JPH0697858B2 - Ultrasonic motor drive circuit - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an ultrasonic motor utilizing ultrasonic vibration, and more particularly to a drive circuit for controlling a piezoelectric body which excites an elastic body.

(Background of the Invention) An ultrasonic motor is composed of an elastic ring 17 and a piezoelectric body 1 as shown in FIGS. 4 and 5 as disclosed in "Nikkei Mechanical, No. 1983.2.28" issued by McGraw-Hill. It is composed of a stator portion 16 and a rotor portion 15 which are configured. Between the terminals Mr-Mg and between the terminals Ml-Mg of this piezoelectric body 1,
It can be regarded as a capacitor each having a certain capacitance Cr and Cl. When the piezoelectric body 1 of the stator portion 16 is excited at a specific frequency fm, a traveling wave having the same frequency as that on the rotor side surface of the elastic ring 17 is generated most efficiently. This specific frequency fm is hereinafter referred to as the mechanical resonance frequency of the ultrasonic motor. This mechanical frequency fm
When the traveling wave is generated in the stator portion 16, the rotor portion 15 is driven.

The drive circuit of this ultrasonic motor, as shown in FIG.
It is composed of a piezoelectric body 1, coils Ll and Lr, and an oscillator 2. The piezoelectric body 1 and the oscillator 2 are connected at terminals Gg and Mg, and are also connected at terminals Gr and Mr, and at terminals Gl and Ml via coils Lr and Ll, respectively.
The oscillator 2 generates a sine wave having an oscillation frequency f having a phase difference of 90 degrees between the terminals Gr-Gg and the terminals Gl-Gg. The coils Ll and Lr are provided to efficiently supply electric power to the ultrasonic motor. Here, the inductance Lr of the coil Lr is set to the mechanical resonance frequency fm of the ultrasonic motor.
, So that the drive circuit resonates in series, Lr = 1 / 4π ² · fm · Cr (where Cr is the capacitance of the capacitor Cr), and similarly, the inductance of the coil Ll
Also select Ll. When a sine wave with an oscillating frequency fm is generated from the oscillator 2, a voltage Vf, Vf = V / ωCr · R (where ω = 2πfm , R is the resistance value of the lead wire, etc.), and the elastic ring is excited to generate the first standing wave. Similarly, very large voltages Vf ′ and Vf ′ = V / ωCl · R (where ω = 2πfm, R is the resistance value of the lead wire, etc.) are applied between the terminals Ml and Mg, and the elastic ring is excited. The second standing wave is generated.

Therefore, the generator 2 generates oscillating frequencies with 90 degrees different phases.
When two sine waves fm are applied to the piezoelectric body 1 at the same time, the first standing wave and the second standing wave are combined in the stator section 16 to generate a traveling wave, and the rotor section 15 is rotated.

However, when the environment in which the ultrasonic motor is driven changes and changes in temperature or changes with time occur, the mechanical resonance frequency fm of the ultrasonic motor is hardly affected, whereas the terminal Mr- Since the capacitances Cr and Cl between Mg and between terminals Ml and Mg change greatly, the electrical resonance frequency fe of the piezoelectric body
Will change. As a result, since the mechanical resonance frequency fm of the ultrasonic motor and the electric resonance frequency fe of the ultrasonic motor do not match, the efficiency of generation of the traveling wave is reduced and the driving efficiency of the motor is reduced.

(Object of the Invention) The present invention solves this drawback, and by making the electric resonance frequency of the drive circuit of the ultrasonic motor substantially match the mechanical resonance frequency of the ultrasonic motor at all times, the ultrasonic motor due to environmental changes It is an object of the present invention to provide a drive circuit for an ultrasonic motor, which functions so as to prevent the drive efficiency of the ultrasonic motor from being lowered even if the drive conditions of the above change.

(Summary of the Invention) In order to achieve such an object, the present invention provides a variable impedance element circuit and its control circuit in order to match the electrical resonance frequency of a drive circuit with the mechanical resonance frequency of an ultrasonic motor. The technical point is that the drive efficiency of the ultrasonic motor is prevented from deteriorating due to changes in temperature and changes with time.

(Embodiment) FIG. 1 to FIG. 3 show a preferred embodiment of the present invention,
FIG. 1 shows a schematic diagram of a drive circuit of an ultrasonic motor. In FIG. 1, the impedance element circuit 3 and the impedance element control circuit 4 are incorporated in the drive circuit, and the change in the electrostatic capacitance of the piezoelectric body 1 is adjusted by controlling the impedance element circuit 3. In order to always match the electric resonance frequency of the drive circuit including the impedance element circuit 3 and the mechanical resonance frequency of the ultrasonic motor, the impedance element control circuit 4 sets the voltage between Mr and Mg of the piezoelectric body 1
_C and the voltage _L of the coil Lr are picked up between the terminals Ig-Ic and between the terminals Ig-Il, and the magnitudes of both voltages are compared.
A control signal for controlling the impedance element circuit 3 is output from the terminal group O. By the control signal from the output terminal group O of the impedance control circuit 4, the impedance element circuit 3 functions to increase or decrease the internal capacitive reactance component and to make the both voltages equal. This principle will be described below.

In FIG. 1 (B), the terminals of the piezoelectric body 1 of FIG. 1 (A)
The capacitor corresponding to Mr-Mg is shown by capacitor Cr, and the voltage of the AC power supply in oscillator 2 in FIG. 1A is the voltage of capacitor Cr, the voltage of coil Lr is _C.
L, and the voltage of the resistor R represents the _L.

Inductive reactance X _L and capacitive reactance X _{C of} this circuit
It is expressed as _{X L = ωLr X C = 1} / ωCr.

Resonance condition of this circuit, since the _{X L = X C | X L} · | = | X C · | | L | = | C | become.

Therefore, the conditions under which the piezoelectric body 1 resonates are as follows: Therefore, the capacitance Cr and the inductance Lr are set so as to satisfy the above equation.

If a temperature change or the like occurs as described above, the capacitance of the piezoelectric body 1 changes. Generally, when the temperature rises, the capacitance Cr of the piezoelectric body 1 increases with Cr = Co + ΔC (Co is the capacitance of the piezoelectric body 1 before the temperature change, ΔC is the change amount of the capacitance due to the temperature change). To do.

Therefore, equation (1) becomes And conversely, when the temperature decreases, the capacitance Cr becomes Cr = Co
When it is decreased as −ΔC, | _L | <| _C |, and the electric resonance frequency and the mechanical resonance frequency are matched by detecting the voltage _{C of the} piezoelectric body 1 and the voltage _{L of the} coil. Can be controlled to

Since the temperature varies depending on the environment in which the ultrasonic motor is driven, the capacitance of the piezoelectric body 1 changes due to the temperature change,
The balance between the voltage of the piezoelectric body 1 (voltage between the terminals Mr and Mg) and the voltage of the coil Lr is lost. In other words, the electric resonance frequency fe of the drive circuit is The electrical resonance frequency fluctuates and does not match the mechanical resonance frequency of the ultrasonic motor. At this time, both voltages are detected between the terminals Ig-Ic and the terminals Ig-Il of the impedance element control circuit 4 as described above, and the impedance element control circuit 4 increases or decreases the capacitive reactance component of the impedance element circuit 3. Then, the control signal is output from the terminal group O. By the control signal output from the terminal group O, the capacitive reactance component of the impedance element circuit 3 is increased or decreased in the direction in which the mechanical resonance frequency of the ultrasonic motor matches the electrical resonance frequency of the drive circuit.

Therefore, the electrical resonance frequency of the drive circuit is always matched with the mechanical resonance frequency of the ultrasonic motor by the impedance element control circuit 4 even if the temperature of the environment changes, and the drive efficiency is not deteriorated by disturbance. It can be prevented.

FIG. 2 is a circuit diagram showing an example of the impedance element circuit 3. In FIG. 2, the impedance element circuit 3
Connects the capacitance elements C1 to C5 and the switches Sw1 to Sw5, respectively, and controls the switches Sw1 to Sw5 by a control signal from the terminal group O (O1 to O5) of the impedance element control circuit 4. I am configuring. If the capacitance of each of these capacitance elements C1 to C5 is C1 to C5, for example, set C2 = C1 / 2, C3 = C1 / 4, C4 = C1 / 8, C5 = C1 / 16 To be done. The switches Sw1 to Sw5 are configured by relay switches, analog switches, and the like.

FIG. 3 is a circuit diagram showing an example of the impedance element control circuit 4. In FIG. 3, the coil Lr is provided between the terminals Ig and Il and between the terminals Ig and Ic of the impedance element control circuit 4.
Voltage _L and the voltage _{C of the} piezoelectric body 1 are input, and both voltages are input to the sample hold circuits 5 and 5 ', respectively. The sample and hold circuits 5 and 5'hold the maximum values ( _L ) _max and ( _C ) _max of the input voltages _L and _C until the reset signal is input from the mono-multivibrator 12 ', and comparators 6 and 6'. Are typing in. This maximum value ( _L ) _max (or _C ) _max )
Is the input voltage for a certain period until the reset signal is output
It is the average value of the maximum values of _L (or _C ). The maximum values ( _L ) _max and ( _C ) _max are compared by the comparators 6 and 6 ', and it is detected that the capacitance of the piezoelectric body 1 has changed due to temperature change, and | _L |> | _C | If so, the terminal 106 outputs an L level signal, and the terminal 107 outputs an H level signal. If | _L | <| _C |, the terminal 106 outputs an H level signal and the terminal 107 outputs an L level signal. Therefore, | _L | ≠ | _C |
If so, the OR gate 9 outputs an H level signal from the terminal 108.

The timing circuit composed of the oscillator 11 and the mono-multivibrator 12, 12 'activates the up / down counter 7 to output the output terminal O of the switch driver 8.
A control signal is output from (O1 to O5) to the impedance element 3. As shown in FIG. 3 (B), the terminal 104
And 103 generate pulse signals based on the pulse signals output from the terminal 105. The H level signal from the terminal 104 at the time point t1 passes through the AND gate 10 only when the terminal 108 of the OR gate 9 is the H level signal to output the H level signal from the terminal 109 to operate the up / down counter 7. As shown in FIG. 3 (B), immediately after the H level signal is output from the terminal 104, the reset signal is output from the terminal 103 of the mono-multivibrator 12 'from the terminal 103 to the time t3 at time t2. The maximum values ( _L ) _max and ( _C ) _max are cut as they are input to 5 '. At time t3, the mono multivibrator 12 '
Since the reset signal from is cut, the sample and hold circuits 5 and 5'output the maximum voltage ( _L ) _max and ( _C ) _max in the section (time points t3 to t4).

At that time, if | _L | ≠ | _C |
Since the H level signal is output from the AND gate 10, the H level signal is output from the AND gate 10 as described above.

In this way, while | _L | ≠ | _C |, the repetitive pulse signal is output to the up / down counter 7.

The internal counter of the up / down counter 7 is increased / decreased by the output signal from the comparator 6, and the terminal 106 becomes H level.
When the internal counter receives one pulse from the AND gate 109 while outputting the level signal, for example, the 5-bit output signal of the up / down counter 7 becomes [10000].
_{If it is (2)} , it will increase one step as [10001] ₍₂₎ . On the contrary, when the terminal 106 outputs the L level signal, when the internal counter receives one pulse from the AND gate 106, the output of the up / down counter 7 becomes [10].
If it is 000] ₍₂₎ , it is configured to be further reduced as [01111] ₍₂₎ . The switch driving driver 8 outputs a control signal for turning on / off the switches Sw1 to Sw5 shown in FIG. 2 to the output terminal O in response to the 5-bit output signal [10000] ₍₂₎ output from the updun counter 7. (O1
~ O5) (the corresponding switches Sw1 to Sw5 are turned on based on '1' of the output signal, and the corresponding switches Sw1 to Sw5 are turned off based on '0' of the output signal). As described above, the output signal of the up / down counter 7 increases from the AND gate 109 for each pulse signal if the terminal 106 outputs the H level signal, or the output signal of the terminal 106.
Outputs an L level signal, it decreases by 1 pulse signal to control the switch driving driver 8 to turn on / off the switches Sw1 to Sw5 of the impedance element circuit 3. In this way, by inputting the control signal from the output terminal O of the impedance element control circuit 4 to the impedance element circuit 3, the switches Sw1 to Sw5 of the impedance element circuit 3 are turned on / off respectively, and as a result, the impedance element circuit Since the combined capacitance of the capacitances C1 to C5 of 3 and the capacitance Cr (and Cl) of the piezoelectric body 1 is created, the electrical resonance frequency is controlled and matched with the mechanical resonance frequency.

Therefore, the impedance element control circuit 4 uses the terminals Ig-Il
By detecting the voltage _L and the voltage _C at the terminals and the terminals Ig-Ic, the maximum voltages ( _L ) _max and ( _C ) _max from the sample hold circuits 5 and 5'are detected by the comparators 6 and 6 '.
, And the switch driving driver 8 is operated as described above to control the impedance element circuit 3 until both voltages match. When the two voltages match, that is, when the electrical resonance frequency and the mechanical resonance frequency match, an L level signal is output from the terminals 106 and 107, and the output of the OR gate 9 becomes an L level signal.

As a result, the up / down counter 7 does not operate, the switch driver 8 does not operate similarly, and the impedance element circuit 3 does not operate.

The present embodiment is not limited to the above-mentioned one,
In the embodiment, the capacitor is used to correct the change in impedance of the piezoelectric body 1, but a coil may be used instead of the capacitor, for example. Further, in the present embodiment, the series resonance circuit in which the piezoelectric body and the coil are connected in series is used, but a parallel resonance circuit in which the piezoelectric body and the coil are connected in parallel may be used.

(Effects of the Invention) According to the present invention, the variable impedance element circuit and the control circuit for controlling the variable impedance element circuit are provided in the drive circuit, so that when the ultrasonic motor is driven, there is a disturbance such as a temperature change or a temporal change due to a change in environment. In addition, since the electric resonance frequency of the drive circuit is always made to substantially match the mechanical resonance frequency of the ultrasonic motor, it is possible to prevent the deterioration of drive efficiency due to disturbance and obtain a highly practical ultrasonic motor. it can.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 (A) is a schematic diagram of a drive circuit of an ultrasonic motor, and FIG. 1 (B) shows the principle of FIG. 1 (A). The principle diagram shown in FIG. 2 is a circuit diagram of the impedance element circuit of FIG.
FIG. 3A is a circuit diagram of the impedance element control circuit of FIG. 1A, and FIG. 3B is an explanatory diagram showing the operation timing of FIG. 3A. FIG. 4 is a perspective view showing a conventional ultrasonic motor, and FIG. 5 is a circuit diagram of the drive circuit shown in FIG. (Explanation of symbols of main parts) 1 ... Piezoelectric body 2 ... Oscillator 3 ... Impedance element circuit 4 ... Impedance element control circuit Lr, Ll ... coil

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-56-133082 (JP, A) JP-A-59-46692 (JP, A) IEICE Technical Report Vol. 84 No. 93 (US84-22) P. 23-30 (July 23, 1984)

Claims (1)

[Claims] 1. A drive circuit of an ultrasonic motor for driving an ultrasonic motor having an elastic body and a piezoelectric body for exciting the elastic body, comprising: a variable impedance element circuit connected in parallel to the piezoelectric body; A control circuit for controlling the variable impedance element so that a mechanical resonance frequency of the ultrasonic motor and an electric resonance frequency of the drive circuit including the variable impedance element circuit are substantially equal to each other. The drive circuit for the ultrasonic motor.