A proposed inchworm actuator, to be designed and fabricated according to the principles of microelectromechanical systems (MEMS), would effect linear motion characterized by steps as small as nanometers and an overall range of travel of hundreds of microns. Potential applications for actuators like this one include precise positioning of optical components and active suppression of noise and vibration in scientific instruments, conveyance of wafers in the semiconductor industry, precise positioning for machine tools, and positioning and actuation of microsurgical instruments.
The inchworm motion would be generated by a combination of piezoelectric driving and electrostatic clamping. The actuator (see figure), would include a pair of holders (used for electrostatic clamping), a slider (the part that would engage in the desired linear motion), a driver, a piezoelectric stack under the driver, and a pair of polymer beams centrally clamped to the flexure beam via a T bar. The holders would be held stationary. One end of the piezoelectric stack would be held stationary; the other end would be connected to the bottom of the driver, which would be free to move up and down. All of these components except the piezoelectric stack and the polymer beams would be micromachined from a 500-μm-thick silicon wafer by deep reactive-ion etching. The inchworm motion would be perpendicular to the broad faces of the wafer (perpendicular to the plane of the figure).
The combination of the polymer beams and the centrally clamped flexure beam would spring-bias the slider into a position such that, in the absence of electrostatic clamping, the gap between the slider on the one hand and both the driver and the holder on the other hand would be no more than a few microns. This arrangement would make it possible to electrostatically pull the slider into contact with either the holders or the driver at a clamping force of the order of 1 N by applying a reasonably small voltage (of the order of 100 V). The actuation sequence would be the following:
- The slider would be electrostatically clamped to the driver.
- The piezoelectric stack would push the driver upward or downward (out of or into the page, respectively).
- The slider would be electrostatically clamped to the holders.
- The slider and the driver would be released from each other.
- The driver would be moved downward or upward by the piezoelectric actuator while the slider remained clamped to the holders. This would complete the sequence for one increment of motion.
- The cycle comprising steps 1 through 5 would be repeated as many times as needed to obtain the desired overall upward or downward travel. The repetition rate could be as high as about 1 kHz.
This work was done by Eui-Hyeok Yang of Caltech for NASA’s Jet Propulsion Laboratory.