¶ Probe
¶ Overview
Probes are used to find the surface of the workpiece. Most commonly this on the Z axis, but FluidNC supports doing it with any axis. The probe circuit is an input to FluidNC, similar to a limit switch. The most common method uses the electrical conductivity of the bit and a metal plate or puck of known thickness on the material to complete a circuit. You could also use any kind of circuit that opens or closes on contact.
FluidNC will move the probe towards the surface. When contact is detected FluidNC will output the location on the serial port and other connected channels. It will then decelerate to a stop to prevent any loss of steps that might occur due to an immediate stop. If you supply the P parameter, FluidNC will zero the axis using the offset provided.
Multipoint surface leveling is not supported by the firmware. A simple Gcode version would have too many parameters to make this practical. A much better solution is to have a GUI prompt you for all the grid parameters. Many gcode senders support this. They then alter the streaming gcode to fit the material profile. FluidNC supports this method.
¶ Config File
- pin:
- Type: Pin (input)
- Range: gpio
- Default: NO_PIN
- Details: This is the signal from the probe.
- toolsetter_pin:
- Type: Pin (input)
- Range: gpio
- Default: NO_PIN
- Details: This is an optional second probe.
- check_mode_start:
- Type: Boolean
- Default: true
- Details: This will force a probe check before a probe is started.
- hard_stop:
- Type: Boolean
- Default: false
- Details: If true the axis will do a hard stop rather than decelerate. This can be used with fragile bits that might break with the overtravel needed for deceleration. It is likely to be less accurate at higher speeds where the motor might skip a few steps without deceleration.
Config Example:
probe:
pin: gpio.34
toolsetter_pin: NO_PIN
check_mode_start: true
hard_stop: false
¶ Setup
Make sure the pin has the right attribute for active high or low. You can verify this by sending the '?' status command. You should not see the a "P" in the status response in the Pn: section. If you see the P invert the active state.
Next, manually activate the probe by triggering the switch, completing the circuit or whatever is needed to activate it. While in the active state you should see the P in the Pn: section when you send the ? command.
Until you pass a manual test, you should not attempt a real probe action.
¶ Using the probe
Basic probing uses a G38.2 command to probe to a switch or electrical contact. You can adjust the active state of the signal with the high/low attribute.
If you set check_mode_start: true it will verify the probe is not touched before the move. If it is you will get an alarm 4
If the probe move completes without activating a probe input it will fail with an alarm 5.
If the probe is successful it will issue a message like this [PRB:151.000,149.000,-137.505:1] with the machine position at the time of the touch specified. The 1 at the end specifies a successful probe. After touching, the machine will decelerate to a stop. This means the machine location will differ from the location in the message after the probe. It is usually only a tiny amount, but you should account for it. The over travel is proportional to the speed. It could break your bit if the over travel is high or the bit is very fragile.
If the probe fails, it will issue a message like this [PRB:0.000,0.000,0.000:0]. The 0 at the end indicates a failed probe.
You need to specify move axis parameters and a feedrate.
- G38.2 Z-5 F200 This would probe towards the work position Z-5 with a feed rate of 200.
- G38.2 G91 Z-5 F200 The G91 parameter will cause it to move down in Z by 5 with a feed rate of 200. Note: Be aware that G91 will persist and affect subsequent g codes. You should reset it to G90 if that was the previous mode.
- G53 G38.2 Z-125 F200 P16 This will probe toward Z-125 in machine space (G53)
You can probe towards any point in any or multiple axes at once. Soft limits will be respected. If the command requests a maximum travel that exceeds the range and soft limits are true for the axis, you will get an alarm.
¶ Setting Work Zero
The value in the PRB message is the exact point where the probe activates. The machine will then decelerate to a stop. The machine will no longer be at the probe point even if the probe is going slowly. The best way to set a work zero is to use the G10 L2 Px command with x being the coordinate system. P0 would be the current system. P1 through P6 would be used to specify G54-G59. To set the current work Z to 0 after getting [PRB:151.000,149.000,-137.505:1] send G10 L2 P0 Z-137.505, using the z value from the PRB message. If you have a plate or other offset, just add that to the PRB value.
¶ Optional P parameter
You can use an optional "P" parameter that specifies the thickness (or offset from 0) of the probe device, like a plate or puck.
Upon successful probe the offset of the current system is zeroed with the P value applied. This will make it much easier for displays and senders to deal with probing.
Example: G38.2 G91 F80 Z-20 P8.00
This will probe an incremental (G91) amount of -20 in Z. It will set the probe location to 8.00 on the Z axis in the current work coordinate system.
Notes:
- After the probe touch, the status will show the axis location to be a little off from the probe location. This is due to the deceleration after the probe touch. The probe location is accurate to the actual touch point. If you want to minimize the over travel use a lower speed (best) or faster acceleration (in your config file).
- You can only specify movement in one axis when you use the P parameter.
¶ Troubleshooting
¶ Testing the probe
The status of the probe is in the Grbl status report. You should see a "P" in the Pn: section of the report. There is no way to determine which probe is active, so test them one at a time.
<Idle|MPos:0.000,0.000,0.000|Pn:P|FS:0,0|WCO:0.000,0.000,0.000>
Test both the active and inactive states.
Pro Tip: If you set
$report/interval=100. The status report will automatically report switch changes for easy testing.
¶ ALARM:4 Probe fail.
Probe is not in the expected initial state before starting the probe cycle when trying to probe. You cannot start a probe cycle if the probe is already active. See the setup section above.
¶ Macros
Macros can be used to probe and set the current work coordinates.
¶ Example using standard gcode
This assumes that you are probing in Z using a touch plate that is on top of the work and in 10mm thick. It also assume you are above the probe location above the plate.
G21 ; use millimeters
G91 ; move in relative motion mode
G38 Z-30 F80 P10; probe a maximum of 30mm down at a rate of 80
G90 ; use absolute motion mode
G0 Z50 ; retract to 30 above work
¶ Using gcode expressions
; dual speed probe macro
; set parameters
#<fast_rate>=160
#<slow_rate>=80
#<probe_dist>=100
#<probe_offset>=10
#<retract_height>=5
G38.2 G91 Z[-#<probe_dist>] F#<fast_rate> ; probe fast
G0 Z3 ; retract a little
G38.2 G91 Z[-#<probe_dist>] F#<slow_rate>; probe slowly
#<wco_z_touch>=#5063 ; save the z touch WCO location
G0 Z[#<retract_height>+#<probe_offset>] ; retract
G10 L2 P0 Z[#<wco_z_touch>+#<probe_offset>]
G91 G0 Z[#<retract_height>+#<probe_offset>]
¶ Examples
¶ Cheap Tool setter
This is a widely available tool setter. It is cheap, but works pretty well. There are various colors and finishes. They have 2 activation points.
- Tool setter signal. This is the first activation point and is probably the most accurate. It should be hooked up to your probe input.
- Overtravel signal. This activates after (lower) than the other signal. It is designed as a warning that you are about to crash. This will save your bit and maybe other things if your Z axis is very strong. You can hook this to any alarm input, like reset or e-stop. You can also hook it up as a Z limit switch if you use hard limits. If you are short on inputs, put it in parallel or serial with an existing limit switch.
The wire colors are pretty random, but the switches are simple mechanical switches so you can easily figure out the wiring with a meter. They sell both N.C. and N.O. switch versions.
This should be mounted to a very flat surface. Tools with different widths could touch at different heights if if the ETS surface is at an angle.