2006 Volume 57 Issue 2 Pages 132-143
Ways for evaluating work burden in an assembly process can be classified into two methods: one for obtaining a torque that is exerted on the joints of the human body, and the other using rapid upper limb assessment (RULA), which is set in accordance with the bend angles of joints. The drawback of the method for obtaining the torque of joints is that it necessitates measuring the elasticity coefficients of a number of muscles in the limbs of a worker. On the other hand, the RULA method is not applied until after the design and construction of a work process is actually completed. This paper proposes a method that makes it possible to analyze work burden even in the process design stage. Our method employs a human body link model. This model has seven joints in the upper half of the body and two joints in the two legs. As constraints, we designate the positions of the fingers at the starting and ending points of a motion, physical characteristics and the range of bend angles of joints established by RULA. Further, we set the sum total of the values obtained by multiplying the bend angles by a coefficient as the objective function. Next, we obtain a solution that minimizes the objective function using the quasi-Newton method to reveal the postures at the starting and ending points of a motion. As an application example, we designed a working area for the assembly of a household appliance. Then we actually manufactured a work table for assembly and carried out the assembly to study the differences between the results of the simulation by this method and actual work burden.
