Auto Level - Auto Calibration Talk
Posted: Wed Oct 30, 2013 12:18 pm
Here's a thread started to keep track on all the related information about auto calibration/auto leveling your Rostock MAX or other delta 3D printer
Well, the truth is, in any current form (as of 2013/10/30), what you think is "auto-level" probably isn't going to help fix your Delta machine. Most likely leveling is not what you're after. Let's start with some definitions. This list assumes a basic understanding of the fundamental Delta terms, such as delta or printer radius, diagonal rod (length), build surface, etc.
Definitions
- (End-) Effector: The device or component located at point of final intended movement of a machine or mechanism that interacts with the environment, i.e., the print-head or nozzle.
- Delta (Printer) Calibration: The iterative tuning process whereby setting the origin location for each of the principle motion axes, in combination with modifying the PRINTER/DELTA_RADIUS parameter in the printer controller's firmware, flat movement of the end-effector over the build surface is achieved. The most common method for setting each axis' origin is through adjustment of an end-stop or limit switch, or by adjusting a movable machine element that contacts the end-stop or limit switch, often a screw. There are firmwares available that offer software adjustment of the origin position. Changing the PRINTER/DELTA_RADIUS parameter in the firmware affects the conversion of the linear motion of the effector to the non-linear movement of each axis. The effects of an incorrectly calibrated radius are manifested through a convex or concave motion of the effector (when it should be flat). This process is commonly referred to as a 4-point calibration, derived from the four points used to check machine movement. Three points, one at the base of each axis (tower), and a single point in the very center of the build area. When the machine can repeatably move to exactly the same measured height above the build surface at each of those four points, all of which are commanded to the same Z position, the machine should [1] be calibrated. Flat is the key term here. This calibration process is often referred to as "printer leveling," and while arguably a correct use of the word, this phrase seems as though it might be the source of some confusion when referred to in the context of z-probes. As such, I propose that the community standardize on "printer calibration" instead of "printer leveling."
- Z-probe: In a generic sense, it is a limit switch attached to the end-effector of a machine-tool that can be used to automatically index the surface of a part or work area. Specifically related to a Delta style 3D printer, the Z-probe is often a mechanical micro-switch, just like the Rostock MAX's end-stops, or a non-contact Hall-effect sensor that is often sold as an end-stop. It can be permanently fixed to the end-effector, in which case it must be manually or automatically "deployed" before use, or user-removable. The micro-switch can be used to directly touch the surface of the probed body or it can be integrated into a mechanism that uses an additional tool or item to physically touch, as in the case of a Hall-effect probe. Essentially, a Z-probe is nothing more than a minimum limit switch for the Cartesian Z-axis of movement.
- Auto-Calibration, or Auto-Radius: An automatic method of performing a printer calibration through the use of a controller-accessible measurement device, such as a Z-probe. A functioning auto-calibration or auto-radius (as in PRINTER/DELTA_RADIUS) routine would be able to use an installed z-probe or other device to measure the movement of the end-effector and determine the corresponding physical parameters that describe the motion. These parameters include the location of each axis' origin, the PRINTER/DELTA_RADIUS, and possibly others.
- Auto-Level, or Surface-Mapping: A method of determining the contour of a surface, also called constructing a surface map, to be used in automatically compensating the motion of the end-effector of a machine, such that an intended flat motion follows the contour of the possibly non-flat surface. For 3D printers, auto-leveling the print surface will produce near-perfect first layer width, resulting in vastly improved and uniform adhesion.
THERE IS NO KNOWN-WORKING AUTO-CALIBRATION ROUTINE AVAILABLE IN ANY FIRMWARE.
Read that last sentence again. That was likely the beef you were looking for, as most people (including myself, several months ago) hear the term "auto-level" and rightfully rejoice. There are only a select few that have been able to, or are capable of, constructing a machine and within only a few calibration iterations can have the perfectly flat motion over the entire build surface that we all so desire. Actually, forget even those edge-cases. Just try to move your machine from one room, even one table, to the next. My bet is that you will have calibration issues. How nice it would be to hit a button and have the machine re-tune itself.
There are currently at least two in-development firmwares that are attempting to implement auto-calibration, for which I have not seen any reports of success. One is the 0.90 development version of Repetier-Firmware and the other that I know of is a custom Marlin version by ScribbleJ. There are likely others of which I am not aware.
User 626Pilot has provided well-documented experimentation with the Repetier 0.90 development branch's auto-calibration in this post: http://forum.seemecnc.com/viewtopic.php ... =20#p21833 Still, there are mixed results.
THERE IS AN IMPLEMENTED, AND WORKING [2], AUTO-LEVEL ROUTINE AVAILABLE IN A SPECIFIC BRANCH OF THE MARLIN FIRMWARE.
Auto-Level is currently implemented via the G29 command in Johann Rocholl's deltabot branch of the Marlin firmware (go here: https://github.com/jcrocholl/Marlin and choose the deltabot branch). Johann called his routine (correctly) auto-leveling, and while I have not read it myself, I have seen others state that he mentioned it should correct for doming (concave or convex effector motion due to an improperly calibrated DELTA_RADIUS), and this likely became the initial source of confusion regarding the automatic capabilities afforded by a Z-probe.
Here is why: It is crucial that the parameters in the firmware governing the calculated motion of the printer match exactly the physical characteristics of the machine. If not, where the printer controller "thinks" the end-effector is located when it is commanded to a point WILL NOT match the actual, physical location. This description exactly defines a calibrated printer. There is no way to get flat, linear, movement otherwise. So while it may seem that a simple adjustment of the Z-motion, via automatically-probed points, could correct doming problems, if the printer can't move in exactly a straight line between two points, then how will any algorithm know how much Z adjustment to make?
Using G29 auto-level, Marlin deltabot edition
When using the auto-level G29 code it must be run before every print job. It does not store the surface map anywhere but in RAM, i.e., no persistent storage in EEPROM. Also, while I can't specifically identify the behavior in the code, I recall the map being reset or over-ridden if I executed a G28 after running G29. I'll need to confirm, but until then, I'd recommend not homing after leveling.
The recommended usage is to insert it into your slicer's start-code, such as this:
Code: Select all
G28 ; home all axes
G1 Z15 F6000 ; prepare for auto-level
G29; call the auto-level probing routine
G1 Z12 F6000 ; lift nozzle
G1 X0 Y0 F6000 ; re-center the machine
G-code confusion
There is a list of dozens of supposedly standardized G-codes for RepRap controllers that can be found here: http://reprap.org/wiki/G-code. As with several other commands, and as the auto-* routines for Deltas are quite new, these have not been added to the list. As such, the G29 routine found in the Marlin deltabot firmware executes a different set of operations than the G29 routine in the Repetier firmware. The specifics of which code to be called for each firmware will need to be investigated by the user, so it would be best to assume that G-code generated with auto-* codes, generated for one firmware, is NOT portable to another firmware.
What all of this means for you and your non-working printer.
If you can't print over (nearly) the entire build surface, YOUR PRINTER NEEDS TO BE CALIBRATED, AND NO MAGICAL Z-PROBE IS GOING TO HELP YOU (FOR NOW).
Anyway, you are almost certainly looking for AUTO-CALIBRATION, so STOP SAYING YOU WANT AUTO-LEVEL!
Maybe that's not what you were wanting to hear, but that's really the answer. Sorry. I went through all of this Z-probe learning process so that you don't have to. I made the mistake of thinking everything would be magically corrected for me. In the end, I had to track down some tiny errors in my tower positions to fully calibrate my machine. Now I don't need the probe, but I use it to auto-level because it is present.
There are certainly firmware developers working on this problem as without it the Delta platform is going to struggle. Whether it is just to ease the setup for new or inexperienced users or to quickly aid in re-calibration after transporting a machine, everyone has a reason why they want some auto-magic in their Delta firmware. If you are a capable coder or knowledgeable firmware tester, I suggest that you fabricate yourself a Z-probe and test the available offerings that currently attempt to use the new device. Provide feedback to the developers of the firmwares you are testing and discuss your results here or elsewhere.
Due to the very experimental nature of the Z-probe's capabilities in any firmware, you are not likely to find much help using one. If you have the time and desire to experiment, your feedback and results will greatly help the community.
[1] There are some conditions where the 4-point calibration will "test positive" yet still yield domed motion in certain locations of the build area. If this is happening on your machine, it likely indicates a larger issue with your geometry. Check tower squareness, tower equi-distance, parallelism of the arms, etc. Ask nicely in the forums and you will find help.
[2] The "working" nature of the Marlin auto-level routine has not been universally observed. The reason for resulting "bad" motion on a well calibrated machine is not yet known.
(Last edited 2013/12/09 12:53 EST: Corrected some typos and added link to 626Pilot's Repetier experimentation results.)
Unfortunately, that method still requires quite a bit of patience, as I'm sure you can attest.