Patent GB-900424-A (GB)
Title: Improvements relating to the inspection of paper
IPC: G01N27/20
Filed: 1959-10-26
Abstract: 900,424. Delivering sheets. WARREN CO., S. D. Oct. 26, 1959 [Nov. 25, 1958], No. 36228/59. Class 100 (1). [Also in Groups XIX and XXXVI] Apparatus for cutting a web of paper into required lengths and sorting faulty lengths from good ones includes a detector, a cutter mechanism, and a gate for rejecting defective sheets arranged consecutively along the path of travel of the web, the detector comprising a driving roller and a series of pivotally-mounted metallic skids, each of which has an insulated shoe which bears on the surface of the web opposite to the roller and moves in response to changes in caliper of the web, means for producing an electrical potential difference between the skids and the roller, and means for generating an electrical signal each time the leakage current between skid and roller exhibits a change of predetermined magnitude and for transmitting this signal to a memory device which transmits a second signal corresponding to the first, and which controls means, operated in synchronizm with the cutter mechanism, for opening the reject gate when a sheet containing a defect reaches it, and closing the gate after the sheet has passed through. General arrangement.-The web of paper P is fed from a supply roll 2 by means of driving rollers 4, 6, 8, 10, 12 which are driven by a common drive system 14. Associated with the roller 8 is a bump detector 16 comprising a number of skids 20, Figs. 2, 6. The skids are electrically connected to one or more amplifier and power supply units 22, each having an output relay 24. When a bump or abrupt change in caliper of the paper occurs it deflects one or more of the skids, which causes the relay 24 of one of the units 22 to close and pass the output signal from an oscillator 28 to a recording head R1 which impresses the signal on a rotating magnetic recording drum D. The relays 24 also operate an auxiliary relay 32 which actuates a web-marking device 34, Fig. 2, which marks the edge of the web adjacent to the bump. A void detector 36 is associated with the roller 10 and consists of a large number of metallic bristles 38, Fig. 3, which engage the web P. The void detector is connected to an amplifier and power supply unit 40 having an output relay 42 which when a void is detected passes the oscillator signal in the form of a pulse to a second recording head R2 which impresses the pulse on the magnetic drum D. Playback heads P1, P2 are associated with the drum D and a permanent magnet E erases the signals on the drum after they have been " read " by the playback heads. A marker 268, Fig. 3, similar to the marker 34 is associated with the void detector. The web P is cut into sheets by a rotary knife 46 driven by a drive 48 which is mechanically linked to and driven by the drive system 14. Also linked to and driven in synchronizm with drive system 14 is a drive system 50 for the drum D. The cut sheets are transported from the knife by a series of co-operating upper and lower endless belts 52, 54 driven, by a system 56, at a linear speed in excess of the speed at which the web P is transported so that as soon as a sheet is cut it is moved away rapidly from the edge of the next sheet to be cut. Sheets free of defects are fed between rollers 60, 62 to a good paper layboy (not shown). The drive system 64 for the rollers 60, 62 is synchronized with the drive system 56. A pivoted reject gate 68 associated with a reject paper layboy 70, is located between the belts 52, 54 and the rollers 60, 62. The gate 68 comprises a series of steel members affixed to and spaced axially along a rotatable shaft 72. The layboy 70 comprises a series of curved metal bars 74 arranged in alternately occurring relation with the steel members forming the gate 68. The gate is normally disposed horizontally and acts as a supporting floor for the sheets moving from the belts 52, 54 to the rollers 60, 62, but it can be pivoted upwards by rotation of shaft 72 to deflect the sheets into the layboy 70. The gate is operated, by a solenoid 78, in response to the signals read by the playback heads P1, P2. These apply the playback signals through an amplifier 80, an output relay 82, a reject relay system 86, and a sheet following system 90 which includes means for tracking successive defective sheets of paper on the belts 52, 54, to a gate relay 94 at the proper time to effect operation of the reject gate 68. In this way sheets containing the defects sensed at rollers 8, 10 are diverted into the reject paper layboy 70. Feelers and detectors.-The bump detector 16, Figs. 2, 6, comprises a beam 102 extending parallel to the roller 8. Pivotally mounted on the beam at 112 are the skids 20, each of which consists of two insulating plates 110a, 110b, e.g. of phenol-formaldehyde resin, between which is sandwiched a conductive metal plate 124. The plate 124 is maintained in a position slightly spaced from the surface of the web P as it passes round the roller 8 by means of an insulating shoe 130 which rides on the web and can be adjusted in relation to the plate 124. Each plate 124 is connected by a cable 146 to one of the amplifier and power supply units 22, which apply a D.C. voltage to the plates. The roller 8 is connected to earth and a capacitative effect is established between the plates and the roller owing to the air gap and paper between them. When a skid is raised by a bump in the paper web the leakage current running from the skid, partly owing to leakage through the insulator 130 but chiefly because of the capacitative effect, to the roller, is decreased, causing the skid voltage derived from the D.C. supply to rise whereby a pulse is transmitted to the electrical control system. The void detector 36 includes an angle iron 230 extending parallel to the roller 10. The bristles 38 which are of copper, bronze or brass are mounted on the angle iron 230 by means of plastic, non-conducting plates 246, the number and size of the plates being variable so as to accommodate webs of different widths. The bristles 38 form a single sensing element by virtue of their physical engagement with each other and are connected by a cable 262 to the amplifier-power supply system 40. The roller 10 is connected to earth. When a hole in the web P passes round the roller 10 it allows one or more bristles to touch the roller whereby current leakage from the bristles to the roller is greatly increased, and the voltage in the bristles falls. In this way a pulse is transmitted to the electrical control system. Means is provided for lifting both the skids 20 and the bristles 38 out of engagement with their respective roller so as to allow the initial threading of the web through the machine. Means is associated with both detectors for counting the number of defects detected. The machine may be adapted to detect other types of defect as well as or instead of bumps and voids, e.g. a photo-electric scanner may be embodied in the machine to determine whether the opacity of the web departs from a predetermined desired standard.