JPH04331481A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To realize accurate step driving without requiring an encoder by switching an ultrasonic oscillation generating means for driving and a standing wave oscillation generating means for stopping appropriately through a switching means. CONSTITUTION:An oscillator ultrasonic wave generating means applies a voltage having frequency in ultrasonic range onto an oscillator piezoelectric element 11. Consequently, the oscillator piezoelectric element 11 is excited to rotate a rotor 17 by a quarter of the standing wave oscillation mode wavelength of the rotor 17. A switching means then switches the oscillator ultrasonic wave generating means to a rotor standing wave generating means which thereby applies a standing wave driving voltage onto a rotor piezoelectric element 16. The rotor 17 is then fed so that the positions of pectinated teeth 13 are aligned with reference to a rotor standing wave oscillation node set at half of the standing wave oscillation mode wavelength. According to the invention, the rotor 17 can accurately be driven in step without requiring any encoder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor that frictionally drives a movable body by ultrasonic vibrations using the expansion and contraction motion of a piezoelectric vibrator.

0002

2. Description of the Related Art A conventional standing wave type ultrasonic motor is shown in FIG. FIG. 5 is an example of a structural diagram of an ultrasonic motor. In the figure, a vibrating body 54 has a vibrating body piezoelectric element 51 bonded to its lower surface. A voltage with a frequency in the ultrasonic band is applied to the vibrating piezoelectric element 51, the vibrating piezoelectric element 51 is expanded and contracted, and the vibrating body base 52 to which the vibrating piezoelectric element 51 is bonded is subjected to bending vibration, and the comb teeth 53 The structure is such that the bending vibration is amplified and the rotor 55 is rotated by the frictional force between the rotor 55 and the upper surface of the tip of the comb teeth 53 which are in face-to-face contact with each other.

In this case, rotation control has been performed by controlling the voltage and frequency applied to the vibrating piezoelectric element 51. For example, conventional structures are disclosed in Japanese Patent Application Laid-open No. 107472/1982 and Japanese Patent Application Laid-Open No. 177874/1999.

0004

[Problems to be Solved by the Invention] However, in conventional ultrasonic motors, an encoder is required to read the position of the rotor when performing accurate step drive such as in an analog clock. This is because the ultrasonic motor is driven by friction, so a simple ON/OFF switch will cause variations in the amount of rotor feed. Therefore, when performing accurate step drive, it is necessary to constantly monitor how far the rotor has moved and issue a stop command the moment it reaches the desired position, so an accurate encoder is required. There was an issue.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to realize an ultrasonic motor that performs accurate step drive without using an encoder, in order to solve the conventional problems.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention includes a piezoelectric vibrator bonded to a rotor, a standing wave vibration generating means for applying to the piezoelectric element bonded to the rotor, and further, By providing an ultrasonic vibration generation means for rotating the rotor and a control means for controlling the timing of the standing wave vibration generation means, and switching between the ultrasonic generation means and the standing wave vibration generation means by the control means, The rotor can be driven accurately in steps without an encoder.

[0007]

[Operation] In the ultrasonic motor configured as described above, the rotor rotates while only ultrasonic vibrations for driving the rotor are generated, and the switching means stops the ultrasonic vibration generating means, causing the rotor to rotate. When a voltage is applied by the standing wave vibration generating means to the piezoelectric element joined to the piezoelectric element to cause the entire rotor to vibrate with a standing wave, the standing wave nodes of the rotor undergoing standing wave vibration stop at the vibrating comb portion.

Therefore, by appropriately switching between the ultrasonic vibration generating means for driving and the standing wave vibration generating means for stopping, accurate step driving is possible without an encoder.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. In order to explain the rotor step drive of the ultrasonic motor of the present invention, FIG. 3 is a cross-sectional view showing the shapes of the vibrating body and the rotor in the circumferential direction developed linearly. In FIG. 3, an insulating friction material 320 is bonded to a first surface of a conductive rotor body 35, and a rotor piezoelectric element 36 is further bonded to the opposite surface. The rotor piezoelectric element 36 has a disk shape or an annular shape, and is divided and polarized in the circumferential direction as shown in the developed state in FIG. It is polarized so that 326 electrode patterns (B) joined to the rotor piezoelectric element 36 and a rotor standing wave generating means 350 to the rotor body 35
When more voltage is applied, the rotor 37 will cause the rotor piezoelectric element 36 to
A standing wave oscillates as shown by the dotted line in Fig. 3 using the boundaries of each polarization region as nodes.

[0010] Here, when the comb teeth 33 are near the nodes of standing wave vibration of the rotor 37, the nodes of the standing wave vibrations are as follows.
It was experimentally confirmed that it moves to the comb tooth position and stays there. Here, it is sufficient that the pitch of the nodes of the standing wave vibration of the rotor 37 is equal to the pitch between the comb teeth of the comb teeth 33, or the number of nodes of the standing wave is an integral multiple of the number of comb teeth. .

[0011] From this, the rotor step angle can be set in various ways by variously setting the number of comb teeth of the vibrating body and the vibration mode of the rotor piezoelectric element, and by changing the nodal pitch caused by the vibration of the rotor. FIG. 4 shows an explanatory diagram of the rotor feed angle control method of the present invention. In Figure 4, the horizontal axis is time T
represents. First, a vibrating body piezoelectric element drive signal is applied to the vibrating body piezoelectric element for a time T1, and the rotor is moved by an amount exceeding one-fourth of the standing wave vibration mode wavelength of the rotor standing wave vibration.
In the next section T2, the vibrating body piezoelectric element drive signal is cut off and the rotor piezoelectric element drive signal is input to cause the rotor to vibrate in a standing wave. The rotor is fed so that the comb teeth position coincides with the rotor standing wave vibration node of 1. T3
is the rest period, T4 (T4 = T1 + T2
+T3) is the interval of one step.

[0012] In the above explanation, it is assumed that the rotor standing wave vibration nodes and the comb tooth positions match, but when the vibrating body piezoelectric element drive signal is applied, the rotor standing wave vibration nodes and the comb tooth positions do not match. It is also possible that there is none. To prevent this, consider inputting the rotor piezoelectric element drive signal immediately before applying the vibrating body piezoelectric element drive signal, aligning the rotor standing wave vibration node and the comb tooth position, and then applying the vibrating body piezoelectric element drive signal. It will be done. Furthermore, it is more reliable to input the rotor piezoelectric element drive signal immediately before applying the vibrator piezoelectric element drive signal for each step so that the rotor standing wave vibration node and the comb tooth position match.

FIG. 2 shows a functional block diagram of the present invention. In FIG. 2, a voltage having a frequency in the ultrasonic band is applied to the vibrating piezoelectric element 21 from the vibrating ultrasonic wave generating means 251, the vibrating piezoelectric element 21 is excited, and the rotor is vibrated by standing wave vibration of the rotor standing wave vibration. Rotate by an amount exceeding 1/4 of the mode wavelength. The drive signal for the vibrating piezoelectric element 21 can be either a standing wave or a traveling wave. Next, the switching means 25 consisting of the clock circuit 23, the switching timing storage circuit 22, and the selection circuit 24 switches between the vibrating body ultrasonic wave generation means 251 and the rotor standing wave generation means 250, and from the rotor standing wave generation means 250, A standing wave driving voltage is applied to the rotor piezoelectric element 26, and the rotor is moved so that the comb teeth position coincides with the rotor standing wave vibration node of one half of the standing wave vibration mode wavelength of the rotor standing wave vibration. do.

T1, T2, and T3 explained in FIG. 4 are stored in the switching timing storage circuit 22. T1, T2, and T3 are measured by the operation of the timing circuit 23,
By operating the selection circuit 24, a drive voltage is supplied to the vibrating body piezoelectric element 21 or the rotor piezoelectric element 26. FIG. 1 is a sectional view showing an embodiment of the present invention. Figure 1
, a support pin 19 is driven into a fixed base 18, and a vibrating body piezoelectric element 11 having an electrode pattern (1) formed on the lower surface is attached to a vibrating body 14 formed by a vibrating body base 12 and comb teeth 13. The fixed vibrating body 14 is driven into the support pin 19. Further, the rotor 17 has an insulating friction material 120 bonded to the lower surface thereof, and the convex portion 119 has 11
An electrode pattern (2) is formed on the upper surface of the rotor body 15 into which lead springs B of 4 are press-fitted, and a piezoelectric element 16 to which lead springs A of 113 are fixed is fixed to the electrode pattern (2). Furthermore, a bearing 111 is integrally fixed to the rotor body 15. This rotor 1
7 is attached as shown in FIG. 1 using the support pin 19 as a guide.

Next, using the support pin 19 as a guide, the spring receiving member 110, the pressure spring 117, and 115 lead patterns A and 116 are connected to the upper and lower surfaces by through holes.
A contact board 112 having a lead pattern B of
Fix with set screw 118. The vibrating ultrasonic wave generating means 2 shown in FIG.
51, the rotor standing wave generating means 250 and the switching means 25 apply the rotor piezoelectric element drive signal and the vibrating body piezoelectric element drive signal using the control method explained in FIG. 4, thereby achieving accurate step drive.

[0016]

As described above, the present invention provides vibrating body ultrasonic wave generation means for rotating a rotor, rotor standing wave generation means for correcting the position of the rotor, and the vibrating body ultrasonic wave generation means for correcting the position of the rotor. By controlling the generating means by the switching means, there is an effect that the rotor can be accurately driven in steps without an encoder.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a functional block diagram of the present invention.

FIG. 3 is a sectional view illustrating the rotor step drive of the present invention.

FIG. 4 is an explanatory diagram of the rotor feed angle control method of the present invention.

FIG. 5 is a cross-sectional view of a conventional ultrasonic motor structure.

[Explanation of symbols]

11 Vibrating piezoelectric element 12 Vibrating body base 13 Comb teeth 14 Vibrating body 15 Rotor body 16 Rotor piezoelectric element 17 Rotor 19 Support pin 110 Spring receiving member 111 Bearing 117 Pressure spring 118 Set screw 25 Switching means 250 Rotor standing wave generation means 251 Vibrating body ultrasonic generation means

Claims (2)

[Claims] 1. A vibrating body ultrasonic wave generating means for supplying a voltage for generating a standing wave or a traveling wave to a vibrating body piezoelectric element fixed to a vibrating body base, and a vibrating body ultrasonic wave generating means that supplies a voltage for generating a standing wave or a traveling wave to a vibrating body piezoelectric element fixed to a vibrating body base; a vibrating body with a plurality of comb teeth formed on the other surface;
A rotor with a rotor piezoelectric element fixed on a first surface, the other surface of which is in contact with the comb teeth, and a rotor in which the rotor piezoelectric element is in contact with the comb teeth of the rotor and the rotor is fixed such that the contact part of the rotor comb teeth becomes a node of a standing wave. rotor standing wave generating means for supplying voltage for generating waves; switching means for switching between driving the vibrating body ultrasonic wave generating means and the rotor standing wave generating means; and pressurizing the rotor against the vibrating body. An ultrasonic motor characterized in that it has means. 2. A ball bearing in which an outer ring is fixed to a rotor and an inner ring is assembled in a supporting member, a spring bearing member integrated with the supporting member, and a spring member that pressurizes the inner ring and the spring bearing member. An ultrasonic motor comprising: