JPH065992B2 - Multi-axis type piezoelectric motor - Google Patents

Description

The present invention relates to a multi-axis piezoelectric motor used as, for example, a joint motor of various robots.

[Conventional technology]

Conventionally, electromagnetic motors such as stepping motors and solenoid motors have been used as robot joint motors. In order to obtain a large torque, the number of rotations is usually reduced by a harmonic gear. Recently, direct drive motors have been developed and are beginning to be used as robot joint motors.

[Problems to be solved by the invention]

Since the electromagnetic motor is based on electromagnetic force, it is unavoidable that a response delay time is caused by the inductance. Further, since the number of poles of the electromagnets provided on the rotor (rotor) and the stator (stator) is finite, the positioning accuracy of the robot hand is naturally limited. Further, if the rotational speed is reduced by a harmonic gear, not only the efficiency of the motor decreases in proportion to the number of gear steps, but also the positioning accuracy decreases due to the accumulation of delicate play in the gear. Was.

The direct drive motor has higher positioning accuracy than the conventional electromagnetic motor, and the accuracy can be increased to several tens of microns. However, this direct drive motor is also a single-axis type motor like the conventional electromagnetic motor,
Moreover, the shaft of the motor is completely fixed, and the rotation around the fixed shaft is used. Therefore, in order to achieve the ultimate goal of the robot, which is to replace all human movements with higher output and higher accuracy than humans, the number of joints must be increased even if a direct drive motor is used. There was no way. In particular, in the case of substituting for assembly and inspection work performed by humans in a factory, the number of joints must be increased.

However, it is generally desirable that the number of joints is small, regardless of the case where an invisible hidden portion is operated.
That is, it is best for the robot to perform the same motion with as few joints as possible. This is obvious in terms of positioning accuracy, moving speed, power consumption, and reliability. In particular, if the length of the arm becomes unnecessarily long as the number of joints increases, it is obvious that any of the above points will be adversely affected.

If the motor rotation shaft can change the tilt angle as needed with almost the same volume, the number of joints can be reduced as compared with the conventional one, and positioning accuracy, moving speed, power consumption,
It is certain that it will turn in the preferred direction in terms of reliability. Therefore, there has been a demand for the realization of a motor capable of changing the direction of the rotating shaft according to such needs.

Therefore, according to the present invention, the inclination angle of the rotation axis of the rotor can be changed,
It is preferable as a motor used for the joints of a robot, for example, it allows the robot to perform a flexible operation with a minimum number of joints, high positioning accuracy, high speed, low power consumption,
It is an object of the present invention to provide a multi-axis piezoelectric motor that can be expected to have high reliability.

[Means for solving problems]

The present invention has taken the following means in order to solve the above problems and achieve the object.

A cereal grain having an opening in one part and a holding part in the other part is provided.

A plurality of ring-shaped piezoelectric motor elements are fixed to the inner wall of this grain through an elastic member.

A sphere is housed in the kernel so as to be supported on the outer peripheral surface by the plurality of ring-shaped piezoelectric motor elements.

On a part of the surface of the sphere, an operating portion is provided which projects outward from the kernel through the opening.

In addition, it is preferable that the plurality of ring-shaped piezoelectric motor elements are applied with a voltage having a phase difference so that one is driven by a traveling wave and the other is driven by a standing wave.

[Action]

By taking such means, the sphere as the rotor can be rotated in any direction and the operating portion can be directed in a desired direction only by controlling the voltage applied to the plurality of ring-shaped piezoelectric motor elements. it can.

The present invention will be described in detail below with reference to the drawings. First, the piezoelectric motor which is the main component of the present invention will be described.

1 (a) (b) to 3 (a) (b) are structural conceptual diagrams of the piezoelectric motor of the present invention. Piezoelectric motors have various structures, but FIGS. 1 (a) and (b) to FIG. 3 (a)
The piezoelectric motor shown in (b) has a ring-shaped piezoelectric motor element as a stator and a spherical body as a rotor. This piezoelectric motor has a completely different structure and operates differently from the conventional electromagnetic motor.

1 (a) and 1 (b) are views showing a piezoelectric motor element.
As shown in the figure, the piezoelectric ceramics 2 having different thicknesses are bonded to the ring-shaped metal plate 1 having a large coefficient of performance Q, and the elastic member 3 is mounted thereon. The piezoelectric ceramics 2 has a pair of opposite polarizations formed adjacent to each other for each wavelength λ, and has a polarization arrangement symmetrical with respect to the center line 4. Then, in the portions through which the center line 4 passes, the non-polarized portions 5 of 3 / 4λ and 1 / 4λ, respectively.
6 is provided. The electrodes corresponding to each polarization are connected so as to be electrically connected to each other on both sides of the center line 4. The lead wire from one side is connected to the terminal A, the lead wire from the other side is connected to the terminal B, and the lead wire from the metal plate 1 is connected to the ground terminal E. Terminal AE
Voltages V1 and V2 having the same amplitude and the same frequency and a phase difference of 90 ° are applied between the terminals and the terminals B and E, respectively.

Now, if voltages V1 and V2 are applied, Am. si
A traveling wave of n (ωt-kx) is generated in the circumferential direction of the piezoelectric motor element as indicated by the arrow in FIG. 1 (b). Where ω
Represents frequency, k represents wave number, t represents time, and x represents position.

FIG. 2 is a diagram showing a state in which the piezoelectric motor element in which the traveling wave is excited is used as a stator, and the sphere 7 as a rotor is placed on the stator. By doing so, each point on the surface of the stator makes a backward elliptical motion with respect to the traveling direction of the traveling wave. The spherical body 7 as a rotor mounted on the stator is always in contact with the top portion of the ellipse, and the displacement direction of this top portion is opposite to the traveling direction of the vibration wave. Therefore, the spherical body 7 rotates around the rotation axis 8 in one direction. When the phase relationship between the applied voltages V1 and V2 is reversed, the direction of the traveling wave is also reversed, so that the rotation direction is reversed. When the phase difference between the applied voltages V1 and V2 is eliminated or when it is deviated by π, a standing wave is generated, so that a spheroidal motion does not occur and a vertical linear motion perpendicular to the circumferential direction is performed. In this state, the friction between the stator and the rotor is extremely small, and the rotor can be smoothly rotated by performing a manual operation or the like. Furthermore, applied voltages V1 and V2
Is not applied at all, the friction between the stator and the rotor becomes maximum, and the chuck state is established.

As described above, FIG. 1 (a) (b) and FIG. 2 (a)
The piezoelectric motor shown in (b) has three states of rotation in both directions, a state of minimum friction (floating state of rotor), and a state of maximum friction (chuck state) due to the application of applied voltages V1 and V2. It has the characteristics that it can be realized with the same structure and that changes between states can be made in an instant. This point is a characteristic point that cannot be expected of conventional electromagnetic motors. The characteristic points of the piezoelectric motor are summarized as follows.

No electromagnetic force is used.

No central axis of rotation (rotating shaft) is required.

Several tens of KHz to 100 generated on the ring as driving force
A traveling wave of KHz is used.

The drive of the rotor is contact friction drive by the stator.

It is voltage driven, high voltage, low current consumption, and has a three-input terminal structure.

A thin shape can be realized.

By changing the vibration wave generated on the ring to a traveling wave, a standing wave, or no vibration, rotor rotation, no resistance,
The three states of the chuck can be realized by a device having the same structure.

The rotation is a low speed, high torque type rotation.

FIGS. 3 (a) and 3 (b) show that the outer surface of one spherical rotor 7 is
It is a figure which shows the case where the individual piezoelectric motor elements M1-M4 are mounted as a stator. As shown in the figure, the plurality of piezoelectric motor elements M1 to M4 are in contact with the rotor 7 so that their centers m1 to m4 are the vertices of a regular tetrahedron as shown in FIG. 3 (b). In the figure, S1, S2, S3, S
Reference numeral 4 is a rotary shaft of each piezoelectric motor element M1 to M4.

For example, now, the voltage V having a phase difference of 90 ° is applied to the piezoelectric motor element M1.
1 and V2 and the other piezoelectric motor elements M2 to M4 are given V1 and V2 with a phase difference of O and all have the same amplitude and frequency, the spherical rotor 7 rotates smoothly around the rotation axis S1. . The piezoelectric motor element M2 has a phase difference of 90
Of the other piezoelectric motor elements M1,
When V1 and V2 having a phase difference of O are given to M3 and M4, they rotate about the rotation axis S2. Piezoelectric motor elements M3, M
The same applies to the case of rotating around each of the four axes S3 and S4. By sequentially applying the voltages V1 and V2 having a predetermined phase difference to the piezoelectric motor elements M1 to M4 in this manner, the rotor 7 rotates about different rotation axes. As a result, one point P on the spherical surface of the rotor 7 can be moved to an arbitrary position on the spherical locus. Since the piezoelectric motor element can be formed in a thin ring shape, even if a fixing member for fixing these piezoelectric motor elements is taken into consideration, the size is slightly larger than the size of the spherical body 7, and there is no fear of increasing the size so much.

〔Example〕

FIG. 4 is a diagram showing an embodiment of the present invention. Numeral 10 is a kernel made of metal such as brass or SUS, and a circular opening 11 is provided in a part thereof. A cylindrical holding portion 12 is attached to another portion of the spheroidizing portion 10, for example, on the opposite side of the opening 11. Four ring-shaped piezoelectric motor elements M1 to M4 are fixed to the inner surface of the kernel 10 via elastic members (for damping and spacers) such as rubber.
These piezoelectric motor elements M1 to M4 are provided at the positions of the vertices of a regular tetrahedron as shown in FIG. 3 (b). Although not shown, the kernel 10 near the fixing portion of the piezoelectric motor elements M1 to M4 is provided with pores for passing the lead wires of the piezoelectric motor elements M1 to M4. A spherical body 13 made of a metal such as brass or SUS or another elastic material is accommodated in the spherical grain 10 while being supported by the piezoelectric motor elements M1 to M4. Therefore, there is a certain gap between the outer peripheral surface of the spherical body 13 and the inner peripheral surface of the spherical grain 10. A shaft 14 as an operation unit for attaching the robot hand is attached to a part of the sphere 13 by means such as screwing. This shaft 14 is a kernel 10
It projects from the opening 11 to the outside.

FIG. 5 is a sectional view showing a part of the piezoelectric motor element. As shown in FIG. 5, an elastic member 15 made of, for example, neoprene rubber or the like and serving as a damping material and a spacer is adhered to the inner peripheral surface of the spherical grain 10, and a ring-shaped piezoelectric ceramic 16 and a ring-shaped piezoelectric ceramic 16 are provided on the elastic member 15. A piezoelectric motor element M formed by superposing the ring-shaped metal plate 17 is joined. The spherical body supporting surface of the ring-shaped metal plate 17 is formed in a concave shape having the same curvature as the outer peripheral surface of the spherical body 13. The spherical grain 10 is formed by integrally joining hemispherical grains so that the spherical body 13 can be easily accommodated.

FIG. 6 is a diagram showing an example in which the multi-axis type piezoelectric motor having the above-mentioned structure is used as a joint of a measuring robot, and is a beam of an ultrasonic probe used for nondestructive inspection or ultrasonic diagnostic equipment. It is an example of arrangement when measuring a pattern. Beam pattern measurement is an important measurement for determining the performance of an ultrasonic probe, particularly lateral resolution and focal length. A reflector 21 having a flat surface or a spherical surface is installed in the water tank 20, and an ultrasonic probe 22 is disposed at a position separated from the reflector 21 by a distance Z. The probe 22 is coupled to the operation unit 14 of the multi-axis piezoelectric motor via a holder 18. A holding portion 12 provided on the kernel 10 of the multi-axis piezoelectric motor
Are connected to the arm 24 of the X, Y, Z Cartesian coordinate robot. The beam pattern is measured by the probe 22 described above.
The ultrasonic beam 23 while moving the X, Y, and Z directions.
Is emitted from the probe 2, the ultrasonic beam 23 reflected by the reflector 21 is made incident again on the probe 22, and the incident beam power is measured. As described above, the probe 22 is linearly moved in the X, Y, and Z directions to perform the measurement. Before this, it is necessary to adjust the central axis of the ultrasonic beam of the ultrasonic probe 22. .

That is, as shown in FIG. 7, it is necessary to accurately orient the ultrasonic beam central axis 23a of the ultrasonic probe 22 toward the reflector 21. For this purpose, it is necessary to rotate the probe 22 around the X, Y, and Z axes by minute angles η, φ, and ξ, respectively. Conventionally, three uniaxial motors were required to swing the η, φ, and ξ. However, if a multi-axis type piezoelectric motor as in the present invention is used, rotation of minute angles such as η, φ and ξ can be performed with high accuracy by a single motor. Since the multi-axis type piezoelectric motor of FIG. 6 is intended to rotate around the orthogonal X, Y, and Z axes,
The piezoelectric motor elements M1 to M4 are arranged so as to be orthogonal to each other. Of the piezoelectric motor elements M1 to M4, M1 and M
Reference numeral 2 is for pressing and the purpose is to suppress the descending force of the sphere due to the gravity, and normally a standing wave is generated and used.

By implementing the measurement system as described above, the measurement can be completely automated, labor saving, and reliable measurement can be performed.

The present invention is not limited to the above-mentioned one embodiment.
For example, in the above-described embodiment, an example in which the present invention is applied to a robot joint motor is shown, but it can be used as other mechanical actuators. Of course, various modifications can be made without departing from the scope of the present invention.

〔The invention's effect〕

According to the present invention, a grain having an opening in a part and a holding part in another part is provided, and a plurality of ring-shaped piezoelectric motor elements are fixed to the inner wall of the grain via an elastic member, An operation of accommodating a sphere in the kernel so that the outer peripheral surface is supported by the plurality of ring-shaped piezoelectric motor elements, and projecting outward from the kernel through the opening in a part of the surface of the sphere. Since the portion is provided, the sphere as the rotor can be rotated in any direction and the operation portion can be directed in a desired direction only by controlling the voltage applied to the plurality of ring-shaped piezoelectric motor elements. Therefore, the tilt angle of the rotation axis of the rotor can be changed, which is preferable as a motor used for robot joints,
For example, it is possible to provide a multi-axis type piezoelectric motor that allows a robot to perform a flexible operation with a minimum number of joints and is expected to have high positioning accuracy, high speed, low power consumption, and high reliability.

[Brief description of drawings]

1 (a) (b) to 3 (a) (b) are structural conceptual diagrams of the piezoelectric motor of the present invention. 4 and 5 are side views and partial sectional views showing an embodiment of the present invention, and FIGS. 6 and 7 are application examples in which the multi-axis piezoelectric motor of the embodiment is used as a joint of a measuring robot. FIG. 10 ... Kernel, 11 ... Opening part, 12 ... Holding part, 13 ... Sphere, 14 ... Shaft (operation part), 15 ... Elastic member, 16
... Piezoelectric ceramics, 17 ... Ring-shaped metal plate, 21 ... Reflector, 22 ... Ultrasonic probe.

Claims (2)

[Claims] 1. A kernel that has an opening in one part and a holder in another part, and a plurality of ring-shaped piezoelectric motor elements fixed to the inner wall of this kernel via an elastic member, and these. A sphere housed in the kernel so that the outer peripheral surface is supported by a plurality of ring-shaped piezoelectric motor elements, and provided on a part of the surface of the sphere and protruding from the opening to the outside of the kernel A multi-axis type piezoelectric motor comprising an operation section. 2. A plurality of ring-shaped piezoelectric motor elements are applied with a voltage with a phase difference set so that one is driven by a traveling wave and the other is driven by a standing wave. The multi-axis type piezoelectric motor according to claim 1.