GB1495272A - Protection apparatus - Google Patents

Abstract

1495272 Machinery safety devices SACOL CONTROLS Ltd 23 April 1975 [26 April 1974] 18422/74 Heading F2J [Also in Divisions G1 and G4] Machinery guarding apparatus comprises a signal generator CPG, a transmitter of radiant energy TX, a receiver RX, gate means TG1 for example, means responsive to the presence for a predetermined period of the output signal from receiver RX to cause the gate means to inhibit passage of the input signal to TX, and thereafter responsive to the absence of said signal for a predetermined period to cause the gate means to enable said passage, and detector DET2 responsive to the cyclic presence and absence of the said output signal to indicate that the radiant energy is not obstructed and the apparatus is functioning correctly. Positive pulses of 10 Ás width at a frequency of 1000 per second from clock pulse generator CPG are transmitted as pulses of radiation to receiver RX. Second gate means TG2 operates alternately with gate TG1 to inhibit and enable passage of the output signal of receiver RX via synchronous detector SD acting as an AND gate and inhibiting electrical interference and spurious light changes. Detector DET1 gives a positive D.C. output when input pulses are present and this is converted to a rectangular waveform by hysteresis circuit H. Bi-stable circuit JK is triggered only by positive-going changes in the output of circuit H. A 1 Ás delay circuit DLY ensures that the circuit JK is triggered before the output of circuit H reaches AND gates &1 and &2. The outputs Q. and Q of circuit JK are complementary alternating signals each with a period of 20 msec., the gates TG1 and TG2 being inhibited alternately every 10 msec. for a duration of 5 msec. When more than two checking loops are required the bi-stable circuit JK may be replaced by a shift register. In a multi-channel embodiment (Fig. 2, not shown) the output signals of three receivers are fed via a channel inhibitor and channel selector to detector DET1. The channel selector is fed with a train of pulses from the generator CPG to provide synchronous gating and selects one channel dictated by binary coded decimal data supplied by a counter (CNTR). This data corresponds to the number of negative going output pulses of an inverter (INV2) which receives the output of circuit H. The channel inhibitor and channel selector inhibit all channels alternately every 10 msec. for a duration of 5 msec., the channel selector changing channels at the start of each inhibit operation. For employing two checking loops on an even number of channels two sets of channels each with an odd number may be interlaced with each other. Preferably with the generator signals to one set out of phase with those to the other set to eliminate cross-talk. The apparatus may be used for machine or security guarding systems.