Environmental constraints on the static exertion of force: PSD analysis in task-design

Abstract

A method of representing the static demands upon forceful exertion of a task, and limitations of performance due to friction, as environmental statements on a chart called the Postural Stability Diagram (PSD), is given. Examples of the technique are drawn from the tasks of handling objects on shelves while standing on a stool, and of supporting a trolley on an incline. When the personal capacity to exert force (the subject of a preceding paper) is-depicted on the same chart as the task-demands, the degree of match between the person and task may be considered by a procedure called PSD analysis. The method is intended for use by task-designers and safety engineers as soon as anthropometric data becomes available.     

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.     

Human strength: measurements of maximum isometric forces in industry

Abstract

Within the framework of an on-going research project, the maximum isometric forces of staff working in production were measured for nine test conditions representative for manual material handling (n = 3600). The technique for the measurement of maximum human forces depending on body posture, the test setup, and the procedures used for data analysis plus the preliminary group results (n = 1245) are described. The results show a marked influence of the initial grip height on the maximum forces achievable for the lifting of a stacking case with both hands. Under comparable grip height and type of grip, small differences between the lifting forces with one or with two hands exist. In comparison to males, females clearly have lower maximum isometric forces than is generally supposed.     

A method for measuring the load imposed on the back of a sitting person

Abstract

A method for calculating the biomechanical load on the spine (at L3) and certain muscles in the back is described. It utilizes a small computer on-line to a force platform and the results are obtainable within a few seconds.

The method, which has been devised to evaluate aspects of industrial seating, deals with vertical forces arising from support of the hands and arms, weight lifting and vertical acceleration as well as trunk movements. It does not deal with horizontally imposed forces. It is shown to be quicker and more accurate than calculations using manual measurements of displacements and can be applied in both the field and the laboratory.     

Grasp stability analysis based on acceleration convex polytopes for multi-fingered robot hands

In this paper, we present the analysis of grasp stability for multi-fingered robot hands that is based on translational and rotational acceleration convex polytopes. The aim of the grasp stability analysis is to find the resistance forces and moments of robot hands that can withstand the external disturbance forces and moments applied on objects. We calculate the resistance forces and moments respectively which are considered the properties of objects and robots. Therefore, the resistance forces and moments depend on the joint driving torque limits, the posture and the mass of robot fingers, the configuration and the mass of objects, the grasp position, the friction coefficients between the object surface and the end-effectors of robot fingers. We produce the critical resistance force and moment which are absolutely stable about external disturbances in all directions, the global resistance force and moment which are whole grasp capability of robot hands, and the weighted resistance forces and moments which can be properly used by controlling two indices according to the importance of robot hands. The effectiveness of this method is verified with simulation examples. Recommended by Editorial Board member Hyoukryeol Choi under the direction of Editor Jae-Bok Song. Myeong Eon Jang received the B.S. and M.S. degrees in Mechanical Engineering from Chonnam National University, Gwangju, Korea in 1987 and 1990, the Ph.D. degree in the Department of Mechatronics Engineering at Chungnam National University, Daejeon, Korea in 2009, respectively. Since 1993, he has been a Researcher in the Agency for Defense Development (ADD), Daejeon, Korea. His research interests include robotics and intelligent control. Jihong Lee received the B.S. degree in Electronics Engineering from Seoul National University, Korea in 1983, and the M.S. and Ph.D. degrees from the Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea, in 1985 and 1991, respectively, all in Electrical and Electronics Engineering. Since 2004, he has been a Professor in the Mechatronics Engineering Department of Chungnam National University, Daejeon, Korea. His research interests include robotics, intelligent control, multi-robot localization and path planning.     

Acclimatization to Severe Dry Heat by Brief Exposures to Humid Heat

Abstract

Maximal static strengths were determined for one-handed exertions in all directions in the fore and aft plane. Data from 12 males and 10 females (mean age 30·7 yrs, standard deviation (SD)=8·9 yrs, n=22) were obtained with handle heights of 1·0 and 1·75 m. Twelve of the subjects also performed two-handed exertions at the same handle heights. The ratio of mean strengths of females to that of males ranged from 0·50 to 0·83 (for absolute forces) and from 0·63 to 1·00 for forces normalized to body weight. The ratios of one-handed to two-handed strengths ranged from 0·64 to 1·04. Two-handed strengths commonly exceeded one-handed strengths at the lower handle height, but showed fewer significant strength differences (p<0·05) according to direction at l·75m. Both female/male and one-handed/two-handed strength ratios were found to be dependent on direction of exertion and handle height. The observed strength dependencies upon number of hands (one or two-handed), direction of exertion, handle height and sex are discussed. The strength data have implications for use in biomechanical models and task analysis.     

Spatial stimulus response compatibility for a horizontal visual display with hand and foot controls

In this study, two experiments were conducted to examine spatial stimulus–response compatibility (SRC) effects for a horizontal visual display with hand and foot controls. In experiment 1, the hand and foot controls were in a hands above and feet below vertical plane, such that the display and controls were orthogonal to each other. In experiment 2, the foot pedals were moved forward and placed directly underneath the front row of signals, resulting in an additional horizontal display and control relationship. The results of experiment 1 revealed a strong orthogonal SRC effect, such that the best performance was for the front signals with hand controls and rear signals with foot pedals, which was not altered with the presence of horizontal location mappings in experiment 2. These findings indicate that the front-hand/rear-foot mapping relationship was quite robust with regard to changes in the relative locations of the hand and foot response devices.

Statement of Relevance: The results of this study provide useful ergonomics recommendations for designing control consoles with visual signals presented in a horizontal plane and control devices operated by hands and feet. They are helpful for improving efficiency and overall system performance in person–machine systems.     

Understanding and Dealing with Common Peer-to-Peer (P2P) Application Security

Abstract

In the early days of the Internet, most computers had a clearly defined role: storage, computation, management, and identity were all responsibilities relegated to servers. This was due primarily to the fact that servers were capable of supporting these functions, and personal computers were capable of little more than running a browser. Additionally, servers were given a static address and name, and maintained a persistent connection to the Internet. In contrast to servers, most Internet-connected personal computers did not have a static identity on the Internet. That is, personal computers did not maintain a regular IP address, name, or persistent presence on the Internet. Based on the unreliable presence of personal computers on the Internet, these machines were incapable of sharing their computing resources to actively participate as a component of a larger system.     

Viewing personal history records: A comparison of tabular format and graphical presentation using LifeLines

Thirty-six participants used a static version of either LifeLines, a graphical interface, or a tabular representation to answer questions about a database of temporal personal history information. Results suggest that overall the LifeLines representation led to much faster response times, primarily for questions which involved interval comparisons and making intercategorical connections. A 'first impression' test showed that LifeLines can reduce some of the biases of the tabular record summary. A post-experimental memory test led to significantly (p< 0.004) higher recall for LifeLines. Finally, simple interaction techniques are proposed to compensate for the problems of the static LifeLines display's ability to deal with precise dates, attribute coding and overlaps.     

The effects of a passive exoskeleton on muscle activity and metabolic cost of energy

ABSTRACT

Nowadays, low back pain has a high incidence during the crowd who work under a long time and repeated stoop condition. Exoskeletons may form a new strategy to reduce the risk of developing low back pain in stressful jobs. A passive exoskeleton device was introduced in this article to apply to the static maintenance of forward bending work, so as to reduce the load of back muscles when wearers work, which plays the role of prevention and subsequent rehabilitation of low back pain. The hypothesis is that these systems would decrease the severity and number of work-related back injuries, while enhancing workers’ safety. Through a preliminary analysis and a substantial number of experiments, we have demonstrated the feasibility of our approach to substantially decrease the forces and muscle activities at the L5/S1 location during bending. In the static holding experiment, we find lower muscle activity (by 35%～61%) and lower metabolic cost of energy (by 22%) when wearing the exoskeleton. The results demonstrate good potential of this passive exoskeleton to reduce muscle activities at the L5/S1 location and metabolic cost of energy.     

Relationship between work constraints and the development of musculoskeletal disorders of the wrist: A prospective study

A 2-year prospective study was conducted on 184 workers about the relationship between the development of musculoskeletal wrist disorders (WD) and the occupational constraint parameters at their job (wrist angles, forces, repetitiveness and angular velocities), taking into account personal and occupational confounding factors. The results demonstrate a greater probability of developing WD for the workers suffering from chronic diseases, from psychological disorders, practising a sport involving the upper limbs and judging their work tiring.All occupational constraint factors are correlated except for the angles. Logistic correlation analyses show that the most significant associations with a greater probability of developing WD are observed for the mean relative EMG value recorded on the finger and hand flexors and the time during which the velocity in flexion–extension is greater than 50°/s. None of the angular parameters shows any association.Relevance to industryThe study shows that the main factor on which to act in order to reduce the risk of WD is clearly the forces exerted by the hand.The objective of the control measures should be to reduce the muscular activity of the finger and hand flexors below 15% of the maximum activity corresponding to the maximum voluntary contraction of the finger flexors.A reduction of these forces appears to be associated with a reduction of the angular velocities of the wrist and of the repetitiveness.     

A Geosat-derived noise spectrum for detecting seamounts in the Arabian Sea

Abstract

Noise power spectral densities (PSDs) have been derived from the analysis often seamount-free Geosat tracks in the Indian seas. The average noise PSD has been fitted by a model function. The model noise PSD has been used in conjunction with a model seamount signature to construct a matched filter for detecting seamounts in the Arabian Sea. Performance of the technique has been verified by successfully detecting the Somali ridge and the Error Seamount which are located in the Arabian Sea. Several uncharted seamounts have also been predicted.     

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     

On-line SPC with consideration of learning curve

This work identifies a link between on-line statistical process control (SPC) and the learning effect for the process standard deviation (PSD) caused by the quality improvement (QI) program. The learning curve (LC) is used to describe and forecast, and the exponentially weighted root mean square control chart is used to monitor the progress in reducing PSD. A modification of the quality control chart (QCC) that considers LC of PSD is proposed. The reduction rate of PSD may be large during the initial stage of the QI program, and influences QCC construction. Simulation is used to compare the shift-detecting ability of the Shewhart- control chart and EWMA- control chart, without- and with- consideration of LC. The EWMA- chart with consideration of LC performs best. In comparison, the Shewhart- chart without LC consideration has almost no shift-detecting ability when the shift magnitude of the process mean is small, leading to rendering quality control ineffective.     

Karamanlidika Digital Library Proposal: Reconstructing the Past of a Specific Diaspora

ABSTRACT

The World Wide Web provides unlimited visibility for the personal documents and cultural artifacts that remain in the hands of families of people belonging to different diasporas. Computer mediated platforms are often the building blocks of their transcendental homelands. This article presents a study aiming to build a model and community around Karamanlides by using digital library technologies. Karamanlides is one of the many interesting communities in need of the creation of a “niche personal/community knowledge environment” as an archetype for similar conceptualizations.     

Automated refactoring to the Strategy design pattern

ContextThe automated identification of code fragments characterized by common design flaws (or “code smells”) that can be handled through refactoring, fosters refactoring activities, especially in large code bases where multiple developers are engaged without a detailed view on the whole system. Automated refactoring to design patterns enables significant contributions to design quality even from developers with little experience on the use of the required patterns.ObjectiveThis work targets the automated identification of refactoring opportunities to the Strategy design pattern and the elimination through polymorphism of respective “code smells” that are related to extensive use of complex conditional statements.MethodAn algorithm is introduced for the automated identification of refactoring opportunities to the Strategy design pattern. Suggested refactorings comprise conditional statements that are characterized by analogies to the Strategy design pattern, in terms of the purpose and selection mode of strategies. Moreover, this work specifies the procedure for refactoring to Strategy the identified conditional statements. For special cases of these statements, a technique is proposed for total replacement of conditional logic with method calls of appropriate concrete Strategy instances. The identification algorithm and the refactoring procedure are implemented and integrated in the JDeodorant Eclipse plug-in. The method is evaluated on a set of Java projects, in terms of quality of the suggested refactorings and run-time efficiency. The relevance of the identified refactoring opportunities is verified by expert software engineers.ResultsThe identification algorithm recalled, from the projects used during evaluation, many of the refactoring candidates that were identified by the expert software engineers. Its execution time on projects of varying size confirmed the run-time efficiency of this method.ConclusionThe proposed method for automated refactoring to Strategy contributes to simplification of conditional statements. Moreover, it enhances system extensibility through the Strategy design pattern.     

Foot deformation during walking: differences between static and dynamic 3D foot morphology in developing feet

The complex functions of feet require a specific composition, which is progressively achieved by developmental processes. This development should take place without being affected by footwear. The aim of this study is to evaluate differences between static and dynamic foot morphology in developing feet. Feet of 2554 participants (6–16 years) were recorded using a new scanner system (DynaScan4D). Each foot was recorded in static half and full weight-bearing and during walking. Several foot measures corresponding to those used in last construction were calculated. The differences were identified by one-way ANOVA and paired Student's t-test. Static and dynamic values of each foot measure must be considered to improve the fit of footwear. In particular, footwear must account for the increase of forefoot width and the decrease of midfoot girth. Furthermore, the toe box should have a more rounded shape. The findings are important for the construction of footwear for developing feet.     

Knee joint moments in work-related situations

Abstract

Circumstantial evidence in the literature points towards a relationship between heavy labour and arthrosis of the knee. The aim of this study was to demonstrate which occupational activities yield the greatest knee moments and thus indicate possible gonarthrosis-inducing occupational hazards. Twelve healthy and uninjured medical students were studied in set occupational situations in a laboratory for gait analysis, using a force plate with video display of force vectors and knee joints (VIFOR). With normal walking as a baseline for moment it was found that activities involving knee flexion, such as lifting objects from one level to the other, climbing stairs and ladders, and jumping down, revealed a significant increase in moment. On the other hand, carrying objects in one or both hands did not yield significant increase in knee moment compared with normal walking. Flexed knee lifting had significantly lower moment than jumping down from a height of 0-5 m on to one or both feet. Three levels of knee moment could thus be identified, i.e., normal walking, flexed knee lifting and jumping down.     

The three-dimensional shapes of underground coal miners’ feet do not match the internal dimensions of their work boots

Mining work boots provide an interface between the foot and the ground, protecting and supporting miners’ feet during lengthy coal mining shifts. Although underground coal miners report the fit of their work boots as reasonable to good, they frequently rate their boots as uncomfortable, suggesting that there is a mismatch between the shape of their feet and their boots. This study aimed to identify whether dimensions derived from the three-dimensional scans of 208 underground coal miners’ feet (age 38.3 ± 9.8 years) differed from the internal dimensions of their work boots. The results revealed underground coal miners wore boots that were substantially longer than their feet, possibly because boots available in their correct length were too narrow. It is recommended boot manufacturers reassess the algorithms used to create boot lasts, focusing on adjusting boot circumference at the instep and heel relative to increases in foot length.

Practitioner Summary: Fit and comfort ratings suggest a mismatch between the shape of underground coal miners’ feet and their boots exists. This study examined whether three-dimensional scans of 208 miners’ feet differed from their boot internal dimensions. Miners wore boots substantially longer than their feet, possibly due to inadequate width.