The present invention relates to an apparatus for building an image by transferring a coloring agent from transfer material to a material to be image transferred.
To facilitate understanding of the invention a typical conventional image building apparatus of the abovementioned type will be schematically illustrated by way of a fragmental side view in FIG. 1. Referring to FIG. 1, the apparatus includes a paper feeding cassette 1 in which a number of cut papers P are received in the layered structure. In the illustrated example the aforesaid material to be image transferred is each of the cut papers P. As the paper feeding roller 2 is rotated, cut papers P are taken out of the cassette 1 one by one and the foremost end of the thus taken cut paper P reaches a pair of aligning rollers 3a and 3b by means of which it is arranged correctly. Thereafter, as both the aligning rollers 3a and 3b are rotated, it is delivered away from them to reach the gate 4 as identified by a solid line. While it is guided by means of the gate 4, it is introduced into the space as defined between the platen roller 5 and the pinch roller 6a so that it is transported further as the platen roller 5 is rotated. At this moment a thermal head 10 on the turnable holder 9 secured to a solenoid 8 is caused to turn about the shaft 11 in the anticlockwise direction whereby the thermal head 10 is displaced away from contact with the platen roller 5. It should be noted that the solenoid 8 is turned on at a time when the foremost end of cut paper P is detected by means of a detector 7 which is located in the vicinity of the outlet side of the aligning rollers 3a and 3b. Next, the platen roller 5 is rotated further while the pinch rollers 6a and 6b rotate in cooperation with the platen roller 5 in the form of follower rollers. As a result, the cut paper P moves forward until its foremost end in clamped between the platen roller 5 and the pinch roller 6b as illustrated in FIG. 2(A). Thereafter, the gate 4 is turned in the anticlockwise direction so that loosening of the cut paper P between both the pinch rollers 6a and 6b is eliminated. Thus, the cut paper P is brought in close contact with the platen roller 5, as illustrated in FIG. 2(B). Thereafter, the gate 4 is turned again in the clockwise direction until the original position is restored. At this moment the solenoid 8 is turned off and thereby the thermal head 10 is caused to turn again in the clockwise direction about the shaft 11 until both the cut paper P and the transfer material, for instance, thermal transfer type ink ribbon R (hereinafter referred to simply as ink ribbon) come in pressure contact with the platen roller one above another, as illustrated in FIG. 2(C). While the above-mentioned operational state is maintained, the platen roller 5 is rotated further whereby transference of a coloring agent is achieved by means of the thermal head 10.
After completion of printing operation on the cut paper P the latter is carried away from the working area toward the paper discharge tray 14 via a paper discharging roller 13, while its upward movement is guided by an opposing pair of guides 12a and 12b (see FIG. 1). It should be noted that the platen roller 5 stops the rotation when its rearmost end part of the cut paper P is firmly clamped between the platen roller 5 and the pinch roller 6a. On the other hand, the thermal head 10 is caused to turn about the shaft 11 in the anticlockwise direction under the effect of energization of the solenoid 8 and thereby it is displaced away from the platen roller 5. This causes the cut paper P and the ink ribbon R to come out of pressure contact with the platen roller 5, as illustrated in FIG. 2(D) and thereafter only the cut paper P can be transported backwardly as the platen roller 5 is rotated in the opposite direction. At this moment the gate 4 is actuated to turn in the anticlockwise direction (to the position shown by the dashed line of FIG. 1) so that the cut paper P is transported away from the platen roller 5 toward an opposing pair of guides 15a and 15b. Then, it is transported in the rightward direction as seen in the drawing while it is guided by means of the guides 15a and 15b. When the foremost end of the cut paper P is restored to its initial position as illustrated in FIG. 2(A), the platen roller 5 stops its rotation and the gate 4 is then turned in the clockwise direction until it resumes the original position as illustrated in FIG. 2(A). Thereafter, by repeating the steps of operations as described above, superimposed printing or transference of various kinds of coloring agents from the ink ribbon R is achieved for the cut paper P. The same steps of operations as described above are repeated further for a plurality of cut papers. After completion of superimposed printing or transference of various coloring agents from the ink ribbon R, cut papers P are carried away on the paper discharging tray 14 on which they are stored in the layered structure.
It should be added that superimposed printing or transfering is usually carried out by using three colors comprising yellow, magenta, cyan or four colors comprising yellow, magenta, cyan and black. FIG. 3 shows an example of ink ribbon to be used for superimposed printing or transfering using four kinds of coloring agents. In FIG. 1, the ink ribbon is identified by reference letter R and arrangement is made such that the ink ribbon R is unreeled from a spool 16 and it is then reeled about another spool 17 via a plurality of guide rollers 18a, 18b, 18c and 18d. The reeling spool 17 is adapted to rotate in synchronization with the platen roller 5 and its rotation is stopped at every time when the rearmost end of the ink ribbon R is detected by means of a color detector 19 located in the proximity of the guide roller 18a after completion of printing or transfering.
It has been found that the conventional thermal transfer type color printer has serious problems from the viewpoint of structure. One of them is concerned with so-called incorrect registering which tends to take place during superimposed printing or transferring. This incorrect registering refers to the case when the printed or transferred position is located offset from an intended one. In view of minimizing an occurrence of incorrect registering, the platen roller 5 is normally made of rubber and the pinch rollers 6a and 6b are also made of rubber so as to inhibit slippage of cut paper P. As schematically illustrated in FIG. 4, a phenomenon of local deformation takes place in the pressure contact area where the pinch rollers 6a and 6b come in pressure contact with the platen roller 5 and the latter comes in pressure contact with the thermal head 10. Due to local deformation of the platen roller 5 and the pinch rollers 6a and 6b, a radius of the platen roller 5 for determining a distance of transportation of cut paper P with the use of the platen roller 5 (which is generally called effective radius) becomes smaller than the nominal radius r of the platen roller 5. Specifically, the effective radius of the platen roller 5 is reduced to r.sub.1 in the pressure contact area where it comes in pressure contact with the thermal head 10 and the same is reduced to r.sub.2 in the pressure contact area where the platen roller 5 comes in pressure contact with the pinch rollers 6a and 6b. For the reasons, the distance of transportation of cut paper P fails to take an amount of 2.pi.r when the platen roller 5 is rotated by one revolution and thereby the cut paper which has been carried by means of the pinch rollers 6a and 6b, and the platen roller 5 becomes loosened particularly with respect to the platen roller 5. Once loosening of the cut paper P has occured, prevention of an occurrence of skewing (moving in the inclined state) of the cut paper P owing to frictional force existent between the platen roller 5 and the cut paper P fails to be achieved. As a result, the cut paper P tends to skew in the course of transportation. Unavoidably, incorrect registering takes place in the printing or transferring area.
To obviate the problem of incorrect registering, there was proposed one measure. Specifically, this measure consists in that both the pinch rollers 6a and 6b are made of the same material in the same dimensions so that they are brought in pressure contact with the platen roller 5 under the condition of the same pressure (Pa=Pb) and moreover hardness of rubber constituting the platen roller 5 and pressure Ph of the thermal head 10 adapted to come in pressure contact with the platen roller 5 are selectively determined to adequate values so as to assure that the distance of transportation of the cut paper P is kept constant. However, it has been found that the platen roller 5 and the pinch rollers 6a and 6b can be fabricated at higher dimensional accuracy only with much difficulty, and therefore incorrect registering in the range of 0.1 to 0.3 mm takes place unavoidably in the printing or transferring area when the conventional method is employed for printing or transferring.
Accordingly, the conventional apparatus as described above has problems that cut paper wound around the platen roller becomes loosened and incorrect registering takes place in the printing or transferring area because of local deformation of the pinch rollers and the platen roller in the pressure contact area, irregular distribution of contact pressure, and reduced dimensional accuracy of parts and components constituting the apparatus.