Ergonomic Challenges in Conventional and Advanced Apparel Manufacturing
Final Report (Phases I through V)
Research Sponsored by:
U.S. Defense Logistics Agency
Michael J. Kelly, Ph.D.,Technical Co-director
Daniel J. Ortiz, Project Director and Technical Co-director
Theodore K. Courtney
Dennis J. Folds, Ph.D.
Jeffery M. Gerth
Georgia Tech Project A-8311
Georgia Institute of Technology
Georgia Tech Research Institute
Environmental Science and Technology Laboratory>
Electronic Systems Laboratory
- Executive Summary 1
- Introduction 2
- Phase I: Ergonomic Survey in the Manufacturing Workplace 3
- Phase II: Low Cost Ergonomic Interventions 7
- Phase III: Explore Higher Technology Manufacturing Technologies 8
- Phase IV: Training Video and Manual 11
- Phase V: Modular Manufacturing Systems 12
- Conclusions and Prospects 13
- References 15
Apparel manufacturing is a labor-intensive, assembly line process requiring significant amounts of repetitive, skilled manipulation. A survey of three typical plants in the southeastern United States identified relatively high frequencies of musculoskeletal discomfort among the sewing operators. Poorly designed and maladjusted workstations contributed to these reported problems. Subsequent research found that ergonomic interventions including redesign and proper adjustment of workstations, use of ergonomically designed seating, and training in low-risk methods and postures substantially reduced these complaints. Other innovations in equipment, job, and organizational design, including adjustable workstations, automation, and modular manufacturing, were also explored. While many of these technologies have potential to improve comfort, safety and efficiency, new ergonomics issues will appear with their introduction. A textbook and videotape to provide manufacturing supervisors instruction in identifying and addressing the most common ergonomic problems in the workplace were developed and are being distributed.
Enclosed in this document is a summary of the five phases or tasks of this endeavor. The appendices contain the detailed reports of Phases I, II, III, and V. Also, a copy of the training handbook and video (Phase IV) is contained in the appendices. Top of the page
The United States apparel manufacturing industry is facing difficult challenges. Apparel manufacturing is a labor-intensive, rather than capital-intensive, endeavor. Because it is possible to start up a factory for a few hundred dollars per employee, it is an ideal industry for developing nations. A ready pool of inexpensive labor in the Pacific Rim and Latin American regions provides strong competition for North American manufacturers. In addition, the industry is experiencing a severe shortage of entry-level sewing workers as the population ages and competition increases for young, relatively unskilled personnel. While some of these challenges might be met by innovations in equipment and manufacturing methods, many existing plants are financially unable to invest in new technology.
A high turnover rate (well over 100% each year in many plants) contributes to escalating costs. Months of on-the-job training are needed by novice operators to learn the complex perceptual motor skills of their trade. On a typical job, novice operators require 12 - 16 weeks of training and practice before their performance reaches established production standards. On especially difficult jobs, as long as 26 weeks may be needed. For most workers, learning curves do not reach asymptote until after one to two years on the job.
Conventional apparel manufacturing is a hand-intensive process as operators rapidly obtain and position parts, guide them through the machine, and dispose of them (Kelly, Ortiz, Folds and Courtney, 1990). As awareness of repetitive motion trauma disorders grows, the industry is experiencing a dramatic increase in reports of upper-extremity injuries and the resulting medical and disability payments. Fines imposed by regulatory agencies for allowing conditions conducive to repetitive motion injuries are expected to add substantially to the already high costs.
A few previous studies have examined ergonomic aspects of the apparel manufacturing industry in the United States and in Europe (e.g., Punnett and Keyserling, 1987; Vihma, Nurminen and Mutanen, 1982). It was desired, however, to broaden the research into an integrated study of ergonomic problems and their potential solutions, covering both conventional and advanced manufacturing, and to disseminate the findings to the industry.
The goals of the research program were to (1) identify and document ergonomic-related problems in the apparel manufacturing workplace, (2) test low cost interventions that would address these problems, (3) identify and explore higher-technology solutions that are beginning to enter the environment, and (4) develop a self-study course in ergonomics specifically designed for apparel manufacturing supervisors. Top of the page
During the first phase of this program, site visits were conducted at three typical apparel manufacturing plants in the southeastern United States. The primary product line for all three plants was trousers. Plant A employed approximately 500 cutting and sewing operators and was considered to be an innovator in the introduction of new technology; Plant B employed approximately 50 operators and would accept new technology after its was thoroughly proven to be of benefit; Plant C employed approximately 120 operators and was considered financially incapable of adopting significant amounts of new technology. These plants provided a representative cross-section of company sizes and opportunities for automation. (Within months after completion of the survey, Plant B ceased operation after over fifty years in business.)
On a preliminary visit to each plant, management, engineers and floor supervisors were interviewed and the plant was toured in order to develop an overall impression of the ergonomic environment and potential problem areas. During these visits, specific target jobs were identified in each plant for extra scrutiny. These were jobs having indications of ergonomic problems including excessive turnover, absenteeism, physical complaints, or unusually long training periods. These jobs were singled out for later video analyses and detailed workstation measurements. Each of the three plants identified between four and six target jobs. Because of differences in product, procedures, and nomenclature between the plants, there was little agreement on the problem jobs.
During a subsequent series of visits, confidential interviews were conducted with 132 volunteer operators representing the target jobs and other jobs in the plants. These interviews covered (1) demographic factors, (2) musculoskeletal discomfort or injuries, (3) characteristics of the work environment, (4) characteristics of the workstation, chair, and job, and (5) training. Environmental measures of illumination, temperature, and noise were taken at sample workstations throughout the three plants. Detailed anthropometric measurements were taken of the 132 (123 female and 9 male) cutting and sewing operators. Measurements used a GPM Model 101 anthropometer and a GPM Model 106 spreading caliper. All measures were taken with shoes removed. Subjects were measured wearing their own working clothing, typically a lightweight summer type clothing such as shorts, t-shirts or cotton skirts. For standing measures, subjects stood erect, facing forward. For sitting measures, subjects sat erect on a firm, flat surface. Operators were measured on each of ten dimensions considered to be most closely related to the desired workstation dimensions.
Results and Discussion
Anthropometric Data Existing anthropometric databases often are not valid for specific populations of workers (Casey, 1989). This may be especially true where job characteristics self-select for certain physical characteristics in the worker. Smith, Smith and McLaughlin (1982) found that a sample of female textile workers, for example, was substantially taller and heavier than the population norm, probably due to the reaching and lifting requirements of the specific job. It was desired to identify (or rule out) any such gross deviation from population norms among sewing operators. The population of male operators was considered to be too small to provide meaningful data and these measures are not included in the study.
It is apparent from comparing these data that female apparel workers do not deviate in any substantial degree from the dimensions of all female workers as summarized on three other published data bases. The sample of apparel workers may be slightly heavier (as suggested by the larger thigh clearance measurement) but none of the other nine measures varied appreciably from the other published norms. This conclusion, however, may not be valid for every plant. Some plants now employ substantial numbers of sewing operators of Asian/American ancestry and have reported difficulty in adjusting workstations to meet the needs of these typically smaller statured workers. Few of these workers were in the population represented in the current study.
Musculoskeletal discomfort. Another major goal of the program was to document patterns of musculoskeletal injury or discomfort experienced by the sewing operators and to begin relating them to job and workplace elements that might have contributed to them. During the interviews, the sewing operators rated the frequency with which they experienced muscle or joint pain in each of 16 areas of their bodies.
Approximately half of all workers reported that they at least sometimes experience pain in their upper back (52%), neck (49%), and right hand (48%). This prevalence of neck, shoulder, and back discomfort is consistent with results of similar surveys on apparel workers in the northeastern United States (Punnett, Robins, Wegman, and Keyserling, 1985) and in Finland (Vihma, Nurminen, and Mutanen, 1982).
The data are also comparable to those we found in a separate study in which a sample (n=12) of seated sewing operators rated their comfort levels at four different points during the day (Courtney, Kelly, Folds, and Ortiz, 1990). Discomfort tended to increase throughout the day and by late afternoon 10 of the 12 were reporting some degree of discomfort in their upper backs, 6 of the 12 were reporting discomfort in their right hands, and 3 of the 12 were reporting discomfort in their necks.
The working posture. Much of the reported discomfort in the back and neck can be attributed to the working posture of the seated operators. In response to job and workstation characteristics, operators typically adopted a hunched working posture. Analyses of videotape records made of thirty subjects in the target jobs indicated that 40 percent stooped forward (i.e., torso flexion) at least 20 degrees throughout the machine cycle. Sixty percent tilted their heads more than 20 degrees throughout the cycle. Several workers stated that this posture is necessary to obtain maximum production and wages. Such postures have been cited as a factor in muscle fatigue, and discomfort (Grandjean, 1982). The tendency of operators to work in this hunched posture can be attributed to at least three factors, the visual demands of the work, the geometry of the workstation, and inadequate seating.
Illumination. Most sewing operations are visually demanding, requiring the precise stitching of thread into a fabric with which there is little or no visual contrast. Overall, 36 percent of operators stated that illumination was insufficient, requiring them to lean toward the point of operation (POO) in order to see their work. To evaluate this complaint, we measured the average illumination at the POO (consisting of general illumination plus supplementary workstation luminaries) for a sample of 396 workstations. The mean value, 168 foot candles (fc), was less than 60 percent of the Illuminating Engineering Society of North America (IESNA) recommended value of 300 fc for visually intensive tasks with low contrast.
Workstation geometry. The tendency of operators to work in the hunched posture also suggested a potential conflict between workstation geometry and operator dimension. Analyses indicated that the machine treadle typically was located too close (mean=15 cm) to the proximal edge of the work surface. Most commonly, operators responded by positioning the chair away from the work surface in order to allow a knee angle of 110 degrees or greater. From this position, the mean distance from the back of the chair to the point of operation (POO) was only 3 cm less than the arm length of the 50th percentile operator. To compensate for these workstation problems, operators leaned forward to maintain adequate visual and manual access to the POO.
Another factor limiting operator access to the workstation was the location of various obstructions (motors, pneumatic equipment, and machine guards) beneath the work surface. While typical recommended knee room averages about 46 cm, (Eastman Kodak Company, 1983) the presence of these obstructions, in some cases, limited available space to less than 26 cm.
Seating. The vast majority of operations were performed in a seated position. Seating encountered in the sewing environment typically consisted of straight-backed wooden or metal chairs. The provided chairs lacked any cushion for reducing compression and fatigue, lacked adjustable backrests, and often were of improper height. Most operators (91%) customized their chairs with homemade cushions on the pan and backrest in order to adjust the height and increase pliancy. Most cushion adjustments increased seat height by 3-6 cm when compressed.
Repetitive Manipulation. One primary risk factor for the development of repeated trauma disorders is the frequency with which motions are repeated. On the basis of observation and interviews with an experienced methods engineer, the sewing jobs were classified as requiring high, medium, or low amounts of repetitive manual manipulation. While the classification was somewhat subjective, it was closely related to the frequency of changes in hand and wrist posture. High degrees of manual manipulation were associated with higher levels of physical discomfort almost throughout the body. Greatest discomfort levels were concentrated in the neck, upper and middle back, right shoulder, and hands. Seventy-three percent of the high manipulation workers reported pain in their right hands, the highest discomfort frequency identified in the analyses. This is consistent with the findings of Vihma, et al. (1982) of a significant relationship between hand pain and repetition rates.
In addition, as many as 100% of operators on certain high manipulation jobs (e.g., top-stitching) reported symptoms that are often associated with repetitive trauma disorders, including nocturnal numbness in the hands and fingers. In the overall population of sewing operators interviewed, the incidence of such reported symptoms was approximately 30%, a somewhat higher incidence than has been previously reported (e.g., Punnett and Keyserling, 1987). Our higher frequency can partially be attributed to the interview sample that was purposely weighted to emphasize problem jobs.
The cycle time of the 14 target jobs ranged from 10 to 109 seconds with most in the 20 to 40 second range, very similar to the cycle times recorded by Punnett, et al. (1987). There were an average of 29 left hand and 25 right hand posture changes per cycle. The most frequent hand and wrist postures included pinch (lateral and pulp), ulnar deviation, flat press, extension, and flexion, respectively.
Training. Initial training of sewing operators was performed on the job in all three of the plants examined. One plant had a specialized training department responsible for initial and continuing training; the other two plants provided training by the floor supervisors. Training periods varied from a few days to as many as six months. None of the plants provided specialized instruction in effective training techniques for their supervisors or training staff.
There was evidence that improvements in operator training are being made, especially for newly hired workers. Higher percentages of younger operators reported receiving job-methods training using visual aids or videotape, training on posture, training on lifting, and training on other safety issues. As suggested by the table, videotape is only infrequently used during initial training but is more commonly used for cross-training the more experienced operators. Training feedback was, at best, inconsistent. After the initial hour or so of intensive training, return visits by the trainer/supervisor were sporadic. One plant posted a daily learning curve chart on the novices' workstations but even this degree of performance feedback was unusual. Top of the page
Relatively low cost solutions are available that can address much of the musculoskeletal discomfort reported by the operators in the initial survey. Badly designed and adjusted workstations can be properly adjusted for the operators; ergonomically-designed seating can replace the hard, unadjustable seats.
While most sewing operators continue to sit on hard, unadjustable seats during the workday, ergonomically designed chairs for the sewing operator are now available (Yu and Keyserling, 1989). These chairs have easily adjustable seat height, seat pans, and backrests. They are adequately padded and promote a lordotic seated posture. Little formal effort had been made to validate the effectiveness of these chairs in the manufacturing environment. The goal of this study was to provide a field evaluation of the effects of workstation adjustments, posture training, and ergonomically designed seating on the comfort, posture, and production efficiency of sewing operators.
Two studies were conducted on the effects of ergonomically designed chairs on posture, comfort, and production efficiency in cut-and-sew manufacturing plants. In the first study, ergonomically designed chairs were tested on the sewing floor of a trouser manufacturing plant (Courtney, et al., 1990). Twelve sewing operators took part in the study. Before initiation of testing, all operators rated their levels of musculoskeletal discomfort in fifteen areas of their bodies at approximately two-hour intervals during the work day to provide baseline comfort/discomfort levels. The subjects were videotaped from the side as they worked so that measures of postural angles could be made.
The operators were divided into two groups of six each. The six operators in the control group then received instruction in proper working posture and were individually given recommendations on adjusting their workstations and chairs to ergonomically appropriate configurations. The six subjects in the experimental group received the same posture training and workstation recommendations; in addition, they were supplied with the ergonomically designed chairs and carefully trained in their use.
After a period of approximately five weeks, the sequence of discomfort surveys and videotaping was repeated.
A subsequent study tested ten sewing operators in two different plants (Peck, 1990). One plant produced active-wear such as sweatshirts; the second produced medical supplies. This study used the same discomfort survey and videotape posture analysis but employed a before-and-after experimental design rather than matched groups.
Results and Discussion
The changes were remarkable. In the first study, the experimental group showed substantial improvements in both posture and frequency of musculoskeletal discomfort. The mean improvement in back angle was 8.3 degrees with five of the six subjects showing improvement. Reported musculoskeletal pain decreased by 90.3 percent. The control group showed a mean 2.5 degree improvement in back posture with three of the six subjects showing improvement. Reported musculoskeletal discomfort decreased by 53.6 percent. No change in production was seen, however, for either group.
In the subsequent seating study, the changes in posture were not as pronounced as those found during the first study. The subjects, however, reported an almost identical 90% reduction in discomfort frequency when using the ergonomically designed chairs. A statistically significant increase in production was experienced by subjects in one of the two plants after introduction of the ergonomic chairs. Given the choice, 15 of the 16 operators who tested the ergonomic chairs during the two studies elected to keep them after the conclusion of the studies.
In field studies of this kind, the experimenter must be mindful of potential contamination of the data by the Hawthorne effect, by the demand characteristics of the study, or by other aspects of the situation that are not under strict control. Traditionally, the Hawthorne effect is most evident in increased production on operator-paced jobs. To explore the possibility of such an effect, we compared production data during the five weeks of the study with historical and post-study data from the same operators. Only one of the three test sites experienced any change in production efficiency that could not be directly attributed to identified outside factors. We attribute the lack of evidence for a Hawthorne effect to at least two factors. First, great care was taken to make the experimental procedures as invisible as possible to the operators. Second, the plants in which the studies took place were relatively innovative and small experiments like this were a typical part of the operators' jobs. Top of the page
Some plants, especially the larger ones, are beginning to recognize and address ergonomic and workstation problems through the introduction of relatively advanced manufacturing technologies. These include such approaches as job automation, automated materials handling, ergonomically improved workstations, and the introduction of modular manufacturing cells. Many of these approaches bring with them new or revisited problems and challenges for the ergonomist. During this phase of the program, we explored and documented emerging technologies in the apparel manufacturing industry through experimentation, interviews with equipment manufacturers, apparel manufacturers, and manufacturing personnel.
Automated Materials Handling
In conventional manufacturing operations, boxes of parts and bundles of approximately 40 unfinished garments are carried, dragged, or wheeled on specially designed carts between workstations. Materials movement is done by the operators, themselves, or by designated "bundle boys." Automation of this materials handling process has received a significant amount of attention, perhaps to the detriment of other automation opportunities (Weissbach, 1986). Various vendors are now introducing automated equipment that is designed to make this materials handling more efficient.
A unit production system (UPS), a computer-controlled overhead conveyor, may be used to move hangers of parts or partially assembled garments from one workstation to the next. Rather than large bundles of parts, each hanger typically carries the components of a single garment or a small number of garments.
In one plant that was surveyed, 100 workstations were connected by a typical automated, ceiling mounted UPS line that carried individual unfinished garments on hangers. A central computer tracked each garment as the bar coded hanger passed by a series of bar code readers on the conveyor line. The garment was automatically moved to the next operation and routed to one of the sewing operators according to the UPS's preprogrammed logic. The garment typically was delivered to the appropriate workstation in a queue near the operator's left shoulder.
Some operators complained about a perceived increase in the noise level and reported temporary auditory threshold shifts during and after the workday. The noise level peaks at the operators' ears, largely produced by impacts between the heavy plastic hangers as they dropped into the queue for the workstation, was measured at between 95 dB and 97 dB at a majority of the workstations. These peaks, occurring every few seconds (depending on the length of the operation cycle at the workstation), were superimposed over a continuous noise level of 82 - 88 dB.
The UPS reduced horizontal reach requirements and all but eliminated heavy lifting by the operators. It resulted, however, in increased vertical reach requirements and increased wrist pronation during acquisition of materials. Interviews on body part discomfort with a sample (n=12) of operators on the conveyor line indicated slightly higher frequencies of hand and leg discomfort among this sample than among their counterparts who utilized conventional materials handling.
Operators on the UPS line expressed dissatisfaction with the "intelligence" of the automated controller. Although the system was designed to be operator paced, faster operators reported that they often experienced empty queues at the same time that work was still being routed to the slower workers. Other difficulties included "ghost hangers" that had dropped their bundles somewhere but were still being moved through the system and counted as units of production. Perhaps the greatest problem with the UPS was its lack of flexibility and the difficulty in making short-term changes in its logic. Slight changes in the production process, for example reassigning a given workstation to do a different operation for a single day, or temporarily changing the work flow for a short run of a different product could not be done economically. This UPS installation was eventually idled and abandoned when the company changed their product line to a different garment and determined that the UPS could not cost-effectively be altered to support the new product.
Many leaders in the industry believe that a solution for some of the training and ergonomic problems lies in partial automation of selected manual manufacturing operations. Automation, for example, can reduce the skill requirements of a complex positioning and guiding task so that novice operators might reach acceptable levels of production within a period of days or weeks rather than the several months currently required. Partial automation can also eliminate many high risk hand and wrist postures and the frequency of hand movements, thereby reducing the exposure to common repetitive trauma disorders.
There are significant technological barriers to the introduction of complete automation to the sewing workstation. Much of the difficulty is due to the nature of the raw material, fabric. Unlike relatively rigid materials such as metal, plastic, or ceramics, a single ply of fabric is difficult to push or pull or to hold in position with the degree of accuracy required in the manufacturing process. Workstation automation, therefore, must (1) concentrate on operations in which precision is not required, (2) find techniques for making the fabric "act" rigid, and (3) use a hybrid approach in which human operators continue to feed and guide the machines during precise tasks.
Automated cutting machines now being introduced into the industry are programmed to cut stacks of fabric parts precisely and in a given order from a "spread" of 100 or more plies of fabric. By creating a partial vacuum under the porous tabletop, air pressure is used to hold the thick stack of fabric rigidly in place. Cutting of the spread is done automatically by a cutting blade, cutting at speeds up to 2000 cm/minute, under control of the computer.
Partial automation of sewing operations can eliminate some of the risk factors for CTDs. As an example, production of a "felled seam," the kind of double overlapped seam found on the side of denim jeans, requires an awkward posture of wrists, hands, and fingers to hold the fabric in position as it is guided through the sewing machine. This job generally requires over six months of training time and it has a disproportionate incidence of hand and wrist injuries. In recent years, a folding attachment for the sewing machine has become available that guides the fabric edges into the appropriate double-overlapped position eliminating many of the operators' motions and awkward hand postures. A more recent innovation, an automated felled seamer, simplifies the job even further, allowing the operator to use nearly neutral wrist and hand postures throughout the operation. In addition to reducing the incidence of repetitive trauma injuries, this is expected to reduce training time by a substantial amount (Textile Clothing Technology Corporation, 1989).
Numerous ergonomists have recommended the use of tilted tabletops to reduce wrist and back angles and to improve visibility during sewing operations. A rapidly adjustable workstation was selected for use in testing this hypothesis. The height of the top was adjustable between 71 cm and 110 cm (28 in and 43 in). The top surface of the workstation could be tilted through angles of +15 degrees through -15 degrees. All adjustments could be made by the operator using a pair of handles below the work surface controlling two hydraulic cylinders. In the Southern Tech AMTC, a Pfaff 463 machine was mounted on the workstation and the operator worked from a seated position.
Tests of the effectiveness of different tilt angles of the work surface were conducted. The sewing operator assigned to that workstation performed the task at worktable angles of 0 degrees, +15 degrees, and -15 degrees. Videotapes of back and wrist posture were taken as the operator worked and the operator was interviewed at the end of the series of trials. Results indicated no significant difference in wrist or seated postures that could be ascribed to the tabletop angle. The operator, however, expressed a strong preference for positions in which the back of the workstation is tilted upward.
Operator Real-Time Information System
Operators who receive near-real-time information feedback about the level of their performance might be expected, according to behavioral principles, to improve their performance. Real-time production management systems are reaching the work floor to track the location and flow of particular bundles, and the status and performance of individual workstations. Terminals at each individual workstation are connected to a central computer system. Managers and supervisors have access to this information to aid in production management and planning. Similar data may be available on the terminals at each workstation but it is not easily obtained and interpreted.
GTRI designed and prototyped a real-time display system that would allow the operator to establish production goals and would provide the operator with continuous information, in bar graph form, of progress toward meeting the established goals. A touch-screen system on the small color monitor could be used to sign on and off, establish goals, change goals, determine total earnings and projected earnings for the day, and perform other display-control functions. The real time display system could be integrated with the information network on a real-time production management system, like those currently in existence, to provide these data at selected workstations. The system would be most cost-effective if used in conjunction with operator training and retraining. Top of the page
Based on the results of the research in the first three phases, a 100 page manual and 30 minute video entitled "A Stitch In Time: The Supervisor's Guide to Ergonomics" were developed as a training package for apparel manufacturing supervisors. Written at approximately the eighth grade comprehension level both manual and video contain 5 corresponding sections. The first is entitled "Making the job fit the worker" and provides a working definition of ergonomics. Section two, entitled " Work station design", focuses on the relationship between posture and the design of the work station. Section three, "What are CTDs", is concerned with defining the major cumulative trauma disorders and discussing the risk factors and possible solutions. Section four, "The work environment", concentrates on the influence of noise and lighting on worker performance and section five, "Training and retraining workers", is primarily concerned with training concepts important to the supervisor.
User testing of the manual at an apparel plant in Georgia suggested that, overall, the manual was written at the right level. The key feature most often noted by participating supervisors was the strategic use of pictures to illustrate the concepts. Over 770 companies and institutions have purchased more than 2100 copies of the training package (Appendix A contains the latest list of companies). The success of the manual and video has been largely due to the tremendous publicity both received in a wide variety of publications and journals (Appendix B contains the list of publications). Top of the page
There are currently significant efforts under way to eliminate the progressive bundle assembly-line process and to introduce the concepts of modular manufacturing cells into the apparel manufacturing workplace. In this concept, a complete garment (or major sub-assembly) is produced in a modular cell of, perhaps, ten operators and twenty machines. Operators are not assigned to a single operation but may move between workstations as the flow of product requires. Individual workstations are typically shared by two or more operators. In contrast to traditional management practices, the team of operators in the cell is responsible for many elements of workflow planning and management, team formation and interpersonal relations, and product quality. Because modular cells are rapidly reconfigurable, modular manufacturing has been promoted as an efficient way of providing a quick response to the common need for a short production run of a particular product.
Attempts to introduce modular manufacturing have produced inconsistent results with both notable successes and distressing failures. Anecdotal reports suggest that, after a period of adjustment, many workers experience significantly decreased levels of musculoskeletal discomfort due to the increased variety in movements, to improved postures at the standing workstations, and to motivational factors. Increased morale and workgroup cohesiveness, along with substantially reduced absenteeism, have also been seen in successful implementations.
Numerous ergonomic questions and challenges appear during the implementation of the modular system. Many traditional workstations will need to be redesigned. Increased adjustability/adaptability will be required for workstations that are shared by two or more operators. Issues of job design, training, organizational design, performance assessment and reimbursement will need to be successfully addressed.
As one example of ergonomic issues in workstation design, some implementations of modular cells have required a switch from a primarily sitting workplace to a primarily standing workplace because of the need for operators to move between the workstations in the module. This necessitates redesign of machine controls since the traditional sewing machine foot treadles are not usable from a standing position and existing standing foot controllers do not provide the necessary level of sensitivity for precise machine control. Several designs of new foot-actuated controllers have recently been introduced but none has proven entirely satisfactory.
In unsuccessful attempts at implementation of modular manufacturing, reduced individual production is often attributed to the lack of specialization by operators and to less efficient material handling techniques. Inability to effectively plan and manage production within the cell, interpersonal problems, and dissatisfaction with new group-incentive pay schemes are also cited as problems. Other ergonomic problems related to job, workstation, and workgroup organization are certain to become apparent as the apparel industry's experience with modular manufacturing systems expands.
Our data indicate that the overall degree of discomfort reported by standing modular operators does not differ significantly from that reported by seated operators in progressive-bundle plants. Standing modular operators report somewhat more foot pain (possibly related to inadequate control devices) and somewhat less pain in other parts of the body (related to posture changes). Operators reported that subjectively they noticed a decrease in musculoskeletal discomfort on moving from bundle to modular processing. For this and other reasons, operators' preference favored modular systems by a wide margin. There is nothing in the discomfort reports that would argue against standup modular work. Substantially more work, however, needs to be done on the development of machine controllers for standup operators. Top of the page
The apparel manufacturing industry in the United States presents significant challenges for the ergonomist. A large percentage of plants are experiencing marginal profitability and can afford no more than quick, band-aid solutions to their ergonomic problems. For these organizations, the ergonomist has much to offer in terms of recommendations for workstation geometry adjustments, improved seating, and improvements in workstation lighting and noise protection. Highly motivated plants are able to develop inexpensive and ingenious solutions to many of the problems that are brought to their attention.
Other, more prosperous organizations are able to experiment with introducing some one or more of the elements of new technology described above. Ergonomically designed seating should be a top priority, but companies often need assistance to distinguish between well designed chairs and those that are "ergonomic" in name only. Other elements of workstation and materials handling automation are becoming popular but managers can certainly use the services of an ergonomist to help lead them through the kinds of pitfalls described above.
Many plants still operate under an unenlightened management philosophy that rejects the application of ergonomics practice. Managers fear that it will "plant seeds of suspicion" in the workforce and lead to increased malingering and frivolous workers' compensation claims. The authors have frequently heard the opinion expressed that cumulative trauma disorders are a contagious psychosomatic affliction spread primarily through contact with union organizers and personal injury attorneys. It is worth noting that even in these plants the sewing operators have a vague recognition of their ergonomic problems. They need not be told, for example, that their chairs are uncomfortable and that their backs ache. They are aware of occupational injuries through media reports and discussions with their coworkers.
An increasing number of apparel manufacturing plants, however, are adopting a more enlightened attitude toward ergonomics. A few large companies have added full-time ergonomists to their management teams; a larger number of companies are using outside consultants to help organize and support inplant ergonomic projects.
One of the most important roles the ergonomist can play is educating the plant management, floor supervisors, and workforce. Managers need to be aware of the importance (for both humanitarian and cost reasons) of a continuous program of surveillance with a goal of detecting ergonomic problems before they are translated into acute or cumulative injuries. Plant floor supervisors need to be educated to support this surveillance program by recognizing symptoms of ergonomic problems including maladjusted workstations, inadequate seating, inadequate illumination, and high-risk working postures and motions, by helping to identify intervention strategies and by training workers to do the same. Ortiz, Kelly, and Davis (1991) have prepared a workbook and accompanying videotape specifically designed to educate the apparel plant floor supervisor in ways to fulfill this role. Top of the page
Casey, S. M., 1989, Anthropometry of farm equipment operators, Human Factors Society Bulletin, 32(7), 1 - 3.
Courtney, T. K., Kelly, M. J., Folds, D. J., and Ortiz, D. J.(1990). The Impact of a Chair as an Ergonomic Intervention in Conventional Trouser Manufacturing. (Georgia Institute of Technology, Atlanta).
Department of the Army, 1981, Human Engineering Design Criteria for Military Systems, MIL-STD-1472C, (Author, Natick, MA).
Grandjean, E., 1982, Fitting the Task to the Man: An Ergonomic Approach, (Taylor and Francis, Ltd., London).
Eastman Kodak Corporation, 1983, Ergonomic Design for People at Work (Van Nostrand Reinhold, New York).
Kelly, M. J., Ortiz, D. J., Folds, D. J. and Courtney, T. K., 1990, Human Factors in Advanced Apparel Manufacturing. In Ergonomics of Hybrid Automated Systems II by W. Karwowski and M. Rahimi (eds.) (Elsevier Science Publishers, Amsterdam), pp. 763 - 768.
Ortiz, D. J., Kelly, M. J., and Davis, N. E., 1991, A Stitch in Time: The Supervisors' Guide to Ergonomics, (Georgia Institute of Technology, Atlanta).
Peck, J. C., 1990, Cheers for chairs, Apparel Industry Magazine, 51(9), 114 - 118.
Punnett, L. and Keyserling, W. M., 1987, Exposure to ergonomic stressors in the garment industry: Application and critique of job-site work analysis methods, Ergonomics, 30(7), 1099 - 1116.
Punnett, L., Robins, J.M., Wegman, D. H., and Keyserling, W. M. (1985). Soft tissue disorders in the upper limbs of female garment workers, Scandinavian Journal of Work Environment and Health, 11, 417 - 425.
Smith, J. L., Smith, L. A., and McLaughlin, T. M., 1982, A biomechanical analysis of industrial manual materials handlers, Ergonomics, 25(4), 299 - 308.
Society of Automotive Engineers, 1983, USA Human Physical Dimensions, SAEJ8333 DEC83, (Author, Warrendale, PA).
Textile/Clothing Technology Corporation, 1989 (September), [TC]2 Report, (Author, Raleigh, NC).
Yu, C. Y. and Keyserling, W. M., 1989, Evaluation of a new work seat for industrial sewing operations, Applied Ergonomics, 20(1), 17 - 25.
Vihma, T., Nurminen, M., and Mutanen, P. (1982). Sewing -machine operators' work and musculo-skeletal complaints. Ergonomics, 25(4), 295-298.
Webb Associates, 1978, Anthropometric Source Book, Volume 1 - Anthropometry for Designers, NASA Reference Publication 1024, (National Aeronautics and Space Administration, Washington, DC).
Weissbach, H. J., 1986, Design and implementation strategies of manufacturing control systems. In Skill Based Automated Manufacturing: Proceedings of the IFAC Workshop by P. Brodner (ed.) (Pergamon Press, New York), pp. 47 - 52.