Transcribed from Behavior and Information Technology, 1987, Vol. 6, No. 3, 363-368.
PAUL T. CORNELL and TERRY WEST
Steelcase, Inc., Grand Rapids, Michigan 49501, USA
Abstract. The Steelcase Sensor chair was introduced in the spring of 1986. It is designed to meet the special needs of modern office workers and their technology by supporting and encouraging movements of the operator while seated. The marketing and research trends that influenced the product philosophy are discussed. The fifteen product criteria achieved in Sensor are described, as are the pertinent ergonomic principles embodied in its design.
The stenographer's chair was developed in the early 1900s. It offered numerous adjustments such as seat depth, back height, and seat height, and typically incorporated box cushions and a swivel base. It was intended for those employed in a 'task-intensive' occupation, and was not meant as a general-purpose chair: the belief was that these workers had special seating needs, and thus required special seating solutions.
Steno chairs are designed today to much the same specification as when first introduced. Despite advancements in seating technology, the stenographer's chair is still recommended in many modern ergonomic texts (e.g.,Woodson 1981,McCormick and Saunders 1982).
The steno chair began to appear more frequently as more workers became task-intensive. This was actually a by-product of the application of the factory model to the design of office jobs. Jobs became more fragmented as office workers found themselves working on the information assembly line. The intense and repetitive nature of the task required one to remain upright and close to the work and materials. The chair was designed to support the operator in this static posture. This situation remained even with the introduction of new technologies in the office.
The importance of ergonomics in the office began to be appreciated in the 1970s. Its role in designing factory jobs and workplaces had long been recognized, but now the marketplace was becoming increasingly aware of the impact ergonomics had on office worker health, comfort, and performance.
This was prompted by several factors. One was the increased number of office workers relative to other workers. A second factor was the need to be competitive and cost-effective. A third contributor was the influx of information technology and its impact on office procedures and design. And finally, ergonomics grew in importance because of the greater concern for quality of work life.
This did not spell the end of the steno chair, but did influence chair design. The ergonomics trend was often manifested in the form of an increased number of chair adjustments. After all, what could be more ergonomic than allowing the operator to individually adjust the various elements of the chair to suit his or her size and preference? The resultant chairs had numerous knobs, dials, and levers, usually located beneath the seat pan and out of sight.
Market feedback and field observation were not very encouraging. People did not use the features regularly. The biggest problem was that many were not aware of the adjustments. Even if they were aware, many did not understand the purpose of the adjustments, how to actuate them, or what the proper setting should be. The location of the control made it difficult to reach, often requiring the user to get out of the chair. Although training programmes and owner's manuals were introduced to educate users, the problem of complexity persisted.
This led to the design and development of the ConCentrx chair line. ConCentrx adjustments are simple, straightforward and designed to be used while seated. More importantly, with this product Steelcase introduced the notion of chair dynamics: rather than requiring manual adjustment, some features adjusted automatically. This was achieved via a 'synchro-tilt' mechanism, which maintained a ratio of tilt between the seat back and the seat pan. This was in contrast to 'swivel-tilt' chairs which had a fixed angle between the seat back and pan.
In spite of the market climate for good ergonomics. ConCentrx took some time to catch on. Accustomed as it was to steno chairs and swivel-tilt technology, the market had to be educated on the benefits inherent in the new design. Soon the superiority of the design was substantiated by its performance in the field. ConCentrx is now the most successful chair line in Steelcase's history.
Soon after the introduction of ConCentrx in mid-1981, Steelcase Marketing and Industrial Design staffs began to discuss the next generation of seating products. It was quickly agreed that the concept of 'dynamics' had to be taken further, while avoiding complexity. To be effective, the chair had to be simple. Many envisioned an enhancement of ConCentrx which embodied greater dynamics in a simpler package.
With the rapid introduction of computers at all job levels, it was evident that most workers had need of support for task-intensive activities. Chairs would not only have to provide the functional support necessary, but also be appropriate for a variety of job classifications.
Introduction of ergonomic features in chairs was usually accompanied by an increase in price. But the market could absorb only so much expense in the name of ergonomics. Steelcase wanted to be a leader in reversing this trend. Cost means more than list price, however; the company wanted to address the cost of ownership over the life of the product. Upgrades and repairs should not be cost-prohibitive.
In 1982, Wolfgang Muller-Deisig, a design consultant from West Germany, contacted Steelcase regarding a new chair concept he was developing. His concept embodied a flexible zone in the lumbar area, provided by the materials instead of an external mechanism. The articulation afforded by this approach approximated the movement of the spine and the rotation of the pelvis that occurs in a seated office worker. After a series of meetings and concept reviews, Steelcase and Muller-Deisig formalized a working relationship.
By this time, the design team had grown to include Steelcase Marketing, Design, Engineering, Research and Development, and Muller-Deisig. Together, these experts contributed to the development of fifteen design criteria reflecting market trends and expectations, recent ergonomic research, standards activities, design trends, and developments in engineering:
(1) chair height adjustment must be 16 to 21 in;
(2) seat angle adjustment must be self-actuating rather than mechanically adjusted;
(3) low-back chairs should have back height adjustment;
(4) the seat tension adjustment should be simple and easy to reach from a seated position;
(5) chair arms had to be field-removable;
(6) upholstery had to be field-detachable;
(7) optional arm height adjustment had to be available;
(8) synchronous seat-pan to seat-back articulation was required;
(9) an optional variable back-stop control was needed;
(10) a five-arm base was required;
(11) seat-back dimensions had to be larger;
(12) the full upholstered version was to be optional;
(13) the column must incorporate a shock absorber that was functional at all seat heights, even the lowest:
(14) a completely new design aesthetic was required;
(15) the cost had to be less than ConCentrx.
With two exceptions, all criteria were eventually met in Sensor. (The adjustable arm rest was deemed too costly and complex, and the adjustable low-back version was judged unnecessary in light of research.) But along the way some new approaches to design and manufacture had to be developed.
Working with a major university, we began drawing from the ergonomics literature and applying it to the design of Sensor. Of particular interest were studies on back support and positioning. As back pain is frequently reported by VDT operators (Smith et al. 1981), it was the key to provide the appropriate kind of dynamic support. In reviewing the research, Steelcase had to keep several issues in mind. First, much of the available research is oriented towards steno chair technology. Since the state of the art had advanced, findings may not be generalizable. Second, many publications concentrated on the 'optimal' upright posture of 90". Field experience and recent studies (e.g.,Grandjean et al. 1983)had established that people do not sit in this posture naturally, and that it may not be all that healthy. Third, while there were studies on sedentary work postures (e.g., Kelsey 1975), the results were often not relevant to office seating. Finally, many 'common knowledge' guidelines on seating are based on older studies that had not been replicated (e.g., Keegan 1953). We had to use caution in generalizing the results of published research.
In performing their office work, people utilize tools in variable unpredictable ways. Most are occasional users of these tools. T o perform a job, workers need to be able to move around easily in their workstation while in a seated position. In terms of the spine, it is important to encourage movement, as this promotes the flow of nutrients through the vertebrae (Holm and Nachemson 1983, Andersson et al. 1984). Minor movement or exercise can prevent the muscle fatigue and discomfort of static sitting postures (Corlett and Eklund 1984,Kelsey1984). Movement can also be beneficial to blood flow in other parts or the body such as the legs and buttocks (Chaffin et al. 1984). These physiological needs are consistent with reports showing the high degree of postural changes during work (Branton 1969). Hence, a design that not only allowed but encouraged movement was desirable from both a task performance and health viewpoint.
The studies by Andersson et al. (1974) examined the relationship between disc pressure and various seated postures. Combined with Keegan's (1953) work, this established the need for lumbar support. Support in the lumbar region promotes lordosis and counteracts the effects of pelvic rotation (Chafin and Andersson 1984). However, the nature of the support remained an issue. With one exception (Branton 1984), little data existed on the location of the apex of the lumbar curve. Studies showed a discrepancy between the theoretical optimum lumbar location and user preference and comfort (Sauter and Arndt 1984). These also appeared to be no correlation between stature and preferred location (Sauter and Arndt 1984). This evidence led us to design a lumbar support that was rounded but not adjustable in height.
Many of the product criteria, though never combined in one chair before, did not pose any particular technological problems. This was not the case with the movement dynamics we were trying to achieve. The challenge was to provide the proper amount of flexibility; too much and the operator has to work to maintain control; too little and the operator has to work against the chair. After several attempts, this was finally achieved with a one-piece inner shell of polypropylene (see figure 1). This provided the right degree or flex both in the seat pan as well as in the scat back.
Figure 1. The Sensor chair: the inner shell, made of a single sheet of polypropylene.
Figure 2. The Sensor chair, in three versions.
To achieve the design aesthetic we were looking for, a new manufacturing process had to be developed. Typically, seat contours are formed by stitching. With Sensor, a bonding technique is used whereby the fabric and foam are bonded together. This provides freedom in the use of different density foams, results in greater comfort, and helps maintain the appearance of the chair throughout its lifecycle (see figure 2).
Product development requires the input of numerous disciplines. In Sensor Steelcase were able to bring together people with backgrounds in marketing, engineering, industrial design, and ergonomics. Though a team effort, a product was developed which met the separate requirements of these disciplines in a cost-effective manner. To date, the results have been very positive.
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Here are some promo pictures showing the inside foam structure:
