For correct operation of the load cells it is necessary to remove the bed, solder the load cells in parallel and plug them into one of the channel connector. Remember/record the channel number, the number can be seen on the last picture.
all photo by (c) ZeyHex
Record/remember which channel number the paralleled load cells were plugged into!
N.B. 1 On the K1 MAX, the board is rotated 180 degrees, not as pictured. Read the channel number either from the main large connector clockwise or refer to the inscriptions on the board:
N.B. 2 You should try to make the wires from the load cells to the main connector the same length.
After all operations, assemble the bed.
Important! when assembling the table and hotbed, either replace the spacers between load cells and the hotbed with higher ones (12+ mm), or carefully arrange the re-soldered wires, especially look carefully at the main wire connection to the MCU board - with standard spacers poorly arranged wires covered with thermal insulation can push the hotbed from below, which negatively affects the correct operation of load cells, in particular, poor repeatability and significantly different accuracy in different parts of the hotbed.
It is necessary to build new firmware for the bed mcu, nozzle and main mcu. Either compile it yourself - or download it from HERE
For firmware compilation you need any Linux distro, here are the instructions using Debian as an example.
sudo apt install build-essential gcc-arm-none-eabi
git clone https://github.com/cryoz/K1_Series_Klipper.git && cd K1_Series_Klipper
./build.sh
If everything builds without errors - the outfw folder with three firmwares will appear:
bed_klipper.bin
mcu_klipper.bin
noz_klipper.bin
Download them to the printer in a temporary folder, e.g. /usr/data/tenso/fw
I used the K1-klipper project mostly because of its easy installation, and then modernized it with necessary modules. But then I decided to fork this repository, adding all necessary modules from garethky and ZeyHex at once
Backup the entire printer config folder (/usr/data/printer_data/config), you can do this via helper-script.
To install the klipper on the printer:
cd /usr/data
wget --no-check-certificate https://raw.githubusercontent.com/cryoz/installer_script_k1_and_max/main/installer.sh
chmod +x installer.sh
./installer.sh
After the installation is complete, do NOT reboot the printer - download all three firmware files to the /usr/data/klipper/fw/K1 folder. If the firmware files were previously downloaded to /usr/data/tenso:
cd /usr/data/tenso/fw && cp *.bin /usr/data/klipper/fw/K1/
It is necessary to backup the log file of the firmware flasher of stock firmware in case of version or revision mismatch:
cp /tmp/mcu_update.log /usr/data/tenso/
N.B. if the Helper-script was used - you need to reinstall all modules that were installed.
Backup the entire printer config folder again, you can use helper-script.
First of all, remove all [prtouch_v2] [prtouch_v1] [fan_feedback] sections from printer.cfg.
Correct load cells settings in /usr/data/printer_data/config/loadcell_probe.cfg file by taking the required pins from the channel into which you soldered the resoldered load cells from this table:
| Channel | dout | sclk |
|---|---|---|
| 1 | PA0 | PA2 |
| 2 | PA1 | PA5 |
| 3 | PA3 | PA6 |
| 4 | PA4 | PA7 |
Change to the required ones in the config file:
[load_cell_probe]
sensor_type: hx711
dout_pin: leveling_mcu:PA4
sclk_pin: leveling_mcu:PA7
Here the load cells are plugged into channel 4, the pins are configured accordingly.
Then add the load cell settings file to printer.cfg:
[include loadcell_probe.cfg]
After that, you need to restart the printer by powering off - the firmware is only flashed in this case.
If the klipper gives errors about obsolete MCU - new firmware has not been flashed, look at the firmware log in /tmp/mcu_update.log.
If the klipper gave errors about configs - look locally: either reinstall the necessary modules via helper-script or delete stock creality sections like prtouch_v2.
If everything starts up and the klipper shows no errors, you can proceed to check the load cells and calibrate them.
to check the functionality of the load cells, run in the console:
$ LOAD_CELL_DIAGNOSTIC LOAD_CELL=load_cell_probe
// Collecting load cell data for 10 seconds...
// Samples Collected: 832
// Measured samples per second: 83.7, configured: 80.0
// Good samples: 832, Saturated samples: 0, Unique values: 464
// Sample range: [0.49% to 0.50%]
// Sample range / sensor capacity: 0.00257%
If the output is anything like this, then the load cells are working
Main docs from the author: https://github.com/garethky/klipper/blob/adc-endstop/docs/Load_Cell.md#calibrating-a-load-cell
In short. Remove the printer head from the work area so that it is out of the way.
Run in console:
$ CALIBRATE_LOAD_CELL LOAD_CELL=load_cell_probe
// Starting load cell calibration.
// 1.) Remove all load and run TARE.
// 2.) Apply a known load, run CALIBRATE GRAMS=nnn.
// Complete calibration with the ACCEPT command.
// Use the ABORT command to quit.
Then:
$ TARE
// Load cell tare value: 0.53% (89146)
// Now apply a known force to the load cell and enter the force value with:
// CALIBRATE GRAMS=nnn
Write the value tare value: 89146
Next you need an item over 1kg and an accurate scale - weigh the item on the scale, memorize and place the item on the printer table. Run in console:
$ CALIBRATE GRAMS=1828
// Calibration value: 0.25% (42719), Counts/gram: 25.39770, Total capacity: +/- 657.07Kg
// ERROR: Tare and Calibration readings are less than 1% different!
// Use more force when calibrating or a higher sensor gain.
!! ERROR: Tare and Calibration readings are less than 1% different!
Due to the peculiarities of the load cells on K1 and the implementation of the algorithm and calibration in the klipper - this error is normal. Write the value Counts/gram: 25.39770
Enter the recorded values into the load cell configuration loadcell_probe.cfg:
reference_tare_counts: 89146
counts_per_gram: 25.39770
Write the following changes to the [stepper_z] section of the printer.cfg file.
Instead of:
endstop_pin: tmc2209_stepper_z:virtual_endstop# PA15
Write:
endstop_pin: probe:z_virtual_endstop
Save and restart klipper.
You can try homing, if all is successful - you can try to build a bed map.
Further fine-tuning of load cells - via graphs https://github.com/garethky/klipper/blob/adc-endstop/docs/Load_Cell.md#viewing-live-load-cell-graphs
At the standard Z-Home speed, the nozzle is pushed into the bed with a force of 1.5kg, which is not conducive to the health of the bed, the coating or the nozzle. Add a parameter to the [stepper_z] section to reduce the homing speed:
homing_speed: 2
Nozzle expansion compensation: https://github.com/garethky/klipper/blob/adc-endstop-k1-debug/docs/Load_Cell_Probe.md#temperature-compensation
Note - the g_code of the load cells contains a limit of nozzle temperature, above which it will refuse to work - to avoid damage to the bed coating. To set the temperature expansion compensation you should temporarily increase the PROBE_TEMP parameter in the loadcell_probe.cfg file:
activate_gcode:
{% set PROBE_TEMP = 150 %}
{% set MAX_TEMP = PROBE_TEMP + 5 %}
{% set ACTUAL_TEMP = printer.extruder.temperature %}
{% set TARGET_TEMP = printer.extruder.target %}
And after adjusting, bring it back up to 140-150 degrees.
ZeyHex added to the firmware reading the temperature from each of the mcu from the built-in sensors - which made it possible to monitor the temperature on the bed, nozzle and main MCUs.
To enable temperature monitoring you need to add sensors to printer.cfg:
[temperature_sensor mcu_temp]
sensor_type: temperature_mcu
sensor_mcu: mcu
min_temp: 0
max_temp: 100
[temperature_sensor nozzle_mcu_temp]
sensor_type: temperature_mcu
sensor_mcu: nozzle_mcu
min_temp: 0
max_temp: 100
[temperature_sensor bed_mcu_temp]
sensor_type: temperature_mcu
sensor_mcu: leveling_mcu
min_temp: 0
max_temp: 100
5.4 Auto Z-Offset calculation with load cells probe and any BLTouch/Microprobe/Cartographer probe (! BETA !)
For this functionality we had to patch Klipper to allow multiple probes to work simultaneously, as well as write a plugin (lc_auto_z_offset.py) for Klipper with GCODE command to determine Z-Offset. To enable this feature you need to use the multiprobe branch from the modified mainline klipper repository.
Required config:
[load_cell_probe lc]
sensor_type: hx711
dout_pin: leveling_mcu:PA4
sclk_pin: leveling_mcu:PA7
z_offset: 0.0
counts_per_gram: 25.39770
reference_tare_counts: 89146
safety_limit: 5000
trigger_force: 160
trigger_count: 1
samples: 2
speed: 2
lift_speed: 5.0
pullback_dist: 0.5
pullback_speed: 0.2
[lc_auto_z_offset]
center_xy_position: 150.0,150.0
secondary_probe: lc
The key point is a named secondary probe, in this case a load cell probe named lc. And this name must be specified in the secondary_probe parameter in the [lc_auto_z_offset] section.
Possibilities:
- to call all commands for a probe by adding a name prefix to the command, for example a probe named
lccan call GCode of the form LCPROBE, LCPROBE_ACCURACY and so on, while the main probe will work with standard commands (PROBE, PROBE_ACCURACY) - use Z-Offset autocalibration via
LC_AUTO_Z_OFFSETcommand - use secondary probe as endstop in
[stepper_z]section by using config likeendstop_pin: lc:z_virtual_endstop, wherelc- name of secondary probe
LC_AUTO_Z_OFFSET command parameters:
NOMOVE - 0/1 (default 0) - do not move when executing the command to the point specified in the plugin's center_xy_position settings - but use the current position
SET - 0/1 (default 0) - set the calculated Z-Offset after executing the command
SAVE - 0/1 (default 0) - save the calculated Z-Offset to the main probe configuration
The other parameters are passed directly to the PROBE command called by the plugin.
Example:
LC_AUTO_Z_OFFSET NOMOVE=1 SAVE=1 SAMPLES=3 PROBE_SPEED=2
In the current position, calculates Z-Offset with probe parameters of 3 samples at speed 2 and stores the calculated value in the main probe config.
Output example:
// LC_AutoZOffset: Probing main probe ...
// probe at 185.000,150.000 is z=0.798340
// probe at 185.000,150.000 is z=0.800684
// probe at 185.000,150.000 is z=0.799316
// LC_AutoZOffset: Probing nozzle probe ...
// probe at 150.000,150.000 is z=-0.019642
// probe at 150.000,150.000 is z=-0.015027
// probe at 150.000,150.000 is z=-0.012001
// LC_AutoZOffset:
// Nozzle: -0.016
// Probe: 0.799
// Diff: 0.815
// Config Manual Adjust: 0.000
// Total Calculated Offset: 0.815
N.B.
- LC_AUTO_Z_OFFSET resets the current Z-Offset to 0.0 on startup
- warm the bed and nozzle to operating temperatures, but no higher than 150 degrees at the nozzle to avoid damaging the bed coating. The command itself does not warm the table or nozzle.
Authors of all modifications, algorithms and improvements:
- ZeyHex
- garethky
Used repos:
- https://github.com/Klipper3d/klipper
- https://github.com/CrealityOfficial/K1_Series_Klipper
- https://github.com/garethky/klipper/tree/adc-endstop
- https://github.com/K1-Klipper/klipper
- https://github.com/K1-Klipper/installer_script_k1_and_max
- https://github.com/hawkeyexp/auto_offset_z
References:
- https://klipper.discourse.group/t/strain-gauge-load-cell-based-endstops/2134
- Klipper3d/klipper#6555
- https://www.loadcells.net/high-temperature-load-cells-connection-methods.html
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