Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2000-05-22
2001-09-04
Ponomarenko, Nicholas (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06285115
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to piezoelectric devices and, more particularly, to an apparatus and method for accurately controlling movement of a piezoelectric device.
BACKGROUND ART
Piezoelectric devices alter their shape in response to an applied electric field. An electric field applied in the direction of polarization effects an expansion of the piezoelectric material in the same direction, while a voltage applied in the opposite direction of polarization will cause a contraction of the material in that same direction. Piezoelectric bending actuators, such as thermally pre-stressed bending actuators, use the “bending” action of the actuator to convert electrical energy into mechanical energy.
While the application of a voltage command signal typically functions well to actuate the piezoelectric device, there are some nonlinearities in operation of the piezoelectric actuator that are reflected in a voltage controlled system. For example, these nonlinearities may cause the actuator to not fully move to a desired position in response to a voltage control signal. Further the control signal may cause the actuator to move or change its position in an abrupt or sluggish manner that does not match the desired actuator movement profile for a particular application.
Thus, the present invention is directed to overcoming one or more of the problems set forth above.
DISCLOSURE OF THE INVENTION
While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, a control system for controlling position and velocity of a piezoelectric device includes a position control circuit that is operable to compare a first control signal corresponding to a desired position of the piezoelectric device to an estimated position of the device. The position control circuit generates a second control signal, such as a position error control signal, that is adapted to drive the piezoelectric device to the desired position.
The control system may further include a velocity control circuit that is operable to receive the position error control signal and generate a third control signal that is adapted to drive the piezoelectric device to the desired position and at a desired velocity. A piezoelectric device control circuit is operatively coupled to the position and velocity control circuits and operable to generate a fourth control signal in response to the third control signal that is adapted to drive the piezoelectric device to the desired position and at the desired velocity so that the piezoelectric device reaches the desired position and moves to that position in accordance with a desired velocity profile.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof.
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Gallmeyer Christopher F.
Waterfield Larry G.
Addison Karen
Caterpillar Inc.
Ponomarenko Nicholas
Wood Herron & Evans LLP
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