US3726381A

US3726381A - Printer ribbon feed

Info

Publication number: US3726381A
Application number: US00120432A
Authority: US
Inventors: J Murphy
Original assignee: Mohawk Data Sciences Corp
Current assignee: DECISION DATA Inc A CORP OF; NationsBank of Texas NA; Mohawk Systems Corp
Priority date: 1971-03-03
Filing date: 1971-03-03
Publication date: 1973-04-10
Anticipated expiration: 1990-04-10
Also published as: DE2208689A1; FR2127827A5; CA936486A

Abstract

A printer having a printhead which moves from left to right across the document to print a line and a ribbon located between the printing end of the printhead and the document. Ribbon supply means is provided at the right side of the document, ribbon takeup means is provided at the left side of the document and means for engaging the ribbon when the printhead moves from right to left is mounted on the printhead. During a printing operation with left-to-right movement of the printhead, the ribbon remains stationary and is traversed by the printhead. This provides a new area of the ribbon for printing each character. When the printhead returns to the left to begin a new line, printing does not occur and the engaging means connected to the printhead pulls the ribbon from the supply means. The resulting slack in the ribbon is taken up at the left side of the document by the takeup means and when the printhead reaches the left margin a new supply of ribbon has been provided for printing the next line. Since the printhead prints when moving toward the right, its velocity is slower in this direction. Preferably, the engaging means is fractionally operable to engage the ribbon at the higher speed during leftward movement but slides with respect to the ribbon at the slower velocity during rightward movement.

Description

United States Patent 1191 'Murphy [54] PRINTER RIBBON FEED [75] Inventor: John B. Murphy, West Roxbury,

Mass.

{73] Assignee: Mohawk Data Sciences Corporation,

Herkirner, N.Y.

2'2 Filed: Mar. 3, 1971 [21 App1.No.:120,432

Primary Examiner-Robert E. Pulfrey Assistant Examiner-R. T. Rader Attorney-Francis J. Thomas, Richard H. Smith and Thomas C. Siekman 1451 Apr. 10, 1973 ABSTRACT A printer having a printhead which moves from left to right across the document to print a line and a ribbon located between the printing end of the printhead and the document. Ribbon supply means is provided at the right side of the document, ribbon take-up means is provided at the left side of the document and means for engaging the ribbon when the printhead moves from right to left is mounted on the printhead. During a printing operation with left-to-right movement of the printhead, the ribbon remains stationary and is traversed by the printhead. This provides a new area of the ribbon for printing each character. When the printhead returns to the left to begin a new line, printing does not occur and the engaging means connected to the printhead pulls the ribbon from the supply means. The resulting slack in the ribbon is taken up at the left side of the document by the take-up means and when the printhead reaches the left margin a new supply of ribbon has been provided for printing the next line. Since the printhead prints when moving toward the right, its velocity is slower in this direction. Preferably, the engaging means is fractionally operable to engage the ribbon at the higher speed during leftward movement but slides with respect to the ribbon at the slower velocity during rightward movement.

4 Claim, 5 Drawing Figures PATENIE APR 1 01975 SHEET 1 [IF 3 Y H P R U M B N H O J ATTORNEY PATENTEU APR 1 0 973 SHEET 3 BF 3 PRINTER RIBBON FEED BACKGROUND OF THE INVENTION This invention relates to printers of the type wherein an inked ribbon is moved with respect to the document so that different areas of the ribbon may be used for printing. More particularly, this invention relates to feeding an inked ribbon in such a printer having a printhead which moves across the document to print a line.

Printers having printheads that move from the left to the right margin as they print a line, character by character, are well known. Upon completing a line, the printhead returns to the left margin to begin a new line while the document being printed upon is stepped to present a new blank area for printing. The necessary ink in many of these printers is provided by a ribbon located between the printhead and document. The ribbon is generally moved between locations adjacent the left and right margins, of the document so that fresh ink is provided for printing successive lines. Such ribbon movement is often accomplished by a continually driven take-up reel at one margin which pulls the ribbon from a supply reel at the other margin. In order to utilize all the ribbon, it is generally moved at a slow speed so that some ribbon is not missed during return leftward movement of the printhead. However, by feeding it at a slow speed, some areas of the ribbon are used twice due to the faster speed of the printhead.

Obviously, those characters printed with this already used areas of the ribbon are lighter than those printed with the new ribbon. Each printed line thus contains characters of different densities.

SUMMARY OF THE INVENTION It is the primary object of this invention to provide a printer, having a printhead which moves across the document, with a ribbon feed that allows printing of each line with characters of uniform density.

It is a further object to provide a ribbon feed for such a printer which is simple, reliable and inexpensive.

These objects and others are achieved by the invention according to which a printer with a printhead that moves between two positions across the document to print a line is provided with a ribbon supply means at one side of the document and ribbon take-up means at the other. Means for engaging the ribbon is connected to the printhead and operable only when the printhead travels toward the take-up means and away from the supply means. During this movement, the ribbon is pulled from the supply means and gathered at the takeup means. Generally, the printhead in such a printer moves at a slower velocity in one direction during which it prints than in the other direction when it returns to begin a new line. Preferably, the engaging means is frictionally operable so that it engages the ribbon at the higher velocity but, at the lower velocity, the ribbon is allowed to slide with respect to it and the printhead. This allows each character of the line to be imprinted with a new supply of ink as the printhead traverses the ribbon while printing. Uniform character densities across the lines are thereby provided. As the printhead returns to begin a new line, the ribbon is engaged and a new supply pulled from the supply means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a printer incorporating a preferred embodiment of the invention.

FIG. 2 is a partial plan view of the printhead and the means connected to the printhead for engaging the ribbon.

FIG. 3 is an elevation view of the elements shown in FIG. 2.

' FIG. 4 is a rear perspective view of the ribbon cassette (with its rear side partially cut-away) from which the ribbon is supplied and into which it is taken up.

FIG. 5 is a view of the spring mechanism for returning the printhead to the left margin.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic rear view of a printer embodying the invention. Thus, the left margin of the document 1 being printed upon is designated 1a and appears at the right side in FIG. 1. Conversely, the right margin of the document is designated 1b and appears at the left in FIG. 1. The printer is of the type which prints characters, one by one, with a printhead 3 which moves across the document 1 from its left margin In to its right margin lb. The printhead shown is of the well known matrix variety and thus contains a plurality of styli wires which are selectively projected out of its printing end 3a in patterns which form the characters on the document 1 as it moves from the left to the right margin (toward the left in FIG. 1). When printing, the styli wires force an inked ribbon 7 against the document 1 and a platen 5 located in back of the document to form their impressions. After printing each line, the printhead is returned to the left margin 1a to initiate a new line. During this carriage return movement, the document 1 is stepped (by means not shown) a one line increment so that a new blank area is provided for printing.

A motor 9 is provided for moving the printhead toward the right margin lb when printing. This drive motor could also be utilized by appropriate means to step the document 1 after each line is printed. However, the document stepping means is not shown in FIG. 1 since any conventional apparatus could be utilized. The output shaft 11 of drive motor 9 having flywheel l3 thereon drives a pulley 14 via another pulley 12 and a belt 15. Pulley 14 via shaft 16 and worm l7 drives gear 18 which is connected to a driving gear 21 via shaft 20, clutch l9, and shaft 22. The motor 9 continually drives gear 18 and the clutch 19 is selectively operable to effect rotation of the driving gear 21. A toothed belt 23 is drivingly connected around the peripheries of the driving gear 21 and a further gear 26 to drivingly connect the two. The printhead 3 is connected to belt 23 by member 24 on which the printhead is mounted and which is rigidly attached to belt 23. Gears 21 and 26 are spaced apart at opposite ends of the document and, with the printhead attached to belt 23, rotation of these gears causes the printhead to move back and forth across the document 1 being printed upon. A pair of guide bars, 24a and 24b are slidably located through the mounting member M to guide movement adjacent to gear 26.

A spring mechanism 25 is mounted adjacent to gear 26. FIG. 5 shows the spring mechanism from the rear of the printer similar to the view of FIG. 1. Referring to both these FIGS., the mechanism 25 comprises a housing 25b within which a helical spring 25a is located. A shaft 27 extends through the spring mechanism 25 and is connected to gear 26 to rotate therewith. Within the housing 25b, the shaft 27 has a keyway 27a (FIG. 5) within which one end of the spring 25a is secured. The other end of the spring 25a is connected to the housing 25b which, in turn, is held fixed by a mount 32 on a base 34. With the shaft 27 connected to gear 26, counter-clockwise rotation of the gear winds up the spring 25a.

During operation of the printer, the drive motor 9 continually operates to drive gear 18 and, when clutch 19 is engaged, gear 21 is rotated counter-clockwise (in FIG. 1) to move belt 23 around gears 21 and 26. As the gears rotate counter-clockwise, the printhead moves from the left la to the right lb margin of the document 1. During this movement of the printhead, a line of characters is printed on the document and spring 25a is wound due to the rotation of shaft 27 from gear 26. After the line has been printed and the printhead has reached the right margin 1b of the document, light from the light source 2a normally received by a photocell 4a is interrupted by a shutter 6 mounted to the printhead mounting 24. The resulting change in the photocells output is utilized by appropriate circuitry to disengage clutch 19. When disengaged, the clutch 19 allows gear 21 to freely rotate and due to the force of spring 25a gears 26 and 21 are caused to rotate clockwise and the printhead 3 is carried to the left margin 1a of the document. Just after reaching this left margin, the shutter 6 interrupts light between a second photocell 4b and light source 2b. The resulting change in the output of photocell 4b appropriate circuitry to now engage the clutch 19. This obviously causes gear 21 to begin to rotate counter-clockwise and initiate printhead movement toward the left in FIG. 1 during which printing occurs.

The circuitry for controlling the clutch 19 in response to the photocells 2a and 2b is not shown or described since any suitable conventional circuit may be utilized and such a circuit forms no part of the invention. Similarly, the printhead itself and the circuits for controlling it are not illustrated since any suitable well known elements could be utilized and these do not form a part of the invention.

Referring again to FIG. 1, the printer contains a ribbon cassette 31 for providing the ribbon 7, which is endless, from its supply end 31a located adjacent the right margin lb of the document. A. shown, the ribbon is guided in a path from the supply end 31a, to around the printhead 3 and, thereafter, to the opposite end 31b of the cassette. At the printhead, the ribbon is engaged such that during movement by the printhead to the right margin lb the printhead slides with respect to the ribbon. However, during movement of the printhead towards the left margin la, the ribbon is engaged at the head and pulled from the supply end 31a of the cassette. This obviously causes slack in the ribbon at the cassettes take-up end 31b which is taken care of by a ribbon drive gear 29 mounted on the shaft 27. As previously disclosed, shaft 27 revolves with printhead movement to the left margin during carriage return. Ribbon drive gear 29 thus rotates during this time and engages a gear 43 shown in FIG. 4 to cause the slack ribbon to be taken-up into the cassette 31.

A mechanical one-way clutch 29a is provided between gear 29 and the shaft 27 so that the ribbon drive gear 29 is not rotated during printhead movement to the right margin. The clutch 29a allows the gear to become drivingly engaged with shaft 27 only when the shaft is being rotated (clockwise in FIG. 1) by the spring mechanism 25 during carriage return when ribbon slack occurs at the left margin and rotation of gear 29 is desired. Any appropriate one-way clutch may be used.

Referring to FIG. 4 which illustrates the cassette with its back side 73 partly cut-away, gear 43 is mounted at the end of a first pinch roller 47 which cooperates with a second pinch roller 42 to engage the ribbon between them and pull it into the cassette during carriage return. However, during printhead movement to the left margin, the two rollers operate to hold the ribbon stationary as it is traversed by the printhead. Between its supply end 31a and take-up end 31b the ribbon is stored in a series of vertical loops. At the supply end, the ribbon travels through an outlet passageway (not 'shown) from which it is pulled by the printhead. This outlet passageway and the inlet passageway (also not shown) at end 31b of the cassette are merely holes in the rear side 44 of the cassette. At the input end 31b, the ribbon 7 enters the input passageway, turns 90, and then travels downwardly to become engaged between

rollers

42 and 47. At the output end 31a, the ribbon 7 passes between a spring 46 and a guide 48, turns 90, and thereafter passes out of the outlet passageway of the cassette. A spring 46 and guide 48 pinch the ribbon between them so that the ribbon may be pulled from the cassette with a constant tension.

As shown in FIG. 1, the ribbon at the printhead takes a substantially U-shaped form since it travels around the printing end 3a of the printhead and passes around a pair of pins 35 located on opposite sides of the printhead 3 but disposed away from the printing end 3a. FIGS. 2 and 3 show the ribbon engaging means located at the printhead which causes the ribbon to take this path. The engaging means frictionally engages the ribbon during carriage return but allows the ribbon to slip with respect to it and the printhead during the printing operation. This action is achieved by and dependent upon the speed with which the printhead is moved across the document. When printing, the printhead necessarily moves at a slower velocity than during carriage return. At this slower speed, slippage occurs while the higher speed of the printhead during carriage return causes the ribbon to be frictionally engagedv With the preferred embodiment disclosed, it has been found that when the printhead is moved to print across the document from left margin 1a to right margin 1b at a relatively constant speed of 10 inches per second and, thereafter, returned to the left margin constantly accelerating from a zero velocity at the right margin lb to a maximum velocity of approximately inches per second at the left margin, the engaging means illustrated frictionally engages the ribbon during carriage return yet slips with respect to the ribbon during the printing operation. During carriage return, the

ribbon becomes engaged and pulled when the printhead reaches the velocity of inches per second.

These results were obtained with a conventional nylon ink ribbon and pins 35 and printhead 3 made of steel.

As noted above, during carriage return when the ribbon is engaged at the printhead, it is pulled from the output end 31a of the cassette and a new length of ribbon is provided for the next line. Since the ribbon is not instantaneously engaged at the start of the carriage return and the printhead must first achieve sufficient velocity (i.e., l5 ips), the ribbon pulled from the supply end of the cassette 31a is not exactly the length required to print a succeeding line. Thus, as indicated above, the output of photocell 4b is changed just after the printhead reaches the right margin la on carriage return. This allows a small additional length of ribbon pin. The printing end 3a of the printhead is about fiveeighth inch wide and the pins are located about 1 %inches from the printing end 3a.

The ribbons path between the pins 35 and

loops

43a and 45a is on an angle of about 15 with respect to the centerline of the printhead. Further, the points on the loops (43a and 45a) contacted by the ribbon are approximately two-sixteenth inch from the printing end of the printer. Also, the width of the ribbon is one-half inch and about half of it is in contact with the printing end 30 of the printhead (as shown in FIG. 3).

It will be appreciated that various changes in the form and details of the above-described preferred emto be pulled from the cassette making up the slippage which occurred when the carriage return was first initiated. Changing of the photocells 4b output at this time may obviously be achieved by placing it and its cooperating light 2b a small distance to the right (as shown in FIG. 1) of the left margin 1a.

FIGS. 2 and 3 show in detail the means at the located on opposite sides of the printhead 3 and the pins 35 project upwardly therefrom. As shown in FIG.

3, each pin 35 has a head 37 at its top and a flange 39 at its bottom where it is connected to ear 33. These heads 37 and flanges 39 help to guide the ribbon should it slip vertically at the pins 35.

FIGS. 2 and 3 also show a guide attached at the printing end of the printhead. This guide comprises a bottom 41, and two sides, 43 and 45, projecting from the bottom 41. As most clearly shown in FIG. 2, the printhead projects over bottom 41 and between

sides

43 and 45.

Sides

43 and 45 and bottom 41 are shaped to correspond to the printheads shape at its printing end. As shown from FIGS. 2 and 3, sides 43 and 45 terminate a distance away from the printing end 3a of the. printer in

loops

43a and 45a respectively.

Loops

43a and 45a provide smooth surfaces for the ribbon to traverse from pins to around the printhead 30. As also shown in FIGS. 2 and 3, the sides 43 and each have a pair of top and bottom flanges. Side 45 has top flange 45b and bottom flange 450 while, similarly, side 43 has top flange 43b and bottom flange 43c. These flanges serve as safety guides so that if the ribbon 7 is displaced vertically from the printhead it is caught and thereafter guided by the top or bottom pair of flanges. Thus, the guide at the end of the printhead shown in FIGS. 2 and 3 together with the pins 35 at the sides of the printhead which project from ears 33 serve to guide the ribbon into a U-shaped form around the printing end 3a of the printhead and to frictionally engage the ribbon at the printheads higher speed while allowing the ribbon to slip around its U-shaped form at the printheads slower speed.

Although the ribbon engaging means shown in FIGS. 2 and 3 is preferred, there obviously are many possible arrangements which could serve to frictionally engage the ribbon at the higher velocity of the printhead while allowing slippage at the lower velocity. In the embodiment shown, the pins each have a diameter of about three-sixteenth inch, are located about 1.4 inches apart and the ribbon makes about a wrap around each bodiment may be effected by persons of ordinary skill without departing from the true spirit and scope of the invention.

Iclaim:

1. In a printer having a reciprocating carriage for generating linear relative movement between a print medium and a print mechanism and further including print control means for causing the print mechanism to print a line of characters on the print medium during movement of said carriage in a first direction, ink ribbon handling means comprising, in combination:

a case containing a loosely folded supply of ink ribbon with a length of said ribbon extending outside of said case through a first slot provided in a side thereof;

drag means acting against said ribbon in an area adjacent said slot;

ribbon guide means supporting said outside-extending length of ribbon along a path lying between said print medium and said print mechanism, a portion of said guide means being mounted on said print mechanism and including at least one relatively sharp edge projecting into the ribbon path; take-up means for holding said ribbon stationary during movement of said carriage in said first direction;

means for moving said carriage in said first direction at a first velocity and for accelerating said carriage in the return direction after completion of said line of printing, whereby the frictional force exerted on said ribbon by said guide means during carriage return exceeding the friction force exerted by said drag means thereby causing said guide means to pull an additional length of ribbon out of said case during said return movement; and

said takeup means taking up the slack in said ribbon caused by the pulling of said ribbon during said return movement.

2. The printer set forth in claim 1 wherein said print mechanism is fixed to and moves with said carriage and said print medium and said case remain stationary during the printing operation.

3. The printer set forth in "claim 1 wherein said takeup means comprises:

a pair of pinch rolls acting on the ribbon; and

means driven by said carriage moving means for rotating said pinch rolls during the return movement of said carriage.

4. The printer set forth in claim 1 wherein:

said ribbon is in the form of an endless band; and

said takeup means operates to feed the ribbon back into said case through a second slot provided on a side of said case opposite said first slot.

Claims

1. In a printer having a reciprocating carriage for generating linear relative movement between a print medium and a print mechanism and further including print control mEans for causing the print mechanism to print a line of characters on the print medium during movement of said carriage in a first direction, ink ribbon handling means comprising, in combination: a case containing a loosely folded supply of ink ribbon with a length of said ribbon extending outside of said case through a first slot provided in a side thereof; drag means acting against said ribbon in an area adjacent said slot; ribbon guide means supporting said outside-extending length of ribbon along a path lying between said print medium and said print mechanism, a portion of said guide means being mounted on said print mechanism and including at least one relatively sharp edge projecting into the ribbon path; take-up means for holding said ribbon stationary during movement of said carriage in said first direction; means for moving said carriage in said first direction at a first velocity and for accelerating said carriage in the return direction after completion of said line of printing, whereby the frictional force exerted on said ribbon by said guide means during carriage return exceeding the friction force exerted by said drag means thereby causing said guide means to pull an additional length of ribbon out of said case during said return movement; and said takeup means taking up the slack in said ribbon caused by the pulling of said ribbon during said return movement.

3. The printer set forth in claim 1 wherein said takeup means comprises: a pair of pinch rolls acting on the ribbon; and means driven by said carriage moving means for rotating said pinch rolls during the return movement of said carriage.

4. The printer set forth in claim 1 wherein: said ribbon is in the form of an endless band; and said takeup means operates to feed the ribbon back into said case through a second slot provided on a side of said case opposite said first slot.