JPH0365077A - Drive controller of ultrasonic motor - Google Patents

Abstract

PURPOSE:To eliminate the necessity of providing an elastic body with a detecting piezoelectric body separate from an exciting piezoelectric body and also to make a wiring for taking out the output signal of an applied voltage- detecting means and conducting current-detecting means unnecessary by making it possible to detect the vibrational state of a vibrator from the output signal. CONSTITUTION:An apparatus is provided with a quantity of state-detecting means composed of an applied voltage-detecting means 6a for detecting an applied voltage to a piezoelectric body 1, a conducting current-detecting means 6b for detecting a conducting current and an operational means 6c for outputting a deviation quantity between the resonance frequency of a vibrator 3' and the frequency of the applied voltage from the output signal of the applied voltage-detecting means 6a and conducting current-detecting means 6b. Then, the oscillation frequency of a power supply means 5 is controlled appropriately to operate an ultrasonic motor stably. Thus, it is made unnecessary to provide an elastic body 2 with a detecting piezoelectric body separate from an exciting piezoelectric body 1 and also a wiring for taking out the signal so that the manufacturing process of a motor is simplified.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a power supply for supplying high-frequency power to the piezoelectric body for an ultrasonic motor having a driving vibrator made of a piezoelectric body and an elastic body. The present invention relates to a drive control device for an ultrasonic motor, which is provided with a state quantity detection means for detecting a vibration state of the vibrator.

More specifically, a stator or a rotor is a vibrator constructed by fixing a piezoelectric body to an elastic body, and the rotor or stator is brought into pressure contact with the vibrator, and the high frequency power supplied to the piezoelectric body causes the elastic body to Drive control for ultrasonic motors that extract rotational force from the action of traveling waves generated in the body, linear ultrasonic motors that have piezoelectric bodies arranged at both ends of a columnar elastic body, and move a slider along the elastic body, etc. Regarding equipment.

[Conventional technology]

Conventionally, this type of ultrasonic motor drive control device is configured by providing the vibrator with a detection piezoelectric body separate from the excitation piezoelectric body as a state quantity detection means for detecting the vibration state of the vibrator. The output voltage corresponding to the vibration amplitude of the vibrator was detected.

In other words, in order to operate the ultrasonic motor with high efficiency and stability, regardless of fluctuations in the mechanical resonance frequency of the vibrator due to fluctuations in the usage environment and conditions such as temperature, load, and drive voltage, It is necessary to maintain the vibration state of the vibrator constant.

For this purpose, the drive control device is provided with a state quantity detection means for detecting the vibration state of the vibrator, that is, some state quantity such as displacement, velocity, acceleration, etc., and based on the detection output,
Drive control was performed to maintain the power frequency applied to the piezoelectric body at an optimal frequency.

[Problem to be solved by the invention]

However, in the above conventional technology, it is necessary to provide the elastic body with a detection piezoelectric body that is separate from the excitation piezoelectric body,
Moreover, wiring is also required to extract the signal.
This method not only complicates the manufacturing process of the motor but also increases the cost of the motor.

Furthermore, such detection piezoelectric bodies may not be able to accurately detect the vibration state of the vibrator due to variations in their characteristics or where they are installed, and as a result, it may not be possible to control the vibration state to the optimum operating state. There was also a drawback.

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

[Means to solve the problem]

In order to achieve this object, the characteristic configuration of the ultrasonic motor drive control device according to the present invention is such that the state quantity detection means includes an applied voltage detection means for detecting the voltage applied to the piezoelectric body, and an energizing current energizing current detecting means for detecting the energizing current detecting means; and calculating means for outputting a deviation amount between the resonant frequency of the vibrator and the frequency of the applied voltage from the output signals of the applied voltage detecting means and the energizing current detecting means. There is something about it.

The applied voltage detection means includes a step-down circuit that steps down the applied voltage to N:1 and detects the applied voltage, and the energized current detection means includes a current transformer with a turns ratio of 1:P and a capacitor connected to the secondary side of the current transformer. It includes a capacitor of C, and these constants are set in the relationship C,=CP/H with respect to the capacitance Cd of the piezoelectric body.

[For production]

In other words, the state quantity detection means detects the drive voltage and current for the piezoelectric body using the applied voltage detection means and the energized current detection means, which have a predetermined relationship, based on the following principle,
By computing these output signals by the computing means, a signal including a term indicating a phase difference caused by a difference between the resonant frequency of the vibrator and the frequency of the applied voltage is output.

By appropriately controlling the oscillation frequency of the power supply means based on the phase difference, the ultrasonic motor can be controlled depending on temperature, load, etc.
Regardless of fluctuations in the mechanical resonance frequency of the vibrator due to fluctuations in the usage environment and conditions such as drive voltage, high efficiency and
This allows for stable operation.

The principle is described below.

Applying the piezoelectric vibrator theory to an ultrasonic motor, the piezoelectric body changes speed divided by the AC voltage applied by the power supply means.
When vibrating at
is expressed by the following equation based on the electroacoustic conversion basic equation.

f=f? +A÷? =-A? +2÷ (1) Here, luck is electrical admittance, A is the conversion coupling coefficient between the electrical system and the mechanical system, which is called the force coefficient, and A is the mechanical impedance. Variables with dots are vector quantities.

As shown in Figure 5, the mechanical terminal has an acoustic impedance of 2
Considering the equivalent circuit of the vibrator system when ′ is connected, the relationship between the vibration speed ÷ and the electric terminal voltage is expressed as ÷=A/(之+之') (2) from equation (1). be done.

Now, consider the oscillator as a lumped model as a single resonant system consisting of mass m, stiffness S, and resistance r, and 2' = r'
+j
(3) Here, ω is the mechanical resonance angular frequency, and ω
is the operating angular frequency.

Therefore, if we pay attention to the phase of ÷ from equation (2), we get v=A/l t-+4' 1-exp [-jφ)・
? (4), and the following three cases are possible.

i, ω〈ω, : ÷ is φ leading in phase, ω=ω, : ÷ is in phase with ω〉ω, : ÷ is φ slow in phase, and the equivalent circuit of the oscillator is As shown in FIG. 6, a series resonant circuit that generates piezoelectric mechanical vibration, C1
It can be expressed as a capacitance C6 that is unrelated to the vibration of the resistance R1, and the equation (1) becomes f=jωC1+A÷ (5). However, ω is the angular frequency of the AC voltage V.

As shown in FIG. 7, the output voltage V of the energizing current detection means for detecting the energizing current to the piezoelectric body.

is Vc=f/jωcp=C,/CP+A÷/jωCP (6). However, the turns ratio of the current transformer is l:P, and the capacitance of the capacitor placed on the secondary side of the current transformer is C.

Further, the output voltage 8 of the applied voltage detection means for detecting the voltage applied to the piezoelectric body is as follows: ,=/N (7). However, the turns ratio of the transformer is N:l.

Next, the output voltage t. , when this is differentially amplified by arithmetic means, the output voltage becomes 2=K(0-RE)=K(C,/CP-1/N)・+KA/(jωCP)・v (8) . however,
K is the differential gain.

Here, if the values of C, P, and N are selected so that C,/CP=1/N (9), equation (8) can be expressed as follows.

Vp = KA/ (j ωc P ) ・v
(10) Here, since KA/(ωCP) is a real number, it does not affect the phase relationship between and ÷.

From equation (10), the output voltage is divided by the vibration speed of the piezoelectric body whose amplitude is proportional and whose phase is delayed by 90°.
will be detected.

Therefore, from equation (4) showing the relationship between velocity ÷ and voltage applied to the vibrator, equation (10) is Vp = KA2/ (ωC
PlZ+Z'l)・exp(-J(Cloveφ))
(11) The phase relationship between and can be divided into the following three cases.

iv. By delaying the voltage applied to the piezoelectric body or the phase of the output signal from the phase difference detection means by 90 degrees, the piezoelectric vibrator is always kept at the resonant frequency ω. Can be driven.

〔Effect of the invention〕

Therefore, in the drive control device for an ultrasonic motor according to the present invention, the vibration state of the vibrator can be detected extremely accurately by detecting the applied voltage and the energizing current. There is no need to provide a separate piezoelectric body for detection, and there is no need for wiring to extract the signal, which simplifies the motor manufacturing process and reduces the cost of the motor due to increased parts and complexity of the manufacturing process. It can now be prevented.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

As shown in Fig. 2, the ultrasonic motor (M) uses a piezoelectric material (
1) to which an elastic body (2) is fixed, a ring-shaped stator (3) that generates traveling waves of ultrasonic waves, and a rotor (4) that rotates in pressure contact with the stator (3). It is composed of That is, the stator (3) becomes a vibrator (3').

The piezoelectric body (1) has regions (A) and (B) in the circumferential direction.
It is divided into two parts, and each region (A) and (B) has a wavelength λ.
Adjacent sections are alternately polarized in the thickness direction at an interval of -2, and these regions (A).

(B) They are arranged with a three-quarter wavelength shift between them.

The region (A) is formed by applying high frequency voltages having a phase difference of 90° to the regions (A) and (B).

The standing waves generated in the stator (3) corresponding to (B) interfere with each other and are combined to form a traveling wave.

That is, the rotor (4) rotates due to the frictional force with the stator (3) based on the traveling waves 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 mechanical unit for the vibrator (3°). phase difference detection means (6) for detecting a phase difference caused by a difference between the resonant frequency and the frequency of the voltage applied to the piezoelectric body (1);
, that is, the state quantity detection means and its phase difference detection means (
The power supply means (6) compares the phase of the output signal with the applied voltage and maintains the phase difference at a set value.
5) frequency control means (7) for controlling the oscillation frequency;
It is comprised of a speed control means (8), etc., which controls 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). be.

The power supply means (5) is configured to vary the output voltage by changing the conduction rate by a switch (B5) via a drive circuit (DI) based on the output signal of the speed control means (8). Based on the output signal of the frequency control means (7), the DC chopper circuit (5a) that controls the frequency An inverter circuit (5b) is provided to vary the voltage.

The inverter circuit (5b) is a combination of two power supply split type half-bridge inverters to output two-phase square waves with a phase shift of 90 degrees, and each output terminal is connected to a step-up transformer (Tl). , via (T2),
The area (A) of the piezoelectric body (1) of the ultrasonic motor (M)
), and are connected to the electrodes provided in (B).

Note that the square wave is generated by the transformer (Tl), (T2)
The waveform is shaped into a sine wave by the leakage inductance.

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

The applied voltage detection means (6a) includes a bootstrap circuit (B1) on the secondary side of a transformer (PT) with a turns ratio of N:1.
The energizing current detection means (6b) is configured by connecting:
A bootstrap circuit (B2) is connected to the secondary side of a current transformer (CT) with a turns ratio of 1:P via a capacitor (C3) with a capacity of
), both of which are connected to the transformer (T2).
It is installed on the secondary side of the

The constants N, P, and C are the piezoelectric body (1
) is set so that Ca "C" P/N.

As a result of differential amplification of the output voltage VN of the applied voltage detection means (6a) and the output voltage Vc of the energizing current detection means (6b) by the calculation means (6c), the output voltage V is as follows. As described in the section above, the term includes a term representing the phase difference caused by the difference between the frequency of the applied voltage V and the resonant frequency of the vibrator (3').

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

The phase comparator (PC) and the low pass filter (LP
A phase correction means (PSC) for correcting the output voltage of the phase comparator (PC) is interposed between the phase comparator (PC) and the phase comparator (PC).

The phase comparator (PC) is connected to the applied voltage detection means (6
The output voltage VN of a) and the output voltage V of the calculation means (6c) are inputted via filters (Fl), (F2), and a comparator (COMI) that shapes the waveform into a square wave (C0M2). As shown in Fig. 3, both mold pressures VN
, VP outputs a voltage corresponding to the phase difference.

As shown in FIG. 4, the voltage controlled oscillator (VCO) makes its output frequency variable in accordance with the output voltage value of the phase comparator (PC) which is inverted by the low pass filter (LPF). be.

In other words, if the phase difference between the two pressures vN and vp is 90 degrees or less, the output voltage of the phase comparator (PC) will decrease.
The output frequency of the voltage controlled oscillator (VCO) increases, and the oscillation frequency of the inverter circuit (5b) increases.

Conversely, if the phase difference between the two types of pressures VN and VP is 90° or more, the output voltage of the phase comparator (PC) increases, so the output frequency of the voltage controlled oscillator (vCO) decreases,
This lowers the oscillation frequency of the inverter circuit (5b).

By the above operation, the phase difference between both mold pressures VN and VP is set to 90°.
In other words, the vibrator (3') can be driven by tracking the resonant frequency that varies due to changes in the temperature, etc. of the vibrator (3').

Furthermore, the frequency control means (7) corrects the output voltage of the phase comparator (PC) with the phase correction means (PSC), so that the ultrasonic motor (M) is most stable and efficient. The oscillation frequency is controlled so that the frequency is slightly higher than the resonance frequency, which is a good driving frequency.

[Another example]

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 constitute the applied voltage detection means (6a), but instead of the transformer (PT), a transformer (PT) with a resistance ratio of N:1 is used to constitute the applied voltage detection means (6a). N-1:1
VN may be taken out by connecting resistors in series.

2. In the previous embodiment, the phase difference detection means (6) is interposed on the secondary side of the transformer (T2) to detect the phase difference in the region (A) of the stator (3). However, the phase detection means (6) may be interposed on the secondary side of the transformer (TI) to detect the phase difference in the region CB). ) may be interposed respectively.

3. In the previous embodiment, the voltage V is applied to the phase comparator (PC).
N, VP: l Nha L/-ta (COMI), (C
0M2), but instead of the voltage VN, the voltage V applied to the piezoelectric body (1) is inputted via a comparator (C
It may also be input via OMI).

46 In the previous embodiment, a rotary type ultrasonic motor in which the stator was configured as a vibrator was explained, but the ultrasonic motor may be one in which the rotor is a vibrator or a linear type. Furthermore, it may be a compound vibrator type ultrasonic motor that controls the motion locus of the mass point by combining two vibrations having different vibration directions, and in this case, the voltage VN.

(2) By maintaining the phase difference of 90°, the most stable and efficient driving is possible.

Incidentally, although reference numerals are written in the claims section for convenient comparison with the drawings, the present invention is not limited to the structure shown in the accompanying drawings.

[Brief explanation of drawings]

The drawings show an embodiment of the ultrasonic motor drive control device according to the present invention, and FIG. 1 is a circuit diagram, and FIG. 2 (A) and ([7]
is the configuration diagram of the ultrasonic motor, Figure 3 is the output characteristic diagram of the phase comparator, Figure 4 is the output characteristic diagram of the voltage controlled oscillator, Figure 5 is the equivalent circuit diagram of the piezoelectric vibrator system, and Figure 6 is the ultrasonic motor. FIG. 7 is an equivalent circuit diagram of the sonic motor, and FIG. 7 is a circuit diagram of the phase difference detection means. (1) Piezoelectric body, (2) Elastic body, (3') Vibrator, (5) Power supply means, (6)...State quantity detection means, (6
a)...Applied voltage detection means, (6b)...
... energizing current detection means, (6c) ... calculation means, (M) ... ultrasonic motor.

Claims (2)

[Claims] 1. For an ultrasonic motor (M) having a driving vibrator (3') consisting of a piezoelectric body (1) and an elastic body (2), a power supply means (for supplying high-frequency power to the piezoelectric body (1)) 5
) and a state quantity detection means (6) for detecting the vibration state of the vibrator (3'), the drive control device for an ultrasonic motor comprising a state quantity detection means (6). an applied voltage detection means (6a) for detecting the voltage applied to the piezoelectric body (1); an energizing current detecting means (6b) for detecting the energizing current; and the applied voltage detecting means (6a) and the energizing current. A drive control device for an ultrasonic motor, comprising a calculating means (6c) for outputting the amount of deviation between the resonant frequency of the vibrator (3') and the frequency of the applied voltage from the output signal of the detecting means (6b). . 2. The applied voltage detection means (6a) includes a step-down circuit that steps down the applied voltage to N:1 and detects the applied voltage, and the energized current detection means (6b) includes a current transformer with a turns ratio of 1:P and its second transformer. 2. The superconductor according to claim 1, further comprising a capacitor having a capacitance C connected to the next side, and whose constants are set in a relationship of C_d=C·P/N with respect to the capacitance C_d of the piezoelectric body (1). Drive control device for sonic motor.