Visualizing Constraints

This chart offers a visual element for the theory of constraints

by Alex Coman and Boaz Ronen

Quality managerial tools are empowered by visual elements such as Pareto charts, control charts, Ishikawa’s fishbone diagram and others.

The theory of constraints (TOC) is a popular five-step continuous improvement method, but it lacks a visual element.

The gate and gear chart (see a populated version in Figure 1) is a simple visual tool that enables quality managers to communicate TOC’s continuous improvement methods to stakeholders and top management.

Figure 1

The gate has two parts: strategic gating, or selecting tasks, and tactical gating, or streamlining those tasks. The gear refers to exploiting and leveraging the bottleneck. The gate and gear chart follows TOC’s five steps:

Identify the system’s constraints. A constraint is any element that prevents the system from achieving better performance. One of the most common constraints is a bottleneck.

Decide how to exploit the constraint. A bottleneck can be exploited in two ways:

Waste reduction: Reducing the bottleneck’s waste or garbage time. Waste reduction is achieved using the Pareto analysis of waste causes.

Strategic gating: Screening tasks that will not be assigned to the system due to constrained bottleneck resources.

Subordinate the whole system to the bottleneck. All other departments should address the bottleneck. Subordination is accomplished using the following tools:

  1. The complete kit policy: Prevent the bottleneck from processing tasks that lack components essential to successful completion.
  2. The small batch concept: Break large batches into small, lean ones to accelerate the flow in the system.
  3. Drum-Buffer-Rope release mechanism: Pace the whole system according to the bottleneck and release tasks to minimize work in process and increase throughput and quality.

Alleviate the bottleneck. The resource is alleviated by offloading bottleneck tasks to non-bottleneck resources.

Reevaluate the constraint. If the current constraint is taken care of and its throughput increases, another resource becomes the constraint.

Consider how the gate and gear chart would look when applying TOC to an IT application development department (Figure 1). In step one, an analysis is performed that identifies system architects
as the constraint.

Step two of TOC is broken into two parts. The first is identifying sources of waste—bad multitasking, scope creep and endless meetings. The second identifies tasks to be eliminated—the system architects will no longer be evaluating the cost of small tasks.

Step three is to subordinate the whole system using three different tools. Enforcing a complete kit policy will ensure that only tasks with complete requirements are fed to the architects. Large tasks are broken into small elements, and tasks are fed to the architects using the Drum-Buffer-Rope method with a maximum of three tasks at a time.

The final step in the chart is to alleviate, or offload, the bottleneck. The programmers will scope small tasks on their own, junior staff will replicate work environments for the architects and project deployment will shift to the operations department.

Alex Coman is a professor of project management at Tel Aviv University and the Academic College of Tel Aviv in Israel. Coman has his doctorate in IT from Claremont Graduate University in California.

Boaz Ronen is a professor of technology management and value creation at Tel Aviv University in Israel. He has his doctorate in business administration from Tel Aviv University and co-authored Focused Operations Management: Achieving More with Existing Resources (Wiley, 2008).

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