Research On Multiple Sensors Control Technology Of Inertial Stabled-Platforms

With the development of related application requirement and technology, the traditional ground based optical tracking systems is developed into motion carrier based systems. Compared with ground based systems, inertial stabilized platforms (ISP) is required in the motion carrier based systems to stable the disturbance of the line of sight that cased by the vehicle vibration. ISP technology becomes a focused research topic as the tracking ability of the whole tracking system depends to a great extent on the disturbances restrain and tracking ability of the ISP.To improve the ISP's disturbance restraint ability and tracking performance, the paper focused on research and discuss on the problem of angular acceleration and angular velocity measure, disturbance restrain and tracking of angle control loop of low sample frequency in the ISP basing on the analyze of the model and basic principle of it. The paper dedicated on providing some efficient technique and method to satisfy the requirement of current project. The result of the research shows that with sufficient disturbance restrain ability of the ISP, the composite axis control of the motion carrier based tracking systems can be regarded as equivalent to that of ground based systems. Therefore, the control scheme of the relatively matured ground based composite axis tracking system can be used to achieve a good tracking ability.First we analyzed the vibration environment, physical model and mathematical model of the ISP and pointed out the factors that affect the disturbance restraint ability. There are two ways to improve the disturbance restraint ability. One way is to improve the restraint ability by improving the restrain factor in low and mid frequency range of the control system without changing the active restrain ability in the circumstance that the ISP's passive restraint ability is sufficient. The other way is to reduce the rotation inertia of the platform and improve the active restraint ability.The accuracy and bandwidth of the inertial sensors is the basis to improve the ISP's active restraint ability. Two MEMS linear accelerators are used to measure the angular acceleration of th ISP for their high bandwidth and low size and weight. The data of the accelerators is used to fuse with the data of MEMS gyroscopes to improve the velocity measure bandwidth. An adaptive noise cancellation method is proposed to eliminate colored noise of the MEMS gyroscope without increase the data latency of the sensor. The experiment shows that the data fusion of the MEMS accelerators and gyroscopes satisfy the requirement for measuring accuracy and bandwidth of the designed ISP control system. In the meantime, the load of the platform is reduced so that the active restraint ability of the platform can be further improved.Based on the analyze of the traditional velocity and position double loop control system, the inserting of a third acceleration control loop is proposed to improve the disturbance restraint ability for the restraint ability of the system is the combination of the three control loops as well as to increase the robustness of the system by providing a fine control target for the velocity loop. The high gain acceleration loop transforms the drive current source to the acceleration source. The control loop of the ISP is a 0 type system and acceleration object loop is of a second order deviation so that the design of an acceleration close loop is very difficult. The paper introduced a method that directly sets up the zeros and poles of the correction function based on the expected close loop transfer function without cancelling the second order resonance of the platform. The experiment shows a close loop bandwidth of 700Hz, which is far wider than that of the velocity control loop. The acceleration loop increases the restrain factor in the frequency range of lower than 20Hz by 15dB.The disturbance feed forward technology is studied to solve the problem that the MEMS gyroscope-based three loop control system's disturbance restraint ability is lower than that of a fiber optic gyroscope based three loop control system. There are multiple choices of the inserting point of the feed forward signal. The velocity loop based feed forward is a little bit better than the acceleration loop based one as the provided target object by the acceleration is nearly flat and is propitious to the design of the velocity loop. The disturbance feed forward control system increases the restrain factor in the frequency range of lower than 20Hz by 1 OdB, which is same as the fiber optic gyroscope based three loop control system.With the stabilization of the ISP, the composite axis control system of the motion carrier based tracking system is approximately the same as that of the ground based system. Referencing the control scheme of the tracking control system of the ground based systems, the method that uses target miss measured by the coarse image sensor to obtain the target's motion trajectory relative to the gimble and then to deduce the position, velocity, acceleration and even the jerk of the target, which can be used in feed forward tracking control to compensate the error introduced by the latency of image sensor data latency and to improve the tracking ability of the system. The experiment shows that the tracking ability of the system can be increased by 5 times with application of velocity and acceleration feed forward scheme.