| 摘要 |
The invention relates to the controlling of the concentration of toner in electrographic developer mixtures, wherein toner concentration is determined by sensing the reflectivity of the developer mixture. An electrographic developer mixture contains toner particles and carrier particles. During use, a proportion of the toner particles become non- transferably attached to the carrier particles, a phenomenon known as scumming, and hence the reflectivity of the mixture is not a true indication of the concentration of toner particles available for transfer to an electrostatic image. The signal produced by measuring the reflectivity of the mixture is modified in dependence upon the expected extent of such scumming, the expected extent of scumming being derived from the usage of a copier in which the developer mixture is employed, for example, from the number of copy making operations carried out by the copier. <IMAGE> |
