Title of Invention

PRINTER

Abstract

A transporting path is adapted to transport a printing medium in a first direction. A guide member forms a part of the transporting path and has an opening. A photosensor is provided with a light emitting element and a light receiving element and is disposed in the opening. A protrusion is protruded from a part of the first guide member, which is adjacent to at least a first edge of the opening that is located in an upstream side relative to the first direction. The protrusion is adapted to shield the light receiving element from ambient light entering the transporting path.

Full Text

PRINTER BACKGROUND OF THE INVENTION The present invention relates to a printer equipped with a reflection type photosensor for detecting a recording sheet being transported along a sheet transporting path. In a printer adapted to perform printing on a rolled sheet, a loading section, into which the rolled sheet is loaded, is opened when a door cover attached to a casing body is opened. After a rolled sheet (recording sheet) is loaded into the loading section, a leading end of the rolled sheet is drawn out and inserted into an inlet located at an upstream end of a sheet transporting path. The inserted rolled sheet is detected by a sheet detector located in the vicinity of the inlet, and a sheet feeding roller located in a downstream side of the sheet detector is rotated to feed the leading end of the rolled sheet to a predetermined position along the sheet transporting path. Thereby, a printing standby state is effected. A reflection type photosensor is generally used as the sheet detector In the absence of the recording sheet, the received light quantity of the photosensor is not higher than a predetermined threshold value. When the recording sheet is passed, the received light quantity of the photosensor is switched into a state exceeding the threshold value by the light reflected on the recording sheet surface. Thus, the presence/absence of the recording sheet is detected on the basis of the change in the received light quantity. In such a printer, at the time of loading or exchanging the rolled sheet, the door cover is opened to open the loading section and the inlet of the sheet transporting path. Thus, the ambient light such as the sunlight may enter the sheet transporting path from the inlet. When the ambient light directly or indirectly irradiates the light receiving face of the photosensor arranged in the sheet transporting path, the received light quantity of the photosensor may exceed the threshold value. Then, a false detection of the insertion of the recording sheet may be made although the recording sheet is not inserted. SUMMARY OF THE INVENTION It is therefore an object of the invention to provide a printer in which a sheet detector (photosensor) of a reflection type can be prevented from being caused to function falsely by disturbance light. In order to achieve the above object, according to the invention, there is provided a printer, comprising: a transporting path, adapted to transport a printing medium in a first direction; a first guide member, forming a first part of the transporting path and having an opening; a photosensor, comprising a light emitting element and a light receiving element and disposed in the opening; and a protrusion, protruded from a part of the first guide member which is adjacent to at least a first edge of the opening which is located in an upstream side relative to the first direction, the protrusion being adapted to shield the light receiving element from ambient light entering the transporting path. At least a second edge of the opening which is located in a downstream side relative to the first direction may have a slant face adapted to reflect light incident thereon so as to deviate from the light receiving element. The light receiving element may be located in the vicinity of the protrusion. The printer may further comprise a second guide member, forming a second part of the transporting path. A part of the second guide member confronting the photo sensor may be recessed. The printer may further comprise a cover, movable between a first position for opening an upstream end of the transporting path and a second position for covering the upstream end. A line extending parallel to the transporting path at the upstream end may cross the cover placed in the first position. The opening may be located in the vicinity of the upstream end of the transporting path. With the above configurations, the light receiving element of the photosensor can be shielded from the direct incidence of the ambient light by the protrusion. In addition, the light receiving element can be shielded from the indirect incidence of reflected light of the ambient light entering the transporting path by the slant face. Therefore, it is possible to reliably prevent the photosensor from being caused to function falsely by the ambient light. BRIEF DESCRIPTION OF THE DRAWINGS The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: Fig. 1 is a perspective view of a printer according to one embodiment of the invention, showing a state that a door cover is closed; Fig. 2 is a perspective view of the printer, showing a state that the door cover is opened; Fig. 3 is a section view taken along a line Ill-Ill in Fig. 2; Fig. 4A is an enlarged section view of a sheet transporting path of the printer; Fig. 4B is a plan view of a sheet guide and a photosensor provided in the sheet transporting path; and Fig. 5 is a schematic side view of a printer according to a second embodiment of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiments of the invention will be described below in detail with reference to the accompanying drawings. A printer 1 according to one embodiment of the invention comprises an elongated box-shaped body 2. This body 2 comprises a casing body 3 and a door cover 4, This door cover 4 is so hinged at its rear end portion to the casing body 3 as to pivot about a pivot shaft extending in the printer width direction, so that it is pivotable between a dosed position 4A shown in Fig. 1 to a fully opened position 4B shown in Fig. 2. A sheet ejecting slot 4a is formed in the center portion of the door cover 4, A printing unit 5 is mounted in the casing body 2 at a front half portion, and a sheet loading section 6 is formed in the rear half portion of the same. When the door cover 4 is opened, the sheet loading section 6 is exposed to the outside so that a rolled sheet (not-shown) can be loaded from above the sheet loading section 6. A sheet transporting path 7 is formed in the printing unit 5. As shown in Fig. 3, the sheet transporting path 7 is defined at its upstream portion by a pair of upper and lower sheet guides 8 and 9 each of which obliquely extends such that a front end thereof is directed downward. These sheet guides 8 and 9 have their upstream side ends opened to form an inlet 7a to accept a recording sheet 10 (represented by a chain line), which is drawn from the sheet loading section 6. At a position near the inlet 7a in the lower sheet guide 9, there is formed an opening 11, in which is mounted a reflection type photosensor 12 for detecting the recording sheet 10-- At the downstream side end portions of the sheet guides 8 and 9, a sheet feeding roller 13 is arranged on the upper side, and a press roller 14 is abutted against the sheet feeding roller 13 from the lower side. A sheet guide 15 extends upward from the sheet feeding roller 13 and serves as a platen 16 confronting a printing head 17. The sheet ejecting slot 4a is positioned above the upper end of the sheet guide 15. A manual cutter 18 is mounted at a position near the sheet ejecting slot 4a. A leading end portion of the recording sheet 10 is cut off, as it is ejected from the sheet ejecting slot 4a, along a blade (or a cutting position) 19 of the manual cutter 18 extending in the printer width direction. The recording sheet 10 drawn from the rolled sheet loaded in the loading section 6 is guided into the sheet transporting path 7 via the inlet 7a. The recording sheet 10 is then transported along the sheet transporting path 7 by the sheet feeding roller 13, and guided to the sheet ejecting slot 4a via the printing position defined by the printing head 17, Finally, the recording sheet 10 is ejected upward from the sheet ejecting slot 4a. The printing head 17 of this embodiment is a dot impact head. The printing head 17 is mounted on a head carriage 21, which can reciprocally move along a guide shaft 22 spanned in the printer width direction. A cassette loading section 23 is formed in front of the head carriage 21. When the door cover 4 is opened, the cassette loading section 23 is exposed so that an ink ribbon cassette 24 can be removably loaded from above. As shown in Figs. 4Aand 4B, on the surface 9a of the sheet guide 9, there are formed ribs 9b arranged at a fixed pitch and extending in the sheet transporting direction, so that their top faces define a lower-side sheet guide face. The surface of the upper-side sheet guide 8 provides a flat sheet guide face in its entirety but for its downstream portion, A part 8a of the sheet guide face 8, opposing the photosensor 12, is recessed. Moreover, a downstream end part 8b continuing downward from the recessed part 8a is so gradually bulged toward the sheet transporting path 7 so that the leading end of the recording sheet 10 may not be caught The sheet guide 9 is formed with an opening 11, which is a rectangular through hole. A detecting section 12c of the photosensor 12, provided with a light emitting element 12a and a light receiving element 12b, is fitted into the through hole from below. A transparent window 12d of the detection unit 12c faces the inside of the sheet transporting path 7 through the opening 11. In this embodiment, the light receiving element 12b is arranged in an upstream side relative to the sheet transporting direction, and the light emitting element 12a is arranged in a downstream side. Moreover, the window 12d of the detection unit 12c is slightly retracted from the surface 9a of the sheet guide 9. Inner faces 11a, 11b, 11c and 11 d of the opening 11 are perpendicular to the surface 9a of the sheet guide 9. A protrusion 11 e (hatched section A in Fig. 4B) is formed so as to protrude from the surface 9a in the vicinity of the upstream inner face 11a of the opening 11. The protrusion 11 e extends so as to connect the ribs 9b. That is, it extends entirely across the opening 11. The height of the protrusion 11e is set, as shown in a chain line in Fig. 4A, such that an ambient light L may not irradiate the light receiving face of the light receiving element 12b of the photosensor 12, when the light L comes-into the sheet transporting path 7. In this embodiment, the protrusion 11 e is made flush with the ribs 9b so that it may not obstruct the transfer of the recording sheet 10. As shown in Fig, 4A, a top end portion of the downstream inner face 11b is entirely tapered so as to form a slope face 11f (hatched section B in Fig. 4B) angled from a normal line of the surface 9a by about 45 degrees. Even if the ambient light L entering the sheet transporting path 7 impinges upon the slope face 11f, the light reflected from the slope face 11f goes in directions away from the light receiving face of the photosensor 12. As a result, the ambient light reflected at the edge portions of the opening 11 will not enter the light receiving face of the photosensor 12. Here, the protrusion 11e for shielding the ambient light may be formed adjacent to the side inner faces 11b, 11c of the opening 11. Further, top end portions of the side inner faces 11b, 11c may be tapered. The areas for forming the protrusion 11e and the slope face 11f may be properly determined in accordance with the incident state of the ambient light. In this embodiment, the door cover 4 is opened at the time of loading a rolled sheet 10 (recording sheet). When the door cover 4 is opened, the loading section 6 and the inlet 7a of the sheet transporting path 7 are opened, as shown in Fig. 2. In this state, the rolled sheet 10 is loaded in the loading section 6. Next, the operator pulls out a leading end portion of the rolled sheet 10 and inserts it into the sheet transporting path 7 from the inlet 7a, When the leading end portion of the recording sheet 10 reaches the nipping portion of the sheet feeding roller 13, it is detected by the photosensor 12. In the-absence-of- the recording sheet 10; more specifically,, the- light emitted from the light emitting element 12a of the photosensor 12 is not received by the light receiving element 12b so that the quantity of the received light remains lower than a threshold value. When the recording sheet 10 is inserted, the emitted light is reflected on the surface of the recording sheet 10 and is incident on the light receiving element 12a. As a result, the quantity of the received light exceeds the threshold value, and it is detected on the basis of the excess that the recording sheet 10 has been inserted. The sheet feeding action by the sheet feeding roller 13 is then started at a predetermined timing, and the recording sheet 10 is transported by a predetermined stroke along the sheet transporting path 7 until its leading end is positioned at the cutting position 19 of the manual cutter 18. This establishes a print ready state. Here, this rolled sheet loading operation is carried in the state that the door cover 4 is opened. As a result, the ambient light, such as sunlight, may come from the inlet 7a of the sheet transporting path 7 in the open state into the sheet transporting path 7, In this embodiment, however, the protrusion 11e is formed adjacent to the upstream edge of the opening 11 in which the photosensor 12 is mounted. As a result, the ambient light toward the light receiving face of the photosensor 12 is shielded by the protrusion 11e. On the other hand, the ambient light reaching the downstream edge of the opening 11 is reflected by the slope face 1if, in a direction different from the light receiving face of the photosensor 12. As a result, the ambient light having entered the inside of the sheet transporting path 7 is prevented from indirectly entering the light receiving face. At the time of loading the recording sheet 10, moreover; either the ambient light reflected on the slope face 11f or the ambient light reflected by the loaded recording sheet 10 may be reflected by the upper sheet guide 8 and becomes incident on the light receiving face, before the leading end portion of the recording sheet 10 covers the light receiving face of the photosensor 12. However, since the part 8a of the upper sheet guide 8, opposing the photosensor 12, is recessed, it is possible to reduce the influences of the reflected light from the upper sheet guide 8 upon the photosensor 12. Especially in this embodiment, the depth of the recessed part 8a is not less than the clearance of the sheet transporting path 7 so that the influences can be substantially neglected. Therefore, even when the ambient light enters the sheet transporting path 7 at the loading time of the recording sheet 10, the ambient light will not be incident on the light receiving face of the photosensor 12. As a result, it is possible to precisely detect whether or not the recording sheet 10 is inserted into the sheet transporting path 7. In this embodiment, since the light receiving element 12b is arranged on the side closer to the protrusion 11e, even if the protrusion 11e is not high, the ambient light can be more reliably prevented from entering the light receiving face of the light receiving element 12b. Next, a second embodiment of the invention will be described. Components similar to those in the first embodiment will be designated by the same reference numerals and repetitive explanations for those will be omitted. In this embodiment, as shown in Fig. 5, the door cover 4 in an opened state serves to shield the ambient light, which might otherwise enter the sheet transporting-path 7; Specifically, in a printer 1A of this embodiment, an extension line 7A extending upstream of the sheet transporting path 7 is set to cross the upper end portion of the door cover 4 at the opened position 4B. In other words, the ambient light in the direction to enter the sheet transporting path 7 is shielded by the upper end portion of the door cover 4, Thus, a disturbance light can be more reliably prevented from being incident onto the light receiving face of the photosensor 12, thereby to more reliably prevent the malfunction of the photosensor due to the disturbance light. Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.

Documents:

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0718-che-2006 abstract-duplicate.pdf

0718-che-2006 claims-duplicate.pdf

0718-che-2006 description (complete)-duplicate.pdf

0718-che-2006 drawings-duplicate.pdf

718-CHE-2006 CORRESPONDENCE OTHERS.pdf

718-CHE-2006 CORRESPONDENCE PO.pdf

718-che-2006-abstract.pdf

718-che-2006-claims.pdf

718-che-2006-correspondnece-others.pdf

718-che-2006-description(complete).pdf

718-che-2006-drawings.pdf

718-che-2006-form 1.pdf

718-che-2006-form 3.pdf

718-che-2006-form 5.pdf

718-che-2006-prioritydocument.pdf