JPH0755064B2 - Ultrasonic actuator drive - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device for an ultrasonic actuator that uses piezoelectric material to generate a driving force.

2. Description of the Related Art In recent years, a vibrating body using a piezoelectric body such as a piezoelectric ceramic is excited by elastic vibration by applying a driving frequency voltage of, for example, several tens of KHz, and this vibrating body is subjected to stretching vibration or thickness vibration, and this vibration is used as a driving force for a rotor, etc. Attention is focused on an ultrasonic actuator in which a driven body (moving body) is pressed and driven to rotate or linearly move the moving body.

Hereinafter, a conventional technique of an ultrasonic actuator will be described with reference to the drawings.

FIG. 3 is a perspective view of an annular ultrasonic actuator,
A ring-shaped piezoelectric body 17 is attached to a ring-shaped elastic body 18 to form a vibrating body 19. Reference numeral 20 is a friction material made of a wear-resistant material, and 21 is an elastic body, which are bonded to each other to form a moving body 22. The moving body 22 is in contact with the vibrating body 19 via the friction material 20. When a voltage is applied to the piezoelectric body 17, bending vibration is excited in the circumferential direction of the vibrating body 19 and becomes a traveling wave, which drives the moving body 22. In addition, a protrusion 23 for extracting a mechanical output is installed on the vibrating body 22 in FIG.

FIG. 4 shows an example of the electrode structure of the piezoelectric body 17 used in the ultrasonic actuator 5 of FIG. In the figure, nine elastic waves are arranged in the circumferential direction. In the figure, A and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is an electrode corresponding to 3/4 wavelength, and D is an electrode corresponding to 1/4 wavelength. Electrodes C and D are positioned in electrode groups A and B
It creates a phase difference of 1/4 wavelength (= 90 °). Electrodes A and B
Adjacent small electrode portions in the inside are electrodes used when the piezoelectric body 17 is polarized, and the bonding surface of the piezoelectric body 17 with the elastic body 18 is the surface opposite to the surface shown in FIG. The electrode is a plane surface electrode. In use, the electrode groups A and B are short-circuited and used as indicated by the hatched lines in FIG.

The electrodes A and B of the piezoelectric body 17 of the ultrasonic actuator 5 configured as described above have different 90 ° phases V1 = V0 · sin (ωt) (1) V2 = V0 · cos (ωt). 2) However, if the voltages V1 and V2 expressed by V0: instantaneous value of voltage ω: angular frequency t: time are respectively applied, ξ ＝ ξ0 ・ (cos (ωt) ・ cos (kX) + Sin (ωt) ・ sin (kX)) = ξ0 ・ cos (ωt−kX) (3) where ξ: amplitude value of bending vibration ξ0: instantaneous value of bending vibration k: wave number (2π / λ) λ: Wavelength X: Bending vibration in the circumferential direction, which can be expressed by position, is excited.
That is, a traveling wave is generated on the surface of the vibrating body 19.
Therefore, when the moving body 22 is brought into pressure contact with the vibrating body 19, the moving body 22 can be moved by the traveling wave.

FIG. 5 shows that the point E on the surface of the vibrating body 19 makes an elliptic motion of the long axis 2W and the short axis 2U by the excitation of the traveling wave, and the moving body 22 installed by pressing on the vibrating body 19 has an elliptical shape. By contacting in the vicinity of the apex, frictional force causes v in the direction opposite to the wave traveling direction.
It shows the motion at the rotation speed of = ωxU. Also,
This speed becomes smaller than v when there is slip between the vibrating body 19 and the moving body 22. The arrow F in the figure indicates a moving body.
22 indicates the traveling direction, and arrow G indicates the traveling direction of this traveling wave. The velocity of the moving body 22 described above can be represented by v = ω · u = k · ω · ξ0 (k: proportional coefficient) and is proportional to ξ0 at the moment of bending vibration.

The electrode D corresponding to 1/4 wavelength in FIG. 4 can be used as a monitor electrode for monitoring the vibration state of the vibration body 19 such as the vibration amplitude and phase.

Now, by applying a frequency voltage such as an alternating current voltage of ultrasonic frequency to the ultrasonic actuator configured as described above,
When excite 19 and get a traveling wave to drive the moving body 22,
It is not efficient if the frequency is not the resonance frequency peculiar to the ultrasonic actuator 5, but if it is driven in the vicinity of this resonance point, the vibration of the vibrating body 19 suddenly stops due to the jumping phenomenon or the hysteresis phenomenon peculiar to the piezoelectric body 17, or the like. The vibration amplitude becomes small and the moving body 22 suddenly stops and the operation becomes unstable. Therefore, it is actually difficult to stably operate the ultrasonic actuator 5 near this frequency. Conventionally, in order to solve this problem, if the piezoelectric body 17 is driven at a frequency higher than this frequency range, the above phenomenon does not occur and it operates stably, and this resonance point is constantly changed depending on environmental conditions such as temperature and humidity and load. Since it fluctuates, the ultrasonic actuator 5 is driven by frequency automatic tracking so that the driving frequency is always higher than the unstable region near the resonance point. In this frequency automatic tracking, the state of the drive frequency can be known by detecting the phase relationship between the frequency voltage applied to the piezoelectric body 17 and the signal obtained from the monitor electrode D described above.
This is realized by controlling the drive frequency so that the phase relationship is maintained at a predetermined value.

FIG. 6 shows a block diagram of an apparatus for driving the ultrasonic actuator 5 by this frequency automatic tracking (phase control).
FIG. 7 is an operation waveform diagram for explaining the operation.
In FIG. 6, 1 is a variable oscillator for generating a signal whose output frequency is controlled by an input voltage value, and 2 is a well-known D flip-flop for generating two signals having 90 ° different phases from the output of the variable oscillator 1. The 90 ° phase shifters 3, 4 composed of a gate circuit and a peripheral gate circuit amplify the signals having different 90 ° phases to a voltage level sufficient to drive the ultrasonic actuator 5, and each of the piezoelectric bodies 17 respectively. , A voltage detector composed of a Schmitt comparator that detects one of the voltages applied to the piezoelectric body 17 and outputs it at a logic level, and 8 represents a signal generated at the monitor electrode D. Monitor signal detector consisting of Schmitt comparator that detects and outputs at logic level, 9
Is a trapezoidal wave generator that creates a trapezoidal wave from a constant current circuit based on the output of the voltage detector 7 by a well-known technique. 13 and 14 are samples at a position delayed by a predetermined time from the output of the monitor signal detector 8. A phase delay device composed of a monostable multivibrator that generates pulses, 15 is a switch (SW) that switches the output of the phase delay devices 13 and 14 according to the direction signal input to the terminal 16, 11 is a trapezoidal wave based on a sample pulse A sample holder consisting of an analog switch that samples and holds a part of the slope of the signal, a hold capacitor and a buffer amplifier. 12 compensates the stability of this frequency auto-tracking loop and its output is applied to the frequency control terminal of the variable oscillator 1. It is a filter, and the above-described frequency automatic tracking (phase control) loop is configured by the above components.

In the operation waveform diagram of FIG. 7, V1 is the output signal of the voltage detector 7, V2 is the output signal of the monitor signal detector 8, V4 is the output signal of the trapezoidal wave generator 9, and V6 and V7 are the phase delay devices 13 respectively. ,
14 output signals.

In the conventional ultrasonic actuator driving apparatus configured as described above, the variable oscillator 1 operates to generate a frequency signal.
When output to the 90 ° phase shifter 2, the 90 ° phase shifter 2 creates two frequency signals having different 90 ° phases based on the signal, and outputs the two frequency signals to the power amplifiers 3 and 4, respectively. Power amplifier circuit 3,
In 4, the signal is increased to a voltage level required to drive the ultrasonic actuator 5 and applied to the piezoelectric body 17 to drive the ultrasonic actuator 5.

When the ultrasonic actuator 5 is driven, the voltage detector 7
Is a trapezoidal wave generated from the output of the power amplification circuits 3 and 4, which detects one of the voltages applied to the piezoelectric body 17 (which is the voltage from the power amplifier 3 in FIG. 2) and which has the waveform shaped into the logic level. To the trapezoidal wave generator 9
Generates a trapezoidal wave V4 with reference to the rising edge of V1 and outputs it to the sample holder 11 as shown in FIG.

On the other hand, the monitor signal detector 8 detects a signal of the monitor electrode D on the piezoelectric body 17 which generates a voltage (hereinafter referred to as a monitor voltage) according to the vibration state of the vibrating body 19 and phase-delays the signal V2 whose waveform is shaped into a logic level. Phase delay unit 1
3 and 14, time TS1 from the rising edge of V2,
The sample pulses V6 and V7 delayed by TS2 are output to the sample holder 11 via SW15.

SW15 is switched by a direction signal that is applied to the terminal 16 and commands the moving direction of the moving body 22. When the moving direction of the moving body 22 is the positive direction (here, clockwise (CW)), V6 is , In the opposite direction (counterclockwise (CCW), V7 is selected. With sample holder 11, sample pulse V6
(V7) samples the position of the slope of the trapezoidal wave V4 according to the phase difference between the applied voltage and the monitor voltage at that time, holds the voltage value until the next sample pulse comes, and outputs it to the compensation filter 12.

The compensating filter 12 performs integral compensation to reduce steady-state deviation and compensation such as phase lead / lag to stabilize the system, and then adds the output signal to the frequency control terminal of the variable oscillator 1 and the variable oscillator 1 receives the input signal. A frequency signal having an oscillation frequency corresponding to the signal (voltage) is output to change the drive frequency of the ultrasonic actuator 5.

In the frequency automatic tracking loop configured as described above, the time relationship between the sample pulse V6 (V7) and the trapezoidal wave V4 is as shown in FIG.
It works like (V7). That is, it is the timing when the sampled and held voltage becomes the center voltage Vc of the system (loop). From this, the amount of delay in the phase delay device 13 (14) determines the relationship between V1 and V2, that is, the phase relationship between the applied voltage and the monitor voltage. Therefore, the delay amount in the phase delay device 13 (14) is determined so that the phase relationship between the applied voltage and the monitor voltage for driving the ultrasonic actuator 5 in a stable state (frequency higher than near resonance) is established. There is. In Figure 7
The delay amount for setting the phase relationship between V1 and V2 to θ1 is Ts1 ((a) in the figure), and the delay amount for setting θ2 is Ts2.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The above-mentioned configuration has the following problems. First, let us first consider generating a traveling wave and driving the ultrasonic actuator 5 in order to move the moving body 22 in the forward direction (CW). At this time, in order to avoid the vicinity of the resonance point and drive the ultrasonic actuator 5 stably and efficiently at a frequency always higher than that, the phase relationship between the applied voltage and the monitor voltage, that is, V1 and V2 is shown in FIG. 7 (a). As described above, it is necessary to perform automatic frequency tracking (phase control) so as to maintain the phase relationship of θ1 (about 45 °). Therefore, the sample pulse V6 input to the sample holder 11 is the output signal V2 of the monitor voltage detector 8. It needs to be adjusted by the phase delay device 13 so as to delay time Ts1 from the rising edge.

Next, when the moving signal of the moving body 22 is instructed by the direction signal V5 to be in the opposite direction, the 90 ° phase lead / lag relationship of the two signals output from the 90 ° phase shifter 2 in the forward direction. Then, the moving body 22 moves in the opposite direction. At this time, as in the forward direction, the ultrasonic actuator 5 is driven stably and efficiently, that is, the vibrating body 19 vibrates in the same direction. In order to maintain the state, the phase relationship of the output signal of the 90 ° phase shifter 2 is reversed, so the phase relationship between V1 and V2 is not set to θ1 but to 90 ° as shown in Fig. 7 (b).゜ (π
/ 2) It is necessary to shift the phase to θ2. Therefore, at this time, the delay amount of the sample pulse V7 selected by SW15 needs to be adjusted to Ts2 by the phase delay device 14 as shown in FIG. 7 (b).

As described above, the conventional drive device for the ultrasonic actuator 5 needs two different sample pulses depending on the moving direction of the moving body 22, and these delay amounts Ts1 and Ts2 must be adjusted separately. However, TS1, T
It is actually difficult to adjust S2 to the same value in practice, and even if it is possible to adjust it accurately, the two phase delay devices have different change characteristics with respect to the environment, so that a delay amount is deviated. From this, in the conventional device, the operation center of the frequency automatic tracking (phase control) loop, that is, the vibration state (operating state) of the vibrating body 19 differs depending on the moving direction of the moving body 22,
When it is attempted to further control the speed or position of the ultrasonic actuator 5 driven in this way, the problem that the control conditions are different in both the forward and reverse directions remains as a design issue. The fact that there are two requirements and that there are two adjustment points remain issues from the viewpoint of the cost and productivity of the device.

In view of such a point, the present invention reduces the number of adjustment points of the phase delay device and the amount of phase delay, and the operation center in the frequency automatic tracking (phase control) loop, that is, the vibration body, regardless of whether the moving direction of the moving body is forward or reverse. It is an object of the present invention to provide a drive device for an ultrasonic actuator in which the same vibration state is obtained.

Means for Solving the Problems The present invention provides an ultrasonic actuator, a vibration state detecting means for detecting a vibration state of a vibrating body, and a phase information output for outputting information on a traveling direction of the elastic traveling wave and a phase of a frequency voltage. Means for comparing the phases of the outputs of the vibration state detecting means and the output of the phase information output means, and frequency changing means for changing the frequency of the frequency voltage by the output of the phase comparing means. The driving device for the ultrasonic actuator.

Operation According to the present invention, by configuring the frequency automatic tracking (phase control) loop by the phase comparison means and the frequency varying means, two types of voltage applied to the piezoelectric body when the traveling direction of the elastic traveling wave is the forward direction are provided. The phase of one of the frequency voltages (or the signal having the phase information of this frequency voltage) is compared with the phase of the detection output, and the frequency of the frequency voltage is changed to reach a predetermined value, and the traveling direction is reversed. In the case of the direction, the phase of the other frequency voltage (or the signal having the phase information of this frequency voltage) is compared with the phase of the above detection output, and the frequency of the frequency voltage is changed so as to become the above predetermined value.

Embodiment FIG. 1 is a block diagram of an ultrasonic motor driving device in an embodiment of the present invention, and FIG. 2 is an operation waveform diagram thereof. In the figure, those given the same drawing numbers as those of the conventional example have the same operation and function, and therefore their explanations are omitted.
Reference numeral 6 denotes a switch (S which switches output voltages Va and Vb of the power amplifiers 3 and 4 (which are applied to the ultrasonic actuator 5) input to the voltage detector 7 by a direction signal V5.
Reference symbols W) and 10 are phase delay devices composed of a monostable multivibrator or the like that generates a sample pulse at a position delayed by a predetermined time from the output of the monitor signal detector 8. In FIG. 2, Va is the output voltage of the power amplifier 3, Vb is the output voltage of the voltage amplifier 4, and V3 is the sample pulse output from the phase delay device 10.

The operation of the ultrasonic actuator driving apparatus of the present embodiment configured as described above will be described below. The variable oscillator 1 operates to operate the 90 ° phase shifter 2 and the power amplifier 3,
When a frequency voltage is applied to the ultrasonic actuator 5 through 4, the moving body 22 is driven. At the same time, if the moving direction is the positive direction, Va selected by SW6 (by the direction signal V5) is detected by the voltage detector 7, and the signal V1 is output as shown in FIG. Wave generator 9 samples trapezoidal wave V4 with reference to rising edge of V1 11
Output to.

Further, when the monitor voltage is detected by the monitor signal detector 8 and the signal V2 is output, the phase delay device 10 causes the ultrasonic actuator 5 to be vibrated in a stable and efficient manner, that is, V1.
The sample pulse V3 whose delay amount is adjusted to Ts1 so that the phase relationship between V2 and V2 (phase relationship between the applied voltage Va and the monitor voltage) maintains θ1 as shown in FIG. 2 (a) is output to the sample holder 11. To do. In the sample holder 11, the slope of the trapezoidal wave V4 is sampled by the sample pulse V3, and the hold voltage is feed-packed to the variable oscillator 1 via the compensation filter 12, as in the conventional case.

Next, when the reverse direction command is issued by the direction signal V5, the 90 ° phase shifter 2 outputs a signal which is the reverse of the 90 ° phase lead / lag relationship of the two signals output in the forward direction. As a result, as shown in FIG. 2B, the 90 ° phase relationship between the output voltages Va and Vb of the power amplifiers 3 and 4 in the ultrasonic actuator 5 is reversed (Vb advances 90 ° with respect to Va). Applied. At the same time, SW6 is switched, and the output Vb of the power amplifier 4 is input to the voltage detector 7, and the trapezoidal wave V4 is created in the trapezoidal wave generation circuit 9 based on this Vb. Therefore, the applied voltage for phase comparison with the monitor voltage is Vb.

By the way, as mentioned earlier, if the vibration is the same as in the positive direction, the phase relationship between the monitor voltage and the applied voltage Va will be 90 ° more than in the positive direction (Va will be delayed by 90 ° with respect to V2). However, since Vb advances 90 ° with respect to Va,
The phase relationship of Vb becomes the same as the phase relationship of Va in the positive direction. Therefore, when moving in the opposite direction as in the present embodiment, the outputs V2 and Vb of the monitor signal detector 8 (actually, Vb when Vb is selected)
If frequency automatic tracking (phase control) is performed so that the phase relationship of 2) is θ1 as in the positive direction as shown in FIG. 2 (b), the vibration state of the vibrating body 19 will be irrespective of the forward and reverse directions. Can be the same. From this, the delay amount of the sample pulse that samples the trapezoidal wave V4 can be the same Ts1
Therefore, only one phase delay device is required.

As described above, according to the present embodiment, the delay amount of the sample pulse is adjusted according to each direction by switching the phase of the applied voltage for phase comparison with the monitor voltage depending on the moving direction of the moving body. Since it is not necessary and the vibration state is the same in each direction, it is not necessary to consider both directions even when trying to perform speed control or phase control, and it is possible to solve the problem in design.

In this embodiment, the applied voltage is directly detected by the voltage detector, and its output and monitor voltage (output of the monitor signal detector)
However, there is no problem even if it is configured to compare the output of the 90 ° phase shifter having the phase information of the applied voltage and the phase of the monitor voltage.

EFFECTS OF THE INVENTION As described above, according to the present invention, it is possible to reduce the number of parts for adjusting the phase delay device and the amount of phase delay, and to perform the frequency automatic tracking (phase control) regardless of whether the moving direction of the moving body is forward or reverse.
It is possible to provide a driving device for an ultrasonic actuator in which the center of motion in the loop, that is, the vibration state of the vibrating body is the same, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic actuator driving device according to an embodiment of the present invention, and FIG. 2 is an operation waveform diagram of the same embodiment.
FIG. 3 is a cutaway perspective view of an ultrasonic actuator, FIG.
FIG. 5 is a plan view showing the shape and electrode structure of the piezoelectric body used in the ultrasonic actuator shown in FIG. 3, FIG. 5 is an explanatory view of the operating principle of the ultrasonic actuator, and FIG. 6 is a conventional ultrasonic actuator. FIG. 7 is a block diagram of the driving device, and FIG. 7 is an operation waveform diagram of the conventional example. 1 ... Variable oscillator, 2 ... 90 ° phase shifter, 3,4 ... Power amplifier, 5 ... Ultrasonic actuator, 6 ... Switch, 7 ... Voltage detector, 8 ... Monitor signal detector, 9 ...
... trapezoidal wave generator, 10 ... phase delay device, 11 ... sample holder, 12 ... compensation filter, 22 ... moving body.

Claims (2)

[Claims] 1. A piezoelectric body is applied with two frequency voltages having the same frequency but different phases to excite an elastic traveling wave on a vibrating body composed of the piezoelectric body and an elastic body. An ultrasonic actuator that moves a moving body that is in contact with the moving body, a vibration state detecting unit that detects a vibration state of the vibrating body, and a two-frequency voltage of the two frequency voltages when the traveling direction of the elastic traveling wave is a forward direction. One of the frequency voltages and the temporal phase of the output of the vibration state detecting means are compared, and when the traveling direction is the opposite direction, the other frequency voltage is compared with the temporal phase of the output of the vibration state detecting means and the comparison is made. An ultrasonic actuator drive device comprising: a phase comparison unit that outputs a signal; and a frequency changing unit that changes the frequency of the frequency voltage according to the output of the phase comparison unit. 2. The ultrasonic actuator drive apparatus according to claim 1, wherein the vibration state of the vibrating body is detected by an output obtained from one electrode on the polarized piezoelectric body.