Precise Position Control of a Gimbaled Camera System

Abstract

In the camera systems mounted on moving platforms such as the surveillance camera of unmanned air vehicles, it is a difficult task to track nonstationary targets. Especially for maneuvering ones, the optical field of view (FOV) of the present cameras is not wide enough to keep the target image within the boundary. Thus, the use of the gimbaled structures is one of the most common ways to enlarge the effective FOV of the cameras. In this sense, the orientation control of the camera supported by the gimbals comes into the picture as a significant issue. In order to make the camera follow the intended target accurately, its orientation should be correctly controlled by means of a convenient control system constructed upon the gimbaled configuration. Here, the most usual control algorithm is the conventional single-loop control system. On the other hand, the two-loop alternatives become more advantageous when the precision requirement from the control system is increased. In this study, the single- and two-loop position control systems are evaluated in the precision control of a gimbaled camera system and relevant computer simulations are carried out. Eventually, it is observed that the two-loop control systems especially regarding the robust control structure in the inner loop yield better results than their single-loop counterparts. Nomenclature ti B = viscous friction coefficient i d = uncertainties defined in the robust control system (i=1, 2, and 3) E = error between the desired and actual gimbal positions j e = penalties defined in the robust control system (j=1 and 2) s f = desired bandwidth of the speed control system () s Gc = controller transfer function () s G v = transfer function of the speed control system I = driver unit output current i J = moment of inertia of the inner gimbal about the rotation axis K = controller of the robust control system d K = derivative gain of the controller i K = integral gain of the controller p K = proportional gain of the controller t K = motor torque coefficient ti K = equivalent stiffness of the connection cables v K = velocity gain of the controller vi