Abstract: A printer having greatly reduced radio frequency interference from the system clock signal therein is provided by angle modulating the system clock signal in accordance with a desired modulation signal. The modulation signal is chosen so as to spread and thereby reduce the energy level of the system clock signal at the carrier and at the harmonics without interfering with proper detection of the system clock signal by the electronic circuits within the printer requiring the clock signal for proper timing. In a first embodiment the angle modulation is provided by an FM modulator responsive to a modulating signal which is either sinusoidal or randomly varying in nature. In a second embodiment the angle modulation is provided by an arrangement which combines a modulated subcarrier with the basic clock frequency in a phase locked loop.

Abstract: In a printer in which a shuttle and a counterbalancing mass are driven in opposing reciprocating fashion by a rotating, generally oval-shaped cam, the cam followers which couple the shuttle and the counterbalancing mass to the cam are castered to prevent skewing of the cam followers relative to the cam. Each of the cam followers is disposed between and rotatably mounted on a pair of opposite arms extending outwardly from a generally planar base of a castered yoke assembly, the planar base being pivotally coupled to a supporting member therefor which is either coupled to the shuttle or forms a part of the counterbalancing mass. In a first embodiment the pair of opposite arms extend from the planar base toward the cam so as to dispose the cam follower between the pivotal mount of the yoke assembly and the cam.

Abstract: In a print hammer mechanism in which a thin, flat hammer spring is mounted at a fixed end thereof to a magnetic structure which includes a permanent magnet and a pole piece having a pole tip facing the opposite free end of the hammer spring on a side of the hammer spring opposite an impact printing tip, a pivot fulcrum is formed by an impact arrangement which faces an intermediate portion of the hammer spring between the fixed and free ends thereof. The permanent magnet normally pulls the hammer spring into a retract position in which the spring impacts and resides against the impact structure with the free end of the spring forming an air gap with the pole tip.

Abstract: A linear motor which mounts and drives a hammer bank shuttle assembly in reciprocating fashion within a dot matrix line printer is controlled by a digital servo. The digital servo includes an encoder for generating a pulse each time the shuttle assembly passes one of a succession of different positions along a linear path of movement therefor together with apparatus for measuring the time intervals between successive pulses, comparing the time intervals with a reference value, generating error signals in accordance with the difference and applying the error signals to vary the durations of driving pulses applied to the linear motor.

Abstract: In a printer system in which hammers mounted along a shuttle assembly which reciprocates relative to a print paper are selectively energized to impact the paper and print dots thereon, the dot density is made variable by an encoder system responsive to the position of the shuttle assembly as it traverses a linear path of motion. The encoder system includes a decoder for generating a succession of fence post pulses as the shuttle assembly reaches each of a succession of different positions along the linear path of motion and circuitry for generating a succession of hammer firing pulses in response to and having a desired phase relationship with the fence post pulses. The hammer firing pulses may occur at a frequency the same as or different from the frequency of the fence post pulses to provide a desired print density. A stored initial offset value is used to initially establish the desired phase relationship between the hammer firing pulses and the fence post pulses.

Abstract: In an impact printer system in which various hammer springs mounted in side-by-side relation along a reciprocating hammer bank are selectively released to cause an impact tip mounted at the upper end of the hammer spring to impact a paper or other printable medium, the hammer springs are divided into two different groups and the release of the hammer springs in the different groups is staggered. Alternate ones of the hammer springs comprise a first group of hammer springs which are selectively released at the beginning of each of a succession of cycles as the hammer bank sweeps across the printable medium. The remaining ones of the hammer springs comprise a second group and are releaseable at a midway point through each cycle.

Abstract: An arrangement for bidirectionally driving a hammer bank shuttle assembly along a linear path in a line printer includes an opposite pair of circular, rotatable elements having an elongated shuttle assembly mounting element and an elongated counterbalancing element extending between the pair of rotatable elements on the opposite sides thereof. Pole pieces and a magnet disposed between and adjacent the shuttle assembly mounting element and the counterbalancing element provide magnetic flux which flows through portions of the opposite elements to attract and maintain the elements in contact with the opposite rotatable elements.

Abstract: In a dot matrix line printer in which selected ones of a plurality of hammers mounted on a reciprocating hammer bank are released in response to successive sets of serial data to print dots on a paper, the changing hammer release characteristics which are caused by different numbers of hammers being released with each new set of serial data are compensated for by an arrangement providing a varying hammer release signal in accordance with the number of hammers being released. The variable release signal is provided in the form of a variation in the time interval during which the drive amplifiers associated with hammer release coils are turned on, thereby effectively varying the length of a current pulse provided to each coil in direct proportion to the number of hammers to be released. A counter is preset, then counted down from the preset value in accordance with the number of hammers to be released as represented by a set of serial data being provided to a shift register.

Abstract: In a print hammer mechanism in which an elongated, resilient hammer element mounted at a fixed end thereof has an opposite free end thereof selectively released from a retract position for impact of a dot imprinting element carried by the free end of the element, an improved magnetic circuit is provided for use in release and retraction of the hammer element. The improved magnetic circuit includes a pair of elongated pole pieces of like configuration having back ends thereof mounted on opposite sides of a rare earth magnet and tips at the opposite front ends thereof disposed adjacent the free end of the hammer element to form a pair of gaps therewith.

Abstract: A counterbalanced bidirectional drive for a hammer bank shuttle assembly within a line printer utilizes a band formed into an endless loop extending around and between an opposite pair of rotatable pulleys on opposite sides of the pulleys. A hammer bank-carrying shuttle assembly is coupled to a portion of the band between the pulleys on one side of the pulleys and is counterbalanced by an elongated bar of similar mass coupled to a portion of the band between the pulleys on the opposite side of the pulleys from the shuttle assembly. A DC motor coupled to one of the pulleys is alternately energized in opposite senses so as to bidirectionally drive the shuttle assembly along a linear path between opposite limits defined by resilient members impacted by an element mounted on the counterbalancing bar.

Abstract: A dot matrix printer having a reciprocating hammer bank prints characters in either a standard or a compressed size using one of two different sets of modulation bits stored in a character generator for each character. A control code byte preceding each line of characters to be printed selects the sets of modulation bits in the character generator to be used and in addition selects the repetitive counts to be made by two different decoders in response to timing pulses designating the different dot column positions during each sweep of the hammer bank to control the application of the modulation bits from the character generator to actuating mechanisms for the hammers within the hammer bank.

Abstract: A print hammer mechanism which forms a magnetic path between the opposite fixed and free ends of an elongated resilient hammer element using a permanent magnet, a first pole piece terminating in a pole tip adjacent the free end of the hammer element and electromagnetic means for cancelling the effects of the permanent magnet employs a second pole piece having a pole tip disposed adjacent the free end of the hammer element between the first pole piece and the fixed end of the hammer element. The relatively short magnetic path of low reluctance along the hammer element between the pole pieces combines with the effect of flux flowing in two gaps perpendicular to the flat surface of the hammer element to significantly improve the magnetic properties of the print hammer mechanism including the ability to quickly release and then retract the hammer element and the ability to increase the resonant frequency and/or the amount of energy stored in the hammer element for a given amount of magnetic flux available.

Abstract: A printer hammer bank for a dot matrix or other type printer is reciprocated at high speed along a printing position by a low mass, low inertia servo-controlled drive. Precise control is maintained even though a positive drive structure is not used. A reciprocable drive mechanism supporting the hammer bank is mounted to undergo free flight with low friction along a selected axis parallel to a printing line. At each limit of movement, the drive mechanism encounters resilient stop members which reverse the direction of motion of the drive mechanism and included hammer bank following a natural cosine function of the spring mass of the stop members and with low kinetic energy loss. Losses occurring during reversal are compensated by an energy impulse from a coupled linear electromagnetic drive and an associated velocity servo system which eliminates the need for close servo control during reversal, allowing the drive mechanism to rebound naturally.

Abstract: An impact printer ribbon drive of the reel-to-reel type, in which a length of ink ribbon extending between and wound around opposite reels is disposed between a reciprocating hammer bank and print paper on a platen, drives the ribbon at substantially constant speed and tension independent of varying ribbon pack diameter on the two reels. Each one of the reels is driven by a different one of a pair of DC permanent magnet motors. The motors are energized by a circuit which maintains the sum of the currents through the two motors substantially constant and which also maintains the voltage at the leading or take-up motor substantially constant. The sum of the currents and the voltage are maintained substantially constant by a pair of servo circuits associated with different ones of the motors and coupled to be alternately actuated in response to external direction commands.

Abstract: A hammer mechanism which undergoes reciprocating motion across platen-supported paper webs in a dot matrix printer effects printing by momentarily energizing coils associated with selected resilient hammer elements mounted on a common magnetic structure to neutralize a magnetic field from the common magnetic structure and release the hammer elements from a retracted position. Each end of the common magnetic structure extends to define dummy hammer positions adjacent the first hammer element on each end, providing uniform magnetic field strength to the end hammer elements and to all hammer elements in between. The hammer elements are fabricated and mounted as individual elements of resilient magnetic material with mounting of the elements being accomplished in pairs using a common plate for each pair and screws which have a portion of reduced diameter directly behind the head thereof to provide easy access to the shaft of the screw in the event of breakage during installation.

Abstract: An improved print hammer actuator for dot matrix printers employs a substantially closed loop magnetic path including a resilient magnetic hammer, a number of such hammers being aligned in a hammer bank assembly which is shuttled back and forth along a printing line at a high rate of speed, while the hammers are individually actuated by energizing coils which overcome a permanent magnetic field normally maintaining the hammers in retracted position. Heat conducting elements are mounted in heat transfer relationship with each of the different ones of the coils in the hammer bank, and high surface area fins on the elements extend into an air flow directed across one side of the hammer bank. For this purpose the hammer bank assembly is configured to define an interior air channel along its length and includes a fixed top cover and spaced apart circuit board forming part of a plenum and directing air frontwardly from a rear mounted fan.

Abstract: Both the operative position of a movable platen and the presence of paper to be advanced past the platen in a line at a time printer are affirmatively sensed by a single mechanism. A cantilevered spring arm extending from a fixed mount includes a terminal switch sensor at its free end in proximity to the paper. At an intermediate region along its length the spring arm traverses adjacent to but spaced apart from the platen, and an adjustable set screw on the arm is disposed for contact with the platen. When the platen is in the operative position, behind the print hammers, and the printer is loaded with paper, the spring arm biases the actuator into contact with the paper, transferring the switch contact to a given position and thereby indicating that both needed prerequisites for printer operation are satisfied.

Abstract: Control of multiple hammer elements in a high speed printing system in which the hammer elements are individually operated by energizing pulses applied to electromagnets is effected by an improved regulation circuit with which additional safety features may be used in cooperative fashion. The additive combination of a full wave rectified signal and the voltage level of a storage capacitor which is being charged by the rectified signal is sensed, converted to a lower level, and compared to a voltage reference. A silicon controlled rectifier which controls charging of the storage capacitor is turned on by this circuit only when current is beginning to flow, thus providing the equivalent of zero crossing initiation and preventing high surge currents from developing. As a further feature, signals generated during times at which printing should not be taking place, such as paper advance, are used to alter the voltage reference level so as to effectively turn off the power during the turnaround interval.

Abstract: A dot matrix printer system utilizes a reciprocating shuttle having a plurality of hammer elements and externally energized hammer controls mounted with the hammers on the shuttle. Each hammer scans a number of dot printing positions within a dot matrix line, and is energized at a high repetition rate during movement to imprint serially the dot patterns in that line for several successive characters. The paper is then advanced and the next dot matrix line is printed in the reverse direction. The shuttle mechanism forms a part of a dynamically balanced system, being in one example driven in a trapezoidal motion from a cam system that also engages an oppositely moving counterweight system. A highly reliable fast acting hammer bank comprises an array of individual spring hammer elements and associated magnetic actuators, the hammer elements normally being magnetically biased to a retract position by a permanent magnet.