JP2009249093A - Paper feeding device and image forming device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variation (deviation) of timing at which paper reaches a predetermined position to be small, and to more accurately correct a paper interval than a conventional one. <P>SOLUTION: Reaching time Ts since paper feeding is started until the paper reaches a carrying sensor is measured, and when the reaching time Ts is smaller than a first threshold value Tth1, paper carrying speed by a carrying roller is reduced from steady speed V to a first deceleration speed Vd1. When the reaching time T2 is larger than the first threshold value Tth1 and smaller than a second threshold value Tth2, the paper carrying speed by the carrying roller is reduced from the steady speed V to a second deceleration speed Vd2. The first deceleration speed Vd1 is set to be a lower speed than the second deceleration speed Vd2, and the most suitable deceleration speed is selected for speed reduction according to the reaching time Ts, thereby correcting the timing at which the paper reaches a timing sensor 16 to be a generally fixed timing. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus that conveys sheets one by one and an image forming apparatus including the same, and more particularly to a technique for adjusting the timing at which a conveyed sheet reaches a predetermined position.

  2. Description of the Related Art Image forming apparatuses such as printer apparatuses and MFPs (Multi Function Peripherals) are provided with a sheet conveying apparatus that conveys sheets one by one to an image forming unit. The sheet conveying device supplies the sheet to the image forming unit at a timing that matches the toner image formed in the image forming unit. In order to improve the productivity of the image forming apparatus, such a sheet conveying apparatus is required to perform continuous sheet feeding at a constant sheet interval as short as possible.

  However, in the paper transport device, the initial position of the paper at the start of paper feed varies and the slip amount of the pickup roller that feeds paper also varies. Variations occur in the arrival timing until a predetermined position on the road is reached. This variation in arrival timing results in a variation in paper interval when continuous feeding is performed. If this variation is large, for example, a paper collision occurs, which causes a paper jam.

  Therefore, conventionally, in order to correct the arrival timing at which the paper reaches the predetermined position, the distance from the trailing edge of the preceding paper to the leading edge of the next paper is measured, and if the distance is less than the predetermined distance, In order to widen the sheet interval to this distance, it has been proposed to reduce the sheet conveyance speed by the roller from a steady speed to a predetermined deceleration speed (Patent Document 1).

JP 2001-341898 A

  Hereinafter, variation correction when the deceleration control disclosed in Patent Document 1 is applied will be described. FIG. 17 is an operation diagram showing an operation locus of the leading edge of a sheet conveyed by conventional deceleration control. In the illustrated example, it is assumed that a pickup roller, a conveyance roller, a conveyance sensor, a timing sensor, and a timing roller are arranged in this order along the sheet conveyance direction. If the paper feed by the pickup roller is started at time T1, the initial position of the paper and the slip amount of the pickup roller vary as described above. The operation line La indicated by a broken line in the figure is traced. When the leading edge of the sheet reaches the conveyance sensor the latest, the operation line Lb indicated by the broken line in the figure is followed, and the timing at which the leading edge of the sheet reaches the conveyance sensor is time T2. Therefore, the variation ΔT occurs at the timing when the leading edge of the sheet reaches the conveyance sensor after the pickup roller starts feeding.

  In order to suppress this variation ΔT, control is performed to reduce the conveyance speed of the conveyance roller from the steady speed V to a predetermined deceleration speed Vd. For example, as indicated by a solid line in the figure, when the leading end of the sheet reaches the transport sensor earlier than time T2 after starting feeding, the transport speed by the transport roller is changed from the steady speed V to a predetermined speed. Control is performed so that the operation line Z1 coincides with the slowest operation line Lb before the leading edge of the sheet reaches the timing sensor after decelerating to the deceleration speed Vd. That is, the goal of deceleration control is to make the timing at which the leading edge of the paper reaches the timing sensor coincide with the timing of the operation line Lb (time T3).

  FIG. 18 is a diagram showing changes in the speed of the carry motor that drives the carry roller. The deceleration control is performed by temporarily decelerating the conveyance motor from the steady speed V to a predetermined deceleration speed Vd as shown in FIG. The area of the shaded portion in the figure is a correction amount that can be corrected by the deceleration control. Therefore, the correction amount is adjusted by increasing or decreasing the speed holding time Tdh at the deceleration speed Vd.

  However, when such deceleration control is performed, there are two restrictions. One of them is that the deceleration speed Vd must be maintained for at least a certain time in order to prevent a conveyance motor constituted by a pulse motor or the like from stepping out. For this reason, the speed holding time Tdh at the deceleration speed Vd must be set to a value that is at least larger than the predetermined time, thereby determining the lower limit value of the correction amount. In this case, as indicated by the operation line Z2 indicated by the solid line in FIG. 19, for example, the leading edge of the fed paper is transported at a timing slightly earlier than time T2 (timing at which the latest operating line Lb reaches the transport sensor). When the above deceleration control is applied, the corrected operation line Z2 is delayed from the slowest operation line Lb, and not only cannot be made to coincide with the target value, but also the sheet interval from the preceding sheet Will open more than necessary.

  For this reason, conventionally, as shown in FIG. 20, a threshold value Tth is set, and when the timing Ts when the leading edge of the paper reaches the conveyance sensor after the start of paper feeding is greater than the threshold value Tth, the deceleration control is not performed. Yes. The threshold value Tth is set based on the lower limit value of the correction amount so that the corrected operation line is not delayed from the slowest operation line Lb even when deceleration control is performed. Therefore, when the conveyance sensor reaches the conveyance sensor at a timing slightly larger than the threshold value Tth as indicated by the operation line Z3, the conveyance speed is not decelerated, and thereafter, the sheet conveyance is performed at the steady speed V of the conveyance motor. A deviation ΔXa from the operation line Lb occurs at the timing when the leading edge of the sheet reaches the timing sensor. The magnitude of this deviation ΔXa depends on the threshold value Tth.

  The second restriction is that it is necessary to return the conveyance speed of the conveyance roller to the steady speed V before the leading edge of the sheet reaches the timing sensor. This is because, in order to force the inclination of the paper, the front end of the paper is brought into contact with the timing roller, the paper is bent by a predetermined amount between the timing roller and the conveyance roller, and in order to stabilize the bending amount, This is because the speed must always be the same speed. Due to this restriction, the timing Te for returning the speed of the transport motor to the steady speed V when the deceleration control shown in FIG. 18 is performed is the time when the leading edge of the sheet reaches the timing sensor at the latest. For this reason, the speed holding time Tdh at the deceleration speed Vd must be set to a time during which the speed of the transport motor can be returned to the steady speed V when the leading edge of the sheet reaches the timing sensor. An upper limit is determined. In this case, as indicated by the operation line Z4 indicated by the solid line in FIG. 21, for example, when the leading edge of the fed paper reaches the transport sensor almost coincident with the earliest operation line La, the above deceleration control is applied. Even if the speed is decelerated from the steady speed V to the deceleration speed Vd, it is necessary to return to the steady speed V before the leading edge of the sheet reaches the timing sensor, so the operation line Z4 cannot be made to completely match the operation line Lb. A deviation ΔXb occurs with respect to the operation line Lb.

  In order to reduce the deviation ΔXb shown in FIG. 21, the deceleration speed Vd may be reduced. That is, if the deceleration speed Vd is decreased, the inclination of the operation line Z4 during deceleration is reduced, so that the operation line Z4 can be matched with the operation line Lb until the leading edge of the sheet reaches the timing sensor. On the other hand, if the deceleration speed Vd is decreased, the correction amount (area of the hatched portion) that can be corrected by the deceleration control shown in FIG. 18 increases. Therefore, the lower limit value of the correction amount is also increased, and it is necessary to set the above-described threshold value Tth to a smaller value. In this case, the deviation ΔXa shown in FIG.

  In this way, in the conventional deceleration control, if the deceleration speed Vd is set to a small value in order to reduce the deviation ΔXb shown in FIG. 21, the deviation ΔXa shown in FIG. 20 increases accordingly. In addition, if the deceleration speed Vd is set to a large value in order to reduce the deviation ΔXa shown in FIG. 20, the deviation ΔXb shown in FIG. 21 increases accordingly. Therefore, conventionally, the value of the deceleration speed Vd is determined so that the deviations ΔXa and ΔXb are approximately the same. Therefore, there is a problem that it is difficult to further reduce each of the deviations ΔXa and ΔXb.

  The present invention has been made for the purpose of solving the above-described conventional problems, and can suppress the deviation of the timing at which the paper reaches a predetermined position, and can correct the paper interval more accurately. It is an object of the present invention to provide a sheet conveying device and an image forming apparatus.

  In order to achieve the above object, the invention according to claim 1 is a sheet conveying apparatus, which conveys a sheet stored in a sheet feeding unit one by one and feeds the sheet, and a sheet conveying path. And detecting means for detecting the paper conveyed by the conveyance mechanism section, and controlling the conveyance speed of the paper by the conveyance mechanism section so that the paper detected by the detection means is further downstream at a predetermined position. Control means for adjusting the timing to reach the sheet, and storage means for storing a plurality of deceleration speeds or acceleration speeds different from the steady speed when the transport mechanism unit transports the paper, the control means, The arrival time from when the paper feeding unit starts feeding the paper by the transport mechanism until the detection unit detects the paper is measured, and the speed of the transport mechanism is changed based on the arrival time. Decide what to do When changing the speed, one deceleration speed or acceleration speed is selected from the plurality of deceleration speeds or acceleration speeds stored in the storage means according to the arrival time, and the selected one By calculating the speed holding time at the time of deceleration or acceleration based on the deceleration speed or acceleration speed and the arrival time and controlling the transport mechanism section, the transport speed by the transport mechanism section is changed from the steady speed. The speed is reduced or increased to the one deceleration speed or acceleration speed, and the transport speed by the transport mechanism is returned to the steady speed after the speed holding time has elapsed.

  According to such a configuration, the storage unit stores a plurality of deceleration speeds or acceleration speeds different from the steady speed, and the control unit measures the arrival time of the sheet and changes the speed of the transport mechanism unit. When the speed is changed, the paper transport speed is reduced by selecting the most appropriate deceleration speed or acceleration speed from the multiple deceleration speeds or acceleration speeds based on the measured arrival time. Alternatively, the speed can be increased. Therefore, compared with the case where only one deceleration speed is set as in the prior art, various speed changes can be made according to the arrival time of the paper, and the paper is set at a predetermined position further downstream of the detection means. It is possible to suppress a deviation in timing to reach the position.

  According to a second aspect of the present invention, in the paper conveying apparatus according to the first aspect, the storage means is one deceleration speed or acceleration speed according to the arrival time from the plurality of deceleration speeds or acceleration speeds. A plurality of threshold values for selecting the control unit, and the control means determines whether to change the speed of the transport mechanism by comparing the arrival time with each of the plurality of threshold values. One deceleration speed or acceleration speed is selected from the plurality of deceleration speeds or acceleration speeds.

  According to such a configuration, the control unit can select the optimum deceleration speed or acceleration speed according to the arrival time of the sheet by comparing the arrival time of the sheet with a plurality of threshold values stored in the storage unit. .

  According to a third aspect of the present invention, in the paper conveying apparatus according to the second aspect, each of the plurality of threshold values corresponds to each of the plurality of deceleration speeds or acceleration speeds, and each threshold value corresponds to it. Deceleration speed or acceleration speed, the steady speed, the deceleration or acceleration transition time required to decelerate or increase from the steady speed to the corresponding deceleration speed or acceleration speed, and the corresponding deceleration speed or Based on the minimum speed holding time that must be kept at the minimum at the acceleration speed and the acceleration or deceleration transition time required to accelerate or decelerate from the corresponding deceleration speed or acceleration speed to the steady speed again It is characterized by being determined.

  According to such a configuration, each threshold is a minimum value (lower limit value of the correction amount) that can adjust the timing of the sheet when the deceleration or acceleration is performed to the corresponding deceleration speed or acceleration speed. To be determined. Therefore, when the deceleration or acceleration is performed at the deceleration speed or the acceleration speed corresponding to each threshold, it is possible to prevent the timing at which the paper reaches the predetermined position from being delayed from the predetermined timing.

  According to a fourth aspect of the present invention, in the paper conveying apparatus according to the second or third aspect, the control means controls the conveyance speed of the paper by the conveyance mechanism unit to be decelerated from the steady speed according to the arrival time. The storage means stores, as the plurality of deceleration speeds, at least two deceleration speeds, a first deceleration speed and a second deceleration speed lower than the steady speed, and the first threshold value as the plurality of threshold values. At least two threshold values, a threshold value and a second threshold value, are stored, the first deceleration speed is lower than the second deceleration speed, and the first threshold value is set to a value smaller than the second threshold value. The control means selects the first deceleration speed when the arrival time is smaller than the first threshold, and the arrival time is larger than the first threshold and smaller than the second threshold. Case It is characterized by performing the deceleration control by selecting the second reduction speed.

  According to this configuration, the control means selects the optimum deceleration speed from at least two deceleration speeds of the first deceleration speed and the second deceleration speed that are lower than the steady speed based on the arrival time of the sheet, and selects the sheet. By decelerating the conveyance speed, the timing at which the paper reaches a predetermined position downstream can be delayed so that it substantially coincides with the predetermined timing.

  According to a fifth aspect of the present invention, in the paper conveyance device according to the second or third aspect, the control unit controls the conveyance speed of the sheet by the conveyance mechanism unit to be increased from the steady speed according to the arrival time. The storage means stores, as the plurality of acceleration speeds, at least two acceleration speeds of a first acceleration speed and a second acceleration speed higher than the steady speed, and the plurality of acceleration speeds. As threshold values, at least two threshold values of a first threshold value and a second threshold value are stored, the first acceleration speed is higher than the second acceleration speed, and the first threshold value is higher than the second threshold value. Is set to a larger value, the control means selects the first acceleration speed when the arrival time is larger than the first threshold, and the arrival time is smaller than the first threshold, And greater than the second threshold It is characterized by performing the speed increasing control by selecting the second speed-increasing speed.

  According to this configuration, the control unit selects an optimum acceleration speed from at least two acceleration speeds of the first acceleration speed and the second acceleration speed higher than the steady speed based on the arrival time of the paper. By selecting and accelerating (accelerating) the conveyance speed of the sheet, the timing at which the sheet reaches a predetermined position downstream can be advanced to almost coincide with the predetermined timing.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus, wherein image formation is performed on the paper conveying device according to any one of the first to fifth aspects and the paper conveyed and supplied by the paper conveying device. And an image forming means for performing.

  According to such a configuration, the timing at which the sheet is supplied from the sheet conveying apparatus to the image forming unit is almost constant, and the deviation is suppressed to be small. Therefore, the image forming unit can form an image on a stable sheet position. Can do. In addition, since the sheet interval is stabilized by the sheet conveying device, the possibility of a paper jam or the like occurring in the image forming apparatus can be reduced.

  According to the present invention, an optimum one deceleration speed or speed increase from among a plurality of speed reduction speeds or speed increases according to the arrival time from the start of paper feeding until the paper is detected by the detecting means. Since the paper conveyance speed can be reduced or increased by selecting the speed, it is possible to suppress the deviation of the timing when the paper reaches a predetermined position further downstream, and to reduce the paper interval more accurately. Correction can be performed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected about the member which is mutually common in some embodiment demonstrated below, and the description which repeats about them is abbreviate | omitted.

(First embodiment)
FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 is an apparatus called a so-called multifunction machine or MFP, and includes a plurality of functions such as a copy, a network printer, a scanner, and a FAX. The image forming apparatus 1 includes a sheet conveying device 2 at a lower portion thereof, and an image forming unit 3 is provided at an upper portion of the sheet conveying device 2. The sheet conveying device 2 and the image forming unit 3 function when image formation is performed in the image forming device 1, that is, when a copy function, a printer function, a FAX function, or the like is used. The sheet transport device 2 stacks and stores sheets serving as image forming media, transports the stored sheets one by one, and feeds them to the image forming unit 3. The image forming unit 3 performs image formation by, for example, an electrophotographic method. The image forming unit 3 is provided on an upper portion of the image forming unit 3 after transferring and fixing a toner image onto a sheet conveyed from the sheet conveying device 2. The paper on which image formation has been performed is sequentially discharged to the discharge unit 5 through the discharge port 4. At this time, the sheet conveying device 2 supplies the sheet to the image forming unit 3 at a timing that matches the toner image of the image forming unit 3.

  FIG. 2 is a diagram illustrating a schematic configuration of the sheet conveying device 2. The sheet conveying device 2 is configured to supply a sheet by storing a plurality of sheets 9 on the sheet feeding unit 8 that stacks and accommodates the sheets 9 and conveying the sheet 9 accommodated in the sheet feeding unit 8 one by one along a predetermined conveying path 11. A transport mechanism unit 10 that performs paper and a control mechanism unit 20 that controls the transport operation of the paper 9 by the transport mechanism unit 10 are provided.

  The transport mechanism unit 10 comes into contact with an uppermost sheet stored in the sheet feeding unit 8 and feeds the sheet from the sheet feeding unit 8 to start feeding, and the sheet is fed by the pickup roller 12. A sheet feeding roller 13 that separates the sheets one by one and feeds only the uppermost sheet to the downstream side, a conveying roller 14 provided at a predetermined position downstream of the sheet feeding roller 13, and a conveying roller 14 And a timing roller 17 provided at a predetermined position on the downstream side. When the pickup roller 12 feeds paper, not only the uppermost sheet but also the lower sheet may move together with the uppermost sheet. The paper feed roller 13 is provided with a paper roller 13 a for picking up the paper that moves together with the uppermost paper. The paper feed roller 13 is configured to convey paper other than the uppermost paper to the downstream side of the paper feed roller 13. To prevent. Accordingly, only the sheet positioned on the uppermost surface of the sheet fed by the pickup roller 12 is conveyed downstream by the sheet feeding roller 13. When the paper transported by the paper feed roller 13 reaches the transport roller 14, it is transported by the transport roller 14 thereafter. The conveyance roller 14 is adjusted in the conveyance speed so that the timing from when the paper is fed until it reaches the timing roller 17 is a predetermined timing. The timing roller 14 is a roller that supplies paper to the image forming unit 3 at a timing that matches the toner image of the image forming unit 3.

  The control mechanism unit 20 includes a controller 21, a paper feed motor drive circuit 31, a paper feed motor 32, a carry motor drive circuit 41, a carry motor 42, a timing motor drive circuit 51, a timing motor 52, and a carry roller. 14 includes a conveyance sensor 15 that detects a sheet at a predetermined position on the downstream side in the vicinity of 14, and a timing sensor 16 that detects a sheet at a predetermined position on the upstream side in the vicinity of the timing roller 17. Each of the paper feed motor 32, the transport motor 42, and the timing motor 52 is configured by, for example, a pulse motor. The paper feed motor 32 is driven by the paper feed motor drive circuit 31 and feeds paper from the paper feed unit 8 by rotating the pickup roller 12 and the paper feed roller 13. The conveyance motor 42 is driven by the conveyance motor drive circuit 41 and conveys the sheet to the timing roller 17 by rotating the conveyance roller 14. The timing motor 52 is driven by the timing motor driving circuit 51 and conveys the sheet to the image forming unit 3.

  The controller 21 controls the paper transport operation in the transport mechanism unit 10 by giving commands to the paper feed motor drive circuit 31, the transport motor drive circuit 41, and the timing motor drive circuit 51. The controller 21 is provided as a CPU 22 provided as a control unit for controlling each part of the transport mechanism unit 10 and a storage unit for storing various parameters and numerical values used when the CPU 22 controls the transport mechanism unit 10. And a timer 24 for generating a clock signal when the CPU 22 measures time.

  In the paper conveyance device 2, when starting paper feeding, the CPU 22 instructs the paper feeding motor drive circuit 31 to start paper feeding. As a result, the paper feed motor 32 is activated, and the paper feed operation by the pickup roller 12 and the paper feed roller 13 is started. At this time, there is a variation W in the initial position of the paper fed. There are also variations in the slip amounts of the pickup roller 12 and the paper feed roller 13. Therefore, there is a variation in the timing from the start of paper feeding until the leading edge of the fed paper reaches the conveyance sensor 15. For this reason, the CPU 22 monitors the output of the transport sensor 15 and gives a transport speed command to the transport motor drive circuit 41 according to the timing at which the transport sensor 15 detects the leading edge of the paper, thereby transporting the paper by the transport motor 14. Control the speed. That is, the CPU 22 changes the conveyance speed of the conveyance roller 14 in accordance with the timing at which the conveyance sensor 15 detects the paper, thereby determining the timing at which the paper reaches the timing sensor 16 further downstream from the conveyance sensor 15. The correction is made so that

  In the present embodiment, in order to correct the timing at which the leading edge of the sheet reaches the timing sensor 16, deceleration control for reducing the sheet conveyance speed by the conveyance roller 14 from the steady speed V is performed as in the conventional case. However, in the present embodiment, a plurality of deceleration speeds are prepared as deceleration speeds that can be adopted when decelerating from the steady speed V, and the plurality of deceleration speeds are stored in the memory 23 in advance. Then, the CPU 22 measures an arrival time Ts from when the conveyance mechanism unit 10 starts feeding the sheet from the sheet feeding unit 8 to when the conveyance sensor 15 detects the leading edge of the sheet, and based on the arrival time Ts. It is determined whether or not to change the speed of the transport roller 14, and in the case of changing the speed, one optimum deceleration speed is selected from the plurality of deceleration speeds stored in the memory 23 according to the arrival time Ts. The speed holding time at the time of deceleration is calculated based on the selected one deceleration speed and arrival time Ts, and the transport operation by the transport roller 14 is controlled. In the following, in order to simplify the description, two deceleration speeds, a first deceleration speed Vd1 and a second deceleration speed Vd2, are prepared as deceleration speeds when decelerating from the steady speed V. The case where the control which decelerates to either one of two deceleration speeds is illustrated.

  FIG. 3 is an operation diagram showing the operation locus of the leading edge of the sheet conveyed by the deceleration control in the present embodiment. Assuming that the pickup roller 12 starts feeding the paper at time T1, as described above, the initial position of the paper and the slip amount of the pickup roller 12 vary, so the leading edge of the paper reaches the transport sensor 15 earliest. In this case, the operation line La indicated by a broken line in the figure is followed. Further, when the leading edge of the sheet reaches the conveyance sensor 15 latest, the operation line Lb indicated by a broken line in the drawing is followed, and the timing at which the leading edge of the sheet reaches the conveyance sensor 15 is time T2. Therefore, a variation ΔT occurs at the timing (arrival time Ts) when the leading edge of the sheet reaches the conveyance sensor 15 after the pickup roller 12 starts feeding.

  In order to suppress this variation ΔT, in this embodiment, two times for evaluating the arrival time Ts from the start of paper feeding from the paper feed unit 8 to when the transport sensor 15 detects the leading edge of the paper are evaluated. Threshold values Tth1 and Tth2 are set. The first threshold Tth1 is set to a value smaller than the second threshold Tth2 (that is, Tth1 <Tth2). The second threshold value Tth2 is set to a value shorter than the timing at which the leading edge of the sheet reaches the conveyance sensor 15 the latest (that is, Tth2 <T2-T1). If the arrival time Ts from when feeding is started until the conveyance sensor 15 detects the leading edge of the sheet is Ts <Tth1, the conveyance speed by the conveyance roller 14 is reduced from the steady speed V to the first deceleration speed Vd1. Take control. If the arrival time Ts is Tth1 ≦ Ts <Tth2, control is performed to reduce the conveyance speed by the conveyance roller 14 from the steady speed V to the second deceleration speed Vd2. Further, if the arrival time Ts is Tth2 ≦ Ts, the conveyance speed by the conveyance roller 14 is not decelerated and the conveyance is performed at the steady speed V.

  In the present embodiment, the first deceleration speed Vd1 is set to be lower than the second deceleration speed Vd2. Therefore, if the arrival time Ts until the fed paper reaches the conveyance sensor 15 is Ts <Tth1, the conveyance speed by the conveyance roller 14 is the steady speed V as indicated by the operation line L1 indicated by the solid line in the figure. To the first deceleration speed Vd1 and the operation line L1 is controlled so as to coincide with the slowest operation line Lb until the leading edge of the sheet reaches the timing sensor 16. If the arrival time Ts until the fed paper reaches the conveyance sensor 15 is Tth1 ≦ Ts <Tth2, the conveyance speed by the conveyance roller 14 is the steady speed as indicated by the operation line L2 indicated by the chain line in the figure. The speed is decelerated from V to the second deceleration speed Vd2, and the operation line L2 is controlled to coincide with the slowest operation line Lb until the leading edge of the sheet reaches the timing sensor 16.

  FIG. 4 is a diagram illustrating a change in speed of the transport motor 42 that drives the transport roller 14. FIG. 4A illustrates a case where the transport motor 42 is temporarily decelerated from the steady speed V to the first deceleration speed Vd 1. Shows a case where the transport motor 42 is temporarily decelerated from the steady speed V to the second deceleration speed Vd2. As shown in FIGS. 4A and 4B, the deceleration control is performed by temporarily decelerating the conveyance motor 42 from the steady speed V to the first deceleration speed Vd1 or the second deceleration speed Vd2. At this time, as shown in each of FIGS. 4A and 4B, the area of the hatched portion is a correction amount that can be corrected by each deceleration control. In other words, the area of these hatched portions is the amount (distance) by which the advancement degree of the leading edge of the sheet can be delayed by each deceleration control when compared with the conveyance at the steady speed V. Therefore, the correction amount is adjusted in each deceleration control by increasing or decreasing the speed holding time Tdh at each deceleration speed Vd1 or Vd2. Here, assuming that the speed holding time Tdh shown in each of FIGS. 4A and 4B is the same, when the vehicle is decelerated to the first deceleration speed Vd1, the speed is reduced to the second deceleration speed Vd2. Since the correction amount becomes large, the timing at which the leading edge of the sheet reaches the timing sensor 16 can be further delayed within a limited time (or distance) range.

  On the other hand, in order to prevent the step-out of the conveyance motor composed of a pulse motor or the like as described above, when the deceleration is performed from the steady speed V to the first deceleration speed Vd1 or the second deceleration speed Vd2, the first The deceleration speed Vd1 or the second deceleration speed Vd2 must be maintained for at least a certain time. When the fixed time is the minimum speed holding time Tdh (min), the lower limit value of the correction amount in each deceleration control is determined by the minimum speed holding time Tdh (min). FIG. 5 is a diagram illustrating a change in the speed of the transport motor 42 when the deceleration control is performed with the minimum speed holding time Tdh (min). FIG. 5A illustrates the transport motor 42 from the steady speed V to the first deceleration speed Vd1. In the case of decelerating, (b) shows the case of decelerating the conveyance motor 42 from the steady speed V to the second deceleration speed Vd2.

  First, as shown in FIG. 5A, when decelerating from the steady speed V to the first deceleration speed Vd1, if the first deceleration speed Vd1 is held for the minimum speed holding time Tdh (min), the correction amount corrected by this deceleration control. Is the area S1 (min) of the shaded portion in the figure. That is, when decelerating from the steady speed V to the first deceleration speed Vd1, an amount smaller than the area S1 (min) cannot be corrected. This area S1 (min) is kept at a minimum at the first deceleration speed Vd1, the steady speed V, the deceleration transition time Tdn required to decelerate from the steady speed V to the first deceleration speed Vd1, and the first deceleration speed Vd1. It is possible to calculate based on the minimum speed holding time Tdh (min) that must be performed and the acceleration transition time Tun required to increase the speed from the first deceleration speed Vd1 to the steady speed V again. The area S1 (min) defines a lower limit value of the correction time that can delay the leading edge of the sheet when decelerating to the first deceleration speed Vd1 as compared with the conveyance at the steady speed V. Therefore, in this embodiment, when the conveyance speed by the conveyance roller 14 is decelerated from the steady speed V to the first deceleration speed Vd1, the speed holding time Tdh at the first deceleration speed Vd1 is ensured more than the minimum speed holding time Tdh (min). The value of the first threshold value Tth1 is determined based on the area S1 (min) so that it can be performed. That is, the first threshold value Tth1 is equal to the operation line L1 (see FIG. 3) even when the first deceleration speed Vd1 is held for the minimum speed holding time Tdh (min) when decelerating from the steady speed V to the first deceleration speed Vd1. ) Is set so as not to be slower than the slowest operation line Lb. The time Th12 shown in FIG. 3 indicates the lower limit value of the correction time defined by the area S1 (min), and the paper leading edge is delayed when the first deceleration speed Vd1 is held for the minimum speed holding time Tdh (min). It is time that can be. Specifically, time Th12 = S1 (min) / V.

  Next, as shown in FIG. 5B, when decelerating from the steady speed V to the second deceleration speed Vd2, if the second deceleration speed Vd2 is held for the minimum speed holding time Tdh (min), the correction corrected by this deceleration control is performed. The lower limit of the amount is the area S2 (min) of the shaded portion in the figure. That is, when decelerating from the steady speed V to the second deceleration speed Vd2, an amount smaller than the area S2 (min) cannot be corrected. This area S2 (min) is kept at a minimum at the second deceleration speed Vd2, the steady speed V, the deceleration transition time Tdn required to decelerate from the steady speed V to the second deceleration speed Vd2, and the second deceleration speed Vd2. It is possible to calculate based on the minimum speed holding time Tdh (min) that must be performed and the acceleration transition time Tun required to increase the speed from the second deceleration speed Vd2 to the steady speed V again. The area S2 (min) defines a lower limit value of the correction time that can delay the leading edge of the sheet when decelerating to the second deceleration speed Vd2 as compared with the conveyance at the steady speed V. Therefore, in this embodiment, when the conveyance speed by the conveyance roller 14 is decelerated from the steady speed V to the second deceleration speed Vd2, the speed holding time Tdh at the second deceleration speed Vd2 is secured for the minimum speed holding time Tdh (min) or more. Thus, the value of the second threshold value Tth2 is determined based on the area S2 (min). That is, the second threshold value Tth2 is equal to the operating line L2 (see FIG. 3) even when the second deceleration speed Vd2 is held for the minimum speed holding time Tdh (min) when decelerating from the steady speed V to the second deceleration speed Vd2. ) Is set so as not to be slower than the slowest operation line Lb. A time Th22 shown in FIG. 3 indicates a lower limit value of the correction time corresponding to the area S2 (min). When the second deceleration speed Vd2 is held for the minimum speed holding time Tdh (min), the leading edge of the sheet is delayed. It is time that can be. Specifically, time Th22 = S2 (min) / V.

  Also in the present embodiment, when control is performed to decelerate the conveyance roller 14 from the steady speed V to the first deceleration speed Vd1 or the second deceleration speed Vd2, the conveyance roller 14 is conveyed until the leading edge of the sheet reaches the timing sensor 16. It is necessary to return the speed of the roller 14 to the steady speed V. That is, when the deceleration control shown in each of FIGS. 4A and 4B is performed, the timing Te for returning the speed of the conveyance motor 42 to the steady speed V is the timing at which the leading edge of the sheet reaches the timing sensor 16 at the latest. Become. Therefore, the speed holding time Tdh in each deceleration control must be set to a time during which the speed of the transport motor 14 can be returned to the steady speed V when the leading edge of the paper reaches the timing sensor 16. The upper limit value of the correction amount in the deceleration control is determined. Hereinafter, the influence of the upper limit value of the correction amount on the timing at which the leading edge of the paper reaches the timing sensor 16 (shift in arrival timing from the latest operation line Lb) will be examined.

  First, FIG. 6 is an operation diagram showing an operation locus of the leading edge of the paper that reaches the conveyance sensor 15 earliest after the paper feeding is started. In this case, as indicated by an operation line L3 indicated by a solid line in FIG. 6, the leading edge of the fed sheet reaches the transport sensor 15 in alignment with the earliest operation line La. Since the arrival time Ts that reaches the conveyance sensor 15 after the start of paper feeding is smaller than the first threshold Tth1, in this case, the CPU 22 makes the speed of the conveyance roller 14 constant at the timing when the conveyance sensor 15 detects the leading edge of the paper. Deceleration control is performed from the speed V to the slowest first deceleration speed Vd1. It is necessary to return the conveyance speed from the first deceleration speed Vd1 to the steady speed V before the leading edge of the sheet reaches the timing sensor 16. Therefore, the CPU 22 calculates the speed holding time Tdh for holding the first deceleration speed Vd1 within the range of the restriction, decelerates from the steady speed V to the first deceleration speed Vd1, and then holds the speed for the speed holding time Tdh. Then, after the speed holding time Tdh has elapsed, the first deceleration speed Vd1 is returned to the steady speed V. By performing such deceleration control, the timing at which the leading edge of the sheet reaches the timing sensor 16 is delayed by time Th11 as compared to the case where deceleration control is not performed. If the operation line L3 cannot be matched with the slowest operation line Lb before the conveyance speed is returned to the steady speed V in such deceleration control, the operation line L3 is finally shifted from the operation line Lb. ΔX1 is generated. This deviation ΔX1 is the maximum deviation when decelerating to the first deceleration speed Vd1, and is represented by ΔX1 = ΔT−Th11. In the case of ΔT−Th11 ≦ 0, the deviation ΔX1 can be made substantially zero by setting the speed holding time Tdh short.

  Next, FIG. 7 is an operation diagram showing an operation locus of the leading edge of the sheet when the timing of reaching the conveyance sensor 15 after the start of sheet feeding is equal to the first threshold value Tth1. In this case, the leading edge of the paper follows a locus indicated by an operation line L4 indicated by a solid line in FIG. Since the arrival time Ts that reaches the conveyance sensor 15 after the start of paper feeding is equal to the first threshold value Tth1, the CPU 22 changes the speed of the conveyance roller 14 from the steady speed V at the timing when the conveyance sensor 15 detects the leading edge of the paper. Deceleration control is performed to a second deceleration speed Vd2 that is lower than the steady speed V and higher than the first deceleration speed Vd1. It is necessary to return the conveyance speed from the second deceleration speed Vd2 to the steady speed V before the leading edge of the sheet reaches the timing sensor 16. Therefore, the CPU 22 calculates the speed holding time Tdh for holding the second deceleration speed Vd2 within the range of the restriction, and after decelerating from the steady speed V to the second deceleration speed Vd2, holds the speed for the speed holding time Tdh. Then, after the speed holding time Tdh has elapsed, the second deceleration speed Vd2 is returned to the steady speed V. By performing such deceleration control, the timing at which the leading edge of the sheet reaches the timing sensor 16 is delayed by time Th21 compared to the case where the deceleration control is not performed. If the operation line L4 cannot be made to coincide with the slowest operation line Lb before the conveyance speed is returned to the steady speed V in such deceleration control, the operation line L4 is finally shifted from the operation line Lb. ΔX2 is generated. This deviation ΔX2 is the maximum deviation when decelerating to the second deceleration speed Vd2, and is represented by ΔX2 = Th12−Th21. In the case of Th12−Th21 ≦ 0, the deviation ΔX2 can be made substantially zero by setting the speed holding time Tdh short.

  Next, FIG. 8 is an operation diagram showing an operation locus of the leading edge of the sheet when the timing of reaching the conveyance sensor 15 after the start of sheet feeding is equal to the second threshold value Tth2. In this case, the leading edge of the paper follows a locus indicated by an operation line L5 indicated by a solid line in FIG. Since the arrival time Ts that reaches the conveyance sensor 15 after the start of paper feeding is equal to the second threshold value Tth2, the CPU 22 does not perform control to decelerate the speed of the conveyance roller 14. For this reason, the sheet reaches the timing sensor 16 with the steady speed V maintained. Finally, the operation line L5 is shifted by ΔX3 from the operation line Lb. The deviation ΔX3 is a maximum deviation value when the deceleration control is not performed, and is represented by ΔX3 = Th22.

  Therefore, in the case of this embodiment, the timing deviation ΔX at which the leading edge of the sheet finally reaches the timing sensor 16 is as shown in FIG.

  In order to reduce the shift ΔX1 when decelerating at the first deceleration speed Vd1, the delay time Th11 that can be corrected by the deceleration control may be increased. Since the delay time Th11 is proportional to the area of the shaded portion shown in FIG. 4A, the first deceleration speed Vd1 may be set to a lower speed in order to increase the delay time Th11. By setting the first deceleration speed Vd1 to a low speed, the inclination at the time of deceleration in the operation line L3 shown in FIG. 6 is reduced, so that the operation line L3 is the slowest operation line Lb before the leading edge of the sheet reaches the timing sensor 16. To be able to match. As a result, the deviation ΔX1 can be suppressed to almost zero. However, in this case, the lower the first deceleration speed Vd1, the better. This is because if the first deceleration speed Vd1 is set too low, the time Th12 = S1 (min) / V that defines the first threshold value Tth1 described above increases. Therefore, the first deceleration speed Vd1 is set so that the leading edge of the paper that reaches the transport sensor 15 at the earliest timing after the start of paper feeding is matched with the time T3 (timing when the latest operation line Lb reaches the timing sensor 16). It is preferable to set the speed so as to reach the timing sensor 16.

  Further, in order to reduce the deviation ΔX2 when decelerating at the second deceleration speed Vd2, the delay time Th21 that can be corrected by the deceleration control may be increased. Since this delay time Th21 is proportional to the area of the hatched portion shown in FIG. 4B, the second deceleration speed Vd2 may be set to a lower speed in order to increase the delay time Th21. By setting the second deceleration speed Vd2 to a low speed, the slope at the time of deceleration in the operation line L4 shown in FIG. 7 is reduced, so that the operation line L4 is the slowest until the second deceleration speed Vd2 returns to the steady speed V. It becomes possible to match the operation line Lb. As a result, the deviation ΔX2 can be suppressed to almost zero. However, in this case as well, the lower the second deceleration speed Vd2, the better. This is because if the second deceleration speed Vd2 is set too low, the time Th22 = S2 (min) / V that defines the second threshold value Tth2 described above increases. Therefore, the second deceleration speed Vd2 is the time T3 (the slowest operation line Lb reaches the timing sensor 16) at the leading edge of the paper that reaches the conveyance sensor 15 at a timing substantially equal to the first threshold value Tth1 after the feeding is started. It is preferable to set the speed at such a level that it can reach the timing sensor 16 in accordance with the timing.

  As described above, the second deceleration speed Vd2 is set at the time T3 (the slowest operation line Lb is sent to the timing sensor 16) at the leading edge of the paper that reaches the conveyance sensor 15 at a timing substantially equal to the first threshold value Tth1 after the feeding is started. By setting the speed at which the timing sensor 16 can be reached in accordance with the timing of arrival, the deviation ΔX3 when the deceleration control is not performed can be reduced. That is, in order to reduce the deviation ΔX3 when the deceleration control is not performed, the time Th22 may be reduced. As described above, this time Th22 is a time during which the leading edge of the sheet can be delayed when the second deceleration speed Vd2 is held for the minimum speed holding time Tdh (min), and is represented by Th22 = S2 (min) / V. The Therefore, in order to reduce the time Th22, the second deceleration speed Vd2 may be set as high as possible. FIG. 7 shows the second deceleration speed Vd2 at which the leading edge of the paper that reaches the conveyance sensor 15 at the timing almost equal to the first threshold Tth1 after the start of paper feeding can reach the timing sensor 16 in time T3. Since this is the fastest deceleration speed at which the deviation ΔX2 can be suppressed to substantially zero, if the second deceleration speed Vd2 is adopted, the deviation ΔX3 when the deceleration control is not performed can be reduced.

  In this case, the deviation ΔX3 when the deceleration control is not performed cannot be suppressed to almost zero, but when compared with the deviation ΔXa or ΔXb (see FIGS. 20 and 21) when there is only one conventional deceleration speed, The deviation ΔX3 in the embodiment is smaller than that, and it is possible to correct the arrival timing of the paper with higher accuracy than before, and to stabilize the paper interval at a constant interval.

  The first deceleration speed Vd1 and the second deceleration speed Vd2 described above are examples. In the above description, the deviation ΔX1 when decelerating at the first deceleration speed Vd1 and the deviation ΔX2 when decelerating at the second deceleration speed Vd2 are suppressed to substantially zero, and the deviation ΔX3 when deceleration control is not performed is as small as possible. Although the preferable example which determines the 1st deceleration speed Vd1 and the 2nd deceleration speed Vd2 in order to suppress was described, this invention is not limited to this. That is, in this embodiment, each of the deviation ΔX1 when the vehicle is decelerated at the first deceleration speed Vd1, the deviation ΔX2 when the vehicle is decelerated at the second deceleration speed Vd2, and the deviation ΔX3 when the deceleration control is not performed, Therefore, the first deceleration speed Vd1 and the second deceleration speed are minimized so as to minimize at least one of these deviations ΔX1, ΔX2, and ΔX3. Vd2 may be determined.

  Further, in order to minimize the deviation that can finally occur, it is necessary to minimize all of the deviations ΔX1, ΔX2, and ΔX3. In this case, the first deceleration speed is set so that ΔX1 = ΔX2 = ΔX3. Vd1 and second deceleration speed Vd2 may be determined.

  When the first deceleration speed Vd1 and the second deceleration speed Vd2 are determined as described above, the first threshold value Tth1 is determined based on the first deceleration speed Vd1, and the second threshold value Tth2 is determined based on the second deceleration speed Vd2. Is determined. The first deceleration speed Vd1, the second deceleration speed Vd2, the first threshold value Tth1, and the second threshold value Tth2 are stored in the memory 23 in advance.

  Next, a specific operation in the sheet transport device 2 will be described. FIG. 10 is a flowchart illustrating an example of a processing procedure when the CPU 22 controls the sheet transport operation by the transport mechanism unit 10. This process is a process performed for each sheet when a plurality of sheets are continuously fed. The CPU 22 drives the paper feed motor 32 by instructing the paper feed motor drive circuit 31 to start paper feed at the timing of paper feed (step S101). As a result, the pickup roller 12 and the paper feed roller 13 are operated, and the paper feed unit 8 starts to feed the paper 9. When instructed to start feeding, the CPU 22 starts measuring time based on the clock signal input from the timer 24 (step S102). And it waits until the conveyance sensor 15 turns on (step S103). The conveyance sensor 15 is turned on when it detects the leading edge of the fed paper, and outputs a detection signal to the CPU 22. When the conveyance sensor 15 is turned on (YES in step S103), the CPU 22 ends the time measurement started in step S102 (step S104). Thereby, the arrival time Ts from the start of paper feeding until the leading edge of the paper reaches the conveyance sensor 15 is determined.

  The CPU 22 reads the first threshold value Tth1 from the memory 23, and determines whether or not the arrival time Ts at the leading edge of the sheet is smaller than the first threshold value Tth1 (step S105). If YES is determined here, it is determined that the speed of the transport motor 42 is decelerated from the steady speed V to the first deceleration speed Vd1. Then, the CPU 22 calculates a speed holding time Tdh when decelerating to the first deceleration speed Vd1 (step S106).

  FIG. 11 is a diagram illustrating a method for calculating the speed holding time Tdh. When calculating the speed holding time Tdh, it is not possible to ignore the acceleration when the transport motor 42 is decelerated from the steady speed V to the first deceleration speed Vd1 and when it is returned from the first deceleration speed Vd1 to the steady speed V again. However, this acceleration can be set in advance as a constant value when the CPU 22 controls the transport motor 42. Therefore, as shown in FIG. 11, the amount (distance) by which the leading edge of the paper is delayed during the deceleration transition time Tdn required to decelerate the transport motor 42 from the steady speed V to the first deceleration speed Vd1 is Ddn, and this value Ddn Can be calculated in advance based on the steady speed V, the first deceleration speed Vd1, and the deceleration transition time Tdn. Further, the amount (distance) by which the leading edge of the paper is delayed during the acceleration transition time Tun required to increase (accelerate) the conveyance motor 42 from the first steady speed Vd1 to the steady speed V is Dun, and this value Dun is also It can be calculated in advance based on the steady speed V, the first deceleration speed Vd1, and the acceleration transition time Tun.

Therefore, when the speed holding time Tdh is held at the first deceleration speed Vd1, the correction amount S that can delay the leading edge of the sheet by this deceleration control is expressed by the following equation (1).
S = Ddn + Dun + (V−Vd1) · Tdh Expression (1)

When the correction amount S calculated by the above equation (1) is related to the correction time, the correction time Th is expressed by the following equation (2).
Th = (Ddn + Dun + (V−Vd1) · Tdh) / V (2)

The correction time Th represented by the above equation (2) corresponds to the time for which the leading edge of the sheet should be delayed by this deceleration control. If time T1 = 0 in FIG. 3, the time to delay the leading edge of the sheet by the deceleration control is represented by (T2−Ts), and therefore the following expression (3) is established.
T2−Ts = Th (3)

Therefore, when the speed holding time Tdh is calculated from the above equations (2) and (3), the following equation (4) is obtained.
Tdh = (V · (T2−Ts) −Ddn−Dun) / (V−Vd1) (4)

  By substituting each value in addition to the arrival time Ts measured on the right side of the above equation (4), the speed holding time Tdh corresponding to the arrival time Ts when decelerating to the first deceleration speed Vd1 can be calculated. . Accordingly, in step S106, the speed holding time Tdh is calculated by performing the calculation of the above equation (4) based on the arrival time Ts measured by the CPU 22. The relationship between the arrival time Ts and the speed holding time Tdh when decelerating to the first deceleration speed Vd1 may be calculated in advance, and the calculated data may be stored in the memory 23 as table data. In this case, since the CPU 22 can immediately obtain the speed holding time Tdh corresponding to the arrival time Ts when decelerating to the first deceleration speed Vd1, from the memory 23, the processing efficiency is improved. When the speed holding time Tdh for deceleration to the first deceleration speed Vd1 is calculated, the process proceeds to step S109, and the CPU 22 executes a deceleration process for the transport motor 42.

  On the other hand, if NO is determined in step S105, the CPU 22 reads the second threshold Tth2 from the memory 23, and determines whether or not the arrival time Ts at the leading edge of the sheet is smaller than the second threshold Tth2 (step S107). If YES is determined here, it is determined that the speed of the transport motor 42 is decelerated from the steady speed V to the second deceleration speed Vd2. Then, the CPU 22 calculates a speed holding time Tdh when decelerating to the second deceleration speed Vd2 (step S108).

The calculation method of the speed holding time Tdh when decelerating to the second deceleration speed Vd2 is also the same as the calculation method described above. That is, the speed holding time Tdh when decelerating to the second deceleration speed Vd2 is expressed by the following equation (5).
Tdh = (V · (T2−Ts) −Ddn−Dun) / (V−Vd2) (5)

  Therefore, by substituting each value in addition to the arrival time Ts measured on the right side of the above equation (5), the speed holding time Tdh corresponding to the arrival time Ts when decelerating to the second deceleration speed Vd2 is calculated. Even in this case, the relationship between the arrival time Ts and the speed holding time Tdh may be calculated in advance, and the calculated data may be stored in the memory 23 as table data. When the speed holding time Tdh for deceleration to the second deceleration speed Vd2 is calculated, the process proceeds to step S109, and the CPU 22 executes a deceleration process for the transport motor 42.

  When NO is determined in step S107 (that is, when the arrival time Ts is larger than the second threshold value Tth2), the CPU 22 sets the transport motor 42 to the steady speed V without performing the deceleration process of the transport motor 42. While being held, the conveyance control of the paper is performed (step S110).

  FIG. 12 is a flowchart illustrating details of the deceleration process of the conveyance motor in step S109. When performing the deceleration process of the transport motor 42, the CPU 22 determines whether or not the deceleration speed is the first deceleration speed Vd1 (step S120). If YES, the CPU 22 outputs a request to reduce the speed of the transport motor 42 to the first deceleration speed Vd1 to the transport motor drive circuit 41 (step S121). Thereby, the conveyance motor drive circuit 41 decelerates the conveyance motor 42 to the first deceleration speed Vd1 at a constant acceleration.

  If NO is determined in step S120, the CPU 22 outputs a request to reduce the speed of the transport motor 42 to the second deceleration speed Vd2 to the transport motor drive circuit 41 (step S122). Thereby, the conveyance motor drive circuit 41 decelerates the conveyance motor 42 to the second deceleration speed Vd2 at a constant acceleration.

  The CPU 22 monitors the transport motor drive circuit 41 and waits until the speed of the transport motor 42 reaches the requested deceleration speed (step S123). When the requested deceleration speed is reached, the CPU 22 sets the speed holding time Tdh calculated in step S106 or S108, and starts time measurement (step S124). Then, it waits until the speed holding time Tdh elapses (step S125). When the speed holding time Tdh elapses, the CPU 22 outputs a request to increase the speed of the transport motor 42 to the steady speed V to the transport motor drive circuit 41 ( Step S126). Thereby, the conveyance motor drive circuit 41 increases the conveyance motor 42 to the steady speed V at a constant acceleration. Thereafter, when the speed of the transport motor 42 reaches the steady speed V, the process is terminated (step S127).

  When the arrival time Ts from the start of the feeding of the paper stored in the paper supply unit 8 to the arrival of the paper at the transport sensor 15 is smaller than the first threshold value Tth1 by the above processing, The speed of the transport motor 42 is decelerated from the steady speed V to the first deceleration speed Vd1. When the arrival time Ts of the paper is longer than the first threshold value Tth1 and smaller than the second threshold value Tth2, the speed of the transport motor 42 is reduced from the steady speed V to the second deceleration speed Vd2. By such deceleration control, the timing at which the leading edge of the fed paper reaches the timing sensor 16 is corrected so as to be substantially constant, and the paper interval is stabilized at substantially constant intervals.

  Thereafter, the CPU 22 determines a timing that can be matched with the toner image of the image forming unit 3 based on the arrival timing of the sheet detected by the timing sensor 16, and drives the timing motor 52 at the determined timing. The paper that has reached the timing roller 17 is supplied to the image forming unit 3.

  As described above, in the present embodiment, when the paper that has started to be fed from the paper feed unit 8 reaches the transport sensor 15 earlier than a predetermined time, the paper is reduced by reducing the transport speed by the transport roller 14. Is controlled so that the timing at which it reaches the timing sensor 16 downstream of the transport sensor 15 is substantially constant. For this deceleration control, in this embodiment, two deceleration speeds, a first deceleration speed Vd1 and a second deceleration speed Vd2, are set. Then, the optimum deceleration speed is selected from the two deceleration speeds of the first deceleration speed Vd1 and the second deceleration speed Vd2 in accordance with the arrival time Ts from the start of paper feeding until the paper reaches the conveyance sensor 15, and the deceleration control is performed. Therefore, the variation (shift) in the timing at which the paper reaches the timing sensor 16 can be suppressed to be smaller than that in the prior art. Even when deceleration control is not performed, the variation (shift) in the timing at which the paper reaches the timing sensor 16 is smaller than that in the prior art.

(Second Embodiment)
Next, a second embodiment will be described. In the first embodiment, when the paper that has started to be fed from the paper feeding unit 8 reaches the transport sensor 15 earlier than a predetermined time, the paper is transported by reducing the transport speed by the transport roller 14. The form which controlled so that the timing which reaches | attains the timing sensor 16 downstream from the sensor 15 becomes substantially constant was demonstrated. On the other hand, in the present embodiment, when the paper started to be fed from the paper feed unit 8 reaches the transport sensor 15 later than a predetermined time, the transport speed by the transport roller 14 is set to a speed higher than the steady speed. A mode of controlling so that the timing at which the sheet reaches the timing sensor 16 downstream of the conveyance sensor 15 by increasing (accelerating) the speed will be described. In the present embodiment, the configuration of the image forming apparatus 1 and the configuration of the paper transport apparatus 2 are the same as those described in the first embodiment.

  FIG. 13 is an operation diagram showing the operation locus of the leading edge of the sheet conveyed by the speed increase control in the present embodiment. Assuming that the pickup roller 12 starts feeding the paper at time T1, as described above, the initial position of the paper and the slip amount of the pickup roller 12 vary, so the leading edge of the paper reaches the transport sensor 15 earliest. In this case, the operation line La shown by a broken line in the figure is followed, and the timing at which the leading edge of the sheet reaches the conveyance sensor 15 is time T2. Further, when the leading edge of the sheet reaches the conveyance sensor 15 the latest, the operation line Lb indicated by a broken line in the figure is followed, and the timing at which the leading edge of the sheet reaches the conveyance sensor 15 is time T3. Therefore, a variation ΔT occurs at the timing (arrival time Ts) when the leading edge of the sheet reaches the conveyance sensor 15 after the pickup roller 12 starts feeding.

  In order to suppress this variation ΔT, in this embodiment, two times for evaluating the arrival time Ts from the start of paper feeding from the paper feed unit 8 to when the transport sensor 15 detects the leading edge of the paper are evaluated. Threshold values Tth1 and Tth2 are set. The first threshold Tth1 is set to a value larger than the second threshold Tth2 (that is, Tth1> Tth2). The second threshold value Tth2 is set to a value that is longer than the timing at which the leading edge of the sheet reaches the conveyance sensor 15 earliest (that is, Tth2> T2-T1). If the arrival time Ts from when feeding is started until the conveyance sensor 15 detects the leading edge of the sheet is Ts> Tth1, the conveyance speed by the conveyance roller 14 is increased from the steady speed V to the first acceleration speed Vu1. Perform fast control. If the arrival time Ts is Tth2 <Ts ≦ Tth1, control is performed to increase the transport speed of the transport roller 14 from the steady speed V to the second acceleration speed Vu2. Further, if the arrival time Ts is Ts ≦ Tth2, the conveyance speed by the conveyance roller 14 is not increased, and the conveyance at the steady speed V is performed.

  In the present embodiment, the first acceleration speed Vu1 is set higher than the second acceleration speed Vu2. Therefore, if the arrival time Ts until the fed paper reaches the conveyance sensor 15 is Ts> Tth1, the conveyance speed by the conveyance roller 14 is the steady speed V as indicated by the operation line L7 indicated by the solid line in the figure. To the first acceleration speed Vu1, and the operation line L7 is controlled to coincide with the earliest operation line La until the leading edge of the sheet reaches the timing sensor 16. If the arrival time Ts until the fed paper reaches the conveyance sensor 15 is Tth2 <Ts ≦ Tth1, the conveyance speed by the conveyance roller 14 is the steady speed as indicated by the operation line L6 indicated by the chain line in the figure. The speed is increased from V to the second acceleration speed Vu2, and the operation line L6 is controlled to coincide with the earliest operation line La until the leading edge of the sheet reaches the timing sensor 16.

  Since the first acceleration speed Vu1 is higher than the second acceleration speed Vu2, the correction amount is larger when increasing to the first acceleration speed Vu1 than when increasing to the second acceleration speed Vu2. The timing at which the leading edge of the sheet reaches the timing sensor 16 within a limited time (or distance) range can be greatly advanced.

  Further, as in the case of the deceleration control, in order to prevent the step-out of the conveyance motor 42 constituted by a pulse motor or the like, the speed is increased from the steady speed V to the first speed increase speed Vu1 or the second speed increase speed Vu2. In this case, the first acceleration speed Vu1 or the second acceleration speed Vu2 must be maintained for at least a certain time. If this fixed time is the minimum speed holding time Tdh (min), the lower limit value of the correction amount that can be corrected when the speed is increased to each of the first speed increase speed Vu1 and the second speed increase speed Vu2 is the minimum speed. It is determined by the speed holding time Tdh (min).

  FIG. 14 is a diagram showing a speed change of the transport motor 42 when the speed increase control is performed with the minimum speed holding time Tdh (min). FIG. 14A shows the speed of the transport motor 42 from the steady speed V to the first speed increase speed. In the case where the speed is increased to Vu1, (b) shows the case where the transport motor 42 is increased from the steady speed V to the second speed increase speed Vu2.

  First, as shown in FIG. 14A, when increasing from the steady speed V to the first speed increase speed Vu1, if the first speed increase speed Vu1 is held for the minimum speed holding time Tdh (min), correction is performed by this speed increase control. The lower limit value of the correction amount is the area S1 (min) in the shaded area in the figure. That is, when increasing from the steady speed V to the first acceleration speed Vu1, an amount smaller than the area S1 (min) cannot be corrected. The area S1 (min) includes the first acceleration speed Vu1, the steady speed V, the acceleration transition time Tun required to increase the speed from the steady speed V to the first acceleration speed Vu1, and the first acceleration speed. It is possible to calculate based on the minimum speed holding time Tdh (min) that must be held at the minimum at Vu1 and the deceleration transition time Tdn that is required to reduce the speed from the first acceleration speed Vu1 to the steady speed V again. is there. Further, the area S1 (min) defines a lower limit value of a correction time during which the leading edge of the sheet can be advanced faster when the speed is increased to the first speed increase speed Vu1 as compared with the conveyance at the steady speed V. . Specifically, the lower limit value of the correction time is expressed as S1 (min) / V. Therefore, in this embodiment, when the conveyance speed by the conveyance roller 14 is increased from the steady speed V to the first acceleration speed Vu1, the speed holding time Tdh at the first acceleration speed Vu1 is set to the minimum speed holding time Tdh (min ) The value of the first threshold value Tth1 is determined based on the area S1 (min) so that the above can be ensured. Specifically, the first threshold value Tth1 = (T2−T1) + S1 (min) / V. Thus, the first threshold value Tth1 is equal to the operation line L7 even when the first acceleration speed Vu1 is maintained from the steady speed V to the first acceleration speed Vu1 and the first acceleration speed Vu1 is maintained for the minimum speed holding time Tdh (min). (See FIG. 13) is set so as not to be earlier than the earliest operation line La.

  Next, as shown in FIG. 14B, in the case of increasing from the steady speed V to the second acceleration speed Vu2, if the second acceleration speed Vu2 is held for the minimum speed holding time Tdh (min), this acceleration control The lower limit value of the correction amount to be corrected is the area S2 (min) of the shaded portion in the figure. That is, when increasing from the steady speed V to the second acceleration speed Vu2, an amount smaller than the area S2 (min) cannot be corrected. The area S2 (min) includes the second acceleration speed Vu2, the steady speed V, the acceleration transition time Tun required to increase the speed from the steady speed V to the second acceleration speed Vu2, and the second acceleration speed. It is possible to calculate based on the minimum speed holding time Tdh (min) that must be held at the minimum at Vu2 and the deceleration transition time Tdn that is required to reduce the speed from the second acceleration speed Vu2 to the steady speed V again. is there. Further, the area S2 (min) defines a lower limit value of a correction time during which the leading edge of the sheet can be advanced faster when the speed is increased to the second speed increase speed Vu2 as compared with the conveyance at the steady speed V. . Specifically, the lower limit value of the correction time is expressed as S2 (min) / V. Therefore, in this embodiment, when the conveyance speed by the conveyance roller 14 is increased from the steady speed V to the second acceleration speed Vu2, the speed holding time Tdh at the second acceleration speed Vu2 is set to the minimum speed holding time Tdh (min The value of the second threshold value Tth2 is determined based on the area S2 (min) so that the above can be ensured. Specifically, the second threshold value Tth2 = (T2−T1) + S2 (min) / V. Thereby, the second threshold value Tth2 is equal to the operation line L6 even when the second acceleration speed Vu2 is maintained from the steady speed V to the second acceleration speed Vu2 and the second acceleration speed Vu2 is maintained for the minimum speed holding time Tdh (min). (See FIG. 13) is set so as not to be earlier than the earliest operation line La.

  With respect to the value of the first acceleration speed Vu1, for example, the leading edge of the paper that reaches the conveyance sensor 15 at the latest timing (time T3) after the start of paper feeding is set to the time T4 (the earliest operation line La is the timing sensor 16). It is preferable to set the speed at which the timing sensor 16 can be reached in accordance with the timing at which the timing sensor 16 is reached. As for the value of the second acceleration speed Vu2, for example, at the time T4 (the earliest operation line La is the timing of the leading edge of the paper that reaches the conveyance sensor 15 at a timing substantially equal to the first threshold value Tth1 after the paper feeding is started). It is preferable to set the speed at which the timing sensor 16 can be reached in accordance with the timing at which the sensor 16 is reached.

  The first acceleration speed Vu1 and the second acceleration speed Vu2, the first threshold value Tth1 and the second threshold value Tth2 are stored in the memory 23 in advance.

  Next, a specific operation in the sheet conveying apparatus 2 of the present embodiment will be described. 15 and 16 are flowcharts illustrating an example of a processing procedure when the CPU 22 controls the sheet transport operation by the transport mechanism unit 10. This process is also a process performed for each sheet when a plurality of sheets are continuously fed. The CPU 22 drives the paper feed motor 32 by instructing the paper feed motor drive circuit 31 to start paper feed at the timing of paper feed (step S201). As a result, the pickup roller 12 and the paper feed roller 13 are operated, and the paper feed unit 8 starts to feed the paper 9. When instructed to start paper feeding, the CPU 22 starts time measurement (step S202) and waits until the conveyance sensor 15 is turned on (step S203). When the transport sensor 15 is turned on (YES in step S203), the CPU 22 ends the time measurement started in step S202 (step S204). Thereby, the arrival time Ts from the start of paper feeding until the leading edge of the paper reaches the conveyance sensor 15 is determined.

  The CPU 22 reads the first threshold value Tth1 set for the acceleration control from the memory 23, and determines whether or not the arrival time Ts at the leading edge of the sheet is larger than the first threshold value Tth1 (step S205). If YES is determined here, it is determined that the speed of the conveyance motor 42 is increased from the steady speed V to the first speed increase speed Vu1. Then, the CPU 22 calculates a speed holding time Tdh when the speed is increased to the first speed increase speed Vu1 (step S206). Here, the speed holding time Tdh is calculated in the same manner as in the case of the deceleration control described in the first embodiment.

That is, assuming that time T1 = 0 in FIG. 13, an amount by which the leading edge of the sheet can be advanced during the acceleration transition time required until the conveyance motor 42 is accelerated from the steady speed V to the first acceleration speed Vu1 ( If the distance (Dun) is Dun and the amount (distance) by which the leading edge of the sheet can be advanced during the acceleration transition time required to decelerate the transport motor 42 from the first acceleration speed Vu1 to the steady speed V is Ddn, the speed is maintained. The time Tdh is expressed by the following equation (6).
Tdh = (V · (Ts−T2) −Ddn−Dun) / (Vu1−V) (6)

  By substituting each value in addition to the arrival time Ts measured on the right side of the above equation (6), the speed holding time Tdh corresponding to the arrival time Ts when accelerating to the first acceleration speed Vu1 is calculated. Can do. When the speed holding time Tdh in the case of increasing to the first acceleration speed Vu1 is calculated, the process proceeds to step S209, and the CPU 22 executes the acceleration process of the transport motor 42.

On the other hand, if NO is determined in step S205, the CPU 22 reads the second threshold Tth2 from the memory 23, and determines whether or not the arrival time Ts of the leading edge of the sheet is larger than the second threshold Tth2 (step S207). If YES is determined here, it is determined that the speed of the transport motor 42 is increased from the steady speed V to the second acceleration speed Vu2. Then, the CPU 22 calculates a speed holding time Tdh when the speed is increased to the second acceleration speed Vu2 (step S208). That is, the speed holding time Tdh when increasing to the second acceleration speed Vu2 is expressed by the following equation (7).
Tdh = (V · (Ts−T2) −Ddn−Dun) / (Vu2−V) (7)

  Accordingly, by substituting each value in addition to the arrival time Ts measured on the right side of the above equation (7), the speed holding time Tdh corresponding to the arrival time Ts when accelerating to the second acceleration speed Vu2 is calculated. can do. When the speed holding time Tdh in the case of increasing to the second acceleration speed Vu2 is calculated, the process proceeds to step S209, and the CPU 22 executes the acceleration process of the transport motor 42.

  When NO is determined in step S207 (that is, when the arrival time Ts is smaller than the second threshold Tth2), the CPU 22 sets the transport motor 42 to the steady speed V without performing the speed increasing process of the transport motor 42. The sheet conveyance control is carried out while holding the sheet (step S210).

  FIG. 16 is a flowchart showing details of the speed-up process of the transport motor in step S209. When performing the speed increasing process of the transport motor 42, the CPU 22 determines whether or not the speed increasing speed is the first speed increasing speed Vu1 (step S220). If YES, the CPU 22 outputs a request to increase the speed of the transport motor 42 to the first acceleration speed Vu1 to the transport motor drive circuit 41 (step S221). Thereby, the conveyance motor drive circuit 41 increases the conveyance motor 42 to the first acceleration speed Vu1 at a constant acceleration.

  If NO is determined in step S220, the CPU 22 outputs a request to increase the speed of the transport motor 42 to the second acceleration speed Vu2 to the transport motor drive circuit 41 (step S222). Thereby, the conveyance motor drive circuit 41 increases the conveyance motor 42 to the second acceleration speed Vu2 at a constant acceleration.

  Then, the CPU 22 waits until the speed of the transport motor 42 reaches the requested acceleration speed (step S223), and when it reaches the requested acceleration speed (YES in step S223), the speed holding time calculated in step S206 or S208. Tdh is set and time measurement is started (step S224). Then, the process waits until the speed holding time Tdh elapses (step S225). When the speed holding time Tdh elapses, the CPU 22 outputs a request to reduce the speed of the transport motor 42 to the steady speed V to the transport motor drive circuit 41 (step S225). S226). Thereby, the conveyance motor drive circuit 41 decelerates the conveyance motor 42 to the steady speed V at a constant acceleration. Thereafter, when the speed of the transport motor 42 reaches the steady speed V, the process is terminated (step S227).

  When the arrival time Ts from when the paper stored in the paper supply unit 8 starts to be fed to the conveyance sensor 15 is longer than the first threshold value Tth1 by the above processing, The speed of the transport motor 42 is increased from the steady speed V to the first speed increase speed Vu1. When the paper arrival time Ts is smaller than the first threshold Tth1 and larger than the second threshold Tth2, the speed of the transport motor 42 is increased from the steady speed V to the second acceleration speed Vu2. By such acceleration control, the timing at which the leading edge of the fed paper reaches the timing sensor 16 is corrected so as to be substantially constant, and the paper interval is stabilized at substantially constant intervals.

  Thereafter, the CPU 22 determines a timing that can be matched with the toner image of the image forming unit 3 based on the arrival timing of the sheet detected by the timing sensor 16, and drives the timing motor 52 at the determined timing. The paper that has reached the timing roller 17 is supplied to the image forming unit 3.

  As described above, in the present embodiment, when the paper that has started to be fed from the paper feed unit 8 reaches the transport sensor 15 later than a predetermined time, the transport speed by the transport roller 14 is increased (accelerated). Thus, the timing at which the paper reaches the timing sensor 16 downstream of the transport sensor 15 is controlled to be substantially constant. For this acceleration control, in this embodiment, two acceleration speeds, the first acceleration speed Vu1 and the second acceleration speed Vu2, are set. Then, the optimum acceleration speed is selected from the two acceleration speeds of the first acceleration speed Vu1 and the second acceleration speed Vu2 according to the arrival time Ts from the start of paper feeding until the paper reaches the conveyance sensor 15. Thus, since the speed increase control is performed, the variation (shift) in the timing at which the paper reaches the timing sensor 16 can be suppressed to be smaller than that in the conventional case. Even when the speed increase control is not performed, the variation (shift) in the timing at which the paper reaches the timing sensor 16 is smaller than that in the prior art.

(Modification)
As mentioned above, although several embodiment regarding this invention was described, this invention is not limited to the content mentioned above. In other words, in addition to the above-described contents, various modifications can be applied to the present invention.

  For example, in the first embodiment described above, the case where two deceleration speeds, ie, the first deceleration speed Vd1 and the second deceleration speed Vd2 are mainly set as the deceleration speed when decelerating from the steady speed V is exemplified. did. However, the set number of deceleration speeds is not limited to two, and may be three or more. When the number of deceleration speeds is set to three or more, it is possible to further reduce the variation in timing at which the leading edge of the paper finally reaches the timing sensor 16. In this case, when n is an integer of 3 or more, the plurality of deceleration speeds are set as Vd1 <Vd2 <... <Vdn <V, and the plurality of threshold values for determining whether to perform the deceleration control are Tth1 < It is set as Tth2 <... <Tthn. If the arrival time Ts when the fed paper reaches the transport sensor 15 is Ts <Tth1, the deceleration control is performed to decelerate from the steady speed V to the deceleration speed Vd1, and if Tth1 ≦ Ts <Tth2, the steady speed V The deceleration control for decelerating to the deceleration speed Vd2 is performed. Thereafter, the same determination is performed. If Tth (n−1) ≦ Ts <Tthn, deceleration control to decelerate from the steady speed V to the deceleration speed Vdn is performed, and if Tthn ≦ Ts, deceleration control is not performed. The sheet is conveyed at the steady speed V. By adopting such a configuration, it becomes possible to perform timing adjustment (that is, correction of the sheet interval) with significantly less variation than in the past.

  In the second embodiment described above, two acceleration speeds, the first acceleration speed Vu1 and the second acceleration speed Vu2, are mainly set as the acceleration speed when increasing from the steady speed V. Exemplified the case. However, the set number of acceleration speeds is not limited to two, and may be three or more. When the number of acceleration speeds set is three or more, it is possible to further reduce the variation in timing at which the leading edge of the paper finally reaches the timing sensor 16. In this case, if n is an integer of 3 or more, the plurality of acceleration speeds are set as Vu1> Vu2>...> Vun> V, and the plurality of thresholds for determining whether to perform the acceleration control are as follows: Tth1> Tth2>...> Tthn. Then, if the arrival time Ts when the fed paper reaches the conveyance sensor 15 is Ts> Tth1, acceleration control for increasing the steady speed V to the acceleration speed Vu1 is performed, and if Tth1 ≧ Ts> Tth2, The speed increase control for increasing the speed from the steady speed V to the speed increase speed Vu2 is performed. Thereafter, the same determination is performed. If Tth (n−1) ≧ Ts> Tthn, acceleration control for increasing from the steady speed V to the acceleration speed Vun is performed, and if Tthn ≧ Ts, the acceleration control is performed. Instead, the sheet is conveyed at the steady speed V. By adopting such a configuration, it becomes possible to perform timing adjustment (that is, correction of the sheet interval) with significantly less variation than in the past.

  In the above-described embodiment, a multifunction peripheral, an MFP, or the like is illustrated as the image forming apparatus 1. However, the image forming apparatus in the present invention is not limited thereto. That is, in the present invention, the image forming apparatus may be a printer dedicated apparatus having only a printer function, or may be a copy dedicated apparatus having only a copy function. Further, a FAX dedicated apparatus having only a FAX function may be used.

1 is an external view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a configuration example of a sheet conveying device. FIG. 6 is an operation diagram illustrating an operation locus of a leading end of a sheet conveyed by the deceleration control according to the first embodiment. It is a figure which shows the speed change of the conveyance motor in the case of performing deceleration control. It is a figure which shows the speed change of a conveyance motor at the time of performing deceleration control in minimum speed holding time. FIG. 10 is an operation diagram showing an operation locus of a leading edge of a sheet that reaches a conveyance sensor at the earliest timing after paper feeding is started. FIG. 10 is an operation diagram illustrating an operation locus of the leading edge of a sheet when the timing of reaching a conveyance sensor after the start of sheet feeding is equal to a first threshold value. FIG. 9 is an operation diagram illustrating an operation locus of the leading edge of a sheet when the timing of reaching a conveyance sensor after the start of sheet feeding is equal to a second threshold value. FIG. 6 is a diagram illustrating a timing deviation in which the leading end of a sheet finally reaches a timing sensor in the first embodiment. 3 is a flowchart illustrating an example of a processing procedure when the CPU controls a sheet transport operation by a transport mechanism unit in the first embodiment. It is a figure explaining the calculation method of speed holding time in a 1st embodiment. 4 is a flowchart illustrating details of a deceleration process of the conveyance motor according to the first embodiment. FIG. 10 is an operation diagram illustrating an operation locus of a leading end of a sheet conveyed by speed increase control according to a second embodiment. It is a figure which shows the speed change of a conveyance motor at the time of performing speed-up control by minimum speed holding time. 9 is a flowchart illustrating an example of a processing procedure when a CPU controls a sheet transport operation by a transport mechanism unit in the second embodiment. It is a flowchart which shows the detail of the acceleration process of the conveyance motor in 2nd Embodiment. It is an operation diagram showing an operation locus of the leading edge of a sheet conveyed by conventional deceleration control. It is a figure which shows the speed change of the conveyance motor by the conventional deceleration control. It is an operation diagram showing an operation locus of the leading end of a sheet for explaining conventional deceleration control. It is a figure which shows the shift | offset | difference of the final timing when not performing deceleration control in the conventional deceleration control. It is a figure which shows the shift | offset | difference of the final timing at the time of performing deceleration control in the conventional deceleration control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper conveying apparatus 3 Image forming part (image forming means)
DESCRIPTION OF SYMBOLS 8 Paper feed part 9 Paper 10 Conveyance mechanism part 14 Conveyance roller 15 Conveyance sensor (detection means)
20 Control Mechanism 21 Controller 22 CPU (Control Unit)
23 Memory (storage means)
42 Conveyance motor V Steady speed Vd1 First deceleration speed Vd2 Second deceleration speed Vu1 First acceleration speed Vu2 Second acceleration speed Ts arrival time Tth1 First threshold Tth2 Second threshold Tdh Speed holding time

Claims (6)

A transport mechanism that transports and feeds the paper stored in the paper feed unit one by one;
A detecting means provided in a paper transport path for detecting paper transported by the transport mechanism;
Control means for adjusting the timing at which the paper detected by the detection means reaches a predetermined position further downstream by controlling the paper transport speed by the transport mechanism;
Storage means for storing a plurality of deceleration speeds or acceleration speeds different from the steady speed when the transport mechanism transports the paper;
With
The control unit measures an arrival time from when the feeding mechanism unit starts feeding a sheet from the sheet feeding unit to when the detection unit detects the sheet, and based on the arrival time, the transport mechanism When the speed change is made, one deceleration speed or acceleration speed is selected from the plurality of deceleration speeds or acceleration speeds stored in the storage means according to the arrival time. And calculating the speed holding time during deceleration or acceleration based on the selected one deceleration speed or acceleration speed and the arrival time, and controlling the transport mechanism unit, thereby The conveyance speed by the mechanism is reduced or increased from the steady speed to the one deceleration speed or acceleration speed, and the conveyance speed by the conveyance mechanism is returned to the steady speed after the speed holding time has elapsed. The sheet conveying apparatus according to. The storage means further stores a plurality of thresholds for selecting one deceleration speed or acceleration speed from the plurality of deceleration speeds or acceleration speeds according to the arrival time,
The control means determines whether to change the speed of the transport mechanism by comparing the arrival time with each of the plurality of threshold values, and determines one of the plurality of deceleration speeds or acceleration speeds. 2. The sheet conveying apparatus according to claim 1, wherein a deceleration speed or an acceleration speed is selected. Each of the plurality of threshold values corresponds to each of the plurality of deceleration speeds or acceleration speeds,
Each threshold includes a corresponding deceleration speed or acceleration speed, the steady speed, a deceleration or acceleration transition time required to decelerate or increase from the steady speed to the corresponding deceleration speed or acceleration speed, and The minimum speed holding time that must be kept at the minimum at the corresponding deceleration speed or acceleration speed, and the acceleration or deceleration required to accelerate or decelerate from the corresponding deceleration speed or acceleration speed to the steady speed again. 3. The sheet conveying apparatus according to claim 2, wherein the sheet conveying apparatus is determined based on the transition time. The control means is for decelerating the sheet conveyance speed by the conveyance mechanism unit from the steady speed according to the arrival time,
The storage means stores at least two deceleration speeds of a first deceleration speed and a second deceleration speed lower than the steady speed as the plurality of deceleration speeds, and the first threshold value and a first threshold value as the plurality of threshold values. At least two threshold values are stored, the first deceleration speed is lower than the second deceleration speed, and the first threshold value is set to a value smaller than the second threshold value,
The control means selects the first deceleration speed when the arrival time is smaller than the first threshold, and when the arrival time is larger than the first threshold and smaller than the second threshold. 4. The sheet conveying device according to claim 2, wherein the second deceleration speed is selected to perform deceleration control. 5. The control means is configured to increase the conveyance speed of the sheet by the conveyance mechanism unit from the steady speed according to the arrival time,
The storage means stores, as the plurality of acceleration speeds, at least two acceleration speeds of a first acceleration speed and a second acceleration speed higher than the steady speed, and as the plurality of threshold values, Storing at least two threshold values of a first threshold value and a second threshold value, wherein the first acceleration speed is higher than the second acceleration speed, and the first threshold value is larger than the second threshold value. Is set,
The control means selects the first acceleration speed when the arrival time is larger than the first threshold, and when the arrival time is smaller than the first threshold and larger than the second threshold. 4. The sheet conveying apparatus according to claim 2, wherein the second speed increasing speed is selected to perform speed increasing control. A paper conveying device according to any one of claims 1 to 5,
Image forming means for forming an image on a sheet conveyed and supplied by the sheet conveying apparatus;
An image forming apparatus comprising:

Images