Patent Application
20080056794
Hereinafter, one embodiment of the invention will be described in detail with reference to the accompanying drawings.
For application to a printer, as is shown in
As is shown in
Although it is not shown in the drawing, a roller that supplies a medium subject to printing (a sheet of paper or the like) into a space between the platen 39 and the print head 31 is provided below the platen 39. This supply roller forms a medium feeding mechanism together with a discharging roller 40 disposed above the platen 39.
As has been described, the print head 31 is mounted on the carrier 32 and opposes the platen fixedly disposed along a specific printing direction. Also, the ribbon cassette 20 is attached to the carrier 32 in such a manner that part of the ink ribbon 22 (portion positioned at the print portion 20a) is positioned in a space between the print head 31 and the platen 39. Further, the medium feeding mechanism having the discharge roller 40 supplies a medium subject to printing in a space between the platen 39 and the ink ribbon 22 as well as the print head 31, and moves the medium in a direction orthogonal to the moving direction of the carrier in association with the movements of the carrier 32.
As is shown in
A medium, such as a sheet of paper, is fed into a space between the print head 31 and the platen 39 by the medium feeding mechanism. Also, the print portion 20a of the ribbon cassette 20 is positioned in a space between the print head 31 and the print medium. A portion of the ink ribbon 22 impregnated with ink is supplied to the print portion 20a. In performing the printing, the print head 31 is activated, so that a wire called a needle is activated to protrude. The tip end of the wire activated to protrude collides on the surface of the medium via the ink ribbon 22. Dot-shaped printing is thus performed on the medium. Arbitrary characters and figures are drawn on the medium by moving the carrier 32 along the platen 34 in association with the operations of the print head 31.
The detailed configuration of the ribbon cassette 20 described above will now be described. Referring to
The ink ribbon 22 is of an endless shape, and the length thereof is sufficiently longer than the length of the circulation path of the ribbon comprising the case main body portion 21a and the pair of arm portions 21b and 21c. Most of the ink ribbon 22 is therefore accommodated in a folded state within a ribbon accommodation chamber 27 defined by a partition wall 21d inside the case main body 21a as is shown in the drawing.
The ink replenishing mechanism 24 has a roller-shaped ink tank 25. The ink tank 25 is shaped like a cylindrical column made of a sponge material or the like impregnated with ink, and it is formed to be rotatable in the shape of a roller. It is preferable for the ink tank 25 to have a larger ink capacity, and there has been a need to increase the volume thereof. To address this need, the ink capacity is increased in this embodiment not by increasing the diameter of the cylindrical column as in the related art, but by increasing the height in the axial direction.
The ink tank 25 is provided in a rotatable manner inside the lower portion case 21a in an upper right portion of
The driving mechanism 23 has a driving roller 23a and a driven roller 23b that together nip the ink ribbon 22. The driving roller 23a is configured to rotate in a clockwise direction in the drawing in association with the movements of the carrier 32, and feeds the ink ribbon 22 into the ribbon accommodation chamber 27 on the left in the drawing through these clockwise rotations.
The driving roller 23a is disposed below the ink tank 25 and the portion of the ink ribbon 22 coming into contact with the transfer roller 26 is stretched over the driving roller 23a, and thereby feeds the ink ribbon 22 replenished with ink into the ribbon accommodation chamber 27 through the clockwise rotations in the drawing together with the driven roller 23b. Also, the driving roller 23a is disposed with a sufficient distance from the outer circumferential surface of the ink tank 25, and the distance will be described below.
As is shown in
The driving roller 23a is used also as a take-up shaft that takes up the slack occurred in the ink ribbon 22. For this reason, as is shown in
As has been described, because the driving roller 23a is disposed with a sufficient distance from the outer circumferential surface of the ink tank 25, the operation knob 29 is naturally positioned with a sufficient distance from the outer circumferential surface of the tank cover portion 28d. Hence, unlike the related art, there is no need to provide the operation knob 29 to be higher than the top surface of the tank cover portion 28d, and as is shown in
In the configuration described above, as is shown in
More specifically, the medium, such as a sheet of paper, is fed into a space between the print head 31 and the platen 39 by the medium feeding mechanism provided with the discharge roller 40 for a portion subject to printing to oppose the print head 31. The print head 31 activates the wire called the needle to protrude toward the platen 39 according to the print information, and causes the tip end thereof to collide on the medium via the ink ribbon 22 of the ribbon cassette 20 positioned at the print portion 20a. Dot-shaped printing is thus performed on the medium. Also, characters and figures according to the print information are printed on the medium as the carrier 32 moves in association with the operations of the print head 31.
During the printing operation, because the driving roller 23a rotates in a clockwise direction in the drawing in association with the movements of the carrier 32 in the ink ribbon 20, the endless ink ribbon 22 is circulated to move in a clockwise direction in the drawing along the length direction. A portion of the ink ribbon 22 used for printing in the print portion 20a (a portion from which ink has been transferred onto the medium) is fed to the ink replenishing mechanism 24 by passing through the arm portion 21c (the outbound path) shown in
Herein, because a tensile force is applied onto the endless ink ribbon 22 by the rotations of the driving roller 23a, the center of rotation of the transfer roller 26 is shifted to the left in the drawing by this tensile force, and the transfer roller 26 is pressed against the outer circumferential surface of the ink tank 25. Ink soaked through the ink tank 25 thus adheres onto the ink ribbon 26 that comes into contact with the outer circumferential surface of the transfer roller 26 to replenish the printed portion with ink via the transfer roller 26. In other words, in a normal state, the transfer roller 26 merely comes into contact with the outer circumstance of the ink tank 25, and does not replenish the ink ribbon 22 with ink. On the contrary, when the ink ribbon 22 is fed, the transfer roller 26 is pressed against the outer circumferential surface of the ink tank 25 by the tensile force of the ink ribbon 22 and replenishes the ink ribbon 22 with ink.
In short, the ink ribbon 22 is replenished with ink only when the ink ribbon 22 is circulated to move in association with the printing operation, and it is not replenished with ink in any other time. It is thus possible to prevent the ink ribbon 22 from being replenished with ink excessively. In addition, because a time for being pressed against the ink tank 25 is shorter than a case where it is kept pressed against the ink tank 25 constantly, it is possible to extend a time until the ink tank 25 undergoes deformation. A satisfactory printing state can be therefore maintained.
In the ribbon cassette 20 configured as above, the occurrence of the slack in the ink ribbon 22 before printing may possibly make satisfactory printing difficult. It is therefore necessary to take up the slack in the ink ribbon 22, for example, when the ribbon cassette 20 is attached onto the carrier 32. The slack in the ink ribbon 22 is thus taken up by rotating the operation knob 29 on the cover main body portion 28a by a manual operation to rotate the driving roller 23a in the feeding direction. In practice, the ink ribbon 22 is fed into the ribbon accommodating chamber 27 to confer the tensile force to the ink ribbon 22 other than the portion accommodated in the ribbon accommodation portion 27 to take up the slack particularly at the print portion 20a.
In this case, the operation knob 29 is provided on the outer circumference surface of the tank cover portion 28d in parallel with the tank cover portion 28d on the same cover top surface on the outer surface of the cover main body portion 28a. Nevertheless, because it is disposed with a sufficient distance from the outer circumferential surface of the tank cover portion 28d, it can be readily operated without any interference with its rotational operation. In addition, because there is no need to provide the operation knob above the tank cover as in the related art, there is a margin in a space above the tank cover 28d of the invention. Hence, a need to increase a tank capacity can be addressed without causing any problem by increasing the volume of the ink tank 25 by making the size of the ink tank 25 in the axial direction larger.
When the axial length of the driving roller 23a becomes longer, the driving roller 23a readily swings, and this swinging may possibly pose a problem in the feeding function of the ink ribbon 22. However, in this embodiment, because the operation knob 29 is provided directly on the top surface of the case main body portion 28sa, it is possible to shorten the rotational axis of the driving roller 23a. In other words, unlike a case in the related art where the operation knob is provided to stand upright on the top surface of the tank case portion, there is no need to increase the rotational axis of the driving roller more than a quantity comparable to the height of the tank case, and the driving roller 23a in this embodiment is able to drive the ink ribbon 22 to be fed in a stable manner without causing swinging. To be more concrete, it is preferable to make the height of the upper edge portion of the operation knob 29 on the case main body portion 28a nearly equal to the height of the top surface of the tank cover portion 28d or lower than the height of the top surface of the tank cover portion 28d.
