Experimental Characterization and Control of a Force Actuator Based on Shape Memory Alloy Wire

This paper presents an experimental design of a force and position controller for a Ni–Ti shape memory alloy actuator. The focus of this work is a measurement device for the characterization of a SMA spring together with the fuzzy controller for position and force that can be quickly and easily implemented. This device makes it possible to develop a mechanism for robotic applications with slow actuation speed, e.g., to mimic a robotic finger. The contribution of our work to the scientific literature is an easy control of force and position, as well as weight reduction when compared to a similar actuator controlled by a traditional electric motor. Ni–Ti wire was winded up to form a coil; an electric current passing through the actuator changes its temperature, which leads to a phase transformation resulting in a length change of the wire. Thus, the actuator behaves as a spring, whose force exerted can be adjusted by an electric current. A closed-loop fuzzy logic controller was programmed in the LabVIEW environment, allowing the control of the force exerted by the actuator, as well as the position of an attached load. The actuator performance was evaluated experimentally before and after a training session.

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