A MAGNETIC AND SHAPE MEMORY ALLOY ACTUATED GRIPPER FOR SURGICAL

This paper presents the development of a novel shape memory alloy (SMA) actuated gripper for use in the biomedical applications. The use of SMA in surgical forceps can allow a surgical robot to accurately and repeatedly apply a force and grip small objects or perform minor surgeries that are less invasive and allow for quicker recovery times. Current designs of thermally actuated grippers use SMAs as the gripping parts, which limits their application due to the transfer of heat to the object being gripped. The design of the gripper illustrated in this paper isolates the SMA coil from the gripping jaws to maintain a constant surface temperature at the gripping end and prevent thermal contamination of soft tissues. Isolating the SMA from the grippers also simplifies automated surgical robots by centralizing all heating elements. A magnetic field exerted between a pair of permanent magnets is used to restore the SMA coil upon cooling. The gripper housing and jaws were fabricated using a 3-D printer to allow for modeling of small features with little down time. A Nitinol SMA wire with a transition temperature of 45 degrees C was wrapped into a 2.5mm diameter coil and heat treated to set the predefined shape. The SMA coil and other parts were assembled to form the gripper. The gripper was successfully tested using an Interlink Electronics Force Sensor and data acquisition card (DAQ), and the forces between the gripper jaws as well as the response time to close and open the jaws were recorded. The gripper produced a force of 0.9N when reaching the transition temperature. The response time for the gripper to close and open the jaws was measured to be approximately 0.16 s and 0.12 s, respectively. It was found that the magnetic field had a faster actuation on the coil than the shape memory alloy force during opening and closing jaws.