Treatment plant for treating workpieces and method for operating such a treatment plant

Abstract

A treatment system (10) for treating workpieces (12) comprises a dryer (14) for drying the workpieces (12) with a dryer housing (16) for receiving the workpieces (12), in which heated air can be circulated as recirculated air and which is connected to at least one exhaust air line (24) for removing exhaust air from the dryer housing (16), at least one heated air line (36) for introducing heated air into the dryer housing (16), and at least one recirculated air line (38) for removing and re-introducing recirculated air from and into the dryer housing (16). A conveying system (18) conveys the workpieces (12) through the dryer (14). There is a heating device (22) for heating the exhaust air or recirculated air from the dryer housing (16) in order to provide heated air to be introduced into the dryer housing (16) via the heated air line (36).A fresh air duct (34) is connected to the exhaust air duct (24), the heated air duct (36), the recirculated air duct (38) and / or directly to the dryer housing (16). At least three process parameters from the following group of process parameters can be controlled interdependently by means of a control device (42): an exhaust air volume, a heated air volume, a fresh air volume, a recirculated air volume, a heating power of the heating device (22), and a conveying speed of the workpieces (12) through the dryer housing (16).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The invention relates to a treatment plant for treating workpieces, in particular vehicle bodies, with a) a dryer for drying the workpieces with a dryer housing for receiving the workpieces, wherein heated heating air can be circulated as recirculating air in the dryer housing, wherein the dryer housing is connected to at least one exhaust air line for discharging exhaust air from the dryer housing, at least one heating air line for introducing heating air into the dryer housing and at least one recirculating air line for discharging and re-introducing recirculating air from and into the dryer housing; b) a conveyor system for conveying the workpieces through the dryer, in particular a conveyor system with a plurality of transport carriages; c) a heating device for heating the exhaust air or recirculated air from the dryer housing in order to provide heated air to be introduced into the dryer housing via the heated air duct; d) a fresh air duct connected to the exhaust air duct, the heating air duct, the recirculation duct and / or directly to the dryer housing for adding fresh air to the exhaust air, the heating air, the recirculation air and / or the recirculation air.

[0002] Furthermore, the invention relates to a method for operating a treatment plant for treating workpieces, in particular vehicle bodies, with the following steps: a) drying the workpieces with a dryer having a dryer housing in which the workpieces are accommodated, wherein heated heating air is circulated as recirculating air in the dryer housing, wherein the dryer housing is connected to at least one exhaust air line for discharging exhaust air from the dryer housing, at least one heating air line for introducing heating air into the dryer housing and at least one recirculating air line for discharging and forwarding recirculating air from and into the dryer housing; b) conveying the workpieces through the dryer using a conveyor system, in particular a conveyor system with a plurality of transport carriages; c) heating the exhaust air or recirculated air from the dryer housing with a heating device in order to provide heated air to be introduced into the dryer housing via the heated air duct; d) Addition of fresh air to the exhaust air, the heated air, the recirculated air and / or the recirculated air via a fresh air duct connected to the exhaust air duct, the heated air duct, the recirculated air duct and / or directly to the dryer housing. 2. Description of the state of the art

[0003] The invention is described below primarily with reference to vehicle bodies as workpieces. However, the invention also relates to treatment systems for other workpieces that require treatment in a production process.

[0004] Such treatment systems in the industrial production of vehicle bodies feature a conveyor system that allows the workpieces to be transported through the treatment system. In order to process a large number of vehicle bodies in a short time, the conveyor systems in state-of-the-art treatment systems feature a large number of transport carriages. The transport carriages, in turn, often feature a support device and a connecting device through which the vehicle bodies can be connected to the transport carriages. A vehicle body connected to a transport carriage is moved through the treatment system by the transport carriage.

[0005] The conveyor system can be designed, for example, as a rail-mounted conveyor system, a chain conveyor, or even a skid conveyor, to name just a few examples. For several years, however, there has been a trend in the industrial production of vehicle bodies and other workpieces toward the use of driverless conveyor systems, in which the transport carriages are designed as free-moving transport carriages. Such free-moving transport carriages carry their own drive system, their own control system, and their own environmental sensor system. They are often supplied with travel instructions by a higher-level system control system and then navigate, controlled by their own control system, to the specified positions in the processing plant.

[0006] In larger vehicle body manufacturing facilities, several different treatment systems are often located one behind the other or follow one another. Such treatment systems may include processing booths, for example, for the mechanical processing of vehicle bodies. However, there are also treatment facilities with paint booths in which painting robots are installed to coat the vehicle bodies with one or more coats of one or more paints.

[0007] The treatment plant under consideration here, as is known from the market, comprises a dryer with a dryer housing in which the workpieces can be accommodated. Heated air is circulated within the dryer housing. It is customary for such dryers to connect at least one exhaust air duct to the dryer housing so that heated air can be discharged as exhaust air from a drying chamber defined by the dryer housing. It is also customary to connect at least one heated air duct to the dryer housing in order to replace the heated air discharged as exhaust air with fresh heated air. In the case of vehicle bodies, one reason why the heated air is discharged from the drying chamber is that solvent-containing pollutants are released into the atmosphere of the drying chamber when freshly painted vehicle bodies are dried.

[0008] This significantly increases the risk of fire and explosion in such dryers, which is why the heating air must be continuously renewed.

[0009] To heat the fresh, heated air before it is introduced into the drying room, treatment systems commonly available on the market feature at least one heating device. The use of heat exchangers at various points within a process air system, which consists of at least the exhaust air duct and the heated air duct, is also common. The use of heat exchangers significantly increases the energy efficiency of dryers, thereby reducing overall operating costs and making the treatment systems more environmentally friendly. For example, heat exchangers transfer part of the thermal energy from the (still warm) exhaust air discharged from the drying room to the fresh, heated air (which still needs to be heated).

[0010] In such treatment systems, the heating device is usually designed as a thermal afterburner with at least one burner, which, on the one hand, heats the hot air introduced into the drying chamber and, on the other hand, oxidizes solvent-containing pollutants in the exhaust air into combustion products through a thermal afterburning process. This serves to reduce the total carbon content in the exhaust and recirculated air, thus reducing the risk of fire and explosion in the dryer and releasing fewer pollutants into the environment. To further reduce this risk, such treatment systems often have at least one fresh air duct connected to the exhaust air duct, the hot air duct, and / or the dryer housing. By introducing fresh air into the recirculation circuit of the treatment system, the concentration of solvent-containing pollutants in the exhaust air is further reduced.The addition of fresh air can take place before or after thermal afterburning.

[0011] Previous plant concepts for the production of workpieces, especially vehicle bodies, are essentially designed for a specific workpiece type and are therefore only partially suitable for other workpiece types. This is due to the lack of flexibility in the dryer controls in existing systems.

[0012] Using vehicle bodies as an example, this can be illustrated as follows: a treatment plant designed for the bodies of conventional cars with combustion engines cannot always treat vehicle bodies intended for vehicles with electric motors with the current concepts, especially not in mixed operation. Likewise, these control systems cannot respond sufficiently well to a rapidly changing number of vehicle bodies conveyed through the dryer. The current actual number of vehicle bodies and the future target number of vehicle bodies are relevant here; the target number is derived from the production or process plan applicable at the time of a query.The problem of the different dryer controls for vehicle bodies designed for vehicles with combustion engines and vehicle bodies designed for vehicles with electric motors (electric vehicle bodies) arises from the fact that the electric vehicle bodies are, or must be, significantly heavier than conventional vehicle bodies due to the batteries that have to be installed in the vehicle floor. This means that, for example, a higher heating output or a longer residence time of the electric vehicle bodies in the dryer housing is required.

[0013] With previous system concepts, switching to other workpiece types or mixed operation with several workpiece types is not possible or only possible under difficult conditions. SUMMARY OF THE INVENTION

[0014] It is an object of the invention to provide a treatment plant and a method for treating workpieces, in particular vehicle bodies, which address the above-mentioned disadvantages of the prior art and make it possible to treat workpieces, in particular vehicle bodies, of different workpiece types, in particular in mixed operation, as well as varying quantities of workpieces in the treatment plant in a cost- and energy-efficient manner, without requiring modifications to the treatment plant or control system updates or hardware or software adaptations.

[0015] The task is solved in the treatment plant for treating workpieces mentioned at the beginning by e) a control device is provided which is designed in such a way that it controls at least three process parameters from the following group of process parameters in a dependent manner: the exhaust air quantity, the heated air quantity, the fresh air quantity, the circulating air quantity, the heating power of the heating device, the conveying speed of the workpieces through the dryer housing.

[0016] A control device designed in this way, which controls at least three process parameters interdependently, makes it possible to respond particularly flexibly to potentially drastically changing process conditions in the dryer, which may be caused, for example, by different workpiece types being dried simultaneously in the dryer and / or by a widely varying number of workpieces being dried simultaneously in the dryer. Different workpiece types, such as vehicle bodies for vehicles powered by an internal combustion engine and electric vehicle bodies, can thus be dried simultaneously in the dryer.

[0017] Until now, it was necessary to provide different treatment systems for such different workpiece types. However, due to increasing demand in the field of e-mobility, there is a growing need to be able to use existing treatment systems for other workpiece types as well. Conventional vehicle bodies are significantly lighter than e-vehicle bodies and require comparatively less heat input and residence time in the dryer to complete the drying of, for example, an applied coating.

[0018] A flexible control device, as specified here, allows for flexible adjustment of dwell times, heat input, and the amount of process air fed into the heating circuit during the ongoing production process, for example, without having to batch workpieces through the dryer according to specific workpiece types or temporarily interrupting the treatment process. Particularly when a conveyor speed can be controlled by the control device, workpieces of certain workpiece types can be fed through the dryer more slowly and, if necessary, even backwards, while, for example, simultaneously increasing or decreasing the heating power of the heating device and the amount of heating air (in relation to the conveyed volume).

[0019] Interdependent control, in this context, refers to the automatic adjustment of interdependently controllable process parameters. In other words, the process parameters that are interdependently controllable exist in a dependent relationship with one another. A change in one process parameter therefore automatically results in a change in at least two other process parameters that depend on this changed parameter. Such a change can involve increasing or decreasing a parameter value. However, it can also include a temporal component, specifically, for example, an extension, shortening, or intermittent change.

[0020] Preferably, the control device is configured such that it controls at least four, five or all six of the process parameters dependently on one another.

[0021] It is advantageous if one of the interdependently controllable parameters is a master parameter, where a change in a master-slave relationship immediately results in a change in at least two other parameters. It is also possible for all interdependently controllable parameters to function as master parameters when certain conditions occur in the dryer.

[0022] It is advantageous if the control device is configured in such a way that it indirectly describes and / or derives the interdependently controllable process parameters from each other by means of at least one plant-specific characteristic curve or a multidimensional plant-specific characteristic map through the respective other interdependently controllable process parameters.

[0023] A characteristic curve therefore reflects the dependence and correlation of two interdependently controllable process parameters of the treatment plant, whereas a characteristic map reflects the dependence and correlation of three or more interdependently controllable process parameters of the treatment plant. The dependencies can either be specified by measuring points that reflect the actual operation of the treatment plant or defined by mathematical functions that, for example, correspond to an idealized operation of the treatment plant, but in each case lead to different characteristic curves or maps.

[0024] An example combination of process parameters that can be adapted to one another or controlled interdependently is the following: recirculation air volume, conveyor speed, and heating power. In a specific scenario, the conveyor speed of the transport trolleys could thus be controlled depending on the recirculation air volume or the heating power. Or conversely, the recirculation air volume and the heating power could be controlled depending on the conveyor speed. In addition to this combination, all other combinations of the specifically mentioned process parameters are conceivable, as are all other combinations of the process parameters not specifically mentioned above that promise a control-related advantage.

[0025] As already indicated in other words, the control device is preferably designed such that, in response to the increase or decrease of a first of the process parameters, it controls the increase or decrease of at least a third of the process parameters depending on a monitored second of the process parameters.

[0026] It is also advantageous if the control device is designed in such a way that, in response to the increase or decrease of a monitored process variable, it controls, in particular increases or decreases, the at least three interdependently controllable process parameters.

[0027] In this context, the monitored process variable is advantageously a process variable from the following group of process variables: a current actual number or a future target number of workpieces within the dryer housing; a specific workpiece type, in particular a workpiece type that is the largest and / or heaviest in terms of volume and / or weight; and a pollutant concentration within the dryer housing. The largest and / or heaviest workpiece type is particularly suitable for dryers as a process variable, depending on which the interdependently controllable process parameters can be controlled. A concrete example of this is the comparison of electric vehicle bodies with conventional vehicle bodies.

[0028] A preferred combination of monitored process variables and adjusted process parameters is, for example, the following: the current actual number of workpieces or workpiece types in the dryer is monitored as a process variable. The following are adjusted depending on this: the recirculation air volume, the heating power, and the conveyor speed. Alternatively, one or more other process variables can of course also be monitored and the process parameters controlled accordingly. Another concrete example is the monitoring of the workpiece types present in the dryer and a dependent control of, for example, the exhaust air volume, the fresh air volume, and the conveyor speed. Here, too, in principle, all control combinations that offer an advantage from a control technology perspective are readily conceivable.

[0029] The control device is preferably designed such that, in addition to the increase or decrease of the second or third of the process parameters, it controls the increase or decrease of a fourth, fifth or sixth of the process parameters.

[0030] Preferably, the control device is designed such that it controls the increase or decrease of the fourth, fifth or sixth of the process parameters depending on the plant-specific characteristic curve or the multi-dimensional characteristic map.

[0031] In the method for operating a treatment plant for treating workpieces, in particular vehicle bodies, the object is achieved in that e) Controlling by means of a control device at least three process parameters from the following group of process parameters in dependence on one another: the exhaust air quantity, the heated air quantity, the fresh air quantity, the recirculated air quantity, the heating power of the heating device, the conveying speed of the workpieces through the dryer housing.

[0032] The advantages resulting from the method for operating the treatment plant correspond to the advantages mentioned above for the treatment method. Likewise, all examples and advantages mentioned above with regard to the other features of the treatment plant naturally also apply to the other features of the method for operating the treatment plant.

[0033] It is advantageous if at least four, five or all six of the process parameters are controlled interdependently by means of the control device.

[0034] Furthermore, an advantage arises if the interdependently controlled process parameters are indirectly described and / or derived from each other by means of at least one plant-specific characteristic curve or a multi-dimensional plant-specific characteristic map through the other interdependently controlled process parameters.

[0035] Preferably, in response to the increase or decrease of a first of the process parameters, the control device controls the increase or decrease of at least a third of the process parameters depending on a monitored second of the process parameters.

[0036] Preferably, the control device controls, in particular increases or decreases, the at least three interdependent process parameters in response to the increase or decrease of a monitored process variable.

[0037] Furthermore, an advantage arises if the monitored process variable is a process variable from the following group of process variables: a current actual number or a future target number of workpieces within the dryer housing, a specific workpiece type, in particular a largest and / or heaviest workpiece type in terms of volume and / or weight, a pollutant concentration within the dryer housing.

[0038] Preferably, in addition to increasing or decreasing the second or third of the process parameters, the control device controls increasing or decreasing a fourth or fifth of the process parameters.

[0039] It is also advantageous if the control device controls the increase or decrease of the fourth or fifth process parameter depending on the at least one plant-specific characteristic curve or the multidimensional characteristic map BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Exemplary embodiments of the invention are explained in more detail below with reference to a single drawing. This shows a schematic side view of a treatment system according to the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] In Fig. Figure 1 shows an embodiment of a treatment system 10 according to the invention for treating workpieces 12. In the present case, only vehicle bodies are illustrated as workpieces 12, which are not specifically provided with a reference symbol. However, other attachments, components, and accessories of vehicle bodies can also be considered as workpieces 12. Of course, any workpieces are equally conceivable, provided they require drying during the manufacturing process, for example, to dry an applied coating (e.g., a paint) or an adhesive bond.

[0042] In the Fig. 1, functionally identical components of the treatment system 10 are each identified only once with a reference symbol.

[0043] The treatment system 10 has a dryer 14 for drying the workpieces 12. The dryer 14, in turn, has a dryer housing 16 in which the workpieces 12 can be accommodated. The dryer housing 16 is thermally insulated so that the heat energy introduced into the dryer housing 16 can be largely contained within the dryer housing 16. The dryer housing 16 contains a drying chamber 17 in which the workpieces 12 can be dried.

[0044] Furthermore, the treatment plant 10 has a conveyor system 18, which in the present embodiment has a plurality of transport carriages 20, by means of which the workpieces 12 can be conveyed through the dryer 14. The transport carriages 20 can be designed either as rail-bound or floor-bound vehicles. Floor-bound transport carriages 20 can be free-moving and carry their own environmental sensor system, their own drive, and their own control device. In the present case, however, the conveyor system 18 is designed as a rail-bound conveyor system, i.e., as a conveyor system 18 in which the transport carriages 20 are moved along a support rail that defines the conveyor path (not specifically provided with a reference symbol).

[0045] Alternatively, the conveyor system 18 in the dryer 14 can also be, for example, a chain conveyor or a roller conveyor on which so-called skids are conveyed, each carrying a workpiece 12.

[0046] The workpieces 12 are conveyed through the dryer 14 in a continuous flow mode. Batch dryers are also conceivable and possible, in which the workpieces 12 are conveyed out again in a direction opposite to the direction in which they were conveyed into the dryer.

[0047] The treatment plant 10 has a process air system 21, which has a heating device 22, by means of which air can be heated for the dryer 14. The components described immediately below are also included in the process air system 21. In this case, exhaust air is discharged from the drying chamber 17 via an exhaust air duct 24 connected to the dryer housing 16 and guided to the heating device 22, where it is heated and fed via a heat recovery / exhaust line 26 to a fresh air heat exchanger 28 and via several heat recovery branch lines 30 to several recirculating air heat exchangers 32.

[0048] In the embodiment shown here, the heating device 22 is designed as a thermal afterburning system, which is not specifically designated by a reference symbol. Its purpose is, on the one hand, to reheat the air coming from the drying chamber 17 and, on the other hand, to largely remove solvent-containing pollutants from the air by burning and oxidizing them. Thus, the thermal afterburning system has several functions: maintaining the temperature in the drying chamber 17, reducing the risk of explosion in the drying chamber 17, and reducing pollutant emissions. In modifications not specifically shown, the heating device 22 can also follow concepts other than thermal afterburning.

[0049] In the present embodiment, the heat recovery / extraction line 26 is not connected to the dryer housing 16. Instead, the thermal energy of the air heated by the heating device 22 is transferred via the fresh air heat exchanger 28 to fresh air, which is supplied to the fresh air heat exchanger 28 via a fresh air line 34. The thus heated fresh air is supplied to the drying chamber 17 as heating air via a heating air line 36, which is connected to the dryer housing 16 and the fresh air heat exchanger 28. This specific heating air line 36 is shown in Fig. 1 as a heating air line 36.1. In embodiments not specifically shown, a heating air line can also branch off directly from the heating device 22, by means of which thermally afterburned heating air can be directly fed back into the drying chamber 17.

[0050] In this case, the fresh air line 34 is connected to the hot air line 36.1. In fact, the fresh air line 34 and the hot air line 36.1 form a continuous line and can only be distinguished by a temperature difference between the air conveyed in the fresh air line 34 and the hot air line 36.1. In embodiments not specifically shown, the fresh air line 34 can also be connected to the exhaust air line 24 or directly to the dryer housing 16.

[0051] Furthermore, a plurality of recirculation air lines 38 are connected to the dryer housing 16, into which exhaust air from the drying room 17 is led, then guided as recirculation air through the recirculation air lines 38 and again led as heated air into the drying room 17.

[0052] For this purpose, a recirculating air heat exchanger 32 is arranged on each of the recirculating air lines 38 in the present case, by means of which heat energy can be transferred from the heated air from the heating device 22 to the recirculating air originating from the drying room 17. In embodiments not specifically shown, fewer or more recirculating air lines 38 than those shown in the figure can be provided, depending on the requirements of the treatment system 10. As already mentioned with regard to the fresh air line 34 and the heated air line 36.1 which is continuous with it, the recirculating air lines 38 leading away from the recirculating air heat exchangers 32 (i.e. leading to the dryer housing 16) also form heated air lines, one of which is designated 36.2 here - here too, there are effectively continuous lines which can be distinguished as recirculating air lines 38 and heated air lines 36.2 due to the temperature difference.

[0053] Accordingly, in the present embodiment, several heating air lines 36 are provided. However, in embodiments not specifically illustrated, fewer or more heating air lines than those shown in the figure may, of course, be provided—depending on the requirements of the treatment system 10.

[0054] In this case, the heating device 22 thus heats both exhaust air and recirculated air. However, in modifications not specifically shown, the heating device or a heating device can also generate heated air using only exhaust air or only recirculated air.

[0055] In addition to the above-mentioned embodiments, the fresh air line 34 is directly connected to one or more of the recirculation lines 38 in embodiments not specifically shown. By introducing fresh air into the process air circuit, the content of solvent-containing pollutants can generally be reduced.

[0056] In the drying room 17 itself, the heated air introduced into it is circulated as recirculating air in order to ensure optimal heat transfer to the workpieces 12.

[0057] The process air system 21 further comprises a plurality of fans 40, of which only one is identified by a reference numeral for illustrative purposes. The fans 40 are distributed within the process air system 21. The fans 40, on the one hand, discharge exhaust air from the drying room 17, and, on the other hand, convey fresh air through the fresh air heat exchanger 28 and recirculated air through the recirculated air heat exchanger 32.

[0058] A control device 42 is provided, which is configured to control at least three process parameters interdependently. The process parameters controlled in this way are selected from the following group of process parameters: the exhaust air flow, the heated air flow, the fresh air flow, the recirculated air flow, the heating power of the heating device 22, and the conveying speed of the workpieces 12.

[0059] In the present treatment system 10, all possible combinations of interdependently controllable process parameters can of course be implemented. In particular, when different workpiece types are treated in the treatment system 10, it is advantageous to control, for example, at least the conveying speed of the transport carriages 20, the heating output of the heating device 22, and the amount of circulating air interdependently. This allows for particularly flexible responses to a wide variety of situations that may arise within the drying chamber 17, e.g., different proportions of workpieces 12 of different workpiece types. For example, the conveying speed of the transport carriages 20 can be increased or decreased, which in turn requires an adjustment of the amount of circulating air fed out of and back into the drying chamber, as well as an adjustment of the heating output of the heating device 22.However, this specific example is only one of many that can be implemented using the control device depending on the situation.

[0060] In further embodiments not specifically illustrated, four, five, or all six of the above-mentioned process parameters can be controlled interdependently. Interdependent control is understood as the automatic adjustment of the other interdependently controlled process parameters when one process parameter is changed by the control device 42.

[0061] In this case, the interdependently controllable process parameters are indirectly described and / or derived from each other by means of at least one plant-specific characteristic curve or a multidimensional plant-specific characteristic map through the other interdependently controllable process parameters. In the case of a plant-specific characteristic map, this means that one process parameter can always be used to determine the at least two other interdependently controllable process parameters, for example, by conversion or by optical reading from the plant-specific characteristic map.

[0062] In practice, such plant-specific characteristic maps are usually created by intensive calibration of the treatment plant 10 before commissioning and, due to changing conditions, also at the commissioning site.

[0063] In the present case, the control device 42 is configured such that, in response to the increase or decrease of a first of the process parameters, it controls the increase or decrease of a third of the process parameters depending on a monitored second of the process parameters. Despite the possibility of indirectly describing or deriving the interdependently controllable process parameters from one another using a plant-specific characteristic curve or a plant-specific characteristic map, it is advantageous to monitor the process parameters and thus be able to detect changes in process parameters not only mathematically but in real time and to react accordingly and automatically.

[0064] To monitor the monitored process parameter, the treatment plant 10 has a corresponding sensor system, which is not specifically shown here.

[0065] Of course, several or all interdependently controllable process parameters can also be additionally monitored with appropriate sensors.

[0066] Furthermore, the control device 42 is configured in this case such that, in response to the increase or decrease of a monitored process variable, it controls the at least three interdependently controllable process parameters. Control in this sense can mean that the process parameters are increased or decreased depending on the monitored process variable. The process variables that can be monitored are selected from the following group of process variables: a current actual number or a future target number of workpieces 12 within the dryer housing 16, a specific workpiece type, or a pollutant concentration within the dryer housing 16.

[0067] In a specific example, the above-mentioned, specifically interdependently controlled process parameters are controlled depending on both the current actual number of workpieces 12 within the drying chamber 17 and the number and ratio of specific workpiece types within the drying chamber 17. However, in embodiments not specifically illustrated, any other combination of process variables and process parameters is also possible. All of the aforementioned process variables can also be monitored, and all of the aforementioned process parameters can be controlled interdependently based on the monitored process variables. In this respect, there are no limits to the control device 42.

[0068] With regard to workpiece types, the volume of the different workpiece types and / or their weight can be particularly important. For example, the conveying speed of the workpieces 12, the heating power of the heating device 22, and the air flow rate in the air circulation lines 36 can be controlled depending on the largest and / or heaviest workpiece type as well as the current actual number of workpieces 12 of the corresponding workpiece type within the drying chamber 17.

[0069] From a control engineering perspective, the control process by the control device 42 proceeds as follows: the value of a process variable is determined. The control device 42 then controls a point in the system-specific characteristic map for all interdependently controllable process parameters that corresponds to an optimal state both in terms of energy and process technology, so that as little energy as possible is consumed at all times during the drying process, while achieving a consistently good drying result.

[0070] For this purpose, the control device 42 is communicatively connected to sub-control units 44, each of which controls the blower 40 or the heating device 22. In the present exemplary embodiment, the control device is connected via communication lines 46 to three sub-control units 44.1, 44.2, and 44.3, each of which controls one or more blowers 40 in order to control the amount of fresh air in the fresh air line 34, the amount of recirculated air in the recirculated air lines 38, or the amount of exhaust air in the exhaust air line 24. Likewise, the control device 42 is connected to a sub-control unit 44.4, which controls the heating device 22. The sub-control unit 44.4 controls, on the one hand, the inflow of exhaust air from the drying chamber 17 to the heating device 22, but, on the other hand, also the amount of fuel gas used in a burner of the heating device 22 (not specifically provided with a reference symbol).

[0071] In addition to the aforementioned sub-control units 44.1 to 44.4, the control device 42 is also connected to a further sub-control unit 44.5 via a communication line 46, which in turn can control the conveyor system 18 and communicate with a higher-level system control system, which is not specifically provided with a reference symbol, in this case via a system-wide radio network 48. The sub-control unit 44.5 can thus, in response to instructions from the control unit 42, control, for example, the conveying speed of the transport carriages 20 through the drying room 17. The sub-control unit 44.5 can thus specifically control the residence time of the workpieces 12 in the drying room 17. Likewise, the current actual number of workpieces 12 simultaneously located in the drying room 17 can be monitored.

Claims

[1] Treatment plant for treating workpieces (12), in particular vehicle bodies, with a) a dryer (14) for drying the workpieces (12) with a dryer housing (16) for receiving the workpieces (12), wherein heated heating air can be circulated as recirculating air in the dryer housing (16), wherein the dryer housing (16) is connected to at least one exhaust air line (24) for discharging exhaust air from the dryer housing (16), at least one heating air line (36) for introducing heating air into the dryer housing (16) and at least one recirculating air line (38) for discharging and recirculating air from and into the dryer housing (16); b) a conveyor system (18) for conveying the workpieces (12) through the dryer (14), in particular a conveyor system with a plurality of transport carriages; c) a heating device (22) for heating the exhaust air or circulating air from the dryer housing (16) in order to provide heating air to be introduced into the dryer housing (16) via the heating air line (36); d) a fresh air line (34) connected to the exhaust air line (24), the heating air line (36), the recirculating air line (38) and / or directly to the dryer housing (16) for adding fresh air to the exhaust air, the heating air, the recirculating air and / or the recirculating air, characterized by , that e) a control device (42) is provided which is designed such that it controls at least three process parameters from the following group of process parameters in a mutually dependent manner: the exhaust air quantity, the heated air quantity, the fresh air quantity, the circulating air quantity, the heating power of the heating device (22), the conveying speed of the workpieces (12) through the dryer housing (16). [2] Treatment plant according to claim 1, characterized bythat the control device (42) is arranged such that it controls at least four, five or all six of the process parameters dependently on one another. [3] Treatment plant according to claim 1 or 2, characterized by that the control device (42) is set up in such a way that it indirectly describes and / or derives the mutually dependently controllable process parameters from each other by means of at least one plant-specific characteristic curve or a multi-dimensional plant-specific characteristic field through the respective other mutually dependently controllable process parameters. [4] Treatment plant according to one of the preceding claims, characterized by that the control device (42) is designed such that it controls the increase or decrease of at least a third of the process parameters in response to the increase or decrease of a first of the process parameters depending on a monitored second of the process parameters. [5] Treatment plant according to one of the preceding claims, characterized by that the control device (42) is designed such that, in response to the increase or decrease of a monitored process variable, it controls, in particular increases or decreases, the at least three mutually dependently controllable process parameters. [6] Treatment plant according to claim 5, characterized by that the monitored process variable is a process variable from the following group of process variables: a current actual number or a future target number of workpieces (12) within the dryer housing (16), a specific workpiece type, in particular a largest and / or heaviest workpiece type in terms of volume and / or weight, a pollutant concentration within the dryer housing (16). [7] Treatment plant according to claim 4, characterized bythat the control device (42) is designed such that, in addition to the increase or decrease of the second or third of the process parameters, it controls the increase or decrease of a fourth, fifth or sixth of the process parameters. [8] Treatment plant according to claim 7 with reference to one of claims 3 or 4, characterized by that the control device (42) is designed such that it controls the increase or decrease of the fourth, fifth or sixth of the process parameters depending on the plant-specific characteristic curve or the multi-dimensional characteristic field. [9] Method for operating a treatment plant (10) for treating workpieces (12), in particular vehicle bodies, comprising the following steps: a) drying the workpieces (12) with a dryer (14) having a dryer housing (16) in which the workpieces are accommodated, wherein heated heating air is circulated as circulating air in the dryer housing (16), wherein the dryer housing (16) is connected to at least one exhaust air line (24) for discharging exhaust air from the dryer housing (16), at least one heating air line (36) for introducing heating air into the dryer housing (16) and at least one recirculating air line (38) for discharging and re-introducing circulating air from and into the dryer housing (16); b) conveying the workpieces (12) through the dryer (14) with a conveying system (18), in particular with a conveying system having a plurality of transport carriages; c) heating the exhaust air or recirculating air from the dryer housing (16) with a heating device (22) in order to provide heating air to be introduced into the dryer housing via the heating air line (36); d) adding fresh air to the exhaust air, the heating air, the recirculating air and / or the recirculating air via a fresh air duct (34) connected to the exhaust air duct (24), the heating air duct (36), the recirculating air duct (38) and / or directly to the dryer housing (16); characterized by e) Controlling by means of a control device (42) at least three process parameters from the following group of process parameters in dependence on one another: the exhaust air quantity, the heated air quantity, the fresh air quantity, the circulating air quantity, the heating power of the heating device (22), the conveying speed of the workpieces (12) through the dryer housing (16). [10] Method according to claim 9, characterized by that at least four, five or all six of the process parameters are controlled interdependently by means of the control device (42). [11] Method according to claim 9 or 10, characterized bythat the interdependently controlled process parameters are indirectly described and / or derived from one another by means of at least one plant-specific characteristic curve or a multi-dimensional plant-specific characteristic map by the other interdependently controlled process parameters. [12] Method according to one of claims 9 to 11, characterized by that the control device (42) controls the increase or decrease of at least a third of the process parameters in response to the increase or decrease of a first of the process parameters depending on a monitored second of the process parameters. [13] Method according to one of claims 9 to 12, characterized by that the control device (42) controls, in particular increases or decreases, the at least three interdependent process parameters in response to the increase or decrease of a monitored process variable. [14] Method according to claim 13, characterized by that the monitored process variable is a process variable from the following group of process variables: a current actual number or a future target number of workpieces (12) within the dryer housing (16), a specific workpiece type, in particular a largest and / or heaviest workpiece type in terms of volume and / or weight, a pollutant concentration within the dryer housing (16). [15] Method according to claim 12, characterized by that the control device (42) controls the increase or decrease of a fourth or fifth of the process parameters in addition to the increase or decrease of the second or third of the process parameters. [16] Method according to claim 15 with reference to one of claims 11 or 12, characterized bythat the control device (42) controls the increase or decrease of the fourth or fifth process parameter depending on the at least one plant-specific characteristic curve or the multi-dimensional characteristic field.

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