THERMAL PRINTER

Abstract: A heat transfer means is used to maintain consistency of the printing performance in a thermal printer by enabling heat produced in the course of the printing process to be removed from the area where the actual printing takes place or from the entire printer, and also enables heating to be applied thereto when required.

Description: BACKGROUND OFTHE INVENTION Field of the Invention This invention relates to a thermal type printer, and particularly to a thermal type printer which enables the prevention of malprinting caused by overheating resulting from the printing or from the external temperature, or caused by overcooling. Description of the Prior Art In general thermal printers are of the type which use thermosensitive paper or of the thermal transfer type which use thermal transfer carbon ribbon. Figure 1 shows an example of a thermal transfer printer. Here, a roll of thermal transfer carbon ribbon 1 is mounted on a feed spindle 2. The thermal transfer carbon ribbon 1 is paid out therefrom and passes via guide roller 3, thermal print head 4, platen 5 and pinch rollers 6 to a take-up spindle 7. The thermal transfer carbon ribbon 1 together with a label strip 8 is held between the thermal print head 4 and the platen 5 where, in accordance with the specific printing signals, heating elements 10 of the thermal print head 4 heat up and cause carbon ink to be transferred from the ribbon onto the label strip 8. The label strip 8 is paid out from the feed spindle 11 and passes via the thermal print head 4, platen 5 and guide roller 12 to the take-up spindle 13. Both types of thermal printer require a heating section of some type, and are provided with a temperature control means or circuit (not shown) to control the heat in the printing zone 14. However, when the printer is used for extended periods of time or when the ambient temperature exceeds the functional limits of the temperature control means, malprinting occurs. For example, if the printer is located where the ambient temperature becomes abnormally high, the thermosensitive paper or the thermal transfer carbon ribbon becomes abnormally hot, smudging the print, and in extreme cases the entire surface of the printing paper may be blackened completely in the printing process. When the printer is located in abnormally cold locations, such as for example a cold storage warehouse or the like, it may be difficult to attain the requisite printing temperature, resulting in the print becoming blurred. These problems arise both with thermosensitive paper and with thermal transfer carbon ribbon types. SUMMARY OF THE INVENTION The object of the present invention is to provide a thermal printer which enables the requisite print quality to be obtained even when the printer is used continuously for long periods or when it is located in factories or cold storage facilities where the temperatures exceed the normal limits. To achieve this object the present invention comprises a thermal printer wherein the printing region or a printer housing is provided with a thermal transfer means comprising a heat pipe having a very high thermal transfer rate and a thermoelectric transducer which enable either heating or cooling to be carried out in accordance with the direction of flow of an electric current therein, thereby enabling temperature control to be exercised by absorbing heat from or supplying heat to the printing region or housing. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an abridged explanatory view of a thermal transfer printer in accordance with an application of the present invention; Figure 2 is an explanatory diagram showing the principal parts of a first embodiment of a first aspect of the present invention; Figure 3 is an explanatory diagram showing the principal parts of a second embodiment of a first aspect of the present invention; Figure 4 is an explanatory view of an example of a control circuit in accordance with the invention; Figure 5 is an explanatory view showing the principal parts of a third embodiment; Figure 6 is an explanatory view showing the principal parts of a fourth embodiment; Figure 7 is an explanatory view showing the principal parts of a fifth embodiment; Figure 8 is an explanatory view showing the principal parts of an example of a different heat pipe arrangement; Figure 9 is an explanatory view showing the principal parts of another example of a heat pipe configuration; Figures 10 to 13 are views showing respectively the first to fourth embodiments of a second aspect of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described with reference to Figure 2 onward. Like parts are denoted with the same numerals used in Figure 1, and only the principal portions are described. The explanation is given with reference to a thermal transfer type printer but it can also apply to a thermal type printer which uses thermosensitive paper. In the first embodiment illustrated in figure 2 a heat pipe 20 is used as the heat transfer means. This embodiment shows an example of when the area of the thermal print head 4 is to be cooled. The heat absorbing portion 20a of the heat pipe 20 is attached to the upper portion of the thermal print head 4 by means of an adhesive 21 that has good thermal conductivity, and the heat discharge portion 20b thereof is located at a position above the heat absorbing portion 20a which is away from the area of the thermal print head 4. After air is removed from the cylindrical member 20c the heat pipe 20 is charged with a specific amount of operating fluid 22 and is then sealed shut. The operating fluid 22, which may be freon, water or the like, absorbs heat at the heat absorbing portion 20a, turns to steam 22a and is moved to the heat discharge portion 20b. This movement is carried out at a very high speed which approaches or exceeds that of sound. Upon reaching the heat discharge portion 20b the steam 22a is turned to liquid 22b, discharging heat, and returns back to the heat absorbing portion 20a in the heat pipe 20. The interior of the heat pipe 20 is provided with grooving or a wick (not shown) or the like to provide a capillary action which facilitates the return of the liquid 22b. The heat discharge portion 20b is provided with a large number of fins 23, increasing the heat discharge area. A fan 24 is also provided to enhance the heat discharge effect. By the above construction the heat generated at the thermal print head 4 portion which constitutes the printing zone 14 is transferred at a very high speed to a position remote therefrom, so that the heat produced at the thermal print head 4 and platen 5 portion is absorbed to provide a cooling of the said portion to the required temperature. If the vertical orientation of the heat pipe 20 is reversed, producing the arrangement indicated in Figure 2 by a phantom line, thermal print head 4 can be heated by heat from elsewhere. Figure 3 illustrates another embodiment wherein a thermoelectric transducer such as for example a thermo-­ module 30 is used as the heat transfer means. This thermo-module 30 comprises n-type semiconductors 31 and p-type semiconductors 32 connected in series by electrical conductors 33 and in series with a power supply 34 and switch 35. The outer surfaces of each of the electrical conductors 33 are provided with electrical insulators 36 and 37. The thermo-module 30 is bonded via the surface of the electrical insulators 37 to the thermal print head 4 by means of an adhesive 21 which has good conductivity, similarly to the case of the first embodiment. The surface of the electrical insulators 36 is provided with fins 23. The thermo-module 30 applies the heating/cooling produced by the Peltier effect between the n-type semiconductors 31 and p-type semiconductors 32; with the direction of current flow illustrated in Figure 3 the side with the insulators 37 is cooled and the insulators 36 on the other side give off heat, which is to say the arrangement provides heating. Therefore, heat produced at the thermal print head 4 is cooled by the cooling provided by the insulators 37 of the thermo-module 30 and the heat of the heat portion is discharged by the fan 24, cooling the thermal print head 4. Changing the direction of the current flow in the thermo-module 30 will cause heat to be produced at the insulators 37 and the insulators 36 to have a cooling effect. Thus, when the printer is being used in a cold storage warehouse or the like all that is required to be done is to reverse the direction of the current flow illustrated in Figure 3 so that the region around the print head 4 is heated. The degree of the heating and cooling can be controlled by the strength of the current used. Use of the type of circuit shown in simplified form in Figure 4 will enable the printer to start up smoothly. Specifically, a sensor S is embedded in the thermal print head 4 (Figure 3) and connected via a bus B with a CPU. Also connected to the CPU via the bus B are a RAM M, in which are stored the optimum printing temperature conditions for the thermal print head 4, and a driver circuit D for the thermo-module 30. Because when the printer starts printing the thermal print head 4 is not yet in its optimum temperature zone, the direction of the driver circuit D current flow is set so that at the start of the printing the thermal print head 4 is heated. When following the start of the printing the sensor S detects that the temperature has reached the required level the direction of the current flow in the driver circuit D is controlled so as to cool the thermal print head 4. By subsequently controlling the direction of current flow in the thermo-module 30 by reference to the optimum temperature setting, printing can be caried out with the thermal print head 4 at the said optimum temperature condition. The thermo-module 30 can be controlled by software or by a hard-wired logic circuit which employs an operational amplifier and other such devices. The effect aimed at by the present invention is attained by providing the heat pipe 20 and thermo-module 30 shown in Figures 2 and 3 in the printing zone 14 which includes the thermal print head 4 and platen 5, and it is also possible to use the two in combination as is shown in Figures 5 and 6. Figure 5 shows a third embodiment wherein the [heat absorbing portion 20a of the] heat pipe 20 is located on the thermal print head 4 and the thermo-module 30 is arranged at the heat discharge portion 20b located away from the thermal print head 4. This arrangement differs from the first embodiment in that the heat discharge portion 20b of the heat pipe 20 can be used to cool the thermo-module 30 more actively, and therefore the thermal print head 4 can be cooled more actively. In addition, as the heat pipe 20 can be formed in any desired length or shape, the thermo-module 30 can be suitably located for the transferring of heat even with printers which are laid out in such a way that the thermo-­ module 30 cannot be located at the printing zone 14. If as indicated by the phantom line in Figure 5 the vertical arrangement of the heat pipe 20 is reversed, and the direction of current flow is reversed, the thermal print head 4 can be heated by heat from the thermo-module 30. In a fourth embodiment illustrated in Figure 6 the thermo-module 30 is affixed to the thermal print head 4 portion and the heat pipe 20 is affixed to the thermo-module 30. With such an arrangement the thermal print head 4 can be cooled directly by the thermo-module 30, providing even more effective cooling than is provided by the third embodiment. Figure 7 shows a fifth embodiment wherein the heat pipe 20 and the thermo-module 30 are used together and in addition it is possible to switch between heating and cooling as desired. In this embodiment, removable retainers 38 are used to fasten the heat discharge portion 20b of the heat pipe 20 so the vertical orientation relative to the thermal print head 4 can be changed. In the arrangement shown by the solid lines in Figure 7 the thermal print head 4 can be cooled, while in the arrangement indicated by the phantom lines the thermal print head 4 can be heated. The heat pipe 20 shown in Figures 2, 5, 6 and 7 may be of various shapes. In accordance with the requirements of the fixing position or the mode of use it may for example be flat, or long and thin, or curved, and may be of any desired size or length. The positioning of the heat pipe 20 is likewise not restricted to the upper part of the thermal print head 4; it may be provided anywhere that is effective in the vicinity of the thermal print head 4 and platen 5 which constitute the printing zone 14. The arrangement may for example be as shown in Figure 8 in which a bearing 40 is provided inside the platen 5 so the heat pipe 20 is supported rotatably relative to the platen 5, so that even when the platen 5 is rotated by a timing belt 41 the heat pipe 20 is maintained in the same position so as to be able to transfer heat from heat absorbing portion 20a to heat the discharge portion 20b. In Figure 9 the heat absorbing portion 20a of the heat pipe 20 is shown incorporated integrally into the thermal print head 4 with the heat discharge portion 20b located away from the thermal print head 4. In Figure 9 the numeral 50 denotes a support bracket for the heat pipe 20. It may moreover be used as desired in the vicinity of a printing zone 14 that is other than at the thermal print head 4 and platen 5. Figures 10 to 13 show embodiments of a second aspect of the invention which enables the overall temperature of the printer to be controlled. Figure 10 shows the first embodiment thereof wherein an entire printer 60 is shut away from contact with the outside atmosphere in an openable housing 70, the heat absorbing portion 20a of the heat pipe 20 being provided inside the housing 70 and the heat discharge portion 20b outside. The heat generated by the printer 60 is discharged by being conducted at high speed from heat absorbing portion 20a of the heat pipe 20 to the heat discharge portion 20b. This allows the inside of the housing 70 to be maintained at a constant temperature. In a second embodiment shown in Figure 11 the thermo-module 30 is provided on the end of the heat pipe 20, thereby providing the same type of active cooling as the arrangement shown in Figure 5. Figure 12 illustrates a third embodiment wherein the interior of the housing 70 is actively cooled by locating the cooling side of the thermo-module 30 inside the housing 70 and the heat discharge side outside. In Figure 13, the heat absorbing portion 20a of the heat pipe 20 is provided on the heat discharge side of the thermo-module 30, thereby providing, similarly to the embodiment shown in Figure 6, a transfer of heat to the heat discharge portion 20b which is at high speed as well as active. With regard to the third and fourth embodiments shown in Figures 12 and 13, the printer 60 may also be heated by changing the direction of the current flow in the thermo-module 30. With regard also to the case of the embodiments shown in Figures 10 to 13, as the temperature control can be carried out with the entire printer 60 sealed off, outside dust and dirt can also be prevented from getting inside. Furthermore, a housing provide with heat transfer means such as heat pipe, thermo-module and the like is not limited to printers but may be used to house any desired device for temperature control.

Claims: 1. A thermal printer provided with a thermal printing zone which includes a platen and a thermal print head for the printing of the required patterns of print on a print medium, and a heat transfer means provided in the vicinity of the said printing zone for the purpose of controlling the temperature in at least the said printing zone. 2. A thermal printer as defined in Claim 1 wherein a heat pipe is employed as the heat transfer means. 3. A thermal printer as defined in Claim 2 wherein the heat absorbing portion of the heat pipe is arranged in the vicinity of the printing zone and the heat discharge portion of the heat pipe is arranged in a position away from the printing zone so that heat generated in the printing zone is discharged away to the said position. 4. A thermal printer as defined in Claim 3 wherein the heat pipe is provided in the vicinity of the thermal print head. 5. A thermal printer as defined in Claim 3 wherein the heat pipe is provided in the vicinity of the platen. 6. A thermal printer as defined in Claims 4 or 5 wherein the heat discharge portion of the heat pipe is provided with fins. 7. A thermal printer as defined in Claim 2 wherein the heat pipe is integrally incorporated into the thermal print head. 8. A thermal printer as defined in Claim 1 wherein a thermoelectric transducer is employed as the heat transfer means. 9. A thermal printer as defined in Claim 8 wherein one surface of the thermoelectric transducer is contacted with the thermal print head and the electric current is controlled so that the said surface is cooled. 10. A thermal printer as defined in Claim 8 wherein one surface of the thermoelectric transducer is contacted with the thermal print head and the electric current is controlled so that the said surface is heated. 11. A thermal printer as defined in Claim 9 wherein the other surface of the thermoelectric transducer is provided with fins. 12. A thermal printer as defined in Claim 1 wherein a heat pipe and a thermoelectric transducer are used in combination as the heat transfer means. 13. A thermal printer as defined in Claim 12 wherein a heat pipe is affixed to the thermal print head and the thermoelectric transducer is affixed to the heat pipe. 14. A thermal printer as defined in Claim 13 wherein the thermoelectric transducer is provided with fins. 15. A thermal printer as defined in Claim 12 wherein the thermoelectric transducer is affixed to the thermal print head and the heat pipe is affixed to the thermoelectric transducer. 16. A thermal printer as defined in Claim 15 wherein the heat pipe is provided with fins. 17. A thermal printer as defined in any of Claims 12 to 16 wherein the direction of current flow in the thermoelectric transducer can be changed and the thermoelectric transducer is used for cooling purposes. 18. A thermal printer as defined in any of Claims 12 to 16 wherein the direction of current flow in the thermoelectric transducer can be changed and the thermoelectric transducer is used for heating purposes. 19. A thermal printer as defined in Claim 12 wherein the heat pipe is provided on the platen and the thermoelectric transducer is affixed to the heat pipe. 20. A thermal printer as defined in Claim 19 wherein the thermoelectric transducer is provided with fins. 21. A thermal printer as defined in Claim 8 or Claim 12 wherein at the start of printing heat is applied to the printing zone by means of the thermoelectric transducer and when the temperature of the printing zone has risen to the required level the thermoelectric transducer is controlled to provide cooling so as to control the temperature of the printing zone to the required level. 22. A thermal printer provided with a thermal printing zone which includes a platen and a thermal print head for the printing of the required patterns of print on a print medium, a housing which encloses the printer unit with the printing zone, and a heat transfer means provided which straddles the interior and exterior of the housing to control the temperature within the said housing. 23. A thermal printer as defined in Claim 22 wherein a heat pipe is used as the heat transfer means. 24. A thermal printer as defined in Claim 23 wherein one end of the heat pipe is provided inside the housing and the other end outside the housing to control the temperature inside the housing. 25. A thermal printer as defined in Claim 24 wherein the heat pipe is provided with fins. 26. A thermal printer as defined in Claim 22 wherein a thermoelectric transducer is employed as the heat transfer means. 27. A thermal printer as defined in Claim 26 wherein one surface of the thermoelectric transducer is provided inside the housing and the other surface is provided outside the housing to control the temperature in the housing. 28. A thermal printer as defined in Claim 27 wherein the thermoelectric transducer is provided with fins. 29. A thermal printer as defined in Claim 22 wherein a heat pipe and a thermoelectric transducer are used in combination as the heat transfer means. 30. A thermal printer as defined in Claim 29 wherein one end of the heat pipe is provided inside the housing and the other end is provided outside the housing and the thermoelectric transducer is provided on the said other end portion. 31. A thermal printer as defined in Claim 30 wherein the thermoelectric transducer is provided with fins. 32. A thermal printer as defined in Claim 29 wherein one surface of the thermoelectric transducer is provided inside the housing and the other surface is provided outside the housing and the heat pipe is provided on the said other surface portion. 33. A thermal printer as defined in Claim 32 wherein the heat pipe is provided with fins.

Inventors: YOKOTA, YUJI
Applicants: KABUSHIKI KAISHA SATO
Application year: 1986
Main classification: B41J2
IPC codes: B41J2, B41J29