EP0640526A1

EP0640526A1 - Method and device for manipulating a stream of products

Info

Publication number: EP0640526A1
Application number: EP94202445A
Authority: EP
Inventors: Adrianus Antonius Joseph Fransen
Original assignee: Kloeckner Haensel Tevopharm BV
Current assignee: Syntegon Packaging Technology BV
Priority date: 1993-08-31
Filing date: 1994-08-26
Publication date: 1995-03-01
Also published as: NL9301496A

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.

Description

The invention relates to a method for manipulating a stream of products, in which the products move successively downstream in a virtually uninterrupted movement, possibly intermittently. The invention also relates to a device for carrying out said method. In particular, the invention relates to the manipulation of astream of products in a packing machine, more particularly a so-called flowpacker. In this case an initially flat continuous web or strip of packaging material is folded or bent with the longitudinal edges towards each other in the form of a tube around the essentially continuously moving product stream, and is then divided into successive pieces or pouches sealed in the lengthwise and crosswise direction and containing one or more products from the product stream. However, the invention is not restricted thereto, and can also be applied to other areas of product stream manipulation, such as in respect of product conveyors with buffer facility etc. In this case the invention is essentially applicable in the field of product streams with relatively high speeds, in the case of which a product passage of, for example, 500 items per min. or more is achieved, as is currently the norm in the foods and consumer industry for articles of relatively small dimensions, such as biscuits, crackers, chocolate bars and pieces of cheese, but also screws, nuts, lamps for light fittings and the like.
It is known from the packaging industry for foods that in the case of the so-called flowpacker the various drive units thereof for supplying the continuous web of packaging material, sealing jaws and cutting elements are speed-controlled depending on the product infeed movement. For this purpose, use is currently being made of an electronic control system in which a detection element on the product supply belt, generally an encoder on the drive shaft, transmits a signal which is used as a reference signal, on the basis of which the drive of the various elements in the packing machine connected downstream are controlled. In control engineering this control is also sometimes called a master-slave control system, in the case of which the master is coupled to the product supply. A flowpacker with such a control system is described in, for example, EP-A-0,339,134.
The disadvantage of this known master-slave control system is the limited capacity of the flowpacker or other type of product processing machine. A machine operating by such a master-slave control system is also subject to fairly abrupt stopping and starting, depending on the product supply. Stopping and starting is often necessary in this case if the known machine has a control system for preventing as far as possible breakdowns resulting from defective product infeed. For example, control systems are known (called "no gap-no seal" or "no product-no bag") for preventing the formation of empty packs, or for preventing a situation in which during the cutting off of the tube and/or sealing thereof the product inside the tube is caught between the cutting and/or sealing elements. For this purpose, the machines controlled in the known manner are provided with detection elements which record a deviation depending on the position of the products on the supply belt, and accordingly stop the flowpacker temporarily, and then restart it virtually immediately. However, in this case the flowpacker as a whole is decelerated/accelerated until synchronization with the product supply has resumed. Accordingly, it is also necessary for the product supply to be as uniform as possible, to which end use is generally made of an infeed chain with pushers (also "driver elements" or "drivers"), which project between the products, have a fixed pitch, and per driver drive along a fixed number of products at a fixed pitch.
However, with the known equipment the production of faulty packs is unavoidable when the product supply is disrupted, a problem which can be solved only to a limited extent by using a "no product-no gap" or "no gap-no seal system".
The object of the invention is to ensure that any breakdowns occurring in the manipulation of a product stream as the result of, for example, a fault in the product supply are largely prevented in an efficient and reliable way, using as little as possible in the way of expensive and labour-intensive means.
For this purpose, the invention proposes a method for manipulating a product stream, in which conveying elements are used to guide the product stream along a conveyor successively past a number of processing elements, said processing elements being controlled depending on a central control system, in order to make the processing elements work 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 processing 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 both the conveying elements and the processing elements if a certain preset threshold value is exceeded. The central control system is, for example, made up of various individual control circuits, one for each type of conveying or processing element, in conjunction with a common basic control circuit for said control circuits which drives said control circuits by means of the reference signal, as explained further in the description of the figures.
Accordingly, in the case of the method according to the present invention, the control is carried out in such a way that it no longer depends on the position of the product infeed, on the basis of which the processing elements are controlled jointly so that they are in phase with the product stream. According to the invention, both the processing elements and the product stream being fed past them are controlled separately on the basis of an independent reference which is essentially constant during operation. It is now possible within certain limits to coordinate the phases of the various elements separately in an optimum manner, in order to ensure that faults, for example of the type described above, are minimized or even eliminated entirely. Since the phase difference between the various elements can be freely selected within a limited range, according to the invention, feedback from the various individual phases occurs, on the basis of which the internal reference signal is adapted if necessary. It is now also possible, for example, to shift the infeed part of the device periodically in phase, in order to form product groups, for example, without the need for additional conveying systems.
The present invention therefore provides an alternative to the known master-slave control system, in which the master is formed by the product supply, and in which the slaves are controlled jointly. In the present invention the master is formed by an internal reference signal, which is largely independent of the environment, and on which only a feedback system acts in order to keep the control within a certain specification. The conveying elements for the control of the product stream are now among the slaves, which are controlled independently within certain limits, each within its own control circuit with feedback.
The method according to the invention can be carried out with a device of which the drivers, preferably individually fed electric motors, coupled to the drive shafts of both the processing elements and the conveying elements are each coupled to an output of the central control unit. A detection element, for example an encoder, is also connected to each of said shafts, which encoders are in signalling communication with an input of the central control unit, in order to form a feedback circuit.
The invention is explained in greater detail below on the basis of a non-limiting example of an embodiment, with reference to the appended drawings, in which:

Fig. 1 shows diagrammatically in prespective view a part of a so-called flowpacker with product infeed according to the present invention; and
Fig. 2 shows a flow chart of the control system for carrying out the method according to the present invention.

Fig. 1 shows diagrammatically a device 1 according to the invention, in which a so-called flowpacker 2 is accommodated, only a part of which is shown here. Said flowpacker is described in greater detail in, for example, EP-A-0,336,012, more particularly in Fig. 10 thereof with the corresponding figure description from Col. 4, line 53. US-A-4,722,168 also describes and illustrates a similar flowpacker.
The device 1 of Fig. 1 has a first supply conveyor 3, by means of which the products 4 lying thereon are conveyed in succession from a source (not shown) lying at a distance, 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 and the like, which are supplied lying one behind the other in a relatively regular stream in the direction of the arrow A. The first conveyor belt 3 is endless, and is driven by means of electric motor M4.
Directly downstream is a relatively short, also endless, second conveyor belt 5, which in a manner known per se consists of two endless conveyor belts placed adjacent to each other with some space between them, in such a way that the top parts thereof lie in one plane, and maintain a gap between them. Said gap (not visible) allows drivers 6 on an endless infeed chain 7 which is known per se to project upwards from underneath between the two top parts of the conveyor belt 5, as shown. These drivers 6, with fixed constant pitch, also project between two successive products 4. Since a slide plate 8 (shown here by dotted lines) abuts the downstream end of the top part of the conveyor belt 5, the products are propelled horizontally onto said slide plate 8 by the drivers 6. Consequently, each product 4 ultimately rests against a driver situated behind it, which provides accurate positioning of the products 4. Both the conveyor belt 5 and the infeed chain 7 are driven by motor M1. The speeds of the conveyor belt 5 and the infeed chain 7 could be varied in relation to each other if desired, for example by means of an infinitely variable transmission (not visible) between motor M1 and belt 5 or chain 7, or both.
The infeed chain 7 is followed by the flowpacker 2, shown only diagrammatically here. As usual, the film 9 is taken from a stock roll 10, and is guided in the form of a continuous web so that it runs downstream at some distance above or below and parallel to the stream of products 4 in the direction of arrow A. During this process, the film 9 passes a conventional folding box 11, by means of which the film 9 is folded or bent in the lengthwise direction around the products 4, so that the longitudinal edges thereof come to rest against or on top of one another, in Fig. 1 at the bottom side of said products 4, in order to form the desired packaging tube 12. As also in the case of EP-A-0,336,012, the film is driven both upstream and downstream of the folding box 11 by means of a drive motor M2. Upstream of the folding box 11, the still essentially flat film 9 is guided between two friction rollers 13, driven so that they rotate in opposite directions. The rotary shafts of said rollers 13 run in the usual manner parallel to the movement track of the products 4, and crosswise to the direction of movement thereof. Downstream of the folding box 11, the overlapping longitudinal edge areas of the film are guided through the gap between one or more pairs of welding rollers 14, driven so that they rotate in opposite directions, only one of each pair of which is visible in Fig. 1, for the formation of the so-called welding rib, which runs in the lengthwise direction of the film tube 12 and projects crosswise. The rotary shafts of said welding rollers 14 run in the usual manner perpendicular to the movement track of the products 4 and at right angles to the direction of movement thereof. An adjustable transmission (not visible) can be provided 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 in order to keep the film 9 taut in the region of the folding box 11. Unlike the film drive described here upstream and downstream of the folding box 11, the drive could be effected, for example, only downstream thereof, by means of the welding rollers 14.
Situated further downstream of the welding rollers 14 are a set of gripping jaws 15, known per se and driven so that they rotate in opposite directions, for sealing lengths of film tube 12 in the crosswise direction and then severing them crosswise at the position of said welds. The rotary shaft of said gripping jaws 15 runs parallel to that of the friction rollers 13. The gripping jaws 15 are driven by electric motor M3. Therefore, by means of the gripping jaws 15, in each case upstream of one or more products 4, which said gripping jaws 15 have passed simultaneously in their position moved apart, the tube 12 is pinched shut in the direction of the arrow A at right angles to the direction of forward movement, and the film parts pressed onto one another are welded together by supplying heat or applying pressure, in which area the tube is subsequently severed in the crosswise direction. After the gripping jaws 15, individual packs (not shown) filled with one or more products 4 are then formed, essentially elongated in shape, and having at their end faces a transverse seam, with a longitudinal seam running between them.
A product detector 16, here a photoelectric cell, is also placed at the level of the infeed chain 7, as shown, for the purpose of controlling the electric motors M1...M4. The detector 16 detects the presence of a product 4, in order to establish whether an empty pack is possibly going to be formed if the operation of the device remains unchanged.
A second product detector 17, likewise a photoelectric cell, is also placed between the welding rollers 14 and the gripping jaws 15. This detector 17 may also be situated further upstream of the gripping jaws 15. With said detector 17 the space between the successive products 4 or groups of products is determined, on the basis of which it is established whether products 4 will be pinched between the gripping jaws 15 if the control of the device 1 is unchanged.
As shown, each servomotor M1...M4 is also linked to a pulse transmitter or so-called resolver R1...R4, for the purpose of the feedback, as will be described in greater detail further on. For this purpose, the respective resolver is also inserted on a respective rotary shaft driven by the motor, as shown in Fig. 1.
Fig. 2 shows the flow chart for control of the drive of the device 1. As shown, each servomotor M1...M4 with its respective resolver R1...R4 is accommodated in a separate control circuit with position regulator P1...P4. These position regulators P1...P4 thus operate independently of each other, and the servomotors M1...M4 are consequently also controlled independently of each other. The position regulators P1...P4 are also coupled to a common basic control circuit 18, which transmits a position control signal to each of the position regulators P1...P4, on the basis of which the latter drive the respective servomotors M1...M4. The position regulators 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 driven in the process by, for example, the infeed chain 7. This control means that each position regulator P1...P4 can determine the optimum current control of the servomotor independently, in order to comply with the internally developed position control signal of the common basic control circuit 18.
In addition to the internal feedback for each individual control circuit with position regulators P1...P4, there is also a feedback for the control unit, for which purpose the detectors 16 and 17 are used. These detectors 16 and 17 are coupled both to the control unit 18 and to the individual control circuits for control of servomotor M2 for the welding rollers 14 and for control of servomotor M3 for the gripping jaws 15 respectively. Directly depending on the feedback signals from the detectors 16 or 17, the position regulators P2 and P3 determine the individual optimum position control signal. The feedback by way of the detectors 16 and 17 to the control unit 18 also ensures that if too great deviations are found between the feedback and the prevailing control, the reference signal coming from the control unit 18 is adapted to the individual control circuits, on the basis of which the individual position regulators P1...P4 determine new optimum position control signals. This ensures that, as a result of the individual control of the motors M1...M4, the device 1 does not run out of control in circumstances deviating greatly from the norm.
Of course, feedback can also be effected for, for example, the separate control circuit for controlling the servomotor M1 of the infeed chain, etc.
A number of potential uses of the device 1 with the control system described above are explained below.

I. Formation of a multipack

The position regulator P1 for the control of the servomotor M1 of the infeed chain 7 can be set in such a way that it accelerates and decelerates alternately relative to the conveyor belts 3 and 5. This control system is such that as soon as a driver 6 is inserted between two products 4 lying on the belt 5 said chain 7 is decelerated for a brief period. Consequently, more than one product 4 behind the last-mentioned driver 6 can pass the upstream end of the chain 7 before the next driver 6 comes up. This means that small groups of products lie between the drivers 6 along the top part of the belt 5 and are pushed against each other by means of the downstream driver 6 when they slide from the downstream end of the top part of the conveyor belt 5 over the slide plate 8. The pitch of the drivers is consequently constant, irrespective of the use of the device 1 for forming single or multipacks.
Should the master-slave control system according to the prior art be used, in which case the servomotors M1...M3 are controlled directly depending on servomotor M4, in this case the formation of product groups with fixed space between the groups would have to have occurred already before arrival at the infeed chain 7, for which purpose it is necessary to have an additional system, which must be switched off when used for obtaining one product per pack. The prior art therefore requires more auxiliaries, and more re-setting time, and consequently involves higher costs.

II. Protection against empty packs

The detector 16 indicates the presence or absence of a product 4 by reading in the space between two successive products 4, and comparing it with a reference space. If a product is absent and the control system is unchanged, an empty pack will be formed. The next upstream product 4 lies, as it were, one product pitch behind the previous one. By delaying the movement of the film 9, and thus the friction rollers 13 and the welding rollers 14, and also the gripping jaws 15, for a brief period relative to the products 4, it is possible to make up this lost ground. For this purpose, on the basis of the signals coming from the detector 16, both the position regulators P1 and P3 determine an optimum deceleration and then acceleration for the servomotors M2, M3 respectively. At a high operating speed of the device 1, for an accurate control, in that case the overall speed of the device 1 is reduced for a brief period, for which purpose the control unit 18 drives the separate control circuits. Within said overall deceleration of the device 1 by means of the control unit 18, the deceleration/acceleration of the servomotors M2 and M3 - which is less than in the situation in which the overall speed of the device 1 is maintained - then occurs, with the result that inaccuracies caused by, for example, mass inertia influences are eliminated. In the case of the known master-slave control circuit depending on the movement of the infeed chain, deceleration and acceleration of the drive rollers and the gripping jaws for a brief period will take place intermittently. In the case of a high machine capacity, there is also no reduction in the overall machine speed for a brief period, and the chance of errors is consequently greater. In the case of the known master-slave control circuit the machine capacity is therefore limited.

III. Remedying faulty product pitch

The detector 17 establishes whether the product 4 is in phase with the gripping jaws 15, so that said product 4 does not become jammed between them. If the pitch is incorrect, a phase shift of the gripping jaws 15 relative to the infeed chain 7 and the rollers 13 and 14 is required. For this purpose, position regulator P3 calculates the necessary control of the servomotor M3 on the basis of signals coming from the detector 17. If the deviation of the pitch is structural, the phase shift will be retained until the original product pitch is established, or a new deviating product pitch. Here again, the operating speed of the entire device 1 is adapted by means of control of the individual control circuits by the control unit 18, if one is operating at high capacity (for example, more than 500 products per minute). For this purpose, the control unit 18 also reacts to signals coming from the detector 17. At a temporarily lower speed of the entire device 1 the phase shift of the gripping jaws 15 is then carried out from the control unit P3. If the phase shift is structural, then after it is executed the overall speed of the device 1 can be returned to the original value, while constantly maintaining the phase shift for the gripping jaws 15.
Of course, other devices for manipulating a product stream also lie within the scope of the present invention. What is important is that the various elements are individually controlled as regards speed, depending on an internal reference signal to which feedback is applicable, which feedback goes into operation as soon as a deviation which exceeds a specific reference range is found.

Claims

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, wherein said central control system controls said control elements and also the conveying elements essentially independently of each other on the basis of an internal, essentially constant reference signal which is adapted, possibly temporarily, depending on detection signals coming from detectors if a certain preset threshold value is exceeded.
Method according to Claim 1 wherein for each individually controlled processing or conveying element an optimum course of the position is calculated within separate control circuits (P1..P4), each of which receives (R1...R4) feedback signals from position and detection elements (R1...R4) which are coupled to the drive elements (M1...M4) controlled by the control circuits.
Method according to Claim 2, wherein one or more of the individual control circuits each receive signals from detectors which indicate the position of the products in the product stream, which signals are used for determining the optimum course of the position of the corresponding processing or conveying element.
Method according to one of the preceding claims, wherein first the reference signal is adapted, as a result of which the speed of each processing and conveying element is first adapted in the same degree and direction, and then the optimum position curve is determined for each of said elements individually.
Device for carrying out the method according to one of the preceding claims, in which the drivers, preferably electric motors (M1...M4), coupled to the drive shafts of both the processing elements (13, 14, 15) and to those of the conveying elements (3, 7) are each coupled to an output of the central control system (19), and a detection element, for example an encoder (R1...R4), is coupled to each of said shafts, which detection elements are in signalling communication with an input of the central control system, in order to form a feedback circuit.