thin wafer handling robot jordan hall, fang li, joel neff, and alex podust
TRANSCRIPT
• 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
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
-1 -0.8 -0.6 -0.4 -0.2 00
0.05
0.1
0.15
0.2
rrel
(m)
For
cegr
ippe
r (N
)
Gripper Force vs. Relative Distance
Gripper Force Balance
Friction force is only active when the wafer is contacting the posts
Gripper – Modelica Code
Gripper - Verification
0.0 2.5 5.00
10
20
30
40
50
60
Mas
s F
low
Rat
e (L
/min
)
Time (sec)
gripper_correct_lift.m_dot_in
0.0 2.5 5.0-0.05
0.00
0.05
0.10
0.15
0.20
[N
]
Time (sec)
gripper_correct_lift.bernoulliForce
Wafer separates
WaferPick-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
Fgripper
Ffriction
Actuator
Electric MechanicalEMFV Torque
DC MOTOR
OutputController(PID)
MotorCommand
+ -
AXIS CONTROLLER
Chassis
Base
Rotating Joint
Lin. joint
Axis 1 θ
Rotating Joint
Rotating Joint
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.