Workload virtualization of the tram driver's vision field.

Jurum-Kipke, Jasna ; Muftic, Osman ; Kovacevic, Drazen 等

1. INTRODUCTION

The first of some hundred low-floor trams of type TMK 2200, was delivered to ZET on 27 April 2005; a tram 32 metres long, that can carry 202 passengers, reaching maximum speed of 70km/h. It is managed from the driver's cab by means of a control lever. The cab also accommodates the monitors that display all the parameters required by the driver during work.

Regular tram traffic operates on 116,346 m of tracks with 191 tram motor cars and 62 trailers operating every day. The total length of the tracks on 15 lines of daily traffic is 148 km, and on four night lines 57 km. There are 167 switches in the city and 255 tram stops. The trams in the City of Zagreb carry annually about 204,000,000 passengers (Zagrebacki Holding, 2009).

The current rolling stock consists of several types of modern trams of different manufacturers. We focus on the Crotram consortium with 110 attractive, modern, hundred percent low-floor trams of type NT 2200, Figure 1.

[FIGURE 1 OMITTED]

2. BIOLOGICAL 3D ANTHROPOMETRY

Knowing the dimensions of the body and some body segments of the driver and their biomechanical action characteristics is the basis of the approach to designing virtual 3D character models. The choice of ergonomic anthropometric measures varies depending on an entire series of factors--first of all depending on the form of the interior of the tram driver's working environment and the functions of individual elements within the working zone. It is therefore necessary to consider also which body parts will be in direct contact with these elements, then to define those parts that are in the close vicinity, or come only occasionally into contact. There are numerous and different sources of anthropometric data that are in principle divided into static, kinematic, and dynamic anthropometric measures (Mijovic et al., 2001).

Determining the anthropometric measures for every individual separately using the conventional method is complex and time-consuming. The introduction of new computer-aided 3D methods allows fast and accurate determination of all the important body dimensions in order to adjust the workplace and ambient dimensions to the anthropometric values of the driver. Consequently, software "ErSABA" was applied, which uses the input data such as body height, weight and gender, as well as the necessary work precision and working postures to determine twenty-two characteristic anthropometric values for the seating and standing working postures of male and female examinees (Tomic et al., 2005).

Regarding the development of virtual models in real correspondence with their actual sources, for the needs of this paper a system of spatial digital three-dimensional body scanning "BodySABA" was applied. Knowing the anthropometric measures, vision fields and reach zones of body parts it is possible to ergonomically design the working ambient systems and to design the workplaces. Table 1 shows the characteristic anthropometric measures for the separate cases of females 160,0 cm tall and males 200,0 cm tall.

3. PHYSIOLOGICAL VISION FIELD ANATOMY

Tram drivers, as traffic participants, express their necessary visual capabilities by recognizing complex structures of horizontal and vertical signalling systems, identifying their distinct forms and colours, observing the movement of vehicles of other traffic participants, resulting eventually in the necessary speed and precision in reacting to the elements of the dynamic traffic environment, based on visual observation. Since trams operate on horizontal urban traffic systems, where all the traffic participants use the same travelling areas, often with increased traffic load, the drivers have to have extremely good visual capabilities, which is decisive for adequate coordination of movements, fast response, and accuracy of performance. The driver's workplace belongs to the closed type with small working area layout and the sitting body posture, so that for adequate design of the workplace, apart from the static and dynamic anthropometric values that refer to the kinematic characteristics of the drivers, the arrangement of work elements is important which provides the necessary level of visual control in performing the working process.

The anatomy of the eye allows transfer of the standard line of vision as the so-called one-eye or two-eye vision. In the plane perpendicular to the standard visual axis, the limit of the upper visual field is 50[degrees], and the limit of the bottom visual field is 70[degrees]. Comfortable eye rotation in the plane perpendicular to the standard line of vision is about 30[degrees] and within this range a normal human eye distinguishes colours. The limit of the right eye vision for one-eye vision in the horizontal plane, Figure 2, is from 94[degrees] to 104[degrees] to the right of the standard line of vision, whereas it is 62[degrees] to the left. With one-eye vision only the anatomic possibilities of the eye are expressed, whereas within the traffic environment the visual inspection is done by means of two-eye vision (Jurum-Kipke et al., 2008).

These considerations are especially important in designing the interior of the control part of the working systems where high level of visual concentration and control is necessary, and the transfer and concentration of vision is significant to make decisions or continue working. The instruments which are the object of visual concentration should be positioned within the visual zone areas, in comfortable area of eyes rotation and head movements, as well as at the same distance from the eyes (dome area of the sphere), thus eliminating the accommodation jump, and determining in this way the favourable arrangement of instruments and control equipment. It is necessary to determine the anthropodynamic characteristics of the driver's body since the angles of sight transfer realized by the front head flexion and eye rotation depend on the working posture during tram control (Maver et al., 2008).

[FIGURE 2 OMITTED]

4. RESEARCH RESULTS

The authors have carried out computer-aided 3D visualisation of ergonomic design of the driver's posture at the driving workplace of the tram CroTram NT2200. The virtualization has been realized by means of a computer-developed 3D model of the tram and computer character animation of the digitally generated persons of different anthropometric structures of male and female gender. The computer scientific visualisation of 3D character in inversely kinematic and dynamic relation with the control and command part of the interior of the tram driving cab, determined the acceptable biomechanical loads of the driver's visual fields.

Figure 3a shows the virtualized 3D presentation of the visual field range of a two-eye vision (recognition of symbols and distinguishing of colours) within the front plane of the tram female driver, 160 cm tall, and Figure 3b shows visualized presentations of the visual fields within the sagital plane of a female examinee 160 cm tall and a male examinee 200 cm tall.

[FIGURE 3 OMITTED]

5. CONCLUSION

During ergonomic modelling of the working conditions and the arrangement of the working elements using virtualization of the workload of the visual field, it was found that in cases when the control by means of the visual system is realized within comfortable anatomic possibilities of the physiological transfer of the line of vision, this contributes to a large extent to a lower level of fatigue and better coordination of movements.

In the working processes the drivers can transfer the standard line of vision, which they use to realize the required control, according to the anatomic possibilities of their visual system, in the following ways: by vertical and horizontal eye rotation, vertical, horizontal or lateral movement of the head, and dually combined movements of the eyes and the head. Therefore, the future research done by the authors will be oriented in this direction.

6. REFERENCES

Jurum-Kipke, J.; Kovacevic, D. & Baksa, S. (2008) Computer Visualisation of Anthropometric Vision Fields of tram Drivers, XV Con. Trans& MOTAUTO 2008, pp. 106-110, Sozopol, September, 2008, Mec. Eng. Union, Sozopol.

Maver, H.; Rudan, P. & Tarbuk, D. (1976). Practical work in anthropology, Ergonomijske Metode, Ant. Bib., Zagreb

Mijovic, B.; Ujevic, D. & Baksa, S. (2001). Visualization of Anthropometric Measures of Workers in Computer 3D Modeling of Work Place. Collegium Antropologicum, 25., 56., (2001), 639-650, ISSN 0350-6134

Tomic, D. ; Muftic, O. & Baksa, S. (2005) Computer 3D Spectral Analysis of Human Movements, CAES 2005, International Ergonomics Conference, Sinay, J., pp. 1-12, Kosice, Slovakia, May, 2005, IEA & SEA, Slovakia.

*** (2009) http://www.zet.hr/tramvaj--Zagrebacki Holding, Podruznica ZET, Accesed on: 2009-04-04 Tab. 1. Anthropo measures of male and female examinees Values (cm) Symbol and name of anthropometric measure Female Male A Body tallness 160,0 200,0 G Arm length (from the back contour) 68,9 98,5 H Length of forearm with hand 41,8 54,3 K Body thickness (chest) 24,2 25,1 M Sitting height 81,5 100,4 N Eyesight height (sitting) 70,9 89,4 O Shoulder height (sitting) 52,3 66,3 P Elbow height (sitting) 20,9 25,1 R Distance from knee to back 54,3 69,3 S Sitting length of thighs 44,8 54,3 T Sitting height above floor 41,8 53,3 U Height of thigh (sitting) 13,6 15,1 X Foot width 8,8 11,0 Y Hand length 16,9 23,2