Parallel Manipulators Towards New Applications Part 3

Tham khảo tài liệu 'parallel manipulators towards new applications part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Quantifying and Optimizing Failure Tolerance of a Class of Parallel Manipulators 53 Table 1 also provides another important inference which is significant from the design perspective. Any redundant manipulator gives very low optimal fault tolerant manipulability values for more than one failures and these values decrease drastically with number of failures. For example for two failures in an octopod the optimal fault tolerant manipulability is and for two and three failures in a nanopod the optimal fault tolerant manipulabilities are and respectively. This means that under the hypothesis of equal probability of failure for each actuator it is not practical to design manipulators optimally fault tolerant to more than one fault. 4. Symmetric orthogonal Gough Stewart platforms Gough Stewart platforms A Gough-Stewart Platform GSP is a parallel manipulator consisting of a base a moving platform or payload and struts. The length of struts is controlled by actuators. The struts have spherical joints at the payload end and U joints at the base. To provide six degrees of freedom six struts are commonly used. Figure 1 is a diagrammatic representation of a GSP. Payload attachment points and base attachment points are represented by p. and q. i e 1 2 3 4 5 6 respectively. Fig. 1. Gough-Stewart Platform OGSPs are a special class of GSPs that provide kinematic and dynamic decoupled control. Therefore OGSPs are being widely used in commercial military and space applications. Scientists at Northrop Grumman Space Technologies NGST are currently experimenting with an 8-strut OGSP. More recent applications of OGSPs include laser tracking and pointing ultra-precise manipulation McInroy Jafari 2006 and robotic surgery Wapler et al. 2003 . The very nature of these applications makes maintenance or repair of manipulators very difficult. Moreover a single failure may compromise the fulfilment of objective or cause costly downtime. As a consequence it is desirable to

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