Geometry mapping

[DieGuy]

Has anyone considered the possiblity of using error mapping in the control software?

Generally good translational formulas exist and with an open source controller software like EMC or turbo CNC it should be possible to build a map to compensate for machine geometry and positioning errors.

Seems positioning errors would be the easiest, With ball screws that the DIY people are using the error is probably pretty linear and an adjustment of the distance per pitch should work.

Geometry is a bit tougher but pitch, yaw, roll and straightness in the vertical and horizontal planes should be doable by a lookup table. The calculations are well known algorythmns.

Seems most NC software offsets the coordinate system to the workpiece but some minor mods to the variable structure in the NC code could run an absolute coordinate system for the machine and a relative coordinate system for the workpiece and display. Most of the computers being used should be more than adequate to do this.

Anyone have any thoughts?

[ger21]

Mach3 has this built in. screw error compensation, and I think Art mentioned some ways to correct for other errors as well.

[alloyspec]

I think several manufacturers use them. Fadal uses "surveys" that sound similar to this. You can correct in 1 inch increments for the whole table. If I remember right Fanuc also uses a table like this on some of their controls but I don't know what they call it.