Finite Capacity Scheduling
Finite Capacity Scheduling Overview
Finite Capacity Scheduling (FCS) software determines operation start and finish times, and eventually order, or requirement, start and finish times. In calculating start and finish times, Finite Capacity Scheduling considers the limited, or finite, capacity of production resources.
To calculate start and finish times, Finite Capacity Scheduling uses time per piece or a fixed time, along with other times such as set up and teardown, to calculate the duration of an operation. The technique then schedules this duration onto the available time (based on shifts and calendars) of a resource or resources (for instance a machine). When resources (machines) are finite, other operations that are also available to be scheduled at the same time are shifted forward, or backward, so they start or finish after the first operation scheduled. In addition to scheduling forward or backward in time, a combination of the two approaches may be used when employing Finite Capacity Scheduling.
The Gantt chart screen view below provides a simple example of scheduling finitely forward in time. In the example, the three machines are available first shift Monday through Friday. Available time is represented by gaps in the Gantt chart, while off time is represented with cross hatching. Two orders, each with three operations, are scheduled. The three operations of Order_1 are represented in blue, while the three operations of Order_2 are represented in cyan, with part of Operation 30 of Order_2 also appearing in red. The red color represents the portion of Operation 30 scheduled to finish after Order_2’s due date.
First Order_1, and then Order_2, were scheduled forward. Since the machines are finite, operations of Order_2 must wait to start until after the scheduled finish of operations of Order_1. The “bottleneck” in this particular example is Machine_2. The time Operation 20 waits to access this machine is what causes Order_2 to be late.
Given the volume of computations involved, computers and associated software are required to implement Finite Capacity Scheduling approaches in “real world” environments. While Finite Capacity Scheduling software has been commercially available for years, the advent of fast affordable computers with graphical user interfaces and software has made Finite Capacity Scheduling software applicable in a wide range of production environments.
Finite Capacity Scheduling software evolved to fill an obvious hole in the MRP II (Manufacturing Resource Planning) paradigm used in most business systems. Under this paradigm, the Master Production Schedule is input into the MRP (Materials Requirement Planning) module, which generates shop orders for the floor to run. Due to inherent problems with Capacity Planning, very seldom could operations departments produce shop orders in a manner that adequately served customers.
Extensions to Finite Capacity Scheduling
As in the example above, initially Finite Capacity Scheduling software only modeled machine constraints. Over time, the Finite Capacity Scheduling software has evolved to become more full-featured. For example, in job shop scheduling environments, there are often more machines than people. Sometimes multiple operations compete for the same machine, but other times there are multiple operations available to run on multiple different machines simultaneously, but not enough labor to staff the machines. In these environments, machine constraints and labor constraints need to be modeled simultaneously by the Finite Capacity Scheduling software.
In other environments, the Finite Capacity Scheduling software needs to model tooling constraints simultaneously with machine and labor constraints. For instance, in stamping or molding operations, by adjusting tooling inserts, two or more different part numbers may be made from the same die or mold. When one such part number is using the die or mold, another must wait.
Finite Capacity Scheduling software has also evolved to consider materials. In its early forms, Finite Capacity scheduling software was able to consider materials in such a way that the ordering of materials is synchronized with the scheduling. So, if the scheduling of operations was delayed due to capacity constraints, the corresponding requirement for material could also be delayed. This synchronization of material and capacity supports concepts such as Lean Production Scheduling, and results in steep reduction of inventory. More recent versions of Finite Capacity Scheduling software include even more robust features for modeling materials.
As Finite Capacity Scheduling software has continued to evolve, and become more feature rich, it has become known as Advanced Planning and Scheduling software (APS software).