Patent GB-921984-A (GB)
Title: Improvements in or relating to devices for constraining the motion of movable members
Inventor: SPENCER DENNIS LINCOLN
IPC: F16D27/02
Filed: 1960-08-25
Abstract: 921,984. Periodic brakes. S. SMITH & SONS (ENGLAND) Ltd. Aug. 25, 1961 [Aug. 25, 1960], No. 29348/60. Class 103 (1). A brake adapted to be applied when a first rotatable part moves a predetermined amount away from a datum position in either sense, but which is released as soon as movement commences in the opposite direction, comprises a second coaxially rotatable part resiliently connected with the first rotatable part, for limited movement either side of a normal position, and also with a third fixed part, and means for actuating the brake carried by the second part which means causes the second part to be locked to the third part. The first part may be fixed and the third part rotatable, the brake performing the same function in this case also. As shown, the first part 1 is a disc formed integrally with a shaft 2 connected through a slip clutch (not shown) with mechanism for operating the control surfaces of an aircraft. A cam formation 10 on the disc 1 normally engages the button 9 of a microswitch 8 carried by the second part 4 which is journalled on the shaft 2, so that the switch contacts 19, Fig. 4 are opened. These contacts with or without other contacts 18, 20, 21, 22, 23, are connected in the circuit of a winding 6 on a magnet member 5 which is stationary and constitutes the third part. The second part 4 acts as an armature which is attracted to and locked on the member 5 when the winding 6 is energized. A resilient connection between the three parts is formed by a pair of arms 14 extending from the ends of a spiral spring 15 loosely engaged around a pillar 16 carried by the part 1, the arms 14 engaging opposite sides of a pin 11 which is secured to the part 4 and projects upwardly through an arcuate slot 12 in the disc 1. The arms also embrace a post 13 secured to the member 5. As a result the parts 1 and 4 are resiliently urged to the datum position shown in which the winding 6 is not energized. Where the additional contacts 18, 20, 21, 22, 23 are omitted, the winding 6 will be energized by angular deflection of disc 1 in either direction as far as the limit position determined by button 9 leaving the cam surface 10, this coinciding with the appropriate end of the slot 12 engaging pin 11. Part 4 is therefore locked to the member 5 and further deflection of the disc 1 prevented. The slot 12, however, allows return movement of the disc 1 sufficient to re-open the contacts 19 so that the parts can then return to their datum position. Where manual switch contacts 18 are additionally provided, these may be opened to remove the limits imposed by the extent of cam surface 10, it still being possible for return to the datum position to occur even if contacts 18 are closed when the deflection of disc 1 exceeds the limits set by the cam surface, the parts 1 and 4 moving alternately in steps to successively open and close the contacts of the microswitch. Contacts 20, 21, 22 may be comprised in further microswitches secured to either part 1 or part 5 and operated by cam surfaces of different length (each longer than the cam surface 10) on either part 5 or part 1, respectively. By this means when selector contacts 23 are connected to one of the contacts 20-22 the contacts 19 are ineffective and the limit of deflection of part 1 is determined by the appropriate one of the contacts 20-22.