Patent Publication Number: US-2013241113-A1

Title: Additive fabrication apparatus and method of layerwise production of a tangible object

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an additive fabrication apparatus for layerwise production of a tangible object. It is known to press a small volume of liquid between a foil and a tangible object to provide a thin liquid layer than can be solidified. The flexible foil is preferably transparent to curing radiation. A firstly formed solid layer of the tangible object is adhered to the underside of the carrier plate by selectively solidifying the liquid. Consecutively formed solid layers are each adhered to a previously formed solid layer, respectively. 
     Each time after solidification of a new layer, a foil guiding stage is moved to peel off the foil from the earlier solidified layers adhered thereon in order to separate the last formed solid layer from the foil. Non-solidified parts of the liquid layer remain on the foil and need to be reconditioned when a new solidification starts. 
     A desire exists to increase the speed of the production process and to enhance the layer quality. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, an additive fabrication apparatus is provided comprising: a carrier plate ( 150 ) capable of supporting a tangible object ( 50 ); a foil ( 6 ) capable of supporting a liquid layer ( 30 ); said carrier plate ( 150 ) and foil ( 6 ) capable of relative movement with respect to each other so as to bring the liquid layer ( 30 ) into contact with the carrier plate or the tangible object ( 50 ); an energy source ( 90 ) arranged for at least partially solidifying at least part of an intersection pattern in the liquid layer arranged on the foil and in contact with the tangible object; and an applicator system ( 2 ) for applying the liquid layer ( 30 ) on the foil ( 6 ) comprising a first applicator, wherein the first applicator is arranged to alternate between providing a supply condition wherein liquid is supplied to the foil via an orifice and providing an uptake condition wherein liquid is taken up from the foil via the orifice. A single orifice may be used for both supply and uptake, or a different orifice may be used in the same applicator for the supply condition and the uptake condition. The applicator may be moveable and the supply condition or uptake condition may be dependent on the movement of the applicator. 
     In another aspect, a method of layerwise production of a tangible object is provided comprising: moving a foil guiding stage having a contact face and comprising on opposite sides of the contact face a pair of upper and lower foil guiding elements, the lower foil guiding element defining a foil height position (H 0 ) distanced from the contact face, to guide a portion of the foil including a liquid layer from the foil height position H( 0 ), along the contact face to contact a tangible object by movement of the foil guiding stage along the tangible object while keeping the portion of the foil contacting the tangible object stationary relative to the object; providing a liquid supply condition by applying the liquid layer on the foil; at least partially solidifying at least part of an intersection pattern in the liquid layer arranged on the foil and in contact with the tangible object by an energy source; and providing a liquid uptake condition wherein liquid is taken up from the foil into an orifice movable with the foil guiding stage; the uptake condition being dependent on a movement direction of the orifice so that liquid is taken up from the foil into the orifice after solidification of at least said part of the intersection pattern. 
     Specific embodiments of the invention are set forth in the dependent claims. 
     These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. 
         FIG. 1  shows a first embodiment of an applicator system; 
         FIG. 2  shows a second embodiment of the applicator system provided on sub stages; 
         FIG. 3  shows a detailed view on an alternative wedged plate configuration; 
         FIG. 4  shows an advantageous position of the liquid supply; 
         FIG. 5  shows a variation of the embodiment of  FIG. 4 ; 
         FIG. 6  shows an embodiment having two pressurized orifices; and 
         FIG. 7  shows a further embodiment of orifices with a controllable tilt angle. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1 , which shows a system  1  according to the invention. While the solidifying method can be applied either in a unidirectional way or in a bidirectional way, an advantage of bidirectional use may be that process time can be gained by avoiding to have to return all the process stages back to their start position before a new cycle can be started. Instead, after a pass in one direction, the stage(s) can reverse instantly and start the process in the opposite direction. This requires a certain mirror symmetry in the machine, so certain elements can switch functions when the direction is switched. 
     In this embodiment, the system  1  comprises a liquid applicator  2  which, in the shown example, is filled with a liquid  3 . 
     The system  1  further comprises a construction shape in the form of a flexible foil  6 . On the foil  6 , a liquid layer is formed of limited height to be brought in contact with the tangible object  50 . The system  1  further comprises a energy source  90  for solidifying a predetermined area  30  of a layer of the liquid  3 , said liquid layer  30  adjoining the construction shape  6 , so as to obtain a solid layer of the tangible object  50 , the solid layer thus having a predetermined shape. 
     In one embodiment, the energy source  90  is an energy source arranged to project a pattern through the foil  6  when the liquid layer  30  contacts the tangible object  50 . In particular, the energy source  90  is arranged for at least partially curing at least part of an intersection pattern in the liquid layer  30 . To enable the light or other radiation of the energy source  90  to solidify the liquid layer  30 , the construction shape  6  (flexible foil  6 ) is preferably substantially transparent to the radiation. 
     In one embodiment, each time after solidification and separation of a new layer, carrier plate (z-stage)  150  together with the tangible object  50  including solidified layers adhered thereon are moved upwards. Hence, the method for layerwise production of a tangible object is a cyclic method, wherein the described steps of positioning, solidifying, and separating together are comprised in a single cycle step of the method. 
     The flexible foil  6  has a liquid contacting side for being in contact with the liquid  3  to form liquid layer  30 . At least a contact face  181  in  FIG. 1  of the guide  180  is in pressing contact with a side of the flexible foil  6  opposite to the liquid contacting side. In the shown example, said pressing contact is realized by a sliding or rolling movement of the guide  180  along said opposite side of the flexible foil  6 . Lower parts in  FIG. 1  of the guide  180  are in rolling contact with a support platform by means of rollers  190 .  191 . Both the guide  180  and the energy source  90  are movable relative to the platform  7  via these rollers  17  in either or both directions indicated by arrow  73  in  FIG. 1 . The energy source  90  may be movable respective to the guide  180 . 
     In the shown example, the foil  6  is transparent to radiation from energy source  90 . As an example it is now assumed that, in the course of time during the performing of a method cycle, the guide  180  and the energy source  90  are synchronously moving in the right-hand direction of arrow  73  in  FIG. 1 . Then, at the instantaneous moment in time shown in  FIG. 1 , there are contacting parts of the layer  30  contacting the tangible object  50  for solidifying certain parts of the layer  30 . During the movement of the guide  180  and the energy source  90 , these contacting parts  30  are time-dependently varying. Thus, over time, the contacting parts  30  may vary depending, in particular, of the position of the guide  180  relative to the tangible object  50 . 
     Two foil guiding elements ( 190 ,  191 ) arranged on the stage  180  define a contact height defined by a height H where the tangible object  50  contacts the liquid layer  30  and at least one position HO distanced from the contact height H, for guiding the foil  6  to or from the contact height to contact the tangible object  50  by movement along the tangible object  50  while keeping the foil fixed relative to the tangible object  50  at least during contacting. 
     The foil  6  can be arranged for carrying the solidifiable layer material  30  supplied from a dispenser  2  to the tangible object  50  and for carrying the removed uncured material away from the tangible object  50 . Typically, the uncured material outside the intersection pattern sticks to the moving foil  6  because the adhesive force between the uncured material and the foil  6  are larger than the adhesive force between the uncured material and the tangible object  50 . 
     In the embodiment of  FIG. 1  the energy source  90  comprises a plurality of individually operable LEDs arranged in rows and columns (not shown). The motion of the energy source  90  may be controlled by a controller, which also controls the lighting of the LEDs. In use, the energy source  90  may be moved rectilinearly in a direction that extends at an angle with the directions of the rows and columns of a LED array to enhance the effective resolution of the system. This technique is described in more detail in copending application EP 07150447.6 in the name of Nederlandse, Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek (TNO), which is incorporated herein by reference for further information regarding this aspect. The energy source  90  may be positioned on the movable foil guiding stage  180 , between the protruding foil guiding elements  190 ,  191  so as to expose the layer of uncured material through the foil  6 . The energy source may be covered by a transparent plate, e.g. a glass plate to improve the guidance of the foil  6 . 
     The combination of using a LED light source comprising a plurality of individually operable LEDs and partially curing at least part of the intersection pattern may be advantageous. Before explaining this further, the LED light source as used in this embodiment will be described in some detail. 
     To shorten the length direction of the stage, an energy source  90  is typically limited in length, for example, for working areas of about 50 cm, only about 6 cm length can be realised with elements (pixels&#39;, each having a LED+microlens) of 2×2 mm2, and still provide a high resolution of about 15 pixels per mm of working-area-width. 
     As used herein, the term ‘solidifiable material’ includes any material which is solidifiable (i.e., which can by polymerized and/or cross-linked) by, for example, a UV light, a laser, ionizing radiation (including but not limited to an electron beam, gamma rays or x-rays), or a combination of any of the foregoing. The term ‘solidifiable material’ shall also be construed to mean a composite material comprising a mixture of both solidifiable and non-solidifiable materials, such as a resin in which fibers and/or fillers are intermixed. 
     Partially curing comprises curing to such a degree that the intersection pattern remains stable while removing the uncured material from the layer outside the intersection pattern. The solidifiable material is not fully cured, but only to such an extent that the material is sufficiently stabilized that it is not removed with the uncured material during the step of removing the uncured material outside the intersection pattern. 
     Fully curing an intersection pattern needs a certain exposure time. Partially curing the intersection pattern means curing the pattern to a lower degree. When the energy source operates at the same power with which the full curing is done, the exposure may be shorter and the speed of the RM and RP processes increases. 
     The transition of a resin cured by UV from liquid to solid passes a so-called gel-point. “At the gel-point, one first observes the visible formation of a gel or insoluble polymer fraction. (The gel point is alternately taken as the point at which the system loses fluidity as measured by the failure of an air bubble to rise in it.) ...The gel corresponds to the formation of an infinite network in which polymer molecules have been crosslinked to each other to form a macroscopic molecule. The gel is in fact considered as one molecule. The nongel portion of the polymer remains soluble in solvents and is referred to as sol. As the polymerization and gelation proceed beyond the gel-point, the amount of gel increases at the expense of the sol as more and more polymer chains in the sol are crosslinked to the gel . . . The reaction mixture is transformed into a polymer of infinite viscosity.” George Odian, “Principles of Polymerization,” 4th ed. 
     More curing forms more bonds, e.g. cross links, to realize a higher E-modulus of the material. The degree of curing desired in partially curing may be defined by curing the solidifiable material to a degree on or near the gel-point degree of the material, where the intersection pattern remains stable while removing the uncured material from the layer outside the intersection pattern. In practice, curing to a degree on or near the gel-point degree may be interpreted as a degree within a range of about 80%-120% of the gel-point degree. 
     Curing at least part of the intersection pattern includes fully curing as well, as opposed to the partially curing being described above, of a raster pattern in the layer of solidifiable material  3 , said raster pattern being dimensioned to hold uncured material. The material may thus be fully cured, but only a raster pattern is cured instead of the complete intersection pattern. 
     The amount of material that has to be exposed for curing a raster pattern is less than for curing the complete intersection pattern. A laser source may e.g. travel a shorter path, which increases the RP and RM speed. 
     A combination of partially curing and curing at least part of an intersection pattern, for example, curing a raster of the intersection pattern to a certain degree only, is also possible. This may further speed up the RP and RM process. 
     To reduce evaporation, it is favorable to remove the resin from the foil in areas where the foil has just been separated (or peeled) from the object  50 . This can be done by adding a remover or squeegee  1001  that moves together with carriage  180 , thus forming a reservoir  3  of material. As can be seen from the drawing, the squeegee is formed as a wedged plate part having a wedge side adjacent the foil. Preferably this squeegee makes an angle alpha of approximately  10  degrees with the foil  6 , that is, the wedge side is angled relative to the plane of foil  6 . This approximate angle was found to have the best scraping capability in one direction and the capability to allow resin to pass in the opposite direction, thus retrieving any resin left on the foil rather than pushing it to the edge of the machine. 
     The wedged plate part retains the resin on a side away from the wedge side. Accordingly, reservoir  3  is enclosed all around: by the squeegee  1001  and by the upward running part of the foil  6 . The squeegee  1001  may include extensions having openings for passing shafts of lower roller  190 , and seals around the shaft passings. In a bidirectional embodiment, a reservoir  3  is formed on each side of the roller  190 . Accordingly, the applicator  2  discloses the wedged plate part  1001  having a wedge side  103 , the wedged plate part  1001  enclosing the resin on a side away from the wedge side  103 , the wedge side adjacent and being angled relative to the plane of foil. 
     There may be a liquid layer  30  providing profiled roller (e.g., a Meyer bar)  190  also on each side of the foil guiding stage. The application roller  190  is arranged to apply the resin layer on the side away from the liquid bath  3 . In this embodiment, the wedged plate part  1001  is arranged opposite profiled application roller  190  to form a resin bath  3 . 
     In an embodiment, the thickness of the liquid layer  30  provided by the coater bars (Meyer bars) is at least equal to the thickness of the next layer, but preferably a bit more. For example, for building with layers of 50 μm, a good value for the liquid layer  30  thickness is around 70-80 μm. Thus when the foil with the liquid layer  30  is moved towards the object, the space of 50 μm between the foil and the previous layer on the object is completely filled with liquid resin. The surplus of resin (20-30 μm) is pressed forward in front of the roller that lifts the foil towards the object, or sideways into spaces that may be present in the object as built so far. 
     The rollers that provide the liquid layer  30  (e.g., Meyer bars) are preferably knurled, or profiled, so that the amount of resin that is transported in the recesses of the Meyer bar from the reservoir side of the Meyer bar to the exposure unit side of the Meyer bar is sufficient to provide the desired (in the example: 70-80 μm) thickness of liquid layer  30 . It is to be noted that the liquid in the recesses only partly remains on the foil behind the Meyer bars, and part stays on the Meyer bar. Therefore the size of the recesses has to be determined experimentally. A typical groove width of the Meyer bar is 0.5 mm and a groove height can be also around 0.5 mm. The outer ridges of the grooves of the bar are about 50 micron distanced from the foil. 
     For the building process to work well, between the exposure and the separation from the foil, the resin should be cured to a certain extent, in order for the newly formed layer to adhere to the previously built layers of the object. For many resins, e.g. DSM Somos® 8120 (an epoxy acrylate), exposed at 365 nm, curing is faster at a higher temperature. In fact, the mentioned resin is found in an embodiment to work well when used above room temperature, preferably approximately between 30 and 40° C. 
     It is noted that the foil side facing the liquid layer  30  should easily separate from (fully or partially) cured resin. Materials that meet this condition include but are not limited to TPX (bulk), silicone (applied as a coating on a foil of different material) and other materials that allow for easy separation. 
     The method and system of the invention have been tested successfully with acrylate and epoxy (and epoxy-acrylate) resins, using exposure with UV light around 365-375 nm. The following commercial types are among these: 
     DSM Somos 8120 (epoxy-acrylate) 
     Envisiontec R5 Profactory (acrylate) 
     To prevent sticking between underside of foil and topside of exposure head; which can occur due to van der Waals forces when these surfaces are very smooth., a very light rubbing with talcum powder or similar may be applied. 
       FIG. 2  provides additional disclosure of a bidirectional embodiment wherein the stage is segmented in sub stages supporting lower and upper rollers  19   a L,  19   a H, energy source  90  and lower and upper rollers  19   b L,  19   b H respectively. In the case of bidirectional use, advantageously separate sub stages for the exposure unit ( 180   c ) and for the equipment on either side of the exposure unit ( 180   a  and  180   b ) are used in contrast to previously disclosed single stages. This has the advantage that the distance between the stage can be optimized for the movement direction, in dependency of the times required for the different subprocesses. 
     As shown here a first process step is carried out in the right-to-left direction  74 . Lower roller  19   a L has the function of providing the liquid layer  30 , upper roller  19   a H has the function of lifting the coated foil up to the level H; 
     On the side of the exposure head  90  opposite rollers  19   a L and  19   a H, upper roller  19   b H has the function of peeling roller, and the lower roller  19   b L has the function of guiding the foil back to the lower level. 
     After a single cycle has been completely performed from right to left (the foil has been completely peeled off from the product, a new cycle can be started immediately from left to right. Now the functions of  19   b H and  19   a H are interchanged, and the functions of  19   b L and  19   a L are interchanged. 
     So upper rollers  19   b H and  19   a H are designed to be suitable for both the lifting and the peeling function. 
     Additionally, lower rollers  19   a L and  19   b L are arranged to be suitable for both providing a liquid layer  30  of correct thickness, and for guiding the foil. A reservoir is present on either sides (X 2   a  and X 2   b ). 
     Note that the squeegees X 4   a  and X 4   b  are preferably both present even in the case of unidirectional use (even in that case the resin must preferably be retained within the space defined by the squeegees). 
       FIG. 3  shows a detailed view on an alternative wedged plate configuration. While in the previous embodiment the wedged plate arranged to retain the liquid on one side of the plate; in another embodiment, the wedge plate can be provided with a second wedge plate to form a slotted orifice  21  arranged to apply the liquid layer  30  with ambient environment exposure only when the liquid layer  30  is formed. In this configuration the exposure of the liquid layer  30  to the ambiance is further reduced relative to the previous embodiment because the liquid volume  3  inside the orifice  21  is unexposed. Plate part  100  is arranged opposite a second wedge shaped plate  101  part to form the orifice  21  for resin supply. For the process to work well, the second wedge shaped plate part  101  defines a smallest distance to the foil in a range of 50-200 micron to apply the resin layer  30  on the side away from the first plate part  100 . The orifice  21  is shaped as a flat rectangular channel of which the bottom and top walls are formed by wedge shaped plate parts  100 ,  101 . 
     The plate part  100  can be slightly distanced from the foil  6 , typically, the wedge side  103  defines a smallest distance to the foil in a range of 10-100 micron. This small gap may result in decreasing foil tension and it may prevent mechanical wear of the applicator foil  6  while still performing a removing function to keep the foil clear from liquid in the area away from the stage  180  and keeping the liquid well conditioned by preventing exposure to the ambient environment so that can be prevented that oxygen diffusion into the liquid layer reaches an unacceptable level. Oxygen can inhibit the radical polymerisation process of resin, which may compromise the curing process. Typically, the resin comprises acrylate components which may evaporate substantially faster than epoxy components, depending on chemical structure. Therefore, longer exposure to the ambient environment may result in evaporation which can change the composition of the resin and increases the viscosity of the resin, which may complicate handling of the resin. 
     Due to the compact nature of the slotted resin supply  21 , having a relatively small width between the opposed plates  100 ,  101 , the supply can be provided on any position between upper and lower foil guiding elements  19   h  and  191  respectively—preferably near upper guiding element  19   h  as close to the contact face  181  as possible. In contrast to the embodiments of  FIG. 1  and  FIG. 2 , transport times of the liquid layer to the curing section can be reduced since the slotted resin supplies  21 ,  22  can be placed very close to the section  181  of the foil  6  that is brought in contact with the object. 
       FIG. 4  shows an advantageous position of the liquid supply  21 , wherein at least one of the plate parts is arranged adjacent an upper foil guiding element. In this respect, the term adjacent is used to indicate that the edges are in near abutment of the foil guiding element  19   h . The gap between the wedged plate&#39;s lower edge  104  and the foil guiding element  19   h , extending in a plane parallel to the wedge plates defines a smallest distance to the foil in a range of 10-200 micron. This distance is small enough to retain the resin on the plate  100  and not damage the foil  6 . The gap between the wedged plate&#39;s upper edge  105  and the foil guiding element  19   h , extending in a plane parallel to the wedge plate  101  defines a smallest distance to the foil in a range of 50-200 micron. The plate thickness may be in the order of 1-3 mm. A typical layer thickness is about 100 micron, preferably in the order of 50-250 micron. 
     This arrangement further reduces the time that the resin layer  30  is exposed to the atmosphere so that evaporation and oxygen diffusion can be reduced and resin quality can be controlled during the whole object building process. 
       FIG. 5  shows a variation of the embodiment of  FIG. 4 . In this embodiment the liquid gap II-II defining the layer thickness is provided between an outer edge  105  of the wedge side  101  and the foil support  19   h  which may enhance the layer thickness stability since it is made substantially independent of the foil tension. In addition, the orifice  21  is has a slight tilt with respect to a normal direction N out of a plane parallel to the foil  6 , so that outflowing resin  3  is directed with a slight velocity component v against the foil movement V relative to the orifice  21 . A realistic foil velocity may be in the order of 50-100 mm/s. The angled resin outflow may prevent instabilities in layer  30  forming such as air inclusions or layer width variations in the resin. A typical angle ranges between 5 and 20 degrees respective to the normal of the foil and can depend on process parameters such as gap width, foil speed, resin viscosity and resin surface tension. 
       FIG. 6  shows an embodiment having two pressurized orifices  21 ,  22  substantially symmetrically arranged adjacent both sides of stage  180 . The resin supply comprises a resin pressurizer P 1 , P 2  to provide a supply or uptake condition depending on a stage movement direction P. Thus, in use, on a side of the stage  180  wherein the foil currently moves towards the contact face  181  (in the figure this shown as the left hand side, with orifice  21  and movement direction P of stage  180  to the left) the resin layer  30  is applied by providing a slight overpressure that is sufficient to allow the layer to be formed. A typical pressure may be in the order of 0.5 bar, typically 3−6×10̂4 Pa with a gradient of about −3×10̂7 Pa/m over the plate thickness. 
     Simultaneously, on the opposite side  22 , where the foil moves away from contact face  181 , a slight underpressure is provided in the orifice such that resin uptake is provided. When the stage movement direction is reversed, in a subsequent cycle, uptake and supply are interchanged by suitably changing the pressure of the liquid in the orifice. This embodiment has the advantage that the liquid is immediately reused in a last first out order while being supplemented with fresh liquid  3  to provide a subsequent layer  30  for solidifying purposes. Thus, liquid degradation is kept minimal. 
       FIG. 7  shows a further embodiment wherein the tilt angle of the orifice is controlled by pivoting the orifice  21 ,  22  on a pivot point that is close to the outer edge  104  of the wedge side defining the smallest gap height relative to the foil  6  (see  FIG. 5 ). In particular the orifices  21 ,  22  are tiltably mounted on the stage to have a tilted orientation depending on the supply or uptake condition. In effect, the orifices on either side of the stage  180  are kept substantially aligned with a slight tilt with respect to a normal direction out of a plane parallel to the foil.  FIG. 7A  illustrates this with the stage  180  moving to right in direction Q: effectively the foil moves in upward direction on the right side, while the orifice  22  is oriented with slight tilt with respect to a normal direction out of a plane parallel to the foil so that outflowing resin is directed with a slight velocity component against the foil movement relative to the orifice as illustrated in detail in  FIG. 5 . Simultaneously, in  FIG. 7A , the left orifice  21  functions as resin uptake by applying a slight under pressure and has a tilt angle which reduces the angle of flow between the liquid layer on the foil and the flow direction in the orifice. It is noted that the angles of left and right orifices in  FIG. 7A  can be favorably mechanically combined but need not be identical. 
       FIG. 7B  shows the reverse direction with the stage  180  moving in a direction P from right to left: here the angles and pressures are reversed dependent on the movement direction respective to  FIG. 7A . The movement direction of the applicator system may be described as, for instance, relative to the tangible object and/or along the foil. 
     The detailed drawings, specific examples and particular formulations given serve the purpose of illustration only. While the specific embodiments of the apparatus  12  described and shown herein concern building the model  5  upside down, the teachings of the present invention may be applied to apparatuses that build models right side up. The aspects of the present invention can also be applied in apparatuses for conventional RP and RM techniques like Selective Laser Sintering (SLS) and Stereo Lithography (SL). 
     The orifices  21 ,  22  may be additionally provided with heating or ultrasound excitation to result in a lower viscosity locally in the slot die, which may improve the liquid supply resin and control over the layer thickness while reducing the over- and underpressures to be provided. 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. Furthermore, the object may have any suitable size and shape. Furthermore, the devices may be physically distributed over a number of apparatuses, while functionally operating as a single device. Also, devices functionally forming separate devices may be integrated in a single physical device. However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. While certain embodiments detail certain optional features as further aspects of the invention, the description is meant to encompass and specifically disclose all combinations of these features unless specifically indicated otherwise or physically impossible.