The objective of this EArly Grant for Exploratory Research (EAGER) project is to develop a method of automatically designing manipulators using as many as eight bars in their linkage to perform a particular specified motion. The approach combines techniques of computational design with those of robotic systems to assist organization of the expanding options for both the design algorithm and the user. This approach forms the basis for a design system for eight-bar linkages, and may be extendable to 10 and 12-bar linkages. It is a high-risk high-reward effort that can yield the first systematic design methodology for eight-bar linkages.
The broader impact resulting from this work is the ability to design new and innovative complex linkage systems that are currently beyond our capabilities. This research also provides effective tools for the design of a new range of devices useful for automation, assistive technology, and a range of applications in aerospace and automotive vehicles.
This EAGER project supported the first effort toward a computer-aided synthesis system for eight-bar linkages. Current research has been limited to four-bar and six-bar linkages. The 16 eight-bar linkage topologies (Figure 1) and the associated large number of design options make computer automation central to the design of these devices. Our design approach relied on the calculation of RR constraints for a designer-specified three degree-of-freedom 6R loop (Figure 2). There are 32 ways these constraints can be applied to obtain as many a 340 eight-bar linkages for a five-position task. The result is a significant opportunity for invention. Analysis of the resulting design is necessary to complete the design process. This computation determines the position of every link in the chain for its entire range of movement. It is a complex calculation that must be adapted to each topology, each link chosen as ground, and each link chosen to be the input crank. Automation of this process proved to be critical to the success of this design system. The initial application of this eight-bar synthesis capability was to the design of linkages that provide rectilinear movement. The design of rectilinear movement is known to result in complex linkages often with more than eight bars, and the designer has little control over the overall movement of the resulting design. Our design system has proven effective at obtaining rectilinear movement with a wide range of features under the designers control. Two examples are (i) an eight-bar linkage that provides support to rectilinear movement of a wheel, which may be useful for a specialized large travel suspension (Figure 3), and (ii) an eight-bar linkage that provides rectilinear movement capable of being sized to micromechanism dimensions for use as a linear suspension (Figure 4).
