GB1212864A - Improvements relating to brakes for power presses and like machines - Google Patents

Abstract

1,212,864. Mechanical presses. BROUGHTON ENG. Ltd. 29 Aug., 1968 [17 June, 1967], No 28032/67. Heading B5F. [Also in Division F2] In a power press or other machine tool, a secondary brake (Division F2) is provided having a first pre-stressed brake-applying device 14, normally held out of operation but released for operation to apply the secondary brake when the crank-shaft of the machine is rotated when over travel of the crank-shaft of the machine occurs to a predetermined degree, a second brake-applying device in the form of a self-energizing or servo device 19, 20 being arranged to derive its brake applying energy when it comes into operation from the kinetic energy of the moving part of the machine such that an over-travel detector 21 is arranged to occupy an operative position when a guard means of the machine tool (not shown) is in an open or unsafe position and to occupy an inoperative position when the guard means is in a closed or safe position. The first brake-applying device 14 comprises a compression spring which is normally held by a latch device 13a in a pre-stressed condition. The self-energizing device comprises a roller 19 disposed between the lever arms 13 of the brake and co-operating with a cam face 20 on one of the lever arms. The over-travel detector includes a detent in the form of a hook element 21 pivoted at its other end 22 to a stirrup 17 and having an upwardly projecting portion 23 co-operating with a rotary catch member 24 rotating with the brake drum 10. The brake drum is formed with frusto-conical edge faces 11 with which similarly shaped brake shoes 12 co-operate. An electrical switch 25, which normally remains closed, is caused to be opened should the secondary brake be brought into operation and the hook element 21 is operatively connected with the barrier member of the guard for the machine. Operation.-The normal stopping position of the crank-shaft corresponds to top dead centre as shown in Fig. 1 and in this position the rotary catch member 24 has a concave face 27 disposed approximately horizontal whilst the hook element 21 has its projecting part 23 engaged beneath the rotary catch member. Since the hook element 21 is operatively connected with the barrier member of the guard for the machine, the guard is operated manually to move the barrier member into its closed position and the hook element is withdrawn to the right so that its projecting part 23 no longer lies beneath the concave face 27 of the rotary catch member 24. The stirrup 17 occupies an approximately horizontal position in which a latch element on the stirrup co-operates with a shoulder outer face 13a of the right hand lever arm 13 to hold the upper end positions of the lever arms against lateral separation to compress the spring means 14. In this position the brake shoes 12 are out of contact with the disc and the switch is closed to permit engagement of the clutch and release of the primary brake (not shown) if the crankshaft rotates clockwise beyond the top dead centre position through a predetermined angle, e.g. approximately 15 degrees, the concave face 27 in engagement with the upper face of the projecting part 23 of the hook element tends to drag the latter downwardly to release the latch element from the step on the shouldered face 13a and permit the upper arm of the lever 13 to move to the right and cause the shoes 12 to be applied against the disc under the pressure derived by the spring means 14. Should the crank-shaft fail to be arrested after a predetermined angle of over-travel, say 25 degrees, continued downward dragging of the hook element causes the roller 19 of the stirrup to exert pressure against the cam face 20 of the right hand lever 13 to increase the frictional effect of the shoes on the brake disc.