CNC
چهارشنبه ۶ فروردین ۱۳۹۳ at ۱۱:۲۵
Before the introduction of our CNC projects, Let’s describe what CNC is?
CNC is an abbreviation of computer numerical control . In Iran just called CNC machine but the translation in Farsi could be numerical control machine.
Nowadays, industrial parts are with complex shapes that can be produced by only high-precision machine. With significant progress in the electronics industry since the seventies, using minicomputers were introduced in the machining industry.
The machine tools which had been directed by computer called CNC. By CNC technology, the precision required to produce complex parts in various industries gradually like aerospace and mold was obtained. With access to very precise tolerances to produce a piece , gradually production speed increased.
Making tools with high hardness, improved the conditions of production. However these days by using high speed machining techniques the parts with accurate tolerances are produced in a very short time. To achieve high speed machining capabilities we should improve in various areas such as structural design, self-motivated vibration control , finding the best rate of chip removal and control the movement and speed.
Motion Control in CNC machines is done in interpolated unit. Most CNC interpolation have the interpolation ability just along line and circle unit.
In the general a curved path for machining by using this type of interpolation needs to break off to curved lines and circles, therefore, these two types of interpolation do not meet all the application requirement such as high speed process.
So using another type of interpolation, ie interpolation along a the curve is necessary. Several researchers in this field have been investigated and have provided several algorithms based on the use of polynomial parametric curves in general.
Korn [1] by expanding the first circular interpolation, has provided interpolation methods for quadratic curves . Korn [4], Yang, Kong [6], Huang, Yang [5] by using a polynomial parametric curve have provided methods for interpolation gave curve, but these methods should be used for the interpolation of a 3rd degree curve and do not have an affect on the higher degree. Gradually by applying the concepts of B-Spline, Bedi [7] and another his assistant have provided another method for interpolation.
At about the same time, Wang [8] Yang [9], based on the parameters of the arc length have provided a useful method for Real-Time interpolation problem along the curves. this method is relatively widespread use in CNC industry.
By improving the arc length parameter method by Wang, Wright [10] , this method was extremely efficient curves of 5th degree. The method developed by Altintas [3] by using different velocity profiles. But all these methods are based on the arc length parameterization and they are not accurate methods.
Using a curve called ? ? (PH) which are the subset of parametric curves the interpolation Real-Time can be solved analytically. These curves that introduced by Farouki, Sakkalis have a special mathematical properties and these properties are able to calculate the arc length of a parametric polynomial expressions. The Different interpolation methods based on instantaneous Real-Time curves by Farouki has been provided. Also, by using the Pythagorean curves – ? , the optimized speed on a curved path can be gained due to the car’s power.
In this study, first we will describe the principles and method of displaying curves. And then will introduce the Pythagorean curves ? and express their mathematical properties, geometric interpolation problem is solved by using such these curves. In addition, describe the interpolation unit, First the variety of linear and circular interpolation are simulated by using velocity profiles.
The combination of different types of velocity profiles for machining a curved path is reviewed and the best velocity for high speed machining is recommended. In the next section will provide the issue of finding the optimal speed curve over a Pythagorean – based on machine ability and will use the different velocity profiles.
While entering the shear forces at the constraints and applying appropriate velocity profiles, a new formulation of the problem is done and the accurate solutions will be presented to solve this problem. The simulation algorithms for interpolation along the lines, circles and curves by using special techniques are actually implementing on the CNC machine.
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