[Solved] Prusa X and Y hits endstop twice before stopping

I'm in the process of a Prusa build. Mechanical endstops, the small 'morse key' rocker type.

I now have my steppers moving on all 3 axes & on the extruder.
When I test 'home' for the X axis , the mechanics moves along , touches the switch as expected , then moves away about an inch, comes back again then stops.
Same process for the switch on Y axis.
(The Z axis switch is not ready to test yet).

Is this normal? If not is it a problem / any ideas what the cause is?

Thanks in advance.


Mike

Reprap Prusa
RAMPS 1.4
Pronterface

Edited 1 time(s). Last edit at 12/31/2011 04:32AM by 3D2B.

Mine does this, so i assume its okay, as long as it returns to the spot its supposed to be in.

All three axis woke that way on mine.

Seems normal.

This is written in the firmware home command. It is an attempt to make the end stop position more accurate and is common on most machine tools. The axis advances quickly to the end stop, then retreats a little then advances more slowly to the stop which makes a more accurate measurement. Its a better way than simply advancing towards the end stops at slow speed as this would make the homing command slow, particularly on large machines.

martinprice2004 got it.

This is written into the firmware, I'd imagine with mechanical endstops in mind, because they can have a variance of about +/- .1 mm (if I recall correctly). Advance very slowly back into the endstop helps to alleviate this problem.

If you scour the code in your firmware I'm sure you can find the lines that govern this action. Hope this helps.

bdc

Stay calm out there.

I use optical sensors and they do the 2 bounce thing as well, described by bdcannon above is exactly what mine does

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That's great guys, makes sense. Thanks.

Mike

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Prusa Mendel /Parcan Mk 2/1280 RAMPS 1.4/PC XP OS/Pronterface/Slic3r

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In marlin I have you can change the seek distance in configuration.h line ~234-237.

//homing hits the endstop, then retracts by this distance, before it tries to slowly bump again:
#define X_HOME_RETRACT_MM 5 
#define Y_HOME_RETRACT_MM 5 
#define Z_HOME_RETRACT_MM 2

I don't see the option in sprinter, but the version I have is a few months old.

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kliment Sprinter

if((home_all_axis) || (code_seen(axis_codes[0]))) {
if ((X_MIN_PIN > -1 && X_HOME_DIR==-1) || (X_MAX_PIN > -1 && X_HOME_DIR==1)){
current_position[0] = 0;
destination[0] = 1.5 * X_MAX_LENGTH * X_HOME_DIR;
feedrate = homing_feedrate[0];
prepare_move();

current_position[0] = 0;
destination[0] = -5 * X_HOME_DIR;
prepare_move();

destination[0] = 10 * X_HOME_DIR;
prepare_move();

current_position[0] = (X_HOME_DIR == -1) ? 0 : X_MAX_LENGTH;
destination[0] = current_position[0];
feedrate = 0;
}
}

This is in the G28 "Home all" command. it attempts to go to -5 so it stops at the end stop, then back to +10 then homes again. It repeats a similar thing for the other axes. Unfortunately it doesn't seem to do the second homing any slower, so this really defeats the object of doing it as far as I can tell.