JP6751997B2 - Drive circuit and drive method - Google Patents

Description

The present invention relates to a drive circuit and a drive method, and particularly relates to a drive circuit and a drive method suitable for driving a piezoelectric element.

Capacitive actuators have the potential to reduce energy loss when applied to robots. Especially in the case of robot limbs, the actuator needs to support the gravitational load. Compared to the kinematic load generated only during exercise, the gravitational load acts continuously for a long time regardless of exercise even under steady conditions.

Inductive actuators such as electromagnetic force consume energy as a function of force because the current corresponds to the force. From this point of view, the electromagnetic force motor is not suitable for application to the limbs of a robot in terms of energy efficiency. Such inconsistency between the load conditions and the actuator characteristics causes insufficient energy utilization efficiency in the robot limbs. Energy efficiency is important for mobile robots, which are increasingly being applied in various fields.

Hydraulic or pneumatic actuators and piezoelectric actuators can be regarded as capacitive actuators that generate force or torque according to the operating state values such as pressure and voltage. In many cases, energy dissipation is caused by flow state values such as fluid flow rate and flow. This means that the energy dissipation in the capacitive actuator does not correspond closely to the output force. Therefore, the capacitive actuator can efficiently support the load, for example, in the limbs of the robot.

However, the energy dissipation of the pump required to drive the hydraulic or pneumatic actuator is generally very large. Also, due to the compliant nature of air, it is difficult for both hydraulic and pneumatic actuators to respond and move at high speeds, such as 50 Hz.

Piezoelectric motors, including ultrasonic motors based on piezoelectric elements, can be efficiently driven by a power source and have high power and output density. However, it is difficult to regenerate the electric energy from the kinetic energy in the piezoelectric element.

Japanese Unexamined Patent Publication No. 10-308542 Japanese Patent No. 4318849

Conventionally, a plurality of piezoelectric elements of a piezoelectric motor do not exchange energy with each other. Therefore, conventionally, energy cannot be reused between a plurality of piezoelectric elements.

Therefore, an object of the present invention is to provide a drive circuit and a drive method capable of reusing energy between a plurality of piezoelectric elements.

According to one aspect of the present invention, it is a drive circuit for driving a plurality of piezoelectric elements, and a transfer path for connecting the plurality of piezoelectric elements via an inductor and a first piezoelectric by controlling the transfer path. A drive circuit with a control unit that transfers charges from a group of elements to a group of second piezoelectric elements is provided.

According to another aspect of the present invention, there is a driving method for driving a plurality of piezoelectric elements, wherein the charge is transferred from one group of piezoelectric elements in which electric charges are stored to another group of piezoelectric elements. A driving method including a step of transferring the electric charge stored in the group of the other piezoelectric elements to a group of piezoelectric elements other than the group of the other piezoelectric elements is provided.

According to one embodiment, energy can be reused between a plurality of piezoelectric elements.

Front view of an example of a piezoelectric motor, A cross-sectional view showing a part of the piezoelectric motor along the alternate long and short dash line AA of FIG. An enlarged cross-sectional view of the gear and input tip of FIG. 1B, Diagram explaining the shape of the gear, The figure which shows an example of the drive system of a piezoelectric motor, Equivalent circuit diagram of piezoelectric element, Schematic diagram illustrating the operation of the drive circuit, A schematic showing a partial example of a drive system, A diagram illustrating an example of a control method for three (3) counter units, Schematic diagram illustrating an example of a drive circuit that drives an even number of piezoelectric element groups, A diagram illustrating the operation of the drive circuit of FIG. Schematic diagram illustrating an example of a drive circuit that drives an odd number of piezoelectric elements. A diagram illustrating the operation of the drive circuit of FIG. Schematic diagram illustrating an example of a drive circuit that uses voltage control, A diagram illustrating a switching method of the drive circuit of FIG. A diagram illustrating a switching state of the drive circuit of FIG. A diagram illustrating an example of a driving method according to an embodiment of the present invention. A block diagram showing an outline of flow and energy transfer in a piezoelectric motor, Diagram showing an example of a work cycle in the mechanical domain, Diagram showing an example of a work cycle in the electrical domain, A diagram showing an example of a low-order mechanical model of a buckling actuator, A diagram showing an example of the calculated output characteristics of a buckling actuator, Schematic diagram showing an example of counter-connection, Schematic diagram showing an example of counter-connection, Schematic diagram showing an example of counter-connection, A diagram showing an example of the force and displacement characteristics output by the counter unit, A diagram illustrating the motor force characteristics generated by one buckling actuator when a unipolar drive gear is used as the gear. The figure which shows the gear force obtained by a single buckling type actuator in various phase switching modes, The figure which shows the gear force obtained by 6 (6) buckling type actuators in various phase switching modes, A block diagram showing an example of a speed control system for a piezoelectric motor, A flowchart illustrating an example of a control method according to an embodiment of the present invention. The figure illustrating the simulation result of the closed loop speed control system when the gear drives only the inertial load, The figure illustrating the simulation result of the closed loop speed control system when the gear drives only the inertial load, The figure illustrating the simulation result of the closed loop speed control system when the gear drives only the inertial load, The figure explaining the simulation result of the closed loop speed control system when a gear drives an inertial load and a constant load, The figure explaining the simulation result of the closed loop speed control system when a gear drives an inertial load and a constant load, The figure explaining the simulation result of the closed loop speed control system when a gear drives an inertial load and a constant load, A diagram showing a first example of a linear piezoelectric motor, A diagram showing a second example of a linear piezoelectric motor, It is a figure which shows the buckling type actuator in the 2nd example of a linear piezoelectric motor in a partial cross section.

The drive circuit and the drive method in each embodiment of the present invention will be described below with reference to the drawings.

1A, 1B and 1C are diagrams illustrating an example of a piezoelectric motor according to an embodiment of the present invention. 1A is a front view of an example of a piezoelectric motor, FIG. 1B is a cross-sectional view showing a part of the piezoelectric motor along the alternate long and short dash line AA of FIG. 1A, and FIG. 1C shows an enlarged view of the gear and input tip of FIG. 1B. It is a sectional view.

As shown in FIG. 1A, the piezoelectric motor 10 includes a rotation transmission gear 11 and three (3) pairs of buckling actuators 12 arranged at an angular interval of 120 degrees about the rotation axis of the gear 11. As shown in FIG. 1B, each buckling actuator 12 includes a pair of piezoelectric elements 121. For example, each piezoelectric element 121 may be formed of a PZT (lead zirconate titanate) piezoelectric element. The base end of each piezoelectric element 121 is connected to the base 13 via an elastic joint 14-1, and the tip of each piezoelectric element 121 is connected to the movable link 15 via an elastic joint 14-2. The movable link 15 has an input tip (or follower) 15A that engages with the gear 11 by sliding with respect to the gear 11. The input tip 15A of the movable link 15 of the pair of buckling actuators 12 constituting the counter unit is connected to the counter connection portion 16, and the movement of the input tip 15A is one (1) according to the movement of the piezoelectric element 121. Limited to the freedom of translational movement. Specifically, the movement of the input chip 15A is limited to the vertical movement in FIGS. 1B and 1C.

As will be described later, the drive system (not shown) drives the piezoelectric elements 121 of the three (3) pairs of buckling actuators 12 in consideration of the gear phase of the gear 11. Therefore, the movement of the input tip 15A in each of the three (3) pairs of buckling actuators 12 causes the gear 11 to rotate along its rotation axis.

FIG. 1C shows a contact state between the gear 11 and the input tip 15A. The input tips 15A of the pair of buckling actuators 12 are firmly connected to each other via the counter-connecting portion 16. The input tip 15A has a counter-connecting portion so that the output energy from the pair of buckling actuators 12 is transmitted via the two input tips 15A, and as a result, the pair of buckling actuators 12 perform a push-pull operation. It may be fixed to 16. In this operation, since the piezoelectric element 121 can transfer energy under the on and off voltage conditions, the energy transfer ability from the piezoelectric element 121 to the gear 11 is enhanced. Therefore, the gear 11 converts the output of the piezoelectric element 121 into the motor output of the piezoelectric motor 10.

By combining the design of the gear 11 and the arrangement design of the pair of buckling actuators 12, the three (3) pairs of buckling actuators 12 can be arranged at the same phase distance with respect to the waveform of the gear 11. The three (3) pairs of buckling actuators 12 are arranged at equal intervals, excluding a multiple of 60 degrees and a multiple of 180 degrees of the gear phase angle. Each pair of buckling actuators 12 is 180 degrees out of phase with the pair of adjacent buckling actuators 12, and a counter unit may be formed.

Further, due to the parallel arrangement of the pair of buckling actuators 12 and the strong connection between the input tips 15A, the movement of the input tip 15A is limited to one (1) degree of freedom of translational motion. This mechanism is similar to a parallel elastic linear motion guide. Therefore, in this example, the piezoelectric motor 10 can omit the external linear motion guide for the input chip 15A, and the weight and size can be reduced by that amount.

For example, a sphere or cylinder having a diameter of 2.5 mm can be used as the input tip 15A for transmitting the output energy of the pair of buckling actuators 12 to the gear 11. The gear shape is designed so that the central locus of the sphere or cylinder forming the input tip 15A has a sinusoidal shape, and both the force transmission by the gear 11 and the movement of the input tip 15A are smooth. The central locus of the sphere or cylinder forming the input chip 15A is an example of the motion locus of the engaging portion of the gear 11 having a shape that engages with the piezoelectric element, and has a sinusoidal component with respect to the gear 11. The height of the locus is set equal to the maximum free displacement amount y _max of the pair of buckling actuators 12. Wavelengths are designed to maintain a continuous shape over the gear shape. In order to realize this, the minimum radius of curvature R _Cmin of the center locus of the sinusoidal shape is set to be larger than the radius of the input chip 15A. The central locus of this sinusoidal shape can be expressed by the following equation (1), assuming that the buckling motion is unipolar. The radius of curvature R _C of the central locus of the sinusoidal shape can be expressed by the following equation (2), and since the minimum radius of curvature R _Cmin deviates from each of the upper and lower parts of the locus of the sinusoidal shape, the minimum radius of curvature R _Cmin can be expressed by the following equation (3).

上記の式（１）乃至（３）中、yは座屈型アクチュエータ１２の出力変位量、xはギア１１のギア位置、λは正弦波形状の中心軌跡の波長、h_gearは一般的に座屈型アクチュエータ１２の最大自由変位量y_maxと同様に設定されるギア１１のギア高さを示す。

In the above equations (1) to (3), y is the output displacement of the buckling actuator 12, x is the gear position of the gear 11, λ is the wavelength of the central locus of the sinusoidal shape, and h _gear is generally the seat. The gear height of the gear 11 set in the same manner as the maximum free displacement amount y _max of the bending actuator 12 is shown.

Further, in the case of the equilateral triangle arrangement of the buckling type actuator 12 shown in FIGS. 1A to 1C, the number of peaks of the waveform cannot be a multiple of 3 (3).

FIG. 2 is a diagram illustrating a gear shape of the gear 11. In FIG. 2, the solid line shows the gear shape, and the alternate long and short dash line shows the central locus of the sinusoidal shape of the input chip 15A.

FIG. 3 is a diagram showing an example of a drive system for the piezoelectric motor 10. In FIG. 3, the drive system 20 includes a control unit 21, a drive device 22, and an inductor L. The drive device 22 includes a plurality of drive circuits 22-1 to 22-N (N is a natural number greater than 1) to which electric charges are supplied by the power source 30 that supplies the power supply voltage. Each drive circuit 22-i (i = 1, ..., N) drives the corresponding buckling actuator 12. The drive system 20 employs a voltage switching function for switching the voltage for controlling the on / off state of each piezoelectric element 121. The drive system 20 also employs a charge recovery function that reuses energy for energy efficiency.

FIG. 4 is an equivalent circuit diagram of the piezoelectric element 121. As described above, the piezoelectric element 121 is a kind of capacitive actuator capable of expressing basic mechanical electrical characteristics by the equivalent circuit of FIG. The components in the upper half shown in FIG. 4 show the properties of the electrical region represented by the capacitance C1. This capacitive property can be simplified by omitting the higher order properties for both voltage and mechanical load. The lower half component shown in FIG. 4 shows the properties of the mechanical region including the inductance L1, the capacitance C1 and the resistor R1. The inductance L1 exhibits mass properties and the capacitance C2 exhibits compliance properties. The resonance characteristic is represented by both the capacitance C2 and the inductance L1. The resistor R1 represents an energy dissipation characteristic. Although not shown in FIG. 4, since the piezoelectric element 121 generally has a hysteresis characteristic according to the electric charge exchanged with the outside of the piezoelectric element 121, energy loss is caused even in a quasi-static state transition. Occurs. Hysteresis characteristics vary in relation to both voltage and mechanical load.

A voltage is applied between the terminals of the piezoelectric element 121 to activate the piezoelectric element 121. Due to this voltage, energy is stored in both the electrical and mechanical regions of the piezoelectric element 121. The energy stored in the mechanical domain can be used for external work. However, the energy stored in the electrical domain does not accomplish external work. This means that when the voltage applied to the piezoelectric element 121 is switched from the on state to the off state, the electrical energy is discarded without being used. In many PZT piezoelectric elements and the like, the capacity of electrical energy is larger than the capacity of mechanical energy, so that the energy efficiency as a whole is significantly reduced by discarding the electrical energy.

The drive circuit 22-i has a configuration in which the electrical energy stored in the piezoelectric element 121 is transferred to the capacitor and the energy from the capacitor is transferred to the piezoelectric element 121. When it is necessary to switch from on to off and from off to on in parallel for two piezoelectric elements, the piezoelectric elements are alternately used as capacitors to transfer energy to one of the piezoelectric elements. Can be transferred directly from to the other piezoelectric element. With such a driving method, energy dissipation can be significantly reduced. Further, the driving method adopting such a charge transfer function can reduce the energy loss generated in the charging circuit between the piezoelectric element 121 and the power supply 30 in FIG.

FIG. 5 is a schematic diagram illustrating the operation of the drive circuits 22-i with respect to the two piezoelectric elements 121. In FIG. 5, the drive circuit 22-i includes switches S _1H , S _1L , S _2H , S _2L , S ₁₂ , S ₂₁ and diodes D ₁₂ and D ₂₁ . Capacitors C _1P and C _2P correspond to the capacitive properties of the two piezoelectric elements 121, and L corresponds to the inductor L shown in FIG. V _S denotes a power supply voltage supplied from the power supply 30 shown in FIG.

In step ST1, the switches S _1H and S _2L are closed (on) so that the capacitor C _1P is charged by the power supply voltage Vs as shown by the broken line arrow and the electric charge stored in the capacitor C _2P is discharged to the ground. ), And the remaining switches S _1L , S _2H , S _2L , S ₁₂ , and S ₂₁ are opened (off). In step ST2, the switch S ₁₂ is closed (on) so that the charge stored in the capacitor C _1P is transferred via the switch S ₁₂ , the diode D ₁₂ and the inductor L as indicated by the arrow of the alternate long and short dash line. Then, the remaining switches S _1H , S _1L , S _2H , S _2L , and S ₂₁ are opened (off). At step ST3, the addition to the charge which the charge remaining in the capacitor C _1P as indicated by the arrows in two-dot chain line is discharged to ground, the power supply voltage V _S is transferred from the capacitor C _1P is supplied to the capacitor C _2P The switches S _1L and S _2H are closed (on) and the remaining switches S _1H , S _2L , S ₁₂ and S are replenished with the amount of charge required to further charge the capacitor C _{2P. 21} is opened (off). Needless to say, the electric charge stored in the capacitor C _2P may be transferred via the inductor L, the diode D ₂₁ and the switch S ₂₁ as in the case of the capacitor C _1P .

The path from the capacitor C _1P to the capacitor C _2P is an example of a transfer path connecting the capacitors C _1P and C _2P via the inductor L. The switches S _1H , S _1L , S _2H , S _2L , S ₁₂ , and S ₂₁ are examples of switching means for switching between transfer and non-transfer of electric charge between the capacitors C _1P and C _2P . The diodes D ₁₂ and D ₂₁ are examples of transfer direction determining means for determining the transfer direction of charges between the capacitors C _1P and C _2P . The switching means and the transfer direction determining means can flexibly determine the necessity of charge transfer and the charge transfer direction.

The path including the switch S _1H between the power supply 30 and the capacitor C _1P and the path including the switch S _2H between the power supply 30 and the capacitor C _2P each transfer the electric charge from the power supply 30 to the capacitors C _1P and C _2P. This is an example of a supply path to supply to. The supply path ensures that the capacitor can be charged. The path including the switch S _1L between the capacitor C _1P and the ground and the path including the switch S ₂₁ between the capacitor C _2P and the ground are the capacitors C _1P and C _2P , respectively, for the charges remaining after the charge transfer. This is an example of a discharge path that discharges from the ground to the ground. The discharge path ensures that the capacitor can be discharged.

FIG. 6 is a circuit diagram showing a part of the drive system 20. In FIG. 6, since the configuration of the drive circuits 22-2 to 22-N is the same as the configuration of the drive circuit 22-1, reference numerals are shown only for the drive circuit 22-1.

In FIG. 6, the drive circuit 22-1 and the circuit unit 221-1 provided for the pair (PZT11) of the piezoelectric elements 121 forming one of the buckling type actuators 12 forming the piezoelectric motor 10. The circuit portion 23 includes a circuit portion 221-2 provided for a pair of (PZT21) piezoelectric elements 121 forming the other one of the buckling actuators 12 forming the piezoelectric motor 10. It is shared by the drive circuits 22-1 to 22-N. The circuit portion 23 may be included in the drive circuit 22-1, or may be provided outside the drive circuit 22-1.

The circuit unit 221-1 includes drivers Drvh11, Drvl11, Drvf11, Drvb11, switches Qh11, Ql11, Qtf11, Qtb11 and diodes Dtf11, Drb11 connected to the pair of piezoelectric elements PZT11 as shown in FIG. On the other hand, the circuit unit 221-2 includes drivers Drvh21, Drvl21, Drvf21, Drvb21, switches Qh21, Ql21, Qtf21, Qtb21 and diodes Dtf21, Drb21 connected to the pair of piezoelectric elements PZT21 as shown in FIG. .. The circuit portion 23 includes drivers Drv1a, Drv1b, Drv2a, Drv2b, switches Q1a, Q1b, Q2a, Q2b and an inductor L connected as shown in FIG.

The drivers Drvh11, Drvl11, Drvf11, Drvb11, Drvh21, Drvl21, Drvf21, Drvb21, Drv1a, Drv1b, Drv2a, Drv2b may be controlled and driven by the signal from the controller 21 shown in FIG. Switches Qh11, Ql11, Qtf11, Qtb11, Qh21, Ql21, Qtf21, Qtb21, Q1a, Q1b, Q2a, Q2b are IGBTs (Insulated Gate Bipolar Transistors) or MOSFETs (Metal-Oxide-Semiconductor Field-Effect) for high efficiency. It may be formed by Transistor).

In this example, only one inductor L is used to transfer the electric charge stored between the two pairs of piezoelectric elements 212 (PZT21 and PZT22) for the following reasons (a1) to (a6).

(A1) The lower the resistance property of the inductor L, the higher the energy transfer characteristic.

(A2) The lower the resistance property of the inductor L, the larger the inductor L generally becomes.

(A3) The switching pattern is restricted by the inductor L connected to each pair of the piezoelectric elements 121.

(A4) In the piezoelectric motor 10, switching is generally required between a pair of buckling actuators 12.

(A5) One inductor L can be used in time division for all buckling actuators 12.

(A6) By using one inductor L, the drive system 20 can be miniaturized and an inductor with a low resistance can be used.

For example, the inductor L has an inductance of 558 μH and a resistor of 19.7 mΩ connected in series. The capacitance that affects the transfer status is, for example, about 14 μF, which is caused by the pair of piezoelectric elements 121. The pair of piezoelectric elements 121 are connected in parallel in the buckling actuator 12, and the two pairs of piezoelectric elements 121 are connected in series via the inductor L. The resistance in the transfer path, including the inductor L, is, for example, about 86 mΩ. Considering the LCR characteristics, it can be seen that the transfer of charges between the buckling actuators 12 in the counter unit is calculated, for example, in about 280 μsec.

As described above, in this example, the piezoelectric motor 10 has six (6) buckling actuators 12 forming three (3) counter units arranged at equal intervals with the phase of the teeth of the gear 11 as a unit. The drive system 20 includes a drive device 22 having a charge transfer function. Considering the features of the piezoelectric motor 10 and the drive system 20, the control method shown in FIG. 7 may be adopted.

FIG. 7 is a diagram illustrating an example of a control method of three (3) counter units A1, A2, and A3, that is, a three-phase switching drive.

As shown in the control method of FIG. 7, the voltage switching is performed between the buckling type actuators 12 that form a pair of the counter units A1, A2, and A3. Lines Sn1 to Sn6 of each sinusoidal waveform indicate gear transitions. The small vertical arrows indicate the output (or drive) directions of the opposing units A1, A2, and A3 in each gear phase. According to this control method, the three (3) counter units A1 to A3 can drive the gear 11 in both the clockwise and counterclockwise directions in FIG. 1A without causing an inoperable point in all gear phases. ..

In this case, the maximum frequency for voltage switching can be set by considering the maximum operating frequency of the piezoelectric element 121 and the estimated resonance frequency of the buckling actuator 12. The voltage switching sequence occurs six (6) times during the switching cycle for each counter unit A1, A2, A3, and each of the three (3) counter units A1 to A3 requires two (2) voltage switching sequences. Therefore, the voltage switching sequence can be performed at a frequency of 1/6 or less of the maximum voltage switching frequency based on the maximum voltage switching frequency. The time division use of the inductor L can prevent the voltage switching sequences from overlapping between different counter units. The voltage switching sequence can be implemented in, for example, an FPGA (Field Programmable Gate Array).

Next, the multi-phase drive of an even number of piezoelectric elements 121 driven with a phase difference of 180 degrees will be described together with FIGS. 8 and 9. FIG. 8 is a schematic diagram illustrating an example of a drive circuit for driving an even number of piezoelectric element groups, and FIG. 9 is a diagram for explaining the operation of the drive circuit of FIG. Each piezoelectric element can exhibit characteristics equivalent to a pair of piezoelectric elements forming the buckling type actuator 12.

FIG. 8 shows a case where the four (4) piezoelectric elements 121A, 121B, 121C, 121D are driven by the four (4) drive circuits 22A, 22B, 22C, 22D having the same configuration. For example, the drive circuit 22A includes a switch _{S H, S L, S 12} , S 21 and diode _{D 12, D 21.} The path 201 connects the output of the diode D ₁₂ of each drive circuit 22A to 22D to one end of the inductor L. The path 202 connects the other end of the inductor L to the input of the diode D ₂₁ of each drive circuit 22A to 22D. The paths 201 and 202 are examples of the first and second paths for connecting the piezoelectric elements 121A to 121D via the switches S ₁₂ and S ₂₁ , and the paths 201 and 202 are connected via the inductor L. The first and second passes allow the piezoelectric element 121 to exchange charges to be flexibly determined.

Switch _S H of the drive circuits 22A to _{22D, S L, S 12,} S 21 , the drive circuit 22A, the piezoelectric element 121A that is driven by 22C, exchanging charge between 121C, driven drive circuit 22B, the 22D The electric charges are exchanged between the piezoelectric elements 121B and 121D in the same manner as described above with FIG. 9, "V" indicates a state in which the piezoelectric element 121 is connected to a power supply 30 for supplying the piezoelectric element 121 is a power supply voltage V _S is charged, "G] is the ground state of the piezoelectric element 121 is grounded In addition, “121A”, “121B”, “121C”, and “121D” indicate the states of the piezoelectric elements 121A, 121B, 121C, 121D driven by the drive circuits 22A, 22B, 22C, and 22D, respectively. The states c1 and c5 are the same. Therefore, the piezoelectric element 121 can continuously drive the motor in one direction by repeatedly transitioning from the state c1 to the state c4 in ascending order. On the contrary, the piezoelectric element 121 can continuously drive the motor in the opposite direction by repeatedly transitioning from the state c4 to the state c1 in descending order.

In the state c1 of the voltage supply sequence (or pattern) shown in FIG. 9, the piezoelectric elements 121A and 121B are connected to the power supply 30, and the piezoelectric elements 121C and 121D are grounded. In the state c2, as a result of the process of transferring the electric charge of the piezoelectric element 121A from the state c1 to the piezoelectric element 121C, the piezoelectric elements 121B and 121C are connected to the power supply 30, and the piezoelectric elements 121A and 121D are grounded. In the state c3, as a result of the process of transferring the electric charge of the piezoelectric element 121B from the state c2 to the piezoelectric element 121D, the piezoelectric elements 121C and 121D are connected to the power supply 30, and the piezoelectric elements 121A and 121B are grounded. In the state c4, as a result of the process of transferring the electric charge of the piezoelectric element 121C from the state c3 to the piezoelectric element 121A, the piezoelectric elements 121A and 121D are connected to the power supply 30, and the piezoelectric elements 121B and 121C are grounded. In the state c5, as a result of the process of transferring the electric charge of the piezoelectric element 121D from the state c4 to the piezoelectric element 121B, the piezoelectric elements 121A and 121B are connected to the power supply 30, and the piezoelectric elements 121C and 121D are grounded. The transfer of electric charge from one piezoelectric element to another piezoelectric process is performed in the same manner thereafter.

Next, the multi-phase drive of the odd number of piezoelectric elements 121 driven by a phase difference other than 180 degrees will be described together with FIGS. 10 and 11. FIG. 10 is a schematic diagram illustrating an example of a drive circuit for driving an odd number of piezoelectric element groups, and FIG. 11 is a diagram for explaining the operation of the drive circuit of FIG. Each piezoelectric element can exhibit characteristics equivalent to a pair of piezoelectric elements forming the buckling type actuator 12.

FIG. 10 shows a case where the three (3) piezoelectric elements 121A, 121B, 121C and the capacitor 231 are driven by four (4) drive circuits 22A, 22B, 22C, 22D having the same configuration. In FIG. 10, the same parts as those in FIG. 8 are designated by the same reference numerals, and the description thereof will be omitted. 10, the power supply voltage _{V S} to supply the power source 30 and the piezoelectric element 121 switches S between a path including a switch _{S H} between (121A, 121B, one of 121C), a power supply 30 and capacitor 231 _The paths including _H are examples of supply paths for supplying the electric charges from the power supply 30 to the piezoelectric element 121 and the capacitor 231 respectively. The capacitor 231 is an example of a storage means for storing electric charges. The power storage means has the same capacitive properties as the piezoelectric element 121. The power storage means can drive an odd number of piezoelectric elements 121 with a phase difference other than 180 degrees.

Switch _S H of the drive circuits 22A to _{22D, S L, S 12,} S 21 is controlled in a manner similar to that described in conjunction with FIG. 5 in the above, the charge from one piezoelectric element to another piezoelectric element The transfer is done via the capacitor 231. For example, in the transfer of electric charge from the piezoelectric element 121A to the piezoelectric element 121B, the electric charge is first transferred from the piezoelectric element 121A driven by the drive circuit 22A to the capacitor 231 controlled by the drive circuit 22D, and then the electric charge is transferred from the capacitor 231. Transfer to the piezoelectric element 121B driven by the drive circuit 22B. 11, "V" indicates a state in which the piezoelectric element 121 or the capacitor 231 is connected to the piezoelectric element 121 or the capacitor 231 power 30 supplies a power supply voltage _{V S} is charged, "G] the piezoelectric element 121 or The grounded state of the capacitor 231 is shown. Further, “121A”, “121B”, “121C” and “231” are of the piezoelectric elements 121A, 121B and 121C driven by the drive circuits 22A, 22B and 22C, respectively. The state and the state of the capacitor 231 controlled by the drive circuit 22D are shown. The states c1 and c7 are the same. Therefore, the piezoelectric element 121 can continuously drive the motor in one direction by repeatedly transitioning from the state c1 to the state c6 in ascending order. On the contrary, the piezoelectric element 121 can continuously drive the motor in the opposite direction by repeatedly transitioning from the state c6 to the state c1 in descending order.

In the state c1 of the voltage supply sequence (or pattern) shown in FIG. 11, the piezoelectric element 121A and the capacitor 231 are connected to the power supply 30, and the piezoelectric elements 121C and 121D are grounded.

In the state c2, as a result of the process of transferring the electric charge of the capacitor 231 from the state c1 to the piezoelectric element 121B, the piezoelectric elements 121A and 121B are connected to the power supply 30, and the piezoelectric element 121C and the capacitor 231 are grounded.

In the state c3, as a result of the process of transferring the electric charge of the piezoelectric element 121A from the state c2 to the capacitor 231 the piezoelectric element 121B and the capacitor 231 are connected to the power supply 30, and the piezoelectric elements 121A and 121C are grounded.

In the state c4, as a result of the process of transferring the electric charge of the capacitor 231 from the state c3 to the piezoelectric element 121C, the piezoelectric elements 121B and 121C are connected to the power supply 30, and the piezoelectric element 121A and the capacitor 231 are grounded.

In the state c5, as a result of the process of transferring the electric charge of the piezoelectric element 121B from the state c4 to the capacitor 231 the piezoelectric element 121C and the capacitor 231 are connected to the power supply 30, and the piezoelectric elements 121A and 121B are grounded.

In the state c6, as a result of the process of transferring the electric charge of the capacitor 231 from the state c5 to the piezoelectric element 121A, the piezoelectric elements 121A and 121C are connected to the power supply 30, and the piezoelectric element 121B and the capacitor 231 are grounded.

In the state c7, as a result of the process of transferring the electric charge of the piezoelectric element 121C from the state c6 to the capacitor 231 the piezoelectric element 121A and the capacitor 231 are connected to the power supply 30, and the piezoelectric elements 121B and 121C are grounded.

The transfer of electric charge from one piezoelectric element to another piezoelectric process via a capacitor is performed in the same manner thereafter.

Next, the switching control sequence of the control unit 21 will be described together with FIGS. 12, 13, and 14. FIG. 12 is a schematic diagram illustrating an example of a drive circuit using voltage control, FIG. 13 is a diagram illustrating a drive circuit switching method of FIG. 12, and FIG. 14 is a diagram for switching the drive circuit of FIG. It is a figure explaining the state.

In FIG. 12, the same parts as those in FIG. 5 are designated by the same reference numerals, and the description thereof will be omitted. The switches S _1O and S _1I and the switches S _2O and S _2I shown in FIG. ₁₂ correspond to the switches S ₁₂ and S ₂₁ shown in FIG. 5, respectively.

The control unit 21 transfers the stored electric charge between the piezoelectric elements 121 (PZT1) and 121 (PZT2), as shown in FIG. 13, for each drive circuit 22-1, 22, 2-2 for the states sw1 to sw9. Generates a control signal that controls the on and off states of the switch.

As shown in FIG. 14, the state sw1, sw9, connected to the piezoelectric element PZT1 power 30 _{(V S),} the piezoelectric element PZT2 is connected to the ground GND. Further, after the transition from the state sw7, a certain amount of electric charge is replenished in the piezoelectric element PZT1, and the remaining electric charge is discharged from the piezoelectric element PZT2.

Further, in the states sw2, sw4, sw6, and sw8, both piezoelectric elements PZT1 and PZT2 are in an insulated state. In the state sw3, the electric charge stored in the piezoelectric element PZT1 can be transferred to the piezoelectric element PZT2. In state sw5, piezoelectric elements PZT1 is connected to ground GND, and the piezoelectric element PZT2 is connected to a power supply 30 _{(V S),} and after the transition from state sw3, supplemented with an amount of electric charge in the piezoelectric element PZT2, piezoelectric element The remaining charge is discharged from the PZT1. Further, in the state sw7, the electric charge stored in the piezoelectric element PZT2 can be transferred to the piezoelectric element PZT1.

Therefore, after the electric charge stored in the first piezoelectric element PZT1 is transferred to the second piezoelectric element PZT2, at least the second piezoelectric element PZT2 is moved at a timing that can be controlled by the control system 50 described later together with FIG. The second piezoelectric element PZT2 is replenished with a certain amount of electric charge for additional charging to a predetermined potential. On the other hand, after the electric charge stored in the second piezoelectric element PZT2 is transferred to the first piezoelectric element PZT1, at least the first piezoelectric element PZT2 is moved at a timing that can be controlled by the control system 50 described later together with FIG. The first piezoelectric element PZT2 is replenished with a certain amount of electric charge for additional charging to a predetermined potential. When the capacitor 231 shown in FIG. 10 is provided in addition to the first and second piezoelectric elements PZT1 and PZT2, the charge transfer between the first and second piezoelectric elements PZT1 and PZT2 is via the capacitor 231. Can be done.

When transferring an electric charge between the piezoelectric elements PZT1 and PZT2, the minimum time for maintaining the state of the switch can be determined according to the LC time constant. On the other hand, when replenishing one of the piezoelectric elements PZT1 and PZT2 with an electric charge, the minimum time for maintaining the state of the switch can be determined according to the RC time constant. Therefore, these minimum times may be set in consideration of the driving performance of the piezoelectric motor 10.

In the multi-phase drive of the piezoelectric element 121, in the state where the electric charge is transferred between the piezoelectric elements forming a certain phase, the control sequence is performed at an arbitrary time point except the state where the electric charge is transferred between the piezoelectric elements forming another phase. Can be done with. For example, in the multi-phase drive of a piezoelectric element, in a certain phase state sw3 and sw7, a control sequence excluding the other phase states sw3 and sw7 can be performed at an arbitrary time point.

In the case of multi-phase drive, the states sw2, sw4, sw6, sw8 in which the piezoelectric element 121 is in an insulated state may be omitted in the switching sequence shown in FIG.

FIG. 15 is a diagram illustrating an example of a driving method according to an embodiment of the present invention. The drive process shown in FIG. 15 for driving a plurality of piezoelectric elements can be performed by the drive device 22 under the control of the control unit 21.

In step S1, the drive device 22 performs the first charge transfer process under the control of the control unit 21, and transfers the charge stored in one piezoelectric element PZT1 to the other piezoelectric element PZT2. In step S2, the drive device 22 performs a second charge transfer device under the control of the control unit 21, and transfers the charge stored in the other piezoelectric element PZT2 to the one piezoelectric element PZT1.

Needless to say, in step S1, the electric charge stored in one piezoelectric element 121A may be transferred to the other piezoelectric element 121B via the capacitor 231 of FIG. In this case, in step S2, the electric charge stored in the other piezoelectric element 121B may be transferred to the piezoelectric element 121A (or 121C) other than the other piezoelectric element 121B via the capacitor 231 of FIG.

According to the drive process described with reference to FIG. 15 above, energy can be reused between the plurality of piezoelectric elements 212.

Next, the drive mechanism related to the piezoelectric motor 10 will be described together with FIGS. 16 and 17.

FIG. 16 is a block diagram showing an outline of energy flow and conversion in the piezoelectric motor 10. In FIG. 16, a part of the power supply 30, the driving device 22, and the piezoelectric element 121 is provided in the electrical region. On the other hand, a part of the piezoelectric element 121, the buckling type mechanism 41, the gear 11 and the load 45 are provided in the mechanical region. The buckling mechanism 41 includes three (3) pairs of buckling actuators 12. For example, the load 45 is a drive target driven by the gear 11 of the piezoelectric motor 10.

17A and 17B are diagrams showing examples of work cycles in the mechanical and electrical regions, respectively. In FIG. 17A, the vertical axis indicates the force F in arbitrary units, and the horizontal axis indicates the position x in arbitrary units. In FIG. 17B, the vertical axis represents the voltage V in arbitrary units, and the horizontal axis represents the charge Q in arbitrary units. For example, by applying a preload exceeding the blocking force of the piezoelectric element to each piezoelectric element of the buckling type actuator to obtain a sufficient allowable tensile stress, the energy characteristics in the mechanical cycle and the electrical cycle are respectively shown in FIG. 17A. And as shown in FIG. 17B.

Based on the above equation (1), the static relationship between the electromechanical state values of the piezoelectric element 121 can be expressed by the following equation (4). Here, d is a value obtained from the piezoelectric coefficient and dimensions of the buckling type actuator 12, c _M indicates mechanical compliance, and c _E indicates the capacitance of the piezoelectric element 121.

予荷重を含めた上記式（４）に基づき、座屈型アクチュエータ１２の機械的領域と電気的領域における仕事サイクルは、夫々図１７Ａ及び図１７Ｂのように表すことができる。機械的及び電気的領域において、○印で囲まれた数字は機械的状態と電気的状態の整合を示す。機械的な仕事サイクルは、圧電素子のブロック力Ｆ_blockと同じ予荷重を含むものとする。図１７Ａの機械的領域においてパス“１”＜−＞“２”及びパス“３”＜−＞“４”がゼロ変位過程であるとすると、図１７Ｂにおいてパス“２”＜−＞“３”及びパス“１”＜−＞“４”は一定電圧過程である。機械的な仕事サイクルと電気的な仕事サイクルの各サイクルの仕事は等しい。圧電モータ１０の出力密度は、座屈型アクチュエータ１２の最大仕事サイクルを適用することで最大化することができる。

Based on the above equation (4) including the preload, the work cycle in the mechanical region and the electrical region of the buckling type actuator 12 can be represented as shown in FIGS. 17A and 17B, respectively. In the mechanical and electrical domain, the numbers circled indicate the alignment of the mechanical and electrical states. The mechanical work cycle shall include the same preload as the block force F _block of the piezoelectric element. Assuming that the paths "1"<->"2" and the paths "3"<->"4" are zero displacement processes in the mechanical region of FIG. 17A, the paths "2"<->"3" in FIG. 17B. And the paths “1” <−> “4” are constant voltage processes. The work of each cycle of the mechanical work cycle and the electrical work cycle is equal. The power density of the piezoelectric motor 10 can be maximized by applying the maximum work cycle of the buckling actuator 12.

Next, the buckling type actuator 12 and the counter unit formed by the buckling actuator 12 will be described. Focusing on the basic mechanism of the buckling actuator 12, the simplified mechanical model can be represented as shown in FIG. FIG. 18 is a diagram showing an example of a low-order mechanical model of the buckling type actuator 12. In FIG. 18, L indicates the distance between the centers of the rotary joint, and L + z indicates the distance between the centers of the rotary joint in consideration of the change in the length of the piezoelectric element 212 during driving. The model of the buckling type actuator 12 shown in FIG. 18 can be represented by the following equation (5). Here, k _θ is the integrated rotational stiffness of the joint of the piezoelectric element 212 connected to the base frame, and k _S is the length of the piezoelectric element 212 obtained by synthesizing the stiffness k _{B of the} substrate frame and the stiffness k _J of the joint along the longitudinal direction. The synthetic stiffness along the direction, k _P is the stiffness along the longitudinal direction of the piezoelectric element 212, z _S is the combined displacement amount of the base frame and the joint, and z _P is the displacement amount of the piezoelectric element 212.

上記の式（５）をまとめると、座屈型アクチュエータ１２が出力する力Ｆ_ｙは、座屈出力変位量ｙと圧電素子２１２の潜在力Ｆ_Ｐから次式（６）のように表すことができる。

To summarize the above equation (5), the force F _y outputting seat屈型actuator 12 may be expressed from the potential F _P of the seat屈出force displacement y and the piezoelectric element 212 by the following equation (6) it can.

座屈型アクチュエータ１２の最大自由変位量ｙ_ｍａｘは、次式（７）で表すことができ、座屈型アクチュエータ１２が外部からの作用を受けることなく圧電素子１２１の駆動のみで発生可能な最大変位量を示す。

The maximum free displacement amount y _max of the buckling type actuator 12 can be expressed by the following equation (7), and the maximum amount that can be generated only by driving the piezoelectric element 121 without the buckling type actuator 12 receiving an external action. Indicates the amount of displacement.

θ＜０．１であると仮定すると、次式（８）で表される近似を用いて上記の式（６）を上記の式（５）から求めることができる。

Assuming that θ <0.1, the above equation (6) can be obtained from the above equation (5) using the approximation represented by the following equation (8).

上記の式と圧電モータ１０に使用される機械的パラメータを用いることで、力変位特性及び変位出力特性を含む座屈型アクチュエータ１２の出力特性を求めることができる。

By using the above equation and the mechanical parameters used in the piezoelectric motor 10, the output characteristics of the buckling type actuator 12 including the force displacement characteristics and the displacement output characteristics can be obtained.

FIG. 19 is a diagram showing an example of the calculated output characteristics of the buckling type actuator 12. In FIG. 19, the vertical axis represents the force F _y output by the buckling actuator 12, and the horizontal axis represents the buckling output displacement amount y.

The counter unit is formed using the buckling actuator 12 as shown in FIGS. 20A, 20B and 20C. 20A, 20B and 20C are schematic views showing an example of counter-connection. In FIGS. 20A to 20C, the circles at both ends indicate side blocks firmly fixed to the substrate structure. The central circle indicates the input chip 15A. The rod-shaped portion indicates the piezoelectric element 121. The rectangular portion between the central circles (input chip 15A) indicates the counter-connecting portion 16 that firmly connects the input chip 15A.

FIG. 20A shows a case where the upper piezoelectric element 121 is on, the lower piezoelectric element 121 is off, and there is no external load. FIG. 20C shows a case where the upper piezoelectric element 121 is off, the lower piezoelectric element 121 is on, and there is no external load. FIG. 20B shows a case where both the upper and lower piezoelectric elements 121 are off and there is no external load. At the input chip positions shown in FIGS. 20A and 20C under the above-mentioned piezoelectric element conditions, the length of the counter-connecting portion 16 is set so as to cancel the interaction force between the input chips 15A. With such a setting, the force and displacement characteristics output by the counter unit are observed as shown in FIG.

FIG. 21 is a diagram showing an example of the force and displacement characteristics output by the counter unit. In FIG. 21, the vertical axis represents the force F _y output by the buckling type actuator, and the horizontal axis represents the buckling output displacement amount y.

The force output by the counter unit can be calculated by adding each buckling force at the same distance as the maximum buckling output displacement amount. In FIG. 21, the thin solid lines “Fy1 ON” and “Fy1 OFF” indicate the characteristics of the force output by the upper buckling actuator 12, and the thin dashed lines “Fy2 ON” and “Fy2 OFF” indicate the lower buckling actuator 12. Shows the characteristics of the force output by. Since the buckling actuator 12 forming the counter unit can realize bipolar motion, this means that the buckling actuator 12 can be displaced from the maximum displacement on the negative side to the maximum displacement on the positive side. However, since the displacement of the counter unit is constrained to a unipolar range, this is because the connected input chip 15A buckles from zero as shown by the thick solid lines "+ Fy" and "-Fy" in FIG. It means that the actuator 12 is displaced to the maximum displacement on the positive side.

Next, the closed loop control of the piezoelectric motor 10 will be described. The open loop control can use the voltage switching frequency as an input to the drive system 20. Such a system configuration can be regarded as a speed input motor, but it is known that the controllability of such a system configuration is low. In order to further improve the controllability of the motor, the input rule can use the pseudo torque control described below.

First, the torque and force characteristics of the piezoelectric motor 10 are considered. FIG. 22 is a diagram for explaining the motor force characteristics generated by one buckling type actuator 12 when a unipolar drive gear is used for the gear 11. In FIG. 22, the plot in the lower right part shows the force displacement characteristic of the buckling actuator 12 for one polarity, and the broken line shows the case where the piezoelectric element 212 (PZT) of the buckling actuator 12 is on (maximum voltage applied). The solid line shows the case where the piezoelectric element 212 (PZT) of the buckling actuator 12 is off (no voltage applied or zero voltage applied).

In Figure 22, by using the centroid of the sinusoidal shape of the input chip 15A with respect to the gear 11 as shown in the upper left portion, a force F _y output by the seat屈型actuator plot in the lower left portion in FIG. 22 Convert to the indicated gear force F _x . Since the tangential angle of the gear surface determines the conversion ratio at each contact, the teeth of the gear 11 also have a sinusoidal pattern in the conversion characteristics with respect to the gear phase indicated by x in the lower left plot of FIG. In the state the piezoelectric element 212 of the seat屈型actuator 12 is turned on, the seat屈型actuator 12 outputs a force F _y in the upward direction. The upward force F _y output by the buckling type actuator is converted into a gear force F _x in the left direction at the first inclination of the teeth of the gear 11 as shown in the upper left portion in FIG. In the second inclination following the first inclination of the gear teeth, the upward force F _y is converted into the right force F _x . The force conversion at other tilts of the gear teeth is similar to the transform at the first and second tilts. In the conversion of the force F _y output by the buckling actuator to the gear force F _{x as} described above, the piezoelectric element 212 of the buckling actuator 12 is continuously turned on and an external action is applied to the buckling actuator 12 and the gear 11. In the absence of, the input tip 15A indicates stability at the top of the gear teeth. On the other hand, when the piezoelectric element 212 of the buckling actuator 12 is off, the downward force F _y output by the buckling actuator 12 is the gear force F _x to the right at the first inclination of the gear teeth. At the second inclination, the downward force F _y is converted into the left force F _x . As a result, in the conversion of the force F _y output by the buckling actuator as described above into the gear force F _x , the piezoelectric element 212 of the buckling actuator 12 is continuously turned off, and the buckling actuator 12 and the gear 11 In the absence of external action, the input tip 15A stabilizes at the bottom of the gear teeth.

Therefore, when the piezoelectric element 212 is switched from the on state to the off state at the upper part (or peak) of the gear tooth, and when the piezoelectric element 212 is switched from the off state to the on state at the lower part (or valley) of the gear tooth. At that time, a continuous leftward gear force F _x is obtained. Similarly, when the piezoelectric element 212 is switched from the off state to the on state at the upper part of the gear tooth, and when the piezoelectric element 212 is switched from the on state to the off state at the lower part of the gear tooth, the direction is continuous to the right. Gear force F _{x of} is obtained.

FIG. 23 is a diagram showing gear forces obtained by a single buckling actuator in various phase switching modes. The upper end of FIG. 23 corresponds to an enlarged upper left portion of FIG. 22.

The first (top) to seventh (bottom) curves shown in FIG. 23 represent continuous left or right gear force characteristics. The fourth (central portion) curve represents the gear force characteristic when the voltage is switched at the midpoint of each gear tooth. From this fourth curve, it can be seen that the force to the left and the force to the right cancel each other out, and the average gear force at each phase length becomes zero. From the fourth curve to the first curve, the average gear force increases to the left as the switching phase changes. On the other hand, in the fourth curve to the seventh curve, the average gear force increases in the right direction according to the change of the switching phase. The switching interval is always maintained at 1/2 of the gear pitch.

FIG. 24 is a diagram showing gear forces obtained by six (6) buckling type actuators 12 in various phase switching modes. The upper end of FIG. 24 corresponds to an enlarged upper left portion of FIG. 22.

The six (6) buckling actuators 12 shall have the same phase spacing at intervals of multiples of the gear cycle other than the same number of multiples as the number of buckling actuators. Figure 24 shows the characteristics of the gear force F _x which is the result by six (6) pieces of the seat屈型actuator 12. As shown in FIG. 24, the switching of each buckling type actuator 12 is performed in consideration of only the gear phase of each buckling type actuator 12. As a result, the same gear force characteristic can be generated from each buckling type actuator 12 only by shifting the gear position with respect to the position of each buckling type actuator 12 with respect to the gear phase. In FIG. 24, a thin solid line indicates the gear force of each buckling type actuator 12. In Figure 24, a curved line indicated by a thick solid line shows the average gear force generated by the six (6) pieces of the seat屈型actuators 12 at each gear phase position which defines the characteristics of the gear force F _x generated as a result ..

For the first (top) and seventh (bottom) curves shown in FIG. 24, which correspond to the case where the piezoelectric element 212 is switched only at the top and bottom of the gear teeth, the average gear force is left or right. It becomes almost constant in the direction. For the fourth (central) curve shown in FIG. 24, which corresponds to the case where the piezoelectric element 212 is switched only at the midpoint of the gear teeth, the average gear force includes some force ripple, but is average regardless of the gear pitch. The power of is zero. In other switching modes, the resulting average force increases with change in switching phase, as in the case of the single buckling actuator 12 described above with FIG. 23.

Assuming that the above equation (1) represents the central locus of the input tip 15A, the contact inclination dy / dx between the gear 11 and the input tip 15A can be expressed by the following equation (9).

上記の式（１）で表される軌跡を上記の式（６）に代入することで、ギア位置に対して座屈型アクチュエータが出力する力をＦ_ｙｘとして定義すると、Ｎ_ｂ個を単位とする座屈型アクチュエータ１２からギア１１に伝達される有効エネルギＥ_Ｇは、次式（１０）で表すことができる。ここで、−１／２≦ｐ＜１／２である。

A trajectory represented by the above formula (1) By substituting the above equation (6), when the force output by the seat屈型actuator against the gear position is defined as F _yx, and N _b number of units valid is transmitted from the seat屈型actuator 12 to the gear 11 energy E _G can be expressed by the following equation (10). Here, −1 / 2 ≦ p <1/2.

上記の式（１０）において、２πｐは１つのグループの圧電素子２１２がオンの状態からこの１つのグループの圧電素子２１２がオフの状態までのギアピッチλの切り替え位相であり、オン・オフの切り替えとオフ・オンの切り替えの間の位相距離がギアピッチの１／２、即ち、λ／２に設定される。Ｆ_Ｐｍａｘは、圧電素子２１２の潜在力Ｆ_Ｐの最大値を示す。有効エネルギＥ_Ｇを用いることで、切り替え位相に応じた平均ギア力Ｆ_{Ｇｍｅａｎ}を次式（１１）で表すことができる。式（１１）において、λはギア１１のギアピッチを示し、ｈ_ｇｅaｒはギア１１のギア高さを示し、Ｌは回転ジョイントの中心間の距離を示し、ｋ_Ｓは長手方向に沿った基体フレームのスチフネスｋ_Ｂとジョイントのスチフネスｋ_Ｊを合成した圧電素子２１２の長手方向に沿った合成スチフネスを示し、ｋ_Ｐは圧電素子２１２の長手方向に沿ったスチフネスを示す。平均ギア力Ｆ_{Ｇｍｅａｎ}は、圧電モータ１０が目標とする推力の一例である。

In the above equation (10), 2πp is the switching phase of the gear pitch λ from the state in which the piezoelectric element 212 of one group is on to the state in which the piezoelectric element 212 of this one group is off, and is the switching phase of on / off. The phase distance between off / on switching is set to 1/2 of the gear pitch, i.e. λ / 2. F _Pmax indicates a maximum value of potential _{F P} of the piezoelectric element 212. By using the effective energy _{E G,} it is possible to represent the average gear force _{F Gmean} in accordance with the switching phase in equation (11). In equation (11), λ indicates the _gear pitch of the gear 11, h _gear indicates the gear height of the gear 11, L indicates the distance between the centers of the rotary joints, and k _S indicates the distance of the base frame along the longitudinal direction. The composite stiffness along the longitudinal direction of the piezoelectric element 212 obtained by combining the stiffness k _B and the stiffness k _J of the joint is shown, and k _P indicates the stiffness along the longitudinal direction of the piezoelectric element 212. The average gear force F _Gmean is an example of the thrust targeted by the piezoelectric motor 10.

上記の式（１１）は、切り替え駆動により駆動されるギア１１の準静的力特性を表し、−１／４≦ｐ＜１／４の範囲内での単調増加特性のため開ループ力制御の可能性をも表す。また、上記の式（１１）は、ギア力特性の直感的な理解をもたらす。式（１１）の２つ目の等号「＝」の後の分数で表される１番目の項は幾何学的性質を表し、２つ目の等号「＝」の後の分数で表される２番目の項はコンプライアンス的性質を表す。この結果、座屈型アクチュエータ１２の曲げスチフネスｋ_θと最大自由変位量ｙ_ｍａｘは、共に準静的平均ギア力に直接的な影響を及ぼさないことが確認された。

The above equation (11) represents the quasi-static force characteristic of the gear 11 driven by the switching drive, and the open-loop force control is performed because of the monotonous increase characteristic within the range of -1/4 ≤ p <1/4. It also represents the possibility. Further, the above equation (11) provides an intuitive understanding of the gear force characteristics. The first term represented by the fraction after the second equal sign "=" in equation (11) represents the geometric property and is represented by the fraction after the second equal sign "=". The second term represents the compliance nature. As a result, it was confirmed that neither the bending stiffness k _θ of the buckling actuator 12 nor the maximum free displacement amount y _max directly affects the quasi-static average gear force.

Next, mounting of the closed loop control on the piezoelectric motor 10 will be described. FIG. 25 is a block diagram showing an example of a speed control system for the piezoelectric motor 10. The closed-loop speed control system 50 shown in FIG. 25 includes a speed control unit (PI) 51, a switch control unit 52, and a control unit 53. For example, at least one of the speed control unit 51, the switch control unit 52, and the control unit 53 may be included in the control unit 21 shown in FIG. The switch control unit 52 includes a first calculation unit 521, a second calculation unit 522, and a phase comparison unit 523. The first and second calculation units 522, 523 may be formed by, for example, a single calculation unit. The control unit 53 may include the drive device 22 shown in FIG. 3, and may further include a voltage amplification function. Each counter unit A1, A2, A3 includes a pair of buckling actuators 12.

The closed loop speed control system 50 is based on the above-mentioned force phase characteristics. The speed control unit 51 calculates the thrust of the piezoelectric motor 10 from the speed of the piezoelectric motor 10 and the target speed of the piezoelectric motor 10, and outputs information indicating the target thrust of the piezoelectric motor 10. The speed of the piezoelectric motor 10 is obtained from a speed sensor (or detector) 802 that detects the speed of the gear 11 by a known means. The configuration of the speed sensor 802 is not limited to a specific type, and any speed sensor 802 may be configured as long as it can detect the speed of the gear 11 and the speed of the piezoelectric motor 10 from the output of the speed sensor 802. The speed of the piezoelectric motor 10 can also be calculated from a position signal measured by a type of position sensor such as an encoder or a resolver. The speed control unit 51 also outputs the gear phase p in the equation (11), and the information indicating the target thrust and the gear phase p may be included in the phase command output from the speed control unit 51. The phase command is output to each of the first and second calculation units 521 and 523.

The first calculation unit 521 controls the on and off states of each piezoelectric element 212 of the buckling actuator 12 based on the information indicating the target thrust included in the phase command, that is, the average gear force F _Gmean in this example. The switching phase 2πp, which is an example of the first phase for switching the voltage, is calculated.

The second calculation unit 522 calculates the second phase with respect to the gear 11 for each piezoelectric element 212 based on the gear phase p included in the phase command and the phase angle of the gear 11. The phase angle of the gear 11 is obtained from a phase sensor (or detector) 801 that detects the phase angle of the gear 11 by a well-known means. The configuration of the phase sensor 801 is not limited to a specific type, as long as the phase angle of the gear 11 can be detected from the output of the phase sensor 801.

The phase comparison unit 523 compares the first phase output from the first calculation unit 521 with the second phase output from the second calculation unit 522, and compares the first and second phases. The switching conditions (or switching modes) of all the buckling actuators 12 shown are output. Switching condition, the voltage switching associated with stored and discharge of electric charge of the piezoelectric element 212 (and if applicable the capacitor 231), that is, each switch (e.g., switch S _H of the embodiment shown in FIGS. 8 and _10, S _L shows the timing of on and off states of _{S 12, S 21).}

The control unit 53 controls the input of the buckling type actuator 12 to the piezoelectric element 212 for each piezoelectric element 212 based on the switching condition output from the phase comparison unit 523. By switching the voltage by the control unit 53, each buckling type actuator 12 is driven to output a force, and each buckling force is subsequently converted according to the inclination of each gear phase of the gear 11. The combined force of the buckling actuator 12 drives the gear 11 and the load 45 to change the phase position applied to each buckling actuator 12.

FIG. 26 is a flowchart illustrating an example of a control method according to an embodiment of the present invention. The control process for controlling the piezoelectric motor having the plurality of piezoelectric elements and the gear for converting the output of the plurality of piezoelectric elements into the motor output, which is shown in FIG. 26, may be executed by the closed loop speed control system 50.

In step S101, the phase sensor 801 performs a detection process for detecting the phase angle of the gear 11. In step S102, the first calculation unit 521 calculates the first phase for switching the voltage for controlling the on / off state of the piezoelectric element 212 based on the information indicating the target thrust of the piezoelectric motor 10. Execute the process. In step S103, the second calculation unit 522 executes a second calculation process for calculating the second phase with respect to the gear 11 for each piezoelectric element 212 based on the phase angle of the gear 11. In step S104, the phase comparison unit 523 executes a comparison process for comparing the first phase and the second phase. In step S105, the control unit 53 executes a process of controlling inputs to the plurality of piezoelectric elements 212 for each piezoelectric element 212 based on the result of the comparison process.

According to the control process described with FIG. 26, the thrust of the piezoelectric motor 10 can be controlled. Further, by controlling the thrust of the piezoelectric motor 10, the controllability of the piezoelectric motor 10 is improved.

27A to 27C and 28A to 28C are diagrams for explaining the simulation results of the closed loop speed control system 50 shown in FIG. 25. In FIGS. 27A-27C and 28A-28C, dashed lines indicate raw data and solid lines indicate filtered data. The simulation considered the compliance properties and weight of the input chip 15A of the buckling actuator 12, the compliance of the interface mechanism between the buckling actuator 12 and the gear 11, and the transmission characteristics and mass of the gear 11. The simulation inserted viscous friction in parallel with each compliance property and Coulomb friction between the gear 11 and the input tip 15A.

27A, 27B and 27C show simulation results when the gear 11 drives only the inertial load and substantially no gear force is output from the gear 11. 27A shows the velocity vs. time characteristic, FIG. 27B shows the phase command vs. time characteristic, and FIG. 27C shows the gear force vs. time characteristic.

The phase of the phase command (1 / lead or wavelength) of FIG. 27B increases with the velocity of FIG. 27A to overcome the energy loss that occurs in the frictional properties. Non-linear characteristics that occur near the maximum average gear force condition for both polarities slow the velocity response compared to the zero average force condition. The ripple of the gear force in FIG. 27C increases with velocity, which is presumed to depend on the inertial force generated by the mass of the input tip.

28A, 28B and 28C show simulation results when the gear 11 drives the inertial load with a constant forced load of 50 N, and the gear force is output from the gear 11 to drive the load 45. FIG. 28A shows the velocity vs. time characteristic, FIG. 28B shows the phase command vs. time characteristic, and FIG. 28C shows the gear force vs. time characteristic.

Offsets occur in both the gear force of FIG. 28C and the phase of the phase command of FIG. 28B. For positive velocity motion, the velocity in FIG. 28A is substantially saturated due to both velocity and forced load. On the other hand, for negative velocity motion, the possibility of regenerative motion was observed.

In the above embodiment, the rotary piezoelectric motor is driven by the drive circuit. However, the above-mentioned drive circuit and drive method, and the above-mentioned control system and control method may be controlled by driving, for example, a linear piezoelectric motor (or actuator) in the same manner as above. An example of a linear piezoelectric motor may include those described below together with FIGS. 29 to 31.

FIG. 29 is a diagram showing a first example of a linear piezoelectric motor. As shown in FIG. 29, the linear piezoelectric motor includes a plurality of buckling actuators 500 _{1 to} 500 _N connected to a linear gear output rod 520 having an improved sinusoidal gear, and the buckling actuator 500 It is driven by a bipolar actuator with a phase of _{1 to} 500 _N.

The reciprocating motion of the output node 514 based on the forces of the plurality of piezoelectric elements forming the buckling actuator 500 _i applies a force F _yi perpendicular to the wavy groove of the gear output rod 520 via the follower 522 _i . By combining the buckling type actuators 500 _{1 to} 500 _N and the gear output rod 520, high motor output efficiency can be obtained during operation, and energy consumption during static holding can be reduced due to its capacitive property. Ripple or nonlinearity of the force that is included in the force F _xi transmitted from the seat屈型actuator 500 _i to the gear output rod 520 can be offset by the phase control of the other seat屈型actuator. That is, the effective output force can be made smooth by combining the node that transmits the zero force and the region where the output force changes by a method using strengthening interference or weakening interference. Further, by operating a plurality of buckling type actuators 500 _{1 to} 500 _N in parallel, the output force is increased, and when the piezoelectric element, the buckling type actuator 500, or a part of the force transmission component fails. Can provide redundancy and fault tolerance.

In FIG. 29, φ _i (shown only for i = 2) indicates the layout position of the i-th buckling actuator 500 _i , the distance between adjacent buckling actuators is the same as φ _i , and x is The gear position of the piezoelectric motor is indicated, y indicates the output displacement amount of the buckling actuator 500 _i , Ψ indicates the output position of the piezoelectric motor, and λ indicates the length of one cycle of the central locus of the follower 522 _i . F _x indicates the gear force.

FIG. 30 is a diagram showing a second example of a linear piezoelectric motor. As shown in FIG. 30, the linear piezoelectric motor includes a plurality of buckling actuators 500 connected to a linear gear output rod 520 having a gear obtained by deforming from a sinusoidal shape, and the plurality of buckling actuators 500. It is driven by a bipolar actuator with phase.

The reciprocating motion along the direction D1 of the output node based on the forces of the plurality of piezoelectric elements forming the buckling actuator applies a force perpendicular to the wavy groove of the gear output rod 520 via the follower. As a result, the linear piezoelectric motor or gear output rod 520 is guided by the linear guide 521 and moves in the output direction D3, and the displacement of the motor is detected by a well-known means using the sensor 523.

FIG. 31 is a diagram showing a buckling type actuator in the second example of the linear piezoelectric motor in a partial cross section. The linear piezoelectric motor includes a buckling actuator 500. The buckling actuator 500 includes a frame 524 and piezoelectric elements 510R and 510L. The piezoelectric element 510R is connected between the side block 512R on the frame 524 and the output unit 514 via the first and second rotary joints. The first rotary joint includes a rotatable member 510Re supported by a support portion 511 on the side block 512R, and the second rotary joint includes a rotatable member 510Rc supported by an output section 514. Similarly, the piezoelectric element 510L is connected between the side block 512L on the frame 524 and the output unit 514 via the third and fourth rotary joints. The third rotary joint includes a rotatable member 510Le supported by a support portion 511 on the side block 512L, and the fourth rotary joint includes a rotatable member 510Lc supported by an output section 514. In FIG. 31, CP1 and CP2 indicate the contact positions of the piezoelectric element 510L, and CP3 and CP4 indicate the contact positions of the piezoelectric element 510R.

The output unit 514 includes a frame 526 having an opening provided with a pair of cylindrical followers 522. PCS (Preload Compensation Spring) 518 having a hexagonal shape is provided on both sides of the frame 526. Each PCS may be fixed to a support portion (not shown) or the like. The linear gear output rod (not shown) penetrates the opening provided in the frame 526 of the output unit 514 and engages with the follower 522. The reciprocating motion along the direction D1 of the output unit 514 based on the force of the piezoelectric elements 510R and 510L forming the buckling type actuator 500 applies a force perpendicular to the wavy groove of the gear output rod via the follower 522. As a result, the linear piezoelectric motor or gear output rod moves in the output direction D3.

Although the present invention has been described above by way of examples, it goes without saying that the present invention is not limited to the above-mentioned examples, and various modifications and improvements can be made within the scope of the present invention.

10 Piezoelectric element 11 Gear 12 Buckling actuator 15A Input chip 20 Drive system 21 Control unit 22 Drive device 22-1 to 22-N Drive circuit 121 Piezoelectric element L inductor

Claims (5)

A drive circuit that drives multiple piezoelectric elements
A transfer path for connecting the plurality of piezoelectric elements and the storage means via one inductor, wherein one end of the inductor is related to each of the plurality of piezoelectric elements and the storage means. A first transfer path connected to each piezoelectric element and one end of the power storage means via a transfer direction determining means and a first switching means, and the other end of the inductor is each of the plurality of piezoelectric elements and the power storage means. In the first transfer path, the first transfer path includes the piezoelectric element and the second transfer path connected to the one end of the power storage means via the second transfer direction determining means and the second switching means related to the above. at the same time when the first switching means Ru is connected to the first transfer direction determination unit, in the second transfer path, said second switching means is connected to said second transfer direction determination means If, of the plurality charge stored in one of the piezoelectric element and the storage means is transferred to the inductor via the first transfer path, before Symbol the charge from the inductor is the second A transfer path, which is transferred to the plurality of piezoelectric elements and the other one of the storage means via the transfer path.
By controlling the transfer path, the electric charge is transferred from the first piezoelectric element to the second piezoelectric element via the power storage means, and then from the second piezoelectric element via the power storage means. It is provided with a control unit that transfers the electric charge to the piezoelectric element.
A drive circuit, characterized in that the first, second, and third piezoelectric elements are different from each other. A supply path for supplying electric charges from the power source to the first piezoelectric element or the second piezoelectric element or the third piezoelectric element or the storage means to which the electric charge is transferred.
It is further provided with an discharge path for discharging the electric charge remaining after the transfer of the electric charge from the first piezoelectric element, the second piezoelectric element, the third piezoelectric element, or the electric storage means to the ground. The drive circuit according to claim 1. A drive circuit that drives multiple piezoelectric elements
A transfer path for connecting the plurality of piezoelectric elements via one inductor, wherein one end of the inductor is a first transfer direction determining means and a first transfer direction determining means related to each of the plurality of piezoelectric elements. A first transfer path connected to one end of each piezoelectric element via the switching means, and a second transfer direction determining means and a second switching in which the other end of the inductor is related to each of the plurality of piezoelectric elements. In the first transfer path, the first switching means is connected to the first transfer direction determining means, including a second transfer path connected to the one end of each piezoelectric element via means. At the same time, in the second transfer path, when the second switching means is connected to the second transfer direction determining means, the electric charge stored in one of the plurality of piezoelectric elements is charged. the first is transferred to the inductor via the transfer path, the charge from the previous SL inductor is transferred to another one of said plurality of piezoelectric elements through the second transfer path, the transfer With the path
A control unit for transferring the electric charge from the first piezoelectric element to the second piezoelectric element by controlling the transfer path is provided.
A drive circuit characterized in that the first and second piezoelectric elements are different from each other. It is a driving method that drives a plurality of piezoelectric elements.
The driving method includes a transfer path in which the plurality of piezoelectric elements and the storage means are connected via one inductor, and the transfer path includes the plurality of piezoelectric elements and the storage means having one end of the inductor connected to the plurality of piezoelectric elements and the storage means. A first transfer path connected to each piezoelectric element and one end of the power storage means via a first transfer direction determining means and a first switching means related to each of the above, and the other end of the inductor is the plurality. Includes each piezoelectric element and a second transfer path connected to the one end of the power storage means via a second transfer direction determining means and a second switching means associated with each of the piezoelectric element and the power storage means. It is, in the first transfer path, at the same time when the first switching means Ru is connected to the first transfer direction determination means, said second switching means is connected to said second transfer direction determination means If the, the charge stored in one of a plurality of piezoelectric elements and said storage means is transferred to the inductor via the first transfer path, the charge is the second from the front Symbol inductor Is transferred to the plurality of piezoelectric elements and the other one of the storage means via the transfer path of
A step of transferring the electric charge stored in the first piezoelectric element to a second piezoelectric element different from the first piezoelectric element via the storage means.
A driving method comprising a step of transferring the electric charge stored in the second piezoelectric element to a third piezoelectric element different from the first and second piezoelectric elements via the storage means. .. It is a driving method that drives a plurality of piezoelectric elements.
The driving method includes a transfer path in which the plurality of piezoelectric elements are connected via one inductor, and in the transfer path, one end of the inductor is associated with each of the plurality of piezoelectric elements. A first transfer path connected to one end of each piezoelectric element via a transfer direction determining means and a first switching means, and a second transfer in which the other end of the inductor is associated with each of the plurality of piezoelectric elements. A second transfer path connected to the one end of each piezoelectric element via a direction determining means and a second switching means is included, and in the first transfer path, the first switching means is the first. at the same time the first Ru is connected to the transfer direction determination unit, in the second transfer path, when said second switching means is connected to said second transfer direction determination unit, among the plurality of piezoelectric elements the charge stored in one is transferred to the inductor via the first transfer path, the other of the plurality of piezoelectric elements through the charge from the previous SL inductors the second transfer path Transferred to one of
A driving method comprising a step of transferring an electric charge stored in the first piezoelectric element to a second piezoelectric element different from the first piezoelectric element.

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