Experimental evaluation of a flexible joint driven by water pressure for underwater robots

We describe here the development a joint mechanism for underwater robotic manipulators. Arms of underwater robots require small-scale bodies and high waterproofing properties. In most of underwater robots, electric motors are used as actuators to drive the robotic arm/arms, but using electric motors for underwater manipulators may be problematic due to the size/weight of the robotic arm and need to waterproof the electric motors. We develop a joint mechanism composed of combinations of rigid and flexible members, which can be deformed by a prismatic actuator fixed onto two rigid parts. We utilize a leaf spring as the flexible joint and a McKibben actuator driven by water hydraulic pressure as the prismatic actuator. The number of members in this mechanism is smaller than that of a mechanism composed of a combination of one pulley and one coil spring. One advantage of this mechanism is the avoidance of gears, thus eliminating sliding parts from the joint.