In this paper, there is a control system which has a strict requirement on the system load and a limited installation space for the sensors. According to the conditions of this system, the scheme by only installing a group of angular position sensors on this system is proposed. Nevertheless, the tracking performance of the system is limited by the time delay of the CCD, the traditional feedback control methods cannot meet the requirements of the system tracking accuracy. The feedforward method can theoretically improve the tracking performance without affecting the dynamic performance of the system. Unfortunately, the feedforward control method requires accurate target state information, and the CCD can only detect the light-of-sight error of the target. Therefore, we propose recovering the target trajectory by combining LOS errors from the CCD and the platform angular position from the angular position sensors, and adding a position feedforward to the system based on a dual-closed loop of angular position sensors and CCD. In addition, there is bad noise in the target state information obtained by the fusion. Then, a Kalman filter is used in this paper to filter and estimate the target state information. Essentially, the Kalman filter is the feedforward controller of the system. In order to design a better feedforward controller, a frequency-domain analysis method for the time-domain filters is proposed. The methods proposed in this paper are verified trough simulations and experiments.
In the spectral imaging system, random jitter and posture change of the aircraft generated random image motion, and flight of aircraft caused forward image motion. Both of image motion can cause image blur in a longer exposure time, which need for image motion compensation. Due to limited field of view of the optical system, limited size and weight, a stable FSM (Fast Steering Mirror) was used for random image motion compensation and a compensation FSM was used for forward image motion compensation. In the random image motion compensation, inertial sensors were used for measuring the random jitter and the posture change of the aircraft. As the advantages and disadvantages for the gyroscope and inclinometer, we used data fusion of the two sensors to complementary advantages with closed-loop mode filter data based on the frequency domain. In this way, we got high linearity, little drift, high bandwidth and little electrical noise inertial measurement sensors. On the other hand, the motion of the compensation mirror was broken down to the amount of displacement within the time required for each interrupt movement. Under strict timing control, macro forward image motion compensation was realized in the exposure time. The above image motion compensation methods were applied to actual spectral imaging systems, aerial experiment results show that image motion compensation obtained good results and met the remaining image motion compensation image error was not more than 1/3 pixel.
Proc. SPIE. 9678, AOPC 2015: Telescope and Space Optical Instrumentation
KEYWORDS: Target detection, Signal to noise ratio, Aerospace engineering, Sensors, Control systems, Optoelectronics, Space telescopes, Optical tracking, Acquisition tracking and pointing, Error control coding
It is inevitable that tracking high-elevation object exists blind region with horizontal gimbal, need to take some control methods to improve the system for high-elevation target tracking capability and reduce the blind region. This paper compares several common tracking control methods, including compound axis control of dual detector, compound axis control of single detector, compound axis control of single detector with modified guidance, analyzes the principle of operation, advantages and disadvantages, and validates by experiments. The experimental results showed that it is stable and reliable using guide modified compound axis control of single detector when the target position information is more accurate. On the other hand, it is able to meet the needs to track target with high speed and high acceleration using improved compound axis control of single detector when the target position information is not very accurate.
Line-of-sight stabilized system, which can be used to isolate the vibration of the moving bed and the disturbance of
environment, is the most important part of an electro-optical tracking system. The steady precision and robustness are the
key issues of recent researches. In this paper, a novel control approach so called 2-Port Internal Model Control (2-PIMC)
for line-of-sight stabilized system is proposed. By adding a parallel feedback control loop on the basis of Internal Model
Control (IMC), the 2-PIMC method can improve precision while it also has strong robustness as the IMC. The
robustness and the static error of 2-PIMC method were subsequently analyzed. Based on this novel method, Simulation
and experiment are both carried out for a gyro stabilized platform of electro-optical tracking system. The experiments
include a shaking table which can generate disturbance as the moving bed and a gyro stabilized platform which is
mounted on the shaking table. The experimental result indicated that the gyro stabilized platform using 2-PIMC method
is accurate and effective. Comparing with PI control, the following error and disturbance restraining error were both
greatly improved at low-frequency and mid-frequency by the 2-PIMC method proposed. The improvement of precision
is more than 10dB at 4Hz. In addition, the 2-PIMC method doesn't need any extra sensors for the platform and it's easy
for parameters regulation. It can be concluded that the2-PIMC method is a new approach for the high-performance gyro
stabilized platform and might have broad application prospect.