DEVICE FOR INDICATING A CERTAIN LIQUID LEVEL IN A CONTAINER

Abstract: A device for indicating when the level of liquid in a container has dropped to a specific level is disclosed. Liquid is drawn from the container via a pump unit (9) through a withdrawal pipe (6). A return conduit (12) is in communication with said withdrawal pipe (6) downstream of said pump unit (9) and, via an ejector assembly (16), causes the liquid to return to the container (1) via a recirculation conduit (7). The ejector assembly (16) is accomodated in a cavity (17) which is in communication with an indicator bowl (8) via a suction tube (18). At least one conduit (3) extends from the indicator bowl into the container (1), with the conduit (3) having its lower end opening at the level in the container which is to be indicated. So long as there is liquid in the container above the lower opening of the conduit (3), the indicator bowl (8) is filled with liquid. Once the liquid in the container (1) drops below the lower opening in the conduit (3), the liquid in the indicator bowl runs into the container (1), thereby indicating that the liquid in the container (1) has reached the predetermined level.

Description: 5 TITLE: Device for indicating a certain liquid level in a container TECHNICAL FIELD: The present invention relates to a device for indicating a 10 certain liquid level in a container according to the preamble of claim 1. The invention further relates to the use of such a device in an ink-jet printer apparatus. BACKGROUND OF THE INVENTION: 15 When operating equipment of the type which is supplied with a liquid from a container, it is often extremely important that the container not be allowed to run dry. Thus, a means of being able to identify when the contents of the container are nearly exhausted is needed. If a transparent 20 container is used, then the operator of the equipment can easily see the liquid level therein, though if the liquid is only very slowly consumed it may be difficult for the operator to identify just when the container should be exchanged for a full one. If the liquid is in an opaque 25 container, then some sort of additional level indicator means is required. One way would be to provide each container with its own built-in level indicator, though in the case of disposable containers the cost of such is prohibitive. 30 SUMMARY OF THE INVENTION: Thus, the object of the present invention is to provide a device for indicating when the level of liquid in a container drops below a predetermined value, which device 35 can be repeatedly used and is easily fitted to the container. This object is achieved by a device according to claim 1. With such a device, when there is sufficient liquid in the container, the indicator bowl is full of the liquid. When, however, the level of liquid in the container drops below a critical level, the indicator bowl rapidly empties, thereby signalling to the operator that the container must be exchanged or replenished. Preferred embodiments of the present invention are detailed in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS: A detailed description of embodiments according to the present invention will be given in the following by way of example only with reference to the drawings in which: Fig. 1 is a schematic representation of an embodiment of the device according to the invention attached to a container of liquid before any liquid is drawn from the container; Fig. 2 is a schematic representation of a preferred embodiment of the present invention connected to a printhead unit of a printing device. Fig. 3 is a schematic sketch showing the principle of operation of an ejector assembly used in the present invention, Fig. 4 shows the device according to Fig. 1 in a steady- state operating mode, and Fig. 5 shows the same device when the liquid level drops below that which is to be indicated. BEST MODE OF CARRYING OUT THE INVENTION: In the figures, a container of liquid is indicated by reference numeral 1. When this liquid is required for use, a connector head 2 is attached to the top of the container by an operator in a conventional manner, e.g. via a screw fit, push fit, etc. The connector head 2 is provided with a plurality of through-bores to which a corresponding number of conduits 3, 4, 5, 6, 7 are connected at either end of said through- bores. Alternatively the through-bores may allow conduits to pass therethrough, as schematically represented in the drawings. In a preferred embodiment shown in Fig. 2, the conduits which extend into the container 1 are surrounded by a section of tube 20 which seals against a ring-seal 21 in the upper surface of the container 1 . Thus, when the connector head 2 is to be attached to the container 1, this section of tube 20 is pushed through the ring-seal 21 in the upper surface of the container, thereby ensuring a rapid yet secure attachment of the connector head. Furthermore, any risk of damage to the conduits 3,4,5,6,7 during insertion is greatly reduced. It is also possible that the section of tube can replace the function of one of the conduits, for example the conduit 5, as shown in Fig. 2. Accordingly, the section of tube 20 is provided with a through hole 22 positioned above the level of liquid in the container. Conduits 3 and 4 pass from the container 1 substantially vertically through the connector head 2 as shown in the drawings and terminate within an indicator bowl 8 sealingly affixed to an upper surface of the connector head 2. The indicator bowl 8 is made from a suitable, transparent or semi-transparent material such as glass or plexiglass so that any liquid contents therein are easily visible. In the container 1, conduit 3 has its lower opening at the height above the base of the container which corresponds to the selected indication level of the liquid. Conduit 4, meanwhile has its lower opening somewhat closer of the base of the container 1. Conduit 5 is optional and in the shown embodiment it provides a connection between the space in the container above the liquid surface and atmosphere. The purpose of this is to equalize the pressure in the container and, as such, any gaseous medium can be used. Conduit 6 has its lower opening at approximately the same level as that of conduit 4. Conduit 6 serves as a withdrawal pipe for withdrawing the liquid from the container and is thus connected to the suction side of a liquid pump unit 9 mounted exteriorally of the container. A delivery pipe 10 runs from the pressure side of the pump unit to a T-connector 11. One conduit 12 from the T- connector forms a part of a recirculation circuit, whilst the other conduit 13 leads to a place of consumption, in this case the print-head 23 of an ink-jet printer. To control the pressure of liquid supplied to the print-head, the pumping pressure of the pump unit 9 may be varied, as schematically indicated in the drawings. The return conduit 12 terminates with a nozzle 15 of an ejector assembly 16 mounted in the connector head 2. The ejector assembly 16 further comprises a cavity 17 from which a suction tube 18 extends into the indicator bowl 8 to a level almost corresponding to the height of said bowl. As is most clearly shown in Fig. 3, a passage forming a second nozzle 19, coaxial with, and of larger diameter than, the first nozzle 15, is provided in the end of conduit 7. Conduit 7 is of larger diameter than the second nozzle 19 and passes through the connector head 2 to emerge into the container to terminate with an opening at approximately the same level as the openings to conduits 4 and 6. This assures that liquid flowing into the container 1 via the conduit 7 is discharged below the level of the liquid already in the container, thereby preventing undesireable frothing of the contents of the container. The method for operation of the level indication device according to the present invention will now be explained with particular reference to Figs. 1, 4 and 5. In Fig. 1, the connector head 2 is shown immediately after having being attaching to the container 1 for the appropriate liquid. In this state, the space above the surface of the liquid in the container is occupied with air at atmospheric pressure. Similarly, the indicator bowl 8 also contains air at substantially atmospheric pressure. The pump 9 is now actuated and liquid is drawn up the withdrawal pipe 6 and through the pump 9 , the delivery tube 10 to the T-connector 11. A major quantity of liquid then flows into the return conduit 12, and the remainder flows under pressure through conduit 13 to its place of consumption. The liquid in the return conduit 12 reaches the ejector assembly 16 in the connector head 2 it is forced at high velocity through the nozzle 15, thereby forming a jet of liquid directed towards the second nozzle 19 in the conduit 7. As is illustrated in Fig. 3, due to the high velocity of the liquid through the nozzle 15 across the cavity 17 into the second nozzle 19, a partial vacuum, or region of lower pressure, is created in the vicinity of the jet of liquid emerging from said nozzle 15. This low pressure region draws the air from the indicator bowl 8 via suction tube 18 into the cavity 17. The air is then removed in the flow of liquid along conduit 7 to the container 1. Due to the evacuation of air from the indicator bowl 8, a sub-atmospheric pressure condition is created therein. Thus, liquid is drawn from the container 1 via the conduits 3 and 4 to the indicator bowl. The indicator bowl fills with liquid until the opening in the upper end of the suction tube 18 is reached. Liquid then flows down the suction tube into the cavity 17 where it is recirculated back to the container 1. This condition is shown in Fig. 4. The operator of the equipment can now see that there is sufficient liquid in the container to allow the equipment to carry on functioning. Advantageously, a float 24 may be included in the indicator bowl to help identify when there is liquid in the bowl. The float may be provided with an electrical contact on its surface facing the upper sur ace of the indicator bowl for cooperation with a corresponding contact positioned thereon, the purpose of which will be explained in the following. The above-mentioned recirculation condition is maintained until the level of liquid in the container 1 falls to just below the level of the lower opening in the conduit 3, i.e. to a level at which the operator should be informed that a replenishment or change of the container is shortly required. This opening is then open to the air in the space above the surface of the liquid. Since the lower end of the other conduit 4 which is in connection with the indicator bowl 8 is still submerged in the liquid in the container, the liquid in the conduit 3 runs up into the indicator bowl 8, allowing air to flow up the conduit 3 and into said bowl 8. As the air enters the indicator bowl, it displaces the liquid therein which is made to flow along conduit 4 to the container 1. This condition is shown in Fig. 5. If the volume of the indicator bowl is chosen to be very much smaller than the volume of the container 1, then the whole indicator bowl 8 is emptied of liquid in a matter of moments. This rapid emptying of the indicator bowl is clearly visible to the operator who is thus informed that the liquid in the container has reached a level at which the container must be replenished or exchanged. To maintain the supply of liquid to the point of consumption, a plurality of containers may be selectively connectable to the pump unit 9 so that when one container is emptied, another may be connected to the system at the throw of a switch. If a float is employed as described above, then the electrical contacts thereon can form the switch for connecting another container when this contact is broken. Such an arrangement is not shown in the drawings. The emptied container can then be decoupled from the connector head and replaced by a full container. A pressure differential sensing means can also be arranged in the indicator bowl which measures the difference in pressure between the indicator bowl and the container 1. Since the difference in pressure is directly proportional to the difference in liquid levels, the depth of remaining liquid in the container 1 can be easily determined. Naturally, the invention is not restricted to the embodiments described above, but may be varied within the scope of the appended claims. For example, although in the drawings two conduits 3,4 pass from the container l into the indicator bowl 8, with certain liquids the device may also function with just one conduit 3 whose lower opening is at the height above the base of the container 1 which corresponds to the selected indicaton level of the liquid. Whether the device will work satisfactorily with one conduit depends upon the viscocity of the liquid in the container 1 and the capillary force generated in the conduit 3 when the level of liquid drops below the lower opening of the conduit 3. In a further not shown embodiment, the outlet from the pump unit 9 may be directly connected to the nozzle 15 of the ejector assembly 16, with liquid being drawn from the container for use at its place of consumption via, for example, an opening in the base of the container. In other words, the pump unit 9 may be used solely to operate the ejector assembly 16. Furthermore, the T-connector 11 and/or the pump unit 9 can be incorporated in/on the connector head 2. Finally, the indicator bowl need not be mounted on the connector head 2, but may be positioned at closer proximity to the operator.

Claims: CLAIMS: 1. A device for indicating a certain liquid level in a container (1) whereby a pump unit (9) is arranged to withdraw liquid from said container (1) via a withdrawal pipe (6), c h a r a c t e r i z e d i n that said device comprises an indicator bowl (8) in direct communication with the liquid in said container (1) via at least one conduit (3) , the lower opening of said conduit (3) being arranged at the level of the liquid in the container which is to be indicated, said indicator bowl also being in communication with a cavity (17) via a suction tube (18) extending from an upper region of said indicator bowl (8) to said cavity, which cavity (17) accommodates an ejector assembly (16) comprising a nozzle (15) at one end of a return conduit (12) whose other end is in communication with said withdrawal pipe (6) downstream of said pump unit (9) , said nozzle (15) being arranged to form a jet of liquid passing across a region of said cavity (17) and directed towards a substantially coaxial second nozzle (19) of larger diameter than said first nozzle (15) , said second nozzle being in communication with a recirculation conduit (7) running from the second nozzle to said container (1) . 2. A device according to claim 1, c h a r a c ¬ t e r i z e d i n that said indicator bowl (8) is sealingly mounted on a connector head (2) which is releasably attached to said container (1) , and, when attached to the container, said indicator bowl is in communication with the contents thereof. 3. A device according to claim l or 2, c h a r a c¬ t e r i z e d i n that a second conduit (4) runs between said indicator bowl (8) and the container (1) and which second conduit (4) has its lower opening arranged closer to the base of the container (1) than that of the first said conduit (3) . 4. A device according to any of claims 1 to 3, c h a r a c t e r i z e d i n that said cavity (17) and ejector assembly (16) are accommodated within said connector head (2) . 5. A device according to any of the previous claims, c h a r a c t e r i z e d i n that a conduit (5) is provided between atmosphere and the interior of the container (1) . 6. A device according to any of the previous claims, c h a r a c t e r i z e d i n that a pressure differential sensing means is located in the indicator bowl (8) . 7. A device according to any of claims 2 to 6, c h a r a c t e r i s e d i n that the conduits extending from said connector head (2) to said container (1) are enclosed by a section of tube (20) . 8. A device according to claim 7, c h a r a c ¬ t e r i z e d i n that said section of tube (20) forms a part of said conduit (5) which connects the interior of the container (1) to atmosphere. 9. The use of the device according to any of the previous claims for indicating when a certain level of liquid has been reached in a container of ink for application in an ink-jet printer apparatus.

Inventors: VONASEK JIRI, VONASEK, JIRI
Applicants: MARKPOINT SYSTEM AB
Application year: 1991
Main classification: G01F23
IPC codes: B41J2, G01F23