actuator

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ECE5320 MechatronicsAssignment01 Literature
Survey on Sensors and Actuators Topic Stepper
Motors

• Prepared by
• Vikranth Ceakala
• Dept. of Electrical and Computer Engineering
• Utah State University

3/9/2007
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Outline

• Reference list
• To probe further
• Actuator
• Major applications
• Basic working principle
• Stepper motors in reality
• Useful animations
• Phase sequence
• Advantages
• Limitations

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Reference list

• Bishop, Robert H The Mechatronics Handbook, CRC
  Press 2002
• http//www.casde.iitb.ac.in/Mechatronics
• http//hibp.ecse.rpi.edu

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To explore further (survival pointers of web
references etc)

• http//www.howstuffworks.com/

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Major Applications

• Computer Peripherals
• Floppy disc position controller
• Carriage drive for printers
• Paper feed mechanism in printers
• Optical Scanner

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Major Applications(continued.)

• 3-dimensional positioning in plotters.
• Air-fuel mixture adjustment in carburetors of
  automobiles.
• ATM Machines

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Major Applications(continued.)

• Film Drive
• Many other applications where precise positioning
  of parts is required.

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Basic working principle

• Magnetism
• - Physical motion produced by
  magnetic attraction and/or repulsion.
• Like poles attract and opposite poles repel

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Basic working principle

• Stepper motor is a digital motor.
• A pulse signal or a sequence of pulse signals are
  used to turn a stepper motor.
• The smallest unit of movement in a stepper motor
  is called a step.

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Basic working principle

• A stepper motor consists of stator and rotor.
• The stator is a series of electromagnets arranged
  to form a circle.
• A rotor is usually a permanent magnet.
• The rotor can be moved by changing polarities of
  the stator in a sequence.

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Basic working principle

• Full Stepper Motor
• This is achieved by energizing two coils at a
  time.
• Next pair of coils are energized just as the
  rotor aligns with one of the stator poles.
• In this example there are 4 steps.

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Basic working principle

• Half Stepper Motor
• This is achieved by energizing two coils first
  and then only one coil and repeating the sequence.

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Basic working principle

• Half Stepper Motor
• (continued)
• A half stepping motor has double the number of
  steps of a full stepper motor.
• The half stepper differs from a full stepper
  motor, in that, the second phase is turned on
  even before the first phase is turned off.
• Thus we will have overlapping of two different
  phases.
• During the overlapped phase stage also called the
  half step the rotor is in between two full step
  positions.
• For this reason a half stepper motor has twice
  the resolution of a full stepper motor.

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Stepper motors in reality

• Examples in previous slides showed the rotor as
  having only 10 poles. In reality a stepper
  motors rotor has as many as 100 poles.
• A rotor with multiple poles is achieved by
  mounting a single magnet in line with the rotor
  axis and staggering the teeth.

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Stepper motors in reality

• In reality even the stators have many teeth.
• These teeth are arranged such that they have a
  phase difference of 90 degrees between two
  phases.
• A stepper motor might not use a permanent magnet.
• Instead it might use a rotor which is made up of
  iron laminates.
• This is also called a switched reluctance motor.

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Animation showing the working of a half stepper
motor
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Animation showing a full stepper motor
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Phase sequence

• Figure shows the phase sequences for a
  full-step motor and a half step motor for a 4
  phase stepper motor.

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Advantages

• Long life - no wear and tear due to the absence
  of brushes
• Can operate in an open loop configuration.
• Inexpensive compared to other motion control
  systems.
• Good torque at low speeds.

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Limitations

• Excessive vibration when full stepping
• Motors suffers from counter electro motive force
  (emf) when switching between phases.
• This gives rise to current even after the motor
  is switched off. This may damage or affect the
  performance of the motor.

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• Thank You
• Vikranth Ceakala