You should be able to connect the MPG to a software encoder and then connect
the velocity output from the software encoder the the feedrate.
Stuart

On Thu, Jun 18, 2009 at 4:13 PM, Leslie Newell <[email protected]>wrote:

> I think a bidirectional jog would be a nice feature. I am thinking of
> doing a crude version of this on my lathe. In jog wheel mode the FRO
> would be tied into the velocity output of an MPG. The faster you turn
> the handle, the faster the code is executed. Stop turning and the
> machine stops. Great for proof testing new code.
>
> One option would be to generate a 'pre-digested' intermediate file. This
>  contains all of the moves after tool compensation, executed code loops
> and any other fancy stuff. It would basically just contain simple linear
> moves, arc moves and triggers for spindle, coolant, I/Os etc. It would
> be easy to design this format so that it can be read in either
> direction. This file is then fed to the TP to generate movement. I
> actually do something similar in SheetCam. The offsets are generated
> then the cut paths are calculated from the offsets, in whatever
> direction is needed.
>
> I think that would be a lot easier than trying to interpret the G-code
> backwards, especially when you take code loops and subroutines into
> account. The only disadvantage is that you would get a delay when you
> load a G-code file as the whole intermediate file (or at least a
> significant portion of it) has to be generated before movement can
> start. For small files the time would be insignificant but it may be an
> issue for multi megabyte 3D contouring code.
>
> Les
>
>
> > There are several applications for going forward or backward through a
> > move or a series of moves (EDM is one).  There are several difficulties
> > though, especially if you allow all the nifty cutter comp features to be
> > turned on while you're "jogging" through the program.  You have to swap
> > G41 and G42 when you go backwards, as well as G2 and G3.  A complete
> > solution would also need to deal with other machine state, such as
> > spindle and coolant.  There have been many discussions on the topic in
> > the past.  If you have a clear vew of what you need, and ideally a good
> > idea of what other applications might need, please write it up and post
> > it :)
> >
>
>
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