Patent GB-1082934-A (GB)
Title: Apparatus for defect analysis and classification of workpieces
IPC: G01N27/90
Filed: 1965-05-05
Abstract: 1,082,934. Detecting defects in metal bars. REPUBLIC STEEL CORPORATION. May 5, 1965 [May 5, 1964], No.18992/65. Heading G1N. The defect content per unit length of metal bars is determined in an apparatus comprising a detector unit 153 (Fig. 14) including a known type of defect sensor operating on the eddy current principle having a search coil 104 (Fig. 14) which is connected to, and determines the frequency of an oscillator 160, the output of which is amplified and a rectified voltage is fed back via a level control and filter 165 which maintains the amplitude of oscillation constant except for changes due to a flaw or defect (e. g. a seam). The filter functions as an integrator so that only voltage impulses greater than a predetermined duration are passed to the oscillator. The detector unit output is a bi-polar waveform the amplitude of which is proportional to the depth of a defect. The pulses from the detector are introduced into a two channel analyzer 154, one channel of which produces a trigger signal for each voltage pulse indicative of a deep defect, and a second channel similarly responds to both deep and shallow defects. These trigger signals are introduced into an analyzer section 156 which counts the number of shallow and deep defects for a given length or area of the workpiece and determines the defect severity as "good", "salvage" or "scrap". A marker unit 155 actuated by the said second channel controls the operation of a carbide cutter whereby the position of each defect is marked. Mechanical Features. Fig. 12 and Figs. 1 to 11, 13 (not shown) The workpiece bars are caused to move longitudinally with a helical motion by means of motor driven rollers the rotational axis of which are at an angle to the longitudinal axis of the bars and the angle is adjustable according to the bar diameter. The bars may progress three inches longitudinally for each revolution thereof. The sensor coil unit 104 (Fig. 12) is universally movable in a gimbal assembly 82 carried by a shaft 105 attached to a piston rod of a pneumatic cylinder 107 controlled by a solenoid actuated control valve. Classifying. (Fig. 14) In the classifier channels each voltage comparator 170d, 170s produces an output pulse when the input to classifier 154 exceeds a certain level. The threshold level of the deep defect comparator 170d is higher than that of 170s so that the "shallow" defect channel produces an output pulse for both shallow and deep defects. Counting. Each shallow defect signal from comparator 170s is fed to a monostable multivibrator 173s which produces a trigger pulse of predetermined duration for each defect signal received. The trigger signal is applied to a timing generator 175s, a reset generator 176s and a dekatron counter 177s. The timing generator produces a sawtooth voltage pulse of adjustable duration set slightly greater than the time required for one revolution of the bar (e. g. 370 rotation). Each time the timing generator receives a pulse it again starts a timing cycle irrespective of the portion of a cycle in which it was previously situated. At the end of each cycle it introduces a signal to the reset generator 176s to reset the dekatron counter 177s. The reset generator prevents the dekatron being reset each time the timing generator is reset to zero time. The voltage appearing at the cathode outputs of the dekatron will continue to advance one position at a time until reset at the end of a timing cycle. The timing generator 175s does not produce a reset pulse to reset the dekatron as long as it receives an input defect trigger pulse before the termination of a timing cycle initiated by a previous pulse. Thus the sensed defects are counted up provided that none of the intervals between two consecutive defects is greater than the period of the timing circuit. A number of closely spaced defects prevents the counter being reset so that it counts the total number of defects. Selecting number of permissable defects. The dekatron 177s outputs are connected to a selector switch and the switch arm 185 is set at one of these outputs according to the permissable number of deep and shallow defect indications, which ever occurs first, e. g. for four permissable defects the switch arm is set at S4. Switch arm 186 is set for a permissable number of deep defects. The scrap defect selector switch 187 position is set for a desired number of deep defects only. When a selected number of defects is counted a memory relay is energized and this retains the energizing signal until the workpiece has cleared the testing section, which causes the workpiece to be directed to an appropriate bin.