Background of the Invention Conveyor weighing has been known weighing technique for quite some time. Conveyor weighing apparatus have mainly been used for weighing of bulk material as grain, rocks and other such materials.

There is however a growing need for accurate and high speed weighing units, both for continuous weighing of bulk material as well as for weighing of individual objects such as food pieces. It is essential in 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 fex. fish filets and trimming of meat. If one had on the other hand to weigh every object individually on a stationary weighing unit, the processing speed would be diminished dramatically.

There is no question that the aforementioned applies not only to processing of fish and meat, but also to other types of food. The main disadvantage of the existing conveyor-type weighing apparatus, especially those available for the food processing industry is lack of accuracy.

From US Patent No. 5.376.950 conveyor weighing unit having an endless conveyor band is known. Further GB-A 2 111 010 describes a similar conveyor weighing unit.

Brief Description of the Invention The object of the invention is to provide accurate conveyor-type weighing unit capable of weighing objects of varying dimension and at the same time, take into-account the disturbance caused by vibrations, friction or other forces caused by the transportation of the conveyor belt.

The so-called link-type belts most commonly used for conveyors, do not have uniform weight over the total length of the belt. The weight of the belt is not uniform and the weight of the belt can change f. ex. due to material pieces being weighed sticking to the belt, slitage etc. To conduct accurate measurements one must take into account the variance in the weight of the respective sections of the belt as well as the vibrations caused f. ex by the reverse (free) conveyance of the conveyor belt.

Detailed description of the invention The conveyor-type weighing unit according to the invention is characterised in that a second guiding unit (18) defining a second reverse conveying direction (19), the second guiding unit (18) supporting the conveyor belt (3) under its reverse revolving conveyance, the second guiding unit (18) thereby absorbing/eliminating the oscillations and force caused by the belt (3).

The invention is also characteristic in that the in the second conveying direction (19) being horizontal.

Further embodiment of the invention is characteristic in that in the second guiding means (18) extending approximately over the whole reverse horizontal conveyance direction (19) of the belt.

The invention is moreover characterised in that the placement of the in the second guiding means (19) being a horizontal and low friction beam like structure.

The invention is further characterised in that the the conveyor belt (3) is supported under its reverse revolving conveyance by a second guiding unit (18) defining a second reverse conveying direction (19), the second guiding unit (18) thereby absorbing/eliminating the oscillations and vertical force of the belt (3).

Brief Description of the Drawings The invention is explained in greater details below with reference to the accompanying drawings, in which Fig. 1 shows a perspective view of the conveyor-type weighing unit according to the invention, and Fig. 2 is a side view of the conveyor-type weighing unit, and Fig. 3 is a sectional view of the conveyor belt and a weighing platform of the weighing means seen from the side, and Figure 4 show a weighing diagram for the sections of the belt, with and without objects being weighed and Figure 5 shows a side view of one possible design of the conveyor belt with support for the reverse conveyance of the conveyor belt.

Detailed description of the presently preferred exemplary embodiments of the Invention The apparatus illustrated in the figure 1-3 comprise 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 two opposite arranged rollers (16.17). A weighing means 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 means.

The section of the belt (Li) placed over the weighing platform (7) is weighed. A computer data processing means (10) is connected to respective parts of the equipment for monitoring and controlling the operation.

Figure 1 shows a perspective view of the conveyor-type weighing-unit according to the invention. Figure 2 shows a side view of the same as fig 1 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 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. A weighing device (4) forms a part of the guiding unit. A computer data processing means (10) is connected to the weighing device (4) and other measuring devices of the apparatus. An object detector (19) is placed along the convevor 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 means. The electrical cabinet of the apparatus is indicated by a square box (21) underneath the computer data processing means (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 (11) over the weighing platform (7).

As the belt moves along and over the weighing platform continuous weighing of the section (L,) of the belt placed over the platform is conducted, with or without objects to be weighed placed 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 other type of belt can be used.

Figure 4 shows the weighing diagram for a weighing unit with one weighing platform and a typical weighing curves for the platform as a single object is transported along the conveyor belt over the platform.

Three curves are drawn. First, the line showing the weighing curve for the total weighing of the object plus the belt section (D). Secondly the curve (E) showing the disturbance caused by the friction, swing and other forces caused by the revolving conveyance of the belt. The third curve (F) show the weighing's when the disturbance caused by the belt friction etc. have been diminished.

Fig. 5 is a sectional side view of one possible design of the conveyor belt guiding units (15,18). The weighing platform (7) is arranged traditionally as a part of the first guiding unit (15). The conveyor belt (3) runs over a first roller (16) defining the input end (22) of the first conveying direction (11). 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. The second guiding unit (18) is situated underneath the first guiding unit (15) and supports the conveyor : belt (3) under its reverse conveyance from the output end (23) to the input end (22). The second guiding unit (18) can be as long as, or of similar length as the first guiding unit (15) and thereby support the entire reverse conveyance of the belt, as shown on the figure. But it can also be shorter and/or made of a number of shorter horizontal support structure and thereby support only partly the conveyor belt (3) under its reverse conveyance.

A second feature of the second guiding unit (18) can be to obtain a support-free section of the belt in-between the end of the guiding unit (18) and the roller (16) of the input end (22).

As shown in fig 1 an identification device is placed on the belt for identification of an certain starting point. By fairly simple measurements, either by using some kind of velocity sensor or by using tachometer connected to the driving unit the transporting speed of the conveyor belt can be measured. By synchronising the speed of the belt and the position of one starting point on the belt the data processing means can without any complicated processing locate where the object is located on the. By simply subtracting the individual weighing of the profile sections (p) from the weighing of the total weight of the belt and the object, very accurate measurements can be obtained.