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diff --git a/docs/Measuring_Resonances.md b/docs/Measuring_Resonances.md new file mode 100644 index 00000000..7d0b3263 --- /dev/null +++ b/docs/Measuring_Resonances.md @@ -0,0 +1,348 @@ +Measuring Resonances +==================== + +Klipper has built-in support for ADXL345 accelerometer, which can be used to +measure resonance frequencies of the printer for different axes, and auto-tune +[input shapers](Resonance_Compensation.md) to compensate for resonances. +Note that using ADXL345 requires some soldering and crimping. ADXL345 can be +connected to a Raspberry Pi directly, or to an SPI interface of an MCU +board (it needs to be reasonably fast). + + +Installation instructions +=========================== + +## Wiring + +You need to connect ADXL345 to your Raspberry Pi via SPI. Note that the I2C +connection, which is suggested by ADXL345 documentation, has too low throughput +and **will not work**. The recommended connection scheme: + +| ADXL345 pin | RPi pin | RPi pin name | +|:--:|:--:|:--:| +| 3V3 (or VCC) | 01 | 3.3v DC power | +| GND | 06 | Ground | +| CS | 24 | GPIO08 (SPI0_CE0_N) | +| SDO | 21 | GPIO09 (SPI0_MISO) | +| SDA | 19 | GPIO10 (SPI0_MOSI) | +| SCL | 23 | GPIO11 (SPI0_SCLK) | + +Fritzing wiring diagrams for some of the ADXL345 boards: + + + + +Double-check your wiring before powering up the Raspberry Pi to prevent +damaging it or the accelerometer. + +## Mounting the accelerometer + +The accelerometer must be attached to the toolhead. One needs to design a proper +mount that fits their own 3D printer. It is better to align the axes of the +accelerometer with the printer's axes (but if it makes it more convenient, +axes can be swapped - i.e. no need to align X axis with X and so forth - it +should be fine even if Z axis of accelerometer is X axis of the printer, etc.). + +An example of mounting ADXL345 on the SmartEffector: + + + +Note that on a bed slinger printer one must design 2 mounts: one for the +toolhead and one for the bed, and run the measurements twice. + +## Software installation + +Note that resonance measurements and shaper auto-calibration require additional +software dependencies not installed by default. You will have to run on your +Raspberry Pi +``` +$ ~/klippy-env/bin/pip install -v numpy +``` +to install `numpy` package. Note that, depending on the performance of the +CPU, it may take *a lot* of time, up to 10-20 minutes. Be patient and wait +for the completion of the installation. On some occasions, if the board has +too little RAM, the installation may fail and you will need to enable swap. + +If installing prerequisites takes too much time or fail for whatever reason, +there is, in principle, another possibility to run a stand-alone script to +automatically tune the input shapers (will be covered later in the guide). + +In order to run stand-alone scripts, one must run the following command to +install the required dependencies (either on Raspberry Pi, or on host, +depending on where the scripts will be executed): +``` +$ sudo apt install python-numpy python-matplotlib +``` + +Afterwards, follow the instructions in the +[RPi Microcontroller document](RPi_microcontroller.md) to setup the +"linux mcu" on the Raspberry Pi. + +Make sure the Linux SPI driver is enabled by running `sudo +raspi-config` and enabling SPI under the "Interfacing options" menu. + +Add the following to the printer.cfg file: +``` +[mcu rpi] +serial: /tmp/klipper_host_mcu + +[adxl345] +cs_pin: rpi:None + +[resonance_tester] +accel_chip: adxl345 +probe_points: + 100,100,20 # an example +``` +It is advised to start with 1 probe point, in the middle of the print bed, +slightly above it. + +Restart Klipper via the `RESTART` command. + +Measuring the resonances +=========================== + +## Checking the setup + +Now you can test a connection. In Octoprint, run `ACCELEROMETER_QUERY`. You +should see the current measurements from the accelerometer, including the +free-fall acceleration, e.g. +``` +Recv: // adxl345 values (x, y, z): 470.719200, 941.438400, 9728.196800 +``` + +Try running `MEASURE_AXES_NOISE` in Octoprint, you should get some baseline +numbers for the noise of accelerometer on the axes (should be somewhere +in the range of ~1-100). Note that this feature will not be available if +`numpy` package was not installed (see +[Software installation](#software-installation) for more details). + +## Measuring the resonances + +Now you can run some real-life tests. In `printer.cfg` add or replace the +following values: +``` +[printer] +max_accel: 7000 +max_accel_to_decel: 7000 +``` +(after you are done with the measurements, revert these values to their old, +or the newly suggested values). Also, if you have enabled input shaper already, +you will need to disable it prior to this test as follows: +``` +SET_INPUT_SHAPER SHAPER_FREQ_X=0 SHAPER_FREQ_Y=0 +``` +as it is not valid to run the resonance testing with the input shaper enabled. + +Run the following command: +``` +TEST_RESONANCES AXIS=X +``` +Note that it will create vibrations on X axis. If that works, run for Y axis +as well: +``` +TEST_RESONANCES AXIS=Y +``` +This will generate 2 CSV files (`/tmp/resonances_x_*.csv` and +`/tmp/resonances_y_*.csv`). + +Note that the commands above require `numpy` to be installed installed. If you +haven't installed it, you can instead pass `OUTPUT=raw_data` argument to the +above commands (2 files `/tmp/raw_data_x_*.csv` and `/tmp/raw_data_y_*.csv` +will be written). One can then run stand-alone scripts on Raspberry Pi +(specify the correct file name on the command line): +``` +$ ~/klipper/scripts/graph_accelerometer.py /tmp/raw_data_x_*.csv -o /tmp/resonances_x.png +$ ~/klipper/scripts/calibrate_shaper.py /tmp/raw_data_x_*.csv -o /tmp/shaper_calibrate_x.png +``` +or copy the data to the host and run the scripts there. See +[Offline processing of the accelerometer data](#offline-processing-of-the-accelerometer-data) +section for more details. + +**Attention!** Be sure to observe the printer for the first time, to make sure +the vibrations do not become too violent (`M112` command can be used to abort +the test in case of emergency; hopefully it will not come to this though). +If the vibrations do get too strong, you can attempt to specify a lower than the +default value for `accel_per_hz` parameter in `[resonance_tester]` section, e.g. +``` +[resonance_tester] +accel_chip: adxl345 +accel_per_hz: 50 # default is 75 +probe_points: ... +``` + +Generated CSV files show power spectral density of the vibrations depending on the +frequency. Usually, the charts generated from these CSV files are relatively easy +to read, with the peaks corresponding to the resonance frequencies: + + + +The chart above shows the resonances for X axis at approx. 50 Hz, 56 Hz, 63 Hz, +80 Hz and 104 Hz and one cross-resonance for Y axis at ~ 56 Hz. From this, one +can derive that a good input shaper config in this case could be `2hump_ei` at +around `shaper_freq_y = 45` (Hz): + +|| +|:--:| +|Input Shaper response to vibrations, lower is better.| + +Note that the smaller resonance at 104 Hz requires less of vibration suppression +(if at all). + +## Input Shaper auto-calibration + +Besides manually choosing the appropriate parameters for the input shaper +feature, it is also possible to run an experimental auto-tuning for the +input shaper. + +In order to attempt to measure the resonance frequencies and automatically +determine the best parameters for `[input_shaper]`, run the following command +via Octoprint terminal: +``` +SHAPER_CALIBRATE +``` + +This will test all frequencies in range 5 Hz - 120 Hz and generate +the csv output (`/tmp/calibration_data_*.csv` by default) for the frequency +response and the suggested input shapers. You will also get the suggested +frequencies for each input shaper, as well as which input shaper is recommended +for your setup, on Octoprint console. For example: + + +``` +Fitted shaper 'zv' frequency = 56.7 Hz (vibrations = 23.2%) +Fitted shaper 'mzv' frequency = 52.9 Hz (vibrations = 10.9%) +Fitted shaper 'ei' frequency = 62.0 Hz (vibrations = 8.9%) +Fitted shaper '2hump_ei' frequency = 59.0 Hz (vibrations = 4.9%) +Fitted shaper '3hump_ei' frequency = 65.0 Hz (vibrations = 3.3%) +Recommended shaper_type_y = 2hump_ei, shaper_freq_y = 59.0 Hz +``` +If you agree with the suggested parameters, you can execute `SAVE_CONFIG` +now to save them and restart the Klipper. + + +If your printer is a bed slinger printer, you will need to repeat the +measurements twice: measure the resonances of X axis with the accelerometer +attached to the toolhead and the resonances of Y axis - to the bed (the usual +bed slinger setup). In this case, you can specify the axis you want to run the +test for (by default the test is performed for both axes): +``` +SHAPER_CALIBRATE AXIS=Y +``` + +You can execute `SAVE_CONFIG` twice - after calibrating each axis. + +However, you can connect two accelerometers simultaneously, though they must be +connected to different boards (say, to an RPi and printer MCU board), or to two +different physical SPI interfaces on the same board (rarely available). +Then they can be configured in the following manner: +``` +[adxl345 adxl345_x] +# Assuming adxl345_x is connected to an RPi +cs_pin: rpi:None + +[adxl345 adxl345_y] +# Assuming adxl345_y is connected to a printer MCU board +cs_pin: ... # Printer board SPI chip select (CS) pin + +[resonance_tester] +accel_chip_x: adxl345_x +accel_chip_y: adxl345_y +probe_points: ... +``` +then one can simply run `SHAPER_CALIBRATE` without specifying an axis to +calibrate the input shaper for both axes in one go. + +After the autocalibration is finished, you will still need to choose the +`max_accel` value that does not create too much smoothing in the printed +parts. Follow [this](Resonance_Compensation.md#selecting-max_accel) part of +the input shaper tuning guide and print the test model. + +## Input Shaper re-calibration + +`SHAPER_CALIBRATE` command can be also used to re-calibrate the input shaper in +the future, especially if some changes to the printer that can affect its +kinematics are made. One can either re-run the full calibration using +`SHAPER_CALIBRATE` command, or restrict the auto-calibration to a single axis by +supplying `AXIS=` parameter, like +``` +SHAPER_CALIBRATE AXIS=X +``` + +**Warning!** It is not advisable to run the shaper autocalibration very +frequently (e.g. before every print, or every day). In order to determine +resonance frequencies, autocalibration creates intensive vibrations on each of +the axes. Generally, 3D printers are not designed to withstand a prolonged +exposure to vibrations near the resonance frequencies. Doing so may increase +wear of the printer components and reduce their lifespan. There is also an +increased risk of some parts unscrewing or becoming loose. Always check that +all parts of the printer (including the ones that may normally not move) are +securely fixed in place after each auto-tuning. + +Also, due to some noise in measurements, it is possible the the tuning results +will be slightly different from one calibration run to another one. Still, it +is not expected that the resulting print quality will be affected too much. +However, it is still advised to double-check the suggested parameters, and +print some test prints before using them to confirm they are good. + +## Offline processing of the accelerometer data + +It is possible to generate the raw accelerometer data and process it offline +(e.g. on a host machine), for example to find resonances. In order to do so, +run the following command via Octoprint terminal: +``` +TEST_RESONANCES AXIS=X OUTPUT=raw_data +``` +(specify the desired test axis and the desired template for the raw +accelerometer output, the data will be written into `/tmp` directory). + +The raw data can also be obtained by running the command `ACCELEROMETER_MEASURE` +command twice during some normal printer activity - first to start the +measurements, and then to stop them and write the output file. Refer to +[G-Codes](G-Codes.md#adxl345-accelerometer-commands) for more details. + +The data can be processed later by the following scripts: +`scripts/graph_accelerometer.py` and `scripts/calibrate_shaper.py`. Both +of them accept one or several raw csv files as the input depending on the +mode. The graph_accelerometer.py script supports several modes of operation: + * plotting raw accelerometer data (use `-r` parameter), only 1 input is + supported; + * plotting a frequency response (no extra parameters required), if multiple + inputs are specified, the average frequency response is computed; + * comparison of the frequency response between several inputs (use `-c` + parameter); you can additionally specify which accelerometer axis to + consider via `-a x`, `-a y` or `-a z` parameter (if none specified, + the sum of vibrations for all axes is used); + * plotting the spectrogram (use `-s` parameter), only 1 input is supported; + you can additionally specify which accelerometer axis to consider via + `-a x`, `-a y` or `-a z` parameter (if none specified, the sum of vibrations + for all axes is used). + +For example, +``` +$ ~/klipper/scripts/graph_accelerometer.py /tmp/raw_data_x_*.csv -o /tmp/resonances_x.png -c -a z +``` +will plot the comparison of several `/tmp/raw_data_x_*.csv` files for Z axis to +`/tmp/resonances_x.png` file. + +The shaper_calibrate.py script accepts 1 or several inputs and can run automatic +tuning of the input shaper and suggest the best parameters that work well for +all provided inputs. It prints the suggested parameters to the console, and can +additionally generate the chart if `-o output.png` parameter is provided, or +the CSV file if `-c output.csv` parameter is specified. + +Providing several inputs to shaper_calibrate.py script can be useful if running +some advanced tuning of the input shapers, for example: + * Running `TEST_RESONANCES AXIS=X OUTPUT=raw_data` (and `Y` axis) for a single + axis twice on a bed slinger printer with the accelerometer attached to the + toolhead the first time, and the accelerometer attached to the bed the + second time in order to detect axes cross-resonances and attempt to cancel + them with input shapers. + * Running `TEST_RESONANCES AXIS=Y OUTPUT=raw_data` twice on a bed slinger with + a glass bed and a magnetic surfaces (which is lighter) to find the input + shaper parameters that work well for any print surface configuration. + * Combining the resonance data from multiple test points. + * Combining the resonance data from 2 axis (e.g. on a bed slinger printer + to configure X-axis input_shaper from both X and Y axes resonances to + cancel vibrations of the *bed* in case the nozzle 'catches' a print when + moving in X axis direction). |