Thin Wafer Handling Robot Jordan Hall, Fang Li, Joel Neff, and Alex Podust
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
Overall System
Bernoulli Gripper
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
Gripper Force Balance Friction force is only active when the wafer is contacting the posts Gripper – Modelica Code
Gripper - Verification Wafer separates Wafer Pick-up
Gripper Model Challenges Required text-based Modelica modeling – No MultiBody sliding friction model –Required pneumatic->mechanical energy conversion –Force balance and direction vectors defined “from scratch.” Interaction between gripper and wafer was highly coupled; required in-depth Dymola experience F gripper F friction
Actuator ElectricMechanical EMF V Torque DC MOTOR Output Controller (PID) Motor Command + - AXIS CONTROLLER
Chassis Base Rotating Joint Lin. joint Axis 1 θ Rotating Joint Arm 1 Arm 2 Arm 3 Axis 2 θ Axis 3 mm Axis 4 θ Axis 5 θ Gripper position ROBOT ARM
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.
Results Energy usage (J) vs time (s) Gripper friction and lateral force (N) vs time (s)
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