Dextrous hands: human, prosthetic, and robotic

The sensory and motor capacities of the human hand are reviewed in the context of providing a set of performance characteristics against which prosthetic and dextrous robot hands can be evaluated. The sensors involved in processing tactile, thermal, and proprioceptive (force and movement) information are described, together with details on their spatial densities, sensitivity, and resolution. The wealth of data on the human hand's sensory capacities is not matched by an equivalent database on motor performance. Attempts at quantifying manual dexterity have met with formidable technological difficulties due to the conditions under which many highly trained manual skills are performed. Limitations in technology have affected not only the quantifying of human manual performance but also the development of prosthetic and robotic hands. Most prosthetic hands in use at present are simple grasping devices, and imparting a "natural" sense of touch to these hands remains a challenge. Several dextrous robot hands exist as research tools and even though some of these systems can outperform their human counterparts in the motor domain, they are still very limited as sensory processing systems. It is in this latter area that information from studies of human grasping and processing of object information may make the greatest contribution.     

Relationship between hand stability and the 10-Hz physiological tremor during various manual tasks

To quantify an individual's ability to perform manual operations stably, the relationship between hand stability and the 10-Hz physiological tremor was investigated. A total of 35 subjects were assessed when performing force and position control tasks, which were representative of ordinary hand movements. Hand stability was analysed as two components: the fluctuation caused by voluntary control (the control error or inaccuracy when voluntarily maintaining a position or force) and the involuntary oscillatory fluctuation (physiological tremor). The control error was defined by the standard deviation of the low frequency component. The tremor was evaluated based on the power spectrum around 10 Hz. A positive correlation between the control error and the 10-Hz tremor was observed in the finger force control tasks. A correlation between finger tremor and arm tremor also was observed; subjects showing small tremors in the finger tasks also exhibited small tremors when performing the arm tasks. Taken together, the results suggested that the 10-Hz tremor can be used as a benchmark to evaluate an individual's ability to use their hands precisely.

Statement of Relevance: It is important to be able to quantify an individual's ability to perform precise manual operations, such as those required for microsurgery. One important aspect is instability when applying force with a finger. The relationship between hand stability and the 10-Hz physiological tremor was investigated in this study. A correlation was found between control error (or inaccuracy when voluntarily maintaining a position or force) and the 10-Hz tremor in the finger force control tasks and the results suggest that the 10-Hz tremor can be used as a measure to evaluate an individual's ability to use their hands precisely.     

Arm posture and human movement capability

Many workers perform manual assembly tasks or use hand tools while the hands are postured above the shoulders or to the side of the body. Experiments were conducted to study the sensitivity of speed-accuracy movement performance to a wide range of hand locations around the shoulder under various levels of hand loads, ratios of work to rest, and task durations. Subjects performed a spatially constrained stylus-to-hole Fitts reciprocal movement task designed to simulate high-incentive manual assembly operations while providing basic information regarding changes in human move and positioning capabilities. Significant decrements in movement performance occurred when hands were postured above shoulder level. Move and positioning times increased 15.3% and 26.5%, respectively, with elevation of the hand from -15 to 60 deg respective to shoulder level. Posturally based decrements in movement capability were unrelated to differences in subject strength capability found among test postures. The consequences of elevated arm postures on human move and positioning capability are presented along with workplace design and methods recommendations for job designers facing work-height decisions in manual assembly environments.     

Hand usage pattern and upper body discomfort of desktop touchscreen users

A laboratory study was conducted to determine how users of different handedness interact with desktop touchscreen displays and how the hand usage pattern influences their body discomfort development. Twenty-one participants in three different handedness groups conducted simple web-browsing for 30 minutes using a 23″ touchscreen display while their subjective body discomfort, frequency of use of each hand and touch area preference were periodically quantified. Participants reported a gradual increase in body discomfort during web-browsing, and the increments in body discomfort varied between handedness groups for some body parts. Results also show that right-handed participants had stronger laterality than the left-handed, and ambidextrous participants used both hands more evenly than other participants, suggesting associations between the hand usage pattern and body discomfort development. Findings of the current study suggest that body discomfort of desktop touchscreen display users could be moderated by user-interface improvements and user training.

Practitioner Summary: Body discomfort development of desktop touchscreen users may be influenced by their hand usage pattern. Findings of this laboratory study suggest that user discomfort may be moderated by placing menu items in the lower area within the display or training users to alternate hands when conducting touch gestures.     

A survey of hand anthropometry of female rural farm workers in Ibadan,Western Nigeria

An anthropometric survey measuring 18 dimensions of the right hand in 37 female rural farm workers living in Ibadan, western Nigeria was conducted. The means, standard deviations and percentile values are reported for these. The means of the collected data are compared with those for females from the UK, from Hong Kong and from America, using data from other published studies. The results suggest that the Nigerian female hand is wider and thicker, but shorter than that of their foreign counterparts. Such differences have implications for design and evaluation of hand tools for the Nigerian female population.     

A survey of hand anthropometry of female rural farm workers in Ibadan, western Nigeria

An anthropometric survey measuring 18 dimensions of the right hand in 37 female rural farm workers living in Ibadan, western Nigeria was conducted. The means, standard deviations and percentile values are reported for these. The means of the collected data are compared with those for females from the UK, from Hong Kong and from America, using data from other published studies. The results suggest that the Nigerian female hand is wider and thicker, but shorter than that of their foreign counterparts. Such differences have implications for design and evaluation of hand tools for the Nigerian female population.     

A Survey of Hand Anthropometry and Biomechanical Measurements of Dentistry Students in Turkey

The objectives of this study were 1) to determine various hand dimensions and biomechanics measurements for Turkish dentistry students, 2) to evaluate the differences between males and females and between the right and left hand, and 3) to compare these data with similar data for other populations (Thai, Indian, Malaysian, British, Jordanian, Nigerian, Mexican, Bangladesh, and Vietnamese). The present study was undertaken to generate hand anthropometric and biomechanics data of 92 male and 73 female students studying at dentistry faculty. Sixty‐seven anthropometric and 26 biomechanics measurements were taken in both hands. The means, standard deviations, and percentile values were tabulated and compared with other populations. The results suggest that the Turkish female fingers are thinner than those of other females except Indians, and that the Turkish male fingers are wider than those of the other males. Furthermore, the results also suggest that the Turkish female strength in handgripping is greater than that of other females except British females, and the Turkish male handgrip strength is greater than that of other males except Americans. This study provides insights about Turkish hand dimensions and biomechanics; it can be a basis for future studies and the design of dental tools meant for the Turkish market. © 2012 Wiley Periodicals, Inc.     

A timeline for hand function following exposure to 2 °C water

In some regions of the North Atlantic Ocean water temperatures are close to 0 °C for half of the year. Individuals who work in this extremely cold water environment will experience hand temperatures that are associated with reduced hand function (e.g. < 8 °C). Despite this reality there is a paucity of research that indicates how long individuals can work in extremely cold waters before their hand temperature drops below the critical thresholds for hand function. The purpose of this study was to investigate the timeline for hand function following exposure to 2 °C water. Participants immersed their hands in 2 °C water and then fine manual dexterity and tactile sensitivity were assessed every 30 s until the index finger temperature dropped below the critical temperature threshold. The results showed that the initial impairment in tactile sensitivity and fine manual dexterity occurred very quickly (90 s of exposure) and the critical temperature threshold was passed at approximately 120 s. These findings demonstrate that hand function will start to deteriorate in less than 2 min during exposure to extremely cold water and therefore the time window for safe and effective use of the hands in cold water is extremely short. Knowledge concerning the timeline for hand function following cold water exposure is relevant to industry because it can inform occupational time management practices, be used as a criterion for assessing occupational manual performance during training, and be used as a guide to modify behaviours and task requirements for cold water work.     

Association between spinal loads and the psychophysical determination of maximum acceptable force during pushing tasks

The objective of this study was to investigate potential associations between an individual's psychophysical maximum acceptable force (MAF) during pushing tasks and biomechanical tissue loads within the lumbar spine. Ten subjects (eight males, two females) pushed a cart with an unknown weight at one push every two minute for a distance of 3.9 m. Two independent variables were investigated, cart control and handle orientation while evaluating their association with the MAF. Dependent variables of hand force and tissue loads for each MAF determination and preceding push trial were assessed using a validated, electromyography-assisted biomechanical model that calculated spinal load distribution throughout the lumbar spine. Results showed no association between spinal loads and the MAF. Only hand forces were associated with the MAF. Therefore, MAFs may be dependent upon tactile sensations from the hands, not the loads on the spine and thus may be unrelated to risk of low back injury.

Practitioner Summary: Pushing tasks have become common in manual materials handling (MMH) and these tasks impose different tissue loads compared to lifting tasks. Industry has commonly used the psychophysical tables for job assent and decision of MMH tasks. However, due to the biomechanical complexity of pushing tasks, psychophysics may be misinterpreting risk.     

Tracking ability in subjects symptomatic of cumulative trauma disorder: does it relate to disability?

Symptoms of upper extremity cumulative trauma disorders (CTDs) often include weakness, discomfort, pain, numbness and stiffness, which are generally assessed clinically by using static tests or isolated movements. Little is known about the dynamic, functional ability of the upper extremity in CTD, yet, more than impairment, performance variables may relate to disability. The objectives of this study were to determine whether a manual tracking task was sensitive to the presence of symptoms associated with CTD and whether tracking performance related to disability. Forty-five volunteers who had frequently experienced one or more symptoms consistent with upper extremity CTD for at least 1 year and 22 control subjects performed the manual tracking task. Using a hand-held stylus over a digitizing tablet, subjects tracked a target that moved pseudo-randomly and was displayed on a computer screen. The root mean square error of the linear difference between target and stylus positions provided a measure of overall performance accuracy. Quadrant specific performance was also calculated to determine whether the location of the target (hence hand and wrist position) influenced performance. Additionally, the symptomatic group completed the Disability of the Arm, Shoulder and Hand (DASH) questionnaire reflecting physical disability level. Performance accuracy was poorer in symptomatic subjects than controls (p<0.001) and was influenced by target location (p<0.0001). The overall performance was associated with physical disability (r = 0.54). The findings suggest that tracking performance is sensitive to the presence of CTD symptoms and related to disability level. Further validation is required to determine whether the performance measure is sensitive to disease progression or intervention-induced changes.     

The principal features of maximal exertion in the sagittal plane

The postural stability diagram (PSD) is a plot of the vertical component of a manual force against the horizontal component. It may be used to assess the interactions of manual strength, frictional limitations at the feet and the forces demanded by a task. This paper presents data on human strength in the form of postural stability diagrams.

The observed features of maximal exertion, in all directions in the sagittal plane, are presented and analysed. Measurements were made on men and women using 12 different combinations of hand and foot placement.

Sex, the position of the hands and feet, and the direction of exertion were important determinants of strength. Evidence is presented to show that, in a minority of conditions, strength is limited by the distribution of body weight and the extent of the foot base. Centres of foot pressure were rarely located at the posterior limits of a subject's anatomical foot base. In certain combinations of hand and foot placement, pronounced peak forces were observed for a narrow range of directions of exertion in the LIFT/PUSH quadrant.     

Evaluation of two wheelchair hand rim models: contact pressure distribution in straight line and curve trajectories

Abstract

Manual wheelchairs are essential for people with disabilities or limited mobility. However, manual propulsion causes biomechanical loads, including contact pressures on the palms of the hands. The hand rim design has received little attention over time, remaining almost unchanged since its creation. This study investigated how two different designs of such devices – one standard and another with a contoured design – influence the contact pressure on the surface of the hands. The procedures included a figure-of-eight shape propulsion task on a regular floor, using both models on a wheelchair. A pressure-mapping system coupled with a pair of fabric gloves recorded the data. The results show that the contoured hand rim provides lower pressure in most of the analysed regions. Considering that manual propulsion is performed during a considerable part of the day as a routine activity, improving the hand rim interface may benefit the user’s comfort and safety during wheelchair use.

Practitioner summary: The design of the hand rim used in wheelchair propulsion influences the contact pressure on the hands. Conventional round tube rims tend to concentrate high levels of pressure on the distal phalanges and metacarpal regions. A contoured design generally provides better stability and promotes the distribution of pressure.

Abbreviations: AT: assistive technology; kPa: kilopascal     

Hand dominance and hand use behaviour reported in a survey of 2437 Koreans

Most tools, utensils, office equipment, home appliances, clothes, medical instruments, sporting goods, weapons and public facilities are made for people who are right-handed. Many left-handed people have to endure a certain amount of inconvenience or difficulty in carrying out daily activities in such an environment. In this study, 2437 Korean male and female participants were randomly selected to collect a variety of data on hand dominance and hand preference when handling diverse products and facilities. Their responses in a questionnaire survey revealed that 5.8% were left-handed and 7.9% were ambidextrous. The younger participants who were from teens to 39 years reported higher percentages of left-handedness than those over 40 years, with those in their thirties reporting the highest proportion of left-handedness (7.3–7.6%) for both men and women. A slightly higher percentage of the male participants (5.9%) said that they were left-handed than did the female participants (5.6%). However, the percentage who were ambidextrous varied with age group, but overall there was a higher percentage of women (8.3%) than of men (7.6%). The analysis of hand use behaviour revealed that the right-handed and ambidextrous people had a tendency to use their right hands more for actions that required accuracy than those that required force. The left-handed people had a strong tendency to use their left hands more often when making a forceful action than for one that required accuracy. Derived from these results, the conclusion is that, depending on their hand dominance, people seem to use their hands differently when they handle objects or use facilities, which should be considered in the design of hand-controlled devices. Depending on which hand is the dominant one, people seem to use their hands differently when they handle objects or use facilities. The left-handed tend to use their left hands more with force-required motions than with accuracy-required motions, while ambidextrous and right-handed people use their right hands more with accuracy-required motions than with force-required motions. Designers of products and facilities will find the results of this study useful for developing hand-controlled devices and systems.     

Measuring consistency of web page design and its effects on performance and satisfaction

Symptoms of upper extremity cumulative trauma disorders (CTDs) often include weakness, discomfort, pain, numbness and stiffness, which are generally assessed clinically by using static tests or isolated movements. Little is known about the dynamic, functional ability of the upper extremity in CTD, yet, more than impairment, performance variables may relate to disability. The objectives of this study were to determine whether a manual tracking task was sensitive to the presence of symptoms associated with CTD and whether tracking performance related to disability. Forty-five volunteers who had frequently experienced one or more symptoms consistent with upper extremity CTD for at least 1 year and 22 control subjects performed the manual tracking task. Using a hand-held stylus over a digitizing tablet, subjects tracked a target that moved pseudo-randomly and was displayed on a computer screen. The root mean square error of the linear difference between target and stylus positions provided a measure of overall performance accuracy. Quadrant specific performance was also calculated to determine whether the location of the target (hence hand and wrist position) influenced performance. Additionally, the symptomatic group completed the Disability of the Arm, Shoulder and Hand (DASH) questionnaire reflecting physical disability level. Performance accuracy was poorer in symptomatic subjects than controls (p<0.001) and was influenced by target location (p<0.0001). The overall performance was associated with physical disability (r = 0.54). The findings suggest that tracking performance is sensitive to the presence of CTD symptoms and related to disability level. Further validation is required to determine whether the performance measure is sensitive to disease progression or intervention-induced changes.     

Evaluation of effects of anti-vibration gloves on manual dexterity

Abstract

The purpose of this study was to evaluate the effects of anti-vibration gloves on manual dexterity and to explore factors affecting the manual dexterity. The manual dexterity of ten different gloves was investigated with 15 adult male subjects via performing two different dexterity tests, namely ASTM F2010 standard test and Two-Hand Turning and Placing Minnesota test. Two-factor repeated-measures analysis of variance was conducted to evaluate the main effects of glove type, test method and their interaction effect on manual dexterity. Results suggested that glove type yielded significant effect on manual dexterity (p?<?.001), while no significant difference was observed between test methods (p?=?.112). The interaction effect of glove type and test method also revealed a significant difference (p?=?.009). The manual dexterity decreased nearly linearly with increase in the glove thickness, which further showed a moderately significant difference on the number of drops during the tests.

Practitioner Summary: Anti-vibration gloves may adversely affect manual dexterity and work precision, which may discourage their usage. This article presented a study of manual dexterity performance of anti-vibration gloves and the design factors affecting the manual dexterity. The results were discussed in view of a design guidance for improved hand dexterity, which would encourage the use of anti-vibration gloves in the workplace.     

A study for determining the optimum diameter of chopsticks

Chopsticks and knives and forks are fundamental utensils used by Asian and Western-oriented people, respectively, in serving food. Although ergonomics studies on the knife handle have been performed, chopsticks, used by at least 1.5 billion people daily, have seldom been examined by ergonomists. This lack of interest may be attributed to the fact that Occidentals, who tend to give more emphasis on empirical research, do not use chopsticks. Nevertheless, from an ergonomics perspective, chopsticks deserve a systematic study in lieu of the large number of users. This study involves 32 male and female university students who served as the control group. According to these results, the diameter of chopsticks significantly influences `food-pinching' efficiency. Also, the smaller and larger diameters of chopsticks are inferior to those of a medium diameter. In addition, chopsticks with 6 mm diameter are optimum for `food-pinching' efficiency. Subjective preference ranking is also used to cross-validate the above performance measures, with these results confirming the effectiveness of `food-pinching' efficiency measure.Relevance to industryHand tools considered as extensions of human hands, are very important in industry. Chopsticks are one of the simplest and most convenient and efficient hand tools. The result of this study reveals that both the diameter of chopsticks and different sizes of food heavily influenced the `food-pinching' efficiency. Thus, the designers must consider human factors, and ergonomic aspects of the user–tool interface when designing a new hand tool.     

Users' intrinsic and extrinsic drivers to use a web-based educational environment

The aim of this study is to gain further insight into the drivers that help in the design of desirable web-based educational environments. The specific objectives are twofold: (1) to explore the main drivers of learners' responses, in terms of their ongoing patronage and recommendation of learning tools to others; and (2) to clarify the significance of exploratory behaviour as a moderator that contributes to users' e-loyalty. Drawing on the fields of design, non-economic satisfaction, and e-loyalty, this quasi-experimental study hinges on analysis of survey data to assess college students' online usage experiences. Aesthetics and usefulness have significant effects on perceptions of the extent to which students' goals and desires are met, and, by extension, extrinsic outcomes and e-loyalty. Making an educational tool simpler to use, however, has hardly any effect on users' perceptions of its usefulness. Furthermore, when usage is more instrumental, expressive issues weaken users' satisfaction-based processes. Our research also indicates that individual differences based on variety-seeking personality traits play an important role in users' decisions to accept e-learning tools. This article may therefore act as a springboard for further empirical research, as well as clarifying and examining the nature of e-learning tools' enduring usage amongst college students.     

Ergonomic design and evaluation of new surgical scissors

The purpose of this study is to design a new surgical scissors handle and determine its effectiveness with various usability indices. A new scissors handle was designed that retains the professional grip but has the shapes of the eye rings modified to fit the thumb and ring finger and finger rests for the index and little finger. The newly designed scissors and traditional scissors were compared by electromyography, subjective evaluation and task performance in experiments using cutting and peeling tasks. The newly designed scissors reduced muscle load in both hand during cutting by the closing action, and reduced the muscle load in the left hand during peeling by the opening action through active use of the right hand. In evaluation by surgeons, task performance improved in addition to the decrease in muscle load. The newly designed scissors used in this study demonstrated high usability.

Practitioner Summary: A new scissors handle was designed that has the eye rings modified to fit the thumb and ring finger. The newly designed scissors reduced muscle load and enabled active use of the right hand. In evaluation by surgeons, task performance improved in addition to the decrease in muscle load.     

PHOEBE: an automation framework for the effective usage of diagnosis tools in the performance testing of clustered systems

The identification of performance issues and the diagnosis of their root causes are time‐consuming and complex tasks, especially in clustered environments. To simplify these tasks, researchers have been developing tools with built‐in expertise for practitioners. However, various limitations exist in these tools that prevent their efficient usage in the performance testing of clusters (e.g. the need of manually analysing huge volumes of distributed results). In a previous work, we introduced a policy‐based adaptive framework (PHOEBE) that automates the usage of diagnosis tools in the performance testing of clustered systems, in order to improve a tester's productivity, by decreasing the effort and expertise needed to effectively use such tools. This paper extends that work by broadening the set of policies available in PHOEBE, as well as by performing a comprehensive assessment of PHOEBE in terms of its benefits, costs and generality (with respect to the used diagnosis tool). The performed evaluation involved a set of experiments in assessing the different trade‐offs commonly experienced by a tester when using a performance diagnosis tool, as well as the time savings that PHOEBE can bring to the performance testing and analysis processes. Our results have shown that PHOEBE can drastically reduce the effort required by a tester to do performance testing and analysis in a cluster. PHOEBE also exhibited consistent behaviour (i.e. similar time‐savings and resource utilisations), when applied to a set of commonly used diagnosis tools, demonstrating its generality. Finally, PHOEBE proved to be capable of simplifying the configuration of a diagnosis tool. This was achieved by addressing the identified trade‐offs without the need for manual intervention from the tester. Copyright © 2017 John Wiley & Sons, Ltd.