U.S. patent application number 11/853755 was filed with the patent office on 2008-01-03 for production line with a series of evenly spaced printhead sets.
This patent application is currently assigned to Silverbrook Research Pty Ltd.. Invention is credited to Kia Silverbrook.
Application Number | 20080001997 11/853755 |
Document ID | / |
Family ID | 30004887 |
Filed Date | 2008-01-03 |
United States Patent
Application |
20080001997 |
Kind Code |
A1 |
Silverbrook; Kia |
January 3, 2008 |
PRODUCTION LINE WITH A SERIES OF EVENLY SPACED PRINTHEAD SETS
Abstract
A production line includes a conveyor configured to move a
substrate at a substantially constant speed in a flat plane. A
series of evenly spaced printhead sets is configured to print
material onto the substrate so that the printhead sets print
respective layers on the substrate. Typically, each printhead set
includes multiple printheads which are arranged to form a
two-dimensional array.
Inventors: |
Silverbrook; Kia; (Balmain,
AU) |
Correspondence
Address: |
SILVERBROOK RESEARCH PTY LTD
393 DARLING STREET
BALMAIN
2041
AU
|
Assignee: |
Silverbrook Research Pty
Ltd.
|
Family ID: |
30004887 |
Appl. No.: |
11/853755 |
Filed: |
September 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10753475 |
Jan 9, 2004 |
7278847 |
|
|
11853755 |
Sep 11, 2007 |
|
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Current U.S.
Class: |
347/40 |
Current CPC
Class: |
B33Y 10/00 20141201;
B41J 2/01 20130101; B41J 3/4073 20130101; H05K 1/185 20130101; H05K
3/125 20130101; Y10S 439/901 20130101; B05C 5/0212 20130101; B41J
11/002 20130101; B33Y 50/02 20141201; B22F 10/10 20210101; B29C
64/112 20170801; B33Y 30/00 20141201; B41J 29/393 20130101; B33Y
70/00 20141201; Y02P 10/25 20151101; B33Y 80/00 20141201; Y10T
29/49144 20150115; H05K 3/4664 20130101; B29C 70/68 20130101; B33Y
40/00 20141201; B41J 3/543 20130101 |
Class at
Publication: |
347/040 |
International
Class: |
B41J 2/15 20060101
B41J002/15 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2003 |
AU |
2003900180 |
Claims
1. A production line comprising: a conveyor configured to move a
substrate at a substantially constant speed in a flat plane; and a
series of evenly spaced printhead sets configured to print material
onto the substrate so that the printhead sets print respective
layers on the substrate.
2. A production line as claimed in claim 1, wherein each printhead
set has multiple printheads.
3. A production line as claimed in claim 2, wherein the multiple
printheads are arranged to form a two-dimensional array.
4. A production line as claimed in claim 1, wherein each layer is
of a constant thickness.
5. A production line as claimed in claim 1, wherein the distance
from each of the printheads to the surface upon which they print is
the same for all printheads.
6. A production line as claimed in claim 1, wherein the conveyor is
configured to move another substrate at a substantially constant
speed in the flat plane and the printhead sets are configured to
print material onto the other substrate.
7. A production line as claimed in claim 1, wherein the melting
point of material printed by one of the printhead sets is different
to the melting point of material printed by another one of the
printhead sets.
Description
[0001] This application is a continuation application of U.S.
application Ser. No. 10/753,475 filed on 9-Jan., 2004, herein
incorporated by reference.
FIELD OF INVENTION
[0002] This invention relates to the creation of objects using
digital additive manufacturing and more particularly to creating
working objects that may be electrically and/or mechanically
active.
CO-PENDING APPLICATIONS
[0003] Various methods, systems and apparatus relating to the
present invention are disclosed in the following co-pending
applications filed by the applicant or assignee of the present
invention simultaneously with the present application:
TABLE-US-00001 7206654 7162324 7162325 7231275 7146236 10/753499
6997698 7220112 7231276 10/753440 7220115 7195475
[0004] The disclosures of these co-pending applications are
incorporated herein by cross-reference.
BACKGROUND
[0005] Digital additive manufacturing is a process by which an
object is defined three dimensionally by a series of volume
elements (hereinafter referred to as voxels). The object is then
produced by creating/laying down each voxel one at a time, in rows
at a time, swaths at a time or layers at a time.
[0006] There exists systems that use modified inkjet type
technology to `print` material onto a substrate, so building the
object. However, these systems typically utilize a single scanning
printhead and are only useful for producing non-working models.
SUMMARY OF INVENTION
[0007] In the present invention we digitally define objects as a
series of voxels and have a production line that creates objects by
creating each voxel. The production line simultaneously creates
different portions of objects with each portion produced by a
separate subsystem. In the preferred embodiments each portion is
for different products and so the system builds up multiple objects
simultaneously. The finished objects may be of identical or of
different designs. The portions may be of any shape that may be
digitally described. Portions produced by different subsystems may
have different shapes.
[0008] In the preferred embodiments each and every voxel has the
same dimension. However, a product may be defined by voxels of more
than one size.
[0009] The portions are preferably created or laid down onto one or
more substrates. In the preferred embodiments one or more
substrates are provided, each having a substantially planar surface
upon which material is deposited. Each of the surfaces preferably
moves in it's own plane past the subsystems but does not otherwise
move relative to the subsystems. Each substrate need not have a
planar surface upon which material is deposited and the surface may
be of any shape desired. The substrate may move past the subsystems
at a constant velocity along a path or may move in steps. The
substrate may also be caused to rotate about one or more axes, as
it moves between subsystems, as it moves past subsystems, as it is
stationary or in combinations of these. In the preferred
embodiments a continuous substrate moves past the subsystems of the
production line at a substantially constant velocity.
[0010] The portions of the object produced by successive subsystems
preferably lie on top of each other but could be spaced apart from
each other, positioned end on end, adjacent to each other or in any
other configuration. As an example, a substrate having a
cylindrical surface may be caused to rotate about its axis as it
moves past a subsystem, so that material deposited extends in a
helix on the cylindrical surface.
[0011] The portions are preferably layers of the object and the
layers are preferably two dimensional, i.e. they lie in a flat
plane. However, the layers need not be planar. The layers may have
a constant thickness. Layers having differing thickness within the
one layer are within the scope of the invention. Similarly objects
may be made with multiple layers that do not have the same
thickness characteristics.
[0012] In the preferred embodiments each layer is planar, is made
up of voxels of constant size and all layers have the same
dimensions. Alternate layers may be offset relative to each other.
Preferably alternate layers are offset by half a voxel in one or
both of two mutually orthogonal directions.
[0013] Because voids may be formed in the object, when we refer to
a `layer` we mean a layer as defined, which may include voids, not
a continuous layer of material or materials.
[0014] In preferred embodiments each layer is created by one or
more printheads. In the preferred embodiments the printheads are
arranged along a longitudinally extending production line and one
or more substrates move past the printheads, and apart from the
first layer, the printheads print onto a previously printed layer
of material(s). The printheads for all layers operate
simultaneously and so whilst the first printhead is printing a
first layer of a first set of one or more products, the second
printhead is printing a second layer of a second set of one or more
products and the third printhead is printing a third layer of a
third set. Thus if we have a product 1000 layers high we have 1000
different subsystems, one for each layer. These 1000 subsystems
operate to simultaneously produce 1000 different layers of 1000
sets of products.
[0015] In the preferred embodiments the printheads extend across
the width of the substrate and are capable of printing across the
full substrate width simultaneously i.e. they do not scan or raster
when printing but are stationary. This enables a substrate to be
moved past the printheads at a substantially constant speed, with
the printheads printing rows of material onto the substrate. The
substrate speed is matched to the row width and printhead cycle
time so that the substrate has moved the width of the rows printed
for each printhead cycle. Thus the next row or rows printed by each
printhead will be printed next to a previously printed row or rows.
In the preferred embodiments the printheads each print two rows
simultaneously for increased substrate speed.
[0016] Whilst substrate width printheads are preferred, scanning
type printheads may be utilized to simultaneously produce multiple
layers of objects.
[0017] The terms "printhead", "print" and derivatives thereof are
to be understood to include any device or technique that deposits
or creates material on a surface in a controlled manner.
[0018] Each layer is printed by one or more printheads. We refer to
the printhead or printheads for a layer as a `layer group`. As used
in the description and claims it is to be understood that a layer
group may have only one printhead that prints one material and the
use of "group" is not to be taken to require multiple printheads
and/or multiple materials.
[0019] Whilst the layer groups may have multiple printheads, each
layer group preferably prints only one layer at any one time, which
may be made of one material or multiple materials. The number of
printheads in each layer is usually determined by the number of
materials to be printed. In the preferred embodiments each material
is printed by a separate printhead and any additional printheads
are only to enable a single layer to have multiple materials within
it. This is because the materials being printed have a relatively
high viscosity compared to water based inks and so require large
supply channels. Thus in the description it is assumed that each
printhead only prints one material. Thus if the system is capable
of printing N different materials, at one printhead per material,
this requires N printheads per layer. However, this is not to
preclude printheads that print multiple materials.
[0020] However, because each printhead could print more than one
material or multiple printheads could print the same material,
there does not have to be a one to one ratio between the number of
printheads and the number of different materials. It is not
critical that all the layer groups are identical, and in some
embodiments it is desirable that different layer groups print
different numbers of materials or different combinations of
materials.
[0021] It will be appreciated that for production efficiency more
than one printhead in a layer group may print the same material.
Where the refill rate of the printheads for different materials is
substantially the same, speed increases can only be achieved when
all materials have the same number of printheads. However if one
material requires a much longer refill time, provision of two or
more printheads for that material alone may allow increased
substrate speed.
[0022] When different materials are printed, they may need to be
printed at different temperatures and so in preferred embodiments
the printheads of a layer group may be maintained at different
temperatures.
[0023] Even if only one material is used there are advantages in
printing material compared to molding. For example, it is possible
to create voids in the finished product. The voids may be of any
complexity that may be digitally described. Thus, any pattern of
dots may be missing from the object created.
[0024] The number of separate products that may be printed
simultaneously depends on the printhead width, the product size
across the substrate, the product size along the substrate and the
longitudinal spacing between products.
[0025] The preferred systems are capable of printing most materials
that are required but there are circumstances where a discrete
object may be incorporated into products. Examples of such discrete
objects include semiconductor microchips, which can be manufactured
in more appropriate materials and in much smaller feature sizes
than in the current systems of the invention. For semiconductor
devices, the device speed is dependant on feature size and
materials used. Whilst preferred embodiments of the invention can
produce organic semiconductors, these are relatively slow compared
to conventional inorganic semiconductors. Thus, for example, where
a high speed integrated circuit is required, insertion of a
separately manufactured integrated circuit chip will be
appropriate, as opposed to printing a low speed circuit.
Mechanically active objects may also be inserted where printing
cannot satisfactorily produce them. In embodiments that create
three dimensional products, the printing process may create the
cavities into which such discrete devices may be inserted.
[0026] The material(s) printed by the printheads may be hot melts.
Typical viscosities are about 10 centipoise. The materials that may
be printed include various polymers and metals or metal alloys. It
is thus possible to print wires, in both two and three dimensions
in products. The material solidifies to a solid, either by freezing
or by other processing to form solid voxels. As used in the
description and claims the terms cured, curing or derivatives are
to be understood to include any process that transforms material or
materials in one state to the same or different material or
materials in a solid state. Different materials may require
different curing techniques or curing conditions.
[0027] The preferred printhead is a Micro Electro Mechanical System
(MEMS) type printhead in which a material is ejected from a chamber
under the control of a movable element. Reference is made to the
following patent specifications that disclose numerous such MEMS
type printheads or printhead components: TABLE-US-00002 6227652
6213588 6213589 6231163 6247795 6394581 6244691 6257704 6416168
6220694 6257705 6247794 6234610 6247793 6264306 6241342 6247792
6264307 6254220 6234611 6302528 6283582 6239821 6338547 6247796
6557977 6390603 6362843 6293653 6312107 6227653 6234609 6238040
6188415 6227654 6209989 6247791 6336710 6217153 6416167 6243113
6283581 6247790 6260953 6267469 6273544 6309048 6420196 6443558
6439689 6378989 6848181 6634735 6623101 6406129 6505916 6457809
6550895 6457812 6428133 6390605 6322195 6612110 6480089 6460778
6305788 6426014 6364453 6457795 6315399 6338548 6540319 6328431
6328425 6991320 6595624 6417757 7095309 6854825 6623106 6672707
6588885 7075677 6428139 6575549 6425971 6383833 6652071 6793323
6659590 6676245 6464332 6478406 6439693 6502306 6428142 6390591
7018016 6328417 6322194 6382779 6629745 6565193 6609786 6609787
6439908 6684503 6755509 6692108 6672709 7086718 6672710 6669334
7152958 6824246 6669333 6820967 6736489 6719406 7246886 7128400
7108355 6991322 10/728790 7118197 10/728970 10/728784 10/728783
7077493 6962402 10/728803 7147308 10/728779
[0028] Such MEMS type printheads may utilize different ejection
mechanisms for different ejectable materials while other MEMS
printheads may utilize different movable shutters to allow
different materials to be ejected under oscillating pressure. It is
to be understood that whilst MEMS type printheads are preferred,
other types of printhead may be used, such as thermal inkjet
printheads or piezoelectric printheads.
[0029] The aforementioned patents disclose printhead systems for
printing ink, but it will be appreciated that the systems disclosed
may be modified to print other materials.
[0030] In the preferred embodiments the data for each layer is
stored in memory on or in or associated with the layer group that
prints that layer. Preferably each layer group also stores data
relating to at least the preceding layer. Thus if an earlier layer
group fails, successive layer groups can all, synchronously, change
to printing the respective preceding layer.
[0031] Preferably, after such a change in which layer(s) a layer
group or groups are printing, the system may automatically transfer
layer data from one layer group to another so as to restore the
layer groups to having data relating to at least the preceding
layer compared to the actual layer being printed.
[0032] In the preferred embodiments each voxel has dimensions in
the order of 10 microns, each layer of the products is about 10
microns high and in a typical system we have about 1000 separate
sub-systems, each creating a separate layer of separate items. Thus
products up to about 1 cm high may be created on a typical
production line of the preferred embodiments.
[0033] Each printhead nozzle ejects a droplet that forms, when
frozen, dried or cured, a volume element (Voxel) that is
approximately 10 microns high. The printheads typically print up to
about 30 cm in width and so print up to about 30,000 droplets in
each line across the substrate. In the preferred embodiments the
voxels are treated as being hexagonal in plan view with an
effective height of about 10 microns.
[0034] If we have a system with 1000 layer groups, each of which is
capable of printing 30,000 voxels transversely and 60,000 voxels
longitudinally, we have a volume of 1800,000,000,000 voxels. Within
that volume we can define as many or as few different products as
we desire that will fit in that volume. Where multiple products are
defined within that volume, their design need not be the same. We
could, for example, define 1000 products within the volume, each
with its own different design. Products may be located
transversely, longitudinally and vertically relative to other
products. Thus products may be created on top of each other, not
just side by side or end on end.
[0035] The preferred embodiments have a print width of about 295
mm, a substrate speed of about 208 mm and an ability to print about
1000 layers, each of which is about 10 microns thick. Thus the
preferred embodiments are able to print products that have a
thickness up to about 1 cm and one of the height and width no more
than 295 mm. The other of the height and width may be up to about
600 mm. As will be explained later, this dimension is limited by
memory considerations.
Product Samples
[0036] Examples of products that may be manufactured using
embodiments of the invention include small electronic devices, such
as personal digital assistants, calculators through to relatively
large objects, such as flat panel display units. The productivity
of a production line is exemplified by the following examples.
Personal Digital Assistant
[0037] An example product that may be produced by a system of the
present invention is a personal digital assistant (PDA) such as
those made by Palm Inc of Milpitas, Calif. USA. A typical PDA has
dimensions of 115 mm.times.80 mm.times.10 mm (H.times.W.times.D).
Using hexagonal voxels 10 microns high and with a side length of 6
microns, a total of about 98 billion voxels are required to define
each product. This requires approximately 98 Gbytes of data, if we
assume that eight different materials are used in the product.
[0038] At a substrate speed of 208 mm per second a typical
production line can produce approximately 4.32 products per second,
373151 products per day or 136 million products per year, assuming
the system runs continuously. Whilst this is greater than the
current market for such products, the system has the potential to
substantially reduce the cost of these products and so increase the
market.
[0039] Whilst the system may print polymer transistors and
displays, these have lower performance than silicon based
transistors and displays. However, as discussed elsewhere, the
system is designed to allow incorporation of made up components
into partially printed objects in the production line.
Flat Panel TV
[0040] A flat panel TV of 53 cm diagonal size is generally the
largest object that can be printed in the typical system. Of course
to print wider objects, wider printheads may be utilized. For
longer objects, more memory is required and for thicker objects the
voxel height maybe increased or more layers printed by providing
more layer groups. Whilst the printheads have the ability to vary
the droplet size slightly, generally if a larger voxel size were
required, different printheads would be required. Of course
increased voxel size results in a higher `roughness` of the
finished product. However, depending on the product, this may be
commercially acceptable.
[0041] A typical 53 cm flat panel TV has dimension of 450
mm.times.290 mm.times.10 mm (H.times.W.times.D). Using hexagonal
voxels 10 microns high and with a side length of 6 microns, a total
of about 1395 billion voxels are required to define each product.
This requires approximately 1395 Gbytes of data, if we assume that
eight different materials are used in the product.
[0042] At a substrate speed of 208 mm per second a typical
production line can produce approximately 0.37 products per second
(.sup.208/450=0.46), 31890 products per day or 12 million products
per year, assuming the system runs continuously.
[0043] The complexity that may be defined by over 1 terabyte of
data is much greater than required by a typical flat panel TV and
the amount of functionality that can be built-in could be very
great. There are very few discrete objects that would need to be
incorporated into the part-printed product.
[0044] From the foregoing it is apparent that the invention thus
has many embodiments and accordingly has many broad forms.
[0045] In a first broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system printing at least part of each of multiple layers
simultaneously.
[0046] In a second broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system printing at least part of each of multiple layers
simultaneously, [0047] wherein each layer is defined by a plurality
of voxels arranged in a regular array and wherein the voxels of
each layer are printed so as to be offset by half a voxel relative
to the voxels of adjacent layers in a first direction, a second
direction perpendicular to the first direct ion or both the first
and second directions.
[0048] In a third broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system including a plurality of printheads, the system
printing at least part of each of multiple layers simultaneously,
[0049] wherein the printheads are configured to enable printing of
at least two different materials in at least one layer.
[0050] In a fourth broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system including a plurality of printheads, the system
printing at least part of each of multiple layers simultaneously,
[0051] wherein the printheads are configured such that at least one
of the layers may be printed with a first set of materials and at
least one other of the layers may be printed with a second set of
materials, and wherein the first and second sets are not the
same.
[0052] Preferably more than 100 layers are printed simultaneously
and more preferably about 1000 layers are printed
simultaneously.
[0053] Preferably pluralities of objects are simultaneously
printed.
[0054] When completed, the objects may have substantially identical
designs.
[0055] Preferably each of the layers that are at least partially
printed simultaneously is for at least one different object.
[0056] Each printhead may print part or all of a predetermined
layer.
[0057] Multiple layers of the same material may be printed
[0058] Multiple materials may be incorporated in each layer.
[0059] Preferably the printheads are inkjet printheads and more
preferably the printheads are fixed inkjet printheads able to
simultaneously print the width of the objects.
[0060] Droplets of material printed may be printed in a hexagonal
close-pack configuration or a face centered cubic
configuration.
[0061] In a fifth broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system including a plurality of printheads, the system
printing at least part of each of multiple layers simultaneously,
[0062] the system configured to enable at least one first printhead
that is initially configured to print at least part of a first
layer to be dynamically reconfigured to print at least part of a
second layer.
[0063] Preferably the at least one first printhead is dynamically
reconfigured if at least one of the at least one printhead
initially configured to print the second layer fails.
[0064] Preferably if a printhead initially configured to print the
second layer fails whilst printing the second layer, the at least
one first printhead is reconfigured to complete the printing of at
least part of said second layer.
[0065] In a sixth broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system including a plurality of printheads, the system
printing at least part of each of multiple layers simultaneously,
[0066] the system configured to enable at least one first printhead
that is initially configured to print at least part of a first
layer to be dynamically reconfigured to print at least part of a
second layer, and [0067] wherein if at least one printhead
initially configured to print the second layer fails whilst
printing said second layer, said at least one first printhead is
dynamically reconfigured to complete the printing of at least part
of said second layer.
[0068] Preferably the reconfiguration is made with no loss of
printed product.
[0069] Preferably the system includes a fault detection system that
automatically detects faults in said system and reconfigures said
at least one first printhead in the event of a failure.
[0070] In a seventh broad form the invention provides a three
dimensional object creation system that prints objects layer by
layer, the system including a plurality of printheads, the system
printing at least part of each of multiple layers simultaneously,
[0071] the system including semiconductor memory and [0072] wherein
data defining at least one layer is stored in the semiconductor
memory.
[0073] Preferably the data defining all of the layers is stored in
the semiconductor memory.
[0074] Preferably each printhead includes at least some of the
semiconductor memory and more preferably the semiconductor memory
of each printhead stores data relating to at least the part of the
layer printed by the printhead.
[0075] Preferably the semiconductor memory of each printhead stores
data relating to at least part of at least another layer and more
preferably the semiconductor memory of each printhead stores data
relating to at least part of the previous layer compared to the
layer currently being printed by the respective printhead.
[0076] The system may include more than 10 Gbytes of semiconductor
memory.
[0077] In a eighth broad form the invention provides a system that
executes a process, the system including a plurality of subsystems,
each of which performs a stage of the process, [0078] each of the
subsystems configured to perform one of a first subset of N.sub.1
of the stages, where N is greater than 1, and to change the stage
of the subset being performed on receipt of a change instruction;
[0079] wherein, in the event that one of the subsystems fails, at
least one of the remaining subsystems synchronously changes to
performing the respective stage of the failed subsystem without
requiring transfer of data relating the respective stage to the
said at least one remaining subsystems, and [0080] when a subsystem
changes to performing a different stage, the system reconfigures
the subsystem to be capable of performing a second subset N.sub.2
of the stages where N.sub.1 and N.sub.2 have the same number of
stages.
[0081] The system may be a pipelined system in which each stage is
dependent on the successful completion of all previous stages.
[0082] Preferably another subsystem is instructed to perform the
stage previously carried out by the first subsystem.
[0083] The reconfiguration may occur by way of replacement of a
component or, in preferred forms, by way of data transfer.
[0084] Preferably each stage is defined by a data set and each
subsystem stores a plurality of data sets. When performing a stage
the subsystem accesses the corresponding data set. To change the
stage being performed, the subsystem merely changes the data set
being accessed. Preferably when a subsystem changes the stage being
performed, the data set relating to the stage previously being
performed is replaced by data relating to a stage not already in
that subsystem's memory.
[0085] In preferred systems, when a subsystem fails, all subsequent
subsystems in the process change the stage being performed and,
when reconfiguration involves a transfer of data, preferably this
occurs as a pipelined data transfer.
[0086] In a ninth broad form the invention provides a printing
system including a least two printheads, wherein a first printhead
is actively maintained at a first temperature and a second
printhead is actively maintained at a second temperature.
[0087] Preferably the system is a three dimensional object creation
system that prints objects layer by layer, the system including a
plurality of printheads, the system printing at least part of each
of multiple layers simultaneously.
[0088] Preferably the first printheads is configured to eject a
metal and the first temperature is above the melting point of the
metal.
[0089] In a tenth broad form the invention provides a printing
system including a least two printheads, a first one of the
printheads printing a first material and a second one of the
printheads printing a second material, the first material being
cured by a first method and the second material being cured by a
second method and wherein the first and second methods are
different.
[0090] The first and second methods may include at least one method
selected from a group including: evaporative drying; freezing of
material ejected when molten; ultra violet curing; addition of a
curing agent.
[0091] The first and second methods may include printing of a
curing agent simultaneously or sequentially with the respective
material.
[0092] The first and second methods may include printing of a
curing agent selected from a group including: a catalyst; a
polymerization initiator; a compound that reacts with the
respective material.
[0093] The system may be a three dimensional object creation system
that prints objects layer by layer, the system printing at least
part of each of multiple layers simultaneously.
[0094] In a eleventh broad form the invention provides a printing
system including [0095] at least one printhead for printing
material to create a printed product, and [0096] an object
incorporation device that incorporates inorganic semiconductors
into the product being printed whilst the at least one printhead
prints the product.
[0097] The inorganic semiconductor may be an integrated
circuit.
[0098] The inorganic semiconductor may comprises silicon.
[0099] The inorganic semiconductor may comprise a Group III-V
semiconductor.
[0100] The inorganic semiconductor may comprises a discrete
device.
[0101] The inorganic semiconductor may be selected from a group
including: transistor; light-emitting diode; laser diode; diode or
silicon controlled rectifiers (SCR).
[0102] The system may be a three dimensional object creation system
and may be a three dimensional object creation system that prints
objects layer by layer, the system printing at least part of each
of multiple layers simultaneously.
[0103] In a twelfth broad form the invention provides a system that
prints three dimensional products, the system including [0104] at
least one object incorporation device that incorporates non-printed
objects into partially completed product, the non-printed objects
not being printed by the system.
[0105] The system may include at least one printhead for printing
material to create a printed product and operate so that
non-printed objects are incorporated into partially completed
product whilst the at least one printhead prints the product.
[0106] Preferably the non-printed objects are incorporated into
partially completed product without stopping the printing
process.
[0107] Preferably the non-printed objects are incorporated into the
partially completed product at a predetermined position and/or a
predetermined orientation on or in the product.
[0108] The system may print electrical connectors to electrically
connect the non-printed objects to other parts of the product.
[0109] The system may print at least part of each of multiple
layers simultaneously. More preferably the system simultaneously
prints objects layer by layer.
[0110] In a thirteenth broad form the invention provides a system
that prints three dimensional products, the system including [0111]
an object incorporation device that inserts non-printed objects
into a cavity created during the printing process, the object
incorporation device incorporating the non-printed object into the
cavity during the printing of the respective printed object.
[0112] Each cavity may be created with substantially the same
height as the non-printed object to be inserted into the respective
cavity.
[0113] Each cavity may be sized so that after insertion of the
object, the top of the non-printed object is substantially flush
with the surrounding material of the partially completed
product.
[0114] Each cavity may be shaped to maintain at least one of the
position and orientation of the non-printed object and preferably
both.
[0115] The shape of each cavity may substantially match the shape
of the non-printed object.
[0116] The system may print at least part of each of multiple
layers simultaneously. More preferably the system simultaneously
prints objects layer by layer.
[0117] In a fourteenth broad form the invention provides a system
that prints three dimensional products, the system including [0118]
at least one printhead that prints electrical connections to at
least one object incorporated in the products.
[0119] Preferably the at least one object does not include a
substrate.
[0120] A drop on demand printing subsystem preferably prints the
electrical connections.
[0121] The electrical connections are preferably printed with
molten metal.
[0122] The system may print at least part of each of multiple
layers simultaneously. More preferably the system simultaneously
prints products layer by layer.
[0123] It will be appreciated that the features of the various
broad forms of the invention may combined together in any
combination and are not limited to any one specific broad form.
BRIEF DESCRIPTION OF DRAWINGS
[0124] FIG. 1 shows a schematic side view of a production line
according to a first embodiment of the invention.
[0125] FIG. 2 shows a schematic side view of a production line
according to a second embodiment of the invention.
[0126] FIG. 3 shows another schematic side view of the production
line of FIG. 2.
[0127] FIG. 4 shows a schematic side view of the production line
according to a third embodiment of the invention.
[0128] FIG. 5 shows a schematic side view of a production line
according to a fourth embodiment of the invention.
[0129] FIG. 6 shows a schematic side view of a production line
including an object insertion device.
[0130] FIG. 7 is a plan view showing a number of voxels of the
preferred embodiments.
[0131] FIG. 8 shows a side view of the arrangement of layers of
voxels produced by preferred embodiments.
[0132] FIGS. 9a, b and c show plan views of an odd layer of voxels,
an even layer of voxels and an odd and even layer of voxels.
[0133] FIG. 10 is a diagram showing how each layer group stores
data relating to multiple layers of material in an initial printing
configuration.
[0134] FIG. 11 is a diagram showing the situation when a first
failure of a layer group has just occurred.
[0135] FIG. 12 is a diagram showing the logical arrangement of
layer groups after a first failure of a layer group when the layer
groups have been remapped.
[0136] FIG. 13 shows the transfer of data after remapping of layer
groups.
[0137] FIG. 14 is a diagram showing the situation when a second
layer group fails.
[0138] FIG. 15 is a diagram showing remapping of layer groups after
the second failure but before all data has been transferred.
[0139] FIG. 16 is a diagram showing the situation when a third
failure occurs before the data transfer relating to the second
failure has completed.
[0140] FIG. 17 is a diagram showing the next actions to accommodate
the second and third failures.
[0141] FIG. 18 shows the next stage in the fault recovery
process.
DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS
Basic Concept
[0142] FIG. 1 schematically shows a simplified production line 100
having many substrate width printheads 102. The printheads 102
print materials onto a moving substrate 104, that is preferably
moved at a substantially constant speed in a flat plane, as
indicated by arrow 106. The printheads 102 extend across the width
of the substrate 104 perpendicular to the direction of travel of
the substrate and are, preferably, spaced along the substrate 104
with substantially constant separations. However, as will be
explained later, constant separation of the printheads is not
critical.
[0143] The printheads 102 print one layer of an object onto the
previously printed layer. Thus the printhead 112 prints the first
layer 110, the second printhead 108 prints a second layer 114 onto
the first layer 110 and the N.sup.th printhead 116 prints an
N.sup.th layer 118 onto the (n-1).sup.th layer 119. For clarity
only one printhead is shown for each layer but in practice there
will be multiple printheads for each layer.
[0144] The layers are of a constant thickness and the printheads
are controlled so that, in plan view, layers are printed on top of
each other.
[0145] The distance from each of the printheads to the surface upon
which they print is also preferably the same for all printheads.
Thus the distance 122 from the first printhead 112 to the substrate
104 is preferably the same as the distance 124 from the seventh
printhead 126 to the sixth layer 128. This may be achieved by
sequentially raising the printhead(s) for each layer by the voxel
height. In this situation, droplets ejected by printheads for
different layers at exactly the same time will arrive at their
destinations at the same time.
Voids
[0146] A product may be produced with voids and/or cavities. These
voids may be utilized for location of separately created objects
that are inserted into the cavities during production. The cavities
may also be provided as fluid passageways or for other purposes and
remain `empty` of printed or inserted materials in the finished
product.
[0147] Cavities that have substantially vertical walls and a roof
can only have the roof printed where there exists solid material in
the cavity. Where an object is inserted, obviously the object
provides the solid surface onto which roof material may be printed.
Where the cavity is to be `empty` in the finished product, it is
necessary to provide a sacrificial material, such as wax, to
provide a solid surface on which the roof material may be printed.
The sacrificial material is then removed by further processing
after the roof has been formed.
[0148] It will be appreciated that many cavity shapes do not
require a sacrificial material and the roof may be closed up
gradually one layer at a time. Examples of such shapes include
ovals and circles, polygons having an odd number of sides, and
other shapes that do not have a horizontal roof portion
significantly greater than the voxel size.
[0149] FIG. 8 shows a product that has had a number of different
cavities or voids formed in various layers. A triangular cavity 830
has been formed that spans 5 layers. As can be seen, printing
successive layers with a smaller opening may close the cavity. The
cavity 830 may extend as a passageway through the product and may
extend vertically and/or longitudinally, not just transversely.
FIG. 8 also shows cavities 832, 834 and 836 that are formed by not
printing in a single layer. Cavity 836 is shown partially completed
and, in cross section has a diamond shape. When the fifth layer is
completed, the cavity will be closed.
[0150] It will be appreciated that the drawing is not to scale and
in practice cavities may extend for 10's of voxels in either the
transverse or longitudinal direction and may also extend for 10's
of layers.
Multiple Materials
[0151] Whilst a system that only prints one material is within the
scope of the invention, to produce functional products made of many
different materials, the ability to print several different
materials on a layer is required. In preferred embodiments this is
achieved by providing multiple printheads for each layer, with at
least one printhead printing a different material compared to the
other printheads provided for that layer.
[0152] Referring to FIG. 2 there is schematically shown a digital
additive manufacturing system 200 for simultaneously creating
multiple multi-material products, one layer at a time. For clarity
some components are omitted.
[0153] The products printed simultaneously may all be of an
identical design or may be of different designs, depending upon
data supplied to the printheads. Different designs of products may
be printed side by side and/or end on end or on top of each other.
Products may be printed on top of each other using sacrificial
material(s) as separating layer(s).
[0154] The system 200 includes a conveyor or substrate 202 that is
caused to move at a substantially constant velocity as indicated by
an arrow 204. The substrate 202 may be directly driven or may be
located on a conveyor system, not shown. The substrate 202
preferably moves in a flat plane. Movement along a non-flat plane
is also possible. A continuous substrate is preferred as this
ensures a consistent velocity past all the printheads. However
because discrete objects are created, a series of discrete carriers
could be conveyed past the printheads.
[0155] Located above the substrate 202 and spaced apart form each
other are a series of "layer groups" 206 of printing devices. Each
layer group 206 includes m printheads 208, which extends
transversely across the substrate 202 perpendicular to the
direction of travel of the substrate. There may be more than one
printhead in each layer group; for a typical system there will be
an average of around eight printheads in each layer group. For
clarity the drawings only show four printheads in each layer group.
There is no theoretical limit to the number of printheads in each
layer group. In the embodiment of FIG. 2 the layer groups are
identical to each other.
[0156] The materials printed by the printheads may include
different polymers, different colored polymers, metals, sacrificial
materials such as wax, various evaporative drying materials and
various two part compounds. A suitable metal that may be used is
indium, which has a melting point of 156.degree. C. Alloys of
Indium and Gallium may be used, with melting points below
156.degree. C. It will be appreciated that other metals or metal
alloys may be used. The ability to print metal enables high
conductivity electrical connections to be printed. Polymers having
melting points in the range of about 120.degree. C. to 180.degree.
C. are preferred, but other polymers may be used. Sacrificial waxes
having a melting point of above 80.degree. C. are preferred. Other
compounds may be printed.
[0157] The layer groups 206 are spaced apart along the longitudinal
direction in which the substrate 202 moves. The spacing of the
layer groups 206 from each other is preferably substantially
constant but this is not essential. The layer groups 206 are spaced
vertically from the substrate 202 and this vertical separation
preferably increases stepwise with each layer group in the
longitudinal direction by .beta. for each layer group. Thus, the
m.sup.th layer group will preferably be .beta.(m-1) further away
from the substrate 202 than the first layer group, where .beta. is
the increase in vertical separation per layer group. The value of
.beta. is preferably at least the voxel height .alpha.,
approximately 10 microns. The step value may be greater than the
voxel height a but in most embodiments cannot be less than the
voxel height. A value greater than a merely results in the
printhead to printing surface increasing. A value less than .alpha.
may result in products contacting the printheads unless the initial
vertical spacing is sufficiently large. However, in practice the
printhead to surface distance is significantly less than the
finished product height. So .beta. needs to be the same or greater
that the voxel height .alpha.. The printheads of each layer group
are preferably the same distance from the substrate so that they
may be synchronized to a single clock and so preferably .beta. is
equal to .alpha.. Variations in vertical position of individual
printheads in each layer group may be compensated for by adjusting
when each of the printheads operate.
[0158] As the substrate 202 moves in the direction of arrow 204,
all of the layer groups operate simultaneously, so that each layer
group lays down a single layer of material or materials of the
products being created. By simultaneously we mean the printheads
operate at substantially the same time; we do not mean that the
printheads eject material at exactly the same time. In fact,
because the printheads of a single layer group are spaced along the
path of travel, by necessity they must eject material at different
times.
[0159] The first layer group 210 prints material directly onto the
substrate 202 to form a first layer 211. Thus as the substrate
passes under the second layer group it will already have material
printed by the first layer group. Thus the second layer group 212
prints a second layer of the object onto that first layer. In
normal operation each layer group prints a layer onto the layer
printed by the previous layer group so that the n.sup.th layer
group 214 prints an n.sup.th layer 216 of the object.
[0160] If the spacing of the layer groups along the substrate is
constant and a single type of object is being produced, the front
edge of all the objects being simultaneously created by the
production line will pass under the first printhead of each layer
group at the same time. If the distances between the first
printhead of each layer group and the surface upon which material
ejected by that printhead are substantially identical, then the
time that material spends traveling from the printhead to the
deposition surface is also the same between the layer groups. Thus,
the layer groups may be synchronized to run off a single clock
without, in normal use, the need for delays in the clock cycles
between layer groups. As will be explained later, the system is
designed to operate with variations with longitudinal spacing
between adjacent operating layer groups and constant longitudinal
spacing or vertical rise is only preferred and is not always
critical.
[0161] To maintain a substantially constant step height between
layer groups, the printheads of the layer groups may be mounted
directly or indirectly on two longitudinally extending support
beams. Assuming the beams are substantially straight, for a
production line of 1000 layer groups, raising the downstream end of
the beams 1 cm compared to the upstream ends will result in a step
height for each layer group of 10 micron, assuming there is a
constant spacing between the layer groups and the layer groups are
all the same size in the longitudinal direction. Where there are
multiple printheads in a layer group the printheads may be mounted
individually to the beams or may be mounted on a common carrier
with the carrier mounted on the beams. Mounting the printheads of
each layer group on a common carrier allows the printheads to be
more easily located substantially in a single plane. In use the
plane is also preferably substantially parallel to the substrate.
This allows the printheads of a layer group to have a common
printhead to printing surface distance where the substrate moves on
a plane. The use of a common carrier also allows the printheads of
a layer group to be assembled on the carrier away from the
production line with the longitudinal spacing between printheads
accurately controlled. Location of the printheads on the beams then
merely requires accurate location of the carrier. Replacement of a
failed layer group is also easier.
[0162] The multiple printheads of each layer group are for printing
a single layer but they are spaced apart from each other. Referring
to FIG. 2, material 218 printed by the m.sup.th printhead 208m may
need to be printed adjacent to material 220 printed by the first
printhead 208a of a layer group. This is achieved by delaying
printing of voxels by the m.sup.th printhead 208m compared to those
printed by the first printhead 208a. This time delay corresponds to
the time the substrate 202 takes to move from the first printhead
208a to the m.sup.th printhead 208m, i.e. the separation of the
printheads divided by the speed of the substrate 202. Since both
the substrate speed and the longitudinal separation of printheads
in a layer group may vary, the time delay is not necessarily
constant. This may be due to temperature variations, variations in
location of printheads and other factors. Accordingly the system
may include sensors that feed data such as temperature, substrate
speed or printhead separation into the timing circuits.
Print Temperatures
[0163] Each of the different materials used may require different
printing and/or post printing processing temperatures compared to
the temperatures required for the other materials. The actual
printing temperatures and post printing processing temperatures
depend on the materials used and so it is conceivable that a multi
material production line could run at one temperature, albeit
unlikely. It also follows that not only must the materials used
must be compatible with the other materials during printing,
processing and in the finished product, but that the printing and
processing temperatures must be generally compatible.
[0164] FIG. 3 shows the production line of FIG. 2 but indicating
print temperatures.
[0165] The printheads of each layer group 206 may print several
different materials, typically materials that are heated above
their melting points. Accordingly, one printhead may print indium
metal at a temperature of 180.degree. C. Sacrificial wax having a
melting point of about 80.degree. C. or lower may be printed by
another printhead to enable the formation of voids. If both indium
and wax are printed, the evaporative temperature of the wax will
need to be below the melting point of indium (156.degree. C.). If
the evaporation temperature of the wax were above 156.degree. C.,
when the product is heated to evaporate the wax, the indium metal
would melt. Accordingly, a wax with an evaporative temperature
below 156.degree. C. (or the lowest melting point of all other
materials used) must be used. The wax also cannot be heated to
180.degree. C. for printing, as at that temperature it is a vapor.
Accordingly, the printhead printing the wax will need to be at a
temperature of about 80.degree. C. whilst the indium printhead will
need to be at about 180.degree. C. Similar considerations apply
when printing materials that are printed in solution and the
solvent evaporates to "cure" the material. These materials may well
be printed at room temperature.
[0166] FIG. 3 shows the first printhead of each layer group, such
as printhead 208a, prints a first material M.sub.1 at a temperature
T.sub.1. The second printhead of each group, such as printhead 208b
prints a second material M.sub.2 at a temperature T.sub.2, etc. The
m.sup.th printhead of each group, such as printhead 208m prints
material M.sub.m at temperature T.sub.m. Some of the values of
T.sub.1 to T.sub.m may be the same.
[0167] Whilst reference is made to the melting point of other
materials, it will be appreciated that some materials, either
before or after printing or curing, may undergo undesirable
temporary or permanent changes if raised about certain
temperatures. If so, the system needs to be configured to avoid
subjecting those materials to temperatures above the relevant
thresholds.
[0168] The temperatures of the materials printed and the
temperature of the exposed layer needs to be maintained within
ranges. The concept of the invention hinges on voxels bonding to
adjacent voxels to form a product of acceptable strength and
durability. Thus, for instance, a droplet of indium metal may be
printed onto a voxel of indium metal or a plastics material. The
droplet of indium will need to be heated to a temperature
sufficiently above its melting point so that it may melt part of
the indium upon which it lands to forming a good mechanical and
electrical bond. However, the indium should not be so hot that it
melts too much of the material that it contacts or otherwise
irreversibly changes the material that it contacts. It will be
appreciated that the requirements for good bonding and avoiding
damage to previously printed material can be accommodated by
adjusting the temperature of material being printed and the
temperature of the material that has been printed, as well as by
appropriate selection of materials.
Curing Methods
[0169] Different materials printed by the system may require a
number of different curing techniques. Two or more materials
usually share a drying/curing technique. FIG. 4 also schematically
shows a number of different curing techniques.
[0170] Curing requirements include simple cooling to cause a
material to solidify, evaporative drying, precipitation reactions,
catalytic reactions and curing using electromagnetic radiation,
such as ultra violet light.
[0171] The materials of each layer need to be cured to a sufficient
degree to be dimensionally stable before the materials of the next
layer are deposited. Preferably the materials are fully cured
before the next layer is deposited but need not be. For example a
material printed as a hot melt may have cooled to be sufficiently
`solid` to allow the next layer to be printed whilst not being
fully solidified. Examples include materials that do not have a
specific melting point but solidify over a temperature range.
[0172] Curing may occur after all materials in a layer have been
printed or may occur at different stages. Thus, in some
embodiments, each layer group may include one or more mechanisms
for effecting curing of the materials printed that are located
between printheads of each group.
[0173] FIG. 4 shows two layer groups of n layer groups of a system
400. The first layer group 402 has four printheads 402 a, b, c
& d requiring two different curing methods. The second layer
group 404 has m printheads printing m materials requiring j
different curing methods. Disposed within the printheads are curing
mechanisms for carrying out appropriate curing methods. The
printheads are preferably arranged so that materials requiring the
same curing method are grouped together upstream of a single
corresponding curing mechanism.
[0174] The materials 403a, 403b of printheads 402a and 402b require
a first curing method and are located upstream of curing mechanism
406, which carries out curing of materials 1 and 2 as they pass
underneath. The materials 403c and 403d printed by printheads 402c
and 402d share a second curing method and so are preferably grouped
together upstream of curing mechanism 408. Thus the materials
printed by printheads 3 and 4 may be cured as they pass under
curing mechanism 408.
[0175] Similarly, the second layer group 404 has materials that
require three different curing methods. Printheads 404a and 404b
print materials 405a and 405b that require curing by the first
curing method and are located upstream of curing mechanism 410. The
third and fourth printheads 404c and 404d print third and fourth
materials 405c and 405d that are cured by curing mechanism 412.
Finally, the fifth to m.sup.th printheads print materials that
require a j.sup.th curing method, which is effected by the curing
mechanism 414.
[0176] By grouping the printheads of materials that share common
curing techniques together, only a single curing mechanism for each
curing method is required in each layer group. Whilst this is
preferred, there is nothing to prevent an arrangement where one
curing method is carried out by more than one curing mechanism in
each layer.
[0177] It will be appreciated that curing methods may conflict and
so the order of printing within each layer group will require
consideration to ensure a curing method does not adversely affect
other materials already printed, whether cured or uncured.
[0178] In some circumstances all curing devices may be located
between layer groups.
[0179] Examples of curing methods include, but are not limited to,
the following [0180] Evaporative drying. [0181] Freezing of ejected
material. [0182] Ultra violet initiated curing using U.V. lamps.
[0183] Printing of reagents.
[0184] Printing of catalysts or polymerization initiators.
Evaporative Drying.
[0185] Evaporative drying may be assisted by passing a hot or dry
(solvent depleted) gas over the material, applying a vacuum or low
gas pressure to the material or by heating, such as by infrared
radiation or combinations of these. It will be appreciated that by
`dry` gas we mean gas that has a relatively low partial vapor
pressure of the relative solvent, whether that solvent is water,
alcohol, another organic solvent, an inorganic solvent, etc.
Freezing of Ejected Material.
[0186] Freezing of ejected material that has been heated above its
melting point is applicable to metals, polymers and waxes. Cooling
may rely on conduction and/or radiation of heat only or may be
enhanced by blowing of cold gas over the layer or any other method
of forced cooling to speed heat removal. Since the preferred
production line has of the order of 1000 layer groups, conduction
and radiation alone will not usually allow sufficient heat loss and
so forced cooling will be required in most situations. As each
layer needs to be cooled, gas(es) will normally be caused to move
transversely across the objects. Cooling gases may be introduced on
one side of the system and caused to flow across the object to the
other side. Alternatively gas may be introduced above the objects
and caused to flow to both sides of the object. It will be
appreciated that these are examples and other systems for gas flow
may be utilized. It will be understood that `cold` is relative and
the gases used may be at or above ambient temperature.
[0187] Where gas is passed over the layer, either for evaporative
drying or for freezing, it will be appreciated that the gas will
need to be compatible with the material or materials being cured.
Where metals are printed, the metal droplets will, generally, need
to fuse with adjacent metal droplets, either in the same layer or
in adjacent layers. As such an inert gas, such as nitrogen, will be
needed for cooling so as to avoid oxidation.
[0188] In most circumstances material ejected as hot melt needs to
be cooled not only below its freezing temperature but also to the
freezing temperature of all the materials printed. Potentially any
of the materials may be printed next to or on top of any other
material. As an example, indium metal may be printed in part of one
layer and the next layer may have sacrificial wax printed onto the
indium metal of the earlier layer. Whilst the indium could be
cooled to about 150.degree. C. to be frozen, this would be too high
for a sacrificial wax with a melting point of about 80.degree. C.
Thus, the indium would need to be cooled to below 80.degree. C. in
this case before reaching the next layer group. In addition,
sacrificial wax may be printed in the same layer and adjacent to
indium metal. In this case the indium metal would need to be cooled
below the melting point of the wax before reaching the wax
printhead of the same layer group. It will be appreciated that a
first voxel of material may be heated by a nearby second voxel even
though the two voxels are not in physical contact with each other.
Whilst wax has been used as an example of a material having a low
melting point, it will be appreciated that the above discussion is
applicable to all materials.
[0189] The effect of high temperatures is not limited to possible
melting. High temperatures may also affect materials that are cured
by other methods, such as evaporation, catalytic reactions or
polymerization reactions.
[0190] It follows from the above discussion that, in most
situations, materials that require a high processing temperature,
whether due to being printed as a hot melt or due to post printing
processing, will need to be printed, processed and cooled to an
acceptable temperature before printing of potentially affected
materials in the same layer, not just in the next layer.
Ultra Violet Initiated Curing Using U.V. Lamps.
[0191] Ultra violet curing may be used with U.V. cured polymers. To
achieve rapid curing high intensity U.V. lamps may be used. To
avoid overheating forced cooling by passing cooled gas may also be
required.
Printing of Reagents and Catalysts or Polymerization
Initiators.
[0192] Reagent printing includes printing of two part polymers or
mixtures in which a precipitation reaction occurs. This may require
special printheads to print the two compounds simultaneously or the
use of two, preferably adjacent, printheads, that each print one of
the compounds. Similarly, use of catalysts or polymerization
initiators requires printing of the material and a catalyst or
polymerization initiator. Thus, again, special `dual` printheads or
two printheads may be required for each such material.
[0193] Where a solid material is produced by use of catalysts,
polymerization initiators, two part polymers, precipitation
reactions or other mechanisms that require two separate components
to be printed separately, the two components may be printed to the
same location or may be printed to adjacent locations with mixing
occurring through contact of adjacent voxels. It will be
appreciated that with two part compounds, one of the compounds,
such as a catalyst, may be required in much smaller qualities than
the other compound.
[0194] It will appreciated that there may be cases where more than
two precursors are printed to form one `finished` material.
[0195] Printing of two or more different materials to the same
location results in more homogeneous voxels of the end material,
but requires greater accuracy than printing to adjacent
locations.
Reduced Capability
[0196] Whilst a production line having identical layer groups
provides maximum flexibility, for many products this is not needed.
For example, many products have a plastic shell. Thus, for example,
the first few hundred layers may only require a single material
forming the base of the shell. Thus the production line may
dispense with printheads that are effectively redundant, so
reducing complexity, size and overall cost of the production line.
Accordingly some of layer groups may have a reduced number of
printheads.
[0197] FIG. 5 shows the first nine layer groups 506 to 522 in a
system 500 having n layer groups.
[0198] The first four layer groups, 506 to 512, only have one
printhead whilst the fifth, sixth and seventh layer groups 514, 516
& 518 have two printheads each. The printheads of each pair
print a different material to that printed by the other printhead
of the pair. The eighth layer group 520 has four printheads,
printing four different materials whilst the ninth layer group 522
has two printheads, again printing two different materials. It will
be appreciated that the number of printheads in other layer groups
does not necessarily dictate the number of printheads in a layer
group.
[0199] The materials printed by each multi-material capable layer
group may be the same or different from each other. Thus, for
example, the fifth and sixth layer groups, 514 & 516, have
printheads 514a and 516a that print material M.sub.1 and printheads
514b and 516b that print a third material M.sub.3.
[0200] The seventh layer group 518 has a printhead 518a that prints
a second material M.sub.2 and a printhead 518b that prints an
n.sup.th material M.sub.n. Printheads 520a, b, c & d of layer
group 520 print materials M.sub.1, M.sub.2, M.sub.3 and M.sub.n,
respectively.
[0201] Whilst FIG. 5 shows layer groups at the start of the
production line having a reduced number of printheads compared to
the maximum number of materials printed, it will be appreciated
that any layer group in the production line may be limited to
printing less materials compared to the maximum number of materials
that are able to be printed by the system.
Insertion of Objects
[0202] At this stage, because the present minimum resolution is
about 10 micron, it is not possible for the system to print all
required components of a product. Some components may require finer
resolution, such as high-speed semiconductors.
[0203] FIG. 6 schematically shows a production line 600 including a
robot 602 for insertion of objects into the products being printed.
For clarity the vertical and horizontal scales are exaggerated.
[0204] The robot 602 has a supply 606 of objects 604 to be
inserted. The robot 602 takes one object at a time and accelerates
the object 604 horizontally to travel at the same speed as the
conveyor. The object 604 is then moved vertically to be inserted
into a cavity 608 previously printed in the product. The cavity 608
is a close fit for the object 604 being inserted and alignment of
the object with the cavity is preferably achieved using vision
systems. The cavity is preferably sized so that the top of the
object does not protrude above the top layer of the object.
[0205] Whilst the drawing shows a cavity five voxels high by nine
voxels long, this is not to scale. Typically, objects to be
inserted have dimensions of the order of millimeters, not microns.
A typical object may have a size of 5.times.5.times.1 mm
(L.times.W.times.H) i.e. 5000.times.5000.times.1000 microns. Whilst
a height of 1 mm may seem small, the clearance between the top
layer of the product and the printheads is typically also only
about 1 mm. Thus, an object placed on the top layer rather than in
a cavity may not clear downstream printheads. Additionally, if the
object extends above the top layer, this may cause unpredictable
airflows and cause unintended displacement of drops subsequently
printed. By inserting, the object into a cavity having a depth at
least as great as the object's height, the highest point of the
object is flush or below with the top of the product and so does
not cause any unexpected results.
[0206] Preferably the cavity is sized so that the object is
securely and correctly located in the cavity. Placing the object in
a cavity also reduces the risk that the object may be moved
unintentionally, which may occur if it were placed on the top
surface. The outline of the cavity preferably matches the object.
Thus, preferably, a rectangular object will be received in a
rectangular cavity. However, it will be appreciated that this is
not essential. The object may be received in a cavity that holds
the object in position but does not have a shape that matches the
object's shape. For example, a rectangular object could be located
in a triangular cavity, so providing free space about the object.
The cavity may be shaped and configured to provide one or more
channels or passageways to other locations within the product or to
the outside of the product. Thus, for instance, a semiconductor
chip may be located in the product and provided with one or more
cooling channels, ducts or passageways that extend to the outside
of the finished product.
[0207] Key types of objects to be inserted typically include
integrated circuits such as main processors, memory etc. Whilst it
is possible to use package chips it is better to use bare dies for
cost, size and weight reasons.
[0208] Preferably known good dies (KGD's) are used. Semiconductor
that may be inserted include but are not limited to transistors;
light-emitting diodes; laser diodes; diodes or SCR.
[0209] As mentioned previously, one of the materials that may be
printed is indium. Another material that may be printed is an
insulator, and accordingly it is possible to print insulated
electrical `wires` 610, 612 & 614 in the product. This may be
carried out both before or after insertion of the device into the
cavity. Whilst the drawing is not to scale, the electrical wires
may have a thickness of 10 to 20 microns, i.e. one or two voxels.
Wires may be placed in the order of 30 microns from each other and
so many millions of wires may be printed in relatively small
volumes.
[0210] Where electrically active devices are inserted, the devices
are preferably inserted with the bond pads 616 facing upwards as
this makes the forming of good quality electrical connections much
easier. With upward facing bond pads, electrical connections may be
formed in the next few layers to be printed. In contrast, bond pads
on the bottom or sides of the object will rely on correct placement
of the object and good contact.
[0211] The device to be inserted may be cleaned by the insertion
robot and the printing may occur in a nitrogen atmosphere, or a
partial or high vacuum. The bond pads may be plated with indium
metal such that when indium is printed onto the bond pads the
indium on the bond pad melts forming a good electrical
connection.
[0212] Once the device has been inserted, downstream layer groups
may then print electrical connections. FIG. 6 schematically shows
four downstream layers part-printed on the object and showing three
electrical connections 610, 612 & 614 printed in upper layers
to join two objects 604a & 604b together. It can also be seen
in FIG. 6 that earlier layers include metal voxels forming
electrical wire 618.
[0213] The invention is not limited to insertion of electrical
devices. Mechanical devices may also be inserted.
Typical System Characteristics
[0214] The following characteristics relate to the preferred
embodiments that utilize MEMS inkjet type printheads as referenced
in the aforementioned specifications.
Voxels
[0215] The building block of the printed object is a voxel. In the
preferred embodiment planar layers are printed that have the same
dimensions and voxels all of the same dimensions. Most preferably
the voxel centers have a hexagonal close pack arrangement.
[0216] In the preferred embodiments the voxels 710 have a side
length 712 of 6 microns, as shown in FIG. 7. The height of the
voxels is nominally 10 micron. This provides a resolution that is
typically 10 times higher than existing systems in each direction,
giving a voxel density typically 1000 times greater than existing
systems. A corresponding nozzle of a printhead prints each voxel
and so the nozzles of the printheads have corresponding spacing.
One or more in rows of voxels 710 are printed by each printhead,
with each row extending across the substrate, ads indicated by
arrow 716. Rows are printed side by side along the substrate, as
indicated by arrow 718. The nozzle pitch 720 is 9 micron, whilst
the row spacing 722 is 10.392 microns
[0217] Each drop of liquid material printed may be treated as a
sphere, which in the typical system has a diameter of about 12
microns. When in position and after becoming solid, each drop forms
a voxel, with a shape approximating a hexagonal prism with a height
of .alpha., the layer height, which in a typical system is about 10
microns.
[0218] The voxels may be printed in a face centered cubic
configuration or in a hexagonal close packed configuration. These
configurations have a number of advantages, including increased
resistance to crack propagation, smaller voids between drops, and
lower resistance of printed conductive lines. Other voxel
configurations are possible, with corresponding voxel shapes.
[0219] FIG. 8 shows a substrate 810 with a number of layers having
been printed is shown. The voxels of even layers 811, 813, 815 and
818 are offset longitudinally by half the voxel spacing relative to
the voxels of odd layers 810, 812, 814 and 816. This results in the
voxels having a hexagonal arrangement in side view. The number of
printheads per layer does not affect the voxel configuration and
for clarity only one printhead per layer group is shown.
[0220] To achieve the longitudinal offsetting of the voxels 820,
the spacing of the printheads 822 in the longitudinal direction is
preferably the same between all layer groups and is more preferably
an integral number of voxels plus half a voxel. This separation is
not critical and it is possible to achieve this half voxel
longitudinal offsetting of the printed layers by adjusting when
each printhead ejects ink or by a combination of physical
offsetting and timing adjustment.
[0221] The preferred printhead utilizes two rows of nozzles to
print a single "row" of voxels. The nozzles for odd drops or voxels
are located in one row and the nozzles for even drops or voxels are
located in another, parallel, row. The two nozzle rows are spaced
half a voxel apart transverse to the row direction and are
staggered half a voxel parallel to the row direction so that when
printed a "row" of odd and even voxels is not a straight line but a
zigzag line. FIG. 9a shows a single "row" 901 shaded for clarity.
If we assume the printed droplets assume a hexagonal shape in plan
view, continuous printing of rows can result in total tiling of the
surface with drops. It will be appreciated that other printhead
configurations are possible. The main requirement is that, when
printed, the droplets can form a substantially continuous
layer.
[0222] FIGS. 9a, b and c show how, in preferred embodiments, odd
and even layers of materials are deposited relative to each other.
For ease of reference, a reference mark 900 is shown to indicate
relative positions. Referring to FIG. 9a, the odd layers 902 are
all printed with no "offset". All even layers 904 are printed with
a constant offset, relative to the odd layers 902. The even layers
are offset by half a voxel in the transverse direction, as shown by
numeral 906 in FIG. 9b. The even layers are also offset half a
voxel in the longitudinal direction, as shown by numeral 908 in
FIG. 9b. The resulting relative positioning of an odd and even
layer is shown in FIG. 9c. This results in each voxel being offset
half a voxel in both the x and y directions. Whilst it is preferred
that offsetting occurs in both the longitudinal and transverse
direction, it will be appreciated that the voxels may be offset in
only one of the longitudinal or transverse directions.
[0223] Transverse offsetting can be achieved by offsetting the
printheads. Thus printheads for odd layers can be offset half a
voxel transversely relative to printheads for even layers.
[0224] Whilst it is preferred that the physical offsetting of the
printheads in the longitudinal and vertical direction is constant,
variations in both directions can be adjusted for by adjusting when
the individual printheads eject ink relative to the others.
Printhead and Layer Group Construction
[0225] A typical system is preferably capable of producing objects
having up to eight different materials and, accordingly, will
preferably have eight printheads per layer group.
[0226] Each printhead of a typical system has a printable width of
295 mm, although this may be more or less, as desired. Each
printhead includes sixteen printhead chips arranged end on end,
with an effective length of 18.4 mm. To increase printing speed
each printhead preferably prints two rows of material
simultaneously, thus requiring two rows of nozzles. In addition,
two additional rows of nozzles are provided for redundancy.
Accordingly, each printhead and printhead chip is provided with
four rows of nozzles.
[0227] Each printhead chip prints 2048 voxels per row and so each
printhead chip has 8192 nozzles and each printhead has 131072
nozzles.
[0228] Where each layer group has eight separate printheads this
requires 128 printhead chips per group and so there are a total of
1,048,576 nozzles per group.
[0229] With a layer height of 10 microns, a typical system requires
1000 layer groups to produce an object 1 cm high and so requires
8000 printheads, 128000 printhead chips and provides 1,049 million
nozzles.
Print Speed
[0230] The nozzle refill time of a typical printhead nozzle is
about 100 microseconds. With two rows of material printed
simultaneously by each printhead, this provides a printed row rate
of 20 kHz. At a row spacing of 10.392 micron in the longitudinal
direction this allows a substrate velocity of 208 mm per second.
Thus, for example, the system can produce an object 30 cm long
about every 1.5 seconds.
[0231] With a print width of 295 mm this provides a maximum print
area of 61 296 mm.sup.2/sec and a maximum print volume (at 10
micron voxel height) of 612963 mm.sup.3/sec per layer, assuming no
voids. For a 1000 layer system this is a total of 0.613 liter/sec.
It will be appreciated that in a multiple material object, most
layers will be made of different materials. Thus, whilst the
maximum volume rate will be this value, each printhead will not be
printing at the maximum rate.
Memory
[0232] In the preferred embodiments we have a system that may
require up to about 98 Gbytes of data. Since we have all the layers
of a defined product(s) being produced simultaneously, all of that
data is being accessed effectively simultaneously. In addition, the
data is being read repetitively. Assuming a product size of about
450 mm longitudinally, each and every layer is printed about every
2.sup.1/2 seconds and so the relevant data needs to be accessed
every 2.sup.1/2 seconds. For shorter layers, the data is read more
frequently.
[0233] The quantity of data and the need to access the data
simultaneously and continuously means that, with present
technologies, it is not practical to store the data in a central
location and/or to use disk drives to store the data that is
accessed by the printheads. If disk drives were used they would be
used continuously and be a major risk of failure. To provide disk
redundancy would also result in unnecessary complexity. As solid
state memory has no moving parts, its failure rate is much lower.
Accordingly, in the preferred embodiments the data is stored in
solid state memory and this solid state memory is distributed
across the layer groups of the system. Each layer group stores data
relating to the layer currently being printed by that layer group
in memory located on or in the layer group. Once the necessary data
has been downloaded to the layer groups, they do not need to access
an external source of data, such as a central data store. By
incorporating the memory in the layer group, and more preferably in
printheads or printhead chips, high speed access to the data for
each and every layer group is readily provided "internally". In the
typical system each layer group normally prints one layer
repeatedly and so, at a minimum, only needs to access the data for
one layer at any one time. In preferred embodiments each layer
group also stores data relating to other layers, for fault
tolerance, as will be discussed later.
[0234] The memory used is preferably Dynamic Random access Memory
(DRAM). Currently available DRAM provides sufficiently fast read
access to meet the requirements of the system. In the preferred
embodiments this memory is located on each printhead.
[0235] In the preferred systems each printhead is constructed of
sixteen printhead chips and those printhead chips each have 4096
active nozzles. Each printhead chip is provided with 256 Mbits of
DRAM to define the relevant portion of the layer to be printed, or
64 Kbits per nozzle. If we allow 2 Kbits to define the layer and
the specific material we have approximately 62 Kbits for voxel
locations per nozzle. Thus we can specify up to about 63,000
(62.times.1024) locations longitudinally. With a longitudinal size
of each voxel of 10.392 micron this equates to a maximum product
length of about 660 mm. This does not allow for redundancy or other
overheads that may reduce the available memory and so the maximum
number of locations.
[0236] Thus, a printhead having 16 printhead chips has 4096 Mbits
of DRAM and with 8 single material printheads per layer group, each
layer group has 32,768 Mbits of DRAM. A production line having 1000
layers groups thus has 32,768,000 Mbits or 4096 Gbytes of DRAM.
Whilst this is a significant amount, the cost is relatively low
compared to the productivity possible with the system.
[0237] It will be appreciated that the total amount of memory
provided is dependant on the total number of different materials
used and the maximum size of objects to be produced. Whilst the
transverse length of the printheads limits the size of objects in
the transverse dimension, there is no limit on the size of objects
in the longitudinal direction. The maximum size is limited by the
memory provided which is also the maximum amount of memory
required. When defining a voxel in the product, the material in the
voxel and the layer in which it occurs needs to be specified.
However, it is possible to dispense with this data at the printhead
level. In the typical system each printhead only prints one
material in only one layer. If the printhead only stores data
relating to voxels that it prints, the data specifying the layer
and material is redundant. Thus, potentially, the amount of data
stored per printhead may be reduced. However, as set out above,
this saving is relatively negligible.
Data Rate
[0238] Each printhead chip operates at 100 KHz, prints two rows of
voxels each of 2048 nozzles and so requires a data rate of 39
Mbits/second so (4096 nozzles at 100 KHz). This is well within the
capabilities of currently available DRAM. This results in data
rates of 625 Mbits/second for each printhead, 5000 Mbits/sec for
each layer and 5,000,000 Mbits/sec (or 625 Gbytes/sec) for the
entire production line. It is thus quite impractical at present to
have a central data store and to pipe the data to the individual
printheads. It will be appreciated that if future developments
allow sufficiently high data transfer rates to be practicable, one
or more centralized data store(s) may be used as the source of
print data, rather than relying on distributed memory residing on
the printheads or printhead chips themselves.
[0239] A central data store defining the products(s) is required
but the data from that store only needs to be downloaded to the
individual layer groups, printheads or printhead chips when the
product(s) being produced change, either totally or when modified.
Whilst the system may require of the order of 4096 Gbytes of memory
in the layer groups, this transfer does not need to be
"instantaneous" as changes will be downloaded when the system is
not operating.
Fault Tolerance
[0240] In a system with approximately 1000 layer groups, 8
printheads per layer group, 16 printhead chips per printhead and
2048 nozzles per printhead chip, there will be about 1 billion
nozzles. As such, it is expected that spontaneous failures will be
a regular occurrence. It is not practicable to stop the
manufacturing process to replace failed printheads, as this will
require scrapping of all partially completed products on the
conveyor. Thus, a 1000 layer manufacturing line may lose thousands
of products every time the system unexpectedly stops. The number of
products on the production line depends on product size, product
spacing on the conveying system and the spacing of layer groups.
Planned stoppages do not result in scrapping of product as each
layer group, commencing with the first, may be sequentially turned
off to stop producing products.
[0241] There are two primary levels of fault tolerance that aim to
prevent unexpected stoppages. One is within the printhead itself
and one is between layer groups.
Printhead Fault Tolerance
[0242] Each printhead provides a level of fault tolerance. In the
preferred embodiments in which stationary printheads are used, the
printhead chips are provided with redundant nozzle arrays. If a
nozzle fails, a corresponding nozzle in one of the redundant nozzle
array(s) may take up its function. However, since the printheads
are fixed, each nozzle prints at the same transverse location and
can only be replaced by one or more specific redundant nozzle(s).
In a printhead with one set of redundant nozzles, each row location
can only have one failure before the printhead becomes unable to
correctly print material at all locations. If a nozzle fails, the
corresponding redundant nozzle replaces it. If that `redundant`
nozzle then fails, it cannot be replaced and so the entire
printhead would be considered to have failed. Whilst the preferred
embodiments only have one redundant nozzle for each location, more
than one set of redundant nozzles may be provided.
[0243] It will be appreciated that in a multi-material system each
printhead does not necessarily print a full row. This depends on
the product or products being printed. Thus many printheads will
only utilize some of the printhead nozzles when producing products.
The status of unused nozzles is not relevant to the ability to
correctly print the current product and so the printheads may be
configured to determine from the product data relating to the layer
being printed which nozzles need to be tested both before printing
and whilst printing is occurring.
[0244] For fault tolerance reasons, as discussed later, a printhead
may need to keep an inventory of failed but unused nozzles, as
these nozzles may be needed if the layer group needs to print
another layer. Thus at initialization, each printhead may test all
nozzles independent of product data. After determining if any
nozzles have failed, those nozzles may be mapped against the
product data to determine if the printhead should be mapped as
failed or not. If a printhead is considered to have failed, then
generally the entire layer group must be considered to have
failed.
Layer Group Fault Response
[0245] The preferred system relies on each layer group carrying out
testing of itself and of the immediately upstream or downstream
layer group. Testing results are passed to a central controller. A
layer group will be declared to have failed and will be
automatically "mapped out" by the central controller if:--
1). the layer group's self-test circuitry or external (to the layer
group) testing detects a fault that cannot be accommodated by
onboard redundancy;
2). the immediately or downstream upstream layer group detects that
the layer group is not responding or not responding correctly to
interrogation, or
3). power fails to the layer group.
[0246] The above list is not exhaustive and other circumstances may
require a layer group to be "mapped out".
[0247] Failure of a layer group must not prevent communication
between its adjacent layer groups and so communication between any
two layer groups is not dependant on intermediate layer groups. The
failure of a layer group should also not cause failure in the
product being printed by that layer group when it fails.
[0248] Referring to FIGS. 10 to 18 there are schematically shown a
number of layer groups of a system 1000 designed for producing
products with up to n layers. Accordingly, the system 1000 has n
active layer groups. The system has a series of spare layer groups
1012, 1013 & 1014 that in `normal` use are not used. These
`spare` layer groups are located downstream of the n.sup.th active
layer group 1011. In the drawings, three `spare` layer groups are
shown. It will be appreciated that the number of spare layer groups
may range from one upwards. In this system all layer groups,
including spare layer groups are functionally identical.
[0249] For the purposes of explanation it is assumed that there is
no transverse offsetting of odd and even layer groups and that an
odd layer can be printed by an `even` layer group and vice
versa.
[0250] Each layer group, as discussed elsewhere, has onboard memory
that stores all the data necessary to define at least one layer. In
the embodiment of FIGS. 10 to 18, each layer group has sufficient
memory to store data for three layers. For ease of explanation the
drawings show each layer group having three separate memory stores,
represented by a separate square in the drawings, labeled a, b
& c, each representing the memory needed to store the data for
one layer. Of course in practice, the memory may be continuous.
[0251] Each layer group stores data for the layer that it is
presently printing and for the two previous layers. Thus, layer
group m stores data for layer m, layer m-1 and layer m-2 in memory
stores a, b and c, respectively. The data for each layer is
represented in the drawings by the code L.sub.n in the memory
squares, where n is the layer number. The first layer group 1001
only stores data L.sub.1 for the first layer, as it has no upstream
layer groups whilst the second layer group 1002 only stores data
L.sub.1 & L.sub.2 for the first and second layers. The indexes
1015 above the boxes represent the layer being printed by each
layer group.
[0252] The spare layer groups are physically identical to the other
layer groups, but, as shown in the FIG. 10, only the first two
spares 1012 and 1013 are initially loaded with data. The first
spare 1012 is initially loaded with data L.sub.n and L.sub.n-1
relating to layers n and n-1 in memory stores 1012b and 1012c. The
second spare 1013 only has data L.sub.n for layer n, stored in
memory store 1013c whilst the third spare 1014 and beyond, if any,
initially have no data in memory.
[0253] The layer groups have data transfer links 1016 configured to
enable layer data in the memory of one layer group to be
transferred to the two immediately adjacent active layer groups,
i.e. an upstream and a downstream layer group. There may be one or
more "inactive" layer groups between active layer groups. Inactive
layer groups are ignored by the system and the system is configured
so that an inactive layer group cannot affect operation of the
system. Typically an inactive group is one that has suffered a
failure that prevents it printing material as required. However,
fully functional layer groups may be mapped out as `inactive` for
other reasons.
[0254] Referring to FIG. 10 the initial configuration is shown and
each layer group prints the corresponding layer, i.e. the first
layer group 1001 prints layer one, the second layer group 1002
prints layer two, etc.
[0255] FIG. 11 shows the situation where the fifth layer group 1005
has been determined to have failed. The system maps out fifth layer
group 1005 and all layer groups downstream of layer group 1005 are
instructed to print an earlier layer. Thus, layer group 1006 is
instructed to print layer five, layer group 1007 is instructed to
print layer six and the n.sup.th layer group is instructed to print
layer n-1. This is achieved by sending an `advance` signal 1018 to
all the downstream layer groups, preferably via the data link 1016
when a layer group fails.
[0256] The advance signal is also propagated to the `spare` layer
groups and so spare layer group 1012 is instructed to print layer
n.
[0257] This is possible as there is sufficient time between failure
being detected and the substrate moving from one layer group to the
next layer group and because each layer group already holds data
defining an earlier layer. The time available to switch over is of
the order of a few hundred milliseconds. Thus, the next layer group
may finish off the part completed layer printed by the upstream
layer group. The layer group 1004 now communicates directly with
layer group 1006 and bypasses layer group 1005, which is no longer
active.
[0258] This switch over may be effectively instantaneous as all the
layer groups already hold data defining the previous layer. Thus,
even if layer group five fails part way through printing its layer,
layer group six may complete that layer as layer group six already
holds data relating to layer five. If there is sufficient gap
between adjacent products, layer groups six onwards may complete
printing of their respective layers before switching to an earlier
layer. In these circumstances, layer group six would complete layer
six on one product, complete the part completed layer five of the
next product and then print layer five on subsequent products.
Layer groups seven onwards would complete their original layers and
then switch to printing the earlier layers.
[0259] Referring to FIG. 12, layer group 1005 is now mapped out and
all downstream layer groups are `moved` upstream one layer, i.e.
layer group 1006 becomes the fifth layer group, layer group 1007
becomes the sixth layer group, layer group n becomes the
(n-1).sup.th layer group and the first spare layer group 1012 is
mapped as the n.sup.th layer group.
[0260] At this time, each layer group downstream of the failed
layer group holds data relating to the layer it is now printing,
the immediate upstream layer and the immediate downstream layer.
Thus, layer group 1006, now mapped as the fifth layer group, has
data for layers four, five and six. The data for the immediate
downstream layers is not required by any of the layer groups and so
may be replaced.
[0261] Transfer of data between the layer groups now occurs via
data link 1016, as shown in FIG. 13. The data L.sub.6 in layer
group 1006 relating to layer six is replaced with data L.sub.3
relating to layer three. This data L.sub.3 is obtained from the
immediate upstream layer group 1004 via data link 1016.
[0262] Simultaneously, layer group 1006 transfers data L.sub.4
relating to layer four to layer group 1007 to replace the now
redundant data L.sub.8 defining layer eight. A similar transfer
occurs simultaneously for all the layer groups downstream of the
failed layer group, i.e. in an active layer group previously mapped
as layer group m+1 and now mapped as layer group m, data relating
to layer m+1 is replaced with data relating to layer m-2 from layer
group m-1. The first spare 1012, now mapped as the n.sup.th layer
group, transfers data relating to layer n-1 to the second spare
1013 and the third spare 1014, which originally held no data,
receives data relating to layer n from layer group 1013.
Simultaneous transfer is possible because all the layer groups hold
the necessary data in memory. Whilst data for all n layers is
transferred substantially simultaneously, the data link 1016 only
carries data for one layer between adjacent layer groups. In
addition, the switchover to accommodate a failed layer group is not
dependant on the completion of this data transfer. Thus, the
capacity of the data link need not be high.
[0263] Referring to FIGS. 14 & 15, assume layer group 1008, now
mapped as the seventh layer group fails. A second `advance` signal
1022 is sent to all active layer groups downstream of layer group
1008 to cause them to print the previous layer, as previously
described i.e. layer group 1009 synchronously takes over printing
layer seven, the first spare 1012 prints layer n-1 and the second
spare 1013 prints layer n, with the third spare 1014 still
unused.
[0264] In the typical system approximately 10.6 Gbytes of data is
required to define all the voxels of each layer and the transfer of
this amount of data takes some time. However, because each layer
group holds data relating to two upstream layers, a failure of a
layer group that occurs whilst the data transfers occurring will
not be fatal.
[0265] Referring to FIG. 16, assume that the transfer of layer data
as a result of the failure of layer group 1008 is still occurring
when layer group 1003 fails. Thus data transfer 1022 is still
occurring. A third `advance` signal 1024 is generated and sent to
all active layer groups downstream of layer group 1003. Layer
groups 1004, 1006 and 1007, now mapped as layer groups four, five
and six are not in the process of replacing data in their memory
and can synchronously commence printing layers three, four and five
respectively. Although mapped layer groups seven to n are in the
process of replacing data in one memory store, they also already
hold in memory data for the immediate upstream layer. Thus, layer
group 1009 already holds data relating to layer six; the eighth
layer group holds data for layer seven, all the way through to the
third spare 1014, which holds data for layer n. Thus all the
downstream layer groups already hold the necessary data and so all
may shift to printing the upstream layer whilst the first data
transfer 1022 is still occurring and on receipt of only an advance
signal. This is shown in FIG. 17.
[0266] An additional instruction is issued to replace the data in
each layer group m relating to layer m+1 with that relating to
layer m-2. Accordingly, as shown in FIG. 17 layer group 1002
transfers data L.sub.1 relating to layer one to layer group 1004.
Layer groups 1009 onwards, now mapped as layer groups six onwards,
continue with the first data transfer 1022, so that layer group
data still populates one of its memory stores with data relating to
earlier layers. The second data transfer 1026 is commenced,
preferably occurring simultaneously with the first transfer 1022,
to transfer data relating to earlier layers. Depending on the
capacity of the data link 1016, the second data transfer may be
delayed until the first transfer has completed. FIG. 18 shows the
layer data in the memory stores of the layer groups after the two
data transfers have been completed.
[0267] Whilst the first data transfer is still occurring, layer
groups 1009 onwards do not hold a complete data set for an upstream
layer. As such, if a fourth failure were to occur before the first
data transfer is completed the system has no layer redundancy.
However, as soon as the first data transfer is complete all of the
layer groups will hold data relating to the current layer being
printed and the immediate upstream layer, so restoring data
redundancy for one failure. When the second data transfer completes
the system is restored to having redundancy for two failures.
[0268] The system can thus cope with two failures occurring in the
time it takes to transfer data relating to one layer between the
layer groups. If greater fault tolerance is required, it is merely
a matter of providing more memory in each layer group. A system in
which each layer group can store data relating to i layers will be
able to continue even if i-1 failures occur in the time to transfer
one layer's data between layer groups.
[0269] If the number of spare layers is greater than i, the number
of spare layer groups does not affect the number of "simultaneous"
failures that may occur before data transfer has completed.
However, the number of spare layer groups does effect the
cumulative number of failures that may be accommodated before the
manufacturing line needs to be stopped in a controlled manner for
replacement of failed printhead or layer groups. It will be
appreciated that in practice the number of spare layer groups maybe
much greater than three.
[0270] In the embodiment shown in FIGS. 10 to 18 all of the layer
groups are identical, with a series of identical spare layer groups
at the downstream end of the n.sup.th layer group. Where a
production line does not have all layer groups identical, it will
be appreciated that the one production line may be treated as a
series of smaller logical production lines placed end on end, in
which the layer groups of each logical production line are
identical. In this situation, spare layer groups may be located at
the downstream end of each logical production line and before the
start of the next logical production line. It will also be
appreciated that a non-identical layer group may replace a layer
group, so long as the replacement is capable of printing all of the
materials printed by the failed layer group. As an example, layer
groups that only print one or two materials can be replaced by
downstream layer groups that can print eight materials, so long as
the eight materials include the first two.
[0271] In the system described, all layer groups can print both odd
and even layers. However, in some cases odd layer groups may not be
able to print even layers and even layer groups may not be able to
print odd layers. An example of such a case is where voxels are
arranged in a hexagonal close pack arrangement and odd layer groups
are physically offset transversely relative to even layer
groups.
[0272] In this case when a layer group fails, the next layer group
would not be able to print the previous layer and need to be mapped
out. Thus, for example, if layer group five fails, both it and
layer group six would be mapped out. Layer group seven would then
print layer five and layer group eight would then print layer six,
and so on. Thus each failure would require the use of two spare
layer groups and so twice as many spare layer groups would be
required to provide the ability to cope with the same number of
failures. It follows that odd layer groups will store data relating
to odd layers and even layer groups will store data relating to
even layers. Thus layer group m will sore data relating to layers
m, m+2 and m+4. Apart from these differences, the system would
function identically to that described.
[0273] As mentioned previously, a printhead may be able to
successfully print material for one layer despite having one or
more failed but unused nozzles. However, one or more failed nozzles
may be required for printing of earlier layers. As each layer group
has memory for multiple layers, it is possible at initialization,
or at other times, to determine if the printhead is capable of
printing all the layers held in memory, not just the layer being
printed. The layer group may then hold a status flag for the other
layers indicating whether it is capable of printing them.
[0274] If a failure occurs in another printhead that requires the
layer group to print a layer that it cannot, the layer group may be
mapped out as well. Effectively this would result in two
simultaneous failures that needed to be accommodated. As such it
may be desirable to increase the number of layers held in memory by
each layer group.
[0275] It will be appreciated that this scenario has the potential
to reduce the number of `failures` and hence the number of spare
layers required but at the same expense of requiring more memory to
provide the same level of simultaneous built in redundancy/fault
tolerance.
[0276] Whilst the present invention has been described with
reference to semiconductor devices printing micron sized voxels, it
is to be appreciated that the invention is not limited to the
printing devices described or the voxel sizes described. Similarly,
whilst preferred forms utilize about 1000 separate subsystems or
layer groups, the invention is not limited to systems having this
many subsystems or layer groups.
[0277] Technologies currently exist that involve the (random)
spraying of molten metal droplets onto a former to form a metallic
structure (see U.S. Pat. No. 6,420,954 for an example). It is
within the scope of the invention to print or otherwise deposit
droplets of metals having melting points significantly above that
of semiconductor materials and in much larger drop sizes, for the
formation of `bulk` objects.
[0278] Many metal objects are cast or otherwise formed to a `rough`
state. The rough casting is frequently then subject to various
machining processes to arrive at the finished article. Printing of
metal objects allows finished products to be produced without the
need for such machining.
[0279] Preferred embodiments of the invention produce voxels of
material that are substantially the same size, independent of
location or material. There is also a one to one relationship
between voxels and `droplets`, i.e. each voxel is constructed of
one cured `droplet` of material. Depending on the product, certain
portions may not need to be produced to the same fineness, such as
the bulk layers of a casing. Accordingly these may be formed of
larger droplets of materials. Accordingly different layer groups
may have printheads printing the same materials but in different
drop sizes to produce either `super size` voxels or multiple
`standard` size voxels.
* * * * *