Forced Control Devices

Forced control effects are preferred over other forms of mistake-proofing effects.

• Wherever possible, use mistake-proofing techniques that lead to a forced control effect.
• With forced control, the action or trigger that leads to the effect is both automatically triggered and compulsory.

There are four families of devices or methods used to achieve a forced control effect:

• Elimination
• Combination
• Use of Guides
• Process Control Systems

These devices do not have to be “high-tech” to work. In fact, many “low-tech” solutions are more elegant and robust than their “high-tech” counterparts.

To use Elimination techniques:

• Eliminate decisions
• Eliminate steps

To use Combination techniques:

• Combine components
• Combine steps

To create forced control effects via the Use of Guides:

• Take advantage of different shapes in the part.
• First, study the size, weight, and shape of the part. Then, use one of those characteristics to develop the guide.
• Keep the shapes simple.
• Check that the guide can only be used one way.
• Leverage asymmetry.
• Use built-in, asymmetrical features.
• Add a new feature or shift/modify existing features to create asymmetry.
• Trade off aesthetics for functionality if needed.

Words of caution

• Make sure the guides are robust.
• They need to be strong, rigid, and wear resistant.
• Guides should be added to the PM (preventive maintenance) schedule.

If using Process Control Systems

• Keep the control system simple.
• The control system does not always need to be electronic.
• Mechanical process control systems can be highly effective.
• Make sure that if the control system fails, that it fails in a “Fail-Safe” mode.
• Allow for expandability to accommodate future process changes.