I took over the Directorship of the Ergonomics Unit in 1979. By then Rachel had already completed the MSc in 1975 (for her MSc Reflections – see Present and Future, Section 9) and had been appointed as lecturer by my predecessor Harry Maule. Rachel is still there to-day. That says much for her loyalty, tenacity and sheer survivability (Harry; John; Harold; Ann…..). Rachel and I were (and still are) a ‘rainbow’ of contrasts – Rachel and myself respectively – physiologist and psychologist by background; teacher and researcher by academic leaning; physical and cognitive ergonomists by preference; intellectual and pastoral carers of students by nature and so on….. For that reason, I think that we made a good team. We covered the waterfront, so to speak, and supported the Unit and the MSc through difficult and sometimes stormy times. (For a personal view on the origins and survival of the Ergonomics Unit – see Rachel’s interview Present and Future, Section 4.) We also had our moments, of course, given the contrasts outlined earlier and the going was not always smooth; but our unquestionable loyalty to the Unit and commitment to (Cognitive) Ergonomics more generally ensured success. I am very pleased to include Rachel’s (and Andre’s (another ex-MSc student)) paper on the website.
PS Thirty-six years on, and Rachel and I are still working together, if only to sort out Unit documents for archiving….. Time passes quickly, when you are enjoying yourself…..
The Hexagon-Spindle Model for Ergonomics
Rachel Benedyk1 and Andrée Woodcock2
1 University College London Interaction Centre, UK
2 Design and Ergonomics Applied Research Group, Coventry University, UK
The concept of ‘work’ in ergonomics may now be applied to the satisfactory completion of any task. Using a systems view of the process, the task consists of a number of transformative interactions, performed simultaneously or successively, to a given level of effectiveness. Such interactions take place at the interface, between the user (or operator) and key components of the system; these encompass not only traditional hardware, software and workstations, but social, managerial, infrastructure and peripheral factors. This paper proposes a new model for Ergonomics, known as the Hexagon – Spindle Model, which represents the multiple factors influencing the effectiveness of interactions at the interface. The model is holistic, multi-dimensional, task-related and transferable across a range of settings. It extends to characterise a time base for serial and simultaneous tasks and highlights areas where operator/system conflicts may arise. The paper illustrates analysis tools for the application of the model in evaluation and design.
Introduction
Traditional work systems approaches in ergonomics (as described originally by Singleton, 1967 and 1974, and more recently by Dowell and Long, 1998) may be applied to the satisfactory completion of any task, not just those conducted as part of ‘formal work’. Using a systems view of the process, the task consists of a number of transformative interactions, performed simultaneously or successively, to a given level of effectiveness. The tasks are accomplished in a ‘workplace’ – the immediate environment in which the user and the work system interact. Each task is defined as one or more processes undertaken by a user or operator while in a dynamic exchange of information (an ‘interaction’) with another or with the key design features of the interface. Here the wider definition of an interface is used, referring to the ‘point of communication between two or more processes, persons, or other (physical) entities’ (Santoro, 2001). This would include concrete or virtual objects such as tools, equipment, networks, furniture, and formal and informal organisational structures.
Task interactions occur in a particular setting, whether in formal spaces such as offices or factories, or informal ones such as sports venues, coffee shops, cyber cafes, or the home. They are task dependent, user specific, and subject to influence from each component of the system; not only from traditional hardware, software and workstations, but also social, managerial, infrastructure and peripheral factors. The overall accomplishment of the task is achieved by the successful and effective completion of task interactions, each of which may be influenced by wider factors beyond the immediate control of the user. The challenge for ergonomists is to find the optimal conditions of all these factors to maximise this effectiveness.
Previous ergonomic models
Traditional models of ergonomics have either represented the interactive nature of the interface or the multiple sources of influential factors. The earliest model, commonly known as Concentric Rings (Shackel, 1969; Galer, 1987), represented an operator-centred focus, and the influence on the operator of factors at levels moving out from there; however, there is no further elaboration in the model of these factors in the system. Girling and Birnbaum (1988) took this further with the Elaborated Concentric Rings model, in which the many influential factors in the outer rings are seen to originate from management, situational or personal sources. These divisions facilitate the diagnosis of multiple sources of design problems and the directions needed for rectification. The enhanced model has since been applied in design problems, ensuring all relevant contributing factors are included (eg Dubois and Benedyk, 1991) and in evaluation problems, providing a holistic framework for scoping the evaluation (eg Naki and Benedyk, 2002).
In parallel, the development of the systems approach to ergonomics has emphasised the purpose (ie the task) and the functions to support that purpose; thus Singleton’s work (1967, 1974) began the ‘closed loop’ system representation of the task interaction at the interface. This exchange of data or information between operator and interface holds true whether operator/machine or practitioner/patient or user/tool. Later authors have developed detailed structures and behaviours to further understand the interface and the nature of this interaction (eg Dowell and Long, 1998).
Combining the two approaches to form a holistic representation would seem to have some advantage: as Wilson (2005, page 10) emphasises: “Human-machine interaction does not take place in a vacuum;…ergonomic techniques are needed to predict, investigate or develop each of the possible interactions, between person-task, person-process, person-environment, person-job, person-person, person-organisation and person-outside world.” In this regard, Singleton (1967) makes passing reference to groups of external factors that could ‘interrupt the closed loop’, and Grey (1987) expands on sources within the rings, placing the task as the innermost ring. Leamon’s (1980) model comes closest to integration, in that it places the Closed Loop inside the Concentric Rings, and attempts to indicate criteria for system effectiveness; however, it elaborates no further on the rings themselves.
In addition to the need for a holistic representation, there is a pressing need for an ergonomic model that can move beyond a systematic construct, to act as a useful tool for practitioners, able to demonstrate the utility of the ergonomic approach. Moreover, no models as yet embrace the complex ergonomic challenges arising from multiple users, from simultaneous or successive tasks, from peripatetic users or from changes in user characteristics over time. The Hexagon-Spindle model presented begins to address all these.
The Hexagon Model
The Hexagon Model has elaborated the Enhanced Concentric Rings model by firstly providing a clearer division of the sectors and the levels; secondly by making explicit the six directions for task interactions and the factors of influence; and thirdly, by differentiating between the constant characteristics of the user (common to any task), which are in the central hexagon of the model, and the individual variables that arise only for that task, which feature in the personal sector. The model was developed in order to elucidate the factors which effect task interactions in learning environments. Using this domain provided a series of specific tasks, interactions and multi-level factors which could be used to validate the model. These developments have been reported by Benedyk, Woodcock and Harder (2006, 2009), and Woodcock, Woolner and Benedyk (2009). In this paper, we wish to test the viability of the generic model by returning it to more traditional domains, using the example of a re-design of a cockpit simulator instructor workstation.
The generic form of the Hexagon Model is shown in Figure 1. This shows that for a specific task, the user performs transformative interactions (in line with his/her requirements) with the interface at the level of the workstation. The workstation consists of all the immediate and relevant tools, materials,
Legend for Figure 1
Shaded areas represent levels
Dotted lines represent porous boundaries
Hashed area represents task interactions at the interface between
user and the workstation level
Sectors provide groupings for sources of factors that potentially
influence the task interactions
Figure 1 A Generic Hexagon Model
technology, furniture, co-workers and other people in the vicinity, facilities and resources. This wider definition of the interface is compound and complex; it is not just limited to the human-machine interface, and its interactions are subject to influence (both positive and negative) from multiple factors at the workplace, work setting and external levels. The subdivisions to the outer rings intend to ensure a sharp focus of analysis, greater rigour and consistency across applications. The model further encourages breadth of consideration, so that all possible influences are addressed. Contextual factors need to be set each time the model is applied, specific to the application under consideration. For a more detailed description of the parts of the model, the reader is referred to Benedyk et al (2009).
To perform a Hexagon Analysis, which is the first stage of the tool for practice, the model is transformed into a matrix (Figure 2) and the key factors of potential ergonomic influence noted for each cell ie, any factor likely to impact on the effectiveness of the task interaction. Every cell in the Analysis Table must be given consideration; this is one of the benefits of the technique, as it encourages this holistic approach. Note that there is no attempt at quantification or comparison here; the inclusion of a factor simply gives it potential significance. If the analysis has an evaluation purpose, the factors noted may be rooted in actual observations of the task in context. However, more often the factors must be extracted from a focused creative discussion between ergonomist and user or designer.
As each analysis is task dependent, the choice and relative weight of factors in the different cells will vary. The acceptable level of effectiveness also needs to be set in advance, using relevant ergonomic criteria and priorities appropriate to that work system. The ergonomic practitioner’s judgment is needed here.
From the range of influencing factors identified, those most critical to task effectiveness are extracted, and an Application Format table (Figure 3) constructed, in which the potential ergonomic problems due to each factor are identified, and solutions suggested. The emphasis of the analysis is on a holistic approach to design and evaluation which recognizes where there are mismatches between ergonomic requirements for effective interaction, and features of the actual system. These issues can then be given professional consideration, with the application of ergonomic techniques as necessary, and recommendations for improvement put forward.
Figure 2 presents an exemplar of the Hexagon Analysis Table; the data here were used for the ergonomic evaluation and re-design of the physical ergonomic aspects of an instructor workstation in a cockpit motion simulator. Figure 3 presents an Application Format table, with an illustrative analysis for the same example.
The Spindle Model
In the second stage of the analysis, multiple Hexagons are combined and compared, using a Spindle Model (Figure 4). The spindle allows the hexagon plates to be stacked or spaced, and the influencing factors on them compared, in order to integrate user requirements over different tasks over time.
Tasks are rarely undertaken singly. The user might move from task to task consecutively, or perform more than one task concurrently. These tasks have the same user in common, and often the same external environment, perhaps even the same organisational management, but they may require different equipment, different settings and entail different user requirements, at different times. Because they are not entirely independent of each other, and relate along a time dimension, it can be useful to see their hexagons arranged as ‘plates’ on a ‘time spindle’ as in Figure 4. The commonality of the user links them at the centre.
For serial tasks, the hexagons will be arranged spaced out along the time dimension as in Figure 4, and for concurrent tasks they will be ‘stacked’ at a single time point. Analysis involves a comparison of the key priority factors (the X’s in Figure 4) on each of the hexagons on the spindle, in order to identify conflict or congruence. The spindle thus can hold user task-independent needs constant while varying user requirements by task-dependent capabilities.
| For time t1 | Organisational Sector | Contextual Sector | Personal Sector | |||
| Management Factors | Infrastructure Factors | Task Factors | Tool factors | Individual Factors | Social Factors | |
| External Level | Businessfunding for training; aviation training policy and standards | Developments in integration of instructor workstations in simulators | Best practice in simulator training facilities and in instructor facilities | Trends and standards in use of integrated cockpit instructor workstations | Instructor recruitment and training in relation to use of simulator workstations | Cultural (national and business) expectations of simulator facilities |
| TaskSetting Level (Pilot training centre) | Allocation of budgetfor simulator facility; costs and benefits ofupgrading | Provision of facilities for simulators; technical support | Syllabus and content of instruction sessions, in relation to use of equipment and interaction of instructor with pilot | Age and antiquity of simulator facilities; flexibility of use of space | Attitudes of instructors to use of different types of simulator workstations | Attitudes and preferences of pilots interacting with instructors in simulators |
| Task Workplace Level (Cockpit simulator) | Procurement and planning choices for design and facilities in training simulators | Overall space, accessibility,temperature, acoustics, lighting, vibration | Style of delivery of instruction for these tasks; equipment and sightline requirements for these tasks | Suitability of workplace configuration to accommodate instructor workstation; effect of environmental factors on workstation usability | Crowding factor; relation of instructor workstation to pilot workstation | Potential interference between instructor’s workstation and fidelity of cockpit simulation |
| TaskWorkstation Level (Instructor’s workstation) | Procurement choice of individual workstation eg adjustability, orientation and size – suitability for this cockpit | Installation, support and power supplies affecting individual workstation; task lighting | Instructor workstation and interface design functionality in relation to required task performance; frequency and extent of use | Instructor workstation and interface design features and their usability; fit to this cockpit; sightlines between instructor and pilot’ instruments | Posture, flexibility of posture, and static loading factors imposed by current configuration; effect of vibration on balance, vision and well-being during these tasks | Sightlines and engagement (both required and unwanted) between instructor and pilot |
| Interaction Level (Task interface) | ||||||
| Interface User Level (Instructor) | Stable personal characteristics, eg anthropometry, skills, abilities, preferences, expectations and knowledge of particular instructor, in relation to these tasks in this cockpit simulator; individual susceptibility to effects of vibration |
Figure 2 The Hexagon Analysis Table: an analysis table for a cockpit flight instructor’s tasks – this figure shows a partial analysis, giving examples filled into the table for physical ergonomics factors relevant to the ergonomic design of a flight instructor workstation
Note the hashed boundaries indicating porosity of influence.
Note also the stable user characteristics (those that are not task dependent) underpinning all sector columns.
Note the interaction level occurs between the user and the workstation, in a direct sense, but is under influence from factors at any level and from any sector.
| Levels: | External | Work-Setting | Workplace | Workstation | Operator |
| Examples of influencing factors at time t1 | Clients from different nations hire this training facility and require different configurations of cockpit to suit. | Motion Simulator instruction must replicate Static Simulator Instruction | Simulator must be as similar to cockpit as possible, so space for instructor is very limitedMovement of flight causes vibration | Instructor must monitor both instructor displays and pilot displaysInstruction takes place in darkness and during flight motion | Instructor workstation is used by many different instructors on different occasions |
| Examples of ergonomics issues at time t1 | Different configurations impose variations in requirements which if not met could impact optimal use of the facility by some users | Do the ergonomic requirements for the instructor in the different facilities cause a conflict? | Are postures too constrained? Could emergency egress be compromised?Can the operator still make fine eye and finger movements without error? | Can the instructor keep sightlines and focus on both displays despite obstructions and distance?Do the darkness, flight motion and isolation of this workplace cause ill effects for these operators? | Given the constrained space in the work area, can the full range of sizes of people who may be instructors be accommodated? |
| Examples of ergonomics approaches to solutions | Ensure use of instructor workstation is compatible with all possible client-preferred cockpit configurations without loss of task quality | Ensure comparison of Motion to Static simulator is not compromised by ergonomic interventions | Assess potential risk of postures and problems with egress, and reduce risk by operator adjustment of layout.Design displays and controls that do not require fine movements. Provide limb supports.Ensure rest breaks are taken outside the work environment. |
Carry out user trials to test that proposed design and layout meet visual task requirements, and build in adjustability where possible.Ensure potential users test their tolerance to the environmental conditions. Ensure operators are adapted to reduce motion sickness. | Ensure anthropometry applied to this design is valid for this user population, and build in adjustability where possible. |
| Figure 3 – The Application Format for the Hexagon-Spindle model: an illustrative example, using the exemplar from Figure 2 |
Legend for Figure 4
t= point in time
x= critical factors on each hexagon
hashed area = common task interactions
Figure 4 A Spindle Model
Provision of generic facilities can sometimes compromise the specific facilities the user needs to perform a variety of tasks. Thus, moving from one task to another or attempting consecutive tasks in the same workstation may entail different user requirements – with the result that the workstation or the materials may be ergonomically optimal for this user for one task but not for others. Similarly, moving a peripatetic workstation (such as a laptop) from one setting or context to another can reveal conflicting requirements for optimal use, even for the same user.
The same analysis technique, stacking the hexagons, can compare different users doing the same task in the same workstation, and accommodate individual differences; highlighting the need for adjustability. For example, in the analysis in Figure 3, if there were two Cockpit Instructors using the same workstation at different times, their individual needs would both have to be accommodated by the workstation design. This perspective can also allow us to return to the wider focus at the workplace level. A single workplace supports not only the tasks of the system user, but also the tasks of the supervisor, the cleaning and maintenance tasks of the janitor, etc; one environment, several users. They have contrasting tasks, and thus demand contrasting user requirements from that environment. The Hexagon-Spindle model would allow us to identify points of conflict that would lead to ergonomic concern (such as increased risk) in such shared environments.
Further, the model can examine the same user over time by comparing factors in the central user hexagon, and point to the changes in the interface necessary to accommodate time-dependant factors such as fatigue, aging, or pregnancy.
Any of the factors in the model can be held constant, and any others varied, and the effect on the task interaction quality or the costs to the user can be examined.
Conclusion
The Hexagon-Spindle model provides a generic framework that enables a practitioner to take a multi-factorial, holistic approach to the design and evaluation of different forms of task material, aids, devices and environments whilst taking into account the requirements of different types of users and tasks. Its approach will lead to a more integrated understanding of each scenario, and an increased confidence in the likely effectiveness of ergonomic interventions and design changes. This is particularly critical in complex settings with multiple tasks, wide ranges of users and budget-limited facilities, which can lack a holistic ergonomic focus.
The flexibility of the spindle provides an opportunity to think outside the rigid box that can sometimes limit other models. A working day for many people now comprises sets of activities, which may or may not occur in the same place, with the same or different colleagues or using the same or different equipment. To create a truly effective working environment requires not just one, but a series of effective environments to be constructed.
The Hexagon-Spindle model explicitly focuses on the effectiveness of the interactions for a single task, thus clarifying conflicts between different task needs. It evaluates the whole complex, multifactorial space as defined by the extended concentric rings and the influence of all factors, whether supportive or limiting, on the task interactions. The Spindle allows for the inclusion of an extra dimension in which to explore and resolve conflicts and priorities over time, over space, or between tasks or users. Not only may the same environment have to cater for the needs of varying users, but also for the other work undertaken in the same environment by other stakeholders. Most importantly, the model extends to provide a usable ergonomics analysis and demonstration tool.
References
Benedyk, R., Woodcock, A. and Harder, A., 2006, Towards a new model of Educational Ergonomics. In: Pro. 2nd Conf on Access and Integration in Schools, (Coventry University, UK)
Benedyk, R., Woodcock, A. and Harder, A., 2009, The Hexagon-Spindle Model for Educational Ergonomics, accepted for publication in Work Journal
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Dubois, S. and Benedyk, R., 1991, An ergonomic review of the usability of the postal delivery bag. In: Designing for Everyone, I. Queinnec and F. Daniellou, Eds., (Taylor and Francis, London)
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Singleton, W., 1974, Man-Machine Systems, Penguin.
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Woodcock, A., Woolner, A. and Benedyk, R., 2009, Applying the Hexagon-Spindle Model for Educational Ergonomics to the design of school environments for children with autistic spectrum disorders, accepted for publication in Work Journal
Wilson, J., 2005, Methods in the understanding of human factors, Chapter 1 in Wilson, J. and Corlett, N., (eds) Evaluation of Human Work, 3rd Edition Taylor and Francis