Optimal Design of Safe Planar Manipulators Using Passive Torque Limiters

This paper presents a synthesis approach to build safe planar serial robotic mechanisms for applications in human–robot cooperation. The basic concept consists in using torque limiting devices that slip when a prescribed torque is exceeded so that the maximum force and the maximum power that the robot can apply to its environment are limited. In order to alleviate the effect of the change of pose of the robot on the joint to Cartesian force mapping, it is proposed to include more torque limiters than actuated joints. The design of isotropic force modules is addressed in order to produce proper force capabilities while ensuring safety. The proposed isotropic module of torque limiting devices leads to such characteristics. In addition to modeling the contact forces at the end-effector, the forces that can be applied by the robot to its environment when contact is taking place elsewhere along its links are also analyzed as well as the power of potential collisions. Examples of manipulator architectures and their static analysis are given. Finally, the design of a spatial serial manipulator using the isotropic planar force modules developed in the paper is illustrated.