U.S. patent application number 16/345376 was filed with the patent office on 2019-08-29 for printing apparatus.
The applicant listed for this patent is TONEJET LIMITED. Invention is credited to Simon John Edwards, Ian Philip Butler Ingham, John Lawton Sharp, Jeffrey Mark Woods.
Application Number | 20190263146 16/345376 |
Document ID | / |
Family ID | 60186314 |
Filed Date | 2019-08-29 |
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United States Patent
Application |
20190263146 |
Kind Code |
A1 |
Sharp; John Lawton ; et
al. |
August 29, 2019 |
PRINTING APPARATUS
Abstract
A printing apparatus for printing onto objects is disclosed. The
apparatus comprises a plurality of carrying devices (104) for
carrying objects (108) to be printed on, the carrying devices (104)
each comprising a rotatable handling device configured to hold and
rotate an object. A track (102) defines a path along which each of
the plurality of carrying devices can be moved. A plurality of
processing stations (106A-106F) are arranged along the track and
comprising at least one printing station (106C). A controller (110)
is configured to independently control the position and speed of
each of the carrying devices (104) with respect to the track. The
handling device is arranged to rotate an object at at least one of
the plurality of processing stations by coupling to a driving
device (610) disposed at the at least one processing station such
that torque is transmitted from the driving device to the handling
device.
Inventors: |
Sharp; John Lawton;
(Cambridge, Cambridgeshire, GB) ; Ingham; Ian Philip
Butler; (Cambridge, Cambridgeshire, GB) ; Woods;
Jeffrey Mark; (Cambridge, Cambridgeshire, GB) ;
Edwards; Simon John; (Cambridge, Cambridgeshire,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TONEJET LIMITED |
Melbourn, Royston |
|
GB |
|
|
Family ID: |
60186314 |
Appl. No.: |
16/345376 |
Filed: |
November 2, 2017 |
PCT Filed: |
November 2, 2017 |
PCT NO: |
PCT/EP2017/078036 |
371 Date: |
April 26, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J 3/4073 20130101;
B41F 17/002 20130101; B41J 11/002 20130101; H02K 49/108 20130101;
B41F 17/20 20130101; F16D 27/01 20130101; B41F 17/18 20130101 |
International
Class: |
B41J 11/00 20060101
B41J011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 2, 2016 |
EP |
16196961.3 |
Nov 2, 2016 |
EP |
16196962.1 |
Nov 2, 2016 |
EP |
16196963.9 |
Nov 2, 2016 |
EP |
16196965.4 |
Claims
1. A printing apparatus for printing onto objects, the apparatus
comprising: a plurality of carrying devices for carrying objects to
be printed on, the carrying devices each comprising a rotatable
handling device configured to hold and rotate an object; a track
defining a path along which each of the plurality of carrying
devices can be moved; a plurality of processing stations arranged
along the track and comprising at least one printing station; and a
controller configured to independently control the position and
speed of each of the carrying devices with respect to the track,
wherein the handling device is arranged to rotate an object at at
least one of the plurality of processing stations by coupling to a
driving device disposed at the at least one processing station such
that torque is transmitted from the driving device to the handling
device.
2. The printing apparatus of claim 1, wherein the controller is
configured to allow at least one of the plurality of carrying
devices to be moved with a first speed, which may be zero speed, on
the track while at least one other of the plurality of carrying
devices is moved with a second speed on the track, wherein the
second speed is not equal to the first speed.
3. The printing apparatus of claim 1, wherein the plurality of
processing stations further comprises one or more of: at least one
drying station, at least one loading station, and at least one
unloading station.
4. The printing apparatus of claim 2, wherein the plurality of
processing stations further comprises at least one drying station,
and wherein the controller is configured to control the position
and speed of each carrying device such that each carrying device is
stationary or moved at a first speed while an object is printed on
at the at least one printing station, and each carrying device is
moved at a second speed through the at least one drying station,
wherein the second speed is not equal to the first speed.
5. The printing apparatus of claim 2 to wherein the controller is
configured to allow one of the plurality of carrying devices to be
stationary or move at a first speed at a printing station while
another of the plurality of carrying devices is moved at a second
speed through a drying station.
6. The printing apparatus of claim 1, comprising a rail or pad
mounted adjacent to the track and wherein the handling device
comprises a wheel configured to contact the rail or pad as it moves
along the track, thereby causing the handling device to rotate as
it is moved along the track.
7. The printing apparatus of claim 1, wherein the track forms a
closed path on which the carrying devices can be moved.
8. The printing apparatus of claim 1, wherein at least one of the
processing stations is repeated on the track, thereby allowing
multiple objects at different positions on the track to undergo the
same process simultaneously.
9. The printing apparatus of claim 8, wherein the controller is
configured to move at least one carrying device such that it passes
through, without processing, a first of a repeated processing
station at which the carried object would normally be processed,
and instead be processed at a second of the repeated processing
station of the same type, thereby allowing the first processing
station to be inoperative without interrupting operation of the
apparatus.
10. The printing apparatus of claim 1, wherein the plurality of
processing stations comprises at least two printing stations that
are disposed parallel to each other but positioned to be offset
along their axis of printing.
11. The printing apparatus of claim 1, wherein the controller is
configured to move a first carrying device along the track at a
first processing station while a second carrying device remains
stationary at a second processing station, wherein both carrying
devices are disposed on the same track.
12. A method of moving objects along a track during a printing
process, the method comprising: moving, along a track, a first
carrying device configured to carry a first object into the
vicinity of a first processing station configured to perform a
first process; moving, along the track, the first carrying device
into an idle position, while moving a second carrying device
configured to carry a second object into the vicinity of the first
processing station; moving, along the track, the first carrying
device to a second processing station configured to perform a
second process, while at the same time moving the second carrying
device to a third processing station also configured to perform the
second process.
13. The method of claim 12, wherein the duration of the second
process is greater than the duration of the first process.
14. The method of claim 12 further comprising moving a third
carrying device configured to carry a third object from the
vicinity of the first processing station into the idle position,
while the first and second carrying devices remain at the second
and third processing stations respectively.
15. The method of claim 12, wherein the first process comprises at
least one of: loading, inspecting, unloading, cleaning, surface
energy modifying, printing, coating, drying, curing or fixing an
object carried by a carrying device.
16. The method of claim 15, further comprising keeping the first
and second carrying devices at the second and third processing
stations while first and second objects held by the respective
carrying devices are printed on.
17. The method of claim 16, further comprising: moving the first
and second carrying devices together into fourth and fifth
processing stations each configured to perform a printing operation
with the same single colour as each other, wherein the colour is
not the same as the colour printed in the second and third
processing stations; and printing onto the first and second objects
held by the first and second carrying devices.
18. The method of claim 12, wherein the track is a closed
track.
19. A method of operating an apparatus comprising: a plurality of
carrying devices for carrying objects to be printed on, the
carrying devices each comprising a rotatable handling device
configured to hold and rotate an object; a track defining a path
along which each of the plurality of carrying devices can be moved;
a controller configured to independently control the position and
speed of each of the carrying devices with respect to the track;
and a plurality of processing stations arranged along the track and
comprising at least one printing station, wherein at least one of
the processing stations is repeated on the track, the method
comprising: moving at least one carrying device such that it passes
through, without processing, a first of a repeated processing
station at which the carried object would normally be processed,
and instead be processed at a second of the repeated processing
station of the same type, thereby allowing the first processing
station to be inoperative without interrupting operation of the
apparatus.
20. The method of claim 15, wherein the second and third processing
stations are printing stations and the second process comprises
printing a single colour onto the surface of the object.
Description
[0001] The present disclosure relates to a printing apparatus in
which objects are carried between processing stations including at
least one printing station for printing an image onto the surface
of an object.
BACKGROUND TO THE INVENTION
[0002] Many industries require high volume complex printing
processes in which a large number of objects are processed in a
succession of treatments. For example, each object in such a
process might receive several ink depositions and finishing
treatments. One example of such an industrial printing process is
digital can printing, in which high resolution digital images are
applied to the bodies of cylindrical cans in a sequence of printing
operations.
[0003] A known problem in the field of high volume complex printing
processes is how to arrange processing stations and carrying
devices for the objects in such a way as to maximize the rate at
which objects are printed (throughput) while minimizing the
physical space required for the apparatus.
[0004] In order to process a large number of objects efficiently,
industrial printing processes typically involve performing
different operations on a number of objects simultaneously. The
objects are carried through a succession of processing stations in
a staggered progression, with each object undergoing a different
process to the other objects at any one time. Processes typically
include the loading and unloading of objects, inspection, the
application of one or more ink depositions, drying and the
application of an over print varnish.
[0005] A known apparatus for carrying objects between printing
stations is a mandrel wheel system (also known as a spindle disc).
In mandrel wheel systems, a plurality of mandrels are fixed at an
equal spacing around a rotating or indexing wheel. The wheel
indexes through a sequence of incremental rotations, during which
objects are carried by mandrels from station to station. In each
incremental rotation of the wheel, each mandrel is moved into the
position previously occupied by a neighbouring mandrel. At any one
time, an object at a given mandrel wheel is undergoing a process
that was performed on an object at the neighbouring mandrel wheel
during the previous step.
[0006] A problem with mandrel wheel systems is that the duration of
each indexing step is limited by the slowest process in the
sequence. Objects that are undergoing a relatively quick process
must therefore be held inactive for some time while the slowest
process is being completed. If, for example, the slowest process
takes twice as long as a faster process, objects will be required
to remain inactive at the faster processing station for twice the
duration that the process takes to perform. This inactive time is a
source of inefficiency in the printing process.
[0007] Mandrel wheel systems are also limited by the requirement
that the minimum distance between neighbouring mandrels be at least
as large as the length of the longest processing station. Hence the
overall circumferential length is at least the length of the
longest processing station multiplied by the number of processing
stations. Where several processing stations have a smaller length
than the longest station, it is necessary to provide redundant
space between the smaller processing stations in order for the
indexing to function. The additional size of the apparatus due to
the redundant space is a further source of inefficiency in mandrel
wheel printing systems.
[0008] There is a need for a printing apparatus that can overcome
the problems with mandrel wheel apparatuses while retaining the
advantages of high volume printing provided by staggered index
processing.
SUMMARY OF INVENTION
[0009] In a first aspect of the present invention, a printing
apparatus for printing onto objects is provided, the apparatus
comprising: a plurality of carrying devices for carrying objects to
be printed on, the carrying devices each comprising a rotatable
handling device configured to hold and rotate an object; a track
defining a path along which each of the plurality of carrying
devices can be moved; a plurality of processing stations comprising
locations at which carrying devices are stationary or moving while
the carried objects undergo a process, arranged along the track and
comprising at least one printing station; and a controller
configured to independently control the position and speed of each
of the carrying devices with respect to each other along the
track.
[0010] This invention therefore allows objects to be moved for
example between processing stations while other objects remain
stationary.
[0011] The provision of an apparatus in which a plurality of
carrying devices can be moved around a track independently of each
other is advantageous over known printing systems as it enables
printing systems in which processes requiring object movement can
occur simultaneously with processes requiring a stationary object,
printing systems in which the distance between neighbouring
processing stations is not limited by the footprint of the largest
processing stations, and printing systems in which parallel
printing operations allow a throughput to be achieved that is not
limited by the throughput of the slowest processing station,
thereby enabling the most optimally compact machine design.
[0012] Preferably, the controller is configured to allow at least
one of the plurality of carrying devices to be moved with a first
speed, which may be zero speed, on the track while at least one
other of the plurality of carrying devices is moved with a second
speed on the track, wherein the second speed is not equal to the
first speed.
[0013] Preferably, the plurality of processing stations further
comprises one or more of: at least one drying station, at least one
loading station, and at least one unloading station.
[0014] Preferably, the controller is configured to control the
position and speed of each carrying device such that each carrying
device is stationary or moved at a first speed while an object is
printed on at the at least one printing station, and each carrying
device is moved at a second speed through the at least one drying
station, wherein the second speed is not equal to the first
speed.
[0015] Preferably, the controller is configured to allow one of the
plurality of carrying devices to be stationary or move at a first
speed at a printing station while another of the plurality of
carrying devices is moved at a second speed through a drying
station.
[0016] Preferably, the handling device is arranged to rotate an
object at at least one of the plurality of processing stations by
coupling to a driving device at the at least one processing station
such that torque is transmitted from the driving device to the
handling device.
[0017] Preferably, the printing apparatus comprises a rail or pad
mounted adjacent to the track and wherein the handling device
comprises a wheel configured to contact the rail or pad as it moves
along the track, thereby causing the handling device to rotate as
it is moved along the track.
[0018] Preferably, the track forms a closed path on which the
carrying devices can be moved.
[0019] Preferably, at least one of the processing stations is
repeated on the track, thereby allowing multiple objects at
different positions on the track to undergo the same process
simultaneously.
[0020] Preferably, the controller is configured to move at least
one carrying device such that it passes through, without
processing, a first of a repeated processing station at which the
carried object would normally be processed, and instead be
processed at a second of the repeated processing station of the
same type, thereby allowing the first processing station to be
inoperative without interrupting operation of the apparatus.
[0021] Preferably, the plurality of processing stations comprises
at least two printing stations that are disposed parallel to each
other but positioned to be offset along their axis of printing.
[0022] In a second aspect of the present invention, a method of
using the printing apparatus of the first aspect is provided, the
method comprising moving a first carrying device along the track at
a first processing station while a second carrying device remains
stationary at a second processing station, wherein both carrying
devices are disposed on the same track. In this way it is possible
for the first processing station to process multiple objects while
the second processing station is processing a single object.
[0023] In a third aspect of the present invention, a method of
printing on objects is provided, the method comprising: moving a
first carrying device configured to carry a first object into the
vicinity of a first processing station configured to perform a
first process; moving the first carrying device into an idle
position, while moving a second carrying device configured to carry
a second object into the vicinity of the first processing station;
moving the first carrying device to a second processing station
configured to perform a second process, while at the same time
moving the second carrying device to a third processing station
configured to perform the second process.
[0024] The above steps provide a method of printing on objects that
allows parallel processes to take place in series with individual
processes on a closed track, thus allowing for an increased
throughput over known methods.
[0025] Preferably, the duration of the second process is greater
than the duration of the first process.
[0026] Preferably, the method comprises moving a third carrying
device configured to carry a third object from the vicinity of the
first processing station into the idle position, while the first
and second carrying devices remain at the second and third
processing stations respectively.
[0027] Preferably, the first process comprises at least one of:
loading, inspecting, unloading, cleaning, surface energy modifying,
printing, coating, drying, curing or fixing an object carried by a
carrying device, and, preferably, wherein the second and third
processing stations are printing stations and the second process
comprises printing a single colour onto the surface of the
object.
[0028] Preferably, the method comprises keeping the first and
second carrying devices at the second and third processing stations
while first and second objects held by the respective carrying
devices are printed on.
[0029] Preferably, the method comprises moving the first and second
carrying devices together into fourth and fifth processing stations
each configured to perform a printing operation with the same
single colour as each other, wherein the colour is not the same as
the colour printed in the second and third processing stations; and
printing onto the first and second objects held by the first and
second carrying devices.
[0030] Preferably, the track is a closed track.
[0031] In a fourth aspect of the invention, there is provided
method of operating a printing apparatus comprising: a plurality of
carrying devices for carrying objects to be printed on, the
carrying devices each comprising a rotatable handling device
configured to hold and rotate an object; a track defining a path
along which each of the plurality of carrying devices can be moved;
a controller configured to independently control the position and
speed of each of the carrying devices with respect to the track;
and a plurality of processing stations arranged along the track and
comprising at least one printing station, wherein at least one of
the processing stations is repeated on the track, the method
comprising: moving at least one carrying device such that it passes
through, without processing, a first of a repeated processing
station at which the carried object would normally be processed,
and instead be processed at a second of the repeated processing
station of the same type, thereby allowing the first processing
station to be inoperative without interrupting operation of the
apparatus.
[0032] By providing an apparatus having duplicated processing
stations, and passing through selected processing stations without
stopping, it is possible for the stations be deactivated during,
for example, maintenance, servicing or replacement of a processing
station, without interrupting operation of the apparatus.
[0033] The apparatus and method of the present invention are
applicable to a wide range of printing processes, including but not
limited to conventional contact means (e.g. offset lithography and
flexography), digital contact means (e.g. electrophotographic
printing, digital offset printing and belt transfer printing) and
digital non-contact means (e.g. inkjet printing, electrostatic
inkjet printing and piezoelectric inkjet printing).
[0034] Printing typically takes place at one or more printing
stations that are arranged along the track. The printing stations
typically form a subset of a greater number of processing stations
arranged along the track, which may also include loading/unloading
stations, drying stations, curing stations and other treatment
stations.
[0035] In some embodiments of the invention different printing
methods are combined. For example, a first printing station may use
offset printing to apply a first printed layer to the object, such
as a white base layer, while subsequent printing stations may use
digital printing, such as inkjet, to print a process colour image
on the surface of the object.
[0036] The apparatus and method of the present invention are
applicable to print processes using one or more of a variety of
inks, including but not limited to water based inks, hydrocarbon
solvent based inks and UV curable inks. Colour printing may be
performed according to a process colour model (e.g. CMYK and
extended gamut models: Hexachrome, CMYKOGV, and CMYKRGB). Spot
colour inks may be used, including white, metallic inks,
fluorescent inks, clear coatings and functional inks (e.g.
magnetic).
[0037] The following disclosure also provides examples of specific
indexing schemes using the apparatus of the present invention which
provide an increased throughput and/or a reduced total size in
comparison with equivalent systems using mandrel wheels.
[0038] The present disclosure describes printing processes with
reference to printing on the body of necked or un-necked
cylindrical monobloc containers, but the apparatus and method of
the present invention is applicable to printing "direct to shape"
on a wide range of objects including such as cans, bottles, tubes,
pots, cups or other containers or caps (e.g. wine bottle screw
caps). Materials that the object is made of may include metal,
coated metal, pre-printed material, plastic, paper, card. The
objects to be printed are preferably cylindrical but may be of
other geometries.
[0039] Aspects of the present invention will now be described by
way of example with reference to the accompanying figures.
BRIEF DESCRIPTION OF THE FIGURES
[0040] FIG. 1 is a schematic block diagram of printing apparatus
according to one embodiment of the invention.
[0041] FIG. 2 is a schematic block diagram of printing apparatus
according to second embodiment of the invention.
[0042] FIG. 3 is a schematic block diagram of printing apparatus
according to third embodiment of the invention.
[0043] FIGS. 4A-E illustrate an example of steps in a sequence
performed during operation of the apparatus shown in FIG. 3.
[0044] FIG. 5 is a schematic block diagram of printing apparatus
according to a fourth embodiment of the invention.
[0045] FIGS. 6a and 6b are perspective views of a magnetic rotation
coupling used to drive the rotation of object handling devices in
some embodiments of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0046] The present invention provides a printing apparatus and
method of printing in which carrying devices are provided along a
track and are independently moveable with respect to each other
along the track. The use of independently moveable carrying devices
provides the possibility for far more flexible indexing schemes
than are possible in known devices.
[0047] The following disclosure provides examples of specific
indexing schemes using the apparatus of the present invention which
provide an increased throughput and/or a reduced total size in
comparison with equivalent systems using mandrel wheels.
[0048] FIGS. 1 and 2 show examples of printing apparatuses 100
according to embodiments of the present invention. In each
embodiment the apparatus comprises a track 102 on which a plurality
of carrying devices 104 (hereafter "carriages") are disposed and
along which the carriages 104 can move.
[0049] A plurality of processing stations 106 are arranged along
the track 102, and each of the plurality of carriages 104 is
configured to carry a container 108 successively into the
vicinities of each of the processing stations 106. In the
embodiment shown in FIG. 1, the processing stations 106 comprise a
loading station 106A, an inspection station 106B, four printing
stations 106C which each print a different colour separation (cyan,
magenta, yellow and black), a drying station 106D, a coating
station 106E and an unloading station 106F. In the embodiment shown
in FIG. 2, the processing stations 106 comprise a loading station
106A, an inspection station 106B, eight printing stations 106C
which each print a different colour separation (white, cyan,
magenta, yellow, orange, green, violet and black), a drying station
106D, a coating station 106E and an unloading station 106F. Each
processing station is configured to perform a process on one
container 108 at a time, other than the drying station 106D which
may process up to five containers 108 simultaneously.
[0050] The series of processing stations 106 of FIGS. 1 and 2 are
chosen to provide a printing apparatus in which objects 108 are
loaded, inspected, printed upon using a four or eight separation
printing process, dried, coated and unloaded. The skilled person
will understand, however, that the number, type and order of
processing stations described with reference to this figure and the
following figures can be varied within the scope of the present
invention for use in other applications. Examples of further types
of processing stations that may be used within the scope of the
present invention are cleaning (contact or non-contact),
pre-coating, pre-treatment for modifying surface energy such as
plasma or flame treatment, curing of a coating or print, and fixing
of print.
[0051] In some embodiments, the apparatuses of FIGS. 1 and 2
comprise a cleaning station (not shown) before the printing
stations 106C for removing dust or other dirt from objects before
printing. The cleaning station may be positioned before the
inspection station 106B, after the inspection station 106B or may
be combined with the inspection station 106B. The cleaning station
may comprise an air-knife cleaner for removing dust particles from
the surface of the object.
[0052] In some embodiments, the apparatuses of FIGS. 1 and 2
comprise a print quality inspection station (not shown) positioned
after the printing stations 106C. The print quality inspection
station comprises one or more cameras arranged to inspect the
quality of the print applied at the printing stations 106C.
[0053] A control device 110 communicates with each of the carriages
104, either directly or via the track 102, in order to control the
position and speed of each of the carriages 104 independently with
respect to the track 102.
[0054] Each carriage 104 is coupled to the track 102 firstly by
means of a constraining force and secondly by means of a motive
force. The constraining force requires the carriage to move only
along the path of the track 102 and allows the carriage 104 to be
guided along the track with high precision. In some embodiments
carriage 104 comprises linear bearings that engage with the track.
The engagement between the linear bearings 104 and the track 102
constrains the motion of the carriage 104 to one degree of
freedom.
[0055] In this example, the motive force between the carriage 104
and the track 102 is provided by a magnetic linear motor system.
The carriages 104 comprise permanent magnet elements that couple
electromagnetically to a system of electromagnets spaced around the
track 102. A position sensing system measures the position of each
carriage 104 on the track 102 and a control device 110 is used to
control the position, speed and acceleration of each carriage 104
on the track 102 by controlling the magnetization of the
electromagnets spaced along the track 102. The control device 110
will typically be programmed to move the carriages 104 between
processing stations 106 according to a predetermined sequence, with
the amount of time that each carriage 104 spends at each station
106 being determined in advance.
[0056] In some embodiments the motive coupling between the
carriages 104 and the track 102 may not be via a magnetic linear
motor system and may instead be via another system that allows each
carriage to move independently with respect to the track 104. In
one alternative embodiment, individually controllable rotational
wheels are mounted on each carriage 104 and are in contact with the
track 102. In another alternative embodiment, the carriages 104 are
mechanically coupled to a track 102 using a clutch system that
allows each carriage speed to be variably controlled. In the above
described alternative embodiments, the controller may communicate
directly with the carriages 104 via a wireless interface or may
communicate via active or passive transponders embedded in the
track.
[0057] Examples of suitable track systems for use in the present
invention are Precision Track Systems from HepcoMotion and the
iTRAK Intelligent Track System produced by Rockwell Automation.
[0058] According to the embodiment of FIG. 1, the track 102 forms a
closed path, which allows carriages 104 to make repeated loops of
the path without a delay at the end of a cycle while the carriage
104 returns to its start position. In this embodiment the track 102
is substantially disco-rectangular in shape, having two horizontal
linear sections, 102A and 102B, that are vertically offset from
each other. A first end of the upper linear section 102A is
connected to a first end of the lower linear section 102B by a
semi-circular arc 102C that lies in a substantially vertical plane.
Similarly, a second end of the upper section 102A is connected to a
second end of the lower section 102B by another such arc 102D.
Other shapes of closed track 102 are possible and may be beneficial
depending on the requirements of the processes being used (e.g. as
a result of preferred orientations of operations of processing
apparatuses). In some other embodiments, the track may have
vertical linear sections along which processing stations are
arranged, and which are connected to each other at their top and
bottom by semi-circular arc sections. In other embodiments, linear
sections may not be parallel nor lie in the same plane.
[0059] The carriages 104 comprise handling devices which in this
embodiment are rotating mandrels adapted to carry containers. Each
mandrel is mounted to its respective carriage 104 via bearings that
allow the mandrel to rotate around its central axis, and thereby
rotate an attached container about its central axis, which is
coaxial with the mandrel.
[0060] In some embodiments, the handling devices may be adapted to
carry objects using a holding device such as internal or external
retaining clips or neck holding chucks. The holding devices may be
adapted for holding other objects to be printed on.
[0061] Handling devices are capable of rotating about their axes
when driven. The drive for rotating a handling device may be
achieved in a variety of ways, including a servo motor mounted on
the carriage, powered and controlled via connections to the
carriage via a power track, data track or wireless means.
Alternatively the carriages 104 may be passive, whereby drive to
the handling device is achieved by coupling rotational motion to
the handling device from a drive device not located on the
carriage. Preferably the carriages 104 are passive requiring no
external services in the form of electrical supply, control wiring,
pneumatic or other connections to retain the object.
[0062] Coupling of rotational motion to the mandrels (or other
handling devices) is provided at processing stations 106 where the
process requires the object to be rotated. The drive (the source of
the rotational motion) may be an individual servo motor, a geared
or belt drive from a common motor that serves a number of adjacent
stations, a stator coil that generates a rotating magnetic field,
etc. The coupling may be provided by a mechanical or by a magnetic
force, or a combination of these. This feature is discussed in more
detail with reference to FIG. 6.
[0063] The drying station 106D may comprise an air pump or fan for
forcing air over the surface of a printed object in order to
evaporate liquid in the deposited ink and extracting evaporated
vapour.
[0064] In other embodiments a pinning or curing station may be
provided instead of or in addition to the drying station 106D. In
some embodiments the pinning or curing station includes a means for
providing one or more of infrared radiation, ultraviolet radiation
and induction heating to the surface of a printed object.
[0065] The drying station 106D may extend along a section of the
track 102 wherein objects are controlled to move continuously
through the drier, rather than indexed between discrete positions.
Drying 106D or pinning or curing stations may be placed between
printing stations 106C if the printing process requires that ink is
dried, pinned or cured between the printing of different colour
separations.
[0066] The coating station 106E applies a layer of over print
varnish (OPV) over the surface of the printed and dried object. The
varnish may be applied by means of a roller or a spray coater. The
OPV itself imparts beneficial properties to the printed object such
as gloss, abrasion resistance, etc, and may be chosen for
compatibility with the object surface material and inks. The
varnish may be thermally curing, UV curing, etc., and curing may be
performed partially or completely as part of the apparatus or by a
separate curing oven downstream of the apparatus.
[0067] As a carriage 104 performs a single loop of the track 102,
it visits selected processing stations 106 sequentially. The steps
set out below describe an example of a series of processes that are
undergone in relation to one carriage during a single loop of the
track 102 in the embodiments shown in FIGS. 1 and 2.
[0068] After unloading a printed container at the end of a previous
cycle, the carriage 104 is brought into the vicinity of a loading
station 106A and stopped while an unprinted container 108 is
brought to the loading station 106A by a conveyor (not shown). The
container 108 is presented in coaxial alignment with the mandrel of
the carriage 104 and transferred onto the mandrel of the carriage
104.
[0069] From the loading station 106A, the carriage 104 carries the
container to an inspection station 106B comprising a defect
inspection device. The carriage 104 stops again at the inspection
station 106B where the container 108 is then rotated through at
least one complete revolution of the mandrel. During this rotation,
the defect inspection device checks for any deformities or
contaminants on the surface of the container 108 that could be
detrimental to the printing process. Rotation of the container 108
is achieved by a magnetic coupling between the rotating motion of a
drive device located at the inspection station 106B and the
mandrel/handling device, which is engaged when the carriage 104 is
stopped at the inspection station 106B. The inspection device may
be an optical camera system, an electrically conducting bar with an
electrical current detection system, or any other suitable surface
inspection device. If a defect is detected the container 108 is
ejected from the mandrel at the inspection station 106B. Before
moving on, the mandrel may be checked to ensure the object has been
unloaded successfully, whereafter the empty mandrel continues
through the apparatus in the normal way except that the processing
steps at each process station are disabled for the empty
mandrel.
[0070] After a successful inspection, the carriage 104 and the
container 108 are moved to a first printing station 106C. There the
container 108 is rotated on the mandrel with a speed and number of
revolutions appropriate to the printing process employed while the
printing process takes place. As described above, the printing
process is not constrained to any one method, but may include any
suitable printing process that is adapted for, or capable of,
printing onto containers. These may be a conventional contact
printing method such as offset lithography, flexography or rotary
screen printing, or a digital method such as electrophotography or
non-contact ink jet printing. For the example of an inkjet method
of printing in which a printhead has ejectors spaced more widely
than the printed pixels on the container surface, the container 108
is rotated over multiple complete revolutions while the carriage is
at the printing station. During each revolution of the container
108, as the printhead is ejecting ink in accordance with the image
to be printed, the printhead is moved in a direction parallel to
the axis of the container for a distance of one pixel spacing. This
continues over the multiple revolutions of the container 108,
resulting in full image coverage on the container 108 surface from
multiple interleaved passes of the container surface beneath the
printhead. During other processes, a different number of
revolutions may be required.
[0071] As with the inspection station 106B, rotation of the
container 108 at a printing station 106C is performed by coupling
the rotating motion or torque of a drive located at the printing
station 106C to the handling device when the carriage is at the
printing station 106C.
[0072] Registration of the print with the container 108 surface
position is performed at a printing station 106C by controlling the
synchronisation of the printhead or print device in accordance with
position signals obtained by a non-contact read-head 611 reading
the angular position of a rotary incremental encoder ring 612
mounted on the handling device.
[0073] The encoder ring 612 has encoded thereon information that
can be used to infer the angular position of the handling device
and, hence, the angular position of a container 108 thereon. A
stationary read-head 611 is mounted separately at a fixed position
with respect to the track 102 at a printing station 106C, where the
handling device is rotated by coupling to a drive device. The
read-head 611 is configured to read the angular position data
encoded in the encoder ring 612, when the carriage 104 is in a
position on the track 102 whereby the encoder ring 602 aligns with
the read head 611, and provide information to the control device
110. Suitable encoder devices are the TONiC.TM. optical read-head
and RESM rotary encoder ring manufactured by Renishaw plc.
[0074] The use of stationary read-heads automatically provides the
process controller at a given processing station the real-time data
it needs about the position of the container 108 currently at that
station 106 without the need to switch data permanently associated
with a particular carriage 104 between processing stations 106 as
it progresses through the apparatus. It further eliminates the need
for power or data connections to the carriage 104 for the purposes
of reading the angular position of the container 108 at a
processing station 106.
[0075] The arrangement of a stationary read-head at a print station
106C, reading from an encoder ring 612 on the carriage 104,
automatically compensates for errors in linear position of the
carriage 104 at a print station 106C, if the encoder ring is the
same diameter as the object being printed. This is because a small
translational error or movement along the track that moves the axis
of the object relative to the printhead, which would otherwise lead
to a print registration error, appears to the read-head in the same
way as a rotation of the encoder ring 602 by the same tangential
distance. Therefore, no print registration error results from a
small translational error of the carriage position at a printing
station.
[0076] The carriage 104 and container 108 are then moved to
subsequent printing stations 106C at which subsequent print
operations are carried out sequentially on the container 108. The
subsequent print operations may use the same or different print
method to the initial print operation in order to add further
process colour separations or spot colours. The subsequent printing
stations 106C may act to increase the width of the print beyond the
width of a single print station by having a second print station of
the same colour ink as the first but displaced with respect to the
first in a direction along the axis of printing (the axis of
printing being defined here as the direction of the line of an
array of ejectors or nozzles of a printhead or contact line with
the container of a print roller, etc.) In general, the sequence of
printing stations 106C that operate on a container may comprise a
variety of printing methods to achieve a desired effect. Control of
the rotation and registration of the print to the container 108
surface are performed at each printing station 106C in the same
manner as in the first printing station 106C.
[0077] In embodiments in which a print quality inspection station
is provided after the printing stations 106C, the object may be
rotated at a lower rotational velocity at the print quality
inspection station than at the printing stations 106C (for example,
3 rps compared with 5 rps) in order to account for a camera data
acquisition speed that is lower than the print speed.
[0078] Once printed, the carriage 104 and container 108 pass
through a drying station 106D. The dryer 106D may be implemented
such that the carriages 104 carrying the printed containers 108
move continuously through the dryer 106D rather than halting in one
or more stations. Drying in this example is by airflow, but other
examples may use heated air, infra-red radiation, induction heating
of the container body, ultraviolet radiation, etc. Because the
carriages 104 of the present invention are independently moveable,
it is possible for one carriage 104 to pass continuously through a
drying station 106D while other carriages 104 are stopped at other
processing stations 106.
[0079] In one embodiment, containers 108 are rotated as the
carriages 104 move through the dryer by the rolling contact of a
wheel mounted on each handling device with a rail mounted parallel
with the track. The wheel is turned by its rolling contact with the
rail as the carriage moves along the track, thereby causing the
container 108 to rotate. Such a rail may be mounted at any position
on the track at which it is desirable to rotate the container 108
as the carriage moves along the track. A short rail or pad may also
be usefully positioned prior to a station 106 at which a handling
device is rotated by a driving device 610, in order to provide some
initial angular momentum in the direction of rotation to provide a
faster synchronisation of the coupling at the station 106.
[0080] Following the drying process, the carriage 104 and printed
container 108 are brought to a coating station 106E where an
over-print varnish (OPV) is applied. The varnish is applied by a
roller that transfers a controlled layer of OPV from an anilox
roller to the container 108 surface. During this operation the
container 108 is rotated at least one complete revolution via the
magnetic coupling in the same manner as at the inspection station.
The OPV is typically a thermally curable formulation, which, when
dried and cured, gives the print a high degree of protection from
handling and abrasion.
[0081] The carriage 104 and the container 108 are then moved to the
unloading station 106, at which the printed container 108 is
removed from the mandrel. In some embodiments the printed container
is transferred onto a vacuum type belt (not shown) that conveys the
printed and varnished containers 108 to a curing oven, which is
separate to the apparatus for curing of the OPV. After the printed
container 108 has been unloaded from the carriage 104, the mandrel
may be checked to ensure that the container has been properly
unloaded, after which the empty carriage 104 returns to the loading
station 106 to begin a subsequent cycle.
[0082] While the carriage 104 and container 108 are undergoing the
processes described above, other carriages 104 and containers 108
undergo the same series of processes at staggered timing. Thus,
while one or more containers 108 are positioned at printing
stations 106C, other containers will be at the inspection 106B and
loading 106A stages of the sequence. In general, each container 108
visits each processing station 106 in sequence. Each processing
station 106 is also visited by each container 108 in the order that
the containers 108 are added to the system. In order to maximise
efficiency of the processes, each processing station 106 should be
active for as great a proportion of the time as possible.
[0083] The above described apparatus and method are advantageous
over the mandrel wheel device described in the background section.
The above device allows one container 108 to be moved continuously
through a drying station while other containers are held at
printing stations 106. This provides greater flexibility in terms
of possible simultaneous processes than in previously known
devices. The above apparatus and process also allow for a system in
which the distance between neighbouring processing stations 106 is
not limited by the footprint of the largest processing station 106.
This is possible because the distance between the individually
controlled carriages 104 can be varied around the track.
[0084] FIG. 3 shows another embodiment of the present invention in
which processing stations 106 that have a slower processing cycle
(i.e. which require a longer time over which to perform a process
on a container) are repeated along a path, while processing
stations 106 with a faster processing cycle are not repeated.
Rather than sequentially visiting each of the processing stations
106 in an apparatus, a carriage 104 stops at every non-repeated
processing station 106, but passes through some repeated processing
stations 106 without stopping. This provides a system in which more
than one container 108 may undergo the same process simultaneously
at repeated processing stations 106, which allows slower processes
to be performed in parallel on a track 102. By performing slower
processes in parallel, while performing faster processes serially,
the throughput of the print process is increased in comparison to
printing apparatuses in which each container 108 visits every
processing station 106.
[0085] The printing apparatus of FIG. 3 comprises a loading station
106A, an inspection station 106B, eight printing stations 106C, a
drying station 106D, a coating station 106E and an unloading
station 106F provided along a track 102. In this example, the
printing process performed by each printing station 6C has a
greater duration than the loading process, the inspection process,
the coating process and the unloading process. The drying process
of a single container 108 may be slower than the printing process;
but, because the drying station 106D is able to process up to five
containers 108 simultaneously, it has a greater throughput than
each of the printing stations 106C.
[0086] The eight printing stations 106C comprise four pairs 112 of
identical stations 106C provided along the track 102. The first
pair 112C comprises a first cyan printing station 112Ci and a
second cyan printing station 112Cii. The second pair 112M comprises
a first magenta printing station 112Mi and a second magenta
printing station 112Mii. The third pair 112Y comprises a first
yellow printing station 112Yi and a second yellow printing station
112Yii. The fourth pair 112K comprises a first black printing
station 112Ki and a second black printing station 112Kii. (The
order C-M-Y-K of the process colours may be chosen differently to
suit the printing process used).
[0087] As each carriage 104 passes through the apparatus, it
sequentially stops at the loading station 106A, the inspection
station 106B, the coating station 106E and the unloading station
106E. Rather than stopping at each printing station 106C, a given
carriage 104 stops at only the first or second printing station
106C of each pair 112 of printing stations. Consecutive carriages
104 stop at alternating printing stations 106C, such that if a
leading carriage 104 stops at the first printing station 106C of
each pair 112, the following carriage 104 will stop at the second
printing station 106C of each pair 112, and the next carriage 104
will again stop at the first printing station 106C of each pair
112, and so on.
[0088] The above arrangement of printing stations 106C has a
greater throughput than an equivalent apparatus in which each
container 108 passes through every printing station 106C of the
apparatus. Such a system is made possible by using a printing
apparatus in which carriages 104 can be individually controlled.
The provision of individually controllable carriages 104 allows a
first set of containers 108 to be sequentially carried through a
series of faster stations (or carried into an idle waiting area),
while other containers 108 are held stationary (with respect to the
track) in a slower processing station 106.
[0089] The skilled person will understand that the principles of
the above described apparatus can be applied to systems having a
different numbers of printheads, e.g. three sets of six printheads.
The combinations of printheads 106 used in a given embodiment will
depend on the relative processing times of different processes in
the apparatus, as well as the specific goals of the user.
[0090] FIGS. 4A-E show the steps in which a plurality of carriages,
A, B, C, D, E and F, carry a plurality of containers through the
inspection station 6B and printing stations of the printing
apparatus of FIG. 3. The positions of carriages and containers
shown in FIGS. 4A-E are shown in the sequence that they occur in a
method according to an embodiment of the invention.
[0091] In FIG. 4A, a first carriage, A, is stationary at the
inspection station 106B where a first container that it is holding
is inspected. At this time, a second carriage, B, is stationary at
the loading station 106A where it is loaded with a second
container.
[0092] In FIG. 4B, carriage A is moved into idle position 402 and
stopped, while the second container held by carriage B is inspected
at the inspection station 106B. At this time, a third container is
loaded onto a third carriage, C.
[0093] In FIG. 4C, after the inspection of the second container is
complete, carriages A and B are moved together to the pair of cyan
printing stations 112C, with carriage A at the second cyan printing
station 112Cii and carriage B at the first cyan printing station
112Ci. The cyan printing stations 112C begin printing on the first
and second containers held by carriage A and carriage B
respectively. At the same time, carriage C is moved to the
inspection station 106B, where the third container inspected, and a
fourth container is loaded onto a fourth carriage, D, positioned at
the loading station 106A.
[0094] In FIG. 4D, carriage C is moved into the idle position 402,
while carriage D is moved to the inspection station where the
fourth container is inspected. A fifth carriage E is moved to the
loading station 106A where it is loaded with a fifth container.
Because the printing process at the printing stations 112Ci and
112Cii has a longer duration than the loading and inspection
processes, carriages A and B remain at, and continue printing, in
the cyan printing stations 112Ci and 112Cii respectively.
[0095] In Figure E, the cyan printing process has been completed
and carriages A and B are moved together to the pair of magenta
printing stations 112M. At approximately the same time, the
inspection of the fourth container is completed, and carriages C
and D are moved together to the cyan printing stations, 112Ci and
112Ci, with carriage C moving from the idle position 402 to the
second cyan printing station 112Cii and carriage D moving from the
inspection station 106B to the first cyan printing station 112Ci
without stopping in the idle position 402. At the same time,
carriage E is moved to the inspection station 106B and a fifth
carriage, F, is loaded with a fifth container at the loading
station 106A.
[0096] For an apparatus in which processes are performed only in
series, the total throughput of the apparatus is limited by the
throughput of the slowest element.
[0097] For example, if the slowest process step is printing, having
a stationary printing duration of 0.8 seconds and a time to index
between printing stations of 0.2 seconds, the maximum throughput
through the printing station, and therefore the entire apparatus,
is 1 container per second (60 containers per minute).
[0098] By using parallel printing processes, the total throughput
of the apparatus can be increased beyond the throughput of a
slowest process in the cycle. Table A below shows a detailed
example of a process sequence using the printing apparatus of FIG.
3 to perform slow processes in parallel. It can be seen that while
the printing stations 106 have a stationary printing duration of
0.8 seconds and a time to index between printing stations of 0.4
seconds, the apparatus is capable of providing a throughput of 2
containers per 1.2 seconds, equivalent to 100 containers per
minute.
[0099] Details of the process timings for each stage of the
sequence are given in Table A.
TABLE-US-00001 TABLE A Process step Distance [ m ] Duration [ s ]
##EQU00001## Simultaneous process step Distance [ m ] Duration [ s
] ##EQU00002## 1 Empty carriage A arrives at Loading station. 2
Carriage A at Loading station while object A is loaded onto holder
A. 0.0 m 0.3 s ##EQU00003## Object A subsequently remains on holder
A for entire machine sequence. 3 Move carriage A to Inspection
station. 0.1 m 0.3 s ##EQU00004## Empty carriage B arrives at
Loading station. 4 Carriage A at Inspection station while object A
is rotated and examined for 0.0 m 0.3 s ##EQU00005## Carriage B at
Loading station while object B is loaded onto holder B. 0.0 m 0.3 s
##EQU00006## defects. If a defect is found Object B subsequently
the object is ejected from remains on holder B for its holder and
the carriage entire machine sequence. continues its sequence with
an empty holder. 5 Move Carriage A to Idle position. 0.1 m 0.3 s
##EQU00007## Move carriage B to Inspection station. 0.1 m 0.3 s
##EQU00008## 6 Carriage A at Idle position. 0.0 m 0.3 s
##EQU00009## Carriage B at Inspection station while object B is
rotated and examined for 0.0 m 0.3 s ##EQU00010## defects. If a
defect is found the object is ejected from its holder and the
carriage continues its sequence with an empty holder. 7 Move
Carriage A through Print 1(i) station without stopping to Print
1(ii) 0.2 m 0.4 s ##EQU00011## Move Carriage B without stopping
through Idle position to Print 1(i) 0.2 m 0.4 s ##EQU00012##
station. station. 8 Carriage A at Print 1(ii) station while object
A is rotated and printed onto. 0.0 m 0.8 s ##EQU00013## Carriage B
at Print 1(i) station while object B is rotated and printed onto.
0.0 m 0.8 s ##EQU00014## 9 Move Carriage A through Print 2(i)
station without stopping to Print 2(ii) 0.2 m 0.4 s ##EQU00015##
Move Carriage B through Print 1(ii) station without stopping to
Print 2(i) 0.2 m 0.4 s ##EQU00016## station. station. 10 Carriage A
at Print 2(ii) station while object A is rotated and printed onto.
0.0 m 0.8 s ##EQU00017## Carriage B at Print 2(i) station while
object B is rotated and printed onto. 0.0 m 0.8 s ##EQU00018## 11
Move Carriage A through Print 3(i) station without stopping to
Print 3(ii) 0.2 m 0.4 s ##EQU00019## Move Carriage B through Print
2(ii) station without stopping to Print 3(i) 0.2 m 0.4 s
##EQU00020## station. station. 12 Carriage A at Print 3(ii) station
while object A is rotated and printed onto. 0.0 m 0.8 s
##EQU00021## Carriage B at Print 3(i) station while object B is
rotated and printed onto. 0.0 m 0.8 s ##EQU00022## 13 Move Carriage
A through Print 4(i) station without stopping to Print 4(ii) 0.2 m
0.4 s ##EQU00023## Move Carriage B through Print 3(ii) station
without stopping to Print 4(i) 0.2 m 0.4 s ##EQU00024## station.
station. 14 Carriage A at Print 4(ii) station while object A is
rotated and printed onto. 0.0 m 0.8 s ##EQU00025## Carriage B at
Print 4(i) station while object B is rotated and printed onto. 0.0
m 0.8 s ##EQU00026## 15 Move Carriage A to start of Drying station.
0.6 m 1.2 s ##EQU00027## Move Carriage B through Print 4(ii)
station without stopping to between Print 0.2 m 0.4 s ##EQU00028##
4(ii) station and start of Drying station Move Carriage B to start
of Drying station 0.5 m 1.4 s ##EQU00029## 16 Move carriage A
through Drying station at constant speed while rotating 0.5 m 2.5 s
##EQU00030## Move carriage B through Drying station at constant
speed while rotating 0.5 m 2.5 s ##EQU00031## object A. object B.
17 Move Carriage A to OPV station. 0.2 m 0.2 s ##EQU00032## Move
Carriage B to OPV station. 0.2 m 0.2 s ##EQU00033## 18 Carriage A
at OPV station while object A is rotated and coated with OPV. 0.0 m
0.4 s ##EQU00034## Carriage B at OPV station while object B is
rotated and coated with OPV. 0.0 m 0.4 s ##EQU00035## 19 Move
carriage A to Unloading station 0.2 m 0.2 s ##EQU00036## Move
carriage B to Unloading station 0.2 m 0.2 s ##EQU00037## 20
Carriage A at Unload station while object A is unloaded from holder
A. 0.0 m 0.3 s ##EQU00038## Carriage B at Unload station while
object B is unloaded from holder B. 0.0 m 0.3 s ##EQU00039## Move
carriage A to Loading station 0.5 m 1.0 s ##EQU00040## Move
carriage B to Loading station 0.5 m 1.0 s ##EQU00041##
[0100] It should be understood that when reference is made to an
object or carriage being stationary, this refers to the position of
the carriage 104 along the track 102. The skilled person will
understand that the term "stationary" in this context includes the
possibility of other motions, including rotation of a handling
device of the carriage and of the object about its axis.
[0101] The above example provides a detailed account of one scheme
of parallel processing according to the present invention. It will
be understood by the skilled person that the above described
concepts can be applied to a wide range of printing apparatuses
with differing functional requirements. The number of processes and
parallel operations will depend on the individual requirements of
the apparatus.
[0102] For example, in another embodiment, pairs of objects to be
printed could be loaded in parallel, inspected in series and then
printed three at a time. In general, parallel processing can be
made most efficient when the ratio of the durations of each
operation most closely matches the ratio of the number of parallel
stations provided for each operation.
[0103] Furthermore, a system as described above, having independent
control of the movement of objects and having replicated processing
stations, provides redundancy that allows selected processing
stations to be passed through without processing, during, for
example, maintenance, servicing or replacement of a processing
station, without interrupting operation of the apparatus.
[0104] FIG. 5 shows an apparatus in which the same set of eight
printing stations 106C used in the apparatus of FIG. 3 may be
configured in an alternative way to increase the width of the print
area rather than the throughput of the machine. In this embodiment,
for each pair of printheads 112, the first and second printheads
are offset to each other in a direction parallel to the axes of the
objects to be printed by a distance of less than or equal to the
print width from a single printhead 106C. An object is indexed
through all eight printing stations, receiving a colour print
process. The resulting print on the object is up to twice the width
of a single printhead 106C.
[0105] FIGS. 6A and 6B show an example of a magnetic rotation
coupling system 600 of a type that can be used at a processing
station to drive the object handling devices 104 of the above
described embodiments. The coupling system comprises a driving
device 610 (shown in FIG. 6A) having a drive disc 601 that is
rotated by a motor (not shown). The driving device 610 is located
at a processing station to drive a passive coupling disc 603 that
forms part of the movable carrying device 104.
[0106] In this example, the coupling comprises two non-magnetic
discs, a drive disc 601 at the processing station and a driven disc
603 on the carriage 104. The two non-magnetic discs, 601 and 603,
carry permanent magnets, 604, inset into the facing surfaces of the
discs, 601 and 603, in complementary patterns. When the axes of the
two discs, 601 and 603, are brought into alignment by the carriage
104 arriving at the processing station, the driven disc 603 angle
self-aligns to the drive disc 601 angle thereby synchronising its
rotation to the rotation of the drive disc 601.
[0107] An advantage of using a driving system that is separate from
the carriages is that the carriages do not require any electrical
connections. The handling devices are passive devices in which
controlled rotation of the container is achieved via a coupling
from a drive device located at a processing station where rotation
of the object to be printed is required. The absence of electrical
connections in the carriages substantially reduces the difficulty
of designing a suitable apparatus in which the carriages can
independently move around a track.
* * * * *