Glossary · Protective devices and interlocks
Two-hand control device
Also known as: two-hand control
German: Zweihandschaltung
In machine safety, a two-hand control device is a device requiring simultaneous use of both hands to initiate and maintain a hazardous machine function, so that the operator's hands are away from the hazard while it runs.
- Machine safety
- Human factors
In one sentence
A two-hand control device keeps the operator's hands on the controls during the hazardous motion; it protects only that operator and needs a safe distance.
Example
On a hydraulic press, the operator must press two buttons within a short time of each other and hold them until the ram reaches the bottom of its stroke.
How it applies
- Machine safety: The controls must be placed far enough from the point of operation that the hazardous motion stops before a hand can reach it after release. The calculation uses the stopping time.
- Design: ISO 13851 specifies two-hand control devices and their types, including requirements for synchronous actuation and protection against defeat, for example operating both buttons with one hand and an elbow.
- Limits: The device protects only the person using it. Helpers or other people near the machine need additional safeguards.
- Technical documentation: Instructions should state that each operator must have their own device if several people work at the machine, and that the buttons must not be blocked or tied down.
Two-hand control device vs. hold-to-run control
A hold-to-run control can be operated with one hand. A two-hand control device ties up both hands and so also keeps them out of the hazard zone.