Image forming apparatus

Abstract: An image forming apparatus having a main body (1) includes an opening portion (20) provided in the side face (1a) of the main body (1), and a thermal transfer printer (2). The thermal transfer printer (2) records desired information additively on a paper whereon a fixing means (17) has fixed a toner image, by using a thermal head (5) to pressure an ink-ribbon (41) on said paper. The thermal transfer printer (2) includes a casing (3) wherein a cassette (4) for housing the ink-ribbon (41) is detachably mounted, a thermal head supporting means (60) for supporting the thermal head (5) and an interlocking mechanism (8). The interlocking mechanism (8) retreats the thermal head (5) by the thermal head supporting means (60) in response to retreat of said casing (3). Thus it is allowed to detach the cassette (4) from the main body (1) through the opening portion (20). It facilitates replacement of cassettes (4) and jam recovery.

Description: The present invention relates to an image forming apparatus including a thermal transfer printer for additively entering specific information like characters that an original image does not include, on paper whereon an image corresponding to an original image has been tranferred and formed. In some cases, it is necessary to make notes of such items as copy date, copier's name, and so forth on paper whereon an image forming apparatus such as an electrostatic copying machine has formed an image. In such cases, it is troublesome to enter said notes by handwriting or stamping. There is known an image forming apparatus wherein for eliminating such troubles, said operation is automatically perfomed inside of the body of the apparatus. Said image forming apparatus is provided with a thermal transfer printer therein. In the thermal transfer printer, a casing wherein a cassette for housing an ink-ribbon and a thermal head are attached is supported by a pair of frame side plates, and a thermal head is pressured through the ink-ribbon to paper passing a platen roller, thereby to heat and transfer characters and such on the paper. There is applied heat meltable ink on said ink-ribbon and said ink is transferred to the paper with heat generated in the thermal head. In said image forming apparatus, however, the cassette whose ink-ribbon is used up is taken out for replacement from a hole provided at the center of either of the frame side plates with a hand inserted through the hole after sliding the cassette in the axial direcdion of the platen roller. Said image forming apparatus suffered difficulty in replacing a used ink-ribbon, because the used ink-ribbon is replaced with a new one with a hand inserted through a narrow through hole. Furthermore, that the cassette is mounted in the vicinity of the thermal head in the casing makes the replacement of the cassette even more difficult. At the same time, there is a problem that jam occurred near the thermal transfer printer is difficult to deal with. Because the ink-ribbon is always placed near a passage for hot paper to pass, the ink-ribbon in said thermal transfer printer is rapidly deteriorated due to the influence of heat and the like, although thermal transferring is performed only when it is necessary. In this connection, there is known a thermal transfer printer, wherein said thermal transferring is performed while the thermal head is protruding the ink-ribbon between a feed reel and a winding reel from the cassette, and after completion of the thermal transferring, slack of the ink-ribbon stemming from the retreat of the thermal head is eliminated, thus keeping the ink-ribbon away from the hot paper passage for the purpose of preventing such deterioration of the ribbon(see, for example, Japanese Laid-open Patent Application No.297085/1988). Meanwhile in thermal transferring, frictional force between the paper and the ink-ribbon is sufficiently greater than frictional force between the ink-ribbon and the thermal head (see, for example, Japanese Laid-open Patent Application No.212977/1983). Therefore there is not a relative shift of the paper from the ink-ribbon. Accordingly, the ink-ribbon is wound out from the feed reel by the length the thermal head travels. There has not been proposed so far any invention or device wherein the length of the ink-ribbon to be wound is precicely regulated when winding the ink-ribbon in thermal transfer operations or when winding the slackened ink-ribbon after completion of thermal transferring. In case a relatively new ink-ribbon is drawn out from a feed reel to be wound on a winding reel, the winding reel with the ribbon wound thereon has a shorter diameter than the feed reel with the ribbon wound thereon. On the contrary, when the ink-ribbon comes near to the end of its use, the winding reel with the ribbon wound thereon has a longer diameter than the feed reel with the ribbon wound thereon. Accordingly, if the winding reel rotates for a given period of time by a predetermined turning angle, the amount of the ribbon wound on the winding reel in the beginning differs considerably from the amount of the ribbon wound on the reel toward the end of its use. In other words, when the ink-ribbon is relatively new, the feed reel with the ribbon wound thereon has a longer diameter, and as the ink-ribbon is used, the diameter of the feed reel with the ribbon wound thereon becomes shorter. The ink-ribbon is wound on the winding reel in thermal transferring or the slackened ink-ribbon after thermal transferring is wound on the winding reel or the feed reel. In such cases, the amount of the ribbon to be wound on the reel differs depending on whether the ink-ribbon is new or has come near to the end of its use. If the operation time of winding the ribbon on the reel is adjusted for the case of a new ink-ribbon, there occurs a problem that as the ribbon draws near to the end of its use, the winding amount increases so that the ribbon is excessively wound on the winding reel. Also in case the slackened ribbon is wound on the winding reel or the feed reel, the ribbon is excessively wound on the reel or the winding amount is not sufficient to eliminate the ribbon slack. In a thermal transfer printer disclosed in said Japanese Laid-open Patent Application No. 297085/1988, when the winding reel stops winding the ribbon thereon, a tension spring urges the feed reel to turn by a predetermined angle in the opposite direction to the winding direction, thereby to eliminate the ribbon-slack by winding the ribbon on the feed reel. Said thermal transfer printer, however, still suffers the same problem with the above that the ribbon slack cannot be eliminated, even though the feed reel is turned by a predetermined angle in the opposite direction; if the amount of the ribbon wound on the feed reel is small, the feed reel does not have a diameter long enough to wind the ribbon by a sufficient length to eliminate the slack. In order to ensure the elimination of the ribbon slack even when the feed reel has a small amount of the ribbon wound thereon as mentioned above, the tension spring is adapted to urge the feed reel to turn by a larger angle. In this structure, however, if the feed reel has a large amount of the ribbon wound thereon, the ink-ribbon is always subject to tension after the slack is eliminated. The tension causes deterioration of the durability of the ink-ribbon. In addition, because thermal transferring is performed by pressuring the ink-ribbon to the paper which is still very hot immediately after a fixing device has heated and fixed an image thereon, and because the ambient temperatures around a thermal transferring device is still very high, said image forming appratus suffers a problem that preferable thermal transferring cannot be achieved because of the ink-ribbon melting in other portion than a pattern to be heated and transferred. To cope with the above problem, it may be suggested that the paper discharged from the fixing device be exposed to wind from a fan thereby to cool the paper. However, if the fan disposed in such a vicinity with the fixing device is operated, the fan circulates the wind, which has become hot due to the heat of the fixing device, within the space between a pair of said frame side plates, deteriorating the efficiency of cooling down the paper. At the same time, the fixing device is deprived of its heat for fixing, resulting in poor effect of heating and fixing an image. It is the object of the present invention to provide an image forming apparatus which ensures to eliminate the slackened ink-ribbon of a thermal transfer printer without deteriorating the durability of the ink-ribbon. Said object is accomplished by the following image forming apparatus: The image forming apparatus is provided with a thermal transfer printer for recording desired information additively on a paper whereon a fixing means has fixed a toner image by pressuring an ink-ribbon to said paper. This thermal transfer printer comprises a cassette for housing the ink-ribbon, a thermal head, a slack eliminating means, a torque limiter, and a resistance loading means. Said cassette has a feed reel for feeding out said ink-ribbon and a winding reel for winding thereon the ink-ribbon fed thereto. Said thermal head moves for thermal transferring to a pressuring position to pressure the ink-ribbon running between said feed reel and said winding reel onto said paper on a platen roller while protruding said ink-ribbon from the cassette, and then after thermal transferring moves to a pressering release position to release pressuring said ink-ribbon. Said slack eliminating means actuates said winding reel to wind said ink-ribbon on said winding reel after completion of thermal transferring, thus eliminating the slack brought about by the thermal head moving to the pressuring release position. Said torque limiter intervenes between said winding reel and said slack eliminating means and restrains slack eliminating meansfrom transmitting a predetermined value or more of drive torque to said winding reel. Said resistance loading means loads on said feed reel braking torque greater than said predetermined torque of said torque limiter. In the above-mentioned structure, the slack eliminating means eliminates the slack of the ink-ribbon by having the winding reel wind the ink-ribbon thereon after completion of thermal transferring, and tensions the ink-ribbon between the winding reel and the feed reel. At this time, the braking torque by the resistance loading means is loaded on the winding reel via the feed reel and the ink-ribbon on tension. However, the winding reel is controled not to accept torque greater than a predetermined torque and because the braking torque is greater than the predetermined torque, unused ink-ribbon from being is not drawn out from the feed reel to be fed to the winding reel. Meanwhile, when the ink-ribbon running between the feed reel and the winding reel is protruded from the cassette by the thermal head for thermal transferring, the ink-ribbon wound on the winding reel on eliminating said ribbon slack is wound out from the winding reel, because like the case of eliminating the ribbon slack, frictional braking torque loaded on the feed reel is greater than the predetermined torque of the torque limiter. Said object is accomplished by the following image forming apparatus as well: The image forming apparatus is provided with a thermal transfer printer for recording desired information additively on a paper whereon a fixing means has fixed a toner image by pressuring an ink-ribbon to said paper. This thermal transfer printer comprises a cassette for housing the ink-ribbon, a thermal head, a slack eliminating means, a torque limiter, and a resistance loading means. Said cassette has a feed reel for feeding out said ink-ribbon and a winding reel for winding the fed ink-ribbon thereon. Said thermal head moves to a pressuring position for thermal transferring to press the ink-ribbon running between said feed reel and said winding reel onto said paper on a platen roller while protruding said ink-ribbon from the cassette, and then after thermal transferring moves to a pressuring release position to release pressuring said ink-ribbon. Said slack eliminating means drives said feed reel to wind said ink-ribbon on said feed reel after thermal transferring, thus eliminating the slack made by the thermal head moving to the pressuring release position. Said torque limiter intervenes between said feed reel and said slack eliminating means and restrains the slack eliminating means from trnsmitting a predetermined torque or more of drive torque to said feed reel. Said resistance loading means loads braking torque greater than said predetermined torque of said torque limiter on said feed reel. In the above-mentioned structure, the slack eliminating means rotates the feed reel for eliminating the ribbon slack brought about by the thermal head moving to the pressuring release position after completion of thermal transferring. At this time, the torque limiter regulates so that a predetermined value or more of drive torque is not transmitted from the slack eliminating means to the feed reel and the resistance loading means loads braking torque greater than said predetermined torque on the winding reel, and therefore the ribbon slack is sure to be eliminated. Furthermore, there never occurs such an error as to wind out the unnecessary ink-ribbon from the winding reel. Thus the slackened portion of the ink-ribbon is wound on the feed reel and in the next thermal transferring, the portion wound on the feed reel is wound out again by the thermal head moving to the pressuring position. Accordingly, it never occurs that the used ink-ribbon is repeatedly used. Fig. 1 is a schematic view illustrating the whole body of a copying machine. Fig. 2 is a side view illustrating the main portion of a copying machine in a state where the casing of a thermal transfer printer is in a retreat position. Fig. 3 is a perspective view showing a state where the side face of the main body of a copying machine is opened by means of a punching unit. Fig. 4 is a perspective view showing the main portion of a thermal transfer printer including an interlocking mechanism. Fig. 5 is a schematic plan view illustrating an operations of replacing cassettes. Fig. 6 is a plan view with portions broken away to reveal the drive means of an ink-ribbon. Fig. 7 is a schematic perspective view of the drive mechanism of an ink-ribbon. Fig. 8 is schematic side view showing a thermal transfer printer in thermal transferring. Fig. 9 is a schematic side view showing a thermal transfer printer directly after completion of thermal transferring. Fig. 10 is a schematic side view showing a thermal transfer printer wherein a slackened ink-ribbon is wound up after completion of thermal transferring. Fig. 11 is a schematic side view showing a thermal transfer printer ready to perform thermal transferring. Fig. 12 is a schematic perspective view showing another example of the drive mechanism of an ink-ribbon. Fig. 13 is a flow chart showing the operations of the drive mechanism of an ink-ribbon. Fig. 14 is a schematic plan view showing the main portion of a winding control means. Fig. 15 is a schematic side view showing the main portion of a winding control means. Fig. 16 is a schematic side view showing the main portion of another example of a ribbon amount detection means. Fig. 17 is a timing chart showing the operations of a thermal transfer printer. Fig. 18 is a schematic side view of a copying machine in a state where the thermal head of a thermal transfer printer is on a pressuring position. Fig. 19 is a schematic side view of a copying machine wherein a thermal head is on a pressuring release position. Fig. 20 is a schematic perspective view showing the periphery of a fixing device in a copying machine. Fig. 21 is a sectional view of a pressuring roller and a pipe. Fig. 22 is a schematic view showing a paper delivery portion. Fig. 23 is a schematic view showing another example of a paper delivery portion. Fig. 24 is a perspective view showing another interlocking mechanism. Detailed description will be given with reference to the accompanying drawings showing preferred embodiments. Referring to Fig. 1, the copying machine of this embodiment includes an optical system 11, a copy processing portion 12 and a paper delivery portion 13 inside of the main body 1 of the copying machine. The optical system forms an electrostatic latent image on a photosensitive material 12a corresponding to an original image. The copy processing portion 12 develops said electrostatic latent image into a toner image and transfers it on paper to form a copy image thereon. The paper delivery portion 13 discharges paper fed from a manual paper feeding portion 10, a paper feeding cassette 15a, or 15b on a discharge tray 19 as a paper discharge portion after successively conveying said paper by way of a copy processing portion 12, a fixing device 17 for heating and fusing an image on the paper, thermal transfer printer 2 and punching unit 18. Between the fixing device 17 and the thermal transfer printer 2, there is provided a paper cooling mechanism 10 for cooling the paper discharged from tha fixing device 17 and for deliverying the paper to the thermal transfer printer 2. The punching unit 18 is disposed between the thermal transfer printer 2 and the side face 1a of the main body 1 of the copying machine. The punching unit 18 is mounted on a cover 1i covering an opening portion 20 of the side face 1a. The punching unit 18 presses punching cutters 18a into the trailing edge of the paper which has passed through the thermal transfer printer 2, thus punching a plurality of holes for filing in the paper. As shown in Figs. 2 and 3, the punching unit 18 is turned on a shaft 18b in the lower end thereof outward from the maind body 1 of the copying machine (counter-clockwise in Fig. 2), thereby to have the opening portion 20 in the side face 1a of the main body 1 of the copying machine. Through this opening portion 20, the maintenance of the thermal transfer printer 2 can be performed. As shown in Fig. 18, the punching unit 18 and the cover 1i normally closes the opening portion 20 on said side face 1a. Referring to Fig. 2 and Fig. 4, the thermal transfer printer 2 includes a casing 3, a cassette 4, a thermal head 5,a thermal head supporting means 60, a thermal head moving means 6, an ink-ribbon drive mechanism 7, an interlocking mechanism 8 and a lock means 9. The casing 3 is turnably supported by a pair of frame side plates 1b, 1d (of which only 1b is shown) of the main body 1 of the copying machine by means of a pair of casing supporting shafts 34 (only one of which is shown). The casing 3 comprises a box 31 with its upper side left open and a pair of near triangle side plates 32a, 32b respectively fastened to both end sides of the box 31. The casing supporting shafts 34 are respectively fixed to the lower end portions of the side plates 32a, 32b, and are turnably attached to said frame side plates 1b ,1d. The casing supporting shafts 34 may be attached directly to said frame side plates 1b, 1d, or may by attached indirectly by means of stays and the like. The casing 3 is turnable on the casing supporting shaft 34 moving between a set position (refer to Fig. 18) and a retreat position (refer to Fig. 2) to allow the cassette 4 to be taken out from the opening portion 20. The cassette 4 is detachably mounted in the casing 3, housing an ink-ribbon 41 in belt. The cassette 4 comprises the ink-ribbon 41 , a body 42, a feed reel 43 and a winding reel 44. The feed reel in3 and the winding reel 44 are attached in parallel in the body 42. In the cassette 4, the ink-ribbon 41 fed from the feed reel 43 is wound on the winding reel 44. The portion of the ink-ribbon 41 which runs between the feed reel in3 and the winding reel 44 accounts for a thermal transfer portion 41a to be used for thermal transferring. The body 42 of the cassette 4 has an opening portion 42b under the thermal transfer portion 41a of the ink-ribbon 41. In the bottom 31a of the box 31 of the casing 3, there is formed an opening portion 33 communicated with said opening portion 42b. The thermal head 5 advances to protrude the thermal transfer portion 41a of the ink-ribbon 41 downward from the cassette 4 and the casing 3 through the opening portion 42b (see Fig. 8 and Fig. 19). The thermal head advancing downward enables the thermal transfer portion 41a of the ribbon to touch a paper on a platen roller 26. The ink-ribbon 41 is a ribbon for thermal transferring whereon heat meltable ink is applied. The ink-ribbon 41 is provided with a silver evaporation portion for light reflection as will be described later. The ink-ribbon 41 before use is wound on the feed reel 43 with its leading edge connected to the core (not shown) of the winding reel 44. As the ink-ribbon 41 is used, the winding reel 44 turns to gradually wind up the ribbon 41 fed from the feed reel 43 on the winding reel 44. By using a mounting member 62, the thermal head 5 is supported on a thermal head supporting shaft 61 turnably mounted in the casing 3. The thermal head supporting means comprises the thermal head supporting shaft 61 and the mounting member 62. The thermal head 5 selectively flows electricity in a plurality of minuscule resistors so as to cause them to generate heat, thereby to form a thermal transfer pattern on the paper. Both ends 61a, 61b of the thermal head supporting shaft 61 are respectively fixed to side plates 32a, 32b. The mounting member 62 is composed of plate and has the thermal head 5 fixed on the upper portion 62a thereof. The lower portion 62b of the mounting member 62 is secured to the center portion 61c of the thermal head supporting shaft 61. The thermal head 5 is turnable on the thermal head supporting shaft 61 moving between a pressuring position (see Fig. 19) to pressure the ink-ribbon 41 to the paper and a retreat position (see Fig. 2) to allow the cassette 4 to be removed from the casing 3. The lock means 9 is disposed inside of the box 31 of the casing 3 and retains the cassette 4 mounted in the casing 3. As shown in Fig. 4 and Fig. 5, the lock means 9 has a stopper 92 shaped like a reveresed letter 'L' which is turnable on a shaft 91 fixed to the bottom 31a of the box 31 of the casing 3. By bringing the end portion 92a of the stopper 92 into contact with the end portion 42a of the body 42 of the cassette 4, the lock means 9 retains the cassette 4 on a predetermined position in the casing 3, thus preventing the cassette 4 from falling off from the casing 3. The removal of the cassette 4 from the casing 3 is performed as follows with reference to Fig. 5. The stopper 92 is turned counterclockwise to a place shown with a two-dots-and-dash line in Fig. 5, to make a space on the right of the cassette 4. Then the cassette 4 is slid rightward from a place shown with a dot-and-dash line to a place shown with a two-dots-and-dash line in Fig. 5. A connecting shaft 76 and the winding reel 44 are disengaged so that the cassette 4 may be taken up out of the casing 3. The cassette 4 may be mounted in the casing 3 in the order reverse to the steps of the above removal operations. INTERLOCKING MECHANISM The interlocking mechanism 8 moves a thermal head 5 to its retreat position when a casing 3 moves to its retreat position. Referring to Fig. 4, the interlocking mechanism 8 comprises a stay 86, a mounting shaft 87, a guided roller 87b, a guiding member 1c and a tension spring 88. The stay 86 comprises a plate spring attached an end portion 61b of a thermal head supporting shaft 61 being integrally turnable with the shaft 61 and extends in the diametral direction of the thermal head supporting shaft 61. The mounting shaft 87 is fastened to an end 86a of the stay 86, extending in parallel to the thermal head supporting shaft 61. The guided roller 87b comprises a roller turnably attached to an end 87a of the mounting shaft 87. The guiding member 1c is a concave plate fastened to a frame side plate 1b of the main body 1 of a copying machine. The tension spring 88 is disposed between a mounting member 62 and a casing 17a of a fixing device 17, tensioning the mounting member 62 toward the casing 17a. A description will be given as to the operations of the interlocking mechanism 8. The punching unit 18 and the cover 1i in a position shown in Fig. 18 is turned on a shaft 18b counterclockwise to the main body 1 of the copying machine and thus an opening portion 20 appears in the side 1a of the main body 1 of the copying machine (see Fig. 2 and Fig. 3). Then the casing 3 of the thermal transfer printer 2 set in a set position (see Fig. 18) is turned counterclockwise on a casing supporting shaft 34 in Fig. 18, thereby to move the casing 3 to its retreat position (see Fig. 2). When the casing 3 turns to its retreat position, referring to Fig. 2 and Fig. 4 the thermal head supporting shaft 61 attached to the casing 3 turns counterclockwise on the casing supporting shaft 34 in Fig. 2. At this moment, the guided roller 87b is engaged with the guiding member 1c to move upward along the guiding member 1c. The thermal head supporting shaft 61 turns clockwise in Fig. 2. Thus, the thermal head 5 supported by the thermal head supporting shaft 61 turns clockwise in Fig. 2, thereby to move to the retreat position shown in Fig. 2. The tensile force of the tension spring 88 engaged with the mounting member 62 facilitates movement of the thermal head 5 to its retreat position and ensures the thermal head 5 to stay at its retreat position. Accordingly, a used cassette 4 can be easily replaced with a new one through the opening portion 20 formed in the side 1a of the main body 1 of the copying machine, and in addition, jam occurred in the periphery of the thermal transfer printer 2 can be easily recovered. Unlike a conventional copying machine wherein the casing 3 is moved in the axial direction of the platen roller 26 by a hand inserted through a narrow through hole in the frame side plate 1b or 1d, the cassette 4 is taken out through a large opening portion 20 in the side face 1a of the main body 1 of the copying machine. Accordingly the cassette 4 can be replaced even more easily. Furthermore a new cassette 4 can be mounted without inflicting any damage on the ink-ribbon of the new cassette 4. The interlocking mechanism 8 retreats the thermal head making effective use of a space above the thermal transfer printer 2. Hence, the main body 1 of the copying machine need not to be made large and can achieve facilitation of the replacement of said cassette 4 or jam recovery. The interlocking mechanism 8 may comprise a stay 86, a mounting shaft 87, a guided roller 87b and a guiding member 1c. The interlocking mechanism 8 may also consist of a tension spring 88 as showing Fig. 24. The interlocking mechanism 8 may comprise a turning transmission mechanism such as a gear setup. The interlocking mechanism 8 may further comprise a step motor for driving a thermal head supporting shaft 61, a movement detection means for detecting retreat of a casing 3 to its retreat position and a control means for having said step motor drive the thermal head supporting shaft 61 according to a signal from the movement detection means, thereby to move the thermal head to its retreat position. A tortion bar engaged with the thermal head supporting shaft 61 may be used in place of the tension spring 88. THERMAL HEAD MOVING MEANS The thermal head moving means 6 selectively moves a thermal head either to a pressuring position (shown in Fig. 19) for the thermal head 5 to pressure the ink-ribbon 41, or to a pressuring release position (shown in Fig. 18) for the thermal head 5 to release pressuring the ink-ribbon 41 after turning for a predetermined length from the pressuring position to the retreat position. This is for preventing rapid deterioration of the ink-ribbon 41 which may occur when the ink-ribbon 41 is close to a passage, through which paper heated to relatively high temperatures by a fixing device 17 passes. That is, when thermal transferring is not performed, the thermal head moving means 6 moves the thermal head 5 to its pressuring release position so as to retreat the thermal head 5, thereby to keep the ink-ribbon 41 away from the hot passage for preventing said deterioration of the ink-ribbon 41. Referring to Fig. 4, the thermal head moving means 6 comprises a roller supporting shaft 81, an eccentric roller 82as a turning means, a compression coil spring 83, said stay 86 and plate spring 84. Both ends of the roller supporting shaft 81 is supported directly or indirectly by the frame side plates 1b, 1d of the main body 1 of the copying machine. The eccentric roller 82 has a long shaft-inserting through hole 82a in the diametral direction thereof. In this shaft-inserting through hole 82a, an end portion 81a of said roller supporting shaft 81 is inserted being movable in the diametral direction. There is further disposed said compression coil spring 83 in the shaft-inserting through hole 82a. The pressure of the compression coil spring 83 keeps the center of the eccentric roller 82 away from the axial line 81b of the roller supporting shaft 81. Due to this the eccentric roller 82 eccentrically turns along with turning of the roller supporting shaft 81. The plate spring 84 has an end portion 84a thereof fastened with a screw 84c to the end portion 61b of the thermal head supporting shaft 61, thus turning in one piece with the thermal head supporting shaft 61. The other end portion 84b of the plate spring 84 extends in the diametral direction of the thermal head supporting shaft 61. This end portion 84b pressures the bottom 31a of a box 31 of the casing 3 when the casing 3 is in a set position. Description will be given as to the operations of the thermal head moving means 6. When a mode to perform thermal transferring is not selected in the copying machine, the compression coil spring 83 is positioned on the upper right of the roller supporting shaft 81 as shown in Fig. 18, and there is no pressure generated between the eccentric roller 82 and the plate spring 86 of the guiding member 85. Therefore in fig. 18, the thermal head 5 is urged to turn clockwise by the restitutive force of the plate spring 84 in Fig. 18 and thus positioned in its pressuring release position. Meanwhile when a mode to perform thermal transferring is selected in the copying machine, the thermal head supporting shaft 61 is turned by 1/2. Then as shown in Fig. 19, the compression coil spring 83 is positioned on the down left of the roller supporting shaft 81. Due to this, the stay 86 is pressured by the eccentric roller 82, and the thermal head supporting shaft 61 is turned counterclockwise in Fig. 18 mainly against the restitutive force of the pressure to the bottom 31a of the plate spring 84. Thus the thermal head 5 is turned counterclockwise in Fig. 18 and moved to its pressuring position shown in Fig. 19. When a mode to perform thermal transferring is canceled again, the eccentric roller 82 releases pressuring to the stay 86 and thus the thermal head supporting shaft 61 is turned clockwise in Fig. 19 by the restitutive force of the plate spring 84, thereby to move the thermal head 5 to the pressuring release position of the thermal head 5. The thermal head supporting shaft 61 may be attached to the frame side plates 1b, 1d of the main body 1 of the copying machine. PAPER DELIVERY PORTION At the outlet of the fixing device 17, there are disposed discharge rollers 21a, 21b for discharging paper with toner image formed thereon from the fixing device 17, and a fusing completion detection switch 22 is disposed on the downstream side of the discharge rollers 21a, 21b in the paper delivery direction. As the leading edge of the paper is discharged from the discharge rollers 21a, 21b, the detection switch 22 in a position shown with a solid line leans down to a position shown with a dot-and-dash line in Fig. 2, thus being turned on. The moment the trailing edge of the paper has passed the detection switch 22, the detection switch 22 returns to a position shown with a solid line, being turned off. That is, the leading edge of the paper having passed the detection switch can be detected by sensing the edge of the detection switch 22 switched from off to on, and the trailing edge of the paper having passed can be detected by sensing the edge of the detection switch 22 switched from on to off. The paper discharged from the discharge rollers 21a, 21b is sent by delivery rollers 23a, 23b to the downstream side of the paper delivery direction. On the downstream side of the paper delivery direction, there is disposed a switching claw 24 in the vicinity of the delivery rollers 23a, 23b. The switching claw 24, when in a position shown with a solid line in Fig. 2, guides the paper to discharge rollers 25a, 25b, and when in a position shown with a dot-and-dach line, guides the paper to a paper refeed passage 13a. According to a signal from the detection switch 22, the discharge rollers 25a, 25b and the platen roller 26 to which the paper is pressured, slow down deliverying the paper to a speed slow enough for the thermal transfer printer 2 to perform thermal transferring. The delivery rollers 23a, 23b, the discharge rollers 25a, 25b and the platen roller 26 are driven by a common step motor (not shown), whose rotating speed is adapted to change. INK-RIBBON DRIVE MECHANISM Referring to Figs. 6 and 7, said ink-ribbon drive mechanism 7 includes a winding reel drive motor 71 as a ribbon slack eliminating means, torque limiter 72, resistance loading means 78 and winding control means 85 serving. The motor 71 drives the winding reel 44 so as to have the winding reel 44 wind the ink-ribbon 41 thereon. The torque limiter 72 intervenes between the winding reel 44 and the winding reel drive means 71, limiting drive torque from the winding reel drive means 71 to the winding reel 44 to a predetermined torque or less. The torque limiter 72 includes the first member 73, the second member 74 and a urging means 75. The first member 73 comprises a gear attached to an end of a connecting shaft 76, being relatively turnable on the connecting shaft 76. The connecting shaft 76 is connected to the winding reel 44 being integrally turnable with the winding reel 44. The first member 73 is engaged with a gear 77 integrally turnable with a motor 71. The second member 74 comprises a ring combined with the connecting shaft 76 through spline. The second member 74 is integrally turnable with the connecting shaft 76 and movable in the axial direction of the connecting shaft 76. The end side 73a of the first member 73 and the end side 74a of the second member 74 are in contact with each other. The urging means 75, which intervenes between the a flange portion 76a provided on the midway of the connecting shaft 76 and the end side 74b of the second member 74, comprises a compression coil for pressuring the end side 74a of the second member 74 to the end side 73a of the first member 73. Driven by the motor 71, the gear 77 drives the first member 73. Meanwhile, the first member 73 and the second member 74 are connected together by means of frictional force, through which drive torque is transmitted from the first member 73 to the second member 74. Due to this, the connecting shaft 76 is actuated to drive the winding reel 44. When said drive torque becomes greater than said torque tansmittable by said frictional force, the end side 73a of the first member 73 slip on the end side 74a of the second member 74, thus relatively turning. Hence the drive torque transmitted from the motor 71 to the winding reel 44 is limited. Said transmittable torque can be set to a desired value by adjusting the roughness of said end side 73a and end side 74a, and the strength of the pressuring force of the urging means 75. In this manner, transmission of the drive torque equal to or greater than a predetermined torque TL thus determined can be limited. This enables to avoid a predetermined value or more of tensile force loaded on the ink-ribbon 41 wound on the winding reel 44. The resistance loading means 78 comprises a compression coil 79 an end portion 79a of which is fastened inside 42a of the body 42 of the cassette 4, and a frictional member 80 which is fastened to the other end portion 79b of the compression coil 79 and which is urged by the compression coil 79 to be pressurized to the end side 43a of the feed reel 43. The resistance loading means 78 generates braking torque TB for regulating the turning of the feed reel 43 from the frictional force between the end side 43a of the feed reel 43 and the frictional member 80. The predetermined torque TL of said torque limiter 72 is set less than the braking torque TB of the resistance loading means 78. By the way, the resistance loading means 78 may be provided outside of the cassette 4. The following description will discuss the operations of eliminating the ribbon slack by means of said motor 71, torque limiter 72 and resistance loading means 78. On completion of thermal transferring in a state shown in Fig. 8, the thermal head 5 retreats as shown in Fig. 9. Retreat of said thermal head 5 brings about slack on the ink-ribbon 41. As shown in Fig. 10, the motor 71 drives the winding reel 44 to wind slackened ribbon 41 thereon, thus eliminating the slack of the ink-ribbon 41 and putting the ink-ribbon 41 between the fedd reel 43 and the winding reel 44 on tension. At this time, the braking torque TB by the resistance loading means 78 is loaded on the winding reel 44 through the feed reel 43 and said ink-ribbon 41 on tension. Transmission of a predetermined value TL or more of the drive torque to the winding reel 43 is checked by the torque limiter 72 and the braking torque TB is greater than the predetermined torque TL. Accordingly, an unused ink-ribbon 41 is not drawn out from the feed reel 43 to be fed to the winding reel 44, therby to ensure the elimination of the ribbon slack beyween the feed reel in3 and the winding reel 44. Then, the motor 71 stops to apply no load on the ink-ribbon 41 between the feed reel 43 and the winding reel 44. Therefore, the ink-ribbon 41 does not suffer deterioration of durablility due to unnecessary tensile load put thereon. Referring Fig. 11, when the thermal head 5 protruds downward the ink-ribbon 41 between the feed reel 43 and the winding reel 44 for thermal transferring, the unused portion of the ink-ribbon 41 wound on the feed reel 43 is not wastefully fed to the winding reel 44, which is economic. This is because the braking torque TB loaded on the feed reel 43 is greater than the predetermined torque TL set by the torque limiter 72, the portion of the ink-ribbon 41 wound on the winding reel 44 in eliminating the ribbon slack is drawn out from the winding reel 44, and the ink-ribbon 41 is returned to the state where thermal transferring is completed. In a conventional example wherein a tension spring winds an ink-ribbon on a feed reel, if a torque limiter is connected with a winding reel while the tensile force of the tension spring is greater than a predetermined torque set by a limiter, thermal transferring results in failure at times. In the conventional example, the portion of the ink-ribbon used for thermal transferring and wound on the winding reel is wound back to the feed reel to be fed again for thermal transferring, thus resulting in a failure of said thermal transferring. On the other hand, the embodiment of the present invention wherein the tensile spring is not employed does not present such a problem. Because during thermal transferring the feeding force which the platen roller 26 applies to the ink-ribbon 41 via paper is greater than the frictional braking torque TB loaded on the feed reel 43, the ink-ribbon 41 is fed from the feed reel 43. The ink-ribbon 41 which passed the thermal head 5 and used for thermal transferring is wound on the winding reel 44. Referring to Figs. 17 to 19, the control operations of a thermal transfer printer 2 will be described. When a mode for the thermal transfer printer 2 to perform thermal transferring is not selected, paper discharged from a fixing device 17 is delivered at paper discharge speed by delivery rollers 23a, 23b and discharge rollers 25a, 25b to be discharged on a discharge tray 19. In this case, a step motor moving the platen roller 26 is rotated at 300 mm/sec. When a mode for the thermal transfer printer 2 to perform thermal transferring by the heating, rotating speed of the step motor is changed as described as follows. When paper is discharged from a fixing device 17 and the trailing edge of the paper which has passed a fusion completion detection switch 22, the detection switch 22 is switched from on to off as shown in Fig. 4-A. Using the off-edge of the detection switch 22 as reference, the thermal transfer printer 2 is operated after a predetermined period of time, thereby to enter additional information at a place a predetermined length inside from the trailing edge of the paper. When a mode for the thermal transfer printer to perform thermal transferring is selected, the step motor is stopped t₁ period of time after the off-edge of the fusing completion switch 22, as shown in Fig. 17. At this time, the trailing edge of the paper stops on 20 mm upstream side, for instance, in the delivery direction from the platen roller 26. After the step motor is stopped, a solenoid (not shown) for lifting up or down a thermal head 5 is turned on to turn an eccentric roller 82 together with a roller supporting shaft 81 by 1/2, thus lowering the thermal head 5 to a pressuring position shown in Fig. 19. While holding the thermal head 5 in said position, the step motor is intermittently driven step by step for 80 steps for instance. Each time the step motor is stopped, the thermal head 5 enters additional information line by line on the paper (see Fig. 17-B). In this case, the additional information is entered on the trailing portion of the paper; or entered when the entire paper is discharged from a fixing device 17. Therefore, there is no possibility that a part of the paper is deformed or burnt due to the heat of the fixing device 17. When the step motor is operated for 80 steps and entering additional imformation is completed, the step motor is stopped for a moment. Then power supply to said solenoid is cut off, and hence the thermal head 5 is lifted up to a pressuring release position by the restitutive force of a plate spring. Corresponding to said step motor turned off, the drive motore 71 for the winding reel inin is turned (see Fig. 17-D), and the ink-ribbon 41 drawn out for thermal transferring is wound on the winding reel 44. Accordingly, the ink-ribbon 41 is free from sticking to the paper or generating unnecessary slack thereon. PAPER COOLING MECHANISM Referring to Fig. 20 and Fig. 21, the paper cooling mechanism 10 allows air to flow inside either of said delivery rollers 23a, 23b disposed near the outlet of the fixing device 17 and cools the delivery roller 23a, 23b thereby to cool the paper. The paper cooling machanism 10 comprises the delivery rollers 23a, 23b, a means for driving these delivery rollers 23a, 23b, and an intake fan 27 for allowing air to flow inside of the delivery roller 23b. The delivery roller 23a comprises an aluminum roller bridged across a pair of the frame side plates 1b, 1d. The delivery roller 23b is a roller for pressuring the paper discharged from the discharge rollers 17a, 17b of the fixing device 17 on the circumference of the delivery roller 23a in the full width thereof. The delivery roller 23b is driven in synch with a paper delivery portion 13 by means of a drive system of the copying machine as a drive means not shown in the figure. The delivery roller 23a is driven and turned by the delivery roller 23b, and the delivery roller 23b along with the delivery roller 23a jointly convey the paper to a passage in the thermal transfer printer 2. Said delivery roller 23a may be driven by the delivery roller 23b through the paper or through a chain or the like. As shown in Fig. 21, the delivery roller 23b comprises an aluminium supporter 28 formed with a plurality of hollow portions 28a extending along the axial direction of the roller and a frictional member 29 made up of rubber or the like which is provided on the circumference of the supporter 28. A supporting shaft 35 is pressed into a shaft-inserting through hole 28b provided in the center portion of the supporter 28. End portions 35a of the supporting shaft 35 are inserted in through holes 1e provided respectively in the frame side plates 1b, 1d, so that the supporting shaft 35 is turnably supported by the frame side plates 1b, 1d. End portions 23c, 23d of the delivery roller 23a go through inserting through-holes 1f provided respectively in the frame side plates 1b, 1d. The end portion 23c communicates with outside of the frame side plate 1b via intake fan 27. The end portion 23d is directly open to outside of the frame side plate 1d. Said inserting through holes 1f have a diameter slightly longer than that of the delivery roller 23a, so that the delivery roller 23a may be free to move in the diametral direction. The end portions 23c, 23d of the delivery roller 23a are elastically pressured toward the delivery roller 23b by a tension spring 36. Thus the clearance between the delivery roller 23b and the delivery roller 23a is adjusted so as to correspond to the thickness of the paper passing through the clearance therebetween. There is a static electricity removal means 38 attached on the frame side plate 1d. The static electricity removal means 38 is for letting out to the frame side plate 1d static electricity occurred in the aluminum delivery roller 23a touching the paper. The static electricity removal means 38 is electrically connected with the frame side plate 1d while has a plurality of brush contact shoe 38a to be brought in contact with the end portion 23d of the delivery roller 23a. That the static electricity removal means 38 conducts out the static electricity in the delivery roller 23a prevents the ink-ribbon 41 from adhering to the paper. Said intake fan 27 is disposed inside of a box 37 attached to the outside of the frame side plate 1b, and is actuated by a motor (not shown) to intake air outside of the frame side plate 1d through the end portion 23d into the inside of the delivery roller 23a. The air drawn into the delivery roller 23a flows from the end portion 23c through the box 37 to be exhausted outside of the frame side plate 1b. The hot paper whereon the fixing device 17 has fused a toner image by heating is discharged by the discharge rollers 21a, 21b and is interposed between the delivery roller 23b and the delivery roller 23a. Then the paper is delivered to the thermal transfer printer 2 while being pressured to the circumference of the delivery roller 23a in the full width thereof. During the conveyance of the paper, the intake fan 27 draws relatively cool air outside of the frame side plate 1d into the the delivery roller 23a, thereby to cool the paper before thermal transferring through the aluminum delivery roller 23a of good heat conductivity. The paper can be effectively cooled partly because relatively cool air outside of the frame side plate 1d is drawn into the the delivery roller 23a and partly because hot air which has absorbed heat from the delivery roller 23a is exhausted out of the frame side plate 1d and does not remain in the periphery of the delivery roller 23a. Due to this, failure of thermal transferring wherein the hot paper melts ink of a portion other than a thermal transferring pattern to transfer the ink on the paper can be prevented. Since the intake fan 27 does not absorb heat of the fixing device 17, the heating efficiency of the fixing device 17 does not deteriorate. The intake fan 27 may be replaced by a blow-in fan for blowing air into the delivery roller 23a. In addition to an intake fan disposed at either of the end portions 23c, 23d of the delivery roller 23a, a blow-in fan may be disposed at the other end portion thereof, thus utilizing two fans for enhancing the cooling efficiency even higher. Further air may be allowed to flow inside of the supporter 28 of the delivery roller 23b. Both the delivery roller 23a and the delivery roller 23b may be actuated in synch. The delivery roller 23a may be actuated to drive the delivery roller 23b. The delivery roller 23b may be replaced by a pressure belt. MODIFICATION OF INK-RIBBON DRIVE MECHANISM Fig. 12 and Fig. 13 show another example of the ink-ribbon drive mechanism 7. The example in Fig. 7 eliminates ribbon slack by winding an ink-ribbon 41 on a winding reel inin, whereas the example in Fig. 12 eliminates said ribbon slack by winding the ink-ribbon 41 on a feed reel 43. In the example in Fig. 12, a ribbon-slack eliminating means comprises a motor gin for driving the feed reel 43. A torque limiter 95 intervenes between the motor gin and the feed reel 43. A resistance loading means 93 intervenes between a drive motor for winding reel 44 and the winding reel 44. The torque limiter 95 has the same structure with the torque limiter 72 mentioned above, wherein it is regulated that a predetermined torque TL or more of the drive torque may not be transmitted from the motor gin to the feed reel 43. The resistance loading means 93 loads the braking torque TB equal to or greater than the predetermined torque TL of the torque limiter 95 on the winding reel 44. Thus it is avoided that the motor gin winds the ink-ribbon 41 by the length more than necessary for eliminating the slack of the ink-ribbon 41. The resistance loading means 93 comprises a solenoid (not shown) whose claw portion can be engaged with a gear portion (not shown) provided on the shaft of the winding reel 44, and said engagement checks reverse turning of the winding reel 44 when the motor 94 starts winding for eliminating the ribbon slack. According to the flow chart in Fig. 13, the operations of thermal transfer printer 2 and a copying machine will be described. In step S1, whether thermal transferring is performed or not is determined. If thermal transferring is not performed, copying is performed and step S2 is completed. If thermal transferring is performed, copying is conducted in step S3 first. Then the motor 71 for driving a winding reel 44 is started (step S4). The thermal head 5 is lowered to be pressured to the paper on the platen roller 26, thus conducting thethermal transferring (step S5). At completion of the thermal tansferring (step S6), the thermal head 5 rises up to the pressuring release position, thus leaving the ink-ribbon 41 slackened (step S7). Next, the motor 94 as the slack eliminating means is started to wind the ink-ribbon 41 on the feed reel 44, thereby to eliminate the slack on the ink-ribbon 41 (step S8). At this time, the ink-ribbon 41 is put on tension, and the drive torque of the motor 94 is applied to the winding reel 44 through this ink-ribbon 41 so that the ink-ribbon 41 will be drawn out from from the winding reel 44. However, the resistance loading means 93 applies the braking torque TB greater than the predetermined torque TL of the torque limiter 95 and therefore, the ink-ribbon 41 is prevented from being drawn out from the winding reel 44. Accordingly, only the ribbon-slack is sure to be eliminated. WINDING CONTROL MEANS A winding control means 10 regulates so that a uniform length of the ink-ribbon 41 is wound in eliminating said salck of the ink-ribbon 41. Referring Fig. 14 and Fig. 15, the winding control means 100 includes a photosensor 96 serving as an ink-ribbon length detection means and a winding time control means 97. The photosensor 96 is disposed in the vicinity of a winding reel 44 so as to detect relative change in the diameter of the ink-ribbon 41 wound on the winding reel 44. The winding time control means 97 comprises a CPU for controling time to drive the drive motor 71 for the winding reel 44 according to a detection signal from the photosensor 96. Along a side portion 41b of the side 41a of the ink-ribbon 41 opposite to a side whereon ink is applied, there is provided a silver evaporation portion 98 as a light reflection face. The photosensor 96 irradiates light on the silver evaportion portion 98 of the ink-ribbon 41 wound on the winding reel 44, thus sensing changes in the amount of the reflected light. As the distance between the photosensor 96 and said silver evaporation portion 98 becomes shorter, the photosensor 96 receives a greater amount of reflected light. The distance between the photosensor 96 and the silver evaporation portion 98 is proportional to the amount of the ink-ribbon 41 wound on the winding reel 44, or the diameter of the ink-ribbon 41 wound on the winding reel 44. A microswitch 99 having an actuator 99a may be used in the place of the photosensor 96, as showing Fig. 16. The microswitch 99 is a switch which is adapted to change its resistance value as the actuator 99a turns to change its position, thereby to induce an output corresponding to the diameter of the ink-ribbon woud on the reel. The winding time control means 97 conducts calculation based on the detection output from the photosensor 96 and changes time to drive the motor 71. Thus, the length of the ink-ribbon to be wound for eliminating a ribbon slack is made uniform when the motor 71 drives the winding reel 44 for eliminating the slack of the ink-ribbon 41. The photosensor 96 may detect the diameter of the ink-ribbon woudn on the feed reel 43, or in other words, a remaining amount of the ink-ribbon 41. In this case, it is required to provide the silver evaporation portion 98 on the ink-ribbon side whereon an ink is applied. If the ink-ribbon 41 has a relatively large width such as approx. 10 cm a narrow silver evaporation portion 98 provided along the side thereof will not exert any bad influence on thermal transferring. Furthermore, if the side whereon ink is applied or the side opposite to said ink applied side has a uniform reflectivity, the photosensor 96 can detect the diameter of the ribbon wound on the reel without providing the silver evaporation portion 98 thereon. MODIFICATION OF THE PAPER DELIVERY PORTION Fig. 22 and Fig. 23 respectively show modifications of the paper delivery portion 13. The paper delivery portion 13 according to said modifications includes a bypass B for guiding the paper discharged from the fixing device 17 to the discharge rollers 25a, 25b without passing through the thermal transfer printer 2, and a distributing means 50 which guides the paper from the fixing device 17 to the thermal transfer printer 2 when using the thermal transfer printer 2, and which guides the paper to said bypass B, when not using the thermal transfer printer 2. With reference to Fig. 22, the fixing device 17 fixes a toner image transferred on paper P delivered from a copy processing portion while catching the paper between a heat roller 211 and a pressure roller 212 thus conveying the paper to the downstream side in the delivery direction. A heater 213 is mounted inside of said heat roller 211. There are provided respectively separation claws 214, 215 for separating the paper P and a pair of delivery rollers 21a, 21b for discharging the paper P from the fixing device 17 on the downstream side in the delivery direction from the heat roller 211 and the pressure roller 212. In addition, an application roller 217 for applying an offset preventive agent such as silicon oil on the pressure roller 212 is brought in contact with the pressure roller 212. Said heat roller 211 and pressure roller 212 or the like are housed in a casing 17a. The thermal transfer printer 2 has the thermal head moving means 6 lift up or down the thermal head 5 disposed above the platen roller 26 opposite to the roller. The thermal head moving means 6 includes the eccentric roller 82 engaged with the fixing member 62 fixed with the thermal head 5. The eccentric roller 82 turns to lift up or down the thermal head 5. A part of the circumference of said platen roller 26 intrudes into a paper delivery passage 5 through the lower guide plate 51a of two guide plates 41a, 51b constituting a paper delivery passage Q. The thermal head 5 intrudes into the paper delivery passage Q through a through-hole formed in the upper guide plate 51b of the two guide plates 51. The distributing means 50 comprises a switching claw 52 disposed on the downstream side of the fixing device 17 in the delivery direction. The distributing means guides the paper P passing through the fixing device 17 to the thermal transfer printer 2 when a thermal transfer mode is selected through a keyboard not shown in the figure, and otherwise guides the paper P to the bypass B. The switching claw 52 is switched to turn by a solenoid not shown in the figure. There are provided the delivery rollers 23a, 23b in the midway of said paper delivery passage Q, and delivery rollers 53a, 53b are provided in the midway of the bypass B. The delivery rollers 23a, 23b, 53a, 53b convey the paper P for the discharge rollers 25a, 25b. S represents a microswitch for checking discharge of the paper P. According to the example in Fig. 22, of the paper P passing through the fixing device 17, only the paper P requiring thermal transferring is guided through the paper delivery passage Q to the discharge rollers 25a, 25b, and the paper P not requiring thermal transferring is guided through the bypass B to the discharge rollers 25a, 25b. Accordingly, the quantity of the paper P passing from the platen roller 26 to the thermal head 5 is reduced, and melting of the ink-ribbon due to radiant heat from the paper P can be prevented. Therefore it is not necessary to provide a long stroke for the thermal head 5 to travel, which enables to perform thermal transferring in a short time. This also leads to fast copying operations. The example in Fig. 23 differs from the example in Fig. 22 in that the paper delivery passage Q and the bypass B are lifted up or down in one piece, and either the delivery passage or the bypass B is selectively connected to the conveyor rollers 21a, 21b the discharge rollers 25a, 25b of the fixing device 17. Referring to Fig. 23, the paper delivery passage Q and the bypass B are provided in parallel. The thermal transfer printer 2, the paper guide plates 51a, 51b constituting the paper delivery passage Q and a pair of guide plates 56a, 56b constituting the bypass B are attached to a pair of side plates 55 movable upward or downward to the main body 1 of the copying machine. Said side plates 55 are designed to be lifted up or down by the distributing means 50. The distributing means 50 comprises a screw member 54 screwed in the side plates 55, and the screw member 54 is driven to turn by the drive system of the copying machine. The example in Fig. 23 has the same effect with the example in Fig. 22.

Claims: An image forming apparatus characterized by: a thermal transfer printer (2) for recording desired information additively on a paper whereon a fixing means (17) has fixed a toner image, by pressuring an ink-ribbon (41) on said paper, said thermal transfer printer (2) including (i) a cassette (4) for housing the ink-ribbon (41) which includes a feed reel (43) for feeding said ink-ribbon (41) and a winding reel (44) for winding thereon the ink-ribbon (41) fed thereto, (ii) a thermal head (5) which moves to a pressuring position to pressure the ink-ribbon (41) between said feed reel (43) and said winding reel (44) to said paper against a platen roller (26), while protruding said ink-ribbon (41) from the cassette (4) for the purpose of thermal transferring, and said thermal head (5) after completion of the thermal transferring, moves to a pressuring release position to release pressuring said ink-ribbon (41), (iii) a ribbon-slack eliminating means (71) for actuating said winding reel (44) to wind the ink-ribbon (41) thereon after thermal transferring is completed, thus eliminating the slack of said ink-ribbon (41) brought about by said thermal head (5) moving to the pressuring release position, (iv) a torque limiter (72) for restraining said ribbon-slack eliminating means (71) from transmitting a predetermined torque or more of drive torque to said winding reel (44), said torque limiter (72) intervening between said winding reel (44) and said ribbon-slack eliminating means (71), and (v) a resistance loading means (78) for loading on said feed reel (43) braking torque greater than said predetermined torque of said torque limiter (72). The image forming apparatus according to claim 1, characterized in that said ribbon-slack eliminating means (71) includes a step motor. The image forming apparatus according to claim 1 or 2, characterized in that said torque limiter (72) includes (i) a first member (73) interlocked and turned with the ribbon-slack eliminating means (71), and (ii) a second member (74) disposed coaxially with the first member (73) and interlocked and turned with said winding reel (44), and both said first member (73) and second member (74) are allowed to move in relative axial direction and to turn relatively, and end sides of the both members, which face each other, are frictionally engaged together by an urging means (75). The image forming apparatus according to any one of claims 1 to 3, characterized in that said resistance loading means (78) includes a frictional member (80) pressured to a predetermined position of said feed reel (43) to generate a frictional force therebetween for braking turn of the feed reel (43), and an urging means (75) for elastically urging the frictional member (80) to said predetermined position. The image forming apparatus according to any one of claims 1 to 4, characterized in that said resistance loading means (78) includes a solenoid whose claw portion can be engaged with a gear portion provided on a supporting shaft of the feed reel (43). An image forming apparatus characterized by: a thermal transfer printer (2) for recording desired information additively on a paper whereon a fixing means (17) has fixed a toner image, by pressuring an ink-ribbon (41) on said paper, said thermal transfer printer (2) including (i) a cassette (4) for housing the ink-ribbon (41) which includes a feed reel (43) for feeding said ink-ribbon (41) and a winding reel (44) for winding thereon the ink-ribbon (41) fed thereto, (ii) a thermal head (5) which moves to a pressuring position to pressure the ink-ribbon (41) between said feed reel (43) and said winding reel (44) to said paper on a platen roller (26), while protruding said ink-ribbon (26) from the cassette (4) for the purpose of thermal transferring, and which after completion of the thermal transferring moves to a pressuring release position to release pressuring said ink-ribbon (41), (iii) a ribbon-slack eliminating means (94) for actuating said feed reel (43) to wind the ink-ribbon (41) thereon after thermal transferring is completed, thus eliminating the slack of said ink-ribbon brought about by said thermal head (5) moving to the pressuring release position, (iv) a torque limiter (95) for restraining said ribbon-slack eliminating means (94) from transmitting a predetermined torque or more of drive torque to said feed reel (43), said torque limiter (95) intervening between said feed reel (43) and said ribbon-slack eliminating means (94), and (v) a resistance loading means (93) for loading on said winding reel (44) braking torque greater than said predetermined torque of said torque limiter (95). The image forming apparatus according to claim 6, characterized in that, said ribbon-slack eliminating means (94) includes a step motor. The image forming apparatus according to claim 6 or 7, characterized in that said torque limiter (95) includes (i) a first member (73) interlocked and turned with the ribbon-slack eliminating means (94), and (ii) a second member (74) disposed coaxially with the first member (73) and interlocked and turned with said feed reel (43), and both said first member (73) and second member (74) are allowed to move in relative axial direction and to turn relatively, and end sides of the both members, which face each other, are frictionally engaged together by an urging means (75). The image forming apparatus according to one of claims 6 to 8, wherein said resistance loading means (93) comprises a solenoid whose claw portion can be engaged with a gear portion provided in a supporting shaft of the feed reel (43). The image forming apparatus according to any one of claims 1 to 9, characterized by a thermal head moving means (6) for selectively moving said thermal head (5) to each of said pressuring position and said pressuring release position. The image forming apparatus according to claim 10, characterized in that, said thermal head (5) is supported by a thermal head supporting shaft (61) being integrally turnable with the thermal head supporting shaft (61), and said thermal head moving means (6) including (i) an urging means (84) for urging the thermal head (5) to the pressuring release position, and (ii) a turning means (82, 86) for turning said thermal head supporting shaft (61) to turn the thermal head (5) to the pressuring position against the force of said urging means (84), and for allowing said urging means (84) to turn the thermal head (5) to the pressuring release position after completion of thermal transferring. The image forming apparatus according to claim 11, characterized in that said turning means includes an eccentric roller (82) for pressuring a member (86) which extends in the diametral direction of the thermal head supporting shaft (61) and is turnable with the thermal head supporting shaft (61). The image forming apparatus according to any one of claims 1 to 12, characterized in that a casing (3) mounting said cassette (4) is supported by a casing supporting shaft (34), and said eccentric roller (82) is provided with a hole (82a) for inserting a roller supporting shaft (81) parallel with said casing supporting shaft (34) in such a manner as to allow the roller supporting shaft (81) to move in the diametral direction thereof, and the hole (82a) is provided with a compression coil spring (83) for keeping the center of the eccentric roller (82) away from the roller supporting shaft (81). The image forming apparatus according to claim 13, further comprising a main body (1), a paper discharge portion (19) formed in the side face (1a) thereof, an opening portion (20) provided in said side face; an opening and shutting means (1i) for opening and shutting said opening portion (20); wherein the cassette (4) is detachably mounted in said casing (3) , said casing (3) being movable between a set position in the main body (1) of the image forming apparatus and a retreat position retreating from said set position so as to allow said cassette (4) to be taken out through said opening portion (20) kept open by said opening and shutting means (1i), wherein a thermal head supporting means (60) is provided for supporting the thermal head (5) turnable about said thermal head supporting shaft (61), and wherein an interlocking mechanism (8) is provided for retreating said thermal head (5) to its retreat position by the thermal head supporting means (60) in response to movement of said casing (3) to its retreat position. The image forming apparatus according to claim 14, characterized in that said casing (3) is turnable about said casing supporting shaft (34) between the set position and the retreat position and said interlocking mechanism (8) keeps the thermal head (5) relatively away from the casing (3) in response to movement of said casing (3) to its retreat position. The image forming apparatus according to any one of claims 14 or 15, characterized in that said interlocking mechanism (8) includes a spring means (88) for urging the thermal head (5) to its retreat position through the thermal head supporting means (60). The image forming apparatus according to claim 16, characterized in that said spring means (88) includes a tension spring or a torsion spring engaged with the thermal head supporting means (60). The image forming apparatus according to any one of claims 14 to 17, characterized in that said interlocking mechanism (8) includes (i) a stay (86) fixed to said thermal head supporting means (60) being integrally turnable with the thermal head supporting means (60), (ii) a guided member (87b) provided at the stay (86), and (iii) a guiding member (1c) which is attached to side plates (1b, 1d) and which is engaged with said guided member (87b) concurrently with the casing (3) turning from its set position to its retreat position, thus guiding the guided member (87b). The image forming apparatus according to claim 18, characterized in that said stay (86) is in contact with said eccentric roller (82), and said eccentric roller (82) moves the thermal head (5) to its pressuring position for thermal transferring. The image forming apparatus according to any one of claims 14 - 19, characterized in that said opening and shutting means (1i) includes a cover turnably mounted on the main body (1) of the image forming apparatus. The image forming apparatus according to claim 20, characterized in that said cover (1i) is connected with a punching unit (18) for punching filing holes in the paper. The image forming apparatus according to any one of claims 14 - 21, characterized in that said opening and shutting means comprises a cover (1i) which is connected with a paper discharging means (25a).

Inventors: HIDEO UMEZAWA, JUNICHI OURA, MITSUHARU YOSHIMOTO, SATOSHI YANO, SEIICHI SHIRASAKI, TAKASHI KONDO, TAKASHI MIYAKE ROOM NAGAO-RYO, YOSHIFUMI OKAUCHI, YOSHITAKE MIYOSHI, YUKIHIRO ITO, YUTAKA SHIGEMURA, HIDEO, UMEZAWA, JUNICHI, OURA, MITSUHARU, YOSHIMOTO, SATOSHI, YANO, SEIICHI, SHIRASAKI, TAKASHI, KONDO, TAKASHI, MIYAKE ROOM 49, NAGAO-RYO, 3-5-1, YOSHIFUMI, OKAUCHI, YOSHITAKE, MIYOSHI, YUKIHIRO, ITO, YUTAKA, SHIGEMURA
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO. LTD.
Application year: 1990
Main classification: G03G15
IPC codes: G03G15, B41J17, B41J25