HK1070689B - Microwave measuring arrangement for product density measurement - Google Patents

Description

Microwave measuring device for measuring product density

Technical Field

The invention relates to a measuring device for measuring the density of a product by means of microwaves, having a first microwave resonator from which microwaves enter a production area during operation, and having a device for compensating for environmental influences and internal and external disturbance variables which influence the measuring signal of the first microwave resonator.

Background

When measuring the density with such a measuring device, the measuring variables used, in particular the resonance frequency and the resonance curve width, depend on different environmental influences and disturbance variables in the first resonator. In order to compensate for the influence of e.g. resonator temperature on systematic measurement errors, it is known to provide a temperature sensor at a certain point of the first resonator and to make a calculation correction from the measured temperature. Since the temperature in the first resonator is only determined at a certain point, the accuracy of the compensation in the first resonator is limited, especially in the case of spatially non-uniform and/or temporally varying temperature distributions.

In general, for example to compensate for the effects of temperature, it is known to use different materials, currently having temperature coefficients of opposite sign for the first resonator. However, in addition to the increasing manufacturing costs, the transition points between different materials, in particular the cans, have a negative effect in microwave technology. It is also known to use special alloys and composites having a coefficient of thermal expansion close to or equal to zero. This also increases the manufacturing cost.

Disclosure of Invention

The invention is based on the problem of reducing, in a measuring device of the type described above, measurement errors introduced by different environmental influences and internal and external disturbance variables in the first resonator.

To this end, the invention provides a compensating device comprising a second microwave resonator, which is shielded towards a production area in connection with the microwave radiation.

Some terms of application are explained first:

"resonator" refers to a region of space within which a continuous microwave field can propagate. The resonator may be a closed or substantially closed resonant cavity or an open resonator.

The product whose density is measured is arranged in a region called the "production region", which has a fixed spatial relationship with the region of the first resonator when the sensor is in operation. The production area may extend partially or completely into the first resonator area; alternatively, it may be spatially separated from the first resonator region. In the latter case, the production region may adjoin the first resonator region; alternatively, it may be arranged spatially remote therefrom and the field may be directed from the resonator to the production area directly via a line. The microwaves enter the production area in order to interact with the product. Typically, the microwaves are thereby able to penetrate the first resonator to the production area. The product can be a continuous and/or endless stream of product, such as fiber strands, fiber bands, staple fibers or individual fibers in a spinning preparation machine, or tobacco strands in a cigarette making machine.

According to the invention, the measured variable is determined by the second resonator-since it has microwave shielding for the production area-and is not influenced by the interaction of the microwave field with the dielectric constant. Since the measured variable of the first resonator is comparable to the corresponding measured variable of the second resonator, the influence of environmental influences and disturbance variables on the measurement signals of the two resonators can be compensated for. One of these environmental influences and disturbance variables is, for example, the thermal effect of the environment, such as the thermal load emitted from the product.

The present invention has realised that for example the temperature distribution in the first resonator may be spatially non-uniform and/or may vary over time. As a result of this knowledge, the invention allows measuring, for example, the integrated temperature, i.e. the average temperature in a region which, with respect to its arrangement, coincides with the first resonator region with respect to the production region and thus has substantially the same temperature distribution as it. This is in contrast to temperature measurements in a small area in relation to the first resonator area.

Especially in the case of time-varying, non-uniform occurring environmental influences and disturbance variables, the temperature of the first resonator is measured regularly at a certain point, for example in special cases may cause distorted measurements with large measurement errors. Let us consider an example as a device in which the temperature sensor is arranged on the side of the first resonator remote from the heat source. As soon as the side of the first resonator facing the heat source is heated, a temperature rise has an effect on the measurement signal; but this cannot be detected and compensated until the side of the first resonator remote from the heat source is heated. During the insertion, no satisfactory temperature compensation takes place.

The invention brings particular advantages when it is combined with a first resonator filled with a dielectric. By "dielectric" is meant herein a dielectric constant of at least 2, preferably at least 5. Thus, for example, the temperature dependence of the measured variable of the first resonator is determined by the temperature dependence of the dielectric constant of the insulating material. Since the thermal conductivity of the medium material is generally poor, a spatially inhomogeneous temperature distribution or a time-varying thermal load has a particularly strong influence, since it takes a long time for the static temperature distribution to form. The second resonator is therefore preferably likewise filled with a corresponding dielectric, which has a similar temperature profile to the insulating material of the first resonator at each measuring instant.

The second resonator preferably has similar characteristics to the first resonator in terms of response to environmental influences and disturbance variables. It applies, for example, to the dimensions and materials of the resonator (claim 3), for example in terms of thermal conductivity, heat penetration value, heat transfer, thermal conduction, heat capacity, thermal expansion and/or other heat-related variables. When the property of the first resonator to be compensated is derived from a material, for example an insulating material, this is generally sufficient to comply with suitable properties in relation to such a material.

The first and second resonators are preferably arranged adjacent to each other (claim 6) and/or form a modular unit (claim 7); it is thereby ensured that both resonators are subjected to the same environmental influences and disturbance variables. Alternatively, however, the two resonators may be arranged spatially separated from one another.

A further great advantage of the invention is that the second resonator can advantageously also be used to simultaneously compensate for the influence of other disturbance variables, such as for example a longer electronic drift or a change in material due to ageing.

Due to the temperature dependence of the dielectric constant of the product, the temperature of the product has a direct influence on the measurement signal. The device can thus advantageously contain a further temperature sensor, for example a PT-100 element or a contactless thermometer, for direct and rapid measurement of the product temperature, in order to be able to correct the measurement signal accordingly in a manner known per se.

The invention can basically be used in both cases, i.e. operating the first resonator on the basis of transmission measurements and operating the first resonator on the basis of reflectometry.

The invention also comprises an advantageous device for use according to the invention and/or for carrying out the measuring method according to the invention, in particular for measuring the density of a sliver of at least one textile fibre, for example cotton, synthetic fibre or the like, wherein the microwave measuring device is used to control and/or regulate the processing device for the at least one textile fibre sliver.

The microwave measuring device is advantageously arranged at the output of the carding machine. At least one microwave measuring device is preferably arranged at the infeed end and/or the output end of the drawing system of the draw frame (draw frame). The drafting system is advantageously a carding machine drafting system at the output end of the carding machine. The textile fibre sliver is preferably a carded sliver. The textile fibre sliver is preferably a draw frame sliver. The microwave measuring device is preferably connected to an electronic control and regulation device, for example a machine control and regulation device. The control and regulation device is advantageously connected to at least one actuator (activator), for example a drive motor, for changing the density of the fiber strand. A display device, for example a screen, a printer or the like, for displaying the density or the density change of the fiber strands is preferably connected to the control and regulating device. The microwave measuring device is advantageously used to monitor the density of the sliver produced on the carding machine or drawing frame.

Another example of an application is the measurement of top compression (the region of higher tobacco density in a cigarette) during the manufacture of cigarettes on a cigarette making machine.

Drawings

The invention is explained below by way of exemplary embodiments and with the aid of the drawings, in which:

FIG. 1 is a cross-sectional view of a measurement device configuration according to the present invention having spatially separated resonators;

FIG. 2 is a cross-sectional view of a measuring device configuration according to the present invention in which two resonators are adjacent to each other and form a modular unit;

FIG. 3 is a schematic side view of a carding machine with a microwave measuring device according to the invention;

FIG. 4 shows a can coiler comprising a fiber can with a microwave measuring device according to the invention, wherein the fiber can has a self-leveling device;

FIG. 5 is a schematic side view of a self leveling draw frame with microwave measuring devices according to the present invention as input and output measuring elements;

FIG. 6 shows a self-leveling draw frame with a closed control loop (closed-loop control) and a measuring device according to the invention;

FIG. 7 shows a self leveling draw frame with an open loop control loop (open loop control);

fig. 8 shows a self-leveling draw frame with a combination of open and closed loop control loops (reference variable input) and two measuring devices according to the invention.

Detailed Description

Exemplary embodiments are shown in fig. 1 and 2, wherein in fig. 1 a spaced-apart measuring device and in fig. 2 a modular measuring device is shown, which contains a microwave sensor 1 (measuring resonator) and a compensation device 2 (reference resonator).

The product is guided through the microwave sensor 1 through two openings.

The microwaves are generated by suitable means 10 (microwave generator) and fed to the resonator 1 through the wire 3. A standing wave is induced in the resonator 1 at a specific frequency. The distribution of the field strength in the region of the resonator 1 is schematically shown in fig. 1 and 2. The microwaves enter the production area 12 and can interact with the products 9 located there. The microwaves are output via the connection 4 and passed to a downstream evaluation device 11 (microwave generator). The reference resonator 2 is arranged directly adjacent to the measurement resonator 1.

Microwaves, preferably tapped off from a transverse feed (fed) 10 by means of a switch 7, are injected and fed into the reference resonator 2 via the wires 5 and 6. The microwaves are passed to the evaluation means 11 via the switch 8. The higher the switching frequency of the switches 7 and 8 can be, the better. Since the reference resonator and the measurement resonator are identical in structure, the state obtained in both resonators 1, 2 is identical at all times, e.g. the temperature distribution is approximately identical.

For the measurement, the field frequency in the resonator 1 is driven by the inclusion of a specific, individual resonance range. The range to be passed depends in particular on the product in question and on the actually occurring moisture content and temperature values (due to the large number of resonance shifts occurring therein). Resonant frequency f₁And the half-value width Γ of the measured resonance₁Is determined in the evaluation device from the start signal. Such a measurement and estimation cycle may be performed in fractions of a second.

At a certain time, a corresponding measurement value is generated in the reference resonator 2. The field frequency in the reference resonator 2 comprises a specific, unique field frequencyVertical resonator range drive; resonant frequency f₂And half-value width gamma₂The same is also measured. f. of₂、Γ₂The value is independent of the product density by the arrangement of the reference resonator 2. f. of₂、Γ₂The values are then converted into corresponding f based on two calibration curves stored in the evaluation device₀、Γ₀The value is obtained. f. of₀、Γ₀The values represent the resonance frequency and the half-value width, respectively, of the resonator 1 without product (without load measurement). These calibration curves clearly determine the variable f for a particular product material₂And f₀And variable Γ₂And Γ₀The correlations between them, which are initially determined in the corresponding calibration measurements by the environmental influences and the changes in the specific disturbance variables within the actually occurring range. In operation, the determination of the variable f may then be omitted₀、Γ₀Is particularly advantageous when measuring a product stream (production stream), wherein no-load measurement is only possible when the product stream is interrupted.

From the variables mentioned above, a variable Ψ (a) ═ f ((f) is derived in a manner known per se₁-f₀)；(Γ₁-Γ₀) Only on the material density a and, as the invention, neither on the material moisture content nor on the environmental impact and the particular disturbance variable. The material density a is determined from the variable Ψ by means of a calibration curve stored in the evaluation device. This calibration curve, which clearly defines the relationship between a and Ψ for a particular product material, is first determined in a corresponding calibration measurement by the change in product density within the range that actually occurs.

In order to avoid diffusion effects, the measurements in the measurement resonator 1 and the reference resonator 2 are preferably carried out at comparatively close frequencies. The reference resonator 2 is preferably dimensioned such that the frequency range to be passed has an average separation of less than 1GHz, preferably less than 100MHz, and preferably less than 10MHz, with respect to the measurement resonator 1 and the reference resonator 2. The measurement is preferably carried out in the range from 0.1 to 20GHz, further preferably from 1 to 5GHz, further preferably from 2 to 3GHz, further preferably from 2.4 to 2.5 GHz.

FIG. 3 shows a carding machine 54, for example a Truetzschler high-performance carding machine DK903, with a feed roll 13, a feed plate 14, a licker-in roll 15₁、15₂、15₃Cylinder 16, small cylinder 17, stripping roller 18, press rollers 19, 20, web guide 21, web funnel 22, feed-out rollers 23, 24, carding machine rotating top cover 25, can 26 and can 27. The direction of rotation of each roller is shown by the corresponding curved arrow. The feed-out rollers 23, 24 draw off the card sliver 28, which passes via guide rollers 29, 30 to the coiler 26 and from there is stored in the can 27. A microwave measuring device 31 according to the invention (see fig. 1, 2) is arranged between the outfeed rollers 23, 24 and the guide roller 29. The microwave measuring device 31 is connected to an electronic control and regulating device 32, for example a microcomputer, which changes the rotational speed of the feed roll 13 by means of a variable-speed drive motor 33. In this way, the density of the card sliver 28 leaving the outfeed rolls 23, 24 at a high speed, for example 200m/min or more, is adjusted. The letter a indicates the working direction.

Referring to fig. 4, a drafting system 34 is mounted above the coiler 26 and corresponds to the drafting system shown in fig. 5; reference is made to the description of the drafting system in figure 5. At the infeed end and the outfeed end of the drawing system 34 there is a corresponding microwave measuring device 48, 49, which is connected to the electronic control and regulating device 32, which is also connected to the drive motors 46, 47 for the drawing system 34 and to the drive motor 21 for the can carousel.

Referring to fig. 5, a draw frame 55, such as a Truetzschler draw frame HSR, has a drawing system 34 upstream of a drawing system inlet 34a and downstream of a drawing system outlet 34b, and a sliver 35 enters a sliver guide 36 from a can (not shown) and is drawn by delivery rollers and delivered to the drawing system 34. The drawing system 34 is designed as an 4/3 drawing system, that is to say it consists of three bottom rollers I, II, III (I being the output bottom roller, II being the intermediate bottom roller, III being the feed bottom roller) and 4 top rollers 33, 38, 39, 40. Drawing (draft)35 ″ of the composite fiber strip comprising the plurality of fiber strips 35 is performed in a drawing system 34. The draft includes a primary draft and a main draft. The roller pairs 40/III and 39/II form the primary drafting zone, while the roller pairs 39/II and 38, 31/I form the main drafting zone. The drawn fiber strands 35 ″ reach a sliver guide 41 at the drawing system outlet and are drawn by delivery rollers 42, 43 through a sliver funnel 44, where they condense into a fiber strand 45, which is then deposited in a sliver can (not shown). The letter C indicates the working direction and 35 "indicates the fiber sliver in the drawing system. For example, a delivery roll, a feed bottom roll III and an intermediate bottom roll II, which are mechanically connected by a toothed belt, can be preset to a desired value by means of a variable-speed motor drive. (the associated top rollers 39 and 40 co-rotate). The output base roller I and the feed rollers 42 and 43 are driven by a main motor 47. At the inlet 34a to the drafting system, a variable proportional to the density of the incoming fiber sliver 35 is measured by the feed-side measuring device 48 according to the invention. At the outlet 34b of the drafting system 34, the density of the fiber sliver is obtained by the discharge-side measuring device 49 according to the invention in connection with the sliver guide trumpet 44. A central computer unit 50 (control and regulation device), for example a microcomputer with a microprocessor, determines the settings for the variables to be adjusted of the variable speed motor 46. The variables measured by the two measuring devices 48 and 49 are transmitted to the central computer unit 50 during drawing. The variables measured by the feed-side measuring device 48 and the desired value for the density of the discharged fiber strand 45 are used to determine an adjustment value for the variable-speed motor 46 in the central computer unit 50. The variable measured by the discharge side measuring device 49 is used to monitor the discharged sliver 45 (monitoring the output sliver). By means of this control system, fluctuations in the density of the incoming fiber sliver 35 can be compensated by corresponding adjustments to the drafting process and the fiber sliver can be smoothed. Reference numeral 51 denotes a display screen, 52 denotes an interface and 53 denotes an input device.

Fig. 6, 7 and 8 show the basic arrangement of the drafting system of the draw frame with different configurations for adjusting the density of the fiber sliver. Figure 6 shows a closed loop control circuit in which a microwave measuring device 49 is installed at the output of the drafting system. The fibre material leaving the drafting system passes through a measuring device 49, the output signal of which is compared with a desired value in an electronic control device 50 and converted so that a corresponding control signal is supplied to the actuator for the roll II (variable speed motor 46. see fig. 5). The output signal corresponding to the density of the discharged fibrous material thereby influences the speed of the pairs of drawing rollers 39/II and 38/I in a manner to flatten the fibrous material. Here, a microwave measuring device 48 is located in the area of the fibre material 35 close to the drafting system and measures the density of the fibre material and the corresponding measurement signal is converted in an electronic control 50 into a control signal which is supplied to the actuator for the roll II (variable speed motor 46, see fig. 5). The time taken for the fibre material 35 to travel from the measuring device 48 to the drafting system can be measured electronically. Fig. 8 shows a combination of open-loop and closed-loop control loops, in which the measurement signal of the measuring device 49 is superimposed on the measurement signal of the measuring device 48.

On a special machine tool, for example a carding machine 54 (fig. 3) and a drawing frame 55 (fig. 5) for control and/or regulation, and also for monitoring the uniformity of the finished fibre slivers 28 and 45, compensation for environmental influences and disturbance variables can be implemented by the reference resonator 2, preferably periodically suspended in production and during machine standstill, for example can be changed, wherein no measurement by the measuring resonator 1 is required. The reference measurements in the reference resonator 2 are made at regular or non-regular intervals. If the environmental influences or disturbance variables have only a relatively slow influence, it may be sufficient to carry out the measurement in the reference regulator 2 after a few minutes, preferably at the latest after a few hours. Thereby not affecting the efficiency of the machine.

When the switching of the switches 7 and 8 (fig. 1 and 2) and the stabilization of the electric field in the resonators 1 and 2 can be realized in a short time, the compensation of the microwave measuring device can be completed in a relatively short time. In this way, environmental impact and disturbance variables can be compensated for during production by the processing machine.

Claims (23)

1. A measuring method for measuring material properties of products (9) in a production area, except for water content, wherein microwaves are input into the production area (12) from a first microwave resonator (1) during operation using said first microwave resonator, and wherein compensation means are used for compensating the measurement signal for environmental influence and disturbance variables, wherein said compensation means comprise a second microwave resonator (2) which is shielded with respect to microwave radiation towards the production area (12).

2. A method of measurement as claimed in claim 1, wherein the method is used to measure the density of a product.

3. A method of measurement according to claim 1, characterized in that the method is used for measuring a fibre bundle.

4. A measuring method as claimed in claim 3, characterized in that the method is used for measuring fibre slivers (26; 35) on a spinning preparation machine.

5. A measuring method as claimed in claim 3, for measuring a tobacco strand in the case of a cigarette manufacturing machine.

6. A measuring method as claimed in claim 1 or 2, characterized in that the first resonator (1) and the second resonator (2) have the same structure.

7. A measuring method as claimed in claim 1, characterized in that the first resonator (1) and the second resonator (2) are at least partly filled with a dielectric, wherein the dielectric constant e of the dielectric is_r＞2。

8. A measuring method as claimed in claim 1, characterized in that the first resonator (1) and the second resonator (2) are fed with microwaves of the same frequency.

9. A measuring method as claimed in claim 1, characterized in that the first resonator (1) and the second resonator (2) are arranged adjacent to each other.

10. A measuring method as claimed in claim 1, characterized in that the first resonator (1) and the second resonator (2) form a modular unit.

11. A measuring method as claimed in claim 1, characterized in that the product (9) extends through the first resonator (1).

12. A measuring method according to claim 1, characterized in that the first resonator (1) and/or the second resonator (2) is a completely shielded resonator with an opening for the entry of the sample.

13. An apparatus for measuring material characteristics of products in a production area, comprising a first microwave resonator (1), from which microwaves are fed into the production area (12) in operation, and compensation means for compensating measurement signals for environmental influences and disturbance variables, wherein the compensation means comprise a second microwave resonator (2), which is shielded with respect to microwave radiation towards the production area (12), for measuring material characteristics, other than moisture content, of products (9) arranged in the production area, characterized in that the microwave measurement means are used for controlling and/or adjusting a processing device (9; 28, 35) for at least one textile fibre sliver.

14. The apparatus of claim 13, wherein the apparatus is adapted to measure the density of the textile sliver.

15. Device according to claim 13, characterized in that the microwave measuring device is arranged at the output of the carding machine (54).

16. The apparatus according to claim 13, characterized in that the microwave measuring device is arranged at the infeed end and/or the output end of the drafting system (34) of the draw frame (55).

17. The apparatus of claim 16, wherein said drafting system (34) is a carding drafting system at the output of the carding machine (54).

18. The device as claimed in claim 13, characterized in that the textile fibre sliver (9) is a card sliver (28).

19. A device according to claim 13, characterized in that the textile fibre sliver (9) is a draw frame sliver (35).

20. The device according to claim 13, characterized in that the microwave measuring device is connected to an electronic control and compensation device (32; 50).

21. Device according to claim 20, characterized in that at least one actuator for varying the density of the fibre sliver (9; 28; 38) is connected to the electronic control and compensation device (32; 50).

22. Device according to claim 20, characterized in that the display means for displaying the density of the fibre sliver (9; 28; 35) are connected to the control and electronic compensation means (32; 50).

23. An apparatus according to claim 13, wherein the microwave measuring device is used to monitor the density of the sliver produced on the carding or drawing frame.