APPARATUS AND METHOD FOR THE DOSED DISPENSING OF A LIQUID

Abstract

The invention relates to an apparatus for the dosed dispensing of a liquid, comprising a dispensing vessel (10) which has a dispensing opening (12) for the liquid and a compressed-air port (14), a compressed-air system (16) for the provision of compressed air, a connecting line (15) by way of which the compressed-air port (14) of the dispensing vessel (10) is connected to the compressed-air system (16); and a sensor device for determining the fill level of the liquid in the dispensing vessel (10). According to the invention, the sensor device is connected by way of the connecting line (15) to the dispensing vessel (10). The dispensing opening (12) is closable. The invention also relates to a method using the apparatus.

Claims

1. An apparatus for the dosed dispensing of a liquid, comprising a dispensing vessel (10) which has a dispensing opening (12) for the liquid and a compressed-air port (14); a compressed-air system (16) for the provision of compressed air; a connecting line (15) by way of which the compressed-air port (14) of the dispensing vessel (10) is connected to the compressed-air system (16); and a sensor device for determining the fill level of the liquid in the dispensing vessel (10), characterized in that the sensor device is connected by way of the connecting line (15) to the dispensing vessel (10), and in that the dispensing opening (12) is closable.

2. The apparatus according to claim 1, characterized in that the sensor device comprises a pressure sensor (34) which measures the pressure in the connecting line (15) and/or in the dispensing vessel (10).

3. The apparatus according to claim 1, characterized in that the sensor device comprises an air quantity sensor (38) which measures the quantity of air flowing through or into the connecting line (15).

4. The apparatus according to claim 2, characterized in that computer means are provided which calculate the fill level in the dispensing vessel (10) from the measurement result of the pressure sensor (34) and/or of the air quantity sensor (38).

5. The apparatus according to claim 1, characterized in that the compressed-air system (16) comprises a pneumatic cylinder (29) which is connected to the connecting line (15).

6. The apparatus according to claim 1, characterized in that the compressed-air system (16) comprises a throttle valve (35) which is connected to the connecting line.

7. The apparatus according to claim 1, characterized in that the pressure system (16) comprises a proportional valve (39) which is connected to the connecting line (15).

8. A method for the dosed dispensing of liquid using an apparatus according to claim 1, wherein, for dispensing liquid, the apparatus is operated in a dispensing mode in which the dispensing opening (12) is open, and wherein, for determining the fill level of liquid in the dispensing vessel (10), the apparatus is operated in a test mode in which the dispensing opening (12) is closed.

9. The method according to claim 8, characterized in that, in the test mode, a pressure change in the dispensing vessel (10) is brought about by the pressure system.

10. The method according to claim 9, characterized in that the pressure change is due to a predetermined change in volume, and the pressure change and/or the pressure in the dispensing vessel (10) is measured.

11. The method according to claim 10, characterized in that a reference pressure change is determined for a reference fill level in the dispensing vessel (10), a measured pressure change being compared with the reference pressure change.

12. The method according to claim 9, characterized in that a predetermined value is predefined for the pressure change or for a pressure in the dispensing vessel (10) and the quantity of air required for the pressure change or for building up the pressure is measured.

13. The method according to claim 12, characterized in that a reference quantity of air is determined for a reference fill level in the dispensing vessel (10), a measured quantity of air being compared with the reference quantity of air.

14. The method according to claim 8, characterized in that the apparatus is operated for a given time in the dispensing mode and then in the test mode in order to determine, via a change in fill level, the quantity dispensed in the given time.

15. The apparatus according to claim 8, characterized in that the dispensing vessel (10) is subjected to different pressures in the dispensing mode depending on the fill level.

Description

[0028] The invention will be explained in greater detail with reference to the exemplary embodiments shown in the drawing, in which:

[0029] FIG. 1 shows a block diagram for a first exemplary embodiment of the apparatus according to the invention;

[0030] FIG. 2 shows a block diagram for a second exemplary embodiment, and

[0031] FIG. 3 shows a block diagram for a third exemplary embodiment.

[0032] FIG. 1 shows a simplified block diagram for a first exemplary embodiment of the invention. A dispensing vessel 10, which is air-tight and rigid, is partially filled with a liquid. A fill level line 11 indicates the fill level of the liquid within the dispensing vessel 10. Air is located above the fill level line 11, and the liquid is located below said line. An air-filled volume V.sub.L (air volume) and a liquid-filled volume V.sub.F (liquid volume) are thus obtained in the dispensing vessel 10 depending on the fill level (see fill level line 11). While the volumes V.sub.L and V.sub.F depend on the fill level in the dispensing vessel 10 and are therefore variable, the sum of the two volumes V.sub.L, V.sub.F is constant and corresponds to a total volume of the dispensing vessel V.sub.G.

[0033] When the dispensing vessel 10 is in the use position shown in FIG. 1, a dispensing opening 12 for the liquid is provided at a lower end of the dispensing vessel. A shut-off valve 13 is assigned to the dispensing opening 12. The dispensing opening 12 can be opened and closed by the shut-off valve 13.

[0034] A compressed-air port 14 is provided at an end opposite the dispensing opening 12. Connected to said compressed-air port 14 is a connecting line 15 which connects the dispensing vessel 10 to a compressed-air system 16. In the exemplary embodiment shown here, the compressed-air port 14 and the dispensing opening 12 are arranged diametrically to one another, which is not absolutely necessary. It is sufficient if the dispensing opening 12 is positioned in such a way that the liquid is in front of this dispensing opening 12 and dispensing without air is possible. In the present case, gravity ensures this.

[0035] When the air-tight dispensing vessel 10 is pressurized by the compressed-air system 16 via the connecting line 15 and the compressed-air port 14, liquid is pressed out of the dispensing vessel 10 through the dispensing opening 12 and the open shut-off valve 13. By way of example, the vessel 10 may be a glue cartridge containing PUR hot-melt adhesive. Hot-melt adhesive can thus be applied by the apparatus to components or surfaces to be bonded. The dispensing vessel 10 must be kept at a temperature such that the hot-melt adhesive remains liquid. It may thus have heating means or connections for a heating medium for heating the liquid in the dispensing vessel.

[0036] The compressed-air system 16 has a first switching valve 17 which is configured as a 3/2-way valve. The switching valve 17 can be switched into a first switching position and into a second switching position. FIG. 1 shows the first switching position, which corresponds to a spring-loaded rest position of the first switching valve 17. This rest position occurs when no signal current is present at the first switching valve (normally closed). In the rest position, a first inlet 18 is connected to an outlet 19. In the second switching position, the first inlet 18 and the outlet 19 are isolated from one another. In this case, in the nomenclature of the block diagram, the outlet 19 is connected to a second inlet 20 of the first switching valve, the second inlet 20 being configured as a blind inlet. In fact, in the second switching position, the first switching valve is thus closed so that no air can escape through the outlet 19 via a node point 21.

[0037] A manually adjustable pressure regulator 22 is disposed upstream of the first inlet 18 of the first switching valve 17. A pressure P.sub.M, which is provided by a pressure supply 24, is applied to an inlet 23 of the pressure regulator 22. From the main pressure P.sub.M, the pressure regulator 22 generates an adjustable pressure P.sub.E. Via a (pressure) line 25, which connects the outlet 24 of the pressure regulator 22 to the first inlet 18 of the first switching valve 17, this pressure P.sub.E can be switched to the dispensing vessel 10 by way of the first switching valve 17. When the shut-off valve 13 is open, liquid is thus pushed out of the dispensing vessel 10 through the dispensing opening 12. If the dispensing of liquid is to be interrupted, the shut-off valve 13 is closed.

[0038] The compressed-air system 16 has a second switching valve 26. This switching valve 26 is also configured as a 3/2-way valve. A first inlet 27 of the second switching valve 26 is connected to the pressure supply 24. An outlet 28 of the second switching valve 26 can be depressurized via a second inlet 29 when the second switching valve 26 is in the switching position shown in FIG. 1 (normally open). This is a first switching position or a spring-loaded rest position. When a signal current is present, the second switching valve 26 switches into a second switching position, in which the first inlet 27 is connected to the outlet 28. The main pressure P.sub.M is thus applied to the outlet 28 of the second switching valve 26.

[0039] Also provided is a pneumatic cylinder 40 which is disposed downstream of the second switching valve 26. The cylinder 40 has an inlet 30 and an outlet 31. If the main pressure P.sub.M is switched to the inlet 30 of the cylinder 40 by way of the second switching valve 26, a piston 32 of the cylinder 40 pushes the air located in the cylinder 40 into the line 32 via the outlet 31. If it is assumed that the cylinder volume V.sub.Z corresponds to the volume that can be pushed out of the cylinder 40 by the piston, the remaining cylinder volume is zero in an upper dead center of the piston 32.

[0040] Connected to the pressure line 33 is a pressure sensor 34, by which the pressure in the pressure line 33 and thus also in the dispensing vessel 10 can be measured.

[0041] The apparatus can be operated in a dispensing mode and in a test mode. In the dispensing mode, the shut-off valve 13 is open. The switching valves 17, 26 are in the switching positions shown in FIG. 1. Liquid is pushed out of the dispensing vessel 10 via the dispensing opening 12 by the pressure P.sub.E generated by the pressure regulator 22. By switching the first switching valve 17, the dispensing can be timed. For example, if the first switching valve 17 is in the open first switching position for 10 seconds, then liquid will be dispensed from the dispensing vessel 10 for these 10 seconds.

[0042] In the test mode, the first switching valve 17 is in the second switching position, in which the outlet 19 is closed. The shut-off valve is closed. At an instant t.sub.1, at which the piston 32 is in the position shown in FIG. 1, a pressure P.sub.1 is determined by the pressure sensor 34. At this instant, a test volume V.sub.1 of a test system is composed of the air volume V.sub.L in the dispensing vessel 10 and the cylinder volume V.sub.Z in the cylinder 40. The volumes V.sub.15, V.sub.33 of the lines 15, 33 or of all line sections located between the cylinder 40 and the dispensing vessel 10 must also be taken into account. The second switching valve 26 is then brought into the second switching position so that the piston 32 pushes the volume V.sub.Z out of the cylinder 40. At the end of the movement of the piston 32 at an instant t.sub.2, a new pressure P.sub.2 thus exists in the dispensing vessel, this new pressure being greater than the pressure P.sub.1 since the test volume of the test system is now smaller. The volume V.sub.2 at instant t.sub.2 corresponds to the volume V.sub.1 minus V.sub.Z. According to the general gas equation (see equation (1)):

(V.sub.L+V.sub.Z+V.sub.33+V.sub.15).Math.P.sub.1=(V.sub.L+V.sub.33+V.sub.15).Math.P.sub.2 (2)

where V.sub.L air volume in the dispensing vessel;

[0043] V.sub.Z cylinder volume;

[0044] V.sub.33 volume of the pressure line 33;

[0045] V.sub.15 volume of the connecting line 15;

[0046] P.sub.1 pressure at the instant t.sub.1;

[0047] P.sub.2 pressure at the instant t.sub.2.

[0048] From equation 2, the air volume V.sub.L can be calculated by transformation. Knowing the total volume V.sub.G of the dispensing vessel 10, the quantity V.sub.F or the fill level to be determined can be obtained directly from the air volume V.sub.L.

[0049] FIG. 2 shows a block diagram for a further exemplary embodiment. Components or features which are similar or identical to components or features of FIG. 1 are provided with the same reference signs. This also applies to the exemplary embodiment shown in FIG. 3.

[0050] The basic structure of the apparatus shown in FIG. 2 corresponds to the structure of the apparatus 1. Reference is therefore made to what has been stated in respect of FIG. 1. Instead of the cylinder 40 shown in FIG. 1, a throttle valve 35 having an inlet 36 and an outlet 37 is disposed downstream of the second switching valve 26. In the first switching position of the second switching valve 26, as is also the case in the exemplary embodiment of FIG. 1, the outlet 28 is connected to the second inlet 29. However, the outlet 28 is not depressurized as a result but rather is closed in an airtight manner.

[0051] Provided in addition to the pressure sensor 34 is an air quantity sensor 38 which measures the quantity of air flowing through the compressed-air line 33. The line 33 connects the outlet 37 of the throttle valve 35 to the connecting line 15.

[0052] The structure differing from the first exemplary embodiment has essentially no effect on the operation of the apparatus of FIG. 2 in the dispensing mode. In other words, the second exemplary embodiment does not differ from the first exemplary embodiment with regard to use in the dispensing mode. In the test mode, on the other hand, the test system is reduced by a predetermined volume V.sub.Z, but a particular quantity of air, which is detected by the air quantity sensor 38, is supplied to the test system. The additional quantity of air leads to a particular pressure increase. Again, the state variables are determined before (instant t.sub.1) and after (instant t.sub.2). The less the dispensing vessel 10 is filled with the liquid, the greater the quantity of air that must be supplied to the test system in order to achieve a particular pressure increase. The quantity of air required for this is thus a measure for the air volume V.sub.L in the dispensing vessel and the fill level in the dispensing vessel. Using the following equation, which is once again based on the general gas equation, the fill level can be determined as a function of the measured quantity of air:

m.sub.D.Math.R.sub.S.Math.T=(V.sub.L+V.sub.15+V.sub.33).Math.(P.sub.2P.sub.1) (3)

where m.sub.D quantity of air supplied in time interval between t.sub.1 and t.sub.2;

[0053] T temperature of the supplied quantity of air;

[0054] R.sub.S specific gas constant;

[0055] V.sub.33 volume of the pressure line 33;

[0056] V.sub.15 volume of the connecting line 15;

[0057] P.sub.1 pressure at the instant t.sub.1;

[0058] P.sub.2 pressure at the instant t.sub.2.

[0059] Compared to the exemplary embodiment of FIG. 1, the exemplary embodiment of FIG. 2 has the advantage that, in order to achieve a predetermined pressure increase or a pressure P.sub.2, the quantity of air required for this is comparatively large in the case of an almost empty or completely empty dispensing vessel 10. The measurement accuracy thus increases as the fill level decreases. This is advantageous when the accurate and reliable determination of the fill level of (almost) completely empty dispensing vessels is of particular importance.

[0060] In the exemplary embodiment of FIG. 3, the functions which are fulfilled by the switching valves 17, 26 and the throttle valve 35 in the exemplary embodiment of FIG. 2 are taken over by a proportional valve 39. When the apparatus is in the dispensing mode, that is to say the shut-off valve 13 is open, the proportional valve 39 provides in the dispensing vessel 10 the pressure that is necessary for dispensing the liquid. However, the proportional valve 39 can also be used in the test mode, in which the shut-off valve 13 is closed. In this case, it supplies an additional quantity of air, which is measured by the air quantity sensor 38, to the pneumatic test system (here: line 33, connecting line 15 and dispensing vessel 10 having the test volume V.sub.33+V.sub.15+V.sub.L. Since with the proportional valve 39 there is the possibility of precisely defining a target pressure value, there is no need for a separate pressure sensor 34. As also in the exemplary embodiment of FIG. 2, the quantity of air required for a pressure increase is measured in order to determine the fill level.

[0061] The test volume of the test system (air-filled portion of the dispensing vessel 10, connecting line 15 and line 33) can be 1 to 2000 ml, preferably 60 to 350 ml. The cylinder volume V.sub.Z can assume values of 1 to 2000 ml. A preferred range for V.sub.Z extends from 12 to 70 ml. The pressures P1 and P2 can be 0.1 to 12, preferably 0.2 to 5 bar. The pressure change P2P1 brought about by reducing the test volume by the cylinder volume V.sub.Z or by the supplied quantity of air can assume values of 0.02 to 5 bar. The supplied quantity of air can be between 80 and 0.25 mg, preferably between 40 and 0.28 mg. The temperature in the dispensing vessel can be 10 to 200, preferably 20 to 180 or 100 to 170 C.

LIST OF REFERENCE SIGNS

[0062] 10 dispensing vessel [0063] 11 fill level line [0064] 12 dispensing opening [0065] 13 shut-off valve [0066] 14 compressed-air port [0067] 15 connecting line [0068] 16 compressed-air system [0069] 17 first switching valve [0070] 18 first inlet [0071] 19 outlet [0072] 20 second inlet [0073] 21 node point [0074] 22 pressure regulator [0075] 23 inlet [0076] 24 outlet [0077] 25 (pressure) line [0078] 26 second switching valve [0079] 27 first inlet [0080] 28 outlet [0081] 29 second inlet [0082] 30 inlet [0083] 31 outlet [0084] 32 piston [0085] 33 (pressure) line [0086] 34 pressure sensor [0087] 35 throttle valve [0088] 36 inlet [0089] 37 outlet [0090] 38 air quantity sensor [0091] 39 proportional valve [0092] 40 cylinder