International Journal of Computer Applications (0975 – 8887) Volume 93 – No 16, May 2014 13 Stabilizing a Gimbal Platform using Self-Tuning Fuzzy PID Controller Nourallah Ghaeminezhad Collage Of Automation Engineering Nuaa Nanjing China Wang Daobo Collage Of Automation Engineering Nuaa Nanjing China Fahad Farooq Collage Of Automation Engineering Nuaa Nanjing China ABSTRACT The aim of the inertial stabilization system is to stabilize the sensor’s line of sight (LOS) toward a target while is isolating the sensor against the disturbances which are caused by the operating environment. The purpose which this paper is following is a model of control servo system for an inertially stabilized gimbal mechanism to improve the performance of system which is using only PID controller by finding a way to tune the PID gains online, for this purpose a self-tuning Fuzzy PID type controller is used. First the relationships that governs gimbals torque will be derived from Newton’s law under consideration of the dynamic mass unbalance and base angular motion. The next step is construction of stabilization loop through designing the proposed self-tuning Fuzzy-PID controller. For simulation and investigate the system performance in different cases of controller, the Matlab/Simulink is used and Based on different performance criteria a comparison study is made. Based on the results in different conditions on proposed controller the system performance is improved. The simulation result shows improvement on transient and the steady-state performance. Keywords Servo control system, inertially stabilized platform, intelligent control, self-tuning Fuzzy PID, Matlab/Simulink. 1. INTRODUCTION An inertial stabilized platform (ISP) or well-known gimbal system is to stabilize the platform which camera or any optical sensing equipment mounted on that, to track a moving or fixed object. The equipment typically is mounted on the moving carrier like UAV or Helicopter. Although requirements for ISPs vary widely depending on the application, they all have a common goal, which is to hold or control the line of sight (LOS) of one object relative to another object or inertial space. [1] In this paper a tracking system’s LOS with nonlinear disturbance is considered. The aim is to track the input velocity command, when the disturbance due to movement of base comes to system. In this paper the pitch (elevation) loop is considered, and it is tried to stabilize one axis platform using a proper controller. Then, it opens a way toward thinking of how to make such a system stable and it can be studied for other axis (yaw) similarly. Concerning the control system, although the researchers tried to utilize and apply many different modern techniques to control servo systems, the conventional PID and its constructors are still the most used approach due to their simple structure, cheap costs, simple design and high performance [2], but when there are nonlinear disturbances or uncertain situation like what in the movement of UAV, the PID gains must tune online during the control. This paper investigates a self-tuning Fuzzy PID controller to deal with mentioned problems. The use of this controller has been proved as an effective tool of many nonlinear systems. [3]- [4] Our paper is divided to two main parts, first is presenting a stabilized gimbal control system in order to simplify the picture of the gimbal platform. And secondly to introduce a self-tuning fuzzy PID controller for related axis gimbal system. 2. FORMULATE THE MODEL 2.1 Problem Statement In principal, all the required thing to prevent an object from rotating with respect to inertial space is to ensure that applied torque is zero. According to, Newton’s second law if a net torque T is applied to a homogenous rigid mass having a moment of inertia J, then the body develops an angular acceleration α,[1], that’s evident in : T=J.α (1) The block diagram in Figure 1 shows the gimbal stabilization system. In this diagram it is tried to null the differences between the rate command input and angular rate of the gimbal, so the proper amount of torque must be forced to gimbal. From Figure 1, it can be seen that:                     , (1) Figure 1 Control loop of LOS stabilized platform Therefore, the paper problem can be briefed into the servo control platform that takes part into two main object. one is command tracking which says about how well the output speed conforms the input command speed. Another is rejection of disturbances that might be anything from the platform movement to rate gyro noise.