Yuh-Chuan Shih

Hand/tool interface effects on human torque capacity

Forty student subjects, involving 20 males and 20 females, participated in this study. Four handle shapes (circular, triangular, square and hexagonal), seven handle sizes, (25.4, 31.8, 38.1, 44.5, 50.8, 57.2 and 63.5 mm), and five types of gloves (surgical, single cotton, double cottons, leather and rubber) were tested for their effects on maximum volitional torque exertion (MVTE) for supination. The results indicated that all the main effects were significant (p < 0.001). Female MVTE is about 62% of male. Triangular shape was the most favorable, followed by square, hexagonal and circular shapes despite of the moment arms being in the ratios of 1.155, 1.414, 1 and 1. The gloved MVTEs are generally found to be superior to without gloves, about 10% to 30% increment. A positive correlation between supination MVTE and glove thickness is also found. For handle size effect, the larger the handle size is, the greater the MVTE is. Female has more effective torque exertion than that of male for handle size less than 44.5 mm (1.75″).

The Relationship between Low Back Discomfort Ratings and the NIOSH Lifting Index

An epidemiological study was performed to evaluate the relation between lowback discomfort ratings and use of the revised NIOSH lifting guide to assess the risk of manual material handling (MMH) tasks. We surveyed 97 MMH workers on site in 15 factories and designed a questionnaire to systematically collect jobrelated information. Approximately 90% of the workers had suffered various degrees of lower back discomfort, and 80% had sought medical treatment. The survey showed that 42 of the 97 jobs analyzed had a recommended weight limit of 0, which was attributed to either a horizontal distance or a lifting frequency that exceeded the bounds of the NIOSH lifting index. Apparently, the limits for horizontal distance and maximum allowable frequency are too stringent to accommodate many existing MMH jobs. For the remaining 55 jobs, the significant positive correlation obtained between the lifting index and the severity of low-back discomfort suggests that the lifting index is reliable in assessing the potential risk of low-back injury in MMH. These findings provide useful information on the application of the NIOSH lifting guide to the assessment of lowback pain.

The influence of gloves during maximum volitional torque exertion of supination

This study focuses on the influence of friction between gloves and handle surface during maximum volitional torque exertion of supination (S-MVTE) and under both friction-controlled and regular friction conditions. Forty student subjects (20 males and 20 females) participated in this study. Five types of gloves (surgical, single cotton, double cotton, leather, and rubber), seven handle sizes (25.4, 31.8, 38.1, 44.5, 50.8, 57.2, and 63.5 mm in diameter) and two handle shapes (cylindrical and hexagonal) were evaluated to determine their combined influences on S-MVTE. The barehanded condition was also included for comparison. The results indicate that all the main effects were significant (P < 0.001). Under friction-controlled conditions (oiled surface handle), the S-MVTEs with gloves were found to be greater than the S-MVTEs of the gloveless, and the thicker the gloves, the greater the S-MVTE. On the other hand, under regular (unoiled) conditions, the S-MVTE was mainly affected by the friction between handle surface and gloves, although the interaction between gloves and handle shape was also a minor influence. A hexagonal handle produced, in all handle diameters, greater S-MVTE than a cylindrical handle. The mean S-MVTE under oiled conditions was about 53% of that of unoiled conditions. The mean S-MVTE of females was about 61% of that of males.

A method for determining the difference threshold of judging weight difference in material handling

Abstract The difference threshold is an important index in psychophysics. A simple and effective method combining the pairwise comparison procedure of AHP (Analytic Hierarchy Process) and the method of constant stimuli is proposed to determine the difference threshold in judging weight difference. The difference thresholds obtained by the proposed approach were 3.87% and 3.96% with the standards weights at 8.2 kg and 20 kg respectively. The results are very close to the findings of carlson, Drury and Webber (1977), as well as Hsia and Drury (1986), which also support the validity of the method. Further, it is interesting to find that wearing gloves has no effect on the difference threshold in judging weight difference. It indicates that humans capability of judging weight difference is not affected when wearing gloves to perform material handling tasks.

Visual Assessment of Camouflaged Targets with Different Background Similarities

The study investigated the effectiveness of different camouflage designs using a computational image quality index. Camouflaged human targets were presented on a natural landscape and the targets were designed to be similar to the landscape background with different levels of background similarity as estimated by the image index. The targets were presented in front of the observer (central 0°) or at different angles in the left (–7°, −14°, −21°) or right (+7°, +14°, +21°) visual fields. The observer had to detect the target using peripheral vision if the target appeared in the left and right visual fields. The camouflage effectiveness was assessed by detection hit rates, detection times, and subjective ratings on detection confidence and task difficulty. The study showed that the psychophysical measures correlated well with the image similarity index, suggesting a potentially more efficient camouflage effectiveness assessment tool if the relationship between the psychophysical results and the index can be quantified in the future.

Psychophysical evaluation of diameter and angle of container handles

Abstract The objectives of this study were, firstly, to apply an efficient approach to assess both optimal handle diameter and angle by subjective perception of heaviness, and secondly, to evaluate one-hand power grip on alternative container handles, using weight discrimination as a criterion. Twelve student subjects (six males and six females) participated in the four experiments designed in this study. Six handle diameters (25.4 mm (1″), 31.8 mm (1.25″), 38.1 mm (1.5″), 44.5 mm (1.75″), 50.8 mm (2″) and 57.2 mm (2.25″)) and six handle angles (radial 20° (R20), radial 10° (R10), neutral (NO), ulnar 10° (U10), ulnar 20° (U20) and ulnar 30° (U30)) were evaluated. The results indicated that the containers were perceived less heavy when handle diameter was about 51 mm (2″) and handle angle was about neutral position. Further, insignificant influences of handle diameter and handle angle on humans ability to discriminate weight difference were found when the standard weight was 8.2 kg. Relevance to industry The results of this study can be applied to handle design in manual material handling tasks.

Evaluating the effects of interface factors on the torque exertion capabilities of operating handwheels

This study intends to assess factors affecting human torque exertion capabilities of operating valve handwheels (maximum volitional torque exertion of wrist radial/ulnar deviation, R/U MVTE). Forty student subjects (20 males and 20 females) participated in this study. In addition to gender and subject factors, gloves (one layer of cotton, two layers of cotton and rubber gloves), operating height (elbow, shoulder and overhead), handwheel size and shape were selected. Barehanded condition was also involved. The results indicate that all the main effects and the first order interactions were significant. The gloved R/U MVTEs were found to be greater than the barehanded R/U MVTE. For operating height, shoulder height gave the greatest R/U MVTE, followed by elbow and overhead heights. The handwheel diameters ranging from 75 to 95 mm for males and 65 to 80 mm for females were found to have the greater R/U shear force. The average R/U MVTE of operating valve handwheel for females was about 63% (3.8/6.05) of that of males.

The effects of weight levels and gloves on the ability to discriminate weight difference

In this study, six different types of gloves commonly used in industry (surgical, cotton, nylon, leather, rubber, and whizard knife hand gloves) were evaluated at four different weight levels (8.2, 3, 1.5 and 0.25 kg). Six males and six females voluntarily took part in this study. The dependent variable was the difference limen (or difference threshold) (abbreviated as DL(%)) of the discriminating weight difference (DWD). A nested-factorial design with the subject nested under gender was employed. The results indicate that the weight level had a negatively significant effect on the DL(%). The mean difference thresholds were 3.49, 5.39, 6.08, and 9.45 for the weight levels at 8.2, 3, 1.5, and 0.25 kg, respectively. The individual difference becomes obvious when the weight level is relatively light (0.25 kg). However, the effects of gender, glove, gender x weight, and weight x glove were found to be insignificant, and there was no significant correlation between the DL(%) and glove characteristics (thickness and weight). Subsequently, four additional weight levels (0.01, 0.5, 1 and 15 kg) were considered, and a psychophysical equation was derived: DL(%) = 34.33 x W(0.238) (R2 = 0.98), where W represents the weight level. These results support the power function. A minimum weight difference with 90% confidence of correct detection was suggested.

Torque levels, subjective discomfort, and muscle activity associated with four commercially available screwdrivers under static and dynamic work conditions.

This study evaluated screwdrivers with different handle designs and blade lengths. 10 men and 10 women voluntarily participated. A repeated-measures experiment design was employed. The three independent factors were sex of user, handle (four types), and blade length (130, 170, and 210 mm). The dependent measures were the maximum supination torque under a static task and the %MVC of EMG responses in biceps brachii and flexor digitorum, and a discomfort rating for the upper extremity under the dynamic task. Analysis showed that the in-line screwdriver with the combined characteristics of large handle diameter (3.8–4.1 cm), smooth rubber covering handle surface, triangular (or circular) shape, and adequate handle length (11 cm) had the greatest supination torque and a smaller discomfort rating than the screwdriver with the pistol-grip handle. Blade length was not significantly related to any dependent measure.

The effect of valve handwheel type, operating plane, and grasping posture on peak torque strength of young men and women.

An experiment was designed to assess the factors affecting the operation of valve handwheels. Forty volunteers (20 men and 20 women) participated in this study. A nested-factorial experimental design was employed. Handwheel type (smooth, curved, or knurled rim), operating plane (sagittal, frontal, or transverse plane), grasping posture (power or precision grasp), and operating direction (clockwise or counterclockwise) were found to have significant effects on the (maximum volitional torque exertion [MVTE)). A power grasp exerted more force than did a precision grasp. A smooth-rim handwheel oriented in the frontal plane resulted in the least MVTE. Counterclockwise torque exertion was significantly greater than clockwise torque exertion, but the difference was not very large. MVTE for women (7.9 Nm) was about 66% of that for men (12.0 Nm).