EP2060400B1

EP2060400B1 - Sheet feed mechanism of printer, and printer

Info

Publication number: EP2060400B1
Application number: EP08017834.6A
Authority: EP
Inventors: Toshiyuki Yamamoto
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 2007-11-15
Filing date: 2008-10-10
Publication date: 2016-02-17
Anticipated expiration: 2028-10-10
Also published as: US20090127777A1; CN101434153A; JP4943997B2; CN101434153B; JP2009120338A; EP2060400A3; EP2060400A2

Description

BACKGROUND

1. Technical Field

The present invention relates to a sheet feed mechanism of a printer according to the preamble of claim 1. This mechanism is constructed such that a sheet is conveyed by rotating a sheet feed roller while the sheet is sandwiched between the sheet feed roller and a sheet pressure-contact member. It also relates to a printer including the sheet feed mechanism.

2. Related Art

In the related art, thermal printers that make a plurality of heat-generating elements of a thermal head generate heat selectively on the basis of recording information, thereby performing recording on a recording medium, are widely utilized.
A sectional view of major portions in a related-art printer which performs desired recording using a thermosensitive recording medium is shown in Fig. 8.
The printer 1 is disposed in a desired position of a frame, and has a platen roller 2 which is rotationally driven under the transmission of the driving force of a driving motor M. A thermal head 3 is arranged above this platen roller 2. The thermal printer 3 is a line-type printer in which a plurality of heater elements are aligned and arranged on a metallic substrate in a direction orthogonal in plan view to a conveying direction of a thermosensitive recording medium (hereinafter simply referred to as "sheet") as a sheet provided for recording is used as this thermal head. At least during recording, the thermal head abuts on the platen roller 2 via the sheet 4. Also, during recording, a color is developed in a predetermined position of the sheet 4 to perform recording, by making each of the heat-generating elements of the thermal head 3 generate heat selectively on the basis of recording information (recording data). Also, during recording, the abutment position where the thermal head 3 abut on the platen roller 2 via the sheet 4 becomes a recording position PP.
Also, the sheet feed roller 6 which is rotationally driven at the same rotating speed as the platen roller 2 under the transmission of the driving force of the driving motor M is arranged on the downstream side (right in Fig. 8) in the conveying direction of the recording position PP. A sheet pressure-contact member 10 is arranged above the sheet feed roller 6 via a spring member 12 within the housing 11 for assembling of a printer such that it can press the sheet along with the sheet feed roller 6, and the sheet 4 pressed by the sheet feed roller 6 by the sheet pressure-contact member 10 is conveyed to the recording position PP along a sheet conveying path with the rotation of the sheet feed roller 6.
Meanwhile, in the printer 1 constructed in this way, when the trailing end of the sheet 4 conveyed is released from the pressure contact between the sheet feed roller 6 and the sheet pressure-contact member 10 (an event that pressing against the sheet 4 is released by conveyance hereinafter referred to as "roller slip-out"), the load to the sheet 4 changes abruptly, and sheet conveyance becomes uneven. Under the influence of these, there is a problem in that white lines are formed in recording results in recording positions. The load change which causes such a problem becomes large as sheet thickness becomes large. Thus, the conveyance of a sheet becomes poor under the influence of the load change. As a result, the possibility that white lines or the like are formed also becomes high.
As measures for solving such a problem, for example, it is considered that the number of steps of a motor which rotationally drive a sheet feed roller is changed by detecting roller slip-out timing by a sensor (Japanese Unexamined Patent Application Publication No. 2005-8343 ), and that selective application of an electric current to each of the heat-generating elements of a thermal head at the time of roller slip-out (Japanese Unexamined Patent Application Publication No. 2007-83500 ) is corrected.
However, in the related art disclosed in Japanese Unexamined Patent Application Publication Nos. 2005-8343 and 2007-83500 , the control for which even a difference in the load change which changes depending on the thickness of sheets to be used is taken into consideration is difficult, and the positive effect that conveyance is stabilized cannot be expected.
Moreover, a method of making the leading end of a sheet sandwiched between a pair of conveying rollers which are arranged to face the downstream in a sheet conveying direction from a recording position, and performing recording in a state where the pressure contact between a sheet feed roller and a sheet pressure-contact member at the trailing end of the sheet is released to remove the load to the sheet is also considered. However, according to the method, a margin equivalent to the distance of a sheet conveyed toward the downstream in the sheet conveying direction from the recording position before the start of recording is formed at the leading end of the sheet on which recording results are formed. Therefore, this method cannot be adopted in a case where recording results in which a margin is not formed are desired. Further, in connection with the sandwiching of a sheet by the conveying roller, a release mechanism which releases the pressing of the sheet pressure-contact member against the sheet feed roller becomes necessary, and the construction of the printer becomes complicated.
US 5 893 556 A discloses a sheet feed mechanism according to the preamble of claim 1. According to this prior art mechanism, a regulating member is disposed on a downstream side of a sheet forward roller and a pinch roller. Said regulating member guides the front end and the back end of the sheet and it also acts as a guide member to maintain the distance between the sheet and an ink jet head constant. The regulating member (sheet trailing end guide portion) extends over the overall width of the sheet and the sheet feed roller. Besides, the regulating member is offset in the downstream direction with respect to said pinch roller.
US 2007/252883 A1 discloses a mechanism in which plural guide rollers are provided at a downstream side of a feeding roller, wherein such guide rollers are disposed above a flat rear sheet guide.

SUMMARY

It is desirable to provide a sheet feed mechanism capable of preventing conveyance unevenness resulting from a change in load to a sheet at the time of roller slip-out, and a printer including the sheet feed mechanism, capable of obtaining excellent recording results.
According to an aspect of the invention, there is provided a sheet feed mechanism of a printer including the features of claim 1.
According to the sheet feed mechanism of the aspect of the invention, the sheet trailing end guide portion gradually guides the trailing end of the sheet released from pressure contact with the sheet feed roller, along the guide surface toward the downstream in the sheet conveying direction. Thereby, an abrupt change in the load applied to a sheet can be suppressed and sheet conveyance unevenness can be reduced. Therefore, generation of poor recording results resulting from an abrupt load change at the time of roller slip-out of the trailing end of a sheet can be prevented. In that case, the sheet trailing end guide portion acts uniformly irrespective of the thickness of the sheet. In addition, in the aspect of the invention having a construction in which the sheet is conveyed by the sheet feed roller, and by the sheet pressure-contact member which makes pressure contact with the sheet feed roller via the sheet, it is possible to form desired recording, without providing a margin at the leading end of the sheet.
Further, in the sheet feed mechanism of the invention, the sheet trailing end guide portion is formed at least at one of both axial ends of the sheet feed roller so as to project a sheet guide surface constituting the sheet conveying path to be lower than the apex of the sheet feed roller, and so as to project toward the downstream in the sheet conveying direction farther than a downstream end of the sheet feed roller in the sheet conveying direction.
According to the sheet feed mechanism of the invention, the sheet trailing end guide portion catches the trailing end of the sheet released from pressure contact with the sheet feed roller, in a position which is higher than the sheet guide surface and lower than the apex of the sheet feed roller, and gradually guides it along the guide surface toward the downstream in the sheet conveying direction. Thereby, an abrupt change in the load applied to a sheet can be suppressed and sheet conveyance unevenness can be reduced.
Further, in the sheet feed mechanism of the aspect of the invention, a plurality of the sheet feed rollers may be arranged in series in the direction orthogonal to the sheet conveying direction, and one or a plurality of sheet feed rollers corresponding to the width dimensions of sheets are used to convey the sheets.
For example, in a case where the sheet feed mechanism is adopted in a printer which enables recording on a plurality of kinds of sheets having dimensions, i.e., width dimensions, which are made different in the direction orthogonal to the sheet conveying direction, it is considered that a plurality of sheet feed rollers are arranged in series in order to correspond to the width dimension of each sheet. Even in this case, the aforementioned operational effects can be obtained by forming a sheet trailing end guide portion at least at one side of both axial ends of each sheet feed roller corresponding to the width dimension of each sheet.
Also, in the sheet feed mechanism of the invention, the sheet trailing end guide portion is formed as a circular-arc convex portion in a section in the sheet conveying direction.
According to the sheet feed mechanism of the invention, the trailing end of a sheet can be gradually guided toward the downstream in the sheet conveying direction along the guide surface which inclines substantially obliquely downward in a circular-arc shape in section in the sheet conveying direction, which constitutes the convex portion.
Moreover, according to another aspect of the invention, a printer includes the sheet feed mechanism having any one of the aforementioned constructions.
According to the printer of the aspect of the invention, the sheet feed mechanism can reduce a change in the load to a sheet at the time of roller slip-out, thereby preventing conveyance unevenness of the sheet. Thus, excellent recording can be obtained.
As mentioned above, according to the printer of the aspect of the invention, a change in the load to a sheet at the time of roller slip-out can be reduced, thereby preventing conveyance unevenness of the sheet, and excellent recording can be obtained. Moreover, according to the printer of the aspect of the invention, including such a sheet feed mechanism, it is possible to exhibit an excellent effect that the printer is suitable as a printer which obtains recording results in which a margin is not formed at the leading end of the sheet in the sheet conveying direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view of major portions in a sheet feed mechanism and a printer according to an embodiment of the invention;
Fig. 2 is a sectional view of the major portions in the sheet feed mechanism and the printer according to the embodiment of the invention (a sectional view of the printer taken along a line II-II of Fig. 1);
Fig. 3 is an enlarged explanatory view (a dimensional view) of the major portions in the sheet feed mechanism and the printer according to the embodiment of the invention;
Fig. 4 shows another arrangement position relationship between a sheet feed roller and sheet trailing end guide portions in the sheet feed mechanism according to a second embodiment;
Fig. 5 shows still another arrangement position relationship between the sheet feed roller and the sheet trailing end guide portions in the sheet feed mechanism according to a third embodiment;
Fig. 6 shows a still further arrangement position relationship between the sheet feed roller and the sheet trailing end guide portions in the sheet feed mechanism according to a fourth embodiment;
Fig. 7 shows a still further arrangement position relationship between the sheet feed roller and the sheet trailing end guide portions in the sheet feed mechanism according to a fifth embodiment; and
Fig. 8 is a sectional view of major portions in a sheet feed mechanism and a printer in the related art.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A printer including a sheet feed mechanism according to embodiments of the invention will be explained with reference to Figs. 1 to 7. In addition, embodiments of the sheet feed mechanism of the invention which become a characterizing portion of the printer of the invention will mainly explained below. Other components of the printer which are not mentioned shall be constructed and act similarly to the aforementioned related-art printer.
A printer of a first embodiment of the invention is a printer which makes an electrical current applied to heat-generating elements of a thermal head made to abut on a thermosensitive recording sheet (hereinafter referred to as a "sheet") with a single width dimension, thereby performing desired recording.
In the printer 1 of this embodiment, as shown in the plan view of major portions of Fig. 1, and in a sectional view (sectional view taken along the line II-II of Fig. 1) of major portions of Fig. 2, one rectangular opening 8 for arrangement of a sheet feed roller extending in a direction (this direction is hereinafter referred to as a "width direction") orthogonal to a sheet conveying direction is formed in a central portion in the width direction in a sheet guide surface 7 which constitutes a sheet conveying path on the downstream side in the sheet conveying direction in the recording position PP, and also serves as a sheet placement base. Also, the sheet feed roller 6 is arranged so as to be rotatable about an axis in the direction orthogonal to the sheet conveying direction in plan view such that its apex is made to project from the opening 8 for arrangement of a sheet feed roller to the sheet guide surface 7, and is made to face the sheet conveying path.
Also, convex sheet trailing end guide portions 9 which project lower than the apex of the sheet feed roller 6 from the sheet guide surface 7, which project toward the lower end in the sheet conveying direction farther than the downstream end of the sheet feed roller 6 in the sheet conveying direction, and which have guide surfaces which gradually guide the trailing end of a sheet released from abutment on the sheet feed roller 6, toward the downstream in the sheet conveying direction from the sheet feed roller 6 are respectively formed at both ends of the opening 8 for arrangement of a sheet feed roller in the sheet guide surface 7 which become both end sides in the axial direction of the sheet feed roller 6. In detail, in this embodiment, the sheet trailing end guide portions 9 are formed in a circular-arc semi-cylindrical shape in a section in the sheet conveying direction, and are integrally formed with the sheet guide surface 7 from a resin material in substantially symmetrical positions in the conveying path from the center in the width direction in the conveying path of a sheet 4. Also, the sheet feed mechanism in this embodiment is constituted by the sheet feed roller 6, the sheet trailing end guide portions 9, and a sheet pressure-contact member 10 arranged via a spring member 12 within the housing 11 for assembling of a printer.
In addition, as the concrete dimensions of the sheet feed mechanism in this embodiment, as shown in Fig. 3, in a case where sheet thickness is set to 0.25 mm, the projecting dimension of the sheet trailing end guide portions 9 which projects from the sheet guide surface 7 is set to 0.3 mm which is large than the sheet thickness, and the projecting dimension of the sheet feed roller 6 which projects from the sheet guide surface 7 preferably has almost the same dimension as a sum of the projecting dimension of the sheet trailing end guide portions 9, and the sheet thickness. In this embodiment, the projecting dimension is set to 0.5 to 0.6 mm.
In the printer 1 including the sheet feed mechanism of this embodiment in which such sheet trailing end guide portions 9 are formed, a single-cut sheet 4 which is paid out one by one from the sheet placement portion is brought into pressure contact with the sheet feed roller 6 by the sheet pressure-contact member 10. The sheet 4 brought into pressure contact with the sheet feed roller 6 by the sheet pressure-contact member is conveyed toward the downstream in the sheet conveying direction by the frictional force with the sheet feed roller 6 and supplied to a printing position PP, with the rotational driving of the sheet feed roller 6 which receives the transmission of the driving force of a driving motor M. As such, in the embodiment of the invention having a construction in which the sheet 4 is conveyed by the sheet feed roller 6, and by the sheet pressure-contact member 10 which makes pressure contact with the sheet feed roller 6 via the sheet 4, it is possible to form desired recording, without providing a margin at the leading end of the sheet 4. That is, in the printing position PP, the leading end of the sheet 4 is sandwiched between the platen roller 2 and the thermal head 3, and an electric current is selectively applied to the heat-generating elements of the thermal head 3 made to abut on the sheet 4, in accordance with the conveyance of the sheet 4 by the rotative force of the sheet feed roller 6, thereby performing desired recording from the leading end of the sheet. Simultaneously with this, the sheet is conveyed toward the downstream in the sheet conveying direction by the rotation of the platen roller 2 which is rotationally driven in synchronization with the sheet feed roller 6 under the transmission of the driving force of the driving motor M.
When the desired recording progresses, and the trailing end of the sheet is released from the pressure contact between the sheet feed roller 6 and the sheet pressure-contact member 10, i.e., at the time of roller slip-out-out of the trailing end of the sheet, in the printer 1 of this embodiment, the pair of sheet trailing end guide portions 9 catches the trailing end of the sheet released from the pressure contact with the sheet feed roller 6 in a position which is higher than the sheet guide surface 7 and lower than the apex of the sheet feed roller 6, and then gradually guides the trailing end of the sheet 4 conveyed by the rotational driving of the platen roller 2, along the circular-arc guide surface toward the downstream in the sheet conveying direction. Thereafter, the sheet 4 conveyed by the rotational driving of the platen roller 2 is subjected to desired recording in the recording position PP, and is ejected from the sheet conveying path.
As such, in the sheet feed mechanism and printer of this embodiment, an abrupt change in the load to be applied to the sheet 4 at the time of roller slip-out-out can be reduced by the sheet trailing end guide portions 9. Therefore, even at the time of roller slip-out-out, the abrupt load change does not affect a recorded state in the recording position PP, but sheet conveyance unevenness can be suppressed to prevent generation of poor recording results. In that case, the sheet trailing end guide portions 9 act uniformly irrespective of the thickness of the sheet 4.
Further, in the sheet feed mechanism of this embodiment, the sheet trailing end guide portions 9 are formed in the substantially symmetrical positions within the conveying path from the center in the width direction in the conveying path of the sheet 4. Thus, after the trailing end of the sheet has slipped out of the roller, the sheet will be caught by the sheet trailing end guide portions 9 in the symmetrical positions from the center in the width direction of the sheet 4. Therefore, an abrupt load change can be reduced substantially uniformly and surely in the width direction of the sheet 4. That is, an abrupt load change can be reduced more substantially uniformly and surely in the width direction of the sheet 4 than the end of the sheet is caught in a cantilevered shape on one side of the sheet 4, by the sheet trailing end guide portions 9.
In addition, in the sheet feed mechanism of the first embodiment, as shown in Fig. 4, the sheet feed roller 6 may be arranged so as to be split into a plurality of pieces in the width direction, and the sheet trailing end guide portions 9 may be arranged on both sides of each sheet feed roller 6 (second embodiment).
In that case, one sheet trailing end guide portion 9 may be arranged between two adjacent sheet feed rollers 6, as shown in Fig. 5 (third embodiment).
Moreover, as shown in Fig. 6, the trailing end guide portions 9 are not formed on both sides of the sheet feed roller 6, respectively, but only one trailing end guide portion may be arranged between two adjacent rollers 6 (fourth embodiment) . However, like Fig. 6, it is preferable that a plurality of sheet trailing end guide portions 9 be formed in the width direction of the sheet 4 rather than forming one sheet trailing end guide portion. It is more preferable that the plurality of sheet trailing end guide portions 9 being arranged with the same dimension and at equal intervals in the width direction of the sheet 4. This is because an abrupt load change can be reduced substantially uniformly and surely in the width direction of the sheet 4.
Moreover, in the printer 1 in which sheets 4 with a plurality of width dimensions can be provided for recording, a plurality of the sheet feed rollers 6 which vary in axial dimension are arranged in series in a direction orthogonal to the sheet conveying direction in order to correspond to the width dimensions of sheets 4 expected to be used, and one or a plurality of sheet feed rollers 6 corresponding to the width dimensions of the sheets 4 may be used to convey the sheets 4 (fifth embodiment). Specifically, as shown in Fig. 7, in the case of the printer 1 using three kinds of sheets including a sheet4 A having "A" as its width dimension, a sheet 4B having "B" as its the width dimension, and a sheet 4C having "C" as its width dimension (the width dimensions are A < B < C), three sheet feed rollers 6 including a sheet feed roller 6A made to correspond to a sheet 4A, a sheet feed roller 6B used simultaneously with the sheet feed roller 6A and made to correspond to the sheet 4B, and a sheet feed roller 6C used simultaneously with the sheet feed rollers 6A and 6B, and made to correspond to the sheet 4C are arranged in series in the direction orthogonal to the sheet conveying direction. In that case, the sheet feed roller 6A is located within the sheet conveying paths of the sheet 4A, the sheet 4B, and the sheet 4C, the sheet feed roller 6B is located within the sheet conveying paths of the sheet 4B and the sheet 4C, and the sheet feed roller 6C is located only within the sheet conveying path of the sheet 4C. In addition, this embodiment is similar to the aforementioned embodiments in that the sheet feed rollers 6A, 6B, and 6C are arranged such that their apexes are made to project from openings 8A, 8B, and 8C for arrangement of sheet feed rollers, which are formed in the sheet guide surface 7, corresponding to the sheet feed rollers, respectively, and the sheet end guide portions 9 are arranged aside the sheet feed rollers 6A, 6B, and 6C in the width direction.
Even in this case, as mentioned above, an abrupt change in the load applied to the sheet 4 can be reduced and sheet conveyance unevenness can be suppressed to obtain excellent recording results, by the sheet trailing end guide portions 9 formed aside the sheet feed roller 6 in the direction orthogonal to the sheet conveying direction of the sheet feed roller corresponding to the width of each sheet 4.
In addition, the invention is not limited to the aforementioned embodiments, and various changes thereof can be made if necessary.
For example, in this embodiment, the printer has been described using a printer which performs desired recording on a thermosensitive recording medium. However, the sheet feed mechanism of the embodiments of the invention can be applied to a thermal printer using ink sheets, etc. Furthermore, the shape of the sheet trailing end guide portions is not limited to the circular-arc semi-cylindrical shape in a section in the sheet conveying direction like the aforementioned embodiment. The guide surface may be an inclined surface which is not circular-arc but flat.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alternations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims.

Claims

A sheet feed mechanism of a printer comprising:
a sheet guide surface constituting a sheet conveying path;

a sheet feed roller (6) arranged so as to be rotatable about an axis in a direction orthogonal to a sheet conveying direction in plan view such that its apex is made to face a sheet conveying path on the downstream side in the sheet conveying direction;

a sheet pressure-contact member (10) arranged to be capable of pressing a sheet (4) against the sheet feed roller (6); and

a sheet trailing end guide portion (9) having a guide surface which catches a trailing end of the sheet released from abutment on the sheet feed roller (6) in a position which is higher than the sheet guide surface and lower than the apex of the sheet feed roller (6) and gradually guides the trailing end of the sheet (4) toward the downstream in the sheet conveying direction,

characterized in that the sheet trailing end guide portion (9) is formed at least at one of both axial ends of the sheet feed roller (6) so as to project from the sheet guide surface and to project toward the downstream in the sheet conveying direction farther than a downstream end of the sheet feed roller (6) in the sheet conveying direction, and the sheet trailing end guide portion (9) is formed as a circular-arc convex portion in a section in the sheet conveying direction.
The sheet feed mechanism of a printer according to claim 1 characterized in that a plurality of the sheet feed rollers (6) are arranged in series in the direction orthogonal to the sheet conveying direction, and one or a plurality of sheet feed rollers (6) corresponding to the width dimensions of sheets are used to convey the sheets (4).
The sheet feed mechanism of a printer according to claim 1 or claim 2.
characterized in that projecting dimension of the sheet feed roller which projects from the sheet guide surface has almost the same dimension as a sum of projecting dimension of the sheet trailing end guide portions (9) and sheet thickness.
A printer that is provided with the sheet feed mechanism according to any of claims 1, 2, and 3.