Patent GB-794341-A (GB)
Title: Method and apparatus for counting imperfections in strand material
IPC: H03K21/02
Filed: 1954-07-05
Abstract: 794,341. Counting imperfections in yarn photo-electrically. WEST POINT MANUFACTURING CO. July 5, 1954 [Feb. 24, 1954], No. 19618/54. Class 40 (3). A method of counting imperfections in a strand of material comprises feeding it progressively through a beam of light, generating voltages instantaneously proportional to the amount of light blocked by the strand, relating the time required for each voltage change to a fixed time base to give signals corresponding to imperfections having different degrees of abrupness, suppressing signals corresponding to less than a certain abruptness, and counting the remaining signals. An image of illuminated slit 36 is formed by lens 37 across the path of the strand 10 which is drawn off a reel 12 by means of a roller 20 covered with resilient material 22 and driven by synchronous motor 24. The amount of light falling on photo-cell 40 is independent of lateral movements of the strand but dependent on changes in its cross-section or opacity. The photo-cell output is passed through an impedance adjusting cathode follower 51 to a CR differentiating network 48, 50, the time constant of which is variable by resistor 50. This circuit produces positive and negative pip pulses of amplitude related to rate of change of photo-cell output and to the magnitude of the change where the rate is high. The pulses are amplified at 54, and either positive or negative pulses removed in clipper 56, and the remaining pulses applied via variable tapping 64 on potentiometer 60 to the grid of valve 68 which gives zero output for pulses below a certain amplitude level and substantially even size output pulses for inputs above this level, which are fed through impedance matching cathode follower stage 96 to an electronic counter of the decade type which sends an output pulse to the solenoid-operated mechanical counter 104 for every 10 input pulses. To count the number of imperfections in a given length of yarn the electronic counter is rendered operative for a fixed period by time switch 120 (30 seconds) or 134 (300 seconds) driven by the 60 c/s. supply. Where switch 120 is being used the counter is started by throwing switch 131 which energizes time switch 120 through contacts 130a and supplies earth potential to the counter through contacts 130b and 120<SP>11</SP>. At the end of the period arm 120<SP>1</SP> of the time switch disengages contacts 120<SP>11</SP> from line 126, so stopping the counter: Throwing switch 131 to its other position applies earth potential to counter resetting line 137 and by breaking the supply to time switch 120 allows it to reset. In an alternative arrangement (Fig. 2, not shown) the voltage derived from the photo-cell is fed to a pair of parallel amplifier circuits of which one includes in its output an integrating network, of time constant variable by selection of various capacitors, which smooths out any abrupt changes in output while not affecting gradual changes, whereas the second circuit gives an output corresponding accurately to its input under all conditions. The two outputs are fed to a difference circuit giving an output corresponding to the difference between them so that for slow changes in the cell illumination there is no output. The output pulses corresponding to imperfections are differentiated by a CR network and fed to a valve which amplifies and acts as a clipper to eliminate the negative pip pulses and yield a single pip per imperfection. The pulses are counted as in the Fig. 1 arrangement, Calibration arrangements.-The first of these (Fig. 3) comprises a wire 288 mounted on reed 270 which is oscillated at the supply frequency by electromagnet 282 fed by rectified current from the supply. The wire is vibrated into and out of the beam of light illuminating photo-cell 40 so that the rate of change of the cell output may be arranged to simulate the rates corresponding to different types of imperfections occurring in the yarn. The constants of the circuits between the cell and electronic counter are then adjusted so that the simulated imperfections each produce a pulse. An alternative arrangement (150 in Fig. 1) comprises diode rectifier 162, voltage stabilizer tube 156 and resistor 154 in series across the power supply to the synchronous motor. The output voltage which comprises clipped positive half-cycles of constant amplitude is differentiated in 168, 170 to give uniform pip pulses across potentiometer 174. The variable tapping enables pulses of amplitude from zero to the maximum amplitude delivered by the differentiator to be fed via switch 178 to the amplifier, clipper, &c. The latter circuits are then adjusted to respond to voltage pulses of known magnitude.