Image formation device

Abstract

To provide an image formation device capable of suppressing step-out of a motor for paper conveyance.SOLUTION: An image formation device comprises: a pair of first conveying rollers for conveying paper along a paper conveyance path; a pair of second conveying rollers for conveying paper in a downstream side rather than the pair of first conveying rollers; a first motor for driving the pair of first conveying rollers; a second motor for driving the pair of second conveying rollers; and a control part for controlling the first and second motors. The control part is provided so as to make acceleration of the pair of first conveying rollers to arrival at predetermined speed, when conveyance of the paper is restarted at the pairs of first and second conveying rollers after the paper stops under a state of being positioned between the pair of first conveying rollers and between the pair of second conveying rollers, larger than acceleration of the pair of second conveying rollers to arrival at the predetermined speed, and to make level difference of frequency transition smaller by limiting a range of an acceleration curve, and to shorten a speed difference between the pair of first conveying rollers and the pair of second conveying rollers.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus. [Background technology]

[0002] It is known that in a paper transport device included in an image forming apparatus, if one of two pairs of paper transport rollers that simultaneously transport paper becomes worn rapidly, the motor will lose synchronization (see, for example, Patent Document 1). In Patent Document 1, the rotation speed of the two pairs of paper transport rollers is slowed down to increase the drive torque of the motor and prevent loss of synchronization. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-214171 Summary of the Invention [Problem to be solved by the invention]

[0004] Differences in the self-starting range due to motor size, differences in the gear ratio of the drive unit, and differences in the rotation speed used can cause a difference in the step width or acceleration of the acceleration curve of the first motor that drives the first pair of transport rollers, and the step width or acceleration of the acceleration curve of the second motor that drives the second pair of transport rollers that transport paper simultaneously with the first pair of transport rollers. This difference can cause the paper to pull against each other during acceleration, increasing the load on the motor and causing it to lose synchronization. The present disclosure has been made in view of the above circumstances, and provides an image forming apparatus that can suppress loss of synchronization of a motor for conveying paper. [Means for solving the problem]

[0005] The present disclosure provides an image forming device comprising a first pair of transport rollers arranged to transport paper along a paper transport path, a second pair of transport rollers arranged to transport paper downstream of the first pair of transport rollers on the paper transport path, a first motor arranged to drive the first pair of transport rollers, a second motor arranged to drive the second pair of transport rollers, and a control unit arranged to control the first and second motors, wherein the control unit is configured to make the acceleration of the first pair of transport rollers until they reach a predetermined transport speed greater than the acceleration of the second pair of transport rollers until they reach the predetermined transport speed when the paper stops while positioned between the first pair of transport rollers and the second pair of transport rollers and then resumes transport of the paper with the first and second pairs of transport rollers, and to reduce the difference that occurs during frequency transition between the two pairs of transport rollers by narrowing the range of the acceleration curves of both pairs of transport rollers. [Effects of the Invention]

[0006] According to the present disclosure, by increasing the acceleration of the first conveying roller pair on the upstream side and narrowing the range of the acceleration curves of both conveying roller pairs, a correction is made to reduce the difference that occurs when the frequencies transition between them, thereby maintaining an appropriate degree of paper deflection between the first conveying roller pair and the second conveying roller pair and suppressing motor out-of-step. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an explanatory diagram of paper transport using a pair of first and second transport rollers. [Figure 3] 10 is a graph showing changes in conveyance speed of first and second conveyance roller pairs driven by first and second motors with different drive outputs. [Figure 4] 6 is a graph showing changes in the shaft rotation frequencies of the first and second motors. [Figure 5] 7A is an enlarged view of the change in shaft rotation frequency of the motor of FIG. 4, and FIG. 7B is an enlarged view of the change in shaft rotation frequency of the motor of FIG. [Figure 6] 10 is a graph showing a change in the conveying speed of the first conveying roller pair and a change in the conveying speed of the second conveying roller pair after correction. [Figure 7] 10 is a graph showing a change in the shaft rotation frequency of the first motor and a change in the shaft rotation frequency of the second motor after correction. [Figure 8] 4 is a flowchart of a method for controlling the first and second motors. DETAILED DESCRIPTION OF THE INVENTION

[0008] The image forming apparatus of the present disclosure comprises a first pair of transport rollers arranged to transport paper along a paper transport path, a second pair of transport rollers arranged to transport paper downstream of the first pair of transport rollers on the paper transport path, a first motor arranged to drive the first pair of transport rollers, a second motor arranged to drive the second pair of transport rollers, and a control unit arranged to control the first and second motors, and the control unit is characterized in that when the paper stops while positioned between the first pair of transport rollers and the first and second pair of transport rollers resume transporting the paper, the acceleration of the first pair of transport rollers until they reach a predetermined transport speed is greater than the acceleration of the second pair of transport rollers until they reach the predetermined transport speed, and by narrowing the range of the acceleration curves of both pairs of transport rollers, the difference that occurs during frequency transition between them is reduced.

[0009] The driving output of the first motor may be smaller than the driving output of the second motor. It is preferable that the control unit is configured to perform a correction to increase the acceleration of the first conveying roller pair until it reaches a predetermined conveying speed when the paper stops while positioned between the first conveying roller pair and the second conveying roller pair and then resumes conveying the paper with the first and second conveying roller pairs, when predetermined conditions are met. It is preferable that the specified conditions include at least one of the following: multiple paper jams related to the first and second motors; the number of sheets of paper passing through exceeds a specified number; loss of synchronization of the first motor is detected; and roller marks are left on the paper due to the paper being pulled against each other.

[0010] The first and second motors may each be a stepping motor, and the control unit may include a first drive circuit configured to supply power to the first motor and a second drive circuit configured to supply power to the second motor. The correction is preferably a correction that compares the acceleration of the first motor with the acceleration of the second motor and modifies the acceleration of the first motor based on the result of the comparison. The control unit may be configured to control rotation of the first motor by a first pulse signal supplied to a first drive circuit, and to control rotation of the second motor by a second pulse signal supplied to a second drive circuit. Preferably, the correction is performed to shorten the time it takes for the frequency of the first pulse signal to reach a target frequency. The correction is preferably a correction that narrows the range of the frequency table used for the first and second pulse signals to reduce the step of the frequency transition.

[0011] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. The configurations shown in the drawings and the following description are examples, and the scope of the present disclosure is not limited to those shown in the drawings and the following description.

[0012] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment, and FIG. 2 is an explanatory diagram showing paper conveyance using a pair of first and second conveyance rollers. The image forming apparatus 50 of this embodiment comprises a first pair of transport rollers arranged to transport the paper 3 along the paper transport path 2, a second pair of transport rollers arranged to transport the paper 3 downstream of the first pair of transport rollers on the paper transport path 2, a first motor 9 arranged to drive the first pair of transport rollers, a second motor 10 arranged to drive the second pair of transport rollers, and a control unit 7 arranged to control the first motor 9 and the second motor 10.The control unit 7 is characterized in that when the paper 3 stops while positioned between the first pair of transport rollers and the second pair of transport rollers and then the first and second pairs of transport rollers resume transporting the paper 3, the acceleration of the first pair of transport rollers until they reach a predetermined transport speed is greater than the acceleration of the second pair of transport rollers until they reach the predetermined transport speed, and by narrowing the range of the acceleration curves of both pairs of transport rollers, the difference that occurs during their frequency transitions is reduced.

[0013] The image forming apparatus 50 is an electrophotographic image forming apparatus that forms images using electrophotographic technology. The image forming apparatus 50 may be a monochrome image forming apparatus capable of forming monochrome images, or an intermediate transfer color image forming apparatus capable of forming color images as shown in FIG. 1 . The image forming apparatus 50 may also be another color image forming apparatus, a copier, a multifunction peripheral, or a facsimile machine. The image forming apparatus 50 is a so-called tandem full-color image forming apparatus having, for example, a toner image forming unit 18a for forming a black toner image, a toner image forming unit 18b for forming a cyan toner image, a toner image forming unit 18c for forming a magenta toner image, and a toner image forming unit 18d for forming a yellow toner image, arranged side by side in a predetermined direction (e.g., horizontally or vertically). The image carrier 20 is a member on whose surface a toner image is formed, and a transfer nip 24 through which the paper 3 passes is formed between the image carrier 20 and the transfer unit 8. When the image forming apparatus 50 is a full-color image forming apparatus, the image carrier 20 is an intermediate transfer belt 20. When the image forming apparatus 50 is a monochrome image forming apparatus, the image carrier is a photosensitive member.

[0014] The control unit 7 is a part that controls the image forming apparatus 50. The control unit 7 may be composed of, for example, a main control circuit 14 having a microcomputer or the like, motor drive circuits (e.g., a first drive circuit 15, a second drive circuit 16), a power supply circuit, etc. The control unit 7 may also have, for example, an arithmetic processing unit (e.g., a CPU), RAM, a storage device (e.g., an HDD), a network controller, a video controller, etc. In addition, the control unit 7 can control the transport of the paper 3 in the paper transport path 2, the transfer timing, etc. by controlling the rotation of the transport roller pairs 4a to 4k, the registration roller 5, the pressure unit 26, the rollers 13a to 13h for the intermediate transfer belt, the roller 12 for the transfer unit, etc.

[0015] The toner image forming units 18a to 18d each include photoconductors 19a to 19d, a charger, an exposure unit 33, a developing unit, a transfer means, and a cleaning unit. The photoconductors 19a-19d are components on whose surfaces latent images and toner images are formed. As the photoconductors 19a-19d rotate, toner images of black toner, cyan toner, magenta toner, or yellow toner are successively formed based on image data. The photoconductors 19a-19d are, for example, photoconductor drums. The charger, exposure unit 33, development unit, transfer means, and cleaning unit are provided in this order along the outer circumferential surfaces of the photoconductors 19a-19d from upstream to downstream in the direction of rotation of the photoconductors 19a-19d. The toner may be negatively or positively charged.

[0016] The toner images of black toner, cyan toner, magenta toner, and yellow toner formed on the photoconductors 19a to 19d are transferred to the intermediate transfer belt 20 by Coulomb force and the like due to the primary transfer electric field (primary transfer), and are superimposed on each other. As a result, color toner images are formed on the intermediate transfer belt 20. The color toner images on the intermediate transfer belt 20, driven by the intermediate transfer belt rollers 13a to 13h, are transferred to the paper 3 conveyed along the paper conveyance path 2 by Coulomb force and the like due to the secondary transfer electric field generated by the transfer voltage in the transfer unit 8 (secondary transfer).

[0017] The transfer unit 8 is a portion provided to transfer the toner image on the intermediate transfer belt 20 (image carrier) to the paper 3. The transfer unit 8 may be a transfer roller, and may have a configuration in which the transfer belt 11 is driven and rotated by a transfer unit roller 12, as shown in FIG. 1. The transfer unit 8 is provided so that the paper 3 passes through a transfer nip 24 between the intermediate transfer belt 20 (image carrier) and the transfer unit 8.

[0018] The paper transport device is a device that transports paper 3 along paper transport path 2. The paper transport device may include paper transport path 2, transport roller pairs 4a to 4k, registration rollers 5, transfer unit 8, fixing unit 28, paper feed tray 21, manual feed tray 22, and paper output tray 23. The paper transport device may also have multiple paper sensors. Paper transport by the paper transport device may be controlled by control signals sent from main control circuit 14 to motor drive circuits for motors that drive each transport roller pair.

[0019] The paper transport device is configured to use a pickup roller to pick up paper sheets 3 one by one from a stack of paper sheets 3 stored in paper feed tray 21 or manual feed tray 22, and to transport the picked-up paper sheets 3 along paper transport path 2 using transport roller pairs 4a to 4k. Paper sheets 3 are transported along paper transport path 2 in the directions indicated by the arrows in FIGS. 1 and 2. When transporting paper sheets 3 from paper feed tray 21, the paper sheets 3 are transported by transport roller pairs 4a, 4b, 4c, 4d, and 4f in this order, and an image is printed on one side of the paper sheets 3. When double-sided printing is to be performed on the paper sheets 3, the paper sheets 3 are transported by transport roller pairs 4i, 4j, 4k, 4h, 4d, 4e, and 4f in this order. When transporting paper sheets 3 from manual feed tray 22, the paper sheets 3 are transported by transport roller pairs 4g, 4h, 4d, 4e, and 4f in this order, and an image is printed on one side of the paper sheets 3. Double-sided printing on the paper sheets 3 is performed as described above. In addition, in the paper transport path 2, the paper 3 is temporarily stopped by the registration rollers 5, and the skew of the paper is corrected. In addition, the paper 3 transported along the paper transport path for double-sided printing by the transport roller pairs 4i, 4j, 4k, and 4h is temporarily stopped by the registration rollers 5, and the skew of the paper is corrected.

[0020] The registration rollers 5 start conveying the paper 3 at the process speed so that the timing when the color toner image reaches the transfer nip 24 due to the rotation of the intermediate transfer belt 20 and the timing when the position on the paper 3 corresponding to the toner image reaches the transfer nip 24 are synchronized. This allows the color toner image on the intermediate transfer belt 20 to be transferred (secondary transfer) to the appropriate position on the paper 3, forming a color toner image on the paper 3. Typically, the process speed is slower than the speed at which the paper 3 is conveyed to the registration rollers 5. Therefore, the conveying speed of the conveying roller pairs 4c, 4d, 4g, 4h, and 4k until the leading edge of the paper 3 reaches the registration rollers 5 is faster than the conveying speed (process speed) of the conveying roller pairs 4c, 4d, 4g, 4h, and 4k when the paper 3 is being conveyed by the registration rollers 5 (when the toner image is being transferred to the paper 3). Also, while a toner image is being transferred to the paper 3, the next paper 3 may temporarily stop upstream of the paper 3 being transferred.

[0021] The fixing unit 28 includes a rotatable heating unit 25, a rotatable pressure unit 26, and a fixing unit motor arranged to rotate the heating unit 25 and the pressure unit 26, and is arranged so that the paper 3 after passing through the transfer nip 24 passes through the fixing nip between the heating unit 25 and the pressure unit 26.

[0022] Each of the conveying roller pairs 4a to 4k is composed of a drive roller and a driven roller, and the paper 3 is sandwiched between the drive roller and the driven roller (at the nip portion), and the paper 3 is conveyed by the rotation of the drive roller and the driven roller. The drive roller is connected to a motor (e.g., first motor 9 or second motor 10) by a gear 29, and the drive roller rotates as the motor shaft rotates. Furthermore, the motor is supplied with power from a motor drive circuit (e.g., first drive circuit 15 or second drive circuit 16) based on a signal from the main control circuit 14, and the rotation of the motor, the rotation of the conveying roller pairs 4a to 4k, and the conveyance of the paper 3 are controlled. This motor is, for example, a stepping motor. The stepping motor is driven in steps based on pulses from the motor drive circuit.

[0023] When the motors driving the pairs of conveying rollers 4a to 4k are stepping motors, the main control circuit 14 sends commands to the motor drive circuits corresponding to the pairs of conveying rollers to be rotated. The main control circuit 14 issues commands to the motor drive circuits regarding various settings, such as the current value to the motor, the current decay mode, the direction of rotation, and the type of phase control, and also outputs step frequency pulses to the motor drive circuits to determine the motor rotation speed. The main control circuit 14 can calculate the value of the acceleration curve used when the motor starts rotating, or record and store this in a table (e.g., in memory). The main control circuit 14 can also calculate the value of the deceleration curve used when the motor stops, or record and store this in a table (e.g., in memory). These acceleration and deceleration curves are necessary to gradually accelerate and decelerate the motor to the target rotation speed when it starts or stops rotating so that the motor does not lose synchronization. The acceleration curve and deceleration curve are the temporal change pattern of the motor's rotation speed until it reaches the target speed, or speed profile. In other words, they are like a predetermined sequence of rotation speeds and timings to be passed through when switching from one rotation speed to another. More specifically, the rotation speed (drive frequency) must be gradually (stepwise) changed until the motor reaches the target rotation speed at a specified acceleration. Information on the rotation speed (drive frequency) is calculated or recorded in a table (frequency table) and stored in the microcomputer of the main control circuit 14. When the motor is actually driven, the rotation speed (drive frequency) of the motor is changed based on the change pattern (acceleration curve or deceleration curve) of the rotation speed (drive frequency) until the target rotation speed is reached. The range of the acceleration curve is the time width from the start to the end of the acceleration curve. The range of the frequency table is the time width from the start to the end of the frequency table. The frequency transition occurs when the drive frequency of an acceleration curve or deceleration curve is changed in stages and a transition occurs from one drive frequency to the next drive frequency. The motor drive circuit outputs pulses of a specified excitation method, current value, and frequency to each phase of the motor based on commands from the main control circuit 14. The stepping motor is driven stepwise based on the pulses from the motor drive circuit. In addition, the motor drive circuit supplies power to the motor based on commands input thereto, causing the motor to rotate and the pair of transport rollers to rotate. Therefore, the commands sent from the main control circuit 14 to the motor drive circuit control the transport of the paper 3 by the pair of transport rollers.

[0024] To rotate the pair of conveying rollers at a predetermined conveying speed, the motor shaft rotation frequency (pps, pulses per second) of the pulse signal sent by the main control circuit 14 to the motor drive circuit is gradually increased until it reaches the motor shaft rotation frequency (pps, pulses per second) corresponding to the predetermined conveying speed. The pair of conveying rollers then conveys the paper 3 at the predetermined conveying speed. Therefore, the acceleration of the pair of conveying rollers until it reaches the predetermined conveying speed can be controlled by the pulse signal sent by the main control circuit 14 to the drive circuit. However, it is difficult to make the acceleration of multiple motors exactly the same. It is particularly difficult to make the acceleration of multiple motors with different drive outputs exactly the same. The number of steps by which the motor shaft rotation frequency of the pulse signal is gradually increased is a specific value (specific number of steps) (for example, 100 steps) due to the memory capacity of the main control circuit 14.

[0025] The control unit 7 is configured so that when the paper 3 stops while positioned between the first pair of conveying rollers on the upstream side and the second pair of conveying rollers on the downstream side and then the first and second pairs of conveying rollers resume conveying the paper 3, the acceleration until the first pair of conveying rollers reaches a predetermined conveying speed is greater than the acceleration until the second pair of conveying rollers reaches the predetermined conveying speed.

[0026] The first conveyance roller pair is one of the plurality of conveyance roller pairs 4a-4k and registration roller 5 that convey the paper 3 along the paper conveyance path 2, and the second conveyance roller pair is one of the plurality of conveyance roller pairs 4a-4k and registration roller 5 (excluding the first conveyance roller pair). The first and second conveyance roller pairs are positioned so that these two conveyance roller pairs simultaneously convey the same paper 3, with the first conveyance roller pair located upstream and the second conveyance roller pair located downstream. The second conveyance roller pair may also be the pair of conveyance rollers next to the first conveyance roller pair. When the paper 3 is temporarily stopped at the registration roller 5 or when the paper 3 is temporarily stopped on the paper conveyance path 2, the paper 3 is positioned between the first conveyance roller pair and the second conveyance roller pair. The first pair of conveying rollers is driven by a first motor 9, and the second pair of conveying rollers is driven by a second motor 10. The control unit 7 may be configured to control the rotation of the first motor 9 by a first pulse signal supplied to a first drive circuit 15, and to control the rotation of the second motor 10 by a second pulse signal supplied to a second drive circuit 16.

[0027] 2 is a diagram illustrating a case where the conveying roller pair 4k is the first conveying roller pair and the conveying roller pair 4h is the second conveying roller pair. For example, when the first conveying roller pair is conveying roller pair 4b, the second conveying roller pair is conveying roller pair 4c; when the first conveying roller pair is conveying roller pair 4c, the second conveying roller pair is conveying roller pair 4d; when the first conveying roller pair is conveying roller pair 4g, the second conveying roller pair is conveying roller pair 4h; and when the first conveying roller pair is conveying roller pair 4h, the second conveying roller pair is conveying roller pair 4d.

[0028] For example, when printing on the back side of paper 3 in double-sided printing, paper 3 conveyed by conveyance roller pairs 4i, 4j, 4k, 4h, and 4d pauses when its leading edge reaches registration roller pair 5 (waiting for process control). At this time, if the trailing edge of paper 3 is upstream of conveyance roller pair 4k, paper 3 pauses while positioned between conveyance roller pair 4k, conveyance roller pair 4h, and conveyance roller pair 4d. In this case, conveyance roller pair 4k is the first conveyance roller pair and conveyance roller pair 4h is the second conveyance roller pair, or conveyance roller pair 4h is the first conveyance roller pair and conveyance roller pair 4d is the second conveyance roller pair. Thereafter, as intermediate transfer belt 20 rotates, conveyance of paper 3 by registration roller pair 5 and conveyance roller pairs 4k, 4h, and 4d begins at process speed so that the timing when the color toner image reaches transfer nip 24 and the timing when the position of paper 3 corresponding to the toner image reaches transfer nip 24 are synchronized. Here, as shown in FIG. 2, a case will be described in which the conveying roller pair 4k is the first conveying roller pair and the conveying roller pair 4h is the second conveying roller pair.

[0029] When the conveyance of the paper 3 is resumed using the first conveyance roller pair 4k and the second conveyance roller pair 4h in this manner, if the conveyance speed or acceleration of the second conveyance roller pair 4h is slightly greater than that of the first conveyance roller pair 4k, the paper 3 may be pulled by the first conveyance roller pair 4k and the second conveyance roller pair 4h, causing the first motor 9 or the second motor 10 to step out. Furthermore, if a tension state occurs during acceleration, this state may continue even after steady rotation is achieved, and a load fluctuation or the like may trigger the first motor 9 or the second motor 10 to step out. If the first motor 9 or the second motor 10 steps out, the first motor 9 or the second motor 10 may stop, causing a paper jam. In particular, if the drive output of the first motor 9 is smaller than the drive output of the second motor 10, the first motor 9 may step out and stop, causing a paper jam. Slight differences in the conveying speed or acceleration can occur, for example, due to deterioration of the motor, conveying rollers, gears, etc. over time, the type of paper 3 being conveyed, and operating conditions such as temperature and humidity. Furthermore, when the roller diameters of the conveying rollers are different and the number of sheets passing through increases, the smaller rollers are more likely to be worn down, resulting in differences in conveying speed. Also, slight differences occur in the step width and acceleration of the acceleration (acceleration curve) of the first motor 9 and the second motor 10 due to differences in the self-orbital region caused by the motor's drive output (motor size), differences in the gear ratio of the drive unit, and differences in the rotation speed used. These differences cause the paper 3 to pull against each other during acceleration, which can increase the load and cause the motor to lose synchronization.

[0030] FIG. 3 is a graph showing the relationship between the conveyance speed of the first conveyance roller pair 4k and the conveyance speed of the second conveyance roller pair 4h and time during acceleration when the drive output of the first motor 9 is smaller than the drive output of the second motor 10. FIG. 4 is a graph showing the relationship between the shaft rotation frequency of the first motor 9 and the shaft rotation frequency of the second motor 10 and time during acceleration when the drive output of the first motor 9 is smaller than the drive output of the second motor 10. The slopes in the graphs of FIGS. 3 and 4 represent acceleration. As shown in the graph of FIG. 3, the acceleration of the second conveyance roller pair 4h, which is driven by the second motor 10 with a larger drive output, is often greater than the acceleration of the first conveyance roller pair 4k, which is driven by the first motor 9 with a smaller drive output. Also, as shown in the graph of FIG. 4, the acceleration at the shaft rotation frequency of the second motor 10 with a larger drive output is often greater than the acceleration at the shaft rotation frequency of the first motor 9 with a smaller drive output.

[0031] 5(a) is an enlarged view of the change in the shaft rotation frequency of the first motor 9 and the change in the shaft rotation frequency of the second motor 10 shown in FIG. 4. Typically, the step height increases as shown in FIG. 5(a) because the motor is accelerated to the shaft rotation frequency corresponding to the maximum operating speed at the specific step number mentioned above. Therefore, during acceleration, the paper 3 is likely to be pulled by the first conveyor roller pair 4k and the second conveyor roller pair 4h, which may cause the motor to lose synchronization.

[0032] In this embodiment, when the first conveyance roller pair 4k and the second conveyance roller pair 4h resume conveying the paper 3 after the paper 3 has stopped while positioned between the first conveyance roller pair 4k and the second conveyance roller pair 4h (for example, when the paper 3 is waiting for process control or when the paper 3 is temporarily stopped due to the presence of another paper 3 downstream on the paper conveyance path 2), the control unit 7 sets the acceleration until the first conveyance roller pair 4k reaches a predetermined conveyance speed (for example, process speed) to be greater than the acceleration until the second conveyance roller pair 4h reaches the predetermined conveyance speed (for example, process speed). This allows the first conveyance roller pair 4k, which is located upstream, to reach the predetermined conveyance speed earlier than the second conveyance roller pair 4h, which is located downstream. Therefore, an appropriate amount of sagging can be formed in the paper 3 between the first conveyance roller pair 4k and the second conveyance roller pair 4h in the short time between when the first conveyance roller pair 4k reaches the predetermined conveyance speed and when the second conveyance roller pair 4h reaches the predetermined conveyance speed. This makes it possible to prevent the first conveying roller pair 4k and the second conveying roller pair 4h from pulling on the paper 3, and to prevent the first motor 9 or the second motor 10 from losing synchronization.

[0033] The control unit 7 may be configured to perform a correction to increase the acceleration of the first conveyance roller pair 4k until it reaches a predetermined conveyance speed when the first conveyance roller pair 4k and the second conveyance roller pair 4h resume conveying the paper 3 after the paper 3 has stopped while positioned between the first conveyance roller pair 4k and the second conveyance roller pair 4h, if a predetermined condition is met. The predetermined condition may be, for example, multiple paper jams related to the first motor 9 and the second motor 10, the number of sheets of paper that have passed through exceeds a predetermined number, loss of synchronization of the first motor 9 is detected, or roller marks left on the paper due to the paper 3 being pulled against each other. If at least one of these predetermined conditions is met, it is highly likely that the paper 3 is being pulled against each other between the first conveyance roller pair 4k and the second conveyance roller pair 4h. Therefore, by correcting the acceleration of the first conveyor roller pair 4k until it reaches a predetermined conveyance speed when the conveyance of the paper 3 is resumed, an appropriate amount of deflection can be created in the paper 3 between the first conveyor roller pair 4k and the second conveyor roller pair 4h, preventing the first motor 9 or the second motor 10 from losing synchronization. For example, the pulse signal sent by the main control circuit 14 to the first drive circuit 15 when the first motor 9 accelerates can be corrected to increase the acceleration of the first motor 9. In this way, simply by changing the software, it is possible to prevent the paper 3 from pulling against each other and prevent motor loss of synchronization. Furthermore, motor loss of synchronization can be prevented without using a high-power motor or increasing the current value. Using a high-power motor increases manufacturing costs, and increasing the current value increases heat generation in the motor drive circuit and the motor, resulting in poor efficiency. When the first motor 9 and the second motor 10 are accelerated simultaneously, the corrected pulse signal is sent to the motor drive circuit, but in normal paper transport, the uncorrected pulse signal is sent to the motor drive circuit.

[0034] For example, when the predetermined conditions are satisfied, the control unit 7 corrects the pulse signal sent by the main control circuit 14 to the first drive circuit 15, correcting the change in the conveying speed as shown in Figure 3 to a change in the conveying speed as shown in Figure 6, thereby increasing the acceleration of the first conveying roller pair 4k, and correcting the change in the motor shaft rotation frequency as shown in Figure 4 to a change in the motor shaft rotation frequency as shown in Figure 7, thereby increasing the acceleration of the first motor 9. This makes it possible to form an appropriate deflection in the paper 3 between the first conveying roller pair 4k and the second conveying roller pair 4h during acceleration.

[0035] The correction may be a correction that compares the acceleration (acceleration curve) of the first motor 9 with the acceleration (acceleration curve) of the second motor 10 and modifies the acceleration (acceleration curve) of the first motor 9 based on the comparison result. For example, the main control circuit 14 may compare a change in the pulse signal (motor shaft rotation frequency) sent to the first drive circuit 15 by the main control circuit 14 when the first motor 9 accelerates with a change in the pulse signal (motor shaft rotation frequency) sent to the second drive circuit 16 by the main control circuit 14 when the second motor 10 accelerates, and correct the pulse signal sent to the first drive circuit 15 by the main control circuit 14 when the first motor 9 accelerates so that the acceleration of the first motor 9 increases. By sending the corrected pulse signal to the first drive circuit 15, the acceleration of the first conveyance roller pair 4k can be increased. The acceleration curve may also be a change in the drive frequency over time during acceleration. For example, the control unit 7 may calculate a slope (acceleration / deceleration) from the time of the lowest frequency and the corresponding frequency, the cumulative time until the maximum frequency is reached, and the corresponding frequency, and use this slope to compare the accelerations (acceleration curves).

[0036] The correction may be a correction that shortens the time it takes for the frequency of the first pulse signal that controls the rotation speed of the first motor 9 to reach the target frequency compared to before the correction. Alternatively, the correction may be a correction that reduces the target frequency of the first pulse signal and the range of the acceleration curve of the second pulse signal that controls the rotation speed of the second motor 10 to reduce the step in the frequency transition, that is, a correction that shortens the correction period and reduces the correction width.

[0037] FIG. 5(b) is an enlarged view of the change in the shaft rotation frequency of the first motor 9 and the change in the shaft rotation frequency of the second motor 10 shown in FIG. 7. For example, as shown in FIGS. 5(b) and 7, the control unit 7 can correct the acceleration curve of the pulse signal sent from the main control circuit 14 to the first drive circuit 15 to a frequency that maximizes the process speed, and can correct the acceleration curve of the pulse signal sent from the main control circuit 14 to the second drive circuit 16 to a frequency that maximizes the process speed. Furthermore, the number of steps required to increase the frequency to the maximum frequency among all frequencies used can be set to the specific number (e.g., 100 steps) due to the memory capacity of the control unit 7. This reduces the step difference in the frequency of the pulse signal during acceleration, as shown in FIG. 5(b), and reduces the difference between the first conveyor roller pair 4k and the second conveyor roller pair 4h. This reduces the pulling of the paper 3 between the first conveyor roller pair 4k and the second conveyor roller pair 4h, and prevents the first motor 9 or the second motor 10 from losing synchronization.

[0038] FIG. 8 is a flowchart showing the control of the first motor 9 and the second motor 10 by the control unit 7. First, in step S1, it is determined whether the target rotation speed of the first motor 9 or the target rotation speed of the second motor 10 is to be changed. If it is to be changed, the process proceeds to step S2. For example, if the paper conveying speed is to be changed to the process speed, the process proceeds to step S2. In step S2, it is determined whether the first motor 9 and the second motor 10 will accelerate simultaneously. If they will not accelerate simultaneously, the process proceeds to step S6, where a clock (pulse signal) of the specified frequency is output to the first drive circuit 15 and the second drive circuit 16 without correction. If they will accelerate simultaneously, the process proceeds to step S3. For example, if the paper 3 is stopped between the first transport roller pair 4k and the second transport roller pair 4h, and the first transport roller pair 4k and the second transport roller pair 4h will accelerate simultaneously, the process proceeds to step S3.

[0039] In step S3, it is determined whether paper jams related to the first motor 9 and the second motor 10 have occurred multiple times. If no jams have occurred, the process proceeds to step S6, where a clock of the specified frequency is output to the first drive circuit 15 and the second drive circuit 16 without correction. If a jam has occurred, the process proceeds to step S4. If a paper jam has occurred multiple times, it is highly likely that the paper 3 is being pulled between the first conveyor roller pair 4k and the second conveyor roller pair 4h. In step S3, it may also be determined whether the number of sheets passed exceeds a predetermined number, whether loss of synchronization of the first motor 9 is detected, or whether roller marks due to the pulling of the paper 3 remain on the paper 3. Loss of synchronization of the first motor 9 can be detected, for example, by a current monitor in an ADC or a motor drive circuit. If roller marks remain on the paper 3, for example, a user or service technician can input information indicating the presence of roller marks to the main control circuit 14 using an input unit (e.g., a touch panel), and the main control circuit 14 can store the information. The determination in step S3 can be made based on this input information.

[0040] In step S4, the acceleration curve of the first motor 9 is compared with the acceleration curve of the second motor 10. For example, the change in the pulse signal (motor shaft rotation frequency) sent by the main control circuit 14 to the first drive circuit 15 when the first motor 9 is accelerating is compared with the change in the pulse signal (motor shaft rotation frequency) sent by the main control circuit 14 to the second drive circuit 16 when the second motor 10 is accelerating.

[0041] In step S5, the acceleration curve of the first motor 9 is corrected. For example, a change in the pulse signal (motor shaft rotation frequency) sent by the main control circuit 14 to the first drive circuit 15 when the first motor 9 is accelerating is corrected so that the acceleration of the first motor 9 becomes faster.

[0042] In step S6, a clock (pulse signal) with the corrected frequency is output to the first drive circuit 15, and a clock (pulse signal) with the specified frequency is output to the second drive circuit 16. This allows an appropriate deflection to be formed in the paper 3 between the first conveying roller pair 4k and the second conveying roller pair 4h during acceleration. [Explanation of symbols]

[0043] 2: Paper transport path 3: Paper 4a to 4k: Pair of transport rollers 5: Registration roller 7: Control unit 8: Transfer unit 9: First motor 10: Second motor 11: Transfer belt 12: Roller for transfer unit 13a to 13h: Roller for intermediate transfer belt 14: Main control circuit 15: First drive circuit 16: Second drive circuit 18a to 18d: Toner image forming unit 19a to 19d: Photosensitive member 20: Intermediate transfer belt (image carrier) 21: Paper feed tray 22: Manual feed tray 23: Paper output tray 24: Transfer nip 25: Heating unit 26: Pressure unit 28: Fixing unit 29: Gear 33: Exposure unit 50: Image forming device

Claims

1. a first pair of transport rollers arranged to transport paper along a paper transport path; a second pair of transport rollers arranged to transport paper on the paper transport path downstream of the first pair of transport rollers; a first motor arranged to drive the first pair of transport rollers; a second motor arranged to drive the second pair of transport rollers; and a control unit arranged to control the first and second motors; The control unit is configured to increase the acceleration until the first pair of conveying rollers reaches a predetermined conveying speed when the paper is stopped while positioned between the first pair of conveying rollers and the second pair of conveying rollers and then resumes conveying the paper with the first and second pairs of conveying rollers, compared to the acceleration until the second pair of conveying rollers reaches the predetermined conveying speed.

2. 2. The image forming apparatus according to claim 1, wherein the driving output of the first motor is smaller than the driving output of the second motor.

3. 3. The image forming apparatus of claim 1, wherein the control unit is configured to perform a correction to increase the acceleration of the first pair of conveying rollers until they reach a predetermined conveying speed when the paper stops in a position between the first pair of conveying rollers and the second pair of conveying rollers and then resumes conveying the paper with the first and second pairs of conveying rollers, when predetermined conditions are met.

4. The image forming apparatus of claim 3, wherein the predetermined conditions include at least one of the following: multiple paper jams related to the first and second motors; the number of sheets of paper passing through exceeds a predetermined number; loss of synchronization of the first motor is detected; and roller marks are left on the paper due to the paper being pulled against each other.

5. each of the first and second motors is a stepping motor; 4. The image forming apparatus according to claim 3, wherein the control unit includes a first drive circuit provided to supply power to the first motor, and a second drive circuit provided to supply power to the second motor.

6. 6. The image forming apparatus according to claim 5, wherein the correction is a correction that compares the acceleration of the first motor with the acceleration of the second motor and corrects the acceleration of the first motor based on the result of the comparison.

7. the control unit is configured to control rotation of the first motor by a first pulse signal supplied to a first drive circuit, and to control rotation of the second motor by a second pulse signal supplied to a second drive circuit; 6. The image forming apparatus according to claim 5, wherein the correction is performed so as to shorten the time it takes for the frequency of the first pulse signal to reach the target frequency compared to before the correction.

8. the control unit is configured to control rotation of the first motor by a first pulse signal supplied to a first drive circuit, and to control rotation of the second motor by a second pulse signal supplied to a second drive circuit; 6. The image forming apparatus according to claim 5, wherein the correction is a correction for reducing a step in frequency transition by narrowing a range of the target frequency of the first pulse signal and an acceleration curve of the second pulse signal.

Images