Description of Invention
[0001] This invention relates to a method of printing.
[0002] In pixel based printing systems such as dot matrix ribbon printing, or thermal transfer
printing which utilises a carrier or web which carries print medium such as ink, (
known in thermal printing, as ribbon or foil), one major expense for a user is the
cost of the ribbon or foil.
[0003] According to the invention we provide a method of printing utilising a printing head
having a plurality of printing elements each of which is operable to transfer a pixel
of print medium from a carrier onto an adjacent substrate, the method comprising the
steps of causing relative movement between the substrate and carrier, and the print
head, such that the print head moves relative to an area of the carrier from a start
position to an end position whilst utilising some or all of the printing elements
to transfer a first set of pixels of print medium from the area of the carrier onto
the substrate, causing relative movement between the print head and the carrier to
replace the print head at the start position, causing relative movement between the
carrier and the substrate such that fresh substrate is presented adjacent to the area
of the carrier, and causing relative movement between the fresh substrate and the
carrier, and the print head, such that the print head moves relative to the area of
the carrier again from the start position to the end position whilst utilising some
or all of the printing elements, to transfer a second set of pixels of print medium
from the area of the carrier, onto the adjacent fresh substrate.
[0004] In all pixel based printing systems, print density is determined by dot resolution.
The invention offers a way for a user to save the cost of thermal printing ribbon
or foil, or other carrier and print medium where the relatively high density print
which can be obtained by at least the higher resolution dot based printing systems,
is not required.
[0005] By "fresh substrate" we mean an entirely fresh substrate, such as a different label,
or a further part of the same substrate, onto which pixels of print medium have not
previously been transferred from the carrier.
[0006] After each printing operation the printing head may be moved e.g. laterally, away
from the carrier and substrate, and held a short distance away from the carrier whilst
the carrier and/or substrate are moved in preparation for the next printing operation,
and then moved e.g. laterally, back towards the carrier and substrate.
[0007] If desired, during printing, during the first relative movement between the substrate
and the carrier, and the print head, a first set only of the printing elements is
employed to transfer the first set of pixels of print medium onto the substrate. Likewise,
during printing, during the relative movement between the fresh substrate and carrier,
and the print head, a second set of printing elements is employed to transfer the
second set of pixels of print medium onto the substrate.
[0008] Thus for example, two separate substrates or separate areas of substrate can be printed
for example, with the same information, but the apparatus only consumes one area of
ribbon or foil.
[0009] Particularly where the printing head includes a high density of printing elements,
the method may be repeated several times for the same area of carrier, with each relative
movement between substrate and carrier, and the print head, utilising different printing
elements to transfer different pixels of print medium onto substrate. During a final
printing operation on a particular area of the carrier all, or substantially all,
the printing elements may be used thus ensuring that, even if there is some misalignment
between the printing elements and the remaining pixels of print medium, the remaining
pixels of print medium will be transferred.
[0010] Alternatively, during printing, during the first relative movement between the substrate
and carrier, and the print head from the start position to the end position, printing
elements are utilised to transfer pixels of print medium from the area of the carrier
onto the substrate, and during printing, during the relative movement between fresh
substrate and carrier, and the print head, printing elements are utilised to transfer
pixels of print medium from the area of the carrier onto the fresh substrate such
that the pixels of print medium are transferred from different pixel positions of
the carrier to the pixel positions from which the print medium was transferred during
the previous relative movement between the substrate and carrier, and the print head.
[0011] In this case, during a final printing operation on a particular area of the carrier,
the printing elements may be used such that printing elements are utilised in pixel
positions at least partially coincidental with pixel positions of the carrier from
which print medium was transferred in a previous printing operation.
[0012] In one embodiment, the relative movement between the substrate and carrier, and the
print head, is produced by movement of the print head whilst the substrate and carrier
are held stationary.
[0013] In another embodiment, the relative movement between the substrate and carrier, and
the print head, is produced by movement of the substrate and carrier whilst the print
head is held stationary.
[0014] The invention is particularly but not exclusively applicable to thermal transfer
printing, where the print medium comprises inkcarried on a carrier comprising a continuous
backing web, and the printing elements are energised to produce heat to transfer pixels
of ink from the carrier onto a substrate.
[0015] In such an application, there are typically at least six, commonly eight or twelve
or more printing elements per millimetre of printing head, arranged in a single line
array. The printing elements may, however, be arranged in a multiple line, or other
non-single line array.
[0016] However the invention may be applied to any other dot based printing system such
as a dot matrix printer which utilises a woven ribbon as a carrier for ink and where
printing elements are arranged in an array.
[0017] According to a second aspect of the invention we provide a printing apparatus comprising
a print head operable to transfer pixels of print medium from a carrier onto an adjacent
substrate, means to maintain the print head during printing, stationary, and to move
the carrier and substrate in a first direction past the print head from a start position
to an end of print position over an area of the carrier and means to cause the carrier,
after a first printing operation, to move relative to the print head in a second direction
generally opposite to the first direction and to present fresh substrate adjacent
to the print head so that in a subsequent printing operation, the fresh substrate
is moved with carrier, in the first direction past the printing head.
[0018] According to a third aspect of the invention we provide a method of printing with
a thermal printer having a print head with an array of heating elements, and a print
ribbon with a layer of thermally sensitive ink for deposition on a print area of a
medium to be printed, wherein the method comprises:
selectively energizing a first set of heating elements to deposit ink from a first
portion of the ribbon onto the print area of the medium to be printed, and then a
second set of heating elements to deposit ink on another print area using ink from
undepleted parts of the first ribbon portion;
displacing the ribbon and repeating the above selective energizing steps on further
print areas using a second ribbon portion.
[0019] The method may include using a printer in which the print head is movable relatively
to the print ribbon and generally parallel to the surface of the ribbon and has an
array of heating elements extending laterally with respect to the direction of print
head movement, and moving the print head in a first stroke whilst selectively energizing
the first set of heating elements, subsequently moving the print medium, and then
moving the print head in a second stroke whilst energizing the second set of heating
elements, using the same ribbon portion for both print head strokes.
[0020] A method may further include using a printer in which the print head is movable relatively
to the print ribbon and has a linear array of heating elements extending laterally
with respect to the direction of movement of the print head, and moving the print
head in a first stoke relative to the print ribbon and the print area of the print
medium, controlling the print head to energize the first set of heating elements during
the first stroke, thereby to heat the first portion of the ribbon and to deposit ink
onto the print medium, controlling the print head to energize the second set of heating
elements during a subsequent print stroke to heat the same first ribbon portion so
as to use ink on the first ribbon portion not used in a previous print stroke, and
displacing the ribbon after the print strokes in which alternate heating elements
are used so that the print head may heat a second portion o f the ribbon during a
subsequent specific number of print strokes.
[0021] The invention will now be described with reference to the accompanying drawings in
which :
FIGURE 1 is a side illustrative view of a printing apparatus which may be operated
by a method in accordance with the invention, without a print medium carrying carrier
being shown, for clarity.
FIGURE 2 is a top plan view of the printing apparatus of figure 1, showing the print
medium carrying carrier.
FIGURE 3 is a front illustrative view of the printing apparatus of figure 1 again
without the print medium carrying carrier for clarity.
FIGURE 4 is a plan view of part of an alternative embodiment of a printing apparatus
in accordance with the invention.
[0022] Referring to Figures 1 to 3, there is shown a printing apparatus 10 comprising a
print head assembly 11 which mounts a plurality of individually energisable thermal
printing elements, preferably provided on an edge of the print head assembly 11, in
a single line array. The print head assembly 11 is movable relative to carrier, being
a web 12 which carries print medium comprising ink, whilst the thermal printing elements
are individually selectively energised under computer control, wherein the elements
will become hot, thus to cause pixels of ink to be removed from the web 12 and deposited
onto a substrate (not shown) to the right hand side of the apparatus 10 as seen in
figure 1. The substrate may for example be a label which is subsequently applied to
an article, or packaging material, or may be the article itself, which substrate moves
past the printing apparatus 10 and is temporarily halted at the printing apparatus
10 whilst printing thereon is effected.
[0023] In this way, information can be printed, in ink, on the substrate.
[0024] The information usually is, one or more alpha-numeric characters, to indicate for
example, a sell-by date. The or each such character is defined by a plurality of pixels
of print medium i.e. ink, transferred from the web 12 or other carrier by the energised
printing elements of the printing head assembly 11 as the print head assembly 11 is
moved relative to the carrier and substrate.
[0025] The web 12 carrying the ink is provided on a supply spool 14 carried on a hub 15,
the web 12 passing around a web guide path comprising idler rollers 16,17,18, around
a further roller 19 between the roller 19 and a drive roller R and then on to a take
up spool mounted on a hub 20. The drive roller R and take up spool are driven, as
hereinafter explained, from a motive means 21 which is in this example, a stepper
motor.
[0026] The hub 15 and hence spool 14 provides some resistance to web 12 being paid out therefrom,
this being provided by a friction means being a clutch material W and a spring S configured
as is well known in the art. The take up spool is also mounted on a hub 20 having
a similar friction means.
[0027] The print head assembly 11 is driven for movement relative to the web 12 by the motor
21 via a transmission. The transmission comprises a pair of generally parallel spaced
apart flexible drive members comprising belts 23,24, which are entrained respectively
about pairs of rollers 25,26, and rollers 27,28.
[0028] The first pair of rollers 25,26, are mounted on respective generally parallel and
vertical drive shafts 30,31, with shaft 31 being driven via a belt 32 or chain drive
or otherwise as required, from an output shaft 33 of the stepper motor 21.
[0029] The second pair of rollers 27,28, are each mounted on respective generally parallel
and vertical shafts 34,35, via bearings so that the rollers 27,28, are free to rotate
relative to their respective shafts 34,35.
[0030] Drive shaft 30 has secured to it, a gear 30a which meshes with a gear 30b on a shaft
L on which roller R is provided.
[0031] As can be seen from figure 1, the print head assembly 11 is of generally rectangular
configuration, and is secured to a mounting structure T which is clamped at screws
36,37, (see figure 3) to the belts 23,24. Upon operation of the motor 21 drive is
transmitted from the drive shaft 33 of the motor to each of the belts 23,24, via the
shaft 31, and hence the print head assembly 11 is caused to move either in the direction
indicated by arrow A, relative to the web 12, or an opposite direction depending upon
the sense of rotation of the output shaft 33 of the motor 21.
[0032] The structure T comprises a slider element V and a bearing B which is fixed relative
to the print head assembly 11 and is slidable relative to the slider element V. Hence
the print head assembly 11 can slide in the direction of arrow B and in an opposite
direction, relative to the slider element V.
[0033] The mounting structure T is also clamped at its rear edge 40 to a third belt 41 as
shown at 42 in figure 2, the third belt 41 being driven in synchronism with belts
23,24, from shaft 31, but being entrained only about the shafts 31 and 30.
[0034] The print head assembly 11 also carries at its rear edge, a guide roller 44 which
is rotatable about a generally vertical axis 45 transverse to the direction A of movement
of the print head assembly 11 during printing. The roller 44 bears on a generally
horizontal post 46 of generally circular cross section, the post being mounted via
a lever arm 47 for rotation about a horizontal axis 48 generally parallel to but spaced
from the post 46, on a bearing 50 which is fixed relative to a body of the printing
assembly 10.
[0035] Hence as the print head assembly 11 moves from side to side, in the direction of
arrow A or oppositely, the print head assembly 11 is guided for movement via the guide
roller 44 and post 46.
[0036] A strong spring 47a is provided between the post 46 and a frame part P of the apparatus
10 to bias the post 46 about axis 48 away from the print head. assembly 11. The print
head assembly 11 carries a hook formation H which engages with post 46 so that as
the post 46 moves in the direction generally opposite to that of arrow B, the print
head assembly 11 is moved with it, and slides relative to the mounting structure T.
[0037] The amount that the post 46 can be moved by the spring 47a is restricted by means
of an air cylinder 50 which is positioned behind the post 46.
[0038] In the figures, the print head assembly 11 is shown in a start position spaced away
from a substrate, but with the web 12 carrying the ink, entrained over an edge of
the print head assembly 11 mounting the thermal printing elements.
[0039] To bring the print head assembly 11 towards the web 12 and substrate to effect printing,
the print head assembly 11 is moved in a direction indicated by arrow B, i.e. laterally,
which is transverse to the direction of movement of the print head assembly 11 during
printing, as indicated by arrow A.
[0040] Movement of the post 46 and hence of the print head assembly 11 in direction B is
achieved by means of the air cylinder 50 and its piston 51, which, when actuated,
rotates the guide post 46 about axis 48, thus to urge the print head assembly 11 towards
the substrate, against the restoring force of the spring 47a. The piston 51 is arranged
to retain the print head assembly 11 in its extended position against the restoring
force of the springs 47a, whilst the print head assembly 11 moves from the beginning,
to end of printing positions in direction of arrow A, to effect printing on the substrate.
[0041] At the end of printing, when the print head assembly 11 is in its end of printing
position, the piston 51 is deactuated and the print head assembly 11 is moved in an
opposite direction to arrow B by the restoring force of the spring 47a away from the
substrate and, by actuating the motor 21 in an opposite sense of rotation, the print
head assembly 11 is moved back to the start position shown in the drawings in a direction
opposite to the direction of arrow A.
[0042] The hub 20 of the take up spool carried by hub 20 is driven from the motor 21 via
a drive belt 80 shown in dotted lines in figure 2, which is fixed to rotate with the
drive roller R. Between drive roller R and the shaft L which is rotated by gear 30b,
there is a mechanical one-way clutch which permits the shaft L to rotate relative
to the roller R as the stepper motor 21 rotates in one sense of rotation (clockwise
in figure 2) during a printing operation. Thus the web 12 and take-up spool 20 remain
stationary during a printing operation as the extended print head 11 moves downwardly
as seen in figure 2. Aone-way clutch suitable for this purpose is well known in itself
and is a purely mechanical unit.
[0043] Of course, when the stepper motor 21 is rotated in an opposite sense of rotation,
in the absence of any other means, the one-way clutch would cause the drive roller
R to rotate clockwise as seen in figure 2, and thus drive the web 12 which is entrained
about it, as well as the take up spool 20, so that the web 12 advances as the print
head assembly 11 is moved back to the start of print position indicated in the drawings.
[0044] To enable the apparatus 10 to operate in accordance with the present invention, there
is provided a further clutch between the gear 30b and shaft L so that during the return
movement of the printing head 11 to the start of print position, the shaft L and hence
the drive roller R can be prevented from rotating with the gear 30b. Such a clutch
preferably comprises an electrically operated clutch which is under the control of
the computer control of the apparatus.
[0045] Further features of the printing apparatus are as follows.
[0046] In this embodiment described, the spools 14 and spool carried by hub 20 as well as
the drive roller R (but not its shaft L) and idler rollers 19, 18 and 17 are carried
by a cassette 55 which can be removed from the body of the printing apparatus 10 to
facilitate replenishing the printing apparatus 10 with web 12.
[0047] The web guide path includes a peeler bar P' behind which the web 12 passes immediately
after passing over the print head assembly 11, the bar P' being operable to ensure
proper separation of ink deposited on the substrate, and remaining web 12.
[0048] The belt 41 is maintained under tension by means of a tensioning roller 59 and the
belts 23,24, can also be kept under constant tension by tensioning rollers 60.
[0049] When the cassette 55 carrying the spools 14 and 20 is removed, a micro switch 61
which feeds power to the stepper motor 21 is tripped so that there is no risk of the
mechanism of the printing apparatus 10 being actuated without the cassette 55 being
in position.
[0050] In the event that the web feed spool 14 becomes empty, an electronic sensor carried
by a clamp 62 past which the web 12 passes, will signal the lack of web 12 to an operator,
and/or disable printing apparatus 10.
[0051] The amount of movement of the print head assembly 11 in a direction opposite to that
of arrow A i.e. the return movement, is restricted by means of a microswitch carried
on a clamp means 63 which senses the print head assembly 11 when returned to its start
position, immediately to stop motor 21.
[0052] It will be appreciated that by virtue of the print head assembly 11 being mounted
on the flexible belts 23,24, and 41 via the mounting structure T, the assembly 11
is able to float to a smaller degree about the central axis of post 46. The roller
44 mounted at the rear of the printing assembly 11 engages with the post 46 to restrict
other movements.
[0053] Hence in the event that the substrate onto which print medium is to be transferred
is not exactly at right angles to the array of printing elements mounted by the print
head assembly 11, the assembly 11 can move slightly about the central axis of post
46 as the print head assembly 11 is moved towards the substrate by the actuator 50
to accommodate such slight misalignment.
[0054] Hence, improved quality of print can be achieved throughout the entire printing operation.
In the absence of some means to accommodate misalignment of the substrate, quality
of print would tend to suffer over at least some of the area of the substrate onto
which information is printed.
[0055] The printing apparatus described above may be operated by a method in accordance
with the first invention as follows.
[0056] In the apparatus described, the print head assembly 11 may comprise at least six,
but possibly eight, twelve, or more energisable printing elements per millimetre width
of the print head assembly 11, with all of the energisable print elements arranged
in a single line array across the printing head assembly 11.
[0057] Rather than utilising all of the printing elements for printing, as the print head
assembly 11 is traversed relative to the webs 12 and substrate, a first set only of
the printing elements may be utilised on a first printing operation. For example,
every alternate printing element may be utilised whilst the print head assembly 11
is traversed over or otherwise moves over an area of the web 12 from its start to
end of print positions to transfer pixels of ink from the web 12 onto the substrate.
[0058] Hence an alpha-numeric character or a plurality of such characters may be printed
on the substrate. However, as only some of the printing elements are utilised, the
print density will obviously be less overall than if all the printing elements of
the print head assembly 11 were used during printing. Whereas this might not be acceptable
for printing machine-readable information such as a bar code, where the information
printed is for example a sell-by date comprising a plurality of alpha-numeric characters,
a human readerwill have little difficulty in reading the information.
[0059] At that stage, rather than advancing the web 12, the print head assembly 11 is moved
as hereinbefore described relative to the web 12 back to the start of print position,
but the electronically operated clutch between the gear 30b and its shaft L is operated
so as to isolate the roller R so that the web 12 is not advanced. The substrate may
be advanced, or an entirely fresh substrate may be presented adjacent to the same
area of the web 12 which was traversed by the print head assembly 11 immediately previously.
[0060] The print head assembly 11 may then be operated to traverse the same area of the
web 12, but different printing elements are utilised during printing to transfer pixels
of ink from the web 12 onto the substrate.
[0061] Thus only some of the printing elements are utilised the first time the print head
assembly 11 traverses the area of the web 12, and only some, and different, printing
elements are utilised the second time the print head assembly 11 traverses the same
area of the web 12.
[0062] At this stage, when the print head assembly 11 is returned to the start of print
position, the clutch between the gear 30b and its shaft L is operated to cause the
roller R and the take-up spool 20 to rotate so that the web 12 is advanced.
[0063] The take up spool 20 may have a slipping clutch which permits differential movement
between the spool 20 and the drive roller R as the spool 20 becomes filled with used
web 12.
[0064] Thus the amount of web 12 utilised for printing will be reduced by half, in this
example, assuming that the web 12 is advanced after the print head assembly 11 has
relatively traversed the web 12 for a second time.
[0065] In arrangements where a large number of printing elements per millimetre are provided,
it might be possible for the print head assembly 11 to traverse or otherwise move
over the same area of the web 12 more than twice, but each traverse of the same area
of the web 12 will utilise different printing elements with a consequent saving in
web 12.
[0066] During second or other the final printing operation using a particular area of web
12all of the printing elements may be used. This ensures that, even if there is some
misalignment between the printing elements and the remaining pixels of ink on the
web 12, sufficient of the remaining pixels of ink will be transferred to achieve satisfactory
printing.
[0067] It will be appreciated that during any printing operation when only alternative printing
elements are thermally energised, it may be necessary to provide added power to the
individually energised printing elements compared with the power supplied when all
the printing elements are utilised in a printing operation. This is because the individual
printing elements may be less able to produce, retain and dissipate heat to the respective
ink pixels of the ink carrier, when a reduced number of the printing elements in a
given area of print head are energised compared with the number which would be utilised
in a conventional method.
[0068] Hence in a printing operation performed by the method of the invention, during a
first printing operation when only alternate printing elements for example are energised
selectively, the individual printing elements may have a first power provided to them,
whereas in a subsequent printing operation using the same area of ink carrier, when
all of the printing elements are energized selectively, a second reduced power may
be provided to each of the printing elements when they are energised.
[0069] Where the print head assembly 11 traverses the same area of the web 12 more than
twice, it will be appreciated that for each such traverse, fresh substrate, being
either a fresh area of substrate, or an entirely different substrate, would need to
be presented adjacent to that area of the web 12.
[0070] The apparatus described with reference to the drawings may alternately be operated
by the method of the invention as follows.
[0071] During a first traverse or other movement of the print head assembly 11 relative
to the web 12 between the start and end positions, each of the printing elements may
be utilised to transfer pixels of print medium i.e. ink, from the web 12 onto the
substrate. However the printing elements may only be operated for certain pixel positions
(rows) between the start and end of printing positions.
[0072] Again the print density will be lower than if the printing elements were all actuated
in all pixel positions, but again, where the information to be printed is intended
for a human reader, the print density will in most instances be sufficient for the
human reader to read the information.
[0073] Once the print head assembly 11 is returned to the start position (without the web
12 having been advanced) and traversed over or otherwise moved relative to the same
area of the web 12 a second time, each of the printing elements may again be utilised,
but by ensuring that each printing element is not operated when in the same pixel
position that the printing element was previously operated during the first traverse
of the print head 11 relative to the web 12, pixels of ink are transferred from different
pixel positions of the web 12 to the pixel positions from which ink was transferred
during the previous traverse of the print head assembly relative to that area of web
12.
[0074] Utilising this method, again the amount of web 12 utilised by the apparatus will
be reduced by half, assuming that the web 12 is advanced after the print head assembly
11 has relatively traversed the web 12 for the second time.
[0075] Again, the method of the invention may cause the print head assembly 11 to traverse
or otherwise move relative to the carrier for more than two times, provided that for
each such movement during printing, no printing element is operated in the same pixel
position between the start and end of printing positions, that the printing element
was operated in a previous printing movement of the print head 11 relative to the
same area of the web 12.
[0076] However, during the final printing operation using a particular area of carrier all
the printing elements may be used in all possible pixel positions to ensure that an
adequate amount of ink is transferred onto the fresh substrate in the event of any
slight misalignment between the web 12 and the printing elements.
[0077] Various modifications may be made to the apparatus described with reference to the
drawings, as follows.
[0078] The printing apparatus 10 may be used in other orientations to that described, as
appropriate to the position and orientation of the substrate.
[0079] For example, although the printing apparatus 10 described has been of the type which
utilises a web 12 carrying ink which is deposited by means of thermal printing elements
onto a substrate, the invention may be applied to any other printing apparatus having
a plurality of selectively operable printing elements to effect printing, such as
a 24 dot matrix printer. The print head assembly 11 may incorporate an array being
a single line of printing elements as described, or an array being a matrix i.e. multiple
lines of such elements.
[0080] Although in the arrangement described, the print head assembly 11 is carried via
the mounting structures T by three drive belts 23,24,41, in another arrangement, less
than three drive belts, or more than three drive belts, may be provided.
[0081] In place of drive belts, any other suitable endless loop members, such as chains,
could be used to provide a transmission and mounting for the print head assembly 11,
or indeed any other suitable flexible or rigid drive member or members which is/are
able to provide drive to, and a means of mounting the print head assembly 11, could
be used.
[0082] Although it is preferred for single stepper motor 21 to be used as a motive means
for the printing apparatus 10, with suitable logic control e.g. utilising a computer,
if desired more than one stepper motor 21 or other motive means may be provided. For
example a separate motor may be provided to drive the drive roller R and take up spool
20 for the web 12.
[0083] Any alternative means to the piston and cylinder arrangement 50 for effecting movement
of the print head assembly 11 towards the substrate, may be provided.
[0084] Although the invention has been described with reference to an apparatus in which
the print head assembly 11 moves relative to the carrier of print medium i.e. web
12, and substrate during printing, the invention may be applied to an apparatus of
the type in which the print head is at a fixed position, and the carrier carrying
print medium, and the substrate are together moved relative to the print head during
printing. In such an embodiment, rather than a print head assembly moving back to
a start position of an area of the carrier in order relatively to traverse or otherwise
move relative to the carrier a second time, the carrier may be arranged to be moved
back relative to the print head assembly whilst fresh substrate is presented adjacent
that area of the carrier, and the carrier and fresh substrate is traversed past the
fixed print head assembly a second, and where appropriate, further, times.
[0085] Referring now to figure 4, a partial view of one embodiment of such an apparatus
100 shows web path and drive components. A web 112 carrying the ink is provided on
a supply spool 114 carried on a hub 115, the web 112 passing around a web guide path
comprising guide roller 116, print head roller 117 against which the print head 111
exerts a force during printing, guide roller 118, web drive roller 119, which is operable
to drive the web 112 and is solely responsible for the amount of web 112 movement
in either direction, as hereinafter explained. The web is then guided on to a take-up
spool 120 carried on a hub 121. Supply spool 114, web drive roller 119, and take-up
spool 120 are driven from a single motive means 122, which in this example is a two-way
stepper motor, via a drive and timing belt 123. Spool 114 is driven through a one-way
clutch and slip clutch and spool 120 is driven through a one way clutch and slip clutch,
the one way clutches operating in tandem such that the two clutches are operable so
that when the stepper motor 122 is operated so as to move the timing belt 122 in a
clockwise direction as seen in figure 4, the take up spool 120 is driven, whilst spool
114 is not driven. Thus web 112 may be paid out from the supply spool 114 and taken
up onto spool 120. Conversely, if stepper motor 122 is operated so as to move the
timing belt 123 in an anti-clockwise direction as seen in figure 4, the supply spool
114 is driven so as to rotate anticlockwise and take-up web 112 onto it, whilst spool
120 is not driven and web 112 can be paid out from spool 120 for a purpose hereinafter
described.
[0086] Additionally, slip clutches are provided for each of these spools 114 and 120 to
accommodate differential movement between the spools 114 and 120 as increasingly,
web is fed out from the supply spool 114 onto the take-up spool 120. The slip clutches
also provide slight resistance (drag) when the respective spools 114,120, are paying
out web 112.
[0087] If desired, at least the one-way clutches may be electrically operated, although
simple mechanical devices are adequate to perform this function.
[0088] A substrate 124 is supplied from a supply spool (not shown) and passes between the
web 112 and print head roller 117. Particularly if the substrate 124 consists of labels
on a web, the path can continue around the print head drive roller 117, around a nip
roller 125 and a guide roller 126. If the substrate is of another form such as polythene
film, the path may continue in substantially the same direction, as indicated by chain
line 127. The substrate 124 is driven by a second motive means (not shown) so that
the substrate 124 moves in synchronism with the web 112 past the print head assembly
which is indicated by arrow 111.
[0089] Movement of the substrate may be continuous or intermittent as desired.
[0090] During printing, the stepper motor 122 drives the timing belt 123 in a clockwise
direction, the one-way clutch and slip clutch of spool 114 offers only slip/drag resistance
to clockwise rotation and spool 114 acts as a supply spool. At the same time, the
one way clutch and slip clutch of spool 120 allow spool 120 to be driven with web
drive roller 119 in a clockwise direction so that the web 112 is taken up on to spool
120. By virtue of the slip clutch on the take-up spool 120, the actual amount of web
112 which traverses the print head 111, is governed entirely by the web drive roller
119 which is directly driven via belt 123 from the motor 122, and preferably comprises
a rubber coated roller which gives good stiction with the web 112.
[0091] After completion of the first printing operation using an area of web 112, the print
head assembly 111 is pulled back a small distance, in the order of half to one millimetre,
from the web 112 in the direction of arrow C, thus releasing the pressure exerted
on roller 117 during printing. This is achieved as the print head assembly 111 is
mounted on an arm 130 which is rotatable about axis 130a of idler roller 16. The arm
130 is spring biased by a spring wound about the central axis 130 of idler roller
116, or otherwise, to urge the arm 130 away from the reaction roller 117.
[0092] The arm 130 and hence the print head 111, can be moved against the force of that
spring by a pneumatically operated actuator which acts on the arm 130 in the direction
of arrow D. Other suitable arrangements are no doubt possible.
[0093] The substrate 124 is then driven on so that an area of fresh substrate is provided
adjacent to the print head 111. At the same time, the stepper motor 122 drives the
timing belt 123 in an anticlockwise direction, the one way and slip clutches of spool
120 offering only slip/drag resistance to web 112 being paid out from spool 120 so
that spool 120 acts as a supply spool whilst the one-way and slip clutches of spool
114 causes the spool 114 to be driven so that spool 114 acts as a pick-up spool. However,
the amount of web 112 driven is again governed by the web drive roller 119. By this
means, the same area of web 112 from which pixels of ink were removed during the previous
printing operation can be aligned with the print head 111 and fresh substrate in preparation
for a second printing operation.
[0094] This process may be repeated as often as required for an area of web 112. When that
area of web 112 has been fully used, the web 112 is not wound back as the substrate
114 is wound on, but a first printing operation is carried out using a fresh area
of web 112.
[0095] The operation of the two-way stepper motor 122 and the second stepper motor which
drives the substrate 124, must be accurately co-ordinated. This may be achieved by
mechanical means but is most conveniently provided by means of computer control. Alternatively,
the stepper motor 122 may be arranged to drive the substrate.
[0096] In each case, the print head assembly 112, where the printing elements are energised
thermally to transfer pixels of print medium i.e. ink from the carrier web 112 onto
the substrate, control is preferably achieved by a computer, together with the relative
movements of the print head and/or carrier and/or substrate as appropriate to cause
either selective printing elements to be energised during each print operation, or
for all or substantially all of the printing elements to be used during each printing
operation but the printing elements are only energised in selected pixel positions
during each printing operation to enable the same area of web 112 or other carrier
respectively to be used to print information, by a method as described in detail above
with reference to the embodiment of figures 1 to 3.
[0097] The mechanism of figure 4, although ideal for performing a method of the first aspect
of the invention, may be used in other apparatus where it is desired to move carrier
in an appropriate direction to the direction the carrier and substrate move during
printing.
[0098] The features disclosed in the foregoing description, or the following claims, or
the accompanying drawings, expressed in their specific forms or in terms of a means
for performing the disclosed function, or a method or process for attaining the disclosed
result, as appropriate, may, separately or in any combination of such features, be
utilised for realising the invention in diverse forms thereof.
1. A method of printing utilising a print head (11) having a plurality of printing
elements each of which is operable to transfer a pixel of print medium from a carrier
(12) onto an adjacent substrate, the method comprising the steps of;
(a) carrying out a first printing operation by means of causing relative movement
between the substrate and carrier (12), and the print head (11), such that the print
head (11) moves relative to an area of the carrier (12) from a start position to an
end position whilst utilising some or all of the printing elements to transfer a first
set of pixels of print medium from the area of the carrier (12) onto the substrate;
(b) causing relative movement between the print head (11) and the carrier (12) to
replace the print head (11) at the start position;
(c) causing relative movement between the carrier (12) and the substrate such that
fresh substrate is presented adjacent to the area of the carrier (12), and
(d) carrying out a second printing operation by means of causing relative movement
between the fresh substrate and the carrier (12), and the print head (11), such that
the print head (11) moves relative to the area of the carrier (12) again from the
start position to the end position whilst utilising some or all of the printing elements,
to transfer a second set of pixels of print medium from the area of the carrier (12),
onto the adjacent fresh substrate.
2. A method according to claim 1 characterised in that after each printing operation,
the print head (11) is moved away from the carrier (12) and substrate and held a short
distance away from the carrier (12), whilst the steps of causing relative movement
between the print head (11) and carrier (12) to replace the print head (11) at the
start position, and causing relative movement between the carrier (12) and the substrate
such that fresh substrate is presented adjacent to the area of the carrier (12), are
performed and then the print head (11) is moved back towards the carrier (12) and
substrate.
3. A method according to claim 1 or 2 characterised in that during printing, during
the first relative movement between the substrate and the carrier (12), and the print
head (11), a first set only of the printing elements is employed to transfer the first
set of pixels of print medium on to the substrate.
4. A method according to claim 3 characterised in that during printing, during the
relative movement between the fresh substrate and carrier (12), and the print head
(11), a second set of printing elements is employed to transfer the second set of
pixels of print medium on to the substrate.
5. A method according to claim 4 characterised in t hat the printing elements of the
second set of printing elements are different from the printing elements of the first
set.
6. A method according to claim 3 characterised in that during the relative movement
between the fresh substrate and carrier (12) all of the printing elements are used
to transfer the second set of pixels of the print medium from the area of the carrier
(12) onto the adjacent fresh substrate.
7. A method according to any one of the preceding claims characterised in that the
method includes performing one or more repetitions of the steps of causing a relative
movement between the print head (11) and the carrier (12) to replace the print head
(11) at the start position, and causing relative movement between the carrier (12)
and the substrate such that fresh substrate is presented adjacent to the area of the
carrier (12), and carrying out a further printing operation by means of causing relative
movement between the fresh substrate and the carrier (12), and the print head (11),
such that the print head (11) moves relative to the area of the carrier (12) again
from the start position to the end position whilst utilising some or all of the printing
elements, to transfer a further set of pixels of print medium from the area of the
carrier (12), on to the adjacent fresh substrate.
8. A method according to claim 7 characterised in that during a final printing operation
on a particular area of the carrier (12), all, or substantially all, the printing
elements are used to transfer pixels of the print medium from the area of the carrier
(12) onto the adjacent fresh substrate.
9. A method according to claim 1 or 2 characterised in that during printing, during
the first relative movement between the substrate and carrier (12), and the print
head (11) from the start position to the end position, printing elements are utilised
to transfer pixels of print medium from the area of the carrier (12) onto the substrate,
and during printing, during the relative movement between fresh substrate and carrier,
and the print head (11), printing elements are utilised to transfer pixels of print
medium from the area of the carrier (12) onto the fresh substrate such that the pixels
of print medium are transferred from different pixel positions of the carrier (12)
to the pixel positions from which the print medium was transferred during the previous
relative movement between the substrate and carrier (12), and the print head (11).
10. A method according to claim 9 characterised in that the pixel positions of the
carrier (12) from which the print medium was transferred during the first relative
movement between the substrate and carrier (12) and the print head (11) are interleaved
with the pixel positions of the carrier (12) from which the print medium is transferred
during the subsequent relative movement between first substrate and carrier (12) and
the print head (11).
11. A method according to claim 9 or claim 10 characterised in that during a final
printing operation on the area of the carrier (12), the printing elements are used
such that printing elements are utilised in pixel positions at least partially coincidental
with pixel positions of the carrier (12) from which print medium was transferred in
a previous printing operation.
12. A method according to any preceding claim characterised in that the relative movement
between the substrate and carrier (12), and the print head (11), is produced by movement
of the print head (11) whilst the substrate and carrier are held stationary.
13. A method according to any one of claims 1 to 11 characterised in that the relative
movement between the substrate and carrier (12), and the print head (11), is produced
by movement of the substrate and carrier (12) whilst the print head (11) is held stationery.
14. A method according to any one of claims 1 to 13 wherein the printing elements
are arranged in a single line array or in a non-single line array.
15. A printing apparatus comprising a print head (11) operable to transfer pixels
of print medium from a carrier (12) onto an adjacent substrate, means to maintain
the print head (11) during printing, stationary, and to move the carrier (12) and
substrate in a first direction past the print head (11) from a start position to an
end of print position over an area of the carrier (12) and means to cause the carrier
(12), after a first printing operation, to move relative to the print head (11) in
a second direction generally opposite to the first direction and to present fresh
substrate adjacent to the print head (11) so that in a subsequent printing operation,
the fresh substrate is moved with carrier (12), in the first direction past the printing
head (11).
16. A method of printing with a thermal printer having a print head with an array
of heating elements, and a print ribbon with a layer of thermally sensitive ink for
deposition on a print area of a medium to be printed, wherein the method comprises:
selectively energizing a first set of heating elements to deposit ink from a first
portion of the ribbon onto the print area of the medium to be printed, and then a
second set of heating elements to deposit ink on another print area using ink from
undepleted parts of the first ribbon portion;
displacing the ribbon and repeating the above selective energizing steps on further
print areas using a second ribbon portion.
17. A method according to claim 16 using a printer in which the print head is movable
relatively to the print ribbon and generally parallel to the surface of the ribbon
and has an array of heating elements extending laterally with respect to the direction
of print head movement, and moving the print head in a first stroke whilst selectively
energizing the first set of heating elements, subsequently moving the print medium,
and then moving the print head in a second stroke whilst energizing the second set
of heating elements, using the same ribbon portion for both print head strokes.
18. A method according to claim 16 using a printer in which the print head is movable
relatively to the print ribbon and has a linear array of heating elements extending
laterally with respect to the direction of movement of the print head, and moving
the print head in a first stoke relative to the print ribbon and the print area of
the print medium, controlling the print head to energize the first set of heating
elements during the first stroke, thereby to heat the first portion of the ribbon
and to deposit ink onto the print medium, controlling the print head to energize the
second set of heating elements during a subsequent print stroke to heat the same first
ribbon portion so as to use ink on the first ribbon portion not used in a previous
print stroke, and displacing the ribbon after the print strokes in which alternate
heating elements are used so that the print head may heat a second portion of the
ribbon during a subsequent specific number of print strokes.