DE20110625U1 - Ultrasonic motor made of piezoelectric components - Google Patents

Description

Ultrasonic motor made of piezoelectric components

The present invention relates to an ultrasonic motor made of piezoelectric components, in which an alternating voltage is fed into the piezoelectric disk. Due to the telescopic ratio of the inverse piezoelectric effect, the piezoceramic generates a push-pull force which causes a metallic back plate to vibrate so that the mechanical waves generated are transmitted radially and along the circumference of the piezoceramic. The traveling waves are deflected in different directions at the outer edge of the piezoelectric disk. In addition, the torque from one of the traveling waves is used to rotate the rotator.

A conventional ultrasonic wave is generated by a piezoceramic made of lead zirconate titanate. When a voltage is applied to the piezoceramic, the ceramic body and the back plate connected to it deform and retract, transferring energy in a wave having the frequency of ultrasonic waves whose wavelength is within one micrometer and is controllable by the applied voltage. Therefore, the piezoceramic can serve as a driving device or system for a precision mechanism or motor.

The above-mentioned ultrasonic motor has an alternating movement. By means of a mechanical design, a moving device can be formed that acts in a certain direction, with the path of movement in each cycle being only a few micrometers long. The oscillation of the ultrasonic frequency produces a displacement of more than ten centimeters. This can be used to drive a more precise device (e.g. camera with automatic

• · ···· ·♦♦

focus adjustment, positioning system in microprocessing).

In addition, the ultrasonic motor has the following characteristics: small volume, light weight, low noise, high torque at low speed, high torsion, responsive, free from interference electromagnetic waves, etc. According to different characteristics, the ultrasonic motor can be used for different products. An ultrasonic motor with small volume and light weight can be used for automatic focus adjustment in a monocular SLR camera. An ultrasonic motor which is low noise, high torque at low speed and high torsion can be used in quiet places in hospitals. A responsive ultrasonic motor can be used to move a coordinate table. An ultrasonic motor which is free from interference electromagnetic waves can be used in magnetic cushion tracks and in biological and medical technology.

Conventional ultrasonic motors or actuators use piezo blocks or stacked piezo pieces. These are expensive due to the high prices of the piezo materials on the market.

Therefore, it is an object of the invention to eliminate the above-mentioned deficiencies and to create an ultrasonic motor made of piezoelectric components, in which an alternating voltage is fed into a piezoelectric disk. Due to the telescopic ratio of the inverse piezoelectric effect, the piezoceramic generates a pressure-tension force which causes a metallic back plate to vibrate, so that the generated

mechanical waves are transmitted radially and along the circumference of the piezoceramic. The traveling waves are deflected in different directions at the outer edge of the piezoelectric disk. In addition, the torque from one of the traveling waves is used to rotate the rotator.

Another object of the present invention is to provide an ultrasonic motor made of piezoelectric components in which a single-phase alternating current is used instead of a two-phase drive current for generating the traveling waves and for coupling the pulses with a high wavelength.

Another object of the present invention is to provide an ultrasonic motor made of piezoelectric devices which is applicable to semiconductor manufacturing equipment, medical instruments, hard disk drives, CD-ROM drives, etc.

Another object of the present invention is to provide an ultrasonic motor made of piezoelectric components that is cost-effective and efficient.

These objects are achieved according to the invention by an ultrasonic motor made of piezoelectric components, which has the features specified in claims 1 to 5. 30

Further features and advantages of the present invention will become apparent from the following description of a preferred embodiment according to the accompanying drawings.

Show it:

Fig. 1 is a schematic representation of an ultrasonic motor according to the invention made of piezoelectric components;

Fig. 2 is a perspective exploded view of the ultrasonic motor according to the invention made of piezoelectric components/

Fig. 3 is an overall perspective view of the ultrasonic motor according to the invention made of piezoelectric components;

Fig. 4 is a plan view of the ultrasonic motor according to the invention made of piezoelectric components;

Fig. 5 is a schematic representation of the cycle voltage fed into a piezoelectric disk;

Fig. 6 is a simulated representation of the piezoelectric disk rotating counterclockwise;

Fig. 7 shows a simulated representation of the piezoelectric disk rotating clockwise;

Fig. 8 shows a simulated vibration representation of the side-sliding actuation principle;

Fig. 9 is a schematic representation of the stator of the side-shifting ultrasonic motor;

Fig. 10 is a perspective view of the rotator of the side-sliding ultrasonic motor;

Fig. 11 is an exploded view of a fabricated side-sliding ultrasonic motor and a test board;

Fig. 12 is a system block diagram of the control circuit; and

Fig. 13 a circuit diagram of a current transformer.

1 to 3, the ultrasonic motor made of piezoelectric components according to the invention mainly comprises a piezoelectric disk 1, a first fixing plate 2, a second fixing plate 3, a torsion spring 4, a plurality of screws 5 and a lead wire 6. The piezoelectric disk 1 is screwed to the first fixing plate 2 with three asymmetric screws 5 inserted through the holes 21. The first fastening plate 2 screwed together with the piezoelectric disk 1 and the torsion spring 4 are screwed to the second fastening plate 3, which has a larger surface area, with several screws 5 being inserted through the holes 21, 31. This forms a spring configuration between the first fastening plate 2 and the second fastening plate 3. In addition, the lead wire 6 is connected to the main electrode 11 of the piezoelectric disk 1. The ultrasonic motor according to the invention is based on an externally excited piezoelectric disk 1, the voltage being applied only to the main electrode 11, while an alternating current is fed between the lead wire 6 of the main electrode 11 and the second fastening plate 3. During use, the second

Mounting plate 3 is held by a hand or attached to a specific device and the piezoelectric disk 1 is brought into contact with a rotator 7, whereby the rotator 7 is set in rotation. 5

With the above components, the operating principle is that the piezoelectric disk 1 serves as a means for converting electrical energy into mechanical energy. An alternating voltage is applied to the piezoelectric disk 1, whereby the piezoceramic generates a compressive-tensile force due to the telescopic relationship of the inverse piezoelectric effect. A metallic back plate 13 is caused to vibrate so that the generated mechanical waves are transmitted radially and along the circumference of the piezoceramic. During wave transmission, all screws 5 serve as a reflection point. By means of the reflection point formed by the three screws 5, the traveling waves are deflected in different directions on the outer edge of the piezoelectric disk 1. In addition, the torque of one of the traveling waves is used to rotate the rotator 7.

The working principle of the travelling waves is that a voltage is applied to the main electrode 11 of the piezoelectric disk 1, so that the stator made of the piezoceramic produces an inverse piezoelectric effect to excite the stator to vibrate in order to transmit waves to the stator. The friction force between the stator and the rotor enables the rotor 7 to move in the advancing direction of the waves. The travelling waves are formed by the disk vibration of a certain frequency at a certain marginal condition producing a multiple reflection, whereby the

Displacement difference of the reflection wave in a
certain area allows the movement of the traveling waves

The working principle of the ultrasonic motor according to the invention is determined according to the FEA method with limited elements

analyzed. If a periodic voltage is applied (see Fig. 5), the stator of the motor is periodically deformed. According to the inverse piezoelectric effect, the direction of deformation of the piezoelectric disk 1 reverses exactly when the applied voltage lies exactly in the positive or negative parabola (see Fig. 5). Therefore,
the four points (a), (b), (c), (d) shown in Fig. 5 in the positive parabola as periodic
Deformation observation points. If the applied

Voltage 20 Vp-p = 2 Vm at a frequency of 66.6 kHz,

The order of periodic change is as follows:

a—»b—>c->d
20

In Fig. 6 the change of the stator of the
ultrasonic motor according to the invention, the sequence of deformation of the stator being shown as follows
is:
25

a-»b->c—»d

In (a) the piezo actuator starts to deform when the applied voltage is 0 V. In (b)

the applied voltage increases to up to 1/2 Vm, whereby the

deformation of the piezo actuator is increased. At (c) the applied voltage increases up to 1 Vm, increasing the deformation of the piezo actuator to the maximum. At (d) the maximum is reached, after which the deformation of the piezo actuator is V = 1/2 Vm

is gradually reduced. In the process or in the negative

»

• .' .: :K.i i i

Parabola, the piezo actuator contracts. In the simulated figure, it is clearly shown that the deformation in R and θ directions is present when the stator of the motor is at the 90° position. When the frequency of the applied voltage is 76 kHz and the rotator is at the 90° position of the stator of the motor, the rotator is rotated clockwise by the stator. The figures of deformation in the ranges of 120° and 150° are in contrast to the figures shown at 66.6 kHz. The drive mechanism of positive and negative rotary motion is essentially obtainable by comparing the vector figures of the simulated deformations of the stator at the input frequency 66.6 kHz and at 76 kHz (see Fig. 8).

At a frequency of 66.6 kHz, a deformation in the direction of R and θ occurs in the region of the drive point. The deformation occurs to the right as shown in Fig. 8a. At the frequency of 76 kHz, the deformation occurs to the left as shown in Fig. 8b. When the rotator is pressed against the drive point, at the frequency of 66.6 kHz, the rotator rotates clockwise, while at the frequency of 76 kHz, it rotates counterclockwise.

Comparing the figures simulated by the constrained element method between 66.6 kHz and 76 kHz, the deformation direction in the 90° range is opposite when the frequency changes, while the direction is reversed when the frequency changes in the 90° range and the 120° range. In the side-pushing ultrasonic motor, the side-pushing force is increased by the 3- and 4-mixing modes.

From the analysis of the vibration mode using the limited element method, it is clear that the displacement of the ultrasonic motor according to the invention of

the wavelength of the alternating voltage on the piezoceramic of the rotator, while the direction of rotation depends on its frequency. In order to drive the ultrasonic motor effectively, a step-down converter and a single-phase half-bridge series resonant circuit (see Fig. 13) are combined in the control circuit shown in Fig. 12. The cycle of the step-down converter is adjusted in such a way that the signals generated by D/A conversion and quasi-adjustment at the output u of the control unit are controlled by the personal computer using a PWM circuit. The converter supplies a variable direct voltage V _dc to the single-phase half-bridge series resonant circuit, whereby the control frequency of the series resonant circuit is selected using the set, defined clockwise and anti-clockwise rotation frequency and the fixed wavelength VCO(I), VCO(2) of the u _p voltage signal. If u _p > 0 (high), fi = 66.6 kHz is selected, whereby the ultrasonic motor is set to rotate clockwise. For u _p = 0 (low), f2 = 76 kHz is selected, whereby the ultrasonic motor is set to counterclockwise rotation.

Fig. 9 shows a rotator of the side-sliding ultrasonic motor of the present invention. The diameter of the screw 91 is 2 mm. In order to ensure wave reflection on a metal back plate 92, the screw 91 must be tightened as tightly as possible. The pre-tensioned spring 93 is fitted to a pivot point 94 to ensure constant contact between the stator and the rotator. The gap between the fixed aluminum plate 95 and the piezoceramic 96 must be securely insulated to prevent a short circuit when the drive cable 97 is passed through by the drive current.

In order to take into account the factors of processing accuracy and rotating balance of the motor,

: If.. {

*; &igr;

The rotator of the motor is designed as a small stepper motor rotator which is inserted into a 13.335 cm (5.25") floppy disk drive (see Fig. 10). The rotator 101 is itself designed as a permanent magnet, the circumference of which is provided with teeth 102 to increase the friction between the stator and the rotator 101 and thus increase the torque. The rotary shaft 104 is provided at two ends with a bearing 103 to support an encoder and a load turntable, the encoder serving to measure the position of the rotator 101 of the motor. Fig. 11 shows an exploded view of a manufactured side-sliding ultrasonic motor and a test board.

The differences between single- and two-phase drive current ultrasonic motors made of piezoelectric components are shown in Table 1.

Table 1:

Differences between single-phase and two-phase
Ultrasonic motors Difference Single-phase
Ultras chal !motor Two-phase
Ultrasonic motor Entering the currents 90° phase difference
differentiated between
High frequency
Signals Single-phase
High frequency
Signals 1 crooked flexible
Wave Traveling wave Standing wave 2 Direction of rotation of
Engines depends on the
shift
two phases. depends on the
Resonance frequency
the specific
Legal and
Turn left. 3

•··♦ ··

4 wavelength depends on the depends on the Control frequency the stator near the adjacent resonance. Voltage off. 5 configuration complicated simply 6 Arrangement of the alternating Unlimited Stator electrode Arrangement of Two-phase electrodes 7 Control circuit complicated simply 8th extent large small 9 Frequency range broad narrow 10 Condition for the no Yes wavelength

Claims (5)

1. Ultrasonic motor made of piezoelectric components, which has:
a piezoelectric disk ( 1 ) for rotating a rotator through which an alternating current flows, thereby generating a traveling wave;
a first mounting plate ( 2 ) for generating reflection and interference waves, to which the piezoelectric disk ( 1 ) is fixed and on which a plurality of screws ( 5 ) are arranged;
a second mounting plate ( 3 ) which is screwed to the first mounting plate ( 2 );
a torsion spring ( 4 ) which serves for a resilient movement of the first and second fastening plates ( 2 , 3 ) and whose two ends are respectively fastened to the first and second fastening plates ( 2 , 3 ); and
a lead wire ( 6 ) connected at one end to the piezoelectric disk ( 1 ) and at the other end to the AC power source; so that an appropriate driving current is supplied, whereby the edge of the piezoelectric disk ( 1 ) is brought into contact with the rotator to cause the rotator to rotate. 2. Ultrasonic motor according to claim 1, characterized in that the piezoelectric disk ( 1 ) has a main electrode ( 11 ), a piezoceramic ( 12 ) and a metallic back plate ( 13 ). 3. Ultrasonic motor according to claim 2, characterized in that the metallic back plate ( 13 ) of the piezoelectric disk ( 1 ) comprises a metal alloy. 4. Ultrasonic motor according to claim 1, characterized in that the first fixing plate ( 2 ) is rectangular in shape to fix the piezoelectric disk ( 1 ). 5. Ultrasonic motor according to claim 1, characterized in that the second mounting plate ( 3 ) is rectangular, a torsion spring ( 4 ) is provided between the first mounting plate ( 2 ) and the second mounting plate ( 3 ) while a screw serves as a pivot, and that the torsion spring ( 4 ) serves for the resilient movement of the first and second mounting plates ( 2 , 3 ).