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Theory of Constraints (TOC)

Theory of Constraints (TOC) is an approach to process management described by Eli Goldratt in The Goal and subsequent books. The basic principle is to find the biggest constraint in a system, fix this, and then move on to the next constraint. It can be thought of as bottleneck management, although this is probably a simplification.

There are five basic parts:

1. Identify the constraint
2. Decide how to address the constraint
3. Subordinate all other processes to this decision
4. Elevate the priority of addressing constraint
5. When the constraint is relieved, return to step 1 to find the next constraint

Constraints include those due to process, policy, equipment and people.

Managing buffers is a critical activity, although this is different in approach to Kanban in the way it considers the whole system simultaneously. Buffers may be flagged as Red (action), Amber (watch) and Green (ok).

Four types of operation may be considered:

• I-plant: flow of one-to-one, with simple sequence of activities.
• A-plant: flow of many-to-one, such as when using sub-assemblies.
• V-plant: flow of one-to-many, such as where raw materials are used in many operations.
• T-plant: flow of many-to-many, with multiple I-plant lines that may use V-plant supply.

Drum-Buffer-Rope (DBR) describes the basic process of managing flow, with:

• Drum setting the synchronized process time.
• Buffers that provide sufficient interface between process points.
• Rope that ties everything together, creating pull.

A simplified form (S-DBR) has a buffer at the shipping point and uses load management across the process.

Not directly related to the above is a problem-solving approach and set of tools called the Theory of Constraints Thinking Processes.

See also:

Buffer, Takt time, Load balancing

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