JP2015003783A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the allowance for a drive motor to operate out of a proper driving range (if it is a stepping motor, allowance to power swing).SOLUTION: When performing the drive control of a drive motor of a resister roller 8 for transporting a sheet 3 so that the sheet reaches a transfer part 9A of a drum 9 in a predetermined image formation start period, so as to increase the speed of the drive motor so as to follow the target speed which gradually increases and then make the drive motor drive at the target steady speed, and executing a fast control mode in which the target steady speed is fast, an image formation device controls the drive of the drive motor so that at least one of the acceleration and initial target speed during through-up becomes smaller than that when a control mode in which the target steady speed is slow is executed.

Description

  The present invention relates to an image forming apparatus such as a printing machine, a printer, and a copying machine, and more particularly to drive control of a conveyance roller that conveys a sheet material.

  Many image forming apparatuses include a registration roller (conveying roller) that conveys the sheet material so that the sheet material reaches the image forming unit at a predetermined image formation start time. The skew of the sheet material is corrected when the leading edge of the fed sheet material comes into contact with the resist roller that has stopped driving. After that, the resist roller starts to be driven at a predetermined drive start timing, and at a predetermined image formation start time. The sheet material reaches the image forming unit. Since high accuracy is required for the conveyance control of the sheet material by the registration roller, a driving source that enables high-precision driving control represented by a stepping motor is used for the registration motor. In such registration motor drive control, at the start of driving, in order to finally drive the registration motor stably at the target steady speed, the registration motor is controlled so as to follow the target speed that gradually increases to the target steady speed. Control called through-up to increase the speed is executed. When executing such control, it is important to increase the speed of the registration motor so that the target steady speed is reached as soon as possible within the range in which the registration motor can be driven properly (appropriate driving range). In particular, when the registration motor is a stepping motor, if the speed is increased too rapidly, the synchronization between the input pulse signal and the motor rotation is lost, and so-called step-out occurs. For this reason, it is necessary to increase the speed of the stepping motor within an appropriate driving range in which such step-out does not occur.

  In Patent Document 1, even when the start of registration roller driving is delayed from the normal driving start timing due to the delay in arrival of the sheet (sheet material), the driving state of the registration roller is adjusted and the transfer position to the transfer position is adjusted. An image forming apparatus is disclosed in which the arrival timing of a sheet is brought close to normal timing. In this image forming apparatus, the following method is proposed as a method of adjusting the driving state at the time of delay. In other words, after reaching the paper (sheet material) without delay, the speed is increased at the same acceleration as in the normal operation when the driving of the registration roller is started at the normal drive start timing, and then the steady target speed in the normal operation. This is a method of providing a period for driving at a large steady target speed and then decelerating to a steady target speed during normal operation. In this method, by providing the period, the paper conveyance time from the registration roller to the transfer position is shortened, and the paper arrival timing at the transfer position is brought close to the normal timing even when the driving start timing of the registration roller is delayed. Can do.

  Many image forming apparatuses in recent years change the image forming speed in accordance with the type of sheet material on which an image is formed. In such an image forming apparatus, it is necessary to change the conveyance speed at which the sheet material is conveyed by the registration rollers in response to the change in the image formation speed. FIG. 8 is a graph showing the target speed immediately after the start of driving the registration roller in each control example according to three different image forming speeds α, β, and γ. In any of the control examples shown in FIG. 8, the registration roller is controlled by a registration motor constituted by a stepping motor. The control example shown in FIG. 8 includes a first control example in which the registration roller driving speed is finally set to the fastest target roller steady speed (for example, 90 [ppm]) and a second fastest target roller steady speed (for example, 60 [ppm]). ppm]) and a third control example of the slowest target roller steady speed (for example, 30 [ppm]). In these control examples, although the target roller steady speeds are different from each other, the increase rate (acceleration) of the target roller speed up to the target roller steady speed is the same.

FIG. 9 is a graph showing the change over time of the load torque applied to the registration motor immediately after the start of driving the registration roller in the second control example (target steady speed = 60 [ppm]).
FIG. 10A is a graph showing the change over time of the load torque applied to the registration motor immediately after the start of driving the registration roller in the first control example (target steady speed = 90 [ppm]).
In FIGS. 9 and 10A, in addition to the change in load torque with time, the control speed of the registration motor (target speed) and the maximum speed at which the registration motor can rotate in synchronization with the input signal. Torque (pull-out torque) is illustrated.

  As shown in FIG. 9 and FIG. 10 (a), in the first control example and the second control example, the largest load torque is generated immediately after the through-up. The load torque converges. Here, it can be said that the greater the difference between the generated load torque and the pull-out torque, the higher the margin for motor step-out. Then, comparing the first control example and the second control example, it can be seen that the first control example having a large target steady speed has a smaller margin than the second control example having a small target steady speed. Actually, in the first control example, a step-out may occur depending on conditions. As described above, when the registration motor is accelerated at the same acceleration, the greater the target steady speed of the registration motor, the smaller the margin for step-out.

  FIG. 10B is a graph showing the change over time of the rotational speed measured on the registration roller shaft in the first control example. FIG. 10B also shows the control speed of the registration motor (converted to the rotation speed of the registration roller shaft) in addition to the temporal change of the rotation speed. As shown in FIG. 10B, immediately after the through-up, the rotational speed of the registration roller shaft gradually converges while periodically moving up and down. Since the time change period of the rotation speed is consistent with the time change period of the load torque shown in FIG. 10A, the time change of the rotation speed of the registration roller shaft is an alternative index indicating the time change of the load torque. Can be used as a value.

  On the other hand, even when drive control is performed at the same target steady-state speed, for example, the size, thickness, material, etc. of the sheet material may change or the contact pressure or separation pressure of the pickup roller may change. A large load torque exceeding the pull-out torque is generated in the registration motor, and the step-out may occur.

  In suppressing the registration motor step-out, even if a large load torque is generated in the registration motor during through-up, the margin for step-out is set so that the load torque does not exceed the pull-out torque. It is important to keep large. However, if, for example, a resist motor having a large pull-out torque is employed in order to increase the margin for the step-out of the resist motor, there is a problem that the motor is increased in size and cost. Further, for example, if the margin for the step-out of the registration motor is increased by controlling the registration motor by increasing the torque current value, problems such as a temperature rise due to heat generation and an increase in power consumption occur. Therefore, it is desired to maintain a large margin for the step-out of the registration motor without causing such a problem.

In the above description, the case where the registration motor is a stepping motor has been described as an example. However, other types of motors may be used as long as they are out of the proper driving range due to excessive load torque being applied. But the same is true.
In the above description, the case where the conveyance roller to be controlled for driving is a registration roller has been described as an example, but the same applies to other conveyance rollers.

  The present invention has been made in view of the above problems, and the object of the present invention is that the drive motor operates out of the appropriate drive range without causing the above-described problems (if it is a stepping motor). It is an object of the present invention to provide an image forming apparatus capable of increasing a margin for step-out).

  In order to achieve the above object, the present invention provides an image forming unit that forms an image on a sheet material, a conveyance roller that conveys the sheet material, a drive motor that rotationally drives the conveyance roller, and a predetermined drive start timing. The drive motor is driven so that the drive motor is driven at the target steady speed after the drive motor is accelerated so as to follow the target speed that increases stepwise. In the image forming apparatus having a drive control unit that performs control, the drive control unit has a plurality of control modes in which the target steady speed is different from each other, and the control in which the target steady speed is fast among the plurality of control modes. When executing the mode, at least one of the acceleration at the time of acceleration and the initial target speed at the start of the acceleration is smaller than at the time of execution of the control mode in which the target steady speed is slow. Kunar so on, and performs the driving control.

  According to the present invention, the acceleration at the time of acceleration and the initial target speed at the start of acceleration are higher than those in the control mode with a slow target steady speed in the control mode with a fast target steady speed in which the drive motor is likely to operate outside the appropriate drive range. By reducing at least one of these, it is possible to obtain an excellent effect that it is possible to maintain a large margin with respect to the drive motor being out of the appropriate drive range.

It is a schematic diagram which shows schematic structure of the stencil printing apparatus in embodiment. 3 is a timing chart showing a paper feeding operation in the stencil printing apparatus. It is the graph which showed the control speed immediately after the drive start of a registration roller in each control example according to three types of printing speeds. 6 is a graph showing changes in the speed of the registration roller shaft when the registration motor is driven and controlled at a predetermined target steady speed and through-up is performed with four types of acceleration. 10 is a graph showing the control speed immediately after the start of driving of a registration roller in each control example corresponding to three types of printing speeds in Modification 1. 6 is a graph showing changes in the speed of a registration roller shaft when the registration motor is driven and controlled at a predetermined target steady speed, and is slewed up at three initial target speeds. 10 is a graph showing the control speed immediately after the start of driving of a registration roller in each control example corresponding to three types of printing speeds in Modification 2. 6 is a graph showing a target speed immediately after the start of driving of a registration roller in each conventional control example corresponding to three different image forming speeds α, β, and γ. It is a graph which shows the time change of the load torque applied to a registration motor immediately after the drive start of a registration roller in the conventional 2nd control example (target steady speed = 60 [ppm]). (A) is a graph which shows the time change of the load torque added to a registration motor immediately after the drive start of a registration roller in the conventional 1st control example (target steady speed = 90 [ppm]). (B) is a graph which shows the time change of the rotational speed measured on the registration roller axis | shaft in the conventional 1st control example.

Hereinafter, an embodiment in which the present invention is applied to a stencil printing apparatus which is an image forming apparatus will be described.
In addition to the stencil printing apparatus, the present invention can be similarly applied to an electrophotographic image forming apparatus, an inkjet image forming apparatus, and the like.

FIG. 1 is a schematic diagram showing a schematic configuration of a stencil printing apparatus 1 according to the present embodiment.
A large number of sheets 3, which are sheet materials, are stacked on the sheet feeding table 2, and the uppermost sheet 3 is fed by a pickup roller 4. The sheet 3 fed in this way is sandwiched between the sheet feeding roller 5 and the friction pad 6 with a predetermined pressure. The friction pad 6 has a large coefficient of friction on the contact surface with the sheet 3, and the contact surface and the sheet come into contact with each other and rub against each other, so that only the topmost sheet 3 is separated by It is sent out to the sheet conveyance path 3A. The pickup roller 4 and the paper feed roller 5 are configured to be rotated by receiving a driving force from a drum motor (not shown).

  A registration roller 8 is disposed in the sheet conveyance path 3A. The registration roller 8 is composed of a pair of rollers, one of which is a driving roller and the other is a driven roller. The drive roller is connected to a registration motor (not shown) constituted by a stepping motor, and is driven to rotate by receiving the driving force of the registration motor. The leading edge of the sheet 3 separated and conveyed by the sheet feeding roller 5 reaches the nip portion of the resist roller 8 that has stopped rotating through the resist sensor 7. The skew of the sheet 3 is corrected when the leading edge of the sheet hits the nip portion of the registration roller 8. Even after the leading edge of the sheet 3 reaches the nip portion of the registration roller 8, a slack is formed between the registration roller 8 and the sheet feeding roller 5 as a result of being conveyed by the sheet feeding roller 5 for a predetermined time.

  The image forming unit of the stencil printing apparatus 1 in the present embodiment is configured by a drum 9. The drum 9 is configured by winding a pre-made master around a plate cylinder. When the registration roller 8 starts to rotate by starting the registration motor at a predetermined drive start timing according to a command from a control device (not shown), the sheet 3 sandwiched between the nip portions of the registration roller 8 is transferred to the drum 9 and the press roller. 10 is conveyed to a transfer portion 9A formed between the two. As a result, the leading edge of the sheet 3 reaches the transfer portion 9A in synchronization with the timing (image formation start time) at which the leading edge of the plate-making image position on the drum 9 reaches the transfer portion 9A.

  In the transfer unit 9A, the paper 3 is pressurized and conveyed between the drum 9 and the press roller 10, and the ink in the drum 9 is made to have pores (holes corresponding to images) provided on the outer peripheral surface (master) of the drum 9. Part) is supplied to the paper 3 and an ink image is formed on the paper 3. The sheet 3 on which the ink image is formed is sucked and held on the back side of the sheet (the side opposite to the image surface on which the ink image is formed) by the suction belt 11 on the downstream side of the sheet conveyance direction of the sheet conveyance path 3A. The paper is discharged to a paper discharge tray 12 outside the apparatus.

Next, the paper feeding operation in this embodiment will be described.
FIG. 2 is a timing chart showing the paper feeding operation.
When the start signal of the image forming operation is turned on, for example, by operating a start key of an operation unit (not shown) of the stencil printing apparatus 1, a drum motor that rotates the drum 9 starts to rotate. . Then, when a detection plate (not shown) provided on the drum 9 rotates together with the drum 9, and the detection plate is detected by a paper supply start sensor (not shown), the output signal of the paper supply start sensor is turned on. . In response to this, the sheet feeding clutch for transmitting the driving force of the drum motor to the pickup roller 4 and the sheet feeding roller 5 is turned on. As a result, the pickup roller 4 and the sheet feeding roller 5 are rotated by the driving force of the drum motor, and the sheet 3 starts to be fed.

  When the leading edge of the sheet 3 reaches the registration sensor 7, the output signal of the registration sensor 7 is turned on. The paper feed clutch is turned off when a predetermined time “a” has elapsed after the output signal of the registration sensor 7 is turned on. This time a is set so that the leading edge of the sheet 3 reaches the nip portion of the registration roller 8 that has stopped rotating, and a predetermined amount of slack is formed between the registration roller 8 and the sheet feeding roller 5. Has been.

  Further, the rotation of the registration motor is started at a timing (driving start timing) when a predetermined time b has elapsed since the output signal of the paper feed start sensor (not shown) is turned ON. Thereby, the rotation of the registration roller 8 is started, and the sheet 3 starts to be conveyed to the transfer unit 9A. This time b is set so that the sheet 3 reaches the transfer portion 9A at the image formation start time when the plate-making image position on the drum 9 reaches the transfer portion 9A.

  In the stencil printing apparatus 1 according to this embodiment, printing modes for printing at three types of printing speeds (image forming speeds) are prepared, and printing is performed by selectively executing these printing modes. If the printing speed is different, it is necessary to change the conveyance speed of the paper 3 in accordance with the printing speed. Therefore, it is necessary to change the conveyance speed at which the sheet material is conveyed by the registration rollers 8.

  FIG. 3 is a graph showing the control speed (target speed) immediately after the start of driving of the registration roller 8 in each control example corresponding to the three types of printing speeds α, β, and γ. In any of the control examples shown in FIG. 3, the registration roller is controlled by a registration motor constituted by a stepping motor. In the control example shown in FIG. 3, the linear speed of the registration roller 8 is finally set to the target roller steady speed (for example, 90 [ppm]) and the target roller steady speed (for example, 60 [ppm]). There are three types of control examples: a second control example and a third control example for setting the target roller steady speed (for example, 30 [ppm]).

  In each control example in this embodiment, not only the target roller steady speed is different from each other, but also the increase rate (acceleration) of the target roller speed up to the target roller steady speed is different from each other as shown in FIG. Specifically, the drive control of the registration roller 8 is performed so that the acceleration in the through-up (acceleration) becomes smaller in the control mode in which the target roller steady speed is faster.

FIG. 4 is a graph showing changes in the speed of the registration roller shaft when the registration motor is driven and controlled at a predetermined target steady speed (about 2000 [pps]) and through-up is performed with four types of acceleration.
As described above, the temporal change in the rotation speed of the registration roller shaft can be used as an alternative index value indicating the temporal change in the load torque generated in the registration motor. In other words, there is a correlation that the greater the variation in the rotational speed of the registration roller shaft, the greater the variation in the load torque generated in the registration motor. As shown in FIG. 4, it can be seen that the smaller the acceleration during through-up, the smaller the variation in the rotational speed of the registration roller shaft. Therefore, the smaller the acceleration during through-up, the smaller the variation in load torque generated in the registration motor. In this embodiment, the acceleration at the time of the through-up is set so as not to be changed. However, other settings such as a setting for changing the acceleration at the time of the through-up to draw an S-shaped curve may be used. Similar results are obtained.

  Therefore, in the present embodiment, as shown in FIG. 3, the acceleration at the time of through-up is smaller as the registration motor drive control is performed when the printing speeds α, β, and γ are higher. As described above, as the printing speeds α, β, and γ increase, the load torque generated by the registration motor increases, and the margin for the step-out of the registration motor decreases. In this embodiment, when the target steady speed at which the load torque generated by the registration motor is large (when the printing speed α is high), the acceleration at the time of through-up is small, so the load torque generated by the registration motor is small. it can. Therefore, even when the printing speed is fast, the registration motor is difficult to step out. On the other hand, when the target steady speed at which the load torque generated by the registration motor is small is low (when the printing speed is γ), the margin for the registration motor step-out is large, so even if the acceleration at the time of through-up is large. The resist motor is difficult to step out. Therefore, in this embodiment, when the printing speed is slow, the acceleration at the time of through-up remains large.

  As described above, according to the present embodiment, even when the printing speed is high, the margin for the step-out of the registration motor is increased. Therefore, the paper size, the paper type, the contact pressure of the pickup roller 4 and the contact of the paper feed roller 5 are increased. By changing the pressure or the like, the occurrence of step-out of the registration motor can be reduced even if a slight fluctuation occurs in the load torque generated in the registration motor. As a result, conventionally, a resist motor having a large torque is selected in consideration of the maximum load torque when the printing speed is high. In this embodiment, a resist motor having a relatively small torque can be selected. Thus, the motor can be reduced in size and cost. In addition, since control for increasing the input current value is not required to obtain a large motor torque, there is no problem of temperature increase and power consumption increase due to heat generation accompanying the increase of the input current value.

[Modification 1]
Next, a modified example of the registration motor drive control in the embodiment (hereinafter referred to as “modified example 1”) will be described.
In the above embodiment, in the control mode with a fast target steady-state speed in which the load torque generated by the registration motor is large, the acceleration is reduced without changing the initial target speed at the time of through-up, and the load torque generated by the registration motor is reduced. Reduced. On the other hand, in the first modification, the initial target speed is reduced without changing the acceleration at the time of through-up, and the load torque generated by the registration motor is reduced.

  FIG. 5 is a graph showing the control speed (target speed) immediately after the start of driving of the registration roller 8 in each control example according to the three types of printing speeds α, β, and γ in the first modification. In each control example in the first modification, not only the target roller steady speeds are different from each other, but also the first target roller speed (initial target speed) immediately after the start of driving is different from each other as shown in FIG. Specifically, the drive control of the registration roller 8 is performed so that the initial target speed at the time of through-up (speed increase) becomes smaller in the control mode in which the target roller steady speed is faster.

FIG. 6 is a graph showing changes in the speed of the registration roller shaft when the registration motor is driven and controlled at a predetermined target steady speed (about 2000 [pps]) and is slewed up at three initial target speeds. . The acceleration at the time of through-up is adjusted to be almost constant.
As shown in FIG. 6, the smaller the initial target speed at the time of through-up, the smaller the fluctuation in the rotational speed of the registration roller shaft. Therefore, it can be seen that the smaller the initial target speed at the time of through-up, the smaller the variation of the load torque generated in the registration motor. Therefore, in the first modification, as shown in FIG. 5, the initial target speed at the time of through-up is smaller as the registration motor drive control is performed when the printing speeds α, β, and γ are higher. As described above, as the printing speeds α, β, and γ increase, the load torque generated by the registration motor increases, and the margin for the step-out of the registration motor decreases. In the first modification, when the target steady speed at which the load torque generated by the registration motor becomes large (when the printing speed α is high), the initial target speed at the time of through-up becomes small, so the load generated by the registration motor Torque can be reduced. Therefore, even when the printing speed is fast, the registration motor is difficult to step out. On the other hand, when the target steady speed at which the load torque generated by the registration motor is small is low (when the printing speed is γ), the initial target speed at the time of through-up is large because the margin for resist motor step-out is large. However, it is difficult for the registration motor to step out. Therefore, in the present embodiment, when the printing speed is slow, the initial target speed at the time of through-up remains large.

  As described above, also in the first modification, even when the printing speed is high, the margin for the step-out of the registration motor increases, so the paper size, the paper type, the contact pressure of the pickup roller 4 and the contact of the paper feed roller 5 are increased. By changing the pressure or the like, the occurrence of step-out of the registration motor can be reduced even if a slight fluctuation occurs in the load torque generated in the registration motor. As a result, conventionally, a resist motor having a large torque is selected in consideration of the maximum load torque when the printing speed is high. In this embodiment, a resist motor having a relatively small torque can be selected. Thus, the motor can be reduced in size and cost. In addition, since control for increasing the input current value is not required to obtain a large motor torque, there is no problem of temperature increase and power consumption increase due to heat generation accompanying the increase of the input current value.

[Modification 2]
Next, another modified example of the registration motor drive control in the embodiment (hereinafter, this modified example is referred to as “modified example 2”) will be described.
In the second modification, in the control mode with a fast target steady speed in which the load torque generated by the registration motor is large, both the acceleration at the time of through-up and the initial target speed are reduced to reduce the load torque generated by the registration motor. It is to reduce.

  FIG. 7 is a graph showing the control speed (target speed) immediately after the start of driving of the registration roller 8 in each control example according to the three types of printing speeds α, β, and γ in the second modification. In each control example in the second modification, not only the target roller steady speeds are different from each other, but also the first target roller speed (initial target speed) immediately after the start of driving and the target roller steady speed as shown in FIG. The increase rate (acceleration) of the target roller speed is different from each other. Specifically, the drive control of the registration roller 8 is performed so that both the initial target speed and acceleration at the time of through-up (during acceleration) become smaller as the control mode has a higher target roller steady speed. According to the second modification, it is possible to further increase the margin for the step-out of the registration motor when the printing speed is higher than in the case of the above-described embodiment and the first modification.

  In the above-described embodiment and the two modifications, the leading edge of the sheet 3 is moved from the start of the registration motor drive since the acceleration and initial target speed at the time of through-up are changed according to the difference in the printing speeds α, β, and γ. The time required to reach the transfer portion 9A varies slightly depending on the printing speeds α, β, and γ. Therefore, in order to reduce such time deviation, the driving start timing of the registration motor may be varied for each of the printing speeds α, β, and γ. Thereby, the image position accuracy in the paper conveyance direction with respect to the paper 3 can be kept good.

  In the above description, the case where the registration motor is a stepping motor has been described. However, the present invention can be widely applied to a motor that requires an acceleration period, such as a DC motor.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image forming unit such as a drum 9 that forms an image on a sheet material such as paper 3, a conveyance roller such as a registration roller 8 that conveys the sheet material, a drive motor such as a registration motor that rotationally drives the conveyance roller, Start driving the drive motor at a predetermined drive start timing, and increase the speed of the drive motor so as to follow a target speed that increases stepwise, so that the drive motor is driven at a target steady speed, In an image forming apparatus such as a stencil printing apparatus 1 having a drive control unit such as a control unit that performs drive control of the drive motor, the drive control unit has a plurality of control modes in which the target steady-state speeds are different from each other, Among the plurality of control modes, when executing a control mode with a high target steady-state speed, the acceleration at the time of acceleration is higher than when the control mode with a low target steady-state speed is executed. So that at least one of the degrees and speed increasing at the start of the initial target speed is reduced, and performs the driving control.
According to this, even in the control mode with a high target steady-state speed at which the load torque becomes large, at least one of the acceleration at the time of acceleration and the initial target speed at the time of acceleration becomes small, so that the actual speed during the acceleration is increased. And the target speed are reduced, and the load torque during acceleration can be reduced. Accordingly, since the margin for the step-out of the drive motor is increased, the load generated in the drive motor due to changes in the paper size, paper type, contact pressure of the pickup roller 4, contact pressure of the paper feed roller 5, and the like. Even if some fluctuations occur in the torque, the occurrence of step-out of the drive motor can be reduced. As a result, in the past, a drive motor with a large torque was selected in consideration of the maximum load torque in the control mode with a high target steady-state speed. According to this aspect, a drive motor with a relatively small torque is selected. This makes it possible to select a motor and reduce the size and cost of the motor. In addition, since control for increasing the input current value is not required to obtain a large motor torque, there is no problem of temperature increase and power consumption increase due to heat generation accompanying the increase of the input current value.

(Aspect B)
In the aspect A, when the load torque applied to the drive motor during conveyance of the sheet material is large, the drive control means includes at least the acceleration at the time of acceleration and the initial target speed at the time of acceleration than when the load torque is small. The drive control is performed so that one becomes smaller.
Even when the target steady speed is low, the load torque applied to the drive motor may be larger than expected. According to this aspect, even when an unexpected excessive load torque is applied to the drive motor, the margin for the drive motor step-out can be increased to reduce the occurrence of the drive motor step-out.

(Aspect C)
An image forming unit that forms an image on a sheet material; a conveyance roller that conveys the sheet material; a drive motor that rotationally drives the conveyance roller; and driving of the drive motor at a predetermined drive start timing; An image forming apparatus having drive control means for controlling drive of the drive motor so that the drive motor is driven at a target steady speed after the drive motor is accelerated so as to follow a target speed that increases in size When the load torque applied to the drive motor during sheet material conveyance is large as in the control mode in which the target steady speed is fast, the load torque is small as in the control mode in which the target steady speed is slow. The drive control is performed so that at least one of the acceleration at the time of acceleration and the initial target speed at the time of acceleration becomes smaller than the time. To.
An excessive load torque exceeding the assumption may be applied to the drive motor. According to this aspect, even when an unexpected excessive load torque is applied to the drive motor, the margin for the drive motor step-out can be increased to reduce the occurrence of the drive motor step-out. Moreover, in the conventional case, a drive motor having a large torque should be selected in consideration of such an excessive load torque. According to this aspect, a drive motor having a relatively small torque can be selected. Can be reduced in size and cost. In addition, since control for increasing the input current value is not required to obtain a large motor torque, there is no problem of temperature increase and power consumption increase due to heat generation accompanying the increase of the input current value.

(Aspect D)
In any one of the aspects A to C, the drive control means changes the predetermined drive start timing according to at least one of the acceleration at the time of acceleration and the initial target speed at the time of acceleration. It is characterized by.
According to this, it is possible to improve the positional accuracy in the sheet conveyance direction with respect to the sheet material, in other words, the deviation of the image positional accuracy, caused by the acceleration at the time of acceleration (through-up) and the difference in the initial target speed.

(Aspect E)
In any one of the aspects A to D, the conveyance roller is a registration roller that conveys the sheet material so that the sheet material reaches the image forming unit at a predetermined image formation start time. To do.
According to this, it is possible to maintain a large margin for the drive motor (registration motor) that drives the registration rollers to be out of the proper driving range.

DESCRIPTION OF SYMBOLS 1 Stencil printing apparatus 2 Paper feed base 3 Paper 3A Paper conveyance path 4 Pickup roller 5 Paper feed roller 6 Friction pad 7 Registration sensor 8 Registration roller 9 Drum 9A Transfer part 10 Press roller 11 Suction belt 12 Discharge stand

JP 2011-128195 A

Claims (5)

An image forming unit for forming an image on a sheet material;
A transport roller for transporting the sheet material;
A drive motor for rotationally driving the transport roller;
Start driving the drive motor at a predetermined drive start timing, and increase the speed of the drive motor so as to follow a target speed that increases stepwise, so that the drive motor is driven at a target steady speed, In an image forming apparatus having a drive control means for performing drive control of the drive motor,
The drive control means has a plurality of control modes in which the target steady speed is different from each other, and when executing a control mode in which the target steady speed is fast among the plurality of control modes, a control mode in which the target steady speed is slow An image forming apparatus that performs the drive control so that at least one of an acceleration at the time of acceleration and an initial target speed at the time of acceleration is smaller than that at the time of executing the above. The image forming apparatus according to claim 1.
The drive control means is configured such that when the load torque applied to the drive motor is large during sheet material conveyance, at least one of the acceleration at the time of acceleration and the initial target speed at the time of acceleration is smaller than when the load torque is small. An image forming apparatus that performs the drive control. An image forming unit for forming an image on a sheet material;
A transport roller for transporting the sheet material;
A drive motor for rotationally driving the transport roller;
Start driving the drive motor at a predetermined drive start timing, and increase the speed of the drive motor so as to follow a target speed that increases stepwise, so that the drive motor is driven at a target steady speed, In an image forming apparatus having a drive control means for performing drive control of the drive motor,
The drive control means is configured such that when the load torque applied to the drive motor is large during sheet material conveyance, at least one of the acceleration at the time of acceleration and the initial target speed at the time of acceleration is smaller than when the load torque is small. An image forming apparatus that performs the drive control. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the drive control unit changes the predetermined drive start timing in accordance with a difference between at least one of acceleration at the time of acceleration and an initial target speed at the time of acceleration. The image forming apparatus according to any one of claims 1 to 4, wherein:
The image forming apparatus, wherein the conveyance roller is a registration roller that conveys the sheet material so that the sheet material reaches the image forming unit at a predetermined image formation start time.

Images