EP0972711B1

EP0972711B1 - Label printer

Info

Publication number: EP0972711B1
Application number: EP19990202303
Authority: EP
Inventors: James William Engel; John Tomasik
Original assignee: ZIH Corp
Current assignee: ZIH Corp
Priority date: 1998-07-17
Filing date: 1999-07-13
Publication date: 2003-10-01
Anticipated expiration: 2019-07-13
Also published as: DE69911694T2; EP0972711A2; EP0972711A3; DE69911694D1

Description

Field of the Invention

The present invention relates generally to imaging forming devices, and more particularly to a printer that automatically separates self-adhesive portions of a printable medium strip from a protective backing of the strip without causing excessive looping or jamming failure of the printer.

Background of the Invention

Self-adhesive labels have been in use for many years. Typically, such self-adhesive labels come in a continuous strip, such as in a roll, and have a front side suitable for writing or printing information, an adhesive back side, and a protective backing forming the strip and adhering to the adhesive back side of the labels. Immediately before using the labels, the labels must be peeled away from the protective backing and adhered to a medium, e.g., an envelope or a box, for labeling.
Conventional devices designed to print information on the self-adhesive labels and to automatically peel off the labels from the protective backing include the Eltron LP-2042 printer. In a typical conventional operation, the continuous strip of the labels enters a conventional device, such as a printer, from a first location of the device--normally the back side of the device. After entering, the strip passes through a contact area between a print head and a platen of the device, and then leaves the device in a second location-normally the front side of the device. Ideally, the labels should be peeled off from the protective backing as it leaves the device. Unfortunately, when certain printing processes (such as thermal transfer) and/or small media are used, such conventional devices tend to fail when the protective backing forms a loop between the print head and an exit roller (which directs the protective backing out of the devices). Such failure may occur before and/or after the labels have been removed from the protection backing and may generally result In either the labels failing to detach and following the protective backing through the exit roller, or the labels only partially separating and adhering to the exit roller.
EP-A-0 416 802 discloses a label separating device comprising a conveyance roller for the conveyance of a paste-board with labels; a separating member disposed downstream with respect to a printing head which holds the pasteboard with labels between the same and a platen, and a pinch roller for holding between the same and the conveyance roller the pasteboard portion which has been bent and separated from a label after printing by the separating member.
Alternatively, other types of conventional devices do not automatically remove the protective backing from the labels and require a user to manually peel the protective backing off of the printed labels. These alternative types of devices however are inconvenient for users and are less efficient in today's busy world. Even so, these alternative types of devices are not immune from the above-noted looping problem as well.

Summary of the Invention

An object of the present invention is to provide an imaging device that will automatically separate detachable adhesive printing media from a protective backing strip without causing excessive looping or jamming failures to the imaging device, as indicated in the claims appended hereto.
One embodiment of the present invention provides the imaging device, e.g., a printer, comprising a print head; a platen for pressing a printing medium, such as a sheet of paper or a series of self-adhesive labels attached to a continuous protective backing strip, against the print head and for moving the printing medium during operation; a stripper bar properly angled upward and adapted to separate the self-adhesive labels from the protective backing when the strip of labels passes over the stripper bar; and a stripper roller positioned under the stripper bar and against a pressure roller or against the platen. The stripper roller has a tube-shaped sleeve and a stepped and generally cylindrically-shaped roller shaft,
wherein the roller shaft is coupled to the first and second wall of said support frame at opposite ends,
wherein the sleeve rotatably encircles the roller shaft,
wherein the roller shaft has a center portion having a length shorter than the length of the sleeve,
wherein the center portion has the largest diameter of the roller shaft, and
wherein only the center portion of the roller shaft touches and presses against said sleeve during operation when the sleeve rotates about the roller shaft. During an initial operation of the printer, the stripper roller causes the protective backing to pass under the stripper roller at a first speed sufficiently different from a second speed of the label strip passing between the print head and the platen to prevent looping or jamming of the protective backing and the label strip.
In a preferred embodiment, the stripper roller includes a stepped stripper roller shaft encircled by a sleeve and adapted to cause the protective backing initially passing the stripper roller at the first speed sufficiently different from the second speed of the strip passing between the print head and the platen, until a tension of the protective backing reaches an equilibrium point which equalizes the first and the second speeds of the protective backing and the strip respectively. The step-stripper roller shaft of the printing device is also designed to have a configuration adapted to prevent looping of the strip or the backing when used in conjunction with a narrow printing medium.
The foregoing and additional features and advantages of this present invention will become apparent by way of non-limitative examples shown in the accompanying drawings and detailed description that follow. In the figures and written description, numerals indicate the various features of the invention, like numerals referring to like features throughout for both the drawing figures and the written description.

Brief Description of the Drawings

Figure 1 shows an isometric view of a lower part of a printer according to the present invention.
Figure 2 shows a top plan view of the printer of Figure 1 according to the present invention.
Figure 3 shows a cross-sectional side view of the printer of Figure 1, with a stripper bar having an upward angle according to the present invention.
Figure 4 shows an exploded view of the stripper roller of Figure 1 according to the present invention.
Figure 5 shows a side elevational view of the stripper roller, a lever, the platen and a cam of the device shown in Figure 1, with the lever in operational position.

Detailed Description of the Invention

Figure 1 shows a preferred embodiment of the present invention where a continuous label strip 14 is fed into a drive part 1 of a printer from a back side of the printer. The continuous label strip 14 comprises sequentially arranged self-adhesive labels 10 attached to a continuous protective backing strip 12. Each of the self-adhesive labels has a printable side and a self-adhesive side adhered to the protective backing 12. Moreover, the continuous label strip 14 is typically wound to form a label roll before being supplied into the printer. After entering the printer, the label strip 14 goes through and between two pathway guides 16, 18 for guiding the label strip 14 toward a front side of the printer. The pathway guides 16, 18 are movably coupled to a shaft 30, as shown in Figure 2, and are equally spaced apart at opposite sides from a midpoint of the shaft 30. The midpoint of the shaft 30 is approximately located at the middle of the shaft 30 having an equal distance from opposite side walls 56, 58 of the drive part 1. As a result, the pathway guides 16, 18 guide the label strip 14 to pass through the printer where the labels passing within the printer are centered therein to provide an optimum printing result.
The shaft 30 is rotatably coupled to the drive part 1 at the bottom by threading through opposite side walls 56, 58 of the drive part 1. The shaft 30 has right and left halves respectively coupled to pathway guides 16, 18, and has a middle part integrally coupled to the left and right halves at opposite ends. The middle part of the shaft 30 is also supported by a middle support rack of the drive part 1 for further supporting the shaft 30. The shaft 30 has worm notches across the left and right halves, but there are no notches on the middle part of the shaft 30. The worm notches have opposite rotational directions respectively on left and right halves of the shaft 30. A rotating nob 20 is securely coupled to the shaft 30 at the one end (left) for rotating the shaft 30. The pathway guides 16, 18 respectively have ring parts at their bottoms. The ring parts of the pathway guides 16, 18 encircle the respective right and left halves of the shaft 30 and have inner worm grooves meshing with the worm notches of the shaft 30. The meshing of the grooves and notches allows the pathway guides 16, 18 to move along the shaft 30 by rotating the shaft 30. However, due to the opposite rotational notch settings of the left and the right halves, the left and right halves of the shaft 30 will respectively cause the pathway guides 16, 18 to move in opposite directions along the shaft 30 when the shaft 30 rotates. Thus, when the shaft 30 rotates in a first direction, the pathway guides 16, 18 will be moved toward each other, and they will be moved away from each other when the shaft 30 rotates in a second direction, opposite to the first rotational direction. A user of the printer may therefore rotate the rotating nob 20 to adjust the relative distance between the pathway guides 16, 18 for accommodating different printing media having different dimensions.
The printer has a platen 22 disposed in the drive part 1, and has a print head (not shown) located in a print part, which is pivotally coupled to the drive part 1 at the back side. Thus, the print part may be pivotally opened from the drive part 1 for a loading position of a printing medium, such as the label strip 14, and may be closely engaged to the drive part 1 for an operation position. The print head is positioned over the platen 22 when the drive part 1 is closely engaged to the print part of the printer during operation. Therefore, in normal operation, the platen 22 will press the printing media, such as the label strip 14, tightly against the print head to allow forming data images on the printable side of the labels. The platen 22 has a platen shaft 23 rotatably coupled to the drive part 1 at opposite side plates 56, 58. Thus, when the platen 22 rotates during operation, it will drag the label strip 14 through the printer, thereby the labels of the label strip 14 could be sequentially printed by the print head.
To load the label strip 14, the label strip 14 is first inserted through an opening near the back side of the drive part 1. The label strip 14 then passes between the pathway guides 16, 18 horizontally and between the print head and the platen 22 vertically wherein the platen 22 is positioned beneath the label strip 14 and the print head is positioned over the label strip 14. The lower side of the label strip 14, that touches the platen 22, comprises the protective backing 12 while the upper side includes the printable surface of the labels 10. As stated, the label strip 14 is tightly trapped in the printer between the print head and the platen 22 when the printer is in the operation position. As a result, when the platen 22 rotates, it will force the label strip 14 to move through the printer in a direction tangential and centrifugal to a rotational direction of the platen 22. In the normal operation, the platen 22 rotates counterclockwise, viewed in from the right side plate 56 of the drive part 1, so that the label strip 14 is pulled by the platen 22 toward the front side of the printer. In addition, the platen 22 is connected by a gear system, having a series of gears including a gear 24 as indicated in Figure 1, to a motor 26 positioned at the right end of the drive part1. The motor 26 drives the gear system to rotates the platen 22 such that the platen 22 will urge the label strip 14 to move through the printer (see also Figure 2).
Normally, the printer has a locking mechanism, which will be explained in the followings, to open up a gap between the print head and the platen 22 for inserting the label strip 14, or to closely engage them for the operation. During the printing operation, the print head is locked into place to contact the upper printable side of the labels 10. With the print head lowered into place and contacting the labels 10, a small amount of friction is created as the label strip 14 passes through and beneath the print head during printing. This small amount of friction is important to the operation of the present Invention, as will be explained more detailedly in the paragraphs that follow.
Just after passing between the print head and the platen 22, the label strip 14 passes over a stripper bar 28 located at the front side of the printer 1, as shown in Figures 1 and 2. The stripper bar 28 is basically a flat panel plate, preferably made by stainless steel or other metal materials, having a wide center portion and two narrow portions, with same length, respectively positioned at opposite ends (left and right) of the stripper bar 28. The overall length of the stripper bar 28 is approximately 14.3 cm (5.63 inches) long, roughly the same length between the left and right side plates 56, 58 of the drive part 1. Thus, the stripper bar 28 may be coupled to the drive part 1 by inserting the narrow portions of the stripper bar 28 into respective receiving slots on the opposite side plates 56, 58. The center portion of the stripper bar 28 is approximately 12cm (4.75 inches) long and is slightly longer than the platen 22, whose length is of approximately 11cm (4.4 inches). The stripper bar 28 is angled upward from a level position with its lower bottom end positioned close to, but not touching on, the platen 22. The lower bottom end of the slanted stripper bar 28 is also positioned slightly above a surface intersection line, which is the tangential intersection line of the platen 22 and a vertical plane, of the platen 22. As will be explained in further details later, the angle of the stripper bar 28 is suitably positioned in order to separate a portion of the protective backing 12 from a label 10 directly over the stripper bar 28. In a preferred embodiment shown in Figure 3, the angle of the stripper bar 28 is of approximately 30° to 50°, preferably at 40°. measured from a level position upward. As can be seen more clearly in the followings, the angle of the stripper bar 28, however, may be of any degree as long as it is suitable to separate the labels 10 from the protective backing 12 when the label strip 14 passes over the stripper bar 28.
After passing over the stripper bar 28, the labels 10 will be allowed to flow straight out of the printer at the front side, while the protective backing 12 will be threaded back underneath the stripper bar 28 and over, behind and then underneath a stripper roller 32. As shown in Figure 4, the stripper roller 32 includes a stripper shaft 38 movably coupled to the drive part 1 at opposite ends and a sleeve 42 rotatably encircling the stripper shaft 38. A pair of roller receiving holes are respectively positioned at opposite side plates 56, 58 of the drive part 1 to receive the opposite ends of the stripper shaft 38. The roller receiving holes are of approximately elliptic shape in a slanted down position .toward the front side, and are slightly larger than a diameter of the stripper shaft 38 to allow the stripper shaft 38 to reciprocally slide therein. The stripper roller 32 is located in front of and lower than the platen 22, thereby the position of the stripper shaft 38 is approximately 45° to 60° angled down from a horizontal plane passing a center axile of the platen shaft 23. In the normal operation, the stripper roller 32 pressed tightly against the platen 22, while in the loading position, the stripper roller 32 is urged away from the platen 22 for threading the protective backing 12 between the platen 22 and the stripper roller 32, as will be explained further.
A pair of left and right cam levers 36 is rotatably coupled to the stripper shaft 38 near the opposite ends inside the respective side plates 56, 58, as shown in Figure 2. The left and right cam levers 36 have extending portions having cam-shape contour and positioned directly underneath the platen shaft 23. In addition, a pair of levers 34, 35 is securely coupled to the stripper shaft 38 at the opposite ends (left and fight) outside of the respective side plates 58, 56 of the drive part 1. Correspondingly, a pair of torsional springs 48, 52 urges the respective levers 34, 35, and thus the stripper roller 32, toward the back end of the drive part 1. Thus, the torsional springs 48, 52 urge the stripper roller 32 tightly against the platen 22 during operation. The lever 34 has an upwardly extending handle, as shown in Figure 1, and a ring shape bottom securely encircling the stripper shaft 38, as shown in Figures 4 and 5. As a result, a user may pull the handle of the lever 34 to rotate the stripper shaft 38, which, in turn, rotates the cam levers 36, thereby the stripper roller 32 may be forced to move toward or away from the platen 22 by the cam levers 36, as will be explained in further details. In a preferred embodiment, the sleeve 42 is made of Teflon due to the properties of the Teflon that are suitable to the operation of the present invention, as will be explained further detailed in the following paragraphs. However, it is possible that other materials may be used for the sleeve 42 as long as they produce similar results as the Teflon does for the present Invention. Moreover, the platen 22 may be made of any suitable materials that are commonly adopted to make platens by persons skilled in the art.
The Teflon provides a number of advantages suitable for the sleeve 42 of the present invention. First, a bearing surface, which is on the outer surface of the sleeve that carries the protective backing 12, of the Teflon sleeve is smooth and offers little friction for the protective backing 12 to pass through. Second, the bearing surface of the Teflon sleeve is a none-sticking bearing surface. Therefore, in some rare cases, if a label is only partially peeled off after passing the stripper bar 28 and follows the protective backing 12 to the stripper roller 32, the label may stick to the sleeve 42 when it approaches the stripper roller 32. By having a none-sticking surface of the sleeve 42, peeling the stuck label off the Teflon sleeve 42 in this rare case of failure would be easier. Finally, a lubricant may be added between the sleeve 42 and the stripper shaft 38 to reduce a rotational friction between the sleeve 42 and the stripper shaft 38. It has been found that the Teflon is suitable to work with most lubricants. All these properties of the Teflon make it particularly suitable to be the material for the sleeve 42.
As can be seen in Figures 5 in conjunction with Figure 1, in order to thread the backing 12 around the stripper roller 32, the user will have to engage the lever 34, which is coupled to the adjacent left end of the stripper shaft 38 and to the cam lever 36. When rotated to a loading position by pulling the lever 34 toward the front end of the printer the lever 34 rotates the cam levers 36 at the ends of the stripper shaft 38. The cam levers 36, together urge the stripper roller 32 away from the platen 22 creating enough room for the protective backing 12 to be threaded through between the platen 22 and the stripper roller 32. Figure 5 shows the lever 34 and the cam lever 36 in their operation position. As stated, the printer also comprises a pair of torsional springs 48, 52 for urging the stripper roller 32 against the platen 22 thereby maintaining a tight pressure between the stripper roller 32 and the platen 22 during operation. The torsional springs 48, 52 are respectively positioned outside of the side plates 58, 56 and before the levers 34, 35. The torsional springs 48, 52 respectively have extruding spring plates contacting the levers 34, 35 to urge the stripper roller 32 against the platen 22.
In an alternative embodiment, the levers 34, 35 and/or the cam levers 36 may also be configured to release the print part from engaging to the drive part 1 of the printer so that the print head may be disengaged from contacting the platen 22 in order to allow the threading of the label strip 14 between the print head and the platen 22. In the above-mentioned alternative embodiment, the levers 34, 35 may respectively have cam-shape latches adjacent to the side plates 58, 56 and slightly higher than the top surface of the side plates 58, 56. Correspondingly, the print part of the printer has a pair of latching cams properly positioned relative to the cam-shape latches of the drive part 1 so that the cam-shape latches will latch with the latching cams of the print part when the two parts are pivotally closed to each other. The torsional springs 48, 52 also serve to urge the levers 34, 35 to lock with the print part during operation. As a result, the user may release the print part from engaging to the drive part 1, and also to simultaneously release the platen 22 from pressing against the stripper roller 32, by pulling the lever 34 toward the front side of the printer.
The labels 10 have printable front sides and adhesive back sides adhered to the protective backing 12. However, the protective backing typically has a gloss surface and most adhesive glue applied on the back side of the labels 10 are often not very sticky in order not to impede peeling off the labels from the protective backing 12. As a result, when the label strip 14 is bent over a certain angle, e.g., 45°, a label just over the bending line of the label strip 14 normally would separate apart from the protective backing 12 and moves in a tangential direction at the bending line relative to the protective backing 12. As noted, the label strip 14 is inserted into the printer through the opening at the back side of the drive part 1. Once entering the drive part 1, the label strip 14 passes through the pathway guides 16, 18 horizontally and between the print head and the platen 22 vertically for receiving printing images on the labels 10 from the print head. After passing through the platen 22, the label strip 14 proceeds over the upwardly angled stripper bar 28 for separating the labels 10 from the protective backing 12. Thereafter, the protective backing 12 is directed backward underneath the stripper bar 28 and over, behind and underneath the stripper roller 32 to come out of the drive part 1 from the bottom of the stripper bar 28, as shown in Figure 1. Since the protective backing 12 is threaded back under the stripper bar 28, the labels 10 will ordinarily move tangentially toward the front side of the printer after passing the stripper bar 28 and will not follow the protective backing 12 to the underside of the stripper bar 28. Thus, the labels 10 will be automatically peeled off the protective backing 12 when they pass the stripper bar 28.
As noted, the protective backing 12 usually has a gloss and smooth surface on one side, which is attached to the adhesive side of the labels 10, to allow the labels 10 to be peeled off easily. Because the protective backing 12 is designed to allow the labels 10 to be peeled off very easily, the labels 10 can be separated from the protective backing 12 by folding the strip 14 at an edge of a label 10 over a certain critical angle. The critical angle of a specific self-adhesive label may be the same as or slightly different from. others. In a preferred embodiment, the present invention comprises a stripper bar 28 having an acute upward angle of approximately 27° to 32° to ensure all labels 10 will be separated from the protective backing 12 when the strip 14 passes the stripper bar 28 while the protective backing is threaded back and underneath the stripper bar 28, as shown in Figure 3.
After protective backing 12 is directed backward under the stripper bar 28, the protective backing 12 is threaded between the platen 22 and the stripper roller 32 to direct it out of the printer in a forward direction. The user will then pivotally fold down the print part to engage the drive part 1, and will move the lever 34 back into its operational position (as shown in Figure 5), that rotates the cam levers 36 and therefore moves the stripper roller 32, the platen 22, and the print head back to its operational position. Thus, the protective backing 12 is trapped between the stripper roller 32 and the platen 22, and the label strip 14 is trapped between the print head and the platen 22. As stated previously, the protective backing 12 may therefore be separated from the labels 10, which move directly out of the printer from over the stripper bar 28, and comes out of the printer through moving underneath the stripper roller 32.
As shown in Figure 4, the stripper roller 32 comprises a stepped stripper shaft 38, surrounded by the sleeve 42. In the preferred embodiment, the stepped stripper shaft 38 is made of any 300 series stainless steel, and the sleeve 42 is made of FEP Teflon, but other suitable materials may be adopted for the stripper shaft 38 or the sleeve 42. The Teflon sleeve 42 has an exterior diameter of approximately 1 cm (0.419 inches), an interior diameter of approximately 0.6cm (0.25 inches), and is approximately 12cm (4.72 inches) in length. The stripper shaft 38 is approximately 15cm (5.98 inches) long. The stripper shaft 38 has a first diameter, measured on the portion of the shaft 38 from either end of the shaft 38 to a set of first steps 44, of approximately 0.4 cm (0.156 inches); a second diameter, measured on the portions of the shaft 38 from either first step 44 to an adjacent second step 46, of approximately 0.5 cm (0.204 inches); and a third diameter, measured on the portion of the shaft 38 between the two second steps 46, of approximately 0.6 cm (0.236 inches). The stripper shaft 38 is generally symmetrical, with the distance between either end and the adjacent first step 44 of approximately 1.57 cm (0.62 inches) the distance between either first step 44 and the adjacent second step 46 of approximately 4.75 cm (1.87 inches), and the distance between the two second steps 46 of approximately 2.5 cm (1.0 inches). As can be seen, even at the point of the greatest diameter, i.e., the third diameter, of the stripper shaft 38 there is a radial clearance between the stripper shaft 38 and the Teflon sleeve 42 of about 0.36 cm (0.014 inches). This clearance (in addition to other inherent properties of Teflon) permits the Teflon sleeve 42 to rotate freely about the stripper shaft 38. As a result, the stripper shaft 38 does not generally rotate during normal operation.
When the printer is In operation, the motor 26 turns the gears of the gear system 24, which, in turn, rotates the platen 22 to urge the label strip 14 moving forward by passing through the print head and platen 22. During the printing, the print head prints data on the labels 10 and creates a small friction on the label strip 14 when it slides over the print head. The small friction has a slight slowing effect on the speed of the label strip 14. Moreover, the pressure from the platen 22 against the protective backing 12 and the stripper roller 32 drives the stripper roller 32 to rotate and thus forces the protective backing 12 to pass underneath the stripper roller 32.
Due partially to the gloss surface of the protective backing 12, it has been found that when the protective backing 12 passes between the platen 22 and the stripper roller 32, it encounters less resistance than the label strip 14 passing between the print head and the platen 22. Therefore, when the printer starts to print, the stripper roller 32 and the platen 22 together will initially pull the protective backing 12 faster than the print head and the platen 22 pulling the label strip 14. As a result, a small tension will be gradually accumulated in a section of the protective backing 12 between the stripper roller 32 and the print head. An equilibrium level of the tension is reached when the stripper roller 32 can no longer overcome the friction created by the print head and move the protective backing 12 at a faster rate than that traveled at by the label strip 14. Therefore, the tension will be kept accumulating until such time that the tension in the protective backing 12 becomes strong enough to counter act the speed differential. At this point, the tension reaches the equilibrium level and the protective backing 12 and the label strip 14 will be moved in a same speed. Once the equilibrium level of the tension is reached, the printer tends to move the protective backing 12 and the label strip 14 at the same speed while maintaining the equilibrium tension level on the protective backing 12 to keep it straight.
Moreover, whenever there is a slack of the protective backing 12 initially, the speed differential will again cause the tension to increase toward the equilibrium level. As a result, the tension built up thereon will help straighten the portion of the protective backing 12 between the stripper roller 32 and the stripper bar 28. This tension on the protective backing 12 will not only straighten the protective backing 12 but also help the printer avoid undesirable looping of the protective backing 12, or other forms of failure of the label strip 14 associated with the slack paper problem.
As labels 10 are printing, the acute angle of the fold of the label strip 14, as it passes over the stripper bar 28 while the protective backing 12 is threaded back and then under the stripper bar 28, continues to separate the protective backing 12 from the labels 10. In addition, the above-noted tension will also help maintaining the proper angle of the fold as the label strip 14 passes over the stripper bar 28. Should the tension become too great, the Teflon sleeve 42 will "slip" against the protective backing 12 and thus maintains the equilibrium level of tension on the protective backing 12 and the label strip 14 for proper printing. The "slip" of the Teflon sleeve 42 is partly due to the lubricants filled in the radial clearance between the Teflon sleeve 42 and the stripper shaft 38.
Most conventional printing devices do not experience the above-mentioned initial speed differential and are subject to failures, particularly the looping of the label strip 14 and/or of the protective backing 12. The conventional devices also have no mechanisms to maintain tension on, and, thus, to straighten, the backing 12. This problem is especially acute with thermal transfer printers, which cause less drags of printing strips than direct thermal printers and do not have the same magnitude of frictions to cause a speed differential that increases the tension of the protective backing 12. A similar problem also exists when a narrow media (e.g., less than 2.5 cm (one inch) wide) is used. Such a narrow printing surface has been found particularly susceptible to looping and failure unless a sufficient tension is maintained between the strip 14 and the protective backing 12. The looping problem of the conventional printing devices when used in conjunction with the narrow media is primarily due to the fact that the conventional printing devices, when designed and built, normally do not take into consideration to accommodate the narrow media.
In contrast, the present invention does not have the above-mentioned problems for the thermal transfer printers and/or for using the narrow printing media. To begin with, it has been found that the present invention causes a sufficient tension on the protective backing 12 to prevent the looping problem in the thermal transfer printers and/or of the narrow printing media. Moreover, stepped stripper shaft 38 of the present invention is particularly suitable to accommodate the narrow media. As previously mentioned and shown in Figure 4, the center portion of the stripper shaft 38, which is between the set of the second steps 46, has the largest diameter on the stepped shaft 38 of approximately 0.6 cm (0.236 inches) and of approximately 2.5 cm (1.0 inches) in length. Only the center portion of the stripper shaft 38 touches and presses against the encircling Teflon sleeve 42 during operation when the Teflon sleeve 42 rotates about the stripper shaft 38. Thus, the stepped stripper shaft 38 helps the stripper roller 32 press against the protective backing 12 by focusing most of the pressure on the center portion of the protective backing 12. When a narrow printing strip is used, even as narrow as one inch long, the present invention will still provide an adequate pressing force more evenly distributed on the narrow strip to move a protective backing of the narrow strip through the printer.
From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made by persons skilled in the art without deviating from the scope of the invention as claimed. For example, the dimensions of the stripper roller, and its relevant parts such as the stripper shaft, may be changed to accommodate different printing devices. The relative proportion of different parts of the stripper shaft may also be changed to accommodate any specific purpose. The sleeve may be made of materials, other than the Teflon, suitable to create speed differential and to "slip." Furthermore, the angle of the stripper bar may be changed to ensure the labels will be separated from the protective backing when the strip passes over the stripper bar while the protective backing is threaded back and underneath the stripper bar. Accordingly, the present invention is not limited except as by the appended claims.

Claims

An image forming device adapted to automatically separate detachable adhesive printing media (10) from a protective backing strip (12) without causing excessive looping or jamming failures to the device, said image forming device comprising:

a support frame having first and second walls (56,58) respectively positioned at opposite sides and having an opening at a back end;

a platen (22) rotatably coupled to the first and second walls of said support frame at opposite ends, said platen being adapted to move the printable medium through the image forming device; and

a stripper roller (32), positioned under and forward of said platen (22), adapted to press the protective strip against the platen;

characterized in that
said stripper roller (32) has a tube-shaped sleeve (42) and a stepped and generally cylindrically shaped roller shaft (38),
wherein the roller shaft is coupled to the first and second wall (56, 58) of said support frame at opposite ends,
wherein the sleeve (42) rotatably encircles the roller shaft (38),
wherein the roller shaft has a center portion having a length shorter than the length of the sleeve,
wherein the center portion has the largest diameter ofthe roller shaft, and
wherein only the center portion ofthe roller shaft touches and presses against said sleeve during operation when the sleeve rotates about the roller shaft.
The image forming device of claim 1, wherein the image forming device is adapted to receive a printable medium having an adhesive printable part adhered to a protective backing part, the image forming device further comprising
a print head; and
a stripper means (28) coupled to the first and second walls (56, 58) of said support frame at opposite ends, said stripper means being positioned forward of said platen, (22) wherein said stripper means is adapted to separate the printable part from the protective backing part of the printable medium,
said stripper roller (32) being disposed under said stripper means (28) and being adapted to press the protective backing part against said platen for pulling the protective backing part at a first speed to cause a tension on the protective backing part.
The image forming device of claim 2 wherein said stripper means comprises a stripper bar (28) of generally flat shape, said stripper bar being upwardly angled of approximately 35° to 50° from a horizontal level and having a lower back edge positioned near and parallel to said platen.
The image forming device of claim 3, in which when the printable medium is moved over said upwardly angled stripper bar, the protective backing part of the printable medium is pulled by said platen and said stripper roller underneath said stripper bar and the printable part is moved directly forward out of a front edge of said stripper bar.
The image forming device of claim 3, wherein said platen is adapted to rotatably press the printable medium against the print head of the image forming device for pulling the printable medium through the print head at a second speed, the print head being adapted to form images on the printable medium.
The image forming device of claim 5, wherein the print head causes, in operation small frictions against pulling of the printable medium by said platen wherein, during an initial operation period, the first speed is slightly faster than the second speed causing the tension on the protective backing part to increase until the tension reaches an equilibrium tension sufficient to overcome the small frictions and, after the initial operation period when the equilibrium tension is reached, the first speed traveled by the protective backing part and the second speed traveled by the printable medium is approximately equalized.
The image forming device of claim 6, in which the tube-shaped sleeve (42) and the roller shaft encircled within the sleeve are in a substantially symmetrical manner, and wherein said stripper, roller has a radial clearance between the tube-shaped sleeve and the roller shaft for the sleeve to rotate freely about the roller shaft (38).
The image forming device of claim 7 wherein the tube-shaped sleeve slips against the protective backing part when the tension level on the protective backing part increases over the equilibrium tension level.
The image forming device of claim 7 wherein said stepped roller shaft comprises:

a first shaft section, said first shaft section being in the center portion of said stripper shaft and having a first diameter slightly smaller than the inner diameter of the sleeve;

second and third shaft sections respectively coupled to said first shaft section at opposite ends, said second and third shaft sections each having a second diameter smaller than the first diameter; and

fourth and fifth shaft sections respectively coupled to said second and third shaft sections at opposite ends of said stripper shaft, said fourth and fifth shaft sections each having a third diameter smaller than the second diameter.
The image forming device of claim 9 wherein said first shaft section is in substantially cylindrical shape and is approximately 2.5 cm (one inch) long.
The image forming device of claim 2 wherein said tube-shaped sleeve is made of FEP Teflon materials.
The image forming device of claim 2, further comprising:

a set of pathway guides (16, 18) positioned at opposite sides in the imaging forming device wherein a distance between said pathway guides is adjustable;

a cam coupled to said stripper roller at opposite ends; and

a lever coupled to said cam and said stripper roller, said lever being adapted to pull said cam such that said cam, in response to the pull of said lever, pulls said roller away from said platen to facilitate loading of the protective backing part under said roller.
The image forming device of claim 12 wherein said cam, in response to the pull of said lever, also pushes said print head away from said platen to facilitate loading of the printable medium between said print head and said platen.
The device of claim 13, further comprising a set of torsional springs (48, 52) located at opposite ends of said stripper roller for urging said roller to press against said platen during operation.
The device of claim 1, further comprising
a print head;
a set of pathway guides (16,18) wherein a distance between said pathway guides is adjustable to accommodate the strip; and
a stripper bar (28) located forward of said platen, said stripper bar being disposed in a suitable upward angle of approximately 40° and being adapted to separate the labels from the protective backing part when the strip passes over said stripper bar while the protective backing part is threaded back and under the stripper bar.
The device of claim 15, further comprising
a cam coupled to said stripper roller;
a set of torsional springs (48, 52) located at both ends of said roller shaft (38) for urging said sleeve (42) against said platen (22); and
a lever (34, 35) coupled to said cam and said roller shaft, said lever being adapted to pull said cam such that said cam, in response to the pull of said lever, pulls said roller shaft away from said platen to facilitate loading of the protective backing part under said sleeve.
Use of the device as claimed in claim 2 for separating self-adhesive labels of a continuous strip inserted in the device from a protective backing (12) of the strip, said use comprising
rotating a platen (22) of the device to move the strip and the protective backing outward of the device;
passing the strip over a stripper bar (28) positioned near a front end of the device in a predetermined upward angle adapted to separate the labels (10) from the protective backing (12);
threading the protective backing backward and under the stripper bar while allowing the labels to continue outward of the device;
passing the protective backing over, behind and underneath a stripper roller positioned forwardly under the platen arid pressing against the platen; and
directing the protective backing out of the device from under the stripper roller (32).
The use of claim 17, further comprising:

moving the strip between a print head and the platen at a first speed;

printing data on the labels by the print head;

moving the protective backing past the stripper roller at a second speed wherein, during an initial operation period of the device, the second speed is slightly faster than the first speed of the strip passed the print head;

increasing a tension level on the protective backing during the initial operation period due to a difference of the first and second speed; and

equalizing the first and second speeds when the tension level on the protective backing reaches an equilibrium level.
The use as claimed in claim 17, comprising the steps of:

moving the media backing strip initially faster between the stripper roller and the platen than between the platen and the printhead to define a speed differential, said speed differential tensioning the media backing strip; and

reducing subsequently said speed differential to zero to allow the tension on the media backing strip to reach an equilibrium state.