Presentation on 1 st year M-tech DEPARTMENT OF CAD-CAM VNIT NAGPUR
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