Abstract
A system and method for cleaning and/or post-exposure of a body manufactured by using an additive manufacturing method from a substance curable by radiation, the system including a cleaning tank for cleaning the body and/or an exposure chamber for post-exposure of the body, the system further including a transport device having a drive for moving a build platform relative to the cleaning tank and/or to the exposure chamber. The transport device includes a force sensor, the force sensor captures a force acting on the build platform and provides a force signal, and is connected to a processing unit for controlling the drive and/or for outputting process parameters based on the force signal.
Claims
1. A system for at least cleaning and post-exposure of a body manufactured using an additive manufacturing method from a substance curable by radiation, the system comprising: a cleaning tank configured to clean the body with a cleaning fluid and an exposure chamber configured for post-exposure of the body; the system further comprising: a transport device having a drive configured to lower a build platform into to the cleaning tank or into the exposure chamber; wherein the transport device comprises a force sensor, wherein the force sensor is configured to capture, during cleaning, a force acting on the build platform being generated due to the drive, the gravity of the body and the buoyancy due to the cleaning fluid displaced during the cleaning, and provide a force signal, and further wherein a processing unit of the system is configured to control the drive and output process parameters based on the force signal.
2. The system according to claim 1, wherein the processing unit is configured to compare the force signal with a predefined expected value for a current process step and to stop the drive and to output an error signal or to set a process parameter as a function of the resulting deviation.
3. The system according to claim 1, wherein the force sensor comprises a strain gauge.
4. The system according to claim 1, wherein the processing unit is configured, based on the force signal, to determine and output at least one of a state of the body, a state of the system, and a state of a part of the system.
5. The system according to claim 1, wherein the processing unit is configured to compare the force signal with an expected value or with a range of an expected value and to adapt at least one of a movement, a movement speed, an acceleration, and a process time of the transport device on the basis of the force signal.
6. A method for cleaning and post-exposure of a body manufactured using an additive manufacturing method from a substance curable by radiation, in a cleaning tank with a cleaning fluid and in an exposure chamber for post exposure respectively, comprising: lowering the body on a build platform into to the cleaning tank for cleaning or into the exposure chamber for post-exposure by a transport device comprising a drive, wherein during cleaning, a force acting on the build platform generated due the drive, due to the gravity of the body and due to the buoyancy of the cleaning fluid displaced during the cleaning is captured using a force sensor, and a force signal is provided, and a processing unit connected to the force sensor controls the drive and outputs a process parameter on the basis of the force signal.
7. The method according to claim 6, further comprising: comparing, by the processing unit, the force signal with a predefined expected value for a current process step and, as a function of the resulting deviation, stopping the drive and outputting an error signal or setting a process parameter.
8. The method according to claim 6, wherein the processing unit determines and outputs at least one of a state of the body a state of the system, and a state of part of the system on the basis of the force signal.
9. The method according to claim 6, further comprising: comparing, by the processing unit, the force signal with an expected value or with a range of an expected value and adapting at least one of a movement, a movement speed, an acceleration, and a process time of the transport device on the basis of the force signal.
10. The method according to claim 6, wherein the processing unit, based on the force sural, deter nines as a process parameter at least one of a deflection of the transport device, a height of the body in relation to the cleaning tank or the exposure chamber, a movement speed of the transport device, and the weight of the body.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The invention is explained in more detail in the following using preferred, non-limiting exemplary embodiments with reference to the drawings. Shown are:
[0045] FIG. 1 schematically a longitudinal section of a system for cleaning and post-exposure of a body built up in layers;
[0046] FIG. 2 schematically a more detailed view transport device of the system according to FIG. 1, this time without a body;
[0047] FIG. 3 schematically the view according to FIG. 2, this time having a body arranged on the build platform;
[0048] FIG. 4 schematically a longitudinal section of a detail of a system having a cleaning tank;
[0049] FIG. 5 schematically a cleaning tank according to FIG. 4 with the acting forces;
[0050] FIG. 6 schematically a diagram having an exemplary time profile of a force signal when immersed in a cleaning fluid as in FIG. 5, with different fluid densities;
[0051] FIG. 7 schematically the system from FIG. 1, the body having come loose during a movement;
[0052] FIG. 8 schematically a diagram having an exemplary time profile of: a force signal when the body is spontaneously detached from the build platform according to FIG. 7;
[0053] FIG. 9 schematically the system from FIG. 1 having a body wetted with cleaning fluid after washing;
[0054] FIG. 10 schematically a diagram having an exemplary time profile of a force signal when the cleaning fluid drips off according to FIG. 9;
[0055] FIG. 11 schematically a diagram having an exemplary time profile a force signal when the cleaning fluid is drained and blown off according to FIG. 9;
[0056] FIG. 12 schematically the system from FIG. 1 having an incompletely drained body;
[0057] FIG. 13 schematically a diagram having an exemplary time profile of a force signal when the cleaning fluid incompletely drips off according to FIG. 12;
[0058] FIG. 14 schematically the system from FIG. 1 having a possible, collision of an incorrectly detached body; and
[0059] FIG. 15 schematically a diagram having an exemplary time profile of a force signal when there is a collision according to FIG. 14.
DETAILED DESCRIPTION
[0060] In the illustrated figures, parts of the device that do not serve to describe the respective figure have been omitted for the sake of clarity.
[0061] System 1 for cleaning and/or post-exposure of a body 2. The body 2 was previously manufactured from a substance curable by radiation by means of an additive manufacturing method. Production takes place on a build platform 3. In the situation illustrated in FIG. 1, the build platform 3 is connected to a transport device 4 of the system 1. For example, an arm 5 of the transport device 4 can have a coupling 6 for connection to a correspondingly configured build platform 3. Using the transport device 4, a connected build platform 3 can be moved in the vertical direction 7 (that is, normal to a building surface of the build platform) and in the horizontal direction 8. For vertical movement, the transport device 4 has a tower 3 which is arranged on a rail (not illustrated) for horizontal movement. The system 1 has a post-exposure unit 10 and two receptacles 11, 12 for cleaning tanks 13, 14 for cleaning the body 2. A circulating device 15 in the form, of a rotor is provided in the cleaning tanks 13, 14 on the bottom 16 of the tank 13, 14. A body 2, and possibly a transport container, can be transported on a build platform 3 between these stations 10, 11, 12 by means of the transport device 4. That is, the body 2 can be lifted vertically out of a transport container, moved horizontally over a cleaning tank 13 and then lowered vertically into the cleaning tank 13. After cleaning, the body 2 can, for example, move over the post-exposure unit 10 and then be lowered vertically into the post-exposure unit 10. The post-exposure unit 10 can, for example, have a (partially transparent) exposure chamber for post-exposure of the body 2 having corresponding light sources directed into the chamber.
[0062] As illustrated in more detail in FIG. 2, the transport device 4 comprises a drive 17 for the above-described vertical and horizontal movement of a connected build platform 3. The transport device 4 also comprises a force sensor 18. The force sensor 18 comprises a strain gauge which is arranged in the arm 5 between the tower 9 of the transport device 4 and the coupling 6 for the build platform 3 and which records a deformation of this arm 5. The force sensor 18 is thus configured to capture a force acting on the build platform 3, the force being generated either by the transport device 4 (for example, by the drive 17) and/or by the body 2 (for example, gravity) and/or from the outside (for example, buoyancy force, see below). The force sensor 18 is connected to a processing unit 19. The processing unit 19 is configured to control the drive 17 and to output process parameters based on the force signal of the force sensor 18 to a user interface 20. The user interface 20 is configured for communication with a data memory 21 which, for example, stores a model of the body 2 and specifications for post-processing the body 2. The data memory 21 can, for example, be part of a transport container. The processing unit 19 is configured to determine and output a state of the body 2, a state of the build platform 3 or a state of a cleaning tank 13, 14 (more precisely: its fill level) on the basis of the force signal. For this purpose, the processing unit 19 is configured to compare the force signal with an expected value or with a range of an expected value and to adapt a movement, a movement speed, an acceleration and/or a process time of the transport device on the basis of the force signal. Particularly, the processing unit 19 can stop the drive 17 and/or output an error signal and/or set a method parameter as a function of a discrepancy between the force signal and the expected value.
[0063] In the situation illustrated in FIG. 2, the build platform 3 is free, that is, no body is connected to the build platform 3. The force signal of the force sensor 18 corresponds to the weight of the build platform 3 when the transport device 4 is stationary. That is, on the basis of the force signal, the processing unit. 19 can determine that a build platform 3 is connected to the transport device 4, as well as the weight of said build platform 3. For a more precise measurement, the build platform 3 having the tower 9 can be set in a vertical movement or oscillation. The inert mass of the build platform 3 can be deduced from the resulting time profile of the force signal.
[0064] In the situation illustrated in FIG. 3, the transport device 4 carries a build platform 3 having a body 2 arranged (adhering) thereon. In this case, the weight of the body 2 together with the build platform 3 can be, derived from the force signal. If the weight of the build platform 3 is known (either as a default or measured beforehand, as in FIG. 2), the weight, of the body 2 can be determined separately. The weight of the body 2 can be compared with an expected weight based on a model. The expected weight is calculated from the density of the material used for manufacture (the photo-reactive substance) and the filled volume of the body 2. The density used can be the density after curing, that is, when the solvent has been completely deposited or separated. The progress of the post-processing can thus be concluded from the difference between the determined and expected weight. In detail, material residues still adhering can be recognized immediately after a washing process and the washing process can be continued. After the washing process, the dripping and draining of the cleaning fluid can be monitored.
[0065] Such a washing process in the cleaning tank 13 is illustrated in more detail in FIG. 4. As can be seen here, the rotor 15 (for example, with permanent magnets) is rotated magnetically by a drive magnet 23 which is arranged below the tank 13 and is connected to an electric motor 22. As a result, the cleaning fluid 24 is circulated and homogenized in the tank 13. Material residues adhering to the body 2, for example, less cured, are rinsed off by the cleaning fluid 24 in this way and collected in the tank 13. During this process, the build platform 3 is lowered onto the cleaning tank 13 and closes tightly with its edge 25 in order to prevent the cleaning fluid from escaping. The contact between the build platform 3 and the tank edge 25 and any contact pressure can be determined and monitored using the force sensor 18. The foody 2 is essentially completely immersed in the cleaning fluid 24 due to the correct fill level of the cleaning fluid 24.
[0066] The acting forces that are captured by the force sensor 18 are delineated in FIG. 5. On the one hand, as in FIG. 3, the force of gravity Fg acts according to the weight of the body 2. On the other hand, and in opposition to the force of gravity Fg, the buoyancy force Fb acts due to the weight of the cleaning fluid 24 displaced by the body. The buoyancy force Fb thus depends, on the one hand, on the immersed volume of the body 2 and also on the density of the displaced cleaning fluid 24. The immersed volume of the body 2 in turn depends or, the fill level of the cleaning fluid 24 in the cleaning tank 13.
[0067] FIG. 6 shows the time profile of the force signal FN when the body 2 is lowered into the cleaning tank 13 for two different situations 26, 27 (solid or dashed line) for the same body 2. The point in time ttouch of the first contact with the cleaning fluid 24 by the body 2, that is, at which the body 2 reaches the fluid level 28 (see FIG. 5), and the point in time tsink of the complete lowering of the body 2 into the cleaning fluid 24 are delineated. The influence of placing the build platform 3 on the edge 25 of the cleaning tank 13 is not illustrated for the sake of simplicity. The point in time ttouch is essentially the same in both situations, that is, the fill level is also the same. Nevertheless, the situations differ in the force signal captured at the point in time tsink, where the force signal in the first case 26 (solid line) drops to a force Fk1 and in the second case 27 (dashed line) drops to a (higher) force Fk2. This difference is due to the different density of the cleaning fluid 24. In the first case 26, this density is higher, that is, the buoyancy force Fb is higher and thus compensates for a larger part of the weight Fg of the body. The resulting force Fk1 is therefore lower. In the second case 27, the density of the cleaning fluid 24 is lower, so that the resulting force Fk2 remains higher. The density of the cleaning fluid 24 which can be determined by the processing unit 19 in this way can be used for diagnostic purposes. For example, an exchange of the cleaning fluid 24 can be recommended to the user when the composition of the cleaning fluid 24 is clearly no longer suitable for washing due to the changed density.
[0068] FIG. 7 shows a situation in which the body 2 is detached from the build platform 3 during transport and falls down. This event can be recognized by the processing unit IS. The time profile of the force signal FN corresponding to this situation is illustrated in simplified form in FIG. 8. The detach point in time tsep is delineated here. The abrupt change in the force signal FN and the deviation from the expected value Fset corresponds to a detachment of the body 2 (or the build platform 3). This case can be recognized, for example, by the fact that the derivation of the force signal (that is, the slope of the flank at point in time tsep) exceeds a limit value of expected changes (for example, when immersing in the cleaning tank).
[0069] FIG. 9 shows a situation after the body 2 has been washed in the cleaning tank 13 according to FIG. 4, the body 2 being completely lifted vertically out of the cleaning fluid 24. Immediately after being lifted out, the cleaning fluid 24 drips off the body 2 and back into the cleaning tank 13. The body 2 is held in this position until most of the cleaning fluid 24 has dripped off. In order to avoid delays, it is advantageous to recognize this point in time as a function of the geometry of the body 2. The force sensor 13 can also be used for this purpose. The time course of the force signal FN during this process is illustrated in FIG. 10. The processing unit 19 monitors the force signal FN and detects a point in time tdrip at which the force signal FN has sufficiently approximated an expected value Fset (that is, up to a predefined acceptable deviation). After the lifting out, the system 1 waits for the point in time tdrip and then continues further post-processing (for example, with post-exposure). Alternatively, the dripping off, after a certain amount of dripping cleaning fluid 24 (recognizable by the change in the captured gravity after lifting it out), can be supplemented by blowing off. This case is illustrated in simplified form in FIG. 11. Here, a blower is switched on at the point in time tdrip and operated until the point in time tdry of sufficient drying. This point in time tdry is recognized by the fact that the force signal FN enters the range Fsetmin-Fsetmax of expected values. The blower can be deactivated at point in time tdry and further post-processing (for example, with post-exposure) is continued.
[0070] An error in the dripping process is illustrated in FIG. 12, exaggerated for the sake of simplicity. In this case, the body 29 forms a “basin” in which cleaning fluid 24 is held. Therefore, in this case, cleaning fluid 24 is scooped up with the body 29 from the cleaning tank 13 and cannot drip off. This case can be recognized by the processing unit 19 from the fact that the force signal FN, as illustrated in FIG. 13, does not sufficiently approximate the expected value Fset for a body 29 that has dripped off. Here, after an expected (or maximum) drip-off time tdrip, the remaining deviation can be recognized and an error can be output and the post-processing can be interrupted or canceled.
[0071] Finally, FIG. 14 shows an error case in which the body 2 has detached itself from the build platform 3 above a cleaning tank 13 and is now lying across the cleaning tank 13. In this case, the build platform 3 will collide with the body 2 when it is lowered into the cleaning tank 13. The corresponding time profile of the force signal FN is shown in FIG. 15. When lowering, the force suddenly begins to increase, the slope corresponding to the force applied by the drive 17 of the transport device 4 and which would also be expected, for example, when it is placed on an edge 25 of the cleaning tank 14. For this reason, the rapid positive change in force in itself is not a reason for cancellation. As soon as the force reaches a predefined maximum value Fmax, however, the processing unit 19 stops the drive 17 of the transport device 4 in order to avoid damage to the system 1. Since at this point in time no immersion in the cleaning fluid 24 as according to FIG. 6 was detected, the processing unit 19 can determine that an error is present and cancel the post-processing and display a corresponding indication with an error message to the user.
