JP3172343B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor using ultrasonic vibration as a driving force, and more particularly, to an ultrasonic motor in which an electric resonance frequency and a mechanical resonance frequency are adjusted.

[0002]

2. Description of the Related Art As a conventional technique on which the present invention is based, attention is paid to the self-capacitance of a vibrating body, and an inductance element is connected in series or in parallel with this capacitance to form a series resonance of this LC circuit. Alternatively, there has been provided an ultrasonic motor optimized for motor characteristics by utilizing parallel resonance (Japanese Patent Application Laid-Open No. 4-281373).

[0003] Here, the equivalent circuit of the ultrasonic motor inductance element are connected in series, the equivalent resistance of the resistance value R _m, consists of the equivalent capacitor of the equivalent coil and the capacitance C _m of the inductance L _m R of mechanical vibration part
And the LC series circuit, a capacitor of inherent capacitance C _d connected in parallel with the RLC series circuit and the inductance element of the serially connected inductances L _e,
It is composed of Ultrasonic motor configured as described above, the mechanical resonance frequency f _m and the electrical resonant frequency f _e and the equivalent circuit constant R of mechanical vibration relationship become as in the ultrasonic motor of the formula (1) _m, L _m, C _m and an inductance L _e, and sets the value of the inherent capacitance C _d. f _m ≦ f _e (1) where f _m is the maximum value (the following equation (3)) of the absolute value | Y | (the following equation (2)) of the admittance Y of the RLC series circuit; _fe is obtained from the following equation (4).

[0004]

(Equation 1)

[0005]

(Equation 2)

[0006]

(Equation 3)

Further, the equivalent circuit of the ultrasonic motor inductance element is connected in parallel, in parallel with the capacitor of the intrinsic capacitance C _d connected in parallel with the RLC series circuit and the RLC serial circuit of the aforementioned the inductance element of the inductance L _p is in the connected configuration. Such ultrasonic motor constructed also, the mechanical resonance frequency f _m and the electrical resonant frequency f _e and the mechanical equivalent circuit constant of the oscillation of the ultrasonic motor so that the following relationship (5) R
_m , L _m , C _m , inductance L _p , intrinsic capacitance C
The value of _d is set. In f _m ≧ f _e · · · · (5) Here, f _m from the above equation (3), f _e is obtained from the following equation (6).

[0008]

(Equation 4)

Furthermore, the inductance element described above
Are connected in series or in parallel or in series and in parallel
In the case of a wave motor, mechanical vibration
Admittance Y of the circuit excluding some RLC series circuit parts
Is equivalent circuit constant R such that the following equation (7) is obtained._m, L_m,
C_mAnd inductance L_eAnd L_p, Intrinsic capacitance C _d
Is set. | 2Y / 2ω | ≧ 0 where ω = 2πf (7)

[0010]

[SUMMARY OF THE INVENTION Incidentally, the frequency of the alternating voltage to drive the ultrasonic motor, mechanical resonance frequency f _m higher frequencies f _s from a mechanical resonance frequency f
It is changed to a frequency around _m . For this reason, as shown in FIG. 4, an ultrasonic motor in which inductance elements are connected in series and has the relationship of equation (1) is used, and an ultrasonic motor in which inductance elements are connected in parallel and has the relation of equation (5) is used. As shown in FIG. 7, the motor consumes a large amount of power at the start of driving (frequency f _s ), so that an overcurrent flows when the motor is started. When the ultrasonic motor is driven continuously for a long time, the temperature of the piezoelectric ceramic, which is the material of the piezoelectric element, rises, and the capacitance Cd between the electrodes increases. Therefore, the electrical resonance frequency f _e ′ is given by the following equation (4).
And the value of C _{d in} equation (6) becomes larger and becomes smaller than f _e . Therefore, power consumption in the mechanical resonance frequency f _m becomes larger as shown by the dotted line in FIG. 4 and FIG.
Therefore, if the ultrasonic motor is driven continuously for a long time,
The power consumption increases, and the heat generated by the drive circuit increases.

Further, the frequency characteristics of the amplitude of the ultrasonic motor inductance element is connected in parallel, since the power supply voltage is applied directly to the motor, regardless of the inductance _{L p, f m ≦ f e} , f m ≧ The same frequency characteristic is obtained in both cases of _fe . Therefore, it can be seen that shift width of the frequency for driving the ultrasonic motor are the same in either case of _{f m ≧ f e, f m} ≦ f e.

Furthermore, when the ultrasonic motor inductance element are connected in series, the mechanical resonance such that the frequency f _m and the electrical resonant frequency f _e is the same, an equivalent circuit of the mechanical vibration of the ultrasonic motor Setting the constants R _m , L _m , C _m , the inductance _Le , and the specific capacitance C _d has the following problems. That is, assuming that the supplied voltage is V _i and the voltage between the electrodes is V ₀ , the voltage V ₀ between the electrodes is represented by the following equation (8). _{V 0 = V i / (1} -ω 2 L e C d) ···· (8) , where the mechanical resonance frequency f _m and the electrical resonant frequency f _e
1-ω ² L _e in the above equation that the same bets (8)
Since C _d is 0, 1-ω ² _Le C _d becomes a positive or negative value if the value of the capacitance between the electrodes slightly changes from the predetermined value C due to disturbance. Therefore, when the value of the capacitance between the electrodes becomes slightly larger than the predetermined value C, the voltage V ₀ between the electrodes becomes negative and the phase is shifted by 180 ° with respect to the input voltage. When the value of the capacitance between the electrodes becomes smaller than the predetermined value C, the voltage V ₀ between the electrodes becomes positive, and the phase difference with respect to the input voltage becomes zero. Therefore, as shown in FIG. 9, when the ultrasonic motor is driven by applying a voltage shifted by 90 ° to the two electrodes of the A phase and the B phase, if the capacitance C _d between the A phase electrodes is slightly However, when it becomes large, a voltage shifted by 180 ° from the input voltage (phase 0 °) is applied. Further, when the value of the capacitance C _d of the B-phase becomes slightly small, a voltage of the same phase (90 °) is applied to the input voltage (voltage shifted by 90 ° by the phase shifter). Therefore, the phase difference between the A-phase and the B-phase changes irregularly from 90 ° to −90 °, and does not function as a motor.

The admittance Y of the circuit excluding the RLC series circuit part of the mechanical vibration part from the equivalent circuit of the ultrasonic motor in which the inductance elements are connected in series or in parallel or in series and in parallel is expressed by the above equation (7). Although the equivalent circuit constants R _m , L _m , and C _m , the inductance _Le , and the specific capacitance C _d are set in such a manner, the above equation (7) takes the absolute value of admittance. This satisfies the above expression (7).

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and has as its object to provide an ultrasonic motor capable of reliably driving by reducing a starting current, reducing power consumption, and suppressing heat generation of a driving circuit. And

[0015]

According to the first aspect of the present invention, there is provided a piezoelectric element or an electrostrictive element which generates mechanical vibration when an alternating voltage is supplied thereto, and the piezoelectric element or the electrostrictive element. A vibrating body that is vibrated by the mechanical vibration of, a plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the piezoelectric element or the electrostrictive element, and each of the plurality of electrodes An inductance element connected in series, and an electrical resonance frequency determined by a capacitance between the electrodes and an inductance of the inductance element is set to be lower than a mechanical resonance frequency of the vibrating body. .

According to a second aspect of the present invention, there is provided a piezoelectric element or an electrostrictive element which generates mechanical vibration when an alternating voltage is supplied, and a vibrating body which is vibrated by the mechanical vibration of the piezoelectric element or the electrostrictive element. A plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the piezoelectric element or the electrostrictive element, and an inductance connected in parallel between the corresponding electrodes in the plurality of electrodes An electric resonance frequency determined by an element and an electrostatic capacitance between the electrodes and an inductance of the inductance element is set to be higher than a mechanical resonance frequency of the vibrator.

According to a third aspect of the present invention, there is provided a piezoelectric element or an electrostrictive element that generates mechanical vibration when an alternating voltage is supplied, and a vibrator vibrated by the mechanical vibration of the piezoelectric element or the electrostrictive element. A plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the piezoelectric element or the electrostrictive element, and a series connection between each of the plurality of electrodes or between electrodes corresponding to the plurality of electrodes. an ultrasonic motor and a inductance element connected in parallel with each between the corresponding electrodes on each of the parallel or more electrodes each in series and the plurality of electrodes of,
From the equivalent circuit of the ultrasonic motor, RL of the mechanical vibration part
The mechanical resonance frequency of the mechanical vibration part is set such that X in the admittance Y = jX (j is an imaginary unit) of the circuit excluding the C series circuit becomes a negative value.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, the ultrasonic motor 80 of this embodiment includes an annular vibrator 82 made of a copper alloy or the like, and a piezoelectric body 84 (see also FIG. 2) is attached to the vibrator 82. To form a stator. Piezoelectric body 8
Reference numeral 4 denotes a piezoelectric material that converts an electric signal into mechanical vibration, and is formed by dividing and arranging in an annular shape by a large number of electrodes. On the other hand, the rotor 86 attached to the drive shaft 85 is formed by bonding an annular slider 90 to a rotor ring 88 made of an aluminum alloy or the like. Have been. As the slider 90, for example, an engineering plastic or the like is used in order to obtain a stable frictional force and a friction coefficient, so that the rotor 86 can be driven with high efficiency. Then, the piezoelectric body 84, the inductance elements 87 and 89 of the inductance L _e are connected in series (see also FIG. 2).

A drive circuit 94 as shown in FIG. 2 is connected to such an ultrasonic motor 80. That is, the drive circuit 94 includes an oscillator 96 including a voltage controlled oscillator (hereinafter, referred to as a VCO). The signal of the predetermined frequency output from the oscillator 96 is branched into two, one of which is amplified by the amplifier 98 and input to the piezoelectric body 84 via the inductance element 87 as a sine wave drive signal, and the other is the phase shifter 100 After the phase is shifted by 90 °, the signal is amplified by the amplifier 102 and input to the piezoelectric body 84 via the inductance element 89 as a cosine-wave drive signal. As a result, in the piezoelectric body 84, a standing wave of ultrasonic vibration caused by a driving signal of a sine wave and a standing wave of ultrasonic vibration having a different phase from the vibration are excited by a driving signal of a cosine wave. 82. When these two standing waves are superimposed, antinodes and nodes of the vibration become vibrating body 8.
Ultrasonic vibrations that move in an annular shape along 2, so-called traveling waves, are generated. The traveling wave is transmitted to the rotor 86 that is in pressure contact with the vibrator 82 as a rotational force in a direction opposite to the traveling direction of the traveling wave, and the rotor 86 and the drive shaft 85 rotate.

The above ultrasonic motor described 80 is a two-phase drive, the phase shifter 1 is a phase of the alternating voltage applied to each phase
Since there is no difference between the first and second phases except for the shift of ± 90 ° at 00, only one phase will be described with reference to FIG. FIG. 3 shows an equivalent circuit for one phase of the ultrasonic motor. As shown in FIG. 3, the equivalent circuit of one phase of the ultrasonic motor, the equivalent resistance of the resistance value R _m 22,
RL of a mechanical vibration part composed of an equivalent coil 24 having an inductance L _m and an equivalent capacitor 26 having a capacitance C _m
A C series circuit; a capacitor 28 having a specific capacitance C _d of a vibrating body connected in parallel to the RLC series circuit;
Inductance connected in series with the inductance element 32 of L _e to the series circuit and the capacitor 28, and a. The equivalent circuit of the ultrasonic motor is an amplifier 9
8 is connected to the power supply voltage.

[0021] In this embodiment, the mechanical resonance frequency f _m and the electrical resonant frequency f _e and the equivalent circuit constant R _m of mechanical vibration relationship become like the ultrasonic wave motor of the formula (9), L
_m , _Cm , inductance _Le , and specific capacitance _Cd are set so that the overall admittance has the frequency characteristics shown in FIG. f _m > f _e (9) The power consumption of the ultrasonic motor of the present embodiment is admittance |
Since Y | is multiplied by the square of the voltage, the result is as shown in FIG. Here, the frequency characteristic of the admittance is f _m
When ≦ f conventional ultrasonic motor power consumption with the relationship _e (FIG. 4) and the power consumption of this embodiment (FIG. 5) and comparing the, whole until you drive from the start of driving the ultrasonic motor for power consumption, in this embodiment, the power consumption during the driving start 'is, the power consumption in the vicinity of the mechanical resonance frequency f _m consecutive driven W _3' W ₁ is. On the other hand, in the conventional art, the power consumption during the driving start is W _1, the power consumption in the vicinity of the mechanical resonance frequency f _m successive driving is W
₃ Therefore, as can be understood from FIGS. 4 and 5, the power consumption of this embodiment is lower than that of the prior art. The power consumption at the start of driving of the ultrasonic motor of this embodiment is W ₁ ′. This power consumption W ₁ ′
Is smaller than the power consumption W ₃ ′ during continuous driving,
At the start of driving of the ultrasonic motor, no overcurrent flows. Furthermore, when continuously driving the ultrasonic motor near a mechanical resonance frequency f _m, smaller than the electrical resonant frequency f _e 'is f _e as described above. For this reason, in the conventional technology in which the admittance has the frequency characteristic shown in FIG.
Power near mechanical resonance frequency f _m becomes larger (W
_2> W _3). On the other hand, in this embodiment, the admittance has the frequency characteristic shown in FIG.
_The power consumption near _m decreases (W ₂ ′ <W ₃ ′). Therefore, as compared with the conventional technique, the circuit current of the drive circuit is reduced, and heat generation of the drive circuit can be suppressed.

Next, a second embodiment of the present invention will be described.
FIG. 6 shows an equivalent circuit of the ultrasonic motor according to the second embodiment. As shown in FIG. 6, the equivalent circuit of the ultrasonic motor of the second embodiment has a structure in which the inductance element 34 of the inductance L _p parallel to the RLC series circuit and the capacitor 28 described above is connected.

[0023] In this embodiment, the mechanical resonance frequency f _m and the electrical resonant frequency f _e and the mechanical equivalent circuit constant of the oscillation R of ultrasonic Namimo over data so that the following relationship (10) _m ,
L _m and C _m , inductance L _p , and specific capacitance C _d are set so that the overall admittance has the frequency characteristics shown in FIG. f _m <f _e (10) The power consumption of the ultrasonic motor of this embodiment is as shown in FIG. Here, the frequency characteristic of the admittance f _m ≧ f _e
Power consumption of a conventional ultrasonic motor having the relationship (Fig. 7)
Compared with the power consumption of this embodiment (FIG. 8), the total power consumption from the start of driving the ultrasonic motor to the end of driving thereof is W _{1 in the} present embodiment at the start of driving. 'is, power consumption of the mechanical resonance frequency f with _m <br/> near continuous driving W _3' is. On the other hand, in the conventional art, the power consumption during the driving start is W _1, the power consumption in the vicinity of the mechanical resonance frequency f _m successive driving is W _3. Therefore, as can be understood from FIGS. 7 and 8, the power consumption of this embodiment is lower than that of the prior art. The power consumption at the start of driving the ultrasonic motor of the present embodiment, 'a, the power consumption W _1' W ₁ so is less than the power consumption W ₃ 'at the time of continuous operation, the ultrasonic motor At the start of driving, no overcurrent flows. Furthermore, when continuously driving the ultrasonic motor near a mechanical resonance frequency f _m, since the electrical resonance frequency f _e as described above 'is less than f _e, admittance a frequency characteristic shown in FIG. 7 in the conventional technology has, the power consumption of around mechanical resonance frequency f _m becomes larger (W _2> W _3). On the other hand, since the admittance in the present embodiment has a frequency characteristic shown in FIG. 8, the power consumption of around mechanical resonance frequency f _m is small _{(W 2 '<W 3'} ). Therefore, in the present embodiment, as compared with the related art, the circuit current of the drive circuit is reduced, the drive efficiency is improved, and the heat generation of the drive circuit can be suppressed.

Next, the magnitude of the admittance Y of the circuit excluding the RLC series circuit part of the mechanical vibration part from the equivalent circuit of the ultrasonic motor in which the inductance elements are connected in series or in parallel or in series and in parallel will be examined. This admittance Y is obtained by the following equation (11). Where j
Is an imaginary unit where j ² = −1. Y = jX (11) First, the admittance Y in which X in Expression (11) is X ≧ 0 is considered. The admittance Y of the ultrasonic motor in which the inductance elements are connected in series is obtained by the following equation (12). Y = j {(1 / ωC _d ) −ωL _e } where ω = 2πf (12) where X ≧ 0, that is, (1 / ωC _d ) −ωL _e ≧ 0
Then, the following equation (13) is obtained. ^{(2πf) 2 ≦ 1 / (} L e C d) ···· (13) that the frequency f of the alternating voltage output from the oscillator is the mechanical resonant frequency f _m near and electrical resonance frequency f _In consideration of _e (formula (4)), the above formula (13) can be transformed into the following formula (14).

[0025]

(Equation 5)

Therefore, if X of the above equation (11) in the admittance Y of the circuit excluding the RLC series circuit part of the mechanical vibration part from the equivalent circuit of the ultrasonic motor is X ≧ 0, f
_It has a relationship of _m ≦ _fe .

The admittance Y of the ultrasonic motor in which the inductance elements are connected in parallel is given by the following equation (15).
Is obtained. Y = j {ωC _d −1 / (ωL _p )} where ω = 2πf (15) where X ≧ 0, that is, ωC _d −1 / (ωL _p ) ≧ 0
Then, the following equation (16) is obtained. ^{(2πf) 2 ≧ 1 / (} L p C d) ···· (16) that the frequency f of the alternating voltage outputted from the oscillator is the mechanical resonant frequency f _m near and electrical resonance frequency f _{In consideration of e} (formula (6)), formula (16) can be transformed into the following formula (17).

[0028]

(Equation 6)

[0029] Thus, if X is X ≧ 0 of the equation (11) in the A Domita <br/> Nsu Y of the circuit except the RLC serial circuit section of the mechanical vibration part from the equivalent circuit of the ultrasonic motor, f
_It has a relationship of _m ≧ _fe .

From the above, when the admittance Y is conditioned by the equation (7), the relationship of f _m ≦ _{fe for} an ultrasonic motor in which inductance elements are connected in series, and the inductance elements connected in parallel It has been for the ultrasonic motor obtained relationship f _m ≧ f _e, so that the problems described problems the invention is to provide occurs.

Therefore, in the above-described first and second embodiments, it is assumed that X in the equation (11) is an admittance Y having a negative value.

That is, in the case of the ultrasonic motor of the first embodiment, X <0, that is, (1 / ωC _d ) −ωL _e.
If <0, the following equation (18) is obtained.

[0033]

(Equation 7)

In the case of the ultrasonic motor according to the second embodiment, X <0, ie, ωC _d −1 / (ωL _p ) <0.
Then, the following equation (19) is obtained.

[0035]

(Equation 8)

From the above, X in the admittance Y (Equation (11)) of the circuit excluding the RLC series circuit portion of the mechanical vibration portion from the equivalent circuit of the ultrasonic motor in which the inductance elements are connected in series or in parallel is X <X If 0, the relations of the equations (9) and (10) when the inductance elements are connected in series or in parallel are obtained.

The first embodiment described above and the second embodiment
In the embodiment, the mechanical resonance frequency f _mAnd electrical resonance frequency
Number f_eOf the ultrasonic motor so that
Equivalent circuit constant R of mechanical vibration_m, L_m, C_mAnd Indak
Tance L_e, Intrinsic capacitance C _dIs set,
The motor actually drives.

[0038]

As described above, according to the first to third aspects of the present invention, according to an ultrasonic motor in which an inductance element is connected in series or in parallel and in series and in parallel,
Since the electric resonance frequency and the mechanical resonance frequency are adjusted so that power consumption is reduced, there is an excellent effect that overcurrent does not flow during driving and power consumption is reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a schematic configuration of an ultrasonic motor.

FIG. 2 is a schematic configuration diagram of a drive circuit of an ultrasonic motor.

FIG. 3 is an equivalent circuit of the ultrasonic motor of the first embodiment in which inductance elements are connected in series.

FIG. 4 is a diagram showing frequency characteristics of admittance and power consumption of an equivalent circuit of a conventional ultrasonic motor having a mechanical resonance frequency smaller than an electric resonance frequency.

FIG. 5 is a diagram showing frequency characteristics of admittance and power consumption of an equivalent circuit of the ultrasonic motor according to the first embodiment having a mechanical resonance frequency higher than an electrical resonance frequency.

FIG. 6 is an equivalent circuit of the ultrasonic motor according to the second embodiment in which inductance elements are connected in parallel.

FIG. 7 is a diagram showing frequency characteristics of admittance and power consumption of an equivalent circuit of a conventional ultrasonic motor having a mechanical resonance frequency smaller than an electric resonance frequency.

FIG. 8 is a diagram illustrating frequency characteristics of admittance and power consumption of an equivalent circuit of the ultrasonic motor according to the second embodiment in which the mechanical resonance frequency is higher than the electrical resonance frequency.

FIG. 9 is a schematic configuration diagram of a drive circuit of an ultrasonic motor in which inductance elements are connected in series.

[Explanation of symbols]

 20 Ultrasonic motor equivalent circuit 32, 34 Inductance element

Claims (3)

(57) [Claims] A piezoelectric element or an electrostrictive element that generates mechanical vibration when an alternating voltage is supplied; a vibrating body that is vibrated by the mechanical vibration of the piezoelectric element or the electrostrictive element; A plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the distortion element; and an inductance element connected in series to each of the plurality of electrodes. An ultrasonic motor in which an electric resonance frequency determined by a capacitance and an inductance of the inductance element is set to be lower than a mechanical resonance frequency of the vibrator. 2. A piezoelectric element or an electrostrictive element that generates mechanical vibration when an alternating voltage is supplied; a vibrator vibrated by the mechanical vibration of the piezoelectric element or the electrostrictive element; A plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the strain element; an inductance element connected in parallel to each of the corresponding electrodes in the plurality of electrodes; An ultrasonic motor in which an electric resonance frequency determined by the capacitance of the above-mentioned and the inductance of the inductance element is set to be higher than the mechanical resonance frequency of the vibrator. 3. A piezoelectric element or an electrostrictive element that generates mechanical vibration when an alternating voltage is supplied; a vibrator vibrated by the mechanical vibration of the piezoelectric element or the electrostrictive element; A plurality of electrodes arranged so that a plurality of alternating voltages having a predetermined phase difference can be applied to the strain element; and a plurality of electrodes in series with each of the plurality of electrodes or in parallel with a plurality of electrodes between corresponding ones of the plurality of electrodes. each an ultrasonic motor and a inductance element connected in parallel with each between the corresponding electrodes in series and the plurality of electrodes, mechanical vibration part from the equivalent circuit of the ultrasonic motor of the electrode RL
An ultrasonic motor in which the mechanical resonance frequency of the mechanical vibration part is set such that X in the admittance Y = jX (j is an imaginary unit) of the circuit excluding the C series circuit becomes a negative value.