JPH01264576A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To stabilize an operation by reducing a friction coefficient between a rotor and a stator. CONSTITUTION:An ultrasonic motor 1 is composed of a stator 2 and a rotor 3, and has a motor support section 2B, an elastic body 2C, etc. A friction coefficient mu generating no hysteresis phenomenon in the resonance characteristic curve K11 of the motor 1 is selected. The friction coefficient is selected in mu<mu0(=0.25). The motor 1 under such conditions does not conduct behavior in which the hysteresis phenomenon is generated in the resonance characteristic curve K11 when the frequency (f) of a driving power is changed from lower limit frequency fMIN to upper limit frequency fMAX.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an ultrasonic motor, and particularly to one that is capable of stable rotational operation.

[Summary of the invention]

The present invention can further stabilize the operation of an ultrasonic motor by selecting the coefficient of friction between the rotor and stator to a value small enough to prevent hysteresis.

[Conventional technology]

A conventional ultrasonic motor having the configuration shown in FIG. 8 has been used. In FIG. 8, I indicates an ultrasonic motor as a whole, and has a stator 2 and a rotor 3.

The annular stator fixing part 2A of the stator 2 is attached to an external base (
(not shown), and an annular elastic body 2C is coaxially supported with respect to the stator fixing part 2A via a flexible stator support part 2B.

The elastic body 2C is made of an elastic metal, and is made to vibrate by a piezoelectric body 2D made of a piezoelectric element attached to the inner surface.

A comb-like uneven surface is formed on the surface of the elastic body 2C, and this uneven surface is pressed against the annular rotor base material 3A of the rotor 3 via a slider 3B made of synthetic resin, for example, and the rotor base material 3A
The rotational force is transmitted to the annular rotational output section 3 via the rotor support section 3C.
Communicate to D.

[Problem that the invention seeks to solve]

However, in the conventional ultrasonic motor 1, in order to increase the drive output from the rotor 3, it is considered necessary to make the friction coefficient μ of the rotor 3 with respect to the stator 2 as large as possible. In consideration of the fact that the wear that occurs at the contact portion between the rotor 3 and the stator 2 increases when the distance is increased, measures have been taken to minimize the wear as much as possible.For example, Japanese Patent Laid-Open No. 62-23379
In the case of JP-A No. 62-100178, a configuration is shown in which the driving efficiency is improved by selecting the friction coefficient μ to be approximately μ>0°4.

However, according to experiments, when the friction coefficient μ between the rotor 3 and the stator 2 is increased, a hysteresis phenomenon occurs in the resonance characteristic curve representing the relationship between the drive output of the ultrasonic motor 1 and the frequency f of the drive power source of the ultrasonic motor 1. It has been found that there is a problem in that the ultrasonic motor 1 cannot be driven stably because of this.

In other words, the ultrasonic motor 1 whose friction coefficient μ is selected to be about μ>0.4 is set with the frequency f of the power source set to the lower limit frequency f MIN at which the ultrasonic motor 1 cannot be started, as shown in FIG. Consider the case where the frequency f is gradually increased from .

When the frequency f is f-fMIN, the amplitude lxl is a value IXMIN representing the lower limit operating point PMIN on the resonance characteristic curve Kl.
It has become l.

When increasing the frequency f from this lower limit operating point P MINO, the frequency fA corresponding to the first transition point PA
In order to maintain the amplitude lxl at approximately lxMIN1 until reaching 1, the ultrasonic motor 1 moves on the first characteristic curve portion KIA representing a stopped state, and as a result, the ultrasonic motor 1 cannot be started.

Eventually, when the frequency f exceeds the frequency fA at the first transition point P, the ultrasonic motor 1 starts and jumps to the point PC on the second characteristic curve section KIB, change above.

Here, as the frequency f becomes higher than the frequency fA of the first transition point PA, the ultrasonic motor 1 responds with an amplitude l.
xl gradually becomes smaller, and eventually the upper limit frequency f
Upper limit operating point P of MAX It enters a stopped state at MAX.

However, once the frequency f of the power supply is changed to the upper limit frequency fM'AX
□If you lower the frequency little by little, the amplitude l
As xl gradually increases and becomes lower than the frequency fA of the first transition point PA, the amplitude 1x1 gradually increases.

Eventually, when the frequency f approaches the frequency f8 of the second transition point P, the amplitude lxl rapidly decreases, and when the frequency f becomes lower than the frequency fll, the value of the amplitude 1xl becomes the first
The ultrasonic motor 1 jumps to a point PD on the characteristic curve portion KIA and reaches the minimum amplitude lXMI'Nl, and the ultrasonic motor 1 eventually stops.

In this way, the ultrasonic motor 1 in which the coefficient of friction μ between the rotor 3 and the stator 2 is large is a drive type.

source frequency f from lower limit frequency f MIN to upper limit frequency f
When increasing the frequency f to WAX, the amplitude IXI changes so as to pass through the characteristic curve section of the point Px+s P - PA PCP MAX as shown in Fig. 10, while the frequency f changes from the upper limit frequency f MAX to the lower limit frequency. When lowering to f MIN, point P, □-P, '-7Ps P
Like D PMIN, it exhibits a hysteresis phenomenon in which the amplitude lxl changes through a different characteristic curve portion than when it rises.

By the way, in order to actually drive the ultrasonic motor 1 with as high efficiency as possible, it is necessary to set the driving frequency fn*v such that the amplitude lxl reaches the driving point P DRY close to its maximum value.
It is necessary to set the power supply frequency f to (FIG. 10).

However, if the drive frequency f DRV decreases due to fluctuations in the power supply frequency f for some reason, or if the resonance characteristic curve Kl itself fluctuates due to temperature changes, load fluctuations, etc., the driving point P DIIV will change. If a fluctuation occurs in the drive conditions of the ultrasonic motor 1 that is below the second transition point P, the ultrasonic motor 1 will immediately stop, and even if the fluctuation condition is resolved, the ultrasonic motor 1 will continue to operate. There is a possibility that it will not be possible to return to the current state.

The present invention has been made in consideration of the above points, and aims to propose an ultrasonic motor that can eliminate the possibility of such unstable behavior.

[Means for solving problems]

In order to solve this problem, the present invention includes a stator 2 in which traveling wave vibration is formed on a first contact surface, and a second contact surface that contacts this first contact surface with a predetermined pressing force No. In the ultrasonic motor 1 having a rotor 3, the friction coefficient μ between the first and second contact surfaces is selected to be a small value to the extent that no hysteresis phenomenon occurs in the resonance characteristic curve Kll.

[Effect]

As the friction coefficient μ between the rotor 3 and the stator 2 is decreased, a hysteresis phenomenon does not occur in the resonance characteristic curve of the ultrasonic motor 1.

Therefore, if the friction coefficient μ is selected to be a small value to the extent that the hysteresis phenomenon does not occur, the driving operation of the ultrasonic motor 1 becomes stable with respect to the frequency f of the power source.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

[1] Driving Principle In FIG. 1, in which parts corresponding to those in FIG. 10 are given the same reference numerals, the ultrasonic motor 1 according to the present invention (FIG. 8) does not cause a hysteresis phenomenon in the resonance characteristic curve Kll. Select a friction coefficient μ such that: As the friction coefficient μ that satisfies this condition, μ×μ. (-0, 25).

Under such conditions, the ultrasonic motor 1 changes the frequency f of the drive power source from the lower limit frequency f MIN to the upper limit frequency f MA
When changed up to X, the resonance characteristic curve no longer behaves in a manner that would cause a hysteresis phenomenon.

For example, the ultrasonic motor 1 when the frequency f is increased from the lower limit frequency f MIN to the upper limit frequency f MAX with the friction coefficient μ selected as μ = μ, (-0, 18).
The behavior of is shown in Figure 1 as follows.

That is, the ultrasonic motor 1 has a lower limit frequency f. Frequency f at which activation starts from the lower limit operating point PMIN corresponding to IN
= f, after passing the low output curve portion KIIA corresponding to the stopped state up to the starting operating point P1, the rising curve portion KIIA is maintained until the amplitude lxl reaches the peak point P2 at the frequency f2.
Rise rapidly through IB.

After passing through the peak point P2, the ultrasonic motor 1 passes through the high output curve part KIIC, passes through an operating state where the amplitude lxl slowly decreases while having a value near the peak value, and then the amplitude lxl stops. It reaches the upper limit operating point P MAX on the low output curve section KIID, which has a low value close to the state.

On the other hand, when the frequency f is lowered from the upper limit frequency f WAX to the lower limit frequency f HIM, the ultrasonic motor 1 reaches the upper limit operating point P MA on the low output curve section KI ID.
From X, high output curve part KI IC2 rising curve part KL
It passes through IB sequentially and moves to the lower limit operating point PMIN on the low output curve section KIIA.

In this way, since no hysteresis phenomenon occurs in the resonance characteristic curve 11 of the ultrasonic motor 1, the ultrasonic motor 1
When the motor is in a driving state, it is possible to prevent unstable operation such as instantaneously dropping into a stopped state.

Incidentally, by driving the ultrasonic motor 1 at the driving frequency f DRV, when driving at the driving point P Dl1%l, the driving frequency f DRV fluctuates, or the resonance characteristic curve collapses due to temperature changes or load fluctuations. As a result, even if the driving point PDRV changes and exceeds the peak point P2 and falls to the rising curve section KIIB or the low output curve section KIIA, the resonance characteristic curve K1.1 does not have a hysteresis loop, so that the ultrasonic wave When the operating state of motor 1 returns to its original state, the driving point P DRV changes to the high output curve section KII.
It can be returned to C.

According to experiments, as described above with reference to FIG. 1, the hysteresis phenomenon did not occur in the ultrasonic motor 1 under conditions such that the friction coefficient μ between the rotor 3 and the stator 2 was 0.25 or less. On the other hand, it was confirmed that a hysteresis phenomenon occurs in an ultrasonic motor having a friction coefficient μ greater than that, and that the depth of the hysteresis operation increases as the friction coefficient μ increases.

That is, the resonance characteristic curve Kll in FIG. 1 is for the case where the friction coefficient μ between the rotor 3 and the stator 2 is μ−μm=0.18, whereas the friction coefficient μ is μ=μ, =0.
．． 34, the resonance characteristic curve in Fig. 3 has a value of 1.
As shown in 2, the first and second
It was found that the occurrence of the transition points PAI and FBI caused a hysteresis phenomenon.

Similarly, if the friction coefficient μ is selected to be 0.45, the first and second transition points pAz and P, as shown at 13 in the resonance characteristic curve in FIG. It was found that a hysteresis phenomenon occurred in the operation of the ultrasonic motor 1 due to the occurrence of I□.

However, in the resonance characteristic curve in the case of FIG. 3 where the coefficient of friction is small, the first and second transition points PAL and PR at 12
+ frequency fAI and the frequency deviation Δf between 184, the frequencies fA2 and fB of the first and second transition points pa2 and PIl□ in the resonance characteristic curve K13 of FIG.
The frequency deviation Δf2 between □ is larger, which means that the ultrasonic motor 1 in the case of FIG. 4 has a deeper hysteresis operation.

Incidentally, generally speaking, the resonance characteristic curve in a vibration system tends to draw a curve with good symmetry centered around the peak point P2 in Fig. 1, for example, whereas in the case of Fig. 1, the resonance characteristic curve Rising curve part KI at a frequency lower than point P2
It has a similar curve as if IB were drawn in a direction approaching peak point P2.

This tendency for the rising curve part to be drawn toward the peak point occurs when the friction coefficient μ is made larger than μ-μm (-〇, 25) (i.e., as in the case of Figures 3 and 4). As a result, the friction coefficient μ becomes μ−μ2
(=0.34 (Figure 3)) larger friction coefficient μ−μ
3 (=0.45 (FIG. 4)), the hysteresis operation becomes deeper.

[2] Experimental results (1) First example Sample number 3 in Fig. 2 has a friction coefficient μ = μ. (−〇、
25) is selected, and the elastic body 2C of the stator 2
As the slider 3B, stainless steel (for example, 5US304) or Invar material (for example, 42% Ni alloy) is used (the same applies to the following examples). A structure made of molecular material was used.

At this time, no hysteresis phenomenon occurred in the resonance characteristic operation of the ultrasonic motor 1.

(2) Second Example In the example of sample number 4 in Figure 2, the friction coefficient μ is selected as μ-μ, (-0, 18) as described above in Figure 1, and the slider 3B was composed of a polymeric material containing 85% polyamideimide, 12% graphite, and 3% PTFE. In this case, as described above with reference to FIG. 1, no hysteresis phenomenon occurred in the resonance characteristic operation of the ultrasonic motor 1.

(3) Third Embodiment In the case of sample number 5 in Fig. 2, an aluminum alloy surface treated with lubricating alumite is used as the slider 3B, and the friction coefficient μ in this case is μ=0. It was 08. Also in this case, no hysteresis phenomenon occurred in the resonance characteristic operation of the ultrasonic motor 1.

(4) Experimental example in which hysteresis phenomenon occurred In the case of specimen number 2 in Figure 2, the friction coefficient μ was selected to be μ - μg (=0.34) as described above with respect to Figure 3. ,
The slider 3B was made of a polymeric material containing bismaleimide triazine and polyamide.

In this case, as described above with reference to FIG. 3, a hysteresis phenomenon occurred in the operation of the ultrasonic motor 1.

In the case of sample No. 1 in FIG. 2, the friction coefficient μ was selected to be μ−μ3 (=0°45) as described above with reference to FIG. 4, and the slider 3B was made of phenol resin.

In this case, as described above with reference to FIG. 4, a fairly deep hysteresis phenomenon occurred in the operation of the ultrasonic motor 1.

(5) Reference example In the case of the "Reference" column in Figure 2, a material with the composition of sample number 4 is used as the slider 3B, and silicone oil is applied to its surface, and the friction coefficient μ is μ− 0,0
It was 5.

At this time, no hysteresis phenomenon occurred in the operation of the ultrasonic motor 1 (and the output of the rotor 3 did not decrease to such an extent that it could not be put to practical use).

[3] Theoretical consideration Considering the various experimental results as mentioned above, if the friction coefficient μ is increased in order to increase the efficiency of rotational output, as has been done in the past, efficiency will increase and The hysteresis phenomenon that occurs in the operation of the ultrasonic motor tends to become deeper, and there is a risk that the operation of the ultrasonic motor 1 becomes unstable due to the hysteresis phenomenon.
By reducing the friction coefficient μ, it is possible to prevent a hysteresis phenomenon from occurring in the resonance characteristic operation of the ultrasonic motor 1, and the operation of the ultrasonic motor can be further stabilized.

Thus, it was confirmed that the rotational output of the ultrasonic motor 1 did not become so small even though the friction coefficient μ was made small.

Regarding this phenomenon, conventionally, as shown in FIG. 5, the relationship between the friction coefficient μ and the output is expressed as the friction coefficient μ between the elastic body 2C of the stator 2 and the slider 3B, and the so-called static friction coefficient is used as a reference for the rotor base material 3A. On the other hand, it is thought that the frictional state between the elastic body 2C and the slider 3B, which are actually in a vibrating state, behaves in a way that cannot be evaluated by the static friction coefficient. Based on the dynamic friction state, even if the static friction coefficient between the elastic body 2C and the slider 3B is small, the rotor base material 3
This is thought to be due to the fact that the driving force on the A side does not decrease much.

That is, the friction coefficient μ is generally expressed by the following formula. N here. is the elastic body 2C and the slider 3
B is the pressure applied when the rotor 3 is in surface contact in a non-vibrating state, and Fo is the pressure applied when the rotor 3 is in surface contact in a non-vibrating state.
is the force necessary to move.

In this way, when the elastic body 2C and the slider 3B are in a stationary state, it is thought that as the coefficient of friction μ increases, the force F0 increases accordingly. Conventionally, based on this idea, the force F0 is increased by increasing the coefficient of friction μ. Efforts have been made to increase the efficiency of the ultrasonic motor 1.

However, the pressure N is the same. Even if the elastic body 2C is in a vibrating state as in the case of Fig. 6,
A traveling wave is generated in the direction of symbol R in the elastic body 2C, and the □ surface of the comb teeth 2E of the elastic body 2C is the slider 3.
The point SA in contact with the surface of B becomes the seventh point as the traveling wave progresses.
As shown in the figure, it is thought to be rotating on an elliptical orbit.

Therefore, at the contact point SA between the elastic body 2C and the slider 3B, a dynamic frictional state different from the static frictional state described above with reference to FIG. The force F required to move the rotor 3 in the static contact condition of FIG. It is believed that a larger force F1 is required to stop the rotor 3 rotating in the direction of the sign.

For these reasons, it is thought that even if the friction coefficient μ is small, the driving force obtained from the rotor 3 will not become so small.

[4] Other embodiments (1) In the above embodiments, the resonance characteristic curve was expressed using the amplitude lxl of the contact surface of the stator 2 with respect to the frequency f of the power supply, but instead of this, Even if it is expressed using the number of revolutions under no load, the current flowing through the piezoelectric body 2D, the pickup voltage obtained by detecting the traveling wave of the elastic body 2C (Japanese Patent Laid-Open No. 59-204477), etc. The same effects as in the above case can be obtained.

(2) In the above embodiment, the slider 3B is provided on the rotor base material 3A of the rotor 3 as the ultrasonic motor 1, so that the contact surface of the slider 3B is brought into contact with the contact surface of the elastic body 2C. I mentioned the case where
The slider 3B may be omitted and the rotor base material 3A may be brought into direct contact.

〔Effect of the invention〕

As described above, according to the present invention, the coefficient of friction between the rotor and stator is selected to a small value that does not cause hysteresis in the resonance characteristic operation of the ultrasonic motor, thereby making the ultrasonic motor more stable. can be driven to

[Brief explanation of the drawing]

Fig. 1 is a characteristic curve diagram showing the resonance characteristic curve of the ultrasonic motor according to the present invention, Fig. 2 is a chart showing an experimental example, and Figs. 3 and 4 are sample numbers of the experimental examples in Fig. 2. Characteristic curve diagrams showing the resonance characteristic curves in cases 2 and 1, Figures 5 and 6 are cross-sectional views for theoretical examination of the fact that practical rotational output could be obtained even with a small friction coefficient, Figure 7 The figure is a route diagram showing the movement of the comb teeth 2E, Figure 8 is a route sectional view showing the configuration of the ultrasonic motor, and Figures 9 and 10 are characteristic curve diagrams for explaining the problems of the conventional method. . 1... Ultrasonic motor, 2... Stator, 3... Rotor, 2C... Elastic body, 2
E...Comb teeth, 3A...Rotor base material, 3
B...Slider. District District

Claims (1)

[Claims] Ultrasonic waves having a stator in which a traveling wave is formed on a first contact surface, and a rotor having a second contact surface that contacts the first contact surface with a predetermined pressing force. An ultrasonic motor, characterized in that the coefficient of friction between the first and second contact surfaces is selected to be small enough not to cause a hysteresis phenomenon in the resonance characteristic curve.