Workplace dimension adaptation to worker as one of tools for increasing human work effectiveness.

Hatiar, Karol ; Caganova, Dagmar

1. INTRODUCTION

Adaptation of workplace dimensions to individual workers provides an opportunity to increase their work effectiveness. Programs available for applying this in the Slovak Republic don't respect specific data of employee population and Slovak legislation. This was the reason why we developed a method enabling to derive expected individual dimensions of workplace for the individual worker on the base of his anthropometric parameters.

2. THE METHOD DESCRIPTION

Expected workplace dimensions for individuals are derived from their anthropometric dimensions by simply mathematical procedures. Anthropometric dimensions used are defined as a direct distance of two anthropometric points (x<->y) or a distances between some of anthropometric points from some of reference planes (tab.1). Next methodical material used is standard ISO 11226:2000.

[FIGURE 1 OMITTED]

Explanatory notes to anthropometric points and plains: "b"-basis; "bs"--basis sedens; "ges"--anthropometric point over patella upper edge in the direction of skin projection prolonged front edge of tibia; "fe"--point femorale; "a"--point acromion; "ol"--point olecranon; "pop" point popliteale.

[FIGURE 2 OMITTED]

We derived data for two strategies of expected parameters of workplaces adjustment parameters (Fig.2): strategy of adjustable table height (A) and strategy of constant table height (B).

This approach allows to the worker a maximum rate of natural changes in basic working postures and prevents the restriction of blood circulation by direct pressure to blood vessels and also supports blood return to the heart by activation of a "muscle pump" function. Practically we can recognize correct chair seat height adjustment if it exist between upper surface of chair seat close to seat edge and under part of thigh in sitting space enough for "fingers of hand" (Fig.3).

On the base of the above mentioned principles, angles of trunk and arms [4], goniometric function cosine and measured anthropometrical parameters of individual workers or 5th, 50th and 95th percentiles we can derive all parameters necessary for evaluation of individual worker, workplace dimensions as well as evaluation of workplace dimensions for a given population. It is necessary to add measured work shoe heel height to all these parameters.

[FIGURE 3 OMITTED]

2.1 Strategy of adjustable table height

In the case of adjustable table height (Fig. 2A) we calculate parameters: adjustable table minimum height abbreviation [TH.sub.min.] calculated according to formula (2); adjustable table maximum height--abbreviation [TH.sub.max.] according to formula (3) on the basis of adjustable chair parameter individually adapted to expected seat height abbreviation ESH, calculated according to formula (1).

ESH = HKst--MTHast (1)

[TH.min] = ESH+ {EHst-[ SHst -(SHst x cos 24[degrees])]} (2)

[TH.sub.max] = ESH+{EHst + [UAL--(UAL x cos 20[degrees])]} (3)

This strategy is very rare in Slovakia, more frequently applied in developed countries e. g. in the USA.

2.2 Strategy of constant table height

In Slovakia we have mostly tables with not adaptable height in required size, but adaptable chairs and leg supports. In this case we can again accept requirements of the ISO standard/CD 11226:2000 related to angles of body segments (Fig. 2 B).

It is necessary to define here two basic parameters: minimum acceptable chair seat height--abbreviation x [ESH.sub.min] calculated according to formula (4) and maximum acceptable chair seat height--abbreviation [ESH.sub.max] calculated according to formula (5) adjusted to the constant measured table height (MTH).

[ESH.sub.min] = [MTH.sub.min]--{EHst + [UAL--(UAL x cos 20[degrees])]} (4)

[ESH.sub.max] = [MTH.sub.max]--{EHst--[SHst--(SHst x cos 24[degrees])]} (5)

Contrary to the strategy of adjustable table height it is necessary to define more parameters.

They are:

Minimum expected adjustable leg support height--abbreviation [ELS.sub.min.]., calculated according to formula (6);

[ELS.sub.min.] = ESH--[ESH.sub.min.]. (6)

Maximum expected adjustable leg support height abbreviation [ELS.sub.max], calculated according to formula (7):

[ELS.sub.max] = ESH--[ESH.sub.max] (7)

Expected range for leg support height adjustment--abbreviation RELS, calculated according to formula (8)

RELS = [ELS.sub.max]--[ELS.sub.min.] (8)

Maximum extreme limit leg support height under chair seat abbreviation MLSu can be calculated for minimum and maximum chair height according to formulas (9 and 10) as difference between chair seat height and anthropometric parameter popliteal height of thigh--below knee in sitting position height fossa poplitea (b [left and right arrow] pop).

MLSu = [ESH.sub.min.]--VFP (9)

MLSu = [ESH.sub.max]--VFP. (10)

3. DISCUSSION AND CONCLUSIONS

A lot of materials and standards recommend values of workplace dimensions as height of seats, height of working tables and dimensions of space for movement of upper and lower extremities.

When a workplace evaluation is directed to looking for causes of musculoskeletal system diseases it is insufficient to find out only adaptation of workplace dimensions to the dimensions requested by standards. The degree of adapting workplace dimensions to the body parameters of individual worker is necessary in this case. This was the reason why we have been looking for methods of expected workplace dimensions for individual workers.

The anthropometric data of workers seem to be adequate for deriving such data. Anthropometric measurements are performed worldwide on the basis of standard methods (Martin and Saller 1957). Some of these parameters have to be adapted to the ergonomic purposes (Hanulik, et al 1978).

This area seems to be hopeful using of digitized video records of human body or laser scanning in measuring of anthropometric parameters for ergonomic purposes.

According to our method, the evaluation of individual adaptation of workplace dimensions to the worker is based on the judgment of differences between expected and measured dimensions of the workplace.

One of the disadvantages of classical anthropometric parameters is that they provide information mainly about the reference posture in which measurements were performed but not about the postures workers assume while working.

This shortcoming can be overcome by using population limit data and the data obtained e.g. by system "VERTEX" (Hatiar, 2008) which enables to analyze digitized video records of body postures of workers at work.

Further it will be necessary to deal with a problem of limit values of workplace dimensions based on expected dimensions derived from body dimensions of workers. It will be necessary to learn more about relations between derived vs. measured workplace parameters and the occurrence of musculoskeletal system troubles.

More information of the method presented and its opportunities for implementation to the practice are published in Hatiar 2008 and Cambal 2009.

4. ACKNOWLEDGEMENTS

This work was supported by KEGA-3-7285-09 "Contents Integration and Design of University Textbook "Specialised Robotic Systems" in Print and Interactive Modules"

5. REFERENCES

Cambal, M. (2008). Long--Term Employee Training as a Basic Prerequisite for the Development of an Optimal Corporate Culture, 1st ed., Kothen : Hochschule Anhalt,, 77 s. ISBN 978-3-86011-023-2

Draft ISO 6682 ISO/CD 11226:2000 Evaluation of static working postures

Martin, R. & Saller, K. (1957). Lehrbuch der Anthropologie. Stuttgart. 661 s

Hanulik, M., et al. (1978). Metodology of ergonomics anthropology. (In Slovak) IPD a Katedra antropologie PF UK, Bratislava 1978. 22 pp

Hatiar, K. (2008). Ergonomics and Technology effectiveness. 1st ed.--Kothen : Hochschule Anhalt, 2008.--83 s. (Scientific monographs).--ISBN 978-3-86011-020-1

Tab. 1. Anthropometric parameter abbreviations used in
definitions, formulas, and calculations (Martin et al., 1957)

 Shortened
 definition
 of
Anthropometric (body) measured
parameters parameters Abbreviation

Height of knee in (b [left and right arrow] ges) HKst
sitting

Max. thigh height (bs [left and right arrow] fe) MTHast
 above the seat

Elbow height in (bs [left and right arrow] ol) EHst
 sitting

Upper arm length (a [left and right arrow] ol) UAL

Shoulder height in (a [left and right arrow] bs) SHst
 sitting

Popliteal height of (b [left and right arrow] pop) FPH
 thigh--below knee
 in sitting