Investigating the effects of physical and cognitive demands on the quality of performance under different pacing levels.

The study was undertaken to investigate the effects of pacing on aspects of performance at an assembly task and on the operators' responses related to work behaviour, perceived workload and perceived stress. A particular objective of the study was to investigate whether physical and cognitive demands may interact in their influences on these effects. An assembly task was simulated in the laboratory and the level of pacing imposed, work height and memory load within the task were all varied. The results showed that the type of pacing commonly imposed (as is common with a lean manufacturing Takt time system in industry) can significantly affect both performance and perceived workload and stress. Physical demands (through work height affecting posture) and mental demand (through memory load) were also found to have significant effects, as would be expected from the many studies of these in the literature. More importantly, some interactions were found between pacing and work height in their effects on quality of assembly and the operator's own rating of performance, and between work height and memory load in their effects on errors. These findings will need to be taken into account by companies when implementing Takt time systems.

Seated work postures for manual, visual and combined tasks.

An awkward and static work posture has been recognized as a risk factor for work-related musculoskeletal problems. The objective of this study was to investigate some of the factors that can influence the posture adopted during work and in particular aspects of the task and how their influence is affected by work height. Three types of task were studied: a peg-hole assembly task, which was largely manual with very little visual component; a visual character identification task; and a combination of the two. Two levels of difficulty were included in each of the manual and visual elements. Postures of the head/neck, trunk and arm were recorded during performance of these tasks. The results showed that type and difficulty of task do influence the posture adopted, and that some of the postural responses (although complex) are predictable so that poor postures could be improved by adjusting task design in addition to workplace layout.

Effect of handle design for cylinder trolleys.

An experiment was carried out to investigate the effects of handle design on the biomechanical stresses imposed in the use of a cylinder trolley. Nine combinations of handle orientations (35 degrees, 50 degrees, 70 degrees)and handle length (1.0, 1.1, 1.2 m) were tested for the initial starting off phase and the steady moving phase. Two weights of cylinder (19 and 37 kg) were used. Measurements were made of wrist angle, elbow flexion, force at the feet and subjective ratings of effort, discomfort and stability as well as the angle at which the trolley was tilted. The biomechanical loads on the spine and joints of the arm were also calculated. High stresses at the elbow and considerable wrist deviations were found to occur during the starting phase. The elbow stresses were significantly affected by the design of the trolley handle, as was the degree to which the trolley was tilted while moving forward with load. For starting, the best configuration proved to be a 35 degrees handle angle and a 1.0 m handle length. The results were, however, less clear in determining the best configuration for pushing the trolley forwards.

Force exertion in awkward working postures--strength capability while twisting or working overhead.

Isometric strength data have been collected for three of the awkward work situations often imposed by workplace constraints in industry, as found in jobs such as maintenance and repair. The effects of the task layout factors (location of the workpiece, reach distance and direction of force exertion) were investigated and the data has been tabulated to show the degree to which strength may be reduced in different situations. Strength measurements in the present study were found to be considerably higher than previous measurements, apparently due to differences in instructions on foot placement that were given to subjects, which indicates that even small constraints on posture within the workplace may have large effects on the ability to exert force.

Strength capability while kneeling.

Work sometimes has to be carried out kneeling, particularly where jobs are performed in confined spaces as is common for miners, aircraft baggage handlers and maintenance workers. In order to assess the risks in performing forceful tasks under such conditions, data is needed on strength capabilities of kneeling subjects. A study was undertaken to measure isometric strength in single-handed exertions for male subjects and to investigate the effects on this of task layout factors (direction of force exertion, reach distance, height of the workpiece and orientation relative to the subject's sagittal plane). The data has been tabulated to show the degree to which strength may be reduced in different situations and analysis of the task factors showed their influence to be complex with direction of exertion and reach distance having the greatest effect. The results also suggest that exertions are weaker when subjects are kneeling on two knees than when kneeling on one knee, although this needs to be confirmed by direct experimental comparison.

Usability of manual handling aids for transporting materials.

Manual transport aids (trucks and trolleys) are in widespread use throughout most industries, but their use does not always result in the anticipated reduction of workload or musculoskeletal stress. A survey of users has shown that many of the aids currently used are poorly designed or inappropriate for the tasks performed. The information gained during the survey has been analysed to identify the most important design features and to provide guidance for their selection and evaluation, in order to ensure that aids are suitable for the tasks for which they are used and that they are effective and safe. It is clear that the first stage in establishing design criteria and guidelines should be developing an understanding of the task requirements and environmental conditions under which materials have to be transported in industry.

Factors affecting posture for machine sewing tasks: the need for changes in sewing machine design.

Sewing machinists suffer from musculoskeletal problems, which have been attributed to poor working postures as well as to the repetitive hand and arm movements. Their posture is constrained by both the visual and the manual aspects of the task, and the design of the sewing machine and table have a considerable influence on the posture adopted. The potential for improvement of industrial sewing machines was investigated in a study of the effects of two design parameters (table inclination and view of the needle). It was shown that both trunk posture and head/neck flexion could be improved significantly by altering these design parameters. Trunk posture was found to be strongly related to the manual aspects of the task, and could be improved by altering the working positions for the arm. Head posture was most influenced by the view of the task/needle and could be improved by improving the visual condition for the task.

Integrating ergonomics and engineering in the technical design process.

Leyland DAF and the University of Nottingham collaborated in establishing an ergonomics team to support the truck design and development process in the company. The project was planned within the framework of a Teaching Company Scheme funded jointly by Leyland DAF and the UK government. This framework provided a training environment in which the team, which was formed of young professional ergonomists and engineers, could quickly acquire the specialist skills needed for work in the automotive industry in addition to gaining practical experience in applying ergonomics, and the programme was structured to promote the integration of ergonomics and engineering considerations within the technical design process. The experience gained in this project has shown the benefits of such an approach to implementing ergonomics in product design, and provided an insight into the ways in which ergonomists and designers can communicate more effectively in a manufacturing organization.

What do we mean by a 'working posture'?

No clear definition of 'posture' can be found in ergonomics literature. It may be regarded as the configuration of the body's head, trunk and limbs in space or as a 'quasistatic biomechanical alignment' (Rohmert and Mainzer 1986), depending on whether the particular context in which it is used is anatomical or biomechanical. The functional aspects of posture are highlighted by the definition of a 'position adopted because it is appropriate for the task being performed' (Corlett 1981). Yet, in any work situation, functional, geometric, and biomechanical aspects are as integral to the concept of posture as they are to the consequences for performance and comfort. A simple task posture model, describing the relationships between the various factors which influence working postures, is presented as an aid to workplace design, and two examples are given to show how the model can be applied to the demands of particular types of task. An analysis is also made of the factors involved in the exertion of force, including physiological, environmental, personal, and task factors, in order to give a better understanding of the influences of task and workplace on strength capability.

Driving for handicapped people.

Physical handicaps often make it difficult to use an ordinary production car. Access can be a major problem for both driver and passenger, while the design of controls has to be matched to the functional capabilities of the individual driver. Provision of an adequate driving posture and storage for a wheelchair also have to be considered. Many of these problems can be overcome by suitable adaptations to the vehicle. Recent work in this field is reviewed to summarize the ergonomic guidelines that are available. The driving task also requires cognitive skills and adequate speeds of reaction as well as physical skills and capabilities. Better methods of assessing these are gradually being developed, but much further work is necessary in this area. Disabled drivers need instructors who are skilled in training for their special needs. New developments have occurred in powered controls and in their mode of operation, allowing greater numbers of severely disabled people to drive. Steering controls can now be produced which require virtually zero force or very little movement to operate, and driving with a single multi-function control can be expected in the very near future.

Dummies for crash testing motor cars.

The paper describes the design and development of the Ogle-MIRA anthropomorphic dummies over the past five years. In the motor industry these dummies are used in safety testing of vehicles and the design of restraint systems. The work started at MIRA in 1969 to produce a dummy which was sufficiently realistic to test steering columns and safety belts for vehicle occupants. The first dummies were manufactured by David Ogle Ltd in 1972 and an advanced dummy (the OPAT Dummy) has now been designed in collaboration with the Transport aand Road Research Laboratory.