The present invention relates to an apparatus for automatically examining and inspecting white resin powder of, for instance, vinyl chloride resins, ABS resins and MBS resins for the presence of foreign substances.
When preparing resin powder or forwarding the powdery product from a manufacturing plant, the product is in general subjected to quality inspection for various predetermined properties. The results are sent back to the manufacturing plant for the improvement of production processes or they are used in the denoration of the quality in order to afford convenience to the destination or the consignee.
In case of, for instance, vinyl chloride resin powder, one of the items for quality inspection thereof is to inspect the resin powder for the presence of foreign substances as contaminants. Conventionally, the inspection of the powdery resin product for the presence of foreign substances has been carried out by spreading a constant amount of the vinyl chloride resin powder and searching for the presence of pigmented foreign substances (such as those colored black, brown and/or red) thus to count the number of foreign substances present therein. However, the results widely vary depending on the visual power and the nature of each inspector. Accordingly, this method never provides objectively measured values, requires much labor and time and accordingly, has low efficiency.
Incidentally, there has recently been used an industrial apparatus for automatic visual inspection which makes use of a video camera. An example of such apparatuses is one which is commercially available from Hajime Sangyo Co., Ltd. under the trade name of FF 4000. This apparatus serves to detect, for instance, defects, stains and foreign substances on the image of a powdery resin sample photographed by the video camera and to specify the positions of the foreign substances on the photograph through blinking modulated bright spots on a monitor. This inspection apparatus permits automatic inspection of a subject for the presence of, for instance, foreign substances and can provide measured values free of any scattering irrespective of inspectors. Moreover, the apparatus does not require much labor and time and ensures efficient inspection.
However, when the aforementioned industrial apparatus for automatic visual inspection which makes use of a video camera is used in the inspection of resin powder easily electrostatically charged such as vinyl chloride resin powder for the presence of colored foreign substances as contaminants thereof, it is often observed that the resin powder to be inspected is not uniformly dropped on a belt conveyor or is unevenly distributed on the belt conveyor due to electrostatic charges generated on the resin powder per se. For this reason, the surface of the spread resin powder layer becomes severely uneven and this leads to a large scattering in the measured values. Consequently, the apparatus does not provide any reproducible result.