<title>Experiences with shape memory alloy: robot grippers for submillimeter hard disk drive components</title>

Abstract

Grippers for an automated assembly cell are being developed for handling individual sub-millimeter hard-disc drive components. Processing requirements dictate positive gripping with a strong actuator that meets clean room specifications. Proof-of-concept testing of shape memory alloy (SMA) as an actuator was performed. The response time of Ni-Ti 0.076 mm diameter shape memory wire was found to be 0.15 seconds under forced air convection conditions. Positioning accuracy was held to steady-state oscillations of 0.076 mm proving that SMA actuators meet performance requirements for a precision microactuator. SMA was then used for the actuation of several candidate gripper designs. One promising design consisted of a two-fingered gripper with integral spring sections at the arm base. SMA wire provided the closing actuation force and the spring sections returned the fingers to their rest position. Another design used an external spring to provide the gripping force, while the SMA wire provided the force required to open the gripper. The paper describes design methodologies and overall results. The addition of closed-loop control and improved heat dissipation mechanisms are needed before SMA materials can be used robustly as actuators for sub-mm robot grippers in high volume applications.