Abstract : The control of the interaction between a robot and the environment is very important in the medical area. The control of this interaction can be realized with a force control, which does not need human intervention, or co-manipulation, where the human operator moves the robot himself. This paper
focuses on a simple hybrid external command allowing to do these two applications by modelling the robot as a rigid structure interacting with the environment thanks to a spring representing the force sensor. After calculation of the correctors with a pole placement, some numerical tests were realized. Some experiments prove the accuracy of the control, for a one degree of freedom robot.