Patent GB-1498417-A (GB)
Title: Optical property of paper
IPC: G06T1/00
Filed: 1974-12-17
Abstract: 1498417 Investigating paper sheets or webs NEKOOSA PAPERS Inc 54423/74 17 Dec 1974 [28 Dec 1973] Heading G1A In a device for sensing the optical properties (e.g. colour, brightness) of a moving web of paper sheet material 14 the paper is transversely scanned by a combination of an upper and a lower sensing heads 11, 12. The heads containing photo-cells 203, 260 and are designed to simultaneously investigate the reflectance and transmittance of the paper at wavelengths determined by a stepwise rotatable filter wheel 210 (also Fig. 4). The photocell outputs are processed by a digital computer. Light from a source 201 passes via lens 202, a filter 281 in the filter wheel 210 and an aperture 130 in the upper sensing head to impinge on the paper web 14. The reflected light passes back through the aperture 130, a filter wheel aperture 221 (which may contain a filter) a pair of lenses 273 and a plate 275 containing a diffusing glass window 276 in front of the photo-cell 203. The transmitted light passes through a window 153 into an integrating cavity 145 containing the photocell 260. The temperature of the sensing heads is maintained substantially constant by heaters 251, 261. The filter wheel 210 is driven by a continuously energized motor 209, but the filter wheel may be retained in selected angular positions by a ratchet arm 230 that co-operates with one of a series of lugs 231-237, the ratchet being lifted momentarily by the action of a solenoid 240. Reed switches are mounted on switching boards 241, 242 and the filter wheel shaft 208 carries a magnet 243 for activating a respective pair of reed switches in each operating position of the filter wheel. The reed switches are used to control the adjustment of amplifiers and actuate relays in the signal processing circuits Fig. 6 (not shown). The description deals at length with the various filters that may be employed on the wheel for investigating paper maker's brightness colour and fluorescence, if any. The description refers to light energy paths having spectral response characteristics simulating the tristimulus function of wavelengths as defined by Commision Internationale de 1' ’'clairage (C.I.E.). It is suggested that the apparatus can be modified to "off-line" single sheet laboratory measurements. The description describes a part of a paper web processing machine Figs. 1 and 2 (not shown) a circuit diagrame Fig. 6 (not shown) of the components in the sensing heads 11 and 12 and the signal processing components and two sets of computer programmes for direct digital control of the system and the data processing together with applying a correction factor. The description refers to and explains a prototype embodiment. In place of the rotatable filter wheel of Fig. 3 and 4 a set of twelve fibre optics light guides may be employed to define six simultaneously operative reflectance light paths in the upper sensing head 11 and six simultaneously operative transmittance light paths in lower sensing head 12. The fibre optics guides would include corresponding filters and be directed to respective photo-cells.