Research On Six-axis Micro Vibration Test Platform

Ground vibration testing is an effective means to detect the performance of aerospace precision equipment. With the increasing demands of aerospace precision equipment, higher accurate ground vibration testing of spacecraft vibration environment simulation is needed. An important means of accurately reproducing simulation of spacecraft environment is multi-axis vibration test. Stewart mechanism is a spatial six degrees of freedom motion platform of high precision. Combining the Stewart mechanism theory and vibration technologies, it is of great strategic significance to develop the study of six-axis vibration technology.Therefore, this paper proposals a six-axis micro vibration testing platform based on Stewart platform. Theory and simulation methods are implemented for the study of the platfrom, The primary work is as following:1. Several dynamic modeling methods are introduced and compared. Then, for the design requirement of the six-axis micro vibration testing platform, Newton-Euler method is adopted under the condition of considering the mounting positions of hooke joints and friction force of hinges to derive the complete dynamic model of the platform. Utilizing the dynamic model of the platform, the influence of hinges friction on the platform dynamic characterize is analyzed. Concretely, the conclusion that the faster the velocity of the platform move, the greater the influence is obvious. Therefore, a new structure design plan using flexure hinges instead of traditional mechanical hinges is proposed.2. Considering the requirement that the platform needs to continuously maintain good structural stiffness in vibration testing, a configuration parameters optimization scheme which uses minimum stiffness of platform as optimization goal is proposed. Meanwhile, the calculation formula of minimum stiffness is derived. Immune genetic algorithm is implemented to optimize the structural parameters of the platform. By optimization, the platform structural parameters satisfied the best and minimum stiffness is obtained.3. By analyzing the characters of flexure ball joints, the relationship between the structural parameters and coefficients of flexural rigidity, torsional stiffness, yield strength is determined. Using the dynamic model of the platform, the maximum rotational angel and stress in vibration testing is solved. Then, the flexure ball joints of the platform is designed. The joints are satisfied the requirement of strength design, which validated through the strength analyses in a finite element software HYPERMESH.4. The theoretic model of the actuator(voice coil motor) of the six-axis micro vibration testing platform. Taking the output displacement of the motor as feedback, PID and robust PID control system are designed. Comparing the step responses of two control system, robust PID control system has better performance. For the testing platform, based on single legs displacements and velocities feedback, a robust PID control algorithm is proposed. Through the simulation of the platform control system in SIMULINK, the designed control system is of good sinusoidal signal tracking and anti-interference performance.