Printronix, Inc.

Leo J Emenaker

Gordon B Barrus

Glen R Radke

Norman E Farb

Raymond F Melissa

Gerold Holzer

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. The opposite portions of each paper feed mechanism terminate in ramps which are angled to facilitate withdrawal of pins on the belt from apertures at the edges of the print paper. A lug arrangement at the end of the ramp prevents the toothed underside of the belt from slipping off of the meshing teeth of a pulley about which the belt extends. Slide members resiliently bear against and maintain the edges of the paper in contact with the belts.

Paper feed system having mechanisms engaging opposite edges of print

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.

Flexure member in cam driven shuttle printer

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. Manual rotation of the thumbknob gradually rotates the lever as the end of the lever is positively positioned in each of the succession of detents. An opposite end of the lever engages a platen handle which is coupled to the platen and which is spring-biased to maintain engagement of the handle with the lever.

Resettable locking platen gap adjustment mechanism

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. The various different color zones are identified by one or more strips which extend across the width of the ribbon adjacent each color zone and which identify the color therein in bar code fashion. The color printer may be operated in a manner which provides multiple passes of each color zone through the print station between the shuttle assembly and the platen to prolong the life of the ribbon and to enable the printer to quickly advance to the next color zone with a minimum amount of search time. The print paper which is driven bidirectionally by tractor drives above the print station is held in tension by an arrangement below the print station which employs a torque motor having an elastomeric wheel engaging a side of the paper opposite an arrangement of non-ink absorbing rollers.

Color printer

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. In a second embodiment the pair of opposite arms extend from the planar base in a direction away from the cam so as to dispose the pivot point of the yoke assembly between the axis of rotation of the cam follower and the cam.

Printer shuttle drive having castered cam followers

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. The hammer mechanism is surrounded by a housing having a front face adjacent the hammer elements which is of magnetic material to increase the flux density for hammer elements of given size and which has an opening therein equipped with a filter to permit the exit of cooling air introduced under pressure into the housing while preventing contaminants from getting inside the housing.

Print hammer mechanism

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. If the platen is disengaged from its normal position, as for paper loading, the spring arm is concurrently moved away from the paper and the switch actuator freed to transfer the switch to its opposite contact. In the absence of paper the switch actuator is also freed regardless of platen position. The length of travel of the spring arm is substantially greater than that of the switch actuator and the spring arm has a greater spring force than the switch actuator arm, insuring both forceful operation of the switch despite variations in paper thickness, and easy vernier adjustment of the trip point of the switch.

Paper feed sensing mechanism for printer

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. The magnetic field is neutralized to permit hammer flight with controlled velocity for imprinting, with hammer return being automatically achieved by the magnetic bias. The system is amenable to generation of a wide variety of dot matrices and arbitrary printing patterns, and provides uniform and well defined characters through a substantial number of copies, but nevertheless operates reliably and at high speed with a low cost mechanism that does not require adjustment.

Growing community of inventors

El Segundo, CA, United States of America

Leo J Emenaker