Patent GB-727914-A (GB)
Title: New or improved safety mechanism for power presses and other power-driven machines or machine tools
Inventor: EVANS FREDERICK ARTHUR
IPC: F16P3/00
Filed: 1952-09-15
Abstract: 727,914. Machinery guards. PRESS GUARDS, Ltd. Oct. 29, 1953 [Sept. 15, 1952], No. 23088/52. Class 80 (4). [Also in Group XXXIV] A safety mechanism for a press or milling or other machine comprises a brake applied to a rotating part by a lever which, in the event of danger to an operator (such as on the opening of a guard, operation of a trip bar, or interruption of a light beam), is moved into the path of a cam or other member on the rotating part and applies the brake through a member having a limited yielding movement to relieve the stresses in the brake. As shown, a pair of brake shoes 12, 13, pivoted on a fixed stud 14 are normally held by a spring 20 in light engagement with a drum on the crank-shaft 11 of a press to bring it to rest when the clutch (not shown) is disengaged. A movable guard (not shown) is linked to a lever 26 so that when the guard is opened a horn 23 on a lever 24 is moved into the path of a cam 22 on the crankshaft. The lever 24 carries a roller 31 engaging a surface 32 on the shoe 13, and is pivoted to a link 30 which is pivoted on a pin 33 slidable, against a frictional resistance provided by spring washers or springs, in a slot in the shoe 12. Should the press over-run while the guard is open, the roller 31 is moved over the surface 32 to give a braking pressure additional to that provided by the spring 20, said pressure being limited by the slidable connection 33. Should the brake fail to stop the crank-shaft, the roller 31 engages a projection 37 to provide a positive stop. The cam 22 may be shaped to hold the guard closed during the down stroke of the press, or during the down stroke and part of the up stroke. A switch 38 controlling the driving motor is carried by a lever 39 pivoted to the link 30 and is normally held closed against a flat on a pin 18 on the shoe 13, the end of the lever 39 bearing on the end of a pin 36 which locks the nut of the connection 33. When the brake intensifier is operated the lever 39 is rocked to open the switch 38 and de-energize the driving motor. The switch 38 also provides a warning that the brake shoes need relining, since if the shoes move together more than a predetermined amount the switch 38 rides off the flat on the pin 18 and the motor cannot be started. Should the brake become locked on the drum the pin 36 may be withdrawn and the connection 33 slackened to release the brake, the pin 36 ensuring that the connection is subsequently returned to its original setting. A spring-pressed radial pawl 41 in the path of the cam 22 prevents reverse rotation of the crank-shaft. In a modification an axially-moving pawl co-operates with a notch in the end face of the brake drum. It is stated that the pawl may be withdrawn by the closing of the guard or by the movement of a clutch lever. In a further construction of brake control, Fig. 3 (not shown), the frictional connection 33 is replaced by a resilient connection comprising a compression spring ; the switch 38 is replaced by a switch carried by the brake shoe 13 and operated by an extension of the link connecting the two shoes ; and the spring- loaded pawl 41 is replaced by a gravity-loaded pawl. It is stated that the brake shoes may be replaced by a band brake. For milling and like machines having a continuously-rotating shaft, the cam is replaced by a toothed wheel or serrated disc adapted to apply the brake. According to the Provisional Specification, a guard is coupled to a bell-crank co-operating with the crank-shaft cam, the bell-crank pivoting on a pin which carries a roller engaging an inclined surface on one brake shoe and is yieldingly linked to the other shoe.