Patent GB-1189169-A (GB)
Title: A Control Device for Periodically Operating Machines
IPC: B23Q15/00
Filed: 1967-12-01
Abstract: 1,189,169. Punching. SAIA A.G. 1 Dec., 1967 [5 Dec., 1966], No. 54832/67. Heading B3W. A control device for periodically operating machines, with a control-signal transducer controllable by the goods to be treated and a test signal transducer adapted to produce a test-signal during each cycle of the machine, characterized by bi-stable trigger circuits of which the one is adapted to be reversed by each control signal or test signal in any desired sequence and the other is adapted to be reversed by each control signal in one direction and by each test-signal in the other direction, the outputs of said trigger circuits being connected to a differential circuit controllable by a difference of the condition of said trigger circuits. A strip of material 35 being fed intermittently through a punching machine has an edge 36 formed transversely of the strip at each cycle of operation. This edge engages a transducer 37 which produces a control signal pulse. The transducer comprises a piezoelectric crystal cemented in a recess in the body of the transducer. The control pulse can also be produced by an ejected workpiece passing in front of, and temporarily shading, a photo-electric cell. Attached to the mainshaft of the press is a test-signal transducer, such as a photo-electric cell, which produces a test-signal pulse of predetermined duration at each cycle of the press. Provided that the control signal, which indicates the proper functioning of the feed or ejector mechanisms, occurs within the duration of the test-signal pulse, the machine continues to operate. If either signal is absent then the machine stops automatically. The bi-stable trigger circuits are two flip-flops 8 and 9, each having two inputs A and B and an output C. The test pulses are shaped to the form shown at 33 and are fed to the input A of flip-flop 8 and to both inputs A and B of flip-flop 9. The control pulses, shaped as shown at 34 are fed to the input B of flip-flop 8 and to both inputs A and B of the flip-flop 9. The output C of flip-flop 8 is connected to the base of transistors 23 and 24 and similarly the output C of flip-flop 9 is connected to the base of transistors 25 and 26. The four transistors together with the diodes 27 and resistor 28 form the differential control circuit. So long as either the transistors 23 and 25 or the transistors 24 and 26 are both conducting then current will flow through the resistor 28 and the output 29 of the differential circuit will be at a positive potential. This positive output is fed to a trigger circuit which extinguishes an alarm lamp and operates a relay to allow the machine to start or continue running. The initial condition of the circuit is set by closing a switch 12 which applies a negative potential to the base of the transistors 18 so that they conduct, and the transistors 17 are cut-off. Transistors 24 and 26 are conducting and transistors 23 and 25 are cut-off. The rear flank of the first control pulse 34 reverses both flip-flops and transistors 23 and 25 conduct instead of transistors 24 and 26. A second complete reversal occurs when the rear flank of the test pulse 33 is applied to both inputs A, thus restoring the circuit to its original condition. If the control pulse 34 is missing, then the first pulse applied is the test pulse 33, and when this reaches the input A of flip-flop 8 is ineffective because transistor 17 is already cut-off. However, the pulse is also applied to input B of flip-flop 9 and reverses this circuit so that transistor 26 is cut-off. The differential circuit 10 is then not conducting in either branch and the trigger circuit to the lamp and relay is reversed. Similarly, if the testpulse 34 is missing, the control pulse 33 reverses only the flip-flop 9 and the trigger circuit acts to stop the machine. The probability that both pulses would be missing at the same time is regarded as very small.