Manual

Linearity Correction 9-1
9 Linearity Correction
Whereas the calibration factors provide an overall stretching or shrinking of the size of a
Calibrated Unit, the Automove System also contains a linearity correction mechanism to
produce small regional adjustments over the entire travel of the motors.
The motor travel is divided up into a rectangular grid. There can be up to twenty grid points
along each axis, for a total of 20 x 20 = 400 grid intersections. The spacing between grid
intersections can be specified. For Rev 3.46 and Revs 3.51 and up, a 49 x 49 grid matrix is
used.
When the Automove System receives an XY motion command, for example MA, it first
multiplies the specified X and Y coordinates by the calibration factors, then adds the
(reverse-corrected) Origin offset to produce the uncorrected microstep location. Then the
System consults the XY Linearity Correction Table.
If the coordinate happens to fall exactly on a grid intersection then the X and Y corrections
specified for that intersection are used. Otherwise, the actual corrections are determined by
interpolating between the corrections specified for the four nearest grid intersections.
("Interpolating" means smoothly blending the effects of the four nearest intersections; the
closer the commanded position is to a particular intersection, the stronger the effect of that
intersection's correction values.)
After determining the appropriate X and Y correction values the System adds them to the
uncorrected microstep location. Then, for example, in the case of the MA command, the
carriage moves directly to the corrected location.
When the host computer asks for the Calibrated Unit equivalent of a physical motor location
(via the OC command or the OT command) the Automove System uses the Linearity
Correction Table "in reverse" to produce the corresponding reverse-corrected values.
Setting Up The Correction
The values in the table are set up via the CR ("Correction") command. The syntax is as
follows:
CR <x index>, <y index>, <x correction>, <y correction>
Each CR command sets the X and Y corrections for one grid intersection. The <x index>
and <y index> parameters determine which grid intersection is being referred to; they can be
in the range 0 through 19. For example, (0, 0) is at the Home switches and (1, 2) is one grid
intersection away in X and two in Y.
The <x correction> and <y correction> parameters determine how much correction is
applied at that grid intersection. They are in microsteps.