Field of the invention The present invention relates to a tear bar assembly or a tear bar arrangement for a printer. In particular, but not exclusively, the present invention relates to a tear bar assembly for a label printer.

Technological background

Label printers are known. An example of a known label printer is the Dymo LabelWriter printer. With the known label printers, a printing mechanism is arranged to print an image on a recording medium such as a label supply.

The printing mechanisms proposed by these known label printers may use a thermal transfer mechanism. In other words, a supply of ink ribbon is used in order to obtain an image on the label supply. In particular, the label supply and the ink ribbon are passed, in an over lapping fashion, past the printing mechanism which prints an image on to the label material. Alternatively, the label material may be of a thermally sensitive nature and accordingly, the need for an ink ribbon can be avoided as the printing mechanism will print an image directly on the thermally sensitive label material. It should be appreciated that other technologies can be used in order to obtain an image on the label material.

In some known label printers the label supply may be fed in both forward and reverse directions. Forward feeding feeds a leading edge of the label supply in a direction outwardly of the printer, and reverse feeding feeds the leading edge of the label supply into the printer.

Reverse feeding may be useful for a number of reasons. For example EP-A- 0573188 (Esselte Dymo N.V.) describes a printing apparatus that is capable of printing an image on an image receiving tape which is wider than the print head. It does this by printing a lower part of a label on a wide image receiving tape, then rewinding the image receiving tape and raising the print head, and then printing an upper part of a label above the tower part.

Reverse feeding may also be used in order to correctly align a label with a print-head prior to a printing operation. Reverse feeding may also be used to control the size of a margin between the edge of a label and the printed output.

The label supply can take the form, for example, of discrete (so called die cut) labels on a backing sheet. Alternatively, the label supply can take the form of a continuous length of tape material on to which an image can be printed. The label material is then cut when the image has been printed.

One known way of cutting the label material is to use a scissor mechanism located at an outlet of the label printer.

Another known way of cutting the label material is by tearing the tape over a knife portion located at the printer outlet. Such a knife portion is commonly known as a "tear bar".

The inventors have identified a problem associated with the latter of these two tape cutting mechanisms. In this respect they have identified that during a tape feeding operation it is likely that a portion of the tape will become caught on the tear bar.

This problem may be exacerbated when the label supply is in the form of die- cut labels since the edges of the labels are raised slightly from the backing sheet to facilitate peeling, and therefore the chance of these edges catching on the tear bar is increased.

There may be a problem during a reverse feeding operation. Before a reverse feeding operation begins it is likely that a portion of the label supply will be hanging unsupported outside of the printer. The angle that this unsupported label portion makes with the tear bar increases the chances of a trailing edge of the die-cut label catching on the tear bar when the label is fed back in to the printer. As a result of this the printer may be unable to feed the label to the correct printing position. In other cases the label may "jump" over the tear bar which results in a loud snapping noise. In still another case the label may completely delaminate from the backing sheet. The printer motor may be caused to stall leading to a printer "time-out", thus requiring the user to restart the printer.

Summary of the. invention

According to a first aspect of the present invention there is provided a tear bar assembly for a printer, the assembly comprising: a tear bar member configured to be positioned at a recording medium outlet of the printer; and a guard member positioned adjacent to the tear bar member; the guard member and the tear bar member having a first relative position in which the guard member is configured to separate the recording medium from a tearing surface of the tear bar member, and a second relative position in which the guard member is configured to allow the recording medium to contact the tearing surface during a recording medium tearing operation.

According to a second aspect of the present invention there is provided a printer comprising: a tear bar member positioned at a recording medium outlet of the printer; and a guard member positioned adjacent to the tear bar member; the guard member and the tear bar member having a first relative position in which the guard member is configured to separate the recording medium from a tearing surface of the tear bar member, and a second relative position in which the guard member is configured to allow the recording medium to contact the tearing surface during a recording medium tearing operation.

According to a third aspect of the present invention there is provided a tear bar assembly for a printer, the assembly comprising: tearing means positioned at a recording medium outlet of the printer; and guard means positioned adjacent to the tearing means; the guard means and the tearing means having a first relative position in which the guard means is configured to separate the recording medium from the tearing means; and a second relative position in which the guard means is configured to allow the recording medium to contact the tearing means during a recording medium tearing operation.

According to a fourth aspect of the present invention there is provided a printer comprising: tearing means positioned at a recording medium outlet of the printer; and guard means positioned adjacent to the tearing means; the guard means and the tearing means having a first relative position in which the guard means is configured to separate the recording medium from the tearing means, and a second relative position in which the guard means is configured to allow the recording medium to contact the tearing means during a recording medium tearing operation.

Brief description of the drawings

For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example only with respect to the accompanying drawings in which:

Figure 1 shows two die cut labels on a backing material;

Figure 2 shows a schematic view of a printer in which the present invention may be embodied;

Figure 3 shows a view of a label printer front cover, in which a tear bar assembly embodying the present invention is partially seen;

Figure 4 is an exploded perspective view of the tear bar assembly which is partially seen in figure 3; Figure 5 is a perspective view of the tear bar assembly of figure 4 when assembled;

Figure 6 is a perspective view of an alternative tear bar assembly;

Figure 7 is a schematic side view of one embodiment of a tear bar assembly embodying the present invention;

Figure 8 is a schematic side view of an alternative tear bar assembly construction;

Figure 9A is a schematic side view of the tear bar assembly of figure 7 further showing a recording medium.

Figure 9B is a schematic side view of the tear bar assembly of figure 9A during a recording medium tearing operation.

Description of the preferred embodiments

Reference will first be made to figure 1 which shows two labels 4 on a backing material 2 defining a label supply 10. The labels 4 are discrete labels i.e. die cut labels. The labels 4 are adhered to the backing material 2. The backing material 2 has a release coating on the side to which the labels are adhered in order to allow the labels to be easily removed from the backing material once a label has been printed. Markings 6 are provided on the side of the backing material 2 opposite to that on which the labels 4 are provided. For schematic purposes, figure 1 shows the labels and markings apparently on the same side as the backing tape. This might occur in embodiments where the markings are invisible to the naked eye. However, in preferred embodiments of the present invention, the markings are on the other side of the backing material 2 to the labels.

The markings each have the same width A and the same separation distance C. The height of the markings is indicated by B and the distance between the edge of the backing material and the start of a marking, as measured across the width of the backing material is D. By way of example only, A may be 3mm, B may be 8mm, C may be 8mm and D may be 11.5mm. However, these measurements are given by way of example only and the size of the measurements may vary.

The markings may extend continuously along the length of the backing material or may be provided in clusters at regular intervals. For example, N markings equally spaced apart from one another may constitute a set of markings. There may be M sets of N markings with the sets of markings being separated by a distance which is greater than the separation of the markings within a set.

It should be appreciated that the size of the markings and/ or the distance there between may be altered to reflect different label sizes and/or materials.

It should be appreciated that in some embodiments, there are no markings provided. In other embodiments of the invention, instead of discrete labels, there is a continuous length of tape onto which an image is printed. There may or may not be a backing sheet provided. The underside of the continuous length of material may or may not be provided with adhesive.

Reference is now made to figure 2 which shows a schematic view of a printer.

The label supply 10 is provided on a supply reel 12. In alternative embodiments of the present invention, the label supply may be provided in a cassette. In other embodiments of the invention, the label supply is provided as a fan-fold stack. In yet another embodiment of the invention, individual labels can be introduced for printing.

The supply reel 12 is mounted on a spindle 14 about which the supply reel can rotate. A print head 18 is provided for printing on the die cut labels 4. The print head 18 is controlled in accordance with data provided from a CPU (Central Processing Unit) 30 or any other suitable processing element and/or print head driver.

The image printed on the label may be input by the user via a keyboard 36. The keyboard 36 is connected to the CPU 30. The CPU processes the input data from the keyboard and puts it into a format suitable for controlling the print head 18.

The print head 18 acts against a platen 20. In this embodiment, the platen 20 is rotatably driven by a motor 16. The print head and/or the platen may be movable apart from one another to allow the easy insertion of the material between the platen 20 and the print head 18. During printing, the platen 20 and print head 18 will be urged one against the other. When the print head 18 and platen 20 are in the printing configuration, rotation of the platen 20 will cause image receiving material to be pulled from the supply roll 12. Alternative printing configurations or technologies may be used in alternative embodiments of the invention. For example a scanning print head or an ink jet print head are just two examples of alternative printing arrangements which can be used in alternative embodiments of the invention.

The motor 16 may be controlled in embodiments of the present invention by the CPU 30 via in put line 32.

Embodiments of the present invention are provided with a sensor arrangement 25, which may be omitted in alternative embodiments. The sensor arrangement 25 comprises a light source 24 which may be a light emitting diode and a light detector 22 which may be in the form of a photo transistor. The phototransistor 22 is arranged to detect light emitted by the light source 24 which is reflected from the rear surface of the image receiving medium i.e. the surface on which the markings are provided. In embodiments of the present invention the markings are darker than the background of the image receiving tape. Thus, more light is reflected from the regions between the markings to the photo transistor than when the light from the light emitting diode 24 impinges a marking.

In some embodiments of the present invention a grating maybe provided between the light emitting diode and photo transistor on the one hand and the backing material on the other hand. The grating is there to improve the quality of the wave form provided by the photo transistor 26. The width of the slit of the grating is selected to have a width generally corresponding to the width of a single line. The provision of the grating can improve the contrast between the light regions and the dark regions. This in turn may provide sharper peaks and troughs in the wave form provided by the photo transistor.

The output of the photo transistor 22 is input via line 26 to the CPU. The CPU 30 may control the light emitting diode 24 via line 28.

Alternative sensing arrangements may be used in alternative embodiments of the invention.

The apparatus also comprises a display 40 which is controlled by the output of the CPU 30 via line 42. In particular, the output of the CPU 30 is input to a display driver 38 which controls the information displayed on the display 40.

In some embodiments, the printer may be connected to a PC (personal computer) or the like. The printer may not have a display. This may be provided by a display connected to the PC. The printer may not have some or all of the processing capability discussed above. This functionality may be provided by the PC and the display of the PC respectively.

A tear bar assembly is not shown in figure 2. However it should be appreciated that a tear bar assembly embodying the present invention may be incorporated into the type of printing system shown in figure 2.

Turning to figure 3, this drawing shows a sub assembly of a label printer front cover 200 for incorporating a tear bar assembly embodying the present invention. The front cover 200 comprises a casing 204. A recording medium (not shown) may be fed forwardly out of the front cover 200 via the outlet 206. The tear bar assembly is shown generally at 202. A guard member, in this case a resilient guard member (explained in greater detail below), which forms part of the tear bar assembly 202, is shown at 220.

The label printer front cover also comprises a form feed button 207. Operation of this button advances the label stock. This button may also or alternatively provide one or more other functions such as: putting the printer into a self test mode when the button is pressed for a certain length of time, or changing the printer from a low power mode to a full power mode when the button is pressed.

The tear bar assembly 202 can be seen in more detail in figures 4 and 5.

The tear bar assembly 202 comprises a mounting frame 210 which is configured to be attachable to the label printer 200 at a position proximate to the outlet 206. The mounting frame 210 has a generally flat portion 212, and a ramp portion 213 along which a recording medium (not shown) is guided between guide projections 215 and 217 when the recording medium is being fed out of or in to the printer.

The mounting frame 210 comprises a series of further projections 214 which project from a front face 216 of the mounting frame. The projections enable a tear bar member 218, a resilient guard member 220 and a securing plate 222 to be attached to the mounting frame 210. The tear bar member 218, resilient guard member 220 and securing plate 222 comprise respective holes 224, 226 and 228 for mounting on to the projections 214 of the mounting frame 210.

The tear bar member 218 is elongate, having long edges 230 and 232 and short edges 234 and 236. Long edge 230 acts as the tearing surface of the tear bar member. In this embodiment the tearing surface is provided with a number of serrations 238, however the tearing surface may comprise a flat blade or any other type of sharp edge. The tearing surface may be metal or any other suitable material such as plastics.

Resilient guard member 220 and securing plate 222 are also elongate.

The resilient guard member 220 can be made of any suitable material, such as silicone rubber. Where silicone rubber is used a thickness of about 0.6mm is optimum. However any thickness between approximately 0.4mm and 0.8mm may be used. Any thickness between 0.3mm and 1 mm may also be used.

The hardness of the silicone rubber is optimally 30 Shore A Durometer. This provides sufficient stiffness to prevent the edge of a label coming in to contact with the tear bar member on reverse feeding, yet provides sufficient flexibility for the resilient guard member to deflect out of the way during a tearing operation (described in more detail with reference to figures 9A and 9B).

Although 30 Shore A Durometer is the optimum hardness, a hardness of anywhere between 20 and 40 Shore A Durometer is effective and may be used. Silicone rubber having a hardness of anywhere between 10 and 60 Shore A Durometer could also be used.

Other materials may be used for the resilient guard member 220. For example the resilient guard member may be made from Buna-N rubber, Mylar or steel. Where Buna-N rubber is used, a thickness of approximately 0.8mm is optimum. Where Mylar or steel are used, a thickness of approximately 0.15mm is optimum.

Resilient guard member 220 comprises long edges 240 and 242 and short edges 244 and 246.

Securing plate 222 comprises long edges 247 and 249 and short edges 248 and 250. The long edges of the resilient guard member 220 are slightly longer than the long edges of the tear bar member 218 to ensure that the serrations 238 do not catch on a recording medium whilst it is being fed. In alternative embodiments of the invention the resilient guard member may be substantially the same length as the tear bar member. The long edges of the securing plate 222 are approximately the same as those of the resilient guard member 220.

It should also be appreciated that the short edges 244 and 246 of the resilient guard member 220 are longer than the short edges 234 and 236 and 248 and 250 of the tear bar member and securing plate respectively. Thus when the tear bar assembly is assembled, as shown in figure 5, the long edge 240 of the resilient guard member is positioned above the long edge (and tearing surface) 230 of the tear bar member, and above the long edge 244 of the securing plate 222.

Thus, in figures 3 and 5, the tear bar member is obscured by the resilient guard member 220.

Preferably the projections 214 are formed from a plastic material. Once the tear bar assembly is assembled (i.e. as per figure 5) the securing plate 222, resilient guard member 220 and the tear bar member 218 are secured to the mounting frame 210 by heat staking. In this process the projections 214 are melted by a heat source (not shown) which causes the projections to melt and splay out, thus creating a secure connection. In this embodiment the resilient guard member 220 is sandwiched between the securing plate 222 and the tear bar member 218 and the resilient guard member is downstream of the tear bar member in the forward feeding direction of the printer.

An alternative technique for achieving the assembly may replace the heat source with an ultrasonic welding operation.

An alternative tear bar sub-assembly is shown in figure 6. In this figure components in common with figures 4 and 5 share like reference numerals. In addition to the components of figures 4 and 5, the embodiment shown in figure 6 comprises a layer of double sided adhesive tape 223 positioned between the tear bar member 218 and the resilient guard member 220, The double sided tape 223 provides an additional securing means to ensure that the tear bar member and resilient guard member do not become detached in use, but allows movement of the unsupported portion of the resilient guard member relative to the tear bar member when assembled.

Figure 7 is a side view of an embodiment of the present invention. The assembly is similar to that shown in figures 4 and 5, and equivalent components share the same reference numerals. In this embodiment the resilient guard member 220 is formed from steel. In this drawing the heat staking process has been carried out, as evidenced by the splayed out projection 214. It can be appreciated from this figure that the resilient guard member 220 and the tear bar member 218 both comprise a crook portion shown generally at 260, The upper ends of the tear bar member 218 and resilient guard member 220 are therefore angled away from the printer outlet. In this embodiment the resilient guard member 220 also comprises a hook portion 262 at one end. In other embodiments the resilient guard member may simply have a squared off end such as the resilient guard member of figure 8.

Figure 8 schematically shows an alternative tear bar assembly construction. Components similar to those shown in figures 4 and 5 are labelled with a reference numeral 100 higher. It can be appreciated from this drawing that the tear bar member 318 and the resilient guard member 320 are not attached to the mounting frame 310 using a heat staking method. Instead the tear bar member 318 and resilient guard member 320 are inserted into a slot 311 formed in the mounting frame 310. The tear bar member 318 and resilient guard member 320 may be vertically or laterally inserted in to the slot 311. The tear bar member 318 and resilient guard member 320 can then be held in place by any appropriate method such as by using an adhesive, screws or compression. This method minimises tooling. It should be appreciated that alternative embodiments of the invention may use alternative or additional methods to secure the elements of the tear bar assembly to one another such as screws, fasteners, adhesive or the like.

The function of the tear bar assembly is best seen in figures 9A and 9B. These figures show the tear bar assembly of figure 7, and additionally a recording medium 252 having a leading edge 254.

It can be appreciated from figure 9A that the recording medium is separated from the sharp edge of the tear bar member 218. Thus when the recording medium is driven in the forward direction (direction A), or the reverse direction

(direction B) the recording medium 252 does not catch on the tear bar member. It can also be appreciated how the leading edge 254 of the recording medium hangs down in front of the tear bar assembly under the force of gravity.

Figure 9B shows the configuration of the tear bar assembly during a tearing operation. During such an operation a downward force P is applied to the leading edge 254 of the recording medium 252. Such a force may for example be applied by the hands of a user wishing to tear the recording medium. As a result of this downward force the recording medium correspondingly pushes down on the resilient guard member, the unsupported portion of which deflects away from the tear bar member 218, thus allowing the recording medium 252 to come into contact with the sharp edge of the tear bar member. A continued downward force therefore enables the sharp edge to penetrate the recording medium and in this manner the recording medium may be torn.

By virtue of its resilience, when the downward force P is removed the resilient member 220 reassumes its position shown in figure 9A.

It should be appreciated that the foregoing merely illustrates the principles of the invention. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. For example, the tear bar may be an integral part of the printer housing. It could for example comprise a sharp edge or serrated edge which is integrally moulded with a portion of the printer body or cover. This reduces the number of components, thus simplifying manufacture.

The tear bar assembly may also be formed by over moulding a printer front cover over a tear bar member. The resilient guard member may also be placed in the mould during the over moulding process or may be fixed after the over moulding process in any appropriate way. Thus the cutting member could be of a material such as a metal or a plastic. The resilient guard member may be of an elastomeric or flexible material which can be over moulded over the cutting member.

Furthermore, there are numerous possibilities for the manner in which the guard member can move relative to the tear bar member. For example the guard member may be linearly movable relative to the tear bar member, or the tear bar member may be linearly movable relative to the guard member, and one or other of the guard member and tear bar member may be movable by means of a motor. If a mechanism is provided to move the guard member and/or the tear bar relative to one another, the guard member may not necessarily be resilient or flexible.

It will thus be appreciated that those skilled in the art will be able to devise numerous techniques which, although not explicitly described herein, embody the principles of the invention and are thus within the spirit and scope of the invention.