Abstract: A toner mass sensor includes a piezoelectric crystal having a resonant frequency, an electrode on a first face of the crystal, an electrically conductive lead connecting the first face of the crystal to an electrical contact point in the vicinity of a second side of the crystal, and a casing closed at one end by the crystal with the first face of the crystal allowed to contact developer outside of the closed casing through the opening of the casing. The casing and crystal defines an interior which is sealed from developer in a development station, within which sealed interior the second face of the crystal is protected from contamination by developer. The electrode is wrapped around the edge of the crystal to be accessible from the second side of the crystal, and the electrode is a metal; preferably aluminum. The interior of the casing is closed by a base member which carries an electrical circuit.

Abstract: A method and apparatus for determining the rate of development characteristic of electroscopic toner particles of the type used in electrostatographic recording to develop electrostatic images. The apparatus has a biased electrode for attracting toner particles and a microprocessor-based logic and control unit for sampling the mass of toner particles attracted to the electrode at preselected times during the accumulation of toner on the biased electrode. This development rate parameter is used by the logic and control unit to control process parameters (e.g. primary charging and exposure levels, development electrode bias, toner concentration) which affect image quality.

Abstract: A densitometer includes a light source positioned to project light rays to a test surface. A photodetector is positioned to receive light rays from the surface, and has an output which is characteristic of the amount of light received. The densitometer includes a voltage source and a photodetector which generates an output signal which is a function of a measured density and of the voltage of the source. A log amp produces a signal which is substantially proportional to the ratio of the output of the photodetector and a second output signal which is also a function of the voltage of the source.

Abstract: Densitometer readings are corrected by obtaining density readings on an untoned area of the interframe region of an image receiver during cycle-up, storing the readings and subtracting the stored readings from subsequent test readings of the same area of the image receiver. Differences between the cycle-up readings and test readings are used to adjust density readings of toned reference patches obtained with the test readings. The procedure can be used during production modes of the machine, with all readings being taken in the interframe regions, or the procedure can be a part of an automatic set-up operation with toned reference patch readings being taken in the image frame areas of the image receiver.

Abstract: A corona discharge device having a first corona wire and a second corona wire parallel to the first corona wire and in physical contact therewith, such that the forces created by the wires during energization prevent the vibration of the wires, thereby eliminating short circuiting and the need for costly wire-damping devices.