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Stepper Motors ME-191 Computer Applications in Mechanical Engineering II Dr. William Farrow Stepper Motor An output transducer that converts a digital signal to discrete rotational motion. Types of Stepper Motors Permanent Magnet Permanent Magnet Rotor (the part that rotates

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stepper motors

Stepper Motors

ME-191

Computer Applications in Mechanical Engineering II

Dr. William Farrow

stepper motor
Stepper Motor
  • An output transducer that converts a digital signal to discrete rotational motion.

ME-191 Computer Applications in Mechanical Engineering II

types of stepper motors
Types of Stepper Motors
  • Permanent Magnet
      • Permanent Magnet Rotor (the part that rotates
        • Smaller size, Faster possible speeds
        • Lower max torques
  • Variable Reluctance
      • Iron or Steel Rotor
        • Larger size, Slower possible speeds
        • Larger max torques

ME-191 Computer Applications in Mechanical Engineering II

permanent magnet
Permanent Magnet
  • Permanent magnet rotor’s magnetic field is driven around by attraction to and repulsion from electrically switched stator field coils (or poles).

ME-191 Computer Applications in Mechanical Engineering II

variable reluctance
Variable Reluctance
  • Steel rotor seeks position of minimum reluctance under influence of the electrically switched stator field coils (or poles).

ME-191 Computer Applications in Mechanical Engineering II

performance
Performance
  • Torque
    • PM limited to ~500 oz-in
    • VR limited to ~2000 oz-in
  • Speed
    • PM smaller rotor size  higher speeds
    • VR larger rotor size  smaller speeds

ME-191 Computer Applications in Mechanical Engineering II

performance7
Performance
  • Input speed
      • Measured in steps/second
      • Some PM’s can reach 30,000 steps/sec
  • Resolution
      • Measured in steps/revolution
      • Commonly 12, 24,144, 180, 200, and 400
      • Or from 30°/step down to 0.9°/step
      • Half-stepping can further enhance resolution

ME-191 Computer Applications in Mechanical Engineering II

important parameters to maintain open loop control
Important Parameters to Maintain Open Loop Control

ME-191 Computer Applications in Mechanical Engineering II

in addition
In Addition:
  • VR – holding torque is zero when power is off
  • PM – holding torque is generated by PM field and steel stators (detent torque)

ME-191 Computer Applications in Mechanical Engineering II

typical stepper motor characterics
Typical Stepper Motor Characterics

ME-191 Computer Applications in Mechanical Engineering II

lab 3 xy table
Lab 3 XY Table
  • Apply the concept of stepper motors to drive a XY positioning table

ME-191 Computer Applications in Mechanical Engineering II

xy table layout
XY Table Layout

ME-191 Computer Applications in Mechanical Engineering II

stepper motor driver
Stepper Motor Driver
  • Digital logic used to command stepper motor
  • This lab applies the UCN5804 IC to control the stepper motor via digital outputs from the LabJack
  • MOSFET power switching transistors used to amplify power to the stepper motor pole coils

ME-191 Computer Applications in Mechanical Engineering II

stepping signals
Stepping Signals
  • X-Axis step
    • D1 - direction
      • Low (0) or High (>0) opposite directions
    • D0 - move one step
      • High (>0) followed by a Low (0)
      • Note: requires two digital output calls
    • D8 & D9 - limit switches for travel
      • Inputs go high when switch is closed

ME-191 Computer Applications in Mechanical Engineering II

lab operation
Lab Operation
  • Connect hardware and test using LJLogger
  • Write m-file to move X-Axis 100 steps

ME-191 Computer Applications in Mechanical Engineering II

lab operation cont
Lab Operation cont.
  • Locate middle of Axis
      • Move x-axis until limit switch A is set
        • Will require While-loop and edigitalin() to monitor switch A
      • Reverse direction and count # of steps to B
        • Will require While-loop
        • Need to increment value in a variable steps
      • Reverse direction and move ½ the # steps
        • Require a For-loop to go ½ of steps

ME-191 Computer Applications in Mechanical Engineering II