Maximum Torque Exertions Research Articles

Effect of Handwheel Height and Angle on Operators' Torque Production Capabilities

OCCUPATIONAL APPLICATIONSFrom investigating the maximum isometric torque exertions of participants on a handwheel set at different heights and angles, it was determined that torque production capability is greatest when the handwheel is set overhead at 45° and is lowest when overhead at 0°. The mean torque production capacity of the participants was substantially lower than the torque demands in the field and in existing standards. Therefore, maximum recommended torque that accommodates the strength of most of the male population was determined for each handwheel height and angle investigated. The findings of this study may be useful for forming guidelines for handwheel-valve system designs, such as in standardizing the height and angle of a handwheel and defining a maximum recommended torque for handwheel-valve systems.TECHNICAL ABSTRACT Background: Handwheel-valve operation is a common task in many workplaces, including power, chemical, water, and oil industries. Handwheels of various angles and heights are common in a typical plant. The torque required to turn a handwheel differs from one valve to another, and there are no well-established torque standards derived specifically from operators' capabilities. Purpose: The purpose of this research was (1) to determine the effects of handwheel height and angle on torque production and (2) to propose maximum recommended torque limits for valve systems. Methods: Sixty male and female college students participated. Handwheel heights included knee, elbow, shoulder, and overhead levels, while handwheel angles included 0°, 45°, and 90°. At each height–angle combination, maximum isometric torque exertions on a handwheel were measured. These data were used to compute maximum recommended torque limits using the 25th percentile torque strength values of the female participants. Results: The mean maximum torque exertions ranged from 51.6 Nm (overhead at 0°) to 74.9 Nm (overhead at 45°). The height–angle and height–gender interaction effects were statistically significant. Male participants produced significantly greater torques (88.1 Nm) than the female participants (44.7 Nm). The 25th percentile torque strength values ranged between 25.2 and 38.9 Nm, depending on the height and angle of the handwheel. Conclusions: The relationship between torque production and handwheel height depends on the handwheel angle and vice versa. Overall, torque production was greatest when the handwheel was at shoulder or overhead levels, at either 45° or 90°, and lowest when overhead at 0°. The mean torque production capacity of the participants was substantially lower than torque demands in the field and even existing standards (about 40% lower). Maximum recommended torque limits for handwheels that would accommodate most of the male population's strength are proposed.

Height of Industrial Hand Wheel Valves Affects Torque Exertion

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. 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). Maximum torque exertions in the clockwise and counterclockwise directions at three heights (knee, chest, and overhead) were tested. 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. 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. Design engineers should avoid placing hand wheel valves at knee height or lower.

Inward Torque and High-Friction Handles Can Reduce Required Muscle Efforts for Torque Generation

The effects of handle friction and torque direction on muscle activity and torque are empirically investigated using cylindrical handles. A torque biomechanical model that considers contact force, friction, and torque direction was evaluated using different friction handles. Twelve adults exerted hand torque in opposite directions about the long axis of a cylinder covered with aluminum or rubber while grip force, torque, and finger flexor electromyography (EMG) were recorded. In addition, participants performed grip exertions without torque, in which they matched the EMG level obtained during previous maximum torque exertions, to allow us to determine how grip force was affected by the absence of torque. (a) Maximum torque was 52% greater for the high-friction rubber handle than for the low-friction aluminum handle. (b) Total normal force increased 33% with inward torque (torque applied in the direction fingertips point) and decreased 14% with outward torque (torque in the direction the thumb points), compared with that with no torque. Consequently, maximum inward torque was 45% greater than maximum outward torque. (c) The effect of torque direction was greater for the high-friction rubber handle than for the low-friction aluminum handle. The results support the proposed model, which predicts a large effect of torque direction when high-friction handles are gripped. Designing tasks with high friction and inward rotations can increase the torque capability of workers of a given strength, or reduce required muscle activities for given torque exertions, thus reducing the risk of fatigue and musculoskeletal disorders.

The effect of torque direction and cylindrical handle diameter on the coupling between the hand and a cylindrical handle

Pheasant and O’Neill's torque model (1975) was modified to account for grip force distributions. The modified model suggests that skin friction produced by twisting an object in the direction of fingertips causes flexion of the distal phalanges and increases grip force and, thus, torque. Twelve subjects grasped a cylindrical object with diameters of 45.1, 57.8, and 83.2 mm in a power grip, and performed maximum torque exertions about the long axis of the handle in two directions: the direction the thumb points and the direction the fingertips point. Normal force on the fingertips increased with torque toward the fingertips, as predicted by the model. Consequently, torque toward the fingertips was 22% greater than torque toward the thumb. Measured torque and fingertip forces were compared with model predictions. Torque could be predicted well by the model. Measured fingertip force and thumb force were, on average, 27% less than the predicted values. Consistent with previous studies, grip force decreased as the handle diameter increased from 45.1 to 83.2 mm. This may be due not only to the muscle length–strength relationship, but also to major active force locations on the hand: grip force distributions suggest that a small handle allows fingertip force and thumb force to work together against the palm, resulting in a high reaction force on the palm, and, therefore, a high grip force. For a large handle, fingertip force and thumb force act against each other, resulting in little reaction force on the palm and, thus, a low grip force.

Evaluation of handle diameters and orientations in a maximum torque task

The effects of gender, handle diameter (25–50 mm), and handle orientation (horizontal and vertical) on the perceived comfort, torque, total finger force, and efficiency of flexor and extensor muscle activity were examined in a maximum torque task. A 16-force sensor glove system was applied to measure finger and phalangeal forces, and a surface EMG was recorded to investigate muscle activities in the torque task. Average maximum torque in the horizontal orientation was about 23.4% more than that in the vertical orientation. The maximum torque was the largest with the 45 and 50 mm diameter handles and least with the 25 mm diameter handle. In both orientations, torque increased as the handle diameter increased, whereas total finger force showed a decreasing pattern which can explain the positive and non-linear correlation between torque output and handle diameter. The efficiency of muscle activity in both orientations followed a similar trend with the torque output for the handle diameters (i.e., the efficiency increased when the handle diameter increased). 35–45 mm handles were rated as the most comfortable for maximum torque exertions. According to a polynomial regression, 37–44 mm and 41–48 mm diameter handles (23.3% of the user's hand length) maximized perceived comfort and were thus recommended for females and males, respectively in this study. Relevance to industry This study will provide guidelines for designing better workstations and hand-tools maximizing performance, muscle efficiency, and user's comfort in manual torque tasks.

Upper-limb surface electro-myography at maximum supination and pronation torques: the effect of elbow and forearm angle

Forearm pronation and supination, and increased muscular activity in the wrist extensors have been both linked separately to work-related injuries of the upper limb, especially humeral epicondylitis. However, there is a lack of information on forearm torque strength at ranges of elbow and forearm angles typical of industrial tasks. There is a need for strength data on forearm torques at different upper limb angles to be investigated. Such a study should also include the measurement of muscular activity for the prime torque muscles and also other muscles at possible risk of injury due to high exertion levels during tasks requiring forearm torques. Twenty-four male subjects participated in the study that involved maximum forearm torque exertions for the right arm, in the pronation and supination directions, and at four elbow and three forearm rotation angles. Surface EMG (SEMG) was used to evaluate the muscular activity of the pronator teres (PT), pronator quadratus (PQ), biceps brachi (BB), brachioradialis (BR), mid deltoid (DT) and the extensor carpi radialis brevis (ECRB) during maximum torque exertions. Repeated measures ANOVA indicated that both direction and forearm angle had a significant effect on the maximum torques ( p<0.05) while elbow angle and the interactions were highly significant ( p<0.001). The results revealed that supination torques were stronger overall with a mean maximum value of 16.2 Nm recorded for the forearm 75% prone. Mean maximum pronation torque was recorded as 13.1 Nm for a neutral forearm with the elbow flexed at 45°. The data also indicated that forearm angle had a greater effect on supination torque than pronation torque. Supination torques were stronger for the mid-range of elbow flexion, but pronation torques increased with increasing elbow extension. The strength profiles for the maximum torque exertions were reflected in the EMG changes in the prime supinators and pronators. In addition, the EMG data expressed as the percentage of Maximum Voluntary Electrical activity (MVE), revealed high muscular activity in the ECRB for both supination (26–43% MVE) and pronation torques (17–55% MVE). The results suggest that the ECRB acts as a stabiliser to the forearm flexors for gripping during pronation torques depending on forearm angle, but acts as a prime mover in wrist extension for supination torques with little effect of elbow and forearm angle. This indicates a direct link between forearm rotations against resistance and high muscular activity in the wrist extensors, thereby increasing stress on the forearm musculo-skeletal system, especially the lateral epicondyle.

Maximum Torque Exertion Capabilities of Korean at Varying Body Postures with Common Hand Tools

A laboratory experiment was conducted to investigate the effects of body posture and of different types of common non-powered hand tools on maximum volitional torque exertion capabilities of Korean, Fifteen males and 15 females were participated in the experiment. Each subject exerted maximum volitional torque in 15 different body postures while using five different common non-powered hand tools. Results of the data analysis showed that, for both males and females, the magnitude of torque exertion is significantly affected by the type of tool and posture. Also the result indicated that females exerted only about 51.5% of torque when compared to that of males. This result is different with the general findings in the field of ergonomics that the muscular strength of female is usually 65% to 75% of male. It suggests that application of same profile of muscular strength of female should be carefully considered in oriental countries since females in this region may possess less physical capability compare to that of western females in terms of percentage muscular strength of males. Profiles of maximum torque capabilities of Koreans are provided.

Glove Size and Material Effects on Task Performance

Two experiments were conducted to measure the effect of glove size and material on task performance. The first experiment tested the glove size and material effects on a maximum torque exertion task while the second experiment tested the glove size and material effect on a small parts assembly task. The results of the first experiment showed that for the maximum exertion task, the glove size had no significant effect while the glove material did have a significant effect. For the assembly task the results indicated that glove size and material combination may be important to performance.