ALLOCATING NONUNITARY RESOURCES IN A CONSTRAINT-BASED SCHEDULER

The new flexibility of industrial plants increases managerial and orga nizational problems. The number of alternatives increases, the mix of products grows, each product can be manufactured on different machines , the trend towards just-in-time production requires that the system r eact quickly, and reduces the temporal intervals for where to allocate activities. So the ''only manual'' approach to scheduling is inadequa te. However, the present level of knowledge and expertise and the solu tions so far used should be carefully considered. From this considerat ion we propose an architecture that could, in a smooth way, integrate the present solution and organization with new knowledge formulation a nd problem solving strategies. We have studied the organization of an Italian company that produces shoe soles for the world market. The hig h mix of products and the flexibility required by the production facil ities impact on the scheduling activity. Here, scheduling could be ini tially approached as a one-machine problem, where the machine is the c uring press and has a non-unitary capacity. The allocation of this mac hine is governed by many constraints that account for a great variety of conditions, both technological and organizational. We have defined the scheduling and resource allocation problem as a constraint satisfa ction problem. We have provided a solution algorithm that orders the c onstraints and applies constraint checking. We have integrated the sch eduling system with the existent PLC automation and with the central d ata and central processor. The result is a real-time system, running o n a PC, and producing the schedules for the next seven days. The sched uler is routinely called once a day, to take into account the data abo ut real production. The production manager can call it in case of disr upting events. Finally, we discuss the implementation and testing of o ur system.