Conventional piezoelectric materials, such as PZTs, have reasonably high electromechanical coupling over 70%, and excellent performance at room temperature. However, their coupling factor (converting electrical to mechanical energy and vice versa) drops substantially at cryogenic temperatures, as the extrinsic contributions (domain wall motions) are almost frozen out below 130 K.
The solution to this problem is to use effective cryogenic piezoelectric stacks that are operational at extreme temperatures, and particularly at cryogenic temperatures, using a flextensional design that can amplify the stack displacement. Significant advances have been made in developing relaxor ferroelectric single crystal piezoelectric materials (such as PMN-PT single crystal) that have much higher electromechanical coupling (over 90%) at room temperature. The properties remain high at extremely low temperatures because their properties are based on the intrinsic/lattice contributions. The heat generated during operation is minimized in order to reduce the heat burden on the thermal control of the instrument or local environment. The motor also has the ability to self-brake while unpowered.
Using these flextensional actuators in an inchworm motor configuration, this design dissipates very little thermal energy with a simple control of driving voltage and/or frequency, and has high stroke that is only limited to the length of the travel guides. In addition, because the flexure frame and guides can be made from the same material with simple structures, unlike conventional electromagnetic motors, the relative thermal mismatch can be minimized. Also, the conceived motor can provide significant precision with minimum displacements in the single-digit nanometer range.
A slider is driven inside a channel that consists of an expanding and contracting flextensional actuator sandwiched between two clamping actuators. The slider is made to move by sequentially releasing the clamping surfaces of the two clamps and alternately contracting or expanding the middle element, depending on the desired moving direction, and which clamp is activated.
This work was done by Stewart Sherrit, Mircea Badescu, Yoseph Bar-Cohen, Xiaoqi Bao, and Hyeong Jae Lee of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49541
This Brief includes a Technical Support Package (TSP).
Piezoelectric Actuated Inchworm Motor (PAIM)
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Overview
The document presents the Piezoelectric Actuated Inchworm Motor (PAIM), a novel cryogenic motor developed by the Jet Propulsion Laboratory (JPL) at the California Institute of Technology. This innovative motor is designed to operate effectively in extreme temperature conditions, making it particularly suitable for NASA missions involving infrared instruments and exploration of celestial bodies with low temperatures, such as Titan and Europa.
The PAIM utilizes a unique inchworm design, where a slider is driven within a channel by an expanding and contracting flextensional actuator, which is sandwiched between two clamping actuators. The movement of the slider is achieved by sequentially releasing the clamping surfaces and alternately contracting or expanding the middle element, depending on the desired direction of movement. This mechanism is powered by piezoelectric stacks that are held in compression by a flexure configuration, allowing for amplified stroke and minimal power dissipation.
One of the key advantages of the PAIM is its ability to generate minimal thermal losses, which is crucial for the operation of sensitive infrared systems at cryogenic temperatures. The motor is designed to operate with low drive voltage and power, minimizing heat generation that could interfere with the performance of infrared instruments or cryo-coolers. Additionally, the motor's holding position does not require continuous activation, further reducing energy consumption.
The document outlines the technical challenges addressed by the PAIM, including the need for actuators that can function at cryogenic temperatures and the thermal mismatch between construction materials. The flextensional design of the motor mitigates these issues, allowing for high precision and minimal thermal energy dissipation. The motor's performance can be optimized by adjusting the driving voltage and frequency, which also helps control power dissipation.
Overall, the PAIM represents a significant advancement in actuator technology, offering a high output torque-to-weight ratio, simple construction without electromagnetic noise, and high electromechanical efficiency. This technology has potential applications not only in space exploration but also in various fields requiring precise motion control in extreme environments. The document serves as a technical support package, providing insights into the development and capabilities of this innovative motor.
