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The Six Axis Wrist (page 1)

This paper describes a novel motion coordination method for redundant robots. The method combines closed-form reverse position analysis and multi-criteria optimization to form a powerful and efficient algorithm. This method of redundancy resolution has been tested (either in simulation or experimentation) on robots with 7, 8, 9, 10, 17, and 21 DOF. This paper presents results for a dual-arm robot with 17 DOF designed and implemented at Oak Ridge National Laboratory.

I. INTRODUCTION
Motion coordination for redundant robots enjoys a rich history as a part of the inverse kinematics problem. 
Dimentberg in the 1950’s and Freudenstein in the 1960’s and 1970’s were seminal authors. With the realization in the late 1960’s that a serial robot could be modelled as a spatial mechanism, the disciplined and analytical theory of mechanisms was applied to the exciting new field of robotics. This work dominated 
inverse kinematics research during the 1970’s as the search for a general closed-form solution for robots 
with six Degrees Of Freedom (DOF) became the “Mount Everest” of kinematics problems (Freudenstein, 1972). Duffy, Pieper, and Roth were at the forefront of inverse kinematics research during this time.

Within the context of redundant robots, the focus shifted towards optimization and linear algebra during the 
1980’s. Much of this work derives from Whitney’s (1969) resolved motion rate control that suggests the use of the pseudo-inverse to resolve redundancy. Liegeois (1977) showed the extension of this method to include self-motions via the null-space. Since then, a large number of researchers have implemented pseudo-inverse based methods. Notable approaches include: Seraji’s (1992) configuration control, Baillieul’s (1986) extended Jacobian, and the Jacobian transpose (Das, Slotine, and Sheridan, 1988). Dubey and Luh (1988) include task-based performance measures in the redundancy resolution. Maciejewski (1989) discusses the kinetic limitations of redundant robots.


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