JP4732623B2 - Ultrasonic motor and electronic device equipped with ultrasonic motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor and an electronic device including the ultrasonic motor, and more particularly to positioning control of the ultrasonic motor.
[0002]
[Prior art]
The ultrasonic motor includes a vibrating body to which a piezoelectric body is bonded, a moving body, a pressing unit that pressurizes and contacts the moving body to the vibrating body, an electrode that applies a high frequency voltage to the piezoelectric body, and the high frequency And an oscillation drive circuit that generates a voltage, and frictionally drives the movable body by a vibration wave generated in the vibration body by the expansion and contraction of the piezoelectric body.
[0003]
Ultrasonic motors have high torque at low speed, large holding torque when no current is applied, high responsiveness and controllability, no magnetic action, small size and light weight, and extremely low operating noise. There are features. For this reason, the ultrasonic motor can be used as a drive source for positioning means of various electronic devices. For example, the present invention can be used for a pointing device that controls movement at a certain angle, mirror angle control, and driving of a pickup (head) of an information device.
[0004]
By the way, the positioning of the ultrasonic motor is performed by a control unit in which a target position is set and a position sensor that detects a current position of a moving body driven by a vibrating body of the ultrasonic motor. When the moving body is a rotor, the position sensor is an encoder attached to the rotor. The positioning operation of the conventional ultrasonic motor is, for example, as shown in FIG. That is, in FIG. 4, the control unit monitors whether or not the current position of the moving body has reached the target position (201), and issues a stop command immediately when the current position of the moving body reaches the target position (202). ), And waits for time t which is a reference waiting period (203). When t time elapses, the control unit checks whether the current position of the moving body is at the target position (204).
[0005]
If it is determined in step 204 of FIG. 4 that the current position of the moving body does not match the target position, the control unit reverses the moving body (205) and returns to the first step 201. Thereafter, the operations from step 202 to 204 are repeated. Each time the reverse rotation operation is repeated, the amount of movement from the target position, that is, the amount of overshoot decreases, and the current position of the moving body converges to the target position after a certain period of time. In this state, that is, when it is determined in step 204 that the current position of the moving body matches the target position, the control unit ends the position correction operation of the ultrasonic motor and turns off the drive power supply. To do.
[0006]
FIG. 5 is a characteristic diagram of the positioning control of the ultrasonic motor, and shows how the moving body converges to the target position after performing the position correction operation by a plurality of reverse rotations after reaching the target position for the first time. (A) is a characteristic diagram when the PWM frequency at the time of position correction is 100 Hz, (B) is a characteristic diagram when the PWM frequency is 1000 Hz, and (C) is a characteristic diagram when the PWM frequency is 10,000 Hz. As shown in FIG. 5, in the positioning control of the ultrasonic motor, the time from the start of positioning until the moving body first reaches the target position, the number of reverse operations, the amount of overshoot, and the settling time differ depending on the PWM frequency. However, what is common is that the amount of overshoot decreases every time reverse rotation is repeated.
[0007]
As described above, in the conventional ultrasonic motor positioning control, when the current position of the moving body reaches the target position, a stop command is issued immediately, and when the controller waits for the reference standby period t time, It is determined whether or not the current position of the moving body is at the target position. However, since the reference standby period is a fixed t time, there is a problem that the settling time cannot be shortened.
[0008]
That is, if the reference waiting period t is shortened, a reverse rotation command is issued at a stage where the movement of the moving body due to inertia or residual vibration is not yet small, and the timing of reverse rotation is too early and the amount of overshoot increases. For this reason, the number of reverse rotations increases and the settling time becomes longer. Such a situation occurs at the stage where the first stop command is issued and at the stage where several stop commands are issued thereafter. In addition, if the reference waiting period t is shortened, after the mobile object is determined to be at the target position, the mobile object may be misaligned due to residual vibration or the like, and accurate positioning may not be performed. Conversely, if the reference waiting period t is lengthened, the reverse rotation timing is too late and a wasteful time is consumed, resulting in an increase in the settling time. Such a situation occurs when convergence is near.
[0009]
[Problems to be solved by the invention]
The problem to be solved is to achieve accurate positioning and shorten the settling time in the positioning control of the ultrasonic motor.
[0010]
[Means for Solving the Problems]
Ultrasonic motor for solving the above problems includes a vibrating member which the piezoelectric element is bonded, and a movable body that moves Ri by the vibration of the vibrating member, and pressure means for pressing contact with the moving body to the vibrator An electrode for applying a high-frequency voltage to the piezoelectric body, an oscillation drive circuit for generating the high-frequency voltage, a position sensor for generating a position signal of the moving body, and a command signal to the oscillation drive circuit to provide the piezoelectric body A control unit that controls the application of a high-frequency voltage to the motor to start / stop the motor and perform normal rotation or reverse rotation. And an ultrasonic motor that stops the supply of the high-frequency voltage when it is determined that the moving body is at the target position for a reference standby period, the feature of which is the reference standby period Lies in that to perform said determination for each divided divided reference waiting period.
[0011]
The reference standby period is a predetermined time interval, and a time when the position of the moving body reaches a target value and the control unit issues a stop command is set as a start time.
[0012]
The division reference standby period is obtained by unevenly dividing the division reference standby period. The division reference waiting period is set to be shorter as the moving amount of the moving body to the target position is shorter. Furthermore, the division reference waiting period is set to be shorter as the speed of the moving body immediately before the stop command is issued is lower. Furthermore, the division reference waiting period is set such that the first is the shortest, the last is the longest, and the time interval is increased in order between the first and last.
[0013]
Furthermore, an electronic apparatus provided with an ultrasonic motor that solves the above-described problems is configured by configuring the ultrasonic motor as described in claim 1.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an ultrasonic motor according to an embodiment of the present invention. That is, the ultrasonic motor shown in FIG. 1 includes a vibrating body 23 to which a piezoelectric body 22 is bonded, a moving body 24 arranged to rotate clockwise or counterclockwise by the vibration of the vibrating body 23, and the moving body 24. A pressurizing unit 25 that pressurizes and contacts the vibrating body 23, a pair of electrodes 21 a and 21 b that apply a high-frequency voltage to the piezoelectric body 22, and an oscillation drive circuit 10 that generates the high-frequency voltage. The electrode 21a is for clockwise rotation, and the electrode 21b is for counterclockwise rotation.
[0015]
The oscillation drive circuit 10 includes a resistor 13, a resistor 14, a capacitor 15, and a capacitor 16. Further, the oscillation drive circuit 10 includes a start / stop inverter 11, a clockwise rotation buffer 12a, and a counterclockwise rotation buffer 12b. The oscillation drive circuit shown in FIG. 1 constitutes a Colpitts oscillation circuit type self-oscillation circuit by these circuit elements and the piezoelectric body 22 as a vibrator. The self-oscillation circuit is described in detail in the paper “Development of Ultra-Small Ultrasonic Motor Using Self-Excited Drive” described in the Journal of Precision Engineering (Vol. 64, No. 8, pp. 1117 to 1121). Is disclosed.
[0016]
The position sensor 30 is an encoder, for example, and constantly detects the current position of the moving body 24 and gives an output signal to the control unit 40. In the control unit 40, the target position of the moving body 24 is set in advance by input means (not shown). Alternatively, the target position of the moving body 24 is always input to the control unit 40 from an external device (not shown). The control unit 40 controls the positioning so that the current position of the moving body 24 always matches the target position by comparing the target position input in this way with the current position from the position sensor.
[0017]
The positioning control described above is performed by giving a control command signal from the control unit 40 to the oscillation drive circuit 10. The control command signals are a start command or stop command signal, a clockwise rotation command signal, and a counterclockwise rotation command signal, which are a start / stop inverter 11, a clockwise rotation buffer 12a, and a counterclockwise rotation command. Each is given to the buffer 12b. The control command signal is an ON / OFF signal.
[0018]
Note that each of the start / stop inverter 11, the clockwise rotation buffer 12a, and the counterclockwise rotation buffer 12b has a control terminal in addition to an input terminal and an output terminal, and a control signal input to the control terminal. In addition to being able to output two voltages of HIGH and LOW at the output terminal, it is a circuit component such as an IC having a tri-state configuration or a three-state configuration capable of bringing the input terminal and the output terminal into a high impedance state.
[0019]
FIG. 2 is a longitudinal sectional view of a main part of the ultrasonic motor of FIG. In FIG. 2, the moving body 24 is a rotor that is rotatably supported on a shaft 27 via a bearing 28. The shaft 27 is erected on the motor substrate 29, and the disk-shaped vibrating body 23 is fixed coaxially to the shaft 27. A plurality of protrusions 26 are integrally formed on the upper surface of the disc-shaped vibrating body 23, and the piezoelectric body 22 is bonded to the lower surface thereof. A pair of electrode plates formed in a predetermined electrode pattern, that is, a clockwise rotation electrode 21a and a counterclockwise rotation electrode 21b are disposed on the lower surface of the piezoelectric body 22. The vibrating body 23 that also functions as a common electrode plate on the upper surface side of the piezoelectric body 22 is electrically connected to the common electrode 21 c through a shaft 27. A spring 25 serving as a pressurizing unit presses the rotor 24 toward the vibrating body 23 and presses the lower surface of the rotor 24 against the upper end surfaces of the plurality of protrusions 26.
[0020]
In the ultrasonic motor having such a configuration, when a high-frequency voltage is applied between the clockwise rotation electrode 21a or the counterclockwise rotation electrode 21b and the common electrode 21c, the piezoelectric body 22 periodically expands and contracts. Vibration is generated in the vibrating body 23. This periodic vibration is a standing wave, and the periodic vibration of the vibrating body 23 is transmitted as power to the rotor 24 pressed against the plurality of protrusions 26 by the spring 25.
[0021]
By the action of the plurality of protrusions 26 formed with a predetermined electrode pattern and a predetermined interval and arrangement, the rotor 24 is frictionally driven by a vibration wave generated in the vibrating body 23 and rotated clockwise or counterclockwise. That is, when a high frequency voltage is applied between the clockwise rotation electrode 21a and the common electrode 21c, the rotor 24 rotates in the clockwise direction, and the high frequency voltage is applied between the counterclockwise rotation electrode 21b and the common electrode 21c. When applied, the rotor 24 rotates counterclockwise. Since the configuration and operation of such a standing wave type ultrasonic motor are disclosed in Japanese Patent Application Laid-Open No. 11-55971 and the like, detailed description thereof is omitted.
[0022]
FIG. 2 shows an embodiment of the position sensor 30. The position sensor 30 is an encoder having a disk-shaped encoder scale 31, a light emitting element 32, and a light receiving element 33. The disk-shaped encoder scale 31 has a large number of slits 34 formed at equal intervals in the circumferential direction. The number of slits 34 corresponds to the resolution required for positioning control. The disk-shaped encoder scale 31 is disposed on the upper surface of the rotor 24. The light emitting element 32 and the light receiving element 33 are disposed at a position where the light beam passes through the slit 34 and are attached to the motor substrate 29 with the disk-shaped encoder scale 31 interposed therebetween.
[0023]
In the ultrasonic motor configured as shown in FIGS. 1 and 2, the positioning control is performed according to the flowchart of FIG. That is, the control unit 40 receives the current position signal from the position sensor 30 and monitors whether the current position of the moving body 24 is the target position (101). When it is detected that the current position of the moving body 24 has reached the target position, the control unit 40 generates a stop command (102) and gives an OFF control signal to the control terminal of the inverter 11 of the oscillation drive circuit 10. Subsequently, the control unit 40 waits for t1 time (103), and determines whether or not the current position of the moving body 24 is at the target position when t1 time elapses (104). The time t1 is the first division reference standby time.
[0024]
If it is determined in step 104 that the current position of the moving body 24 exceeds the target position, the control unit 40 reverses the moving body 24 (109) and moves it in the target position direction. In this case, the controller 40 cancels the stop command and gives an ON control signal to the control terminal of the inverter 11, and the controller 40 issues a reverse command to the respective control terminals of the buffers 12a and 12b. This is done by switching the control signal.
[0025]
When it is determined in step 104 that the current position of the moving body 24 is at the target position, the control unit 40 further waits for t2 hours (105), and when the time t2 has elapsed, the current position of the moving body 24 becomes the target position. It is determined again whether or not (106). The second division reference standby period t2 is set longer than the first division reference standby period t1.
[0026]
When it is determined in step 106 that the current position of the moving body 24 exceeds the target position, the control unit 40 reverses the moving body 24 (109) and moves it in the target position direction. In this case, the controller 40 cancels the stop command and gives an ON control signal to the control terminal of the inverter 11, and the controller 40 issues a reverse command to the respective control terminals of the buffers 12a and 12b. This is done by switching the control signal.
[0027]
When it is determined in step 106 that the current position of the moving body 24 is at the target position, the control unit 40 further waits for t3 hours (107), and when the time t3 has elapsed, the current position of the moving body 24 is changed to the target position. It is determined again whether it is in (108). The third division reference standby period t3 is set longer than the second division reference standby period t2.
[0028]
When it is determined in step 108 that the current position of the moving body 24 exceeds the target position, the control unit 40 reverses the moving body 24 (109) and moves it in the target position direction. In this case, the controller 40 cancels the stop command and gives an ON control signal to the control terminal of the inverter 11, and the controller 40 issues a reverse command to the respective control terminals of the buffers 12a and 12b. This is done by switching the control signal.
[0029]
When it is determined in step 108 that the current position of the moving body 24 is at the target position, the control unit 40 ends the position correction operation and turns off the drive power supply. In this way, the positioning operation according to the present invention is completed. And the control part 40 waits until a new target position is input next.
[0030]
In the present invention, not only when the first division reference waiting period t1 has elapsed since the stop command was issued and when the second division reference waiting period t2 has elapsed, the third division reference waiting period t3 has elapsed. Even at the time, it is confirmed that the current position of the moving body 24 is at the target position. The reference waiting period t, which is the total period of the first divided reference waiting period t1, the second divided reference waiting period t2, and the third divided reference waiting period t3, is an optimum time interval depending on the positioning characteristics of the target ultrasonic motor. Is set as That is, the reference standby period t is set to be approximately the same as the most desirable time interval in the conventional ultrasonic motor positioning control. The division reference waiting period is set to be shorter as the moving amount of the moving body 24 to the target position is shorter. Furthermore, the division reference waiting period is set shorter as the speed of the moving body immediately before the stop command is issued is lower. This is based on the reason that the amount of overshoot of the moving body is small when the moving amount is short or the speed is low, and the time until stopping is short. Based on these, the optimum reference waiting period t is selected in the range of several milliseconds to several hundred microseconds.
[0031]
As described above in detail, in the positioning control of the ultrasonic motor according to the present invention, the reference waiting period t elapses to determine that the moving body 24 has reached the target position and keeps the position stably. At the same time, it is determined whether or not reversal for position correction is necessary for each of a plurality of divided reference standby periods obtained by dividing the reference standby period t. In the plurality of division reference waiting periods, the first is the shortest, the last is the longest, and the time interval is set to be longer between the first and last. As described above, since it is determined whether or not reverse rotation for position correction is necessary, during the reference standby period t, useless standby time is eliminated and settling time in positioning control is shortened. . Further, when the reference waiting period t of the optimal time interval has elapsed, it is determined that the moving body 24 keeps the target position stably, so that more accurate positioning is possible. It was.
[0032]
In the present invention, the control unit 40 can of course be configured by a CPU, but it is also a feature of the present invention that it can be configured using inexpensive logic circuit elements. In this case, the setting means for the division reference standby period is also configured using the logic circuit elements. Further, the present invention is not limited to the standing wave type ultrasonic motor, but can of course be applied to a traveling wave type ultrasonic motor or the like. Of course, the oscillation drive circuit 10 is not limited to one using a self-excited oscillation circuit, but may be one using a separately-excited oscillation circuit.
[0033]
【The invention's effect】
According to the present invention, an ultrasonic motor capable of accurate positioning and shortening the settling time is provided. In addition, since the control unit for positioning control can be configured using logic circuit elements, the cost can be reduced. Furthermore, an electronic device employing such an ultrasonic motor as a positioning control drive source has been improved in positioning accuracy and shortened settling time.
[Brief description of the drawings]
FIG. 1 is a block circuit diagram of an ultrasonic motor according to an embodiment of the present invention.
2 is a longitudinal sectional view of a main part of the ultrasonic motor of FIG. 1. FIG.
FIG. 3 is an example of a flowchart of the positioning operation of the ultrasonic motor according to the present invention.
FIG. 4 is a flowchart of a positioning operation of a conventional ultrasonic motor.
FIG. 5 is a characteristic curve showing the overshoot and settling time when correcting the position of the ultrasonic motor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Oscillation drive circuit 11 Inverter 12a Clockwise rotation buffer 12b Counterclockwise rotation buffer 13, 14 Resistance 15, 16 Capacitor 21a Clockwise rotation electrode 21b Counterclockwise rotation electrode 21c Common electrode 22 Piezoelectric body 23 Vibration body 24 Moving body or rotor 25 Pressurizing means or spring 26 Protrusion 27 Shaft 28 Bearing 29 Motor substrate 30 Position sensor 31 Encoder scale 32 Light emitting element 33 Light receiving element 34 Slit 40 Control unit

Claims (7)

A vibrating body to which a piezoelectric body is bonded; a moving body that moves by vibration of the vibrating body; a pressurizing unit that pressurizes and contacts the moving body to the vibrating body; and an electrode that applies a high-frequency voltage to the piezoelectric body; An oscillation drive circuit that generates the high-frequency voltage; a position sensor that generates a position signal of the moving body; and a command signal that is supplied to the oscillation drive circuit to control application of the high-frequency voltage to the piezoelectric body. And a control unit that performs start / stop and forward rotation or reverse rotation, and monitors the position signal and is controlled so that the position of the moving body coincides with a target position input in advance, and the oscillation drive circuit Is to stop the generation of the high-frequency voltage when a stop command signal is input from the control unit, and the control unit determines the time when the moving body reaches the target position and issues the stop command signal as a start time. In each divided reference waiting period obtained by dividing the reference waiting time to be determined, it is determined whether the moving body is at the target position, and when it is determined that the moving body has exceeded the target position, the moving body is reversed. In addition, when it is determined that the moving body has been at the target position over the entire reference waiting period, the positioning motor is terminated . Ultrasonic motor according to claim 1, wherein the reference waiting period is a predetermined time interval. The ultrasonic motor according to claim 1, wherein the divided reference waiting period is an uneven division of the reference waiting period.   The ultrasonic motor according to claim 3, wherein the division reference waiting period is set to be shorter as the moving amount of the moving body to the target position is shorter.   The ultrasonic motor according to claim 3, wherein the division reference waiting period is set to be shorter as the speed of the moving body immediately before the stop command is issued is lower.   The ultrasonic motor according to claim 3, wherein the division reference waiting period is set such that the first is the shortest, the last is the longest, and the time interval is longer in order between the first and last. Electronic apparatus having an ultrasonic motor according to any one of claims 1 to 6.

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