FAQ: How are the Electronic Gear Ratio parameters, Pn202 and Pn203, set for linear motors?
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The positioning resolution of the linear motor when used with the Sigma II SGDH servo amplifier in position mode is equal to the linear encoder scale pitch divided by 256. For a 20 micron pitch linear encoder (i.e. Renishaw RGH22B), the positioning resolution is 20 micron/256.
The incoming position reference is scaled by the Electronic Gear Ratio. Pn202 is the Electronic Gear Ratio numerator, set to a default of 4. Pn203 is the Electronic Gear Ratio denominator, set to a default of "1". Therefore, with these these default settings, for every reference input pulse, the linear motor will move (4/1) x (20 microns/256) or 0.3125 microns, assuming a 20 micron pitch linear encoder. The Electronic Gear Ratio can be changed to allow for "friendlier" positioning units.
For example, assuming a 20 micron pitch linear encoder:
1.) The desired position reference resolution is one micron (or 0.001mm). For every reference pulse, the linear motor moves one micron.
To achieve this resolution, set Pn202=256 and Pn203=20. Now, for every reference pulse, the linear motor will move (256/20) x (20 microns/256) or one micron.
2.) The desired position reference resolution is 0.001 inch.
Set Pn202=8128 and Pn203=25. Now for every reference pulse, the linear motor will move (8128/25) x (20 microns/256) x (25.4 inches/0.001mm), which is equal to 0.001 inch.
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