Re: what is POSTPROCESSOR? a fundamental question

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jerry Kimberlin
<kimberln@a...> wrote:

> "doug98105 " wrote:
>
> > In some cases a post processor can be more than a translator from
> > the CAM program's internal data format to a language that is

machine

> > specific.
>
> What are the characteristics of a machine that makes it different
> from any other machine? That is if you have one brand of 5-axis
> machine and another brand of 5-axis machine and both use stepper
> motors and stepper drivers, where are the differences that
> constitute machine specificity with regard to a post processor?
>

Following are 2 machines with the same definition, 5 axis. The
programming of each is entirely different, even ignoring simple
controller syntax requirements or options.

1) 5 axis mill. normal x-y-z linear and then a rotary table mounted
on a trunnion, attached to the mill table. The rotary table has 7200
degrees of movement (10 revs) and the trunnion has only 90 degrees.
Simple positioning or surface contouring cannot attempt to program
the trunnion past 90 degrees.

2) 5 axis gantry mill. Normal x-y-z linear and then an articulated
spindle with a B axis with 45 degrees of freedom, and a C with 180.

A "simple" program like VectorCam will properly output 5 axis rotary
positioning and 3 axis rotary contouring for either of these
machines. This is done with special add-on programs
that "postprocesses" what would normally be X-Y-Z coordinate data
representing lines and arcs. These postprocessors(actually dll's in
the case of Vector) takes into account the rotational effects needed
for the rotary axes. They interact instantaneously during the
program generation and create the desired output wihtout any
intermediate files and processing steps.


Another example is the high speed machining option. With this
feature Vector evaluates the geometry to be cut and creates feed
reductions and increases within the CNC program to compensate for
cutting conditions encountered when approaching a sharp corner. Some
machines will simply slew around the corners at high feed rates.The
Vector hsm places feed reductions at a predefined distance before and
after the corner, so that instead of having to go into a dead-stop
exact positioning mode, you can reduce the corner errors, while at
the same time continue cutting at high speeds with continuous
contouring in areas that have long straightaways. Different materials
and geometry require different sets of parameters and this allows one
to specify them without having to reset the actual machine operating
parameters.

You don't see it, because the process of geometry creation through
CNC code creation is all accomplished by directly generating the
program. You see a picture and you see a CNC program that will turn
the picture into a real part. The postprocessing has become an
integral part of the process, instead of an external "red headed step
child". ;-)

Best Regards, Fred Smith- IMService

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