Patent GB-1425605-A (GB)
Title: Method and apparatus for scanning lumber cants
IPC: B27B31/06
Filed: 1973-05-09
Abstract: 1425605 Scanning lumber cants photo-electrically BLACK CLAWSON CO 9 May 1973 [9 May 1972] 22231/73 Heading G1A The location of the leading and trailing edges of lumber cants and the orientation of the cants in a saw mill are determined photo-electrically by directing light beams at a low angle of incidence across the cants.  Saw-mill Logs 10 to be cut into studs are moved past a first optical scanner 15 to measure the diameter of each log at a plurality of positions along its length Unacceptable logs are conveyed along conveyers 17, 18 whereas acceptable logs are passed between slab chippers 22, 23 and then through adjustable band-saws 28, 29 which cut 2" or 4" cants, under the control of a computer to which the output of the scanner 15 is applied, the sawn cants being conveyed to pans 35, 36, 44, 45, The sawn cants are then conveyed to a second optical scanner 15 which controls the position of adjustable stops 56, 57 to orient each cant with respect to cant  chippeis 58, 59 so that the wane is removed from the cant in such a way as to maximize the number of studs available therefrom. After removal of the wanes the 2" cants are conveyed by 61 through edger 62 to conveyer 65 and the 4" cants via edger 68 to the conveyer 65.  Optical scanner 55, Fig. 3 Each cant 70 is carried to the optical scanner on a first conveyer 50 moving at a first speed and in the region of the scanner engages a set of lugs 80, 81 of a plurality of sets spaced along a second conveyer 85 moving at a second slower speed so that the lugs are pressed into positive contact with the lugs. Light from a first source 71 is directed at a low angle of incidence across cant 70 so as to illuminate thetrailing wane and the top, sawn, portion of the cant and the light reflected is sensed by a first set-of photo-detectors arranged transverse to the conveyers, the output from the photodetectors being a rectangular waveform Fig. 7 (not shown). Similarly light from a second source 91 is directed across the sawn piece of the cant and' the leading wane and the reflected light detected by a second set of photo-detectors, a movable baffe being provided so that only one light source at a time illuminates the cant. The outputs from the individual photo-detectors are combined with the output from tachometer 90 providing the speed of the second conveyer to provide a rectilinear representation of the available wood in the cant, and which is transmitted to the central computer 140. Since the leading edge of each cant need not necessarily be straight a reference co-ordinate against which the information is referenced is established ahead of each cant by a detector located below the second conveyer and sensing the passage of one of the logs.  A single set of photo-detectors may be used, Fig. 8 (not shown), extending transversely across the conveyers. In this case each light source includes a set of LED's with each set being energized alternately. Once the grid co-ordinates of the leading and trailing edges of the sawn portion of the cants are determined the cant is then orientated in accordance therewith relative to fixed chipper 58 and movable chipper 59. The orientation is achieved by suitable positioning of stops 56, 57 in line with lugs 80, 81.