Investigation of a shape memory alloy actuator for dextrous force-feedback masters

Multifingered dextrous robot hands can perform more complex tasks than simpler end effectors. Teleoperation, in which a robot mimics the motion of a remote operator, provides a convenient method for controlling these robot hands. Damage to the object being manipulated by the robot hand may result in the case of open-loop control if there is no force-feedback sensation to the operator from the robot hand. The need arises for new actuator technology to provide force feedback to the hand master. These actuators have to meet the tight space and light weight requirements of a dextrous master. One candidate is the shape memory alloy (SMA) actuator. SMAs, such as Nitinol, are materials with a unique 'mechanical memory' and high force/weight ratio. A prototype SMA actuator and its hardware interface were designed and tested. Results showed that the actuator met the space and weight limitations of the master (Exos DHM™) and provided adequate reactive force feedback to the operator. However, the actuator had a low bandwidth of operation, due to relatively slow engagement and disengagement motions. This makes it unusable in real-time control situations.