Abstract:
This invention relates to a spool for a supply of printing material, said spool comprising a first part, said first part comprising a shaft on which the supply of printing material is mountable, a second part, said second part having an opening and being arranged to retain a supply of printing material on the first part, said opening being arranged to engage said shaft, wherein one of said opening and the shaft is resilient and the other of the opening and the shaft has at least one part which extends towards the said one of said opening and the shaft more than at least one other part thereof to thereby cause said opening to engage with said shaft.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a spool for supporting a supply of printing material.  
       DESCRIPTION OF RELATED ART  
       [0002]     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 label supply.  
         [0003]     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.  
         [0004]     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 a 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.  
         [0005]     The label supply is supported on a spool. One known spool structure comprises a first part and a second part. The first part comprises a disc with a shaft. The second part comprises a disc. The label supply is supported on the first part with the second part slid over the shaft of the first part. The position of the disc of the second part of the shaft of the first part will depend on the width of the label material. In this way, a common spool structure can be used with a range of different sizes of label supply and/or tolerances in the size of the label material can be accommodated.  
         [0006]     With the known design, the second part stays in position on the shaft as a result of friction between the second part and the shaft. To increase the friction between the second part and the shaft, the second part is resilient around its opening which help to retain the second part in position on the smooth shaft.  
         [0007]     However, this design has a problem. In particular, this mechanism has a tendency to allow the second part to move out of the correct position. If the second part moves out of position, the label material will not be positioned optimally in the printer. This means that the text which is printed on the labels may not be printed on the optimum position on the label material. In other words the quality of printing on the labels may be reduced.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an aim of embodiments of the present invention to address this problem.  
         [0009]     According to a first aspect of the present invention, there is provided a spool for a supply of printing material, said spool comprising a first part, said first part comprising a shaft on which the supply of printing material is mountable, a second part, said second part having an opening and being arranged to retain a supply of printing material on the first part, said opening being arranged to engage said shaft, wherein one of said opening and the shaft is resilient and the other of the opening and the shaft has at least one part which extends towards the said one of said opening and the shaft more than at least one other part thereof to thereby cause said opening to engage with said shaft.  
         [0010]     According to a second aspect of the present invention, there is provided a cassette comprising a spool for a supply of printing material, said spool comprising a first part, said first part comprising a shaft on which the supply of printing material is mountable, a second part, said second part having an opening and being arranged to retain a supply of printing material on the first part, said opening being arranged to engage said shaft, wherein one of said opening and the shaft is resilient and the other of the opening and the shaft has at least one part which extends towards the said one of said opening and the shaft more than at least one other part thereof to thereby cause said opening to engage with said shaft.  
         [0011]     According to a third aspect of the present invention, there is provided a spool for a supply of printing material, said spool comprising a first part, said first part comprising a disc for supporting said supply of printing material and a shaft on which the supply of printing material is mountable, a second part, said second part having an opening and being arranged to retain a supply of printing material on the first part, said opening being arranged to engage said shaft, wherein said shaft comprises a plurality of grooves parallel to said shaft and in uses said opening is arranged to be received in one of said grooves.  
         [0012]     Alternately, according to another third aspect of the present invention, there is provided a spool for a supply of printing material, said spool comprising: 
        a first part, said first part comprising a disc for supporting said supply of printing material and a shaft on which the supply of printing material is mountable, wherein said shaft comprises a plurality of grooves formed on the circumference of the shaft and having a portion with a reduced radius (measured from the axis of the shaft) bounded by portions having an enlarged radius, each groove running approximately perpendicular to the axis of said shaft; and     a second part, said second part having an opening and being arranged to retain said supply of printing material on the first part, said opening being arranged to engage at least one groove on said shaft. By the term “portion with the reduced radius” we mean reduced relative to the “portion having an enlarged radius.” In practice, the radius of the portion with the reduced radius can, for example, be the same or smaller than the radius of another portion of the shaft which does not have grooves. Similarly, the radius of the portion with the enlarged radius can, for example, be the same or larger than the radius of another portion of the shaft which does not have grooves.       
 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]     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 to the accompanying drawings in which:  
         [0016]      FIG. 1  is a block diagram of a label printing system for printing information on to a label of a label supply in accordance with an embodiment of the present invention;  
         [0017]      FIG. 2  shows the spool structure embodying the present invention with the first part and the second part separated;  
         [0018]      FIG. 3  shows a spool structure of  FIG. 2  with the second part positioned on the first part;  
         [0019]      FIG. 4  shows a detail of the shaft of the first part shown in  FIG. 2  in more detail;  
         [0020]      FIG. 5  shows the construction of the second part in more detail;  
         [0021]      FIG. 6   a  shows the disc of the second part in more detail; and  
         [0022]      FIG. 6   b  shows a cross section of the disc of  FIG. 6   a  along line AA.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]      FIG. 1  schematically shows a label printing system  10  embodying the present invention.  
         [0024]     The label printing system  10  includes a label printer  100  and a computer system  120 . The label printer  100  accepts a spool of labels  102  and prints information onto labels of the spool of labels. The label material on the spool  102  may comprise discrete or die cut labels carried on a backing layer of a continuous length of material or tape onto which an image can be printed.  
         [0025]     The label printer  100  includes a top of form (TOF) sensor  104 , a label size indicator (LSI) sensor  106 , a platen  108 , a motor  109 , a print head  110 , an exit point  112  and a processor  116 . The processor  116  includes a memory module  118  for storing information including data that printer  100  collects. The TOF sensor  104  is arranged to detect TOF marks (not shown) on the label material. The TOF sensor  104  also detects the presence or absence of the label material. The LSI sensor  106  is able to detect LSI marks (not shown) on the label material and the presence or absence of the label material.  
         [0026]     The motor  109  drives the platen  108  such that the platen turns in a clockwise or counter-clockwise direction. Rotation of the platen  108  causes the label material to advance in a forward direction if the platen  108  rotates in a counter-clockwise direction or to advance in a reverse direction if the platen  108  rotates in a clockwise direction.  
         [0027]     Print head  110  prints information onto the label material. The print head  110  is arranged such that the information is printed at a pinch point  114  of the platen and the print head  110 .  
         [0028]     In one embodiment, the memory module  118  includes volatile and non-volatile memory. In another embodiment, the volatile memory is random access memory. In yet another embodiment, the non-volatile memory may include flash memory.  
         [0029]     The computer system  120  sends print requests to the label printer  100 . The label printer  100  sends information to the computer system  120  describing the types of labels contained on the label supply  102 , whether or not the label printer  100  is ready to print and the like. This information allows the computer system  120  to format print requests to the label printer  100 .  
         [0030]     In one embodiment, the label material  102  on the spool may be accommodated in a cartridge or cassette. Use of a cartridge or cassette containing the label material allows a user to insert and/or remove labels from the label printer  100  with ease. Once the cartridge or cassette is inserted into the label printer, the label printer begins processing the label material from the cartridge or cassette. The label material is processed through the label printer in substantially the same manner as if the label material was not contained with the cartridge of cassette.  
         [0031]     In preferred embodiments of the invention, the spool is not accommodated in a cassette or cartridge.  
         [0032]     It should be appreciated that depending on the printing technology used, an ink ribbon may be present. If an ink ribbon is present, then that ink ribbon may be accommodated on a spool, which may or may not be in a cassette. In the case that the ink ribbon is provided in a cassette, this may be the same or different to one accommodating the label material.  
         [0033]     The embodiment shown in  FIG. 1  shows a label printer which is used in conjunction with a computer system such as a PC. It should be appreciated that in some embodiments of the present invention, the label printer may be a stand alone printer or have two modes of operation in which it is able to operate as a stand alone printer or be controlled by a computer system.  
         [0034]      FIG. 2  shows the spool  102  used to support the label material in more detail. It should be appreciated that a similar structure for the spool for supporting ink ribbon, if present, can be used. This spool may be provided as a stand alone supply reel, in a casing or in a cassette or cartridge.  
         [0035]     The spool  102  comprises two parts  12  and  14 . The first part  14  comprises a circular disc  16  with a shaft  18  extending perpendicular to the plane of the disc  16 . The label material is in a roll and one end of the roll will be supported on the disc  16 . The shaft  18  will extend through the roll of label material. Spacer elements  20  are provided around the shaft  18 , at the end of the shaft  18  attached to the disc  16 . These spacer elements are sized such that the inner circumference of roll of tape supply will snugly fit around the ends of the spacer elements  20  remote from the shaft. The spacer elements thus maintain the orientation of the label supply roll with respect to the shaft  18 .  
         [0036]     Reference is made to  FIG. 4  which shows the outer circumference of the shaft  18  in more detail. In particular, as can be seen from  FIG. 2 , section  80  is shown in more detail in  FIG. 4 . In particular, the outer circumference of the shaft  18  comprises a plurality of grooves. The grooves  22  are generally circular and are each contained in a plane parallel to the disc  16 . The grooves may take any suitable form. It should be appreciated that in alternative embodiments of the present invention, the grooves may take the form of a screw threading.  
         [0037]     As can be seen from  FIG. 3 , the second part comprises a disc  12  which is mounted on the shaft  18 . The plane of disc  12  is arranged in use to be parallel to that of disc  14 . The disc  12  will now be described in more detail. The disc  12  can be seen in more detail in  FIGS. 5, 6   a  and  6   b . The disc  12  is arranged to be the same on both sides. Accordingly, the disc has cut out portions  24  which extend from a central opening. These cut out portions  24  are arranged to provide resilience. The opening  26  is sized so as to be slightly smaller than the outer circumference of the shaft  18 . The cut out portions  24  thus mean that when the disc  12  is pushed onto the shaft, the opening  26  can be expanded so that it can accommodate the shaft. The cut out portions  24  then provide a resilient effect urging the sides of the opening  26  against the sides of the shaft.  
         [0038]     In embodiments of the invention, the periphery of the opening  26  is sized to be accommodated in one of the grooves  22 . The opening is thus preferably sized so as to be slightly smaller than the inner circumference of the groove  20 . This means that when the edge of the opening  26  is accommodated in a groove  22 , the cut out portions  24  will urge the sides of the opening  26  into the groove  22  thus retaining the disc  12  securely in place.  
         [0039]     The cut out portions or openings can take any suitable shape and size and will depend on the material used to make the disc  12 . In one embodiment of the invention, six cut out portions are provided, arranged in pairs around the opening of the disc. The cut out portions in one embodiment of the present invention are not arranged to extend along a radius of the disc but instead extend from the opening  26  in a dog leg manner. The second part of the dog leg is arranged to cross a number of different radii of the disc. It will be appreciated by the skilled man that any suitable configuration and shape for the cut out portions can be adopted.  
         [0040]     The shape of the cut out portions is optimised to move over the grooves, but only when a predetermined minimum force is applied. When the disc is to be moved from one groove to the next, the cut out portions give in a radial direction. The torque to rotate each cut and portion about its virtual point of rotation is maximized when the second part of the dog leg of each cut out portion is generally perpendicular to the radial force on this cut out portion. For example line  29  which follows the second part of the dog leg of one cut out portion is perpendicular to the radial force along line A-A. The length of the cut out portions in combination with their shape determines the required force to move the disc from one groove to another.  
         [0041]     Additionally, the disc  12  has three pegs  28  on each side of the disc, around the opening. These pegs  28  are arranged to retain a ring shaped cap  30  in place. In practice, one cap is provided on each side of the disc  12 . The caps force the cut out portions to move in a radial direction and not in an axial direction. The caps also help retain the label supply in position. It should be appreciated that in some embodiments of the present invention one or more of these caps may be omitted. However preferred embodiments of the invention use two caps to keep the second part symmetrical and avoid that the second part is used in the wrong position.  
         [0042]     The caps comprise ring like structures which have holes, e.g., three holes  32 , to accommodate the respective pegs  28 . The inner circumference of the ring is sized so as to be slightly larger than the circumference of opening  26 . The inner circumference of the ring is advantageously at least as large as the portions of the shaft which will pass through the ring. This is because the ring  30  will not have resilience and accordingly must be big enough to accommodate the largest outer circumference of the shaft  18 .  
         [0043]     The outer circumference  30  of the ring is sized to provide a similar function to the spacers  20 . In other words, the outer circumference  30  of the ring on the lower side of the disc will be accommodated internally of the supply of labels.  
         [0044]     The spool shown in the figures is arranged to be reusable. Accordingly, the user can place a supply of labels over the shaft and put the disc  12  over the end of the shaft. The disc is pushed down until it makes contact with the label spool. Since the edge of the opening  26  is engaged in a groove, when the disc is retained in its final position, against the end of the label supply, it will remain in that position during use. Accordingly, the problems of the prior art, namely that the disc  12  moves, are avoided. In this way, it can be ensured that the position of the label supply with respect to the print head remains unchanged and accordingly the resulting quality of print can be improved as compared to the prior art.  
         [0045]     The supply of labels can be replaced by a supply of labels having a different dimension. The disc will then be moved accordingly to take into account the different supply of labels.  
         [0046]     In alternative embodiment of the present invention, the spool is arranged to be used once only. However, the same spool can be used with a range of different label supply sizes. This makes the manufacture of the label supplies much easier.  
         [0047]     In preferred embodiments of the present invention, the spool is made of a suitable plastics material. In one preferred embodiment of the present invention, the first part of the spool comprises a one piece structure.  
         [0048]     Embodiments of the present invention have described the opening of the second part as being resilient. It should be appreciated that the shaft may be of a resilient material such as rubber or plastics or may be coated with a resilient layer of material.  
         [0049]     In some embodiments of the invention, both the opening and the shaft may be resilient.  
         [0050]     In preferred embodiments of the invention, the resilience of the opening has been provided by the shape of the cut away portions. It should be appreciated that in some embodiments of the invention, the second part may be made of a resilient material.  
         [0051]     In preferred embodiments of the invention, the shaft is provided with grooves. The grooves may be replaced by at least one projection or at least one recess which is engagable by the opening.  
         [0052]     In one embodiment of the invention, the support disc of the first part may be omitted. For example, the second part may be provided with one cap only. The diameter of the shaft would then match the internal dimension of the label supply. The second part could then be supported on the shaft with the cap to the outside. Alternatively or additionally at least part of the function of the support disc may be provided by the label printer.