JP4313604B2 - Ultrasonic motor drive circuit and electronic device with ultrasonic motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic motor and an electronic device using the ultrasonic motor, and more particularly, to an ultrasonic motor driving circuit and an electronic device with an ultrasonic motor driven by the driving circuit.
[0002]
[Prior art]
Various types of ultrasonic motors expected as next-generation actuators have been devised, and recently, linear type ultrasonic motors are attracting attention. As the driving principle, for example, longitudinal vibration and bending vibration of a rectangular plate are often used. In this case, by applying two signals to the piezoelectric element, an elliptical motion is generated on the side surface of the vibrating body, and the moving body in contact with the vibrating body is driven. In order to generate this elliptical motion, and to switch the direction of the elliptical motion and switch the driving direction of the moving body, the phases of the two signals are changed (see, for example, Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-116162 (pages 5-7 and 4-5)
[0004]
[Problems to be solved by the invention]
However, the difference between the resonance points of two different vibrations, for example, longitudinal vibration and flexural vibration, is different for each motor and the excitation force of the two vibrations is also different, so the phase of the vibration displacement generated for the input signal is driven by each vibration mode. It changes with frequency. From these, in the driving method using the conventional driving circuit, the output characteristics such as the moving speed and the propulsive force of the moving body differ depending on the moving direction. And even in the individual ultrasonic motors, the natural frequency of the two vibration modes is slightly different, so that the output characteristics also vary greatly. The degree of influence of these phenomena also changes depending on the drive frequency, and the change in output characteristics caused by the external environment such as temperature and load is large.
[0005]
[Means for Solving the Problems]
Therefore, in order to solve the above-described problem, in the present invention, an ultrasonic motor that drives a moving body in contact with the vibrating body by applying a first signal and a second signal to the piezoelectric element of the vibrating body having a piezoelectric element. In the driving circuit, the second signal has a phase setting circuit that shifts the phase from the first signal by a first phase amount, and an output signal from the phase setting circuit is advanced or delayed by a second phase amount. The driving circuit is characterized in that it is a signal obtained through a phase switching circuit for switching between the two. According to this, variation in output characteristics with respect to individual motors and moving directions is reduced. In particular, motor efficiency is improved by setting the second phase amount to 90 degrees.
[0006]
In the driving circuit of the ultrasonic motor that drives the moving body in contact with the vibrating body by applying the first signal and the second signal to the piezoelectric element of the vibrating body having the piezoelectric element, the second signal is A phase setting circuit that shifts the phase from the first signal by a first phase amount, and whether the output signal from the phase setting circuit is delayed by a second phase amount or whether the output signal is advanced by a second phase amount The drive circuit is characterized in that it is a signal obtained through a phase switching circuit for switching whether or not. According to this, variation in output characteristics with respect to each motor and the moving direction is reduced, and the configuration of the drive circuit is simplified.
[0007]
In particular, by setting the second phase amount to 180 degrees, the motor efficiency is improved, the configuration of the drive circuit is simplified, and the application to the self-excited oscillation circuit is facilitated.
[0008]
In the circuit configuration described above, the first phase amount or the second phase amount can be varied according to the driving state of the vibrating body or the moving body, so that the temperature, load, etc. have changed. Even in this case, there is little difference in the output characteristics depending on the change of the motor output characteristics and the moving direction.
[0009]
By mounting these drive circuits and ultrasonic motors driven by these on an electronic device, it is possible to realize an electronic device that is small in size and has low power consumption and is not easily affected by the external environment and has little variation among individual products.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0011]
(Embodiment 1)
FIG. 5 shows an example of the configuration of an ultrasonic motor driven by the drive circuit of the present invention. The vibrating body constituted by the piezoelectric element 1 is supported by a support member (not shown), and pressure is applied in the direction of the arrow in the drawing by a pressure mechanism 26 (not shown) between the friction member 24 and the moving body 6. Appropriate frictional force works. The moving body 6 is guided by a guide member 25. Here, the vibrating body may be constituted only by the piezoelectric element 1 or may be constituted together with an elastic body such as metal. Displacement in the moving direction of the moving body 6 and displacement in the pressurizing direction are simultaneously generated in the friction member 24 provided on the vibrating body by exciting the vibration body with longitudinal vibration and bending vibration simultaneously. Driven. Further, the movable body 6 may be fixed and the vibrating body may be driven.
[0012]
A configuration of a vibrating body applicable to the ultrasonic motor of the present invention will be described with reference to FIGS. In FIG. 4, the vibrating body is composed only of the piezoelectric element 1. The piezoelectric element 1 is configured by laminating piezoelectric elements 1a and 1b. One of the piezoelectric elements 1a is provided with quartered electrodes 2a, 2b, 2c, and 2d to constitute the first electrode 2 of the piezoelectric element 1. On one surface of the piezoelectric element 1b, an electrode 3 is provided over almost the entire surface, and constitutes a second electrode of the piezoelectric element 1. An electrode 4 is provided on the joint surface between the piezoelectric elements 1a and 1b, and serves as a common electrode for the piezoelectric elements 1a and 1b. The piezoelectric element 1a is polarized in the thickness direction in the + and-directions in the figure. The piezoelectric element 1b is polarized in the same direction in the thickness direction throughout. When a drive signal is applied between the electrode 2 of the piezoelectric element 1a and the common electrode 4, secondary bending vibration is excited in the entire piezoelectric element 1, and when a drive signal is applied between the electrode 3 and the common electrode 4 of the piezoelectric element 1b. A primary longitudinal vibration is excited. Incidentally, here, the number of piezoelectric elements 1a and 1b and the order of lamination are not concerned.
[0013]
In order to configure an ultrasonic motor using this vibrating body and change the moving direction of the moving body 6, it is necessary to reverse the phase of the drive signal applied to the piezoelectric elements 1a and 1b. For example, the frequency signal from the frequency generation circuit 8 is amplified by the amplification circuit 1a and applied to the piezoelectric element 1a, and the frequency signal from the frequency generation circuit 8 passes through the transfer circuit 13 and then is amplified by the amplification circuit 9b to be piezoelectric. Add to element 1b. By reversing the phase by the transfer circuit 13, two different vibrations, that is, the phase of longitudinal vibration and bending vibration are reversed, and the moving direction of the moving body 6 is changed. However, as described above, the output characteristics of the ultrasonic motor may differ depending on the moving direction. By the way, FIG. 6 shows an example of measuring the change in propulsive force when the amount of phase changed by the transfer circuit 13 is gradually changed (increased), and propulsion is performed at 90 degrees or −90 degrees (270 degrees). The force is not maximized, but is maximized at a point shifted from a certain phase to 90 degrees or -90 degrees. This tendency shifts with the driving frequency. When the driving frequency is 83 kHz, the right driving force is maximum at 150 degrees, and the left driving force is maximum at 330 degrees (−30 degrees). Taking a drive frequency of 85 kHz as an example, the difference in the output characteristics of the ultrasonic motor due to the moving direction is eliminated by shifting the phase by ± the same amount around the phase amount of 120 degrees. In particular, the largest driving force can be obtained by setting the phase amount to be shifted to 90 degrees. Further, by selecting whether the phase amount shifted by the transfer circuit 13 is a certain value, or by shifting a certain amount of phase from that value, the difference in the output characteristics of the ultrasonic motor due to the moving direction is eliminated. For example, in the case of a driving frequency of 83 kHz, the amount of phase to be shifted may be set to 150 degrees, or may be further shifted 180 degrees therefrom, that is, shifted by 330 degrees (-30 degrees). By the way, + and-in a figure show the difference in the moving direction of a moving body.
[0014]
Next, a specific configuration of the drive circuit will be described with reference to FIGS. In FIG. 1, a signal of a specific frequency obtained by the frequency signal generation circuit 12 is amplified by the amplification circuit 9a and then applied to the first electrode 2 of the piezoelectric element 1, and the phase setting circuit 11 The phase is shifted by the phase amount, and an external control signal (not shown) is received and the phase switching circuit 10 determines whether to advance or delay the phase by the second phase amount.
[0015]
In the previous example (drive frequency 85 kHz), for example, the phase setting circuit 11 sets the first phase amount to 120 degrees, and the phase switching circuit 10 sets the second phase amount to 90 degrees. This signal is applied to the second electrode 3 of the piezoelectric element 1. The moving direction of the moving body 6 is determined by whether the phase is advanced or delayed by the phase switching circuit 10.
[0016]
In FIG. 1, the phase setting circuit 11 shifts the phase by the first phase amount, and the phase switching circuit 10 determines whether the phase is advanced or delayed by the second phase amount. It may be a method. In the previous example (driving frequency 85 kHz), the phase setting circuit 11 sets 210 degrees, and the phase switching circuit 10 determines whether or not to delay the second phase amount by 180 degrees. In this case, the phase switching circuit 10 only needs to select whether or not to shift the second phase amount, and the drive circuit is simplified.
[0017]
By the way, although the signal shifted in phase from the frequency signal generation circuit 12 is applied to the second electrode here, this signal is applied to the first electrode, and the same phase as the frequency signal generation circuit 12 is applied to the second electrode. You may add the signal.
[0018]
If the first phase amount and the second phase amount are set for each motor, for example, at the manufacturing stage, the variation in characteristics of each motor becomes extremely small. For example, these settings may be changed by a variable resistor or a variable capacitor on the drive circuit.
[0019]
In the vibrating body shown in the present embodiment, the longitudinal vibration and the bending vibration are independently excited by two signals, so that the effect of the present invention is great. However, even if the system uses both the longitudinal vibration and the bending vibration with the same signal, the same effect can be expected if the system is driven using two signals having different phases.
[0020]
(Embodiment 2)
FIG. 2 shows a modification of the first embodiment. Here, only the differences from FIG. 1 will be described. As described above, the relationship between the amount of phase shift of the signal applied to the second electrode 3 and the output varies depending on the drive frequency. That is, it is estimated that this relationship changes depending on the environment such as temperature and load. Therefore, in the present embodiment, the first phase amount and the second phase amount in the first embodiment are optimized by feeding back the driving state of the moving body 6 and the vibration state of the vibrating body.
[0021]
That is, the speed of the moving body 6 is measured by a sensor 7 such as an encoder, or a signal obtained from the third electrode provided on the piezoelectric element 1 is detected to detect the vibration state of the vibration body, and these are set to an optimum state. In order to be maintained, either the frequency of the frequency signal generation circuit 12, the first phase amount in the phase setting circuit 11, the second phase amount in the phase switching circuit 10, or a plurality of setting values are varied. This stabilizes the motor characteristics regardless of the external environment.
[0022]
(Embodiment 3)
FIG. 3 shows an example in which the first and second embodiments are applied to a self-excited oscillation circuit. The piezoelectric element 1 and the capacitors 22 and 23 constitute a resonance circuit whose phase changes by 180 degrees. A signal obtained through the common electrode 4 and the capacitor 23 is amplified by an amplifier circuit composed of a resistor 14 and a three-state inverter 15. Then, it returns to the second electrode 2 through the capacitor 22 and the buffer 16, and constitutes a self-excited oscillation circuit in which oscillation continues in the vicinity of a predetermined resonance frequency. By the way, this oscillation signal is taken out through an inverter 17 serving as a buffer, and the phase is shifted by a first phase amount by a low-pass filter including a resistor 18 and a capacitor 19, and either the three-state buffer 20 or the three-state inverter 21 is used. Whether the phase is reversed or not is determined and applied to the second electrode 3.
[0023]
Thus, the self-excited oscillation circuit constitutes the frequency signal generation circuit 12, the inverter 17, the resistor 18, and the capacitor 19 constitute the phase setting circuit 11, and the three-state buffer 20 and the three-state inverter 21 constitute the phase switching circuit 10. Constitute. The buffer 16, the three-state buffer 20, and the three-state inverter 21 also function as amplifier circuits 9a and 9b.
[0024]
According to the present embodiment, the self-excited oscillation circuit is configured with a simple configuration as described above.
[0025]
(Embodiment 4)
FIG. 7 shows a block diagram in which an ultrasonic motor 100 driven by the drive circuit of the present invention is applied to a drive source of an electronic device, and friction is caused by the piezoelectric element 1 and the friction member 24 joined to the piezoelectric element 1. The movable body 6 to be driven includes a transmission mechanism 27 that operates integrally with the mobile body 6, and an output mechanism 28 that operates based on the operation of the transmission mechanism 27.
[0026]
Here, the transmission mechanism 27 uses a transmission wheel such as a gear train and a friction wheel, for example. As the output mechanism 28, a paper feed mechanism in a printer, a shutter drive mechanism, a lens drive mechanism, a film winding mechanism in a camera, a pointer in an electronic device or a measuring instrument, an arm mechanism in a robot, a machine tool In this case, a tooth tool feeding mechanism, a processing member feeding mechanism, or the like is used.
[0027]
Note that an electronic timepiece, a measuring instrument, a camera, a printer, a printing machine, a robot, a machine tool, a game machine, an optical information device, a medical device, a moving device, and the like can be realized as the electronic device in this embodiment. Furthermore, if the moving body 6 is provided with an output shaft and has a power transmission mechanism for transmitting torque from the output shaft, an ultrasonic motor driving device can be realized.
[0028]
【The invention's effect】
In the present invention, a phase reference point is set by the phase setting circuit when changing the moving direction of the moving body, and the phase is switched based on the reference point. With such a configuration, it is possible to reduce a difference in output characteristics caused by a difference in moving direction of the moving body. In addition, by setting the phase set by the phase setting circuit for each motor, it is possible to reduce the difference in characteristics of each motor. Furthermore, feedback of information on the driving state such as the speed of the moving body or the vibration state of the vibrating body, and the driving frequency, the phase amount set by the phase setting circuit, or the phase amount set by the phase switching circuit can be varied. Therefore, the optimum driving state is always achieved, so the difference in the output characteristics of the motor is small even with changes in the external environment such as temperature and load. Variation can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a circuit configuration of an ultrasonic motor driving circuit according to the present invention.
FIG. 2 is a diagram showing another example of the circuit configuration of the ultrasonic motor drive circuit of the present invention.
FIG. 3 is a diagram showing an example in which the driving circuit of the ultrasonic motor of the present invention is applied to a self-excited oscillation circuit.
FIG. 4 is a diagram showing an example of a vibrating body of the ultrasonic motor of the present invention.
FIG. 5 is a diagram showing an example of the configuration of an ultrasonic motor according to the present invention.
FIG. 6 is a diagram showing the relationship between the phase difference of the drive signal and the propulsive force of the ultrasonic motor of the present invention.
FIG. 7 is a block diagram when the ultrasonic motor of the present invention is applied to an electronic device.
[Explanation of symbols]
1 Piezoelectric element 2, 3, 4, 5 Electrode 6 Moving object

Claims (6)

A piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration. A drive circuit of an ultrasonic motor that drives a moving body that contacts the vibrating body by applying a second signal to
A phase setting circuit for shifting the phase from the first signal by a first phase amount;
A phase switching circuit for switching whether the output signal from the phase setting circuit is advanced or delayed by 90 degrees ;
The ultrasonic motor drive circuit, wherein the second signal is a signal obtained through the phase setting circuit and the phase switching circuit. A piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration, and a piezoelectric element that excites only the longitudinal vibration. A drive circuit of an ultrasonic motor that drives a moving body that contacts the vibrating body by applying a second signal to
The second signal is a phase setting circuit that shifts the phase from the first signal by a first phase amount, and whether or not to delay the output signal from the phase setting circuit by 180 degrees,
Or it has a phase switching circuit that switches whether to advance,
An ultrasonic motor drive circuit, wherein the second signal is a signal obtained through the phase setting circuit and the phase switching circuit. 3. The ultrasonic motor drive according to claim 1, wherein the vibrating body is configured by stacking a piezoelectric element that excites only bending vibration and a piezoelectric element that excites only longitudinal vibration. 4. circuit. The drive circuit for an ultrasonic motor according to any one of claims 1 to 3, wherein the bending vibration is a secondary vibration, and the longitudinal vibration is a primary vibration .   5. The ultrasonic motor driving circuit according to claim 1, wherein the first phase amount is variable according to a driving state of the vibrating body or the moving body. 6. Driven by the drive circuit of the ultrasonic motor according to any one of claims 1 to 5,
A piezoelectric element;
A moving body frictionally driven by a friction member joined to the piezoelectric element;
A transmission mechanism that operates integrally with the moving body;
An electronic apparatus with an ultrasonic motor comprising an output mechanism that operates based on the operation of the transmission mechanism.

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