An automatic braking system which is not dependant on external power and which is smooth in operation is offered by our customer EA Group. The automatic braking transmission prevents overspeeding of revolving doors which could be the result of wind effects and/or misuse by individuals resulting in speeds in excess of c.12 rpm for example.
The braking system comprises a single stage helical speed increaser (available in ratio up to 1:7.46) directly coupled to a 3 shoe centrifugal brake hub. Our customer has fitted an appropriate brake housing and the whole unit is foot mounted from the gearbox.
To achieve an appropriate transmission the 12 rpm door speed is increased by an "open" gear set of 1:5.41 and in conjunction with the speed increaser ratio of 1:7.46 the resultant brake shaft speed becomes approximately 484 rpm (Combidrive advised that this would be around the minimum speed that a centrifugal brake could be embodied cost effectively).
EA Group decided on brake engagement starting at c.300 rpm. Our customer found the transmission to be quiet and smooth in operation, in addition to including this in their own door product they suggest that it can be applicable to other door products (new or retro fitted).
Photos/drawings with kind permission of EA Group. Patent applied for by EA Group.