Ribbon tracking system

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to printer ribbon tracking systems and more particularly to a ribbon tracking system for a thermal transfer printer which uses a plate for covering printer wiring under the ribbon frame which has a head portion gimbaled centrally on a small integral neck portion and adapted to deflect according to the movement of the ribbon.

2. Prior Art

Various attempts have been made in the past to provide effective means for correcting errors in ribbon tracking during printer operation. Most attempts, however, have either been implemented with limited success, or have been associated with high manufacturing costs, or both.

For example, U.S. Pat. No. 4,084,683 to Moss discloses a ribbon tracking system which includes guide means and roller means thereon which automatically tilts with the moving ribbon to correct errors in tracking of the ribbon. The system also includes a crowned pulley which is floatingly supported and journaled on a curved guide post with the pulley being axially moved along the guide post in a direction generally opposite the tracking error to correct the attitude of the moving ribbon. When a tracking error occurs due to an unbalance of forces acting on the ribbon and the centerline of the ribbon does not align with the radius of curvature of the guide post, the forces on the crowned pulley cause the pulley to center itself with respect to the moving ribbon. A ribbon tracking system of this kind is rather costly to manufacture, assemble and/or maintain due to its complex design.

Another example is commonly assigned U.S. Pat. No. 6,123,471 to Harb et al, which discloses a medium tracking bar mounted on a printer ribbon mechanism by way of La V-shaped metal flange which has a central aperture for receiving a compression spring-loaded screw. The screw and the compression spring function as a central pivot means for the medium tracking bar. The compression spring provides a force that resists pulling in and/or pushing away the medium tracking bar from a balanced central position. the resisting force is used to counteract the uneven stresses on a misaligned moving ribbon. This type of centrally pivoted and spring loaded medium tracking bar, although an improvement over the above-described Moss setup, involves a number of relatively costly components and requires a certain amount of assembly time which adds to the overall manufacturing cost of the system.

SUMMARY OF THE INVENTION

The present invention is directed to a ribbon tracking system for use in an image forming device having a printhead coupled to a ribbon frame comprising a plate including a first portion coupled to the ribbon frame downstream from the printhead and a second portion spaced apart from the first portion and adapted to contact a moving ribbon at a first edge. The plate also comprises a substantially small integral neck region between the first and second portions adapted to permit the second portion to deflect toward and/or away from the first portion to help equalize stress differentials between various portions of the moving ribbon to prevent wrinkling of the ribbon.

These and other aspects of the present invention will become apparent from a review of the accompanying drawings and the following detailed description of the preferred embodiments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is shown by way of example in the accompanying which:

FIG. 1

is a top perspective view of a ribbon tracking system in accordance with the present invention;

FIG. 2

is a bottom perspective view of the ribbon tracking system of

FIG. 1

mounted on the underside of a printer ribbon frame in accordance with the present invention;

FIG. 3

is a cross-sectional view taken along section line

3

—

3

of

FIG. 2

;

FIG. 4

is a bottom plan view of the ribbon tracking system of

FIG. 1

; and

FIG. 5

is a partial cross-sectional view taken along section line

5

—

5

of FIG.

2

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, some preferred embodiments of the present invention will be described in detail with reference to the related drawings of

FIGS. 1-5

. Additional embodiments, features and/or advantages of the invention will become apparent from the ensuing description or may be learned by the practice of the invention.

In the figures, the drawings are not to scale and reference numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the description.

The following description includes the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention.

The present invention is directed to a ribbon tracking system for use in a printer, scanner or the like which comprises a plate (or shroud) for covering printer wiring under the ribbon frame which has a first portion coupled under the printer ribbon frame downstream from the printhead, a second portion spaced apart from and generally parallel to the first portion wherein the second portion is in contact with a moving ribbon at a curved front edge during printer operation, and a substantially small integral neck region coupled centrally between the first and second portions. The first portion, the second portion and the integral neck region are injection molded as one integral unit from a rigid carbon fiber plastic composition. The neck region functions as a living hinge and permits the second portion to deflect toward and/or away from the first portion during printer operation to automatically equalize stress differentials between various portions of the moving ribbon so as to prevent wrinkling of the ribbon during printer operation.

Turning to

FIGS. 1-2

, a ribbon tracking system, generally referred to by a reference numeral

10

, comprises a plastic polygonal plate (or shroud)

12

used to cover printer wires under a printer ribbon frame

26

which is preferably adapted on one side to provide automatic ribbon tracking capability to prevent wrinkling of a moving ribbon during printer operation. Automatic ribbon tracking is achieved by providing an integral generally rectangular gimbaling plate

14

coupled centrally to a front side

15

of wire shroud

12

by means of an integral substantially small neck portion or region

16

which is generally of the same thickness as the body of wire shroud

12

and gimbaling plate

14

. Integral gimbaling plate

14

has a right side

17

(disposed to the right of neck portion

16

) and a left side

19

(disposed to the left of neck portion

16

) spaced apart at a predetermined determined distance from and generally parallel to side

15

of wire shroud

12

as illustrated in FIG.

1

. Gimbaling plate

14

is generally of the same width but of shorter length relative to the body of wire shroud

12

. Wire shroud

12

has a width W and a length L, respectively, as generally shown in

FIGS. 1

,

4

.

Integral gimbaling plate

14

and neck portion

16

are preferably made of the same plastic material as wire shroud

12

. Wire shroud

12

is provided with mounting slots

18

,

20

,

22

for screw-mounting wire shroud

12

to an underside

24

of printer ribbon frame

26

such that gimbaling plate

14

is preferably disposed proximate to and to a certain extent under a thermal transfer printhead

28

mounted to underside

24

of ribbon frame

26

upstream as depicted in FIG.

2

.

As generally illustrated in

FIG. 3

, printer ribbon frame

26

is disposed over a printer base

30

of a thermal transfer printer (not shown) and supports a ribbon supply roll

32

and a ribbon take up roll

34

which generally define a ribbon path

36

for a moving ribbon

38

which is conventionally made of thin web-like material. During the printing operation ribbon

38

passes between a rotating platen

40

(which is rotatably mounted to printer base

30

) and thermal printhead

28

which is mounted on a metal printhead bracket

42

removably coupled to underside

24

of ribbon frame

26

(

FIGS. 2

,

3

). Ribbon

38

is pulled by a motor (not shown) and associated gear train (not shown) from ribbon Supply roll

32

over gimbaling plate

14

, which is substantially in contact with ribbon

38

during printer operation by way of its curved front edge

44

(FIGS.

1

-

3

), between rotating platen

40

and thermal printhead

28

, to ribbon take up roll

34

as generally shown by ribbon path

36

of FIG.

3

.

In accordance with a preferred embodiment of the present invention, the width and length of integral neck portion

16

are picked small enough to allow each side (right side

17

and left side

19

) of gimbaling plate

14

to deflect horizontally within a predetermined range A (

FIG. 4

) or vertically within a pre-determined range B (FIG.

5

), or in any combination of directions thereof within the respective pre-determined ranges, under pressure from moving ribbon

38

to automatically prevent wrinkling of moving ribbon

38

during printer operation. Integral neck portion

16

functions generally as a “living hinge” allowing gimbaling plate

14

to automatically track moving ribbon

38

. The automatic ribbon tracking capability provided by gimbaling plate

14

helps equalize existing stress differentials between various portions of moving ribbon

38

so as to prevent undesirable wrinkling, buckling of moving ribbon

38

along ribbon path

36

.

Since integral neck portion

16

and gimbaling plate

14

are made of the same plastic material as the body of wire shroud

12

, a person skilled in the art would readily recognize that plastic materials suitable for practicing the present invention must be sufficiently stiff to prevent premature breakage of substantially small neck portion

16

and/or the right and left sides (

17

,

19

) of gimbaling plate

14

during ribbon tracking. In this regard and in accordance with another preferred embodiment of the present invention, wire shroud

12

, neck portion

16

and gimbaling plate

14

are injection molded as one integral unit from a carbon fiber/polycarbonate material

46

(

FIGS. 1-2

) which has a high enough flexural modulus to allow neck portion (“living hinge”)

16

and right and left sides (

17

,

19

) of gimbaling plate

14

to perform as described hereinabove. A material suitable for practicing the present invention may be purchased from LNP Engineering Plastics, Inc. of Exton, Pennsylvania and is available commercially under the trademark name STAT-KON™. The preferred chemical composition of material

46

is currently sold is STAT-KON™ DCL-4413 and contains about 15% carbon fiber, about 2% silicone with the rest being polycarbonate. In general, an approximate range of 5%-30% carbon fiber may be utilized in a material of this kind. Other materials, including other plastic carbon fiber-based compositions, may be used to manufacture ribbon tracking system

10

provided such other materials do not depart from the intended purpose of the present invention.

As ribbon

38

slides over and contacts curved front edge

44

of gimbaling plate

14

, each side (

17

,

19

) of gimbaling plate

14

deflects accordingly to provide the necessary tolerance to prevent wrinkling/buckling of moving ribbon

38

, i.e. to automatically correct for errors in tracking. The extent to which the right and left sides (

17

,

19

) of gimbaling plate

14

deflect horizontally and/or vertically generally depends on the type of ribbon used, the speed of the ribbon (different ribbon speeds produce different moments on gimbaling plate

14

) and the specific type of material used to manufacture gimbaling plate

14

.

In accordance with yet another preferred embodiment of the present invention, vertical and horizontal stops are provided to limit the extent of travel or deflection of gimbaling plate

14

in each direction. In this regard, thermal printhead

28

serves as a vertical stop for a vertically deflecting gimbaling plate

14

(FIG.

5

), while front left side

15

a

of wire shroud

12

serves as a horizontal stop for left side

19

of gimbaling plate

14

(

FIG. 4

) and front right side

15

b

of wire shroud

12

serves as a horizontal stop for right side

17

of gimbaling plate

14

(FIG.

4

).

In one example, and as generally illustrated in

FIG. 4

, the range of travel A in the horizontal direction (

FIG. 4

) for each side (

17

,

19

) of gimbaling plate

14

may be about 0.08 inches which is equal to the length L″ of neck portion

16

and the range of travel B in the vertical direction (

FIG. 5

) may be about 0.027 inches. In the same example, the width W of wire shroud

12

may be about 4.98 inches which is equal to the width W′ of gimbaling plate

14

, the length L of wire shroud

12

may be about 2.35 inches, the length L′ of gimbaling plate

14

may be about 0.48 inches, i.e. 6 times larger in length than neck portion

16

, and the width W″ of neck portion

16

may be about 0.19 inches, i.e. more than 26 times smaller in width than gimbaling plate

14

.

The above-described novel ribbon tracking system provides a cost efficient automatic ribbon tracking solution to printer manufacturers which can be easily incorporated in a variety of printers, scanners, fax machines and the like. The ribbon tracking system of the present invention includes a single integral ribbon tracking unit which is made of a rigid carbon fiber plastic composition and does not use any screws and/or compression springs to track the ribbon during printer operation. A person skilled in the art would immediately appreciate the fact that assembly time for the integral ribbon tracking, unit itself has been reduced to zero.

Other components and/or configurations may be utilized in the above-described embodiments, provided that such components and/or configurations do not the intended purpose and scope of the present invention.

While the present invention has been described in detail with regards to the preferred embodiments, it should also be appreciated that various modifications and variations may be made in the present invention without departing from the scope or spirit of the invention. In this regard it is important to note that practicing the invention is not the applications described hereinabove. Many other applications and/or alternations may be utilized provided that such other applications and/or alterations do not depart from the intended purpose of the present invention.

It should also be appreciated by a person skilled in the art that features illustrated or described as part of one embodiment can be used in another embodiment to provide yet another embodiment such that the features are not limited to the specific embodiments described above. It is, therefore, intended that the present invention cover all such modifications, embodiments and variations as long as they come within the scope of the appended claims and their equivalents.