FR2568181A1 - Paper-tensioning device for a printer - Google Patents

Abstract

The invention relates to a printer, in which a length of paper is advanced towards a printing station by a paper-driving device. The printer comprises a paper-tensioning device having a torque motor 294, a first roller 298 connected to the torque motor and bearing against the length of paper 302 and a second roller 304 bearing against the side of the length of paper opposite the side where the first roller 298 is located. The field of use of the invention is particularly colour printing.

Description

 The invention relates to color printers and more particularly to color printers of the dot matrix impact type, in which the zones of different colors of an ink ribbon are struck one after the other to carry out a printing in color.

 It is known to use a color printer of the dot matrix impact type in which the zones of different colors of an ink ribbon are successively struck in order to produce a color printing. Examples of such a printer are described in US Pat. Nos. 4,289,069 and NO. 4,336,751. These patents describe a color printer comprising an ink ribbon, the length of which is basically divided into three zones. different colors. A color printing is carried out by advancing a first of the color zones of the ribbon to a printing station between a cylinder and a shuttle assembly with directional reciprocating movement containing striking hammers. A page or other document of suitable length is then printed in the color contained in the first area of the ink ribbon. Pin drives are used to advance the paper to be printed in a first direction through the printing station while the page is printed in the first color. After printing the page in the first color, the paper advance is reversed to bring the page in preparation for printing using the second color area of the ink ribbon which is advanced in the printing station . After printing the page in the second color, the paper is inverted again in preparation for printing the page of a third color using the third color area of the ribbon which is advanced in the printing station. By using different color combinations and the dots printed using these combinations, multiple color printing can be achieved.

 Despite the fact that it produces multi-color printing, the color printer described in the aforementioned patents is affected by a number of drawbacks. One of these drawbacks relates to the arrangement of the colored zones on the ink ribbon. It has been found that the best results are obtained if the printing is carried out by starting with the lightest color and then using the increasingly dark colors. If the darker colors are printed first, the dark ink already deposited on the printed paper tends to detach from the paper and thus contaminate the lighter areas of the ribbon when these areas are used for printing. In the three-zone ribbon described in the aforementioned patents, it is fairly simple to arrange the colors of the three zones so that the three colors presented become more and more dark when the ribbon is advanced longitudinally in a given direction. However, if you then drag the ribbon in the opposite direction, the reverse becomes true and the darkest colors are presented first. The same problem exists when the combination of the three basic colors is repeated several times along the length of the ribbon. As before, the desired order of color presentation is obtained in one direction of movement of the ribbon, but the opposite is true in the opposite direction. It is desirable that the ribbon be driven bidirectionally from one end to the other during printing so that speed and efficiency are optimal. However, the arrangement of the ribbon with three color zones described in the aforementioned patents is limited to advancing the ribbon in one direction if the color contamination is to be minimized.

 It is therefore desirable to have a multi-colored ribbon in which the lighter colored areas are presented first, followed by the darker colored areas, in each direction of ribbon entrainment.

 In the printer shown and described in the aforementioned patents, the ribbon is advanced from a first reel to a second reel. Initially, the ribbon is wound entirely on the first reel. It is then driven in a first direction until it is almost completely wound on the second reel, after which the direction of drive is reversed and the ribbon is brought from the second reel to the first reel. The ribbon generally follows a path extending between the opposite reels and comprising various guides.

While the ribbon is being wound on one of the spools, sections of two zones of different adjacent color are arranged in contact with each other or at least in close proximity to each other. It has been found that, over time, the ink of a color area can permeate parts of the adjacent color area and vice versa, causing contamination of the ribbon. It also appeared that the ink coming from the various color zones tends to deposit on the various guides of the path of the ribbon. This ink can then pass guides over areas of different colors, causing contamination of the ribbon.

 It is therefore desirable to provide an ink ribbon designed so as to mumize or eliminate the contamination of the various areas of color following the winding or the emmaqasinaae of the ribbon on each of the opposite reels. It is further desirable to provide a tape capable of cleaning part or all of the ink from the tape path guides in order to minimize or eliminate contamination of this tape.

 In the color printer described in the aforementioned patents, the areas of different colors of the ribbon which are generally welded together to form the ribbon are identified using a device having openings in the opposite edges of the ribbon. In this way, the printer is able to identify the particular color presented to the printing station at any given time. However, although the arrangement of apertures is capable of identifying the areas of different colors, it may be desirable to provide a simpler and more reliable means of identifying the areas of color using markers which are easily reported on the ribbon, together with a standard combination of coding. It is also desirable to provide a tape which does not have any welds or other joints liable to break.

 As described above, in the color printer described in the aforementioned patents, the ribbon is advanced in a given direction in order to present successively each of the three different color zones of this ribbon at the printing station. It has been found that the single pass resulting from each of the color areas can result in a relatively short ribbon life due to the uneven ink depletion that results. For example, the ribbon can be fed at a speed causing a single pass of a given color area in the printing station for the time required to print a full page. However, if you print a certain number of pages of which only a first part of each of them receives an impression, only the first corresponding part of each color zone of the ribbon is then used. This results in an exhaustion of the ink in this first part of each color zone, while the ink of the remaining part of each color zone is used little or not at all. A device capable of using a ribbon and depleting the ink in a more uniform manner would significantly extend the life of the ribbon. In addition, a single pass of each color zone is not always suitable for fast and efficient operation, in particular when the pages are only printed on certain parts and the printer has to wait for the ribbon to advance to the next ribbon zone at a certain nominal ribbon drive speed.

 In color printers such as those of the type described in the aforementioned patents, it is necessary to reverse the progress of the paper after printing a page in a first color so that the same page can be printed in colors remaining. One method is to use conventional pairs of spikes placed both above and below the printing station. This gives a fairly satisfactory bidirectional advance of the paper, but at the cost of two separate pairs of pin drivers. In this regard, it is desirable to provide a device for driving the paper requiring only a pair of spike feeders at the same time as the paper is advanced directionally under a desired tension so that it remains taut and aligned as desired. .This should be done without risk of smearing by ink of the parts of the paper already printed.

 The invention relates to a color printer in which the ink ribbon is designed and arranged so as to minimize or prevent its contamination and also to have an extended useful life. In addition, each color area of the ribbon is advanced through the printer in multiple passes, which also extends the life of the ribbon and at the same time allows relatively quick and efficient printing in the case of printing. pages printed in varying degrees, on less than one full page. The paper advances inside the printer in a bidirectional manner using two relatively simple torque motor devices which hold the paper taut without the ink smearing the parts already printed on this paper.

 In an advantageous embodiment of the ink ribbon according to the invention, the zones of different colors formed over the length of a continuous non-welded fabric are arranged in a progression which is repeated over the length of the ribbon. The progression or combination begins with the lightest area of color at one end of the ribbon, then progresses through the immediately darkest area of color to the darkest area. Then the immediately darker area of color is repeated, followed by the lighter colored area which ends the progression or combination. Consequently, when the ribbon advances in one direction or the other, it is sufficient to skip an intermediate color zone. Otherwise, the various color zones are presented to the printing station in a given order starting with the color the lighter and progressing with the increasingly dark colors.

As an example, the progression or combination begins with yellow and is followed by red, blue, black, then red again, after which the progression or combination is repeated. At the opposite ribbon end, a yellow area is added at the end of the progression or combination.

 According to the invention, the contamination problems due to the fact that the inks filter through the ribbon between the color zones during the storage of the ribbon on a reel are minimized or eliminated by the incorporation of two stop zones or barrier areas between each pair of adjacent color areas of the ribbon. The stop zones are advantageously coated with a non-wetting material such as a fluorine-containing polymeric silicone in order to prevent the ink from filtering through them. Each stop zone advantageously has a length at least equal to the outer circumference of the ribbon spool so that no part of a color zone of the ribbon can overlap another part of the ribbon than the adjacent stop zone. A blank ribbon zone is provided between the two stop zones separating the adjacent color zones of each pair. The virgin zone consists of a section of raw ribbon which rubs against the guides and other elements lying in the path of the ribbon and which thus effectively removes the ink having deposited on these guides and elements.

 The areas of different colors of ribbons in accordance with the invention can be identified by different groups of marks consisting of lines extending over the width of the ribbon and arranged in the format of a normal bar code. Each of these groups of markers is advantageously located in the stop zone adjacent to one end of each color zone. The marks include a desired number of lines of selected width to identify the color of the area in a bar code fashion, as well as the opposite ends of the ribbon. The lines are advantageously applied to the ribbon by hot foil stamping. The resulting barcode formation is easily read using optical sensors placed on the tape path.

 Color printers in accordance with the invention are advantageously implemented so that each of the various color zones located along the ribbon makes several different passes through the printing station when the color of each of these zones is printed on a page. An odd number of these passes is necessary and, in general, the ribbon undergoes at least two direction reversals to establish a minimum of three different passes of the color area through the printing station. Larger numbers of passes, for example five or seven, can also be used when desired. The advantage of using several passes is to distribute the wear more evenly over the length of each color zone.

Another advantage lies in the possibility of printing quickly and efficiently in the event that the pages are not printed in their entirety. The quantity of material to be printed on each page is determined and, in the meantime, the ribbon is advanced so that the color zone makes at least one pass or one pass. When the printing of the page using the color zone is then completed, the printer is prepared to quickly reverse the direction of ribbon feed if the printing ends after an odd number pass, then to immediately advance the ribbon to the start of the next color area. When desired, the tape speed can be increased by a nominal speed during the search for the next color area to further reduce the color selection time.

 According to the invention, the bidirectional advancement of the paper can be achieved using a conventional pin driver using a paper tensioning device which bears against the paper, on the opposite side of the printing station with respect to the pin driver, and which moves in the same direction as the pin driver, but at a different speed in order to keep the paper stretched to a desired degree through the printing station. In a first embodiment, this device can comprise a torque motor connected to a wheel having an elastomeric surface which bears against the printing paper, on one side of the latter opposite several rollers mounted so as to be able to rotate side by side. The outer surfaces of the rollers are advantageously made of non-wetting material such as "Teflon" or "Delrin" in order to oppose the action of any ink from the parts already printed on the paper, which could otherwise cause contamination. The torque motor and the associated drive wheel are mounted on the lower end of a support which has an opposite upper end which can pivot on the pivot drive and an intermediate part carrying a permanent magnet. The permanent magnet is clamped: normally by itself on the rear side of the cylinder in order to pivot the support towards a position for picking up the paper in which the drive wheel associated with the torque motor presses the paper against the rollers. loading and unloading the paper, the cylinder can be rotated so that the permanent magnet is moved away by cam action and thus rotate the lower end of the support, comprising the torque motor and the drive wheel , to a position clear of the paper. The rollers are mounted so as to be able to rotate in a generally rectangular frame which includes opposite paper guides, converging towards each other upwards to a zone of minimum spacing situated immediately below the rollers, thus than the torque motor and the drive wheel connected to it.

 In another embodiment of the paper tensioning device, a torque motor is coupled to a first roll extending over the width of the paper, on its rear face, in opposition to a second roll of non-wetting material which extends over the width of the paper, on the front. The second roller, which is normally biased in a direction pressing the paper against an elastic surface of the first roller by means of two springs bearing against two supports in which the opposite ends of the second roller are mounted so that they can rotate, can be moved away from the paper and the first roller to allow loading and unloading of the paper. The second roller is moved away from the paper by manual actuation of a lever starting from one of the two supports so as to rotate the two supports and an incorporated rod, of square section, on which the supports are mounted, in a direction moving the second roll of the paper against the resistance of the springs. The lever can be locked in the loading-unloading position of the paper by being disposed against a rim of an opening formed in the frame of the tensioning device. paper from which the lever protrudes. When the lever is released from the edge of the opening, the springs can rotate the two supports and thus act on the second roller so that it forces the paper against the first roller.

 The ink ribbon follows a path which passes through the printing station and through one or more guides located on each side of the printing station. The guides may include guide rollers which each have a rotating core carrying opposite flanges and having an outer surface made of a material generally not absorbing ink. In another embodiment of a tape guide avoiding certain drawbacks of both rotary guides and fixed guides, each guide can rotate over an angular range which corresponds to a substantial part of one turn of the guide. of the ribbon drive direction, any ink having accumulated on the guide, at the upstream end of the ribbon guide interface, because the ribbon is pulled on a non-rotating guide, is redeposited on the ribbon during that the guide rotates over a substantial part of a revolution, and that it then stops under the effect of the new direction of entrainment of the ribbon.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting examples, in which
- Figure 1 is a perspective view of a color printer according to the invention
- Figure 2 is a plan view of part of the printer of Figure 1, and it also shows a simplified diagram of a servo device for driving the ribbon of this printer;
- Figure 3 shows a conventional ribbon of the prior art having several areas of different colors;
- Figure 4 shows a ribbon having color zones arranged so as to present the colors in decreasing order of clarity in the two directions of ribbon drive, in accordance with the invention;
- Figure 5 is a representation of a section of the ribbon of Figure 4, illustrating how adjacent color zones are separated by barrier or stop zones and by a blank ribbon zone and whose colors are identified using of lines arranged in the format of a bar code
- Figure 6 is a representation of a section of the ribbon of Figure 4 illustrating an operating mode of the color printer of Figure 1 in which each color area makes several passes through the printer's printing station
- Figure 7 is a representation of the ribbon of Figure 4, similar to that of Figure 6, showing different examples of multiple passages of the color zones
- Figure 8 is a representation of a section of the ribbon of Figure 4 illustrating how different numbers of passes of each color area can be used to perform printing at different dot densities for a given nominal speed of the ribbon and a dimension nominal given of the color zones;
- Figure 9 is a representation of a section of the ribbon of Figure 4, illustrating how different numbers of passes of a color area are chosen for different dot densities and different numbers of hammers of the printer shuttle mechanism of FIG. 1, at a given nominal speed of the ribbon and at a given length of the color zone;
- Figure 10 is a front view of a part of the printer of Figure 1, illustrating an arrangement for maintaining the paper to be printed under a desired tension during its bidirectional advancement
- Figure 11 is a cross section of the arrangement of Figure 10 and a part of the printer of Figure 1;
- Figure 12 is a front view of part of the arrangement of Figure 10
- Figure 13 is a partial perspective view of a guide roller used on the path of the tape;
- Figure 14 is a perspective view of a variant of the guide device to be used on the path of the tape;
- Figure 15 is a perspective view of the guide of the device of Figure 14; ;
- Figure 16 is a top view of the guide device of Figure 14, the upper part of the mounting frame is removed
- Figure 17 is a top view of part of Figure 15, showing how an ink buildup is returned to the ribbon
- Figure 18 is a perspective view of another embodiment of the paper tensioning device for maintaining the paper to be printed under a desired tension during its bidirectional advancement
- Figure 1 9 is a section of the mechanism of Figure 18, along line 19-19 of this figure
- Figure 20 is a view similar to that of Figure 9, the second roller of the mechanism is spaced from the first roller to facilitate loading and unloading of the paper; and
- Figure 21 is a perspective view of a part of the mechanism of Figure 18 which provides temporary positioning of the second roller away from the first roller to facilitate loading and unloading of the paper.

 Figure 1 shows the color printer 10 according to the invention. The printer 10 comprises a relatively flat base 12 mounted on a support leg 14.

The foot 14 has a front portion 16 intended to support a stack 18 of paper 20 for printing multiple copies, with perforated edges, folded in accordion. The printing paper 20 is raised from the stack 18 so as to pass through a generally rectangular body 22 to arrive at a printing station 24.

 The printing station 24 is defined by the interface between an elongated cylinder 26 and a shuttle assembly 28. The printing paper 20 passes through the printing station 24 to arrive at a conventional pimpled driving device comprising two opposite coaches s 30 and 32 with pins. The coaches 30 and 32, which are mounted on shafts 30 and 34 extending between opposite mounting brackets 38 and 40 arranged approximately vertically on the base 12, engage with the perforations of the opposite edges of the paper 20 in order to train the latter in the well known manner. The opposite edges of the printing paper 20 are only partially shown above the printing station 24 in FIG. 1, for reasons of clarity.

 An elongated console 42 can pivot by its upper end 44 on the shaft 36. Hdlicoldaux springs 46 and 48, arranged around the outer surface of the shaft 36 between the upper end of the console 42 and the opposing spikes 30 and 32, are intended to keep the console 42 centered between the coaches 30 and 32. As described below, the console 42 carries a torque motor and an associated drive wheel (not shown in FIG. 1) intended to take the printing paper 20 at a point below the printing station 24. The torque motor and the associated drive wheel move in the same direction as the drives 30 and 32, but at a different speed in order to keep the printing paper 20 stretched to a desired degree in the printing station 24.

 The shuttle assembly 28 is mounted so as to execute a bidirectional reciprocating movement with respect to the cylinder 26, as indicated by an arrow 50.

The shuttle assembly 28 is disposed on the side of two rotary pulleys opposite the side of a counterweight bar 52. A first 54 of the two pulleys is shown in FIG. 1 and can rotate on a vertical axis 56. The second 57 pulleys, which is not shown in Figure i, but which is shown in Figure 2, is mounted so that it can rotate on a vertical axis 58 spaced from the first vertical axis 56. The axes 56 and 58 rotate in a horizontal frame element 60.

 As indicated above, the shuttle assembly 28 performs a bidirectional reciprocating movement as indicated by the arrow 50. During this movement, the shuttle assembly 28 moves on the two rotary pulleys 54 and 57. At the same time, the counterweight bar 52, which is disposed on the other side of the pulleys 54 and 57 with respect to the shuttle assembly 28, performs an alternating movement in the opposite direction to that of the shuttle assembly 28, as indicated by a arrow 62.The shuttle assembly 28 and the counterweight bar 52 are connected to thin flexible bands (not shown) which pass around the opposite pulleys 54 and 57 and which hold, with one or more suitable magnetic devices (not shown) disposed between the shuttle assembly 28 and the bar 52 against weight, the shuttle assembly 28 and the bar 52 in contact with the two pulleys 54 and 57.

Such an arrangement is described in detail in US Patent No. 4,359,289.

 The aforementioned patent NO 4 359 289 also describes a mechanism suitable for driving the device comprising the shuttle assembly 28 and the counterweight bar 52, in an alternative and bidirectional manner. Such a mechanism comprises permanent magnets disposed in the immediate vicinity of the interior side. of the counterweight bar 52 in order to produce a magnetic interaction with two coils 64 and 66 which surround sections of the counterweight bar 52. As described in the aforementioned patent No. 4,359,289, the coils 64 and 66 are excited by signals which control the shuttle assembly 28 and the counterweight bar 52 at a relatively constant speed over a substantial part of their course between the opposite direction reversal points. In the present example, the opposite direction reversal points directions are established by buffers 68 and 70 mounted on the base 12 and disposed near the ends of the shuttle assembly 28 of the counterweight bar 52, respectively. The shuttle assembly 28 and the bar 52 strike alternately against the stops 68 and 70 in order to reverse the direction of their movement.

 The shuttle assembly 28 contains several printing hammers in the form of elastic springs mounted side by side along its length and each comprising a printing point by striking intended to print a point on the paper 20. Each spring of hammer is controlled by an associated hammer mechanism located within the shuttle assembly 28, which uses a permanent member to hold the hammer spring in a withdrawn position and a coil which momentarily overcomes the magnetic effect of the permanent magnet when energized so that the hammer spring is ejected from the withdrawn position to come into contact with an ink ribbon 72 disposed between the shuttle assembly 28 and the cylinder 26. This has the effect on the tip printing the hammer spring to make it strike the ink ribbon 72 against the printing paper 20 supported by the cylinder 26 in order to print a dot on the paper 20. Then, the mart spring water returns to the withdrawal position under the effect of the permanent magnet. The excitation current of the various coils of the various printing hammer mechanisms of the shuttle assembly 28 is supplied by a flexible wire bus 74 which extends between the shuttle assembly 28 and a bracket 76 with mounted terminals on the frame element 60. The various wires of the bus 74 leaving from the bracket 76 are connected to an appropriate circuit housed in a box 78 located at the rear of the base 12 of the printer. The hammer spring and associated mechanisms of the shuttle assembly 28 are described in U.S. Patent No. 3,941,051.

 The color printer 10 includes a ribbon tray 80 mounted on the base 12 at its front end.

The ribbon plate 80 has two opposite spools 82 and 84 mounted so as to be able to rotate on this plate and carrying the ink ribbon 72. The ribbon 72 extends from the spool 82 to the opposite spool 84 along a path which includes the printing station 24. As can best be seen in FIG. 2, the ribbon path comprises two guides 86 and 88 arranged at opposite ends of the printing station 24. Each of the guides 86 and 88 may contain an electrical sensor intended to determine the presence of the end of the ribbon 72 at this sensor.

Each of the opposite ends of the tape 72 may have a conductive section which, when present at one of the guides 86 and 88, indicates that the end of the tape 72 has been reached and that the direction of drive of the tape must be reversed. The ribbon path also includes two opposite guides 90 and 92 arranged in the immediate vicinity of guides 86 and 8ss. Two optical sensors 94 and 96 are arranged at the opposite ends of the printing station 24, in the immediate vicinity and just inside the guides 86 and 88. The optical sensors 94 and 96 detect marks carried by the ribbon 72 by identifying the color of the various color zones of the ribbon 72. The latter may also contain markers indicating its opposite ends, in which case the optical sensors 94 and 96 also supply this data in place of the electrical sensors located inside the guides 86 and 88.

The color identification and end of ribbon markers and the composition of the ribbon 72 having the arrangement of the various color zones are described below.

 The coils 82 and 84 are driven by motors 98 and 100, respectively shown in FIG. 2.

The motors 98 and 100 are mounted inside the plate 80 of ribbon, and are coupled to a servo-system 102 also shown in FIG. 2. The servo-system or servo-control device 102 comprises, with the motors 98 and 100, in the present example, the ribbon drive device described in United States Patent No. 4,177,731. This patent describes a printer ribbon drive device which includes a servo system or device servo comprising two motors intended to drive the opposite ribbon spools.

The servo system drives the coil motors in response to external control signals to give the tape substantially constant speed and tension.

 Likewise, the servo-system 102 shown in FIG. 2 controls the motors 98 and 100 in order to advance the ribbon 72 between the coils 82 and 84 at a substantially constant speed and at a substantially constant voltage. Practically all of the ribbon 72 is wound on one of the coils 82 and 84, the servo-system 102 drives the coils 82 and 84 in order to advance the ribbon 72 from the substantially full coil to the substantially empty coil. Thus, if the tape 72 is wound almost entirely on the reel 82, the servo-system 102: drives the reels 82 and 84 in order to advance the tape 72 from the reel 82 to the reel 84. When the tape 72 has been transferred almost entirely from the reel 82 to the reel 84, the optical sensor 94 detects marks carried by the ribbon, identifying that the end of the ribbon 72 has been reached. This has the effect of transmitting an "end of ribbon" signal to the servo-system 102 and the latter reacts by reversing the drive direction of the coils 82 and 84. This causes the ribbon 72 to return from the reel 84 to the reel 82 When the ribbon 72 is wound almost entirely on the reel 82, the optical sensor 96 detects marks located at the opposite end of the ribbon 72 by indicating that this end of the ribbon 72 has been reached. The resulting "end of ribbon" signal transmitted to the servo-system 102 has the effect of the latter making it again reverse the direction of ribbon 72 drive.

 As mentioned previously, the optical sensors 94 and 96 detect on the tape 72 marks identifying the zones of different colors of the tape.

This allows the system 102 to determine the particular color presented by the ribbon in the printing station 24 at any given time. It also allows the servo-system 102 to drive the coils 82 and 84 in order to pass each color zone several times through the printing station 24 described below. This multiple pass operation represents a notable difference from the conventional operation in which the tape 72 is driven at a nominal speed in the same direction until its end is reached. In a multiple pass operation, the direction ribbon drive is reversed a number of times to repeatedly pass each color area of the ribbon 72 through the printing station 24 and, as described below, there is the possibility of a search to high speed on the ribbons, allowing the ribbon drive to operate at high speed to the next color area.

 As previously described in the aforementioned patent No. 4,359,289, the shuttle assembly 28 is driven along the printing station 28 in a bidirectional reciprocating movement under the action of a linear motor which comprises the coils 64 and 66 mounted on the counterweight bar 52. While the shuttle assembly 28 moves along the printing station 24, the various printing hammers it contains are selectively actuated or "triggered" by an electronic circuit contained in the housing 78 in order to strike the printing paper against the cylinder 26 through the ribbon 72 to print dots. The two-way reciprocating movement of the shuttle assembly 28 drives the latter over a distance sufficient for the various printing hammers that 'It contains can print almost the entire width of the paper 20. The scanning or the stroke of the shuttle assembly 28 through the' printing station 24 is determined in part by the number of printing hammers contained in the assembly 28. Thus, in the case where the shuttle assembly 28 contains seventeen printing hammers, this assembly 28 must carry out a stroke or a sweep of 20.32 mm to adequately cover printing paper generally having a width of 377.83 mm. When the shuttle assembly 28 contains 33 printing hammers, the required stroke or sweep is 10.16 mm.

 Each time the shuttle assembly 28 sweeps across the printing paper 20 in one direction or another, a row of dots is printed on the paper 20. During the opposite intervals of inversion of direction of the shuttle assembly 28, when this assembly 28 strikes against the stopper 68 or when the counterweight bar 52 strikes against the stopper 70, the paper 20 is advanced one step upward by the pin-type coaches 30 and 32 to the position of the next row of dots which is then printed during the next scan of the shuttle assembly 28 across the width of the printing paper 20. At the same time as the shuttle assembly 28 reciprocates on the width of the printing paper 20, the ribbon 72 is driven through the printing station 24 by the servo-system 102 at a desired nominal speed, for example at 7.62 or 15.24 cm per second. The movement of the ribbon 72 at a certain nominal speed is necessary to prevent a noticeable shortening of the life of the ribbon, a shortening which would otherwise occur as a result of ink running out from the struck areas of the ribbon, if the ribbon remained stationary or was driven at too low a speed.

 Color printing requires that the information printed be in several inks of different colors.

 A minimum of three colors is usually preferred for obtaining acceptable color quality and flexibility, printing in four or five colors is preferred for certain applications to improve the quality and variety of colors. Initially, a page of the printing paper 20 is brought into the positions of its various rows of dots in the printing station 24 by the pin drives 30 and 32 so that a predetermined combination of dots of a first color is printed on paper 20.

During the printing of this first color, the servosystem 102 ensures, by means of signals detected by the optical sensors 94 and 96, that the first correct color carried by the ribbon 72 is present in the printing station 24. After printing the page in the first color, the spindle drives 30 and 32 reverse the direction of movement of the paper and bring the printing paper 20 back to the beginning of the page in preparation for printing a second color. Meanwhile, the servo system 102 advances the ribbon 72 in high speed search mode so that a color zone of this ribbon containing the second color to be printed is placed in the printing station 24.

The spindle coaches 30 and 32 again advance the page through the printing station 24, through the various positions of the rows of dots, while the assembly at.

shuttle 28 reciprocating prints a predetermined combination of dots of the second color on the page. The process is then repeated for a third color and for any additional colors to be printed on the page. When the last color has been printed on the page, the pin drives 30 and 32 do not bring the beginning of the page to the printing station 24, but are, on the other hand, continue to advance the printing paper 20 towards the top through post 24 when printing of the next page begins.

 The color printer described in the aforementioned patents NO 4 289 069 and NO 4 336 751 uses a ribbon divided into three zones of different colors along its length. Color printing is achieved by printing a page in a first color, printing during which the area of the first color is advanced through the printer's printing station, followed by printing of the same page of a second color while the area of the second color of the ribbon is advanced through the printing station, then in a third color while the area of the third color of the ribbon is advanced through the printing station . Figure 3 shows a similar ribbon device having four different colors.

 FIG. 3 represents an ink ribbon 104 which can be used in the same way as the ink ribbon 72 in the printer such as the color printer 10, and which is divided into four zones of different colors along its length, between first and second opposite ends 106 and 108, respectively. The ribbon 104 includes an area 110 of a first color which begins at the first end 106 and which contains yellow ink. The first color area 110 is followed by a second color area 112 containing red ink and a third color area 114 containing blue ink and a fourth color area 116 which is at the second end 108 of the ribbon 104 which contains black ink. When the ribbon 104 is advanced in a first direction or forwards "between the coils 82 and 84, the resulting advance sequence consists in passing the yellow zone 110 through the printing station 24, followed by the red zone 112, the blue zone 114 and finally the black zone 116. This sequence is desirable because it has the lightest color first, followed by the other three colors in the decreasing order of clarity. Each time a page is printed on paper 20, some of the ink previously printed on the page tends to come off the ribbon. When the ink previously printed is lighter in color than the one being printed, l The fact that this lighter colored ink comes off and is applied to the ribbon poses a relatively minor contamination problem with regard to the ribbon. However, when the ink previously deposited on the page is darker in color than that being printed, even very small amounts of the darker ink will cause contamination of the lighter color area of the page. ribbon in use for printing.

 This is the reason why the advance cycle, shown in Figure 3 in the case of ribbon 104 is desirable. Yellow is lighter than red which is itself lighter than blue which itself is lighter than black. However, a problem occurs when the second end 108 of the tape 104 is reached. If the ribbon feed direction is simply reversed, the print order is then reversed, with black being printed first, followed by blue, then red and yellow. If the ribbon 104 is driven in one direction for printing so that the advance cycle is performed, then the problem is avoided. However, this requires delaying printing while the ribbon 104 is being driven in reverse from the second end 108 to the first end 106 so that printing can resume. Other problems such as uneven wear of the ribbon appear also because the printing always begins at the same end of each of the color zones 110, 112, 114 and 116. Consequently, when the drive speed of the ribbon 104 is established chronologically in order to pass each of the color zones 110 , 112, 114 and 116 through the printing station 24 during the time it takes to print a complete page from top to bottom, in a given color, the pages which are not printed at their full height result in a repeated use of one end of each color area, excluding the opposite end of that area.

 These problems are avoided, according to the invention, by arranging the color zones along the length of the ribbon so that the desired sequence or printing cycle, from the lightest colors to the most dark, or basically observed in both directions of ribbon drive. For this purpose, certain areas of color are repeated according to a predetermined progression or combination over the length of the ribbon, then certain areas are skipped while the ribbon is drawn through the printing station 24 during printing.

An example of such a ribbon 118 is shown in FIG. 4.

The ribbon 118, which has first and second opposite ends 120 and 122, respectively, can have substantially the same length as the ribbon 104 in FIG. 3. Instead of having only four color zones as is the case with the ribbon 104 of FIG. 3, the ribbon 118 of FIG. 4 has a much larger number of color zones of reduced size.

 We see that the ribbon 118 of FIG. 4 begins at the first end 120 with a yellow colored area (Y) 124 followed by a red colored area (R) 126, a blue colored area (BL) 128 and a black area (BK) 130. This combination is the same as that found on the ribbon 104 of FIG. 3. However, before repeating the sequence YR-BL-BK along the ribbon 118, an additional zone 132 of red color is added. The combination of light to dark then repeats itself with a yellow area 134, a red area 136, a blue area 138 and a black area 140. As before, an additional red area 142 is added after the black area 140. Then the combination of light to dark is repeated with a yellow area 144, a red area 146, a blue area 148 and an area 150 of black color. As previously, a red area 152 is added to the black area 150. Finally, a yellow zone 154 is added to complete the length of the ribbon 118.

 The ribbon advance sequence 118 consists in passing the area 124 of yellow color to the printing station 24, followed by the area 126 of red color of the area 128 of blue color, then of the area 130 of black color. At this stage, the red area 132 is advanced rapidly through the printing station 24, without printing. Then printing is resumed using the yellow area 134, the red area 136, the blue area 138 and then the black area 140. As before, the additional area 142 of red color is quickly passed through the printing station 24, without printing.

Then the printing is resumed using the zone 144 of yellow color, the zone 146 of red color, of the zone 148 of blue color then of the zone 150 of black color. At this stage, the zone 152 of red color is again skipped and the printing begins using the zone 154 of yellow color.

 The yellow zone 154, which is at the second end 122 of the ribbon 118, can be advanced through the printing station 24 in the front direction or in the opposite direction, as appropriate. A typical example is to advance the ribbon 118 to its end 122 after printing the black area 150, after which the drive of the ribbon 118 is reversed and printing is performed using the area 154 yellow in color.

 Then printing is continued in the opposite direction, passing through the red zone 152, the black zone 150 and the blue zone 148. Although the black zone 150, which is darker, is printed before the blue zone 148, which is somewhat little clearer, the effects of contamination are minimal due to the relatively small difference in clarity between blue ink and black ink. It is important that the printing of the relatively dark blue ink and the even darker black ink does not precede a printing done with the red ink, which is lighter, and that this last impression does not itself precede a printing made with yellow ink which is even lighter.

 After the printing carried out using the blue area 148, the red area 146 is skipped and the sequence YR-BK-BL is then repeated by printing using the colored areas 144, 142, 140 and 138. The red area 136 is then skipped and printing is resumed using the yellow area 134, the red area 132, the black area 130 then the area 128 blue.

The red area 126 is skipped and printing using the yellow area 124 is then started, backward or forward, as appropriate.

 We see that the ribbon 118 of FIG. 4 presents a repetitive progression or combination which begins with the lightest color, which is yellow, followed by the immediately darker color, which is red, then, finally, of a or several areas of the darkest colors which, in this example, are blue and black.

The intermediate red color is then repeated before the sequence starts from the lightest to the darkest,
YR-BL-BK. The lightest color, which is yellow, appears at each of the opposite ends of the ribbon 118 which ensures that printing begins, in both directions of ribbon entrainment, with the lightest color. This is also advantageous because the lightest colors tend to be the fastest to run out.

 The number and length of the various color zones of the ribbon 118 are determined at least in part by the printing speed of the color printer 10 and by the speed of the ribbon drive. In the case of an example of the printer 10 shown in Figure 1, which has 33 print hammers located in the shuttle assembly 28, it takes approximately 30 milliseconds to print each row of dots across the width of the paper 20, with an additional 6 milliseconds required to complete the reversal of direction of the shuttle assembly 28 and the advancement of the printing paper 20 from a row of dots position by the spindle drives :: 30 and 32.

If printing is done at a dot density of 40 x 40 per cm, the time required to print a page 28 cm long is approximately 40 seconds. At a lower dot density of 20 x 20 per cm, the time required to print a 28 cm page is approximately 11.3 seconds. If the minimum allowable ribbon speed for a reasonable ribbon life is determined to be 7.6 cm per second, then 3.05 m of ribbon is required to print a 28 cm page in one color with a density of 40 x 40 dots per cm, and 0.86 m of ribbon to print the same page in one color with a point density of 20 x 20.

 In another example of the color printer 10, the shuttle assembly 28 contains 17 print hammers instead of 33 hammers. In this case, the total time required to print a row of dots and make a change of direction becomes 66 milliseconds. This brings to 73 seconds the time required to print a 28 cm page at a point density of 40 x 40 per cm, and to 25 seconds the time required to print the page at a point density of 20 x 20 per cm.

At a nominal ribbon speed of 7.6 cm per second, you need 5.5 m ribbon to print the page in one color at a dot density of 40 x 40 per cm, and 1.92 m ribbon for one point density of 20 x 20 per cm.

 When a ribbon containing several zones of different colors such as ribbon 118 is wound on the reels 82 and 84, the inks of the sections of the ribbon ser # atn7ant tend to pass one inside the other at the interface between two zones of adjacent colors, which poses a contamination problem. To avoid this problem, the interface between the adjacent color zones of each pair of the tape 118 comprises at least one barrier zone or stop zone. In a preferred embodiment shown in FIG. 5, two barrier zones 156 and 158 are placed between the two color zones 160 and 162 forming each pair. The color zones 160 and 162 can constitute any adjacent pair of color zones inside the ribbon 118 such as the color zones 124 and 126 situated at the first end 120 of the ribbon 118 or the color zones 138 and 140 d 'an intermediate part of the ribbon 118. The barrier 156 interfaces with the color zone 160, while the barrier zone 158 interfaces with the color zone 162. A single cleaning zone 164, consisting of a length of virgin or raw tape, is placed between the two barrier zones 156 and 158.

 During the operation of the ribbon plate 80 shown in FIGS. 1 and 2, ink coming from the various zones of different colors tends to deposit to a certain degree on the guides 86, 88, 90 and 92. This ink can be rub on a different colored area and thus pose a contamination problem. The cleaning zone 164 minimizes or eliminates this problem by eliminating by friction or by absorbing most of the ink from the guides 86, 88, 90 and 92.

Consequently, if the color zone 160 passes over the guide 86, 88, 90 and 92 and a certain part of the ink coming from the color zone 160 is deposited by friction on these elements, the next passage of the section of raw tape comprising the cleaning area 64 by sweeping away or otherwise absorbing most or all of the ink from the guides 86, 88, 90 and 92 before the passage of the next color area 162 through the station 24 and on guides 86, 88, 90 and 92.

This prevents contamination of the color area 162 by ink from the previous color area 160.

 Each of the barrier zones 156 and 158 advantageously has a length at least equal to the external circumference of the coils 82 and 84. This makes it possible to compensate for the most unfavorable case in which the section of ribbon shown in FIG. 5 is located at the external part of a complete ribbon wound on one of the reels 82 and 84 and filling practically the whole of the reel. By giving the barrier zones 156 and 158 this minimum length, it is possible for the barrier zone 156 to prevent any overlap of the color zone 160 with the cleaning zone 164, and to the barrier zone 158 to prevent any overlap of the color area. 162 with the cleaning zone 164. The barrier zones 156 and 158 and the cleaning zone 164 together prevent any overlapping of the color zones 160 and 162. The barrier zones 156 and 158 are advantageously coated with a non-wetting agent applied, for example example, by spraying a fluoropolymer. This prevents ink from filtering through barrier areas 156 and 158 entering adjacent segments of the ribbon.

 Unlike certain multi-colored ribbons of the prior art, which consist of different segments of fabric welded to each other at their limits, the ribbon 118 consists of a continuous length of fabric having no solder, seam or other joint. The ribbon is thus less subject to breaks, tears or other deterioration.

As shown in FIG. 5, each of the barrier zones 156 and 158 carries a different set of marks 166 and 168. The set of marks 166 serves to identify the color contained in the area 160, while the set of marks 168 serves to identify the color contained in the zone 162. Each of the sets of marks 166 and 168 comprises one or more lines extending over the width of the ribbon, between the opposite edges of the latter. The lines, which are of a reflective nature so as to be able to be detected by optical sensors 94 and 96 and which are advantageously applied by hot stamping in thin sheet, vary in number and can also vary in width in order also to identify the colors of the various zones in the manner of a conventional bar code
The use of a hot foil stamping process gives very thin opaque films formed on the ribbon without appreciable increase in the thickness of the latter, so as not to obstruct the path of travel of the paper in the passage through the printing station.

Sets or groups of markers similar to sets 166 and 168 can also be used to identify the opposite ends of the ribbon, as indicated above, which avoids having to put in place conductive segments at the opposite ends of the ribbon, segments associated with electrical sensors placed inside the guides 86 and 88 as described above.

 An example barcode diagram for identifying the four different colors of the ribbon of the examples described, as well as opposite ends of the ribbon, uses five lines to identify yellow, four lines to identify red, three lines to identify blue, two lines to identify black and a single line to identify the end of the ribbon.

 Yellow, red, blue and black colors are cited only for illustrative purposes and to simplify the description of the ribbons in the present examples. As indicated above, different numbers of colors and different combinations of colors can be used to perform color printing according to the invention. In addition, in the example described with four colors, red is more technically of magenta shade and blue color of cyan shade.

The operation of the color printer 10 has so far been described as making a single pass of each color area of the ribbon through the printing station 24 while the ribbon is being fed in a given direction. As a result, printing of a given page begins at the same edge of each color area
o used in the printing of this page, for a given direction of ribbon entrainment. If all or substantially all of the page contains printed information, each color area is used almost entirely during printing. On the other hand, if the page is printed on a surface much smaller than its totality, only the first part of each color zone is then used, since a large number of the pages printed by a printer such as the color printer 10 are not entirely printed, the ribbon tends to wear unevenly. Consequently, a more equal use of the color zones of the ribbon would have the effect of extending the useful life of this ribbon.

 Another problem may arise with regard to the speed or efficiency of printing when a single pass of each color zone is made through the printing station. As before, when the printing carried out on a given page does not cover the whole of this page1 only the first part of the passage through each color zone is then accompanied by a printing. The printer must rotate freely during the second part of this passage, waiting for the arrival of the next color zone in the printing station 24, before printing of the next color can begin.

 A printing technique according to the invention, which tends to distribute the wear of the ribbon more evenly and, at the same time, to speed up the printing process and to make it more efficient, uses multiple passes or passes of each color zone of the ribbon through the printing station 24 of the color printer 10. This technique is illustrated in FIGS. 6 and 7. The example in FIG. 6 relates to three different passages of each color zone through the printing station 24. Thus, a yellow-colored zone 170 makes a first passage 172 through the printing station 24, in a first direction, followed by a second passage 174 through the station 24, in the opposite direction. The second passage 174 is followed by a third passage 176 which is again in the first direction. A similar sequence of three different passages is used with each of the following areas of red, blue and black 178, 180 and 182 during the continuation of the sequence.

 The three different passages of each of the colored zones, such as the passages 172, 174 and 176 of the yellow zone 170, are executed by the servo-system or servo device 102 which reacts to the barcode signals coming from optical sensors 94 and 96 and indicating the arrival at the opposite ends of the various color zones. Thus, in the case of the yellow area 170, the servo-system 102 passes the area 170 through the printing station 24 until the first pass 172 "is completed. When one end 184 of the yellow-colored zone 170 reaches the printing station 24, this condition is detected by one of the sensors 94 and 96 and the servo-system 102 reacts by reversing the direction of the ribbon drive to start the second pass 174. The second pass 174 continues until an opposite end 186 of the yellow area 170 is reached. 'When the end 186 is reached, the associated barcode marks are detected by one of the sensors 94 and 96 and the servo-system 102 reacts by reversing the ribbon drive direction again to start the third pass 176 of the yellow area 170 through the printing station 24. At the end of the third pass 176, the servo system 102 ignores the arrival of the end 184 due to the presence nce of a counting circuit which determines that the three passages of the zone 170 of yellow color have taken place. The servo system 102 simply continues in the red-colored zone 178 for which the process of the three passes is repeated.

 It can be seen that the three pass technique shown in Figure 6 tends to use the two ends of each colored area as well as the intermediate parts of the area. This technique is also suitable, by its nature, for faster and more efficient printing, as illustrated in FIG. 7 which also shows the four color zones 170, 178, 180 and 182 of the example in FIG. 6. In the technique illustrated in FIG. 7, the quantity of information to be printed on a given page is determined. This is easily done because the information to be printed is generally entered and stored in the printer 10 before printing, as described in the aforementioned patent No. 3,941,051. Consequently, it can be determined before or at least at end of the first scan by the first colored area, during the printing of a given page, if the printing of the page has been completed or if passages; additional are necessary The example shown at the bottom of the figure 7 assumes a case where only the upper end of the given page is to be printed. Since the length of the printed information is less than a third of the page, a single pass from each of the four color zones 170, 178, 180 and 182 is required to print the page. This condition is illustrated by line 187 at the bottom of FIG. 7. A preliminary determination of the length of the page to be printed allows the servo-system 102 to carry out a single pass of each of the color zones.

In addition, the high speed search mode of operation can be used to advance the ribbon to the next color area at a higher speed after completion of printing.

 Since multiple passes of each of the color zones are provided in the examples of Figure 7, the various color zones of the ribbon can be shortened, or the nominal speed of the ribbon can be increased compared to the single-thread process passage described above. Therefore, even when the printing is partially completed using each of the color areas 170, 178, 180 and 182, the time required to move to the next color area is considerably less than that taken in the case of the single pass.

 FIG. 7 shows, at its upper part, another example according to which it is determined that the information to be printed on a given page occupies only about half of the page. In this example, a first passage 188 of the yellow color zone 170 is carried out, followed by an inversion of the direction of entrainment of the ribbon and the beginning of a second passage 190. About halfway through the second passage 190 it is determined that the yellow printing of the page is complete. At this instant, the direction of entrainment of the ribbon is again reversed and the system passes directly to the zone 178 of red color by making a third shortened passage 192 of the second half of the zone 170 of yellow color. The high speed search mode is advantageously established so that the third pass 192 is carried out at high speed. A similar three pass process is performed for each of the remaining color areas 178, 180 and 182 to complete the printing of the given page.

 It appears that in the case where a multiple-pass printing technique is used, an odd number of passes from each group of four color zones is produced in the example described. It is possible to make a single pass of each of the four color zones, as indicated by line 187 of the example at the bottom of Figure 7. In addition, as shown in Figure 6 and at the top in FIG. 7, three different passages of each color zone are also possible, in which case the passages can be complete passages in the sense that they relate to the entire length of each color zone, as is the case on the Figure 6, or they may include several shortened passages as in the example illustrated at the top of Figure 7. In all cases, two reversals of the ribbon drive direction are made in each color area, except in cases where a single pass is required for a page of relatively short length.

 As described below with reference to Figure 9, a multi-pass operating technique is not necessarily limited to three passes, but may include other odd numbers of passes, for example five, seven or nine passes.

 FIG. 8 explains how the lengths of the various color zones of a ribbon can be chosen so that a ribbon of desired overall length is obtained, taking into account the different densities of points that can be used. In the example of a shuttle assembly 28 comprising 17 printing hammers, a single passage of the color zone requires approximately 25 seconds at a tape speed of 7.36 cm per second if the color zone has a length about 1.83 m and that the density of the impression is 20 x 20 points per cm. When the print density is high at 40 x 40 dots per cm, we can then determine that it takes 73 seconds in the color zone if the latter is approximately 1.83 m in length and the ribbon speed is 7.62 cm per second. This can be achieved without extending the color area by 1.83 m, by three passes of this color area.

 Thus, as shown in FIG. 8, a zone of color 194 having a length of 1.83 m and moving at a nominal speed of 7.62 cm per second must pass only once in the case of a density d print of 20 x 20 dots per cm and three times in the case of a print density of 40 x 40 dots per cm. As before, this assumes a shuttle assembly 28 to 17 printing hammers.

 In the example of a shuttle assembly 28 to 33 printing hammers, the printing speed is practically doubled. However, each of the colored areas such as the area 194 shown in Figure 8 can be maintained to the length of 1.83 m, simply by doubling the nominal speed of the ribbon to bring it to 15.24 cm per second. Therefore, the techniques illustrated in Figure 8 apply to a 33 hammer system as well as to a 17 hammer system if the nominal speed of the tape is doubled to 15.24 cm per second.

 The nominal length of 1.83 m of a color zone can be used to make a ribbon similar to the ribbon 118 shown in FIG. 4, but having a total of 26 color zones. The 26 color zones require a total length of 47.55 m of ribbon, and the intermediate stopping and cleaning zones such as those shown in Figure 5 require an additional 7.3 m of ribbon length. This gives the ribbon a total length of 54.85 m, which is the standard length of ribbon used in dot-matrix printers of this type.

 Figure 9 provides another illustration of how a multiple pass operation can be used, with a nominal speed of the ribbon and a nominal length of the color areas, so that the same ribbon is suitable for different dot densities and can be used in printers with different numbers of print hammers. In the example of FIG. 9, the ribbon is driven at a nominal speed of 20.32 cm per second and the area 1 96 of color shown has a length of 1.83 m. The approximate times required to make one, three, five, seven and nine passes of this color zone are indicated. On this basis, it can be determined that, in a printer with 17 hammers, three passages of each color zone are necessary. for a point density of 20 x 20 points per cm and nine passes of each color zone for a point density of 40 x 40 points per cm. A 33 hammer printer requires a single pass from each color zone for a density of 20 x 20 dots per cm and five passes from each color zone for a point density of 40 x 40 per cm.

 As indicated above, the pin drives 30 and 32 advance the printing paper 20 upwards step by step through each of the positions of successive rows of dots on a page during the printing thereof. in a given color, after which the paper is fed in reverse to return to the top of the page in preparation for printing in the next color. It is desirable to be able to keep the printing paper 20 stretched as it is moved through the printing station 24 in either direction. This is achieved using the device shown in Figures 10 to 12 which includes the elongated console 42 and the rectangular frame 22 mentioned previously with regard to Figure 1. As shown in Figure 1, the elongated console 42 is mounted so to be able to pivot on the shaft 36 of the spindle drives 30 and 32, by its upper end 44. The pivoting assembly is produced by means of a hinge element 98 connected to the upper end 44 of the console 42 and having an opening 200 intended to receive the shaft 36.

 A torque motor 202 is mounted on the console 42, at its lower end 204 opposite the upper end 44. The torque motor 202 comprises a drive wheel 206 mounted so that it can be rotated by this motor. The wheel 206 has an outer surface of elastomer, for example rubber, so that traction is established between the wheel 206 and the printing paper 20. A permanent magnet 208 of rectangular shape is mounted on the console 42, at a intermediate part thereof, between the upper 44 and lower 204. The permanent magnet 208 is normally fixed on the rear face of the cylinder 26 by magnetic attraction in order to maintain the pivoting console 42 in a working position in which the wheel 206 of the torque motor 202 bears against the back of the printing paper 20.

 With the console 42 in the working position, the drive wheel 206 presses the printing paper 20 against a set of rollers 210. The rollers 210 are mounted so that they can rotate side by side along the length of axis 212 extending between the opposite ends of the rectangular frame 22, ends on which this axis is mounted. Therefore, the various rollers 210 extend across the width of the printing paper20. These rollers 210 are made of non-wetting material, for example "Delrin", so as to present an external surface which does not absorb ink. This is important because the rollers 210 come into contact with certain parts of the paper. printing which have already been printed in one or more colors, when the progress of the paper 20 is reversed and the paper descends to the top of a given page during printing, in preparation for printing in color next.

The drive wheel 206, which pushes the rear face or the back of the printing paper 20 against the rollers 210, need not necessarily have a non-wetting external surface since it bears against a face of the paper which does not contain ink.

 In operation, the torque motor 202 is started in the same direction as the pin drives 30 and 32, but at a different speed. When the printing paper 20 is driven upward by the pin drives 30 and 32, the torque motor 202 rotates the drive wheel 206 in the upward movement of the paper, at a lower speed. This generates a desired degree of tension in the printing paper 20, inside the printing station 24.

When the printing paper 20 is driven downward by the pin drives 30 and 32, the torque motor 202 is controlled so as to rotate the drive wheel 206 in the direction of movement of the paper downward at a speed slightly higher than that produced by the pin drives 30 and 32. This has the effect of keeping the paper 20 stretched as desired in the printing station 24.

 As indicated previously, the permanent magnet 208 is fixed on the rear side of the cylinder 26 in order to manten.ir console 42 in the working position in which the drive wheel 206 presses the printing paper 20 against the rollers 210. can withdraw, by rotating it, the console 42 from its working position in order to move the drive wheel 206 away from the printing paper 20 and thus facilitate loading and unloading of the paper in the printer 10. This is achieved by the action of a relatively flat cam 214 which is mounted on top of the cylinder 26 and which has a slightly inclined edge, bearing against the permanent magnet 208 in order to push this magnet 208 and the console 42 of which it is integral towards the outside when the cylinder 26 rotates. The cylinder 26 is made so as to be able to rotate on an axis 216 which passes through it, as indicated by an arrow 218. Since the axis 216 is offset from the cylinder 26, the rotation of the latter has the effect of l move away from the shuttle assembly 28 and thus facilitate the loading and unloading of the printing paper 20. Consequently, at the same time as the cylinder 26 is rotated to open such a space, the cam 214 against the permanent magnet 208 so as to push the console 42 outwards and thus move the drive wheel 206 which is coupled to the torque motor 202 away from the rollers 210.

 The rectangular frame 22 comprises a paper guide assembly comprising a pair of opposing paper guides 220 and 222. The paper guides 220 and 222, which extend along the length of the rectangular frame 22 inside the latter , rise in the direction of the drive wheel 206 and the rollers 210. The paper guides 220 and 222 converge towards each other upwards until they reach a zone of minimum spacing between them, immediately below the drive wheel 206 and the rollers 210, as shown in FIG. 11.

 The paper guides 220 and 222 facilitate loading the printing paper into the color printer 10. As shown in FIG. 1, a stack of paper 18 is normally placed on the front part 16 of the support leg 14. The stack 18 includes a length of folded printing paper 20. The paper 20 is loaded by pulling it upwards and introducing it into the underside of the rectangular frame 22. At this stage, the guides 220 and 222 of the paper serve to guide the edge of the paper while it is moved towards the high between the drive wheel 206 and the rollers 210, in an opening in the base 12, between the cylinder 26 and the shuttle assembly 28 and towards the inside of the spindle drives 30 and 32.

 FIG. 13 represents a guide roller which can be used for the guides 86, 88, 90 and 92 shown in FIG. 2. The guides used in a tape tray of this type normally include a fixed element or a small column around which the tape is pulled. In practice, this results in the deposition by friction of a certain part of the ink of the ribbon on the guide.

This does not pose any particular problem in the case where an entirely black ribbon is used in a black and white printing. On the other hand, in the case of color printing, ink coming from a color zone deposited on a guide and then passing by friction over a different color zone, poses a contamination problem.

 This problem can be mitigated by using the guide roller 224 shown in FIG. 13. The guide roller 224 comprises a core 226 having opposite cheeks 228 and 230 of larger diameter and mounted so as to be able to rotate on a vertical axis 232 which is itself mounted on the plate 80. The rotary core 226 can rotate freely with the ribbon 72 during the bidirectional drive of the latter. The rotation of the core 226 with the ribbon 72 has the effect of significantly reducing the quantity of ink depositing from the ribbon 72 on the core compared to the case of the fixed ribbon guides of the prior art. In addition, the outer surface of the core 226 is made of a non-wetting material such as "Teflon" which does not absorb the ink from the ribbon 72. This also significantly reduces the amount of ink depositing from the ribbon 72 on the core 226.

 As indicated above with reference to FIG. 13, the guides used in a ribbon drive mechanism of the type shown in FIG. 2 normally include a fixed element or a column around which the ribbon is pulled. The problem posed by these fixed guides lies in the large quantities of ink which can pass by friction of the ribbon on the guide. This does not pose any particular problem in the case of a single-colored ribbon but, in the case of a multi-colored ribbon, at least a certain part of the ink deposited on the guide can be transferred to a colored area. even when the tape has an intermediate cleaning area such as area 164, which results in contamination. The guide roller 224 shown in Figure 13 alleviates this problem because its core 226 can rotate freely with the ribbon 72 during its bidirectional drive.

 However, the guide roller 224 shown in Figure 13 is not without itself posing a possible problem of its own. If the central axis of the core 226 around which the guide 224 rotates is precisely positioned with respect to the moving ribbon, the ribbon then tends to pass over the guide 224 by rotating the latter in a gentle, continuous and deformation-free manner. tion. However, the rotating core 226 of the guide 224 tends, as is the case with any rotating ribbon guide, to direct or force guide the ribbon passing over it, and this may result in a tendency of a portion of the ribbon end up folding in on itself or completely escaping from the guide in certain extreme cases, in particular when the central axis of the core 226 is not precisely positioned. This is not a problem in the case of fixed guides. that don't spin. However, as indicated above, the fixed guides pose the problem of a possible accumulation of the ink, with possible contamination of other areas of color in the case of ribbons with multiple colors.

 FIGS. 14 to 17 show another embodiment of a tape guide 240 which avoids the orientation or guiding problem present in the case of rotary tape guides, while attenuating the possibility of contamination when this guide is used with a ribbon made up of a series of zones of different colors.

The tape guide 240 is characterized by its ability to rotate over a limited range of angular movement which, in the present example, is an important part of a full turn of the tape guide 240. Therefore, each time the ribbon feed direction is reversed, the ribbon guide 240 rotates with the ribbon over a substantial portion of a full turn, after which the guide 240 remains stationary so that the ribbon slides over it.

 As shown in FIG. 14, the partially rotary guide 240 of tape is carried by a fixed mounting frame 242 comprising opposite upper and lower parts 244 and 246 respectively and an intermediate part 248 extending between the upper and lower parts 244 and 246. The upper part 244 has an opening 250 intended to receive the guide 240 of the tape. The lower part 246 has a similar opening (not shown) intended to receive the guide 240. The intermediate part 246 is of generally elongated shape and ends in a rounded front edge 252 adjacent to the guide 240 of the ribbon.

 FIG. 15 shows the guide 240 in detail.

As shown in FIG. 15, the guide 240 comprises an elongated, generally cylindrical core 254 disposed between two opposite cheeks 256 and 258. the abutment element 260 has a generally disc-shaped part mounted on the cheek 256, on the other side with respect to the core 254 and a projection or tab 262 projecting outwards from this disc-shaped part. A pin 264, which extends towards the outside of the stop element 260, on the other side of the cheek 256, has a central axis which coincides with the central axis of the core 254. A second pin 266, of which l the central axis also coincides with that of the core 254, is disposed on the opposite side of the lower cheek 258 relative to the core 254. The pin 264 is housed so as to be able to rotate in the opening 250 of the upper part 244 of the frame 242 mounting. The opposite pin 266 is housed so that it can rotate in the opening of the lower part 246 of the mounting frame 242.

 The ribbon guide 240 is configured so as to receive an ink ribbon such as the ribbon 72 on the core 254, between the opposite cheeks 256 and 258 of the latter. In the absence of the stop element 260 ′, the guide 240 of the ribbon can rotate freely continuously under the effect of the movement of this ink ribbon. However, as shown in FIG. 16, in which the upper part 244 of the mounting frame 242 is not shown for clarity, the abutment element 260 and its tab 262 limit the rotational movement of the guide 240 of the tape at an angular range less than one full turn of this guide. This results from the contact of the tab 262 with the opposite sides of the intermediate part 248 of the mounting frame 242 when the tape guide 240 rotates in opposite directions. At one end of the movement, the tab 262 bears against a first side 268 of the front edge 252 of the intermediate part 248, as shown in solid lines in FIG. 16. At the other end, the tab 262 bears against a second opposite side 270 of the front edge 252 of the intermediate part 248, as shown in dotted lines in FIG. 16. An arrow 272 shows there that the guide 240 of the ribbon can rotate between the opposite limit positions shown, in which the tab 262 bears against one or the other of the sides 268 and 270 of the front edge. 252 of the intermediate part 248.

 Due to the limited range of rotation movement of the ribbon guide 240, it can be seen that the problem of orientation or guiding of the ribbon, generally present in the case of freely rotatable guides, is minimal or nonexistent. Each time the ribbon is turned in the opposite direction, the ribbon guide 240 then rotates over a large part of a revolution to the opposite limit position, after which the guide 240 stops and remains motionless while the ribbon slides over it, like a fixed or non-rotating guide. When the direction of the ribbon guide reverses again, the guide 240 again rotates with the ribbon for a substantial part of a revolution to the opposite limit position in which the guide 240 stops and remains stationary for as the ribbon slides on it. Since the ink ribbon tends to fold in on itself or to escape completely from the guide only after numerous rotations of the guide, this problem is practically nonexistent with the guide 240 which cannot rotate only over a limited interval. At the same time, the small amplitude of possible rotation of the ribbon guide 240 appreciably mitigates the contamination problems of the ribbon which would otherwise appear with a fixed or non-rotating guide, as explained with reference to FIG. 17.

 FIG. 17 represents the core 54 of the guide 240 of the ribbon on which a length of ink ribbon such as the ribbon 72 is wound. It is assumed that the tape 72 is driven in the direction indicated by the arrows 274 and that the guide 240 has been turned so that the tab 262 of the stop element 260 is against the first side 258 of the front edge 252 of the intermediate part 248. A line 276 drawn on the core 254 represents the orientation of the tab 262 when it is in this position.

While the ribbon 72 continues to be driven in the direction of the arrows 274 and the core 254 remains stationary, the scraping effect of the ribbon 72 passing over the fixed core 254 causes an amount of ink 278 to form. upstream end of the interface between the ribbon 72 and the core 254. If the direction of drive of the ribbon 72 is now reversed and the core 254 continues to remain stationary, the quantity of ink 278 carried by the core 254 rest. This is of no consequence as long as the same color area of the ink ribbon 72 continues to be drawn on the core 254. However, when a different color area of the ribbon 72 is drawn towards and on the core 254, at least some part of the quantity of ink 278 is transferred to this zone of different color and causes it to be contaminated.

 In the case of the ribbon guide 240, the inversion of the ribbon drive direction 72 in relation to that indicated by the arrows 274 has the effect of rotating the ribbon guide 240 and the incorporated core 254 over a large portion of a turn, as indicated by an arrow 280. During this rotation, the tab 262 passes from the orientation indicated by the line 276 to an opposite position on the second side 270 of the front edge 252 of the intermediate part 248, as shown by a dashed line 282 in FIG. 17. When the core 254 rotates in this way under the effect of the reversal of the direction of drive of the ribbon 72, the quantity of ink 278 previously deposited on the core 254 is brought in by rotation to a point 284 located at the opposite end of the interface between the ribbon 72 and the nogau 254. Then, while the core 254 continues to undergo the slight rotation necessary to complete its movement between the opposite limits, the quantity ink 278 carried by this core 254 comes into contact with the ribbon 72, which has the effect of transferring most or practically all of the quantity of ink 278 onto the ribbon 72.

Since the same color area of the ribbon 72 is still present on the ribbon guide 240, this is of no consequence
If the ribbon 72 then continues to be driven in the opposite direction to that indicated by the arrows 274, the movement of the ribbon 72 on the fixed core 254 results in the accumulation of an amount of ink on the surface of the core 254, at point 284. If the movement of the ribbon 72 is now reversed so that the ribbon is driven in the direction of the arrows 274, the ribbon guide 240 and the incorporated core 264 rotate, entraining this quantity of ink and then bringing it into contact with the ribbon 72, which has the effect of returning this quantity of ink to the ribbon 72.

 The advantages of the limited rotational movement produced by the ribbon guide 240 are best used when the ribbon 72 is driven so that each color zone of the ribbon makes several different passes through the printing station 24, nearby tape guide 240. It appeared that this multi-pass operating mode produced relatively large quantities of ink at the interface of the ribbon 72 and of the core 254, which quantities are not completely removed from the core 254 by the intermediate zone 164 for cleaning the ribbon. 72 before the arrival of the next color zone on the core 254. In the case where the ribbon 72 is continuously driven from one end to the other so as to produce only one pass of each color zone on the ribbon guide 240 and through the printing station 24, the core 254 remains stationary during the advance of each of the successive color zones towards the ribbon guide 240. However, in these cases, the accumulation of ink at the interface of the ribbon 72 and the core 254 has been found to be minimal, and these amounts of ink are usually reduced or eliminated by the intermediate cleaning zones of the ribbon 72. , so contamination is not a problem.

 The preceding description of FIG. 1 has referred to a paper tensioning mechanism contained in a rectangular frame or housing 22 and which is described in detail with reference to FIGS. 10 to 12. Another relatively simpler embodiment of the mechanism paper tensioner according to the invention is illustrated in Figures 18 to 21. These figures show a paper tensioning mechanism 290 which is housed in a generally rectangular housing 292 designed to be fixed to the underside of the base 12 of the printer 10 in color, like the rectangular box 22 shown in FIG. 1.

 The housing 292 contains a torque motor 294 comprising a shaft 296 connected to a first roller 298.

One end of the first roller 298, opposite the torque motor 294, has a journal 300 which is housed so that it can rotate in the housing 292 so that the first roller 298 can rotate under the control of the torque motor 294. The first roller 298, which extends over the width of the printing paper 302, on its rear face, is mainly made of foam rubber in order to present an elastic outer surface. This elastic outer surface of the first roller 298 facilitates the taking of the printing paper 302 by the first roller 298 so that the paper 302 is driven by the action of the torque motor 294.

 A second roller 304 extends over the width of the printing paper 302 and bears against the face of the paper 302 opposite to that in contact with the first roller 298. As in the case of the rollers 210 of the previous embodiment shown in Figure 10, the second roller 304 is made of a material not wetted by the ink so as not to act on the ink already transferred on the adjacent surface of the printing paper 302. The second roller 304 is mounted so as to be able to rotate between two opposite supports 306 and 308 which are themselves mounted so as to be able to pivot inside the housing 292 as described below. A helical spring 310 extends between an inner wall of the housing 292 and the support 306 so as to normally return the latter in the direction of the printing paper 302 and the first roller 298. A helical spring 312, mounted between the inner wall of the housing 292 and support 308, normally recalls the latter towards the printing paper 302 and the first roller 298. In this way, the coil springs 310 and 312 act on the second roller 304 so as to hold the printing paper 302 in contact with the first roller 298. This position is illustrated in FIG. 19.

 The manner in which the supports 306 and 308 are mounted so that they can pivot inside the housing 292 is illustrated in FIG. 21. The supports 306 and 308, on an upper end of each of which journals a different end of the second roller 304 , are each mounted by a lower end on an axis 314 of generally square section. The axis 314 has a first end 316 adjacent to the support 306 and which pivots in an opening 318 of a support 320. thle second end 322, opposite to the previous one, of the axis 314 is mounted so that it can rotate in a opening 324 of a support 326. The opposing supports 320 and 326 are mounted inside opposite ends of the rectangular housing 292 so that the axis 314, the supports 306 and 308 and the second roller 304 are arranged at the inside of this rectangular box 2 92.

 As previously mentioned, the coil springs 310 and 312 normally recall the upper ends of the supports 306 and 308 and the second roller 304 in a direction compressing the printing paper 302 against the first roller 298, as illustrated in Figure 1 9. However , the second roller 304 can be moved away from the printing paper 302 and the first roller 298, against the resistance of the helical springs 310 and 312, by a downward movement of a lever 328 forming part of the lower end of the support 306 and which passes through an opening 330 of the rectangular housing 292 as shown in FIG. 18. The downward movement of the lever 328 causes the support 306 to rotate against the helical spring 310 in order to move the upper end of the support 306 away from the associated end of the second roller 304 of the printing paper 302 and the first roller 298, against the resistance of the coil springs 310. At the same time, the axis 314, which is f fixed to the lower end of the support 306, rotates in the openings 318 and 324 formed in the supports 320 and 326. This results in a rotation of the support 308 in the same direction and substantially at the same angle as the rotation of the support 306 against the resistance of the coil springs 312. Consequently, the second roller 304 moves away from the printing paper 302 and the first roller 298 in a generally uniform manner and parallel to this roller, in response to a downward movement of the lever 328. This is illustrated in FIG. 20 and this is the position that the second roller 304 takes to allow loading and unloading of the printing paper 302. The second roller 304 and the supports 306 and 308 can be locked in the position shown in FIG. 20 by bending the lever 328 towards the left part of the opening 330 shown in FIG. 18 so that the lever 328 engages with a flange 332 situated in the opening 330.

 As shown in FIGS. 19 and 20 as well as in FIG. 18, the paper tensioning mechanism 290 comprises convergent and opposite paper guides s 334 and 336 whose functioning is similar to that of the paper guides 220 and 222 of the previous form of embodiment shown in FIGS. 10 to 12, in order to facilitate the insertion of the printing paper 302 into and through the tensioning mechanism 290. Once the printing paper 302 has been placed in the tensioning mechanism 290, the second roller 304 and the supports 306 and 308 are brought back to the position shown in FIG. 19 by a movement of the lever 328 to the right inside the opening 330 shown in FIG. 18, so that this lever disengages from the edge 332. This allows the lever 328 to rise inside the opening 330 while the helical springs 310 and 312 point out the upper ends of the supports 306 and 308 and the second roller 304 towards the printing paper. 302, then in contact with the latter, opposite the first roller 298.

 During operation, the torque motor 294 is controlled so as to drive the printing paper 302 via the first roller 298, in the same direction as the spindle drives 30 and 32 shown in FIG. 1 and at a speed slightly different from that of these coaches. While the printing paper 302 is advanced upward by the pin drives 30 and 32, the torque motor 294 moves the first roller 298 in a direction allowing an upward movement of the printing paper 302, but at a speed slightly lower in order to maintain a desired degree of tension in the printing paper 302, in the area of the printing station 24. Conversely, when the pin drives 30 and 32 drive the printing paper 302 downward, the torque motor 294 drives the first roller 298 in one direction and at such a speed that the printing paper 302 is moved downwards at a slightly higher speed, thus conferring as before a desired degree of tension on the printing paper 302 in the area of the printing station 24. Unlike the paper tensioning mechanism shown in FIGS. 10 to 12, which automatically takes the position of loading and unloading of paper in response to the rotation of the cylinder re 26, the paper tensioning mechanism 290 of FIGS. 18 to 21 requires an independent actuation of the lever 328 to bring the second roller 304 into the position of loading and unloading of the paper shown in FIG. 20. However, at the same time, the tensioning mechanism 290 is much simpler in construction and operation.

 It goes without saying that many modifications can be made to the ribbon and to the printer described and represented without departing from the scope of the invention.

Claims (19)

 1. Printer in which a length  of paper (20) is advanced towards a printing station (24) by a paper drive device arranged on a first side of the printing station, characterized in that it comprises a paper tensioning device arranged  on an opposite side of the printing station from the paper drive, the tensioning device bearing against the paper to generate tension therein as it is advanced through the printing station.  2. Printer according to claim i, characterized in that the paper drive device is bidirectional in order to drive the paper in opposite directions through the printing station and in that the paper tensioning device has the effect generate tension in the paper as it moves back and forth through the printing station.  3. printer according to claim 2, characterized in that the paper tensioning device comprises a torque motor (202) and a drive wheel (206) connected to the motor and bearing against the paper.  4. Printer according to claim 3 ,. characterized in that it comprises several rollers (210) mounted so as to be able to rotate on the side of the paper opposite to that where the drive wheel is located.  5. Printer according to claim 4, characterized in that the drive wheel has an outer elastomer surface and in that the rollers  mounted so that it can rotate on the opposite side of the  paper generally have non-wetting surfaces.  6. Printer according to claim 1,  characterized in that the paper tensioning device  comprises a rotary element (206) in contact with the  length of paper and is implemented in order to turn  in the same direction as the paper; and at a different speed.  7. Printer according to claim 6, characterized in that the paper tensioning device comprises a torque motor (202) connected to the rotary element.  8. Printer according to claim 6, characterized in that it further comprises several rollers (210) mounted so as to be able to rotate, side by side, on the opposite side of the length of paper relative to the rotary element.  -9. Printer according to claim 8, characterized in that it comprises a paper guiding device comprising two opposite paper guides (220, 222), mounted below the rollers and the rotary element and converging towards each other. 'other upwards to a minimum spacing zone located below and near the rollers and the rotating element.  .10. Printer according to claim 8, characterized in that the rollers have external surfaces made of material which practically do not absorb the ink and in that the rotary element comprises a wheel having an external elastomer surface.  11. Printer according to claim 8, characterized in that the paper tensioning device comprises an elongated console (42) on the lower end of which the rotary element is mounted and whose opposite upper end (44) is articulated on the pin drive device (30, 32), a part of this console, located between the opposite upper and lower ends, being intended to bear against the cylinder (26) which is mounted so that it can rotate and which can make pivot the console so as to move the rotary element away from the length of paper when said cylinder rotates.  12. Printer according to claim 11, characterized in that it further comprises a permanent magnet (208) mounted on the part of the console situated between the opposite upper and lower ends in order to be applied against the cylinder, and an element cam (214) mounted on the cylinder which can bear against the permanent magnet when the cylinder is turned.  13. Printer according to claim 1, characterized in that the paper tensioning device comprises a torque motor (294), a first roller (298) connected to the torque motor and bearing on the length of paper (302), and a second roller (304) bearing against the side of the length of paper opposite to that where the first roll is located.  14. Printer according to claim 13, characterized in that the first roller has an outer surface of elastic material and the second roller has a generally non-wetting surface.  15. Printer according to claim 14, characterized in that the paper tensioning device comprises a first roller (298) having an outer surface of elastic material in contact with the length of paper, over the width of the paper, a torque motor (294 ) connected to the first roll, and a second roll (304) having an outer surface of material practically not absorbing ink, in contact with the length of paper, on the side of the paper opposite to that where the first roll is located .  16. Printer according to claim 15, characterized in that it also comprises a paper guide device comprising two opposite paper guides s (220, 222) mounted below the first and second rollers, the converging paper guides towards each other and upwards to a minimum spacing zone located under and in the immediate vicinity of the rollers and the rotary element.  17. Printer according to claim 15, characterized in that it comprises means intended to momentarily distance the second roller from the first roller to facilitate the loading and unloading of the paper.  18. Printer according to claim 17, characterized in that it further comprises a housing (292) in which the first roller is mounted so as to be able to rotate, a rod (314) mounted so as to be able to rotate in the housing, two brackets (306, 308) mounted on the rod, at a distance from one another and carrying between them the second roller so that it can rotate, and two springs (310, 312) each arranged between the housing and one, different, consoles.  19. Printer according to claim 18, characterized in that it further comprises a lever (328) starting from one of the two brackets and an opening <330) formed in the housing in order to receive the lever, the opening comprising a flange (332) intended to receive the lever in order to maintain the second roller in a position separated from the first roller against the resistance of the two springs.