WO1986000405A1

WO1986000405A1 - Automatic weighing machine

Info

Publication number: WO1986000405A1
Application number: PCT/DK1984/000061
Authority: WO
Inventors: Per Flöj LINDEGREN
Original assignee: Bilwinco Aps
Priority date: 1984-06-28
Filing date: 1984-06-28
Publication date: 1986-01-16
Also published as: EP0188407A1

Abstract

In an automatic weighing machine for weighing portions of a product (1) composed of individual articles, comprising a product feeding device (2) and at least one weighing line having a vibratory conveyor and a weigh hopper (6), the vibratory conveyor comprises a first (4) and a second, vibratory chute (5) closest to the weigh hopper (6), each respective one being provided with a drive mechanism (7, 8) in connection with a control device (9). The second chute (5) is energized to vibrate at constant amplitude and frequency, while the control device (9) in dependence on the actual values of the feeding rate (v1) of the first chute (4) and the weight (Makt) of a product portion discharged to the weight hopper (6) is adapted to adjust solely the product feeding rate (v1) of the first chute (4) for discharging a substantially constant amount of product (delta2) per unit of time to the weigh hopper (6). In order to stop the discharge of product to the weigh hopper (6) the control device (9) supplies stop signals to both drive mechanisms (7, 8) at a predetermined stopping moment dependent on a desired value of portion and an arresting delay.

Description

Automatic weighing machine.

This invention relates to an automatic weighing machine for weighing individual, uniform portions of a product composed by individual articles, comprising a product feeding device and at least one weighing line having a vibratory conveyor one end of which is located at the product feeding device for receiving said articles, while in connection with the other end of the conveyor there is positioned a weigh hopper adapted to receive and weigh the articles fed from the conveyor, the vibratory conveyor comprising a first vibration chute closest to the product feeding device and a second vibration chute positioned closest to the weigh hopper, said second chute having its product feeding end located beneath a product discharge end of, the first chute, said chutes being connected with a drive mechanism with an associated control device to energize the chutes to vibrate with controllable vibration amplitude and/or frequency to control the product feeding rate of the conveyor. Weighing machines of said type are used in the production of batch pac agings of a series of different products within the foodstuffs industry, for instance in the form of vegetables, cakes, confectionery and the like, within the field of other branches of industry e.g. when packaging certain fittings goods like nails, screws and the like. Such weighing machines are available in the form of single-weighing lines where a weigh hopper in such a line collects the final batch quantity as well as in the form of combinatory weighing plants in which the total batch content with a view to

• increasing the capacity and the weighing accuracy is composed of sub-portions selected by combinative methods of calculation from a number of weighing lines that may be connected with the same product feeding system. Such combinatory weighing plants are for instance known from US patents Nos. 3,939,928 and 4,397,364. In prior weighing machines the weighing lines may be time-controlled, whereby the time of dosing, i.e. the time consumed for collecting and weighing a single por¬ tion and thus also the capacity defined as the number of weighed batches per unit of time, will be dependent on the batch size. In many prior weighing machines the time of dosing is further prolonged in that the feeding rate of the vibratory conveyor must be considerably reduced at the end of the weighing of each batch in order to obtain sufficient accuracy. This drawback can be remedied to a certain extent by making use of a vibratory conveyor with two independently controlled sub-chutes as stated by way of introduction, whereby the time delay when stopping the chutes can be reduced. Also as regards product handling, the utilization of two chutes positioned as stated by way of introduction with a gradient course at the transition between the chutes may entail practical advantages as blocking of the chu¬ tes are easier eliminated and the product is better levelled. It is the object of the invention to provide a new design of a weighing machine of the kind concerned to be used in line weighing plants as well as in com¬ binatory weighing arrangements by which a considerably improved weighing accuracy and a considerable increase of capacity are obtained through utilization of a self- adjusting feed-back.

In order to achieve this, a weighing machine ac¬ cording to the invention is characterized in that the control device is connected by signal with the weigh hopper and with individual drive mechanisms, respective- ly, for the first and the second chute, that the second chute is energized by its drive mechanism to vibrate at a constant amplitude and frequency and that the control devcice is adapted to supply, in response to inlet con- trol signals derived from the actual values of the feeding rate of the first chute and the weight of pro¬ duct portion received and weighed in the weigh hopper, respectively, a vibration control signal to the drive mechanism for the first chute for controlling solely the product feeding rate of said chute for adjustment of the product level in the second chute for discharging a substantially constant amount of product per unit of time to the weigh hopper, and to supply stop signals to the drive mechanisms of both chutes for stopping the product discharge from the second chute to the weigh hopper at a predetermined stop moment dependent on a desired value of the weight of said uniform portions and a substantially constant arresting delay.

By driving solely the first vibratory chute posi- tioned closest to the product feeding device at varying speed and letting the following second chute, from which the product is discharged to the weigh hopper, operate at a constant speed that is preferably faster than the speed of the first chute there is - besides an advan- tageous product levelling in the second chute - obtained security against overfilling of said chute without the requirement of particular feed-back arrangements as is the case in certain prior weighing machines by use of a weight suspension or a product level sensor in asso- ciation with the second chute.

This together with control of the speed of the first chute through a pure weight control on the basis of an input control signal supplied from the accurate weighing system which is associated with the weigh hopper provides for obtaining a capacity of the machine defined as weighed batches per unit of time within a variation range whose upper limit is determined by the total product accommodation capacity of the second chute which will be substantially independent of the batch size, thereby entailing considerable, practical advan¬ tages to the subsequent handling of the packagings to which the batches discharged from the machine are trans¬ ferred from the weigh hopper. In comparison with prior time-controlled weighing machines a further contribution to an increase in capacity is that the machine operates at full speed until the vibratory conveyor stops, i.e. without any requirement of a decrease in speed.

Finally, the invention provides for obtaining an improved weighing accuracy due to the fact that the weight of the individual batches is adjusted around a average value corresponding to the desired value of the batch weight.

A preferred embodiment of the weighing machine according to the invention is characterized in that said stop moment is determined so that when stopping the discharge of product to the weigh hopper after said arresting delay, a total time of dosing (T3) is obtained determined by

in which s is a predetermined stop point factor defined by

Particularly as a consequence of the improved weighing accuracy of the weighing line the embodiment according to the invention is extremely suitable for combinatory weighing arrangements where a batch of the product to be weighed is composed of sub-portions from a suitable combination of a sub-number of weigh hoppers for a larger amount of weighing lines. Due to the improved weighing accuracy according to which sub- portions of all weighing lines will be of about the same average weight, a considerable reduction of the comput¬ ing time used to select a combination of sub-portions resulting in the desired batch size is obtained, co - pared to prior combination weighing arrangements of the kind disclosed in the aforementioned US patents.

In this respect, an embodiment in which the weighing machine comprises a number of weighing lines in a combinatory weighing arrangement in which the weigh hoppers of the weighing lines may be selectively emptied to a common collecting weigh hopper adapted to receive a total product batch composed of sub-portions from weigh hoppers in a sub-number of weighing lines, charac¬ terized in that the control device for selecting a com- bination of weigh hoppers up to said sub-number compri¬ ses a combinatoric computerunit which from the weigh hoppers of the weighing lines receive the input control signals derived from said actual portion weight values and is adapted to calculate and select a combination of sub-portions within the prescribed minimum and maximum limits for the weight of the total portion through sorting of the applied batch portion weight values according to size and examining combinations containing a number of portion weight values between the limits 1 and m = n/s, wherein n is the said sub-number corres¬ ponding to the ratio between a desired weight value of the total product portion in the collecting container and a common desired weight value of the sub-portions, in which examination as to combination of a determined number of sub-portions within said limits, is only effected of all possible combinations including said number, if the conditions

Wj, in < W_tot, max og Wj, max > W_tot, min 1 < j < m are fulfilled, wherein Wj min and Wj max are the lowest and highest value, respectively, of the total weight of said number (j) of sub-portions, and by said examination of all possible combinations of one or more determined numbers (j) of sub-portions by fulfilment of said condi- tions, is practised by putting an end to the examination as soon as a combination having a total weight equal to the desired weight of the total batch has been found or, if such a combination cannot be found, selecting from all said combinations the combination whose total weight is closest to said desired value.

Compared to prior combinatory weighing arrange¬ ments a considerable limitation is obtained of the number of combinations to be examined, thereby limiting the total computing time and as a result a reduction is obtained of the time the product resides in the indivi¬ dual weigh hoppers. Such a combinatory weighing arrange¬ ment is particularly suited for weighing batches of deep-frozen goods, for which there may otherwise be a considerable risk that the individual articles in the products stick together by freezing.

In such a combination weighing arrangement a further measure of precaution with respect to the time used by the products in the weigh hoppers is obtained in that a work storage associated with the combinatorial unit is fed with said input control signals together with a clock indication about the arrival of each con¬ trol signal generated internally, and that the unit is adapted to effect the examination as to combination of any given number of weigh hoppers or possible inter- mediate collecting containers in time order, starting by the earliest. Due to this assignment of priority it is ensured by the selection of combinations of sub-portions that the sub-portions which at the time of selection have stayed for the longest time in the individual containers have a preferential position.

In the following the invention is explained in detail with reference to the schematical drawings, in which

Fig. 1 shows an embodiment of a weighing line in a weighing machine according to the invention,

Fig. 2 is a graphic representation illustrating the course of time for discharging a product batch from the weigh hopper in a weighing line as shown in Fig. 1,

Fig. 3 is a corresponding graphic representation illustrating the speed control,

Fig. 4 is a flow diagram explaining the speed control, and

Figs 5 and 6 illustrate an embodiment of the weighing machine according to the invention as a com- binatory weighing arrangement.

In the embodiment schematically illustrated in Fig. 1 of a single weighing line a product 1 composed of individual articles is accommodated in a container 2 with product outlet 3. Through the product outlet 3 the product 3 is discharged to one end of a first vibratory chute 4 in a vibratory conveyor. The opposite end of the chute 4 is positioned higher than a product supply end of a second vibratory chute 5, from the opposite end of which the flow of product fed from the container 2 through the chutes 4 and 5 is discharged to a weigh hopper 6.

The conveyance of product in the vibratory chutes

4 and 5 is effected in a known manner in that the chutes are vibrated transversely by means of a drive mechanism 7. and 8, respectively, associated with either chute. Control signals to the drive mechanisms 7 and 8 are supplied from a control device 9 for adjusting the amplitude and/or frequency of vibration with a view to control the product feeding rate, as well as with stop signals for arresting the vibratory chutes 4 and 5 when a product batch of desired size has been collected and weighed in the weigh hopper 6.

According to the invention the control device 9 is signal-connected with the weigh hopper 6 and with the individual drive mechanisms 7 and 8 and receives as input control signals the actual values of the feeding rate vi for the first chute and the weight of a product batch 10 received and weighed in the weigh hopper. In response to said input control signals the control device 9 generates a vibration signal for the drive mechanism 7 of the first chute 4 to control solely the feeding speed vi of said chute, whereas the second chute 5 is energized by the drive mechanism 8 to vibrate at constant amplitude and frequency, thereby feeding the product at a constant rate V2, that is preferably faster than the upper limit of the variation range of the rate i.

As explained in the following the control device 9 is further adapted to supply stop signals to the drive mechanisms 7 and 8 of both chutes at a predetermined stop moment defined by the desired value M of the batch weight and a substantially constant arresting delay.

The division known per se of the vibratory con¬ veyor into two partial chutes 4 and 5 in extension of each other but with such a difference in level that a fall path 11 is provided at the transition from the chute 4 to the chute 5 through which the product is transferred at a velocity Δ » causes an advantageous product levelling in the second chute 5, so that the product is discharged from said chute to the weigh hopper in a uniform flow at a product rate Δ2« The schematical time diagram in Fig. 2 illustra¬ tes the discharge of a product batch to the weigh hopper 6 from the vibratory conveyor 4, 5. Supposed the product discharge is effected at a constant rate Δ2 correspond- ing to the inclination of the oblique curve portion in Fig. 2, the desired total product quantity having the batch weight P will be collected in the weigh hopper 6 after a dosing period T_<j.

In order that the desired product quantity P may be fed to the weigh hopper 6 just in the course of the period 3, the vibratory conveyor 4, 5 must be stopped for a time interval, the arresting delay Tf, before the expiry of the period of time T3. Said arresting delay Tf that is composed of the response time caused by the mechanical inertia of the vibratory chutes 4 and 5 with associated drive mechanisms 7 and 8, and the period of dropping of fall path 12 through which the product is discharged from the chute 5 to the weigh hopper 6 together with the delay in a possible low-pass filter of an amplifier 9a connected between the weigh hopper 6 and the drive mechanism 9 is typically of the order of the magnitude 0,3 sec.

Said circumstance is according to the invention utilized for introducing as a control parameter a stop point factor s defined so that s • P designates the pro¬ duct quantity collected in the weigh hopper 6 in the period of time T^ - Tf. Since the stop point factor is defined by

Δ T s = 1 2—- ø wherein M is the desired value of the batch weight the following equation thus applies to the relation between the periods of time T3 and Tf T, = 1 - s

As the second chute 5 is driven at constant speed, the arresting delay Tf is a substantially constant magni¬ tude so that also the time of dosing ^ will be constant and independent of the product quantity P for a given value of the stop point factor s. As already mentioned, this implies that the capacity of the weighing machine according to the invention defined by the amount of weighed batches per unit of time is substantially inde¬ pendent of the batch size within a variation range limited by the total capacity of product in the the chute 5. It appears from Fig. 2 that for a given value of the stop factor s there will only exist one definite value of the product feeding rate Δ2 from the second chute 5 to the weigh hopper 6 at which the desired amount of product P is actually collected in the weigh hopper within the time of dosing 3.

As explained in the following by means of Fig. 3 this circumstance can be utilized for control the rate of the first chute 4 through establishment of a feed¬ back by which the product discharge rate Δ2 is adjusted to the value corresponding to a given desired value of the stop factor s.

In this respect it is firstly remarked that due to the fact that the second chute 5 is driven at a con¬ stant rate V2» the product discharge rate Δ2 will be defined by the product height or level in the second chute 5, and at the constant rate V2 this incidentally solely depends on the product feeding rate Δ_ in full path 11 and thus on the rate vi of the first chute.

Curves a, b and c in Fig. 3 shows the course at three different values of the product feeding velocity, i.e. the curve inclination Δ2« The curve b indicates the ideal dosage at which the product quantity P_D collected and weighed in the weigh hopper 6 actually corresponds to the desired weight Mø. As to the curve b there will thus be discharged, as explained with reference to Fig. 2, in the course of the arresting delay Tf the ideally correct product quantity (1 - s) M to the weigh hopper 6.

On the contrary, as a result of the changed inclination Δ2 there will, as regards the curves a and c, be discharged the product quantities P_a - s M and P_c - s Mø, respectively, in the course of the arresting delay Tf. If the designation M_a]_ζt s applied generally as actual weight value for the product quantities P_a and P_c, it will be seen that an adjustment of the courses defined by the curves a and c requires that the inclina¬ tion or the product feeding rate Δ2 in such cases be multiplied by

1 - s ^Makt ø wherein _a]ζt as stated is the actual collected batch weight, in the above mentioned case P_a or P_D. With the above mentioned relation beween the product feeding rate Δ2 and the product feeding rate vτ_ for the first chute 4 there will consequently by controlling said velocity according to the equation

be effected a regulation of the product level in the second chute 5 in order to correct the product feeding velocity Δ2» With a view to carrying out the velocity control the drive mechanism 9 includes a microprocessor which at suitable regulation intervals makes a calculation of the velocity value v_ny on the basis of the applied input information about the actual rate value v^t and the actual batch weight M_{a t} weighed in the weigh hopper 6, since the desired value Mø of the batch weight and the stop factor s for a given weighing operation are con¬ stant magnitudes which at the start of the machine are recorded in the microprocessor by means of a keyboard by which rate values for vi and V2 are programmed that by experience are appropriate for the product desired to be weighed and the intended batch weight Mø.

After comparatively few batch weighings the machine will have adjusted itself by the described velo¬ city regulation to the correct value of the feeding rate vi for the first chute 4.

As it is merely a regulation of said velocity value that is effected resulting in a control of the product flow Δ]_ from the first chute 4 to the second chute 5 it is according to the invention preferred that the supply of the vibration signal from the control device 9 to the drive mechanism 7 is effected at regula¬ tion intervals corresponding to a regulation delay rela- tive to the time at which the control device 9 receives the batch weight signal M_aζ_f corresponding to the time of dosing for a number of batch weighings between the product capacity of the second chute 5 and the desired value of batch weight Mø, whereby the product quantity which at the time of receiving said signal is located in the second chute 5, is batchwise discharged to the weigh hopper 6 before adjustment of a new velocity value of vi.

To achieve this, the velocity control is effected in accordance with the flow diagram shown in Fig. 4, in which the upper block indicates the input information ^Makt' ^Mø' ^{s n< v}akt available to the microprocessor in the control device 9.

In view of the above described desired regulation delay a further information N is applied to the micro¬ processor about the number of weighings carried out since the latest preceding adjustment of a new value of velocity for vi. In the example illustrated in the flow diagram five weighings have been chosen as a regu- lation delay which means that the product quantity accommodated in the second chute 5 when the control device 9 receives the signal M_a]ς . corresponds to five batches of product in the weigh hopper 6, thereby ensuring that the effect of the preceding regulation of velocity is fully in force.

In the following block 14 of the flow diagram it is examined whether the figure N is greater than 5. If not, 1 is added to the figure N, and return is made to the starting point of the flow diagram. Due to the fact that the flow diagram illustrates the velocity regulation during operation, there can as an expression of the actual batch weight value M_a t i-ⁿ the preceding equation advantageously be chosen an average value M_ac of the actual batch weight values in a number of the closest preceding weighings, for instance twenty, implying an extension of the interval of regula¬ tion up to twenty-five weighings. If the examination in block 14 shows that the figure n is greater than 5, it is examined in the successive block 15 whether figure N is greater than or equal to 25. If this is not the case, yet a new velocity value has^" hot yet to be calculated according to the preceding equation, but in the follow¬ ing block 16 the batch weight M_a of the actual weigh¬ ing is added to the accumulated weight of the preceding N-l weighings, following which figure N is increased by 1 and return is made to the starting point of the flow diagram.

If the examination in block 15 shows that the figure N exceeds or is equal to 25, the average value M_ac is calculated to be inserted in the preceding equation, and in the following block 18 the new velocity value v_ny is calculated in dependence on the preceding equation, said velocity value being applied to the drive mechanism 7, following which both magnitudes MJJ and N are brought to zero in the following block 19, and in the subsequent block 20 a figure is added to the number N in the same manner as stated above, following which return to the starting point of the flow diagram is effected. The rather considerable interval of regulation according to the flow diagram implying that a new adjustment only takes place after the most recently adjusted value of velocity of vi has been practised for a certain period of time, has a considerably stabilizing effect on the whole regulation, causing that the weigh¬ ing machine discharges continuously batch sizes to the weigh hopper 6 at slight variations about the average value Mø.

The design illustrated in Figs 5 and 6 of a com- binatory weighing arrangement comprises eight weighing lines 21 to 28 each designed as explained in the pre¬ ceding and arranged in pairs in a cross arrangement in relation to a central product supply device 29 in con¬ nection with a container 30 having a product storage, as it appears most clearly from Fig. 6. The weigh hoppers 31 of the weighing lines 21 to 28 are provided, as illustrated in Fig. 5, with individual closing means 32 and are adapted to be emptied via inclined conveying chutes 33 to a common collecting container 34. Said con- figuation of a combination weighing arrangement corres- ponds in principle to the one disclosed in the aforemen¬ tioned US patents. Such a combination weighing arrange¬ ment provides for obtaining the desired total batch of the product in the collecting container 34 by com- bination of a number of sub-portions from the weigh hop¬ pers of the individual weighing lines 21 to 28, said number being lower than the number of weighing lines, as a combinatoric selection of such sub-portions whose total weight approaches most the desired value of the weight of the total batch is carried out by examining the batch weights of the sub-portions.

With the purpose of carrying out said examination of the sub-portions and the combinatoric selection the microprocessor in the control device of the weighing machine according to the invention is programmed as a combinatoric computing unit.

In a combination weighing arrangement as illu¬ strated in Figs 5 and 6 the weight-controlled regulation of the individual weighing lines provided by the inven- tion, by which said weighing lines are caused to dis¬ charge sub-portions whose weight shows an average value corresponding to the desired value of the batch weight, entails, however, that, contrary to prior combination weighing arrangements a considerably higher degree of uniformity is obtained of the sub-portions discharged from the individual weighing lines of which the total batch is to be composed.

Thereby, in comparison with prior combination weighing arrangements wherein the combinatoric selection of sub-portions as a result of their non-uniformity makes it necessary to examine all possible combinations of sub-portions from the total amount of weighing lines with a resulting very long time of combinatoric calcula¬ tion, the possibility is opened that it will be suf- ficient to examine a substantially smaller number of combinations, thereby obtaining a considerable reduction of the time of combinatoric calculation and so also a reduction of the time the product batches reside in the weigh hoppers, that is in particular of importance when using such a weighing arrangement for batch weighing of deep-frozen products.

According to the invention the combinatoric cal¬ culation unit calculates and selects a combination of sub-portions within predetermined minimum and maximum limits W-t₀t,min ^{and w}tot»^max °f ^{tϊ e} weight W_tot of the total batch through examination of combinations con¬ taining a number of sub-portions or batch weight values between the limits 1 and m = n/s, wherein n is the ratio of the desired weight value of the total product batch in the collecting container 34 to the common desired weight value of the sub-portions in the weigh hoppers 31 and thus indicates the number of sub-portions envisaged to form part of the total batch. For a given number j of sub-portions between said limits examination is, however, only effected of all possible combinations of said number of sub-portions if the conditions

Wj, min < -fcof ^max °9

Wj, max > Wt₀-t, min, 1 < j < m are fulfilled, wherein Wj, min and Wj, . max are the lowest and the highest value, respectively, for the total weight of the sub-portions j, i.e. the weight of the hightest j and the heaviest j sub-portions.

The upper limit m = n/s for the number of sub- portions in the combinations to be examined expresses a safety margin determined by the fact that the weigh hop¬ pers of the individual weighing lines will always col¬ lect a minimum batch weight s • mø as a result of the weight controlled regulation of the individual weighing lines. Furthermore, the examination of the combinations for such numbers of sub-portions, in which the said conditions are fulfilled, is effected in such a manner that it is stopped as soon as a combination having a total weight equal to the desired value has been found or, if such a combination cannot be found, selection is made among all the combinations of the said sub-numbers whose total weight is closest to the desired value of the total batch.

As the weight-controlled regulation of the indi¬ vidual weighing lines in practice provides for a consi- derable probability of finding a combination having a total weight equal to the desired value a reduction of the time of calculatng the combination can thus also be achieved.

Supposed that by means of a combination weighing arrangement as illustrated in Figs 5 and 6 having eight weighing lines total batches with a desired weight of 300 g shall be provided, and that a desired weight of 100 g is chosen for the weighing lines corresponding to three sub-portions in a total batch, and a stop point factor of s = 0.7, there is obtained m * 4.3. With this value for the combinatoric selection there should according to the invention be effected examination of combinations containing at least one and not more than four sub-portions. The weight values of the batches from the indivi¬ dual weighing lines are fed into a working memory in the micro-processor of the control device the examination programme of which is so developed that a sorting of the weight values of the batches according to size from the lightest to the heaviest is at first carried out. Sub¬ sequently, the fulfilment of the above conditions for combinations comprising one, two, three and four sub- portions, respectively, is examined, so that it is exa¬ mined for each of said steps whether the weight of the lightest sub-portion or the summary weight of the two, three and four lightest sub-portions, respectively, lie beneath the maximum limit of the total weight, and whether the weight of the heaviest sub-portion and the summary weight of the two, three and four heaviest sub- portions exceed the minimum limit of the total weight.

Only if both of the above mentioned conditions are fulfilled in a given examination step, indicating that possible combinations having the number concerned of sub-portions are available, said sub-portions lying between the minimum and the maximum limit of the weight of the total batch, all combinations of the number of sub-portions are examined.

In a plant having M weighing lines there should for each examining step with combinations of j sub- portions, wherein j < m < M , be examined a number of combinations

M j 1 (M - j) !

The uniformity of the weight values of the sub- portions achieved by the invention entails, however, that said number of combination shall only be examined in practice for quite few examining steps out of the number m forming part of the total examination. In the present example with eight weiging lines and four exa¬ mining steps it is not conceivable that the above men¬ tioned conditions can be fulfilled by the examining steps comprising combinations with one, two and four sub-portions, respectively, due to the fact that the weight of the heaviest or the two heaviest sub-portions will be less than the minimum limit of the total weight, and the weight of the four lightest sub-portions will exceed the maximum limit of the total weight. As to each of said examining steps only the two combinations com- prising the lightest and the heaviest sub-portions are to be examined, while as far as the examining step with combinations of three sub-portions are concerned subject to fulfilment of the above mentioned conditions in all 56 combinations are to be examined, i.e. a total of 62 different combinations. In the combination weighing arrangements disclosed in the aforementioned US patents prescribing examination of all possible combinations it is, necessary to examine 255 different combinations, contrary to this case with eight weighing lines. In the combination examination of that or those examination step(s) wherein the above mentioned con¬ ditions are fulfilled, it is practised that the examina¬ tion is stopped if a combination of a total weight equal to the desired value of the total batch is available. If such a combination does not exist, the combination of all the combinations in that or those examining step(s) is selected whose total weight is closest to the desired value.

For further reducing the time the product stays in weigh hoppers or possible intermediate collecting containers the examination of combination for the examation step(s) may be effected so that it is started as soon as input control signals are available from a predetermined number of weigh hoppers or possible inter- mediate collecting containers which number is at least equal to the said sub-number n but is less than the total amount of weigh hoppers or possible intermediate collecting containers. If the above mentioned conditions are not fulfilled for any combination within said prede- termined number of weigh hoppers or possible inter¬ mediate collecting containers which by the stated numerical example for instance may be four, a new exami¬ nation is started upon receipt of the next control signal indicating that a new sub-portion has been collected in a weigh hopper or possible intermediate collecting containers. Contrary to the above, the examination of com¬ bination in prior combination weighing arrangements is effected only after sub-portions are available in all the weigh hoppers of the weighing lines or possible intermediate selecting containers associated therewith.

A further measure of reducing the stay of the duct in weigh hoppers or possible intermediate collecting containers may consist in utilizing a general system of preference so that the examination of com- bination also takes into consideration how long the sub- portions have stayed in the individual weigh hoppers or possible intermediate collecting containers. With respect thereto the micro-processor of the combinatoric computing unit may be programmed so that its working memory receives input control signals together with an indication of time generation internally in the control device about the arrival of each control signal, and so that the examination of combination is carried out in time order for any given number of sub-portions, start- ing by the earliest.

According to the invention an additional measure may be attached to the above principle of preference i.e. that the said indications of time for the input signals are compared to a time of priority prescribed for compulsory emptying the weigh hoppers in the weighing lines or possible intermediate collecting con¬ tainers so that, if said time of priority is exceeded for one or more sub-portions, compulsory use is made of that or those sub-portions by approval of the best com- bination having a total weight between the minimum and the maximum limit of which that or those sub-portions form part.

It is remarked that US patent No. 4,418,771 discloses a combinatoric weighing method by which a reduction of the number of combinations to be examined is obtained by allowing a deviation from the desired value of the total weight within a minimum and a maximum limit, in the same manner as according to the present invention, thereby reducing the number of examining steps in comparison with prior combination weighing arrangemnents according to the aforementioned US patents. Said prior method implies, however, examination of any combination of any used examining steps, combined with a selection of the first combination of sub-por- tions the summary weight of which lies between the mini¬ mum and the maximum limit of the total weight so that it is ignored whether there exist one or more in the suc¬ cessive unexamined combinations that is/are closer to the desired value of the total weight. The improvement obtained according to the inven¬ tion in relation to the prior combination weighing arrangements, in which all combinations are examined is more pronounced, the greater the maximum number of sub- portions is. Besides the number of weighing lines an increase in the maximum number of sub-portions with the purpose of increasing the number of combination possi¬ bilities and thereby improve the possibility of select¬ ing a combination of sub-portions very close to the desired value of the total weight may be obtained in that several, for instance two, intermediate collecting containers are -associated with the weigh hopper of each weighing line and are adapted to be emptied selectively and individually to the common collecting container 34 in the same manner as actually known from the latter US patent.

The said utilization of intermediate collecting containers in connection with the weighing lines may, however, according to the invention be practised with respect to the examination of combination in that the control device is adapted to subject also a sub-portion disposed in the weigh hopper of the weighhing line to the examination of combination at the presence of an input control signal for the sub-portion in at least one of the intermediate collecting containers associated with a weighing line, so that the last mentioned sub- portion may only be selected together with a sub-portion from the intermediate collecting container(s) concerned. Particularly in connection with the above men¬ tioned measures of preference and in particular if a compulsory emptying of a sub-portion is to be effected from one of said intermediate collecting containers an important increase of the combinatorial possibilities is obtained.

It will appear from the above that the number m indicating the upper limit of the number of examining steps will generally not be an integer, typically implying that the examination of combination must comprise two or more examining steps with the above defined numerical example, for instance the steps with three and four sub-portions, respectively. A measure for further reduction of the time of calculation may accord¬ ing to the invention consist in that the control device is adapted to adjust the pre-programmed desired value of the weight of the individual sub-portions in the weighing lines in dependence on whether the examination is carried out for one or more determined number of sub- portions. In the above described numerical example it will typically be necessary to examine combinations con¬ taining three and four sub-portions, respectively, even though the number of sub-portions envisaged by calcula¬ tion is solely three. Moreover, it may occur that also combinations comprising only two sub-portions fulfil the above mentioned conditons so that also such combinations must be involved in the examination. On the basis of the number of sub-portions in the actual selected com- binations an adjustment of the desired value may for instance be effected to reduce the number of examining steps, in the numerical example for instance from the selected value of 100 g to 95 g.

Claims

PATENT CLAIMS 1. An automatic weighing machine for weighing machine for weighing individual, uniform portions of a product (1) composed by individual articles, comprising a product feeding device (2) and at least one weighing line having a vibratory conveyor one end of which is located at the product feeding device (2) for receiving said articles, while in connection with the other end of the conveyor there is positioned a weigh hopper (6) adapted to receive and weigh the articles fed from the conveyor, the vibratory conveyor comprising a first vibration chute (4) closest to the product feeding device (2) and a second vibration chute (5) positioned closest to the weigh hopper (6), said second chute having its product feeding end located beneath a product discharge end of the first chute (4), said chutes being connected with a drive mechanism with an associated control dvice to energize the chutes (4, 5) to vibrate with controllable vibration amplitude and/or frequency to control the product feeding rate of the conveyor, characterized in that the control device (9) is con¬ nected by signal with the weigh hopper (6) and with individual drive mechanisms (7, 8), respectively, for the first and the second chute (4, 5), that the second chute (5) is energized by its drive mechanism (8) to vibrate at a constant amplitude and frequency and that the control devcice is adapted to supply, in response to inlet control signals derived from the actual values of the feeding rate (Vi) of the first chute (4) and the weight (M_a^t) of product portion received and weighed in the weigh hopper (6), respectively, a vibration control signal to the drive mechanism (7) for the first chute (4) for controlling solely the product feeding rate (VT.) of said chute (4) for adjustment of the product level in the second chute (5) for discharging a substantially constant amount of product (Δ2) per unit of time to the weigh hopper (6), and to supply stop signals to the drive mechanisms (7, 8) of both chutes (4, 5) for stopping the product discharge from the second chute (5) to the weigh hopper (6) at a predetermined stop moment dependent on a desired value (Mø) of the weight of said uniform portions and a substantially constant arresting delay (Tf) .

2. A weighing machine as claimed in claim 1, characterized in that said stop moment is determined so that when stopping the discharge of product to the weigh hopper (6) after said arresting delay, a total time of dosing (T_<j) is obtained determined by _Λ T_d = 1 - s

in which s is a predetermined stop point factor defined by

Δ₂ T_f

1 - Mø

3. A weighing machine as claimed in claim 2, characterized in that said vibration control signal for adjustment of the product feeding rate (V]_) of the first chute is calculated in dependence on said actual values according to the following equation

^ ⁼5ϋ ₃ ^{' Vakt} M₀

wherein ( ^^) is the actual product feeding rate of the first chute and that the control device (9) is adapted to supply the vibration control signal to the drive me- chanism (7) of the first chute (4) with an adjusting delay relative to the moment when the control device (9) receives the input control signal derived from the actual portion weight value (M^t), corresponding to the time of dosing for a number of portion weighings deter- mined by the relation between the product capacity of the second chute (5) and said desired value of the por¬ tion weight (Mø).

4. A weighing machine as claimed in claim 3, characterized in that the actual portion weight value for controlling the product feeding rate of the first chute (4) is constituted by an average value of the individual portion weight values of a number of weigh¬ ings and that the vibration control signal is supplied at regulation intervals defined by said adjusting delay with addition of the total time of dosing for said number of weighings.

5. A weighing machine as claimed in any of the preceding claims, comprising a number of weighing lines (21 to 28) in a combinatory weighing arrangement in which the weigh hoppers (31) of the weighing lines may be selectively emptied to a common collecting weigh hopper (34) adapted to receive a total batch portion composed of sub-portions from weigh hoppers in a sub- number of weighing lines, characterized in that the control device for selecting a combination of weigh hop¬ pers up to said sub-number comprises a combinatoric com¬ puter unit which from the weigh hoppers (31) of the weighing lines (21 to 28) receive the input control signals derived from said actual portion weight values and is adapted to calculate and select a combination of sub-portions within the prescribed minimum and maximum limits (W-t_oτ_, min,

max) for the weight of the total portion through sorting of the applied portion weight values according to size and examining com- binations containing a number of portion weight values between the limits 1 and m = n/s, wherein n is the said sub-number corresponding to the ratio between a desired weight value of the total product portion in the col¬ lecting container (34) and a common desired weight value of the sub-portions, in which examination as to com¬ bination of a determined number (j) of sub-portions within said limits, is only effected of all possible combinations including said number, if the conditions

Wj, min < -tof ^max °9 Wj, max > W-to_f ™in, 1 < j < m are fulfilled, wherein Wj min and Wj max are the lowest and highest value, respectively, of the total weight of said number (j) of sub-portions, and by said examination of all possible combinations of one or more determined numbers (j) of sub-portions by fulfilment of said condi¬ tions, is practiced by putting an end to the examination as soon as a combination having a total weight equal to the desired weight of the total portion has been found or, if such a combination cannot be found, selecting from all said combinations the combination whose total weight is closest to said desired weight.

6. A weighing machine as claimed in claim 5, characterized in that the control device is adapted to start the examination as to combination as soon as input control signals are available from a predetermined number of weigh hoppers or possible intermediate col¬ lecting containers said numbers being at least equal to said sub-number (n) but less than the total number of weigh hoppers or possible intermediate collecting con- tainers and in that, if said condition is not fulfilled for any combination within the said predetermined number, a new examination is started at the following received control signal, indicating that a new sub- portion has been collected in a weigh hopper or an intermediate collecting container.

7. A weighing machine as claimed in claim 5 or 6, characterized in that a work storage associated with the combinatorial unit is fed when said input control signals together with a clock indication about the arri- val of each control signal generated internally in the control device, and that the unit is adapted to effect the examination as to combination of any given number of weigh hoppers or possible intermediate collecting con¬ tainers in time order, starting by the earliest.

8. A weighing machine as claimed in claim 7, characterized in that said clock indications for the input signals are compared to a priority period pre¬ scribed for compulsory emptying of the weigh hoppers of the weighing lines or possible intermediate collecting containers so that, if said priority period is exceeded for one or more sub-portions, compulsory use is made of that or those sub-portions by approval of the best com¬ bination having a total weight between the minimum and the maximum limit of which that or those sub-portions form part.

9. A weighing machine as claimed in any of claims 5 to 8, characterized in that a number of intermediate collecting containers is connected with each weigh hopper, that the input control signals from the weigh hoppers are supplied to the control device with an indi¬ cation of the intermediate collecting container to which the sub-portion concerned has been transferred, and that the examination as to combination is effected on the basis of the sub-portions transferred to the inter- mediate collecting container.

10. A weighing machine as claimed in claim 9, characterized in that the control device is adapted to incorporate also a sub-portion disposed in the weigh hopper of the weighhing line to the examination as to combination at the presence of an input control signal for the sub-portion in at least one of the intermediate collecting containers associated with a weighing line, so that the last mentioned sub-portion may be selected only together with a sub-portion from the intermediate collecting container(s) concerned.

11. A weighing machine as claimed in any of claims 5 to 10, characterized in that the control device is adapted to adjust the desired value of the sub-por¬ tions of the weighing lines in dependence on the number of sub-portions in the actually selected combinations.