Patent Application
20070237887
In the drawing:
The dosing pump 4 is connected via a hose line 5 to a varnish output device 6 which dispenses the conveyed varnish through a valve 7. The varnish output device 6 is handled by an only schematically depicted robot 8. The robot 8 can guide the valve 7 along a predetermined movement path in order to cover, for example, certain components with a varnish layer. Accordingly, the hose line 5 has to have certain flexibility. In order to ensure this flexibility, the hose line 5 is normally made of an elastomer material. The hose line 5 of an elastomer material, however, changes the volume of its interior 9 according to the pressures present in the interior. If the pressure rises, the volume of the interior 9 increases slightly. If the pressure in the interior 9 diminishes, the volume of the interior 9 decreases accordingly up to a minimal value.
A control device 10 is provided which controls the varnish repository 2 as well as the dosing pump 4. The control device 10 is also connected to the varnish output device 6 in order to, for example, close a there present valve when a varnish output should be terminated.
The control device 10 is also connected to the robot 8 so that the control device 10 is always informed about the position of the varnish output device 6 and the valve 7.
When the control device 10, because of a preset varnishing program, knows that in a predetermined movement segment of the varnish output device 6 a higher varnish mass has to be applied, for example, because a spray beam of the varnish with a greater width should be produced, while the applied layer thickness remains the same, the dosing pump 4 is adjusted to an appropriately higher delivery rate. The dosing pump 4 reacts very fast so that theoretically immediately after the change of the delivery rate of the dosing pump 4 the then required varnish mass should be available at the varnish output device 6.
Due to the extensibility of the hose line 5 this is not the case. If, for example, the dosing pump 4 delivers a greater conveyance mass, the pressure in the interior 9 of the hose line 5 initially rises, because the flow resistance which the varnish output device sets against the varnish does not change. The pressure increase, in turn, causes a slight volume increase in the hose line 5, so that the additional mass of the varnish conveyed by the dosing pump 4 has to be used first in order to fill up this volume increase.
This time lag brings forth that the increased varnish mass is not immediately available at the varnish output device 6, but rather only a short while later. Even if this short while is only the fraction of a second, for example, a fourth of a second, through this delay a relatively large transition area is produced, if one considers that the robot 8 moves the varnish output device 6 at a speed in the magnitude of 1 m/s. At a delay of a fourth of a second one ends up with a transition area of 25 cm in length, in which the deployed varnish amount is increased. A transition area of this size is in many tasks, particularly in the lacquering of motor vehicle parts, no longer acceptable. Incidentally, the length of the transition area increases according to the length of the hose line 5. Since in the varnishing of big parts, for example, truck bodies or bus bodies, one needs by all means hose lines with a length in the magnitude of 15 to 20 m, the length of the transition area would become too large.
In order to facilitate a faster change of the varnish mass deployed through the varnish output device 6, a volume compensation device 11 is arranged at the end of the hose line 5 where the dosing pump 4 is mounted, and whose configuration is illustrated in more detail in
The volume compensation device 11 is connected via a line 12 with a pressure fluid repository 13. The pressure fluid repository 13 is preferably a compressed air repository. The pressure reaching the volume compensation device 11 from the compressed air repository 13 is adjusted via a proportional valve 14 which is controlled by the control device 10.
The volume compensation device 11 has an input 15 which is connected to the dosing device 4, and an output 16 which is connected to the interior 9 of the hose line 5. Between the input 15 and the output 16 a compensation volume 17 is arranged which is delimitated, on the one hand, by a housing part 18 and, on the other hand, by a diaphragm 19. The diaphragm 19 is elastically deformable. When it is moved toward the housing part 18, the compensation volume 17 decreases. When it is moved away from the housing part 18, the compensation volume 17 increases.
A pressure port 20 is connected with the line 12. It empties through an only schematically illustrated valve 21 which is normally open into a pressure chamber 22 arranged on the side of the diaphragm 19 facing away from the compensation volume 17. The diaphragm 19 is moved in the direction of the compensation volume 17 and diminishes the compensation volume 17, when the pressure in the pressure chamber 22 is greater than the pressure in the compensation volume 17 and thus in the interior 9 of the hose line 5.
Thus, the compensation volume 17 is arranged in series with the interior 9 of the hose line 5. This is advantageous for cleaning. In case of a change of color the hose line 5 can be scraped, i.e., one can push a scraper from the varnish output device 6 to the volume compensation device 11 and transport the varnish residues present in the hose line 5 back to the varnish repository. In this manner, in a subsequent rising procedure not only the interior 9 of the hose line 5 but also the interior of the volume compensation device 11 gets flushed.
The control device 10 now does not only actuate the dosing pump 4 but also the volume compensation device 11.
When, for example, the dispensary volume of the varnish through the varnish output device 6 should be augmented, the output of the dosing pump 4 is increased. Simultaneously, through the proportional valve 14 a pressure is produced in the pressure chamber 22 that corresponds to the pressure which pertains to the then preset output or it rises slightly above it. Through this pressure, varnish fluid is eliminated from the compensation volume. The compensation volume is at least as great as the volume difference of the hose line 5 between a minimum pressure and a maximum pressure. Thus, the varnish volume from the compensation volume 17 is definitely sufficient to compensate for the volume increase of the interior 9 in the hose line 5. Since no varnish is used for this compensation that would need to be conveyed first by the dosing pump, but rather varnish that is already present in the compensation volume 17, the required varnish volume is practically available at the varnish output device 6 with the start of the dosing pump 4.
If the varnish volume to be dispensed should be decreased, the dosing pump 4 is shut down. Simultaneously, the control device 10, through the proportional valve 4, sets a pressure in the pressure chamber 22 which corresponds to the then valid output or lies slightly below. The hose line 5 contracts somewhat because of the reduced pressure. The thereby displaced varnish fluid is received in the compensation volume 17, wherein the diaphragm 19 moves away from the housing part 18 and thereby increases the compensation volume.
Since the diaphragm 18 is controlled through pressure, steady state conditions are quickly recovered in the hose line 5. Within a very short time after the change of pressure in the pressure chamber 22 a pressure is reached in the interior 9 which corresponds to an output volume dispensed through the dosing pump 4.
The control device 10 has a storage device 23 which is organized, for example, in the form of a “look-up” table. For every conveyance mass that can be preset in the dosing pump 4 there is a pressure value stored which then develops in the interior 9 of the hose line 5. The control device can now in the case of increase set a slightly higher pressure or, in the case of decrease of the output set a slightly lower pressure in the pressure chamber 22.
While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 016 950.6 | Apr 2006 | DE | national |
