Hi all, While this list is essentially a list for EMC controller discussion an occasional passing word on precision and accuracy might be appropriate.
Definitions: accuracy : the ability to hit the blueprint values precision: your repeatability You can adjust your code to hit the spec dead on but only if you have a VERY accurate way of measuring your part independent of the machine you made it on! Now after you get accuracy you can start to worry about the variability (scatter) around the target value. Here is where you get to play with statistics both on the production end and on the measurement end. Do many of do this; I suspect not. We make parts that are good- enough. That is good enough for the intended use. If they don't fit we try again. IMO - only those in a production mode worry much about dimensions to spec. Control issues: On servo machines you really have two values to worry about. Position of the bed ... and most of the time 0.0002" or 0.0001" is way better than the tightness of the machine. Ten times that might be more realistic. The other is machine velocity usually taken off an encoder and used in the PID loop. Experience tends to indicate that this can and should be a high as you can get and not over-run the max frequency for either the encoder or the encoder counter. Often these are the same device and you use what you can afford. High counts/machine unit tend to help the quantization error and lead to better control. OK you're next. Dave ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
