FR2680722A1 - THERMAL PRINTHEAD. - Google Patents

Abstract

Thermal printhead comprising a holder (1), a head circuit board (2) mounted on the holder, a connector board (3) overlapping the head circuit board, and a pressure piece (4) for press the connector board against the head circuit board. The support (1) is flexible and its modulus of elasticity is between 9.8 x 104 and 4.9 x 106 N / mm2. The head circuit board has a comb-shaped end portion (8) placed in a limited central region whose length is substantially smaller than the head circuit board. The connector board also has a comb-shaped end part (18) corresponding to the end part of the head circuit board, and the length of the connector board is substantially smaller than that of the head circuit board. .

Description

THERMAL PRINTHEAD

  The present invention relates to a print head.

  thermal pressure which is used for example for im-

  primer on heat-sensitive paper or to cause

  ink transfer between a thermal transfer ribbon or film

  miqueetun papier papier More particularly, the present invention relates to improvements of a thermal print head of the type in which a connector board overlaps a head circuit board for

  connection to external circuits.

  As we know, thermal print heads

  that are widely used in fax machines for printing

  sea information transmitted on thermosensitive paper

  ble The thermal print head is also used

  in printers of the type in which the ink of a ru-

  ban or ink transfer film is thermally trans-

on a printing paper.

  There are various types of thermal print heads which include line type heads and

  matrix type heads The thermal print head

  that of the in-line type comprises a row (line) of multiple heating points, as described for example in the open Japanese patent application No. 63-151466 or

  NO 63-221055 The matrix type thermal print head has a plurality of heating points

  created in a matrix, as described, for example, in US Pat. No. 3,855,448 to Hanagata et al. The main object of the present invention is to

  online type thermal print head

  rifier objects of the present invention, we now refer to Figures 10 and 11 which show a head

  thermal printing of the usual line type.

  As shown in Figures 10 and 11, the prior art thermal print head includes an elongated head circuit board 100 fixed by bonding to an elongate support 101 which is made of aluminum

  for example, to also serve as a heat evacuator.

  The head circuit board 100 carries a longitudinal row (line) of multiple heaters 102 located near a longitudinal edge of the circuit board

  head The head circuit board also carries a

  comb-shaped terminal tie 103, located near the other longitudinal edge of the circuit board, and a series of

  control integrated circuits 104 to activate selective-

  the hot spots 102 Although not shown, the head circuit board further includes

  a complex conductive configuration.

  The print head further includes a card

  connector 105 in the form of a flexible strip which is

  forced by a back 106 made for example of resin

  forced by glass fibers In the assembled state, the back

  106 rests directly on the support 101, as shown

  felt in FIG. 11 The flexible card 105 comprises a front marginal part which projects beyond the back 106 so as to partially overlap the card

  head circuit 100 The underside of the mar-

  protruding from the flexible card 105 has a comb-shaped end portion 107 which corresponds to the end portion 103 of the head circuit board 100. An elongated pressure cover 108 is placed above the connector board 105 and it is fixed to the support 101 by mounting screws 109 which pass through the pressure piece and the connector board and are screwed

  in the holder The underside of the press cover

  sion is equipped with an elastic rod 110 which presses the comb-shaped end part 107 of the connector card in intimate contact with the comb-shaped end part 103 of the head circuit board 100

  when the fixing screws 109 are tight.

  During the operation of the printer, the line of heating points 102 of the head circuit board 100 is maintained in intimate contact with the heat-sensitive paper which is supported on a roller 114 (FIG. 11). To allow loading (or reloading) of

  heat-sensitive paper and / or maintenance of the print head

  pressure, the print head or roller is mounted on

  one pivoting part of the printer, the other of these

  nes being mounted on a fixed part of the printer,

  so you can move the print head closer and farther apart

  the roller and each other so it is necessary to

  re to provide guide means to guide the wheel

  the water and bring it to a predetermined position relative to the line of heating points 102 when the print head and the roller are brought closer to each other, this

  which ensures good print quality.

  The guide means shown in FIGS. 10 and 11 comprise two L-shaped roller guides 111, placed at the respective ends of the support 101 Each plate guide 111 has a guide cutout 112 for removably receiving a shaft end roll 114, and it's

  fixed to the support 102 by screws 113.

  The thermal print head of the prior art

  laughter, described above, has a serious bending disadvantage during the printing operation The reason for

this bending is as follows.

  Generally, the support (heat evacuator)

  101 and pressure cover 108 are both manufactured

  aluminum because this material is light and can

  during easily be formed to the desired configuration.

  Therefore, these two pieces have the same coefficient of

  linear expansion However, the support 101 receives im-

  mediately the heat coming from the head circuit board 100, while the pressure cover 108 receives the heat indirectly via the fixing screws 109, with a certain delay Thus, at the instant of activation activation from the line of heating points 102 or the sudden change in the activation voltage, the delay in heat transmission

  leads to a difference in longitudinal expansion in

  be the support and the pressure cover, at least

before reaching steady state.

  In accordance with the provision of prior art

  Laughter shown in Figures 10 and 11, since the comb-shaped end portion 103 of the card

  head circuit 100 extends substantially over the entire length

  head circuit board, connector board

  flexible tor 105 and pressure cover 108 must also have a length substantially equal to that

  head circuit board In addition, the length to-

  pressure cover 108 must be mounted in a

  fixed lesson on the support 101 by the fixing screws 109.

  Consequently, when the pressure cover and the support expand longitudinally to different degrees, the

  thermal print head as a whole bends

  gitudinally, as a result of the so-called "bimetal" phenomenon.

  Another drawback lies in the fact that all the fixing screws 109 must be tightened in a well-adjusted manner in order to ensure uniform electrical contact between the two end parts 103, 107 over their entire length.

  length, which consequently increases the time required

  to be used in the manufacture of the thermal print head.

  The thermal print head according to art

  There is another disadvantage in the prior art.

  identifies the roller guides 111 More specifically,

  each roller guide 111 must be manufactured in one

  tal tal, such as a ferrous alloy, because the guide of

  roller must be mechanically strong enough to resist

  ter in repetitive contact with the shaft of the roller On the other hand, the support 101 should preferably be made of light metal, such as aluminum, in order to reduce the

  weight So the roller guide should be initial-

  separate from the support and then fixed to the support by

  the screws 113 As a result, the total number of components

  sants increases and more time is required for assembly In particular, the roller guide must be strictly adjusted in position to ensure good print quality, so careful assembly of the roller guide is necessary ,

  which results in increased assembly time.

  Theoretically, the support 101 can be manufactured

  made of a ferrous alloy and made integral with the guide

  roller 111 However, the support 101 must be ri-

  gide (i.e. thick enough) to minimize the fle-

  thermal xion, described above, of the print head.

  Consequently, if the support is made of such an alloy,

  the total weight of the print head increases

  unacceptable lesson Consequently, in reality,

  fabricate the support from a light metal, such as aluminum

  nium, without integrating it into the roller guide.

  US Patent No. 4,963,886 describes a printer head.

  improved thermal pressure which incorporates a head circuit board carrying a comb-shaped terminal block arranged only in a limited central length which is appreciably smaller than that of the head circuit board itself With such an arrangement, the length d '' a flexible connector card is correspondingly reduced and a pressure cover presses the connector card and puts it in contact with the comb-shaped terminal block of the head circuit board only in the limited central length of the board head circuit assembly Thus, although a plurality of fixing screws are used to mount the pressure cover on a support (heat evacuator), only the screws which are in the limited central length must be tightened in a way well adjusted The other screws can be inserted freely in larger holes of the pressure cover, in order to allow

  the longitudinal expansion of the pressure cover in-

depending on the medium.

  With the arrangement described in the US patent pre-

  cited, we can avoid thermal bending of the head

  since the pressure cover can become

  later regardless of the support, with the exception of a

  tie located in the limited central length of the head circuit board In addition, those of the fixing screws

  which lie outside this central length li-

  muffled don't need to be tightened well

  set, so that the print head can be assembled

  faster than the next print head

  the prior art shown in Figures 10 and 11.

  However, the print head of the patent

  US mentioned above remains to be improved on the following points:

  touts. First, the support is provided relatively thick, in order to be rigid. Consequently, if the support is longitudinally curved or wavy in its natural state, the head circuit board mounted on the support cannot

  not be brought into uniform linear contact with the wheel

  water and therefore results in a deterioration in print quality.

  We can of course obtain a linear contact

  uniform area between the head circuit board and the roller by increasing the elastic load applied

  to the support, since the rubber of the roller can loosen

  form elastically and come into intimate contact with the

  head circuit board under the effect of the elastic load

  that increased However, in this case, it is necessary to apply a

  high traction on the printing paper to do so before

  cer between the head circuit board and the roller, which requires a high torque motor to advance the

  paper and also increases the risk of tearing the paper

  pier. Second, the pressure cover still has a length substantially equal to that of the card.

  head circuit, despite the fact that the length of the car-

  flexible connector has been greatly reduced

  done, the pressure cover fulfills both functions

  flexible connector card pressure on

  the head circuit board, and a circuit cover

  Rie of integrated excitation circuits which are sensitive to external shocks Generally, the series of integrated excitation circuits extends substantially over the entire length of the head circuit board and this is for

  this is why the pressure cover must remain long.

  However, it is very advantageous for the reduction in weight to at least partially reduce the length of the pressure cover It is also advantageous, for the simplification of the assembly, to reduce the total number of fixing screws required, as a result of

  reducing the length of the pressure cover.

  Third, the support (heat sink)

  consists of a relatively thick aluminum plate-

  se As a result, separate roller guides must

  be screwed to the respective ends of the support at the

  of incorporation into the printer, so that

  the same problem that was written about the head of im-

  pressure according to the prior art of FIGS. 10 and 11

is inevitable.

  The object of the present invention is therefore to provide

  rer a thermal print head in which a

  te of circuit head can be uniformly maintained in intimate contact with a roller, under a normal elastic load, even if a support is longitudinally curved

  or wavy, which improves print quality.

  In accordance with the present invention,

  holds a thermal print head comprising a support; and a head circuit board mounted on the support, the head circuit board carrying a line of heating points and a series of excitation elements for activating the heating points, the circuit board

  additionally carrying a terminal part or a terminal

  deny for exterior connections;

  characterized in that the support is elastically fle-

  xib Ie, with a modulus of elasticity between 9.8 x 104

and 4.9 x 106 N / mm 2.

  The idea of the present invention is that

  that the support itself is elastically flexible so that

  that it can easily flex under an elastic load

  normal, to bring the head circuit board into con-

  uniform tact with the roller This idea is directly contrary to the prior art, in which a roller is made so as to elastically deform under increased elastic load, in order to come into uniform contact with a head circuit board which is mounted on a

rigid support.

  According to a preferred embodiment, the terminal part of the head circuit board is

  locally arranged in a limited length which is sufficient

  considerably smaller than that of the head circuit board, the print head further comprising: a connector board carrying a terminal part or a terminal block which corresponds to the terminal part of the head circuit board, the connector board having a length sufficiently shorter than that of the head circuit board; and35 a pressure piece mounted on the support for pressing the end portion of the connector board in intimate contact with the end portion of the head circuit board, the pressure piece having a pressure portion of sufficiently short length than that of the head circuit board. The pressure piece may also include a cover part intended to cover the series of excitation elements, in order to protect them In this case, the cover part must have a length not

  lower than that of the series of excitation elements.

  Alternatively, the pressure piece may not have a covering part. Instead, the series of excitation elements can be protected only by enclosing it in an elongated protective body in

  hard resin In this case, the pressure piece is released

  of the series of excitation elements and the pressure piece as a whole is sufficiently smaller in length than the head circuit board. Such an arrangement contributes to further reducing the total weight of

the print head.

  In accordance with another preferred embodiment of

  sation of the present invention, each end of the sup-

  port is formed integrally with a roller guide comprising a guide cutout for removably receiving a corresponding shaft end of the roller. Such a one-piece construction is advantageous in that the roller guide does not need to be subsequently fixed to the support, which removes the position adjustment and the

associated screwing.

  Preferably, the support can be provided with at least one marking indication located near the roller guide, the marking indication being in the form

  a marking hole for example As a variant, the guide

  roller age itself can have at least one indication

  locating cation which can be in the form of a window

  identification mark In all cases, the identification indication

  rage can advantageously be used for adjusting the position of the head circuit board relative to the

roller guide.

  Other objects, aspects and advantages of the present invention will become more apparent in the light of the

  detailed description below of preferred modes of realization

  sation, with reference to the accompanying drawings in which Figure 1 is an exploded perspective view 1 O of a thermal print head according to the present invention; _ Figure 2 is a section along the lines

  II-II of Figure 1, showing the same print head

  sion in an assembled state; Figure 3 is a section along the lines

  III-III of figure 1, representing the same print head-

  sion in an assembled state; Figure 4 is a section similar to Figure 2 but showing the same printhead incorporated in a printer;

  Figure 5 is a perspective view illus-

  trant the mode of assembly of the print head; Figure 6 is an exploded perspective view

  another thermal printhead according to the pre-

invention;

  Figure 7 is a side view of the printer head

  close to Figure 6, in an assembled state; Figure 8 is an exploded perspective view

  another thermal printhead according to the pre-

invention;

  Figure 9 is a side view of the printer head

  pressure of Figure 8, in an assembled state; Figure 10 is an exploded perspective view of a thermal print head according to the prior art; and there figure 11 is a section along the lines

  XI-XI of Figure 10, representing the print head

  sion of the prior art in an assembled state.

  Reference is now made to FIGS. 1 to 3 which represent a thermal printing head of the online type which mainly comprises an elongated support 1,

  an elongated head circuit card 2, a fle card

  xible of connector circuit 3 and a pressure piece

  4 The details of these main parts are described below.

blades.

  The head circuit board 2 includes a sub-

  insulating stratum, made for example of a ceramic material

  mique such as alumina The upper or front surface

  of the head circuit board carries internal circuits

  excitation rigs 5 enclosed in a protective body al-

  length 6 which is made, for example, of a soft resin

  very soft, such as a silicone resin, and an electrical resistance line 7 extending along a longitudinal side of the head circuit board, near this edge The linear resistance 7 is excited in a divided manner, by the integrated excitation circuits 5, to form a line of heating points The front surface of the head circuit board also comprises a terminal connection part in the form of a comb 8,

  adjacent to the other longitudinal side of the circuit board

cooked overhead.

  Although not shown in Figure 1, the front surface of the head circuit board

  2 further comprises a conduction circuit configuration

  tor, substantially as described in the US patent

  n O 4 963 886 The conductive configuration, not shown

  tee, allows the comb-shaped terminal connection part 8 to have a reduced number of terminals and to be accommodated locally in a limited central part of the

head circuit board.

  Support 1, which also serves as an evacuator

  heat for the head circuit board 2, is fa-

  briquished by pressing a metal plate or sheet

  laterally thin which is for example a ferrous alloy such as steel Each end of the support has a

  roller guide 9, substantially vertical, which is so-

  support frame The roller guide has a

  guide cutout 10 for receiving a piece of cor-

  corresponding to a roller 11, as shown in the

Figures 2 and 3.

  As already described in connection with the prior art, the thermal printing head or the roller II is mounted on a fixed part of the printer, while the other

  of these organs is mounted on a pivoting part of the im

  primante Thus, the roller 11 can be brought in and away selectively in the active position relative to the head

  thermal printing, by tilting the pi-

  printer printer The roller guide 9 of the

  port 1 is used to position the roller 11 exactly

  compared to the thermal print head when the

  the water is brought to its working position.

  Rely, in the working position shown in Figures 2 and 3, the roller 11 must come into contact with

  the head circuit board 2 (i.e. the thermal paper

  mosensible) along a line of contact which exactly coincides with the linear resistance 7 of the card

head circuit.

* Support 1 also has two ta-

  threaded 14 respectively to positions that are not

  hidden by the head circuit board 2 The support

  further carries two positioning holes 15 near the respective tapped holes 14 The function of these holes

14.15 is described below.

  The flexible connector card 3 is made for example from a polyimide film and is reinforced by a back 16 which can be made of epoxy resin reinforced with glass fibers Since the terminal connection part in the form of a comb 8 of the head circuit board 2 is arranged in the limited central region, the flexible board 3 and the reinforcement back 16 only need to have a reduced length of

  correspondingly The back 16 supports, on its side

  lower, at least one connector 17 which can be glued

on the back 16.

  The flexible connector card 3 has a front marginal part which projects beyond the

  reinforcement back 16 The underside of this part

  front marginal tie has a terminal portion of con-

  comb-shaped connection 18 in correspondence with the

  connection terminal in the form of a comb 8 of the head circuit board After assembly, the terminal connection portions 8, 18 of the circuit board

  head 2 and flexible connector card 3, respectively

  intimately overlap, as described more

far.

  The flexible connector card 3, provided with the reinforcing back 16, has two through holes

  14 'in correspondence with the tapped holes 14 of the support 1.

  In addition, the associated connector board and back include

  carry two positioning holes 15 'in correspond-

  this positioning holes 15 of the support.

  The pressure piece 4 comprises a pressure part 19 and a cover part 20 The pressure part 19 has a length which corresponds substantially

  to that of the flexible connector card 3 and it

  vauche this one, cdmme represented on figures 2 and 3.

  On the other hand, the cover part 20 has a length which corresponds substantially to that of the elongated protective body 6 and it extends beyond the flexible card 3 so as to completely cover the protective body.

lying down 6.

  The underside of the pressing part 19

  has an elongated recess 21 adjacent to the neck portion

  verture 20, to receive an elastic rod 22 which

  poses on the front marginal part of the connection card

  flexible tor 3 Thus, after assembly, the elastic rod

  tick 22 presses the comb-shaped end part

  18 of the flexible card 3 in intimate contact with the

  comb-shaped terminal tie 8 of the head circuit board 2, to ensure electrical conduction between

these parts.

  The pressure part 19 of the pressure piece

  4 also has two through holes 14 "in cor-

  correspondence of the respective threaded holes 14 of the support 1.

  The pressure part further comprises two holes for

  positioning 15 "in correspondence with those of the support.

  Two clamping screws 23 are inserted in the through holes

  respective sides 14 ', 14 "of the connector board 3 and the pressure part 19 and they are screwed into

  the tapped holes 14 of the support 1.

  The thermal print head described above

  above is assembled by means of an assembly apparatus comprising a pallet 24 which has two positioning pins 25 and two reference marks or marks 26, as shown in FIG. 5 The positioning pins 25 and the marks 26 have positions precise relative, to allow precise adjustment of

the position.

  More particularly, in the operation of as-

  appearance, the support 1 is placed on the pallet 24 so as to introduce the positioning pins 25 into

  the respective positioning holes 15 of the support 1.

  As a result, the respective guide cutouts 10 of the roller guides 19 are positioned exactly

  relative to the marks 26 on the pallet 24.

  Then the head circuit board 2 is

  placed on the support 1 and adjusted in position relative to

  port to it, using the linear resistor 7 of the head circuit board 2 on the one hand and the pins 26 of the pallet 24 on the other hand As a result, the linear resistor 7 is positioned exactly relative to the

  roller 11 which is then received by the guiding cutouts 10 of the support 1.

  Preferably, the head circuit board 2

  is glued to the support 1 only in its central part.

  Such an arrangement is advantageous in that the support 1

  and head circuit board 2, although having coef-

  different linear thermal expansion factors,

  wind will expand substantially independently of any other

  very when the temperature rises, without causing

  longitudinal bending due to the "bimetal" phenomenon.

  After adjusting the position and gluing the head circuit board 2 relative to the support 1,

  the flexible connector card 3 is placed overlapping

  ment on the head circuit board 2, and the pressure piece 4 associated with the elastic rod 22 is placed overlapping on the connector board 3 At this time, the positioning pins 25 of the pallet 24 are inserted into the holes respective positioning 15 ', 15 "of the connector board 3 and of the pressure piece 4, which exactly positions these pieces 3.4 relative to

the head circuit board.

  Finally, the clamping screws 23 are inserted

  in the through holes 14 ', 14 "of the connection card

  tor 3 and the pressure piece 4 and they are screwed into the tapped holes 14 of the support 1 As a result, the comb-shaped end portion 18 of the connector card 3 is brought into intimate contact with the end portion.

  comb shape of the head circuit board 8.

  When incorporated into the printer, the support 1 is pressed towards the roller 11 by springs 27, as shown in FIG. 4 Thus, the resistance

  line 7 of the head circuit board 2 can be ame-

  born in intimate linear contact with the roller 11.

  The embodiment described above benefits from the basic advantages described in US Patent No. 4,963,886, since the present invention is based on

  This patent In particular, the basic advantages com-

  take the prevention of thermal bending, which is

  obtained from the fact that the terminal part in the form of a pei

  gen 8 of the head circuit board 2 is located alone-

  ment in the limited central part thereof.

  The embodiment shown in the figures

  gures 1 to 3 also has the additional advantages

res below.

  First, while the covering part of the pressure piece 4 has a length which corresponds substantially to that of the head circuit board 2,

  the pressure part 19 of the pressure piece is much

  blow shorter than the head circuit board so

  the weight of the pressure piece can be greatly reduced

  duit, compared to US patent 4,963,886 in the-

  which the whole (including the pressure part) of the

  pressure piece has a length that matches sensitive-

  to that of the head circuit board What is

  core more important is that the shortened pressure part

  cie 19 does not require fastening means near the ex-

  respective hoppers of the cover part 20 This is very different from US patent n 4,963,886 according to which the pressure piece is fixed by screws (in addition to the central clamping screws) near the respective ends

of the cover part.

  Second, the roller guide 9 for the roller 11 is formed integrally with the support 1. Thus, no separate roller guide needs to be attached to

  each end of the support by screws and no adjustment

  no position is required between the guide

  water and support The only need for precise positioning of the roller 11 is to fix the head circuit board 2 exactly with respect to the support.

  reduce the total number of components required, with a reduction

  corresponding reduction in assembly cost.

  Third, since the comb-shaped end portion 8 of the head circuit board 2 is disposed only in the limited central region thereof, to avoid thermal bending, it is not necessary for the support 1 itself is rigid to avoid thermal bending Thus, the support 1 can be provided relatively thin, so as to have a reduced modulus of section (i.e. rigidity), and it can be made of a ferrous alloy For example, the support 1 can be manufactured by pressing a sheet of steel. As a result, the total weight and thickness of the thermal printing head can be greatly

  reduced, and press forming makes it easy to

  Lement the vertical roller guides 9 by folding.

  Fourth, because of the reduced thickness, the support 1 can be made elastically flexible. This elastic flexibility of the support 1 can be used to bring the linear resistance 7 into intimate contact with the roller 11 under the pressure force of the springs 27 (FIG. 4) even if the roller 11 is not perfectly cylindrical or if the support 1 or the head circuit board 2 are not perfectly flat, which improves

  therefore the print quality It should be noted that the

  gure 3 represents the linear resistance 7 at a short distance from the roller 11, while FIG. 4 represents the linear resistance maintained in intimate contact with the roller.

  As results of tests carried out by the in-

  fans, we found that support 1 must have a mo-

  dule of elasticity (representative of the rigidity longitu-

  dinal) between 9.8 x 104 and 4.9 x 106 N / mm 2 In this range, the head circuit board 2 (linear resistance 7) mounted on the support 1 can be brought into uniform linear contact with the roller 11 under a total elastic load of approximately 3 da N in the case of a

  paper size JIS A 4 (JIS: industrial standards ja-

  poles) or about 4 da N in the case of a paper of

  JIS B 4 dimension, which ensures good quality

  pressure. If the modulus of elasticity is less than 9.8 x 104 N / mm 2, the support 1 becomes too flexible and it

  results in deterioration of the print quality Au-

  above 4.9 x 106 N / mm 2, the support is then too rigid

  of, so that the head circuit board 2 placed on the support cannot come into uniform linear contact with the roller if the support is longitudinally curved

or wavy in its natural state.

  Normally, the usual supports for thermal print heads have an elastic modulus included

  between 9.8 x 106 and 9.8 x 108 N / mm 2, which is many

  times larger than the support module according to the present invention Within this usual range of the module

  elasticity, it is difficult to obtain a li-

  uniform with a roller if the support is long

  tudinally curved or wavy In this case, if we apply

  a strong elastic load to try to obtain a con-

  uniform tact with the roller, you must exert a strong

  pulling on the printing paper, which requires the

  use of a high torque motor to advance the

  paper and also increases the risk of tearing the paper

pier.

  The material for support 1 according to the pre-

  sente invention is not limiting For example, the sup-

  port 1 can be made of spring steel or

  galvanized steel Other materials are also accepted

  tables, provided that the flexibility condition of the support

be respected.

  In the case where the support 1 is made of galvanized steel

  1 mm thick, the elastic modulus of the sup-

  port is 1.274 x 106 N / mm 2 In this case, we can obtain

  nir good print quality even if the support in its natural state is longitudinally curved, with a deviation reaching + 400 µm from the exact flatness in the center On the contrary, with a rigid support

  usual, it is difficult to obtain a good quality of im-

  pressure when the support is longitudinally curved with a deviation of not less than + 100 µm from the

exact flatness.

  Figures 6 and 7 show another head

  thermal printing according to the present invention.

  This print head is similar to the embodiment

  previous tion but it differs from the latter on more

several points.

  The print head in Figures 6 and 7 includes

  takes a support 1 'which is manufactured for example by

  press mage of a steel sheet Support 1 'is

  formed integrally, along the longitudinal edges res-

  pectifs, with edges turned downward ', for reinforcement In fact, the support 1' must be moderately flexible but moderately rigid and one can determine the

  height of each ledge according to various conditions

  tions (for example the wall thickness of the support) If the support is too flexible, a greater number will be required

  springs (see Figure 4) to ensure proper contact

  time between the head circuit board 7 and the roller (see Figures 2 to 4) over the entire length of the print head As a result, the presence of the flanges la 'is important in that flexibility (or rigidity ) of

  support can be adjusted appropriately by

the height of the edges.

  The support 1 'also has two parts

  narrower ends lb 'which are mechanically reinforced

  forced by indentations 28 Each end part

  lb 'is formed with a vertical roller guide 9' pre-

  feeling a guide cutout 10 'The support comprises

  further two locating holes 29 located near the guides

  respective roller dages 9 'and usable as markers

  reference points for adjusting the position of the head circuit board 2 relative to the support, such as

described below.

  The diameter of each locating hole 29 can

  be optionally chosen but preferably it does not

  pass 1 mm (for example approximately 0.5 mm) in order to allow

  be a precise position adjustment Of course, the locating hole must be offset towards a longitudinal edge of the support 1 so that the locating hole is not

  hidden by the head circuit board 2 fixed to the support.

  The head circuit board 2 shown on

  Figures 6 and 7 differs from that of the embodiment

  previous point, only on a more specific point

  lier, a series of integrated excitation circuits (not shown in Figures 6 and 7 but shown in Figure 1) are contained in a protective body

  elongated 6 'which is made of hard resin instead of

  sine tender (for example a silicone resin) An example

  preferred hard resin is a poly- type resin

  etheramide, but other hard resins may be suitable.

  Thanks to the use of hard resin, the protective resin body 6 'can in itself completely protect the

  integrated excitation circuits placed inside

  be external shocks, which makes it unnecessary to predict

additional protection.

  The pressure piece 4 'illustrated on the fig-

  res 6 and 7 does not include a cover part for

  integrated circuits of excitation, since the body pro-

  6 'hard cover alone can provide sufficient protection

  The weight of the pressure piece can therefore be greatly reduced and the entire pressure piece is used only to press the flexible connector card 3 in intimate contact with the circuit board.

head 2.

  With the previous embodiment (see FIG. 5), the position adjustment between the support 1

  and the head circuit board 2 is done by utili-

  sation of the positioning pins 25 and the marks 26 provided on the pallet 24 This position adjustment mode can be precise only when the pins 25 are intimately adjusted in the positioning holes 15 of the support because otherwise the support may deviate slightly compared to the marks 26 However, the diameter D1 of the pins 25 must be slightly smaller than the diameter D 2 of the positioning holes 15, to allow their mutual coupling. Consequently, the pins 25 and the positioning holes 15 must be machined with very high precision in order to minimize tolerance

  diametral (D 2-D 1) for precise position adjustment.

  This strict requirement leads to an increase in the manufacturing cost. In addition, the strict diametrical tolerance (i.e. the tight fit) between pins 25 and

  the positioning holes 15 makes it difficult to attach them

  fast and separate, causing

  sharp slowdown in production operations.

  In the embodiment of Figures 6 and 7, use the locating holes 29 which are directly

  provided on the support 1 'in predefined position relation

  finished with the roller guides 9, for adjusting the position of the head circuit board 2 relative to the support More particularly, the support is placed on

  pallet 24 (see figure 5) by inserting the pins

  positioning pins 25 in the positioning holes of the support and the head circuit board 2 is adjusted in position with reference to the linear resistance 7 of the head circuit board on the one hand and to the holes

  locating 29 of the support on the other hand.

  Of course, during the position adjustment, the positioning pins 25 of the pallet 24 can be accommodated with play in the positioning holes 15 of the support 1 'since the position relation between the locating holes 29 and the roller guides 9 is fixed, whatever the movement of the support 1 'relative to the pallet 24 Thus, the position adjustment becomes

  safer and more accurate The benchmark brands 26 on the

  lette 24 are no longer used for position adjustment

  tion, so you can remove these marks for sim-

fold the pallet.

  It is understood that the locating holes 29 may

  wind be formed at the same time as the press forming of the support 1 'itself Thus, the creation of these holes does not lead to an increase in price In addition, since the function of the marking holes 29 is to provide reference points for position adjustment, these holes can be replaced by other marks, such as

  locating projections and locating troughs.

  Figures 8 and 9 show a slight mo-

  definition which differs from the embodiment of the figures

6 and 7 only on one point.

  More particularly, the support 1 ′ of the modified printhead has two marking slots 29 ′ respectively located in the roller guides 9 ′

  near the guide cutouts 10 '.

  As already indicated, the position adjustment between

  support 1 'and head circuit board 2 is required

  to bring the roller 11 (see Figure 2) into contact

  intimate linear tact with the linear resistor 7 of the head circuit board For this purpose, a central line L (figure 7) must coincide, crossing the guide cutout 10 'of each roller guide 9', with the resistor linear 7 Of course, the reference mark or reference point must be placed as close as

  possible from the central line L, in order to increase the pre-

position adjustment cision.

  In the embodiment of Figures 6 and 7, each locating hole 15 is located relatively far

  of the corresponding guide cutout 9 ', in the direction

  transverse tion of the support 2 'On the other hand, each locating slot 29' in FIGS. 8 and 9 is located much closer to the corresponding guide cutout 9 ', which provides a better reference point for an adjustment

precise position.

  Furthermore, in the embodiment of the figures

  Figures 8 and 9, even if each roller guide 9 'is

  incorrectly folded, the positional relationship between the

  guide cut 10 'and the locating slot 29' is invisible

  variable since the locating slot is formed directly

  on the roller guide As a result, the recess slot

  perage 29 'always serves as a precise reference point with respect to the central line L of the cutout In the embodiment of FIGS. 6 and 7, the position relation between the guide cutout 10' and the hole of

  marking 29 varies when the roller guide 9 'is not

  correctly folded, which does not allow a point to be obtained

precise reference.

  The width of the marking slot 29 ′ can be optionally chosen, but preferably it is not more than 1 mm (for example 0.5 mm).

  of course, you can replace the marking slot with

  very indications, in particular a locating projection.

  The present invention being thus described, it is understood that various modifications can be made thereto.

  These modifications should not be considered as departing from the spirit and the scope of the invention5 and it is understood that all the modifications which will appear to those skilled in the art must enter into the scope of the invention.

of the appended claims.

Claims (1)

CLAIM   1. Thermal print head, comprising a support (1); and a head circuit board (2) mounted on   the support, the head circuit board carrying a   heating points (7) and a series of control elements (5) for activating the heating points, the card   of the head circuit further comprising a termi-   nale (8) for external connections; characterized in that the support (1) is elastically flexible and its modulus of elasticity is between 9.8 x 104 and 4.9 x 106 N / mm 2.