Trapped-key interlocking systems

Hazardous machines and systems are frequently equipped with safety elements (safety doors) with a locking mechanism to protect the operator. Their function is to prevent hazardous machine functions if the safety door is not closed and locked and to keep the safety door closed and locked until the risk of injury has passed. A general example: A machine has one or more maintenance openings (part-body access) or is accessible through one or more doors (full-body access). On the one hand, it has to be secured that the machine is switched off, before one of these openings or doors can be opened.

Haake Technik GmbH is the ONLY trapped-key interlocking system manufacturer certified in accordance with the Machine Directive 2006/42/EC Annex X. According to this Machine Directive trapped-key interlocking systems are logic units to secure safety functions.

Trapped-key interlocking system HST: Safety of machinery
On the other hand, the machine must only be re-set into operation, if all openings and doors are closed, and nobody is present inside the machine. Such guard locking devices are for instance key-operated mechanical interlocks, also called trapped-key systems. They are based on the easy-to-understand premise that a key cannot be in two places at the same time - it can for instance be inserted in a switch OR be used for opening a guard. Another safety-relevant feature is that a key can only become free in a safe condition, when there are no hazards - a switch is turned off, a guard interlock is closed and locked. The big advantage of the system is the fact that a certain sequence of steps can be pre-determined when designing the system. It is not possible to deviate from this sequence - thus a high degree of integrity is achieved. So virtually any hazard can be eliminated. The system consists of a central electrical part (for instance in the control panel) and mechanical units at the guards. Therefore, the devices are very often used in areas, where due to space conditions or other environmental conditions and explosion hazards electrical components are not suitable or expensive to integrate. The devices can be supplied with individual codes (engraving up to 5 digits). Thus a higher degree of safety and a better protection against tampering is obtained.
  • high degree of safety, individual codes
  • only pre-determined secure safety sequences are possible
  • no spare actuator 'in the pocket'
  • no cables to individual safety doors (cost savings, fault prevention)
  • easy retro-fitting
  • door interlocks have a locking feature
  • particularly suited when there are different energy types on the machine (electric, pneumatic, ...)
  • in areas where people can be trapped: personal safety key
  • simple option for realizing safety conditions for setup
  • time delay due to key transfer between the switch and interlock
Guard locking mechanisms

Guard locking mechanisms

Guard locking devices comprises a lock portion and a lateral locking bolt. It is used as guard locking device on hinged, sliding or removable doors and flaps. Inserting and trapping the coded key in the releases the locking bolt allowing the door to ...
Interlocking device HST® B

Interlocking device HST® B

Interlocking device HST® B is used for locking switching devices (circuit breakers, earthing switches). By turning the key, the bolt moves into a corresponding recess on the handle or the control unit of the switching device and locks.
Switching devices

Switching devices

The Switching element with locking mechanism HST-S1 is used to switch off the power supply to the load circuits of machines or plants without shutoff delays, with rated currents up to 20A. Other applications are prohibited.
Switching element with locking mechanism

Switching element with locking mechanism

The Switching element with locking mechanism is used to switch off the power supply to the load circuits of machines or plants with shut-off delays, with rated currents up to 20A.
Key Exchange Stations

Key Exchange Stations

The key exchange stations are used to safely trap keys of a machine or system. No secondary keys can be removed from the exchange station until all primary keys have been inserted and trapped. The primary keys remain trapped until all secondary keys ...