Thin Wafer Handling Robot

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Thin Wafer Handling Robot
Jordan Hall, Fang Li, Joel Neff, and Alex Podust
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• Background
• Handling of thin silicon wafers for solar cells
• Reducing handling stress and characterizing
  residual stresses are part of manufacturing
  research
• Objective
• Design a robot to move wafers between conveyor
  and inspection station without dropping or
  imposing large gripping forces
• Minimize energy consumption and handling time

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Overall System
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Bernoulli Gripper

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Bernoulli Gripper Model

• Used an mass flow input to create a vertical
  lift force
• Gripper force depends on distance to wafer
• Rubber pads keep wafer from impacting gripper
  frame
• The friction of the pads keeps wafer stuck to
  the gripper as the robot accelerates

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Gripper Modelica Code
Gripper Force Balance
Friction force is only active when the wafer is
contacting the posts
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Gripper - Verification
Wafer separates
Wafer Pick-up
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Gripper Model Challenges

• Required text-based Modelica modeling
• No MultiBody sliding friction model
• Required pneumatic-gtmechanical energy conversion
• Force balance and direction vectors defined from
  scratch.
• Interaction between gripper and wafer was highly
  coupled required in-depth Dymola experience

Fgripper
Ffriction
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Actuator
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Chassis
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Model Limitations

• Inflexibility - Path hard coded as joint angle
  start and end values.
• Multiple simplifying assumptions s.a.
• Motor
• Gripper
• Chassis
• Cost of robot components not considered.
• Hard to determine safety factor for wafer flying
  off gripper.

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Results
Energy usage (J) vs time (s)
Gripper friction and lateral force (N) vs time (s)
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Lessons learned

• Value of using simulation software to solve
  engineering design problems
• Gained appreciation for information economics
• Do not underestimate complexity of modeling
  details of a system
• How to make good decisions under uncertainty