Stereolithography apparatus with oscillatory agitation to prevent three-dimensional object from adhering to vat

Abstract

A stereolithography apparatus (1) for generating a three-dimensional object (2) from a photo-curable substance (3), comprising a vat (4) for storing the photo-curable substance (3), and a platform (5) for supporting the three-dimensional object (2), wherein the platform (5) is movable relative to the vat (4), an optical unit (6) for sequentially projecting layer images towards the photo-curable substance (3) in order to harden the photo-curable substance (3) deposited between the three-dimensional object (2) and the bottom of the vat (4), further comprising an oscillation unit (7) adapted to horizontally oscillate the vat (4) with a substantially constant amplitude simultaneously with the projection of the layer images in order to prevent the three-dimensional object (2) from adhering to the bottom of the vat (4).

Description

TECHNICAL FIELD

[0001] The invention relates to a stereolithography apparatus for generating a three-dimensional object from a vat of photo-curable substance. The invention more particularly relates to a technique for preventing the three-dimensional object from adhering to the bottom of the vat. BACKGROUND

[0002] Stereolithography apparatuses are used to manufacture three-dimensional objects having a desired shape by stepwise or continuously exposing a photo-curable substance, for example a liquid monomer in a vat, with a layer image which can be generated for example by a digital mask or by a scan of a laser beam in an ultraviolet region. The basic principle of stereolithography is also commonly known as rapid prototyping or three-dimensional printing. For stereolithography manufacturing, a layer image, in particular a pixel-based layer image, is projected into a reference surface of the photo-curable substance, using alternatively a pixel-based display creating a digital mask or a laser beam in combination with a controllable micro-mirror, to make it harden stepwise or continuously. The reference surface is defined by a focus layer in which the solidification of the photo-curable substance takes place and a solidified layer is formed. Depending on the application, the solidified layer can have a rigid or flexible consistency and is generally positioned within the volume of the fluid photo-curable substance on the bottom of the vat. The solidified layer is first transferred onto a platform which is relatively movable with respect to the vat, by adhesion during the polymerization process. During the exposure, the solidified layer also adheres to the bottom of the vat. After the exposure, the solidified layer has to be separated from the bottom of the vat so that fresh photo-curable substance can flow between the last solidified layer, i.e. the polymerization front, and the bottom of the vat. The solidified layer is generally separated from the bottom of the vat by tilting or moving the vat with respect to the platform holding the three-dimensional object. Thereafter, the flowed-in photo-curable substance is solidified by a subsequent exposure. These steps are repeated until the three-dimensional object is generated according to the projected layer images. In a well-known technique, the bottom of the vat is covered with an elastic film from which the three-dimensional object can be peeled off more easily when the vat is tilted or moved. In another well-known technique, a specific material permeable to oxygen is used at the bottom of the vat which can prevent the three-dimensional object model from adhering to the bottom of the vat. However, such oxygen-permeable vat is relatively expensive.

[0003] US 2017 / 0210072 Al discloses a system for additive manufacturing of homogeneous optical elements with reduced scattering and diffraction effects by a DLP projector and a quasi-random lateral vibration of the resin tank. The random amplitude is 1.5 pixels in size.

[0004] WO 2016 / 172788 Al discloses a stereolithography system with a resin tank having a pair of ultrasonic transducers that vibrate up and down for tilting the resin tank after exposure to peel off the manufactured object.

[0005] US 2018 / 0243987 A1 discloses an additive manufacturing system having an ultrasonic vibrator connected to a vat, which is vibrated after the slicing is completed to separate the manufactured object from a window of the vat.

[0006] WO 2018 / 187874 A1 discloses a stereolithography system having a strategic transducer placed on a corner of a vat of resin to facilitate the release of the solidified object from the vat with a certain amplitude of vibration in the direction of the print layer thickness. EP 3205484 A1 discloses a three-dimensional printer having a vibration device to facilitate the separation of the printed object from the bottom of the resin tank after printing. SUMMARY

[0007] It is an object of the present invention to overcome the disadvantages of the prior art to provide a stereolithography apparatus in which the adhesion of the three-dimensional object on the bottom of the vat can be effectively prevented during exposure in a less complex manner.

[0008] This object has been achieved by a stereolithography apparatus as defined in claim 1. The dependent claims relate to further developments.

[0009] The stereolithography apparatus of the present invention is suitable for generating a three-dimensional object from a light-curable substance, comprising a vat for storing the light-curable substance, a platform for supporting the three-dimensional object, wherein the platform is movable relative to the vat, an optical unit for sequentially projecting layerwise images towards the light-curable substance in order to harden the light-curable substance deposited between the three-dimensional object and the bottom of the vat, and an oscillation unit adapted to horizontally oscillate the vat with a substantially constant amplitude simultaneously with the projection of the layerwise images, said amplitude being smaller than the pixel size of the layerwise images in the horizontal direction, in order to prevent the three-dimensional object from adhering to the bottom of the vat.

[0010] The main advantageous effect of the present invention is that by the simultaneous oscillation excitation, the three-dimensional object can be prevented from adhering to the bottom of the vat during exposure. Thus, the need to tilt or move the vat after exposure can be eliminated, so that the manufacturing process can be further accelerated. Moreover, the need to use a vat permeable to oxygen, an elastic foil can be dispensed with, and the manufacturing costs can be relatively reduced.

[0011] According to the present invention, the vat can also be continuously oscillated between successive exposures, i.e. during the generation pause, to fill the gap between the last solidified layer and the bottom of the vat with the fluid light-curable substance, i.e. resin, more quickly. Thereby, the generation pause time can be relatively shortened, the manufacturing process can be further accelerated.

[0012] According to an embodiment of the present application, the oscillation unit horizontally oscillates the vat during the generation process and / or in the generation pause. Thus, the fluid light-curable substance can be more effectively prevented from adhering to the vat. And the gap can be more effectively refilled with the fluid light-curable substance.

[0013] According to an embodiment of the present application, the oscillation unit oscillates the vat with an amplitude smaller than a pixel size of the layered image and a frequency higher than an exposure frequency of the layered image. Thereby, blurring of the three-dimensional object can be effectively reduced.

[0014] According to an embodiment of the present application, the oscillation unit has at least one actuator oscillating the vat. The actuator can be directly connected to the vat or a support of the vat. The vat is preferably exchangeably mounted to the support. The actuator is controlled by a control unit of the stereolithography apparatus based on the layered image, the pixel size, the exposure time, the viscosity of the light-curable substance, etc. The actuator can be piezoelectric. Other types of actuators known to the skilled person can be used alternatively. BRIEF DESCRIPTION OF DRAWINGS

[0015] In the following description, further aspects and advantageous effects of the present application will be described in more detail by using exemplary embodiments and with reference to the accompanying drawings in which,

[0016] Figure 1 A stereolithography apparatus according to an embodiment of the present application is shown.

[0017] The reference signs shown in the drawings represent elements listed below and will be referred to in the following description of exemplary embodiments:

[0018] 1. Stereolithography apparatus

[0019] 2. Three-dimensional object

[0020] 3. Light-curable substance

[0021] 4. Vat

[0022] 5. Platform

[0023] 6. Optical unit

[0024] 7. Oscillation unit

[0025] 8. Actuator

[0026] 9. Control unit

[0027] 10. Drive unit DETAILED DESCRIPTION

[0028] Figure 1A stereolithography apparatus (1) for generating a three-dimensional object (2) from a photocurable substance (3) is shown. All processes in the stereolithography apparatus (1) are controlled by a control unit (9). The photocurable substance (3) is stored in a vat (4). The vat (4) is arranged on a support. An optical unit (6) projects a layer image sequentially towards the photocurable substance (3) in order to harden the photocurable substance (3) deposited between the three-dimensional object (2) and the bottom of the vat (4). Simultaneously with the projection of the layer image, an oscillation unit (7) oscillates the vat (4) in order to prevent the three-dimensional object (2) from adhering to the bottom of the vat (4). The three-dimensional object (2) is supported by a platform (5). The platform (5) is movable relative to the vat (4) by a drive unit (10).

[0029] The oscillation unit (7) oscillates the vat (4) along a horizontal direction, preferably in the X-direction and / or the Y-direction. The amplitude and the frequency of the oscillation are controlled by the control unit (9) based on the type of the photocurable substance (3) and the layer image, in particular the pixel size and the exposure frequency. The amplitude of the oscillation is preferably smaller than the pixel size of the layer image. The frequency of the oscillation is preferably higher than the exposure frequency of the layer image. The exposure frequency is inversely proportional to the exposure time of each layer image.

[0030] According to an embodiment of the present invention, the oscillation unit (7) has at least one actuator (8) oscillating the vat (4). The actuator (8) can be directly connected to the vat (4). Alternatively, the actuator (8) can be connected to a support of the vat (4).

[0031] According to an embodiment of the present invention, the actuator (8) can comprise an electromechanical actuator. A piezoelectric actuator can be used. Alternatively, an electroactive polymer actuator can be used. Alternatively, a magnetostrictive actuator can be used.

Claims

1. A stereolithography apparatus (1) for generating a three-dimensional object (2) from a photocurable substance (3), said stereolithography apparatus comprising: a vat (4) for storing said photocurable substance (3); a platform (5) for supporting said three-dimensional object (2), wherein said platform (5) is movable relative to said vat (4); an optical unit (6) for sequentially projecting layerwise images towards said photocurable substance (3) in order to harden said photocurable substance (3) deposited between said three-dimensional object (2) and the bottom of said vat (4); characterized in that said stereolithography apparatus further comprises: an oscillation unit (7) adapted to horizontally oscillate said vat (4) with an amplitude simultaneously with the projection of said layerwise images, said amplitude being smaller than the pixel size of said layerwise images in horizontal direction, in order to prevent said three-dimensional object (2) from adhering to the bottom of said vat (4) and in order to reduce blurring of said three-dimensional object (2).

2. The stereolithography apparatus (1) according to claim 1, characterized in that said oscillation unit (7) is further adapted to oscillate said vat (4) with a frequency equal to or higher than the exposure frequency of said layerwise images.

3. The stereolithography apparatus (1) according to claim 1 or 2, characterized in that said oscillation unit (7) comprises at least one actuator (8) adapted to oscillate said vat (4), wherein said at least one actuator (8) is directly connected to said vat (4) or to a support of said vat.

4. The stereolithography apparatus (1) according to claim 3, characterized in that said at least one actuator (8) is piezoelectric.

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