Alarm 9 Homing fail error

LightBurn Hardware Compatibility GRBL
1

I assembled my laser engraver using CNC Shield and GRBL, I have already tested cutting and engraving, everything works. But as soon as I connected the limit switches, it stopped driving. When idle, I click on the limit switches and the program writes “ALARM: 1
A hard limit has been triggered. The machine’s position is likely lost due to the sudden and immediate stop. Re-targeting is strongly recommended.” Both limit switches work, but after $H it doesnt move and the console displays “ALARM:9
Pointing error. The limit switch could not be found within the search distance. Defined as 1.5 * max_travel during search and 5 * offset during search stages.
ok”

My $$

$0=10
$1=25
$2=0
$3=1
$4=0
$5=0
$6=0
$10=1
$11=0.010
$12=0.002
$13=0
$20=0
$21=1
$22=1
$23=1
$24=25.000
$25=100.000
$26=244
$27=6.000
$30=1000
$31=0
$32=1
$100=100.000
$101=100.000
$102=100.000
$110=400.000
$111=400.000
$112=500.000
$120=10.000
$121=10.000
$122=10.000
$130=500.000
$131=500.000
$132=200.000

2

Looks like the switches are recognized to be activated all the time. Try to invert them ($5=1). You can test by sending a question mark “?” in the console window and check the output. There is a section Pn: which shows the activated limit switches.

3

I checked

With 5=0
<Idle|MPos:0.000,0.000,300.000|FS:0,0|WCO:0.000,0.000,0.000>

With 5=1
<Idle|MPos:0.000,0.000,300.000|FS:0,0|Pn:XYZ|Ov:100,100,100>

4

When i set $5=1, then i have another error
“ALARM:8
Pointing error. During the cycle, it was not possible to reset the limit switch when moving. Try increasing the tap setting or check the wiring.
ok”

5

I just read your post again and I got it wrong. Your setting was correct and the output shows that all switches work. So $5=0 is correct. If you hit the switches and get the hard stop message, that’s fine and should be like this. Be aware, that after a hard limit trigger event, you probably need to power cycle the board to make it work again.

Regarding homing:
You set a workspace size of 500x500, is that correct? Your speeds are extremely slow compared to that size. Which driving mechanism do you use? If it is a standard mechanics, set
$24=50
$25=1000
$110=5000
$111=5000
$120=500
$121=500

Since you are driving such slow, you might run in a timeout.

6

Slow speed for safety only.
When i hit “home” button - nothing happens. The motors “knock” once, entering hold mode, but do not move.

7

Then my next guess would be that the motors don’t get enough power to run simultaneously. But you said you tested normal movement already?

8

Yep, i already cut and engrave some plywood, they works normal (with turned off hard limits), problem only with homing + hard/soft limits (G28, $H doesnt matter it always says the same)

9

Ah, another idea. Which firmware version did you use? Standard grbl from the GitHub repository? Or something else? Maybe it tries to home Z first. Check if you can home a single axis via $HX or $HY (but the single commands also need to be enabled in firmware).

10

Thanks for the hint!
Redact config.h in the GRBL firmware

From:
#define HOMING_CYCLE_0 (1<<Z_AXIS)
#define HOMING_CYCLE_1 ((1<<X_AXIS)|(1<<Y_AXIS))
To:
#define HOMING_CYCLE_0 (1<<X_AXIS)
#define HOMING_CYCLE_1 (1<<Y_AXIS)

And now homing works perfect

11

Great! Though, I’d change it to

#define HOMING_CYCLE_0 ((1<<X_AXIS)|(1<<Y_AXIS))

This will make both axis home simultaneously, instead of one after another.

12

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