JPH0519393B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an ultrasonic motor that generates driving force using a piezoelectric body.

BACKGROUND OF THE INVENTION In recent years, ultrasonic motors have attracted attention in which elastic vibrations are excited in a drive body using a piezoelectric material such as piezoelectric ceramic, and the vibrations are used as driving force.

The principle of the ultrasonic motor will be explained below with reference to the drawings.

FIG. 3 shows an example of an ultrasonic motor, in which a piezoelectric driving body 3 is constructed by bonding a circular piezoelectric ceramic 2 to one of the circular surfaces of a circular elastic body 1. 4
is a slider made of wear-resistant material, 5 is an elastic body,
They are pasted together to form a moving body 6. The moving body 6 is in contact with the driving body 3 via the slider 4. When an electric field is applied to the piezoelectric ceramic 2, a traveling wave of bending vibration is excited in the circumferential direction of the driving body 3, thereby driving the moving body 6. Note that the arrow in the figure indicates the direction of rotation of the moving body 6.

FIG. 4 shows an example of the electrode structure of the piezoelectric ceramic 2 used in the ultrasonic motor of FIG. In the figure, nine waves of bending vibration are applied in the circumferential direction. In the same figure, A and B are each 1/2
This is an electrode group consisting of a small area corresponding to a wavelength, and C and D are electrodes with a length of three-quarter wavelength and one-quarter wavelength, respectively. Therefore, there is a phase shift of a quarter wavelength (=90 degrees) between the electrode group A and the electrode group B in the circumferential direction. Adjacent small electrode portions in electrode groups A and B are polarized in mutually opposite directions in the thickness direction. The adhesive surface of the piezoelectric ceramic 2 with the elastic body 1 is the opposite surface to the surface shown in FIG. 4, and the electrodes are solid electrodes. During use, the electrode groups A and B are short-circuited as shown by diagonal lines in FIG. 4, and the solid electrode is used as a common electrode.

The operation of the ultrasonic motor configured as above will be described below. When a voltage V=Vo・sin(ωt) (1) (V: voltage, Vo: instantaneous value of voltage ω: angular frequency, t: time) is applied to the electrode group A of the piezoelectric body 2, the driving body 3 causes bending vibration in the circumferential direction. FIG. 5 is a perspective view of the driving body of the ultrasonic motor shown in FIG. 3 when it is approximated by a straight line. FIG. This shows what happens when voltage is applied.

FIG. 6 is an enlarged depiction of the contact situation between the moving body 6 and the driving body 3. In the electrode group A of the piezoelectric body 2
By applying voltages Vo・sin(ωt) and Vo・cos(ωt) whose phases are shifted by π/2 to the electrode group B, a traveling wave of bending vibration can be created in the circumferential direction of the driving body 3. can. In general, if the amplitude of a traveling wave is ξ, it can be expressed as ξ=ξo・cos(ωt−kx) (2) (ξo: instantaneous value of amplitude, k: wave number, λ: wavelength, x: position). Equation (2) can be rewritten as ξ=ξo・(cos(ωt)・cos(kt) +sin(ωt)・sin(kx)...(3), and equation (3) shows that the traveling wave is π/2 in time. waves cos(ωt) and sin(ωt) that are out of phase by π/2, and cos(kx) and sin(kx) that are positionally out of phase by π/2.
It shows that it can be obtained by the sum of the products of each. From the above explanation, the piezoelectric body 2 has electrode groups A, which are positioned out of phase by π/2 (=λ/4),
B, a traveling wave of bending vibration can be created in the driving body 3 by applying voltages with a phase difference of π/2 to each of the electrode groups.

Figure 6 shows that point A on the surface of the driving body 3 is moving in an ellipse with the long axis 2w and the short axis 2u due to the excitation of the traveling wave, and the moving body 6 placed on the driving body 3 is at the apex of the ellipse. The figure shows how the waves move at a speed of v=ω·u in the opposite direction to the direction of wave travel. That is, the moving body 6 is pressed against the driving body 3 with an arbitrary static pressure, contacts the surface of the driving body 3, and is driven at a speed v in the opposite direction to the direction of wave propagation due to the frictional force between the moving body 6 and the driving body 3. be done. When there is slippage between the two, the velocity will be smaller than v above.

Problem to be solved by the invention The speed v of the moving body 6 is v=ωu∝ωξoh...(4) (ξo: amplitude value of bending vibration h: distance between the neutral surface of the driving body 3 and the contact surface). It is proportional to the amplitude value ξo of the driving body 3 and the distance h. The maximum value of the amplitude value ξo is determined by the allowable strain limit value of the piezoelectric ceramic, and the distance h is determined once the materials and thicknesses of the piezoelectric body 2 and elastic body 1 that constitute the driving body 3 are determined, so that the maximum speed of the moving body 6 is decided,
It is difficult to obtain a larger value than that.

The present invention has been made in view of these points, and an object of the present invention is to provide an ultrasonic motor that has a simple configuration and can move a moving object 6 at a high speed.

Means for solving the problem Avoiding the positions of the two elastic stationary antinodes that constitute the elastic traveling wave excited by the driving body, the number of protrusions that are an integer multiple of 4 per wavelength of the elastic traveling wave is is placed on the contact surface side of the elastic body constituting the drive body 3 with the moving body, and the moving body is pressurized so as to come into contact with the tip of the protrusion.

Effect The speed of the moving object can be increased by increasing the distance between the neutral surface and the contact surface without interfering with the excitation of the two standing waves that make up the elastic traveling wave excited by the moving object. .

Embodiment Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cutaway perspective view of an ultrasonic motor according to an embodiment of the present invention. In the figure, 7 is a protrusion provided on the contact surface side of the elastic body 1 constituting the drive body 3 with the movable body 6, and the movable body 6 comes into pressure contact with the tip of the protrusion 7 via the slider 4. will be placed. When an alternating electric field near the resonant frequency of the driving body 3 is applied to the piezoelectric ceramic 2, a traveling wave of bending vibration is excited in the driving body 3, and the moving body 6 is moved by the protrusion 7.

FIG. 2 is a cross-sectional view of the driving body 3 in FIG. 1 when it is straightened for explanation. In the figure, a sine wave voltage is applied to electrode group A, and a cosine wave voltage is applied to electrode group B.
A wave voltage is applied to the driving body 3, creating standing waves of bending vibrations A' and B' in the figure, respectively. These two standing waves A' and B' are superimposed to form a traveling wave.

The neutral surface when there is no protrusion 7 is located at the position indicated by L in the figure, and the distance between the neutral surface L and the contact surface with the moving object 6 is h. When the projections 7 are provided on the surface of the elastic body 1, the change in the position of the neutral surface is smaller than the change in the distance to the contact surface. The position of the neutral surface after the protrusion 7 is installed is indicated by L', and the distance from the neutral surface to the contact surface is indicated by h'. In other words, piezoelectric ceramic 2
Since the effect of increasing the distance h is greater than the fact that the amplitude ξo at a strain rate within the allowable limit of the piezoelectric ceramic 2 becomes smaller as the distance from the neutral surface becomes longer, a larger speed is obtained from equation (4). You can see what you can get.

The bending rigidity at the protrusion 7 is large;
The bending stiffness is small where there is no . Therefore, if the protrusion 7 comes to the position of the antinode of the two standing waves A' and B' that create the traveling wave of bending vibration, this position is actually difficult to bend, so the position of the antinode of the standing wave changes to a place where it is easy to bend, and it becomes impossible to drive efficiently, which is different from the optimal standing wave position as seen from the electrode position. Therefore, as shown in FIG. 2, efficient driving can be achieved if the protrusion 7 is installed so as not to be located at the antinodes of the standing waves A' and B'. To satisfy this condition, 1
It is also possible to create one or two protrusions per wavelength, but in this case, the lateral component of the traveling wave of the bending vibration of the driving body 3 will not be transmitted steadily to the moving body 6, and the moving speed of the moving body 6 will decrease. On the contrary, it decreases.

Although this embodiment has been described using an annular ultrasonic motor as an example, similar effects can be obtained with other ultrasonic motors that use elastic traveling waves.

Effects of the Invention According to the present invention, it is possible to provide an ultrasonic motor that can obtain a high speed with a simple configuration.

[Brief explanation of the drawing]

Fig. 1 is a cutaway perspective view of an ultrasonic motor according to an embodiment of the present invention, Fig. 2 is a linear model diagram of a driving body in the embodiment of Fig. 1, and Fig. 3 is a conventional annular ultrasonic motor. 4 is a plan view showing the electrode structure of the piezoelectric body used in the ultrasonic motor of FIG. 3, and FIG. 5 is a model diagram showing the vibration state of the driving body of the ultrasonic motor. FIG. 6 is a diagram explaining the principle of an ultrasonic motor. 1... Elastic body, 2... Piezoelectric body, 3... Drive body,
4...Slider, 5...Elastic body, 6...Moving body, 7
...Protrusion.

Claims (1)

[Claims] 1. By exciting an elastic traveling wave in a driving body consisting of an elastic body and a piezoelectric body, which have a projection on the side of the contact surface with the moving body, the driving body is placed in pressure contact on the projection of the driving body. In the ultrasonic motor for moving the moving object, the number of the protrusions is 1 of the traveling waves.
An ultrasonic motor characterized in that the protrusion is arranged at a position that is an integer multiple of 4 per wavelength and is outside the antinode of two elastic standing waves constituting the elastic traveling wave.