On Thu, Mar 25, 2010 at 2:59 AM, Mark Wendt (Contractor) < [email protected]> wrote: <snip>
> The Z axis was > dead nuts on, but I was get varied responses to jogs on the X > axis. I tried it at .001, .05, .01 and .1 on the jog movement. At > .001, sometimes I'd get no movement (I'd here stepper motor noise but > no movement on the dial indicator), other times I'd get a half-thou, > and other times it would jump .002" - .004". At .01, the first > couple of jogs would show about .001" - .002" short of the full .01" > movement, then occasionally move the full .01", and then sometimes > slightly more than .01". About the same for the .05" movement. At > .1", the movement for the first few times was .003" - .004" short, > but then would move almost dead nuts on to .1" each jog. I don't > think backlash would come into play since all the moves were in the > same direction. > <snip> I've seen this before and it was caused by the microstepping of the stepper motors. Stepper motors want to rest at their natural step increments, usually 200 increments per revolution. Microstepping can hold them in between their natural step increments but it is not consistent with heavy loads. To test if this is happening in your situation, setup the machine to jog in 0.001" increments. Watch the pulley on the stepper motor closely and begin jogging in 0.001" steps. If you notice that on some steps the pulley does not move and then a few steps later the pulley suddenly catches up to where it should be and then a few steps later stops moving again and this repeats every 4 or 8 steps then your problem is caused by the microstepping not having enough torque to hold between the stepper motors natural increments. This error is not cumulative as each time hit a natural step position the motor will catch up. To make it easier to see, you can exaggerate the motion by cutting a large cardboard disk and taping it to the pulley and making some hash marks on the outer perimeter. The larger diameter of the disk will cause small rotational movements to be much more noticeable. If the pulley moves on each and every 0.001" step consistently then your problem is mechanical. Lawrence ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
