A key role of the CNC is to perform the feedrate interpolation which consists in generating the setpoints sent to each axis of a machine tool based on a NC program. In high speed machining, the feedrate is limited by the velocity, acceleration and jerk of each axis of the machine tool. The algorithm presented in this paper aims to obtain an optimized feedrate profile which makes best use of the kinematical characteristics of the machine. This minimum time feedrate profile is computed by intersecting all the constraints due to the drives in an iterative algorithm. It is worth noting that both tangential jerk and axis jerk are taken into consideration. The proposed VPOp (Velocity Profile Optimization) method is universal and can be applied to any articulated mechanical structure as it is demonstrated in the examples. Moreover the algorithm has been implemented for various formats: linear interpolation (G1) and NURBS interpolation in 3 and 5-axis. The effectiveness of the algorithm is demonstrated thanks to a comparison with an industrial CNC and can be freely tested using the VPOp software which is available on the internet http://webserv.lurpa.ens-cachan.fr/geo3d/premium/vpop.
Many sources of errors exist in the manufacturing process of complex shapes. Some approximations occur at each step from the design geometry to the machined part.The aim of the paper is to present a method to evaluate the effect of high speed and high dynamic load on volumetric errors at the tool center point.The interpolator output signals and the machine encoder signals are recorded and compared to evaluate the contouring errors resulting from each axis follow-up error. The machine encoder signals are also compared to the actual tool center point position as recorded with a non-contact measuring instrument called CapBall to evaluate the total geometric errors. The novelty of the work lies in the method that is proposed to decompose the geometric errors in two categories: the quasi-static geometric errors independent from the speed of the trajectory and the dynamic geometric errors, dependent on the programmed feed rate and resulting from the machine structure deflection during the acceleration of its axes.The evolution of the respective contributions for contouring errors, quasi-static geometric errors and dynamic geometric errors is experimentally evaluated and a relation between programmed feed rate and dynamic errors is highlighted.
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