Door interlock with silent motor drive

Door interlocks are still used for revolving and automatic lift shaft doors in the fields of residential housing and industry. The actuation of the door interlock is usually made by a retiring cam mounted on the lift car. The retiring cam is retracted electromagnetically in order to prevent the unlocking of a shaft door during the travel. When reaching the stop the retiring cam drops, thus actuates the rubber roller of the door interlock, the shaft door is released and can be opened.

More and more frequently the retiring cam is replaced by smaller solenoids that are directly connected to the door interlock or even integrated in the door lock. The elimination of the retiring cam and the rubber rollers with the levers offers space saving, considerably easier solutions and improves the optical appearance of glass lifts.

Further applications arise from the area of the Machinery Directive for hoists, lifting platforms and other protections against falls.

If by a retiring cam only the door that is behind the lift car can be unlocked, this condition has to be rebuilt by a safety circuit at directly actuated door interlocks. Thus additional effort is necessary for the safe electrical control of the solenoids, so that such solutions are most suitable at low floor numbers, single additional doors as for example at a through loading facility or for special requirements. For retiring cams relatively large sized solenoids are used that often weigh some kilograms. The electromagnetic force is proportionate to the product of windings and current. Thus at large magnets more windings can be realized and at the same current higher forces resp. a better efficiency is achieved. Furthermore, the big volume can absorb higher power losses and the magnet can be loaded higher and longer. The magnets of the retiring cams often have an excellent air damping for effective noise reduction. In addition the lifting power is saved by a spring assembly and can be applied permanently.

All these features cannot be integrated in a significantly smaller door interlock that easily. Compromises between the features as e.g. construction size, costs, power reserves, power loss and sound level have to be found. Thus the existing solutions on the market are often associated with disadvantages as for example excessive sound level, additional space requirement, additional mounting or wiring effort, high power consumption, low forces etc..

For a newly developed Kronenberg door interlock a small three-phase motor is used instead of the solenoid integrated in the door interlock. This motor offers considerable advantages compared to the previous solution with a solenoid. The entire technology was integrated in the type series of the DLF1 that has proven itself for decades.

Compared to the previous door interlock DLF1EM with integrated solenoid the attraction force of the motor driven door interlock DLF1MO is three times higher, although the starting current could be reduced by considerable 88%. Also the holding current could be reduced by 50%. Through the low power loss the attraction force can be applied over a longer period on request without overloading any components. A latch bolt temporarily blocked by incorrect operation can thus still be attracted.

Due to the intelligent motor electronics the acceleration and deceleration of the latch bolt and the increase and decrease of the motor current are controlled. Nevertheless the motoric unlocking process only takes about a second. The damped and flowing motion frequencies lead to low noise emissions, the unlocking and locking are hardly audible. The currently often discussed sound insulation requirements of rooms needing particular protection can be adhered to without any problem. For this reason the door interlock is predestined for the use in domestic constructions.

By the optional possibility to couple an external emergency release via a bowden cable, the installation place can be selected flexibly and opens additional scope to optimize the use of space or for additional applications.

According to the lift directive door interlocks for landing doors count among the few safety components in the lift that have to be approved. The motoric door interlocks with and without faulty closure device type DL1MO and DLF1Mo were tested accordingly by the notified body and their conformity with the EG type approval certificates was certified. Furthermore they also comply with the new lift directives EN81-20 and EN81-50.

Dipl-Ing. Holger Klaus (Hans & Jos. Kronenberg GmbH)