Switching between Continuum and Discrete States in a Continuum Robot with Dislocatable Joints

Abstract

Rigid linkages allow robots to lift heavy loads but prevent them from gently stretching and bending their bodies. Continuum robots without rigid linkages have a wide range of motion, safety, shape adaptability, and compliance. To combine the benefits of both continuum and rigid robots, we propose a method of switching between discrete and continuum states by a dislocatable joint. This mechanism is driven by three wires. It has a cup joint in an upper section and a ball joint in a lower section, and the two sections are connected by a spring. The cup and ball joints are separated, and the manipulator is a flexible continuum one. When the wires through the sections are pulled, the two joints are connected as a discrete state. To clarify the design methodology of the manipulator, we build a model of the joint and consider three collision cases in the simulation and experiment. The model reveals the relationship between the robot's shape parameters and the manipulator's range of motion, and it visualizes an area where the positioning is uncertain due to the collision between the ball and cup joints. We build a prototype manipulator and experimentally verify that the stiffness is improved by the connection.