Patent Description:
There is a known conventional mechanism that drives a contact member using a plurality of vibrators. The plurality of vibrators employ electromechanical energy conversion elements, such as piezoelectric devices and electrostriction elements, and are driven by a common drive circuit. This reduces a circuit structure as compared with a case where individual drive circuits are respectively installed for the plurality of vibrators. As a related technique, a vibration driving device in which three plate-shaped vibrators are arranged at angular intervals of <NUM> degrees so as to drive a ring-shape driven body is proposed (see <CIT> (<CIT>)). Moreover, a driving device in which two piezoelectric devices arranged on a straight line drive a tabular single movable body is proposed (see <CIT> (<CIT>)).

The vibrators of the vibration driving device of <CIT> are connected in parallel. Accordingly, since the vibrators vibrate at different amplitudes and phases because of difference in the resonance frequencies of the respective vibrators, sliding loss occurs between the vibrators and the contact member according to the vibration velocity difference between the respective vibrators. If the resonance frequencies of the vibrators are made uniform when manufacturing the vibration driving device of <CIT>, the sliding loss is reduced to some extent. However, this needs the operation to select vibrators according to the frequency and cannot eliminate the difference of the vibration velocities of the respective vibrators due to the difference in load.

In the meantime, the vibrators of the driving device of <CIT> are connected in series. Accordingly, the vibrators connected in series vibrate as one resonance system. Accordingly, vibration phases of the vibrators are made uniform to some extent. And since a balance of applied voltage depends on the amount of load, the sliding loss becomes small. However, since the resonance frequencies of the vibrators depend on the load, the difference of the vibration velocities of the vibrators cannot be eliminated. Further cited prior art documents are <NPL>, featuring a vibration actuator according to the preamble of claim <NUM>, <CIT> showing a piezoelectric element drive circuit and robot, <CIT> showing a piezoelectric element, vibratory actuator and drive unit, <CIT> showing a driving device, piezoelectric motor, electronic component conveyance apparatus, and robot and <CIT> showing a vibration type driving apparatus, interchangeable lens and imaging apparatus including vibration type driving apparatus, and method for adjusting vibration type driving apparatus, <CIT> showing a piezoelectric element driving circuit and pump device, and <CIT> showing a vibration wave driving device, image pickup device, optical apparatus, liquid discharge device, and electronic apparatus.

The present invention provides a vibration actuator and a system further including a driving device therefor that are capable of reducing difference of vibration velocities when a contact member is driven using a plurality of vibrators.

Accordingly, aspects of the present invention provide a vibration actuator and a system as specified in claims <NUM> and <NUM>, respectively.

According to the present invention, the difference of the vibration velocities of the vibrators when the contact member is driven using a plurality of vibrators can be reduced.

Hereafter, examples not covered by the claimed invention and embodiments according to the present invention will be described in detail by referring to the drawings. Configurations described in the following embodiments are only examples, and the scope of the present invention is not limited by the configurations described in the embodiments but solely by the appended claims.

<FIG> are views showing an example of a configuration of a vibrator device <NUM> concerning a first example not covered by the claimed invention. The vibrator device <NUM> contacts a contact member and moves relative to the contact member. Thereby, the vibrator device <NUM> drives the contact member. <FIG> shows a circuit configuration in which three vibrators <NUM>, <NUM>, and <NUM> are connected in series. Piezoelectric members, electrostriction elements, etc. that are electric-mechanical energy conversion means are joined to the vibrators <NUM>, <NUM>, and <NUM>. Hereinafter, the following description assumes that a piezoelectric member is joined to each of the vibrators. <FIG> is an equivalent circuit diagram of the vibrator device <NUM> in <FIG>.

As shown in <FIG>, inductors are respectively connected in parallel to the vibrators <NUM>, <NUM>, and <NUM>. In the example of <FIG>, an inductor <NUM> is connected in parallel to the vibrator <NUM>, an inductor <NUM> is connected in parallel to the vibrator <NUM>, and an inductor <NUM> is connected in parallel to the vibrator <NUM>. Moreover, the inductor <NUM>, the inductor <NUM>, and the inductor <NUM> are connected in series. Although this example describes the case where the piezoelectric members are joined to the vibrators <NUM>, <NUM>, and <NUM>, the vibrators <NUM>, <NUM>, and <NUM> themselves may be configured by piezoelectric members. Moreover, a piezoelectric member may be a lamination piezoelectric member. The number of the vibrators of the vibrator device <NUM> and the number of inductors are not limited to three.

Next, an example of a vibrator device of a comparative example will be described. <FIG> are views showing the example of a configuration of the vibrator device of the comparative example. As shown in <FIG>, the vibrator device of the comparative example is configured by connecting three vibrators <NUM>, <NUM>, and <NUM> to which piezoelectric members are joined in series. No inductor is not connected in parallel to the vibrators <NUM>, <NUM>, and <NUM>.

<FIG> is an equivalent circuit diagram of <FIG>, and a circuit that consists of C0, L1, C1, and R1 indicates the equivalent circuit of the vibrator <NUM>. A circuit that consists of C0, L2, C2, and R2 indicates the equivalent circuit of the vibrator <NUM>. A circuit that consists of C0, L3, C3, and R3 indicates the equivalent circuit of the vibrator <NUM>. The damping capacitance C0 of each equivalent circuit indicates the electric characteristic of the piezoelectric member that is joined to each of the vibrators <NUM>, <NUM>, and <NUM>. The series resonant circuits that consist of Lx, Cx, and Rx (x is an integer of <NUM> to <NUM>) indicates mechanical characteristics of the vibrators <NUM>, <NUM>, and <NUM>. Reference symbols IE1, IE2, and IE3 show values of electric currents that flow through the damping capacitances C0 of the vibrators <NUM>, <NUM>, and <NUM>. Reference symbols IM1, IM2, and IM3 show values of electric currents that flow through the series resonant circuits (Lx, Cx, and Rx) of the vibrators <NUM>, <NUM>, and <NUM>. Then, a value of an electric current Io becomes equal to "IE1 + IM1", "IE2 + IM2", and "IE3 + IM3 ".

<FIG> are graphs showing electric current amplitude characteristics with respect to a frequency corresponding to the configuration of <FIG>. <FIG> is the graph showing electric current amplitude characteristics with respect to a frequency in cases where the same alternating voltages are applied to the vibrators <NUM>, <NUM>, and <NUM>. The vibrators <NUM>, <NUM>, and <NUM> have the electric current amplitude characteristics that the amplitudes are maximized at different resonance frequencies Fr1, Fr2, and Fr3. <FIG> is the graph showing the amplitudes of the electric currents IM1 (an alternate long and short dash line), IM2 (a solid line), IM3 (a broken line), and Io (a dotted line) with respect to the frequency of the alternating voltage applied to the series resonant circuits (Lx, Cx, and Rx) in <FIG>.

As shown in <FIG>, when the alternating voltages are applied to the series resonant circuits (Lx, Cx, and Rx) in <FIG>, the amplitudes of the electric currents IM1, MI2, and IM3 that represent vibration velocities of the vibrators <NUM>, <NUM>, and <NUM> are maximized at the resonance frequency Fr0. However, the maximum amplitudes of the respective electric currents are different. When the maximum amplitudes of the electric currents of the vibrators <NUM>, <NUM>, and <NUM> differ at the resonance frequency Fr0, the vibration velocities of the vibrators <NUM>, <NUM>, and <NUM> differ. When the vibrators <NUM>, <NUM>, and <NUM> press the contact member to drive in the state where the vibration velocities of the vibrators <NUM>, <NUM>, and <NUM> differ, sliding amounts at the contact positions of the contact member differ. When the sliding amounts differ, loss that does not contribute to the driving occurs, which reduces driving efficiency of the contact member. Moreover, as shown in <FIG>, the variation of the electric current Io that flows through the vibrator device <NUM> differs from the variations of the electric currents IMx (x is an integer of <NUM> to <NUM>) greatly. Accordingly, it is difficult to accurately detect the amounts of the electric currents IMx by detecting the electric current Io.

In light of the above problem, in this example, as shown in <FIG>, the inductors L01, L02, and L03 are respectively connected in parallel to the damping capacitances C0 of the vibrators <NUM>, <NUM>, and <NUM>. Each inductor connected in parallel to the damping capacitance C0 resonates in parallel at a predetermined frequency. Accordingly, the amounts of the electric currents IEx' (x is an integer of <NUM> to <NUM>) that flow through the parallel circuits that consist of the inductors L0x (x is an integer of <NUM> to <NUM>) and the damping capacitances C0 approach zero. When the electric currents IEx' become about zero, the electric currents IMx'+IEx' (x is an integer of <NUM> to <NUM>) become approximately equal to the electric currents IMx'. Accordingly, the electric current Io' that flows through the vibrator device <NUM> shown in <FIG> becomes approximately equal to the electric currents IMx'.

<FIG> is a graph showing the amplitudes of the electric currents IM1' (an alternate long and short dash line), IM2' (a solid line), IM3' (a broken line), and Io' (a dotted line) with respect to the frequency of the alternating voltage applied to the series resonant circuits (Lx, Cx, and Rx) in <FIG>. The amplitudes of the electric currents IM1', IM2', and IM3' are approximately equal and are maximized at the same resonance frequency Fr0'. The resonance frequency Fr0' is approximately equal to an average value of the resonance frequency Fr1 of the vibrator <NUM>, the resonance frequency Fr2 of the vibrator <NUM>, and the resonance frequency Fr3 of the vibrator <NUM>. Moreover, the amplitude of the electric current Io' becomes approximately equal to the amplitudes of the electric currents IMx' in a frequency range in which the amplitudes are more than a predetermined value.

This example employs the configuration that the inductors are connected in parallel to the respective vibrators connected in series. Accordingly, since the above-mentioned electric currents IMx'+IEx' are approximately equal to the electric currents IMx', the amplitudes and phases of the vibrators <NUM>, <NUM>, and <NUM> are made uniform even if the plurality of vibrators are vibrated with one drive voltage. This is capable of reducing the difference between the vibration velocities of the vibrators and is capable of transferring the forces generated by the respective vibrators to one contact member at a sufficient efficiency. Moreover, the contact member can be driven with the high thrust using the plurality of vibrators.

<FIG> is a view showing a configuration of the vibration actuator that contacts the vibrators <NUM>, <NUM>, and <NUM> around the cylindrical shaft <NUM> to rotate the cylindrical shaft <NUM>. <FIG> is a view showing the electric connection relation thereof. <FIG> is a view showing the configuration of the vibration actuator that rotates the cylindrical shaft <NUM>. The vibrators <NUM>, <NUM>, and <NUM> vibrate in a vertical direction (a direction of an arrow). The cylindrical shaft <NUM> is an example of a contact member and is driven by the vibrators <NUM>, <NUM>, and <NUM>. The vibrators <NUM>, <NUM>, and <NUM> are arranged around the cylindrical shaft <NUM> at nearly equal intervals of <NUM> degrees. Then, the vibrators <NUM>, <NUM>, and <NUM> press the cylindrical shaft <NUM> equally by pressure mechanisms (not shown). In the example of <FIG>, the cylindrical shaft <NUM> is rotated clockwise by vibrations in the vertical direction that are excited by the vibrators <NUM>, <NUM>, and <NUM>.

<FIG> is a view showing the electric connection relation in the vibrator device <NUM>. The inductors <NUM>, <NUM>, and <NUM> are connected in parallel to the piezoelectric members joined to the vibrators <NUM>, <NUM>, and <NUM>, respectively. The vibrator device <NUM> is provided with a connector <NUM> to input an alternating voltage. The vibrators <NUM>, <NUM>, and <NUM> are connected in series and both sides of a series circuit of the vibrators are connected to the connector <NUM>.

The vibrators <NUM>, <NUM>, and <NUM>, the cylindrical shaft <NUM>, and the inductors <NUM>, <NUM>, and <NUM> are stored in a ring-shape casing <NUM>, and these are united to constitute the vibrator device <NUM>. Moreover, the vibrators <NUM>, <NUM>, and <NUM> have projection members that press the cylindrical shaft <NUM> that passes a hollow cylindrical part of the casing <NUM>. The projection members are arranged at angular intervals of <NUM> degrees in the hollow cylindrical part. Each of the projection members is pressed to the cylindrical shaft <NUM> by a support member including a spring structure (not shown) at a fixed pressure. Moreover, the projection amount and pressure of each projection member are adjustable by a rotation-linear motion conversion mechanism that is provided in the casing <NUM>.

<FIG> is a graph showing relationships between a rotation angle and amplitudes of alternating voltages applied to the respective vibrators <NUM>, <NUM>, and <NUM> when the cylindrical shaft <NUM> is driven by applying the alternating voltages to the vibrator device <NUM>. Load fluctuation of one cycle occurs in synchronization with the rotation of the cylindrical shaft <NUM> because of load fluctuation under the influence of decentering of the cylindrical shaft <NUM>. Accordingly, the voltage amplitude increases with increasing of the load, and the voltage amplitude decreases with decreasing of the load.

Since the vibrators <NUM>, <NUM>, and <NUM> are arranged around the cylindrical shaft <NUM> at the nearly equal intervals of about <NUM> degrees, rotation phases of the three waveforms (waveforms showing the voltage amplitudes of the vibrators <NUM>, <NUM>, and <NUM>) in <FIG> are shifted by about <NUM> degrees. Moreover, the averages of the voltage amplitudes of the vibrators <NUM>, <NUM>, and <NUM> during the rotation of the cylindrical shaft <NUM> are different to each other. This is mainly attributed to difference in internal loss and/or resonance frequency between the vibrators <NUM>, <NUM>, and <NUM>.

As mentioned above, since the vibrator device <NUM> of this example includes the inductors connected in parallel to the respective vibrators <NUM>, <NUM>, and <NUM>, the amplitudes and phases of the electric currents flowing through the vibrators <NUM>, <NUM>, and <NUM> are made uniform, which reduces the difference of the vibration velocities of the vibrators. Thereby, even if a difference in the resonance frequency occurs between the vibrators <NUM>, <NUM>, and <NUM> or the load fluctuation occurs, the amplitudes of the alternating voltages applied are automatically adjusted. As a result, the vibration velocities of the vibrators <NUM>, <NUM>, and <NUM> are made uniform and the cylindrical shaft <NUM> can be driven at high efficiency.

<FIG> is a view showing an example of a drive circuit for the vibration actuator that uses the vibrator device <NUM> concerning the first example. The drive circuit for the vibration actuator corresponds to the driving device for the vibration actuator. The drive circuit for the vibration actuator shown in <FIG> has the vibrator device <NUM>, a drive signal generator <NUM>, a resistance <NUM>, an amplitude detector <NUM>, a comparator <NUM>, and a drive signal controller <NUM>.

The vibrator device <NUM> corresponds to a part surrounded by a dotted line in <FIG>. In the vibrator device <NUM>, the vibrators <NUM>, <NUM>, and <NUM> are connected in series. The inductor <NUM> is connected in parallel to the vibrator <NUM>, the inductor <NUM> is connected in parallel to the vibrator <NUM>, and the inductor <NUM> is connected in parallel to the vibrator <NUM>.

Values of the inductors <NUM>, <NUM>, and <NUM> connected in parallel to the respective vibrators are matched at a predetermined frequency near the resonance frequency of the vibrator device <NUM> (a frequency within a predetermined range including the resonance frequency of the vibrator device <NUM>). That is, a relation between a matching frequency F0, the damping capacitance C0, and a value L0 of the inductor is represented by the following formula <NUM>.

The drive signal generator <NUM> generates the alternating voltage applied to the vibrator device <NUM>. The resistance <NUM> is connected to the vibrator device <NUM> in order to measure the electric current that flows through the vibrator device <NUM>. The resistance <NUM> outputs the voltage proportional to the vibration velocity of the vibrators <NUM>, <NUM>, and <NUM>. Although the vibration amplitude of the vibrator is proportional to a value obtained by integrating the vibration velocity by time in fact, the following description assumes that the vibration amplitude shall be controlled by controlling the amplitude of the vibration velocity because the amplitude of the vibration velocity is approximately proportional to the vibration amplitude.

The amplitude detector <NUM> detects the amplitude of the vibration velocity detected by the resistance <NUM>. The comparator <NUM> compares a vibration amplitude command from a vibration amplitude command unit (not shown) with the output from the amplitude detector <NUM>, and outputs a comparison result to the drive signal controller <NUM>. The drive signal controller <NUM> controls the drive signal generator <NUM> on the basis of the comparison result which the comparing unit <NUM> outputted.

The drive signal controller <NUM> outputs a frequency command or an amplitude command to the drive signal generator <NUM>. The electric current that flows through the vibrator device <NUM> is approximately proportional to the vibration velocity of the vibrators <NUM>, <NUM>, and <NUM> owing to the effects of the inductors <NUM>, <NUM>, and <NUM>. Since the resistance <NUM> detects the electric current that flows through the vibrator device <NUM> and the drive signal controller <NUM> controls the alternating signal, the amplitudes of the vibrators <NUM>, <NUM>, and <NUM> are stably controlled with quick response.

Although an inductor is connected in parallel to each vibrator in the example of <FIG>, according to an embodiment of the invention, a parallel circuit consisting of an inductor and a capacitor is connected in parallel to each vibrator. A plurality of inductors that are connected in series or parallel may be connected in parallel to each vibrator in order to enable frequency matching at high accuracy. However, if a plurality of large-size inductors are used, the whole size of the vibrator device <NUM> will be enlarged. To avoid this, a capacitor may be added in parallel to the damping capacitance C0 instead of adjusting an inductor so as to adjust the value of the damping capacitance C0. This reduces enlargement of the vibrator device <NUM>.

Next, failure of the vibrator device <NUM> in this example will be described. Since the inductors <NUM>, <NUM>, and <NUM> are connected in series, the vibrator device <NUM> is able to continue to drive a contact member (for example, the cylindrical shaft <NUM>), even if failure, such as a short circuit or disconnection, occurs in the vibrators <NUM>, <NUM>, and <NUM>. Even if a part of the vibrators <NUM>, <NUM>, and <NUM> in <FIG> short-circuits electrically, the alternating voltage is continuously applied to the other vibrators. Since the short-circuited vibrator stops vibration, the loads to the other vibrators become heavy for that. Since the number of the available vibrators decreases, a thrust lower if the applied voltage does not change. In the meantime, when the number of available vibrators decreases, feedback control that increases the voltage applied to the available vibrators so as to maintain the thrust starts automatically. Thereby, the drive control of the vibrator device <NUM> is continuable.

Next, a case where disconnection occurs in a connection with a vibrator will be described. The inductors <NUM>, <NUM>, and <NUM> are connected in parallel to the respective vibrators. Accordingly, even if connection between a piezoelectric member and wiring in a vibrator breaks under the influence of vibration, the alternating voltage is continuously applied to the other vibrators as long as connection between the inductors that are connected in series does not break. Since the broken vibrator stops vibration, the loads to the other vibrators become heavy for that. Since the number of the available vibrators decreases, the thrust lowers if the applied voltage does not change.

In the meantime, when disconnection occurs between the piezoelectric member joined to the vibrator and the wiring, a high impedance state by the parallel resonant circuit of the damping capacitance C0 and the inductor causes a state where the damping capacitance C0 disappears. This lowers the impedance and causes a state that is similar to the state where a vibrator short-circuits in greater or lesser degrees. Accordingly, since the voltage applied to the available vibrators increases, exciting force increases automatically as well as the case where a vibrator short-circuits. Thereby, the drive control of the vibrator device <NUM> is continuable.

When the short circuit or disconnection occurs in the vibrator device <NUM> as mentioned above, the electric current that flows through the vibrator device <NUM> increases as compared with the case where neither short circuit nor disconnection occurs. The resistance <NUM> is measuring the electric current that flows through the vibrator device <NUM>. When the increase in the electric current that flows through the resistance <NUM> is detected, occurrence of failure such as short circuit and disconnection is detected. For example, when an amount of increase of the electric current that flows through the resistance <NUM> is more than a predetermined amount, the amplitude detector <NUM> detects that failure occurs in the vibrator device <NUM>.

Next, a drive circuit for a vibration actuator to which an amplifier circuit is added will be described. <FIG> is a view showing an example of a drive circuit for a vibration actuator that is configured by adding a transformer <NUM> to the circuit of <FIG>. The transformer <NUM> as an amplifier circuit is a boosting transformer and is connected to the output side of the drive signal generator <NUM>. A capacitor <NUM> for frequency matching is connected in parallel to a secondary side of the transformer <NUM>. A relation between a value Lt of inductor at the secondary side of the transformer <NUM>, an electrostatic capacity Ct of the capacitor <NUM>, and the matching frequency Ft that is decided by the driving frequency range of the vibrator device <NUM> is represented by the following formula <NUM>.

When the frequency matching at the secondary side of the transformer <NUM> is appropriately taken so as to satisfy the above-mentioned formula <NUM>, the electric current that is approximately proportional to a secondary-side current flows at a primary side of the transformer <NUM> within the driving frequency range mentioned above. Accordingly, the same operation as <FIG> is achievable by detecting the primary-side current of the transformer <NUM> by the resistance <NUM> like the drive circuit of <FIG>.

<FIG> is a view showing another configuration example of the vibrator device <NUM> of <FIG>. As shown in <FIG>, the transformer <NUM> and the capacitor <NUM> are built in the vibrator device <NUM>. Since the transformer <NUM> is built in the input side of the vibrator device <NUM>, the vibrator device <NUM> can be driven at relatively low voltage.

<FIG> are views showing examples of the vibration actuators concerning the first example. <FIG> is a view showing an example of the vibration actuator that is constituted by connecting three vibrator devices <NUM>, <NUM>, and <NUM> in series. <FIG> is a view showing an example of the vibration actuator that is constituted by connecting the three vibrator devices <NUM>, <NUM>, and <NUM> in parallel.

The number of the vibrator devices <NUM> connected in series or in parallel is not limited to three. Since one vibrator device <NUM> has three vibrators as mentioned above, the vibration actuator in <FIG> employs nine vibrators. Nine vibrators connected in series may be built in one vibrator device. In the meantime, when the vibrators are divided into a plurality of vibrator devices, there is a merit that output torque is adjusted by adjusting the number of vibrator devices according to required output torque. The vibrator devices <NUM> and <NUM> are the same as the vibrator device <NUM>. Three vibrators connected in series are built in each of the vibrator devices <NUM>, <NUM>, and <NUM>, and the average of the resonance frequencies of three vibrators falls within the predetermined frequency range.

Hereinafter, an example of manufacturing of the vibrator devices <NUM>, <NUM>, and <NUM> shown in <FIG> will be described. The vibrator devices <NUM>, <NUM>, and <NUM> may be manufactured manually or automatically. For example, when the fixed number (tens through hundreds, for example) of vibrators are manufactured, a list of resonance frequencies is created on the basis of measuring results of the resonance frequencies of the respective vibrators. Next, on the basis of the list of resonance frequency, the fixed number of vibrators are classified into some classes corresponding to the frequency ranges by referring to the resonance frequency list. For example, the fixed number of vibrators are classified every <NUM>. Then, three vibrators are selected at random from the same class and the average of the resonance frequencies of the three vibrators is calculated. Random selection of three vibrators is repeated until obtaining a combination of three vibrators of which the average of resonance frequencies falls within a frequency range (for example, a predetermined frequency ± <NUM>) that is beforehand decided for every class. When three vibrators of which the average of resonance frequencies falls within the frequency range that is beforehand decided for every class are obtained, one vibrator device is constituted by these three vibrators.

Accordingly, three vibrators of which the average of the resonance frequencies falls within the above-mentioned frequency range are built in one vibrator device. It is difficult to prepare many vibrators of which resonance frequencies are close. In the meantime, the method for preparing vibrators using the average of the resonance frequencies like this example enables to prepare relatively large number of vibrators.

Moreover, vibrators that constitute one vibrator device may be selected using dispersion of resonance frequencies instead of the average. That is, in this case, vibrators of which the dispersion of the resonance frequencies falls within a predetermined dispersion range are built in one vibrator device. When the dispersion is set to a large value to some extent, there is unevenness of the resonance frequencies of the selected vibrators, which stabilizes the characteristic of the vibrator device. As mentioned above, when a vibration actuator is constituted by combining a plurality of vibrator devices of the same class, a high-power and high-efficiency vibration actuator is manufactured stably.

In the case in <FIG>, the three vibrator devices <NUM>, <NUM>, and <NUM> are connected in series. When the number of the vibrator devices connected in series increases, it is necessary to enlarge the amplitude of the alternating voltage, which increases the applied voltage. When the applied voltage becomes high, the entire vibrator device is enlarged for applying an insulation countermeasure etc. This increases a cost.

Accordingly, the configuration in which the vibrator devices <NUM>, <NUM>, and <NUM> are connected in parallel can be employed as shown in <FIG>. In this case, since the three vibrator devices <NUM>, <NUM>, and <NUM> are connected in parallel, the vibrator devices are driven by the alternating voltage of the amplitude that is one third of the amplitude of the case where the three vibrator devices <NUM>, <NUM>, and <NUM> are connected in series.

The vibrator devices <NUM>, <NUM>, and <NUM> belong in the same class as mentioned above, the resonance frequencies (averages of the resonance frequencies of the built-in vibrators) of the vibrator devices are approximately equal. Moreover, since the three vibrators are equally arranged around the cylindrical shaft <NUM>, the loads of three vibrators are equalized. Accordingly, there is little load fluctuation during rotation. This reduces the difference between the vibration velocities of the vibrator devices and achieves efficient drive.

<FIG> are views showing attachment phases of the respective vibrator devices <NUM>, <NUM>, and <NUM> to the cylindrical shaft <NUM>. The three vibrator devices are attached so that the rotation phases are shifted every <NUM> degrees. Since the vibrator devices <NUM>, <NUM>, and <NUM> are equally arranged around the cylindrical shaft <NUM> by shifting the phases by the predetermined angle as shown in <FIG>, rotation of the cylindrical shaft <NUM> with few torque fluctuation is achieved. The three vibrators are connected in series in each of the vibrator devices <NUM>, <NUM>, and <NUM> in the example shown in <FIG>, the vibrators are arranged every <NUM> degrees. When the vibrator device has two vibrators, two vibrators are preferably arranged every <NUM> degrees. Moreover, when the vibrator device has four vibrators, four vibrators are preferably arranged every <NUM> degrees.

<FIG> is a view showing a drive circuit for the three vibration actuators of <FIG>. Each of the vibrator devices <NUM>, <NUM>, and <NUM> has three vibrators connected in series and inductors connected in parallel to the three vibrators. The value of the inductor connected in parallel to each vibrator is matched at a predetermined frequency within the frequency range of the alternating voltage that the drive signal generator <NUM> outputs. That is, a relation between the matching frequency F0, the damping capacitance C0, and the value L0 of the inductor is represented by the above-mentioned formula <NUM>.

The drive signal generator <NUM> generates the alternating voltage applied to the vibrator devices <NUM>, <NUM>, and <NUM>. The resistance <NUM> is used to measure the total electric current that flows through the vibrator devices <NUM>, <NUM>, and <NUM>. Since the resonance frequencies of the vibrator devices <NUM>, <NUM>, and <NUM> are made uniform, an almost equivalent average load is applied to each of the vibrators that are equally arranged around the cylindrical shaft <NUM>. Accordingly, the phase of inflow electric current does not deviate largely.

Accordingly, the amplitude detector <NUM> outputs the voltage proportional to the sum of the amplitudes of electric currents that flow through the vibrator devices <NUM>, <NUM>, and <NUM>. Then, the comparator <NUM> compares the sum of the amplitudes of electric currents with the vibration amplitude command from the command unit (not shown). The drive signal controller <NUM> controls the frequency or amplitude of the alternating voltage that the drive signal generator <NUM> outputs on the basis of the comparison result.

Although the example that the plurality of vibrator devices drives the same contact member is described in this example, the plurality of vibrator devices may respectively drive different contact members. In this case, although it is difficult to drive the contact members at the completely same speed, the circuit structure can be reduced because the plurality of contact members are simultaneously driven at the similar vibration velocities.

Moreover, although the example in which the vibrators of the same configuration are applied to each vibrator device is described in this example, the vibrators of different configurations may be applied to each vibrator device as long as the resonance frequencies of the vibrators fall within the predetermined range.

Moreover, <FIG> respectively show the vibration actuators in which the plurality of vibrator devices <NUM>, <NUM>, and <NUM> are connected in series and in parallel. Conditions of the contact member may differ according to the positions that the vibrator devices <NUM>, <NUM>, and <NUM> contact. For example, the diameter of the cylindrical shaft <NUM> may differ according to the positions that the vibrator devices <NUM>, <NUM>, and <NUM> contact. In such a case, it is preferable to set different vibration velocities for the respective vibrator devices <NUM>, <NUM>, and <NUM> in order to drive the contact member properly. For this reason, the configuration that the transformer <NUM> is provided inside each of the vibrator devices <NUM>, <NUM>, and <NUM> as shown in <FIG> is employed. Then, the ratio of the vibration velocities is adjusted by adjusting the winding ratios of the transformers <NUM>. That is, the vibration velocity of each of the vibrator devices <NUM>, <NUM>, and <NUM> is properly controlled by changing the winding ratio of each of the transformers <NUM> according to the condition of the contact member.

Next, a second example not covered by the present invention will be described. <FIG> is a view showing an example of a vibration actuator concerning the second example. As shown in <FIG>, each of three shaft-output vibration actuators <NUM>, <NUM>, and <NUM> has one vibrator and joins to a rotation shaft 33A using a bevel gear mechanism to rotate the rotation shaft 33A. A bevel gear <NUM> is attached at a front end of an output shaft <NUM> of the vibration actuator <NUM>. A bevel gear <NUM> is attached at a front end of an output shaft <NUM> of the vibration actuator <NUM>. A bevel gear <NUM> is attached at a front end of an output shaft <NUM> of the vibration actuator <NUM>. The bevel gears <NUM>, <NUM>, and <NUM> engage with a larger bevel gear <NUM> attached to the rotation shaft 33A at angular intervals of <NUM> degrees.

The vibrators of the respective vibration actuators <NUM>, <NUM>, and <NUM> are electrically connected in series. Alternating voltages of which phases are shifted by <NUM> degrees are applied to drive voltage lines of phases A, NA, B, and NB. Thereby, vibrations are excited and the bevel gear <NUM> connected indirectly is driven. <FIG> is a view showing one example of a configuration of the vibration actuator <NUM> concerning the second example. The vibration actuator <NUM> has a rotor <NUM>, ceramic elastic body <NUM>, piezoelectric member <NUM>, and friction member <NUM>. The output shaft <NUM> is joined to the center of the rotor <NUM>. The output shaft <NUM> and rotor <NUM> are supported rotatably. The ceramic elastic body <NUM> is a non-conductive member that has a comb-like projection structure. The piezoelectric member <NUM> is adhered to the ceramic elastic body <NUM>. Moreover, the friction member <NUM> is adhered on the projection structure of the ceramic elastic body <NUM>. The material of the friction member <NUM> is selected so that a contact portion to the rotor <NUM> slowly and stably wears out.

<FIG> is a view showing an electrode structure of the circular piezoelectric member <NUM>. <FIG> shows a connection state between electrodes <NUM>, <NUM>, <NUM>, and <NUM> of the piezoelectric member <NUM> on its front surface and the drive voltage lines of the phases A, B, NA, and NB.

<FIG> is a view showing a wiring structure of the piezoelectric member <NUM>. Electrodes of the piezoelectric member <NUM> on its back surface are also distributed as well as the electrodes <NUM>, <NUM>, <NUM>, and <NUM> shown in <FIG>. A back electrode of the phase NA is opposite to the electrode <NUM> of the phase A. A back electrode of the phase BA is opposite to the electrode <NUM> of the phase B. As shown in <FIG>, an inductor <NUM> is connected in parallel between the phases A and NA and an inductor <NUM> is connected in parallel between the phases B and NB. The phase difference between the alternating voltages applied to the phases A and NA is equal to <NUM> degrees, and the phase difference between the alternating voltages applied to the phases B and NB is the same as it.

<FIG> is a view showing a first example of a drive circuit for the vibration actuator concerning the second example. In the vibration actuator <NUM>, a plurality of vibration sections of which phases are different are formed by the alternating voltages that have the phase difference of <NUM> degrees and are input by the phases A and NA and the phases B and NB. The two vibration sections of which phases are different are indicated by two vibrators in <FIG>. The inductor <NUM> is connected in parallel between the phases A and NA and the inductor <NUM> is connected in parallel between the phases B and NB.

The vibration actuators <NUM> and <NUM> are connected similarly, and the vibration actuators <NUM>, <NUM>, and <NUM> are connected in series for each phase. In the example in <FIG>, the three vibration actuators <NUM>, <NUM>, and <NUM> are connected in series and constitute one vibration actuator <NUM> that has terminals A, NA, B, and NB as a whole. An area surrounded with a broken line indicates each vibration actuator <NUM>, <NUM>, and <NUM>. An area surrounded by a dotted line indicates the vibration actuator <NUM>.

The capacitor <NUM> for frequency matching and the secondary side winding of the transformer <NUM> for amplification are connected in parallel between the terminals A and NA of the vibration actuator <NUM>. Moreover, the capacitor <NUM> for frequency matching and the secondary side winding of the transformer <NUM> for amplification are connected in parallel between the terminals B and NB of the vibration actuator <NUM>. The drive signal generator <NUM> generates an alternating voltage. H-bridge circuits (power amplification circuits, not shown) are respectively connected between the terminals A and NA and between the terminals B and NB of the drive signal generator <NUM>.

Waveforms of pulse drive signals that the H-bridge circuits output are shaped by series resonant circuits constituted by inductors <NUM> and <NUM> and capacitors <NUM> and <NUM> that are inserted between the transformers <NUM> and <NUM> and the drive signal generator <NUM>. Then, the pulse drive signals after the waveform shaping are amplified by the transformers <NUM> and <NUM>, and are applied to the vibration actuator <NUM>. The series resonant circuits constituted by the inductors <NUM> and <NUM> and the capacitors <NUM> and <NUM> are subjected to matching adjustment at a predetermined frequency within a driving frequency range of the vibration actuator <NUM>. This suppresses large fluctuation of the drive voltage amplitude of the vibration actuator <NUM> within the driving frequency range.

Resistances <NUM> and <NUM> for current measurement are respectively connected to source terminals for electric current detection of the H-bridge circuits of the drive signal generator <NUM>. The resistances <NUM> and <NUM> are measuring the electric currents corresponding to the vibration velocities of the vibrators included in the vibration actuator <NUM>. The amplitude detector <NUM> detects the amplitude of the vibration velocities of the vibrators on the basis of the measurement values of the resistances <NUM> and <NUM>. The comparator <NUM> compares the vibration amplitude command from the vibration amplitude command unit (not shown) with the detection results (amplitude velocities of the vibrators) of the amplitude detector <NUM>. The drive signal controller <NUM> outputs at least one command among commands about the frequency, pulse width, and voltage amplitude to the drive signal generator <NUM> according to the comparison result.

Generally, a vibration actuator has irregularity or fluctuation in a resonance frequency or an internal loss under the influence of manufacture irregularity of a friction member or pressure irregularity owing to plane accuracy of a vibrator. In addition, since there are variation depending on a rotation angle and variation with time resulting from progress of wear, it is difficult to make vibration characteristics of a plurality of vibration actuators uniform. As a countermeasure for this, an inductor is connected in parallel to each of the vibrators that are connected in series in this embodiment as mentioned above. This makes the amplitude characteristics of the vibrators uniform, allows to transmit the comparatively equal force to the bevel gear <NUM>, and enables the efficient drive with little wear of the gears.

Although the vibration actuator <NUM> does not include the transformers <NUM> and <NUM>, the inductors <NUM> and <NUM>, and the capacitors <NUM> and <NUM> in the example in <FIG>, some or all of these components may be included in the vibration actuator <NUM>. Since the vibration actuator <NUM> includes the components that are subjected to the frequency matching in accordance with the inherent resonance frequency, adjustment at the time of using the vibration actuator <NUM> becomes unnecessary. This reduces variation in performance and improves convenience of the user who uses the vibration actuator <NUM>. Moreover, either of the inductor <NUM> and the capacitor <NUM> may be connected in series to the primary side of the transformer <NUM>. Similarly, either of the inductor <NUM> and the capacitor <NUM> may be connected in series to the primary side of the transformer <NUM>. A capacitor is used to intercept direct current and an inductor has an effect to smooth a waveform.

Moreover, in this embodiment, the entire configuration including the three vibration actuators <NUM>, <NUM>, and <NUM> that are connected in series and are united by the bevel gear <NUM> is described as the one vibration actuator <NUM>. Assuming that the vibration actuator <NUM> is one vibrator device, a configuration in which the vibrator devices are connected in series or in parallel can be also employed. Thereby, a high-output vibration actuator is constituted. In this case, it is preferable that the average of the resonance frequencies of the vibrators in each of the vibration actuators, which constitute the vibrator devices, be approximately equal to the average of the resonance frequencies of the three vibrators in the vibration actuator <NUM>.

Moreover, the above-mentioned vibrator devices may be mechanically combined by connecting a plurality of complex vibration actuators as shown in <FIG> in a state where a plurality of gears equivalent to the bevel gear <NUM> are fixed to the same shaft 33A. Alternatively, the vibrator devices may be combined through other gears.

<FIG> is a view showing a second example of a drive circuit for the vibration actuator concerning the second example. In the drive circuit for the vibration actuator of the second example, two vibrator devices <NUM> and <NUM> are connected in series. The vibrator device <NUM> has the vibration actuators <NUM>, <NUM>, and <NUM> and the transformers <NUM> and <NUM>. The vibrator device <NUM> has vibration actuators <NUM>, <NUM>, and <NUM> and transformers <NUM> and <NUM>. In the drive circuit for the vibration actuator in <FIG>, the ratio of the rotational speeds of the vibrator devices is adjustable by changing the winding ratios of the transformers of the vibrator devices.

Moreover, the three vibration actuators <NUM>, <NUM>, and <NUM> connected in series in the vibrator device drive one shaft through the bevel gears <NUM>, <NUM>, and <NUM> in the second example. In the meantime, the vibration actuators may drive different contact members, respectively. For example, when a plurality of dolls, which are contact members that are not necessary to move synchronously, decorated in a show window are driven, a plurality of vibration actuators are applicable to drive the dolls. This case is effective because the plurality of vibration actuators are stably driven at an appropriate speed.

For example, a doll is attached in place of the bevel gear <NUM> of the vibration actuator in <FIG>. When three vibration actuators to which different dolls are respectively attached are electrically connected in series, the three dolls are rotated at the almost same speed. Moreover, the drive circuit for the vibration actuator in <FIG> is able to change the rotation speeds of the dolls for every vibrator device by adjusting the winding ratio of each transformer. Moreover, when the gear ratio of the engaged gears is adjusted while adjusting the winding ratio of each transformer, the adjustment depending on required torque is also available.

Next, a third example not covered by the claimed invention will be described. <FIG> are views showing a configuration and vibration modes of a vibrator concerning the third example. As shown in <FIG>, a vibrator <NUM> has a plate shape and is manufactured from non-conductive material. Two projections that contact a contact member are provided in the surface of the vibrator <NUM>. A piezoelectric member <NUM> constitutes a part of the vibrator <NUM> and vibrates the vibrator <NUM>. <FIG> shows electrodes <NUM> and <NUM> provided in the piezoelectric member <NUM>. The electrodes <NUM> and <NUM> are electrically insulated. Two alternating voltages of which phases vary independently are respectively applied to the electrode <NUM> and the electrode <NUM>. Two similar electrodes are also provided on a back surface of the piezoelectric member <NUM> and are configured so as to enable energization from the front surface through via holes (not shown) provided in parts of the electrodes <NUM> and <NUM>.

<FIG> shows a vibration form in a vibration mode excited when alternating voltages of the same phase are applied to the electrodes <NUM> and <NUM>. <FIG> shows a vibration form of the vibration mode excited when alternating voltages of opposite phases are applied to the electrodes <NUM> and <NUM>. When the phase difference between the alternating voltages applied to the electrodes <NUM> and the electrode <NUM> is <NUM> degrees, the vibration mode of <FIG> is excited. When the phase difference between the alternating voltages applied to the electrodes <NUM> and the electrode <NUM> is <NUM> degrees, the vibration mode of <FIG> is excited.

Moreover, when the phase difference of alternating voltages is an angle between <NUM> degrees and <NUM> degrees, both the vibration modes are excited simultaneously. The phase difference of alternating voltages is an angle between <NUM> degrees and <NUM> degrees in many cases. Then, a contact member that presses the projections provided in the vibrator <NUM> moves. When the contact member is a rectangular parallelepiped, the contact member that presses the projections provided in the vibrator <NUM> moves in a rectangular longitudinal direction.

<FIG> are views showing a first example of a linear-motion vibration actuator of the third example. <FIG> is a figure viewed from a direction that intersects perpendicularly with a moving direction of a contact member <NUM>. Projections of the two vibrators <NUM> and <NUM> are arranged face to face mutually and are configured so that the contact member <NUM> will move in a direction of an arrow in <FIG> in a state where the projections put the contact member <NUM> therebetween from the vertical direction. <FIG> is a figure viewed from the moving direction of the contact member <NUM>. The vibrators <NUM> and <NUM> are arranged symmetrically in the vertical direction (are arranged equally at angular intervals of <NUM> degrees on the circumference) with respect to the contact member <NUM>.

<FIG> is a view showing a first example of the drive circuit for the vibration actuator concerning the third example. As shown in <FIG>, the piezoelectric members of the vibrator <NUM> and the piezoelectric members of the vibrator <NUM> are connected in series for each phase, and the inductors are respectively connected in parallel to the vibrators <NUM> and <NUM>. The vibrators <NUM> and <NUM> are connected to the H-bridge of the drive signal generator <NUM> through the series resonant circuit that consists of the inductors <NUM> and <NUM> and the capacitors <NUM> and <NUM>.

The series resonant circuit may consist of inductors only or capacitors only. The drive signal generator <NUM> outputs pulse signals of four phases that differ every <NUM> degrees. A thrust detector <NUM> detects thrust to the contact member <NUM> and outputs the detected thrust to a comparator <NUM>. The comparator <NUM> compares the detected thrust with a thrust command from an command unit (not shown) and outputs a comparison result. A vibration amplitude command unit <NUM> controls the vibration amplitudes of the vibrators <NUM> and <NUM> according to the comparison result that the comparator <NUM> outputs.

Moreover, the resistance <NUM> and <NUM> for measuring the electric currents corresponding to the vibration velocities of the vibrators <NUM> and <NUM> are connected to the source terminals for electric current detection of the H-bridges of the drive signal generator <NUM>. The amplitude detector <NUM> detects the vibration amplitudes from the electric currents that the resistances <NUM> and <NUM> measure. The comparator <NUM> compares the detected vibration amplitudes and the vibration amplitude command from the vibration amplitude command unit <NUM>. The drive signal controller <NUM> controls at least one of the frequency, pulse width, and voltage amplitude of the pulse signals that the drive signal generator <NUM> generates according to the comparison result.

For example, when the thrust of the vibrators <NUM> and <NUM> is smaller than a target value, the frequency of the alternating voltage that the drive signal generator <NUM> outputs approaches the resonance frequency of the vibrators <NUM> and <NUM>, and the vibration amplitudes of the vibrators <NUM> and <NUM> increase. Thereby, the thrust of the vibrators <NUM> and <NUM> increases. The moving speed of the contact member <NUM> can be controlled when a configuration in which the thrust detection part <NUM> is replaced with a speed detector that detects the speed of the contact member <NUM> and the comparator <NUM> compares the detected speed with a speed command from a command unit (not shown) is employed.

Moreover, although the vibrator device is constituted by the upper and lower two vibrators <NUM> and <NUM> that put the contact member <NUM> therebetween in the example of <FIG>, the contact member <NUM> may be a prism having a square section and the vibrators <NUM> and <NUM> may be configured so that the four projections respectively press the four sides of the prism. <FIG> are views showing a second example of a linear-motion vibration actuator concerning the third example. As shown in <FIG>, four vibrators <NUM>, <NUM>, <NUM>, and <NUM> are equally arranged around a contact member <NUM> that is a prism having a square section at angular intervals of <NUM> degrees on the circumference. The vibrators <NUM>, <NUM>, <NUM>, and <NUM> shown in <FIG> are connected in series for each phase of the alternating voltage that is applied to two electrodes (not shown) of a piezoelectric member of each vibrator. And the inductors are respectively connected in parallel to the vibrators. The contact member <NUM> may be a cylindrical shape having a circular section.

Although one vibrator device is constituted by connecting the four vibrators in series in the example of <FIG>, a configuration in which two vibrator devices each of which is constituted by two vibrators that are opposite to each other are connected in series or in parallel may be employed. Moreover, a configuration in which a plurality of vibrator devices each of which is constituted by four vibrators are arranged along the moving direction of the contact member <NUM> and are connected in parallel or in series may be employed.

Moreover, a configuration in which a plurality of vibrators in which projections are provided on the same plane are equally arranged along a circumferential direction of a ring-shaped contact member or a circular contact member may be employed. <FIG> is a view showing an example of a rotary-motion vibration actuator concerning the third example. As shown in <FIG>, three vibrators <NUM>, <NUM>, and <NUM> are equally arranged along a circular contact member <NUM>. The vibrators <NUM>, <NUM>, and <NUM> are electrically connected in series, and inductors are respectively connected in parallel to the vibrators <NUM>, <NUM>, and <NUM> for each phase. Although the plurality of vibrators are driving one contact member in the example of <FIG>, the plurality of vibrators may respectively drive different contact members. Moreover, when the plurality of vibrators are divided into a plurality of vibrator devices, the respective vibrator devices may drive different contact members.

Next, an embodiment of the present invention will be described. <FIG> is a view showing a first example of a vibration actuator concerning the embodiment. As shown in <FIG>, two vibrators <NUM> and <NUM> and two vibrators <NUM> and <NUM> respectively constitute vibrator devices. The vibrators <NUM> and <NUM> constitute a Y-axis vibrator device that drives a contact member <NUM> in a Y-axis direction. The vibrators <NUM> and <NUM> are electrically connected in series, and inductors are respectively connected in parallel to the vibrators <NUM> and <NUM>.

The vibrators <NUM> and <NUM> constitute an X-axis vibrator device that drives the contact member <NUM> in an X-axis direction. The vibrators <NUM> and <NUM> are electrically connected in series, and inductors are respectively connected in parallel to the vibrators <NUM> and <NUM>. The resonance frequency of the X-axis vibrator device is fully apart from the resonance frequency of the Y-axis vibrator device so as not to affect mutually. And the shapes of the vibrators are adjusted so that the driving frequency ranges may not overlap.

<FIG> is a view showing a first example of a drive circuit for the vibration actuator concerning the embodiment. The vibrators <NUM> and <NUM> of the X-axis vibrator device and the vibrators <NUM> and <NUM> of the Y-axis vibrator device are connected in series for each phase. Moreover, an inductor and a capacitor are connected in parallel to each vibrator. Values of the inductors and capacitors of the Y-axis vibrator device are subjected to frequency matching to a frequency Fy for a Y-axis. And values of the inductors and capacitors of the X-axis vibrator device are subjected to frequency matching to a frequency Fx for an X-axis.

<FIG> is a graph showing electric current amplitude characteristics of the vibrator devices in the embodiment. A solid line shows the vibration characteristic of the X-axis vibrator device, and a broken line shows the vibration characteristic of the Y-axis vibrator device. Driving frequency ranges are set at the higher sides of the respective maximum-amplitude frequencies. The frequency Fx for the X-axis and the frequency Fy for the Y-axis are set within the respective driving frequency ranges.

The drive signal generator <NUM> in <FIG> generates two-phase alternating voltages in the respective frequency ranges by compositing the alternating voltages in the two frequency ranges including the frequency Fx for the X-axis and the frequency Fy for the Y-axis, respectively. An amplitude detector <NUM> detects the vibration amplitudes in the frequency range for theX-axis and the frequency range for the Y-axis on the basis of the sum signal of the two-phase electric currents that flow according to the vibration velocities of the vibrators that the resistance <NUM> for current detection measures, and outputs the detection results. Comparators <NUM> and <NUM> respectively compare a vibration amplitude command for the X-axis and a vibration amplitude command for the Y-axis from a command unit (not shown) with the detection results that the amplitude detector <NUM> outputs. Drive signal controllers <NUM> and <NUM> respectively control the frequencies of the alternating voltages applied to the X-axis vibrator device and Y-axis vibrator device on the basis of the comparison results of the comparators <NUM> and <NUM>.

Moreover, the command unit monitors position signals output from a two-dimensional position detector (not shown) that detects a two-dimensional position of the contact member <NUM>. And the command unit compares the position signals with target positions in the respective axes. Then, the command unit switches the phases of the alternating voltages applied to the X-axis vibrator device and Y-axis vibrator device to <NUM> degrees or -<NUM> degrees according to signs (+/-) of the comparison results and sets up a vibration amplitude command for the X-axis and a vibration amplitude command for the Y-axis according to the absolute values of the comparison results. As a method of separating the signals in the two frequency ranges, there are a method of separating the signals with a filter, a method of finding frequencies and amplitudes by the FFT computation, and a method of performing synchronous detection of the synchronizing signal that the drive signal generator <NUM> generates.

Moreover, when the respective vibration velocities of the X-axis vibrator device and Y-axis vibrator device are detected from the sum signal of the electric currents, an error occurs in measurement of the amplitudes if the frequencies are merely separated. In view of this problem, an offset value for an amplitude for every frequency obtained beforehand is stored in the amplitude detector <NUM>. This enables detection of a vibration velocity at high accuracy by performing a correction calculation based on the offset value to the obtained information about the amplitude and frequency.

<FIG> is a view showing a second example of a drive circuit for the vibration actuator concerning the above invention embodiment. The vibrator devices of which the driving frequency ranges differ are individually connected to the drive signal generator <NUM> through the transformers, respectively. A series circuit that consists of an inductor and a capacitor that are subjected to frequency matching at a predetermined frequency within a driving frequency range decided for each vibrator device is inserted between each transformer and the drive signal generator <NUM>.

<FIG> is a view showing a second example of the vibration actuator concerning the above invention embodiment. A plurality of vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> shown in <FIG> have a plurality of vibrators connected in series and inductors connected in parallel to the respective vibrators. The vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are constituted by having the vibrators of which driving frequency ranges do not overlap, respectively. The vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are electrically connected in parallel and are driven by two-phase alternating voltages A and B.

Each of the vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> nips a linear-motion contact member with a plurality of vibrators that are electrically connected in series as with the examples shown in <FIG>, <FIG>. And a wire bundle <NUM> is combined with the contact member. The wire bundle <NUM> is engaged with a tube-shaped bending driver <NUM> that imitates a finger. The bending driver <NUM> is constituted so as to bend and stretch a plurality of pseudo joints by pulling and pressing wires of the wire bundle <NUM>. One wire of the wire bundle <NUM> corresponds to each of the vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. A wire may be configured to combine with a vibrator device so as to be relatively movable with respect to a contact member. That is, the wire is constituted to be movable by the vibrator device and contact member that move relatively and mutually.

The bending driver <NUM> can be driven by linearly moving the contact members included in the vibrator devices <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> as if a finger bends and stretches. Accordingly, since a plurality of wires are driven even if the number of wiring lines is small, it is effective in the driving of a complicated robot hand having a plurality of joints.

Claim 1:
A vibration actuator comprising:
a vibrator device (<NUM>); and
a contact member (<NUM>; <NUM>)
that moves relative to the vibrator device (<NUM>),
wherein the vibrator device (<NUM>) comprises:
a plurality of vibrators (<NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, <NUM>) that are electrically connected in series, and
a plurality of inductors (<NUM>, <NUM>, <NUM>) that are connected in parallel to the respective vibrators (<NUM>, <NUM>, <NUM>; <NUM>, <NUM>, <NUM>, <NUM>),
characterised in that the vibrator device further comprises a plurality of capacitors, each capacitor connected in parallel to a respective inductor.