A METHOD AND CONTROL SYSTEM FOR CONTROLLING A CONVEYOR SYSTEM AND A PLANT FOR BALING PAPER PULP

Abstract: In a method and control system for controlling a conveyor system comprising a plurality of conveyors, each of which is allocated a control unit (44, 46, 48), the conveyors are controlled in accordance with status data from the conveyors. Each conveyor is brought to communicate (via 50, 52, 53, 54) only with its adjacent conveyors, which are in turn brought to communicate only with their adjacent conveyors, etc. The communication comprises the control units (44, 46, 48) of each conveyor transmitting and receiving control information, said information being created on the basis of the conveyor's own status data and control information from its adjacent conveyors. Control signals for controlling the conveyor are created on the basis of the conveyor's own status data and the control information received by the conveyor's control unit from control units of adjacent conveyors. The control units can be standardized and dimensioned for a maximum number of adjacent conveyors. A plant for baling paper pulp comprises a conveyor system having such a control system.

Description: A method and control system for controlling a conveyor system and a plant for baling paper pulp The present invention relates to a method for controlling a conveyor system, comprising a plurality of conveyors, as described in the preamble to claim 1, and a control system for such a conveyor system comprising a plurality of conveyors, each of which is allocated a control unit in communication with sensing means for the supply of status data. On the basis of these status data and on the basis of status data from other conveyors, the control unit generates control signals to control the conveyor. The invention also relates to a plant for baling paper pulp having such a conveyor system. The sensing means of a conveyor may consist of mechanical limit sensors or inductive transducers. The status data obtained from the sensing means of a conveyor provide combined information concerning the status of the conveyor, i.e. if the conveyor is free or if it is carrying a load (e.g. a bale), as well as the location of the conveyor . In this context "conveyor" shall also be understood to mean machines in the conveyor system other than true conveyors. From a communication point of view, all such machines must function as conveyors. Conveyor equipment in the pulp baling line for the manufacture of board, for instance, is seldom the same from case to case. This is primarily because the premises in which the conveyor equipment is to be installed are seldom similar, but also because the form of the load (bale) and the capacity required for the conveyor system differs from plant to plant. Each plant is specifically designed, thus requiring extensive engineering work upon delivery. In a typical case approximately half the engineering work is devoted to the conveyors and half to the other machinery included in the plant. Control systems in modern conveyor systems of the type under discussion are also constructed so that the control unit for each conveyor is arranged in a central computer common to the conveyor system. The central computer thus includes a control unit for each conveyor wherein each control unit is in reality a program module. Each conveyor communicates via its control unit with all other conveyors on which the conveyor in question may be dependent. The control unit receives status data from the conveyors on which it is dependent. A conveyor is dependent on the conveyors whose status affects how the conveyor in question shall be controlled. Purely theoretically a conveyor may be dependent on an infinite number of other conveyors. In practice, however, a conveyor is usually dependent on not more than about 15 other conveyors and its control unit thus receives status data from 15 other conveyors. On the basis of the status data the control unit creates control signals to control the conveyor pertaining to the control unit. Since each conveyor in a conveyor system has its own set of conveyors on which it is dependent, and since two conveyor systems are hardly ever alike, extremely complex, customer-unique solutions are required for each conveyor system. In principle, therefore, a unique control unit is required for each conveyor. If for some reason the plant is to be altered, by a conveyor being removed, for instance, or being given a slightly altered function, the control unit of this conveyor and the control units of all conveyors dependent on this conveyor must be reprogrammed. The object of the present invention is to avoid these problems and thereby, amongst other things, to greatly reduce the engineering work, and consequently the costs. This object is achieved with a method and a control system of the type described in the introduction which has been given the characterizing features defined in claims 1 and 2, respectively. Recurrence is exploited in the invention, i.e. each conveyor communicates only with conveyor(s) adjacent to it, which in turn communicate with their adjacent conveyors, and so on. An adjacent conveyor is deemed to be one which the conveyor can deliver a load to or receive a load from. The communication comprises the control unit of each conveyor receiving or transmitting control information from or to the control unit of each of its adjacent conveyors. The control information of each conveyor is created from the conveyor's own status data and the control information of its adjacent conveyors. Each conveyor does not therefore possess direct information concerning the status of its adjacent conveyors, but instead is in possession of control information created on the basis of status data from several conveyors. A chain of conveyors is thus searched and status data are returned in the form of control information. Control signals are created for controlling the conveyor in question on the basis of the conveyor's own status data and the control information possessed by the conveyor's control unit. The control units of the conveyors can thus be standardized. The scope of the control information between adjacent conveyors is always the same, regardless of the type of conveyor used. From the communication point of view turning and travelling operations are equivalent and a stationary conveyor is treated as a travelling conveyor with only one position. Thus only one program is required for moving the load between conveyors. All transport systems will be identical from the programming aspect and subsequent alterations of existing plants are as simple as building a new plant. When expanding or altering an existing plant it is only necessary to specify the new adjacent conveyors. From the communication aspect a stationary conveyor can easily be changed to a travelling conveyor by entering information about the new adjacent conveyors. Great savings can be achieved with the present invention since the control units of the conveyors are built as complete, standardized units. Engineering work such as programming prior to delivery of a new conveyor system, as well as engineering work upon installation of the conveyors will be reduced to typically one tenth of that previously required. This saving in labour applies both when converting an existing conveyor system in accordance with the invention and when building new installations. Even existing plants with different types of control systems can be converted to control systems according to the invention. The control unit according to the invention is dimensioned for communication with control units pertaining to a maximum number of adjacent conveyors. This means, therefore, that the control unit is dimensioned for the "worst case" which, in the case of a conveyor system for the baling line for paper pulp, consists of a travelling conveyor with five different positions, each position having two adjacent conveyors. The same standardized unit is used in the simplest case, i.e. a straight conveyor with one adjacent conveyor, but in this case its capacity is only partially used. In the control system according to the invention, for instance, the control unit of a conveyor may be connected directly to the control units of its adjacent conveyors, or arranged to communicate with the control units of the adjacent conveyors by way of a field bus. The cable laying is minimised if a field bus is used for communication between the conveyors. Physical inputs and outputs are arranged on each conveyor, used for communication with motors, lamps, signal equipment, sensing means, etc. The inputs generate status data to the control unit and the outputs transmit control signals supplied from the control unit. The input and output can also be standardized. According to an advantageous embodiment of the control system according to the invention each conveyor comprises a control unit, a communication processor for the field bus and physical inputs and outputs. According to another embodiment of the control system according to the invention the control units are realised as program modules in a central computer and the communication with the conveyors occurs via a communication processor in the central computer. In this case the central computer comprises a program module for each conveyor. This program module then forms the control unit for the conveyor in question. To further explain the invention, embodiments of the control system according to the invention, selected by way of example, will now be described with reference to the accompanying drawings, in which Figure 1 shows a part of a conveyor system for baling paper pulp and Figures 2-4 illustrate the principle structure of three different embodiments of the control system for the conveyor system shown in Figure 1. Figure 1 shows part of a baling line for paper pulp with a cutter 2 situated at the far left of the figure, from which bales are transported sideways and swung by swivel conveyors 7, 9 to the conveyors 4 or 5. In the figure the swivel conveyors 7, 9 are shown in a waiting position for receipt of bales from the cutter 2. The bale is transported from conveyor 4 to conveyor 6 and then on to conveyors 8 and 10. The framed part 11 after the conveyor 10 comprises a weighing machine, a bale press and then another conveyor for transporting the bale to a following wrapping machine 13. The wrapping machine 13 wraps the bale in a wrapping sheet supplied by conveyors 15, 20, 22, as will be discussed later. The wrapping machine 13 is followed by a first binding machine 17 in which the bale is bound with wire 19. After the binding machine 17 is a marking machine 21 and a folding machine 12 with a turntable for lifting and turning the bale in order to fold in the corners of the wrapping sheet, after which the bale is supplied to a second binding machine 23 to complete wrapping by binding with a wire 25 passed from the other direction as compared with the wire in the first binding machine 17. Naturally additional conveyors are provided for gradual transportation of the bales between the above-mentioned machines for wrapping. These wrapping operations, the subsequent stapling operations and further handling of the bales are not described in the detail here. Each conveyor is associated with a control unit comprising physical inputs and outputs, as well as sensing means. Status data from the sensing means, inter alia, are supplied to the control unit via the physical inputs, and control signals, inter alia, are supplied from the control unit to the conveyor via the outputs. The control unit of the conveyor is arranged, in a manner described in more detail below, to communicate with the control units of the conveyors adjacent to it. Each control unit generates control information which is created on the basis of the status data of its own conveyor, and also on control information from adjacent conveyors. Via the control units of the adjacent conveyors, thus, control information is gathered which, together with its own status data, is used to create control signals to control its own conveyor. The conveyor 6 thus obtains control information from the conveyors 4, 8, 14 and 15 and the conveyor 8 obtains control information from the conveyor 10 as well as the conveyor 6, etc. A sequence might have the following appearance where the starting position is a bale on conveyor 6, which bale is to be transported further. If the control unit for conveyor 6 receives control information from the control unit for conveyor 8 that the latter is unable to receive the bale, the bale will be carried on conveyor 6 to conveyor 14 if the control information of its control unit indicates that there is room for it to be temporarily stored on conveyor 14, 16 or 18. Assume that conveyors 14 and 16 are occupied but conveyor 18 is free. The status data of conveyor 14 then indicate that it is occupied. The control unit for conveyor 14 asks the control unit for conveyor 16 if there is room. The status data of conveyor 16 indicate that it is occupied. The control unit for conveyor 16 asks the control unit for conveyor 18 if there is room. The status data of conveyor 18 indicate that it is free. The control unit for conveyor 18 responds with control information to the control unit for conveyor 16 that it is free. The control unit for conveyor 16 responds with control information to the control unit for conveyor 14 that there is room. The control unit for conveyor 14 responds with control information to the control unit for conveyor 6 that there is room. As soon as there is room on conveyors 8 and 10 to transport bales to subsequent wrapping and further handling, and conveyor 4 and the swivel conveyor 7 are empty of bales, bales are returned from temporary storage on conveyors 14, 16, 18 to conveyor 6, and so on. The baling line normally operates more quickly than the cutter and temporary storage is therefore only required in the event of disturbances in the operation of the baling line. The arrangement shown in Figure 1 has duplicate baling lines, with a lower line in the figure that is identical to the line described in the upper part of the figure. Wrapping material is supplied between these lines by the conveyors 15, 20, 22 and 24. The supply of wrapping material is common to both baling lines. Figure 2 shows an embodiment of the control system according to the invention having a number of control units 26, 28, 30, each of which is arranged on a conveyor. Each control unit 26, 28, 30 is directly connected to the control unit of adjacent conveyors via physical inputs and outputs 32, 33, 34 and cables 36, 38. Sensing means 27, 29, 31 are connected to the inputs to sense the status of the conveyor and supply status data to the relevant control unit 26, 28, 30. Figure 3 shows an embodiment in which each of the control units 44, 46, 48 is arranged on a conveyor and all communicate with each other via a coinmunication processor 50, 52, 53 arranged on each conveyor, by way of a field bus 54. Figure 4 shows another alternative embodiment in which control units 70, 72, 74 are arranged in a central computer 66 and where each conveyor is allocated its own control unit 70, 72, 74. The status data of each conveyor are transmitted with the aid of a communication processor 60, 62, 64, via a field bus 56, via a communication process 58 in the central computer 66 to respective control units 70, 72, 74. Control signals are transmitted from the central computer 66 by the communication processor 58, by way of the field bus 56 and via the communication processors 60, 62, 64, to the conveyors. In this embodiment control information is transmitted directly between the control units 70, 72, 74 in the central computer 66. In this embodiment also, recurrence is implemented in the central computer 66, i.e. the control unit of each conveyor communicates only with the control units of its adjacent conveyors. The embodiments exemplified in Figures 3 and 4 also comprise inputs, outputs, and sensing means as described with reference to Figure 2. In the control system according to the invention the control information is transmitted between the control units cyclically. The control units are therefore constantly in possession of all requisite information and the above sequences describing how information is transmitted thus occur instantaneously. Conveyor systems for baling lines of the type described above normally comprise the following types of conveyors: stationary swivel travelling stationary with turntable tiltable angular overloader, stationary angular overloader, travelling. Examples of signals that are transmitted for control of the conveyor system are: bale on conveyor, conveyor position 1, conveyor position 2, conveyor position 3, etc. , bale position 1, bale position 2, bale position 3, etc. , ready to receive bale forward position 1, ready to receive bale forward position 2, ready to receive bale forward position 3, etc. , ready to receive bale back position 1 , ready to receive bale back position 2, ready to receive bale back position 3, etc. , supply bale forwards position 1, supply bale forwards position 2, supply bale forwards position 3, etc., supply bale backwards position 1, supply bale backwards position 2, supply bale backwards position 3, etc., and conveyor forward, conveyor back, chain forward, chain back, etc.

Claims: C L A I M S 1. A method for controlling a conveyor system comprising a plurality of conveyors, each of which is dependent for its control on the status of at least a number of the other conveyors in said plurality, in which method each conveyor is controlled in accordance with its own status data and status data from the conveyors on which the conveyor in question is dependent, c h a r a c t e r i z e d i n t h a t each conveyor is brought to communicate only with adjacent conveyors, which are in turn brought to communicate only with their adjacent conveyors, etc. , and in that the communication comprises each conveyor transmitting and receiving control information, where the control information of each conveyor is created on the basis of the conveyor's own status data and status data from the other conveyors on which the conveyor in question is depending, status data from said other conveyors being supplied through recurrence to the conveyor in question in the form of control information from the adjacent conveyors. 2. A control system for a conveyor system comprising a plurality of conveyors, each of which is allocated a control unit in communiction with sensing means for supply of status data, each control unit being arranged to control the associated conveyor and for this control being arranged to generate control signals depending on the conveyor's own status data and status data from that number of the other conveyors of said plurality of conveyors on which the conveyor in question is dependent, c h a r a c t e r i z e d i n t h a t the control unit of each conveyor is arranged to communicate only with the control units of its adjacent conveyors, which units are in turn arranged to communicate only with the control units of their adjacent conveyors, etc., and in that the communication comprises the control unit of each conveyor transmitting and receiving control information, which control information is created on the basis of the conveyor's own status data and status data from those other conveyors on which the conveyor in question is dependent, status data from said other conveyors being supplied through recurrence to the control unit of the conveyor in question in the form of control information from adjacent conveyors. 3. A control system as claimed in claim 2, characterized in that each control unit is designed as a standard unit, dimensioned for communication with control units pertaining to a maximum number of adjacent conveyors. 4. A control system as claimed in claim 2 or claim 3, characterized in that the control unit of each conveyor is arranged on the conveyor. 5. A control system as claimed in any of claims 2, 3 or 4, characterized in that the control unit of each conveyor is connected via cables to the control units of the adjacent conveyors. 6. A control system as claimed in any of claims 2, 3 or 4, characterized in that each control unit is arranged to communicate with the control units of the adjacent conveyors via a communication processor arranged at each control unit, by way of a field bus. 7. A control system as claimed in claim 2 or claim 3, characterized in that the control units of the conveyor are realised as program modules in a common central computer. 8. A control system as claimed in claim 7, characterized in that the control units in the central computer communicate with respective conveyors via a communication processor arranged on the central computer, by way of a field bus and a communication processor arranged on each conveyor. 9. A plant for baling paper pulp, characterized in that it comprises a conveyor system with control system in accordance with any of the preceding claims.

Inventors: EDSTROEM TOMAS, EDSTROEM, TOMAS
Applicants: EDSTROEM TOMAS, SUNDS DEFIBRATOR IND AB, EDSTROEM, TOMAS, SUNDS DEFIBRATOR INDUSTRIES AB
Application year: 1999
Main classification: B65G43
IPC codes: B65G43, B65G47