Steered Mirror using HDD Actuators

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Steered Mirror using HDD Actuators

• ME 433 Adv. Mechatronics
• October 11, 2005
• Mark Locascio
• Brian Quist

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Steered Mirror 2002

• Voice coil actuators from loudspeakers
• Mirror rotates around universal joint

http//www.mech.northwestern.edu/courses/433/2002/
Projects/SteeredMirror/index.htm
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Problem Statement

• We will design a device to steer a point of light
  generated by a laser pointer by moving an optical
  assembly with the actuators used in standard
  computer hard disk drives.

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Equipment

• Actuator consists of a coil layer between two
  strong magnet layers
• Applying a current to the coils causes the head
  to sweep across the platters

http//www.pcguide.com/ref/hdd/
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Inside the HDD
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Design Options

• Sensor
• Potentiometers
• Linear
• Rotational
• Accelerometers
• Hall Effect Sensors
• Rotary Encoders
• Optics
• Prisms
• Mirrors

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Proposed Design

• Two actuators, two mirrors
• One mirror rotates around a vertical axis, one
  rotates around a horizontal axis

But the beam from mirror 1 MUST stay
perpendicular to the axis of mirror 2!
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Proposed Design

• Sensors
• Linear Hall Sensors are being used
• Attach a magnet to the actuator
• Hall Sensor remains stationary
• Movement of the actuator/magnet assembly causes
  change in the output voltage of the sensor

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Sample Sensor Data
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Proposed Design

• Control System
• The sensors will provide feedback that allow us
  to control the movement of the head
• Provide the system with desired mirror angles ?1
  and ?2
• Move to desired position with as fast a response
  as possible
• Minimize overshoot and steady-state error
• PID control is a relatively straightforward
  method
• Allows us to specify rise time and overshoot
• Easily tunable