Patent GB-1375144-A (GB)
IPC: D06H7/00
Filed: 1973-03-01
Abstract: 1375144 Detecting breakage of cutter blades TEIJIN Ltd 1 March 1973 [3 March 1972] 10008/73 Headings G4D D7X D6Y D6C1 D6C2 D6L and D1D5 Apparatus for detecting breakage of at least one of the n radially displaced blades of a rotary cutter 9 for a tow comprises a first detector 12 producing a pulse for each pass of a cutter blade 10, a second detector 13 (coacting with 23) producing n or one or 1/m pulses per rotation of the cutter and means for producing an output when the number of pulses from the first detector between two pulses from the second detector is less than a predetermined number. The detectors may be inductive or photo-electric and the output may actuate an alarm or stop the cutter drive. N pulses per revolution of cutter, Fig. 4 (not shown).-In this case the first detector produces the same number of pulses as the second. Cutter rotation pulses P B  are inverted at 102, differential (rising edge) at 103 and fed to the set input of flipflop 104. The flip-flop output is fed to AND gate 105, the other input of which is pulse train P B . Cutter blade pulses P A  are fed via OR gate 107 to the reset input of flip-flop 104. The output of gate 105 sets flip-flop 106 the output Q2 of which is the alarm. Both flip-flops can be reset by a pulse on the RESET lead. When all cutter blades are present, flip-flop 104 is set by S 2  (derived from P B ) and reset by P A  and the output of Q 1  and P B  do not coincide to enable AND gate 105. When a blade is broken, one pulse Po of train P A  is missing, 104 is not reset and the 1 outputs of Q 1  and P B  coincide, producing on output S 3  which sets flipflop 106, producing an output which sounds on alarm or stops the cutter drive. In alternative embodiments, Figs. 5 and 6 (not shown), P A  or P B  may be fed to the trigger input of JK flip-flop. One pulse per revolution of cutter, Fig. 7 (not shown).-In this case the first detector produces n pulses for each pulse from the second detector. Pulses PB are fed to AND gate 135 and after differentiation to set flip-flop 138 and reset JK flip-flop 134. Pulses PA trigger flip-flop 134. The input to gate 135 is from Q 5  when n is even and Q 5  when n is odd. Normally the squarewave output of flip-flop 134 and pulses PB are out of phase and there is no output from gate 135, but a broken cutter removes one pulse PA and changes the relative phase of the signals producing an alarm output. In an alternative embodiment, Fig. 8 (not shown), a ring counter with n stages is used and and output is produced when the pulses P B  do not coincide with the energizing of one particular counter stage. One pulse per m counter revs, Fig. 9 (not shown).-In this case there are n x m (6 x 4 as described) cutter blade pulses per counter rev pulse. Pulse train PB of one pulse per cutter revolution is divided by four at 151 (P B <SP>1</SP>) and fed to set flip-flop 155 which enables AND gate 157, to clear the binary counter comprising flip-flop Q A  to QE and to set flip-flop 159 which enables AND gate 160. Pulses PA are fed to the counter via AND gate 157 and when a predetermined count between (n-1)m and nm is reached, a signal from gate 158 resets flip-flop 159 disenabling gate 160. When a cutter tooth is broken, only (n-1)m pulses will be received by the counter before the next pulse PB<SP>1</SP> and this will pass gate 160 to set flip-flop 106 and produce alarm signal Q2.