Serial impact calculator printer

Claim 2

In a printing apparatus having a frame, a print head selectively actuated by actuating means associated with said head to impress characters on a recording medium, a pair of record medium advancing rollers mounted for rotation on spaced parallel axes with the external roller surfaces engageable with one another to define a common guide path for advancement of the recording medium therebetween and advancing means associated with said print head drive means to incrementally drive one of said print medium advancing rollers in a direction causing advancement of the recording means, the improvement comprising: print head drive means rotatable to reversibly drive said print head in a print and return direction transversely of the direction of advancement of the recording medium, a pair of ribbon spools disposed for rotation at opposite ends of travel of said print head, a print ribbon wound on said spools for passage between said print head and recording medium, each spool including ratchet means thereon to cause each spool to undergo rotation when said ratchet means are positively advanced, and ratchet drive means pivotally mounted on said print head for travel therewith, said ratchet drive means alternately movable into engagement with one of said spools to wind said printing ribbon onto one spool and responsive to resistance of the one spool to rotation to pivot away from engagement with the one spool and into engagement with the other spool to reverse the travel of said printing ribbon whereby to unwind it from the one spool and wind it onto the other spool.

Claim 3

In a printing apparatus according to claim 1, said ratchet drive means defined by a pair of oppositely directed pawl arms extending in opposite directions from said print head, and means centrally supporting said pawl arm on said print head being responsive to resistance of each of said spools to rotation to selectively shift one of said pawl arms into engagement with the other of said ribbon spools at opposite ends of travel of said print head.

Claim 4

In a printing apparatus according to claim 2, said central support means for said ratchet drive means defined by biasing means normally urging each of said pawl arms rearwardly and a pivot pin, said pawl arms being displaceable in a direction substantially parallel to the direction of travel of said print head to shift the pivot point between said pawl arms so as to permit one of said biasing means to overcome the urging of said other biasing means to pivot one of said pawl arms into engagement with one of said ribbon spools while pivoting the other of said pawl arms away from engagement with the other of said ribbon spools.

Claim 5

In a printing apparatus according to claim 1, each of said ribbon spools including a spool body for winding of said print ribbon thereon, a ratchet wheel disposed beneath said spool body, and downwardly projecting legs beneath said ratchet wheel frictionally engaging the edge of a spool-mounting opening on said frame.

Claim 6

In a printing apparatus according to claim 4, said spool-mounting opening defined by a bushing having a downwardly projecting sleeve, said downwardly projecting legs on said ribbon spool including a pair of diametrically opposed leg portions having a transverse interconnecting beam member resiliently urging said legs outwardly into frictional engagement with the inner surface of said sleeve.

Claim 7

In a printing apparatus according to claim 5, said downwardly projecting legs including a pair of legs displaced at 90° from said first pair of legs having means movable into snap-fitting engagement with said sleeve.

Claim 8

In a printing apparatus according to claim 1, said ratchet means for each ribbon spool correspondingly designed by upper and lower ratchet wheels of different diameters, ratchet teeth on one wheel extending in a direction opposite to the ratchet teeth on the other wheel, said ratchet drive means having pawls at opposite ends, the pawl at one end being aligned for engagement with a ratchet wheel of one diameter on one of said ribbon spools and the pawl at the opposite end being aligned for engagement with a ratchet wheel of the other diameter on the other ribbon spool.

Claim 9

In a printing apparatus according to claim 7, said ratchet drive means being pivotal a greater distance in one direction to permit alignment of the one pawl with the ratchet wheel of lesser diameter than the pivotal displacement of the other pawl for engagement with the ratchet wheel of a greater diameter.

Claim 10

A printing apparatus comprising in combination: a frame including spaced-apart, upright side frame portions and a horizontal bed extending between said side frame portions and rigidly interconnecting said side frame portions, a motor drive assembly affixed to one of said side frame portions, a paper supply roll disposed between said side frame portions rearwardly of said horizontal bed, paper advancing means including a platen journaled between said side frame portions above and in closely spaced relation to a concave guide surface at the rearward end of said bed so as to form an arcuate guide path between said platen and said concave guide surface, a pressure roll seated in a recess disposed in said bed forwardly of said concave guide surface, means yieldably supporting said pressure roll in said recess whereby to yieldingly urge said pressure roll against the external surface of said platen, a detent engaging ring at one end of said platen mounted for rotation therewith and provided with a plurality of circumferentially spaced detent engaging grooves along its outer peripheral surface, a ratchet member at one end of said platen opposite to said detent engaging ring mounted for rotation therewith and provided with a plurality of circumferentially spaced ratchet teeth on its outer peripheral surface, a print head including a head carrier, a print head drive member journaled for rotation between said side frame portions in a recess formed in said horizontal bed forwardly of said platen and said pressure roll, said print head drive member including an outer cylindrical surface provided with a helical groove therein, rotatable drive means between said motor drive and said print head drive member operative to rotate said drive member at a predetermined rate of speed whereby to reversibly drive said print head in a print and return direction transversely of the direction of advancement of the paper forwardly along said arcuate guide path and upwardly between said pressure roll and said platen, a detent member mounted for limited rotation at one end of said platen adjacent to said detent engaging ring, said detent member including a detent arm movable into engagement with one of said detent engaging grooves and a manual release level engageable to release said detent arm from engagement with said detent engaging ring, and means normally urging said detent arm in a direction forcing it into engagement with one of said detent engaging grooves, incremental drive means for said platen including an eccentric member mounted for rotation with said print head drive means and a ratchet drive arm journaled for rotation on said eccentric member and extending rearwardly therefrom, said ratchet drive arm including a pawl at its rearward distal end movable into and away from engagement with one of the ratchet teeth on said ratchet wheel in response to rotation of said eccentric member whereby to advance said platen a predetermined distance as said print head is driven in the return direction, and a pair of ribbon spools disposed for rotation at opposite ends of travel of said print head, a print ribbon wound on said spools for passage between said print head and the path of advancement of said paper above said pressure roll, and ribbon spool drive means between said head and said ribbon spool, said ribbon spool drive means being responsive to resistance of rotation of each spool to rotation to move into driving engagement with the other spool for reversibly advancing said print ribbon back and forth between said ribbon spools in response to travel of said print head.

Claim 11

A printing apparatus comprising in combination: a frame including spaced-apart, upright side frame portions and a horizontal bed extending between said side frame portions and rigidly interconnecting said side frame portions, a motor drive assembly affixed to one of said side frame portions, a paper supply roll disposed between said side frame portions rearwardly of said horizontal bed, paper advancing means including a platen journaled between said side frame portions above and in closely spaced relation to a concave guide surface at the rearward end of said bed so as to form an arcuate guide path between said platen and said concave guide surface, a pressure roll seated in a recess disposed in said bed forwardly of said concave guide surface, means yieldably supporting said pressure roll in said recess whereby to yieldingly urge said pressure roll against the external surface of said platen, a detent engaging ring at one end of said platen mounted for rotation therewith and provided with a plurality of circumferentially spaced detent engaging grooves along its outer peripheral surface, a ratchet member at one end of said platen opposite to said detent engaging ring mounted for rotation therewith and provided with a plurality of circumferentially spaced ratchet teeth on its outer peripheral surface, a print head including a head carrier, a print head drive member journaled for rotation between said side frame portions in a recess formed in said horizontal bed forwardly of said platen and said pressure roll, said print head drive member including an outer cylindrical surface provided with a helical groove therein, rotatable drive means between said motor drive and said print head drive member operative to rotate said drive member at a predetermined rate of speed whereby to reversibly drive said print head in a print and return direction transversely of the direction of advancement of the paper forwardly along said arcuate guide path and upwardly between said pressure roll and said platen, a detent member mounted for limited rotation at one end of said platen adjacent to said detent engaging ring, said detent member including a detent arm movable into engagement with one of said detent engaging grooves and a manual release level engageable to release said detent arm from engagement with said detent engaging ring, and means normally urging said detent arm in a direction forcing it into engagement with one of said detent engaging grooves, incremental drive means for said platen including an eccentric member mounted for rotation with said print head drive means and a ratchet drive arm journaled for rotation on said eccentric member and extending rearwardly therefrom, said ratchet drive arm including a pawl at its rearward distal end movable into and away from engagement with one of the ratchet teeth on said ratchet wheel in response to rotation of said eccentric member whereby to advance said platen a predetermined distance as said print head is driven in the return direction, and a pair of ribbon spools disposed for rotation at opposite ends of travel of said print head, a print ribbon wound on said spools for passage between said print head and the path of advancement of said paper above said pressure roll, and ribbon spool drive means between said head and said ribbon spool, said ribbon spool drive means being responsive to resistance of rotation of each spool to rotation to move into driving engagement with the other spool for reversibly advancing said print ribbon back and forth between said ribbon spools in response to travel of said print head.