is an OHP sheet. As shown in FIG. 2, since the OHP sheet is transparent, the resist sensor 28 cannot detect the OHP sheet when the inclination of the OHP sheet surface intersecting with the optical axis of the emitted light of the resist sensor 28 exceeds ± 15 °.

  FIG. 3 is a diagram illustrating a state of the registration roller pair 27 and the OHP sheet S. FIG. 4 is a diagram illustrating an example of a detection signal from the registration sensor 28 when the plain paper and the OHP sheet are conveyed. is there. In FIG. 3, the registration roller pair 27 includes a metal roller 27a and a rubber roller 27b. The metal roller 27a is a metal roller, and the rubber roller 27b is a rubber roller. In FIG. 4, a detection signal A is a detection signal when plain paper is conveyed, and a detection signal B is a detection signal when an OHP sheet is conveyed. When the detection signal is high, it indicates that the registration sensor 28 is detecting paper, and when it is low, it indicates that no paper is detected.

  As shown in FIG. 3A, when the OHP sheet S is first conveyed from the paper feeding unit 130, the registration sensor 28 detects the leading edge of the OHP sheet S, and the detection signal B is high as shown in FIG. It becomes a level (time t1). Since the light emitted from the registration sensor 28 is reflected near the cross section of the tip of the OHP sheet S, the registration sensor 28 can detect the tip even if the OHP sheet S is transparent.

  Subsequently, as shown in FIG. 3B, when the OHP sheet S reaches the registration roller pair 27 and is bent, an angle at which the OHP sheet S can be detected by the registration sensor 28 (emitted from the registration sensor 28). The range of the angle of the OHP sheet surface intersecting with the optical axis of the light is very narrow, and the OHP sheet S is transparent, so that the detection of the OHP sheet S by the resist sensor 28 becomes unstable and cannot be detected. That is, as shown in FIG. 4, the detection signal B is at a low level (time t2). Until the registration roller pair 27 is driven, that is, while the OHP sheet S is bent, the registration sensor 28 cannot detect the OHP sheet S even though the OHP sheet S is in front of the registration sensor 28. The detection signal continues to be at a low level.

  Next, as shown in FIG. 3C, when the registration roller pair 27 starts driving, the metal roller 27a rotates so as to bite into the rubber roller 27b. By this bite, the rear end of the OHP sheet S comes close to the registration sensor 28. Thereby, the registration sensor 28 detects the OHP sheet S, and the detection signal becomes high level (time t3). Then, the OHP sheet S passes in front of the registration sensor 28 and the detection signal becomes low level (time t4).

  On the other hand, when the plain paper is conveyed, even if the plain paper is bent as shown in FIG. 3 (b), the range of angles that can be detected by the registration sensor 28 is wide. Since it is not transparent, the registration sensor 28 can detect plain paper stably. Accordingly, the detection signal is at a high level from the time when the plain paper passes in front of the registration sensor 28 to the time when the trailing edge passes (from time t1 to time t4).

  Here, the detection result of the registration sensor 28 is often used for paper jam detection. A control unit described later captures a detection signal output from the registration sensor 28, and determines whether the paper is jammed based on the presence or absence of the detection signal. In this case, while the OHP sheet S is conveyed and is bent by the registration roller pair 27 and the OHP sheet S cannot be detected by the registration sensor 28 (from time t2 to time t3 in FIG. 4), the registration sensor Since no detection signal is output from the control unit 28, the control unit erroneously determines that a paper jam has occurred even though there is an OHP sheet in front of the registration sensor 28. The misjudgment of a paper jam has hindered stable continuous paper feeding and reduced productivity.

  Therefore, in the present invention, by detecting the paper jam using the detection signal output from the registration sensor 28 until the registration sensor 28 detects the leading edge of the paper or the OHP sheet and immediately before detecting the trailing edge, We propose a method to realize stable continuous paper feeding.

  This will be described in detail below. FIG. 5 is a block diagram showing an electrical configuration of the image forming apparatus 1. The same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted. The image forming apparatus 1 includes a control unit 61, a storage unit 62, an image memory 63, an image processing unit 64, an image forming unit 65, a paper transport unit 66, an input operation unit 67, and a network I / F unit 68. Yes.

  The control unit 61 is configured by a CPU (Central Processing Unit) or the like, reads a program stored in the storage unit 62 and executes processing, and outputs instruction signals to each functional unit, data transfer, and the like. The image forming apparatus 1 is comprehensively controlled. In addition, the control unit 61 includes a paper jam determination unit 611. The paper jam determination unit 611 takes in the detection signal output from the registration sensor 28 and determines whether there is a paper jam. For example, if a detection signal is not output from the registration sensor 28 even after a predetermined time has elapsed since the driving of the intermediate roller pair 29, the paper jam determination unit 611 determines that a paper jam has occurred on the upstream side of the registration sensor 28. The paper jam determination unit 611 includes a timer 612 that counts time.

  The storage unit 62 stores programs, data, and the like for realizing various functions provided in the image forming apparatus 1. The image memory 63 temporarily stores image data transmitted from an external device via the network I / F unit 68. The image processing unit 64 performs image processing such as image correction and enlargement / reduction on the image data stored in the image memory 63.

  The image forming unit 65 includes an intermediate transfer unit 92, an image forming unit 93, an exposure unit 94, a fixing unit 97, and the like. The paper transport unit 11 includes a paper supply unit 130, an intermediate roller pair 29, a registration sensor 28, a registration roller pair 27, and the like. The input operation unit 67 includes a power key, a reset key, a numeric keypad, a display panel for displaying various messages, and the like. The network I / F unit 68 includes a communication module such as a LAN board, and transmits / receives various data to / from an external apparatus connected to the network I / F unit 68.

  FIG. 6 is a diagram illustrating an example of a detection signal output from the registration sensor 28 when the OHP sheet is conveyed, and ON / OFF of a paper jam determination operation by the paper jam determination unit 611. In FIG. 6, when the paper jam determination operation is on, it is a period during which the paper jam determination unit 611 determines whether there is a paper jam using the detection signal, and when it is off, the determination of whether there is a paper jam is stopped. The period during which

  When a detection signal is output from the registration sensor 28, the paper jam determination unit 611 turns off the paper jam determination operation and does not perform the paper jam determination operation based on the detection signal. Here, the paper jam determination unit 611 receives the detection signal output from the registration sensor 28 and turns off the paper jam determination operation. Therefore, the paper jam determination unit 611 can recognize that the leading edge of the OHP sheet has passed in front of the registration sensor 28. At least at this stage, it can be confirmed that no paper jam has occurred.

  The judgment operation by the paper jam judgment unit 611 continues to be in an off state until a timing earlier than the timing at which the detection signal is turned off (time t4) as the trailing edge of the OHP sheet passes in front of the registration sensor 28. At t, it is turned on again and the paper jam determination operation is resumed. Hereinafter, the period T during which the paper jam determination operation is off is referred to as a paper jam non-detection period. By restarting the paper jam determination operation at a timing (time t) earlier than the timing at which the detection signal is turned off (time t4), the paper jam determination unit 611 ensures that the trailing edge of the OHP sheet passes in front of the registration sensor 28. I can recognize that.

  As a setting method of the time t for determining the end of the paper jam non-detection period T, (Example 1) A method of calculating and setting according to the length of the OHP sheet in the conveyance direction and the conveyance speed, (Example 2) Registration sensor There is a method of setting when the detection signal 28 continues to output the detection signal for a preset time.

  First, Example 1 will be described in detail. First, the time from when the OHP sheet reaches the registration roller pair 27 to when the trailing edge passes the registration sensor 28 is measured or calculated from the length of the OHP sheet in the conveyance direction and the sheet conveyance speed. The time obtained by subtracting the time (time t4-t) for the registration sensor 28 to detect the trailing edge of the OHP sheet from the time obtained by the measurement or calculation is defined as a paper jam non-detection period T. This determination method of the paper jam non-detection period T is an example, and other methods may be used. Further, since the paper jam non-detection period T differs depending on the paper size, each size is determined in advance and stored in advance in a storage unit 62, a work memory (not shown) in the control unit 61, or the like.

  FIG. 7 is a flowchart illustrating the flow of a paper jam determination process performed by the paper jam determination unit 611 according to the first exemplary embodiment. First, when a sheet is conveyed from the sheet supply unit 130 (step S11; YES), the paper jam determination unit 611 determines whether a detection signal is output from the registration sensor 28 (step S12). The conveyance of the sheet by the sheet supply unit 130 is determined by driving the sheet feed roller 32 and the pickup roller 35 or the like.

  When a detection signal is output from the registration sensor 28 (step S12; YES), the paper jam determination unit 611 turns off the paper jam determination operation, and the timer 612 starts time measurement (step S13). When the count of the timer 612 reaches the paper jam non-detection period T (step S14; YES), the paper jam judgment unit 611 resumes the paper jam judgment operation (step S15). If the count of the timer 612 has not reached the paper jam non-detection period T (step S14; NO), the timer 612 continues to measure time, and the paper jam judgment unit 611 repeats the process of step S14.

  On the other hand, when the detection signal is not output from the registration sensor 28 (step S12; NO), the paper jam determination unit 611 determines that a paper jam has occurred and displays a warning message on the display panel of the input operation unit 67 or the like. Is performed (step S16).

  Next, the second embodiment, which is a method for setting when the registration sensor 28 continues to output the detection signal for a preset time, will be described in detail. Under the control of the paper jam judgment unit 611, the timer 612 measures the time during which the detection signal is at a high level, and when the time reaches a predetermined time t0 (see FIG. 6), the paper jam judgment unit 611 performs the paper jam judgment operation. Resume. That is, when the detection signal is stably output from the registration sensor 28 for the predetermined time t0, the paper jam determination unit 611 starts the paper jam determination operation.

  FIG. 8 is a flowchart illustrating the flow of the paper jam determination process of the paper jam determination unit 611 according to the second embodiment. First, when a sheet is conveyed from the sheet supply unit 130 (step S11; YES), the paper jam determination unit 611 determines whether a detection signal is output from the registration sensor 28 (step S12).

  When a detection signal is output from the registration sensor 28 (step S12; YES), the paper jam determination unit 611 turns off the paper jam determination operation, and the timer 612 starts time measurement (step S13). Hereinafter, the paper jam determination unit 611 controls the operation of the timer 612 according to the level of the detection signal. That is, when the detection signal is at a high level (step S21; high level) and the count of the timer 612 is not 0 (counting operation is in progress) (step S23; NO), the paper jam determination unit 611 determines the timer 612. It is determined whether or not the count has reached a predetermined time t0 (step S23). If the count of the timer 612 has reached the predetermined time t0 (step S23; YES), the paper jam determination unit 611 resumes the paper jam determination operation to indicate that the registration sensor 28 has continued to output the detection signal for the predetermined time t0. (Step S24). If the count of the timer 612 has not reached the predetermined time t0 (step S23; NO), the timer 612 continues to measure time, and the paper jam determination unit 611 shifts the processing to step S21.

  On the other hand, when the detection signal is at a high level (step S21; high level) and the count of the timer 611 is 0 (step S22; YES), the paper jam determination unit 611 causes the timer 612 to start measuring time. (Step S26), the process proceeds to Step S21.

  If the detection signal is at a low level (step S21; low level), the paper jam determination unit 611 resets the timer 612 to stop time measurement (step S25), and the process proceeds to step S21. Thus, when the detection signal is at a low level, the timer 612 is reset and stopped, and when the detection signal is at a high level, the timer 612 is operated to measure the time during which the detection signal has remained at a high level, and the measurement time is predetermined. When the time t0 is reached, the paper jam judgment unit 611 restarts the paper jam judgment operation.

  In the above embodiment, the OHP sheet has been described as an example, but it is also possible to deal with plain paper or the like.

  As described above, when the detection signal is output from the registration sensor 28, the paper jam determination unit 611 turns off the paper jam determination operation, so that the OHP sheet is bent by the registration roller pair 27. Sometimes, the misregistration of a paper jam due to the fact that the registration sensor 28 cannot detect the OHP sheet can be prevented. Therefore, various types of paper can be stably and continuously passed. Further, by restarting the paper jam determination operation at a timing earlier than the timing when the detection signal is turned off as the rear end of the paper passes in front of the registration sensor 28, the paper jam determination unit 611 moves from the front end of the paper to the rear. It can be recognized that the end has surely passed in front of the registration sensor 28.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 130 Paper supply part 24 Paper conveyance path 27 Registration roller pair 28 Registration sensor 29 Intermediate roller pair 611 Paper jam determination part (determination means)
612 Timer (Measuring means)

Claims (5)

An intermediate roller for conveying the recording medium;
A registration sensor arranged downstream of the intermediate roller and outputting a detection signal while detecting the recording medium;
A registration roller disposed downstream of the registration sensor;
Determining means for determining whether the recording medium is jammed based on the presence or absence of a detection signal output from the registration sensor;
And the judgment means outputs the detection signal when the registration sensor passes the leading edge of the recording medium and then stops outputting the detection signal when the trailing edge of the recording medium passes. A paper conveying apparatus that uses a paper jam detection period as an early timing, and stops judging whether the recording medium is jammed during the paper jam detection period.   The non-paper jam detection period is a time set in advance according to the length of the recording medium in the conveyance direction and the conveyance speed of the recording medium, and the determination unit outputs the detection signal from the registration sensor. 2. The paper according to claim 1, further comprising a measuring unit that measures time from a time point, and restarting the determination of a paper jam of the recording medium immediately after the measurement result by the measuring unit reaches the preset time. Conveying device.   The no-paper jam detection period is a time until the registration sensor continues to output the detection signal for a preset time, and the determination means measures the time when the detection signal is continuously output. 2. The sheet transport device according to claim 1, further comprising: a unit that restarts the determination of a paper jam of the recording medium immediately after the measurement result of the measurement unit reaches the preset time.   The paper conveying apparatus according to claim 1, wherein the recording medium to be conveyed includes a transparent sheet, and the registration sensor optically detects the presence of the recording medium. A paper conveying device according to any one of claims 1 to 4,
Image forming means for forming an image on a recording medium conveyed by the paper conveying device;
An image forming apparatus.

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