JPH0667233B2 - Ultrasonic motor device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor device that uses piezoelectric material to generate a driving force.

2. Description of the Related Art In recent years, attention has been paid to the fact that an ultrasonic motor, which uses piezoelectric ceramics or the like to excite various ultrasonic vibrations using an electro-mechanical conversion element to obtain rotational or traveling motion, has a high energy density. ing.

FIG. 5 shows an exploded perspective view of the ultrasonic motor.

As shown in JP-A-60-190178, on the bottom surface of the vibrating body, a piezoelectric body 18 and a piezoelectric body 19 which are circularly divided into, for example, eight parts and are polarized in opposite directions at intervals of 45 ° are provided. Of the piezo-electric bodies 18 and 19 by applying drive signals 27 and 28 of several tens of kHz, which are different from each other in temporal phase by 90 deg. In addition, a standing wave with a phase difference of 90 ° occurs spatially. When the vibrations of the two standing waves are made equal, the standing waves are combined in the vibrating body 25 to generate a bending vibration wave that advances in the circumferential direction. 26 is a moving body, 29 is a spring, and 30 is a screw.

FIG. 6 shows that the point A of the vibrating body 25 depends on the traveling wave and the long axis 2w,
It shows a state in which an elliptic motion of a minor axis 2u is performed, and a moving body 26 pressurized and installed on a vibrating body 25 makes contact with the apex of the ellipse, whereby V = w · u in the direction opposite to the traveling wave of the wave. …… (1) (w
Indicates that it is moving at the speed of the traveling wave). The moving body 26 is driven in the direction opposite to the traveling wave of the wave by the frictional force between the moving body 26 and the vibrating body 25, and when the work done to the outside cannot be ignored for this frictional force, the moving body 26 and the vibrating body A slip occurs between 25 and the velocity becomes lower than V.

FIG. 7 is an electrical equivalent circuit diagram of the piezoelectric body 18 or 19.
Capacitance C ₀ that does not contribute to the piezoelectric effect and L that contributes to the piezoelectric effect,
It is considered that they are connected in parallel with C ₁ and R. The current flowing in C ₀ is called the electric arm current, and the current flowing in L, C ₁ and R is called the mechanical arm current. The mechanical arm current and the amplitude 2u of the short axis have a proportional relationship.

Even if the voltage and frequency applied to the piezoelectric bodies 18 and 19 of FIG. 5 are constant, the electrical admittance of the piezoelectric bodies 18 and 19 changes due to fluctuations in ambient temperature and mechanical load, and the rotation speed changes. Resulting in.

Problems to be Solved by the Invention As described above, the moving speed of the ultrasonic motor is determined by the product of the frequency w of the traveling wave and the short axis u of the elliptic motion, and the size of the short axis u is the mechanical arm current. Proportional to.

The fluctuation width of the minor axis u is larger than the fluctuation width of the frequency w, and the rotation speed is almost determined by the machine arm current. Piezoelectric 18,1
If the mechanical load of 9 is constant, the electrical impedance is constant, and if the voltage is constant and the frequency is constant, the mechanical arm current is constant. However, in reality, because the moving body is moving, the mechanical arm load fluctuates, and the electrical impedance fluctuates due to temperature change, and as a result, the mechanical arm current changes and the rotational speed fluctuates greatly. There is a problem.

Further, even if the mechanical arm current is kept constant, there is a problem that the rotational speed fluctuates finely due to mechanical arm load and temperature fluctuations, making precise control of the rotational speed difficult. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an ultrasonic motor device capable of performing precise rotation speed control with respect to changes in mechanical load and temperature.

Therefore, according to the present invention, a piezoelectric body is driven by an alternating voltage to excite an elastic wave in a vibrating body composed of the piezoelectric body and an elastic body, thereby applying the elastic wave to the vibrating body. An ultrasonic motor that moves a moving body that is in pressure contact with the moving body, mechanical arm current detection means that detects the mechanical arm current flowing into the piezoelectric body, and the mechanical arm current and the mechanical arm current reference value are compared. Mechanical arm current comparing means, ultrasonic motor driving means for driving the ultrasonic motor according to the output of the mechanical arm current comparing means, speed detecting means for detecting the moving speed of the moving body, and the speed detecting means. A speed comparison means for comparing the output with a speed reference value, and the output of the speed comparison means is the machine arm current reference value, and the machine arm current reference value is changed according to the output of the speed detection means. Ultrasound configured to It is a motor device.

Operation With the above configuration, by changing the machine arm current reference value according to the moving speed reference value of the ultrasonic motor detected by the speed detecting means, the machine arm current reference value and the machine arm current detecting means The ultrasonic motor can be driven according to the output to control the speed of the moving body.

Example An example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic motor device of the present invention. 4 is an ultrasonic motor, 6 is a mechanical arm current detector for detecting the mechanical arm current of the ultrasonic motor 4, and 2 is a mechanical arm current 9 output from the mechanical arm current detector 6 and a mechanical arm current reference value 8. A mechanical arm current comparator 3 to be compared is an ultrasonic motor drive circuit that drives the ultrasonic motor so that the mechanical arm current 9 becomes constant based on the output of the mechanical arm current comparator. 5
Is a speed detector such as a well-known frequency generator that detects a change in magnetic flux proportional to the moving speed from a magnet in the form of a plastic attached to the periphery of the moving body 26, and 1 is a speed detector. The speed signal 10 of the moving body 26 obtained by 5
And a speed reference value 7 and the output thereof is used as a machine arm current reference value 8 for speed comparison.

Figures 2a and 2b are frequency characteristics of the mechanical arm current and the phase with respect to the applied voltage. From this figure, when the voltage is constant, the mechanical arm current changes with the drive frequency, and if the drive frequency is the same, For example, the mechanical arm current increases as the drive voltage increases. Therefore, it can be understood that the driving frequency or the applied voltage may be changed in order to drive with a constant mechanical arm current.

FIG. 3 is an example of an ultrasonic motor drive circuit that changes the drive frequency to keep the mechanical arm current constant, and FIG. 4 is an ultrasonic motor that changes the applied voltage to keep the mechanical arm current constant. It is an example of a drive circuit.

Before explaining the overall operation, the operation of the closed loop (inner loop in FIG. 1) constituted by the mechanical arm current comparator 2, the ultrasonic motor drive circuit 3, the ultrasonic motor 4, and the mechanical arm current detector 6 will be described. explain. First, the mechanical arm current detector of FIG. 3 will be described. The the electrode section A to the piezoelectric A of 18 and the resistance element R _A1 are connected in series, a capacitor -C _A volume equal to the capacity C ₀ of the electric arm impedance of the piezoelectric body in FIG. 7
Wherein the resistance element R _A1 equal resistance element R _A2 are connected in series with,
The piezoelectric body and the resistance element are connected in parallel with the series connection body. The same applies to the electrode portion B. By obtaining the difference between the potentials of the resistance element R _A1 and the resistance element R _A2 of the electrode portion A using the differential amplifier 20, the electric arm current is canceled and the mechanical arm current 9 is detected.

Next, the overall operation of FIG. 3 will be described. The machine arm current comparator compares the machine arm current 9 converted to direct current using the smoothing device 21 with the machine arm current reference value 8. The variable oscillator 14 changes the drive frequency 13 according to the output of the mechanical arm current comparator. The 90 ° phase shifter 15 outputs two AC signals having mutually different 90 ° phases and is connected to the power amplifiers 16 and 17, respectively. With this configuration, the drive frequency is changed so that the mechanical arm current 9 is constant, and the ultrasonic motor is driven. 22 is an integral filter.

FIG. 4 is an example of an ultrasonic motor drive circuit that changes the applied voltage to make the mechanical arm current constant, and the operation will be described.
The contents of the mechanical arm current detector and the mechanical arm current comparator are the same as in FIG. Using the phase difference detector 24 and the phase comparator 23,
The drive frequency is determined so that the phase difference of the mechanical arm current 9 with respect to the drive voltage becomes constant, and the output of the mechanical arm current comparator is used as the gain control signal of the power amplifier so that the mechanical arm current 9 becomes constant. The ultrasonic motor is driven by changing the drive voltage.

As described above, the ultrasonic motor drive circuit 3 drives the ultrasonic motor by changing the drive frequency or the drive voltage so that the magnitude of the mechanical arm current 9 becomes constant.
Both examples shown in FIGS. 4 and 4 can be used.

Next, the overall operation will be described with reference to FIG. As described above, the mechanical arm current comparator 2, the ultrasonic motor drive circuit 3, the ultrasonic motor 4, and the mechanical arm current detector 6 constitute a closed loop (inner loop in FIG. 1) of the ultrasonic motor 4. The arm current 9 is driven to be constant, and its constant value is determined by the mechanical arm current reference value 8. The rotation speed of the ultrasonic motor 4 is almost determined by keeping the mechanical arm current constant, but the rotation speed is not precisely determined due to load fluctuation, temperature fluctuation, and the like. Therefore, a closed loop (the outer loop in FIG. 1) is configured by using the speed comparator 1 and the speed detector 5, and the machine arm current reference value is changed so that the speed signal 10 becomes precisely constant and the rotation speed control is performed. I do.

As described above, the ultrasonic motor is driven so that the machine arm current becomes constant according to the machine arm current reference value, and the machine arm current reference value is changed so that the speed signal becomes precisely constant. The control becomes possible, and the controllability of the ultrasonic motor becomes extremely high because the rotation speed is controlled by controlling the magnitude of the mechanical arm current, which is a parameter closely related to the rotational speed of the ultrasonic motor.

Although the present embodiment has been described by using the disc type ultrasonic motor, the present invention is not limited to the disc type ultrasonic motor, and may be a ring type ultrasonic motor or a linear moving linear ultrasonic wave. It can also be applied to motors.

As described above, according to the present invention, by driving the ultrasonic motor so that the mechanical arm current becomes constant according to the mechanical arm current reference value, it is possible to achieve a higher voltage than driving at a constant voltage and a constant frequency. The fluctuation of the rotation speed of the sonic motor is greatly reduced, and the rotation speed can be precisely controlled by changing the mechanical arm current reference value so that the speed signal becomes precisely constant. In the present invention, the controllability of the ultrasonic motor is very high because the mechanical arm current, which is a parameter closely related to the rotational speed of the ultrasonic motor, is detected and the rotational speed is controlled by controlling the magnitude of the mechanical arm current. It becomes high and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic motor device according to an embodiment of the present invention, FIGS. 2a and 2b are frequency characteristic diagrams of a phase difference with respect to a magnitude of a mechanical arm current and a driving voltage, and FIG. FIG. 4 is a block diagram of an ultrasonic motor drive circuit when the machine arm current is controlled to be constant by changing the frequency, and FIG. 4 is an ultrasonic motor when the machine arm current is controlled to be constant by changing the drive voltage of the motor. FIG. 5 is a block diagram of a drive circuit, FIG. 5 is an exploded perspective view of a disc type ultrasonic motor used in an embodiment of the present invention, FIG. 6 is a principle explanatory diagram of the motor, and FIG. 7 is an electric equivalent circuit of the motor. It is a figure. 1 ... Speed comparator, 2 ... Machine arm current comparator, 3 ... Ultrasonic motor drive circuit, 4 ... Ultrasonic motor, 5 ... Speed detector, 6 ... Machine arm current detector.

Claims (1)

[Claims] 1. A moving body installed on the vibrating body under pressure contact by driving the piezoelectric body with an alternating voltage to excite an elastic wave on the vibrating body composed of the piezoelectric body and the elastic body. An ultrasonic motor for moving the mechanical arm, a mechanical arm current detecting means for detecting a mechanical arm current flowing into the piezoelectric body, a mechanical arm current comparing means for comparing the mechanical arm current with a mechanical arm current reference value, and a mechanical arm. Ultrasonic motor driving means for driving the ultrasonic motor according to the output of the current comparing means, speed detecting means for detecting the moving speed of the moving body, and speed for comparing the output of the speed detecting means with a speed reference value. An ultrasonic motor device comprising: a comparison unit, wherein the output of the speed comparison unit is the mechanical arm current reference value, and the mechanical arm current reference value is changed according to the output of the speed detection unit.