Sheet feeding apparatus

Abstract: The present invention provides a sheet feeding apparatus, comprising a pair of rotary convey members (101, 102), and control means (121) having a first mode in which a sheet (105) fed in a predetermined direction is pinched between the pair of rotary convey members (101, 102), the sheet (105) is then fed in a reverse direction, a leading end of the sheet is then abutted against a nip between the rotary convey members (101, 102), and then the sheet (105) is fed in the predetermined direction, and a second mode in which the fed sheet (105) is further fed to the predetermined direction by the pair of rotary convey members (101, 102) without returning the sheet (105) and adapted to control the pair of rotary convey members (101, 102) to feed the sheet (105) in either the first or second mode.

Description: The present invention relates to a sheet feeding apparatus according to the preamble of claim 1. Such a sheet feeding apparatus is used for feeding a sheet (normal sheet, cut sheet, print sheet, transfer sheet, photosensitive sheet, electrostatic recording sheet, printing sheet, OHP sheet, envelope, post card, original and the like), with preventing the skew feed of the sheet, to a sheet processing station such as a printing station, image forming station, exposure station, working station and the like in an image forming system and other various sheet using devices such as a recording system (printer), copying machine, facsimile and the like as an information output equipment such as a word processor, computer and the like. From the document PATENT ABSTRACTS OF JAPAN, Vol. 12, No. 141, 28 April 1998 (& JP-A-62 259944) a generic sheet feeding apparatus is known which has a sheet supply member and a pair of rotary convey members performing a forward and reverse rotary movement, so as to allow a first operating mode of the apparatus. In this first operating mode a sheet can be pinched between the pair of rotary convey members and the sheet supply member in order to form a loop therebetween. The same analysis also applies to the sheet feeding apparatus disclosed in the document EP-A-0418515 upon which the preamble of claim 1 is based. In the past, various means for feeding a sheet, with preventing the skew feed of the sheet, to a sheet processing station such as a printing station of a recording system have been proposed. In an exemplary sheet feeding means, the skew feed of the sheet is prevented by utilizing flexion reactive force of the sheet. That is to say, the sheet feeding means-comprises a first sheet feeding means for feeding a sheet to a sheet processing station, and a second sheet feeding means including a pair of urgingly contacted rollers disposed between the first sheet feeding means and the sheet processing station, and is so designed that a leading end of the sheet is abutted against a nip between the paired rollers of the second sheet feeding means now stopped by the normal rotation of the first sheet feeding means, and a further normal rotation of the first sheet feeding means forms a predetermined loop in the sheet between first and second sheet feeding means in opposition to the resilience of the sheet. With this arrangement, even when the sheet is skewfed from the first sheet feeding means, the whole length of the leading end of the sheet is abutted against the nip line between the paired rollers of the second sheet feeding means, thereby registering the leading end of the sheet with the nip line. Then, when the paired rollers of the second sheet feeding means are rotated in the normal direction, the leading end of the sheet enters into the nip of the paired rollers in parallel with the nip line, with the result that the sheet is sent to the sheet processing station without the skew feed of the sheet. On the other hand, there are conventional sheet feeding apparatuses wherein the first and second sheet feeding means are operated as follows. In Fig. 5, the reference numeral 303 denotes a sheet supply roller; 304 denotes a sheet stacker; 305 denotes a recording medium; 301 denotes a convey roller; and 302 denotes a driven roller. When the sheet supply roller 303 and the convey roller 301 are rotated in the normal direction, the recording medium 305 on the sheet stacker 304 is picked up. These rollers 303, 301 are rotated normally until a leading end of the recording medium 305 has passed through a nip between the convey roller 301 and the driven roller 302. Thereafter, the sheet supply roller 303 is stopped while abutting against the sheet stacker 304, and then, the convey roller 301 is rotated reversely, thereby returning the leading end of the recording medium 305 to a position upstrear of the nip between the convey roller 301 and the driven roller 302 (Figs. 6 and 7). In this condition, since a trailing end of the recording sheet 305 is pinched between the sheet supply roller 303 and the sheet stacker 304 urged against the sheet supply roller which are now stationary, the recording medium is flexed or bent between the sheet supply roller 303 and the convey roller 301 by an amount corresponding to the returning distance of the leading end of the recording medium, with the result that the leading end of the recording medium is wholly abutted against the nip line between the convey roller 301 and the driven roller 302. Thereafter, by rotating the convey roller 301 and the sheet supply roller 303 normally by a predetermined amount, the recording medium is fed to a printinc position. However, in the above-mentioned sheet feeding apparatus and its control, the leading end of the recording medium is returned toward the upstream side from the nip between the convey roller 301 and the driven roller 302, and then, is abutted against the nip, thereby preventing the skew feed of the recording medium. Thus, although the skew feed preventing ability is highly ensured in case of the cut sheet and the like a thickness of which is uniformly controlled, regarding sheets having no uniform thickness such as envelopes folded several times over and having different thickness folded portions, as shown in Fig. 8, when the leading end of the sheet is returned toward the upstream side from the nip between the convey roller 301 and the driven roller 302 and then is abutted against the nip, since positions on the leading end of the sheet are different from point to point along a line perpendicular to a plane of Fig. 8, this feeding method causes the skew feed of the sheet more noticeably than the case where the sheet is directly forwarded without returning it toward the upstream side. Further, regarding sheets having the greater thickness and high resilience, when the convey roller is rotated reversely to return the sheet toward the upstream side from the nip between the convey roller 301 and the driven roller 302, because of the high resilience of the sheet, the loop cannot be formed in the sheet between the convey roller and the sheet supply roller, but the convey roller is slipped without returning the sheet, with the result that, when the convey roller is then rotated normally by the predetermined amount to send the sheet to the print start position, the sheet will be fed excessively. Further, in the conventional sheet feeding apparatus having the above-mentioned skew feed preventing ability, a greater space is required between the first and second sheet feeding means for permitting the formation of the predetermined loop in the sheet, because if such a space is small the sheet will be bent or folded. As a result, it was hard to make the apparatus small-sized. Further, in a recording system of serial type wherein the main scan is effected along a direction transverse to a recording sheet feeding direction (sub scanning direction), after the An object of the present invention is to provide a sheet feeding apparatus in which the above-mentioned conventional drawbacks obstructing the compactness of a sheet feeding apparatus are eliminated. The object of the present invention is achieved by the combination of features according to claim 1. Preferred further developments of the subject-matter according to claim 1 are set forth in the dependent claims. According to the invention, the feeding of a sheet is permitted with preventing the skew feed of the sheet and without requiring a space for the formation of a loop in the sheet between first and second sheet feeding means. According to an aspect of the present invention, a sheet feeding apparatus comprises first sheet feeding means for feeding a sheet to a sheet processing station, second sheet feeding means disposed between the first sheet feeding means and the sheet processing station and including a pair of rollers urged against each other, drive and drive transmitting means for the first and second sheet feeding means, and control means for controlling the drive and drive transmitting means. The control means controls the drive and drive transmitting means for the first and second sheet feeding means in such a manner that the first and second sheet feeding means are rotated normally to feed the sheet from the first sheet feeding means to the second sheet feeding means until a leading end of the sheet exceeds a nip between the paired rollers of the second sheet feeding means by a predetermined distance L, then, the drive transmission to the first sheet feeding means is stopped and the second sheet feeding means is rotated reversely to feed the sheet reversely until the sheet is returned more than the predetermined distance L, and then the paired rollers of the second sheet feeding means are rotated normally again to enter the sheet into the nip again and to further feed the sheet normally toward the sheet processing station. A sheet holding or urging force of the first sheet feeding means which is stopped when the sheet is fed reversely is so selected that the sheet fed reversely by the second sheet feeding means can be slipped with respect to the first sheet feeding means not to flex the sheet between the first and second sheet feeding means. In the following, embodiments of the present invention are described in detail with reference to the figures. Fig. 1 is a schematic elevational sectional view of a sheet feeding apparatus according to an embodiment of the present invention; Fig. 2 is a control block diagram for the sheet feeding apparatus; Fig. 3 is a flow chart for operating the sheet feeding apparatus; Fig. 4 is a control block diagram according to another embodiment; Figs. 5 to 7 are partial sectional views of a conventional sheet feeding apparatus for explaining a sheet supplying operation; and Fig. 8 is a partial sectional view of the conventional sheet feeding apparatus in a condition that an envelope is supplied. Fig. 1 shows an embodiment of the present invention. In this embodiment, the reference numeral 101 denotes a convey roller (platen) for holding a recording-medium (sheet) in a recording position and for feeding the recording sheet in a sub scanning direction; 102 denotes a driven roller for urging the recording sheet against the convey roller 101 to generate a feeding force; 103 denotes a sheet supply roller; 104 denotes a sheet stacker on which the recording sheets are stacked; 105 denotes the recording sheet; 106 denotes a recording sheet sensor such as a photosensor of reflection type for detecting the presence/absence of the recording sheet; and 107 denotes a recording sheet thickness sensor such as a supersonic sensor for detecting a thickness of the recording sheet. When a sheet supplying operation is started by a sheet supply start signal, the convey roller 101 and the sheet supply roller 103 are rotated normally, thus picking up the recording sheet 105 on the sheet stacker 104 by the sheet supply roller 103. At the same time when a leading end of the sheet is detected by the recording sheet sensor 106, a thickness of the sheet is read by the recording sheet thickness sensor 107. Since a thickness of a cut sheet is in the order of 0.1 mm and a thickness of an envelope is in the order of 0.5 mm or more, these can easily be discriminated. If the kind of the sheet is discriminated as the cut sheet, the skew preventing control similar to the conventional one is effected. To the contrary, if the kind of the sheet is discriminated as the thicker sheet such as the envelope, the convey roller 101 and the sheet supply roller 103 continue to be rotated in the normal direction by a predetermined amount, thereby feeding the leading end of the sheet 105 to a predetermined print start position A. The convey roller 101 also acts as a platen. In this embodiment, a recording head 110 is of bubble jet type wherein ink droplets are discharged by utilizing energy generated by evaporating the ink by thermal energy. The recording head 110 is guided by guides 111 so that the recording head 110 can be moved in a direction transverse to the sheet feeding direction. Incidentally, the reference numerals 112, 113 denotes sheet guides. Fig. 2 shows a control block diagram. The reference numeral 121 denotes a control portion for controlling the feeding of the sheet; 122 denotes a motor for driving the sheet supply roller; and 123 denotes a motor for driving the convey roller 101. Next, an operation of the recording system according to this embodiment will be explained with reference to a flow chart shown in Fig. 3. When the sheet supply start signal is emitted, in a step S11, the motors 122, 123 are activated to rotate the sheet supply roller 103 and the convey roller 101 in an anti-clockwise direction in Fig. 1. In a step S12, the leading end of the sheet is detected by the sensor 106 and the thickness of the sheet is detected by the thickness sensor 107. The thickness sensor 107 measures a distance between it and a surface of the sheet by utilizing the supersonic wave. And, if the distance is smaller than a predetermined value, it is judged that the sheet is the thicker sheet. In case where the thickness of the sheet is below the predetermined value (i.e., cut sheet), the sheet is fed in the normal direction until the leading end of the sheet exceeds the nip (abutment point) between the paired rollers 101, 102 by a distance L1 toward a downstream side of the sheet feeding direction (step S14), and then the sheet supply roller 103 and the convey roller 101 are stopped. Then, the convey roller 101 is rotated reversely (clockwise direction) by a predetermined amount sufficient to return the sheet in the reverse direction by a distance more than the distance L1, thereby drawing the leading end of the sheet out of the nip (step S15). As a result, a loop is formed in the sheet between the paired convey rollers 101, 102 and the sheet supply roller 103 while abutting the leading end of the sheet against the nip of the rollers 101, 102. Then the convey roller 101 is rotated normally again until a portion of the sheet on which the image segment for the first line is to be printed reaches the recording position between the convey roller 101 and the recording head 110. Whenever the one-line printing is effected by the recording head 110, the sheet is line-spaced by a predetermined amount. After the printing operation is finished, the sheet is ejected out of the system. In the step S13, if the thickness of the sheet is greater than the predetermined value, the sheet continues to be fed to the recording position, where the printing is effected on the sheet. In this way, since the thickness of the sheet is detected and the sheet supply mode is changed in accordance with the thickness of the sheet, it is possible to provide the accurate sheet supplying operation with minimum skew-feed of the sheet, regardless of the thickness of the sheet. In the above embodiment, while the sheet supply mode was changed through the recording sheet thickness sensor, it is to be understood that, in place of the recording sheet thickness sensor, an operator may change the sheet supply mode through an operation panel of the recording system (alteration). Such alteration is shown in Fig. 4. This alteration differs from the embodiment of Fig. 2 in the point that a switch 107a is provided in place of the thickness sensor 107 and the operator can change the sheet supply mode between a plain paper mode and a thicker sheet mode via the switch. When the plain paper mode is selected via the switch 107a, after the step S12, the control sequences of the steps S14 - S16 are effected; whereas, when the thicker sheet mode is selected, the control sequence of the step S17 is effected. Incidentally, in the aforementioned embodiments, while the present invention was applied to the ink jet recording systems, the present invention can be applied to various recording systems such as wire dot recording systems, laser beam recording systems, thermal transfer recording systems and the like, as well as the ink jet recording systems, regardless of the types of the recording means (recording heads), with providing the same advantages. Further, in the aforementioned embodiments, while the recording system of serial type wherein the recording head(s) mounted on the carriage is shifted in the main scanning direction along the recording sheet was explained, the present invention can similarly be applied to recording systems of line type wherein the recording is effected by a recording means of line type through the whole or part of the recording width of the recording sheet, with providing the same advantages. Further, in the aforementioned embodiments, while the color recording systems utilizing a plurality of recording heads for the different colors were explained, the present invention can be applied to a mono-color recording system utilizing a single head or a gradient color utilizing a plurality of recording heads for same color inks having different density, or the like, regardless of the number of recording heads, with providing the same advantages. Furthermore, regarding the recording head, it may be formed integrally with an ink tank to constitute a cartridge or it may be formed independently from an ink tank and connected to the latter via an ink supply tube, regardless of the relation between the recording head and the ink tank, with providing the same advantages. Incidentally, when the present invention is applied to the ink jet recording systems, it can be applied to an ink jet recording system having a recording head utilizing electrical/thermal converters such as piezo electric elements. Particularly, when the present invention is applied to an ink jet recording head having a recording means of the type wherein the ink is discharged by utilizing thermal energy, the excellent advantage can be expected, since it is possible to achieve the recording with high density and high resolving power. It is preferable to employ the typical structure and the principle of structures disclosed in, for example, U.S.P. No. 4,723,129 and U.S.P. No. 4,740,796. This system can be adopted in a so-called "On-Demand" type and "Continuous" type structures. In this system, an electrothermal conversion member disposed to align to a sheet or a liquid passage in which liquid (ink) is held is supplied with at least one drive signal which corresponds to information to be recorded and which enables the temperature of the electrothermal conversion member to be raised higher than a nuclear boiling point, so that thermal energy is generated in the electrothermal conversion member and film boiling is caused to take place on the surface of the recording head which is heated. As a result, bubbles can be respectively formed in liquid (ink) in response to the drive signals. Due to the enlargement and contraction of the bubble, liquid (ink) is discharged through the discharge port, so that at least one droplet is formed. In a case where the aforesaid drive signal is made to be a pulse signal, a further satisfactory effect can be obtained in that the bubble can immediately and properly be enlarged/contract and liquid (ink) can be discharged while exhibiting excellent responsibility. It is preferable to employ a drive signal of the pulse signal type disclosed in U.S.P. 4,463,359 and U.S.P. 4,345,262. Furthermore, in a case where conditions for determining the temperature rise ratio on the aforesaid heated surface disclosed in U.S.P. No. 4,313,124 are adopted, a further excellent recording operation can be performed. In addition to the structure (a linear liquid passage or a perpendicular liquid passage) of the recording head formed by combining the discharge ports, the liquid passage and the electrothermal conversion member as disclosed in the aforesaid specifications, a structure disclosed in U.S.P. No. 4,558,333 and U.S.P. 4,459,600 in which the heated portion is disposed in a bent portion is included in the scope of the present invention. Furthermore, the present invention can effectively be embodied in a structure in which a common slit is made to be the discharge portion of a plurality of electrothermal conversion members and which is disclosed in Japanese Patnet Laid-Open No. 59-123670 and a structure in which an opening for absorbing thermal energy pressure wave is formed to align to the discharge port and which is disclosed in Japanese Patent Laid-Open No. 59-138461. That is, the recording can be carried out effectively irrespective of embodiment of the recording head. Further, the present invention can effectively be applied to a recording head of full-line type having a length corresponding to a maximum width of a recording sheet (recording medium) to be recorded. As such recording head, the construction wherein such length is attained by combining a plurality of recording heads or a single recording head integrally formed may be adopted. In addition, among the above-mentioned serial types, the present invention is effectively applicable to a recording head secured to the recording system, or to a removable recording head of chip type wherein, when mounted on the recording system, electrical connection between it and the recording system and the supply of ink from the recording system can be permitted, or to a recording head of cartridge type wherein an ink tank is integrally formed with the head. Further, it is preferable that a head recovering means and an auxiliary aiding means are added to the recording head according to the present invention, since the effect of the present invention is further improved. More concretely, these means include a capping means for capping the recording head, cleaning means, pressurizing or suction means, and an auxiliary heating means comprising electrical/thermal converters or other heating elements or the combination thereof. Further, it is effective for the stable recording to perform an auxiliary discharge mode wherein the ink discharge regardless of the recording ink discharge is effected. Further, as to the kind and number of the recording head to be mounted, each recording head may correspond to each different color ink, or a plurality of recording heads can be used for a plurality of inks having different colors and/or different density. That is to say, as the recording mode of the recording system, the present invention can effectively be applied not only to a recording mode with a single main color such as black, but also to a system providing a plurality of different colors and/or a full-color by mixing colors by using an integrated recording head or the combination of plural recording heads. Further, in the illustrated embodiments, while the ink was liquid, the ink may be solid in a room temperature or less, or may be softened at a room temperature. In the above-mentioned ink jet recording system, since the temperature control is generally effected in a temperature range from 30°C to 70°C so that the viscosity of the ink is maintained within a stable discharging range, the ink may be liquidized when the record signal is emitted. In addition, ink having a feature that is firstly liquidized by the thermal energy, such as solid ink which serves to prevent the increase in temperature by absorbing energy in changing the ink from the solid state to the liquid state or which is in the solid state in the preserved condition to prevent the vaporization of ink and which is liquidized into ink liquid to be discharged in response to the record signal comprising the thermal energy, or ink which has already been solidified upon reaching the recording medium, can also be applied to the present invention. In such a case, the ink can be held in the liquid state or solid state in recesses or holos in porous sheet as disclosed in the Japanese Patent Laid-Open Nos. 54-56847 and 60-71260, in confronting relation to the electrical/thermal converters. Incidentally, in the present invention, the above-mentioned film boiling principle is most effective for each ink. Furthermore, the ink jet recording system according to the present invention can be embodied as an image output terminal of an information processing equipment such as a computer, a copying machine combined with a reader and the like, a facsimile having the communication ability, or the like.

Claims: A sheet feeding apparatus, comprising a sheet supply member (103), a pair of rotary convey members (101, 102), and a control means (121) having a first mode in which a sheet (105) fed in a predetermined direction by means of the sheet supply member (103) and the pair of rotary convey members (101, 102) is pinched between said pair of rotary convey members (101, 102), is then fed in a reverse direction by means of the pair of rotary convey members (101, 102) until a leading end of the sheet is abutted against a nip between said rotary convey members (101, 102) so as to form a loop in the sheet between said nip and the sheet supply member (103), and in which the sheet (105) is then fed in said predetermined direction, characterized in that the control means (121) has a second mode in which the sheet (105) is fed in said predetermined direction by said pair of rotary convey members (101, 102) without returning the sheet (105), and is adapted to control said pair of rotary convey members (101, 102) to feed the sheet (105) in either said first or second mode corresponding to a kind of the sheet. A sheet feeding apparatus according to claim 1, further comprising a detection means (107) for detecting a thickness of the fed sheet (105), and wherein said control means (121) is designed so as to change the modes in response to a signal from said detection means. A sheet feeding apparatus according to claim 1, further comprising a changing means (107) for changing the control modes of said control means. A sheet feeding apparatus according to claim 1, further comprising a switch (107a) for changing the control modes of said control means.

Inventors: KAWAGUCHI KOICHIRO, YOKOI KATSUYUKI, KAWAGUCHI, KOICHIRO, YOKOI, KATSUYUKI, Kawaguchi, Koichiro, c/o Canon Kabushiki Kaisha, YOKOI, KATSUYUKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: B65H5
IPC codes: B65H5, B65H9