Xubair Khan

Agenda:

• Introduction to Stepper Motors• Types of Stepper Motors• Main components of a stepper motor• How do these components work together• Control sequence to turn a stepper motor• Advantages and disadvantages of stepper motors• Practical Applications of stepper motor• Step Angle• Summary

Introduction to Stepper Motors:• A stepper motor is a brushless, synchronous electric motor that converts digital pulses

into mechanical movement.

• The stepper motor rotates a specific incremental distance per each step. The number of steps that are executed controls the degree of rotation of the motor’s shaft. This characteristic makes step motors excellent for positioning applications.

• For example, a 1.8° stepper motor executing 100 steps will rotate exactly 180° with some small amount of non-cumulative error. The speed of step execution controls the rate of motor rotation. A 1.8° step motor executing steps at a speed of 200 steps per second will rotate at exactly 1 revolution per second.

Types of Stepper Motors:

Permanent Magnet

Variable Reluctance

Hybrid

Non-magnetic, geared rotor

Magnetic rotor

Combines characteristics from PM and VRmagnetic, geared rotor

Permanent magnet motor:The permanent magnet (PM) or tin can (fig. 2) motor is perhaps the most widely used stepping motor in non-industrial applications. In it's simplest form the motor consists of a radially magnetized permanent magnet rotor and a stator similar to the V.R. motor. Due to the manufacturing techniques used in constructing the stator they are also sometimes known as 'claw pole' motors

The variable reluctance motor:The variable reluctance or V.R. (fig 1) motor consist of a rotor and stator each with a different number of teeth. As the rotor does not have a permanent magnet it spins freely i.e. it has no detent torque. Although the torque to inertia ratio is good, the rated torque for a given frame size is restricted. Therefore small frame sizes are generally used and then very seldom for industrial applications.

Energized A & A’ Energized C & C’

Advantages and disadvantages of stepper motors:

Advantages

• Low cost for control achieved• Simplicity of construction• Can operate in an open loop control system• Low maintenance (no brushes)• Less likely to stall or slip• Will work in any environment

Disadvantages

• Require a dedicated control circuit• Use more current than D.C. motors• High torque output achieved at low speeds

Stepper Motor Construction:

YouTube Video link : www.youtube.com/watch?v=MHdz3c6KLrg

How to Stepper motor works?

YouTube Video link : www.youtube.com/watch?v=t-3VnLadIbc

Two Main Configuration of Stepper Motors :

Two Phase Bipolar Stepper Motor:

• Leads on each coil can be brought out in two ways• Each lead taken separately• Bi-directional current flow through entire winding

Applying a voltage to lead A’ and grounding lead A generates current flow resulting in the stator polarities shown above.

Applying a voltage to lead A and grounding lead A’ generates current flow resulting in the stator polarities shown above.

Applying a voltage to lead B and grounding lead B’ generates current flow resulting in the stator polarities shown above.

Applying a voltage to lead B’ and grounding lead B generates current flow resulting in the stator polarities shown above.

Four Phase Unipolar stepper Motor:

• A center tap added between the two leads• Center Tap connected to Ground or Voltage source• Unidirectional current flow in each ½ of winding

Driving one of the leads on winding A to ground allows current to flow in one half of the winding generating a

polarity on the stator poles and the rotor rotatesaccordingly.

Driving one of the leads on winding B to ground allows current to flow in one half of the winding generating a

polarity on the stator poles and the rotor rotatesaccordingly.

Driving one of the leads on winding A to ground allows current to flow in one half of the winding generating a

polarity on the stator poles and the rotor rotatesaccordingly.

Next, the grounding source is removed from the winding A lead and one of winding B’s leads is driven to ground. Again, current flows in half the winding and the appropriate stator poles are energized. This continues to rotate the motor 360

degrees.

Let’s compare both winding configurations.

Unipolar and Bipolar Motors

• Bipolar uses entire winding −Unipolar uses half the winding at one time

• Unipolar motor coil wire is thinner − More wire needed = increased resistance

• Bipolar requires more complex circuitry − Increased cost − More real estate

Application :

• Paper Feeder On Printers• CNC Machine• Stepping Motor to move read-write head in computer CD drive• Labeling Machine• Moving Positioning System• Medical Equipment• Automotive and scientific equipment etc.• Packing Machine• Robotic Arm • Fiber Optic Splicing Machine

Stepper motor move clockwise:

Stepper motor move counter clockwise:

Step Angle:How much movement is associate with a single step ? This depends on the internal construction of the motor in particular the number of teeth on the stator and the rotor. The step angles for various motor have different step angles table shown

Notice the term steps per revolution this is the Total number of steps needed to rotate one complete rotation or 360 degrees (e.g.,180 steps x 2 degrees = 360)

Stepper Motors Interface With microcontroller :

How Can I Determine Stepper Motor Wiring Without the Stepper Motor Pin out?

1. Each of the two phases should have the same resistance when measured with a multimeter. When measuring the resistance across one wire from each of the two phases, the resistance should be infinite because the circuit is open. Locate the two pairs of wires that represent the two phases; both pairs of wires will have similar internal resistance.

2. Connect each phase to the amplifier and ignore the polarity (+ / -), for now. You have a 50 percent chance of guessing right.

3. Send a command to move the motor. If the motor rotates in the wrong direction, then switch either phase A and A- or B and B- (effectively reversing directions).

Determine Stepper Motor Wiring using color code chart:

Thank You!!

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