JPH11215860A - Traveling-wave motor and measuring method for its temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple and precise temperature measuring method for traveling-wave motors and their stators. SOLUTION: A traveling-wave motor has a stator having a piezoelectric ceramic 1 excitable electrically, and a rotor touchable to the stator with friction. And the piezoelectric ceramic 1 is composed of two groups of piezoelectric areas polarized alternately and so as to be different, and both groups of piezoelectric areas are excited by AC voltages 2, 3 whose phases are shifted by 90 deg. mutually. Two electrodes 5, 6 are formed at least at an interval of λ/4 for detecting the motor condition sensor-technically, in a first part range 4 of the piezoelectric ceramic 1 unutilizable for the generation of a traveling wave. Similarly, a measuring electrode 8 is formed in a second part range 7 of the piezoelectric ceramic 1 unutilizable for the generation of a traveling wave, and a capacitor having a temperature-stable capacitance value is connected to it, so that the measuring electrode 8 and the temperature-stable capacitor may form a capacity-type voltage divider.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a traveling wave motor having a stator having an electrically excitable piezoelectric ceramic and a rotor capable of frictionally contacting the stator.

[0002]

BACKGROUND OF THE INVENTION Traveling wave motors of known construction, mode of operation, and preferred use utilize mechanical vibrations to produce rotational motion. For this purpose, the stator has a piezoelectric element which makes it possible to convert electrical vibrations into mechanical traveling waves.

A traveling wave motor, also called an ultrasonic motor, is disclosed, for example, in US Pat. No. 4,562,374, Yuk.
ihiko Ise "Travelling Wav
e Ultrasonic Motors Offer
High Conversion Efficien
cy "(JEE, June 1986, PP66-7
0) and Schadebrodt and Salom
on "Piezo Traveling Wave
Motor-A New Element in A
ctuation (Control Engineer)
ing, May 1990, PP10-18).

For the excitation of traveling waves, an annular piezoelectric ceramic structure is used for symmetry reasons. This structure is divided into two groups of piezoelectric areas, which are alternately positively and negatively prepolarized, and these piezoelectric areas are spaced apart by λ / 4 and 3λ / 4.
Form two electrodes. Both groups are excited with AC voltages that are phase shifted from each other by 90 °. Known drive circuit for driving the traveling wave motor is used, an oscillator to effectively drive the stator to generate electrical frequency f _e, which is tuned to the mechanical resonant frequency f _m of the stator. Rotation of the rotor is performed by a traveling wave propagating in a direction opposite to the rotation direction.

A first sub-range of the piezoceramic, which cannot be used for the generation of traveling waves, comprises at least 2 at intervals of λ / 4.
Two electrodes are formed and these electrodes are utilized using the opposite piezoelectric effect to detect the ratio of standing wave component to traveling wave component or vibration amplitude.

[0006] Traveling wave motors can be used in a variety of ways, for example, as joints for mobile operators or robot systems. Particularly in applications requiring power requirements, high heat generation must be considered.

[0007] Currently traveling wave motors reach a mechanical power of about 50 W with an efficiency of about 25%. The desired operating temperature range is between -40C and + 80C. Additional boundary conditions, such as different load requirements with respect to speed or torque, result in large and relatively fast temperature changes in the motor. With increasing motor temperature, a decrease in the stator resonant frequency f _m is observed. Similarly, the capacitance of the piezoelectric ceramic exhibits extremely remarkable and reproducible temperature characteristics. As can be seen from FIG.
In the desired operating temperature range of -40 ° C to + 800 ° C, the capacity of the piezoelectric ceramic increases by about 50% with respect to the value at -40 ° C.

[0008] Therefore, detection of temperature change is extremely important for optimal driving of the motor, protection of overload, and prevention of failure due to peeling of the piezoelectric ceramic.

In the traveling wave motor described in US Pat. No. 5,585,686, a temperature sensor is mounted around the stator to monitor a predetermined stator temperature set via a heating element. . Another traveling wave motor having a temperature sensor is described in U.S. Pat. No. 5,477,100. The traveling wave motor disclosed in Japanese Patent Application Laid-Open No. 2-7879 has a temperature measuring device, and a temperature sensor, a comparison resistor and a capacitor form a resistance voltage divider.

[0010]

It is an object of the present invention to provide a method which allows a simple and accurate measurement of the traveling wave motor and the stator temperature.

[0011]

According to the invention, this object is achieved by a traveling wave motor having the features of claim 1 and a method having the features of claim 8.

The mounting of the measuring electrodes in a sub-area of the piezoceramic, which is not available anyway for the generation of traveling waves, saves space and allows for very precise measurements of the direct measurement at the point to be measured. I do. Furthermore, a special temperature sensor to be additionally mounted is not required, and the associated problem of contacting the temperature sensor with a vibrating measuring object is also avoided.

The temperature-related signal determined by the method according to the invention is indicated as a temperature-related voltage value. This indication makes it possible to use the temperature detection for the control and regulation of the traveling wave motor, so that overheating protection is also realized.

Further advantageous embodiments and developments of the traveling wave motor according to the invention and the temperature measurement method according to the invention are set out in the dependent claims.

A preferred embodiment of the present invention is shown in the drawings and will be described below.

[0016]

FIG. 1 shows a possible configuration of an electrically excitable piezoelectric ceramic 1 provided on a stator. The piezoelectric ceramic 1 is divided into two groups of alternating piezoelectric areas, which are polarized differently.
The positively polarized piezoelectric area and the negatively polarized piezoelectric area are provided in an angular range of 2/13 · π or 1/13 · λ, respectively. Other angular ranges that are advantageous for the arrangement are, for example, 2/9 · π or 2/11 · π or 1/9 · λ or 1/11 · λ.

In the first partial area 4 of the piezoelectric ceramic 1, which is not used for the generation of traveling waves, two electrodes 5 and 6 are provided for detecting the state of the motor with a sensor technology. Thereby, for example, the vibration amplitude can be obtained. Electrode 5,
Numerals 6 are formed at least at intervals of λ / 4 or an odd multiple of λ / 4, and are used, for example, for detecting vibration amplitude. 6 each
Pairs or five or four pairs of positive and negative pre-polarized areas form working electrodes or excitation systems on both sides of the sensor electrodes 5,6. The working electrodes 2, 3 are excited by alternating voltages that are phase shifted from one another by 90 °.

A measuring electrode 8 is mounted in the second partial area 7 of the piezoelectric ceramic 1, which is likewise not used for generating traveling waves. The measuring electrode 8 can occupy only a partial area of the second partial area 7 that is not available for the generation of traveling waves, or it can occupy the entire area of this second partial area 7.
The measuring electrode 8 can be provided symmetrically or asymmetrically in a partial area of the second partial area 7 that cannot be used for generating a traveling wave. The second sub-region 7 of the piezoelectric ceramic 1, which is not available for the generation of traveling waves, can likewise be polarized as part of the piezoelectric area, but need not be.

For adjacent zones that are polarized differently, the measuring electrode 8 must always maintain a minimum insulation distance.

As can be seen from the circuit diagram of FIG. 2, the capacitor 9 is connected so that the measuring electrode 8 and the capacitor 9 form a capacitive voltage divider. Connected capacitor 9
Can be housed in an electronic measurement and evaluation device. The working electrodes 2 and 3 and the measuring electrode 8 are thermally connected via the piezoelectric ceramic 1. The capacity of the piezoelectric ceramic 1 is shown in FIG.
As can be seen, in the normally desired operating temperature range of -40 ° C to + 80 ° C, it shows remarkable temperature characteristics. Here, the capacity of the piezoelectric ceramic increases by about 50% with respect to the value at -40 ° C. The result of this measurement is
The capacity is calculated by the configuration of the capacity voltage divider, which makes it possible to determine the stator temperature. Accordingly, a capacitor having a temperature-stable capacitance value is selected as the capacitor 9 to be connected. For the purpose of calculating the capacitance, it is advantageous if the capacitance value of the temperature-stable capacitor 9 is as large as the corresponding capacitance value of the measuring electrode 8 at a predetermined temperature, for example, room temperature.

The temperature-stable capacitor 9 and the measuring electrode 8 can be connected in series or in parallel. In the circuit diagram of FIG. 2, for example, the capacitor 9 and the measurement electrode 8 are connected in series. To measure the temperature of the stator, the capacitive voltage divider is _{supplied with} an alternating voltage of constant amplitude and frequency _fmess generated by a digital oscillator. If the second partial area 7 of the piezoelectric ceramic 1, which is not available for the generation of traveling waves, is not polarized, when applying an AC voltage to the capacitive voltage divider,
An AC voltage having an arbitrary frequency f _mess can be selected. It is advantageous to choose a frequency between the available frequency bands.
If the second sub-range 7 of the piezoelectric ceramic 1, which cannot be used for the generation of traveling waves, is polarized, when applying an AC voltage to the capacitive voltage divider, the AC voltage of a specific first sub-range 4 is selected. I have to. The frequency f _mess must be in the range between two frequencies that occur as a multiple of the operating frequency used to drive the traveling wave motor.

Signal C relating to temperature from measuring electrode 8
(T) is extracted, and a temperature-stable reference signal C _ref is extracted from the temperature-stable capacitor 9. The two signals are compared with one another in a subtraction circuit 10 and the temperature-related signal C (T) thus determined is supplied to the amplifier 12 and possibly additionally to the analog-to-digital converter 13 and the microprocessor 14. After the passage, as shown in FIG. 4, it is expressed as a temperature-related voltage value U _mess (T).

If the piezoelectric ceramic 1, which cannot be used for the generation of traveling waves, is polarized, it is _advisable to use a bandpass filter 11 which passes only the measuring signal _Umess . Thereby,
During the operation of the motor, a disturbance voltage which appears on the measurement electrode and has a frequency for driving the motor can be removed. If the second sub-region 7 of the piezoelectric ceramic 1, which is not available for the generation of traveling waves, is not polarized, the complexity of the filter is reduced or
Or it can be completely eliminated. This is because only a small disturbance appears in this case.

Expressing the temperature-related signal as a temperature-related voltage value U _mess allows a simple use of the measuring method for control. Effective overheating protection is also provided by a simple shut-off mechanism, for example, microprocessor 14.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a piezoelectric ceramic for a traveling wave motor.

FIG. 2 is a schematic diagram of a circuit having elements important for implementing a temperature measuring method.

FIG. 3 is a characteristic curve diagram of capacitance of a piezoelectric ceramic related to temperature.

FIG. 4 is a diagram showing a signal related to temperature as a voltage value related to temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric ceramic 2, 3 AC voltage (operating electrode) 4 First partial range not usable for generation of traveling wave 5, 6 Detection electrode in motor state 7 Second partial range not usable for generation of traveling wave 8 Measurement electrode 9 Capacitor

Claims (11)

[Claims] A traveling wave motor includes a stator having a piezoelectric ceramic (1) which can be electrically excited and a rotor capable of frictionally contacting the stator, wherein the piezoelectric ceramics (1) alternate with each other. And two groups of piezoelectric zones which are polarized differently, both groups are excited by alternating voltages (2,3) which are phase-shifted from one another by 90 ° and are not available for the generation of traveling waves. First sub-range (4) of ceramic (1)
In order to detect the state of the motor using a sensor technology, a piezoelectric ceramic (1) that cannot be used to generate a traveling wave in a motor having two electrodes (5, 6) formed at least at an interval of λ / 4. A measuring electrode (8) is mounted in a second sub-region (7) of the first and second capacitors (9), so that the measuring electrode (8) and the temperature-stable capacitor (9) form a capacitive voltage divider. A traveling wave motor, wherein a capacitor (9) having a value is connected. 2. A temperature-stable capacitor (9) and a measuring electrode (8) are connected in series,
The traveling wave motor according to claim 1. 3. A temperature-stable capacitor (9) and a measuring electrode (8) are connected in parallel,
The traveling wave motor according to claim 1. 4. The capacitor according to claim 1, wherein the capacitance of the temperature-stable capacitor is the same as the capacitance of the measuring electrode at a predetermined temperature. 3. The traveling wave motor according to claim 1. 5. The method according to claim 1, wherein the measuring electrode occupies a partial area of the second partial area which is not available for the generation of a traveling wave. 3. The traveling wave motor according to claim 1. 6. The measuring electrode (8) is provided with a minimum insulation distance to the adjacent polarized piezoelectric area and to cover the entire area of the second sub-region (7) that is not available for the generation of traveling waves. Traveling wave motor according to one of the claims 1 to 4, characterized in that the traveling wave motor is occupied. 7. The method according to claim 1, wherein the second sub-region of the piezoelectric ceramic which is not available for the generation of a traveling wave is unpolarized. Traveling wave motor. 8. A traveling wave motor has a stator having an electrically excitable piezoelectric ceramic (1) and a rotor capable of frictionally contacting the stator, wherein the piezoelectric ceramics (1) are alternately arranged. It consists of two groups of piezoelectric areas to be polarized, both groups being excited by alternating voltages (2,3), which are phase-shifted from one another by 90 °, of a piezoelectric ceramic (1) not available for the generation of traveling waves. In the first partial range (4), two electrodes (5, 6) used for detecting the sub-amplitude are formed at an interval of at least λ / 4, and the piezoelectric ceramics ( A measuring electrode (8) is mounted in the second sub-region (7) of 1), and the temperature-stable capacitor (9) forms a capacitive voltage divider with the measuring electrode (8). A capacitor (9) with a certain capacitance value is connected, and the stator of this device is To measure the temperature, applying an AC voltage to the capacitive divider, it retrieves the signal C (T) related to the temperature from the measuring electrode (8), and a temperature-stable reference signal C _ref with temperature stability The temperature-related signal C (T) taken out of the capacitor (9) is compared with a temperature-stable reference signal C _ref by a subtraction circuit (10), and the temperature-related signal C (T) thus obtained is obtained.
As a voltage value U _mess related to temperature, wherein the temperature of the stator of the traveling wave motor is measured. 9. An AC voltage having an arbitrary frequency when an AC voltage is applied to a capacitive voltage divider without polarizing a second partial range (7) of a piezoelectric ceramic (1) that cannot be used for generating a traveling wave. The method according to claim 8, characterized in that: 10. A driving device for driving a traveling wave motor when a second partial range (7) of a piezoelectric ceramic (1) that cannot be used for generating a traveling wave is polarized and an AC voltage is applied to a capacitive voltage divider. 9. The method according to claim 8, wherein an AC voltage having a frequency lying between several times the frequency to be applied is selected. 11. The method according to claim 10, further comprising: after extracting the temperature-related signal and the temperature-stable reference signal, passing the extracted signals C (T) and C _ref through a band filter. The method described in.