JP2008100824A - Paper feeding mechanism and image forming device having the mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper feeding mechanism and an image forming device having this mechanism, capable of stably and quickly performing paper feeding operation, by restraining the occurrence of a rubbing sound and paper double feeding, when a pickup roller is always brought into pressure contact. <P>SOLUTION: The pickup roller 29 and a paper feeding roller 30a are unitized into a frame body 41, and the frame body 41 is vertically rotatably supported around a rotary shaft of the paper feeding roller 30a. A first detecting sensor 49 detects whether or not paper 26 passes through paper feeding roller pairs 30. After starting paper feeding, a paper loading plate 28 is lowered by rotating a lift plate 33 in the timing when the tip of the uppermost paper 26 passes through the paper feeding roller pairs 30, and the paper loading plate 28 is lifted again in the timing when the rear end of the paper 26 passes through the paper feeding roller pairs 30. A paper feeding position for lifting the paper loading plate 28 is determined by a detecting result of a second detecting sensor 50. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a paper feed mechanism that is used in a paper feed cassette or an original transport device of an image forming apparatus such as a digital copying machine or a laser printer and separates and feeds paper one by one from a paper bundle.

  A configuration of a conventional paper feed cassette will be described. FIG. 6 is a side sectional view of the paper feed cassette 10. In the cassette base 25, a paper stacking plate 28 supported so as to be rotatable around a fulcrum 28a is disposed, and the paper 26 is placed on the paper stacking plate 28. Reference numeral 31 denotes a rear end cursor for aligning the rear ends of the paper 26, and is provided so as to be movable in parallel with the paper transport direction (from left to right in FIG. 6). A lift plate 33 that rotates together with the sector gear 32 is disposed below the sheet stacking plate 28, and a cassette side gear 34 is connected to the sector gear 32.

  The sheet cassette 10 is inserted into the apparatus main body, and the cassette side gear 34 is engaged with a gear 36 on the apparatus main body side (hereinafter referred to as apparatus main body side gear) 36 connected to a motor (not shown). The driving force is transmitted to the sheet stacking plate 28 via the lift plate 33. Further, the image forming apparatus 100 is provided with a sensor (not shown) that detects whether or not the upper surface of the paper 26 is at a predetermined paper feed position, and rotates the motor by a predetermined amount according to the detection result of the sensor. By gradually raising the tip of the lift plate 33, the paper 26 set on the paper stacking plate 28 is pressed against a pickup roller 29 provided on the apparatus main body side with a predetermined pressure. Here, when the copy start button of the image forming apparatus is turned on, the pickup roller 29 and the paper feed roller 30a of the paper feed roller pair 30 are rotationally driven in the direction of the arrow in the figure.

  One or a plurality of sheets 26 are usually fed to the paper feed roller pair 30 by the pickup roller 29. The plurality of sheets sent to the pair of paper feed rollers 30 are separated or transported toward the paper transport path 12 by the separation roller 30b that stops or rotates in the same direction as the paper feed roller 30a. The Reference numeral 35 denotes a cassette cover, the front side of which is exposed to the outside and constitutes a part of the exterior surface of the image forming apparatus 100 main body.

  In such an image forming apparatus, in order to replenish paper, the paper feed cassette 10 is pulled out from the apparatus body in the horizontal direction (rightward in FIG. 6), and after replenishing the paper, the paper feed cassette 10 is again reversed (see FIG. 6 to the left) and insert into the main body. FIG. 7 is a perspective view showing a state in which the paper feed cassette 10 is pulled out from the image forming apparatus main body.

  Guide ribs 41a and 41b that engage with cassette guides 40a and 40b provided on the inner side surface of the apparatus main body are provided on both the left and right sides of the cassette base 25. The paper feed cassette 10 is slid in the direction of the arrow AA '. The attachment / detachment operation from the main body of the image forming apparatus 100 is performed. Here, the guide rib 41b is not shown.

  As described above, in the conventional paper feeding mechanism, the pickup roller 29 is brought into contact with the upper surface of the stacked paper 26 and rotated in the paper feeding direction to feed the paper to the pair of paper feeding rollers 30 on the downstream side. Is. At this time, if the pickup roller 29 is pressed against the surface of the sheet even after the uppermost sheet is fed to the pair of sheet feeding rollers 30, noise is generated due to friction between the sheets due to a load during sheet conveyance. Double feed (double feed) occurs, or the paper separated by the separation roller 30b cannot be reliably returned into the cassette base 25.

  Therefore, for example, as disclosed in Patent Document 1, the pickup roller can be moved up and down, the pickup roller is lowered during the paper feeding operation and pressed against the paper, and the paper is raised by raising the pickup roller during the time other than the paper feeding operation. A sheet feeding device that is separated from the sheet is used. Further, the pressure contact force of the pickup roller is an important factor that affects the double feeding of sheets and the non-feeding (feeding error). That is, when the pressure contact force is higher than the optimum value, double feeding is likely to occur, and conversely, when it is lower than the optimum value, no paper feeding is likely to occur. Therefore, in Patent Document 2, a means for detecting the rotation amount (lifting amount) of the pickup roller in three or more stages is provided so that the rising amount of the paper stacking plate can be controlled according to the detection result.

  However, the method disclosed in Patent Document 1 requires a complicated cam mechanism as a lifting mechanism for the pickup roller, which causes a problem in that the configuration of the sheet feeding apparatus is complicated. There is also a problem that noise and vibration are generated due to an impact when the pickup roller falls on the upper surface of the paper. Further, in the method of Patent Document 2, the sheet height can always be maintained at a height suitable for paper feeding by controlling the rising amount of the paper stacking plate. Accordingly, since the pickup roller is pressed against or separated from the paper, noise or vibration may occur due to the weight of the roller when the pickup roller is pressed.

On the other hand, Patent Document 3 discloses a paper feeding device that raises and lowers a paper stacking plate in conjunction with a paper feeding start timing and a timing when a paper passes through a pair of conveyance rollers instead of raising and lowering a pickup roller. However, in the method of Patent Document 3, since the paper stacking plate does not rise after the previous paper is fed and until the next paper feed start signal is transmitted, the next paper feed is used as the paper feed start signal. It cannot be performed at the same time, and it has not been possible to meet the demand for high speed image forming apparatuses in recent years.
Japanese Patent No. 3787760 JP 2005-239294 A JP-A-3-2888731

  SUMMARY OF THE INVENTION In view of the above problems, the present invention includes a paper feed mechanism that suppresses the occurrence of rubbing noise and double paper feed due to constant pressure contact of a pickup roller, and a stable and quick paper feed operation, and the same. An object is to provide an image forming apparatus.

  In order to achieve the above object, the present invention is configured to press and contact a paper stacking plate that can be rotated up and down around the upstream end in the transport direction, and an upper surface of the paper stacked on the paper stacking plate. A feeding unit that sequentially feeds sheets by moving the surface in a predetermined direction; a sheet feeding roller that is disposed on the downstream side in the transport direction of the feeding unit; and a separation member that is disposed to face the sheet feeding roller, A sheet feeding mechanism comprising: a separating and conveying unit that conveys the sheets sent from the feeding unit one by one; an elevating unit that rotates the sheet stacking plate; and a control unit that controls driving of the elevating unit. A first detection unit that is disposed in the vicinity of the downstream side in the conveyance direction of the separation conveyance unit and that detects the passage of a sheet; and a second detection unit that detects the height of the delivery unit, and The control means is configured such that the first detection means is the leading edge of the paper. After the elevating means is driven at a timing when the passage is detected and the sheet stacking plate is lowered by a predetermined amount from the paper feed position, the elevating means is detected at a timing when the first detection means detects the passage of the trailing edge of the paper. Is driven to raise the paper stacking plate to the paper feed position, and the paper feed position is determined based on the detection result of the second detection means.

  The present invention also provides an image forming apparatus equipped with the paper feed mechanism having the above-described configuration.

  According to the first configuration of the present invention, the pressure contact force of the sending means is relaxed or released at the timing when the leading edge of the paper passes through the separating and conveying means, and the sending means is again at the timing when the trailing edge of the paper passes through the separating and conveying means. Is pressed against the upper surface of the sheet, so that the load during sheet conveyance can be reduced without lowering the sheet feeding speed, and noise due to sheet rubbing and double sheet feeding can be effectively suppressed. Further, since the sending means is pressed and separated by raising and lowering the paper stacking plate, the impact between the sending means and the upper surface of the paper can be mitigated, and noise and vibration can be suppressed. Furthermore, since the paper feed position for raising the paper stacking plate is determined based on the detection result of the second detection means, there is no possibility that the pressure contact force of the delivery means will vary.

  In addition, according to the second configuration of the present invention, it is possible to effectively prevent problems such as a paper feed error and printing misalignment by mounting the paper feed mechanism of the first configuration, and image forming efficiency. In addition, the image forming apparatus is excellent also in quietness.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus provided with a paper feed mechanism of the present invention. In the image forming apparatus (here, a color printer) 100, when performing a copying operation, the photosensitive drum 1 that rotates counterclockwise in the drawing is uniformly charged by the charging unit 2 in the apparatus main body. The exposure unit 3 irradiates the photosensitive drum 1 with a laser beam based on the original image data input to an image input unit (not shown) from a personal computer or the like, and the electrostatic latent image on the photosensitive drum 1. Is formed.

  The photosensitive drum 1 is formed, for example, by laminating a photosensitive layer on an aluminum drum, and the surface is charged by a charging unit 2. Then, an electrostatic latent image in which charging is attenuated is formed on the surface that has received the laser beam from the exposure unit 3. As the photosensitive material for forming the photosensitive layer, an amorphous silicon photoreceptor or a positively charged organic photoreceptor (positive OPC photoreceptor) is used. When positive OPC is used as the photosensitive layer, the generation of ozone or the like is small and charging is stable. In particular, the positive OPC having a single-layer structure has little change in photosensitive characteristics even when the film thickness changes after long-term use. Since the image quality is stable, it is preferably used in a system having a long life.

  Reference numeral 4 denotes a rotary developing unit that supplies toner onto the photosensitive drum 1. The developing unit 4 includes cartridge-type yellow, magenta, cyan, and black developing devices 4a, 4b, 4c, and 4d in which a developing device and a toner container are integrated, and the developing devices 4a to 4d are photoreceptors. By sequentially rotating to a position facing the drum 1, positive polarity toner is attached to the electrostatic latent image on the photosensitive drum 1 to form toner images of each color.

  Reference numeral 5 denotes an intermediate transfer belt onto which a toner image is transferred. The intermediate transfer belt is passed over intermediate transfer rollers 6a and 6b, a belt driving roller 8 and a driven roller 9, and is in contact with the photosensitive drum 1 by a driving means (not shown). Rotate clockwise. A sheet made of dielectric resin is used for the intermediate transfer belt 5, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used.

  When the user inputs image formation start, a yellow toner image is formed on the photosensitive drum 1 at a predetermined timing. The yellow toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 5 by the intermediate transfer rollers 6a and 6b to which a negative transfer bias is applied (primary transfer). Thereafter, the toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning roller 7a and the cleaning blade 7b, and the developing unit 4 rotates by a predetermined amount (here, 90 °), and this time, the magenta toner image is the same as described above. Are formed on the photosensitive drum 1 and transferred onto the intermediate transfer belt 5.

  Thereafter, cyan and black toner images are transferred onto the intermediate transfer belt 5 from the photosensitive drum 1 by the same method as described above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. A transfer roller 15 is positioned below the intermediate transfer belt 5, and a belt cleaning blade 16 removes residual toner on the surface of the intermediate transfer belt 5.

  As described above, the paper 26 is directed from the paper feed cassette 10 to the intermediate transfer belt 5 on which the toner image is formed via the pickup roller 29, the paper feed roller pair 30, the transport rollers 11, 13, and the registration roller pair 14. The full color toner images that are conveyed and sequentially formed on the surface of the intermediate transfer belt 5 are transferred onto the paper 26 at a time (secondary transfer) by the transfer roller 15 to which a negative transfer bias is applied. The paper 26 onto which the toner image has been transferred is conveyed to a fixing device 17 having a heating roller 17a and a pressure roller 17b to fix the toner image. The paper 26 that has passed through the fixing device 17 is discharged to the discharge tray 20 via the paper conveyance path 18 and the discharge roller pair 19.

  FIG. 2 is a side view of the paper feed mechanism of the present invention. Portions common to FIG. 1 and FIG. 6 of the conventional example are denoted by the same reference numerals, and description thereof is omitted. The paper feed mechanism 40 of the present invention includes a paper stacking plate 28, a pickup roller 29, a paper feed roller pair 30, a lift plate 33, a first detection sensor 49, a second detection sensor 50, and the like. When 10 is inserted into the image forming apparatus 100 (see FIG. 1), the pickup roller 29 is disposed so as to contact the upper surface end on the downstream side in the transport direction of the paper 26 stacked on the paper stacking plate 28. . Here, the fan-shaped gear 32, the cassette side gear 34, and the apparatus main body side gear 36 (all of which are shown in FIG. 6), which are the rotation means of the lift plate 33, are omitted.

  The pickup roller 29 and the paper feed roller 30a are unitized in a frame body 41, and the frame body 41 is supported so as to be rotatable up and down around the rotation axis of the paper feed roller 30a. One end of a compression spring 42a is connected to the upper surface of the frame 41, and the other end of the compression spring 42a is fixed to a main body frame (not shown). Thereby, the frame body 41 is urged toward the paper stacking plate 28.

  Further, the separation roller 30b and the transport roller 13 are pressed against the paper feed roller 30a and the transport roller 11 with a predetermined pressure by compression springs 42b and 42c, respectively. The separation roller 30b has a built-in torque limiter 43 that controls the rotation of the separation roller 30b when a plurality of sheets are fed to the nip portion between the sheet feeding roller 30a and the separation roller 30b.

  Reference numeral 49 denotes a first detection sensor that detects the conveyance of the sheet 26 stacked on the sheet stacking plate 28, and is disposed in the vicinity of the downstream side in the conveyance direction of the pair of paper feed rollers 30. A detection result by the first detection sensor 49 is transmitted to a control unit (described later), and it is detected whether or not the paper 26 has passed the pair of paper feed rollers 30 based on the detection result. As the first detection sensor 49, various sensors capable of detecting whether or not a sheet has passed can be used. In this example, an arm-type sensor that directly detects a sheet and detects the sheet is used. Instead of the arm type sensor, for example, a reflection type sensor that emits light from the light emitting unit to the paper and detects reflected light from the paper surface by the light receiving unit may be used.

  Reference numeral 50 denotes a second detection sensor that detects the height of the pickup roller 29, and a detection unit 50a including a light emitting unit and a light receiving unit is provided on the opposed inner surfaces of the U-shape in plan view. When the flag 51 protruding from the tip of the frame body 41 passes through the detection unit 50a and the optical path is blocked or opened, the light reception signal level of the detection unit 50a is switched to LOW or HIGH, and the rotation of the frame body 41 is performed. The moving position, that is, the height of the pickup roller 29 can be detected. In FIG. 2, the detection unit 50 a is blocked by the flag 51 and the light reception signal of the second detection sensor 50 is LOW, and the state where the upper surface of the paper 26 is raised to a predetermined paper feed position is detected.

  3 is a side view of the paper feed mechanism showing a state in which the lift plate 30 is rotated counterclockwise to lower the paper stacking plate 28, and FIG. 4 is a block diagram showing a control path of the paper feed mechanism of the present invention. FIG. 5 is a flowchart showing a paper feed control procedure by the paper feed mechanism. With reference to FIGS. 2 to 4, the lifting control of the pickup roller 29 will be described according to the steps of FIG. 5. First, when a print signal is received by the control unit 57 in response to a print start command or the like (step S1), the second detection sensor 50 confirms that the pickup roller 29 is at a predetermined paper feed position (the light reception signal is LOW level). (Step S2). Next, the roller drive motor 53 is rotationally driven by the control signal transmitted from the control unit 57, and the pickup roller 29 and the paper feed roller 30a are rotated counterclockwise in FIG. 2 to start paper feeding (step S3). .

  Next, as shown in FIG. 3, it is determined whether or not the uppermost sheet 26a has been conveyed by a predetermined amount and the first detection sensor 49 is turned on at the leading end of the sheet (step S4). When the ON signal of the first detection sensor 49 is transmitted to the control unit 57, the leading end of the paper 26a passes through the pair of paper feed rollers 30, so the control signal is transmitted from the control unit 57 and the lift plate drive motor 55 is rotated by a predetermined amount. Accordingly, the lift plate 33 is rotated by a predetermined amount counterclockwise in FIG. 3, and the paper stacking plate 28 is lowered from the position (paper feed position) in FIG. 2 (step S5).

  When the paper stacking plate 28 is lowered by a predetermined amount, the urging force of the compression spring 42a is applied to the weight of the pickup roller 29 and the frame body 41, and the frame body 41 is also moved downward from the paper feed position (the broken line position in FIG. 3). At this time, since the flag 51 is retracted downward from the detection unit 50a of the second detection sensor 50 and the light reception signal becomes a HIGH level, it is detected that the sheet stacking plate 28 has been lowered to a predetermined lowered position (step S6). .

  When the detection result is transmitted to the control unit 57, a control signal is transmitted from the control unit 57, the lift plate driving motor 55 is stopped, and the lowering of the sheet stacking plate 28 is stopped (step S7). At this time, as shown in FIG. 3, since a gap is formed between the upper surface of the sheet and the pickup roller 29, the rotational load of the roller drive motor 53 can be reduced, and the sheet can be conveyed smoothly. Occurrence of rubbing noise between sheets and double feeding of sheets can also be suppressed.

  Next, it is determined whether or not the sheet 26a is further conveyed by a predetermined amount, the trailing edge of the sheet passes through the first detection sensor 49, and the first detection sensor 49 is turned off again (step S8). When the OFF signal of the first detection sensor 49 is transmitted to the control unit 57, the rear end of the sheet 26a passes through the pair of paper feed rollers 30, and therefore a control signal is transmitted from the control unit 57 to generate a roller drive motor. 53 is stopped, and the rotation of the pickup roller 29 and the paper feed roller 30a is stopped (step S9).

  Accordingly, the lift plate drive motor 55 is reversely rotated by a predetermined amount, whereby the lift plate 33 is rotated by a predetermined amount clockwise in FIG. 3, and the paper stacking plate 28 is raised to the position (feeding position) in FIG. (Step S10). At this time, since the flag 51 shields the detection unit 50a of the second detection sensor from below, the light reception signal becomes the LOW level again, and it is detected that the paper stacking plate 28 has been raised to the paper feed position. Then, the control signal is transmitted to stop the lift plate driving motor 55, and the lifting of the paper stacking plate 28 is stopped.

  Then, it is determined whether or not the paper feeding is completed (step S11). If the paper feeding is finished, the process is finished as it is. On the other hand, if continuous printing is input and paper feeding continues, the process returns to step S2, and the same procedure is repeated thereafter (steps S2 to S11).

  According to the above control procedure, the pickup roller 29 and the upper surface of the sheet are separated from each other when the leading edge of the sheet passes the pair of paper feeding rollers 30, and the pickup roller 29 is moved to the upper surface of the sheet when the trailing edge of the sheet passes the pair of feeding rollers 30. Therefore, the load of the roller drive motor 53 does not increase when the paper is fed, and the rubbing between the papers and the double feeding of the paper can be effectively reduced. In addition, since the time during which the pickup roller 29 and the upper surface of the paper are separated is short, there is no risk of reducing the paper feeding efficiency, and the present invention can be applied to an image forming apparatus with a high printing speed.

  Further, by raising and lowering the paper stacking plate 28 using the lift plate 33 and the lift plate drive motor 55, the pickup roller 29 has less impact when coming into contact with the upper surface of the paper than the configuration in which the pickup roller 29 is raised and lowered, and noise. And the occurrence of vibrations can be reduced. Since the paper feed position at which the paper stacking plate 28 is stopped is determined each time based on the detection result of the second detection sensor 50, the pressure contact force of the pickup roller 29 varies even if the paper 26 on the paper stacking plate 28 decreases. There is no risk.

  The lowering position of the paper stacking plate 28 may be set as appropriate according to the type of paper used, such as the paper size and thickness, or the specifications of the paper feed mechanism. For example, as shown in FIG. 3, the pressure contact force of the pickup roller 29 may be relaxed without being lowered to a position where the upper surface of the sheet and the pickup roller 29 are completely separated from each other. However, if the upper surface of the sheet and the pickup roller 29 are in contact with each other even a little, there is a possibility that the sheet will be double fed due to friction. Therefore, it is preferable to lower the paper stacking plate 28 to a position where the upper surface of the paper and the pickup roller 29 are completely separated from each other.

  In the above embodiment, both the rising position (paper feeding position) and the lowering position of the paper stacking plate 28 are determined based on the detection result of the second detection sensor 50. However, the lowering position of the paper stacking plate 28 is The upper surface of the paper 26 and the pickup roller 29 need only be separated from each other and need not be strictly controlled as compared with the paper feed position. For example, even if the control is performed by the drive amount (rotation speed) of the lift plate drive motor 55. good.

  Further, the arrangement of the first detection sensor 49 is not limited to the vicinity of the downstream side in the conveyance direction of the pair of paper feed rollers 30, and may be arranged further downstream in the conveyance direction. However, as shown in FIGS. 2 and 3, in order to prepare for feeding the next sheet by re-raising the sheet stacking plate 28 as soon as possible after the previous sheet is fed, as shown in FIGS. 30 is preferably arranged as close as possible to the downstream side in the conveyance direction.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the pickup roller 29 and the paper feed roller 30a are unitized. However, the pickup roller 29 may be provided separately from the paper feed roller 30a. A configuration in which a separation pad is arranged instead of the separation roller 30b is also possible.

  In the above embodiment, the lift plate 33 is rotated by the sector gear 32, the cassette side gear 34, the apparatus main body side gear 36, and the lift plate drive motor 55, but a drive coupling mechanism is provided at the rotation fulcrum of the lift plate 33. It is good also as a structure which is directly connected to a motor and rotates.

  Further, here, a printer is described as an example of the image forming apparatus. However, if the paper feed mechanism of the present invention has a configuration in which the paper feed cassette is detachable in the horizontal direction, other image formation such as a copying machine or a facsimile machine is possible. It can also be applied to devices. Furthermore, in the above-described embodiment, the paper feeding mechanism that is mounted on the image forming apparatus and used as the paper supply source has been described as an example. Needless to say, the present invention can also be applied to an automatic document feeder that sequentially feeds a plurality of sheet documents.

  According to the present invention, a sheet stacking plate that can be rotated up and down around the upstream end in the transport direction and a top surface of the sheet stacked on the sheet stacking plate are pressed against each other, and the pressing surface is moved in a predetermined direction. A sheet feeding unit that sequentially feeds the sheet, a sheet feeding roller that is disposed on the downstream side of the sheet feeding direction of the sheet feeding unit, and a separation member that is disposed to face the sheet feeding roller. In a paper feed mechanism comprising separation and conveyance means that conveys and conveys the sheets one by one, lifting and lowering means for rotating the paper stacking plate, and control means for controlling driving of the lifting and lowering means, the separation and conveyance means downstream in the conveyance direction A first detection unit disposed near the side for detecting the passage of the paper and a second detection unit for detecting the height of the sending unit are provided. Used to drive the lifting means at the timing of detecting the passage of the tip After the stacking plate is lowered from the paper feeding position by a predetermined amount, the lifting / lowering unit is driven to raise the paper stacking plate to the paper feeding position at the timing when the first detection unit detects the passage of the trailing edge of the paper. The paper position is determined based on the detection result of the second detection means.

  As a result, it is possible to provide a paper feeding mechanism that can effectively suppress an increase in load during paper conveyance and double feeding of paper without reducing the paper feeding speed with a simple configuration. In addition, since the pressure contact force of the sending means is adjusted by raising and lowering the paper stacking plate, the impact between the sending means and the upper surface of the paper can be alleviated to suppress noise and vibration. Further, since whether or not the paper stacking plate has been raised to the paper feed position is determined by the second detection means, there is no possibility that the pressure contact force of the sending means will fluctuate.

  In addition, when the paper feed mechanism of the present invention is installed, it is possible to reduce the load on the motor and the occurrence of double paper feed during paper transport without reducing the image formation efficiency, paper feed errors, printing misalignment, etc. Therefore, it is possible to realize an image forming apparatus that is less likely to cause the above problem and that is excellent in quietness.

FIG. 2 is a side cross-sectional view showing the overall configuration of an image forming apparatus equipped with a paper feed mechanism of the present invention. FIG. 3 is a side view of the paper feed mechanism of the present invention (in a state where the paper stacking plate is raised). FIG. 3 is a side view of the paper feed mechanism of the present invention (a state where the paper stacking plate is lowered). These are block diagrams which show the control path | route of the paper feed mechanism of this invention. These are the flowcharts which show the raising / lowering control procedure of the paper stacking board by the paper feed mechanism of this invention. These are side surface sectional drawings which show the structure of the conventional paper feed cassette and paper feed mechanism. FIG. 5 is a perspective view showing a state in which the paper feed cassette is pulled out from the apparatus main body.

Explanation of symbols

10 Paper Feed Cassette 28 Paper Loading Plate 29 Pickup Roller (Sending Out)
30 Paper feed roller pair (separation transport means)
30a Paper feed roller 30b Separation roller (separation member)
33 Lift plate (lifting means)
DESCRIPTION OF SYMBOLS 40 Paper feed mechanism 41 Frame 42a-42c Compression spring 43 Torque limiter 49 1st detection sensor (1st detection means)
50 Second detection sensor (second detection means)
53 Roller drive motor 55 Lift plate drive motor (lifting means)
57 Control unit (control means)
100 Image forming apparatus

Claims (2)

A paper stacking plate that can rotate up and down around the upstream end in the transport direction;
Sending means that is pressed against the upper surface of the paper stacked on the paper stacking plate, and that sequentially transfers the paper by moving the pressure contact surface in a predetermined direction;
Separation and conveyance, comprising a sheet feeding roller disposed downstream in the conveyance direction of the feeding means and a separating member disposed to face the sheet feeding roller and conveying the sheets fed from the feeding means one by one Means,
Elevating means for rotating the paper stacking plate;
A control mechanism for controlling the driving of the lifting and lowering means,
A first detection unit that is disposed near the downstream side of the separation conveyance unit in the conveyance direction and detects the passage of the paper; and a second detection unit that detects the height of the sending unit;
The control means drives the elevating means at a timing when the first detection means detects the passage of the leading edge of the paper to lower the paper stacking plate by a predetermined amount from the paper feed position, and then performs the first detection. When the means detects the passage of the trailing edge of the paper, the lifting / lowering means is driven to raise the paper stacking plate to the paper feed position, and the paper feed position is determined based on the detection result of the second detection means. A paper feed mechanism characterized by determining.   An image forming apparatus comprising the paper feed mechanism according to claim 1.

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