HP Labs Technical Reports
A 2D Study of Hybrid Position/Force Control
Fisher, William D.; Mujtaba, M. Shahid; Sinha, Pramath
Abstract: We examine and explain why the hybrid control scheme of Craig and Raibert is stable for certain manipulator configurations and not for others. We use the general two dimensional manipulator configutation to establish the basis vector of interest b sub (sj) (super T) for a given S and generalized J, and show how the space for the selected joint position vector theta sub e sub s in general is spanned by b sub (SJ) super T and a vector orthogonal to b sub (SJ) super T. In particular, a two revolute joint manipulator has unstable configurations whereas the polar and Cartesian type manipulators are never unstable. A comparative analysis with the same manipulator geometries using a corrected version of the hybrid position/force control scheme is given to show that the space for the selected joint position vector theta sub e sub s is always spanned by the b sub (SJ) super T basis vector. Experimental results on a two dimensional case illustrates well-behaved performance with the corrected (SJ)+ position formulation over a region that has been shown to cause difficulty using the original J super-1 S position formulation.
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