Re: [CAD_CAM_EDM_DRO] Newb question....

At 06:59 PM 10/1/2004, Jon Elson wrote:

>John Trevick wrote:
>
> >
> >Jon, can you clarify this for me. I am using your USC with steppers with
> >encoders and EMC. If a stepper loses a step it does not recover? Or is
> >what you said above not apply to the USC because it is more like a servo
> >system?
> >
> >
>If a stepper were to lose a step (or however much it takes to accumulate
>more
>axis error than the deadband value) at a low speed, it would recover so
>well you
>might never be aware of it. This could possibly happen due to the step
>to direction
>change timing not matching what the drive needed at a direction reversal.
>
>If a stepper were to lose a step under heavy load at moderate to high speed,
>the drive and motor could never recover until you slowed down or reduced
>the load.
>The motor would simply stall, and no amount of rapid step pulses would
>get it
>to pick up the pace as long as the load remains. As soon as the load or
>speed was
>reduced, then it could resume moving. Most likely, you would get a
>following error
>in this case before the motor could get out of the stalled condition.
>If you want to
>experiment with it, try reducing the motor current. With a Gecko drive,
>you would
>chage the resistor value, for instance. But, if the following error
>limit is wide, or
>the stall exists for only a small instant, then it would recover with
>only that hesitation
>in the motion. At any rate, even if EMC goes into E-stop, or the drives
>fault out,
>the position EMC is showing on the "actual position" display will still
>be correct,
>and it can resume operation without re-homing after the cause of the
>stall is corrected.
>
>Jon

Ok, this is what I thought.

With all the questions about Stepper vs Servo what might be interesting to
try is taking the Pico Systems USC with the Gecko Servo Interface and
compare the performance of a Stepper motor vs a DC motor (I say DC motor
instead of servo to try and avoid confusion). The point being to have a
servo environment with as many elements the same like the software, encoder
resolution, power supply size, etc. in order to measure the "efficiency"
(for lack of a better term) of each motor. Perhaps using motors of the
same frame size. I realize that the Gecko 2xx and 3xx series don't work at
all the same way to move the motor but it would look the same to
EMC. Also, I realize that Steppers and Servos don't usually work in the
same voltage/amperage range but the bigger power supplies also cost more so
it may be a fair handicap. I suspect the result would be that the DC motor
works better at medium to higher RPM but at least all the other elements
which confuse the issue would be eliminated (like the general assumption
that Stepper systems are open loop).



- John