Patent Application
20110063395
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-214874 filed on Sep. 16, 2009, the contents of which are incorporated herein by reference.
An embodiment described herein relates to a thermal head mechanism that prints on an object that is conveyed, a printing device using the same, and a method of supporting a thermal head.
In printing devices such as a thermal printer, there is known a printing device incorporating a head-pressing mechanism that causes a printhead having lined heat elements to abut on a paper sheet conveyed in a predetermined direction by pressing the printhead in a direction orthogonal to the paper-conveyance direction. This type of printer is typically provided with a printhead mechanism having a supporting mechanism supporting the printhead so as to slidably move in the head-pressing direction to maintain an appropriate print pressure to the paper. In such printers and mechanisms, a rotational moment is produced in a pressing part by virtue of a frictional force caused between the printhead, and a paper sheet or ink ribbon.
Aspects of this disclosure will become apparent upon reading the following detailed description and upon reference to the accompanying drawings. The description and the associated drawings are provided to illustrate embodiments of the invention and not limited to the scope of the invention.
A printhead mechanism in one embodiment of the present application includes a thermal head supported while being pressed to an object that moves in a predetermined object-conveyance direction, a pressing part pressing the thermal head in a direction orthogonal to the object-conveyance direction, and a supporting part supporting the thermal head movably in the head-pressing direction, wherein an acting point of pressing force at which the thermal head is pressed is disposed downstream of a supporting point at which the thermal head is supported.
According to one embodiment of the present application, an adequate printing pressure can be obtained.
Description will be made for the printing device in one embodiment in conjunction with
A printing device 1 is, for example, a thermal printer used as a label printer, barcode printer, receipt printer, etc., which has a printhead mechanism 10. Printing device 1 includes a pair of side frames 11, a thermal head 12 (printhead) that is supported between the pair of side frames 11, a platen roller 13 opposed to thermal head 12, a printhead supporting mechanism 20 (support part) that slidably supports thermal head 12, and a pressing mechanism 30 (pressing part) that presses thermal head 12 onto platen roller 13.
A paper sheet 14 and an ink ribbon 15 are interposed between a heater line 12a of thermal head 12 and platen roller 13 at a print section P1, at which printing is performed with the ink ribbon 15 heated by heater line 12a as paper sheet 14 and ink ribbon 15 are conveyed in a predetermined paper-conveyance direction along the X-axis in the figure. For illustration, paper sheet 14 and ink ribbon 15 are omitted in
A pair of side frames 11 each is provided at both ends in the paper-width direction along the Y-axis in the
Thermal head 12 includes heater line 12a composed of multiplex heat elements arranged in a line in the paper-width direction having a predetermined length covering the width of paper sheet 14. Thermal head 12 is pressed onto platen roller 13 by head-pressing mechanism 30 in the head-pressing direction (z-axis direction) orthogonal to the paper-conveyance direction of paper sheet 14 with paper sheet 14 and ink ribbon 15 interposed between the thermal head and the platen roller 13. The head-pressing direction is along the diameter of platen roller 13. Thermal head 12 is supported by head support mechanism 20 so as to slidably move in the head-pressing direction.
Platen roller 13 is formed in a cylinder extending to the paper-width direction, which is composed of, for example, a cylindrical roller 13a of an elastic material such as NBR (nitrile rubber) and a platen shaft 13b. Platen roller 13 is rotatably supported by support member 11b of side frames 11 through a pair of shaft receiving parts 13c. Platen roller 13 is driven by a motor, not indicated, to rotate on a rotation shaft extending in the paper-width direction (Y direction).
Head support mechanism 20 is comprised of supporting shaft members 21, a head support frame 22 that is fixed to the upper surface of thermal head 12 and a pair of head support plates 23, each of which is fixed to each of the ends in the width direction of head support frame 22.
Head support frame 22 is composed of, for example, a metal plate formed bent in a shape of a one-end open rectangular in its front view, each end of which is fixed to the paired head support plates 23 by a fixing member 24 such as a screw.
Paired head support plates 23, which, for example, are each composed of a flat metal plate, each have two slots 25 provided in parallel in the head-pressing direction. The plural slots 25 are shaped in an ellipse, the length of which is oriented in the head-pressing direction. Supporting shaft members 21 of side frames 11 are engaged with the slots 25 so as to move relatively in the head-pressing direction. Accordingly, thermal head 12 is supported by head support mechanism 20 allowing its movement in the head-pressing direction relative to the side frames 11.
Pressing mechanism 30 is comprised of a cum shaft 31 extending in the paper-width direction, a cum 32 provided in the middle part of cum shaft 31 in the paper-width direction, a press-spring 33 provided so as to contact with the lower part of cum 32, and a transmission frame 34 that transmits a pressing force W between this press-spring 33 and head support frame 22 of head support mechanism 20.
Cum shaft 31 is rotatably supported on support member 11a of side frames 11 through the pair of both ends shaft receiving part. Cum 32 is composed of a noncircular plate, of which distance from cum shaft 31 to the peripheral varies, and serves to press press-spring 33 downwardly as cum shaft 31 rotates. Press-spring 33, which is composed of, for example, a resiliently deformable leaf spring, deforms by being pressed by cum 32, pressing transmission frame 34 downwardly by the load caused by the deformation. Transmission frame 34, which is formed by an one-open ended rectangular plate member viewed from its front, presses head support frame 22 downwardly averaging the pressing force W from cum 32. Thermal head 12 is pressed downwardly by thus configured pressing mechanism 30 through head support frame 22 in the head-pressing direction against paper sheet 14 (or ink ribbon 15).
Referring to
In printing device 1, there arises a pressing force W by pressing mechanism 30 that presses thermal head 12 in the head-pressing direction downwardly in the figure. There also arises a frictional force F at print section P1 in the paper-conveyance direction along the X-axis by thermal head 12 and the conveyance of ink ribbon 15 or paper sheet 14. Based on a support point P3 at which thermal head 12 is supported by head support mechanism 20, there are produced a second rotational moment M2, by friction force F, that acts clockwise in the figure, and a first rotational moment M1, by pressing force W, that acts counterclockwise in the figure.
A pressing-force acting point P2 at which pressing force W is exerted to thermal head 12 is provided downstream of a supporting point p3, at which the thermal head is supported, in the paper-conveyance direction. That is, for example, as illustrated in
Furthermore, in printing device 1, the arrangement of head support mechanism 20, pressing mechanism 30, and print section P1 are set so that first rotational moment 141 produced by pressing force W and second rotational moment M2 produced by frictional force F between the printhead and, ink ribbon 15 or paper sheet 14 are cancelled by each other.
For example, in the example of
0.7≦M1/M2≦1.3 Expression 1
M1=(F′×L1) Expression 2
M2=(W′×L2) Expression 3
F′=μW cos θ1 Expression 4
W′=W cos θ2 Expression 5
where, θ1 denotes an angle subtended between the paper-conveyance direction and the line (dashed line) passing through print section P1 perpendicular to the line connecting supporting point p3 with print section P1, while θ2 denotes an angle subtended between the head pressing-direction and the line (arrowed dashed line) passing through pressing-force acting point P2 perpendicular to the line connecting supporting point p3 with pressing-force acting point P2, and μ denotes a dynamic friction coefficient between thermal head 12 and paper sheet 14 (ink ribbon 15).
According to the configuration described above, when platen roller 13 rotates in a state that thermal head 12 is pressed onto paper sheet 14 (or ink ribbon 15) with pressing force W exerted by press-spring 33, first rotational moment M1 derived from press-spring 33 that presses thermal head 12 to paper sheet 14 (or ink ribbon 15) and second rotational moment M2 derived from frictional force F that thermal head 12 receives by the sliding with paper sheet 14 (or ink ribbon 15) are mutually cancelled. Thus, the drag against pressing force W can be alleviated, and hence good printing pressure can be attained.
It is more preferable that first rotational moment M1 is set to be equal to second rotational moment M2 as meeting the expression below.
M1=M2 Expression 6
With this setting made, first rotational moment M1 can be balanced with second rotational moment M2 so that the two moments are mutually cancelled. Thus, the drag attributed to pressing force W can be eliminated and more suitable print pressure can be attained.
According to printing device 1 of the above-mentioned embodiment, a suitable print pressure can be easily attained only by adjusting the positions of head support mechanism 20, pressing mechanism 30, and print section P1. That is, since the setting is made so that pressing-force acting point P2 is positioned downstream of supporting point p3 in the paper-conveyance direction and first rotational moment M1 is balanced with second rotational moment M2, frictional force F between supporting shaft members 21 and slots 25 at supporting point p3 becomes reduced and hence the drag against pressing force W can be reduced. Consequently, the loss of pressing force W can be reduced or eliminated, and thus, a stable pressure can be provided. Accordingly, even when printing conditions by the nature of paper sheet 14 or environmental conditions are changed, stable printing can be performed.
Since the setting value of pressing force W can be lowered compared with the value given in the case that the drag occurred by the rotational moments, the energy required for the sheet conveyance can be reduced and hence a stable print pitch between pixels can be achieved. Moreover, since there is no need for setting a large value of pressing force W, adverse effects, such as cocking on ink ribbon 15, that are caused by application of an excess pressure onto an ink ribbon or else can be prevented. Thus, the print quality can be improved.
In the above embodiment expressions 1 to 6 are used. However, for example, conditional settings for the reference positions P1 to P3 as the references, the magnitudes or directions of forces F′ and W′ may be appropriately altered as needed depending upon various conditions of configurations or arrangements of printing devices or paper sheet 14.
In the above embodiment, pressing mechanism 30 was exemplified by the configuration using cum 32 and press-spring 33. However, other type of a pressing mechanism, e.g., a coil spring expandable by a magnitude of a load can be used. Furthermore, an example for head support mechanism 20 was shown by supporting by the engagement of supporting shaft members 21 in plural slots 25. However, the mechanism need not be restricted to this. Head support mechanisms with different configurations, e.g., a structure having mutually slidable rails can be employed.
In the above embodiment, an example was shown in which ink ribbon 15 as the object is provided between thermal head 12 and paper sheet 14. In place of this example, a thermosensitive recording paper having a thermal sensitive layer developing color by heat can be used as the object instead of an ink ribbon.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-214874 | Sep 2009 | JP | national |
