EFFECTIVENESS OF INPUT SHAPING AND REAL-TIME NURBS INTERPOLATION FOR REDUCING FEEDRATE FLUCTUATION

In modern CAD/CAM system, NURBS (Non-Uniform Rational B-Spline) interpolation is adopted for the purpose of achieving high speed and high accuracy performance. The main problem with using NURBS curve is the relationship approximation between arc length and spline parameter. In case the toolpath planning can be assumed with no feed fluctuations, implementing of driving mechanism still can lead CNC system to vibrate. Input shaping is a method of preshaping control input to reduce residual vibration in the flexible systems. Input shaping alters the reference command by convolving it with an impulse sequence. The convolution product is then used to drive the system. In this paper, NURBS curve representation was employed to generate the planning trajectory for a two axis gantry crane which is considered as a CNC system. The effectiveness of input shaping based on genetic algorithm was investigated by following the desired NURBS curve.