| 摘要 |
1,213,781. Photo-electric detection of foreign matter in powders. TOKYO SHIBAURA ELECTRIC CO. Ltd. Jan.23, 1969 [Jan. 24, 1968], No. 3766/69. Heading G1A. [Also in Division B8] Powdered or granular material, such as sugar, is scanned photo-electrically and particles of foreign matter which have a different reflectivity from the mass of the material are detected. The beam from a He-Ne gas laser 24 passes through half-silvered mirror 26 to rotating mirror drum 25 which causes the beam to repetitively scan across the width of a conveyer 22 carrying the powdered or granular material. A photo-electric detector e.g. a photo-multiplier 28, is positioned with respect to mirror 26 such that it detects only diffusely-reflected light, from the material and the mirror drum, which has travelled back along the same path as the incident beam. In this way the detector does not view any shadows thrown by the incident beam and detect these as particles of foreign matter. The detector 28 has associated therewith an interference filter so that only the wavelengths of the laser beam are passed. The output of the photo-multiplier is amplified and may be inverted before being supplied to a gate. This receives synchronizing pulses from a generator comprising light source 36, photo-cell 37 and slotted disc 35 which rotates in synchronism with drum 25. In this way, only photo-multiplier signals generated while the laser beam is incident in the actual material 21 are passed to a threshold device e.g. a Schmitt circuit or comparator, operating on an alarm. Instead of half-silvered mirror 26, an ordinary mirror may be provided, having a hole for passage of the laser beam. Figs. 4 and 5 (not shown) illustrate a suitable vibratory shoot and dam arrangement whereby only a thin layer of material is scanned and thus substantially all foreign particles are detected (see Division B8). |
