in an electrophotographic copying machine of the type utilizing a single - component developer applied to a photosensitive member through the use of a magnetic brush ; a regulating plate is positioned across the sleeve of the brush immediately prior to the juxtaposition of the sleeve and the photosensitive member in order to prevent spill - over of excess magnetic toner . this plate is preferably in addition to another regulating plate placed across the sleeve upstream of the first regulating plate where the developer is fed to the sleeve . both plates have wider outer edges closely spaced to the sleeve to prevent rising of the developer over these outer edges when the magnetic force of the brush is weak and does not hold the developer to the sleeve .