Study On Orientation Singularity And Singularity-Avoidance Of 6/6-Stewart Platform With Redundant Actuation

Singular configuration is an intrinsic property of mechanisms. The moving platform would achieve one or more than one local degree of freedom when the parallel manipulator lies in singular configuration. The motion ability and dynamics performance would have even great changes when the parallel manipulator nears the singular configuration. Not only should the manipulator avoid singular configuration, but also should be far away from it. Therefore, singular configuration should be further researched so as to decrease its effects. The main contributions of the paper are as follows:Basic theories of the parallel manipulators have been introduced, consisting of descriptions of rigid bodies' position and orientation, especially the concepts of quaternion and the descriptions of the orientation of body using unit quaternion, descriptions of mobility and force using screw, basic concepts of singular configuration, forces' analysis of the 6/6-Stewart platform and the discriminance of singular configuration using force Jacobian matrix.As the view of researching objects, singular configuration can be classified as position- singularity and orientation-singularity. The orientation-singularity, which has been researched by few literates, has been researched with description of orientation using unit quaternion in the dissertation. A polynomial expression, which represents the orientation-singularity loci of manipulator at a fixed position, has been derived, and then is described in three dimensional space. Finally, the effects of manipulator's geometry configuration and the position of the moving platform on orientation-capability have been researched in the dissertation.Orientation-workspace of the 6/6-Stewart platform has been researched with description of orientation using unit quaternion in the dissertation. The concepts and the algorithms of orientation-workspace, nonsingular orientation-workspace, practical orientation- workspace and practical orientation-capability are represented. Examples of a 6/6-Stewart platform are presented to demonstrate the correctness of these algorithms, and then the practical orientation-capability versus the position of moving platform in the the work space of original orientation has also been represented.Finally, the theory of redundant actuation to avoid singular configuration has been introduced in the dissertation, and then it has been applied to the singularityavoidance of the 6/6-Stewart platform. A given exsample is used to demonstrate thevalidity of this method.