Patent GB-750367-A (GB)
Title: Safety devices for press and like machinery guards
IPC: F16P3/04
Filed: 1953-12-02
Abstract: 750,367. Machinery guards. WILKINS & MITCHELL, Ltd., and WILKINS, E. W. Nov. 10, 1954 [Dec. 2, 1953], No. 33432/53. Class 80(4) A safety device for a press or like machine controlled by a fluid-pressure-operated clutch ensures that the clutch cannot be engaged until the guard is closed and that the guard cannot be opened while the machine is running, and provides for automatic opening of the guard at the end of a working cycle, the latter being initiated by manual closing of the guard. The press shown has vertically-slidable pairs of guards 12, Fig. 2, at the front and rear thereof, the guards in each pair being moved toward and away from each other by side chains passing over sprockets 14 on a shaft 15, Fig. '3 coupled by discs 16, 17 and a pin 20 to a coaxial shaft 18. On the shaft 18 a disc 22 having a slot 23 co-operates with a lever 24 which is acted upon by a spring-loaded plunger 31 and the plunger of a safety valve 27. As the guards are closed the shaft 15 is rotated and a cam on the disc 17 closes a switch 47 energizing a solenoid (not shown) to open a main delivery valve supplying fluid to the safety valve 27. Provided the guards have been properly closed so that the slot '23 registers with the lever 24, the fluid pressure in the valve 27 causes the descent of its plunger, thereby uncovering a port 29 to supply fluid to the clutch mechanism starting the press, and simultaneously pushing the lever 24 into the slot 23 (as shown) to lock the guards closed. At the end of a working cycle a trip switch (not shown) operated by the press mechanism de-energizes the afore-mentioned solenoid and the main delivery valve is closed, thereby cutting off the fluid supply to the valve 27 and allowing the plunger 31 to raise the lever 24 and unlock the guards. To effect the automatic opening of the guards a pawl 32 on the disc 22 co-operates with a ratchet tooth integral with a pinion which is free on the shaft 18 and is rotated by a rack 35 operated by a pneumatic cylinder 36. A valve 37 actuated by the lever 24 is connected to the cylinder 36 so that when the lever enters the slot 23 and the press starts the valve 37 supplies air to the lower end of the cylinder and exhausts the upper end, causing the rack 35 to be raised quickly, the pawl 32 allowing the disc 22 to remain stationary. At the end of a working cycle, when the lever 24 is raised the valve 37 supplies air to the upper end of the cylinder 36 and connects the lower end to a throttled exhaust, so that the rack 35 is slowly lowered and, through the pawl 22, rotates the shaft 15 and opens the guards. The mechanism comprising the pneumatic cylinder 36 with the rack and ratchet gearing the valve 37, switch 47 and the lever 24 is duplicated at the front and rear of the press, the two levers 24 being on a common shaft 30 so as to operate simultaneously under the control of a single safety valve 27. The coupling 16, 17, 20 enables said mechanism to be disconnected and removed without disturbing the guards 12. Specifications 604,374 and 689,655 are referred to. Reference has been directed by the Comptroller to Specifications 604,374 and 689,655.