Abstract: A printing machine, having operating parameters associated therewith, for producing prints is provided. The printing machine includes a controller for controlling the operating parameters and an operator replaceable sub-assembly adapted to serve as a processing station in the printing machine. The operator replaceable sub-assembly includes a memory device, communicating with the controller when the replaceable sub-assembly is coupled with the printing machine, for storing a value which varies as a function of the usage of the replaceable sub-assembly, the controller adjusting a selected one of the operating parameters in accordance with the stored value for maintaining printing quality of the printing machine.

Abstract: In a laser printer, in which a latent image is generated on a circulating imaging member in accordance with digital image signals and subsequently developed with toner, the number of pixels to be toned is used as an indication of the rate at which toner is being depleted from the developer mixture. The device for dispensing fresh toner to the developer mixture is operated in dependence on the number of pixels to be toned so that there is a pre-established relationship between the pixel count and the length of time for which the dispensing device is in operation. If the efficiency of the dispensing device falls, the pre-established relationship is adjusted so that the toner density in the developed images remains constant. If a predetermined level of adjustment is reached, it is taken as an indication that the supply of toner in the printer is low, and should be replenished.