My laser does not home correctly or the limit switches do not work

[Gene Uselman]

This is a work in progress- please comment below if I have errors or you think something would help people- this subject is confusing to a lot of people and I am hoping this will help... not the confusion... clear it up a bit. Gene

This behavior is called homing and homing can be to any corner of the machine. I 'think' right rear is most common. The limit switches will typically
be found in that corner but as always there are exceptions. The 'X' axis is on the gantry [left and right] and the limit switch will determine if you home
to the left or right side of the bed. The 'Y' axis is toward/away from you and the limit switch will be on the front or back of the machine- that determines
if your home is on the front corner or rear corner. They are commonly in the same corner but do not have to be.

Switches are momentary contact switches or inductive switches or proximity switches and either mechanically set or set in response to ferrous metal contact being in close relationship.
Any of the switches may be normally open or normally closed [NO or NC] and must be connected as appropriate to the controller for the homing to function correctly.

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Limit Switches.jpg

Proximity switches have a light built in to them to indicate when the switch completes the circuit or not. In instance where the switch
does not appear to function an adjustment to the flag or switch may be required. They do not need to touch and in fact you want a few mm clearance.

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Homing behavior for RDw-LB.jpg

To verify proper function and validate the controller sees the switch completing or breaking the circuit:

Move the head to the middle of the table using the controller. Place a ferrous screw driver next to one of the switches and make sure it lights up.

If it doesn't ...either you have a power to the switch problem or the switch is bad.

If it does - Now go back and look at the lights on the Ruida controller. There is a light for the x axis and a light for the y axis. If you move the screwdriver/magnet away from the switch the light should go out.
Move the screw driver/magnet a couple of times to confirm light corresponds to the correct axis. If the light go on and off then the controller can see the signal. Do this for both x & y and z if you have it.

If not there may be a break in the wiring or it is hooked up to the wrong terminal.

Normal Homing Behavior


1. The laser head and gantry move quickly towards the limit switches. Each axis stops when the limit switch detects (lights up).

2. After both limit switches detect, the laser head & gantry moves slowly away from the limit switches. Each axis stops when
the limit switch no longer detects (light goes out).

3. The laser head & gantry then move very slowly until the limit switches detect again (lights up).

4. The X & Y will then move to the offset that is programmed in the setup




Troubleshooting switches

Common problem #1: the head or gantry moves AWAY from the limit switches instead of towards them. This will be corrected in the Machine setup above.

Common problem #2: the limit switch detects the laser head and gantry (both switches light up), but the motors don't stop. This is due to the controller not reacting to the activation of the limit switch(es). First check the software to be sure the limit switches are enabled in the software. Second, check to see that the limit switches are actually wired to the RuiDa controller (see 644x wiring diagram). Most limit switches need +24V, GND, and the output of the limit switch connected to X- or Y- connector.

Common problem #3: the limit switch fails to detect the laser head and/or gantry (doesn't light up). First I'd test to see if the limit switches work. You can use any large piece of ferrous metal - a screwdriver, a wrench, etc. When you put it near a magnetic limit switch (within 5mm), the switch should light up. If it doesn't, check to see if the limit switch is actually connected to the RuiDa controller and if the wire is good (there have been cases of broken / intermittent wires). Otherwise, replace the limit switch (they're not expensive).
If the limit switch works with your piece of metal, but doesn't detect the laser head, try adjusting the mechanical position of the switch so that it is closer to the piece of metal that it's supposed to detect (Or sometimes the metal on the moving part it should be sensing).

Common problem #4: be sure your limit switch is attached to the proper terminal- this pict is of a 6445 controller and on this one the X & Y limiters attach to the CN4 terminal- one wire will always go to ground and the other to either the axis [+] or [-] this is why we have different polarity choices in the software and why sometimes it is necessary to try to change the polarity. Other controllers will be similar but the CN# may be different.

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RDC6445G.jpg

[Jeffrey Aley]

Looks great - you did a fine job of merging all the different comments together into a coherent whole.

It might be useful to include a sentence in there somewhere to "Verify that the switch is correctly wired to the RuiDa controller." You could probably insert it somewhere near where it says that the switches need +24V, GND and a connection to X- or Y-.

I mention it since the most recent issue was caused by the switch being mistakenly wired to OUT2 instead of GND.

Thanks,

-Jeff

Thanks Jeff