Probing Description and Operation - synthetos/TinyG GitHub Wiki

placeholder for documenting G38 command

This section describes edge-0.97 build 449.01.

G38.2 moves toward the programmed X, Y and/or Z point at the current feed rate until the probe input becomes active, then stops and records the position. G38.3, G38.4 and G38.5 are not supported (status 131). Format:

G38.2 Z-10 F100

• Set the mode of exactly one X, Y or Z switch input (min or max) to 4 (probe), e.g. $zsn=4.
• $prbp sets the probe input polarity independently of $st: 0 = normally open (active low, the default), 1 = normally closed. It can only be changed while no cycle is running and the planner is empty; otherwise it fails with status 117 ("Setting refused: stop the job first") and keeps its value.

• At least one of X, Y or Z must be present (status 134 if not). A, B or C words are not allowed (status 135).
• A feed rate must be in effect; it may have been set on an earlier line (status 142 if not). G93 inverse time mode is not allowed (status 143).
• In G91 the axis words are distances from the current position; in G90 they are work coordinates. Axes that are not programmed do not move.
• The probe travel must be at least 0.254 mm (status 251).
• No probe input configured: status 252. More than one: status 253. A probe input on the A axis: status 254.
• During the probe move the homing jerk ($xjh etc.) is used for X, Y and Z. Jerk and the G90/G91 distance mode are restored afterwards, and the motion mode is set to G80.

When the probe move ends TinyG sends a report as a top-level object (not inside an r response):

{"prb":{"e":1,"x":10.000,"y":20.000,"z":-3.512,"a":0.000,"b":0.000,"c":0.000}}

• e is 1 if the probe tripped during the move and 0 if it did not.
• x ... c are the machine coordinates (G53: not shifted by G54-G59, G92 or the tool length offset) where the machine stopped, in millimetres (degrees for A, B and C) whatever G20 or G21 is active, with 3 decimals, as g2core reports them. A value that is not a finite number is sent as null. To get the work position, subtract the active offsets, or read posx ... posz after the probe.
• The report follows the $js setting (relaxed or strict JSON). The same values can be read later with {prb:n}.

• If the probe input is already active before the move starts, the move is not made, e is 0, and the machine goes to ALARM with status 250 ("Probe already tripped").
• If the move ends without the probe tripping, the machine goes to ALARM with status 250 ("Probe did not trip").
• If the probe move itself is refused (for example by the soft limits), the machine goes to ALARM.
• An alarm that happens before or during the probe ends the probe cycle.

See Alarms for how to clear an alarm.