JPH0759155B2 - Drive controller for ultrasonic motor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic motor having a driving vibrator including a piezoelectric body and an elastic body, and a power supply for supplying high frequency power to the piezoelectric body. And a vibration speed detecting means for detecting the vibration speed of the vibrator.

[Conventional technology]

Conventionally, in this type of ultrasonic motor drive control device, as a vibration velocity detecting means for detecting the vibration velocity of a vibrator, a piezoelectric body for detection, which is separate from a piezoelectric body for excitation, is provided on the vibrator. In some cases, the output voltage corresponding to the vibration amplitude of the vibrator is detected.

That is, in order to operate the ultrasonic motor in a highly efficient and stable manner regardless of changes in the mechanical resonance frequency of the vibrator due to changes in operating environment such as temperature, load, drive voltage, and conditions, It is necessary to keep the vibration state of the vibrator constant.

For that purpose, the drive controller is provided with a vibration state of the vibrator,
That is, it is necessary to detect some state quantity such as displacement, speed, and acceleration. For that purpose, a vibration speed detecting means is provided,
Based on the detected vibration speed, drive control is performed so that the power supply frequency applied to the piezoelectric body is maintained at an optimum frequency.

However, according to the above-mentioned conventional technique, it is necessary to provide the elastic body with a detection piezoelectric body separate from the excitation piezoelectric body,
Not only does the manufacturing process of the motor become complicated and the cost increases, but also the vibration state of the vibrator cannot be detected accurately depending on the installation location due to variations in characteristics.

Therefore, an ultrasonic motor drive control for detecting the mechanical arm current to the piezoelectric body and adjusting the output voltage of the power supply means or adjusting the frequency so as to maintain the amplitude of the detected mechanical arm current at a set value. An apparatus has been proposed (Japanese Patent Laid-Open No. 1-16
No. 0379).

[Problems to be Solved by the Invention]

However, in the one that detects the mechanical arm current to the piezoelectric body, attention is paid to the fact that the fluctuation width of the minor axis of the elliptical motion of the traveling wave is proportional to the mechanical arm current, and that value is maintained at the set value. In order to adjust the output voltage of the power supply means or to adjust the frequency, and not to detect the vibration speed itself of the piezoelectric body, it is not necessary to control due to factors such as fluctuations in the frequency of the traveling wave. There is a drawback that the drive device does not have good characteristics.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks.

[Means for Solving the Problems]

In order to achieve this object, a first characteristic configuration of a drive control device for an ultrasonic motor according to the present invention is configured such that the vibration speed detection means is an applied voltage detection means for detecting an applied voltage to the piezoelectric body, and a conduction current. And a means for calculating a differential signal of the output signals of the applied voltage detection means and the applied current detection means, the applied voltage detection means, the applied voltage N: A step-down circuit for stepping down and detecting is provided at 1, and a current transformer having a winding ratio of 1: P and a capacitor having a capacitance C connected to the secondary side thereof are provided at the energization current detecting means, and the constants thereof are set to the piezoelectric body. (1) with respect to the capacitance C _d of lies in that is set on the relation of _{C d = C · P / N} .

A second characteristic configuration is that in the above-described configuration, speed control means for adjusting the output voltage of the power supply means is provided so as to maintain the detected vibration speed by the vibration speed detection means at a set value.

Furthermore, according to the third characteristic configuration, the phase difference between the differential signal by the arithmetic means and the voltage applied to the piezoelectric body is detected, and the power supply means of the power supply means is maintained so as to maintain the detected phase difference at a set value. The point is that frequency control means for adjusting the oscillation frequency is provided.

According to the fourth characteristic configuration, the set value is 90 °.

According to the fifth characteristic configuration, the frequency control means is provided with a phase correction means for correcting the set value.

[Work]

That is, the vibration velocity detecting means detects the drive voltage and the current for the piezoelectric body by the applied voltage detecting means and the energizing current detecting means having a predetermined relationship, and calculates the output signals by the calculating means based on the following principle. by doing,
A signal including a term indicating a phase difference caused by a difference between the resonance frequency of the vibrator and the frequency of the applied voltage is output.

Based on the phase difference, by appropriately controlling the oscillation frequency of the power supply means, the ultrasonic motor, temperature, load,
High efficiency, regardless of changes in the mechanical resonance frequency of the vibrator due to changes in operating environment and conditions such as drive voltage, and
It operates stably.

The principle will be described below.

When the theory of the piezoelectric vibrator is applied to the ultrasonic motor, when the piezoelectric body vibrates at a speed due to the AC voltage applied by the power supply unit, the piezoelectric body and the elastic body are applied to the vibrator. The electric current and the exciting force flowing into the are expressed by the following equations based on the electroacoustic conversion basic equations.

= + A = -A + (1) Here, is electric admittance, A is a conversion coupling coefficient of an electric system and a mechanical system, called a force coefficient, and is mechanical impedance. In addition, the dot is attached to the variable is the vector quantity.

As shown in FIG. 5, considering the equivalent circuit of the vibrator system when the acoustic impedance 'is connected to the mechanical terminal, the relationship between the vibration speed and the electric terminal voltage is expressed as follows: It is expressed as (+ ') (2).

Now consider the oscillator as a lumped model as a single resonance system consisting of mass m, stiffness s, and resistance r, and ′ = r ′ + j
Let x ′ be + ′ = r + r ′ + jx ′ + jωm + s / jω ω _r = {− x ′ + (− x ′ ² + 4ms) ^1/2 } / 2m (3) where ω _r is the mechanical resonance angular frequency And ω is the operating angular frequency.

Therefore, paying attention to the phases of and from the equation (2), it follows that: = A / | + '| exp {jφ} · (4), and the following three cases can be considered.

i.ω <ω _r : is a phase advance with respect to ii.ω = ω _r : is in phase with iii.ω> ω _r : is a phase delay with respect to As shown in, L and C of a series resonance circuit that generates piezoelectric mechanical vibration, resistance R, and electrostatic capacitance C _d irrelevant to vibration can be expressed as
The equation (1) is: jj C _d + A (5) However, ω is the angular frequency of the AC voltage V.

As shown in FIG. 7, the output voltage _c of the energization current detecting means for detecting the energization current to the piezoelectric body is _c = / jωCP = Cd / CP + A / jωCP (6). However, the turns ratio of the current transformer is 1: P, and the capacity of the capacitor arranged on the secondary side of the current transformer is C.

The output voltage _N of the applied voltage detecting means for detecting the applied voltage to the piezoelectric body is _N = / N (7). However, the turns ratio of the transformer is N: 1.

Next, when the output voltages _C and _N are differentially amplified by the calculating means, the output voltage _P is _P = K ( _C − _N ) = K (C _d / CP−1 / N) · + KA / (jωCP)・
(8) However, K is a differential gain.

Here, when the values of C, P and N are selected so that C _d / CP = 1 / N (9), the equation (8) can be expressed as follows. _P = KA / (jωCP) · (10) Here, since KA / (ωCP) is a real number, it does not affect the phase relationship with _P. Output voltage from equation (10)
The amplitude of _P is proportional to the amplitude of _P , and the phase of the piezoelectric element is delayed by 90 ° to detect the vibration speed of the piezoelectric material.

Therefore, from equation (4) showing the relationship between the speed and the applied voltage to the vibrator, equation (10) is Therefore, the phase relationship with _P can be divided into the following three cases.

iv.ω <ω _r : _P is 90 ° -φ retarded with respect to v.ω ＝ ω _r : _P is 90 ° retarded with respect to vi.ω> ω _r : _P is 90 ° + φ retarded with respect to From the above, _P , that is, by delaying the phase of the output signal from the vibration velocity detecting means by 90 ° from the voltage applied to the piezoelectric body, the piezoelectric vibrator can always be driven at the resonance frequency ω _r .

〔The invention's effect〕

Therefore, according to the first characteristic configuration of the present invention, the vibration velocity of the piezoelectric body can be accurately detected indirectly by the vibration velocity detecting means.

Then, according to the second characteristic configuration, by adjusting the output voltage of the power supply means so as to maintain the above-described detected vibration speed at a set value, even if a load fluctuation occurs, the ultrasonic wave is generated. The motor can now be controlled stably.

According to the third characteristic configuration, the oscillation frequency of the power supply means is adjusted so as to maintain the phase difference between the differential signal by the arithmetic means and the voltage applied to the piezoelectric body at a set value, thereby oscillating. The frequency can now be controlled stably by tracking the mechanical resonance frequency that fluctuates due to temperature changes and load fluctuations.

According to the fourth characteristic configuration, by setting the set value to 90 °, particularly, the driving at the mechanical resonance frequency which is the most stable and efficient in the composite vibrator type ultrasonic motor is guaranteed. It became so.

According to the fifth characteristic configuration, the traveling wave type ultrasonic motor is most stable by correcting the set value by the phase correction means and adjusting the oscillation frequency to a frequency slightly higher than the mechanical resonance frequency. Moreover, it is possible to drive at an efficient drive frequency.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 2, an ultrasonic motor (M) has a ring-shaped stator (3) for fixing an elastic body (2) to a piezoelectric body (1) to generate a traveling wave of ultrasonic waves, and It is composed of a rotor (4) which rotates in pressure contact with the stator (3).
That is, the stator (3) becomes the vibrator (3 ').

The piezoelectric body (1) is divided into two regions (A) and (B) in the circumferential direction, and each of the regions (A) and (B) alternates between adjacent sections at intervals of half the wavelength λ. Is polarized in the thickness direction, and these regions (A) and (B) are arranged with a shift of three quarter wavelengths.

By applying high frequency voltages having 90 ° different phases to the regions (A) and (B), the standing waves generated in the stator (3) corresponding to the regions (A) and (B) are mutually generated. They cause interference and are combined into a traveling wave.

That is, the rotor (4) is rotated by the frictional force with the stator (3) based on the traveling wave generated in the stator (3).

As shown in FIG. 1, the drive control device for the ultrasonic motor (M) includes a power supply means (5) for supplying high frequency power to the piezoelectric body (1) and a machine for the vibrator (3 ′). Phase difference detecting means (6) for detecting a phase difference caused by the difference between the typical resonance frequency and the frequency of the voltage applied to the piezoelectric body (1), that is, the vibration velocity detecting means and the phase difference detecting means (6). ) Output signal and the applied voltage are compared, and a frequency control means (7) for controlling the oscillation frequency of the power supply means (5) so as to maintain the phase difference at a set value; It comprises speed control means (8) for controlling the output voltage of the power supply means (5), that is, the voltage applied to the piezoelectric body (1) based on the output signal of the phase difference detection means (6).

The power supply means (5) changes the output voltage in the preceding stage by changing the conduction ratio by the switch (S5) via the drive circuit (D1) based on the output signal of the speed control means (8). The direct current chopper circuit (5a) and the switch (S1) to the switch (S4) are opened / closed via the drive circuit (D2) on the basis of the output signal of the frequency control means (7). Inverter circuit that changes the voltage (5b)
Is provided and configured.

The inverter circuit (5b) is a combination of two sets of power-supply-divided half-bridge inverters and outputs a two-phase square wave whose phase is shifted by 90 °.
Regions (A) and (B) of the piezoelectric body (1) of the ultrasonic motor (M) through the boosting transformers (T1) and (T2)
It is connected to the electrodes provided in.

The square wave is shaped into a sine wave by the leakage inductance of the transformers (T1) and (T2).

The phase difference detecting means (6) is an applied voltage detecting means (6a) for detecting an applied voltage V to the piezoelectric body (1), an energizing current detecting means (6b) for detecting an energizing current I, and outputs thereof. It is composed of arithmetic means (6c) for differentially amplifying signals.

The applied voltage detecting means (6a) is a transformer (P
The bootstrap circuit (B1) is connected to the secondary side of (T), and the energization current detection means (6b) has a capacity C on the secondary side of the current transformer (CT) with a turns ratio of 1: P. A bootstrap circuit (B2) is connected via a capacitor (C3), both of which are provided on the secondary side of the transformer (T2).

The constants N, P and C are set so that C _d = C · P / N with respect to the capacitance C _d of the piezoelectric body (1).

As a result of differentially amplifying the output voltage V _{N of the} applied voltage detection unit (6a) and the output voltage V _C of the energization current detection unit (6b) by the calculation unit (6c), the output voltage V _P is ], The term represents a phase difference caused by the difference between the frequency of the applied voltage V and the resonance frequency of the vibrator (3 ′).

The frequency control means (7) includes a phase comparator (PC), an output inverting low-pass filter (LPF), and a voltage controlled oscillator (V).
The output of the voltage controlled oscillator (VCO) is connected to the drive circuit (D2).

The phase comparator (PC) and the low pass filter (LPF)
A phase correction means (PSC) that corrects the output voltage of the phase comparator (PC) is interposed between and.

The phase comparator (PC) includes the applied voltage detecting means (6a).
Of the output voltage V _N of the calculation means (6c) and the output voltage V _P of the calculation means (6c) are input through the filters (F1), (F2) and the comparators (COM1), (COM2) for waveform shaping into a square wave. As shown in FIG. 3, a voltage corresponding to the phase difference between the two voltages V _N and V _P is output.

The voltage controlled oscillator (VCO), as shown in FIG.
The output frequency is made variable according to the output voltage value of the phase comparator (PC) inverted by the low pass filter (LPF).

That is, when the phase difference between both voltages V _N and V _P is 90 ° or less, the output voltage of the phase comparator (PC) decreases, so the output frequency of the voltage controlled oscillator (VCO) increases, and Increase the oscillation frequency of the inverter circuit (5b).

On the contrary, when the phase difference between the two voltages V _N and V _P is 90 ° or more, the output voltage of the phase comparator (PC) increases, so that the output frequency of the voltage controlled oscillator (VCO) decreases, The oscillation frequency of the inverter circuit (5b) is lowered.

By the above-mentioned operation, the phase difference between the two voltages V _N and V _P can be maintained at 90 °, that is, the resonance frequency fluctuated by the change of the temperature of the vibrator (3 ′) can be tracked and driven. .

Further, the frequency control means (7) corrects the output voltage of the phase comparator (PC) by the phase correction means (PSC), so that the ultrasonic motor (M) is most stable,
Moreover, the oscillation frequency is controlled so as to be a frequency slightly higher than the resonance frequency which is an efficient drive frequency.

[Another embodiment]

 Another embodiment of the present invention will be described below.

1. In the previous embodiment, a transformer (PT) with a turns ratio of N: 1 is used to configure the applied voltage detection means (6a),
Instead of the transformer (PT), V _N may be taken out by connecting resistors having a resistance ratio of N-1: 1 in series.

2. In the previous embodiment, the phase difference detecting means (6) is provided on the secondary side of the transformer (T2) to detect the phase difference in the area (A) of the stator (3). However, the phase detecting means (6) may be installed on the secondary side of the transformer (T1) to detect the phase difference in the region (B), and further, both the transformers (T1), ( You may intervene in T2) respectively.

3. In the previous embodiment, the voltage V _N , V is applied to the phase comparator (PC).
_{Although P} is input via the comparators (COM1) and (COM2), even if the applied voltage V to the piezoelectric body (1) is input via the comparator (COM1) instead of the voltage V _N. Good.

4. In the above embodiment, the rotary ultrasonic motor in which the stator is configured as the vibrator has been described. However, the ultrasonic motor is not limited to the one in which the rotor is the vibrator or the linear type. Good.

Further, it may be a composite oscillator type ultrasonic motor that controls the locus of motion of a mass point by combining two vibrations having different vibration directions. In this case, the voltage V _N , V _P Most stable by maintaining the phase difference at 90 °,
In addition, efficient driving is possible.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

The drawings show an embodiment of a drive control device for an ultrasonic motor according to the present invention. FIG. 1 is a circuit diagram, FIGS. 2 (a) and 2 (b) are configuration diagrams of the ultrasonic motor, and FIG. 3 is a phase comparison. Output characteristic diagram of the device, Fig. 4 output characteristic diagram of voltage controlled oscillator, Fig. 5 equivalent circuit diagram of piezoelectric vibrator system, Fig. 6 equivalent circuit diagram of ultrasonic motor, Fig. 7 phase difference detection It is a circuit diagram of a means. (1) ... Piezoelectric body, (2) ... elastic body, (3 ') ... vibrator, (5) ... power supply means, (6) ... state quantity detection means, (6a) ... applying Voltage detecting means, (6b) ... energizing current detecting means, (6c) ... calculating means, (M) ... ultrasonic motor.

Claims (5)

[Claims] 1. An ultrasonic motor (M) having a vibrator (3 ') for driving, which comprises a piezoelectric body (1) and an elastic body (2), and supplies high frequency power to the piezoelectric body (1). A drive control device for an ultrasonic motor, comprising: a power supply means (5) for controlling the vibration speed; and a vibration speed detection means (6) for detecting the vibration speed of the vibrator (3 ′). (6) is an applied voltage detecting means (6a) for detecting an applied voltage to the piezoelectric body (1), an energizing current detecting means (6b) for detecting an energizing current, the applied voltage detecting means (6a) and The energizing current detecting means (6b) and an arithmetic means (6c) for obtaining a differential signal of the output signals of the energizing current detecting means (6b) are detected by the applied voltage detecting means (6a) by stepping down the applied voltage to N: 1. And a current transformer with a turns ratio of 1: P in the energizing current detecting means (6b). Ultrasonic waves of a capacitor of capacitance C connected to the secondary side is provided, relative to the capacitance C _d of the their constant piezoelectric (1), it is set in a relationship of C _d = C · P / N Motor drive control device. 2. A speed control means (8) for adjusting the output voltage of the power supply means (5) so as to maintain the vibration speed detected by the vibration speed detection means (6) at a set value. 1. The drive control device for the ultrasonic motor according to 1. 3. The power supply means () for detecting a phase difference between a differential signal by the calculating means (6c) and a voltage applied to the piezoelectric body (1) and maintaining the detected phase difference at a set value. 5)
3. The drive control device for the ultrasonic motor according to claim 1, further comprising frequency control means (7) for adjusting the oscillation frequency of the ultrasonic motor. 4. The drive control device for an ultrasonic motor according to claim 3, wherein the set value is 90 °. 5. The frequency control means (7) is provided with a phase correction means (PSC) for correcting the set value.
A drive control device for the ultrasonic motor described.