Fault-tolerant strategy and workspace of the subreflector parallel adjusting mechanism

Parallel mechanism has been widely used in large-scale and heavy-duty attitude adjustment equipment. In order to improve the work reliability of the subreflector parallel adjusting mechanism, a fault-tolerant strategy based on the redundant degree-of-freedom and a workspace boundary identification method are proposed in this paper, which can realize the proper function of the subreflector parallel adjusting mechanism when it has a driven fault. The configuration and parameters of the parallel adjusting mechanism are introduced firstly, then the degrees-of-freedom of the parallel adjusting mechanism is calculated when it has a driven fault, and the principle of the fault-tolerant strategy based on the redundant degree-of-freedom is deduced in detail. Next, the method to solve the workspace boundary identification problem for the parallel adjusting mechanism in fault tolerance conditions is proposed, the maximum and minimum workspaces of the parallel adjusting mechanism at fault tolerance conditions in different frequency bands are analyzed. The results showed that the workspace calculated by the fault-tolerant strategy in the fault condition can completely meet the needs of the subreflector, where this method can also be applied to other parallel mechanisms. Lastly, an experiment is conducted to verify the correctness and effectiveness of the fault-tolerant strategy, in which the results showed that the fault-tolerant strategy can effectively improve the work reliability of the parallel adjusting mechanism. The fault-tolerant strategy and workspace boundary identification method can make the subreflector parallel adjusting mechanism work normally when it has a driven fault, which can significantly improve the work reliability and work efficiency and the maintenance cost can also be reduced. The fault-tolerant strategy and workspace boundary identification method can also be well applied to the research and development for this kind of parallel mechanical equipment.

Workspace Investigation of Cable-Driven Robots With Non-Negligible Cable Mass and Antipodal Method

The significance of gravity, cable density and elasticity on cable tension and manipulator workspace is investigated. Formulations of the cable tension vector are discussed. In addition, implementation of the antipodal theorem criteria for the workspace boundary characterization of planar cable-driven robot manipulators is presented when the mass and elasticity of cables are included. It is demonstrated that unlike the linear model, the external force could have more prominent effect on the workspace. Specifically, depending on the cable properties, platform orientation and manipulator design constraints, for the catenary cable model, the extended workspace due to external wrench may be divided into disjoint regions.

The Analysis of PPP-δ Robot Workspace Based on Boundary Search Method

There are two ways to solve workspace boundary, analytic geometry method and numerical method. In this paper, boundary search method is used to wok out the PPP-δ parallel robot workspace. And the relevant points coordinates and motion displacement of expression S1, S2, S3 is worked out. And the PPP-δ parallel robot graphical workspace is also obtained.