ANALYSIS AND DESIGN FOR TWO-HANDED HEAVY PART ASSEMBLY METHODS

摘要

In spite of advances in industrial automation, manual assembly tasks continue to be an important feature of many industrial operations. In heavy part assembly, some pieces of raw material or equipment are too heavy to be safely handled by just one operator. Material handling devices such as Jib cranes or overhead cranes are employed to help operators work safer and, in some cases, faster. However, during full-load productions, access to these devices could become limited due to insufficient resources and hence, delay or extend the cycle times. The authors studied how people perform the assembly and subsequently applied Fitts' Index of Difficulty to develop a model which indicates factors that increase the task difficulty. This model can also be used as an assembly time predictor. Since improving the efficiency of an overhead crane could significantly reduce the total cycle times and production costs, the authors modified the crane by adding a spring between the hook and the gripper to help support the weight. Two sets of experiments were conducted. The first set was to investigate the effect of spring stiffness on assembly time. The result indicated that using a spring that was too soft could create a parasitic oscillation, which increases the assembly time. The objective of the second set was to compare the assembly time of using the regular crane to that of the modified crane in situations where the part weights and the task difficulty vary. As a result of the modifications, assembly performance tended to increase by approximately 250% from using the modified crane.