문제) Consider the system shown in Figure 1. This is a PID control of a second-order plant P(s). Assume that disturbances d(s) enter the system as shown in the diagram. It is assumed that the reference input R(s) is normally held constant, and the response characteristics to disturbances are a very important consideration in this system. Design a control system such that the response to any step disturbance will be damped out quickly (in 2 to 3 sec in terms of the 2% settling time). Choose the configuration of the closed loop poles such that there is a pair of dominant closed-loop poles. Then obtain the response to the unit-step disturbance input. Obtain also the response to the unit-step reference input.