N_Cook wrote:
Andrew May wrote in message
...
On 09/02/2012 15:50, N_Cook wrote:

I'm just wondering if something has gone wrong with microstepping.
Course
back and forth movement and then at near focus dropping into
microstepping
mode and not enough drive/wrong phasing / interaction with that spring


It cold well be. I had a closer look last night and found the following
with the spring removed:

When starting up and finding the home position it will move the carriage
backwards and forwards with sufficient force that it is not possible to
easily stop it.

While scanning it moves the carriage from the rear towards the front,
basically from the home position over the slide and does this with
sufficient force that it is not easy to stop.

Having finished the scan it returns to the home position but this time
just putting a finger in the way will stop the movement and results in a
squealing sound.

What I can not figure out is, if this is a micro-stepping problem, why
it is using micro-stepping to return the carriage to the home position.
I can understand it when scanning but not when it has finished. But then
I have no experience of stepper motors.

I assume the motor is OK. Is this indicative of a problem with the drive
circuitry? I don't have a service manual or circuit diagram but the PCB
which I assume does the driving is not very large and could probably be
traced out.

Andrew




If this was mine , I'd connect a small spring or cord with that spring to
reduce its effect, but allow continued use while you obtain info &
stepper/driver replacement


Could it be wear or dirt on the carriage or tracks, with the off centre
force from the spring making it wedge in position? As the problem is in
one direction only, I'd be suspecting a mechanical cause rather than
electonics failure, bearing in mind the tolerances involved.

--
Tciao for Now!

John.