Center of rotation estimation for rocket nozzle by infrared reflective makers and image sequences

The determination of an accurate center of rotation of rocket motor nozzle or other object to be measured is of great interest across a wide range of applications, such as rocket, missile, robotics, industry, spaceflight, aviation and human motion analysis fields, particularly for clinical gait analysis. A new approach was proposed to estimate the moving objects' instantaneous center of rotation and other motion parameters. The new method assumes that the two segment of object to be measured are rigid body which rotates around a center of rotation between each other relatively. The center of rotation varies with time in the global coordinate system but is fixed in the local coordinate system attached to each segment. The models of rocket motor nozzle and its movement were established. The arbitrary moving object' s corresponding to motion equations were deduced, and the least square closed-form solutions of the object' s motion parameters were figured out. It is assumed that the two high speed CCD cameras mounted on the 750 nm infrared (IR) filter are synchronized and calibrated in advance. The virtual simulation experiment using 3D coordinates of markers was conducted by synchronized stereo image sequences based on 6-DOF motion platform and the experimental results prove the feasibility of our algorithm. The test results show that the precision of x, y, z component on center of rotation is up to 0. 14 mm, 0. 13 mm, 0. 15 mm.