Analysis Of Anthropometric Data For Design And Development Of Computer Workstation

Transcription

1 Analysis Of Anthropometric Data For Design And Development Of Computer Workstation Pratima.S.Joshi, Dr.Shashidhar.S.Kalashetty, Dr.S.M.Qutubuddin Dept. of Industrial & Production, P.D.A.College of Engineering Kalaburagi,Karnataka In this work carried for to study the Computer Workstation to establish the current practices with reference to the use of Anthropometry. It also leads to the Re-design of the workstation,in order to improve Productivity, Health safety and comfort of the operators in the Workstation. Optimizing the Anthropometric data for computer workstation design can be a complex task because of the number of design parameters that must be put into consideration. This Problem has recently been made much easier to solve as a result of the development of some design principles like design for extreme, design for average sizes and design for adjustable range. Because of the nature of the selected workstations, design for adjustable range principle is used. Anthropometric dimensions of the operators were used to design chair and table which can accommodate 5%-95% of the operators. The workstations were examined and analyzed under the combination of different anthropometric parameters. The analysis of the results indicates some deficiencies in the design of the workstation based on the design parameters and standard values from the literatures. Based on the analysis of these results the operators and their clients may likely be exposed to fatigue, workstress and other related diseases. For demonstration of the application of the adjustable range design approach, a computer workstation has been redesigned as a real case. It is hoped that the new design will contribute to improvement in Productivity, Health safety and Comfort of the operators in the workstation. In the proposed adjustable range design approach, suggested to every organization operating with workstation. Before any decision took on making or buying equipments and tools, Industrial Engineers are to be consulted depending on the design factor, for proper guidance. Anthropometric dimensions of the workers should also be considered for any workstation that requires chair and table design. Many works were done on anthropometry as a design factor for computer operator workstation were done on simple system, where design for extreme and average are always resonable. The work was also done on multiple complex systems like computer workstation in the departments and laboratories where many people of different sitting positions of different heights were considered. In view of these, design for adjustable range is most economical and ergonomic appropriate. NCADOMS-2016 Special Issue 1 Page 319

2 Keywords: Anthropometry, Computer workstation, Design parameters. Introduction: The word ergonomic was derived from the Greek word, ergon, meaning work, and nomos, meaning law or usage. The literature suggests that the word Ergonomics was independently used in 1949 by a British Scientist, K.R.H. Murrell (Kroemer, 2003).During the past decade, research in ergonomics had led to heightened interest in the technology of work and furniture design based on biomechanics of the human body. These researches were focused on the development of new principles for the design of chairs and desks in the workplace (Parcells et al, 1999).Bridger (1995) and Chou and Hsiao (2005) believed anthropometry is a research area in ergonomics dealing with the measurement of human body dimensions and certain physical characteristics. Anthropometric data can be used in ergonomics to specify the physical dimensions of workspaces, workstations, and equipment as well as applied to product design.presently, the importance of safety and ergonomic in the design and manufacture of consumer products had grown significantly. The latest technology had increased the option to broaden the ergonomic and safety features of certain consumer products. However, it will also pose new risks which are more complicated to manage. Therefore, it is important for the product designer and manufacturer to use anthropometric data and ergonomic knowledge in making decision during designing of machines, equipment, products and systems (Mattila, 1996). Visual discomfort and musculoskeletal discomfort, particularly in the neck and shoulders, are occupational health concerns for people who work with computers (Bergqvist and Knave, 1994; Bergqvist et al, 1995; Hunting et al, 1981). In terms of ergonomics, comfort integrates a sense of wellbeing with health and safety; conversely, discomfort could be related to biomechanical factors involving muscular and skeletal systems (Zhang et al, 1996).Over the last two decades, ergonomics in work environments has gained much attention from researchers; this is because ergonomics had played a very important role in preventing and controlling work-related injuries and illnesses (Piegorsh et al, 2006). According to Wang et al. (1999) anthropometry has been considered as the very basic core of ergonomics in an attempt to resolve the dilemma of fitting people to machines. Computers have almost totally replaced typing machines, and facilitated intensive research activities of various sorts through their screens using keyboard and mouse. Therefore, continuous and NCADOMS-2016 Special Issue 1 Page 320

3 repetitive nature of computer applications, normally involving long hours of work for on the job usage or for leisure, engaging mostly one hand (and about three middle fingers of the right hand in the case of using mouse)[1] in almost hanging situation, and sewing the eyes to shiny jungle of shambles and hieroglyphs on the improperly proportioned screens, etc are bound to inflict multitude of very complicated injuries, mostly of persisting kind, to the user. Carpal tunnel syndrome [2-4], eyestrains [5-7], and musculoskeletal complaints [8-11] are known major problems ensuing from the repetitive use of computers involving several components. In the opinion of the present authors, by the increased and flooding use of computers, as time goes by, will aggravate injuries and human force will greatly suffer to the point of permanent disability in its major organs, unless a critical remedying action be taken by introducing engineering design principles and practice in the corresponding educational and industrial establishments. That is, the hardware and software should be designed by professionals who have passed courses on total engineering design at relevant institutions. As far as the present authors are aware, such courses are non-existing in computer and electronics engineering and science courses in even major universities or colleges around the world. In order to give the matter a heavier degree of due importance, advice of lawsuits to computer-use-inflicted injuries are suggested. Although, not a frequent computer user as such, but one or more hours of continuous sessions at the desk is enough to give eye fatigue and dryness, musculoskeletal fatigue, pain on my hand and wrist, dry fingers, back and spine hump, and headache. Moreover, as a trained eye for beauty of shapes and color and characters matching, looking at aesthetically non-proportioned components, specially the screen gives me mental unease, recovery from which need some extra effort. We therefore feel the gravity of bad design effects on the user to the bone. Although the present authors do not claim to have succeeded in developing a completely effective desk design, because we did not fully follow engineering design principles, but we hereby propose our concerned points in the form of a geometry which may arise some further thoughts to assist in the future developments. Applying practical interviews, and remembering the tilt angle that draftspersons used to provide for themselves of their drawing boards, we have proposed a totally different angle for the screen in respect to the desk surface, and a stepped desk, which can include useful components that lack in most present designs. There are good directives to the frequent user in the literature who can benefit from them as injury preventive measures. All the same, good design certainly eliminates or, at least can alleviate the use inflicted problems to a great extent. New conceptual look and redesign of certain items, NCADOMS-2016 Special Issue 1 Page 321

4 such the seat, mouse, keyboard, etc. using advantages of developments in the science of mechatronics is a vital necessity before too late. Fig. 1 Continuous step desk design Figure 2(a): Computer workstation Figure 2(b): Computer workstations in laboratories NCADOMS-2016 Special Issue 1 Page 322

5 Desk design In order to alleviate hand, wrist, arm and back strains, we have been approved by the interviewees to locate the mouse and keyboard at a lower height than the desk s main surface (Fig. 1). This lower desk surface is considered continuous lengthwise, in our design, to provide enough free space for some of the periphery to be moved about. Considering the anthropometrics standards our proposed design also facilitates serial arrangements of desks (Fig. 2), which are suitable for most of the work environments as generally practiced now. The height of the desk step provides just enough room for some compartmentalization purposes (Fig. 1). These compartments, though limited in size, facilitate design of lockers for the user, space for writing paper, CDs, etc. The best location of the tower for right-handed users, which is an established practice now, is underneath the desk at the right hand. PC screen issues Due to the most PC terminals being notoriously too voluminous and bulky, and the trend of development seemingly is toward monitors of the LCD type, we have concentrated our study on the latter type of designs. Most of the on-the-job and frequent users tend to adjust the screen angle of their bulky terminals to about 75 degrees plus to the desk, due to the positional restrictions imposed by their stand designs. Our department secretaries hard at work in front of the screen of their voluminous PCs interviewed, despite their tendencies to first defend their habit of using the aforementioned large angle, gradually came to agree with the suggestion of degrees screen angle to the desk giving their sight, head, and back a more comfortable position. According to the interviews, position of the reference material was preferred aligned with the screen angle. The screen center at their 75 degrees plus terminal orientation, they were more at ease, not at the center portion, but at a slightly lower section of the proposed degrees angle screen. At this position screen top is viewed even more comfortably. In all the interviews, the approximately perpendicular viewing distance to the screen was about 50 cm. Figure (3) shows a proposed rough angular position of the bulky and LCD kind of terminals and corresponding viewing angles in respect to horizon. Dimensions given by the manufactures of LCD 15 and 17 inch terminals and the provision of some of them for adjustability of tilt angle, we find that the lower surface of the proposed desk is approximately a favorable base for these kinds of terminals (Fig. 4). When not in use terminals can be locked in the left hand compartment underneath the desk (Fig. 1). All wiring would be hidden from the scene, which is a measure to remedy the wires syndrome. NCADOMS-2016 Special Issue 1 Page 323

6 Fig 3: Proposed screen position Figure 4: Proposed desk design Ergonomic Chair Design Computer chair is the most important part of computer work station. The chair has to fit user and suit the tasks that is been done. One style of chair may not suit every worker. For example, the average chair is designed in some instances to fit the average male and may not suit other users. A chair is only ergonomic if it can be adjusted to fit the user. The following features are part of a good computer chair: I. 5 Caster Swivel base II. Arm rest III. Height adjustable seat pan IV. Tilt adjustable back rest V. Ability to make adjustments easily while sitting in the chair VI. Firm padding covered with non slip, breathable fabric The special features include: Seat Pan: the seat pan should be the type with rounded front edge, wide and deep enough to fit the user Comfort ability, and with adjustable in angle. Back rest: the back rest contains padding for the low back area that is curved to fit the shape of the back of the user. It must be of adjustable height and angle with locking mechanism, wide and high enough to fit the back of the user. It should be noted that, when seated, the back tends to lose some of its natural curvature. An effective lumber support of a chair is designed to help maintain the natural curvature of the spine when sitting. It is important to provide appropriate support for the spine so that there is no discomfort or pain. NCADOMS-2016 Special Issue 1 Page 324

7 Figure 5: Chair with Lumber support The arm rest should be designed in such a way to eliminate interference with the work surface and will provide height and width adjustability. The chair height is designed in a way that allows the feet of the user to rest comfortably on the floor and even pressure is felt from the seat pan both on the back of the seat (buttock region) and under the thighs (near the knees). To carter for the chair range of motion, the seat and back rest should allow for varied seated postures. This can be accomplished by allowing a rearward tilt on the back. A minimum of 10 0 rearward tilt (between 90 0 and ) is preferable [13]. The only guidelines for seat tilt measurement is to ensure the torso-to thigh angle is not less than 90 0, and that the seat angle is between rearward tilt. Figurer 6: Measurements for Ergonomic Chair NCADOMS-2016 Special Issue 1 Page 325

8 Table 1 Specific Chair design guideline Measurements (all dimensions in cm) Measurement Guideline (cm) All Steel Sum Chair (cm) Seat Height A Popliteal Height + Shoe allowance Seat Depth B Buttock- Popliteal No deeper than length- Clearance allowance (fixed), 16.9 include (adjustable) Seat Width C Hip breadth, No less than Sitting + Clothing allowance Back rest D None At least Height Back rest E Waist breadth Width Back rest Lumber Arm rest Height F None Most prominent point from seat pan, in and out1 G Elbow rest Height Infinite through height of back Arm rest Length Distance between Arm rest H None None 10.5 I Hip breath, Sitting + Clothing allowance 18 (fixed) 18 (adjustable) Methodology Designing a computer workstation requires more than just putting a computer on a standard office desk and providing an adjustable chair. The design of computer workstation includes the work envelope (range of movement), work surfaces (such as desks, tables, etc.), and seats as well as the design and location of computer screen, keyboard, and mouse. The design of the computer workstation should clearly be rooted in the use of anthropometric data. In this study, we have specifically developed a questionnaire based on the occupational Safety and Health (NIOSH) Symptoms Survey and the Nordic Musculoskeletal Questionnaire to gather data on upper limb symptoms. The questionnaire covers the usual background information (age, sex, occupational history), the present job position, the nature of symptoms (ache, numbness, tingling, burning, pain, weakness, cramping, swelling, loss of color, stiffness), trouble and discomfort areas (neck, shoulders, elbows, wrists/hands, upper back, lower back, NCADOMS-2016 Special Issue 1 Page 326

9 hips/thighs/buttocks, knees, ankles/feet), the notification and duration of the problems, plus medical history asking about any medical treatment for the problem. Figure7: Seated body dimensions computer user Anthropometric Dimensions for Desk and Chair Design The data was collected under the following body dimensions: 1. Sitting Height: with the subject sitting erect, distance from sit to vertex of the hair pressed down. 2. Shoulder Width: the distance from the edge of one shoulder to the next in the sitting position. 3. Hip Width (Seat Width): distance between the outer part of the right and left hips in a seated position. 4. Elbow Rest Height (Arm rest Height): with subject sitting erect, distance from seat to bottom of elbow. 5. Knee Height (Seat Height): distance from the knee to the sole in sitting position. 6. Buttock-Knee Length (Seat Depth): distance from the back of the buttocks to the foremost point of the patellar. NCADOMS-2016 Special Issue 1 Page 327

10 7. Thigh Clearance: with subject sitting, distance between the right and left thigh. 8. Eye Height: with subject sitting erect, distance from the seat to the eye level. 9. Lower Arm-Hand Length (Arm rest Length): in sitting position, distance from the elbow to the mid finger tip. 10. Back rest Lumber: distance between the lower back rest curvature to the tip of the seat pan. 11. Back rest Height: distance between the topmost edge and bottom edge of the back rest. 12. Back rest Width: distance between the top most right side to the top most left side of the back rest. 13. Distance between the Arms rests: in sitting position, hip width with clothing allowance. Selection of statistic and Error Rate The primary statistical procedure used was one - way analysis of variance (ANOVA). The general linear model in SPSS 16.0 was used for analyzing data. The SPSS 16.0 Software program includes an additional column labeled sig. for significance. Several assumptions were made for the one -way ANOVA statistical procedures in the study. (a) Samples were randomly collected from the population and randomly assigned to group (b) There was homogeneity of variance (c) the error rate selected was 0.05 type 1 Figure 8: The computer workstations Desk & PC dimensions in AutoCAD As shown in above figure it explains about the computer workstation dimensions in AutoCAD. The proper ergonomic positioning with the body positioned using a static seated posture with the body positioned using the rule in which the back-thigh angle was 90 degrees, the thighleg angle 90 degrees, and the leg-foot angle was 90 degrees. Movement, such as leaving your workstation at least once an hour for 5-10 minutes, needed to be performed since frequent position changes help prevent work-related musculoskeletal disorders. Today, good ergonomics NCADOMS-2016 Special Issue 1 Page 328

11 practice dictates that some computer workers should work in a variety of postures to include sitting. Some of the awkward postures as shown in below figures: Figure 9(a): Wrist pain Figure 9(b): Height of footrest Figure 9 (c): Unreached of the hand (can t reach due to collapse with wall) NCADOMS-2016 Special Issue 1 Page 329

12 Figure 9(d): The touching of knees to the keyboard platform Figure 9(e): No foot rest NCADOMS-2016 Special Issue 1 Page 330

13 Figure 9(f): No armrest WORKING CONDITIONS The workstation is designed or arranged for doing VDT, video display terminal, tasks so it allows the employee s,students,lecturers,professors... Yes No A. Head and neck are about upright (not bent down/back). B. Head, neck and trunk face forward (not twisted). C. Trunk is about perpendicular to floor (not leaning forward/backward). D. Shoulders and upper arms are about perpendicular to the floor (not stretched Forward) and relaxed (not elevated). E. Upper arms and elbows are close to the body (not extended outward). F. Forearms, wrists, and hands are straight and parallel to the floor (not Pointing up/down). G. Wrists and hands are straight (not bent up/down or sideways toward little Finger). H. Thighs are about parallel to the floor and lower legs are about perpendicular to Floor. I. Feet rest flat on the floor or are supported by a stable footrest. NCADOMS-2016 Special Issue 1 Page 331

14 J. VDT tasks are organized in a way that allows the employee to vary VDT tasks with other work activities, or to take micro-breaks or recovery pauses while at the VDT workstation. 2. SEATING The chair... Yes No 1. Backrest provides support for employee s lower back (lumbar area). 2. Seat width and depth accommodate specific employee (seat pan not too big/small). 3. Seat front does not press against the back of employee s knees and lower legs (seat pan not too long). 4. Seat has cushioning and is rounded/has a waterfall front (no sharp edge). 5. Armrests support both forearms while employee performs VDT tasks and do not interfere with movement. 3.KEYBOARD/INPUT DEVICE The keyboard/input device is designed or arranged for doing VDT tasks so that... Yes No 6. Keyboard/input device platform(s) is stable and large enough to hold keyboard and input device. 7. Input device (mouse or trackball) is located right next to keyboard so it can be operated without reaching. 8. Input device is easy to activate and the shape and size fit the hand of the specific employee (not too big/small). 9. Wrists and hands do not rest on sharp or hard edge. 4.MONITOR The monitor is designed or arranged for VDT tasks so that... Yes No 10. Top line of the screen is at or below eye level so the employee is able to read it without bending head or neck down/back. (For employees with bifocals/trifocals, see next item). 11. Employee with bifocals/trifocals is able to read screen without leaning head, neck or trunk forward/backward. 12. Monitor distance allows employee to read screen without leaning head, neck or trunk forward/backward. 13. Monitor position is directly in front of employee so employee does not have to twist head or neck. NCADOMS-2016 Special Issue 1 Page 332

15 14. No glare (e.g., from windows, lights) is present on the screen that might cause employee to assume an awkward posture to read screen. 5.WORK AREA The work area is designed or arranged for doing VDT tasks so that... Yes No 15. Thighs have clearance space between chair and VDT table/keyboard platform (thighs are not trapped). 16. Legs and feet have clearance space under VDT table so employee is able to get close enough to keyboard/input device. 6.ACCESSORIES Yes No 17. Document holder, if provided, is stable and large enough to hold documents that are used. 18. Document holder, if provided, is placed at about the same height and distance as monitor screen so there is little head movement when employee looks from document to screen. 19. Wrist rest, if provided, is padded and free of sharp and square edges. 20. Wrist rest, if provided, allows employee to keep forearms, wrists and hands straight and parallel to ground when using keyboard/input device. 21. Telephone can be used with head upright (not bent) and shoulders relaxed (not elevated) if employee does VDT tasks at the same time. 7.GENERAL Yes No 22. Workstation and equipment have sufficient adjustability so that the employee is able to be in a safe working posture and to make occasional changes in posture while performing VDT tasks. 23. VDT workstation, equipment and accessories are maintained in serviceable condition and function properly. PASSING SCORE = Yes answer on all working postures items A-J and no more than two No answers on remainder of checklist (items 1-23). Figure 10 shown below explains about the exact computer workstations after the approach of questionnaire. NCADOMS-2016 Special Issue 1 Page 333

16 Figure 10: The exact dimension of computer workstation after questionnaire NCADOMS-2016 Special Issue 1 Page 334

17 The survey exercise was 100% response; all the questionnaires given out were attended to. The majority of the respondents were male, which was 53.33% while the female was 46.67%. The age limit of most of the respondents fell in between years with a percentage of 33.33%, followed by the age limit between 30 40years with a percentage of 30%. Age years limit was 16.67%, 50 years and above was 13.33% and 20% of the respondents were below 20 years. Most of the respondents were 56.67% and 50% in height and weight respectively. The extremely tall respondents of above 1.7meters were 23.33%, followed by those respondents below 1.5 meters with 20% quota. All the respondents were frequent computer user, so 100% computer operators were recorded. In the area of daily working hour of the respondents, the highest number of the respondents uses computer between 3 6hours per day with 50% quota, while the least users were below 3 hours per day. Full working hour respondents fell in between the two, with 26.67%. Almost half of the respondents experiences pain sometimes during and after work with 43.33%. Always and rarely pain experience user were both 20%, 16.67% of the respondents neither experience pain during nor after work. All the respondents preferred sitting position while at work on computer. The respondents experiences pain mostly o the buttock, neck region, spinal cord and shoulder with 18.42%, 17.11%, 15.79% and 13.16% respectively. The thigh and hand muscles both shared the same level of 9.2%, while hips, leg muscles and elbow/forearm were 3.95%. The respondents rarely experience pain on the legs and wrist with 2.63%. None of the respondent experience pain on the finger. In the ergonomic awareness part of the result from the questionnaire, 36.67% of the respondent sometimes experiences fatigue at work, mostly at the neck region with 33.33%, while 26.67% rarely experience fatigue. 20% always experience, and 16.67% never experience at all. The percentage of respondents that also experienced fatigue causing pain on the spinal cord, buttocks, leg muscles and hand muscles were 24.24%, 15.15%, 12.12% and 9.10% respectively. The level of implementation of ergonomic in the existing design was evaluated by the respondents using liker scale. 23% of the respondents agreed to moderately conformed, 30% agreed to slightly conformed, 16.67% consented to strongly conformed, while only 6.67% chose not conformed. The respondents rated their productivity and efficiency on the existing design. 40% consented to be good, 33.33% consented to be average performance, 20% believed to be excellent, and only 6.67% agreed to not conform. NCADOMS-2016 Special Issue 1 Page 335