JPH0352573A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To reduce set driving frequency and the resonance frequency of a stator by providing a vibrator being stuck to the stator and generating progressive waves, a means pushing a rotor against the stator by specified welding force and an adjusting means diminishing welding force when load torque is increased. CONSTITUTION:When a piezoelectric vibrator 9 is supplied with AC power, the piezoelectric vibrator 9 is expanded and contracted, and progressive-wave vibrations are generated on a stator 7. A stabilizer 12 is disposed between a rotor 10 and a belleville spring 11 so that the welding force of the belleville spring 11 is applied uniformly onto the whole circumferential surface of the rotor 10, a welding-force adjusting mechanism is composed of cam faces 6b, 16b and steel balls 17a, 17b, 17c, 17d, and the magnitude of load torque is converted into displacement in the axial direction of a holder 16. The rotor 10 is pushed against the stator 7 by weak welding force on large load. Accordingly, the difference of set driving frequency and the resonance frequency of the stator can be held at a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an ultrasonic motor that rotates a rotor by a traveling wave generated on a stator.

(Prior Art) Conventionally, an ultrasonic motor has been developed in which a piezoelectric vibrator is bonded to a stator, a traveling wave is generated in the stator by supplying a predetermined alternating current power to the piezoelectric vibrator, and the rotor is rotated by the traveling wave. It has been known. Such an ultrasonic motor is disclosed in, for example, Japanese Patent Application Laid-Open No. 59-204477.

In the ultrasonic motor disclosed in Japanese Unexamined Patent Publication No. 59-204477, etc., a sensor for detecting the strength of a traveling wave is attached to the stator. A monitor signal detected by this sensor is input to a control circuit for adjusting the frequency of AC power supplied to the piezoelectric vibrator. The control circuit uses the monitor signal obtained from the sensor to adjust the frequency of the AC power applied to the piezoelectric vibrator so that the strength of the traveling wave generated in the stator is approximately constant.

When the load acting on the ultrasonic motor increases, the energy extracted from the rotor increases.
The traveling waves generated in the stator become weaker. At this time, the control circuit brings the frequency of the AC power applied to the piezoelectric vibrator close to the resonant frequency of the stator, which is preset in the control circuit, so that the strength of the traveling wave on the stator remains approximately constant. do.

Conversely, when the load acting on the ultrasonic motor becomes smaller, the energy extracted from the rotor becomes smaller, so the traveling waves generated in the stator become stronger. This special,
The control circuit controls the frequency of the alternating current fL power applied to the piezoelectric vibrator away from the resonant frequency of the stator, which is preset in the control circuit, so that the traveling wave on the stator becomes approximately constant.

(Problems to be Solved by the Invention) Incidentally, the resonant frequency of the stator changes depending on the magnitude of the load acting on the ultrasonic motor.

Therefore, if the size of the load becomes too large, the difference between the drive frequency set in the control circuit and the actual resonant frequency of the stator will become small, or the magnitude relationship between the drive frequency and the actual resonant frequency of the stator will be reversed. As a result, the control circuit may not operate properly. For this reason, in conventional ultrasonic motors, when the load becomes large, the rotor suddenly stops, or in extreme cases, the rotor begins to rotate in reverse.

The present invention has been made to solve these problems in the prior art, and by suppressing changes in the resonance characteristics of the stator, the difference between the drive frequency set in the control circuit and the actual resonance frequency of the stator is reduced. The technical challenge is to keep the difference small.

[Precepts of invention]

(Means for solving the problem) The technical means taken to achieve the above-mentioned technical problem are a pressurizing means that presses the rotor toward the stator with a predetermined pressurizing force, and a load torque applied to the rotor. This is because an adjusting means is provided to reduce the pressurizing force of the pressurizing means as the pressure increases.

(Operation) According to the above-mentioned technical means, when the load acting on the ultrasonic motor increases, the pressing force between the rotor and the stator is reduced. The resonant frequency of the stator changes as the applied force decreases. For this reason, even when the load increases, the actual resonant frequency of the stator is held approximately constant, and the intended technical problem is achieved.

(Example) Hereinafter, an example apparatus to which the present invention is applied will be described with reference to the accompanying drawings.

First, the structure of an ultrasonic motor to which the present invention is applied will be explained with reference to FIG. A case 2 is fixed to the base material l. A ball bearing 3 is placed in the center of the base material 1.
is embedded. Furthermore, a disc spring 4 is fitted into the recess 2a of the case 2. A ball bearing 5 is supported on the disc spring 4. A rotating shaft 6 is rotatably supported by ball bearings 3 and 5. A pusher 20 is disposed between the ball bearing 3 and the rotating shaft 6.

A fixed portion 7a of the stator 7 is firmly fixed to the base member 1 with countersunk screws 8 so that it cannot vibrate. A ring-shaped piezoelectric vibrator 9 is bonded to one surface of the stator 7 .

The stator 7 has a shape in which a fixed part 7a and a vibrating part 7c are integrated by a thin supporting part 7b. A large number of protrusions 7d are formed on the surface of the vibrating portion 7c at a constant pitch over the entire circumference. The stator 7 is made of a metal material with excellent conductivity (such as phosphor bronze), and is electrically connected to the base material l.

The piezoelectric vibrator 9 is an element for generating a traveling wave on the stator 7, and is polarized to efficiently generate a traveling wave on the stator 7. The piezoelectric vibrator 9 for the ultrasonic motor has already been introduced in many documents and is well known.
A detailed explanation will be omitted. Piezoelectric vibrator 9 to 90
``When AC power with a phase difference is supplied, the piezoelectric vibrator 9
expands and contracts, causing traveling wave vibrations on the stator 7.

The rotor 1G is constantly pressed against the stator 7 by the pressing force of the disc spring 11. The rotor 10 and the disc spring 1 are arranged so that the pressing force of the disc spring 11 is uniformly applied to the entire circumferential surface of the rotor 10.
1, a stabilizer l2 is disposed between the two. A rubber seat 13 is provided between the countersunk spring 11 and the stabilizer 12.
A rubber seat 14 is installed between the stabilizer 12 and the rotor 1G.
are sandwiched between each.

The rotor IO has a shape in which an outer circumferential portion 10a and an inner diameter portion 10c are integrated through a thin wall portion 10b. A ring-shaped friction material film l5 is adhered to the lower surface of the outer peripheral portion 10a of the rotor 10.

The friction material film l5 is attached to the lower surface of the outer circumferential portion 10a and the stator 7.
It is sandwiched between the vibrating parts 7c.

The stabilizer l2 of this embodiment is made of iron material and has a larger mass than the rotor lO made of aluminum material. Here, if the mass of the stabilizer l2 is made larger than the mass of the rotor 10, the vibration of the rotor 10 is
It becomes difficult to convey to 1.

Further, it is desirable that the squib riser l2 be made of a material with high rigidity. This is because if the stabilizer l2 has low rigidity, vibrations of the rotor 10 will be absorbed.

A ring-shaped protrusion 12a is formed on the outer periphery of the stabilizer l2. This protrusion 12a is located inside the contact surface between the rotor 10 and the stator 7, and presses down the rotor 10. Since the protrusion 12a is shaped with a certain dimensional accuracy, the pressing force of the disc spring 11 is uniformly distributed along the circumference of the protrusion 12a.

The disc spring 11 is held by a collar portion 16a of the holder l6. A rotating shaft 6 is inserted into the center of the holder l6. The rotating shaft 6 is rotatably supported by a push l9 pressed into the case 2 and a ball bearing 3. There is a spacer l between the holder l6 and the pole bearing 5.
8 has been inserted. The holder l6 can freely rotate around the rotating shaft 6.

FIG. 2 shows an exploded perspective view depicting the holder l6 and the rotating shaft 6. A cam surface 16b having four substantially V-shaped bottoms is formed at the center of the holder l6.

On the other hand, a flange 6a is formed on the rotating shaft 6.
a has a cam surface 6b having a shape corresponding to the cam surface 16b;
is in great shape. Between the cam surface 6b and the cam surface 16b, four steel balls 17a, 17b, 17c, 1
7d is held in between. The driving force of the rotor lO is transmitted to the holder l6 through the stabilizer l2 and the disc spring 11,
Furthermore, the steel ball 1 sandwiched between the cam surface 16b and the cam surface 6b
It is transmitted to the rotating shaft 6 through 7a, 17b, 17c, and 17d.

Force/mu surface sb, tab and steel ball 17a. 17b, IT
c and 17d are the pressure adjustment mechanism, and the rotating shaft 6
The magnitude of the load torque acting on the holder l6 is converted into an axial displacement of the holder l6.

When the load acting on the rotating shaft 6 is small, the relative displacement between the holder l6 and the rotating shaft 6 is small, so the steel ball IT
a. 17b, ITc. ITd moves near the substantially V-shaped bottom of the cam surfaces 16b, 6b. At this time, since the holder l6 moves in a direction approaching the stator 7 (downward in FIG. 1), the rotor 10 is pressed against the stator 7 with a strong pressing force.

- Conversely, when the load acting on the rotating shaft 6 is large, the relative displacement between the holder l6 and the rotating shaft 6 becomes large.
Steel balls 17a, 17b, 17c, 17d are cam surface 16b,
Move towards the top of 6b.

At this time, the holder l6 moves toward the stator 7 (upward in FIG. 1), so the rotor 10 is pressed against the stator 7 with a weak pressing force.

When the load acting on the rotor 10 increases, the stator 7
The resonant frequency of increases. However, in the device of this embodiment, the pressurizing force adjustment mechanism operates and the pressurizing force acting on the stator 7 is weakened so that the resonance frequency of the stator 7 is lowered. As a result, the resonant frequency of the stator 7 is maintained substantially constant.

FIG. 3 shows the control circuit of the device of this embodiment. Control circuit 30
are a power supply circuit 31, a human power circuit 32, a microcomputer 33, a D/A conversion circuit 34, a voltage controlled oscillation circuit 35,
It includes a phase shift circuit 36, a driver circuit 37.3g, a step-up transformer 39.4G, and a smoothing circuit 4l.

The power supply circuit 31 is connected to the battery 8TT and supplies power at a constant voltage into the control circuit 30.

The input circuit 32 includes a microcomputer 33 and a switch S.
It inputs to the microcomputer 33 whether the switch SW is set to the ON side or the OFF side.

The piezoelectric vibrator 9 bonded to the stator 7 has a
A pair of drive electrodes 9a, 9 for generating a traveling wave above
b is joined. The phase is set to 90 by the phase shift circuit 36.
When a pair of electric signals shifted by 6 is applied to drive electrodes 9a and 9b, a traveling wave is generated on stator 7. The amplitude of the traveling wave generated on the stator 7 is determined by the voltage controlled oscillation circuit 35.
It changes depending on the oscillation frequency. That is, as the oscillation frequency of the voltage controlled oscillation circuit 35 approaches the resonant frequency of the stator 7, the amplitude of the traveling wave increases, and conversely, as the oscillation frequency of the voltage controlled oscillation circuit 35 moves away from the resonant frequency of the stator 7, the amplitude of the traveling wave increases. decreases.

The traveling wave generated on the stator 7 generates a monitor voltage on the sensor electrode 7c that is approximately proportional to the amplitude. The monitor voltage is smoothed by the smoothing circuit 41 and input to the microcomputer 33. The microcomputer 33 controls the D/A converter circuit 34 according to the average amplitude of the stator 7 input manually from the smoothing circuit 41, and controls the voltage controlled oscillation circuit so that the amplitude on the stator 7 is almost constant. Adjust the oscillation frequency of 35.

An example of a program executed by the microcomputer 33 is shown in FIG. When the battery BTT is connected to the power supply circuit 31, the microcomputer 33 starts executing the program shown in FIG. 4 from step S1.

In step 31, initialization necessary for executing subsequent processing is performed.

After this, in step S2, it is determined whether the switch SW is turned on. The process of step S2 is repeated until the switch SW is turned on.

In step S3, the standard drive frequency f. A code corresponding to is stored in the control flag f. Note that the driving frequency f0 is determined based on the resonant frequency of the stator 7 at the rated load.

Thereafter, in step S4, when the code stored in the control flag f is output to the D/A conversion circuit 34, the standard drive frequency f0 is output from the voltage controlled oscillation circuit 35, and the rotor 6 starts rotating.

Thereafter, in step S5, at this moment, the sensor electrode 4c
The magnitude of the monitor voltage V generated in is read,
In step S6, it is compared with the standard voltage V0. Note that the standard voltage V0 is equal to the magnitude of the monitor voltage detected when the drive frequency f0 is supplied to the stator 7 at a rated load.

If the standard voltage V0 and the read electrode voltage V are equal, the process of step S7 is omitted.

If they are not equal, the process of step S7 is executed,
The code of the control flag f is increased or decreased so that the monitor voltage V matches the standard voltage V0.

In step S8, it is determined whether the switch SW remains on the ON side. If the switch SW is on the ON side,
The process of step S4 can be executed again. switch S
If W is on the OFF side, the process of step S9 is executed, the oscillation of the voltage controlled oscillation circuit 35 is stopped, and the rotor 6 is stopped.

The control circuit 30 and microcomputer 33 described above
In this example device, the program executed in
The amplitude of the traveling wave generated in the stator 7 is adjusted to be approximately constant.

In the control circuit 30 described above, control is performed using the resonance characteristics of the stator 7 at the rated load as a standard. Therefore, if the resonance characteristics of the stator 7 change significantly depending on the load, correct control cannot be performed. However, according to the device of this embodiment, the resonant frequency of the stator 7 is mechanically maintained substantially constant, so electrical control is always correctly executed and the output characteristics of the ultrasonic motor are extremely stable.

〔Effect of the invention〕

In the ultrasonic motor of the present invention, variations in load torque are mechanically detected and the pressing force between the rotor and stator is adjusted. Therefore, the resonant frequency of the stator can be held substantially constant regardless of variations in load torque. As a result, the ultrasonic motor to which the present invention is applied can obtain extremely stable output characteristics.

[Brief explanation of drawings]

FIG. 1 is an illustrative cross-sectional view of an ultrasonic motor illustrating a device according to an embodiment of the present invention. FIG. 2 is a perspective view depicting a pressurizing force adjustment mechanism of an apparatus according to an embodiment of the present invention. FIG. 3 is a circuit diagram depicting a control circuit of an apparatus according to an embodiment of the present invention. FIG. 4 is a flowchart showing an example of a program executed by the control circuit depicted in FIG. l...Base material, 2...Case, 3...Pole bearing, 4...Fish plate, 5...Pole bearing, 6
... Rotating shaft (adjustment means), 7 ... Stator, 8 ... Screw, 9 ... Piezoelectric vibrator (vibrator), 11 ... Belleville spring (pressure means), 12 ... Stabilizer, 13, l5...Friction material film, l4...Rubber seat, IO...[J Ichiyo, l6...Holder (adjustment means), 17a, 17b, 17c, 17d...Steel ball (Adjustment means), 1B... Spacer, 19.20... Push 30.
... Control circuit, 3l... Power supply circuit, 32... Human power circuit, 33... Microcomputer, 34... D/
A conversion circuit, 35... Voltage controlled oscillation circuit, 36...
Phase shift circuit, 37.38...driver circuit, 39.40
...Step-up transformer, 4L...Smoothing circuit.

Claims (1)

[Scope of Claims] A stator, a vibrator attached to the stator and generating a traveling wave on the stator, a rotor in contact with the stator, and a predetermined pressing force to direct the rotor toward the stator. An ultrasonic motor comprising: a pressure means for pressing the rotor; and an adjustment means for reducing the pressing force of the pressure means as the load torque applied to the rotor increases.