Sheet feeding device

This Nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2008-144139 filed in Japan on Jun. 2, 2008, the entire contents of which are hereby incorporated by reference.

The present invention relates to a sheet feeding device for feeding recording sheets to a copier or the like.

A sheet feeding device of a certain type includes a restricting section, a displacement section, and a link section and identifies the size of a recording sheet placed on a sheet support (see Japanese Patent Laid-Open Publication No. HEI 11-139572). The restricting section restricts the position of the recording sheet placed on the sheet support by abutting against an edge of the recording sheet. The link section interlinks the restricting section and the displacement section to displace the displacement section in accordance with a sliding movement of the restricting section. The position of the displacement section is detected by a sensor.

Japan and European countries generally adopt ISO•JIS as industrial standards for recording sheets, while North American countries generally adopt International Standards. Sizes of recording sheets conforming to ISO•JIS include A4 size and B5 size. Sizes of recording sheets conforming to International Standards include letter size and legal size. A4 size is 210×297 mm. B5 size is 182×257 mm. Letter size is 215.9×279.4 mm. Legal size is 215.9×355.6 mm.

A standard sheet of A4 size (hereinafter will be referred to as “A4 sheet”), a standard sheet of letter size (hereinafter will be referred to as “letter sheet”) and a standard sheet of B5 size (hereinafter will be referred to as “B5 sheet”) have their respective long side dimensions which are approximate to each other. The difference in long side dimension between A4 sheet and letter sheet is smaller than the difference in long side dimension between letter sheet and B5 sheet. For this reason, a sheet feeding device meeting both of ISO•JIS and International Standards is likely to cause an error in identifying the sizes of A4 sheet and letter sheet. If the linkage between the displacement section and the restricting section is highly precise and, at the same time, the resolution of the sensor is high, the sheet feeding device mentioned above can realize size identification with high precision. However, some levels of dimensional precision of each of the restricting section, gear member and displacement section make it difficult to link the position of the displacement section to that of the restricting section.

A feature of the present invention is to provide a sheet feeding device capable of identifying the sizes of standard sheets with high precision irrespective of the level of dimensional precision of each of the restricting section, gear member and displacement section.

A sheet feeding device according to the present invention includes a sheet support, a restricting section, a displacement section, and a link section. A recording sheet is placed on the sheet support. The restricting section slides along a line passing through at least three restricting points on the sheet support. The restricting section restricts the position of the recording sheet by abutting against an edge of the recording sheet when the restricting section is positioned at each of the restricting points. The displacement section is provided with the sheet support, and the position of the displacement section is detected by a sensor. The link section, which interlinks the restricting section and the displacement section, is configured to change a ratio of a distance that the displacement section travels as the restricting section travels a fixed distance, wherein the ratio of the distance between those restricting points which define a relatively large spacing therebetween becomes longer than the ratio of the distance between those restricting points which define a relatively small spacing therebetween.

The foregoing and other features and attendant advantages of the present invention will become more apparent from the reading of the following detailed description of the invention in conjunction with the accompanying drawings.

FIG. 1 is a schematic front elevational view showing a copier provided with a sheet feeding device according to a first embodiment of the present invention;

FIG. 2A is a schematic plan view showing a sheet feed cassette included in the sheet feeding device;

FIG. 2B is a schematic bottom view of the sheet feed cassette;

FIG. 2C is a schematic side elevational view showing a side of the sheet feed cassette indicated by a dashed double-dotted line of FIG. 2B ;

FIG. 2D is a schematic side elevational view showing a side of the sheet feed cassette indicated by a dashed dotted line of FIG. 2B ;

FIG. 3 is a view illustrating the positional relationship between a rack included in the sheet feed cassette and switches of a sensor for detecting the position of the rack;

FIG. 4 is a table showing the relationship between positions of the switches and classifications of standard sheets;

FIG. 5 is a schematic bottom view showing a gear member included in the sheet feed cassette;

FIG. 6 is a schematic sectional view of the gear member;

FIG. 7A is a view illustrating the gear member in a state assumed when A4 sheets are placed in the sheet feed cassette;

FIG. 7B is a view illustrating the gear member in a state assumed when letter sheets are placed in the sheet feed cassette;

FIG. 7C is view illustrating the gear member in a state assumed when B5 sheets are placed in the sheet feed cassette;

FIG. 8A is a diagram illustrating a first example of angles formed between the gear member and peripheral structures;

FIG. 8B is a diagram illustrating a second example of angles formed between the gear member and the peripheral structures;

FIG. 9A is a view illustrating the state of the gear member and the state of a comparative example which are assumed when A4 sheets are placed in the sheet feed cassette;

FIG. 9B is a view illustrating the state of the gear member and the state of the comparative example which are assumed when letter sheets are placed in the sheet feed cassette; and

FIG. 10 is a view illustrating an arrangement of a sheet feed cassette included in a sheet feeding device according to a second embodiment of the present invention.

Hereinafter, a sheet feeding device according to a first embodiment of the present invention will be described based on a copier provided with the sheet feeding device. FIG. 1 is a schematic front elevational view showing a copier according to the present embodiment.

A copier 100 forms a color or monochrome image in accordance with image data on a recording sheet by using four color (i.e., yellow, magenta, cyan and black) developers of a two-component system.

The copier 100 includes a sheet feed unit 110 , image forming units 130 A to 130 D, a laser scanning unit (LSU) 180 , an intermediate transfer unit 140 , a secondary transfer unit 150 , a fixing unit 160 , and a document reading unit 170 .

The document reading unit 170 reads color image data from a document placed on a platen. The color image data is color-separated into simple color image data items corresponding to respective of cyan, magenta, yellow and black by a non-illustrated image processing section. The LSU 180 applies laser beams to the image forming units 130 A to 130 D in accordance with the respective simple color image data items. The image forming units 130 A to 130 D form toner images of the respective colors. The intermediate transfer unit 140 includes an endless intermediate transfer belt. The toner images are transferred from the image forming units 130 A to 130 D to the intermediate transfer belt. The sheet feed unit 110 feeds each of recording sheets accommodated therein to the secondary transfer unit 150 . The secondary transfer unit 150 transfers a resulting toner image from the intermediate transfer belt to a recording sheet. The fixing unit 160 fixes the toner image onto the recording sheet by heat.

The sheet feed unit 110 , which is equivalent to the sheet feeding device defined by the present invention, includes a sheet feed cassette 1 . The sheet feed cassette 1 accommodates therein standard sheets of any one of the types including A4 sheet, B5 sheet and letter sheet.

FIG. 2A is a schematic plan view of the sheet feed cassette 1 . In FIG. 2A , the arrow indicates a sheet feed direction X toward a right-hand side surface of the sheet feeding device.

The sheet feed cassette 1 includes a sheet support 11 , wall portions 12 A to 12 D, slot portions 13 A to 13 C, and restricting portions 14 A to 14 C. The sheet support 11 is shaped like a rectangular flat plate. The wall portion 12 A extends along a side of the sheet support 11 which extends perpendicular to the sheet feed direction X and which lies on the side closer to the right-hand side surface of the device. The wall portion 12 B extends along a side of the sheet support 11 which extends parallel with the sheet feed direction X and which lies on the side closer to a front side surface of the device. The wall portion 12 C extends along a side of the sheet support 11 which extends perpendicular to the sheet feed direction X and which lies on the side closer to a left-hand side surface of the device. The wall portion 12 D extends along a side of the sheet support 11 which extends parallel with the sheet feed direction X and which lies on the side closer to a rear side surface of the device. The slot portion 13 A is vertically cut through the sheet support 11 and linearly shaped to extend parallel with the sheet feed direction X. The slot portions 13 B and 13 C are open on an upper surface of the sheet support 11 and are linearly shaped to extend perpendicular to the sheet feed direction X. The restricting portion 14 A, which is equivalent to the restricting section defined by the present invention, is mounted so as to be slidable along the slot portion 13 A. The restricting portion 14 B is mounted so as to be slidable along the slot portion 13 B. The restricting portion 14 C is mounted so as to be slidable along the slot portion 13 C.

When the restricting portion 14 A restricts the position of a standard sheet by abutting against a short side of an A4 sheet, the restricting portion 14 A is positioned at a first restricting point spaced about 297 mm from the wall portion 12 A, while the restricting portions 14 B and 14 C positioned as spaced about 210 mm from each other. When the restricting portion 14 A restricts the position of a standard sheet by abutting against a short side of a letter sheet, the restricting portion 14 A is positioned at a second restricting point spaced about 280 mm from the wall portion 12 A, while the restricting portions 14 B and 14 C positioned as spaced about 216 mm from each other. When the restricting portion 14 A restricts the position of a standard sheet by abutting against a short side of a B5 sheet, the restricting portion 14 A is positioned at a third restricting point spaced about 257 mm from the wall portion 12 A, while the restricting portions 14 B and 14 C positioned as spaced about 182 mm from each other.

The restricting portion 14 A may be configured to be capable of restricting standard sheets of other sizes, such as legal size, also. The restricting portion 14 A may be configured to abut against a long side of a standard sheet in order to restrict the position of the standard sheet. It is preferable that at least three restricting points defining adjacent spacings therebetween which are not equal to each other are established to restrict standard sheets.

FIG. 2B is a schematic bottom view of the sheet feed cassette 1 .

The sheet feed cassette 1 includes a gear member 17 , a slider 15 and a rack 21 which are disposed on the bottom side of the sheet support 11 .

The gear member 17 , which is equivalent to the link section defined by the present invention, has a teardrop outside shape as can be obtained by combining a semicircular shape and a substantially triangular shape. The semicircular portion has a toothed peripheral surface 19 , while the triangular portion defines a slit 18 therein. The gear member 17 is supported by a rotating shaft 20 extending through the center of the semicircular portion from a lower surface of the sheet support 11 .

The slider 15 is joined to the restricting portion 14 A through the slot portion 13 A and is slidable along the slot portion 13 A with movement of the restricting portion 14 A. The slider 15 has a slider pin 16 . The slider pin 16 is fitted in the slit 18 of the gear member 17 to form a sliding structure. As the restricting portion 14 slides, the slider pin 16 slides in the slit 18 of the gear member 17 with movement of the slider 15 , so that a component of a force exerted by the slider pin 16 on the internal wall of the slit 18 works as a torque to cause the gear member 17 to pivot about the rotating shaft 20 . The slider 15 and the slot portion 13 A are located substantially centrally of the sheet feed cassette 1 so as to provide a space around the sliding structure for preventing the tip of the gear member 17 from interfering with peripheral members.

FIG. 2C is a schematic side elevational view showing a side of the sheet feed cassette 1 indicated by a dashed double-dotted line as viewed in the direction of arrows C of FIG. 2B .

The rack 21 , which is equivalent to the displacement section defined by the present invention, has a portion projecting downwardly from a bottom surface of the sheet feed cassette 1 and formed with a toothed surface (not shown) meshing with the toothed peripheral surface 19 of the gear member 17 . The rack 21 , together with the gear member 17 , forms a rack and pinion mechanism. The rack 21 has a rack slot 21 A extending parallel with the sheet feed direction. The rack slot 21 A is fitted over a pin 31 projecting laterally from the wall portion 12 D. Therefore, the rack 21 is slidable along the sheet feed direction parallel with the slot portion 13 A. As the gear member 17 pivots clockwise, the rack 21 slides in the direction opposite to the sheet feed direction. As the gear member 17 pivots counterclockwise, the rack 21 slides in the sheet feed direction. Since the rack and pinion mechanism has a very small backlash, the position of the rack 21 follows varying angle of the gear member 17 with high precision.

FIG. 2D is a schematic side elevational view showing a side of the sheet feed cassette 1 indicated by a dashed dotted line as viewed in the direction of arrows D of FIG. 2B .

A sensor 22 is provided on the housing of the copier 100 and includes switches 22 A to 22 C on a track on which the rack 21 slides. When the rack 21 contacts any one of the switches 22 A to 22 C, the switch contacted by the rack 21 is pressed into the sensor 22 . The sensor 22 outputs standard size detection signals in accordance with positions of the switches 22 A to 22 C pressed in or not. Such a standard size detection signal is outputted to a control section of the copier 100 , which in turn performs a control meeting the standard size of a recording sheet thus detected.

FIG. 3 is a view illustrating the positional relationship between the rack 21 and the switches 22 A to 22 C. In FIG. 3 , the solid line depicts the rack 21 in a position assumed when the restricting portion 14 A restricts the position of an A4 sheet, while the dashed line depicts the rack 21 in a position assumed when the restricting portion 14 A restricts the position of a letter sheet.

FIG. 4 is a table showing the relationship between positions of the switches and classifications of standard sheets.

When the rack 21 is in the position assumed when the restricting portion 14 A restricts the A4 sheet, the rack 21 does not contact any one of the switches 22 A to 22 C and, hence, all the switches 22 A to 22 C are in their positions projecting from the sensor 22 . When the switches 22 A to 22 C assume these positions, the sensor 22 outputs a standard size detection signal indicative of A4 size to the control section of the copier 100 .

When the rack 21 is in the position assumed when the restricting portion 14 A restricts the letter sheet, the rack 21 contacts the switch 22 A and fails to contact the switches 22 B and 22 C and, hence, only the switch 22 A is pressed into the sensor 22 while the other switches 22 B and 22 C are in their positions projecting from the sensor 22 . When the switches 22 A to 22 C assume these positions, the sensor 22 outputs a standard size detection signal indicative of letter size to the control section of the copier 100 .

When the rack 21 is in the position assumed when the restricting portion 14 A restricts a B5 sheet, the rack 21 contacts the switches 22 A and 22 B and, hence, the switches 22 A and 22 B are pressed into the sensor 22 while the switch 22 C is in its position projecting from the sensor 22 . When the switches 22 A to 22 C assume these positions, the sensor 22 outputs a standard size detection signal indicative of B5 size to the control section of the copier 100 .

When the rack 21 is in the position in which the rack 21 contacts all the switches 22 A to 22 C, all the switches 22 A to 22 C are in their positions pressed into the sensor 22 . When the switches 22 A to 22 C assume these positions, the sensor 22 outputs to the control section of the copier 100 a standard size detection signal indicating that a sheet of A4 size is placed in a portrait orientation with its long side contacted by the restricting portion 14 A.

FIG. 5 is a schematic bottom view of the gear member 17 .

The gear member 17 has a plurality of punched portions around a rotating shaft bearing for reducing the weight thereof. The slit 18 of the gear member 17 includes a region 18 A on the outer peripheral side and a region 18 B on the inner peripheral side. The regions 18 A and 18 B are joined to each other in a bending fashion at a bending position 18 C. The region 18 B is a linear region extending along a peripheral surface of the gear member 17 . The region 18 A is a linear region extending outwardly from the bending position 18 C toward an outer peripheral surface in a direction inclined relative to the circumferential direction.

FIG. 6 is a schematic sectional view, taken on a dashed dotted line of FIG. 5 , of the gear member 17 .

The slit 18 has ribs 17 A and 17 B. The ribs 17 A and 17 B enhance the strength of the periphery of the slit 18 to prevent the gear member 17 from being broken. The slider pin 16 has a sectional shape with a large-diameter portion 16 A and a small-diameter portion 16 B. The slit 18 has a sectional shape similar to that of the slider pin 16 . This feature ensures a sufficient contact area between the slider pin 16 and the slit 18 , thereby inhibiting rattling of the slider pin 16 against the inner wall of the slit 18 .

FIG. 7A is a view illustrating the gear member 17 in a state assumed when A4 sheets are placed in the sheet feed cassette 1 . When A4 sheets are placed in the sheet feed cassette 1 , the restricting portion 14 A and the slider 15 are positioned at the first restricting point in the slot portion 13 A. At that time, the gear member 17 has pivoted to assume an orientation at an angle such as to position the slider pin 16 in the region 18 A, while the rack 21 is positioned at an extremity of its slidable range which lies on the side closer to the right-hand side surface of the device.

FIG. 7B is a view illustrating the gear member 17 in a state assumed when letter sheets are placed in the sheet feed cassette 1 . When letter sheets are placed in the sheet feed cassette 1 , the restricting portion 14 A and the slider 15 are positioned at the second restricting point in the slot portion 13 A. The second restricting point in the slot portion 13 A is located closer to the right-hand side surface of the device than the first restricting point in the slot portion 13 A. At that time, the gear member 17 has pivoted to assume an orientation at an angle such as to position the slider pin 16 at the bending position 18 C, while the rack 21 is positioned closer to the left-hand side surface of the device than the position thereof shown in FIG. 7A .

FIG. 7C is view illustrating the gear member 17 in a state assumed when B5 sheets are placed in the sheet feed cassette 1 . When B5 sheets are placed in the sheet feed cassette 1 , the restricting portion 14 A and the slider 15 are positioned at the third restricting point in the slot portion 13 A. The third restricting point in the slot portion 13 A is located closer to the right-hand side surface of the device than the second restricting point in the slot portion 13 A. At that time, the gear member 17 has pivoted to assume an orientation at an angle such as to position the slider pin 16 substantially centrally of the region 18 B, while the rack 21 is positioned closer to the left-hand side surface of the device than the position thereof shown in FIG. 7B .

FIG. 8A is a diagram schematically illustrating a first example of angles formed between the gear member 17 and peripheral structures. In FIG. 8A , the dotted line indicates the center line of the slit 18 ; the dashed line indicates the center line of the slot portion 13 A; and the long dashed line indicates a line perpendicular to the slot portion 13 A.

In FIG. 8A , angle θ 0 is an angle formed between the center line of the slit 18 and the perpendicular line when the slider pin 16 slides in the region 18 A; angle θ 1 is an angle formed between the center line of the slit 18 and the center line of the slot portion 13 A when the slider pin 16 slides in the region 18 A; and angle θ 2 is the angle of the corner formed between the regions 18 A and 18 B.

The angles θ 0 to θ 2 have the following relationship:

θ0=360−90−θ1−θ2.

FIG. 8B is a diagram schematically illustrating a second example of angles formed between the gear member 17 and the peripheral structures. In FIG. 8B , the dotted line indicates the center line of the slit 18 ; the dashed line indicates the center line of the slot portion 13 A; and the long dashed line indicates a line perpendicular to the slot portion 13 A.

In FIG. 8B , angle θ 0 ′ is an angle formed between the center line of the slit 18 and the perpendicular line when the slider pin 16 slides in the region 18 B; and angle θ 1 ′ is an angle formed between the center line of the slit 18 and the center line of the slot portion 13 A when the slider pin 16 slides in the region 18 B.

The angles θ 0 ′ and θ 1 ′ have the following relationship:

θ0′=180−90−θ1′.

The angle θ 1 formed when the slider pin 16 slides in the region 18 A is closer to a right angle than the angle θ 1 ′ formed when the slider pin 16 slides in the region 18 B. Therefore, even when the restricting portion 14 travels the same distance in the slot portion 13 A, the angle through which the gear member 17 pivots when the slider pin 16 slides in the region 18 A is larger than the angle through which the gear member 17 pivots when the slider pin 16 slides in the region 18 B. On the other hand, when the gear member 17 pivots through a fixed angle, the distance that the rack 21 travels is constant. Therefore, even when the restricting portion 14 travels the same distance in the slot portion 13 A, the distance that the rack 21 travels as the slider pin 16 slides in the region 18 A becomes longer than the distance that the rack 21 travels as the slider pin 16 slides in the region 18 B.

The slit 18 is preferably bent such that the angle at which the slit 18 and the slot portion 13 A cross each other when the restricting portion 14 A travels between those restricting points which define a relatively small spacing therebetween is closer to a right angle than the angle at which the slit 18 and the slot portion 13 A cross each other when the restricting portion 14 A travels between those restricting points which define a relatively large spacing therebetween.

In the present embodiment, the angle θ 2 at which the slit 18 is bent is preferably within a range from about 120° to about 135°. When the angle θ 2 is too small, the resistance to sliding of the restricting portion 14 A becomes so large that smooth sliding of the restricting portion 14 A is difficult. When the angle θ 2 is too close to 180°, the variation in the angle θ 1 (or θ 1 ′) which occurs as the slider pin 16 slides around the corner of the slit 18 is so small that the distance that the rack 21 can travel is difficult to prolong.

FIG. 9A is a view illustrating the state of the gear member 17 and the state of a comparative example having a straight slit which are assumed when A4 sheets are placed in the sheet feed cassette 1 . In FIG. 9A , the dashed line depicts the comparative example and the solid line depicts the gear member 17 of the present embodiment.

FIG. 9B is a view illustrating the state of the gear member 17 and the state of the comparative example having the straight slit which are assumed when letter sheets are placed in the sheet feed cassette 1 . In FIG. 9B , the dashed line depicts the comparative example and the solid line depicts the gear member 17 of the present embodiment.

When the restricting portion 14 A travels between the first and second restricting points in the slot portion 13 A, the gear member 17 of the present embodiment pivots through a larger angle than in the conventional art. For this reason, the rack 21 travels a longer distance than in the conventional art. Therefore, the rack 21 of the present embodiment can be located farther from the switch 22 A than in the conventional art. By so doing, it is possible to reduce the danger of erroneously detecting the sizes of standard sheets even when there are variations in the dimensional precision of the members associated to each other.

Description will be made of a second embodiment of the present invention.

FIG. 10 is a bottom view illustrating an exemplary link structure according to the present embodiment. Though the foregoing embodiment employs the rack and pinion mechanism for interlinking the gear member and the rack, the present embodiment employs a slit mechanism.

A sheet feed cassette includes a slot 113 A, sliders 115 and 121 , and a link section 17 . The link section 117 has an outside shape as can be obtained by combining two arms together. The link section 117 has slits 118 A and 118 B in the respective arms. The link section 117 is supported by a rotating shaft 120 extending through the center of a semicircular portion from a lower surface of a sheet support.

The slot 113 A is linearly shaped and vertically cut through the sheet support. The slider 115 is joined to a restricting portion provided on an upper surface of the sheet support through the slot 113 A and is slidable in the slot 113 A with movement of the restricting portion. The slider 115 has a slider pin 116 A which is fitted in the slit 118 A of the link section 117 . As the restricting portion slides, the slider pin 116 A slides in the slit 118 A of the link section 117 with movement of the slider 115 , so that a component of a force exerted by the slider pin 116 A on the internal wall of the slit 118 A works as a torque to cause the link section 117 to pivot about the rotating shaft 120 .

The slot 113 B is linearly shaped and vertically cut through the sheet support. The slider 121 , which is equivalent to the displacement section defined by the present invention, is slidable in the slot 113 B with pivoting movement of the link section 117 . The position of the slider 121 is detected by a sensor. The slider 121 has a slider pin 116 B which is fitted in the slit 118 B of the link section 117 . As the link section 117 pivots, the slider pin 116 B slides in the slit 118 B of the link section 117 . The slider 121 is caused to slide in the slot 113 B by the slider pin 116 B pressed against the inner wall of the slit 118 B.

The slit 118 B of the link section 117 has a bent shape. Therefore, the distance that the slider travels as the link section 117 pivots through a fixed angle is locally prolonged when the slider pin 116 B slides in the vicinity of the tip of the slit 118 B.

The slit 118 B may be similar to or different from the slit 118 A in bending position and angle. It is also possible that the link section is provided with a pin while the slider provided with a slit. The slit may be gently curved.

The foregoing embodiments are illustrative in all points and should not be construed to limit the present invention. The scope of the present invention is defined not by the foregoing embodiments but by the following claims. Further, the scope of the present invention is intended to include all modifications within the scopes of the claims and within the meanings and scopes of equivalents.