1. Design
Mitigating Bearing Failure Through Automation
Lifeloc Technologies Inc. - University of Colorado at Boulder
Trevor Roberts, Jared Foland, Chris Womack, Thomas Andress, Alex Peters, Marco Gardi and Kyle Suleski
● Lifeloc’s passive breathalyzer pump assembly test had a
20% failure rate
● Hypothesis: Failure in pump assembly is caused by faulty Lead
Screw Assemblies (LSA)
● Results in increased rework time, rejected components and loss
of capital
Motor Pump Assembly:
Current Process:
● Press fit uses a hand-operated arbor press to apply force to
manually aligned molds
● Multiple points of failure within the pump assembly
Background
● Achieves order of magnitude
improvement in alignment
● Detects measurable
difference in LSA’s
● Press fit cycle = 35 sec
Full operation = 70 sec
● Potential savings
of $5,000/year
Results
The Lead Screw
Assembly
(LSA)
To the following people
for their help over the
course of this project:
Brandon Wellborn
Dan Underkofler
Daria Kotys-Schwartz
Julie Steinbrenner
Greg Potts
Pat Maguire
Shirley Chessman
and
Thanks
The Process
Fully Automated
Loose Bearing
Friction Test
Press Fit Lead
Screw into Bearing
LSA Friction
Test
Inputs
User Places
Components
User Selects
Mode with GUI
Outputs
LSA Returned to
User
Friction Values
Displayed
Improve Current Press Fit Process
● Create reliable process that assembles the LSA
Develop Friction Test
● Test friction before and after press fit
● Measure the difference between ‘good’ and ‘bad’ LSA’s
● Quantify the change in friction between bearing and LSA
Decrease Assembly Time
● Reduce their original assembly time of 60 seconds per LSA while
adding friction tests
Implement Automation
● Provide testing data on a part-by-part basis rather than by batch
● Improve alignment accuracy and press fit repeatability
Objectives
Bad LSA’s
Free Spinning
Friction Test
Good LSA’s
The PressTestinator
Graphic User Interface (GUI)
● Allows for touch and go operation
● User chooses any combination of:
○ Press Fit, Bearing Friction Test,
LSA Friction Test, Calibration
Press Fit Fixture
● Applies press fit force to the
inner race of bearing
● Spring bob aligns bearing during
press fit and retracts to
accommodate lead screw
● Returns the LSA to the bearing
plate for friction testing
● Replaces manual arbor press
with pneumatic automation
Embedded System
● mbed software controls automation
● Uses custom C++ libraries and
functions
● Runs at 120 MHz
Friction Test Fixture
● Spins up bearing or LSA
to 500 RPM
● Encoder counts revolutions
after electric clutch disengages
● Analyzes spin down to quantify
friction relative to ‘good’ LSA’s
● Indicates how detrimental the
press fit process was
XY Track
● Software accounts for backlash
● Has a movement resolution of 0.000025”
Component Fixture
● Automatically aligns bearing
to lead screw within 0.0009”
● Three linear bearings guide
the press fit motion
● Accommodates press fit
and friction test
The Spring
Bob
Inner
Race Lip
SpringCalibration
Plate
Multiple future uses for the fixture
● Determine allowable change in
friction due to press fit
● Define acceptable baseline friction
for loose bearings
● Specify failure criteria for LSA’s in
the pump assembly test
Improvements
● Integrate linear encoders
● Upgrade friction test bearings
Moving Forward
Electric
Clutch
Encoder
Pressure
Cone and
Flat Head
Stepper
Motor