Composable Flexible Small Actuators Built from Thin Shape Memory Alloy Sheets

Alternatives to traditional actuators such as electromagnetic motors are needed in applications where space and weight are limited, for example, laparoscopic medical probes, miniature robotics, and micro-lens positioning systems. We present a family of small light-weight actuators that can be composed out of a basic unit-cell to yield linear, rotational, and surface actuation. The unit-cell actuator is built using Shape Memory Alloy (SMA) sheets. It is activated by electrical current and the resultant heating. Depending on the combination of these unit-cells, the designer can control the direction of actuation, the amount of force generated, and the expansion (stroke) of the actuator. The unit-cell design overcomes limitations of actuators built with SMA wires. For example, the heat needed to activate the SMA is localized in a specific area by controlling the geometry of the electrical conduction path. This geometry is easily constructed by laser-cutting the desired pattern. Additionally, the SMA can be mounted by its non-heating areas. In this paper, we characterize the new actuator, compare its performance with that of a traditional electromagnetic motor, and report on results of endurance tests. We also demonstrate a robotic system driven by these actuators.