Printing apparatus

Abstract: A colour printer has a print unit (1) with a continuous roll (4) of paper which passes over a platen roller (2) beneath a print head (3) with interposed ink transfer ribbon fed between reels (6) and (6'). The end of the paper roll (13) is clamped between jaws (9,10) of a clamping carriage (5) which is movable to position (5') to draw out length (L) of paper (4). During this action the print head (3) is operative to deposit or transfer an appropriate colour from ribbon (6) onto the paper. Roll (4) then rewinds the paper and draws clamp (5) back to the start position. The print operation is repeated for each colour required after which rollers (12a,12b) cause the paper to be discharged through guides (18a,18b) and through sheet cutter (7).

Description: This invention relates to a means for reproducing or printing text, drawings, photographs and the like onto a roll of paper wound on a drum. This invention is especially useful as a colour printer using a colour sublimation type of ribbon and a thermal print head. Printers are known in the art which apply selectively an impact force to a ribbon material using a solid ball or a print wire or which form an ink jet using heat, vibration, electric or magnetic field, or which selectively apply heat to an inked transfer material using a thermal head or which selectively supply heat to a heat sensitive printing paper using a thermal head. There is a need to provide for colour printing to a professional standard for business use and in the field of CAD and computer graphics. In known devices, because many conventional printers use cut paper, the transfer path of paper inside the unit becomes complex, and as a result, makes the change in the size of paper and maintenance difficult. These matters are important especially in the case of a colour printer. In a colour printer which prints up to three colours and black, four printing operations are needed and the complex paper transfer path makes it difficult to improve the positioning accuracy, and colour image quality is often poor. To improve the known devices more complex mechanisms for improving positioning and picture quality are required. A method is known from US 5110227A for using a roll of paper instead of cut sheets and to print four times on the same sheet portion by clamping and rolling the printing paper around a large size drum and turning the drum forward and back. In this method the print unit size becomes larger because a large size drum is required for printing a large sheet and thus a plurality of drum diameters are needed for obtaining various sizes of printed image. This disclosure also requires pinch roller units following the print platen roller and which operate to transport the paper in a curved path and repeatedly pull and feed the paper non-linearly several times in a forward and a reverse run direction. This paper feeding mechanism can create practical problems in use. In Fig 3 of this disclosure a modification is shown using a clamp moving a section of the paper in a linear manner. However the clamp is not attached to the free end of the paper and operates at an intermediate point and drive of the pinch rollers is still necessary to pull the paper through the print head. One object of this invention is to provide a printer unit especially for colour printing, wherein the construction is simple, printing accuracy is high due to improved positioning accuracy using linear motion without the need for pinch rollers and a roll of paper is used to provide good printing or image quality at high resolution. According to this invention there is provided a printing unit having a continuous roll of paper or like medium to be printed, transport means to draw paper from the roll to pass over a platen, and a print head adjacent the platen to produce an image on the paper, characterised in that the transport means includes a clamp operable to grip the free end of the roll, said transport means being movable to draw-off a length of paper from the roll, the roll being operable in a reverse direction to rewind and pull-back the paper whereby the transport means moves in a linear reciprocating manner, the print head producing an image during the reciprocating movement. By such means it has been found that many problems can be overcome by using a clamp unit for holding the free end of a roll of printing paper and effecting a linear reciprocating movement over a designated number of cycles. The printing unit of this invention may use a print head of any conventional kind. For example the print head may operate by heat sensitive printing by making the head contact the printing paper and colouring same by heating, or heat transfer printing may be used for transferring an ink from a film to the paper by heating same. Heat transfer printing can be classified into a fusion heat transfer using a sublimation type ink carrier sheet which is fused by heat application or the sublimation type heat transfer using a sublimation type ink sheet wherein a dye sublimes by heat application from the rear face of a dye layer and is diffused and fused into the receiving layer of the printing paper to colour same. For printing using pressure as the energy source, there is pressure sensitive printing using colouring through chemical change under pressure and the ink jet system for controlling the release of a jet of ink under pressure to adhere same to the paper. Various systems have been developed in the ink jet system, but such systems can be generally classified into an on-demand type and the continuous type. The on-demand type uses electrical and mechanical switch systems, electrical and heat switch systems and electrostatic suction systems. Among these the bubble jet system and thermal ink jet system using a thermal head are suitable for this invention. There is also electric heat sensitive printing and electrostatic printing using electric current and printing using optical (laser) and magnetic systems as the energy source. A variety of printing systems can be used with this invention. Among such systems are those using the thermal head which is especially suitable for the printing unit of this invention and in respect of the controllability, resolution and graduation (tone), and heat sensitive printing systems using fusion type thermal transcription, thermal sublimation and bubble jet techniques. The sublimation type thermal transfer has advantages due to the wide gradation and high reproducibility of picture density, the gradation in low density areas is uniform and high density can be obtained. In addition to the picture quality, high resolution is possible and the unit is comparatively compact and can be made at lower cost. The maintenance is easy, and throughput time is short so that higher speed is possible and these features are especially important for the colour printer of this invention. The paper roll used in this invention is wound around the core of the reel or drum and is continuous instead of the usual cut sheets. In the case of a sublimation type thermal transfer, image receiving paper is used where the receiving surface, which is designed to absorb the dye, is provided on a smooth base material and a parting layer for preventing thermal fusion with the transfer film is provided on the receiving layer surface. The roll type recording paper is printed on by each of said recording systems when it passes between the printing head and the platen roller. In the sublimation type of thermal printing, in addition to the image receiving paper, an ink ribbon is used with the dye layer containing a sublimation dye on one side of a base of thin polyester film, the transcription film being provided with a heat resistant smooth layer rolled onto the rear surface. The film is overlapped by image receiving paper, and when it is passed between the thermal head and the platen roller, the dye sublimes and is dispersed and fused into the receiving paper layer to colour same by heating the dye layer instantaneously from the rear face using a high temperature. A full colour picture can be obtained by overprinting each of the colours yellow, magenta, cyan and black in sequence using the thermal print head. For a printing system using an ink ribbon such as in the sublimation type thermal printing then a single colour ribbon in the case of a single colour or a multi-colour ribbon in the case of multi-colours is used. In the case of a multi-colour ribbon, there is provided a strip coating system using non-uniform layers, and a sequential system for printing the image as a line or raster system using the dye layers yellow, magenta, cyan and black in sequence. The order of the dye layers applied may be different. The ink ribbon which is to be wound on a spool is turned sequentially with the spool together with the passage of the printing head. The printer paper is clamped at the end and linearly pulled out in the main run direction by the length necessary for one image area by the clamp unit. The action of the clamp unit is a feature of this invention, and first the end of the roll of paper is pressed against a metal part of the clamp by one or more rubber strips using a releasing mechanism to apply pressure to the end of the paper. Secondly, the clamp unit pulls out the printer paper which is pulled back by the reverse turning force of paper roll drum. The clamp unit makes a linear reciprocating movement between the initial position and the remote position (pull-out position) relative to the platen roller and the printing head. The unit draws out the paper prior to the actual printing, once in the case of single colour and four or three times in the case of multi-colours. This initial or idle feed of paper means that, after the end of the roll of paper is clamped and without printing by the head, the paper is pulled out to the length necessary for one image. The paper is then rolled back. This achieves compensation for the paper skew at right angles to the main run direction from the correct position and corrects distortion of the paper itself. The paper is then rolled back to the original position by reverse turning of the paper roll drum. Regardless of whether single colour or multi-colour printing is used and after the end of printing of one image, the clamp unit returns to the original position and a roller inside the unit turns after release of the clamp to feed the paper to the paper discharge channel. As described above, the drum on which the roll of paper is wound turns in the forward direction to allow feed out of the paper when the end is pulled out by the clamp but when the clamp returns to the initial position from the pull-out position, the said unit winds back the printer paper by one image frame by the reverse turning force applied to the paper drum. The function and construction of the printing head, in this invention, can be changed by adopting any known printing system. The function and construction of the head may change depending on the type of printing system. For example, some printer systems depend on electrical energy, pressure, heat, light and magnetic forces. The thermal print head is especially useful not only for printing high density and at high speed with low noise and controllability but also has structural features of compact size. In this invention, the drive force for linearly reciprocating the clamp unit between the initial position and the pull-out position requires a high accuracy in order to enhance the paper positioning accuracy. A pulse stepping roller has a high accuracy but is very expensive. It is possible to obtain the required linear reciprocating movement with the desired high accuracy by providing gears for linearly moving the clamp unit, fitting a toothed belt where teeth are provided at constant spacing on a rubber belt and by moving the belt with a pulse stepping motor. The roll of paper, on which printing is finished after the designated number of cycles, is unclamped at the initial position and fed in a paper discharge direction by a set of paper discharging rollers arranged on upper and lower sides adjacent to the clamp. The paper may then be cut manually or automatically or using a cutter unit in the path midway from the clamp unit at the initial position to the paper discharge outlet. One set or more than one set of rollers can be provided, if necessary, before and after the cutter unit in the channel to the paper discharge outlet. The cutter unit enables the roll of paper to be sequentially accumulated in cut sheet form. In addition, sensors may be provided for detecting the position of the paper, ink ribbon, clamp unit and the end of the paper, as well as a head driving logic and memory, cooling fan, input/output connectors, circuit breakers, motors for driving various parts, switches for testing which may all be installed as necessary into the printing unit of this invention. One embodiment according to this invention is described and shown by way of example with reference to the drawings, wherein:- Figure 1 shows a schematic sectional side view of a sublimation type thermal colour printer, and Figure 2 shows in more detail the reciprocating paper transport clamp means. Referring to Figure 1, there is shown a sectional view of a colour printer of the sublimation type using a thermal transfer process. The roll of paper 4 to be printed is wound around a drum and a sublimation type ink film or ribbon 6 which has dye layers in sequence of yellow, magenta, cyan and black is drawn out and fed between the platen roller 2 and thermal print head 3 inside the unit 1. The end of the paper 4 is held by a transport device 5 with a clamp capable of opening and closing. The transport device 5 linearly reciprocates between the initial position 5 and the drawn out position 5' over the maximum length indicated by arrow L. The drive source for the transport device is not shown in the drawing, but a linear reciprocating movement of high accuracy can be obtained by use of gear drives or through a toothed belt driven by a stepping motor. A cutter unit 7 is provided between the transport clamp 5 and a paper discharge port 8 where the cut paper sheet of the required length is discharged from the port. The ink ribbon is fed in sequence of yellow, magenta, cyan and black between two drums 6 and 6'. Figure 2 shows in more detail a section through the transport clamp 5. The transport clamp 5 has an upper unit 5a and the lower unit 5b, and for maintenance, the upper unit 5a may be opened. The end 13 of the paper drawn out from the roll of paper 4 is held by a two part clamp with rubber clamp strip 10 on the clamp arm 11 against a metal clamp plate 9. The entire clamp unit 5 in the paper clamping state linearly reciprocates in the direction L. The clamp rubber 10 need not be one piece, and for equalising the pressure, six pieces of clamp rubber can be arranged spaced according to the width of paper. The clamp arm 11 is operated by the moving lever 15 which is turned in the direction D by a gear 17 and cam 16. The lever 15 operates the clamp arm 11 to move in the direction O against the spring 14 to release the clamp 9,10. The pressure of the clamp is in the reverse direction to arrow O and the paper 13 is held between the clamp rubber 10 and the clamp plate 9 by the force of spring 14. A set of paper discharging rollers 12a and 12b are provided adjacent the clamp 9, 10 and the paper 13, after printing a complete image or picture, is fed to the cutter 7 installed in the paper discharge path between upper and lower paper guides 18a and 18b. The printing operation is now described in more detail. The clamp unit 5 which has clamped the end 13 of the paper by release and then closing of the clamp in the initial position moves the paper by the length L in the draw-out direction to the left linearly and during idle feed out of the paper over the roller 2 without activating the printing head. The feed is through a belt and the stepping motor which are not shown in the drawing. After this, because of a reverse turning force applied to the roll 4, the printing paper 13 returns to the initial position without any sagging. On this operation, distortion of skew to the paper 13 is corrected with the end portion of the paper moving in a direction at right angles to the main run direction so that the paper is aligned and returns to the correct position. This idle feed action of the paper is important for correcting the skew and achieving alignment and correct positioning. This is especially important for colour printing and contributes greatly to the enhancement of picture quality when four or three colour printing is effected requiring accurate alignment. After this operation the printing is effected once for a single colour and four times or three times in the case of multi-colour. The end of the printing paper 13 is clamped and the clamp unit 5 again pulls out the paper from the initial position using the belt and the stepping motor. During this action, the first printing, for example black in the case of a single colour and the yellow in the case of colour, will be printed on the paper by the thermal head 3 from the ink ribbon 6. As the paper is drawn out, the ink ribbon passes between the paper 4 and the thermal head 3, and is transported from roll 6 to reel 6'. When the pull-out and the first printing has finished and the clamp has reached the end of the pull-out position, the said unit pulls back the paper with the end of the paper remaining clamped. Not only does the clamp unit return to the original position but the pull-back also returns the paper correctly to the original position by the reverse rotation given to the paper drum 4. After this process follows the paper discharge operation if the printing is in a single colour, or in the case of multi-printing, the clamp unit repeats the action as for the magenta colour, followed by cyan and black, then returns to the initial position and effects the paper discharging action after the printing has been completed. For reference, the black is sometimes omitted from a colour print. In the paper discharging operation paper discharging rollers 12a and 12b arranged adjacent to the clamp 9, 10 inside the clamp unit 5 start rotating and the end of the clamped paper 13 is fed in the discharge direction by the paper discharging rollers. The paper may be directly guided to the paper discharge port and accumulated in a tray or the like, but it is usually convenient to use cut paper of designated sizes and hence, in the embodiment, the paper guided by upper and lower guides 18a and 18b is cut across the main run direction using cutter unit 7, and sequentially accumulated in the tray through the paper discharge port 8. As described above, the printing unit of this invention has a simple mechanism which can be used even with large sizes of paper. For this reason, the unit can have a compact size and maintenance is simple. The positioning accuracy is much enhanced and the printing accuracy and resolution are higher through repeating the reciprocation movement of the clamp and by using the idle feed mechanism for first correcting the skew. Thus printing is of excellent quality. When using the cutter unit, continuous roll paper can be used to produce a final printed cut sheet. Due to the use of paper rolls this invention enables paper to be loaded and aligned.

Claims: A printing unit (1) having a continuous roll (4) of paper or like medium to be printed, transport means (5) to draw paper from the roll (4) to pass over a platen (2), and a print head (3) adjacent the platen to produce an image on the paper, the transport means (5) including a clamp (9,10) operable to grip the free end (13) of the roll (4), said transport means (5) being movable to draw-off a length of paper (L) from the roll (4), the roll (4) being operable in a reverse direction to rewind and pull-back the paper and the transport means (5) whereby the transport means (5) moves in a linear reciprocating manner, the print head (3) producing an image during the reciprocating movement. A printing unit in accordance with Claim 1, characterised in that the transport means (5) and paper (13) reciprocate a defined number of cycles, the image being produced or built up by the print head (3) during the or each cycle. A printing unit in accordance with Claim 1 or 2, wherein the image is printed during the movement of the paper (13) in the draw-off direction. A printing unit in accordance with any preceding claim characterised in that the transport means (5) reciprocates either four times and the print head (3) produces a yellow, magenta, cyan and black image at each operation, or three times to produce a yellow, magenta and cyan image, or once to produce a black image. A printing unit (1) in accordance with any preceding claim, characterised by the continuous roll (4) of paper passing over the platen comprising a roller (2) beneath the print head (3) with interposed colour ink transfer ribbon fed between reels (6) and (6'), the end of the paper (13) being clamped between jaws (9,10) of a transport carriage (5) which is movable to a position (5') to draw out linearly a length (L) of paper from the roll (4), the print head (3) being operative to deposit or transfer an appropriate colour from the said ribbon onto the paper, roll (4) being rewound to draw the paper and clamp (5) back to the initial position, the print operation being repeated for each colour required after which rollers (12a,12b) cause the paper to be discharged through guides (18a,18b) and through sheet cutter (7), to a paper discharge port (8). A printing unit in accordance with any preceding claim characterised in that a thermal transfer printing unit (3) is used with a thermal print head. A printing unit according to claim 6, characterised in that the said thermal transfer printing unit (3) is a sublimation thermal transfer type and includes an ink ribbon mechanism (6',6) for moving the said ribbon between the thermal print head (3) and the paper (13). A printing unit according to any preceding claim characterised by the paper sheet cutter unit (7) being located between the transport means (5) and the paper discharge port (8). A printing unit according to any preceding claim, characterised in that the clamp (9,10) comprises a clamp plate (9) for receiving the end (13) of the paper roll (4), resilient means (10) on a clamp arm (11) pressed by a spring (14) against clamp plate (9), a clamp releasing lever (15) for releasing the pressure of clamp arm (11), a cam (16) with gear (17) for operating the release lever (15) and including the discharging rollers (12a,12b) for feeding the paper to the cutter unit (7). A printing unit as claimed in any preceding claim, characterised in that the clamp (9,11) has a mechanism for holding the end (13) of the paper with rollers (12a,12b) for correcting distortion in the paper and for feeding the paper in the paper discharge direction. A printing unit as claimed in any preceding claim characterised by a stepping or pulse motor with a toothed belt drive forming the transport means (5) to effect the linear reciprocation movement over the designated number of cycles at every printing operation in accordance with the length of the paper. A printing unit in accordance with any preceding claim characterised in that the platen comprising the roller (2) turns in synchronism with the movement of the transport means (5) and paper (4). A printing unit in accordance with any preceding claim, characterised in that the first reciprocating movement of the transport means is used to align the free end (13) of the paper particularly to correct skew and preferably to index position, the printing being effected during the second and subsequent reciprocating movements of the transport means (5). A colour printing apparatus including the printing unit of any preceding claim.

Inventors: TAMURA TOSHIHARU, YOSHIDA NAOKI, TAMURA, TOSHIHARU, YOSHIDA, NAOKI, Tamura, Toshiharu, c/o Syst.Int. Products Co. Ltd., Yoshida, Naoki, c/o Syst. Int. Products Co. Ltd.
Applicants: ALTECH COMPANY LIMITED
Application year: 1995
Main classification: B41J15
IPC codes: B41J11, B41J2, B41J15