Device for determining a fluid pressure

Abstract

A hot-beverage preparation apparatus for domestic purposes, having a pump for conveying preparation water, fluid lines (4) for supplying preparation water to preparation units, and a sensor unit (1; 10) on a fluid line (4) for detecting a pressure state in the fluid line (4), is developed such that the fluid line (4) is enclosed on more than four sides in a radial plane in the region of the sensor unit (1; 10).

Description

[0001] Device for determining a fluid pressure

[0002] The invention relates to a hot beverage preparation device, in particular for household purposes, having a fluid system comprising at least one pump for conveying preparation water, fluid lines for supplying preparation units of the preparation device, such as a heater or a brewing chamber, with preparation water, and a sensor unit on at least one fluid line for detecting a change in a flow state in the fluid line.

[0003] EP 2 628 421 B1 describes a device for preparing a milk-containing beverage, comprising a conveying device configured to convey the milk, which comprises a conveying channel. A detection unit with a sensor is configured in and / or on the conveying channel, with which a change in the fill and / or flow state in the conveying channel can be detected. The conveying channel has a flexible section. The sensor, as an electromechanical sensor, for example in the form of a piezoelectric sensor, a Hall sensor, or a load cell, is positioned such that it can be used to measure a change in position, expansion, pressure, and / or shape of / on the flexible section(s) in order to detect the change in the fill and / or flow state in the conveying channel.

[0004] The object of the invention is to provide a sensor unit for detecting a brewing pressure in a hot beverage preparation device which is sufficiently sensitive to provide accurate values.

[0005] This object is achieved according to the invention in the hot beverage preparation device mentioned at the outset in that the fluid line in the area of ​​the sensor unit is enclosed on more than four sides. The enclosure of the fluid line is directed towards its circumference. The enclosure thus lies in a radial plane of the fluid line. The invention therefore moves away from contacting the fluid line in the area of ​​the sensor unit on more than four sides, but only on a maximum of four sides, as is occasionally done in medical technology. This is because with only a four-sided, tangential contact with the fluid line, four corners remain into which the fluid line can expand under the influence of pressure, without the pressure causing the expansion being able to be detected by sensors. With each additional tangential enclosure side, another corner is created, but this corner covers a significantly smaller proportion of the circumference of the fluid line and offers a significantly smaller expansion depth.An increasing number of enclosing sides thus reduces the circumferential sections that can deform undesirably and thus increases the accuracy of the pressure values ​​that the sensor unit can record.

[0006] According to an advantageous embodiment of the invention, the fluid line in the region of the sensor unit can be essentially completely enclosed on the circumference. According to the invention, the enclosure can ideally be annular, so that it acts essentially over the entire length of the circumference of the fluid line. The invention therefore moves away from contacting the fluid line in the region of the sensor unit only tangentially or in partial sections. Instead, it follows the principle of enclosing the circumference of the fluid line almost completely, which does not exclude small gaps between enclosing elements. The complete enclosure almost completely prevents the cross-section of the fluid line from expanding, so that no deformation of the fluid line is "lost" but can be detected by the sensor.

[0007] Enclosing the fluid line essentially along its entire circumference significantly increases the detection accuracy of the sensor unit. This is because, in the event of a pressure change, the fluid line or its casing cannot deflect under the pressure, for example, due to deformation, in those circumferential sections where the fluid line or its casing is not enclosed. The sensor unit can therefore detect pressure changes much more accurately. For example, in the case of a linear pressure change, it can provide significantly better, largely linear, characteristic values ​​for a force-pressure curve. This is because conventionally determined force-pressure curves are regularly subject to a non-negligible non-linearity that must be corrected using correction factors.

[0008] The above inventive structure of the sensor device and the fluid line provides significantly lower nonlinearity. This simplifies, or can even eliminate, subsequent corrections that compensate for material changes in the fluid line over time, drifts (i.e., slow changes in the output variable that are unrelated to the input variable), and fluctuations in the measuring device. In the simplest case, namely with particularly reliable sensor values, instead of a curve with changing gradient values, a straight line of the force-pressure characteristic curve can result, which can be determined exclusively from two points. The determined gradient rates and, if applicable, correction factors are stored in the preparation device. A software algorithm can then be used to regularly adjust the corrections to compensate for material changes, drifts, and fluctuations.For readjustment, almost pressureless system states in the preparation device or system states with known pressures can be used.

[0009] According to a further advantageous embodiment of the invention, the sensor unit can directly enclose and contact the fluid line. For this purpose, it can comprise two shell elements that almost completely surround the fluid line circumferentially in a radial plane. The shell elements can be designed in the form of two opposing, one-dimensionally curved half-shells, whose curvature and inner radius are adapted to the outer radius of the fluid line. This results in the shell elements being in large-area contact with the jacket of the fluid line. The two half-shells thus almost completely surround the fluid line. They can leave only a minimal gap at their joints in order to offer minimal movement space relative to one another. A sensor unit designed in this way leads to a very precise force-pressure characteristic curve.

[0010] The shell elements can be formed integrally with the sensor unit. For this purpose, the two half-shell-shaped shell elements can be formed in a body of the sensor unit where the sensor unit contacts the circumference of the fluid line. The integral design of the damage elements and the sensor unit results in a simple structure. Alternatively, the shell elements can be formed as separate components of the sensor unit. They can then be more precisely adapted to the diameter of the fluid line and are interchangeable.

[0011] The sensor unit is preferably located in a cold water area of ​​the fully automatic coffee machine to minimize temperature influences. The cold water area is usually located between the pump and the heater.

[0012] The principle of the invention is therefore based on practically completely enclosing the circumference of the fluid line within the sensor device in order to prevent the fluid line from "deviating" due to deformation in the event of a pressure change. By preventing the fluid line from deforming, the measured values ​​of the sensor unit are not falsified. According to an advantageous embodiment of the invention, the fluid line can also be protected against radial deformation, in particular against radial expansion, at least in a section upstream and / or downstream, i.e. outside or beyond the sensor unit, in a protected section. The invention is therefore thanks to the realization that deformation of the fluid line outside the sensor unit can also impair the measured values ​​within the sensor unit.

[0013] According to a further advantageous embodiment of the invention, the fluid line can be surrounded, at least in the protected section, by a non-deformable or pressure-resistant protective tube. For this purpose, the actual fluid system, in particular the existing fluid line, does not need to be modified or removed. Rather, the non-deformable protective tube can also be retrofitted to or on the fluid line, if necessary. This allows conventional fluid systems to be equipped according to the invention and hot beverage preparation devices to be retrofitted cost-effectively.

[0014] According to an alternative embodiment of the invention, the wall of the fluid line, at least in the protected section, can contain a non-deformable material as a support structure or can consist entirely of it. The fluid line itself can thus be designed to be pressure-resistant. In fluid lines whose sheath contains non-deformable material, the sheath consists of an inherently deformable material such as PVC or rubber and contains a fabric or grid or a spiral made of plastic, glass or carbon fiber or metal embedded therein, which can also be attached to the outside of the sheath. The sheath can also be made entirely of these or similar materials, but can then have a greater wall thickness or be less flexible.By using a pressure-resistant fluid line, manufacturing steps for the protected section can be reduced because instead of two components—namely, the fluid line on the one hand and a protective tube on the other—a single fluid line according to the invention can be installed. Reducing the number of components to a single one also leads to space savings.

[0015] According to a further advantageous embodiment of the invention, the fluid line in the protected section can be subjected to radial compressive prestress. This prevents the non-prestressed fluid line or its casing from expanding under pressure to its load limit before the pressure is transmitted to the sensor unit. Conversely, the fluid line can relax again upon a subsequent pressure drop. In both cases, the change in tension in the casing of the fluid line can "absorb" portions of the pressure change. Factory-prestressed compressive prestressing of the initially depressurized fluid line in the protected section can anticipate such potential deformation, helping the sensor unit achieve greater sensitivity to pressure changes.

[0016] The largely complete enclosure of the fluid line according to the invention thus protects and supports the fluid line, at least in its section within the sensor device, against unwanted radial expansion. In a simple embodiment, the fluid line itself can be designed and installed without prestress. Alternatively, according to a further advantageous embodiment of the invention, the fluid line can also be prestressed within the sensor device. This makes it possible to compensate for manufacturing-related tolerance fluctuations, e.g., with regard to the diameter or wall thickness of the fluid line. Furthermore, influences from creep of the material of the fluid line can be eliminated by subjecting the fluid line to a suitable prestress before installation, advantageously one that corresponds to the later prestress in the installed state.

[0017] According to a further advantageous embodiment of the invention, the fluid line can also be designed to be pressure-resistant within the sensor device. The wall of the prestressed fluid line can contain pressure-resistant material for this purpose. The wall of the fluid line can comprise a support structure as described above to make the fluid line pressure-resistant. Under a compressive prestress, the support structure can be relieved so that it no longer absorbs any compressive forces from the fluid line. The remaining material of the wall, on the other hand, can offer a certain amount of expansion space under the pressure load to be sensed. The compressive prestress of the inherently pressure-resistant fluid line essentially deactivates the support structure so that, under a pressure load on the fluid line, it does not absorb any pressure load components that might otherwise be missed by the sensor unit.

[0018] Due to the lack of deformation losses in the fluid line or its casing, the sensor unit according to the invention also generates significantly higher sensed force values. Higher force values ​​are helpful for improved resolution of a force-pressure characteristic curve determined by the sensor unit.

[0019] To the extent that the pressure preload of the fluid line deactivates its support structure, a fluid line that is not pressure-resistant could also be installed in the area of ​​the sensor unit, i.e., one without preload. However, this would require additional coupling points between pressure-resistant and non-pressure-resistant fluid line sections. The combination of a pressure-resistant fluid line on the one hand and a pressure preload of the fluid line within the sensor on the other hand makes it possible to install a fluid line of the same type, namely pressure-resistant, both upstream, within, and possibly downstream of the sensor unit. According to the invention, the pressure preload for deactivating the support structure thus has a completely different function than in the prior art.

[0020] According to the invention, the sensor unit can be equipped with two opposing, one-dimensionally curved half-shells, whose curvature and inner radius are adapted to the outer radius of the fluid line. In principle, they can correspond to one another. According to a further advantageous embodiment of the invention, the inner diameter of the shell elements can be adapted to the outer radius of the fluid line in that it can be smaller or smaller in size than the outer radius. The installation of the fluid line in the sensor unit then leads to a constraint on the fluid line, which causes its compressive preload. This simplifies the application of the compressive preload to the fluid line in the sensor device.

[0021] The sensor unit can fundamentally be constructed relatively simply, namely in one piece, whereby the fluid line is drawn in to apply the prestress while overcoming a certain deformation resistance of its casing. To facilitate the assembly of the fluid line under prestress, the sensor unit can also be constructed in two or more parts in an alternative embodiment of the invention. The prestress can then be applied by at least two parts of the sensor unit being mounted to one another with the fluid line enclosed around the circumference in such a way that the fluid line is constrained. The shell elements as contact points for the fluid line can also be constructed in one piece with the sensor unit and thus directly on it. The sensor unit can therefore offer a small number of parts, which can simplify its handling.In an alternative embodiment of the invention, the shell elements can also be formed separately. They can be specifically designed for easy assembly and / or dimensioned more precisely to the dimensions of the fluid line. This also makes it easier to adapt the sensor unit to different diameters of different fluid lines.

[0022] The principle of the invention is explained in more detail below using a drawing as an example. The drawing shows:

[0023] Figure 1: a first embodiment of a sensor unit according to the invention,

[0024] Figure 2: a second embodiment of the sensor unit according to the invention,

[0025] Figure 3: two pressure-force curves.

[0026] The first embodiment of a sensor unit according to the invention, as shown in Figure 1, is designed as a force sensor and specifically as a type of fork-shaped load cell 1 made of metal with two prongs 2, 3 running parallel to one another. The fluid line 4 of a beverage preparation device is arranged in a linear gap 6 between the prongs 2, 3, which occupies approximately two-thirds of the transverse extent of the load cell 1 and is shown larger than necessary for clarity. The fluid line 4 has an outer radius A. As the pressure in the fluid line 4 increases, it expands, so that the prongs 2, 3 in the fluid line 4 are spread apart relative to one another.

[0027] The lower prong 3 serves as a largely rigid abutment. The upper prong 2 is shaped to resemble a spring body, whose geometry changes or deforms slightly under the influence of the expanding force of the fluid line 4. A strain gauge 5 is attached to the top of prong 2, which records the elastic deformation of prong 2 and converts it into an electrical signal.

[0028] At their free ends 7, the prongs 2, 3 have two cutouts in the form of one-dimensionally curved half-shells 8 on their mutually facing surfaces at the gap 6. The half-shells 8 have a curvature or inner radius 1 and almost completely enclose the fluid line 4 mounted in the load cell 1 on the outside. Only in the area of ​​the gap 6 do insignificantly small sections of the casing of the fluid line 4 remain uncovered. Therefore, the fluid line 4 can hardly avoid increasing pressure through undetected deformation. Rather, its pressure-induced deformation is almost completely absorbed by the half-shells 8 and recorded as a deformation of the prong 2.

[0029] The fluid line 4 consists of an inner silicone tube 9 and an outer textile sheath 11, which are firmly bonded together. The sheath 11 consists of a non-stretchable fiberglass fabric as a support structure, so that the fluid line 4 is pressure-stable – even outside the load cell 1. To ensure that the sheath 11 cannot absorb any compressive forces within the load cell 1 that could escape detection by the load cell 1, the fluid line 4 is pre-stressed.

[0030] The compressive prestress of the fluid line 4 is generated during its assembly in the load cell 1. For this purpose, the curvature or inner radius I of the half-shells 8 is slightly smaller than the outer radius A of the fluid line 4. Thus, during its assembly in the load cell 1 and through the load cell 1 itself, the fluid line 4 experiences circumferential constraint, which imparts the inventive prestress to its casing made up of the silicone hose 10 and the cover 11.

[0031] The fluid hose 4 is mounted in the load cell 1 by pulling the fluid hose 4 into the half shells 8. To do this, a certain deformation resistance of the fluid hose 4 must be overcome, which largely corresponds to the preload force on the fluid hose 4 within the load cell 1.

[0032] The load cell 10 shown in Figure 2, thanks to its two-part design, facilitates the assembly of the preloaded fluid line 4: For this purpose, the prongs 2, 3 are designed separately from one another and are rigidly clamped together at a shaft section 12. The prongs 2, 3 are only assembled on the shaft section 12 once the fluid line 4 is positioned in the half-shells 8.

[0033] After the load cell 1, 10 is factory-installed in a hot beverage preparation device, it is calibrated as a force measuring device and adjusted if necessary. Adjustment or calibration of the load cell 1, 10 to the fluid line 4 is performed by pressure calibration, for example, on a final test bench in production. Pressure-force characteristic curves are determined in this process.

[0034] Determined gradient values ​​of the pressure-force characteristic curves and correction factors are stored in a control unit of the preparation device. Using a software algorithm, material changes, for example, due to aging, particularly of the fluid line over time, or drifts and fluctuations in the measuring device, i.e., the load cell 1, 10, can be readjusted at regular intervals. Readjustment can be performed under largely pressureless conditions or under conditions with known pressures in the preparation device.

[0035] Figure 2 shows two example pressure-force curves a and b. The abscissa indicates the values ​​for an internal pressure in the fluid line 4 in the unit "bar," while the ordinate indicates the resulting force, measured by the load cell 1.10, in the unit "Newton." The dotted line c indicates linearity with respect to both curves a and b starting at a value of 1 bar.

[0036] The characteristic curve a is generated by a conventional, state-of-the-art load cell. It exhibits a pronounced nonlinearity resulting from the lateral deflection of the pressurized fluid line, which in a conventional load cell rests on parallel, flat surfaces of the tines. This nonlinearity requires the storage of numerous individual values ​​to map the characteristic curve a or the storage of correction factors.

[0037] Characteristic curve b, on the other hand, is created by a load cell 1, 10 according to the invention. Due to the almost complete enclosure of the fluid line 4, the expected linear relationship between the internal pressure in the fluid line 4 and the resulting and detectable force in the load cell 1, 10 arises. Characteristic curve b significantly simplifies the evaluation of the force values ​​required during calibration; for some measurement tasks, correction can be omitted entirely. In the simplest case, characteristic curve b can be specified using only two points, which significantly simplifies calibration.

[0038] Since the load cells 1, 10 and the fluid line 4 described in detail above are exemplary embodiments, they can be modified to a wide extent by a person skilled in the art without departing from the scope of the invention. In particular, the specific designs of the half-shells 8 can also be implemented in a form other than that described here, for example separately. Likewise, the fluid hose 4 can be configured in a different shape if this is necessary for reasons of space or design. Furthermore, the use of the indefinite articles "a" or "an" does not exclude the possibility that the features in question can also be present multiple times or multiple times.

[0039] List of reference symbols

[0040] 1 load cell

[0041] 2 upper tines

[0042] 3 lower prongs

[0043] 4 Fluid line

[0044] 5 strain gauges

[0045] 6 gap

[0046] 7 free end

[0047] 8 half shells

[0048] 9 Hose

[0049] 10 load cell

[0050] 11 Cover

[0051] 12 Shaft section

[0052] A outer radius

[0053] I inner radius a, b pressure-force characteristics c linear progression

Claims

PATENT CLAIMS 1. Hot beverage preparation device for domestic purposes with a pump for conveying preparation water, with fluid lines (4) for supplying preparation units with preparation water and with a sensor unit (1; 10) on a fluid line (4) for detecting a pressure state in the fluid line (4), characterized in that the fluid line (4) is enclosed on more than four sides in a radial plane in the region of the sensor unit (1; 10).

2. Hot beverage preparation device according to claim 1, characterized in that the fluid line (4) is completely enclosed on the circumference.

3. Hot beverage preparation device according to one of claims 1 or 2, characterized in that the sensor unit (2) comprises two shell elements (8) which almost completely surround the fluid line (4) in a radial plane.

4. Hot beverage preparation device according to one of the above claims, characterized in that the fluid line (4) is protected against radial expansion in a protected section at least in a section upstream and / or downstream of the sensor unit (1; 10).

5. Hot beverage preparation device according to claim 4, characterized in that the fluid line (4) is surrounded in the protected section by a non-deformable protective tube 6. Hot beverage preparation device according to claim 4, characterized in that the wall of the fluid line (4) in the protected section contains or consists of a non-deformable material (11).

7. Hot beverage preparation device according to one of the above claims, characterized in that the fluid line (4) is subjected to radial prestress in the region of the sensor unit (1; 10).

8. Hot beverage preparation device according to one of the above claims, characterized in that the fluid line (4) is protected against radial expansion at least in the section within the sensor device (1; 10).

9. Hot beverage preparation device according to claim 7 or 8, characterized in that the fluid line (4) within the sensor device (1; 10) is pressure-resistant.

10. Hot beverage preparation device according to one of claims 3 to 9, characterized by an inner diameter (I) of the shell elements (8) which is smaller than the outer diameter (A) of the fluid line (4).

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