Actuators are critical to all the robotic and manipulation mechanisms that are used in current and future NASA missions, and are also needed for many other industrial, aeronautical, and space activities. There are many types of actuators that were designed to operate as linear or rotary motors, but there is still a need for low-force, low-noise linear actuators for specialized applications, and the disclosed mechanism addresses this need.

The Actuator is driven by shape memory alloy as a primary active element. Electrical connections to points A and B are used to apply electrical power in the resistive NiTi wire, causing a phase change that contracts the wire on the order of 5%.
A simpler implementation of a rotary actuator was developed where the end effector controls the motion of a brush for cleaning a thermal sensor. The mechanism uses a SMA (shape-memory alloy) wire for low force, and low noise. The linear implementation of the actuator incorporates a set of springs and mechanical hard-stops for resetting and fault tolerance to mechanical resistance. The actuator can be designed to work in a pull or push mode, or both. Depending on the volume envelope criteria, the actuator can be configured for scaling its volume down to 4×2×1 cm3. The actuator design has an inherent fault tolerance to mechanical resistance. The actuator has the flexibility of being designed for both linear and rotary motion. A specific configuration was designed and analyzed where fault-tolerant features have been implemented. In this configuration, an externally applied force larger than the design force does not damage the active components of the actuator. The actuator housing can be configured and produced using costeffective methods such as injection molding, or alternatively, its components can be mounted directly on a small circuit board.

The actuator is driven by a SMA -NiTi as a primary active element, and it requires energy on the order of 20 Ws(J) per cycle. Electrical connections to points A and B are used to apply electrical power in the resistive NiTi wire, causing a phase change that contracts the wire on the order of 5%. The actuation period is of the order of a second for generating the stroke, and 4 to 10 seconds for resetting. Thus, this design allows the actuator to work at a frequency of up to 0.1 Hz.

The actuator does not make use of the whole range of motion of the SMA material, allowing for large margins on the mechanical parameters of the design. The efficiency of the actuator is of the order of 10%, including the margins. The average dissipated power while driving at full speed is of the order of 1 W, and can be scaled down linearly if the rate of cycling is reduced. This design produces an extremely quiet actuator; it can generate a force greater than 2 N and a stroke greater than 1 cm. The operational duration of SMA materials is of the order of millions of cycles with some reduced stroke over a wide temperature range up to 150 ºC.

This work was done by Mircea Badescu, Stewart Sherrit, and Yoseph Bar-Cohen of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47991

Topics:
Electric power Forming Manufacturing processes Mechanical Components Mechanics Molding Off-board energy sources Sensors and actuators
This Brief includes a Technical Support Package (TSP).
Document cover
Compact, Low-Force, Low-Noise Linear Actuator

(reference NPO-47991) is currently available for download from the TSP library.

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NASA Tech Briefs Magazine

This article first appeared in the September, 2012 issue of NASA Tech Briefs Magazine (Vol. 36 No. 9).

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Overview

The document presents a technical support package for a Compact, Low-Force, Low-Noise Linear Actuator developed by NASA's Jet Propulsion Laboratory (JPL). This actuator utilizes shape memory alloy (SMA) technology, specifically NiTi (Nickel-Titanium), to achieve efficient actuation with minimal noise and force. The actuator is designed for applications that require precise movement and reliability, making it suitable for aerospace and other technological fields.

The actuator operates by applying electrical power to the resistive NiTi wire, which induces a phase change that allows the wire to contract by approximately 5%. This contraction generates a force greater than 2 N and a stroke exceeding 1 cm. The actuation cycle requires about 20 Joules of energy, with an average power consumption of around 4 Watts over a 10-second period. The actuator can operate at a frequency of up to 0.1 Hz, with a reset time of 4 to 10 seconds, making it efficient for various applications.

The design emphasizes cost-effectiveness, allowing for production through methods such as injection molding or direct mounting on circuit boards. The actuator's housing is robust enough to withstand externally applied forces without damaging its components, ensuring durability and reliability. The operational lifespan of the SMA materials is estimated to be in the millions of cycles, even under varying temperature conditions up to 150°C.

Figures included in the document illustrate the actuator's configuration, prototype designs, and performance metrics, such as voltage and current plots during actuation. The actuator's quiet operation and efficiency are highlighted, making it an attractive option for applications requiring low-noise solutions.

The document also acknowledges the research's sponsorship by NASA and the California Institute of Technology, emphasizing the collaborative effort in developing this technology. It serves as a resource for potential commercial applications and further research in the field of aerospace technology.

In summary, this technical support package outlines the development and capabilities of a novel linear actuator that leverages SMA technology, showcasing its potential for broader applications beyond aerospace, while also providing insights into its design, performance, and operational characteristics.