Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

14.3.3 Constraint-Oriented Finite Loading

Intended learning outcomes: Identify bottleneck capacities and the drum-buffer-rope technique. Describe the drum, the buffer, and the rope. Present an evaluation of the technique. Identify its limitations and typical areas of application.

In constraint-oriented finite loading, orders are planned around bottlenecks, or bottleneck capacities, which are work centers with a capacity utilization of 100% or more.

Bottlenecks depend on the given order volume and not upon the master data for the work center.

Drum-buffer-rope is a technique of production control that accords with the theory of constraints (TOC). See also Section 5.1.5 and [GoCo14].

The drum-buffer-rope technique includes the components shown in Figure

Fig.       The drum-buffer-rope technique.

The drum stands for the rate or pace of the system. The “drumbeat” results from the drum schedule, that is, the master production schedule for the system, set by the throughput of the constraint, which should be balanced with the customer demand. The constraint controls the throughput of all products that it processes. Feeder workstations, that is, work centers feeding bottlenecks, should be scheduled at a rate that the bottleneck can process.

A buffer in front of the constraint absorbs potential disturbances during a certain period of time. Buffer management expedites material in time buffers (that is, protection against uncertainty that takes the form of time) in front of constraints and helps to avoid idleness at the constraint. To avoid idle time due to disturbances of the succeeding operations, buffer management can also include the maintenance of a space buffer after the constraint. Compare here Figure

The rope is an analogy for the communication process: the set of planning, release, and control instructions for bringing the necessary material for production to the constraint in due time. This can be achieved using any technique: pull (e.g., Kanban or reorder point type, or generic Kanban, i.e., a card that only serves to release the next order, for whatever item ID) or push (MRP type; for example, by releasing material at the right time into the system), or any other appropriate intuitive or heuristic technique for the specific case.

Evaluation of the drum-buffer-rope technique: The following prerequi­sites must be satisfied for use of this planning technique:

  • Our picture of the capacity and load must be accurate, that is, the planning data and reported work progress must “tally.”
  • Bottleneck capacities must be known and remain stable. Any change requires replanning of the elements drum, buffer, and rope.
  • The order due dates must have a degree of flexibility, since the completion date for an order is determined by the way in which the orders come together at bottleneck capacities and by the subsequent forward scheduling.
  • In fact, most work centers must have somewhat flexible capacity, or they would all become bottleneck work centers.

The following limitations apply:

  • There must not be too many bottleneck capacities. In particular, the technique is unsuitable for situations where for a single order there are multiple bottleneck capacities, which may not follow in succession or may even be located at other production stages. Other­wise, it would become difficult or even impossible to determine the “rope” part of the technique in detail. This means that the techniques are applicable mainly for simple — for example, one-level — product structures.

Typical areas of application are the following:

  • The technique is suited to mature line production running at a fixed rate, for example, simple chemical products, food processing, or production of simple parts.
  • The technique is especially suited for machine-limited capacity, or a production en­vironment where a specific machine limits throughput of the process (cf. [ASCM22]).

Course section 14.3: Subsections and their intended learning outcomes