Apparatus and method for three-dimensional mapping and modeling

FIELD OF THE INVENTION

The present invention relates to three-dimensional mapping and modeling.

BACKGROUND OF THE INVENTION

Various techniques are known for three-dimensional mapping and modeling. Commercial 3־D digitizers are currently used for inputting the precise contour of physical objects into CAD/CAM systems. Reference is made in this connection to Graphic-Input Devices for CAD/CAM by Thomas A. Nobbe, Machine Design, February 21, 1985, ΡΡ. 109 111 ־. Such devices are available from McDonnell-Douglas Electronics Company, P.O.Box 516, St. Louis, MO 63166, U.S.A.; Micro Control Systems, 143 Tunnel Road, Vernon, CT 06066, U.S.A.; and Science Accessories Corp., 970 Kings Highway West, Southport, CT 06490, U.S.A.

There are also known various techniques for automated three-dimensional modeling, including numerically controlled machining, such as milling, grinding and turning. The capability of these techniques to generate 3D configurations is limited by their restricted degree of freedom, by the physical size of the cutting fixture and by the mechanical forces that these methods apply on the material. As a result, the geometry of the models realizable is restricted.

SUMMARY OF THE INVENTION

The present invention seeks to provide threedimensional mapping and modeling apparatus, which is relatively fast and inexpensive.

There is thus provided in accordance with a preferred embodiment of the present invention three-dimensional mapping and modeling apparatus comprising apparatus for providing coordinate information with respect to ,a three-dimensional element, workstation apparatus arranged to receive the coordinate information from the providing apparatus and to permit manipulation of the coordinate information, and apparatus responsive to manipulated coordinate information for automatically providing a three-dimensional model of a desired three-dimensional element. . ¹

The term manipulation is used throughout to refer to all possible workstation functions in relation to coordinate information, including generation of coordinate information at the workstation as well as editing received ' coordinate information.

The apparatus for providing a three-dimensional model may comprise apparatus for producing the model of superimposed layers of radiation dimensionable material, apparatus for selective solidification of portions of a volume of one or more liquids, one of which may have higher specific gravity than the other, apparatus for selectable dimensioning of wrapped or rolled material, or any other suitable technique.

In accordance with the present invention, the apparatus for selective solidification of portions of a volume of liquid may include apparatus for carrying out at least one of the following processes: cationic polymerization, electron beam curing, photopolymerization, UV curing, UV polymerization, photocrosslinking, laser polymerization, photoinitiation, photoreactivity, or visible light curing.

Further in accordance with a preferred embodiment of the present invention there is provided automatic modeling apparatus comprising apparatus for sequentially providing layers of polymerizable material onto a substrate, such that they join to define a solid mass, apparatus for providing selected polymerization of regions on each of the layers of polymerizable material prior to application of a subsequent layer thereon, and including radiation apparatus for producing radiation responsive polymerization. Also provided is apparatus . for forming isolated parts or objects of substantially any spatial geometry, including apparatus for generating a random supporting mesh to support such isolated parts or objects without deforming them during the process.

Further in accordance with a preferred embodiment of the invention, apparatus is provided for restriction of the polymerization process to the uppermost active layer, thus avoiding distortion of the object by excessive radiation which might penetrate the completed layers.

In accordance with one embodiment of the invention, the polymerizable material comprises an epoxy. According to an alternative embodiment of the invention, the polymerizable material comprises an acrylic. Further in accordance with an embodiment of the invention, the polymerizable material may be selected from among the following materials: epoxy resin, epoxy acrylate copolymer, cyclaliphatic epoxide , methacrylate polymer, oligomer, acrylic resin, dissolved polymer.

According to yet another embodiment, the polymerizable material comprises two such materials, such that one of them has higher specific gravity than the other.

In accordance with this preferred embodiment of the invention there is provided a technique for three-dimensional modeling comprising the steps of receiving information describing the configuration of a three-dimensional object to be modeled; repeatedly defining superimposed layers of a laser dimensionable coating on a substrate, whereby they join to form a solid mass; and following definition of each layer, radiation dimensioning the layer in accordance with the received configuration information, thereby building up, layer by layer, a radiation dimensioned solid mass defining three-dimensional model of the three-dimensional object.

In accordance with the dual-liquid embodiment of the invention, there is also provided apparatus for adding additional quantities of both liquids subsequent to the definition of each layer, in order to define the next layer.

In accordance with a preferred embodiment of the invention, the radiation dimensioning step is carried out essentially as a two-dimensional process, using conventional twodimensional radiation dimensioning equipment presently available.

In accordance with an alternative embodiment of the present invention there is provided automatic modeling apparatus comprising apparatus for providing a volume of a laser solidifyable liquid; apparatus for laser radiation at selected regions of the volume for causing local polymerization and crosslinkage at the selected regions, thereby to define a desired solid model; and means for removing the excess liquid.

In accordance with one embodiment of the invention, the liquid comprises a liquid monomer mixed with a photoinitiator. A dye or a liquid crystal may also be included.

In accordance with this preferred embodiment of the invention there is provided a technique for three-dimensional modeling comprising the steps of receiving information describing the configuration of a three-dimensional object to be modeled; providing a volume of a laser solidifyable liquid; providing laser radiation at selected regions of the volume for causing local polymerization and cross-linkage at the selected regions, thereby to define a desired solid model; and removing the excess liquid.

In accordance with a further alternative embodiment of the present invention there is provided automatic modeling apparatus comprising apparatus for rolling laser dimensionable web material in a generally cylindrical configuration and apparatus for laser writing on the rolled material as it is rolled to selectably dimension it.

In accordance with one embodiment of the invention, the web material comprises a self-adhesive film having the chemical properties of photo-resist.

In accordance with this preferred embodiment of the invention there is provided a technique for three-dimensional modeling comprising the steps of receiving information describing the configuration of a three-dimensional object to be modeled, rolling laser dimensionable web material in a generally cylindrical configuration, and laser writing on the rolled material as it is rolled to selectably dimension it.

According to this embodiment, the laser writing normally takes place on the external layer of the cylinder in a line parallel to the cylindrical axis. After the laser writing, there is normally provided a development stage, wherein the external layer is chemically processed to render the exposed areas of that layer insoluble and leave the non-exposed portions of the layer soluble. Following wrapping of the entire cylinder, writing and developing, it is removed from the writing apparatus and rinsed such that the soluble material is dissolved and eliminated, leaving the desired model.

Additionally in accordance with a preferred embodiment of the present invention, the configuration information is provided initially in a viewable editable format and is converted subsequently to a slice-by־slice or cylindrical coordinate format for governing the laser dimensioning step.

In accordance with another preferred embodiment of the invention, two liquids are employed in the liquid solidification modeling technique described above. A first, relatively light, solidifiable liquid is selectably solidified layer by layer according to any of the techniques described hereinabove. A second, relatively heavier liquid, is non-solidifiable under the conditions that produce solidification of the first liquid and serves as a support for the first liquid, protecting the already configured layers of the model from undesired modification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:

Fig. 1 is a block diagram illustration of a threedimensional mapping and modeling system constructed and operative in accordance with a preferred embodiment of the present invention;

Fig. 2 is a part-schematic, part-pictorial side view illustration of three-dimensional modeling apparatus useful in the system of Fig. 1;

Fig. 3 illustrates the layer spreading apparatus of the apparatus of Fig. 2 and a partially completed three-dimensional model;

Fig. 4 is a pictorial illustration of apparatus for three-dimensional modeling in accordance with an alternative embodiment of the present invention;

Fig. 5 is a pictorial illustration of apparatus for three-dimensional modeling in accordance with a further alternative embodiment of the present invention;

Fig. 6 is a flow chart illustrating the steps of threedimensional modeling employed in accordance with a preferred embodiment of the present invention, employing the apparatus of Fig. 2;

Fig. 6A is a flow chart illustrating the steps of three-dimensional modeling employed in accordance with a preferred embodiment of the present invention, employing the apparatus of Figs. 2 and 15A.

Fig. 7 is a flow chart illustrating the steps of three dimensional modeling employed in accordance with another preferred embodiment of the present invention, employing the apparatus of Fig. 4;

Fig. 8 is a flow chart illustrating the steps of threedimensional modeling employed in accordance with yet another preferred embodiment of the present invention, employing the apparatus of Fig. 5;

Fig. 8A is a flow chart illustrating the steps of three-dimensional mileling employed in accordance with yet another preferred embodiment of the present invention, employing the apparatus of Figs. 5. 16 and 17;

Fig. 9 is a pictorial flow chart illustrating the steps of three-dimensional modeling employed in accordance with still another preferred embodiment of the present invention;

Fig. 10 is a pictorial illustration of apparatus for layer dimensioning in three-dimensional modeling in accordance with a further alternative embodiment of the present invention;

Fig. 11 is a pictorial illustration of apparatus for layer dimensioning in three-dimensional modeling in accordance with yet another alternative embodiment of the present invention;

Fig. 12 is a pictorial illustration of apparatus for layer dimensioning in three-dimensional modeling in accordance with still another alternative embodiment of the present invention;

Figs. 13A and 13B are illustrations of respective partially completed and fully completed states of a modeled object which has isolated portions during an intermediate stage in the modeling process;

Fig. 14 is a pictorial illustration of a modeled object comprising two parts spatially separated from each other;

Fig. 15 is a top view sectional illustration of a random supporting mesh provided in accordance with a preferred embodiment of the present invention;

Fig. 15A is a schematic illustration of apparatus for modeling in accordance with an embodiment of the invention, including apparatus for the generation of the random supporting mesh;

Fig. 16 is a schematic illustration of apparatus for modeling in accordance with an embodiment of the invention employing an inert liquid; and

Fig. 17 is a view of a partially completed modeled object produced in accordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Reference is now made to Fig. 1, which illustrates, in general block diagram form, a three-dimensional mapping and modeling system constructed and operative in accordance with a preferred embodiment of the present invention.

The system typically comprises configuration information input apparatus 10, such as a conventional 3־D digitizer. An example of such a digitizer is a 3SPACE Digitizer manufactured and sold by McDonnell Douglas Electronics Company. Other suitable types of information input apparatus 10, such as those described hereinabove in the Background of the Invention, may alternatively be employed. Additional input sources may be three-dimensional computer aided design (CAD) files, and interactively sculptured objects generated at a workstation.

Further in accordance with a preferred embodiment of the invention, the output of a Computerized Tomography scanner, such as a General Electric GE8800 CT Scanner, in the form of a multi-slice sequential data file, may be employed by the system to genreate a physical replica of a scaned object. Such a replica can be useful in diagnosis and surgery planning.

A workstation and processing center 12, receives configuration information inputs from apparatus 10 and provides a viewable display of such information,, preferably in raster format, to an operator, and enables the operator to edit such information or to generate such information at the workstation.

The principal functions performed by workstation and processing center 12 are as follows:

a. VOXELIZATION

Voxelization is an automatic function that converts the solid model taken from a CAD (Computer Aided Design) system into a compact voxel enumeration format, such as OCTREE, which inherently allows for variable resolution spatial data treatment. In practice, this means converting data from three-dimensional vector presentation into a collection of voxels located at specific locations in space.

b. VOXEL EDITING

Voxel editing is a working tool in the hands of the operator, enabling manipulation of the shape of an object presented on a screen. This is done by offering the operator direct access to the voxels, allowing him to add, delete or change the values of voxels by means of a suitable control device, such as a lightpen, ball, joystick, etc. The principal features realized by this function are drawing, line choice, cross-section determination, space fill, trimming, copying and mirror imaging.

c. FREE HAND SCULPTURING

In contrast to the voxel editing function described in the preceding paragraph, which is based on a CAD file converted into voxels, this function permits creation of a model from scratch, i.e. without using input apparatus 10. The operator creates the model by using sculpturing techniques based either on building up or subtracting material.

In addition to free-hand sculpting, the operator will have at his disposal simulated machining tools, that will enable him to shape the object. The software tools employed by the operator include tool definition (drill, lathe, mill, nozzle, etc.), a build up/subtract option, etc.

d. CONVERSION INTO SOLID MODELS

This function is the reverse process of the voxelization process. A file describing a body as a group of voxels in space is converted into three-dimensional constructive solid geometry (CSG) based on voxels as primitive cubes in a selected CAD format. This enables a model to be created on the present apparatus for further CAD analysis and operations to be carried out on an associated CAD system on the same model.

A plurality of model creation operands are available to the operator, prior to generating the physical model. These include scale setting, resolution setting, physical grid creation, supporting rib creation (where needed to support an object at a desired location in space), nesting (to provide most efficient use of the modeling medium), and definition of drainage conduits (where needed).

Workstation and processing center 12 interfaces with conventional 3־D computer aided design apparatus 14 and software such as. GEOMOD of General Electric/Calma, CADDS of Computervision, UNIGRAPHICS of McAuto, MEDUSA of Prime Computer or CIS. A description and listing of CAD programs appears in

Engineering without Paper by John K. Krouse, High Technology,

Mar. 1986, at pages 38 46 ־. Workstation and processing center 12 also provides an output to three-dimensional modeling apparatus

16.

A preferred embodiment of three-dimensional modeling apparatus 16 is illustrated in Figs. 2, 3 and 4 and is seen to include a modeling chamber 20 having associated therewith a model support mechanism 22, typically including a Z-axis motion drive 24 for selectably raising or lowering the model. Z-axis drive 24 is typically operated by a Z-axis controller 26.

A model layer definition device 28, available from International Polymer Industries as Ty. 5410200־, receives a supply of modeling material, such as a laser polymerizable material, for example a suitable epoxy, acrylic, polyacrylate, polyester, silicone, or polyurethane, from a container 3θ via a feed pump 32, which is controlled by a pump controller 34.

According to an alternate embodiment of the invention, the modeling material may consist of a mixture of two or more raw materials, such that the majority of the material is a dissolved polymer, and only a small portion of the material is an active photopolymer. The presence of the dissolved polymer in the modeling material contributes to the performance of the system in the following ways:

1. Reduction of solidification-shrinkage of the mixture, since the dissolved polymer does not shrink when it becomes a part of the solid.

2. Improvement of the sensitivity of the reaction, since the dissolved polymer does not absorb the radiated energy, so the energy density on the photoinitiator increases.

3. Reduction in the cost of the raw material, since the additives are less expensive than the active material.

In yet another embodiment of the invention, the modeling material comprises a mixture containing solid powder (such as silicon powder, IMSIL A-25 by Illinois Mineral Co., 2035 Washington Ave., Cairo, Illinois, 62914), which powder contributes to reducing the shrinkage and improving the sensitivity of the process.

In another embodiment, similar to the last, the grains of the added powder have a substantially spherical shape, thus having a lens effect on the radiated light energy. The lens effect generates multiple focal points, one per each spherical grain, with local high concentrations of energy, thus triggering the photochemical reaction while the average radiation intensity is beneath the required level.

The modeling material or combination of modeling materials is referred to as modeling material throughout this description.

The modeling material is applied as a multiplicity of layers 36 (Fig. 3)» each of a typical thickness of 100 microns, onto a support 38, which is mounted onto apparatus 22. The thickness of each of the layers determines the vertical (Z-axis) resolution of the process. As each layer is applied, a blanket of nitrogen or other suitable inert gas may be provided over the surface of the modeling material to prevent the inhibitory effect produced by an oxygen-containing atmosphere. The nitrogen is supplied from a container 40 via a suitable gas valve 42.

A radiation energy source, such as a laser beam 43 (Fig. 3) is operative to scan the layer, line by line in a raster mode, through the blanket of nitrogen. The laser beam is provided by laser radiation apparatus 44, including a laser energy source 46 such as a helium cadmium laser which is available from Omnichrome or an argon laser which is. available from Spectral Physics, laser optics 48 and a laser modulator 50, which is controlled by a modulator controller 52.

Definition device 28 is translated along the Y axis relative to the model by means of a Y axis motion drive 54, such as a screw drive, which is controlled by a Y-axis controller 56.

The laser beam is modulated so as to provide radiation only to locations identified by the model generating data file. Typically laser radiation will be provided at locations at which the model is to exist, thus producing solidification of the modeling material. Simply stated, the laser energy triggers a photoinitiator that causes a monomeric material in the modeling material to polymerize and cross-link, thus solidifying the material in the close vicinity of the selected location. The chemical mechanism of solidification initiated by laser radiation is described, for example, in the following references:

V.D. McGinnis, Org. Coatings Appl. Polym. Sci, 48 2314־ (Mar. 1983)

J.G. Kloosterboer, G.J. M. Lippits, Polym. Preprints, 26 [2], 351, 352 (Sept. 1985)

In accordance with the present invention, the apparatus for selective solidification of portions of a volume of liquid may include apparatus for carrying out at least one of the following steps: cationic polymerization, electron beam curing, photopolymerization, UV curing, UV polymerization, photocrosslinking, laser polymerization, photoinitiation, photoreactivity, visible light curing.

The process is repeated layer after layer until the entire model is generated.

It is possible to employ a modeling material or mixture of materials which will not expand or shrink in the process, thus maintaining high tolerances. It is also possible to add a selectably colorable material such as silver halide to the modeling material, so as to enable every location on the model to be selectably colored by application thereto of a suitable wavelength or energy level of radiation.

Additionally or alternatively, the entire model or certain layers thereof may be uniformly color tinted. In such a way, by periodically alternating between two shades, an appropriate scale may be defined on the model.

The technique employed in accordance with the embodiment of Figs. 2 and 3 is set forth in summary form in the flow chart of Fig. 6.

Reference is now made to Fig. 4, which illustrates an alternative embodiment of the present invention. The apparatus of Fig. 4 employs a feeding roll 51 of self-adhesive film having the chemical properties of a photo-resist. Film of this type is conventionally available from 3M Corporation. Alternatively nonself-adhesive material may be use'd when a light polymerizable adhesive is applied thereto. UV curable adhesives may be employed for this purpose.

The film 53 is unrolled from feeding roll 51» and a protective paper or coating 55 is peeled off. Film 53 is then rolled onto an output cylinder 57! such that each layer sticks to the underlying layers. The output cylinder 57 is preferably rotated at a controlled speed, such that its outer perimeter has a constant tangential speed. The cylinder 57 is constantly repositioned such that its outer layer is always located at the focus of the laser writing apparatus.

A laser dimensioning system 58, which may be similar in all relevant respects to apparatus 44 shown in Fig. 2, is operative to write on the external layer of the cylinder in a line parallel to the rotation axis 60 of the cylinder. After the writing step, the layer passes through development, symbolized by a bath 62, and is subsequently covered by additional layers.

The resulting solid dimensioned cylinder contains portions that were irradiated by the laser and became insoluble under development and portions which were not irradiated and are soluble. The soluble portions are rinsed away, leaving the desired solid model.

The technique employed in association with the apparatus of Fig. 4 is set forth in summary form in the flow chart of Fig. 7.

Reference is now made to Fig. 5 which illustrates a further alternative embodiment of the present invention. In this embodiment an input file is generated as in the above-described embodiments. Two generally horizontally aimed, perpendicularly directed laser sources 70 are mounted for movement along respective x and y axes and arranged such that their output beams intersect at selected locations inside a volume 2ך of laser dimensionable liquid, such as Cyracure UVR 6100, available from Union Carbide, or any other appropreate photoinitiator. Intersection of the laser beams produces solidification of the liquid.

By producing intersection of the laser beams at a set of locations determined by the input file, a complete solid body of predetermined configuration is produced. The non-solidified liquid is drained and may be recycled.

The technique employed in association with the apparatus of Fig. 5 is set forth in summary form in the flow chart of Fig. 8.

Reference is now made to Fig. 9, which illustrates in pictorial block diagram form an alternative technique for automatic three-dimensional modeling. In contrast to the techniques described hereinabove, this technique employs laser dimensionable layers of solid material, such as as polycarbonate or aluminum. Each layer is individually laser dimensioned by a laser operating on the basis of a vectorial file containing the dimension information for each layer.

Undesired portions of each layer are removed, as by vacuum techniques, and their space is temporarily filled by a liquid to prevent spatial distortions in layers placed thereover. The various layers are bonded to each other using adhesive or any other suitable technique and the liquid is drained by means of suitable conduits formed in the completed model.

Reference is now made to Fig. 10 which illustrates an alternative embodiment of layer writing apparatus constructed and operative in accordance with the present invention. A computer 90 generates a two-dimensional image defining the layer configuration on a graphics display 92. This image is photographed by conventional techniques. The process is repeated for each of the layers making up the model and the photographs may be conveniently made by synchronized stepwise operation of a movie camera 94. The film is developed and sequentially projected by a suitable projector 96 onto a plurality of layers 98 in the order corresponding to the order in which the photographs were made. The slides are positioned at such locations that their projected images will register correctly.

Alternatively, the film may be produced directly from the computer using conventional computer generated slide producing apparatus.

Alternatively, the film may be generated by a digital laser plotter such as Scitex ELP that writes directly on the film.

Reference is now made to Fig. 11, which illustrates yet another layer writing technique. Here a computer 100 produces a sequence of images, each corresponding to a layer, on a high resolution liquid crystal display 102. The image on the display is reflected onto the various layers 104 for photodimensioning thereof. Alternatively, the image can be projected directly onto the layer using a conventional large screen computer display projector.

Reference is now made to Fig. 12, which illustrates still another layer writing technique. Here a computer 110 operates a line array 112 of light switching elements (LISA) available from Philips Valve, Hamburg, West Germany. The line array modulates light from a high intensity linear light source 114, and scans each layer for photodimensioning thereof.

Reference is now made to Figs. 13A -15. A unique feature of this system is it's ability to generate objects of practically any space geometry. This may include isolated parts that are not anchored to the base of the container (Fig. 13A), which may or may not eventually be anchored to the container through later layers (Fig. 138); such parts may stay isolated through the end of the dimensioning process, as shown in Fig. 14. Due to difference of specific gravity between the solidified parts and the liquid (among other reasons), such isolated parts may drift from their original place in space and create deformations in the dimensioning of the object. The proposed system eliminates this error in one of the following ways:

1. By adjusting the chemical contents of the raw materials to almost equate the specific gravity of the solid to that of the liquid. One possible mixture is the addition of dissolved polymers to the liquid as hereinabove discussed.

2. By detecting (in software) layers that have isolated islands, and treating them in the following specific manner:

Such a layer will be uniformly illuminated through a special mesh slide, indicated at reference numeral 144 in Fig. 15A, for a short duration prior to the active writing of the information onto it. The mesh slide is one of two possible slides on the slide tray 146, the other slide being the current data slide 149. When the need for a supporting mesh is detected by the software, the slide tray moves, so that the active layer 148 of the model 130 is illuminated through the mesh slide 144, rather than through the current data slide 149 (which is a part of the film and advanced after each layer).

The software will detect the need for a supporting mesh by identifying closed contours on the layer, that do not overlap, pixel per pixel, any contour of the previous layer. A layer containing such non-overlapped closed contours will require the support of a supporting mesh.

The mesh slide will contain a dense random pattern of narrow lines, indicated at reference numeral 116 (Figs. 15 and 15A). The thickness of the lines on the slide determines the thickness of the lines of the actual mesh, and the duration of the illumination determines the depth of the mesh fibres. These two parametes are adjusted so that the result is a mesh of thin polymerized fibers 117. The thickness of the fibers can be a fraction of the layer thickness (i.e. if the layer thickness is 100 microns, the fiber thickness will be around 20 microns}. When the active information is written on that layer, the mesh will be integrated into the layer, and will hold the isolated parts, indicated at reference numeral 118 in Fig. 15, in place. The mesh may be moved slightly successive to completion of each mesh layer, to ensure isolation of the fibers from each other. After the completion of the whole object, the support fibers 117 will be rinsed away, since their individual resistance to tear is very low. The software will decide if a given layer requires support as described above and will activate it.

3. The mesh may be replaced with a thin membrane (not shown), and the illumination will be of short duration, without a slide.

4. Supporting ribs (not shown) may be added, in the computerized description of the object, so that the isolated parts are suspended from the main structure, thus changing the geometry of the object to include no isolated parts. An alternate embodiment of the invention is shown in Figs. 16 and 17. In this embodiment, the repetitive addition of liquid layers is done by lowering the container with the liquid and partially solidified object by the amount of one layerthickness (typically 0.1 mm), and injecting an appropriate amount of fresh liquid into the container, so that the level of the liquid resumes its vertical position, which happens to be the focal plane for the radiated energy.

This embodiment comprise a container 120 resting upon a pedestal 122, control by a motor 124, which is operative to lower the container by the designated amount after the formation of each layer. Container 120 contains two liquid substances: an active liquid 126 and an inert liquid 128. Successive to the formation of each layer of the object 130, additional amounts of liquids 126 and 128 are injected into container 120 through liquid injection tubes 132 and 134 respectively, controlled by liquid injection controls 136 and 138, respectively. Liquids 126 and 128 are stored in liquid source containers 140 and 142, respectively. Due to the difference in the specific gravities of liquids 126 and 128, liquid 126 forms a thin layer upon the surfaces of liquid 128 with the container. The next layer of object 130 is thus formed, when radiation is applied, of active liquid 126, while the existing layers are protected by inert liquid 128.

The liquids 126 and 128 can be injected anywhere within the volume of container 120. The injection tubes can come from the open top of the container, so as to dispense with the need to pass through the wall of the container. The open ends of the injection tubes can be kept at a fixed level under or above the active level; The container can be disposable or reusable, and it can be removed from the machine and taken to a rinsing/drying/final curing station after completion of dimensioning of object 130. A disposable container ensures that no other part of the machine, except the container, comes into contact with the liquids, which keeps the machine dlean and facilitates the changing of material formulations between jobs, such as changing color or other physical properties of the solidified object.

It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather the scope of the invention is defined only by the claims which follow: