| Electrically-actuated torsional dynamic stiffness tester is a test equipment which is desperately needed for the design of high-performance transmission systems in the field of shipbuilding, aerospace, guided weapons. In order to study the dynamic stiffness characteristics of the measured objects throughly, the tester with wide loading frequency band is required. However, the improvement of loading frequency would lead to low loading accuracy and small torque amplitude for the electric loading test equipment. Therefore, this thesis takes the loading platform of torsional dynamic stiffness testers as study object, researches mechanical system and loading system of the loading platform, and solves the influence of wide loading frequency band to loading accuracy and torque amplitude from structure and control, with the aim of theoretical and practical guidances for the improvement of high performance electric test equipment.The overall scheme of the electric loading platform are proposed according to design requirements, which is based on the principle and method of torsional dynamic stiffness test. The electric loading platform is divided as mechanical system and loading system to be designed and analyzed. For the mechanical system of loading platform, frame structure and three-DOF repeat positioning mechanism are designed to solve the problem of versatility, and the structural performance is also analyzed by FEA software. To avoid the structure resonance affecting test accuracy, this thesis takes the way of enhancing stiffness and reducing weight, then the modal frequency of loading platform is improved effectively. For the loading system of loading platform, the loading motor and measuring sensors are selected according to the working principle, then the mathematical model of loading system is established. The influence of transmission part stiffness to the characteristics of loading system is analyzed, and suitable transmission shaft is designed based on the result. In order to improve the control performance of the system, and solve the problem of disturbed torque, torque closed-loop PID control and feedforward compensation element based on structure invariance theory are designed. The decentralized loading mode used double motor is proposed, and simulation results indicate that this way could improve the output torque amplitude to 40 Nm under the premise of 120 Hz loading frequency.Finally, the performance of loading platform is tested and simulated. Through the modal experiment, modal parameters of the loading platform are obtained. The result is consistent with simulation, and it reveals that the first-order modal frequency of the mechanical system is 233.1Hz, much more highly than the maximum loading frequency 120 Hz. In addition, the simulation analysis reveals that the loading system has good torque tracking performance in the frequency band of 120 Hz, the amplitude error of loading torque is within 10%. |
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