Abstract: A novel parallel machine-tool mechanism based on the compound-sphere-joint is presented. The parallel machine tool consists of a moving spindle system and a fix base connected by 5-SPS serial chains. The moving spindle system is made up of two compound-sphere-joints, one of them is a three-layer sphere-joint connecting three SPS serial chains; the other is a two-layer sphere-joint connecting two SPS serial chains. The two-sphere-joints spindle system replaces the general moving platform and the main axis of the parallel machine tool is collinear with the centerline of two sphere-joints. Compared with Stewart platform, the novel 5-SPS parallel machine tool has the same necessary degree-of-freedom, and its structure will be simple and has decoupling of the position and orientation. In addition, inverse position resolution is convenient, and its con-trol is easier. The novel structure of the parallel machine tool is proposed, and the structure of the compound-sphere-joint is analyzed. Inverse position resolution is obtained. Posing reachable workspace is also analyzed and calculated. The novel parallel mechanism machine tool has a wide prospective outlook in three-dimension surface manufacturing fields.

Key words: Compound-sphere-joint, Inverse position resolution, Parallel mechanism, Reachable workspace