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Unraveling The Mystery of Stepper Motor Technology
Presented By: Prince , Mubeen,
What will you learn after this presentation =>
What Are Stepper Motors
How Do Stepper Motors Work
Applications of Stepper Motors
in robotics.
Motors Need Maintenance Steppers “ Not So Much
Stalled motors burn up
Steppers operate in stall condition
Most brushes go bad
Steppers are brushless
All bearings go bad
Quality Stepper bearings are rated from 90-100K hours
People break them
Hammers donâ„¢t fix Steppers
Problems with Stepper Motors
Very low torque to weight ratio
Torque decreases with increase in the stepping frequency
For sufficiently high stepping speed the stepper motor may skip steps due to overshoot
Types of Stepper Motors
Permanent-Magnet (PM)
PM rotor & electromagnetic coil
Variable Reluctance (VR)
No PM, no residual torque
Hybrid “ NEMA Sizing
Combined PM & VR Technology
Microstepping A Stepper Motor
Full step can be broken into as many as 512 parts
Current is limited through each winding.
Unequal pull on the magnet means it moves toward the weaker winding
Torque falls rapidly as speed increases
Steps are not constant for positioning
Microstepping should only be used for smooth movement.
What is a Robot
Electro-mechanical device.
Performs Various tasks.
May be human controlled or automated.
It finds itâ„¢s uses in all aspects of our life.
How a Robot Can Help
An automatic industrial machine replacing the human in hazardous work environment.
An automatic mobile sweeper machine at a modern home.
An automatic toy car for a child to play with.
A machine removing mines in a war field all by itself and many more¦
Basic Parts of a Robot
Mechanical system
Power supply system
Actuators
Sensory devices for feedback
Sensor Data processing unit
Control system
Mechanical System
The most basic and important part of the robot.
It comprises of chassis, motors, wheels and their placement.
This system decides the locomotion of the robot.
Wheeled Locomotion Systems
Differential drive
Car type drive
Skid steer drive
Synchronous drive
Pivot drive
Differential Drive
This is the most commonly used form of locomotion system used in robots as itâ„¢s the simplest and easiest to implement.
It has free moving wheel(s) in the front accompanied with a left and right wheel. The two wheels are driven by different motors.
Differential Drive: An Analysis
Simplicity and ease of use makes it the most preferred system by beginners
Independent drives makes it difficult for straight line motion. The differences in motors and frictional profile of the two wheels cause them to move with slight turning effect
The above drawback must be countered with appropriate feedback system. Suitable for human controlled remote robots
Car Type Drive
It is characterized by a pair of driving wheels and a separate pair of steering wheels.
The translation and rotation are interlinked, hence this system faces severe path planning problem.
Skid Steer Drive
A close relative of the differential drive system.
It is mostly used in tracked machines e.g. tanks. Also finds application in some four / six wheeled robots
The left and right wheels are driven independently.
Steering is accomplished by actuating each side at a different rate or in a different direction, causing the wheels or tracks to slip, or skid, on the ground.
Synchronous Drive
As the name suggests, it uses synchronous rotation of its wheels to achieve motion & turns
It is made up of a system of motors. One set of which drive the wheels and the other set turns the wheels in a synchronous fashion
The two sets can be directly mechanically coupled as they always move in the same direction with same speed
Pivot Drive
The most unique type of Locomotion system
It is composed of a four wheeled chassis and a platform that can be raised or lowered
The wheels are driven by a motor for translation motion in a straight line
For rotation one motor is needed to lower/raise the platform & another to rotate the chassis around the platform
This system can guarantee perfect straight line motion as well as accurate in “ place turns to a desired heading
Power Systems
Power Supply System
Suitable power source is needed to run the robots.
Robots are most suitably powered by batteries.
The weight and energy capacity of the batteries may become the determinative factor of its performance.
Actuators
They convert the electrical energy into meaningful mechanical work
Mechanical output can be rotational or linear (straight line)
Motors provide rotational motion
Electromagnets provide linear motion
Motors are of various kinds
AC Motors : Not used much in robotics
Stepper Motors : For controlled rotation
DC Motors : Finds extensive general use
Servo Motors : DC motor with in built feedback & error compensation
Stepper Motors
Used for measured rotation.
Can be held at a particular position of the shaft.
Ideal for many autonomous robots requiring higher precision.
DC Motors
As the name suggests, a motor which uses a DC (Direct Current) power
Can run in both directions
Speed Controllable
DC Motor Characteristics
DC Motors are high“speed, low-torque devices.
Using gears, the high speed of the motor is traded off into torque
DC Motor Drivers
These are current amplifying circuits.
A low current control signal is converted into a proportionally higher current signal that can drive the motor
Control Systems
Open Loop Control System
There is no error correction. No way to check if the actuator was able to take the desired action
Simple system to design, not very reliable
Requires regular calibration of the system
Sensors
Analogous to human sensory organs
Eyes, ears, nose, tongue, skin
Sensors help the robot knowing its surroundings better
Improves its actions and decision making ability
Provides feedback control
Examples
Light Dependent Resistor
Thermistor
IR Photo Sensor
Line Follower
A line follower is a robot capable of tracking a line drawn on a surface
Optical sensors capture the line position at the front end of the robot
The robot is steered to keep it always over the line
