Improvement of brushless DC motor actuators
Today, the use of brushless DC motors (BDCM) in robotic applications is only at its beginning in spite of their remarkable features. This is due to the increased complexity of the control with respect to the conventional DC motors, but also to the parasitic torques of the BDCM, i.e. the Cogging, the Ripple and the Hyteresis Drag torques which limit their full potential when accurate control is required. In this paper, we deal with the digital compensation of the parasitic torques. The main novelty presented is the compensaction of the ,magnetic hysteresis drag. As the effect of this drag is similar to that of the static mechanical friction, the proposed compensation algorithm allows greater positioning precision in robotic applications. The importance of this compensation is vital in the field of teleoperators for position error based force reflecting servomanipulators. Electronic offsets compensation and the ways to partially compense the static mechanical friction are also compensate the static mechanical friction are also considered. Besides, we present a procedure for the quick automatic determination of the two independant look-up tables needed to compensate the cogging torque an torque ripple. This procedure can be carried out directly on a servomanipulator and probably on most robotic joints.