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« on: November 02, 2010, 08:59:56 PM »
Interesting thread to follow, that said, i am going to make some comments FWIW.
1.The software is the begining of the controlling process. It could be buggy, but, one dosen't know without some physical indication.
2. It can be useless looking for an electronic step / pulse without the proper equipment.
Ideally it would be nice to have a pulse counter which could simultaneously take and compare say the following:
PC to PP - PP output - drive input - drive output to the motor ....and compare the electronics. Not manny folks have
access to such an instrument or one of high enough quality that it can be trusted as the "last word". Of course the signal quality
along the way by itself can contribute to a problem.
3. The motor acts as a converter to mechanical motion. So anything downstream of it becomes motion / distance.
The motor by itself can be a contributor.So now you have all the variables like timing gear, belt, bearing, screw, nut and
each has it owne level of quality relative to the motion. Yes ....a belt can create what would apear to be a lost step.
So if one wanted to be annal about all this, they would need to isolate each part of the system , define the error against some standard,
put it into perspective to the final outcome namely , motion. Good grief... thats only about 20 tests and it dosn't even include
other devices a user may be using or software influences. All of them need to be done in a very disciplined way and to higher degree than the
min resolution of the system.
Considering the above the user needs to work with what they have and can do and in most cases that is not much.
So what can you do quite accurately?
Minimise the electronics to only that which is needed for motion. PC/PP/drive/ then a motion measuring device upstream of the
mechanics. Simply put, you put out pulses and measure them at motor output shaft. To do that one can make mechanical ( not electronic )
indicator and see what that "block" of the system is doing. ie;
A simple disc of 6 " diameter would have a circumference of 18.849". At 20000 steps per inch, the resolution / single step is equal to 0.00005"
if all was perfect and 18.849 / 20000= 0.0001" of circumferential movement of the disc. An 8" disc would give you 0.0013" of circumferential movement.You need to make at least a 1 rev of the motor since the non linearinty of the stepper should repeat. You can figure out what commanded movement
is required for one complete revolution of the disc. Make note that if you fall in a micro step you may be +- in cicumferential distance.
So the user can check a drive with micro step or without ( use the same motor ) , then swap the cables and compare other drives. Forward and reversemotion.Try the same with a different motor. Try a different PP port. But make note of the data of each test. Not all motors are the same!
At least this way you are comparing electronics to a motion standard without influences of the mechanical system.
Just some thoughts FWIW on testing,
RICH
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