TABLE OF CONTENTS The program address G identifies a preparatory command, often called a G-code. This address has one and only objective - that is to preset or to prepare the control system to a certain desired condition, or to a certain mode or a state of operation. For example, address G00 presets a rapid motion mode for the machine tool but does not move any axis, address G81 presets the drilling cycle but does not drill any holes, etc. The common term preparatory command indicates its meaning - a G-code will prepare control unit to accept the programming instructions following the G-code, in a specific way.
One block example will illustrate the need for preparatory commands in the following program entry:
N7 X13.0 Y10.0
Even a casual look at this block shows that the coordinates X13.0Y10.0 relate to the cutting tool end position, when block N7 is executed ( i.e., processed by the control). Block N7 does not indicate whether the coordinates are in absolute or incremental mode. It does not indicate whether X13.0Y10.0 are in metric or imperial units. Neither it indicates whether the actual motion to this specified target position is a rapid motion or a linear motion. If evaluation of such a block cannot establish the meaning of its contents, control system does not have enough information. The supplied information in such a block is incomplete, therefore unusable by itself. Some additional...
