JP2000184760A - Driver for oscillatory motor and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillatory wave driver in which stabilized driving is ensured by reducing the possibility of stoppage even if the driving frequency is fluctuated due to fluctuation of load. SOLUTION: An oscillatory wave driver comprises an oscillatory wave motor 1 for moving an oscillator exciting a driving oscillation relatively by bringing a contactor into pressure contact therewith, and drive control sections 404, 412 performing feedback control by delivering a drive signal to the oscillator in order to excite driving oscillation wherein the drive control section is set with a lower limit of controlling the fluctuation of driving frequency during operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device and an image forming apparatus for a vibration type motor, and more particularly, to a vibration type (vibration wave) motor which is a driving means having good rotational accuracy and a photosensitive drum, a transfer belt and a transfer device. The present invention can be applied to an electrophotographic apparatus for rotating a transfer body such as a drum, for example, an apparatus such as a printer apparatus, a copying apparatus, and a facsimile apparatus.

[0002]

2. Description of the Related Art A vibration type motor, for example, a vibration wave motor,
As proposed in Japanese Patent Application Laid-Open No. 58-148682, a motor that generally excites a plurality of vibrations to a vibrating body at a frequency exceeding an audible range and obtains a driving force by combining them. The driving is described in JP-A-63-1379.
JP, JP-A-60-176470, JP-A-60-176470
As described in detail in JP-A-204477 and the like, stable rotation at a constant speed is realized.

[0003]

In the above prior art, an electrophotographic apparatus for rotating a photosensitive drum or a transfer belt by using a vibration wave motor which is a driving means having good rotational accuracy is provided.
When the recording paper enters the transfer belt or when the paper on the transfer belt enters the fixing device, a sudden load change occurs.

At this time, in the case of a vibration wave motor provided with a normal speed control, if the load of the vibration wave motor suddenly increases,
In order to increase the torque corresponding to the load,
The operation is performed so as to rapidly reduce the driving frequency given to the vibration wave motor, and the vibration wave motor is stopped in a region where the vibration wave motor cannot be operated.

FIG. 11 shows such a situation, in which the horizontal axis represents time and the vertical axis represents drive frequency. This shows a case where the speed is stabilized from the start. In the case of the present embodiment, the drive frequency moves up and down in a certain cycle as shown in FIG. 12, but this is due to the inertia of the load or the like, and there are various cases depending on the load.

[0006] Such a vibration wave motor is provided in an image forming apparatus,
For example, it is used for driving a photosensitive drum in a color electrophotographic apparatus (photosensitive drums of each color are arranged along a transfer direction of a transfer material) and for driving an endless transfer material transport belt for transporting the transfer material. In this case, as shown in FIG. 12, when the vibration wave motor is driven in a steady state, a transfer material such as a recording sheet adheres to a transfer material transport belt or heats and presses a toner image on the transfer material. For example, when a fuser enters a fixing device where fixing occurs, a sudden change in load is caused. Therefore, depending on the control response characteristic, the drive frequency changes abruptly as indicated by “a” in FIG.

[0007] Further, when the load is heavy, the driving frequency may be reduced to a range as shown in "b" and to a region where the vibration wave motor cannot rotate.

For this reason, in the case of the stop state, it is necessary to return the drive frequency to the initial start frequency and then restart it, and it is necessary to perform a special process. In a normal control state, the drive is not restarted. become unable.

[0013] The above-mentioned inoperable region of the vibration wave motor is, as shown in FIG. 13, a portion that cannot be rotated when the drive frequency is lowered, and the resonance frequency f of the vibration wave motor is reduced.
It is said to be c. Since it is known that the resonance frequency fc differs not only for each vibration wave motor but also for the temperature of the motor, if the lower limit value of the drive frequency is set low so that the drive frequency does not become lower than this lower limit value, However, the resonance frequency itself may be higher than the lower limit, and the lower limit cannot be set lower. Therefore, if the above lower limit is set to a high value, the above problem can be solved. However, the normal fluctuation of the frequency in the normal driving state (for example, a slight additional fluctuation or the fluctuation of the frequency in the constant speed control) causes this problem. There is a possibility that the frequency variation may be lower than the lower limit, and the frequency variation range that should be originally permitted is restricted.

An object of the invention according to the present application is to provide a driving device and an image forming apparatus for a vibration type motor capable of performing stable driving by reducing the possibility of stopping even if a driving frequency fluctuates due to a load fluctuation. What you want to do.

[0011]

SUMMARY OF THE INVENTION A driving apparatus for a vibration type motor which realizes the object of the present invention is an electric motor provided on a vibrating body.
In a driving device for a vibration type motor that obtains a driving force by applying a frequency signal to a mechanical energy conversion element unit,
Limit value setting means for setting a lower limit value of a driving frequency determined according to a change state of the frequency of the frequency signal in a driving state of the motor; and a limit set by the setting means during driving of the motor. Prohibition means for prohibiting the frequency of the frequency signal from shifting in a direction lower than the value is provided.

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: one or more image carriers; an exposing unit configured to expose the image carriers with image light to form a latent image; Developing means for developing the image with toner, conveying means for conveying the transfer material toward the transfer position and transferring the toner image carried on the image carrier to the transfer material, and electro-mechanical device provided on the vibrator The apparatus has one or a plurality of vibration-type motors that obtain a driving force by applying a frequency signal to an energy conversion element unit, and the vibration-type motor is used as a drive source of the one or more image carriers and the conveyance unit. In the image forming apparatus used, a lower limit value setting unit configured to set a lower limit value of a driving frequency determined according to a change state of the frequency of the frequency signal in a driving state of the motor, and the setting during driving of the motor. Set by means It is provided with a prohibiting means for prohibiting the frequency of the said frequency signal than the limit value shifts to lower direction.

With the above-described configuration, it is possible to provide a vibration wave driving device and an image forming apparatus that are less likely to stop when a load change is instantaneously applied.

In addition, not only the minimum control frequency is determined from the minimum or average drive frequency in the control state, but also the maximum or average value is obtained to determine the maximum control frequency and the speed is determined by the control characteristics. Can be prevented from abnormally lowering, thereby enabling further stable driving.

When the minimum value, average value, and maximum value are obtained, the average value and the like may be simply obtained. However, instead of simply obtaining the minimum value, the average value, and the maximum value, the vibration wave motor At startup, there is a sudden change in frequency, and by taking into account the change in control frequency due to the temperature change and load system behavior at startup, it is possible to obtain a more stable control limit, and it is possible to obtain a more stable control limit. Thus, it is possible to provide a vibration wave driving device and an image forming apparatus that rotate.

[0016]

1 to 5 show a first embodiment of the present invention.

FIG. 4 shows the overall schematic configuration of the color image forming apparatus. First, the configuration of the color reader will be described.

Reference numeral 101 denotes a CCD, 311 denotes a substrate on which the CCD 101 is mounted, 312 denotes a printer processing unit, 301 denotes a platen glass (platen), and 302 denotes a document feeder (note that
There is also a configuration in which a mirror pressure plate or a white pressure plate (not shown) is mounted in place of the document feeder 302), 303 and 3
04 is a light source of a halogen lamp or a fluorescent lamp for illuminating the original, 305 and 306 are reflectors for condensing the light of the light sources 303 and 304 on the original, 307 to 309 are mirrors, 310
Is a lens for condensing reflected light or projection light from the original on the CCD 101; 314, a carriage for housing the halogen lamps 303, 304, reflectors 305, 306, and the mirror 307; 315, a carriage for housing the mirrors 308, 309; An interface 313 with another IPU or the like (I
/ F) section. Note that the carriage 314 has a speed V,
The carriage 315 scans (sub-scan) the entire surface of the document by mechanically moving at a speed V / 2 in a direction perpendicular to the electrical scanning (main scanning) direction of the CCD 101.

Next, the configuration of the printer unit in FIG. 4 will be described. Reference numeral 317 denotes a magenta (M) image forming unit, 318 denotes a cyan (C) image forming unit, 319 denotes a yellow (Y) image forming unit, and 320 denotes a black (K) image forming unit. The unit 317 will be described in detail, and description of other image forming units will be omitted.

In the M image forming unit 317, reference numeral 342 denotes a photosensitive drum, on which a latent image is formed by light from the LED recording head 210. Reference numeral 321 denotes a primary charger, which charges the surface of the photosensitive drum 342 to a predetermined potential.
Prepare for latent image formation. Reference numeral 322 denotes a developing device for the photosensitive drum 3
The latent image on 42 is developed to form a toner image. Note that the developing device 322 includes a sleeve 345 for applying a developing bias to perform development.

A transfer charger 323 is a transfer material transport belt 3.
Discharge is performed from the back surface of the transfer roller 33, and the toner image on the photosensitive drum 342 is transferred to a recording sheet or the like on the transfer material transport belt 333. In this embodiment, since the transfer efficiency is good, the cleaner portion is not provided, but it goes without saying that there is no problem even if the cleaner portion is attached.

Next, a procedure for transferring a toner image onto a transfer material such as recording paper will be described. Transfer materials such as recording paper stored in cassettes 340 and 341 are pick-up rollers 33.
9 and 338, the sheet is supplied onto the transfer material transport belt 333 by the sheet feed rollers 336 and 337 one by one. The supplied recording paper is charged by the adsorption charger 346. Reference numeral 348 denotes a transfer material transport belt roller that drives the transfer material transport belt 333 and charges the recording paper or the like in pairs with the attraction charger 346 so that the recording paper or the like is attracted to the transfer material transport belt 333. The transfer material transport belt roller 348 may be a drive roller for driving the transfer material transport belt 333, and a drive roller for driving the transfer material transport belt 333 may be disposed on the opposite side.

Reference numeral 347 denotes a paper edge sensor which detects the edge of a recording paper or the like on the transfer material transport belt 333. The detection signal of the paper leading edge sensor 347 is sent from the printer unit to the color reader unit, and is used as a sub-scanning synchronization signal when a video signal is sent from the color reader unit to the printer unit.

Thereafter, the recording paper and the like are transferred to the transfer material transport belt 3.
The toner image is formed on the surface of the image forming units 317 to 320 in the order of MCYK. The transfer material such as recording paper that has passed through the K image forming unit 320 is separated from the transfer material transport belt 333 after the charge is removed by the charge removing charger 349 in order to facilitate separation from the transfer material transport belt 333. Reference numeral 350 denotes a peeling charger, which prevents image disturbance due to peeling discharge when recording paper or the like is separated from the transfer material transport belt 333. The separated recording paper and the like are charged by pre-fixing chargers 351 and 352 in order to compensate for toner attraction and prevent image disturbance,
After the toner image is thermally fixed by the fixing device 334, the toner image is discharged to a paper discharge tray 335.

In this embodiment, a vibration type (vibration wave) motor is used as a drive motor for rotating the photosensitive drums 342 to 345, and a drive roller for driving the transfer material conveying belt 333 is used. A vibration type (vibration wave) motor is also used as a drive motor for rotating.

A vibration type (vibration wave) motor is one that applies a frequency signal having a different phase to an electro-mechanical energy conversion element such as a piezoelectric body disposed on a vibrating body to excite the vibrating body to obtain a driving force. That is, it utilizes a plurality of vibrations that are excited by the vibrating body by the frequency of the ultrasonic region, and according to a speed detection signal for stably rotating at a constant speed detected by a speed sensor detecting a driving speed of the motor. The drive frequency / drive voltage of the frequency signal and the pulse width of the drive voltage are controlled.

FIG. 1 is an operation flowchart of the present embodiment, FIG. 2 is a control block of the vibration wave motor, and FIG. 3 is a flowchart of obtaining a drive frequency of the control block.

A method for obtaining the lower limit value of the drive frequency during rotation of the motor will be described below with reference to FIG.

1-1: The rotation operation of the vibration wave motor starts.

1-2: At the time of starting the vibration wave motor, the drive frequency is set to the drive frequency control unit 404 of the five vibration wave motors.
(The control unit 404 is provided for each motor.)

1-3: A pulse having a frequency corresponding to the drive frequency signal set in the drive frequency control unit 404 is applied to the vibration wave motor, and the vibration wave motor starts.

1-4: Set the target speed α (control the driving frequency so as to reach the target speed α).

1-5: It is determined whether or not the drive speed has reached the target speed, that is, whether or not the start-up has been completed. At the time of start-up, it is determined whether or not the speed is the target speed in order to sequentially control the vibration wave motor so as to reach the target speed. At startup, since the speed is lower than the target speed, the control system performs an operation of decreasing the drive frequency in 1-6 in order to sequentially increase the drive frequency.

As a method at this time, a method of subtracting a predetermined amount is also possible, but it is also possible to set a target speed and control the drive frequency according to the current speed with respect to the target speed. Needless to say.

In this way, the drive frequency is reduced so as to reach the target speed.
Then, the lower limit of the driving frequency is measured.

The drive system is not limited to the vibration wave motor but has a certain period of operation.
One vibration wave motor is used, and one vibration wave motor is used as a recording paper transport motor.

For this reason, in 1-9, the rotation time of one rotation of the drum is set to one cycle time for the vibration wave motor for the drum, and one rotation of the recording paper conveyance motor is set to one rotation for the vibration motor of the recording paper conveyance motor. Set the cycle time. Thereafter, the lowest frequency of the drive frequency in each cycle is obtained.

1-10: Clear the lowest driving frequency measurement register Fminr.

1-11: In order to define the measurement cycle, for a drum, one rotation time of the drum is detected, and for recording paper conveyance, one rotation time of the recording paper conveyance belt is detected, and driving is performed every cycle. Find the lowest frequency.

1-16 to 1-18 are the measurement routines, and 1-16 performs averaging processing to reduce the influence of "a" (the minimum value of the driving frequency during operation) in FIG. I have. This average amount needs to be adjusted according to the load fluctuation amount.

F0 represents the previous driving frequency, and f-1 represents the driving frequency two times before, and the averaged result is expressed by F
a. (The lowest frequency <f in FIG. 5> every time the drive frequency in one cycle goes up and down is detected as each frequency, and the average value is Fa.) 1-17: The magnitude of Fa and Fminr is determined, and Fa is determined. If is smaller, go to 1-18, otherwise return to 1-11. In the first case, since Fminr is cleared by 1-10, the drive frequency at the time of startup is within Fminr.

1-18: The operation of replacing the value of Fminr with Fa is performed within one cycle. This gives 1
The minimum value of Fa in the cycle falls within Fminr.

On the other hand, in 1-11, when one cycle time elapses, in 1-12, the Fm calculated above is obtained.
memorize inr, and proceed to 1-13.

1-13: To set a control lower limit value for the value of Fminr, fc (for example, 100 Hz) is further subtracted from the lowest value of the currently operating drive frequency. Find Fcmin.

1-14: The value of Fcmin is set in the vibration wave drive frequency control unit, and is used as a limit value of the lowest frequency of drive control described with reference to FIG.

1-15: After setting Fcmin, Fmin
Fminr is cleared to obtain r for the next one cycle. At that time, Fminr is set to the drive frequency at the time of startup.

FIG. 14 is a characteristic diagram showing the relationship between the driving frequency of the vibration wave motor and the torque of the motor.

Normally, the drive system has an assumed load torque (design value or study value), which corresponds to Ts, and the drive frequency at that time is fs. In this embodiment, the load of the drive system is Tsmax with Ts as the center.
To Tsmin.

In this state, a method of setting fc will be described below.

In the system for finding the lowest frequency, (1) fc = fsmin-fm fm is intermediate between Tmax and Tsmax.

(2) fc = fsmax-fsmin The width of the frequency that can normally swing when controlling the drive system. (3) fc = (fs-fmax) / 2 (4) fc = fconmax-fsmin This is the maximum possible frequency. In fact, the oscillatory wave motor has fconmax to f
As it approaches max, there is a frequency at which the rotor and stator begin to slip and become uncontrollable.

(5) δc = (fconmax−fsmin) −α α is a margin amount for a margin.

The speed control of the vibration wave motor will be described with reference to FIGS. One of the vibration wave motors 1 to 4 for rotating the photosensitive drums 342 to 345 and the vibration wave motor 5 for conveying the recording paper is taken as an example, and there are actually a plurality of blocks in FIG. . Reference numerals 1 to 5 in FIG. 2 represent the vibration wave motor, and this time, the description will be made as the recording paper conveyance vibration wave motor 5.

The vibration wave motor is provided with a coaxial rotary encoder 10 for detecting a rotational speed (the other vibration wave motors 1 to 4 are similarly provided with coaxial rotary encoders 6 to 9). ), A pulse is generated according to the rotation speed of the vibration wave motor 5, and in the present embodiment, this pulse is input to the drive frequency control unit. A speed difference detector 403 detects a speed difference from a signal from the rotary encoder 10 and a target speed.

In the present embodiment, as a method of detecting the current rotational speed of the vibration wave motor, the rotational speed of the vibration wave motor is detected by detecting the time from the rise of the pulse of the rotary encoder to the next rise. Detected. In addition to the present embodiment, it is needless to say that the rotational speed of the vibration wave motor can be detected even if the pulse accuracy of the rotary encoder is high, even with the number of pulses in a predetermined time.

The speed difference detector 403 calculates the difference between the detected speed and the target value set by the arithmetic and control unit 412, and sends the speed difference from the target to the drive frequency detection unit 405. Here, as will be described later (FIG. 3), the frequency is obtained so as to decrease the drive frequency when increasing the drive frequency with respect to the current drive frequency, and to increase the drive frequency when decreasing the speed with respect to the current drive frequency. After the control lower limit setting unit 407 that sets the lower limit of the frequency is checked whether the lower limit of the frequency is lower than the set lower limit, the frequency is sent to the drive frequency generator 406.

The driving frequency generating section 406 generates a clock having the obtained driving frequency,
Zero generates a specified number of pulses. Then, the drive pulse is boosted in an AC voltage generation section 411 to generate an AC voltage, and the AC voltage is applied to the piezoelectric element of the vibrating body of the vibration wave motor to control the rotation of the vibration wave motor.

The actual control flow will be described with reference to FIG.

At 3-1 the start of the vibration wave motor is started by the arithmetic and control unit 412, and at 3-2 the initial drive frequency at the time of startup for the vibration wave motors 1 to 5 is set in the drive frequency control unit 404. Then, the target speed is set in 3-3. According to this target speed, the speed is increased by the following flow.

3-4: The speed detector 403 compares with the target speed. If the target speed has not been reached,
Proceeding to 7, the speed detector 403 obtains the speed difference Sp.

3-8: According to the value of the speed difference, calculation is performed so as to lower the drive frequency by βSp so as to lower the drive frequency with respect to the current drive frequency.

Although the description has been made with the proportional control this time,
It goes without saying that the method of calculating the value to be corrected by Sp may be a combination of general PID control in the control theory, and the values of parameters such as the calculation method and β depending on the control target may be variously assumed depending on the case. Needless to say.

3-9: The drive frequency obtained in 3-8 is set in the drive frequency generator 406, and the speed of the vibration wave motor is increased. Then, in order to step up the speed of the vibration wave motor, when the target speed is reached in 3-4, the process proceeds to 3-5, and it is determined whether or not the start is completed.

3-5: In order to sequentially increase the speed,
Judge whether it is the final speed, and if it is starting up, 3-6
To increase the target speed and start the vibration wave motor to the final speed. When the final speed is reached, the control enters the constant speed control. (Note that the start-up operation is an operation of shifting to the final target speed while gradually increasing the target speed.) 3-10: Obtain the speed difference Sp and compare the absolute values of the values. When this value is smaller than Sm (in the case of a small speed difference), the process proceeds to 3-12, and otherwise, the process proceeds to 3-13.

3-12: Operate with the drive frequency kept as it is (this step is not provided, and there is no problem even in a control system with only 3-13).

3-13: It is determined whether the speed difference is plus or minus. If the difference is plus, the process proceeds to 3-14. If not, the process proceeds to 3-18.

That is, a positive value indicates that the current speed is lower than the target speed, which indicates that the current speed is lower than the target speed. Perform processing.

If the value is negative, the current speed is higher than the target speed, indicating that the current speed is higher. In 3-18, the drive frequency is calculated to increase the drive frequency.
Proceed to -17.

3-15: A comparison is made with the lowest frequency (Fcmin) obtained in the flowchart of FIG. 1 and set in the control section. The drive frequency is replaced with the lowest frequency. If not, the drive frequency is set in the drive frequency generator 406 to drive the vibration wave motor at the determined drive frequency in 3-17. And 3-
Returning to FIG. 10, by repeating this, stable driving of the vibration wave motor can be realized.

FIG. 5 shows the driving frequency of the vibration wave motor thus obtained by a solid line, the obtained minimum value by a dotted line, and the lower limit of the driving frequency obtained by calculation by a dashed line. is there.

As a result, what has conventionally been stopped due to over-correction of control or the like due to load fluctuation as shown in "b" of FIG. 12 can be operated without stopping. In addition,
The flowchart for obtaining the lowest frequency in FIG. 1 is performed for a predetermined time when the power of the apparatus is turned on, or as a mode of the apparatus shown in FIG.
A mode for executing the flowchart of FIG. 1 is provided, and the mode is executed when this mode is selected. Alternatively, during execution of the constant speed control operation after the start-up of the flowchart of FIG. From 1 to 18 may be performed. Also, the flowcharts of FIGS. 1 and 3 illustrate the functions of the drive frequency control unit of FIG. 2 except for the drive pulse generation unit and the functions of the arithmetic control unit when the computer processes the functions. What is necessary is just to make it set as a program.

[Second Embodiment] In the second embodiment, a drive frequency upper limit is added to the drive frequency control state in the above-described embodiment, and abrupt control due to a transient control response is performed. FIGS. 6 and 7 are flowcharts for explaining this, and FIG. 8 shows the result.

The entire flowchart will be described with reference to FIG. 6, but the same parts as those described with reference to FIG. 1 will be omitted.

Since steps 1 to 9 in FIG. 6 are the same as those in FIG.

1-10: The values of Fminr and Fmaxr (registers for obtaining the maximum value of the driving frequency) are cleared to the starting frequency.

1-11: It is determined whether or not the time of one cycle has elapsed. If the time has not elapsed, the process proceeds to 1-16. If the time has elapsed, the process proceeds to 6-12.

Here, one cycle of the vibration wave motor or the drive system is measured, and the maximum value Fmaxr and the minimum value Fminr of the drive frequency for n + 1 times of the drive frequency for one cycle are measured.
Ask for.

1-16: The average value Fa of the (n + 1) driving frequencies is obtained, and the magnitude of Fminr is compared with that of Fa in 1-17. If Fa is small, go to 1-18 and Fmi
The value of nr is replaced with Fa. Otherwise, the process of 1-18 is skipped and the process moves to 6-17. This processing corresponds to 1 in FIG.
Although the description is omitted because it is the same as -16, 1-17, and 1-18, the average value Fa of the lowest frequency is obtained. 6-
In step 17, the frequency is detected as the highest frequency (F in FIG. 5) every time the drive frequency increases or decreases in one cycle, and the average value is set to Fb. Note that f0 represents the previous drive frequency, and f-1 represents the drive frequency two times before.

6-18: The magnitude of Fmaxr is compared with the Fb obtained in 6-17, and if Fb is large, the value of Fmaxr is replaced with Fb in 6-19. Otherwise, skip 6-19 and return to 1-11.

When one cycle is detected in 1-11, 6-12
Frequency Fminr and maximum frequency Fma obtained by
xr is stored, and in step 6-13, fc is subtracted from the obtained Fminr to obtain Fcmin and Fcmax actually used in the control, and the obtained Fmaxr is obtained.
Is added to fc.

Then, in 6-14, the values are stored in the vibration wave motor control block in the lowest drive frequency Fcmin and the lowest drive frequency Fcma of the vibration wave motor.
Set x.

Thereafter, the control system gives a limit value to the drive frequency of control based on this value. In 6-15,
Fminr and Fmaxr are cleared (set to the starting frequency).

FIG. 7 is a flow chart for obtaining the driving frequency of the vibration wave motor. The maximum frequency can be limited with respect to the first embodiment. The process up to -11 is the same as that of FIG.

In step 3-13 in FIG. 7, it is determined whether Sp is positive or negative. If it is positive, control for lowering the driving frequency is performed in the same manner as in the first embodiment.
Proceed to 18.

Therefore, in the case of a negative value, the target speed is lower than the current speed, so that the speed is higher.

In 3-18, in order to increase the driving frequency of the vibration wave motor (when the driving frequency is increased, the speed decreases), the value of βSp is added to the current driving frequency (beta is a control parameter. A) Find a new drive frequency.

At this time, in step 7-15, this value is compared with the maximum frequency set in the control device.
If the obtained drive frequency is higher than the maximum frequency (Fcmax) set in 6-14, the obtained drive frequency is replaced with the maximum frequency in 7-16.

If it is small, and when the replacement is completed,
Returning to 3-17, the speed can be controlled by setting the value in the drive frequency generator.

FIG. 8 shows an example of the result described above.

The solid line in FIG. 8 represents the change in the actual drive frequency. “A” indicates a sudden load burden and the drive frequency suddenly decreases. “C” indicates a direction in which the speed rapidly increases. This is a case where the drive frequency suddenly rises due to the load applied to the motor.

In fact, even in the case of "c", if the control is overcorrected, the operation is almost stopped. Therefore, as in the present embodiment, the upper and lower limits of the drive frequency are set by providing the upper and lower limits. In addition, it is possible to control the drive frequency that can operate stably even when the load change is abrupt and overcorrected, within the upper limit value and the lower limit value of the drive frequency (one point in FIG. 8 is a line). Note that the dotted lines in FIG. 8 indicate the maximum and minimum values of the obtained driving frequency.

[Third Embodiment] In the present embodiment, a specified amount of control range is provided for the currently controlled drive frequency. However, the first and second embodiments are described above. In the embodiment, the maximum and minimum drive frequencies for each vibration cycle of the drive system are obtained, and the upper and lower limits of the drive frequency are determined based on the values. On the other hand, in the present embodiment, the averaging process is simply performed. The dashed line in FIG. 9 indicates the average value obtained by the averaging process.

In this embodiment, since the averaging time takes a considerable amount, the fluctuation of the average value represents a change in the long-term range of the driving frequency. An example of a value obtained by setting only the lower limit of the driving frequency or the lower and upper limits of the driving frequency with respect to this average value is a line in FIG. 9.

In the present embodiment, it is needless to say that the lower limit may be limited only to the lower limit in the case where the lower limit is determined by the control system. As for the average amount, as shown in FIG. 9, it is possible to take a considerable amount of time or to shorten it.
As in the case of “a” in FIG. 9, there is a case where the control range is determined based on the value of the position where the “a” is lowered. As a result, a case may occur where it is not suitable as the lowest frequency limit for control.

For this reason, it is desirable to obtain the average value of at least two or more drive frequencies before the drive frequency (the average number depends on the load fluctuation condition of the drive system).

The average number of average values needs to be such that "a" in FIG. 9 can be removed, and it is sufficient to take an average value of data several times as long as "a".

FIG. 10 shows the result when the average number is reduced. The lower and upper limits of the drive frequency obtained at this time are indicated by dashed lines.

[Fourth Embodiment] The present embodiment is different from the third embodiment in the method for obtaining the average value of the driving frequency. At the time of start-up, when driving last time, an average value of the drive frequency after a lapse of a predetermined time (for example, after 5 seconds) from the start-up is set as a control minimum drive frequency of the vibration wave motor,
When, for example, 5 seconds have elapsed from the start, the vibration wave motor that is currently operating is driven at the average value of the drive frequency.

In this embodiment, the predetermined elapsed time is 5
After the start-up sequence (operation of starting the drive frequency to a predetermined speed while sequentially controlling the drive frequency from the startable frequency), the averaging process is performed, and the time until the average number reaches the required number is obtained. no problem.

Furthermore, in an actual apparatus, there is a preparation time until the motor or the like rotates and the actual paper can be fed, and the condition of the motor at this time may be different from that at the time of actual image formation. There is no problem if the measurement mode is started from the start of image formation.

When the motor is driven for the first time (for example, when replacing the motor), there is no previous data. Therefore, only in this case, the motor is driven without limiting the minimum frequency for a predetermined time.
Hereafter, it can be used as the data.

For this reason, the apparatus has a storage means for storing the average value obtained after the lapse of the predetermined time obtained above.

Further, by providing a temperature detecting means in the apparatus, the temperature obtained by the left-hand calculation and the current temperature can be compared with the average value obtained after the lapse of the predetermined time obtained last time due to environmental changes. If the temperature has changed from the predetermined temperature (for example, 10 deg), there is a fact that the drive frequency of the vibration wave motor decreases due to the temperature rise. Therefore, the amount may be different for each motor, but a general value or By having a correction table for the amount of change, it is possible to further improve accuracy by correcting the average value according to the amount of change in temperature.

[0104]

As described above, according to the present invention,
Even if a transient load fluctuation occurs in a vibration wave drive unit such as a vibration type motor, it is possible to drive the vibration wave without stopping.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an operation according to a first embodiment of the present invention;

FIG. 2 is a control block diagram showing a first embodiment of the present invention.

FIG. 3 is a flowchart for obtaining a drive frequency according to the first embodiment;

FIG. 4 is a schematic diagram of an image forming apparatus according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a relationship between a drive frequency swing and a lower limit of the drive frequency according to the first embodiment;

FIG. 6 is a flowchart showing the operation of the second embodiment.

FIG. 7 is a flowchart for obtaining a drive frequency according to the second embodiment;

FIG. 8 is a diagram showing the relationship between the drive frequency swing and the drive frequency upper and lower limit values according to the second embodiment.

FIG. 9 is a diagram showing the relationship between the drive frequency swing and the upper and lower limits of the drive frequency according to the third embodiment.

10 is a diagram showing the relationship between the drive frequency swing and the drive frequency upper and lower limit values when the average number in FIG. 9 is reduced.

FIG. 11 is a diagram showing a fluctuation of a driving frequency of a vibration wave motor.

FIG. 12 is a partially enlarged view of FIG. 11;

13A is a diagram illustrating a relationship between a driving frequency and a speed of a vibration wave motor, and FIG. 13B is a diagram illustrating a change in a driving frequency due to a temperature change.

FIG. 14 is a diagram showing a relationship between a driving frequency and a torque of a vibration wave motor.

[Explanation of symbols]

 1-5 Vibration wave motor 6-10 Rotary encoder 300 Display unit 342-345 Photosensitive drum 333 Transfer material transport belt 403 Speed difference detector 404 Driving frequency control unit 405 Driving frequency detection unit 406 Driving frequency generation unit 407 Control lower limit setting unit 410 Drive pulse generation unit 411 AC voltage generation unit 412 Operation control unit

Claims (34)

[Claims] 1. A driving device for a vibration-type motor for obtaining a driving force by applying a frequency signal to an electro-mechanical energy conversion element provided on a vibrating body, wherein Limit value setting means for setting a lower limit value of the driving frequency determined according to the change state of the frequency of the signal, and the frequency of the frequency signal is higher than the limit value set by the setting means during driving of the motor. A driving device for a vibration-type motor, comprising a prohibition unit for prohibiting a shift to a lower direction. 2. The vibration type according to claim 1, wherein the lower limit value is a value corresponding to a change state of the frequency number when the drive of the motor is controlled under predetermined specific conditions. Drive for the motor. 3. The speed controller according to claim 2, wherein the specific condition is a speed control state in which a driving speed of a motor is monitored and the frequency signal is adjusted so that the monitored speed becomes a specific speed. 3. A driving device for the vibration type motor according to 2. 4. The driving device for a vibration type motor according to claim 1, wherein the lower limit value is a value corresponding to a lower extreme value at the time of the frequency change. 5. The driving device according to claim 4, wherein the lower limit value is an average value of the extreme values. 6. The driving device for a vibration-type motor according to claim 1, wherein the lower limit is a value corresponding to an average value of the frequency fluctuation. 7. The vibration type motor according to claim 4, wherein the lower limit is a value determined according to a fluctuation state in N (N is an integer) cycles of rotation of the motor. Drive. 8. The vibration type motor according to claim 4, wherein the lower limit is a value determined according to an extreme value in N (N is an integer) cycles of the rotation of the motor. Drive. 9. The vibration type according to claim 6, wherein the lower limit is a value determined according to an average value of extreme values in N (N is an integer) cycles of rotation of the motor. Drive for the motor. 10. The motor control apparatus according to claim 1, wherein the lower limit is N (N
7. The driving device for a vibration type motor according to claim 6, wherein the value is determined according to an average value of fluctuations in a period. 11. The limit value setting means sets an upper limit value of a drive frequency determined according to a change state of a frequency of the frequency signal in a drive state of a motor together with the lower limit value, and 2. The vibration type motor according to claim 1, wherein the prohibition unit prohibits the frequency of the frequency signal from shifting in a direction higher than the upper limit set by the setting unit during driving of the motor. Drive for the. 12. The vibration-type motor according to claim 11, wherein the upper limit value is a value corresponding to a change state of a frequency when drive control of the motor is performed under predetermined specific conditions. Drive for the. 13. The specific condition is a speed control state of monitoring a driving speed of a motor and adjusting the frequency signal so that the monitored speed becomes a specific speed. A driving device for the vibration-type motor according to claim 12. 14. The driving device for a vibration motor according to claim 11, wherein the upper limit value is a value corresponding to a higher extreme value when the frequency changes. . 15. The driving device according to claim 14, wherein the upper limit value is an average value of the extreme values. 16. The apparatus according to claim 11, wherein the upper limit value is a value corresponding to an average value of the frequency fluctuation.
A driving device for the vibration type motor according to 2 or 13. 17. The method according to claim 5, wherein the calculation for obtaining the average value is performed a number of times capable of removing a transient change.
A driving device for the vibration type motor according to 6, 9, 10, 15 or 16. 18. The vibration-type motor according to claim 5, wherein the calculation for obtaining the average value is performed based on a time during which a long-term change can be detected. Drive. 19. The driving device for a vibration type motor according to claim 1, wherein the calculation of the limit value is not performed when the motor is started. 20. The vibration type motor according to claim 1, wherein the calculation of the limit value is performed after a lapse of a predetermined time after the start-up processing of the motor is completed. Drive. 21. A storage unit for storing the limit value from a start of the motor to a predetermined time, and the value stored in the storage unit is stored from the next start to the end of the calculation of the limit value. 2. The method according to claim 1, wherein the value is used as a limit value.
21. The driving device for a vibration type motor according to any one of claims 20 to 20. 22. A temperature detecting device for detecting an environmental temperature when the limit value is calculated, and a storage device for storing temperature information of the temperature detecting device, wherein the temperature information corresponds to the temperature information stored in the storage device. 22. The driving device for a vibration-type motor according to claim 21, wherein the threshold value is used at the time of startup. 23. The driving device for a vibration type motor according to claim 1, wherein the motor is a vibration wave motor. 24. The driving device for a vibration type motor according to claim 23, wherein the limit value is set each time with one rotation of the vibration wave motor as one cycle. 25. One or more image carriers, exposure means for exposing the image carrier to image light to form a latent image, developing means for developing the latent image with toner, and transfer material To the transfer position, and applies a frequency signal to a conveying unit for transferring the toner image carried on the image carrier to a transfer material, and an electro-mechanical energy conversion element unit provided on the vibrator. An image forming apparatus including the one or more vibration type motors for obtaining a driving force by using the vibration type motor as a drive source of the one or more image carriers and the transporting means; Limit value setting means for setting a lower limit value of the drive frequency determined according to the change state of the frequency of the frequency signal at the frequency signal, and a frequency lower than the limit value set by the setting means during driving of the motor. If the signal frequency is An image forming apparatus characterized in that a prohibition means for prohibiting to migrate in a direction have. 26. The image forming apparatus according to claim 25, wherein the lower limit value is a value according to a change state of the frequency number when the driving of the motor is controlled under predetermined specific conditions. apparatus. 27. The specific condition is a speed control state in which a driving speed of a motor is monitored and the frequency signal is adjusted so that the monitored speed becomes a specific speed. 27. The image forming apparatus according to 26. 28. The image forming apparatus according to claim 25, wherein the lower limit is a value corresponding to a lower extreme value at the time of the frequency change. 29. The image forming apparatus according to claim 28, wherein the lower limit is an average of the extreme values. 30. The apparatus according to claim 25, wherein the lower limit is a value corresponding to an average value of the frequency fluctuation.
28. The image forming apparatus according to 6 or 27. 31. The lower limit value of N (N
29. The image forming apparatus according to claim 28, wherein the image forming apparatus is a value determined according to a fluctuation state in a period. 32. The lower limit is set to N (N
29. The image forming apparatus according to claim 28, wherein the image forming apparatus is a value determined according to an extreme value in a period. 33. The lower limit value of N (N
31. The image forming apparatus according to claim 30, wherein the image forming apparatus is a value determined according to an average value of extreme values in a period. 34. The lower limit value of N (N
31. The image forming apparatus according to claim 30, wherein the image forming apparatus is a value determined according to an average value of fluctuations in a period.