Assembly system and method for assembling workpieces

Abstract

Assembly system for assembling workpieces (100, 200, 300, 400), comprising several assembly stations (10, 20, 30) and at least one rework station (40), wherein each workpiece (100, 200, 300, 400) is to be arranged in a predetermined temporal sequence, first in an i = j-th and then in an i = j+1-th assembly station (10, 20, 30), wherein, in the event that a defect is identified for a workpiece (200) in the j-th assembly station (20), the assembly system is configured to remove this workpiece (200) from the j-th assembly station (20) and to insert a workpiece (400) from a rework station (40) of the at least one rework station (40) into the j+1-th assembly station (30), wherein the removed defective workpiece (200) is arranged in the same post-processing station (40) of the at least one post-processing station (40) from which the workpiece (400) that is fed in as a replacement,is taken from it.

Description

[0001] The invention relates to an assembly system for mounting workpieces and a method for mounting workpieces.

[0002] In an assembly process, workpieces are processed sequentially at different assembly stations. Errors can occur during this process, creating gaps in the manufacturing flow and disrupting it.

[0003] In this context, the dissertation “Novel logistics concepts for flexible automobile production without a conveyor belt” by Julian Popp (Institute for Materials Handling and Logistics at the University of Stuttgart), the dissertation “Method for planning modular, product-flexible assembly configurations in variant-rich series assembly, using the automotive industry as an example” by Christian Küber (Fraunhofer Institute for Production Engineering and Automation IPA, Stuttgart) and the article “Self-controlled driverless transport systems” by Christoph Schwarz et al. (Logistics Journal) are known.

[0004] German patent application DE 102 32 402 A1 describes a buffer system for the production of mass-produced goods. Through the complete decoupling of process steps via the random use of buffer locations, each buffer location can be used for any process step. Furthermore, flexible call sequences between process steps and process connections at different levels are possible. Process steps can also be repeated. An item to be processed can be randomly inserted into the process chain or a transport flow. Conversely, it can also be removed from the process chain or the transport flow.

[0005] From publication DE 10 2008 038 760 A1, a method for machining a large number of first and second workpieces is known, which are sequentially fed into a common machining process. The workpieces are machined in several machining steps in spatially separated machining areas, with transport of the workpieces between the machining areas being carried out by a conveyor system.

[0006] An automated manufacturing station for body components is known from German patent application DE 20 2017 101 643 U1. This station comprises a manufacturing area with one workstation and several program-controlled manufacturing robots, whereby the body components are fed to the manufacturing station from the outside on production load carriers.

[0007] Against this background, it was a task to compensate for any errors during the assembly of workpieces.

[0008] This problem is solved by an assembly system and a method with the features of the independent claims. Embodiments of the assembly system and the method are described in the dependent claims and the description.

[0009] The assembly system according to the invention is designed for assembling workpieces or components and comprises several assembly stations and at least one post-processing station. Each workpiece is to be arranged successively in the assembly stations spatially distributed within the assembly system, first in an i = j-th and then in an i = j+1-th assembly station, according to a predetermined schedule or defined sequence, during a designated occupancy time. Schedules or sequences, which are to be provided or defined for all workpieces, define a production flow of the assembly system. The assembly system can have a sensor assigned to each assembly station, which is designed to identify any defects that may be present in a workpiece. For example, if...If a defect is identified, detected, or recognized by a sensor for a workpiece located in the j-th assembly station, the assembly system is designed to remove this defective workpiece from the j-th assembly station and thus from the production flow, usually removing it from the production flow in terms of time and space, and to insert a workpiece from a post-processing station of at least one post-processing station into the subsequent j+1-th assembly station and thus into the production flow, usually inserting it into the production flow in terms of time and space.

[0010] The assembly system is designed to arrange the workpiece removed from the production flow in the rework station of at least one rework station from which the workpiece was taken that was introduced into the production flow, i.e., into the j+1th assembly station, to replace the defective workpiece.

[0011] Furthermore, each assembly station is designed to process the workpiece placed therein during a processing time and to bring it to a setup state assigned to the respective assembly station within the production flow.

[0012] The assembly system may also include at least one self-driving or automated driverless transport vehicle designed to transport a workpiece from one station to another, i.e., from one assembly station to another, from one assembly station to the at least one post-processing station and / or from the at least one post-processing station to an assembly station, taking into account the intended schedule.

[0013] Furthermore, the assembly system may have a computing unit that is designed to control, e.g., to steer and / or regulate, the assembly system, the procedure described below, the schedule or assembly sequence for the workpieces and / or the production flow.

[0014] The method according to the invention is provided for assembling workpieces with an assembly system, for example, an embodiment of the assembly system described above, which comprises several assembly stations and at least one post-processing station. Each workpiece is arranged successively in the assembly stations spatially distributed within the assembly system, first in an i = j-th and then in an i = j+1-th assembly station, according to a predetermined schedule or defined sequence, during a designated occupancy time. The production flow of the assembly system is defined by schedules or sequences that are determined for all workpieces. If a defect is detected for a workpiece in the j-th assembly station, for example, by a sensor in that assembly station, the workpiece is removed.If a defective workpiece is identified, it is removed from the production flow and thus from the j-th assembly station, typically both spatially and temporally. Instead, a workpiece from a rework station (or at least one rework station) is fed into the j+1-th assembly station, i.e., the assembly station that follows the j-th assembly station from which the defective workpiece was previously removed. The workpiece from the rework station is then reintroduced into the production flow, typically both spatially and temporally.

[0015] In this process, assembly stations can be numbered using a first running parameter i = 1,..., j,... and assembly states for workpieces using a second running parameter m = 1,..., n,..., taking the production flow into account. Each workpiece is brought to an nth assembly state, production state, or assembly state assigned to the j-th assembly station where it is positioned, after completion of assembly or processing. The assembly state of each workpiece or component is further developed, e.g., incremented, as it passes through the assembly stations according to the schedule or sequence from assembly station to assembly station within the production flow. For example, it can...In a j-1th assembly station, which precedes the j-th assembly station in the sequence, the workpiece is brought to an n-1th assembly state, and in a j+1th assembly station, which follows the j-th assembly station in the sequence, it is brought to an n+1th assembly state. The starting point for numbering the assembly stations and assembly states can be defined as needed. Thus, depending on the definition, it is conceivable, for example, that a defect is identified in a workpiece when it is in the j+1th assembly station, from which it is then removed, with the replacement workpiece being fed from the rework station into the subsequent j+2th assembly station.

[0016] The rejected defective workpiece is brought to the same nth assembly state in the same rework station as the workpiece that has already been reworked in the rework station and is fed into the j+1th assembly station as a replacement. The previously defective workpiece is also fed into the j+1th assembly station after rework, since it has already been brought to the nth assembly state in the rework station—the state it could or should have been brought to in the jth assembly station if it were functioning correctly and did not have a defect that, for example, would have been identified by the sensor of the jth assembly station.

[0017] A workpiece can be placed in the rework station of at least one rework station until a gap arises again within the production flow in the j+1 assembly station, if another workpiece with a defect is identified in the j-th assembly station before the j+1 assembly station, which is removed from this j-th assembly station and leaves a gap in the j+1 assembly station into which the now reworked workpiece is inserted as a replacement.

[0018] In this method, the workpiece is initially in an n-1 assembly state before being placed in the j-th assembly station, where the defect is identified or confirmed. The workpiece that is reworked in the rework station and is introduced into the j+1-th assembly station (which follows the j-th assembly station in the production flow) as a replacement for the defective workpiece is already brought to the n-th assembly state in the rework station, the same state to which the defective workpiece should have been brought in the j-th assembly station. Furthermore, the previously reworked workpiece is brought to the n+1-th assembly state in the j+1-th assembly station, into which it was introduced from the rework station.

[0019] Each workpiece is positioned in a specific station during an occupancy period, i.e., an assembly station and, if applicable, at least one post-processing station. An occupancy period comprises an entry time, an actual processing time during which the workpiece is assembled or processed, and an exit time. In the case of at least one post-processing station, it is possible for a workpiece that is initially defective, after being assembled during the processing time, to be stored in a buffer or storage area of ​​the post-processing station until a gap arises in the production flow, typically at the j+1th assembly station, into which it can be inserted.

[0020] The assembly system and process enable the buffering of workpieces or workpiece carriers, in which workpieces can be arranged within the assembly system, as well as the integration of returned workpieces from post-processing into the modular assembly system. The assembly system and its stations, designed for assembly, processing, and / or post-processing, can be used to assemble or process workpieces such as electrical machines and / or components for vehicles, e.g., motor vehicles. Regardless of the specific characteristics of the workpieces to be assembled or that can be assembled, each workpiece is arranged and assembled or processed sequentially in various assembly stations.

[0021] The assembly system enables the modular assembly of workpieces using multiple assembly stations. These stations are designed to assemble the workpieces in their respective partial stages, with each workpiece being moved from one assembly station to its corresponding assembly stage to provide a complete stage. Depending on the definition, the assembly system may include an automated guided vehicle (AGV) system for transporting workpieces between the stations—that is, between the assembly stations and at least one post-processing station—where the workpieces are transported between stations by self-propelled and / or automated guided vehicles (AGVs). The at least one post-processing station is also configured as an assembly station or can be designated as such.The rework station can perform a rework operation on each defective workpiece, restoring it to the assembly state it could not reach at the assembly station where the defect was detected and from which it was rejected. The at least one assembly station designed as a rework station for performing each rework operation has a buffer for at least one reworked workpiece.

[0022] The assembly system includes a control unit designed to generate schedules for the autonomous transport vehicles for a future time period. Furthermore, the control unit is intended to close unexpected gaps in the production flow or the respective schedule that arise when a defective workpiece is removed from an assembly station for rework. This is achieved by utilizing the buffer of the respective rework station, from which a previously reworked workpiece is selectively introduced into the production flow, thus closing the gap and preventing such gaps from occurring in the future.

[0023] In one embodiment of the method, if a workpiece carrier with a workpiece is removed from the production flow to post-processing, another workpiece or component that has already been in post-processing can be reintroduced into the production flow as a replacement for the removed workpiece, thereby closing the gap created by the removed workpiece.

[0024] Gaps in the production flow, and thus in the planned schedule, which arise when workpieces or components are diverted to or destined for rework, can be filled, for example, by workpieces being returned from rework to production that have a configuration that matches the gap in the production flow. A workpiece from rework, once it has been processed in the rework station, can be held there until a gap appears in the production flow into which it can be inserted. The workpiece is then transported from the rework station to the corresponding assembly station or workstation with the gap (either empty or occupied) using an automated guided vehicle (AGV).The workpiece from the post-processing station is available to the control algorithm for scheduling in the production flow, provided that it has been or has been completely post-processed.

[0025] Such logic can also be used, for example, in the event of machine malfunctions, to temporarily prevent inevitable gaps in the production flow and thus in the planned schedule. In the case of a machine malfunction, which is considered a potential disruption in the production process, a buffer conveyor continues to process the workpiece, which is normally being transferred from the post-processing station to an assembly station, until the malfunction (e.g., the machine malfunction) is resolved, or until further production is no longer possible due to a lack of available resources, in this case, gaps caused by defective workpieces or already post-processed workpieces.Once the machine malfunction is resolved, the excess workpieces in the workpiece carriers can be slowly removed from the production process until a nominal quantity of workpieces, as specified in the production flow (e.g., a target quantity for a given time), is reached again. This takes into account that removing a workpiece too quickly from an assembly station would create a gap in that station.

[0026] These two processes are automated by the assembly system's computing unit or by a control computer and controlled without human intervention.

[0027] In one embodiment of the method, gaps in the manufacturing or production plan caused by defective and rejected workpieces can be avoided by replacing them with reworked, substitute workpieces. Despite potential disruptions, such as machine malfunctions, the input of workpieces or components into the production flow can be optimized. Furthermore, workpieces from rework can be integrated without negatively impacting ongoing production, such as daily output. This also allows for the smoothing of production capacity peaks, thereby optimizing the utilization of all involved resources and increasing the overall equipment effectiveness (OEE) of the entire assembly system. Finally, optimal utilization of resources, typically the assembly stations, can reduce the risk of bottlenecks within the assembly system.

[0028] A self-driving, automated guided vehicle (AGV) can be used to remove a defective or faulty workpiece from an assembly station and transport it to a rework station. In the rework station, the defective workpiece is restored to the assembly state it should have been in at the station where the defect was identified. This also applies to transporting a reworked workpiece from a rework station and inserting it into a gap in an empty assembly station. This allows for the efficient implementation of different assembly sequences for various workpieces. The process also reduces the risk of workpieces or workpiece carriers becoming jammed.

[0029] This method makes it possible to transport a component or workpiece in a timely manner from, for example, the j-th assembly station to the next, for example, the j+1-th assembly station. This method addresses the issue that, in the case of different assembly sequences, transport does not occur in the same order as when a workpiece is placed at the first assembly station at the start of assembly, but rather in a modified sequence and therefore, depending on the definition, can be quite chaotic.

[0030] To mitigate this chaos and optimize workpiece output across the entire assembly system, the process can utilize a schedule that considers travel times for workpieces between assembly stations, processing times and / or station occupancy, as well as potential machine malfunctions, quality issues, and / or rework processes. For example, the processing unit can always plan ahead for a certain period. The planned schedule can be optimized using mathematical optimization methods or genetic algorithms to ensure the entire schedule or manufacturing process is as short as possible, thus maximizing the number of workpieces processed per unit of time.

[0031] This method addresses the issue that machine malfunctions, quality problems, or other disruptions would otherwise prevent adherence to the production schedule, such as that calculated by the processing unit. A machine malfunction can cause a defective workpiece, which has already passed through an affected assembly station, to continue through the process, potentially creating gaps in subsequent assembly stations. In one embodiment of the method, workpieces initially diverted to rework are then systematically fed into the next assembly station designated in the production flow. This allows gaps or holes in the production flow caused by defective workpieces to be filled, maintaining a continuous production flow and preventing output losses.

[0032] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0033] The invention is schematically illustrated with reference to embodiments in the drawings and is described schematically and in detail with reference to the drawings. Fig. Figure 1 shows a schematic representation of an embodiment of the assembly system according to the invention for carrying out an embodiment of the method according to the invention in different situations.

[0034] The figures are described in a coherent and comprehensive manner; identical components are assigned the same reference symbols.

[0035] The embodiment of the assembly system according to the invention comprises three assembly stations 10, 20, 30 and a post-processing station 40, as well as a self-propelled or driverless transport vehicle 50, which is designed for the automatic transport of workpieces 100, 200, 300, 400 or components to be assembled, namely a first workpiece 100, a second workpiece 200, a third workpiece 300 and a fourth workpiece 400, between the stations, wherein the workpieces 100, 200, 300, 400 are here designed as electric machines. At least the first three workpieces 100, 200, 300 are fed successively to the three assembly stations 10, 20, 30 according to a schedule provided for assembly and are assembled or processed by a respective assembly station 10, 20, 30. Furthermore, the assembly system has a computing unit, e.g. a computer (not shown here), which is used for controlling, i.e.is designed to control and / or regulate the execution of the procedure.

[0036] All three Fig. 1a, Fig. 1b and Fig. Figure 1c schematically represents a production flow according to a schedule for the assembly of workpieces 100, 200, 300, 400. The figure features an abscissa 2 and an ordinate 4, where time is represented along abscissa 2 and occupancy times, during which each workpiece 100, 200, 300, 400 is located in an assembly station 10, 20, 30, respectively, are represented by bars along the ordinate 4. Each workpiece 100, 200, 300, 400 is thus brought to a setup or production state within the production flow that is assigned to the respective assembly station 10, 20, 30, 40.

[0037] Fig. Figure 1a shows a state of the assembly system with error-free assembly of workpieces 100, 200, 300. Each occupancy time for a workpiece 100, 200, 300 in an assembly station 10, 20, 30 comprises an entry time, during which the workpiece 100, 200, 300 is fed into or positioned in the assembly station 10, 20, 30; an actual processing time, during which the workpiece 100, 200, 300 is processed by the assembly station 10, 20, 30; and an exit time, during which the workpiece 100, 200, 300 is removed from or taken out of the assembly station 10, 20, 30, with the reference numerals listed below being assigned to these times.

[0038] Initially, each workpiece 100, 200, 300 is assembled for the first time in an i = j-th assembly station 10. For the first workpiece 100, an entry time of 111, a processing time of 112, and an exit time of 113 are planned for the first assembly. For the second workpiece 200, an entry time of 211, a processing time of 212, and an exit time of 213 are planned for the first assembly in the j-th assembly station 10. For the third workpiece 300, an entry time of 311, a processing time of 312, and an exit time of 313 are planned for the first assembly in the j-th assembly station 10. Each workpiece 100, 200, 300 is thus brought to one of the m = n-th assembly states assigned to the j-th assembly station 10 for the first assembly.

[0039] Subsequently, each workpiece 100, 200, 300 is assembled in an i = j+1-th assembly station 20. For the first workpiece 100, an entry time 121, a processing time 122, and an exit time 123 are scheduled. For the second workpiece 200, an entry time 221, a processing time 222, and an exit time 223 are scheduled in the j+1-th assembly station 20. For the third workpiece 300, an entry time 321, a processing time 322, and an exit time 323 are scheduled in the j+1-th assembly station 20. Each workpiece 100, 200, 300 is thus brought to one of the m = n+1-th assembly states assigned to the j+1-th assembly station 20.

[0040] First, each workpiece 100, 200, 300 is assembled a second time, i.e., again in the j-th assembly station 10. For the first workpiece 100, the second assembly time is scheduled as follows: an entry time of 114, a processing time of 115, and an exit time of 116. For the second workpiece 200, the second assembly time in the j-th assembly station 10 is scheduled as follows: an entry time of 214, a processing time of 215, and an exit time of 216. For the third workpiece 300, the second assembly time in the j-th assembly station 10 is scheduled as follows: an entry time of 314, a processing time of 315, and an exit time of 316. In this process, each workpiece 100, 200, 300, when it is arranged and assembled for the second time in the j-th assembly station 10, is brought to one of the m = n+2-th assembly states still assigned to the j-th assembly station 10, which differs from the n-th assembly state to which the workpiece 100, 200, 300 was brought by the j-th assembly station the first time.

[0041] Finally, each workpiece 100, 200, 300 is assembled in an i = j+2-th assembly station 30. For the first workpiece 100, an entry time 131, a processing time 132, and an exit time 133 are planned. For the second workpiece 200, an entry time 231, a processing time 232, and an exit time 233 are planned in the j+2-th assembly station 30. For the third workpiece 300, an entry time 331, a processing time 332, and an exit time 333 are planned in the j+2-th assembly station 30. Each workpiece 100, 200, 300 is thus brought to one of the m = n+3-th assembly states assigned to the j+2-th assembly station 30.

[0042] When the workpieces have reached the n+3 assembly stage, workpieces 100, 200, and 300 are fully assembled, which is indicated here by two crossed hammers. Since each workpiece 100, 200, and 300 is arranged and processed twice in the j-th assembly station 10, but only once each in the j+1-th and j+2-th assembly stations 20 and 30, according to a sequence specified here within the production flow, the number of a respective assembly station 10, 20, or 30 can differ from the assembly stage number of a respective workpiece 100, 200, or 300 if it has been processed by that assembly station 10, 20, or 30. It is further provided here that each workpiece 100, 200, 300, before it is arranged for the first time in the j-th assembly station 10, is still in an m = n-1-th assembly state within the manufacturing flow.Before the workpiece is positioned for the second time in the j-th assembly station 10, it is already in the n+1-th assembly state. The assembly stations 10, 20, 30 are numbered according to a first running parameter i, starting from 1 to j, etc. The assembly states are numbered according to a second running parameter m, starting from 1 to n, etc.

[0043] Fig. Figure 1b illustrates a situation where, for example, a sensor in the assembly system detects that the second workpiece 200 is defective upon arrival at the j-th assembly station 10, and / or has been incorrectly assembled. This results in a fault or defect being identified during a processing time of 212x for the second workpiece 200, and the second workpiece 200 is therefore not OK (not OK). In this case, the second workpiece 200 is removed from the j-th assembly station 10 and the intended production flow and transported by the transport vehicle 50 to the rework station 40, as indicated by arrows 601. The second workpiece 200 is then fed into the rework station 40, i.e., positioned and assembled there, and subsequently reworked.As a result, a gap 500 is subsequently created in the j-th assembly station 10 (on the second time) as well as in the j+1-th and j+2-th assembly stations 20, 30, since the second workpiece 200 is located in the post-processing station 40, while waiting for a partial production loss (arrow 602).

[0044] Such gaps, 500 in number, are, as in Fig.Figure 1c illustrates this, as it is compensated by the fourth workpiece 400, which is mounted as a replacement for the defective second workpiece 200 during the execution of the procedure. Here, the fourth workpiece 400 is removed from the post-processing station 40, transported by the transport vehicle 50 to the j+1th assembly station 20, and inserted into the gap 500 created by the second workpiece 200 to be mounted, as a replacement for the second workpiece 200, into the j+1th assembly station 20 and thus into the intended production flow (arrows 700).For this fourth workpiece 400, the following are provided in the j+1th assembly station 20: an input time 421, a processing time 422 and an output time 423; in the j-th assembly station 10: an input time 414, a processing time 415 and an output time 416; and in the j+2th assembly station 30: an input time 431, a processing time 432 and an output time 433, until it is fully assembled.

[0045] In this embodiment, it is provided that if the error or defect is detected for the second workpiece 200 at the j-th assembly station 10 during the failed machining time 212x, it is by definition not yet in the n-th assembly state provided for in the production flow, but is still in the n-1-th assembly state when it is removed from the production flow and fed into the rework station 40. In the rework station 40, once the second workpiece 200 has been assembled or reworked, it is brought from the n-1-th assembly state to the originally intended n-th assembly state, in which the fourth workpiece 400 is already located after it has been reworked by the rework station 40. REFERENCE MARK: 2 Abscissa 4 ordinates 10, 20, 30 assembly station 40 post-processing stations 50 transport vehicles 100, 200, 300, 400 workpieces 111, 114, 121, 131, 211, 214, 221, 231, 311, 314, 321, 331, 414, 421, 431 Entry time 112, 115, 122, 132, 212, 212x, 215, 222, 232, 312, 315, 322, 332, 415, 422, 432 Processing time 113, 116, 123, 133, 213, 216, 223, 233, 313, 316, 323, 333, 416, 423, 433 Exit time 500 gap 601, 602 700 Arrow

Claims

[1] Assembly system for assembling workpieces (100, 200, 300, 400), comprising several assembly stations (10, 20, 30) and at least one post-processing station (40), wherein each workpiece (100, 200, 300, 400) is to be arranged in a predetermined temporal sequence, first in an i = j-th and then in an i = j+1-th assembly station (10, 20, 30), wherein, in the event that a defect is identified for a workpiece (200) in the j-th assembly station (20), the assembly system is configured to remove this workpiece (200) from the j-th assembly station (20) and to insert a workpiece (400) from a post-processing station (40) of the at least one post-processing station (40) into the j+1-th assembly station (30), wherein the removed defective workpiece (200) is arranged in the same rework station (40) of the at least one rework station (40) from which the workpiece (400)which is introduced as a replacement, is removed. [2] Assembly system according to claim 1, wherein each assembly station (10, 20, 30) is configured to process the workpiece (100, 200, 300, 400) arranged therein and to bring it to an assembly state assigned to the respective assembly station (10, 20, 30). [3] Assembly system according to claim 1 or 2, comprising at least one driverless transport vehicle (50) designed to transport a workpiece (100, 200, 300, 400) from one station to another station. [4] Assembly system according to one of the preceding claims, comprising a computing unit configured to control the assembly system. [5] Method for assembling workpieces (100, 200, 300, 400) with an assembly system comprising several assembly stations (10, 20, 30) and at least one post-processing station (40), wherein each workpiece (100, 200, 300, 400) is arranged successively in an i = j-th and then in an i = j+1-th assembly station (10, 20, 30) according to a predetermined temporal sequence, wherein if a defect is identified for a workpiece (200) in the j-th assembly station (20), this workpiece (200) is removed from the j-th assembly station (20) and a workpiece (400) from a post-processing station (40) of the at least one post-processing station (40) is inserted into the j+1-th assembly station (30), wherein the removed defective workpiece (200) is arranged in the same post-processing station (40) of the at least one post-processing station (40) from which the workpiece (400) that is fed in as a replacement,is taken from it. [6] Method according to claim 5, wherein a workpiece (200, 400) is arranged in the post-processing station (40) of the at least one post-processing station (40) until a gap (500) is created in the respective j+1-th assembly station (20), into which the workpiece (200, 400) is inserted. [7] Method according to one of claims 5 or 6, wherein it is provided that the workpiece (200) is still in an n-1-th assembly state before it is arranged in the j-th assembly station (20) in which the defect is identified for the workpiece (200), wherein the workpiece (400), which is reworked in the post-processing station (40) and fed into the j+1-th assembly station (30) as a replacement for the defective workpiece (200), is brought to an n-th assembly state in the post-processing station (40).

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