Paper-end detector

Abstract: A printing unit using a paper roll (4) has a paper end detector comprising swinging arm (12) with roller (10) maintained in contact with the surface of the paper (4) wound on core (9) by spring (13). The paper is drawn-off through printing head (3) with ribbon (6) and platen (2). The core (9) has a colour or shade contrasting with the paper (4) and a photo-sensitive detector (11) is provided on the arm (12) adjacent roller (10) in order to detect the change in reflected light from the paper (4) to the core (9) when the paper end is reached. The light source illuminating the paper surface may be integral with the detector (11) or separate therefrom.

Description: This invention relates to machines using paper or film rolls and more particularly a paper roll end detecting device and method for use in recording or printing units for text, drawings, tables and pictures on a paper roll coiled around a core or drum. This invention may be applied conveniently to a colour printer using a colour sublimation ribbon and being equipped with a thermal print head. Reference is made to our copending application 95305887.2(EP), published as EP6gg538A. Printers are known that provide print head impact force to transfer ink to the paper by means of a solid ball, type face or a print wire. Ink jet means using heat, vibration, electric field and magnetic field are also known. Thermal print heads comprise another class where heat is used to mark a heat sensitive recording paper. There is a need to provide colour printing and a universal printer catering for professional use as well as business use such as for CAD and computer graphics is desirable. Many conventional printers use cut sheet paper and the paper feed and transfer path of the paper inside the unit becomes complex, and as a result, makes the use of larger sizes of paper and also the maintenance difficult. In the case of a colour printer for three colours and black, four print passes are needed and the complex paper transfer paths make it difficult to provide positioning accuracy. Thus the colour picture quality may prove insufficient and more complex mechanisms are needed for improving the positioning and picture quality. A method and apparatus as disclosed and claimed in EP95305887.2 (EP6gg538A) uses, instead of cut paper for the recording paper, a roll of recording paper wound around the periphery of a drum wherein printing on the same surface is effected four times by turning the drum back and forth. In this construction a plurality of roller units are located both before and after the platen roller to pull and feed the recording paper several times in forward and reverse directions after pulling the paper off the roll. In JP-A-58095061 there is disclosed a paper end detecting apparatus in a printing or recording unit wherein a change in reflectivity between the paper and the core is used to signal the paper end as detected by a sensor maintained in contact with the paper surface. In our prior application EP95305887.2 (EP6gg538A) we disclose and claim, and referring to Figure 1 herein, 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, characterised in that the transport means (5) includes 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 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. In such a printing unit using roll paper, attention must be paid to the replacement of the roll when it has been consumed and the location of the roll and the maintenance should be simple. One object of this invention is to provide for easier and secure detection of the terminal end of the roll of paper wound around the core in a printer as aforesaid, especially for a colour printer. According to this invention there is provided a printing or recording 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, and including a paper roll end detecting unit for detecting the terminal end of a roll of paper wound around a core in said printing or recording unit wherein the outside surface of said core is of a different colour or shade than the paper of the roll, said paper roll end detecting unit comprising a photo sensor for detecting a change in characteristic or intensity of light reflected from the paper, a first means for maintaining a constant distance between the photo sensor and the paper surface during reduction in the paper roll diameter and a second means for maintaining the said first means in contact with the surface of the paper, the arrangement being such that in operation the terminal end of the roll of paper is detected through the change in the characteristic or intensity of reflected light detected by the sensor, characterised in that said first means comprises a pinch roller and that the said 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 and transport means whereby the transport means moves in a linear reciprocating manner the print head producing an image during the reciprocating movement. In this invention it has been found surprisingly that the problem can be solved by detecting, by means of a sensor, colour change of the core around which the recording paper is wound. Preferably the paper roll recording unit is a sublimation type colour printer. In the paper roll recording unit, the paper wound around the core is fed out to the print head section continuously from the cut end and printing is effected on the paper. Because the roll is a consumable item the paper rolled around the core is reduced during use. The outside diameter of the paper roll is continuously decreased, and when the paper has entirely been consumed the roll is the same diameter as that of the core. In this invention, the outside surface of the core of the paper roll is made darker in colour than the paper. The paper is usually white, but if the paper should be coloured then the core may be darker or the outside surface of the core may be contrastingly coloured but need not be especially coloured if it has a darker colour than the roll paper due to the material from which the core is made. The paper roll end detection forming part of this invention is effected by the intensity of light reflected from the paper and the core by use of a photo sensor. For example the extent of the consumption of paper is assessed by detecting a change from the strong reflected light from white or pale colour of the paper to a lower reflected light due to the dark colour, for example black or brown colour, of the outside surface of the core. The detected result is signalled by means such as a light, a buzzer or liquid crystal display. Usually the paper is white whereas the core is black, brown or dark brown so that the difference in shade is large which is preferable because the detection of the change in intensity of reflected light becomes easier. The paper end detecting unit forming part of this invention may be formed by a pinch roller being pressed against the paper roll and following the rotation to keep the distance between a photo sensor and the surface constant during the reduction in roll diameter. The photo sensor may be positioned in the vicinity of the pinch roller with a support unit and a spring for assisting tracking of the photo sensor and to press it against the paper surface whose outside diameter is decreasing. In addition to this basic structure, the light source such as a lamp, light emitting diode (LED), semi-conductor laser or other light emitting element for illuminating the paper surface is arranged in the vicinity of the photo sensor. These light emitting sources may be a single mono-block unit reflected light sensor in combination with the light receiving element such as a photo diode. The paper terminal end detecting unit of this invention can be used with various constructions of paper roll recording units. For example, a variety of printers and instrumentation equipment can be adapted by including the unit of this invention. An example of a colour printer to which this invention can be applied is the printing unit disclosed and claimed in EP95305887.2 (EP6gg538A). The paper roll terminal end detecting unit and method forming part of this invention may be applied to a printing or recording unit using a print head of any 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 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 useful for paper roll printing according to this invention. 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 to which this invention can be applied, and Figure 2 shows in more detail and in section the paper end detector 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'. In the said mechanism, as the printing operation progresses, the roll of recording paper reduces in outside diameter. Both the maximum outside diameter state, when the roll is new and at a maximum diameter and the minimum outside diameter state, when the paper has been consumed, are shown in Figure 1. In the figure, references 10 and 10' are the pinch roller positions when pressed against the roll of paper and following the rotation. The pinch roller position 10 shows when the outside diameter of roll paper is a maximum, the roller always following the change in outside diameter of the roll, down to the position of the roller 10' when the outside diameter is a minimum. Figure 2 shows a detailed sectional view in the vicinity of the paper roll 4 and pinch roller 10. The paper roll which is wound around the core 9 is printed by the thermal head 3 via the ink ribbon 6 which is fed through the platen roller 2. The pinch roller 10 follows the rotation of the paper roll and touches the surface of the roll. The roller 10 is always pressed against the surface of the paper roll by the carrier arm 12 urged by spring 13 pulling the arm 12 towards the roll. A photo sensor 11 is installed on the arm 12 in the vicinity of roller 10. The pinch roller 10 may be fixed and the roll 4 made movable. Light from a light source (not shown) is reflected by the paper surface and the intensity is detected by the light receiving element 11. The photo sensor 11 and the pinch roller 10 approach the core 9 as the paper is used and following a reduction in the outside diameter of the roll. When the roll reaches the terminal end and the outside face of the core appears, the photo sensor 11 detects the change in intensity of reflected light because of the dark colour of core 9, and signals that the paper roll has been consumed. In the embodiment the light source may be carried by the arm 12 adjacent the sensor 11 or may be separate from the arm 12 and pinch roller 10 and arranged to illuminate an appropriate area on the paper surface. As described above, the paper roll terminal end detecting unit forming part of this invention is mechanically simple and for this reason the unit can be designed to a compact size with the arrangement inside the printing unit being simple and trouble free, requiring little maintenance. This invention can be very effectively applied to a colour printer using a colour sublimation type ribbon and a thermal head.

Claims: A printing or recording 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, and including a paper roll end detecting unit for detecting the terminal end of a roll of paper (4) wound around a core (9) in said printing or recording unit (1) wherein the outside surface of said core (9) is of a different colour or shade than the paper of the roll (4), said paper roll end detecting unit comprising a photo sensor (11) for detecting a change in characteristic or intensity of light reflected from the paper (4), a first means (10) for maintaining a constant distance between the photo sensor (11) and the paper surface (4) during reduction in the paper roll diameter and a second means (13) for maintaining the said first means (10) in contact with the surface of the paper (4), the arrangement being such that in operation the terminal end of the roll of paper is detected through the change in the characteristic or intensity of reflected light detected by the sensor (11), characterised in that said first means comprises a pinch roller (10) and that the said transport means (5) includes 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 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 as claimed in Claim 1, characterised in that the said unit (1) is a sublimation type colour printer. A printing unit as claimed in Claim 1 or 2 characterised in that the outside surface of said core (9) is made darker than the paper (4); the pinch roller (10) is pressed by a spring (13) against the surface of the rotating paper roll; and the terminal end of the paper roll is detected by the change in intensity of reflected light between the paper (4) and core (9), detected by said photo sensor (11). A printing unit as claimed in any preceding claim, characterised in that the light reflectivity characteristic of the paper (4) is substantially different to that of the core (9) around which the paper is wound, said light detecting sensor (11) being maintained in constant position relative to the paper surface during unwinding from the roll (4); and a paper end signal is generated by said sensor (11) on a significant and preselected change in the characteristic of reflected light detected by the sensor (11). A printing unit as claimed in any preceding claim, characterised by a light source illuminating the paper in the zone of the photo-sensor (11). A printing unit as claimed in Claim 5, characterised in that the light source is adjacent and integrated with the photo sensor (11). A printing unit as claimed in any preceding claim, characterised in that the photo sensor (11) detects a change in light intensity or a change in colour or a combination thereof.

Inventors: TAMURA TOSHIHARU, YOSHIDA NAOKI, TAMURA, TOSHIHARU, YOSHIDA, NAOKI
Applicants: ALTECH COMPANY LIMITED
Application year: 1995
Main classification: B41J29
IPC codes: B41J29, B65H23, B41J15, B65H26, B41J11