G34 automatic point assignment (#16473)

Marlin/Configuration_adv.h

@@ -668,11 +668,37 @@
  */
 //#define Z_STEPPER_AUTO_ALIGN
 #if ENABLED(Z_STEPPER_AUTO_ALIGN)
-  // Define probe X and Y positions for Z1, Z2 [, Z3]
-  #define Z_STEPPER_ALIGN_XY { {  10, 190 }, { 100,  10 }, { 190, 190 } }
+  // Define probe X and Y positions for Z1, Z2 [, Z3 [, Z4]]
+  // If not defined, probe limits will be used.
+  // Override with 'M422 S<index> X<pos> Y<pos>'
+  //#define Z_STEPPER_ALIGN_XY { {  10, 190 }, { 100,  10 }, { 190, 190 } }
+
+  /**
+   * Orientation for the automatically-calculated probe positions.
+   * Override Z stepper align points with 'M422 S<index> X<pos> Y<pos>'
+   *
+   * 2 Steppers:  (0)     (1)
+   *               |       |   2   |
+   *               | 1   2 |       |
+   *               |       |   1   |
+   *
+   * 3 Steppers:  (0)     (1)     (2)     (3)
+   *               |   3   | 1     | 2   1 |     2 |
+   *               |       |     3 |       | 3     |
+   *               | 1   2 | 2     |   3   |     1 |
+   *
+   * 4 Steppers:  (0)     (1)     (2)     (3)
+   *               | 4   3 | 1   4 | 2   1 | 3   2 |
+   *               |       |       |       |       |
+   *               | 1   2 | 2   3 | 3   4 | 4   1 |
+   *
+   */
+  #ifndef Z_STEPPER_ALIGN_XY
+    //#define Z_STEPPERS_ORIENTATION 0
+  #endif
 
   // Provide Z stepper positions for more rapid convergence in bed alignment.
-  // Currently requires triple stepper drivers.
+  // Requires triple stepper drivers (i.e., set NUM_Z_STEPPER_DRIVERS to 3)
   //#define Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS
   #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
     // Define Stepper XY positions for Z1, Z2, Z3 corresponding to
@@ -680,23 +706,16 @@
     // Define one position per Z stepper in stepper driver order.
     #define Z_STEPPER_ALIGN_STEPPER_XY { { 210.7, 102.5 }, { 152.6, 220.0 }, { 94.5, 102.5 } }
   #else
-    // Amplification factor. Used to scale the correction step up or down.
-    // In case the stepper (spindle) position is further out than the test point.
-    // Use a value > 1. NOTE: This may cause instability
-    #define Z_STEPPER_ALIGN_AMP 1.0
+    // Amplification factor. Used to scale the correction step up or down in case
+    // the stepper (spindle) position is farther out than the test point.
+    #define Z_STEPPER_ALIGN_AMP 1.0       // Use a value > 1.0 NOTE: This may cause instability!
   #endif
 
-  // Set number of iterations to align
-  #define Z_STEPPER_ALIGN_ITERATIONS 3
-
-  // Enable to restore leveling setup after operation
-  #define RESTORE_LEVELING_AFTER_G34
-
   // On a 300mm bed a 5% grade would give a misalignment of ~1.5cm
-  #define G34_MAX_GRADE  5  // (%) Maximum incline G34 will handle
-
-  // Stop criterion. If the accuracy is better than this stop iterating early
-  #define Z_STEPPER_ALIGN_ACC 0.02
+  #define G34_MAX_GRADE              5    // (%) Maximum incline that G34 will handle
+  #define Z_STEPPER_ALIGN_ITERATIONS 5    // Number of iterations to apply during alignment
+  #define Z_STEPPER_ALIGN_ACC        0.02 // Stop iterating early if the accuracy is better than this
+  #define RESTORE_LEVELING_AFTER_G34      // Restore leveling after G34 is done?
 #endif
 
 // @section motion

Marlin/src/feature/z_stepper_align.cpp

@@ -0,0 +1,137 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2019 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+/**
+ * feature/z_stepper_align.cpp
+ */
+
+#include "../inc/MarlinConfigPre.h"
+
+#if ENABLED(Z_STEPPER_AUTO_ALIGN)
+
+#include "z_stepper_align.h"
+#include "../module/probe.h"
+
+ZStepperAlign z_stepper_align;
+
+xy_pos_t ZStepperAlign::xy[NUM_Z_STEPPER_DRIVERS];
+
+#if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+  xy_pos_t ZStepperAlign::stepper_xy[NUM_Z_STEPPER_DRIVERS];
+#endif
+
+void ZStepperAlign::reset_to_default() {
+  #ifdef Z_STEPPER_ALIGN_XY
+
+    constexpr xy_pos_t xy_init[] = Z_STEPPER_ALIGN_XY;
+    static_assert(COUNT(xy_init) == NUM_Z_STEPPER_DRIVERS,
+      "Z_STEPPER_ALIGN_XY requires "
+      #if NUM_Z_STEPPER_DRIVERS == 4
+        "four {X,Y} entries (Z, Z2, Z3, and Z4)."
+      #elif NUM_Z_STEPPER_DRIVERS == 3
+        "three {X,Y} entries (Z, Z2, and Z3)."
+      #else
+        "two {X,Y} entries (Z and Z2)."
+      #endif
+    );
+
+    constexpr xyz_pos_t dpo = NOZZLE_TO_PROBE_OFFSET;
+
+    #define LTEST(N) (xy_init[N].x >= _MAX(X_MIN_BED + MIN_PROBE_EDGE_LEFT,  X_MIN_POS + dpo.x) - 0.00001f)
+    #define RTEST(N) (xy_init[N].x <= _MIN(X_MAX_BED - MIN_PROBE_EDGE_RIGHT, X_MAX_POS + dpo.x) + 0.00001f)
+    #define FTEST(N) (xy_init[N].y >= _MAX(Y_MIN_BED + MIN_PROBE_EDGE_FRONT, Y_MIN_POS + dpo.y) - 0.00001f)
+    #define BTEST(N) (xy_init[N].y <= _MIN(Y_MAX_BED - MIN_PROBE_EDGE_BACK,  Y_MAX_POS + dpo.y) + 0.00001f)
+
+    static_assert(LTEST(0) && RTEST(0), "The 1st Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
+    static_assert(FTEST(0) && BTEST(0), "The 1st Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+    static_assert(LTEST(1) && RTEST(1), "The 2nd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
+    static_assert(FTEST(1) && BTEST(1), "The 2nd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+    #if NUM_Z_STEPPER_DRIVERS >= 3
+      static_assert(LTEST(2) && RTEST(2), "The 3rd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
+      static_assert(FTEST(2) && BTEST(2), "The 3rd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+      #if NUM_Z_STEPPER_DRIVERS >= 4
+        static_assert(LTEST(3) && RTEST(3), "The 4th Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
+        static_assert(FTEST(3) && BTEST(3), "The 4th Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
+      #endif
+    #endif
+
+  #else // !defined(Z_STEPPER_ALIGN_XY)
+
+    const xy_pos_t xy_init[] = {
+      #if NUM_Z_STEPPER_DRIVERS >= 3  // First probe point...
+        #if !Z_STEPPERS_ORIENTATION
+          { probe.min_x(), probe.min_y() }, // SW
+        #elif Z_STEPPERS_ORIENTATION == 1
+          { probe.min_x(), probe.max_y() }, // NW
+        #elif Z_STEPPERS_ORIENTATION == 2
+          { probe.max_x(), probe.max_y() }, // NE
+        #elif Z_STEPPERS_ORIENTATION == 3
+          { probe.max_x(), probe.min_y() }, // SE
+        #else
+          #error "Z_STEPPERS_ORIENTATION must be from 0 to 3 (first point SW, NW, NE, SE)."
+        #endif
+        #if NUM_Z_STEPPER_DRIVERS == 4    // 3 more points...
+          #if !Z_STEPPERS_ORIENTATION
+            { probe.min_x(), probe.max_y() }, { probe.max_x(), probe.max_y() }, { probe.max_x(), probe.min_y() }  // SW
+          #elif Z_STEPPERS_ORIENTATION == 1
+            { probe.max_x(), probe.max_y() }, { probe.max_x(), probe.min_y() }, { probe.min_x(), probe.min_y() }  // NW
+          #elif Z_STEPPERS_ORIENTATION == 2
+            { probe.max_x(), probe.min_y() }, { probe.min_x(), probe.min_y() }, { probe.min_x(), probe.max_y() }  // NE
+          #elif Z_STEPPERS_ORIENTATION == 3
+            { probe.min_x(), probe.min_y() }, { probe.min_x(), probe.max_y() }, { probe.max_x(), probe.max_y() }  // SE
+          #endif
+        #elif !Z_STEPPERS_ORIENTATION     // or 2 more points...
+          { probe.max_x(), probe.min_y() }, { X_CENTER, probe.max_y() } // SW
+        #elif Z_STEPPERS_ORIENTATION == 1
+          { probe.min_x(), probe.min_y() }, { probe.max_x(), Y_CENTER } // NW
+        #elif Z_STEPPERS_ORIENTATION == 2
+          { probe.min_x(), probe.max_y() }, { X_CENTER, probe.min_y() } // NE
+        #elif Z_STEPPERS_ORIENTATION == 3
+          { probe.max_x(), probe.max_y() }, { probe.min_x(), Y_CENTER } // SE
+        #endif
+      #elif Z_STEPPERS_ORIENTATION
+        { X_CENTER, probe.min_y() }, { X_CENTER, probe.max_y() }
+      #else
+        { probe.min_x(), Y_CENTER }, { probe.max_x(), Y_CENTER }
+      #endif
+    };
+
+  #endif // !defined(Z_STEPPER_ALIGN_XY)
+
+  COPY(xy, xy_init);
+
+  #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+    constexpr xy_pos_t stepper_xy_init[] = Z_STEPPER_ALIGN_STEPPER_XY;
+    static_assert(
+      COUNT(stepper_xy_init) == NUM_Z_STEPPER_DRIVERS,
+      "Z_STEPPER_ALIGN_STEPPER_XY requires "
+      #if NUM_Z_STEPPER_DRIVERS == 4
+        "four {X,Y} entries (Z, Z2, Z3, and Z4)."
+      #elif NUM_Z_STEPPER_DRIVERS == 3
+        "three {X,Y} entries (Z, Z2, and Z3)."
+      #endif
+    );
+    COPY(stepper_xy, stepper_xy_init);
+  #endif
+}
+
+#endif // Z_STEPPER_AUTO_ALIGN

Marlin/src/feature/z_stepper_align.h

@@ -0,0 +1,41 @@
+/**
+ * Marlin 3D Printer Firmware
+ * Copyright (c) 2019 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+#pragma once
+
+/**
+ * feature/z_stepper_align.h
+ */
+
+#include "../inc/MarlinConfig.h"
+
+class ZStepperAlign {
+  public:
+    static xy_pos_t xy[NUM_Z_STEPPER_DRIVERS];
+
+    #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+      static xy_pos_t stepper_xy[NUM_Z_STEPPER_DRIVERS];
+    #endif
+
+  static void reset_to_default();
+};
+
+extern ZStepperAlign z_stepper_align;

Marlin/src/gcode/bedlevel/G26.cpp

@@ -707,7 +707,7 @@ void GcodeSuite::G26() {
     if (location.valid()) {
       const xy_pos_t circle = _GET_MESH_POS(location.pos);
 
-      // If this mesh location is outside the printable_radius, skip it.
+      // If this mesh location is outside the printable radius, skip it.
       if (!position_is_reachable(circle)) continue;
 
       // Determine where to start and end the circle,

Marlin/src/gcode/calibrate/G34_M422.cpp

@@ -24,6 +24,8 @@
 
 #if ENABLED(Z_STEPPER_AUTO_ALIGN)
 
+#include "../../feature/z_stepper_align.h"
+
 #include "../gcode.h"
 #include "../../module/planner.h"
 #include "../../module/stepper.h"
@@ -45,68 +47,6 @@
 #define DEBUG_OUT ENABLED(DEBUG_LEVELING_FEATURE)
 #include "../../core/debug_out.h"
 
-//
-// Sanity check G34 / M422 settings
-//
-constexpr xy_pos_t test_z_stepper_align_xy[] = Z_STEPPER_ALIGN_XY;
-
-#if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
-
-  static_assert(COUNT(test_z_stepper_align_xy) >= NUM_Z_STEPPER_DRIVERS,
-    "Z_STEPPER_ALIGN_XY requires at least three {X,Y} entries (Z, Z2, Z3, ...)."
-  );
-
-  constexpr float test_z_stepper_align_stepper_xy[][XY] = Z_STEPPER_ALIGN_STEPPER_XY;
-  static_assert(
-    COUNT(test_z_stepper_align_stepper_xy) == NUM_Z_STEPPER_DRIVERS,
-    "Z_STEPPER_ALIGN_STEPPER_XY requires three {X,Y} entries (one per Z stepper)."
-  );
-
-#else
-
-  static_assert(COUNT(test_z_stepper_align_xy) == NUM_Z_STEPPER_DRIVERS,
-    #if NUM_Z_STEPPER_DRIVERS == 4
-      "Z_STEPPER_ALIGN_XY requires four {X,Y} entries (Z, Z2, Z3, and Z4)."
-    #elif NUM_Z_STEPPER_DRIVERS == 3
-      "Z_STEPPER_ALIGN_XY requires three {X,Y} entries (Z, Z2, and Z3)."
-    #else
-      "Z_STEPPER_ALIGN_XY requires two {X,Y} entries (Z and Z2)."
-    #endif
-  );
-
-#endif
-
-constexpr xyz_pos_t dpo = NOZZLE_TO_PROBE_OFFSET;
-
-#define LTEST(N) (test_z_stepper_align_xy[N].x >= _MAX(X_MIN_BED + MIN_PROBE_EDGE_LEFT,  X_MIN_POS + dpo.x) - 0.00001f)
-#define RTEST(N) (test_z_stepper_align_xy[N].x <= _MIN(X_MAX_BED - MIN_PROBE_EDGE_RIGHT, X_MAX_POS + dpo.x) + 0.00001f)
-#define FTEST(N) (test_z_stepper_align_xy[N].y >= _MAX(Y_MIN_BED + MIN_PROBE_EDGE_FRONT, Y_MIN_POS + dpo.y) - 0.00001f)
-#define BTEST(N) (test_z_stepper_align_xy[N].y <= _MIN(Y_MAX_BED - MIN_PROBE_EDGE_BACK,  Y_MAX_POS + dpo.y) + 0.00001f)
-
-static_assert(LTEST(0) && RTEST(0), "The 1st Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
-static_assert(FTEST(0) && BTEST(0), "The 1st Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
-static_assert(LTEST(1) && RTEST(1), "The 2nd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
-static_assert(FTEST(1) && BTEST(1), "The 2nd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
-#if NUM_Z_STEPPER_DRIVERS >= 3
-  static_assert(LTEST(2) && RTEST(2), "The 3rd Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
-  static_assert(FTEST(2) && BTEST(2), "The 3rd Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
-  #if NUM_Z_STEPPER_DRIVERS >= 4
-    static_assert(LTEST(3) && RTEST(3), "The 4th Z_STEPPER_ALIGN_XY X is unreachable with the default probe X offset.");
-    static_assert(FTEST(3) && BTEST(3), "The 4th Z_STEPPER_ALIGN_XY Y is unreachable with the default probe Y offset.");
-  #endif
-#endif
-
-//
-// G34 / M422 shared data
-//
-static xy_pos_t z_stepper_align_pos[] = Z_STEPPER_ALIGN_XY;
-
-#if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
-  static xy_pos_t z_stepper_align_stepper_pos[] = Z_STEPPER_ALIGN_STEPPER_XY;
-#endif
-
-#define G34_PROBE_COUNT COUNT(z_stepper_align_pos)
-
 inline void set_all_z_lock(const bool lock) {
   stepper.set_z_lock(lock);
   stepper.set_z2_lock(lock);
@@ -201,11 +141,11 @@ void GcodeSuite::G34() {
     // iteration this will be re-calculated based on the actual bed position
     float z_probe = Z_BASIC_CLEARANCE + (G34_MAX_GRADE) * 0.01f * (
       #if NUM_Z_STEPPER_DRIVERS == 3
-         SQRT(_MAX(HYPOT2(z_stepper_align_pos[0].x - z_stepper_align_pos[0].y, z_stepper_align_pos[1].x - z_stepper_align_pos[1].y),
-                   HYPOT2(z_stepper_align_pos[1].x - z_stepper_align_pos[1].y, z_stepper_align_pos[2].x - z_stepper_align_pos[2].y),
-                   HYPOT2(z_stepper_align_pos[2].x - z_stepper_align_pos[2].y, z_stepper_align_pos[0].x - z_stepper_align_pos[0].y)))
+         SQRT(_MAX(HYPOT2(z_stepper_align.xy[0].x - z_stepper_align.xy[0].y, z_stepper_align.xy[1].x - z_stepper_align.xy[1].y),
+                   HYPOT2(z_stepper_align.xy[1].x - z_stepper_align.xy[1].y, z_stepper_align.xy[2].x - z_stepper_align.xy[2].y),
+                   HYPOT2(z_stepper_align.xy[2].x - z_stepper_align.xy[2].y, z_stepper_align.xy[0].x - z_stepper_align.xy[0].y)))
       #else
-         HYPOT(z_stepper_align_pos[0].x - z_stepper_align_pos[0].y, z_stepper_align_pos[1].x - z_stepper_align_pos[1].y)
+         HYPOT(z_stepper_align.xy[0].x - z_stepper_align.xy[0].y, z_stepper_align.xy[1].x - z_stepper_align.xy[1].y)
       #endif
     );
 
@@ -216,31 +156,39 @@ void GcodeSuite::G34() {
     current_position.z -= z_probe * 0.5f;
 
     float last_z_align_move[NUM_Z_STEPPER_DRIVERS] = ARRAY_N(NUM_Z_STEPPER_DRIVERS, 10000.0f, 10000.0f, 10000.0f),
-          z_measured[G34_PROBE_COUNT] = { 0 },
+          z_measured[NUM_Z_STEPPER_DRIVERS] = { 0 },
           z_maxdiff = 0.0f,
           amplification = z_auto_align_amplification;
 
     uint8_t iteration;
     bool err_break = false;
+
+    #if DISABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+      bool adjustment_reverse = false;
+    #endif
+
     for (iteration = 0; iteration < z_auto_align_iterations; ++iteration) {
       if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPGM("> probing all positions.");
 
       SERIAL_ECHOLNPAIR("\nITERATION: ", int(iteration + 1));
 
       // Initialize minimum value
-      float z_measured_min = 100000.0f,
+      float z_measured_min =  100000.0f,
             z_measured_max = -100000.0f;
 
       // Probe all positions (one per Z-Stepper)
-      for (uint8_t i = 0; i < G34_PROBE_COUNT; ++i) {
+      for (uint8_t i = 0; i < NUM_Z_STEPPER_DRIVERS; ++i) {
         // iteration odd/even --> downward / upward stepper sequence
-        const uint8_t iprobe = (iteration & 1) ? G34_PROBE_COUNT - 1 - i : i;
+        const uint8_t iprobe = (iteration & 1) ? NUM_Z_STEPPER_DRIVERS - 1 - i : i;
 
         // Safe clearance even on an incline
         if (iteration == 0 || i > 0) do_blocking_move_to_z(z_probe);
 
+        if (DEBUGGING(LEVELING))
+          DEBUG_ECHOLNPAIR_P(PSTR("Probing X"), z_stepper_align.xy[iprobe].x, SP_Y_STR, z_stepper_align.xy[iprobe].y);
+
         // Probe a Z height for each stepper.
-        const float z_probed_height = probe.probe_at_point(z_stepper_align_pos[iprobe], raise_after, 0, true);
+        const float z_probed_height = probe.probe_at_point(z_stepper_align.xy[iprobe], raise_after, 0, true);
         if (isnan(z_probed_height)) {
           SERIAL_ECHOLNPGM("Probing failed.");
           err_break = true;
@@ -279,15 +227,15 @@ void GcodeSuite::G34() {
         // This allows the actual adjustment logic to be shared by both algorithms.
         linear_fit_data lfd;
         incremental_LSF_reset(&lfd);
-        for (uint8_t i = 0; i < G34_PROBE_COUNT; ++i) {
-          SERIAL_ECHOLNPAIR("PROBEPT_", int(i + 1), ": ", z_measured[i]);
-          incremental_LSF(&lfd, z_stepper_align_pos[i], z_measured[i]);
+        for (uint8_t i = 0; i < NUM_Z_STEPPER_DRIVERS; ++i) {
+          SERIAL_ECHOLNPAIR("PROBEPT_", i + '1', ": ", z_measured[i]);
+          incremental_LSF(&lfd, z_stepper_align.xy[i], z_measured[i]);
         }
         finish_incremental_LSF(&lfd);
 
         z_measured_min = 100000.0f;
         for (uint8_t i = 0; i < NUM_Z_STEPPER_DRIVERS; ++i) {
-          z_measured[i] = -(lfd.A * z_stepper_align_stepper_pos[i].x + lfd.B * z_stepper_align_stepper_pos[i].y);
+          z_measured[i] = -(lfd.A * z_stepper_align.stepper_xy[i].x + lfd.B * z_stepper_align.stepper_xy[i].y);
           z_measured_min = _MIN(z_measured_min, z_measured[i]);
         }
 
@@ -309,8 +257,8 @@ void GcodeSuite::G34() {
       // Correct the individual stepper offsets
       for (uint8_t zstepper = 0; zstepper < NUM_Z_STEPPER_DRIVERS; ++zstepper) {
         // Calculate current stepper move
-        const float z_align_move = z_measured[zstepper] - z_measured_min,
-                    z_align_abs = ABS(z_align_move);
+        float z_align_move = z_measured[zstepper] - z_measured_min;
+        const float z_align_abs = ABS(z_align_move);
 
         #if DISABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
           // Optimize one iteration's correction based on the first measurements
@@ -318,10 +266,14 @@ void GcodeSuite::G34() {
         #endif
 
         // Check for less accuracy compared to last move
-        if (last_z_align_move[zstepper] < z_align_abs - 1.0) {
+        if (last_z_align_move[zstepper] < z_align_abs * 0.7f) {
           SERIAL_ECHOLNPGM("Decreasing accuracy detected.");
-          err_break = true;
-          break;
+          #if DISABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+            adjustment_reverse = !adjustment_reverse;
+          #else
+            err_break = true;
+            break;
+          #endif
         }
 
         // Remember the alignment for the next iteration
@@ -342,6 +294,13 @@ void GcodeSuite::G34() {
           #endif
         }
 
+        #if DISABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+          // Decreasing accuracy was detected so move was inverted.
+          // Will match reversed Z steppers on dual steppers. Triple will need more work to map.
+          if (adjustment_reverse)
+            z_align_move = -z_align_move;
+        #endif
+
         // Do a move to correct part of the misalignment for the current stepper
         do_blocking_move_to_z(amplification * z_align_move + current_position.z);
       } // for (zstepper)
@@ -406,12 +365,13 @@ void GcodeSuite::G34() {
  *   Y<pos>   : Y position to set (Unchanged if omitted)
  */
 void GcodeSuite::M422() {
+
   if (!parser.seen_any()) {
-    for (uint8_t i = 0; i < G34_PROBE_COUNT; ++i)
-      SERIAL_ECHOLNPAIR_P(PSTR("M422 S"), i + 1, SP_X_STR, z_stepper_align_pos[i].x, SP_Y_STR, z_stepper_align_pos[i].y);
+    for (uint8_t i = 0; i < NUM_Z_STEPPER_DRIVERS; ++i)
+      SERIAL_ECHOLNPAIR_P(PSTR("M422 S"), i + '1', SP_X_STR, z_stepper_align.xy[i].x, SP_Y_STR, z_stepper_align.xy[i].y);
     #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
       for (uint8_t i = 0; i < NUM_Z_STEPPER_DRIVERS; ++i)
-        SERIAL_ECHOLNPAIR_P(PSTR("M422 W"), i + 1, SP_X_STR, z_stepper_align_stepper_pos[i].x, SP_Y_STR, z_stepper_align_stepper_pos[i].y);
+        SERIAL_ECHOLNPAIR_P(PSTR("M422 W"), i + '1', SP_X_STR, z_stepper_align.stepper_xy[i].x, SP_Y_STR, z_stepper_align.stepper_xy[i].y);
     #endif
     return;
   }
@@ -427,9 +387,9 @@ void GcodeSuite::M422() {
 
   xy_pos_t *pos_dest = (
     #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
-      !is_probe_point ? z_stepper_align_stepper_pos :
+      !is_probe_point ? z_stepper_align.stepper_xy :
     #endif
-    z_stepper_align_pos
+    z_stepper_align.xy
   );
 
   if (!is_probe_point
@@ -451,7 +411,7 @@ void GcodeSuite::M422() {
   int8_t position_index;
   if (is_probe_point) {
     position_index = parser.intval('S') - 1;
-    if (!WITHIN(position_index, 0, int8_t(G34_PROBE_COUNT) - 1)) {
+    if (!WITHIN(position_index, 0, int8_t(NUM_Z_STEPPER_DRIVERS) - 1)) {
       SERIAL_ECHOLNPGM("?(S) Z-ProbePosition index invalid.");
       return;
     }

Marlin/src/module/configuration_store.cpp

@@ -37,7 +37,7 @@
  */
 
 // Change EEPROM version if the structure changes
-#define EEPROM_VERSION "V75"
+#define EEPROM_VERSION "V76"
 #define EEPROM_OFFSET 100
 
 // Check the integrity of data offsets.
@@ -66,6 +66,10 @@
   #include "../feature/bedlevel/bedlevel.h"
 #endif
 
+#if ENABLED(Z_STEPPER_AUTO_ALIGN)
+  #include "../feature/z_stepper_align.h"
+#endif
+
 #if ENABLED(EXTENSIBLE_UI)
   #include "../lcd/extensible_ui/ui_api.h"
 #endif
@@ -252,6 +256,16 @@ typedef struct SettingsDataStruct {
   #endif
 
   //
+  // Z_STEPPER_AUTO_ALIGN, Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS
+  //
+  #if ENABLED(Z_STEPPER_AUTO_ALIGN)
+    xy_pos_t z_stepper_align_xy[NUM_Z_STEPPER_DRIVERS];             // M422 S X Y
+    #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+      xy_pos_t z_stepper_align_stepper_xy[NUM_Z_STEPPER_DRIVERS];   // M422 W X Y
+    #endif
+  #endif
+
+  //
   // ULTIPANEL
   //
   int16_t ui_preheat_hotend_temp[2],                    // M145 S0 H
@@ -801,6 +815,13 @@ void MarlinSettings::postprocess() {
       #endif
     }
 
+    #if ENABLED(Z_STEPPER_AUTO_ALIGN)
+      EEPROM_WRITE(z_stepper_align.xy);
+      #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+        EEPROM_WRITE(z_stepper_align.stepper_xy);
+      #endif
+    #endif
+
     //
     // LCD Preheat settings
     //
@@ -1669,6 +1690,13 @@ void MarlinSettings::postprocess() {
         #endif
       }
 
+      #if ENABLED(Z_STEPPER_AUTO_ALIGN)
+        EEPROM_READ(z_stepper_align.xy);
+        #if ENABLED(Z_STEPPER_ALIGN_KNOWN_STEPPER_POSITIONS)
+          EEPROM_READ(z_stepper_align.stepper_xy);
+        #endif
+      #endif
+
       //
       // LCD Preheat settings
       //
@@ -2474,6 +2502,14 @@ void MarlinSettings::reset() {
   #endif
 
   //
+  // Z Stepper Auto-alignment points
+  //
+
+  #if ENABLED(Z_STEPPER_AUTO_ALIGN)
+    z_stepper_align.reset_to_default();
+  #endif
+
+  //
   // Servo Angles
   //