JP6356461B2 - Control system and control method - Google Patents

Description

  The present invention relates to a control system and a control method, and more particularly, to a control system and a control method suitable for controlling a piezoelectric element.

  Capacitive actuators may reduce energy loss when applied to robots. Especially in the case of robot limbs, the actuator needs to support gravity loads. Compared to kinematic loads that occur only during exercise, gravity load works continuously for a long time regardless of movement, even under steady-state 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 limb of the robot in terms of energy efficiency. Such mismatch between the load condition and the actuator characteristics causes insufficient energy utilization efficiency in the limb of the robot. Energy efficiency is important for mobile robots that are increasingly being applied in various fields.

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

  However, the energy dissipation of the pump required to drive a hydraulic or pneumatic actuator is generally very large. Also, because of the compliance 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 force and power density. However, the controllability of the piezoelectric motor is not always satisfactory.

JP 2007-12049 A JP 2008-271667 A

  Conventionally, the controllability of the piezoelectric motor is not always satisfactory because the thrust of the piezoelectric motor is not taken into consideration.

  Accordingly, an object of the present invention is to provide a control system and a control method that can improve the controllability of a piezoelectric motor by considering the thrust of the piezoelectric motor.

  According to one aspect of the present invention, there is provided a control system that controls a motor including a plurality of piezoelectric elements and a gear that converts the outputs of the plurality of piezoelectric elements into motor outputs, the target thrust of the motor being A first calculation unit that calculates a first phase for switching a voltage based on information to be expressed; and a second calculation that calculates a second phase for the gear for each of the plurality of piezoelectric elements based on a phase angle of the gear. A comparison unit comparing the first phase with the second phase, and a comparison result between the first phase and the second phase by the comparison unit. A control system including a control unit for controlling each of the plurality of piezoelectric elements is provided.

  According to another aspect of the present invention, there is provided a control method for controlling a motor including a plurality of piezoelectric elements and a gear for converting outputs of the plurality of piezoelectric elements into motor outputs, and detecting a phase angle of the gears. A first calculation step of calculating a first phase for switching a voltage based on information representing the target thrust of the motor, and a gear for each of the plurality of piezoelectric elements based on a phase angle of the gear To the plurality of piezoelectric elements based on the result of comparison in the second calculation step of calculating the second phase with respect to the first phase, the step of comparing the first phase with the second phase, and the step of comparing. A control method including a control step of controlling the input of each of the plurality of piezoelectric elements is provided.

  According to one embodiment, the controllability of the piezoelectric motor can be improved by considering the thrust of the piezoelectric motor.

Front view of an example of a piezoelectric motor, Sectional drawing which shows a part of piezoelectric motor along the dashed-dotted line AA of FIG. 1A. Sectional drawing which expands and shows the gear and input chip of FIG. 1B, A 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 explaining the operation of the drive circuit, A circuit diagram showing an example of a part of a drive system, The figure explaining an example of the control system of three (3) counter units, A schematic diagram for explaining an example of a drive circuit for driving an even number of piezoelectric element groups, The figure explaining operation | movement of the drive circuit of FIG. A schematic diagram for explaining an example of a drive circuit for driving an odd number of piezoelectric element groups, The figure explaining operation | movement of the drive circuit of FIG. Schematic diagram illustrating an example of a drive circuit using voltage control, The figure explaining the switching method of the drive circuit of FIG. The figure explaining the switching state of the drive circuit of FIG. The figure explaining an example of the drive method in one Example of this invention, Block diagram showing the outline of flow and energy transmission in a piezoelectric motor, A diagram showing an example of a work cycle in the mechanical area, A diagram showing an example of a work cycle in the electrical domain, A diagram showing an example of a low-order machine model of a buckling actuator, The figure which shows an example of the output characteristic of the buckling type actuator calculated, A schematic diagram showing an example of a counter connection, A schematic diagram showing an example of a counter connection, A schematic diagram showing an example of a counter connection, The figure which shows an example of the force and displacement characteristic which a counter unit outputs, The figure explaining the motor force characteristic produced | generated by one buckling type actuator when a unipolar drive gear is used for a gear, The figure which shows the gear force obtained by the single buckling type actuator in various phase change modes, The figure which shows the gear force obtained by six (6) buckling type actuators in various phase switching modes, A block diagram showing an example of a speed control system of a piezoelectric motor, The flowchart explaining an example of the control method in one Example of this invention, The figure explaining the simulation result of a closed loop speed control system when a gear drives only an inertia load, The figure explaining the simulation result of a closed loop speed control system when a gear drives only an inertia load, The figure explaining the simulation result of a closed loop speed control system when a gear drives only an inertia load, The figure explaining the simulation result of a closed loop speed control system in case a gear drives inertial load and constant load, The figure explaining the simulation result of a closed loop speed control system in case a gear drives inertial load and constant load, The figure explaining the simulation result of a closed loop speed control system in case a gear drives inertial load and constant load, The figure which shows the 1st example of a linear piezoelectric motor, The figure which shows the 2nd 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.

  Hereinafter, a driving circuit and a driving method in each embodiment of the present invention will be described with reference to the drawings.

  1A, 1B and 1C are diagrams for explaining an example of a piezoelectric motor in one embodiment of the present invention. FIG. 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 one-dot chain line AA of FIG. 1A, and FIG. 1C is an enlarged view of the gear and input chip of FIG. It is sectional drawing.

  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 around 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 end 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 chip (or follower) 15 </ b> A that engages with the gear 11 by sliding with respect to the gear 11. The input chip 15A of the movable link 15 of the pair of buckling actuators 12 constituting the counter unit is connected to the counter connector 16, and the movement of the input chip 15A is one (1) according to the movement of the piezoelectric element 121. Limited to the degree of freedom of translation. 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. For this reason, the movement of the input chip 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 chip 15A. The input chips 15 </ b> A of the pair of buckling actuators 12 are firmly connected to each other via the counter connection portion 16. The input chip 15A receives the output energy from the pair of buckling actuators 12 via the two input chips 15A, so that the pair of buckling actuators 12 perform a push-pull operation. 16 may be fixed. This operation enhances the energy transmission capability from the piezoelectric element 121 to the gear 11 because the piezoelectric element 121 can transmit energy under on and off voltage conditions. 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 except for a multiple of 60 degrees and a multiple of 180 degrees of the gear phase angle. Each pair of buckling actuators 12 may be 180 degrees out of phase with the adjacent pair of buckling actuators 12 to form a counter unit.

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

For example, a sphere or cylinder having a diameter of 2.5 mm can be used as the input chip 15 </ b> A that transmits the output energy of the pair of buckling actuators 12 to the gear 11. The gear shape is designed so that the center locus of the sphere or cylinder forming the input chip 15A has a sine wave shape, and both the transmission of force by the gear 11 and the movement of the input chip 15A are smooth. The center locus of the sphere or cylinder forming the input chip 15A is an example of the movement locus of the engaging portion of the gear 11 having a shape that engages with the piezoelectric element, and has a sine wave 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. The wavelength is designed to maintain a continuous shape on the gear shape. In order to realize this, the minimum radius of curvature R _Cmin of the center locus of the sine wave shape is set larger than the radius of the input chip 15A. This sinusoidal center locus can be expressed by the following equation (1) assuming that the buckling motion is unipolar. Further, the radius of curvature R _C of the sinusoidal center locus can be expressed by the following equation (2), and the minimum radius of curvature is deviated from each of the upper and lower portions of the sinusoidal locus with the minimum radius of curvature R _Cmin. R _Cmin can be expressed by the following equation (3).

In the above formulas (1) to (3), y is the output displacement amount of the buckling actuator 12, x is the gear position of the gear 11, λ is the wavelength of the center locus of the sine wave shape, and h _gear is generally seated. The gear height of the gear 11 set similarly to the maximum free displacement amount y _max of the bent actuator 12 is shown.

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

  FIG. 2 is a diagram illustrating the gear shape of the gear 11. In FIG. 2, the solid line indicates the gear shape, and the alternate long and short dash line indicates the center locus of the sine wave shape of the input chip 15A.

  FIG. 3 is a diagram illustrating an example of a drive system of 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 charges are supplied by a power supply 30 that supplies a 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 a voltage for controlling the on and off states 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 type of capacitive actuator that can represent basic mechanical and electrical characteristics by the equivalent circuit of FIG. The upper half component shown in FIG. 4 indicates the nature of the electrical region represented by the capacitance C1. This capacitive property can be simplified by omitting 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 resistance R1. The inductance L1 indicates a mass property, and the capacitance C2 indicates a compliance property. Resonance characteristics are represented by both the capacitance C2 and the inductance L1. Resistor R1 represents energy dissipation characteristics. Although not shown in FIG. 4, the piezoelectric element 121 generally has a hysteresis characteristic corresponding to the electric charge exchanged with the outside of the piezoelectric element 121, so that energy loss is also caused in a quasi-static state transition. Arise. 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. With this voltage, energy is stored in both the electrical region and the mechanical region of the piezoelectric element 121. The energy stored in the mechanical area 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 greater than the capacity of mechanical energy, so the overall energy efficiency is greatly 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 perform switching from on to off and switching from off to on in parallel for two piezoelectric elements, the piezoelectric elements are alternately used as capacitors, so that energy is supplied to one piezoelectric element. Directly to the other piezoelectric element. With such a driving method, energy dissipation can be greatly reduced. In addition, the driving method employing such a charge transfer function can reduce energy loss that occurs in the charging circuit between the piezoelectric element 121 and the power supply 30 in FIG.

FIG. 5 is a schematic diagram for explaining the operation of the drive circuit 22-i for 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 , D ₂₁ . The 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 indicates a power supply voltage supplied from the power supply 30 shown in FIG.

In step ST1, the capacitors C _1P are charged by the power supply voltage Vs as indicated by the broken line arrows, and the switches S _1H and S _2L are closed (ON) so that the electric charge stored in the capacitors C _2P is discharged to the ground. The remaining switches S _1L , S _2H , S _2L , S ₁₂ and S ₂₁ are opened (off). At step ST2, the as charge stored in the capacitor _{C 1P} as shown by dashed-line arrow is transferred via a switch _{S 12,} the diode _{D 12} and the inductor L, the switch _{S 12} is in a closed (ON) Then, the remaining switches S _1H , S _1L , S _2H , S _2L , S ₂₁ are opened (off). In step ST3, as indicated by the two-dot chain line arrow, the charge remaining in the capacitor C _1P is discharged to the ground, and the power supply voltage V _S is supplied to the capacitor C _2P and added to the charge transferred from the capacitor C _1P. Thus, the switches S _1L and S _2H are closed (turned on) so that the charge necessary for further charging the capacitor C _2P is replenished, and the remaining switches S _1H , S _2L , S ₁₂ , S ₂₁ is opened (off). Needless to say, the charge stored in the capacitor C _2P may be transferred through 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 that connects 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 an example of a switching unit that switches whether charges are transferred or not transferred between the capacitors C _1P and C _2P . The diodes D ₁₂ and D ₂₁ are an example 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 source 30 and the capacitor C _1P and the path including the switch S _2H between the power source 30 and the capacitor C _2P respectively _store charges from the power source 30 in the capacitors C _1P and C _2P. FIG. 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, respectively, charge remaining after the transfer of the charges to the capacitors C _1P and C _2P. It is an example of the discharge path which discharges from the ground to the ground. The discharge path ensures that the capacitor can be discharged.

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

  In FIG. 6, the drive circuit 22-1 includes a circuit unit 221-1 provided for a pair of (PZT11) piezoelectric elements 121 forming one of the buckling actuators 12 forming the piezoelectric motor 10. A circuit portion 23 including a pair (PZT 21) of piezoelectric elements 121 that form another one of the buckled actuators 12 that form the piezoelectric motor 10. The driving circuits 22-1 to 22-N are shared. 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, and switches Qh11, connected to the pair of piezoelectric elements PZT11 as shown in FIG.
Includes Ql11, Qtf11, Qtb11 and diodes Dtf11, Drb11. On the other hand, the circuit unit 221-2 includes drivers Drvh21, Drvl21, Drvf21, Drvb21, switches Qh21, connected to the pair of piezoelectric elements PZT21 as shown in FIG.
Includes Ql21, Qtf21, Qtb21 and diodes Dtf21, Drb21. The circuit portion 23 includes drivers Drv1a, Drv1b, Drv2a, Drv2b, switches Q1a, Q1b, connected as shown in FIG.
Includes Q2a, Q2b and inductor L.

Driver Drvh11,
Drvl11, Drvf11, Drvb11, Drvh21, Drvl21, Drvf21, Drvb21, Drv1a, Drv1b, Drv2a,
Drv2b may be driven by being controlled by a signal from the controller 21 shown in FIG. Switch Qh11,
Ql11, Qtf11, Qtb11, Qh21, Ql21, Qtf21, Qtb21, Q1a, Q1b, Q2a, Q2b are IGBT (Insulated Gate Bipolar Transistor) or MOSFET (Metal-Oxide-Semiconductor) for high efficiency
(Field-Effect 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 resistive properties of the inductor L, the higher the energy transfer characteristics.

  (A2) In general, the inductor L is larger as the resistance property of the inductor L is lower.

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

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

  (A5) One inductor L can be used for all buckling actuators 12 in a time-sharing manner.

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

  For example, the inductor L has an inductance of 558 μH and a resistance of 19.7 mΩ connected in series. The capacity that affects the transfer status is, for example, about 14 μF, and is attributed to 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 is about 86 mΩ including the inductor L, for example. Considering the LCR characteristics, it can be seen that the charge transfer between the buckling type actuators 12 in the counter unit is performed at, for example, about 280 μsec.

  As described above, in this example, the piezoelectric motor 10 has six (6) buckling actuators 12 forming three (3) opposing units arranged at equal intervals with the tooth phase of the gear 11 as a unit. The driving system 20 includes a driving device 22 having a charge transfer function. In consideration of the characteristics 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 for explaining 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 is switched between the buckling actuators 12 forming a pair of the opposing units A1, A2, and A3. Each sinusoidal line Sn1 to Sn6 represents a gear transition. A small vertical arrow indicates the output (or drive) direction of each counter unit A1, A2, A3 in each gear phase. According to this control method, the three (3) opposing units A1 to A3 can drive the gear 11 in both the clockwise and counterclockwise directions in FIG. 1A without causing inoperable points during all gear phases. .

  In this case, the maximum frequency of 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 opposing unit A1, A2, A3, and each of the three (3) opposing units A1 to A3 requires two (2) voltage switching sequences. Therefore, the voltage switching sequence can be performed at a frequency equal to or lower than 1/6 of the maximum voltage switching frequency based on the maximum voltage switching frequency. By using the inductor L in a time-sharing manner, it is possible to prevent voltage switching sequences from overlapping between different opposing units. The voltage switching sequence can be implemented in, for example, an FPGA (Field Programmable Gate Array).

  Next, multiphase driving of an even number of piezoelectric elements 121 driven with a phase difference of 180 degrees will be described with reference to FIGS. FIG. 8 is a schematic diagram for explaining 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 actuator 12.

FIG. 8 shows a case where four (4) piezoelectric elements 121A, 121B, 121C, 121D are driven by four (4) drive circuits 22A, 22B, 22C, 22D having the same configuration. For example, the drive circuit 22A includes switches S _H , S _L , S ₁₂ , S ₂₁ and diodes D ₁₂ , D ₂₁ . Path 201 connects the output of the diode _{D 12} of the drive circuits 22A to 22D to one end of the inductor L. Path 202 connects the other end of the inductor L to the input of the diode _{D 21} of the respective drive circuits 22A through 22D. The paths 201 and 202 are examples of first and second paths that connect 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 make it possible to flexibly determine the piezoelectric element 121 whose charge is to be exchanged.

The switches S _H , S _L , S ₁₂ , and S ₂₁ of the drive circuits 22A to 22D exchange electric charges between the piezoelectric elements 121A and 121C driven by the drive circuits 22A and 22C, and are driven by the drive circuits 22B and 22D. Control is performed in the same manner as described above with reference to FIG. 5 so as to exchange charges between the piezoelectric elements 121B and 121D. 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 states of the piezoelectric elements 121A, 121B, 121C, and 121D that are driven by the drive circuits 22A, 22B, 22C, and 22D, respectively. States c1 and c5 are the same. Therefore, the motor can be continuously driven in one direction by the piezoelectric element 121 by repeatedly transitioning from the state c1 to the state c4 in ascending order. On the contrary, the motor can be continuously driven in the reverse direction by the piezoelectric element 121 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 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 source 30, and the piezoelectric elements 121A and 121D are grounded. In the state c3, as a result of the process of transferring the 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 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 source 30, and the piezoelectric elements 121B and 121C are grounded. In the state c5, as a result of the process of transferring the 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 charges from one piezoelectric element to another piezoelectric process is performed in the same manner.

  Next, multi-phase driving of an odd number of piezoelectric elements 121 driven with a phase difference other than 180 degrees will be described with reference to FIGS. FIG. 10 is a schematic diagram for explaining 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 actuator 12.

FIG. 10 shows a case where three (3) piezoelectric elements 121A, 121B, 121C and a capacitor 231 are driven by four (4) drive circuits 22A, 22B, 22C, 22D having the same configuration. 10, parts that are the same as the parts shown in FIG. 8 are given the same reference numerals, and explanation thereof is 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 path including _H is an example of a supply path that supplies the electric charge from the power supply 30 to the piezoelectric element 121 and the capacitor 231. The capacitor 231 is an example of a power storage unit that stores electric charges. The power storage means has a capacitive property similar to that of 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.

The switches S _H , S _L , S ₁₂ , and S ₂₁ of each of the drive circuits 22A to 22D are controlled in the same manner as described above with reference to FIG. 5, except that charges from one piezoelectric element to another piezoelectric element are controlled. The transfer is performed via the capacitor 231. For example, the charge is transferred from the piezoelectric element 121A to the piezoelectric element 121B by first transferring the charge from the piezoelectric element 121A driven by the drive circuit 22A to the capacitor 231 controlled by the drive circuit 22D, and then transferring the charge from the capacitor 231. Transfer is made 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 This indicates a grounded state in which the capacitor 231 is grounded, and “121A”, “121B”, “121C”, and “231” indicate 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. States c1 and c7 are the same. Therefore, the motor can be continuously driven in one direction by the piezoelectric element 121 by repeatedly transitioning from the state c1 to the state c6 in ascending order. On the contrary, the motor can be continuously driven in the reverse direction by the piezoelectric element 121 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 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 source 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 to the capacitor 231 from the state c2, the piezoelectric element 121B and the capacitor 231 are connected to the power source 30, and the piezoelectric elements 121A and 121C are grounded.

  In the state c4, as a result of the process of transferring the 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 source 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 source 30, and the piezoelectric elements 121A and 121B are grounded.

  In the state c6, as a result of the process of transferring the 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 source 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 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 source 30, and the piezoelectric elements 121B and 121C are grounded.

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

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

In FIG. 12, the same parts as those in FIG. 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.

  In order to transfer the stored charges between the piezoelectric elements 121 (PZT1) and 121 (PZT2), the control unit 21 performs driving circuits 22-1 and 22-2 for the states sw1 to sw9 as shown in FIG. A control signal for controlling the on and off states of the switches is generated.

As shown in FIG. 14, in the states sw1 and sw9, the piezoelectric element PZT1 is connected to the power supply 30 (V _S ), and 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 supplemented to the piezoelectric element PZT1, and the remaining electric charge is discharged from the piezoelectric element PZT2.

In the states sw2, sw4, sw6, and sw8, both the 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 the state sw5, the piezoelectric element PZT1 is connected to the ground GND, the piezoelectric element PZT2 is connected to the power supply 30 (V _S ), and after the transition from the state sw3, the piezoelectric element PZT2 is supplemented with a certain amount of charge. The remaining charge is discharged from PZT1. Furthermore, 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 controlled at a timing that can be controlled by the control system 50 described later with reference to FIG. A certain amount of charge is replenished to the second piezoelectric element PZT2 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 with reference to FIG. A certain amount of charge is replenished to the first piezoelectric element PZT2 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 PZT 1 and PZT 2, charge transfer between the first and second piezoelectric elements PZT 1 and PZT 2 is performed via the capacitor 231. Can be done.

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

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

  In the case of multiphase driving, the states sw2, sw4, sw6, and sw8 in which the piezoelectric element 121 is in the insulated state may be omitted in the switching sequence shown in FIG.

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

  In step S1, the driving device 22 performs a 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 driving device 22 performs the 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 charge stored in one piezoelectric element 121A may be transferred to the other piezoelectric element 121B via the capacitor 231 in FIG. In this case, in step S2, the 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 in FIG.

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

  Next, a driving mechanism related to the piezoelectric motor 10 will be described with reference to 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 source 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 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 driving target driven by the gear 11 of the piezoelectric motor 10.

  FIG. 17A and FIG. 17B are diagrams showing examples of work cycles in the mechanical region and the electrical region, 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 indicates the voltage V in arbitrary units, and the horizontal axis indicates the charge Q in arbitrary units. For example, by obtaining a sufficient allowable tensile stress by applying a preload exceeding the blocking force of the piezoelectric element to each piezoelectric element of the buckling actuator, the energy characteristics in the mechanical cycle and the electrical cycle are shown in FIG. 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 actuator 12, c _M indicates mechanical compliance, and c _E indicates the capacitance of the piezoelectric element 121.

Based on the above formula (4) including the preload, the work cycles in the mechanical region and the electrical region of the buckling actuator 12 can be expressed as shown in FIGS. 17A and 17B, respectively. In the mechanical and electrical areas, the numbers surrounded by circles indicate the matching between the mechanical state and the electrical state. 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. The paths “1” <−> “4” are constant voltage processes. The work of each mechanical work cycle and 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 actuator 12 and the counter unit formed thereby will be described. Focusing on the basic mechanism of the buckling actuator 12, a simplified machine model can be expressed as shown in FIG. FIG. 18 is a diagram illustrating an example of a low-order machine model of the buckling actuator 12. In FIG. 18, L indicates the distance between the centers of the rotary joints, and L + z indicates the distance between the centers of the rotary joints in consideration of the change in the length of the piezoelectric element 212 during driving. The model of the buckling actuator 12 shown in FIG. 18 can be expressed by the following equation (5). Here, k _θ is the joint rotation stiffness of the joint of the piezoelectric element 212 connected to the base frame, and k _S is the longitudinal length of the piezoelectric element 212 obtained by synthesizing the base frame stiffness k _B and the joint stiffness k _J along the longitudinal direction. The combined stiffness along the direction, k _P indicates the stiffness along the longitudinal direction of the piezoelectric element 212, z _S indicates the combined displacement amount of the base frame and the joint, and z _P indicates the displacement amount of the piezoelectric element 212.

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.

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

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

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

FIG. 19 is a diagram illustrating an example of the output characteristics of the buckled actuator 12 to be calculated. In FIG. 19, the vertical axis represents the force F _y output from the buckling actuator 12, and the horizontal axis represents the buckling output displacement amount y.

  The counter unit is formed using a buckled actuator 12 as shown in FIGS. 20A, 20B and 20C. 20A, 20B, and 20C are schematic diagrams illustrating an example of a counter connection. 20A to 20C, the circles at both ends indicate the side blocks firmly fixed to the base structure. The center circle indicates the input chip 15A. The bar-shaped portion shows the piezoelectric element 121. A rectangular portion between the center circles (input chip 15A) indicates a counter connection 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 the upper and lower piezoelectric elements 121 are both off and there is no external load. In the input chip position shown in FIGS. 20A and 20C under the piezoelectric element conditions as described above, the length of the opposing connection portion 16 is set so as to cancel the interaction force between the input chips 15A. With this setting, the force and displacement characteristics output from the opposing unit are observed as shown in FIG.

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

  The force output by the counter unit can be calculated by adding the buckling forces at the same distance as the maximum buckling output displacement. In FIG. 21, thin solid lines “Fy1 ON” and “Fy1 OFF” indicate the characteristics of the force output by the upper buckling actuator 12, and thin broken lines “Fy2 ON” and “Fy2 OFF” indicate the lower buckling actuator 12. Shows the characteristics of the force output by. This means that the buckling actuator 12 that forms the counter unit can realize a bipolar motion, so 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 opposing unit is constrained to a unipolar range, this means that the connected input chip 15A is buckled from zero as indicated by the thick solid lines “+ Fy” and “−Fy” in FIG. This means that the actuator 12 is displaced to the maximum displacement on the positive side.

  Next, closed loop control of the piezoelectric motor 10 will be described. 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, pseudo torque control described below can be used as the input rule.

  First, the torque and force characteristics of the piezoelectric motor 10 are considered. FIG. 22 is a diagram illustrating motor force characteristics generated by one buckling actuator 12 when a unipolar drive gear is used as the gear 11. In FIG. 22, the lower right plot shows the force displacement characteristics 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 application). A solid line indicates a case where the piezoelectric element 212 (PZT) of the buckling actuator 12 is off (no voltage application or zero voltage application).

In FIG. 22, the force F _y output from the buckling actuator is plotted in the lower left portion of FIG. 22 by using the center locus of the sine wave shape of the input chip 15A with respect to the gear 11 as shown in the upper left portion. converting the gear force _{F x} shown. Since the tangential angle of the gear surface determines the conversion ratio at each contact point, the teeth of the gear 11 also have a sinusoidal pattern in the conversion characteristics related to the gear phase indicated by x in the plot in the lower left part 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 from the buckling actuator is converted into a leftward gear force F _x at the first inclination of the teeth of the gear 11 as shown in the upper left part of FIG. In the second inclination following the first inclination of the gear teeth, the upward force F _y is converted into a right force F _x . The force conversion at the other inclination of the gear teeth is similar to the conversion at the first inclination and the second inclination. The conversion of the force F _y output from the buckling actuator as described above into the gear force F _x is such that 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. If there is no, it indicates that the input chip 15A is stable at the upper part of the gear teeth. On the other hand, in a state where 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. In the second inclination, the downward force F _y is converted to the left force F _x . As a result, the conversion of the force F _y output from the buckling actuator as described above into the gear force F _x is such that the piezoelectric element 212 of the buckling actuator 12 is continuously off and the buckling actuator 12 and the gear 11 are turned off. If there is no external action, the input tip 15A is stabilized at the lower part of the gear teeth.

Accordingly, when the piezoelectric element 212 is switched from the on state to the off state at the upper part (or crest) of the gear tooth, and at the lower part (or valley) of the gear tooth, the piezoelectric element 212 is switched from the off state to the on state. In the event of a failure, a continuous leftward gear force _Fx 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 continuously to the right. The gear force _Fx is obtained.

  FIG. 23 is a diagram illustrating a gear force obtained by a single buckling actuator in various phase switching modes. The upper end portion of FIG. 23 corresponds to an enlargement of the upper left portion of FIG.

  The first (uppermost) to seventh (lowermost) curves shown in FIG. 23 represent continuous left or right gear force characteristics. The fourth (center 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 in the left direction and the force in the right direction cancel each other, and the average gear force in each phase length becomes zero. From the fourth curve to the first curve, the average gear force increases in the left direction according to the change of the switching phase. On the other hand, in the fourth to seventh curves, the average gear force increases in the right direction according to the change of the switching phase. The switching interval is always held at ½ of the gear pitch.

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

The six (6) buckling actuators 12 have equal phase intervals at intervals of multiples of the gear period other than the same multiple as the number of buckling actuators. FIG. 24 shows the characteristics of the resulting gear force F _x by six (6) buckling actuators 12. As shown in FIG. 24, the switching of each buckling actuator 12 is performed considering only the gear phase of each buckling actuator 12. As a result, the same gear force characteristic can be generated from each buckling actuator 12 simply by shifting the gear position relative to the position of each buckling actuator 12 with respect to the gear phase. In FIG. 24, a thin solid line indicates the gear force of each buckling 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 (uppermost) curve and the seventh (lowermost) curve shown in FIG. 24 corresponding to the case where the piezoelectric element 212 is switched only at the upper and lower portions of the gear teeth, the average gear force is leftward or rightward. It becomes substantially constant toward the direction. For the fourth (center) curve shown in FIG. 24, which corresponds to the case where the piezoelectric element 212 is switched only at the middle point of the gear teeth, the average gear force includes a certain amount of force ripple, but the average regardless of the gear pitch. The power of is zero. In other switching modes, the resulting average force increases with changes in switching phase as in the case of the single buckling actuator 12 described above with FIG.

  If the above equation (1) represents the center locus of the input chip 15A, the contact inclination dy / dx between the gear 11 and the input chip 15A can be represented by the following equation (9).

By substituting the locus represented by the above equation (1) into the above equation (6), if the force output by the buckling actuator with respect to the gear position is defined as F _yx , N _b 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.

In the above formula (10), 2πp is a switching phase of the gear pitch λ from the state where one group of piezoelectric elements 212 is turned on to the state where one group of piezoelectric elements 212 is turned off. The phase distance between switching off and on is set to 1/2 the gear pitch, ie 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 represents the gear pitch of the gear 11, h _gear represents the gear height of the gear 11, L represents the distance between the centers of the rotary joints, and k _S represents the length of the base frame along the longitudinal direction. The synthesized stiffness along the longitudinal direction of the piezoelectric element 212 obtained by synthesizing the stiffness k _B and the joint stiffness k _J is shown, and k _P shows the stiffness along the longitudinal direction of the piezoelectric element 212. The average gear force F _Gmean is an example of a target thrust of the piezoelectric motor 10.

The above equation (11) represents the quasi-static force characteristic of the gear 11 driven by the switching drive, and because of the monotonically increasing characteristic within the range of −1 / 4 ≦ p <¼, It also represents the possibility. Moreover, said Formula (11) brings about intuitive understanding of a gear force characteristic. 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 property. As a result, stiffness k _theta and maximum free displacement y _max bending of the seat屈型actuator 12, it was confirmed that both do not have a direct impact on the quasi-static average gear force.

  Next, mounting the closed-loop control on the piezoelectric motor 10 will be described. FIG. 25 is a block diagram illustrating an example of a speed control system of the piezoelectric motor 10. A 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 controller 51, the switch controller 52, and the controller 53 may be included in the controller 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 and 523 may be formed by a single calculation unit, for example. The control unit 53 may include the driving device 22 illustrated 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 force phase characteristics. The speed control unit 51 outputs information indicating the target thrust of the piezoelectric motor 10 by calculating the thrust of the piezoelectric motor 10 from the speed of the piezoelectric motor 10 and the target speed 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, as long as the speed of the gear 11 and the speed of the piezoelectric motor 10 can be detected 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 kind 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 information indicating the target thrust included in the phase command, that is, in this example, the average gear force F _Gmean. A switching phase 2πp, which is an example of a 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 and the phase angle of the gear 11 included in the phase command. 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 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 and the second phase output from the second calculation unit 522, and obtains a comparison result between 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 , S ₁₂ , S ₂₁ ) shows the timing of the on and off states.

  The control unit 53 controls the input to the piezoelectric element 212 of the buckling actuator 12 for each piezoelectric element 212 based on the switching condition output from the phase comparison unit 523. Each buckling actuator 12 is driven to output a force by voltage switching by the control unit 53, and each buckling force is then 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, and changes 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 a piezoelectric motor having a plurality of piezoelectric elements and a gear for converting the outputs of the plurality of piezoelectric elements into motor outputs shown in FIG. 26 may be executed by the closed loop speed control system 50.

  In step S <b> 101, the phase sensor 801 performs a detection process for detecting the phase angle of the gear 11. In step S <b> 102, the first calculation unit 521 calculates a first phase for switching a voltage for controlling the on / off state of the piezoelectric element 212 based on information indicating the target thrust of the piezoelectric motor 10. Execute the process. In step S <b> 103, 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 S <b> 104, the phase comparison unit 523 executes comparison processing for comparing the first phase and the second phase. In step S <b> 105, the control unit 53 executes a process for 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 processing described with FIG. 26, the thrust of the piezoelectric motor 10 can be controlled. Furthermore, the controllability of the piezoelectric motor 10 is improved by controlling the thrust of the piezoelectric motor 10.

  FIGS. 27A to 27C and FIGS. 28A to 28C are diagrams for explaining the simulation results of the closed-loop speed control system 50 shown in FIG. In FIGS. 27A to 27C and FIGS. 28A to 28C, broken lines indicate raw data, and solid lines indicate filtered data. The simulation considered the compliance property 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. In the simulation, viscous friction was inserted in parallel to each compliance property, and Coulomb friction was inserted between the gear 11 and the input chip 15A.

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

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

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

  An offset occurs in both the gear force in FIG. 28C and the phase of the phase command in FIG. 28B. For positive speed motion, the speed of FIG. 28A is nearly saturated due to both speed and forced loading. On the other hand, the possibility of regenerative motion was observed for negative velocity motion.

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

FIG. 29 is a diagram illustrating a first example of a linear piezoelectric motor. 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, as shown in FIG. ₁ is driven by a bipolar actuator having a phase of 500 _N.

The reciprocating motion of the output node 514 based on the force 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 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 properties. The ripple or non-linearity of the force included in the force F _xi transmitted from the buckling actuator 500 _i to the gear output rod 520 can be canceled out by phase control of other buckling actuators. In other words, the effective output force can be made smooth by combining the node transmitting zero force and the region where the output force changes by a method using the interference that increases or decreases. In addition, when a plurality of buckling actuators 500 _{1 to} 500 _N are operated in parallel to increase the output force, a part of the piezoelectric element, the buckling actuator 500, or the force transmission component fails. In addition, redundancy and fault tolerance can be provided.

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 Indicates the gear position of the piezoelectric motor, y indicates the output displacement amount of the buckling actuator 500 _i , Ψ indicates the output position of the piezoelectric motor, λ indicates the length of one cycle of the central locus of the follower 522 _i , F _x represents the gear force.

  FIG. 30 is a diagram illustrating a second example of the linear piezoelectric motor. 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, as shown in FIG. Driven by a bipolar actuator with phase.

  The reciprocating motion along the direction D1 of the output node based on the force 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. Thereby, the linear piezoelectric motor or the 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 known means using the sensor 523.

  FIG. 31 is a partial cross-sectional view of the buckling actuator in the second example of the linear piezoelectric motor. 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 the support portion 511 on the side block 512R, and the second rotary joint includes a rotatable member 510Rc supported by the output portion 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 rotation joint includes a rotatable member 510Le supported by the support portion 511 on the side block 512L, and the fourth rotation joint includes a rotatable member 510Lc supported by the output portion 514. In FIG. 31, CP1 and CP2 indicate contact positions of the piezoelectric element 510L, and CP3 and CP4 indicate contact positions of the piezoelectric element 510R.

  The output unit 514 includes a frame 526 having an opening in which a pair of cylindrical followers 522 are provided. 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. A linear gear output rod (not shown) passes through an opening provided in the frame 526 of the output portion 514 and engages with the follower 522. The reciprocating motion along the direction D1 of the output portion 514 based on the force of the piezoelectric elements 510R and 510L forming the buckling actuator 500 applies a force perpendicular to the wave-like groove of the gear output rod via the follower 522. As a result, the linear piezoelectric motor or the gear output rod moves in the output direction D3.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made within the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Piezoelectric element 11 Gear 12 Buckling-type actuator 15A Input chip 20 Drive system 21 Control part 22 Drive apparatus 22-1 to 22-N Drive circuit 50 Control system 51 Speed control part 52 Switch control part 53 Control part 121 Piezoelectric element 521 1st 1 calculation unit 522 second calculation unit 523 comparison unit 601 phase sensor 602 speed sensor L inductor

Claims (4)

A control system for controlling a motor comprising a plurality of piezoelectric elements and a gear for converting the outputs of the plurality of piezoelectric elements into motor outputs,
A first calculation unit for calculating a first phase for switching a voltage based on information representing the target thrust of the motor;
A second calculation unit for calculating a second phase for the gear for each of the plurality of piezoelectric elements based on the phase angle of the gear;
A comparator for comparing the first phase and the second phase;
A control unit that controls input to the plurality of piezoelectric elements for each of the plurality of piezoelectric elements based on a comparison result obtained by comparing the first and second phases in the comparison unit ;
The controller transfers the electric charge stored in the capacitor of the first piezoelectric element of the plurality of piezoelectric elements to the capacitor of the second piezoelectric element of the plurality of piezoelectric elements based on the comparison result. A control system for adjusting on / off timing of a switch for performing Wherein the speed control unit for outputting the information by calculating the thrust of the motor and a speed of the motor to speed and the target of the motor to the first calculation unit is further provided, according to claim 1 The described control system. Wherein the first calculation unit, when each of the plurality of piezoelectric elements, movement locus of the engagement portion of the shape and engagement of the gear has a sine wave component with respect to the gear, on the basis of the following equation Calculate 2πp, which is the first phase ,
E _G represents an effective energy transmitted from the plurality of piezoelectric elements to N _b number of units in the gear, lambda indicates the gear pitch of said gear, h _gear indicates the gear height of the gear, L is K _S is the distance between the centers of the rotary joints, k _S is the combined stiffness along the longitudinal direction of each piezoelectric element that combines the stiffness of the base frame along the longitudinal direction and the stiffness of the joint, and k _P is the combined stiffness of each piezoelectric element shows the stiffness in the longitudinal direction, 2Paipi the plurality of piezoelectric elements of the one group a plurality of piezoelectric elements of one group from the on state indicates a switching phase of the gear pitch λ to off, F _Pmax is the maximum value of potential F _P of the piezoelectric element, wherein the phase distance between the switching of the switching and off-on on or off is set to lambda / 2 Claim 1 or 2 control system according. A control method for controlling a motor comprising a plurality of piezoelectric elements and a gear for converting the outputs of the plurality of piezoelectric elements into motor outputs,
Detecting a phase angle of the gear;
A first calculation step of calculating a first phase for switching a voltage based on information representing a target thrust of the motor;
A second calculation step of calculating a second phase for the gear for each of the plurality of piezoelectric elements based on the phase angle of the gear;
Comparing the first phase and the second phase;
Based on the result of comparison in the step of the comparison, viewed including a control step for controlling input to said plurality of piezoelectric elements for each of the plurality of piezoelectric elements, the control unit, based on the comparison result, said plurality Adjusting the on / off timing of a switch for transferring the charge stored in the first capacitor of the plurality of piezoelectric elements to the capacitor of the second piezoelectric element of the plurality of piezoelectric elements. Control method.