and this free end pushes the linkage bar 35 and the sliding bar 36 towards the electromagnet 33 as shown in fig3 b this will cause the sliding bar 36 to be moved against the spring 37 potential energy and makes the retracted plate 38 to be retracted on the electromagnet 33 while the grip 34 a of the crank arms 34 clamps the aperture 20 b of the intermediate piece 20 through action of the linkage bar 35 as shown in fig3 c on the other hand in a event of power failure no matter what causes the event the sliding bar 36 is released and the spring 37 pushed the linkage bar 35 and causes the grip 34 a of the crank arms 34 to release the intermediate piece 20 as shown in fig3 d and the brake of the door operator is released due to release of the cord 10 fig4 and 5 illustrate the second embodiment of the central release device 1 for a safety door the components include a cord 10 of which one end is a passive end 10 a and the other end is an active end for example the active end is connected with the brake releasing bar not shown or.