Automatic Case Feeder
REV C MGNZ shield PCB's (Red boards) can be used to operate an automatic rotary case feeder that will pick cartridges from a hopper and deliver them to the annealing coil at the correct moment in the sequence. The automatic case feeder enables high throughput as the automated case picking is very fast and repeatable.
At the heart of the case feeder is a NEMA17 stepper motor. The NEMA17 motor delivers sufficient torque to pick large calibre cases and move them smoothly and quietly to the delivery tube. Using NEMA17 motors enables us to leverage the vast array of open source motors and hardware made for the 3D printer and CNC markets.
Stepper Motor Selection:
There are basically 2 options ~
1) Standard open loop NEMA17 motor
2) A closed loop NEMA17 motor and controller
The difference between the 2 is that open loop motor control has no position feedback and so the absolute position of the case feeder is unknown. A real world example is that if the motor gets a case jam and causes it to lose 10 steps, it will never recover from this. The control board thinks the 10 steps were successful so from that moment the feeder will be slightly misaligned. The way to rectify this is to power the controller off and re-align the case feed wheel.
A closed loop stepper motor has circuitry that tracks the motor shaft angle as well as the winding current pulses etc. to determine if the motor actually moved after it was commanded to step. This is great for our case feeder application as we can be sure that the cases will always be picked and fed at the correct moment.
Standard NEMA17 motor
Closed loop NEMA17 motor by BigTreeTech
Micro stepping allows for angular position steps that are finer than the physical motor pole count. For example, a 200 step motor has 1.8 degree steps. If microstepping is enabled, this can be reduced by a factor of 2, 4, 8, 16... etc. giving position steps of 0.1 degree or better.
The default MGNZ v3.0.0 software on Github is configured to have microstepping of 16. If you are using a closed loop stepper motor, these typically come pre-configured to also have 16 microsteps. These motors also ship with an OLED display and can be reconfigured by the user. If you are running an open loop motor using an A4988 motor driver or similar, you will need to rebuild the software and change the #define STEPPER_MICROSTEPS value to 1.
Closed loop motor settings:
The MGNZ controller has been tested with the BigTreeTech S42B closed loop stepper motor and the Makerbase MKS SERVO42B. Each motor is available with an OLED display so that you can adjust the motor parameters prior to installing into the case feeder. Recommended settings are:
- 16 microsteps
- en pin logic
- motor current limit - set to ~1200mA
Some software changes may be required depending on the closed loop motor you choose. The Makerbase motor takes 200 control steps per revolution when used on a 200 step motor, however, the BigTreeTech motor requires 256 steps to complete 1 complete revolution on a 200 step motor. To configure this, there is a Macro in the MGNZ software to edit:
#define STEPPER_STEPS_PER_TURN 200*STEPPER_MICROSTEPS
The Case Feeder:
The case feeder mechanism consists of a few 3D printed parts.
CAD files for all the parts are available here: https://www.thingiverse.com/thing:4902058/files
The parts are:
1) Main Body
3) Backing Wheel
4) Feeder Wheel
6) Mounting base