[0001] The invention relates to a sheet handling device comprising: a sheet support plate
made of a heat conductive material having a first heat capacity, said plate having
at least one cavity formed between a top wall defining a top surface of the plate
and a bottom wall defining a bottom surface of the plate; and a temperature control
system including a circulating system for circulating a temperature control fluid
through said cavity.
[0002] In the copying and printing industry, a temperature controlled sheet support plate
is frequently used for supporting an image receiving sheet and at the same time controlling
the temperature thereof. For example, in a hot melt ink jet printer, a sheet, e. g.
a sheet of paper, is advanced over a sheet support plate while the image is being
printed. At room temperature, the hot melt ink is solid, and it is therefore necessary
that the ink is heated in the printer above its melting point, before it can be jetted
onto the paper. The ink droplets that have been jetted onto the paper tend to spread-out
more or less before the ink solidifies. In order to obtain a suitable and constant
amount of spreading of the ink droplets, the temperature of the sheet support plate
and hence the temperature of the paper should be controlled such that the ink cools
down at an appropriate rate.
[0003] In an initial phase of the print process, when a new sheet has been supplied, it
is generally desirable to heat the sheet and to keep it at a suitable operating temperature.
However, in the further course of the print process, it is necessary to dissipate
the heat of the ink that solidifies on the paper. To that end, a temperature control
fluid, e. g. a liquid, may be passed through the cavity in the plate in order to control
the temperature of the plate.
[0004] Moreover, in order to obtain a good print quality, the surface of the sheet support
plate should be perfectly flat, at least in the region where the image is being printed.
Thus, the support plate should have a sufficient strength so that it will not bend
under mechanical or thermal stress. As a result, the plate must have a certain minimum
thickness, and this implies a certain minimum volume of the cavity.
[0005] For reasons of power consumption, it is required that the printer enters into a so-called
sleep mode, when the printer is not operating for a certain time, and in the sleep
mode, among others, the heating system for the sheet support plate is switched off.
As a result, like in US 2002/0071016, when a new image is to be printed, it will take
a certain time until the sheet support plate has been heated to its operating temperature.
[0006] It is an object of the invention to provide a sheet handling device in which the
sheet support plate can quickly be brought to its operating temperature.
[0007] According to the invention, this object is achieved by a sheet handing device of
the type indicated above, wherein the cavity contains a displacement body which is
spaced apart from the top wall of the cavity and is made of a material having a second
heat capacity which is smaller that said first heat capacity of the material of the
plate.
[0008] The displacement body reduces the effective volume of the cavity but, thanks to its
smaller heat capacity, does not significantly increase the overall heat capacity of
the plate. As a result, the volume of the temperature control fluid that is needed
for filling the cavity is reduced and, consequently, less time and/or heating power
is needed for heating the fluid and hence the plate to its operating temperature.
[0009] As an additional advantage, the Reynolds number for the flow of fluid through the
cavity is increased, which results in an improved heat exchange between the fluid
and the plate.
[0010] Useful details and further developments of the invention are indicated in the dependent
claims.
[0011] When the displacement body is spaced apart from both the top wall and the bottom
wall of the cavity, the fluid may circulate through hollow spaces near both the top
wall and the bottom wall of the cavity, so that the top and bottom surfaces of the
plate may always be kept on the same temperature and a thermal distortion of the plate
is prevented.
[0012] In a preferred embodiment, the sheet support plate has a plurality of elongated cavities
which extend in parallel through the plate and are separated by separating walls.
This assures a high rigidity of the plate. The separating walls may be formed with
trough-holes which connect the top surface of the plate to a suction chamber provided
at the bottom surface thereof, so that the sheet may be sucked against the top surface
of the plate. This assures a perfectly flat configuration of the sheet, especially
in the region where the image is being formed, and at the same time assures a good
thermal contact between the sheet and the plate.
[0013] The displacement bodies may then simply be formed by bars made of synthetic resin
such as polystyrene, which are inserted into each of the cavities and may easily be
manufactured as extruded profiles or the like. Preferably, the displacement bodies
are in contact with the separating walls of the plate, so that each cavity is divided
into two passages which extend near the top surface and the bottom surface, respectively,
of the plate and are only connected to one another and to the circulating system at
the respective ends of the cavities.
[0014] According to a further development of the invention, the displacement bodies may
be made of a material which shows a phase transition with a relatively high latent
heat at a transition temperature close to the operating temperature of the plate.
For example, the transition may be one between a liquid state and a crystalline, semi-crystalline
or amorphous solid state. Thus, when the temperature of the plate exceeds the transition
temperature, the displacement bodies or at least parts thereof may melt, with absorption
of latent heat, so that the temperature of the plate is returned to the operating
temperature. Conversely, when the temperature drops below the transition temperature,
the displacement bodies will solidify and will release the latent heat. Thus, the
temperature of the plate is stabilized at the operating temperature.
[0015] In a particularly preferred embodiment, at least part of the material of the displacement
bodies, is in the high-temperature state, e. g. the molten state, when the plate has
its operating temperature. Then, when the printer enters into the sleep mode and the
heating system for the plate, i. e. the heating system which heats the temperature
control fluid, is switched off, the displacement bodies will release their latent
heat, and the cooling-down of the plate is delayed. As a result, when the printer
is activated again after a short interval, the plate will still have a high temperature,
and the operating temperature may quickly be re-established with reduced energy consumption.
[0016] Preferred embodiments of the invention will now be described in conjunction with
the drawings, in which:
- Fig. 1
- is a schematic perspective view of a hot melt ink jet printer;
- Fig. 2
- is a partial cross-section of a sheet support plate in the printer shown in Fig. 1;
- Fig. 3
- is a partial cross-section of a sheet support plate according to a modified embodiment;
and
- Fig. 4
- is a temperature/heat-diagram for a material used in the plate shown in Fig. 3.
[0017] As is shown in Fig. 1, a hot melt ink jet printer comprises a platen 10 which is
intermittently driven to rotate in order to advance a sheet 12, e. g. a sheet of paper,
in a direction indicated by an arrow A over the top surface of a sheet support plate
14. A number of transport rollers 16 are rotatably supported in a cover plate 18 and
form a transport nip with the platen 10, so that the sheet 12, which is supplied from
a reel (not shown) via a guide plate 20, is paid out through a gap formed between
an edge of the cover plate 18 and the surface of the sheet support plate 14.
[0018] A carriage 22 which includes a number of ink jet printheads (not shown) is mounted
above the sheet support plate 14 so as to reciprocate in the direction of arrows B
across the sheet 12. In each pass of the carriage 22, a number of pixel lines are
printed on the sheet 12 by means of the printheads which eject droplets of hot melt
ink onto the sheet in accordance with image information supplied to the printheads.
For the sake of simplicity, guide and drive means for the carriage 22, ink supply
lines and data supply lines for the printheads, and the like, have not been shown
in the drawing.
[0019] The top surface of the sheet support plate 14 has a regular pattern of suction holes
24 which pass through the plate and open into a suction chamber 26 that is formed
in the lower part of the plate 14. The suction chamber is connected to a blower 28
which creates a subatmospheric pressure in the suction chamber, so that air is drawn-in
through the suction holes 24. As a result, the sheet 12 is sucked against the flat
surface of the support plate 14 and is thereby held in a flat condition, especially
in the area which is scanned by the carriage 22, so that a uniform distance between
the nozzles of the printheads and the surface of the sheet 12 is established over
the whole width of the sheet and a high print quality can be achieved.
[0020] The droplets of molten ink that are jetted out from the nozzles of the printheads
have a temperature of 100°C or more and cool down and solidify after they have been
deposited on the sheet 12. Thus, while the image is being printed, the heat of the
ink must be dissipated with a sufficient rate. On the other hand, in the initial phase
of the image forming process, the temperature of the sheet 12 should not be too low,
because otherwise the ink droplets on the sheet 12 would be cooled too rapidly and
would not have time enough to spread-out. For this reason, the temperature of the
sheet 12 is controlled via the sheet support plate 14 by means of a temperature control
system 30 which circulates a temperature control fluid, preferably a liquid, through
the plate 14. The temperature control system includes a circulating system with tubes
32 that are connected to opposite ends of the plate 14. One of the tubes passes through
an expansion vessel 33 containing a gas buffer for absorbing temperature-dependent
changes in the volume of the liquid. As will be readily understood, the temperature
control system 30 includes heaters, temperature sensors, heat sinks, and the like
for controlling the temperature of the fluid, as well as a pump or other displacement
means for circulating the fluid through the interior of the sheet support plate 14,
as will now be described in detail in conjunction with Fig. 2.
[0021] The sheet support plate 14, which has been shown in cross-section in Fig. 2, is made
of a material, such as a metal, having a relatively high heat conductivity and also
a relatively high heat capacity. A number of elongated cavities 34 are formed in the
interior of the plate 14 so as to extend in parallel with one another and in parallel
with the direction (B) of travel of the carriage 22 between opposite ends of the plate
14, where they are connected to the tubes 32 through suitable manifolds. Each cavity
34 is delimited by a top wall 36, a bottom wall 38 and two separating walls 40. The
top walls 36, together, define the top surface 42 of the plate 14 which is machined
to be perfectly flat. Between each pair of two separating walls 40, which delimit
to adjacent cavities 34, a hollow space 44 is formed, through which the suction holes
24 pass through into the suction chamber 26.
[0022] As is further shown in Fig. 2, a bar-shaped displacement body 46 having a rectangular
cross-section has been inserted in medium height in each of the cavities 34, so that
each cavity is divided, over its entire length, into two separate passages 48, 50,
and the effective volume of the cavity 34 is reduced significantly. The displacement
bodies 46 are made of polystyrene, for example, and in any case have a heat capacity
that is significantly lower than that of the material of the plate 14. Thus, the bodies
46 do not substantially add to the overall heat capacity of the sheet support plate
14 and, accordingly, do not increase the amount of time and energy needed for heating
the plate 14 to a predetermined temperature. On the other hand, since the volume of
the cavities 34 is reduced, a comparatively small amount of temperature control fluid
is sufficient for filling the channels 48, 50 completely, and only this reduced amount
of fluid needs to be heated or cooled in order to control the temperature of the plate
14. Moreover, since the cross-sectional area of the cavity 34 is reduced to that of
the passages 48, 50, the Reynolds number for a given volume flow rate of the fluid
is increased, and this improves the efficiency of heat exchange between the fluid
and the walls of the plate 14.
[0023] The displacement bodies 46 may be held in place in the cavities 34 by means of an
adhesive, for example. As an alternative, the profile of the plate 14 may be modified
such that the separating walls 40 are provided with ribs for guiding and supporting
the displacement bodies 46. In yet another alternative, only the end portions of the
bar-shaped displacement bodies 46 may be held in position in the manifolds at both
ends of the plate 14.
[0024] Preferably, the fluid flows through the passages 48 and 50 of each cavity 34 in the
same direction, so that the temperature of the bottom wall 38 of the cavities will
always be equal to temperature of the top wall 36, and the plate 14, as a whole, is
not caused to bend due to differential thermal expansion.
[0025] In a modified embodiment, a more complex circulating system may be used which causes
the fluid in adjacent cavities 34 to flow in opposite directions, so as to minimize
a possible temperature gradient in lengthwise direction (arrow B) of the plate 14.
In this case, it is also possible to connect the passages 48, 50 with one another
at one end of the cavity 34 and to connect the two passages to different tubes 32
at the opposite end, so that the fluid is caused to circulate in countercurrent fashion
within each of the cavities 34, but with opposite sense in adjacent cavities.
[0026] When the printer is switched on, the heater integrated in the temperature control
system 30 will heat the fluid, and the fluid will be circulated through the passages
48, 50 until the plate 14 has been brought to its operating temperature, i.e. a temperature
which assures an appropriate cooling rate for the droplets of hot melt ink that have
been jetted onto the paper. Since the volume of fluid to be heated is small, the required
operating temperature can be reached in a reduced time and with reduced power consumption.
[0027] As the print process continues, the sheet 12 and the plate 14 will be heated by the
ink deposited on the sheet, and the temperature control system 30 switches from a
heating mode to a temperature control mode in order to keep the temperature of the
plate 14 constant. Since at least one half of the fluid circulating through the cavities
34 is forced to pass through the passages 50 near the bottom walls 38 of the cavities,
these bottom walls 38, which are exposed to the suction chamber 26, may efficiently
be used as heat sinks which prevent the temperature of the fluid from increasing beyond
a tolerable limit. Moreover, the reduced volume of fluid shortens the response time
for the thermostatic control.
[0028] Fig. 3 shows a modified embodiment of the sheet support plate 14, in which displacement
bodies 46' in the cavities 34 are hollow bodies which enclose a material 52a, 52b,
e. g. a wax or the like, which, at a certain transition point or in a transition temperature
range, undergoes a transition between a high-temperature phase 52b and a low temperature
phase 52a with release of latent heat. The transition point or range is equal to or
close to the operating temperature of the plate 14. In the condition shown in Fig.
3, which corresponds to the operating condition of the plate 14, only part of the
material contained in the bodies 46' is in the low-temperature phase 52a and forms
a solid core, whereas the rest of the material is in a molten state, i. e. the high-temperature
phase 52b.
[0029] In Fig. 4, the temperature T of the material 52a, 52b has been shown as a function
of the heat content Q of a given volume of this material. It can be seen that, within
a narrow transition temperature range from T
1 to T
2, the heat content increases drastically from Q
1 to Q
2, corresponding to the latent heat of the phase transition. As a result, the temperature
of the material 52a, 52b and, therewith, the temperature of the plate 14 can easily
be stabilized in the range between T1 and T2, i. e. at the operating temperature.
[0030] When the printer enters into a sleep-mode and the heater in the temperature control
system 30 is switched off, the core 52a grows on the cost of the molten phase 52b
and the latent heat is released, so that the plate 14 will essentially retain its
operating temperature for an extended time period. When the printer becomes operative
again before this time period has lapsed, the print process can start immediately,
because the plate 14 still has its operating temperature. If the sleep-mode continues
for a longer time period, the temperature drops below T
1, but when the heater is switched on again, the temperature T
1 and hence the operating temperature can quickly be recovered by supplying only a
little amount of heat.
[0031] In more general terms, what is proposed here is a paper handling device comprising
a sheet support plate 14, heating and temperature control means 30 for heating the
sheet support plate 14 to a predetermined operating temperature and keeping it at
that temperature, and buffer bodies 46' integrated in the sheet support plate 14,
said buffer bodies containing a material 52a, 52b, which, at a temperature point or
in a temperature range T
1 - T
2 at or near the operating temperature, undergoes a phase transition from a high-temperature
phase 52b to a low-temperature phase 52a with release of latent heat.
1. A sheet handling device comprising a sheet support plate (14) made of a heat conductive
material having a first heat capacity, said plate having at least one cavity (34)
formed between a top wall (36) defining a top surface (42) of the plate (14) and a
bottom wall (38) defining a bottom surface of the plate; and a temperature control
system (30) including a circulating system (32) for circulating a temperature control
fluid through said cavity (34) characterized in that the cavity (34) contains a displacement body (46; 46') which is spaced apart from
said top wall (36) and is made of a material having a second heat capacity which is
smaller than said first heat capacity.
2. The sheet handling device of claim 1, wherein said displacement body (46) is also
spaced apart from the bottom wall (38) of the cavity (34).
3. The sheet handling device of claim 1 or 2, wherein said displacement body (46) is
made of synthetic resin.
4. The sheet handling device of claim 3, wherein the displacement body (46) is made of
polystyrene..
5. The sheet handling device of any of the preceding claims, comprising a plurality of
cavities (34) arranged in parallel to one another and separated by separating walls
(46) of said material with said first heat capacity.
6. The sheet handling device of claim 5, wherein the sheet support plate (14) comprises
suction holes (24) passing through from the top surface (42) to the bottom surface
of the plate and separated from the cavities (34) by the separating walls (40).
7. The sheet handling device of any of the preceding claims, wherein the displacement
body (46') comprises a material (52a, 52b), which, at a predetermined temperature
or within a predetermined temperature range (T1 - T2), undergoes a phase transition from a high-temperature phase (52b) to a low-temperature
phase (52a) with release of latent heat.
8. A hot melt ink jet printer comprising a sheet handling device according to one of
the claims 1 to 7.
1. Bogenhandhabungsvorrichtung mit einer Bogenträgerplatte (14) aus einem wärmeleitfähigen
Material, das eine erste Wärmekapazität aufweist, welche Platte wenigstens einen Hohlraum
(34) aufweist, der zwischen einer oberen Wand (36), die eine obere Oberfläche (42)
der Platte (14) definiert, und einer unteren Wand (38) gebildet ist, die eine untere
Oberfläche der Platte definiert, und einem Temperatursteuersystem (30) mit einem Umwälzsystem
(32) zum Umwälzen eines Temperatursteuerfluids durch den Hohlraum (34), dadurch gekennzeichnet, daß der Hohlraum (34) einen Verdrängungskörper (46; 46') enthält, der von der oberen
Wand (36) beabstandet ist und aus einem Material besteht, das eine zweite Wärmekapazität
hat, die kleiner ist als die genannte erste Wärmekapazität.
2. Bogenhandhabungsvorrichtung nach Anspruch 1, bei der der Verdrängungskörper (46) auch
von der unteren Wand (38) des Hohlraums (34) beabstandet ist.
3. Bogenhandhabungsvorrichtung nach Anspruch 1 oder 2, bei der der Verdrängungskörper
(46) aus Kunststoff besteht.
4. Bogenhandhabungsvorrichtung nach Anspruch 3, bei der der Verdrängungskörper (46) aus
Polystyrol besteht.
5. Bogenhandhabungsvorrichtung nach einem der vorstehenden Ansprüche, mit mehreren Hohlräumen
(34), die parallel zueinander angeordnet und durch Trennwände (40) aus dem Material
mit der genannten ersten Wärmekapazität getrennt sind.
6. Bogenhandhabungsvorrichtung nach Anspruch 5, bei der die Bogenträgerplatte (14) Sauglöcher
(24) aufweist, die von der oberen Oberfläche (42) zur unteren Oberfläche der Platte
durchgehen und durch die Trennwände (40) von den Hohlräumen (34) getrennt sind.
7. Bogenhandhabungsvorrichtung nach einem der vorstehenden Ansprüche, bei der der Verdrängungskörper
(46') ein Material (52a, 52b) enthält, das bei einer vorbestimmten Temperatur oder
innerhalb eines vorbestimmten Temperaturbereiches (T1 - T2) einen Phasenübergang von einer Hochtemperaturphase (52b) in eine Tieftemperaturphase
(52a) unter Freisetzung von latenter Wärme erfährt.
8. Tintenstrahldrucker für heißschmelzende Tinte, mit einer Bogenhandhabungsvorrichtung
nach einem der Ansprüche 1 bis 7.
1. Dispositif de traitement de feuilles comprenant une plaque de support pour feuilles
(14) constituée d'un matériau thermoconducteur ayant une première capacité calorifique,
ladite plaque comprenant au moins une cavité (34) formée entre une paroi supérieure
(36) définissant une surface supérieure (42) de la plaque (14) et une paroi inférieure
(38) définissant une surface inférieure de la plaque et un système de régulation de
la température (30) comprenant un système de circulation (32) permettant de faire
circuler un fluide régulateur de température à travers ladite cavité (34), caractérisé en ce que la cavité (34) contient un organe de déplacement (46, 46') séparé de ladite paroi
supérieure (36) et constitué d'un matériau ayant une seconde capacité calorifique
inférieure à ladite première capacité calorifique.
2. Dispositif de traitement de feuilles selon la revendication 1, dans lequel ledit organe
de déplacement (46) est séparé de la paroi inférieure (38) de la cavité (34).
3. Dispositif de traitement de feuilles selon la revendication 1 ou 2, dans lequel ledit
organe de déplacement (46) est constitué de résine synthétique.
4. Dispositif de traitement de feuilles selon la revendication 3, dans lequel l'organe
de déplacement (46) est constitué de polystyrène.
5. Dispositif de traitement de feuilles selon l'une quelconque des revendications précédentes
comprenant une pluralité de cavités (34) disposées parallèlement l'une à l'autre et
séparées par des parois de séparation (46) dudit matériau présentant ladite première
capacité calorifique.
6. Dispositif de traitement de feuilles selon la revendication 5, dans lequel la plaque
de support pour feuilles (14) comprend des orifices d'aspiration (24) traversant depuis
la surface supérieure (42) jusqu'à la surface inférieure de la plaque et séparés des
cavités (34) par les parois de séparation (40).
7. Dispositif de traitement de feuilles selon l'une quelconque des revendications précédentes,
dans lequel l'organe de déplacement (46') comprend un matériau (52a, 52b) qui, à une
température prédéterminée ou dans un intervalle de températures (T1 - T2) prédéterminé, subit une transition de phase d'une phase (52b) de température élevée
à une phase (52a) de faible température avec libération de chaleur latente.
8. Imprimante à jet d'encre thermofusible comprenant un dispositif de traitement de feuilles
selon l'une quelconque des revendications 1 à 7.