Vibration motors

Details Vibration motors Vibration motors

1999-08-12

2001-03-20

Ramirez, Nestor (Department: 2834)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S317000, C310S323020, C310S328000

Reexamination Certificate

active

06204590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns vibration motors.
2. Description of the Prior Art
Vibration motors are also known as ultrasound motors, referring to their preferred frequency, or piezo-active motors, referring to their preferred excitation material.
Several vibration motor structures having a high power to weight ratio combined with the ability to generate much higher mechanical powers than prior art vibration motors have already been proposed. See, for example, French patent applications 95-14.1169 and 97-10.948.
One particularly advantageous application of these motors concerns secondary flight controls in aircraft.
An aim of the invention is to propose improvements to vibration motors and in particular to optimize the efficiency of these motors.
Vibration motors conventionally combine tangential vibration modes, which correspond to deformations in directions parallel to the surface of contact between the rotor and the stator, and normal vibration modes, which correspond to deformations in directions normal to the surface of contact between the rotor and the stator.
Vibratory mechanical energy is taken from the tangential vibration modes to be converted into continuous movement (torque and angular speed) by the non-linear friction mechanism. These modes are therefore optimized primarily for efficient energy transfer.
In contrast, the normal vibration modes do not contribute to the final supply of energy. Their role is limited to supplying the oscillation of the rotor-stator contact bearing force needed to convert the tangential oscillatory movement of the stator into continuous tangential movement of the rotor. Consequently, the only loss of energy to which a normal oscillator is subjected is that due to its internal losses.
The tangential oscillators of the motor must be made to operate at their resonant frequency to optimize the main transfer of energy. This is known in itself.
The invention proposes to make the normal oscillators operate at their resonant frequency as well, i.e. to dimension the motor so that the normal and tangential modes have very similar resonant frequencies or even the same resonant frequency.
This minimizes dielectric losses in the active material and also minimizes losses in the electronic circuits feeding it.
SUMMARY OF THE INVENTION
For this reason, the invention proposes a vibration motor including a stator and a rotor and excitation means for deforming said stator in vibratory modes combining tangential vibrations and normal vibrations intended to drive rotation of the rotor, wherein the rotor and the excitation means have dimensions such that the normal and tangential modes have similar resonant frequencies, or even the same resonant frequency, and correspond substantially to the excitation frequency.
However, even with very close manufacturing tolerances, it is not possible to prevent fluctuation of various parameters (dimensions of parts, Young's modulus, density, etc) on which the resonant frequencies of the normal and tangential modes depend, for example because of temperature variations to which the motor may be subjected or because of ageing or wear of the various components of the motor.
For this reason, another aim of the invention is to propose a vibration motor structure that alleviates this drawback and automatically corrects any drift in the difference between the two frequencies, and possibly all or part of fixed differences.
To this end, the vibration motor structure proposed by the invention advantageously includes means for correcting the resonant frequency of the normal mode and/or the tangential mode in operation.
In particular, if the excitation means that generate the normal vibrations include piezo-electric active components, the electrical means driving the active components can be means for modifying the Young's modulus of said active components.
Advantageous examples of the embodiment of such means are described below.
Another object of the invention is to simplify the device for mechanically prestressing the piezo-electric material exciting the normal mode in the case of a motor including in a frame at least two pairs of stator plates which comprise tangential deformation active components, as well as two rotor disks which lie between the plates of both pairs, piezo-electric active members for generating a normal force which lie between the plates of both of the facing pairs, spring means being disposed between said pairs of plates and the frame.
In the solution proposed to this end, the active components for generating a normal force are excited so that the masses on opposite sides of the same rotor disk are in antiphase and the masses on opposite sides of the active component are also in antiphase.
The active components can be dimensioned in this case so as to satisfy the prestressing conditions.
Other features and advantages of the invention will emerge further from the following description. The description is purely illustrative and is not limiting on the invention. It must be read in conjunction with the accompanying drawings.


REFERENCES:
patent: 4608506 (1986-08-01), Tanuma
patent: 4980599 (1990-12-01), Kuwabara et al.
patent: 5783898 (1998-07-01), Wu
patent: 6060816 (2000-05-01), Audren
patent: 0 907 213 (1999-04-01), None

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