Keywords

1 Introduction

Seating comfort is an important issue in long distance transportation vehicles.

The survey form Institute of Occupational Safety and Health (2003) pointed out that up to 86.3% of bus drivers have musculoskeletal discomfort, owing to that truck drivers have to maintain a fixed position for a long to in the limited space. Over time poor posture results in pain, muscle aches, tension and headache and can lead to long term complications such as osteoarthritis (2009).

1.1 Neck and Shoulder Stress

When travelling, passengers maintain a fixed posture for hours and often complain about neck and back pain. According to the observation, most of seat designs are using a pillow-like headrest on chair back which might force user’s head forward. According to Cailliet (1993) M. D., former director of the department of physical medicine and rehabilitation at the University of Southern California, maintaining a forward head posture causes stress concentration in the neck and shoulder.

In recent years, most of seat designs are more emphasis on innovative design, generous seat space; comfort features such as seat material, and rarely pay attentions to ergonomics like the neck and back pain caused by long time use.

1.2 Preventing a Forward Head Posture

According to the shortcomings of the traditional passenger seat which users familiar with, the most uncomfortable issue is difficult to sleep in the seat. One of reasons is hard to stably rest the head in the headrest which cause to neck and shoulder stress.

Traditional cabin seats provide a pillow-like head support for user as an ergonomics feature, which forces the user’s head forward. Maintaining a forward head posture it will causes stress concentration in the neck and shoulder, resulting in neck and shoulder pain (Fig. 1).

Fig. 1.
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Static muscular efforts caused by an improper headrest that forces head forward.

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2 Design Research

2.1 For Neck and Shoulder Stress Improvement

A tilted backward angle at about 22° on the seat from the shoulder height will keep the center of gravity of the head in a straight line on spine. Moreover, a proper neck support leads the head gravity, neck and spine in a naturally straight line, significantly reduce neck stress (Fig. 2).

Fig. 2.
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To prevent a forward head posture (FHP), a backward angle from neck support of chair back was proposed.

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2.2 For Head Fix

Moreover, maintaining a sitting posture for a long period of time might lead to static muscular efforts which cause discomfort. When shifting upper trunk, the passenger’s head rest in different position on the headrest. A design of wide headrest with three V-shape notches would provide passengers with better head support following the upper trunk shifting (Fig. 3).

Fig. 3.
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A three V-shape notch was designed for passenger’s head rest in different position when shifting upper trunk.

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3 Design Improvement

Chairs of the prior art are usually structured from a chair base, a chair cushion and a chair back, wherein the chair cushion is disposed on the chair base, and the chair back is joined to the chair cushion at an appropriate angle of inclination, thereby enabling the back of the user to lean against the chair back when sitting on the chair cushion.

However, chair backs of chairs of the prior art are unable to effectively support the cervical vertebra, resulting in poor head postures when sitting, thereby causing pressure on the peripheral nerves of the cervical vertebra when sitting or slee** on chairs of the prior art for long periods of time and affecting development of the central nervous system.

In addition to the head and neck support, other ergonomics feature will be integrated to achieve a comfortable cabin seat design. The proposed design features of cabin seat are as follows:

3.1 Headrest

A backward angle from neck support of chair back could shift the head gravity forward to keep head and trunk in a straight. It would decline the stress from the forward head posture (Fig. 4).

figure 4

Fig. 4.

3.2 V-Shape Notches

The three V-shape headrest notches in various angles would enable the passenger to maintain a comfortable sitting posture when shifting upper trunk (Fig. 5).

figure 5

Fig. 5.

3.3 Neck Support

A proper convex cylindrical neck support would effectively relieve the neck stress (Fig. 6).

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Fig. 6.

4 Conclusion

The present invention relates to an improved ergonomic chair for transportation cabin, and more particularly to an ergonomic chair which enables a chair back to appropriately support the cervical vertebra, and thereby avoid neck pains when sitting.

The design research is based on the question that the traditional passenger seat headrest is the main factor leading to neck and back pain. The severity of the neck issue may depend on the amount of tension on the cord or tension on the nerves. The design solution maintains a nature cervical curve which supports a relaxed spinal cord.

After design improvement, the seat headrests changed from forward to backward, users head and spine can maintain in a nature curve, these design features effectively improve the neck and back pain conditions.

In summary, the improvement of head and neck support design is new to the market, the user’s experiences after functional model test are also positive. Although the user’s experience is positive, professional ergonomic testing is required in order to achieve the optimal specifications.

The innovative design would benefit airlines and bus companies for better customer satisfaction in seating (Fig. 7).

Fig. 7.
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Seat design rendering

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