Patent Grant
7331728
1. Field of the Invention
The present invention relates to a printer provided with an impact type print head and a platen located opposite to the print head. To be more specific, the invention relates to the structure of a platen which receives an impact from a print head at the time of printing on a print medium.
2. Description of the Related Art
For example, an impact type printer comprises a print head which is linearly moved over a print medium, and a platen which supports the print medium. The print head has a number of wires projecting toward the print medium. When the wires hit an ink ribbon upon the print medium, characters, marks or the like are printed on the print medium. The platen extends in the moving direction of the print head, and is located opposite to the print head with respect to the print medium. The platen is hit by the wires of the print head at the time of printing on the print medium. Thus, the platen is required to have a sufficient strength to withstand the impacts from the print head.
It should be noted that a passbook which is an example of a print medium is thicker than an ordinary recording paper sheet, and it has a print region whose thickness is not uniform. The print head prints a row of characters, marks or the like each time it performs printing while being moved in its width direction. Thus, if the print medium has a print region whose thickness varies as in the passbook, the distance between the print head and the print medium varies as the print head is moved to print the print medium. As a result, the print density of a thick part of the print medium is different from that of a thin part of the print medium. Inevitably, the print quality is low.
In view of the above circumstances, a printer which handles a thick print medium such as a passbook uses a print head provided with rollers for pushing the print medium against the platen. In addition, both ends of the platen are elastically supported by respective springs. Thereby, the platen is displaced in a direction toward or away from the platen in accordance with the position of the print head. As a result, the positional relationship between the print head and the print medium is constant, thus improving the print quality.
Also, in a conventional printer, both ends of the platen are supported by respective springs as in the above printer. In this structure, the pressure acting on the center of the platen toward the print head is double that on each end of the platen. In other words, the reactive force of the platen against the wires of the print head is locally high, i.e., that of the center of the platen is great. Inevitably, the print density of the part of the print medium which corresponds to the center of the platen is high, and that of the parts of the print medium which correspond to the ends of the platen is low.
In order to solve such a problem, a conventional impact printer uses a flexible platen. This platen is formed of a material having an elastic modulus, and its height increases from either of its ends toward its center. The moment of inertia of a horizontal surface extending through the center of gravity of the platen increases from either of the ends toward the center. An impact printer having such a platen is disclosed in, e.g., U.S. Pat. No. 5,879,091.
In the impact printer disclosed in the U.S. patent, although the both ends of the platen are supported by respective springs, the reactive force of each of the ends of the platen is equivalent to that of the center of the platen. This feature thus prevents increasing of the print density of part of a print medium which corresponds to the center of the platen.
However, if a platen is easily warped such that the reactive forces of the ends of the platen are equivalent to that of the center of the platen, the reactive forces of parts of the platen which are located between the center of the platen and the ends of the platen, respectively, are increased.
Consequently, when a print head reaches each of the above parts of the platen which are located between the center of the platen and the ends of the platen, the print medium is strongly pushed against the rollers of the print head. Thus, especially if a pressure sensitive copying paper sheet is used as a print medium, the marks of the rollers are transferred onto the paper sheet. On the other hand, if the reactive force of the platen is lowered in order to avoid the above problem, the print density of the entire print region of the print medium decreases. Consequently, printing is unclear, and the print quality drops.
The object of the present invention is to provide a printer in which the reactive force of the platen is made uniform over the entire length thereof, and the print quality is improved.
In order to attain the above object, a printer according to an embodiment of the present invention comprises a print head and a platen. The print head is linearly moved along a print medium to print the print medium. The platen supports the print medium, and is located opposite to the print head. The platen includes a first end portion, a second end portion and an intermediate portion, and is formed of material having stiffness. The first and second end portions are located at respective ends of the platen in the moving direction of the print head. The intermediate portion is located between the first and second end portions. The first and second end portions are supported by spring members such that they can be elastically displaced in the moving direction of the platen toward or away from the print head. The intermediate portion is formed to be more easily warped than the first and second end portions.
In the above structure, when the print head is moved along the platen, the platen is warped balanced by the pressures of the spring members, such that the intermediate portion of the platen is displaced by a given amount. Thus, the reactive force of the platen at the time of printing can be uniformized over the entire length of the platen. Therefore, the print density is kept constant, and printing of high quality is achieved.
Objects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention.
The accompanying drawings illustrate embodiments of the invention, and together with the general description given above and the detailed description given below, serve to explain the principles of the invention.
An embodiment of the present invention will be explained with reference to
In this embodiment, a passbook 6 is used as the print medium. The passbook 6 is inserted into the transfer path 3 through the insertion slot 4, while it is open. As shown in
In the transfer path 3, a first roller unit 7 and a second roller unit 8 are provided in given positions, respectively. They are spaced apart from each other in the transferring direction of the passbook 6. The first roller unit 7 includes a pair of rollers 7a and 7b, and the second roller unit 8 includes a pair of rollers 8a and 8b. The pair of rollers 7a and 7b and the pair of rollers 8a and 8b are provided to transfer the passbook 6 while holding it. These rollers are rotated when receiving torque from a transfer motor 9.
The transfer path 3 includes a print section P for printing on the passbook 6. The print section P is located between the first roller unit 7 and the second roller unit 8. At the print section P, a carrier 11 is provided. To be more specific, the carrier 11 is located above the transfer path 3, and can be linearly reciprocated in the direction perpendicular to the transferring direction of the passbook 6.
The carrier 11 is provided with a print head 12 and an ink ribbon cassette 13. The print head 12 includes a number of wires not shown. At the time of printing, the wires are projected toward the print region 6a of the passbook 6. An ink ribbon is guided from the ink ribbon cassette 13 into the gap between the distal ends of the wires and the print region 6a of the passbook 6. Thus, when being linearly moved, e.g., in the width direction of the passbook 6, the print head 12 hits the ink ribbon on the print region 6a of the passbook 6 to print a row of characters, marks or the like on the print region 6a.
Furthermore, the print head 12 includes a pressing roller 14. The pressing roller 14 is intended to keep constant the distance between the print head 12 and the print region 6a of the passbook 6, and is projected more downwardly toward the passbook 6 than the print head 12.
As shown in
The platen 16 is made of material such as glass-reinforced plastic, which has a sufficient stiffness, so that it can withstand the impacts from the print head 12. As shown in
The first and second end portions 17 and 18 of the platen 16 are supported by the apparatus body 2, with compression coil springs 20 interposed between the first and second end portions 17 and 18 and the apparatus body 2, respectively. Each of the compression coil springs 20 is an example of a spring member. The compression coil springs 20 continuously push the first and second end portions 17 and 18 of the platen 16 upwardly toward the print head 12. Thus, the platen 16 can be elastically displaced from its original position toward the print head 12 or away from the print head 12 in accordance with the thickness of the passbook 6.
The platen 16 includes a main body 22 and a beam 23. The main body 22 extends in the moving direction of the print head 12, and is also formed in the shape of a plate which is flat and elongated in the transferring direction of the passbook 6. The main body 22 includes two ends 24a and 24b and a supporting surface 25. The end 24a is located at the first end portion 17 of the platen 16. The end 24b is located at the second end portion 18 of the platen 16. That is, the ends 24a and 24b are separated from each other in the longitudinal direction of the main body 22. The supporting surface 25 is intended to support the passbook 6, and is interposed between the ends 24a and 24b.
The beam 23 extends between the ends 24a and 24b of the main body 22. The beam 23 projects downwards from a center portion of the main body 22, which is located at the center of the main body 22 in the width direction thereof. The beam 23 has a cross section which is narrower in width than that of the main body 22. The beam 23 has a greater section modulus than that of the main body 22. The stiffness of the beam 23 is higher than that of the main body 22. Therefore, the platen 16 has a T-shaped cross section.
The beam 23 includes a pair of ends 26a and 26b. The end 26a is located at the first end portion 17 of the platen 16. The end 26b is located at the second end portion 18 of the platen 16. The ends 26a and 26b of the beam 23 are pushed upwards by the compression coil springs 20.
The end 26a of the beam 23 and the end 24a of the main body 22 are formed integral with each other. Similarly, the end 26b of the beam 23 and the end 24b of the main body 22 are formed integral with each other. Thus, the main body 22 and the beam 23 are formed as a single body. As a result, the platen 16 is stabilized with respect to the strength. In addition, the inertia of the platen 16 is increased, since the weight of the beam 23 is added to the main body 22.
As shown in
As shown in
As shown in
The elastic members 28a and 28b are different from the platen 16 in modulus of elasticity. In the embodiment, the modulus of elasticity of each of the elastic members 28a and 28b is higher than that of the platen 16. Thus, the elastic members 28a and 28b are elastically deformed in accordance with the impact applied to the supporting surface 25 of the platen 16.
The beam 23 of the platen 16 includes a front surface 30a and a rear surface 30b located opposite to the front surface 30a. To the front surface 30a of the platen 16, a first mass member 31 formed as shown in
The beam 23 includes pairs of boss portions 33 which are located adjacent to ends 26a and 26b. As shown in
As shown in
The bracket 38 supports a second mass member 40. The second mass member 40 is formed of, e.g., a steel plate, and is smaller than the first mass member 31. The mass of the second mass member 40 is greater than that of the platen 16, and the stiffness of the second mass member 40 is higher than that of the platen 16. The second mass member 40 is exposed toward the rear surface 30b of the beam 23, and is located in the center of the beam 23 in the longitudinal direction.
In such a manner, the first and second mass members 31 and 40 and the platen 16 are formed as a single body to form a platen assembly 41.
As shown in
The platen 16 having the above structure is pushed downwards against the urging forces of the compression coil springs 20, so as not to interfere with transferring of a thick print medium like the passbook 6, at the time of transferring it.
As shown in
The arms 51 and 52 include engagement portions 54 and cam followers 55. The engagement portions 54 extend through the first mass member 31, and are engaged with a pair of engagement holes 56 formed in the beam 23 of the platen 16. The cam followers 55 extend toward positions below the pivot shafts 53.
A cam shaft 58 is provided below the arms 51 and 52. The cam shaft 58 includes a pair of cams 59. The cams 59 include base circles 59a and cam noses 59b projecting from the base circles 59a. The base circles 59a and the cam noses 59b contact the cam followers 55.
A driving wheel 60 is fixed to one of the ends of the cam shaft 58. The driving wheel 60 is driven along with a relay wheel not shown in interlock with a driving motor 61 shown in
When the cam followers 55 are shifted from the base circles 59a onto the cam noses 59b, the arms 51 and 52 are rotated downwards. Due to this rotation of the arms 51 and 52, the platen 16 is forcibly pushed downwards by the engagement portions 54 of the arms 51 and 52. Thus, the platen 16 is retreated to a level lower than that at which the paper guide 50 is located.
When the cam followers 55 are shifted from the cam noses 59b onto the base circles 59a, the platen 16 is released from downward pushing by the arms 51 and 52. Thus, the platen 16 is pushed upwards by the compression coil springs 20. As a result, the platen 16 is moved up and down each time a row of characters, marks or the like are printed on the passbook 6.
In the impact printer 1 having the above structure, when the passbook 6 reaches the print section P, the platen 16 is pushed upwards by the compression coil springs 20. Thereby, the passbook 6 is held between the supporting surface 25 of the platen 16 and the pressing roller 14 of the print head 12. Thus, the passbook 6 is fixed to the supporting surface 25, and at the same time the distance between the print region 6a of the passbook 6 and the print head 12 is set at the predetermined value.
In the case of printing on the print region 6a of the passbook 6, for example, when the print head 12 is moved from the right side to the left side in
The intermediate portion 19 of the platen 16 is more easily warped than the first and second end portions 17 and 18, since its section modulus is smaller than those of the first and second end portions 17 and 18. Furthermore, the elastic members 28a and 28b provided between the beam 23 and the main body 22 of the platen 16 are elastically deformed to absorb warping of the main body 22 which occurs when the main body 22 supports the passbook 6, and finely adjust the degree of deformation of the main body 22 in accordance with the position of the print head 12.
That is, at the first and second end portions 17 and 18 of the platen 16 which receive the urging forces of the compression coil springs 20, the platen 16 has a double-deck structure in which the main body 22 and the beam 23 are provided, and at the intermediate portion 19 of the platen 16 which is easily warped, the platen 16 has a three-deck structure in which the main body 22, the beam 23 and the elastic members 28a and 28b are provided.
The intermediate portion 19 of the platen 16 is warped balanced, against the pressures of the compression coil springs 20 supporting the platen 16, such that the main body 22 and the elastic members 28a and 28b are displaced in accordance with the position of the print head 12, and generates a reactive force toward the print head 12.
Therefore, when the print head 12 is moved to print a row of characters, marks or the like on the print region 6a of the passbook 6, the reactive force of the platen 16 toward the print head 12 can be made uniform over the entire length of the platen 16. As a result, the print densities of the characters, marks or the like printed on the print region 6a are equivalent, thus achieving printing with a high quality.
When the intermediate portion 19 of the platen 16 is easily warped, there is a possibility that the main body 22 of the platen 16 may be deformed to be warped toward the print head 12. Thus, the main body 22 of the platen 16 includes the stopper 42 at the center of the platen 16 in the longitudinal direction thereof. The stopper 42 is in contact with an upper edge of the opening portion 44 of the first mass member 31, with the elastic ring 43 interposed between the stopper 42 and the upper edge of the opening portion 44. The elastic ring 43 contacts the first mass member 31 to restrict free deformation of the main body 22 toward the print head 12.
Thus, though the intermediate portion 19 of the platen 16 is easily warped, the supporting surface 25 of the main body 16 is formed to be uniformly flat. Therefore, clear printing can be achieved, and the printing quality is improved.
By virtue of the above structure, the reactive force of the platen 16 is kept optimal for printing, and is made uniform over the entire length of the platen 16. Thus, for example, even if a pressure sensitive copying paper sheet is used as the print medium, the pressing rollers 14 are prevented from leaving marks on the paper sheet when the print head 12 is moved. In addition, when the stepped portion 6b of the passbook 6 reaches the print head 12, the platen 16 is smoothly moved downwards in accordance with the thickness of the passbook 6, and the platen 16 warps balanced. Thus, the print head 12 is not caught by the stepped portion 6b of the passbook 6.
Furthermore, the weight of the beam 23 is added to the platen 16, since the main body 22 of the platen 16 is reinforced by the beam 23, which has a higher stiffness than that of the main body 22. Also, the weights of the first and second mass bodies 31 and 40 are added to the platen 16, since the first and second mass members 31 and 40, each of which has a higher specific gravity than that of the platen 16, are attached to the beam 23 of the platen 16. Thus, the inertia of the platen 16 is increased.
Therefore, when the passbook 6 is printed, fine vibration, which would occur at the platen 16 when the print head 12 repeatedly hits the platen 16, can be suppressed. Furthermore, the vibration of the beam 23 is absorbed by the elastic rings 35 provided between the first mass member 31 and the beam 23.
Therefore, vibration of the platen 16 at the time of printing can be efficiently reduced, thus preventing noise.
In the above embodiment, the beam and the main body of the platen are formed integral with each other. However, in the invention, the structure of the beam and the main body are not limited to such a structure. For example, the beam and the main body may be formed separately, and be connected with each other by screws or the like.
Furthermore, the main body and the beam may be formed of different materials. In this case, it is preferable that material having a high modulus of vertical elasticity be used as the material of the beam.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the inventive as defined by the appended claims and their equivalents.
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