Patent Grant
7971868
1. Field of the Invention
The present invention relates to a sheet feeding apparatus which feeds a sheet such as an original or a recording sheet to an image forming apparatus such as a printer, a facsimile machine or a copier, and to an image forming apparatus including the sheet feeding apparatus.
2. Description of the Related Art
Some conventional image forming apparatuses such as printers, copiers and facsimile machines have a feeding apparatus which feeds a sheet to the image forming apparatus. In the sheet feeding apparatus, sheets are stacked on a sheet stacking member (middle plate) which is vertically movably provided in a sheet storage portion, the sheets are lifted to a feeding position, and then the sheets are sent out toward the image forming portion by a sheet feeding member.
In such a sheet feeding apparatus, when sheets are to be stacked on a sheet storage portion for adding or exchanging sheets, the sheet storage portion can be pulled out from the sheet feeding apparatus. In association with the pulling-out operation of the sheet storage portion, the sheet stacking member can be lowered to a predetermined sheet stacking position.
The sheet feeding apparatus connected to a printer, for example, is provided with a sheet upper surface detection sensor which detects a height position of the top sheet stacked on the sheet stacking member. Based on the detection information of the sheet upper surface detection sensor, the sheet stacking member moves. With this, the height position of the top sheet is always maintained at a given height.
As the sheet feeding member, if a sheet-feed signal is sent from the image forming apparatus, the sheet-feed roller abuts against the top sheet and rotates, and the top sheet is fed to a next pair of separation rollers.
The pair of separation rollers separately feeds sheets sent by the sheet-feed roller one-sheet at a time, and sends out the sheets to the image forming apparatus. At that time, if the sheet-feed roller sends out the sheet to the pair of separation rollers, the sheet feed roller retracts above the sheet so that the sheet feed roller does not hinder when the pair of separation rollers separate the sheets from each other and does not abut against the sheet. Whenever the sheet-feed signal is sent from the image forming apparatus, the above operation is repeated and sheets are sent out to the image forming apparatus sheet by sheet.
The roller holder 1110 is provided with a sensor flag 1110a. The sensor flag 1110a moves to a position where sensor light of the optical sensor 1111 can be blocked. A position where light projection/light shield of the optical sensor 1111 is switched by the sensor flag 1110a is a position at which an appropriate sheet feed pressure is applied to an upper surface of a sheet by the sheet-feed roller 1053 when sheets are fed (position shown in
The middle plate 1101 supports a sheet Sa and can be vertically moved by a push-up plate 1102. As shown in
In the conventional sheet feeding apparatus, after a sheet is sent out, the sheet-feed roller 1053 is moved upward and separated from the upper surface of a sheet. This is the same also when the last sheet in the sheet cassette is sent out. Therefore, if the last sheet is sent out, the sheet-feed roller 1053 is moved to its original position above the sheet cassette shown in
The sheet-feed roller 1053 is located at the initial position also when sheets are added and the sheet cassette is attached to the apparatus body. When the sheet-feed roller 1053 is in the initial position, the light of the optical sensor 1111 is blocked by the sensor flag 1110a.
Since the light of the optical sensor 1111 already is blocked when the sheet cassette is to be attached, even if the upper surface of a sheet does not reach the predetermined height range at which an appropriate sheet feeding pressure is applied, a control section determines that the apparatus is in a state where a sheet can be fed. Therefore, when the sheet cassette is attached, the middle plate 1101 can not be moved upward or an upper surface of a sheet can not be moved to the predetermined height range at which the appropriate sheet feeding pressure is applied.
In this case, the sheet feeding operation is started even though a sheet S does not reach a position where a sheet can be fed (“sheet-feeding position”, hereinafter). As a result, there is a fear that a sheet-feeding failure may be caused, or the middle plate 1101 may be brought higher than necessary depending upon control, and inconvenience such as deformation of parts may be caused.
As a method for solving such a problem, there is a conventional technique as shown in
However, according to the technique in which the lift up of the sheet-feed roller 1053 is mechanically released when the sheet cassette is inserted, since the lift-up mechanism is required, the cost is increased. The mechanism is constituted such that it works when the cam member 1112 is in a standby position. Therefore, when the cam member 1112 is not in the standby position due to a jam, the lift up of the sheet-feed roller 1053 can not be released even if the sheet cassette 1052 is inserted and as a result, there is a possibility that the detector can not detect.
The present invention provides a sheet feeding apparatus capable of reliably feeding a sheet with an inexpensive structure, and provides an image forming apparatus including said sheet feeding apparatus.
The sheet feeding apparatus of the present invention has the following elements.
A sheet feeding apparatus comprising a sheet stacking member on which a sheet can be stacked, a lifter mechanism which configured to lift the sheet stacking member towards a sheet feeding member, a sheet feeding member which is moveable, and which is configured to engage with a sheet stacked on the sheet stacking member to feed the sheet, and a detector, operable to output a detection signal based on a position of the sheet feeding member, in which the sheet stacking member is adapted to be lifted by the lifter mechanism based on detection of the detector, such that an upper surface of the topmost stacked sheet is moved to a sheet-feeding position, wherein in a sheet feeding standby state the sheet feeding member is positioned at a standby position above the sheet feeding position, when the sheet feeding operation of the sheet is started from the sheet feeding standby state, the sheet feeding member is lowered from the standby position towards the sheet feeding member, the sheet stacking member is lifted by the lifter mechanism based on detection of the detector, and the upper surface of the sheet stacked on the sheet stacking member is moved to the sheet-feeding position.
A sheet feeding apparatus for feeding a sheet stacked on a sheet stacking member using a sheet feeding member, comprising a sheet stacking member on which a sheet can be stacked, a lifter mechanism which is adapted to lift the sheet stacking member, a sheet feeding member which is configured to feed a sheet stacked on the sheet stacking member, and which is operable to move to a first position retracted from the sheet stacked on the sheet stacking member, a second position lower than the first position for feeding the sheet, and a third position lower than the second position, and a detector operable to output a detection signal based on a position of the sheet feeding member, wherein the sheet feeding apparatus has a position control mode in which when a sheet is fed, the sheet feeding member is moved from the first position to the third position and stopped there, the sheet stacking member is moved by the lifter mechanism toward the sheet feeding member, the sheet stacked on the sheet stacking member is brought into engagement with the sheet feeding member, and the sheet stacking member is moved until the detector outputs the detection signal that the sheet stacking member is in the second position.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An image forming apparatus having a sheet feeding apparatus according to an embodiment of the present invention will now be described with reference to the drawings.
In this embodiment, a laser beam printer is indicated as the image forming apparatus, and the embodiment will be explained using a sheet feeding apparatus connected to the printer.
[Image Forming Apparatus]
The entire structure of the image forming apparatus will be explained together with an image forming operation with reference to
In
A known process member concerning image formation is incorporated in a process cartridge 7, and the process cartridge 7 is detachably attached to the apparatus body. A photosensitive drum 7a as an image bearing member is incorporated in the process cartridge. The photosensitive drum 7a is irradiated with laser light in accordance with image information by a laser exposure apparatus 8, an image is written, and a toner image is formed.
A transfer roller 9 is pressed on the photosensitive drum 7a, and a toner image on the drum surface is transferred to a sheet S when the sheet S passes between the photosensitive drum 7a and the transfer roller 9. A fixing apparatus 10 fixes (fuses) the transferred images by applying heat and pressure to the sheet S after the image was transferred to the sheet S. The sheet S after the images was fixed (fused) is conveyed and discharged into a discharge tray 12 formed on an upper surface of the apparatus by a pair of discharge rollers 11 such that a surface of the sheet S on which the images was formed points downward.
[Sheet Feeding Apparatus]
Next, the sheet feeding apparatus will be explained. A sheet feeding apparatus 51 of the embodiment is constituted as a three-cassette deck. The sheet feeding apparatus 51 also functions as a mounting stage of the image forming apparatus body 1, and the sheet feeding apparatus 51 is disposed on a lower portion of the image forming apparatus. Casters are mounted on four locations of a lower surface of the sheet feeding apparatus 51 so that the sheet feeding apparatus 51 can move in a state where the image forming apparatus body 1 is placed thereon.
The sheet feeding apparatus 51 has three sheet feeding members and sheet cassettes 52a, 52b and 52c. Each sheet cassette is constituted such that sheets of various sizes and weights can be stacked. If the sheet feeding apparatus receives a sheet-feed signal from the image forming apparatus body, the sheet feeding apparatus selects a sheet cassette on which sheets suitable for the sheet-feed signal are stacked, and the sheet feeding apparatus can feed the sheets S to the image forming apparatus body 1 from the sheet cassette one-sheet at a time.
Here, the sheet feeding members and the sheet cassettes provided in the sheet feeding apparatus 51 will be explained. Since the three sheet feeding members and the sheet cassettes 52a, 52b and 52c have the same structure, the top sheet feeding member and the top sheet cassette will be explained. Unless it is necessary to distinguish them from one another, added alphabets a, b and c added to the drawings for expressing elements of the sheet feeding members and the sheet cassettes will be omitted from the description.
As shown in
The detailed structure of the sheet feeding portion of the embodiment will now be described.
In the drawings, a snaggletooth gear 103 rotates the feed roller 54, and a flapper member 105 is operated by a solenoid 104. The feed roller 54 is rotated several times by one rotation control of the snaggletooth gear 103 by the flapper member 105. Rotation of the feed roller 54 is transmitted to the sheet-feed roller 53 through a planet gear 106.
The middle plate 101 supports the stacked sheets. The middle plate 101 is provided on a sheet cassette 52 such that the middle plate 101 can turn (move) around retaining portions 101a and 101b shown in
A lift motor (not shown) is driven and controlled by a control section. The control section rotates the pinion 108 using the lift motor based on a detection signal from a later-described position detection sensor, and moves the middle plate 101 toward the sheet-feed roller 53 through a gear portion and the push-up plate. With this, one end of the middle plate 101 is lifted to provide a given height at which an appropriate pressure is applied between an upper surface of a sheet supported when the sheet is fed and the sheet-feed roller 53.
The sheet-feed roller 53 is rotatably held by a roller holder 110 which is turnably mounted on a shaft 109 of the feed roller 54 shown in
A cam member 112 engages the snaggletooth gear 103 and rotate in unison when the snaggletooth gear 103 rotates. An abutting portion 110b (see
If the abutting portion 110b abuts against a cam member 112 by its own weight or via a biasing member such as a spring (not shown), and one rotation control of the snaggletooth gear 103 is carried out, the sheet-feed roller 53 drops (rotates) due to the shape of the cam member and moves to a position where the sheet-feed roller 53 abuts against a sheet S. Then, the sheet-feed roller 53 retracts from the sheet halfway through the sending motion of the sheet, and returns to the initial position (first position) shown in
If the sheets S are fed one-sheet at a time by such a control, the number of sheets Sa stacked on the middle plate 101 is reduced and the height of the upper surface of the sheets is reduced. With this, the sheet-feed roller 53 is lowered together with the roller holder 110, block of light of the position detection sensor 111 by the sensor flag 110a is released by the lowering of the roller holder 110 as shown in
If the roller holder 110 lowers to the position where the blocking of light from the position detection sensor 111 ceases, i.e., the position where the position detection sensor 111 is brought into the non-detection state, the appropriate sheet feeding pressure can not be applied to the upper surface of the sheet S by the sheet-feed roller 53. Therefore, if the position detection sensor 111 is brought into the non-detection state, the control section drives the lift motor and again moves up one end of the middle plate 101 to a position (second position) using the push-up plate 102 of the lifter mechanism where the appropriate pressure is applied when a sheet is fed and an upper surface of the sheet Sa reaches a substantially constant height. Here, the second position is a position where the sheet-feed roller 53 is lowered to the position shown in
If the position detection sensor 111 is brought into the non-detection state while sheets are sequentially fed in a state where the position of the roller holder 110 (sheet-feed roller 53) is detected by the position detection sensor 111, the middle plate 101 is moved by the lifter mechanism. Sheets can reliably fed until the last sheet is fed by repeating the control such that the upper surface position of a sheet comes to a predetermined position. Although the control is performed such that the sheet-feed roller 53 moves from the sheet feeding position to the standby position whenever one sheet is sent in this embodiment, if sheets are continuously fed, the sheet-feed roller 53 may be maintained in the sheet feeding position of sheets. In this case, after the last one of sheets to be fed continuously is fed, the sheet-feed roller 53 is moved to the standby position.
[Control after Sheet Cassette is Inserted]
Next, control when sheets are set in the sheet cassette 52 of the sheet feeding apparatus of the embodiment will be described.
The sheet feeding apparatus of the embodiment has a position control mode for controlling the height of the top sheet after sheets are set in the sheet cassette 52 and the sheet cassette 52 is inserted. The position control mode is driven and controlled by a control section as shown in
If the sheet cassette 52 is pulled out from the sheet feeding apparatus as shown in
Since the sheet-feed roller 53 is at the initial position (first position) in the state shown in
In this embodiment, the flapper member 105 is operated by the solenoid 104 at that time, the snaggletooth gear 103 is rotated a given angle by the sheet-feed motor 121, and the position detection sensor 111 is brought into the non-detection state. In this state, a sheet on the middle plate 101 is moved toward the sheet-feed roller 53 by driving the lift motor 122 of the lifter mechanism, and if the position detection sensor 111 detects the detection state, the driving of the lift motor of the lifter mechanism is stopped.
More specifically, as shown in the flowchart in
That is, as shown in
Next, the lift motor 122 of the lifter mechanism is driven and the middle plate 101 is pushed up by the push-up plate 102 (S6). With this, a surface of the top one of the sheets Sa stacked on the middle plate 101 abuts against the sheet-feed roller 53 and rises. The position detection sensor 111 is brought into detection state (ON state) and if it is detected that the sheet-feed roller 53 is in the second position, the driving of the lift motor 122 is stopped and is brought into the sheet feeding standby state (S7 and S8).
With this, the middle plate 101 can rise to the substantially constant height position where the appropriate pressure is applied between the sheet-feed roller 53 and an upper surface of a sheet which is supported when the sheet is fed.
With this, the height of the top sheet on the middle plate 101 can fall within the predetermined range without providing any special mechanism, and a sheet can be moved to the sheet-feeding position with a simple structure without increasing the cost.
In the above embodiment, the position control mode in which the insertion of the sheet cassette is detected by the cassette sensor and the movements of the sheet-feed roller 53 and the middle plate are controlled is executed. However, when the sheet cassette is inserted, the position control may not be carried out, and when a sheet-feed signal is sent thereafter and the first sheet feeding operation is carried out, the position control mode may be carried out. That is, the control of the present invention may be carried out when the first sheet-feed signal is input in the sheet feeding-standby state.
The sheet feeding apparatus of the present invention for achieving the above object has the following elements.
A sheet stacking member on which a sheet is stacked, a lifter mechanism which vertically moves the sheet stacking member, a sheet feeding member which can vertically move, and which abuts against the sheet stacked on the sheet stacking member to feed the sheet, and a detector which outputs a detection signal based on a position of the sheet feeding member. The sheet stacking member is vertically moved by the lifter mechanism based on detection of the detector, an upper surface of the stacked sheet is moved to a sheet-feeding position by the sheet feeding member. The sheet feeding member is positioned on a standby position above the sheet feeding position in a sheet feeding standby state. When the sheet feeding operation of the sheet is started from the sheet feeding standby state, the sheet feeding member is lowered from the standby position, the sheet stacking member is lifted by the lifter mechanism based on detection of the detector, and the upper surface of the sheet stacked on the sheet stacking member is moved to the sheet-feeding position.
A sheet feeding apparatus which feeds a sheet stacked on a sheet stacking member by a sheet feeding member has the following elements.
A sheet stacking member on which a sheet is stacked, a lifter mechanism which vertically moves the sheet stacking member, a sheet feeding member which feeds a sheet stacked on the sheet stacking member, and which can move to a first position retracted from the sheet stacked on the sheet stacking member, a second position lower than the first position for feeding the sheet, and a third position lower than the second position, and detector which detects a position of the sheet feeding member. The sheet feeding apparatus has a position control mode in which when a sheet is fed, the sheet feeding member is moved from the first position to the third position and stopped there, the sheet stacking member is moved toward the sheet feeding member by the lifter mechanism, the sheet stacked on the sheet stacking member is brought into abutment against the sheet feeding member, the sheet stacking member is moved until the detector detects that the sheet feeding member is in the second position, and a height of the sheet is controlled.
According to the present invention, when the sheet stacking member is accommodated in the apparatus body and a sheet is fed, the sheet feeding member is lowered from a sheet feeding position and then, the sheet stacking member is moved and the height of the sheet is controlled. With this, the height of the top sheet on the sheet stacking member can be located within a predetermined range without providing any special mechanism, and a sheet can be moved to a sheet-feeding position with a simple structure without increasing the cost.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structure and functions.
This application claims the benefit of Japanese Patent Application No. 2007-232260, filed Sep. 7, 2007, which is hereby incorporated by reference herein in its entirety.
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