126 lines
6.1 KiB
Markdown
126 lines
6.1 KiB
Markdown
This document describes Klipper's stepper phase adjusted endstop
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system. This functionality can improve the accuracy of traditional
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endstop switches. It is most useful when using a Trinamic stepper
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motor driver that has run-time configuration.
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A typical endstop switch has an accuracy of around 100 microns. (Each
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time an axis is homed the switch may trigger slightly earlier or
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slightly later.) Although this is a relatively small error, it can
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result in unwanted artifacts. In particular, this positional deviation
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may be noticeable when printing the first layer of an object. In
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contrast, typical stepper motors can obtain significantly higher
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precision.
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The stepper phase adjusted endstop mechanism can use the precision of
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the stepper motors to improve the precision of the endstop switches.
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When a stepper motor moves it cycles through a series of phases until
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in completes four "full steps". So, a stepper motor using 16
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micro-steps would have 64 phases and when moving in a positive
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direction it would cycle through phases: 0, 1, 2, ... 61, 62, 63, 0,
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1, 2, etc. Crucially, when the stepper motor is at a particular
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position on a linear rail it should always be at the same stepper
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phase. Thus, when a carriage triggers the endstop switch the stepper
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controlling that carriage should always be at the same stepper motor
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phase. Klipper's endstop phase system combines the stepper phase with
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the endstop trigger to improve the accuracy of the endstop.
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In order to use this functionality it is necessary to be able to
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identify the phase of the stepper motor. If one is using Trinamic
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TMC2130, TMC2208, TMC2224 or TMC2660 drivers in run-time configuration
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mode (ie, not stand-alone mode) then Klipper can query the stepper
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phase from the driver. (It is also possible to use this system on
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traditional stepper drivers if one can reliably reset the stepper
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drivers - see below for details.)
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Calibrating endstop phases
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==========================
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If using Trinamic stepper motor drivers with run-time configuration
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then one can calibrate the endstop phases using the
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ENDSTOP_PHASE_CALIBRATE command. Start by adding the following to the
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config file:
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```
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[endstop_phase]
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```
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Then RESTART the printer and run a `G28` command followed by an
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`ENDSTOP_PHASE_CALIBRATE` command. Then move the toolhead to a new
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location and run `G28` again. Try moving the toolhead to several
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different locations and rerun `G28` from each position. Run at least
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five `G28` commands.
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After performing the above, the `ENDSTOP_PHASE_CALIBRATE` command will
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often report the same (or nearly the same) phase for the stepper. This
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phase can be saved in the config file so that all future G28 commands
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use that phase. (So, in future homing operations, Klipper will obtain
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the same position even if the endstop triggers a little earlier or a
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little later.)
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To save the endstop phase for a particular stepper motor, run
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something like the following:
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```
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ENDSTOP_PHASE_CALIBRATE STEPPER=stepper_z
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```
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Run the above for all the steppers one wishes to save. Typically, one
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would use this on stepper_z for cartesian and corexy printers, and for
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stepper_a, stepper_b, and stepper_c on delta printers. Finally, run
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the following to update the configuration file with the data:
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```
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SAVE_CONFIG
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```
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Additional notes
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----------------
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* This feature is most useful on delta printers and on the Z endstop
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of cartesian/corexy printers. It is possible to use this feature on
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the XY endstops of cartesian printers, but that isn't particularly
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useful as minor differences in XY position rarely impact print
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quality. It is not valid to use this feature on the XY endstops of
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corexy printers (as the XY position is not determined by a single
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stepper on corexy kinematics). It is not valid to use this feature
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on a printer using a "probe:z_virtual_endstop" Z endstop (as the
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stepper phase is only stable if the endstop is at a static location
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on a rail).
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* After calibrating the endstop phase, if the endstop is later moved
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or adjusted then it will be necessary to recalibrate the endstop.
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Remove the calibration data from the config file and rerun the steps
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above.
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* In order to use this system the endstop must be accurate enough to
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identify the stepper position within two "full steps". So, for
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example, if a stepper is using 16 micro-steps with a step distance
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of 0.005mm then the endstop must have an accuracy of at least
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0.160mm. If one gets "Endstop stepper_z incorrect phase" type error
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messages than in may be due to an endstop that is not sufficiently
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accurate. If recalibration does not help then disable endstop phase
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adjustments by removing them from the config file.
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* If one is using a traditional stepper controlled Z axis (as on a
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cartesian or corexy printer) along with traditional bed leveling
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screws then it is also possible to use this system to arrange for
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each print layer to be performed on a "full step" boundary. To
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enable this feature be sure the G-Code slicer is configured with a
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layer height that is a multiple of a "full step", manually enable
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the endstop_align_zero option in the endstop_phase config section
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(see config/example-extras.cfg for further details), and then
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re-level the bed screws.
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* It is possible to use this system with traditional (non-Trinamic)
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stepper motor drivers. However, doing this requires making sure that
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the stepper motor drivers are reset every time the micro-controller
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is reset. (If the two are always reset together then Klipper can
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determine the stepper phase by tracking the total number of steps it
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has commanded the stepper to move.) Currently, the only way to do
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this reliably is if both the micro-controller and stepper motor
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drivers are powered solely from USB and that USB power is provided
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from a host running on a Raspberry Pi. In this situation one can
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specify an mcu config with "restart_method: rpi_usb" - that option
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will arrange for the micro-controller to always be reset via a USB
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power reset, which would arrange for both the micro-controller and
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stepper motor drivers to be reset together. If using this mechanism,
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one would then need to manually configure the "endstop_phase" config
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sections (see config/example-extras.cfg for the details).
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