Drum-Buffer-Rope Scheduling

Introduction

This is the Theory of Constraints method for scheduling and managing operations that have a consistent internal constraint or capacity-constrained resource. In "Drum-Buffer-Rope", the “Drum” is the consistent constraint that sets the pace of the rest of the non-constrained Resources. The Drum limits the amount of Throughput for the company. The “Buffer” is a time-based work backlog that is purposely maintained before a Drum Resource to avoid starving the Drum, which is undesirable since that would reduce the Throughput achieved by the system. The “Rope” is the information flow from the Drum to the front of the line material release, which regulates the release of materials to match the flow through the constraint. This avoids unnecessary build-up of work-in-process inventory beyond what is needed to protect the Drum. The “Rope” is calculated automatically for each Manufacturing Order so that it is released at the right time to reach the Drum buffer-time before it needs to be there for on time delivery (and taking the Shipping Buffer into account).

Using the Drum-Buffer-Rope Optimize Release Rule will direct APS to schedule according to this method.

Key Concepts

Each MO is released on its DBR Release Date minus the JIT Slack Days specified in the Optimize Settings. This is the EARLIEST that the Optimize will start the MO. It can start later if there are other constraints or if other MOs are scheduled ahead of it.

DBR Release Date: If the MO uses a Drum Resources then this is the Drum Due Date minus the Drum Buffer. Otherwise it is the JIT Start Date minus the MO Shipping Buffer.

Drum Due Date: The JIT Start Date of the Drum Operation minus the MO Shipping Buffer. This is only valid for MOs scheduled on a Drum.