812,618. Blank punching; sub-press mechanism. STANDARD TELEPHONES & CABLES Ltd. Feb. 13, 1956, No. 16999/56. Divided out of 812,617. Class 83 (4). In apparatus for controlling a machine such as a metal working press which carries out a series of mechanical movements, electrical contacts are provided to detect whether the various operations have been correctly executed and supervisory equipment, including indicator lamps, tests the cordition of the contacts and responds to their operation. A mechanical press for shearing and punching plates 1, Fig. 1, having holes 3 has a sub-press assembly with a series of electric contacts which are closed to permit operation of the machine only when, (a) metal strip is located in the feed to the machine, (b) the strip is correctly fed up to an end stop, (c) the stripper block has operated and returned to normal position, and (d) the ejector has operated and returned to normal position. In the event of faulty operation the machine is automatically stopped and an indicating lamp goes out in the relevant circuit. A pair of strips to be punched is fed over a die-block 44, Fig. 4, on the lower part 6b, Fig. 2, of a sub-press assembly and is punched by a top part 6a of the assembly which is guided over pillars 10a, 10b. The strips pass over a block 24 through which a pair of plungers 23a, 23b project and are depressed by the strips to actuate electrical changeover switches 27a, Fig. 5, through levers 28a to provide means for detecting the presence or absence of material. The strips are clamped on a feed slide 31 by penumatic cylinders 32a, and are intermittently moved forward by a double-acting pneumatic cylinder 39 which reciprocates the slide 31 over guide rods 38a. Spririg-loaded grippers 43a hold the strips in position during the return stroke of the slide 31. The ends of the strips engage a stop plate 46 through which plungers 47a project to operate electrical changeover switches 48a to provide a means for detecting whether the strips have been fed into position. An ejector blade 50 operated by a double-acting pneumatic cylinder 53 moves across the die block 44 to eject the finished clamp plates into a shoot 52. Changeover switches 55, 56 actuated by a projection 59 on the ejector blade 50 at each end of its stroke provide means for indicating whether the blade 50 has completed an operation and returned to its retracted position or is jammed in an intermediate position. The upper part 6a, Fig. 3, of the sub-press assembly comprises a punch block 15 carrying the punches (not shown) from which the blanks are ejected by a stripper block 14 under the action of springs 16. A further changeover switch 17 operated through a lever 19 from the stripper block 14 provides a means for detecting that the block has retracted or has returned to its normal position. The press is controlled from a control unit 62, Fig. 2, to which the switches are connected through cables 109 and to which the pneumatic cylinders are connected through pipe lines 108. For normal operation the press crank-shaft 12 is rotated under the control of a one revolution clutch (not shown) which is engaged by the operator on the depression of a pedal 102 connected to a pneumatic control valve 104. With the control unit 62 in operation the supply of air to the control valve 104 is automatically cut off from its supply pipe 106 to prevent operation of the press in the event of any of the various switches on the sub-press assembly 6a, 6b being incorrectly positioned as is shown by the indicator lamps. The various operations of the press are controlled from a series of cams described in Specification 812,617, mounted in the control unit and rotated in unison with the press crank-shaft through a flexible drive 83. The cams open and close electrical relays which control the operation of the clutch control valve 104, clamping cylinders 32, feeding cylinder 39 and ejection cylinder 53 through a series of solenoid-operated valves and relays. Failure of any of the various switches detecting mechanical movements of the press results in the relay for the clutch-control valve 104 being short-circuited.