WO2000042390A2

WO2000042390A2 - Method for measuring free-flowing materials and device therefor

Info

Publication number: WO2000042390A2
Application number: PCT/IL2000/000025
Authority: WO
Inventors: Anatoly Likhtser
Original assignee: I.D.M. Engineering Ltd.
Priority date: 1999-01-13
Filing date: 2000-01-12
Publication date: 2000-07-20
Also published as: IL128038A0; WO2000042390A3; IL128038A

Abstract

A method for measuring a predetermined amount of a free-flowing material. The method includes the steps of (a) calculating the desired amount of a preliminary dose of material which is less than the predetermined amount of material; (b) dispensing a preliminary dose of material from a source of free-flowing material into a first measuring apparatus (7); (c) measuring the actual amount of the preliminary dose in the first measuring apparatus (7) in a state of static equilibrium which is less than the predetermined amount of material; (d) calculating the desired amount of corrective dose of material; (e) dispensing a corrective dose of material from a source of free-flowing material to a second measuring apparatus (8); (f) coincidentally with step (e), emptying the preliminary dose of material from the first measuring apparatus (8) into a receptacle (9); (g) measuring the actual amount of the corrective dose of material; and (h) emptying the corrective dose of material from the second measuring apparatus (8) into the receptacle (9).

Description

METHOD FOR MEASURING FREE-FLOWING MATERIALS AND DEVICE THEREFOR

FIELD OF THE INVENTION

The present invention relates, in general, to the field of packaging and/or processing of free-flowing materials, such as food, grain, chemicals and the like and, in particular, to the measuring and packaging of free-flowing materials which are dispensed by weight

BACKGROUND OF THE INVENTION

Those skilled in the art are familiar with various methods of measuring or dosing of a free-flowing material, wherein the term free-flowing should be understood as including both liquid and solid materials which are to be measured, such as juice, rice, sugar, candy bars, etc. According to known methods, in order to supply a predetermine dose, the material is fed, or dispensed, first by a bulk or rough flow and then by a dribble or fine flow The rough flow delivers the material at a relatively rapid rate until a predetermined desired weight has been delivered, at which point the rough flow stops and the fine flow begins This fine flow continues until a second predetermined weight has been reached

Known devices for implementing this method generally utilize separate rough flow and fine flow dispensers, with a single load receiver located beneath the two dispensers, wherein the rate of dispensing may be controlled so as to provide first relatively rapid feed and then slower feed of the material

Disadvantages of this method and of known devices are relatively low accuracy and productivity, as well as the dependence of measurement error on the type of material (granules, powder, etc ) These disadvantages are due to various factors, such as measurement of a material which is not in a state of static equilibrium, due to vibration of the material on a weight meter, and the like This, together with the dynamic pressure of falling material, results in a large measurement error Further, known methods and devices may require that, after the rough flow has been dispensed, there remains a significant portion of material which still has to be dispensed by the fine flow, which is much slower This greatly reduces productivity US Patent No 4, 100,984 attempts to overcome some of these problems by providing a device wherein a product to be packaged is fed from a hopper into a feed tray By vibrating the feed tray, the product is fed continuously, first at a relatively rapid rate and then at a slower rate, along the surface of the feed tray, from which it drops into a receptacle, such as a bucket The bucket is provided with a weight sensor to determine when a first desired weight has been reached, at which point the rough, relatively rapid feed stops and a fine, slower feed of the product begins The fine feed continues until a second desired weight has been reached, at which point the vibrator stops, thus stopping the fine feed Due to vibration, impact of the product on the bucket, and response time, the weight determined by the weight sensor will seldom be equal to the true weight In order to more accurately determine the actual weight of the product which has been fed, the product may be checkweighed by one of two methods First, after a desired time delay, when the product has been allowed to reach a state of substantial equilibrium, it may be checkweighed A second method is to provide a motion sensor such that, when motion of the bucket has stopped, the checkweighing device is activated

A checkweighing means disclosed in US 4,100,984 detects the relationship between the weight sensed and the desired weight If it is determined that the weight sensed is less than a desired weight setting, then additional product is fed into the receptacle If the checkweighing means determines that the weight sensed is equal to or more than the desired weight setting, then the product is discharged from the receptacle, after which is may be packaged

While checkweighing enables more accurate measuring of material which has been fed into a receptacle, there is still some error in weighing the material Also, since the product is fed first by a rough feeder and then by a fine feeder, the process of feeding is relatively slow There is, therefore, a need for an improved process and device which will increase the rate of feeding materials and which will provide more accurate weighing of material which has been fed SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method and device which will allow a reduction of the measurement error and an increase in productivity of the measurement and packaging of free-flowing materials, so as to eliminate the disadvantages of prior art.

There is thus provided, in accordance with a preferred embodiment of the invention, a method for measuring a predetermined amount of a free-flowing material, the method including the steps of:

(a) calculating the desired amount of a preliminary dose of material, the desired amount of the preliminary dose being less than the predetermined amount of material;

(b) dispensing a preliminary dose of material from a source of free-flowing material into a first measuring apparatus;

(c) measuring the actual amount of the preliminary dose in the first measuring apparatus in a state of static equilibrium, the actual amount of the preliminary dose being less than the predetermined amount of material;

(d) calculating the desired amount of corrective dose of material;

(e) dispensing a corrective dose of material from a source of free-flowing material to a second measuring apparatus;

(f) coincidentally with step (e), emptying the preliminary dose of material from the first measuring apparatus into a receptacle;

(g) measuring the actual amount of the corrective dose of material in the second measuring apparatus; and

(h) emptying the corrective dose of material from the second measuring apparatus into the receptacle. Additionally in accordance with a preferred embodiment of the present invention, step

(g) includes dynamically measuring the actual amount of the corrective dose of material in the second measuring apparatus.

Further in accordance with a preferred embodiment of the present invention, the calculated desired amount of the corrective dose is adjusted to compensate for at least one of the group which consists of the following factors: bulk density, whether the material is a liquid or a free-flowing solid, the desired amount of material, the amount of the preliminary dose, and the dynamic pressure of falling material into the second measuring apparatus. Yet further in accordance with a preferred embodiment of the present invention, the sum of the error of measurement of the actual amount of the preliminary dose and the error of measurement of the actual amount of the corrective dose is substantially equal to the error of measurement of the actual amount of the corrective dose. Still further in accordance with a preferred embodiment of the present invention, there is provided a method for packaging a predetermined amount of a free-flowing material, the method including measuring a predetermined amount of a free-flowing material according to steps (a) through (h), and including the following additional step: (i) packaging the contents of the receptacle. In accordance with a preferred embodiment of the invention, there is provided a device for measuring a predetermined amount of a free-flowing material, the device including: apparatus for calculating the desired amount of a preliminary dose of material, the desired amount of the preliminary dose being less than the predetermined amount of material; apparatus for dispensing a preliminary dose from a source of free-flowing material into a first measuring apparatus; apparatus for measuring the actual amount of the preliminary dose in the first measuring apparatus at a state of static equilibrium, the actual amount of the preliminary dose being less than the predetermined amount of material; apparatus for calculating the desired amount of a corrective dose of material; apparatus for dispensing a corrective dose of material from a source of free-flowing material to a second measuring apparatus; apparatus for emptying the preliminary dose of material from the first measuring apparatus into a receptacle, the apparatus for emptying being actuatable during operation of the apparatus for dispensing the corrective dose; apparatus for measuring the actual amount of the corrective dose of material in the second measuring apparatus; and apparatus for emptying the corrective dose of material from the second measuring apparatus into the receptacle.

Additionally in accordance with a preferred embodiment of the invention, the apparatus for measuring the actual amount of the corrective dose of material in the second measuring apparatus includes apparatus for dynamically measuring the actual amount of the corrective dose of material in the second measuring apparatus.

In a system for packaging a predetermined amount of a free-flowing material, in accordance with a preferred embodiment of the invention, use of a device for measuring a predetermined amount of a free-flowing material further includes: apparatus for packaging the contents of the receptacle.

Yet further in accordance with a preferred embodiment of the invention, the sum of the error of measurement of the actual amount of any preliminary dose and the error of measurement of the actual amount of the corresponding corrective dose is substantially equal to the error of measurement of the actual amount of the corresponding corrective dose.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings, in which:

Fig. 1 is a schematic representation of measuring device, constructed and operative in accordance with the present invention, including a single device;

Fig. 2 is schematic representation of a measuring system having a plurality of the measuring devices of Fig. 1, constructed and operative in accordance with the present invention;

Fig. 3 is an illustration of the primary components of a measuring device in accordance with a preferred embodiment of the present invention;

Fig. 4 is a schematic representation of a combination of measuring devices, in accordance with the present invention; Figs. 5 A, 5B, and 5C illustrate graphically a preliminary dose delivery cyclogram, a corrective dose delivery cyclogram, and a combined preliminary dose and corrective dose delivery cyclogram, respectively, in accordance with the method of the present invention;

Figs. 6A and 6B are illustrations of a corrective dose feeder and of a corrective dose receiver, in accordance with the present invention, wherein the dependence of the measurement of a corrective dose mass on the material fall height is indicated for the case of the maximum fall height and for the case of the minimum fall height, respectively; and Figs. 7A and 7B are illustrations showing the influence of dynamic pressure change on the mass of corrective doses for the cases of the maximum fall height and minimum fall height, respectively.

DETAILED DESCRIPTION OF THE INVENTION

With reference to Fig. 1, there is schematically shown the relationship among components of a measuring device 20, according to the present invention, by which the method of the present invention may be carried out. The device 20 includes a controller, such as a microprocessor 1; a preliminary dose weight meter 2, such as any suitable load cell; a corrective dose weight meter 3; a preliminary dose (rough flow) feeder 4; and a corrective dose (fine flow) feeder 5. The microprocessor 1 controls operation of the weight meters 2, 3 and of the feeders 4, 5 as will be discussed below.

Fig. 2 is schematic representation of a the relationship among components of a system of devices, according to the present invention. System 30 is composed of a combination of four identical measuring devices 20, and a central control system or microprocessor 6 is provided for controlling operation of each of microprocessors 1. The provision of a plurality of identical measuring devices provides a system having increased productivity. It will be appreciated by persons skilled in the art that the system 30 according to the present invention has been shown and described as having four identical measuring devices. In order to further increase the productivity of the system, there may be provided any number N of identical devices 20 which are controlled by a central control system or microprocessor.

Fig. 3 illustrates the components of a measuring device 20 in accordance with a preferred embodiment of the present invention. Device 20 includes a preliminary dose feeder 4, and corrective dose feeder 5. Under feeder 4 there is disposed a preliminary dose receiver 7, which is mounted onto a weight meter 17. Under feeder 5 there is disposed a corrective dose receiver 8, which is mounted onto a weight meter 18.

The dose feeders, weight meters, and dose receivers employed in accordance with the present invention are similar to components known to persons skilled in the art and, as such, are not described in detail herein. A common receiving bin 9 into which the measured doses are emptied is rigidly mounted beneath preliminary dose receiver 7 and corrective dose receiver 8. Operation of device 20 is controlled by a microprocessor 1, as noted above. The device is operated as follows: At the start of operation of device 20, preliminary dose feeder 4 and corrective dose feeder 5 are maintained closed by means, such as is known in the art. Similarly, gates 27, 28 maintain respective dose receivers 7 and 8 in closed configuration by means (not shown), such as is known in the art. A desired amount M₂ of material is calculated, as will be discussed below, and its value is transmitted by microprocessor 1 to weight meter 17. Preliminary dose feeder 4 is opened, thus releasing material therefrom so that it falls into dose receiver 7. The material that is being released into dose receiver 7 is measured, as it falls into receiver 7, by weight meter 17. Once the weight meter 17 senses that the amount M₂ of the preliminary dose has been dispensed, feeder 4 is closed, and the preliminary dose is allowed to reach a state of static equilibrium. Once this state has been reached, the actual mass M₄ of the preliminary dose in receiver 7 is determined. The value of M₄ is transmitted to the microprocessor 1 where the mass M₃ of the corrective dose is calculated, as will be discussed below. The value of M₃ is transmitted by microprocessor 1 to weight meter 18. Then the gate 27 of preliminary dose receiver 7 is opened so that the preliminary dose material falls into receiving bin 9, and, simultaneously, corrective dose feeder 5 is opened, thus releasing material therefrom so that it falls into dose receiver 8. The material that is being released into dose receiver 8 is measured, as it falls into receiver 8, by weight meter 18. Once the weight meter 18 senses that the amount M₃ of the corrective dose has been reached, feeder 5 is closed, and gate 28 of dose receiver 8 is opened so that the corrective dose material falls into receiving bin 9, where it is added to the preliminary dose that was previously supplied from the dose receiver 7. From receiving bin 9 the full dose may be transferred, for example, to a storage bag or container (not shown), by means known in the art. If desired, receiving bin 9 may be utilized as a storage container and may be removed so that a new, empty receiving bin may be positioned under dose receivers 7 and 8. The gates 27, 28 of respective dose receivers 7, 8 are then closed, and the entire cycle may be repeated.

It should be noted that the device of the present invention, as shown and described with reference to the embodiment of Fig. 3, includes feeders 4 and 5 which, when opened, allow material to fall into respective dose receivers 7 and 8. Also, this device includes dose receivers 7 and 8 having respective gates 27 and 28 which, when opened, allow material to fall into receiving bin 9. It will be appreciated, however, that any other suitable means for transferring material from the feeders and dose receivers, such as vibrating means, conveyor means, or any other mechanical means may be utilized, without departing from the scope of the present invention.

Fig. 4 illustrates schematically a combination of devices, according to the present invention, wherein four devices 20 have a common receiving bin 19 into which all the devices 20 are successively unloaded. Utilization of this embodiment of the invention enables repeated cycles of delivery, measurement, and unloading of a preliminary dose and delivery (during unloading of the preliminary dose), measurement, and unloading of a corrective dose, by each of the devices 20. Such a combination of devices 20 allows an increase in productivity of the unit. For example, if each device 20 has a cycle of 2.0 seconds, then each device will measure 30 doses per minute. By utilizing a combination of four devices 20, as described above, productivity is increased to 120 doses per minute. Additionally, such a combination of devices could be employed in the measuring of a plurality of free-flowing materials which are to be packaged together. For example, for dry soup which consists of salt, pepper, pasta, and garlic, each ingredient could be measured by a device 20 and unloaded into receiving bin 19, after which the combination of ingredients is packaged together.

Figs. 5A, 5B, and 5C illustrate graphically three cyclograms according to the method for measuring free-flowing materials of the present invention. Each cyclogram represents a measured amount of material, M, delivered or unloaded during a time interval T.

According to the cyclogram of Fig. 5 A, the delivery of a preliminary dose M₂ via a rough flow takes place during a time interval Tt, and terminates at point A. During the time from point A to point B, or time interval T₂, movement of the preliminary dose material which has been unloaded slows and then substantially stops. Thus, during time interval T₂, which may be, for example, 0.05 seconds, the material is allowed to come to a state of static equilibrium. The actual mass M₄ of the preliminary dose is then measured. The difference in measurement between masses M and M is due to the pressure of the flow of the preliminary dose material falling on the device, which will be discussed further below, such that the initial measurement of the mass of material, at point A, is greater than its actual measurement, at point B. During time interval T₃. which terminates at point C, the delivered material is unloaded, e.g., to a receiving bin or packaging station. Repeated cycles of the delivery of a preliminary dose, measurement of the actual mass, and unloading of the delivered material are shown in Fig 5A

According to the cyclogram of Fig 5B, the delivery of corrective dose via a fine flow is started at point D, and continues during time interval T₄, terminating at point E After delivery of the corrective dose has been completed, at point E, it is measured The corrective dose is then unloaded during time interval T₅, which terminates at point F The cycle of delivery of a corrective dose, its measurement, and its unloading is repeated as shown in the cyclogram of Fig 5B

It should be noted that, according to prior art methods, the delivery of a material, via a rough flow, into a receiving bin is followed by delivery of the material, via a fine flow, into the same bin, after which the entire amount is measured and then unloaded In contrast, according to the method of the present invention, a corrective dose is delivered during time interval T₄ which begins at the end of time interval T₂, such that the delivery of corrective dose M₃ (point D) begins at the same time that the unloading of the preliminary dose material is begun (point B). Thus, the method of the present invention enables delivery of material at an increased rate, as compared with delivery of a material according to prior art methods.

Fig. 5C shows a cyclogram representing a combination of the cyclograms of Figs 5 A and 5B, wherein a dose Mi consisting of two components, the preliminary dose and the corrective dose, is delivered during time interval T₆ Thus, the mass Mi is equal to the combination of the mass of the preliminary does Mi and the mass of the corrective dose M₃ Time interval T₆ is the total time required for delivery of a preliminary dose, allowing the preliminary dose to come to a state of static equilibrium, delivery of a corrective dose, during which time the preliminary dose is unloaded; and unloading of the corrective dose Thus, time interval T₆ is equal to the combination of time intervals Tι+T₂+T₄+T₅. The cyclogram of Fig 5C shows repeated cycles of delivery and unloading of preliminary and corrective doses. Due to the fact that unloading of the preliminary dose and delivery of the corrective dose are begun simultaneously, the method according to the present invention thus reduces the amount of time required per cycle as compared with prior art methods This enables a significant increase in the productivity of a device which utilizes the method of the present invention over devices which utilize prior art methods A particularly advantageous feature of the present invention is that the total measurement error is relatively small, as compared with that of prior art devices This is due to several factors First, while the corrective dose is measured dynamically, the preliminary dose is measured in a state of static equilibrium Thus, the measurement error may be calculated as the sum of the measurement error of the preliminary dose M₄, which is small, and the measurement error of the corrective dose M-, Thus, the error of the entire dose, according to the present invention, is substantially determined by the error of measurement of the corrective dose M₃ Second, the provision of separate dose receivers and weight meters for the preliminary and corrective doses enables the provision of weight meters having different measurement ranges While the accuracy of any weight meter will inherently have a certain margin of error, since the present invention enables the error in measurement to be substantially limited to the error of the corrective dose measurement only, then the total error will be substantially within the margin of error of the corrective dose, which is relatively small, as compared with the total amount of the combined dose Mi In light of these advantages, the present invention represents a significant improvement over prior art devices, wherein a single weight meter is employed for measuring both preliminary dose and corrective dose When utilizing prior art devices, the resulting error of the entire dose is determined by combining the measurement error of the preliminary dose (rough flow) weight meter with the measurement error the corrective dose (fine flow) weight meter, both of which are significant due to the fact that measurement is carried out under dynamic conditions

In order to illustrate the importance of the present invention in limiting the total dose error to the error in corrective dose measurement only, it should first be understood that the relationship between the amount of the preliminary dose and the amount of the corrective dose will affect the amount of the total error of measurement The smaller the amount of the preliminary dose, the greater is the corrective dose required, thus increasing the total error Conversely, the greater the amount of the preliminary dose, the less is the total error

By utilizing known measuring techniques and devices, margins of error depending on the desired dose may be established The relationship between the preliminary and corrective doses is illustrated by the following examples, wherein it is desired to measure 50,000g of a material and 1 ,000g of a material When it is desired to measure 50,000g of a material, it has been found that, using known material weighing devices, the dose error will be in the range of from 0 1% - 2 0%, i e 50g - lOOOg Thus, in order to ensure that no more than the desired amount of material is fed, the amount of the preliminary dose M₂ should be in the range of from 49,950g - 49,000g, and the amount of the corrective dose M₃ should be in the range of from 50g - l,000g The ratios of corrective dose to preliminary dose may be calculated as follows for minimum preliminary dose error 50/49950 = 1/999 for maximum preliminary dose error 1000/49000 = 1/49

When it is desired to measure l,000g of the same material, it has been found that, using known material weighing devices, the unit dose error will be in the range of from 0 5 % to 2 0%, i e 5g - 20g Thus, in order to ensure than no more than the desired amount of material is fed, the amount of the preliminary dose M should be in the range of from 995g - 980g and the amount of the corrective dose M₃ should be in the range of from 5g - 20g The ratios of corrective dose to preliminary dose may be calculated as follows' for minimum preliminary dose error 5/995 = 1/199 for maximum preliminary dose error 20/980 = 1/49

Based on these examples, the ratio of volumes of maximum corrective and preliminary doses has been calculated as ranging from 1 49 to 1 999 For ratios greater than 1 49, the proportion of corrective dose increases, thus reducing the productivity and increasing the measurement error Ratios less than 1 999, i e , cases where the measurement error is less than 0 1 %, are unattainable by known methods

Experimental trials of the device according to the present invention and of prior art devices have been conducted and studied A comparison of results shows that the advantageous features of the present invention enable a reduction in the measurement error by a factor of 6 - 10 (which results in material savings) and an increase in the rate of productivity by a factor of 1 5 - 2 (depending on amount of desired dose), over prior art devices.

This is illustrated in the following example, wherein the desired total dose is lOOOg and the preliminary dose measurement error is ±2% The desired preliminary dose is determined by M₂ = M, - M, x 2% = 1000 g - 20 g = 980 g The range of the actual preliminary dose is determined by 980 ±2% x 980 = 980 g ±19 6 g Thus, the actual measurement of the preliminary dose may be in the range of from 960 4 g to 999 6 g If, for example, the actual measurement of the preliminary dose is 972 g, i e , 960 4 < 972 < 999 6, then the corrective dose mass Ms is determined by Ms = 1000 g - 972 g = 28 g, the corrective dose error being ±2% x 28 g = ±0 56 g Even if the error actually obtained is 0 56g, this represents a corrective dose error of only 2%, such that an increase in the productivity and reduction of the cost of material waste are attained The total mass of the dose may be determined by Ms + M, = 28^{+0 56} + 972^{+0 ]} = 1000^{τ0 66} g, wherein the superscript 0 56 indicates the margin of error for the measurement of the corrective dose and the superscript 0 1 indicates a typical margin of error for the preliminary dose weight meter Therefore, the total measurement error is 0 66/1000, or approximately 0 07 % of the desired total dose of 1000 g

A method of measuring free-flowing materials according to the present invention is implemented as follows The desired mass Mi of a dose to be measured is given, the mass M₂ of a preliminary dose is determined using the microprocessor The mass M₃ of a corrective dose is determined as the difference between the desired mass Mj and the actual mass M₄ of the preliminary dose, i e., M₃ = Mi - M₄ The value of Ms is transmitted by the microprocessor to a corrective dose weight meter The mass M₄ of the preliminary dose is found to be within the range of from MUmax to MUmm, and the mass M₃ of corrective dose will vary accordingly

Figs 6A and 6B illustrate the distances between the corrective dose feeders 5 and the topmost points, Oj and O₂, respectively, of corrective doses which have been dispensed into dose receivers 8 These distances by which the corrective doses must fall may be referred to as 'falling distances,' and may be represented by D Fig 6A illustrates that, for a maximum preliminary dose

the amount of corrective dose required is minimal, i e , M_3rnιn, and that the falling distance, D_ma is maximal Fig 6B illustrates that, for a minimum preliminary dose M-i_rmn, the amount of corrective dose required is maximal, i e , M_3ma , and that the falling distance, D„„„, is minimal It should be understood that the distance by which any given corrective dose must fall will be within the range of from D_mιn to D_ma

In the prior art, the influence of falling distance of a free-flowing material on a weighing device is not taken into account when measuring each dispensed dose In contrast, Applicant has considered that differences in the falling distances of corrective doses of a material being dispensed will result in variations of dynamic pressure exerted on a weight meter, from Pdyn _m3 to Pd_>n mm, and that these variations in dynamic pressure should be taken into account when measuring each of the corrective doses. Consequently, the method of the present invention enables the desired amount of corrective dose to be adjusted, as will be discussed below with reference to Figs. 7A and 7B, references to Fig. 7B shown in parentheses. Figs. 7A and 7B illustrate the influence of dynamic pressure change on the mass of corrective doses for the cases of the maximum fall height and minimum fall height, respectively. These graphs have been plotted using values based on standard theoretical data, depending on various factors, such as amount of dose, type of material, falling height, etc. Specifically, there are shown graphs representing changes in pressure P which may be exerted by a corrective dose falling on a corrective dose weight meter over time T, wherein the pressure of a corrective dose having mass M₃ may be measured as P = M₃ ^#g, where g is the acceleration due to gravity.

The curve I (F) represents the measurement of pressure exerted by a corrective dose being dispensed onto a weight meter during time T, without regard to dynamic pressure of the falling material, i.e., as if each point of the curve corresponds to a measurement of actual mass of corrective dose at a state of static equilibrium. On curve I (F), K (K') and Q (Q') are points at which the amount of corrective dose that has been dispensed is equal to the desired amount and is less than the desired amount, respectively. The curve II (IF) represents the measurement of pressure exerted by a corrective dose being dispensed onto a weight meter during time T, with regard to dynamic pressure, i.e., while the material is falling onto the weight meter. On curve II (IF), L (L') and N (N') are points at which the amount of corrective dose that has been dispensed is equal to the desired amount and is less than the desired amount, respectively.

Fig. 7A (7B) shows that, at point K (K') on curve I (F), since the amount of pressure being exerted by dispensing of the corrective dose is P₂ (P₂'), a weight meter will indicate that the desired mass of corrective dose has been dispensed, since it does not take into account dynamic pressure exerted by the falling of the corrective dose into the corrective dose receiver. However, due to the presence of dynamic pressure, the amount of pressure at point K (K') corresponds to point N (N') on curve II (IF), at which the actual mass of the corrective dose is less than the desired mass. In fact, the actual mass of the corrective dose at point N (N'), sensed due to the exertion of dynamic pressure, is represented on curve I (V) by point Q (Q'). Thus, in accordance with the present invention, when the amount of pressure sensed by a weight meter is P₂ (P₂'), this will indicate that the desired amount of corrective dose has not yet been dispensed.

To compensate for this measurement error which would otherwise result, so as to allow for the proper amount of corrective dose to be dispensed, point L (L') may be determined on the graph, by drawing a vertical line segment from point K (K') until it intersects curve II (IF). As noted above, L (L') corresponds to the point at which the desired amount of corrective dose has been dispensed, when dynamic pressure is considered. Thus, in order to compensate for the error which would otherwise result, the present invention determines Ps (P₃'), the pressure at which the desired amount of corrective dose has been dispensed, and determines point L (L'). A signal is then sent to the corrective dose weight meter, the signal representing point L (L'), such that the corrective dose will be dispensed until the dynamic pressure P₃ (P₃') has been sensed, indicated that the desired amount of corrective dose has been dispensed.

In addition to this adjustment, the present invention takes into consideration the fact that the amount of a corrective dose will vary, depending on the type of material (sugar, wheat, etc.) and desired total dose (1 kg, 50 kg,...), and, once a desired amount of material is known, also on the actual amount of the preliminary dose. Thus, a compensating factor λ , depending on the amount of the corrective dose, is determined and introduced into the microprocessor program. Thus, the actual amount of the corrective dose mass M₃ will be M_3act = λ x M.s, where λ < 1 is an experimental factor accounting for the compensating mass (the dynamic pressure of falling material and the mass of material remaining in the air between the feeder and dose receiver after cutting out the feed); and M₃ is the amount of corrective dose measured by the weight meter.

In contrast to prior art methods, where the dose is fed in two consecutive doses (flows), the preliminary (rough) and corrective (fine) flows, the method of the present invention partitions the total desired dose into the preliminary and corrective doses, two unequal doses which are delivered in parallel, and not consecutively. This results in an increase in productivity over prior art methods.

The method of measuring free-flowing materials according to the present invention was subjected to tests which yielded promising results. I.D.M Engineering Ltd. (Be'er Sheva, Israel) has designed and manufactured a device for measuring free-flowing solid materials with a desired total dose of 1000 g Tests conducted by 1 D M Engineering Ltd yielded the following results

1 Measurement error • Preliminary dose 0 1 g

• Corrective dose 0 3 g • Total error 0 4 g

2 Productivity rate 30 doses per minute

For comparison, the CB2-3, a 1000 g batching machine manufactured by OPTIMA, a leading German company, has a total error of up to 5 g and a productivity rate of 15 doses per minute Thus, it is apparent that the method and device of the present invention are advantageous over prior art, both with regard to accuracy of total dose and speed of operation

It will be appreciated by persons skilled in the art the scope of the present invention is not limited by what has been particularly shown and described above Rather, the scope of the invention is limited solely by the claims, which follow

Claims

C L A I M S

1 A method for measuring a predetermined amount of a free-flowing material, said method including the steps of (a) calculating the desired amount of a preliminary dose of material, the desired amount of the preliminary dose being less than the predetermined amount of material,

(b) dispensing a preliminary dose of material from a source of free-flowing material into a first measuring apparatus,

(c) measuring the actual amount of said preliminary dose in said first measuring apparatus in a state of static equilibrium, the actual amount of the preliminary dose being less than the predetermined amount of material,

(d) calculating the desired amount of corrective dose of material,

(e) dispensing a corrective dose of material from a source of free-flowing material to a second measuring apparatus, (f) coincidentally with step (e), emptying the preliminary dose of material from the first measuring apparatus into a receptacle,

(h) emptying the corrective dose of material from the second measuring apparatus into the receptacle.

2 A method according to claim 1, wherein said step (g) includes dynamically measuring the actual amount of the corrective dose of material in the second measuring apparatus

3. A method according to claim 1 , wherein the desired amount of the preliminary dose is calculated as the difference between the predetermined amount of material and a predicted margin of error of the preliminary dose

4. A method according to claim 3, wherein the predicted margin of error of the preliminary dose is dependent on the accuracy of measuring in step (c)

5. A method according to claim 1 , wherein the desired amount of the corrective dose is calculated as the difference between the predetermined amount of the free-flowing material and the actual amount of the preliminary dose.

6. A method according to claim 5, wherein the calculated desired amount of the corrective dose is adjusted to compensate for at least one of the group which consists of the following factors: bulk density, whether the material is a liquid or a free-flowing solid, the desired amount of material, the amount of the preliminary dose, and the dynamic pressure of falling material into the second measuring apparatus.

7. A method according to claim 1, and wherein the sum of the error of measurement of the actual amount of the preliminary dose and the error of measurement of the actual amount of the corrective dose is substantially equal to the error of measurement of the actual amount of the corrective dose.

8. A method according to claim 1, wherein each of the ratios of the amount of desired corrective doses to the amount of desired preliminary doses is within the range 1 :49 to 1:999.

9. A method for packaging a predetermined amount of a free-flowing material, said method including measuring a predetermined amount of a free-flowing material according to steps (a) through (h) of claim 1, and including the following additional step: (i) packaging the contents of said receptacle.

10. A device for measuring a predetermined amount of a free-flowing material, said device including: apparatus for calculating the desired amount of a preliminary dose of material, the desired amount of the preliminary dose being less than the predetermined amount of material; apparatus for dispensing a preliminary dose from a source of free-flowing material into a first measuring apparatus; apparatus for measuring the actual amount of the preliminary dose in said first measuring apparatus at a state of static equilibrium, the actual amount of the preliminary dose being less than the predetermined amount of material; apparatus for calculating the desired amount of a corrective dose of material; apparatus for dispensing a corrective dose of material from a source of free-flowing material to a second measuring apparatus; apparatus for emptying the preliminary dose of material from said first measuring apparatus into a receptacle, said apparatus for emptying being actuatable during operation of said apparatus for dispensing the corrective dose; apparatus for measuring the actual amount of the corrective dose of material in said second measuring apparatus; and apparatus for emptying the corrective dose of material from said second measuring apparatus into said receptacle.

11. A device according to claim 10, wherein said apparatus for measuring the actual amount of the corrective dose of material in said second measuring apparatus includes apparatus for dynamically measuring the actual amount of the corrective dose of material in said second measuring apparatus.

12. A device according to claim 10, wherein said apparatus for measuring the actual amount of the preliminary dose includes a first weight meter and said apparatus for measuring the actual amount of corrective dose includes a second weight meter.

13. A device according to claim 10, including control apparatus for controlling operation of each of said apparatus for dispensing the preliminary dose, said apparatus for dispensing the corrective dose, and said apparatuses for measuring the preliminary and corrective doses.

14. In a system for packaging a predetermined amount of a free-flowing material, use of a device for measuring a predetermined amount of a free-flowing material according to claim 10, and further including: apparatus for packaging the contents of said receptacle.

15 A system for measuring a plurality of predetermined amounts of a free-flowing material, said system including a plurality of devices for measuring according to claim 13, said plurality of microprocessors being controlled by a central microprocessor

16 A system for packaging a plurality of predetermined amounts of a free-flowing material, said system including the system for measuring a plurality of predetermined amounts of a free-flowing material according to claim 10, and further including apparatus for packaging the contents of said plurality of receptacles

17 A device according to claim 10, wherein each of the ratios of the amount of desired corrective doses to the amount of desired preliminary doses is within the range of from 1 49 to 1 999

18 Use of a device or of a system, according to claim 10, and wherein the sum of the error of measurement of the actual amount of any preliminary dose and the error of measurement of the actual amount of the corresponding corrective dose is substantially equal to the error of measurement of the actual amount of the corresponding corrective dose

19 A device for packaging a plurality of predetermined amounts of at least one free-flowing material, said device including

(a) apparatus for calculating the desired amounts of preliminary doses of the at least one material, each of the desired amounts of the preliminary doses being less than a corresponding one of the plurality of predetermined amounts of material,

(b) a plurality of apparatuses for dispensing a plurality of preliminary doses of the at least one material to a corresponding plurality of first receptacles,

(c) apparatus for measuring the actual amounts of each of the plurality of preliminary doses of the at least one material at a state of static equilibrium in each of said plurality of first receptacles, the actual amount of each of the plurality of preliminary doses being less than a corresponding one of the plurality of predetermined amounts of material, (d) apparatus for calculating the individual desired amounts of a plurality of corrective doses of the at least one material, each of the desired amounts corresponding to one of the plurality of preliminary doses;

(e) a plurality of apparatuses for dispensing a plurality of corrective doses of the at least one material to a corresponding plurality of second receptacles;

(f) apparatus for emptying each of the plurality of preliminary doses from said plurality of first receptacles into a third receptacle, said apparatus for emptying being operable coincident with operation of said plurality of corrective dose dispensing apparatuses; (g) apparatus for dynamically measuring the actual amounts of each of the plurality of corrective doses in each of said plurality of second receptacles;

(h) apparatus for emptying each of the corrective doses of the at least one material from said corresponding plurality of second receptacles into said third receptacle; and (i) apparatus for packaging the contents of said third receptacle.

20. A device according to claim 19, wherein each of said apparatuses for measuring the actual amounts of the preliminary doses and each of said apparatuses for dynamically measuring the actual amounts of the corrective doses includes a weight meter.

21. A device according to claim 19, said plurality of preliminary dose dispensing apparatuses, said plurality of corrective dose dispensing apparatuses, and said plurality of weight meters being controlled by a plurality of microprocessors.

22. A device according to claim 21, said plurality of microprocessors being connected to a central microprocessor.

23. A device according to claim 19, wherein each of the ratios of the amount of desired corrective doses to the amount of desired preliminary doses is within the range of from 1 :49 to 1 :999.

24. Use of a device or of a system, according to claim 19, and wherein the sum of the error of measurement of the actual amount of any preliminary dose and the error of measurement of the actual amount of the corresponding corrective dose is substantially equal to the error of measurement of the actual amount of the corresponding corrective dose.