STEP-compliant CNC with T-spline enabled toolpath generation capability

The STEP-compliant CNC (STEP-CNC) system has been under research for years, and has been considered to be able to undertake various intelligent functions that cannot be performed by conventional CNC operations based on G-code (ISO 6983). However, the toolpath generation capability requires great developing and computing efforts, thus has gradually become a major obstacle on the future path of STEP-CNC. Due to the complexity and inherent flaws of the currently used tensor-product parametric surface (such as NURBS), the freeform surface machining in recent STEP-CNC prototypes mostly relies on the off-line toolpath generator in a CAM system. This paper explores the possibility to implement T-spline in a STEP-CNC system, so as to enhance the on-line toolpath generation capability for machining freeform surfaces. A set of toolpath generation algorithms with high robustness and efficiency is proposed for T-spline according to the machining strategy defined in ISO 14649. A practical STEP-CNC system has been developed, which parses the ISO 14649-based STEP-NC code with the T-spline extension, generates the toolpath on-line, and drives the servo axes directly. Some examples have been tested to show the feasibility as well as the efficiency of the STEP-NC compliant T-spline direct interpolation technology for the STEP-CNC system.