JP3192029B2 - Ultrasonic motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic motor, and more particularly, to an ultrasonic motor driven by two electro-mechanical energy conversion elements fixed to an elastic body.

[0002]

2. Description of the Related Art In recent years, an ultrasonic motor has attracted attention as a new motor replacing an electromagnetic motor. This ultrasonic motor has the following advantages over a conventional electromagnetic motor. (1) High thrust at low speed can be obtained without using gears. (2) Large holding force. (3) Long stroke and high resolution. (4) It is quiet. (5) It does not generate magnetic noise and is not affected by the noise.

[0003] Ultrasonic motors having such various advantages can be roughly classified into rotary type and linear type according to the driving method. An example of a linear type ultrasonic motor among these is disclosed in Japanese Patent Application No. 4-321 proposed by the present applicant.
No. 096.

A conventional ultrasonic linear motor will be described below based on Japanese Patent Application No. 4-321096.
In an ultrasonic transducer, two laminated piezoelectric elements are arranged on one end face of a basic elastic body at a portion corresponding to a substantially antinode of secondary resonance bending vibration, and these are sandwiched by a holding elastic body to form the basic elastic body. It is configured to be fixed to the body. An ultrasonic motor is configured by holding such an ultrasonic vibrator by a vibrator holding member so as to adjust the contact pressure with respect to a driven member.

When such an ultrasonic vibrator is operated, an alternating voltage having a phase shifted by 90 degrees or -90 degrees is applied to the two laminated piezoelectric elements, thereby making it possible to obtain primary resonance longitudinal vibration and secondary resonance. The next resonance bending vibration is excited, and the clockwise or counterclockwise ultrasonic elliptical vibration can be excited by the combination thereof. At this time, by appropriately adjusting the dimensions of the ultrasonic vibrator, the primary resonance longitudinal vibration and the secondary resonance bending vibration are excited at substantially the same frequency. Then, the driven member relatively moves rightward or leftward by pressing a sliding member provided at a portion where the ultrasonic elliptical vibration is applied to the driven member.

As described above, the conventional ultrasonic motor is basically driven by making the resonance frequency of the longitudinal vibration substantially equal to the resonance frequency of the bending vibration.

[0007]

However, in the case where the driving is performed with the resonance frequency of the longitudinal vibration and the resonance frequency of the bending vibration substantially coincident as described above, the characteristic curve of the speed with respect to the driving frequency has the maximum speed. Is asymmetric on both sides of the frequency at which the frequency is obtained, and the speed drops sharply on the low frequency side, resulting in a problem that the movable frequency range of the ultrasonic motor becomes very narrow. Accordingly, for example, when the ultrasonic motor is driven in an open loop, the resonance frequency changes according to the temperature fluctuation of the operating environment, and the ultrasonic motor may stop even with a small temperature change. Was.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an ultrasonic motor that has a wide movable range with respect to a driving frequency and operates stably.

[0009]

In order to achieve the above object, an ultrasonic motor according to the present invention comprises an elastic body, two electro-mechanical energy conversion elements fixed to the elastic body, and a pressing force applied to the elastic body. And an ultrasonic wave that drives the driven member by applying an AC voltage to each of the two electro-mechanical energy conversion elements to generate longitudinal vibration and bending vibration in the elastic body. In the motor, the electro-mechanical energy conversion element is configured by a laminated piezoelectric element, and the laminated piezoelectric element is fixed so as to be sandwiched by a part of the elastic body, and the resonance frequency of the bending vibration is vertically increased. Characterized by being lower than the resonance frequency of the vibration, and the resonance frequency of the bending vibration,
The elastic body is characterized by being about 3% lower than the resonance frequency of the longitudinal vibration, and the elastic body has a substantially rectangular parallelepiped basic elastic body partially having a projection, and two auxiliary bodies fixed to the basic elastic body. An elastic body, each of the laminated piezoelectric elements is disposed along a portion of the basic elastic body on which the protrusion is formed, one end of which contacts the protrusion, and the other. The end is fixed in contact with the auxiliary elastic body.

[0010]

By applying an AC voltage to each of the two electro-mechanical energy conversion elements, a longitudinal vibration and a bending vibration having a resonance frequency lower than the resonance frequency of the longitudinal vibration are generated in the elastic body. Drive the member.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show a first embodiment of the present invention. First, the configuration of the ultrasonic transducer will be described with reference to FIG.

The ultrasonic vibrator 2 according to the first embodiment has a structure shown in FIG.
As shown in (1), a laminated piezoelectric element 4 is fixed on an upper part of a basic elastic body 3 by an auxiliary elastic body 6 to constitute a main part thereof.

As shown in FIG. 1A, the basic elastic body 3 is formed of a brass material in a substantially rectangular parallelepiped shape, and projects upward from a central convex portion 3a of the upper end surface thereof. Has been established. The dimensions of this basic elastic body 3 are
Except for a, a prototype having a width of 30 mm and a depth of 4 mm and a height (height indicated by reference numeral H in FIG. 1) in the range of 7.25 mm to 9 mm was prototyped. Also,
The dimensions of the protrusion 3a are, for example, 4 mm in width and 2.5 m in height.
m, depth 4 mm. Further, the basic elastic body 3 includes
A pin 3b made of a stainless steel material having a diameter of 2 mm is driven into the center portion of the basic elastic body in the width direction and at a position 6 mm from the bottom surface by press fitting.

A laminated piezoelectric element 4 is attached to such a basic elastic body 3 so as to sandwich the convex portion 3a from both sides.
It is sandwiched by the auxiliary elastic body 6 formed to 5 mm and 4 mm in depth, and fixed by screws 12.
The laminated piezoelectric element 4 is formed by laminating tens to hundreds of thin plate-shaped piezoelectric elements that have been subjected to electrode treatment. In the first embodiment, a laminated piezoelectric element NLA-2 × 3 × 9 manufactured by Tokin Co., Ltd. is used, and its dimensions are 2 mm × 3.1 mm × 9 mm. Portions other than both ends of the laminated piezoelectric element are covered with an epoxy resin (not shown) with a coating thickness of about 0.5 mm, for example.

Next, a method of assembling the above-described ultrasonic vibrator 2 will be described. First, as shown in FIG. 1, the laminated piezoelectric element 4 is placed on both sides of the convex portion 3a of the basic elastic body 3. And it is held and fixed on the basic elastic body 3 by being sandwiched from both sides by the holding elastic member 6. Although not shown, the basic elastic body 3 has screw taps at two places, and as shown in FIG.
Are fixed to the basic elastic body 3 by fastening two screws 12, and are bonded with an epoxy-based adhesive. At this time, the multi-layer piezoelectric element 4 is held and fixed between the convex portion 3a of the basic elastic body 3 and the holding elastic body 6 in an applied state or under a compressive force.

The laminated piezoelectric element 4 includes the basic elastic body 3
The portion which comes into contact with the convex portion 3a and the holding elastic body 6 is fixed by applying an epoxy adhesive.
The lower surface portion in contact with the basic elastic body 3 is also bonded using an epoxy adhesive. Further, the contact portion between the holding elastic body 6 and the basic elastic body 3 is also joined by an epoxy-based adhesive.

A position (resonant bending vibration) 9 mm from both ends of the surface of the basic elastic body 3 opposite to the surface on which the laminated piezoelectric element 4 is disposed (that is, the surface in contact with the driven member). At a position where the vibration amplitude of the sample has a maximum value), a stainless steel material, for example, SUS440C, having a Vickers hardness of 800
Rectangular parallelepiped sliding member 5 formed by quenching
However, the dimensions are, for example, 3 mm in width, 4 mm in depth, and 1 mm in thickness.

Next, the operation of the ultrasonic transducer 2 will be described. In FIG. 1, electrical terminals connected to the left-side laminated piezoelectric element 4 are denoted by A and G (referred to as A-phase), and electric terminals connected to the right-rear laminated piezoelectric element 4 are denoted by A and G. B and G (referred to as B phase). If the ultrasonic vibrator 2 is formed in the above-described size and shape, the primary resonance longitudinal vibration and the secondary resonance bending vibration can be substantially the same frequency Fr (5
(About 3 kHz to 56 kHz).
As a result of computer analysis of these vibrations using the finite element method, it was found that a resonance longitudinal vibration state as shown in FIG. 2A and a resonance bending vibration state as shown in FIG. 2B were taken. As a result of actual vibration measurement, it was verified that such a vibration state was attained.

First, an A phase having a frequency Fr and an amplitude of 10 Vp-
When the alternating voltage of p is applied and the alternating voltage of the same frequency, the same amplitude and the same phase is applied to the B phase, the primary resonance longitudinal vibration as shown in FIG. 2A is excited.

Next, in the A phase, a frequency Fr and an amplitude of 10 Vp-
When the alternating voltage of p is applied and the alternating voltage of the same frequency, the same amplitude, and the opposite phase is applied to the B phase, the secondary resonance bending vibration as shown in FIG. 2B is excited.

Next, with reference to FIG. 3, an ultrasonic linear motor 1 constituted by using the ultrasonic transducer 2 will be described. As shown in FIG. 3, the ultrasonic vibrator 2 is sandwiched and held by two holding plates 21 via the pins 3b from both sides. That is, a hole 21a having a diameter substantially equal to the diameter of the pin 3b is formed in the holding plate 21, and the pin 3b is engaged with the hole 21a. By holding in this manner, the ultrasonic vibrator 2 has a degree of freedom only for rotation around the pin 3b.

The holding plate 21 has a screw 23 at its upper end.
The linear bush 24 is erected upward on the holding plate fixing member 22. The linear bush 24 is
It moves linearly in the vertical direction along the.

The shaft 25 is erected downward from the lower end surface of the shaft fixing member 26.
6 is fixed to the base 27 by screws 26a. A tap penetrating vertically is cut at a substantially central portion of the shaft fixing member 26, and a pressing screw 28 is screwed into the tap. A pressing spring 29 is interposed between the lower end surface of the screw portion of the pressing screw 28 and the holding plate fixing member 22.

On the other hand, a cross roller guide 30 as a driven member is fixed to the base 27 by a screw 31a at a fixing portion 31 thereof. The cross roller guide 30 has a moving part 32 attached to the fixing part 31, and a sliding member holding part 33 is fixed to the moving part 32 by a screw (not shown). For example, it is configured by bonding a sliding member 34 formed of zirconia ceramics subjected to HIP processing.

The sliding member 34 is provided with a plurality of grooves at regular intervals in a direction perpendicular to the moving direction, the pitch of the grooves being 0.4 mm, and the width of the grooves. Is 0.15 mm and the depth is 0.1 mm.

According to the structure of the pressing mechanism, the pressing force of the ultrasonic vibrator 2 on the sliding member 34 of the cross roller guide 30 can be adjusted by adjusting the pressing screw 28.

Next, the operation of the ultrasonic linear motor 1 according to the first embodiment will be described. As described above, the frequency Fr and the amplitude of 10 V are applied to the A-phase and the B-phase of the ultrasonic vibrator 2.
When an alternating voltage of pp and a phase difference of +90 degrees or −90 degrees is applied, a clockwise or counterclockwise ultrasonic elliptical vibration is generated at the position of the sliding member 5 of the ultrasonic transducer 2. The moving part 32 of the cross roller guide 30
Are driven rightward or leftward, respectively, according to the rotation direction.

In the operation of the ultrasonic linear motor 1 as described above, the dimension indicated by the reference numeral H in FIG. 1, which is the height of the portion of the basic elastic body 3 excluding the convex portion 3a, was variously changed. An ultrasonic transducer 2 was prototyped and its motor characteristics were evaluated. Table 1 shows the results.

[0029]

[Table 1] In Table 1, those indicated by a circle in the motor operation indicate that the motor has operated, and those indicated by a cross indicate that the motor does not operate, or that even when the motor operates, little speed and thrust appear. . From this result, it became clear that the operation would not be performed unless the bending vibration resonance frequency was lower than the longitudinal vibration resonance frequency.

Next, the prototype No. No. 1 to prototype No. FIG. 4 shows the measurement results of the characteristics of the moving speed with respect to the driving frequency of the ultrasonic motor (that is, the operating ultrasonic motor) up to 5. FIG. 4A shows the characteristics when there is no load, and FIG. 4B shows the characteristics when 1.86 N is applied as the load.

By comparing the data shown in FIG. 4 with the data shown in Table 1 above, (1) the frequency at which the maximum speed occurs is almost equal to the resonance frequency of the longitudinal vibration. (2) As the resonance frequency of the bending vibration becomes lower than the resonance frequency of the longitudinal vibration, there is a tendency that the velocity characteristics on both sides of the frequency that generates the maximum velocity become more symmetric. It turns out that. In order to further increase the symmetry on both sides of the frequency at which the maximum velocity is generated, it is desirable to lower the resonance frequency of the bending vibration by about 3% from the resonance frequency of the longitudinal vibration. Is obtained.

According to the first embodiment, the ultrasonic motor whose bending vibration resonance frequency is lower than the longitudinal vibration resonance frequency and whose drive frequency is near the longitudinal vibration resonance frequency is movable with respect to the drive frequency. An ultrasonic motor that has a wide range and has symmetrical speed characteristics on both sides of the frequency of the maximum speed, and can obtain the maximum characteristics in both the thrust and the speed.

FIGS. 5 and 6 show a second embodiment of the present invention. In the second embodiment, the description of the same parts as those in the first embodiment will be omitted, and different points will be mainly described. The ultrasonic vibrator 2 of the second embodiment is different from the first embodiment mainly in that a vibration detecting piezoelectric element 41 is newly bonded to the basic elastic body 3. This detecting piezoelectric element 41
As shown in FIG. 5, is formed of, for example, PZT ceramics having a thickness of 0.3 mm in a belt shape having a length slightly shorter than the length of the basic elastic body 3 in the longitudinal direction, and is polarized in the thickness direction. Then, both surfaces of the detection piezoelectric element 41 are subjected to silver electrode treatment.

The piezoelectric element 41 for detection is provided with a pin 3
It is adhered to almost the upper half of the basic elastic body 3 on the upper side of b and below the laminated piezoelectric element 4 over substantially the entire width. According to such a configuration, when the ultrasonic transducer 2 is vibrating, it is possible to detect only the longitudinal vibration. Further, the lead terminal F
On the other hand, although not shown, a common ground terminal is derived from the basic elastic body 3.

Next, the operation of the second embodiment will be described. According to the method described in the first embodiment, the multilayer piezoelectric element 4
To excite the primary longitudinal vibration. At this time, a substantially sine wave signal proportional to the vibration amplitude was obtained from the lead terminal F.

Similarly, an alternating voltage is applied to the laminated piezoelectric element 4 by the method described in the first embodiment to excite secondary bending vibration. At this time, almost no signal was obtained from the lead terminal F.

Next, an alternating voltage is applied to the laminated piezoelectric element 4 by the method described in the first embodiment to simultaneously excite the primary longitudinal vibration and the secondary bending vibration. At this time, a sinusoidal signal was obtained from the lead terminal F. In this case, the signal from the lead terminal F is considered to be proportional to the primary longitudinal vibration.

When the ultrasonic vibrator 2 is operated in various temperature environments, the resonance frequency changes depending on the temperature of the ultrasonic vibrator. Therefore, in order to keep the vibration state of the vibrator constant, it is necessary to track the frequency. FIG. 6 shows an example of a drive circuit of an ultrasonic motor capable of tracking this frequency. The alternating voltage near the longitudinal vibration frequency Fr output from the oscillator 43 is amplified by an amplifier (abbreviated as Amp in the figure) 47 and applied to the A-phase. At the same time, the phase is shifted by, for example, +90 degrees or -90 degrees through the phase shifter 45, and then amplified by the amplifier 48 and applied to the B phase. The output signal from the lead terminal F is amplified by the amplifier 46, compared with the signal of the oscillator 43 by the comparator 44 as a monitor voltage, and the oscillator 43 is controlled so that the phase difference between them is constant. Adjust the frequency or adjust the oscillation frequency so that the monitor voltage is always maximum.

When an ultrasonic motor as shown in FIG. 3 was operated using an ultrasonic vibrator provided with a drive circuit capable of automatically tracking such a frequency, the speed and thrust were varied over a wide temperature environment. An ultrasonic motor that does not deteriorate was obtained.

According to the second embodiment, the first
The ultrasonic motor has almost the same effect as the embodiment, and performs the motor drive by performing frequency tracking on the resonance frequency of the longitudinal vibration, so that even when the temperature changes, the thrust and speed are less likely to decrease. It can be.

In each of the above embodiments, only the linear type ultrasonic motor has been described. However, the present invention is not limited to this. If the moving body is a rotary body using an ultrasonic vibrator, the present invention is not limited to this. It can also be applied to a rotary ultrasonic motor.

[0042]

As described above, according to the present invention, it is possible to provide an ultrasonic motor having a wide movable range with respect to the driving frequency and operating stably.

[Brief description of the drawings]

FIG. 1 is a perspective view of an ultrasonic transducer according to a first embodiment of the present invention.

FIG. 2 is a diagram showing (A) a resonance longitudinal vibration state and (B) a resonance bending vibration state of the ultrasonic vibrator of the first embodiment.

FIG. 3 is a front view showing an ultrasonic linear motor configured using the ultrasonic transducer of the first embodiment.

FIG. 4 shows an ultrasonic linear motor according to the first embodiment.
(A) When no load is applied, (B) When load is applied,
FIG. 4 is a diagram showing characteristics of speed with respect to frequency of FIG.

FIG. 5 is a front view of an ultrasonic transducer according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a drive circuit of an ultrasonic motor capable of tracking a frequency according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ultrasonic linear motor 2 ... Ultrasonic transducer 3 ... Basic elastic body 4 ... Laminated piezoelectric element 30 ... Cross roller guide 41 ... Piezoelectric element for detection

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-45173 (JP, A) JP-A-3-261385 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02N 2/00

Claims (3)

(57) [Claims] 1. An elastic body, two electro-mechanical energy conversion elements fixed to the elastic body, and a driven member pressed by the elastic body. In an ultrasonic motor that drives the driven member by generating a longitudinal vibration and a bending vibration in the elastic body by applying an AC voltage, the electro-mechanical energy conversion element is configured by a laminated piezoelectric element. An ultrasonic motor, wherein the laminated piezoelectric element is fixed so as to be sandwiched by a part of the elastic body, and a resonance frequency of the bending vibration is lower than a resonance frequency of the longitudinal vibration. 2. The ultrasonic motor according to claim 1, wherein a resonance frequency of the bending vibration is lower than a resonance frequency of the longitudinal vibration by about 3%. 3. The elastic body includes a substantially rectangular parallelepiped basic elastic body partially having a projection, and two auxiliary elastic bodies fixed to the basic elastic body. Is formed with the protrusion in the basic elastic body
2. The ultrasonic motor according to claim 1, wherein the ultrasonic motor is arranged along the portion , one end of which is in contact with the protrusion, and the other end is in contact with and fixed to the auxiliary elastic body.