Hybrid Stepper Motor - Construction & Working


     The word hybrid means combination or mixture. The hybrid stepper motor is a combination of the both of the variable reluctance stepper motor and permanent magnet stepper motor i.e., it had both features of permanent magnet and variable reluctance stepper motor, hence smooth control of motion can be achieved.



Construction :


     The hybrid stepper motor uses the principles of the permanent magnet and variable reluctance stepper motor.


     Hybrid motors are available with step resolutions of 0.9°, 1.8° or 3.6°, the standard being 1.8°. They exhibit high static and dynamic torque and run characteristics at very high step rates, therefore, hybrid motors are the preferred type for industrial applications.

Hybrid Stepper Motor - Construction & Working


     Both the rotor and the stator assembles of hybrid motors have tooth like projections. These 'teeth' align in various configurations during rotation.

     The stator construction is same as that of variable reluctance or permanent magnet stepper motor. The rotor consists of two identical stacks of soft iron attached to the north and south poles of an axially magnetised round permanent magnet. The rotor teeth are machined on the soft iron poles mounted on the shaft. Thus, the rotor teeth on one end become north pole and the other end become south pole. The rotor teeth at both north and south poles are displaced by some angle for proper alignment of the rotor pole with that of the stator.



Operation :


     Torque is created in the hybrid motor by the interaction of the magnetic field setup by the rotor permanent magnets and the magnetic field setup by the stator phases. To understand the rotor's interaction with the stator, examine the construction of 8 stator poles hybrid step motor. Each pole has 2 to 6 teeth. The rotor is made up composed tooths cups of permanent magnet.

Stepper Motor

     The stator has a two phase construction ( Phase-A and Phase-B ). The winding coils are placed at 90° from each another with one phase. Poles 1, 3, 5 and 7 form phase A and poles 2, 4, 6 and 8 form phase B. Each phase is wound so that the poles 180° apart are the same polarity, while the poles 90° apart are of the opposite polarity. When the current in a phase is reversed, the axis of the poles also be changed from north pole to south pole or vice-versa.


     When phase A is energized, the windings at pole 1 and 5 are north poles and the windings at pole 3 and 7 are south poles. The windings at 1 and 5 would attract the teeth of the magnetically south end of the rotor, and windings at 3 and 7 would attract the teeth of the magnetically north end of the rotor. The desired direction of travel determines the next set of poles to be energised.



Advantages :


1. Very small step angles upto 1.8°.

2. Higher torque per unit volume.

3. Presents of detent torque.



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