MEASURING METHOD FOR THE CREATION OF A THREE-DIMENSIONAL BODY

Description

[0001] The invention generally relates to a stereolithography device for producing a three-dimensional body by layer-by-layer curing of a photosensitive material and a method for accelerating the production process by a spatially and temporally resolved measurement method; the device comprises: a reference layer; a radiation source for generating the specific radiation required for curing; a sensor; and at least one passive radiation source for generating measuring radiation.

[0002] More specifically, the invention relates to a method for producing a three-dimensional body in a stereolithographic process, wherein a photosensitive material is cured by radiation.

[0003] In stereolithography systems (see, for example, EP 2 173 538 B1), a photosensitive liquid is converted into a layer of a three-dimensional body by exposure to suitable radiation, e.g., UV radiation. The invention concerns the acceleration of such a stereolithographic process by means of an optical measurement method that can be used in such a system.

[0004] Stereolithography is commonly understood as a process that allows the creation of a three-dimensional object by arranging individual layer formations. This basic principle is also known by terms such as rapid prototyping, 3D printing, additive manufacturing, etc.

[0005] In stereolithography processes, in addition to controllable laser sources, radiation sources are also used that generate the layer formation using digital mask exposure systems, so-called MEMS or DLP chips, or displays. The advantage of pixel-based exposure systems is that the entire layer formation is generated at once, whereas in laser-based systems the laser beam must traverse the geometry of the layer. The photosensitive material is cured in a reference layer or reference plane: this can be the surface of a floor or another suitable defined area, and it can be solid, flexible, or liquid depending on the application. After a layer has solidified, it must be separated from the reference layer as gently as possible by a relative movement between the reference layer and a support surface to which the generated layer is to adhere.After the successful separation of the generated layer, new material suitable for solidification is added between the reference layer and the last layer formed. This can be achieved, for example, by a simple lifting movement of the support surface. The newly added photosensitive material can then be cured again by irradiation. To create the desired three-dimensional object, the described individual process steps are repeated until all layers necessary to form the body or object have been created.

[0006] The disadvantages of such a stereolithography process are the long processing times and waiting times that occur during the separation of a layer. These times account for a large portion of the total process time. Further disadvantages include the inability to detect exposure errors and the inability to adhere to the substrate. Adjusting the start and zero positions of the system is also problematic.

[0007] It is known from the prior art to integrally measure the peel forces in a stereolithography process during the separation of the generated layer from the reference layer on the carrier platform. An example of such a method is described in EP 2 043 845 B1, wherein a force measuring sensor is attached to a build platform or carrier platform. This sensor enables the measurement of the peel forces that occur during the separation of a newly formed component layer or the component from a reference layer. This can accelerate the build process. The force sensor described in EP 2 043 845 B1, which can be designed as a strain gauge, for example, measures the sum of the forces generated on the generated layers during separation in the described arrangement.The disadvantage is that only the sum of the forces that occur when separating multiple component layers can be recorded, not the separation force of a specific component or layer. Furthermore, only the total separation force occurring as a function of time can be recorded. Furthermore, no statements or conclusions can be made about the dependence of the force on the layer geometry of an individual body, and thus no statements can be made about whether, in the case of simultaneous generation of multiple bodies, all bodies will be built reliably and completely. Furthermore, the known methods do not allow any conclusions to be drawn about the polymerization process of the layer or body.

[0008] EP2178694A1 discloses a method for producing a lens from a reactive mixture on a substrate by means of a source of actinic radiation which can be controlled to cure a definable part of a volume of the reactive mixture

[0009] The aim of the invention is therefore to eliminate the above-mentioned disadvantages by means of an improved technology (device, method) and to enable a simple, fast, trouble-free, continuous, economical and self-checking production of three-dimensional bodies.

[0010] More specifically, it is the object of the invention to provide a method as initially stated, in which a precise statement about the process status is continuously possible, and in which the production of several bodies simultaneously in a stereolithographic process is made possible, wherein the status of the individual processes or produced bodies / layers is also made possible.

[0011] This goal was achieved by the measuring method according to claim 1.

[0012] The following embodiments in which a measuring radiation is coupled into a reference layer do not fall within the scope of the claimed invention.

[0013] In more detail, an interaction between a reference surface / layer and the respective formed layers should be able to be recorded.

[0014] According to the invention, the present method for producing a three-dimensional body is characterized primarily by the fact that measurement radiation is coupled into a reference layer and remains predominantly within the reference layer due to internal reflection, and that the measurement radiation is recorded by a sensor with spatial and temporal resolution. This procedure makes it possible to continuously monitor and record the layer production process, thus the 3D printing process and its progress, practically point-by-point or region-by-region, thereby avoiding unnecessary waiting times.

[0015] It is particularly advantageous if the internal reflection is disrupted by deformation of the reference layer, causing measurement radiation to escape from the reference layer. This allows for particularly precise recording of the process progress, especially in specific areas.

[0016] In order to improve the measurement, it is also advantageous if the sensor detects the outgoing measuring radiation in several measuring ranges simultaneously.

[0017] For measurement performance, it is also advantageous if the reference layer is flexible and at least partially transparent to the measurement radiation. Due to the flexible design of the reference layer, the application of forces causes deformation of this reference layer, which influences the measurement radiation and thus prevents accurate measurement.

[0018] Particularly advantageous results can be achieved if the reference layer is made of silicone. It is also advantageous for the measurement if total internal reflection occurs within the reference layer.

[0019] Finally, a particularly advantageous embodiment of the present method is characterized by the use of infrared radiation as the measuring radiation. Thus, if the sensor is additionally designed to detect the thermal radiation that occurs during the solidification of a layer of at least one body on the reference layer, the curing can be advantageously monitored.

[0020] In the present method or the associated stereolithography device, at least two measuring radiation sources, ie passive radiation sources, and at least one associated measuring sensor can be provided.

[0021] According to the invention, by detecting the coupled-out, location- and time-dependent measurement radiation from the reference layer, it is possible to infer, at least qualitatively, the presence of an intermediate phase within the photoreactive substance. This intermediate phase, which has no or only very low reactivity, at least partially due to at least one inhibitor (e.g., oxygen), forms a type of "inert" lubricating film. As a result, the adhesive forces normally occurring during the process can be greatly reduced and / or almost completely eliminated. Since the escaping measurement radiation is related to the adhesive forces, the method according to the invention can be used to infer the presence of an intermediate phase during the process, both spatially and temporally resolved.

[0022] The invention will be further explained below using preferred embodiments and with reference to the drawing. The drawing shows in detail in schematic form: Fig. 1 is a schematic view of an example of a stereolithography system to illustrate the present method; Fig. 2 is a view of a modified stereolithography system; Fig. 3 is a schematic diagram of an arrangement for illustrating the measurement of scattered radiation; Fig. 3a is a Fig. 3 simplified arrangement; Fig. 4 shows another embodiment with a modified position of the passive (measurement) radiation source; Fig. 4a which in Fig. 4 illustrated embodiment, but without a separate base; Fig. 5 schematically shows an example of radiation information detected by the sensor; Fig. 6 schematically shows a section through part of a system, with a modified measuring arrangement; Fig. 7a a schematic diagram of a measuring arrangement for determining the presence of an intermediate phase, where, for example, it can be assumed that the forces are very small; and Fig. 7b a schematic diagram in which the intermediate phase has the height, where h < H and measuring radiation is coupled out.

[0023] Fig. 1 shows an example of an embodiment of a stereolithography system 1, partly in section, whereby this system 1 is used to produce one or more three-dimensional bodies 3 (see also Fig. 2 bis 4 ) consists of individual layers that are cured by means of actinic radiation by partially solidifying a photosensitive material 9 located in a trough 2 forming a receiving space 14. The photosensitive material 9, which is located in the receiving space 14, is liquid, whereby the term "liquid" here refers to liquids of any viscosity, including suspensions and pasty substances.

[0024] One or more passive radiation sources 10, 11 are arranged such that a radiation difference resulting from the deformation of a reference layer 80 can be detected by at least one sensor 5. According to Fig. 1 A base 8 and the reference layer 80, including associated walls, form a trough 2, which serves as a receiving space 14 for the photosensitive liquid material 9. "Passive radiation source" is understood here to be the radiation source that serves as a measuring means, wherein its radiation is not capable of solidifying the photosensitive material 9 due to either the intensity and / or the wavelength used. A controllable radiation source, in particular a light source 60, is arranged, for example, below the trough 2, wherein the emitted beam of the light source 60 is deflected, for example, by a mirror 7. The mirror 7 can be designed such that it only reflects the radiation of the light source 60, but is transparent for other wavelength ranges. The radiation source 60 is, according to Fig. 1 For example, an optical element 61, e.g., a lens, is arranged in front of the device, and the radiation unit thus formed is designated overall by 6. The radiation source 60 can emit, for example, conventional light, but also IR or UV radiation.

[0025] A support surface 4 can be moved relative to the receiving space 14 by an actuator 12, for example a stepper motor drive. The tray 2 is advantageously designed such that it can be precisely aligned and centered with respect to the passive light source(s), e.g., 10, 11, as well as with respect to the radiation unit 6 when inserted into the stereolithography system, and can assume a specific position advantageous for the measurement method relative to the passive light source(s) 10, 11, which are located in the system space 15. Advantageously, the sensor 5 can also assume any position within the system space 15 that is appropriate for the measurement method. The tray 2 itself can also be designed such that it is capable of redirecting the beam path of the passive light sources 10 and 11, respectively; see also Fig. 6 , for example, in a specific embodiment to enable a space-saving arrangement of the passive light sources 10, 11.

[0026] According to Fig. 1 the passive radiation is coupled from the side into the reference layer 80 in order to be reflected, for example, by total internal reflection (cf. Fig. 3 ) within the reference layer 80. A control device 13, for example a control computer, controls the movements of the support surface 4 as well as the entire process sequences necessary for producing the body 3 in the system 1, including the light source 60 or 6, and detects the passive measuring radiation via the at least one sensor 5 in order to evaluate it.

[0027] Fig. 2 shows in comparison to Fig. 1 a variant of a stereolithography system 101, in which the passive radiation sources 110, 111 are located below the tank 2 in the system room 15 and irradiate the underside of the tank 2 and preferably illuminate it uniformly. The at least one sensor 5 is also located in the system room 15 and detects the reflection or scattered radiation from the underside of the tank 2, which is formed at least by the reference surface 80, possibly also by a base 8. In this embodiment, the passive radiation is not necessarily coupled into the reference layer 80 or the tank 2, and the tank 2 does not have to be fully transparent to the passive radiation; the reference layer 80 merely needs to have a certain reflectivity for the passive radiation.

[0028] Deviating from the embodiments according to Fig. 1 and 2The system, e.g., 1, may also comprise a sensor 5 capable of detecting the exothermic solidification processes triggered by the radiation source 60. This allows at least partial detection of the polymerization state of the formed layer, e.g., 30, 31, 32, and the recording of the radiation by the sensor 5 can also provide information about the possible separation process of the produced layer, e.g., 30, 31, 32.

[0029] Fig. 3 shows a detailed section through the recording room 14, in which two bodies 60, 70 are created. In this Fig. 3 For better understanding, the reference layer 80 and the passive radiation of the passive radiation sources 10, 11 coupled into it and transported by total internal reflection are shown schematically using exemplary, zigzag-shaped geometric beam paths. Fig. 3 also shows the deformation of the elastic reference layer 80 caused by separation forces F1 and F2 on the bodies 60 and 61, respectively. The - optional - base 8 merely serves as a support for the elastic reference surface 80. The separation forces F1 and F2 are not equal in the illustration shown, since the body 60 has a substantially larger cross-sectional area than the body 70, and thus in this example F1 > F2 applies, whereby the deformation of the reference layer 80 is also different as a result.

[0030] Due to the different deformation, the total reflection within the reference layer 80 is also disturbed depending on the location, and radiations 40, 50 are accordingly coupled out of the reference layer 80 in a certain ratio to the respective separating force F1, F2. For optimal adjustment of the total reflection within the reference layer 80, the position of the passive light sources 10, 1 can be positioned, for example, by an angle α in the system room 15; however, it is understood that the passive radiation sources 10, 11 can be freely positioned in all spatial coordinates. The sensor 5 thereby detects the position and the temporal behavior (intensity curve) of the scattered radiation 40 or 50, which depends on the respective force, e.g., F1 or F2.

[0031] Fig. 3a shows an embodiment of the system 1 without a separate floor 8, also in a schematic section. The elastic reference layer 80 simultaneously forms the floor of the tub 2. This offers the advantage that the Fig. 3a The scattered radiation 40, 50 shown in FIG. 1 is not attenuated by a further layer. In addition, the reference layer 80 can be designed in its elasticity and thickness such that a desired load-bearing capacity of the tub 2 (in Fig. 1 and 2 ) for the photosensitive liquid 9, with a simultaneous "membrane-like" behavior of the reference layer 80, which promotes the separation of the bodies 60, 70 and minimizes the separation forces F1, F2. Also, for example, a thicker reference layer 80 can more easily couple passive radiation into this reference layer 80, and the position of the tank 2 or the passive radiation sources 10, 11 in the system room 15 (see Fig. 2 ) needs to be adjusted less precisely.

[0032] Fig. 4 also illustrates a section through the receiving space 14 of a system in which the passive radiation sources 110, 111 are arranged below the trough 2 in a position in the system space 15 and illuminate at least the reference layer 80 and the optional floor 8 more or less uniformly. The elastic reference layer 80 is deformed, at least as shown, by the separating forces F1, F2, which depend on the cross-sectional area of ​​the formed body(s) 60 or 70. The illustration again illustrates, for example, that the body 60 has a larger cross-sectional area than the body 70, and thus it can be assumed that the separating force F1 is greater than the separating force F2. The elastic reference layer 80 is in turn deformed by the separating forces F1, F2 depending on the location, resulting in a change in the illumination by the passive radiation sources 110, 111 depending on the magnitude of the deformation of at least the reference layer 80.The deformation causes a different time- and location-dependent reflection behavior of the tub 2 or the reference layer 80 and / or the floor 8, which in turn can be detected by the sensor 5.

[0033] Fig. 4a shows a variant, starting from the system according to Fig. 4 , where again the floor 8 was omitted, similar to the case of the Fig. 3a in relation to Fig. 3 . Here again, it can be assumed that the reference layer 80 is sufficiently stable to support the liquid 9 and the shaped bodies 60, 70. Furthermore, similar to Fig. 4 The beams of radiation sources 110 and 111 are schematically illustrated at 202 and 203. Finally, the respective radiation 50 and 40 is also illustrated.

[0034] Fig. 5 illustrates by way of example a location- and time-dependent change in the intensity distribution of the passive radiation caused by an outcoupled radiation, detected by the sensor 5, e.g. by the action of the forces F1, F2 and the resulting time- and location-dependent deformation of the reference surface 80 and possibly also of the bottom 8 of the trough 2 (see Fig. 3 , Fig. 3a ) or by a change in reflection (see Fig. 4 and Fig. 4a ) in the measuring space 15 detected by at least one sensor 5. In this case, for example, in the area detected by the sensor 5, depending on the deformation of the elastic reference layer 80 that occurs, areas 61, 71 occur which each depend on the intensity distribution that differs from the respective body 60, 70; these intensity distributions are detected by the sensor 5 as a function of location and time and are related to the separating forces F1, F2 that occur. If, for example, the sensor 5 is designed as an infrared camera and infrared radiation is used as passive radiation, the sensor 5 detects a specific measuring area of ​​the measuring space 15 as image information or video information which represents the geometric characteristics of the cross-sectional areas, an intensity distribution corresponding to the separating forces F1, F2 that occur, either in predetermined time-resolved steps or continuously.In this case, for example, in regions 72 in which no or less deformation occurs, less passive radiation is detected by the sensor 5, and these therefore appear, for example, darker in the overall image detected by the sensor 5 than, for example, the regions 61, 71 in which a deformation of the elastic reference layer 80 occurs.

[0035] It goes without saying that the person skilled in the art can easily make various modifications and additions to the embodiments of the invention disclosed here.

[0036] In Fig. 6 is shown schematically, with the trough 2 partially illustrated, an embodiment in which radiation sources 210, 211 provided below the trough 2 couple radiation upwards into the bottom 8 of the trough 2, which in turn is formed by the reference layer 80. In this reference layer 80, in the beam path of the radiation sources 210, 211, obliquely arranged mirrors or light guide elements 212 and 213, which are preferably formed directly from the material of the reference surface, are attached or formed in order to deflect the measuring radiation emitted by the radiation sources 210, 211 and thereby couple it into the bottom 8 or the reference layer 80. Even if this is not described in more detail in Fig. 6 As illustrated, this coupling can again be achieved, similar to Fig. 3 , with an angle such that a total reflection of the reference layer 80 results (in Fig. 6 not shown).

[0037] Furthermore, a sensor 5 on the underside can be used, as shown in the Fig. 1 bis 5 shown, and a control device 13, as shown in Fig. 1 and 2 shown, be appropriate. Fig. 7a shows a detailed section through a recording space 14 in which two bodies 60, 70 are produced. The photosensitive material 9 has, as in Fig. 7a shown an intermediate phase 9A. This intermediate phase 9A has a reduced reactivity compared to the material 9. This reactivity difference, which leads to the formation of the intermediate phase 9A in the photoreactive material 9, can be achieved, for example, by chemical inhibitors, such as oxygen. The thickness H of the intermediate layer 9A has, as shown in Fig. 7a As shown, a value (such as 30, 50, 100 micrometers, etc.) is selected such that the intermediate layer 9A at least largely prevents, if not completely suppresses / prevents, the formation of the separation forces F1, F2. Due to the absence of the separation forces, ideally no coupling of measuring radiation occurs. Thus, a conclusion can be drawn regarding the presence of a sufficient intermediate layer.

[0038] Fig. 7b shows how Fig. 7aa detailed section through the receiving space 14, wherein this schematic diagram shows a case in which the intermediate layer 9A has a thickness h. Here, h is smaller than H (h <H). In der dargestellten Prinzipskizze ist beispielhaft also ein möglicher Grenzfall dargestellt in der die Zwischenschicht 9A auf einen Grenzwert h abgefallen ist, beispielsweise durch Konsum des Inhibitors oder durch Prozessgrößen, so dass erstmals messbare Trennkräfte F1 und F2 auftreten. Dadurch kann im Rückschluss - und dies ggf. orts- und zeitaufgelöst - festgestellt werden, wo der Grenzfall der Zwischenschichtdicke erreicht wurde, um ggf. prozesstechnische Schritte auszulösen um die Zwischenschicht 9A entsprechend zu regenerieren und / oder aktiv nachzubilden.For example, this can be achieved by additional and / or increased supply of at least one inhibitor, by changing an inhibitor concentration (e.g. oxygen-enriched air), by appropriately varying the process variables such as the exposure energy, waiting times, stroke speed, etc., and / or by deliberately introducing pauses.

[0039] These changes, individually or in combination, contribute to increasing the height of the intermediate layer 9'. Using the described measurement method, changes in the intermediate layer 9A can also be recorded with spatial and temporal resolution, for example, through a targeted, spatially resolved supply of inhibitor, which only occurs in the area where the intermediate layer is to be specifically increased or regenerated. This targeted supply could also be dependent on the geometric extension of the body or depending on the exposure area. Thus, using the described measurement method, the thickness of the intermediate layer 9A can be specifically recorded and increased locally, if necessary, depending on the extension of the body to be generated.

Claims

1. Measurement method during the production of a three-dimensional body (60, 70) in a stereolithographic process, wherein a photosensitive material (9) is cured by radiation from a radiation source (60), characterized in that the exothermic solidification processes triggered by the radiation source (60) are detected by a sensor (5) in order to at least partially detect the polymerization state of the layer (30, 31, 32) formed and the detection of radiation by the sensor (5) also enables conclusions to be drawn about the separation process of the produced layer (30, 31, 32), wherein the sensor (5) is designed as an infrared camera.