Patent Application
20080271993
The invention relates to an electro-dip lacquering device with
In electro-dip lacquering, also termed electrophoretic lacquering, the lacquer components in the lacquer bath are deposited on the workpieces under the influence of an electric field. It has proved advisable not to keep the electric field constant during the passage of the workpieces through the lacquer bath, but to vary it along the movement path, in particular to let it increase with the distance covered. A reason for this measure inter alia is that the lacquer coating building up represents an electrical resistance, which makes the further build-up of the lacquer coating difficult.
The problem thus arises of how the voltage can be changed for each workpiece as it passes through the lacquer bath. In electro-dip lacquering devices of the type named at the beginning, such as described for example in DE 199 42 556 C2, the current is supplied to the workpiece via a contact rail divided into individual sections in the movement direction of the workpieces to be lacquered; the sections are galvanically separated and connected to one pole of a voltage source assigned to each section. The electrodes arranged along the movement path of the workpieces in the lacquer bath are connected to the other pole of the voltage source. It is disadvantageous in this case that it is relatively difficult to track the path of each individual workpiece along the various sections of the contact rail in control terms and to effect the transition of the workpiece from one section to another section without “jump” in potential. Since the charge flowing between electrode and workpiece is used as a measure for the coating thickness applied, it is necessary to “activate” the measurement of the current flowing to the workpiece section-wise too with the movement of the workpiece. After all, the “cuts” in the contact rails which cause the galvanic separation also represent unevennesses in the contact rail which lead to wear of the contact devices that are moved together with the workpieces.
In the event of changes in the workpiece, e.g. in the length of the workpiece, or in the event of a change in the dipping curve, the positions of the cuts between the contact rail sections change, so that an installation change is necessary for an optimum coating.
The object of the present invention is to configure an electro-dip lacquering device of the type named at the beginning in such a way that it can be controlled more easily, is flexible, and causes less wear on the contact devices.
This object is achieved according to the invention in that
According to the invention, therefore, the division of the contact rail into sections, which is associated with rail cuts, is dispensed with and a galvanically continuous contact rail is used. In order now to be able to apply different potentials, and even potentials that change in the course of the movement, to the various workpieces, which all draw their voltage from the same contact rail, a separate voltage adjusting unit is assigned to each workpiece. This is activated according to the position of the workpiece such that the workpiece is always at the desired potential. In this way a very much more sensitive adjustment of the potentials at the workpieces can be accomplished than in the case of the known division of the contact rail into individual sections. A changeover to a different type of workpieces is possible without any problems solely by means of programming measures. The absence of cuts in the contact rail has a favourable effect on the lifetime of the contact devices.
The at least one control system can be the central control system of the device. This is possible in particular where the conveying device comprises a chain conveyor and all workpieces move at the same velocity.
Modern devices have conveying systems with independently moving carriages each carrying at least one workpiece. Since these carriages are themselves generally “intelligent”, thus have a decentralised control system, this can also be used for the purposes according to the invention.
In a particularly preferred embodiment of the invention, the position indicating device has a position code rail as well as a reading head for each workpiece, which head is moved together with the workpiece and is able to read the local code of the position code rail. Position code rails suitable for this are obtainable relatively cheaply in the trade and have a high level of accuracy.
Alternatively a navigating system, for example a laser-controlled or GPS-based system, can be used as a position indicating device.
Furthermore, it is also possible for the position indicating device to comprise a presence sensor at the start of the movement path of the workpieces through the lacquer bath and velocity sensors for the workpieces, wherein the control system is designed so that it can calculate the momentary position for each workpiece from the velocities recorded and the time that has elapsed since the response of the presence sensor.
Instead of the velocity and the time that has elapsed since the presence sensor was passed, the distance covered can also be recorded directly and the momentary position of each workpiece calculated from this. In conveying systems operating with a transport chain, the distance measurement can take place by counting the chain links that have run past, while in the case of conveying systems operating with wheels, by counting the revolutions of the wheels.
An embodiment of the invention is explained in greater detail below with reference to the drawing; the single FIGURE shows schematically the voltage supply of vehicle bodies in an electro-dip lacquering bath.
The drawing shows three vehicle bodies 1a, 1b, 1c in all, which can be thought of as dipped into a lacquer pool filled with lacquering liquid, as described in DE 199 42 556 C2 already mentioned above. The lacquer pool is not shown in
In the lacquer pool (not shown), counter electrodes, in particular anodes, are positioned in a known manner along the movement path of the vehicle bodies 1a, 1b, 1c, as is likewise to be inferred from DE 199 42 556 C2. In the electric field created within the lacquering liquid between the counter electrodes and the vehicle bodies 1a, 1b, 1c, the deposition of the lacquer components onto the vehicle bodies 1a, 1b, 1c takes place. The ampere hour number that has flowed between the counter electrodes and the vehicle bodies 1a, 1b, 1c on the passage through the lacquer pool represents a direct measurement of the thickness of the lacquer coat deposited.
In order to produce the electric field required for the electrophoretic deposition of the lacquer, the vehicle bodies 1a, 1b, 1c must be connected during their movement through the lacquer bath to the corresponding pole of a direct voltage source 20, in the current case of cataphoretic dip lacquering to its negative pole.
This connection is made in the following manner:
Along the movement path of the vehicle bodies 1a, 1b, 1c leading through the lacquer pool, but outside the lacquering liquid, a contact rail 2 extends. This contact rail 2 is uninterrupted over its entire length, thus does not have the “cuts” customary in the prior art, i.e. points at which different sections of the contact rail are attached, electrically insulated, to one another. The contact rail 2 is connected to a pole, preferably the negative pole, of the direct voltage source 20. It generally suffices if the direct voltage source 20 emits a constant output voltage, which corresponds to the maximum voltage to be applied to the vehicle bodies 1a, 1b, 1c. The other pole of the direct voltage source 20 is connected to the electrodes, preferably anodes, arranged along the movement path.
Each vehicle body 1a, 1b, 1c has a contact shoe 3a, 3b, 3c assigned to it, which shoe, creating an electrical connection, slides along the contact rail 2. The contact shoes 3a, 3b, 3c are not connected directly to the respective vehicle bodies 1a, 1b, 1c, but via a controllable voltage adjusting unit 4a, 4b, 4c. The voltage adjusting units 4a, 4b, 4c are formed so that according to a control signal supplied to them by a control system 5 via a line 6a, 6b, 6c, they can route the voltage present on the contact rail 2 in unchanged or changed, generally reduced, form to the corresponding vehicle body 1a, 1b, 1c.
Running in parallel to the contact rail 2, likewise outside the lacquering liquid, is a position code rail 7. This carries along its longitudinal extension at all points a readable code, which denotes the position of the point in question. Each vehicle body 1a, 1b, 1c has a reading head 8a, 8b, 8c assigned to it which is able to read the momentary position of the corresponding vehicle body 1a, 1b, 1c from the position code rail 7. The signals read by the reading heads 8a, 8b, 8c are supplied via a line 9a, 9b, 9c respectively to the control system 5.
The control system 5 contains a memory in which it is stored in a suitable manner for each vehicle body 1a, 1b, 1c, or at any rate for each type of vehicle body 1a, 1b, 1c that is to be treated on the device, which voltage is to be applied at which point along the movement path to the vehicle body 1a, 1b, 1c in question.
The electro-dip lacquering device described above operates as follows:
As soon as one of the vehicle bodies 1a, 1b, 1c reaches the area of the contact rail 2 and thus the area of the lacquer pool, an electrical connection is made with the contact rail 2 with the aid of the contact shoe 3a, 3b, 3c; the respective reading head 8a, 8b, 8c enters the vicinity of the position coding rail 7 and detects the momentary position of the vehicle body 1a, 1b, 1c. The appropriate information is now emitted to the control system 5, which reads from its memory the desired voltage that is to prevail at the vehicle body 1a, 1b, 1c in question at the respective point. The control system 5 now emits a corresponding signal to the corresponding voltage regulating unit 4a, 4b, 4c via the line 6a, 6b, 6c, which signal ensures that the voltage adjusting unit 4 actually produces the desired voltage from the voltage prevailing on the contact rail 2 and applies it to the vehicle body 1a, 1b, 1c.
This process is repeated constantly during the passage of the vehicle body 1a, 1b, 1c through the lacquer pool. The reading head 8a, 8b, 8c here transmits the respective position either continuously or through small path increments following transit and the control system 5 readjusts the voltage present at the related vehicle body 1a, 1b, 1c via the voltage adjusting units 4a, 4b, 4c.
Obviously it is possible in this way to set a very precise voltage characteristic for all vehicle bodies 1a, 1b, 1c which are connected to the same contact rail 2 during their travel through the lacquer pool.
The positioning device, which was formed in the embodiment described above by the position code rail 7 and the reading heads 8a, 8b, 8c, can naturally also be replaced by other position indicating devices. For example, a navigating system based on a laser control system or on GPS can be used. In the simplest case a sensor can even be arranged at the entrance to the movement passage through the lacquer pool, which sensor reports the entry of a vehicle body. From there the respective position of the vehicle body is calculated from its velocity, which is ascertained and monitored continuously, and the elapsed time.
Instead of a central control system, decentralised control systems can also be used, which are assigned to the individual vehicle bodies and move together with these.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 037 174.4 | Aug 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2006/007561 | 7/31/2006 | WO | 00 | 5/13/2008 |
