JPH0815398B2 - Ultrasonic motor drive - Google Patents

Description

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

2. Description of the Related Art In recent years, an ultrasonic motor that rotates, moves linearly or curvedly by exciting ultrasonic vibration using a piezoelectric body such as a piezoelectric ceramic has been announced, and has attracted attention because of its features such as simple structure, small size and light weight. ing.

Hereinafter, a conventional technique of an ultrasonic motor will be described with reference to the drawings.

FIG. 5 shows an example of an ultrasonic motor, in which a ring-shaped piezoelectric ceramic 2 is bonded to one of the ring-shaped surfaces of a ring-shaped elastic body 1 as a piezoelectric body to form a piezoelectric drive body 3. Reference numeral 4 is a slider made of a wear resistant material, and 5 is an elastic body, which are bonded to each other to form a moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 4. When an electric field is applied to the piezoelectric body 2, bending vibration is excited in the circumferential direction of the driving body 3 and becomes a traveling wave, whereby the moving body 6 rotates.

FIG. 6 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, the bending vibration has 9 wavelengths in the circumferential direction. In the figure, A and B are electrode groups each consisting of a small region corresponding to a half wavelength, C is a quarter wavelength, and D is a quarter wavelength electrode. Therefore, the A electrode group and the B electrode group have a phase shift of a quarter wavelength (= 90 degrees). Adjacent small electrode portions in the electrode groups A and B are polarized in the thickness direction opposite to each other. The bonding surface of the piezoelectric ceramic 2 with the elastic body 1 is the surface opposite to the surface shown in FIG. 6, and the electrode is a solid electrode. In use, the electrode groups A and B are short-circuited and used as indicated by the diagonal lines in FIG.

The operation of the ultrasonic motor configured as described above will be described below. In the electrode group A of the piezoelectric body 2, V ₀
When a voltage represented by sin (ωt) is applied (where V ₀ is an instantaneous voltage value, ω is an angular frequency, and t is time), the driving body 3 vibrates in the circumferential direction.

FIG. 7 is a perspective view of a part of the ultrasonic motor of FIG. 5, and FIG. 7A shows the state when no voltage is applied to the piezoelectric body 2, and FIG. 7 shows that a voltage is applied to the piezoelectric body 2. The situation of time is shown.

FIG. 8 is an enlarged view of the contact state between the moving body 6 and the driving body 3. In the electrode group A of the piezoelectric body 2, V ₀ · sin (ω
t), if a voltage of V ₀ · cos (ωt) with a phase difference of π / 2 is applied to the other electrode group B, a traveling wave of bending vibration can be generated in the circumferential direction of the driving body 3. . In general, if the vibration of a traveling wave is ξ, then ξ = ξ ₀ · cos (ωt−kx) (1) where ξ ₀ : instantaneous value of wave size k: wave number (= 2π / λ) λ: wavelength x : Can be expressed by position. Equation (1) can be rewritten as ξ = ξ ₀ · (cos (ωt) · cos (kx) + sin (ωt) · sin (kx)) …… (2), and equation (2) shows that the traveling wave is π temporally. Obtained as the sum of the products of cos (ωt) and sin (ωt), which are out of phase by / 2, and cos (kx) and sin (kx), which are in phase out of phase by π / 2 Is shown. From the above description, since the piezoelectric body 2 has the electrode groups A and B which are phase-shifted from each other by π / 2 (= λ / 4), the piezoelectric body 2 has a frequency output equal to the resonance frequency of the driving body 3. From the output of the oscillator,
If an alternating voltage is generated with a phase shift of π / 2 in each of them and applied to the electrode group, a progressive wave of bending vibration can be generated in the driving body 3.

FIG. 8 shows that the point A of the driving body makes an elliptical motion of the long axis 2w and the short axis 2u by the traveling wave, and the moving body 6 placed on the driving body 3 comes into contact with the apex of the ellipse. , Shows a state of moving at a velocity of v = ωu in the direction opposite to the traveling direction of the wave. That is, the moving body 6 is pressed against the driving body 3 by an arbitrary static pressure and comes into contact with the surface of the driving body 3, and the moving body 6 and the driving body 3
It is driven at a speed v in the direction opposite to the traveling direction of the wave by the frictional force between and. When there is a slip between the two, the speed becomes smaller than v above.

The speed v of the ultrasonic motor shown above can be represented by v = ωt∝ωξ ₀ (3) and is proportional to the maximum amplitude ξ ₀ of the bending vibration of the driving body 3. The magnitude of the bending vibration amplitude is different if the driving frequency is different even if the applied voltage is the same. FIG. 9 shows frequency characteristics of impedance and sensitivity (amplitude / applied voltage, that is, an amplitude value at a unit applied voltage) of the driving body 3. From the figure, when the piezoelectric body having the electrode structure of FIG. 6 is used, the resonance of the driving body 3 has one relatively large resonance below the original resonance frequency f ₀ and one resonance above the original resonance frequency f ₀ , and the sensitivity is the resonance of each resonance. It has a maximum at the frequency and a maximum at the original resonance frequency f ₀ .

Therefore, in order to drive the ultrasonic motor efficiently, it is preferable to drive the ultrasonic motor at the resonance frequency of the driving body 3.

However, as shown in FIG. 4, the resonance frequency of the driving body 3 changes depending on the static load and the load for pressing the driving body 3 and the moving body 6, and also depends on the temperature of the driving body 3. Change. Generally, the higher the temperature of the driver, the lower the resonance frequency. Since the driving body 3 generates heat due to mechanical loss during driving, the resonance frequency changes momentarily due to load fluctuation and heat generation.
That is, when the driver 3 is driven by using the oscillation circuit having a constant frequency as described above, efficient and optimum driving cannot always be performed.

The present invention has been made in view of the above points, and an object of the present invention is to provide an ultrasonic motor receiving device that can always perform efficient and optimal driving even if the resonance frequency of the driving body changes.

Means for solving the problem A driver including a piezoelectric body is driven by the output of a voltage controlled oscillator circuit, the mechanical arm current component of the current flowing into the piezoelectric body is detected by a detection circuit, and the above detection value is set for a set time. It is stored in the storage circuit at every timing, and the comparison result is compared with the storage result of the storage circuit at the previous timing and the current storage result, and the oscillation is performed on the side where the detected value becomes large according to the comparison result. The oscillation frequency of the voltage controlled oscillation circuit is set by changing the voltage value of the control terminal of the circuit.

When the stored result of the detected value of the previous mechanical arm current is larger than the stored result of the detected value of the current mechanical arm current,
From the control voltage of the control terminal at the time of storage just before the oscillation circuit,
When the control voltage for the current memory is being increased, the control voltage for the control terminal of the oscillation circuit is made smaller, and conversely, the control voltage for the current memory is made smaller than the control voltage for the previous memory. When it is on, the control voltage of the control terminal of the oscillation circuit is increased.

When the storage result of the detected value of the previous mechanical arm current is smaller than the storage result of the detected value of the current mechanical arm current, and the control voltage of the control terminal at the time of the previous storage of the oscillation circuit is Therefore, when the control voltage for the current memory is increased, the control voltage for the control terminal of the oscillation circuit is further increased, and conversely, the control voltage for the current memory is set to be higher than the control voltage for the previous memory. When the voltage is reduced, the control voltage at the control terminal of the oscillator circuit is further reduced. By controlling the machine arm current in this way, it is possible to control the machine arm current in the vicinity of the maximum value.

Therefore, even if the resonance frequency of the driver changes due to the load or the temperature, the output frequency of the oscillation circuit is always adjusted to the resonance frequency. That is, the piezoelectric driver can be driven at the resonance frequency at which the in-phase current becomes the largest for the same applied voltage.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 shows the piezoelectric driver 3 shown in FIGS. 5 and 6.
2 is an equivalent circuit near the resonance frequency viewed from the electrode group A or B of the piezoelectric body 2 in FIG. 2, (a) of FIG. 2 shows an equivalent circuit near the resonance frequency, and (b) of FIG. 2 shows an equivalent circuit at the resonance frequency. . In the figure, C ₀ represents the electric capacity, C ₁ is the mechanical elasticity, L ₁ is the mass, R ₁ is the mechanical loss, the C ₀ of the electric arm, C ₁ , L ₁ and R ₁ of The series circuit is called a mechanical arm. At the resonance frequency, C ₁ and L ₁ resonate. And ie is the electrical current,
im represents a mechanical current (that is, speed). Therefore, the driver 3
If is driven at the resonance frequency, im will flow to the maximum at the same voltage. That is, the maximum displacement can be obtained, and the maximum velocity of the moving body 6 can be obtained from the equation (3).

In FIG. 1, R ₁ is a resistor for detecting an inflow current to the piezoelectric ceramic 2 connected to the piezoelectric ceramic 2 of the piezoelectric driving body 3, and C ₁ and C ₂ are the electrode groups A and B of the piezoelectric ceramic 2 and the back surface thereof. A capacitor having the same value as the electric capacitance between the electrodes, and R ₂ is a resistor having the same value as the resistor R ₁ . Therefore, if the difference between the terminal voltages of the resistors R ₁ and R ₂ is taken by the differential amplifier 10, the electric current ie is canceled and only the mechanical current im is taken out as an output, and this im is controlled to be maximum. By doing so, the amplitude ξ ₀ can be maximized with the same applied voltage, and optimum driving can be performed.

Reference numeral 7 is a voltage controlled oscillation circuit, and the oscillation frequency can be changed by the voltage value of the oscillation frequency control terminal 7a as shown in FIG. 8 is a 90 ° phase shifter for shifting the output of the oscillation circuit 7 by 90 °. The output of the oscillator 7 and the signal phase-shifted by 90 ° are amplified by the power amplifiers 9a and 9b, respectively, and input to the two electrode groups A and B which are different in phase by 90 °. Reference numerals 12a and 12b denote storage circuits, which store the value obtained by converting the output of the differential amplifier 10 into a direct current by the rectifying circuit 11. A timing circuit 13 controls the time to be stored in the storage circuits 12a and 12b.

If the control circuit 14 applies a control voltage to the control terminal 7a at a certain time, the oscillator 7 oscillates at a frequency determined by the control characteristic of the oscillation frequency of the third oscillator.
For example, if the voltage at the control terminal is V ₁ , then the oscillation frequency is f ₁ . This oscillation output is input to the 90 ° phase shifter 8 and phase-shifted by 90 °, or directly to the power amplifiers 9a and 9b, respectively, to obtain the level required for rotating the moving body 6 at a predetermined speed. Is amplified to. Amplified signal is electrode group
It is input to A and B, and as described above, a traveling wave of bending vibration is generated in the driving body 3. The mechanical current im flowing at this time is obtained by the differential amplifier 10, the AC value is converted to DC by the rectifier circuit 11, and the storage circuit 12a is generated at the timing created by the timing circuit 13.
To memorize.

Next, the control circuit 15 to V ₃ of FIG. 3 by increasing the control voltage applied to the terminal 7a by the set value. Then, the oscillation frequency of the oscillator 7 becomes f ₃ . Drive-like mechanical current due to this f ₃
Im is stored in the memory circuit 12b by the timing circuit 13, and compared with the memory result of the immediately previous memory circuit 12a by the comparator 14,
When mechanical current im becomes smaller than the control voltage V ₃
When returning to V ₁ and increasing, V ₂ is again increased by the set value, and the mechanical current im at that time is stored in the memory circuit 12a and compared by the comparator 14.

In this way, when the control voltage is increased and the mechanical current im at that time increases, the control voltage increases again by the set value, and similarly, the control voltage increases, and when the mechanical current im decreases, the control voltage increases. Is decreased by the set value. Also, when the control voltage is decreased and the mechanical current im increases, the control voltage is further decreased by the set value, and similarly, the control voltage is decreased and the control voltage is decreased by the set value when the mechanical current im decreases. To increase. As a result, if the variable range of the control voltage is matched with the range in which the resonance frequency of the driving body 3 changes, the control circuit 15 always outputs the output frequency of the oscillator 7 so that the driving frequency of the driving body 3 matches the resonance frequency. To control. Therefore, the maximum mechanical current is always the same for the same applied voltage.
It can drive im with good efficiency.

EFFECTS OF THE INVENTION According to the present invention, even if the impedance characteristics and the resonance frequency of the piezoelectric driver change due to temperature, static load, load fluctuation, etc., optimum driving can always be performed stably.

Also, when changing the drive frequency of the ultrasonic motor in the direction in which the machine arm current value increases, this is done at regular intervals, so the processing algorithm can be greatly simplified and the processing system can be simplified. Can be

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic motor drive device according to an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram in the vicinity of a resonance frequency seen from one electrode group of a piezoelectric body, and FIG. 3 is FIG. FIG. 4 is a control characteristic diagram of the voltage controlled oscillator circuit used in the embodiment of FIG. 4, FIG. 4 is a characteristic diagram showing a change in impedance characteristic of the driver with a load,
FIG. 5 is a cross-sectional view of a conventional ultrasonic motor, FIG. 6 is a plan view showing the shape and electrode structure of the piezoelectric body used in FIG. 1, and FIG. 7 is vibration of the drive body portion of the ultrasonic motor. FIG. 8 is a model diagram showing the state, FIG. 8 is an explanatory diagram of the principle of the ultrasonic motor, and FIG.
The figure is a frequency characteristic diagram of the impedance and sensitivity of the driver. 7 ... Voltage controlled oscillator, 8 ... 90 degree phase shifter, 9a, 9b ...
Power amplifier, 10 ... Differential amplifier, 11 ... Rectifier circuit, 12a,
12b ... memory circuit, 13 ... timing circuit, 14 ... comparator, 15 ... control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Tokushima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Hiroshi Ouchi, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-60-22480 (JP, A) JP-A-58-36684 (JP, A) Actual development 57-148472 (JP, U)

Claims (1)

[Claims] 1. An elastic body and a piezoelectric body are bonded together to form a piezoelectric drive body, and by applying an AC voltage to the piezoelectric body, an elastic wave is generated in the piezoelectric drive body and applied to the piezoelectric drive body. In an ultrasonic motor that moves a moving body that is brought into pressure contact with the moving body, a variable oscillation in which the output frequency that is the drive frequency of the AC voltage is always changed during operation of the ultrasonic motor at fixed intervals. Circuit, in synchronization with the set time, by subtracting the current value flowing in the piezoelectric body and the current value flowing in the capacitive element equal to the electric capacitance value of the piezoelectric body, the current flowing in the mechanical arm of the piezoelectric body A mechanical arm current detection circuit that detects an amplitude, a storage circuit that stores the amplitude of a current that flows in the mechanical arm in synchronization with the set time, an amplitude of the mechanical arm current of the storage circuit, and a previous storage. The resulting mechanical arm A comparison circuit that compares the amplitude of the current, the variable direction of the output frequency of the variable oscillation circuit, and the comparison direction of the comparison circuit controls the variable direction of the next step of the output frequency of the variable oscillation circuit. An ultrasonic motor drive device having an oscillation control circuit.