NL9301496A - Method and device for manipulating a product flow. - Google Patents

Abstract

Method for manipulating a product stream, in which the product stream is guided by means of conveying elements along a conveyor successively past a number of processing elements, said processing elements being controlled depending on a central control system for making the control elements operate in phase with the product stream, and for this purpose the central control system transmits control signals and receives detection signals on the position of the conveying elements, and in which according to the invention said central control system controls said control elements and also the conveying elements essentially independently of each other on the basis of an internal reference signal which is adapted, possibly temporarily, depending on detection signals coming from detectors if a certain preset threshold value is exceeded. <IMAGE>

Description

Method and device for manipulating a product flow.

The invention relates to a method for manipulating a product flow, wherein the products move downstream successively in a virtually continuous movement, optionally in a jerky manner. The invention furthermore relates to an apparatus for operating that method. In particular the invention relates to the manipulation of a product flow in a packaging machine, more in particular a so-called "flow packer". In the process, an initial flat web or strip of packaging material is folded or bent with the longitudinal edges together into a tubular shape around the substantially continuously moving product flow, to be divided into successive longitudinally and transversely sealed pieces, within which one or more products are the product flow. However, the invention is not limited to this, and it also applies to other areas of product flow manipulation, such as with regard to product conveyors with buffer capability, etc. The invention is mainly concerned with product flows with relatively high speeds, wherein a product passage of, for example, 500 pieces / min. or more, as is common in the food and consumer industry today for items of relatively small dimensions, such as biscuits, biscuits, bars, cheese pieces, as well as screws, nuts, lamps for lighting fixtures, etc.

The so-called "flowpacker" is known from the food packaging industry that the various drive units thereof for supplying the web of packaging material, sealing jaws and cutting elements, are speed-controlled in dependence on the product infeed movement. An electronic control system is currently used for this purpose, whereby a detection device on the product supply belt, usually an encoder on the drive shaft, gives a signal that is used as a reference signal, by means of which the drive of the various elements in the downstream packaging machine is controlled. In control technology this control is also referred to as master-slave control, where the master is coupled to the product supply A flowpacker with such a control is described, for example, in EP-A-0 339 13 ^ ·

A disadvantage of this known master-slave control is the limited capacity of the "flowpacker" or other product processing machine. Furthermore, a machine operating according to such a master-slave control has a fairly abrupt stop and start depending on the product supply. Stopping and starting is frequently necessary when the known machine has an arrangement to prevent malfunctions as a result of incorrect product entry as much as possible. For example, regulations (known as no gap-no seal or no product-no bag) are known to prevent the formation of empty packaging, or to prevent the hose inside the hose from being cut off and / or sealed product enters between the cutting and / or sealing members. For this purpose, the machines controlled in the known manner are provided with detection means, which, depending on the position of the products on the supply belt, register a deviation, and accordingly temporarily stop the "flow packer", to restart almost immediately. However, the "flowpacker" is hereby slowed down / accelerated in its entirety, until the cadence with the product feed is resumed. Accordingly, it is also necessary that the product feed be as uniform as possible, for which use is often made of an infeed chain with pushers (also or "catchers" or "catches") which insert between the products, have a fixed pitch, and move a fixed number of products with a fixed pitch per catch.

However, with the known equipment in the event of a disrupted product supply, the production of faulty packaging is inevitable, which problem can be solved within limited limits using a "no product-no gap" or "no gap-no seal" system.

The object of the invention is to prevent any malfunctions which occur during the manipulation of a product flow, for instance as a result of an error in the product supply, in an efficient and reliable manner, using as little cost and labor-intensive means as possible.

To this end, it is proposed a method for manipulating a product flow, wherein the product flow is conveyed successively along a conveyor track past a number of processing members by means of transport members, wherein these processing members are controlled in dependence on a central control system, in order to phase the processing members with the product flow to operate, and the central control system sends control signals for this purpose, and receives detection signals about the position of the transport members, and in accordance with the invention that central control system controls those processing members, as well as the transport members, substantially independently of one another by means of an internal reference signal, that, depending on detection signals from both the transport members and the processing members, adjustment is made, if necessary temporarily, if a certain preset threshold value is exceeded. For example, the central control system is composed of several separate control circuits, one for each type of conveyor or processor, in combination with a basic control circuit common to those control rings, which controls those control circuits with the reference signal, as further explained in the figure description.

Accordingly, in the method of the present invention, the control is performed so that it no longer depends on the position of the product input, by which the processors are controlled together so that they are in phase with the product flow. According to the invention, both the processors and the product stream passing thereon are individually controlled by means of an independent reference which is essentially constant during operation. Within certain limits, it is now possible to optimally tune the phases of the various elements individually, in order to largely or even completely eliminate disturbances, such as those as referred to above. Since the mutual phase difference of the different members within a limited range is freely selectable, according to the invention feedback takes place of the different individual phases, on the basis of which the internal reference signal is possibly adjusted. Furthermore, it is now also possible, for example, to periodically shift the input part of the device in phase, for example to form product groups without the need for additional transport systems.

The present invention thus provides an alternative to the known "master-slave" controller, in which the master is formed by the product supply, and in which the "slaves" are controlled jointly. With the present invention, the "master" is constituted by an internal reference signal, which is largely independent of the environment, and on which only a feedback system operates to keep the control within a certain specification. The transport means for controlling the product flow now also belong to the "slaves", which are independently controlled within certain limits, each within their own control loop with feedback.

The method according to the invention can be operated with a device, the actuators of which are coupled to the drive shafts of both the processing members and those of the transport members, preferably separately powered electric motors, each of which is coupled to an output of the central control unit. Furthermore, a detection member, for example an encoder, which is in signaling connection with an input of the central control unit, is coupled to each of these axes to form a feedback loop.

In the following the invention is further elucidated on the basis of a non-limiting exemplary embodiment, with reference to the annexed drawings. Hereby shows:

Fig. 1 is a schematic side view of a part of a so-called "flow packer" with product input according to the present invention; and

Fig. 2 is a basic schematic of the control diagram for performing the method of the present invention;

Fig. 1 schematically shows a device 1 according to the invention, in which a so-called "flowpacker" 2 is included, of which only a part is shown here. This "flow packer" is described in more detail in, for example, EP-A-0 336 012, more particularly fig. 10 thereof with the corresponding figure description from col. 4, r. 53. Also US-A-4 722 168 describes and shows a similar "flowpacker".

The device 1 of Fig. 1 has a first supply conveyor 3, with which the products 4 lying thereon are successively supplied from a remote source (not shown), such as a product stock or a production machine, to the flowpacker 2. These products 4 are, for example, pieces of cheese, bars of chocolate, biscuits, etc., which are supplied in succession in a relatively regular flow in the direction of the arrow A. The first conveyor belt 3 is endless and is driven by electric motor M4.

Immediately downstream is a relatively short, also endless, second conveyor belt 5, which in known manner consists of two endless conveyor belts placed next to each other with some space between them, such that the upper parts thereof lie in one plane and between them in a gap to keep. This slit (not visible) allows that, between the two upper parts of the conveyor belt 5, carriers 6 can stick to an endless feed chain 7 known per se, as shown. These cleats 6 with fixed, constant pitch, are always placed between two consecutive products 4. Since a sliding plate 8 (shown here in dotted lines) connects to the downstream end of the upper part of the conveyor belt 5, the products are propelled lying on that sliding plate 8 by the drivers 6. As a result, each product 4 bears against a carrier located behind it, which provides an accurate positioning of the products 4. Both the conveyor belt 5 and the feed chain 7 are driven by motor M1. The speeds of the conveyor belt 5 and the feed chain 7 can optionally be mutually varied, for instance by means of an adjustable variable transmission (not visible) between motor M1 and one or both belt 5 and chain 7.

The infeed chain 7 is followed by the "flowpacker" 2, which is only schematically represented here. As usual, the foil 9 is taken from a supply roller 10, and guided as a continuous path to pass some distance parallel above or below the flow of products 4 in the direction of arrow A downstream. The foil 9 thereby passes a conventional folding box 11, with which the foil 9 is folded or bent in the longitudinal direction around the products 4, so that the longitudinal edges thereof lie against or on top of each other, in Fig. 1 on the underside of those products 4. formation of the desired packaging hose 12. As also according to EP-A-0 336 012, the foil is driven upstream and downstream of the folding box 11 by a drive motor M2. Upstream of the folding box 11, the still substantially flat film 9 is guided between two oppositely rotating driven friction rollers 13. The rotary axes of said rollers 13 are in the usual manner parallel to the path of movement of the products 4 and transverse to the direction of movement thereof focused. Downstream of the folding box 11, the overlapping longitudinal edge regions of the film are guided between one or more pairs of counter-rotating, driven welding rollers 14, only one of which is visible per pair in FIG. 1, to form the so-called welding fin, which runs in the longitudinal direction of the foil hose 12 and protrudes transversely. The axes of rotation of said welding rollers 14 are oriented perpendicularly to the path of movement of the products 4 and perpendicular to the direction of movement thereof. An adjustable transmission (not visible) can be arranged between the drive motor M2 and the friction rollers 13 and / or the welding rollers 14, for example for setting a speed difference between the friction rollers 13 and the welding rollers 14, for example around the foil 9 in the region of keep the folding box 11 under pretension. Contrary to the foil drive described here upstream and downstream of the folding box 11, the drive can optionally be, for example, only downstream thereof.

by means of the welding rollers 14.

Further downstream of the welding rollers 14 there are known per se, oppositely rotationally driven set of clamping jaws 15 for sealing transversely therebetween and subsequently transversely cutting lengths of foil hose 12 at the location of those welds. The axis of rotation of said clamping jaws 15 is parallel to those of the friction rollers 13. The clamping jaws 15 are driven by electric motor M3. Thus, with the clamping jaws 15 upstream of one or more products 4, which said clamping jaws 15 have simultaneously passed in their moved position, the hose 12 is squeezed in the direction transverse to the direction of movement according to the arrow A, whereby heat supply or pressure the foil parts pressed together are welded together, in which area the hose is subsequently cut transversely. After the clamping jaws 15 separate packages (not shown) filled with one or more products 4 are formed, of substantially elongated shape, with a transverse seam at the end ends, and a longitudinal seam running between them.

For the control of the electric motors M1 ... M4, a product observer 16, here a photocell, is also placed at the position of the infeed chain 7 as shown. The observer 16 detects the presence of a product 4 to determine whether an empty package will possibly be formed if the operation of the device 1 remains unchanged.

Furthermore, a second product observer 17 is placed between the welding rollers 14 and the clamping jaws 15. This observer 17 may also be located further upstream of the clamping jaws 15. With that observer 17 the spacing between the successive products 4 or groups of products is determined, on the basis of which it is determined whether products 4 will be squeezed between the clamping jaws 15 without unchanged control of the device 1.

Furthermore, as shown, each servomotor M1 ... M4 is coupled to a pulse generator or so-called "resolver" R1 ... R4, for the purpose of feedback, as described further below.

Fig. 2 shows the circuit diagram for controlling the drive of the device 1. As shown, each servomotor M1 ... M4 with its respective resolver R1 ... R4 is included in a separate control circuit with position controller P1 ... P4 . These position controllers P1 ... P4 thus operate independently of each other, and consequently the servomotors M1 ... M4 are also independently controlled. The position controllers P1 ... P4 are further coupled to a common basic control circuit 18, which supplies a position control signal to each of the position controllers P1 ... P4, by means of which they control the respective servomotors M1 ... M4. The position controllers P1 ... P4 and the common basic control circuit 18 form the central control system 19 · The common basic control circuit 18 produces the position control signal internally, without being controlled by, for example, the input chain 7 · This control means that each position controller P1 ... P4 can independently determine the optimum instantaneous control of the servomotor, in order to comply with the internally developed position control signal of the common basic control 18.

In addition to the internal feedback on each individual control circuit with position controllers P1 ... P4, there is also a feedback for the control unit, for which the observers 16 and 17 have been used. These observers 16 and 17 are coupled both to the control unit 18 and to the separate control circuits for controlling the servo motor M2 for the welding rollers 14 and for controlling the servo motor M3 for the clamping jaws 15. The position controllers P2 and P3 determine directly depending on the feedback signals from the observer 16 resp. 17 the separate optimum position control signal. Furthermore, the feedback via the observers 16 and 17 to the control unit 18 ensures that, in the event of too great anomalies found between the feedback and the prevailing control, the reference signal from the control unit 18 is adapted to the individual control circuits, on the basis of which the individual position controllers P1 ... P4 determine new optimal position control signals. In this way it is prevented that, as a result of the separate control of the motors M1 ... M4, device 1 runs out of the control under conditions which deviate from the regularity.

It is of course also possible to provide feedback for, for example, the separate control circuit for controlling the servo motor M1 of the input chain, etc.

In the following some uses of the device 1 with the above-described control are explained.

I. Forming a multinack.

The position controller PI for the control of the servo motor M1 of the infeed chain 7 can be set such that it is alternately accelerated and decelerated relative to the conveyor belts 3 and 5. This control takes place in such a way that as soon as a driver 6 between two on the belt 5 lying products 4 have been inserted, which chain 7 is briefly delayed. As a result, more than one product 4 can pass behind the latter driver 6 past the upstream end of the chain 7 before another driver 6 rises. Between the carriers 6 along the upper part of the belt 5 there are therefore groups of products which are pushed together by means of the downstream carrier 6 when they slide over the slide plate 8 from the downstream end of the upper part of the conveyor belt 5. As a result, the pitch of the flights is constant regardless of the use of the device 1 for forming single or multipacks.

If the prior art master-slave control had been used, the servomotors' M1 ... M3 being controlled in direct dependence on the servomotor M4, in this case the formation of product groups with fixed space between the groups would already be arrival at the infeed chain 7 must have taken place, which requires an additional system which can be turned off when used to obtain one product per package. Therefore, the prior art requires more tools, more changeover time, and consequently higher costs.

II. Protection against empty packaging.

Observer 16 signals the presence or absence of a product 4 by reading in the spacing between two consecutive products 4, and comparing it to a reference spacing. If a product is absent, empty packaging will be formed with unchanged control. The next upstream product 4 is, as it were, one product pitch behind the previous one. By delaying the movement of the foil 9 and thus the friction rollers 13 and the welding rollers 14, as well as the clamping jaws 15, relative to the products 4, this delay can be made up. For this purpose, on the basis of the signals from the observer 16, an optimum deceleration and then acceleration for the servomotors M2, resp. M3 determined. At a high operating speed of the device 1, for an accurate control, the total speed of the device 1 is then briefly slowed down, for which purpose the control unit 18 controls the individual control circuits. Within that global deceleration of the device 1 by means of the control unit 18, the - compared to the situation in which the global speed of the device 1 is maintained, then a relatively smaller deceleration / acceleration of the servomotors M2 and M3 takes place, whereby inaccuracies are caused, for example, by influences of mass inertia are eliminated. With the known master-slave control, depending on the movement of the infeed chain, the drive rollers and the clamping jaws will slow down and accelerate briefly. Furthermore, with high machine capacity, there is no short-term reduction in the global machine speed, and the chance of errors is therefore higher. In the known master-slave control, the machine capacity is therefore limited.

III. Fix incorrect product stitch.

It is determined with observer 17 whether the product 4 is in phase with the clamping jaws 15, so that this product 4 does not get clamped between them. If the pitch deviates, a phase shift of the clamping jaws 15 relative to the infeed chain 7 and the rollers 13 and 14 is required. Position controller P3 calculates the required control of the servomotor M3 on the basis of signals from the observer 17. Is if the deviation of the stitch is structural, the phase shift will be maintained until the original product stitch is detected, or a new deviating product stitch. Again, the operating speed of the entire device 1 is adjusted by controlling the individual control circuits by the control unit 18 when working at high capacity (for example, more than 500 products per minute). To this end, the control unit 18 also responds to signals from the observer 17. At a temporarily lower speed of the entire device 1, the phase shift of the clamping jaws 15 is then carried out from the control unit P3. If the phase shift is structural, then the global the speed of the device 1 to its original value, while maintaining the phase shift for the clamping jaws 15.

Of course, other devices for manipulating a product stream are also included in the present invention. It is important that the different members are individually speed-controlled in dependence on an internal reference signal, to which a feedback applies, which activates as soon as a deviation has been detected which exceeds a certain reference area.

Claims (5)

A method for manipulating a product flow, wherein the product flow is conveyed successively along a transport path past a number of processing members (13, 14, 15) by means of transport members (6), wherein these processing members are controlled in dependence on a central control system, for operating the processors in phase with the product stream (4), and the central control system sends control signals thereto, and receives detection signals about the position of the transporters, characterized in that the central control system (19) processes those processers, as well as the transporters control substantially independently of one another by means of an internal, substantially constant, reference signal, which, depending on detection signals from observers (16, 17), is adjusted, if necessary temporarily, if a certain preset threshold value is exceeded. Method according to claim 1, characterized in that for each individually controlled processing or conveying means an optimum position variation is calculated within separate control circuits (P1 ... P4), each of which receives feedback signals (R1 ... R4) originating from position detecting members (R1 ... R4) which are coupled to the drive members (M1 ... M4) controlled by the control circuits. Method according to claim 2, characterized in that one or more of the separate control circuits each receive signals from observers (16, 17) which signal the position of the products (4) in the product stream, which signals are used for determining the optimal course of the position of the associated processing or transporting member. Method according to any one of the preceding claims, characterized in that first the reference signal is adjusted, as a result of which first the speed of all processing and conveying members is adjusted in equal measure and direction, and then the optimum for each of those members individually position course is determined. Device (1) for operating the method according to any one of the preceding claims, of which the actuators, preferably electric motors, are coupled to the drive shafts of both the working members (13, 14, 15) and those of the transport members (3, 7) (M1 ... M4), each coupled to an output of the central control system (19), and coupled to each of these axes is a detector, for example an encoder (R1 ... R4), which are in signaling connection with an input from the central control system, to form a feedback loop.