Modeling of frictions in the transmission elements of a robot axis for its identification

Control in robotics needs more and more precise models of the mechanical parts of the structure and specially for a complex system such as a biped robot. An important but difficult aspect of this work is the modelling of the mechanical loss due to friction in the chain of transmission from the motor to the axis. The loss of each part is defined as a sum of three terms, one constant, another depending only on the speed and the last depending on the torque transmitted in the part. The robot joint kinematic chain is modeled with three elements: the motor, the gearbox and a rotational joint at the leg. The results show a good adequacy between the measurement and the simulation with the proposed identification method in comparison with a classic least square identification method.