JP3872337B2 - Ultrasonic motor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-excited drive type ultrasonic motor that drives a vibrating body by self-oscillation.
[0002]
[Prior art]
The basic principle of an ultrasonic motor is to cause mechanical resonance generated in a vibrating body having a piezoelectric element and to extract the rotational force or thrust of the moving body from the vibration through friction. However, the resonance point of the vibrating body shifts depending on the driving environment such as temperature. Therefore, in order to realize stable driving, it is necessary to control the frequency of the alternating voltage applied to the motor, that is, the driving frequency, according to the driving environment. Specifically, a temperature sensor and a voltage sensor are built in the drive circuit, and based on the information, the drive point is automatically tracked according to the characteristics of each motor written in the memory to obtain a stable output.
[0003]
In addition, a method of automatically tracking a driving point by detecting a current flowing in a motor or a phase difference between a voltage and a current is used, and the circuit is inevitably complicated. In this case, a method of detecting a signal from a detection piezoelectric element provided separately from the drive is widely used. However, such a complicated circuit and configuration are not preferable when considering the size and cost of the circuit when the motor is downsized.
[0004]
Self-excited drive type ultrasonic motors are provided as desired. This self-excited drive type ultrasonic motor is an attempt to drastically simplify the drive circuit of the ultrasonic motor by applying the Colpitts type oscillation circuit, which is well-known as the crystal oscillation circuit used as the time reference for watches. . An oscillation circuit using a piezoelectric vibrator such as a crystal oscillation circuit is composed of a vibration body having a piezoelectric body, a feedback circuit including an external element, and an amplification circuit. As the various noise components when the power is turned on, only a specific resonance frequency component is selected by the feedback circuit, and the oscillation is continued by amplifying it by the amplifier circuit.
[0005]
By the way, the condition for the self-excited oscillation of the ultrasonic motor is called the Bauhausen condition regarding oscillation, and is as follows when the value of the amplifier circuit is G and the value of the feedback circuit is H.
[0006]
About gain ｜ G × H ｜ ＞ 1 (1)
About phase angle ∠G + ∠H = 2πn (n = 0, 1, 2) (2)
With such a circuit configuration, the motor can be driven stably by automatically tracking the change in the resonance frequency due to the change in temperature, voltage, and external load.
[0007]
The ultrasonic motor disclosed in Japanese Patent Laid-Open No. 8-251952 “Ultrasonic Motor and Electronic Device with Ultrasonic Motor” belongs to such a self-excited drive type ultrasonic motor.
[0008]
As shown in FIG. 11, the ultrasonic motor includes at least two electrode groups each including a pressure spring 109 disposed so as to press the movable body 108 against the vibrating body 101 and a plurality of electrodes on the surface. And a piezoelectric element 102 on which 103a and 103b are formed. An output terminal is connected to each of at least two sets of electrode groups 103 a and 103 b formed on the piezoelectric element 102. Furthermore, this ultrasonic motor includes an oscillation drive circuit 405 having at least two power amplifiers 501a and 501b that independently drive each electrode group 103a and 103b, and forward and reverse rotation for setting the rotation direction of the moving body 108. Forward / reverse signal generating means 110 for generating a signal is provided. Further, the ultrasonic motor has a switching circuit 106 for selecting at least one of at least two power amplifiers 501a and 501b of the oscillation drive circuit 405 based on an output signal from the forward / reverse signal generation means 110. And by having such a structure, the ultrasonic motor which can perform forward / reverse control by a simple drive system and has high environmental reliability was realized.
[0009]
Here, when the ultrasonic motor is driven by self-excited vibration, the crystal oscillator or the like is intended for the source, and the oscillation is started and sustained because the vibration due to the self-excited oscillation is used as mechanical power. Only with the oscillation power amplifier intended for this purpose, sufficient power to function as a motor cannot be obtained. Therefore, in the self-excited drive circuit of the ultrasonic motor, the motor output is improved by providing the drive power amplifier in addition to the oscillation power amplifier. Such a configuration is also adopted with respect to the above prior art.
[0010]
However, when the self-excited drive circuit is configured by using two or more power amplifiers of the oscillation power amplifier and the drive power amplifier as described above, the oscillation power amplifier and the drive There is a difference in the operating point level between the two power amplifiers, and as a result, a minute signal at the time of rising of the self-excited oscillation cannot be transmitted smoothly, and there is a problem that an oscillation failure is likely to occur.
[0011]
[Problems to be solved by the invention]
It is an object of the present invention to eliminate an oscillation failure caused by a difference in operating point level between an oscillation power amplifier and a drive power amplifier due to manufacturing variations in a self-excited drive type ultrasonic motor aiming at miniaturization of the ultrasonic motor. An object of the present invention is to provide an ultrasonic motor having a novel self-excited drive circuit that can be avoided.
[0012]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, according to the present invention, a self-excited drive circuit includes a pre-power amplifier for oscillation and an output terminal on an electrode provided on the surface of the piezoelectric element. Connected drive power amplifier, phase adjusting capacitor with one end connected to the power amplifier input terminal and the other end, inserted between the output terminal of the power amplifier and the input terminal of the power amplifier And an LC resonance circuit for stabilizing self-excited oscillation between the input terminal of the pre-power amplifier and the power amplifier.
[0013]
According to the present invention, the Q obtained by the LC resonance circuit of the capacitor and the coil increases the amplitude of the output signal of the pre-power amplifier, and the operating point level of the power amplifier is slightly different from the operating point level of the pre-power amplifier. Even in this case, it is possible to reliably amplify the output signal of the pre-power amplifier, and as a result, it is possible to avoid an oscillation failure and provide a highly reliable ultrasonic motor with excellent start-up stability.
[0014]
The invention according to claim 2 is a self-excited drive circuit comprising: a pre-power amplifier for oscillation; a power amplifier for driving in which an output terminal is connected to an electrode provided on the surface of the piezoelectric element; Consists of a phase adjusting capacitor with one end connected to the input terminal of the power amplifier and the other end installed, and a resistor and a coil inserted in series between the output terminal of the pre-power amplifier and the input terminal of the power amplifier An LCR resonance circuit for stabilizing self-excited oscillation is formed between the input terminal of the pre-power amplifier and the power amplifier while protecting the input terminal of the power amplifier.
[0015]
According to the present invention, in addition to the effect based on the invention of the first aspect, the input terminal of the driving power amplifier is further protected, and an ultrasonic motor with higher reliability can be provided.
[0016]
According to a third aspect of the present invention, in the ultrasonic motor according to the first or second aspect, the resonance frequency of the vibration mode of the vibrating body used for driving the motor is f, the value of the capacitor is C, and the value of the coil. When L is L
f = 1 / (2π√ (LC))
The values of the capacitor and the coil are set so that the above is substantially satisfied.
[0017]
According to the present invention, the Q of the LC resonance circuit can be utilized to the maximum, and more stable oscillation starting characteristics can be obtained.
[0018]
According to a fourth aspect of the present invention, in the ultrasonic motor according to any one of the first to third aspects, at least one of the pre-power amplifier and the power amplifier is an inverting power amplifier. It is characterized by being.
[0019]
According to the present invention, in addition to the effects of the first to third aspects of the invention, the amount of phase shift in the feedback circuit portion of the self-excited drive circuit can be reduced by using the inverting power amplifier. Is effective.
[0020]
According to a fifth aspect of the present invention, in the ultrasonic motor according to any one of the first to fourth aspects, the pre-power amplifier and the power amplifier are in an active state or an inactive state based on a control signal. The state control is possible, and the pre-power amplifier and the power amplifier are activated by a control signal to cause the vibrator to self-oscillate to drive the motor.
[0021]
According to the present invention, in addition to the effects obtained by the inventions according to the first to fourth aspects, the control of the self-excited drive circuit can be realized very simply.
[0022]
According to a sixth aspect of the present invention, in the ultrasonic motor according to any one of the first to fifth aspects, the piezoelectric element has at least two sets of electrode groups formed of a plurality of electrodes on the surface. An output terminal connected to each of the electrode groups, and a power amplifier for independently exciting and driving each of the electrode groups, wherein the rotation direction of the moving body is switched by selecting the electrode group for exciting and driving. To do.
[0023]
According to the present invention, in addition to the effects of the first to fifth aspects of the invention, switching between forward and reverse rotation of the motor can be realized with an easy and simple configuration.
[0024]
According to a seventh aspect of the present invention, in the ultrasonic motor according to any one of the first to fifth aspects, the pre-power amplifier is a CMOS tri-state inverter having a control terminal. The power amplifier is a CMOS tri-state buffer with a control terminal, and the tri-state inverter and the tri-state buffer are in an active state or an inactive state based on a control signal input to the control terminal. Control is possible, and the motor is driven by causing the vibrator to self-oscillate by making the tri-state inverter and the tri-state buffer active.
[0025]
According to the present invention, in addition to the effects of the first to fifth aspects of the invention, a simple self-excited drive circuit can be obtained.
According to an eighth aspect of the present invention, in the ultrasonic motor according to the sixth aspect, the pre-power amplifier is a CMOS tri-state inverter having a control terminal, and is provided on the surface of the piezoelectric element. The power amplifier is a CMOS tri-state buffer with a control terminal provided for at least two electrode groups, and the tri-state inverter and the tri-state buffer are input to the control terminal. The state can be controlled to the active state or inactive state based on the control signal generated, and the motor is driven by causing the tri-state inverter and the tri-state buffer to be in the active state to self-oscillate the vibrator. And select a tri-state buffer to be activated, that is, select an electrode group to be driven. In wherein the switching the rotational direction of the moving body.
According to the present invention, in addition to the effect of the invention described in claim 6, a self-excited drive circuit capable of simple forward and reverse rotation can be realized.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
First, the basic configuration of the self-excited drive type ultrasonic motor of the present invention will be described. FIG. 1 is a longitudinal sectional view of a self-excited drive type ultrasonic motor of the present invention. In FIG. 1, a center shaft 202 is fixed to the fixed base 201. The vibrating body 101 to which the piezoelectric element 102 is bonded is fixedly supported in the vicinity of the central portion so as to be integrated with the fixing base 201 by the central shaft 202. The moving body 108 is rotationally guided by the central shaft 202 through a ball bearing 208, and is further applied to a protrusion 107 provided on the surface of the vibrating body 101 by a pressure spring 109 through the ball bearing 208 with a predetermined pressure. It comes to contact.
[0027]
Specifically, a pressure spring is sandwiched between the pressure spring receiving member 106 fixed to the central shaft 202 and the inner ring of the ball bearing 208, and the moving body 108 is pressed against the protrusion 107 by the outer ring of the ball bearing 208. . The piezoelectric element 102 has a disk shape, and two sets of electrodes 103a and 103b are formed on one side as shown in a plan view in FIG. As shown in the plan view of FIG. 2B, a common electrode is formed on the entire surface. One surface of the piezoelectric element 102 is integrally joined to the vibrating body 101 by means such as adhesion or thin film formation.
[0028]
When the vibrating body 101 is divided into 12 regions a1 to a6 and b1 to b6 corresponding to the two sets of electrodes 103a and 103b formed on the piezoelectric element 102, as shown in a plan view in FIG. , B1, a2, b2,..., Six projections 107 for transmitting power to every other position near the boundary between a6 and b6.
[0029]
FIG. 4 shows a cross-sectional developed view of the integrated piezoelectric element 102 and vibrating body 101 at a radius portion where the protrusion 107 exists. The piezoelectric element 102 forms a first electrode group 103a and a second electrode group 103b every other electrode divided into twelve times the wave number in the circumferential direction, as shown in FIGS. Are subjected to polarization treatment (+) and (-). In the figure, the piezoelectric elements 102 are divided into groups (1) and (2). (1) corresponds to the first electrode group 103a and (2) corresponds to the second electrode group 103b. Is.
[0030]
By applying a voltage of a predetermined frequency to the piezoelectric element 102, the vibrating body 101 is driven by exciting a standing wave of three wavelengths in the circumferential direction. The first electrode group 103a is composed of six electrodes, and each electrode is short-circuited by the first connecting means 104a. The second electrode group 103b is also composed of six electrodes, and each electrode is short-circuited by the second connection means 104b.
[0031]
Here, the vibrator 101 is driven by applying a high-frequency voltage near the resonance frequency of the vibration mode of the vibrator 101 used for driving to one of the two electrode groups 103a and 103b. The rotating direction of the moving body 108 to which the rotational force is applied by driving the vibrating body 101 is switched depending on which electrode group the vibrating body 101 is driven. That is, when a drive signal is applied to the first electrode group 103a, the vibrating body 101 bends and vibrates as shown in FIG. The positions of the peaks and valleys in this vibration are changed every half cycle as indicated by the solid line, but the protrusion 107 tilted to the right rises and the protrusion tilted to the left descends, so the rotor tilts to the right. It always comes in contact with the protrusion of the book and moves to the right. On the other hand, when a drive signal is applied to the second electrode group 103b, the positional relationship between the peaks, valleys, and protrusions changes as shown in FIG. The rotor moves in the opposite direction.
[0032]
By selecting the electrode pattern to which the drive signal is applied in this way, the forward / reverse rotation direction can be easily switched, and the forward / reverse of the single-phase drive type (standing wave type) motor, which has been considered difficult in the past. Easy rotation switching. The ultrasonic motor disclosed in Japanese Patent Laid-Open No. 8-251952 is basically the same in terms of the above configuration and operation, and further the self-excited drive type ultrasonic motor.
[0033]
As described above, the present invention provides a novel self-excited drive circuit capable of avoiding an oscillation failure due to a difference in operating point level between a pre-amplifier for oscillation and a power amplifier for drive due to manufacturing variations. It is a problem to provide. An output signal (INV output signal) of an inverting power amplifier 502 as a pre-power amplifier for oscillation in an ultrasonic motor disclosed in Japanese Patent Laid-Open No. 8-251952, which is a prior art, and power as a driving power amplifier The output signal (BUF output signal) of the amplifiers 501a and (501b) is shown in a graph in FIG.
[0034]
As can be seen from the graph, the amplitude of the frequency signal of the INV output signal is small, and the relationship between the INV operating point level and the BUF operating point level is delicate. A difference in level between the INV operating point and the BUF operating point due to manufacturing variations causes a defective oscillation. Incidentally, in the case shown in FIG. 6A, since the INV output signal does not fall to the BUF operating point level, the BUF which is a non-inverting amplifier receives the input signal level as the H level and outputs the H level. That is, the BUF cannot amplify the frequency signal output from the INV, and cannot oscillate.
[0035]
Therefore, in order to solve the above-described problem, the self-excited drive circuit in the ultrasonic motor of the present invention is a drive in which an output terminal is connected to an electrode provided on the surface of a pre-power amplifier for oscillation and a piezoelectric element. A power amplifier, a capacitor having one end connected to the input terminal of the power amplifier and the other end installed for phase adjustment, a coil inserted between the output terminal of the pre-power amplifier and the input terminal of the power amplifier, In this configuration, an LC resonance circuit for stabilizing self-excited oscillation is formed between the input terminal of the pre-power amplifier and the power amplifier.
[0036]
According to this, Q (resonance) obtained by an LC resonance circuit composed of a coil and a capacitor, a desired frequency from the output signal of the oscillation pre-power amplifier, that is, vibration of the vibrating body used for driving the motor The amplitude of a signal having a frequency near the resonance frequency of the mode is secured, and the signal having an unnecessary frequency is cut while being easily transmitted to the driving power amplifier. By doing this, even if there is a difference in operating point level between the pre-power amplifier and the power amplifier due to manufacturing variations, only the frequency required for driving the motor is surely amplified, Oscillation can be stabilized and sustained.
[0037]
A graph of the frequency characteristics of the gain and phase of the LC resonance circuit is shown by a solid line in FIG. The two-dot chain line shows the characteristics of conventional RC coupling. As can be understood from this graph, the gain is raised so as to show a maximum value at the oscillation drive frequency by the action of the LC resonance circuit, and the phase also crosses −90 ° at the oscillation drive frequency and the oscillation drive. It shows a steep characteristic that the phase is inverted in the vicinity of the frequency. As a result, as shown in FIG. 6B, the output signal of the INV as the pre-power amplifier is amplified and transmitted to the BUF as the power amplifier. This ensures that the output signal from INV crosses the operating point level of the BUF only for the desired frequency component while cutting unnecessary frequency components, which is effective against problems caused by manufacturing variations. To work.
[0038]
Here, the oscillation drive frequency fosc shown in FIG. 7 means the resonance frequency of the vibration mode of the vibrating body used for driving, and the self-excited drive circuit oscillates at this frequency to drive the motor. Made. And the capacitor and coil are
fosc = 1 / (2π√ (LC))
Is set to be The LC resonance circuit also serves as a phase shift circuit of the self-excited drive circuit, and the phase shift amount when the values of the capacitor and the coil are set as shown in the above equation is −90 °. .
[0039]
[Example 1]
FIG. 8 shows an embodiment of a self-excited drive circuit incorporated in the ultrasonic motor of the present invention.
[0040]
In FIG. 8, a piezoelectric element 102 in which two sets of electrode groups 103a and 103b formed of a plurality of electrodes are formed on one plane is joined to the vibrating body 101 by means such as adhesion. The self-excited drive circuit is configured using a vibrating body 101 to which a piezoelectric element 102 is bonded. The inverter 502 inverts and amplifies an electrical signal as excitation information from the electrode 103c formed on the surface opposite to the surface on which the two sets of electrode groups 103a and 103b of the piezoelectric element 102 are formed, or from the vibrating body 101. It plays the role of an inverting power amplifier.
[0041]
Resistor 503 is connected in parallel to inverter 502 and stabilizes the operating point of inverter 502. The output terminal of the inverter 502 is connected to the input terminals of the two sets of buffers 501a and 501b via the coil 504. Each of the output terminals of the two buffers 501a and 501b is connected to two sets of electrode groups 103a and 103b formed on one plane of the piezoelectric element 102, respectively. In addition, one end of each of the two capacitors 505 and 506 is connected to the input terminal of the inverter 502 and the output terminal via the resistor 503, and the other end is grounded, and performs phase adjustment in the self-excited drive circuit.
[0042]
The two buffers 501a and 501b are arranged immediately before the two electrode groups 103a and 103b formed on the piezoelectric element 102, respectively, for the purpose of phase adjustment and DC blocking at the input terminal and the output terminal of the inverter 502. In addition to the capacitors 505 and 506 being connected, the piezoelectric element 102 is basically a capacitive load, which is very effective for obtaining a high output from the ultrasonic motor. In addition, it is effective for facilitating switching of the rotation direction of the motor and for preventing the motor output from being lowered by means for switching the rotation direction.
[0043]
Here, the inverter 502 and the two buffers 501a and 501b each have a control terminal in addition to the input terminal and the output terminal, and the output terminal is in a high impedance state depending on the H / L level signal input to the control terminal. It uses a tri-state inverter and buffer.
[0044]
The ultrasonic motor control circuit 601 outputs an H / L level drive / stop signal and a forward / reverse rotation signal, and includes two tri-state buffers 501a and 501b and a tri-state of the self-excited drive circuit. Each is connected to the control terminal of the inverter 502. Based on the forward / reverse rotation signal from the ultrasonic motor control circuit 601, one of the two tri-state buffers 501a and 501b functions as a normal buffer, that is, in an active state, and the output terminal of the other buffer has a high impedance. The state is made inactive.
[0045]
The vibrating body 101 is selected based on the forward / reverse rotation signal output from the ultrasonic motor control circuit 601 and is excited by one tri-state buffer that is in an active state, thereby driving the ultrasonic motor. Here, when the buffer that takes the active state based on the forward / reverse rotation signal is replaced, the rotation direction of the ultrasonic motor is switched.
[0046]
The difference in configuration between the ultrasonic motor disclosed in Japanese Patent Laid-Open No. 8-25952 and the present embodiment is connected between the output terminal of the inverter 502 and the capacitor 506, and is input to two sets of buffers 501a and 501b. It may appear that the resistor connected to the terminal has just been replaced by the coil 504. However, the replacement of the coil 504 constitutes an LC resonance circuit by coupling with the capacitor 506, and as described above, the LC resonance circuit simply filters and self-excited drive circuit for the oscillation drive frequency value desired. It is not only the role of phase adjustment of the feedback circuit section.
[0047]
In other words, as another role, the Q (resonance characteristics) of the LC resonance circuit eliminates an oscillation rise defect caused by a difference in operating point level due to manufacturing variations of the oscillation inverter 502 and the driving buffers 501a and 501b. Sometimes improving reliability. This is the aim of the present invention, and has realized the provision of a self-excited drive type ultrasonic motor that is suitable for miniaturization required for application to electronic equipment and ensures reliable operation.
[0048]
[Example 2]
Next, FIG. 9 shows a second embodiment of the self-excited drive circuit incorporated in the ultrasonic motor of the present invention. The difference between this embodiment and the previous embodiment is that a resistor 507 is interposed between the tri-state inverter 502 and the coil 504. That is, the LC resonance circuit is configured by the coil 504 and the capacitor 506 in the previous embodiment, but the present embodiment is different in that an RLC series resonator is configured by the resistor 507, the coil 504, and the capacitor 506. .
[0049]
When this configuration is adopted, the gain characteristic indicated by the solid line in FIG. 7 does not change in that the maximum value is obtained at the oscillation drive frequency, but the lifting width is reduced according to the resistance value. Further, the phase does not change at a point where −90 ° is crossed in the oscillation drive frequency, but the characteristic that the phase is inverted at the oscillation drive frequency is not a steep slope but from a frequency separated from the oscillation drive frequency according to the resistance value. The reversal operation is started and a gentle inclination characteristic is exhibited. That is, when the resistor 507 is interposed, both the gain characteristic and the phase characteristic tend to be dull.
[0050]
In this embodiment, the reason why such a dull characteristic is adopted is that when the Q (resonance) value increases, the amplitude of the INV output signal as the pre-amplifier for oscillation shown in FIG. Becomes larger. If it is input to the BUF as a driving power amplifier, the BUF input terminal may be destroyed. Considering only the oscillation operation, it is preferable that the gain is large and the phase characteristics are steep. However, by adding an appropriate resistance value R from the viewpoint of protecting the BUF, higher reliability can be obtained.
[0051]
[Example 3]
Next, FIG. 10 shows a third embodiment of the self-excited drive circuit incorporated in the ultrasonic motor of the present invention. This embodiment is different from the first and second embodiments in the electrode structure of the piezoelectric element of the ultrasonic motor and the basic configuration of the self-excited drive circuit.
[0052]
As shown in FIG. 10, two sets of electrode groups 803a and 803b and a detection electrode 803d are provided on one surface of the piezoelectric element 802, and a common electrode 803c is provided on the other surface. Yes. The electrode 803 is bonded to the vibrating body 801 and is grounded via the vibrating body 801. A CMOS inverter 702 as a pre-amplifier for oscillation inputs a signal generated in the piezoelectric element 802 via the detection electrode 803d and inverts and amplifies it. Output terminals of CMOS buffers 701a and 701b as drive power amplifiers are connected to the two sets of electrode groups 803a and 803b of the piezoelectric element 802, respectively. Furthermore, one end is grounded, and the other end is connected to the input terminals of the buffers 701a and 701b, and a capacitor 706 for adjusting the phase of the self-excited driving circuit is connected in series between the output terminal of the inverter 702 and the buffers 701a and 701b. And a coil 704 inserted into the.
[0053]
The inverter 702 and the buffers 701a and 701b have a tri-state configuration similar to that used in the first and second embodiments. The drive / stop signal and the normal / reverse rotation signal output from the ultrasonic motor control circuit 601 are input to the inverter 702 and the control terminals of the buffers 701a and 701b to drive / stop the motor and switch the rotation direction. The carrying of the control is the same as in the first and second embodiments. Here, the coil 702 forms an LC resonance circuit with the capacitor 706, and brings about the same operation as that of the first embodiment.
[0054]
【The invention's effect】
The present invention is an ultrasonic motor having a vibrating body joined with a piezoelectric element and frictionally driving a moving body by a vibration wave generated in the vibrating body due to expansion and contraction of the piezoelectric element. In an ultrasonic motor provided with a self-excited drive circuit for driving a motor, the self-excited drive circuit includes a pre-power amplifier for oscillation and an output terminal connected to an electrode provided on the surface of the piezoelectric element. A power amplifier, a phase adjusting capacitor having one end connected to the input terminal of the power amplifier and the other end installed, and a coil inserted between the output terminal of the pre-power amplifier and the input terminal of the power amplifier In the self-excited drive type ultrasonic motor, a configuration in which an LC resonance circuit for stabilizing the self-excited oscillation is formed between the input terminal of the pre-power amplifier and the power amplifier is adopted. It is possible to avoid the oscillation failures due to the difference in operating point level of the power amplifier for driving the front 置電 force amplifier for oscillation due to manufacturing variations of which was IC is. In addition, this LC resonance also has an effect of suppressing spurious oscillation by giving a strong band limitation.
[0055]
Further, the present invention adopts a configuration in which a resistor and a coil are connected in series between the output terminal of the pre-power amplifier and the capacitor of the feedback circuit, and an LCR resonance circuit is formed by the resistor, the coil and the capacitor. The purpose of this is to adjust both the gain characteristic and phase characteristic of the LC resonance circuit by dulling and adjusting it, so that the input terminal of the driving power amplifier is not destroyed by a large amplitude signal due to the Q (resonance) effect of the LC resonance circuit. Thus, in the form of the LCR resonance circuit, in addition to the effect of avoiding the oscillation failure due to the manufacturing variation of the IC, the function of protecting the input terminal of the driving power amplifier is possessed, thereby further increasing the reliability. It can be secured.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an ultrasonic motor according to the present invention.
FIG. 2 is a plan view showing double-sided electrodes of the piezoelectric element of the present invention.
FIG. 3 is a diagram showing region sections and protrusion positions of the vibrating body according to the present invention.
FIG. 4 is a cross-sectional developed view of an integrated piezoelectric element and a vibrating body of the present invention at a radius portion where a protrusion exists.
FIG. 5 is a diagram illustrating rotational driving of the ultrasonic motor of the present invention.
FIG. 6 is a graph showing the relationship between inverter output, inverter operating point level and buffer amplifier operating point level, and buffer output signal, where (A) is a conventional device and (B) is for the present invention. is there.
FIG. 7 is a graph showing frequency characteristics of gain and phase of a self-excited drive circuit.
FIG. 8 is a diagram for explaining a first embodiment of a self-excited drive circuit incorporated in the ultrasonic motor of the present invention.
FIG. 9 is a diagram for explaining a second embodiment of the self-excited drive circuit incorporated in the ultrasonic motor of the present invention.
FIG. 10 is a diagram for explaining a third embodiment of the self-excited drive circuit incorporated in the ultrasonic motor of the present invention.
FIG. 11 is a circuit configuration diagram of a conventional ultrasonic motor.
[Explanation of symbols]
101 Vibrating body
102 Piezoelectric element
103a, 103b Electrode group
103c electrode
104a, 104b Connecting means to electrodes
107 protrusion
108 Mobile
109 Pressure spring
201 fixed base
202 Central axis
501a, 501b Power amplifier
502 Inverting power amplifier (inverter)
503 Resistor
504 coil
505, 506 Phase adjustment capacitor
507 resistor

Claims (9)

A vibrating body having a piezoelectric element;
A preamplifier circuit in which an input terminal is electrically connected to an electrode provided on one surface of the piezoelectric element;
A coil having one end electrically connected to the output terminal of the preamplifier circuit;
A power amplifier in which an input terminal is electrically connected to the other end of the coil, and an output terminal is electrically connected to an electrode provided on the other surface of the piezoelectric element;
A capacitor having one end electrically connected to the other end of the coil and the other end grounded;
A capacitor having one end electrically connected to the input terminal of the preamplifier circuit and the other end grounded;
A self-excited drive circuit that self-oscillates the vibrating body at
An ultrasonic motor that frictionally drives a moving body with vibration waves generated in the vibrating body . A piezoelectric element having an electrode on one surface and the other surface, the electrode on the one surface being grounded;
A vibrator having the piezoelectric element;
A preamplifier circuit in which an input terminal is electrically connected to a detection electrode provided on the other surface of the piezoelectric element;
A coil having one end electrically connected to the output terminal of the preamplifier circuit;
A power amplifier in which an input terminal is electrically connected to the other end of the coil, and an output terminal is electrically connected to an electrode provided on the other surface of the piezoelectric element;
A capacitor having one end electrically connected to the other end of the coil and the other end grounded;
A self-excited drive circuit that self-oscillates the vibrating body at
An ultrasonic motor that frictionally drives a moving body with vibration waves generated in the vibrating body . The ultrasonic motor according to claim 1, wherein a resistor is provided in series with the coil between an output terminal of the power amplifier circuit and an input terminal of the power amplifier. The ultrasonic motor according to any one of claims 1 to 3, wherein a resonance frequency of a vibration mode of the vibrating body used for driving the motor is f, a value of the capacitor is C, and a value of the coil is L. When
f = 1 / (2π√ (LC))
The ultrasonic motor is characterized in that the values of the capacitor and the coil are set so that is generally established. The ultrasonic motor according to any one of claims 1 to 4, among the front置電force amplifier and the power amplifier, and at least one of is inverted power amplifier, ultrasound, characterized in that motor. The ultrasonic motor according to any one of claims 1 to 5, wherein the front置電force amplifier and the power amplifier are those capable state control to the active state or inactive state on the basis of the control signal The ultrasonic motor is characterized in that the pre-power amplifier and the power amplifier are activated by the control signal to drive the motor by self-oscillating the vibrating body. The ultrasonic motor according to any one of claims 1 to 6 , wherein at least two sets of electrode groups each including a plurality of electrodes are formed on a surface of the piezoelectric element,
An output terminal is connected to each of the electrode groups, and a power amplifier for independently exciting and driving each electrode group is provided, and the rotation direction of the movable body is switched by selecting the electrode group to be excited and driven. And an ultrasonic motor. The ultrasonic motor according to any one of claims 1 to 6, wherein the front置電force amplifiers are CMOS tri-state inverter having a control terminal, said power amplifier having a control terminal A CMOS tri-state buffer, wherein the tri-state inverter and the tri-state buffer can be controlled in an active state or an inactive state based on a control signal input to the control terminal. An ultrasonic motor characterized in that the tri-state inverter and the tri-state buffer are activated to drive the motor by causing the vibrator to self-oscillate. 8. The ultrasonic motor according to claim 7 , wherein the pre-power amplifier is a CMOS tri-state inverter having a control terminal, and at least two sets of electrodes provided on the surface of the piezoelectric element. Each of the power amplifiers is a CMOS tri-state buffer having a control terminal, and the tri-state inverter and the tri-state buffer are connected to a control signal input to the control terminal. Based on this, state control is possible to an active state or an inactive state, and the tri-state inverter and the tri-state buffer are made active to cause the vibrator to self-oscillate to drive the motor. At the same time, select a tri-state buffer to be activated, that is, select a group of electrodes to be driven. Switching the rotational direction of the moving body in Rukoto, ultrasonic motors, characterized in that.

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