A friction identification approach based on dual-relay feedback configuration with application to an inertially stabilized platform

• The proposed method is applied for friction identification in a low-velocity servo system.
• The low-velocity frictional behavior can be described by the proposed friction model.
• Properties of limit cycles are proposed as bases of friction identification approach.
• A systematic friction identification procedure consists of four phases.
• The friction identification approach improves the low-velocity motion performance of servo system.

The low-velocity motion performance of servo system tends to be deteriorated greatly by friction due to its relay nonlinearity and Stribeck effect in low-velocity state. To achieve better low-velocity motion performance, an effective friction identification approach based on the dual-relay feedback configuration is presented for a typical low-velocity servo system, an inertially stabilized platform (ISP). An improved piecewise friction model derived from Tustin model is used to describe the frictional behaviors including static, Coulomb, viscous friction and especially Stribeck effect, so that the frictional behaviors can be appropriately formulated through describing functions. The dual-relay feedback configuration is designed to excite limit cycles in a velocity feedback loop, rather than in the position loop, so as to avoid noise arisen from the derivative of the position response signal. Properties of the limit cycle oscillations are analyzed for proper selections of dual-relay gains, based on which a systematic procedure for friction identification is proposed. Simulations and experiments on a servomechanism of ISP verify the effectiveness of the proposed approach.