Computer Optimized Manufacturing

Energy Expenditure

It is important to consider the workers so that fatigue does not accumulate。 The accumulation of fatigue causes a decrease in operational performance of the workers,   and   also   may   cause   industrial accidents。

Digital manufacturing Though the fatigue phenomenon is complicated by mental and physiological factors, only physical or muscular fatigue is examined in this paper。

The energy consumption during work can be calculated in “Jack”, based on the study of Garg et al。 (Garg, 1978)。  The  energy  expenditure  rate  is  given  in   the

effectively used here for the simulation。 A biomechanics-based human model is shown in Fig。2; a human body is assumed as a system of links and connected joints, considering the dimension and weight of each segment, and the equilibrium of moment and force is calculated。 “Jack” models a mechanical human body with 69 segments and 68 joints (135 freedoms)。

Where Eposi is obtained by static strength, considering the gender,  body  weight  and  posture。  Task  energy Δ Etaskj is gained experimentally for each task in accordance with the parameter such as carrying-weight and height, speed, load, frequency, etc。 This is given for

25 specific jobs by the experimental formulas。 For example, the task energy to lift something is

Fig。2: Virtual Human Model (Skeleton)

Static Strength Prediction

The static strength on a human body is predicted by one of the modules of “Jack”。 The torque on human body joints can be obtained by solving the equilibrium of self-weight of each segment and the loaded weight on both hands, considering the possible rotation angle of each segment, which was gained by statistical analysis。 The human posture, body size and weight are inputted。 Furthermore, the proportion of the population to be able to bear this calculated torque is calculated as a result of statistical data of American people。 This value is called percent capable (P。C。) hereafter。

BW：Body weight(kgf)

L：lifting weight(kgf) S：Coefficient，male;1，female;0 h1：Start height(m)

h2：End height(m)

The effects of the temperature, humidity, environment, etc。 are not considered in the analysis。

Simulation of Welding Work

Human model of Welder

As a result of observing welding work in shipyards, three postures are selected as shown in Fig。3- Fig。5; flat position, vertical position, and overhead position。 The human model is 165cm tall and 61。6kg in weight which are mean values for Japanese men。

Though many types of welds have been introduced recently, CO2 semi-automatic welding is widely applied。

In this case, a welder has a torch connected with cables

in his right hand and a shield (mask) in his left hand 1

usually。  Hence the  hand  loads  on  a human  model are 1

taken to be 3kg in right hand and 1。5kg in left hand。

(a)Actual posture (b) Human model

Fig。3: Flat Position

Static Strength Analysis

The results of the static strength analysis for each posture are shown in Fig。 6 (for torque on each joint) and Table 1 (for percent capable)。

In the flat position, the largest torque occurs on the lower body, especially on the trunk (flex/ext), because the trunk turns extremely in front, and it exceeds 100 Nm。 However, the percent capable(P。C。) was negligible because the trunk has enough strength to endure this position。 The torque on the knee reaches 50 Nm, and this value corresponds to 92% P。C。 in population rate (i。e。 8 percent of people can't bear the torque)。 The P。C。 on hip and ankle in the flat position were 97。5% and 99 % respectively。