Friction identification of ball-screw driven servomechanisms through the limit cycle analysis

Friction degrades the positioning accuracy of servomechanisms. Friction compensators are required to fabricate high-performance servomechanisms. In order to compensate for the friction in the servomechanism accurately, identification of the friction is required first. This paper proposes a friction identification method of a ball-screw driven servomechanism in the frequency domain. A nonlinear friction model including static, Coulomb, and viscous friction as well as Stribeck effect is formulated by using describing functions. Friction elements are estimated through the limit cycle analysis in a velocity control loop. In order to increase the accuracy of the friction identification process, a Butterworth filter is incorporated into the velocity feedback loop. Validity of the proposed method is confirmed through the numerical simulation and experiment in a ball-screw driven servomechanism. In addition, a model-based friction compensator is applied as a feedforward controller to compensate for the nonlinear characteristics of the servomechanism and to verify the effectiveness of the proposed identification method.