Presentation on

1st year M-techDEPARTMENT OF CAD-CAM

VNIT NAGPUR

What is Motor?

It may be DC or AC depending upon the type of power supply.

Stepper motor also stepping motor because this motorrotates through a fixed angular step in response to each i/pcurrent pulse received by its controller.

Stepper motor popularity is due to fact that they can becontrolled directly by computer, microprocessors andprogrammable controller.

Stepping are ideally suited for situation where eitherprecise positioning or precise speed control or both arerequired in automation system.

Servomotor also called control motor and have hightorque capability.

The servo motor is paired with some type of encoder toprovide position/speed feedback.

Servo motor

AC Servo motor

DC Servo motor

Brushless Servo motor

Magnets are basically two types:

1. Permanent magnet: It exhibits its

magnetic field for longer period

2. Electromagnet: It is a temporary

magnet, A coil having some

number of turns is wound over

piece of unmagnetized iron.

Passing a D.C current through

this coil is described as exciting

the electromagnet.

A stepper motor is an electromechanicaldevice which converts electrical pulses intodiscrete mechanical movements.

Stepper motor

Variable-reluctance

Permanent magnet

Hybrid

The angle through which the motor shaft rotates for each command pulse is called the step angle.

• smaller the step angle, greater the number of step per revolution and higher the resolution or accuracy of positioning obtained.

• the step angles can be as small as .72 or as large as 90 degree.

•RESOLUTION⁼ No. of steps /Revolution

Rotor

Stator

Coils

2

1

S

N

1

2

Outside Casing

Stator

Rotor

Internal components of a Stepper

Motor

Full Step Operation

Four Steps per revolution i.e. 90 deg. steps

Half Step Operation:

Eight steps per. revolution i.e. 45 deg. steps

Servomotor differ in application capabilities from largeindustrial motor in following respect:-1. They produce high torque at all speeds including zero

speed.2. They are capable of holding a static (i.e. no motion)

position.3. They do not overheat at standstill or lower speed.4. Due to low-inertia, they are able to reverse direction

quickly.5. They are able to accelerate and de-accelerate quickly.

Servo motor

AC Servo motor

DC Servo motor

Brushless Servo motor

Difference withOtherConventionalMotor:Basic construction andoperation principlesof the servo motor arethe same as generalconventionalinduction motors. Butthey have beenredesigned to meethigh precision, highspeed, high frequencypositioning and speedcontrol of mechanicalfacilities

Characteristics Servo Motor (DC Brushed) Stepper (Hybrid)

Cost HIGHER LOWER

Reliability how well the motor is protected. HIGHER because it does not require an encoder which may fail.

Frame Sizes Servo motors are available in a wide variety of frame sizes

Stepper motors do not have as many size selections as servo motors in the large sizes.

Setup Complexity Little complex almost plug-and-play

Motor Life

The brushes on servo motors must be replaced every 2000 hours of operation. Also encoders may need replacing.

The bearing on stepper motors are the only wearing parts. That gives stepper motors a slight edge on life.

Overload SafetyServo motors may malfunction if overloaded mechanically.

Stepper motors are unlikely to be damages by mechanical overload.

Characteristics Servo Motor (DC Brushed Stepper (Hybrid)

Power to Weight/Size ratio excellent power to weight ratio

smaller power to weight/size ratio

Efficiency Servo motors are very efficient. Yielding 80-90% efficiency given light loads

Stepper motors consume a lot of power usually about 70% efficient

Least Heat production

Since the current draw of a servo motor is proportional to the load applied, heat production is very low.

Stepper motors draw excess current regardless of load. The excess power is dissipated as heat.

Resonance and VibrationServo motors do not vibrate or have resonance issues.

Stepper motors vibrate slightly and have some resonance issues

Availability

Servo motors are not as readily available to the masses as are stepper motors.

Stepper motors are far easier to find than quality servo motors.

Application Use

Plotter paper feed

Plotter X-Y-Z positioning

Tape Reader index tape

Printer position matrix print head

Printer paper feed

Printer rotate character wheel

Printer carriage drive

Floppy Disc position magnetic pickup

Printer ribbon wind/rewind

Computer Peripherals:Application Use

Carburetor Adjusting air-fuel mixture adjust

Conveyor main drive

Assembly Lines parts positioning

Mail Handling Systems

feeding and positioning letter

Valve Control fluid gas metering

Process Control:

Machine Tool:

Application Use

Milling Machines X-Y-Z table positioning

Drilling Machines X-Y table positioning

Grinding Machines down feed grinding wheel

Grinding Machines automatic wheel dressing

Electron Beam Welder

X-Y-Z positioning

Laser Cutting X-Y-Z positioning

Lathes X-Y positioning

Sewing X-Y table positioning

Stepper motor Advantages:

Advantage of stepper

motor

StableNeed No feedback

Inexpensive

Standardized frame size

Plug and play

safeLong life

Excellent low speed

torque

Excellent repeatability

Overload safe

Stepper motor disadvantages

Motor get very hot

Low torque to inertia

ratio

No feed back

Prone to resonance

Low efficiency

Stepper Disadvantages

High output power relative to motor size and weight

Motor stays cool, Current draw

proportional to load.

High efficiency

High torque to inertia ratio. It can rapidly accelerate

loads

Encoder determines

accuracy and resolution

Resonance and vibration free operation

DC Servo motor

Advantages

Poor motor cooling. Ventilated motors

are easily contaminated

Motor can be damaged by

sustained overload

Brush wear out limits life to 2,000 hrs. Service is then

required

Complex. Requires encoder

Requires "tuning" to stabilize feedback

loop

Motor "runs away" when something

breaks. Safety circuits are required

DC Servo motor

Disadvantages

a text book of ELECTRICAL TECHNOLOGY Vol.2 by B.L. THERAJA and A.K. THEREJA

a text book of BASIC ELECTRICAL ENGINEERING by S.B. BODKHE and N.M. DESHKAR

Electromechanical Systems & Actuators BY Dr.AdelGastli