JP2989887B2 - Ultrasonic motor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor, and more particularly, to an improvement in an ultrasonic motor that applies a motor drive voltage to a piezoelectric element of a stator unit to rotate a rotor unit.

[Conventional technology] Conventionally, ultrasonic motors have low operating noise, low inertia, and can be instantaneously stopped and started. Simple motor structure Higher operating speed than traveling wave ultrasonic motors with larger shaft torque than electromagnetic motors Possible Single-phase drive is possible (traveling-wave type ultrasonic motor is two-phase drive), so it can be expected to improve the performance of products by applying it to existing motor-based products. ing.

FIG. 6 shows an example of such an ultrasonic motor.

The ultrasonic motor 10 is formed in a cylindrical shape, and a bolt 12 is provided at the center thereof. This bolt 12
The block bodies 14 and 16 are screwed at the upper and lower positions. Each of the blocks 14 and 16 is formed in a cylindrical shape, and is threaded at its center so as to be screwed to the bolt 12.

And, between the blocks 14 and 16, two piezoelectric elements
18a and 18b are arranged. That is, the two piezoelectric elements 18a and 18b are sandwiched between the blocks 14 and 16.

Electrodes 20 are attached to the upper and lower surfaces of one of the piezoelectric elements 18b, and an AC power supply (not shown) is connected to the electrodes 20, so that a motor driving voltage of a predetermined frequency is applied. .

When an AC voltage having a predetermined frequency is applied to the electrode 20 in this manner, the piezoelectric element 18 is applied to the upper and lower thickness directions (arrows).
(100 directions). At this time, block body 14
This longitudinal vibration is transmitted to
And 16 are screwed to the bolt 12, so that the screw generates torsional vibration. In this way, a combined vibration of the longitudinal vibration and the torsional vibration is generated on the end surfaces of the block bodies 14 and 16. Therefore, by attaching a rotor (not shown) to the upper end of the block 14,
The rotor is rotationally driven by the combined vibration generated on the end face of the rotor 14, whereby a rotational driving force can be obtained.

Various improvement techniques of such an ultrasonic motor are disclosed in JP-A-63-217984 and JP-A-1-76193.

[Problems to be Solved by the Invention] As described above, the ultrasonic motor generates a rotational force by applying a single-phase AC voltage to the piezoelectric element 18 as a motor drive voltage. Varies greatly depending on the frequency of the motor drive voltage, and the rotational force generation efficiency becomes maximum at a specific frequency (hereinafter, referred to as an optimum drive frequency).

This optimum drive frequency is a frequency unique to each motor, and the bandwidth of this frequency is very narrow.

Further, the value of the optimum driving frequency is not always constant during operation, but changes at any time depending on operating conditions such as a temperature change of an element and a size of a load. Therefore, in order to drive the ultrasonic motor with high efficiency, it is necessary to detect the constantly changing optimal driving frequency and perform feedback control of the frequency of the motor driving voltage.

However, in the conventional technology, the changing optimal driving frequency cannot be electrically detected for the feedback control. Therefore, the frequency of the motor driving voltage is always set to a constant value, or is set to a value near the frequency considered to be the optimal driving frequency. The motor drive voltage must be set, and the frequency of the motor drive voltage cannot be feedback-controlled following the changing optimal drive frequency.

Therefore, the conventional ultrasonic motor has a problem in that the efficiency of generating the rotational driving force is poor, and it is not possible to exhibit sufficient performance.

The present invention has been made in view of such a conventional problem, and has as its object to perform feedback control so that the frequency of a motor drive voltage always follows an optimum drive frequency that changes according to operating conditions, so that the optimum An object of the present invention is to provide an ultrasonic motor that can be driven in a state.

Means for Solving the Problems To achieve the above object, the present invention provides an ultrasonic wave in which a motor drive voltage is applied to a piezoelectric element of a stator unit, and a rotor unit is rotated by the obtained longitudinal vibration and torsional vibration. In the motor, a torsional vibration sensor disposed at or near the antinode of the torsional vibration generated in the stator portion and extracting the torsional vibration as an electric signal; and a motor drive voltage applied to a piezoelectric element of the stator portion Phase comparing means for outputting a phase difference from the electric signal taken out of the torsional vibration sensor as a phase angle φ; and a phase angle φ output from the phase comparing means, wherein a predetermined angle α ゜ at which a preset maximum efficiency is obtained. Frequency adjusting means for adjusting the frequency of the motor drive voltage applied to the piezoelectric element so that

Also, the present invention provides an ultrasonic motor that rotates a rotor unit by longitudinal vibration obtained by applying a motor drive voltage to a piezoelectric element of a stator unit and torsional vibration generated by a bolt based on the longitudinal vibration, A torsional vibration sensor that extracts a torsional vibration of the stator portion as an electric signal; and a phase that outputs a phase difference between a motor drive voltage applied to the piezoelectric element of the stator portion and the electric signal extracted by the torsional vibration sensor as a phase angle φ. Comparing means, frequency adjusting means for adjusting the frequency of the motor drive voltage applied to the piezoelectric element so that the phase angle φ output from the phase comparing means is a constant angle α ゜ at which a preset maximum efficiency is obtained. And characterized in that:

[Operation] The present inventor conducted various experiments from the viewpoint that if the frequency of the motor drive voltage deviates from the optimal drive frequency, this can be detected indirectly.

As a result of this experiment, no matter how the optimal driving frequency changes, as long as the frequency of the motor driving voltage is controlled to the optimal driving frequency, the phase difference between the motor driving voltage and the torsional vibration generated in the stator section, and so on. That is, it has been found that the phase angle φ always has a constant value α ゜.

FIGS. 5A and 5B are explanatory diagrams for that purpose.

Figure 5 (A) is an explanatory diagram showing a motor drive voltage signals V ₁ and generated the phase of the torsional vibration signal V ₂ is applied to the piezoelectric element. The phase difference between these two signals is the phase angle φ in the portion shown by the broken line in the figure.

Further, FIG. 5 (B) is a graph showing the relationship between frequency f and the phase angle φ of the motor drive voltage V ₁ applied to the voltage element in certain conditions, when the optimum drive frequency f _M The phase angle φ is α ゜.

According to the inventor's experiments, this when the operating conditions are variously changed, but changes to various also curves on the diagram showing the relationship between the frequency f and the phase angle phi, the phase with respect to the optimum drive frequency f _M It has been confirmed that the fact that the angle φ is α ゜ does not change under any conditions.

The present invention has been made based on such a fact.

In the present invention, and the phase angle φ is first phase difference between the motor drive voltage V ₁ of the electric signal V ₂ and the predetermined frequency based on torsional vibration obtained by the torsional vibration sensor detected by the phase comparing means . Then, the frequency of the motor drive voltage is feedback-controlled by the frequency adjusting means so that the phase angle φ obtained from the phase comparing means becomes α ゜, which is the phase angle at which the maximum efficiency is obtained.

Thus, according to the present invention, the frequency of the motor drive voltage is always controlled to the optimum drive frequency.

As described above, according to the present invention, the ultrasonic motor can always be driven with the highest efficiency by adjusting the frequency of the motor driving voltage so that the phase angle φ always becomes α ゜.

Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of an ultrasonic motor to which the present invention is applied. This example is a bolted Langevin type ultrasonic motor. The same members as those of the ultrasonic motor shown in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

The ultrasonic motor 10 according to the embodiment includes a stator portion 11 and a rotor (not shown) attached to an end surface of the stator portion 11, and the stator portion 11 includes piezoelectric elements 18a and 18b, and block members 14 and 16. And bolts (not shown).

The piezoelectric element 18a, 18 are sandwiched between the block body 14, a predetermined motor drive voltages V ₁ through the electrode 20 from the terminal T ₃ and T ₄ are configured to be applied.

Therefore, the application of a motor driving voltage V ₁ of the predetermined frequency to the terminals T ₃ and T _4, the longitudinal vibration is generated piezoelectric element 18a, by 18b, the longitudinal vibration will be transmitted to the block body 14, 16 . Then, the bolts screwed into the blocks 14 and 16 generate torsional vibration by the bolts, and the combined vibration of the torsional vibration and the longitudinal vibration is transmitted to the end face of the stator. A rotor (not shown) in contact with the end face of the motor 11 is driven to rotate.

One of the features of the ultrasonic motor 10 of the present invention is that
11 is provided with a torsional vibration sensor 30 for detecting the torsional vibration generated in 11 as an electric signal. In this embodiment, the torsional vibration sensor 30 composed of a piezoelectric element and an electrode is used as the torsional vibration sensor. ing.

Further, as is well known, the torsional vibration generated in the stator portion 11 includes an abdomen showing a vibration peak and a node having a vibration value of zero, and the positions of the abdomen and the node are determined by the stator portion. Once the shape of 11 is determined, it will always be constant.

For this reason, it is preferable that the torsional vibration sensor 30 is attached to the stator portion 11 so as to be located on the antinode of the generated torsional vibration. In the present embodiment, the predetermined side surface of the block body 16 is designed to satisfy such conditions. Fixed in position.

Thus, the torsional vibration generated in the stator 11, the piezoelectric torsional vibration sensor 30 well detected by this is as torsional vibration signal V _2, the output from the terminal T ₁ and T ₂ is pulled out from the sensor electrode become.

FIG. 2 shows a drive circuit of the ultrasonic motor according to the embodiment.

The ultrasonic motor 10 of the present embodiment has a VCO 32 called a voltage-controlled oscillator, and an AC voltage of a predetermined frequency output from the VCO 32 is amplified by a power amplifier 34 to a motor drive voltage, and the terminals T ₃ and T _{3 It} is applied to the piezoelectric element 18 via ₄ and drives the ultrasonic motor 10.

The driving circuit of the embodiment, the drive voltage signal input circuit 36 to the motor drive voltage V ₁ output from the power amplifier 34 is input, the output V ₂ of the piezoelectric torsional vibration sensor 30 which is fixedly attached to block 16 And a torsional vibration sensor signal input circuit 38 to which the input signals V ₁ and V ₂ are respectively converted into appropriate voltage levels and directed to corresponding phase circuits 40a and 40b. Output.

Each of these phase shift circuits 40a and 40b converts only the phase of the input signal and outputs the converted signal.
If the V ₁ and V ₂ are in phase, the output of the phase shifting circuit 40b is performing the phase adjustment so delayed α ° with respect to the output of the phase shift circuit 40a.

The outputs of the phase shift circuits 40a and 40b are input to waveform shaping circuits 42a and 42b, where the input sine wave signal is converted into a square wave signal having the same phase as that of the sine wave signal, and a phase comparator 44
Is input to

The phase comparator 44 is formed so as to detect the phase difference between the two input signals thus input, and to output a positive / negative pulse signal proportional to the phase difference to the loop filter 46.

Thus, in the present embodiment, the drive voltage signal input circuit 36, the torsional vibration sensor signal input circuit 38, the phase shift circuits 40a and 40b, the waveform shaping circuits 42a and 42b, and the phase comparator 4
4 constitutes the phase comparison means as a whole.

The loop filter 46 is formed so as to remove high-frequency components and noise from the input signal in this way and output a DC voltage obtained by integrating the input pulse signal,
The output voltage is input to the VCO 32. That is, the VCO 32 outputs an AC voltage having a frequency corresponding to the output voltage output from the loop filter 46 to the power amplifier 34. As described above, in the present embodiment, the loop filter 46 and the VCO 32 constitute frequency adjusting means.

The embodiment has the above configuration, and its operation will be described below.

First, when the power supply (not shown) of the circuit is turned on, the VCO32
Outputs the AC voltage of the initial frequency f _i. Then, the AC voltage is amplified output as the motor drive voltages V ₁ required to drive the ultrasonic motor 10 by the power amplifier 34, is applied to the terminal T ₃ and T ₄ for driving the ultrasonic motor 10. The application of this voltage, the torsional vibration is generated in block 14 and 16, piezoelectric torsional vibration sensor 30 by the torsional vibration is generated torsional vibration signal V ₂ corresponding to the torsional vibration.

At this time, the motor drive voltage signal V ₁ output from the power amplifier 34 is supplied to the drive voltage signal input circuit 36, it is dropped to a voltage level suitable for control output. On the other hand, the torsional vibration signal V ₂ is supplied to the torsional vibration sensor signal input circuit 38 is also dropped to a voltage level suitable for control output.

Next, the respective signals in the phase shift circuits 40a and 40b are:
A phase change adjustment is performed. That is, the phase shift circuit is set to 40a.
And when the input signals V ₁ and V ₂ are in phase, the phase of the output of the phase shift circuit 40b is adjusted with respect to the output of the phase shift circuit 40a so that the output always delays α ゜ even if the frequency changes. I have. Thus, if the feedback control so that the output signal of the phase shifting circuit 40a and the phase shift circuit 40b is in phase, and V _1, the phase difference between V ₂ can be α °, the frequency of the current drive voltage Can always be controlled to the optimum driving frequency.

Next, the outputs of the phase shift circuits 40a and 40b are supplied to waveform shaping circuits 42a and 42b, respectively, and shaped into square wave signals.

FIG. 3 shows a waveform diagram when the frequency of the drive voltage is feedback-controlled to the optimum drive frequency.

FIGS. 7A and 7B show the waveform shaping circuits 42a and 42a.
2b shows an output signal. In the figure, portions of the Z ₁ represents a phase delay of the output signal of the waveform shaping circuit 42b to the output of the waveform shaping circuit 42b. In this state, the current frequency of the motor drive voltage is not the optimal drive frequency, and the phase angle φ has a value larger than α ゜.
In this case, the phase comparator 44, and outputs relative to the high impedance as shown in FIG. (C), as a pulse width corresponding negative pulse signal Z ₁ is the phase difference.
Also since the output signal of similarly waveform shaping circuit 42b also Z ₂ in FIG. (B) there is a phase lag, and outputs a negative pulse signal having a width corresponding to the delay.

Next, the keep part of Z ₃ in FIG (B), the waveform shaping circuit
The phases of the output signals of 42a and 42b match. When the phases of the output signals of the waveform shaping circuits 42a and 42b match, as described above, the phase difference between the input signals V ₁ and V ₂ of the phase shift circuits 40a and 40b is α ゜. Therefore, the frequency of the motor drive voltage in the state of Z ₃ is
The optimum driving frequency is obtained. At this time, the output of the phase comparator 44 maintains the high impedance state, and no pulse signal is output.

Next, the keep part of Z ₄ and Z ₅ in FIG (B), a phase delay occurs in the output signal of the waveform shaping circuit 42a side. In this case, the phase comparator 44 outputs a positive-side pulse signal having a width corresponding to the delay width.

The loop filter 46 receives a positive or negative pulse signal or a high impedance maintaining signal from the phase comparator 44 as described above, and outputs a predetermined analog voltage signal. FIG. 4D shows the output signal of the loop filter 46. When the input signal of the loop filter 46 is Z ₁ , Z ₂
In the case of a negative pulse as in the state of (1), the output DC voltage decreases. When the output of the phase comparator 44 has a high impedance, the output DC voltage is in a state where the state is maintained. When the input signal is a positive pulse, such as in the case of the Z ₄ and Z _5, the DC voltage at the output rises.

That is, when the phase angle φ is larger than α ゜, it is necessary to increase the frequency of the driving voltage, and conversely, the Z ₄
If and has a small phase angle than the phase angle α ° as in the case of Z _5, it is necessary to lower the frequency of the driving voltage (see the graph of FIG. 5 (B)). Therefore, the VCO 32 changes and adjusts its output frequency according to the input voltage.In the present embodiment, the frequency increases when the voltage of the loop filter 46 decreases, and conversely, when the output voltage of the loop filter 46 increases. Adjust to lower the output frequency.

FIGS. 4 (A), (B) and (C) show the case where the frequency of the drive voltage is adjusted and the motor drive voltage signal is adjusted.
The phase angle between V ₁ and the torsional vibration sensor signal V ₂ is maintained at α ゜,
The output waveform of each part of the circuit when the motor is operating at the voltage of the optimum driving frequency is shown.

In FIG. (A) has a motor drive voltage signal V ₁ which is actually applied, the torsional vibration signal V ₂ generated on the basis of the motor drive voltage is shown. Since the current drive voltage has the optimum drive frequency, the phase angle φ of both is adjusted to α ゜.

FIG. 7B shows signal waveforms output from the drive voltage signal input circuit 36 and the torsional vibration sensor signal input circuit 38 at this time, and each signal waveform is adjusted to a voltage level suitable for control. This indicates that the waveform has changed. The phase angle φ is α ゜.

FIG. 3C shows signal waveforms output from the waveform shaping circuits 42a and 42b at this time. Here, the waveforms of both outputs are completely in phase. That is, by making the phases of the output signals of the waveform shaping circuits 42a and 42b completely in phase, the phase difference between the input signals V ₁ and V ₂ of the phase shift circuits 40a and 40b is controlled to be α ゜. is there.

Thus, in this embodiment, a torsional vibration signal V ₂ to the motor drive voltage signal V _1, is an adjustment that delays the α ° phase resulting. That is, feedback control of the frequency of the motor drive voltage, by the phases of the two signals V ₁ and V ₂ is adjusted to be in phase, and controls the frequency of the motor drive voltage to keep the phase angle α ° as a result be able to. By controlling in this way,
The frequency of the motor drive voltage can be adjusted so as to always follow the optimum drive frequency that varies depending on the size of the load and the temperature of the motor, so that it is possible to drive the ultrasonic motor efficiently.

Note that the present invention is not limited to the above embodiment,
Various modifications can be made within the scope of the present invention.

For example, in the above-described embodiment, the case where the drive circuit of the ultrasonic motor 10 is configured by an analog circuit has been described as an example.
The present invention is not limited to this, and may be configured by a digital circuit as needed, or may be configured to be performed by computer control such as a CPU.

Further, in the above embodiment, using the phase shift circuits 40a and 40b,
Was configured to provide a phase difference α ° into two signals V ₁ and V _2, the present invention is not limited thereto, the phase shift circuit 40a as necessary, without using a 40b, phase comparator 44 There compares the phase of the direct both signals V ₁ and V _2, it is also possible that the phase angle is configured to control such that α °.

[Effects of the Invention] As described above, according to the ultrasonic motor according to the present invention, the frequency of the motor drive voltage can be feedback-controlled so as to always follow the optimal drive frequency that varies based on the operating conditions. Thus, the driving of the ultrasonic motor can always be performed in a good state, and the performance of the ultrasonic motor can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of an ultrasonic motor according to the present invention, FIG. 2 is a circuit configuration diagram of the entire driving device of the embodiment, and FIGS. FIGS. 4 (A), (B) and (C) are output or input waveform diagrams. FIGS. 4 (A), (B) and (C) are output waveform diagrams of each part when operating at the optimum driving frequency adjusted according to the embodiment. B) is an explanatory diagram for explaining the basic principle of the present invention, and FIG. 6 is an explanatory diagram showing an example of a conventional ultrasonic motor. 10 ... ultrasonic motor, 12 ... bolt, 14 and 16 ... block body, 18 ... piezoelectric element, 20 ... electrode, 22 ... rotor, 30 ... piezoelectric torsional vibration sensor, 32 ... VCO, 34 …… Power amplifier, 36 …… Drive voltage signal input circuit, 38 …… Torsion vibration sensor signal input circuit, 40a, 40b …… Phase shift circuit, 42a, 42b …… Waveform shaping circuit, 44 …… Phase comparator, 46 …… Loop filter.

Continued on the front page (72) Inventor Keisuke Honda 20th Oyamazuka, Oiwa-cho, Toyohashi-shi, Aichi Prefecture Inside Honda Electronics Co., Ltd. Inside the Electronics Co., Ltd. (72) Inventor Masanori Sato 20th Oyamazuka Oiwa-cho, Toyohashi-shi, Aichi Prefecture Inside Honda Electronics Co., Ltd. In-house (56) References JP-A-2-228275 (JP, A) JP-A-63-234881 (JP, A) JP-A-3-40773 (JP, A) JP-A-4-210784 (JP, A) JP-A-49-59627 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02N 2/00

Claims (2)

(57) [Claims] 1. An ultrasonic motor in which a motor drive voltage is applied to a piezoelectric element of a stator part and a rotor part is rotated by the obtained longitudinal vibration and torsional vibration, wherein an antinode of torsional vibration generated in the stator part is provided. Or a torsional vibration sensor disposed near the torsion vibration sensor to extract the torsional vibration as an electric signal; and a phase difference between a motor drive voltage applied to the piezoelectric element of the stator unit and the electric signal extracted from the torsional vibration sensor. A phase comparison unit that outputs the angle φ, and a frequency of a motor drive voltage applied to the piezoelectric element such that the phase angle φ output from the phase comparison unit becomes a constant angle α ゜ that obtains a preset maximum efficiency. An ultrasonic motor, comprising: frequency adjusting means for adjusting the frequency. 2. An ultrasonic motor for rotating a rotor part by longitudinal vibration obtained by applying a motor drive voltage to a piezoelectric element of a stator part and torsional vibration generated by a bolt based on the longitudinal vibration, Vibration sensor that extracts the torsional vibration of the portion as an electric signal, and a phase comparison that outputs the phase difference between the motor drive voltage applied to the piezoelectric element of the stator portion and the electric signal extracted by the torsional vibration sensor as a phase angle φ. Means, and frequency adjustment means for adjusting the frequency of the motor drive voltage applied to the piezoelectric element so that the phase angle φ output from the phase comparison means becomes a constant angle α ゜ at which a preset maximum efficiency is obtained. An ultrasonic motor, comprising: