Abstract:
An ink dispensing device for selectively dispensing ink pellets into an ink reservoir which comprises casing and a slide, said casing and said slide defining therebetween a first sluice and a second sluice, each of which is adapted to accommodate at least one ink pellet, and means for moving the slide and/or the casing relative to each other whereby a pellet is discharged from the first sluice into the second sluice and simultaneously a pellet is discharged from the second sluice into the ink reservoir.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ink jet device comprising an ink reservoir and a dispenser for ink pellets, wherein the dispenser comprises a sluice for discharging the pellets one by one into the ink reservoir. 
     In an ink jet device, such as an ink jet printer, an ink reservoir is incorporated in the printhead or in a separate cartridge and serves to accommodate a certain amount of liquid ink which is to be supplied to a nozzle system of the printhead. In case of a hot melt ink jet device the ink reservoir is heated in order to keep the temperature of the ink above its melting point, e.g., at a temperature of about 100° C. or more. Research Disclosure Bulletin, March 1999, No. 41973, pages 374 to 376 discloses an ink jet device in which hot melt ink can be supplied in pellet or tablet form. The dispenser used for supplying the ink tablets one by one into the ink reservoir of the printhead may be mounted on the same carriage as the printhead so as to travel back and forth along the printing medium. Alternatively, the dispenser or at least an actuating mechanism thereof may be disposed stationarily above one of the end positions of the carriage, so that an ink tablet can be supplied into the reservoir each time the carriage has performed a complete stroke and stops in the end position. 
     The supply of ink in tablet form has the advantage that the amount of ink to be melted in the ink reservoir can be metered with high precision and, accordingly, the temperature of the molten ink within the ink reservoir can be kept stable. 
     The dispenser of known ink jet devices has a simple sluice mechanism of the type generally known in dispensers of candy. Such sluice mechanisms are, however, not fully reliable, and it may happen that the dispenser, although it has been actuated, fails to discharge a tablet. This may give rise to a shortage of ink, in particular in the case where the dispenser can be actuated only after each stroke of the carriage. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the present invention to provide an ink jet device in which ink tablets can be supplied more reliably. 
     In order to achieve this object, there is provided an ink jet device wherein the dispenser comprises an output chamber for accommodating a single pellet discharged from the sluice, and a shutter for opening and closing the output chamber towards the ink reservoir. 
     According to the present invention, the pellet or tablet which needs to be timely supplied to the ink reservoir is held readily available in the output chamber and can reliably be transferred into the ink reservoir, simply by opening the shutter. Simultaneously or at a later instant, the sluice mechanism is actuated in order to supply another single pellet to the output chamber. If the sluice mechanism fails, it can be actuated repeatedly until a pellet is discharged into the output chamber, so that the next pellet will be reliably available when it is needed. 
     As is generally known, the dispenser comprises a storage chamber for accommodating a number of tablets and a slide movably disposed in said chamber and forming the sluice mechanism together with a portion of a bottom wall of the storage chamber. Preferably, the output chamber is also formed by a portion of the bottom wall of the storage chamber and a portion of the slide, and the shutter is also formed by a portion of the slide of the sluice mechanism, so that the shutter and the sluice mechanism can be easily actuated in a single operation. More specifically, the shutter and the output chamber may form a second sluice which has essentially the same construction as the first sluice. The reason why the sluice mechanism is not fully reliable is mainly due to the fact that a plurality of tablets present in a supply passage above the sluice tend to become clogged in the supply passage. Since the second sluice will not receive more than a single tablet at a time, a reliable and fail-safe function of the second sluice is assured. 
     In a preferred embodiment, a sensor, e.g., an optical sensor, is provided for detecting the presence or absence of a tablet in the output chamber, and when no tablet is detected after the sluice mechanism has been actuated, a signal is generated for actuating the sluice mechanism once again. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a longitudinal section of an ink reservoir and an ink dispenser of an ink jet device; and 
     FIGS. 2 to  6  are sectional views of the ink dispenser in different operating states. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An ink reservoir  10  in an ink cartridge or a printhead of a hot melt ink jet printer is formed by a casing having a bottom wall  12 , two parallel longer side walls  14  and two parallel shorter side walls  16 . In the top part of the ink reservoir, the side walls  14 , 16  define an inlet port  18  which has an elongated rectangular cross-section when viewed from above. Outlet ports  20 , through which the ink is supplied to a nozzle system (not shown) of the printhead, are formed as elongate slots in the side walls  14  close to the bottom wall  12 . 
     The inlet port  18  is separated from the lower portion of the ink reservoir including the outlet ports  20  by a tubular filter element  22  which can also be flat. The filter element is inserted into the ink reservoir through an opening  24  formed in one of the side walls  16  and closed by a plug  26 . In the shown embodiment, a rod-like sensor element  28  is embedded in the plug  26  and extends coaxially in the tubular filter element. This sensor element  28  may, for example, serve as a level detector for detecting the level of the ink liquid in the ink reservoir and/or as a temperature sensor for monitoring the temperature of the hot-melt ink. 
     The ink reservoir  10  is heated, and the ink is supplied in a solid state in the form of small pellets or tablets which are so sized that the supply of a single tablet which then has to be melted in the ink reservoir will not cause a significant change in the temperature of the liquid ink. 
     FIGS. 1 and 2 further show an ink dispenser  30  which is used for supplying ink tablets  32  into the ink reservoir. In the shown embodiment the ink tablets  32  have a flat cylindrical shape. The dispenser  30  has a casing  34  defining a storage chamber  36  that is sealingly closed by a cover  38 . The lower portion of the storage chamber  36  which can accommodate a large number of tablets  32  is formed as a narrow funnel  40 , the width of which (in the direction normal to the plane of the drawing) is only slightly larger than the thickness of the tablets, so that the tablets are oriented as is shown in the drawing. 
     The bottom of the funnel  40  is formed by inclined walls which converge downwardly towards a narrow passage  42  the width of which is only slightly larger than the diameter of the tablets  32  and still slightly decreases towards the bottom end, so that only one tablet can pass through the passage  42  at a time. One of the inclined walls of the bottom of the funnel  40  and one wall of the passage  42  are formed by the casing  34 , whereas the other of the inclined walls of the funnel and the adjacent wall of the passage  42  are formed by a slide  44  which is guided in the casing  34  and the cover  38  and is slidingly movable in the vertical direction. The slide  44  is biased upwardly by a pressing member such as a spring (not shown) so that it is normally held in the position shown in FIGS. 1 and 2. 
     At the lower end of the passage  42  the slide  44  and the casing  34  form a first sluice  46  and a second sluice  48 . 
     The first sluice  46  comprises a cavity  50  formed in the slide  44  and shaped to accommodate a single tablet. The lower wall of the cavity  50  merges into a downwardly inclined ramp surface  52 . When the slide  44  is in the position shown in FIG. 1, the ramp surface  52  and another ramp surface  54  on the opposing side of the passage  42  converge and hold the lower end of the first sluice  46  closed. 
     The second sluice  48  has essentially the same configuration as the first sluice and, accordingly, comprises another cavity formed in the slide  44  and shaped to accommodate a single tablet. This cavity serves as an output chamber  56  for the dispenser. The lower wall of the output chamber  56  merges into a downwardly inclined ramp surface  58 . When the slide  44  is in the position shown in FIGS. 1 and 2, the ramp surface  58  and the other ramp surface formed by the nose  60  of the casing  34  converge and hold the lower end of the second sluice  48  in a closed position. Thus, the ramp surface  58  and the nose  60  cooperate to form a shutter for opening and shutting the second sluice  48 . 
     The top portion of the slide  44  projects through the cover  38  and forms a push button  62  which can be depressed by means of an actuator  64 . 
     The output chamber  56  has an optical sensor  66  or at least a transparent window for an optical sensor which detects the presence or absence of a tablet  32  in the output chamber and delivers a detection signal to a control system for the actuator  64 . Also a mechanical switch could be used. 
     The bottom wall of the casing  34  forms a projection  68  which fits into the open end of the ink reservoir  10 , as is shown in FIG.  1 . When the dispenser  30  is disposed on the ink reservoir  10  in this manner and the push button  62  is depressed, the slide  44  moves downward, as is shown in FIGS. 3 and 4. 
     FIG. 3 shows that the lowermost one of the tablets  32  is deflected by the ramp surface  54  so that it is accommodated in the cavity  50  and can move downward into the second sluice  48 . 
     FIG. 4 shows the slide  44  in its lower extreme position. In this state, the ramp surfaces  52  and  54  are vertically offset from one another so that the tablet  32  that has previously been accommodated in the cavity  50  is now dropped into the second sluice via the ramp surface  52 . At the same time, the tapering walls of the passage  42  prevent the next tablet from entering into the cavity  50 . Thus, it is assured that only a single tablet is supplied to the second sluice  48 . This tablet is at first caught by the nose  60  in a position above the output chamber  56 , as is shown in FIG.  4 . 
     When the push button  62  is released again, the spring-biased slide  44  moves upward, and when it reaches the position shown in FIG. 5, the next tablet enters into the cavity  50  so that the dispenser is ready for a subsequent supply operation. At the same time the tablet that has dropped into the second sluice  48  is accommodated in the output chamber  56 . 
     The tablet in the output chamber  56  is supported on the one hand by the ramp surface  58  of the slide  44  and on the other hand by the ramp surface of the nose  60  and is held in a position in front of the optical sensor  66 . 
     Once the slide  44  has been actuated in the manner described above, the sensor  66  should indicate the presence of a tablet  32  in the output chamber  56 . When however, the first sluice  46  has failed to supply a tablet, this is also indicated by the sensor  66 , and the actuator  64  is operated once again in order to make another attempt to supply a tablet into the second sluice  48 . This attempt may be repeated as often as required. 
     The state illustrated in FIG. 5 corresponds to the normal operating state of the dispenser. In this state, one tablet is accommodated in the output chamber  56  of the second sluice  48  and another tablet is present in the cavity  50  of the first sluice  46 . When it is detected, for example by means of the sensor element  28 , that another tablet needs to be supplied into the ink reservoir  10 , the slide  44  is depressed once again, as is shown in FIG.  6 . Then the tablet  32  which has been in a stand-by position in the second sluice  48  is reliably released into the inlet port  18  of the ink reservoir  10 , and simultaneously the next tablet is transferred from the first sluice  46  to the second sluice  48 . This cycle is repeated whenever there is demand for another ink tablet. Should the first sluice  46  fail to supply a tablet into the second sluice  48 , the actuator  64  will cause the slide  44  to perform one or more extra strokes in response to the signal supplied from the sensor  66 . 
     The dispenser  30  and the actuator  64  may be permanently mounted on the ink reservoir  10  when the ink jet device is operating. In the shown embodiment, however, the dispenser  30  is removably disposed on the ink reservoir  10 . The dispenser can be manufactured at low costs from cheap recycling materials such as recycled plastic material and may form a disposable refill package in which the ink tablets are delivered to the user. The dispenser mostly forms part of the ink reservoir and moves together with the ink jet head on the carriage. However, it is also possible to fix this dispenser at the frame of the print-engine, thereby minimizing the weight of the carriage. 
     The actuator  64  is preferably held at a machine frame (not shown) of the printer, so that it need not be removed when the refill package is replaced. In this case, the actuator is ready to depress the push button  62  only when the carriage on which the ink reservoir  10  and the dispenser  30  are mounted stops in a predetermined position, e.g. at one end of the carriage stroke. The amount of ink contained in a single tablet  32  will be sufficient for a plurality of carriage strokes, so that the actuator will normally be operated only every second, third, or n-th stroke of the carriage. Only when the sensor  66  detects that the output chamber  56  is empty will the actuator  64  be operated again after the next stroke of the carriage. It is also possible to hold the separation unit at the machine frame. In this case only a cassette holding the pills or pellets or tablets has to be replaced. 
     Similarly, the sensor  66  can be disposed stationarily at the frame of the printer in a position which corresponds to the position of the transparent window of the output chamber  56  when the carriage stops in the position in which the push button  62  is aligned with the actuator  64 . 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.