Synergy Hand Using Fluid Network: Realization of Various Grasping/Manipulation Styles

Synergy hands absorb the complexity of control and mechanisms inherent in multi-fingered hands, enabling human-like grasping with simple mechanisms and low-dimensional control. However, they struggle with functional object grasping and dexterous manipulation expected of multi-fingered hands. In this study, we propose a synergy hand using a fluid network that can balance functional grasping and manipulation with low-dimensional control. The fluidic network comprises actuators attached to the joints of the hand, a single hydraulic pump, connecting flow tubes, and solenoid valves attached at various points in the flow tubes. Switching the network configuration via solenoid valves makes it possible to choose whether each joint is under synergy control or remains fixed while pressurized. This allows for allocating grasping and manipulation functions to each finger, enabling control appropriate to the function. Furthermore, by controlling the flow rate to each actuator with proportional control solenoid valves, the system can precisely express various grasping postures using a single pressure source. Experimental validation of the proposed synergy hand demonstrated its ability to grasp objects of various shapes. The use of proportional control valves for joint position control resulted in about 1.5% improvement in accuracy compared to the method using standard solenoid valves. It was also confirmed that the system could functionally grasp and manipulate objects with degrees of freedom, which had been difficult with conventional synergy hands.