METHOD AND APPARATUS FOR WEIGHING

Abstract: The invention concerns a method and apparatus for weighing by a conveyor-type weighing unit (2). A conveyor belt (3) forming an endless loop is transported along a first guiding unit (15), defining a first conveying direction (11) and extending in-between the top sides of opposite arranged rollers (16, 17). The belt is driving in a revolving manner and transported over a weighing device (4). The weighing device is a part of the first guiding unit and performs weighing of the objects transported along the conveyor. The conveyor-type-weighing unit is characterised in the weighing unit comprising two or more weighing-platforms (7). The platforms are arranged side by side as a part of the first guiding unit (15). Each of the platforms measures the weight on the conveyor belt placed over them. A data processing unit (10) is connected to the platforms and continuously compares the measurements sent thereto.

Description: Method and apparatus for weighing Technical Field The invention relates to a method and apparatus for weighmg by conveyor-type weighing unit, where a conveyor belt forming an endless loop is transported along a first guiding unit, defining a first conveying direction and extending in-between the top sides of a opposite arranged rollers. The belt is driving in a revolving manner by a driving unit and transported over a weighing device in a downstream direction. The weighing device being a part of the first guiding unit and perform weighing of objects transported along the conveyor. Background of the Invention Conveyor weighing has been known weighing technique for quite some time. Such apparatus have mainly been used for weighing of bulk material such as grain, rocks and other like materials. There is a growing need for accurate and high speed weighing units, both continuous weighing of bulk material as well as for weighing of individual objects such as food pieces. It is essential in the food processing to measure as exact as possible the weight of the object being processed prior to various types of operations such as sorting, cutting, or packaging. The weighing of individual food pieces transported along a conveyor is today an important operation in processing of f.ex. fish filets and trimming of meat to mention two. If one had to weigh every object individually on a stationary weighing unit, the processing capacity would be diminished dramatically. There is however no question that the aforementioned applies not only to processing of fish and meat but also to other types of food and/or objects. The main disadvantage of the existing conveyor-type weighing apparatus, especially those available for the food processing industry is lack of accuracy and low processing capacity. Further disadvantage as commonly known, is the use of one weighing platform, where the length of the platform determines the processing capacity of the weighing apparatus. If a number of single objects, are to be weighed successively and without disturbance to a next adjacent object the distance between two successive objects must be equal or greater than the length of the platform. This results in low processing capacity as the maximum length of platform needed determines the distance between adjacent objects. One can only increase the processing speed by decreasing the length of the weighing platform. By decreasing the length of a platform a larger number of objects can not be successively weighed. On the other hand by increasing the length of a platform, the distance between the objects on the conveyor must be increased and thereby the process capacity will be decreased. From US Patent No. 4.526.244 it is known to use three or more, but spaced apart weighing stations or areas disposed along a conveying path and a comparator (computer) for comparing the weighings from each weighing station. However the 244 Patent do not teach the use of side by side arrangement of weighing platforms. Brief Description of the Invention The object of the invention is to provide accurate and high-speed conveyor- type weighing unit capable of weighing objects of varying dimension at high- speed and operating performance. The conveyor-type-weighing unit according to the invention is characterised in; the weighing device comprising; two or more side by side, in said conveying direction arranged weighing platforms, each platform having a pre-defined platform length, each weighing platform continuously weighing the conveyor belt section placed there over and/ or the object transported there on, one, two or more adjacent arranged weighing platforms constitutes at each time a weighing unit having a total platform length equal or greater than the object length to be weighed, said weighing platforms being operatively connected to a data processing unit, said data processing unit receiving and processing data from said weighing platforms, and based thereupon, the length/ weight of the object is determined and accordingly appropriate number of adjacent platform selected, having total length at least equal or greater than the object to be weighed and thereby enabling minimal spacing between adjacent objects and maximum operational capacity. As a result it is possible to perform weighings of objects of varying length with the minimum distance between the objects. And thereby obtain high processing speed. By this arrangement the distance between adjacent objects does only need to be equal or larger that the length of one of the platform, or added length of two or more adjacent platforms. By this arrangement objects of varying length can be weighed with minimum distance between them at high speed and with great accuracy. The invention is moreover characterised in that the a predetermined limits, is when the first derivative of two successive measurements equals to zero. The invention is further characterised in that the number of weighing platforms is three or more. Moreover according to the invention it is particularly preferred that the platforms have different length. According to the invention it is particularly preferred that the number of platforms is unlimited. Moreover the number of platforms is unlimited and two or more of the platforms form a weighing unit which added platform length is larger than the length of the object to be weighed Finally according to the invention the method is characterised in that the object is moved along the conveyor belt in a downstream direction over a weighing device comprising two or more weighing platforms. The platforms are arranged side by side in the downstream direction. Each of the platforms continuously measure the weight of the conveyor belt transported over them. The weighing measurements are continuously sent to a data processing unit, where the measurements from one or more platforms are processed and continuously compared. If a certain number of repeated measurements from the platforms forms a weighing measurements within a prescribed minimum time- and/ or weighing range, such measurement represent the weighing of the respective object. Moreover according to the invention it is particularly preferred that the prescribed time- and/ or weighing minimum is when the first derivative (Δy/Δx) of two or more repeated weighing measurements equal to zero, then such measurement constitute the weighing of the object. And last according to the invention it is particularly preferred that the prescribed time and/ or weighing minimum is when the first derivative (Δy/Δx) of the added weighing of two or more weighing platforms equal to zero, then such measurement constitute the weighing of the object. Brief Description of the Drawings The invention is explained in greater details below with reference to the accompanying drawings, in which Fig. la shows a diagram for the weighing capacity of a conveyor weighing unit with one platform of varying length, Fig. lb shows a diagram for the weighing capacity of a conveyor weighing unit with three platforms of different length, Fig. 2a shows a perspective view of the conveyor-type weighing unit according to the invention, Fig. 2b is a side view of the conveyor-type weighing unit, Fig. 3 is a sectional cut view of the conveyor belt and a weighing platform of the weighing device seen from the side, Fig. 4 is a front view of the conveyor-type weighing unit seen from the in-feed end, Fig. 5 is a side view of one possible design of the conveyor belt with three weighing device of different length, Figure 6 is a side view of a possible line up of three weighing platforms, and Figure 7 shows a weighing diagram for the weighing of individual objects using three platforms, Detailed description of the presently preferred exemplary embodiments of the Invention The apparatus illustrated in the figure 2 - 6 comprises a conveyor-type weighing unit (2) arranged on a stationary supporting frame structure (41). A conveyor belt (3) being a part of the conveyor- type weighing unit forms an endless loop driven in a revolving manner by a driving unit (6). The conveyor belt is transported along a first guiding unit (15) arranged horizontally in direction extending downstream in-between to top sides of reversing rollers (16, 17). A weighing device (4) is incorporated as a part of the first guiding unit and thereby forming a part of a platform the conveyor belt is transported along. As the belt is transported along the first guiding unit (15) continuous weighing measurement are made by the weighing device. The section of the belt (Li) placed over the weighing platform (7) is weighed at each time. A computer data processing unit (10) is connected to respective parts of the equipment for monitoring and controlling the operation. Figure la, shows a diagram for the weighing capacity of a conveyor weighing unit with one platform of varying length. The number of weighing pr. minutes (O s ) are shown on the y-axis and the length of the platform on the x-axis. If the conveyor belt speed (V c ) is set as constant, the number of weighing pr. minutes can be found by the formula O s = N c * L where the (L) is the length of the platform. If the conveyor belt speed is increased or decreased the curve will be set aside. To be able to conduct accurate weighing by a conveyor-type weighing unit, the length of the weighing platform must be greater or equal the length of the object to be weighed. This is due to the fact that when the object is transported along the conveyor it is only when the whole object is placed on the weighing platform that a total weight can be measured. If the object is longer than the platform and rests on some other parts of the conveyor it is never possible to place the whole object on the platform and conduct weighing of the whole object. This results also in that the distance between two adjacent objects must be equal or greater than the length of the platform. The diagram shows how the number of weighing pr. minute (O s ) will be decreased if the length of the platform is increased. On the other hand one can se how the number of weighing can only be increased by decreasing the length of the platform. This however will result in that the weighing device will only be able to weigh shorter object. As the platform becomes shorter a greater number of objects will not be weighed. Figurer lb shows as figure la, the weighing capacity of a conveyor- weighing-unit, but now with three platforms each of different length. The number of weighing pr. minutes (O s ) is shown on the y-axis and the length of the platforms on the x-axis. By using three platforms of varying length 1, 3 and 5, the operational capacity is increased dramatically. The distance between adjacent objects are no longer determined by the platform long enough to weigh the longest object, but only by the length of the platform the next preceding object will be weighed on. If an object is weighed successively on the first platform, then the distance two adjacent objects on the conveyor is determined by the length of the first platform. If the object is successively weighed on the second platform, then the distance between that object and the next adjacent is determined by the length of the second platform, and so on. Based on the above one can see, that by using unlimited number of platforms the operational performance will be variable according to the length of the objects. As often is the case f.ex. in fish processing, number of species of fish of different lengths are processed at each time. This result in the length variation is different from one time to another. By using the multiple weighing platform principle, it is possible to perform weighing of fish or other objects of varying length, and even different length variation with the same apparatus without any adjustment or amendments of the equipment and with optimal processing performance. Figurer 2a shows a perspective view of the conveyor-type weighing-unit according to the invention. Figure 2b shows a side view of the same as fig 2a but where a side protecting plate (29) have been removed. A conveyor-type weighing unit (2) supported by a frame (41) is illustrated. The weighing unit (2) comprise a conveyor belt (3) forming a endless loop which is driven in a revolving manner by a driving unit (6) in a direction downstream (11) from an in-feed end (22) to an out- feed end (23). The driving unit (6) can be equipped with cogged driving wheel for interception with the belt and can be located anywhere along the conveyor path of the belt and either push or pull the belt over the horizontal first guiding unit. The belt (3) rests on a guiding unit (15) from a first- (16) to a second reversing roller (17). The rollers can be with or without sprockets for interception with conveyor belt or for example non-rotating round end-units which the belt slide over (as shown in fig 5) . A weighing device (4) forms a part of the guiding unit. A computer data processing unit (10) is connected to the weighing device (4) and other measuring unit of the apparatus. An object detector (19) is placed along the conveyor belt to detect objects to be weighed and transported along the belt. Further a belt placement detector (8) is arranged for example underneath the belt path to located a starting point (12) of the belt as the belt is transported along the first guiding unit. By having a certain detectable starting point of the conveyor belt the data processing unit is able to locate what part of the belt is placed on the weighing device. The electrical cabinet of the apparatus is indicated by a square box (21) underneath the computer data processor ( 10) . Figure 3 shows a sectional view of the conveyor belt (3) and a weighing device (4) including a weighing platform (7). The conveyor belt (3) is moved in the downstream direction ( 1 1) over the weighing platform (7). As the belt moves along and over the weighing platform continuous weighing of the section (Li) of the belt placed over the platform is conducted, with or without objects to be weighed on it. The most preferable belt as shown on the figure is so called link-type belt. An unlimited number of links (27) are connected together by nit-type joint (26). Each link is turnable around the joints. However almost any other type of belt can be used without foreseeable problems. Fig. 4 shows a front end view of the conveyor-type-weighing unit seen from the in-feed end (22). The placement of the conveyor belt (3), the supporting frame (41), the computer data processing unit (10) and the electrical cabinet (21) of the apparatus as illustrated. Fig. 5 is a sectional side view of one possible design of the conveyor belt guiding unit (15) with three weighing platform (7). The platforms are arranged one after the other in the conveying direction ( 1 1). The conveyor belt (3) runs over a first roller (16) defining the input end (22) of the first conveying direction ( 1 1). The belt runs further over the weighing platforms (7) being a part of the guiding unit (15) and then over the second roller (17) defining the output end (23) of the first horizontal conveying direction. The roller ( 16, 17) does not necessarily need to be rotable but can be curve or semi-circular on the end so the belt slides easily over them. The conveyor belt (3) is f.ex. driven by a toothed driving wheel (6) situated underneath the output end (23). The driving wheel pulls the conveyor belt (3) along the guiding unit (15) over the two rollers. Figure 6 is a side view of a possible line up of three weighing platforms. The conveyor belt (3) is pushed or pulled over the guiding unit (15) in the first conveying direction ( 1 1) and over the weighing device (4), including the three weighing platforms (7) all being a part of the guiding unit for the conveyor belt. The sections (LA, LB and Lc) of the belt placed over the platforms are weighed. Figure 7 show a number of weighing diagrams for the weighing of individual objects transported along the conveyor belt and over the weighing platforms. The first of the diagrams shows three curves each representing the weighing of the platforms (A), (B) and (C). The length of the platforms is defined as A = 2, B = 3 and C = 6. The length of the objects to be weighed is varied from S = 2 in the first diagram and then increased by one until for the last diagram S = 6. By using three platforms of varying length and use them as single weighing platforms as well as in added combination, it is possible to obtain so many as six different platform length. A = 2, B = 3, A + B = 5, C = 6, B + C = 9 and A + B + C = 1 1 As for the first one the length of the objects is 2 which is equal to the length of the first platform. The weighing on the first platform (A) shows a curve where the gradient of the curve is either larger or smaller than zero. In the maximum point, the gradient is equal to zero for one measurement. The weighing of the second platform (B) shows a curve where the gradient is equal to zero for a number of measurements, or for the time it takes the conveyor belt to move the object one unit length e.g. the platform length minus the object length. The weighing of the last platform (C) show a curve where the gradient of the curve is equal to zero for a larger number of measurements, and longer than for platform (B). The interval where the gradient is zero equals the time it takes the conveyor belt to travel with the whole object placed on the platform. As a result it is possible to determine the placement of the objects on the platform based on the gradient of the curve for the weighing measurements. If the gradient (first derivative) (dy/dx) of the curve is zero for two or more successive weighings that is an indication that the maximum weight of the objects is reached and all the whole object is placed on the platform. The following diagram shows the curves for the repeated measurements but the length of the objects is increased by one in each diagram. On the second diagram both the curve for platform (A) and (B) show only one measurement where the gradient of the curve is zero. The curve does not get flat in the top section and therefor no valid measurements can be conducted. On platform (B) the curve shows one point where the gradient (dy/dx) is zero. The third platform (C) however show a curve where the gradient is zero for repeated number of measurements. The platform length is 5 but the object length (L) is still shorter than that or 3. A new curve is however shown. This is the combined, or added weighing of platform (A) and (B). The curve is plotted by dotted line and marked (A+B). By adding the weighing of the two platforms it is possible to conduct measurements on a platform longer than the object and therefor obtaining the gradient (dy/dx) to zero for a number of repeated measurements. This is then repeated as the length of the object is increased and as shown on the last diagram when the length of the objects is greater that the length of each of the individual platforms. By adding either platforms (B + C) or even (A+B+C) it is possible to obtain repeated measurements where the gradient (first derivative) of the curve (dy/dx) is zero. The diagram therefor shows that as long as the objects is shorter than length of one, two or even the added length of all three of the platform accurate weighing measurements can be obtained. The diagram represent the weighing of a single object. The situation becomes more complex when a row of objects are transported over the weighing platforms. Then all of the platform can show weighings at the same time. Further two or more objects can be placed on one and the same platform at the same time. To solve the problems arising, an object detector or sensor is placed in front of the first platform. The sensor will transmit information about that a new object is arriving to the data processing unit. By knowing the placement and time of arrival of the object onto the platform the data processing unit can organize and sort out the measurements from the platforms. The invention has been described with reference to a preferred embodiment. Many modifications can be carried out without thereby deviating from the scope of the invention. The length of the weighing platforms as well as the number of platforms can be varied in many ways without thereby deviating from the invention described herein. A number of measuring method can also be used to detect the object on the conveyor as well as detecting the starting point of the conveyor belt. By using taco-meter on the driving unit instead the belt detecting sensor one will obtain the same results.

Claims: Patent Claims: 1. Conveyor- type weighing unit (2) for weighing objects transported along a conveyor, comprising; a frame (41), a conveyor belt (3), forming an endless loop, a first guiding unit (15), defining a first conveying direction (11) extending in-between the top sides of two opposite arranged rollers (16, 17), a weighing device (4) being a part of the first guiding unit, said belt being driven in a revolving manner by a driving unit (6) and transported over said weighing device (4) in said conveying direction, c h a ra c t e r i s e d in the weighing device (4) comprising; two or more side by side, in said conveying direction (11) arranged weighing platforms (7), each platform having a pre-defined platform length, each weighing platform (7) continuously weighing the conveyor belt section placed there over and/ or the object transported there on, one, two or more adjacent arranged weighing platforms (7) constitutes at each time a weighing unit (2) having a total platform length equal or greater than the object length to be weighed, said weighing platforms (7) being operatively connected to a data processing unit (10), said data processing unit receiving and processing data from said weighing platforms, and based thereupon, the length/weight of the object is determined and accordingly appropriate number of adjacent platform selected, having total length at least equal or greater than the object to be weighed and thereby enabling minimal spacing between adjacent objects and maximum operational capacity. 2. Conveyor- type weighing unit (2), according to claim 1, characterised in the number of weighing platforms (7) being three or more. 3. Conveyor-type weighing unit (2), according to claim 1 or 2, characterised in the platforms having different length. 4. Conveyor-type weighing unit (2), according to claim 1, 2, or 3, characterised in the number of platforms is unlimited. 5. Conveyor- type weighing unit (2), according to claim 1, 2, 3 or 4, characterised in the number of platforms is unlimited and two or more of them form a weighing unit which added platform length is larger than the object to be weighed. 6. Conveyor- type weighing unit (2), according to one or more of claim 1 - 5, characterised in the number of weighing platforms performing each weighing is variable as well as the individual platform length depending on the length of the object to be weighed. 7. Conveyor- type weighing unit (2), according to one or more of claim 1-6, characterised in the weighing unit (2) comprising a object detecting sensor (19) connected to the data processing unit for collecting information of the placement of objects arriving on the conveyor belt. 8. Conveyor- type weighing unit (2), according to one or more of claim 1-7, characterised in the weighing unit (2) comprising a conveyor belt detecting sensor (8) connected to the data processing unit for collecting information of the placement of the conveyor belt transporting the objects arriving. 9. Method of weighing objects by a conveyor-type weighing unit (2), where the conveyor belt (3), forming a endless loop, is transported along a first guiding unit (15), defining a first horizontal conveying direction (11) extending in-between the top sides of a opposite arranged rollers (16, 17), a weighing device (4) being a part of the first guiding unit (15), said belt driven in a revolving manner by a driving unit (6) and transported over said weighing device in said conveying direction, c h a ra c t e r i s e d in, conveying the object along the conveyor belt (3) in said conveying direction over the weighing device (4), said weighing device (4) comprising two or more side by side, in said conveying direction (11) arranged weighing platforms (7), each weighing platform (7) continuously weighing the conveyor belt section placed there over and/ or the object transported there on, one, two or more adjacent arranged weighing platforms (7) constitutes at each time a weighing unit (2) having a total platform length equal or greater than the object length to be weighed, said weighing platforms (7) being operatively connected to a data processing unit (10), said data processing unit receiving and processing data from said weighing platforms, and based thereupon, the length/weight of the object is determined and accordingly appropriate number of adjacent platform selected, having total length at least equal or greater than the object to be weighed and thereby enabling minimal spacing between adjacent objects and maximum operational capacity. 10. Method according to claim 9, characterised in that the prescribed time- and/ or weighing range is when the first derivative (dy/dx) of two or more repeated weighing measurements is equal to zero. 11. Method according to claim 9 or 10 characterised in that if the first derivative (dy/dx) of the added weighing of two, three or more weighing platforms is equal to zero, such measurement constitute the weighing of the object.

Inventors: OLAFSSON JON THOR, OLAFSSON, JON, THOR
Applicants: MAREL HF, OLAFSSON JON THOR, MAREL HF., OLAFSSON, JON, THOR
Application year: 1999
Main classification: G01G11
IPC codes: G01G11