The Study Of Movement Controller For Open CNC

Recently, open CNC is becoming the main trend of new generation NC. To exploreCNC based on PC and consisting of open programmable movement controller has a niceperspective. This article proposes a primary project of open programmable controller whichuses DSP as its controlling core and is aided with CPLD, and designs parts of controllerinvolving interpolation and speed detecting. The project using DSP as central processing chip and aided with CPLD to communicatewith pc and dual port ram as interfaces to peripheral equipments makes full use of advantagesof hardware and software .It is also very helpful in machining performance and make thewhole system have high real-time ability, less components, compact structure and highanti_jamming ability. Proposing a full numerical speed-detecting system project. This system is realized byCPLD which can get rid of the disadvantages in one-time design including property liable tojamming, long sampling period, and poor working stability. Its sampling period is up to 500nsat least and output delay is only 19.5ns. A stable period of pulse coming out ofquadruple-frequency differential circle belongs to it. This interpolation module uses the popular and advanced NURBS interpolationtechnology. The procedures of math processing for NURBS, preprocessing for interpolationand real-time interpolating running on DSP are presented in this article. The interpolatingprocedure uses an advanced self-adjusting interpolation method, which can automaticallyadjust the length of interpolation according to machining speed, acceleration and the toleranceof bow height. A real-time interpolator for NURBS curves based on parameter prediction andcorrection is applied. The proposed approach provides good performance in two respects tomeet the requirements of high-speed and high accuracy machining. First, the calculation timeis significantly reduced by applying preprocessing, avoiding computing the derivative andradius of curvature of curves. Second, feed-rate can adapt to the curve's curvature to limit thecontour error and feed-acceleration within the allowable range. At last, this article presents the project for position correction during machining, itcompare instruction position with feedback position by software and correct the position errorwith PID control method.