The postprocessor translates certain AutoCAD drawing elements. When an AutoCAD .DXF file is created by AutoCAD, every type of element currently in the drawing is in the .DXF file. The Router-CIM postprocessor will filter out the AutoCAD elements that do not have meaning to the NC translation process. Due to the large list of element types available in AutoCAD, the following list contains only those data elements that the postprocessor will process. AutoCAD drawing elements processed by postprocessor are:
Circle (later broken up into an arc)
Polyline (later broken up into arcs and lines)
Spline (later broken up into lines or arcs)
Ellipse (later broken up into lines or arcs)
All other AutoCAD drawing elements are filtered out during the post processing step and ignored.
During the Geoshape step in Router-CIM the geometry elements listed above are reduced to their smallest elements. That means that a polyline, for instance, will be broken down into lines and arcs as necessary for the translation into NC Code. Since most machine tools will only be capable of making either a linear or arc motion, all elements eventually turn into these geometric pieces.
The postprocessor translates AutoCAD .DXF data in a specific manner. This manner of processing AutoCAD data to NC code is outlined in this section.
The process of translation is a sequential process. Each time a piece of data is encountered, a specific NC code is developed for that piece of data. This basic concept is applied to every AutoCAD element in the input .DXF file.
Since NC code is based on motion blocks (sometimes referred to as command blocks), the "trigger" that outputs NC code is a motion by the machine tool. This motion is any X, Y, or Z AutoCAD entity, such a line, arc, circle, polyline, spline, ellipse or point. Even though the motion may not physically move the machine tool, a command block is developed. An AutoCAD data element that is considered a tool motion but does not physically move the machine is a point at a location where the machine tool is currently located.
A text line of NC code (command block) is produced every time the postprocessor encounters a physical AutoCAD element. A physical element is a line, point, arc, circle, polyline, ellipse, or spline.
AutoCAD text statements are "collected" by the postprocessor and then output as NC code when a physical AutoCAD element is processed.
Understanding the two facets of processing outlined above, we can combine text statements with AutoCAD geometry to yield certain results. An example would be two text statements followed by a line element.
These three AutoCAD elements would be in the order of TEXT, TEXT, and LINE. These three elements would produce one text line or motion block of NC code. The postprocessor would sequentially "collect" the two text statements, then encounter the line element. The line element would cause an NC text output. The format of the command block with the two text statements and the line is governed by the .$PP file.
This section only touches on the concept. The "Configuration" section provides a technical description of the various formatting features of the program.