Hardware Experiments In Feedback Control Systems Using A Geared Dc Motor

One of the difficulties in teaching control systems to engineering and technology students is to relate classroom theory and computer simulation to experimental results. Students tend to focus on analyzing feedback control systems without understanding where the transfer functions of real life systems come from. This effect is exacerbated by textbooks in control systems, where authors often assume that variables such as moment of inertia, damping coefficients and gear ratios are readily available when determining the transfer function of a system. The purpose of this paper is to present a series of experiments with a geared dc motor which is coupled to a rotary potentiometer. In the first experiment, the students look at the impulse response of the motor to determine the transfer function of the motor. Since an ideal impulse function cannot be provided, the students provide a short duration pulse to the motor to approximate an impulse. The results of experimentally determining the transfer function can then be used in a software package, such as Matlab, to compare simulation results to hardware results. In the second experiment, the students build a position control system for the geared dc motor and again compare results with simulation results. Non-linear effects such as saturation of operational amplifiers can be considered as part of both hardware and simulation. Students are able to gain a wealth of understanding from these labs, whereby the transfer functions in the textbook become more than just numbers and variables.