A human-friendly robot (HFR) is described to realize human safety, and a collision-tolerant control method is also proposed to achieve task performance. The HFR consists of an arm covered with viscoelastic materials and a trunk with mechanical elements, such as springs and dampers. In an unexpected or expected collision with a human, the passive viscoelastic trunk of the HFR passively deforms in response to the collision/contact forces. It is difficult, however, for the end effector to perform a desired task owing to the deformation of the passive trunk. In order to deal with this problem, the joint configurations of the arm are directly calculated according to the passive trunk deformation. The HFR with the passive viscoelastic trunk is compared with a conventional industrial robot with a rigid trunk for evaluation. Simulation and experimental results confirm that the proposed control method is useful for the end-effector position control and the passive viscoelastic trunk suitable for the suppression of collision/contact forces.
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