Periodic reconfiguration of general-purpose fixtures in a dedicated FMS

Fixtures dedicated to a given part type in an FMS can sometimes become bottlenecks to some FMSs as demand variability increases. Past research indicates that the increased operating flexibility associated with general-purpose fixtures may be a key to the efficient scheduling of even those FMSs dedicated to producing a small number of part types over a known planning horizon. However, the increased time required to reconfigure general-purpose fixtures to meet current demand may also create a bottleneck in the loading area. Increases in the defect rate associated with improper fixture assembly and part alignment are also possible. One solution may be to reconfigure general-purpose fixtures off line according to specific demand schedules for the period, and then to treat them as ‘pseudo-dedicated’ fixtures until the next period. This would utilize some of the flexibility associated with general-purpose fixtures, while reducing drawbacks associated with incremental loading time and alignment errors. The research reported in this article simulates an existing FMS, using fixtures dedicated to individual part types, and compares the results to those collected using a group of general-purpose fixtures that are reconfigured each week, based on current demand for each part type, and used in a pseudo-dedicated fashion. Three simulation experiments are run with increasing coefficients of variation in the input distributions used to generate demand. Performance is measured by system throughput, proportion of parts tardy, and average tardiness. The simulation results show that while overall system performance decreases as the level of demand mix variability increases, this negative impact is significantly less severe when using pseudo-dedicated, general-purpose fixtures.