Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Patent
1998-12-15
2000-11-14
Budd, Mark O.
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
H01L 4108
Patent
active
061474363
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a piezoactive motor equipped with one or more stator modules designed to vibrate to cause relative movement of a driven part over a large travel according to a dynamic operating mode, and possibly step by step operation by means of drive means by friction, said stator modules, by deforming, in addition enabling fine positioning of the driven part according to a direct actuator operating mode, each stator module comprising at least: so as to deform and produce small longitudinal movements, are applied, said element being formed by a ring shaped as a shell and made of a deformable flexible material, surrounding each pair of actuators by fixing at two opposite points.
STATE OF THE ART
The document EP-A-313,072 A1 describes a piezoactive motor using a dynamic operation, whose stator is formed by a head animated by one or two piezoactive actuators whose direction of actuation is inclined at an oblique angle with respect to the direction of movement of the driven part. It requires a particular driving configuration suitable for driving pliable and flexible objects such as sheets of paper and based on a roller whose friction coefficient with respect to the driven part is lower than that of the head with respect to the driven part.
A major drawback of this stator is to cause flexion of the piezoactive actuators at the same time as their extension. Such a flexion is detrimental on account of the stress limits of the active materials and reduces the power performances of the motor. Another drawback is to require a particular driving configuration which considerably limits the field of application of the motor. Finally, the absence of any decoupling between the stator and frame results in vibrations on the frame which disturb its operation.
The document EP-A-313,072 A1 also describes a process which consists in performing fine positioning by means of operation as a direct actuator after rough positioning has been performed by means of dynamic high frequency operation. Direct actuator operation involves a movement which must be able to be in two directions, which leads to constraints on the electronics which are penalising in terms of cost. The piezoelectric actuator(s) must be able to be deformed in elongation and in contraction. However in practice, this contraction is much smaller than the elongation because of the coercive field limit, which limits the micro-positioning travel. Furthermore, it is not possible in this known process to make use of step by step operation, useful for a rough positioning approach, in order to make a subsequent saving in consumption in direct actuator operation.
The document U.S. Pat. No. 5,424,597 describes a piezoactive motor using a step by step operation, whose stator is based on two parallel piezoactive arms, each being formed by a translator and a monitoring element and using links with flexible pivots. This motor operates by making a first arm establish a connection with the driven part by gripping, while the second arm moves and establishes a connection point a little further on before the first arm moves in turn, and so on. This step by step operation is possible in quasi-static manner, that is to say according to cycles whose frequency is low, from 50 to 100 Hz, and results in a maximum speed equal to 1 mm/s.
A major drawback of this motor is not to be able to use a dynamic operating mode because of the necessary overlap times and of the vibrations which would be transmitted to the frame, which limits its speed and efficiency.
The document FR-A-2,564,912 describes a piezoactive motor composed of two colinear piezoactive actuators and a mechanical coupler in the form of an elliptical annular shell. The shell receives the vibrations produced by the actuators via heads, which generates at its peak movements with an elliptical trajectory. The figure presenting the principle of the stator shows that the rear of the actuators is fixed to a stationary frame. According to this principle, the document describes in detail numerous
REFERENCES:
patent: 4950135 (1990-08-01), Tojo et al.
patent: 5424597 (1995-06-01), Gloss et al.
Patent Abstracts of Japan, vol. 009, No. 325 (E-368), Dec. 20, 1985, Publication No. JP-A-60156283.
Patent Abstracts of Japan, vol. 12, No. 254 (E-634), Jul. 16, 1988, Publication No. 63039478.
Claeyssen Frank
Le Letty Ronan
Lhermet Nicolas
Budd Mark O.
Cedrat-Recherche
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