Generic control functions were studied in relation to PID feedback control. It was noted that the block diagram of a PID control system is basically equivalent to the damped oscillation model of a mechanical system with a spring, mass, and damper, and that energy conversion in PID control is a conversion of potential energy, the value of which is given as a change of the target quantity to thermal energy. However, thermal energy is difficult to measure. A residual energy was therefore defined as a sum of potential energy and kinetic energy. When the residual energy becomes zero, it can be considered that all the energy put into the system has been converted to thermal energy, so residual energy was evaluated by a smaller-the-better type of S/N ratio. Parameter design was carried out by this evaluation method. As a result, the S/N ratio improved substantially and good reproducibility of the gain was obtained. From these results it was concluded that when energy changes form but remains in the system,reproducibility of the gain can be secured by evaluating the entire residual energy in the system.
