Analysis of Interpolator in CNC Machines with High Speed Machining Ability, Mohammad Javad Barakchi Fard, 2002

Abstract:

Today’s CNC machines have superior features in machining of free-form surface encountered in dies, ­moulds, automotive parts and aerospace industry. The most important and demanding one is High Speed Machining (HSM) of free-form surfaces. In order to implement HSM along a free-form path, it is necessary for the controller unit to generate sequence of reference points according to a prescribed feedrate function. To achieve a desired fixed or variable feedrate along a given curved path, CNC machines employ independent motors to drive each of their axes in a time-coordinated manner resulting desired path. In HSM the important aspects that must be taken into consideration are physical constraints of the axes driver motors. These constraints limit velocity and acceleration that can be physically realized. In this thesis, PH curves are incorporated for generating of reference point according to desired feedrate function. The algorithm implemented in the software interpolator of an open-architecture CNC milling machine. Several feedrate profiles are investigated and the proper one is suggested for HSM. Feedrate and acceleration along a desired path are maximized subjected to motor limits and cutting forces constraint. Variation of feedrate in the vicinity of two PH curves junction point is investigated and then suggestions are proposed and implemented.