Laser Beam Steering with Precision Galvanometers

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Laser Beam Steering with Precision Galvanometers
M. N. Missaghi and G. A. WuisanME 433 Advanced
MechatronicsOctober 11, 2005
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Project Objectives

• To control the path of a visible laser beam with
  a fast-acting optomechanical device
• To stabilize a laser beam against random
  fluctuations in laser position (i.e. hand tremor)
• To enable a user to generate useful images with a
  laser beam through gestures
• Underlining
• Arrows
• More complex figures

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System Geometry

• A rigid object can be located with six
  coordinates
• Three for position (x, y, z)
• Three for orientation (a, ß, ?)
• However, the symmetry of the laser beam reduces
  the number of variables

ß
?
a
The roll axis ? and cylindrical axis z are
unimportant
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Block Diagram (Open Loop)
Orientation Sensor
AbsoluteOrientation(x,y,a,ß)
Galvanometer(s)
Controller
Relative BeamOrientation(?,d)
d
?
Scanner
Laser
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GalvanometersTheory of Operation

• Electric current flows through a coil of wire,
  inducing a magnetic field
• This field interacts with a permanent magnet to
  produce a magnetic force on the moving element
• In precision galvanometers, the coil should be
  stationary
• Bandwidth gt 1 kHz is easily attainable, and we
  require gt 100 Hz for beam stabilization

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Orientation MeasurementGyroscope vs.
Accelerometer

• MEMS Gyroscopes are
• Usually single-axis devices
• Relatively expensive (50)
• Quite accurate
• A pair of MEMS two-axis accelerometers can
• Give position and orientation changes
• Have lower total cost than gyros, but
• Angular sensitivity is unknown

Analog Devices iMEMS ADXL203 2-axis accelerometer
(12k/1000)
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Future Plans

• Calculate sensitivity requirements for
  orientation sensor
• Design a multiple-axis galvanometer system to
  steer laser beam
• Test gyros and accelerometers for accuracy and
  response time
• Write control algorithm for galvanometer