Treatment system for treating workpieces

Abstract

The present invention relates to a treatment plant (100) for treating workpieces (102), in particular vehicle bodies (104), wherein the treatment plant (100) comprises the following: - at least one treatment tank (106), in particular at least one immersion tank, for treating the workpieces (102) with at least one treatment fluid, and - at least one conveyor system (108) for conveying the workpieces (102), each of which is arranged on a workpiece carrier (132), wherein the conveyor system (108) comprises: - at least one roller conveyor device (130) for conveying the workpieces (102) in a transfer conveying direction (114); and - at least one lifting conveyor device (120, 122), preferably at least two lifting conveyor devices (120, 122), which can be individually moved laterally along the at least one treatment tank (106) in the transfer conveying direction (114), wherein the at least one lifting conveyor device (120, 122) comprises at least one lifting arm (126) which can be individually moved in a lifting direction (128) and is designed to at least partially receive a workpiece carrier (132) and / or a workpiece (102).

Description

The present invention relates to a treatment system for treating workpieces, in particular vehicle bodies.It is known in practice that conveyor systems for cathodic dip coating (CDL) or pretreatment (VBH) of vehicle bodies, for example, are generally designed as a line conveyor system, in which the process steps take place continuously or in cycles in the longitudinal direction of the conveyed vehicle body.Above all in clocked installations there are restrictions with regard to the throughput capacity, which are usually attributable to the structure of the conveying installation, in particular to the transfer between the processes of the vehicle bodies to be treated which has hitherto been required.The transfer of the vehicle bodies in the region of the respective treatment process inlet is dependent on the main conveyor device which is set up. In this regard, on the one hand, roller conveying devices are known which use transport carriages, also called "skids", as workpiece carriers, i.e. as carriers for the vehicle bodies. On the other hand, chain conveying devices are used which use cross bars, also called "cross bars", as carriers for the vehicle bodies. The vehicle bodies are thus conveyed to the actual treatment process either by means of a roller conveyor device or by means of a chain conveyor device, in order to then be transferred to the process conveyor device in the region of the corresponding process inlet.The main conveying device can itself be designed as a roller conveying device or chain conveying device or the main conveying device can comprise a transfer device which is designed as a roller conveying device or chain conveying device. The transfer device is then in turn movable or movable along a main conveying direction, wherein the transfer conveying direction then preferably runs transversely, in particular perpendicularly, to the main conveying direction. In the event that the workpieces are conveyed into the treatment process by the main conveying device and / or are conveyed out of the latter, the transfer conveying direction and the main conveying direction preferably coincide.The process conveying device may be, for example, a reciprocating conveying device, a rotary conveying device, or a modification thereof.The actual transfer of the vehicle bodies into the treatment process can take place in various ways. On the one hand, the vehicle body can be taken over by a vertically immovable element of the main conveying device, wherein the body remains statically on the transfer device or the main conveying device on the skid or on the cross member and is taken over by raising or raising the process conveying device.On the other hand, the transfer can also take place from a vertically movable element of the main conveying device. In this case, the corresponding element of the transfer device or of the main conveying device is raised or lowered in order to transfer the vehicle body mounted on a skid or a cross member to the process conveying device.This transfer process has hitherto generally been located before the process, i.e. in the case of the CTL in front of the process basin or the immersion basin, and takes a certain time, as a result of which the throughput of the vehicle bodies to be treated is limited, since the transfers require a stop-and-go operation or interrupt the conveying flow. In addition, it has been technically necessary up to now to spatially separate the transfer / take-over area and the treatment process area and accordingly also to provide the necessary space, wherein a transfer area is usually provided before and after the process area.The monitoring of the transfer process and of the actual treatment process is furthermore generally based on digitally switching sensors, which can be interconnected to form one or more monitoring functions in combination with other digitally switching sensors. In other words, the monitoring functions used have hitherto been carried out on purely sensory signals, wherein there are defined switching thresholds and triggering trigger points for the activation of monitoring functions in the case of digitally switching sensors. Consequently, firstly changes in a variable to be monitored below the switching thresholds are not detected and secondly no anomalies in the movement profile can be detected.The object of the present invention is therefore to provide a treatment system with which more efficient workpiece treatment is possible.This object is achieved according to the invention by a treatment plant having the features according to claim 1.The treatment system serves for the treatment of workpieces. The treatment plant is preferably a paint shop for vehicle bodies.According to a first aspect of the invention, the treatment plant comprises the following:at least one treatment basin, in particular at least one immersion basin, for treating the workpieces with at least one treatment fluid, andat least one conveying system for conveying the workpieces, which are each arranged on a workpiece carrier, wherein the conveying system comprises the following:at least one main conveying device for conveying the workpieces in a main conveying direction and / or in a transfer conveying direction; andat least one lifting conveyor device, preferably at least two lifting conveyor devices, which can be individually moved laterally of the at least one treatment basin along the latter in the main conveying direction and / or transfer conveying direction,wherein the at least one lifting conveyor device comprises at least one lifting arm which is individually movable in a lifting direction and is configured to at least partially receive a workpiece carrier and / or a workpiece.According to the first aspect, the present invention is based on the basic idea that, when a workpiece is transferred into a treatment process and when the workpiece is moved through the treatment basin filled with treatment fluid, certain monitoring functions must be provided, which ensure the required precision in the coordination of the components of the conveyor system even at high conveying speeds and additionally ensure a high quality of the treated workpieces. The latter is achieved in particular by protecting the workpieces against dropping, colliding with parts of the treatment plant and / or against deformation due to mechanical overloading.With respect to the total conveying flow of the workpieces in the treatment plant, main conveying devices are arranged upstream and / or downstream of the treatment processes, i.e. of the treatment basins, whereas lifting conveying devices are assigned to a treatment process, i.e. a treatment basin.Preferably, two lifting conveyor devices are provided per treatment basin, wherein these are preferably designed as lifting towers.In the case where only one lifting conveyor device is used, it is conceivable that this one lifting conveyor device comprises at least two lifting arms which are connected to one another, for example, via a transverse beam or the like which is mounted in a rotating manner and can be moved in the lifting direction, in order to enable a transfer between the main conveyor device and the lifting conveyor device.The lifting conveyor devices assigned to a treatment basin have the task of, on the one hand, accepting the workpiece to be treated for the treatment process or releasing the treated workpiece from the treatment process and, on the other hand, bringing the workpiece to be treated into one or more treatment positions in the region of the corresponding treatment process, in particular lowering and / or raising it into the treatment basin filled with treatment fluid.The main conveying direction and the transfer conveying direction are preferably aligned horizontally, whereas the lifting direction of the lifting conveying devices is preferably aligned vertically.Preferably, the lifting conveyor devices are moved, i.e. linearly moved, along a rail element or along a predetermined straight path.By means of the lifting arms, the workpiece and / or a workpiece carrier which carries the workpiece is picked up by the main conveying device, i.e. in particular docked and raised, and / or deposited on the main conveying device, i.e. lowered and docked.The terms "docking" and "docking" are to be understood in the broadest sense in this description and the appended claims as the establishment of a contact and the removal of a contact, respectively. The workpiece carriers are preferably locked on the lifting arms after being received thereon, so that the workpiece carrier with the workpiece arranged thereon remains securely connected to the lifting arms for the duration of the treatment.The term "individually movable" is to be understood in this description and the appended claims such that in treatment installations with more than one lifting conveyor device and / or more than one lifting arm each lifting conveyor device or each lifting arm can be moved independently of the other lifting conveyor devices or lifting arms, wherein a synchronous or coupled movement of the lifting conveyor devices or lifting arms is not to be excluded thereby.It should be understood that the main conveying direction, the transfer conveying direction and the lifting direction essentially represent axis profiles along which movements in both directions are possible, whereby it should be at the same time made clear that the movement processes or movement sequences described in this description and the appended claims are preferably also reversible.Consequently, a workpiece can be conveyed into a treatment process by being transferred from a main conveying device to the lifting conveying devices, and the workpiece can also be conveyed out of a treatment process again by being transferred from the lifting conveying devices to the original or a further main conveying device.Preferably, the two lifting conveyors are arranged consecutively along the main conveying direction or along the transfer conveying direction.Thus, the workpiece and / or the workpiece carrier can be picked up by the lifting conveyor devices at at least two sections in the corresponding conveying direction. As a result, the lifting conveyor devices can be moved along to receive the respective section of the workpiece or of the workpiece carrier, aligned optimally and optionally corrected individually in their position.It can be advantageous if the conveying system is configured to transfer a workpiece arranged on a workpiece carrier between the at least one main conveying device and the at least one lifting conveying device.It can furthermore be advantageous if the workpieces can be brought by means of the at least one lifting conveyor device into at least one treatment position, in particular at least one immersion position, in the at least one treatment basin.In a further embodiment of the invention, it can be provided that the at least one lifting arm is L-shaped or U-shaped.The lifting conveyor devices can preferably be designed as vertically oriented columns or towers. In combination with lifting arms of L-shaped design, which are connected at the upper end of their L-shape to the respective lifting conveyor device, the advantage results that a picked-up workpiece can be discharged below the horizontal displacement plane of the lifting conveyor devices, i.e. the plane of the track guide of the lifting conveyor devices, when the lifting arms are displaced downward along the lifting direction. Accordingly, the workpiece can be lowered into a dipping basin of a KTL or VBH, which is arranged essentially below the lifting conveyor devices.Lifting arms of U-shaped design are preferably used when in each case two lifting conveying devices are arranged opposite one another with respect to the conveying direction, i.e. opposite one another on both sides of a treatment process region, wherein the upper ends of the U-shape of a lifting arm are movably mounted on in each case one lifting conveying device and the workpiece and / or the workpiece carrier are accordingly received in the depression of the U-shape.In a further embodiment of the invention, it can be provided that the workpiece carriers are designed as cross members and / or skids.It can furthermore be provided that a transfer position of the at least one lifting arm can be adapted to a transfer movement of a workpiece to be transferred.The transfer position is preferably the position in which the lifting arms docks onto the workpiece or the workpiece carrier and lifts the latter from the main conveying device. In order to achieve a suitable transfer position, i.e. a position which causes a very slight interruption of the conveying flow, the lifting arms must be moved in at least two directions which are preferably oriented perpendicular to one another, such as the main conveying direction or transfer conveying direction and the lifting direction. In other words, the transfer position of a lifting arm is adapted, in particular continuously adapted, by the displacement of the lifting conveyor device in the main conveying direction or transfer conveying direction and the displacement of the associated lifting arm in the lifting direction.It can be advantageous if the at least one lifting conveyor device and / or the at least one lifting arm can be moved together with a workpiece to be transferred for at least approximately uninterrupted transfer of the same.The synchronization of the movement of the lifting conveyor devices with the movement of the workpiece in the conveying direction, i.e. the main conveying direction or the transfer conveying direction, enables the smallest possible interruption of the conveying flow, for which purpose the lifting conveyor devices must be movable together with the conveying movement of the workpiece.In a further embodiment of the invention, it can be provided that the conveying system comprises at least one control and / or regulating device, by means of which the transfer of a workpiece between the at least one main conveying device and the at least one lifting conveying device and / or the movement of the workpiece to be treated in the at least one treatment basin can be controlled and / or regulated.By coordinating the movement or the current position of the main conveying device and the lifting conveying devices, correction movements and / or waiting times are preferably avoided and the conveying flow is interrupted as little as possible.It can furthermore be advantageous if the treatment system comprises at least one radar measuring device and / or at least one laser measuring device for detecting the workpiece carrier position and / or the workpiece position, in particular during the transfer of a workpiece between the at least one lifting conveyor device and the main conveyor device.When conveying the workpiece to be treated into the treatment process or when conveying the treated workpiece out of the treatment process, i.e. during the transfer process of the workpiece between the main conveying device and the two lifting conveying devices, the transfer position must preferably be present continuously with a high precision on account of the prevailing conveying speed.It should be taken into account here that the main conveying device is preferably designed as a roller conveying device or comprises such a device, in particular for transfer. An indirect detection of the workpiece position via the drive rollers of the roller conveying device is, however, too inaccurate due to the slip.A classic detection method for detecting the workpiece carrier by digital sensors also seems unsuitable, since, as explained, the digital sensors switch only after a limit value or threshold value has been reached. In addition, digital sensors generally do not have sufficient space at the usual measurement points of a workpiece carrier.Therefore, the workpiece carrier position and / or the workpiece position, preferably from the rear side of the workpiece carrier or of the workpiece, is measured with at least one radar measuring device and / or at least one laser measuring device, both of which have a sufficiently high measurement accuracy and sufficiently high range.The rear side of the workpiece carrier or of the workpiece is preferably understood to be the side which is directed away from the treatment basin during the transfer into the treatment process. Accordingly, the front side is the side which points to the treatment basin during the transfer into the treatment process.The measuring devices can be part of the conveying installation. Preferably, the measuring devices are arranged on the main conveying device or the transfer device. An arrangement of the one or more measuring devices on the main conveying device or the transfer device is to be considered as less expensive overall.However, it is also conceivable that the measuring devices are arranged outside the conveying installation, i.e. the measuring devices are arranged in a stationary manner in the treatment installation and are not moved together with a component of the conveying installation.A radar measuring device and a laser measuring device are preferably used for position detection, whereby the strengths and weaknesses exhibited by both methods under different ambient conditions are mutually compensated. Nevertheless, it is conceivable that other devices based on a different measuring method can also be used.In real operation of the treatment system, the conveying system is in moist, warm and possibly noble atmosphere, so that a secured measured value of the workpiece carrier position or of the workpiece position may not be ensured at any time during the transfer. Therefore, the measured values of the two different measuring methods, i.e. the laser measured value and the radar measured value, are compared for plausibility checking the actual measured value.Alternatively or additionally, further sensor systems can be provided in the treatment system, such as, for example, measuring devices which monitor the slip of the individual workpiece carrier. A workpiece carrier can also clamp or even plug in the main conveying device, which can also be measured and / or monitored. It is therefore particularly favorable if the equipped sensor system monitors a constant and continuous movement of the workpiece carriers.It can furthermore be advantageous if the conveying system comprises at least one distance sensor, in particular at least one inductive distance sensor, for detecting the distance between the at least one main conveying device and a workpiece carrier and / or a workpiece, in particular during the transfer of a workpiece between the at least one lifting conveying device and the main conveying device.The transfer of the workpiece carrier with the workpiece to be treated arranged thereon by means of the lifting arms of the lifting conveyor devices is effected by the superposition of two movement sequences: a horizontal conveying of the workpiece carrier by the main conveyor device or the transfer device which is comprised by the main conveyor device, and a vertical conveying in the lifting direction by the upward lifting movement of the lifting arms along the respective lifting conveyor device.During the threading of the lifting arms into the receiving hoppers on the workpiece carrier, inaccuracies can lead to a short lifting of the workpiece carrier from the main conveying device before the workpiece carrier slides over the hopper slopes of the receiving sections of the lifting arms as a result of gravity into the final position in which the workpiece carrier is preferably locked.This brief lifting of the workpiece carrier during the threading movement is preferably detected by at least one distance sensor, in particular an inductive distance sensor, which can thereby provide a measure for the threading accuracy.It is conceivable that the determined threading accuracy is matched to the position measurement values of the laser measurement and radar measurement device. All three values provide a quality of the transfer precision.If the distance measured by the at least one distance sensor exceeds a predetermined threshold value or limit value, a warning and / or fault signal is preferably output or generated.In a further embodiment of the invention, it can be provided that each lifting conveyor device comprises at least one acceleration sensor for monitoring the conveying movement.Preferably, for each workpiece treatment, a driving program of the lifting conveyors is predetermined or measured, which program comprises a specific movement profile and / or acceleration profile of the lifting conveyors along the treatment basin.During the actual treatment of a workpiece, the current acceleration profile, which is detected by means of the at least one acceleration sensor per lifting conveyor device, is matched to the predetermined acceleration profile in order to detect anomalies from which, for example, exceeding limit values or tolerance thresholds can be predicted.In the case of detected or determined anomalies, a warning or fault signal is preferably output or generated.It can be provided that the maximum acceleration of the lifting conveyor devices is defined overall or is individually predefined for the different types of workpieces.It can furthermore preferably be provided that at least one, preferably all, lifting conveyor devices comprise at least one vibration sensor for monitoring a treatment vibration profile.Similarly to the acceleration sensors, a typical vibration profile is preferably determined or measured for each lifting conveyor device, which is used as a reference profile for the vibration profile measured during the treatment in order to detect anomalies from which, for example, exceeding limit values or tolerance thresholds can be predicted.In the case of detected or determined anomalies, a warning or fault signal is preferably output or generated.Both in the case of the vibration sensors and in the case of the acceleration sensors, it may be advantageous to make the abnormality detection dependent on the type of workpiece transported or conveyed, i.e. in particular the vehicle body type, since the treatment installation is also suitable for treating a wide variety of body shapes and therefore also for driving along different travel profiles.For example, different vibration and / or acceleration patterns can also result from different workpiece weights or body weights. Different vibration and / or acceleration patterns are also conceivable when different, body-specific driving curves are present.It can furthermore be advantageous if the at least one lifting conveyor device is configured to prevent a collision between the workpiece to be treated and the at least one treatment basin.During the treatment process, the workpiece moves through the treatment basin on the basis of a predefined movement curve. The workpiece moves within a predetermined basin geometry.The contour and position data of the workpiece determined by the dimensions of the workpiece to be treated and by the movement curve are matched with the basin geometry in a software-assisted manner in order to avoid a collision of the workpiece with the treatment basin.In other words, the movement of the workpiece within the treatment basin is limited by geometric calculation, so that the movement of the workpiece stops in time before it touches the basin wall.As already in the case of vibration and / or acceleration monitoring, different geometric calculations can also result on account of different body types.In a further embodiment of the invention, it can be provided that the at least one lifting conveyor device is configured to detect an unlocking of the picked workpiece carrier and / or of the workpiece to be treated during the treatment in the at least one treatment basin.By an unfavourable concatenation of events, it cannot be completely ruled out that the workpiece to be treated is released from the locking of the lifting arms during the treatment in the treatment basin.In order to detect this and to be able to take appropriate countermeasures for protecting the workpiece, a locking monitoring system can be provided, for example, which can be provided in particular by locking sensors on the lifting arms.Alternatively or additionally, a torque monitoring device can also be provided, which monitors the torque about a transverse axis of the workpiece, which is oriented transversely, preferably perpendicularly, to the movement axis of the lifting conveyor devices along the treatment basin.It can furthermore be advantageous if the speed and / or the acceleration of the workpiece can be limited for at least one direction of movement during the treatment.As a result of the movement of the workpiece by the treatment fluid in the treatment basin, forces act on the workpiece, which likewise increase with increasing speed and / or acceleration. It is therefore advantageous if the forces are limited to the workpiece to be treated, which can preferably be realized with software assistance on the basis of virtual workpiece positions.In this case, it is possible to distinguish between limit values for speeds of the workpiece to be treated outside the treatment basin, i.e. outside the treatment fluid, and inside the treatment basin. The same applies to the acceleration or the rotation of the workpiece.In a further embodiment of the invention, it can be provided that the at least one main conveying device comprises at least one transfer device for transferring and / or accepting workpieces along the main conveying direction and / or along the transfer conveying direction.The transfer device itself is preferably movable in or on the main conveying device along the main conveying direction.It can be advantageous if the main conveying direction and the transfer conveying direction are oriented at least approximately perpendicular to one another.However, it is also conceivable that the main conveying direction and the transfer conveying direction are aligned at least approximately parallel to one another, as a result of which a workpiece is first conveyed along the main conveying direction and, when an end position of the main conveying device is reached, is conveyed further by the transfer device in the same direction, i.e. in an extension of the main conveying direction.The alignment of the main conveying direction and the transfer conveying direction is substantially determined by the circumstances at the installation location of the conveying installation.It can furthermore be provided that the main conveying device is a transverse conveying device, by means of which the workpieces can be conveyed in a transverse orientation, wherein the workpieces are oriented in the transverse orientation such that a longitudinal direction, in particular a longitudinal axis, of the workpieces is oriented transversely, in particular at least approximately perpendicularly, to the main conveying direction and / or at least approximately horizontally.As a result, the workpiece can be transferred from the transfer device in its longitudinal direction to the lifting conveyors, as a result of which as a rule more path or distance is available for the transfer movement and the workpiece is held more stably on the lifting conveyors, provided that the longitudinal extent of the workpiece is greater than the transverse extent.It is advantageous in particular if the transfer device is a chain conveying device or a roller conveying device or if the transfer device comprises a chain conveying device and / or a roller conveying device.The object is furthermore achieved according to the invention by a method for treating workpieces.The method serves in particular for the treatment of vehicle bodies, wherein these are treated with at least one treatment fluid in at least one treatment basin of a treatment plant.The vehicle bodies are preferably treated with a dip paint in a dip basin of a paint shop.In principle, the treatment method would also be suitable for VBH. Instead of dip tanks with dip paint, different VBH tanks would be used which are generally filled with VBH-specific fluids.The method comprises the following steps:transferring a workpiece from at least one main conveyor device to at least one lifting conveyor device;moving the at least one lifting conveyor device together with the workpiece to be transferred as soon as the workpiece and / or a workpiece carrier on which the workpiece is arranged has reached an initial position for the transfer;receiving the workpiece to be transferred and / or the workpiece carrier during the movement by means of at least one lifting arm of the at least one lifting conveyor device; andtransferring the workpiece into at least one treatment position by means of the at least two lifting conveyor devices, wherein the received workpiece is lowered in particular into at least one immersion position.Since the treatment installation is preferably suitable for conveying and treating different types of workpiece or vehicle body, in practice the corresponding type of workpiece or vehicle body is determined before the transfer of the workpieces to the lifting conveyor devices and the appropriate dive curve is selected therefrom.The workpiece or vehicle body type can be determined by many detection methods in front, of which only a few are listed in the following by way of example:RFID data carriers or the like on the workpiece carrier or on the workpiece; and / orlight barriers; and / orWorkpiece number coding by sheets or plates on the workpiece carrier.Furthermore, it can be provided that during the transfer of a workpiece to be treated from the at least one main conveyor device to the at least one lifting conveyor device a) the workpiece position and / or the workpiece carrier position is detected by means of at least one radar measuring device and / or at least one laser measuring device; and / or b) the distance between the main conveyor device and the workpiece and / or the workpiece carrier is detected by means of at least one distance sensor, in particular at least one inductive distance sensor.In a further embodiment of the invention, it can be provided that during the treatment of the workpiece a) the conveying movement of the at least one lifting conveyor device is monitored in each case by means of at least one acceleration sensor; and / or b) a vibration profile of at least one, preferably all, lifting conveyor devices is monitored by means of at least one vibration sensor; and / or c) the movement path of the workpiece to be treated is monitored in order to avoid collision between the workpiece to be treated and the at least one treatment basin; and / or d) the locking of the workpiece to be treated and / or of the workpiece carrier on the at least one lifting arm is monitored; and / or e) the torque of the workpiece to be treated about a transverse axis is monitored; and / or f) the speed and / or the acceleration of the workpiece is limited for at least one movement direction.In particular, the above monitoring options a), b), c), e) and f) may be different depending on the type of workpiece.The workpiece can either be picked up by a main conveying device or a transfer device by means of the at least one lifting conveying device or deposited on a main conveying device or a transfer device by means of the at least one lifting conveying device. Accordingly, the picking is preferably to be understood as a transfer and the depositing is preferably to be understood as a transfer.In a further embodiment of the invention, it can be provided that two lifting conveyor devices, which each have a lifting arm, are arranged successively along the main conveying direction or along the transfer conveying direction, wherein only the lifting conveyor device leading in the conveying direction is moved together with the workpiece and receives a front portion of the workpiece and / or of the workpiece carrier with the lifting arm, and wherein then the lifting conveyor device following in the conveying direction is moved together with the workpiece and receives a rear portion of the workpiece and / or of the workpiece carrier with the lifting arm.The receiving movement of the lifting arms takes place substantially in the lifting direction.In a further embodiment of the invention, it can be provided that two lifting conveyor devices, which each have a lifting arm, are arranged successively at an at least approximately constant distance from one another along the main conveying direction or along the transfer conveying direction, wherein both lifting conveyor devices are moved together with the workpiece after reaching the initial position and receive a front and a rear section of the workpiece and / or of the workpiece carrier at least approximately simultaneously.It should be understood that the distance between the lifting conveyors is either already taken up at the beginning of the transfer or is taken up dynamically during the conveying movement of the workpiece and the synchronization of the movement of the lifting conveyors and the workpiece associated therewith.Preferably, the lifting conveyor device and the workpiece move in the conveying direction at least approximately without interruptions, i.e. in particular approximately continuously, during the entire reception of the workpiece. The docking of the lifting arms to the respective section of the workpiece and / or of the workpiece carrier is here minimal in time, since in particular the movement of the lifting conveyor device and of the workpiece are synchronized.The method preferably has individual or several of the features and / or advantages described in connection with the treatment plant. Preferably, the treatment plant also has individual or several of the features and / or advantages described in connection with the method.According to a second aspect of the invention, the treatment plant comprises the following:at least one treatment basin, in particular at least one immersion basin, for treating the workpieces with at least one treatment fluid, andat least one conveying system for conveying the workpieces, which are each arranged on a workpiece carrier, wherein the conveying system comprises the following:at least one roller conveyor device for conveying the workpieces in a transfer conveying direction; andat least one lifting conveyor device, preferably at least two lifting conveyor devices, which can be individually moved laterally of the at least one treatment basin along the latter in the transfer conveying direction,wherein the at least one lifting conveyor device comprises at least one lifting arm which is individually movable in a lifting direction and is configured to at least partially receive a workpiece carrier and / or a workpiece.It can furthermore be provided that the workpiece carrier comprises the following:two longitudinal beams which are arranged at a distance from one another and are aligned parallel to one another;four bell-shaped contact devices; andat least one mounting strut for mounting the workpiece on the workpiece carrier,wherein two bell-shaped contact devices are arranged on a longitudinal beam.According to the second aspect, the present invention is based on the basic idea that each workpiece carrier is designed as a skid and comprises two pairs of oppositely arranged bell-shaped contact devices. One of these pairs is arranged close to a front end of the skid in order to allow a steep penetration of the workpiece after the transfer of the skid from the roller conveyor device to the lifting conveyor devices. The bell-shaped contact devices also function according to the principle of a submerged bell. This means that the bell-shaped contact devices are only partially filled with treatment fluid when the skid is immersed in the treatment basin and a dry region remains in which the free end of an electrically conductive contact element contacts the inner surface of the bell-shaped contact device in order to allow an electric current flow to the workpiece which forms the cathode in a CTL. The contact element is part of an associated locking device, which is likewise arranged in pairs on the lifting arms. In addition, the locking devices of the lifting arms and the bell-shaped contact devices cooperate in such a way that, starting from a certain angle of inclination being exceeded, floating of the workpiece in the treatment basin is blocked. The skids are also preferably equipped with a tilting protection element which prevents the workpiece carrier from tilting over with workpiece during the transfer from the roller conveyor device to the two lifting conveyor devices.It can be advantageous if the bell-like contact devices are arranged opposite one another in pairs.It can furthermore be advantageous if the two pairs of mutually opposite, bell-like contact devices are arranged asymmetrically with respect to a longitudinal extent of the two longitudinal beams.As mentioned, the front pair of bell-type contact means, i.e. the pair arranged at the leading end of the workpiece carrier, is arranged as close as possible to the leading end of the workpiece carrier, whereby the entire workpiece carrier does not have to be brought too far into an overhanging or overhanging position until the lifting arm of the leading lifting conveyor device can receive the front pair of bell-type contact means.In a further embodiment of the invention, it can be provided that each bell-shaped contact device has at least one counter element and one bearing journal on an inner side surface.Preferably, each contact device comprises on its inner side face two counter elements which are designed as flat iron.These flat bars are arranged at a distance from one another with respect to the longitudinal extent of the workpiece carrier and together form an axially symmetrical V-shape, the lower end of which is open by the spacing.It can be advantageous if each lifting arm comprises at least one locking device, preferably two locking devices, wherein each locking device is configured to receive and lock a bell-like contact device.In a further embodiment of the invention, it can be provided that each locking device comprises the following:a receiving element, by means of which the bearing pin of a bell-shaped contact device can be received; anda contact element, by means of which an electrically conductive dry contact can be formed within a bell-shaped contact device.The free end of the contact element, which points away from the associated lifting arm, projects into the received bell-shaped contact device and forms a frictional contact with the inner surface of this bell-shaped contact device. The frictional contact ensures that portions of the inner surface which have been covered with the treatment fluid during dip coating and have therefore been coated are freed of the coating as soon as the inclination of the workpiece carrier is changed. This ensures that the electrical current flow to the workpiece can be established and maintained via the contact element.It can be advantageous if the receiving element comprises a blocking element, wherein the blocking element acts on the at least one counter element of the received bell-shaped contact device to prevent the workpiece carrier and / or the workpiece from floating as soon as the workpiece carrier exceeds an angle of inclination in the range from 10 degrees to 15 degrees.A geometric arrangement of the elements of the locking device and of the bell-like contact devices which interact against floating and which, for mutual locking, must first have overcome a certain angle of inclination of the workpiece carrier facilitates the threading of the bell-like contact devices into the respective locking device during the transfer of the workpiece carrier from the roller conveying devices to the lifting conveying devices.It can furthermore be advantageous if the workpiece carrier comprises a tilting protection element, by means of which tilting over of the workpiece carrier and / or of the workpiece during the transfer from the roller conveyor device to the at least one lifting conveyor device can be prevented.In a further embodiment of the invention, it can be provided that the anti-tilting element is arranged between the longitudinal supports, wherein the roller conveying device has a roller guide with at least one overlapping roller pair, in which the anti-tilting element can be guided.The anti-tipping element is preferably of a sword-like design and has two lateral guide edges on which the overlapping roller pairs of the roller guide, which is preferably arranged at a position adjacent to the treatment basin on the roller conveying device, roll.According to a third aspect of the invention, the treatment plant comprises the following:at least one treatment basin, in particular at least one immersion basin, for treating the workpieces with at least one treatment fluid, andat least one conveying system for conveying the workpieces, which are each arranged on a workpiece carrier, wherein the conveying system comprises the following:at least one transfer device for conveying the workpieces in a transfer conveying direction; andat least one lifting conveyor device, preferably at least two lifting conveyor devices, which can be individually moved laterally of the at least one treatment basin along the latter in the transfer conveying direction,wherein the at least one lifting conveyor device comprises at least one lifting arm which is individually movable in a lifting direction and is configured to at least partially receive a workpiece carrier and / or a workpiece.It can be advantageous if each lifting arm comprises two round support pipes and one round central pipe, wherein the round central pipe is arranged between the two round support pipes with respect to the transfer conveying direction.According to the third aspect, the present invention is based on the basic idea that the lifting arms projecting on one side into the treatment tank in a CTL impair the field lines between the anodes arranged on the inside of the tank and the workpiece as a cathode, whereby the coating quality of the treated workpieces is also influenced. This can be counteracted in that the lifting arms cause as little shading as possible, which can be realized by a reduced and / or at least partially permeable cross section. Nevertheless, a certain rigidity of the lifting arms is required, so that they do not permanently deform as a result of the dynamic load during the workpiece treatment. For this reason, round tubes are preferably used for the lifting arms, the curved surface of which on the one hand less strongly influences the field lines and on the other hand makes it difficult for particles of the treatment fluid to adhere. It has also been found that if three round tubes are arranged in such a way that they form a triangular shape at least in the predominantly vertical section of the lifting arm, with respect to a horizontal cross-sectional plane, sufficient rigidity is achieved and at the same time an acceptable impairment of the field lines is brought about.In a further embodiment of the invention, it can be provided that one or more electrical lines are guided in the central round tube, which are electrically conductively connected to at least one locking device of the lifting arm.It can be advantageous if the cross section of the central round tube is larger than the cross section of the support round tubes.It can furthermore be advantageous if the central round tube and the support round tubes are arranged triangularly in a horizontal cross-sectional plane at least in sections along the lifting arm.Triangular is intended to mean that the central axes of the round tubes preferably span a triangle.In a further embodiment of the invention, it can be provided that the central round tube and the support round tubes are arranged at least in sections spaced apart from one another, wherein at least one intermediate plate is arranged between the round tubes and is connected thereto.The intermediate plate thus fixes the spacing between the round tubes, whereby the rigidity of the lifting arm is increased.It can be advantageous if the lifting arm corresponds at least in sections to an adjoining inner contour of the treatment basin.Since the treatment basin is tapered in order to reduce the required volume and thus to save treatment fluid, preferably in the lower region at least on two opposite sides, it is advantageous if the lifting arms also follow this taper in their shape, so that the complete vertical length of the lifting arms is available during movements in the lifting direction.In a further embodiment of the invention, it can be provided that each lifting arm comprises at least one locking device, preferably two locking devices, for locking a workpiece carrier, wherein each locking device has at least one electrically conductive clamping element.It can be advantageous if each clamping element has a guide, in particular a horizontal guide, for receiving a receiving pin of the workpiece carrier.It can furthermore be advantageous if the open ends of the guides of one lifting arm point in the direction of the other lifting arm, with respect to the transfer conveying direction.Such locking devices are preferably provided for inventory workpiece carriers.By means of the clamping elements and their guides it is possible to lock a workpiece carrier on the lifting arms in that the lifting conveyor devices are moved towards each other as soon as the lateral receiving pins of the workpiece carriers have been threaded into the guides.In a further embodiment of the invention, it can be provided that the transfer device a) is designed as a roller conveyor device and the workpiece carriers are designed as skids; or b) is designed as a chain conveyor device and the workpiece carriers each comprise at least two cross-members.The treatment plants of the three aforementioned aspects of the present invention preferably have individual or a plurality of the features and / or advantages described in connection with the respective other treatment plants.Further features and / or advantages of the invention are the subject matter of the following description and the graphical representation of exemplary embodiments.The figures show: FIG. 1 shows a schematic, perspective illustration of a first embodiment of a treatment system according to the invention at the beginning of a workpiece transfer; FIG. 2 shows a schematic, perspective illustration of the first embodiment from FIG. 1 without workpiece carrier and workpiece; FIG. 3 shows a schematic, perspective illustration of the first embodiment from FIG. 1 during the treatment of the workpiece in the treatment basin; FIG. 4 shows a schematic, perspective illustration of a second embodiment of a roller conveyor device and a skid; FIG. 5 shows a schematic, perspective illustration of a bell-like contact device of the skid from FIG. 4 at the beginning of a coupling with a second embodiment of a locking device of a lifting arm; FIG. 6 shows a schematic, perspective illustration of a bell-like contact device of the skid from FIG. 4 at the end of a coupling to the second embodiment of a locking device of a lifting arm; FIG. 7 shows a schematic vertical sectional illustration of a bell-like contact device of the skid from FIG. 4 in two differently inclined states, wherein the bell-like contact device is locked to the second embodiment of a locking device; FIG. 8 is a schematic vertical sectional view of a bell-type contact device of the skid of FIG. 4, wherein the skid is in a non-inclined state and the bell-type contact device is coupled to the second embodiment of a locking device; FIG. 9 is a schematic vertical sectional view of a bell-type contact device of the skid from FIG. 4, wherein the skid is inclined by approximately 15 degrees and the bell-type contact device is locked to the second embodiment of a locking device; FIG. 10 shows a schematic vertical sectional illustration of a bell-like contact device of the skid from FIG. 4, wherein the skid is at least approximately maximally inclined and the bell-like contact device is locked on the second embodiment of a locking device; FIG. 11 shows a schematic, perspective vertical sectional illustration of a second embodiment of a treatment system with a second embodiment of lifting arms; FIG. 12 shows a schematic vertical partial sectional illustration of the second embodiment from FIG. 11 along the line A-A; FIG. 13 shows a schematic horizontal sectional illustration of the second embodiment along the line B-B from FIG. 12 ; FIG. 14 shows a schematic, perspective side view of a third embodiment of a treatment plant according to the invention with a chain conveying device and a third embodiment of locking devices during the locking of the cross members; FIG. 15 shows a schematic, perspective illustration of the third embodiment from FIG. 14 ; FIG. 16 shows a schematic, perspective side view of a fourth embodiment of a treatment system according to the invention with the second embodiment of a roller conveyor device from FIG. 4 and the third embodiment of the locking devices during the lowering of a conventional skid into the treatment basin; and FIG. 17 shows a schematic, perspective illustration of the fourth embodiment from FIG. 16.Identical or functionally equivalent elements are provided with the same reference numerals in all figures.FIG. 1 shows the start of a transfer process of a first embodiment of a treatment plant designated as a whole as 100.The treatment system 100 serves for treating workpieces 102.In addition, FIG. 2 shows the treatment system 100 from FIG. 1 without the workpiece 102.The workpieces 102 are in particular vehicle bodies 104, wherein the treatment plant 100 is preferably a painting shop for coating vehicle bodies.The treatment plant 100 comprises a treatment basin 106 and a conveying plant 108.The treatment plant 100 enables at least approximately uninterrupted transfer of workpieces 102 into a treatment process or out of a treatment process, i.e. the conveying flow of the workpieces 102 along the treatment plant 100 or within a treatment plant 100 is optimized to the effect that temporal losses due to transfer processes of the workpieces 102 are minimized.The treatment process takes place in the treatment basin 106, which is with a treatment fluid (not shown).The conveying installation 108 comprises a main conveying device 110 for conveying the workpieces 102 in a main conveying direction 112 and a transfer conveying direction 114.The main conveying device 110 is preferably a transverse conveying device 116, by means of which the illustrated vehicle body 104 is conveyed in a transverse orientation in the main conveying direction 112. The transverse orientation is oriented in such a way that the longitudinal axis of the vehicle body 104 runs transversely to the main conveying direction 112 or parallel to the transfer conveying direction 114.The main conveying device 110 comprises a transfer device 118 for transferring and / or accepting the workpieces 102 along the transfer conveying direction 114.The conveying installation 108 further comprises, with respect to the transfer conveying direction 114, a guiding lifting conveying device 120 and a subsequent lifting conveying device 122, which are preferably displaceable independently of one another.The lifting conveyor devices 120, 122 can preferably be moved linearly along a rail element 124.Both lifting conveyor devices 120, 122 each have a lifting arm 126, which are both movable in a lifting direction 128 along the respective lifting conveyor device 120, 122.FIGS. 1 to 3 show an embodiment of the lifting arms 126. Another preferred embodiment of the lift arms 126 is shown in conjunction with Figs. 5-19.The lifting arms 126 are L-shaped.The lifting direction 128 is preferably vertical, while the main conveying direction 112 and the transfer conveying direction 114 are preferably horizontal.The transfer device 118 is a roller conveyor 130 in the embodiment in FIGS. 1 to 3.The workpiece 102 is mounted on a workpiece carrier 132, by means of which it can be conveyed and transferred.The workpiece carrier 132 is in particular a so-called skid 134, i.e. a transport slide.In FIGS. 1 and 2, the roller conveyor device 130 has reached an end position 136 along the main conveying direction 112, from which end position the workpiece 102 can be transferred to the lifting conveyor devices 120, 122.FIG. 3 shows the first embodiment of a treatment system 100 during the treatment of a workpiece 102 in the treatment basin 106.In FIG. 3, the workpiece 102 or the workpiece carrier 132 is completely accommodated by the lifting arms 126 of the lifting conveyor devices 120, 122 and preferably locked to these.The lifting arm 126 of the guiding lifting conveyor device 122 is at least partially lowered in the lifting direction 128, as a result of which the front section of the workpiece 102 to be treated dips into the treatment fluid of the treatment basin 106.For transferring the workpiece between the roller conveyor 130 and the two lifting conveyors 120, 122, the workpiece carrier 132 with the workpiece 102 arranged thereon is brought into a projecting position.During the cantilever movement of the workpiece carrier 126 or of the workpiece 102, a detection device (not shown) determines an initial position of the workpiece carrier 132 and / or of the workpiece 102, from which the guiding lifting conveyor device 120 moves along, preferably synchronously with the workpiece carrier 132 or the workpiece 102.The initial position can be reached, for example, when the workpiece 102 and / or the workpiece carrier 132 contact a stop as a detection device or a detection device designed as a light barrier is triggered. The detection device can also be a proximity switch or comprise a proximity switch.However, it is also possible for the initial position to be a measured workpiece carrier position which was detected by means of a measuring device. In particular, a measuring device as is explained in greater detail below.When the guiding lifting conveyor 120 is moved along, the lifting arm 126 of this lifting conveyor 120 is moved upwards in the lifting direction 128 and receives a front section of the workpiece carrier 132.In this case, in particular, two different sequences are conceivable. In the first sequence of receiving the front section of the workpiece carrier 132, the conveying movement of the workpiece carrier 132 with the workpiece 102 in the transfer conveying direction 114 is interrupted for a short time, so that the lifting arm 126 can receive or dock the front section of the workpiece carrier 132 and lift it out of the roller conveying device 130. Since the lifting arm 126 has already been brought into the correct position along the transfer conveying direction 114 during the movement along, the actual picking takes place in a minimum time interval. In a second case, the conveying movement of the workpiece carrier 132 or of the workpiece 102 is not interrupted, but rather the coordination quality of the movement of the lifting arm 126 in the transfer conveying direction 114 and in the lifting direction 128 is so high that both can be effected in parallel.The front section is received before the workpiece carrier 132 with the workpiece 102 protrudes beyond the roller conveyor 130 to such an extent that it is imminent that it might tip over.The receiving movement of the lifting arm 126 in the lifting direction 128, with which the workpiece carrier 132 with the workpiece 102 is lifted by the roller conveyor 130, is preferably so small that tilting of the workpiece 102 on the workpiece carrier 132 is prevented. In other words, after the front section of the workpiece carrier has been received, the horizontal orientation or orientation of the workpiece 102 is at least approximately maintained.After the front section of the workpiece carrier 132 has been received, the detection device determines a further initial position of the workpiece carrier 132 and / or of the workpiece 102, from which the following lifting conveyor device 122 moves along, preferably synchronously with the workpiece carrier 132 or the workpiece 102.It is conceivable that the introduction or termination of the reception of the front section already initiates the movement of the following lifting conveyor device 122.When the following lifting conveyor device 122 is moved along, the lifting arm 126 of this lifting conveyor device 122 is moved upwards in the lifting direction 128, and in the process receives a rear section of the workpiece carrier 132.The receiving of the rear section of the workpiece carrier 132 is in particular completed before the roller conveyor device 130 has completely conveyed down the workpiece carrier 132, so that the workpiece carrier 132 does not sag with the workpiece 102.After the front and the rear sections of the workpiece carrier 132 have been received, the lifting conveyors 120, 122 move further in the transfer conveying direction 114 via the fluid bath contained in the treatment basin until a starting position for the treatment process is reached.Following the treatment process, the workpiece 102 can be conveyed back to the main conveying device 110 in a correspondingly reversed sequence, wherein it is transferred to the roller conveying device 130 or deposited thereon.However, it is also conceivable that workpiece carriers 132 and workpiece 102 are conveyed further along the transfer conveying direction 114 by means of the lifting conveying devices 120, 122 after the treatment process, in order to then be transferred to a further main conveying device (not shown) in an outlet region of the treatment process, which outlet region is situated opposite an inlet region of the treatment process, wherein the inlet region is that region in which the first transfer from the main conveying device 110 to the lifting conveying devices 120, 122 takes place.The transfer between the main conveying device 110 or transfer device 118 and the lifting conveying devices 120, 122 is controlled and / or regulated by at least one control and / or regulating device (not shown). In this case, the movement or the movement sequence of the main conveying device 110 and the lifting conveying devices 120, 122 must be coordinated with the conveying movement of the workpiece 102 or of the workpiece carrier 132.Furthermore, different values are detected and monitored during the transfer and the treatment, by means of which sufficient precision of the movement sequence is ensured, anomalies in the movement sequence are detected early and a high treatment quality of the workpiece is ensured.For this purpose, the control and / or regulating device preferably comprises one or more sensors and / or one or more measuring devices, wherein the control and / or regulating device preferably operates in a software-assisted manner, such that, for example, desired profiles can be matched to actual profiles in real time.A profile is to be understood in particular as the preferred or ideal temporal profile of a variable to be measured, which has been determined, for example, under ideal boundary conditions of the treatment process.It can be seen in FIGS. 1 to 3 that a radar measuring device 138 and a laser measuring device 140 are arranged on the roller conveyor device 130.Alternatively, the radar measuring device 138 and the laser measuring device 140 can also be arranged outside the conveying installation 108, such as behind the rear of the vehicle body 104 available for transfer.The two measuring devices 138, 140 detect the workpiece carrier position and / or the workpiece position from the rear side thereof according to their arrangement in the embodiment in FIGS. 1 to 3, wherein both measuring devices 138, 140 have a sufficiently high measurement accuracy and sufficiently high range.The redundant measurement setup of two different measurement techniques or measurement methods compensates for the strengths and weaknesses exhibited by both techniques or methods under different ambient conditions.The radar measuring device 138 and the laser measuring device 140 supply precise values with respect to the workpiece carrier position and / or workpiece position, as a result of which a precise transfer can be realized even at high conveying speeds.Furthermore, a distance sensor 142, which is preferably designed as an inductive distance sensor, is arranged on the roller conveying device 130, said distance sensor detecting the distance between the roller conveying device 130 of the main conveying device 110 and the workpiece carrier 132 and / or the workpiece 102. If this monitored distance exceeds a predetermined threshold or limit value, a warning and / or an interfering signal is output or generated, for example.The lifting conveyors 120, 122 further each comprise an acceleration sensor 144, by means of which the acceleration along the rail element 124 can be monitored.The acceleration of both lifting conveyor devices 120, 122, measured along the rail element 124, i.e. along the treatment basin 106, is matched to a predetermined acceleration profile in order to detect anomalies in the acceleration at an early stage and thus to be able to prevent damage from the workpiece to be treated in good time.Here too, it applies that detected anomalies in the acceleration of one or both lifting conveyor devices 120, 122 can cause a warning and / or fault signal.The control and / or regulating device can furthermore be configured to prevent a collision between the workpiece 102 to be treated and the treatment basin 106.During the treatment process, the workpiece 102 moves through the treatment basin 106 on the basis of a predefined movement curve. The workpiece 102 moves within a predetermined basin geometry.The contour and position data of the workpiece determined by the dimensions of the workpiece 102 to be treated and by the movement curve are therefore preferably matched with the basin geometry in a software-assisted manner in order to avoid a collision of the workpiece 102 with the treatment basin 106. In other words, the movement of the workpiece 102 within the treatment basin 106 is limited by geometric calculation, so that the movement of the workpiece 102 stops in time before it touches the basin wall.The lifting arms 126 each preferably have two locking devices 146, which secure the received workpiece carrier 132 to the lifting arms 126 at least for the duration of the immersion in the treatment basin 106.The locking of the locking devices 146 is preferably also monitored in order to be able to identify a tilting down of the workpiece 102 in good time and to take appropriate countermeasures.By means of the locking devices 146, which are only schematically illustrated in FIGS. 1 to 3, not only is the workpiece carrier 132 including the workpiece 102 secured at least temporarily to the lifting arms 126, i.e. in particular prevented from floating during the dip treatment in the treatment tank 106, but the electrical current flow to and through the workpiece 102 is also realized via the locking devices 146, which preferably forms the cathode in the case of cathodic dip coating, whereas the associated anodes are arranged within the treatment tank 106.The interaction between a skid 134 according to the invention and the corresponding locking devices 146 of the lifting arms 126 will be discussed in more detail below.FIG. 4 shows, on the one hand, an exposed transfer device 118 which is designed as a roller conveyor device 130. On the other hand, the workpiece carrier 132 provided for the roller conveyor device 130 is shown, which is designed as a skid 134.The skid 134 comprises on its longitudinal beams 148 four bell-shaped contact devices 150 which are arranged opposite one another in pairs.The bell-type contact devices 150 will be described in detail in connection with FIGS. 5 to 10.In FIG. 4, the left side of the roller conveyor 130 is the side which-when the roller conveyor 130 has been moved into the transfer position-adjoins the treatment basin 106, whereas the right side is the side which points away from the treatment basin.The illustrated skid 134 is also oriented in the same direction, that is to say the left side of the skid 134 in FIG. 4 is the side or the end of the skid 134, which is conveyed first into the treatment region of the treatment basin 106.For convenience, the left side or end of the skid 134 and the roller conveyor, relative to the plane of the drawing in FIG. 4, will be referred to herein as the front side or end, and the opposite side or end will be referred to herein as the rear side or end. This is also consistent because workpieces 102 which are designed as a vehicle body 104 are usually introduced with their front, i.e. with the region of the engine hood, first into the treatment region of the treatment basin 106.It can thus be seen that the front pair of bell-shaped contact means 150 is arranged closer to the front end of the skid 134 than the rear pair with respect to the rear end of the skid 134.Such an asymmetry of the bell-shaped contact devices 150 with respect to the longitudinal axis of the skid 134, which is preferably oriented parallel to the transfer conveying direction 114, has the advantage that the workpiece 102 mounted on the skid 134 and to be treated can be immersed very steeply in the treatment fluid at the beginning of the treatment in the treatment basin 106 and overall a deeper immersion into the treatment basin is possible.In addition, the front pair of bell-like contact devices 150 offers the advantage in an arrangement close to the front end of the skid 134, that the skid 134 does not have to project beyond it until the lifting arm 126 of the guiding lifting conveyor device 120 can receive the skid 134 on the front pair of bell-like contact devices 150. That is, the overhang of the skid 134 beyond the roller conveyor 130 is kept as low as possible during the transfer.As mentioned above, a radar measuring device 138 and a laser measuring device 140 are arranged on the roller conveying device 130 in order to be able to detect the position of the workpiece carrier 132, i.e. of the skid 134, in the transfer conveying direction 114.Furthermore, the skid 134 comprises three cross struts 152, of which at least one cross strut 152 has two measuring plates 154, preferably vertical measuring plates, by means of which the position of the skid 134 can be detected by the radar measuring device 138 and the laser measuring device 140, which are both arranged on the roller conveying device 130, during the transfer between the two lifting conveying devices 120, 122 and the roller conveying device 130.Moreover, the skid 134 preferably comprises four fork lift truck receptacles 156, which are likewise opposite one another in pairs, such that in each case one fork lift truck tine can be guided through an opposite receptacle pair in order to lift, transport and / or deposit the skid 134.The skid 134 illustrated in FIG. 4 furthermore preferably has a tilt protection element 158 which is arranged in a rear section of the skid 134.In the present case, this anti-tilting element 158 is designed in the manner of a tongue and is fastened to the two rear cross struts 152.In the embodiment shown, the anti-tipping element 158 comprises two lateral guide edges 160.The anti-tipping element 158 with its lateral guide edges 160 interacts with a roller guide 162 which is arranged in a front section of the roller conveyor device 130.The roller guide 162 comprises at least one, preferably a plurality of overlapping roller pairs 164 which roll on the lateral guide edges 160 of the anti-tipping element 158, while the anti-tipping element 158 is guided by the roller guide 162. This ensures that, when a projecting position is reached at the end of the transfer process between the roller conveyor 130 and the lifting conveyors 120, 122, the skid 134 together with the workpiece 102 does not tip over in the direction of the treatment basin 106, but preferably maintains an approximately horizontal position until the transfer is completed.The roller conveyor device 130 furthermore comprises a plurality of lateral guide rollers 166 which roll on the lateral outer surfaces of the longitudinal members 148 during the transfer of the skid 134, as a result of which the skid 134 does not yaw about a vertical axis during the transfer and accordingly remains aligned approximately parallel to the transfer conveying direction 144. As a result, the precession of the locking process between the locking devices 146 and the skid 134 is improved.The skid 134 in FIG. 4 further comprises two mounting struts 167, by means of which the connection between the skid 134 and the workpiece 102 is realized.In the following FIGS. 5 to 10, a bell-shaped contact device 150 of a skid 134 is illustrated by way of example in order to explain the process of threading, locking and dry contacting between the skid 134 and the lifting arms 126 of the lifting conveyors 120, 122.The bell-shaped contact device 150 is shown, which is arranged at the front end of the skid 134 and, with respect to the transfer conveying direction 114 into the treatment process, on the right side of the skid 134. Thus, with respect to a vehicle body 104 to be treated, there is shown the bell-type contact means 150 and associated locking means 146 of the lifting arm 126 of the leading lifting conveyor 120 which are located in the vicinity of the wheel house of the right front tyre.The locking device 146 comprises a base 168, via which the locking device 146 is connected to the associated lifting arm 126, an internally arranged receiving element 170 which is of fork-shaped design, and an externally arranged contact element 172 for electrically contacting the inner surface of the bell-like contact device 150.The receiving element 170 comprises two guide prongs 174 and a guide joint 176 arranged therebetween.The guide tines 174 are preferably bent inwardly at their tips 175 by an angle in the range of 10 degrees to 45 degrees with respect to a longitudinal axis of the receiving element 170.On the side of the receiving element 170 which points outwards, i.e. in the direction of the contact element 172, a blocking element 178 is arranged below the guide joint 176.The bell-shaped contact device 150 of the skid 134 shown has a bearing pin 182 and two counter elements 184 on its inwardly facing side surface 180.The counter elements 184 are preferably designed as flat iron and are arranged so that they together form a V-shape, the tip of the V-shape being open at the bottom, as can be seen in FIG. 8.The bell-shaped contact device 150 preferably has a circular shape which is open at least in sections downwards, i.e. facing away from the workpiece 102.The bearing pin 182, which is preferably formed at least in sections in a cylindrical manner, is preferably arranged in the center of the circular side surface 180 of the bell-like contact device 150 and has a counter piece 186 at its opposite, free end, as can be seen in FIG. 4.FIG. 5 shows the beginning of the threading between the skid 134 and the lifting arm 126, i.e. the skid has already been conveyed by the roller conveying device 130 in the transfer conveying direction 114 into a projecting position and the lifting arm 126 of the guiding lifting conveying device 120 has been moved in the lifting direction 128 in the direction of the skid 134.The bearing pin 182 of the bell-shaped contact device 150 is located above the guide joint 176 of the receiving element 170 in this transfer stage.The guide prongs 174 taper in the direction of their respective tip 175, for which reason the guide joint 176 is widened in its upper section, whereby more space is available for the initial threading of the bearing journal 182 into the guide joint 176 in the transfer conveying direction 114.During the threading according to FIG. 5, the contact element 172 reaches at least partially into the volume or the cavity of the bell-shaped contact device 150.FIG. 6 shows the state in which the skid 134 has been completely accommodated by the lifting arm 126. In this state, the journal 182 is located in a lower, narrow portion of the guide groove 176 and a free end 188 of the contact element 172 contacts the inner surface of the bell-shaped contact device 150.By the contact between the free end 188 of the contact element 172 and the inner surface of the bell-shaped contact device 150, an electric current flow from the anodes in the treatment basin 106 to the workpiece 102 as cathode is now possible.The bell-shaped contact device 150 is preferably designed such that treatment fluid at least partially penetrates into the bell-shaped contact device 150 when the skid 134 and the workpiece 102 are immersed in the treatment fluid of the treatment basin 106. However, the geometry of the bell-shaped contact device 150, which preferably functions according to the principle of a submerged bell, ensures that the free end 188 of the contact element 172 is arranged in a drying region 190, i.e. a region without treatment fluid, independently of the angle of inclination of the skid 134. In other words, the region around the free end 188 of the contact element 172 is not flushed by the treatment fluid, even at different angles of inclination of the skid 134, as can be seen in FIG. 7.The angle of inclination is preferably to be understood as the angle between the longitudinal axis of the workpiece carrier 132 or of the skid 134 and a horizontal.The inclined state of the skid 134 on the left in FIG. 7 represents a maximum possible inclination, in which the contact element 172 contacts a front stop 192 on the foot of the bell-like contact device 150.The bell-shaped contact device 150 also has a rear stop 194, which enables the same angle of inclination of the skid 134 only with the opposite sign. However, it is also conceivable that the stops 192, 194 make possible different, maximum possible angles of inclination, based on the amount of the angle of inclination.The angle of inclination of the skid 134 in the left-hand state of FIG. 7 is approximately 60 degrees.In this state, the drying area 190 is greatly reduced, but still sufficient such that the free end 188 of the contact element 172 is not in the treatment fluid.The inclined state of the skid 134 on the right in FIG. 7 represents a smaller inclination than in the left state in which the contact element 172 is located between the front stop 192 and the rear stop 194 of the bell-like contact device 150.The angle of inclination of the skid 134 in the right-hand state is approximately 30 degrees.In this state, the drying area 190 is larger, since only about two-thirds of the volume in the bell-type contact device is filled with fluid.Cathodic dip coating may result in portions of the inner surface of bell contact 150 contacting the treatment fluid during a dip coating operation being coated.However, the frictional contact between the free end 188 of the contact element 172 and the inner surface of the bell-type contact device 150 ensures that no paint adheres permanently to the surface section of the inner surface of the bell-type contact device 150, over which the free end 188 of the contact element 172 rubs by adjusting the angle of inclination of the skid 134.The counterpart 186 at the end of the bearing journal 182, which is designed, for example, in the form of a triangle, preferably interacts with the bent tips 175 of the guide prongs 174, in particular when the skid 134 is transferred back from the treatment process to the roller conveyor 130. This cooperation has the effect that the skid 134 does not tilt in a lateral direction such that a transfer to the roller conveyor device 130 is impeded.FIGS. 8 to 10 show the interaction of the blocking element 178 with the counter elements 184 designed as flat iron, for example at different angles of inclination.FIG. 8 shows the state at the end of the threading, i.e. after the lifting arm 126 of the guiding lifting conveyor device 120 has taken up the skid 134 and the free end 188 of the contact element 172 projects so far into the bell-shaped contact device 150 that it contacts the inner surface thereof.In this state, the skid 134 would in principle have the possibility of floating and becoming detached from the lifting arm 126 or the locking device 146, since the blocking element 178, which is preferably trapezoidal in cross section, is not hindered or blocked by the counter elements 184 in a vertical movement or in an upward movement.The angle of inclination of the skid 134 is approximately 0 degrees in FIG. 8.The two counter elements 184 are preferably arranged in an axially symmetrical manner with respect to one another and each enclose an angle of approximately 60 degrees with a horizontal in the non-inclined state of the skid 134.In FIG. 9, the skid 134 is inclined by approximately 10 degrees to 15 degrees. In other words, the lifting arm 126 of the guiding lifting conveyor device 120 is lowered in the lifting direction 128 relative to the lifting arm 126 of the following lifting conveyor device 122 to such an extent that the angle of inclination of the skid 134 assumes a value in the range from 10 degrees to 15 degrees.In this state, the skid 134 is already prevented from floating or from a fluid-induced lifting movement, since the front counter element 184, which is the left-hand one of the two counter elements 184 in FIGS. 8 to 10, is held by the blocking element 178 during a vertical upward movement.The skid 134 is thus locked on the locking devices 146 or the lifting arms 126 from an angle of inclination in the range from 10 degrees to 15 degrees.In FIG. 10, the maximum inclination of the skid 134 is shown, comparable to the left-hand state in FIG. 7, in which the contact element 172 bears against the front stop 192 of the bell-like contact device 150. The angle of inclination of the skid 134 in this state is approximately 60 degrees, for which reason the front counter element 184 is now oriented approximately horizontally and is arranged below the blocking element 178 in such a way that the blocking element 178 can act with its complete underside on just this counter element 184 in order to block or prevent the skid 134 from floating.As indicated above, FIGS. 11 to 13 show a preferred second embodiment of the lifting arms 126, which can already be seen at least partially in FIGS. 5 to 10. In order to be able to better address the details of this embodiment of the lifting arms 126, the lifting conveyor devices 120, 122 have been omitted.Because the lifting conveyor devices 120, 122 are preferably arranged one behind the other on one side of the treatment basin 106 and are moved along this basin side in the transfer conveyor direction 114, the associated lifting arms 126 are dynamically loaded on one side.Plate-shaped anodes 196 are arranged in the treatment tank 106 for dip coating on the side walls.The one-sided arrangement of the lifting arms 126 causes some of these anodes 196 to be at least partially shaded by the lifting arms 126, as a result of which the field lines in the affected region are disturbed and the quality of the treatment of the workpiece 102, in particular the coating of a vehicle body 104, can be impaired.It is therefore advantageous to keep the shading caused by the lifting arms 126 as low as possible, which can be realized in particular by the geometry of the lifting arms 126.The lifting arms 126 according to the preferred second embodiment therefore each comprise two outer round support pipes 198 and one central round pipe 200 which is arranged between the two round support pipes 198 with respect to the transfer conveying direction 114.By selecting round tubes for the lifting arms 126, the field lines are impaired to the smallest extent or to a significantly lesser extent in comparison with other cross-sectional shapes. In addition, particles in the treatment fluid adhere less well to the curved surface of the round pipes.The cross section of the central round tube 200 is preferably larger than the cross section of the two support round tubes 198, the cross section of which is preferably at least approximately the same size.As can be seen by way of example in FIGS. 9 and 13, one or more electrical lines 201 are led inside the central round tube 200, which are electrically connected to one or both locking devices 146 of a lifting arm 126 in order to ensure an electrical current flow through the workpiece 102 as cathode.The lifting arms 126 preferably have four sections, which will be discussed in detail below.If position information such as, for example, "upper" or "upper" and "lower" or "lower" is used in the following, the image plane of the respective figure or figures is referred to, unless otherwise stated.In an upper section 202 of a lifting arm 126, the central round tube 200 and the supporting round tubes 198 are firmly connected to a base unit 204, which is preferably designed as a mounting plate and oriented vertically.By means of the base unit 204, a lifting arm 126 is connected to the associated lifting conveyor device 120, 122.In the upper section 202, the support round tubes 198 are simply angled in the direction of the base unit 204 or the lifting conveyors 120, 122, preferably by an angle of 45 degrees.Below the bend, each of the support round tubes 198 is supported against the base unit 204 by a transverse round tube 206, which is preferably oriented approximately horizontally.The transverse round tubes 206 prevent a deformation of the lifting arms 126 in the direction of the adjoining side wall of the treatment basin 106 as a result of the takeover and treatment of a skid 134 with the workpiece 102.The central round tube 200 is preferably angled twice in the direction of the respective lifting conveyor device 120, 122 in the upper section 206 so that the plane of the base unit 204 and the central round tube 200 are connected to one another approximately perpendicularly.The upper section 202 is adjoined at the bottom by a vertical section 208 in which the central round tube 200 and the support round tubes 198 run substantially vertically and parallel to one another, wherein the support round tubes 198 are arranged at the same height with respect to a horizontal which runs perpendicular to the transfer conveying direction 114, that is to say parallel to the main conveying direction 112, and the central round tube 200 is arranged at an inward distance, that is to say is offset further in the direction of the workpiece 102 to be treated.In the upper region of the vertical section 208, the central round tube 200 and the two support round tubes 198 are preferably connected to one another by a horizontal intermediate plate 209.This horizontal intermediate plate 209 fixes the spacing of the central round tube 200 and the support round tubes 198 from one another and increases the rigidity of the lifting arm 126 without promoting shading.The vertical section 208 of the lifting arms 126 is adjoined at the bottom by a corner section in which the central round tube 200 and the support round tubes 198 are also angled, namely in the direction of the central longitudinal axis of the treatment basin 106, which runs parallel to the transfer conveying direction 114.The respective angle through which the central round tube 200 and the two support round tubes 198 are angled inward is likewise in the range of approximately 45 degrees. However, the bending of the round support pipes 198 from above begins earlier and a bent section 212 of both round support pipes 198 is longer than a corresponding section of the central round pipe 200. In addition, the angled sections 212 are brought together downwards in the direction of the central round tube 200, so that these sections 212 are fastened, preferably welded onto the central round tube 200, adjoining one another at their lower end.The bending of the central round tube 200 and the support round tubes 198 in the corner section 210 follows a taper 216 of the treatment basin 106 in the lower basin region, by means of which treatment fluid can be saved.The corner portion 210 is finally adjoined by a horizontal portion 218, in which the central round tube 200 runs at least approximately horizontally.The two locking devices 146 are arranged in the horizontal section 218, wherein the locking device 146, which is arranged further by the lifting conveyor devices 120, 122, preferably has electrically supplied or acted upon.These locking devices 146 have an insulating plate 220 between the respective base 168 and the central round tube 200, for which reason their receiving element 170 and contact element 172 are preferably shorter by the thickness of the insulating plate 220 than the receiving element 170 and the contact element 172 of the adjacent locking device 146, i.e. of the other locking device 146 of the same lifting arm 126.From the upper section 202 to the corner section 210, the central round tube 200 and the support round tubes 198 are thus arranged in such a way that a triangular arrangement is always obtained in cross section through all three tubes, which arrangement firstly ensures a high rigidity of the lifting arm 126 and secondly minimally impairs the field lines between the anodes 196 and the workpiece 102 as cathode.The triangular arrangement can be seen by way of example in FIG. 13, which shows a horizontal cross section at the height of the corner section 210.FIGS. 14 to 17 show a third and a fourth embodiment of a treatment system 100, in which a third embodiment of the locking devices 146 is equipped, which are provided in particular for inventory workpiece carriers 132.Inventory workpiece carriers 132 are to be understood as known or conventional workpiece carriers 132 which do not have the advantages of the workpiece carriers 132 according to the invention described further above.In the third embodiment of a treatment system 100 in FIGS. 14 and 15 and in the fourth embodiment of a treatment system 100 in FIGS. 16 and 17, the second embodiment of the lifting arms 126 as presented and explained in connection with FIGS. 5 to 13 is used in each case.Whereas in FIGS. 14 and 15 the transfer device 118 of the treatment plant 100 is designed as a chain conveying device 222, for which two cross-beams 224, also called "crossbars", are used as workpiece carriers 132 for each workpiece 102, the transfer device 118 is designed in the embodiment in FIGS. 16 and 17 as a roller conveying device 130, for which, however, conventional or known skids 134 are used as workpiece carriers 132, i.e. in particular without bell-shaped contact devices 150 and without a tilt protection element 158.Both for the embodiment of the treatment system 100 in FIGS. 14 and 15 with a chain conveying device 222 which telescope the workpiece 102 to be treated into an overhang over the treatment basin 106 for the transfer to the lifting arms 126, and for the embodiment of the treatment system 100 in FIGS. 16 and 17 with a roller conveying device 130, the locking devices 146 are designed such that accommodation and electrical contacting are realized in a clamping element 226.Each clamping element 226 preferably has a guide 228 which receives the associated lateral receiving pin 230 of the cross member 224 or of the skid 134.The guide 228 preferably extends horizontally, so that the lifting arms 126 do not have to perform any additional vertical movement when locking and unlocking the workpiece carrier or carriers 132.The guides 228 of the clamping elements 226 of the lifting arm 126 arranged on the guiding lifting conveyor 120 are open to the rear, i.e. pointing towards the transfer device 118, whereas the guides 228 of the clamping elements 226 of the lifting arm 126 arranged on the following lifting conveyor 122 are open to the front, i.e. pointing away from the transfer device 118.Consequently, the guides 228 of the two lifting arms 126, which are opposite one another in the transfer conveying direction 114, are open with respect to one another, as a result of which the workpiece 102 can be locked to the lifting arms 126 by the lifting conveying devices 120, 122 being moved towards one another as soon as the receiving pins 230 of the workpiece carrier or carriers 132 bear against the guides 228 of the clamping elements 226.Conversely, the treated workpiece 102 is unlocked by the two lifting conveyor devices 120, 122 moving apart and thus releasing the clamping of the workpiece carriers 132.In the case of a chain conveying device 222, as depicted in FIGS. 14 and 15, the workpiece 102 designed as a vehicle body 104, which in each case has a mounted cross-member 224 in the region of the wheel arch, is first telescoping over the treatment basin 106.Subsequently, the lifting arms 126, which have previously been lowered below the plane of the chain conveying device 222 in the lifting direction 128 and sufficiently spaced apart from one another, preferably parallel to the telescoping, are lifted in the lifting direction 128, such that the receiving pins 230 of the cross members 224 are positioned directly in front of the guides 228 of the clamping elements 226 or bear against a lower protrusion 232 of the guides 228.Then, the lifting conveyor devices 120, 122 are finally moved towards each other until the receiving pins 230 have reached the end of the respective guides 228 and thus the workpiece 102 or the vehicle body 104 has been locked on the lifting arms 126 by means of the cross members 224 for the treatment.In a roller conveyor 130, as depicted in FIGS. 16 and 17, the used skid 134 or the two front lateral receiving pins 230 are first threaded into the guides 228 of the clamping elements 226 of the lifting arm 126 of the guiding lifting conveyor 120 by conveying the skid 134 into a projecting position. In this case, the two lifting conveying devices 120, 122 are positioned as close as possible to the roller conveying device 130, with the result that the skid 134 protrudes beyond as little as possible in order to avoid tilting of the skid 134 in the direction of the treatment basin 106.Meanwhile, the lifting arm 126 of the following lifting conveyor 122 is positioned such that the locking devices are positioned below the skid 134.Subsequently, the skid 134 is conveyed further by the roller conveying device 130 in the transfer conveying direction 114 via the treatment basin 106, wherein the guiding lifting conveying device 120 is moved synchronously therewith.At the same time, the lifting arm 126 of the following lifting device 122 is lifted in the lifting direction 128, namely up to the height of the lifting arm 126 of the guiding lifting device 120, wherein the lifting is matched in such a way that, when the height of the lifting arm 126 of the guiding lifting device 120 is reached, the guides 228 of the clamping elements 226 of the lifting arm 126 of the following lifting device 122 are situated behind the lateral receiving pins 230 of the skid 134 or the receiving pins abut the projection 232 of the guides 228.Finally, the lifting conveyors 120, 122 are moved towards one another for locking the skid 134, namely until the receiving pins 230 have reached the end of the respective guide 228.The unlocking takes place in the correspondingly reversed sequence if the treated workpiece 102 is returned to the original transfer device 118.It is also preferably the case for the locking devices 146 of the embodiments in FIGS. 14 to 17 that only that locking device 146 is energized per lifting arm 126, which locking device is arranged on the side of the lifting arm 126 which is arranged further away from the lifting conveyor devices 120, 122.Nevertheless, it is also conceivable that only the locking devices 146 are energized, which are arranged closer to the lifting conveyor devices 120, 122, or that alternatively two locking devices 146 are energized, the positions of which on the respective lifting arm 126 are different.List of reference characters100 Treatment installation 102 Workpiece 104 Vehicle body 106 Treatment basin 108 Conveying installation 110 Main conveying device 112 Main conveying direction 114 Transfer conveying direction 116 Transverse conveying device 118 Transfer device 120 Guiding lifting conveying device 122 Following lifting conveying device 124 Rail element 126 Lifting arm 128 Lifting direction 130 Roller conveying device 132 Workpiece carrier 134 Skid 136 End position 138 Radar measuring device 140 Laser measuring device 142 Distance sensor 144 Acceleration sensor 146 Locking device 148 Longitudinal carrier 150 Bell-shaped contact device 152 Transverse strut 154 Measuring plate 156 Fork-lift truck receptacle 158 Anti-tilting element 160 Guide edge 162 Roller guide 164 Overlapping roller pair 166 Lateral guide rollers 167 Mounting strut 168 Base 170 Receiving element 172 Contact element 174 Guide tine 175 Tip of a guide tine 176 Guide joint 178 Blocking element 180 Inner side surface 182 Bearing journal 184 Counter element 186 Counterpart 188 Free end of the contact element 190 Dry area 192 Front stop 194 Rear stop 196 Anode 198 Support round tube 200 Central round tube 201 Electrical line 202 Upper section of a lifting arm 204 Base unit 206 Transverse round tube 208 Vertical section 209 Intermediate plate 210 Corner section 212 Angled section of a support round tube 214 Angled section of a central round tube 216 Narrowing of the treatment basin 218 Horizontal section 220 Insulating plate 222 Chain conveying device 224 Cross bar 226 Clamping element 228 Guide 230 Receiving pin 232 Projection

Claims

Treatment installation (100) for treating workpieces (102), in particular vehicle bodies (104), wherein the treatment installation (100) comprises: - at least one treatment basin (106), in particular at least one immersion basin, for treating the workpieces (102) with at least one treatment fluid, and - at least one conveying installation (108) for conveying the workpieces (102), which are each arranged on a workpiece carrier (132), wherein the conveying installation (108) comprises: - at least one roller conveying device (130) for conveying the workpieces (102) in a transfer conveying direction (114); and - at least one lifting conveyor device (120, 122), preferably at least two lifting conveyor devices (120, 122), which can be individually moved laterally of the at least one treatment basin (106) along the latter in the transfer conveyor direction (114), wherein the at least one lifting conveyor device (120, 122) comprises at least one lifting arm (126), which can be individually moved in a lifting direction (128) and is configured to at least partially receive a workpiece carrier (132) and / or a workpiece (102).Treatment installation (100) according to Claim 1, characterized in that the workpiece carrier (132) comprises: - two longitudinal members (148) which are arranged at a distance from one another and are aligned parallel to one another; - four bell-like contact devices (150); and - at least one mounting strut (167) for mounting the workpiece (102) on the workpiece carrier (132), wherein in each case two bell-like contact devices (150) are arranged on one longitudinal member (148).Treatment plant (100) according to claim 2, characterised in that the bell-shaped contact devices (150) are arranged opposite each other in pairs.Treatment plant (100) according to Claim 3, characterized in that the two pairs of mutually opposite, bell-like contact devices (150) are arranged asymmetrically with respect to a longitudinal extent of the two longitudinal beams (148).Treatment plant (100) according to one of Claims 2 to 4, characterized in that each bell-shaped contact device (150) has, on an inner side face (180), at least one counter element (184) and a bearing journal (182).Treatment plant (100) according to any one of claims 2 to 5, characterised in that each lifting arm (126) comprises at least one locking device (146), preferably two locking devices (146), each locking device (146) being adapted to receive and lock a bell-shaped contact device (150).Treatment installation (100) according to Claim 6, characterized in that each locking device (146) comprises: - a receiving element (170), by means of which the bearing pin (182) of a bell-like contact device (150) can be received; and - a contact element (172), by means of which an electrically conductive dry contact can be formed within a bell-like contact device (150).Treatment installation (100) according to claim 7, characterised in that the receiving element (170) comprises a blocking element (178), wherein the blocking element (178) acts on the at least one counter element (184) of the received bell-shaped contact device (150) for preventing the workpiece carrier (132) and / or the workpiece (102) from floating as soon as the workpiece carrier (132) exceeds an angle of inclination in the range from 5 degrees to 20 degrees, preferably from 10 degrees to 15 degrees.Treatment installation (100) according to one of Claims 1 to 8, characterized in that the workpiece carrier (132) comprises a tilt protection element (158), by means of which it is possible to prevent the workpiece carrier (132) and / or the workpiece (102) from being overturned during the transfer from the roller conveyor device (130) to the at least one lifting conveyor device (120, 122).Treatment plant (100) according to claim 9, characterised in that the anti-tilting element (158) is arranged between the longitudinal beams (148), wherein the roller conveying device (130) has a roller guide (162) with at least one overlapping roller pair (164), in which the anti-tilting element (158) can be guided.

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