Re: Lost steps

Hi,

Something else you might want to check for is noise. If your motor
drive is a switching type (chopper, PWM, etc.)then you may be getting
noise pickup from the motor phase wires into the STEP and DIRECTION
inputs. This can happen if these wires are bundled in a common cable
with the motor leads even for a few inches.

Noise is always additive. The motor will move the required number of
steps plus whatever are contributed by noise. Obviously with missed
steps you will be short of your position. This makes it easy to test
for.

Home the axis in question. Check that position accurately. Make a
large move away from home position. Measure that position accurately.
Repeat many times. If you are consistently "long" by a variable
amount each time, it is almost certainly noise.

How to correct. Check your cable routiong. Keep the outputs at least
an inch away from inputs. Check the step input with a scope if you
have one. Verify a 0 to 5VDC swing on the input. See that the rise
and fall times on the edges are clean and fast. Route the Step,
direction and common inputs thru a shielded cable. Check the power
supply voltage for spikes. Bypass the supply with a capacitor at the
drive if spikes are noted. Hope that helps.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, Ozzie@h... wrote:
> After a long slow process I now have CNC mostly setup on my
Shoptask
> machine. The setup includes EMC running on Linux Redhat 5.2,
> Camtronics 5A chopper driver in half step mode, and 150 in-oz
motors.
>
> In repeated attempts to determine the backlash on the axis, I find
no
> consistency in dial indicater readings. On the X axis I lose
> .002-.003" cumalatively in one direction. On the Y axis the
readings
> are erratic with variations in the.002" area.
>
> Before beginning I partially disassembled the carriges and cleaned
> and
> lubricated the ways, and adjusted the gibs. All seems to work
> smoothly.
>
> I understand these motors are not power-houses, but they should
> certainly operate the machine with no load on it.
>
> I'm using moves of a half inch each direction at 6 ipm for the
tests.
>
> The motors came with the machine when I bought it used and were
> powered by a box, one axis at a time, with "The Motion Group, Inc."
> on
> it.
>
> The Camtronics driver tests well and puts out the correct voltages.
>
> Any ideas, and how should I go about finding the problem????
>
> I'm a total newbie-dummy.