Patent ID: 12188828

DETAILED DESCRIPTION

FIG.1is a schematic drawing of the lateral cross section of a 3D printer2according to the invention for a stereolithography process or digital light processing process, having a build platform4, a receiving or holding device10for printing material8, a thermal imaging camera12and a control device14. In this embodiment, printing material6cured on the lower face of the build platform4is represented schematically. The cured printing material6can take on different forms depending on the printed object, and is represented here by columns of different thickness. Further, an arrow indicates the direction of movement of the build platform4, which can be displaced vertically up and down.

Below the build platform4, there is a receiving device10for printing material8, the fill level of the printing material8being represented by a dashed line. The lower boundary11of the receiving device10consists of a transparent material, preferably a transparent film.

A thermal imaging camera12is directed onto the outer and lower surface9of this film11, and is in turn connected to a control device14. Using this thermal imaging camera12, the temperature of the part of the surface9of the foil11to be inspected can be measured. For this purpose, the thermal imaging camera is directed onto or at the lower surface9of the very thin film11, and the heat emission during and between illuminations is recorded. In this case, the part is a dental restoration and the area of the foil11to be monitored is approximately 5 cm×5 cm. The control device14can generate a 2-dimensional temperature distribution over the part of the surface9of the foil11to be checked from the data recorded by the thermal imaging camera12, taking into account the thermal conductivity and thermal capacity of the materials used—the translucent foil11and the printing material8.

In the event of abnormalities in the 2-dimensional temperature distribution between two or more layers and/or other unexpected changes in temperature, the control device14emits a signal to warn of errors. Possible errors include, for example, the absence of a sudden increase in heat emission when exposure is started, or the absence of a sudden decrease in temperature when the cured printing material is released from the film. It is also possible that upon comparison of the 2-dimensional temperature tracking, and thus the comparison of the illuminated and cured areas of two or more layers, an excessive area increase or decrease in the cured layer is recorded.

In the event that errors are recorded in the printing process, this can be optionally automatically adjusted by the control device14. However, it is more common that if a warning signal is emitted, the control device14pauses the printing process until all errors have been eliminated by the user and the user triggers the printing process again.

FIG.2shows a schematic representation of the lateral cross-section of a further embodiment of a 3D printer2according to the invention. Here, an active printing process, i.e., a layer being exposed, is shown by means of a 3D printer according toFIG.2. The columns shown herein of the cured printing material6, which are intended to represent schematically the already printed object, are immersed or dipped into the printing material8. Centrally below the receiving device10, a light source18having a conical illumination region20is schematically shown. A light source of this type may be a high-precision laser which emits the optimum wavelength as appropriate for the respective photoinitiator, or else preferably an LED light source. For simplicity, the entire possible detection region is shown here, although the capture may take place in a spatially resolved manner using a focus mark of for example 0.5 mm×0.5 mm. Between the already cured printing material6and the transparent film11, newly cured material16is schematically shown.

For simplicity, conical illumination20is shown. However, it would also be possible to illuminate only the desired regions (1 pixel for example 20×20 μm) between the already cured material6and the transparent film11using a plurality of light sources, which illuminate smaller regions or appropriate deflection mirrors, optionally with a slight increase or decrease in area. In this embodiment, the thermal imaging camera12is only directed onto the illuminated region or exposed region of the film surface9, even if this is not shown in detail in the drawings, and is focused and therefore only receives or records the heat emission of this small region. By way of illustration, this is shown using dot-dash lines. As a result of this concentration on the important region, i.e., the exact region of the 3D-printing process, it is possible to avoid unnecessarily large datasets and thus slow processing by the control device14.

FIG.3graphically displays the light output, the temperature progression and the z-position of the build platform4, i.e., the internal vertical displacement of the build platform4with respect to the transparent film11, during the 3D-printing process.

Line a) gives information about the light output of the light source18in [mW/cm2]. When the light source18is switched on, the light output increases linearly with a steep gradient, optimally jumping up. During the illumination, the light output or power is kept constant and subsequently switched off, which results in a sudden drop in the light power.

Line b) shows the progression of the room temperature during the 3D-printing process. This should optimally be kept constant so as to avoid incorrect measurement of the temperature progression at the film surface9.

Line c) shows an optimum temperature profile at the surface9of the transparent film11during the printing process. This temperature progression is recorded by the thermal imaging camera12and evaluated by the control device14. The temperature increases at the time when the light source18is switched on. This is caused by the incident light power of the light source18, as well as the onset of exothermic polymerization of the printing material8. When the change in temperature dT/dt approaches a particular value as close as possible to zero, in particular a zero value, the maximum of the temperature during the polymerisation process Tmaxis approximately reached. The value dT/dt=0 cannot be reached within a finite time, and therefore a value close to zero is resorted to in order to keep the illumination duration as short as possible and nevertheless to achieve appropriate curing of the printing material8. At this point, the light source18is switched off and the temperature of the surface9of the transparent film11slowly returns to its initial value.

Line d) provides information about the z-position of the build platform4, i.e., the internal vertical displacement of the build platform4with respect to the transparent film11, during the progression of a 3D-printing process. The build platform4is moved or displaced close to the light-transmissive/transparent film11prior to exposure or illumination in order to achieve a defined gap of x mm (where x may be adapted depending on the requirements).

After completion of the exposure process, the build platform4is moved away from the film11again to achieve a detachment of the cured material6from the light-transmissive film11.

Moreover, time periods1to5are marked inFIG.3. These denote the individual stages of the 3D-printing process. Region1is the initial value and represents the starting position and the temperature without illumination or exposure. This point is optimally reached again for all of curves a) to d) after the printing process.

Region2shows the approach of the build platform4towards the transparent film11. At this point, the light source18is switched off and the temperatures correspond to the starting value. At the end of region2, i.e., when the build platform4is optimally approaching the film11, the light source18is switched on and the polymerisation starts. This can be recognized by the beginning temperature increase of line c).

In region3, the maximum heating temperature Tmaxof the film surface9is reached during exposure. Here, the temperature change dT/dt approaches a certain value, in particular the value zero. When this value is reached, the light source18is switched off and the temperature of the surface9of the transparent film11starts to fall again.

Region4denotes the cooling process of the film surface9, after the illumination has terminated and the polymerisation is thus ended. When the starting temperature of the film surface9is reached, time period5starts, at which point the build platform4travels back to its starting position and the polymerised printing material6is thus detached from the transparent film11. At the end of region5, all the parameters return to their initial values (region1).

FIG.4shows a modified embodiment compared to that shown inFIG.3. In this context, the light output, the temperature profile and the Z-position of the build platform4, i.e., the internal vertical displacement of the build platform4with respect to the transparent film11, during the 3D-printing process, are again graphically shown.

Compared toFIG.3, the Z-position of the build platform4is different. Line a) shows the Z-position of the build platform4, i.e., the internal vertical displacement of the build platform4with respect to the transparent film11, during the progression of a 3D-printing process. The build platform4is moved away from the light-transmissive film11after curing (exposure) and then approached again to achieve a defined gap of x mm (x can be adjusted according to the requirements).

Line b) shows the progression of the light output18in mW/cm2. When the light source18is switched on, the light output jumps up. While the build platform4is moving, the light source is switched off and thus has an output of 0 mW/cm2. During illumination, the light power is kept constant.

Line c) shows, similarly to inFIG.3, an optimum temperature progression at the surface9of the transparent film11during the printing process. The temperature increases at the time when the light source18is switched on and the build platform4is displaced in the Z-direction, and remains constant when a particular value is reached, in particular the temperature of the liquid printing material8. If the light source is switched on again, the temperature increases again. This is caused by the incoming light output of the light source18and the onset of the exothermic polymerisation of the printing material8. After the curing has ended, the temperature remains constant again (change in temperature dT/dt approaches a zero value). This corresponds to the maximum of the temperature during the polymerisation process Tmax.

The room temperature (in this case line d)) during the 3D-printing process should be kept as constant as possible to avoid erroneous measurement of the temperature progression at the film surface9.

Moreover,FIG.4shows time periods I to III. These denote the individual portions of the 3D-printing process.

Region I shows the Z-position of the build platform4during the illumination process. In this context, the light source18is switched on and the film surface9shows the maximum heating temperature Tmaxreached during the illumination. The change in temperature dT/dt approaches a zero value here.

Region II shows the change in the Z-position of the build platform4between two illumination processes. The build platform4is raised. At the start of the movement of the build platform4, the light source18is switched off, causing the temperature at the surface9of the transparent film11to decrease sharply and remain constant until the end of this region II when a certain temperature is reached, in particular the temperature of the liquid printing material8.

Region III again shows the lowering of the Z-position of the build platform4at the start of an illumination progress. The light source is switched on again, in such a way that the temperature at the surface9of the transparent film11increases again. This is caused by the incoming light output of the light source18and the onset of the exothermic polymerisation of the printing material8.

After the curing is complete, the temperature again takes on the constant value Tmaxin accordance with region I (change in temperature dT/dt approaches a zero value). This indicates the end of the polymerisation process, so that the cycle can start again.

FIG.5is a schematic drawing of a further embodiment of a 3D printer2according to the invention. The special feature here is the optics or optical system used for guiding the light radiation towards the printed object or printing material6, i.e., towards the surface9of the transparent film11, and to guide the thermal or IR radiation from the printed object/printing material6towards the thermal imaging camera12.

The light source18is located next to the object to be printed in this embodiment, and is shown above said object inFIG.5. Radiation19exiting the light source18and used for illumination is deflected via a mirror30to a converging lens28.

In an advantageous embodiment, the mirror30is designed with an edge filter, in such a way that the radiation19is reliably reflected but natural light can pass freely through the mirror. The lens28is suitable for converging and parallelizing the individual light rays of the illumination radiation19, and optionally also the additional natural light radiation. The now parallel rays of the illumination radiation19are passed on from the (converging/collecting) lens28to two laminated prisms25and26and a DMD unit24.

In this embodiment, the two prisms25and26together form a “Total Internal Reflection” prism (TIR prism)27. Total Internal Reflection is a physical phenomenon occurring in waves, such as light rays, and occurs when light strikes a flat interface with another transparent medium in which the propagation speed of the light is greater than in the original medium. If the angle of incidence is varied continuously, this effect occurs relatively abruptly at a particular value of the angle of incidence. This specific angle of incidence is known as the critical angle of total internal reflection. The light mostly no longer passes over into the other medium, but instead is (more or less) totally reflected back into the starting medium from this angle onwards. The TIR prism, i.e., the optical element, which is composed of the two laminated prisms25and26, can thus be used as a mirror. If the refractive index of the TIR prism27is high enough, total internal reflection (TIR) is achieved, and the TIR prism27acts like a mirror with 100% reflection.

As a combination of two laminated prisms25and26, the TIR prism27deflects/directs the incident light onto the DMD unit24, and the image to be produced is projected using the light ray reflected from the DMD unit24. The use of a TIR prism27thus allows a considerable savings of space since the same effect could only be achieved with a highly complex combination of mirrors. Moreover, this greatly increases the contrast achieved by the system.

The radiation exiting the TIR prism continues onwards to a projection lens22, which again splits the parallel rays of the illumination radiation19into a conical illumination region20. For simplicity, a possible illumination region20is shown here, but the illumination may be spatially resolved using a focus mark of for example 0.5 mm×0.5 mm.

The radiation of the conical illumination region20is subsequently directed to a semi-transparent mirror32, known as a splitter or divider mirror, through which the illumination radiation19can pass. Subsequently, the illumination radiation19is incident on a transparent film11, and illuminates a desired region between said film and the already cured material6. The resulting thermal radiation13, i.e., the IR radiation, is emitted by the material6and guided back through the transparent film11to the semi-transparent mirror32.

In an advantageous embodiment, the mirror32is formed as a splitter mirror, i.e., in such a way that the thermal radiation13, i.e., the IR radiation, is re-reflected towards the thermal imaging camera12, but the illumination radiation19, for example UV radiation, can pass through the mirror unchanged.

For simplicity, a conical illumination region20is shown. However, by using a plurality of light sources which illuminate smaller regions, it is also possible to illuminate only the desired region or areas (1 pixel for example 20×20 μm) between the already cured material6and the transparent film11, optionally with a slight increase or decrease in area.

In an advantageous embodiment, the DMD unit24can further switch individual pixels of the illumination region on or off depending on completeness of curing. This makes it possible to prevent overexposure of already cured regions.

In all places, the film can be light-transmissive, light transmitting, translucent or transparent. Illumination and exposure are interchangeable.

In some embodiments, the innovations may be implemented in diverse general-purpose or special-purpose computing systems. For example, the computing environment can be any of a variety of computing devices (e.g., desktop computer, laptop computer, server computer, tablet computer, gaming system, mobile device, programmable automation controller, etc.) that can be incorporated into a computing system comprising one or more computing devices.

In some embodiments, the computing environment includes one or more processing units and memory. The processing unit(s) execute computer-executable instructions. A processing unit can be a central processing unit (CPU), a processor in an application-specific integrated circuit (ASIC), or any other type of processor. In a multi-processing system, multiple processing units execute computer-executable instructions to increase processing power. A tangible memory may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two, accessible by the processing unit(s). The memory stores software implementing one or more innovations described herein, in the form of computer-executable instructions suitable for execution by the processing unit(s).

A computing system may have additional features. For example, in some embodiments, the computing environment includes storage, one or more input devices, one or more output devices, and one or more communication connections. An interconnection mechanism such as a bus, controller, or network, interconnects the components of the computing environment. Typically, operating system software provides an operating environment for other software executing in the computing environment, and coordinates activities of the components of the computing environment.

The tangible storage may be removable or non-removable, and includes magnetic or optical media such as magnetic disks, magnetic tapes or cassettes, CD-ROMs, DVDs, or any other medium that can be used to store information in a non-transitory way and can be accessed within the computing environment. The storage stores instructions for the software implementing one or more innovations described herein.

Where used herein, the term “non-transitory” is a limitation on the computer-readable storage medium itself—that is, it is tangible and not a signal—as opposed to a limitation on the persistence of data storage. A non-transitory computer-readable storage medium does not necessarily store information permanently. Random access memory (which may be volatile, non-volatile, dynamic, static, etc.), read-only memory, flash memory, memory caches, or any other tangible, computer-readable storage medium, whether synchronous or asynchronous, embodies it.

The input device(s) may be, for example: a touch input device, such as a keyboard, mouse, pen, or trackball; a voice input device; a scanning device; any of various sensors; another device that provides input to the computing environment; or combinations thereof. The output device may be a display, printer, speaker, CD-writer, or another device that provides output from the computing environment.

The scope of protection of the present invention is given by the claims and is not limited by the features explained in the description or shown to the figures.