JPH0591767A - Drive circuit for composite vibrator type ultrasonic motor - Google Patents

Abstract

PURPOSE:To provide a drive circuit for composite vibrator type ultrasonic motors which can eliminate the possibility of thermal destruction of the ultrasonic motors by suppressing the heat generation of the motors by reducing the input power which is wastefully spent in a no-load state. CONSTITUTION:In this drive circuit which drives an ultrasonic motor provided with a stator equipped with torsional vibrators 2 and 3 and a longitudinal vibrator and rotor, a high-frequency oscillation circuit 15 and DC power source 14 are connected in parallel with the vibrators 2 and 3 through a transformer 13 and a current limiter which decides the upper limit value of the electric current supplied to the vibrators 2 and 3 is connected between the transformer 13 and power source 14. Therefore, no excessive input power is continuously inputted to the ultrasonic motor, because the current limiter limits the electric current supplied to the vibrators 2 and 3 at no-load time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite vibrator type ultrasonic motor using an electrostrictive vibrator.

[0002]

2. Description of the Related Art Conventionally, an ultrasonic motor having a structure shown in FIG. 3 is known as an example of the structure of this kind of ultrasonic motor. The ultrasonic motor A shown in FIG. 3 includes a bottom nut 1, annular torsional vibrators 2 and 3, a hollow holder 4, an annular vertical vibrator 5, a hollow head 6, a friction material 8 and a rotor 9. Are integrated by a central shaft 10. In the above structure, the bottom nut 1, the torsional vibrators 2, 3, the holder 4, the vertical vibrator 5, and the head 6 constitute a stator 7. Further, a spring member 11 is attached to the central shaft 10 to press the rotor 9 against the head 7 via the friction material 8, and
A bearing 12 is incorporated in a penetrating portion of the central shaft 10 at.

In the ultrasonic motor A having the above structure, the torsional vibrators 2 and 3 generate the rotational driving force of the rotor 9,
The vertical vibrator 5 controls contact between the stator 7 and the rotor 9. That is, when a voltage is applied to the torsional vibrators 2 and 3 while the head 6 and the rotor 9 are pressed and touched by the spring force of the spring member 11,
Due to the torsional force of 3, the rotors 9 are displaced in the circumferential direction and the rotor 9 rotates by a small angle. After the rotation, the pressing force of the rotor 9 against the head 6 is reduced. The amount of twist between them cancels out and disappears. When voltage is again applied to the torsional vibrators 2 and 3, the rotor 9 rotates again by a minute angle. By repeating the above operation, the rotor 9 can be rotated in a fixed direction, and the ultrasonic motor of this structure has a characteristic that a high torque can be easily obtained at a low speed and the operating noise is quiet. is doing.

FIG. 4 shows an example of the structure of a drive circuit for the composite vibrator type ultrasonic motor A constructed as described above. In FIG. 4, reference numerals 2 and 3 denote torsional oscillators, and the primary sides of the transformer 13 are electrically connected to these oscillators 2 and 3,
DC power supply 14 is provided on the secondary side of the transformer 13 via an FET.
And the high-frequency oscillation circuit 15 are connected. Although the drive circuit for the vertical vibrator 6 of the ultrasonic motor A is omitted in the drawing, a power source is actually connected to the vertical vibrator 6 so that a desired voltage can be applied.

[Problems to be Solved by the Invention]

In the composite vibrator type ultrasonic motor having the drive circuit having the above-mentioned structure, an AC voltage of several 100V to 1000V is applied to the vertical vibrator 6 and the torsional vibrators 2 and 3 at a frequency of about 20 kHz. And is driving. Here, FIG. 5 shows the relationship between the input power (W) and the torque (kg · cm) for the torsional vibrators 2 and 3 of the ultrasonic motor having the above-described configuration. As is clear from FIG. 5, the torsion element 2,
The power input to 3 becomes maximum when the torque = 0, and becomes smaller as the torque increases. Therefore, in the case of a drive circuit that applies a constant voltage, the maximum current is flowing when the torque is 0, that is, when there is no load on the ultrasonic motor, resulting in extremely large loss.

Here, for example, in the case of manufacturing a drive circuit for operating the ultrasonic motor in a sufficiently satisfactory manner in all the operating states of the ultrasonic motor, a capacity of a drive device capable of sufficiently driving the maximum power when the torque = 0 is set. You have to make a drive circuit. However, as shown in FIG. 5, for example, 8 kg
・ When driving a motor that requires a cm torque with an ultrasonic motor, a power of less than half the maximum power is sufficient, so the drive circuit for maximum input power will obviously have an excessive output circuit. There is a problem that the manufacturing cost is increased accordingly. However, conversely, when a drive circuit for 8 kg · cm is designed and the ultrasonic motor is continuously driven under no load for some reason (for example, the rotor of the ultrasonic motor is disconnected and the In this case, if the maximum input power is continuously input, the fuse of the drive circuit may be blown, and in the worst case, electronic components such as the transistor of the drive circuit may be destroyed. is there.

Further, when no load is applied, even though the maximum power is input to the ultrasonic motor, since the ultrasonic motor is not working, most of the input power is changed to heat, This may cause the ultrasonic motor to overheat, leading to deterioration or destruction of the ultrasonic motor itself.

The present invention has been made in view of the above-mentioned problems, and it is possible to reduce the input power wasted in the no-load state to suppress the heat generation of the ultrasonic motor and eliminate the risk of thermal destruction. It is an object to provide a drive circuit for a motor.

[0009]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a stator having a torsional vibrator and a longitudinal vibrator, and a rotor, and the torsional vibrator has a high frequency. In a circuit that drives a composite oscillator ultrasonic motor that applies a current to generate rotational force in the rotor and applies a predetermined voltage to the vertical oscillator to control contact between the stator and rotor, A high-frequency oscillation circuit and a DC power supply are connected in parallel via a transformer, and a current limiter that regulates the upper limit of the current value applied to the torsion element is incorporated between the transformer and the DC power supply.

[0010]

In the configuration of the present invention, the ultrasonic motor is supplied with the input power inversely proportional to the torque from the power source as in the conventional case. However, when the ultrasonic motor is unloaded for some reason and the maximum power is continuously input, the current limiter operates to limit the input. Therefore, the maximum power is not continuously input to the ultrasonic motor, the driving circuit is not overpowered, and the ultrasonic motor itself is not overheated or damaged.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the drive circuit of the present invention. In the drive circuit of this example, the same components as those of the conventional drive circuit shown in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. The difference between this embodiment and the conventional example is that a current limiter 16 is incorporated in series between the DC power supply 14 and the transformer 13. The drive circuit of this embodiment is also used by being connected to the composite drive ultrasonic motor A having the configuration shown in FIG. 3, like the conventional drive circuit.

The current limiter 16 is an ultrasonic motor A.
If a power more than the allowable value is input to the DC power supply 14
Is to reduce the voltage that is loaded. FIG. 2 shows an example of the configuration of the current limiter 16. The device of this example has a circuit configuration in which a resistor R, a transistor Tr ₁ , a transistor Tr ₂ and a reference voltage source are incorporated between an input terminal and an output terminal. According to this circuit configuration, the potential of the transistor Tr ₁ in the direction indicated by the arrow is VBE = i ₀ × R
Therefore, the relationship of i ₀ = VBE / R≈0.6 / R holds. Here, for example, when the resistance R is set to 1Ω,
At i ₀ = 0.6 / 1 = 0.6A, Tr ₁ is turned on and Tr ₂
In order to short the base emitter of Tr ₂ , Tr ₂ is turned off and the current is cut off. This can prevent an excessive current load on the ultrasonic motor.

If the ultrasonic motor A is driven by a drive circuit incorporating the current limiter 16, the ultrasonic motor A will be in a no-load state for some reason, and the ultrasonic motor A will be supplied with a large power from the DC power supply 14. When the power is about to be input, the current limiter 16 operates at a predetermined power value, and the voltage applied to the torsional vibrators 2 and 3 from the DC power supply 14 is not increased more than that value. That is, the power value applied to the ultrasonic motor A does not exceed a predetermined value. Therefore, no excessive power is input to the ultrasonic motor A, abnormal heat generation of the ultrasonic motor A does not occur, and no load is applied to the electronic components of the drive circuit and the components of the ultrasonic motor A. Therefore, even if the ultrasonic motor is in a no-load state, failure of the drive circuit and destruction of parts will not occur, and the ultrasonic motor itself will not be overheated and damaged. Further, since the drive circuit can be designed in accordance with the maximum load of the ultrasonic motor A when designing the drive circuit, it is not necessary to design a circuit with a wasteful capacity in consideration of a margin, and there is no such waste. Even if the circuit is used, the ultrasonic motor A is not deteriorated or destroyed.

[0014]

As in the conventional ultrasonic motor, the ultrasonic motor according to the present invention is supplied with the input power inversely proportional to the torque from the power source. However, even if the ultrasonic motor is unloaded for some reason and the maximum power is continuously input, the current limiter operates to limit the input power. Therefore, excessive input power is not continuously input to the ultrasonic motor. Therefore, under no load, not only the electronic components attached to the ultrasonic motor but also the electronic components attached to the drive circuit are not damaged by heat, and it is possible to prevent the ultrasonic motor itself from being overheated or damaged. Further, since the circuit can be designed without considering the excessive current, the cost of the electronic parts used for the circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a current limiter according to the present invention.

FIG. 3 is a cross-sectional view of an example of an ultrasonic motor.

FIG. 4 is a circuit diagram showing a configuration example of a conventional drive circuit.

FIG. 5 is a graph showing the relationship between input power applied to an ultrasonic motor and torque.

[Explanation of symbols]

 A Ultrasonic motor 2, 3 Torsional vibrator 5 Vertical element 7 Stator 9 Rotor 10 Center axis 13 Transformer 14 DC power supply 15 High frequency oscillation circuit 16 Current limiter

Claims (1)

[Claims] 1. A stator comprising a torsional oscillator and a vertical oscillator, and a rotor, wherein a high frequency current is applied to the torsional oscillator to generate a rotational force in the rotor, and a predetermined voltage is applied to the vertical oscillator. In a circuit that drives a composite vibrator type ultrasonic motor that controls the contact between the stator and rotor by applying a voltage, a high-frequency oscillator circuit and a DC power supply are connected in parallel via a transformer to the torsional vibrator. Between
A drive circuit for a composite vibrator type ultrasonic motor, characterized in that a current limiter for regulating the upper limit of the current value applied to the torsional vibrator is incorporated.