Indirect estimation of cutting force in milling machine tools

This work investigates the indirect and online estimation of the cutting forces from spindle integrated displacement sensor (SIDS) in addition to current of feed drive by two approaches. In the first approach, an FEM model of the spindle integrated sensor is used to measure relative displacement between the sensor head and the rotating spindle shaft under cutting load. In order to increase the bandwidth of the indirect force measurement and compensation for the spindle dynamics, the design of a state estimator, namely “Kalman filter” scheme, has been used. The second approach is the indirect estimation of cutting forces from feed drive of servo motors. Current of the machine tool feed drive has direct contributes to the torque generated by the motor and the external resistant loads. The total external load torque to the servo motor consists of the torque induced from the cutting force and that from the friction force in the guide way. The main idea is to estimate the disturbance load which is exerted to the feed drive system due to the cutting force. Hence, a Kalman filter is implemented as a model based disturbance observer for indirect estimation of cutting forces in milling process. The estimation of cutting forces is performed based on Matlab/Simulink software. The simulation results of the spindle integrated displacement sensor model are reported by applying step and simulated real cutting forces to the system. Nevertheless, the simulation results of the feed drive models are presented based on closed loop and open loop systems model, applying step force input.