JP2014204666A - Motor, control system and control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve thrust controllability of a piezoelectric motor.SOLUTION: A motor includes: a plurality of actuators having elastic characteristics and including a plurality of quantitative actuators; and a gear which converts output of the plurality of actuators into the output of a motor. The gear is formed so as to have a shape in which the movement locus with respect to the gear of an engagement part of the plurality of actuators engaged with the gear contains at least a sine wave component. The plurality of actuators are arranged at a phase interval such that at least a part of the elastic characteristics is cancelled.

Description

  The present invention relates to a motor, a control system, and a control method, and more particularly, to a motor, a control system, and a control method suitable for driving a motor such as a piezoelectric motor.

  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 movement, gravity loads work 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 sufficiently 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 elastic properties of air, it is difficult for both the hydraulic and pneumatic actuators to respond and move at a high speed, 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 thrust controllability of a piezoelectric motor is not always satisfactory.

JP 2007-12049 A JP 2008-271667 A

J. Torres and H. Asada, "A Non-Flexure Type Displacement Amplification Mechanism for Piezoelectric Stack Actuators Utilizing Rolling Contact Joints", 2013 IEEE International Conference on Robotics and Automation (ICRA)

  Conventionally, the thrust controllability of a piezoelectric motor is not always satisfactory.

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

  According to an aspect of the present invention, the apparatus includes a plurality of actuators having elastic characteristics and including a plurality of capacitive actuators, and a gear that converts outputs of the plurality of actuators into motor outputs, and the gear is associated with the gear. A phase interval that cancels at least a part of the elastic characteristics, and the movement trajectory of the engaging portions of the plurality of actuators to be combined has a shape including at least a sine wave component. A motor arranged in is provided.

  According to another aspect of the present invention, there is provided a control system for controlling the motor described above, wherein a control system for inputting a voltage corresponding to a phase angle of the corresponding gear to the plurality of actuators.

  According to still another aspect of the present invention, there is provided a control method for controlling the motor described above, wherein a control method for inputting a voltage corresponding to a phase angle of the corresponding gear to the plurality of actuators.

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

The figure which shows an example of a buckling type actuator, The figure which shows the 1st example of the linear motion piezoelectric motor in one Example. The figure which shows an example of the instantaneous displacement gain with respect to joint angle (theta), The figure explaining the structure of a buckling type actuator, The figure explaining the description of the buckling type actuator shown in FIG. The figure explaining the description of the buckling type actuator shown in FIG. The figure explaining the elastic characteristic of the buckling actuator in the machine model, The figure which shows an example of the output characteristic of a buckling type actuator, The figure which shows an example of contact rigidity fluctuation, The figure which shows an example of the force characteristic of the buckling type actuator converted by the gear output rod, The figure which shows an example of the maximum output characteristic of the linear motion piezoelectric motor according to the number of buckling type actuators used, The block diagram which shows an example of the control system in one Example, The flowchart explaining an example of the control processing which employ | adopts the control method in one Example, The figure which shows the 2nd example of the linear motion piezoelectric motor in one Example. It is a figure which shows the 3rd example of the linear motion piezoelectric motor in one Example.

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

  One of the goals when designing an actuator is to provide sufficient force, displacement and speed for a given application. Another goal is to improve system performance considering power or force density, responsiveness and energy consumption characteristics. These predefined characteristics typically dominate the actuator design, but reducing actuator energy consumption makes it less dependent on large energy sources and much without consuming excess energy. These actuators can be coordinated. Balancing these goals is particularly important for mechatronics and robotic systems where a specific force and displacement output is desired, but in the case of mobile devices, the power supply may only provide a limited energy supply. It is difficult to satisfy these goals of actuator design at the same time.

  Many conventional actuators developed for robots and mechatronic systems that maximize the density of forces and displacements cannot simultaneously achieve high speed response and low power consumption. These conventional actuators are generally regarded as dielectric or capacitive actuators. For dielectric actuators such as magnetic force motors that typically have a high bandwidth, the torque output is a function of current and power consumption is high when large torque is provided regardless of actuator speed. Instead, capacitive actuators such as hydraulic and pneumatic actuators typically operate at a low bandwidth, but output force as a function of an action variable such as pressure. Thus, these actuators consume limited energy when providing a small or zero displacement amount of force. This can improve, for example, the energy efficiency of a ground-mounted robot that must support large gravity or other static loads for long periods of time during operation.

Piezoelectric actuators are a type of capacitive actuator that can provide a high operating bandwidth in excess of 10 kHz and a power density of about 10 ⁸ W / m. Because of these important performances of piezoelectric actuators, there are increasing opportunities to use piezoelectric actuators in small applications such as acoustics, vibration control and precision positioning. On the other hand, the output stroke of the piezoelectric actuator is still very small. The unamplified strain that can be achieved with a piezoelectric stack actuator such as PZT (lead zirconate titanate) is on the order of 0.1%. Due to such a small strain, the amount of displacement that can be realized is on the order of 4 × 10 ⁻² mm, which is insufficient for application to a typical robot or mechatronics, and it is necessary to use a displacement amplifier.

  Piezoelectric strain amplification is generally classified into internal leverage design, external leverage design, and frequency leverage design. Internal leverage actuators such as stack, vendor and unimorph actuators have appropriately selected the piezoelectric material geometry for displacement amplification. Stroke output is limited by the internal stiffness of the actuator. A stack actuator is a simple and effective internal leverage actuator that can maintain a high power density and can be used as a building block for both external and frequency leverage mechanisms.

  In a frequency leverage mechanism, also known as USM (ultrasonic motor), the piezoelectric actuator is driven at a resonant frequency to add motion to the actuator output by friction drive. In the case of the rotary USM, this output is an unrestricted rotation, while the linear motion device uses an “inch worm” motion to amplify the displacement so as to slide along the track. Since USM operates as a direct drive motor, it is generally low speed and high torque. However, the driving force and torque can be adversely affected by wear of the friction drive material.

  Several types of external leverage or mechanical amplification actuators have been proposed, including flexural actuators. These actuators are typically capable of generating displacement amplification that is an order of magnitude larger in magnitude than the displacement amplification amount of the stack actuator building block. In recent years, external leverage research has been conducted on an amplification mechanism that effectively utilizes the buckling of a nonlinear structure. According to such a buckling of a nonlinear structure, a displacement amplification in which the order of amplitude is two orders of magnitude larger by one stage of the actuator. Can be realized.

  FIG. 1 is a diagram illustrating an example of a buckling actuator. The buckling actuator 500 includes a pair of piezoelectric elements 501, a side block 600 and an output node (or keystone) 514. Each piezoelectric element 501 has one end connected to the side block 600 and the other end connected to another piezoelectric element 501 via an output node 514. The joint between the piezoelectric element 501 and the side block 600 is a rolling joint (or a rotary joint), and the joint between the piezoelectric element 501 and the output node 514 is a rolling joint. The piezoelectric element 501 is shown as a cylinder for convenience of explanation.

  When activated, the piezoelectric element 501 moves to the position indicated by the broken line in FIG. 1 and moves the output node 514 in the y direction. Thereby, the buckling actuator 500 forms a buckling amplification mechanism that generates a unipolar stroke 505 or a bipolar stroke 506 of the output node 514 and generates a non-linear force output described later. Control of the output displacement direction can be managed by additional restrictions described later.

  The piezoelectric element 501 causes the same restrictions as the conventional capacitive actuator. However, the piezoelectric element 501 that forms the buckling type amplification mechanism exhibits a level of performance that is one level higher. The design and analysis of an efficient, high force density linear motion piezoelectric motor in one embodiment is described below. The linear motion piezoelectric motor includes a plurality of buckling actuators 500 that engage with rods having gear teeth (hereinafter also referred to as “gear output rods”). The gear output rod will be described later with reference to FIG. The plurality of buckling actuators 500 are arranged with a predetermined phase difference along the gear output rod, and a substantially constant force is generated regardless of the rod position by adjusting the movement of the plurality of buckling actuators 500. To do. The rolling contact buckling mechanism formed by a plurality of buckling actuators 500 has a high energy transfer rate and low loss from the buckling actuators 500 to the gear output rod, and can provide a large displacement amplification amount. This direct acting piezoelectric motor has the characteristics of a capacitive actuator and can efficiently support a static load. In addition, the actuator architecture of the direct acting piezoelectric motor including the polyactuator architecture can be flexibly improved in function and performance by a modular design.

  First, engagement of the buckling type amplification mechanism with a PAS (Phased Array Shaped) gear output rod will be described together with an analysis of output force and displacement characteristics.

  Direct-acting piezoelectric motors are preferably driven by actuators containing piezoelectric elements with high power density to achieve the force requirements, large displacements and low energy consumption when holding static loads required by standard robots and mechatronics . The direct acting piezoelectric motor preferably satisfies the following additional constraints i) to vi).

i) Long stroke output,
ii) High power density output,
iii) High energy efficiency that can support static load at any actuator output position without using almost electric power,
iv) Force controllability over typical frequency leverage actuators,
v) Fault tolerance that does not impair actuator function due to individual mechanical work element failures, and
vi) Reverse drive performance that minimizes motor stroke impedance during reverse drive.

  Linear motion piezoelectric motors operate by bipolar activation with the phase of a rolling contact buckling mechanism connected to a linear shaped gear output rod. As shown in FIG. 2, a force input perpendicular to the wavy groove of the linear gear output rod is applied by the reciprocating force of the buckling actuator via the buckling mechanism.

FIG. 2 is a diagram illustrating a first example of a linear motion piezoelectric motor in one embodiment. The linear motion piezoelectric motor includes a plurality of buckling actuators 500 _{1 to} 500 _N connected to a PAS linear gear output rod 520 having a sinusoidal gear (or cam) as shown in FIG. It is driven by a bipolar actuator having a phase of the bent actuator 500 _{1 to} 500 _N. The plurality of buckling actuators 500 _{1 to} 500 _N are arranged at a constant phase interval with respect to the gear (or cam) of the gear output rod 520 that converts the output of the buckling actuators 500 _{1 to} 500 _N into a motor output. Has been.

The reciprocating motion of the output node 514 based on the force of the plurality of piezoelectric elements 501 forming the buckling actuator 500 _i causes a force F _yi perpendicular to the wavy groove of the gear output rod 520 via the follower 522 _i of the output node 514. Apply. The gear (or cam) of the gear output rod 520 has a movement locus of an output node 514 _i that is an example of an engagement portion of the buckling actuator 500 _i that engages with the gear (or cam) of the gear output rod 520. The gear output rod 520 has a shape that is sinusoidal with respect to the gear (or cam). 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 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. Further, by operating the plurality of buckling actuators 500 _{1 to} 500 _N in parallel, the output force is increased, and part of the piezoelectric element 510, the buckling actuator 500, or the force transmission component has failed. In some cases, redundancy and fault tolerance can be provided.

In FIG. 2, φ _i (shown only for i = 2) indicates the layout position of the i-th buckling actuator 500 _i , x indicates the gear position of the direct-acting piezoelectric motor, and y indicates the buckling actuator 500. _{i represents} the output displacement amount, Ψ represents the output position of the linear motion piezoelectric motor, λ represents the length of one cycle of the movement trajectory of the center of the follower 522 _i , and F _x represents the continuous gear force in the right direction. Show.

As the constituent blocks of the actuator architecture, the rolling contact, buckling and displacement amplification mechanisms proposed in Non-Patent Document 1 can be used. This proposed displacement amplification mechanism can transmit mechanical work at a high rate between the piezoelectric element and the external load of the motor. By combining this proposed displacement amplification mechanism with the gear output rod 520 having the shape as described above, the efficiency of linear motor output during operation can be increased, and the capacitive property is energy consumption during static holding. The above-mentioned Non-Patent Document 1 also describes the adverse effects of the structural elasticity of the rolling contact joint and the frame structure of the proposed displacement amplification mechanism. In this embodiment, the rigidity of the rolling contact is improved in order to improve the force output by the buckling actuator and the frame rigidity. In the following, some rolling contact geometries are considered.

  Secondary structural elasticity resulting from the frame structure can be improved by using an anisotropic material that increases the stiffness of the material along the load direction. This embodiment uses a main load structure of a carbon fiber having a high elastic modulus.

  The modular polyactuator architecture of a piezoelectric motor can provide the following functions: First, by using a plurality of buckling actuators in parallel, the output of the linear motor force can be controlled with high resolution. The ripple or non-linearity of the force transmitted to the buckling actuator 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. Secondly, by operating a plurality of buckling actuators in parallel, the output force is increased, and when some of the piezoelectric elements, buckling actuators or force transmission components fail, the redundancy is increased. And can provide fault tolerance.

  In order to effectively use the bipolar movement of the buckling amplification mechanism, it is necessary to handle the reciprocal displacement at the output node and the application of a non-linear force to the gear output rod. In order to input a smooth force to the load to be driven while minimizing the ripple of force on the gear output rod, the phase shape parameter of the gear output rod is controlled. In addition, mechanical transmission occurs in the buckling amplification mechanism between the output of the force of the actuator and the output of the force of the buckling type mechanism, but by adjusting the length and amplitude of the gear pitch of the gear output rod, Further improved mechanical transmission is possible.

  Since the bipolar output of the buckling amplification mechanism is required to drive the gear output rod, the output direction of the buckling actuator needs to be controlled to move in a predetermined direction at an appropriate rod position. Since the motion singularity in each buckling mechanism, that is, the buckling singularity, is not deterministic, the predetermined direction or direction must be controlled from the outside. External control can be achieved by continuous contact engagement between the output of the buckling mechanism and the shape surface of the gear output rod. In the region away from the buckling singularity, the movement of the buckling mechanism is deterministic and drives the gear output rod. At the buckling singularity, the gear output rod moves across the singularity to energize the buckling mechanism with substantially zero impedance. The output direction of the buckling actuator then becomes deterministic again.

Next, force characteristics of the buckling actuator of the direct acting piezoelectric motor shown in FIG. 2 will be described with reference to FIG. The force F _x of the static output of the direct acting piezoelectric motor can be generally expressed by the following equation (1), where i is the i-th buckling actuator 500 _i and N is the buckling actuator. The maximum value of the numbers 500 _{1 to} 500 _N , Ψ is the output position of the linear motion piezoelectric motor represented by the phase angle of the gear output rod 520, and φ _i is the i th buckling actuator at the phase angle of the gear output rod 520 The layout position of 500 _i , F _xi is the biasing force of the i-th buckling actuator 500 _i to the output force of the linear motion piezoelectric motor, and G is the follower of the buckling actuator 500 along the profile of the gear output rod 520. 522 _i , the movement locus of the center of _i , R is the inclination angle of the movement locus G with respect to the actual output position x of the linear motion piezoelectric motor, F _yi is the output of the i-th buckling actuator 500 _i , U _i is an input to the i-th buckling actuator 500 _i , and λ is the length of one cycle of the movement locus G of the actual output position.

座屈型アクチュエータ５００_１乃至５００_Ｎは、ギア出力ロッド５２０を介して並行に接続されているので、座屈型アクチュエータ５００_１乃至５００_Ｎの全ての出力はギア出力ロッド５２０による変換後に加算される。上記の式（１）は、直動圧電モータの設計に以下の４つの自由度ａ）乃至ｄ）があることを表している。

Since the buckling actuators 500 _{1 to} 500 _N are connected in parallel via the gear output rod 520, all outputs of the buckling actuators 500 _{1 to} 500 _N are added after conversion by the gear output rod 520. . The above equation (1) indicates that the linear motion piezoelectric motor has the following four degrees of freedom a) to d).

a) Characteristics of buckling actuators 500 _{1 to} 500 _N ;
b) A movement locus G determined by the gear shape of the gear output rod 520,
c) layout of buckling actuators 500 _{1 to} 500 _N for gear output rod 520;
d) Input to buckling actuators 500 _{1 to} 500 _N.

The above formula (1) also indicates that all buckling actuators 500 _{1 to} 500 _N have an interaction through the gear output rod 520. For example, when the value of N is small, the interaction of the buckling actuators 500 _{1 to} 500 _N via the gear output rod 520 is considered. On the other hand, when the value of N is large, the impedance of a group of seats屈型actuator 500 ₁ through 500 _N is greater than the individual impedances of the seat屈型actuators 500 ₁ to 500 _N, each seat屈型actuators 500 ₁ to 500 Consider the individual interaction between _N and the gear output rod 520.

Next, the geometric characteristics of the buckling actuator will be described. The buckling actuator can be analyzed by the analysis method described in Non-Patent Document 1, for example. In the seat屈型actuator shown in FIG. 1, assuming to have an ideal rigid base structure and an ideal joint, the instantaneous displacement amplification factor R _B for the joint angle θ is determined based on the following equation (2) be able to.

図３は、ジョイント角度θに対する瞬間的変位増幅率Ｒ_Ｂの一例を示す図である。

Figure 3 is a diagram showing an example of instantaneous displacement amplification factor R _B for a joint angle theta.

  Due to the presence of singularities, locally infinite amplification theoretically occurs in a zero angle / displacement configuration. According to the configuration of this linear motion piezoelectric motor, a very large amplification factor can be obtained in the vicinity of the singular point as compared with the other one-stage leverage mechanism.

Next, a joint mechanism provided between the output node 514 and the piezoelectric element 501 in FIG. 1 and between the piezoelectric element 501 and each block 600 will be described with reference to FIGS. 4, 5A, and 5B. FIG. 4 is a diagram illustrating the configuration of the buckling actuator 500. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. For convenience of explanation, the joint 501Rc, 501Re, 501Le, 501Lc round is of the same radius _{r 2,} or have a hemispherical shape, the output node 514 and the side blocks 600R, 600L round is of the same radius _{r 1,} or, a hemispherical It has a shape. Due to the symmetrical actuator structure, the output node 514 can move in the direction of the output axis D1 without rotating in FIG.

  5A and 5B are diagrams for explaining the notation of the buckling actuator 500 shown in FIG. 5A shows the horizontal state of the piezoelectric element 501L, and FIG. 5 shows the activated and inclined state of the piezoelectric element 501L. 5A and 5B, d indicates the distance between the centers of the curvature radii of the joints 501Le and 501Lc, z indicates the amount of displacement of the piezoelectric element 501L, and b indicates the distance between the perpendiculars at the contact points CP1 and CP2 of the joints 501Le and 501Lc. Indicates the distance.

If the sum of the distance d and the displacement amount z is zero (0), the distance b is also zero (0). However, since the displacement amount z changes according to the activation of the piezoelectric element 501L and the distance d is constant, the distance b cannot be kept at zero (0) in all operating states. If the distance b is not zero (0) and the interaction force in the system is not zero (0), the contact points CP1, CP2 between the joint 501Le and the side block 600L and between the joint 501Lc and the output node 514 A frictional force is generated at, and the balance between the moment and the force can be maintained by the normal force and the distance b acting on the contact points CP1 and CP2. The resulting interaction force is F _z , the distance between the contact points CP1 and CP2 is L, and the angle between the imaginary line connecting the contact point CP1 and the center of the radius of curvature of the side block 600L and the horizontal axis is θ. As shown, the frictional force F _Fric can be obtained from the following equation (3).

摩擦は、接触点ＣＰ１，ＣＰ２における滑りを引き起こすモーメントを打ち消すことができる。しかし、転がり接触の場合は微小な滑りが起こること、及び、微小な滑りは各動作毎に蓄積されることは、既に知られている。座屈動作を不安定にする滑りを防止するため、距離ｄをゼロ（０）に設定してｚ＜＜Ｌにより摩擦を無視できる程度に小さいθの領域に低減しても良い。この条件が、ジョイント５０１Ｌｅ，５０１Ｌｃの曲率半径の中心が同一であることを表すことは、次式（４）から確認することができる。次式（４）は、例えば０．１ラジアン未満といった、無視できる程度に小さいθの領域において、三角関数の近似により定義することができる。

Friction can counteract the moment that causes slip at the contact points CP1, CP2. However, it is already known that a minute slip occurs in the case of rolling contact, and that a minute slip is accumulated for each operation. In order to prevent slippage that makes the buckling operation unstable, the distance d may be set to zero (0) and reduced to a region of θ that is small enough to ignore friction by z << L. It can be confirmed from the following formula (4) that this condition represents that the centers of the curvature radii of the joints 501Le and 501Lc are the same. The following equation (4) can be defined by approximation of a trigonometric function in a region of θ that is negligibly small, for example, less than 0.1 radians.

座屈型アクチュエータ５００における予荷重については、関連した制約がある。第１の制約は、圧電素子５０１Ｒ，５０１Ｌの出力を最大化することである。この例において用いられている圧電素子５０１Ｒ，５０１Ｌは、圧電セラミックと電極の薄膜が積層されているので、圧電素子５０１Ｒ，５０１Ｌは、許容圧縮力に比べて大きな引張力に対する耐性が不十分である可能性がある。しかし、十分に大きな予荷重の力が印加されると、結果的に得られる圧電素子５０１Ｒ，５０１Ｌの力及び予荷重の力により、高い引張力及び高い圧縮力を許容し、座屈型アクチュエータ５００から圧縮力及び引張力の両方を出力させることができる。第２の制約は、各圧電素子５０１Ｒ，５０１Ｌの全ての変位領域において一定の力を維持することであり、これは、予荷重の剛性が出力変位量を減少させ、各圧電素子５０１Ｒ，５０１Ｌから抽出可能な仕事が減少してしまうからである。第３の制約は、各接触面に作用する圧縮力を維持することであり、これは、各接触面に作用する圧縮力を維持することで摩擦力により圧電素子５０１Ｒ，５０１Ｌ及び出力ノード５１４の位置を保持できるからである。第４の制約は、接触面における非線形剛性を利用して直列的な弾性を低減することである。

There are related constraints on the preload in the buckling actuator 500. The first constraint is to maximize the output of the piezoelectric elements 501R and 501L. Since the piezoelectric elements 501R and 501L used in this example are formed by laminating a piezoelectric ceramic and an electrode thin film, the piezoelectric elements 501R and 501L have insufficient resistance to a large tensile force as compared with an allowable compressive force. there is a possibility. However, if a sufficiently large preload force is applied, the resulting piezoelectric elements 501R and 501L and the preload force allow a high tensile force and a high compressive force, and the buckling actuator 500 Thus, both the compressive force and the tensile force can be output. The second constraint is that a constant force is maintained in all the displacement regions of the piezoelectric elements 501R and 501L. This is because the rigidity of the preload decreases the output displacement amount, and the piezoelectric elements 501R and 501L This is because the work that can be extracted is reduced. The third constraint is to maintain the compressive force acting on each contact surface. This is because the friction force causes the piezoelectric elements 501R and 501L and the output node 514 to maintain the compressive force acting on each contact surface. This is because the position can be maintained. The fourth constraint is to reduce the series elasticity by using the non-linear stiffness at the contact surface.

To satisfy each of the above constraints, as shown in FIG. 6, a linear preload compensation spring (PCS) k _PCS is connected to the output node 514 in the machine model, and between the frame 624 and each side block 600R, 600L. A preload force _FPL is applied horizontally to. FIG. 6 is a diagram illustrating the elastic characteristics of the buckling actuator 500 in the machine model.

The preload is generated by the shortened distance between the output node 514 and the side blocks 600R and 600L. Since the displacement amounts of the piezoelectric elements 501R and 501L are smaller than the distance between the output node 514 and the side blocks 600R and 600L, the displacement amounts of the joints 501Le, 501Lc, 501Re, and 501Rc are joints having the same center of curvature radius. It can be regarded as a change in the diameter of 501Le, 501Lc, 501Re, and 501Rc. As a result, the balance of forces between the forces generated by the preload force F _PL and PCSK _PCS can be expressed by the following equation (5). Here, L represents the distance between the center of the output node 514 and the center of each side block 600R, 600L. Relationship between the preload force _{F PL} and _{PCSK PCS} may be due approximation of a trigonometric function expressed by the following equation (6).

図６に示す弾性の、機械モデルは、圧電素子５０１Ｒ，５０１Ｌにより駆動される座屈型アクチュエータ５００の静的出力特性を計算するのに用いることができる。ＰＣＳｋ_ＰＣＳと、各圧電素子５０１Ｒ，５０１Ｌと、各ジョイント５０１Ｌｅ，５０１Ｌｃ，５０１Ｒｅ，５０１Ｒｃと、フレーム６２４とには、４つの弾性特性が存在する。次式（７）で表される基本的な関係から、静的出力特性を表し座屈型アクチュエータ５００から出力される力Ｆ_ｙは、次式（８）から求めることができる。

The elastic mechanical model shown in FIG. 6 can be used to calculate the static output characteristics of the buckling actuator 500 driven by the piezoelectric elements 501R and 501L. The PCSK _PCS , the piezoelectric elements 501R and 501L, the joints 501Le, 501Lc, 501Re, and 501Rc, and the frame 624 have four elastic characteristics. From the basic relationship expressed by the following equation (7), the force F _y that represents the static output characteristic and is output from the buckling actuator 500 can be obtained from the following equation (8).

上記の式（７）及び式（８）において、Ｆ_ＰＺＴは圧電素子５０１Ｒ，５０１Ｌへの入力電圧Ｖ_ＰＺＴにより定義され、圧電素子５０１Ｒ，５０１Ｌの逆圧電効果を表す係数ｅ_ＰＺＴは次式（９）で表すことができる。

In the above equations (7) and (8), F _PZT is defined by the input voltage V _PZT to the piezoelectric elements 501R and 501L, and the coefficient e _PZT representing the inverse piezoelectric effect of the piezoelectric elements 501R and 501L is expressed by the following equation (9) ).

上記の式（８）における予荷重の力Ｆ_ＰＬとＰＣＳｋ_ＰＣＳとの間の関係は、弾性特性により上記の式（６）の関係から変化する。

Relationship between the preload force _{F PL} and _{PCSK PCS} in the above formula (8) is changed from the relationship of the above formula (6) by the elastic properties.

  Based on the above equation (8), the output characteristics of the buckling actuator 500 are as shown in FIG. FIG. 7 is a diagram illustrating an example of output characteristics of the buckling actuator 500. In FIG. 7, the vertical axis indicates the thrust of the piezoelectric elements 501R and 501L of the buckling actuator 500, and the horizontal axis indicates the displacement amount of the piezoelectric elements 501R and 501L. In FIG. 7, solid lines indicate a state where the piezoelectric elements 501R and 50L are activated and turned on, and broken lines indicate a state where the piezoelectric elements 501R and 501L are deactivated and turned off. In FIG. 7 and FIGS. 8 to 10 described later, “a.u.” represents an arbitrary unit.

One characteristic characteristic of the buckling actuator 500 is that the piezoelectric elements 501R and 501L are shown in FIG. 1 from the “zero output position” in which all the joints 501Le, 501Lc, 501Re, and 501Rc are aligned in a horizontal line in FIG. 1 is a so-called “bidirectional movement” that naturally moves in both the upper and lower directions. Bidirectional movement of the buckling actuator 500 is possible when the above-mentioned singular point is generated at the zero output position. Due to this specificity, the buckling actuator 500 can amplify the displacement amount by, for example, 50 times. Bidirectional movement creates a displacement amplification of approximately 100 times, for example, by doubling the stroke. The maximum output displacement y _max is defined by a distance between positions at which the force output at the minimum input (F _PZT = 0) and the maximum input F _PZT = F _PZTmax ) to the piezoelectric elements 500R and 500L becomes zero. It can be obtained from equation (10).

ヘルツの接触定理によれば、転がり接触ジョイントの剛性ｋ_Ｊは、曲面間の接触剛性として次式（１１）で表すことができる。ここで、Ｆ_Ｊは接触力を示し、δは接触線近傍に主に発生する変形を示し、Ｌ_Ｊは各圧電素子５０１Ｒ，５０１Ｌを表す円柱の長さを示し、Ｅは円柱材料のヤング率を示し、ｖはポアソン比を表す。

According to Hertz's contact theorem, the stiffness k _J of the rolling contact joint can be expressed as the following equation (11) as the contact stiffness between the curved surfaces. Here, F _J represents a contact force, δ represents a deformation mainly occurring near the contact line, L _J represents a length of a cylinder representing each of the piezoelectric elements 501R and 501L, and E represents a Young's modulus of the column material. Where v represents the Poisson's ratio.

上記の式（１１）で表されているように、転がり接触ジョイントの剛性ｋ_Ｊは、圧電素子５０１Ｒ，５０１Ｌ及び予荷重の力Ｆ_ＰＬの合力と等しい接触力Ｆ_Ｊに応じて変動する。しかし、座屈増幅機構を介して印加される予荷重により、動作状態における転がり接触ジョイントの剛性ｋ_Ｊの変動は極めて小さく、図８に示すように例えば１０％のオーダである。図８は、転がり接触ジョイントの剛性ｋ_Ｊ、即ち、接触剛性変動の一例を示す図である。図８中、縦軸は接触剛性を示し、横軸は接触力を示す。図８において、梨地で示す領域は、動作状態で使用される領域を示す。

As represented by the above formula (11), the stiffness _{k J} of rolling contact joint, varies depending on the piezoelectric element 501R, 501L and preload force equal contact force _{F J} heavy force _{F PL.} However, the preload applied through the seat屈増width mechanism, the variation of stiffness k _J Contact joint rolling in operative position is extremely small, for example 10% of the order as shown in FIG. FIG. 8 is a diagram illustrating an example of the stiffness k _J of the rolling contact joint, that is, the contact stiffness variation. In FIG. 8, the vertical axis indicates the contact rigidity, and the horizontal axis indicates the contact force. In FIG. 8, a region indicated by a satin surface indicates a region that is used in an operating state.

Various PAS gear output rods can be used depending on the general characteristics of the linear motion piezoelectric motor that generates the static output force F _x represented by the above formula (1). In this embodiment, the gear output rod 520 used is of the gear and roller follower type shown in FIG. Similar to conventional design methods, the minimum radius of curvature of the follower trajectory must be greater than the radius of the follower 514 in order to allow continuous transitions when the direction of movement of both the gear and follower 514 changes. Further, in this embodiment, in order to enable smooth energy transfer between the gear and the follower 514 and natural reciprocation of the follower 514, the gear output rod 520 has a sinusoidal movement path at the center of the follower 514. To. The movement locus of the follower center can be expressed by the following equation (12). Here, y _FC indicates a position along the gear output rod 520 in the output direction of the linear motion piezoelectric motor, y _FCmax indicates the maximum displacement amount of the follower center, λ indicates the wavelength of the gear output rod 520, x Indicates a relative displacement amount between the buckling actuator 500 and the gear output rod 520 in the output direction of the linear motion piezoelectric motor.

上記の式（８）及び式（１２）を考慮すると、ギア出力ロッド５２０により変換された座屈型アクチュエータ５００の力特性は、次式（１３）で表すことができる。

Considering the above formulas (8) and (12), the force characteristics of the buckling actuator 500 converted by the gear output rod 520 can be expressed by the following formula (13).

図９は、ギア出力ロッド５２０により変換された座屈型アクチュエータ５００の力特性の一例を示す図である。図９において、左側の縦軸は直動圧電モータの推力を示し、右側の縦軸は図２中ｙ方向へのフォロワの軌跡を示し、横軸はフォロワ中心の図２中ｘ方向への変位量を示す。また、図９において、実線は圧電素子５０１Ｒ，５０１Ｌが活性化されてオンである状態を示し、一転鎖線は圧電素子５０１Ｒ，５０１Ｌが非活性化されてオフである状態を示し、破線はフォロワの軌跡を示す。

FIG. 9 is a diagram illustrating an example of force characteristics of the buckling actuator 500 converted by the gear output rod 520. In FIG. 9, the left vertical axis indicates the thrust of the linear motion piezoelectric motor, the right vertical axis indicates the locus of the follower in the y direction in FIG. 2, and the horizontal axis indicates the displacement of the follower center in the x direction in FIG. Indicates the amount. In FIG. 9, the solid line indicates that the piezoelectric elements 501R and 501L are activated and turned on, the alternate long and short dash line indicates that the piezoelectric elements 501R and 501L are deactivated and turned off, and the broken line indicates the follower Show the trajectory.

The term including the above formulas _(13), the _{F PZT} represents the effect of the energy from the power supply inputted via the piezoelectric element 501R, the 501L. The other term in equation (13) represents the action of the energy stored by the elastic characteristics of the buckling actuator 500. The effect of the elastic properties is separated into two periodic components that are twice and four times the wave cycle of the gear output rod 520.

The coefficients A _Fx and A _Fpzt in the above equation (13) can also be expressed by the following equation (14).

ｙ_{ＦＣｍａｘ}がｙ_ｍａｘと等しい場合、Ｆ_ＰＺＴがＦ_{ＰＺＴｍａｘ}と等しいと、（Ａ_Ｆｐｚｔ・Ｆ_ＰＺＴ）は４になり、図９に示すように圧電素子５０１Ｒ，５０１Ｌのオン状態とオフ状態の間で水平及び垂直方向に対称なＦ_ｘｕ特性が得られる。係数Ａ_ＦｘはＲ_ｙ ^２と共に増加するが、これと同時に、弾性特性の静的出力の力Ｆ_ｘに対する影響もＲ_ｙ ^４と共に増加する。従って、パラメータＲ_ｙが大きくなるにつれて、静的出力の力Ｆ_ｘの制御がより難しくなることがわかる。

When y _FCmax is equal to y _max and F _PZT is equal to F _PZTmax , (A _Fpzt · F _PZT ) becomes 4, and between the on-state and off-state of the piezoelectric elements 501R and 501L as shown in FIG. F _xu characteristics that are symmetrical in the horizontal and vertical directions are obtained. The coefficient A _Fx increases with R _y ² , but at the same time, the influence of the elastic properties on the static output force F _x also increases with R _y ⁴ . Therefore, it can be seen that the control of the static output force F _x becomes more difficult as the parameter R _y increases.

  By substituting the above equation (13) into the above equation (1), the force characteristics of the buckling actuator 500 can be obtained from the following equation (15).

上記の式（１５）から、静的出力の力Ｆ_ｘは１ＰＡＳ波長λ内で２サイクル及び４サイクルの成分を含み、ＰＡＳの波形サイクルに対してπ／２ラジアンの距離を有する二（２）つの座屈型アクチュエータ５００により、効率的にギア出力ロッド５２０の位置にかかわらず静的出力の力Ｆ_ｘを生成できることがわかる。

From equation (15) above, the static output force F _x includes components of 2 and 4 cycles within 1 PAS wavelength λ, and has a distance of π / 2 radians with respect to the PAS waveform cycle. It can be seen that the two buckled actuators 500 can efficiently generate the static output force F _x regardless of the position of the gear output rod 520.

  From the sine and cosine theorem, the following equation (16) is obtained. Here, k = 1,. . . , N.

上記の式（１６）は、次式（１７）に一般化することができる。

The above equation (16) can be generalized to the following equation (17).

上記の式（１７）は、式（１７）の位相セットから発生する剰余を２πラジアンで除算すると、上記の式（１６）の位相セットと同じになることを示している。

The above equation (17) indicates that when the remainder generated from the phase set of equation (17) is divided by 2π radians, the phase set of equation (16) is the same.

Considering the above equations (15) and (17), several types of layout designs can be obtained that produce different static output forces F _x as shown below.

Case 1. Complete cancellation of elastic action:
When φ _i has only a phase set expressed in radians with respect to the PAS waveform cycle, terms other than the term including FPZT _{, i} are between the buckling actuators 500, as can be seen from the following equation (18). Negate each other.

この場合、静的出力の力Ｆ_ｘは、次式（１９）で表すことができる。

In this case, the force F _{x of the} static output can be expressed by the following equation (19).

上記の式（１９）は、ＰＡＳ波形の位相のみに依存する他の出力の項を考慮するだけで、Ｆ_{ＰＺＴ，ｉ}を調整することで静的出力の力Ｆ_ｘを制御できることを表している。直動圧電モータからのモータ出力が不要である場合には、大きなエネルギ損失を発生することなくＦ_{ＰＺＴ，ｉ}を一定に維持することができる。

The above equation (19) indicates that the static output force F _x can be controlled by adjusting _{FPZT, i} only by considering other output terms that depend only on the phase of the PAS waveform. . When the motor output from the direct acting piezoelectric motor is unnecessary, _{FPZT, i} can be kept constant without generating a large energy loss.

  The force characteristics described above are obtained from various combinations of phase sets expressed in radians for a cycle of a PAS waveform including the original phase set and other phase sets having a phase shift, as represented by the following equation (20). Can do.

ケース２．弾性作用の部分的な打ち消し：
φ_ｉがＰＡＳ波形サイクルに対してラジアンで示される位相セットのみを有する場合、Ｆ_{ＰＺＴ，ｉ}を含む項以外の項は、次式（２１）からもわかるように、座屈型アクチュエータ５００間で打ち消し合う。

Case 2. Partial cancellation of elastic action:
When φ _i has only a phase set expressed in radians with respect to the PAS waveform cycle, terms other than the term including FPZT _{, i} are between the buckling actuators 500, as can be seen from the following equation (21). Negate each other.

この場合、静的出力の力Ｆ_ｘは、次式（２２）で表すことができる。

In this case, the force F _{x of the} static output can be expressed by the following equation (22).

上記の式（２２）は、直動圧電モータが圧電素子５０１からの力の入力を受けることなく周期的な力を生成することを示している。このような力特性により、直動圧電モータは、自己の位置を自己で保持する自己保持機能を有する。

The above equation (22) indicates that the linear motion piezoelectric motor generates a periodic force without receiving the force input from the piezoelectric element 501. Due to such force characteristics, the direct acting piezoelectric motor has a self-holding function of holding its own position by itself.

  The above-mentioned force characteristics are obtained from various combinations of phase sets expressed in radians for a cycle of a PAS waveform including the original phase set and another phase set having a phase shift, as represented by the following equation (23). Can do.

他のレイアウト設計では、モータ出力にＰＡＳ波形サイクルに対して４倍のサイクル成分を含んでも良い。しかし、４倍成分の蓄積は、力に大きなリップルを発生させる可能性があり、モータ出力の制御を難しくする。このため、本実施例で用いられているようなタイプの直動圧電モータの場合は、上述のレイアウト設計が好ましい。

In other layout designs, the motor output may include four times as many cycle components as the PAS waveform cycle. However, the accumulation of quadruple components can cause large ripples in the force, making it difficult to control the motor output. For this reason, in the case of the direct acting piezoelectric motor of the type used in this embodiment, the above layout design is preferable.

  From FIG. 9, each buckling actuator 500 directly switches the input to the piezoelectric element from the on state to the off state at each λ / 4 position with respect to the phase of the PAS waveform, and from the off state to the on state. It can be seen that forces in both the positive and negative directions can always be output as the motor output of the dynamic piezoelectric motor. Also, by canceling the action of the preload force and the PCS force on the force output of the buckling actuator, the force when the piezoelectric element is on and the output node moves from zero to the end point, such as from the peak to the valley of the PAS waveform, The transition is the same as the force transition when the piezoelectric element is off and the output node moves from the end point of the PAS waveform to zero.

  The maximum output from the direct acting piezoelectric motor can be obtained by the positive resultant force of the forces output from all the buckling actuators of the direct acting piezoelectric motor. FIG. 10 is a diagram illustrating an example of the maximum output characteristic of the linear motion piezoelectric motor according to the number of buckling actuators used. In FIG. 10, the left vertical axis represents the maximum thrust of the linear motion piezoelectric motor, the right vertical axis represents the follower locus along the y direction, and the horizontal axis represents the displacement amount of the follower center along the x direction. In FIG. 10, the solid line indicates the case where six (6) buckling actuators 500 are used, the rough broken line indicates the case where four (4) buckling actuators 500 are used, and the fine broken line indicates the follower locus. Indicates. The above-described phase layout was employed both when six (6) buckling actuators 500 were used and when four (4) buckling actuators 500 were used. As the number of buckling type actuators 500 used increases, the average value of the thrust output from the direct acting piezoelectric motor increases, and the fluctuation of the maximum thrust of the direct acting piezoelectric motor decreases.

  The average output from the linear motion piezoelectric motor by changing the switching position at which the input to the piezoelectric element is switched from the on state to the off state and from the off state to the on state from each λ / 4 position with respect to the phase of the PAS waveform. Thrust can be controlled.

  Next, continuous voltage drive control of the direct acting piezoelectric motor will be described.

When the voltage supplied to each piezoelectric element of the direct acting piezoelectric motor is continuously changed, the direct acting piezoelectric motor exhibits a specific force characteristic. As described above with Equation (9), the analysis may take into account that the input voltage of the piezoelectric element is proportional to _FPZT . For this reason, in the following description, a pattern of _FPZT will be described instead of the input voltage. A specific pattern of _FPZT can be expressed by the following formula (24). Here, F _PZTin the amplitude of the force of the piezoelectric element input (hereinafter, also referred to as "piezoelectric force Input") indicates, P _in denotes a phase specified by the phase command.

上記の式（２４）を上記の式（１５）に代入することで、静的出力の力Ｆ_ｘは次式（２５）で表すことができる。

By substituting the above equation (24) into the above equation (15), the static output force F _x can be expressed by the following equation (25).

上記の式（２５）中、３番目の和の項は一定入力条件と全く同じであり、これは、３番目の和の項に依存する力が上述のレイアウト設計に依存する力とは多少異なる性質を有することを表す。この違いにより、圧電素子の力入力Ｆ_{ＰＺＴｉｎ}による作用が１／２になる。上記の式（２５）の１番目の項は、位相Ｐ_ｉｎによりλ／２波長に対して制御可能な静的出力の力Ｆ_ｘを生成する直動圧電モータから出力される力の平均出力を決定する。上記の式（２５）の１番目の項における位相Ｐ_ｉｎの役割を考慮すると、位相Ｐ_ｉｎは好ましくは上記の式（２５）の２番目の項と３番目の和の項のバランスを制御するのには使用されない。さらに、座屈型アクチュエータが上述のケース１またはケース２のレイアウト設計に応じて配置されており、正弦波成分のサイクルがＰＡＳ波形の４倍である場合、レイアウト位相は互いに打ち消し合う。

In the above equation (25), the third sum term is exactly the same as the constant input condition, which is that the force depending on the third sum term is slightly different from the force depending on the layout design described above. It represents having properties. Due to this difference, the action of the force input _FPZTin of the piezoelectric element is halved. The first term of the above equation (25), the average output of the force output from the linear piezoelectric motor for generating a force F _x of the controllable static output to lambda / 2 wavelength by the phase P _in decide. Considering the role of phase P _in in the first term of equation (25) above, phase P _in preferably controls the balance of the second and third sum terms of equation (25) above. Not used for. Further, when the buckling actuator is arranged according to the layout design of the case 1 or the case 2 described above and the cycle of the sine wave component is four times the PAS waveform, the layout phases cancel each other.

In this case, the static output force F _x can be defined in consideration of the layout design as follows.

Case 1. Complete cancellation of elastic action:
In this layout design, the static output force F _x can be obtained from the following equation (26).

上記の式（２６）は、静的出力の力Ｆ_ｘが、力のリップルを生じることなく、圧電力入力Ｆ_{ＰＺＴｉｎ}及び位相Ｐ_ｉｎの両方により制御可能であることを表している。

Equation (26), the force F _x static output, without causing ripples of force, indicating that is controllable by both the piezoelectric force input F _PZTin and phase P _in.

Case 2. Partial cancellation of elastic action:
In this layout design, the static output force F _x can be obtained from the following equation (27).

上記の式（２７）は、圧電力入力Ｆ_{ＰＺＴＩｉｎ}がＦ_{ＰＺＴｍａｘ}と等しくＲ_ｙがＡ_ＦｐｚｔとＦ_{ＰＺＴｉｎ}の積を２にする場合、静的出力の力Ｆ_ｘが、力のリップルを生じることなく、位相Ｐ_ｉｎのみにより制御可能であることを表している。その他の場合には、上記の式（２７）の２番目の項がある程度のレベルを有し、力のリップルを発生する可能性がある。

When the piezoelectric power input F _PZTIin is equal to F _PZTmax and R _y is _set to 2 as the product of A _Fpzt and F _PZTin , the force F _{x of the} static output does not cause a force ripple. , it indicates that is controllable only by the phase P _in. In other cases, the second term of the above equation (27) has a certain level and may generate a force ripple.

  FIG. 11 is a block diagram illustrating an example of the control system 50 in one embodiment. A control system 50 shown in FIG. 11 includes a power source 51, a driving device 52, a plurality of piezoelectric elements 53, a buckling type mechanism 54, a gear 55, a load 56, and a controller 57. The driving device 52 is supplied with a power supply voltage from the power supply 52 and drives the piezoelectric element 53. The piezoelectric element 53 may correspond to the piezoelectric element 501 (501R, 501L) of the above-described direct acting piezoelectric motor, and may form the above-described buckled actuator 500. Based on the command from the controller 57, the driving device 52 controls the voltage condition of each piezoelectric element 53, such as an on and off state or a sinusoidal transition.

  The buckling mechanism 54 may include a plurality of buckling actuators having elastic characteristics, such as the buckling actuator 500 described above. The plurality of buckling actuators are arranged at a constant phase interval with respect to the gear 55, and the phase interval cancels at least part of the elastic characteristics. When the nonlinear component of the elastic characteristic is approximated by a polynomial, the phase interval may cancel at least a part of the harmonic component of the motor thrust generated by the harmonic component of the polynomial. Therefore, the driving device 52 drives the buckling mechanism 54 by driving the piezoelectric element 53 that forms the buckling actuator of the buckling mechanism 54. The gear 55 may correspond to the linear gear output rod 520 described above, and converts the outputs of a plurality of buckling actuators into motor outputs. The gear 55 has a shape such that the movement locus of the engaging portions of the plurality of buckling actuators that engage with the gear 55 has a sine wave shape with respect to the gear 55.

  The drive device 52, the piezoelectric element 53, the buckling type mechanism 54, and the gear 55 can form a direct-acting piezoelectric motor. The load 56 may be a drive target driven by a gear 55 of a direct acting piezoelectric motor. The load 56 may include a part of a direct acting piezoelectric motor. The controller 57 can be formed by a processor such as a CPU (Central Processing Unit).

  In the example illustrated in FIG. 11, the load 56 includes a sensor unit 560. However, the sensor unit 560 may be provided with respect to the gear 55 to form a part of the direct acting piezoelectric motor. For example, the sensor unit 560 may include a speed sensor that detects the speed of the gear 55 by a known means and a phase sensor that detects the gear phase angle of the gear 55 by a known means. The configuration and method used by the speed sensor are not limited to a specific type, and it is sufficient that the speed of the gear 55 and the speed of the linear motion piezoelectric motor can be detected from the output of the speed sensor. For example, when other types of sensors such as a position sensor are used, it is sufficient that the speed of the gear 55 and the speed of the direct-acting piezoelectric motor can be observed based on signals from these sensors. The configuration and method used by the phase sensor are not limited to a specific type, and it is sufficient that the gear phase angle of the gear 55 and the rotational phase angle of the direct acting piezoelectric motor can be detected from the output of the speed sensor. For example, when other types of sensors such as a position sensor are used, the gear phase angle of the gear 55 and the rotational phase angle of the linear motion piezoelectric motor can be observed based on signals from these sensors. good.

  The controller 57 can generate the target thrust of the direct acting piezoelectric motor based on the target speed of the direct acting piezoelectric motor and the speed of the direct acting piezoelectric motor received from the sensor unit 560. The controller 57 can generate the target gear phase angle and the target amplitude of the voltage input to the piezoelectric element based on the gear phase angle of the gear 55 and the gear phase angle of the gear 55 received from the sensor unit 560. Therefore, the controller 57 adjusts the voltage of each piezoelectric element 53 of the buckling actuator that forms the buckling mechanism 54 based on the target thrust, the target gear phase angle, and the gear phase of the gear 55. Based on the angle, the second phase for each piezoelectric element 53 can be determined. Further, the controller 57 may compare the first phase and the second phase to generate a voltage condition for the buckling actuator of the buckling mechanism 54 that indicates the comparison result of the first and second phases. it can.

  Therefore, the controller 57 can output a command to the driving device 52 and control voltage input to the plurality of piezoelectric elements 53 based on the voltage condition. As a result, the driving device 52 inputs a voltage including, for example, a sine wave component corresponding to the corresponding phase angle of the gear 55 to the plurality of piezoelectric elements 53. The voltage input to the plurality of piezoelectric elements 53 can be determined so as to adjust the motor thrust according to the amplitude of the sine wave component and / or the difference between the shape of the gear 55 and the waveform shape. In this way, each buckling actuator of the buckling mechanism 54 is driven to output a buckling force, and then each buckling force is converted according to the inclination of the gear 55 at each gear phase. The resultant force of the plurality of buckling actuators of the buckling mechanism 54 can drive the gear 55 and further drive the load 56.

  FIG. 12 is a flowchart illustrating an example of a control process that employs a control method according to an embodiment. The control process shown in FIG. 12 includes a linear motion piezoelectric motor having a plurality of buckling actuators having elastic characteristics and including a plurality of piezoelectric elements, and a gear for converting outputs of the plurality of buckling actuators into motor outputs. Control. The control process may be executed by, for example, the control system 500 illustrated in FIG.

  In step S101 shown in FIG. 12, the controller 57 generates the voltage condition of the buckling actuator of the buckling mechanism 54 by the method described in conjunction with FIG. In step S <b> 102, the controller 57 outputs a command for controlling voltage input to the plurality of piezoelectric elements 53 to the driving device 52 based on the voltage condition. Specifically, the controller 57 controls the driving device 52 to input a voltage including, for example, a sine wave component corresponding to the phase angle corresponding to the gear 55 to the plurality of piezoelectric elements 53. The voltage input to the plurality of piezoelectric elements 53 can be determined so as to adjust the motor thrust according to the amplitude of the sine wave component and / or the difference between the shape of the gear 55 and the waveform shape. In this way, each buckling actuator of the buckling mechanism 54 is driven to output a buckling force, and then each buckling force is converted according to the inclination of the gear 55 at each gear phase. The resultant force of the plurality of buckling actuators of the buckling mechanism 54 can drive the gear 55 and further drive the load 56.

  The controller 57 may control the driving device 52 to input a voltage including, for example, a rectangular wave component according to the phase angle corresponding to the gear 55 to the plurality of piezoelectric elements 53.

  The above-described control system and control method can drive and control a direct-acting piezoelectric motor other than the direct-acting piezoelectric motor (or actuator) shown in FIG. 2, for example. Examples of linear motion piezoelectric motors may include those described below in conjunction with FIGS.

  FIG. 13 is a diagram illustrating a second example of the direct acting piezoelectric motor in the embodiment. The linear motion piezoelectric motor includes a plurality of buckling actuators 500 connected to a linear gear output rod 520 having an improved sinusoidal gear, 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. Accordingly, the linear motion piezoelectric motor or gear output rod 520 is guided by the linear guide 521 and moved in the output direction D3, and the displacement of the motor is detected by a known means using the sensor 523.

The maximum rated speed v _xmax can be set in consideration of the thermal characteristics of the piezoelectric element. The voltage and frequency affect energy loss and thermal excitation in the buckled actuator 500. The material used for the piezoelectric element loses its piezoelectric properties when it exceeds the Curie temperature of the material. For these reasons, the practical operating conditions of the direct acting piezoelectric motor may be determined in consideration of temperature.

  The wavelength λ of the PAS can be determined in consideration of the contact stress between the PAS and the follower driven by the buckling actuator 500. Since the maximum contact stress occurs at the tooth ridge of the PAS, the radius of curvature of the joint is greater than a certain radius, and the joint is preferably formed of hardened tool steel, for example.

  FIG. 14 is a diagram illustrating a third example of the direct acting piezoelectric motor in the embodiment. The direct acting 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. 14, 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. Thereby, the linear motion piezoelectric motor or the gear output rod moves in the output direction D3.

  Although the above embodiment is applied to a linear actuator, the above embodiment can be similarly applied to a rotary actuator.

  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.

50 control system 51 power supply 52 drives 53,501,501R, 501L piezoelectric element 54 seats屈型mechanism 55 gear 56 load 57 control unit 500, 500 ₁ to 500 _N seat屈型actuator 514 output node 520 linear gear output rod 560 sensor Part

Claims (10)

A plurality of actuators having elastic properties and including a plurality of capacitive actuators;
A gear for converting the outputs of the plurality of actuators into motor outputs;
The gear is formed such that a movement locus of the engaging portions of the plurality of actuators engaged with the gear with respect to the gear has a shape including at least a sine wave component,
The motor is characterized in that the plurality of actuators are arranged at a phase interval that cancels at least a part of the elastic characteristics.   The motor according to claim 1, wherein at least some of the plurality of actuators are arranged at a constant interval with respect to the gear. The nonlinear component of the elastic property is approximated by a polynomial,
3. The motor according to claim 1, wherein the phase interval cancels at least a part of a harmonic component of a motor thrust generated by a higher-order component of the polynomial. A control system for controlling the motor according to any one of claims 1 to 3,
A voltage according to a phase angle of the corresponding gear is input to the plurality of actuators.   The control system according to claim 4, wherein the voltage has a waveform including a sine wave component.   The control system according to claim 4, wherein the voltage has a waveform including a rectangular wave component.   The control system according to claim 4, wherein the voltage is determined so as to adjust a motor thrust according to an amplitude of the sine wave component.   The control system according to claim 4, wherein the voltage is determined so as to adjust a motor thrust according to a phase difference between the shape of the gear and the sine wave component.   7. The voltage according to claim 4, wherein the voltage is determined so as to adjust a motor thrust by a combination of an amplitude of the sine wave component and a shape of the gear and a phase difference of the sine wave component. The control system according to any one of claims. A control method for controlling the motor according to any one of claims 1 to 3,
A voltage according to a phase angle of the corresponding gear is input to the plurality of actuators.

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