GB1497289A - Multi-process control system for an electrophotographic printing machine - Google Patents

Abstract

1497289 Electro-photography; automatic control systems XEROX CORP 17 March 1975 [18 March 1974] 11005/75 Headings G2H and G3R Xerographic drum 10 includes a probe 16, which may be either fixed in the drum or movably mounted on it, and is so constructed as to mimic the response of the photo-conductive surface of the drum as it passes through xerographic processing stations and to generate outputs representative of the response. The probe may comprise a transparent, electrically conductive sheet 73 secured over the photo-conductive material 12 of the drum by a layer of insulating cement 80, with an electrically conductive lead 81 secured to the sheet 73. The voltage between the sheet 73 and electrically conductive substrate 74 is monitored, and gives an indication of the condition of the material 12. Comparison of the voltage produced with a succession of references gives a corresponding succession of error signals, as the probe passes the processing stations, and enables the processing stations to be controlled. Control. The processes controlled are (i) voltage of initial charge by a corona device, (ii) intensity of lamps which illuminate the document to be copied, (iii) development of the image by magnetic toner, by control of the voltage on developer rolls (three colour), (iv) the voltage on a transfer roller and (v) the concentration of toner particles in the developing medium. In each case, measurement of the variable controlled is by detection of the charge remaining on the probe after the respective process; this is sampled once per revolution at the appropriate point and stored on a capacitor for the next repetition of the operation. It is then compared with a respective reference voltage, and if greater than the reference a silicon control switch locks in, to change the state of a flip-flop, the output of which operates a controller for the process.