The application is a divisional application of an invention patent application named as a 'rapid prototyping device', with an application date of 2004, 5/2 and an application number of 200810171073.1, and the applicant is obujit geometry ltd.
Disclosure of Invention
One aspect of an embodiment of the present invention relates to an inkjet-type Rapid Prototyping Apparatus (RPA) having improved operating characteristics.
One aspect of an embodiment of the present invention is directed to an RPA that includes a carriage with a printhead assembly, wherein each printhead is removably mounted in the printhead assembly and is independently replaceable relative to other printheads in the assembly.
According to one embodiment of the invention, the carriage and the print head have a structure that can be automatically aligned by an alignment structure included in the print head assembly and the print head when the print head is replaced. According to one embodiment of the invention, the printhead is coupled to a memory having stored profile data defining operational characteristics of the printhead, and the controller in the RPA controls the printhead via the profile data. In some embodiments of the invention, the memory is included in the printhead.
One aspect of an embodiment of the present invention relates to an RPA having an improved lamp that emits radiation to cure photopolymer build material.
The photopolymer build material at the edges of the RPA shaped build layer is often difficult to polymerize and still in a soft and tacky state, resulting in poor edge definition. A radiation lamp according to an embodiment of the invention provides relatively much radiation energy, so that the radiation is incident into the building layers at relatively large angles to the plane normal. Large incident angle radiation may polymerize the material of the build-up layer edges more efficiently than small incident angles. One aspect of an embodiment of the present invention is directed to an RPA having an improved cleaning sheet for removing polymer debris collected on the surface of the RPA.
There is thus provided in accordance with an embodiment of the invention apparatus for fabricating an object by successively forming thin layers of build material layer by layer in accordance with data defining the object, the apparatus including:
a plurality of print heads, each print head having a surface forming a plurality of output orifices, and the print heads controllably causing each output orifice to dispense build material independently of the other output orifices;
a carriage on which the print head is mounted;
a support surface; and
a controller adapted to control the carriage to reciprocate across the support surface and, as the carriage moves, to control the printheads to dispense build material through their respective output ports in accordance with the data to form a first layer on the support surface before continuing to form further layers; wherein
Each printhead is removably mounted on the carriage and is independently replaceable relative to the other printheads.
Optionally, each printhead includes at least one alignment structure that mates with an alignment structure included in the carriage, and when the printhead is mounted on the carriage, the at least one alignment structure on the printhead contacts a corresponding carriage alignment structure to accurately position the printhead in the carriage. Alternatively, the orifices in each print head are linearly arranged at equal intervals, with the first orifice being at a first end of the arrangement. Optionally, at least one alignment structure included in each printhead and its corresponding carriage alignment structure are used to position the printheads, with their respective columns of orifices being parallel. Alternatively, the rows of outlets are arranged in a direction perpendicular to the rows of outlets. Optionally, at least one alignment structure included in each print head and its corresponding carriage alignment structure are used to position the print heads so that the first orifices in each print head are accurately positioned relative to the first orifices in the other print head. Alternatively, projections on the support surface of parallel lines through the centres of the outlets are substantially equally spaced from each other, wherein the parallel lines through the centres of the outlets are perpendicular to the columns of outlets. Alternatively, the distance of the first output port from the same plane perpendicular to the column of output ports is given by the equation y (n) = C + n (d)yN), where y is the distance from the plane, C is a constant, N is the number of printheads, dyIs the distance between adjacent output ports on the same printing head, N is different integer for each printing head, and N is more than or equal to 0 and less than or equal to (N-1). Alternatively, the controller controls the carriage to move in a direction perpendicular to the columns of orifices as build material is dispensed from the orifices in the printhead during formation of the layer. Alternatively, the distance y (N) is such that the print head deposits droplets at specific locations of a given line on a build-up layer parallel to the columns of orifices, the droplets being deposited at such specific locations that the droplets do not substantially abut any droplets of material previously deposited on the given line by the other N print heads. Alternatively, on a given line, each droplet deposited between two nearest previously deposited droplets is equidistant from the two previously deposited droplets.
In some embodiments of the invention, the at least one alignment structure in each printhead includes at least one alignment pin that protrudes from the printhead and has an end that is precisely positioned relative to the row of orifices.
Alternatively, the respective carriage alignment structure is a surface, the alignment pin and the alignment surface being positioned such that when the printhead is mounted on the carriage, the tip of the pin abuts against the alignment surface. Alternatively or additionally, the at least one alignment pin comprises three alignment pins. Optionally, wherein a line between the tips of two of the alignment pins is exactly parallel to the row of output orifices. Alternatively, the tip of the third alignment pin is displaced parallel to the row of outlets and away from the position of all outlets by an accurate distance from the first outlet.
In some embodiments of the invention, each print head is connected to a memory. Optionally, the memory is included in the printhead. Additionally or alternatively, the memory includes profile data specifying operating characteristics specific to the printhead, and the controller uses the data to control the printhead. Alternatively, the profile data is automatically made accessible to the controller when the print head is mounted on the carriage. Additionally or alternatively, each outlet is associated with its own actuator which can be controlled to control dispensing of build material from the outlet, wherein the profile data comprises data which can be used to control the actuator.
In some embodiments of the invention, the apparatus includes a temperature monitor that generates a signal responsive to a temperature of the printhead. Optionally the memory includes calibration data (calibration) which relates the characteristics of the signal to the temperature of the print head.
In some embodiments of the invention, the printhead includes a heat source that is controllable to maintain the printhead at a desired temperature, and the memory includes data that is usable to control the heat source.
In some embodiments of the invention, the memory includes data that can be used to determine the position of the orifices relative to the orifices of other print heads in the carriage.
In some embodiments of the invention, the build material comprises a photopolymer. Optionally, the apparatus includes a lamp that emits radiation to polymerize the photopolymer. Optionally, the lamp emits a substantial portion of the radiation so as to be incident on the build-up layer at a substantially non-normal angle (non-normals) with respect to its plane.
There is also provided, in accordance with an embodiment of the present invention, apparatus for manufacturing an object by successively forming thin material layers layer by layer in accordance with data defining the object, the apparatus including:
at least one print head having a surface defining at least one orifice, the print head controllably causing the orifice to dispense a photopolymer material in a liquid state;
a lamp that controllably emits radiation that polymerizes the photopolymer; and
a controller adapted to control the print head to dispense the photopolymer and continuously form a layer, control the lamp to irradiate and polymerize the dispensed photopolymer; wherein
A substantial part of the radiation emitted by the lamp is directed such that it is incident on the layer at an angle substantially not at right angles.
Optionally, the lamp comprises a radiation source and a reflector for reflecting light emitted by the radiation source such that the light is incident on the layer at a substantially non-right angle. Additionally or alternatively, the magnitude of the angle is greater than 20 ° relative to a normal to the layer. In some embodiments of the invention, the magnitude of the angle is greater than 30 ° relative to the normal. In some embodiments of the invention, the magnitude of the angle is equal to about 45 ° relative to the normal.
In some embodiments of the invention, the reflector comprises at least one parabolic reflector and at least part of the light source is located at a focal point of the reflector. Alternatively, the reflector is a polygonal reflector approximating a parabolic reflector. Alternatively, the angle of incidence of the portion of light is positive and the angle of incidence of the portion of light is negative.
In some embodiments of the invention, the radiation source is a discharge bulb. Alternatively, the bulb is a mercury or xenon discharge bulb.
In some embodiments of the invention, the lamp includes a light emitting diode that controllably emits radiation that polymerizes the photopolymer.
There is also provided, in accordance with an embodiment of the present invention, apparatus for manufacturing an object by successively forming thin material layers layer by layer in accordance with data defining the object, the apparatus including:
at least one printhead that controllably dispenses a photopolymer material in a liquid state;
a lamp that controllably emits radiation that polymerizes the photopolymer; and
a controller adapted to control the print head to dispense the photopolymer and continuously form a layer, control the lamp to irradiate and polymerize the dispensed photopolymer; wherein
The lamp includes an array of light emitting diodes that controllably emit radiation that polymerizes the photopolymer.
Optionally, the device includes a microlens that transforms light emitted by the light emitting diode into a cone-shaped beam having a relatively large cone angle. Optionally the taper angle is greater than about 80. Optionally the taper angle is greater than about 100.
In some embodiments of the invention, the array of light emitting diodes is arranged relatively far from said layer, and each light emitting diode in the array has a radiation conductor for conveying radiation from the light emitting diode to a position relatively close to said layer, where said radiation irradiates an area of said layer.
In some embodiments of the present invention, the controller controls the intensity of the ultraviolet light emitted by the light emitting diodes in the array and makes the intensity of the ultraviolet light emitted by the light emitting diodes independent of the intensity of the ultraviolet light emitted by other light emitting diodes in the array.
In some embodiments of the invention, the controller turns the light emitting diodes in the array on and off to reduce radiation emitted by the array that is not effective to polymerize the photopolymer in the layer.
In some embodiments of the invention, the device comprises a wiper blade, wherein the controller is adapted to move the at least one print head over the wiper blade to clean a surface of the print head where the outlet opening is formed.
There is also provided, in accordance with an embodiment of the present invention, apparatus for manufacturing an object by successively forming thin material layers layer by layer in accordance with data defining the object, the apparatus including:
at least one print head having a surface defining at least one orifice, the print head controllably dispensing a photopolymer material in a liquid state through the orifice;
scraping a blade; and
a controller adapted to control the printhead to dispense the photopolymer and form a layer continuously and to move the printhead over the wiper blade to clean the surface of the printhead where the output opening is formed.
Additionally or alternatively, the blade includes at least one cleaning blade, an edge of which scrapes excess build material from a surface of the printhead as the controller controls the surface to move over the blade.
Alternatively, the edge of at least one cleaning sheet contacts the surface of the printhead as the surface moves over the blade.
Alternatively, the cleaning sheet is formed of an elastic material so that the edge of the contact surface resiliently contacts the surface. Optionally, the edge is scalloped and each printhead corresponding to the at least one printhead has a different scalloping.
In some embodiments of the invention, the at least one printhead comprises a plurality of printheads.
Optionally, the cleaning sheet is formed with at least one slot dividing the cleaning sheet into a plurality of teeth, each tooth having an edge contacting the outlet orifice surface of a different one of the plurality of printheads for scraping excess build material on the surface.
Additionally or alternatively, the at least one cleaning sheet comprises at least two cleaning sheets. Optionally, a cleaning sheet of the at least two cleaning sheets has an edge that does not contact the exit orifice surface of the printhead, but moves along and close to the surface as the controller controls the surface to move over the wiper blade. Optionally, as the surface moves over the blade, an area of the surface moves past the edge that is not in contact with the surface before contacting the edge that is in contact with the surface.
In some embodiments of the invention, the apparatus comprises an obstacle detection system for detecting defects in the layer that protrude from the surface of the layer. Optionally, the obstacle detection system comprises: a laser emitting a laser beam, wherein the laser beam contacts or is positioned proximate to a surface of the layer along its length; and a detector receiving the laser beam; wherein light received by the detector from the laser is at least partially blocked by defects protruding from said surface.
One aspect of an embodiment of the present invention is directed to a novel build material for inkjet RPA that provides improved structural strength of objects made using the material as compared to existing inkjet build materials.
Detailed Description
Fig. 1 schematically illustrates an inkjet RPA20 for fabricating an object 22 on a build platform 24, in accordance with an embodiment of the present invention. In accordance with an embodiment of the present invention, the RPA20 includes a controller 26 and a carriage 28, the carriage 28 including a printhead assembly 50, leveling rollers 27, and optionally two radiation sources 120 for polymerizing photopolymer used by the RPA for fabricating the object. Alternatively, the build platform 24 is mounted on a table 25 and is controllably lowered and raised relative to the table.
During manufacture of the object 22, the controller 26 of the RPA20 periodically moves the carriage 28 to a service area 220 on the table 25, where it includes a waste pit 222 and at least one cleaning sheet. Illustratively, the service area 220 includes two cleaning sheets, a first cleaning sheet 225 and a second cleaning sheet 227. At service area 220, controller 26 executes a cleaning routine to remove waste build material "debris" that has accumulated on the printheads of printhead assembly 50. The service area 220 and the cleaning procedure will be described below.
For simplicity, it is assumed that the photopolymer used by RPA20 is UV curable and that the radiation source 120 is a UV lamp. The RPA20 is shown schematically in the figure, with only the features and components of the RPA relevant to the description being shown in fig. 1. Coordinate system 21 is used to represent the arrangement and location of features and components of RPA 20.
To fabricate object 22, controller 26 controls carriage 28 to reciprocate, optionally parallel to the x-axis, over build platform 24 in directions indicated by block double arrow 31. After reversing one or more directions along the x-axis, the controller advances the carriage 28 parallel to the y-axis by an incremental distance, optionally in the direction indicated by block arrow 32. As carriage 28 moves over build platform 24, controller 26 controls printheads to dispense build material (desired building material BM and/or support material SM) in accordance with build data defining object 22 to form build layer 34 for fabrication of the object.
After the build material has just been printed to form an area of a given build layer 34, the leveling rollers 27 contact the area and flatten and level the build layer to a desired thickness by scraping off the upper portion of the printed material. To achieve the scraping action, the roller 27 is rotated in the direction of rotation thereof, which occurs when rolling on the construction material in the direction of advance of the carriage 28, but at a rotational speed greater than the corresponding linear speed of advance of the carriage. Suitable wipers and waste "concentrators" (not shown) are mounted in the carriage 28 for cleaning the waste build material on the roller 27.
Build layers 34 are stacked in a stacking direction perpendicular to build platform 24, parallel to the z-axis. After forming a given build layer 34, build platform 24 is optionally lowered a distance equal to the thickness of another build layer to be formed on the given build layer. The thickness of the build-up layer 34 is shown enlarged in fig. 1 for ease of illustration.
By way of example, the object 22 is a replica of the vase 36 shown in the inset 38, and a portion of it that has been made is shown on the build platform 24. The schematically illustrated vase 36 is formed by a "data cross section" layer 40, the layer 40 being defined by construction data of the vase. Block arrows 42 schematically represent the input of construction data into controller 26 and/or the generation of construction data in the controller from the input data and arranged to control the formation of structural layer 34.
Fig. 2A is a perspective view, shown from the bottom, schematically showing the carriage 28. In the perspective view of fig. 2A, the x-axis and z-axis of the coordinate system 21 are in opposite directions to those shown in fig. 1.
The printhead assembly 50 is optionally formed with a plurality of slots 51 each adapted to receive a printhead 52, the insertion and removal of a printhead into and from a slot being independent of the insertion and removal of other printheads into and from the slot. The slot 51 is more clearly shown in fig. 2B and 2C, which show the carriage with and without the printhead 52 inserted into the slot, respectively, from the bottom of the carriage 28. Figure 2D schematically illustrates a single printhead 52 according to one embodiment of the invention, which more clearly shows the details of the printhead in comparison to figures 2A-2C.
By way of example, the assembly 50 includes eight sockets 51. Alternatively, different printheads 52 or different groups of printheads 52 are used to print different build materials. For example, some printheads 52 may print BMs or certain types of BMs only, while other printheads 52 may print SMs or certain types of SMs only. The print head 52 may be designed and constructed as a BM or SM specific print head by any method. For example, the number of printheads 52 used to print BM may be different than the number of printheads 52 used to print SM. Additionally or alternatively, adjacent printheads 52 may be used to print different materials of construction, one for printing BM and the other for printing SM.
For example, in the print head assembly 50, it is assumed that four print head 52 groups in the insertion slot 51 indicated by the bracket 54 are used for printing BM and four print head 52 groups in the insertion slot 51 indicated by the bracket 53 are used for printing SM. For ease of authorization, slot 51, indicated by bracket 53, may also be denoted as slot 53, and slot 51, indicated by bracket 54, may also be denoted as slot 54.
According to one embodiment of the present invention, printhead assembly 50 and printhead 52 are constructed such that each printhead can be replaced relatively easily, such as due to damage or replacement required for maintenance. Alternatively, all of the printheads 52 are approximately the same.
Each printhead 52 includes a housing 56, best shown in fig. 2D, on which is formed a plurality of co-linear, optionally equally spaced, output ports 58 through which the build material is dispensed. For simplicity, dashed lines 59 are shown in FIG. 2D, as are some of the print heads 52 in FIGS. 2A and 2B, along which collinear output orifices 58 are aligned. A method and apparatus for supplying build material to printhead 52 in accordance with an embodiment of the present invention will be described with reference to fig. 2E and 2F.
Circuit board 55 includes circuitry 57 that controls piezoelectric actuators (not shown) located in housing 56 and actuated to dispense build material through output port 58 and other components of printhead 52. Connector 47 connects circuit board 55 to circuitry in printhead assembly 28, which is connected to controller 26 (see FIG. 1). According to one embodiment of the invention, the circuit board 55 includes a memory 49 in which data, i.e., "profile data" (profile), representing the operating characteristics of the printhead 52 is stored. Alternatively, the profile data stored in the memory 49 will be described hereinafter.
Printhead 52 and printhead assembly 50 have corresponding alignment features. The alignment features cooperate to automatically align the print head 52 when it is inserted into either slot 51 so that the lines 59 of its output 58 are parallel to the same line, optionally the y-axis. The lines 59 of the output openings 58 in all the print heads 52 mounted on the print head assembly 50 are therefore parallel to each other and have a relatively high accuracy. Alternatively, the lines 59 of the orifices 58 in the printhead 52 are equally spaced from one another.
Corresponding alignment features cooperate to align printheads 52 so that, optionally, the y-coordinates of the output orifices on different printheads for printing the same build material are different. For example, according to one embodiment of the invention, the y-coordinates of the orifices 58 on different printheads 52 inserted into the slots 53 (i.e., the slots 51 indicated by bracket 53) are different. Similarly, the y-coordinate of the orifices 58 in the print head 52 inserted into the slot 54 (i.e., the slot 51 indicated by bracket 54) may be the same as the y-coordinate of the orifices in the print head 52 inserted into the slot 53, with the y-coordinates of the orifices 58 in two different print heads 52 in the slot 54 being different. Alternatively, the structure of the print head in the slot 54 is the same as that of the print head in the slot 53, and therefore it will be understood that the following description of the print head in the slot 54 applies to the print head in the slot 53.
Assuming that the first orifices 58 in each print head 52 are the orifices closest to the xz plane (see FIG. 2A), the distance between adjacent orifices on the same print head is "dy". Alternatively, the value of the y-coordinate of the first outlet on each print head 52 located in the slot 54 passes belowThe expression is given in the formula,
y=C+n(dy/N)=C+nΔdy
where N represents the number of slots 54, Δ dy＝dyN, N is a different integer for each slot, and the condition 0. ltoreq. n.ltoreq.N-1 is satisfied.
Optionally, the alignment features of each printhead 52 include two x-alignment pins 60 and one y-alignment pin 62 (best shown in fig. 2B and 2D). Alternatively, each x-pin has a rounded end with a tip 61 and each y-pin 62 has a rounded end with a tip 63. The tip 61 of each x-pin 60 is offset along the x-axis by the same precise distance ax with respect to the x-coordinate of line 59. Alternatively, Δ x is approximately the same for all printheads 52. The tip 63 of the y-pin 62 is offset along the y-axis by a precise distance deltay relative to the y-coordinate of the first delivery orifice on the print head 52. Alternatively, Δ y is approximately the same for all printheads 52.
Each slot 54 includes two x-alignment buttons 64 and one y-alignment button 66 that correspond to the x-alignment pins 60 and the y-alignment pins 62, respectively, on each printhead 52. The X-align button 64 is not shown in fig. 2A, but is shown schematically in fig. 2B and more clearly in fig. 2C. Each x-alignment button 64 has the same precision control length and ends in a flat "alignment surface" 65. Each socket 54 comprises at least one resilient element 68, such as a leaf spring or a helical spring. When the printhead 52 is inserted into the slot 54, the at least one resilient element 56 presses against the printhead such that the tip 61 of the x-alignment pin 60 contacts the x-alignment surface 65 of the alignment button 64 in the slot. The configuration of the X alignment pins 60 and buttons 64 is such that the lines 59 of the outlets 58 in the printhead 52 inserted into the slot 51 are relatively precisely parallel.
Each y-button 66 in the slot 54 has a different length, optionally given by equation 1, with the ends of the buttons lying in flat alignment surfaces 67. The elastic member 69 is included in each of the slots 54 for elastically pressing the punch inserted into the slotThe print head 52 such that the y-alignment tip 63 of the print head presses against the y-alignment surface 67 of the alignment button in the slot. The configuration of the y-alignment pin 62 and the button 66 is such that the first ejection port 58 of each printhead 52 inserted into a different slot 54 has a different y-coordinate, which can alternatively be derived from equation 1. The orifices 58 of each printhead 52 in the slot 54 are thus offset (d) relative to the orifices of the other printheads in the slot 54y/N)＝ΔdyDifferent multiples of (a). The projections of the orifices 58 on all the print heads 52 in the slot 54 on a line parallel to the y-axis are equally spaced along that line by a distance equal to deltady. For example, for the configuration of slot 54 and y-alignment button 66 shown in FIG. 1, the displacement of printhead 54 along the y-axis decreases linearly as the x-coordinate of the printhead relative to the x-coordinate of the fixed feature of printhead assembly 50 increases.
Fig. 2E is a perspective view schematically showing the upper right side of the printhead assembly 50, in which the printhead 52 mounted in the assembly is connected to hoppers 401, 402, 403 and 404 included in the printhead assembly for storing build material supplied to the printhead. The printhead and the hopper are visible through the printhead assembly indicated by the dashed line. Fig. 2F schematically shows a cross-section of the printhead 52 shown in fig. 2E.
A printhead 52 located in a slot 54 (see fig. 2B and 2C) and optionally used to print construction material (BM) is indicated by the bracket designation "BM" and acts as a BM printhead. Each BM print head 52 is connected to hoppers 401 and 403 which store BMs and supply BMs to the print heads. A feed conduit 409 connects the stocker 401 to a "feed" pump (not shown) that is optionally used to pump BM into the stocker 401 from a BM supply box located a distance from the printhead assembly 50. Alternatively, the back-flow relief valve 411 connects the hopper 403 to a vacuum pump (not shown) to maintain a certain vacuum in the hoppers 401 and 402.
Similarly, "SM" indicated in brackets indicates a print head 52 positioned in slot 53 and optionally used to print Support Material (SM), which acts as an SM print head. Each SM print head 52 is connected to hoppers 402 and 404 that store SMs and supply SMs to the SM print heads. A feed conduit 410 connects the hopper 402 to a pump that pumps SM material out of the SM feed box. A back-flow relief valve 412 connects the hopper 404 to a vacuum pump (not shown).
Alternatively, the operation of the stockers 401 and 403 supplying BM to the BM print head 52 is the same as the operation of the stockers 402 and 404 supplying SM to the SM print head 52, and the operation procedure of the stockers will be described below with reference to the stockers 401 and 403 and the BM print head 52.
Referring to fig. 2F, the housing 56 of the BM print head 52 has a manifold 420 that connects the reservoirs 401 and 403 and allows BM pumped by the feed pump into the reservoir 401 to flow freely into the reservoir 403. A sensor (not shown) generates a signal responsive to the level of BM in hoppers 401 and 403. A feed pump control circuit (not shown) controls the operation of the feed pump to maintain the desired level of BM in the reservoirs 401 and 403. Fig. 2F schematically shows the hoppers 401, 403 and the manifold 420 filled with BM indicated by the shading 418.
Alternatively, the small feed conduits 422 have different diameter portions, as is known in the art, connecting each output port 58 to the manifold 420 and to a piezoelectric actuator (not shown). The controller 26 (see fig. 1) controls the piezoelectric actuator connected to each feed conduit 420 to extract the BM418 from the manifold 420 and expel a desired amount of BM from the corresponding output port 58 of the feed conduit.
To prevent inadvertent dripping of BM from the port 58, a vacuum pump is optionally connected to the hopper 403 and maintained at a vacuum level in the hoppers 401 and 403. The backflow relief valve 411 prevents BM in the hopper 403 from being accidentally sucked into the vacuum pump. The back-flow relief valve 411 may function by various methods and devices known in the art. Optionally, the backflow relief valve includes a float that rises to close off the port through which the vacuum pump draws air when the BM enters the valve and rises above a predetermined level.
The inventors have found that a pressure of about 2mm to 9mm water column below atmospheric in the holding tanks 401 and 403 is advantageous in preventing BM from accidentally flowing out of the outlet 58. The monitoring of the vacuum level in the hoppers 401 and 403 and the control of the vacuum pump that maintains the pressure can be accomplished by any known method and device. In some embodiments of the invention, the vacuum pump is continuously operated to draw air out of the hopper 403 and slowly flow the air into the hopper 401 and/or 403 through the at least one outlet. Suitable control circuitry controls the vacuum pump to balance the rate at which air is drawn from the reservoir 403 by the pump and the rate at which air flows into the reservoirs 401 and/or 403 through the at least one outlet, thereby maintaining the required vacuum level. In some embodiments of the invention, the control circuit controls the vacuum pump to operate only when the pressure in the reservoir 403 exceeds a predetermined pressure.
As carriage 28 moves along the x-axis to dispense build material to print build layer 34 (see fig. 1), droplets of build material are dispensed from each output 58 of printhead 52 onto build platform 24, or previously formed layer 34, along a line parallel to the x-axis, hereinafter referred to as a "deposition line". The deposition lines of orifices 58 on the same printhead 52 (i.e., orifices on printhead 52 in slot 54) that distribute BM are spaced the same distance Δ d from each othery(equation 1). Spatial resolution along the y-axis, hereinafter referred to as "primary" y-resolution PRyEqual to Δ dyAlternatively, the build material may deposit sufficient material in the form of droplets such that the material deposited along adjacent deposition lines mixes to form a smooth build layer of approximately uniform thickness.
The deposition lines of some of the output ports 58 of the printhead 52 in the slot 54 are schematically represented by lines 70 in fig. 3A. Although the deposition lines 70 are lines along the structured surface formed by RPA20, they are projected onto the bottom of the printhead assembly 50 for ease of illustration and to show their relationship to the orifices 58 that determine their location. Fig. 3B is a partial enlarged view of fig. 3A, and the deposited lines 70 and their relative positions can be more easily seen compared to fig. 3A.
Conveniently by indexing PkRespectively, the print heads 52 in the slots 54 are shown, where 1. ltoreq. k.ltoreq.4, with index DL1、DL2…DLMRepresenting deposition line 70, as shown in FIG. 3B (M equals printhead P)kThe number of medium orifices 58 multiplied by the number of printheads (optionally four)). All fourth deposition lines 70 are identical to the same printhead P in slot 541、P2、P3Or P4The upper output port 58 corresponds. E.g. DL1、DL5、DL9… and printhead P1And correspondingly.
Because of the distance between adjacent lines 59 of orifices 58 on print assembly 50, a build layer is dispensed by different printheads at different times at the same given x-coordinate on the build layer as carriage 28 moves, for example, in the positive x-axis direction. Suppose the speed at which the carriage 28 moves in the x direction is VSThe distance d between the rows 59 of orifices in adjacent print heads 52xThen the time delay "t" between two dispensing of build material by adjacent printheads 52 at the same given x-coordinate build layer locationd"is equal to dx/Vs。
For example, if the print head P1At time t1Along the deposition line DL1、DL5、DL9… deposit build material at a given x-coordinate, the printhead P2At time t2I.e. tdAfter a second, along the deposition line DL2、DL6、DL10… deposit build material at the same given x coordinate. Print head P1、P2、P3And P4Relative time t at which the build material is dispensed from output port 58 at the same given x-coordinate1、t2、t3And t4Represented by the length of each deposition line extending to the right in fig. 3A and 3B. In FIG. 3B, the end of line 70 is deposited and the relative time t1、t2、t3And t4Represented by the lines labeled relative time.
Droplets of liquid build material deposited adjacent to each other have an affinity for each other, with a tendency to bind. This tendency to bond can be in a build layer, such as that shown in FIG. 1The build-up layer 34 formed by RPA20 creates defects. In particular, this tendency to coalesce may cause the build-up layer to striate parallel to the deposition line 70 (RPA 20 deposits build-up material along deposition line 70). When streaks occur, the streaks tend to occur in the vicinity of the deposition line 70, and the print head P4Along the deposition line (i.e., DL)4、DL8、DL12… deposit the build material.
Fig. 4A illustrates a method by which striations may be formed in a build-up layer. This figure shows time-sequential cross-sectional views 81, 82, 83 and 84 of the build layer along a plane parallel to the xz-plane at a given x-coordinate. The time-sequential cross-sectional views show the passage of droplets past the print head P1-P4Along deposition line 70 to form a build-up layer. Suppose that time profiles 81, 82, 83 and 84 are each at a continuous time t1、t2、t3And t4Intercepted, wherein the time t is continuous1、t2、t3And t4Time delay t of transition betweend. The deposition line of the droplet deposition is indicated by the ring-shaped indication DLm. Print head P1－P4The deposited droplets of build material are represented by representations Dr1-Dr4, respectively.
At time t1In the time section 81, the print head P1Along the deposition line DL at a given x-coordinate1、DL5… deposit droplet Dr 1. At time t2In time section 82, print head P2 is along deposition line DL at the given x coordinate2、DL6… deposit droplet Dr2, each droplet Dr2 being adjacent to previously deposited droplet Dr1 and tending to coalesce with droplet Dr 1. At time t3In time section 83, print head P3 is along deposition line DL3、DL8… and adjacent to droplet Dr3, droplet Dr2 is deposited, droplet Dr3 merging with previously deposited droplets Dr1 and Dr2 as shown in the timing diagram.
It can be seen that the material in the bound droplet does not readily flow to the deposition line DL shown in time section 834、DL8、DL12… …, bonding empty regions 86 between the droplets. At the time oft4In the time section 84, when the print head P4As droplet Dr4 is deposited in void region 86, the material in each droplet is pulled to both sides of the droplet away from each group of droplets previously joined. The pulled material will create a small void 88 near the deposition line DL4 as shown in the time cross section 84. Voids 88 may create streaks in the build layer formed by RPA 20.
To avoid streaking, the structure of the y-align button 66 in the slot 54, according to one embodiment of the invention, is such that after the first printhead deposits material at the x-coordinate, each droplet dispensed at a given x-coordinate is deposited equidistantly between previously deposited droplets. The inventors have found that when droplets are deposited using an "isometric" method to form a build layer, striations in the build layer that occur when droplets are deposited as shown in FIG. 4A are mitigated or nearly eliminated. It is noted that the deposition of droplets of build material can be accurately and absolutely equidistant deposition only if the number of deposition lines for the build layer is equal to a power of two (apowerofwo). Otherwise only approximately equidistant deposition is possible.
FIG. 4B schematically illustrates a method of depositing build material "equidistantly" to form a build-up layer of an object, according to an embodiment of the invention. This figure is similar to figure 4A and shows cross-sectional views 91, 92, 93 and 94 in chronological order. The cross-sectional view is taken along a plane parallel to the xz-plane at a given x-coordinate and shows sequential at time t according to an equidistant deposition method1、t2、t3And t4Droplets of build material are deposited along a deposition line.
At time t1In time section 91, along deposition line DL1、DL5、DL9… deposit droplet Dr 1. At time t2In time section 92, along deposition line DL2、DL6… deposition droplet Dr2In which the droplet Dr2Not in contact with droplet Dr1Adjacent but equally spaced along the deposition line DL3、DL5… between deposited droplets. At time t3In the time section 93, optionallyAlong the deposition line DL2、DL4… deposition droplet Dr3. From time t1And t2To t3Droplet Dr1And Dr2The material in (a) will diffuse. Diffusion of droplets Dr1 and Dr2 will locally cover along deposition line DL4、DL8、DL12And region 96. In the time section 94, when at time t4Along the deposition line DL4、DL8、DL12Deposition droplet Dr4In this case, since the deposition line is partially covered, a void is not formed along the deposition line, and thus a stripe is not formed.
Figure 4C is a bottom view schematically illustrating a printhead assembly 50 that performs the isometric deposition method shown in figure 4B. The length of y-align button 66 in slot 54 (and optionally slot 53) does not decrease linearly as it increases relative to the x-coordinate of the fixed feature of printhead assembly 50. Thus, the print head P1、P2、P3、P4Will not follow the deposition line DL shown in fig. 3B and 4A1、DL2、DL3And DL4And depositing the material. In contrast, the print head P1、P2、P3、P4Along the deposition line DL shown in FIG. 4B1、DL2、DL3And DL4And depositing the material.
However, the alignment features of the printhead assembly 50 and the printhead 52 are such that the printhead 52 in the printhead assembly does not need to be adjusted or calibrated for alignment when replaced, and a given printhead typically has unique operating characteristics. In order to properly operate a given printhead 52, it is advantageous for controller 26 to control each printhead according to its unique operating characteristics. In accordance with one embodiment of the present invention, each printhead 52 is represented by profile data that represents operating parameters specific to the printhead. Optionally, the profile data is stored in a memory 49, optionally included in a circuit board 55 of the printhead. When the print head 52 is mounted in the slot 51, a data line between the controller 26 and the print head 52 is implemented by a connector 47 included in the circuit board, wherein the controller receives profile data of the print head through the data line.
Profile data representing printhead 52 includes, for example, operational data specifying the operation of each piezoelectric actuator in the printhead that controls the deposition of build material through output 58. Generally, the operational data for the actuators specifies that the characteristics of the actuators are a function of the voltage applied to the actuators and the characteristics and temperature of the build material dispensed by the printhead 52. This data is typically used to determine the lift time, fall time, and voltage pulse amplitude that controller 26 applies to the actuator to control the weight of the droplets of build material and/or the jetting velocity dispensed by output port 58, where the actuator is in communication with output port 58. Optionally, the profile data includes operating characteristics of a heater (optionally included in printhead 52) that heater controller 26 controls to maintain a desired temperature of build material in the printhead hopper.
The profile data may also include dimensional data of the print head. For example, in some embodiments of the present invention, the length of the x-alignment pins 60 (see fig. 2D) of a printhead 52 relative to another printhead can be varied widely, where the length can be controlled so that the length of the x-pins Δ x on the same printhead 52 remains the same with high accuracy. Thus, the estimated length of x-pins 60 for each printhead 52 may be presumptively unknown for the accuracy of the required sharpness of RPA 20. For such embodiments, the profile data for the printhead includes data defining its x-alignment pin length.
Whereas in the embodiments described above the memory 49 optionally located on the print head circuit board 55 (see figure 2D) stores the print head profile data, in some embodiments of the invention the print head 52 profile data is stored in a memory device separate from the print head. Such as an optional floppy disk, CD, or portable flash memory, which stores profile data for printhead 52. When the printheads are inserted into the slots 51 of the printhead assembly 50 (see fig. 2A-2C), data is downloaded from the memory device to the controller 26 by various methods and means known in the art.
In the above embodiment, the print head 52 is inserted into the single slot 51 of the print head assembly 50. In some embodiments of the present invention, the printhead assembly does not have a slot. Fig. 5 is a bottom view schematically illustrating printhead assembly 100, where printhead assembly 100 does not include a single slot for mounting each printhead in the assembly, but rather has a single mounting cavity 102 for receiving printheads 104.
Optionally, the printheads 104 are identical and each has two x alignment pins 60 and one y alignment pin 62. In addition, each printhead 104 has two x-alignment buttons 106. The mounting cavity 102 includes y-alignment buttons 108 and corresponding resilient members 110 that correspond to the y-alignment pins 62 in the printheads 104 (e.g., eight printheads 104). Alternatively, the length of the y-alignment button increases linearly as its x-coordinate increases relative to the x-coordinate of the fixed feature of printhead assembly 100. The mounting cavity 102 also includes two x-alignment buttons 112 and corresponding resilient members 114.
When eight print heads 104 are inserted into the mounting cavity 102, the elastic member 114 presses the print heads in the x direction and presses the print heads one by one against the other. As a result, the x-pin 60 of one printhead presses the x-button 106 of the next printhead and the x-pin of the last printhead presses the x-alignment button 114 in the cavity. The resilient element 110 presses the print head 104 so that its y-pin presses against the y-button in the cavity 102. The x and y alignment pins of printhead 104 cooperate with the corresponding x and y buttons and resilient elements in mounting cavity 102 to align the printhead.
Each radiation lamp 120 (such as shown in fig. 2A) included in carriage 28 optionally includes an ultraviolet light bulb 122 that emits the build material dispensed by ultraviolet photopolymerization printhead 52, a reflector 124, and a housing 126 that supports and contains the reflector and bulb. The ultraviolet light bulb 122 may alternatively be a discharge bulb, such as a mercury or xenon discharge bulb. Optionally, the lamp 120 includes a protective cover plate 128 through which ultraviolet light from the bulb 122 is transmitted and which covers an aperture 129 through which the lamp provides light.
Fig. 6A is an enlarged view schematically illustrating the carriage 28 of fig. 1, wherein components of a lamp 120 according to an embodiment of the invention are visible through a lamp housing 126, the lamp outline being indicated by dashed lines. The reflector 124 is shown partially cut away. Fig. 6B and 6C show cross-sections of lamp 120 along lines AA and BB.
The uv light emitted by lamp 120 and reflected by the surface of the build layer or build platform 24 (see fig. 1) formed by RPA20 back toward printhead 52 (see fig. 2A) or build material on other components of carriage 28. The polymerized build material on the print head 52 may block the output port 58 or output ports on the head. In addition, hardened masses or partially hardened build-up material on printhead 52 or other areas of carriage 28 may land on or impact an object, such as object 22 (see fig. 1) fabricated by RPA, thereby damaging the object.
The inventors have found that the amount of light reflected from the build layer to the carriage 28 is a function of the build layer and the height above the surface area of the build platform 24 at which the lamp provides light. The functional relationship between the amount of reflected light reflected to the carriage 28 and the height is similar to a graph 180 shown in fig. 6D, which shows the amount of reflected light "RR" reaching the carriage as a function of the height "H".
However, for both a relatively large and a relatively small height H, the amount of reflected light is relatively small, and it is of course advantageous to make the height relatively small instead of relatively large, so that the light emitted by the lamp 120 can be effectively utilized. Thus, according to one embodiment of the present invention, lamps 120 are mounted on carriage 28 such that when a build layer is printed by RPA20, their respective apertures 129 are relatively close to the build layer. In some embodiments of the present invention, aperture 129 is less than about 10mm from the structural layer fabricated by RPA 20. In some embodiments of the present invention, aperture 129 is less than about 15mm from the structural layer fabricated by RPA 20. In some embodiments of the present invention, aperture 129 is less than about 10mm from the structural layer fabricated by RPA 20. In some embodiments of the present invention, aperture 129 is approximately 5mm from the structural layer fabricated by RPA 20.
A problem is often encountered when shaping objects using inkjet RPAs, such as RPA20, even though the objects are relatively difficult to shape with sharp edges and features. The material of the build layer edges of RPA fabricated objects tends to "melt" during the fabrication process, with the result that the edge deformation loses clarity. The present inventors have found that the material polymerization of the edge surfaces of the build layers of the object is relatively slow and inefficient, which results in unclear edge and object image detail. The otherwise inefficient polymerization may leave the edges of the object unhardened and still "tacky".
Inefficient, slow or localized polymerization of the edge surface material of objects fabricated from prior art RPAs is caused by the relatively low intensity of the polymerizing light emitted by the lamps and the relatively strong reflectivity of the edge surfaces in prior art RPAs.
Increasing the intensity of the polymerizing light emitted by the UV lamp does not generally solve this problem. Most of the material in the body of the RPA-shaped object build layer polymerizes relatively quickly at certain uv light intensities, but this intensity is not sufficient to polymerize the build material of the edge surfaces of the build layer quickly and efficiently. Thus, increasing the intensity of the ultraviolet light wastes energy, and most of the increased intensity is used to heat the already polymerized material in the bulk of the build layer. The increased heat increases thermal stresses in the RPA components and build-up layers, tending to deform the build-up layers, impairing the accuracy of the object formation and the quality of the object.
According to an embodiment of the invention, to increase the efficiency of the build material at the edges of the photopolymerizable build layer from the UV lamp without excessive heating to waste energy, the light from the lamp is at a relatively large angle to the normal plane of the build layer. The ratio between the intensity of light incident on the edge surface of the structured layer and the intensity of light incident on the surface parallel to the layer surface increases with increasing angle of incidence, given the intensity of light emitted by the lamp. Thus as the angle of incidence increases, the efficiency of polymerisation of the edge build material increases relative to the efficiency of polymerisation of the material in the bulk of the build layer. Thus, according to one embodiment of the invention, the proper angle of incidence and intensity of the ultraviolet light are determined so that the light efficiently polymerizes the edge material and the bulk material of the build-up layer without excessive heating and wasting energy. The edge material of the construction layer made of RPA with a UV lamp according to an embodiment of the invention is relatively efficiently polymerized. As a result, the edges do not melt and deform as easily as the edges of prior art RPA-made construction layers, and clarity is improved.
For example, the incident angle of the majority of the ultraviolet light emitted by the UV lamp 120 included in the carriage 28 may alternatively be approximately equal to 45 °. Optionally, the reflector 124 in the UV lamp includes an edge reflector 130 and a planar reflector 132, which may optionally be a treated surface of the housing 126 so that it reflects light emitted by the bulb 122. Optionally, the edge reflector 130 includes two mirrored parabolic reflectors 134 that intersect at a common edge 136 and are positioned such that their respective focal points are approximately coincident. The radiation bulb 122 is optionally mounted on the edge reflector 130 through a suitable hole in the reflector. The contact end 138 of the light bulb 122 is mounted to an electrical socket (not shown) on the housing 126 that is in electrical contact with the light bulb 122 to supply electrical power (not shown). Optionally, the socket supports the light bulb 122 and holds the light bulb in place in the housing 126.
The bulb 122 has a fixed position "hot spot" 140 from which most of the light emitted by the bulb emanates, the hot spot 140 being located approximately at the focal point of the parabolic reflector 134. Each parabolic reflector 134 is positioned such that a majority of the light emitted by hot spot 140 is reflected at an angle of approximately 45 deg. onto cover plate 128, and the light emitted by lamp 120 passes through cover plate 128 to be incident on the shaping fabric of RPA 20.
The cross-sectional view of the lamp 120 in fig. 6B schematically shows the parabolic reflector 134 reflecting ultraviolet light rays 150 from the hot spot 140 so that light emitted from the lamp passes through the cover plate 128 at an angle of about 45 ° to the plane of the cover plate. The reflected light is incident on the regions of the build layer 152 fabricated by RPA 20. The edge 154 of layer 152 is shown enlarged in inset 156. According to one embodiment of the invention, ultraviolet light (emitted from lamp 120 at an angle of about 45 ° relative to the plane of build-up layer 152) is incident on the surface area of edge 154 in a direction close to the normal of the edge surface (as indicated by block arrow 158). As a result, the relative intensity of light incident on the surface of the edge 154 is increased, and a majority of the incident light is incident on the build material along the edge, effectively polymerizing the material.
Fig. 6C schematically illustrates a planar reflector 132 that reflects light rays 159 from the hot spot 140 and causes them to exit the cover plate 128. In order to provide relatively intense light to polymerize the RPA 20-shaped build-up layer material, the mirrors are optionally brought relatively close to each other so that the light emitted from the lamp 120 by the bulb 122 is concentrated in a relatively small surface area of the build-up layer. The inventors have found that relatively close to planar reflectors reduce the amount of ultraviolet light emitted by the lamp 120 that is reflected toward the output port in the print head in the carriage 28.
Fig. 7A and 7B are cross-sectional views schematically showing examples of deformation of the UV lamp 120. The cross-sectional view is taken along line AA in fig. 6A and is similar to that shown in fig. 6B. In FIG. 7A, the edge reflector 160 according to an embodiment of the invention is similar to the edge reflector 124, including four parabolic reflectors 161, 162, 163, and 164. The parabolic reflectors 161 and 163 are mirror images of each other, and the parabolic reflectors 162 and 164 are mirror images of each other. The focal points of all parabolic reflectors approximately coincide with the hot spot 140 of the bulb 122. In FIG. 7B, an edge reflector 170 according to an embodiment of the invention is similar to the edge reflector 124, including two "prismatic" parabolic reflectors 171 and 172 and planar reflectors 173 and 174. The parabolic reflectors 171 and 172 are mirror images of each other and each comprises two planar plates 175. The planar reflectors 172 and 174 are mirror images of each other.
Conventional discharge bulbs used for emitting ultraviolet light, such as mercury and xenon discharge bulbs, typically require a high voltage power supply and a complex ignition system in operation, which generates a significant amount of heat and cannot be turned on and off quickly.
In some embodiments of the invention, the UV lamp comprises a light emitting diode that emits ultraviolet light for polymerizing the build material. UV light emitting diodes generate a small amount of thermal energy compared to the UV energy they deliver and can be turned on and off relatively quickly while still providing UV radiation with a relatively small required radiation bandwidth. The output intensity of the light emitting diodes can be relatively easily controlled and they can be arranged in close packing to provide the required ultraviolet light intensity for rapid polymerization of the RPA forming build material.
The leds can be turned on and off quickly without delay or RF (radio frequency) interference with the radiant operation of the discharge bulb. The process of manufacturing the object can be started quickly and the process itself is made more reliable because the aforementioned light emitting diodes can be turned on/off quickly.
Furthermore, the use of light emitting diodes reduces the deformation of the printing model for the following reasons: for example, significant differences in the temperature of the object and the room during manufacture are one cause of distortion of the final printed object upon cooling, especially when cooling is rapid and uneven throughout the process. When the led array emits only a small amount of heat per unit curing amount, the object to be manufactured is manufactured at a lower temperature than when a discharge lamp is used, and deformation of the object, which tends to occur when the object is cooled, is alleviated.
Fig. 8 schematically shows the carriage 28 including UV lamps 190, optionally each UV lamp 190 including an array 191 of closely spaced UV emitting light emitting diodes 192. Alternatively, the LEDs 192 are in the DIE state (i.e., a semiconductor block, in this case unpackaged LEDs) and are arranged at a pitch of about 1 mm. Alternatively, the LEDs 192 are SMD LEDs with a pitch in the array 191 of less than 2 mm. In order to allow UV radiation to be incident on the structured layer shaped by RPA20 at relatively large angles of incidence, each led 192 is optionally connected by known means to a microlens, which converts the light emitted by the led into a cone-shaped beam having a relatively large cone angle. Optionally, the taper angle is greater than about 80 ° (full taper angle). Optionally the cone angle is greater than about 100 (full cone angle). Alternatively, the controller 26 controls the intensity of light emitted by the UV LEDs 192 by controlling the current or voltage applied to the LEDs. Alternatively, the controller 26 delivers electrical energy to the LED 192 in the form of a series of current or voltage pulses, and the controller controls the duty cycle of the pulses to control the intensity of the UV light emitted by the LED.
According to one embodiment of the invention, the controller 26 (see fig. 1) that controls the operation of the carriage 28 controls the intensity of the ultraviolet light emitted by the light emitting diodes 192 in the array 191 independently of the intensity of the light emitted by the other light emitting diodes in the array. In particular, the controller controls the individual light emitting diodes 192 to limit the location and timing of the UV radiation emitted by the lamp 190. For example, when a build layer 34 is printed, the layer has unprinted areas where no build material is deposited. Alternatively, the controller 26 controls the light emitting diodes 192 so that the unprinted region receives little or approximately no ultraviolet light. During manufacture of an object, such as object 22 described above, controller 26 periodically executes a service routine that moves carriage 28 away from build platform 24 into service area 200 for cleaning. During the performance of the maintenance program, the controller 26 selectively turns off the light emitting diodes 192.
However, the LEDs 192 generate a small amount of heat, and they and/or the circuitry to which they are connected do not generate heat, which is beneficial in a densely packed array to improve the heat dissipation characteristics of the lamp 190. In some embodiments of the invention, the leds 192 are mounted on and/or connected to a seebeck effect device (peltier device) and/or equipped with a suitable fan to dissipate heat.
In some embodiments of the invention, the RPA includes a sledge with light emitting diodes positioned relatively far from the build layer being manufactured by the RPA, similar to RPA20 according to an embodiment of the invention. The ultraviolet light emitted by the light emitting diode is transmitted into the structural layer through an optical cable or an optical fiber.
Fig. 9A and 9B are perspective views schematically showing a carriage 194, the carriage 194 including a light emitting diode 196 positioned relatively far from a structural layer to be printed by the carriage. Fig. 9A is a bottom perspective view of the carriage 194. Fig. 9B is a perspective view showing the "upper right side" of the carriage and the build layer 198. The light emitting diode 196 is connected to an optical fiber or cable 200 that transmits light from the light emitting diode to the build layer. Ultraviolet light emitted by the leds 196 exits the cable 200 through an end 202, which end 202 is supported adjacent the build layer 198 (see fig. 9B) by a suitable support structure or housing (not shown). Optionally, the end 202 is coupled to or formed with a suitable lens such that the ultraviolet light of the cone beam has a relatively large cone angle. The leds 196 and the circuitry optionally associated with the leds are supported or mounted in a housing (not shown) that is an "open" structure to facilitate heat dissipation.
As described above, during manufacture of the object, the controller 26 periodically moves the carriage 28 to the service area 220 (see fig. 1) and performs a cleaning procedure. The cleaning procedure typically includes a clean-out procedure that scrapes build material off all of the output ports of the carriage to restore the flow of material through the print head. Controller 26 controls carriage 28 to contact and move in a direction approximately perpendicular to the edge of at least one of first cleaning blade 225 and second cleaning blade 227 so that the cleaning blade scrapes off droplets of residual material remaining on the exit port surface after the cleaning process is completed and excess material "debris" and dust that has accumulated on the surface of print head 52 during the manufacturing process.
Fig. 10A and 10B are an enlarged perspective view and a cross-sectional view, respectively, schematically showing the bottom of the carriage 28 when a cleaning process according to an embodiment of the present invention is performed. Cleaning sheets 225 and 227 are shown removing build material debris 229 from a surface 230 (hereinafter "port surface") of the printhead 52 having the output port 58 and cleaning the surface.
Cleaning sheets 225 and 227 have "cleaning" edges 226 and 228, respectively, optionally parallel to each other and to the x-axis. Optionally, the cleaning edge 226 of the first cleaning sheet 225 is proximate to but not in contact with the port surface 230. Cleaning edge 228 of second cleaning sheet 227 contacts port surface 230. The carriage 28 moves parallel to the y-axis in the direction indicated by block arrow 232. As the carriage 28 moves, the edge 226 of the first cleaning sheet 225 removes relatively large debris deposits protruding from the mouth surface 232. The edges 228 of the second cleaning sheet 227 remove residual debris and scrape the cleaning surface.
Debris 229 removed from the surface of the printhead 52 by the cleaning sheets 225 and 227 falls or falls into the waste pit 222 as shown by the dashed lines. The spaced first and second cleaning sheets 225 and 227 are maintained at a sufficient distance such that debris removed from the mouth surface 230 by the cleaning edges 226 and 228 of the sheets will fall or fall smoothly into the waste pit 222. During the performance of the maintenance procedure, a suitable vacuum pump (not shown) removes debris accumulated in the waste pit 222.
The inventors have found that by using two cleaning sheets, a pre-cleaning sheet, i.e. a first cleaning sheet 225 that does not contact the surface 230 of the print head 52, and a wiping sheet, i.e. a second cleaning sheet 227 that contacts and wipes the surface, the likelihood of debris being deposited between the print heads during the cleaning process is reduced.
In some embodiments of the invention, the edges of the cleaning sheet are not straight but crenulated or scalloped. Figure 10C schematically shows a cleaning sheet 240 having a scalloped edge 242. A straight cleaning blade edge tends to push the portion of debris scraped from the print head 52 laterally along the blade edge. Debris forced along the edges tends to collect in the spaces between the printheads. The scalloped edges may prevent lateral movement of the removed debris, but instead direct the debris into the scrap pit 222.
Scalloped edges are not the only edge shape that prevents debris from moving laterally along the edge. Figure 10D schematically shows a cleaning sheet 244 with edges 246 shaped like a series of triangular pulses, which has a similar function.
In some embodiments of the present invention, the cleaning region 220 (see fig. 1) comprises a single cleaning sheet. Fig. 11A and 11B are a perspective view and a cross-sectional view, respectively, schematically illustrating maintenance cleaning of the carriage 28 during maintenance cleaning of the carriage, optionally using a single cleaning sheet 248 to clean the mouth surface 230 of the printhead 52.
Alternatively, the cleaning sheet 248 is a thin flexible sheet formed of plastic, rubber, or metal. Alternatively, the cleaning sheet 248 is formed from a thin steel plate that is approximately 50 microns thick. The cleaning sheet 248 is mounted above the waste pit 222 so that it is at an angle relative to the surface 230 of the printhead 52. During a cleaning process, the controller 26 (see FIG. 1) positions the carriage 28 so that the surface 230 (see FIG. 11B) presses down on the cleaning sheet 248, causing the sheet to contact the surface at an acute angle to the surface, and the cleaning edge 250 of the sheet resiliently presses against the surface. As the carriage 28 moves in the direction of block arrow 232, the cleaning edge 250 effectively scrapes the debris 229 off of the surface 230 and causes the debris to fall into and/or be dumped into the waste pit 222.
In some embodiments of the present invention, a cleaning sheet similar to cleaning sheet 248 according to an embodiment of the present invention has a groove that includes a plurality of individual resilient teeth. Figure 11C schematically illustrates a cleaning sheet 260 having grooves for cleaning the carriage 28, in accordance with one embodiment of the present invention. The cleaning sheet 260 includes a plurality of teeth 262 having a cleaning edge 264. During cleaning, each tooth 262 contacts the surface 230 of a different printhead 52 at an acute angle and the edge 264 of the tooth resiliently presses against the surface. Because each tooth 262 is resilient independent of the other teeth, each tooth 262 can adjust the height, i.e., the z-coordinate, of the surface 230 of the print head 52 that it is cleaning independent of the other teeth. The cleaning sheet 260 can effectively compensate for slight differences in the height of the surface 230.
It should be noted that the cleaning sheets 248 and 260 are not only provided with grooves according to embodiments of the present invention. Cleaning sheets similar to sheets 225 and 227 (see fig. 10A) and sheets 242 and 246 can also have slots, such that each sheet includes a plurality of small cleaning sheets (i.e., teeth), each tooth cleaning a different printhead 52, and can be independently adjusted to compensate for differences in the elevation of printhead upper surface 230.
Despite periodic maintenance cleaning of print head 52, build material debris can fall onto the build layer during the manufacture of an object or leveling of the build layer, in both cases leaving undesirable bumps in the build that damage the layer. When this occurs, the bumps on the layer not only damage the quality of the next layer to be deposited on the damaged layer, but also can collide with the bumps and be damaged as the carriage 28 moves over the build layer.
Thus, an RPA, such as RPA20, according to an embodiment of the present invention optionally includes an obstacle detection system. The detection system generates a signal responsive to the formation of an unwanted bump on the build layer and transmits the signal to the controller 26. The controller 26 either performs corrective action, such as leveling the layer using the leveling rollers 27, or stops the manufactured object and issues an alert indicating that user intervention is required.
Fig. 12A and 12B are perspective and cross-sectional views, respectively, schematically representing an RPA300 similar to RPA20, RPA300 including an obstacle detection system 302 in accordance with an embodiment of the present invention. Only the components and features of RPA300 relevant to the description are shown in fig. 12A and 12B. In the figure, RPA300 is shown forming a layer of build material 304 during fabrication of an object (not shown) and detecting bulging of a top build layer 306.
Obstacle detection system 302 may optionally include a laser 308 and corresponding optics (not shown) as desired, and controller 26 may control laser to generate laser beam 310. The detection system includes an optical detector 312 and corresponding optics (not shown) as needed to detect the light emitted by laser 308. Alternatively, laser 308 and detector 312 are mounted on brackets 314 and 315, respectively, with brackets 314 and 315 being positioned in slots 316 and 317 formed in table 25. Brackets 314 and 315 are optionally mounted on threaded shafts 318 and 319, respectively, located in slots 316 and 317. The slot may alternatively be parallel to the y-axis. The controller 26 controls at least one motor (not shown) to rotate the shafts 318 and 319 to position the brackets 314 and 315 in the appropriate position along their respective slots 316 and 317 and thus in the appropriate y-coordinate. Alternatively, laser 308 and detector 312 may be controlled by controller 26 to be raised and lowered in a direction perpendicular to stage 25 (i.e., parallel to the z-axis).
To detect a bulge in the top build-up layer 306, the controller 26 positions the laser beam 10 to contact the layer surface along the length of the laser beam and moves the carriage 314 along the groove 316 so that the bulge present on the layer at least partially blocks the laser beam as it moves. As the controller 26 moves the laser 308, its movement detector 312 detects the laser beam 10. When the beam is blocked, the detector 312 generates a signal from the laser beam 10 to indicate the presence of a bump. Fig. 12C schematically shows a case where the laser beam is blocked by the ridge 320. Alternatively, controller 26 moves laser 308 and detector 312 so that laser beam 10 is in front of carriage 28 as it moves along the y-axis and "scans" the elevation of the area of top layer 306 before the carriage's printhead dispenses build material to print the area again for another build layer.
It is noted that the configuration of the obstacle detection system 302 shown in fig. 12A and 12B limits the movement of the laser 308 and detector 312 in the z-axis. This limitation does not affect the ability of detection system 302 to detect top build layer elevations because build platform 24 decreases the distance by approximately the thickness of the layer as RPA300, e.g., RPA20, prints each new build layer. Thus, all build layers produced by RPA300 are performed at approximately the same height from stage 25, i.e., the same z-coordinate, or within the same small height range on the stage.
However, in some RPAs according to embodiments of the present invention, the build layers are not all fabricated at the same z coordinate. Instead, the carriage of the RPA is raised by the thickness of the layer for each build layer of at least some new layers produced by the RPA. In such an embodiment, it may be advantageous, but not necessary, to have the range of motion of the obstacle detection system along the z-axis be greater than the range of motion of detection system 302. Of course, if desired, it may be advantageous for an obstacle detection system according to an embodiment of the present invention to be configured with a range of motion along the z-axis that is greater than the range of motion of detection system 302.
Fig. 12D schematically illustrates an obstacle detection system 330, which is a modified example of the system 300, according to an embodiment of the invention. The range of motion of the obstacle detection system 330 along the z-axis is greater than the range of motion of the system 302. The optional detection system 330 includes carriages 332, each having a slider 334 that can be controlled to rise and fall. The laser 308 and detector 312 are mounted on a slider 334 on different supports 332 and are selectively controlled to be positioned at different locations along the z-direction length of the slider. The range of motion of positioning laser 308 and detector 312 is approximately equal to the range of motion of slider 334 in the z-direction plus the length of the slider in the z-direction. Alternatively, as another example, the laser and detector for detecting the bump are mounted on the carriage 28 so that they move with the carriage parallel to the z-axis.
It should be noted that the obstacle detection systems according to embodiments of the present invention, such as detection systems 302 and 330, are not only used to detect bumps on a build layer, but also to detect obstacles on build platform 24. Such an obstacle may be, for example, a first object part manufactured by the RPA that is inadvertently left on the RPA build platform to interfere with the RPA's manufacture of a second, later object.
Optionally, in accordance with an embodiment of the present invention, the RPA includes a collision detection system for detecting whether and when a carriage of the RPA collides with an obstacle. When a collision occurs, the controller 26 optionally stops the manufactured object and generates an alarm to alert the user that the collision occurred, requiring user intervention.
12A-12D includes a crash detection system 340, which may optionally be mounted on the carriage 28. Alternatively, the crash detection system 340 includes an accelerometer (not shown) that generates a signal responsive to the acceleration of the carriage 28. A crash will generally generate a force that causes an undesirable acceleration of the carriage, which has a characteristic curve for identifying the acceleration generated by the crash. For example, a crash typically results in a thrust force acting on the carriage, thereby producing a corresponding recognizable acceleration.
Whereas the impact system 340 shown in fig. 12A-12D is mounted on the carriage 28, an impact detection system according to an embodiment of the present invention may be mounted in or on other components of the RPA. For example, the impact detection system may be mounted on a component of the RPA (other than the carriage) to detect vibrations of the component due to an impact. In some embodiments of the invention, the collision detection system includes a microphone and corresponding algorithm that identifies sounds emitted by collisions.
The print definition of the RPA dispensed build layer droplets (i.e., the droplet density of the build material printed in the x and y directions) and other "operational" parameters that define the RPA operational specifications typically have a complex relationship with each other. For example, "loss rate" generally refers to the ratio of the amount of build material removed from the printed build layer by the leveling rollers 27 (see fig. 1) to the amount of material of the printed build layer. As the loss rate increases, the thickness of the layer decreases, the quality of the construction increases (the definition of the construction in the stacking direction, i.e., the z-direction increases), the production speed decreases, and the cost increases. For the RPA to operate effectively, the values of its operating parameters are determined based on the relationships between the parameters. Due to the complex relationships between the RPA operating parameters, it is often difficult to determine the values of the operating parameters that cause the RPA to operate efficiently. The sharpness and other operating parameters of the RPA are therefore typically set by the manufacturer and cannot be adjusted by the user. Thus limiting the user's flexibility in determining production specifications (hereinafter "object specifications"), and thus limiting the quality and characteristics required of the RPA to manufacture the object.
In order to allow the user to flexibly control the operating parameters of the RPA and thus the object specifications, the controller of the RPA has an "RPA" operating algorithm and data according to an embodiment of the present invention. The RPA operating algorithms and data enable a user to adjust the RPA operating parameters according to the desired specifications for the object being manufactured by the RPA. The user inputs information into the RPA defining the desired object specifications and the controller adjusts the operating parameters of the RPA based on the RPA data and algorithms to ensure the object specifications. If a particular contour of an object specification cannot be met, the controller will inform the user that it cannot be met, and will instruct him or her which object specification is applicable, and how to set an acceptable object specification contour.
For example, controller 26 of RPA20 may optionally have data relating to Layer Thickness (LT), x and/or y-axis Print Resolution (PR), and printhead 52 Drive Voltage (DV) values, where printhead 52 controls the volume of the droplets of build material dispensed by the printhead. Fig. 13 schematically illustrates a graph 350 of RPA data available to the controller 26. Graph 350 shows a surface 360 that correlates to layer thickness LT, sharpness PR, and printhead 52 operating voltage DV values. (e.g., the operational data represented by graph 350 may be different for different printheads-as described above, memory 49 in printhead circuit board 55 feeds these operational data for each printhead 52 to controller 26 in accordance with one embodiment of the present invention). It is assumed that the definition is expressed in units of dpi, i.e., the number of units of inches of dots or droplets that dispense build material along the x or y axis shown in FIG. 1 to produce a build layer. Lines 361 and 362 on surface 360 are used to visualize the plane and lie in a plane parallel to the DV-LT and PR-LY planes, respectively, in graph 350. Line 361 and the other lines lying in a plane parallel to the DV-LT plane represent the layer thickness LT at different sharpness PR constants, and the layer thickness LT is a function of the drive voltage DV. Line 362 and other lines in surface 360 that are parallel to the PR-LT plane represent LT at different DV constants, and layer thickness LT is a function of PR. When the user selects the desired build layer LT and print definition PR, the controller 26 determines the drive voltage according to the RPA algorithm determined from the data in the graph 350. If the user selected LT and PR do not have corresponding drive voltages, the controller 26 will alert the user while displaying to the user the range of LT and PR options.
From the graph 350 it can be seen that at a given drive voltage DV, the layer thickness LT of the build-up layer in the object produced by RPA increases with increasing print definition PR. This is because, given DV, the volume of droplets of build material dispensed by printhead 52 is approximately the same, with the density of droplets dispensed per inch along the x and/or y axes increasing as the resolution increases. However, as build layer thickness increases, build clarity along the z-axis decreases and the fidelity of the RPA-fabricated object decreases compared to its replicated object. Surface tension of the build material printed into the build layer can also reduce fidelity and quality of the manufactured product. The surface tension of the build material has a tendency to deform the edges of the build layer, which tends to increase with increasing layer thickness.
According to an embodiment of the present invention, an RPA-fabricated object having relatively high print definition, fidelity, and quality along the x and/or y axis is formed from relatively thin build layers.
The x-pitch and y-pitch of an object build layer are the distances between the coordinates of building material droplets dispensed along the x-and y-axes, respectively, used to form the build layer. (x-pitch and y-pitch are the inverse of x and y print resolution, respectively). Layers in an object are printed with relatively low x and/or y definition (not necessarily the same) and relatively large x-pitch and/or y-pitch, so that the printed layer is relatively thin and is not as susceptible to the effects of surface tension as thick layers. However, according to one embodiment of the present invention, the x and/or y coordinates of the deposited droplets of build material in adjacent build layers are offset from each other by a fraction (fraction), the "pitch fraction", less than one of the droplet x-pitch or y-pitch. (the pitch segments need not be identical in both x and y coordinates).
The inventors have found that the fidelity and quality of an object approximates that of a relatively thin layer fabricated object having an "effective" x and/or y definition equal to the relatively low definition at the time the layer is actually printed multiplied by the reciprocal of the corresponding pitch segment. Since the pitch segment is less than 1, the effective sharpness is increased.
FIG. 14 schematically shows a print layer according to an embodiment of the invention. A cross-sectional view of a build layer 381, 382, 383 formed from an RPA in accordance with an embodiment of the present invention is shown and is, for example, a cross-section parallel to the xz plane. Layers 381, 382, and 383 are formed from droplets of build material 391, 392, and 393, respectively. Shown schematically in the figure are the droplets after mixing and after correction by leveling rollers, such as leveling roller 27 (see fig. 1). The printing of build layers 381, 382, and 383 is repeated every third layer, so that every third layer thereafter has the same x-coordinate.
Layers 381, 382, and 383 are printed with relatively low resolution Ndpi along the x-axis and corresponding x-pitch, where "Δ x" is 1/N inchesCun. The pitch segment is denoted by "1/P", where "P" is a number greater than 1. The x coordinate of the droplet 391 in the "n-th" row printed on the RPA is therefore (x)o+ (n-1) Δ x) where xoIs the x-coordinate of the first droplet in layer 381 along the x-axis. In accordance with one embodiment of the present invention, the corresponding x coordinate of droplet 392 in layer 382 is (x)o+ (n-1) Δ x + (1/P) Δ x), the corresponding x coordinate of droplet 393 in layer 383 is optionally (x)o+(n-1)Δx+Δx)。
The x-coordinates of the droplets in each layer 381, 382, 383, from which the layer is printed, correspond to the x-coordinates of similar voxels (homologusvoxels) defined by the object build data. The construction data elements corresponding to the droplets in the adjacent layer are offset with respect to each other by a distance equal to (1/P) ax.
In some embodiments of the invention, the droplets in each layer correspond to similar voxels in the respective layer defined from the construction data, wherein the construction data is segmented into voxels having an x-pitch equal to Δ x and corresponding to a "low" print definition N. Build-up layers are "thin layers" having a thickness corresponding to the thickness of build-up layers 381, 382, and 383.
In some embodiments of the present invention, all of the droplets in the three layers correspond to similar voxels of a "thick" layer defined from the build data, where the thickness of the "thick" layer corresponds to the sum of the thicknesses of all three layersoThe voxels of + (n-1) Δ x) correspond. Droplets 392 and 393 in build layers 382 and 383, respectively, and the x coordinate in the build data layer equals (x) respectivelyo+ (n-1) Δ x + (1/P) Δ x) and (x)oThe droplet of + (n-1) Δ x + Δ x) corresponds.
The inventors have found that the effective print definition of layers 281, 282, and 283 is approximately equal to P × N, corresponding to an effective x-pitch equal to Δ x/P. The effective x-pitch Δ x/P of layers 281, 282, and 283 is shown in FIG. 14.
To illustrate a few examples, P in FIG. 14 is equal to 2 and the pitch segment is 0.5. If the low print definition N along the x-axis is equal to 600dpi, with a corresponding x-pitch of 1/600 inches, the effective print definition of the build layer along the x-axis is 2 x 600 — 1200dpi, with a corresponding high definition x-pitch equal to 1/1200 inches.
An RPA manufacturing apparatus for manufacturing an object includes one or more RPAs that define and provide limited throughput. When the device receives instructions to manufacture an object, the device must determine how to allocate and arrange its production capacity to meet the requirements. Each production order defines the fabrication of at least one object according to a set of object specifications that define a set of RPA operating parameters (e.g., sharpness, layer thickness, loss rate, production time …) that are generally different from the operating parameters of the other production orders. Allocating and scheduling production capacity is often complicated and often requires a production manager to monitor and execute production schedules with the aid of computer programs.
According to one embodiment of the present invention, allocating and scheduling the production capacity of the RPA devices is performed by a task management algorithm (JMA), which allows a user to allocate and schedule production capacity through an interface without intervention from a production manager.
When a user wants to set the order in which devices manufacture objects, the user accesses the JMA. JMA responds to a user and displays a plurality of virtual build platforms on a computer screen through a user interface. Each virtual build platform represents, for example, build platform 24 shown in fig. 1. The RPA in the RPA device on the platform manufactures the object in the order of the RPA devices.
Each virtual build platform has a plurality of "platform parameters". Example platform parameters include estimated start and end times for manufacturing an object on the platform, available production space on the platform, and space costs. Optionally, the platform parameters include RPA operating parameters such as layer thickness, sharpness, and loss rate, and the RPA device manufactures the object on the platform according to the platform parameters.
The user selects a platform having sufficient available space for fabricating the object, RPA operating parameters that correspond to the object specifications for fabricating the object and provide the user with the appropriate scheduling and cost. Once the user has completed the step of selecting a platform, the user proceeds with the management requirements, such as paying or signing purchase orders, to determine and save the manufacturing space and time he or she has reserved.
In some embodiments of the invention, a user may define at least some platform parameters of the platform. For example, the JMA may optionally provide the user with at least one "empty" build platform so that the user may define platform parameters. Alternatively, the user-defined platform parameters may include priorities, and if the priorities are high enough, certain tasks of the user may be performed out of order, but before a prior task that has been scheduled. JMA selectively generates corresponding production space costs on the platform based on user-defined platform parameters. For example, if a user sets a very high priority for a platform over other tasks, the JMA will determine the cost of space (spaceost) on the platform.
In many cases, users cannot readily determine the RPA operating parameters, platform space, cost, and other parameters (hereinafter "task data") needed to perform user tasks. For this reason, the JMA optionally provides the user with production guidance to assist the user in determining the task data parameters. Alternatively, the wizard assists the user through an interactive query interface (interactive inquiry), wherein the wizard presents the user with questions, the answers to which are used to determine the task data. Alternatively, the user transmits configuration data defining the object that the user wants to produce, and the wizard determines the task data based on the transmitted configuration data. Once the task data has been determined, the wizard highlights or indicates which production platforms are appropriate for the user's tasks.
In the description and claims of this application, each verb, such as "comprise," "include," "have," and related words mean that the object or verb object does not necessarily list all of the elements, components, elements of the subject or the subject of the verb.
The present invention has been illustrated by the detailed embodiments, but does not limit the scope of the present invention. The described embodiments comprise different features, not all of which are required to be comprised in all embodiments of the invention. Some embodiments of the invention use only some of the features or combinations of the features. It will be appreciated by a person skilled in the art that the described variant embodiments of the invention and the embodiments of the invention comprise various combinations of features described in the above embodiments. The scope of the invention is limited only by the claims.
This application claims priority to U.S. provisional application 60/466,731 filed on 5/1/2003, the disclosure of which is incorporated herein in its entirety.