Abstract: An image forming apparatus which forms an image on a recording medium at a number of different dot densities.

Abstract: An ink jet printer includes a pump which pressurizes an ink to be supplied to a nozzle, which projects an ink jet. When the ink pressure which is supplied to the nozzle exceeds a given value or when the deflection of the ink jet is improper, pressure oscillations are applied to the nozzle by alternately and repeatedly driving and ceasing to drive the pump in order to remove a plugging of the nozzle. If the repeated operation does not result in a reduced ink pressure, the nozzle is connected to a low pressure ink vessel, causing the pressure prevailing within the nozzle to be reduced.

Abstract: A charge detecting electrode unit is disclosed which is coupled to a platen shaft of an ink jet printer so as to be rotatable relative thereto for detecting a deflected position of charged ink particles. It includes a housing having an internal space in which a charge detecting electrode is centrally located. The housing is formed with an opening which receives flying ink particles, in its front surface. An electrically conductive layer is formed on and continuously extends across the internal wall surfaces and the external surface of the housing around the opening, and an electrically conductive and water absorbing sheet is attached to the outer periphery of the housing and is in contact with the conductive layer located around the opening which is connected to a grounding wire. The housing also includes a compartment which houses a water absorbing pad and which is open to the exterior of the housing.

Abstract: A thermal printer for printing characters or the like on a recording medium, heat-sensitive paper or plain paper, by a thermal printhead which is mounted on a carriage movable along the recording medium in a reciprocating manner is provided. The printhead is pressed against the recording medium while the carriage is moving in a printing direction and the printhead is kept away from the recording medium while the carriage is moving in a returning direction opposite to the printing direction. A cassette containing therein heat-sensitive ink ribbon is substantially elongated in shape and it bridges between a pair of side plates forming part of a frame of the printer when detachably mounted in position. The cassette is provided with a supply port at one end and a take-up port at the opposite end and thus the ribbon is lead outside through the supply port and lead inside through the take-up port. And the ribbon is taken up in association with the returning motion of the carriage.

Abstract: A control system for a stepping motor in which a current (or voltage) to be fed to each excitation coil of the motor at the timing for an m-phase excitation is different from a current (or voltage) to be fed at the timing for an n-phase excitation. This difference in current (or voltage) causes a same torque to develop both in the m-phase excitation and n-phase excitation.

Abstract: In an impact printing apparatus including a carriage which carries a rotary type element, the length of time required for a motor drive system for the carriage stop hunting and stabilize at a desired printing position depends on variables including the distance the carriage was moved, character pitch and the like. The apparatus senses these variables and delays hammering of the type element for printing for a length of time calculated to reduce the displacement of the carriage from the desired printing position caused by hunting to an acceptable value while maximizing the effective printing speed.

Abstract: A stepping motor (31) drives a load (33) such as an ink ribbon in a printer which exerts reverse torque on the motor shaft (32) thus displacing the shaft (32) slightly in the reverse direction when a low hold current is applied to a motor phase. Prior to switching the motor (31) to a next phase for rotation, a high drive current is applied to the present phase. After a certain length of time which is sufficient for the shaft (32) to be moved to the correct present position, the phases are sequentially switched while the high drive current is applied for rotating the shaft (32) and load to a new position.

Abstract: A type element (22) is driven across a sheet of paper (24) and a hammer is driven at desired space positions for printing without stopping the type element (22). A length of time required for the type element (22) to select a new character is computed, and a type element drive speed for a next space is computed as a function of the selection time and the present drive speed so that the type element (22) will reach the next space in a length of time substantially equal to the selection time, thereby compensating for acceleration or deceleration of the type element (22).

Abstract: A coil (12), when electrically energized, magnetically drives a printing hammer to impact a type element against paper for printing a character. The coil (12) is connected to a power source (+V) for a predetermined time (T1) during which the hammer moves toward the paper and the current (I) through the coil (12) increases exponentially. Then, the coil (12) is energized for another predetermined time (T2) in response to logically high portions of a train of high frequency drive pulses (B). A diode (23) connected in parallel with the coil (12) maintains current flow through the coil (12) due to counter electromotive force during the logically low portions of the drive pulses (B) by providing a low resistance path across the coil (12).The average value of current through the coil (12) decreases exponentially during the time the drive pulses (B) are applied.

Abstract: A monolithic photosensor array comprises first, second and third identical photodiodes. A light emitting diode illuminates the third photodiode continuously. An occluder disc is rotatably driven from the shaft of a servo motor between the light emitting diode and the first and second photodiodes. The disc is formed with a plurality of circumferentially spaced apertures which alternately cover and uncover the photodiodes which produce quasisinosoidal position signals in response thereto, the position signals of the first and second photodiodes being relatively 90.degree. out of phase. A computing circuit produces a motor shaft velocity command signal corresponding to the number of steps the shaft must rotate from the initial position to the new desired position and progressively reduces the magnitude of the velocity signal in response to the position signals.

Abstract: A disc rotatable with the motor shaft has circumferentially equally spaced slots formed therethrough. A light source and receiver assembly are operatively arranged relative to the slots to produce pulses representing a predetermined angular displacement of the motor shaft determined by the width of the slots as the motor shaft rotates. The duration of the pulses decreases as the motor shaft speed increases. A multivibrator is triggered by the leading edges of the pulses to generate reference pulses of a predetermined duration. The motor phases are excited in a normal sequence as long as the duration of the pulses is longer than the duration of the reference pulses. When the pulse duration becomes less than the reference pulse duration, coincidence sensing means alter the phase excitation during the times between the termination of the pulses and the termination of the respective reference pulses to apply a torque to the motor shaft in such a manner as to prevent the motor shaft from accelerating further.

Abstract: A disc rotatable with the motor shaft has circumferentially equally spaced slots formed therethrough between the motor step positions. A light source and receiver assembly are operatively arranged relative to the slots to produce position pulses when the motor shaft is positioned between steps. Since the motor shaft varies during operation, the widths of the position pulses also vary in proportion to the motor shaft speed. Timing pulse generators are arranged to generate timing pulses of fixed duration at various motor shafts spacings before the desired stopping position. The coincidence between the timing pulses and the position pulses is sensed, and the motor phases are switched to apply reverse torque to the motor shaft during the intervals of coincidence or non-coincidence of the timing pulses and position pulses.