Accumulation, control and accounting of fluid by-product from a solid deposition modeling process

A by-product waste material removal system for solid deposition modeling. As excess build and support material is removed during the build as a by-product waste the removal system accumulates, measures, and releases the by-product waste material into a waste receptacle for disposal. The by-product waste material removal system requires no mechanical vacuum systems and allows operator intervention to remove and replace waste receptacles without interrupting an ongoing build.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a system and a method for accurately metering, accumulating, and accounting for the by-product waste stream generated from a solid deposition modeling process. In addition, the system allows operator intervention during the fabrication process and can be integrated with a sealed waste removal system wherein reactive materials can be employed without special handling procedures.

2. Description of the Prior Art

Recently, several new technologies have been developed for the rapid creation of models, prototypes, and parts for limited run manufacturing. These new technologies can generally be described as solid freeform fabrication, herein referred to as “SFF”. Some SFF techniques include stereolithography, selective deposition modeling, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, fused deposition modeling, particle deposition, laser sintering, and the like. In SFF, complex parts are produced from a modeling material in an additive fashion as opposed to conventional fabrication techniques, which are generally subtractive in nature. For example, in conventional fabrication techniques material is removed by machining operations or shaped in a die or mold to near net shape and then trimmed. In contrast, additive fabrication techniques incrementally add portions of a build material to targeted locations, typically layer by layer, in order to build a complex part.

SFF technologies typically utilize a computer graphic representation of a part and a supply of a build material to fabricate the part in successive layers. SFF technologies have many advantages over the prior conventional manufacturing methods. For instance, SFF technologies dramatically shorten the time to develop prototype parts and can quickly produce limited numbers of parts in rapid manufacturing processes. They also eliminate the need for complex tooling and machining associated with the prior conventional manufacturing methods, particularly when creating molds for casting operations. In addition, SFF technologies are advantageous because customized objects can be produced quickly by processing computer graphic data.

There are a wide variety of build materials that are used in various SFF techniques. These materials are typically applied in the form of a powder, liquid, gas, paste, foam, or gel. Recently, there has developed an interest in utilizing highly viscous paste materials in SFF processes to achieve greater mechanical properties. In addition, an interest has recently developed in reproducing visual features such as color on the three-dimensional objects produced by SFF processes. This has produced a need to develop special additives for the build materials along with new dispensing systems to enable the production of these visual features when building the three-dimensional objects.

One category of SFF that has emerged is selective deposition modeling, herein referred to as “SDM”. In SDM, a build material is physically deposited in a layerwise fashion while in a flowable state and is allowed to solidify to form an object. In one type of SDM technology the modeling material is extruded as a continuous filament through a resistively heated nozzle. In yet another type of SDM technology the modeling material is jetted or dropped in discrete droplets in order to build up a part. In one particular SDM apparatus, a thermoplastic material having a low-melting point is used as the solid modeling material, which is delivered through a jetting system such as those used in ink jet printers. One type of SDM process utilizing ink jet print heads is described, for example, in U.S. Pat. No. 5,555,176 to Menhenneft, et al.

Because ink jet print heads are designed for use in two-dimensional printing, special modifications must be made in order to use them in building three-dimensional objects by SFF techniques. This is generally because there are substantial differences between the two processes, thus requiring different solutions to different problems. For example, in two-dimensional printing a relatively small amount of an ink is jetted and allowed to dry or solidify with a significant interest being given to print resolution. Because only a small amount of material is jetted in two-dimensional printing, the material reservoir for the liquid material can reside directly in the ink jet print head while providing the ability to print numerous pages before needing to be refilled or replaced. In contrast, in SDM utilizing an ink jet printhead, a large amount of normally solid material, such as a thermoplastic or wax material, must be heated to a flowable state, jetted, and then allowed to solidify. Furthermore, in SDM dispensing resolution is not as critical as it is in two-dimensional printing. This is generally because, for each targeted pixel location, the amount of material to be jetted in SDM techniques is substantially greater than the amount to be jetted in two-dimensional printing techniques. For example, it may be required to deposit six droplets on a particular pixel location in SDM compared to just one or two droplets in two-dimensional printing. Although the targeting accuracy may be the same, the actual resolution achieved in SDM techniques is generally somewhat less than in two-dimensional printing because the six droplets dispensed may droop or slide towards adjacent pixel locations.

The differences mentioned above are significant and create a number of problems to be resolved. For instance, the amount of material deposited in ink jet based SDM techniques, both in volume and in mass, can be so substantial that it is generally considered impractical to mount a reservoir directly on the ink jet print head to hold all of the material. Thus, it is typical in most SDM systems to provide a large reservoir at a location remote from the print head that is in communication with the ink print head via a material delivery system having a flexible umbilical tube. However, the large container and umbilical tube must be heated to cause at least some of the build material to become or remain flowable so that the material can flow to the dispensing device. Start up times are longer for SDM techniques using ink jet print heads than in two-dimensional printing with ink jet print heads due to the length of time necessary to initially heat the solidified material in the large remote reservoir to its flowable state. In addition, a significant amount of energy is required to maintain the large quantity of material in the flowable state in the reservoir and in the delivery system during the build process. This generates a significant amount of heat in the build environment.

Another problem that is unique to SDM techniques is that the layers being formed must be shaped or smoothed during the build process to establish a uniform layer thickness. Normalizing the layers is commonly accomplished with a planarizer that removes a portion of the material dispensed in the layers. One such planarizer is disclosed in U.S. Pat. No. 6,270,335 to Leyden et al. However, the planarizer produces waste material during the build process that must be handled. This is less of a concern when working with non-reactive materials; however, it is a greater concern when reactive materials are used. For example, most photopolymers are reactive, and excessive contact to human skin may result in sensitivity reactions. Thus, most SFF processes that utilize photopolymer materials require some additional handling procedures in order to minimize or eliminate excessive physical contact with the materials. For example, in stereolithography, operators typically wear gloves when handling the liquid resin and when removing finished parts from the build platform. However, SDM operators who normally handle even non-reactive materials consider additional handling procedures inconvenient and, if possible, would prefer they be eliminated. For reactive materials in SDM systems the issue is compounded and rises above mere inconvenience. Thus, there is a need to provide a material feed and waste system for SDM that can handle reactive materials without requiring the implementation of special handling procedures.

A by-product waste handling system for dealing with the aforementioned waste stream from an SDM process is described in U.S. patent application Ser. No. 09/970,956, entitled “Quantized Feed System For Solid FreeForm Fabrication” and assigned to the assignee of the present invention. In that system the by-product waste material collects in an in-line reservoir and flows from it by gravity for delivery through actuated solenoid valves into waste receptacles. Although workable, that system is improved significantly by the instant invention. A lack of sufficient buffering capacity can result in too much by-product waste material backing up in the system. The amount of by-product waste is not known so the amount of energy (optical or thermal) needed to cure or solidify the material collected is not known. A system is needed that reliably captures all of the waste material, accurately measures it, and delivers measured amounts to a waste collection container without the use of large and expensive vacuum systems. In addition, a system is needed that allows operator intervention to remove and replace waste containers without interrupting a build.

These and other difficulties of the prior art are overcome according to the present invention by providing a new and simpler by-product waste removal system for a solid deposition modeling system utilizing on an automated collection reservoir.

BRIEF SUMMARY OF THE INVENTION

The instant invention provides its benefits across any SFF process that requires removal of excess build and/or support material during a build. This is done by providing a reliable and precise system for accumulating, accounting for, and removing by-product waste material from a SFF device for forming three-dimensional objects.

It is one aspect of the instant invention to provide an improved by-product waste removal system for SFF systems that overcomes the earlier mentioned disadvantages of prior art systems.

It is another aspect of the instant invention to provide an improved by-product waste removal system for SFF systems that does not require a mechanical vacuum pumping system.

It is another aspect of the instant invention to provide an improved by-product waste removal system that allows intervention in removing collected waste during the SFF build process without interrupting the build.

It is still another aspect of the instant invention to provide an improved by-product waste removal system that can accurately account for by-product waste removed.

It is a feature of the present invention that at least one container holding a discrete amount of material is delivered to a queue station and the material is removed from the container for delivery to the dispensing device.

It is an advantage that the by-product waste removal system of the present invention is lower in cost, simpler and more effective than prior by-product waste removal systems.

These and other aspects, features and advantages are provided by a method for delivering at least one material and removing waste material in a solid freeform fabrication apparatus to form a three-dimensional object, the method including at least the steps of: delivering material to a dispensing device; dispensing the removed material from the dispensing device in a layerwise fashion to form the three-dimensional object; producing waste material from the dispensed material and depositing the waste material in a waste receptacle, wherein the depositing step includes at least collecting the waste material in an intermediate vessel, then releasing from the intermediate vessel to the waste receptacle the collected waste material when a pre-set amount of the waste material has been collected and then repeating the collecting and releasing steps until a three-dimensional object is formed.

The invention also includes a material feed and waste system for a solid freeform fabrication apparatus, the system including at least a means for delivering at least one material to at least one dispensing device; a means for dispensing the discrete amount of material by the dispensing device in a layerwise fashion to form via a plurality of layers a three-dimensional object; a means for normalizing the layers of the three-dimensional object wherein waste material is produced; means for depositing the waste material in a waste receptacle; wherein the means for depositing the waste material comprises: means for collecting the waste material in an intermediate vessel and a means for releasing from the intermediate vessel to the waste receptacle the collected waste material when a pre-set amount of the waste material has been collected; and a means for repeating said collecting and releasing means until three-dimensional object is formed.

These and other aspects, features, and advantages are achieved according to the method and apparatus of the present invention that employs a unique waste by-product removal system that automatically and reliably transfers measured amounts of by-product waste material to a final collection container.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides its benefits across a broad spectrum of SFF processes. While the description which follows hereinafter is meant to be representative of a number of such applications, it is not exhaustive. As will be understood, the basic apparatus and methods taught herein can be readily adapted to many uses. It is intended that this specification and the claims appended hereto be accorded a breadth in keeping with the scope and spirit of the invention being disclosed despite what might appear to be limiting language imposed by the requirements of referring to the specific examples disclosed.

While the present invention can be applicable to other SFF techniques and objects made therefrom, the invention will be described with respect to solid deposition modeling (SDM) utilizing a build material dispensed in a flowable state. However it is to be appreciated that the present invention can be implemented with any SFF technique that requires the continuous or intermittent removal of by-product waste during a build. For example, the build material can be a photocurable or sinterable liquid or powder material that is heated to a flowable state but when solidified may form a high viscosity liquid, a semi-solid, a gel, a paste, or a solid. In addition, the build material may be a composite mixture of components, such as a mixture of photocurable liquid resin and powder material such as metallic, ceramic, or mineral, if desired.

As used herein, the term “a flowable state” of a build material is a state wherein the material is unable to resist shear stresses that are induced by a dispensing device, such as those induced by an ink jet print head when dispensing the material, causing the material to move or flow. Preferably the flowable state of the build material is a liquid state, however the flowable state of the build material may also exhibit thixotropic properties. The term “solidified” and “solidifiable” as used herein refer to the phase change characteristics of a material where the material transitions from the flowable state to a non-flowable state. A “non-flowable state” of a build material, as used herein, is a state wherein the material is sufficiently self-supportive under its own weight so as to hold its own shape. Build materials existing in a solid state, a gel state, a paste state, or a thixotropic state are examples of a non-flowable state of a build material for the purposes of discussion herein. Further, the term “cured” or “curable” refers to any polymerization reaction. Preferably the polymerization reaction is triggered by exposure to radiation or thermal energy.

Most preferably the polymerization reaction involves the cross-linking of monomers and oligomers initiated by exposure to actinic radiation in the ultraviolet or infrared wavelength band. Further, the term “cured state” refers to a material, or portion of a material, in which the polymerization reaction has substantially completed. It is to be appreciated that as a general matter the material can easily transition between the flowable and non-flowable state prior to being cured. However, once cured, the material cannot transition back to a flowable state and be dispensed by the apparatus.

Additionally, the term “support material” refers to any material that is intended to be dispensed to form a support structure for the three-dimensional objects as they are being formed, and the term “build material” refers to any material that is intended to be dispensed to form the three-dimensional objects. The build material and the support material may be similar materials having similar formulations but, for purposes herein, they are to be distinguished only by their intended use.

A preferred method for dispensing a curable phase change material to form a three-dimensional object and for dispensing a non-curable phase change material to form supports for the object is disclosed in the co-pending U.S. patent application Ser. No. 09/971,337 entitled “Selective Deposition Modeling with Curable Phase Change Materials”, assigned to the assignee of the present invention. A preferred curable phase change material and non-curable phase change support material are disclosed in the co-pending U.S. patent application Ser. No. 09/971,247 entitled “Ultra-Violet Light Curable Hot Melt Composition”, also assigned to the assignee of the present invention. An SDM system and method using powder is disclosed in U.S. Pat. No. 6,416,850 and a method of using an ink jet printhead to deliver a binder to layers of powdered material is described in U.S. Pat. No. 5,204,055.

Referring particularly toFIG. 1there is illustrated generally by the numeral10a prior art solid freeform fabrication apparatus of the SDM type that can be adapted to incorporate the waste removal system of the instant invention. This apparatus10is schematically shown including a material feed and waste system indicated generally by the numeral86. The build platform15is reciprocally driven by conventional drive means29. The dispensing trolley21is precisely moved by actuation means17vertically to control the thickness of the layers of the object20. The actuation means17comprises precision lead screw linear actuators driven by servomotors. The ends of the linear actuators17reside on opposite ends of the build environment13and in a transverse direction to the direction of reciprocation of the build platform. However, for ease of illustration inFIG. 1they are shown in a two-dimensionally flat manner giving the appearance that the linear actuators are aligned in the direction of reciprocation of the build platform15. Although they may be aligned with the direction of reciprocation, it is sometimes preferred they be situated in a transverse direction so as to optimize the use of space within the apparatus.

In the build environment illustrated generally by numeral13inFIG. 1, there is shown by numeral20a three-dimensional object being formed with integrally formed supports53. The object20and supports53both reside in a sufficiently fixed manner on the build platform15so as to sustain the acceleration and deceleration effects during reciprocation of the build platform15while still being removable from the platform. In order to achieve this, it is desirable to dispense at least one complete layer of support material on the build platform15before dispensing the build material since the support material is designed to be removed at the end of the build process. In this embodiment, the build material identified by numeral23A is dispensed by the dispensing device14that is in fluid flow communication with the material feed portion of system86to form the three-dimensional object20. The support material, identified by numeral23B, is dispensed in the same manner by dispensing device14to form the supports53. Containers identified generally by numerals42A and42B, respectively hold a discrete amount of these two materials23A and23B. Umbilicals51A and51B, respectively deliver the material to dispensing device14, which in the preferred embodiment is an ink jet print head having a plurality of dispensing orifices27.

Preferably the materials23A and23B ofFIG. 1are phase change materials that are heated to a liquid state, and heaters (not shown) are provided on the umbilicals51A and51B to maintain the materials in a flowable state as they are delivered to the dispensing device14. In this embodiment the ink jet print head14is configured to dispense both materials from a plurality of dispensing orifices27so that both materials can be selectively dispensed in a layerwise fashion to any location in any layer being formed. When the dispensing device14needs additional material23A or23B, extrusion bars46A and46B, respectively are engaged to extrude the material from the containers42A and42B, through the umbilicals51A and52B, and to discharge orifices27of the dispensing device14.

The dispensing trolley21in the embodiment shown inFIG. 1includes a heated planarizer39that removes excess material23A and23B from the layers being dispensed to normalize the dispensed layers. The heated planarizer39contacts the build and support materials23A and23B in their non-flowable state and, because it is heated, locally transforms some of the materials to a flowable state. Due to the forces of surface tension, the excess flowable materials23A and23B adhere to the surface of the planarizer39, and as the planarizer39rotates the adhered materials are brought up to the skive90which is in contact with the planarizer39. The skive90separates the excess materials23A and23B that are now waste material from the surface of the planarizer39and directs the flowable material into a waste reservoir, identified generally by numeral94located on the trolley21. A heater96and thermistor98on the waste reservoir94operate to maintain the temperature of the waste reservoir at a sufficient level so that the Waste material58in reservoir94remains in a flowable state.

Waste reservoir94is connected to a heated waste umbilical tube56for delivery of the Waste material58to the waste receptacles60A and60B. Waste material58is allowed to flow via gravity down to the waste receptacles60A and60B. Although only one umbilical tube or line56with a splice connection to each waste receptacle is shown, it is preferred to provide a separate waste umbilical line56between the waste reservoir94and each waste receptacle60A and60B.

For each waste receptacle60A and60B, there is associated a solenoid valve100A and100B, for regulating the delivery of waste material to the waste receptacles. Preferably the valves100A and10B remain closed, and only open when the respective extrusion bars46A and46B are energized to remove additional material. For example, if only extrusion bar46A is energized, only valve100A is opened to allow waste material58to be dispensed into the waste receptacle60A. This feedback control of the valves prevent delivery of too much waste material to either waste receptacle by equalizing the delivery of waste material in the waste receptacles in proportion to the rate at which material23A and23B is fed from the containers42A and42B to the dispensing device14. Thus, the delivery of waste material58to the waste receptacles60A and60B is balanced with the feed rates of build material23A and support material23B of the feed system.

In the prior art system ofFIG. 1, an additional detection system is provided in the waste system to prevent the waste material58from overflowing the waste reservoir94. The system comprises an optic sensor102provided in the waste reservoir94that detects an excess level of waste material58in the reservoir94. If the level of the waste material58in the waste reservoir94raises above a set level, it is detected by the sensor102. The sensor102in turn provides a signal to a computer controller (not shown), which shuts down the apparatus. This prevents waste material from flooding the components inside the apparatus10in the event of a malfunction of the feed and waste system86. The apparatus10can then be serviced to correct the malfunction, thus preventing excessive damage to the apparatus.

In the prior art system shown inFIG. 1, the build material23A is a phase change material that is cured by exposure to actinic radiation. After the curable phase change material23A is dispensed in a layer it transitions from the flowable state to a non-flowable state. After a layer has been normalized by the passage of the planarizer39over the layer, the layer is then exposed to actinic radiation by radiation source88to cure the build material23A. Preferably the actinic radiation is in the ultraviolet or infrared band of the spectrum. It is important, however, that planarizing occurs prior to exposing a layer to the radiation source88. This is because the preferred planarizer car only normalize the layers if the material in the layers can be changed from the non-flowable to the flowable state. This cannot occur if the material23A is first cured.

In conjunction with the curable build material23A, a non-curable phase change material is used for the support material23B. Since the support material23B cannot be cured, it can be removed from the object and build platform, for example, by being dissolved in a solvent. Alternatively the support material23B can be removed by application of heat to return the material to a flowable state, if desired.

In this prior art system the by-product waste material58comprises both materials23A and23B as they accumulate during planarizing. Preferably, a second radiation source70is provided to expose the waste material in the waste receptacles to radiation to cause the material23A to cure so that there is no reactive material in the waste receptacles.

This prior art system has containers42A and42B for use in the by-product feed and waste system86. Each container42A and42B comprises a syringe portion62A and62B and plunger portion64A and64B. The syringe portion forms a cylinder having a small opening at one end for dispensing the material23A or23B, as appropriate. As the plunger portion64A and64B is driven into the syringe portion62A and62B, the material23A or23B in the syringe portion of the corresponding container is expelled through the small opening.

Unique to each container is a waste receptacle60A and60B that is provided on the plunger portion64for accepting delivery of waste material58. There is a corresponding waste receptacle60A or60B for each plunger portion64A and64B. The appropriate extrusion bar46A or46B acts on the plunger portion64A and64B to drive the plunger into the syringe portion62A and62B and thereby remove the build material23A and support material23B from the appropriate container42A and42B. As this occurs, the waste material58is deposited into the waste receptacles60A and60B of the plunger portions64A and64B. Once substantially all of the build and support materials23A and23B have been delivered from their containers42A and428to the dispensing device14, the waste material58is sealed within the depleted containers for safe disposal.

Now referring toFIG. 2, the SDM apparatus schematically shown inFIG. 1is shown as10. To access the build environment, a slideable or retractable door104is provided at the front of the apparatus. The door104does not allow radiation within the machine to escape into the outside environment. The apparatus is configured such that it will not operate or turn on with the door104open. In addition, when the apparatus10is in operation the door104will not open. A support material feed door106is provided so that the support material containers (not shown) can be inserted into the apparatus10. A build material feed door108is also provided so that the build material containers (not shown) can be inserted into the apparatus. A waste drawer68is provided at the bottom end of the apparatus10so that expelled waste containers can be removed from the apparatus10. A user interface110is provided which is in communication with an internal computer (also not shown), which tracks receipt of the print command data from an external computer. That typically is the user's workstation computer or a computer network.

Turning toFIG. 3, a schematic of a similar SDM device is shown but with the by-product waste removal system86replaced by the by-product removal system of the present invention. In this design the build and support material feed containers shown earlier as42A and42B inFIG. 1have been replaced by simpler container systems42C and42D that do not require the feature of storing waste material in the used feed containers.

InFIG. 3the complete build apparatus of the SDM device operates as described inFIG. 1in building parts. Therefore that aspect of the description of the method and apparatus will not be repeated here, but it will be understood to be the same as the description given with respect toFIG. 1. In addition the schematic shown inFIG. 3operates within the same industrial design shown in the perspective view ofFIG. 2.

Beginning with the waste umbilical tube or line56inFIG. 3, the by-product waste material removal system of the instant invention is shown generally by the numeral150and will be described hereafter as accumulator150. By-product waste material58from the waste reservoir94flows by gravity through line56and into intermediate vessel or holding tank162of accumulator150through inlet line160. Vessel162is a tank that has sealable openings at the base or bottom and the top with o-ring seals that open and close when actuator164moves a central rod174up or down. When rod174is moved to the up position, top vent176is opened to the atmosphere and base drain172is sealed to allow vessel162of accumulator150to fill with by-product waste. A level detector168senses when the level of by-product waste material166rises to the level detector. Level detector168then activates actuator164to move central rod174down, closing top vent176and opening base drain172. When drain172opens the by-product waste material58rapidly empties through drain172by gravity flow into waste material receptacle180. Because top vent176is closed at this time the flow of liquid waste creates a slight negative pressure, effectively pulling any residual by-product waste material58from line56. Earlier work with systems of this type required bulky and expensive vacuum pump systems to ensure that line56would remain clear and not plug during SDM builds. In this instant invention that function is performed by the slight vacuum created by the gravity flow of the by-product waste from vessel162of accumulator150.

After vessel162empties actuator164is activated to move central rod174up, closing the bottom seal172and opening top vent176to vent to the atmosphere to thereby allow vessel162to begin refilling for the next cycle.

Because level detector168always activates actuator164at the same level accumulator150can easily be calibrated so that the system computer can monitor the exact amount of by-product waste material fed into waste material receptacle180.

It should be recognized that the preferred design described herein of a central shaft that activates the vent and drain seals could be replaced by any appropriate design that opens and closes the seals in the same manner, such as spring loaded valves or solenoid controlled valves.

Waste material receptacle180, in a preferred embodiment, is a disposable polypropylene bag with a zipper closure that can be easily removed for disposal. It should be recognized that the use of a polypropylene bag is only one embodiment and that other bags or bottles may be employed in the instant invention. Because of the capacity of accumulator150and its vessel162, the design of the instant invention allows the operator to intervene to remove and replace waste receptacle180without interrupting the SDM build.

In another embodiment (not shown) a source of actinic radiation could be mounted near waste receptacle180to cure the by-product waste material in waste receptacle180.

Turning toFIG. 4, a schematic side sectional view of the accumulator150of FIG.3is illustrated generally by the numeral200. The schematic shows a metal accumulator tank232with a metal rod228passing completely through tank232and connected to actuator204, which is mounted to the top of accumulator tank232by actuator support frame208. An inlet hole220in accumulator tank232is the entry point for by-product waste material58(not shown) from the SDM device. Hole224in accumulator tank232is the entry point for a level detector that is preferably a reflective object optical IR sensor adapted to sense liquid. The unadapted sensor is available commercially from Optek Technology, Inc. of Carrollton, Tex. 75006. Adaptations include a glass cone-shaped reflector lens and an insulating housing. An o-ring seal216is located at top of accumulator tank232around central rod228and acts to seal the top of accumulator tank232when actuator204is activated into down position. A second o-ring seal236and a ball seal240are located at bottom of accumulator tank232around central rod228and act to seal the bottom drain hole of accumulator tank232when the actuator204is activated into up position.

FIG. 5is a perspective rendering showing a preferred design of the accumulator tank represented generally by the numeral300. The accumulator tank structure is a machined aluminum block308with a hollow center and sealed cap302. It is surrounded by insulation312the block also has heating elements (not shown) to aid in keeping the by-product waste material in a flowable state. An actuator support frame316mounted on cap302on block308supports the actuator290used to drive the central shaft298that operates to close and open the atmospheric vent seal320and the base or drain (not visible), depicted inFIG. 3as base drain172. Also shown are the inlet line296for by-product waste material and the level sensor housing294.

Although this preferred design is made from aluminum it should be recognized that the materials of construction are not critical to the instant invention and any number of materials could be used.

In operation the instant invention operates as follows. Referring toFIG. 3, once a SDM build is in progress waste material58is generated and flows from the waste reservoir94down line56by gravity. Inlet port160to accumulator150is always in an open state, allowing the flow of waste material into the tank. During this filling cycle base drain172is in a closed position and atmospheric vent176is in an open position. Waste material166accumulates in vessel162of accumulator150until the level of waste material eventually reaches the level of the level sensor168. When the waste level reaches level detector168the sensor transmits a signal (not shown) to actuator164, which acts to move central shaft174downwardly, closing atmospheric top vent176and opening base drain172. With atmospheric top vent176sealed the rapid draining of waste material166through base drain172into waste receptacle180creates a negative pressure that effectively pulls waste material58from line56, keeping line56clear for the next cycle. After vessel162and line56are drained, actuator164is energized again to move central shaft174upwardly, closing base drain172and opening atmospheric top vent176, allowing, gravity flow of further waste material to accumulate in vessel162of accumulator150. Continued operation allows reliable removal of waste material in accurately measured batches and keeps line56clear without use of vacuum pumps.

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 form the inventive concept disclosed herein. Accordingly, the spirit and broad scope of the appended claims is 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.