[BUG] SCARA axis homing

[Sejkorka]

Did you test the latest bugfix-2.1.x code?

Yes, and the problem still exists.

Bug Description

Hi, I have a problem with marlin and its SCARA function, it's my graduation paper, I have already printed the complete scara, most things work, if not at least half.
But what doesn't work is the homing of the "X" axis, the limit switches work normally and M119 shows them as triggers when they should be.
The "X" axis does not homing, it seems to me that once the "Y" axis is homed so is the "X" axis.

Bug Timeline

No response

Expected behavior

No response

Actual behavior

No response

Steps to Reproduce

No response

Version of Marlin Firmware

2.0.9

Printer model

MP_SCARA

Electronics

BOARD_RAMPS_14_EFB

LCD/Controller

No response

Other add-ons

No response

Bed Leveling

None

Your Slicer

None

Host Software

Repetier Host

Don't forget to include

• A ZIP file containing your Configuration.h and Configuration_adv.h.

Additional information & file uploads

Config adv.txt
Config.txt

[thinkyhead]

This part of the code doesn't get enough attention. When I was last working on a SCARA style robot it had a single free arm, so it had to home both its first and second joints. I've never seen the Morgan and MP SCARA robots do their homing, but the provided code is supposed to have done the right thing at one time.

Anyway, it sounds like you'll need to dig into the homing code and debug it to work for your machine, or recruit some help to figure it out. The Marlin Discord server is a pretty good place to find help. Once you have it sorted out it would be great if you could submit the fix to the main project. SCARA is a rare thing, but we do want it to work!

[ellensp]

MP_SCARA is quite broken in bugfix 2.1.x

I Enabled debugging
#define DEBUG_LEVELING_FEATURE
M111 S32

All the following G28 test where done on a freshly reset board.

G28 gives me this log on a standard G28, Z axis moves up and then it errors..

G28
18:54:25.501 > >>> G28 X0.00 Y199.07 Z0.00
18:54:25.501 > Machine Type: SCARA
18:54:25.501 > Probe: NONE
18:54:25.501 > remember_feedrate_scaling_off: fr=66.67 100%
18:54:25.501 > Raise Z before homing:
18:54:25.501 > do_z_clearance(5.00 [0.00 to 5.00], 0)
18:54:25.501 > do_blocking_move_to_z(5.00, 4.00)
18:54:25.501 > >>> do_blocking_move_to X0.00 Y199.07 Z0.00
18:54:25.501 > > X0.00 Y199.07 Z5.00
18:54:25.501 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
18:54:25.501 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
18:54:27.481 > echo:busy: processing
18:54:27.858 > <<< do_blocking_move_to X0.00 Y199.07 Z5.00
18:54:27.858 > current_position= X0.00 Y0.00 Z5.00 : sync_plan_position
18:54:27.858 > do_blocking_move_to_xy(-300.00, -300.00, 28.28)
18:54:27.858 > >>> do_blocking_move_to X0.00 Y0.00 Z5.00
18:54:27.858 > > X-300.00 Y-300.00 Z5.00
18:54:27.858 > <<< do_blocking_move_to X0.00 Y0.00 Z5.00
18:54:27.858 > echo:Homing Failed
18:54:27.858 > Error:Printer halted. kill() called!

G28 Z works as expected

G28 Z
19:08:29.178 > >>> G28 X0.00 Y199.07 Z0.00
19:08:29.178 > Machine Type: SCARA
19:08:29.178 > Probe: NONE
19:08:29.178 > remember_feedrate_scaling_off: fr=66.67 100%
19:08:29.178 > >>> homeaxis(Z)
19:08:29.178 > Home Fast: -150.00mm
19:08:29.178 > >>> do_homing_move X0.00 Y199.07 Z0.00
19:08:29.178 > ...(Z, -150.00, [4.00])
19:08:29.178 > current_position= X0.00 Y199.07 Z0.00 : sync_plan_position
19:08:31.158 > echo:busy: processing
...
19:08:59.142 > echo:busy: processing
19:08:59.377 > <<< do_homing_move X0.00 Y199.07 Z-150.00
19:08:59.378 > Move Away: 3.00mm
19:08:59.378 > >>> do_homing_move X0.00 Y199.07 Z-150.00
19:08:59.378 > ...(Z, 3.00, [4.00])
19:08:59.378 > current_position= X0.00 Y199.07 Z0.00 : sync_plan_position
19:09:00.928 > <<< do_homing_move X0.00 Y199.07 Z3.00
19:09:00.928 > Re-bump: -6.00mm
19:09:00.928 > >>> do_homing_move X0.00 Y199.07 Z3.00
19:09:00.928 > ...(Z, -6.00, 1.00)
19:09:00.928 > current_position= X0.00 Y199.07 Z0.00 : sync_plan_position
19:09:01.151 > echo:busy: processing
19:09:03.148 > echo:busy: processing
19:09:04.182 > <<< do_homing_move X0.00 Y199.07 Z-6.00
19:09:04.182 > >>> set_axis_is_at_home(Z)
19:09:04.182 > current_position= X0.00 Y199.07 Z0.00 :
19:09:04.182 > <<< set_axis_is_at_home(Z)
19:09:04.182 > current_position= X0.00 Y199.07 Z0.00 : sync_plan_position
19:09:04.182 > <<< homeaxis(Z)
19:09:04.182 > current_position= X0.00 Y199.07 Z0.00 : sync_plan_position
19:09:04.182 > >>> do_move_after_z_homing X0.00 Y199.07 Z0.00
19:09:04.182 > do_z_clearance(5.00 [0.00 to 5.00], 1)
19:09:04.182 > do_blocking_move_to_z(5.00, 4.00)
19:09:04.182 > >>> do_blocking_move_to X0.00 Y199.07 Z0.00
19:09:04.182 > > X0.00 Y199.07 Z5.00
19:09:04.182 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:09:04.201 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:09:05.144 > echo:busy: processing
19:09:06.554 > <<< do_blocking_move_to X0.00 Y199.07 Z5.00
19:09:06.554 > <<< do_move_after_z_homing X0.00 Y199.07 Z5.00
19:09:06.554 > restore_feedrate_and_scaling: fr=66.67 100%
19:09:06.554 > X:0.00 Y:199.07 Z:5.00 E:0.00 Count A:2581B:2581 Z:8000
19:09:06.554 > SCARA Theta:90.01 Psi:90.01
19:09:06.554 >
19:09:06.554 > <<< G28 X0.00 Y199.07 Z5.00
19:09:06.554 > ok

G28 Y moves Z up 5mm as expected, but then does nothing.

G28 Y
19:11:21.900 > >>> G28 X0.00 Y199.07 Z0.00
19:11:21.900 > Machine Type: SCARA
19:11:21.900 > Probe: NONE
19:11:21.900 > remember_feedrate_scaling_off: fr=66.67 100%
19:11:21.900 > Raise Z before homing:
19:11:21.900 > do_z_clearance(5.00 [0.00 to 5.00], 0)
19:11:21.900 > do_blocking_move_to_z(5.00, 4.00)
19:11:21.900 > >>> do_blocking_move_to X0.00 Y199.07 Z0.00
19:11:21.900 > > X0.00 Y199.07 Z5.00
19:11:21.900 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:11:21.900 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:11:23.865 > echo:busy: processing
19:11:24.254 > <<< do_blocking_move_to X0.00 Y199.07 Z5.00
19:11:24.254 > current_position= X0.00 Y199.07 Z5.00 : sync_plan_position
19:11:24.254 > restore_feedrate_and_scaling: fr=66.67 100%
19:11:24.254 > X:0.00 Y:199.07 Z:5.00 E:0.00 Count A:2581B:2581 Z:8000
19:11:24.254 > SCARA Theta:90.01 Psi:90.01
19:11:24.254 >
19:11:24.254 > <<< G28 X0.00 Y199.07 Z5.00
19:11:24.254 > ok

G28 X moves Z up 5mm as expected, but then does nothing.

G28 X

19:18:41.893 > >>> G28 X0.00 Y199.07 Z0.00
19:18:41.893 > Machine Type: SCARA
19:18:41.893 > Probe: NONE
19:18:41.893 > remember_feedrate_scaling_off: fr=66.67 100%
19:18:41.893 > Raise Z before homing:
19:18:41.893 > do_z_clearance(5.00 [0.00 to 5.00], 0)
19:18:41.893 > do_blocking_move_to_z(5.00, 4.00)
19:18:41.893 > >>> do_blocking_move_to X0.00 Y199.07 Z0.00
19:18:41.893 > > X0.00 Y199.07 Z5.00
19:18:41.893 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:18:41.893 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:18:43.857 > echo:busy: processing
19:18:44.247 > <<< do_blocking_move_to X0.00 Y199.07 Z5.00
19:18:44.247 > current_position= X0.00 Y199.07 Z5.00 : sync_plan_position
19:18:44.247 > restore_feedrate_and_scaling: fr=66.67 100%
19:18:44.247 > X:0.00 Y:199.07 Z:5.00 E:0.00 Count A:2581B:2581 Z:8000
19:18:44.247 > SCARA Theta:90.01 Psi:90.01
19:18:44.247 >
19:18:44.247 > <<< G28 X0.00 Y199.07 Z5.00
19:18:44.247 > ok

Im not sure that G28 X or Y should actually do anything since there isn't really a X or a Y endstop.
But G28 should most definely home all axies.

[ellensp]

disabling #define VALIDATE_HOMING_ENDSTOPS does allow G28 to complete, but does not move X or Y steppers

G28
19:43:25.835 > >>> G28 X0.00 Y199.07 Z0.00
19:43:25.835 > Machine Type: SCARA
19:43:25.835 > Probe: NONE
19:43:25.835 > remember_feedrate_scaling_off: fr=66.67 100%
19:43:25.835 > Raise Z before homing:
19:43:25.835 > do_z_clearance(5.00 [0.00 to 5.00], 0)
19:43:25.835 > do_blocking_move_to_z(5.00, 4.00)
19:43:25.835 > >>> do_blocking_move_to X0.00 Y199.07 Z0.00
19:43:25.835 > > X0.00 Y199.07 Z5.00
19:43:25.835 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:43:25.835 > destination= X0.00 Y199.07 Z5.00 : prepare_fast_move_to_destination
19:43:27.800 > echo:busy: processing
19:43:28.194 > <<< do_blocking_move_to X0.00 Y199.07 Z5.00
19:43:28.194 > current_position= X0.00 Y0.00 Z5.00 : sync_plan_position
19:43:28.194 > do_blocking_move_to_xy(-300.00, -300.00, 28.28)
19:43:28.194 > >>> do_blocking_move_to X0.00 Y0.00 Z5.00
19:43:28.194 > > X-300.00 Y-300.00 Z5.00
19:43:28.194 > <<< do_blocking_move_to X0.00 Y0.00 Z5.00
19:43:28.194 > >>> homeaxis(Z)
19:43:28.194 > Home Fast: -150.00mm
19:43:28.194 > >>> do_homing_move X0.00 Y0.00 Z5.00
19:43:28.194 > ...(Z, -150.00, [4.00])
19:43:28.194 > current_position= X0.00 Y0.00 Z0.00 : sync_plan_position
19:43:29.807 > echo:busy: processing
19:43:31.804 > echo:busy: processing
19:43:32.452 > <<< do_homing_move X0.00 Y0.00 Z-150.00
19:43:32.453 > Move Away: 3.00mm
19:43:32.453 > >>> do_homing_move X0.00 Y0.00 Z-150.00
19:43:32.453 > ...(Z, 3.00, [4.00])
19:43:32.453 > current_position= X0.00 Y0.00 Z0.00 : sync_plan_position
19:43:33.810 > echo:busy: processing
19:43:34.003 > <<< do_homing_move X0.00 Y0.00 Z3.00
19:43:34.003 > Re-bump: -6.00mm
19:43:34.003 > >>> do_homing_move X0.00 Y0.00 Z3.00
19:43:34.003 > ...(Z, -6.00, 1.00)
19:43:34.003 > current_position= X0.00 Y0.00 Z0.00 : sync_plan_position
19:43:35.808 > echo:busy: processing
19:43:37.172 > <<< do_homing_move X0.00 Y0.00 Z-6.00
19:43:37.172 > >>> set_axis_is_at_home(Z)
19:43:37.172 > current_position= X0.00 Y0.00 Z0.00 :
19:43:37.172 > <<< set_axis_is_at_home(Z)
19:43:37.172 > current_position= X0.00 Y0.00 Z0.00 : sync_plan_position
19:43:37.172 > <<< homeaxis(Z)
19:43:37.172 > current_position= X0.00 Y0.00 Z0.00 : sync_plan_position
19:43:37.172 > >>> do_move_after_z_homing X0.00 Y0.00 Z0.00
19:43:37.172 > do_z_clearance(5.00 [0.00 to 5.00], 1)
19:43:37.172 > do_blocking_move_to_z(5.00, 4.00)
19:43:37.172 > >>> do_blocking_move_to X0.00 Y0.00 Z0.00
19:43:37.172 > > X0.00 Y0.00 Z5.00
19:43:37.172 > destination= X0.00 Y0.00 Z5.00 : prepare_fast_move_to_destination
19:43:37.191 > destination= X0.00 Y0.00 Z5.00 : prepare_fast_move_to_destination
19:43:37.798 > echo:busy: processing
19:43:39.545 > <<< do_blocking_move_to X0.00 Y0.00 Z5.00
19:43:39.545 > <<< do_move_after_z_homing X0.00 Y0.00 Z5.00
19:43:39.545 > restore_feedrate_and_scaling: fr=66.67 100%
19:43:39.545 > X:0.00 Y:0.00 Z:5.00 E:0.00 Count A:-2147483648B:-2147483648 Z:8000
19:43:39.545 > SCARA Theta:-74893488.00 Psi:-74893488.00
19:43:39.545 >
19:43:39.545 > <<< G28 X0.00 Y0.00 Z5.00
19:43:39.545 > ok

[ellensp]

This answer that question, only G28 Z will fuction

  void homeaxis(const AxisEnum axis) {

    #if ANY(MORGAN_SCARA, MP_SCARA)
      // Only Z homing (with probe) is permitted
      if (axis != Z_AXIS) { BUZZ(100, 880); return; }

[ellensp]

I want back to 2.0.5 to find one that can home, and I notice that is_scara is not set for the mp_scara,

ie 2.0.5 does not limit homeaxis to Z_AXIS

void homeaxis(const AxisEnum axis) {

  #if IS_SCARA
    // Only Z homing (with probe) is permitted
    if (axis != Z_AXIS) { BUZZ(100, 880); return; }
  #else

So I regressed bugfix 2.1.x to just the following and allowed it to home X and Y

#if ENABLED(MORGAN_SCARA)  

And the large arm actually homed, but very very slowly. then after homing it flung itself wild to the other end of travel.
So it seems like the axis is not being setup correctly.
...

no solution yet.

[Sejkorka]

This answer that question, only G28 Z will fuction

  void homeaxis(const AxisEnum axis) {

    #if ANY(MORGAN_SCARA, MP_SCARA)
      // Only Z homing (with probe) is permitted
      if (axis != Z_AXIS) { BUZZ(100, 880); return; }

But there has to be soome way to do it, i look at the video from "How To Mechatronics" he build SCARA and for him MARLIN worked, but his MARLIN not working for me..

[shimaode]

I commented out the return code for SCARA

  void homeaxis(const AxisEnum axis) {

    #if ANY(MORGAN_SCARA, MP_SCARA)
      // Only Z homing (with probe) is permitted
      // if (axis != Z_AXIS) { BUZZ(100, 880); return; }

And in my case, the x axis can home in normal speed but it's not guaranteed to back to home position every time, sometimes it just stops before it even hit the endstop. And the y axis is going wild in an unnormal speed.

Looking into the homing code, this should be causing the problem:

const float move_length = 1.5f * max_length(TERN(DELTA, Z_AXIS, axis)) * axis_home_dir;
if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPGM("Home Fast: ", move_length, "mm");
do_homing_move(axis, move_length, 0.0, !use_probe_bump);

This commands the head to move 1.5f * max_length of each axis

And in do_homing_move:

  #if IS_SCARA
    // Tell the planner the axis is at 0
    current_position[axis] = 0;
    sync_plan_position();
    current_position[axis] = distance;
    line_to_current_position(real_fr_mm_s);

line_to_current_position will call into planner.buffer_line and finally call into MP_SCARA's inverse_kinematics to translate this target position into MP_SCARA's arm angles.

The problem of the above code is that this homing target position calculated from 1.5 * max_length of axis is not guaranteed to get a valid arm angles after being sent into MP_SCARA's inverse_kinematics, it could be beyond the reach of the arms and get you a wrong arm angle, depends on your settings of the SCARA.

That's why in my case, the x axis can do homing normally and the y axis can not, because this homing position for x axis happens to be in the reach of the arms but the y axis is not so lucky.

Also this homing position for x axis just rotate my arm for under 90 degrees in my case, so when the arm is too far away from the endstop, it just stops before hits the endstop.

I think for SCARA, homing should be just keep rotating the arm until the endstops are hit instead of trying to use a far away position and do IK to that position for homing.

Not sure my ideas are right, correct me if I'm wrong. :-)

[ellensp]

Ascii art of the mp_scara (shoulder joint)<==upper arm==>(elbow joint)<== forearm with a fixed hand==>
So we are using same terminology...

I have this homing but the arm must be positioned so the upper arm hits its endstop first, ie the forearm should point away from the endstops. (I can see no way around this as the upper arm must be in correct location before the forearm can get near its endstop)

diff --git a/Marlin/src/module/motion.cpp b/Marlin/src/module/motion.cpp
index 820089d7ee..4e9cec1003 100644
--- a/Marlin/src/module/motion.cpp
+++ b/Marlin/src/module/motion.cpp
@@ -2467,7 +2467,7 @@ void prepare_line_to_destination() {
       #endif
     }

-    #if ANY(MORGAN_SCARA, MP_SCARA)
+    #if ENABLED(MORGAN_SCARA)
       // Tell the planner the axis is at 0
       current_position[axis] = 0;
       sync_plan_position();
@@ -2665,7 +2665,7 @@ void prepare_line_to_destination() {

   void homeaxis(const AxisEnum axis) {

-    #if ANY(MORGAN_SCARA, MP_SCARA)
+    #if ENABLED(MORGAN_SCARA)
       // Only Z homing (with probe) is permitted
       if (axis != Z_AXIS) { BUZZ(100, 880); return; }
     #else
@@ -3054,7 +3054,7 @@ void set_axis_is_at_home(const AxisEnum axis) {
     }
   #endif

-  #if ANY(MORGAN_SCARA, AXEL_TPARA)
+  #if IS_SCARA
     scara_set_axis_is_at_home(axis);
   #elif ENABLED(DELTA)
     current_position[axis] = (axis == Z_AXIS) ? DIFF_TERN(HAS_BED_PROBE, delta_height, probe.offset.z) : base_home_pos(axis);

Config files needs this added #define FEEDRATE_SCALING (without this the homing feed rate are all over the place)
Also disable #define VALIDATE_HOMING_ENDSTOPS

The XY homing procedure is it does a quick home on X and Y ie both move at once (this is required to keep the forearm pointing in the same direction during moving home)

Then the upper arm is re-homed, then the forarm is homed.

finally scara_set_axis_is_at_home is called to set home position to homeposition = { SCARA_OFFSET_THETA1, SCARA_OFFSET_THETA2} from Configuration.h

The homes reliably for me, but I have not tested anything else, especially not the sacra kinematics.

[Sejkorka]

This is my scara

[ellensp]

This is the MP_SCARA https://www.thingiverse.com/thing:2487048 which is also what I tested on

[Sejkorka]

Technically they are the same.

[ellensp]

MP_SCARA has endstops in a weird location

ie.

Yours is much more like https://howtomechatronics.com/projects/laser-engraving-with-diy-arduino-scara-robot-complete-guide/

The video https://www.youtube.com/watch?v=1QHJksTrk8s shows the endstops are independent. So a little different from the MP_SCARA