Synthesis of Useful Eight-Bar Linkages as Constrained 6R Loops

Abstract

This paper formulates a methodology for designing planar eight-bar linkages for five task positions, by adding two RR constraints to a user specified 6R loop. It is known that there are 32 ways in which these constraints can be added, to yield as many as 340 different linkages. The methodology uses a random search within the tolerance zones around the task specifications to increase the number of candidate linkages. These linkages are analyzed using the Dixon determinant approach, to find all possible linkage configurations over the range of motion. These configuration trajectories are sorted into branches. Linkages that have all the five task configurations on one branch, ensure their smooth movement through the five task positions. The result is an array of branch-free useful eight-bar linkage designs. An example is provided to illustrate the results. INTRODUCTIONIn this paper a design methodology is described for generating useful eight-bar linkages for five finitely separated task positions or poses. The user first discretizes the desired motion requirement into five task positions. In addition, the user also specifies a three degree-of-freedom planar 6R (6 Revolute joints) parallel robot, that can reach all the five task positions. A 6R parallel robot (6R loop) is shown in Fig.1 along with its graph.The eight-bar linkage is obtained by synthesizing two RR constraints that constrain the 6R loop to a single degree-of-

Synthesis of eight-bar linkages by constraining a 6R loop

“…This paper is an extension of research on eight-bar linkage design system presented in Sonawale and McCarthy (2014); . The initial results in this area focused on adding three RR dyads to a 4R serial chain can be found here, .…”

Design of Eight-Bar Linkages With an Application to Rectilinear Motion

“…Their method couples two four-bar legs, to guide a coupler through 11 task positions. Our work follows the design procedure of constraining the user defined open or closed chain using RR constrains, introduced by Soh and McCarthy (2007) [12,13] and further developed by Sonawale and McCarthy [14,15]. Soh and Ying (2013) [16] followed this procedure to design an eight-bar linkage with prismatic joints.…”

Flexure Design for Eight-Bar Rectilinear Motion Mechanism

“…Continuing research on finding all possible ways of applying the RR constraint was presented by Sonawale and McCarthy (2014) [9]. In our research, we specified the five task positions on a straight line.…”

“…The synthesis of an eight-bar linkage to reach five task positions has been presented by Soh and McCarthy (2007) [6] and Sonawale and McCarthy (2014) [9]. This method starts from two 3R chain robots and by adding two RR constraints to get one degree-of-freedom eight-bar linkage.…”