JP2020190657A - Image forming apparatus and sheet conveying device - Google Patents

Abstract

To reduce the rotation speed of a motor while maintaining the stability of a conveying operation.SOLUTION: An image forming apparatus executes speed control of changing the rotation speed of a motor according to the timing at which sheet detection means detects a sheet, during execution of a conveying operation to cause the motor to drive conveying means to convey the sheet. The image forming apparatus executes acceleration change processing of changing the acceleration of the motor in the speed control based on the magnitude of load torque detected by torque detection means when the apparatus causes the motor to drive the conveying means.SELECTED DRAWING: Figure 10

Description

The present invention relates to an image forming apparatus for forming an image on a sheet and a sheet conveying device for conveying a sheet.

In image forming devices such as printers, copiers, and multifunction devices, sheets used as recording materials are fed one by one from a feeding cassette or the like, and an image is formed on the sheets by an image forming unit such as an electrophotographic method or an inkjet method. To do. Inside the image forming apparatus, the sheet is conveyed by a transfer roller driven by a motor. The sheet transfer speed inside the device is not always constant, and may be accelerated or decelerated during the transfer operation.

Patent Document 1 describes that, in an electrophotographic apparatus that transfers a fed paper to a transfer unit without pausing the transfer, the image transferred to the paper and the paper are transferred by accelerating or decelerating the transfer speed of the paper. It is described that alignment is performed. In this device, the productivity of the image forming device is improved by transporting the paper to the transfer section at regular intervals in accordance with the interval of the write-out start timing of the electrostatic latent image in the image forming section.

Japanese Unexamined Patent Publication No. 2008-287236

By the way, conventionally, the speed profile of the motor (time series of the target speed of the motor) when the sheet transfer speed is changed in the middle of the transfer operation is premised on accelerating or decelerating the motor at a preset constant acceleration. Was created. As this acceleration, in order to realize stable transfer operation, the maximum load torque that can act on the motor under normal operating conditions is assumed, and even if such load torque acts, the value is small enough to start the motor. (Slow acceleration) was selected.

However, on the premise that the rotation speed of the motor is changed at a gradual acceleration, the target speed may have to be set to a high value in order to deliver the sheet to a predetermined position at a predetermined timing. In general, the higher the speed at which a motor is rotated, the greater the noise associated with the rotation of the motor and the power consumption of the motor.

Therefore, an object of the present invention is to provide an image forming apparatus and a sheet conveying apparatus capable of suppressing the rotation speed of a motor while maintaining the stability of the conveying operation.

One aspect of the present invention includes an image forming means for forming an image on a sheet at an image forming position, a conveying means for conveying the sheet toward the image forming position, a motor for driving the conveying means, and the conveying means. The sheet detecting means for detecting the sheet on the sheet conveying path toward the image forming position via the motor, the torque detecting means for detecting the load torque applied to the motor, and the conveying operation for conveying the sheet by the conveying means are being executed. A control means for executing speed control for changing the rotation speed of the motor according to the timing when the seat detecting means detects the seat, and the control means causes the motor to drive the conveying means. The image forming apparatus is characterized in that an acceleration change process for changing the acceleration of the motor in the speed control is executed based on the magnitude of the load torque detected by the torque detecting means.

In another aspect of the present invention, a transport means for transporting the sheet toward a predetermined position, a motor for driving the transport means, and a sheet on a transport path of the sheet toward the predetermined position via the transport means. The sheet detecting means for detecting, the torque detecting means for detecting the load torque applied to the motor, and the sheet detecting means according to the timing when the sheet is detected during the execution of the transporting operation of transporting the sheet by the transporting means. A control means for executing speed control for changing the rotation speed of the motor is provided, and the control means determines the magnitude of the load torque detected by the torque detecting means when the motor drives the transport means. Based on this, the sheet transfer device is characterized in that an acceleration change process for changing the acceleration of the motor in the speed control is executed.

According to the present invention, the rotation speed of the motor can be suppressed while maintaining the stability of the transport operation.

The schematic diagram of the image forming apparatus which concerns on Example 1. FIG. The schematic diagram which shows the drive structure of the feeding mechanism which concerns on Example 1. FIG. The schematic diagram of the feed motor which concerns on Example 1. FIG. The figure which shows the control circuit of the feed motor which concerns on Example 1. FIG. The figure which shows the arrangement (a) of the sheet transport path which concerns on Example 1 and the position (b, c) of a sheet in the sheet feeding operation. The diagram which shows the transition of the sheet tip position and the sheet transfer speed in a reference example. The graph which shows the relationship between the acceleration of the feed motor which concerns on Example 1 and the acceleration magnification. The graph which shows the relationship between the load torque and acceleration of the feed motor which concerns on Example 1. FIG. FIG. 6 is a diagram showing a transition of a sheet tip position and a sheet transport speed in the first embodiment. The flowchart which shows the control method of the image forming apparatus which concerns on Example 1. The figure which shows the drive circuit of the feed motor which concerns on Example 2. FIG. The flowchart which shows the control method of the image forming apparatus which concerns on Example 2.

Hereinafter, exemplary embodiments for carrying out the present invention will be described with reference to the drawings.

First, the overall configuration of the image forming apparatus according to the first embodiment will be described. FIG. 1 is a schematic view of a printer 100, which is an image forming apparatus according to this embodiment. The printer 100 is an electrophotographic image forming apparatus having an image forming unit 101 including four process cartridges 5Y, 5M, 5C, and 5K that can be attached to and detached from the printer body, and an intermediate transfer unit 102.

Although the process cartridges 5Y to 5K differ in that they form a toner image of yellow (Y), magenta (M), cyan (C), and black (K), the structure related to image formation is the same. Therefore, in the following description, the process cartridge 5Y will be taken as an example. The process cartridge 5Y includes a toner container 23Y for containing toner, a photoconductor 1Y, a charging roller 2Y, a developing roller 3Y, a drum cleaner 4Y, and a waste toner container 24Y. An irradiation unit 7Y of the exposure apparatus 7 is arranged below the process cartridge 5Y.

Photoreceptor 1Y is a rotatable drum-shaped member. When the process cartridge 5Y creates a toner image, the charging roller 2Y uniformly charges the surface of the rotating photoconductor 1Y to a predetermined polarity and a predetermined potential. The surface of the charged photoconductor 1Y is exposed by the exposure apparatus 7, and an electrostatic latent image corresponding to the yellow color component image is written. The developing roller 3Y carries and rotates a developer containing toner contained in the toner container 23Y, and supplies toner to the photoconductor 1Y. As a result, the electrostatic latent image supported on the photoconductor 1Y is developed into a toner image. By performing the same process in parallel in the other process cartridges 5M to 5K, toner images of each color are formed on the surfaces of the photoconductors 1Y to 1K.

The intermediate transfer unit 102 includes an intermediate transfer belt 8, a drive roller 9, a secondary transfer opposed roller 10, a belt cleaner 21, and a waste toner container 22. Further, the intermediate transfer unit 102 is provided with primary transfer rollers 6Y to 6K at positions inside the intermediate transfer belt 8 and facing the photoconductors 1Y to 1K of each process cartridge 5Y to 5K. The drive roller 9 is rotated by a motor (not shown) to rotate the intermediate transfer belt 8 in the direction of the arrow α in FIG.

The toner images supported on the photoconductors 1Y to 1K are sequentially transferred to the intermediate transfer belt 8 by the primary transfer rollers 6Y to 6K, and transferred to the secondary transfer roller 11 in a state where the toner images of four colors are superimposed. Will be done. The drum cleaner 4Y, which is a blade-shaped cleaning member, removes deposits such as residual toner remaining on the photoconductor 1Y without being transferred to the intermediate transfer belt 8 from the surface of the photoconductor 1Y, and collects them in the waste toner container 24Y. ..

When the toner image supported on the intermediate transfer belt 8 reaches the secondary transfer portion, which is the nip portion formed between the secondary transfer roller 11 and the intermediate transfer belt 8, the bias formed by the secondary transfer roller 11 The toner image is secondarily transferred to the sheet by the electric field. The intermediate transfer belt 8 is the image carrier of this example, the secondary transfer roller 11 is the transfer member of this example, and the position of the secondary transfer portion is the image forming position of this example. The belt cleaner 21, which is a blade-shaped cleaning member, removes deposits such as residual toner remaining on the intermediate transfer belt 8 without being transferred to the sheet from the belt surface, and collects them in the waste toner container 22.

In parallel with such an image forming process, a transport operation is executed in which the sheets P loaded on the feed cassette 13 are fed one by one and transported toward the secondary transfer unit. The sheet P loaded on the feeding cassette 13 which is an example of the sheet loading section is sent out from the feeding cassette 13 by the feeding roller 14 in order from the highest sheet. The transport roller 15 receives the sheet P from the feed roller 14 and transports it toward the registration roller (hereinafter referred to as a registration roller) 16.

The separation roller 15a as a separation member is connected to a shaft fixed to the printer body via a torque limiter, and forms a separation nip with the transfer roller 15. The separation roller 15a applies a frictional force to the sheet P at the separation nip, and regulates that a sheet other than the uppermost sheet in contact with the transfer roller 15 passes through the separation nip. As a result, the sheets P are delivered to the registration roller 16 in a state of being separated one by one. The separation roller 15a is an example of a separation member, and a pad-shaped friction member that abuts on the transfer roller 15 and a torque limiter that applies a driving force in a direction opposite to the rotation of the transfer roller 15 (counterclockwise direction in FIG. 1). You may use the retard roller which is input through.

The registration roller 16 conveys the sheet P toward the secondary transfer unit. In this embodiment, the register roller 16 adopts a configuration in which the image is aligned in the sheet transport direction (sub-scanning direction) by controlling the transport speed of the sheet P without stopping the sheet tip.

As described above, the sheet P to which the toner image is transferred in the secondary transfer unit is conveyed to the fixing device 17. The fixing device 17 comprises a heating roller 18 and a pressure roller 19 which are a pair of rotating bodies that sandwich and convey the sheet P, and a heating element such as a halogen lamp that heats a toner image on the sheet via the heating roller 18. Have. The toner image on the sheet is heated and pressurized when passing through the nip portions of the heating roller 18 and the pressurizing roller 19 to melt, and then fixed to the sheet P.

The sheet P sent out from the fixing device 17 can switch the transport path by the flap-shaped switching member 30. The sheet P guided to the transport path (A) toward the discharge roller 20 is discharged to the outside of the printer body by the discharge roller 20 and loaded on the discharge tray provided on the upper surface of the housing of the printer 100. When double-sided printing is performed, the sheet P whose image is formed on the first surface is guided by the switching member 30 to the transport path (B) toward the reversing roller 31. Then, the sheet P is switchback-conveyed by the reversing roller 31 and fed to the double-sided transport path (C). Then, it is conveyed again toward the secondary transfer unit via the refeed roller 32 arranged in the double-sided transfer path, an image is formed on the second surface opposite to the first surface, and then the discharge roller 20 It is discharged to the outside of the printer body.

The printer 100 is equipped with a control unit 25 which is a control board on which a control circuit (electronic circuit) is formed. A central processing unit (CPU) 26 and a memory 27 are mounted on the control unit 25, which is the control means of this embodiment. The CPU 26 controls the operation of the printer 100 by reading the control program from the memory 27 and executing the control program. For example, the CPU 26 controls a drive source (for example, a feed motor 34 described later) related to the sheet transfer operation, controls the drive source of the process cartridges 5Y to 5K, controls the exposure apparatus 7, and further controls the failure detection. ing. The memory 27 includes a non-volatile storage device and a volatile storage device, and serves as a storage place for the control program and data necessary for executing the control program, and also provides a work place for the CPU 26 to execute the control program.

The control unit 25 operates by the electric power supplied from the switching power supply 28. The switching power supply 28 is a device that converts an alternating current power supply voltage input from a power cable 29 connected to a commercial power supply into a direct current (DC) voltage used in each part of the printer 100, and operates with the control unit 25 and other electric power. Is supplying to.

The above image forming unit 101 and intermediate transfer unit 102 are examples of image forming means, and a direct transfer type electrophotographic unit that directly transfers a toner image formed on a photoconductor to a sheet without an intermediate transfer body is used. May be good. The image carrier in this case is a photoconductor, a transfer roller or the like that transfers a toner image from the photoconductor to a sheet is a transfer member, and a position where the photoconductor and the transfer member face each other is an image forming position. Further, not limited to the electrophotographic unit, an image forming unit such as an inkjet method or an offset printing method may be used as the image forming means.

(Feeding mechanism)
Next, the feeding mechanism 33 provided in the printer 100 will be described. The feeding mechanism 33 of this embodiment includes a feeding roller 14, a transport roller 15, a register roller 16, a refeeding roller 32, a drive source for driving these roller members, and a drive transmission configuration. Point to. The feed roller 14, the transport roller 15, the register roller 16, and the refeed roller 32 are all examples of transport means for transporting the sheet driven by a motor.

FIG. 2 shows a driving force transmission configuration of the feeding mechanism 33. The feed motor 34 is a direct current (DC) motor that is a drive source for the feed mechanism 33. The driving force of the feed motor 34 is directly transmitted to the register roller 16 and the transfer roller 15 via a gear train (not shown). In other words, the register roller 16 and the transfer roller 15 are always connected to the feed motor 34 and are rotationally driven in conjunction with the rotation of the rotor of the feed motor 34.

On the other hand, a feed clutch 35 is arranged in the drive transmission path from the feed motor 34 to the feed roller 14. The feed clutch 35 has an engaged state (ON state) in which the driving force of the feed motor 34 is transmitted to the feed roller 14 and a non-engaged state (OFF state) in which the drive transmission is cut off by a command signal from the CPU 26. It switches to. As the feed clutch 35, for example, an electromagnetic clutch can be used.

Further, sensors for detecting the passage of the sheet are arranged at at least one place on the transfer path of the sheet transported by the feeding mechanism 33. In this embodiment, the transfer sensor 15S that detects the sheet at a detection position substantially the same as the position where the transfer roller 15 contacts the sheet, and the registration sensor (registration sensor) that detects the sheet at a detection position substantially the same as the position where the registration roller 16 contacts the sheet. ) 16S and are arranged. Each of the transport sensor 15S and the registration sensor 16S is composed of, for example, a mechanical flag protruding into the seat transport path (the space through which the seat passes) and a photo interrupter for detecting that the mechanical flag is pressed by the seat and swings. A sensor unit is used. Both the transport sensor 15S and the registration sensor 16S are examples of sheet detection means for detecting a sheet at a predetermined detection position on the transport path.

FIG. 3 is a schematic view of the feed motor 34 according to this embodiment. The feed motor 34 is an inner rotor type brushless motor which is a kind of synchronous motor. That is, the feed motor 34 is composed of a stator 34S in which the rotation drive unit (motor body) 34M is fixed to the motor case 34C, and a rotor 34R in which permanent magnets are attached to a plurality of positions in the rotation direction. It is a motor unit. The rotation drive unit 34M is configured so that the rotor 34R rotates when a plurality of coils attached to the stator 34S are energized in a predetermined order.

An output gear 41 is attached to one end in the axial direction and an encoder disk 42 is attached to the opposite end of the rotating shaft 40 to which the rotor 34R is attached. Further, the feed motor 34 is provided with a driver board 43 on which a drive circuit (a driver circuit unit described later) for driving a rotation drive unit by passing a current through the coil of the stator 34S is mounted. Further, the driver board 43 is provided with an encoder detection unit 44 that detects the rotation speed of the encoder disk 42, and a connector 45 that serves as an interface for supplying power to the feed motor 34 and transmitting a signal to the CPU 26.

The command signal transmitted from the CPU 26 to the feed motor 34 includes a signal used for controlling the rotation speed of the feed motor 34, a rotation direction signal instructing the rotation direction, and a brake signal instructing deceleration. In this embodiment, a pulse width modulation signal (PWM signal) is used for speed control of the feed motor 34. On the other hand, as a signal transmitted from the feed motor 34 to the CPU 26, there is an encoder signal (detection signal of the encoder detection unit 44) indicating the rotation speed of the feed motor 34.

FIG. 4 shows a control circuit that controls the drive of the feed motor 34. The control unit 25 includes a speed / position control unit 50, a gain setting unit 49, a target speed / target position setting unit 47, a rotation direction setting unit 51, and a brake setting unit 52 as functional units related to the control of the feed motor 34. It includes a speed / position measuring unit 48 and a PWM duty recording unit 53.

The speed / position control unit 50 is a PID control unit that controls the rotation speed and position (rotation angle) of the feed motor 34 by PID control. That is, the speed / position control unit 50 transmits a PWM signal to the feed motor 34 based on the deviation between the target value of the rotation speed and position of the feed motor 34 and the current value, and the integration and differentiation of the deviation. Calculate (generate). The target speed / target position setting unit 47 sets the rotation speed and the target value of the position used for PID control. For example, in the acceleration / deceleration control described later, the target speed / target position setting unit 47 sets the rotation speed and the target value of the position of the feed motor 34 at each time point during the sheet transport operation according to the speed profile of the acceleration / deceleration control. .. The speed / position measuring unit 48 acquires the current values of the rotation speed and the position used for PID control based on the encoder signal received from the feed motor 34. The gain setting unit 49 sets each control gain used for PID control.

The driver circuit unit 46 of the feed motor 34 drives the rotation drive unit according to the received control signal. Specifically, the driver circuit unit 46 includes a switching circuit (inverter circuit) including a plurality of switching elements such as a field effect diode (FET), and a control circuit such as a microcomputer that operates the switching elements. The driver circuit unit 46 drives the rotation drive unit 34M by switching the path through which the current flows with respect to the coil of the stator in a predetermined order to generate a rotating magnetic field. The driver circuit unit 46 has a function of generating a pseudo sine wave voltage by controlling the switching circuit based on the encoder signal and applying it to the rotation drive unit 34M. In this case, the PWM signal is a sine wave. This means that the amplitude of is specified. That is, the PWM signal is an example of a command signal capable of controlling the input power to the feed motor 34. However, the control method of the rotation drive unit 34M by the driver circuit unit 46 is not limited to this, and for example, a rectangular wave may be output to drive the rotation drive unit 34M.

Further, the rotation direction setting unit 51 and the brake setting unit 52 set the value of the rotation direction signal for designating the rotation direction of the feed motor 34 and the value of the brake signal for decelerating the feed motor 34, respectively. These control signals (PWM signal, rotation direction signal, brake signal) are transmitted from the control unit 25 to the driver circuit unit 46 of the feed motor 34. The driver circuit unit 46 switches the rotation direction of the feed motor 34 based on the value of the rotation direction signal, and decelerates the rotation of the rotor of the feed motor 34 based on the value of the brake signal.

Here, the amount of current supplied to each coil of the stator 34S is controlled by the PWM signal. The PWM signal is a modulation method in which the period is constant and the signal strength is expressed by the length of the period (also called pulse width or duty ratio) during which the current is ON in one cycle. As the pulse width increases, a large amount of current flows through the coil, and the drive torque output by the rotary drive unit 34M increases. The speed / position control unit 50 changes the duty ratio of the PWM signal at any time by PID control so that the feed motor 34 outputs a drive torque corresponding to the magnitude of the load torque.

As described above, the duty ratio of the PWM signal transmitted from the speed / position control unit 50 to the driver circuit unit 46 reflects the magnitude of the load torque applied to the feed motor 34. Therefore, in this embodiment, the magnitude of the load torque applied to the feed motor 34 is increased by monitoring the duty ratio of the PWM signal transmitted by the speed / position control unit 50 to the driver circuit unit 46 of the feed motor 34. Can be detected. The PWM duty recording unit 53, which is the torque detecting means of this embodiment, records the duty ratio of the PWM signal transmitted by the speed / position control unit 50 to the driver circuit unit 46 of the feed motor 34, and is used for the control described later. The average value (PWM_AVE) of the signal is acquired.

The encoder detection unit 44 provided on the driver board 43 of the feed motor 34 detects the rotational state of the rotation shaft 40 of the feed motor 34 and transmits the encoder signal to the control unit 25. The speed / position measurement unit 48 of the control unit 25 calculates the current rotation speed and rotation position of the feed motor 34 by monitoring the encoder signal.

Each of the above-mentioned functional units in the control unit 25 may be implemented as a module of a control program executed by the CPU 26, or may be implemented as a dedicated circuit such as an ASIC. For example, the CPU 26 can set the target speed and the target position by the target speed / target position setting unit 47, set the control gain by the gain setting unit 49, and record the duty ratio of the PWM signal by itself.

(Acceleration / deceleration control in sheet transfer operation)
Subsequently, acceleration / deceleration control (speed control of this embodiment) for changing the sheet transfer speed during the sheet transfer operation will be described with reference to FIG. Hereinafter, the "tip" of the sheet refers to the downstream end of the sheet in the sheet transport direction, and the "rear edge" of the sheet refers to the upstream end of the sheet in the sheet transport direction. Regarding the two sheets that are continuously fed from the feed cassette 13, the sheet that is fed in advance is referred to as the "preceding sheet", and the sheet that is fed after the preceding sheet is referred to as the "successor sheet". .. Further, the transfer speed of the sheet in the secondary transfer unit is defined as the "process speed". Further, the rotation speed of the feed motor 34 such that the peripheral speed of the register roller 16 becomes equal to the process speed is also referred to as a "reference speed" of the feed motor 34.

In the printer 100 of this embodiment, the sheet spacing in the secondary transfer unit is set to 10 mm, and the sheet spacing at the time of feeding is set to 25 mm. However, the sheet spacing in the secondary transfer section is the distance in the sheet transport direction from the rear end of the preceding sheet to the tip of the succeeding sheet when the tip of the succeeding sheet reaches the secondary transfer section. The sheet interval at the time of feeding is the distance in the sheet transporting direction from the front end of the succeeding sheet to the rear end of the preceding sheet at the time when the feeding of the succeeding sheet is started. Specifically, when the feeding of the succeeding seat is started, the feeding clutch 35 is switched from OFF (non-engaged) to ON (engaged) while the feeding motor 34 is rotating. This is the time when the rotary drive of the feed roller 14 is started.

By the way, the above-mentioned numerical value (25 mm) of the sheet spacing at the time of feeding is a design value, the preceding sheet and the succeeding sheet are set at predetermined positions of the feeding cassette 13, and the feeding of the succeeding sheet is started. If there is no delay or the like, the seat spacing at the time of actual feeding is also 25 mm. However, in the actual sheet transport operation, the sheet spacing at the time of feeding may not be 25 mm. Factors that cause the seat spacing during feeding to be wider than 25 mm are the slip of the feeding roller 14 and the response characteristics of the feeding clutch 35 (from the ON command from the control unit 25 to the start of rotational drive of the feeding roller 14). Delay). Further, when the uppermost sheet in the feeding cassette 13 deviates from a predetermined set position in the sheet transporting direction, it also becomes a factor for changing the sheet spacing at the time of feeding.

On the other hand, from the viewpoint of improving the productivity of the image forming apparatus, it is preferable to keep the sheet spacing in the secondary transfer unit as constant as possible. This is because if the process speed is constant, productivity can be increased by narrowing the sheet spacing.

In particular, in this embodiment, the register roller 16 adopts a configuration in which the image is aligned in the sheet transport direction (sub-scanning direction) by controlling the sheet transport speed without stopping the sheet tip. In this configuration, it is important to keep the sheet spacing constant not only from the viewpoint of improving productivity but also from the viewpoint of improving the accuracy of the image position.

Therefore, in this embodiment, by executing the acceleration / deceleration control during the sheet transport operation, the sheet spacing in the secondary transfer unit is 10 mm even if the sheet spacing during feeding deviates from 25 mm. Change the transport speed of.

FIG. 5A shows the positional relationship between the rollers on the transport path from the feed roller 14 to the secondary transfer unit. In this embodiment, the distance from the feeding roller 14 to the separation nip is 25 mm, the distance from the separation nip to the nip portion of the registration roller 16 is 35 mm, and the distance from the nip portion of the registration roller 16 to the secondary transfer portion is 100 mm. To do.

FIG. 5 (b, c) shows the transfer of the preceding sheet and the succeeding sheet in the case of continuous single-sided printing in which a plurality of sheets are continuously fed from the feeding cassette 13 to form an image on one side of the sheets. It shows the state of operation. In this embodiment, since the seat spacing during feeding is set to 25 mm, the feeding clutch 35 is turned on when the rear end of the preceding seat P1 passes through the separation nip as shown in FIG. 5 (b). It is switched to and the feeding of the succeeding sheet P2 is started. At this point, since the rear end of the preceding seat has not passed through the register roller 16 driven by the feed motor 34, the rotation speed of the feed motor 34 needs to be maintained at a speed at which the peripheral speed of the register roller 16 becomes the process speed. There is. If the rotation speed of the feed motor 34 is changed at the start of feeding the succeeding sheet P2, the peripheral speed of the register roller 16 becomes larger than the process speed, and the sheet bends between the register roller 16 and the secondary transfer unit. This is because it may lead to the disorder of the transferred image.

As shown in FIG. 5C, when the rear end of the preceding sheet P1 passes through the registration roller 16, the rotation speed of the feed motor 34 is temporarily accelerated to a speed higher than the reference speed corresponding to the process speed, and then. , It is decelerated to the reference speed. As a result, the tip of the succeeding sheet P2 approaches the rear end of the leading sheet P1 being conveyed at the process speed up to 10 mm. After that, the subsequent sheet P2 passes through the secondary transfer unit while being conveyed at the process speed, so that the toner image is transferred to a predetermined position on the sheet.

(Speed profile of acceleration / deceleration control)
Subsequently, the basic contents of the acceleration / deceleration control will be described with reference to FIG. The upper part of FIG. 6 is a diagram showing an example of transition of the tip position of the subsequent sheet in the case of continuous single-sided printing using the sheet loaded on the feeding cassette 13, and the lower part of FIG. 6 is a diagram showing a transition example of the tip position of the succeeding sheet. It shows the transition of the rotation speed of. The horizontal axes (time) of the upper and lower rows of FIG. 6 are common.

It is assumed that the preceding sheet is in a state of being transported at a constant process speed before the feeding of the succeeding sheet is started. Therefore, the rear end of the preceding sheet (thin broken line in the upper part of FIG. 6) passes through the positions of the feeding roller 14, the transport roller 15, the register roller 16, and the secondary transfer roller 11 in order at the process speed.

In the case of continuous single-sided printing, the feeding clutch 35 is engaged at the timing Ta when the distance between the preceding sheet and the succeeding sheet is 25 mm, so that the feeding roller 14 starts feeding the succeeding sheet. At this time, if the feeding of the succeeding sheet is delayed due to the slip of the feeding roller 14, the actual tip of the succeeding sheet is separated from the rear end of the leading sheet by more than 25 mm (the sheet interval at the time of feeding is 25 mm). In some cases, the subsequent seats are delivered in a more expanded state). At the upper end of FIG. 6, the solid line represents the case where there is almost no delay in the succeeding sheet, the alternate long and short dash line represents the case where a relatively small delay occurs in the succeeding sheet, and the broken line represents the case where a relatively large delay occurs in the succeeding sheet.

On the other hand, since the target value (target interval) of the sheet spacing in the secondary transfer section is set to 10 mm, even if there is no delay in the feeding of the succeeding sheet, the subsequent sheet reaches the secondary transfer section. It is necessary to narrow the seat spacing. In this embodiment, the sheet spacing is narrowed to 10 mm from the secondary transfer roller 11 to a position 30 mm upstream so that the tip of the sheet can be pushed into the secondary transfer section while the sheet transfer speed is stable. explain. That is, the position 30 mm upstream from the secondary transfer roller 11 (the position 30 mm upstream from the secondary transfer portion) corresponds to the target point for speed control in this embodiment that controls the sheet transfer speed.

Hereinafter, the state of acceleration / deceleration control according to the degree of delay of the succeeding seat will be described. However, in the reference example (FIG. 6) described here, it is assumed that a predetermined constant value is used for the acceleration when the feed motor 34 is accelerated or decelerated in the acceleration / deceleration control.

1. 1. When there is no delay in the succeeding sheet When there is almost no delay in the feeding of the succeeding sheet, that is, when the succeeding sheet is fed with the sheet spacing with respect to the preceding sheet approximately equal to 25 mm, the sheet spacing is reduced from 25 mm to 10 mm. Acceleration / deceleration control of the feed motor 34 may be performed as described above. At the time of timing Ta, since the preceding sheet is sandwiched between the registration rollers 16, the rotation speed of the feed motor 34 is the reference speed Vp corresponding to the process speed. After that, at the timing Tb when the rear end of the preceding sheet passes through the registration roller 16, acceleration of the feed motor 34 is started with a target speed (V1) faster than the reference speed Vp.

At the target speed V1, the distance between the preceding sheet and the succeeding sheet is reduced to 10 mm by the time the tip of the succeeding sheet reaches the target point (30 mm upstream of the secondary transfer roller 11) based on the delay amount of the succeeding sheet. Is set. More precisely, the difference between the moving speed of the succeeding seat and the moving speed (= process speed) of the preceding seat during execution of acceleration / deceleration control including during acceleration and deceleration of the feed motor is determined by the acceleration / deceleration control. The value integrated over the execution period becomes the seat interval shortened by the acceleration / deceleration control. Therefore, when there is almost no delay in feeding the succeeding seat, the seat interval (distance for catching up the succeeding seat to the preceding seat by the acceleration / deceleration control) is 25-10 = 15 [mm]. The target speed V1 for acceleration / deceleration control is determined.

After the feed motor 34 is accelerated to the target speed V1 and maintained at the target speed V1, the feed motor 34 is decelerated to the reference speed Vp. At this time, the deceleration start timing is determined according to the magnitude of the target speed V1 so that the deceleration of the feed motor 34 is completed at the timing Tc when the tip of the succeeding sheet reaches the point 30 mm upstream of the secondary transfer roller 11. Has been done. The acceleration / deceleration control of the feed motor 34 in this embodiment refers to a process from the start of acceleration of the feed motor 34 at the timing Tb to the completion of the deceleration of the feed motor 34 at the timing Tc.

When the tip of the succeeding sheet reaches a point 30 mm upstream of the secondary transfer roller 11 (Tc), the distance from the rear end of the preceding sheet to the tip of the succeeding sheet is reduced to 10 mm. After that, the rotation speed of the feed motor 34 is maintained at the reference speed Vp corresponding to the process speed until the rear end of the succeeding sheet passes through the register roller 16, and the succeeding sheet reaches the secondary transfer unit at the timing Td. Therefore, the succeeding sheet is conveyed at a process speed while maintaining a sheet spacing of 10 mm with respect to the preceding sheet, passes through the secondary transfer section, and the toner image is transferred to the sheet surface.

2. 2. When a relatively small delay occurs in the feeding of the succeeding sheet The alternate long and short dash line in FIG. 6 is an example of a case where a relatively small delay occurs in the feeding of the succeeding sheet, which is about 35 mm away from the rear end of the preceding sheet. It represents the case where the sheet is fed (when the delay amount of the succeeding sheet is about 10 mm). For example, if the timing at which the tip of the succeeding sheet is detected by the transport sensor 15S is delayed by 25 mm from the rear end of the preceding sheet and is delayed from the timing when the succeeding sheet is fed, the succeeding sheet is fed. It can be seen that there is a delay.

The delay amount of the succeeding sheet can be acquired, for example, based on the timing when the transport sensor 15S (FIG. 5) detects the tip of the succeeding sheet. For example, "the delay amount of the succeeding sheet is 10 mm" means that the tip position of the succeeding sheet is at the timing when the position of the succeeding sheet is determined by the transport sensor 15S or the like when there is no delay in the feeding of the succeeding sheet. It means that it is delayed by 10 mm. Further, in FIG. 6, by extrapolating the graph based on the delay amount of the succeeding sheet detected by the transport sensor 15S or the like, the tip of the succeeding sheet is also set in the time zone before the transport sensor 15S or the like detects the succeeding sheet. The position is illustrated. However, in reality, there is a period in which the tip of the succeeding seat stays in the vicinity of the feed roller 14 due to the slip of the feed roller 14 and the response delay of the feed clutch 35, so that the feed of the succeeding seat is delayed.

If there is a delay in the feeding of the succeeding seats, it is necessary to increase the seat interval to be shortened by the acceleration / deceleration control. Here, since it is assumed that the delay amount is about 10 mm, the target speed V2 of the acceleration / deceleration control is determined so that the seat interval shortened by the acceleration / deceleration control is 25 mm. This target speed V2 is a value larger than the target speed V1 for acceleration / deceleration control when there is almost no feed delay.

Except that the target speed V2 is different, the content of the acceleration / deceleration control is the same as when there is almost no feed delay. That is, the process of accelerating the feed motor 34 from the reference speed Vp to the target speed V2 is started at the timing Tb. After that, the feed motor 34 is moved at a timing corresponding to the magnitude of the target speed V2 so that the feed motor 34 is decelerated to the reference speed Vp at the timing Tc when the tip of the succeeding sheet reaches the target point. The process of decelerating from the target speed V2 to the reference speed Vp is started. As a result, when the tip of the succeeding sheet reaches the target point, the distance from the rear end of the preceding sheet to the tip of the succeeding sheet is reduced to 10 mm.

3. 3. When a relatively large delay occurs in the feeding of the succeeding sheet The broken line in FIG. 6 shows an example of a case where a relatively large delay occurs in the feeding of the succeeding sheet, which is about 95 mm away from the rear end of the preceding sheet. Indicates the case where is fed (when the delay amount of the subsequent sheet is about 70 mm). When such a large delay occurs, it is necessary to further increase the seat interval to be shortened by the acceleration / deceleration control. Specifically, the target speed V3 of the acceleration / deceleration control is determined so that the seat spacing shortened by the acceleration / deceleration control is 85 mm. This target speed V3 is a value even larger than the target speed V2 for acceleration / deceleration control when the feed delay is relatively small.

Except that the target speed V3 is different, the content of the acceleration / deceleration control is the same as when there is almost no feed delay. That is, the process of accelerating the feed motor 34 from the reference speed Vp to the target speed V3 is started at the timing Tb. After that, the feed motor 34 is moved at a timing corresponding to the magnitude of the target speed V3 so that the feed motor 34 is decelerated to the reference speed Vp at the timing Tc when the tip of the succeeding sheet reaches the target point. The process of decelerating from the target speed V3 to the reference speed Vp is started. As a result, when the tip of the succeeding sheet reaches the target point, the distance from the rear end of the preceding sheet to the tip of the succeeding sheet is reduced to 10 mm.

When the feeding of the succeeding sheet is significantly delayed as shown by the broken line, the transport sensor 15S may not detect the tip of the succeeding sheet even at the timing Tb. Even in such a case, in this embodiment, it is determined that a feeding delay has occurred in the succeeding seat based on the fact that the transport sensor 15S does not detect the seat, and the acceleration / deceleration control of the feeding motor 34 is performed at the timing Tb. Shall start. When the acceleration / deceleration control is started, the feed motor 34 is accelerated to a temporary target speed V3 which is faster than the reference speed Vp. In this case, when the transport sensor 15S detects the tip of the succeeding seat after the timing Tb, the seat spacing is shortened to 10 mm by the acceleration / deceleration control, so that a more appropriate target speed is reset.

Further, if the transport sensor 15S still does not detect the succeeding sheet even after a predetermined time has elapsed from the timing Tb, it is determined that an abnormality in the transport operation (feeding failure) has occurred and the job is interrupted. The length of the predetermined time determined to be poor feeding corresponds to, for example, a delay amount in which the seat interval cannot be shortened to 10 mm by the target point even if the feeding motor 34 is accelerated to the maximum speed. .. Such resetting of the target speed can be executed even when there is almost no delay in feeding the succeeding sheet or when it is relatively small.

(Rotation speed of motor in acceleration / deceleration control)
As described above, by controlling the acceleration / deceleration of the feed motor 34 based on the degree of feed delay of the succeeding sheet detected by the transport sensor 15S or the like, it is possible to bring the sheet spacing in the secondary transfer unit close to a constant value. Is.

However, as shown in the lower part of FIG. 6, as the delay amount of the succeeding seat increases, the target speed of acceleration / deceleration control required to recover the delay is set to a larger value (V1 <V2 <V3). In general, the higher the rotation speed of the motor, the higher the operating noise and power consumption of the motor. Therefore, it has been required to suppress the maximum speed of the motor in acceleration / deceleration control.

One of the factors that causes the maximum speed of the motor to become a large value in acceleration / deceleration control is that a relatively small value is predetermined as the acceleration of the motor, and acceleration and deceleration must be performed at a relatively gentle acceleration. there were. If the acceleration of the motor is set to a large value, the motor may not rotate at the desired rotation speed when a large load is applied to the motor, for example, when transporting a sheet having a large basis weight and a high transport resistance. .. Specifically, when a synchronous motor is used as in the feed motor 34 of this embodiment, the motor stops when step-out occurs due to load torque. Further, even if the motor is not stopped, irregularities that cause noise are likely to occur in a state where the load torque is large. Therefore, in order to realize stable transport operation, the maximum load torque that can act on the motor under normal operating conditions is assumed, and even if such load torque acts, the value is small enough to start the motor (gentle). Acceleration) was selected.

However, the magnitude of the load torque acting on the feed motor 34 when actually transporting the sheet differs depending on conditions such as the material and size of the sheet, the presence or absence of curvature of the transport path, and environmental conditions (particularly humidity). .. Therefore, it is considered that even if the acceleration / deceleration control is performed at an acceleration larger than the preset relatively small acceleration, the stability of the transport operation may not be substantially affected.

Therefore, the inventors investigated the relationship between the magnitude of the load torque applied to the motor and the magnitude of the acceleration that can be used in the acceleration / deceleration control, and examined a method of suppressing the maximum speed of the motor in the acceleration / deceleration control.

FIG. 7 is a graph showing the relationship between the acceleration of the feed motor 34 and the acceleration magnification in the acceleration / deceleration control when the seat interval shortened by the acceleration / deceleration control is fixed to a constant value. Here, it is assumed that the delay of 60 mm is shortened by the acceleration / deceleration control. The acceleration of the feed motor 34 on the horizontal axis is the acceleration when the feed motor 34 is accelerated from the speed corresponding to the process speed to the target speed, and the acceleration of the feed motor 34 from the target speed to the speed corresponding to the process speed. Refers to the acceleration (deceleration) when decelerating. The acceleration of the feed motor 34 is an acceleration when the rotation speed of the feed motor 34 is converted into the peripheral speed of each roller, and the unit is [mm / s ² ]. The acceleration ratio on the vertical axis is the ratio of the target speed of the feed motor 34 in acceleration / deceleration control to the rotation speed (reference speed Vp) before acceleration.

Each point in FIG. 7 indicates the magnitude of the target speed of the feed motor 34, which is required when acceleration / deceleration control is performed under a specific acceleration (horizontal axis coordinates) to reduce a delay of a predetermined amount. (Vertical axis coordinates). As can be read from the figure, if acceleration / deceleration control is performed with a larger acceleration, the acceleration ratio can be suppressed to a smaller size. That is, it can be seen that the maximum speed of the motor in the acceleration / deceleration control can be suppressed if the acceleration / deceleration control can be performed with a larger acceleration.

Subsequently, FIG. 8 shows the relationship between the load torque of the motor and the acceleration. The horizontal axis represents the magnitude of the load torque applied to the motor, and the vertical axis represents the magnitude of the acceleration that the motor can output under the load torque. Similar to FIG. 7, the acceleration of the feed motor 34 is the acceleration when the rotational speed of the feed motor 34 is converted into the peripheral speed of each roller. As can be read from the figure, it can be seen that the larger the load torque applied to the motor, the smaller the acceleration of the motor. In other words, when the load torque applied to the motor when transporting the seat is relatively small, the stability of the transport operation is maintained even if acceleration / deceleration control is performed after setting the acceleration to a relatively large value. It is possible.

Therefore, considering the relationship between the acceleration and the acceleration magnification as shown in FIG. 7, when the load torque applied to the motor is relatively small, the acceleration in the acceleration / deceleration control is set to a large value to accelerate. It is possible to suppress the magnification (suppress the maximum speed). On the other hand, when the load torque applied to the motor is relatively large, the acceleration in the acceleration / deceleration control is set to a small value from the viewpoint of maintaining the stability of the transport operation. In this way, by changing the acceleration in acceleration / deceleration control according to the magnitude of the load torque actually applied to the motor when transporting the seat, the maximum speed of the motor can be suppressed, and the motor can be made quieter and save power. It becomes possible to obtain benefits such as conversion.

Since the magnitude of the load torque applied to the motor changes depending on the various conditions described above, it is determined based on the measured value of the load torque (or the physical quantity that correlates with the load torque) measured when the seat is actually conveyed. It shall be. As will be described in detail later, in this embodiment, the second and subsequent sheets are based on the average value of the duty ratios of the PWM signals to the feed motor 34 when the transfer operation is executed for the first sheet in the job. The acceleration of acceleration / deceleration control for the seat is changed.

(Control example)
FIG. 9 shows an operation example of acceleration / deceleration control to which this embodiment is applied. The upper part of FIG. 9 is a diagram showing an example of transition of the tip position of the succeeding sheet in the case of continuous single-sided printing using the sheet loaded on the feeding cassette 13, and the lower part of FIG. 9 is a diagram showing a transition example of the tip position of the succeeding sheet. It shows the transition of the rotation speed of. The horizontal axes (time) of the upper and lower rows of FIG. 9 are common.

Similar to the reference example described with reference to FIG. 6, the preceding sheet is conveyed at a constant process speed, and the feeding of the following sheet is set to start at the timing when the sheet spacing with respect to the preceding sheet becomes 25 mm. There is. Here, the change in acceleration / deceleration control due to the difference in the set value of the acceleration will be described on the assumption that the feeding delay is caused in the succeeding seat due to the slip of the feeding roller 14.

In the upper part of FIG. 9, the solid line (a) shows the transition of the seat tip position when it is determined that the load torque applied to the feed motor 34 is large. In this case, a relatively small value is selected as the acceleration in the acceleration / deceleration control, and the inclination of the acceleration portion and the deceleration portion of the speed profile becomes gentle as shown in the lower part of FIG. However, the acceleration part of the speed profile is a section in which the rotation speed of the motor is accelerated from the first speed (here, Vp) before the acceleration / deceleration control to the second speed (here, Va) faster than the first speed. is there. The speed reduction section of the speed profile is a section for decelerating the rotation speed of the motor from the second speed (here, Va) to the third speed (here, Vp) slower than the second speed. The target speed Va of the speed profile is set so that the seat spacing can be reduced to 10 mm by acceleration / deceleration control under the selected acceleration.

In the upper part of FIG. 9, the broken line (b) represents the transition of the seat tip position when it is determined that the load torque applied to the feed motor 34 is small. In this case, a relatively large value is selected as the acceleration in the acceleration / deceleration control, and the inclination of the acceleration portion and the deceleration portion of the speed profile becomes steep as shown in the lower part of FIG. The target speed Vb of the speed profile is set so that the seat spacing can be reduced to 10 mm by acceleration / deceleration control under the selected acceleration.

Comparing the solid line (a) and the broken line (b) in the lower part of FIG. 9, even if the seat spacing shortened by the acceleration / deceleration control is the same, the maximum speed can be suppressed by setting the acceleration to a larger value (Va). > Vb) can be seen. This is because the steeper the inclination of the acceleration portion and the deceleration portion of the speed profile, the longer the time during which the feed motor 34 can be maintained at the target speed is longer than in the case where the inclination is gentle. In other words, the area of the trapezoid surrounded by the straight line and solid line (a) of V = Vp (constant) and the area of the trapezoid surrounded by the straight line and broken line (b) of V = Vp (constant) in the lower part of FIG. As long as they are equal, the height of the trapezoid becomes smaller when the upper side is longer (b).

Therefore, as shown in FIG. 9, it can be seen that the maximum speed of the motor can be actually suppressed by changing the acceleration in the acceleration / deceleration control according to the magnitude of the load torque applied to the motor when the seat is conveyed. .. In FIG. 9, the change due to the difference in acceleration in the acceleration / deceleration control was described for the case where the feeding delay of the succeeding sheet is relatively large, but in this embodiment, the acceleration / deceleration control is performed even when the feeding delay of the succeeding sheet is small. Change the magnitude of acceleration in.

A control method of the image forming apparatus for realizing the above operation will be described with reference to FIG. FIG. 10 is a flowchart of a process for determining the acceleration of acceleration / deceleration control in this embodiment. It is assumed that each step of this process is processed by the CPU 26 (FIG. 1) reading and executing the control program stored in the memory 27. Further, this process is started when the CPU 26 executes the image forming job.

When there is a feed instruction for the first (first) sheet in the job (S101), the CPU 26 rotates the feed motor 34 and engages the feed clutch 35 to cause the feed roller. The feeding of the first sheet according to 14 is started (S102). During the period from the start of feeding the first sheet to the arrival of the tip of the sheet at the secondary transfer section, the CPU 26 records the duty ratio (PWM duty) of the PWM signal transmitted to the driver circuit section 46 of the feeding motor 34. (S103, S104). Then, when the tip of the sheet reaches the secondary transfer portion, the average value PWM_AVE of the PWM duty is calculated (S105).

The CPU 26 determines the acceleration of the feed motor 34 used for acceleration / deceleration control for the second and subsequent sheets according to the value of PWM_AVE acquired in the above procedure by performing the transfer operation for the first sheet. (S106 to S112). At this time, when the value of PWM_AVE becomes large, the condition is set so that the value of the motor acceleration in the acceleration / deceleration control becomes small. In the example shown in FIG. 10, the settings are as follows.
Motor acceleration when PWM_AVE is less than 20% ... a1
Motor acceleration when PWM_AVE is 20% or more and less than 40% ... a2
Motor acceleration when PWM_AVE is 40% or more and less than 60% ... a3
Motor acceleration when PWM_AVE is 60% or more ... a4

The motor accelerations a1 to a4 satisfy the relationship of a1 ≧ a2 ≧ a3 ≧ a4 and a1> a4. The following can be used as specific motor acceleration setting values.
a1 = 10000 [mm / s ² ]
a2 = 5000 [mm / s ² ]
a3 = 3000 [mm / s ² ]
a4 = 3000 [mm / s ² ]

That is, in this embodiment, when the variable (PWM_AVE) representing the magnitude of the load torque is the first value, the motor acceleration is set to the second value, and the third value is larger than the first value. It is configured so that the motor acceleration is set to be smaller than the fourth value when it is present. When the examples of the first value and the third value are 15% and 35%, respectively, the second value and the fourth value under the above setting conditions are 10000 [mm / s ² ] and 5000 [mm / mm, respectively. s ² ].

When the value of the motor acceleration in the acceleration / deceleration control is determined by the above processing, in the acceleration / deceleration control for the second and subsequent sheets in the job, the speed is determined according to the determined motor acceleration and the detection timing of the transfer sensor 15S or the like. The profile is determined. As a result, as shown in FIG. 9, even when the seat spacing shortened by the acceleration / deceleration control is constant, the speed profile is determined under different accelerations, and when the acceleration is large (b), the maximum motor is used. The speed (Vb) decreases.

In S104 of this process, the timing at which the tip of the first sheet reaches the secondary transfer portion is, for example, the elapsed time after the registration sensor 16S (FIG. 2) detects the tip of the sheet and the first sheet. It can be determined based on the transport speed of. Further, when the first sheet is conveyed, acceleration / deceleration control is not performed to bring the sheet interval closer to the target interval, but acceleration / deceleration control is performed to align the image with the image in the secondary transfer unit. May be done. For the acceleration of the acceleration / deceleration control in this case, a preset fixed value may be used, or the value of the acceleration when the previous job is executed may be referred to.

Further, the selection condition of the motor acceleration according to the average value PWM_AVE of the PWM duty and the above-mentioned values of the motor accelerations a1 to a4 are merely examples and can be changed as appropriate. For example, the value of PWM_AVE may be divided into five or more classes, and the value of the motor acceleration corresponding to each class may be determined in advance. Further, the motor accelerations a3 and a4 may be set to values such that the relationship a3> a4 holds.

Further, in the control example shown in FIG. 10, the acceleration used in both the acceleration unit and the deceleration unit in the speed profile of acceleration / deceleration control is changed, but only one of the acceleration of the acceleration unit and the acceleration of the deceleration unit is set to PWM_AVE. It may be changed accordingly. Further, the magnitudes of the acceleration of the acceleration unit and the acceleration of the deceleration unit need not be the same.

(Summary of this embodiment)
As described above, in this embodiment, the process of changing the value of the motor acceleration used for acceleration / deceleration control based on the measurement result of the PWM duty when the feed motor 34 is rotated (S106 to S112 in FIG. 10). It is carried out. In other words, an acceleration change process for changing the acceleration of the motor when speed control is performed during the transfer operation is executed based on the magnitude of the load torque detected by the torque detection means when the motor drives the transfer means. To do. As a result, it is possible to set the motor acceleration to a value as large as possible while avoiding that the load torque applied to the motor when the seat is conveyed with respect to the motor acceleration increases and the stability of the transfer operation is impaired. It becomes. That is, as described with reference to FIG. 9, since the motor acceleration is set to a larger value within the range in which the stability of the transport operation can be maintained, the maximum speed of the motor in acceleration / deceleration control is suppressed to improve quietness. It is possible to obtain benefits such as power saving and power saving.

Further, in this embodiment, when executing a job of forming an image on a plurality of sheets, the second sheet is based on the load torque applied to the feed motor 34 when the transfer operation for the first sheet is executed. The motor acceleration used for acceleration / deceleration control for the subsequent seats is determined. This makes it possible to determine an appropriate motor acceleration value each time a job is executed, and control with high accuracy from the viewpoint of suppressing the maximum speed of the motor in acceleration / deceleration control while maintaining the stability of the transfer operation. It can be carried out.

In addition, instead of the method of changing the value of the motor acceleration based on the detection result of the load torque when the motor is actually rotated as in this embodiment, the value of the motor acceleration is set in advance for each condition. An alternative configuration is conceivable in which the value is selected according to the job execution conditions. For example, when the basis weight of the sheet is smaller than the threshold value, a large acceleration may be selected, and when the basis weight of the sheet is equal to or more than the threshold value, a small acceleration may be selected.

However, even if this alternative configuration is used, the magnitude of the load torque when the motor is actually rotated will vary. Factors that cause the load torque of the motor to fluctuate include, for example, the component tolerance and assembly tolerance of the drive transmission mechanism that connects the motor and the roller member that transports the seat, and the seat and transport due to environmental conditions (for example, humidity) during job execution. Changes in the frictional resistance of the guide can be mentioned. Therefore, in the method of selecting a value from a predetermined set of acceleration values according to the job execution conditions, the motor acceleration may be excessively large or small due to the variation in the load torque when actually executing the transfer operation. There is. On the other hand, in this embodiment, since the set value of the motor acceleration is changed based on the magnitude of the load torque detected when the motor is actually rotated after the image forming apparatus is installed, the influence of such fluctuation factors It is possible to control the speed with a more appropriate motor acceleration without receiving it.

(Modification example)
The timing of changing the motor acceleration according to the load torque (the time of acquiring the load torque used for the acceleration change processing) is not limited to the case where the first sheet in the job is conveyed. For example, if it is known that the feed cassette 13 is loaded with the same sheet as the one used when the previous job was executed, the motor acceleration set when the previous job was executed is used this time. It is possible to continue using it in jobs. The “same sheet” means, for example, that the size and type (basis weight, material, presence / absence of coat layer, etc.) are the same, and the information input via the operation panel of the image forming apparatus or the feeding cassette 13 is provided. It is possible to make a judgment based on the information acquired by the size detection sensor. Further, after the job was input, during the preparation period (during the initial operation) before feeding the first sheet, the feeding motor 34 was rotated for a certain period of time with the feeding clutch 35 in the disengaged state. The motor acceleration may be determined based on the PWM duty.

Further, in this embodiment, the motor acceleration is determined based on the average value of the PWM duty for a predetermined period (from the start of feeding to the arrival at the secondary transfer unit) in the transport operation for the sheet, but a method different from this is used. The load torque of the feed motor 34 may be detected. For example, the average value of the PWM duty in the period from the detection of the tip of the sheet by the transport sensor 15S to the detection by the registration sensor 16S (another example of a predetermined period) is the magnitude of the load torque applied to the feed motor 34. It may be treated as a sensor. Further, instead of the average value of the PWM duty, the motor acceleration may be determined based on the maximum value of the PWM duty during a predetermined period.

Further, instead of using the measurement result of the load torque when one sheet is conveyed, the motor acceleration may be determined based on the average value of the measurement results of the load torque when a plurality of sheets are conveyed. Good. In addition, by determining the motor acceleration for the succeeding sheet according to the load torque when the preceding sheet (not necessarily the first sheet) is conveyed, the motor acceleration can be changed at any time during job execution. May be good.

Next, the configuration of the image forming apparatus according to the second embodiment will be described. This embodiment is different from the first embodiment in that a brushless motor (brushless DC motor) driven by a square wave drive is used and that the load torque of the motor is detected by measuring the current flowing through the motor. .. Other elements having the same configuration and operation as in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

FIG. 11 shows a drive circuit of the feed motor 34A which is a drive source of the feed mechanism 33 according to the present embodiment. The feed motor 34A is a brushless DC motor, and includes a rotary drive unit composed of a stator having coils 110 to 112 connected in Y and a rotor 106 rotatable with respect to the stator. Further, the feed motor 34A includes Hall elements 107 to 109 as a position detecting means of the rotor 106. The Hall elements 107 to 109 are elements in which a voltage appears at both ends of the semiconductor piece by detecting a magnetic field, and the output voltage changes according to the position (rotation angle) of the rotor 106. The outputs of the Hall elements 107 to 109 are amplified by the amplifier 113 and input to the input port of the drive control circuit 46A.

The operation of the rotary drive unit of the feed motor 34A is controlled by the drive circuit unit 43A. The drive circuit unit 43A includes a drive control circuit 46A composed of a microcomputer or the like, high-side FETs 100 to 102 and low-side FETs 103 to 105, which are switching elements. A power supply voltage Vcc converted to direct current by the switching power supply 28 (FIG. 1) is input to the drive circuit unit 43A. The FETs 100 to 105 are connected to the terminals of the coils 110 to 112 of each of the U, V, and W phases in the pattern shown in the figure. The FETs 100 to 105 are ON / OFF controlled by the phase switching signal output from the drive control circuit 46A, so that the path through which the current flows through the coils 110 to 112 changes depending on the power supply voltage Vcc.

The drive control circuit 46A outputs a phase switching signal from the output ports (FETs 1 to 6) based on the drive signal received from the CPU 26 and the output signals of the Hall elements 107 to 109 (signals representing the positions of the rotor 106). As a result, the energization pattern for the coils 110 to 112 is automatically switched every time the rotor 106 is rotated by 60 degrees, and the rotor 106 is rotated by the rotating magnetic field generated by the coils 110 to 112. Since the energization period of each switching element during one rotation of the rotor 106 is 120 degrees, the control method of the feed motor 34A by the drive control circuit 46A is also called 120 degree energization control.

The current flowing through the feed motor 34A flows through the current detection resistor 114, is converted from current to voltage, is input from the input port of the CPU 26, and is converted into a current value. The current value detected by this correlates with the magnitude of the load torque applied to the feed motor 34A, and the higher the current value, the higher the load torque is applied to the feed motor 34A. That is, the current detection resistor 114 functions as a torque detection means.

The current value flowing through the feed motor 34A is controlled by, for example, the drive control circuit 46A outputting a pulse width-modulated phase switching signal to the coils 110 to 112. In this case, the drive control circuit 46A compares the target speed and the target position specified in the drive signal received from the CPU 26 with the position information of the rotor 106 detected from the output signals of the Hall elements 107 to 109. Based on this comparison result, the drive control circuit 46A changes the PWM duty of the phase switching signal so that the required drive torque can be obtained. As a result, even when the feed motor 34A is driven at a constant target speed, the output voltage of the drive control circuit 46A (time average of pulse width modulated voltage values) becomes large when a large load torque acts on the motor. , A larger current flows through the coils 110-112. It should be noted that such pulse width modulation may be performed by the CPU 26, which is a control unit higher than the drive control circuit 46A, as in the first embodiment. In this case, the drive control circuit 46A controls the FETs 100 to 105 ON / OFF by a simple logical product of the rectangular wave signal by the 120-degree energization control and the signal whose pulse width is modulated by the CPU 26.

FIG. 12 is a flowchart of a process for determining the acceleration of acceleration / deceleration control in this embodiment. Each step of this process is processed by the CPU 26 (FIG. 1) reading and executing the control program stored in the memory 27. Further, this process is started when the CPU 26 executes a series of tasks (image forming job, hereinafter simply referred to as a job) for forming and discharging an image while feeding a predetermined number of sheets one by one. ..

When there is a feed instruction for the first (first) sheet in the job (S201), the CPU 26 rotates the feed motor 34 and engages the feed clutch 35 to cause the feed roller. The feeding of the first sheet according to 14 is started (S202). During the period from the start of feeding the first sheet to the arrival of the tip of the sheet at the secondary transfer unit, the CPU 26 records the current value flowing through the feeding motor 34A detected by using the current detection resistor 114 (S203). , S204). Then, when the tip of the sheet reaches the secondary transfer unit, the average value I_AVE of the current flowing through the feed motor 34A is calculated (S205).

The CPU 26 determines the acceleration of the feed motor 34 used for acceleration / deceleration control for the second and subsequent sheets according to the value of I_AVE acquired in the above procedure by performing the transfer operation for the first sheet. (S206 to S212), the process ends. At this time, when the value of I_AVE becomes large, the condition is set so that the value of the motor acceleration in the acceleration / deceleration control becomes small. In the example shown in FIG. 12, the settings are as follows.
Motor acceleration when I_AVE is less than 0.5A ... a1
Motor acceleration when I_AVE is 0.5A or more and less than 1.0 ... a2
Motor acceleration when I_AVE is 1.0A or more and less than 2.0A ... a3
Motor acceleration when I_AVE is 2.0A or more ... a4

The motor accelerations a1 to a4 satisfy the relationship of a1 ≧ a2 ≧ a3 ≧ a4 and a1> a4. The following can be used as specific motor acceleration setting values.
a1 = 10000 [mm / s ² ]
a2 = 5000 [mm / s ² ]
a3 = 3000 [mm / s ² ]
a4 = 3000 [mm / s ² ]

As described above, in this embodiment, the process of changing the value of the motor acceleration used for acceleration / deceleration control based on the measurement result of the motor current when the feed motor 34A is rotated (S206 to S212 in FIG. 12). It is carried out. Therefore, as in the first embodiment, the motor acceleration is set to a large value as much as possible while avoiding that the load torque applied to the motor when the seat is conveyed with respect to the motor acceleration increases and the stability of the transfer operation is impaired. It is possible to set to. That is, as described with reference to FIG. 9, since the motor acceleration is set to a larger value within the range in which the stability of the transport operation can be maintained, the maximum speed of the motor in acceleration / deceleration control is suppressed to improve quietness. It is possible to obtain benefits such as power saving and power saving.

(Other embodiments)
In the first and second embodiments, the configuration in which the sheet fed from the feeding cassette 13 is conveyed to the secondary transfer unit without stopping has been described, but the present technology also has a configuration in which the sheet transfer is temporarily stopped. Applicable. For example, there is known a configuration in which a motor for driving the register roller 16 is provided independently of the feed motor, the tip of the seat is abutted against the stopped register roller 16 to correct skew, and then the control roller 16 is started to be driven. There is. In this case, the image and the seat are aligned according to the drive start timing of the registration roller 16, but the point that productivity can be improved by bringing the interval at which the seat reaches the registration roller 16 close to a certain value is the first embodiment. It is the same as 2.

Further, in Examples 1 and 2, the case where a brushless motor is used as an example of the motor has been described, but the present technology can also be applied to the case where a synchronous motor (for example, a stepping motor) other than this is used. Further, even in an induction motor in which a slip occurs between the rotating magnetic field and the rotor, it is possible to control the rotation speed and the position with relatively high accuracy by using vector control. Therefore, this technique may be applied to an image forming apparatus using an induction motor.

Further, in Examples 1 and 2, the case where the present technology is applied to the operation of the electrophotographic apparatus to convey the sheet toward the image forming position (transfer position) has been described. However, even if it is not an image forming device, the present technology is applied to a sheet transfer device that performs a transfer operation for transporting a sheet toward a predetermined position, and the motor is controlled in the transfer operation based on the detection result of the torque detecting means. It is possible to change. Examples of such a sheet transporting device include an automatic document feeding device that transports a sheet as a document toward a scanning position by an image sensor in an image reading device.

The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

8: Image carrier (intermediate transfer belt) / 11: Transfer member (secondary transfer roller) / 14, 15, 16: Transfer means (feed roller, transfer roller, registration roller) / 15S, 16S: Sheet detection means (Convey sensor, registration sensor) / 25: Control means (control unit) / 34, 34A: Motor (feeding motor) / 53: Torque detection means (PWM duty recording unit) / 100: Image forming device (printer) / 114: Torque detection means (current detection resistance)

Claims (12)

An image forming means for forming an image on a sheet at an image forming position,
A transport means for transporting the sheet toward the image forming position, and
The motor that drives the transport means and
A sheet detecting means for detecting a sheet on a sheet conveying path toward the image forming position via the conveying means, and a sheet detecting means.
Torque detecting means for detecting the load torque applied to the motor and
A control means for executing speed control for changing the rotation speed of the motor according to the timing at which the sheet detection means detects the sheet is provided during the execution of the transfer operation for conveying the sheet by the transfer means.
The control means executes an acceleration change process for changing the acceleration of the motor in the speed control based on the magnitude of the load torque detected by the torque detecting means when the motor drives the transport means. To do,
An image forming apparatus characterized in that. The control means
When the load torque detected by the torque detecting means is the first value when the motor drives the conveying means, the acceleration of the motor in the speed control is set to the second value.
When the load torque detected by the torque detecting means is a third value larger than the first value when the motor is driven by the transport means, the acceleration of the motor in the speed control is the said. The acceleration change process is executed so as to be set to a fourth value smaller than the second value.
The image forming apparatus according to claim 1. When the control means executes a job that repeatedly executes the transfer operation on a plurality of sheets, the load torque detected by the torque detecting means when the transfer operation is performed on the first sheet. By executing the acceleration change process based on the magnitude of the above, the acceleration of the motor when the speed control is performed during the execution of the transfer operation for the second and subsequent sheets is determined.
The image forming apparatus according to claim 1 or 2. The control means
In the speed control, the acceleration unit that accelerates the rotation speed of the motor from the first speed to the second speed that is faster than the first speed, and the rotation speed of the motor is slower than the second speed from the second speed. It is configured to change the rotational speed of the motor according to a speed profile that includes a speed reducer that decelerates to a third speed.
The inclination of the acceleration unit and the inclination of the deceleration unit are determined based on the acceleration set by the acceleration change process, and
The magnitude of the second speed of the sheet is changed according to the timing when the sheet detecting means detects the sheet.
The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus is characterized in that. When the control means executes a job of repeatedly executing the transfer operation on a plurality of sheets, the control means so that the interval at which the plurality of sheets pass through the image forming position approaches a predetermined target interval. Determining the magnitude of the second velocity,
The image forming apparatus according to claim 4. The control means measures the load torque detected by the torque detecting means during the period from when the motor drives the conveying means to start conveying the sheet until the tip of the sheet reaches the image forming position. The acceleration change process is executed based on the average value.
The image forming apparatus according to any one of claims 1 to 5, wherein the image forming apparatus is characterized in that. The image forming means has an image carrier that carries a toner image and rotates.
A loading section on which the sheet transported by the transport means is loaded, and
A transfer member that faces the image carrier and transfers the toner image carried on the image carrier to the sheet at the image forming position is further provided.
The control means conveys the sheet supplied from the loading unit without stopping until the sheet reaches the image forming position, and the toner image carried on the image carrier and the transfer. The speed control is executed so that the timing at which the sheet conveyed by the means reaches the image forming position is synchronized.
The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus is characterized in that. The control means is configured to be able to control the input power to the motor by transmitting a command signal to the drive circuit of the motor.
The torque detecting means detects the command signal.
The image forming apparatus according to any one of claims 1 to 7, wherein the image forming apparatus is characterized. The command signal is a pulse width modulated signal.
The torque detecting means detects the duty ratio of the command signal.
The image forming apparatus according to claim 8. The torque detecting means detects a current flowing through the motor.
The image forming apparatus according to any one of claims 1 to 7, wherein the image forming apparatus is characterized. The motor is a brushless motor.
The image forming apparatus according to any one of claims 1 to 10. A transport means for transporting the sheet to a predetermined position and
The motor that drives the transport means and
A sheet detecting means for detecting a sheet on a sheet conveying path toward the predetermined position via the conveying means, and a sheet detecting means.
Torque detecting means for detecting the load torque applied to the motor and
A control means for executing speed control for changing the rotation speed of the motor according to the timing at which the sheet detection means detects the sheet is provided during the execution of the transfer operation for conveying the sheet by the transfer means.
The control means executes an acceleration change process for changing the acceleration of the motor in the speed control based on the magnitude of the load torque detected by the torque detecting means when the motor drives the transport means. To do,
A sheet transfer device characterized by this.

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