Abstract: This paper implements a real-time NURBS(Non-Uniform Rational B-Spline) path interpolator for a six-axis arc welding robot.An open architecture robot controller is used as the testbed.The NURBS curve is calculated with an ICP(Iterated Closest Point)-based fitting algorithm.The reason that the end-effector velocity can be controlled in this motion interpolator is analyzed,and the situation is discussed when the velocity profile is a trapezoid which is commonly used in the end-effector movement.Finally,an example is given to prove the applicability of this method.After comparing with the commonly used point-to-point approximation technique,it can be observed that this mothod has great advantages.