| 摘要 |
PURPOSE:To avoid the effect on a photodetector, of spectral reflected light due to a color toner on a conductive mask by providing a light emitting element with a luminous flux aperture to control the extension of the light incident on a conductive probe. CONSTITUTION:An AC square wave is applied to a conductive member 13 constituting a conductive mask 11, and when voltage same in polarity as a developer is applied, the mask 11 is kept clean, but the moment an opposite voltage is applied, a color tonr and a carrier having so far electrostatically attracted each other are separated and the toner is attached only to the surface of the member 13. Light emitted from a light emitting element 9a is controlled with a luminous flux aperture 9c in the extension of the flux, transmitted through a transparent glass plate 12, reflected with a conductive probe 8, again transmitted through the glass 12, and falls on photodetector 9b. Since the amt. of the incident light corresponds to an amt. of color toner attracted to the member 13, i.e. the concn. of the toner, the color toner concn. can be fetched as an electric signal. |
