Piezoelectric actuator and method for driving the same
View Patent ↗The piezoelectric actuator includes a piezoelectric element structure ( 100 ) which has at least one piezoelectric element ( 120 ), and a working edge ( 130 ) for directing driving force on a driven body (MB), wherein the working edge ( 130 ) oscillates in response to deformation of the piezoelectric element ( 120 ). The piezoelectric actuator further includes a driver circuit ( 300 ) for applying voltage to the piezoelectric element ( 120 ); and a drive control circuit ( 200 ) for inducing oscillation of the working edge ( 130 ) by supplying a drive signal (DV, #DV) of rectangular waveform to the driver circuit ( 300 ). The drive control circuit (200) is capable of reversing the drive direction of the driven body (MB) by changing the duty ratio of the drive signal (DV, #DV).
1. A piezoelectric actuator that drives a driven body, comprising:
a piezoelectric element structure having at least one piezoelectric element and a working edge that directs driving force to act on the driven body, wherein the working edge oscillates in response to deformation of the piezoelectric element;
a driver circuit that applies voltage to the piezoelectric element; and
a drive control circuit that includes oscillation of the working edge by supplying a drive signal of rectangular waveform to the driver circuit,
wherein the drive control circuit reverses the drive direction of the driven body through a change in a duty ratio of the drive signal.
2. The piezoelectric actuator according to claim 1 , wherein the drive control circuit:
(i) drives the driven body in a first direction by setting the duty ratio of the drive signal to a value less than 50%;
(ii) stops the driven body by setting the duty ratio of the drive signal to 50%; and
(iii) drives the driven body in a second direction opposite the first direction by setting the duty ratio of the drive signal to a value exceeding 50%.
3. The piezoelectric actuator according to claim 2 , wherein
relationship between the duty ratio of the drive signal and driving force of the working edge shows a non-linear characteristic exhibiting a smaller slope of change of the driving force where the duty ratio is close to 50%, and a larger slope of change of the driving force at locations where the duty ratio is further away from 50%.
4. The piezoelectric actuator according to claim 1 , wherein
the piezoelectric element structure has a sensor that detects oscillation of the piezoelectric element structure, and
the drive control circuit includes:
a resonance frequency signal generator that generates, in response to a sensor output of the sensor, a resonance frequency signal having a resonance frequency at which the piezoelectric element structure resonates; and
a duty controller that generates the drive signal so as to have the same frequency as the resonance frequency signal, and have a duty ratio dependent on the driving direction of the driven body.
5. The piezoelectric actuator according to claim 1 , wherein
the piezoelectric element structure includes:
two piezoelectric elements of generally rectangular tabular shape;
a common electrode interposed between the two piezoelectric elements; and
first and second electrodes which are interconnected and disposed at corresponding locations on outside faces of the two piezoelectric elements,
and wherein the first and second electrodes are positioned along one of the two diagonals on the outside surfaces of the piezoelectric elements.
6. A method that drives a piezoelectric actuator that drives a driven body, the piezoelectric actuator having at least one piezoelectric element and a working edge that directs driving force to act on the driven body, the working edge oscillating in response to deformation of the piezoelectric element, the method comprising:
reversing a drive direction of the driven body through a change in a duty ratio of a drive signal that drives the piezoelectric element.
7. The method according to claim 6 , further comprising:
(i) driving the driven body in a first direction by setting the duty ratio of the drive signal to a value less than 50%;
(ii) stopping the driven body by setting the duty ratio of the drive signal to 50%; and
(iii) driving the driven body in a second direction opposite the first direction by setting the duty ratio of the drive signal to a value exceeding 50%.
8. The method according to claim 7 , wherein
relationship between the duty ratio of the drive signal and driving force of the working edge shows a non-linear characteristic exhibiting a smaller slope of change of the driving force where the duty ratio is close to 50%, and a larger slope of change of the driving force at locations where the duty ratio is further away from 50%.
9. The method according to claim 6 , wherein
the piezoelectric element structure has a sensor that detects oscillation of the piezoelectric element structure, and
the method further comprises:
generating, in response to a sensor output of the sensor, a resonance frequency signal having a resonance frequency at which the piezoelectric element structure resonates; and
generating the drive signal so as to have the same frequency as the resonance frequency signal, and have a duty ratio dependent on the driving direction of the driven body.
10. The method according to claim 9 , wherein
the piezoelectric element structure includes:
two piezoelectric elements of generally rectangular tabular shape;
a common electrode interposed between the two piezoelectric elements; and
first and second electrodes which are interconnected and disposed at corresponding locations on outside faces of the two piezoelectric elements,
and wherein the first and second electrodes are positioned along one of the two diagonals on the outside surfaces of the piezoelectric elements.