Investigation on the basic principles of human-machine contact force, based on screw theory

In this paper, to introduce a spatial rigid body mechanics analytical method and start the analysis, the human-machine contact force is equivalent to a spatially rigid body: the mechanism and skin surfaces are equivalent to two different rigid planes, and the motion between the mechanism and skin surfaces is equivalent to virtual branches motion. By considering the elastic deformation of each virtual branch axis, an equivalent human-machine contact force model is established, along with the deformation coordination equation of each virtual branch. The analytical solution of the tension/compression and the expression of the internal force of each virtual branch are obtained by solving the pseudo inverse and weighted generalized inverse solutions of the human-machine contact force. The physical meaning of the internal force of each virtual branch is also denoted. In addition, this paper contains an experimental platform for testing human-machine contact force, in which the linear stiffness of each branch is evaluated, therefore simulating and verifying the theoretical model introduced above. The contact force model proposed in this paper provides a theoretical basis for the development of human-machine synergetic motion.