2. What is Ergonomics
A Primer
R.W. Marklin, Ph.D, CPE
Certified Professional Ergonomist
Dept. of Mechanical Engineering
Marquette University
3. Etymology of Ergonomics
Ergo: work from Greek
Nomos: laws, customs
Ergonomics is etymologically laws or
customs of work
But we need a less abstruse definition in
order to understand ergonomics in the
contemporary world
4. Definition of Ergonomics
Ergonomics is the science of evaluating
and designing products and work
environments around the strengths and
limitations of the human user in order to:
Maximize occupational health
Maximize ease of use
Maintain productivity of user
5. PsychoSocial
Work Organization
Worker Satisfaction
Mgmt-Worker Rel.
Compensation.
Cognitive Factors
Mental workload
Physical Factors
Tools and Equipment
Methods of Task
Measure external
and internal forces (EMG)
Human
Operator
Industrial Hygiene
Noise
Heat/Cold
Chemicals R.W. Marklin is a
Physical Ergonomist
Three Spheres of Ergonomics
7. Cab Design
Seat Travel- Forward and Rear
Seat to Bulkhead Distance
Steering Wheel Height
Cab Ceiling Height
Pedal Location
Height between Cab Floor and IP
7
8. Insufficient Rear Travel
Site Visit vehicle
95th
percentile male
modeling by
Siemens Jack
Worker’s legs
rotated outward
Safety hazard and
postural discomfort
8
9. Insufficient Forward Seat Travelavel
Site Visit vehicle
5th
percentile female
modeling by
Siemens Jack
Worker does have
full support from seat
back
9
10. Calculating Seat Travel
Accelerator to Seat
Ref Point (SRP)
SAE J4004 method
for calculating
forward and rear
seat travel
EPRI 2010 utility
workers’ male
anthropometry
Gen. pop female
anthropometry 10
15. Recommendation
At least 42 in. height
from Seat Ref. Point
to cab ceiling
Ht from cab floor to
SRP can vary –
reason to use SRP
Based on 99th
percentile male utility
workers
15
16. Pedal Location
Insufficient distance
between brake and
accelerator
Toe stuck under
pedal
Boot overlaps both
pedals
Workers have larger
feet than gen. pop
Some workers drive
vehicles without
boots
16
This cab has sufficient distance
between brake and accelerator but
not between accelerator and hump.
17. Recommendation
EPRI 2010
anthropometry study:
99th
percentile shoe
size was 14D
2 in. clearance
added to ½ of boot
width
Center of accelerator
used to
accommodate big
boots (overlap with 17
23. Epidemiology & Keyboards
Tittirandonda, Burastero, and Rempel
(1999) summary
Consistent relationship between
computer-related risk factors and MSDs,
specifically sustained awkward postures
of wrist
This presentation will address how
alternative keyboard designs can reduce
awkward postures risk factor
24. How Do MSDs’ Risk Factors Relate
to Conventional Computer
Keyboards?
Posture
Extended wrist
Ulnarly deviated wrist
Repetition
3 key strokes per second
Up to 50,000 to 100 000 key strokes
per day
Force
Minimal forces but exerted many times
27. Biomechanical Consequences
of a Deviated Wrist Position
Friction of tendons across the carpal tunnel
Requires more muscular effort due to friction and
contact forces
May lead to tenosynovitis (friction causes irritation
of tendons, leading to inflammation, pain and
swelling)
May lead to carpal tunnel
syndrome (swelling in the
carpal tunnel leads to
increased carpal
tunnel pressure)
28. Carpal Tunnel Pressure
Pressure against median nerve in carpal
tunnel could cause carpal tunnel
syndrome
Pressure against tendons and their
sheaths could cause tenosynovitis
38. Summary of Split Keyboards
Split keyboards with opening angle of
20˚ to 25˚reduced ulnar deviation by
>10˚
Within 2˚ of neutral for right
Within 5˚ of neutral for left
Reduced wrist factor of ulnar deviation
No decrease in typing speed or accuracy
47. Removing and Replacing Manhole Covers:
Current Work Practice
Manholes provide access to
underground vaults and utility corridors
Square: up to 3 ft x 4 ft
Round: up to 4 ft in diameter
123 to 209 lbs
48. Removing and Replacing Manhole Covers:
Current Work Practice
Hook and chain
Steel lifting hook
49. Removing and Replacing Manhole Covers:
Current Work Practice
1st
class lever with a magnet
50. Removing and Replacing Manhole Covers:
Current Work Practice
1st
class lever with a magnet
52. Removing and Replacing Manhole Covers:
Problems
High forces on shoulder and trunk
muscles – particularly using the hook
and chain and steel lifting hook
53. Removing and Replacing Manhole Covers:
Recommended Ergonomic Recommendations
1st
class lever with magnet
2nd
class lever
54. Removing and Replacing Manhole Covers:
Benefits of 1st
class lever with magnet
Based on field study with 32.5 inch 175 lbs
cover
Peak force with handle attached to 175 lbs
cover: 177 lbf
Peak force with 1st
class lever: 68 lbf
55.
56. Removing and Replacing Manhole Covers:
Benefits of 1st
class lever with magnet
University of Michigan 3D SPPP based
on field study with 32.5 in. 175 lb cover:
Spinal compression with hook and chain:
over 2800 lbf
Spinal compression with 1st
class lever and
magnet: < 433 lbf
NIOSH safe limit = 770 lbf
59. Mobile Computer Laboratory Study
Investigate the effects of different laptop
PC locations in a utility vehicle cab
Biomechanical effects
Performance and safety effects
Subjective assessment
65. Laboratory Study:
Dependent Variables
Biomechanical
Body segment angles
Neck angle (rotation and flexion)
Shoulder (abduction and flexion)
Elbow (flexion)
Wrist (radial/ulnar deviation and
flexion/extension)
Trunk (rotation and flexion)
Muscle force: EMG activity of major trunk,
shoulder and arm muscles
65
66. Laboratory Study:
Dependent Variables
Comfort and effort
Assessed using ordinal subjective
assessment forms
Performance
Time to complete tasks on PC
Accuracy of tasks
Preference
Rank order of placement from worst to best
Selection of best placement
66
67. Left Erector Spinae EMG
67
Laptop on and in
front of passenger
seat (A & B)
increases left back
muscle force
substantially for both
tasks
L e ft E r e c to r S p in a e
N = 7
L o c a t i o n * T a s k ; W e i g h t e d M e a n s
V e rt i c a l b a rs d e n o t e 0 . 9 5 c o n f i d e n c e i n t e r v a l s
K e y b o a rd
T o u c h s c r e e n
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9
A B C D
L o c a t i o n
0 . 0 0
0 . 0 5
0 . 1 0
0 . 1 5
0 . 2 0
0 . 2 5
0 . 3 0
Mean
0 . 1 7 5 2
0 . 1 0 3
0 . 0 4 0 4
0 . 0 6 0 1
0 . 1 8 2 6
0 . 1 4 5 8
0 . 0 8 8 0 . 0 8 7 9
68. Right Deltoid EMG
68
Laptop on and in
front of passenger
seat (A & B)
increases right
shoulder force
substantially for
touchscreen tasks
R ig h t D e lto id
N = 2 2
L o c a t i o n * T a s k ; W e i g h t e d M e a n s
V e r t i c a l b a r s d e n o t e 0 . 9 5 c o n f i d e n c e i n t e rv a l s
K e y b o a r d
T o u c h s c re e n
A B C D
L o c a t i o n
0 . 0 0
0 . 0 5
0 . 1 0
0 . 1 5
0 . 2 0
0 . 2 5
0 . 3 0
Mean
70. Subjective Assessment
Subjects
overwhelmingly
liked the locations
near driver seat
Disliked the locations
near passenger seat
Q u e s t io n 3 : M e d ia n R e s p o n s e
N = 2 2
4 . 0
5 . 0
5 . 5
2 . 0
0 1 2 3 4 5 6
BC
D A
4 . 0
5 . 0
5 . 5
2 . 0