I’ve been working on a belted z-axis setup on the SolidCore 3D Printer. The stepper motor will turn the belt that moves the lead screw. I’m not an engineer but I think that the belt and pulley ratio gives the steppers more torque and increases resolution. The belt to lead screw arrangement also minimizes and vibrations that might be transferred from the motors to the z-axis. Each lead screw will be constrained by an MGN12 linear rail. With the Duet Wifi we can drive 3 steppers and run an auto bed leveling routine using a proximity sensor or probe.
Many 3d printer users frown upon the idea of multiple steppers for Z-axis motion due to syncing issues. But with the 32 bit Duet board and RepRap Firmware keeping the three lead screws in sync should be fine. When powered up stepper motors tend to jump to the four steps that match the phase current. Some will jump forwards or backward after a number of power cycles.
While a single NEMA 17 motor can use a continuous closed loop belt routing to all three lead screws in sync. This can be avoided by adding code in RepRap Firmware to detect a power down moving the motors to the correct position ready for power-up. The Duet WiFi has two power monitor circuits onboard but it doesn’t matter because the machine will run an auto-leveling at startup.