JPH07108105B2 - Ultrasonic motor driving method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ultrasonic motor or an ultrasonic linear motor that uses ultrasonic vibration as a drive source.

2. Description of the Related Art Regarding motors utilizing ultrasonic vibration, various structures and principles have already been patented or presented at academic conferences. The basis of those technologies is when a voltage is applied to a piezoelectric body,
It uses elongation or contraction. Basically, an electric field of several tens of kilohertz is applied to a ring-shaped or disk-shaped piezoelectric body, and the mechanical displacement generated in the piezoelectric body at that time is taken out through a frictional force.

Further, a linear motor in which a disk-shaped piezoelectric body is linearized has also been reported and operates with the same driving principle.

Problems to be Solved by the Invention The ultrasonic motor as described above has many drawbacks,
There is no report of practical application yet. The characteristics of the ultrasonic motor are similar to the characteristics of the DC motor, and the rotation speed changes depending on the load applied or the voltage applied to the motor. As a result, the rotation angle and the moving distance are not constant, and some means must be used and externally controlled in order to keep them constant. However, since adding a rotation speed detector to the outside increases the cost for the operation of the ultrasonic motor, it has been considered that such usage is not suitable.

It is possible to greatly expand the application range of the ultrasonic motor by providing the function of controlling the speed of the ultrasonic motor or providing the function of moving the rotation angle according to an external signal, but it is possible to inexpensively obtain a highly accurate position or speed. There was no technology to realize a controllable ultrasonic motor.

Means for solving the problem At the same time as measuring the wave number of the ultrasonic vibration for driving, the wave number of the output signal of the rotation speed detector provided in the ultrasonic motor is measured to detect the rotation speed from the rotation speed of the ultrasonic motor. From the relationship between the wave number of the output signal of the detector and the number of vibrations of the ultrasonic vibration, the position of the ultrasonic motor or Control the speed.

Action Simultaneously measure the wave number of ultrasonic vibrations excited in the stator, and at the same time measure the wave number of the output signal of the rotation speed detector installed in the ultrasonic motor, and measure the wave number of the output signal of the rotation speed detector and the wave number of the ultrasonic vibrations. From the relationship, the speed or rotation angle of the ultrasonic motor is controlled by interpolating between the output signals of the rotation speed detector by the wave number of ultrasonic vibration.

Example An ultrasonic drive motor uses ultrasonic vibration as a driving force, and vibrates the stator at an audible frequency of several tens of kilohertz per second or more, and a very small mechanical feed on the stator surface is used as the driving force of the motor. To do. The feed amount per vibration is extremely small, i.e., 1 micron or less. However, since a large number of feeds are made, a rotational speed of several hundred revolutions per minute is obtained.

The present invention uses a rotational speed detector having a relatively low resolution, and by interpolating during one resolution by the wave number of ultrasonic vibrations excited in the stator, that is, the wave number of the driving AC electric field, the position of the ultrasonic motor or This makes it possible to control the speed with high accuracy.

As an example, a motor operating at a rotation speed of 360 revolutions per minute makes 6 revolutions per second. If you are driving the stator of this ultrasonic motor at a frequency of 30 kHz,
Frequency (wave number) of ultrasonic vibration required for one rotation of the rotor
Is 30k / 6 = 5k, that is, the number of ultrasonic vibrations required to rotate the rotor once is 5000. As a result, the feed amount per rotor (movement amount of rotor) is 360 ° ÷ 5000 = 0.072 °, which is a single ultrasonic vibration of the stator.
It indicates that the feed is 072 °.

In order for the ultrasonic drive motor to rotate accurately, it is a condition that the ultrasonic drive motor starts correctly at the same time as the ultrasonic vibration starts, and also stops correctly when it stops. With conventional motors, such a concept has not been established.

There are pulse motors and step motors as motors that relatively meet these requirements. However, since the number of gaps for performing magnetic coupling is finite, the movement does not continue and vibrations called cogging occur. Not easy to use.

Since the pulse motor cannot obtain a high pulse response speed, a pulse motor having a high-speed response characteristic has been demanded.

When driving an ultrasonic motor, the generation of ultrasonic vibration
The motor torque is directly generated. Furthermore, the stop of ultrasonic vibration is instantaneously activated as a braking action, so that it is characterized by immediate stop.

Next, an embodiment of the ultrasonic motor according to the present invention will be shown. First
In the figure, 1 is a rotor which is a rotation take-out portion, and 2 is a stator which generates ultrasonic vibrations and serves as a motor driving portion, and is constituted by laminating a piezoelectric body 3 on an elastic body such as metal or ceramic. Reference numeral 4 indicates a fixed base of the motor. An encoder 5 for detecting the speed or position of the ultrasonic motor is attached to the rotor 1. Reference numeral 6 denotes a detector including a light emitting diode and a photodiode for optical detection. The light emitted from the light emitting diode of the detector 6 is reflected by the encoder 5 and received by the photodiode of the detector 6.

In the embodiment shown in FIG. 1, 360 ° is set to 1 as the encoder 5.
The structure body, which is divided into 024 and has slits, is integrated with the rotor 1 at a position where it is searched into the stator 2.

As mentioned above, the characteristics of ultrasonic motors are
Although it is characterized by the responsiveness of stopping and stopping, FIG. 2 shows current and voltage waveforms of rotating and stopping. The horizontal axis represents the time axis and the vertical axis represents the output waveform. Fig. 2 shows rotation speed 200r.pm, torque 100g-
Regarding the characteristics under the load of cw, it is shown how excellent the stopping characteristics of the ultrasonic motor are.

In FIG. 2, (a) shows the voltage-current characteristics at the time of rising, and (b) shows the voltage-current characteristics at the time of falling. It was confirmed that the measurement data was correct by the fact that the data of both of them coincided with the measurement by the rotary and the encoder.

In FIG. 2, the wave number of ultrasonic wave drive is about 200 waves during the output of one pulse of the encoder. This is an ultrasonic motor with an AC electric field of 30 kHz described as an example on page 4 of the present specification. It corresponds to the case where the rotation speed of the ultrasonic motor becomes 8.789 rpm when is driven. To explain this, the number of revolutions per second of the ultrasonic motor is 8.789 ÷ 60 = 0.1465rps Therefore, the wave number of ultrasonic vibration required for one revolution of the rotor 1 is 30k ÷ 0.1465 = 204.78k, that is, one revolution of the rotor. The wave number of the ultrasonic vibration required to make it is 204780 waves. From this, the wave number of ultrasonic vibration per pulse of the rotary encoder is 204780 ÷ 1024 = 200.

Therefore, the accurate position can be known from the output of the rotary encoder, and during one output pulse of the rotary encoder, the wave number of the ultrasonic vibration of the stator 2 is used as the position signal to increase the resolution of the rotary encoder by 200 times. Can be increased to That is, in the embodiment, theoretically, a resolution of 360/1024/200 = 0.00176 ° can be realized, but a resolution of 0.01 ° was actually realized.

That is, the output of the rotary encoder is usually used as a position or speed signal for position or speed control, and the wave number of ultrasonic vibration of the stator 2 is used as a position or speed signal during one output pulse of the rotary encoder. By using it, it is possible to realize an ultrasonic motor capable of highly accurate position or speed control even when a rotary encoder having a low resolution is used.

The experiment evaluated the cumulative number of revolutions and the deviation from the set value over 40,000 revolutions, but the cumulative error was 1/40000 or less. From this result, it was confirmed that the stop was performed within the setting range of 360 ° with an accuracy of 0.01 ° or less.

Further, FIG. 3 shows the characteristics when position control is performed by using the rotary encoder with 1024 resolution per rotation described above and dividing the resolution into 200 equal parts by the wave number of ultrasonic vibration of the stator. From the figure, it can be seen that the position control can be performed with good linearity even during the output pulse corresponding to one resolution of the rotary encoder with respect to the rotation angle during one rotation of the rotor.

EFFECTS OF THE INVENTION According to the present invention, even if a rotary position detector having a low resolution is used, one resolution of the rotary position detector is interpolated by the wave number of ultrasonic vibration of the stator and used for the position or speed control signal. It is possible to provide an ultrasonic motor capable of highly accurate position or speed control even at low cost.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of an ultrasonic pulse motor according to an embodiment of the present invention, FIG. 2 is a graph showing rise and fall characteristics of voltage and current of the motor, and FIG. 3 is a rotation angle of the motor. It is a graph which shows a pulse number characteristic. 1 ... Rotor, 2 ... Stator, 3 ... Piezoelectric body, 4 ...
Support base, 5 ... Encoder, 6 ... Detector.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Kawasaki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References: Shou 58-54709 (JP, U)

Claims (1)

[Claims] 1. A rotor, which is movably contacted with a stator composed of an elastic body and a piezoelectric body, is applied with an AC electric field to the piezoelectric body to excite ultrasonic vibrations on the stator to move the rotor. A driving method of an ultrasonic motor to be driven, wherein a rotation position detector of the rotor is installed, and a position information output signal of the rotation position detector and the position information output signal
An ultrasonic wave characterized in that an interpolation signal obtained by interpolating between resolutions based on the wave number of ultrasonic vibrations excited in the stator within the position information output time of the one resolution is used as a position control signal of the rotor. Motor driving method.