JP2006246551A - Control device for ultrasonic motor, and control method of ultrasonic motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for ultrasonic motor that can improve the accuracy of the stop position. <P>SOLUTION: A controller 10 for driving the ultrasonic motor 3, that controls the movement of a moving body comprises: a displacement sensor 5 that detects the moving state of the moving body; a deviation calculation means (a step S4) that operates deviation ΔLd between a detected position Ld detected by the displacement sensor 5 and a target position L<SP>*</SP>; an integration operation means (a step S12) that integrates and calculates the deviation operated by the deviation calculation means; and an amplifier 4 that drives the ultrasonic motor 3, on the basis of an integration output outputted from at least the integration calculation means. The integration calculation means, comprises integration constant setting means (steps S5 to S9) each of which varies an integration constant ki into at least three stages, according to the degree of reduction, when the deviation ΔLd calculated by the deviation calculation means is in a downward trend. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic motor control device and an ultrasonic motor control method.

Ultrasonic motors, also called piezoelectric motors, cause vibrations in piezoelectric elements that change shape when a voltage is applied, and move the moving body by the vibrations. In recent years, attempts have been made to use an ultrasonic motor that is small and can provide a large holding force to a moving body when stopped.
Incidentally, feedback control is known as normal motor control. And, for example, PI control comprising two operations of P operation and I operation, that is, PI calculation means having a proportional term (P) and an integral term (I), and based on a control output from the PI calculation means A control device that controls movement of a motor is known. The PI control is generally used widely because it can be expected to be simple and highly accurate (for example, see Non-Patent Document 1).
High-precision positioning control technology, issued by General Technology Center Co., Ltd.

Here, FIG. 6 shows an example of the driving locus of the moving body when the PI control used in a normal motor is applied to an ultrasonic motor.
As can be seen from the figure, in the ultrasonic motor, since the coefficient of static friction is large, there is a dead zone T1 until the moving body starts to move. Furthermore, from the time when the moving body starts to move to the vicinity of the target position, a region T2 that requires a driving force for instantaneously driving a long distance, and from the vicinity of the target position to the completion of positioning to the target position, There is a region T3 in which a minute region needs to be finely controlled.

In normal motor movement control, even if PI control with an integral constant that is considered to minimize the positioning time that is generally performed is performed, the motor is stopped due to the relatively large static friction force inherent to the ultrasonic motor. There was a problem that the accuracy of the position was insufficient.
The present invention has been made paying attention to such problems, and an object thereof is to provide an ultrasonic motor control device and an ultrasonic motor control method capable of improving the accuracy of the stop position.

  In order to solve the above-mentioned problem, the invention according to claim 1 is an ultrasonic motor control device for driving an ultrasonic motor for controlling the movement of a moving body, and a moving state detecting means for detecting a moving state of the moving body; Deviation calculation means for calculating a deviation between the movement state detection value detected by the movement state detection means and the target position, integration calculation means for integrating the deviation calculated by the deviation calculation means, and at least the integration calculation means Motor driving means for driving the ultrasonic motor based on the output integral output, and the integration calculating means integrates according to the degree of decrease when the deviation calculated by the deviation calculating means tends to decrease. It has an integral constant setting means for changing the constant in at least three stages.

  The invention according to claim 2 is the ultrasonic motor control device according to claim 1, wherein the integral constant setting means determines whether or not the deviation calculated by the deviation calculating means converges within a predetermined range. Convergence determination means for determining whether or not the convergence determination means sets the integral constant to a first value when the deviation does not converge within a predetermined range, and the deviation is predetermined. When it is detected that the deviation has converged within the range and the deviation is less than or equal to the first threshold, the integration constant is set to a second value different from the first value, and the deviation converges within the predetermined range. In addition, when the deviation is detected to be equal to or smaller than the second threshold value, the integral constant is set to a third value different from the second value.

  The invention according to claim 3 is the ultrasonic motor control device according to claim 2, wherein the motor driving means selects either the resonance drive mode or the non-resonance drive mode for the ultrasonic motor. The resonant drive mode is selected when the integral constant is set to the first value and the second value, and the non-resonant drive is selected when the integral constant is set to the third value. It is characterized by selecting a mode.

  According to a fourth aspect of the present invention, in an ultrasonic motor control method for driving an ultrasonic motor that controls movement of a moving body, a moving state detecting step for detecting a moving state of the moving body, and the moving state detecting step A deviation calculating step for calculating the deviation between the movement state detection value detected in step 1 and the target position, and when the deviation calculated in the deviation calculating step tends to decrease, the integration constant is set to at least a first value corresponding to the degree of decrease. An integration constant setting step for changing the value to the second value and the third value, an integration calculation step for integrating the deviation calculated in the deviation calculation step using the integration constant, and at least the integration calculation step Based on the output integral output, when the integral constant is set to the first value and the second value, the ultrasonic motor is driven to resonate, and the integral constant is the third value. It is characterized in the that it comprises a motor drive steps in a non-resonant drive the ultrasonic motor when set to.

  ADVANTAGE OF THE INVENTION According to this invention, the ultrasonic motor control apparatus and ultrasonic motor control method which can improve the precision of a stop position can be provided.

Hereinafter, an embodiment of an ultrasonic motor control device according to the present invention will be described with reference to the drawings as appropriate.
FIG. 1 is an explanatory diagram showing an example of a configuration of a positioning device to which an ultrasonic motor control device according to the present invention is applied.
As shown in FIG. 1, the positioning device 1 includes a positioning table 2, an ultrasonic motor 3, an amplifier 4, a displacement sensor 5, and a controller 10.

  In the positioning table 2, a stage 2a, which is a moving body, is mounted and fixed on a linear motion guide device 2b, and can move on one axis along a linear track 2c of the linear motion guide device 2b. Yes. A friction plate 6 is attached to the stage 2 a of the positioning table 2, the entire ultrasonic motor 3 is preloaded toward the friction plate 6, and the mover 3 a of the ultrasonic motor 3 is moved to the friction plate 6. Is pressed.

  The ultrasonic motor 3 is connected to the controller 10 via the amplifier 4. In the ultrasonic motor 3, the signal output from the controller 10 is amplified by the amplifier 4 and applied to the piezoelectric element in the ultrasonic motor 3. At this time, since the voltage applied to the piezoelectric element in the ultrasonic motor 3 can be adjusted by the positive / negative of the control output by the controller 10, the piezoelectric element in the ultrasonic motor 3 causes a desired vibration and the vibration. Thus, the moving body can be moved in a desired moving direction.

Amplifier 4 amplifies a signal outputted from the controller 10, based on the control output from the controller 10, the resonance frequency f _u or the ultrasonic motor 3, switches the non-resonant frequency f _L of the ultrasonic motor 3 Output is enabled.
The displacement sensor 5 is attached to the side of the gantry portion of the positioning table 2 at a position where the displacement amount of the stage of the positioning table 2 can be measured. The displacement sensor 5 is a linear scale, and a sensor having a resolution corresponding to the application is used. For example, in the present embodiment, a sensor having a minimum resolution of a nanometer level is used. The displacement amount of the stage of the positioning table 2 can be output to the controller 10 as a movement state detection value (a detection position Ld described later). Here, the displacement sensor 5 corresponds to the moving state detecting means.

Next, the controller 10 will be described in more detail.
FIG. 2 is a block diagram showing the configuration of the controller 10.
The controller 10 of the ultrasonic motor is composed of, for example, a microcomputer MC, and executes an ultrasonic motor positioning process.
Specifically, as shown in the figure, the microcomputer MC includes a CPU 30 that controls operations and the entire system based on a predetermined control program, a ROM 32 that stores a control program of the CPU 30 in a predetermined area, and a ROM 32. The RAM 34 for storing data read from the CPU and the calculation result necessary for the calculation process of the CPU 30 and an I / F 38 for mediating input / output of data to / from an external device are included. The buses 39, which are signal lines for transfer, are connected to each other so as to be able to exchange data.

The I / F 38 is connected with a system control device 42 constituted by a personal computer or the like that controls the entire positioning device 1, the displacement sensor 5, and the amplifier 4 as external devices.
The CPU 30 starts a predetermined program stored in a predetermined area of the ROM 32, and executes the ultrasonic motor positioning process shown in the flowchart of FIG. 3 according to the program.

FIG. 3 is a flowchart for explaining the ultrasonic motor positioning process by the controller 10.
The ultrasonic motor positioning process includes PI calculating means having a proportional term (P) and an integral term (I) when positioning the stage 2a (moving body) of the positioning table 2 to the target position L ^* , This is a process for controlling the movement of the ultrasonic motor based on the control output V from the PI calculation means. When the process is executed in the CPU 30, first, as shown in FIG. Yes.

In step S1, it is determined whether or not the system control device 42 a target position from the L ^* is input, if the target position L ^* is inputted (Yes) the process moves to step S2, the target position L ^* is input If not (No), the process waits in step S1. The subsequent step S2 is a movement state detection step for detecting the movement state of the stage 2a (moving body). The detection position Ld, which is the movement state detection value detected by the displacement sensor 5, is read, and the process proceeds to step S3.

In step S3, the target position L ^* and the detection position Ld are compared. If the target position L ^* = Ld ± X, the positioning is terminated. If the target position L ^* and the detection position Ld are different values, the process proceeds to step S4. Transition. “± X” is a convergence range (final deviation) with respect to the final target value.
Step S4 is a deviation calculation step for calculating a deviation ΔLd between the movement state detection value (detection position Ld) and the target position L ^* . That is, in step S4, a deviation ΔLd (= L ^* −Ld) between the target position L ^* and the detection position Ld is calculated.

In step S5, it is determined whether or not the deviation | ΔLd | is equal to or less than a first threshold value ΔL _SH . That is, if the deviation | ΔLd | is equal to or smaller than the predetermined range ΔL _SH (Yes), the process proceeds to step S7. If the deviation | ΔLd | exceeds the predetermined range ΔL _SH (No), the process proceeds to step S6.
In step S6, the proportional constant kp of the proportional term (P) is set to the initial proportional constant kp _L (kp = kp _L ), and the integral constant ki of the integral term (I) is set to the first value ki _L (ki = ki _L ), and the process proceeds to step S10.

At step S7, the absolute value of the deviation ΔLd determines whether the following second threshold [Delta] L _SL. That is, if the deviation | ΔLd | is equal to or smaller than the predetermined range ΔL _SL (Yes), the process proceeds to step S9. If the deviation | ΔLd | exceeds the predetermined range ΔL _SL (No), the process proceeds to step S8. Note that the second threshold value ΔL _SL is a value smaller than the first threshold value ΔL _SH .
In step S8, the proportional constant kp of the proportional term (P) is set to the second proportional constant kp _M (kp = kp _M ), and the integral constant ki of the integral term (I) is set to the second value ki _M (ki = Ki _M ), and the process proceeds to step S10.

In step S9, the proportional constant kp of the proportional term (P) is set to the third proportional constant kp _H (kp = kp _H ), and the integral constant ki of the integral term (I) is set to the third value ki _H (ki = set to ki _H), the process proceeds to step S11.
Here, in the ultrasonic motor positioning process, the change of the integral constant ki of the integral term (I) is set so that the influence of the integral operation becomes larger as the deviation ΔLd becomes smaller. That is, when the stage (moving body) of the positioning table 2 is positioned at the target position L ^* , the integration constant ki of the integral term (I) is changed in three steps according to the deviation ΔLd. Specifically, three stages of integration constant ki of the integral term (I), when the deviation ΔLd becomes [Delta] L _SH within less than a predetermined range (set value [Delta] L _SH), the first value ki (set value ki _When the deviation ΔLd is within a second threshold (set value ΔL _SL ) smaller than a predetermined range (set value ΔL _SL ), the first value is changed to a second value (set value ki _M ) different from _L 1. Is changed to a second value (set value ki _H ) different from the value (set value ki _M ).

In step S10, the process proceeds to step S12 to set the driving frequency f of the piezoelectric element to the resonant frequency _{f u.} In step S11, sets the driving frequency f of the piezoelectric element to the non-resonance frequency f _L, the process proceeds to step S12 and the movement control of the ultrasonic motor driving by non-resonant frequency f _L. Incidentally, when switching the driving method from the resonance frequency f _u to a non-resonant frequency f _L, switching for switching the output frequency of the amplifier 4 connected to the ultrasonic motor 3 from the resonance frequency f _u to a non-resonant frequency f _L A command is output.

In step S12, calculation of the following equation (1) is performed to calculate the control output V, and then the process proceeds to step S13, where a signal set based on the control output V is output to the amplifier 4 and the original processing is performed. Return.
V = kp · ΔL + ki · ∫ΔL (1)
With the above configuration, the controller 10 constantly monitors the deviation ΔLd and switches the integral constant ki of the integral term (I) to increase in three stages according to the value of the deviation ΔLd. The control output V can be controlled while setting the proportionality constant kp and the integral constant ki of the integral term (I) to predetermined values.

Here, in the flowchart described above, step S4 corresponds to the deviation calculation means, and step S12 corresponds to the integration calculation step. The integral constant setting means corresponds to step S5, step S7, and the integral constant setting step, step S6, step S8, and step S9. Further, step S3 corresponds to the convergence determination means, and positioning ends when the detection position Ld converges with an accuracy of ± X with respect to the target position L ^* .
Note that the motor drive means and the motor drive step correspond to the amplifier 4 and steps S10, S11, and S13, and the frequency setting in the amplifier 4 is performed by ultrasonic waves in steps S10 and S11. The frequency f of the piezoelectric element that drives the motor is set to a desired frequency.

  Next, the positioning operation of the ultrasonic motor using this controller will be described with reference to FIGS. 4 and 5 as appropriate. FIG. 4 is an explanatory view schematically showing the positioning operation of the ultrasonic motor using the controller of the present invention. FIG. 5 is an explanatory diagram showing an example of the driving locus of the moving body when the control in the ultrasonic motor positioning process by the controller 10 of the present invention is applied to the ultrasonic motor 3.

As shown in FIG. 5, according to this controller 10, until the deviation ΔLd becomes small to some extent (| ΔLd | ≧ ΔL _SH ), the ultrasonic motor 3 is driven by resonance driving which is a normal driving state (same as above). Areas indicated by P1 and I1 in the figure). At this time, the proportional term (P) is a proportional constant kp _L, the PI control by the integral term (I) is an integration constant ki _L, the target position ^{L *} of the mobile as shown in FIGS. 4 and 5 (final target position) Positioning is performed.

Next, as shown in FIG. 4, when the deviation ΔLd becomes smaller than the predetermined range ΔL _SH set in advance (time t0 has elapsed) (step S5), the integration constant of the integral term (I) is set to the first integration constant. The value ki _L is largely changed from the value ki _L to the second value ki _M (step S8), and the remaining deviation is operated. Here, as a guideline for setting the second threshold value ΔL _SL , it is preferable that the deviation ΔLd be an area where the resonance Δ can be reduced.

Next, as shown in FIG. 4, when ΔLd ≦ ΔL _SL is satisfied (time t1), the deviation ΔLd becomes sufficiently small so that the deviation ΔLd can be reduced only by the displacement of the piezoelectric element ( Deviation ΔLd ≦ ΔL _SL ), and the integration constant of PI control is switched from the second value ki _M to the third value ki _H. That is, in order to perform positioning with higher accuracy, when the deviation ΔLd becomes smaller than the preset second threshold value ΔL _SL (step S7), the integration constant of the integral term (I) is changed from ki _M to ki. _A large change is made to _H (step S9), and the remaining deviation is operated to be smaller. At this time, the ultrasonic motor 3, as shown in FIG. 5, a rather resonant frequency f _u is a normal driving state, the stage 2a of the positioning table 2 by applying a voltage to the non-resonance frequency f _L to the piezoelectric element Can be finally positioned (step S11).

Next, the operation and effect of this ultrasonic motor control device will be described.
As described above, the controller 10 for the ultrasonic motor sets the integral constant ki of the integral term (I) to the deviation ΔL when positioning the stage 2a (moving body) of the positioning table 2 to the target position L ^*. Accordingly, the number is increased to three levels.
That is, the three-stage integration constant ki is changed to a second value ki _M different from the first value ki _L when the deviation ΔLd becomes the first threshold value ΔL _SH smaller than the initial deviation. When the deviation ΔLd becomes the second threshold ΔL _SL smaller than the first threshold ΔL _SH , the deviation ΔLd is changed to the third value ki _H larger than the second value ki _M. At this time, when the deviation ΔLd with respect to the target position L ^* tends to decrease, when the integration constant ki is increased according to the degree of decrease and the integration constant ki is changed to the third value ki _H , ultrasonic waves the motor 3, so that driven by the ultrasonic resonance of a piezoelectric element for driving the motor 3 frequencies f lower than the _u non-resonance frequency f _L.

Thus, if driving at a non-resonance frequency f _L, since it is possible to position the stage of positioning the table 2 by only displacement of the piezoelectric element, the deviation ΔLd can be reduced to the minimum resolution that can be measured by the displacement sensor 5. Therefore, positioning control can be performed more suitably. Therefore, for example, the minute region can be controlled more finely in the region T3.

As described above, according to the ultrasonic motor control device of the present invention, it is possible to provide an ultrasonic motor control device that can improve the accuracy of the stop position.
The ultrasonic motor control device according to the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the ultrasonic motor control device is configured by the microcomputer MC, and the ultrasonic motor positioning process is described as an example executed as a control program on the microcomputer MC. However, the present invention is not limited to this. Instead, the ultrasonic motor control device may be configured by an analog circuit having a proportional arithmetic circuit, an integral arithmetic circuit, or the like, for example.

Moreover, in the said embodiment, although calculation with a proportional term (P) and integral term (I) is performed together, it is not limited to this, Each may be calculated separately and may be added later.
Further, in the above embodiment, the integration constant ki of the integral term (I) that can be switched by the controller 10 has been described in the example of three stages, but is not limited thereto, and may be, for example, four stages or four stages or more. .

In the above embodiment, the ultrasonic motor positioning process shown in FIG. 3 has been described with an example in which the integral constant ki of the integral term (I) is changed. However, the present invention is not limited to this, and the proportional term (P) The proportionality constant kp may be appropriately changed according to the deviation ΔLd. For example, in FIG. 4, the proportional term (P) is changed from the proportional constant kp _L to the proportional constant kp _M. However, in the present invention, the proportional constant kp of the proportional term (P) does not necessarily need to be increased. Further, the proportionality constant kp of the proportional term (P) is not limited to changing in a stepwise manner, and need not be changed.

  Moreover, in the said embodiment, although the displacement sensor 5 which is a movement state detection means is an example which uses a linear scale, if the displacement amount of the positioning table 2 can be measured, various displacement sensors can be used. For example, a laser reflection type displacement sensor may be used. Moreover, although the displacement sensor 5 was demonstrated in the example attached to the side part of the positioning table 2, if the attachment position of a displacement sensor is a position which can measure the displacement amount of the positioning table 2, for example, the positioning table 2 The central part of the The format of data sent from the displacement sensor 5 is not particularly limited as long as it can be read by the controller.

It is explanatory drawing which shows an example of a structure of the positioning device to which the ultrasonic motor control apparatus which concerns on this invention is applied. It is a block diagram which shows the structure of the ultrasonic motor control apparatus which concerns on this invention. It is a flowchart explaining the ultrasonic motor positioning process by the ultrasonic motor control apparatus which concerns on this invention. It is explanatory drawing which modeled the positioning operation | movement of the ultrasonic motor using the ultrasonic motor control apparatus which concerns on this invention. It is explanatory drawing which shows the example of the drive trace of a moving body at the time of applying PI control by the ultrasonic motor control apparatus of this invention to an ultrasonic motor. It is explanatory drawing which shows the example of the drive trace of a moving body at the time of applying PI control by the conventional ultrasonic motor control apparatus to an ultrasonic motor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positioning device 2 Positioning table 3 Ultrasonic motor 4 Amplifier (motor drive means)
5 Displacement sensor (moving state detection means)
6 Friction plate 10 Controller (Ultrasonic motor controller)
30 CPU
32 ROM
34 RAM
38 I / F
39 Bus 42 System controller

Claims (4)

In an ultrasonic motor control device that drives an ultrasonic motor that controls movement of a moving object,
A moving state detecting means for detecting a moving state of the moving body; a deviation calculating means for calculating a deviation between a moving state detection value detected by the moving state detecting means and a target position; and a deviation calculated by the deviation calculating means. An integral calculation means for performing an integral calculation, and a motor drive means for driving the ultrasonic motor based on at least an integral output output from the integral calculation means,
The ultrasonic motor has an integral constant setting means for changing the integral constant in at least three stages according to the degree of decrease when the deviation calculated by the deviation calculator tends to decrease. Control device. The integral constant setting means has a convergence determining means for determining whether or not the deviation calculated by the deviation calculating means converges within a predetermined range,
The convergence determination means sets the integration constant to a first value when the determination result shows that the deviation does not converge within a predetermined range, the deviation converges within the predetermined range, and the deviation is the first The integration constant is set to a second value different from the first value when it is detected that the value is less than or equal to a threshold value, the deviation converges within a predetermined range, and the deviation is less than or equal to the second threshold value. 2. The ultrasonic motor control device according to claim 1, wherein the integral constant is set to a third value different from the second value when the signal is detected. 3.   The motor drive means is configured to drive the ultrasonic motor by selecting either a resonance drive mode or a non-resonance drive mode, and the integration constant is set to a first value and a second value. 3. The ultrasonic motor control device according to claim 2, wherein a resonance drive mode is sometimes selected, and a non-resonance drive mode is selected when the integral constant is set to a third value. In an ultrasonic motor control method for driving an ultrasonic motor that controls movement of a moving body,
A moving state detecting step for detecting a moving state of the moving body, a deviation calculating step for calculating a deviation between the moving state detection value detected in the moving state detecting step and the target position, and a deviation calculated in the deviation calculating step An integration constant setting step for changing the integration constant to at least the first value, the second value, and the third value in accordance with the degree of decrease, and the deviation calculated in the deviation calculation step when there is a decreasing tendency; The ultrasonic motor when the integration constant is set to the first value and the second value based on an integration calculation step for performing an integration calculation using a constant, and at least an integration output output from the integration calculation step. And a motor drive step for non-resonantly driving the ultrasonic motor when the integration constant is set to a third value. Control method.

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