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 PERFORMANCE PERSON GAP ESSENTIAL WITH TASK DISABILITY FUNCTIONS ACCOMMODATION SYSTEM SYSTEM INPUTS + OUTPUTS ENVIRONMENT 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 Disadvantages Mounting Individual -access to and from machine at -access to only one machine Machine any location Independent -access to an unlimited number of -machinery can only be accessed machines from the location of the lift Type Standing -least expensive option -operator must be able to stand Platform Wheelchair -access to wheel chair at all times -large and bulky Platform -long transfer distances Parallel -simple to design and construct -minimal reach and lifting Linkage distances Chair Lift rail/slide -inexpensive to design and -relies on winch for power construct swing arm -greater reach (horizontal and -cost vertical) -greater range of motion in all directions Power Hydraulic -escape capacity -requires additional modifications to attach -more durable in harsh -more expensive components environments Electric winch -least expensive option -safety (see safety section) linear -made to order -limited range of motion actuator chain -easy to repair -larger power requirement screw -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 The design should begin with a thorough user. understanding of the user and the user's task. 2.Consistency, consistency, Things that look the same should act the same. consistency. 3.Everyone makes mistakes, so every The user should have feedback on what they mistake should be fixable. 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 Behavioral Basis (error mode) Countermeasure (potential or Response (errors and violations) implemented) purchase set-up and installed in wrong location damage to machine k nowledge-based: step-by-step instructions installation freq : low severity : moderate (user did not know where to telling user where to mount lift mount) effectiveness : high freq : moderate judgement-based: provide easy to use instructions (user decided in a hurry) effectiveness : high freq : moderate ordinary use using lift for inappropriate use damage to machine judgement-based: provide warings (lift capacities) (pulling fence posts) severity : moderate (inappropriate use) in user's manual and on lift freq : moderate freq : moderate effectiveness: low running lift into tractor damage to machine sk ill-based: modify product freq : low severity : moderate (user lacks skill in operating) use limit switches to prevent freq : low contact personal injury effectiveness: high severity : low modify product decrease speed of lift movement effectiveness: moderate troubleshooting maintenance and repair emergency attempt to use lift when system potential injury judgment-based : warning label procedures looses power in emergency severity : high (user knew better, but decided (do not use in emergency) freq: high to try anyway) effectiveness : low freq : high disposal 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 Effect Behavioral Basis Countermeasure (potential Missing (error mode) or implemented) Response (errors and violations) purchase error: select the wrong effect: lift won't get used knowledge countermeasure: consult style of lift (chair with manufacturer or platform) freq: low severity: high freq: high effectiveness: high error: fit to clients effect: lift won't get used knowledge / countermeasure: educate needs, tractor, judgment based consumers with a storage brochure with limitations specifications freq: moderate severity: high freq: moderate effectiveness: moderate error: wrong features effect: won't use knowledge / countermeasure: inform judgment / skill consumer based freq: low / moderate / severity: low / moderate / freq: low / moderate / effectiveness: low / high high high moderate / high error: installing the lift effect: exposure to more judgment based countermeasure: clearer on a less hazards recommendations accessible tractor through personal contacts freq: low severity: moderate freq: low effectiveness: low Panel of Experts EMEA (cont.) set-up and error: install the unit in effect: difficulty in knowledge / skill countermeasure: provide installation the wrong transfers based clear instructions / location provide standardized mounting freq: low / moderate / severity: low / moderate / freq: low / moderate / effectiveness: low / high high high moderate / high error: improper wiring effect: fire hazard skill based countermeasure: clear instructions freq: moderate severity: moderate freq: moderate effectiveness: moderate error: improper effect: damage to the judgment countermeasure: modify modifications to tractor with caution the tractor freq: moderate severity: moderate freq: moderate effectiveness: high Panel of Experts EMEA (cont.) Task Stage Inappropriate or Effect Behavioral Basis (error Countermeasure Missing mode) (potential or Response implemented) (errors and violations) set-up and error: select the wrong effect: lift won't get used knowledge / judgment / countermeasure: consult installation style of lift (chair skill based with manufacturer or platform) 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 ordinary use error: difficulty effect: fall skill based countermeasure: transferring experience freq: moderate severity: high freq: low effectiveness: moderate error: activating wrong effect: move wrong skill based countermeasure: better switch direction labels freq: high severity: moderate freq: high effectiveness: moderate error: failure to wear effect: fall judgment countermeasure: warning seatbelt label freq: moderate severity: high freq: moderate effectiveness: low Panel of Experts EMEA (cont.) trouble-shooting error: fusing in control effect: failure to operate knowledge based countermeasure: better panel wiring freq: low severity: moderate freq: moderate effectiveness: moderate error: improper dealing effect: damage to unit knowledge / judgment / countermeasure: with failure skill based troubleshooting manual freq: moderate severity: moderate freq: moderate effectiveness: moderate maintenance error: no instructions effect: knowledge / judgment / countermeasure: manual and repair for maintenance skill based freq: severity: freq: effectiveness: emergency error: power failure / effect: stranded / death knowledge based countermeasure: backup procedures fire 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.
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