All-in-one CNC machine controller (stepper motors)
I've invested the time I have saved from my forum abstinence the last two months to make an new P2 controller board. It's designed to handle everything that needs to be controlled in a small milling machine or lathe, especially
- up to five stepper motors for positioning
- one induction motor to drive the tool or workpiece
- drive relays or solenoids for coolant, tool changer etc.
- handle sensor inputs for home switches, tool length probe etc.
- provide safety features (door lock, emergency stop, limited jog speed...)
The controler consists of a main board holding several plug-in cards with power stages for the stepper motors.
The single-row pin header on the left side is for the power stage for the induction motor (VFD, not shown) which runs directly from mains voltage (230VAC). I plan to use the power stage of this old P1 project which is a simple "sixpack" driver (3 phase bridge) with some additional protection features.
All data is transmitted from a PC via ethernet (100Mbit) so the P2 doesn't need much RAM and no display. Well... almost. I'll connect a small OLED display module so that status and diagnostics can be displayed as plain text and without cryptic LED blinking codes.
The stepper motors are powered from a 48V SMPS. Power to the 48V supply and the VFD is cut off completely for emergency stop and slow jog mode (when safety doors are open) with two relays. The relay contacts are monitored with a special redundant circuit so that any posiible failures of one relay can be detected before the second also fails. All safety related circuits (door switches and emergency stop) are also monitored for faults and cross conduction.
I know, I have already designed many boards for the P2 but haven't managed to really finish a single project. I hope I'll have more luck, this time. But one of my bigger customers already showed interest, so I'm optimistic. Integrating the safety features should result in a competitive price. Chinese drives are damn cheap but you have to add all those safety devices externally which not only costs money but also adds complexity and work to the assembly and wiring.