【正文】 Cutter path interval 1. INTRODUCTION Parallel Machine Tool (PMT) is a creative application of parallel mechanism, NC technology and puter control technology in the area of machine tool [16]. As a newstyle machine tool, PMT has advantages of simple structure, low cost, low moving inertia, high velocity, agile mobility, high techniques, etc. PMT plements the traditional NC machine tool perfectly and especially it is suitable for machining parts with plicated surfaces such as vane, impeller and propeller, etc[2]. However, as the existing PMT which only adopts parallel architecture is restrained by hinge and interfered by chain, particularly is affected by some factors such as coupling of position and orientation, the mobile platform has a limited ability to realize orientation. Therefore, it is very difficult to meet the needs of multicoordinate NC machining with large working space and plex surface. In order to solve this problem, researchers have made efforts on exploring new architectures. Many researchers begin to pay their attention to less than 6 ,degree of freedoms (DOFs) PMTs, especially hybrid machine tools (HMTs)[4], another important developing trend of PMT is that translatory DOF and rotary DOF are implemented individually by utilizing bined mechanism. This configuration not only releases the coupling between translatory control and rotary control, but also has advantages of large working space and better reconfiguration ability. Specially, as there is an analytic solution for position and orientation in forward kinematics, so it provides a great convenience for NC programming, control and error pensation. 1PS+4TPS mechanism is a novel 4 DOFs hybrid mechanism[8], among the abbreviations ‘1PS+4TPS’, P represents prismical joint, S represents spherical joint, T represents hooke joint, it can implement one translatory movement and three rotary movements. The core architecture of novel HMT is a serial and parallel pound architecture which is posed of above 4 DOFs hybrid mechanism and a xy worktable, shown as . Mechanism design and kinematic analysis for this novel hybrid machine tool are described first, then a CNC system scheme for HMTs is designed, a realtime fiveaxis interpolator for path control of HMTs is proposed. Cutter path interval calculation and interpolate error analysis are also discussed . 2. DESCRIPTION OF NOVEL HMT’s ARCHITECTURE A 4DOF hybrid mechanism is shown in Fig. 1. . Structure scheme of novel hybrid machine tool hybrid mechanism consists of five kinematic subchains, including four variable length driving legs with identical topology and one passive leg, connecting the fixed base to a moving platform. In this 4DOF hybrid mechanism, each of the four identical legs consists of a fixed Hooke joint, an driving prismatic joint, a moving link and a spherical joint attached to the moving platform. The fifth chain, which connects the fixed base center to the moving platform center, is a passive leg with a different structure from the other four identical chains. It consists of a prismatic joint attached to the base, a moving link and a universal joint attached to the platform. Above hybrid mechanism can be bined with twoaxis systems, such as x–y tables, to form fiveaxis machines. 3. INVERSE DISPLACEMENT ANALYSIS MODEL AND INVERSE KINEMATIC MODEL FOR HMTs . Inverse displacement analysis model A fixed reference coordinate system and a movable reference coordinate system are set up on the center of fixed platform and movable platform respectively, shown as Fig 2. Position of four hooke joints of fixed platform with respect to the fixed frame can be described by ,position of four spherical joints of movable platform with respect to the movable frame can be described by ,position of four spherical joints of movable platform with respect to the fixed frame can be described by ,original point of movable frame can be described by is orientation rotation matrix of the movable platform with respect to the fixed platform described by three Euler angle. . The coordineate of spherical joint in movable platform with respect to the fixed frame can be denoted by Inverse displacement analysis equation can be written as where is the 3x3 rotation transformation matrix of coordinate system which can be obtained using three sustain rotation transformation by three Euler angles and as follows (shown as Fig 3.) . . Inverse ki