This is a custom designed Brushless DC motor that is used on a commercial bakery packaging machine to twist-tie plastic bag closures. It uses a flux ring to achieve hall effect type commutation, without the use of a magnet.
Typical DC Brushless motor designs use a separate hall effect magnet and hall effect devices to provide positional feedback to the control. This magnet must be aligned with the main rotor magnet in positioning applications. The control then switches the coils appropriately to provide rotation of the motor.
This unique design incorporates a steel flux ring to provide accurate positioning, which eliminates the need for a separate hall effect magnet. In this case, the hall effect devices are placed in close proximity to the outer diameter of the flux ring, and use the rotor flux commutator. With no hall effect magnet, it eliminates the inherent problems related to accuracy of magnet positioning and magnetization.
Due to the flux path from the rotor magnet to the flux ring, the magnet transition points are always properly aligned to the rotor. Proper alignment ensures no errors in commutation timing due to any inaccuracies in the manufacture of the motor.
Instead of a hall effect magnet, this Brushless DC motor uses an easily fabricated steel ring as a flux sink to capture the rotor magnet flux which in turn provides accurate positional feedback for commutation. This is a highly cost-effective solution with a more compact design, which greatly improves the ability to manufacture the design.