Ergonomic Evaluation of
Commercially Available Operator
Lifts for Farmers with Disabilities
Aaron M. Yoder, Ph.D.
Penn State University,
Purdue University &
Breaking New Ground
Resource Center
Background
 692-1,697 persons in agriculturally related
occupations or industries with a spinal
cord injury.
 An estimated 4,500 persons with spinal
cord injuries presently in the agricultural
population.
 Innumerable others (~19%) with mobility
restrictions. (e.g. strokes, arthritis,
amputations, back injuries, and others)
Background (cont.)

Assistive technology
allows them to return
to work
• motor vehicles
• agricultural
equipment
• agricultural
workplaces
Background (cont.)

Many will, however,
return to work without
the appropriate
technology
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)

Purdue University’s
Breaking New Ground
Resource Center has
taken a leadership
role in assisting
farmers and ranchers
with disabilities
continue farming
safely.
Background (cont.)
Background (cont.)
Background (cont.)
Background (cont.)
Purpose
 To develop and administer a systems
approach for evaluating ergonomic and
safety issues related to the application of
commercially available operator lifts used
on agricultural and other off-road
machinery to provide a means for
operators with restricted mobility to gain
access to the operator’s station.
Objective 1
 Develop and administer a standardized
approach to conduct 11 on-site visits to
collect observational and interview data
from individuals who currently own and
use both locally made and commercially
available operator lifts to access and
operate their agricultural equipment.
Objective 2
 Conduct a formal ergonomic analysis, with
an emphasis on safety and usability, of two
configurations of commercially available
LifeEssentials operator lifts designed for
accessing agricultural equipment.
Objective 3
 Develop a standardized user survey
instrument for obtaining user
demographics and feedback on operator
lifts being used on self-propelled
agricultural equipment and to test the
following hypotheses:
• Ho1: A majority of the lift users have spinal cord injuries.
• Ho2: A majority of the lift users have use of their upper body.
• Ho3: Owning a lift allows the lift users to continue to be productive
in an agricultural operation.
• Ho4: Commercially manufactured lifts are safer than home built
models.
Objective 4
 Validate the analysis strategies and survey
instrument by utilizing a panel of experts in
the field of assistive technology to conduct
an independent ergonomic evaluation of
the operator lifts.
Objective 5
 Collect ergonomic and demographic data
from agricultural operator lift users using
the survey instrument previously
mentioned in Objective 3.
Related Literature
 Secondary Injury
 Systems Approach
 Machinery Ergonomics in Agriculture
 Related Standards
 Expert Panels
 Lift Design Characteristics
Secondary Injury
 17% of farm operators had physical
disabilities that prevented them from
completing essential farm tasks.
 Increasing mean age of farm operators has
led to a higher prevalence of disabling
conditions.
 Secondary injury risk is more severe for
individuals with SCI.
The Systems Approach
 To ensure completeness in the ergonomic
evaluation of operator lifts.
 Hagel – “The whole is more than the sum of
its parts”
 Gestalt psychologists recognized the
importance of “objectiveness” or
wholeness to human perception.
The Systems Approach (cont.)
 Explosion in use during WW II in Human
Factors
 In 1973, Meredith et al. emphasized that the
systems approach warranted attention and
respect as a stand alone philosophy,
worthy of study, separate from the
engineering discipline.
 Used by scientists, engineers and
agricultural safety specialists.
The Systems Approach (cont.)
TOOLS
EQUIPMENT
WORKSTATION
INFORMATION
PERSON
WITH
DISABILITY
PERFORMANCE
GAP
ESSENTIAL
TASK
FUNCTIONS
ACCOMMODATION
SYSTEM
INPUTS
ENVIRONMENT
+
SYSTEM
OUTPUTS
Machinery Ergonomics in
Agriculture
 ASAE Publication- Human Factors (1991)
 An Ergonomic Checklist for Tractors and
Agricultural Machinery. (Hansson, 1991)
 Cab Accessibility: How important is it?
(Latif and Christianson, 1988)
 Safe access to farm tractors and trailers.
(Hammer, 1991)
Machinery Ergonomics in
Agriculture (cont.)
 Risks in using modified tractors by
operators with SCI and their co-workers
(Willkomm, 1997)
 Assessment of work-related injury risk for
farmers and ranchers with physical
disabilities (Allen et al., 1995)
Related SAE Standards
• SAE J2092 – Testing of Wheelchair Lifts for Entry to or
Exit from a Personally Licensed Vehicle
• SAE J2093 – Design Considerations for Wheelchair
Lifts for Entry and Exit from a Personally Licensed
Vehicle
• SAE J1725 – Structural Modifications for Personally
Licensed Vehicles to Meet the Transportation Needs
of Persons with Disabilities
• SAE J185 – Access Systems for Off-Road Machines
Expert Panels
Lift Design Characteristics
Advantages
Mounting
Individual
Machine
Independent
Type
Standing
Platform
Wheelchair
Platform
Parallel
Linkage
Chair Lift
rail/slide
swing arm
Power
Hydraulic
-access to and from machine at
-access to only one machine
any location
-access to an unlimited number of -machinery can only be accessed
machines
from the location of the lift
-least expensive option
-operator must be able to stand
-access to wheel chair at all times -large and bulky
-long transfer distances
-simple to design and construct
-minimal reach and lifting
distances
-inexpensive to design and
construct
-relies on winch for power
-greater reach (horizontal and
vertical)
-greater range of motion in all
directions
-cost
-escape capacity
-requires additional modifications
to attach
-more expensive components
-more durable in harsh
environments
Electric
winch
linear
actuator
chain
screw
Disadvantages
-least expensive option
-made to order
-safety (see safety section)
-limited range of motion
-easy to repair
-larger power requirement
-generates large amounts of force -cost
-prevents freewheeling or falls
Methodology
 Objective 1 – Observational and Interview
Analysis
 Objective 2 – Initial Ergonomic Analysis by
the Researcher
 Objective 3 – Preliminary Questionnaire
Development
 Objective 4 – Panel of Experts
 Objective 5 – Questionnaire Administration
Observational and Interview
Analysis

Telephone
Conversations
• Informal survey

11 Site Visits
• Photographs
• Informal survey
Initial Ergonomic Analysis by the
Researcher
Heuristic Analysis and
EMEA conducted on
LifeEssentials
operator lift system.
 Results used for the
initial development of
the lift user’s
questionnaire.

Heuristic Analysis
Rule
Description
1.Know thy user, and YOU are not thy
user.
2.Consistency, consistency,
consistency.
3.Everyone makes mistakes, so every
mistake should be fixable.
The design should begin with a thorough
understanding of the user and the user's task.
Things that look the same should act the same.
The user should have feedback on what they
did, they should have help in finding errors and
knowing how to correct them, and they should
easily be able to correct the errors.
4.When the tool is needed, it should be Information for decisions, about options, and so
at hand.
on needs to be there when needed; and if not
visible, users should know where and when to
find it.
5.Make error messages useful to the
Error messages should be written in the user's
user.
language, and tell the user how to fix the
problem.
6.Every action should have a reaction. Part of this rule implies subjectively fast and
recognizable feedback.
7.Don't overload the user's buffers.
Minimize the need to maintain information in
memory (esp. short term/working memory) in
order to complete a task.
8.Keep it simple.
Don't include things users don't need. Make it
easy to find the things they do need. Don't
clutter the design with features or attributes a
given user doesn't want. In general, one simple
useful thing is going to have more value than
when it is buried in enhancements.
9.Make it easy to be fast.
The more you do something, the easier it should
be to do.
10.Treat the user as manager.
The user should feel like they are in control.
The user should always know what is
happening, in terms that are useful to them.
Table 2. Ameritech Top 10 Rules of Thumb for Usability. (Ameritech, 2000)
Error Modes and Effects Analysis
(EMEA)
Task Stage
Inappropriate or Missing
Effect
Response (errors and violations)
Behavioral Basis (error mode)
Countermeasure (potential or
implemented)
installed in wrong location
freq : low
k nowledge-based:
(user did not know where to
mount)
freq : moderate
step-by-step instructions
telling user where to mount lift
effectiveness : high
judgement-based:
(user decided in a hurry)
freq : moderate
provide easy to use instructions
effectiveness : high
purchase
set-up and
installation
ordinary use
damage to machine
severity : moderate
using lift for inappropriate use
(pulling fence posts)
freq : moderate
damage to machine
severity : moderate
judgement-based:
(inappropriate use)
freq : moderate
provide warings (lift capacities)
in user's manual and on lift
effectiveness: low
running lift into tractor
freq : low
damage to machine
severity : moderate
sk ill-based:
(user lacks skill in operating)
freq : low
modify product
use limit switches to prevent
contact
effectiveness: high
personal injury
severity : low
modify product
decrease speed of lift movement
effectiveness: moderate
troubleshooting
maintenance
and repair
emergency
procedures
disposal
attempt to use lift when system potential injury
looses power in emergency
severity : high
freq: high
judgment-based :
(user knew better, but decided
to try anyway)
freq : high
warning label
(do not use in emergency)
effectiveness : low
Preliminary Questionnaire
Development
 Based on key areas identified from the
preliminary observations, interviews and
ergonomic analyses
• Demographics
• Ergonomic Information
– controller usability
– transfers
• Mail
Panel of Experts
 Four Members
 Mailed Information
 Met for Two Days
 Heuristic Analysis
and EMEA
 Validation of
Questionnaire
Findings
 Observational and Interview Analysis
 Ergonomic Analysis by the Researcher
 Questionnaire Development
 Panel of Experts
 Questionnaire Administration
Panel of Experts
Heuristic Analysis
Heuristic #1: Know thy user. Is the lift/control designed logically based on the
user?
Comments:










The lift appears to be designed for a person with "normal"
upper body strength.
Awkward placement of controller and cable routing.
Sling is uncomfortable.
Handholds would be useful for transferring.
The swivel seat is a good idea, but it is hard to operate.
The seat shape is hindering.
The controller needs better labeling.
It would be hard to use for someone with visual limitations.
Could it be used for more than ingress and egress?
Awkward placement of controller storage.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #2: Consistency. Does everything that looks the same act the same?
Comments:




All the controls on the controller look the same.
Use pictorials on the controller.
The control orientation could be improved.
When the operator is in different locations, their perspective of
the controller changes.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #3: Everyone makes mistakes, so every mistake should be fixable.
Are they?
Comments:






Use redundancy for the wiring.
Location visibility is difficult at times.
What can be done in case of power failure?
A learning curve is needed.
Many pinch and crush points are present.
Can the random rotation on the sling lift be reduced?
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #4: When the tool is needed, it should be at hand. Are they?
(remote, seatbelt, etc.)
Comments:







The controller is hard to reach and store.
An intermittent location for the controller would be useful.
Handholds are needed for transfers.
It would be useful if the lift could be used for maintenance.
A different restraint system may be useful (bar).
Could a circuit breaker be used in place of the main fuse?
It would be useful to be able to access the electronics box
without tools.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #5: Make error messages useful to the user. Are they?
Comments:








Trouble shooting instructions may be useful.
A failsafe backup should be used.
General directions would help.
Are error messages needed?
There is no positioning feedback.
Interference warnings could be used.
Audible signals could be used.
Limits would be helpful.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #6: Every action should have a reaction. Is there feedback?
Comments:





All O.K.
No!
Bumping and dragging may not be notice.
Controls are not intuitive.
Dampen the swing in the sling.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #7: Don’t overload the user’s buffers. Is the user’s memory load
high?
Comments:



Leg positioning depends on the user.
Controls are not intuitive.
It is mainly a simple system.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #8: Keep it Simple. Are any of the controls or is any part of the lift
complex?
Comments:



The seat is too simple.
Controller is too complex.
There are no simple emergency procedures.
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #9: Make it easy to be fast. Are there any points where speed could
be improved?
Comments:





Variable lift speeds would help.
Improve controller design.
Use smart logic to program the lift to go up and in.
Use transfer aids to speed up transfers.
Fast is sometimes bad (Injuries, Sensation of poor control).
Panel of Experts
Heuristic Analysis (cont.)
Heuristic #10:Treat the user as manager. Is there any point where the user
doesn’t feel in control?
Comments:



Swinging high in the air is very uncomfortable.
Lack of positioning sensations.
Use a joystick control.
Panel of Experts
EMEA
Task Stage
Inappropriate or
Missing
Response
(errors and
violations)
Effect
Behavioral Basis
(error mode)
Countermeasure (potential
or implemented)
purchase
error: select the wrong
style of lift (chair
or platform)
effect: lift won't get used
knowledge
countermeasure: consult
with manufacturer
freq: low
severity: high
freq: high
effectiveness: high
error: fit to clients
needs, tractor,
storage
limitations
effect: lift won't get used
knowledge /
judgment based
countermeasure: educate
consumers with a
brochure with
specifications
freq: moderate
severity: high
freq: moderate
effectiveness: moderate
error: wrong features
effect: won't use
knowledge /
judgment / skill
based
countermeasure: inform
consumer
freq: low / moderate /
high
severity: low / moderate /
high
freq: low / moderate /
high
effectiveness: low /
moderate / high
error: installing the lift
on a less
accessible tractor
effect: exposure to more
hazards
judgment based
countermeasure: clearer
recommendations
through personal
contacts
freq: low
severity: moderate
freq: low
effectiveness: low
Panel of Experts
EMEA (cont.)
set-up and
installation
error: install the unit in
the wrong
location
effect: difficulty in
transfers
knowledge / skill
based
countermeasure: provide
clear instructions /
provide standardized
mounting
freq: low / moderate /
high
severity: low / moderate /
high
freq: low / moderate /
high
effectiveness: low /
moderate / high
error: improper wiring
effect: fire hazard
skill based
countermeasure: clear
instructions
freq: moderate
severity: moderate
freq: moderate
effectiveness: moderate
error: improper
modifications to
the tractor
effect: damage to the
tractor
judgment
countermeasure: modify
with caution
freq: moderate
severity: moderate
freq: moderate
effectiveness: high
Panel of Experts
EMEA (cont.)
Task Stage
Inappropriate or
Missing
Response
(errors and
violations)
Effect
Behavioral Basis (error
mode)
Countermeasure
(potential or
implemented)
set-up and
installation
error: select the wrong
style of lift (chair
or platform)
effect: lift won't get used
knowledge / judgment /
skill based
countermeasure: consult
with manufacturer
freq: moderate
severity: moderate
freq: moderate
effectiveness: high
error: controller wiring
effect: end pulls off
judgment
countermeasure: better
wiring techniques
freq: high
severity: high
freq: high
effectiveness: high
error: difficulty
transferring
effect: fall
skill based
countermeasure:
experience
freq: moderate
severity: high
freq: low
effectiveness: moderate
error: activating wrong
switch
effect: move wrong
direction
skill based
countermeasure: better
labels
freq: high
severity: moderate
freq: high
effectiveness: moderate
error: failure to wear
seatbelt
effect: fall
judgment
countermeasure: warning
label
freq: moderate
severity: high
freq: moderate
effectiveness: low
ordinary use
Panel of Experts
EMEA (cont.)
trouble-shooting
maintenance
and repair
emergency
procedures
error: fusing in control
panel
effect: failure to operate
knowledge based
countermeasure: better
wiring
freq: low
severity: moderate
freq: moderate
effectiveness: moderate
error: improper dealing
with failure
effect: damage to unit
knowledge / judgment /
skill based
countermeasure:
troubleshooting
manual
freq: moderate
severity: moderate
freq: moderate
effectiveness: moderate
error: no instructions
for maintenance
effect:
knowledge / judgment /
skill based
countermeasure: manual
freq:
severity:
freq:
effectiveness:
error: power failure /
fire
effect: stranded / death
knowledge based
countermeasure: backup
system
freq: low
severity: high
freq: low
effectiveness: high
error: poor planning
effect: entrapment
knowledge based
countermeasure: develop
plan
freq:
severity:
freq:
effectiveness:
Questionnaire
Administration
 Initial mailing sent to 127 potential lift
users
 40 returned due to incomplete or invalid
addresses
 60 (69%) of the remaining 87 were
completed and returned
 4 did not qualify, leaving 56 to analyze
Questionnaire
Administration (cont.)

Survey Comments
Question 13 – Were you able to use the same piece of machinery after your injury
without a lift? If yes, how did you access it?

Pull myself up on tractor with my wife helping me, also with leg braces.

Yes, but it requires someone (usually) to lift my legs for me. I can usually pull
myself up and down, but it is safer with another person.

Bought both after accident

Had to park close to a bank and walk a plank.

Prior to intallation of the lift I was only able to use this tractor with assistance
from someone else.
Questionnaire
Administration (cont.)

Survey Comments (cont.)

Dangerously used end loader to lift me up on a platform then transfer. Not
recommended.

I pulled myself up on the tractor (broke leg doing it).

It would have been hard.

I had an electric winch hooked to the rafters in my pole barn. I used that a long
with a hoyer seat pad to connect to the lift. Once on the tractor you had to pull the
tractor back in the same spot to get off.

Until 50, I was able to get on my tractors using brute strength However, I should
have used a lift as I injured both shoulders. I have arthritis and rotator cuff tears.
Questionnaire
Administration (cont.)

Survey Comments (cont.)
Question 37 – Have you ever had to use the lift in an emergency situation, such as
a fire or accident?

I broke my femur (left) after bracing – removed myself from the tractor

Caught combine on fire, could smell it burning, called for help save combine.

In the event of a fire, I would not be able to get off the tractor quickly enough to
save myself. I would have to fall off and take my chances.
Questionnaire
Administration (cont.)

Survey Comments (cont.)
Question 38 – Have you ever been injured or almost injured while you were using
the lift?

The nut that holds the seat on became loose and the seat slid and I almost fell off.

Was bush hogging and lift arm on tractor broke while I was making a turn to the
left on a 20-25% incline. The bush hog climbed up on wheel, but lift stopped it
from coming up on me, but roll bar may also have stopped it, too.

Always try to be careful to watch feet, legs, fingers, body parts when using
(manlift).

Not me, but there was a sheer point on one of the lifts we built and my brother
broke a toe when using it improperly once. The sheer point has been eliminated.

The screw broke when I was about half way up.
Questionnaire
Administration (cont.)

Survey Comments (cont.)

The screw broke when I was about half way up.

I don’t dairy farm anymore. The two tractors are sold and the lifts are in my
machine shed. I can't operate tractors anymore because of recurrent pressure sores
problems. Everything is hired done.

I was on the lift and it started going down itself. If my leg had been in the way I'm
not sure what I would have done. The only happened once in five years. No
injuries, though. Not complaining just answering the question.

The lift broke and fell on the tractor wheel. That is why you have to brace the lift
to the tractor to make it solid. There is to much vibration on a tractor and not have
it braced.
Questionnaire
Administration (cont.)

Survey Comments (cont.)
Question 39 – Have you ever used the lift for any other purpose than lifting the
operator into the operator’s station?

Yes, lifting out

My brother uses the lift to lift heavy boulders out of the field to place on the rear
axel of the 4wd. When convenient.

Pull fence posts, carry stuff, works great.

I had to sell out 99 so I don't farm any more.

It lifts a lot of stuff in my shop.

Getting from tractor cab to van seat.

I fell off of wheelchair. I used the lift to get back on wheelchair.
Questionnaire
Administration (cont.)

Survey Comments (cont.)

I fell off of wheelchair. I used the lift to get back on wheelchair.

Used it to lift quick hitch on tractor and other implements

Putting fuel in tractor, checking water.

I now use it to stand up.

For adjusting mirrors and reaching equipment.

I used the lift to reach the side of my pole barn.

To get into truck or tractors

I transfer from wheelchair to lift and swing into my wood front deck mower.

For access to pecan trees to graft the tree
Conclusions
 Observational and Interview Analysis
•
•
•
•
Introduction to users and types of lifts
Collected user data
Initiated ideas of problems with lifts
Aided in the development of the Questionnaire
Conclusions
 Ergonomic Analysis by Researcher
• Heuristic and EMEA
• Identified additional areas of concern
• Aided in the development of the Questionnaire
Conclusions
 Panel of Experts
• Heuristic and EMEA
– Identified areas of concern
• Validated analysis strategies
• Validated questionnaire
Conclusions
 Questionnaire Administration
•
•
•
•
H01: 75% of the lift users had SCI
H02: 76% of the lift users had full use of arms
H03: 17% could use same machinery before
H04: Low response by locally fabricated
– 8(16%) of 49 commercially manufactured
– 1 (14%) of 7 locally fabricated
Recommendations


An adaptation of the questionnaire and
ergonomic analyses used in this study could be
used to assess other assistive technology
devices used in the agricultural population.
A standard aimed at the testing and use of
operator lifts to access agricultural and other
off-road equipment by operators with physical
disabilities should be submitted to the Adaptive
Standards Committee of the Society of
Automotive Engineers. An initial draft has been
developed based on the review of ASAE and SAE
standards and the findings of this study.
Recommendations (cont.)


The information gained from this study should
be used to justify the safety and applicability of
operator lifts in agriculture to organizations
that supply funding for the use of and research
pertaining to assistive technology.
Additional studies in the area of secondary
injuries involving assistive technology should
be conducted to gain a clearer perspective on
the issue.