Method of detecting impurities in molten resin utilizing scattering light and the shadows of the impurities

A method of detecting impurities in a molten resin comprising:

• providing at least two devices used in carrying out the method of detecting impurities in a molten resin by passing the molten resin through a passage having a window through which light can pass and emitting light from a light source through said window and the molten resin flowing through said passage and sensing, by means of a sensor, shadows produced when the light from said light source is interrupted by an impurity contained in the molten resin and measuring a size of the impurity from a width of the shadow and an intensity of light in the shadow, detecting the shadows of impurities contained in the molten resin by means of at least two sensors of said at least two devices to determine three-dimensional positions of the impurities, and correcting a size of the impurities according to the three-dimensional position thus obtained.

A method of detecting impurities in a molten resin comprising:

• combining a device used in carrying out the method of distinguishing impurities in a molten resin wherein shadows of impurities contained in the molten resin are detected by passing light from a light source through the molten resin, and wherein judgment is made that if optical signals obtained by detecting the light that has passed through the molten resin indicate that a bright area exists around a dark area, the said dark area is determined to be a shadow of an impurity with a focus-adjustable camera, detecting a position of the shadow of an impurity in the molten resin, and recording an image of the impurity by means of said camera after adjusting its focusing point according to said detected position of the shadow of the impurity.

A method of distinguishing impurities in a molten resin wherein shadows of impurities contained in the molten resin are detected by passing light from a light source through the molten resin, and wherein judgment is made that if optical signals obtained by detecting the light that has passed through the molten resin indicate that a bright area exists around a dark area, then said dark area is determined to be a shadow of an impurity.

A method, of distinguishing impurities in a molten resin wherein shadows of impurities contained in the molten resin are detected by passing light from a light source through the molten resin, and wherein judgment is made that if optical signals obtained by detecting the light that has passed through the molten resin indicate that a bright area exists around a dark area, the said dark area is determined to be a shadow of an impurity, further comprising:

• binarizing said optical signals by comparing said optical signals with a first threshold for a dark level;
• binarizing said optical signals by comparing said optical signals with a second threshold for a bright level;
• and determining that a dark area represented by the optical signals binarized according to the first threshold indicates a shadow of an impurity if there exists bright areas represented by the optical signals binarized according to the second threshold at both ends of said dark area.