U.S. patent application number 16/152065 was filed with the patent office on 2019-01-31 for print head maintenance.
This patent application is currently assigned to MUTRACX INTERNATIONAL B.V.. The applicant listed for this patent is MUTRACX INTERNATIONAL B.V.. Invention is credited to Jacobus Hendricus Johannes JANSSEN, Joost Anne VEERMAN, Henk Jan ZWIERS.
Application Number | 20190037704 16/152065 |
Document ID | / |
Family ID | 47664395 |
Filed Date | 2019-01-31 |
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United States Patent
Application |
20190037704 |
Kind Code |
A1 |
ZWIERS; Henk Jan ; et
al. |
January 31, 2019 |
PRINT HEAD MAINTENANCE
Abstract
A maintenance unit for an inkjet system with a print head
assembly having at least one print head being an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the at least one print head towards a substrate
includes a wiper to wipe along the surface of the at least one
print head; a force actuator to apply a force to the wiper in a
direction perpendicular to the surface of the at least one print
head; a force measuring unit configured to determine a wiping force
with which the wiper is pressed against the surface of the at least
one print head; and a controller configured to control the force
applied by the force actuator in dependency of an output of the
force measuring unit in order to press the wiper against the
surface of a print head with a predetermined wiping force.
Inventors: |
ZWIERS; Henk Jan; (Venlo,
NL) ; JANSSEN; Jacobus Hendricus Johannes; (Haps,
NL) ; VEERMAN; Joost Anne; (Grubbenvorst,
NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MUTRACX INTERNATIONAL B.V. |
Nuenen |
|
NL |
|
|
Assignee: |
MUTRACX INTERNATIONAL B.V.
Nuenen
NL
|
Family ID: |
47664395 |
Appl. No.: |
16/152065 |
Filed: |
October 4, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
15677926 |
Aug 15, 2017 |
10123427 |
|
|
16152065 |
|
|
|
|
15148780 |
May 6, 2016 |
9769932 |
|
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15677926 |
|
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|
14370195 |
Jul 1, 2014 |
9363899 |
|
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PCT/NL2012/050934 |
Dec 28, 2012 |
|
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|
15148780 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 3/061 20130101;
H05K 1/092 20130101; H01L 21/288 20130101; H01L 23/544 20130101;
H05K 3/125 20130101; H05K 2203/1572 20130101; G01N 2021/95615
20130101; H05K 2203/163 20130101; G01N 21/95607 20130101; H05K
2203/1563 20130101; H05K 2203/16 20130101; B41J 2/16544 20130101;
H05K 3/22 20130101; H05K 2203/162 20130101; B05B 1/08 20130101;
B41J 2/16538 20130101; H05K 2203/1461 20130101; B41J 2/2132
20130101; H01L 2924/0002 20130101; H05K 3/0079 20130101; B41J
25/001 20130101; H05K 2203/013 20130101; H01L 22/12 20130101; B05B
13/0221 20130101; H01L 2924/0002 20130101; H01L 2924/00
20130101 |
International
Class: |
H05K 3/12 20060101
H05K003/12; B05B 1/08 20060101 B05B001/08; B05B 13/02 20060101
B05B013/02; B41J 2/165 20060101 B41J002/165; B41J 2/21 20060101
B41J002/21; B41J 25/00 20060101 B41J025/00; H01L 21/66 20060101
H01L021/66; B05B 12/16 20180101 B05B012/16; H01L 21/288 20060101
H01L021/288; H05K 3/00 20060101 H05K003/00; H05K 1/09 20060101
H05K001/09; H05K 3/22 20060101 H05K003/22; H01L 23/544 20060101
H01L023/544; G01N 21/956 20060101 G01N021/956 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 2, 2012 |
NL |
2008063 |
Jan 2, 2012 |
NL |
2008064 |
Jan 2, 2012 |
NL |
2008065 |
Jan 2, 2012 |
NL |
2008066 |
Jan 2, 2012 |
NL |
2008067 |
Jan 2, 2012 |
NL |
2008068 |
Claims
1. A maintenance unit for an inkjet system with a print head
assembly, said print head assembly comprising at least one print
head, the at least one print head being an integral unit configured
to eject droplets of ink fluid from nozzles arranged in a surface
of the at least one print head towards a substrate, the maintenance
unit comprising: a wiper to wipe along the surface of the at least
one print head; a force actuator to apply a force to the wiper in a
direction perpendicular to the surface of the at least one print
head; a force measuring unit configured to determine a wiping force
with which the wiper is pressed against the surface of the at least
one print head; and a controller configured to control the force
applied by the force actuator in dependency of an output of the
force measuring unit in order to press the wiper against the
surface of a print head with a predetermined wiping force.
2. The maintenance unit for an inkjet system according to claim 1,
wherein the maintenance unit further comprises: a position sensor
to measure the position of the wiper relative to the surface of the
at least one print head; and a set point generator for generating a
set point corresponding to a desired position of the wiper relative
to the surface of the at least one print head seen in a direction
perpendicular to the surface of the at least one print head,
wherein the controller is arranged to drive the force actuator in
dependency of an output of the position sensor and the set point,
wherein, in order to wipe along the surface of the at least one
print head, the set point generator is configured to output a set
point corresponding to a position in which the wiper is at least
partially inside the at least one print head, and wherein the
controller is configured to limit the maximum applicable force of
the force actuator to the predetermined wiping force.
3. The maintenance unit according to claim 1, further comprising a
wiper moving device for moving the wiper, wherein the controller is
configured to drive the wiper moving device such that the wiper is
moved along the surface of the at least one print head.
4. The maintenance unit according to claim 1, further comprising a
frame and a guide to guide movement of the wiper with respect to
the frame in a direction parallel to the wiping force.
5. The maintenance unit according to claim 3, wherein the wiper
moving device is configured to operate on the frame to move the
wiper.
6. The maintenance unit according to claim 1, wherein the force
actuator is an electromagnetic actuator.
7. The maintenance unit according to claim 6, wherein the
electromagnetic actuator is a Lorentz actuator.
8. The maintenance unit according to claim 3, wherein the guide is
configured to guide movement of the wiper without applying
significant forces to the wiper, or wherein the guide guides
movement of the wiper while applying a constant force to the
wiper.
9. The maintenance unit according to claim 3, wherein the wiper
moving device is configured to move the wiper in two degrees of
freedom in a plane parallel to the surface of the at least one
print head.
10. The maintenance unit according to claim 1, wherein multiple
wipers are arranged on a common wiper support frame.
11. The maintenance unit according to claim 10, wherein respective
wiper moving devices are provided in between the respective wiper
and the support frame, such that movement of each wiper can
individually be controlled by the controller.
12. The maintenance unit according to claim 10, wherein the wiper
support frame is moveable relative to the print head assembly in
one direction only, and wherein the wiper moving devices on the
wiper support frame are configured to move the respective wiper in
a direction different from said one direction of the wiper support
frame such that the wiper is moveable in a two dimensional plane
parallel to the surface of the at least one print head.
13. The maintenance unit according to claim 1, comprising a heating
device to heat the wiper in order to melt ink fluid that has
accumulated on the wiper, thereby removing the ink fluid from the
wiper.
14. An inkjet system comprising: a print head assembly with at
least one print head, the at least one print head being an integral
unit configured to eject droplets of ink fluid from nozzles
arranged in a surface of the at least one print head towards a
substrate; and the maintenance unit according to claim 1 to perform
maintenance on the at least one print head.
15. The inkjet system according to claim 14, wherein the wiper of
the maintenance unit is moveable between an operational position in
which the wiper is able to perform a wiping action with respect to
the at least one print head, and a non-operational position in
which the wiper is arranged at a distance from the print head
assembly, such that the maintenance unit is not interfering with
normal printing activities.
16. The inkjet system according to claim 15, wherein a printing
direction is defined which corresponds to a direction in which
substrates pass the print head assembly for printing purposes, and
wherein the maintenance unit is moveable in a horizontal direction
perpendicular to the printing direction.
17. A method to perform maintenance on a print head of a print head
assembly, said print head being an integral unit configured to
eject droplets of ink fluid from nozzles arranged in a surface of
the print head towards a substrate, said method comprising the
following steps: providing a wiper which is moveable along the
surface of the print head to remove ink from said surface; moving
the wiper along the surface of the print head while pressing the
wiper against the surface of the print head with a force actuator;
determining a wiping force with which the wiper is pressed against
the surface of the print head by the force actuator; and driving
the force actuator based on the determined wiping force in order to
press the wiper with a predetermined wiping force against the
surface of the print head.
18. The method according to claim 17, further comprising the
following steps: urging the wiper to an unreachable position inside
the print head with a force actuator while moving the wiper along
the surface of the print head; and while urging the wiper to said
position, keeping the maximum by the force actuator applied force
below a predetermined value.
19. The method according to claim 17, wherein ink fluid is purged
out of the nozzles prior to moving the wiper along the surface of
the print head.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation of U.S. application Ser.
No. 15/677,926, filed on Aug. 15, 2017, which is a Continuation of
U.S. application Ser. No. 15/148,780, filed on May 6, 2016 (now
U.S. Pat. No. 9,769,932 issued on Sep. 19, 2017), which is a
Continuation of U.S. application Ser. No. 14/370,195, filed on Jul.
1, 2014 (now U.S. Pat. No. 9,363,899 issued on Jun. 7, 2016), which
is the National Phase of International Application No.
PCT/NL2012/050934, filed on Dec. 28, 2012, which claims the benefit
under 35 U.S.C. .sctn. 119(a) to Dutch Patent Application Nos.
2008068, 2008067, 2008066, 2008065, 2008064, 2008063, filed on Jan.
2, 2012, all of which are hereby expressly incorporated by
reference into the present application.
BACKGROUND OF THE INVENTION
[0002] In general, the present invention relates to devices,
methods and uses, for manufacturing a substrate comprising an ink
pattern. In particular, the present invention relates to several
aspects of a method and an inkjet system for manufacturing a
printed circuit board by printing an ink pattern onto a
substrate.
[0003] The invention relates to an inkjet system, in particular a
drop-on-demand inkjet system for industrial applications.
[0004] Drop-on-demand inkjet systems are well-known, especially in
the consumer market where inkjet printers for paper applications
have proven to be very successful over the years. An advantage of
inkjet systems over other printing techniques such as impact
printing is that no direct contact is required between inkjet
system and substrate to provide the substrate with a desired
pattern. Also part of the success of consumer inkjet printers is
that manufacturers found ways to develop small and relatively cheap
inkjet printers.
[0005] Recent developments have been directed to make use of inkjet
systems in other applications than traditional paper applications
as well. However, these developments have not been very successful,
especially not when a high accuracy and reliability is
required.
[0006] Examples of applications where inkjet systems are considered
to be a promising manufacturing tool due to its simplicity and
speed are:
[0007] providing etch resist masks on printed circuit boards
(PCB);
[0008] providing solder masks for PCB manufacturing;
[0009] providing masks for electrode patterning for solar cells;
or
[0010] manufacturing of active or passive circuit components,
display components, antennas and/or electronic components on
substrates including flexible substrates.
[0011] Inkjet systems can be used to deposit the required mask
layers or structures in a desired pattern, e.g. a pattern
corresponding to the electronic wiring on a PCB. Depending on the
desired line width of the electronic wiring and the size of the
droplets used, a missing or misplaced droplet may have an enormous
impact on the working of the electronic wiring and thus the PCB.
For instance, a missing droplet may cause a wire to have a
undesirably high local electrical resistance which may even cause
electromigration.
[0012] Inkjet systems usually comprise a print head assembly with
at least one print head, said print head being an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the print head towards a substrate. Misplacement of
droplets may occur as a result of ink fluid that has accumulated on
the surface of the print head and that interacts with the ink fluid
inside the nozzle or interacts with a droplet leaving the nozzle
thereby changing the intended trajectory of the fired droplet.
[0013] Missing droplets may be caused by a nozzle that is blocked
by dried or solidified ink fluid. This can be solved by purging the
nozzles with an overpressure which forces ink fluid out of the
nozzle, thereby removing the ink fluid portion blocking the nozzle.
A disadvantage is that the purging may result in ink fluid
accumulating on the surface of the print head which in turn may
cause misplacement of the droplets.
[0014] In order to prevent the misplacement of droplets due to ink
fluid on the surface of the print head, prior art inkjet systems
use a maintenance unit with a wiper, which wiper is moved relative
to the surface of the print head to remove ink fluid that is
present on the surface, either by moving the wiper while keeping
the print head stationary, moving the print head while keeping the
wiper stationary, or by moving both the wiper and print head.
[0015] A disadvantage of currently used maintenance units is that
the wiping performance is unsatisfactory, for instance due to
changing properties of the wiper, which may be caused by aging of
the wiper. As a result, not all ink fluid may be removed from the
surface of the print head during a wiping action, which negatively
influences the obtainable accuracy and reliability of the inkjet
system and thus limits the number of industrial applications for
which the inkjet system can be used.
SUMMARY OF THE INVENTION
[0016] It is therefore an object of the invention to provide a
maintenance unit with an improved wiping performance, thereby
preferably resulting in a more accurate and reliable inkjet
system.
[0017] According to a first subaspect of the invention, this object
is achieved by providing a maintenance unit according to clause 1.
The first subaspect of the invention is based on the insight that
an important parameter of the wiping action is the force, i.e. the
wiping force, with which the wiper is pressed against the surface
of the print head, and that the wiping force has to be controlled
in order to cope with the changing properties of the wiper. Prior
art position control of the wiper can not be used to reliably
control the wiping force, because when for instance the properties
of the wiper change, e.g. due to aging, the wiping force with which
the wiper presses against the surface of the print head is usually
also undesirably changed and not corrected for as the wiper remains
in the same position.
[0018] The maintenance unit according to the first subaspect of the
invention is configured to apply a wiping force at a substantially
predetermined value, thereby resulting in a constant wiping
performance and thus a more accurate and reliable inkjet system.
The substantially predetermined value of the wiping force is
obtained by position control using a set point that cannot be
reached by the wiper due to the presence of the print head, in
combination with a limitation in the maximum applicable force of
the force actuator. As a result, the controller will continuously
apply the maximum force to the wiper in order to urge the wiper to
the position corresponding to the set point. When for instance the
properties of the wiper change, the controller will automatically
change the position of the wiper, such that the maximum force is
still applied by the force actuator and no change in wiping
performance occurs.
[0019] When the wiper does not have to wipe, the set point
generator is preferably configured to provide a set point to the
controller that corresponds to a position of the wiper at a
distance from the surface of the at least one print head seen in a
direction perpendicular to the surface of the at least one print
head. In this way, the wiper is positioned in a retracted position
when no wiping action is required. Consequently, when the wiper is
required to perform a wiping action, the set point generator will
again provide a set point corresponding to a position of the wiper
at least partially inside the at least one print head seen in the
direction perpendicular to the surface of the at least one print
head.
[0020] In an embodiment, the maintenance unit comprises a wiper
moving device for moving the wiper, wherein the controller is
connected to the wiper moving device, and wherein the controller is
configured to drive the wiper moving device in order to move the
wiper along the surface of the at least one print head thereby
removing ink from said surface with the wiper.
[0021] Preferably, the force actuator is provided to only control
the position in a direction perpendicular to the surface of the at
least one print head, thereby only being able to press the wiper
against the surface of the at least one print head, while the wiper
moving device is only provided to move the wiper parallel to the
surface of the at least one print head. In such an embodiment, the
wiping action is a combination of operating the force actuator and
operating the wiper moving device.
[0022] In an embodiment, the wiper is guided by a guide, i.e.
moveably supported, with respect to a frame in a direction
perpendicular to the surface of the at least one print head, i.e. a
direction parallel to the wiping force applied by the force
actuator. Preferably, the wiper is guided in said direction only.
The guide defines a moving range in which the wiper is allowed to
move.
[0023] In an embodiment, the maintenance unit comprises a frame,
wherein the wiper moving device is configured to operate on the
frame of the maintenance unit in order to move the wiper. The force
actuator can then be positioned in between the frame and the wiper
in order to be independently controlled with respect to the wiper
moving device.
[0024] In an embodiment, the force actuator is an electromagnetic
actuator, preferably a Lorentz actuator, preferably such that the
force generated by the electromagnetic actuator is proportional to
the current applied to the force actuator. The controller may then
limit the maximum applicable force of the force actuator by
limiting the current applied to the force actuator. Preferably, the
current-force relationship is substantially constant in the moving
range of the wiper, so that the current is representative for the
applied force in the entire moving range.
[0025] In an embodiment, the guide applies no significant forces to
the wiper in the direction parallel to said wiping force, or in
case the guide applies a force, this force is preferably constant
and independent of the position of the wiper within the moving
range. As a result, once the constant force is compensated for if
necessary, the force applied by the force actuator is proportional
to the wiping force with which the wiper is pressed against the
surface. Hence, regulating the maximum applicable force to be
applied by the force actuator will automatically regulate the
wiping force with which the wiper is pressed against the
surface.
[0026] In an embodiment, the guide is configured to guide the wiper
substantially hysteresis-free, for instance by using leaf springs,
e.g. leaf springs arranged parallel with respect to each other,
thereby providing a linear guide.
[0027] In an embodiment, the force actuator comprises two parts,
namely a first part mounted to the frame and a second part mounted
to the wiper, wherein the first and second part interact with each
other in order to apply a force in between the first and second
part. For instance, the first part may be a coil and the second
part may be a permanent magnet interacting with the coil via
respective magnetic fields.
[0028] In an embodiment, the position sensor is configured to
measure the position of the wiper relative to the frame of the
maintenance unit. For instance, the position sensor measures the
position of the second part relative to the first part. Preferably,
the distance between frame and surface of the at least one print
head is known and constant, so that measuring the position of the
wiper relative to the frame is representative for the position of
the wiper relative to the surface of the at least one print
head.
[0029] In an embodiment, the wiper moving device is configured to
move the wiper in a single direction along the surface. This
requires some initial alignment between the wiper moving device and
the surface of the print head when the maintenance unit is provided
in an inkjet system, but has the advantage that control of the
wiper is relatively simple.
[0030] In an embodiment, the wiper width is larger than the width
of the surface, wherein the wiper moving device is configured to
move the wiper in a longitudinal direction of the surface.
[0031] The wiper moving device may additionally be configured to
move the wiper in two degrees of freedom, which reduces the
required alignment accuracy, but may increase the control
demand.
[0032] In an embodiment, the wiper moving device is configured to
move the wiper in one or more directions parallel to the surface of
the at least one print head.
[0033] In an embodiment, multiple wipers with respective wiper
moving devices are provided on a common wiper support frame, so
that each wiper is moveable independent of the other wipers.
Alternatively, the multiple wipers may be stationary mounted to the
common wiper support frame, which wiper support frame as a whole is
moved in order to move the wipers simultaneously. This reduces the
control complexity of the maintenance unit considerably, but does
not allow for individual control of the movement of the wipers.
[0034] In an embodiment, the wiper support frame is moveable in a
direction, where the wiper moving devices are configured to move
the respective wiper in another direction, thereby obtaining two
degrees of freedom moving possibilities of the wipers while keeping
the control relatively simple.
[0035] In an embodiment, the wiper support frame is controllable in
a stepwise manner to position the wiper support frame relative to
the print head assembly after which the wiper moving devices are
driven to let the wiper carry out a wiping action while the wiper
support frame remains stationary relative to the print head
assembly. After performing the wiping action, the wiper support
frame may be moved to another position to allow the wiper to
perform a wiping action with respect to another print head.
Alternatively, the wiper support frame may be configured to be
moved during the wiping action to cooperate with the wiper moving
device in order to provide the required movement of the wiper. The
mode of operation of the wiper support frame may depend on the
orientation of the print heads. In case all print heads are
oriented in a similar way, the stepwise mode may be applied, but
when the print heads have different orientations, it may be
necessary to move the wiper support frame during the wiping
action.
[0036] In an embodiment, a heating device is provided in order to
heat the wiper. This is especially advantageous when the ink fluid
is a hot-melt ink fluid having a melting temperature above room
temperature, so that ink fluid may remain behind on the wiper,
which may negatively influence the wiping performance of the wiper.
By heating the wiper to a temperature above the melting temperature
of the ink fluid, the ink fluid may be removed thereby improving
the wiping performance of the wiper.
[0037] The first subaspect of the invention also relates to an
inkjet system comprising a print head assembly and a maintenance
unit for the print head assembly, said print head assembly
comprising at least one print head, wherein the at least one print
head is an integral unit configured to eject droplets of ink fluid
from nozzles arranged in a surface of the at least one print head
towards a substrate, and said maintenance unit being a maintenance
unit according to an embodiment of the first subaspect of the
invention.
[0038] In an embodiment, the wiper of the maintenance unit is
moveable between a maintenance position in which the wiper is able
to perform a wiping action with respect to the at least one print
head, and a non-operational position in which the wiper is arranged
at a distance from the print head assembly such that the
maintenance unit is not interfering with normal printing activities
which usually concerns the moving of a substrate below the print
head assembly.
[0039] In an embodiment, the mentioned moveability of the wiper is
provided via the wiper moving device.
[0040] Preferably, the mentioned moveability of the wiper is
provided in a plane parallel to the surface of the at least one
print head.
[0041] In an alternative embodiment, the wiper is provided
stationary and the print head assembly is moved between an
operational position in which the print head assembly is able to
perform printing activities, and a maintenance position in which
the print head assembly is positioned close to the maintenance unit
to allow maintenance of the at least one print head by the
maintenance unit.
[0042] The inkjet system may define a printing direction, which
printing direction indicates the direction in which the substrates
pass the print head assembly for printing purposes. In an
embodiment, the moveability of either the maintenance unit or the
print head assembly for maintenance purposes is perpendicular to
the printing direction, and preferably in a horizontal
direction.
[0043] The first subaspect of the fourth aspect of the invention
also relates to a method to perform maintenance on a print head of
a print head assembly, said print head being an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the print head towards a substrate, said method
comprising the following steps, [0044] providing a wiper which is
moveable relative to the surface of the print head to remove ink
from the surface of the print head, [0045] urging the wiper to an
unreachable position inside the print head with a force actuator
while moving the wiper along the surface of the print head; [0046]
while urging the wiper to said position, keeping the maximum by the
force actuator applied force below a predetermined value.
[0047] As a result, the wiping force with which the wiper is
pressed against the surface of the print head is substantially
constant during the wiping action, but also relative to subsequent
wiping actions over time, and thus independent of property changes
of the wiper.
[0048] In an embodiment, ink fluid is purged out of the nozzles
prior to moving the wiper along the surface of the print head.
[0049] In an embodiment, the wiper is moved to a position away from
the surface of the print head when no maintenance is to be carried
out.
[0050] According to a second subaspect of the invention, the object
of the invention is achieved by providing a maintenance unit for an
inkjet system with a print head assembly, said print head assembly
comprising at least one print head, which print head is an integral
unit configured to eject droplets of ink fluid from nozzles
arranged in a surface of the at least one print head towards a
substrate, wherein the maintenance unit comprises a wiper, wherein
the maintenance unit further comprises a force actuator to press
the wiper against the surface of the at least one print head, a
force measuring unit configured to determine a wiping force with
which the wiper is pressed against the surface of the at least one
print head, and a controller configured to control the force
applied by the force actuator in dependency of an output of the
force measuring unit in order to press the wiper against the
surface of a print head with a predetermined wiping force.
[0051] The second subaspect of the invention is based on the
insight that an important parameter of the wiping action is the
force, i.e. the wiping force, with which the wiper is pressed
against the surface of the print head, and that the wiping force
has to be controlled in order to cope with the changing properties
of the wiper. If the properties of the wiper change due to aging,
the wiping force with which the wiper presses against the surface
of the print head is usually also changed. The maintenance unit
according to the second subaspect of the invention is configured to
adjust its settings automatically, such that the wiping force is
kept at a predetermined value, thereby resulting in a constant
wiping performance and thus a more accurate and reliable inkjet
system.
[0052] The difference between the first and second subaspect of the
invention is that the more or less predetermined wiping force is
obtained in different ways. In the first subaspect of the fourth
aspect of the invention, smart use of position control in
combination with a limited force applied by the force actuator
results in a predetermined wiping force, while in the second
subaspect of the fourth aspect of the invention, the predetermined
wiping force is obtained by properly controlling the applied force
of the force actuator.
[0053] In an embodiment, the maintenance unit comprises a wiper
moving device for moving the wiper, wherein the controller is
connected to the wiper moving device, and wherein the controller is
configured to drive the wiper moving device such that the wiper is
moved along the surface of the at least one print head thereby
removing ink from said surface with the wiper
[0054] In an embodiment, the wiper is guided by a guide, i.e.
moveably supported, with respect to a frame in a direction parallel
to the by the force actuator generatable wiping force. Preferably,
the wiper is guided in said direction only. The guide defines a
moving range in which the wiper is allowed to move.
[0055] In an embodiment, the wiper moving device is configured to
operate on the frame of the maintenance unit in order to move the
wiper. The force actuator can then be controlled independently from
the wiper moving device. In an embodiment, the wiper moving device
is configured to move the wiper in a direction perpendicular to the
direction of the by the force actuator generatable wiping
force.
[0056] In an embodiment, the guide applies no significant forces to
the wiper in the direction parallel to said wiping force, or in
case the guide applies a force, this force is preferably constant
and independent of the position of the wiper within the moving
range. As a result, once the constant force is compensated for if
necessary, the force applied by the force actuator is proportional
to the wiping force with which the wiper is pressed against the
surface. Hence, regulating the force to be applied by the force
actuator will automatically regulate the wiping force with which
the wiper is pressed against the surface. It is then sufficient for
the force measurement unit to directly or indirectly measure the
force applied by the force actuator.
[0057] In an embodiment, the force actuator is an electromagnetic
actuator, preferably a Lorentz actuator, such that the force
generated by the electromagnetic actuator is proportional with the
current applied to the force actuator. The force measurement unit
is then able to determine the by the force actuator applied force
by measuring the current applied to the force actuator. Preferably,
the current-force relationship is substantially constant in the
moving range of the wiper, so that the current is representative
for the applied force in the entire moving range.
[0058] In an embodiment, the guide may comprise resilient members
which apply a non-constant guiding force to the wiper, for instance
a guiding force depending on the position of the wiper within the
moving range, e.g. the guide having a spring-like behaviour. An
advantage of the resilient members is that the wiper may be urged
towards an equilibrium position, which may be advantageous
especially in case the wiper is non-operational. However, the
guiding force applied by the resilient members can be a significant
disturbance force counteracting the force applied by the force
actuator, so that the force applied by the force actuator to the
wiper no longer is proportional to the wiping force with which the
wiper is pressed against the surface of the print head.
[0059] In order to determine the wiping force with which the wiper
is pressed against the surface of the print head, it may be
necessary for the force measuring unit to measure a parameter
representative for a guiding force applied to the wiper by the
guide and combine this information with a measured force applied by
the force actuator in order to determine the wiping force with
which the wiper is pressed against the surface. In case the guiding
force applied by the guide is dependent on the relative position of
the wiper with respect to the guide, the force measuring unit may
comprise a position sensor to measure said relative position. This
allows the controller to drive the force actuator in such a manner
that the guiding force applied by the guide can be compensated.
[0060] In other words, the guide comprises resilient members which
urge the wiper towards an equilibrium position, wherein the force
measuring unit is configured to determine the guiding force applied
to the wiper by the guide in order to allow compensation of said
guiding force by the force actuator. Preferably, the force
measuring unit is configured to measure the level of deviation from
the equilibrium position to determine the guiding force applied to
the wiper by the guide.
[0061] In an embodiment, the force measuring unit determines the
force applied by the force actuator and subtracts from that force
the determined guiding force to determine the wiping force, which
wiping force is supplied to the controller for control of the
wiping force.
[0062] In an embodiment, the direction in which the force actuator
is able to apply a force to the wiper is substantially
perpendicular to the surface of the print head.
[0063] In an embodiment, the wiper moving device is configured to
move the wiper in a single direction along the surface. This
requires some initial alignment between the wiper moving device and
the surface of the print head when the maintenance unit is provided
in an inkjet system, but has the advantage that control of the
wiper is simple.
[0064] In an embodiment, the wiper width is larger than the width
of the surface, wherein the wiper moving device is configured to
move the wiper in a longitudinal direction of the surface.
[0065] The wiper moving device may additionally be configured to
move the wiper in two degrees of freedom, which reduces the
required alignment accuracy, but may increase the control
demand.
[0066] In an embodiment, the wiper moving device is configured to
move the wiper in one or more directions parallel to the surface of
the at least one print head.
[0067] In an embodiment, multiple wipers with respective wiper
moving devices are provided on a common wiper support frame, so
that each wiper is moveable independent of the other wipers.
Alternatively, the multiple wipers may be stationary mounted to the
common wiper support frame, which wiper support frame as a whole is
moved in order to move the wipers simultaneously. This reduces the
control complexity of the maintenance unit considerably, but does
not allow for individual control of the movement of the wipers.
[0068] In an embodiment, the wiper support frame is moveable in a
direction, where the wiper moving devices are configured to move
the respective wiper in another direction, thereby obtaining two
degrees of freedom moving possibilities of the wipers while keeping
the control relatively simple.
[0069] In an embodiment, the wiper support frame is controllable in
a stepwise manner to position the wiper support frame relative to
the print head assembly after which the wiper moving devices are
driven to let the wiper carry out a wiping action while the wiper
support frame remains stationary relative to the print head
assembly. After performing the wiping action, the wiper support
frame may be moved to another position to allow the wiper to
perform a wiping action with respect to another print head.
Alternatively, the wiper support frame has to be moved during the
wiping action to cooperate with the wiper moving device in order to
provide the required movement of the wiper. The mode of operation
of the wiper support frame may depend on the orientation of the
print heads. In case all print heads are oriented in a similar way,
the stepwise mode may be applied, but when the print heads have
different orientations, it may be necessary to move the wiper
support frame during the wiping action.
[0070] In an embodiment, a heating device is provided in order to
heat the wiper. This is especially advantageous when the ink fluid
is a hot-melt ink fluid having a melting temperature above room
temperature, so that ink fluid may remain behind on the wiper,
which may negatively influence the wiping performance of the wiper.
By heating the wiper to a temperature above the melting temperature
of the ink fluid, the ink fluid may be removed thereby improving
the wiping performance of the wiper.
[0071] The second subaspect of the invention also relates to an
inkjet system comprising a print head assembly and a maintenance
unit for the print head assembly, said print head assembly
comprising at least one print head, wherein the at least one print
head is an integral unit configured to eject droplets of ink fluid
from nozzles arranged in a surface of the at least one print head
towards a substrate, and said maintenance unit being a maintenance
unit according to an embodiment of the invention.
[0072] In an embodiment, the wiper of the maintenance unit is
moveable between a maintenance position in which the wiper is able
to perform a wiping action with respect to the at least one print
head, and a non-operational position in which the wiper is arranged
at a distance from the print head assembly such that the
maintenance unit is not interfering with normal printing activities
which usually concerns the moving of a substrate below the print
head assembly.
[0073] In an embodiment, the mentioned moveability of the wiper is
provided via the wiper moving device.
[0074] In an alternative embodiment, the wiper is provided
stationary and the print head assembly is moved between an
operational position in which the print head assembly is able to
perform printing activities, and a maintenance position in which
the print head assembly is positioned close to the maintenance unit
to allow maintenance of the at least one print head by the
maintenance unit.
[0075] The inkjet system may define a printing direction, which
printing direction indicates the direction in which the substrates
pass the print head assembly for printing purposes. In an
embodiment, the moveability of either the maintenance unit or the
print head assembly for maintenance purposes is perpendicular to
the printing direction, and preferably in a horizontal
direction.
[0076] The second subaspect of the invention also relates to a
method to perform maintenance on a print head of a print head
assembly, said print head being an integral unit configured to
eject droplets of ink fluid from nozzles arranged in a surface of
the print head towards a substrate, said method comprising the
following steps, [0077] providing a wiper which is moveable
relative to the surface of the print head to remove ink from the
surface of the print head,
[0078] moving the wiper along the surface of the print head while
pressing the wiper against the surface of the print head with a
force actuator,
[0079] determining a wiping force with which the wiper is pressed
against the surface of the print head by the force actuator,
[0080] driving the force actuator based on the determined wiping
force in order to press the wiper against the surface of the print
head with a predetermined wiping force.
[0081] In an embodiment, ink fluid is purged out of the nozzles
prior to moving the wiper along the surface of the print head.
[0082] In an embodiment, determining the wiper force is indirectly
done by measuring a parameter of the force actuator representative
for the force applied to the wiper by the force actuator when the
wiper is guided by a guide introducing substantially no disturbance
forces to the wiper.
[0083] In an embodiment, determining the wiper force is indirectly
done by measuring a parameter of the force actuator representative
for the force applied to the wiper by the force actuator and by
measuring a parameter of the guide representative for the force
applied to the wiper by the guide, and combining the results of
both measurements when the wiper is guided by a guide introducing
significant disturbance forces to the wiper during guiding of the
wiper.
[0084] Embodiments of the invention may be defined by the following
clauses:
[0085] Clause 1. A maintenance unit for an inkjet system with a
print head assembly, said print head assembly comprising at least
one print head, which print head is an integral unit configured to
eject droplets of ink fluid from nozzles arranged in a surface of
the at least one print head towards a substrate, wherein the
maintenance unit comprises a wiper to wipe along the surface of the
at least one print head, characterized in that the maintenance unit
further comprises a force actuator to apply a force to the wiper in
a direction perpendicular to the surface of the at least one print
head, a position sensor to measure the position of the wiper
relative to the surface of the at least one print head, a set point
generator for generating a set point corresponding to a desired
position of the wiper relative to the surface of the at least one
print head seen in a direction perpendicular to the surface of the
at least one print head, and a controller to drive the force
actuator in dependency of an output of the position sensor and the
set point, wherein, in order to wipe along the surface of the at
least one print head, the set point generator is configured to
output a set point corresponding to a position in which the wiper
is at least partially inside the at least one print head, and
wherein the controller is configured to limit the maximum
applicable force of the force actuator to a predetermined
value.
[0086] Clause 2. A maintenance unit according to Clause 1, wherein
the maintenance unit comprises a wiper moving device for moving the
wiper, and wherein the controller is configured to drive the wiper
moving device such that the wiper is moved along the surface of the
at least one print head.
[0087] Clause 3. A maintenance unit according to Clause 1, wherein
the maintenance unit comprises a frame and a guide to guide
movement of the wiper with respect to the frame in a direction
parallel to the wiping force.
[0088] Clause 4. A maintenance unit according to Clause 2 and
Clause 3, wherein the wiper moving device is configured to operate
on the frame to move the wiper.
[0089] Clause 5. A maintenance unit according to Clause 1, wherein
the force actuator is an electromagnetic actuator, preferably a
Lorentz actuator.
[0090] Clause 6. A maintenance unit according to Clause 3, wherein
the guide is configured to guide movement of the wiper without
applying significant forces to the wiper or the guide guides
movement of the wiper while applying a constant force to the
wiper.
[0091] Clause 7. A maintenance unit according to Clause 2, wherein
the wiper moving device is configured to move the wiper in two
degrees of freedom in a plane parallel to the surface of the at
least one print head.
[0092] Clause 8. A maintenance unit according to Clause 1, wherein
multiple wipers are arranged on a common wiper support frame.
[0093] Clause 9. A maintenance unit according to Clause 8, wherein
respective wiper moving devices are provided in between the
respective wiper and the support frame, such that movement of each
wiper can individually be controlled by the controller.
[0094] Clause 10. A maintenance unit according to Clause 8, wherein
the wiper support frame is moveable relative to the print head
assembly in one direction only, and wherein the wiper moving
devices on the wiper support frame are configured to move the
respective wiper in a direction different from said one direction
of the wiper support frame such that the wiper is moveable in a two
dimensional plane parallel to the surface of the at least one print
head.
[0095] Clause 11. A maintenance unit according to Clause 1,
comprising a heating device to heat the wiper in order to melt ink
fluid that has accumulated on the wiper, thereby removing the ink
fluid from the wiper.
[0096] Clause 12. A maintenance unit for an inkjet system with a
print head assembly, said print head assembly comprising at least
one print head, which print head is an integral unit configured to
eject droplets of ink fluid from nozzles arranged in a surface of
the at least one print head towards a substrate, wherein the
maintenance unit comprises a wiper, characterized in that the
maintenance unit further comprises a force actuator to press the
wiper against the surface of the at least one print head, a force
measuring unit configured to determine a wiping force with which
the wiper is pressed against the surface of the at least one print
head, and a controller configured to control the force applied by
the force actuator in dependency of an output of the force
measuring unit in order to press the wiper against the surface of a
print head with a predetermined wiping force.
[0097] Clause 13. An inkjet system comprising a print head assembly
with at least one print head, which print head is an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the at least one print head towards a substrate,
wherein the inkjet system further comprises a maintenance unit
according to one or more of Clause 1-Clause 12 to perform
maintenance on the at least one print head.
[0098] Clause 14. An inkjet system according to Clause 13, wherein
the wiper of the maintenance unit is moveable between an
operational position in which the wiper is able to perform a wiping
action with respect to the at least one print head, and a
non-operational position in which the wiper is arranged at a
distance from the print head assembly, such that the maintenance
unit is not interfering with normal printing activities.
[0099] Clause 15. An inkjet system according to Clause 14, wherein
a printing direction is defined which corresponds to a direction in
which substrates pass the print head assembly for printing
purposes, and wherein the maintenance unit is moveable in a
horizontal direction perpendicular to the printing direction.
[0100] Clause 16. A method to perform maintenance on a print head
of a print head assembly, said print head being an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the print head towards a substrate, said method
comprising the following steps:
[0101] providing a wiper which is moveable along the surface of the
print head to remove ink from said surface;
[0102] urging the wiper to an unreachable position inside the print
head with a force actuator while moving the wiper along the surface
of the print head<
[0103] while urging the wiper to said position, keeping the maximum
by the force actuator applied force below a predetermined
value.
[0104] Clause 17. A method to perform maintenance on a print head
of a print head assembly, said print head being an integral unit
configured to eject droplets of ink fluid from nozzles arranged in
a surface of the print head towards a substrate, said method
comprising the following steps:
[0105] providing a wiper which is moveable along the surface of the
print head to remove ink from said surface;
[0106] moving the wiper along the surface of the print head while
pressing the wiper against the surface of the print head with a
force actuator;
[0107] determining a wiping force with which the wiper is pressed
against the surface of the print head by the force actuator;
[0108] driving the force actuator based on the determined wiping
force in order to press the wiper with a predetermined wiping force
against the surface of the print head.
[0109] Clause 18. A method according to Clause 16 or Clause 17,
wherein ink fluid is purged out of the nozzles prior to moving the
wiper along the surface of the print head.
[0110] Thus, this patent application presents several measures,
features and aspects of the invention which may be considered as
stand-alone inventions or aspects, but which inventions or aspects
may also be combined in one embodiment as complementary to each
other and/or to reinforce obtainable effects.
BRIEF DESCRIPTION OF THE DRAWINGS
[0111] The invention will be explained in more detail with
reference to the appended drawings. The drawings show a practical
embodiment according to the invention, which may not be interpreted
as limiting the scope of the invention. Specific features may also
be considered apart from the shown embodiment and may be taken into
account in a broader context as a delimiting feature, not only for
the shown embodiment but as a common feature for all embodiments of
falling within the scope of the appended claims, in which:
[0112] FIG. 1 depicts an inkjet system according to an embodiment
of the invention;
[0113] FIG. 2 depicts a part of the inkjet system of FIG. 1 and
shows schematically a maintenance unit according to an embodiment
of the invention;
[0114] FIG. 3A depicts in more detail a part of a maintenance unit
according to an embodiment of the first subaspect of the fourth
aspect of the invention, which is suitable to be used in the inkjet
system of FIG. 1;
[0115] FIG. 3B depicts in more detail a part of a maintenance unit
according to an embodiment of the second subaspect of the fourth
aspect of the invention, which is suitable to be used in the inkjet
system of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0116] FIG. 1 depicts an inkjet system IS according to an
embodiment of the invention for depositing ink fluid in a desired
pattern on a substrate S by jetting liquid droplets DR of the ink
fluid in a jetting direction JD towards the substrate S. The inkjet
system is preferably a drop-on-demand inkjet system in which a
droplet is only jetted when required. This is in contrast to
continuous inkjet systems in which droplets are continuously jetted
at a predetermined frequency and wherein droplets required to form
the pattern are directed towards the substrate and the remaining
droplets are captured and thus prevented from reaching the
substrate.
[0117] The inkjet system of FIG. 1 is an industrial inkjet system,
for instance an inkjet system used to deposit resist material as a
mask layer on a printed circuit board (PCB) as an alternative to
the more traditional process of providing a mask layer using
lithography. Because the mask layer can be deposited directly by
the inkjet system, the amount of process steps can be reduced
dramatically and thus the time for PCB manufacturing. However, such
an application requires a high droplet placement accuracy and a
high reliability (substantially every droplet counts).
[0118] To provide a high accuracy inkjet system, the inkjet system
IS comprises a force frame FF which supports a metrology frame MF
from the ground GR. Between the force frame FF and the metrology
frame MF a vibration isolation system VIS is provided to support
the metrology frame MF from the force frame FF while isolating the
metrology frame MF from vibrations in the force frame FF. As a
result, a relatively steady and quiet printing environment can be
created on the metrology frame MF which is advantageous for
accuracy.
[0119] The inkjet system further comprises a print head assembly
with one or more print heads PH which are held by a print head
holder H, and a substrate holder SH to hold the substrate S. The
print heads PH each comprise one or more, typically dozens of,
nozzles from which droplets DR can be ejected towards the substrate
S. The nozzles are preferably arranged in an array, i.e. in one or
more rows. The print heads together define a printing plane
perpendicular to the jetting direction JD, said printing plane
indicating where the substrate has to be positioned in order to
receive jetted droplets from the print heads.
[0120] The substrate holder SH is moveable relative to the print
heads PH in a printing direction PD parallel to the Y-direction and
thus parallel to the printing plane in order to let a substrate S
pass below the print head assembly. In this application a
distinction is made between passing the print head assembly while
moving from left to right in FIG. 3, i.e. moving the substrate
holder in the positive Y-direction, and passing the print head
assembly while moving from right to left, i.e. moving the substrate
holder in the negative Y-direction. The right to left movement will
be referred to as a forward swath and the left to right movement
will be referred to as a backward swath.
[0121] In order to be able to cover the entire top surface TS of
the substrate S, many configurations are possible. In a first
configuration, the printing plane in the X-direction is at least as
large as the largest possible dimension in X-direction of a
substrate S that can be held by the substrate holder SH. In that
case, a single swath of the substrate holder SH may suffice to
cover the entire top surface with droplets. In a second
configuration, the printing plane in X-direction is smaller than
the largest possible dimension in X-direction of a substrate S that
can be held by the substrate holder SH. In that case, multiple
parallel swaths are necessary to cover the entire top surface TS of
the substrate S. To allow multiple parallel swaths, the print head
assembly and/or the substrate holder SH is moveable in the
X-direction perpendicular to the printing direction PD.
[0122] In case of the printing plane in the X-direction being at
least as large as the largest possible dimension in X-direction of
a substrate S that can be held by the substrate holder SH, multiple
swaths may still be necessary in order to obtain the required
printing resolution, because the nozzles in the print heads PH may
be arranged at a larger distance than the corresponding pitch from
each other, e.g. to prevent or reduce cross talk between adjacent
nozzles. The substrate is then passing the print head assembly
multiple times, wherein each time the substrate has been moved in
X-direction corresponding to the resolution in order to print the
entire pattern.
[0123] In this embodiment, the print head assembly has a printing
plane with a dimension in X-direction at least as large as the
largest possible dimension in X-direction of a substrate the
substrate holder SH can handle. As a result, the print head
assembly can be mounted stationary with respect to the metrology
frame MF.
[0124] In the embodiment of FIG. 1, the substrate holder SH is
supported by a substrate positioning stage PS, which substrate
positioning stage PS in turn is supported by the metrology frame
MF. The substrate positioning stage PS is supported by the
metrology frame such that it is moveable in the printing direction
PD, thereby allowing to position the substrate holder SH and thus
the substrate S in the Y-direction. Positioning of the substrate
positioning stage PS is done using a stage positioning device SD,
which is able to apply forces F between the substrate positioning
stage PS and the force frame FF. As a result, the forces F do not
introduce disturbances to the metrology frame MF, but are
transmitted to the ground via the force frame FF, which results in
a higher obtainable accuracy of the inkjet system.
[0125] Between the substrate positioning stage PS and the substrate
holder SH, a holder positioning device HD is provided in order to
position the substrate holder SH in one or more degrees of freedom,
preferably at least in the printing direction PD, relative to the
substrate positioning stage PS. Using this configuration, the stage
positioning device SD can be used for coarse positioning the
substrate holder SH in the printing direction while the holder
positioning device HD can be used for fine positioning of the
substrate holder in the printing direction relative to the print
head assembly. If required, the holder positioning device HD may
also be used for fine positioning of the substrate holder in other
directions as well, e.g. the X-direction and/or the Z-direction,
and may even fine position the substrate holder in rotational
directions such as Rx, Ry and Rz as well. Preferably, the holder
positioning device HD is able to position the substrate holder
relative to the substrate positioning stage in six degrees of
freedom.
[0126] Position information about the substrate holder SH relative
to the metrology frame MF is measured by a measurement system MS.
The measurement system is at least configured to measure a position
quantity, i.e. actual position, velocity or acceleration, of the
substrate holder in the printing direction PD. In an embodiment,
the measurement system measures position information about the
substrate holder in six degrees of freedom, depending on the level
of control that is applied/required.
[0127] The output of the measurement system MS is provided to
control electronics CE. The control electronics are here depicted
as a black box that controls all processes in the inkjet system IS.
As an example, the output of the measurement system MS can be used
by the control electronics to drive the stage positioning device SD
and the holder positioning device HD (as shown in dashed lines) in
order to position the substrate holder accurately relative to the
print head assembly. The control electronics may further send
driving signals to the print heads PH (see dashed lines) in order
to print a desired pattern on the substrate while the substrate S
passes the print heads PH.
[0128] The inkjet system IS further comprises a droplet detection
device DD which measures the position of placed droplets on the
substrate, e.g. by emitting light towards the substrate and
detecting the reflected light. The obtained information is also
send to the control electronics, which may comprise a calibration
unit in order to adjust the position of the print heads relative to
each other based on the droplet position information obtained by
the droplet detection device. The droplet detection device DD may
further be used to calibrate the timing for firing the nozzles.
[0129] The FIGS. 1, 2, 3A and 3B relate in particular to the
invention.
[0130] The inkjet system IS as shown in FIG. 1 further comprises a
maintenance unit MU (see FIG. 2) configured to remove ink fluid
from the surfaces SU of the print heads PH in which the nozzles are
arranged, because ink fluid may accumulate on said surface during
printing which reduces the obtainable accuracy and reliability.
[0131] The surfaces SU of the print heads PH are shown with
reference to FIG. 2 in which the print head assembly is shown from
below. The printing direction PD is also indicated by the
respective arrow to indicate the transport direction of the
substrates for printing. Only a few print heads and a few surfaces
SU are indicated by the respective reference numerals PH and SU for
clarity reasons.
[0132] Also schematically shown in FIG. 2 are a wiper support frame
WSF of the maintenance unit MU that can be moved between a
non-operational position NOP as shown in FIG. 2 in which no
maintenance can be performed on the print heads and a maintenance
position MP (see dashed box) below the print heads in which the
maintenance unit is able to perform maintenance actions on the
print heads. For this purpose guides G1, G2 are provided along
which the wiper support frame is able to move between the
non-operational position and the maintenance position. Movement of
the wiper support frame may be caused by a respective actuation
system provided between the wiper support frame and the guides G1,
G2.
[0133] The non-operational position of the wiper support frame is
in this case adjacent the transport area of the substrates, i.e.
the movability of the wiper support frame is in a direction D1
perpendicular to the printing direction PD, which has the advantage
that the maintenance unit can be moved to a position in which the
maintenance unit does not interfere with the printing activities,
i.e. does not collide with passing substrates or substrate
holders.
[0134] The maintenance unit MU further comprises multiple wipers
with respective wiper moving devices to move the wipers in a
direction D2 relative to the wiper support frame WSF. Direction D2
is in this embodiment parallel to the longitudinal direction of the
surfaces SU of the print heads PH. The wipers and wiper moving
devices are schematically indicates by dashed boxes W as they are
operational at the other side of the wiper support frame, i.e. the
side of the wiper support frame facing towards the surfaces of the
print heads when being in the maintenance position MP.
[0135] This configuration allows the wiper support frame to be
positioned in the direction D1 such that the wipers are aligned
with the surfaces SU of a first column of print heads after which
the wipers are subsequently moved by the wiper positioning devices
along the surfaces of the print heads. After performing the wiping
action, the wipers can subsequently be positioned properly with
respect to a second column of print heads for a next wiping action,
and so forth until all print heads of the print head assembly are
wiped clean. In such a case, the wiper support frame is moved
stepwise and the wiping action is performed by the wiper moving
devices while the wiper support frame is kept stationary relative
to the print head assembly. It will be apparent to the person
skilled in the art of maintenance units for inkjet systems that
other configurations for moving the wiper are also envisaged.
[0136] So far, the maintenance unit can be according to the first
or second subaspect of fourth aspect of the invention. An example
of a maintenance unit according to the first subaspect of the
fourth aspect of the invention will be given with reference to FIG.
3A, and an example of a maintenance unit according to the second
subaspect of the invention will be given with reference to FIG.
3B.
[0137] FIG. 3A schematically depicts a part of a maintenance unit
MU according to an embodiment of the first subaspect of the
invention, which maintenance unit can be used in the inkjet system
of FIGS. 1 and 2. Shown are a wiper support frame WSF which
moveably supports a frame FR. In between the frame FR and the wiper
support frame WSF, a wiper moving device WMD is operable to
generate a force F1 to position the frame FR relative to the wiper
support frame WSF.
[0138] Arranged on the frame FR is a wiper W1 to be moved along the
surfaces of the print heads. Movement of the wiper W1 is guided by
a guide with two parallel leaf springs LF which together form a
linear guide allowing the wiper only to move up and down. Connected
to the wiper W1 is a permanent magnet PM as part of a force
actuator. The permanent magnet is arranged inside a coil CO being
another part of the force actuator, so that supplying a current I
to the coil by an appropriate energy source, e.g. a current source,
will generate a force on the permanent magnet due to the
interaction between the respective magnetic fields of the magnet
and coil. This force can be used to position the wiper in a
direction perpendicular to a surface SU of a print head PH with
respect to the surface SU of the print head PH, which print head is
shown in dashed lines.
[0139] The position of the wiper W1 relative to the surface SU is
indirectly measured using a position sensor PS based on the
assumption that the distance between frame FR and surface SU is
substantially the same each time. The output of the position sensor
is fed to a controller CON which based on the output of the
position sensor provides driving signals to a current source CS to
apply a current I to the force actuator, and to the wiper moving
device WMD. In order to provide a predetermined wiping force to the
surface SU, the maintenance unit comprises a set point generator SG
which provides a set point corresponding to a location of the wiper
W1 inside the print head PH as shown by wiper W1'. However, the
wiper W1 is not able to reach that location, so that the controller
will continuously urge the wiper W1 to the position W1' using the
force actuator. The controller comprises a limiter LI which keeps
the maximum applicable force applied by the force actuator within a
predetermine value, in this embodiment by limiting the maximum
current that can be generated by the current source. As a result,
substantially the same wiping force is applied to the wiper
independent of occurring variations in properties of the wiper.
[0140] FIG. 3B schematically depicts a part of a maintenance unit
MU according to an embodiment of the second subaspect of the fourth
aspect of the invention, which maintenance unit can be used in the
inkjet system of FIGS. 1 and 2. Shown are a wiper support frame WSF
which moveably supports a frame FR. In between the frame FR and the
wiper support frame WSF, a wiper moving device WMD is operable to
generate a force F1 to position the frame FR relative to the wiper
support frame WSF.
[0141] Arranged on the frame FR is a wiper W1 to be moved along the
surfaces of the print heads. Movement of the wiper W1 is guided by
a guide with two parallel leaf springs LF which together form a
linear guide allowing the wiper only to move up and down. Connected
to the wiper W1 is a permanent magnet PM as part of a force
actuator. The permanent magnet is arranged inside a coil CO being
another part of the force actuator, so that supplying a current I
to the coil by an appropriate energy source, e.g. a current source,
will generate a force on the permanent magnet due to the
interaction between magnet and coil. This force can be used to
press the wiper against the surface of the print heads during a
wiping action.
[0142] Preferably, the force actuator is configured such that a
substantially constant current-force relationship is obtained in
the working range of the wiper. This allows an open loop kind of
control, wherein controlling the current through the coil properly
controls the force applied to the wiper by the force actuator. The
current can be measured using a measurement resistance R1 and
measuring the voltage V1 over the resistance R1. The measured
current can be supplied to a controller CON, which is able to
control the current source CS based on said measured current.
[0143] In case the leaf springs of the guide do not apply a
significant force to the wiper while guiding the wiper in the
working range of the wiper, the force applied by the force actuator
corresponds to the wiper force with which the wiper will be pressed
against the surface of the print heads independent of the stiffness
of the wiper, the actual position of the wiper etc. In some
embodiment, it may be necessary to overcome a known or determinable
constant force, e.g. gravity, but this constant force can easily be
compensated for.
[0144] In case the forces applied by the guide to the wiper are
significant and non-constant or when the current-force relationship
is not constant, the mentioned open-loop control may not suffice.
Usually, the current-force relationship is dependent on the
position of the permanent magnet inside the coil, so that adding a
position sensor PS for determining the position of the magnet can
be beneficial for accurately determining the force applied to the
wiper by the force actuator.
[0145] The position sensor PS can alternatively or additionally be
used to determine the position of the guide. In case the stiffness
of the leaf springs in vertical direction is too high, the
disturbance force applied by the guide to the wiper is also
dependent on the position of the wiper relative to the guide.
Hence, measuring the position allows to determine the disturbance
force of the guide which when fed to the controller can be
compensated for.
* * * * *