An investigation on robust biped walking using compliant force control and a online walking pattern generator

This paper discuses biped walking which is robust to external disturbances and how it could be realized by means of achieving compliance and dynamic trajectory generation. A method of limiting the ground reaction forces is presented. It is mathematically equivalent to a conventional position control system when the ground reaction forces are within the set limits, therefore in this case the positioning performance is the same. This method only requires the tooltip position reference, joint states and force sensor data as inputs. As an application it can be used to limit the ZMP of a biped robot to be within the foot sole, limiting the lateral forces to prevent sliding and limiting the downwards foot force after a jumping maneuver to prevent breaking the leg mechanism. It could be considered to be more general than the conventional ZMP controller method of stabilizing biped walking yet it is compatible and can be used in conjunction with such a method. A method of calculating the foot and COM trajectories online is also discussed. A walking simulation is presented to show the effectiveness of the ground reaction force limiter in the case where the input trajectory is inappropriate for the robot. A different simulation shows how the robot can attain compliance to external forces while keeping the ZMP in a predefined sub-region of the foot. Finally a simulation is shown to demonstrate the proposed walking pattern generator.