Abstract: A developing apparatus for xerography including a developing roll, a regulator member for controlling developer thickness located proximate to the developing roll, and an elastic plate member arranged to elastically apply pressure to uniformly spread the developer on the developing roll.

Abstract: In a perfecting printing machine, a switch-back mechanism moves backwardly each sheet delivered out of the printing section, and a switching gate provided immediately after the switch-back mechanism selects a first sheet path to return the sheet whose one side has been printed to the printing section and a second sheet path so that the sheet whose both sides have been printed is delivered to the stacker after being moved backwardly by the switch-back mechanism.

Abstract: In an electrophotographic developing device, its doctor blade disposed adjacent to a magnetic roll so as to control the thickness of a layer of magnetic developing agent conveyed by the magnetic roll has an edge which is curved in such a manner that the gap between the edge and the magnetic roll is a minimum in the vicinity of the middle of the magnetic roll, whereby the layer of magnetic developing agent is made uniform in thickness and the printing density is made uniform despite gravitational sagging of the roll.

Abstract: A dot printer in which vibration is eliminated without the use of a separate counterweight. The printer includes first and second hammer banks each holding a plurality of dot printing elements. The first and second hammer banks are spaced apart from each other a predetermined distance in the direction in which a printing sheet passes. A motor and oppositely-phased drive cams reciprocate the two hammer banks in opposite directions parallel to a dot printing direction.

Abstract: A printing apparatus including a plurality of drive coils for driving printing hammers arranged longitudinally in side-by-side relation at one side of a core of the U-shape. A first cooling fluid passageway is defined inside the core of the U-shape to allow a cooling fluid for cooling the drive coils to flow therethrough, and a second cooling fluid passageway is defined outside the core by a duct to allow the cooling fluid for cooling the drive coils to flow therethrough without escaping to the outside by diffusion. A current of cooling fluid is forcibly fed into these cooling fluid passageways by a fluid machine.

Abstract: In a high speed impact printer of the type arranged to impact a plurality of print hammers against given types carried by a type carrier by energizing corresponding solenoids, the energization of given solenoid or solenoids is started from a given point of time. The given solenoid(s) is/are continuously energized for a predetermined interval which is accurately determined by digital circuitry having a counter. A memory for storing data each indicative of a place in a print line in each address thereof, is provided, where a given address of the memory is periodically read and written at a given interval in response to the output signal of the counter which periodically counts the number of clock pulses. The data stored in the memory is decoded to terminate the energization of the given solenoid(s).

Abstract: The print timing, with which a print hammer impacts a desired type moving on a type carrier, is advanced and then retarded or vice versa during test printing to find an ideal print timing. The amount of advancing and retarding respectively correspond to the negative and positive tolerance limits of the variation in flight time of the print hammer. During test printing the print timing is further advanced and/or retarded so that printed samples are perfect, and then the timing, which has been further advanced or retarded, is used to determine the ideal print timing. Circuit arrangements for performing the method are also disclosed as embodiments of the invention.