docs: Add Delta_Calibrate.md guide with "enhanced delta calibration"

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Delta_Calibrate.md

@@ -0,0 +1,212 @@
+This document describes Klipper's automatic calibration system for
+"delta" style printers.
+
+Delta calibration involves finding the tower endstop positions, tower
+angles, delta radius, and delta arm lengths. These settings control
+printer motion on a delta printer. Each one of these parameters has a
+non-obvious and non-linear impact and it is difficult to calibrate
+them manually. In contrast, the software calibration code can provide
+excellent results with just a few minutes of time. No special probing
+hardware is necessary to get good results.
+
+Basic delta calibration
+=======================
+
+Klipper has a DELTA_CALIBRATE command that can perform basic delta
+calibration. This command probes seven different points on the bed and
+calculates new values for the tower angles, tower endstops, and delta
+radius.
+
+In order to perform this calibration the initial delta parameters (arm
+lengths, radius, and endstop positions) must be provided and they
+should have an accuracy to within a few millimeters. Most delta
+printer kits will provide these parameters - configure the printer
+with these initial defaults and then go on to run the DELTA_CALIBRATE
+command as described below. If no defaults are available then search
+online for a delta calibration guide that can provide a basic starting
+point.
+
+During the delta calibration process it may be necessary for the
+printer to probe below what would otherwise be considered the plane of
+the bed. It is typical to permit this during calibration by updating
+the config so that the printer's `minimum_z_position=-5`. (Once
+calibration completes, one can remove this setting from the config.)
+
+There are two ways to perform the probing - manual probing and
+automatic probing. Automatic probing utilizes a hardware device
+capable of triggering when the toolhead is at a set distance from the
+bed. Manual probing involves using the "paper test" to determine the
+height at each probe point. It is recommended to use manual probing
+for delta calibration. A number of common printer kits come with
+probes that are not sufficiently accurate (specifically, small
+differences in arm length can cause effector tilt which can skew an
+automatic probe). Manual probing only takes a few minutes and it
+eliminates error introduced by the probe.
+
+To perform the basic probe, make sure the config has a
+[delta_calibrate] section defined and run:
+```
+DELTA_CALIBRATE
+```
+After probing the seven points new delta parameters will be
+calculated.  Save and apply these parameters by running:
+```
+SAVE_CONFIG
+```
+
+The basic calibration should provide delta parameters that are
+accurate enough for basic printing.  If this is a new printer, this is
+a good time to print some basic objects and verify general
+functionality.
+
+Enhanced delta calibration
+==========================
+
+The basic delta calibration generally does a good job of calculating
+delta parameters such that the nozzle is the correct distance from the
+bed. However, it does not attempt to calibrate X and Y dimensional
+accuracy. It's a good idea to perform an enhanced delta calibration to
+verify dimensional accuracy.
+
+This calibration procedure requires printing a test object and
+measuring parts of that test object with digital calipers.
+
+Prior to running an enhanced delta calibration one must run the basic
+delta calibration (via the DELTA_CALIBRATE command) and save the
+results (via the SAVE_CONFIG command).
+
+Use a slicer to generate G-Code from the
+[docs/prints/calibrate_size.stl](prints/calibrate_size.stl) file.
+Slice the object using a slow speed (eg, 40mm/s). If possible, use a
+stiff plastic (such as PLA) for the object. The object has a diameter
+of 140mm. If this is too large for the printer then one can scale it
+down (but be sure to uniformly scale both the X and Y axes). If the
+printer supports significantly larger prints then this object can also
+be increased in size. A larger size can improve the measurement
+accuracy, but good print adhesion is more important than a larger
+print size.
+
+Print the test object and wait for it to fully cool. The commands
+described below must be run with the same printer settings used to
+print the calibration object (don't run DELTA_CALIBRATE between
+printing and measuring, or do something that would otherwise change
+the printer configuration).
+
+If possible, perform the measurements described below while the object
+is still attached to the print bed, but don't worry if the part
+detaches from the bed - just try to avoid bending the object when
+performing the measurements.
+
+Start by measuring the distance between the center pillar and the
+pillar next to the "A" label (which should also be pointing towards
+the "A" tower).
+
+![delta-a-distance](img/delta-a-distance.jpg)
+
+Then go counterclockwise and measure the distances between the center
+pillar and the other pillars (distance from center to pillar across
+from C label, distance from center to pillar with B label, etc.).
+
+![delta_cal_e_step1](img/delta_cal_e_step1.png)
+
+Enter these parameters into Klipper with a comma separated list of
+floating point numbers:
+```
+DELTA_ANALYZE CENTER_DISTS=<a_dist>,<far_c_dist>,<b_dist>,<far_a_dist>,<c_dist>,<far_b_dist>
+```
+Provide the values without spaces between them.
+
+Then measure the distance between the A pillar and the pillar across
+from the C label.
+
+![delta-ab-distance](img/delta-outer-distance.jpg)
+
+Then go counterclockwise and measure the distance between the pillar
+across from C to the B pillar, the distance between the B pillar and
+the pillar across from A, and so on.
+
+![delta_cal_e_step2](img/delta_cal_e_step2.png)
+
+Enter these parameters into Klipper:
+```
+DELTA_ANALYZE OUTER_DISTS=<a_to_far_c>,<far_c_to_b>,<b_to_far_a>,<far_a_to_c>,<c_to_far_b>,<far_b_to_a>
+```
+
+At this point it is okay to remove the object from the bed. The final
+measurements are of the pillars themselves. Measure the size of the
+center pillar along the A spoke, then the B spoke, and then the C
+spoke.
+
+![delta-a-pillar](img/delta-a-pillar.jpg)
+
+![delta_cal_e_step3](img/delta_cal_e_step3.png)
+
+Enter them into Klipper:
+```
+DELTA_ANALYZE CENTER_PILLAR_WIDTHS=<a>,<b>,<c>
+```
+
+The final measurements are of the outer pillars. Start by measuring
+the distance of the A pillar along the line from A to the pillar
+across from C.
+
+![delta-ab-pillar](img/delta-outer-pillar.jpg)
+
+Then go counterclockwise and measure the remaining outer pillars
+(pillar across from C along the line to B, B pillar along the line to
+pillar across from A, etc.).
+
+![delta_cal_e_step4](img/delta_cal_e_step4.png)
+
+And enter them into Klipper:
+```
+DELTA_ANALYZE OUTER_PILLAR_WIDTHS=<a>,<far_c>,<b>,<far_a>,<c>,<far_b>
+```
+
+If the object was scaled to a smaller or larger size then provide the
+scale factor that was used when slicing the object:
+```
+DELTA_ANALYZE SCALE=1.0
+```
+(A scale value of 2.0 would mean the object is twice its original
+size, 0.5 would be half its original size.)
+
+Finally, perform the enhanced delta calibration by running:
+```
+DELTA_ANALYZE CALIBRATE=extended
+```
+This command can take several minutes to complete. After completion it
+will calculate updated delta parameters (delta radius, tower angles,
+endstop positions, and arm lengths). Use the SAVE_CONFIG command to
+save and apply the settings:
+```
+SAVE_CONFIG
+```
+
+The SAVE_CONFIG command will save both the updated delta parameters
+and information from the distance measurements. Future DELTA_CALIBRATE
+commands will also utilize this distance information. Do not attempt
+to reenter the raw distance measurements after running SAVE_CONFIG, as
+this command changes the printer configuration and the raw
+measurements no longer apply.
+
+Additional notes
+----------------
+
+* If the delta printer has good dimensional accuracy then the distance
+  between any two pillars should be around 74mm and the width of every
+  pillar should be around 9mm. (Specifically, the goal is for the
+  distance between any two pillars minus the width of one of the
+  pillars to be exactly 65mm.) Should there be a dimensional
+  inaccuracy in the part then the DELTA_ANALYZE routine will calculate
+  new delta parameters using both the distance measurements and the
+  previous height measurements from the last DELTA_CALIBRATE command.
+
+* DELTA_ANALYZE may produce delta parameters that are surprising. For
+  example, it may suggest arm lengths that do not match the printer's
+  actual arm lengths. Despite this, testing has shown that
+  DELTA_ANALYZE often produces superior results. It is believed that
+  the calculated delta parameters are able to account for slight
+  errors elsewhere in the hardware. For example, small differences in
+  arm length may result in a tilt to the effector and some of that
+  tilt may be accounted for by adjusting the arm length parameters.

docs/Features.md

@@ -77,8 +77,10 @@ Klipper supports many standard 3d printer features:
   manipulating the Z steppers. Most Z height probes are supported,
   including servo activated probes.
 
-* Automatic delta calibration support. The calibration can be done
-  with a Z height probe or via manual probing.
+* Automatic delta calibration support. The calibration tool can
+  perform basic height calibration as well as an enhanced X and Y
+  dimension calibration. The calibration can be done with a Z height
+  probe or via manual probing.
 
 * Support for common temperature sensors (eg, common thermistors,
   AD595, PT100, MAX6675, MAX31855, MAX31856, MAX31865). Custom

docs/G-Codes.md

@@ -152,6 +152,8 @@ section is enabled:
   - `NEXT`: If manual bed probing is enabled, then one can use this
     command to move to the next probing point during a DELTA_CALIBRATE
     operation.
+- `DELTA_ANALYZE`: This command is used during enhanced delta
+  calibration. See [Delta Calibrate](Delta_Calibrate.md) for details.
 
 ## Bed Tilt
 

docs/Overview.md

@@ -10,7 +10,9 @@ settings in the config file.
 
 The Klipper configuration is stored in a simple text file on the host
 machine. The [config/example.cfg](../config/example.cfg) file serves
-as a reference for the config file. The
+as a reference for the config file. See the
+[Delta Calibrate](Delta_Calibrate.md) document for information on
+calibrating delta printers. The
 [Pressure Advance](Pressure_Advance.md) document contains information
 on tuning the pressure advance config.