Compliantly underactuated hands based on multiport networks

In this paper, we outline a design framework that can be used to evaluate and select elastic transmissions between a robotic hand's actuators and its fingers. This framework is based on compliant mechanisms modeled as multiport networks. By analyzing the principal eigenvectors of the stiffness matrix of the multiport, it is possible to approximate the response of the fingers to given actuator inputs. The outlined design process is general, and may be used to design hands with any number of actuators or fingers. An anthropomorphic robotic hand with an elastic transmission mechanism based on a coil spring is presented that superimposes the actions of each actuator across its fingers. The analytically computed multiport stiffness matrix of the transmission mechanism matched the experimentally determined one to within 17%. Because the hand has two actuators that are compliantly coupled, it not only conforms to and grasps objects but can also deliberately vary the finger contact forces during grasping.