Browsing by Author "Dr. Carolyn M. Sommerich, Committee Member"

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    Predicting Trunk Kinematics from Static Task Parameters
    (2002-07-25) Nay, David Todd; Dr. David A. Dickey, Committee Member; Dr. Gary A. Mirka, Committee Chair; Dr. Carolyn M. Sommerich, Committee Member
    Many of the current ergonomic assessment tools available to industry take static "snapshots" of manual material handling (MMH) tasks to assess the hazards of a job. These tools are valuable to industry in that they provide a quick and inexpensive assessment of the task. However, these tools do not evaluate the trunk kinematics occurring during the task. As previous research has shown, trunk kinematics play an important role in assessing the stress placed on a person's low back. The goal of this study was to provide a model that predicts the trunk kinematics as a result of static task parameter inputs. A three-dimensional electrogoniometer worn on the subject's low back (Lumbar Motion Monitor (LMM)) was used to record the effects of task parameters on trunk kinematics during a lifting task. Task parameters consisted of the inputs to the NIOSH Lifting Equation: the beginning and ending asymmetry location (five levels), horizontal distance (two levels), vertical height (three levels), and weight (two levels). Study results showed a good ability to predict the trunk kinematics in the sagittal plane, but a very low ability in the coronal and transverse planes. Using the results of this study to calculate the LMM Model's Probability of High Risk Group Membership (PHRGM) resulted in an average absolute error of 8.07. Improvements in the ability to accurately predict the PHRGM were achieved when the MMH lifts evaluated were kept within the parameters of this research. The results of this research provide ergonomists with trunk kinematics information from the static task parameters that can be used during the ergonomic assessment of a MMH lift.
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    Productivity and Ergonomic Investigation of Bent-Handle Pliers.
    (2002-07-02) Duke, Kelly Scott; Dr. Michael S. Woglater, Committee Member; Dr. Carolyn M. Sommerich, Committee Member; Dr. Gary A. Mirka, Committee Chair
    Musculoskeletal disorders (MSDs) cost industry billions of dollars in workers' compensation costs each year. Ergonomics is concerned with understanding the causes of MSDs and developing solutions to reduce these costs. Awkward postures have been implicated as a risk factor for the development of some MSDs, and a design principle to "bend the tool, not the wrist" has been advocated in many ergonomic textbooks. However, despite numerous laboratory investigations showing positive outcomes of application of this design principle to various hand tools, there is indication of lack of acceptance in industry for these bent-handle tools. In an attempt to understand the lack of industry acceptance, this investigation sought to determine if this design principle imposed constraints on users and/or negatively affected productivity, which may explain why they are not being widely used in industry. The experiment used two different tasks (a computer-jumper installation task, and a spring assembly task) to compare the use of bent-handle pliers versus straight-handle pliers. Additionally, the effects of work surface orientation (vertical versus slanted at 45°) was evaluated, as was the effect of constraining the user's coupling of the tool. The dependent variables in the experiment were productivity and postural outcomes (arm elevation, wrist deviation in the radial/ulnar plane, and wrist deviation in flexion/extension). An important point that must be made is that overall the results clearly suggested that the expected outcomes (both productivity and postural) are very task specific. This in itself says a lot about the general recommendation to "bend the tool", that being that the recommendation cannot be made without clearly understanding the other task characteristics involved, and that it should therefore not be proposed as a general design recommendation. For the computer-jumper task the bent-handle pliers resulted in 5.3% faster task performance compared to the straight-handle pliers, while for the spring assembly task the performance was 4.9% faster with the straight-handle pliers. The explanation provided is that the bent-handle pliers seem to be preferable for tasks that require minimal or no tool rotation out of the sagittal plane, losing their advantage when multi-plane rotation is required. When subjects were constrained to holding the pliers with a power grip or oblique grip (modified power grip) arm elevation was reduced 50% and ulnar deviation was reduced by 12% when using the bent-handle pliers on the computer-jumper task, while on the spring assembly task ulnar deviation was reduced 22%. These results suggest that there are postural advantages to the bent-handle pliers (for the tasks used in this experiment) when the pliers-coupling is restricted to these grips. In the test of constrained versus unconstrained the results showed that for the computer-jumper task the postural benefits of the bent-handle pliers were lost when the subject could hold the straight-handle pliers any way desired, while for the spring assembly task this was not seen. In addition to showing that the postural benefits may only be seen when the pliers are held in a specific way, these results (along with others discussed in the paper) illustrate that the expectations associated with this design concept are very task-specific. Finally, removal of the coupling constraint also showed that subjects were more likely hold the straight-handle pliers in unconventional manners. In summary, it appears that the specificity of the bent-handle tool design, may make it better in very specific circumstances, but if the use requires increasing degrees of manipulation, it is less likely to be superior to a simpler design.
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    Visual Posture Observation Error and Training
    (2003-06-04) Covalla, Elizabeth Danielle; Dr. Gary A. Mirka, Committee Chair; Dr. Nelson Couch, Committee Member; Dr. Carolyn M. Sommerich, Committee Member
    The purpose of this study was to determine people's ability to visually estimate postural angles of the shoulder, trunk, and wrist. One application of these findings is to determine the effect of estimation error on common risk analysis tools that incorporate posture. Considerations are given to the effect of training, video mode, gender, body region, and subject characteristics on estimation error. Absolute error, algebraic error, and subject confidence are used to characterize visual estimation abilities. Results indicate that visual estimation error ranges between 7 and 10 degrees. Error further increased with wrist postures and female observers. Due to estimation errors, analysis tools that include posture are less accurate in predicting risk of injury. Eight, 12, and 14 percent of shoulder, trunk, and wrist postures, respectively, were misclassified causing Rapid Upper Limb Assessment (RULA) scores to shift by at least one point. For the Strain Index, forty percent of wrist postures were misclassified by participants causing as much as a two-thirds change in the final score.