Modeling and control of a finger-like mechanism using bending shape memory alloys

In this research a biologically inspired finger-like mechanism similar to human musculoskeletal system is developed based on Shape Memory Alloys (SMAs). SMA actuators are inspiring the design of a modular finger part with compact and compliant actuation. A three-segmented finger-like mechanism is designed and fabricated. This mechanism is composed of six bending Shape Memory Alloy (SMA) actuators. As a result, our finger mechanism is compact and compliant. The insider three SMA actuators are used for finger flexion while the outsider three SMA actuators are for extension. Each segment of this mechanism can be bent and/or extended independently by actuating a corresponding bending SMA actuator. Furthermore, full bending motion can be achieved by applying coordinated control of the three SMA actuators. Toward this goal a mathematical model of the SMA combined finger has been developed. The developed mathematical model is then used to design a proportional-derivative controller for control compliant actuation of the finger-mechanism. The performance of this mechanism has been experimentally evaluated. Our experimental results verify that the SMA-based finger module can achieve the desired postures similar to a human finger.