Variation in compliance in two classes of two-link underactuated mechanisms

The compliance of an underactuated robotic hand, or a robotic hand with fewer actuators than degrees of freedom, is a function of the mechanism type, the design parameters, and the operational control mode. The transmissions used in underactuated mechanisms can be divided into two main classes based on the self adaptive transmission used to route actuation to the various degrees of freedom, namely the single-acting transmission and the double-acting transmission. While both transmission classes can be represented using a kinematic constraint equation that defines the relationship between actuator and joint motion, the main difference between the two transmission classes is that the kinematic constraint is always active in double-acting mechanisms while there are specific combinations of external disturbances and mechanism parmeters that render the constraint inactive in single-acting mechanisms. While previous studies have only explored the performance of underactuated mechanisms with the constraint always active, this paper identifies the benefits for robotic grasping (such as better disturbance rejection) that arise when the constraint becomes inactive in single-acting mechanisms.