Figure 1

Block diagram of the feed drive system of a concerned axis (R and P are the reference position and the actual position. \(K_\text{f}\), \(K_\text{p}\), \(K_\text{v}\) and \(T_\text{v}\) are the velocity feedforward coefficient, the position loop gain, the velocity loop gain, and the integral time constant. \(T_\text{s}\) is the sampling interval. \(u_\text{c}\) is the compensation signal of friction. ZOH is short for zero-order holder. \(T_\text{f}\) is the friction torque. \(K_\text{a}\), \(K_\text{t}\), \(r_\text{g}\), J and B are the current amplification factor, torque amplification factor, lead screw gain, equivalent inertia and viscous damping)