Saturday, 17 November 2018
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Door interlock with quiet motor drive

Door interlocks are used in residential buildings and in industry for hinged doors and automatic landing doors. Kronenberg GmbH has developed a new interlock, in which in the place of the solenoid integrated in the door interlock, a three-phase a.c. motor with motor electronics is used.


Activation of the door interlocks normally occurs through a retiring cam attached to the lift car. The retiring cam is retracted electromagnetically during the journey to prevent unlatching of the landing door during the passage. Upon arriving at the stop, the retiring cam is released, as a result of which the rubber roller of the door interlock is activated, the landing door is unlatched and can be opened.


However, it is becoming increasingly common for the retiring cam to be replaced by small solenoids, which are directly coupled to the door interlock or even integrated in the door interlock. The elimination of the retiring cam and the rubber rollers with levers facilitates space-saving and mechanically much simpler solutions and improves appearances in glass lifts. Additional possible uses arise in the area of the Machine Directive for lifting platforms, platform lifts and other safeguards against crashes.

In cases where a retiring cam only unlatch the door behind which the lift car is located, this condition must be reproduced in the case of directly activated door interlocks by a safety circuit. Consequently, additional effort is required for the secure electric triggering of the solenoids so that such solutions make sense especially in the case of low floor numbers, individual additional doors, as in the case of through loading or special requirements.

Improved efficiency

HandwerkRetiring cams use relatively large solenoids, which often weigh several kilograms. The electromagnetic power is proportional to the product of turns and electricity. More turns can be realised in large magnets and this produces greater power and improved efficiency with the same current.

Moreover, as a result of the large volume, greater power loss can be absorbed and the magnet can be loaded for longer and at higher levels. Retiring cam magnets usually have outstanding air damping for effective noise insulation. Moreover, the lifting power is stored by a spring assembly and is permanently available.

It is not so easy to integrate all of these characteristics in a much smaller door interlock. Compromises have to be found between characteristics like size, cost, power reserves, power loss or noise. Consequently, the current solutions on the market are often associated with disadvantages such as excessive noise, additional space requirements, additional installation and wiring effort, greater power consumption or lower force.

Low noise emissions

In the newly developed Kronenberg door interlock a small three-phase a.c. motor with motor electronics is used instead of the solenoid integrated in the door interlock, which has considerable advantages compared to the previous solution with a solenoid. At the same time all of the technology has been integrated in the dimensions of the DLF1 door interlock series, which has been tried-and-tested over decades. Thanks to the low power loss, the traction force can now also be kept available for a lengthy period without parts being overloaded. Hence a bolt that has been briefly blocked by incorrect operation can still be operated.

Thanks to the intelligent motor electronics, accelerating and braking of the bolt and increasing and decreasing of the motor current can be controlled during the traction and halt phase. Nevertheless, the motor unlatching process only takes about a second. The damped and flowing movements result in especially low noise emissions; the unlatching and latching is almost inaudible.

Flexible installation location

As a result, the noise insulation requirements for rooms worthy of protection that are currently much talked about are easy to realise. The door interlock with motor drive is also especially suitable for use in residential construction. Thanks to the option of attaching an external emergency unlatching mechanism via a Bowden cable, flexibility is possible regarding the installation location and opens up additional room for manoeuvre in optimising the use of space or for additional uses.

The DLF1MO and DLF1MO motor latching mechanism types with and without safety latching mechanisms have been tested at the TÜV SUD office mentioned and their conformity with the appropriate EC type approval certificates confirmed. They also comply with the new lift standards EN81-20 and EN81-50.

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

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