3DPrinting
3DPrinting is a place where makers of all skill levels and walks of life can learn about and discuss 3D printing and development of 3D printed parts and devices.
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Have you looked into Trinamic's fancy stepper drivers that have feedback for step counting and skipped steps and other things? They might be suitable because industrial optical encoders are like $800 and I've never seen one small enough to go on a nema 17 stepper.
Also, what tolerances are you trying to hold here? My ender 3 repeats within a thousandth of an inch. I haven't upgraded the limit switches, but I got a new main board with trinamic drivers.
Given the physical properties of FDM, I don't think chasing tolerances lower than that will actually improve the quality of prints at all, and surely one thou is close enough for what you're trying to do.
As I mentioned, virtual end stops are nowhere near accurate. This is the trinamic system. It is using over current detection as an end stop.
This is a precision verses accuracy type of problem. If you haven't worked through these kinds of issues and ideas before it can be a struggle. Accuracy and precision are very very different things. All of our printers are precision; none of them are accurate.
Optical encoders are simple and cheap devices. You are likely limited to the shiternet's echo chambers when it comes to searching for information. There are a half dozen optical encoders built into most cheap inkjet printers. The system needed to locate each head on a printer is cheap, the tricky part is the software and designing the second head to be adjustable to match Z offset with changes like nozzles.
The main point is not tolerances; it is alignment. Alignment requires accuracy. Printers are cheap and simple because they are only precision machines. This is a fundamental design thing. If you want to build an accurate design, this needs to be engineered into every aspect of the machine from the beginning. This affects every aspect from hardware to software.
No, the trinamic system I'm talking about is end stop phase counting in tandem with physical limit switches. It's pretty accurate, one thou repeatability, like I said.
But like you point out, repeatability of the home position is not so useful if the axes of the two heads aren't aligned in the first place. That's a hardware issue that's not going to be solved with encoders or software.