CA2015021A1 - Differential friction media drive - Google Patents
Differential friction media driveInfo
- Publication number
- CA2015021A1 CA2015021A1 CA 2015021 CA2015021A CA2015021A1 CA 2015021 A1 CA2015021 A1 CA 2015021A1 CA 2015021 CA2015021 CA 2015021 CA 2015021 A CA2015021 A CA 2015021A CA 2015021 A1 CA2015021 A1 CA 2015021A1
- Authority
- CA
- Canada
- Prior art keywords
- medium
- drive
- moving
- drive roller
- printer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
- B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
- B41J13/00—Devices or arrangements of selective printing mechanisms, e.g. ink-jet printers or thermal printers, specially adapted for supporting or handling copy material in short lengths, e.g. sheets
- B41J13/02—Rollers
Landscapes
- Delivering By Means Of Belts And Rollers (AREA)
- Feeding Of Articles By Means Other Than Belts Or Rollers (AREA)
- Handling Of Cut Paper (AREA)
- Handling Of Sheets (AREA)
Abstract
DIFFERENTIAL FRICTION MEDIA DRIVE
ABSTRACT OF THE DISCLOSURE
An apparatus for providing motive force to a medium (14), including a high friction drive surface (16) and a drive plate (20) which is surfaced with an extremely low friction material (30) is provided. The friction differ-ential produced by the surface variations is sufficient to furnish superior transfer of motive force and to avoid problems of jamming and mishandling. Placement of a print-head (12) near the drive surface (16) allows for high qual-ity printing, and very small top and bottom margin dis-tances.
ABSTRACT OF THE DISCLOSURE
An apparatus for providing motive force to a medium (14), including a high friction drive surface (16) and a drive plate (20) which is surfaced with an extremely low friction material (30) is provided. The friction differ-ential produced by the surface variations is sufficient to furnish superior transfer of motive force and to avoid problems of jamming and mishandling. Placement of a print-head (12) near the drive surface (16) allows for high qual-ity printing, and very small top and bottom margin dis-tances.
Description
2015~21 PATENT
P~-188429 ~IFFERENTIAL FRICTION MEDIA DRIVE
TECHNICAL FIE$D
The present invention relates to medium drive mecha-10nisms for computer hard copy printers. The predominant current usage of the improved medium drive ~echanism is as a means for causing a medium such as paper to move through the printer and past the printing area in a thermal ink-jet printer.
BACKGROUND ART
A num~er of various means have ~een employed to move a medium such as paper through computer hard copy printers.
20The first of these was the traditional typewriter roller arrangement. This arrangement proved unsatisfactory for automated computer printers, however, because it was not well suited for automatically accepting single sheets of medium as they were fed into the printer.
25Other methods that have been tried have included trac-tor feed mechanis~s wherein drive sproc~ets engage holes in the medium. This method works ~ell for form-feed type doc-uments and other ~edia; however, it is not adaptable for use with single sheets of media.
30Current drive mechanis~s for ther~al ink-jet printers frequently include roller mechanis~s wherein the medium is passed between two opposing rollers as in the rollers of an old ~ashioned washing machine. This arrangement works well because it provides a positive feed ~or the mediuc and al-3Slows the medium to exit the drive area in a straight line.
' Case 188429 ~,~ ' ,'::: . . , .
P~-188429 ~IFFERENTIAL FRICTION MEDIA DRIVE
TECHNICAL FIE$D
The present invention relates to medium drive mecha-10nisms for computer hard copy printers. The predominant current usage of the improved medium drive ~echanism is as a means for causing a medium such as paper to move through the printer and past the printing area in a thermal ink-jet printer.
BACKGROUND ART
A num~er of various means have ~een employed to move a medium such as paper through computer hard copy printers.
20The first of these was the traditional typewriter roller arrangement. This arrangement proved unsatisfactory for automated computer printers, however, because it was not well suited for automatically accepting single sheets of medium as they were fed into the printer.
25Other methods that have been tried have included trac-tor feed mechanis~s wherein drive sproc~ets engage holes in the medium. This method works ~ell for form-feed type doc-uments and other ~edia; however, it is not adaptable for use with single sheets of media.
30Current drive mechanis~s for ther~al ink-jet printers frequently include roller mechanis~s wherein the medium is passed between two opposing rollers as in the rollers of an old ~ashioned washing machine. This arrangement works well because it provides a positive feed ~or the mediuc and al-3Slows the medium to exit the drive area in a straight line.
' Case 188429 ~,~ ' ,'::: . . , .
2~15021 However, the problem with this arrangement is that there is frequently insufficie~t room to ea~ily include a pair o~
opposed rollers. This problem is particularly acute as re-gards the top roller, as it may interfere with the movement of the printhead if it is placed too near.
It is desirable to place the drive mechanism as close to the printhead as possible, because the less distance the medium has to travel from the drive mechanism to ~he print-head, the less chance there is of it buckling in that in-terval. Further, if the printhead could be placed nearerto the drive area, necessary top and bottom margins could be greatly reduced. This is considered to be a highly de-sirable feature. Therefore, printer designers have been faced with the dilemma of having to place the drive mecha-lS nism as close as possible to the printhead to avoid buc~-ling and to reduce necessary top and bottom margin sizes, and also having to remove the drive mechanism from the printhead sufficiently far to provide room for a top rol-ler. This dilemma has been compounded by the fact that the height of the printhead above the medium must also be mini-mized, as this is an important factor in print quality.
Obviously, it would be desirable to provide a means for driving media through printers which did not include a top roller and therefore could be placed as close as is de-sired to the printhead. However, previous attempt~ to de-sign such a mechanism have been less than successful. For instance, if the top roller is replaced with a flat sur-face, the medium has tended to feed improperly and to jam in the drive mechanism unless an additional pair of drive rollers is provided, thereby allowing for a clearance be-tween the drive roller and the flat surface.
To the inventor's knowledge, no prior art mechanism for driving medium through a printer has successfully met desirable size restrictions so as to reduce the overall size of the printer and also to allow the drive mechanism Case 188429 ., - , .
201~021 to be placed very close to the printhead. All successful medium drive mechanisms to date have used either a combina-tion of rollers or other complex mechanisms in order to avoid the problems of mediu~ buckling, and also to avoid the problems of mediu~ misfeed and jamming, and further to cause the medium to exit the drive mechanism in a straight line parallel to the printhead. Further, no prior art mechanism for driving medium through a printer has allowed for producing top and bottom margins as small as 2 to 3 millimeters.
DISC~OSURE OF INVENTION
This invention relates to a medium drive mechanism for a computer hard copy printer having an extremely low fric-tion surface opposed to a high friction drive surface.
This combination provides a positive medium drive formerly available only with dual roller drive systems.
Briefly, the preferred embodiment of the present in-vention is a medium drive mechanism constructed such that a high friction rubber drive roller imparts a motive force to a sheet print medium. The medium is held in place against the rubber drive roller by means of a guide plate including a structural backing mechanism and an extremely low friction surface. In the preferred embodiment of the present invention, the low friction surface is constructed of ultra-high molecular weight (UHMW) polyethylene. Al-though other very low friction materials such as Teflon could be used in the manufacture of the inventive drive mechanism, ~HNW polyethylene has been found by the inventor to provide the best combination of low ~riction properties and wear resistance. It has been found by the inventor that drive mechanism$ so constructed are no more prone to ~amming or medium misalignment than are dual roller drive mechanisms.
Case 188429 201~02~
The superior drive qualities of the inventive drive mechanism are largely due to the fact that the sum of forc-es on the medium produced by the inventive drive actually produces a greater total force in the intended drive direc-tion than have simil~r prior art drive mechanisms.
The inventive medium drive mechanism subassembly may be placed closer to the printhead in a printer assembly than is possible with a dual roller medium drive mechanism, because the guide surface does not interfere with the move-ment of the printhead as does a top roller. Of course, the greater distance the medium has to travel after leaving the drive mechanism and before getting to the printing area of a printer, the greater the liXelihood that buckling or oth-er medium misalignment may occur. But the primary advan-lS tages of the inventive drive mechanism are that the amount of necessary top and bottom margins are greatly reduced, and that high image_quality may be maintained by allowing placement of the printhead close to the medium and to the drive assembly.
Therefore, the inventive method is conducive to the highest print quality possible, since medium orientation to the printhead is optimized. That placement of the drive mechanism close to the printhead is desirable has long been known. However, prior attempts to design mechanisms which could be placed closer to the printhead have failed because all such attempts have resulted in mechanisms that were more prone to jamming or other problems than were the con-ventional dual roller drive mechanisms. Therefore, prior to the present invention, dual roller mechanis~s have been incorporated into ink-~et printer assemblies.
Another desirable factor of the present invention is that a drive mechanism constructed according to the inven-tion may be made smaller than conventional mediu~ drive mechanisms, there~y facilitating a reduction in overall printer size.
Case 188429 ~,~.. .. . .
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2~15~21 An advantage of the present invention is that the size of top and bottom margins on the print medium may be de-creased.
Another advantage of the present invention is that a printer medium drive mechanism may be placed horizontally closer to an ink-jet printer printhead.
Yet another advantage of the present invention is that image quality is improved by allowing placement of the printhead vertically closer to the medium.
A further advantage of the present invention is that a tendency of medium to jam in the drive mechanism is re-duced.
A still further advantage of the present invention is that the unsupported area between a drive mechanism and a printhead wherein a medium might buckle is reduced.
Yet another advantage of the present invention is that overall printer size may be reduced.
These and other objects and advantages of the present invention will become clear to those sXilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as il-lustrated in the several figures of the drawing.
FIG. 1 is a diagrammatic representation of a side view of a portion of a printer including the drive mechanism o~
the present invention:
FIG. 2 is a diagrammatic representation similar to FIG. 1, showing the low friction surface o~ the present in-vention replaced with a prior art pinch roller; and FIG. 3 is a representation of the various forces ex-erted on a print ~edium by a drive mechanism.
Case 188429 ~-'''''' ' ~
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2~5~1 , BE~T MODES FOR CARRYI~G QUT INVENTION
The best presently known mode for carrying out the in-vention is a thermal ink-jet printer incorporating a con-ventional printer per. and pen traversing mechanism, but al-so using a medium drive mechanism in accordance with the present invention, wherein motive force is transferred to the medium via a high friction surface and the medium is held against the high friction surface by an opposing low friction surface. The medium drive mechanism of the pres-ent invention is more compact then comparable prior art drive mechanisms, and also provides for more accurate me-dium placements than has been considered to be feasible us-ing compact drive mechanisms. In the best presently known embodiment of the present invention, the friction differen-tial necessary to the succe~s of the invention is achieved by use of an ultrahigh molecular weight (UHMW) polyethylene tape on the low friction suxface. The sum of the resultant forces produced on the medium by the inventive drive mecha-nism is greater in a desired drive direction than thatwhich is produced by comparable prior art drive mechanisms.
The predominant expected usage of the inventive medium drive mechanism is in thermal ink-jet printers, wherein clearance of the drive mechanism to the printhead pen is critical, and especially in applications, wherein the height O~r the combined assembly is a concern, such as in a portable or small desk top units, and in applications wherein minimal top and bottom margins are required.
A portion of the thermal ink-jet printer assembly o~
the presently preferred embodiment o~ the present invention is illustrated in diagrammatic form in a side view in FIG.
1 and is designated therein by the general reference char-acter lO. In most of its substantial components, the printer lO does not differ signi~icantly from conventional thermal ink-jet printers.
Case 188429 .:,rr, .-~;~r~r " ~ ' :
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The conventional elements of the printer 10 include a printhead 12 and a printhead traversing mechanism (not shown) for moving the printhead 12 across a piece of medium 14, thus positioning the printhead 12 for printing upon the medium 14.
The medium 14 is moved through the printer by means of a high friction drive surface 16. In the presently pre-ferred embodiment of the present invention, the drive sur-face 16 is made of high friction rubber and constitutes the surface 16 of a drive roller 18. A drive plate 20 is pro-vided to hold the medium 14 firmly against the drive sur-face 16. A means for pressing the drive plate 20 toward the drive surface 16 in a force direction 22 is provided in the presently preferred embodiment of the invention by con-structing the drive plate 20 of spring steel and tensioning it against the drive roller 18 in force direction 22.
The tangent point 24 of the drive roller 18 to the drive plate 20, according to the present invention, trans-fers motive force to the medium 14 in a medium advance di-rection 26 as the drive roller 18 rotates in a rotationaldirection 28. Therefore, normal force in force direction 22 must be sufficiently great to prevent slipping and mis-handling of the medium 14. The actual amount of necessary normal force in force direction 22 may vary depending upon the type of medium 14 used and other variables, but this can be guickly and easily adjusted according to the exact application to which the present invention is applied.
Contrary to previous beliefs about printer drive mech-anisms, the inventor has found that sufficient normal force in force direction 22 may be applied to prevent slippage and resultant ~amming of the medium 14 when tangent point 24 is the point of transfer of motive force from the high friction drive surface 16 to the medium 14. In t~s best presently known embodiment of the present invention, an ul-Case 188429 ~ ~., -. -2015~21 trahigh molecular weight (UHMW) polyethylene tape 30 is ap-plied to the drive plate 20.
Using the UHMW polyethylene tape 30, friction differ-ential as between th~ first junction 32 of the high fric-5tion drive surface 16 to the medium 14, and the second junction 34 of drive plate 20 to the medium 14, sufficient to prevent problems previously believed to be unavoidable in such an application, may be created. UHMW polyethylene tape may be obtained from 3M Company, Industrial Tape Divi-10sion, St. Paul, Minnesota, under their part number 5425.
The tape is provided with a solvent-resistant acrylic adhe-sive backing (not shown) for adhering the UHMW polyethylene tape 30 to the drive plate 20.
As opposed to prior art mechanisms, as depicted in 15FIG. 2, wherein a pinch roller 44 is used to reduce drag, the UHMM polyethylene tape of the presently preferred embo-diment of the present invention allows the printhead 12 (FIG. l and FIG. 2) to be placed closer to the tangent point 24 while not necessitating raising the printhead 12 20higher above the medium. ~his is an important advantage in thermal ink-jet printers, since maintaining the printhead 12 at a minimal height above the medium 14 is necessary to print quality, and since placement of the printhead 12 close to the drive tangent point 24 allows printing on a 25greater portion of the medium 14, thereby reducing the size of top and bottom margins (not shown).
Referring now to F~G. 3, wherein is depicted a drive force 46, a drag force 48, and two normal forces 50 acting on a print medium 14, it can be seen that the sum of forces 30~6, 48, and 50 will influence movement of the medium 14 in the medium advance direction 26. The normal forces 50 are produced, in the best presently known emkodiment of the present invention, by tensioning of the drive plate 20 to-ward the drive roller 18. Since the drive plate 20 and the 35drive roller 18 are immobile in the plane of the normal Case 188429 :? ~
:"j., -:: :-201~21 , .
forces 50, the two normal forces 50 are necessarily equal in magnitude and opposite in direction. The drive force 44 in medium advance direction 26 acting on the medium 14 is a function of the product of the normal force 50 and a friction factor between the high friction drive surface 16 and the medium. The drag force 46 acting in a direction opposite to medium advance direction 26 is a function of the product of the normal force 50 and a friction factor between the low friction surface 30 and the medium 14. As can be appreciated by one skilled in the art, greatly re-ducing the friction factor between the medium 14 and the drive plate 20 by addition of the low friction surface 30, causes the ratio of the drive force 44 to the drag force 46 to be greatly increased. The sum of forces acting on the medium 14 in a plane parallel to the medium drive direction 26 is the drive force 44 minus the drag force 46. The nor- -mal force 50 can be increased, in accordance with the pres-ent invention, to a value necessary to provide sure and positive handling of various types of medium 14 without slippage or other mishandling of the medium 14.
various modifications may be made to the invention without altering its value or scope. For example, the high friction drive surface 16 may be part of a flat sliding plate, rather than a roller. Another conceivable altera-tion would be to use another very low friction surfacingmaterial as a substitu~e for the UHMW polyethylene tape 30.
All of the above are only some of the examples of available embodiments of the present invention. Those skilled in the art will readily observe that numerous other modifications, alterations, and adaptations may be made without departing from the spirit and scope of the inven-tion. Accordingly the above disclosure is not intended as limiting and the appended claims are to be intarpreted as encompassing the entire scope o~ the invention.
Case 188429 ' ' - 201~2~
INDUSTRIAL APPLICABILITY
Thermal ink-jet printers have found wide acceptance in the marketplace. Among the many desirable qualities of thermal ink-jet printers are the high print quality and the ease of use of these printers. The present invention has been found to enhance both of these qualities. The print quality of thermal ink-jet printers is enhanced through use of the drive mechanism of the present invention by virtue of the fact that the printhead may be placed at a height which is relatively close to the medium as compared with prior art arrangements, and because the height relationship of the medium to the printhead is held relatively constant by virtue of the fact that the medium is supported close to the printhead by the inventive drive assembly.
Since printing is accomplished in a thermal ink-jet printer by ejecting droplets of ink onto the medium, any vari~tions in the plane of the medium relative to the sur-face of the printhead from which the ink is ejected will result in a reduction of print quality. Since the market-place for thermal ink-jet printers is quite competitive and since one of the major differentiating factors of such printers is the print quality, any innovation such as the present invention which will enhance quality will greatly enhance the utility of the printer in the marketplace.
Furthermore, since the printhead may be placed very close to the drive assembly, according to the present in-vention, the top and bottom margins (unprinted areas) may be greatly reduced. These margins are a function of the distance from the drive assembly to the printhead, since the medium must necessarily be supported in the drive as-sembly when printing is being accomplished, ~nd since the absolute minimum margin would be the distance from the printhead to point at which the medium is supported by the drive assembly. It is thought that this factor alone will Case 188429 .,,, . ,. :
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provide a major benefit to the users of printers employing the inventive drive mechanism.
Ease of use of thermal ink-jet printers is greatly reduced by any jamming or mishandling of medium within the printer. Minor variations in medium handling will result in print being improperly placed upon the medium. Major mishandling problems require operator intervention and are considered to be extremely detrimental to user satisfac-tion. For this reason, dual roller type medium drive mech-anisms have been used in spite of the fact that they are less than ideal for other reasons discussed herein.
However, the inventive mechanism has been found to be as conducive to error-free medium handling as have prior art dual roller mechanisms. Therefore, it is anticipated that medium drive ~echanisms according to the present in-vention will greatly enhance the usability of thermal ink-jet printers.
Another factor which may increase the acceptance and usefulness of the inventive drive mechanism is that the need for smaller printers is increasing. In fact, portable printers to accompany portable computers may be a future application.
Since the medium drive mechanisms of the present in-vention may bs readily constructed and are easily incorpo-rated into printer designs, it is expected that they will be accepted in the industry as substitutes for conventional medium drive mechanisms.
For these and other reasons, it is expected that the utility and industrial applicability of the invention will both sign$ficant in scope and long lasting in duration. `
Case 188429 .~;,, ~ .: -~?~1 . ` .. .
opposed rollers. This problem is particularly acute as re-gards the top roller, as it may interfere with the movement of the printhead if it is placed too near.
It is desirable to place the drive mechanism as close to the printhead as possible, because the less distance the medium has to travel from the drive mechanism to ~he print-head, the less chance there is of it buckling in that in-terval. Further, if the printhead could be placed nearerto the drive area, necessary top and bottom margins could be greatly reduced. This is considered to be a highly de-sirable feature. Therefore, printer designers have been faced with the dilemma of having to place the drive mecha-lS nism as close as possible to the printhead to avoid buc~-ling and to reduce necessary top and bottom margin sizes, and also having to remove the drive mechanism from the printhead sufficiently far to provide room for a top rol-ler. This dilemma has been compounded by the fact that the height of the printhead above the medium must also be mini-mized, as this is an important factor in print quality.
Obviously, it would be desirable to provide a means for driving media through printers which did not include a top roller and therefore could be placed as close as is de-sired to the printhead. However, previous attempt~ to de-sign such a mechanism have been less than successful. For instance, if the top roller is replaced with a flat sur-face, the medium has tended to feed improperly and to jam in the drive mechanism unless an additional pair of drive rollers is provided, thereby allowing for a clearance be-tween the drive roller and the flat surface.
To the inventor's knowledge, no prior art mechanism for driving medium through a printer has successfully met desirable size restrictions so as to reduce the overall size of the printer and also to allow the drive mechanism Case 188429 ., - , .
201~021 to be placed very close to the printhead. All successful medium drive mechanisms to date have used either a combina-tion of rollers or other complex mechanisms in order to avoid the problems of mediu~ buckling, and also to avoid the problems of mediu~ misfeed and jamming, and further to cause the medium to exit the drive mechanism in a straight line parallel to the printhead. Further, no prior art mechanism for driving medium through a printer has allowed for producing top and bottom margins as small as 2 to 3 millimeters.
DISC~OSURE OF INVENTION
This invention relates to a medium drive mechanism for a computer hard copy printer having an extremely low fric-tion surface opposed to a high friction drive surface.
This combination provides a positive medium drive formerly available only with dual roller drive systems.
Briefly, the preferred embodiment of the present in-vention is a medium drive mechanism constructed such that a high friction rubber drive roller imparts a motive force to a sheet print medium. The medium is held in place against the rubber drive roller by means of a guide plate including a structural backing mechanism and an extremely low friction surface. In the preferred embodiment of the present invention, the low friction surface is constructed of ultra-high molecular weight (UHMW) polyethylene. Al-though other very low friction materials such as Teflon could be used in the manufacture of the inventive drive mechanism, ~HNW polyethylene has been found by the inventor to provide the best combination of low ~riction properties and wear resistance. It has been found by the inventor that drive mechanism$ so constructed are no more prone to ~amming or medium misalignment than are dual roller drive mechanisms.
Case 188429 201~02~
The superior drive qualities of the inventive drive mechanism are largely due to the fact that the sum of forc-es on the medium produced by the inventive drive actually produces a greater total force in the intended drive direc-tion than have simil~r prior art drive mechanisms.
The inventive medium drive mechanism subassembly may be placed closer to the printhead in a printer assembly than is possible with a dual roller medium drive mechanism, because the guide surface does not interfere with the move-ment of the printhead as does a top roller. Of course, the greater distance the medium has to travel after leaving the drive mechanism and before getting to the printing area of a printer, the greater the liXelihood that buckling or oth-er medium misalignment may occur. But the primary advan-lS tages of the inventive drive mechanism are that the amount of necessary top and bottom margins are greatly reduced, and that high image_quality may be maintained by allowing placement of the printhead close to the medium and to the drive assembly.
Therefore, the inventive method is conducive to the highest print quality possible, since medium orientation to the printhead is optimized. That placement of the drive mechanism close to the printhead is desirable has long been known. However, prior attempts to design mechanisms which could be placed closer to the printhead have failed because all such attempts have resulted in mechanisms that were more prone to jamming or other problems than were the con-ventional dual roller drive mechanisms. Therefore, prior to the present invention, dual roller mechanis~s have been incorporated into ink-~et printer assemblies.
Another desirable factor of the present invention is that a drive mechanism constructed according to the inven-tion may be made smaller than conventional mediu~ drive mechanisms, there~y facilitating a reduction in overall printer size.
Case 188429 ~,~.. .. . .
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2~15~21 An advantage of the present invention is that the size of top and bottom margins on the print medium may be de-creased.
Another advantage of the present invention is that a printer medium drive mechanism may be placed horizontally closer to an ink-jet printer printhead.
Yet another advantage of the present invention is that image quality is improved by allowing placement of the printhead vertically closer to the medium.
A further advantage of the present invention is that a tendency of medium to jam in the drive mechanism is re-duced.
A still further advantage of the present invention is that the unsupported area between a drive mechanism and a printhead wherein a medium might buckle is reduced.
Yet another advantage of the present invention is that overall printer size may be reduced.
These and other objects and advantages of the present invention will become clear to those sXilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as il-lustrated in the several figures of the drawing.
FIG. 1 is a diagrammatic representation of a side view of a portion of a printer including the drive mechanism o~
the present invention:
FIG. 2 is a diagrammatic representation similar to FIG. 1, showing the low friction surface o~ the present in-vention replaced with a prior art pinch roller; and FIG. 3 is a representation of the various forces ex-erted on a print ~edium by a drive mechanism.
Case 188429 ~-'''''' ' ~
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2~5~1 , BE~T MODES FOR CARRYI~G QUT INVENTION
The best presently known mode for carrying out the in-vention is a thermal ink-jet printer incorporating a con-ventional printer per. and pen traversing mechanism, but al-so using a medium drive mechanism in accordance with the present invention, wherein motive force is transferred to the medium via a high friction surface and the medium is held against the high friction surface by an opposing low friction surface. The medium drive mechanism of the pres-ent invention is more compact then comparable prior art drive mechanisms, and also provides for more accurate me-dium placements than has been considered to be feasible us-ing compact drive mechanisms. In the best presently known embodiment of the present invention, the friction differen-tial necessary to the succe~s of the invention is achieved by use of an ultrahigh molecular weight (UHMW) polyethylene tape on the low friction suxface. The sum of the resultant forces produced on the medium by the inventive drive mecha-nism is greater in a desired drive direction than thatwhich is produced by comparable prior art drive mechanisms.
The predominant expected usage of the inventive medium drive mechanism is in thermal ink-jet printers, wherein clearance of the drive mechanism to the printhead pen is critical, and especially in applications, wherein the height O~r the combined assembly is a concern, such as in a portable or small desk top units, and in applications wherein minimal top and bottom margins are required.
A portion of the thermal ink-jet printer assembly o~
the presently preferred embodiment o~ the present invention is illustrated in diagrammatic form in a side view in FIG.
1 and is designated therein by the general reference char-acter lO. In most of its substantial components, the printer lO does not differ signi~icantly from conventional thermal ink-jet printers.
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The conventional elements of the printer 10 include a printhead 12 and a printhead traversing mechanism (not shown) for moving the printhead 12 across a piece of medium 14, thus positioning the printhead 12 for printing upon the medium 14.
The medium 14 is moved through the printer by means of a high friction drive surface 16. In the presently pre-ferred embodiment of the present invention, the drive sur-face 16 is made of high friction rubber and constitutes the surface 16 of a drive roller 18. A drive plate 20 is pro-vided to hold the medium 14 firmly against the drive sur-face 16. A means for pressing the drive plate 20 toward the drive surface 16 in a force direction 22 is provided in the presently preferred embodiment of the invention by con-structing the drive plate 20 of spring steel and tensioning it against the drive roller 18 in force direction 22.
The tangent point 24 of the drive roller 18 to the drive plate 20, according to the present invention, trans-fers motive force to the medium 14 in a medium advance di-rection 26 as the drive roller 18 rotates in a rotationaldirection 28. Therefore, normal force in force direction 22 must be sufficiently great to prevent slipping and mis-handling of the medium 14. The actual amount of necessary normal force in force direction 22 may vary depending upon the type of medium 14 used and other variables, but this can be guickly and easily adjusted according to the exact application to which the present invention is applied.
Contrary to previous beliefs about printer drive mech-anisms, the inventor has found that sufficient normal force in force direction 22 may be applied to prevent slippage and resultant ~amming of the medium 14 when tangent point 24 is the point of transfer of motive force from the high friction drive surface 16 to the medium 14. In t~s best presently known embodiment of the present invention, an ul-Case 188429 ~ ~., -. -2015~21 trahigh molecular weight (UHMW) polyethylene tape 30 is ap-plied to the drive plate 20.
Using the UHMW polyethylene tape 30, friction differ-ential as between th~ first junction 32 of the high fric-5tion drive surface 16 to the medium 14, and the second junction 34 of drive plate 20 to the medium 14, sufficient to prevent problems previously believed to be unavoidable in such an application, may be created. UHMW polyethylene tape may be obtained from 3M Company, Industrial Tape Divi-10sion, St. Paul, Minnesota, under their part number 5425.
The tape is provided with a solvent-resistant acrylic adhe-sive backing (not shown) for adhering the UHMW polyethylene tape 30 to the drive plate 20.
As opposed to prior art mechanisms, as depicted in 15FIG. 2, wherein a pinch roller 44 is used to reduce drag, the UHMM polyethylene tape of the presently preferred embo-diment of the present invention allows the printhead 12 (FIG. l and FIG. 2) to be placed closer to the tangent point 24 while not necessitating raising the printhead 12 20higher above the medium. ~his is an important advantage in thermal ink-jet printers, since maintaining the printhead 12 at a minimal height above the medium 14 is necessary to print quality, and since placement of the printhead 12 close to the drive tangent point 24 allows printing on a 25greater portion of the medium 14, thereby reducing the size of top and bottom margins (not shown).
Referring now to F~G. 3, wherein is depicted a drive force 46, a drag force 48, and two normal forces 50 acting on a print medium 14, it can be seen that the sum of forces 30~6, 48, and 50 will influence movement of the medium 14 in the medium advance direction 26. The normal forces 50 are produced, in the best presently known emkodiment of the present invention, by tensioning of the drive plate 20 to-ward the drive roller 18. Since the drive plate 20 and the 35drive roller 18 are immobile in the plane of the normal Case 188429 :? ~
:"j., -:: :-201~21 , .
forces 50, the two normal forces 50 are necessarily equal in magnitude and opposite in direction. The drive force 44 in medium advance direction 26 acting on the medium 14 is a function of the product of the normal force 50 and a friction factor between the high friction drive surface 16 and the medium. The drag force 46 acting in a direction opposite to medium advance direction 26 is a function of the product of the normal force 50 and a friction factor between the low friction surface 30 and the medium 14. As can be appreciated by one skilled in the art, greatly re-ducing the friction factor between the medium 14 and the drive plate 20 by addition of the low friction surface 30, causes the ratio of the drive force 44 to the drag force 46 to be greatly increased. The sum of forces acting on the medium 14 in a plane parallel to the medium drive direction 26 is the drive force 44 minus the drag force 46. The nor- -mal force 50 can be increased, in accordance with the pres-ent invention, to a value necessary to provide sure and positive handling of various types of medium 14 without slippage or other mishandling of the medium 14.
various modifications may be made to the invention without altering its value or scope. For example, the high friction drive surface 16 may be part of a flat sliding plate, rather than a roller. Another conceivable altera-tion would be to use another very low friction surfacingmaterial as a substitu~e for the UHMW polyethylene tape 30.
All of the above are only some of the examples of available embodiments of the present invention. Those skilled in the art will readily observe that numerous other modifications, alterations, and adaptations may be made without departing from the spirit and scope of the inven-tion. Accordingly the above disclosure is not intended as limiting and the appended claims are to be intarpreted as encompassing the entire scope o~ the invention.
Case 188429 ' ' - 201~2~
INDUSTRIAL APPLICABILITY
Thermal ink-jet printers have found wide acceptance in the marketplace. Among the many desirable qualities of thermal ink-jet printers are the high print quality and the ease of use of these printers. The present invention has been found to enhance both of these qualities. The print quality of thermal ink-jet printers is enhanced through use of the drive mechanism of the present invention by virtue of the fact that the printhead may be placed at a height which is relatively close to the medium as compared with prior art arrangements, and because the height relationship of the medium to the printhead is held relatively constant by virtue of the fact that the medium is supported close to the printhead by the inventive drive assembly.
Since printing is accomplished in a thermal ink-jet printer by ejecting droplets of ink onto the medium, any vari~tions in the plane of the medium relative to the sur-face of the printhead from which the ink is ejected will result in a reduction of print quality. Since the market-place for thermal ink-jet printers is quite competitive and since one of the major differentiating factors of such printers is the print quality, any innovation such as the present invention which will enhance quality will greatly enhance the utility of the printer in the marketplace.
Furthermore, since the printhead may be placed very close to the drive assembly, according to the present in-vention, the top and bottom margins (unprinted areas) may be greatly reduced. These margins are a function of the distance from the drive assembly to the printhead, since the medium must necessarily be supported in the drive as-sembly when printing is being accomplished, ~nd since the absolute minimum margin would be the distance from the printhead to point at which the medium is supported by the drive assembly. It is thought that this factor alone will Case 188429 .,,, . ,. :
.. i :
~, ;-20~502~
provide a major benefit to the users of printers employing the inventive drive mechanism.
Ease of use of thermal ink-jet printers is greatly reduced by any jamming or mishandling of medium within the printer. Minor variations in medium handling will result in print being improperly placed upon the medium. Major mishandling problems require operator intervention and are considered to be extremely detrimental to user satisfac-tion. For this reason, dual roller type medium drive mech-anisms have been used in spite of the fact that they are less than ideal for other reasons discussed herein.
However, the inventive mechanism has been found to be as conducive to error-free medium handling as have prior art dual roller mechanisms. Therefore, it is anticipated that medium drive ~echanisms according to the present in-vention will greatly enhance the usability of thermal ink-jet printers.
Another factor which may increase the acceptance and usefulness of the inventive drive mechanism is that the need for smaller printers is increasing. In fact, portable printers to accompany portable computers may be a future application.
Since the medium drive mechanisms of the present in-vention may bs readily constructed and are easily incorpo-rated into printer designs, it is expected that they will be accepted in the industry as substitutes for conventional medium drive mechanisms.
For these and other reasons, it is expected that the utility and industrial applicability of the invention will both sign$ficant in scope and long lasting in duration. `
Case 188429 .~;,, ~ .: -~?~1 . ` .. .
Claims (11)
1. An assembly for moving a print medium through a printer, comprising:
a high friction moving surface for transmitting motive force to the medium;
means for imparting motive force to said high friction moving surface;
an extremely low friction stationary surface for causing the medium to be pressed against said high friction moving surface; and means for tensioning said extremely low friction stationary surface toward said high friction moving sur-face.
a high friction moving surface for transmitting motive force to the medium;
means for imparting motive force to said high friction moving surface;
an extremely low friction stationary surface for causing the medium to be pressed against said high friction moving surface; and means for tensioning said extremely low friction stationary surface toward said high friction moving sur-face.
2. The assembly for moving a print medium of claim 1, wherein:
said high friction moving surface is affixed to a round drive roller; and said means for imparting motive force to said high friction moving surface is a means for causing said round drive roller to turn upon the cylindrical axis of said round drive roller.
said high friction moving surface is affixed to a round drive roller; and said means for imparting motive force to said high friction moving surface is a means for causing said round drive roller to turn upon the cylindrical axis of said round drive roller.
3. The assembly for moving a print medium of claim 1, wherein:
said extremely low friction stationary surface includes an ultrahigh molecular weight polyethylene tape.
said extremely low friction stationary surface includes an ultrahigh molecular weight polyethylene tape.
4. The assembly for moving a print medium of claim 1, wherein:
said means for tensioning said extremely low friction stationary surface toward said high friction mov-ing surface includes a spring steel backing plate on said extremely low friction stationary surface.
said means for tensioning said extremely low friction stationary surface toward said high friction mov-ing surface includes a spring steel backing plate on said extremely low friction stationary surface.
5. A printer drive mechanism, comprising:
a print medium;
a drive roller;
a means for causing said drive roller to rotate;
a drive plate opposed to said drive roller; and a low friction surface attached to said drive plate at least at an area tangent to said drive roller.
a print medium;
a drive roller;
a means for causing said drive roller to rotate;
a drive plate opposed to said drive roller; and a low friction surface attached to said drive plate at least at an area tangent to said drive roller.
6. The printer drive mechanism of claim 5, wherein:
said low friction surface attached to said drive plate is an ultrahigh molecular weight polyethylene materi-al.
said low friction surface attached to said drive plate is an ultrahigh molecular weight polyethylene materi-al.
7. The printer drive mechanism of claim 6, wherein:
said ultrahigh molecular weight material is ad-hered to said drive plate by means of a solvent resistant acrylic adhesive.
said ultrahigh molecular weight material is ad-hered to said drive plate by means of a solvent resistant acrylic adhesive.
8. The printer drive mechanism of claim 5, wherein:
said drive plate is made of spring steel.
said drive plate is made of spring steel.
9. A print medium feeder, comprising:
a means for propelling a medium; and an ultrahigh molecular weight polyethylene sur-face for holding the medium against said means for propel-ling the medium.
a means for propelling a medium; and an ultrahigh molecular weight polyethylene sur-face for holding the medium against said means for propel-ling the medium.
10. The print medium feeder of claim 9, wherein:
said means for propelling the medium includes:
a flat plate;
a high friction surface on said flat plate;
and a means for moving said flat plate parallel to said ultrahigh molecular weight polyethylene surface.
said means for propelling the medium includes:
a flat plate;
a high friction surface on said flat plate;
and a means for moving said flat plate parallel to said ultrahigh molecular weight polyethylene surface.
11. The print medium feeder of claim 9, wherein:
said means for propelling the medium includes:
a round drive roller;
a high friction surface on said round drive roller; and a means for causing said round drive roller to rotate.
said means for propelling the medium includes:
a round drive roller;
a high friction surface on said round drive roller; and a means for causing said round drive roller to rotate.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41482989A | 1989-09-29 | 1989-09-29 | |
| US414,829 | 1989-09-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2015021A1 true CA2015021A1 (en) | 1991-03-29 |
Family
ID=23643149
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2015021 Abandoned CA2015021A1 (en) | 1989-09-29 | 1990-04-20 | Differential friction media drive |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0419800B1 (en) |
| JP (1) | JPH03152039A (en) |
| CA (1) | CA2015021A1 (en) |
| DE (1) | DE69015082T2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4220175C2 (en) * | 1991-06-21 | 1994-12-01 | Ricoh Kk | Printing mechanism for a printer |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4938468A (en) * | 1985-10-24 | 1990-07-03 | Xerox Corporation | Non-rotating paper path idler |
-
1990
- 1990-04-20 CA CA 2015021 patent/CA2015021A1/en not_active Abandoned
- 1990-07-26 EP EP90114394A patent/EP0419800B1/en not_active Expired - Lifetime
- 1990-07-26 DE DE1990615082 patent/DE69015082T2/en not_active Expired - Fee Related
- 1990-09-27 JP JP25879190A patent/JPH03152039A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| EP0419800B1 (en) | 1994-12-14 |
| JPH03152039A (en) | 1991-06-28 |
| DE69015082T2 (en) | 1995-08-03 |
| DE69015082D1 (en) | 1995-01-26 |
| EP0419800A1 (en) | 1991-04-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |