JPH06315283A - Drive circuit for ultrasonic motor - Google Patents

Abstract

PURPOSE:To provide a drive circuit for ultrasonic motors that follows up the optimum frequency even in case of the fluctuation of resonance frequency due to temperature variation, and that prevents stalls and overcurrent due to steep load fluctuation. CONSTITUTION:A drive circuit for ultrasonic motors 4 is provided with an oscillation circuit 1 and a temperature sensor 5 installed in proximity to the ultrasonic motor 4. It also includes memory 9 that stores the lower limit of driving frequency corresponding to temperature; an oscillation control circuit 8 that controls the oscillation frequency of the oscillation circuit 1 according to detected temperature and the lower limit; a current detector 7 that monitors the currents fed into the drive circuitry; and memory 9 that stores the upper limit of the range of frequency lower than the motor anti-resonance point of the fed current and the upper limit of the range of frequency higher than that. When the detected current exceeds the upper limit of the lower frequency range, the frequency of alternating current voltage is shifted toward higher values; when the detected current exceeds the upper limit of the higher frequency range, the frequency of alternating current voltage is shifted toward lower values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for an ultrasonic motor, and more particularly to a drive circuit for an ultrasonic motor that drives a predetermined amount at high speed and accurately regardless of temperature changes.

[0002]

2. Description of the Related Art In recent years, ultrasonic motors have attracted much attention as compared with electromagnetic motors because they have a small outer dimension and can obtain a strong driving force. This ultrasonic motor uses ultrasonic vibration generated by applying an AC voltage to a piezoelectric element as a driving force for a driven member.

The temperature of such an ultrasonic motor often gradually rises when it is driven by applying a voltage. However, since the optimum driving frequency for driving the ultrasonic motor changes depending on the temperature, it remains as it is. The optimum driving frequency could not always be obtained.

In consideration of these problems, various driving circuits for ultrasonic motors have been proposed in the past, which can drive a predetermined amount at high speed and accurately regardless of temperature changes. No. 264579. The technical means described in this publication detects the temperature of the vibrating body and sets the optimum drive frequency for driving the ultrasonic motor accordingly. This allows
It is possible to track changes in frequency due to temperature changes.

[0005]

However, in the above-mentioned conventional example, when a large load is applied, the resonance frequency transiently fluctuates, and the resonance frequency enters into a lower frequency region than the unstable resonance frequency and stops. , Excessive current may damage the circuit.

The present invention has been made in view of the above problems, and it is possible to follow the optimum frequency even if the resonance frequency fluctuates due to a temperature change, and it is possible to prevent a stop or an excessive current due to a sudden load change. It is an object of the present invention to provide a drive circuit for an ultrasonic motor.

[0007]

In order to achieve the above object, the drive circuit of the ultrasonic motor according to the present invention is an electric motor.
A drive circuit for an ultrasonic motor that generates a driving force by ultrasonic vibration generated by applying an AC voltage to a mechanical energy conversion element, the oscillation means for setting the frequency of the AC voltage, and the ultrasonic wave. Temperature detection means provided in the vicinity of the motor, and first storage means for storing the lower limit value of the drive frequency corresponding to the temperature of the ultrasonic motor,
A control means for controlling the oscillating frequency of the oscillating means based on the detected temperature and the lower limit value; and a current monitoring means for monitoring a current flowing into these drive circuits, and a motor anti-resonance point of the inflow current. The second storage means stores the upper limit value in the low frequency region, and the frequency shift means that shifts the frequency of the AC voltage to the higher frequency side when the detected current exceeds the upper limit value.

The ultrasonic motor drive circuit according to the present invention is an ultrasonic motor drive circuit for generating a driving force by ultrasonic vibration generated by applying an AC voltage to an electro-mechanical energy conversion element. An oscillating means for setting the frequency of the AC voltage; a temperature detecting means provided in the vicinity of the ultrasonic motor; and a lower limit value of a driving frequency corresponding to the temperature of the ultrasonic motor.
The storage means and the control means for controlling the oscillation frequency of the oscillation means on the basis of the detected temperature and the lower limit value are further provided. Further, the current monitoring means for monitoring the current flowing into these drive circuits and the motor for the inflow current are provided. A second storage means for storing an upper limit value in a frequency region higher than the anti-resonance point and a frequency shift means for further shifting the frequency of the AC voltage to a lower frequency side when the detected current exceeds the upper limit value are provided. ing.

[0009]

When the driving circuit of the ultrasonic motor generates the driving force by the ultrasonic vibration generated by applying the alternating voltage to the electromechanical energy conversion element, the oscillating means sets the frequency of the alternating voltage, The temperature detection means detects the temperature of the ultrasonic motor, the first storage means stores the lower limit value of the drive frequency corresponding to the temperature of the ultrasonic motor, and the control means oscillates based on the detected temperature and the lower limit value. The current monitoring means monitors the current flowing into these drive circuits, and the second storage means stores the upper limit value of the inflow current in the frequency region lower than the motor anti-resonance point. When exceeds the upper limit value, the frequency shift means shifts the frequency of the AC voltage to the higher frequency side.

Further, when the driving circuit of the ultrasonic motor generates the driving force by the ultrasonic vibration generated by applying the AC voltage to the electro-mechanical energy conversion element, the oscillating means sets the frequency of the AC voltage. Then, the temperature detection means detects the temperature of the ultrasonic motor, the first storage means stores the lower limit value of the drive frequency corresponding to the temperature of the ultrasonic motor, and the control means based on the detected temperature and the lower limit value. The oscillating frequency of the oscillating means is controlled, the current monitoring means monitors the current flowing into these drive circuits, and the second storage means stores the upper limit value of the inflow current in a frequency range higher than the motor anti-resonance point, When the detected current exceeds the upper limit value, the frequency shift means shifts the frequency of the AC voltage to the lower frequency side.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 show a first embodiment of the present invention. As shown in FIG. 1, the drive circuit of the ultrasonic motor of the first embodiment has an oscillator circuit 1 as an oscillating means for generating a basic pulse φUSR having a frequency about four times the drive frequency.
And a pulse conversion circuit 2 for dividing the generated basic pulse φUSR into four types of pulses φ1, φ2, φ3, φ4
And a power amplifier circuit 3 that uses these pulses φ1, φ2, φ3, and φ4 as switching pulses to generate a two-phase AC signal of an A-phase and a B-phase, and these two-phase AC signals A-phase and B-phase. A traveling wave type ultrasonic motor (abbreviated as USM in the figure) which rotates by applying a phase 4
And a temperature sensor 5 which is provided in the vicinity of the ultrasonic motor 4 and which detects the temperature of the motor 4 and which is a temperature detecting means composed of, for example, a temperature sensitive resistor or various thermistor chips.
A rotary encoder 6 configured by, for example, an MR sensor or a photo interrupter for detecting the rotation of the ultrasonic motor 4, a current detector 7 serving as a current monitor means for detecting the current consumed by the power amplification circuit 3, An oscillation control circuit 8, which is a control means for controlling the oscillation circuit 1 based on the outputs from the temperature sensor 5, the rotary encoder 6, the current detector 7 and the output of the memory 9, constitutes a main part thereof.

As shown in FIG. 2, in the power amplifier circuit 3, the transformers Tr1 and Tr2 are switched by the pulses φ1 and φ2 and the pulses φ3 and φ4 using the transistors Q1 and Q2 and the transistors Q3 and Q4, respectively. ,
It is for generating A phase and B phase which are drive voltages of the ultrasonic motor.

The current detector 7 is composed of a resistor R1 and an AD converter AD1 as shown in FIG.
The electric current of the power system flowing through is detected as a voltage value.

The power amplifier circuit 3 and the current detector 7 are connected via a filter composed of the coil L1 and the capacitor C1. The filter constituted by the coil L1 and the capacitor C1 is a filter whose time constant is sufficiently larger than the drive frequency of the ultrasonic motor 4, and prevents noise from being mixed in the power supplies indicated by reference symbols VBOL and PGND. The current detection by the resistor R1 and the AD converter AD1 is based on the pulse φ1,
It does not fluctuate due to switching of φ2, φ3, and φ4.

A time chart of the components shown in FIG. 2 is shown in FIG. As described above, four basic pulses φUSR make up one cycle of the drive frequency. Of the four pulses that make up one cycle of this drive frequency, pulse φ1 is the first rectangular pulse and pulse φ2 is the third rectangular The pulse and pulse φ3 are obtained by dividing the second rectangular pulse, and the pulse φ4 is obtained by dividing the fourth rectangular pulse. Further, the A phase and the B phase are out of phase with each other by 90 degrees as shown in the figure.

Next, the principle of driving will be described with reference to FIG. Reference numeral LIφ in FIG. 4A indicates a current-frequency curve at a certain temperature x, and reference numeral LNφ in FIG. 4B indicates a rotation speed-frequency curve at the same temperature x. As shown in the figure, on the lower frequency side than the maximum rotation frequency Aφ corresponding to the maximum point of the rotation speed-frequency curve LNφ, the current value rapidly increases as shown by the current-frequency curve LIφ, while the rotation is extremely high. It becomes unstable and is easily stopped when the load changes. Therefore, if the lower limit frequency fminxn corresponding to each temperature xn is experimentally obtained and the ultrasonic motor 4 is driven at a frequency higher than the lower limit frequency fminxn, stable rotation can be obtained. Therefore, the lower limit frequency fminxn is stored in the memory 9, and when the ultrasonic motor 4 is driven, the lower limit frequency fminxn corresponding to the temperature xn is read out so that the frequency does not fall below this value. Have control.

However, if the load increases suddenly,
The current-frequency curve LIφ is a curve indicated by reference symbol LIφ ′,
The characteristics of the rotation speed-frequency curve LNφ are shifted to the curves indicated by the symbol LNφ ′. At this time, if the ultrasonic motor 4 is continuously driven at the conventional lower limit frequency fminxn, the unstable region is entered, which causes the rotation to stop and the current value to increase. In this case, if the driving frequency is shifted to the high frequency side when the current value is larger than the predetermined value Ilφ, it is possible to enter the stable driving region in which the rotation is stable and the current is small. The frequency corresponding to this current value Ilφ is fminxφ. In addition to setting the lower limit frequency by temperature in this way,
If the upper limit current value is provided and the lower limit value of the frequency is shifted when the upper limit current value is exceeded, the ultrasonic motor drive circuit can cope with both temperature fluctuation and load fluctuation.

Next, the operation of the oscillation control circuit 8 will be described with reference to FIG.
This will be described with reference to the flowchart in FIG. First, when an instruction to drive the ultrasonic motor 4 is input by a drive switch (not shown) or the like (S1), the temperature of the ultrasonic motor 4 is detected by the temperature sensor 5 (S2), and the detected temperature xn is detected. The upper limit current value Ilφ that is determined regardless of the lower limit frequency fminxn and the temperature is read from the memory 9 (S
3). Next, the oscillation frequency is set to the starting frequency fstart, which is a frequency higher than any fminxn (S4),
The ultrasonic motor 4 is turned on (S5) to start driving.

When the driving of the ultrasonic motor 4 is started, the current value is detected by the current detector 7 (S6), and it is determined whether the value is larger or smaller than the upper limit current value Ilφ read from the memory 9 in step S3. Check (S7). If it is large, the frequency is shifted to the higher side than the present frequency (S8), and the process returns to step S6. On the other hand, when the current value detected in step S7 is smaller than the upper limit current value Ilφ, the rotation encoder 6 measures the output pulse interval to detect the rotation speed (S9).

Next, it is checked whether the detected speed is higher or lower than the target speed (S10), and if it is higher, the frequency is increased (S13). On the other hand, if the detected speed is lower than the target speed, it is checked whether the frequency is lower than the lower limit frequency fminxn read from the memory 9 in step S3 (S1).
1), if not small, decrease the frequency (S1
2). Then, it is checked whether or not a stop switch (not shown) is turned on (S14), and if it is not turned on, the process returns to step S6. If it is turned on, the ultrasonic motor 4 is turned off (S15) to stop the rotation. (S16).

According to the first embodiment as described above, not only is the frequency limited by temperature detection for optimization, but a stable drive frequency is provided when a current value upper limit value is provided and it is exceeded. Since the frequency is shifted, the ultrasonic motor can be driven stably regardless of temperature and load fluctuations.

Next, FIGS. 6 and 7 show a second embodiment of the present invention. The second embodiment is substantially the same as the above-mentioned first embodiment except that the values stored in the memory 9 and the operation at the time of driving are slightly different, and other parts are almost the same. Therefore, only different points will be described and the same parts The description is omitted.

FIGS. 6A and 6B show current-frequency characteristics and rotation speed-frequency characteristics of the ultrasonic motor 4. The curves denoted by reference numerals LI1 and LI2 are current-frequency curves at high temperature and low temperature, respectively, and the curves denoted by reference numerals LN1 and LN2 are, respectively.
These are the rotational speed-frequency characteristics at high temperature and low temperature, respectively.

As shown in FIG. 6A, when the temperature changes from low temperature to high temperature, for example, the current curve changes from LI2 to LI.
The characteristics of the curve change greatly, such as changing to 1 and shifting to the low frequency direction, and the peak value of the current value rising. Therefore, instead of the constant upper limit current value Ilφ provided in the first embodiment, the upper limit current value Il1xn that is changed according to the temperature is provided, and for example, at high temperature, Il
1x1 and Il1x2 at low temperature. The frequencies corresponding to these upper limit current values are lower limit frequencies fminx1 and fminx2, respectively.

FIG. 7 is a flow chart showing the operation of the second embodiment. The operation of steps S21 to S36 shown in FIG. 7 is almost the same as the operation of steps S1 to S16 shown in FIG. 5, except that the upper limit corresponding to the temperature xn at step S23 is different. That is, the current value Il1xn is being read, and accordingly, in step S27, the current detected by the current detector 7 is compared with the upper limit current value Ilxn. The other parts are almost the same as those in the first embodiment.

According to the second embodiment as described above, the ultrasonic motor has substantially the same effect as that of the above-mentioned first embodiment, can reliably realize stable driving, and can use up to the maximum rotation at that temperature. Can be used as a drive circuit.

Next, FIG. 8 shows a third embodiment of the present invention. The third embodiment is similar to the second embodiment described above except that the values stored in the memory 9 and the operation at the time of driving are slightly different, and other parts are substantially the same, so only different points will be described and similar parts will be described. Is omitted.

As shown in FIG. 6A, when the drive frequency is shifted to a higher frequency side than the antiresonance frequencies furx1 and furx2 corresponding to the antiresonance point where the current value becomes a minimum, Although the current increases, the corresponding rotation speed decreases as shown in FIG. 6 (B).
The driving speed is reduced. Since it is not preferable that the current increases too much even though the driving speed is low and the output of the ultrasonic motor 4 is small, in the third embodiment, the upper limit current value is set on the higher frequency side than the anti-resonance point. The frequency is shifted to the lower frequency side when a current exceeding this value flows. That is, in the third embodiment, in addition to the lower limit value fminxn of the frequency and the upper limit current value Il1xn in the region lower than the antiresonance point, the antiresonance frequency furxn which is different with respect to the temperature and The upper limit current value Il2xn at the high upper limit frequency fmaxxn is stored in the memory 9.

Next, the operation of the third embodiment will be described with reference to FIG. The operation of steps S41 to S59 shown in FIG. 8 is the same as that of step S41 shown in FIG.
The operation is almost the same as that of steps 21 to S36, but there are some differences. First, step S4
3, the lower limit value fmin of the frequency corresponding to the detected temperature value xn
xn, the upper limit current value Il1xn, the antiresonance frequency furxn, and the upper limit current value Il2xn are read from the memory 9. In step S47, it is checked whether the current frequency is higher or lower than the anti-resonance frequency furxn, and if it is lower, the process proceeds to step S51. On the other hand, if it is large, the detected current is Il2 × n in step S48.
Whether it is larger or smaller is checked. If it is smaller, the process proceeds to step S52, and if it is larger, the process proceeds to step S49 to decrease the frequency. The other parts are almost the same as those in the second embodiment.

According to the third embodiment, the same effect as the first and second embodiments described above is obtained, and the current value becomes excessive in the region where the current increases and the efficiency decreases. In addition, since the upper limit of the frequency is limited so that a required low speed can be obtained, it is possible to provide an ultrasonic motor drive circuit capable of suppressing power consumption.

In the first to third embodiments as described above, the configuration for generating the A-phase and B-phase AC signals from the oscillation circuit is not limited to that shown in FIG. 2 and other configurations. But good. Further, if the temperature detection by the temperature sensor is performed during driving, the driving circuit of the ultrasonic motor can more accurately follow the temperature change. Further, while the ultrasonic motor is being driven, the speed may not be controlled and may always be driven at the maximum rotation, or the driving frequency may be fixed to the lower limit frequency and the speed may be controlled by a method such as power control. Is also good. Further, the present invention is not limited to the traveling wave type ultrasonic motor as described above, but can be widely applied to other types of ultrasonic motors.

[0032]

As described above, according to the present invention, it is possible to follow the optimum frequency even if the resonance frequency fluctuates due to temperature changes, and to prevent stoppage or excessive current due to a sudden load change. A drive circuit for a motor can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of a drive circuit for an ultrasonic motor showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a power amplifier circuit and a current detector according to the first embodiment.

FIG. 3 is a timing chart showing each signal of the first embodiment.

FIG. 4 is a diagram showing (A) current value and (B) rotational speed with respect to the frequency of the ultrasonic motor of the first embodiment.

FIG. 5 is a flowchart showing the operation of the first embodiment.

FIG. 6 is a diagram showing (A) current value and (B) rotational speed with respect to frequencies of the ultrasonic motors of the second to third embodiments of the present invention.

FIG. 7 is a flowchart showing the operation of the second embodiment.

FIG. 8 is a flowchart showing the operation of the third embodiment of the present invention.

[Explanation of symbols]

 1 ... Oscillation circuit 4 ... Ultrasonic motor 5 ... Temperature sensor 7 ... Current detector 8 ... Oscillation control circuit 9 ... Memory

Claims (2)

[Claims] 1. A drive circuit of an ultrasonic motor for generating a driving force by ultrasonic vibration generated by applying an AC voltage to an electro-mechanical energy conversion element, for setting the frequency of the AC voltage. Oscillation means, temperature detection means provided in the vicinity of the ultrasonic motor, first storage means for storing the lower limit value of the driving frequency of the ultrasonic motor corresponding to temperature, and the detected temperature and lower limit value. A control means for controlling the oscillating frequency of the oscillating means, and a current monitoring means for monitoring the current flowing into these drive circuits, and a frequency lower than the motor antiresonance point of the inflow current. Second storage means for storing the upper limit value in the region, and a frequency shifter for shifting the frequency of the AC voltage to a higher frequency side when the detected current exceeds the upper limit value. Driving circuit of the ultrasonic motor, characterized by comprising a preparative means. 2. A drive circuit for an ultrasonic motor, which generates a driving force by ultrasonic vibration generated by applying an AC voltage to an electro-mechanical energy conversion element, for setting the frequency of the AC voltage. Oscillation means, temperature detection means provided in the vicinity of the ultrasonic motor, first storage means for storing the lower limit value of the driving frequency of the ultrasonic motor corresponding to temperature, and the detected temperature and lower limit value. A control means for controlling the oscillation frequency of the oscillating means, and a current monitoring means for monitoring the current flowing into these drive circuits; and a frequency of the inflow current higher than the motor antiresonance point. Second storage means for storing the upper limit value in the region, and a frequency shifter for further shifting the frequency of the AC voltage to the lower frequency side when the detected current exceeds the upper limit value. Driving circuit of the ultrasonic motor, characterized by comprising a preparative means.