From 5a7356b6fca1eb588e804f7feafd870bd4af827e Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Wed, 22 Jul 2015 20:23:40 -0700
Subject: [PATCH] Patch for G29 final Z position
Include all the necessary pieces to get the final Z position after
probing the bed, and add commentary about other possible changes.
---
Marlin/Marlin_main.cpp | 23 ++++++++++++++++++++---
1 file changed, 20 insertions(+), 3 deletions(-)
diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index b7ad8f49ac..3321b8c433 100644
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -2744,11 +2744,28 @@ inline void gcode_G28() {
float x_tmp = current_position[X_AXIS] + X_PROBE_OFFSET_FROM_EXTRUDER,
y_tmp = current_position[Y_AXIS] + Y_PROBE_OFFSET_FROM_EXTRUDER,
z_tmp = current_position[Z_AXIS],
- real_z = st_get_position_mm(Z_AXIS); //get the real Z (since the auto bed leveling is already correcting the plane)
+ real_z = st_get_position_mm(Z_AXIS); //get the real Z (since plan_get_position is now correcting the plane)
apply_rotation_xyz(plan_bed_level_matrix, x_tmp, y_tmp, z_tmp); // Apply the correction sending the probe offset
- //line below controls z probe offset, zprobe_zoffset is the actual offset that can be modified via m851 or is read from EEPROM
- current_position[Z_AXIS] = z_tmp - real_z - zprobe_zoffset; // The difference is added to current position and sent to planner.
+
+ // Get the current Z position and send it to the planner.
+ //
+ // >> (z_tmp - real_z) : The rotated current Z minus the uncorrected Z (since homing)
+ //
+ // >> zprobe_zoffset : Z distance from nozzle to probe (set by default, M851, EEPROM, or Menu)
+ //
+ // >> Z_RAISE_AFTER_PROBING : The distance the probe will have lifted after the last probe
+ //
+ // >> Should home_offset[Z_AXIS] be included?
+ //
+ // Discussion: home_offset[Z_AXIS] was applied in G28 to set the starting Z.
+ // If Z is not tweaked in G29 -and- the Z probe in G29 is not actually "homing" Z...
+ // then perhaps it should not be included here. The purpose of home_offset[] is to
+ // adjust for inaccurate endstops, not for reasonably accurate probes. If it were
+ // added here, it could be seen as a compensating factor for the Z probe.
+ //
+ current_position[Z_AXIS] = -zprobe_zoffset + Z_RAISE_AFTER_PROBING + (z_tmp - real_z);
+ // current_position[Z_AXIS] += home_offset[Z_AXIS]; // The probe determines Z=0, not "Z home"
sync_plan_position();
}
#endif // !DELTA
--
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