JPH03261385A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To drive an ultrasonic motor with a required speed while a highly efficient operation is maintained by a method wherein a detecting means which detects the fluctuation information of a load and a phase control means which controls the phase of an input voltage applied to an oscillator in accordance with the output of the detecting means are provided. CONSTITUTION:The electrode 26 of a first piezoelectric unit 22 and the electrodes 27a and 27b of second piezoelectric units 23a and 23b are connected to amplifiers 60a and 60b. A phase detecting circuit 63 is electrically connected to the amplifiers 60a and 60b and phase information is supplied to a control circuit 64. Further, the speed variation of an ultrasonic motor 30 is detected by a speed detecting means such as an optical encoder 65a and, at the same time, speed information is supplied to the control circuit 63. If the load of the ultrasonic motor fluctuates, the phase of an input voltage applied to an oscillator is controlled in accordance with the fluctuation.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ultrasonic motor drive device that uses ultrasonic vibration energy as a drive source, and more particularly to an ultrasonic motor whose speed can be controlled. It is.

[Prior art] In recent years, various types of ultrasonic motors have been developed that utilize the high-frequency mechanical vibration energy of ultrasonic vibrators and use frictional force as a driving source.
Applied research is underway. In this method, a movable element is pressed against an ultrasonic vibrator, and thrust is generated by frictional force caused by the pressing force to perform relative motion. As a conventional example, a standing wave type ultrasonic motor is shown in FIG.

In the linear ultrasonic motor 1, an ultrasonic vibrator 3 is fixed to a yoke 2, and a drive section 4 is formed at one end of the ultrasonic vibrator 3. A movable element 5 is pressed onto the drive section 4 by a rubber roller 6, and the movable element 5 is attached to the yoke 2.
It is supported by linear hair rings 7a and 7b fixed to.

In the linear ultrasonic motor 1 configured as described above,
When the ultrasonic transducer 3 is excited, the movable element 5 receives a driving force due to the substantially elliptical vibration of the ultrasonic transducer 3, and moves in the direction of arrow A in the figure. This driving force is generated by the frictional force between the drive section 4 and the movable element 5.

In order to perform high-speed drive or constant-speed drive in such an ultrasonic motor, for example, Japanese Patent Application Laid-Open No. 59-2044
As seen in Japanese Patent No. 77, in many cases, an ultrasonic vibrator is provided with a piezoelectric element for detecting a vibration state, and speed control is performed by controlling the vibration amplitude or drive frequency of the ultrasonic vibrator.

[Problems to be Solved by the Invention] In the above-mentioned ultrasonic motor, the vibration amplitude, drive frequency, etc. are controlled according to the desired speed.

However, this alone did not allow the ultrasonic motor to be driven under optimal conditions, and it could not necessarily be said that the ultrasonic motor was controlled under highly efficient operating conditions. In other words, the standing wave type ultrasonic motor has a problem in that the optimal input voltage phase changes due to load fluctuations, which affects the drive characteristics.

The present invention has been made to solve the above-mentioned problems, and maintains high efficiency operation in a standing wave type ultrasonic motor by controlling the phase of the input voltage during load fluctuations. The purpose of this invention is to obtain a standing wave type ultrasonic motor that can be driven at a desired speed.

[Means for Solving the Problems] In order to achieve this object, the speed control device for an ultrasonic motor of the present invention includes a stationary vibrator that is excited with at least two vibrations whose vibration directions are substantially orthogonal to each other. In the wave type ultrasonic motor, a detection means for detecting load variation information of the standing wave type ultrasonic motor, and a detection means for controlling the phase of the input voltage applied to the vibrator according to the output of the detection means. and phase control means.

[Operation] The speed control device for a standing wave type ultrasonic motor having the above configuration changes when the vibration mode of the compound vibrator changes at startup or when the load fluctuates, and as a result, the load on the ultrasonic motor fluctuates. , the phase of the input voltage applied to the vibrator is controlled according to its fluctuation.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

The composite vibrator used in the present invention is disclosed in Japanese Patent Application No. 1-468, for example.
A composite vibrator including a mechanical resonator as proposed in the specification and drawings attached to application No. 66 may be used. An example of the configuration will be described below with reference to FIG.

The composite vibrator 11 has a first oscillator on the upper surface of an elastic body 21 having a rectangular prism shape for exciting bending vibration in the elastic body 21.
A piezoelectric body 22 is also attached. In the elastic body 21,
Second piezoelectric bodies 23a and 23b for exciting longitudinal vibration in the elastic body 21 are attached to the side surfaces substantially perpendicular to the attachment surface.

The longitudinal center of the elastic body 21 is fixed by fixing bolts 24a and 24b for fixing the elastic body 21. The other ends of the fixing bolts 24a and 24b are
It is fixed to bases 25a and 25b.

Electrodes 27a and 27b are provided on the upper surface of the first piezoelectric body 22.
has been installed. The elastic body 21 itself also serves as a ground electrode, and is grounded to the bases 2Sa and 25b via the fixing bolts 24a and 24b.

Furthermore, the elastic body 21 has a predetermined frequency f in its thickness direction.
The shape and dimensions are adjusted so that it bends in a secondary mode at both free ends, and longitudinally vibrates in a primary mode at both free ends in the longitudinal direction at the same frequency f.

Generally, the resonant frequency of longitudinal vibration propagating in an elastic body is
Depends on the length of the elastic body. Further, the resonance frequency of bending vibration in the thickness direction of the elastic body depends on the length and thickness. Therefore, since it is easy to design the elastic body 21 as described above, the details thereof will be omitted.

The operation of the composite vibrator 11 configured as described above will be explained below. First, when an alternating current voltage of the frequency f is applied to the first piezoelectric body 22 to cause it to vibrate, the elastic body 21 resonates in the second-order mode of bending vibration, and a standing wave is excited. Then the second
When the piezoelectric bodies 23a and 23b are vibrated by applying an alternating current voltage of the frequency f, the elastic body 21 vibrates in the first-order mode of longitudinal vibration, and a standing wave is excited. In other words, the positions fixed by the fixing bolts 24 and 24 are the nodes of each standing wave.

At this time, the first piezoelectric body 22 and the second piezoelectric bodies 23 and 23
By adjusting the amplitude and phase of the voltage applied to the elastic body 21, it is possible to generate approximately elliptical vibration of any shape in the elastic body 21.

In the above embodiment, a compound vibrator was described that excites the first-order mode of longitudinal vibration and the second-order mode of bending vibration, and generates substantially elliptical motion vibration by combining them, but the present invention is not limited to this. , bending vibration, shear vibration, torsional vibration, etc., can be considered, and higher-order modes may also be used.

The basic operating principle of an ultrasonic motor that suitably utilizes the above-mentioned composite vibrator 11 will be explained with reference to FIGS. 2 and 3. In this figure, each member given the same reference numeral as in FIG. 1 indicates that it is the same as each component described in detail above.

In FIG. 2, the ultrasonic motor 30 is connected to the composite vibrator 1.
A driver element 32 is formed at both ends giving a maximum amplitude of 1,
Furthermore, it is configured to be in contact with a rail 34 which is a second elastic body.

FIG. 3 shows the piezoelectric bodies 22 and 23a, 2 of the composite vibrator 11.
3b is a diagram showing a voltage waveform of an input signal applied to the terminal 3b.

When an AC electric signal is applied to the composite vibrator 11 to excite it, the composite vibrator 11 generates a driving force by repeating vertical and bending vibrations as shown in FIGS. 2(a) to (d). . That is, in FIG. 2(a), the phases of both vibrations are adjusted so that the left end of the drive section 32 comes into contact with the rail 34 during expansion and contraction of the longitudinal vibration. Next, as the shape of the composite vibrator 11 changes as shown in FIGS. 2(a), (b), and (c) over time, the drive unit 3
The right end of 2 touches the rail 34. When the driver 32 and the rail 34 come into contact with each other, they receive a driving force due to the frictional force between them and generate thrust in a predetermined direction.

The directions always point in the same direction, as shown by arrows A and B in the figure. The speed of the composite vibrator 11 is
adjustable by the voltage and phase of the input signal;
Further, the driving direction can be arbitrarily changed depending on the phase.

Next, a specific example of the configuration of the linear ultrasonic motor 30 will be described with reference to FIGS. 4 and 5.

In FIG. 4, the composite vibrator 11 has support members 40 formed at its nodes. The support member 40 is supported by a groove 42 provided in a yoke 41 so as to have a degree of freedom in the vertical direction. The yoke is fixed on a base 44 by two linear bearings 43a and 43b, and is movable in the direction of the arrow in FIG.

On the other hand, on the upper part of the composite vibrator 11, a crimping mechanism is formed which includes a leaf spring 50, a spring presser 51, a spring guide 52, and a holder 53.

These are the spring guides 52 supported by the holder 53.
By rotating the spring presser 51 along the screw groove formed in the plate spring 50, the height of the leaf spring 50 is adjusted and the pressing force is controlled.

Further, the rail 34 is installed on the base 44 so as to come into contact with the driver 32 of the composite vibrator 11. However, since the optical encoders 65a and 65b will be described in detail later, they will be omitted here.

With the above configuration, the above-mentioned ultrasonic motor 30 has no structural restrictions on the rail 34 on the stator side, and can create a trajectory of any curvature by simply providing a simple support mechanism. can be configured. Also, the ultrasonic motor is
When not driven, it is held by frictional force, and this force is usually 2 to 5 times larger than that of the ultrasonic motor, so it can form slopes of any angle from 0 to 90 degrees. It is.

Here, the configuration of the speed control device provided in the ultrasonic motor 30 will be explained below with reference to FIG. 6.

The electrode 26 of the first piezoelectric body 22 and the second piezoelectric body 23
The amplifier 60 is connected to the electrodes 27a and 27b of a and 23b.
a and 60b, and the amplifiers 60a and 6
An oscillator 62 is connected to the input terminal 0b through a phase shifter 61. Moreover, the amplifiers 60a and 60
A phase detection circuit 63 is electrically connected to b and is configured to send phase information to a control circuit 64.

On the other hand, as shown in FIG. 4, a slit 65b of an optical encoder is formed in 43b, which is one of the two linear bearings 43a and 43b. It is provided on the yoke 41. Its electrical output is connected to the control circuit 64. Furthermore, a phase shifter 61 is connected to the control circuit 64 to enable phase control.

In reality, the relationship between the speed and phase of the ultrasonic motor is as shown in the speed-phase characteristics in Figure 7. If no speed control is performed, the load changes only from 0 to 0.3 kgf. The speed varies considerably and also shows a strong dependence on phase, with the phase at which maximum speed is obtained depending on the load. In other words, when driving at a phase θ = ±90 degrees that provides the maximum speed in a no-load state, at a load of 0°3 kgf, if the phase is controlled, the speed will be approximately 0.0°.
1m/S is obtained, whereas without control it is 0.08
There is a problem in that it is not possible to obtain 5 m/sL, and in some cases it does not work at all. Therefore, the ultrasonic motor can be driven at a stable speed at all times by adjusting the phase at startup or when the load fluctuates, and the speed change can be reduced even when the load fluctuates.

The speed control method will be explained below.

Initially, the ultrasonic motor 30, which was driven at a speed v1 with an input voltage phase θl, changes due to various factors such as changes in the contact state between the composite vibrator 11 and the rail 34 due to load fluctuations. The vibration mode of the vibrator 11 changes, and as a result, the speed of the ultrasonic motor 30 changes from ■1 to V2.
Changes to This speed change is detected by the optical encoder 6.
5 or the like, and simultaneously sends speed information v1 and v2 to the control circuit 63. At this time, if the speed is decreasing (1>v2), the control circuit 63 sends a signal to the face shifter 61 to change the input voltage phase θ1 of the composite vibrator 11 to near the initial phase value θ1. send. Then, the speed change accompanying the phase change is detected again by the optical encoder 65, and speed information v3 is sent to the control circuit 64 again. As a result, the speed information is compared and the control circuit 64 detects the phase θ2 when the maximum speed is obtained. Then, the control circuit 64 determines the phase of the phase shifter 61 so that the ultrasonic motor 30 is driven at the phase θ2.

A similar operation is performed when the speed is yl<v2.

In other words, since load and speed generally have a correlation, the change in speed of the ultrasonic motor is used as an example of load change information.

With the above configuration, the ultrasonic motor 30
In this case, it is possible to always drive at a desired speed, here the maximum speed, regardless of load fluctuations. In other words, a standing wave type ultrasonic motor has an advantage over a traveling wave type ultrasonic motor in that the input terminal phase can be controlled, and the present invention makes it possible to fully utilize this advantage, and as a result,
You can get an excellent ultrasonic motor. The above-mentioned relationship between speed and phase can be clearly expressed by using a prismatic composite resonator with a very simple structure. In other words, the prismatic composite resonator 11 is considered to be very suitable for this speed control. On the other hand, in a Langevin type vibrator that combines a plurality of elastic bodies or uses a bolted structure, speed changes are likely to occur due to conditions other than phase due to the complexity of the structure.

In this embodiment, an example in which phase control is performed based on speed information has been described, but the present invention is not limited to this. The change in amplitude is detected by attaching the electrodes 27a and 27b above the electrodes 27a and 27b, which are easy to detect.Since the magnitude of the amplitude is correlated with the magnitude of the speed, the phase control is performed using the same control as the speed control described above. It is also possible to do this.

Also, the speed-phase characteristics that change depending on the load are stored in memory in advance, the load value is detected, and the phase that provides the desired speed at that load is recalled from the memory and the phase is controlled. Good too.

Furthermore, in this embodiment, the optical encoder 63 has been described as an example of a speed change detection means, but the present invention is not limited to this, and various other methods such as a magnetic encoder can be used.

On the other hand, although the above embodiments have been described using a prismatic composite resonator as an example, the present invention is not limited thereto, and similar effects can be obtained by using a substantially flat resonator.

Further, in this embodiment, a piezoelectric body is used as an excitation source for the elastic body, but its shape is not limited to a flat plate, but various shapes such as a disk shape and a laminated shape can be considered.

Further, in this embodiment, the crimping mechanism has been described using a leaf spring as an example, but the present invention is not limited to this, and various springs such as coil springs, application of magnetic force, etc. can be considered.

In addition, various modifications can be made without departing from the spirit of the present invention.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, by performing phase control during load fluctuations in a standing wave type ultrasonic motor, high efficiency operation can be maintained. A standing wave type ultrasonic motor that performs speed control at a desired speed can be realized.

[Brief explanation of drawings]

1 to 7 show embodiments embodying the present invention. FIG. 1 is an explanatory diagram of a composite vibrator used in this embodiment, and FIG. 2 is an illustration of an ultrasonic motor. FIG. 3 is a diagram showing the voltage waveform of the input signal applied to the piezoelectric body of the composite vibrator; FIG. 4 is a diagram showing the top and side views of the ultrasonic motor of the present invention. FIG. 5 is a diagram showing a CC cross section in FIG. 4, FIG. 6 is a diagram showing a speed control device for an ultrasonic motor, and FIG. FIG. 3 is a diagram showing speed-phase characteristics of a motor. FIG. 8 is a diagram showing a conventional example of an ultrasonic motor. 1 Composite vibrator 1 2 23a and 23b 3 4 5 Prismatic elastic body First piezoelectric body Second piezoelectric body Phase detection means Phase control means Speed detection means FIG.

Claims (1)

[Claims] 1. In a standing wave type ultrasonic motor equipped with a vibrator that is excited with at least two vibrations whose vibration directions are substantially orthogonal to each other, a detection means for detecting load fluctuation information of the standing wave type ultrasonic motor; and a phase control means for controlling the phase of the input voltage applied to the vibrator according to the output of the detection means.