1. Field of the Invention
The present invention related to a toner concentration measuring apparatus that measures the concentration of toner in a developer of an electrostatic copying apparatus.
2. Description of Prior Art
Various electrostatic copying apparatuses, such as a copier, a printer or a facsimile, have been used. These electrostatic copying apparatuses form a latent image on the surface of photosensitive material which is identical with an original image, brings toner-dispersed developer into contact with the surface of this photosensitive material, and sticks toner particles only on the latent image with electrostatic forth to form a copied image on a recording paper. In order to maintain the copy concentration on the recording paper, there are several types of concentration measuring apparatuses for measuring the concentration of the toner in the developer.
Japanese Patent Laid-Open Publication No. Sho 62-235544 (disclosed on Oct. 15, 1987 in Japan) discloses a toner concentration measuring method for electrostatic photography developer.
The publication discloses only the principle of transmittance measurement of infrared rays which are transmitted through the developing layer of wet-type developer. The publication does not disclose its practical configuration.
However, merely applying the above-described principle of the transmittance measurement of the infrared rays through the developer to the copying apparatus with no technical modification added, this technique creates some problems. For example, in a configuration in which the transmittance of the infrared rays through a developer-supplying duct is measured, the problems described below arise.
First, when a plurality of color developers are used for a color printer, a plurality of color toners are sometimes blended in the developer. In such a case, the transmittance of a specific wavelength band is significantly decreased, and an incorrect toner concentration which is higher than the actual concentration is obtained.
Second, the toner particles in the developer are precipitated or stagnated easily in a duct. This results in an incorrect toner concentration that is higher than the actual concentration.
Third, in a configuration in which the transmittance is measured with a light emitting device and a light receiving device across the duct, the attenuation of the transmitting light becomes significantly large because the transmittance of toner-dispersed developer is very low. As a result, the detection sensitivity becomes very low, producing a large measurement error in the measured toner concentration.
Fourth, because the attenuation of the transmitting light is very large in the configuration described in the above-described third problem, a small positioning error in installing the light emitting device and the light receiving device in the duct would results in a large measurement error in the toner concentration.
The toner concentration measuring apparatus according to the present invention, provided along a duct through which developer containing toner particles is supplied, includes a light emitting device for emitting light; a first light guiding device having an end surface projecting into the duct for guiding the light emitted from the light emitting device; a second light guiding device having an end surface projecting into the duct and opposed to the end surface of the first light guiding device for guiding light emitted from the end surface of the first light guiding device and transmitted through the developer in the duct; and a light receiving device for receiving light transmitted to the second light guiding device.
thus the toner concentration measuring apparatus according to the present invention has a pair of the opposing small-diameter light guiding devices in the duct with a small interval between them to reduce the attenuation of the light transmitted through the developer. This structure allows the concentration of the toner in the developer to be measured precisely.