JPH0654561A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To make it possible to position a moving body at a desired position, by changing the amplitude of a standing wave generated in a vibrating body through a plurality of electrical-to-mechanism energy conversion elements. CONSTITUTION:An operation microcomputer 4 issues commands to an oscillator 5 so as to output an AC voltage having a certain frequency. Then, the AC voltage E1 having the certain frequency outputted from the oscillator 5 is applied to a piezoelectric element 3A for A-having driving through a gain controller 7A and an amplifier 8A. Also, the AC voltage E1 is applied to a piezoelectric element 3B for B-phase driving through a phase-shifting circuit 6, a gain controller 7B and an amplifier 8B. The phase-shifting circuit 6 moves a phase shift of the AC voltage E1. Next, the gain controllers 7A and 7B amplify the inputted AC voltage with a gain according to a signal from the microcomputer 4, and output the amplified voltage as AC voltages E3 and E4. Now, in the gain controllers 7A and 7B, an input gain is controlled according to the signal from the microcomputer 4 in order to generate a standing wave at a desired position in a stator 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor used for driving a lens, feeding a paper for a printer, feeding a print head and the like.

[0002]

2. Description of the Related Art There have been proposed many ultrasonic motors for generating traveling waves in a vibrating body and driving a moving body in contact with the vibrating body, and further commercialization has been realized. On the other hand, various types of ultrasonic motors for driving a moving body by using a standing wave include, for example, JP-A-3-261383.
It is proposed in the issue publication.

An example of an ultrasonic motor for driving a moving body using a standing wave will be described below with reference to the drawings.

FIG. 14 is a diagram showing a positional relationship between a vibrating body and a moving body of a conventional ultrasonic motor. In addition, FIG.
FIG. 3 is a diagram showing the polarization directions of respective regions of a two-phase piezoelectric element as a drive source of the ultrasonic motor shown in FIG.

In FIG. 14, 1 is a moving body, and 1a
Is a protrusion provided on the surface side of the moving body 1 in contact with the vibrating body,
Reference numeral 2 is a vibrating body in an excited state. When the vibrating body 2 is excited by the standing wave, a node of the standing wave (N in the figure) shown in the figure is formed in the vibrating body 2. Then, the protrusion 1a of the moving body and the vibrating body 2 contact each other near the node of the standing wave (see FIG. 14), and the moving body 1 is positioned. further,
By moving the node of the excited standing wave, the moving body 1 also moves following the node. Incidentally, in order to excite the vibrating body 2 with a standing wave, the piezoelectric element 3 arranged as shown in FIG. 15 (A) is used. The piezoelectric element 3 is composed of two piezoelectric elements 3A for driving the A phase and 3B for driving the B phase, and the electrodes 3A and 3B are arranged so as to be 90 degrees apart from each other. Similarly to the known voltage element, polarization processing in opposite directions is alternately performed.

Next, details of the known conventional ultrasonic motor driving method will be described. In FIG. 15A, 3A, 3
It shows a state in which an AC signal is simultaneously applied to both piezoelectric elements of B. As a result, the vibrating body 2 is excited by the two combined waves. The dotted line in FIG. 15A is the standing wave generated in the vibrating body 2 when excited by only 3A, the dashed-dotted line is the standing wave when only 3B, and the solid line is the standing wave formed by combining them. . Also, in FIG.
It is a standing wave when only one is driven. Next, FIG.
(C) shows a standing wave that is generated by exciting both 3A and 3B and by the difference in the amplitude of both phases. Then, FIG. 15D shows the standing wave generated in the vibrating body 2 when the AC signal is applied only to 3B. The vibrating body 2 in the order of FIGS. 12 (a), 12 (b), 12 (c), and 12 (d) described above.
When you excite the

[0007]

[Outer 1] The moving body 1 moves step by step, and as a result, the moving body 1 pressed against the vibrating body 2 also moves at the same step as the node position of the standing wave generated in the vibrating body 2 moves. The above is the drive principle of the above-described known ultrasonic motor that drives a moving body using a standing wave.

[0008]

In the conventional ultrasonic motor using the standing wave, when controlling the movement of the moving body,

[0009]

[Outside 2] You can only control each. That is, it is impossible to position the moving body at an arbitrary position and continuously control it. The present invention solves the above problems and provides an ultrasonic motor that can be controlled with higher precision.

[0010]

According to the present invention, a plurality of electro-mechanical energy conversion elements arranged on a vibrating body excite the vibrating body with a standing wave and move a node of the standing wave of the vibrating body. As a result, in an ultrasonic motor that moves a moving body having a protrusion that is in contact with the vibrating body near the node of the standing wave, the standing wave generated in the vibrating body by each of the plurality of electro-mechanical energy conversion elements. By providing a means for changing the amplitude of, the moving body can be positioned at any position.

[0011]

1 is a perspective view of a stator and a rotor of an annular ultrasonic motor according to an example of the present invention. Reference numeral 1 is a rotor and 2 is a stator. The rotor 1 is provided with a convex portion 1a (a black portion in the figure) having twice the number of standing waves generated in the stator 2. Reference numeral 3 is a piezoelectric element attached to the stator 2. FIG. 2 shows a pattern of electrodes of the piezoelectric element 3 attached to the stator 2. The piezoelectric element 3 is composed of two phases, that is, a piezoelectric element 3A that generates an A-phase standing wave and a piezoelectric element 3B that generates a B-phase standing wave, and is similar to a piezoelectric element of a known ultrasonic motor. , The phase generated by each piezoelectric element

[0012]

[Outside 3] They are arranged in a staggered manner. The inside of each phase is divided into regions as shown in the drawing, and the regions are alternately polarized in opposite directions. Further, in the present embodiment, the piezoelectric element 3 is polarized so that seven standing waves are provided all around the stator 2 and the number of electrodes in each phase is determined. The rotor is positioned by bringing the convex portion 1a of the rotor into contact with the node portion of the standing wave generated in the stator 2. The operation will be described below.

FIG. 3 is a block diagram of a circuit for driving the ultrasonic motor of this embodiment shown in FIGS. 3, the same members as those in FIGS. 1 and 2 are designated by the same reference numerals. 4 is an arithmetic microcomputer, 5 is an oscillator, 6 is a phase shifter, 7A and 7B are gain controllers, and 8A and 8B are amplifiers.

Next, the control when the ultrasonic motor of this embodiment is driven by a standing wave will be described.

The arithmetic microcomputer 4 gives a command to the oscillator 5 to output an AC voltage of a certain frequency. The alternating current E ₁ of a certain frequency output from the oscillator 5 is applied to the A-phase driving piezoelectric element 3A via the gain controller 7A and the amplifier 8A. At the same time, the AC voltage E ₁ is applied to the B-phase driving piezoelectric element 3B via the phase shift circuit 6, the gain controller 7B and the amplifier 8B. Phase shift circuit 6
Is a circuit for shifting the phase of the AC voltage E1 (E ₁ =
E ₂ ). Then the gain controller 7A, 7B is for outputting an AC voltage input as an AC voltage E _3, E ₄ are amplified by a gain according to the signal from the microcomputer 4. Here, in order to generate a standing wave at an arbitrary position in the stator 2, the gain controllers 7A and 7B control the input gain according to the following equation according to the signal from the microcomputer 4.

E ₃ = cos (θ) E ₁ E ₄ = sin (θ) E ₂ = sin θE ₁ (E ₁ = E
₂ when the phase shift circuit 6 does not operate) Here, the gains in the gain controllers 7A and 7B are cos (θ) and sin (θ), respectively, and θ is the standing wave to be generated in the stator 2. It is a variable that changes depending on the position. That is, the position of the node of the standing wave generated in the stator 2 can be controlled by controlling θ. Further, since the position of the convex portion of the rotor that is in contact with the node can be positioned, the position of the rotor itself can be controlled. Since E ₁ (= E ₂ ) is an AC voltage, E ₁ = Esin
(Wt) (E: amplitude of AC voltage).
Therefore, the exchange formula in the gain controllers 7A and 7B is as follows.

E ₃ = cos (θ) · Esin (ωt) E ₄ = sin (θ) · Esin (ωt)

Next, the output voltages from the gain controllers 7A and 7B are amplified by the amplifiers 8A and 8B at the same amplitude rate, and the A phase driving piezoelectric elements 3A and 3A, respectively.
It is output to the B-phase driving piezoelectric element 3B. Amplifier 8 here
If the amplification rates of A and 8B are both a, then E _A = a · cos (θ) · Esin (ωt) = cos (θ) · aEsin (ωt) = cos (θ) · C · sin (ωt) E _B = a · sin θ · E sin (ωt) = sin θ · aE sin (ωt) = sin (θ) · C · sin (ωt) (assuming aE = C). 4, 5 and 6 show the driving process when the gain controllers 7A and 7B are appropriately controlled according to the above equation to drive the ultrasonic motor.

FIG. 4 (a) shows θ when θ = −90 °.
= −90 °, the AC voltages E _A and E _B applied to the piezoelectric elements 3A and 3B are: E _A = cos (−90 °) C sin (ωt) = 0 E _B = sin (−90 °) C sin (Ωt) = − Csin (ωt). Therefore, the stator is excited only by the B-phase piezoelectric element, and a standing wave as shown in FIG. Here, one node of the standing wave is N, and the convex portion of the rotor that is in contact with the stator 2 in the vicinity of the node is 1as. Hereinafter, the operation of the present invention will be described while paying attention to the movement of the convex portion 1as. The electric circuit drawn on the right side of FIG. 4 schematically shows the piezoelectric elements 3A and 3B and the voltages E _A and E _B applied thereto.

Next, FIG. 4B shows the case of θ = −60 °.

At θ = −60 °, applied voltages E _A , E
_Each of _B is

[0022]

[Outside 4] Becomes Since the A-phase and the B-phase are displaced by 90 °, the standing waves generated by the respective phases are as shown in the figure (A-phase: see dotted line, B-phase alternate long and short dash line).

The amplitude of the standing wave generated in each phase is proportional to the applied voltages E _A and E _B. In this case, the amplitudes of E _A and E _B are

[0024]

[Outside 5] Therefore, the ratio of the amplitudes of E _A and E _B is

[0025]

[Outside 6] Becomes From the above, the amplitude ratio of the piezoelectric elements A phase and B phase is also

[0026]

[Outside 7] Becomes When such a phase shift is 90 °, the amplitude ratio is

[0027]

[Outside 8] 2 are present in the stator, and as a result, the stator 2 is excited by a composite wave of these two standing waves (solid line in the figure). And in this composite wave, the node N is at the position shown in the figure, that is, θ = -90 °
Move to the right from when. Further, along with this, the convex portion 1as also moves.

Next, FIG. 4C shows the standing waves generated in the vibrating body (stator) and the positions of the convex portions 1as due to each phase when θ = 45 °.

At θ = -45 °, each piezoelectric element 3
The voltages E _A and E _B applied to A and 3B are

[0030]

[Outside 9] Becomes In this case, the ratio of the amplitude of the vibration generated in the stator by the A phase and the B phase is 1: 1. The composite wave of such two-phase vibration is as shown by the solid line in the figure, and N of one node is θ =
It moves further to the right than at -60 °.

Further, FIG. 5A shows the case where θ = −30 °.

At θ = −30 °, the above E _A and E _B
Respectively

[0033]

[Outside 10] Becomes In this case, the amplitude ratio of the A phase and the B phase is √3: 1, the composite wave is as shown by the solid line in the figure, and one node N is θ =
Move further to the right than at -45 °.

Further, FIG. 5B shows the case where θ = 0 °.

At θ = 0 °, E _A and E _B are E _A = cos (0 °) Csin (ωt) = Csin (ωt) E _B = sin (0 °) Csin (ωt) = 0 Therefore, only phase A is excited. One node N moves further to the right than when θ = −30 °.

Further, similarly, the process of sequentially changing θ to θ = 90 ° is shown in FIGS. 5 (c) and 6 (a)-(c). That is, comparing FIG. 4 (a) (θ = −90 °) with FIG. 6 (c) (θ = 90 °), the position of the node N is moved by half a wavelength, and the convex portion 1as is also moved by half. It has moved by the wavelength. By repeating the operation of FIG. 4, the rotor 1 can be further driven. In the case of this embodiment, the electrodes of the piezoelectric elements for driving the A-phase and the B-phase are arranged so that seven wavelengths can be formed around the circumference of the stator.
By repeating the operation of FIG. 6 (c) 14 times, the rotor 1
It can be rotated.

In FIGS. 4, 5 and 6, θ = 0, ± 30 °,
Although shown as ± 45 °, ± 60 °, and ± 90 °, they are not limited to these variables θ. The same control can be performed for any θ, that is, the node position of the stator can be arbitrarily changed by arbitrarily changing the amplitudes of the A phase and the B phase, and the rotor can be positioned at any position. Is.

By thus allowing the standing wave to be generated at a free position, the positional relationship between the stator and the rotor can be determined without using a sensor such as an encoder.

In the present invention, ideally, the resolution can be increased as much as possible. Therefore, an ultrasonic motor with high stopping accuracy can be obtained.

Although the case where the rotor is driven by the standing wave has been described, the traveling wave is used to rotate the rotor as in the case of the conventional traveling wave type ultrasonic motor, and the standing wave is first held when the rotor is stopped at a desired position. The motor may be configured to use waves, and the driving method of the present invention described above may be applied when the standing wave drive is performed. When a traveling wave is to be generated in such a configuration, the phase shift circuit 6 shown in FIG. 3 shifts the phase of the input AC voltage E ₁ and outputs it as an AC signal E _2. Can be generated. Further, when the rotor which is rotating by the traveling wave is stopped at a desired position, in the phase shift circuit 6, the phases of E ₁ and E ₂ are returned to be the same, and the standing wave is generated in the stator. Thereafter, FIG. 4, FIG. 5, and FIG.
Control as follows.

Further, although two sets of piezoelectric elements for exciting the vibrating body (stator) are provided in the present embodiment, the present invention is also applicable when three or more sets of A phase, B phase and C phase are provided. Is applicable.

Next, a second embodiment of the present invention will be described. The first embodiment is an example of the ring type ultrasonic motor,
The present embodiment is an example in which the present invention is applied to a rod-shaped ultrasonic motor as disclosed in JP-A-3-1-11981.

FIG. 7 is a diagram showing a schematic structure of the rod-shaped ultrasonic motor of the second embodiment described above. 9 is a rotor, P,
Q is a convex portion provided on the diagonal line of the substantially circumferential position of the rotor 9. Reference numeral 10 is a stator, 11 is a piezoelectric element group, and 11A in the piezoelectric element group is an A-phase driving piezoelectric element and 11B is a B element.
Piezoelectric elements constituting a phase driving piezoelectric element, each of which is divided into two and polarized to the polarity shown in the figure like the known piezoelectric element (see FIG. 7B). This piezoelectric element 11A, 11B
By applying a voltage to the stator 10, a desired standing wave is generated in the stator 10, and the protrusions P and Q of the rotor are formed at the nodes of the standing wave.
The rotor 9 is positioned by contacting. The elements 11A and 11B are arranged so as to be shifted by 90 ° as shown in the figure, and further, each vibrates in the X and Y directions as shown in the bottom diagram of FIG. 7B. These piezoelectric elements 11A, 1
Each of 1B excites the stator 10 by a standing wave, and as a result, the rotor 9 is excited by the combined wave of the standing waves generated by 11A and 11B. The position of the node of this composite wave can be changed by the ratio of the amplitudes of 11A and 11B. FIG. 8 is a block diagram showing a circuit for performing the control.

The same parts as those in FIGS. 3 and 7 are designated by the same reference numerals. The operation of the circuit is the same as in the case of FIG. 3 of the first embodiment. Here, only the relationship between the gain values in the gain controllers 7A and 7B and the standing wave generated in the stator 10 will be described. A phase of the first embodiment similarly stator, respectively the voltage applied to the B phase _{E A = cos (θ) ·} Csin (ωt) E B = sin (θ) · Csin (ωt) C: the amplitude. cos (θ) and sin (θ) are gains given by the gain controllers 7A and 7B. FIG. 9 is a diagram showing changes in the standing wave with changes in the value of θ. Figure 7
The same parts as in are marked with the same numerals.

FIG. 9A shows the case of θ = 0 °. At θ = 0 °, E _A = C · sin (ωt) E _B = 0. Therefore, the vibrating body (stator) 10 is a piezoelectric element for driving the A phase. A standing wave is generated where the boundary between the positive electrode and the negative electrode of the element is the node. Then, at this time, the convex portion P of the rotor stably stops at the position N where a node is formed, which is the minimum vibration amplitude.

FIG. 9B shows the case of θ = 45 °.

[0047]

[Outside 11] Therefore, the vibrating body 10 generates a standing wave with the center of the portion where the positive electrode of the A-phase driving piezoelectric element and the positive electrode of the B-phase driving piezoelectric element overlap as the antinode. The node portion of this standing wave is deviated from that by 90π / 180 rad, and the convex portion P of the rotor is stabilized there.

FIG. 9 (c) shows the case of θ = 90 ° At θ = 90 °, E _A = 0 E _B = C · sin (ωt) Therefore, the vibrating body 10 is a piezoelectric element for driving the B phase. A standing wave is generated so that the boundary between the positive electrode and the negative electrode becomes a node. Then, at this time, the convex portion P of the rotor stably stops at the node N.

FIG. 9 shows (d) when θ = 135 °. At θ = 135 °

[0050]

[Outside 12] Therefore, in the vibrating body 10, a standing wave is generated with the center of the portion where the positive electrode of the A-phase driving piezoelectric element and the negative electrode of the B-phase driving piezoelectric element overlap. At this time, the node N can be positioned as shown in the figure, and the convex portion P of the rotor is stabilized there.

FIG. 10A shows the case where θ = 180 °.

At θ = 180 °, E _A = C · cos (180 °) sin ωt = −C sin ωt E _B = 0. Therefore, in the stator, the boundary between the positive electrode and the negative electrode of the piezoelectric element for driving the A phase serves as a node. Standing waves are generated. Then, at this time, the convex portion P of the rotor stably stops at the position N where a node is formed, which is the minimum vibration amplitude.

As described above, FIGS. 9 (a) to 9 (c) and 10 (a)
Thus, the rotor 9 has rotated half a turn. Do the same action another 1
By repeating the process once, the rotor makes one revolution.

By thus allowing the standing wave to be generated at any position, the positional relationship between the stator and the rotor can be determined without a sensor such as an encoder.

In addition, FIGS. 9A to 9C and 10A.
As you can understand by focusing on a certain point (P),
The rod-shaped ultrasonic motor 10 can be moved stepwise by sequentially changing θ from 0 to 135π / 180 rad.

Moreover, in the above description, 45π / 180 rad
Although the motor is sent in steps, ideally, the resolution can be increased in the present invention. Therefore, a rod-shaped ultrasonic motor with a high stopping accuracy can be obtained.

FIG. 11 shows a rotor used in the second embodiment and a rotor having another shape.

In FIG. 11 (a), the stator is provided with two steps.
11 (b), the stator hits the stator at two points P in the drawing in a smooth curved shape. With such a shape, it is possible to easily make it by processing in a state of being folded in two.

FIG. 11C shows an example in which a thin sheet-like material is attached to the two friction surfaces of the rotor. This also facilitates processing.

FIG. 11D shows an example in which the friction surface of the rotor is flat, but the hardness of the brim spring is hard in only two places. With this method, the present invention can be carried out without reducing the motor efficiency.

FIG. 12 is an exploded perspective view of the vibrator of the third embodiment of the present invention.

The driving piezoelectric element groups a1, a2 and the electrode plate groups A1, A2, G1, G2, G3 are the same as those in FIG. 7, but in this example, there are two vibration detecting piezoelectric elements. Each of them is divided into one capable of detecting the excited vibration of the piezoelectric element a1 (s1) and one capable of detecting the excited vibration of the piezoelectric element a2 (s2). An insulating sheet d-1 is inserted between s1 and s2 so as not to short-circuit each other. When a standing wave is generated in the vibrating body by using the vibrating bodies a ₁ and a _{2 according} to the second embodiment, the A-phase direction vibration detecting piezoelectric element S1 and the B-phase direction vibration detecting piezoelectric element S2 are The direction of the standing wave can be detected from the output ratio, and by feeding back this, the constant wave can be generated at an accurate position even if there is a difference in the resonance frequency of the A phase and the B phase, the force coefficient, and the like. The formula is shown below. Since the output of each of S1 and S2 is V _S1 = b · cos (θ) · sin (ω + ψ) V _S2 = b · sin (θ) · sin (ω + ψ)

[0063]

[Outside 13] Then, θ can be obtained.

FIG. 13 shows a block diagram of the circuit of the third embodiment. 4 to 8 are the same as those in the first embodiment, and the amplitude and phase difference detector 12 is connected to the rod-shaped ultrasonic motor 13 having two vibration detecting means.

The state of the standing wave is detected from the signal of the detector 12 and feedback is applied.

[0066]

As described above, according to the present invention, it is possible to improve the accuracy of the method of positioning an ultrasonic motor without a sensor such as an encoder. Moreover, it is possible to use this to enable step driving with fine resolution.

[Brief description of drawings]

FIG. 1 is a diagram showing a moving body and a vibrating body of a ring type ultrasonic motor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the vibrating body of FIG.

FIG. 3 is a block diagram of a circuit according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the operation of the ultrasonic motor according to the first embodiment of the present invention.

FIG. 5 is a diagram showing the operation of the ultrasonic motor according to the first embodiment of the present invention.

FIG. 6 is a diagram showing the operation of the ultrasonic motor according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a rod-shaped ultrasonic motor according to a second embodiment of the present invention.

FIG. 8 is a block diagram of a circuit according to a second embodiment of the present invention.

FIG. 9 is a diagram showing the operation of the ultrasonic motor according to the second embodiment of the present invention.

FIG. 10 is a diagram showing an operation of the ultrasonic motor according to the second embodiment of the present invention.

FIG. 11 is another rotor shape of the ultrasonic motor according to the second embodiment of the present invention.

FIG. 12 is an exploded perspective view of a vibrating body according to a third embodiment of the present invention.

FIG. 13 is a block diagram of a circuit according to a third embodiment of the present invention.

FIG. 14 is a diagram showing a moving body and a vibrating body of an ultrasonic motor using a conventional standing wave.

FIG. 15 is a diagram showing an operation of a conventional ultrasonic motor using a standing wave.

[Explanation of symbols]

1 Rotor of ring-shaped ultrasonic motor 2 Stator of ring-shaped ultrasonic motor 3 Piezoelectric element arranged on stator of ring-shaped ultrasonic motor 4 Microcomputer 5 Oscillation circuit 6 Phase shift circuit 7 Gain controller 8 Amplifier 9 Rod-shaped ultrasonic wave Motor rotor 10 Rod-shaped ultrasonic motor stator 11 Rod-shaped ultrasonic motor piezoelectric element 13 Rod-shaped ultrasonic motor having a vibration detection piezoelectric element

Claims (1)

[Claims] 1. A standing wave is excited by a plurality of electric-mechanical energy conversion elements arranged on the vibrating body, and the nodes of the standing wave of the vibrating body are moved to move the standing wave. In the ultrasonic motor for moving a moving body having a protrusion in contact with the vibrating body in the vicinity of the node, a means for varying the amplitude of the standing wave generated in the vibrating body by each of the plurality of electro-mechanical energy conversion elements is provided. An ultrasonic motor characterized by being provided.