Adaptive friction compensation based on the LuGre model for a pneumatic rodless cylinder

This paper deals with an adaptive friction compensation strategy based on the LuGre model for a pneumatically driven rodless cylinder. Due to their high dynamics, good force-to-weight characteristic, and their relatively small price pneumatic positioning systems offer an attractive alternative to electrical drives. However, pneumatic positioning systems also involve some difficulties like the nonlinear characteristic of the air mass flow through the servovalves and friction forces acting on the piston. To consider nonlinear friction in the control structure, a LuGre observer has been implemented. The update law for the estimated observer parameters is obtained by adaptive backstepping control. The employed control approach has a cascade structure: In an underlying control loop, the internal pressures of the left and right chamber of the cylinder are controlled, whereas the carriage position and the mean pressure of the two chambers represent the control variables of the outer loop. Experimental results from an implementation on a test rig show a high control performance.