Switching Between Continuum and Discrete States in a Continuum Robot With Dislocatable Joints

Ayato Kanada,Tomoaki Mashimo

doi:10.1109/access.2021.3062284

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.

Highlights

Conventional industrial robots require a high level of stiffness to execute tasks with agility and accuracy in manufacturing
Vertebrates have relatively high payloads, but they do not actively disengage their joints. Snakes can separate their jaws to open their mouth widely and have highly mobile jaw joints, whose left and right anterior ends are joined by a flexible ligament [24]. Inspired by these animals and biology, we propose a concept for a variable stiffness manipulator that can shift between discrete and continuum states by dislocatable joints
A certain type of soft robots with rigid mechanical elements shows a higher payload and better responsiveness, but the dislocatable joints that we propose in this paper have not been reported [25]

Summary

INTRODUCTION

Conventional industrial robots require a high level of stiffness to execute tasks with agility and accuracy in manufacturing. Vertebrates change their stiffness by antagonizing their muscles through their joints They are similar to conventional rigid robots, which transmit high power through discrete joints. They have small bone fragments scattered on the surface of their bodies and in their arms They can change their rigidity and range of motion by altering the stiffness of the elastic connective tissue (catch connective tissue) that connects their bone fragments [22], [23]. Snakes can separate their jaws to open their mouth widely and have highly mobile jaw joints, whose left and right anterior ends are joined by a flexible ligament [24] Inspired by these animals and biology, we propose a concept for a variable stiffness manipulator that can shift between discrete and continuum states by dislocatable joints.

KINEMATIC MODELING

JOINT AND SPRING

CONCLUSION