EP0099763B1 - Toner powder applicator on the imaging roller of a non-impact printer - Google Patents

Description

The present invention relates to a device for applying solid developer particles to the recording element of a non-impact printer.

In modern equipment which is used for data processing, fast printers are used more and more in which the printing of the characters is carried out without for that calling upon the impact of types of relief printing on a sheet of receiving paper. These printing machines, known as non-impact or even without impact transfer, generally include a recording element generally constituted by a rotary drum or an endless belt, on the surface of which one can form, electrostatic or magnetic, sensitized areas also called latent images which correspond to the characters or images to be printed. These images are then developed, that is to say made visible, using a powdery developer which, deposited on the recording element, is only attracted by the sensitized areas thereof. . After which, this recording element is brought into contact with a sheet of paper in order to allow the developer particles which have been deposited on these areas to be transferred onto this sheet to be definitively fixed there.

In order to apply this powdery developer to the recording element of a printing machine of this kind, various application devices have been used in the prior art. Thus, for example, a device was used which comprises a casing containing the powder developer, this casing having an opening in front of which the recording element passes, the inking of this element being produced by a cylindrical brush which, rotating inside the casing, projects the developer particles towards the surface of the element which passes in front of this opening. However, this device does not give complete satisfaction to the use of the fact that it causes, on the one hand the formation of a cloud of developer particles which spreads outside the casing, which is particularly unpleasant for people who, being near the printer, are reached by this cloud, on the other hand, an undesirable electrification of the particles which, projected towards the recording element, can then remain on the non-sensitized areas of that - as a result of an electrostatic attraction.

In the case where the developer is capable of being attracted magnetically, one can use, to apply this developer, a magnetic roller of the type which has been described and represented in French patent FR-A-1,566,007 and which comprises a series of elongated magnetic elements, arranged one next to the other, around a tree, parallel to this one, each of these magnetic elements being magnetized radially so as to have a constant magnetic polarity throughout its length, the polarities magnetic presented by two contiguous magnetic elements being opposite. However, this magnetic roller which gives good results when used in an electrostatic charge latent image development apparatus for transporting a powdery developer capable of being attracted magnetically, is not entirely satisfactory when wants to use it as a powdery developer transport roller in a magnetic latent image development apparatus such as, for example, a magnetic printing machine. This is because, in fact, because this magnetic roller is placed in the immediate vicinity of the element for recording the latent magnetic images, this recording element is necessarily subjected to the action of the magnetic fluxes generated by the elements. magnetic tape of this roller, so that the information recorded on this recording element may be greatly altered as it passes in front of this developer applicator roller. This drawback can be eliminated by interposing, between the applicator roller and the recording element, a deflector intended to collect the developer particles transported by the roller, this deflector having one of its edges disposed in the immediate vicinity of the recording element to constitute therewith a bucket, having substantially the shape of a dihedral, in which the developer particles collected by the deflector accumulate. This produces a developer application device of the type which has been described and represented in French patent Fr-A-2 408 462 and in which the recording element is moved in a direction such that the particles accumulated in the bucket are entrained towards the edge of the dihedral, the particles entrained beyond this edge remain applied only on the sensitized zones of the recording element. However, it has been observed that, in the case where this application device comprises a transport roller of the type described in the aforementioned French patent FR-A-1,566,007, the developer particles are aligned along the lines of external forces which, on the surface of the transport roller, leave each of the magnetic elements having a north magnetic polarity to join each of the neighboring magnetic elements which have a south magnetic polarity. Since these external lines of force thus form arches oriented perpendicular to the axis of rotation of the roller, the developer particles, by being placed along these lines of force, therefore form chains of particles arranged perpendicular to this axis. . Under these conditions, when chains of particles are stopped in passing by the deflector, they break but continue to form, inside the bucket, fragments of chains having an orientation which is practically perpendicular to the surface of the recording element. As a result, these particles, when they come to be applied to the sensitized areas of this element, tend to associate with each other to form particle-shaped aggregates of particles which results in the appearance of streaks of particles at the surface of the recording element and, consequently, by streaks which are particularly unpleasant to the sight for the characters formed during the transfer of these particles to the paper.

This same drawback still appears when, in the application device mentioned above, the transport roller of the type described in the aforementioned French patent FR-A-1,566,007 is replaced by a transport roller of the type which is incidentally described in United States patent US-A-4,185,130, this latter roller comprising a rotating cylinder coated on its outer cylindrical surface with a strip of magnetic material, this strip being magnetized so as to present on its outer surface magnetic poles forming equidistant magnetic lines, the north or south magnetic polarity of which alternates from one magnetic line to the other, each of these lines extending along a helix with constant pitch.

The present invention overcomes this drawback and proposes a device which makes it possible to apply developer particles to the recording element of a non-impact printer, without thereby causing or altering the information recorded on this element, nor streaks of particles on the surface of this element.

More specifically, the present invention relates to a device for applying, onto the recording element of a non-impact printer, solid developer particles contained in a reservoir, this device comprising, on the one hand a roll of transport arranged to bring these particles to the vicinity of the surface of this element, on the other hand a deflector interposed between this element and this transport roller to collect the particles transported by this roller, this deflector having one of its edges disposed at immediate proximity of said element to constitute with this element a bucket having substantially the shape of a dihedral, in which the particles thus collected accumulate, this element being moved in a direction where it entrains these particles towards the edge of said dihedral, the particles entrained beyond this edge remaining applied only to the sensitized areas of said recording element, said developer being capable of being attracted magn ethically, said transport roller being constituted by a rotating cylinder coated, on its outer cylindrical surface, with a magnetic material magnetized so as to present, on its outer face, magnetic poles forming equidistant magnetic lines whose north magnetic polarity or south alternates from one magnetic line to another, these magnetic lines extending along portions of propellers with constant pitch, said device being characterized in that there are a plurality of bands of said magnetic material, arranged in parallel to the axis of rotation and contiguous to each other, the arrangement of the propellers being such that, on two contiguous bands, the pitch of the propeller portions of one of these two bands is opposite to that of the propeller portions from the other band.

The present invention will be better understood and other objects, details and advantages thereof will appear better in the following description, given by way of nonlimiting example and with reference to the appended drawings in which:

• la figure 2 est une vue schématique, à grande échelle montrant certains détails de réalisation du dipositif d'application représentée su la figure 1;
• la figure 3 est une vue en perspective, avec parties arrachées, d'un rouleau magnétique utilisé dans l'art antérieur pour l'application d'un révélateur sur l'élément d'enregistrement d'une imprimante magnétique, cette vue montrant la façon dont s'orientent les particules de révélateur à la surface de ce rouleau;
• la figure 4 représente un premier mode de réalisation d'un rouleau magnétique faisant partie du dispositif d'application qui équipe la machine imprimante représentée sur la figure 1,
• la figure 5 représente un second mode de réalisation d'un rouleau magnétique faisant partie du dispositif d'application qui équipe la machine imprimante représentée sur la figure 1,
• la figure 6 est une vue en perspective et en coupe partielle, suivant un plan perpendiculaire à l'axe de rotation, d'une partie du rouleau représenté sur la figure 4.

FIG. 1 represents a partial schematic view of a magnetic printing machine equipped with a developer application device produced according to the present invention:

• Figure 2 is a schematic view, on a large scale showing certain details of embodiment of the application device shown in Figure 1;
• FIG. 3 is a perspective view, with parts broken away, of a magnetic roller used in the prior art for applying a developer to the recording element of a magnetic printer, this view showing the way which orient the developer particles on the surface of this roller;
• FIG. 4 represents a first embodiment of a magnetic roller forming part of the application device which equips the printing machine shown in FIG. 1,
• FIG. 5 represents a second embodiment of a magnetic roller forming part of the application device which equips the printing machine shown in FIG. 1,
• FIG. 6 is a perspective view in partial section, along a plane perpendicular to the axis of rotation, of a part of the roller shown in FIG. 4.

The printing machine, part of which has been shown diagrammatically in FIG. 1, comprises a recording element which is constituted, in the example described, per a magnetic drum 10. This magnetic drum 10 is rotated, in the direction of the arrow F, by an electric motor (not shown). The recording of information on this drum is carried out by a magnetic recording member 11 which is arranged near the external surface of the drum. In the example described, this recording member 11 is formed of an assembly comprising several magnetic recording heads which, placed one next to the other, are aligned parallel to the axis of rotation 12 of the drum 10. Each of these heads generates, when it is excited repeatedly by an electric current, a variable magnetic field, which has the effect of creating magnetized domains or "magnetic points" on the surface of the drum which passes in front of the organ d recording 11. The moments of excitation of these heads are moreover established, in a known manner, so as to obtain on the surface of the drum sets of magnetic domains 13, called magnetized zones or latent magnetic images, the shape of which corresponds to that of the characters to be printed. These magnetized zones 13 then pass in front of an application device 14 which is arranged below the drum 10 and which makes it possible to apply to the surface of the drum particles of a powdery developer contained in a reservoir 1 5. The particles of developer which are thus applied to the drum 10 adhere, in principle, only on the magnetized areas thereof, so that the magnetized areas which have passed in front of the application device 14 appear coated with a layer of developer , this layer forming, on the drum 10, the image of the characters which are to be printed. It should be noted here that this developer consists of magnetic particles in picks of a thermoplastic resin. which, by heating, is capable of melting and fixing on a paper on which it has been deposited. By way of example, the developer contained in the reservoir 15 may be the one which was the subject of the patent application filed in France by the Applicant on March 20, 1980 and published FR-A-2 478 839. As well as As indicated above, this developer which is applied to the drum 10 mainly adheres to the magnetized zones 13, thus forming deposits 16 of particles on the surface of this drum. These deposits 16 then pass in front of a retouching device 17 which has the role of eliminating the particles which have adhered elsewhere on the magnetized zones 13, as well as the particles which are found in excess in these zones. After which, the developer particles which remain on the drum 10 are transferred, almost entirely, onto a sheet of paper 18 which is applied to the drum 10 by means of a pressure roller 19. The residual developer particles which when this transfer is produced, are still on the drum 10 and are then removed by means of a cleaning device 20, of known type, for example with a brush. After which, the magnetized zones which have passed in front of the cleaning device 20 pass in front of an erasing device 21 where they are then erased, which allows the demagnetized portions of the drum 10 to be able to be magnetized again when they arise next before the registration body 1 1.

As can be seen in FIG. 1, the application device 14 comprises, on the one hand, a transport element 22 which picks up developer particles from the reservoir 15 to bring them near the surface of the drum 10, on the other hand, a fixed deflector 23 which is interposed between the transport element 22 is the drum 10 to collect the particles transported by this element 22 and apply them to the surface of the drum 10. An application device 14 of this kind has in particular been described and represented in French patent FR-A-2 408 462. The transport element 22 which equips such an application device usually consists of a magnetic roller which will be described later, the axis of rotation 24 of this roller being parallel to the axis of rotation 12 of the drum 10. The deflector 23 which is associated with this magnetic roller 22 is a part which, fixed to the two lateral faces of the reservoir 15, has, as we seen in Figure 2, a he flat face 40 limited by first and second edges 41 and 42 parallel to the axes 12 and 24, the second edge 42 preferably forming a sharp edge to avoid an accumulation of particles on said edge. This deflector 23, which has its first edge 41 practically in contact with the magnetic roller 22 is arranged in such a way that its second edge 42 is in close proximity to the surface of the drum 10 and that its face 40 forms with the plane defined by the axis 12 of the drum and the axis 24 of the magnetic roller a dihedral whose angle is less than forty five degrees.

The magnetic roller 22 is rotated, in the direction indicated by the arrow R in Figures 1 and 2, by an electric motor (not shown), this direction being such that the developer particles transported by the magnetic roller 22 are driven towards the face 40 of the deflector 22 and are stopped in passing, at least for most of them, by this deflector. The particles which are thus stopped then accumulate in a trough 43 delimited by the surface of the drum 10 and by the face 40 of the deflector 23. The direction of rotation of the drum 10, indicated by the arrow F, is chosen so that the particles accumulated in the bucket 43 are entrained towards the sharp edge 42 of the deflector 23 so that some of them can come to be applied to the magnetized zones 13 of the drum 10. However, the particles thus entrained by the drum 10 are not stopped in passing by the deflector 23, because it does not touch the drum and that it therefore leaves, between the sharp edge 42 and the drum 10, an opening whose width is sufficient to allow the developer particles entrained by this drum to leave the trough 43. The developer particles which, applied to the magnetized areas of the drum, come out of the trough 43, continue to adhere to these areas and thus make them visible the characters that must be printed, while those which leave the bucket 43 without being retained by the drum generally fall back into the reservoir 15.

The magnetic roller which has been shown with parts broken away in FIG. 3, is of known type and has been described in French patent FR-A-1,566,007. It will be recalled here that this roller comprises a fixed shaft 25 made up of a material having a high magnetic permeability such as soft iron for example. Magnetic elements 26 are arranged around the shaft 25, these elements being arranged one beside the other, parallel to the shaft 25, so as to form a ring around this shaft. For obvious reasons of simplification, only two magnetic elements referenced 26A and 26B have been shown in FIG. 3, but it should be noted that the number of these elements is much greater than two, this number being chosen so as to be a multiple of two. Thus, in the example illustrated in Figure 3, the roller has eight magnetic elements. This roller further comprises a cylindrical sleeve 27 placed around the ring formed by the magnetic elements and mounted so as to be able to rotate around the shaft 25 in a direction indicated by the arrow R in FIG. 3. This sleeve is produced in a non-magnetic material, such as aluminum for example. The magnetic elements 26 are, as can be seen in FIG. 3, radially magnetized, that is to say in a direction perpendicular to the axis 24 and so that each magnetic element has, on its face 28 located opposite the sleeve 27, a magnetic polarity which is reversed when moving from one magnetic element to the next magnetic element. Thus, for example, the magnetic element 26A shown in FIG. 3 has, on its face located opposite the sleeve 27, a north magnetic polarity (N) while the magnetic element 26B which is contiguous to the element 26A has, on its face 28 located opposite the sleeve 27, a south magnetic polarity (S). Under these conditions, the external lines of force of the magnetic field pro duit by the magnetic elements 26 depart from the faces 28 having a north magnetic polarity to join the faces 28 which have a south magnetic polarity. In FIG. 3, only some of these external lines of force, referenced 29 have been shown in dashed lines for reasons of simplification. If the magnetic roller that has just been described is placed in contact with a powder developer capable of being attracted magnetically, the outer surface of the sleeve 27 is covered, during its rotation, with a layer of developer particles . During this operation, some of the developer particles adhere directly to the surface of the sleeve 27, while others will be placed outside this surface, along the external lines of force 29, thus forming chains of particles whose some, indicated by 30 in FIG. 3, are in the form of arches and the others, indicated by 31 in this figure, have the form of portions of arches oriented substantially perpendicular to the surface of the sleeve. As can be seen in FIG. 3, all these chains of particles are contained in planes perpendicular to the axis of rotation 24 of the roller. As a result, when the developer particles deposited on this sleeve are stopped in passing by the deflector 23, they continue to form chains or fragments of chains 32 which pile up on the face 40 of the deflector 23 while remaining practically parallel to each other as shown in Figure 3. These particles, which thus remain associated with each other, therefore form when they are then applied to the surface of the drum 10, filiform aggregates of particles which not only then cover the areas magnetized from this drum, but even extend beyond these areas, so that, when these aggregates are subsequently transferred to the paper 18, they form streaks of particles which seriously affect the quality of printing.

The magnetic roller of the present invention overcomes this drawback. In the embodiment which is illustrated in FIG. 4, this magnetic roller 22 is formed by a cylinder 50 provided with a shaft 51 allowing it to rotate in bearings, not shown, mounted on the lateral faces of the reservoir 5, these bearings being arranged so that the axis of rotation 24 of this roller is parallel to the axis of rotation 12 of the drum 10. This cylinder 50 is made of a non-magnetic material, such as, for example, copper, glass or plastic. In the example described, it will be considered that this cylinder 50 is made of aluminum. FIG. 4 shows that this cylinder 50 is coated, on its outer cylindrical surface, with bands 52 of flexible magnetic material, these bands being contiguous to each other and arranged parallel to the axis of rotation 24 of the cylinder 50. In the example illustrated by FIG. 4, six bands 52 are thus arranged on the cylinder 50, each of these bands extending over the entire length of the cylinder. The flexible magnetic material which constitutes these bands is well known and is generally constituted by an elastomer in which magnetic particles have been incorporated. Thus this flexible magnetic material can be that which is manufactured industrially under the name of "Ferriflex" (registered trademark) by the company of Chemicals Ugine-Kuhlmann. As can be seen in Figure 6 which shows in section, along a plane passing through the axis of rotation 24, a portion of the magnetic roller of Figure 4, each of the strips 52 is magnetized permanently, in a perpendicular direction at its thickness, in order to present on its external face, magnetic poles forming magnetic lines such as 53A, 53B, 53C which are equidistant from each other, the north or south magnetic polarity of these lines alternating from a magnetic line to the other. Thus, for example, the magnetic lines 53A and 53C shown in FIG. 6 have a north magnetic polarity (N), while the magnetic line 53B has a south magnetic polarity (S). In FIGS. 4, 5 and 6 these magnetic lines have been symbolically represented in broken lines and are designated in FIGS. 4 and 5 by the general reference 53. The equidistance of these magnetic lines depends on the thickness of the strip 52. It will be noted, by way of example, that, for a strip thickness of 1 millimeter, these magnetic lines 53 are separated from each other by a distance equal to 2.54 millimeters and that, for a strip thickness of 2 millimeters, these magnetic lines are separated from each other by a distance equal to 5.08 millimeters. FIG. 4 also shows that these magnetic lines 53 are oriented on the surface of the magnetic roller, according to portions of propellers of the same pitch, one of these propellers referenced H, being represented in dashed lines in FIG. 4. In a more particularly advantageous embodiment, the pitch P of these propellers is chosen so as to be numerically equal to the | ungueurπ D of a cross section of the cylinder 50, D being the diameter of this cylinder. Under these conditions, the angle under which the magnetic lines 53 intersect the generatrices of the cylinder is equal to 45 degrees. It should also be noted that, as can be seen in FIG. 4, the portions of propellers formed by the different magnetic lines 53 do not all have the same winding direction. In other words, the pitch of these propeller portions is such that, on two contiguous bands 52, the pitch of the propeller portions of one of these two bands is opposite to that of the propeller portions of the 'other band. The number of bands 52 arranged on the cylinder 50 is also chosen so as to be always even, so that the characteristic which has just been stated concerning the pitch of the propeller portions can always be respected.

Naturally, various embodiments of the magnetic roller of the invention can be envisaged. Thus, in the embodiment illustrated by FIG. 5, the strips 52 of flexible magnetic material each have a length less than the length of the cylinder 50. In the particular case represented in FIG. 5, the length of each of the bands 52 is equal to half that of the cylinder 50, so that when two of these bands, oriented so that their long side is parallel to the axis of rotation 24 of the cylinder, are placed. end to end on this cylinder, touching by their short side, these two bands extend over the whole the length of the cylinder. In other words, if we consider the cylinder 50 fictitiously divided, perpendicular to its axis of rotation 24, into two portions 50A and 50B of the same length, each of these cylinder portions is covered with 2n bands 52, 2n being a number peer. In FIG. 5, the bands covering the cylinder portion 50A have been referenced 52A and those covering the cylinder portion 50B have been referenced 52B. It can also be seen, in FIG. 5, that the pitch of the propeller portions along which the magnetic lines 53 of the bands 52A and 52B are oriented is such that, on any two contiguous bands, the pitch of the propeller portions of the one of these two bands is inverse to that of the propeller portions of the other band.

It should also be noted that, in the more general case where the cylinder 50 is assumed to be divided, perpendicular to its axis of rotation 24, in p equal portions and where the length of each of the strips 52 of flexible magnetic material is equal to the length of each of these p cylinder portions, each of these p cylinder portions is covered by an even number (equal to 2n) of bands 52. The 2n bands which cover each of the p cylinder portions are contiguous with one another and oriented in parallel to the axis of rotation of the cylinder. In addition, the 2n bands of the same cylinder portion are themselves contiguous to the 2n bands of the adjacent cylinder portion and are aligned with the latter. The strips 52 of magnetic material which cover the cylinder 50 do not necessarily consist of flexible material incorporating magnetic particles. Thus, in another embodiment, these strips 52 may be made of a non-flexible magnetic material, for example of ferrite, molded so as to have the shape of a hollow cylinder (or of cylinder portions hollow, such as 52 for example) whose internal diameter corresponds to the external diameter of the cylinder 50, this hollow cylinder being magnetized so as to present, on its external face, magnetic poles, forming magnetic lines extending along portions d propeller arranged analogously to that illustrated in FIGS. 4 and 5.

By using the magnetic roller which has just been described in an application device of the type described in French patent FR-A-2 408 462, it has indeed been found that no bundles of particles of developer inside the bucket formed by the deflector and the recording element and that, as a result, the subsequent transfer of these particles to the paper practically did not cause particles streaks, so that the print quality was greatly improved.

Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of example. On the contrary, it includes all the means constituting the technical equivalents of those described and illustrated, considered in isolation or in combination, and used in the context of the claims which follow.

Claims (7)

1. Device forthe application, on the recording element (10) of a non-impact printer, of solid particles of developer (toner) contained in a reservoir (15), this device on the one hand comprising a transporting roller (22) arranged to carry these particles close to the surface of the element (10), and on the other hand a deflector (23) interposed between this element and this transporting roller for collection of the particles carried by this roller, this deflector having one of its edges (42) positioned in the immediate proximity of the said element (10) so that it forms with this element a trough (43) having substantially the shape of a dihedron, in which are accumulated the particles thus collected, this element being displaced in one direction (F) in which it entrains these particles towards the edge of this dihedron, the particles carried along beyond this edge remaining applied only on the sensitised areas of the said record element, the said developer being able to be attracted magnetically, the said conveyor roller (22) comprising a rotary cylinder (50) covered on its external cylindrical surface with magnetic material magnetised in such a manner that on its outer surface it has magnetic poles forming equidistant magnetic lines (53) of which the magnetic north (N) or south (S) polarity alternates from one to another, these magnetic lines extending along helix portions of constant pitch, the said device being characterised in that there is a plurality of strips (52) of the said magnetic material arranged parallel to the axis of rotation (24) of the said cylinder and contiguous to each other, the arrangement of the helices (H) being such that, on two contiguous strips (52), the pitch of the helix portions of,the one of these two strips is the opposite of that of the helix portions of the other strip.

2. Applicator device according to claim 1, characterised in that the magnetic lines (53) are so directed as to intersect the generatrices of the cylinder (50) at an angle equal to 45 degrees.

3. Applicator device according to either of claims 1 and 2, characterised in that each of the strips (52) is formed from flexible magnetic material and extends throughout the length of the rotary cylinder (50).

4. Applicator device according to either of claims 1 and 2, characterised in that, assuming the rotary cylinder (50) to be divided, perpendicular to its axis of rotation (24), into p cylinder portions (such as 50A and 50B) of the same length, each of the strips (52) formed from magnetic material has a length equal to the length of each of the said p cylinder portions, and the number of these strips (52) is equal to 2pn, so that each of these p cylinder portions is covered by 2n of the said strips, all these strips being contiguous to each other.

5. Applicator device according to claim 3, characterised in that the rotary cylinder (50) has a diameter equal to 25 mms and in that the number of strips (52) covering the same is equal to 4.

6. Applicator device according to claim 4, characterised in that the rotary cylinder (50) has a diameter equal to 25 mms and in thatthe number of strips (52) covering each of the portions of this cylinder is equal to 4.

7. Applicator device according to either of claims 1 and 2, characterised in that each of the strips (52) is formed from rigid magnetic material moulded in such a manner as to have the form of a hollow cylinder - or of hollow cylinder portions (52) - of which the inner diameter corresponds to the outer diameter of the rotary cylinder (50).

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