DE19924738A1 - Load cell, especially for measuring yarn tension, uses a lever attached to a diaphragm which seals a housing containing sensors and damping fluid - Google Patents

Abstract

The load (2) is applied to a lever (3) attached to a membrane (7) that forms the spring unit (4). The membrane (7) seals (8) against the housing (9), which is filled with damping fluid (22) and encloses deflection sensors (5) and transmitter (20). The membrane deflection signals are transferred to the outside by radio transmission (20,21). The interior end (16) of the lever (3) can be free within an overload clearance (19). Alternatively it can be held stationary, with additional sensors measuring the lever deflection. The membrane shape can be varied to suit the application and is machined as a single component.

Description

The following invention relates to a measuring cell according to Ober concept of the main claim.

Such a measuring cell is known for example from DE-PS 41 10 429.

In the case of such measuring cells, a measuring load over a Fixed lever introduced into the measuring cell and on transfer an elastically deformable spring structure. The Ver The formation of the spring structure is recorded using suitable measured values mer detected and given to an evaluation circuit.

To do this, the measuring cell must be connected to a stationary machine stell be attached. A rigid Ge is used for this purpose housing, which with suitable devices for befe the machine frame.

Such measuring cells are often used for measuring tasks where there is a risk of decontamination, because, for example, vapors, oil mist, volatilized sub punch any type on the measuring cell over time len.

It is therefore essential to measure the measuring cell against such shield against environmental influences.  

For this purpose, bellows are known in the prior art, whose stroke is detected and converted into a measurement signal.

The problem with such bellows is the relatively large one Such constructions are unsuitable for mass and consequently for measuring small forces and especially small forces under high frequency changes over time.

Although this is not a limitation of the invention process, the problem of decontamina arises tion in particular in the textile sector. There serve such Measuring cells for example the detection of small thread forces that are subject to highly dynamic vibrations. Especially here must be considered that the running thread with a Preparation or finishing is provided, which is in the Very thin ver spreads and thus the risk of incorrect measurements on the measuring cell le evokes.

One can try to encapsulate such measuring cells. Then, however, there is the additional problem of incorrect measurements and nonlinearities to the fore since the encapsulation also include the lever's entry point into the measuring cell must and must also be tight at this point.

It is therefore an object of the present invention, the be known measuring cell so that avoiding obi leak tightness problems can still be resolved in a highly dynamic manner the sensor for small forces arises which has a linear out provides output signal from a bending deformation.

This task is solved by the characteristics of the An saying 1.

The advantage of the invention is that the cell len are hermetically sealed from the environment and  form a self-contained pot, the one Wall of the pot, which is the lever for initiating the measuring load carries, was recognized as a linearly deformable spring structure.

This spring structure is used in the present application referred to as a flat membrane that is rigid on its circumference the housing is coupled. About to one side of the mem Outstanding lever is the respective measuring load in the Membrane initiated, in turn, as a result of the rigid A tension on the circumference at least in the plane in which besides the lever there is also the measuring load, an S-shaped Aus steering experience.

It can therefore be the proven measuring principle of the so-called Double beam can also be applied to the invention. As a result of the rigid coupling of the membrane to the housing are the coupled edge zones of the membrane bending moments kept stiff so that the membrane when the Lever an S-shaped deflection is impressed.

On the other hand, the membrane is parallel to the effective never the respectively introduced measuring load very stiff, so that in the zones lying to the side of the lever are parasitic Deformation is practically not to be taken into account. The even any deformations that occur are also symme tric to each other and therefore falsify the measurement result Not.

The invention therefore uses the general tendency of the mem bran to elastically deform under the respective measuring load the relevant deformations on suitable Turn off the membrane.

This membrane is in principle a flat structure, wel besides the function of an elastic deformation also the Function of the sealing of the surface behind the membrane  mes fulfilled. This is tightly enclosed by the housing and the actual space of the measuring cell, in which also the transducers are therefore convenient also for liquids with strong creeping properties inaccessible.

The space closed behind the membrane can open used in various ways to achieve predetermined effects become. This space can be more suitable with an oil, for example Viscosity can be filled. This can be done agreed damping or a defined Fre achieve quenzgang. To increase the damping can also a perforated partition may be provided so that closed damping fluid due to the reduced flow cross sections of the perforation on the free back and forth flow is additionally prevented.

The measuring cell according to the invention is therefore particularly suitable especially for use with nominally small nominal measurements forces in processes for the production of threads, in particular Endless threads, because the natural vibration behavior of the sensor is practical table can be steamed as desired.

Another advantage is the possibility of a loading filling under higher pressure than atmospheric pressure. This measure prevents any creeping liquid from entering sustainable, so that the creep behavior of the measuring cell can be reliably predicted.

The measuring cell also enables detection in addition to a detection solution of the S-shaped bending of the membrane also a detection solution of their torsion.

For this purpose, it is proposed that the front view Sensor on a parallel to the line of action of the Measuring load and arranged in pairs on both sides of the lever  are and also additional sensors on a for this purpose transverse line are provided. The latter measured value transducers are expediently made as torsion transducers designed, for example in the form of strain gauges, de ren orientation is less than 45 ° to the cross line.

Since the measuring cell at hand is easy to spot be designed metrically or rotationally symmetrical complete balancing can be achieved.

This measuring cell is therefore especially for the one suitable in the rotating area.

Counterweights are used in the interior for balancing range of the measuring cell, these can also be used in another radio serve as an overload-limiting stop.

In addition, the measuring cell according to this invention offers the possibility of different attachments to the machine frame, for example via a threaded sleeve, one on the outside screw thread attached to the housing, a smooth and cylindrical surface in connection with axial clamping facilities, fastening via a revolving Flange ring etc.

It is provided in training that the lever Membrane pierces and ver until shortly before the bottom of the pot running. In this way, an overload can easily limiting stop can be installed. For this purpose, Bo anchored to that of the pot, its inner diameter larger than the outer diameter of the lever on the pot side Is end so that the lever with its pot-side end in To a certain extent it is freely movable before being attached to the inside catch of the attached ring bumps.  

In addition, the displacement of the pot-side end of the lever under the respective measuring load also relative just tap and send it out as a measurement signal. For this come especially capacitive measuring methods or Hall probes into consideration, since they work without contact and thus the respective measurement signal easily brought out of the measuring cell can be.

Also take into account that the sensor with a small stroke is to provide a high output signal is additionally provided beat the self-contained peripheral edge of the membrane to form as a stable massive ring, on the inside seen a relatively thin measuring zone of only a few tenths Millimeters thick follows. It closes after the measuring zone in again a thick solid area, which is the opening lever is used.

Such a sensor offers a relatively high resolution even with small forces, whereby compared to the thick ones massive zones with considerable material accumulation the pure Deflect measuring zones very sensitively.

The membrane is expediently a one-piece construction part, so that any internal tension etc. avoided become.

For better transfer of the respective measuring load, it is proposed entirely, the membrane ge each two flatten opposite areas and the respective housing se also so that within the membrane under the measuring load an essentially uniform build-up of voltage takes place can.

In addition, the invention offers the advantage that in addition to the deformation of the membrane also a deformation of the Lever can be tapped. This is more convenient  wise by catching the pot-side lever end using egg a firm support on the pot. The He then between the clamping point on the pot and the fastening in the manner of a spiral spring weakens, so that ei under the given measuring load ne Bend the lever in the closed pot area will put.

This deflection can be tapped in a suitable manner and overlay for measurement evaluation.

In the following the invention based on execution examples explained in more detail. Show it:

Fig. 1 shows a first embodiment of the invention with a freely movable end of the lever,

Fig. 2 shows a possible front view of the measuring cell,

Figure 3 is a further possible frontal view cell. On the measurement,

Fig. 4 frontal plan view of a modified membrane with flattened Einspannzonen,

Fig. 5 shows a schematic representation of a further measuring cell with a lever clamped in the head.

Unless otherwise stated below, the following description always for all figures.

The figures show a measuring cell 1 for measuring Kräf th by means of a fixed lever 3 to initiate the respective measuring load 2nd The lever 3 transmits the respective measuring load 2 to an elastically deformable spring structure 4 . On the spring structure 4 , transducers 5 are provided, which detect the respective deformation of the spring structure and convert it into a measurement signal.

The measuring cell 1 sits within a rigid housing 9 . The housing 9 has devices for attachment to the machine frame. This can include, for example, clamping devices on the outer casing of the housing. If necessary, screw-on flanges can be provided. In the exemplary embodiment shown, a circumferential thread is provided on the circumference of the housing, which thread is screwed to the machine frame 6 via suitable pairs of clamping nuts.

It is now essential that the spring structure 4 has the shape of a flat membrane 7 ner. The membrane 7 has a umlau fenden and self-contained edge 8 and is tightly attached to the inner periphery of the housing 9 with the sem edge 8 and rigidly attached there. For this purpose, the tight fastening joint 10 serves between the outer circumference of the closed rim 8 and the inner circumference of the housing 9 . Metal, Teflon, plastic, for example, can be used to seal the closed edge on the housing. Metal ring seals, solder joints, adhesive joints, weld seams are also conceivable. The membrane can also be made in one piece with the connection area of the housing 9 . Suitable manufacturing processes are stamping, milling, turning, eroding or processes from micromechanics.

The membrane 7 extends in side view (see Fig. 1) substantially parallel and in frontal view (see Fig. 2 to 4) lengthways and transversely to the direction of the measuring load 2 , where the measuring load 2 from the actual measuring point on the membrane bran takes a predetermined distance 32 . This distance 32 is essential since it causes an S-shaped deflection of the membrane 7 , the deformations of which are to be detected by the sensors 5 .

To one side of the membrane, the housing 9 is closed like a pot, so that a closed cavity 11 is formed between the inside of the membrane 7 and the pot-like part of the housing 9 . The lever 3 for introducing the measuring load 2 is rigidly fixed in the center of the membrane 7 and projects freely accessible on the other side of the membrane 7 in the room. At its free end, the measuring load acts on it. Between the center of the membrane 7 and the He bel 3 will create a connection via the clamping point 12 ge, which is if possible in relation to the measuring zones to which the transducers 5 are attached, is resistant to bending and deformation.

Due to the flexurally and deformation-resistant connection between the lever 3 and the center of the membrane 7 , the entire measuring load 2 is converted into corresponding deformations of the membrane 7 in wesentli, where the transducers 5 are brought to.

As shown in FIGS. 2 to 4, the line of action 13 of the measuring load 2 runs essentially centrally through the center of the membrane 7 . A transverse line 14 lying transversely to this can be useful for an additional measured value tap, since a precisely defined deformation will also take place here.

Namely, while the areas above and below the force application point experience an S-shaped bend, there is a torsion around the area of the transverse line 14 , which can be gripped with suitably oriented transducers.

The center line of the lever 13 expediently runs through the point of intersection 15 between the action line 13 of the measuring load and the transverse line 14 , since defined attack and deformation conditions are present in this way.

In addition, FIGS . 1 and 5 show the arrangement of the transducers 5 on the surface of the membrane 7 facing the interior of the pot. Since there is a tight joint between the membrane 7 and the inner circumference of the pot, harmful spray mist and so on remain outside the transducer. The Mem bran therefore serves in addition to a tap for the measured values also the sealing of the transducers ge against the environment.

Furthermore, the Fig. 2 to 4 show in front view, that the sensors 5 are on a line parallel to the line of action 13 of the measuring load and are arranged in pairs on both sides of the He bels. 3 In addition, torsion measuring strips can be provided on the transverse line 14 , which is oriented transversely to the parallel to the line of action of the measuring load. In this case too, the transducers should be provided in pairs on both sides of the lever.

Although the outline shape of the membrane 7 can be selected as desired, point-symmetrical shapes are particularly preferred. These include in particular the square outline shape and the circular outline shape according to FIG. 3. The latter offers the additional advantage of being relatively simple to manufacture on a lathe. Nonetheless, elliptical or diamond-shaped floor plans are also easily considered.

In addition to this, FIGS. 1 and 5 show that the lever 3 pierces the membrane 7 and extends with a second lever end 16 to just before the bottom 17 of the pot, but does not touch it. This case is shown in Fig. 1. There, the second lever end 16 is freely movable within certain limits. 5 Notwithstanding the above, FIG. An exemplary case in which the second lever end opposite the bottom 17 of the pot is clamped. There is also a bending zone 30 between the end 29 and the membrane 7 seen before. This bending zone serves to accommodate suitable transducers 31 , so that the deformations present there can also be tapped and evaluated.

In addition to the embodiment shown, the end fixing can also be designed as a fixed clamping. In this case, a turning point would arise in the region of the bending zone 30 , at which the curvature of the second lever of the 16 changes direction. It would accordingly form an at least substantially S-shaped curved beam.

In addition to this, FIG. 1 shows a housing-fixed stop 18 , which is provided in the vicinity of the bottom end of the lever 3 . The fixed stop to the second lever end 16 with a predetermined distance, so that for the second lever end 16 a free Bewegungsbe rich 19 is created.

The second lever end 16 can be moved freely within this movement range 19 . The range of motion 19 is determined by the distance that arises between the outer circumference of the second lever end 16 and the inner circumference of the stop 18 fixed to the housing.

This distance is so limited that the bo the end of the lever still during the elastic Membrane deformation takes place.

In this case, the stop 18 serves as an overload limiter to avoid deformations on the measuring cell 1 , which would lead to their destruction.

In addition, this distance, which naturally changes over time when the lever 3 is acted upon, can be tapped, for example, by a capacitive or inductive measuring method. The current distance is therefore also a measure of the force acting on the measuring cell 1 .

In addition to this, provision can be made for the measured values to be conducted from the interior of the measuring cell 1 to the outside via a wireless radio connection. For this purpose, a transmitter 20 is to be provided in the interior, which is suggested by corresponding transducer lines gene from the transducers 5 and 31, respectively. The signals transmitted by the transmitter 20 are passed on to an evaluation circuit via an external receiver 21 .

The pot-like housing can expediently be provided with a filling 22 . This includes, for example, an inert shielding gas. Such filling can reliably prevent the occurrence of decontaminating atmospheric constituents.

In addition, a filling 22 with damping properties can also be filled. These include, for example, highly viscous oils, for example silicone oils.

Since, when the diaphragm 7 is always acted on, a certain displacement of the filled damping liquid is also followed, a defined damping or a defined frequency response can be set by appropriate selection of the liquid.

By arranging damping projections 23 which are moved together with the lever 3 and which are immersed in the respective damping liquid, an additional damping can be achieved. The degree of damping can be further increased by using an additional damping wall 24 which is fitted into the interior of the housing 9 . The damping wall has perforations to allow the enclosed damping fluid to have a considerably restricted flow inside the interior.

In addition, the figures show membranes 7 , in which the self-contained edge 25 has considerable material accumulations and the central area as well, with very thin measuring zones 27 being provided between the edge 25 and the center 26 , from which the resilient deformation is picked up.

So while the material accumulations are essentially provided in the edge area and in the center of the membranes 7 , the zones in between are practically only millimeters thin or less, so that the small forces occurring in particular with textile machines can be detected highly dynamically. With such a membrane design, parasitic deformations practically do not occur.

In addition to this, FIG. 4 shows a membrane which is flattened at two opposing locations, the connecting lines of the opposing flattenings being perpendicular to one another.

Here, the flattened portions 28 serve as the fixed tension of the membrane 7 over a relatively wide longitudinal area, so that even outside the line of symmetry, which is parallel to the line of action of the measuring load, reliably predictable membrane deformations occur.

In addition to this, FIGS. 2 to 4 show in dashed form membranes in which the circumferential edge 25 is connected via measuring elements which run vertically and transversely. The fields not occupied by transducers 5 are not involved in the measurement results and in particular only serve to seal on the one hand and to stiffen the horizontally and vertically mounted measuring strips.

As can be seen from these figures, the transducers 5 can be arranged on two mutually perpendicular axes on the membrane, so that a measurement can be carried out simultaneously in both axes. Such measures have the advantage that, with the measurement of the current measurement load, statements can also be made, for example, about the coefficient of friction at the measurement point 2 .

Such a sensor has the additional advantage that it can be balanced around its central axis. As a result, such a sensor can also be easily installed in the Insert the rotating area. You can see the balance weight in the interior of the sensor before, this can also be considered as over serve to limit the load.

Overall, the present invention therefore offers the advantage of making such sensors hermetically sealed with a very small nominal measuring force and still making them very compact. Since the measuring cell with the exception of the measuring zones 27 can be designed to be very resistant to bending and deformation, sensors of this type also have a very high system natural frequency and are therefore particularly suitable for measurements in the highly dynamic range, for example for fast-running plastic threads (10,000 m per minute and more) on spinning machines.

List of reference symbols

1

Measuring cell

2nd

Measuring load

3rd

lever

4th

Feather structures

5

Sensor

6

Machine frame

7

membrane

8th

closed edge

9

casing

10th

tight fastening joint

11

closed cavity

12th

Clamping point of the lever

13

Line of action of the measuring load

14

Cross line to the line of action

15

Intersection between line of action and cross line

16

second lever end

17th

Bottom of the pot

18th

Fixed stop

19th

Range of motion

20th

Channel

21

receiver

22

filling

23

Damping advantage

24th

additional damping wall

25th

edge

26

center

27

Measuring zone

28

Flattening

29

end determination

30th

Bending zone

31

Sensor in the bending zone

32

distance

Claims (19)

1. Measuring cell ( 1 ) for measuring forces by means of a stationary lever ( 3 ) for introducing the measuring load ( 2 ), which receives the respectively acting measuring load ( 2 ) on an elastically deformable spring structure ( 4 ) with the measured value attached to it ( 5 ) transmits, wherein the measuring cell ( 1 ) sits in egg nem rigid housing ( 9 ) which has Vorrichtun conditions for attachment to the machine frame ( 6 ), characterized in that the spring structure ( 4 ) is a flat membrane ( 7 ) extends in a side view essentially parallel and in a frontal view longitudinally and transversely to the measuring load and which has a closed edge ( 8 ) on which it is tightly enclosed by the housing ( 9 ), with the housing ( 7 ) on one side of the membrane ( 7 ) 9 ) is closed like a pot and that the lever ( 3 ) for introducing the measuring load ( 2 ) is rigidly attached to the membrane ( 7 ) and protrudes to the other side of the membrane ( 7 ). 2. Measuring cell according to claim 1, characterized in that the transducers ( 5 ) sit on the surface of the membrane ( 7 ) facing the pot. 3. Measuring cell according to claim 1 or 2, characterized in that the transducers ( 5 ) are arranged on a parallel to the line of action ( 13 ) of the measuring load and in pairs on both sides of the lever ( 3 ) in a frontal view. 4. Measuring cell according to one of claims 1 to 3, characterized in that the transducers ( 5 ) on a transverse line ( 14 ) transverse to the parallel to the line of action of the measuring load ( 2 ) and in pairs on both sides of the lever ( 3 ) are arranged. 5. Measuring cell according to one of claims 1 to 4, characterized in that the membrane ( 7 ) is point-symmetrical with respect to the tellinie of the lever ( 3 ). 6. Measuring cell according to one of claims 1 to 5, characterized ge indicates that the membrane with respect to the Mittelli the lever is never rotationally symmetrical. 7. Measuring cell according to one of claims 1 to 6, characterized in that the lever ( 3 ) pushes through the membrane ( 7 ) and with a second lever end ( 16 ) until just before the bottom ( 17 ) of the pot. 8. Measuring cell according to claim 7, characterized in that the second lever end ( 16 ) does not touch the bottom of the pot and that in the vicinity of the bottom En of the lever ( 3 ) a housing-fixed stop ( 18 ) is seen in front of the bottom end of the lever takes a dimensioned distance ( 19 ) that an abutment of the bottom end of the lever ( 3 ) takes place during ela-elastic membrane deformations. 9. Measuring cell according to claim 7 or 8, characterized net that the deflection of the bottom end of the He bels from the centered zero position and as Measured value is given to the outside. 10. Measuring cell according to claim 7, characterized in that the bottom end of the lever is held by a stop fixed to the housing, which prevents displacement of the bottom end of the lever and that between the bottom end of the lever and the membrane ( 7 ) has a bending zone ( 30 ) is provided, the deformation of which is detected by transducers ( 31 ) and given to the outside as a measured value. 11. Measuring cell according to one of claims 1 to 10, characterized in that the measured values are given to the outside via a wireless radio device ( 20 , 21 ). 12. Measuring cell according to one of claims 1 to 11, characterized in that the pot-like housing ( 9 ) is filled with an inert protective gas. 13. Measuring cell according to claim 12, characterized in that the protective gas is under excess pressure. 14. Measuring cell according to one of claims 1 to 11, characterized in that a damping fluid ( 22 ) is filled in the pot-like housing ( 9 ). 15. Measuring cell according to claim 14, characterized in that coupled to the movement of the membrane Dämpfungsvor jumps ( 23 ) are provided, which protrude into the Dämpfungsflüs liquid ( 22 ). 16. Measuring cell according to claim 14 or 15, characterized in that a perforated damping wall ( 24 ) is hen between the membrane and the bottom ( 17 ) of the pot. 17. Measuring cell according to one of claims 1 to 16, characterized in that the membrane ( 7 ) has a closed edge ( 25 ) and a center ( 26 ) each with considerable union material accumulations and that between the edge ( 25 ) and center ( 26 ) very thin measuring zones ( 27 ) are provided, the resilient deformation of which is tapped. 18. Measuring cell according to claim 17, characterized in that the membrane ( 7 ) is a one-piece component. 19. Measuring cell according to one of claims 1 to 18, characterized in that the membrane ( 7 ) at two opposing locations has flats ( 28 ) and that the connecting lines of the two opposing flats ( 28 ) perpendicular to each other stand.