JP3926523B2 - Driving frequency control method of piezoelectric actuator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a configuration of a piezoelectric actuator that can easily drive a moving body.
[0002]
[Prior art]
As a general piezoelectric actuator, there is known a piezoelectric actuator that uses a piezoelectric element as a driving source and drives a moving body by pressing and contacting the surface of a vibrating body made of an elastic body. As an example, there are an ultrasonic motor and a micromotor (Patent Application Publication No. 7-184382) for moving an object.
[0003]
The operation principle of such a piezoelectric actuator is as follows. A piezoelectric element polarized for driving is provided on one surface of the vibrating body, and an electric field is periodically applied to the piezoelectric element. As a result, longitudinal vibration and flexural vibration are excited and propagated to the entire vibrating body, and are transmitted to the moving body as a traveling wave from the phase difference of the applied electric field. This traveling wave is converted into a lateral motion by the thickness of the vibrating body, and causes an elliptical motion on the surface of the vibrating body. By placing the moving body in pressure contact with the vibrating body, the frictional force between the moving body and the vibrating body transmits the lateral movement of the surface of the vibrating body to the moving body, and the moving body moves.
[0004]
Such conventional piezoelectric actuators are characterized in that (1) the structure is simple, (2) the generated force is large with respect to the actuator size, (3) the response is excellent, and (4) it can be made of a nonmagnetic material.
On the other hand, in the conventional piezoelectric actuator, since the vertical vibration amplitude value of the vibrating body is as small as several microns, the vibrating body and the moving body are contacted in the state where the amplitude is the maximum value, that is, the resonance state of the vibrator. It was important to take out the machine output.
[0005]
[Problems to be solved by the invention]
As described above, in the conventional piezoelectric actuator and ultrasonic motor, the resonance phenomenon of the vibrator in which the amplitude of the vibrating body is increased is used in order to efficiently extract the mechanical output. For this reason, the drive frequency is limited to a specific narrow range, and there is a problem that fluctuation of the drive frequency greatly affects the operation. In addition, the piezoelectric element constituting the displacement mechanism has a characteristic that its resonance frequency changes depending on the surrounding environment, particularly temperature. For this reason, even when driven at a constant drive frequency, there is a problem that the resonance frequency of the displacement mechanism section changes and the operation of the piezoelectric actuator changes.
[0006]
[Means for Solving the Problems]
In view of the above, the present invention has been made in view of the above, and provides a piezoelectric actuator that expands the range of the movable frequency and can stably operate against fluctuations in the resonance frequency and drive frequency of the displacement mechanism section. The purpose is to do.
In order to achieve the above-mentioned object, in the present invention, the shape, material (density, rigidity, etc.), tempering treatment (including surface treatment), and fixing location of the vibrator and piezoelectric element constituting a plurality of displacement mechanism portions By changing the method and the like by the displacement mechanism unit, the resonance frequency of all the displacement mechanism units is not made the same. Therefore, the range of the movable frequency of the piezoelectric actuator composed of a plurality of displacement mechanisms can be expanded, and stable operation is possible.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
(Embodiment 1)
FIG. 1 is an assembly diagram of a piezoelectric actuator according to Embodiment 1 of the present invention, and FIG. 2 is a detailed explanatory view of a support portion in the present embodiment.
[0008]
The piezoelectric actuator 100 includes a rotation shaft 110, a support body 120 having an L-shaped vibrator 121, a rotation body 130, and a spring 140 that holds the contact between the rotation body 130 and the support body 120 at a constant pressure. It is composed of The displacement mechanism unit 123 includes a vibrator 121 and a piezoelectric element 122 attached thereto, and the piezoelectric element 122 is provided with an electrode 124 on a surface opposite to the attachment surface. The three displacement mechanism parts 123 in the support body 120 are configured such that the dimensions in the longitudinal direction become smaller in the order of 123a, 123b, and 123c. In addition, the piezoelectric elements 122a, 122b, and 122c attached to each displacement mechanism portion 123 have the same shape and size. In addition, the number of the displacement mechanism parts comprised in the support body 120 is not limited to three.
[0009]
The electrode 124 is connected to the drive circuit 150 via an electric wire or the like. The drive circuit 150 is connected to the control circuit 160 and amplifies the signal input from the control circuit 160 and inputs the amplified signal to the piezoelectric element 122. The control circuit 160 is grounded through a contact. The support 120 is grounded through a contact 125.
The spring 140 has a structure in which the central portion 141 and the beam portion 142 are thinner than the outer peripheral portion 143. Therefore, by joining the center portion 141 to the rotating shaft 110, the beam portion 142 is elastically deformed, and the outer peripheral portion 143 generates a force that pressurizes the rotating body 130 toward the support body 120. For this reason, the support 120 and the rotating body 130 can obtain stable adhesion.
[0010]
FIG. 3 shows a behavior in which the displacement mechanism unit 123 vibrates when an AC voltage is applied. When an AC voltage is applied to the piezoelectric element 122, the piezoelectric element 122 expands and contracts. However, since the attached displacement mechanism portion 123 has a free end, the expansion and contraction causes the piezoelectric element 122 and the displacement mechanism portion 123 to move. Appears as a bending force including. The displacement mechanism unit 123 generates a vibration in which a minute displacement and a force are mixed depending on the application condition of the input AC voltage, and excites longitudinal vibration and elliptical motion. Since the absolute value of the vibration amplitude is maximized at the free end of the displacement mechanism portion 123, the motion is transmitted from the displacement mechanism portion 123 to the rotating body 130 via a frictional force. Therefore, the moving direction of the rotating body 130 is determined by the lateral component of the elliptical motion in FIG.
[0011]
Further, in order to obtain a larger rotational force, it is necessary to increase the vibration amplitude of the displacement mechanism portion 123. Therefore, it is desirable that the frequency of the voltage applied to the piezoelectric element is close to the resonance frequency of the displacement mechanism unit 123. The resonance frequency of the displacement mechanism is determined by the shape, density, and rigidity of the vibrator and the piezoelectric element constituting the displacement mechanism, the relative positional relationship between the vibrator and the piezoelectric element, the support position and method of the displacement mechanism, and the like. The factors that determine the resonance frequencies of the piezoelectric elements 122a, 122b, and 122c in the present embodiment are the same, but the factors (shapes) of the vibrators 121a, 121b, and 121c are different. Therefore, the resonance frequencies of the displacement mechanism parts 123a, 123b, and 123c are different from each other.
[0012]
In this embodiment, a stainless steel material is used for the rotating body 130, but other materials such as beryllium copper, phosphor bronze, brass, duralumin, titanium, and silicon may be used.
A piezoelectric element 122 made of PZT (lead zirconate titanate) is attached to one surface of the displacement mechanism portion 123. In this embodiment, PZT is used for the piezoelectric element 122, but other piezoelectric materials such as barium titanate and lithium niobate may be used.
[0013]
FIG. 4 shows the vibration amplitude at the free end of each displacement mechanism 123 with respect to the drive frequency. Since the displacement mechanisms 123 have different resonance frequencies, the vibration amplitudes at a certain drive frequency are different. When the sum of the vibration amplitudes of the displacement mechanism portions is a certain value or more, the rotating body 130 can move, and therefore the movable frequency has a certain range. As shown to Fig.4 (a), when the resonant frequency of the several displacement mechanism part 123 is the same, a movable frequency range is narrow. For this reason, when the resonance frequency of the displacement mechanism part 123 is set to have a slight difference, the movable frequency range can be expanded (FIG. 4B). In addition, the resonance frequency of the piezoelectric element 122 changes depending on the ambient temperature and the like, and the resonance frequency of the displacement mechanism section changes accordingly. For this reason, by increasing the movable frequency range, it is possible to operate more stably than the piezoelectric actuator constituted by the displacement mechanism unit having the same resonance frequency.
(Embodiment 2)
FIG. 5 is a diagram showing a support body 220 including displacement mechanism portions 223a, 223b, and 223c in the configuration of the piezoelectric actuator according to the second embodiment of the present invention. Other configurations are the same as those of the first embodiment.
[0014]
Since the vibrators 221a, 221b, and 221c in the present embodiment are made of the same shape and material, the resonance frequencies of the individual vibrators are the same. However, the lengths of the piezoelectric elements 222a, 222b, and 222c attached to the vibrators 221a, 221b, and 221c are shortened in that order. For this reason, the displacement mechanisms 223a, 223b, and 223c including the vibrators 221a, 221b, and 221c and the piezoelectric elements 222a, 222b and 222c have different resonance frequencies. As described above, the drive frequency can be increased as in the first embodiment, and the piezoelectric actuator can be stably operated.
(Embodiment 3)
FIG. 6 is a diagram showing a support 320 including displacement mechanism portions 323a, 323b, and 323c in the configuration of the piezoelectric actuator according to Embodiment 3 of the present invention. Other configurations are the same as those of the first embodiment.
[0015]
Since the vibrators 321a, 321b, and 321c and the piezoelectric elements 322a, 322b, and 322c in the present embodiment are made of the same shape and material, the resonance frequencies of the individual vibrators and the piezoelectric elements are the same. However, in the displacement mechanism portions 323a, 323b, and 323c, the piezoelectric element 322 is pasted in a short distance from the fixed end of the vibrator 321 in that order. For this reason, the displacement mechanism parts 323a, 323b, and 323c that are configured have different resonance frequencies. As described above, the drive frequency can be increased as in the first and second embodiments, and the piezoelectric actuator can be stably operated.
(Embodiment 4)
FIG. 7 is a diagram showing supports 420a and 420b including displacement mechanism portions 423a, 423b, and 423c in the configuration of the piezoelectric actuator according to Embodiment 4 of the present invention. Other configurations are the same as those of the first embodiment.
[0016]
In this embodiment, the displacement mechanism portions 423a and 423b are formed on the same support, and the displacement mechanism portion 423c is formed on another support. Further, the fixing positions 426a and 426b for supporting the supports 420a and 420b are also present on the same radius. The vibrators 421a, 421b, 421c and the piezoelectric elements 422a, 422b, 422c constituting the displacement mechanism units 423a, 423b, 423c are made of the same shape and material, respectively. The supports 420a and 420b that constitute the displacement mechanism are made of different materials. For this reason, although the displacement mechanism parts 423a and 423b to be configured have the same resonance frequency, the displacement mechanism part 423c has a resonance frequency different from that of the other displacement mechanism parts. For this reason, similarly to the first to third embodiments, the drive frequency can be increased, and the piezoelectric actuator can be stably operated.
[0017]
Note that it is possible to change the characteristics of the material by manufacturing the supports 420a and 420b with the same material and then performing a tempering process such as annealing on one of the supports. Therefore, the resonance frequency of the displacement mechanism unit 423 can be changed, and the same effect as described above can be expected.
Further, the resonance frequency of the displacement mechanism portions 423a, 423b, and 423c can be changed by changing the support method of the fixing positions 426a and 426b, for example, by using different adhesives.
(Embodiment 5)
FIG. 8 is a diagram showing supports 520a and 520b including displacement mechanism portions 523a, 523b, and 523c in the configuration of the piezoelectric actuator according to Embodiment 5 of the present invention. Other configurations are the same as those of the first embodiment.
[0018]
In the present embodiment, the displacement mechanism portions 523a and 523b are formed on the same support, and the displacement mechanism portion 523c is formed on another support. The vibrators 521a, 521b, 521c and the piezoelectric elements 522a, 522b, 522c constituting the displacement mechanism portions 523a, 523b, 523c are made of the same shape and material, respectively. Further, the fixing positions 526a and 526b for supporting the supports 520a and 520b are different from each other. For this reason, although the displacement mechanism parts 523a and 523b to be configured have the same resonance frequency, the displacement mechanism part 523c has a resonance frequency different from that of the other displacement mechanism parts. For this reason, similarly to the first to fourth embodiments, the drive frequency can be increased, and the piezoelectric actuator can be stably operated.
[0019]
Further, even in the vibrator 521 and the piezoelectric element 522 having the same shape and material, the resonance frequency of the displacement mechanism unit 523 can be changed by changing the method of attaching the piezoelectric element, for example, by changing the bonding method or the adhesive in each displacement mechanism unit. Can be changed.
(Embodiment 6)
FIG. 9 is an assembly view showing a piezoelectric actuator according to Embodiment 6 of the present invention. In the piezoelectric actuator 600, displacement mechanisms 623a, 623b, and 623c are arranged so that the moving body 630 moves linearly. The piezoelectric actuator 600 includes a support body 620 having displacement mechanism portions 623a, 623b, and 623c, and a moving body 630. The displacement mechanisms 623a and 623c have the same shape of the vibrator 621, but the size of the piezoelectric element 622 is different. Further, the displacement mechanism portions 623a and 623c and 623b are different from each other in the shape of the vibrator and the size of the piezoelectric element 622.
[0020]
Since the piezoelectric actuator 600 according to the present embodiment actively follows a change in the resonance frequency due to an environmental change or the like, the piezoelectric element 622 is connected to the sensing circuit 680 and the drive circuit 650 via the switching circuit 670. Further, connection is made so that the output of the sensing circuit 680 is input to the control circuit 660 and the output of the control circuit 660 is input to the drive circuit 650.
[0021]
When the AC voltage output from the drive circuit 650 is connected to the piezoelectric elements 622a and 622b by the switching circuit 670, the displacement mechanisms 623a and 623b generate vibrations due to expansion and contraction of the piezoelectric elements 622a and 622b. This vibration is transmitted to the moving body 630 and the support body 620, and excites the vibration in the displacement mechanism portion 623c. A piezoelectric element 622c is attached to the displacement mechanism portion 623c, and an electromotive force is generated in the piezoelectric element 622c due to the induced vibration of the displacement mechanism portion 623c. The generated electromotive force is connected to the sensing circuit 680 by the switching circuit 670c, whereby the frequency output from the drive circuit 650 through the control circuit 660 can be controlled. The above operation is performed only when driving frequency sensing (amplitude detection) is required.
[0022]
The vibration amplitudes of the displacement mechanism portions 623a, 623b, and 623c are maximized when the relationship between the frequency of the AC voltage input from the drive circuit 650 and the resonance frequency of the displacement mechanism portion becomes constant. The resonance frequency is determined by the characteristics of each of the piezoelectric elements 622a, 622b, and 622c. In addition, the resonance frequency slightly changes depending on the pasting state with the displacement mechanism portions 623a, 623b, and 623c, the contact state with the moving body 630, the environmental temperature, and the like. When the relationship with the frequency of the AC voltage input due to the change in the resonance frequency is not constant, the vibration amplitudes of the displacement mechanism units 623a, 623b, and 623c become small. Therefore, according to the circuit configuration of the present embodiment, the maximum value of the electromotive force induced in the piezoelectric elements 622a, 622b, and 622c is changed by the vibration amplitude of the displacement mechanism portions 623a, 623b, and 623c. The amplitude of the electromotive force induced in 622a, 622b, and 622c is detected, and the frequency of the AC voltage output from the drive circuit 650 through the control circuit 660 is changed so that the amplitude always has a peak value. The relationship between the frequency and the resonance frequency can be kept constant.
[0023]
However, in order to track the resonance frequency, it is necessary to track the maximum value of the output voltage value of the displacement mechanism units 623a, 623b, 623c, but even if the drive frequency shifts from the resonance frequency to the high frequency side, Even if there is a deviation, the voltage similarly decreases, so it cannot be determined whether the frequency should be controlled high or low (FIG. 10A). Therefore, for example, the piezoelectric element connected to the sensing circuit 680 is switched from 622b to 622c using the switching circuits 670b and 670c. Thus, as shown in FIG. 10 (b), by releasing the frequency of sensing (amplitude detection) from the resonance frequency of the displacement of mechanism, by increasing or decreasing the vibration amplitude, moving direction reveals the resonant frequency. Therefore, the control direction of the drive frequency becomes clear, and the control speed can be increased. In order to increase the control speed, it is necessary to obtain in advance the relationship between the resonance frequencies of the displacement mechanisms 623a, 623b, and 623c or the vibration amplitude at the drive frequency. As an example, FIG. 11 shows a detailed control method when the resonance frequency of the displacement mechanism units 623a, 623b, and 623c is 623a <623b <623c. In this control method, a constant reference value X is provided for the amplitude, and the drive frequency f is controlled by comparing with a vibration amplitude of each displacement mechanism section. Therefore, it is necessary to appropriately determine the drive frequency increment Δf and the processing speed of the control circuit 650 according to the responsiveness and controllability of the piezoelectric actuator.
[0024]
【The invention's effect】
As described above, according to the piezoelectric actuator of the present invention, the resonance frequency of each displacement mechanism section differs by making a difference in the shape or size of the plurality of displacement mechanism sections and piezoelectric elements. Thus, the range of the movable frequency of the piezoelectric actuator can be expanded, and a stable operation that is not affected by fluctuations in the resonance frequency is possible.
[0025]
Further, by attaching a sensing circuit and a switching circuit, it is possible to actively follow fluctuations in the resonance frequency. As a result, the range of the movable frequency can be further expanded, and the operational stability can be further improved.
Furthermore, since a stable operation can be obtained without providing a drive circuit or a control circuit for each of a plurality of piezoelectric elements, the piezoelectric actuator configuration can be reduced in size.
[Brief description of the drawings]
FIG. 1 is an assembly diagram illustrating a piezoelectric actuator according to a first embodiment of the present invention.
FIG. 2 is an enlarged explanatory view showing a support shown in FIG. 1;
FIG. 3 is an explanatory diagram showing the driving principle of the piezoelectric actuator of the present invention.
FIG. 4 is an explanatory diagram showing a range of a movable frequency according to the present invention.
FIG. 5 is an enlarged explanatory view showing a support of the present invention.
FIG. 6 is an enlarged explanatory view showing a support of the present invention.
FIG. 7 is an enlarged explanatory view showing a support of the present invention.
FIG. 8 is an enlarged explanatory view showing a support of the present invention.
FIG. 9 is an assembly diagram illustrating a piezoelectric actuator according to a second embodiment of the present invention.
FIG. 10 is an explanatory diagram showing a control direction of a drive frequency according to the present invention.
FIG. 11 is an explanatory diagram showing a driving frequency control method according to the present invention;
[Explanation of symbols]
100, 600 Piezoelectric actuator 110 Rotating shafts 120, 220, 320, 420, 520, 620 Supports 121, 221, 321, 421, 521, 621 Vibrators 122, 222, 322, 422, 522, 622 Piezoelectric elements 123, 223 323, 423, 523, 623 Displacement mechanism part 124 Electrode 125 Electrode 426, 526 Fixed position 130 Rotating body 140 Spring 141 Central part 142 Beam part 143 Outer part 150, 650 Driving circuit 160, 660 Control circuit 630 Moving body 670 Switching circuit 680 Sensing circuit

Claims (2)

A plurality of displacement mechanisms each having a piezoelectric element attached to one surface of a vibrator having a free end;
A moving body in contact with the other surface of the vibrator;
At least one of the plurality of displacement mechanism portions has a resonance frequency different from the others,
A drive circuit for outputting a drive signal to each of the piezoelectric elements of each of the plurality of displacement mechanisms;
A sensing circuit that detects an amplitude of an electromotive force of the piezoelectric element due to vibration of the plurality of displacement mechanism parts;
Switching means for selectively connecting the drive circuit and the sensing circuit to the piezoelectric element;
A method for controlling the drive frequency of a piezoelectric actuator comprising a control circuit for changing the drive frequency output from the drive circuit based on the amplitude of the electromotive force detected by the sensing circuit,
When changing the driving frequency,
The frequency for amplitude detection by the sensing circuit is left as it is,
Switching the piezoelectric element connected to the sensing circuit by the switching means,
A drive frequency control method for a piezoelectric actuator, wherein a control direction of the drive frequency is obtained by increasing or decreasing an amplitude of the electromotive force detected by the sensing circuit after switching, and the drive frequency is changed by the control circuit. A plurality of displacement mechanisms each having a piezoelectric element attached to one surface of a vibrator having a free end;
A moving body in contact with the other surface of the vibrator;
At least one of the plurality of displacement mechanism portions has a resonance frequency different from the others,
A drive circuit for outputting a drive signal to each of the piezoelectric elements of each of the plurality of displacement mechanisms;
A sensing circuit that detects an amplitude of an electromotive force of the piezoelectric element due to vibration of the plurality of displacement mechanism parts;
Switching means for selectively connecting the drive circuit and the sensing circuit to the piezoelectric element;
A method for controlling the drive frequency of a piezoelectric actuator comprising a control circuit for changing the drive frequency output from the drive circuit based on the amplitude of the electromotive force detected by the sensing circuit,
When changing the driving frequency,
The vibration amplitude and the reference amplitude at each drive frequency of each of the plurality of displacement mechanism sections are respectively compared, a control direction of the drive frequency is obtained from each comparison result, and the drive frequency is changed by the control circuit. A drive frequency control method for the piezoelectric actuator.

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