GB906862A - Improvements in or relating to machinery safety devices - Google Patents

Abstract

906,862. Machinery safety devices. PARKES, G. W. Dec. 29, 1958 [Dec. 31, 1957], No. 40449/57. Class 80 (4). A safety device associated with a guard or door 13, Fig. 1, movable relatively to a fixed part 12 of an electrically operated machine comprises a bolt 22 on a pivoted armature 18 on the part 12 adapted to be actuated by an electromagnet 14, 15 on the movable part 13. When the coil 15 is energized, with the guard or door 13 in its safety position, the armature 18 is attracted and the bolt 22 engages in a recess 17 in the part 13 to prevent movement of that part. The armature 18 closing on to the core 14 of the electromagnet forms a transformer to induce a secondary current in a winding 23, thereon which operates a relay Y, Fig. 2, to close contacts Y1 in the control circuit of the machine. This circuit comprises also between A.C. supply lines 28, 29 a stop switch 26, start contacts 27 for energizing coil 15 through a transformer. 30 and start contactors 25 for the machine. Holding contacts M1 are operated by the contactors 25 and cam-operated contacts 37 control D.C. current from a rectifier 31 to a solenoid 36 which actuates a locking member 32 for the armature 18 so that only when the rotating parts of the machine have stopped can the armature 18 be released and withdrawn by a spring 21.