Method and apparatus for thermal printing suitable for large printing area

Abstract: A method and an apparatus for thermal printing capable of thermally printing diverse patterns on large printing areas at a high accuracy. In the apparatus, the carbon ribbon (1) is moved along a first track and then along a second track which are spatially separated from the first track; a printing object is carried along the second track below the carbon ribbon (1); the desired printing patterns are imprinted on the carbon ribbon (1) moving along the first track by a printing head (19) placed on the first track; and the carbon ribbon (1) is pressed onto the printing object by thermal transfer roller (23) placed on the second track so as to thermally transfer the desired printing patterns on the carbon ribbon to the printing object.

Description: The present invention relates to an apparatus and a method for thermally printing desired printing patterns on a printing object by using a carbon ribbon having thermally transferable carbon black on its front side as set forth in the Preambles of Claims 1 and 6, respectively. An apparatus and a method of this kind is known from US-A-4 739 343. In this document, a thermal printing system for postage meter mailing machine application is disclosed in which the carbon ribbon is imprinted from its rear side by a printing heading having the pattern of an extraneous image. This extraneous image is transferred by the printing head onto a scavenging roller so that positive printing pattern remains on the carbon ribbon which is subsequently transferred by thermally printing onto a printing object. A blade is associated to the scavenging roller which dislodges the ink transferred thereto from the carbon ribbon so that the scavenging roller is always prepared to receive ink from the carbon ribbon. From US-A-4 740 798 a transfer-type thermal printing device is known making use a carbon ribbon which is imprinted by a printing head so that a predetermined pattern of ink is removed from the ribbon, so that a printing pattern remains on the ribbon which is subsequently transferred by application of heat to a printing object. The ink of the predetermined pattern initially removed from the ribbon is transferred by the printing head onto the rear side of the ribbon expended by the utilization in the printing station where the ribbon is brought in contact with the printing object. It is the object of the present invention to provide an apparatus and a method for thermal printing as set forth in the Preamble of Claim 1 and 6, respectively, which make it possible to print patterns on large printing areas at a high accuracy. This object is attained by the features of Claim 1, as far as the apparatus is concerned, and by the features of Claim 6, as far as the method is concerned. Preferred embodiments thereof are subject matter of the dependent claims. Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings. Figure 1 is a schematic diagram of an embodiment of an apparatus for thermal printing according to the present invention, and Figure 2 is a perspective view of a roll of a carbon ribbon and a polyester film to be utilized in the embodiment of Figure 1. Referring to Figure 1, there is shown an embodiment of an apparatus for thermal printing according to the present invention. In this embodiment there is provided a ribbon winding reel 3, rotatable around an axis 5 which is connected to a motor (not shown), for winding a carbon ribbon 1, and a ribbon supplying reel 7, rotatable around an axis 9 which is connected to another motor (not shown), around which the carbon ribbon 1 is initially wound and from which the carbon ribbon 1 is taken out as it is wound around the ribbon winding reel 3. The carbon ribbon 1 is accompanied by a transparent polyester film 2, which are rolled together at the ribbon supply reel 7. The carbon ribbon 1 is suspended downwards from the ribbon winding reel 3 and the ribbon supplying reel 7 in a U-shape by means of a pair of guiding rollers 15 and 17 provided below the ribbon supplying reel 7 and the ribbon winding reel 3, respectively, so that starting from the ribbon supplying reel 7 the carbon ribbon 1 moves along its U-shaped track first along a first vertical track of a sufficient length in a vertical direction and then along a horizontal track of a sufficient length in a horizontal direction before wounded by the ribbon winding reel 3 along a second vertical track. The carbon ribbon 1 has a front surface covered by carbon black which is facing outwards from an outer circumference of the U-shaped track. At the middle of the first vertical track extending from the ribbon supplying reel 7, there is provided a printing head 19 for imprinting desired patterns on the carbon ribbon 1. This printing head 19 is pivotally supported such that it can be separated from the carbon ribbon 1, and is controlled by a printing controller unit 27 in which predetermined printing patterns are pre-programmed such that various desired printing patterns can be obtained from combinations of the pre-programmed printing patterns. On the opposite side of the printing head 19 with respect to the carbon ribbon 1, there is provided a platen roller 21 for maintaining an accuracy in printing by the printing head 19 on the carbon ribbon 1. Between this platen roller 21 and the carbon ribbon 1 the polyester film 2 is disposed on which extraneous negative (or positive) images are transferred by the heat from the printing head 19 so as to leave positive (or negative) images of the printing patterns on the carbon ribbon 1. The polyester film 2 is turned at the platen roller 21 and wound around film winding reel 4, rotatable around an axis 6 which is connected to a motor (not shown), provided behind the platen roller 21. This motor is controlled by a motor control unit 25 along with the ribbon winding reel 3 and the ribbon supplying reel 7. Underneath the horizontal track for the carbon ribbon 1 a belt conveyor 13 is provided on which a printing object 11 is carried along the horizontal direction with a printing surface facing the front surface of the carbon ribbon 1. On the opposite side of the belt conveyor 13 with respect to the carbon ribbon 1, between the pair of guiding rollers 15 and 17, a thermal transfer roller 23 is disposed which rotates at a circumferential speed which equals that of the carbon ribbon 1, and is vertically movable so that at its lower position the carbon ribbon 1 moving underneath the thermal transfer roller 23 is pressed down onto the printing surface of the printing object 11 moving below the carbon ribbon 1 on the conveyor belt 13. Thus, in this embodiment, the printing head 19 and the thermal transfer roller 23 are arranged to be spatially separated from each other substantially, as they are arranged along the vertical and horizontal directions, respectively. This feature allows this embodiment of an apparatus for thermal printing to print large printing patterns on a large printing surface, since the imprinting by the printing head 19 can be done for the carbon ribbon 1 over a length of the vertical track beyond the printing head 19, while the thermal transfer by the thermal transfer roller 23 takes place at the spatially separated horizontal track. According to the invention, the supply of the carbon ribbon 1 and the polyester film 2 is done at the same rate, so that they can be replaced by new ones at the same time, which in turn secures a continuous operation of the apparatus for the entire length of the carbon ribbon 1. The drives of the ribbon winding reel 3, the ribbon supply reel 7 and the film winding reel 4 are controlled by the motor control unit 25 so as to obtain a smooth and desirably controlled motion of the carbon ribbon 1 along its U-shaped track and of the polyester film 2. The operation of the thermal printing is performed by the apparatus as follows: First, by turning on a switch (not shown) of the apparatus, the carbon ribbon 1 and the polyester film 2 are set into an intermittent motion from the supplying reel 7 under the control by the motor control unit 25. Then, while the carbon ribbon 1 and the polyester film 2 are at rest at the first vertical track, the desired printing patterns are imprinted on the carbon ribbon 1 by the printing head 19 held in a position to make contact with the rear surface of the carbon ribbon 1, under the control of the printing controller unit 27. Here, the negative (or positive) images of the printing patterns are formed on the carbon ribbon 1 by means of the heat from the printing head 19 which transfers the extraneous carbon black from the carbon ribbon 1 onto the polyester film 2 such that desired positive (or negative) images of the printing patterns are left on the carbon ribbon 1 as it moves away from the printing head 19. As the carbon ribbon 1 moves on to the horizontal track, the carbon ribbon 1 carrying the imprinted positive (or negative) images of the printing patterns come into contact with the printing surface of the printing object 11 carried by the conveyer 13, and the carbon ribbon 1 and the printing object 11 move at the same speed along the horizontal track. Then, at an appropriate timing the thermal transfer roller 23 is lowered to its lowered position such that the carbon ribbon 1 is pressed onto the printing surface of the printing object 11, so as to have the desired printing patterns printed on the desired locations on the printing surface of the printing object 11. The printing object 11 is then carried away from the apparatus by the belt conveyer 13, while the carbon ribbon 1 is wound around the ribbon winding reel 3. Thus, according to this embodiment, it is possible to thermally print diverse patterns on large printing areas, because the imprinting of the printing patterns on the carbon ribbon 1 by the printing head 19 and the thermal transfer of the printing patterns from the carbon ribbon 1 to the printing object 11 by the thermal transfer roller 23 are performed at spatially separated positions, i.e., on the vertical track and the horizontal track, respectively. Moreover, the thermal transfer takes place on the printing surface lying on a flat surface of the belt conveyer 13, so that the sufficient stability for achieving a high accuracy required for printing bar codes or other printing patterns requiring a high accuracy. Furthermore, by adopting this embodiment into a handy type apparatus rather than a fixed type described above, the printing of a part of patterns at later time can easily be furnished. In addition, in this embodiment, the printing head 19 does not contact the printing surface of the printing object 11 directly, so that there is no need to make special protection for its logical circuits against any contact with the hard printing surface. It is to be noted that the printing head 19 and the printing controller unit 27 may be combined into a single controllable printing head. It is also to be noted that although the thermal printing roller 23 described above is of vertically movable type, this can be replaced by a horizontally movable one which moves along with the carbon ribbon 1 and the printing object 11 in the horizontal direction while pressing the carbon ribbon 1 onto the printing surface of the printing object 11.

Claims: An apparatus for thermally printing desired printing patterns on a printing object (11) by using a carbon ribbon (1) having thermally transferable carbon black on its front side, comprising: means (3, 7, 15, 17) for moving the carbon ribbon (1) along a first track and then along a second track which is spatially separated from the first track, conveyor means (13) for carrying a printing object (11) along the second track below the carbon ribbon (1); printing head means (19) placed on the first track for creating the desired printing patterns on the carbon ribbon (1) on the first track by imprinting the rear side of said ribbon (1); a platen roller (21) placed on an opposite side of the printing head means (19) with respect to the carbon ribbon (1); and thermal transfer roller means (23) placed on the second track for pressing the front side of the carbon ribbon (1) onto the printing object (11) on the conveyor means (13) so as to thermally transfer the desired printing patterns from the carbon ribbon (1) to the printing object (11); characterized by further comprising: transparent sheet means (2) for taking extraneous images in which the printing patterns are excluded, the sheet means (2) being a polyester film (2) rolled together with the carbon ribbon (1) and inserted between the platen roller (21) and the front side of the carbon ribbon (1) in the vicinity of the printing head means (19), and moved along with the carbon ribbon (1) until the carbon ribbon (1) has passed through the printing head means (19). The apparatus of Claim 1 wherein the first and second tracks are oriented along different directions. The apparatus of Claim 2, wherein the first and second tracks are oriented along mutually perpendicular directions. The apparatus of Claim 1 wherein the second track is oriented along a horizontal direction. The apparatus of any one of the preceding claims, wherein the extraneous images are negative extraneous images such that the printing patterns appear blank while an outline of the printing patterns appears inked on the printing object (11). A method of thermally printing desired printing patterns on a printing object by using a carbon ribbon having thermally transferable carbon black on its front side, comprising the steps of: moving the carbon ribbon along a first track and then along a second track which are spatially separated from the first track; carrying a printing object along the second track below the carbon ribbon; creating the desired printing patterns on the carbon ribbon on the first track by imprinting the rear side of said ribbon; pressing the front side of the carbon ribbon onto the printing object on the second track and concurrently applying heat to said pressed ribbon so as to thermally transfer the desired printing patterns on the carbon ribbon to the printing object; characterized by further comprising the step of: taking extraneous images in which the printing patterns are excluded, by a transparent polyester film rolled together with the carbon ribbon and moved along with the carbon ribbon until the carbon ribbon has passed through the printing head means. The method of Claim 6 wherein the first and second tracks are provided along different directions. The method of Claim 7, wherein the first and second tracks are provided along mutually perpendicular directions. The method of Claim 7, wherein the second track is provided along a horizontal direction. The method of Claim 7, wherein the extraneous images are negative extraneous images such that the printing patterns appear blank while an outline of the printing patterns appears inked on the printing object.

Inventors: TOHDO MICHIHARU, TOHDO, MICHIHARU
Applicants: TOHDO MICHIHARU, TOHDO, MICHIHARU
Application year: 1989
Main classification: B41J2
IPC codes: B41J2, B41M3, B41M5