Abstract: Each of a pair of spaced apart paper feed mechanisms within the paper feed system of a dot matrix line printer has opposite upper and lower portions thereof slightly angled relative to each other and disposed on opposite sides of and close to an elongated print station having a platen at one side thereof on which the paper feed mechanisms are mounted. Guides within the print station direct a length of paper introduced onto one portion of the paper feed mechanism through the print station and onto the other portion. Each paper feed mechanism is locked in a desired position on the platen using a manually operated lever arm arrangement having a mechanical advantage. Phasing or pitch adjustment between the opposite portions of each paper feed mechanism is accomplished by either of two arrangements which vary the position of a pulley engaging an endless belt between the opposite portions in combination with an opposite spring mounted pulley which bears against the inside of and tensions the endless belt.

Abstract: The specification describes a low reluctance magnetic circuit for a dot matrix line printer for retaining hammersprings by the magnetic circuit having pairs of pole pieces formed of magnetically conductive sheets having a space for receipt of a permanent magnet. A coil is wrapped around a portion of each of the pole pieces between the magnet and the ends to provide a reverse magnetic field to the magnetic field provided by the permanent magnet. A magnetic shunt is established between the pole pieces to provide a greater magnetic effect. The pole pieces are sized and plated at the ends, with a spaced wear bar between them to provide improved performance and longer wear.

Abstract: The specification sets forth a hammerspring for a dot matrix printer having a plurality of such hammersprings spaced along a hammerbank with permanent magnetics to draw said hammersprings into a retracted and uniformly stressed mode through a spring portion which are released by overcoming the magnetic retention, the hammerspring formed with a base portion connected to the hammerbank with a spring portion extending from said base portion having a decreasing transverse cross sectional area extending to an enlarged end portion for improved magnetic retention against said permanent magnets.

Abstract: An improved hammerbank in a dot matrix line printer has two different sets of staggered apertures therein along the length thereof for drawing pressurized air at the outside of the hammerbank therein to provide turbulent, high velocity cooling air in the region below the magnetic coils of the magnetic hammer actuators. The cooling air is confined to passage over the magnetic coils by enlarged flanges on the coil bobbins which form an air dam. The air dam discourages escape of the cooling air through spaces between the hammer springs.Magnetic interaction between adjacent magnetic hammer actuators is minimized due to the absence of common magnetic materials extending therebetween, except for the permanent magnets which hold the hammer springs in the retracted position. The permanent magnets are common to a plurality of the magnetic hammer actuators and by physically extending therebetween serve to prevent substantial leakage flux from occurring.

Abstract: In a printer in which a shuttle is driven in reciprocating fashion by a rotating cam, a counterbalance assembly disposed on the opposite side of the cam from the shuttle and having a cam follower disposed along a common axis extending through the cam and a cam follower of the shuttle includes a mass in the form of a generally rectangular block mounting the cam follower at one of a pair of opposite ends thereof. Reciprocating movement of the block in response to rotation of the cam is provided by a pair of tapered flex pivots coupled to opposite ends of a base and extending upwardly and coupled to the opposite ends of the block. The end of the block opposite the cam follower receives a spring disposed against a reference surface to bias the cam follower against the cam.

Abstract: A printer tractor drive assembly is specified having a belt with pins which engage paper which is to be moved across a print station. The assembly includes a split lid covering the paper being driven. One portion of the split lid can be opened to expose and remove the paper along its perforations, while the other portion of the split lid retains the paper on the tractor pins.

Abstract: A dot matrix line printer is disclosed in which the amount of wear of an ink ribbon is measured by continuously compiling data representing impacting action of the printer as the printer prints.In one embodiment, this is accomplished by initially determining a dot count based on the length of the ribbon and representing the maximum theoretical useful life of the ink ribbon and then decreasing the initial dot count as printing thereafter commences. The dot count remaining is continuously divided by the initial dot count to determine the percentage of ribbon life remaining. When the dot count has been increased substantially to zero, a worn ribbon indication is provided to initiate an audible or visible alarm and to prevent further printing until the worn ribbon is replaced. As printing occurs the dots actually printed are counted, and this count is applied to reduce the initial dot count at a rate determined by the type of printing being undertaken.

Abstract: A dot matrix line printer is disclosed in which the amount of wear of an ink ribbon is measured by continuously compiling data representing impacting action of the printer as the printer prints.In a first embodiment, this is accomplished by initially determining a dot count based on the length of the ribbon and representing the maximum theoretical useful life of the ink ribbon and then decreasing the initial dot count as printing thereafter commences. The dot count remaining is continuously divided by the initial dot count to determine the percentage of ribbon life remaining. When the dot count has been decreased substantially to zero, a worn ribbon indication is provided to initiate an audible or visible alarm and to prevent further printing until the worn ribbon is replaced. As printing occurs the dots actually printed are counted, and this count is applied to reduce the initial dot count at a rate determined by the type of printing being undertaken.

Abstract: In a printer in which a plurality of hammers mounted along the length of an elongated hammerbank are selectively fired as the hammerbank is reciprocated relative to an elongated platen to impact a length of ink ribbon against at least one length of print paper supported by the platen to effect printing in dot matrix fashion, the platen being rotatable about an axis of rotation to vary the size of a platen gap between the plurality of hammers and the platen, a mechanism is provided for positively locking the platen in any one of a succession of different rotational positions to provide locking platen gap adjustment. The Positions are identified in order to facilitate resetting of the platen to a desired gap size. The mechanism includes a rotatable knurled thumbknob having mounted thereon a cam having a succession of eccentric or radially varying detents in an outer surface thereof which receives the end of a pivotally mounted, spring-biased lever.

Abstract: In a printer in which drive transistors coupled to hammer drive coils control energization of the coils within each of a plurality of magnetic print hammer actuators to provide firing of hammer springs associated with the print hammer actuators, leakage of one or more of the drive transistors when they are switched off is detected by a testing circuit which flags a fault condition to turn off the driver circuits if the current at a junction common to all of the drive transistors exceeds a predetermined threshold value. This provides an early warning system in which faulty transistors are routinely detected well before they have a chance to fail and thereafter burn out the associated coil included within a hammerbank of the printer.

Abstract: In a printer in which an elongated shuttle is driven in reciprocating fashion across a print paper with hammers mounted along the length of the shuttle being selectively fired to print dots on the paper, a timing system provides hammer fire pulses denoting the positions of the shuttle at which hammer firing should be initiated to print in the proper dot positions. Proper timing is maintained so as to allow for printing during acceleration and deceleration as well as during constant velocity movement of the shuttle by determining the average shuttle velocity between each successive pair of fence post pulses generated by a shuttle-coupled encoder. The average velocities are represented by the time lapses between occurrence of the pairs of fence post pulses which are measured and stored during each startup of the printer as well as each time the nominal operating shuttle velocity is changed as part of a change in printer operation.

Abstract: In a dot matrix line printer in which a plurality of hammer springs mounted along the length of an elongated reciprocating hammerbank are selectively released or fired to impact dot printing impact tips mounted thereon against a print paper through a length of ink ribbon to print dots, the wear that would otherwise occur each time one of the hammer springs rebounds back into contact with a pair of pole pieces against which the hammer spring resides when in its retracted position is greatly minimized by chromium masses plated on the tip of the hammer spring and on the tips of the pole pieces. Chromium platings on each hammer spring are confined to the end of the spring and comprise either a pair of masses adjacent the different pole tips or a single mass encompassing both pole tips. The chromium masses are of convex contour and of hexavalent chromium composition to provide the masses with hard and smooth surfaces that slide over and do not abrade one another upon impacting.

Abstract: In a dot matrix line printer in which an elongated hammerbank and an opposite conunterbalancing assembly are driven in opposing reciprocating fashion by a motor driven cam, the size of the cam drive motor and the current requirements thereof during startup of the printer are greatly reduced by applying current pulses to the motor in a pattern synchronous with the resonant frequency of the reciprocating cam driven system. The current pulses which are considerably smaller in amplitude than the continuous current conventionally used to produce startup are generated during alternate half cycles of the resonant frequency, causing the cam to rock back and forth until eventually the peak resistance presented by opposite lobes on the cam and the consequent maximum compression of springs within the cam followers coupling the cam to the hammerbank and the counterbalancing assembly is overcome.

Abstract: In a color printer in which a shuttle assembly containing a plurality of impacting print hammers is reciprocated in bidirectional fashion relative to an opposing platen to impact a print paper against the platen through the different color zones of an ink ribbon to print in color, the different color zones of the ribbon are arranged in a repeating pattern along the length thereof enabling the lightest color to be printed first followed by successively darker colors as the ribbon is advanced bidirectionally between the opposite ends thereof. A pair of barrier zones having a blank ribbon zone therebetween are disposed between each adjacent pair of color zones on the ribbon to prevent ribbon contamination due to bleeding of ink between adjacent color zones when the ribbon is wound on a reel. Ribbon contamination is further prevented by the blank ribbon zones which absorb ink that rubs off onto the ribbon guides.

Abstract: A ribbon fault detection system within an impact printer has a pair of resilient electrical contacts disposed in spaced-apart relation across the width of an ink ribbon within each of a pair of ribbon guides located between the opposite ends of a print station and a pair of spools for receiving the opposite ends of the ink ribbon and driving the ink ribbon. Each of the electrical contacts which is silicone coated to minimize ink migration and which is normally held out of engagement with a mating contact due to engagement by the ribbon is coupled in parallel with the other resilient electrical contacts so that closure of any one of the resilient electrical contacts onto its mating contact will generate an indication of a ribbon fault condition.

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.