Parity equation-based friction compensation applied to a rolling mill

This paper presents a friction compensator design based on parity equations applied to a single stand of a hot strip rolling mill. For the purpose of control, the force acting on the rolled metal piece is measured. However, this measurement is affected by friction, which, due to its strongly nonlinear character, leads to limit cycles. The algorithm presented here utilises the parity equations of a linearised and discretised plant model in order to obtain a residual, which is proportional to the friction force. Based on this proportionality a friction compensator is developed. The performance of the plant with a compensator in the control loop is tested using a MATLAB/Simulink model. A structured residual approach and input/output measurement sensor fault isolability are also investigated.