Transcript COST ROBOT Bryan DallAs, Andrew Loveless, Eric Osborne

Reliability and Safety
Analysis
Abstract
Design and build a compact robot to
traverse a maze
 Use the robot to generate an ASCII
representation of the entire maze
 Mark light locations on map as they are
discovered
 Revisit lights intelligently
throughout the maze in
a user-defined order

Reliability Analysis
PIC18F4550 Microcontroller
Model Equation: λP= (C1πT+C2πE)πQπL
Parameter name
Description
Value
Comments
C1
Die complexity failure rate
.14
Based on the MIL-Hdbk-217f [1] for 8
bit microcontrollers
πT
Temperature factor
.98
Assuming a worst case junction
temperature of 85C based on worst
operating temp of microcontroller
C2
Package failure rate
.016676
Based on equation from MIL-Hnbk-217f
page 5-14 [1] for SMT with 44 pins
πE
Environment factor
4
Handbooks value for mobile devices
πQ
Quality factor
10
Assumed from the notes that this is the
value to use, most likely the value is too
large
πL
Learning factor
1
Number used for devices older than 2
years in production
λP
Failure rate per 10^6 hours
2.039032
MTTF
Mean Time To Failure
490428.7917
Approximately 55 years to a failure for
one device
Reliability Analysis
MIC29150 Low Dropout Regulator
Model Equation: λP= (C1πT+C2πE)πQπL
Parameter name
Description
Value
Comments
C1
Die complexity failure rate
.01
Based on the MIL-Hdbk-217f [1] for
devices with 100 or less bipolar
transistors
πT
Temperature factor
58
Assuming a worst case junction
temperature of 125C based on worst
junction temp of the regulator
C2
Package failure rate
.00092
Based on equation from MIL-Hnbk-217f
page 5-14 [1] for SMT with 3 pins
πE
Environment factor
4
Handbooks value for mobile devices
πQ
Quality factor
10
Assumed from the notes that this is the
value to use, most likely the value is
too large
πL
Learning factor
1
Number used for devices older than 2
years in production
λP
Failure rate per 10^6 hours
5.8368
MTTF
Mean Time To Failure
171326.7544
Approximately 19.5 years to a failure
for one device
Reliability Analysis
TI L293 Quadruple Half-H Driver
Model Equation: λP= (C1πT+C2πE)πQπL
Parameter name
Description
Value
Comments
C1
Die complexity failure rate
.01
Based on the MIL-Hdbk-217f [1] for
devices with 100 or less bipolar
transistors
πT
Temperature factor
58
Assuming a worst case junction
temperature of 125C based on worst
estimated junction temp of the H-bridge
C2
Package failure rate
.0056
Based on equation from MIL-Hnbk-217f
page 5-14 [1] for SMT with 16 pins
πE
Environment factor
4
Handbooks value for mobile devices
πQ
Quality factor
10
Assumed from the notes that this is the
value to use, most likely the value is too
large
πL
Learning factor
1
Number used for devices older than 2
years in production
λP
Failure rate per 10^6 hours
6.024
MTTF
Mean Time To Failure
166002.656
Approximately 19 years to a failure for
one device
Reliability Analysis
CTS CB3 HCMOS/TTL Clock Oscillator
Model Equation: λP= λb*πQ*πE
Parameter name
Description
Value
Comments
λb
Base failure rate
.027
πQ
Quality factor
2.1
πE
λP
Environment factor
Failure rate per 10^6 hours
10
MTTF
Mean Time To Failure
1763668.43
Based on the MIL-Hdbk-217f [1] for
devices with 20 MHz frequency
Based on devices with a non MILSPEC
Handbooks value for mobile devices
Based on a quartz oscillator
calculation
Approximately 201 years to a failure
for one device
.567
Criticality Analysis

5 Subsection
 Microcontroller
 Fuel Gauge
 User I/O
 Power
 Motor contoller
Criticality Levels

High Criticality
 Over discharge of the battery
 Over heating of components
 Over charge of battery
 Erratic movement of robot

Low Criticality
 No power
 No input/output
 Does not run
Criticality Analysis – Micro
Controller
Failure Mode: Output stuck at ‘1’
 Possible causes: Overvoltage to the
micro
 Effects: LEDs always off, H-bridge
shorted
 Detection: Observation – Overheated HBridge, no LEDs
 Criticality: High

Criticality Analysis – Fuel Gauge
Failure Mode: Reading battery
discharging too quickly
 Possible causes: Rsense shorted, Cf
shorted
 Effects: Misinformation to user about
battery state
 Detection: Observation – Battery
indicator drops quickly
 Criticality - Low

Criticality Analysis – Fuel Gauge
Criticality Analysis – User I/O
Failure Mode: User input fails
 Possible causes: R13/14/15 open
 Effects: User buttons are floating
 Detection: Observation – Erratic button
presses
 Criticality - Low

Criticality Analysis – User I/O
Criticality Analysis – Power
Failure Mode: 5 V rail > 5V
 Possible causes: Linear regulator failed
 Effects: Damage to 5V components
 Detection: Observation – Regulator too
hot, smoke
 Criticality - High

Criticality Analysis – Motor
Control
Failure Mode: No output to motors
 Possible causes: Digital isolators failed,
H-bridge failed
 Effects: Motors will not run
 Detection: Observation – robot does not
move
 Criticality - Low
