1. Development of Posture Analysis Software for Continuous Farm Work
Masafumi Mitarai1, Hironori Matsuoka1, Julius Caesar Sicat2,Tomohiro Mino1, Sayaka Hosoyamada1
1Faculty of Agriculture,Miyazaki University,Miyazaki City,Japan
2Department of Science and Technology Regional Office No.3, Pampanga, Philippines

2. Background and Objective of the Study
Manual farm work is often accompanied by intense work load. Aging farmers doing agriculture in present-day Japan are gradually increasing in number. As a result, problems of accumulated physical stress and weariness increase as well. Therefore, to solve these problems, it is necessary to improve farm working postures as related to the amount of work loads.
To date, various ways of evaluating working postures were developed. Examples are OWAS, RULA, NIOSH and Bless Pro. However, evaluation of work processes and working moments using these softwares is a bit complicated. Also, they are not able to measure the forces and bending moments associated with continuous farm work operations.
A software which analyzes work posture and determines the optimum working posture was developed to solve the problems mentioned above. It can evaluate continuously the forces and bending moments acting on critical body parts of the worker. The body angle data were continuously measured using a work posture monitor VM

3. Work Posture Monitor (VM12-512)
Mac Enaduo (VM12-512) made by VINE company was used as work posture monitor. It was developed to measure the posture of the worker moving continuously. It can measure the inclination angle of each part of the body (body trunk, upper arm, forearm, thigh and portion below the thigh) by angle sensors.
　The angle sensors detect the angular change of measured part relative to the vertical line.
Incidentally, the posture analysis software is limited to the capacity of the work posture monitor, but it can analyze continues work of 27 minutes at intervals of 0.5 seconds.
Figure 1. The angle sensors　 Table 1. Specification of work posture monitor

4. Work Posture Display and Analysis
　The posture analysis software assumes farm work to be two-dimensional. Also, the study focuses on the L5/S1 joint where waist ailment called lumbago frequently occurs. The software analyzes a load that divides the body into two: the upper part of the body trunk and the lower part of the body trunk.
(1)　The work posture display
(2)　Joint bending moment analysis
(3)　Estimation of forces on lumbar vertebrae
L5/S1
Figure 2. The human body model for calculating the various forces and moments on the different joints

5. Forces Acting on L5/S1 L5/S1 Shearing force at L5/S1 disc :Fs
Force at erector spinal :Fm
Compression force at L5/S1 disc :Fc
Abdominal pressure :Fa
L5/S1
Figure 3. Biomechanical model of lumbar loads

6. Calculation of Lumbar Loads
Angle between L5/S1 and the thigh joint - shoulder joint line：
　　　　　　θb= *H *H^ *K^ *H*K 　･･･(3)
Angle between L5/S1 and the shoulder joint - thigh joint line：
θa=sin^-1{(L30*sinθb)/L31}　･･･(4)
Inclination angle of lower body trunk：θp=θ3-θb　･･･(5)
Inclination angle of upper body trunk：θq=θ3+θa　･･･(6)
Force at erector spinal：Fm = (pmp * Fa * D) / e　･･･(7)
Compression force at L5/S1 disc：Fc = Twp* * Cos(Ra) + Lw * * Cos(Ra) - Fa + Fm　･･･(8)
Shearing force at L5/S1 disc：Fs = Twp * * Sin(Ra) + Lw * * Sin(Ra)　･･･(9)
where、
pmp：Bending moment at L5/S1　　　　　　　 Fa：Abdominal pressure　　
　　 D： Lever arm of L5/S1 (abdominal pressure) e：Lever arm of the force at erector spinal
　　 Twp：Weight above L5/S1 　　　　　 Ra：Inclination angle of L5/S1 joint surface　　
　　　Lw：Weight of hand load

7. Posture Analysis Software
START…?
Figure 4. the menu screen of the posture analysis software

8. Conclusion
The work posture analysis software was found effective in the following conditions:
Continuous analysis and evaluation when the work positions of legs and hands are different and loads on both hands are different as well.
Evaluation and improvement of work posture which bends forward and down and momentary overloaded postures such as in manual farm work.
Evaluation and improvement of difficult farm work such as carrying and lifting heavy load.
Analysis and improvement of unstable farm work in inclined places.