More than ever, human factors engineers and ergonomists need to justify our practice’s value to management. How can we effectively communicate with management? How should we present a Return on ...Investment (ROI) that leadership will find useful that addresses company profits, cost savings, productivity, first time quality, and turnover? What else does management care about other than ROI? This second panel in a two panel series will specifically highlight case studies in which presenters give examples of situations in which ROI for ergonomics was investigated from a business value. The session will start with four case study lectures followed by a panel discussion led by the moderators. The audience will be encouraged to participate with their own questions and comments.
A joint study was conducted by a manufacturer of dental stools in the Midwest of the United States and Marquette University to measure the occupational postures of dentists and dental hygienists. The ...postures of 10 dentists and 10 dental hygienists were assessed using work sampling and video techniques. Postural data of the neck, shoulders and lower back were recorded from video and categorized into 30-degree intervals: o (neutral posture of respective joint), 30, 60 and 90 degrees. Each subject's postures were observed while they were treating patients during a four-hour period, during which 100 observations of postures were recorded at random times. Compared to standing, dentists and dental hygienists were seated 78 percent and 66 percent of the time, respectively. Dentists and dental hygienists flexed their trunk at least 30 degrees more than 50 percent of the time. They flexed their neck at least 30 degrees 85 percent of the time during the four-hour duration, and their shoulders were elevated to the side of their trunk (abducted) at least 30 degrees more half of the time. The postures of the trunk, shoulders, and neck were primarily static. This database of postures can be used by dental professionals and ergonomists to assess the risk dentists and dental hygienists are exposed to musculoskeletal disorders, such as low back pain or shoulder tenosynovitis, from deviated joint postures. They could use these data to select dental furniture or dental devices that promote good body posture, i.e., reduce the magnitude and duration of deviated joint postures, which, in theory, would decrease the risk of musculoskeletal disorders.
Overhead line workers have anecdotally reported elevated levels of fatigue in forearm muscles when operating the pistol grip control that maneuvers an aerial bucket on a utility truck. Previous ...research with surface electromyographic (sEMG) recordings of forearm muscles corroborated these reports of muscle fatigue. A new pistol grip was designed that reduces the applied force by 50% in all directions of movement. In laboratory testing, sEMG signals were recorded from the upper extremity muscles of twenty subjects, who operated a conventional-force pistol grip and the 50% reduced-force control to move a 1/15 scale model of an aerial truck boom. The muscle that resulted in the greatest sEMG activity (extensor digitorum communis (EDC)) was the muscle that workers typically pointed to when they reported forearm muscle fatigue from using the control. The reduced-forced pistol grip decreased EDC sEMG by an average of 5.6%, compared to the conventional control, increasing the maximum endurance time by 38% according to muscle fatigue models. This study was the first to quantify muscular activity of a new aerial bucket pistol grip control and the results show promise for improving the occupational health of electric utility overhead line workers, specifically reducing muscle fatigue. Before the new design of the pistol grip can be commercialized, it must be tested in the field on actual equipment.
Objective: A shovel with a blade perforated with small holes was tested to see whether a worker would use less whole-body energy to dig wet clay than with a shovel with an opaque blade.
Background: A ...perforated shovel is hypothesized to require less whole-body energy on the basis of adhesion theory; a smaller surface area would require less physical effort to dig and release soil from the blade.
Method: The study involved 13 workers from an electric utility who dug wet clay with two 1.5-m long-handled point shovels, which differed only in blade design (perforated and opaque). Oxygen consumption was measured with a portable system while each worker dug wet clay at a self-regulated pace for 10 min.
Results: There was no significant difference in number of scoops dug during the 10-min sessions, but workers dug 9.5% more weight of clay with the perforated shovel than with the conventional shovel (404 kg vs. 369 kg, respectively). Furthermore, stable oxygen uptake normalized to weight of participant and to the weight of clay dug revealed that participants expended 11.7% less relative energy per kilogram of clay dug with the perforated shovel.
Conclusion: A point shovel with a perforated blade is recommended for digging and shoveling wet clay. However, the extra weight that workers chose to dig with the perforated shovel may increase the loading on the spine and may offset the metabolic advantages.
Application: Manual shoveling is a common task, and workers may experience less whole-body and muscle fatigue when using a perforated shovel.
Motorcycle Clutch Grip Strength Conrad, Megan O.; Marklin, Richard W.
Proceedings of the Human Factors and Ergonomics Society Annual Meeting,
09/2014, Letnik:
58, Številka:
1
Journal Article
Recenzirano
The purpose of this study was to evaluate the maximum grip force a user can exert on a motorcycle clutch. In a laboratory setting subjects (57 male; 34 female, 95% right-handed) were asked to exert ...maximum grip strength using their left hand on an actual motorcycle clutch that was instrumented with a load cell. The clutch was capable of being fixed in 5 different positions, allowing maximum grip measurements at A=5.0 cm, B=6.5 cm, C=8.0 cm, D=9.5 cm, E=11.0 cm grip spans. Average maximum grip force for females (179 N) was exerted at the 5.0 and 6.5 cm grip spans, while males exerted their highest force (334 N) at the 6.5 and 8.0 spans. For all grip spans, male subjects exerted significantly higher grip forces than female subjects (p<0.05). Additionally, females ranked 6.5 cm span (B) as the most comfortable grip span, while males ranked the 8 cm span (C) as highest for comfort. Data collected in this study can be applied to motorcycle clutch design or other lever controls that require a planar grip operated by the hands, particularly the left hand.
Electric utility line workers report high levels of fatigue in forearm muscles when operating a conventional pistol grip control in aerial buckets. This study measured the applied force and surface ...electromyographic (sEMG) signals from four upper extremity muscles required to operate the pistol grip control in two tasks. The first task was movement of the pistol grip in six directions (up/down, forward/rearward, clockwise/counter-clockwise), and the second task was movement of the bucket from its resting position on the truck bed to an overhead conductor on top of a 40 ft tall pole. The force applied to the pistol grip was measured in 14 aerial bucket trucks, and sEMG activity was measured on eight apprentice line workers.
The applied force required to move the pistol grip control in the six directions ranged from 12 to 15 lb. The sEMG activity in the extensor digitorum communis (EDC) forearm muscle was approximately twice as great or more than the other three muscles (flexor digitorum superficialis, triceps, and biceps). Line workers exerted 14 to 30% MVCEMG to move the pistol grip in the six directions. Average %MVCEMG of the EDC to move the bucket from the truck platform to an overhead line ranged from 26 to 30% across the four phases of the task. The sEMG findings from this study provide physiologic evidence to support the anecdotal reports of muscle fatigue from line workers after using the pistol grip control for repeated, long durations.
Ergonomics analysis of line workers in the electric power industry who work overhead on utility poles revealed some tasks for which less than 1% of the general population had sufficient strength to ...perform. During a 2-year study, a large Midwestern US electric utility provided a university with a team of represented workers and management. They evaluated, recommended, and monitored interventions for 32 common line worker tasks that were rated at medium to high magnitude of risk factors for musculoskeletal disorders (MSDs). Two of the recommended ergonomic interventions—the battery-operated press and cutter—were selected by the team as having the greatest potential for reducing risk factors of MSDs. Only overhead distribution line worker tasks were evaluated. A business case was formulated that took into account medical injury and illness statistics, workers’ compensation, replacement worker and retraining costs. An outline of a business case formulation and a sample intervention payback calculation is shown. Based on the business case, the utility committed over $300,000 to purchase battery-operated presses and cutters for their overhead distribution line crews.
This study aimed to compare and analyse rubber-dome desktop, spring-column desktop and notebook keyboards in terms of key stiffness and fingertip typing force. The spring-column keyboard resulted in ...the highest mean peak contact force (0.86N), followed by the rubber dome desktop (0.68N) and the notebook (0.59N). All these differences were statistically significant. Likewise, the spring-column keyboard registered the highest fingertip typing force and the notebook keyboard the lowest. A comparison of forces showed the notebook (rubber dome) keyboard had the highest fingertip-to-peak contact force ratio (overstrike force), and the spring-column generated the least excess force (as a ratio of peak contact force). The results of this study could aid in optimizing computer key design that could possibly reduce subject discomfort and fatigue.
Advancements in fastener technology have been complemented by the development of new types of screwdriver bits. While designs may vary, so may the force application requirements placed on the tool ...user. The primary objective of this experiment was to analyze the relationship between user applied torque and screwdriver bit design. A further objective was to utilize the results to develop an effort metric by which bits of different designs can be compared. Three types of screwdriver bit designs (straight, Phillips, and combination of straight/Phillips (ECXTM)) were tested to determine how the design affects the amount and type of force applied by the user when performing a fastening task. The designs were tested to simulate fastener tightening and loosening operations. Sixteen participants were tested in this study. The data suggest there is no difference in user torque exertion between the ECXTM bit, Phillips, and the straight bit designs in either direction, 2.61-2.97 Nm for pronation and 2.63 -2.85 for supination. Mean axial force was significantly less for the Phillips (67 N) than the other 2 bits (72 and 80N). Although there was no significant effect of bit head design on maximal torque and axial force, the data suggest that the Phillips bit design may allow subjects to exert less axial force, which would result in a higher biomechanical effort ratio. A greater effort ratio would produce greater torque for the same axial force or the same torque for a lower axial force. Mean effort ratio for the Phillips bit was 3.6 N/N (Sup) and 4 N/N (Pro) and approximately 3.0 for the other two combinations of bits and directions. Subjective assessment indicated that users overwhelmingly preferred the Phillips bit design
Objective: The aim of this study was to determine how height of a hand wheel affects maximum torque production and risk of injury to the shoulders and back of workers. Background: Workers in the ...processing, refinery, and energy generation industries manually open and close valves with hand wheels that require high torque. This task is physically strenuous and can lead to shoulder musculoskeletal disorders (MSDs). Method: Maximum torque exertions in the clockwise and counterclockwise directions at three heights (knee, chest, and overhead) were tested. Results: The torque production in the counterclockwise (left) direction was greater than that of the clockwise (right) direction (150.5 N·m vs. 141 N·m). This main effect was independent of valve height, as there was no interaction between direction and valve height (p = .686). Participants exerted at least 10% greater torque at the overhead level than at the chest level (means of 153.2 N·m vs. 138.3 N·m). There was no difference in maximum torque between knee and overhead levels and between knee and chest levels. Conclusion: According to ergonomics principles, the risk of MSDs affecting the shoulder and trunk from turning valves should be lowest at chest height because the postures of the shoulder and trunk are at or near neutral. However, workers exerted greatest torque when the valve was located overhead. Whether valves located at overhead height, compared with chest height, present greater risk of MSDs to workers is not known. Application: Design engineers should avoid placing hand wheel valves at knee height or lower.
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