Patent Application
20160303616
Embodiments of the invention relate generally to three-dimensional printing (“3D printing”) and in particular to methods and equipment for 3D printing.
Three dimensional printers are divided into several categories based on the methods used for dispensing materials. One of these categories encompasses the use of ink-jet printing with a powdered or granular substrate. An exemplary granular-substrate ink-jet method is described in U.S. Pat. No. 5,204,055, incorporated herein by reference in its entirety. A moving ink-jet printhead is used to dispense, e.g., print, a liquid ink onto a stationary level substrate comprising a granular material, e.g., a powder, confined to a region of the machine referred to as the build area. Motion of the printhead relative to the substrate and other stationary components is provided by a robot to which the printhead is attached. The union of the ink and the powder forms a solid portion of material in the location printed. A three dimensional article is formed by first printing a cross sectional layer on the substrate, then spreading a further layer of powder over the first layer, and printing a second cross-sectional layer in the same general location as the first. Layers bond together in sequence, forming a solid three-dimensional article. After a relatively large number of layers are printed in this manner, the solid article may be removed from loose, unbound powder (i.e., powder that has not received a dose of ink) after a suitable curing time has passed.
A persistent difficulty encountered with 3D printing equipment, especially those using ink-jets over a powdered substrate, is maintenance of the printing element. This arises from the combination of several requirements for building accurate 3D articles: (1) The printing element preferably travels relatively close to the substrate to ensure accurate printing; (2) the powder is preferably relatively flowable in its unprinted state to facilitate the formation of flat layers on the substrate; and (3) the combination of ink and powder typically form a durable solid when they mix. The combination of these three factors ensures the ambient environment around the printing element tends to be dusty and the dust tends to form tenacious deposits on the printing elements of the machine.
In an aspect, a 3D printing apparatus includes a printing element, and a manifold configured to receive the printing element. A gasket is disposed proximate the printing element. The manifold and gasket together enclose the printing element, and the gasket defines a liquid-tight seal that isolates the printing element from ambient.
One or more of the following features may be included: The gasket may include a highly flexible, hydrophobic material, such as EPDM rubber, fluoroelastomers, and/or polydimethylsiloxane.
The gasket may include a flexible component coupled with a rigid support. The gasket may be adapted to become distorted when it is mated to the printing element in an interference fit, the distortion causing the liquid-tight seal to become compressed at an interface between the gasket and the manifold.
The apparatus may include a robot adapted to move the printing element, manifold, and gasket. The robot may be adapted to move a plurality of assembled printing elements, manifolds, and gaskets.
In another aspect, a 3D printing apparatus includes a manifold configured to receive a printing element, and a gasket disposed at a lower portion of the manifold. The manifold and gasket are adapted to together enclose the printing element, and the gasket defines a liquid-tight seal that isolates the printing element from ambient.
A service station may be adapted to service the printing element. The service station may include a parking element having at least one surface, e.g., a flat surface.
In another aspect, a method for capping a printing element is provided. A 3D printing apparatus may be provided, including a printing element, a manifold configured to receive the printing element, a gasket disposed proximate the printing element, and a service station adapted to service the printing element, the service station including a parking element having at least one surface. The manifold and gasket together enclose the printing element, and the gasket defines a liquid-tight seal that isolates the printing element from ambient. The printing element is positioned against the surface of the service station. The printing element is pressed against the surface, with the surface compressing the gasket to tighten the liquid-tight seal.
In still another aspect, a service apparatus for washing a printing element is provided. The apparatus includes a parking element having at least one surface, e.g., a flat surface, and a frame defining a plurality of channels or tubes for introducing and draining a liquid solution when the printing element is parked against the parking element.
In another aspect, a method for washing a printing element is provided. In accordance with the aspect, a 3D printing apparatus is provided, including a printing element, a manifold configured to receive the printing element, and a gasket disposed proximate the printing element. The manifold and gasket together enclose the printing element, and the gasket defines a liquid-tight seal that isolates the printing element from ambient.
The 3D printing apparatus is positioned against a service apparatus including a parking element having at least one surface, and a frame defining a plurality of channels for introducing and draining a liquid solution when the printing element is parked against the surface of the parking element. The channels are in fluidic communication with a space between the gasket and an orifice plate of the printing element. A fluid is supplied from at least one inlet channel to a space between the gasket and the orifice plate. A negative pressure is applied to an outlet channel. The fluid is drained through the outlet channel.
One or more of the following features may be included. Supplying the fluid may include pressurizing the fluid in the printing element. The printing element may apply the negative pressure. A first fluid may be supplied through the inlet channel, a second fluid may be supplied through the printing element, and the product of reaction between the two fluids effects cleaning of an orifice plate on the printing element.
Acoustic energy from an acoustic energy source may be applied to the fluid occupying the space between the gasket and orifice plate. The source of acoustic energy may be a piezoelectric actuator of the printing element.
In still another aspect, a method for preserving and storing a printing element is provided. In accordance with the aspect, a 3D printing apparatus is provided, including a printing element, a manifold configured to receive the printing element, and a gasket disposed proximate the printing element. The manifold and gasket together enclose the printing element, and the gasket defines a liquid-tight seal that isolates the printing element from ambient.
The 3D printing apparatus is positioned against a service apparatus that includes a parking element having at least one surface, and a frame defining a plurality of channels for introducing and draining a liquid solution when the printing element is parked against the surface of the parking element. The channels are in fluidic communication with a space between the gasket and an orifice plate of the printing element. A storage fluid is supplied from at least one channel to the space between the gasket and the orifice plate.
One or more of the following features may be included. A vacuum may be applied to the printing element, to cause the storage fluid to replace at least a portion of an ink disposed in the printing element, the storage fluid including a nonvolatile, inert solvent miscible with the ink, and the ink including a binder for 3D printing. The printing element may be positioned against an impermeable surface to seal the storage fluid within the printing element.
As used herein, the term “powder” means granular material used as a substrate in a 3D printing process. The term “ink” means a liquid component dispensed onto the powder to define a three-dimensional article in a 3D printing process. An ink can include a chemical substance that activates adhesive components contained in the powder, or it may itself include an adhesive, or it may include a fluid with no adhesive action, e.g. a conventional dye-based ink used for marking the substrate.
As used herein, the term “print” means the action of dispensing a liquid ink over a powdered substrate.
As used herein, the term “printhead” means an assembly of printing hardware that is manipulated as a unit in a 3D printer to dispense ink during the printing process. An example of a commercially available printhead suitable for use with embodiments of the invention is RHB-12, available from 3dbotics, Inc of Woburn, Mass. The term “printing element” means a subcomponent of the printhead, i.e., a single device that ejects ink when it receives electronic signals. An example of a commercially available printing element is a QS80 “Sapphire” available from Fujifilm/Dimatix of Lebanon, N.H.. A printhead may include several printing elements, mounting hardware, fluid connections, electronic connections, and components attached to the printhead to protect the printing elements from damage and facilitate maintenance. Components of a printing element include an “orifice plate,” i.e., a mechanical component defining one or several holes through which ink is ejected in the form of a jet. Other components include fluid inlets through which ink is supplied, a stimulation device that may include a piezoelectric element providing acoustic energy that ejects liquid ink through the orifice plate, and electronic components that receive signals from the outside and control the flow of ink through the orifice plate.
An embodiment of the instant invention also includes a service station. This is a component that sits in a particular location outside of the build area and includes a set of devices for cleaning the printhead, most particularly the orifice plates on individual printing elements and areas immediately surrounding them. The service station may additionally include a capping station, whose purpose is to cover the orifice plates when they are not in use, to protect them from ambient dust, and to prevent them from drying out or otherwise reacting with the ambient atmosphere.
In U.S. Patent Publication No. 2015/0251354 A1, incorporated herein by reference in its entirety, a geometric arrangement of printing elements in a printhead is disclosed that ensures nearly all of the dust ejected by the printing process moves away from the printing elements. Embodiments of the instant invention provide an additional mechanical means for protecting the printhead from dust, and for cleaning it when dust happens to collect on it.
The principal method for cleaning a printhead that has accumulated some dust is to wash the orifice plates of the printing elements with a liquid. This may be accomplished either by supplying a stream of liquid from an external source, or by pressurizing the ink within the head (a process known as pressure-priming) to expel deposits from the vicinity of the orifice plates. In both of these methods, a stream of liquid arrives at the external surface of the printhead that greatly exceeds the quantity expelled during normal printing. This liquid is preferably excluded from the vicinity of the electronic components and cleared away at the conclusion of the cleaning process to make a free path between the individual ink jets and the powder.
Embodiments include a rigidly supported flexible gasket that forms a liquid-tight seal around the orifice plates and is integrated with the printhead, combined with a stationary service station that sits in a particular location outside of the build area of the 3D printer. The gasket that surrounds the orifice plate forms a barrier to protect electronic components, protects the fragile orifice plate while facilitating wiping of the head, and provides an interface with the service station. The service station includes a fixed arrangement of components. All motion of the printhead relative to the service station may be provided by a robot.
In a preferred embodiment, printhead components are encapsulated in a modular envelope (i.e., a manifold) that allows convenient supply of fluid and electronic signals, and allows accurate alignment and support of individual printing elements in an array that includes the printhead. The gasket described herein is preferably integrated into the manifold and travels with it. It provides a liquid-tight barrier between the electronic components of the head and the path taken by the fluid, and provides mechanical protection of the delicate printing elements of the printhead during operation, assembly, handling, and service.
Referring to
To make an effective seal around a slender rectangular orifice plate, a soft rubber gasket 106 is preferably mechanically supported around its entire circumference. The design of the gasket 106 that travels with the manifold 102 preferably incorporates a rigid structure that provides support. In one embodiment, the mechanical support is provided by a metallic plate that carries multiple printing elements 104 that project through narrow slots in the plate. In a preferred embodiment the gasket support element 108 is a slotted bar of metal (referred to herein as a “dogbone” design) that attaches to the manifold 102 containing a single printing element 104. This configuration may provide the advantage of enabling the single assembly to be used as a modular component in different printhead configurations. By way of example, a dogbone gasket support element 108 is shown in
A typical multi-channel printing element is exemplified by the U-Series products manufactured by FujiFilm/Dimatix. The orifice plate may be a rectangle with a width selected from a range of 0.5 mm to 20 mm and a length of 0.5 mm to 200 mm. One or more holes, e.g., 1 to 4096 holes may be defined in the orifice plate, each hole having a diameter selected from a range of 0.005 mm to 0.5 mm, with spacing of 0.005 mm to 0.5 mm between the holes. In a particular embodiment, the orifice plate may be a rectangle 5 mm wide and 80 mm long with 256 holes etched into it in a single line with 0.01 inches between holes.
A gasket 106 appropriate for this printhead possesses a rectangular slot that slightly overlaps the orifice plate, for example the slot may be 3.5 mm wide and 77 mm long, in the case of the exemplary plate of 5 mm wide and 80 mm long. The bottom surface of the gasket 106 may be flat, while the top surface may have depressions and asperities that enclose various physical features of the printing element 104. Most particularly, the gasket 106 may include a rectangular ridge that fits the outside dimensions of the orifice plate, e.g., 5 mm×80 mm in this example. This provides a sealing surface around the circumference of the orifice plate and retards the flow of fluid upwards from the orifice plate to the regions where active electronic components.
The gasket 106 is typically made of a soft, flexible material such as silicone rubber. To hold it in the proper orientation with respect to the orifice plate, a rigid support is provided by the dogbone gasket support element 108. The dogbone support element 108 is essentially a metallic object with a rectangular slot that surrounds the orifice plate with a clearance of at least a few millimeters. By way of example, the slot in the dogbone 108 may be 88 mm long and 13 mm wide to provide 4 mm of clearance around an orifice plate having dimensions of 5 mm×80 mm, allowing enough space for the contours of the rubber gasket 106. The gasket 106 may be molded over the dogbone gasket support element 108 such that the dogbone support element 108 is embedded in the rubber and holds the gasket 106 securely in place.
The rubber gasket 106 supported by each dogbone support element 108 preferably defines a narrow slot through which the jets of the printing element 104 may eject fluid onto the powder. The width of the slot is preferably slightly less than the width of the orifice plate, and may be provided with a positioning feature such as a ridge. This positioning feature permits the orifice plate to mate with a corresponding slot or other locating feature in the flexible gasket 106 around its entire circumference. The rubber gasket 106 and dogbone support element 108 may be coupled to the orifice plate with coupling elements 110, 110′. The coupling elements form the end pieces for the rubber gasket/dogbone support element assembly, and provide the anchoring points for the structure supporting the gasket. The coupling elements are integral parts of the metallic portions of the dogbones, forming the end pieces of the structure that support thinner members that support the narrow slot in the rubber gasket and pass along the length of the orifice plate. The dogbone is aligned and attached to the manifold by screws threaded through holes in the coupling elements into threaded inserts pressed into the lower corners of the manifold, adjacent to the slot that contains the printing element. In the event of a collision between the printhead and an external object, these anchoring points transfer the force of impact away from the printing element, through the manifold, and into the frame of the machine.
When the gasket 106 and dogbone gasket support element 108 are assembled with the printing element 104 and manifold block 102, it may be preferred that the printing element 104 press into the mating slot in the gasket 106 a short distance, with a small ‘interference’ fit of, e.g., roughly 1 mm. This provides some extra mechanical force against the mating surface and ensures a liquid-tight seal.
Referring to
As used herein, a ‘parking element’ 210 is a solid feature located on a stationary structure that stands outside of the build area of the machine. This feature provides a mating surface for the dogbone gasket 208 at times when the printhead is not in use. In a particular embodiment, the parking element 210 may be a body of flexible material with a flat upper surface against which the dogbone gasket support element 208 (that travels with the printhead) may be placed. It provides mechanical compression of the dogbone gasket 208 around the orifice plate and ensures a seal against the edges of the plate, preventing drying of the printing element 204. This mode of compression is illustrated in
The parking element 210 may include a supporting frame that forms a portion of a printhead service station. The frame 322 may define a plurality of channels for introducing and draining a liquid solution when the printing element is parked against the parking element. In some embodiments, the channels may be defined by tubes. In a preferred embodiment, the frame may be constructed from stainless steel or a plastic material that is stiff enough to support the flexible parking element under the load imposed by parking the printhead. Channels for carrying fluid to and from the parking element may, for example, be sealed by hoses and hose-barbs or compression fittings attached to inlet points molded into the parking element. Tubes may, for example, have an inside diameter approximately the size of the slot in the dogbone gasket, and may project vertically downward from the inlet and outlet orifices disposed in the parking element.
In an exemplary configuration, the frame may include a fluid supply and drain to flush away accumulated dust. The design of the dogbone gasket 208 accommodates all to the complexity of the lower extent of the printhead and printing element 204. The dogbone gasket 208 provides an interface to a more simplified surface that includes the parking element 210. A simple geometry for the parking element 210 may be a flat sheet of flexible rubber. That shape is relatively easy to clean, and allows the printhead to park within a broad area without the need to register with any special topography. As an example, in
The printhead is the travelling component of the 3D printing system. A robot effects the motion of the printhead during the manufacturing of 3D printed parts. A suitable robot is, for example, an IRB 260 or an IRB 140 industrial robot manufactured by ABB, Inc.
The service station is a stationary component that rests outside of the build area of the machine, but inside the region where the robot is capable of moving the printhead. When it is desired to park, clean, prime, or wipe the printhead, the robot may be used to move the printhead to the appropriate component of the service station.
The lip of the gasket surrounding the slot provides a surface away from the printing element where ejected powder can collect and be easily wiped away without contacting (and possibly damaging) the orifice plate.
The soft, flexible material from which the gasket 206 is made is chosen to easily shed foreign material. Particularly useful materials for this component are chemically resistant hydrophobic elastomeric materials such as natural or synthetic rubber, EPDM rubber, fluoroelastomers such as VITON, polydimethylsiloxane, and associated polymers.
Advantageously, the projecting lip of the gasket 206 provides a useful feature for capping a printhead (or printing element) when it is not in use. In an embodiment, a parking station 210 is provided, including a flat sheet of flexible rubber that may be made from a material chosen from the same set as that given for the gasket, i.e., natural or synthetic rubber, EPDM rubber, fluoroelastomers such as VITON, polydimethylsiloxane, and associated polymers The printhead is capped by moving the printhead to a point over the flat sheet and lowering it vertically until the flat sheet compresses against the lips of the gaskets 206 that surround the orifice plates of the individual printing elements 204.
Referring to
In a typical washing operation, the printhead is parked with the slot in the dogbone gasket aligned with the two orifices, 312, 314, in the irrigation site 301. The washing fluid may be supplied under a modest pressure to the space such that particles of dust or deposits ejected from the build area are dissolved or carried away from the orifice plate. A suitable washing fluid is, e.g., a low-viscosity solvent whose action serves to soften solidified deposits on the printhead, such as water containing a surfactant, alcohol, ethoxy ethanol, or dipropylene glycol monomethyl ether. The washing fluid may be supplied through a tube connection to the fluid supply orifice 312 on the upper surface of the parking element. Excess fluid may be drained from the space through the drain orifice 314, to a waste collection system via, e.g., a tube connection (not shown). Most preferably, the two orifices 312, 314, in the illustrated embodiment are located at points on opposite ends of the orifice plate.
Referring to
Referring to
In use, a printing element may be washed as follows. The 3D printing apparatus described may be positioned against the service apparatus described above such that the channels 312, 314 are in fluidic communication with a space 324 between the gasket and the orifice plate of the printing element. A fluid is supplied from at least one channel to the space between the gasket and the orifice plate. A vacuum or fluid drain to the channel or tube is provided. The fluid is subsequently drained away.
Service station functions that may be provided by embodiments of the invention include:
1. Capping: During times when the printhead is idle, for example, when other components of the machine are undergoing maintenance, the printhead is preferably protected from the ambient environment. Configurations in accordance with embodiments of the invention permit the capping element to have a very simple shape that is easy to keep clean, e.g., a surface of a flat rubber sheet.
2. Wiping: By providing a non-sticky target for the majority of dust deposits to collect, embodiments of the invention facilitate cleaning of the outside of the printhead.
3. Protection: The gasket provides a fluid-tight seal against the orifice plate that excludes washing fluids from the fragile electronic components of the printing elements.
4. Washing: Fluids supplied to the orifice plate to facilitate cleaning are confined to the area where they are most needed. Washing fluids may be supplied externally, or they may be supplied from the printing elements by pressure priming.
The presence of an external source of wash fluid and drainage in close proximity to the orifice plate offers numerous opportunities for efficiently cleaning and preserving the printing elements. Besides the irrigation method described above, one may additionally use the printing element itself as a source of fluid by forcing ink out through the orifice plate into the irrigation site. Alternatively, one may use the printing element as a drain for the wash fluid. In the former case, the strategy is useful for removing particles of material that may have become lodged on the outer surface of the orifice plate. In the latter case, the wash fluid may be used to perform some detergent action on the interior channels of the printing element to dislodge, for example, deposits that may have accumulated from drying of the ink.
The mixing of the wash fluid and the ink during the process described above may be utilized to provide some further benefit. A chemical reaction may be caused to occur between the ink and the wash fluid when the two are mixed during irrigation. The wash fluid may contain an inhibitor for the solidification reaction that softens deposits on the orifice plate; and it may also include a buffer to adjust the pH of the mixed ink and wash fluid for purposes of dispersing particles.
One may additionally use acoustic energy to further stimulate the dispersion and/or softening of deposits in the presence of the wash fluid. A suitable acoustic energy source may be piezoelectric elements that may be included in the printing element.
For purposes of preserving the printing elements during occasional idle periods, a mechanism may be provided for replacing the ink in the printing elements with an inert storage fluid that displaces reactive inks with a medium in which the printing elements can rest for long periods, e.g., several days to a few months without damage.
A procedure for preparing a printing element for storage may be as follows:
1. Provide a 3D printing apparatus, including a printhead having a printing element, a manifold configured to receive the printing element, and a gasket disposed proximate the printing element.
2. Position the printhead against the service station 300 by moving the printing element against the parking station of the service station, over the irrigation site 301 that is configured to supply an inert, nonvolatile storage fluid that is miscible in an ink disposed in the printhead after use, e.g., after 3D printing. For example the storage fluid may be diethylene glycol, propylene glycol, or polyethylene glycol, and the ink may be CSTRed available from 3dbotics, Inc of Woburn, Mass.
3. Irrigate the space outside the orifice plate of the printhead with the storage fluid by supplying the storage fluid;
4. Apply a vacuum to fluid channels inside the printing element to cause the storage fluid to enter the channels inside the printing element;
5. Supply a quantity of the storage fluid sufficient to dilute an ink inside the printing element by no less than one volume of storage fluid per volume of ink, thereby replacing at least a portion of an ink disposed in the printing element;
6. Stop the supply of storage fluid;
7. Optionally one may seal the printing element by parking against a flat portion of the parking station.
If the printhead is to be stored for a relatively long period of time, for example, more than a few days, it may be desirable to either resupply the printhead with storage fluid periodically or to close off the ink supply with a valve or stopcock to prevent the ink from migrating back into the printing elements through the ink supply. When service is resumed, the storage fluid may be purged from the head either through internal channels in the head or out of the head into a drain.
Those skilled in the art will readily appreciate that all parameters listed herein are meant to be exemplary and actual parameters depend upon the specific application for which the methods and materials of the present invention are used. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described.
This application claims the benefit of priority to U.S. Provisional Application Ser. No. 62/149,297 filed Apr. 17, 2015, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62149297 | Apr 2015 | US |
