This study focuses on approximate function synthesis of the three types of overconstrained Bennett 6R mechanisms using Chebyshev approximation. The three mechanisms are the double-planar, double-spherical and the plano-spherical 6R linkages. The single-loop 6R mechanisms are dissected into two imaginary loops and function synthesis is performed for both loops. First, the link lengths are employed as construction parameters of the mechanism. Then extra construction parameters for the input or output joint variables are introduced in order to increase the design points and hence enhance the accuracy of approximation. The synthesis formulations are applied computationally as case studies. The case studies illustrate how a designer can compare the three types of Bennett 6R mechanisms for the same function. Also we present a comparison of the spherical four-bar with the double-spherical 6R mechanism and show that the accuracy is improved when the 6R linkage is used.

In this paper, the problem of function generation synthesis of planar 5R mechanism is studied using the least squares approximation method with equal spacing of the design points. The study represents a case study for analytical function generation of multi-degrees-of-freedom systems. The planar 5R mechanism is designed with a fixed input joint and a moving input joint adjacent to the first input, whereas the remaining fixed joint is the output joint. The input/output relationship of the mechanism is expreseed as an objective function in polynomial form with four unknown construction parameters. . The objective function involves nonlinearities, however the problem is linearized using Lagrange variables. The linear system is solved and finally the construction parameters of the mechanism are determined. A numerical example is presented as a case study.

Abstract. This study addresses the approximate function generation synthesis with an overconstrained two degrees-of-freedom double spherical 7R mechanism using least squares approximation with equal spacing of the design points on the input domain. The 7R mechanism is a constructed by combining a spherical 5R mechanism with a spherical 4R mechanism with distant centers and a common moving link and then removing the common link. This construction allows the analysis and synthesis of the resulting single-loop mechanism by decomposing it into fictitious 5R and 4R loops. The two inputs to the mechanism are provided in the 5R loop and the output is in the 4R loop. The fictitious output of the 5R loop is an input to the 4R loop this intermediate variable is used to also decompose the function to be generated. This decomposition provides the designer extra freedom in synthesis and enables decreasing the error of approximation. A case study is presented at the end of the study where the 7R design is compared with an equivalent spherical 5R mechanism; hence the advantage of the 7R mechanism is demonstrated.