  The estimation of the motor torque and friction parameters are crucial for
implementing an efficient low level joint torque control. In a set of coupled
joints, the actuators torques are mapped to the output joint torques through a
coupling matrix, such that the motor torque and friction parameters appear
entangled from the point of view of the joints. As a result, their
identification is problematic when using the same methodology as for single
joints. This paper proposes an identification method with an improved accuracy
with respect to classical closed loop methods on coupled joints. The method
stands out through the following key points: it is a direct open loop
identification; it addresses separately each motor in the coupling; it accounts
for the static friction in the actuation elements. The identified parameters
should significantly improve the contribution of the feed-forward terms in the
low level control of coupled joints with static friction.
