Method and device for calibrating a scale for determining the weight per unit length of an elongate object strand as seen in the conveying direction

Abstract

The invention relates to a method for calibrating a scale (3) for determining the weight per unit length (g / m) of a quasi-endless object strand (11) which is elongate in the conveying direction (x), in particular a rubber strand for producing tyres, wherein the scale has a weighing section with a weighing device (5) and a preload-forming load receptacle (7) which is arranged thereon and which forms a conveying plane (x-y) and comprises conveying element conveying devices (9a, 9b) which are arranged (directly) upstream and downstream of the weighing section (5, 7) and do not form a preload, in which, for calibrating the scale (3), a test strand (13) is used as a test body, wherein the test strand, by way of complete travelling-over, runs onto the weighing section (5, 7), passes over the weighing section (5, 7), and runs off same, wherein, as seen in the conveying direction (x), the length of the test strand (13) projects beyond the length of the load receptacle (7) to such an extent that there is, during complete travelling-over, at least one position of the test strand (13) at which said test strand is supported by the load receptacle (7) and the conveying element conveying devices (9a, 9b) arranged upstream and downstream, and there is thus a force shunt, during complete travelling-over the dynamic weight of the test strand (13) is determined, the total weight of the test strand (13) is previously known or is determined substantially without a force shunt and is compared with the determined dynamic weight of the test strand (13), a possible deviation is detected in a determined manner, and the possible deviation is compared with a specified target value. The invention also relates to a device for carrying out the method.

Description

[0001] Method and device for calibrating a scale for determining the weight per unit length of an elongated object strand seen in the conveying direction

[0002] The invention relates to a method for calibrating a scale for determining the weight per unit length (g / m) of an elongated object strand as seen in the conveying direction, and to a device for carrying out such a method.

[0003] Such processes are used, for example, in tire manufacturing. To determine the so-called weight per meter, or the weight per unit length (g / m), of a (virtually) continuous rubber strand for tire production, a strand scale is typically used to continuously measure the weight per unit length (i.e., the mass flow). To ensure the overall quality of tires in terms of total weight and, if applicable, imbalance, the tire manufacturer requires the most accurate and reliable weight per meter information possible.

[0004] The strand scales or meter weight scales used in tire production do not meet the increasingly stringent requirements or do so only partially.

[0005] The present invention is therefore based on the object of creating an efficient and cost-effective method and a device with which the accuracy of scales for determining the weight per unit length is increased.

[0006] This object is achieved according to the invention by a method having the features of claim 1 and a device having the features of claim 10.

[0007] According to the invention, a special calibration method is created for a scale for determining the weight per unit length of a quasi-endless object string, the weight determination of which is subject to force shunt effects. This calibration method takes these force shunt effects into account in an improved form. Any weighing device with a load suspension, in particular with at least one load cell, can be used as a scale. Even an X-ray scale, i.e. weighing using X-rays (where the weight is determined from gray values), would be conceivable. In this case, the preload-generating load suspension would be a conveyor element, in particular a belt, on which the object string is transported and penetrated by the X-rays. The belt attenuates the X-rays or is taken into account in the gray value determination as a preload.

[0008] When weighing by X-ray, it is even conceivable to dispense with a preload-forming load sensor, for example, if the sensor is arranged in a belt gap. The following advantageous embodiments are therefore applicable not only to weighing with a preload-forming load sensor, but also to weighing by X-ray without a preload-forming load sensor.

[0009] According to the invention, a test string is used as a test body for calibration, which, viewed in the conveying direction, projects beyond the length of the effective load-bearing device of the scale to such an extent that at least one position of the test string exists during a complete overrun in which it is supported simultaneously by the load-bearing device and by the upstream and downstream conveying devices, thus creating a force shunt on both sides.

[0010] This test string can preferably be a production-like test body or test specimen of finite length, which in its properties, such as dimensions, specific weight, elasticity, etc., corresponds to or at least comes very close to the (quasi-) endless object string to be weighed in ongoing production, except for the length.

[0011] In a preferred embodiment of the invention, the test strand can have a length of, for example, up to 1.5 times, preferably up to 3 times, particularly preferably up to 5 times, or even up to 10 times the length of the load-bearing section or weighing section, thus significantly exceeding it. In any case, the test strand is significantly shorter than the virtually endless object strand. In a particularly preferred embodiment of the invention, the length of the test strand can correspond to the product length required for further processing of the respective tire type.

[0012] Any load-bearing device, such as belt conveyors, chain conveyors, roller conveyors, or friction plates, can be used to convey a test string. The load-bearing devices are preferably non-driven to avoid negative drive influences, such as vibration, on the weight determination. However, the upstream and downstream conveyor devices can also be driven.

[0013] The scale is then subjected to a complete overrun in a calibration run (before, during or after ongoing operation with an object string), whereby the test string moves towards the weighing section, in particular the load support, over it and away from it in the conveying direction.

[0014] The complete overrun, especially the beginning and end, can be read, for example, from the weight signal curve (rise from and fall to a constant "zero line") or detected by sensors such as at least one light barrier. Positions and thus the beginning and end of the measuring cycle (complete overrun) can also be detected using encoders (e.g., located on the drive of the conveyor elements).

[0015] During the complete overflow, the dynamic weight of the test strand is determined, wherein the test strand is conveyed during the overflow, preferably continuously, in particular at the same speed, for example 0.5 m / s to 0.75 m / s, as the quasi-endless object strand.

[0016] The dynamic weight calculated in this way, for example by summing or integrating continuously determined individual values, i.e. the total weight dynamically determined with the scale, is compared with the (actual) total weight of the test strand. The total weight of the test strand can be determined without or at least essentially without force shunt, or it can be known in advance, for example in the form of a standard test strand or even a calibrated test strand. The total weight can be determined, for example, by means of a separate weighing process using a scale on whose weighing support or load receptor the test strand rests completely, i.e. spread out, rolled up, folded, or at least partially hanging down or upright. The total weight is preferably determined statically, i.e. with a static load.

[0017] For example, the separate weighing process could also take place during a production break, whereby the test strand is weighed statically on the scale while completely lying down (e.g. folded) to determine the weight per unit length of the object strand.

[0018] According to the invention, any deviation between total weight and dynamic weight is determined or recorded and / or ascertained, for example by means of a control and / or evaluation device, for example a process control unit, and compared with a predetermined target value.

[0019] This makes it possible to ensure and even prove the accuracy of the scale.

[0020] In a further embodiment of the invention, the determined deviation is output to a higher-level process control or an operator.

[0021] Of course, it is also conceivable to log one or more results, e.g. as a trend, whether the deviation is within the specified tolerance, i.e. below the target value, and, especially in the negative case, to issue a notification or even an alarm depending on the deviation or even to stop processing.

[0022] In a preferred embodiment of the invention, at least one correction factor is determined from a specific deviation, for example by means of the control and / or evaluation device, in order to correct the dynamic weight determination of an elongated, quasi-endless object string. This advantageously allows the scale to be adjusted and thus the accuracy and quality of the weight determination as well as the efficiency and degree of automation to be increased. The at least one correction factor can be determined separately for the upstream and / or overflow and / or downstream processes. In particular, this can take into account the fact that the upstream and downstream behavior is particularly responsible for incorrect measurements due to different influences of the force shunt. In addition, unavoidable variations in the structural design (height difference or alignment of the rollers) can be compensated for by the at least one correction factor.

[0023] In a particularly preferred embodiment of the invention, the total weight of the product is determined on a separate scale. This separate scale can also be part of the production line, allowing automated weighing without manual intervention by an operator.

[0024] In a further embodiment of the invention, the test strand is separated from a target strand in ongoing production before, during, or after ongoing operation. This advantageously ensures that the test strand corresponds in its properties – except for its length – to the target strand. The test strand can be separated from the beginning or end of the target strand, so that a single cut, for example, using a cutting device, is sufficient. If the test strand is separated from a different area of ​​the target strand, two cuts are naturally required.

[0025] In a preferred embodiment of the invention, the test string is cut from an object string during operation, creating a gap of at least one length equal to the load-bearing device or the weighing section length before and / or after the test string. Providing the gap of the specified length advantageously ensures that the dynamic weight of the test string is determined without the influence of preceding or following parts of the object string.

[0026] In the case of an X-ray scale, the length of the load support or the weighing section corresponds to the detector width, for example, the extension of the line sensor or the group of line sensors or the area sensor in the conveying direction. Thus, only very short gaps, e.g., a few mm, are necessary. The term "load support" in this case refers to the weighing section and not to the load support for a load cell (load support is only necessary for trouble-free conveying).

[0027] Such a gap can be created, for example, by two cuts or by punching. If sections are created by cutting out, these sections can be removed manually or, preferably, automatically (using a ejection or sorting device).

[0028] Of course, it is also conceivable to create a gap by cutting and then warping, i.e., conveying the separated parts of the object string at different speeds (up to a brief stop). If the test string is not cut at the beginning (gap after test string) or at the end (gap before test string) of the object string, two gaps are naturally required.

[0029] In a particularly preferred embodiment of the invention, the test strand is removed from a production line to determine its total weight manually or, preferably, automatically (for example, using the aforementioned or another removal device). Automatic removal can be achieved, for example, by a pivoting or folding conveyor device or by a so-called lift-up weighing system, in which the test strand is completely lifted out using a suitable lifting device, in particular a fork.

[0030] In a further embodiment of the invention, the discharge can be performed only temporarily, so that the test strand is reinserted into the production line for further processing (using an infeed device). In this case, the infeed and outfeed can take place after, but also before, a complete overflow of the weighing section. For example, in lift-up weighing, the test strand can be discharged and reinserted before the complete overflow.

[0031] This advantageously means that no material is wasted.

[0032] In a preferred embodiment of the invention, the dynamic weight of the test string is determined by summing or integrating consecutively sampled individual values. These values ​​are advantageously already available in a meter scale or its control and / or evaluation device, so that the dynamic weight of the test specimen can be determined easily (dynamically).

[0033] According to the invention, the device comprising a scale for carrying out the method explained above has at least one, but at most one group of a maximum of three, conveying elements adjacent to the weighing section and lowered with respect to the conveying plane before and / or after the weighing section.

[0034] These lowered conveyor elements, particularly rollers, prevent the object string from resting on them and reduce the negative influence of height differences between the load-bearing device and upstream and downstream, non-preload-generating conveyor devices or their conveyor elements on the theoretical force shunt (ideally assumed without height differences). In this case, the distance to the next conveyor element forming the force shunt is increased in the conveying direction, so that a significantly smaller possible height difference (perpendicular to the conveying plane) compared to this increased distance has a lesser effect on the measurement result, thus increasing measurement accuracy.

[0035] Because the conveying elements, in particular rollers, are only lowered (for example a few millimeters, preferably at most 5 mm, in particular at most 3 mm) and are not completely missing, a beginning of the object string is guided sufficiently to pass over the weighing section, so that undesired threading (outside the conveying plane), in particular submerging of the string beginning under a conveying track, in particular roller track, is avoided.

[0036] As already explained above, the device comprising a scale may have a cutting device (upstream) to produce a test strand.

[0037] Furthermore, as explained above, the device can have a discharge device and preferably an infeed device in order to automatically discharge the test strand before or after the complete overflow of the test strand over the weighing section (upstream and / or downstream) and preferably also to infeed it again.

[0038] In a further preferred embodiment of the invention, the load receiving device and thus the weighing section has, as inlet and outlet, a conveying device connected upstream and downstream, which, together with the weighing section, have a common base frame as a module.

[0039] The common base frame ensures a common attachment to the mainland, thus facilitating a highly precise height adjustment of the conveyor elements of the conveyor devices and the load handling system, especially the rollers, to each other.

[0040] The invention is explained in more detail below using an embodiment shown in the drawing.

[0041] The drawing shows:

[0042] Fig. 1 is a perspective view of a scale according to the invention;

[0043] Fig. 2 is a schematic side view of a production line with a scale according to Fig. 1 and an endless object string;

[0044] Fig. 3 is a schematic side view of the production line according to Fig. 2 with a test string in position on the weighing section;

[0045] Fig. 4 is a schematic side view of the production line according to Fig. 2 and Fig. 3 with a test strand in position during the discharge; Fig. 5 is a schematic side view of the production line according to Fig. 2 to Fig. 4 with a test strand in position on a separate scale and

[0046] Fig. 6 is an enlarged schematic view of detail D from Fig. 5.

[0047] The scale 3 shown in Fig. 1 comprises a weighing device 5 with, for example, at least one load cell (not shown in the drawing). Located above the weighing device 5, as viewed in the z-direction, is a load-bearing device 7 with conveyor elements designed as rollers.

[0048] The load holder 7 thus forms the preload for the weighing device 5 with a conveying plane xy.

[0049] Viewed in the conveying direction x, the scale 3 has an immediately adjacent upstream conveying device 9a upstream and an immediately adjacent downstream conveying device 9b downstream.

[0050] These conveying devices are not mechanically directly connected to the load receiving device 7 or the weighing device 5 and therefore do not form a preload for weighing.

[0051] As can be seen from Fig. 1, the load receiving device 7 and the conveying devices 9a, 9b with their conveying elements in the form of rollers form a common conveying plane xy for the continuous conveying and weighing of an object string 11 (see Fig. 2).

[0052] The scale 3 and the upstream and downstream conveyor devices 9a, 9b are arranged in a common housing 37, ensuring joint attachment to the mainframe or to a machine frame in the sense of a mainframe. This facilitates highly precise height adjustment, for example, in the range of a few micrometers, of the conveyor elements (in this example, the rollers) of the conveyor devices 9a, 9b and the load-bearing device 7 relative to one another. The housing 37 represents a module that can be inserted or mounted into a production line 1.

[0053] Fig. 2 shows such a production line 1 with a scale 3 on which a quasi-endless object strand 11 is conveyed in the conveying direction x.

[0054] The scale 3 is followed upstream by a conveyor line 21 and downstream by a conveyor line 23, which are only examples of a production line 1 that can be continued in any desired manner.

[0055] As can be seen from Fig. 2, the endless object strand is continuously conveyed over the entire conveying section (scale 3, conveying sections 21, 23) in the conveying direction x and the weight per unit length (g / m) of the object strand 11, for example a rubber strand for tire production, is determined by means of the scale 3.

[0056] The conveyor elements in the illustrations in Fig. 2 to Fig. 5 are only shown schematically in the form of endless belts, even if they are preferably rollers.

[0057] Upstream of the scale, a cutting device 35 is arranged, by means of which a test strand 13 can be cut from the object strand 11. In order to create a test strand 13 and gaps of length L before and after it during ongoing operation, the cut-out parts can be removed or ejected in a manner not shown in detail, preferably automatically.

[0058] Fig. 3 shows a snapshot of a position in which a test string 13 with a length P significantly greater than the length W of the weighing section or the load-bearing device 7 rests both on the load-bearing device 7 and at least partially on the upstream and downstream conveyor devices 9a, 9b. Since the conveyor devices 9a, 9b do not form a preload, in the position shown, a force shunt exists due to the resting of the test string 13 on both conveyor devices 9a, 9b during weighing.

[0059] The length L of the gaps is at least slightly greater than the length W of the weighing section, so that the leading and trailing ends of the object string 11 are never located at the same time (in any instantaneous position) as the test string 13 in the weighing section or on the load support 7.

[0060] During the complete overrun, in which the test string moves in the conveying direction x onto the weighing section or the load receiving device 7, overruns the weighing section and moves away from it, the dynamic weight of the test string 13 is determined, wherein the test string 13 preferably moves at the same speed, for example 0.5 m / s to 0.75 m / s, as the object string 11.

[0061] By summing or integrating continuously determined individual values, the dynamic weight of the test string 13 is calculated or determined dynamically (as dynamic weight).

[0062] As can be seen in Fig. 4, in the production line 1 there is a pivotable conveyor device 17, for example a folding belt, which is guided by a conveyor belt shown in Fig.

[0063] 2 and Fig. 3 can be pivoted upwards in the conveying direction x into a (discharge) position shown in Fig. 4.

[0064] In the discharge position, the test string 13 is discharged from the production (ongoing operation) of the object string 11 after a complete overflow of the weighing section or the load receiving device 7 and is guided to a separate scale 15 via a feeding conveyor device of any type.

[0065] If the test string 13 comes to rest on the weighing support 25 of the separate scale 15, as shown in Fig. 5, or rests completely on it, the movement of the test string 13 is preferably stopped.

[0066] The weighing support 25 is at least as long as the test string, so that the total weight of the test string can be determined without (or at least essentially without) force shunt, preferably statically (with a static load).

[0067] Of course, it is also conceivable that the test strand 13 is weighed in motion, preferably at a speed slower than the production speed of the production line 1. By means of a control and / or evaluation device not shown in the drawing, for example a process control unit, the total weight determined in this way is compared with the dynamic weight.

[0068] In the case of a deviation or difference, it is determined whether the deviation is within a specified tolerance (below a target value).

[0069] If the result is positive, this confirms that the scale is in a calibrated state.

[0070] If the reading is negative, the scale can be (readjusted). For this purpose, a correction factor can be determined from the aforementioned comparison of total weight and dynamic weight and applied to the weight determination of scale 3 directly or in the control and / or evaluation device.

[0071] As shown in Fig. 6, the conveyor elements immediately adjacent to the load receiving device 7, in particular rollers 31, 33, are lowered relative to the conveyor plane xy (i.e., relative to the remaining rollers of the conveyor devices 9a, 9b and load receiving device).

[0072] By lowering the load by a few millimeters, in particular 3 mm, the object strand 11 no longer rests on the rollers 31, 33, so that the distance between the load support 7 and the nearest rollers increases. This advantageously reduces the influence of existing height differences between the rollers on the "theoretical" force shunt (in which only half of the material is weighed between the weighing and non-weighing rollers).

[0073] Since the rollers are not omitted but are only lowered, they still act as a threading aid for the beginning of an object string, so that an undesired sinking or diving below the load suspension 7 is prevented.

[0074] The number of lowered rollers and thus the aforementioned distance can of course be adapted to the properties, in particular the elasticity, of the object strand in order to prevent resting on the lowered rollers on the one hand and to ensure that the distance is as large as possible on the other.

[0075] To prevent negative effects, such as vibrations, on the weighing process, the conveyor elements of the weighing section are not driven.

[0076] As already explained in relation to Fig. 1, Fig. 6 only schematically shows that the load receiving device 7 and the upstream and downstream non-preload-forming conveying devices 9a, 9b have a common base frame 37.

[0077] List of reference symbols:

[0078] I Production / manufacturing line

[0079] 3 scales

[0080] 5 Weighing device

[0081] 7 preload-forming (preferably non-driven) load suspension

[0082] 9a, b upstream and downstream non-preload-forming conveying devices

[0083] II Object strand

[0084] 13 test string

[0085] 15 separate scales

[0086] 17 pivoting conveyor device

[0087] 19 feeding conveyor device

[0088] 21 Upstream conveyor line

[0089] 23 Conveyor line downstream

[0090] 25 Weighing support of the separate scale

[0091] 27 Weighing device of the separate scale

[0092] 31 lowered conveyor element

[0093] 33 lowered conveyor element

[0094] 35 Cutting device

[0095] 37 Base frame x Conveying direction y Transverse direction to the conveying direction xy Conveying plane of the scale z Height direction of the scale perpendicular to the conveying plane xy

[0096] P Length of test string

[0097] W Length of the weighing section

[0098] L Length of gaps

[0099] D Detail

Claims

Patent claims 1. Method for calibrating a scale (3) for determining the weight per unit length (g / m) of a quasi-endless object strand (11) which is elongated in the conveying direction (x), in particular a rubber strand for tire production, wherein the scale comprises a weighing section with a weighing device (5) and a preload-forming load receiver (7) arranged thereon Twhich forms a conveying plane (xy) and comprises conveyor devices (9a, 9b) arranged (immediately) upstream and downstream of the weighing section (5, 7) and which do not form a preload, a) in which a test strand (13) is used as a test body for calibrating the scale (3), b) wherein the test strand travels in the conveying direction in the form of a complete overflow onto the weighing section (5, 7), travels over the weighing section (5, 7) and travels away from it, c) wherein, viewed in the conveying direction (x), the length of the test strand (13) exceeds the length of the load receiver (7) by so much that at least one position of the test strand (13) exists during the complete overflow in which it is supported by the load receiver (7) and the upstream and downstream conveyor devices (9a, 9b) simultaneously and thus a force shunt exists on both sides of the load receiver (7), d) during the complete overflow the dynamic weight of the test string (13) is determined,e) the total weight of the test string (13) is known in advance or is determined essentially without force shunt and is compared with the determined dynamic weight of the test string (13), f) any deviation is determined and g) any deviation is compared with a specified target value.

2. Method according to claim 1, characterized in that the determined possible deviation is output to a process controller or an operator.

3. Method according to claim 1 or 2, characterized in that at least one correction factor is determined from a specific deviation in order to correct the dynamic weight determination of an elongated, quasi-endless object strand (11).

4. Method according to claim 3, characterized in that the at least one correction factor is determined separately for run-up and / or overflow and / or run-off.

5. Method according to one of the preceding claims, characterized in that the determination of the total weight of the test strand (13) takes place on a separate scale.

6. Method according to one of the preceding claims, characterized in that the test strand is separated from an object strand (11) of the ongoing production.

7. Method according to claim 6, characterized in that the test strand (13) is cut off from an object strand (11) during operation, wherein a gap (L) of at least one length of the load support (W) is created before and / or after the test strand (13).

8. Method according to claim 6 or 7, characterized in that the test string (13) is manually or automatically discharged from a production line (1) to determine the total weight.

9. Method according to one of the preceding claims, characterized in that the dynamic weight of the test strand (13) is calculated by summation or integration of continuously determined individual values.

10. Device for carrying out a method according to one of the preceding claims, characterized in that the device has at least one, but at most one group of a maximum of three, conveyor elements (31, 33) located lower with respect to the conveyor plane (xy) before and / or after the weighing section (5, 7).

11. Device according to claim 10, characterized in that the device comprises a cutting device (35) to produce a test strand (13).

12. Device according to claim 10 or 11, characterized in that the device has a discharge device (17) in order to automatically discharge the test strand (13) before or after the complete overflow of the test strand (13) over the weighing section (5, 7).

13. Device according to one of claims 10 to 12, characterized in that the load receiving device (7) has an upstream and downstream conveyor device (9a, 9b) as an inlet and an outlet, and these conveyor devices (9a, 9b) together with the weighing section (5, 7) have a common base frame as a module.

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