JP4495274B2 - Ultrasonic motor drive control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for driving and controlling an ultrasonic motor at an optimum frequency, and more particularly to an ultrasonic motor driving control apparatus that enables simplification of circuit configuration and real-time control.
[0002]
[Prior art]
An ultrasonic motor applies two alternating voltages with different phases to a piezoelectric element such as piezoelectric ceramics to excite two standing waves with different phases, and forms a circular or elliptical motion on the surface particles of the drive surface by synthesis. The moving body that is in pressure contact with the drive surface is moved by friction drive, so that the moving body rotates and functions as a motor. In such an ultrasonic motor, it is considered that if the motor is driven at a frequency that maximizes the amplitude on the driving surface, the maximum capacity of the motor can be exhibited. It is known that the correlation characteristic of the rotational speed with respect to the frequency of the ultrasonic motor is FIG. 4A, and the correlation characteristic of the amplitude voltage (voltage corresponding to the amplitude) with respect to the frequency is also FIG. 4B. Therefore, it is preferable to detect the rotation speed or amplitude of the motor and control the driving frequency of the motor based on the detected value. Among these, parts such as an encoder are required to detect the rotation speed, and the structure of the ultrasonic motor drive control device becomes complicated. On the other hand, since the ultrasonic motor can easily detect the amplitude as an amplitude voltage by the sensor electrode provided on the stator, a technique for feeding back the driving frequency based on the amplitude output is conceivable.
[0003]
[Problems to be solved by the invention]
However, even if such a peak value of the amplitude voltage is detected and the drive frequency is controlled to the frequency of the peak value, a complicated circuit such as a peak hold circuit is required to detect the peak value. This is contrary to the purpose of simplifying the circuit configuration. In this case, it is not impossible to detect the peak value by program control using a control microcomputer, but the response to control the drive frequency is delayed by the time required for program processing, and control is performed in real time. It is difficult. Even if it is possible to control the drive frequency based on peak detection in real time with a simple circuit configuration, the frequency of the ultrasonic motor can be understood from the correlation characteristics shown in FIG. The characteristic of the amplitude voltage with respect to is a characteristic that gradually increases from the high frequency region toward the low frequency region and rapidly decreases when the amplitude voltage peak Vp is exceeded. For this reason, when the drive frequency is feedback controlled based on the amplitude voltage, the amplitude voltage becomes a voltage close to zero as soon as the peak of the amplitude voltage is exceeded from the high frequency side toward the low frequency side. Thus, the feedback control becomes unstable by deviating from the controllable voltage range, and it becomes difficult to control the rotational drive of the ultrasonic motor in a stable state. In particular, as shown in FIG. 4B, the amplitude voltage has temperature dependence, and the frequency at which the peak voltage Vp is changed is changed by the environmental temperature. When the peak fluctuates, the control instability as described above becomes remarkable.
[0004]
SUMMARY OF THE INVENTION An object of the present invention is to provide an ultrasonic motor drive control device capable of performing rotational drive control of an ultrasonic motor stably with a simple circuit configuration and in real time.
[0005]
[Means for Solving the Problems]
The ultrasonic motor drive control device according to the present invention includes a frequency control means capable of changing and controlling a drive frequency of a signal for driving the ultrasonic motor, and an amplitude voltage detection means for detecting the vibration amplitude of the ultrasonic motor as an amplitude voltage. And comparing means for comparing the detected amplitude voltage with a preset reference voltage and changing and outputting the comparison result as a comparison signal, wherein the comparing means is a voltage on the lower limit side of the signal waveform of the amplitude voltage. The comparison signal is changed when it is detected that the voltage is lower than a reference voltage, and the frequency control means controls the drive frequency based on the comparison signal, and the comparison signal has changed a predetermined number of times. The drive frequency change control is sometimes stopped. By controlling the drive frequency of the ultrasonic motor based on the amplitude voltage, an encoder for detecting the motor rotation speed becomes unnecessary. Further, since the drive frequency change control is stopped when the voltage on the lower limit side of the signal waveform of the amplitude voltage falls below the reference voltage, the drive frequency is fixed even when the comparison signal temporarily changes due to noise or the like. Therefore, stable control without the influence of noise or the like is possible. Further, since the amplitude voltage is compared with the reference voltage to control the drive frequency, it is not necessary to detect the peak of the amplitude voltage, and the circuit configuration is prevented from becoming complicated. Further, since it is not necessary to detect the peak of the amplitude voltage and control the drive frequency based on this peak, the drive frequency is not controlled to the low frequency side beyond the peak of the amplitude voltage, and due to temperature change. It is possible to perform stable control in real time without being affected by changes in the characteristics of the amplitude voltage.
[0006]
Here, in the present invention, the comparison means is configured to change and output the comparison signal when the voltage on the lower limit side of the signal waveform of the amplitude voltage is lower than the reference voltage. Further, as the amplitude voltage detecting means, by using the voltage detected by the sensor electrodes are attached to the ultrasonic motor, there is no need to newly provide the amplitude voltage detection means. Further, the frequency control means includes a voltage controlled oscillator whose oscillation frequency is changed based on a control voltage, and supplies the voltage controlled oscillator with the control voltage changed over time, and a comparison signal from the comparison means The drive control device according to the present invention can be realized by utilizing generally provided circuit components by including the CPU for fixing the control voltage based on the above.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the ultrasonic motor drive control apparatus of the present invention. The ultrasonic motor 1 has a pair of drive electrodes A and B, although the description of the specific configuration is omitted here, and by applying frequency signals whose phases are different by 90 degrees to these drive electrodes, The vibrating body as a stator vibrates to excite the traveling wave of elastic vibration, and the moving body pressed against the vibrating body is frictionally driven by the lateral component of the wavefront of the traveling wave, and is proportional to the amplitude of the traveling wave. Moved at speed. The ultrasonic motor 1 is provided with a sensor electrode S, from which an amplitude voltage VD proportional to the amplitude when the vibrating body vibrates elastically is detected. .
[0008]
A CPU (microcomputer) 2 is provided as a control circuit for driving and controlling the ultrasonic motor 1, and a drive for outputting a signal for driving the ultrasonic motor 1 to the output side of the CPU 2. An output port Pout, a control voltage output port PVCO that outputs a drive frequency signal for driving the ultrasonic motor 1 as a frequency control voltage, and a reference voltage output port PREF that outputs a reference voltage in the comparison circuit 7 described later. have. Further, on the input side of the CPU 2, there is a drive input port Pin to which a comparison output obtained by comparing the detection output of the sensor electrode S with a reference voltage is input.
[0009]
The drive output port Pout of the CPU 2 is connected to one input of the AND gate 3. The output of the control voltage output port PVCO is input to a control voltage terminal of a voltage controlled oscillator (VCO) 4 to control the oscillation frequency of the VCO 4 in accordance with the output voltage. The output of the VCO 4 is connected to the other input of the AND gate 3. Then, the drive frequency signal SD which is the output of the AND gate 3 is branched into two, and one output is input to the A electrode side power amplifier circuit 5A, the power is amplified and supplied to the drive electrode A of the ultrasonic motor 1. The The other output branched into two is input to the 90-degree shifter 6 where the phase is shifted by 90 degrees. The phase-shifted output is input to the B electrode side power amplifier circuit 5B, where the power is amplified and supplied to the drive electrode B of the ultrasonic motor 1. Each of the power amplifying circuits 5A and 5B includes power amplifying transformers T1 and T2, switching transistors TR1 to TR4, and inverters I1 and I2, and performs a power amplifying operation based on a motor driving power supply voltage Vm. It is configured.
[0010]
On the other hand, a comparison circuit 7 is connected to the sensor electrode S of the ultrasonic motor 1, and a comparison output of the comparison circuit 1 is input to the drive input port Pin of the CPU 1. The comparison circuit 7 includes a comparator COMP, resistors R1 to R5, and a capacitor C, and the amplitude voltage VD that is the output of the sensor electrode S falls within the circuit power supply voltage by the resistance ratio of the resistors R4 and R5. In addition, an amplitude voltage VD ′ that is level-shifted so that the center level thereof becomes a voltage that is ½ of the circuit power supply voltage V is input to the negative input terminal of the comparator COMP. The reference voltage VREF from the reference voltage output port PREF of the CPU 2 is input to the positive input terminal of the comparator COMP. The comparator COMP compares the amplitude voltage VD ′ obtained from the sensor electrode S and level-shifted with the reference voltage VREF, and the voltage on the lower limit side of the signal waveform of the amplitude voltage V D ′ is the reference voltage. At a timing when the voltage becomes lower than the voltage V REF , a high level output is output as the comparison signal SC and input to the drive input port Pin of the CPU 2.
[0011]
Here, in the CPU 2, based on the correlation characteristics between the frequency and amplitude voltage of the ultrasonic motor 1 to be controlled, the amplitude at the driving frequency at which the ultrasonic motor 1 exhibits the maximum capability or the driving frequency in the vicinity thereof. The voltage is obtained by calculation or measurement, the lower limit value of the voltage waveform slightly smaller than the obtained amplitude voltage is obtained as the reference voltage VREF, and this reference voltage VREF is set to be output from the reference voltage output port PREF. Has been.
[0012]
The drive control operation by the ultrasonic motor drive control apparatus having the above configuration will be described with reference to the flowchart of FIG. 2 and the timing chart of FIG. When a motor drive command is input to the CPU 2 (S101), the CPU 2 sets the built-in counter to “i = 0” (S102). Next, the CPU 2 outputs the preset reference voltage VREF of FIG. 3 from the reference voltage output port PREF and inputs it to the positive input terminal of the comparator COMP (S103). At the same time, the control voltage output port PVCO outputs a control voltage VVCO whose voltage gradually increases as time passes as shown in FIG. 3 (S104). In response to this control voltage VVCO, as shown in FIG. 3, the VCO 4 outputs a drive frequency signal SD whose oscillation frequency is changed from the initial high frequency toward the low frequency side. Note that this oscillation frequency is a region where the amplitude voltage is changed with respect to the frequency shown in FIG. 4B, and more than a frequency fp of the peak voltage Vp that exhibits the maximum capability of the ultrasonic motor 1 by a predetermined frequency. Needless to say, the frequency is set on the high frequency side. Further, a high level drive signal SH is output from the drive output port Pout (S105). With the output of the drive signal SH, the output SD of the oscillation frequency of the VCO 4 is output from the AND gate 3 as a drive frequency signal, one of which is input to the A side power amplifier circuit 5A, and the other is phase shifted by 90 degrees and Input to the side power amplifier circuit 5B. Then, the respective frequency outputs are power amplified in the power amplification circuits 5A and 5B and supplied to the drive electrodes A and B of the ultrasonic motor 1 as drive signals whose phases are different by 90 degrees to rotationally drive the ultrasonic motor 1 ( S106).
[0013]
When the ultrasonic motor 1 is driven to rotate, the sensor electrode S detects an amplitude corresponding to the motor driving frequency, and outputs an amplitude voltage VD. The amplitude voltage VD is level-shifted in the comparison circuit 7 to become an amplitude voltage VD ', and is output as an AC signal corresponding to the drive frequency as shown in FIG. Since the amplitude voltage VD ′ has a correlation with the driving frequency as shown in FIG. 4B, when the driving frequency of the ultrasonic motor 1 is reduced, the amplitude voltage VD ′ is accordingly increased. The absolute value of is gradually increased. Then, the amplitude voltage VD 'is compared with the reference voltage VREF in the comparator COMP, and at the time t1 when the voltage on the lower limit side of the signal waveform of the amplitude voltage falls below the reference voltage, the comparator COMP outputs a high level as the comparison signal SC. Is done. During this time, the control voltage VVCO in the CPU 2 is gradually increased until a high level is output from the comparator COMP, and as a result, as shown in FIG. SD (S107, S108).
[0014]
When the high-level signal SC is output from the comparator COMP, the CPU 2 sets the built-in counter to “i = i + 1” (S109), and the count number i is a preset value N (N is an integer of about 1 to 5). (S110). When the count number i has not reached the set value N, the process returns to step S108, the control voltage VVCO is further increased, and the drive frequency of the ultrasonic motor 1 is further lowered. As a result, the amplitude voltage VD ′ obtained from the sensor electrode S further increases. When the above steps are repeated and the count number i reaches the set value N, the increase in the control voltage VVCO is stopped thereafter. As a result, the ultrasonic motor 1 is controlled so as to continue driving at a driving frequency corresponding to the control voltage at that time.
[0015]
As described above, the amplitude voltage VD ′ is obtained by using the sensor electrode S attached to the ultrasonic motor 1, and the driving frequency of the driving frequency signal SD of the ultrasonic motor 1 is controlled based on the amplitude voltage. Therefore, an encoder or the like for detecting the motor rotation speed is unnecessary, and the circuit configuration is not complicated. In controlling the driving frequency, when it is detected that the voltage on the lower limit side of the signal waveform of the amplitude voltage VD ′ is lower than the preset reference voltage VREF, the driving frequency signal SD is set to the frequency at that time. Since it is fixed, it is not necessary to detect the peak of the amplitude voltage, and there is no need for circuit components for that purpose, and the circuit configuration is not complicated. At this time, since the drive frequency is fixed when the state in which the voltage on the lower limit side of the signal waveform of the amplitude voltage VD ′ is lower than the reference voltage VREF reaches the predetermined number N, for example, temporarily due to noise or the like. When the amplitude voltage is increased or decreased , the driving frequency is not fixed and the driving frequency can be controlled stably. Furthermore, even if the correlation characteristics between frequency and amplitude voltage change due to environmental temperature, if the reference voltage has a predetermined margin, the drive control of the ultrasonic motor can be stably maintained even if the temperature changes. is there.
[0016]
It should be noted that according to the inventor's experiment in setting the reference voltage, as described above, the characteristics of the ultrasonic motor to be controlled are measured in advance, and the amplitude voltage with respect to the drive frequency as shown in FIG. For example, a voltage of about 80% to 90% is set as the reference voltage VREF with respect to the peak voltage Vp obtained from the correlation characteristic, and the value of N is set to about 5. In this case, in a general ultrasonic motor, it is possible to drive and control the ultrasonic motor at a driving frequency corresponding to an amplitude voltage of 90 to 95% of the peak voltage. These values are variations in the types and the individual characteristics of the ultrasonic motor to be controlled, yet it is not needless to say those which differ by the detection characteristics of the sensor electrode.
[0017]
In the embodiment, the comparator COMP is set to the high level when the voltage on the lower limit side of the signal waveform of the amplitude voltage VD ′ is lower than the reference voltage VREF as the setting of the comparator COMP . The comparator output may be inverted to a high level or a low level when the voltage on the upper limit side of the signal waveform exceeds the reference voltage. In the above embodiment, the AND gate 3 is used to calculate the logical sum of the output SD of the VCO and the drive output SH to obtain the drive frequency signal SD. The VCO may be controlled by the output, and the ultrasonic motor may be driven by directly using the output of the VCO.
[0018]
【The invention's effect】
As described above, according to the present invention, while the drive frequency for driving the ultrasonic motor is controlled by the frequency control means, the vibration amplitude of the ultrasonic motor is detected as the amplitude voltage by the amplitude voltage detection means, and this detection is performed. A comparison means compares the measured amplitude voltage with a preset reference voltage. In this comparison, the comparison signal is changed when it is detected that the voltage on the lower limit side of the signal waveform of the amplitude voltage is lower than the reference voltage. Since the drive frequency is controlled based on the comparison signal as the comparison result, and the change control of the drive frequency of the frequency control means is stopped when the comparison signal is changed a plurality of times. temporarily comparison signal without driving frequency is changed also changes due to noise or the like, that Do enabling stable control without the influence of noise. Also, according to the present invention, an encoder for detecting the motor speed will not be required, in order to control the drive frequency by comparing the amplitude voltage reference voltage, it is necessary to detect the peak voltage amplitude Thus, the circuit configuration is prevented from becoming complicated. In addition, since it is not necessary to detect the peak of the amplitude voltage and control the drive frequency based on the peak, the drive frequency may be controlled to the low frequency side beyond the peak of the amplitude voltage. In addition, it is possible to suppress the influence of fluctuations in the correlation characteristics of the amplitude voltage due to temperature changes, and to realize stable control of the ultrasonic motor in real time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the overall configuration of an ultrasonic motor drive control device of the present invention.
FIG. 2 is a flowchart for explaining a control operation in the apparatus of FIG. 1;
FIG. 3 is a timing chart showing signal waveforms at various parts in FIG. 2;
FIG. 4 is a diagram showing a correlation characteristic between the rotation speed and the amplitude voltage with respect to the drive frequency of the ultrasonic motor.
[Explanation of symbols]
1 Ultrasonic motor 2 CPU
3 And Gate 4 Voltage Controlled Oscillator (VCO)
5A, 5B Power amplification circuit 6 90 degree shifter 7 Comparison circuit S Sensor electrode COMP Comparator

Claims (4)

Frequency control means capable of changing and controlling the drive frequency of a signal for driving the ultrasonic motor, amplitude voltage detection means for detecting the vibration amplitude of the ultrasonic motor as an amplitude voltage, and the detected amplitude voltage and the preset value And comparing means for comparing the measured reference voltage and outputting the comparison result as a comparison signal, wherein the comparing means detects that the voltage on the lower limit side of the signal waveform of the amplitude voltage is lower than the reference voltage. The frequency control means controls the drive frequency based on the comparison signal, and stops the change control of the drive frequency when the comparison signal changes a predetermined number of times. A drive control apparatus for an ultrasonic motor. The frequency control unit is configured to gradually decrease the drive frequency from the start of driving the ultrasonic motor, and the frequency control unit is configured to stop the decrease of the drive frequency based on a change in the comparison signal. The ultrasonic motor drive control device according to claim 1 , wherein: The ultrasonic motor is provided with a sensor electrode that outputs a voltage corresponding to the vibration amplitude of the motor, and the amplitude voltage detecting means detects the amplitude voltage based on the voltage detected by the sensor electrode. The drive control apparatus of the ultrasonic motor according to claim 1 or 2 . The frequency control means is a voltage-controlled oscillator whose oscillation frequency is changed based on a control voltage, supplies the control voltage to the voltage-controlled oscillator with a change over time, and based on a comparison signal from the comparison means 4. The drive control apparatus for an ultrasonic motor according to claim 1, further comprising a CPU for fixing the control voltage.

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