STEPPER MOTOR

CHAPTER 7

Stepper Motor

Stepper motor is a brushless, synchronous electric motor and an electromagnetic device that uses magnetic field to move the rotor with the aid of digital pulses that drives power solid state devices ON and OFF

Three types of stepper motor:

-Permanent magnet

-Hybrid

-Variable reluctance

Variable reluctance Permanent magnet Hybrid

1) Soft iron multipole rotor and a laminated core in the wound stator2) Has four "stator pole sets" (A, B, C,) set 15 degrees apart3) Rarely use in industry because of less detent torque.

1) Rotor has no teeth and and a laminated core in the wound stator2) Has four phase and 90 degrees apart.3) Ideal choice for non industrial application such as a line printer print wheel positioner and operate at fairly low speed.

1) Standard Hybrid motor has 200 rotor teeth and bifilar stator windings.2) Standard Hybrid motor move at 1.8 step angles.Other Hybrid motor available in 0.9ºand 3.6º step angle configurations.3) Wide variety used for industrial applications because of high static and dynamic torque and run at very high step rates.

Types of stepper motor

Stepper Motor

-Stepper motor “step modes” include full step,half step and microstep.

Full Step

ONE-ON full step operation

Full Step

Two-ON full step operation

Half Step(also known as one ON,two ON operation)

Four operational mode of stepper motor Rest mode – the stator windings are de-energized

and the motor is not running, resisting movement until a load-originating torque exceeds the detent torque.

Stall mode – the stator windings are energized and the rotor is not running resisting movement until a load-originating torque exceeds the holding torque.

Bidirectional mode – the rotor turns continually then stops. It can continue in the same direction or the reverse direction

Unidirectional mode – the rotor is accelerated (ramped up) beyond the bidirectional rate and cannot be reversed instantaneously. In some of the literature this mode is called the slew mode

Stepper motor resolution

The resolution of stepper motor depends on the type and energize method of the stepper motor. Res = 360 βWhere : Res = resolution of the stepper motor (step/rev) β = step angle 360 = conversion factor ( 360°/rev)Example: Determined the resolution of a four-phase hybrid stepper motor with a 1.8° step angle if the stepper motor operated:a) full stepB)half stepAnswer:(a) β = 1.8° for full step rotation Res = 360/1.8 = 200 steps/rev(b) Half step, β = 0.9°. Res = 360/0.9 = 400 steps/rev.

Stepper Motors Sequence

Full step sequence showing how binary numbers can control

the motor

Half step sequence of binary control numbers