In this paper, displacement analysis of a general spatial open-loop system and a computer algorithm for the workspace of the system are developed by applying the direction cosine matrix method. In using this method, one global coordinate system and two joint local coordinate systems must be predefined in order to formulate the direction cosine transformation matrices of the unit vectors of each joint axis and link vector. The 3 × 3 direction cosine transformation matrices for each joint axis and link vector are established based on the known geometric configurations, the preceding unit vectors, and the cofactor property of the direction cosine matrix. The use of cofactor property will provide a unique solution for the transformation matrix. A computer algorithm is developed to illustrate the workspace of spatial n-R open-loop systems projected onto the coordinate X-Y, Y-Z, and X-Z planes. Numerical examples are demonstrated for an industrial robot, an application to human upper extremity, and a hypothetical 9-link open-loop system.

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