JPS62201071A - Ultrasonic wave motor - Google Patents

Abstract

PURPOSE:To start smoothly and enhance reliability, by providing the voltage application circuit of an ultrasonic wave motor with positive characteristic thermistors. CONSTITUTION:Into the driving voltage application circuit of the main unit 10 of an ultrasonic wave motor, positive characteristic thermistors 11, 12 are inserted respectively in series, and the main unit is composed so that an input voltage V1, V2 with the phase difference of 90 deg. via the positive characteristic thermistors 11, 12 may be applied to. When the driving voltage V1, V2 is applied to, then great rush voltage is applied to because the thermistors 11, 12 resist low on the initiation, and the main unit 10 of the ultrasonic wave motor is exactly started. After that, a resistance value is suddenly increased by the self-generated heat of the thermistors 11, 12, and with the value and the impedance of the main unit 10 of the motor, voltage is divided, and given limited voltage is applied to.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic motor formed by integrating a piezoelectric element and a diaphragm, and particularly to an improvement in initial rush voltage application means.

[Conventional technology]

FIGS. 5(a) and 5(b) are diagrams showing a rotary ultrasonic motor using traveling plate waves. In the figure, 1 is a piezoelectric element, 2 is an elastic ring, 3 is a slider, and 4 is a rotor. Such an ultrasonic motor has the following advantages over an electromagnetic motor.

■Does not require a central axis.

■Thin and lightweight.

■There is no exchange of magnetic influence.

■The component structure is simple and highly reliable.

■Low speed and high torque can be obtained without gears.

■There is no backlash and positioning is easy.

■The rotor rotates and chucks against the stator.

It can take on three states: floating.

In order to take advantage of these advantages, various applied techniques are being researched. One example of this is considered to be camera lens drive.

FIG. 6 is a diagram showing one example. That is, piezoelectric element 1
, an elastic ring 2, a rotor 4, etc., is incorporated into the lens barrel of the camera, and the rotation of the ultrasonic motor is converted into forward and backward movement of the lens barrel to drive the lens. When using an ultrasonic motor to drive a camera lens in this way, the problem is how to set the driving voltage of the ultrasonic motor. That is, since the camera is used in various postures, the driving voltage varies depending on the posture. Therefore, if the drive voltage is set too low, a phenomenon may occur in which the device operates normally in one orientation but does not operate normally in another orientation. Furthermore, if the drive voltage is set too high, the device will operate normally regardless of its orientation, but it will always supply excessive energy, which will require a battery with a large capacity.

As a means to eliminate such problems, there is a means of applying a rush voltage only at the initial stage of rotation. In this type of conventional rush voltage application means, the rush voltage application time is set by a timer circuit, and a large rush voltage is applied only for a set period as shown in FIG. is applied to drive the ultrasonic motor. In addition, in FIG. 7, time points t1 to t3
is a motor drive period, and time t3 to t4 is a motor stop period.

[Problems to be Solved by the Invention] The conventional rush voltage applying means described above requires a timer circuit, etc., so it is difficult to incorporate it into a small camera due to space considerations. There was a risk of malfunction, and there were problems with reliability.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an ultrasonic motor equipped with a rush voltage applying means that can be easily incorporated into a small camera, etc., has no risk of malfunction, and can be expected to operate with high reliability. purpose.

[Means for solving problems]

In order to solve the above-mentioned problems and achieve the object, the present invention takes the following measures. That is, in an ultrasonic motor that integrates a piezoelectric element and a diaphragm, a positive temperature coefficient thermistor is inserted and connected in a voltage application circuit for excitation of traveling waves.

[Effect]

By taking such measures, the number of component parts is extremely small, making it possible to reduce the size of the device, and since there is no switch section, failures hardly occur.

〔Example〕

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

In the figure, 10 is an ultrasonic motor main body, and 11 and 12 are a pair of positive temperature coefficient thermistors. That is, in the drive voltage application circuit of the ultrasonic motor main body 10, a positive temperature coefficient thermistor 11.
12 are interposed and connected in series, and an input voltage Vl having a phase difference of 90° is applied via these positive characteristic thermistors 11 and 12.

V2 is applied.

Positive characteristic thermistors 11 and 12 are made of barium titanate,
Rare earth elements such as samarium, strontium, manganese, etc. are added and sintered at 1300°C to 1400°C,
Nickel is vapor-deposited on both sides.

FIG. 2 is a diagram showing the resistance-temperature characteristics of the PTC thermistor 11.12, and FIG. 3 is a diagram showing the resistance temperature characteristics of the PTC thermistor 11.12.
12 is a diagram showing current-voltage characteristics of No. 12. As shown in the figure, the positive temperature coefficient thermistors 11 and 12 have a characteristic that the resistance value increases rapidly when the temperature exceeds a predetermined temperature Tc. The temperature Tc is preferably about 60° C. in consideration of the influence of ambient temperature, and the strontium content is determined so as to achieve the above temperature. Note that in the temperature range from normal temperature to Tc, that is, 60° C., it is desirable that the resistance value is set to be approximately constant and 10Ω or less. On the other hand, the impedance of an ultrasonic motor is usually 100 to 100 in the driving frequency range.
It is about 200Ω.

Therefore, the slope of the resistance temperature characteristic is determined so that the resistance value after the resistance increases due to self-heating of the positive temperature coefficient thermistors 11 and 12 is equal to or less than the impedance of the ultrasonic motor. When applied to devices other than Naorimara, etc., where there are no particular restrictions on power supply capacity, there is no need for special restrictions on the resistance value after self-heating as described above. In other words, the basic condition is that the specific resistance at room temperature is small.

In this embodiment configured as described above, the drive voltage V
When l and V2 are applied, a large rush voltage is applied because the positive temperature coefficient thermistors 11 and 12 initially have low resistance. Therefore, no matter what posture the camera or the like is used in, the ultrasonic motor main body 10 is reliably activated. When current flows through the PTC thermistor 11.12 when the rush voltage is applied, the temperature of the PTC thermistor 11.12 rises due to self-heating due to Joule heat, and when the temperature reaches Tc, the resistance value of the PTC thermistor 11.12 increases. or rise rapidly. Therefore, after this, the ultrasonic motor main body 10
A certain limited voltage divided by the impedance of the positive temperature coefficient thermistor 11 and the resistance value of the positive temperature coefficient thermistor 11, 12 is applied.

In other words, a large rush voltage is applied only at the initial stage of application of the drive voltage.

In the above operation, if the response time of the positive temperature coefficient thermistors 11 and 12 is long, the next drive cannot be performed effectively. Therefore, in this embodiment, the positive temperature coefficient thermistor 11.1
The heat capacity of 2 is made small so that it generates heat instantly and cools down instantly, thereby shortening the response time. According to the experimental results, it was confirmed that a response time of 100 m5ec or less could be obtained.

As described above, according to this embodiment, the positive temperature coefficient thermistor 11.
By simply adding 12, the desired purpose can be achieved, so
It is small and lightweight. Moreover, since it does not have a switch section, failures are less likely to occur and reliability is high.

FIG. 4 is a diagram showing a second embodiment of the present invention.

This second embodiment is an example in which a coil 13 is inserted into one side of the excitation circuit and only one positive temperature coefficient thermistor 11 is used as a means for applying a drive voltage having a phase difference of 90°. This embodiment also provides the same effects as the first embodiment.

-The present invention is not limited to the above embodiments,
Of course, various modifications can be made without departing from the gist of the invention.

〔Effect of the invention〕

According to the present invention, in an ultrasonic motor formed by integrating a piezoelectric element and a diaphragm, a positive temperature coefficient thermistor is inserted and connected in a voltage application circuit for excitation of traveling waves, so that it does not matter what the orientation of the motor body is. Not only can startup be performed smoothly, but the number of component parts is extremely small, making it possible to achieve miniaturization, and since there is no switch section, there are almost no occurrences of failures. In this way, it is possible to provide an ultrasonic motor equipped with a rush voltage applying means that can be easily incorporated into a small camera, etc., has no risk of malfunction, and can be expected to operate with high reliability.

[Brief explanation of drawings]

Figures 1 to 3 are diagrams showing a first embodiment of the present invention.
The figure is a circuit diagram showing the configuration, FIG. 2 is a resistance-temperature characteristic diagram of a positive temperature coefficient thermistor, and FIG. 3 is a current-voltage characteristic diagram. FIG. 4 is a circuit diagram showing a second embodiment of the present invention. Figure 5 (a
)(b) to FIG. 7 are diagrams for explaining the prior art. DESCRIPTION OF SYMBOLS 1... Piezoelectric element, 2... Elastic ring, 3... Slider, 42 rotor, 10... Ultrasonic motor main body, 11
．． 12...Positive characteristic thermistor, 13...Phil. Applicant's agent Patent attorney Atsushi Tsuboi Figure 1 Figure 2 Figure 3 Figure 4 Special 81 Office Official Tuition fees Shield department Toshiro 1. Indication of the matter lt'y Application No. 61-0711063 2, Name of the invention Ultrasonic motor 3, Person making the amendment Relationship to the case Patent applicant (037) Olympus Optical Industry Co., Ltd. 4, Agent Tokyo Minato No. 17 Mori Building, 1-26-5, Toranomon, 1-10
5 Telephone: 03(502)3181 (main representative)
6. Subject of correction

Claims (1)

[Claims] An ultrasonic motor formed by integrating a piezoelectric element and a diaphragm, characterized in that a positive temperature coefficient thermistor is inserted and connected in a voltage application circuit for excitation of traveling waves.