METHOD AND MASKING DEVICE

CROSS-REFERENCE

The present application claims priority to Swedish patent application no. 0701935-9, filed 27 August 2007, and US patent application number 60/968,1 15, filed 27 August 2007, both of which are incorporated herein by reference as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a method of creating a temporary computer-controlled mask adapted to selectively transmit electromagnetic radiation, preferably for use in equipment designed to perform Free Form Fabrication (FFF), and more preferably Solid Freeform Fabrication (SFF).

TECHNICAL BACKGROUND

It is known from United States Patent No. 6,531,086 to use a developer device that electrostatically applies a masking powder onto a transparent plate. Present-day developer devices are primarily intended to print toner on paper via a roller, onto which an electrostatic image has been deposited (such as a photoconductive drum in a laser printer). This takes place using a number of rollers that allow corona-charged toner to jump over different air gaps. See e.g., United States Patent No. 5,532,100. This method impairs the accuracy of the toner positioning and its edge sharpness. For each "jump" of the toner, less and less toner is transferred and the electrostatic charge must be adapted thereto. If an excessively high "jump voltage" is applied, so-called "blooming" is created, whereby the toner is spread in the pixels.

The present invention is directed, at least in part, to improving or overcoming one or more aspects of prior methods of forming a temporary computer-controlled mask adapted to selectively transmit electromagnetic radiation.

An object of the present invention is to overcome at least one of the above-mentioned drawbacks and to provide a sharp and accurate mask. SUMMARY OF THE INVENTION

According to a first aspect of the present disclosure, a method of creating at least one temporary computer-controlled mask or masking pattern adapted to selectively transmit electromagnetic radiation may comprise providing a transparent plate having two sides, wherein a capacitive layer is arranged or defined on one of the sides of the transparent plate and providing a powder chamber, wherein masking powder particles adapted to form, or suitable for forming, a masking pattern are stored. The masking powder particles preferably are selected for prohibiting radiation impinging on a masking pattern formed by the masking powder particles deposited on the transparent plate from reaching certain areas of particulate build material. A solid body comprising a large number of layers of melted, sintered or otherwise fused particulate build material is preferably manufactured from this particulate building material using the masking pattern formed by this method, as will be further discussed below.

Further, the method may also comprise the steps of fluidising or suspending the powder particles in the powder chamber, so that at least a part of the powder particles in the powder chamber are in a floating or suspended state and depositing or applying electrostatic charges, e.g., electrons or ions, in and/or on the capacitive layer of the transparent plate. Further, an electrostatic field may be formed in the powder chamber in order to electrostatically charge at least some of the suspended powder particles. In addition, at least some of the charged, suspended powder particles are directly applied or adhered to the transparent plate, which has the electrostatic charges deposited or printed thereon in a predetermined pattern, so that the desired masking pattern is formed from masking powder particles that electrostatically adhere to the transparent plate.

According to an exemplary embodiment, the electrostatic charges may be applied in, on or to the capacitive layer of the transparent plate using an electron beam imaging print head. Preferably, electrons are applied to the transparent plate, although an ion implant print head optionally may be utilised with the present teachings.

According to a further exemplary embodiment, the method may also include using the masking pattern to perform a SFF method, i.e. to form a fused or bonded layer of particulate build powder in order to form a three-dimensional volume body having a desired shape. The volume body is preferably designed using computer-aided design (CAD) techniques and may represent any arbitrary three-dimensional shape(s).

According to a further exemplary embodiment, at least one corona electrode is used to form the electrostatic field in the powder chamber.

According to a further exemplary embodiment, one or more electrodes may be used to fluidise or suspend the powder particles in the powder chamber and to generate a fluidised or suspended bed of the powder particles using a high- voltage, alternating electric field.

According to a further exemplary embodiment, a fluidised or suspended bed of the masking powder particles may be formed by flowing a gas medium into the masking powder particles disposed within the powder chamber. In addition or in the alternative, a suspension of masking powder particles may be formed by agitation of the powder chamber.

According to a further exemplary embodiment, the method may include mechanically scraping the transparent plate in order to remove a previously-formed masking pattern and returning or recycling the scraped-off powder particles to the powder chamber for reuse in a subsequent masking pattern forming method. Preferably, the mechanical scraping is achieved by movement of the plate relative to a scraping device.

According to a further exemplary embodiment, an electrostatic alternating electric field is applied to the transparent plate after removal of the powder particles forming the previous masking pattern, so that the transparent plate is electrically discharged and thereby prepared for a subsequent application of electrostatic charges for forming a new masking pattern on the transparent plate.

According to a further exemplary embodiment, the capacitive layer of the transparent plate may comprise at least one electrically-conductive layer and at least one outer electrically-insulating layer arranged outside the conductive layer. Further, the method may comprise depositing the electrostatic charges on the transparent plate using an attractive force generated by grounding or earthing the electrically-conductive layer.

According to another aspect of the present disclosure, a masking device for creating a temporary computer-controlled mask or masking pattern adapted to selectively transmit electromagnetic radiation may comprise a transparent plate having two sides, wherein a capacitive layer is arranged on one of the two sides. A powder chamber is adapted to store masking powder particles which are adapted to prohibit radiation impinging on a masking pattern formed by the powder particles deposited on the transparent plate from reaching certain areas of a particulate building material, from which a solid body comprising a large number of layers of melted, sintered or otherwise fused particulate building material is manufactured. Further, the device may comprise fluidizing or suspending means adapted to bring at least some of the masking powder in the powder chamber into an at least partly floating or suspended state. A printer device is adapted to deposit electrostatic charges, e.g., electrons or ions, in or on the capacitive layer.

Application means is adapted to generate an electrostatic field in the suspended powder that charges at least some of the powder particles and achieves direct transfer or application of the charged powder particles to the transparent plate.

According to a further exemplary embodiment, the device may comprise at least one corona electrode disposed in the powder chamber that is electrically connected, e.g., to a high-voltage direct current circuit and is adapted to charge and/or transfer the masking powder particles.

According to a further exemplary embodiment, the capacitive layer of the transparent plate may comprise at least one electrically-conductive layer and at least one outer electrically-insulating layer arranged outside the conductive layer, both layers being at least substantially transparent to the spectrum of wavelengths of the electromagnetic radiation. For example, the transparent plate is preferably transparent to the spectrum of infra red wavelengths. However, in other embodiments, the transparent plate may be transparent for another wavelength or ranges of wavelengths that is/are utilized in a volume body forming device, as will be further explained below.

According to a further exemplary embodiment, the capacitive layer of the transparent plate may comprise a computer-controlled matrix that is transparent to IR radiation.

According to a further exemplary embodiment, the fluidizing or suspending means may include one or more electrodes adapted to generate a fluidised or suspended bed of powder particles by application of a high- voltage alternating electric field to the powder particles. According to a further exemplary embodiment, the fluidizing or suspending means may include one or more air permeable devices adapted to agitate the marking powder particles, e.g., by application of a pressurized air source to the air permeable device(s).

According to a further exemplary embodiment, at least one of the air permeable devices may contain the corona electrode therein.

According to another aspect of the present disclosure, an apparatus adapted to manufacture a volume body formed by a plurality of mutually-connected layers of build powder particles that are bonded or fused to each other, e.g., using radiant heat or another type of radiation source, may comprise a support on which the volume body is built, an applying device adapted to apply or dispose a layer of not bonded build powder particles onto the support or onto a previously bonded layer of build powder particles. The device may also comprise a masking device as mentioned above and described in more detail below, and an irradiation device adapted to irradiate a layer of non-yet bonded build powder particles through a masking pattern generated by the masking device, so that only defined areas of the layer of build powder particles are melted, sintered, fused, bonded or otherwise mutually connected.

Moreover, the electrical charges applied or deposited in or on the capacitive layer of the transparent plate may be cleared or electrically discharged by application of an alternating electric field (a so-called Eraser).

In one embodiment, the present teachings provide the advantage that, by directly transferring the masking powder onto the transparent plate, the above mentioned drawbacks of the prior art may be reduced or eliminated, and a sharp and accurate mask or masking pattern may be generated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be explained in greater detail with reference to exemplary embodiments shown in the appended drawings. The invention is not limited to the depicted embodiments, but also comprises other embodiments that fall within the scope of the claims.

Fig. 1 shows a schematic perspective view of a first embodiment of a device according to the present teachings, as seen obliquely from above,

Fig. 2 shows a cross-section of the device according to Fig. 1,

Fig. 3 shows a schematic view of a part of the device shown in Fig. 2, which depicts further details of the electrical connection of the device,

Fig. 4 shows an alternative electrical connection according to the present disclosure,

Fig. 5 shows another alternate electrical connection according to the present disclosure, and

Fig. 6 shows a schematic view of an apparatus adapted to manufacture a volume body formed by a plurality of mutually-connected layers of powder particles that are bonded to each other using a radiation source, which apparatus includes a device according to Figs. 1-5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

In a preferred embodiment of the present disclosure, electrostatic charges 11 are first deposited on a capacitive surface 9, 10 of an essentially planar, transparent plate 1, e.g., using an electron beam imaging print head 2. The electrostatic charges 1 1 are printed or applied or deposited in a pattern that directly or indirectly (e.g., a "negative" image) represents a desired masking pattern for a subsequent volume body forming step. Then, corona-charged, non-meltable masking powder particles 4, which act as a radiation shield or filter during the volume body forming step, are directly transferred to the plate 1 in order to form a mask pattern 4a on the plate 1.

After the mask pattern 4a is utilized in the volume body forming step to form a fused or bonded layer of build powder particles, wherein radiation is transmitted through unmasked portions of the plate 1, the mask pattern 4a is removed from the plate 1, e.g., by mechanically removing the masking pattern 4a and/or by applying an alternating current and/or voltage to electrically discharge the capacitive layer 9, 10 such that a new mask 4a can be formed on the transparent plate 1 for a subsequent volume body forming step.

A first representative structure and some preferred aspects of a device capable of implementing a method according to the present teachings are further elucidated in Figs. 1, 2 and 3.

Fig. 1 shows a perspective view from above of a device comprising a substantially horizontally-arranged, transparent plate 1. This plate 1 can be moved back and forth relative to, preferably in or close to, a powder chamber 3 comprising masking powder 4. The powder chamber 3 is preferably arranged below the plate 1 and inside a machine casing (not shown). The machine casing is preferably designed according to the teachings of United States Patent No. 6,531,086, which teachings are incorporated herein by reference.

One or more electrodes 5, e.g. coil electrode(s), is/are preferably arranged inside the powder chamber 3 and are adapted to fluidize and/or suspend masking powder 4 stored inside the powder chamber 3. Further, a corona electrode 6 is preferably arranged between the transparent plate 1 and the bottom of the powder chamber 3. A corona electrode 6 is an electrode capable of generating a corona discharge, as is well known in the art and need not be further described herein.

A scraping device 7 is preferably disposed adjacent to the corona electrode 6 and even closer to the plate 1. The electrode 6, the scraper 7 and the powder chamber 3 preferably extend in a direction that is generally perpendicular relative to the direction of movement of the plate 1. A printer device 2, e.g., an electron beam imaging print head 2, is disposed adjacent to the powder chamber 3 and adjacent to the underside of the transparent plate 1. The printer device 2 is in electrical communication with and is controlled by a computer unit (not shown) so as to apply or print a predetermined print pattern to the plate 1. The print pattern is preferably controlled by or generated from a CAD drawing stored in the computer unit. A so-called eraser 8 is also close by or next to the lower surface of the plate 1 between the printer 2 and the powder chamber 3.

As shown in Fig. 3, the lower surface of the plate 1 has a capacitive layer that preferably comprises two layers 9, 10, e.g. at least one conductive layer 9 and at least one insulating layer 10. A direct current, high- voltage circuit 13 charges or energizes the corona electrode 6 and an alternating voltage (or current) circuit 14 charges or energizes the one or more coils 5. The alternating voltage and/or current is/are selected so as to fluidize or suspend at least some of the masking powder 4 in the chamber 3.

In a preferred embodiment, the method is utilised to form a masking device for a FFF (Free Form Fabrication) machine, more preferably a Solid Freeform Fabrication (SFF) machine, similar to the one described in United States Patent No. 6,531 ,086. In this reference, a glass plate 1 that is transparent to IR (infrared radiation) has a surface coating comprising an electrically-conductive layer 9, such as an ITO (indium tin oxide) layer 9, and an outer, electrically-insulating layer 10, such as glass, aluminium oxide or a similar electrically-insulating material. During transport of the plate 1 over the electron beam imaging print head 2, the print head 2 deposits, prints or applies electrostatic charges 11, e.g. electrons, in or on the insulating layer 10 due to an attractive force generated by electrically grounding or earthing the electrically conductive layer 9. The electrostatic charges 1 1 are deposited in a pattern (an electrostatic mask) that corresponds to a given layer/section of a three-dimensional CAD drawing, such as is known from the method described in United States Patent No. 6,002,415, which is also incorporated herein by reference.

Thereafter, the portion of the plate 1 having the electrostatic charges disposed thereon is moved over the powder chamber 3, wherein at least some of the masking powder 4 stored therein has been put into a floating or suspended state. In one preferred, but non- limiting embodiment, a suspended bed 4' of masking powder 4 is generated by applying a high-voltage alternating current to the coil electrodes 5, which generates an alternating electric field in the powder chamber 3. The electrodes 5 are preferably provided with an electrically-insulating layer in order to prevent electrical arcing or flash-over. One advantage of fluidizing or suspending the masking powder 4 by applying an alternating current to the coil(s) 5 is that the electrostatic potential of the charged masking powder, which is subsequently recycled into the powder chamber 3, is discharged when it comes into contact with the electric field generated by the coil electrodes 5.

A rectified high-voltage circuit 13 is electrically connected to the corona electrode 6 and to the conductive layer 9, thereby generating an electrostatic field that negatively charges at least some of the suspended masking powder 4' in accordance with the lines of force or electric field 6a directed towards the conductive layer 9, such as is known, e.g., from the method of GB 1,400,175, which is also incorporated herein by reference. In the areas Ib of the plate 1 where electrostatic charges (e.g., electrons) 11 are attached, the charged masking powder particles 4 are repelled. In the areas Ia where there are no electrostatic charges 11 , the charged masking powder particles 4 attached to the transparent plate 1 such that a mask pattern 4a is formed with IR-transparent portions and IR-blocking portions. That is, the powder particles 4 are attracted to and/or attach to the areas Ib in which the printing unit 2 did not apply or deposit the electrostatic charges 11 , such that a non-transparent or radiation-blocking coating or mask 4a is formed at the non-charged areas Ib of the plate 1.

In a further preferred embodiment of the present teachings, the mask pattern 4a applied to the plate 1 may thereafter be used in a known manner to sinter, melt or otherwise fuse a surface of IR-absorbing, meltable (or fusible) powder (preferably made of a synthetic resin) by applying or transmitting IR radiation (not shown) through the plate 1. For example, the transparent plate 1 may be moved from a mask generating device 18 to a volume body forming device 21, as shown in Fig. 6. When the mask pattern 4a on the plate 1 is disposed in relation to a volume body 19, the uppermost layer of "build powder" 20 (i.e. a powder material that melts, sinters, fuses, bonds, cures or solidifies upon application of radiation in order to form a solid body 19) is irradiated through the transparent portions of the masking pattern 4a. The masking powder 4, which is arranged on the transparent plate 1 according to the masking pattern 4a, blocks or filters the radiation applied by the irradiating device 17, so that little or no radiation passes through the plate 1 at the locations covered with the masking powder 4. As a result, the build powder 20 does not solidify (e.g., melt, sinter, fuse, etc.) in the non-irradiated areas.

After the irradiation step, the plate 1 may be returned to the mask forming device 18 for the application of a new mask pattern 4a to the plate 1. At this time, an applying or smoothing device 16 may be utilized to form a smooth or level upper surface of build powder 20 in the volume body forming device 21 for the next irradiation step. The portions of the uppermost layer of build powder 20, which are irradiated in the next irradiating step, will form the next solidified layer of the growing volume body 19.

After the plate 1 has been returned to the mask forming device 18, the electrostatically held powder mask 4a can be scraped off using the pivotal scraper 7 that acts against the lower surface of the plate 1. The removed masking powder 4 is thus preferably returned to the powder chamber 3 and can be used again for forming the next mask pattern 4a. The scraped off glass plate 1 is electrically-discharged when it passes over the eraser 8, which generates a high-voltage, alternating electric field, as was discussed above.

Thereafter, the print unit 2 can apply a new layer of electrostatic charges 11 in an appropriate pattern that represents or corresponds to the next layer/section from the CAD drawing, and thereby generate a new mask pattern 4a in order to fuse a new layer of build powder 20 with the preceding fused or solidified layers of the growing volume body 19. This process of forming mask patterns in the masking device 18 and irradiating the build powder 20 in the volume body forming device 21 is repeated until all layers/sections of the CAD drawing have formed one or more finished solid bodies 19.

Figs. 4 and 5 show alternative electrical connections in accordance with modified embodiments of the present teachings. Fig. 4 shows that the alternating current coil electrodes 5 can be connected to an insulated screen 12 via the high-voltage, alternating electric field circuit 14 instead of being connected to the direct current circuit 13 (as in Fig. 3). Fig. 5 shows that the alternating current coil electrodes 5 can also be connected to the corona electrode 6 via the high-voltage alternating current circuit 14. Both of these connections have the same function, i.e. the coils 5 cause at least a portion of the masking powder 4 to be suspended or fluidised in the powder chamber 3 so that the floating powder particles 4 can be attracted by the polar field 6a of force generated by the corona electrode 6, i.e. to create an efficient fluidized powder bed 4'.

It is noted that no special atmosphere is required inside of the powder chamber 3 for most applications of the present teachings. However, a skilled person will understand that an inert environment, such as nitrogen gas or a noble gas, may be suitable for particular applications, depending upon the masking powder 4 and electrical fields that are utilized. The invention is not limited to what has been taught above but may be modified in various ways that still fall within the scope of the claims. The person skilled in the art will understand that the transparent plate 1 can be manufactured from a variety of different materials, with the purpose of obtaining desired properties for the chosen electromagnetic radiation to be transmitted. According to a preferred embodiment, a glass material is used as the base material for the transparent plate, although other suitable materials may be utilised. It is furthermore understood that the computer- controlled mask pattern is in no way limited to a particular type of software or type of file. Any type of CAD program may be suitably used to generate the design of the volume body according to present engineering standards. It is also understood that the print head 2 can be of various types, as long as it is capable of depositing or printing electrostatic charges on the plate 1, and that the technology may be suitably based on an existing developed application, although future-developed applications may also be utilized with the present teachings as appropriate.

It is furthermore understood that the powder chamber 3 can be of various designs without departing from the basic principles of the present disclosure. The person skilled in the art will understand that the latter is true also for the designs of the electrodes 5, the corona electrode 6, the pivotal scraper 7, the eraser 8 and other component parts of the device. It can be mentioned, for example, that the person skilled in the art will understand that one or more of the same or different types of mechanical scraping devices can be used, in addition or in the alternative to the scraper 7 shown in the figures. For example, an additional scraper may be reversed in relation to the first scraper 7 and may be disposed at the other end of the powder chamber 3, which will then clean the glass surface one final time just before new masking powder is to be applied.

It is also understood that the materials of the insulating layer 10 and the electrically- conductive layer 9, respectively, can be chosen from a wide range of materials depending on the prerequisites of a particular application of the present invention and the skilled person can readily choose the appropriate materials based upon system requirements. With respect to the electrodes 5 that are intended to create a fluidized powder bed 4', it is also understood that other types of known techniques can be used to create the fluidized powder, such as an agitating bed, in which the agitation is achieved by air, etc. In a preferred embodiment, a porous/air permeable tube may be used (such as is, e.g., used in aquariums) to suspend the masking powder particles 4. The corona electrode 6 may be positioned inside the porous tube in this case, which tube can be positioned such that the powder 4 covers the tube with the electrode 6 disposed therein. According to this alternate design, efficient powder fluidization is achieved in combination with a clean environment that prevents contamination of the electrode 6, and the powder 4 can be given a "starting position" closer to the glass plate 1.

As an alternative to an electron beam imaging print head, an external ion implant print head may be utilised. In addition or in the alternative, a computer-controlled matrix that is transparent to IR radiation can be applied directly onto or disposed in the transparent plate 1, primarily as an alternative to the electrically conductive layer 9. In this case, the attractive, electrostatic fields of force 6a can be generated directly by the computer, e.g., using screen drivers. It will roughly be the same as when an image is formed on a flat computer screen but it does not become visible until the masking powder 4 builds up the mask 4a via the corona electrode 6.

Finally, although the preferred embodiments utilise negative charges deposited on the transparent plate and negatively-charged masking powder, any combination of polarities may be utilized according to the requirements of a particular design. For example, it would be possible in principle to apply negative charges to the transparent plate and then positively-charge the masking powder, in which case the masking powder would adhere to the transparent plate at the negatively charged locations. Thus, the present teachings are not limited in this regard as well.