Electrostatic motor

Details Electrostatic motor Electrostatic motor

1997-07-01

1999-10-12

Dougherty, Thomas M.

Electrical generator or motor structure

Non-dynamoelectric

Charge accumulating

310309, H02N 100

Patent

active

059659688

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention generally relates to an electrostatic motor and to its method of production. The motor of the invention can have a size of the order of a centimeter or a micrometer. Hence, the invention relates also to micromotors, that is to say motors which, because of their size, are likely to be produced according to the techniques of microelectronics. The electrostatic motors of the invention can find numerous applications in the fields of integrated optics to carry out, for example a scanning of laser beams, in medical fields, to produce, for example, microscalpels, in the field of the automobile and in a more general way for any application where movement of a small load or a microscopic load is necessary.


PRIOR ART

Motors or micromotors are usually classified either in relation to the nature of the movement that they bring about, or in relation to the physical principles that they involve.
Hence, distinction can be made between, for example, rotary micromotors and linear micromotors. Rotary micromotors are essentially made up of a fixed part that is called a stator and a rotary part in relation to the fixed part, called a rotor. Linear micromotors also comprise a moving part and a fixed part. Also, by extension, in the rest of this description, rotor will designate both the moving part of a rotary motor and that of a linear motor and stator the fixed part equally for the rotary motor and for the linear motor.
Micromotors are able to function by involving different physical principles. Hence, distinction can be made, for example, between micromotors of the electrostatic type, micromotors of the electromagnetic type and micromotors of the piezoelectric type.
In a micromotor, or an electrostatic motor, putting the rotor into motion uses electrostatic forces linked to the accumulation of charges in electrodes. Capacitive forces result from this which tend to bring together conductive plates or electrodes subjected to a difference of potential. For example, in a linear electrostatic motor, the rotor and the stator each include a series of electrodes. The electrodes of each series, that is to say that of the stator and that of the rotor are arranged periodically with a different step. The application of a voltage thereby induces a displacement of the rotor with respect to the stator.
Among the electrostatic micromotors, three categories may be distinguished mainly. A first category includes motors called "side drive motors". These motors utilise the tangential electrostatic forces on the electrodes to drive the motor. These electrostatic forces tend to align the electrodes of the rotor and of the stator. The rotor propelled by these forces rotates about a central axis. These motors permit very high rotational speeds. On the contrary, the torque of these motors and their performance are very poor, essentially because of the useful capacitive surface area of these motors and hence the useful forces, which are very small. Furthermore, the radial component of the capacitive forces, that is to say the component of the forces which is of no use for causing the motor to turn is clearly greater than the useful tangential component. This radial force induces friction and rapid wear of these motors.
A second category includes micromotors called "top drive motors". This type of motor also uses tangential electrostatic forces, but the useful capacitive surface area is situated above and below the poles of the rotor. The electric energy is stored in an air space formed by the overlapping of the poles of the stator and the rotor. To cause the motor to turn, a three phase excitation, for example, is applied to the rotor which turns around a central axis. As the capacity of this type of motor is greater, this motor can supply an interesting torque; however, vertical forces tend to hold the rotor on the poles of the stator. Hence a high vertical instability of the rotor.
A third category of micromotors includes rotary micromotors called "harmonic" or "wobble" micromotors. This category is distinguished

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