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Copy of Microstepping

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Hafza Daniele

on 10 September 2013

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Transcript of Copy of Microstepping

Micro stepping of Stepper motor for positional accuracy
stepper motor
Brushless DC motor
Rotates in steps.
Multiple toothed electromagnets arranged around a central gear shaped iron piece
Electromagnets are given power to attract the teeth.
Two types: Unipolar and Bipolar
Shaft encoder
gray code
Grey code has got the advantage over the other types of coding as only one bit changes between the adjacent positions as the rotor moves
Functions of PIC18F4520
Controls the motor
Decode the sensor output to determine the position of motor
Error correction if the motor is not in the right position
Stepper motor driver
Two types: Constant current drive, Constant voltage drive
Constant current drive is chosen over the constant voltage drive as it can maintain the torque even at higher speeds.
3.5A Two Phase Hybrid Stepper Motor Driver – HY DIV168N
A3967SLB Easy driver V4.3
Easy implementation with simple code
Less expensive and readily available
thermal shutdown
over voltage look out current protection
How to set up?
Operating voltage 12-36v
On board voltage regulator for 5V
Microstepping upto 8 steps achieved by setting pins MS1 and MS2
The other pins to be configured are STEP, DIR and Enable
1.8 degree stepper motor
7.5 degree stepper motor
Choice of stepper motors
A gear system is connected between motor and the disc.
One pattern on disk should have a minimum angle of 2 degree to accomodate the optical sensors above it.
The small angle rotations made my the motor is mapped to a higher angle rotation by the disc.
Gear system
Project by: Hafza Kareem K V

Supervised by: Dr. Andrew.J.Tickle,
Joseph Grindley

Coventry University
This project is based on the micro stepping of stepper motor for positional accuracy.

In order to get a positional accuracy, optical shaft encoders are designed for various resolutions in two different motors.
An electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code
Two types- Optical and Mechanical
Mechanical shaft encoders succeptible to wear due to the use of brush type contacts.
In an optical shaft encoder, A light source and photo detector array reads the pattern on the optical disk that results from the disc's position at any time
Motor Control
Depending upon the driver used the code for motor control changes.
The motor is made to rotate in full step, half step or micro step mode by setting the desired combination of pins on the driver high or low.
Reading encoder disk
The optical sensors gives the ouptut according to the black and white pattern on the disk.
The sensor values are decoded by the PIC to find out the position of the motor

Full step
Half step
Micro stepping
Different modes of Operation
•Torque ripple is negligible
•Zero vibration and negligible noise
•The stability and value of torque during high speed is greater than the other constant current drives, and hence giving it an upper hand in maintaining positional accuracy.

How to set up?
Operating voltage 12-36V
Switches to set the micro stepping mode and current
Enable works on negative logic
The pulse and direction with +ve and -ve allows to change the pulse and direction of rotation
Error Correction
According to the target position of the motor, the pattern on which the motor should stop can be determined
Once the motor stops, the controller cross checks if the current pattern on disk is same as the required pattern.
If not, the motor is made to take microsteps forward or backward untill it reaches the required position
4 bit grey coded disc
Optical encoder

Repetitive patterns
Different bit grey coded pattern used according to the number of micro steps in one step.
Full transcript