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.

This Piezoelectric/Electrostatic Actuator would produce motion of the slider into or out of the page in small increments.

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:

  1. The slider would be electrostatically clamped to the driver.
  2. The piezoelectric stack would push the driver upward or downward (out of or into the page, respectively).
  3. The slider would be electrostatically clamped to the holders.
  4. The slider and the driver would be released from each other.
  5. 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.
  6. 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.

Topics:
Microelectromechanical devices Motion Control Noise Optics Physical Sciences Polymers Semiconductors Sensors and actuators Vehicle drivers Vehicle occupants
This Brief includes a Technical Support Package (TSP).
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MEMS-Based Piezoelectric/Electrostatic Inchworm Actuator

(reference NPO-30672) is currently available for download from the TSP library.

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Motion Control Tech Briefs Magazine

This article first appeared in the June, 2003 issue of Motion Control Tech Briefs Magazine (Vol. 27 No. 6).

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Overview

The document presents a technical report on a MEMS-based micro inchworm actuator developed by Eui-Hyeok Yang at NASA's Jet Propulsion Laboratory. This innovative actuator is designed to achieve both large travel distances (on the order of hundreds of microns) and nanometer-scale precision in motion, addressing limitations found in conventional inchworm actuators.

Traditional inchworm actuators, often composed of multiple piezoelectric elements, tend to be bulky and unsuitable for microsystems that require compact actuation solutions. Previous MEMS-based technologies have not successfully combined large travel capabilities with fine resolution. The proposed actuator overcomes these challenges by utilizing a combination of compliant polymer beams and precision silicon micromachining techniques.

The actuation mechanism involves a sequence of steps that utilize electrostatic clamping and piezoelectric driving. Initially, the slider is electrostatically clamped to a driver, which is then moved upward or downward by a piezoelectric stack. Following this, the slider is clamped to holders, and the driver is released. The driver is subsequently moved while the slider remains clamped to the holders, completing one increment of motion. This cycle can be repeated at a high frequency, up to approximately 1 kHz, allowing for rapid and precise positioning.

The design incorporates a centrally clamped flexure beam, which enhances the actuator's performance by allowing for larger travel distances while maintaining the necessary precision. The actuator's ability to achieve small gaps (a few microns) between the slider and other components facilitates effective electrostatic clamping with a modest voltage (around 100 V) and a clamping force of about 1 N.

This technology has significant implications for various applications, including micro-manipulation, precision positioning in scientific instruments, and potential use in space exploration systems. The report emphasizes the novelty of this actuator in the micro actuator field, highlighting its potential to revolutionize how precise movements are achieved in compact systems.

Overall, the document outlines a significant advancement in actuator technology, showcasing a solution that combines large travel capabilities with high precision, making it a valuable contribution to the field of micro-electromechanical systems (MEMS).