Decoupling Point Weight Measurement

Abstract

An apparatus or method for weighing and/or measuring the flow rate of quantity of a particulate flowing out of a hopper wherein the hopper is isolated from the other components of the apparatus. The apparatus and method are adapted to generate a decoupling point boundary that demarcates the total amount of particulate in the hopper into portions that are not fully supported and portions that are fully supported by the hopper. The particulate is in continuous contact with itself from the inlet to the outlet, with the particulate contained between the isolated hopper and the rest of the components of the system by a flexible coupling or some other method of containment. The invention has the advantages of higher accuracy, decreased cost and complexity, and greater reliability than other solid particulate weighing systems of the prior art, particularly when dealing with low density particulates.

Claims

1. A method of accurately weighing a quantity of a particulate placed in a shaped vessel, such as a hopper of the type having an inlet and an oppositely positioned outlet, the outlet being positioned over a platen and comprising: weighing the empty shaped vessel with at least one scale; while weighing the shaped vessel, introducing the particulate into the vessel through the inlet and allowing the particulate to exit though the outlet on to the platen and determining when the decoupling point occurs to determine the decouple weight of the particulate; while still weighing the shaped vessel, filling the shaped vessel with the remaining quantity of the particulate matter; and calculating the total weight of the particulate matter by adding the weight of the particulate matter prior to the decoupling point with the remaining quantity of the particulate matter; whereby the time required to empty the vessel can be determined and vessel refill times determined.

2. The method of claim 1, further including a valve operatively associated with the outlet to control the rate of particulate flow out of the vessel.

3. The method of claim 2, wherein the valve is selected from the group comprising a rotary valve, slide gate valve and screw feeder.

4. An apparatus for accurately weighing a quantity of a particulate and comprising: a shaped vessel, such as a hopper of the type having an inlet and an oppositely positioned outlet, the outlet adapted to be positioned over a platen; a scale operatively associated with the shaped vessel and to weigh said shaped vessel and adapted to output a signal representative of the combined weight of the vessel and of the particulate entering therein; a computer operatively associated with said scale, said computer adapted to continuously receive said output signal and to determine the point at which the particulate weight is transferred from the platen to said vessel thereby defining the decoupling point and to calculate the total weight of the particulate matter by adding the weight of the particulate matter prior to the decoupling point with the remaining quantity of the particulate matter.

5. The apparatus of claim 1, further including a valve operatively associated with the outlet to control the rate of particulate flow out of the vessel.

6. The apparatus of claim 2, wherein the valve is selected from the group comprising a rotary valve, slide gate valve and screw feeder.

7. A weight measurement apparatus, comprising a supporting component selected from a list comprising a platen, an electromagnetic shaker table, a slide gate valve, and a rotary valve, a platen supporting an initial weight within a gravity-conveyor, that weight being a partial weight of a volume of loose material substantially retained within said gravity conveyor, that portion supported by said supporting component being the excess weight beyond a decoupling weight for said conveyor.

8. The apparatus of claim 7, wherein said gravity conveyor comprises a hopper supported by plural scales and adapted to contain an initial amount of material that is contiguous with an amount that is supported above said supporting component, wherein an amount of the initial amount is a discharge decoupling weight, that amount being supported only by said conveyor, the remaining weight being an excess that is supported by only the supporting component.

9. The apparatus of claim 7, wherein said apparatus is adapted to generate a decoupling point and resist measurement of erroneous material that flows out of a hopper for a duration before generation of said decoupling point, which measurement of said material supported within the hopper is unaffected by the weight of material geometrically within the conveyor but which is not supported by said conveyor, and which does not require inference about the flow rate derived from a decrease in weight of said entire apparatus while discharging, said entire apparatus meaning one that includes components that are supported by surfaces or objects that do not apply a load to said scales.

10. A method of measurement, comprising a step of initiating a run of a solid particulate from a shaped hopper, comprising a step of supporting the hopper upon plural one scales, and a step of locating all other mechanisms downstream with respect to said hopper on support which is not supported by said scales.

11. The method of claim 10, wherein an initial amount of particulate falls out of the hopper upon initiating flow of solid particulate, for a period in which the scales do not register a decrease in weight.

12. The method of claim 11, wherein the scale begins to register an accurate amount of weight of solid particulate, after some amount of particulate has exited the hopper, following initiation of the run.

13. The method of claim 12, wherein the subsequent weight measurements report a consistent decrease in weight, until the weight in the hopper falls below a discharge decoupling weight.

14. The method of claim 13, wherein the initial weight in the hopper was sufficient to generate a decoupling point boundary.

15. The method of claim 14, comprising a further step of filling the hopper with a sufficient amount to reach a fill decoupling point.

16. The method of claim 10, generating a decoupling point ascertaining the inception of a decoupling point, and tracking the amount of time which passes before a change in measured weight of a gravity conveyor, in order to integrate an amount of weight which is a fill decoupling point.

17. The method of claim 10, filling to a sufficient amount sufficient to generate a discharge decoupling point.

18. The method of claim 10, wherein said apparatus is unaffected by type of material, and allows subsequent runs of such system to be accurately measured without locating a scale which is at least partially loaded with substantially all of the weight of a vibratory conveyor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Some of the features and advantages of the invention having been briefly described, others will appear from the detailed description which follows, when taken in connection with the accompanying drawings in which—

[0020] FIG. 1a illustrates schematically a prior art method of determining product weight by weighing the empty hopper, the feed mechanism and all of the supporting structure.

[0021] FIG. 1b illustrates schematically a prior art method of determining product weight by weighing the hopper containing product, the feed mechanism and all of the supporting structure.

[0022] FIG. 1c illustrates schematically a prior art method of inferring hopper level by product weight by weighing the hopper containing product, the feed mechanism and all of the supporting structure.

[0023] FIG. 1d illustrates schematically a prior art method of determining hopper level by direct measurement.

[0024] FIG. 2a illustrates schematically a prior art method of determining hopper level by weighing the hopper containing the product, the feed mechanism and all of the supporting structure by supporting the apparatus atop a scale.

[0025] FIG. 2b illustrates schematically a prior art method of determining hopper level by weighing the hopper containing the product, the feed mechanism and all of the supporting structure by supporting the apparatus atop a scale.

[0026] FIG. 2c illustrates schematically a prior art method of determining hopper level by weighing the hopper containing the product, the feed mechanism and all of the supporting structure by suspending the apparatus from a scale.

[0027] FIG. 2d illustrates schematically a prior art method of determining hopper level by weighing the hopper containing the product, the feed mechanism and all of the supporting structure by suspending the apparatus from a scale.

[0028] FIG. 3a illustrates schematically a method of directly weighing hopper level by product weight by weighing the hopper containing product, with all other mechanisms being supported by a distinct and unweighed supporting surface

[0029] FIG. 3b illustrates schematically a method of directly weighing hopper level by product weight by weighing the hopper containing product, with all other mechanisms being supported by a distinct and unweighed supporting surface

[0030] FIG. 4a illustrates an expanded view of a graph of weight data collected during filling of a dischargeable vessel.

[0031] FIG. 4b illustrates a graph of weight data collected during filling of a dischargeable vessel.

[0032] FIG. 5a illustrates an expanded view of a graph of weight data collected during fillings of a dischargeable vessel for three alternative dischargeable materials.

[0033] FIG. 5b illustrates a graph of weight data collected during fillings of a dischargeable vessel for three alternative dischargeable materials.

[0034] FIG. 6a illustrates an expanded view of a graph of weight data collected during the timed discharge of a dischargeable vessel.

[0035] FIG. 6b illustrates a graph of weight data collected during the timed discharge of a dischargeable vessel.

[0036] FIG. 7a illustrates an embodiment of the present invention, a gravity-conveyor decoupling point solid-particulate flow-weighing system, having a slide-gate valve and actuator

[0037] FIG. 7b illustrates an embodiment of the present invention, a gravity-conveyor decoupling point solid-particulate flow-weighing system, having a rotary valve with a motor and a flexible coupling.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a particular embodiment is shown, it is to be understood at the outset that a person skilled in the art may modify the invention herein described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as a broad teaching disclosure directed to persons of skill in the appropriate arts and not as limiting upon the present invention.

[0039] Referring now to the figures and particularly to FIG. 1a, the prior art method of determining hopper, bin or silo weight is to weigh the entire mechanism, which includes the hopper, the feed mechanism and all supporting structure. The first step is to weigh the mechanism without the product as shown in FIG. 1a. The mechanism with the product is then weighed as shown in FIG. 1b; the difference being the product weight. This method is not without its inherent drawbacks and deficiencies in that often, the weight of the mechanism (hopper, feed mechanism and supporting structure) is many times the weight of the product. This requires a very high resolution in order to measure small changes in product weight which is consequently, expensive and necessarily complex. This is particularly an issue when low density products such as cat litter must be measured. Another method is to employ a level detector to measure the height of the product, but this method is also unreliable due to clumping or when especially low density product is present.

[0040] Another method of determining hopper level or fill is to infer hopper level based on fill weight. Measurement of weight is normally considered a good method of determining hopper level since bulk density of a given material usually fairly consistent, and it “integrates” the uneven surface level of the product and does not rely on material characteristics. The main drawback of this method is that some of the material may not be in the “Fixed Shape” zone, as shown by the dotted lines in FIG. 1c. If this is the case some degree of error may be introduced by unknown or variable volume of the product not in the Fixed Shape zone. Notwithstanding the foregoing, level by weight is still considered the most accurate method of solid particle level measurement, albeit the most expensive.

[0041] Hopper level may also be measured directly as shown in FIG. 1d by employing a level sensor positioned above the hopper, but this method can be unreliable due to product shape. In addition, the surface characteristics of some materials make it difficult to reliably sense the location of the surface. Note that in connection with the above methods, the vibratory conveyor is not running.

[0042] Another method of weight measurement is to measure a batch amount of product delivered to the hopper. If the time required to deliver a batch amount is known, then the flow rate can be determined. A change in weight with respect to time is the flow rate, or in other words, the first derivative of the weight with respect to time yields the flow rate. There are currently two measurement methods or techniques in general use—supported and suspended. In both cases, the entire weight of the mechanism (the hopper, vibratory tray and the electromagnetic drive) plus the weight of the product is measured.

[0043] The most commonly employed method for measuring small weights is shown in FIG. 2a and FIG. 2b. The flow begins with a full hopper, as shown in FIG. 2a and as product flows out of the hopper on the vibratory conveyor, the hopper level drops after a measured time period as shown in FIG. 2b. This is an inference of product level during weight measurement. However, the actual measurement is all of the material plus the equipment, except that which is in “free fall” as shown in FIG. 2b. Since product flow is the first derivative of the weight measurement, and the “loss in weight” is a vary small part of the total, very high weight resolutions must be averaged over time in order to obtain a good signal representative of the product flow rate.

[0044] When the hopper is large, all of the weight is measured, including the supports and base as described in FIG. 2a and FIG. 2b. This is very little difference in the output of the two methods and as actual product weight can be a very small percentage of the total weight measurement, a very high measurement resolution is needed in order to be meaningful. FIG. 2c and FIG. 2d illustrate the use of only two scales, however, the actual minimum would be three for actual use.

[0045] As seen from the foregoing, the methods and apparatus described above generally require, in one form or another, that the entire mechanism (hopper, base, and driver) be weighed along with the material in order to measure the weight or flow rate of a product contained in the hopper. The present invention, in contrast, enables weighing only the hopper and the product, which results in a much improved and more accurate weight measurement. More specifically, the present invention hinges around a concept that, for the purposes stated herein, shall be referred to as the “decoupling point”.

[0046] The decoupling point may be defined as the point at which the weight of particulate in a hopper, bin, or some other container (generally tapering) with an opening at the bottom, transfers the preponderance of the additional material's weight to the walls of the container, and not to the material below that point which is supported by a surface (e.g., a “platen”) or other supporting means. Stated otherwise, there is a point at which sufficient material is added to the bin so that a “material bridge” is formed across the hopper and the weight of the material transfers from the platen below to the container itself. Also, the material is in continuous contact with itself from the top of the material until it contacts the bottom surface. There are two generally accepted methods of containing the material between the hopper discharge and the receiving container—angle of repose (shown in FIG. 2a) and some type of flexible coupling as shown in FIG. 7b, with angle of repose being the most prevalent.

[0047] For most particulate matter in a shaped vessel, such as a hopper shown in FIG. 3a and FIG. 3b, there exists a point above which the weight of the material is transferred to the hopper, and below which its weight is transferred to the material below, which is supported by the base. In FIG. 3a, both the scale and the base support product weight while in FIG. 3b, only the scale supports the weight as the product below the illustrated decoupling line is supported by the base. Only product added above the decoupling point shown will be subject to being weighed. Again, the decoupling point, illustrated in the difference between FIG. 3a and FIG. 3b, is the point at which above all the material weight is transferred to the hopper or support vessel, and below which a transition starts that transfers the product weight from the hopper to the material below, as will be discussed herein below.

[0048] The decoupling point for a particular material may be determined by measurement. FIG. 4a illustrates the point at which the decoupling point occurs. More specifically, FIG. 4a is an expanded graph of the actual weight (act Weight) of a hopper vs. the measured weight (mea Weight), as shown in FIG. 4b. In experiments that were performed, the decoupling point is shown at an actual weight of 4.85 and a measured weight of 1.7, and it is at this point where the relationship between the actual weight and the measured weight becomes linear. Referring now to FIG. 4a and FIG. 4b, the measured weight was set to zero (tare weight) with the hopper completely empty. As material was first added to the hopper, the measured weight did not indicate any weight. As more and more material is added to the hopper (see the section of FIG. 4a below the Decoupling Point), the measured weight approaches a linear relationship with the actual weight.

[0049] Once the level in the hopper reaches the decoupling point, the added weight of the material is supported by the hopper and the measured weight is the actual weight. FIG. 4b illustrates the linear relationship between the weight of the material transferred to the hopper as it is filled up from the decoupling point. Note that the relationship remains the same (linear) as the hopper is filled to the maximum level. With respect to the foregoing, note that most of the error observed between the actual weight and the measured weight is due to the method of actually measuring the material in the hopper. In experiments that were performed, the actual weight of the material in the hopper was measured using a CentriFlow® flow meter (available from Eastern Instrument Laboratories, Inc., Wilmington, N.C.) and integrating the signal to determine the weight of the material in the hopper. Since the meter is positioned at the free fall end of the vibratory feeder, the material in the feeder is weighed and any small change in the vibratory feeder level would contribute to error, however, over the entire weight of the hopper, the difference is small.

[0050] Referring now to FIGS. 5a and 5b, the fill decouple weight varies for different materials (See Table 1).

TABLE-US-00001 TABLE 1 bulk density Decouple wt Decouple vol Longest side Material lb/ft.sup.3 lb in.sup.3 inches Almonds 37.1 3.38 .0911 0.75″ Plastic pellets 35.9 2.24 .0676 0.15 Kitty litter 24.7 1.24 .050 .0625

[0051] FIG. 5a is an expanded view about the origin, with respect to FIG. 5b, to illustrate the start of the process. Table 1 illustrates three very different possible fill materials and their respective characteristics. As previously noted, the decouple weight is the weight that must be added to the measured weight to give the correct weight. It is normally determined by a best fit straight line through the data, and then the actual weight indicated at zero measured weight. Also, note that in FIGS. 4a and 4b, the decouple weight is the actual weight minus the measured weight, assuming that the measured weight is “zeroed” with the hopper completely empty. It should be noted that once the measured is “zeroed” with the hopper empty, and the offset of the decoupled weight is added, the measured weight is still not accurate until the actual weight is above the decouple point. It is preferred, in best modes, to presume that a measured weight will be accurate when the actual weight is twice (2×) the decoupled weight.

[0052] As shown in FIG. 5b, over a weight range of approximately 100 lbs, the best fit lines of all three materials (almonds, plastic pellets and kitty litter) are parallel, indicating that only the offset is affected by different materials. This means that the calibration of the scale is not affected by material selection, only the offset, which is a procedural “zero.”

[0053] The decouple volume data in Table 1 is calculated from the decouple weight and bulk density. The decouple volume point is the actual physical point at which the material couples to the hopper. Comparing almonds to plastic pellets, the larger almonds require more volume to support itself on the hopper wall than the plastic pellets. Also, the size variation range is over 10:1 and the density 2:1, and the decouple weight changed approximately ±1 lb. The hopper employed for this measurement was small and can hold approximately 100 lbs, making the offset change no more than one percent (1.0%) over the product range. No decoupling point change was detected from maximum to minimum material weight for this hopper.

[0054] Referring now to FIGS. 6a and 6b, with respect to discharge decouple weight, a reasonable assumption would be that the fill and discharge weights differ, i.e., as one fills a hopper from empty, more weight would be supported by the base, and when discharge begins, some of the fill decouple weight is transferred to the hoppers walls or the discharge decouple weight. FIG. 6a illustrates this effect. In the illustrated example, note the 2.3 lb difference between the measured hopper weight and the actual weight integrated by the CentriFlow® flow meter, which is assumed to be the actual weight. From Table 1, the fill decouple weight was 3.38 lbs, so the discharge decouple weight is 3.38−2.3=1.08 lbs.

[0055] The hopper weight measurement is “calibrated,” as shown in FIG. 6a, by adding fill or discharge decouple weight to the empty run hopper weight, which yields the measured product weight. The cMF weight is the actual weight integrated by the CentriFlow® flow meter and is assumed to be the correct weight. With respect to FIG. 6a, it is important to note that the “calibrated” measured product weight joins the actual weight and also that the measured product weight rises almost immediately to the correct weight (note the dotted circle in FIG. 6a), so that it would be easy in software to find the peak if an accurate discharge batch weight were required. FIG. 6b illustrates a full run of 40 lbs of almonds that was delivered in a batch. Note that if software is employed to pick the maximum and minimum, batch weight is accurate to at least one percent, and possibly 0.25%.

[0056] It will be noted that the data presented herein was derived using a vibratory feeder, which is considered one of the most widely used short term flow variable feed devices. Furthermore, another factor contributing to flow variation by the decouple weight method is the volume of material below the decouple point, which as previously mentioned, is not weighed. Actual small flow rate changes contribute to the variation in the volume or weight below the decouple point, increasing the indicated variability. The variability introduced by the decouple unweighted volume is time dependent, so longer product runs tend to reduce measurement error.

[0057] While the disclosure discussed herein above refers to the use of the decouple system of the present invention used in conjunction with a vibratory feeder, other feeder mechanisms may be employed with equal efficacy. For example, a slide gate valve, a rotary valve and a screw feeder. Since the screw feeder is similar to the vibratory feeder, a detailed discussion thereof is not deemed necessary.

[0058] FIG. 7a illustrates schematically the present system employed in combination with a slide gate valve. When a slide gate valve is used the decoupling point remains unchanged, but the volume of material supported by the base decreases significantly (as compared to the vibratory feeder of FIG. 3a). Another advantage of the slide gate feeder is that the material flow is the most constant which results in making the flow calculation smoother.

[0059] FIG. 7b illustrates schematically the present system employed in combination with a rotary valve feeder and the supported volume is small, similar to the slide gate valve discussed herein above. The rotary valve supplies a pulsating material flow, which by its nature is not as good, in terms of the flow rate measurements, as the slide gate valve. In some circumstances, the rotary valve is superior to the vibratory conveyor, if sized correctly.

[0060] The foregoing embodiments and examples are to be considered illustrative, rather than restrictive of the invention, and those modifications which come within the meaning and range of equivalence of the claims are to be included therein.