JPH07123748A - Drive circuit of ultrasonic motor - Google Patents

Abstract

PURPOSE:To drive an ultrasonic motor so that the motor can be stabilized in a desired driving state. CONSTITUTION:The voltage level detecting circuit 44 of a drive circuit 30 is connected to the output terminals of power amplifier circuits 38 and 40 and the two-phase drive signals supplied to piezoelectric bodies 14A and 14B of an ultrasonic motor from the circuits 38 and 40 are inputted to the circuit 44. The circuit 44 detects the mean value of the voltage levels of the two-phase drive signals. A drive control circuit 42 controls the voltage levels of the two- phase drive signals outputted from the amplifier circuits 38 and 40 so that the mean value of the voltage levels of the two-phase drive signals indicated by a signal inputted from the circuit 44 can coincide with the target voltage level value of the drive signals indicated by a signal inputted from an external control circuit 43. Therefore, the output of the ultrasonic motor can be controlled with accuracy so that the output cannot deviate largely from a desired output even when the voltage levels of the two-phase drive signals are different from each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor drive circuit, and more particularly to an ultrasonic motor drive circuit for driving an ultrasonic motor by supplying drive signals of a plurality of phases to the ultrasonic motor.

[0002]

2. Description of the Related Art Ultrasonic motors using ultrasonic vibration as a driving force have been conventionally known. In a traveling wave type ultrasonic motor, which is a type of ultrasonic motor, a piezoelectric body is attached to a ring-shaped elastic body to form a stator, and a rotor attached to the drive shaft makes pressure contact with this stator. Has been done. The drive circuit of the ultrasonic motor supplies two-phase drive signals (sin wave and cos wave) having a predetermined frequency and a phase difference of 90 ° to the piezoelectric body. Due to the mechanical vibration of the piezoelectric body generated by these two drive signals,
Ultrasonic vibration (traveling wave) in which an antinode and a node of vibration move annularly along the elastic body is excited in the elastic body. The traveling wave causes the rotor and the drive shaft, which are in pressure contact with the elastic body, to rotate in a direction opposite to the traveling direction of the traveling wave.

Further, the rotational speed and torque of the rotor of the ultrasonic motor change according to the amplitude of ultrasonic vibration, that is, the voltage level of the drive signal. Therefore, in order to efficiently and stably rotate the rotor and the like at a predetermined rotation speed and torque, the voltage level of either one of the two-phase drive signals is detected, and the voltage level of the drive signal or the voltage level of the drive signal is detected based on the detection result. It has been proposed to control the frequency of a drive signal (see, for example, JP-A-3-239168 and JP-A-3-277184).

By the way, a driving signal of a relatively high voltage level is required to drive the ultrasonic motor. Therefore, a booster circuit as shown in FIGS. 22A to 22D is provided in the drive circuit of the ultrasonic motor, and a two-phase drive signal obtained by turning on / off the switching elements 120A and 120B. Is boosted by inductance elements (coils) 122 and 124 (see FIGS. 22A and 22B) or transformers 126 and 128 (see FIGS. 22C and 22D) and the piezoelectric body 1 of the ultrasonic motor.
It is supplied to each of 30A and 130B.

However, since the inductance elements and the transformers have different phases of inductance and the plurality of drive signal input terminals of the ultrasonic motor also have different impedances, they are supplied to the ultrasonic motor. The voltage levels of the phase drive signals are not necessarily equal. The drive circuits described in the above publications each detect the voltage level of either one of the two-phase drive signals,
Since the detected voltage level is controlled so as to match the target value, there is a drawback in that it is difficult to drive the ultrasonic motor so that the ultrasonic motor stabilizes in the target driving state. For example, when driving the ultrasonic motor so as to obtain a target output (rotational speed or torque),
If the voltage levels of the two-phase drive signals are greatly different, the rotation speed and the torque are significantly different from the target values, and the rotation speed and the torque cannot be controlled with high accuracy.

Further, when the ultrasonic motor is driven with high output (high rotation or high torque), it is necessary to raise the voltage level of the drive signal, but if the voltage level is too high, the vibration of the piezoelectric body becomes excessive. , The piezoelectric body is destroyed or deteriorates. As an example, in order to drive an ultrasonic motor in which the piezoelectric element breaks when the voltage level of the drive signal is 500 V or higher, only the voltage level of one drive signal is detected and, for example, the voltage level of the two-phase drive signal is detected. Even if the voltage level of the other drive signal exceeds 500V (for example, about 550V), even if the detected voltage level is controlled to be 450V with a margin of 50V in mind, the piezoelectric body may be destroyed or deteriorated. Inconvenience may occur. Further, if the voltage level of the detected drive signal is controlled to be 400V with a further allowance, the ultrasonic motor cannot be driven at a sufficiently high output when the voltage level of the other drive signal is 400V or a value close to 400V. There is a problem.

On the other hand, when the ultrasonic motor is driven with low output (low rotation or low torque), it is necessary to lower the voltage level of the drive signal, but if the voltage level is too low, the piezoelectric body will not vibrate. , The ultrasonic motor may not start and the rotor may not rotate. As an example, in order to drive an ultrasonic motor that does not start when the voltage level of the drive signal is 100 V or less at a low output, only the voltage level of one drive signal is detected, and the difference between the voltage levels of the two-phase drive signals is detected, for example. Even if the voltage level of the other drive signal becomes 100 V or less (for example, about 80 V) even if the detected voltage level is controlled to be 120 V with a margin of 20 V expected, the ultrasonic motor drive stops. Or it may not be activated. In addition, the voltage level of the drive signal detected with a further allowance
Controlling to 140V has a disadvantage that the ultrasonic motor cannot be driven at a low output when the voltage level of the other drive signal is 140V or a value close to 140V.

In order to solve the above-mentioned drawbacks, JP-A-5-64
Japanese Patent Laid-Open No. 30-230 discloses that a means for controlling the gain of each booster circuit of the two-phase drive signals is provided so that the voltage levels of the two-phase drive signals are almost equal. When each gain is changed to make the voltage levels equal to each other, the voltage levels interfere with each other and the voltage levels change, so there is a problem that it is difficult to make the voltage levels converge to the same value. Have difficulty. Even if it can be realized, complicated control is required, which leads to a significant increase in cost.

The present invention has been made in consideration of the above facts, and an object thereof is to obtain an ultrasonic motor drive circuit capable of driving an ultrasonic motor so as to be stable in a target drive state. .

[0010]

In order to achieve the above object, the invention according to claim 1 is a drive signal output means for outputting drive signals of a plurality of phases for driving an ultrasonic motor, and a drive signal output means of the plurality of phases. Average value detection means for detecting the average value of the voltage levels of the drive signals, and the voltage levels of the drive signals of the plurality of phases so that the average value detected by the average value detection means matches or approaches the target value of the voltage level. And a control means for controlling each of the above.

According to a second aspect of the present invention, drive signal output means for outputting a plurality of phase drive signals for driving the ultrasonic motor, and a maximum value for detecting a maximum voltage level of the plurality of phase drive signals. And a control unit that controls the voltage levels of the drive signals of the plurality of phases so that the maximum value detected by the maximum value detection unit does not exceed an allowable maximum value of the ultrasonic motor. is doing.

According to a third aspect of the present invention, there is provided drive signal output means for outputting a plurality of phase drive signals for driving the ultrasonic motor, and a minimum value for detecting a minimum voltage level of the plurality of phase drive signals. And a control unit that controls the voltage levels of the drive signals of the plurality of phases so that the minimum value detected by the minimum value detection unit does not become smaller than the allowable minimum value of the ultrasonic motor. is doing.

[0013]

According to the first aspect of the present invention, the average value of the voltage levels of the drive signals of the plurality of phases for driving the ultrasonic motor is detected, and the detected average value matches or approaches the target value of the voltage level. The voltage levels of the drive signals of a plurality of phases are controlled respectively. As the voltage level, the average value of the amplitude (instantaneous value) of the drive signal, the effective value of the voltage of the drive signal, or the like can be used. The average value of the voltage levels of the multi-phase drive signals substantially corresponds to the amplitude of the ultrasonic vibration excited in the ultrasonic motor by the multi-phase drive signals, that is, the output (rotation speed, torque) of the ultrasonic motor. .

Thus, when the ultrasonic motor is driven with the voltage level corresponding to the predetermined output as the target value of the voltage level so that a predetermined output can be obtained, for example, the voltage levels of the drive signals of a plurality of phases are Even if they are different, the voltage levels of the drive signals of the multiple phases are controlled so that the average value of the voltage levels matches or approaches the target value of the voltage level, so the voltage levels of the drive signals of the multiple phases match. Even if it is not controlled so that the output of the ultrasonic motor is not greatly deviated from the predetermined output, the output of the ultrasonic motor can be controlled with high accuracy. Therefore, the ultrasonic motor can be driven so as to be stable in the target driving state without requiring complicated control.

According to the second aspect of the invention, the maximum value of the voltage levels of the drive signals of the plurality of phases for driving the ultrasonic motor is detected by the maximum value detecting means, and the detected maximum value is allowable by the ultrasonic motor. The control means controls the voltage levels of the drive signals of a plurality of phases so that the maximum values are not exceeded.
As a result, even if the voltage levels of the drive signals of the multiple phases are different when driving the ultrasonic motor at high output, for example, the voltage level of one of the drive signals of the multiple phases will not exceed the maximum allowable value of the ultrasonic motor. If the value exceeds the value, the piezoelectric motor of the ultrasonic motor will not be damaged, and the deterioration of the life of the ultrasonic motor will not cause any inconvenience. It is possible to drive the ultrasonic motor so that the ultrasonic motor is stable even in the state of being kept.

According to the third aspect of the invention, the minimum value of the voltage levels of the drive signals of the plurality of phases for driving the ultrasonic motor is detected by the minimum value detecting means, and the detected minimum value is allowable by the ultrasonic motor. The voltage levels of the drive signals of the plurality of phases are controlled so as not to become smaller than the minimum value. As a result, for example, when the ultrasonic motor is driven at a low output, even if the voltage levels of the drive signals of a plurality of phases are different,
If the voltage level of any of the multi-phase drive signals falls below the allowable minimum value of the drive signal voltage level, the ultrasonic motor will not be driven or the ultrasonic motor will not be started. Since it is possible to maintain the operating state, it is possible to drive the ultrasonic motor so as to be stable even in the state of being driven at a low output.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings. Although the following description will be given using numerical values that do not hinder the present invention, the present invention is not limited to the numerical values shown below.

[First Embodiment] FIG. 1 shows a traveling wave type ultrasonic motor 10 according to the first embodiment. The ultrasonic motor 10 includes an annular elastic body 12 made of a copper alloy or the like, and a piezoelectric body 14 is attached to the elastic body 12 to form a stator.

The piezoelectric body 14 is made of a piezoelectric material that converts an electric signal into mechanical vibration, and is divided into a ring shape by a large number of electrodes.
It is arranged and configured. On the other hand, the rotor 18 attached to the drive shaft 16 is formed by adhering an annular slider 22 to a rotor ring 20 made of an aluminum alloy or the like, and the slider 22 is brought into pressure contact with the elastic body 12 by a spring 24. Has been done. An engineering plastic or the like is used as the slider 22 in order to obtain a stable frictional force and coefficient of friction, and the rotor 18 can be driven with high efficiency.

The elastic body 12 has a piezoelectric element 26 (see FIG. 2).
(See) is attached. As shown in FIG. 2, the piezoelectric element 2
One end of 6 is connected to the terminal 30A of the ultrasonic motor drive circuit 30, and the other end is grounded. The piezoelectric element 26 detects the vibration of the elastic body 12 and outputs an AC signal having an amplitude and a cycle corresponding to the vibration to the drive circuit 30. The terminal 30A is connected to the input end of the frequency control circuit 32. The output terminal of the frequency control circuit 32 is connected to the signal input terminal of the voltage controlled oscillator circuit (VCO) 34. The voltage controlled oscillator circuit 34
A signal having a frequency corresponding to the voltage level of the signal input to the signal input terminal is output.

The output end of the voltage controlled oscillator circuit 34 is branched into two parts, one of the branched ends is connected to the input end of the power amplifier circuit 38, and the other branched end is connected via the phase shifter 36. It is connected to the input end of the power amplification circuit 40. The phase shifter 36 changes the phase of the input signal by 90 ° and outputs it. Therefore, signals having the same frequency and amplitude but different phases by 90 ° are input to the power amplification circuits 38 and 40. Also,
The control ends of the power amplification circuits 38 and 40 are respectively the drive control circuit 4
Connected to 2.

Each of the power amplification circuits 38 and 40 is configured to include an inductance element, a transformer, or the like,
The signal input from the voltage control oscillation circuit 34 is boosted to a voltage level corresponding to the level of the voltage control signal input from the drive control circuit 42 and output as an ultrasonic motor drive signal. Note that, hereinafter, for convenience, the drive signal output from the power amplification circuit 38 is referred to as an A phase, and the drive signal output from the power amplification circuit 40 is referred to as a B phase. Power amplifier circuits 38, 40
The output end of the piezoelectric body 14A via terminals 30B and 30C,
It is connected to one end of 14B. Piezoelectric bodies 14A, 14B
The other end of is grounded. The piezoelectric bodies 14A and 14B form the piezoelectric body 14 of the ultrasonic motor 10. In the ultrasonic motor 10 of the present embodiment, for example, the maximum allowable voltage level of the drive signal is 500V and the minimum allowable voltage level is 100V.
It is said that.

The terminals 30B and 30C are connected to the input terminals of the voltage level detection circuit 44. In the first embodiment, the voltage level detecting circuit 44 is composed of the detecting circuit 44A corresponding to the average value detecting means of the present invention (see FIG. 3). That is, the detection circuit 44A has two input terminals 56.
A and 56B are provided, and the terminal 30B has an input end 56A.
Further, the terminals 30C are connected to the input ends 56B, respectively.
The anode of the diode 46 is connected to the input end 56A, and the anode of the diode 48 is connected to the input end 56B. The cathode of the diode 46 is a resistor 50.
, And the cathode of the diode 48 is connected to one end of the resistor 51. The resistors 50 and 51 have the same electric resistance value. Resistance 50, 5
The other ends of ₁ are connected to each other at a P ₁ point, and one end of a resistor 52, one end of a capacitor 54 and an output end 56C are connected to this P ₁ point. Resistor 52 and capacitor 54
The other end of each is grounded.

The output end 56C of the detection circuit 44A, that is, the output end of the voltage level detection circuit 44 is connected to the drive control circuit 42 as shown in FIG. Drive control circuit 42
Corresponds to the control means of the present invention. Drive control circuit 42
An external control circuit 43 configured to include a microcomputer is connected to the external control circuit 43, and a signal representing a target value of the voltage level is input from the external control circuit 43. The drive control circuit 42, based on the signal input from the voltage level detection circuit 44 and the signal input from the external control circuit 43,
The power amplification circuit 3 by changing the level of the voltage control signal
Output to 8 and 40.

Next, the operation of the first embodiment will be described. When the driving of the ultrasonic motor 10 is started, the frequency control circuit 32
Outputs a frequency control signal of a relatively low voltage level, and the voltage controlled oscillation circuit 34 of the drive circuit 30 corresponds to the voltage level of the frequency control signal and is higher than the drive frequency band of the ultrasonic motor 10 (see FIG. 4). A signal having a sufficiently high frequency (frequency at the start of driving shown in FIG. 4) is output. The signal output from the voltage controlled oscillator circuit 34 is branched into two signals, one of which is changed in phase by 90 ° by the phase shifter 36 and amplified (boosted) by the power amplifier circuits 38 and 40, respectively, so that sin
Wave and cos wave two-phase drive signals are generated, and these two-phase drive signals are applied to the piezoelectric bodies 14A and 14B of the ultrasonic motor 10.
Is supplied to.

This drive signal is converted into mechanical vibration by the piezoelectric bodies 14A and 14B, and a traveling wave is excited in the elastic body 12 of the ultrasonic motor 10 to rotate the drive shaft 16 and the rotor 18. Further, the vibration of the elastic body is converted into an electric signal by the piezoelectric element 26 and input to the frequency control circuit 32 of the drive circuit 30. In the frequency control circuit 32, the voltage level of the frequency control signal is adjusted so that the frequency of the drive signal supplied to the ultrasonic motor 10 becomes the optimum drive frequency of the ultrasonic motor 10 based on the signal input from the piezoelectric element 26. To control.

Specifically, for example, the applicant has already filed a patent application
As proposed in 4-330215, the voltage level of the frequency control signal is gradually lowered only during the period when the amplitude of the signal rectified from the signal input from the piezoelectric element 26 exceeds the reference level. The frequency of the drive signal rises), and the voltage level of the frequency control signal is gradually increased only during the period when the amplitude of the signal is below the reference level (thereby causing the frequency of the drive signal to decrease). As a result, the frequency of the drive signal output from the voltage controlled oscillation circuit 34 and supplied to the ultrasonic motor 10 is set to follow the optimum drive frequency of the ultrasonic motor 10 regardless of load fluctuations, ambient temperature fluctuations, and the like. Controlled.

On the other hand, A output from the power amplifier circuit 38
The phase drive signal is input to the diode 46 via the input terminal 56A of the detection circuit 44A that constitutes the voltage level detection circuit 44, half-wave rectified by the diode 46, and output. The B-phase drive signal output from the power amplification circuit 40 is also input to the diode 48 via the input end 56B, half-wave rectified by the diode 46, and output. Here, the cathode of the diode 46 and the cathode of the diode 48 are connected via resistors 50 and 51, respectively.
Because it is connected with P ₁ points shown, the voltage level at _point P is a voltage level at the input via the input terminal 56A diode 46 half-wave rectified and divided by the signal by the resistor 50 and 52 , The voltage level of the signal input through the input terminal 56B, half-wave rectified by the diode 48, and divided by the resistors 51 and 52, and the average value.

Further, when viewed from the output terminal 56C, the fluctuation of the voltage level at the point P ₁ is smoothed by the capacitor 54, so that the voltage level corresponding to the average value of the voltage levels of the two-phase drive signals is output from the output terminal 56C. Then, a signal with almost no level fluctuation is output (hereinafter, the signal output from the voltage level detection circuit 44 is referred to as signal X). On the other hand, the external control circuit 43 includes an ultrasonic motor 10
Data indicating the relationship between the voltage level of the drive signal supplied to the ultrasonic motor 10 and the output of the ultrasonic motor 10 is stored in advance, and represents the target value of the voltage level of the drive signal for obtaining the desired output from the ultrasonic motor 10. The signal is output to the drive control circuit 42.

In the drive control circuit 42, the average value of the voltage level of the drive signal represented by the signal X input from the voltage level detection circuit 44 is higher than the target value of the voltage level represented by the signal input from the external control circuit 43. When it is small, the voltage level of the drive signal output from the power amplification circuits 38 and 40 is high, and when the average value of the voltage levels is higher than the target value, it is output from the power amplification circuits 38 and 40. The level of the voltage control signal is changed so that the voltage level of the drive signal becomes smaller, that is, the average value of the voltage levels matches the target value.

This voltage control signal is supplied to the power amplifier circuits 38, 4
The voltage levels of the drive signals input to and output from the respective 0s are similarly changed. As a result, even if the voltage levels of the two-phase drive signals output from the power amplifier circuits 38 and 40 are greatly different from each other, the accuracy of the output of the ultrasonic motor 10 does not greatly deviate from the desired output. The ultrasonic motor 10 can be well controlled, and the ultrasonic motor 10 can be driven so as to be stable in a target driving state.

Further, the external control circuit 43 considers the difference between the voltage levels of the two-phase drive signals, and sets the target value of the voltage level of the drive signals to a predetermined value whose upper limit is slightly smaller than the maximum allowable value of the ultrasonic motor 10. And the lower limit is set to a value within a predetermined range, which is a predetermined value slightly larger than the allowable minimum value of the ultrasonic motor 10. This prevents the voltage levels of the two-phase drive signals from exceeding the allowable maximum value of the ultrasonic motor 10 or becoming smaller than the allowable minimum value of the ultrasonic motor 10.

In the above description, the voltage level detection circuit 44 for outputting the signal corresponding to the average value of the voltage levels of the two-phase drive signals is composed of the detection circuit 44A shown in FIG. 3, but it is shown in FIG. You may comprise by the detection circuit 44B. That is, in the detection circuit 44B, the resistors 50 and 51 are omitted, the resistor 60 is inserted between the anode of the diode 46 and the input end 56A in place of the resistor 50, and the anode of the diode 48 and the input end is placed in place of the resistor 51. The resistor 62 is inserted between 56B. The cathode of the diode 64 is connected to the anode of the diode 46,
The cathode of the diode 66 is connected to the anode of the diode 48. The anodes of the diodes 64 and 66 are grounded.

Also in the detection circuit 44B, the input 2
The phase drive signals are half-wave rectified by the diodes 46 and 48, respectively, but when the voltage level of the drive signals is negative, a current flows through the diodes 64 and 66 and the resistor 6
0,62 so that the diodes 46,4
As the element 8, an element having poor frequency characteristics can be used. On the other hand, the voltage level at point P ₁ is
Voltage level of the signal that is input through the resistors 60 and 52 and is half-wave rectified, and voltage level of the signal that is input through the input terminal 56B and is divided and half-wave rectified by the resistors 62 and 52. Equal to the average of the levels and. Therefore, the output terminal 56C outputs the signal X having a voltage level corresponding to the average value of the voltage levels of the two-phase drive signals and having almost no level fluctuation, and the same effect as that obtained when the detection circuit 44A is used. can get.

[Second Embodiment] Next, a second embodiment of the present invention will be described. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In the second embodiment,
As the voltage level detection circuit 44, a detection circuit 44C (see FIG. 6) corresponding to the maximum value detection means of the present invention is used.

The anode of a diode 70 is connected to the input end 56A of the detection circuit 44C, and the diode 70
One end of a resistor 74 is connected to the cathode of the. The other end of the resistor 74 is connected to one end of the resistor 76,
The other end of 6 is grounded. The resistor 74 and the resistor 76 are connected to the non-inverting input terminal of the operational amplifier 86. Further, one end of the capacitor 82 is also connected to the non-inverting input end of the operational amplifier 86, and the other end of the capacitor 82 is grounded. The output terminal of the operational amplifier 86 is connected to the anode of the diode 90, and the cathode of the diode 90 is connected to the output terminal 56C and the inverting input terminal of the operational amplifier 86. Further, one end of the resistor 94 is connected to the output end 56C, and the other end of the resistor 94 is grounded.

A circuit having the same structure as the circuit connected to the input end 56A is also connected to the input end 56B. That is,
The anode of the diode 72 is connected to the input end 56B, and one end of the resistor 78 is connected to the cathode of the diode 72. The other end of the resistor 78 is connected to one end of the resistor 80, and the other end of the resistor 80 is grounded. The resistor 78 and the resistor 80 are connected to the non-inverting input terminal of the operational amplifier 88. Further, one end of the capacitor 84 is also connected to the non-inverting input terminal of the operational amplifier 88,
The other end of the capacitor 84 is grounded. Operational amplifier 8
The output terminal of 8 is connected to the anode of the diode 92, and the cathode of the diode 92 is connected to the output terminal 56C and the inverting input terminal of the operational amplifier 88.

Next, the operation of the detection circuit 44C will be described. The A-phase drive signal input via the input end 56A is half-wave rectified by the diode 70, divided by the resistors 74 and 76, smoothed by the capacitor 82, and input to the non-inverting input end of the operational amplifier 86. Since the output terminal of the operational amplifier 86 is connected to the anode of the diode 90 and the cathode of the diode 90 is connected to the inverting input terminal of the operational amplifier, the operational amplifier 86 and the diode 90 have the anode on the input terminal 56A side and the cathode on the output terminal 56C. It is equivalent to an ideal diode arranged on the side, and only when the voltage level of the signal input to the non-inverting input terminal of the operational amplifier 86 is higher than the voltage level at the point P ₁ (that is, the cathode voltage of the diode 90). , results in a current flowing from the output terminal of the operational amplifier 86, the voltage level of the P ₁ point is raised so that the voltage level of the P ₁ point is equal to the voltage level of the non-inverting input terminal side.

On the other hand, B input through the input terminal 56B
The phase drive signal is also half-wave rectified by the diode 72, divided by the resistors 78 and 80, smoothed by the capacitor 84, and input to the non-inverting input terminal of the operational amplifier 88. The operational amplifier 88 and the diode 92 are also equivalent to an ideal diode in which the anode is arranged on the input end 56B side and the cathode is arranged on the output end 56C side, and the voltage level of the signal input to the non-inverting input end of the operational amplifier 88 is Only if it is higher than the voltage level at P ₁
Flows out current from the output terminal 8, the voltage level of the P ₁ point is raised so that the voltage level of the P ₁ point is equal to the voltage level of the non-inverting input terminal side.

Since the other end of the resistor 94 whose one end is grounded is connected to the point P _1, the voltage level of the signal X output from the output end 56C is high at the cathode voltage of the diode 90 and the diode 92. Will be matched with the other value. Therefore, the detection circuit 44C outputs a voltage level signal corresponding to the maximum value of the voltage levels of the two-phase drive signals. The drive control circuit 42 of the second embodiment uses the signal X
Based on the maximum value of the voltage level of the two-phase drive signal represented by and the target value of the voltage level of the drive signal represented by the signal input from the external control circuit 43, as in the first embodiment The voltage level of the drive signal is controlled respectively.

In the external control circuit 43 of the second embodiment, the upper limit of the target value of the voltage level of the drive signal is different from that of the first embodiment, and the upper limit of the target value of the voltage level of the ultrasonic motor 10 is set. The value is very close to the maximum allowable value (500V in this embodiment).

Thus, for example, even when the voltage levels of the two-phase drive signals are different when the ultrasonic motor 10 is driven at a high output, one of the two-phase drive signals is driven. It is possible to surely prevent the piezoelectric body 14 of the ultrasonic motor 10 from being destroyed or exceeding its allowable maximum value of the voltage level of the signal, and it is possible to surely prevent disadvantages such as shortening of the life due to deterioration. 1
0 can be driven so as to be stable in a high output driving state.

In the above description, the voltage level detection circuit 44 for outputting the signal X corresponding to the maximum value of the voltage levels of the two-phase drive signals is composed of the detection circuit 44C shown in FIG. It may be configured by the detection circuit 44D shown.

That is, in the detection circuit 44D, the operational amplifiers 86 and 88 are omitted from the detection circuit 44C shown in FIG. 6, and a circuit equivalent to an ideal diode composed of the operational amplifier 86 and the diode 90 and the operational amplifier 88 and the diode 92 is used.
The simple diodes 90 and 92 are used instead. This detection circuit 44D also has the same effect as the detection circuit 44C. However, there is a voltage drop in the diode even when a current flows in the forward direction, and the magnitude of this voltage drop fluctuates due to fluctuations in the ambient temperature and variations in the diode itself (especially for silicon diodes, the forward voltage drop). The detection accuracy is lower than that of the detection circuit 44C of FIG. 6 because of the large fluctuation range of (1). However, since the operational amplifier can be omitted, the configuration is simple and the cost can be kept low.

[Third Embodiment] Next, a third embodiment of the present invention will be described. The same parts as those in the first and second embodiments are designated by the same reference numerals and the description thereof will be omitted. In the third embodiment, as the voltage level detecting circuit 44, the detecting circuit 44E (see FIG. 8) corresponding to the minimum value detecting means of the present invention is used.

This detection circuit 44E has substantially the same configuration as the detection circuit 44C (see FIG. 6) described in the second embodiment, but the directions of the diodes 90 and 92 are different, and the output of the operational amplifier 86 is different. The cathode of the diode 90 is connected to the end, and the anode of the diode 90 is connected to the output end 56C and the inverting input end of the operational amplifier 86. Similarly, the output terminal of the operational amplifier 88 is connected to the cathode of the diode 92, and the anode of the diode 92 is connected to the output terminal 56C and the inverting input terminal of the operational amplifier 88. The other end of the resistor 94, one end of which is connected to the output end 56C, is connected to a constant voltage power source (not shown), and the voltage level of the output end 56C is raised (pulled up) to a predetermined level (for example, about 5V). There is.

Next, the operation of the detection circuit 44E will be described. Entering
The A-phase drive signal input via the input terminal 56A is
Half-wave rectified by the terminal 70, and divided by the resistors 74 and 76
Is smoothed by the capacitor 82, and the
It is input to the inverting input terminal. The output terminal of the operational amplifier 86 is
It is connected to the cathode of the ion 90
The anode is connected to the inverting input of the op amp
Therefore, the cathode of the operational amplifier 86 and the diode 90 is
The anode is arranged on the input end 56A side and the output end 56C side is arranged.
It is equivalent to an ideal diode. Therefore, the input end 5
The current flowing from the 6A side to the output end 56C side is blocked, and
The voltage level on the non-inverting input terminal side of the amplifier 86 is P₁To the point
Forward the diode 90 when the voltage level is lower than
Current flows in the direction of P₁The voltage level at the point is the non-inverting input end side
P to match the voltage level of ₁Low voltage level at point
Be sent down.

On the other hand, B input through the input end 56B
The phase drive signal is also half-wave rectified by the diode 72, divided by the resistors 78 and 80, smoothed by the capacitor 84, and input to the non-inverting input terminal of the operational amplifier 88. The operational amplifier 88 and the diode 92 are also equivalent to an ideal diode in which the cathode is arranged on the input end 56B side and the anode is arranged on the output end 56C side, and a current flowing from the input end 56B side to the output end 56C side is blocked, When the voltage level at the non-inverting input terminal side of the operational amplifier 88 is lower than the voltage level at the P ₁ point, current flows in the diode 92 in the forward direction, and the voltage level at the P ₁ point matches the voltage level at the non-inverting input terminal side. As a result, the voltage level at point P ₁ is lowered.

From the above, P ₁ point, that is, the output end 56C
The voltage level of the signal X output from the diode 90
And the lower value of the anode voltage of each of the diodes 92. Therefore, the detection circuit 44C outputs a signal having a voltage level corresponding to the minimum voltage level of the two-phase drive signals. The drive control circuit 42 of the third embodiment sets the minimum value of the voltage level of the two-phase drive signal represented by the signal X and the target value of the voltage level of the drive signal represented by the signal input from the external control circuit 43. Based on this, the voltage levels of the two-phase drive signals are controlled respectively, as in the first and second embodiments.

In the external control circuit 43 of the second embodiment, the lower limit of the target value of the voltage level of the drive signal is different from that of the first embodiment, and the lower limit of the target value of the voltage level of the ultrasonic motor 10 is. The value is very close to the allowable minimum value (100V in this embodiment).

As a result, even if the voltage levels of the two-phase drive signals are different when the ultrasonic motor 10 is driven at a low output, either one of the two-phase drive signals is driven. It is possible to reliably prevent the occurrence of inconveniences such as the driving of the ultrasonic motor 10 being stopped or not being started when the voltage level of the signal falls below the allowable minimum value, and the ultrasonic motor 10 is driven at a low output. It can be driven to stabilize in the state.

The voltage level detection circuit 44 that outputs the signal X corresponding to the minimum voltage level of the two-phase drive signals as described above is not limited to the detection circuit 44E shown in FIG. The detection circuit 44F shown in FIG. 9 can also be configured.

That is, in the detection circuit 44F, the operational amplifiers 86 and 88 are omitted from the detection circuit 44E shown in FIG. 8, and like the detection circuit 44D described above, an ideal operational amplifier 86 and diode 90 and an operational amplifier 88 and diode 92 are ideal. A circuit equivalent to a diode is simply a diode 90,
92 is substituted. In this case as well, the detection accuracy is lower than that of the detection circuit 44E of FIG. 8 due to the influence of the forward voltage drop of the diode, but the operational amplifier can be omitted, so that the configuration is simple and the cost can be kept low.

[Fourth Embodiment] Next, a fourth embodiment of the present invention will be described. The same parts as those in the first to third embodiments are designated by the same reference numerals and the description thereof will be omitted. In the fourth embodiment, the voltage level detection circuit 44 is composed of a detection circuit 44G including a microcomputer as shown in FIG.

The anode of the diode 70 is connected to the input terminal 56A of the detection circuit 44G as in the case of the detection circuits 44C to 44F, and one end of the resistor 74 is connected to the cathode of the diode 70. The other end of the resistor 74 is the resistor 7
6 and one end of the resistor 76 is grounded. The other end of a capacitor 82 whose one end is grounded is connected between the resistor 74 and the resistor 76, and the analog signal input end A / D _{IN of the} microcomputer 98 is further connected.
It is connected to A. Microcomputer 98 is A /
It has a built-in D converter (not shown) and converts an analog signal input through the analog signal input terminal A / D _IN A into digital data and takes in the digital data.

The detection circuit 44C is also provided for the input terminal 56B.
The anode of the diode 72 is connected in the same manner as ~ 44F, and one end of the resistor 78 is connected to the cathode of the diode 72. The other end of the resistor 78 is connected to one end of the resistor 80, and the other end of the resistor 80 is grounded. Further, between the resistor 78 and the resistor 80, the other end of the capacitor 84 whose one end is grounded is connected, and further connected to the analog signal input end A / D _IN B of the microcomputer 98. The analog signal input through the analog signal input terminal A / D _IN B is converted into digital data by the A / D converter in the same manner as described above, and then taken into the microcomputer 98.

The analog signal output terminal D / A _OUT of the microcomputer 98 is connected to the output terminal 56C, and the logic output terminal L _OUT is connected to the output terminal 56D. The microcomputer 98 converts data representing the detected value of the voltage level of the drive signal obtained by the processing described later into an analog signal (signal X) by a built-in D / A converter and outputs the analog signal output terminal D / Output via A _OUT . Further, as will be described later, when the driving of the ultrasonic motor 10 is stopped, an ultrasonic motor drive stop instruction (digital signal) is output via the logical output terminal L _OUT .

The power supply terminal V _CC of the microcomputer 98 is connected to a constant voltage power source (not shown), and is connected to the ground terminal GND.
Is grounded. The anodes of diodes 100 and 102 are connected to the analog signal input terminals A / D _IN A and A / D _IN B of the microcomputer 98, respectively.
The cathodes of the diodes 100 and 102 are connected to the power supply terminal V _CC . Further, the output terminal 56D is connected to the drive control circuit 46 and the voltage control oscillation circuit 34 as shown in FIG. 11, and the ultrasonic motor drive stop instruction output from the microcomputer 98 is the drive control circuit 42 and the voltage control oscillation. It is input to the circuit 34.

Next, the operation of the fourth embodiment will be described with reference to the flowchart of FIG. 12 showing the processing in the microcomputer 98. Input terminal 56A of the detection circuit 44G
The A-phase drive signal input to A is half-wave rectified by the diode 70, divided by the resistors 74 and 76, smoothed by the capacitor 82, and input to the analog signal input terminal A / D _IN A of the microcomputer 98. It Also, the input terminal 5
The B-phase drive signal input to 6B is half-wave rectified by the diode 72, divided by the resistors 78 and 80, smoothed by the capacitor 84, and input to the analog signal input terminal A / D _IN B of the microcomputer 98. To be done.

In the microcomputer 98, steps
Analog signal input terminal A / D at 200 _INA, A / D_INB
Obtained by converting the analog signal input via
Imported data (hereinafter referred to as input data A and B)
Mu. The value of this input data A, B is the analog signal input terminal
Voltage level of analog signal input to the
Of the two phases input to the input terminals 56A and 56B of the circuit 44G
It corresponds to the voltage level of the drive signal. Step 202
Then, the value of input data A is larger than the value of input data B.
Determine whether or not. The determination in step 202 is positive
In case of step 204, the data V_HInput data A to
The data V_LSubstitute the input data B for each. Also,
If the determination in step 202 is negative, the step
Data V at 206_HInput data B, data V_LEnter
The force data A is substituted for each.

According to the above, the data V _H is the input data A, B
Of these, the larger value is set, and the data V _L is set to the smaller value. In the next step 208, it is determined whether or not the value of the data V _H is a relatively large value. In the ultrasonic motor 10 of the present embodiment, the maximum allowable voltage level of the drive signal is set to 500V as an example, and in the flowchart of FIG. 12, it is determined whether the data _VH is 450V or more. Step 20
If the determination in step 8 is affirmative, the next step 21
At 0, it is determined whether the data V _L has a relatively small value. As an example, the ultrasonic motor 10 of the present embodiment has an allowable minimum value of the voltage level of the drive signal of 100 V, and in the flowchart of FIG. 12, it is determined whether the data V _L is 120 V or less. If the determination in step 210 is negative, the data V _H is adopted as the output data X in step 212,
Go to step 220.

When the determination in step 208 is negative, it is determined in step 214 whether or not the data V _L is a relatively small value (120 V in FIG. 12, similar to the above). When the determination in step 214 is affirmative, the data V _L is adopted as the output data X in step 216. If the determination in step 214 is negative, the output data X is set as the data V _{H in} step 218.
A value obtained by dividing the sum of the data V _L and the data V _L , that is, the average value of the data V _H and the data V _L is adopted. Step 22
At 0, the output data X of which the value is determined above is converted into an analog signal by the D / A converter and output as the signal X,
Return to step 200.

As described above, the microcomputer 9
The signal X output from 8 is input to the drive control circuit 42. The drive control circuit 42 determines the voltage of the two-phase drive signal based on the voltage level of the drive signal represented by the input signal X and the target value of the voltage level of the drive signal represented by the signal input from the external control circuit 43. Control each level. In addition, in the external control circuit 43 of the fourth embodiment, the upper limit of the target value of the drive signal voltage level is equal to that of the second embodiment, and the lower limit of the target value of the drive signal voltage level is equal to that of the third embodiment. ing.

On the other hand, if the determination in step 210 is affirmative, the difference between the data V _H and the data V _L is so large that it is determined to be in an abnormal state. In step 222, the drive control circuit 42 and the voltage control are controlled. An ultrasonic motor drive stop instruction is output to the oscillation circuit 34. As a result, the drive control circuit 4
2 and the operation of the voltage controlled oscillation circuit 34 are stopped, and the driving of the ultrasonic motor 10 is stopped.

The above control is summarized in Table 1 below.

[0066]

[Table 1]

As described above, the output of the ultrasonic motor 10 can be accurately controlled so as not to deviate largely from the desired output, and the voltage level of the drive signal is high when the ultrasonic motor 10 is driven at a high output. It is possible to reliably prevent the voltage level of the drive signal from falling below the allowable minimum value of the ultrasonic motor 10 when it is driven at a low output, or the output (rotational speed, torque) is large or small. Regardless of this, the ultrasonic motor 10 can be driven so as to be in a stable driving state. Therefore, it is particularly suitable when the target value of the output of the ultrasonic motor 10 changes greatly depending on the situation, for example, when the ultrasonic motor is used as the drive source of the power window of the vehicle.

In the above description, when the voltage levels of the two-phase drive signals are significantly different (when the determination in step 210 is affirmative), it is determined that the state is abnormal and the drive of the ultrasonic motor 10 is stopped. However, it is not limited to this. For example, as shown in Table 2 below, the output data X may be regarded as a normal state and the smaller value may be adopted.

[0069]

[Table 2]

Specifically, as shown in the flowchart of FIG. 13, the control shown in Table 2 adopts the data V _L as the output data X in step 222 when the determination in step 210 is affirmative. It suffices to execute the processing. As a result, even if the voltage levels of the two-phase drive signals are greatly different, it is possible to more reliably prevent the inconvenience such as the drive of the ultrasonic motor 10 being continued and the drive of the ultrasonic motor 10 being stopped. it can. FIG. 14 shows an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 2 is performed.

When the voltage levels of the two-phase drive signals are greatly different, it is regarded as a normal state as shown in Table 3 below, and the data having the larger value is adopted as the output data X. May be.

[0072]

[Table 3]

Specifically, the control shown in Table 3 can be realized by adopting the data V _H as output data in step 22 in the flowchart of FIG. This makes it possible to more reliably prevent the piezoelectric body 14 of the ultrasonic motor 10 from being broken or deteriorated. FIG. 15 shows an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 3 is performed.

Further, when the voltage levels of the two-phase drive signals are greatly different, it is regarded as a normal state as shown in Table 4 below, and the average value of the voltage levels of the two-phase drive signals is output data X. May be adopted.

[0075]

[Table 4]

Specifically, the control shown in Table 4 can be realized by adopting the average value of the data V _H and the data V _L as the output data X in step 22 in the flowchart of FIG. As a result, the output of the ultrasonic motor 10 can be controlled more accurately even when the voltage levels of the two-phase drive signals greatly differ. FIG. 16 shows an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 4 is performed.

[Fifth Embodiment] Next, a fifth embodiment of the present invention will be described. The same parts as those in the fourth embodiment are designated by the same reference numerals and the description thereof will be omitted. In the fifth embodiment,
The value of the output data X is determined by fuzzy inference by the microcomputer 98. Therefore, in the ROM (not shown) of the microcomputer 98, as an example, FIG.
A membership function for evaluating the voltage level of the drive signal as shown in 7 and a fuzzy rule are stored. The fuzzy rule is composed of the following nine rules based on Table 2 described above.

If the A-phase voltage is "low" and the B-phase voltage is "low", the output data X is matched with the lower one of the A-phase voltage and the B-phase voltage.

If the A-phase voltage is "medium" and the B-phase voltage is "low", the output data X is matched with the B-phase voltage.

If the A-phase voltage is "high" and the B-phase voltage is "low", the output data X is matched with the B-phase voltage.

If the A-phase voltage is "low" and the B-phase voltage is "medium", the output data X is matched with the A-phase voltage.

When the A-phase voltage is "medium" and the B-phase voltage is "medium", the output data X is the average value of the A-phase voltage and the B-phase voltage.

If the A-phase voltage is "high" and the B-phase voltage is "medium", the output data X is matched with the A-phase voltage.

If the A-phase voltage is "low" and the B-phase voltage is "high", the output data X is matched with the A-phase voltage.

When the A-phase voltage is "medium" and the B-phase voltage is "high", the output data X is matched with the B-phase voltage.

If the A-phase voltage is "high" and the B-phase voltage is "high", the output data X is matched with the higher one of the A-phase voltage and the B-phase voltage.

Next, the operation of the voltage level detecting circuit 44 in the fifth embodiment will be described with reference to the flowchart of FIG. At step 250, the input data A and the input data B are fetched. In step 252, the input data A and B are evaluated based on the above-mentioned membership function.
Specifically, the voltage level of the drive signal represented by the input data A and B is plotted on the horizontal axis of the membership function, and “low”,
The degree of agreement with each evaluation of "medium" and "high" is obtained.
As an example, in the membership function shown in FIG. 17, when the voltage level is 120V or less, the degree of agreement with the evaluation of “low” is 1.0, the degree of agreement with the evaluations of “medium” and “high” is 0, and the voltage level is 120V. If it is higher than 285V and is 285V or less, the degree of agreement with the evaluation of `` low '' and `` medium '' is 0 to 1.
A value between 0 and the degree of coincidence with the evaluation of "high" are 0.

At the next step 254, based on the evaluation result of the input data A, B obtained above, the input data A,
Fuzzy inference is performed to find the goodness of fit for each of the nine fuzzy rules of B. This goodness of fit is a coefficient for weighting each rule, and the "low" of the input data A and B,
It can be obtained by using the degree of coincidence with respect to each evaluation of “medium” and “high”. In step 256, the value of the output data X determined by each rule is given a weight corresponding to the goodness of fit for each rule, and the weighted average is calculated to determine the value of the output data X. In step 258, the determined output data X is converted into an analog signal by the D / A converter and output as the signal X, and the process returns to step 250.
Thus, the signal X output from the microcomputer 98 is input to the drive control circuit 42, and the voltage levels of the two-phase drive signals are controlled based on the signal X.

FIG. 19 shows an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the fuzzy rule based on Table 2 and the membership function shown in FIG. 17 are used. Shown in. When this relationship is compared with the relationship shown in FIG. 14 described in the fourth embodiment, the value of the output data X changes smoothly with respect to changes in the voltage levels of the A-phase and B-phase drive signals. Therefore, in the control shown in FIG. 19, since the value of the output data X is changed smoothly with respect to the fluctuation of the voltage level of the drive signal, the rotor 1 of the ultrasonic motor 10 is changed.
It is clear that the rotation of 8 is stable.

The fuzzy rules used in this embodiment are not limited to the rules based on the control shown in Table 2, but the rules based on the control shown in Table 3 and the rules shown in Table 4. Can be used. For example, if the rule based on the control shown in Table 3 is used, A
The voltage levels of the drive signals of the phase B and the phase B and the output data X have the relationship shown in FIG. 20, which is compared with the relationship shown in FIG. 15 described in the fourth embodiment. It is clear that the value of the output data X changes smoothly with respect to the change of the voltage level of, and the rotation of the rotor 18 of the ultrasonic motor 10 is stable.

Further, for example, when the rule based on the control shown in Table 4 is used, the voltage levels of the drive signals of the A phase and the B phase and the output data X have the relationship shown in FIG. Compared with the relationship shown in FIG. 16 described in the embodiment, the value of the output data X changes smoothly with respect to the change in the voltage level of the drive signals of the A phase and the B phase, so that the ultrasonic wave is the same as above. It is clear that the rotation of the rotor 18 of the motor 10 is stable.

Although the value of the output data X is determined by fuzzy inference in the fifth embodiment, the present invention is not limited to this, and the microcomputer 98
The relationship shown in FIG. 19 or FIG. 20 or FIG. 21 is stored in advance in a ROM or the like as a map, and the value of the output data X is searched by using the values of the input data A and B as keys in the map. The value of X may be obtained.

Further, in the fourth and fifth embodiments, the microcomputer 98 outputs the signal X representing the voltage level of the drive signal to the drive control circuit 42, but the present invention is not limited to this. Alternatively, the drive control circuit 42 and the external control circuit 43 may be configured to have the functions of the external control circuit 43 and the voltage control signal for controlling the voltage level of the drive signal may be directly output to the power amplification circuits 38 and 40. Good.

Further, in the above, the voltage controlled oscillator circuit (VC
Although the drive circuit 30 that obtains a high frequency analog signal for driving the ultrasonic motor 10 by (O) 34 has been described as an example, the boosted signal generated by turning on / off the switching element is supplied to the ultrasonic motor as a drive signal. The present invention can also be applied to a type (see FIG. 22) drive circuit.

Although the traveling wave type ultrasonic motor driven by the two-phase driving signals has been described above as an example, the number of phases of the driving signal and the type of the ultrasonic motor are not limited to the above. The number of phases of the drive signal may be “3” or more, and the present invention can be applied to drive, for example, a standing wave type ultrasonic motor.

[0096]

As described above, according to the first aspect of the invention, the average value of the voltage levels of the drive signals of the plurality of phases for driving the ultrasonic motor is detected, and the detected average value is the voltage level. Since the voltage levels of the drive signals of the multiple phases are controlled so as to match or approach the target value, the excellent effect that the ultrasonic motor can be driven so as to be stable in the target drive state is provided. can get.

According to the second aspect of the invention, the maximum value of the voltage levels of the drive signals of the plurality of phases for driving the ultrasonic motor is detected, and the detected maximum value does not exceed the allowable maximum value of the ultrasonic motor. Since the voltage levels of the drive signals of a plurality of phases are individually controlled as described above, it is possible to obtain an excellent effect that the ultrasonic motor can be driven so as to be stable even in a state of being driven at a high output.

According to the third aspect of the present invention, the minimum value of the voltage levels of the drive signals of a plurality of phases for driving the ultrasonic motor is detected, and the detected minimum value does not become smaller than the allowable minimum value of the ultrasonic motor. Since the voltage levels of the drive signals of a plurality of phases are individually controlled as described above, it is possible to obtain an excellent effect that the ultrasonic motor can be driven in a stable manner even when it is driven at a low output.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an ultrasonic motor.

FIG. 2 is a block diagram schematically showing an overall configuration of an ultrasonic motor drive circuit.

FIG. 3 is a circuit diagram showing an example of a detection circuit for detecting an average value of voltage levels of two-phase drive signals according to the first embodiment.

FIG. 4 is a diagram showing a change in impedance of the ultrasonic motor with a change in frequency of a drive signal.

FIG. 5 is a circuit diagram showing another example of a detection circuit that detects an average value of voltage levels of two-phase drive signals.

FIG. 6 is a circuit diagram showing an example of a detection circuit for detecting a maximum value of voltage levels of two-phase drive signals according to the second embodiment.

FIG. 7 is a circuit diagram showing another example of a detection circuit that detects the maximum value of the voltage levels of two-phase drive signals.

FIG. 8 is a circuit diagram showing an example of a detection circuit for detecting a minimum value of voltage levels of two-phase drive signals according to a third embodiment.

FIG. 9 is a circuit diagram showing another example of a detection circuit for detecting the minimum value of the voltage levels of two-phase drive signals.

FIG. 10 is a circuit diagram showing a detection circuit according to a fourth embodiment.

FIG. 11 is a block diagram schematically showing an overall configuration of an ultrasonic motor drive circuit according to a fourth embodiment.

FIG. 12 is a flowchart illustrating an example of processing in the microcomputer of the voltage level detection circuit according to the fourth embodiment.

FIG. 13 is a flowchart illustrating another example of processing in the microcomputer of the fourth embodiment.

FIG. 14 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 2 is performed in the fourth example.

FIG. 15 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 3 is performed in the fourth example.

FIG. 16 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 4 is performed in the fourth example.

FIG. 17 is a diagram showing an example of a membership function for evaluating the voltage level of the drive signal used in the fifth embodiment.

FIG. 18 is a flow chart for explaining the processing in the microcomputer of the voltage level detection circuit of the fifth embodiment.

FIG. 19 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 3 is performed in the fifth example.

FIG. 20 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 4 is performed in the fifth example.

FIG. 21 is a diagram showing an example of the relationship between the voltage levels of the A-phase and B-phase drive signals and the output data X when the control shown in Table 4 is performed in the fifth example.

22A to 22D are circuit diagrams showing a portion for boosting a drive signal in the ultrasonic motor drive circuit.

[Explanation of symbols]

 10 ultrasonic motor 30 drive circuit 38 power amplification circuit 40 power amplification circuit 42 drive control circuit 44 voltage level control circuit 44A detection circuit 44B detection circuit 44C detection circuit 44D detection circuit 44E detection circuit 44F detection circuit 44G detection circuit

Claims (3)

[Claims] 1. A drive signal output means for outputting drive signals of a plurality of phases for driving an ultrasonic motor, an average value detection means for detecting an average value of voltage levels of the drive signals of the plurality of phases, and the average. A control circuit for controlling the voltage levels of the drive signals of the plurality of phases so that the average value detected by the value detection means coincides with or approaches the target value of the voltage level. 2. A drive signal output means for outputting drive signals of a plurality of phases for driving an ultrasonic motor; a maximum value detection means for detecting a maximum value of a voltage level of the drive signals of the plurality of phases; An ultrasonic motor drive circuit, comprising: control means for controlling the voltage levels of the drive signals of the plurality of phases so that the maximum value detected by the value detection means does not exceed an allowable maximum value of the ultrasonic motor. 3. A drive signal output means for outputting drive signals of a plurality of phases for driving an ultrasonic motor; a minimum value detection means for detecting a minimum value of a voltage level of the drive signals of the plurality of phases; An ultrasonic motor drive circuit comprising: control means for controlling the voltage levels of the drive signals of the plurality of phases so that the minimum value detected by the value detection means does not become smaller than the allowable minimum value of the ultrasonic motor.