Interfacing Stepper motor to 8051 microcontroller

A A stepper motorstepper motor is a special type of electric motor that is a special type of electric motor that moves in increments, or steps, rather than turning smoothly as a moves in increments, or steps, rather than turning smoothly as a conventional motor does.conventional motor does.

Typical increments are 0.9 or 1.8 degrees, with 400 or Typical increments are 0.9 or 1.8 degrees, with 400 or 200 increments thus representing a full circle. 200 increments thus representing a full circle.

The speed of the motor is determined by the time delay The speed of the motor is determined by the time delay between each incremental movement.between each incremental movement.

Stepper motor usesStepper motor uses Permanent Magnet (PM) and Variable Reluctance (VR)Permanent Magnet (PM) and Variable Reluctance (VR)

Motor Moves Each Time a Pulse is Motor Moves Each Time a Pulse is ReceivedReceived

Can Control Movement (Direction and Can Control Movement (Direction and Amount) EasilyAmount) Easily

Can Force Motor to Hold Position Against Can Force Motor to Hold Position Against an Opposing Forcean Opposing Force

ConstructionConstructionPermanent Magnet RotorPermanent Magnet Rotor– Also Called the Also Called the ShaftShaft

StatorStator– Surrounds the ShaftSurrounds the Shaft– Usually Four Stator Windings Paired with Usually Four Stator Windings Paired with

Center-Tapped CommonCenter-Tapped CommonKnown as Four-Phase or Unipolar Stepper MotorKnown as Four-Phase or Unipolar Stepper Motor

Stepper motorsStepper motors can be used in various areas of your can be used in various areas of your microcontroller projects such as making microcontroller projects such as making robots, robotic arm, robots, robotic arm, automatic door lock systemautomatic door lock systemTypes of Stepper motor:Types of Stepper motor:1 . Unipolar stepper motor 1 . Unipolar stepper motor – 6 wires= 4 coils and 2 common– 6 wires= 4 coils and 2 common2 . 2 . Bipolar stepper motor – 4 wires= 4 coils and no common Bipolar stepper motor – 4 wires= 4 coils and no common terminals. terminals.

Working of Stepper Motor Working of Stepper Motor

When only 1 coil is energizedWhen only 1 coil is energized When 2 coil is energizedWhen 2 coil is energized

Half SteppingHalf SteppingFull SteppingFull Stepping

Stepper motors can be driven in two different patterns or sequences. namely, Stepper motors can be driven in two different patterns or sequences. namely,

1. Full Step Sequence1. Full Step Sequence

2. Half Step Sequence2. Half Step Sequence

we will go through these sequences one by one.we will go through these sequences one by one.

8051_Mazidi\stepper motor\8051_Mazidi\stepper motor\fig\3_full-step.giffig\3_full-step.gif

8051_Mazidi\stepper motor\8051_Mazidi\stepper motor\fig\4_half-step.giffig\4_half-step.gif

Steps/RevolutionSteps/Revolution = 360° = 360° Step AngleStep AngleIn 1 full step sequence, motor rotates by 1 tooth pitch.In 1 full step sequence, motor rotates by 1 tooth pitch.So, So, Number of Rotor teethNumber of Rotor teeth = Steps/ Revolution = Steps/ Revolution 44

Construction (con’t)Construction (con’t)

Center Tapped CommonCenter Tapped Common

Moving the RotorMoving the Rotor

Unstable Stable

Rotor will ALWAYS seek a stable position.

Single-Coil ExcitationSingle-Coil Excitation - Each successive coil is energised in turn. - Each successive coil is energised in turn.

Two-Coil Excitation - Each successive pair of adjacent coils is Two-Coil Excitation - Each successive pair of adjacent coils is energised in turn. energised in turn.

Interleaving the two sequences will cause the motor to half-step 8 step sequence = normal 4 step + wave drive 4 step.

Two-Coil Excitation

                                                          

Single-Coil Excitation

Interleaved Single- and Two-Coil Excitation

                                                          

Half-Stepping

How Far Does It Move?How Far Does It Move?

Step AngleStep Angle– Arc Through Which Motor Turns With ONE Arc Through Which Motor Turns With ONE

Step Change of the WindingsStep Change of the Windings– Varies With Model of Stepper MotorVaries With Model of Stepper Motor(Depending on the number of teeth on stator (Depending on the number of teeth on stator

and rotor)and rotor)– Normally in DegreesNormally in Degrees– Step angle = 360/No. of Steps per RevolutionStep angle = 360/No. of Steps per Revolution– Commonly available no. of steps per Commonly available no. of steps per

revolution are 500, revolution are 500, 200200, 180, 144, 72, 48, 24, 180, 144, 72, 48, 24

How Fast?How Fast?Revolutions per Minute (RPM)Revolutions per Minute (RPM)

volutionperSteps

SecondperStepsrpm

Re

60

The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet 2.

The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6° (1.8’)(1.8’)

in this example.

The bottom Electromagnet (3) is energized; another 3.6° (1.8’)(1.8’)

rotation occurs.

The left electromagnet (4) is enabled, rotating again by 3.6° (1.8’)(1.8’). When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25(50)(50) teeth, it will take 100(200)(200) steps to make a full rotation in this example.

Common Stepper Motor TypesCommon Stepper Motor Types

DriversDrivers

May Need a Driver CircuitMay Need a Driver Circuit– Same Problem as Relays – May Draw Too Same Problem as Relays – May Draw Too

Much CurrentMuch Current

TypesTypes– Transistor DriversTransistor Drivers

Usually a Darlington PairUsually a Darlington Pair

– Darlington ArraysDarlington Arrays– CanCan Build It Yourself Build It Yourself

Using Using Transistors Transistors for Stepper for Stepper

Motor Motor DriverDriver

ApplicationsApplications::Used inUsed in In instrumentation such as watches, clocks, etc.In instrumentation such as watches, clocks, etc.Computer peripherals such as card readers, teleprinters, teletypes, Computer peripherals such as card readers, teleprinters, teletypes, dot matrix printers, etc.dot matrix printers, etc.RoboticsRobotics