WO1998005932A1

WO1998005932A1 - Multi-recipe dosing system

Info

Publication number: WO1998005932A1
Application number: PCT/IL1996/000177
Authority: WO
Inventors: Josef Simchoni; Gilad Gozani; Yaacov Gozani
Original assignee: Simchoni Automation Systems
Priority date: 1996-08-01
Filing date: 1996-12-10
Publication date: 1998-02-12
Also published as: ZA97291B; IL118993A0; AU7707796A; TW348144B

Abstract

A multi-recipe, gravimetric, batch dosing system comprising a hopper stage (20) containing a plurality of raw substance materials and fitted with feeding units (60) adapted for dispensing measured quantities of the raw materials, a weighing stage (22) below the hopper stage (20) for receiving and weighing the measured quantities of raw material, and a mixing stage (24) below the weighing stage (22) for mixing and dispensing batches of raw material. The weighing stage (22) and the mixing stage (24) each comprise a plurality of cells, each for handling a single recipe. The arrangement is such that at least one of the weighing stage (22) and the mixing stage (24) is rotatable by a drive mechanism (94).

Description

MULTI-RECIPE DOSING SYSTEM

FIELD OF THE INVENTION

The present invention is in the field of dosing systems and more specifically it is directed to a batch dosing system for simultaneously preparing a plurality of recipes on a gravimetric basis.

BACKGROUND OF THE INVENTION

Dosing systems are generally divided into two groups, namely, systems in which recipes are prepared on a volumetric basis and systems in which recipes are prepared on a gravimetric basis. Although volumetric systems are, in principle, essentially cheaper than gravimetric systems, however, they are not accurate and are thus not suitable for preparing precise recipes.

The gravimetric dosing systems also fall into two principle categories, one for continuous preparation of a recipe and the other for preparation of batches, the latter being more popular, in particular in the plastics industry e.g. , for supplying raw material to extrusion and injection molding machines, etc. at times referred to as consumer machines.

A variety of gravimetric dosing systems have been proposed. However, a series drawback of such prior art systems is that they are usually adapted for preparing one pre-selected recipe at a time. Thus, in a plant where several extrusion or injection molding machines work simultaneously, each requiring a different recipe of raw material, it is necessary to dedicate a dosing system per machine, with an integral control system, which arrangement is space consuming and expensive. Another serious drawback of prior art dosing systems is that each time a recipe is changed, the system should be thoroughly cleaned from remains of material in order not to contaminate batches prepared according to a new recipe. The above is in particular important with additives such as pigment materials which even in very small quantities are noticeable, ultraviolet screeners, etc.

It is an object of the present invention to provide a gravimetric dosing system for simultaneous preparation of a plurality of multi-recipe batches, in which the above drawbacks are substantially reduced or overcome. It is still an object of the present invention to provide a highly accurate dosing system.

SUMMARY OF THE INVENTION

According to the present invention there is provided a multi recipe, gravimetric, batch dosing system comprising: a hopper stage containing a plurality of raw substance materials and fitted with feeding units adapted for dispensing measured quantities of the raw materials; a weighing stage bellow said hopper stage for receiving the measured quantities of raw material and weighing same; and a mixing stage bellow said weighing stage for mixing and dispensing batches of raw material; wherein each of the weighing stage and the mixing stage comprises a plurality of cells, each for handling a single recipe and where at least one of said weighing stage and said mixing stage is adapted for rotation by a drive mechanism.

According to a preferred embodiment of the invention, the hopper stage comprises a plurality of hoppers disposed along one or more concentric circular paths, each hopper being capable of containing a raw substance material and each fitted at a bottom outlet thereof with a feeding unit adapted for dispensing measured quantities of the raw material; the weighing stage comprises a plurality of circularly disposed weighing buckets mounted on a first platform positioned, an inlet opening of each weighing bucket being in flow communication with at least one feeding unit and comprising a gate assembly at a bottom outlet thereof; the mixing stage comprises a plurality of mixer units circularly mounted on a second platform, each mixer unit is in flow communication with a weighing bucket and comprises a mixing device and a discharge gate; where at least one of said first and said second platforms is adapted for rotation by a drive mechanism.

By still a preferred embodiment of the present invention the dosing system further comprises: at least one first sensor associated with each hopper for generating at least one respective signal indicative to the status of raw material in the hopper; at least one weight transducer associated with each weighing bucket for generating a weight signal indicative to the status of raw material within the weighing bucket; at least one second sensor for generating at least one respective signal indicative to the rotative position of the rotating platform; at least one third sensor associated with each mixer for generating at least one signal responsive to a status of raw material in the mixer; a first activator associated with each feeding unit, adapted for controlling at least one function of the feeding unit responsive to a first control signal; a second activator associated with each gate assembly of the weighing buckets for controlling the gate assembly responsive to a second control signal; a rotary activator associated with each rotating platform for controlling the platforms rotative position responsive to a third control signal; at least one third activator fitted with each mixer for controlling the discharge gate and the mixing device, responsive to a fourth control signal; and a programmable controller being selectively responsive to said signals and adapted for selectively emitting said control signals so as to obtain a pre-selected recipe at a predetermined accuracy and speed.

By using the term "selectively responsive" it is meant that the programmable controller may be adapted to receive all said signals but may be programmed so as to respond to only a selected group of signals, or none, all depending on a pre-selected mode of operation.

By using the term "strike-off gate " it is referred to a "flap-type " gate comprising one or two gates, suitable for discharging essentially large amounts of raw material within a short time and at essentially low accuracy. By using the term "linear vibrating feeding unit" it is referred to a linear vibrator suitable for discharging essentially small quantities of raw material at high accuracy. Such a feeding unit is suitable, in particular, for additives and may be adapted for controlled dispensing as few as several grains at a time.

By using the term "status " it is referred to different capacity parameters, e.g. amount of raw material, flow rate of raw material, overflow of raw material, shortage of raw material, etc.

By using the term "activator" it is referred to a component which is responsive to a control signal for carrying out mechanical operations, e.g. by means of pneumatic pistons, solenoids, motors, etc. In a most preferred embodiment, the dosing system according to the invention has a carousel-like layout and has a constant supply of raw material into the hoppers as known er se, e.g. by pneumatic loaders. The dosing system is connected via suitable conduits, (preferably by pneumatic conduits) to consumer machines (plastic extrusion, injection molding machines, etc.), wherein the programmable controller ensures preparation of the required recipes at maximum accuracy and efficiency, i.e., minimum time, depending on a pre-defined priority list.

By still a preferred embodiment of the invention, the hopper stage comprises hoppers arranged in two or three circles, at least one circle comprising hoppers provided with strike-off gate-type feeding units , suitable for fast dispensing of raw material, where at least one other circle of hoppers is fitted with linear vibrating feeding units, suitable for slow and essentially accurate raw material dispensing.

BRIEF DESCRIPTION OF THE DRAWINGS

For better understanding, the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is an isometric view, partially sectioned of a first embodiment of a dosing system according to the present invention;

Fig. 2 is a top view of the embodiment seen in Fig. 1 ; Fig. 3 is a side view of the embodiment seen in Fig. 1 ; Fig. 4a is a perspective view of a hopper fitted with a strike-off gate- type feeding unit; Fig. 4b is a perspective view of a hopper fitted with a two-stage strike-off gate-type feeding unit;

Fig. 5 is a perspective view of a hopper fitted with a linear vibrating feeding unit, shown in its so-called cleaning position;

Fig. 6 is a perspective view, partially sectioned of a weighing bucket used with a dosing system according to the present invention, with the gates in their open position;

Fig. 7 is a perspective view, partially sectioned of a weighing bucket used with a dosing system according to the present invention, with the gates in their closed position; Fig. 8 is a perspective view of a weighing bucket fitted with a calibrating plate and with a calibrating weight;

Fig. 9 is a perspective view of a mixer unit with an airflow regulator for use in a dosing system in accordance with the present invention. Fig. 10 is an isometric view of a further embodiment of the dosing system according to the present invention;

Fig. 11 is a side view of the embodiment seen in Fig. 10;

Fig. 12 is a top view of the dosing system seen in Fig. 10;

Fig. 13 is an isometric view of still a further embodiment of the dosing system according to the present invention;

Fig. 14 is a side view of the embodiment seen in Fig. 13;

Fig. 15 is a top view of the embodiment seen in Fig. 13.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS It should be realized that peripheral equipment, e.g. , conduits leading from the mixers to the consumer machines, source feeding equipment, construction supporting the system, wiring, etc. is not shown in any of the figures and it is appreciated that an artisan is well familiar with the peripheral equipment which does not form an essential part of the invention. Additionally, in some of the Figures some components are not shown, for sake of clarity.

Attention is first directed to Figs. 1-3 of the drawings illustrating a first embodiment of a dosing system according to the present invention. As seen in the figures, the dosing system consists of three stages, namely, hopper stage 20, weighing stage 22 and mixing stage 24. Hopper stage 20 comprises a fixed circular plate 26 supporting a first array of hoppers 28 circularly disposed adjacent the periphery of platform 26, and a second array of hoppers 30, circularly arranged along an inner, coaxial path. Each of the hoppers 28 and 30 comprises a flange 32 useful for attachment to the platform 26 by means of bolts or rivets as known per se. As seen in Fig. 1, a raw material source generally designated 38 is positioned above each of the plurality of hoppers 28 and 30, although in the figures represented by a single element, to avoid cluttering the Figure. Typically, such feeders are pneumatic and are equipped with a pneumatic gate for dispensing raw material upon a control signal received from a controller, or by manual operation, all as known per se.

A second platform 40 is spaced apart from platform 26 and is supported by protective cylinders 42 coaxial with hoppers 30 and 28, and fixed to the platforms 26 and 40 by a top flange (not seen) and a bottom flange 44. As seen in Fig. 3, platform 40 has a plurality of openings 45 and a plurality of downwardly projecting funnels 46 fixed by bolts 48 to the platform 40, coaxial with hoppers 30 and protective cylinders 42.

Each of hoppers 28 is provided at its bottom end with a linear vibrator feeding unit, generally designated 50, pivotally supported at 52 and having a dispensing end 54 projecting through an opening 56 in protective cylinders 42, essentially above opening 45 of platform 40. The construction and operation of the linear vibrator 50 will hereinafter be explained in more detail, in particular with reference to Fig. 5.

Each of hoppers 30 is provided with a feeding unit generally designated 60 which is a strike-off gate-type feeder, adapted for dispensing essentially large amounts of raw material at a short period. The specific construction and operation of feeding unit 60 will hereinafter be described in more detail.

The weighing stage 22 comprises a platform 66 coaxially rotatable with respect to the hopper stage 20 by means of driving motor 68. The platform 66 is formed with a plurality of openings 73, each accommodating a weighing unit generally designated 72 attached below the platform 66, wherein each weighing unit 72 corresponds with a funnel 46 of the hopper stage 20. As can be seen in Fig. 3 and as hereinafter will be explained in more detail with respect to Figs. 6-8, each weighing unit 72 comprises a weighing bucket 74 provided with a weighing transducer 76 and a gate assembly 78. Each weighing unit 72 is coaxially accommodated within a cylindric housing 80 provided at its bottom end with a funnel 84 having an outlet opening 86. It should be noted that the hoppers of the first stage may be arranged in various configurations, e.g. in Fig. 3 it can be seen that the hoppers are arranged in couples consisting of a hopper 28 and a hopper 30, and in trios, consisting of two hoppers 28 and one hopper 30, although this arrangement is only a specific embodiment and the invention is not restricted thereto.

As can further be seen in Fig. 3, mixing stage 24 comprises a platform 90 coaxial with the weighing stage 22 and rotatable by means of motor 94. A plurality of mixer units 96 are attached at a bottom face of platform 90 along a circular path, corresponding with that of weighing units 72 and in register with openings 97. Each mixer unit 96 comprises a mixing blade 98 rotatable by means of motor 100 as known per se. At a bottom end of each mixer there is an outlet 102 provided with a gate 103 connected to a conduit 104 via an air regulator 105 as will hereinafter be explained in more detail. The conduits 104 extend upwards through central openings within all the platforms and centrally project from the top platform 26 and are then directed each to a designated consumer machine, e.g. , an extrusion or an ejection molding machine, etc. (not shown).

As can further be seen in Fig. 3, above platform 66 of the weighing stage 22 and above platform 90 of mixing stage 24, there is provided a lid assembly 110 and 112 respectively, each being a rotatable plate comprising a number of openings corresponding in size and location with openings 73 in platform 66 of weighing units 72 and openings 97 in platform 90 of mixer units 96. Each of lid assemblies 110 and 112 is rotatable between a first position in which the plurality of openings is aligned with a corresponding opening within platform 66 and 90, respective- ly and, a second position in which the lid assemblies are rotated, whereby openings of the lid plates are offset with respect to those of platforms 66 and 90. The object of the closure plates is to prevent accidental contamination of batches within the weighing stage 22 or the mixing stage 24 by unintentional spillage of raw material from an upper stage. Preferably, the plates of the lid assemblies have an inclined peripheral surface, to allow grains of raw material to fall of the plates.

The dosing system seen in the figures further comprises a control system, the compounds of which are only schematically illustrated in the figures, and it should be obvious to a person versed in the art that the type and location of the components of the control signal may vary from application to application.

Each of hoppers 28 and 30 is provided with a sensor 120 near a top end thereof and a sensor 122 near an outlet end thereof, for indicating the existence and flow rate of flow material within the hopper and for signaling shortage or over-flow of raw material. Platform 66 of the weighing stage 22 is provided with a sensor 124 indicating its angular position with respect to hopper stage 20 and lid assembly 110 is provided with a sensor 126 for indicating its rotative position with respect to platform 66. Platform 90 of the mixing stage 24 also comprises a sensor 128 for indicating its angular position with respect to the weighing stage 22 and lid assembly 112 comprises a sensor 130 for generating a signal indicating its rotative position with respect to platform 90. Each of the mixing units 96 comprises a top sensor 132 and a bottom sensor 134 for generating signals responsive to existence and flow rate of raw material within the mixer units.

Each of the above-mentioned sensors and any other sensors which are provided in the system may be connected via brush-type pick-ups to a programmable controller 140 which may be programmed for emitting control signals for activating the system as will hereinafter be explained in more detail. Activators for activating various components are connected in turn to the programmable controller 140, e.g. pistons and vibrators activating the feeding units, servo motors rotating the platforms and the lid assemblies, pistons activating the gates of the weighing units and of the mixing units, etc.

Attention is now directed to Fig. 4a of the drawings for understanding a specific embodiment of a strike-off gate-type hopper, suitable for dispensing main components, i.e., for dispensing essentially large amounts of raw material within a short period such as hopper 30 in the embodiment referring to Figs. 1 to 3. The hopper comprises a flange 32 for attaching to the plate 26 as hereinabove explained. At a bottom end of the hopper, there is a tube portion 160 closable by a strike-off type gate generally designated 162, comprising a gate member 164 pivoted at 166 to the tube 160. It should be noted that hinge 166 is offset from the longitudinal axis of tube 160 for the reason soon to be explained. A pneumatic piston 168 is pivotally attached near its top end 169 to the hopper 30 with an extendible piston rod 170 pivotally attached at a bottom end thereof to an arm 171 projecting from gate member 164. Piston 168 constitutes the activator of the feeding unit, whereupon retraction of piston rod 170 entails swinging of gate 164 in the direction of arrow 172, wherein the offset of hinge 166 ensures rapid opening and closure of the gate 164 for striking off flow of raw material.

Further attention is directed to Fig. 4b of the drawings illustrating an alternative hopper 173 differing from the hopper 30 seen in Fig. 4a by a two-stage pneumatic piston 174 consisting of a first piston stage 175 pivoted at a top end 176 to the hopper, and a second piston stage 177 pivoted at a bottom end 179 to the hopper, each piston stage being independently operable and constituting together the activator of the feeding unit. The arrangement is such that the first piston stage 175 is adapted for essentially long strokes of piston rod 175', whereas the second piston stage 177 is adapted for essentially short strokes of piston rod 177'. As can readily be understood, retraction of the first piston rod 175' entails swinging of gate 164' in the direction of arrow 172' to an essentially large opening for dispensing large quantities of raw material, whereas retraction of the first piston rod 177' entails swinging of gate 164' at an essentially narrow opening, suitable for dispensing small and essentially accurate quantities of raw material.

Attention is now directed to Fig. 5 illustrating a hopper 28 equipped with a feeding unit of the linear vibrating type generally designat- ed 180. The linear vibrating feeding unit 180 consists of a trough-like conduit 182 having a U-like longitudinal cross-sectional shape. The conduit 182 is connected to a vibrator 184 constituting the activator of the feeding unit 28. Conduit 182 with vibrator 184 are supported by a structure member 186 which is swingingly pivoted at 188 to an arm 190 and which is in turn attached to platform 40 (see Fig. 1 ).

The conduit 182 is tiltable between a first position referred to as a "feeding position " wherein upon dispensing of raw material from the hopper and vibrating of vibrator 184, grains of raw material 192 are vibrated along conduit 182 and will progress along the conduit until they depart from the fore end 194 of the conduit 182. However, upon seizing the vibration of vibrator 184 grains of raw material 192 will stop their advancing. Conduit 182 may be tilted to a second position referred to as a "cleaning position " wherein the conduit is tilted about pivot 188 (position not shown) for removing residual grains of raw material, for example, prior to starting a new recipe, for avoiding contamination of the new recipe.

Reference is now made to Figs. 6 to 8 of the drawings illustrating a weighing unit in accordance with the present invention. As can be seen, the weighing unit generally designated 72 consists of a cylindrical weighing bucket 74 supported within a cylindrical protective housing 80, the latter being attached by flange 200 below platform 66, in register with openings 73, as seen in Fig. 3. Weighing bucket 74 is fitted with a weight transducer 76 projecting through the housing 80, for generating a weight signal indicating the weight of raw material within the weighing bucket 74. Weighing bucket 74 is further provided with two gate flaps 202 pivotally connected at 203 to the weighing bucket 74 and swingable between a closed situation as in Fig. 7 and an open position as in Fig. 6. Two pneumatic pistons, constituting the activator of the gate assembly of the weighing buckets, are pivoted at a top end 206 to the weighing buckets and at a bottom end of piston rods 208 hingedly connected to the gates 202, whereby extension of piston rods 208 from pistons 204 entails opening of gates 202 and vice versa.

As can be seen in Fig. 8 of the drawings, the protective housing 200 of weighing unit 72 comprises an opening 210 opposite hinge 203 of gate 202. The opening 210 serves as a service opening and for hanging a calibration plate 212 by means of bracket 214 for calibrating the weight transducer 76 with a calibration weight 216 as known per se. The advantage of this arrangement is that calibration of the weighing transducers can be easily carried out without having to dismantle any components of the system. In Fig. 9 of the drawings, there is shown a lower end of a mixer unit 96 fitted at a top end with a flange 230 for connecting to a motor constituting the activator of the mixing unit (schematically illustrated in Fig. 3). The mixer unit comprises a mixing blade 232 rotatable within the mixing unit 96 and provided with a projecting coupling end 234 for coupling to the motor 100. At a bottom end of the mixing unit, there is connected, via mating flange members 238, a gate assembly 103 which in turn is connected to an airflow regulator 106 having an inverted T-like shape, the vertical leg portion 240 being provided with a rotatable disk 242 for regulating the cross-sectional area of apertures 242 whereby, the airflow into the supply tubes 104 is regulated, for controlling suction forces within the system.

Attention is now directed to Figs. 10 to 12 of the drawings illustrating a further embodiment of the present invention wherein, for the sake of clarity some of the components were removed, e.g. supply feeders, some of the rotating plates, lid assemblies, control components, etc. As can be seen in the figures, the hopper stage 260 comprises a plurality of hoppers 262 arranged along a circular path above the mixing stage 264. As can be seen, the hoppers are arranged in pairs, each pair consisting of a hopper 268 provided with a linear vibrating feeding unit 270 and a hopper 272 provided with a strike-off type gate feeding unit 274 at the end of an extension tube 276. The arrangement is such that an opening 282 of each weighing unit 284 may be supplied with raw material from either one or both hoppers 262 and 272, one supplying small, accurate quantities of additive raw material and the other supplying large quantities of the main raw material, as hereinabove explained. The other components of the system are essentially similar with those explained in connection with previous embodiments including the various control means.

Reference is now made to Figs. 13 to 15 of the drawings, illustrating still another embodiment of the present invention, the difference residing in the hopper stage generally designated 300. In this embodiment too, various elements of the system have been removed, for the sake of clarity only.

As can be seen, hopper stage 300 comprises a plurality of hoppers arranged along three concentric circular paths, the innermost and outer hoppers collectively referred to as 302 and 304, respectively, being provided with linear vibrating feeding units 306, whereas the hoppers positioned along the middle circle and collectively designated at 310 are fitted with feeding units of the strike-off gate-type, as hereinabove described. The arrangement of preferred embodiments according to the present invention is such that hoppers provided with strike-off gate-type feeding units are disposed essentially above the weighing buckets whereas hoppers provided with linear vibrating feeding units are slightly offset with respect to the weighing buckets, as can be readily be understood.

Attention is now directed again to Figs. 1 to 3 for understanding the steps of preparing pre-elected recipes. At a first stage, the various components of the system are cleaned from any remains of raw material. Then, a plurality of recipes is selected from a pre-programmed list of recipes within the programmable controller 140 or, new recipes may be programmed ad hoc. The programmable controller is also suitable for making decisions of priority depending on consumption and accordingly, if required, a list of quantity or time-based priorities should be entered too. Then the hoppers are filled with raw material via the pneumatic feeders 38.

Then, a first stage of the process takes place wherein plate 66 starts rotating and each weighing bucket 72, in its turn, takes place beneath a funnel 46 of a suitable hopper 28 or 30 and the required quantities of raw material are fed into the weighing unit. Preferably, first main raw material from hoppers 30 are fed into the weighing units (at essentially large quantities) and only then, the additive raw material is added from hoppers 28 (at essentially small and accurate quantities). This arrangement enables a more accurate process since the quantity of additive raw material is calculated according to the actual main raw material within the weighing unit. However, the process may also be performed by first feeding raw material from the hoppers 30 (at essentially small and accurate quantities) and then feeding raw material from hoppers 28 fitted with the two-stage pneumatic piston 174 as in Fig. 4b, wherein raw material may be accurately measured. Typically, in a dosing system according to a preferred embodiment of the invention the gravimetric accuracy of the strike-off gate-type feeding units is about 2% ± 0.1 %, wherein the gravimetric accuracy of the linear vibrating feeding units is better than about ± 0.2% . Each time the weighing stage 22 rotates, the lid assembly 110 rotates so as to cover the openings 73 of the weighing units 72. As soon as a weighing unit has finished collecting all the raw materials from the hoppers, it revolves to a station above the suitable mixing unit, the second lid assembly 112 comes into a suitable position and gates 78 open, allowing dispensing of a batch into a mixing unit 96 wherein the batch is mixed and then transferred to the consuming machine via tube 104.

In the embodiment of Figs. 1 to 3, the mixing stage 24 is also rotatable for shortening the period of time required for a weighing bucket to reach the matching mixing unit. However, a rotatable mixing stage may be omitted.

It should be obvious to a person versed in the art that the teachings of the present invention are applicable mutatis mutandis to a large variety of dosing systems according to the present invention.

Claims

CLAIMS:

1. A multi recipe, gravimetric, batch dosing system comprising: a hopper stage containing a plurality of raw substance materials and fitted with feeding units adapted for dispensing measured quantities of the raw materials; a weighing stage bellow said hopper stage for receiving the measured quantities of raw material and weighing same; and a mixing stage bellow said weighing stage for mixing and dispensing batches of raw material; wherein each of the weighing stage and the mixing stage comprises a plurality of cells, each for handling a single recipe and where at least one of said weighing stage and said mixing stage is adapted for rotation by a drive mechanism.

2. A dosing system according to claim 1 , wherein the hopper stage comprises a plurality of hoppers disposed along one or more concentric circular lines, each hopper being capable of containing a raw substance material and each fitted at a bottom outlet thereof with a feeding unit adapted for dispensing measured quantities of the raw material; the weighing stage comprises a plurality of circularly disposed weighing buckets mounted on a first platform positioned bellow said hoppers, an inlet opening of each weighing bucket being in flow communication with at least one feeding unit and comprising a gate assembly at a bottom outlet thereof; the mixing stage comprises a plurality of mixer units circularly disposed bellow said weighing buckets and mounted on a second platform, each mixer comprises a mixing device and being in flow communication with a weighing bucket and being fitted with a discharge gate; where at least one of said first and said second platforms is adapted for rotation by a drive mechanism.

3. A dosing system according to claim 2 further comprising: at least one first sensor associated with each hopper for generating at least one respective signal indicative to the status of raw material in the hopper; at least one weight transducer associated with each weighing bucket for generating a weight signal indicative to the weight of raw material within the weighing bucket; at least one second sensor for generating at least one respective signal indicative to the rotative position of the rotating platform; at least one third sensor associated with each mixer for generating at least one signal responsive to a status of raw material in the mixer; a first activator associated with each feeding unit, adapted for controlling at least one function of the feeding unit responsive to a first control signal; a second activator associated with each gate assembly of the weighing buckets for controlling the gate assembly responsive to a second control signal; a rotary activator associated with each rotating platform for controlling the platforms rotative position responsive to a third control signal; at least one third activator fitted with each mixer for controlling the discharge gate and the mixing device, responsive to a fourth control signal; and a programmable controller being selectively responsive to said signals and adapted for selectively emitting said control signals so as to obtain a pre-selected recipe at a predetermined accuracy and speed.

4. A dosing system according to claim 2, wherein said feeding units consist of at least one of strike-off gate-type gravimetric feeders adapted for fast dispensing of raw material into the weighing buckets, and linear vibrating feeders adapted for slow dispensing of raw material into the weighing buckets at essentially high accuracy.

5. A dosing system according to claim 4, wherein the strike-off gate-type feeding units are provided with a flap swingably hinged near the outlet opening of the hopper, the hinge point being offset from a longitudinal axis of the outlet opening.

6. A dosing system according to claim 5, wherein said flap is activated by pneumatic pistons.

7. A dosing system according to claim 5, wherein said flap is activated by two-stage pneumatic piston, a first stage of which adapted for essentially widely opening the flap and a second stage adapted for essentially narrow opening of the flap.

8. A dosing system according to claim 2, wherein each gate assembly of the weighing buckets comprises two flaps swingable in opposite directions between a closed and an open position.

9. A dosing system according to claim 8, wherein said flaps are activated by pneumatic pistons.

10. A dosing system according to claim 8, wherein said flaps are hinged to the weighing bucket wherein at least one flap is removable for attaching a weight calibration device to the weighing bucket.

11. A dosing system according to claim 2, wherein each weighing bucket is supported within a housing securely mounted on the first platform, the housing being formed with at least one opening.

12. A dosing system according to claim 2, wherein said linear vibrating feeders comprises a trough-like vibrating conduit having a V-like shaped longitudinal cross-section and positioned bellow an outlet opening of a hopper; the linear vibrators being tiltable between a feeding position and a cleaning position.

13. A dosing system according to claim 4, wherein the gravimetric accuracy of the strike-off gate-type feeding units is about 2 % ± 0.1 % .

14. A dosing system according to claim 4, wherein the gravimetric accuracy of the linear vibrating feeding units is better than about ± 0.2 % .

15. A dosing system according to claim 3, wherein the pre-selected recipe is selected from a given list or programmed for a specific task.

16. A dosing system according to claim 3, wherein said at least one first sensor is provided near a bottom end of each hopper for determining when it empties.

17. A dosing system according to claim 3, wherein said third sensor comprises an inlet sensor fitted adjacent a mixer inlet for emitting a signal responsive to deficiency of material within the mixer.

18. A dosing system according to claim 3, wherein said third sensor comprises an outlet sensor fitted adjacent a mixer outlet for emitting a signal in response to an empty mixer.

19. A dosing system according to claim 2, wherein each of said mixers comprises a service opening.

20. A dosing system according to claim 2, wherein said first and said second platforms are carousel-like rings suitable for rotating through a full circle in any direction.

21. A dosing system according to claim 2, wherein said first and said second platforms are provided with brush-type pickups for transferring electric signals.

22. A dosing system according to claim 4, wherein said gravimetric feeders dispense main components of the recipe, whereas the vibrating feeders dispense additives.

23. A dosing system according to claim 2, wherein an actual amount of a main component that has been fed into a weighing bucket sieves as a basis for calculating the amount of additive components to be fed into the weighing bucket.

24. A dosing system according to claim 3, wherein in response to a weight signal emitted from said weight transducer responsive to an amount of a main component that has been fed into a weighing bucket, the programmable controller calculates the amount of additive component to be fed into the weighing bucket and emits said first control signal.

25. A dosing system according to claim 2, further comprising a lid member above at least one of the weighing buckets and the mixing units.

26. A dosing system according to claim 25, wherein said lid is a rotatable member having a plurality of apertures corresponding with inlet openings of the weighing buckets and the mixing units, respectively, and being rotatable between an open position in which said apertures are in register with said inlet openings and a closed position in which the apertures are shifted from said inlet openings.