Mechanism Design And Study On Performance Of Heavy-Duty Parallel Dynamic Simulator With Six-Dimension Movement

One of typical applications of a large and heavy-duty dynamic simulator with special 6-dimension movement is using as earthquake simulator equipment. Earthquake simulator system is one of the key equipments in the research field of vibration engineering. By means of inputting the data from the record of a natural earthquake or artificial seismic waves, an earthquake simulator can reproduce the earthquake motion under which failure mechanisms and collapse processes of various kinds of structures can be studied. This is help to establish the resistance standards, find the methods of earthquake resistance and reduce the cost of earthquake seismic hazards. Most of the traditional earthquake simulators are driven by hydraulically-actuated system and have redundant chains to enhance the driving force and bearing capacity. This drive mode brings about some shortcoming, such as huge system, limited application environment, high cost, undesirable characteristic of low frequency and difficult to control, and so on. Based on the analysis of disadvantages of the current earthquake simulators, this paper presents a novel motor-driven earthquake simulator which has not any redundant chains but has the characteristic of redundant-driven and fault-tolerant ability. Meanwhile, this paper focuses on several key problems, such as the actuator with redundant and fault-tolerant function, the method of designing a novel mechanism for simulating earthquake motions, building the mathematic models and its simplified strategy for real-time control, analysis of the performance index, developing the control and measure system and performing the experiments. The main contributions are as following.1. In consideration of the disadvantages of large hydraulic drive and redundant kinematic chains, a novel redundant and fault-tolerant actuator (RFTA) driven by motors is presented. This actuator is appropriate for heavy-payload equipments, including earthquake simulator. The kinematics of RFTA is built and its 12 working models are given. The translation mechanism characteristics are studied and three design guidelines are obtained. The reliability of this RFTA is also analyzed. Experiments for verifying are done and the results show the RFTA has the desirable functions of double supply and fault-tolerant.2. Based on summarizing the engineering characteristics of general seismic motion, the basic parallel mechanis as earthquake simulator is designed. This parallel mechanis has the following features: ability of 6-dimention motion in space for simulating a real earthquake motion, simple mechanism without over-constraint for responding to three essential earthquake elements, stong driving power and bearing capacity for getting the collapsing force of earthquakes. Applying the RFTA to the basic parallel mechanism, many different earthquake simulator with multi-motor are designed, which adapt to the development tendency of large earthquake simulator system.3. The relationship between the mechanical topology parameters of an earthquake simulator and its kenimatic characteristics is researched. The research consists of three parts, that is the relationship of mechanical topology parameters and inverse kinimatics, how the mechanical topology parameters affecting characteristics of the decoupling and the isotropy, and the position-errors in different mechanical topology parameters under decoupled control. The feasibility of decoupled control is discussed4. The relationship between the mechanical and structural parameters of an earthquake simulator and its dynamic characteristics is researched. The stiffness model of the whole earthquake simulator is built. The relationship between the mechanical and structural parameters of an earthquake simulator and its stiffness is discussed. The force analysis of every parts of an earthquake simulator is studied by using Newton-Euler method. The dynamics model is derived and the mechanical and structural parameters of meeting the requirement of general decoupled output forces are obtained. The dynamic simulations based on the dynamic model are performed and the results show the mechanism has the desirable dynamic characteristic under low-frequency motion.5. In view of nonlinearity, multi-variate coupling, difficulty of real-time control, this paper analyses the complexity of computing the closed dynamic model and presents a decoupled method to simplify dynamic model according to the orthogonal fearture of the parallel mechanism. Based on the simplified dynamic model, the control of computed torque method is simulated in the earthquake simulator. The result shows the control of computed torque method based on the simplified dynamic model not only meets the requirement of computing precision but also improves the computing efficency, which makes controlling a parallel mechanism based on its dynamics possible.6. An earthquake simulator system for experiments is developed. The multi-axis control system with redundant and fault-tolerant function is built for simulating seismic waves. The software system is written according to the working fearture of the equipment. The 3-D laser tracker is used to measure the position of the moving platform and the acceleration of every direction is tested by single-direction accelerometer. A typical earthquake wave, named El-Centro, is simulated on three translation-directions of the earthquake simulator. The harmonic motions with fixed-frequency are performed on its three rotation-directions. The results of experiments display the earthquake simulator is able to simulate 6-dimention motions of a natural earthquake and satisfies precision, which shows the earthquake simulator is appropriate for using as earthquake simulator.