On the other hand, the calculation results for the vertical position and overhead position show similar tendency。 However, in the vertical position, the torque exceeding 80 Nm occurred at the knee, and this resulted in more severe result corresponding to 68 P。C。 (32  percent people can't bear the torque)。

Among the three positions, the flat position seems to be the hardest posture of work。 Though it is a basic concept in welding planning that the overhead position and vertical position should be avoided as much as possible in order to obtain a good quality of weld, it is learned here that the overhead position is a comparatively easy posture for a human body, while this  calculation does not include symptoms such as stiff shoulder, stiff neck and so on。

Energy Expenditure Analysis

Referring to the result of observations using a video camera in the shipyard, 10 minutes was assumed to  be 1 cycle, which includes 8 minutes of welding work and 2 minutes of movement to the next place。 The work- model is illustrated in Fig。7 for the flat position as an example。 Energy expenditure calculations were carried out for the three positions using the same  model of work cycle as Fig。7。 The calculation results are shown in Fig。8。

In the figure, the total task energy means the energy consumption by a task using both hands, while bent posture energy, sitting posture energy, and standing posture energy show the energy to maintain such work postures。Walk（1min）

Crouching - down

Flat position （0。5min）

Time (hour)

Fig。7: Work Cycle (flat position)

Fig。9: Allowable Energy Expenditures

Simulation of Grinding Work

Flat Vertical Overhead

Fig。8: Calculated Energy Expenditures

Human Model of Grinding Worker

Referring to the many postures on-site, 7 kinds of representative models were selected as shown in Fig。10。 In grinding, the analysis was carried out using 10kgf maximum value as the reaction force from the tool by field measurement。 Body size is taken to be the same as before。

From Fig。8, the bent posture energy is comparatively high for the flat position due to its posture, while the overhead position only involves standing posture energy。

The energy consumption is high in the flat position (2。87kcal/min), vertical position (2。76 kcal /min), and overhead position (2。69kcal/min) in order, which reflects the static strength calculation。 However, the difference among these three positions is not so large。

Fig。9 shows the calculated allowable values by “Jack”; 2。72kcal/min for 8 hours continuous work and 3。11kcal/min for 4 hours work。 Comparing Fig。8 with Fig。9, the energy expenditures of the flat position and vertical position exceed the allowable value in the case of 8 hours, and that of the overhead position is close to the allowable value。

In the case of 4 hours, it is understood that the energy expenditures of any of the 3 positions are sufficiently under the allowable value。 Therefore, accumulation of physical fatigue does not seem to occur for welding in this case, if the sufficient rest is taken in a half day (for 4 hours)。

This result does not take boundary conditions such as temperature, humidity, and equipments of the welder into consideration。 Hence, the energy consumption in actual work seems to rise a little。

(a)Squat-L (b)Squat-H (c)Squat-U (d)Stoop

(e)Standing-H (f)Standing-U