JPH04109881A - Ultrasonic motor - Google Patents

Abstract

PURPOSE:To suppress a friction loss and improve an efficiency and suppress an internal loss which is created in a moving unit such as a rotor when the moving unit is brought into contact with a driving part by a method wherein a difference between a taper angle and a vibration angle is made to be as small as possible. CONSTITUTION:The possible of the part of a vibrator made of electric material such as metal or plastic where a tapered contact driving part A is provided and the taper angle psi of the contact driving part A are so predetermined as to have a difference between the taper angle psi and a vibration angle alpha sufficiently small. As the friction angle of the tapered contact driving part A is 22 deg. when its friction coefficient is 0.4, depending on the shape of a rotor, a slip along a direction within the tapered surface can be almost suppressed if ¦psi-2¦ is not larger than 22 deg.. Therefore, although ¦psi-2¦ is not larger than 1-2 deg. in the present embodiment, it may be about 20-30 deg. practically. Naturally, if a slip caused by an external disturbance and the influences of errors in processes and assemblies are taken into consideration, the smaller ¦psi-2¦, the better.

Description

Detailed Description of the Invention [Industrial Application Fields] The present invention vibrates an elastic body as a rod-shaped vibrator by supplying electrical energy to an electric-mechanical energy conversion element provided on the rod-shaped elastic body. The present invention relates to an ultrasonic motor that generates circular or elliptical motion in the mass point of a vibrator and frictionally drives a moving body pressed against the vibrator, and is particularly suitable for optical equipment such as cameras and office equipment such as printers. .

[Prior art] Conventional ultrasonic motors have been of the type that causes bending vibrations in an annular elastic body and uses frictional force to drive a moving body for driving a lens, but these motors have not been put to practical use in AF mechanisms for cameras, etc. There is. However, since this conventional type is ring-shaped, it cannot be used as a unit including a pressurizing mechanism.
It is relatively expensive and is disadvantageous in terms of cost for motor applications that do not require a hollow space. Therefore, a type of motor as shown in FIGS. 2 and 3 has been proposed in recent years, which is a solid type and has an easy configuration such as a pressurizing system.

Here, the proposed motor will be briefly explained using FIGS. 2 to 4.

Fig. 2 is an external view of a rod-shaped ultrasonic motor, Fig. 3 is a sectional view of the central part of the motor shown in Fig. 2, and Fig. 4 is a diagram schematically showing the vibration state of the vibrating body of the motor shown in Fig. 2. show. Furthermore, the γ direction in FIG. 4 refers to the Z direction (vibrating body a) shown in FIG.
, b axis), and the γ-Z plane refers to a plane formed by the γ direction and the Z direction. The rod-shaped ultrasonic motor as shown in the second figure has a hollow metal upper vibrating body a and a hollow metal lower vibrating body.
Two hollow disk-shaped piezoelectric elements (PZT) are inserted, and threaded portions aa are provided on the inner periphery of each of the upper vibrating body a and the lower vibrating body.

bb are provided, and the piezoelectric element C is held between the bolts e by screwing them into the respective threaded portions (aa, bb).

[Problems to be Solved by the Invention] However, in such a motor, the vibration angle in the γ-Z plane of a point in the tapered contact drive section A provided on the vibrating body (due to the direction of vibration that occurs when the motor operates) angle)
(see FIG. 5) and the taper angle ψ of the tapered contact drive portion A (see FIG. 5) were quite apart. That is, the vibration direction of the tapered contact drive section A is not perpendicular to the surface (tapered surface) formed by the tapered contact drive section A. For this reason,
The vibration displacement fb of the tapered surface includes a component d parallel to the tapered surface in addition to a component c perpendicular to the tapered surface.

This component d causes sliding friction on the rotor f, which may increase sliding loss and reduce efficiency.

Also, due to this frictional force, the rotor f near the contact drive part A
was deformed in the in-plane direction of the taper, resulting in unnecessary internal loss.

Note that f is a hollow rotor having a protrusion ff that contacts the vibrating body a, and h is a pressure member that frictionally engages the rotor f with the vibrating body a via a bearing g by a spring i.

[Means for solving the problem (and operation)] The present invention aims to solve the problem, and in order to solve the problem,
It consists in reducing the difference between the taper angle ψ and the vibration angle α.

When the difference between the taper angle φ and the vibration angle α is small, the vibrating body a
, the component d of b (see Figure 5) is small (becomes).

Therefore, slippage in the component element d direction within the tapered surface is less likely to occur between the rotor and the vibrating body (stator), reducing sliding loss and improving efficiency.

Figure 1 shows a vibrating body a of a rod-shaped ultrasonic motor to which the present invention is applied.
, b, the arrows indicate the vibration displacement at each point of the vibrating body during operation. The other constituent elements of the motor shown in the first figure are the same as those of the motor shown in FIGS. 2 and 3, so their explanation will be omitted here.

In the first embodiment, the difference between the taper angle ψ (see FIG. 1) and the vibration angle α in the tapered contact drive portion A provided in a part of the vibrating body made of an elastic body such as metal or plastic is sufficiently small. (The position and taper angle of the contact drive part A are set so that If 1ψ−21 is less than 22°, then
Sliding in the inward direction of the tapered surface can be suppressed.

Therefore, in this embodiment, 1ψ-21 is set to 1 to 2 degrees or less, but in practice, it is considered that a range of about 20 to 30 degrees is allowed. Of course, it is considered that the smaller 1ψ-21 is, the better, considering the effects of slippage due to external disturbances and processing/assembly errors.

[Other Embodiments] Figures 6 to 9 are front views of main parts of the vibrating bodies a and b of an ultrasonic motor according to other embodiments of the present invention, and the arrow fb indicates the point when the motor is in operation, as in the first figure. FC indicates the vibration displacement at each point of the vibrating body, and FC indicates the position of the node of vibration generated in each vibrating body a, b, that is, the position on the vibrating body where the vibration direction changes, and C indicates the same as in the first embodiment. , a piezoelectric element as an electromechanical energy conversion element.

These two piezoelectric elements have the same configuration as the piezoelectric element of the second illustrated motor described above, and are each polarized to (+) and (-) across the center line of the annular piezoelectric element. They are laminated with a positional phase difference of 90°. Then, electric signals having a phase difference (usually a phase difference of 90°) are applied to each of these two piezoelectric elements from a drive circuit (not shown), thereby causing the vibrating body a.

Vibration is excited in a plurality of different planes in b and has a predetermined phase difference in time, and as a result, vibrations in the vibrating body a
, b perform circular or elliptical motion.

FIG. 6 shows an example in which the tapered contact drive portion A is located near the antinode position of the vibration where the vibration angle α is relatively small.

Further, FIG. 7 shows an example in which the contact drive section A is set near the node position in vibration where the vibration angle α is around 90'', and FIG. In the example of part A, Fig. 9, the vibration angle α is 90.
Examples are shown in which the contact drive portion A is located near the antinode position of the vibration between 180° and 180°. Of course, in these embodiments as well, the vibration angle α and taper angle ψ of each vibration are designed to be sufficiently close values.

Further, since the other components of the motor are the same as those in the first embodiment, their explanation will be omitted.

[Effects of the Invention] As explained above, the present invention allows the vibration angle and the taper angle of the tapered contact drive section to substantially match, in other words, the direction of vibration in the drive section and the direction of the tapered surface of the drive section. Since they are substantially the same, the present invention has various advantages in that sliding loss is small, efficiency is high, and when a moving body such as a rotor is brought into contact with the drive section, internal loss occurring in the moving body is reduced. It is effective.

In the above embodiment, the vibrating body is fixed and the rotor side is moved, but this may be reversed.

[Brief explanation of drawings]

FIG. 1 is a front view of a main part of a vibrating body of an embodiment of an ultrasonic motor to which the present invention is applied, FIG. 2 is an external view of a conventional ultrasonic motor, and FIG. 3 is a sectional view of the motor shown in the second figure. Figure 4 is a diagram schematically showing the mass points on the vibrating body surface of the motor shown in the second diagram from each direction, Figure 5 is a diagram schematically showing the vibration state of the motor shown in the second diagram, and Figures 6 to 9 are the main FIG. 7 is a front view of main parts of another embodiment of the invention. In the figure, A...Tapered contact drive section, a, bl.

Claims (1)

[Claims] (1) Excite vibrations in a plurality of different planes of the elastic body by applying an electric signal to an electro-mechanical energy converting element provided on a rod-shaped elastic body, and add a predetermined time to each vibration. In an ultrasonic motor that generates rotational motion on the surface of the elastic body by providing a phase difference and frictionally drives a moving body that is pressure-engaged with a tapered contact drive portion of the elastic body, vibrations in the drive portion are reduced. An ultrasonic motor characterized in that the direction of vibration and the direction of the tapered surface of the drive section are substantially perpendicular.