JP2023169644A - Image forming apparatus and method for controlling motor used for the same - Google Patents

Abstract

To obtain, in feedback control of a motor operating while switching between a plurality of rotation speeds, stable following of the motor when a target is switched to a lower speed without using a special speed detector or circuit.SOLUTION: An image forming apparatus comprises: a driving circuit that drives a motor upon reception of a driving signal; a speed detector that outputs a rotation signal at a time interval according to the rotation speed of the motor; and a feedback control unit that obtains the current rotation speed of the motor from the rotation signal output from the speed detector, and sequentially updates and outputs the driving signal to the driving circuit so that the motor rotates at a target speed. When the rotation signal from the speed detector is not output within a period from the previous update of the driving signal until the update this time, the feedback control unit considers that the speed detector has output a rotation speed lower than a target rotation speed and updates the driving signal.SELECTED DRAWING: Figure 6

Description

This disclosure relates to an image forming apparatus and a method of controlling a motor used therein.

An image forming apparatus uses one or more motors to drive a mechanism related to an image forming process and also to transport a document or printing paper related to image formation.
Some motors are driven by speed feedback control. A typical motor to which speed feedback control is applied is a DC motor.
Speed feedback control detects the actual rotational speed of the motor using a speed generator such as a speed generator that detects the rotational speed of the motor, an encoder that detects the rotational angle, and adjusts the detected rotational speed to a predetermined speed. The drive of the motor is controlled to bring the object closer. If the rotation speed is faster than the target speed, the drive is weakened and decelerated according to the speed difference with the target, and conversely, if the rotation speed is slower than the target speed, the drive is driven according to the speed difference with the target. strengthen and accelerate. By performing appropriate feedback control, the rotation of the motor can be maintained at a predetermined speed despite changes in load.

By the way, some motors used in image forming apparatuses need not only to rotate at a constant speed but also to vary the speed or stop at a predetermined timing.
For example, the following rotation control method is known regarding stop control. This relates to control of a registration operation that transports paper to a transfer position in accordance with the timing of image formation.
In the registration operation, the paper is brought into contact with a registration roller that is stopped on the downstream side in the paper transport direction in order to transport the paper to the transfer position in time with the timing of image formation. At this time, when a deflection is formed on the leading edge of the paper to correct the skew, the upstream conveyance roller is temporarily stopped, and both the conveyance roller and the registration roller start rotating in accordance with the timing of image formation. .

Here, when the conveyance roller is temporarily stopped, the interval between pulse signals from the encoder becomes longer as the rotation range becomes lower, and the time required to wait for pulse input becomes longer. During this waiting time, feedback control that performs acceleration and deceleration by determining the magnitude relationship between the actual speed and the target speed during deceleration based on the size of the interval between pulse signals cannot be executed. Therefore, the stopping distance may not be stable and the stopping time may become long.
Therefore, from the start of deceleration, the rotation speed is lowered to the reference speed by repeating braking and at least one of power running (coasting) and coasting, and then braking is continued until the stop (for example, (See Patent Document 1).

Japanese Patent Application Publication No. 2014-139636

The technique disclosed in Patent Document 1 aims to suppress variations in the stopping distance (paper carrying distance) and stopping time from when the registration sensor detects the leading edge of the paper until the carrying roller stops.
However, when controlling the conveyance of a document or printing paper, there are cases where the motor is not only stopped but also controlled to quickly switch the target speed. For example, there is control to reduce the conveyance speed immediately before ejecting the printing paper to the ejection tray. It is preferable to decelerate the printing paper sufficiently in order to deposit the printing paper on the ejection tray in an orderly manner before ejecting the paper. Further, when the printing paper after an image has been printed on one side is switched back and guided to the duplex printing path for printing on the other side, the switchback is performed after the conveyance speed is reduced. When the trailing edge of the printing paper overlaps with the leading edge of the subsequent printing paper during these decelerations, a paper jam occurs. In order to avoid paper jams, it is necessary to ensure a sufficient distance between the following printing sheets, but if the distance between the sheets is too large, the productivity of image formation will decrease. Therefore, when temporarily decelerating the conveyance speed as described above, it is preferable to decelerate as quickly as possible to make the deceleration period as short as possible. Therefore, feedback control is desired in which the target speed is changed substantially stepwise and the rotation of the motor is made to follow the change.

Although the example of printing paper has been described, the same can be said for controlling the document conveying device that conveys the document.
However, if the target speed after the change is lower than before the change, an undershoot occurs in the rotational speed of the motor that attempts to follow the change to the target speed. If the time interval of the pulse signals from the encoder at the target speed is comparable to the response time of the motor, then during the period of undershoot there may be moments when the time interval of the pulse signals becomes longer than the response time of the motor. Here, the response time of the motor is, for example, a time expressed as a mechanical time constant of the motor in a load driving state.

Feedback control is preferably performed at time intervals shorter than the response time of the motor in order to achieve stable control of the system. However, if the time interval of the pulse signal is longer than the response time of the motor, the information that serves as the basis for feedback control that accelerates or decelerates the motor based on the pulse signal cannot be obtained, and feedback control at a predetermined time interval becomes difficult. I can't go to
By using an encoder with high resolution to shorten the pulse interval, a pulse interval shorter than the response time of the motor may be obtained even when changing to a lower target speed. However, the use of a high-resolution encoder reduces the time interval between pulses not only when the motor rotates at low rotational speeds, but also at high rotational speeds. At high rotational speeds, processing related to pulse signals will be performed more frequently than necessary.

The above-mentioned deceleration period when printing paper or originals is ejected or when switching back is only a small part of the entire conveyance control, and therefore pulse signals are processed more frequently than necessary. This may also be considered unreasonable.
This disclosure was made in consideration of the above circumstances, and it is possible to lower the target without using a special speed detector or circuit in feedback control of a motor that operates by switching between multiple rotational speeds. This provides a method that allows stable motor tracking when switching speeds.

This disclosure includes a drive circuit that receives a drive signal and drives a motor, a speed detector that outputs a rotation signal at time intervals according to the rotation speed of the motor, and a rotation signal that is output from the speed detector. a feedback control unit that obtains the current rotational speed of the motor and sequentially updates and outputs a drive signal to the drive circuit so that the motor rotates at a target speed, the feedback control unit If the speed detector does not output a rotation signal during the period from the previous update of the signal to the current update, it is assumed that the speed detector has output a rotation speed lower than the target rotation speed, and the drive An image forming apparatus that updates signals is provided.

In addition, from a different perspective, this disclosure includes a step in which a control unit that controls a motor used in an image forming apparatus obtains a rotation signal at a time interval corresponding to the rotation speed of the motor using a speed detector; obtaining the current rotation speed of the motor from a rotation signal output from a detector; sequentially updating and outputting a drive signal to a drive circuit so that the motor rotates at a target speed; If the speed detector does not output a rotation signal during the period from the previous update of the signal to the current update, it is assumed that the speed detector has output a rotation speed lower than the target rotation speed, and the drive updating the signal;
A method for controlling a motor is provided.

In the image forming apparatus according to this disclosure, when the current rotation speed cannot be obtained because the rotation signal is not output from the speed detector during the period from the previous update of the drive signal to the current update, the feedback control section Since the drive signal is updated by regarding a rotational speed lower than the rotational speed of It is possible to obtain stable motor tracking.
The motor control method according to this disclosure also provides similar effects.

1 is a perspective view showing the external appearance of a multifunction peripheral as an example of an image processing device according to this disclosure. FIG. 2 is a sectional view showing the configuration of the multifunction peripheral shown in FIG. 1. FIG. FIG. 3 is a block diagram showing a configuration related to control and transport drive of the multifunction device shown in FIGS. 1 and 2. FIG. FIG. 4 is an explanatory diagram showing motors arranged in the image reading section and the printing section shown in FIGS. 1 to 3. FIG. FIG. 4 is an explanatory diagram showing a motor arranged in the document conveyance unit shown in FIGS. 1 to 3. FIG. It is an explanatory view showing an example of composition of a motor and a feedback control part in this embodiment. 2 is a flowchart illustrating an example in which a processor executes processing of a feedback control unit in this embodiment. FIG. 3 is an explanatory diagram showing a relationship between an example of the waveform of a rotation signal output from an encoder and a current rotation speed derived by a rotation speed measuring section based on the rotation signal in this embodiment. 9 is a waveform diagram showing an example of a transient response waveform during deceleration operation according to the conventional method shown as a comparative example in FIG. 8. FIG. FIG. 10 is a waveform diagram showing an example of a transient response waveform during deceleration operation according to the method of this embodiment.

Hereinafter, this disclosure will be further explained in detail using the drawings. Note that the following description is illustrative in all respects and should not be construed as limiting this disclosure.
<<Configuration example of image forming apparatus>>
FIG. 1 is a perspective view showing the appearance of a digital multifunction peripheral, which is an embodiment of the image forming apparatus of this disclosure. FIG. 2 is a sectional view showing the mechanical configuration of the multifunctional device shown in FIG. 1. FIG. FIG. 3 is a block diagram showing a configuration related to control and transport drive of the multifunction device shown in FIGS. 1 and 2. As shown in FIG.

As shown in FIGS. 1 to 3, the multifunction device 100 includes an image reading section 111 that reads a document, an operation section 105 that accepts user operations, a communication circuit 107 (see FIG. 3), and a printing section 115 that forms an image. We are preparing for The operation unit 105 notifies the operator of the status and settings of the device and receives instructions. The communication circuit 107 allows the control unit 101 to communicate with external equipment.
Furthermore, paper feed trays 18A, 18B, 18C, and 18D are provided below the printing section 115. An ejection tray 39A is provided above the printing section 115 and below the image reading section 111, and an ejection tray 39B protruding from the right end of the printing section 115 is provided.
A document transport unit 103 is provided on the main body to transport the document to the reading section.
The multifunction device 100 also includes a control unit 101 that controls operations (see FIG. 3).

Here, the internal configuration of the main body of the multifunction device 100 shown in FIG. 2 will be described.
The multifunction device 100 forms four-color toner images of yellow (Y), magenta (M), cyan (C), and black (BK) using an electrophotographic process, and prints a color image on a print sheet by overlapping them. . Alternatively, a monochrome image using a single color (for example, black) is printed on the print sheet. Therefore, four developing units 12, four photosensitive drums 13, four chargers 14, four drum cleaners 15, and the like are provided. The photosensitive drum 13, charger 14, and drum cleaner 15 are integrally configured as a removable process unit. An optical scanning unit 11 is arranged below the process unit 30 to scan and expose a photosensitive drum 13 corresponding to each color with a laser beam polarized by a polygon mirror 11M.

The multifunction device 100 includes process units 30y, 30m, 30c, and 30k for each color, but in FIG. 2, only the components of the yellow process unit 30y are labeled, and the other colors are omitted. The process unit may also be expressed as a process unit 30 using a representative symbol. It should be understood that the description using representative symbols applies to each of the colors Y, M, C, and K.

Above the process unit 30, toner storage units 27 corresponding to each color are arranged. Similar to the process unit 30, the developing unit 12 and the toner storage unit 27 have units for each color, but only the yellow unit is labeled and the other colors are omitted.

The multifunction device 100 further includes an image processing circuit 41 that generates an input signal to the optical scanning unit 11 (see FIG. 3). The image processing circuit 41 processes the image data of the document read by the image reading section 111 to generate exposure data related to the exposure pattern of the photoreceptor drum 13. The exposure data corresponds to a pattern of an electrostatic latent image formed on the surface of the photoreceptor drum 13.
Under the control of the control unit 101 shown in FIG. , C, or K toner image is formed.

The toner images formed in Y, M, C, and K on the photosensitive drum 13 are transferred onto the intermediate transfer belt 21 in an overlapping manner by the primary transfer roller 16 via the intermediate transfer belt 21 . The control unit 101 rotates the intermediate transfer belt 21 in synchronization with the rotation of the photosensitive drums 13 of each color, and sends the toner image transferred onto the intermediate transfer belt 21 to a position where it contacts the secondary transfer unit 23 at the right end. The control unit 101 rotates the transfer belt stretched across the secondary transfer unit 23 in synchronization with the intermediate transfer belt. Then, the toner image on the intermediate transfer belt 21 is transferred to the print sheet fed from the paper feed trays 18A to 18D.

The control unit 101 transports the print sheet onto which the toner image has been transferred by the secondary transfer unit 23 to the fixing unit 17 . The fixing unit 17 heats and presses the printing sheet that passes between the opposing heating roller R11 and pressure roller, thereby fixing the toner image transferred to the printing sheet onto the printing sheet.

The control unit 101 discharges the print sheet that has passed through the fixing unit 17 to the discharge tray 39A. Alternatively, the paper is switched back at one end by the discharge roller R13 and discharged to the discharge tray 39B on the right side through the discharge roller R14. Alternatively, the switched-back printing sheet is guided to a double-sided conveyance path where double-sided conveyance rollers R15, R16, and R17 are arranged, and returned to the transfer section where the secondary transfer unit 23 is arranged. Then, the toner image is transferred to the back side of the print sheet, and the print sheet is ejected to the ejection tray 39A or 39B via the fixing unit 17.

As shown in FIG. 3, the control unit 101 includes devices such as a processor 121, a RAM 122, and a nonvolatile memory 123 as hardware resources. The nonvolatile memory 123 stores control programs and data in a rewritable manner. The functions of the control unit 101 are realized by the processor 121 executing a control program stored in advance in the nonvolatile memory 123 and cooperating with hardware resources. The control unit 101 includes a motor control unit 125 that controls a plurality of motors as described later. The motor control section 125 may include a feedback control section 127. However, the configuration is not limited to this, and the feedback control unit 127 may be configured using hardware resources different from those of the control unit 101.

The block of the printing unit 115 shown in FIG. 3 mainly shows motors as drive sources related to sheet conveyance and original document conveyance, and loads (rollers, etc.) driven by each motor. The order of the rollers shown in FIG. 3 corresponds to some extent to the arrangement of the rollers in FIG. FIG. 2 shows the arrangement of each load with reference numerals, and FIGS. 4 and 5 show the arrangement of each motor.
As shown in FIG. 3, the paper feed motor 50 drives a paper feed roller R01, a pickup roller R02, and a separation roller R03 via a paper feed clutch 52. Note that when the paper feed solenoid 53 is turned on, the pickup roller R02 descends and contacts the uppermost print sheet stored in the paper feed tray 18A, and transfers the print sheet between the paper feed roller R01 and the separation roller R03. send out.

Paper feed motor 50 also drives transport rollers R04, R05, R06, and R07 via transport clutch 54.
The developing motor 58 drives the developing unit 12 and the process unit 30.
The transfer conveyance motor 60 drives a secondary transfer drive roller R09, an intermediate transfer drive roller R10, a heating roller R11 of the fixing unit 17, and a conveyance roller R12.
The registration motor 56 drives the registration roller R08 to perform a registration operation related to the print sheet.

Further, the discharge reversing motor 64 drives the discharge rollers R13 and R14 in a reversible manner. Note that the discharge roller R13 can be shifted by a shift motor 65 in a direction perpendicular to the conveying direction of the print sheet (towards the front and back with respect to the paper surface of FIG. 2). By shifting, the positions of print sheets discharged onto the discharge tray 39A can be shifted and deposited on a set-by-set or job-by-job basis.
The double-sided conveyance motor 62 drives double-sided conveyance rollers R15, R16, and R17.

Additionally, there are several motors for the printing section 115 that are not shown in FIG. For example, a lift-up motor that lifts up the print sheets stored in the paper feed trays 18A to 18D may be used. Further, there are a motor that rotationally drives the polygon mirror 11M of the optical scanning unit 11, a toner motor that replenishes the toner stored in the toner storage unit 27 of each color to the corresponding developing unit 12, and the like.

Further, the image reading section 111 of the multifunction peripheral 100 includes a document scanning unit 68 that scans a document placed on a transparent document table 67 arranged on the top surface of the image reading section 111, as shown in FIG. A scan motor 69 for driving a document scanning unit 68 is provided.
Further, the document transport unit 103 arranged so as to cover the top of the document table 67 includes a document feed motor 71, a document registration motor 73, and a document conveyance motor 75, as shown in FIGS. 3 and 5.

The document feed motor 71 drives a document feed roller R31, a document pickup roller R32, and a document separation roller R33 (see FIGS. 2 and 3). Note that when the document feed solenoid 72 is turned on, the document pickup roller R32 descends and contacts the uppermost document placed on the document feed tray 43, and transfers the document to the document feed roller R31 and the document separation roller R33. Send it between.
The document registration motor 73 drives the document registration roller R34 to perform a registration operation related to the print sheet. That is, the skew of the original fed from the original feeding tray 43 and conveyed is corrected.
The document conveyance motor 75 drives document conveyance rollers R35 and R36 and document discharge roller R37.

<<Motor feedback control>>
The plurality of motors included in the multifunction device 100 are of different types depending on the required performance. Feedback-controlled DC motors are used for applications that switch between different rotational speeds over a wide range.
In this embodiment, the DC motor subjected to feedback control shall be applied to the following. In the printing unit 115, the present invention is applied to a paper feed motor 50, a registration motor 56, a developing motor 58, a transfer conveyance motor 60, a double-sided conveyance motor 62, and an ejection reversal motor 64. It is assumed that a stepping motor is applied to the shift motor 65.
A stepping motor is applied to the scan motor 69 included in the image reading section 111.
The feedback-controlled DC motor is further applied to a document feed motor 71, a document registration motor 73, and a document conveyance motor 75 included in the document conveyance unit 103.

We will now discuss control that greatly changes the rotational speed and decelerates it.
The discharge reversing motor 64 reduces the conveyance speed just before the print sheet finishes passing through the discharge roller R13. Then, the print sheet is slowly discharged to the discharge tray 39A so as not to fly far from the position of the discharge roller R13. In the case of double-sided printing, the conveyance speed is decelerated just before the printing sheet whose first side has been printed finishes passing through the discharge roller R13, and then conveyed in the opposite direction to be guided to the double-sided conveyance path. Furthermore, just before the print sheet finishes passing through the discharge roller R14, the conveyance speed is reduced. Then, the print sheet is slowly discharged to the discharge tray 39B so as not to fly far from the position of the discharge roller R14.
Further, the document conveyance motor included in the document conveyance unit 103 reduces the conveyance speed immediately before the document finishes passing through the document discharge roller R37. Then, the document is slowly discharged to the document discharge tray 45 so that the document does not fly far from the position of the document discharge tray 45.

FIG. 6 is an explanatory diagram showing a configuration example of a motor and a feedback control section in this embodiment.
As shown in FIG. 6, the feedback control section 127 includes a target rotation speed acquisition section 129, a rotation speed measurement section 131, a detection lower limit processing section 133, and a motor drive section 135. The motor drive unit 135 generates and outputs a drive signal to the driver circuit 137. A driver circuit 137 drives a DC motor 138 equipped with an encoder 139.
As described in the explanation of FIG. 3, the feedback control unit 127 may be configured using the hardware resources of the control unit 101, or may be configured using another hardware resource. That is, the processor 121 of the control section 101 may perform processing as the feedback control section 127, but it may also be constituted by a circuit separate from the control section 101.

Further, in the examples shown in FIGS. 3 and 6, it is assumed that the functions of the feedback control unit 127 are realized using a processor, but this is only one aspect. All or part of the functions of the feedback control section 127 may be realized using a hardware circuit.
The feedback control unit 127 basically repeatedly executes processing related to feedback control at time intervals shorter than the mechanical time constant of the DC motor 138 when driving the load.
It should be understood that the DC motor 138 shown in FIG. 6 corresponds to, for example, the discharge reversing motor 64. Alternatively, it should be understood that it corresponds to the document transport motor 75. However, the present invention is not limited thereto, and it is not understood that the DC motor corresponds to various motors to which the DC motor is applied in this embodiment. Further, the configuration shown in FIG. 6 is not limited to a DC motor, but may be any motor to which feedback control is applied.

The driver circuit 137 shown in FIG. 6 receives a drive signal from the feedback control section 127 and drives the DC motor 138. That is, the driver circuit 137 corresponds to a drive circuit that drives a motor.
Further, the encoder 139 corresponds to a speed detector that outputs a rotation signal at intervals according to the rotation speed of the motor.
In FIG. 6, a target rotational speed acquisition unit 129 acquires a target rotational speed from a processor 121 serving as a motor control unit 125 that performs higher-level control.

The rotation speed measurement unit 131 acquires a rotation signal from the encoder 139. Then, the time at which the rotation signal was obtained is stored. The rotation speed measurement unit 131 stores at least the most recent time when the rotation signal was obtained from the encoder 139 and the time when the previous rotation signal was obtained.
The rotational speed measurement unit 131 performs processing to derive the current rotational speed of the DC motor 138 based on the time interval between the time when the most recent rotational signal was obtained and the time when the previous rotational signal was obtained. .

However, as described above, when the feedback control unit 127 repeatedly executes processing related to feedback control, if the rotational speed of the DC motor 138 is low, the time interval of the signals output from the encoder 139 is too wide. It may happen that no rotation signal is obtained between this time and the current processing time. Alternatively, it may happen that no rotation signal is obtained in a period that goes back from the current processing time by the response time of the feedback control system, such as the mechanical time constant of the motor in the load driving state. This can also be said to be a state in which the most recent rotation signal cannot be obtained. When such a state occurs, the rotational speed measurement unit 131 cannot derive the current rotational speed of the DC motor 138 based on the most recent rotational signal.
In that case, the detection lower limit processing section 133 outputs a predetermined rotation speed instead of the current rotation speed that should be derived by the rotation speed measurement section 131.
The motor drive unit 135 determines the deviation between the target speed output from the target rotation speed acquisition unit 129 and the current rotation speed of the DC motor 138 output from the rotation speed measurement unit 131 via the detection lower limit processing unit 133. , outputs a drive signal according to the deviation to the driver circuit 137.

≪Flowchart≫
The processing procedure when the processor executes the processing related to the feedback control described above will be described with reference to a flowchart.
FIG. 7 is a flowchart showing an example in which a processor executes processing as the feedback control unit 127 in this embodiment. The processor may be the processor of the control unit 101, or, unlike that, may be a processor dedicated to the feedback control unit 127, for example.

As shown in FIG. 7, the processor acquires the target rotational speed at that point from the higher-level motor control unit 125 (step S11). The higher-level motor control unit 125 provides a target rotational speed at each point in time in accordance with the progress of a printing job or the like.
After acquiring the target rotation speed, the processor checks whether a rotation signal is acquired from the encoder 139 (step S13). Here, it is determined whether the most recent rotation signal has been acquired during a predetermined period going back from the current time (step S15). An example of the predetermined period is a period from the time when the feedback control unit last updated the drive signal to the present time. Alternatively, as another example, it may be a period corresponding to the response time of the motor, that is, a period corresponding to the mechanical time constant of the motor in a load driving state.

If the processor determines that the most recent rotation signal has been acquired in a predetermined period (Yes in step S15), the processor determines the time at which the most recent rotation signal was acquired and the rotation signal immediately before that time. The current rotational speed of the motor is calculated based on the time interval from the time (step S17). The rotation speed is determined by taking into account the resolution of the encoder 139 (the rotation angle of the motor shaft from when one rotation signal is output until the next rotation signal is output, which can also be called the time interval between rotation signals for a certain rotation speed). Calculated. Then, the process proceeds to step S21, which will be described later.
On the other hand, if it is determined that the most recent rotation signal has not been acquired within the predetermined period (No in step S15), the processor determines that the current rotational speed of the motor cannot be calculated, and instead calculates a predetermined rotational speed. is output (step S19). Then, the process proceeds to step S21, which will be described later.

We will further discuss the adverse effects when the most recent rotation signal is not acquired within a predetermined period. If a rotation signal obtained further back than the predetermined period is taken as the latest rotation signal, it will eventually have the same value as the current rotation speed at the time of the previous update. If the target speed is the same as last time, the same drive signal as the last updated drive signal will be output as a result, and even if the target speed is not the same as last time, the rotation signal is the same as last time, so the current Feedback control does not reflect the rotational speed of the motor.
The problems that emerge in that case are the same as those already mentioned. That is, if the time interval of the rotation signal from the encoder 139 becomes longer than the response time of the motor during undershoot when the target speed is changed and deceleration is performed, stable control of the feedback system cannot be realized.

In this embodiment, the processor outputs a predetermined rotational speed to ensure stable motor tracking. The predetermined rotation speed is a rotation speed lower than the target rotation speed. Preferably, the rotational speed is lower than the rotational speed at which the time interval of the rotational signal from the encoder 139 falls within the period from the previous feedback control processing to the current feedback control processing.
The specific effects will be described later, and the processing of the processor will be explained here.
In step S21, the processor calculates the difference between the target speed and the current rotational speed of the motor to determine the deviation of the current speed. According to the determined deviation, a drive signal to be provided to the driver circuit 137 is determined and outputted to the driver circuit 137 (step S23). That is, it performs processing as a feedback control controller to update the drive signal. For the drive signal according to the deviation, gain characteristics and filter characteristics suitable for the control system may be determined by applying a known feedback control theory method, for example. However, the present invention is not limited thereto, and methods other than classical feedback control theory may be used.

After updating the drive signal, the processor determines whether to continue driving the motor (step S25). That is, it is determined whether an instruction to stop driving has been received from the higher-level motor control unit 125. If an instruction to stop the drive is received (No in step S25), the drive of the DC motor 138 is stopped (step S27), and the feedback control process ends.
If the DC motor 138 is to continue to be driven (Yes in step S25), the process waits for a predetermined period to elapse (loop in step S29) and returns the process to step S11.
The above is an example of processing by a processor that performs feedback control.

≪Obtaining the current rotation speed≫
The rotation speed measurement unit 131 obtains the current rotation speed of the DC motor 138 based on the rotation signal from the encoder 139, and a conventional method (comparative example) and a method according to this embodiment will be described.
FIG. 8 is an explanatory diagram showing the relationship between an example of the waveform of the rotation signal output from the encoder 139 and the current rotation speed derived by the rotation speed measuring section 131 based on the rotation signal. As shown in FIG. 8, the encoder 139 outputs a binary rotation signal that changes from low level to high level and from high level to low level when the rotation shaft of DC motor 138 rotates by a predetermined angle. Note that the horizontal axis in FIG. 8 indicates time.

In one example, it is assumed that the encoder 139 changes the rotation signal from a low level to a high level and from a high level to a low level every time the rotation axis of the DC motor 138 rotates by 3.6 degrees. In other words, the rotation signal transitions from low level to high level 100 times while the rotating shaft rotates once (360 degrees). Transition from high level to low level is also performed 100 times, and 100 pulse signals are output.
In the rotation signal shown in FIG. 8, the interval between transitions gradually increases. This indicates that the DC motor 138 is gradually decelerating. A plurality of dashed lines extending in the vertical direction in FIG. 8 indicate times t0 to t10 at 1 millisecond intervals. In this embodiment, the feedback control unit 127 performs processing related to feedback control at time intervals of 1 millisecond. In other words, the "predetermined period" in the process shown in step S29 in FIG. 7 corresponds to the 1 millisecond time interval shown in FIG. 8.

(1) to (4) shown in the pulse signal waveform of the rotation signal indicate the time interval between each transition from a low level to a high level, that is, a rising edge of the rotation signal. [1] to [4] shown on the right side of case 1 to case 3, which are comparative examples below the rotation signal in FIG. Indicates rotation speed. For example, [1] is the current rotation speed derived by the rotation speed measurement unit 131 from the time interval (1), and as in the numerical example above, the encoder 139 generates a rotation signal having 100 rising edges in one rotation. The rotational speed V[1] when outputting is,
V[1] = 1/(100 x time interval (1)) (rps)
= 60/(100 x time interval (1)) (rpm)
It is calculated by
The same applies to [2] to [6].
[C] shown in FIG. 8 indicates that when the detection lower limit processing unit 133 determines that the time interval of the rotation signals is wide and the current rotation speed cannot be derived, the detection lower limit processing unit 133 performs detection lower limit processing instead of the current rotation speed. The predetermined rotational speed output by the section 133 is shown.

The comparative example shown in FIG. 8 is a method of deriving the current rotational speed in the feedback control process from time t0 to t10 every millisecond as follows. Even if the rising edge of the most recent rotation signal is not input between the previous process and the current process, that is, even if the most recent rotation signal is before the previous process, the previous rotation signal and the previous one are Derive the current rotation speed based on the time interval of the rotation signal.
For example, in the process at time t4, the most recent rising edge of the rotation signal has not been input in the period from the current time t4 to the previous time t3. The most recent rising edge of the rotation signal was input before time t3. However, the rotation speed measurement unit 131 derives the current rotation speed [2] based on the time interval (2) between the most recent rotation signal and the previous rotation signal. As a result, the current rotational speeds derived at time t2 and time t3 are both [2]. The same holds true for times t4, t6 to t8, and time t10.

On the other hand, "Case 1" shown in FIG. 8 is one of the methods according to this embodiment (first embodiment), in which the most recent rotation signal and the previous rotation signal are both processed by the previous process. It is assumed that the current rotation speed cannot be derived unless it has been input in the period dating back to that time.
For example, in the process at time t2, the rising edge of the most recent previous rotation signal has not been input in the period from the current time t2 to the previous time t1. Therefore, the rotational speed measurement unit 131 determines that the current rotational speed cannot be derived. In response to this determination, the detection lower limit processing unit 133 outputs a predetermined rotation speed [C]. The same thing can be said about the processing after time t3.

By the way, the reason why both the most recent rotation signal from the encoder 139 and the previous rotation signal can be input in the period going back to the previous processing is because the time interval of the rotation signal from the encoder 139 is different from the feedback control processing. This is a case where the repeating time is equal to or shorter than 1 ms. At a rotation speed where the time interval of rotation signals exceeds 1 ms, the rotation speed measurement unit 131 cannot derive the current rotation speed in case 1. In this embodiment, the lower limit rotation speed, ie, the rotation speed at which the time interval of the rotation signals is 1 ms, is 10 ps, or 600 rpm.

“Case 2” shown in FIG. 8 refers to a method different from “Case 1” according to this embodiment (second embodiment). If both the most recent and previous rotation signals satisfy the following conditions, it is determined that the current rotation speed can be derived. Regarding the most recent rotation signal, the condition is that it has been input in a period dating back to the previous feedback control process. Further, the rotation signal immediately before the most recent rotation signal must be input in a period that goes back to the feedback control process before the previous one. If both conditions are met, the current rotation speed is derived based on the time interval between the most recent rotation signal and the previous rotation signal.
In the case of "Case 2", for example, in the process at time t2, the most recent rotation signal is input during the time from the current time t2 to the previous time t1. Furthermore, the rotation signal immediately before the most recent rotation signal is input within a period that goes back to time t0 before the previous rotation signal. Therefore, the rotational speed measurement unit 131 determines that the current rotational speed can be derived based on the time interval (2). This can be said to be a looser standard than "Case 1" in which it is determined that the current rotational speed cannot be derived through the processing at time t2.

“Case 3” is an example of a more lenient standard (third embodiment). In case 3, if the most recent rotation signal has been input during the period from the current processing time to the previous processing, the current rotation speed is calculated based on the time interval from the previous rotation signal. It is a method of guiding. It does not matter when the most recent rotation signal was input.

For example, in the process at time t5, the most recent rotation signal is input in the period from the current time t5 to the previous time t4. Therefore, the rotational speed measurement unit 131 determines that the current rotational speed can be derived based on the time interval (3). The same thing can be said about time t9.

The criterion for determining whether or not the current rotation speed can be derived based on the rotation signal is not limited to the above-mentioned cases 1, 2, and 3, and various modifications can be considered.
For example, as a case located between Case 2 and Case 3, which has a looser standard, the rotation signal immediately before the most recent rotation signal goes back three or more predetermined times (for example, two times before the previous one). It is also possible to consider a determination criterion that it is sufficient that the information is input in the period (fourth embodiment).
Furthermore, a modification may be considered in which the response time of the DC motor 138 in the load driving state is used as the reference instead of the time interval of the feedback control processing shown in steps of 1 millisecond in FIG. 8 (fifth embodiment). In order to realize stable feedback control, the time interval at which the feedback control process is repeated is usually set to a shorter interval than the response time of the system described above. In the example shown in FIG. 8, the time interval of the feedback control process is 1 millisecond, but an example of a mechanical time constant representing the response time of the DC motor 138 is 3.8 milliseconds. For example, if the most recent rotation signal and the previous rotation signal were both input during a period that goes back to the time represented by this mechanical time constant, the current degree of rotation transfer can be derived, but this is not the case. This method assumes that the current rotational speed cannot be determined without the rotation speed.

≪Effect on feedback control by detection lower limit processing section≫
The advantages of the feedback control according to this embodiment with respect to the comparative example shown in FIG. 8 will be explained below while showing an example of a response waveform of the feedback control.
FIG. 9 is a waveform diagram showing an example of a transient response waveform during deceleration operation according to the conventional method shown as a comparative example in FIG. On the other hand, FIG. 10 is a waveform diagram showing an example of a transient response waveform during deceleration operation according to the method of this embodiment. Note that the feedback control methods shown in FIGS. 9 and 10 correspond to the comparative example and case 1 shown in FIG. 8, respectively; however, the rotation signal waveform shown in FIG. 8 is an example; It does not directly correspond to the waveform shown in .

In FIGS. 9 and 10, the target rotational speed changes stepwise from the initial rotational speed of 2446 rpm to 623 rpm. In FIGS. 9 and 10, the time period changes from 3.5 ms to 4.5 ms on the time axis. The sudden change in the target rotational speed to a low speed corresponds to, for example, deceleration control in which the discharge reversing motor 64 is decelerated immediately before the trailing edge of the print sheet finishes passing through the discharge roller R13.
In FIG. 9, the actual rotational speed of the DC motor 138 is constant, approximately equal to the initial rotational speed of 2446rpm, from 3.5ms on the time axis when the target rotational speed changes to 623rpm to 6.5ms on the time axis. It's speed. This can be said to be a response delay of the feedback control system. Thereafter, at 6.5 ms on the time axis, deceleration begins toward the target rotational speed of 623 rpm. Each point on the waveform represents a step of 1 ms, and corresponds to a time point at which the feedback control process is repeated. In the process at 10.5 ms on the time axis, the actual rotational speed of the DC motor 138 is reduced to 877 rpm. The feedback control unit 127 performs the next feedback control process at a time point of 11.5 ms, which is 1 ms later.

At 11.5 ms on the time axis, the actual rotational speed of the DC motor 138 has fallen to 500 rpm. In other words, the rotation speed is lower than 600 rpm, which is the lower limit rotation speed at which two rising edges of the most recent rotation signal and the previous rotation signal can exist during the 1 ms time step period during which feedback control processing is repeated. . At 500 rpm, which is lower than the lower limit rotation speed of 600 rpm, the rotation speed measurement unit 131 detects the current The same rotational speed as in the previous feedback control process is derived as the speed. As a result, the same drive signal as before is output. In other words, since no new rotation signal is input from the encoder 139 during the time interval during which feedback control is repeated, the current rotation speed is not updated and the past state is maintained, and the drive signal is also maintained at the past state. Ru.

In FIG. 9, the waveform of "current rotational speed on control" after 10.5 ms on the time axis indicates a state in which the rotational speed is not updated and the past rotational speed is maintained. For example, at a time point of 11.5 ms on the time axis, the motor drive unit 135 sets the past rotation speed that is not updated as the current rotation speed for control purposes. As a result, it is determined that the DC motor 138 is rotating at a rotation speed faster than the target rotation speed, and a drive signal is outputted to further reduce the rotation of the DC motor 138.
The "DUTY of the drive signal" at the time point of 11.5 ms on the time axis shown in FIG. 9 indicates the state. Note that DUTY of the drive signal is zero, which corresponds to a non-driving state in which the DC motor 138 is not driven at all, and 100, which corresponds to a state in which the DC motor 138 is fully driven. Even after 11.5 ms on the time axis, the DUTY of the drive signal continues to be substantially zero (no drive). This is simply because a new rotation signal is not input from the encoder 139, and the current rotation speed cannot be derived. As shown by "actual current rotational speed" in FIG. 9, the actual rotational speed of the DC motor 138 drops below the target rotational speed, and the DC motor 138 eventually stops.

In this way, if the time interval between the rotation signals from the encoder 139 is too wide during the undershoot period during deceleration and the current rotation speed cannot be updated, the rotation speed of the DC motor 138 is made to follow the target rotation speed. I can't. As a result, a situation may arise in which the DC motor 138 stops.
According to the method according to this embodiment, such problems can be avoided with a simple configuration.

The waveform shown in FIG. 10 shows an example corresponding to feedback control using the method of "Case 1" in FIG. At a point after 11.5 ms on the time axis when two rising edges of the most recent rotation signal and the previous rotation signal cannot exist within a time interval of 1 ms, the rotation speed measuring unit 131 determines the current rotation speed. It is determined that it is not possible to guide the Upon receiving the determination, the detection lower limit processing unit 133 outputs the predetermined rotation speed as the current rotation speed for control. In the example shown in FIG. 10, the predetermined rotational speed value is zero. Note that the value of the rotational speed output by the detection lower limit processing unit 133 in FIG. 10 is an example. The predetermined rotational speed output by the detection lower limit processing unit 133 when the rotational speed measurement unit 131 determines that the current rotational speed cannot be determined is set by the designer to a value suitable for each feedback control system based on experiments. do it.
A preferred range of rotational speeds has a lower limit of zero. The upper limit value is a rotation speed at which two rising edges of the most recent rotation signal and the previous rotation signal cannot exist in the time interval (1 ms in this embodiment) in which feedback control processing is repeated.
In the example shown in FIG. 10, the rotation speed at which the two rising edges of the most recent rotation signal and the previous rotation signal are equal to the 1 ms time interval for repeating the feedback control process is 1000 rotation signals per second. Corresponds to the output rotation speed. Since the encoder 139 outputs 100 rotation signals in one rotation, its rotation speed corresponds to 10 rps, that is, 600 rpm. Therefore, the upper limit of the preferred range of the predetermined rotational speed is 600 rpm.

At time points of 11.5 ms and 12.5 ms on the time axis shown in FIG. 10, the rotation speed measuring unit 131 detects that the latest and previous rotation signals have not been input during the 1 ms period, and therefore the current rotation speed cannot be measured. It is judged that it cannot be guided. In response to this determination, the detection lower limit processing unit 133 outputs zero as the current rotational speed for control. The motor control unit 125 determines that the current rotational speed is lower than the target rotational speed and outputs a drive signal to accelerate the DC motor 138. In FIG. 10, the value of the drive signal DUTY output at 11.5 ms on the time axis is 34, and the value of the drive signal DUTY output at 12.5 ms on the time axis is 42.

By outputting such a DUTY drive signal, the actual rotational speed of the DC motor 138 changes from deceleration to acceleration at 12.5 ms on the time axis. Then, at 13.5 ms on the time axis, the actual rotational speed increases to 650 rpm. After that, the actual rotation speed exceeds the target rotation speed of 623 rpm and overshoots, and then almost converges to the target rotation speed.
As shown in FIG. 10, according to this embodiment, even if there is a temporary undershoot during deceleration, the DC motor 138 rotates following the target rotation speed without stopping, achieving stable feedback control. has been done.

As mentioned above,
(i) The image forming apparatus according to this disclosure includes a drive circuit that drives a motor in response to a drive signal, a speed detector that outputs a rotation signal at a time interval according to the rotation speed of the motor, and a a feedback control unit that obtains the current rotation speed of the motor from the output rotation signal and sequentially updates and outputs the drive signal to the drive circuit so that the motor rotates at a target speed; The feedback control unit is configured to output a rotation speed lower than a target rotation speed when the rotation signal is not output from the speed detector during a period from the previous update to the current update of the drive signal. The drive signal is updated by taking this into consideration.

In this disclosure, the motor is used in an image forming apparatus and is subject to feedback control. A typical type of motor is a DC motor, but it is not particularly limited as long as feedback control is applicable; for example, an induction motor or a synchronous motor may be used.
Further, the speed detector outputs a rotation signal indicating that the motor is rotating at a time interval corresponding to the rotation speed of the motor. A specific example of this is, for example, an encoder that outputs a signal every time it rotates by a predetermined angle.
Furthermore, the feedback control section updates and outputs the drive signal so that the motor rotates at a target speed based on the rotation signal. A specific example of this is, for example, a mode in which the feedback control section is configured using a processor. However, some or all of the functions may be configured by hardware (circuits).

The feedback control section sequentially updates the drive signal. The time interval is basically a time interval shorter than the time during which the motor can respond.

Furthermore, preferred embodiments of this disclosure will be described.
(ii) If at least one rotation signal is output from the speed detector between the previous update of the drive signal and the current update, the feedback control unit is configured to control the rotation signal and the immediately preceding rotation. The current rotational speed of the motor may be obtained based on the time interval with the signal.
According to this aspect, the current rotational speed of the motor is based on at least one rotational signal that was input while tracing back to the previous update, so it reflects the most recent state.

(iii) The feedback control unit may execute a process of updating the drive signal based on the current rotational speed of the motor at preset time intervals.
According to this aspect, the feedback control section updates the drive signal at predetermined time intervals, so that feedback control of the motor is continuously and substantially continuously performed.

(iv) The time interval may be set based on response characteristics of the motor.
According to this aspect, since the drive signal is updated by repeatedly performing feedback control processing at time intervals according to the response characteristics of the motor, substantially continuous feedback control of the motor is performed.

(v) When the rotation signal from the speed detector is not output during the period from the previous update to the current update of the drive signal, the feedback control unit may adjust the time interval of the rotation signal from the speed detector to The drive signal may be updated by assuming that the speed detector has output a rotational speed that is lower than the rotational speed that falls within the period from the previous update to the current update.
According to this aspect, even if the rotation signal is not output from the speed detector during the period from the previous update to the current update because the rotation speed is low, the rotation signal from the speed detector is output during that period. By performing control on the assumption that a rotation signal corresponding to a rotation speed further than the rotation speed at which the motor is accommodated is output, stable feedback control can be realized without stopping the motor.

(vi) If the rotation signal is not output from the speed detector during the period from the previous update of the drive signal to the current update, the feedback control unit assumes that the motor is stopped and The drive signal may be updated.
According to this aspect, even if the rotation signal is not output from the speed detector during the period from the previous update to the current update because the rotation speed is low, the motor is stopped during that period. By controlling based on this assumption, stable feedback control can be achieved without stopping the motor.

(vii) The motor may be a motor related to transporting paper or a document in an image forming apparatus.
According to this aspect, stable feedback control can be achieved without stopping the motor even when the transport speed of the paper or document is temporarily decelerated.

(viii) One aspect of this disclosure includes the step of a control unit that controls a motor used in an image forming apparatus using a speed detector to obtain rotation signals at time intervals corresponding to the rotation speed of the motor; obtaining the current rotation speed of the motor from a rotation signal output from a speed detector; sequentially updating and outputting a drive signal to a drive circuit so that the motor rotates at a target speed; If the speed detector does not output a rotation signal during the period from the previous update of the drive signal to the current update, it is assumed that the speed detector has output a rotation speed lower than the target rotation speed, and the updating the drive signal;
including a method of controlling a motor that performs.

Aspects of this disclosure also include combinations of any of the multiple aspects described above.
In addition to the embodiments described above, there may be various modifications to this disclosure. Such variations are not to be construed as falling outside the scope of this disclosure. This disclosure is to include the meaning of equivalents of the claims and all modifications within the said scope.

11: Optical scanning unit, 11M: Polygon mirror, 12: Developing unit, 13: Photosensitive drum, 14: Charger, 15: Drum cleaner, 16: Primary transfer roller, 17: Fixing unit, 18A, 18B, 18C, 18D: Paper feed tray, 21: Intermediate transfer belt, 23: Secondary transfer unit, 27: Toner storage unit, 30, 30y, 30m, 30c, 30k: Process unit, 39A, 39B: Ejection tray, 41: Image processing circuit , 43: Document feed tray, 45: Document output tray, 50: Paper feed motor, 52: Paper feed clutch, 53: Paper feed solenoid, 54: Transport clutch, 56: Registration motor, 58: Developing motor, 60: Transfer Conveyance motor, 62: Double-sided conveyance motor, 64: Ejection reversal motor, 65: Shift motor, 67: Document table, 68: Document scanning unit, 69: Scan motor, 71: Document feed motor, 72: Document feed solenoid, 73: Original registration motor, 75: Original transport motor 100: Multifunction device, 101: Control unit, 103: Original transport unit, 105: Operation unit, 107: Communication circuit, 111: Image reading unit, 115: Printing unit, 121: Processor, 122: RAM, 123: Non-volatile memory, 125: Motor control unit, 127: Feedback control unit, 129: Target rotation speed acquisition unit, 131: Rotation speed measurement unit, 133: Detection lower limit processing unit, 135: Motor drive 137: Driver circuit, 138: DC motor, 139: Encoder R01: Paper feed roller, R02: Pick up roller, R03: Separation roller, R04, R05, R06, R07, R12: Conveyance roller, R08: Registration roller, R09 : Secondary transfer drive roller, R10: Intermediate transfer drive roller, R11: Heat roller, R13, R14: Ejection roller, R15, R16, R17: Double-sided conveyance roller, R31: Document feed roller, R32: Document pickup roller, R33 : Original separation roller, R34: Original registration roller, R35, R36: Original transport roller, R37: Original discharge roller

Claims (8)

a drive circuit that receives a drive signal and drives the motor;
a speed detector that outputs a rotation signal at time intervals according to the rotation speed of the motor;
a feedback control unit that obtains the current rotation speed of the motor from the rotation signal output from the speed detector and sequentially updates and outputs a drive signal to the drive circuit so that the motor rotates at a target speed; , comprising;
The feedback control unit is configured to control whether the speed detector outputs a rotation speed lower than a target rotation speed when the rotation signal is not output from the speed detector during a period from the previous update to the current update of the drive signal. An image forming apparatus that updates the drive signal by regarding the drive signal as an object. If at least one rotation signal is output from the speed detector between the previous update of the drive signal and the current update, the feedback control unit is configured to control the rotation signal between the rotation signal and the immediately preceding rotation signal. The image forming apparatus according to claim 1, wherein the current rotational speed of the motor is obtained based on a time interval. The image forming apparatus according to claim 1 , wherein the feedback control unit executes a process of updating the drive signal based on the current rotational speed of the motor at preset time intervals. The image forming apparatus according to claim 3, wherein the time interval is set based on response characteristics of the motor. The feedback control unit is configured to adjust the time interval of the rotation signal from the speed detector so that the time interval of the rotation signal from the speed detector is the same as that of the previous update when the rotation signal is not output from the speed detector during the period from the previous update to the current update of the drive signal. The image forming apparatus according to claim 1, wherein the drive signal is updated by regarding the speed detector as outputting a rotational speed lower than a rotational speed that falls within a period from 1 to the current update. If the rotation signal is not output from the speed detector during the period from the previous update to the current update of the drive signal, the feedback control unit assumes that the motor is stopped and changes the drive signal. The image forming apparatus according to claim 1, wherein the image forming apparatus is updated. The image forming apparatus according to claim 1, wherein the motor is a motor for transporting paper or original documents in the image forming apparatus. The control unit that controls the motor used in the image forming apparatus is
obtaining rotation signals at time intervals according to the rotation speed of the motor using a speed detector;
obtaining the current rotational speed of the motor from the rotational signal output from the speed detector;
sequentially updating and outputting a drive signal to a drive circuit so that the motor rotates at a target speed;
If the speed detector does not output a rotation signal during the period from the previous update to the current update of the drive signal, it is assumed that the speed detector has output a rotation speed lower than the target rotation speed. updating the drive signal;
How to control a motor that performs.