Modeling and worker motivation in Just In Time production systems

This paper concerns the modeling of low inventory lines. Currently, most models assume that processing times are independent. We consider the differences in behavior of workers in low- and high-inventory production lines. Using a laboratory experiment we show that workers speed up when they are the cause of idle time on the line. This means that processing time distributions are not independent of the size of the buffer, of the processing speed of co-workers, or of the amount of inventory in the system. We show that the direction of these effects is predictable and that the magnitude is significant. In particular, there is less idle time and higher output than would be predicted using assumptions of independence. In this experiment the effect completely cancelled productivity loss due to blocking and starving. This work is important in understanding both the motivation of workers in low-inventory systems and the implications of models of manufacturing flow lines.