A stepping motor maximum torque is limited by the flux level that saturates the rotor and stator teeth. But improved stepper motor is available now, reduced saturation effects and produces 50 to 100% more torque than conventional stepper motors for the same power consumption.

 

Both conventional and improved stepper motors develop maximum torque when the rotor teeth are offset by one-quarter tooth pitch of opposite poles in the energized phase. The stepper motor pole pairs develop appreciable torque even at zero current. Torque increases current approaches in face value.

 

At or near the rated current in conventional stepping motors, a larger part of the air-gap flux of the gap to the rotor stator traverses slot instead of teeth, resulting in less torque.

 

The improved stepper motor used to circumvent a relatively new stator design problem. Here samarium-cobalt or neodymium-iron-boron magnets are embedded in slots between the teeth. Concentrated flux lines result between the stepping motor rotor and the stator teeth with less lost flux lines to the slotted air gap. This new slot magnet focus air-gap flux, reduce leakage and ensure that the stepper motor to produce more torque.

 

Torque is placed by a second pair of poles of the same phase 180 ° apart and 90 ° from the first pair produces. The second pair of poles of the conventional stepping motor generates a torque which is opposite to the positive-acting pair. These large negative torque at low currents, but will close the rated current.

 

Improved step motors also have large negative torques at low currents. But positive effect flux from the permanent magnets in the stator to overcome the small negative torque at rated current generated. The resulting torque will help the production of pole pairs of the primary positive torque.

 

The slot in the expanded magnet stepper motors provide peak torques reach twice that of conventional stepper motors. Moreover, these stepper motors manipulate three rated current compared to only twice for conventional stepper motors. Depending on the load inertia, these new stepper motors reach speeds of 5,000 to 10,000 steps / sec Corresponding torque is 200 oz-in. to 3,100 oz-in. in 2 to 4-in.-diameter packages. Hybrid stepper motors usually also high inertia (30 to 40,000 g-cm2), small step angles (0.5 to 15 °) and high accuracy (± 3%).