Abstract:
An improved apparatus for forming three-dimensional objects using multiple chambered resin vats and a photopolymer resin leveling system to permit concurrent use of multiple, photopolymer build materials and easy change over of resin vats is disclosed. The apparatus ensures the same level of photopolymer resin is maintained in each chamber during multiple chambered vat use.

Description:
FIELD OF INVENTION  
       [0001]     The present invention is directed to an apparatus for forming three-dimensional objects on a layer-by-layer basis and, more particularly, is directed to a method and an apparatus utilizing a leveling system for an apparatus having multiple solidifiable fluid medium vats or containers to permit more than one part building location to be utilized during the building of three-dimensional objects. The leveling system is particularly useful in stereolithography with multiple resin vats or containers and an improved mounting system.  
       BACKGROUND OF THE INVENTION  
       [0002]     In recent years, many different techniques for the fast production of three-dimensional models have been developed for industrial use. These are sometimes referred to as rapid prototyping and manufacturing (“RP&amp;M”) techniques. In general, rapid prototyping and manufacturing techniques build three-dimensional objects layer by layer from a working medium utilizing a sliced data set representing cross-sections of the object to be formed. Typically, an object representation is initially provided by a Computer Aided Design (CAD) system.  
         [0003]     Stereolithography, presently the most common RP&amp;M technique, may be defined as a technique for the automated fabrication of three-dimensional objects from a fluid-like material utilizing selective exposure of layers of the material at a working surface to solidify and adhere successive layers of the object (i.e. laminae). In stereolithography, data representing the three-dimensional object is input as, or converted into, two-dimensional layer data representing cross-sections of the object. Layers of material are successively formed and selectively transformed or solidified (i.e. cured) using a computer controlled laser beam of ultraviolet light (UV) into successive laminae according to the two-dimensional layer data. During transformation, the successive laminae are bonded to previously formed laminae to allow integral formation of the three-dimensional object. More recent designs have employed the use of visible light to initiate the polymerization reaction to cure the photopolymer build material that is commonly referred to as resin.  
         [0004]     Stereolithography represents an unprecedented way to quickly make complex or simple parts without tooling. Since this technology depends on using a computer to generate its cross-sectional patterns, there is a natural data link to CAD/CAM. Such systems have encountered and had to overcome difficulties relating to shrinkage, curl and other distortions, as well as resolution, accuracy, and difficulties in producing certain object shapes.  
         [0005]     Although stereolithography has shown itself to be an effective technique for forming three-dimensional objects, various improvements addressing the technology&#39;s difficulties and expanding the potential manufacturing applications have been desired for some time. Many improvements have addressed the aforementioned difficulties and have been made to object accuracy, speed and appearance of the build object over the years. A recent area of expansion of stereolithographic applications has been into the area of hearing aid shell manufacturing where digital data of a patient&#39;s ear is used to create a customized hearing aid shell. This is done on a large scale with as many as 160 hearing aid shells being manufactured in a single build using a stereolithography system. Many patients have two hearing aid shells made, one for each ear. Other patients require only a single hearing aid shell. Regardless, a convention has arisen among some manufacturers to color code the hearing aid shells according to which ear in which the shell is to be used. With the advent of biocompatible colored resins or build materials, a need has arisen for the ability to manufacture in a single build cycle hearing aid shells for both the left and the right ears. This requires the use of at least two separate vats within the context of the traditional stereolithography systems. Therefore there is the need for a stereolithography or similar three-dimensional imaging system to accommodate a second vat or resin material container so that hearing aid shells of two different colors can be manufactured in a single build cycle. Further, there is a need to ensure that the levels of the photocurable resins in each vat are the same when a multiple vat or multiple chamber configuration is employed.  
         [0006]     These problems are solved in the design of the present invention.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an aspect of the present invention that a apparatus for forming three-dimensional objects is provided which permits the concurrent use of multiple chambered resin vats or photopolymer material containers during a single build cycle.  
         [0008]     It is another aspect of the present invention that an improved photopolymer resin leveling system for maintaining the resin in multiple vats to multiple chambered vats at the same level during operation of the stereolithography apparatus.  
         [0009]     It is a feature of the present invention that multiple resin vats or photopolymer material containers can be used concurrently during a single build cycle and the photopolymer resin in each is maintained at the same level to create three-dimensional parts in a stereolithography system.  
         [0010]     It is another feature of the present invention that the photopolymer resin leveling system employs a master resin vat or photopolymer material container and a slave resin vat or photopolymer material container.  
         [0011]     It is yet another feature of the present invention that the slave resin vat or photopolymer material container has resin added to or removed from it to maintain the photopolymer resin at the same level as the photopolymer resin in the master resin vat or photopolymer material container.  
         [0012]     It is still another feature of the present invention that the resin level within the multiple chambered resin vats or photopolymer containers is at the same level in each chamber during operation.  
         [0013]     It is yet another feature of the present invention that the photopolymer resin level in the master resin vat or photopolymer material container is measured by sensors in baffles within each resin vat.  
         [0014]     It is still another feature of the present invention that a refill reservoir provides photopolymer resin to the slave resin vat or photopolymer container and receives excess resin back from the slave resin vat or photopolymer container in the leveling process.  
         [0015]     It is an advantage of the present invention that multiple resins, including differently colored resins, can be utilized concurrently in a stereolithography system to produce three-dimensional objects with different physical properties.  
         [0016]     It is another advantage of the present invention that a simple resin leveling system maintains the same photopolymer resin level in the resin vats or material containers during to multiple chambered vat operation.  
         [0017]     These and other aspects, features, and advantages are obtained by the present invention through the use of a photopolymer resin leveling system with a multiple chambered resin vat or multiple resin vats.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0018]     These and other aspects, features and advantages of the invention will become apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the following drawings wherein:  
         [0019]      FIG. 1  is a front perspective view of a stereolithography system;  
         [0020]      FIG. 2  is a diagrammatic illustration of the operation of a stereolithography system;  
         [0021]      FIG. 3  is a partial perspective view of the multiple resin vat configuration of the frame and supporting structure of a stereolithography system of the present invention;  
         [0022]      FIG. 4  is a top plan view of the stereolithography system having two resin vats mounted for concurrent operation;  
         [0023]      FIG. 5  is a side perspective view of the quick disconnect elevator arms of a stereolithography system of the present invention;  
         [0024]      FIG. 6  is a front elevational view of the quick disconnect elevator arms and the locking device moved between an unlocked position shown in solid lines and a locked position shown in dotted lines of a stereolithography system of the present invention;  
         [0025]      FIG. 7  is a side elevational view of the quick disconnect elevator arms and the locking device moved in a locked position of a stereolithography system of the present invention;  
         [0026]      FIG. 8  is a side perspective view of a two resin vat system showing the separate drains for each vat of a stereolithography system of the present invention; and  
         [0027]      FIG. 9  is a partial perspective view of the single resin vat configuration of the frame and supporting structure of a stereolithography system of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     Additive technology for creating three-dimensional objects involve the layer by layer build-up of material until a finished object is completed. Stereolithography is one example of an additive technology. Stereolithography typically involves the layer by layer build-up of articles from a vat or container of liquid monomer. Stereolithography parts are preferably built on structures known as supports rather than directly on an elevator platform that moves the build object or part up and down as successive layers or laminae are formed during the stereolithography process. The vat of liquid photopolymer material provides a fresh material to create new layers as the object is built. The invention will be described in the context generically of a traditional stereolithography system, although it is to be understood the invention is applicable to any technology utilizing multiple containers to hold a solidifiable fluid medium to form a three-dimensional object.  
         [0029]     A typical stereolithography system is represented by the numeral  10  shown in  FIG. 1 . Such a system is offered commercially by 3D Systems, Inc. of Valencia, Calif. as the Viper si2™ SLA® system. The system  10  includes a computer console  11  with a control computer, computer terminal, and monitor. The system  10  also has a laser housing  12  that includes a laser, mirrors, crystal and other components of the laser system of the type described in U.S. Pat. No. 6,157,663 to Wu et al. and assigned to the assignee of the present invention. The laser system projects a beam onto the surface of the photocurable liquid or resin material in the vat to cure or solidify the liquid in the cross section or layer being formed. This photocuring operation takes place in an enclosed process chamber  14  and the part with its underlying support structure is formed on a support platform  15  that is moveable up and down in the vat of material by an elevator assembly.  
         [0030]     Looking now at  FIG. 2 , there is shown in a diagrammatic illustration a stereolithographic system that makes solid objects by successively creating thin layers of a solidified material one on top of the other by use of a programmable moveable spot beam of light shining on the surface of the UV curable liquid.  FIG. 2  shows a laser  20  projecting a laser beam  21  onto the surface of the resin  19  to form the three dimensional object  17  that is supported on the support platform  15 . The support platform  15  is raised and lowered by means of an elevator  18  which extends down into the vat  16  that contains the photocurable resin  19 . Data is sent to the stereolithography system from a CAD station indicated by the numeral  22  that converts the CAD data to a suitable digital stereolithographic layer data format and feeds it to a computer control system  24  where the object data is manipulated to optimize the data and provide output vectors. The stereolithographic layer data format or STL file is a tessellated object description consisting of the X, Y, and Z coordinates of the three vertices of each surface polygon, as well as an index that describes the orientation of the surface normal. The surface polygons preferably are triangles. The manipulated data will reduce stress, curl and distortion, and increase resolution, strength, accuracy, speed and economy of reproduction, even for rather difficult and complex object shapes. The interfacing computer control system  24  generates layer data by slicing, varying layer thickness, rounding polygon vertices, filling, scaling, cross-hatching, offsetting vectors, ordering of vectors, and generating flat skins, near-flat skins, up-facing and down-facing skins.  
         [0031]     The vector data and parameters from the computer control system  24  are directed to a controller subsystem for operating the system stereolithographic laser, mirrors, elevator and the like which permit the solid individual laminae that represent cross-sections of the build object or part to be generated and the laminae to be successfully combined to form the three-dimensional part. The part is generated by the application of an appropriate form of energy stimulation as a graphic pattern according to these vector data and parameters at the fluid medium surface to form the thin individual layers or laminae. Each solid layer or individual lamina represents an adjacent cross-section of the three-dimensional object to be produced. Successive adjacent layers or laminae are superimposed as they are formed to generate the three-dimensional object or part.  
         [0032]     The programmable source of energy stimulation, in this instance the ultraviolet (“UV”) light, is provided by a laser. Alternatively, new systems employing visible light such as DLP, systems may be used to cure the photocurable resin  19 . Photomasks also can be utilized in either approach to selectively apply the energy stimulation, which may be any other appropriate form of energy to stimulate change from a liquid to a solid such as electron beam particle bombardment or application of chemically reactive materials. Operation of the SLA system  10  of  FIG. 1  and its diagrammatic illustration in  FIG. 2  is described in greater detail in U.S. Pat. No. 5,184,307 to Hull et al. and assigned to the assignee of the present invention.  
         [0033]     Turning now to  FIG. 3 , there is shown in a partial front perspective view the interior frame of an SLA system with its elevator and Z-stage assembly  25  holding a dual vat or resin container  31 . The elevator and Z-stage assembly indicated generally by the numeral  25  has frame  26  that supports it and includes a machined aluminum vat rim  28  that encloses all four sides of the frame and to which a rim support  29  is bolted. Rim support  29  is also fastened to the frame (not shown) of the system  10 . Rim support  29  has a bottom onto which the vat rim  28  sealingly seats. Vat rim  28  is kinematically mounted on three balls (not shown) to the frame  26 .  
         [0034]     A recoater device  30  is movably mounted onto the frame for movement front-to-back along the vat rim  28 . However, in the dual vat configuration the recoater device is not employed. A recoater device  30  is employed where a single vat is utilized in the stereolithography system  10  and its operation is described in greater detail in U.S. Pat. No. 5,902,537 issued to Almquist et al. and assigned to the assignee of the present invention. An advantage of the present invention is that cleaning of the stereolithography system and especially the recoater device is not required during change over or exchange of multiple chambered vats to a single chamber vat.  
         [0035]     The dual vat  31  illustrated in  FIG. 3  has handles  34  (only one of which is shown) on both sides mounted to flanges  33 , fastened to the side of the vat  31 . A vat divider  32 , best seen in  FIGS. 4 and 8 , separates the two chambers  31 A and  31 B of the vat (see briefly  FIG. 4 ). Vat  31  with its two chambers thus can hold two different resins, such as a resin colored red or blue, or different pigmented or clear resins. A resin refill reservoir  35  is connected in fluid flow communication with one of the two vats in dual vat  31 . In this configuration it is connected in fluid flow communication with vat chamber  31 A that is known as the slave vat chamber as opposed to the master vat chamber  31 B. Manually actuated ball valves  36 , best seen in  FIGS. 3 and 8 , connect to the bottom of slave vat chamber  31 A and master vat chamber  31 B to permit resin to be drained through drain holes  37  when desired. The floors of vat chambers  31 A and  31 B slope downwardly toward the drain holes  37  to facilitate draining resin from the vat chambers. The manually actuated valves  36  are opened using vat drain handles  38 .  
         [0036]     As seen in  FIG. 8 , there is a baffle  78  that is used to contain liquid resin during the vat leveling operation. The baffle  78  contains a single chamber and is open bottomed on its left side in master vat chamber  31 B, but is closed on the bottom in slave vat chamber  31 A. The slave vat chamber  31 A also has an open bottomed baffle  79 . Within baffle  78  a diode beam from leveling diode spy sensor assembly  42  and from laser leveling diode  93  senses the height of the resin in master vat chamber  31 B. Sensor  93  causes the hoist to move the master vat chamber  31 B to the correct height. Spy sensor assembly  42  uses the sensing of sensor  93  as a reference, records the height and provides a comparative value for laser diode assembly  41  to adjust the height of resin in slave vat chamber  31 A to the same height as the resin in master vat chamber  31 B. Sensor assemblies  41  and  42  are employed to ensure the level of resin in both vat chambers  31 A and  31 B are exactly the same height. Both laser diode sensor assemblies  41  and  42  employ an OMRON ZXLD30 optical sensor  43  to sense the height of the resin in slave vat chamber  31 A and the master vat chamber  31 B as described. Sensor assembly  41  senses the height of the resin in slave vat  31 A inside baffled  79 . A baffle is used to prevent gas bubbles in the vat chambers from interfering with obtaining exact resin height readings. Sensor assembly  41  compares the sensing from its sensor  43  with the signal from spy sensor assembly  42  to either add more resin from resin refill reservoir  35  or pump resin back into resin refill reservoir  35 , as appropriate.  
         [0037]     Dual vat  31  is raised up and down by a vat hoist (not shown) under the vat and which can be used to lower the vat to a fully lowered position when removal is needed in a manner to be described with respect to disconnection of the elevator legs  48 .  
         [0038]     Also seen in  FIG. 3 , attached to the vat rim is a ceramic laser beam rest stop  39  that permits the laser beam for the stereolithography system  10  to rest on a target that cannot be harmed when not imaging on the surface of the resin  19 . A rim support  40  is shown adjacent ceramic laser beam rest  39  that helps fasten the rim support  29  to the vat rim  28 .  
         [0039]     The elevator, indicated generally by the numeral  57 , is best seen in  FIGS. 5-7 . For the dual vat configuration with dual vat or split vat  31 , a pair of mounting brackets  45  are secured via four bolts through bolt holes  47  (see briefly  FIG. 5 ) into mounting block  44  of the Z-stage saddle  66 . Elevator legs  48  are connected to the mounting plates  45  in a manner to be described hereafter. Each platform  62  (see briefly  FIG. 4 ) in the split vat  31  is supported by a pair of elevator legs  48  that are fastened to a welded stainless steel elevator frame  50 . Frame  50  has a cross bar  51  connecting its opposing sides allowing the platform  62  to rest on top of it.  
         [0040]     A vat quick disconnect locking lever  46 , best seen in  FIGS. 5 and 6 , is pivotally or rotatably mounted to each mounting bracket  45  via a locking lever pivot screw  52 . Lever  46  has a handle  53  and on its opposing end a rolling pin  54  fastened to the locking lever  46  by a mounting screw  55 . An elevator leg locking bar  49  connects the two opposing elevator legs  48  for each elevator assembly supporting each elevator platform  62 . As best seen in  FIG. 6 , the locking lever  46  is moveable between a locked position, shown in solid lines and an unlocked position shown in dotted lines. In the locked position, the rolling pin  54  is pressed in cam-like fashion against the locking bar  49  to secure the elevator in place. In the unlocked position the rolling pin  54  is pivoted up into the rolling pin recess  56 . In the locked position, the locking lever  46  is stopped in its fully locked position by stop pin  58 . As best seen in  FIG. 7 , the platform elevator legs  48  (only one of which is shown) fit over a pressed in pin or dowel  59  that extends about 2.5 inches from both sides of mounting plates  45 . Elevator leg mounting groove  60  for each elevator leg  48  then fits over and hangs on pin  59 . If locking lever  46  is not in the locked position, the elevator legs  48  are free to swing on pins  59 . However, when locking lever  46  is in the locked position, rolling pin  54  presses against the locking bar  49  to hold the elevator legs  48  and the elevator assembly  57  and platform  62  firmly in position. A spring loaded ball detent  63  in the outer side of each mounting plate  45  pushes the outer elevator leg  48  of each pair outwardly to bias the elevator assembly  57  so it repeatably will be seated with the opposing elevator leg pulled snugly against mounting plate  45 . Also as seen in  FIG. 7 , an elevator frame mounting pin  61  connects elevator frame  50  to the bottom of each elevator leg  48 .  
         [0041]     Returning now to  FIG. 4 , there is also shown in connection with the resin refill reservoir  35  a refill reservoir pump  64  that is driven by a pump electric motor  65 . This motor turns a peristaltic pump or positive displacement pump that pumps resin in both directions between the reservoir  35  and the slave vat chamber  31 A. As described previously, two sensors  42  and  41  match the height of the resin in the slave vat chamber  31 A to the height of the resin in the master vat  31 B by pumping resin into or removing it from slave vat chamber  31 B. This is necessary because in the dual vat  31  configuration both vats must have the exact same level of resin. Resin recoating of the three dimensional part  17  being built in the dual vat  31  occurs by the deep dip process whereby after exposing and solidifying a layer of the object, the elevator assembly  57  is lowered with the platform  62  by the z-stage stepper motor  68  so that fresh resin flows over the top of the just exposed layer. The z-stage stepper motor  68  then raises the platform  62  with the recoated part on it to a height one layer thickness beneath the surface of the resin  19  in vat  31  and the laser beam than repeats the imaging to from the next layer.  
         [0042]     As seen  FIG. 4 , the z-stage includes a saddle  66  and a z-stage stepper motor  68  mounted to a stepper motor mount  69  that raises and lowers the elevator assembly  57 . The stepper motor  68  is connected to a ball screw that is connected to the z-stage saddle  66 . The z-stage moves up and down on linear bearings  72  that ride in two vertical tracks (not shown). The stepper motor mount  69  is connected to a z-stage base  70  that is connected to the stereolithography system frame by a connecting bar  71 . A z-stage flag  74  is sensed by an upper limit switch  75  to limit raising the height of the z-stage to its maximum. A corresponding lower limit switch and flag assembly  95  are shown briefly in  FIG. 3 .  
         [0043]     When a single vat is desired to be utilized, the locking levers  46  are moved to the unlocked position and the elevator arms  48  are removed from the mounting plate pins  59  by sliding the arms  48  off of the pins  59  and out of the grooves  60  to permit the elevator assembly  57  and the platform  62  in each vat chamber  31 A and chamber  31 B to be lowered into the vat. The vat hoist (not shown) then lowers the dual vat  31  and a cart is used to remove the dual vat  31  from the stereolithography system  10 . A single chambered vat  80  is then moved into place by means of a cart rolling the vat into the frame  26 . As seen in  FIG. 9 , the two outer mounting plate pins  59  on mounting plates  45  are employed with the single vat elevator legs locking bar  84  to lock the elevator legs  82  into place in the grooves  60  that are machined into the elevator legs  82  in the same manner as with the dual vat  31 . The elevator legs  82  are similarly connected to a frame  50  that supports a support platform  81  on which three dimensional parts are built. The recoater blade  30  can then optionally be employed to recoat a fresh layer of resin over a just formed layer of the three dimensional part, if desired. Alternatively, the deep dip method can be employed. The laser diode leveler  93  is utilized in conjunction with baffle  94  to sense the level of liquid in the single chambered vat  80  and provide additional resin as required from the resin refill reservoir  35 . This leveling operation is described in greater detail in U.S. Pat. No. 5,258,146 to Almquist et al., assigned to the assignee of the present invention.  
         [0044]     Any suitable fluid medium capable of solidification in response to the application of an appropriate form of energy stimulation may be employed in the practice of the present invention. Many liquid state chemicals are known which can be induced to change to solid state polymer plastic by irradiation with ultraviolet light or other forms of stimulation such as electron beams, visible or invisible light, or reactive chemicals applied by ink jet or via a suitable mask. Suitable photopolymers that may be employed in the practice of the present invention include any commercially available photopolymer manufactured by 3D Systems, Inc. of Valencia, Calif. These include, but are not limited to, SI10, SI20, SI 40, and SI 50 resins for use in any 3D Systems&#39; commercially available SLA® system. Especially suitable for manufacturing hearing aid shells are the 7400, 7500, 7100 and 7300 series resins available from Dreve-Otoplastik GmbH of Unna, Germany. When manufacturing hearing aid shells the resin vats  31  or  80  are shallow, having a depth of about 2 to 3 inches.  
         [0045]     The present invention can be practiced on any stereolithographic equipment, but has been discussed in the context of a Viper si2™ SLA® system available commercially from 3D Systems, Inc., the assignee of the present invention.  
         [0046]     While the invention has been described above with references to specific embodiments thereof, it is apparent that many changes, modifications and variations in the materials, arrangements of parts and steps can be made without departing from the inventive concept disclosed herein. For example, of the present invention can equally well be applied to photopolymer material leveling in the individual chambers in dual vat  31  by having the dual vat chambers be separately formed in two separate and distinct containers each supported by their own elevator assembly. Further, while only a dual chambered approach has been illustrated it is possible to employ a vat having more than two chambers or more than two separate and distinct chambers each supported by their own elevator assembly and individually removable. Additionally, the source of energy to initiate photocuring or polymerization of the fluid medium capable of solidification can be any appropriate form of energy stimulation, as described above, delivered by a laser, electron beam gun, a light projector such as a digital light projector, an x-ray or gamma ray emitter, or infrared lamp. Accordingly, the spirit and broad scope of the appended claims are intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.