| Because the Cable-driven parallel mechanism is actuated by cables instead of link, it has the characteristics of high rigidity, high precision, high load capacity,compact structure and high-speed operation capacity. However, since the cable can only withstand tension but not compression and are flexible, the workspace of Cable-Driven Parallel Robot is not just determined by length of cables. Cables should be kept tight in process of driving actuator. Not all Point in workspace determined by length of cables can satisfy the state of keeping tension, so the workspace of cable driven parallel robot is limited. If more cables are added to the Cable-Driven Parallel Robot, the driving control must be very complicated. So, if springs are added into the proper position between end-effecter and frame of Cable-Driven Parallel Mechanism in the form of Cable-Spring Mechanism, the number of cable of this mechanism that can keep certain tension and movement, with spring providing passive force, is equal to that of degree freedom and the structural performance of this mechanism is improved without changing the number of cable. So it is necessary to analyze the structure characteristics of the Cable-Spring Parallel Robot.This thesis is base on the working performance of the Cable-Spring Parallel Robot and concentrates on the analysis of the influence of the parameter of springs on the distribution of stiffness and the tension of cables. And base on this, an algorithm program is proposed to optimize the structure parameters of the Cable-Spring Parallel Robot to achieve the largest workspace which meet the requirements of the stiffness distribution and the cable tension distribution of the mechanism. Then the analysis of the motion control of the Cable-Spring Parallel Robot with the center-of-gravity shift is proposed. This dissertation mainly includes the following aspects:First, the structure model of Cable-Spring Parallel Robot is established. Second, based on the wrench closure workspace of three degree-of-freedom restrained Cable-Driven Parallel Robot, a method is put forward to solve feasible workspace of the Cable-Spring Parallel Robot, and then the stiffness and cable tension at point in workspace is calculated.It is analyzed that the effects of the stiffness distribution and the cable tension distribution by altering the spring location, the initial length and stiffness. The stiffness distribution and the cable tension distribution of the mechanism are used to evaluate the quality of the workspace, and then the genetic algorithm is used for optimizing the spring’s parameters of the Cable-Spring Parallel Robot to achieve the largest workspace which meets the requirements of the quality of the workspace.Passively Guided Deflection Units is added to Cable-Driven Parallel Robot, that the fixed hinge join of the spring branch is replace by slide connected with two springs along a straight track. The effect of passive Guided deflection Units on the performance of the workspace is studied. The structure of the Passively Guided Deflection Units is designed by comparing the influence on workspace, the distribution of stiffness and cables tension.According to the structural characteristics o f the Cable-Spring Parallel Robot, the dynamic model under ideal conditions and the dynamic with gravity and center-of-gravity changes of the moving platform are established. Considering that the gravity and centre-of- gravity of the robot is always unknown and time-varying, a robust compensation control strategy with H?tracking performance is developed, which aimed to solve the tracking performance of the Cable-Spring Parallel Robot with the time-varying and unknown of the centre-of-gravity shift. According to the desired motion of the moving platform, the simulation calculation of the motion process of the Cable-Spring Parallel Robot is carried out, and the dynamic characteristics and the stability of the robot in motion are studied. Then the reasonable control method is proposed. |
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