Pneumatic variable stiffness soft robot end effectors

Al Abeach, LAT

Abstract

Traditionally, robots have been formed from heavy rigid materials and have used stiff actuator technologies. This means they are not well suited to operation near humans due to the associated high risk of injury, should a collision occur. Additionally, rigid robots are not well suited to operation in an unstructured environment where they may come into contact with obstacles. Furthermore, traditional stiff robots can struggle to grasp delicate objects as high localised forces can damage the item being held.

The relatively new field of soft robotics is inspired by nature, particularly animals which do not have skeletons but which still have the ability to move and grasp in a skilful manner. Soft robotics seeks to replicate this ability through the use of new actuation technologies and materials.

This research presents the design of a variable stiffness, soft, three-fingered dexterous gripper. The gripper uses contractor pneumatic muscles to control the motion of soft fingers. The soft nature of the gripper means it can deform if it collides with obstacles, and because grasping forces are spread over a larger area the chance of damaging the object being held is reduced. The gripper has the ability to vary its stiffness depending upon how it is to be used, and in this regard two methods of varying the stiffness are explored. In the first method, the finger is formed from an extensor muscle which acts antagonistically against the contractor muscles. Increasing the total pressure in the system increases the stiffness of the fingers. The second approach uses granular jamming to vary the stiffness of the actual finger structure.

This thesis explores the behaviour of both extensor and contractor pneumatic muscles and develops a new simplified mathematical model of the actuator’s behaviour. The two methods of stiffness variation are then assessed experimentally. A number of multi-fingered grippers are then designed and their kinematics determined before prototypes are presented. Control of the grippers was then explored, along with the ability to adjust the stiffness of the grasp.

Citation

Al Abeach, L. Pneumatic variable stiffness soft robot end effectors. (Thesis). University Of Salford

• Thesis Type: Thesis
• Deposit Date: Feb 20, 2018
• Publicly Available Date: Nov 3, 2019
• Award Date: Jun 1, 2017