Tuesday, January 6, 2009

More on End Stops

I previously blogged on my X & Y end stop’s being Hall Effect Limit sensors, so I thought I would write more on using the standard RepRap optical sensors on ExMrClean for my Z axis.

In a bit of reading at the CNC zone about the Hall Effect sensors the author mentioned that they are real easy to position to set limits since they in them selves are magnetic.

This got me to thinking as how I would implement a similar functionality on my Z stage since I am planning a lot of dirty activities for ExMrClean.

Since my Z stage is most aluminum I hit on using flexible magnetic strips that I picked up for a buck at the hobby store.

From ExMrClean

Since the strips have magnetic poles you should see how they best join together to not reduce have them fight each other and reduce the attraction power before you peel off the paper over the adhesive. In my case I have two strips on top of each other at maximum travel and two sets of two at minumum travel.

I then took a nylon screw and attached it to a metal strip to dock on to the magnetic strips. I used a nylon screw since it was easy to sand down to a flat surface.

From ExMrClean

Then by moving the status LED to the other side of the board it cleared up the mounting hole on the optical sensor to attach the metal plate too. A little bit of injected hot glue to make the assembly more ridged so it wouldn’t pivot on the screw and I was done.

From ExMrClean

Here’s a picture of the minimum/home sensor magnetically attached. It's simple to slide the sensor up and down to adjust the home position.

The optical interrupter plate/vane is a plastic tool tag from a punch that I brought that I simply mounted on the side of the movement stage.

From ExMrClean

Further thoughts

When I finally getting to extruding I should make a guide to align the metal strip laterally, right now if I do not test after a repositioning the moving stage can knock the sensor loose.

The RJ-45 cables are a bit too stiff to use in this mode, even though they are ok once they aquire a set in the approximate location. I should really use more a flexible cable or wires that will not try to drag the sensor around.

1 comment:

  1. I used stranded RJ45 cable for the moving stages, it seemed a lot more flexible. No problems so far, but the plastic filament I used as a cable guide and strain relief broke from all the repeated bending!

    Also, I've been adjusting my Z home position by hand, but I find it very difficult to get the nozzle height exact. I often get it close, and then add a fraction of a mm to the homing sequence to fix it, but it's an iterative process, and slow. Nophead had a better solution, to home away from the bed, and then calculate the offset. You can usually tell when the bed height is off by the density of the first layer of the raft.

    Depending on how your extruder is set up, you might find that it expands half a mm or so after the PTFE gets warm (say 20 minutes of operation or so).