Soft hands based only on an actuator system using a motor, air compressor, or smart material show obvious shortcomings due to the characteristics of each actuator. In this article, to overcome the weaknesses of each actuator system, a novel soft hand with a hybrid actuator system is presented to improve the grasping capacity and complete complex tasks, as the individual actuators can complement each other. First, the structure and actuation system of the soft hand are presented. DC motors are used to output sufficient torque to bend the soft fingers. Shape memory alloy wires are used to rotate the fingertips. The electromagnets embedded in the soft fingers are actuated to bond the fingers to improve the load capability without changing the fingers' stiffness. Then, four different grasping methods are tested to manipulate objects: (1) the soft hand actuated only by motors is tested in terms of its ability to grasp objects of different shapes; (2) the soft robot can grasp the inside of the objects using rotated fingertips; (3) grasping involving the fingers tightly bonded by an electromagnetic force is tested; and (4) small objects are also secured and prevented from falling from the fingers by a gap-filling grasping method. In conclusion, the soft hand actuated by the hybrid system should be a viable alternative to soft manipulators that can compensate for the weaknesses of each actuator and improve the grasping capacity relative to that of individual actuators.
Keywords: SMA; electromagnetic force; hybrid actuator; soft hand.