Title of Invention

CONTINUOUS WEIGHING METER

Abstract

The continuous weighing meter according to the invention has a conveyor belt (1) driven by a motor (3) and running over a guide roller (4), which is loaded via an input funnel (6) from a feed arrangement (9) . In addition to a first weighing arrangement (11), which determines the gross loading of the loaded conveyor belt (1), the continuous weighing meter has a second weighing arrangement (15), which determines the tare loading of the empty, but possibly dirty and inhomogeneous conveyor belt (1). The weighing distances have the lengths SB (11) or ST (15) and are separated by a distance L between homologous points. The weighing results are converted to digital form in evaluation equipments (22, 21) and taken to a computer (25) which calculates the net loading of the conveyor belt (1). Additionally the computer (25) monitors the running of the belt for slip using increment transmitters (17, 23) and associated counters (18, 24) and generally controls the feed arrangement (9).

Full Text

-1A- Continuous weighing meter The present invention relates to a continuous weighing meter for bulk materials with zero adjustment control according to the preamble to Claim 1. Several processes and devices for the monitoring and recalibration of the zero point of continuous weighing meters are known. WO 91/14927 (Dl) and WO 95/29390 (D2) may be cited as representing the large number of descriptions, which border the state of the technology. The aim of the aforementioned inventions and also of the present one is to increase the accuracy of the determination of the flow of material by a continuous weighing meter. On the one hand - to determine the zero point of the weighing returned by the empty belt - the supply of bulk material to be measured is periodically interrupted (Dl), and on the other two weighing stations are provided downstream from the despatching station. Within certain tolerances the two weighing results are applied to form an average (D2). The periodic interruption of the supply obviously permits the calculation of the possibly varying zero point. This is however troublesome for many applications, since the despatch to another processing station of the material being weighed cannot be interrupted repeatedly without consequence. Added to this the last calculated zero point remains stored for the period between two such interruptions. In the case of problematical bulk materials such as chocolate solids, flour and other partly sticky - 2 - substances the zero point can vary relatively quickly. The process described in D2 does not contribute anything to the absolute accuracy of the weighing when residues of the materials mentioned - possibly even on the underside of the conveyor belt - build up slowly and remain there. The aim which is to be addressed by the present invention, is the production of a continuous weighing meter, with which the zero point can be continuously and permanently determined and is always up to date and available for the processing of the gross weighing. The solution of the set aim is given in the characterising part of Claim 1 with respect to its essential features, in Claims 2 to 9 regarding further advantageous developments. The invention is more closely described using the accompanying drawins. These show: Fig. 1 a schematic representation of the continuous weighing meter according to the invention, Fig. 2 a block schematic of the electrical equipment. In Fig. 1 the metering continuous weighing meter is represented in its mechanical and electrical construction in a rather schematic form. A conveyor belt 1 is driven by an electric motor 3 via a drive roller 2 and runs over a guide roller 4. The guide roller 4 is also formed as a tensioning roller in a known manner. This construction is similarly well - 3 - known and so configured that the even running of the conveyor belt 1 can be effected with it. Further the positions of the drive roller 2 and the guide roller 4 can be interchanged. An input funnel 6 guides the mass stream of a bulk material 7 to be metered onto the conveyor belt 1. The bulk material 7 is taken to the input funnel in a known manner, using for instance a feed screw, vibrator, a conveyor belt or other known conveying method. These known and possible conveying methods are shown schematically as boxes and given the reference number 9. Direct abstraction from a silo by the conveyor belt 1 also comes into consideration. In the last modification the conveyed quantity is controlled only by the speed of the conveyor belt 1; if additionally a feed arrangement 9 is considered, then this is also controlled as well as the belt speed. In the direction of flow of the conveyor belt 1, after the input funnel 6 there is a weighing arrangement 11, comprising a force measuring cell 12, which measures the force on a rod 13 stretching across the entire width of the conveyor belt 1. The actual measurement distance, designated here by the letter S, at whose centre the rod 13 is positioned, is limited by two further rods 14. The relationship between the force measured by the measurement cell 12, the length of the measurement distance, the speed of the belt VB and the flow of material m is known and does not need to be discussed here. The flow of material m determined in this manner is in any - 4 - case a gross value, since the weight of the conveyor belt 1 is continuously weighed in with it. Added to this there are influences of the belt tightness, since for instance the rod 12 lies somewhat higher than the two rods 14. The gross value m has thus to be cleaned up by a tare value, which is given by the measurement of the empty conveyor belt 1. Now instead of periodically interrupting the flow of the bulk material 7, to obtain the tare value, which remains stored until the next determination, according to the arrangement shown in Fig. 1 a second weighing arrangement 15 is provided, in the preferred example of construction fully identical to the weighing arrangement 11. This is positioned before the input funnel 6 in the direction of the movement of the conveyor belt 1 and comprises similarly two rods 14 defining the measurement distance S and a weighing force accepting rod 13, which for its part impacts on a force measurement cell 16. The signals generated by the force measurement cells 12, 16 are each converted into digital weight signals in following evaluation equipments 21, 22 and taken to a computer 25. The interaction between the two weighing arrangements 11 and 15 is explained first in summary, bringing in the further elements shown in Fig. 1, and then in greater detail using Fig. 2. On the motor 3 - or on a drive connected to it, not separately shown - an increment transmitter 17 is connected, with the aid of which a digital signal is generated in a - 5 - counter 18, corresponding to the speed of rotation of the drive roller 2, Additionally an increment transmitter 23, corresponding to the increment transmitter 17 can measure the rotational speed of the guide roller 4; the signals of the increment transmitter 23 are then converted into a digital signal corresponding to the speed of rotation of the guide roller 4 in a second counter 24 connected after it. In so far as the conveyor belt 1 exhibits no slip on the drive roller 2, the signals generated by the counters 17 and 23 and passed to the computer 25 are of the same amplitude; a difference between the two signals means that there is slip in the conveyor belt 1; in this event the computer 25 generates a corresponding signal, which for example can be used for an automatic stopping of the arrangement according to Fig. 1. From the measures described, it is known exactly what time is required on the one hand for a particular point on the conveyor belt 1 to pass over the measurement distance S, and on the other hand also how much time expires for the same point to pass over the distance L where the distance L designates the distance between the two rods 13 lying in the middle of the weighing arrangements 11, 15, in the preferred example of construction the distance in general between homologous points in the two weighing arrangements 11 and 15. For the general case, where the weighing arrangements 11, 15 are not identically constructed, the measurement distance of the weighing arrangement 11 is designated SB and that of the - 6 - weighing arrangement 15 ST. A weighing process for each of the force measurement cells 12, 16 requires a certain, even if a short, time interval, which may be to form an average, or it may be, as in the case of string force measurement cells, for systematic reasons. In the stated time interval the conveyor belt 1 moves forward past the weighing arrangement 11 by a certain distance SB/kB under the assumption that in the time during which the conveyor belt 1 covers the distance SB, kB weighings are undertaken. The weighing arrangement 15 has the measurement distance ST and similarly a certain, possibly differing, time interval for a weighing, so that in the same time, when the weighing arrangement 11 performs kB weighing operations, kT weighings are available from the weighing arrangement 15. It is expedient that kB = kT. As discussed further below, however it is possible that kT = kB/h; i.e. the weighing arrangement 15 works with a lower time resolution than weighing arrangement 11. If further SB ? ST, then for the calculation of the tare loading by the computer the measurement distance ST of the weighing arrangement 15 and the number kT.ST/SB completed by the travel of the conveyor belt 1 over this measurement distance are brought in. Analog to this consideration, during the time in which the conveyor belt 1 passes over the distance L, j weighing operations occur in the weighing arrangement 11. Fig. 2 shows in block schematic form, how the different - 7 - PKT-963 digital signals quoted are processed. The computer is shown in Fig. 1 as a box identified by the reference 25. It comprises a central processing unit 30, which undertakes all the arithmetic and logic operations and also contains the control program in file. An input/output unit 32 is connected to the central processing unit 30 by data feeder lines 36, 37, via which the control quantities such as belt speed, bulk flow, on and off commands and - if provided in the program -limit values (for instance for target deviation and maximum tare value) can be input. Inputs are effected via the input/output unit 32 using a schematically represented keyboard 35; output values are shown by numerical magnitudes and operating conditions on a visual display unit 34. The input values covering motor revolutions (18), belt running speed (24) and gross weighing (22) are fed in directly to the central processing unit 30 over bidirectional data lines 38, 39, 40; bidirectional because the central processing unit 30 outputs at least the central timing for the elements referenced as 18 to 24. The evaluating unit for tare weighing, that is for the weighing arrangement 15, is connected via a further bidirectional line 41 to a shift register 31. This includes, for example, j counting stages, whose content is shifted by one stage forward at each pulse with the reasonable assumption, that the weighing arrangements 11, 15 carry out their weighing operations at the same clock speed. The result output from the last stage with the number - 8 - j is processed with the result of the gross weighing of weighing arrangement 11 in the central processing unit 30 to give a net result; the entry read into the counting stage with the number 1 is the current weighing of weighing arrangement 15. It is included in the scope of the invention, that the number of counting stages j might be reduced by a factor h with a simultaneous reduction of the shift timing by the same factor h. This has the consequence that a certain tare result of the weighing arrangement 15 is used for h gross weighings. This can be indicated, when the positional and time variations of the tare result is small. Instead of a shift register 31, the use of an addressable RAM with j numbered store locations is similarly within the scope of the invention, whereby the reduction to j/h store locations - as previously mentioned - is similarly included in the scope. In this at each weighing, gross as well as tare, the corresponding store location is addressed and at the same time the address selector is advanced by one number. The running speed of the belt (Motor 3) and the feed arrangement 8 controlling the flow of the bulk material 7 can be controlled by the process program in the central processing unit; processes and devices for this purpose are of themselves known; likewise the processing of the data from the devices designated 17 to 24. The advantage of the application described here of the second weighing cell 15 evaluating the running tare value is - 9 - that a tare weighing, which is currently determined, is available for every gross weighing and also periodical variations of the tare, such as inhomogeneities of the conveyor belt 1, and also irregularities such as dirtying of the belt (including the build-up of encrustations) are egually captured and considered. On the one hand this obviates the periodic empty running of the conveyor belt 1, and on the other hand one is not working with an average tare value, but with a multiplicity of individual and currently updated values. The measures under the invention also increase the availability of the feed mechanism, which forms the decisive part of the continuous weighing meter. A further advantage of the continuous weighing meter according to the invention is that spliced conveyor belts can be used instead of circular woven or otherwise homogeneous manufactures. Spliced conveyor belts exhibit an inhomogeneity at the spliced section, which cannot be taken into account using stored tare values. Using the arrangement according to the invention mass inhomogeneities - irrespective of their cause - are effectively subtracted and thereby the resolution and accuracy of the continuous weighing meter is increased with simultaneous reduction of the cost of the conveyor belt as a welded part. -10- WE CLAIM: 1. A continuous weighing meter for bulk materials (7) with zero point correction with a drive roller (2) driven by a motor (3), a guide roller (4) and a conveyor belt (1) running around them, an input funnel (6) for the bulk material (7) to be weighed, a first weighing arrangement (11) positioned after the input funnel (6) with a first force measuring cell (12) with an evaluation equipment (22), at least one device for determining the running speed of the conveyor belt (1), and a computer (25) with a central processing unit (30) and computing and control programs for the evaluation of all values arising to be determined and an input/output unit (32) and data lines to all measurement positions, Characterized in that, a second weighing arrangement (15) with a second force measuring cell (16) with an evaluation equipment (21) is present, however positioned before the input funnel (6) in the running direction of the conveyor belt (1) and thus determines the tare loading due to the empty conveyor belt(l), - in the computer (25) means are present to determine the loading of the bulk material (7) on the conveyor belt (1) from the weighing results of the first weighing arrangement (11) and that of the second weighing arrangement (15). -11- 2. A continuous weighing meter as claimed in claim 1, wherein - the two weighing arrangements (11,15) are so constructed that they have two rods (14) at right angles to the direction of movement of the conveyor belt (1), extending across its width, which exhibit the mutual separation SB for the first weighing arrangement (11) and the mutual separation ST for the second weighing arrangement (15), whereby SB and ST represent the measurement distances of the two weighing arrangements (11,15) and that a further similar rod (13). parallel to the aforementioned rods (14) is present in each case, each of which impacts on a force measuring cell (12,16). 3. A continuous weighing meter as claimed in claim 2, wherein the distance between the rods (13) lying in each case in the centre of the measurement distance has the value L. 4. A continuous weighing meter as claimed in claim 2 and claim 3, wherein the two weighing arrangements (11,15) are constructed essentially identically, so that SB = ST = S. 5. A continuous weighing meter as claimed in claim 3, wherein - the means available in the computer (25) to determine the net loading of the conveyor belt (1) comprise in that a shift register (31) is present with j/h counting stages, where j and h are whole numbers and the count j corresponds to the number of weighings which are undertaken by the first weighing arrangement (11) in the time that the conveyor belt (1) covers the distance L , 12- - each weighing result of the second weighing arrangement (15) is read into the shift register (31), and the j/h weighing result of the second weighing arrangement (15) already in there is shifted further by a counting stage, - the weighing result from the last counting stage of the shift register (31) from the second weighing arrangement (15) is available as tare value for the gross value determined from the first weighing arrangement (11), whereby the determination of the net value is undertaken in the central processing unit. 6. A continuous weighing meter as claimed in claim 5, wherein the two weighing arrangements (11, 15) are essentially constructed identically and h = 1 and the two weighing arrangements operate with the same timing. 7. A continuous weighing meter as claimed in claim 3, wherein - the means available in the computer (25) for determining the net loading of the conveyor belt (1) comprise in that an addressable RAM with j/h store locations is present, where j and h are whole numbers and the count j of the number of weighings corresponds to those undertaken by the first weighing arrangement (11) in the time during which the conveyor belt (1) passes through the distance L, - each weighing result from the second weighing arrangement (15) is read into the RAM, whereby the address is increased by the value of 1, - the weighing result read out from the store location with the address j/h from the second weighing arrangement (15) is available as tare value for the gross value determined from -13- the first weighing arrangement (11), whereby the determination of the net value is undertaken in the central processing unit (30). 8. A continuous weighing meter as claimed in claim 7, wherein the two weighing arrangements (11,15) are essentially constructed identically and h = 1 and the two weighing arrangements operate with the same timing. 9. A continuous weighing meter as claimed in claim 1, wherein the computer (25) has an input/output unit (32) connected to the central processing unit (30) with a keyboard (35) for the input of operationally required parameters and control values and a visual display unit (34) for the representation of operational data and conditions. The continuous weighing meter according to the invention has a conveyor belt (1) driven by a motor (3) and running over a guide roller (4), which is loaded via an input funnel (6) from a feed arrangement (9) . In addition to a first weighing arrangement (11), which determines the gross loading of the loaded conveyor belt (1), the continuous weighing meter has a second weighing arrangement (15), which determines the tare loading of the empty, but possibly dirty and inhomogeneous conveyor belt (1). The weighing distances have the lengths SB (11) or ST (15) and are separated by a distance L between homologous points. The weighing results are converted to digital form in evaluation equipments (22, 21) and taken to a computer (25) which calculates the net loading of the conveyor belt (1). Additionally the computer (25) monitors the running of the belt for slip using increment transmitters (17, 23) and associated counters (18, 24) and generally controls the feed arrangement (9).

Documents:

00051-cal-1998-abstract.pdf

00051-cal-1998-claims.pdf

00051-cal-1998-correspondence.pdf

00051-cal-1998-description (complete).pdf

00051-cal-1998-drawings.pdf

00051-cal-1998-form-1.pdf

00051-cal-1998-form-2.pdf

00051-cal-1998-form-3.pdf

00051-cal-1998-pa.pdf

51-CAL-1998-FORM 27.pdf

51-CAL-1998-FORM-27-1.pdf

51-cal-1998-granted-abstract.pdf

51-cal-1998-granted-acceptance publication.pdf

51-cal-1998-granted-claims.pdf

51-cal-1998-granted-correspondence.pdf

51-cal-1998-granted-description (complete).pdf

51-cal-1998-granted-drawings.pdf

51-cal-1998-granted-examination report.pdf

51-cal-1998-granted-form 1.pdf

51-cal-1998-granted-form 2.pdf

51-cal-1998-granted-letter patent.pdf

51-cal-1998-granted-others.pdf

51-cal-1998-granted-pa.pdf

51-cal-1998-granted-reply to examination report.pdf

51-cal-1998-granted-specification.pdf