The Acceleration And Deceleration Control And The Application Of High Speed Machining Of The CNC System

The acceleration and deceleration control is an important part of interpolator and the key of CNC system development. In the traditional acceleration and deceleration control, the motion stability of CNC system is reduced because of the discontinuous acceleration or jerk. The complex curve need to be discretized into a large number of continuous micro line blocks before interpolation, which will lead to frequent change of acceleration and deceleration that has a serious impact on machining efficiency. Accordingly, the acceleration and deceleration control of CNC system is deeply studied in this paper trying to realize high speed and high accuracy machining on the condition of system stability.Firstly, the traditional acceleration and deceleration controls are compared and analyzed finding out the advantages and disadvantages. In order to overcome these disadvantages, a new cubic S-shape curve acceleration and deceleration control is introduced which provides the expression of jerk, acceleration, feedrate and displacement. Feedrate planning method is carried out to deal with various conditions that may occur in acceleration and deceleration control based on optimization theory. The simulation result shows that the proposed algorithm can guarantee smooth change of acceleration and jerk so the intense impact is avoided and the higher motion stability of the CNC system is obtained, and it can re-plan the feedrate adaptively according to chord length so the machining efficiency is improved by the simple and intelligent algorithm.Secondly, the acceleration and deceleration of complex curve machining are studied. The look-ahead algorithm of continuous micro line blocks and space arc transition algorithm are studied in order to avoid frequent feedrate changes in interpolation. The transition vector angle mathematical model of geometric element is established and the velocity constraint conditions and solving method are provided. The arc transition model of adjacent lines is established, and according to the chord error conditions, the calculation method of transition velocity is provided. The feedrate does not slow down to zero in the acceleration and deceleration in these two algorithms so the frequent feedrate changes are eased in a certain extent and the machining efficiency is improved.Finally, the NURBS curve interpolation and its acceleration and deceleration are studied. Three kinds of equivalent definition of NURBS curve is provided with the principle and method of NURBS curve direct interpolation. A look-ahead adaptive acceleration and deceleration control is introduced as it has no obvious start and end point and hard to make feedrate planning in NURBS curve interpolation. Velocity constrain conditions is established according to chord error. This algorithm can find velocity sensitive points by looking ahead a certain distance and calculate and adjust the feedrate of each sensitive point, and then complete the feedrate planning and acceleration and deceleration control according to cubic S-shape curve acceleration and deceleration control. The look-ahead adaptive acceleration and deceleration control that combined look-ahead control and cubic S-shape curve acceleration and deceleration is a good solution to the velocity control problem in NURBS curve interpolation.