GB2228627A

GB2228627A - Ultrasonic wave linear motor

Info

Publication number: GB2228627A
Application number: GB8926830A
Authority: GB
Inventors: Kazumasa Ohnishi; Koichi Naito; Toru Nakazawa
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1988-12-16
Filing date: 1989-11-28
Publication date: 1990-08-29
Anticipated expiration: 2009-11-28
Also published as: JP2582145B2; GB2228627B; GB8926830D0; JPH02164286A

Abstract

An ultrasonic wave linear motor includes an oscillatory element (3) which oscillates an elastic intermediate member (2) to drive a body such as a rail (1) in a linear direction the direction of oscillation of element 3 being at an angle to the axis of the member 2. The oscillatory element (2) may be forced to drive the oscillatory member (3) at its resonance frequency. <IMAGE>

Description

ULTRASONIC WAVE LINEAR MOTOR This invention relates to an ultrasonic wave linear motor. Such motors are used for obtaining linear displacement by employing the ultrasonic wave oscillation of a piezoelectric element as a drive power supply.

Recently, an ultrasonic wave motor has been developed which uses ultrasonic oscillation of a piezoelectric element made of piezoelectric ceramics as its driving power supply, and which is used as an actuator for various kinds of apparatus. Such an ultrasonic wave motor is of compact size and high torque and, beneficially, has no influence on electromagnetic media etc due to not generating electromagnetic waves.

In such an ultrasonic wave motor, the oscillation of a drive body in its feed direction is arranged to be transmitted to a driven body, by aid of friction, by placing the oscillatory drive body in the vicinity of the driven body. The oscillation of the drive body is in the form of either a slant linear oscillation composed of mutually orthogonal oscillatory components or an elliptical oscillation.

Therefore, the drive body can be classified in three types, that is, an oscillatory piece type, a torsional oscillator type and an advance wave type.

An ultrasonic wave motor of the oscillatory piece type drives in the manner shown in Figure 8, in which a piezoelectric oscillator 11 making longitudinal oscillations and an oscillatory piece 12 attached thereto are set slant to the contact surface of driven body 13 so as to push the driven body 13 in a fixed direction so that high speed operation can be carried out with high conversion efficiency.

An ultrasonic wave motor of the torsional vibrator type is formed in such a manner, as shown in Figure 9 that an elliptical oscillation may be generated, rather than the linear oscillation of the oscillatory piece type, by attaching a torsion coupling element 15 to a piezoelectric oscillator 14.

An advance wave type ultrasonic motor forces a contact surface with a rotor 18 to make an elliptical oscillation by coupling a piezoelectric element 17 to an oscillatory body 16 formed in an annular or disc shape giving a flexural oscillation wave advancing in the circumferential direction to an oscillating body 16 as shown in Figure 10. This motor possesses the merit of resulting in less wear due to having a large contact area.

However, problems are involved with the above-mentioned motors.

Firstly, in the case of an oscillatory piece type ultrasonic wave motor, the oscillation is unstable and the driving direction of a driven body is fixed, because the contact between the oscillatory piece 12 and a driven body 13 is intermittent.

Furthermore, a rotor oscillatory piece 12 involves the problem of severe wear of its tip.

A torsional oscillatory piece type ultrasonic wave motor involves such drawbacks as difficulty, from view of its structure, to control oscillation for feeding and oscillation for controlling friction separately and to require a linear motion conversion mechanism so that it can be used as a linear motor.

An advance wave type ultrasonic wave motor has such drawbacks as requiring a linear conversion mechanism, as stated above, in addition to low efficiency of energy conversion. Also, it can be taken into account, in the case of an advance wave type ultrasonic wave linear motor, that a linear oscillatory body is installed instead of an annular or disc-shaped oscillatory body 16 so as to transmit the oscillation to a driven body by applying the advance wave thereto, but it may involve, in this case, such drawbacks as increasing the energy loss to deteriorate the efficiency because of excitation of advance wave required on the total length of a rail.

According to the present invention there is provided an ultrasonic wave linear motor constituted in such a way that an oscillatory element for making oscillation in a direction crossing the shaft line of an oscillatory member is attached to the oscillatory member made of an elastic body formed in a rod shape and a driven body capable of making free relative movement in a direction crossing the shaft line in relation to the above oscillatory member is arranged to abut the end of the above oscillatory member.

According to the present invention there is further provided a driving process that, the ultrasonic wave linear motor makes linear movement by exciting flexural oscillation and longitudinal oscillation on the above oscillatory member by means of the oscillation of an oscillatory element so that an elliptical oscillation composed of flexural oscillation and longitudinal oscillation may take place on the surface of the oscillatory member in contact with the driven body.

The present invention also provides a process for driving the oscillation frequency of the oscillatory element by means of the resonance frequency of the oscillatory member as the most efficient driving process in terms of energy.

In such an ultrasonic wave linear motor and its driving process, the oscillation of one oscillatory element is divided and transmitted in two components, one of which is parallel to and the other of which is perpendicular to the shaft line in relation to the oscillatory body.

Of these components, the one perpendicular to the shaft line gives flexural oscillation to the oscillatory member and the other one parallel to the shaft gives longitudinal oscillation thereto, resulting in a stationary wave, properly amplified in compliance with the material, configuration and size of the oscillatory member. On the contact surface of the end of the oscillatory member with the driven body, an inclined linear or elliptical oscillation is generated on the front most surface due to mutual phase differences among these oscillations and this oscillation is transmitted to the driven body which abuts one end of the oscillatory member and the driven body or the oscillatory member makes linear movement in one direction.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a perspective view of one embodiment of the present invention: Figure 2 shows a cross sectional view of another embodiment; Figure 3 to Figure 5 show analytical results of the process of oscillation carried out by a simulation; Figure 6 shows a graph of the relationship between the load and speed of an ultrasonic wave linear motor; Figure 7 shows a yet further embodiment; and Figure 8 to Figure 10 show conventional ultrasonic wave linear motors.

Figure 1 shows one embodiment of the present invention, in which a running body 4 composed of a rod shaped oscillatory member 2 and a longitudinal oscillatory element 3 fixed to the top end of the oscillatory member 2 is movably placed on a smooth rail (driven body) 1.

The oscillatory member 2 is formed of an elastic material having proper rigidity and elasticity for which a metal such as aluminium may be used. Alternatively, ceramics or resin etc may be selected as occasion requires. The oscillatory member 2 has a rectangular cross section (square, in the illustrated example). Its bottom edge is formed in a smooth contact surface 5 perpendicularly intersecting the shaft line and its top edge is formed in a slant surface 6 (slant by 45 degrees to the shaft line, in the illustrated example) ascending as advancing in the running direction (direction of rail). Its dimension is determined, as described below, by considering the balancing of a longitudinal oscillation in the axial directon of the oscillatory member 2 caused from excitation by the longitudinal oscillatory element 3 with the flexural oscillation caused from excitation in the direction perpendicularly intersecting the shaft. The longitudinal oscillatory element 3 is fixed to the centre of the slant surface 6 by using a bonding agent. This longitudinal oscillatory element 3 of is a well known type which is formed by stacking piezoelectric ceramics plates, polarized in their thickness direction, while sandwiching electrodes therebetween and applying AC voltage thereon so that it can make longitudinal oscillation.

The oscillatory member 2 in the embodiment illustrated in the figure is made of a raw material such as aluminium and has dimensions 5mm square cross sectional area, and 12.5 mm height. The dimensions of the longitudinal element are 5 mm square cross sectional area, and 9 mm height. It is also allowed to reduce its wear rate so as to attempt smooth running by applying a frictional material consisting of composite material etc belonging to polyimide system on the contact face of the oscillatory member 2 with a rail 1.

An illustrated example relates to the surface of the rail 1 on which a guide groove 7 is formed for regulating the running direction of the running body, but such a guide groove 7 is not necessarily desirable because it increases the friction between the running body 4 and rail 1. In addition, the running body 4 is pressed on the rail 1 by its dead weight, but this press-contact force is not sufficient for this purpose as a rule and is preferably controlled properly in response to a load or the like. Therefore, it may be desireable to install closely aside a mechanism for pressing the running body onto the rail at a prescribed pressure as well as to maintain a constant attitude of the running body in relation to the rail.

One example of this structure A is shown in Figure 2. This structure comprises a supporter 11 for surrounding the running body 4, a vehicle frame 13 provided with a pair of front and rear rollers 12 rolling along the lower surface of a rail 1, and connecting members 15 for connecting the above supporter 11 to the vehicle frame 13 via resilient or elastic members (coil springs) 14. The supporter 11 has a structure including guide arms 18 for holding the posture of the oscillatory member 2 in contact with four walls of the oscillatory member 2 and is also provided with a press-pushing member 20 suspended from the ceiling plate 19 of a box body 16 and press-pushing the oscillatory member 2 from upside so as to hold the running body 4 onto the rail 1 in a fixed posture and support it movably along the rail 1 as well as to protect it.A ball bearing (not shown) is buried in the tip of each guide arm 18 so as to reduce a frictional resistance against the oscillation of the oscillatory member 2.

Also, each connecting member 15 is provided with a nut 22 for adjusting the position of the spring receiver 21 of the coil spring 14, so that the contact surface 5 of the oscillatory member 2 may be press-pushed onto the rail 1 under a fixed pressure by adjusting the energizing power of the coil spring 14 by turning the nut 22.

The action of an ultrasonic wave linear motor constructed in such a way as described above will now be described, principally based upon the results of FEM (simulation by a computer, using finite element method).

Figure 3 and Figure 4 show the results of simulation obtained by applying AC voltage having a resonance frequency close to that of the oscillatory member 2 to a longitudinal oscillatory element 3.

A synthetic oscillation consisting of a longitudinal oscillation and a flexural oscillation is excited by applying AC voltage of a resonance frequency to the longitudinal oscillatory element 3.

The oscillatory components are taken into account after being separated from each other and the outline thereof shall be described.

The longitudinal oscillation is of an odd number degree with its node in the centre of the oscillatory member 2 and the maximum amplitude on both ends, while the flexural oscillation is of an even number degree with its nodes in positions equal distances away from the centre in opposition directions and its maximum amplitude on both ends.

Figure 3(a) to Figure 3(d) display this process while thin lines in the figures show the original configuration, (a) shows the state of the longitudinal oscillatory element 3 in its most extended state, (b) shows the state of the same element a little contracted from the state shown in item (a), (c) shows its state thereof contracted from its original size, (d) shows its most contracted state and the element returns from the state (d) to the state (a) and repeats this change of state sequentially. Thereby, since the bottom end makes its lateral oscillation simultaneously with its longitudinal oscillation, the bottom end makes an elliptical oscillation as shown in Figure 4 as a resultant oscillation.

This elliptical oscillation is inclined according to a phase difference between the longitudinal oscillation and the flexural oscillation. Also, different oscillations appear on the bottom end of the oscillatory member 2 and at the same time, the configuration of the oscillation also varies depending upon the oscillatory-frequency of the longitudinal oscillatory element 3. The flatness of the ellipse is determined principally according to the following two points.

1) phase difference between longitudinal oscillation and flexural oscillation 2) amplitude difference between longitudinal oscillation and flexural oscillation, and differences in these phase and amplitude change depending upon parameters such as material, dimensions and configuration of the oscillatory member 2 and the dimensions, configuration, weight, material and oscillatory frequency etc of the longitudinal oscillatory element 3 itself.

Since the modes of the longitudinal oscillation and the flexural oscillation change, resulting in a change of phase difference when the frequency of oscillation is changed, the orientation of the ellipse can be changed. Figure 5 displays the result of simulation with the oscillatory frequency set to 82.0 kHz and it is known that the linear motor advances in opposite direction when the frequency is 92.7 kHz.

With regard to the material of the oscillatory member 2, the larger the modulus of elasticity, the smaller the energy loss, but the displacements by the longitudinal oscillation and flexural oscillation become small. Therefore, the material having the best energy efficiency is selected from general standpoint of view.

Also, in terms of size and configuration, the amplitude of the flexural oscillation increases as the height of the oscillatory member 2 increases, the cross sectional area decreases and becomes flatter in the direction perpendicular to the running direction. Further, the analysis of oscillation is carried out in a structure comprising integrated configuration of the oscillatory member and the oscillatory element.

The relationship between load and speed generated when a driving voltage of 12V, press contact force of 3 kg and load of O to 0.3 kg are applied to a longitudinal oscillatory element 3 of the emodiment shown in Figure 1 is shown in Figure 6.

It was found that the maximum speed and the maximum thrust are 0.4 m/sec and 0.8 kg respectively under no load.

Further, provided that the driving voltage is set to 5.OV between its peak and the press-contact force is set to 0.5 kg, the linear motor runs in the normal direction (toward the bottom side of the longitudinal oscillatory element 3) within a range of frequency from 90.0 to 113.0 kHz and runs in the reverse direction within a range thereof from 85.8 to 87.3 kHz. The resonant frequency of this embodiment was 92.7 kHz as the result of analysis through FEM but the results of measurement on a practical test model by using an impedance analyzer showed 94.7 kHz.

The present invention is not limited to the above-mentioned embodiments but a ratio between a vertical component and a horizontal component of oscillation can be changed by properly setting the slant angle of a slope instead of fixing it to 45 degrees. Also, although the cross section is shown as a rectangle, the length ratio between adjacent sides can be set conveniently and the cross section can be formed in a shape other than a rectangle.

A requirement for an oscillatory member is to have only its local part formed in a rod, eg this oscillatory member has such a structure including an inclined part 26 integrally formed on the top end of a rod part 25 and a longitudinal oscillatory element 3 installed on the upper end of the inclined part.

The purpose of the present invention is to install an oscillatory element which makes oscillation in a direction intersecting the axial line of an oscillatory member, on the oscillatory member formed in an elastic body of a rod shape by using an elastic material, so that a driven body capable of making free movement relative to the above-mentioned oscillatory member in a direction intersecting the axial line may be brought in contact with one end of the above oscillatory member, and also to realize an excellent effect representing the possiblity of an ultrasonic wave linear motor having high efficiency of energy obtained by ultilizing the resonant oscillation of the oscillatory member of a simple structure, by transmitting the ultrasonic wave oscillation of an oscillatory element to the oscillatory member so as to excite elliptical oscillations with enlarged values of amplitude on the end of the oscillatory member.

Claims

1. An ultrasonic wave linear motor wherein an oscillatory element which makes oscillation in a direction for crossing the shaft line of an oscillatory member, is attached to the oscillatory member formed in a rod shaped elastic body and a driven body, capable of making free movement relative to the oscillatory member in the direction intersecting its axial line, is brought in contact with one end of the oscillating member.

2. A process of driving an ultrasonic linear motor wherein an oscillatory element which makes oscillation in a direction for intersecting the shaft line of an oscillatory member is attached to the oscillatory member formed in a rod shaped elastic body and a driven body capable of making free movement relative to the above-mentioned oscillatory member in the direction for intersecting its axial line is brought in contact with one end of the said oscillatory member, and both deflective and longitudinal oscillations are excited on the said oscillatory member by means of the oscillatory element so as to generate an elliptical oscillation produced by combining the deflective oscillation with the longitudinal oscillation on a contact face between the oscillatory member and the driven body.

3. A process of driving an ultrasonic linear motor according to Claim 2, further comprising forcing said oscillatory element to make oscillation at the resonance frequency of the oscillatory member.

4. An ultrasonic wave linear motor substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 7 of the accompanying drawings.

5. A process of driving an ultrasonic linear motor substantially as hereinbefore described with reference to, and as illustrated by, Figures 1 to 7 of the accompanying drawings.