JP4144428B2 - Sheet feeding device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sheet supply apparatus for supplying a recording sheet to a printing unit of a copying machine or a printer that forms a recorded image using an electrophotographic method or the like, and more specifically, various types supplied to the printing unit The present invention relates to an improvement for forming a recorded image with better image quality on the recording sheet.
[0002]
[Prior art]
[Patent Document 1]
JP-A-5-330696 [Patent Document 2]
Japanese Patent Laid-Open No. 9-6066 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-68528
In an image forming apparatus such as a copying machine or a printer that forms a recorded image using an electrophotographic method, a toner image corresponding to image information is formed on a photosensitive drum, and then transferred to a recording sheet. The toner image is fixed on the recording sheet by inserting the recording sheet through a heat fixing device. In recent years, instead of directly transferring a toner image from a photosensitive drum to a recording sheet, the toner image is primarily transferred from the photosensitive drum to a belt-shaped or drum-shaped intermediate transfer member, and the toner image on the intermediate transfer member is transferred. Is often used for color copying machines and color printers that require superposition of toner images of a plurality of colors.
[0004]
As a method of transferring a toner image from a photosensitive drum or an intermediate transfer member to a recording sheet, a transfer electric field is formed between the photosensitive drum or the like and a transfer member disposed on the back side of the recording sheet so as to have a predetermined polarity. A method is generally performed by applying an electrostatic attraction to the charged toner. However, there are a plurality of types of recording sheets such as plain paper, glossy paper, OHP film, and the resistance value is different for each recording sheet. Therefore, a constant voltage is always applied between the photosensitive drum and the transfer member. In this case, a transfer electric field having an appropriate magnitude for the transfer of the toner image cannot be formed, and the transfer voltage applied to all the transfer members needs to be controlled according to the type of the recording sheet. Is done. Also, in fixing a toner image by a heat fixing device, since the heat capacity varies depending on the type of recording sheet, for example, when fixing a toner image on an OHP film, sufficient heat energy can be applied. It is necessary to control such that the temperature of the heat fixing device is set higher or the OHP film is inserted into the heat fixing device at a lower speed than other recording sheets. Therefore, if a higher-quality recorded image is to be formed, the type of recording sheet to be used is discriminated, and image forming conditions such as transfer voltage, heating and fixing temperature, and process speed are appropriate according to the type of recording sheet. It is desirable to set to.
[0005]
In order to determine the type of recording sheet in a copier or printer, there is a method of directly specifying the type of recording sheet to be used by a user who uses these, but JP-A-5-330696 and JP-A-9-6066. Japanese Patent Laid-Open No. 2002-68528 discloses a technique in which a sensor for detecting the surface state of a recording sheet is provided in the course of the recording sheet conveyance path, and the type of the recording sheet is optically detected using the surface detection sensor. Disclosure. The surface detection sensor is composed of a light emitting unit composed of an LED element that illuminates the surface of the recording sheet, and a light receiving unit such as a photodiode that receives reflected light from the recording sheet, and is generated on the surface of the recording sheet. The type of the recording sheet is determined by measuring the intensity of the regular reflection light or irregular reflection light. For example, when comparing plain paper and OHP film, the OHP film generates almost no irregularly reflected light, whereas plain paper has a larger amount of irregularly reflected light than regular reflected light, and glossy paper is used for OHP. Although it is not as much as a film, it has a feature that specular reflection light is larger than that of plain paper. Therefore, according to this method, it is possible to determine the type of the recording sheet by measuring the amount of either regular reflection light or irregular reflection light, and using the determination result, the toner image It is possible to set image forming conditions such as a transfer voltage, a heat fixing temperature, and a process speed that are optimum for a recording sheet on which transfer is performed.
[0006]
[Problems to be solved by the invention]
However, all of the conventionally known surface detection sensors are provided in the middle of the recording sheet conveyance path, and the surface of the recording sheet being conveyed is measured. The positional relationship between the detection sensor and the measurement surface of the recording sheet is not stable, and even if the same type of recording sheet is conveyed, the detection signal of the surface detection sensor varies greatly, and the type of the recording sheet is correctly determined. There was a problem that it was not possible.
[0007]
Japanese Laid-Open Patent Publication No. 9-6066 discloses a method of using the surface detection sensor in which, for example, the type of a recording sheet designated by a user in a print job is different from the type of recording sheet detected by the surface detection sensor. In such a case, it is disclosed that a warning message is displayed to the user. However, as disclosed in the publication, when the surface detection sensor is provided in the middle of the conveyance path of the recording sheet, specifically, in the middle of the conveyance path from the paper feed tray to the toner image transfer portion, Even if the warning is displayed because the type of the recording sheet is different, the recording sheet has already been taken into the printing unit from the paper feed tray at that time, and the user must remove this recording sheet before recording the correct type. There is a problem that printing cannot be performed on a sheet.
[0008]
The present invention has been made in view of such problems, and an object of the present invention is to provide a recording sheet before supplying the recording sheet to a printing unit of an image forming apparatus such as a copying machine or a printer. An object of the present invention is to provide a sheet supply apparatus that can accurately determine the type and contribute to the convenience of the user.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a sheet feeding apparatus according to the present invention includes a sheet feeding tray on which recording sheets are stacked, and a sheet feeding roll that feeds a recording sheet on the sheet feeding tray toward a printing unit in the image recording apparatus. And a sheet separating member that is opposed to the paper feed roll across the conveyance path of the recording sheet and prevents double feeding of the recording sheet, and is pressed against the paper feed roll and stopped on the paper feed tray A surface detection sensor that illuminates the surface of the recording sheet in a state, receives the reflected light and outputs a detection signal corresponding to the surface state of the recording sheet, and determines the type of the recording sheet from the detection signal of the surface detection sensor It comprises a sheet discriminating means for discriminating.
[0010]
According to such technical means, the surface detection sensor detects the surface state of the stationary recording sheet set on the paper feed tray, not the recording sheet being conveyed. In addition, since the surface detection sensor performs detection in a state where the recording sheet is pressed against the paper feed roll, the surface of the recording sheet detected by the surface detection sensor always exists at a certain position. recording sheet and a is kept in a fixed positional relationship but could do al discovery. As a result, when the same type of recording sheet is set in the paper feed tray, the amount of reflected light generated on the surface of the recording sheet is prevented from being different, and the detection signal of the surface detection sensor is prevented from varying. This makes it possible to more accurately determine the type of recording sheet.
[0011]
Here, in order to prevent erroneous detection by the surface detection sensor, the recording sheet may be set at a predetermined position on the paper feed tray before the surface detection sensor detects the surface state of the recording sheet. From this point of view, a sheet confirmation sensor for detecting that the recording sheet is set at a predetermined position on the paper feed tray is provided, and after the sheet confirmation sensor detects the presence of the recording sheet, It is preferable that the sheet discriminating means is configured to read the detection signal of the surface detection sensor.
[0012]
For the same reason, in a sheet feeding apparatus having a bottom plate that lifts the leading end of a recording sheet toward the sheet feeding roll in the sheet feeding tray, the bottom of the sheet feeding apparatus is set after the recording sheet is set on the sheet feeding tray. It is preferable that the sheet discriminating unit reads the detection signal of the surface detection sensor after the plate is completely lifted, that is, after the uppermost recording sheet comes into contact with the paper feed roll.
[0013]
Further, from the viewpoint of stabilizing the positional relationship between the uppermost recording sheet stored on the paper feed tray and the surface detection sensor, the surface detection sensor is arranged in the axial direction of the paper feed roll. It is preferable to be arranged so as to overlap with the paper roll. By arranging the surface detection sensor in such a position, the recording sheet can be detected the surface state of the recording sheet in the vicinity of a position in contact with the sheet feed roller, further detection signal of the surface detection sensor Variations can be eliminated.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the sheet feeding apparatus of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 shows an example of a full-color laser beam printer M to which the sheet feeding apparatus of the present invention can be applied. The full-color printer M includes a printing unit 10 that forms a recording image according to image information on a recording sheet, and includes a paper feed cassette 20 and a manual feed tray 30 that supply the recording sheet to the printing unit 10. Yes.
[0015]
A process cartridge 11 for forming a toner image by an electrophotographic process is mounted on the printing unit 10, and a raster scanning unit 12 is provided adjacent to the process cartridge 11. The process cartridge 11 includes four photosensitive drums corresponding to yellow Y, magenta M, cyan C, and black K, and these photosensitive drums are arranged in a vertical row. The raster scanning unit 12 emits four laser beams modulated in accordance with the image information of each color, and these laser beams expose the photosensitive drums of the respective colors, respectively, and the image data on the photosensitive drums according to the image information. An electrostatic latent image is formed. On the other hand, around each photosensitive drum of the process cartridge 11, a charging roll for charging the photosensitive drum to a uniform background potential prior to exposure by the laser beam, and an electrostatic latent formed on the photosensitive drum. A developing unit for developing the image with toner and a cleaner for cleaning the photosensitive drum are provided, and a toner image corresponding to image information of each color is formed on the photosensitive drum by an electrophotographic process. Reference numerals 13Y, 13M, 13C, and 13K in the figure are toner cartridges for supplying toner to the color developing devices of the process cartridge 11.
[0016]
Of the four photosensitive drums, two photosensitive drums corresponding to yellow Y and magenta M are in contact with the first primary intermediate transfer drum 14, and yellow Y and The magenta M toner image is primarily transferred to the first primary intermediate transfer drum 14. The two photosensitive drums corresponding to cyan C and black K are in contact with the second primary intermediate transfer drum 15, and the cyan C and black K toner images formed on these photosensitive drums are the first ones. 2 is primarily transferred to the primary intermediate transfer drum 15. Further, the first and second primary intermediate transfer drums 14 and 15 are in contact with the secondary intermediate transfer drum 16, and the two-color multiple toner images formed on the primary intermediate transfer drums 14 and 15 are secondary intermediate images. Secondary transfer to the transfer drum 16 is performed, and a multi-toner image of four colors is formed on the secondary intermediate transfer drum 16 so as to overlap each other. The four-color multiple toner images transferred onto the secondary intermediate transfer drum 16 in this way are transferred onto the recording sheet P by the final transfer roll 17.
[0017]
The recording sheet P is fed from the paper feed cassette 20 housed in the lower part of the printer casing 1 or from the manual feed tray 30 provided on the front side of the printer casing 1 to the printing unit 10 of the printer, specifically, the secondary intermediate transfer drum. 16 and supplied to a transfer position between the final transfer roll 17. The sheet feeding cassette 20 is configured to be pushed into the lower portion of the printer housing 1 from the front side and set, and the recording sheet P accommodated in the cassette 20 is placed on the upper portion of the set sheet feeding cassette 20. A pickup roll 21 for pulling out is provided. Further, a paper feed roll 22 that feeds the recording sheet P and a retard roll 23 that faces the paper feed roll 22 and prevents double feeding of the recording sheet P are arranged at the front end of the paper feed cassette 20. It is installed.
[0018]
On the other hand, the manual feed tray 30 is provided so as to be freely opened and closed as a part of the front cover of the printer. When used, the recording sheet P is placed on the manual feed tray 30 that is pulled down along the one-dot chain line arrow in the figure. In addition, only the leading end portion of the recording sheet P is inserted into the manual feed port formed by opening the manual feed tray 30 for use. A paper feed roll 31 and a retard roll 32 that is in pressure contact with the paper feed roll 31 are disposed immediately inside the manual paper feed slot. By the functions of the paper feed roll 31 and the retard roll 32, the paper feed roll 31 is placed on the manual feed tray 30. The set recording sheets P are separated one by one and supplied to the toner image transfer position.
[0019]
The recording sheet P supplied from the paper feed cassette 20 or the manual feed tray 30 in this way is aligned with respect to the toner image transfer timing by the registration roll 18 disposed in front of the transfer roll 17, and is then The sheet is fed between the next intermediate transfer drum 16 and the transfer roll 17, and a four-color multiple toner image corresponding to the image information is transferred onto the recording sheet P. The recording sheet P to which the toner image has been transferred is inserted into the fixing device 19 and the toner image is fixed. Then, the recording sheet P passes through the discharge roll 40 and faces the discharge tray 1a provided on the upper portion of the printer casing 1. It is discharged in the down state. A reference numeral 41 in FIG. 1 denotes a sheet reversing path for double-sided printing, and is configured to pull back the recording sheet P discharged from the fixing device 19 and re-feed it to the registration roll 18.
[0020]
FIG. 2 is a perspective view showing the paper feed roll 31 and the retard roll 32 disposed around the manual paper feed port of the printer housing 1 and the periphery thereof. Between the manual feed tray 30 (not shown in FIG. 2) and the retard roll 32, a bottom plate 34 that swings around a support shaft 33 is disposed, and the bottom plate 34 is set on the manual feed tray 30 for recording. The leading end of the sheet P is pushed up from below and is brought into contact with the paper feed roll 31. For this reason, when the paper feed roll 31 rotates, the recording sheets P set on the manual feed tray 30 are sequentially drawn from the uppermost recording sheet P toward the registration roll 18, and the set recording sheets P As the number of sheets decreases, the bottom plate 34 rises toward the paper feed roll 31.
[0021]
A surface detection sensor 35 is provided adjacent to the paper feed roll 31 in the axial direction of the paper feed roll 31. The surface detection sensor 35 is generated on the surface of the recording sheet P by the illumination means such as an LED element that illuminates the surface of the uppermost recording sheet P among the recording sheets P set in the manual feed tray 30. It includes a light receiving element such as a photodiode that receives reflected light and outputs a detection signal having an intensity corresponding to the amount of light received. Reflected light generated when the surface of the recording sheet is illuminated can be classified into regular reflection light and irregular reflection light, and the amount of reflected light increases depending on the surface state of the recording sheet. Since the surface of the film is extremely smooth, almost no irregular reflection light is generated, and most of the illumination light is regularly reflected. Also, plain paper is the opposite, and the amount of diffusely reflected light tends to be overwhelmingly larger than the amount of specularly reflected light. Therefore, by receiving the one of the regularly reflected light or diffuse reflection by the light receiving element, if outputs a detection signal corresponding to the light quantity of its, by comparing such detected signal with a predetermined threshold level, a manual The surface state of the recording sheet P set on the tray 30 can be grasped, and the type of the recording sheet P can be determined.
[0022]
In particular, the surface detection sensor 35 of this embodiment has a light receiving element that receives specularly reflected light generated on the surface of the recording sheet P and a light receiving element that receives diffusely reflected light in order to increase the accuracy of determining the type of the recording sheet P Are provided separately so that detection signals output from the respective light receiving elements can be compared. That is, by grasping the ratio of the amount of specularly reflected light and the amount of diffusely reflected light generated on the surface of the recording sheet P, it is more accurate than when the type of the recording sheet P is determined using only one of the light amounts. In addition, many types of recording sheets P can be discriminated.
[0023]
FIG. 3 is a block diagram showing a control system for detection signals of the surface detection sensor 35. The surface detection sensor 35 outputs a current value corresponding to the amount of light received by the light receiving element. The current value is converted into a voltage value via an amplifier 36 and amplified, and is input to the sheet determination unit 37 as a detection signal. The The sheet discriminating means 37 is configured as a part of a controller 38 that controls the printing unit. The controller is configured as a computer system, and the nonvolatile memory of the recording sheet P that can be used by the printer is provided. A table indicating the type and the ratio of the specular reflection light detection signal and the irregular reflection light detection signal corresponding to each recording sheet P is stored in advance. As a result, the sheet discriminating means 37 reads the detection signals of the pair of light receiving elements provided in the surface detection sensor 35, and then applies the ratio of these detection signals to the table to thereby set the recording set on the manual feed tray 30. The type of the sheet P can be discriminated.
[0024]
When the type of the recording sheet P is discriminated by the sheet discriminating means 37, a transfer voltage corresponding to the type of the recording sheet P is set for the high voltage power source 50, or the process speed corresponding to the type of the recording sheet P is set. Is set in the main motor 51 for driving the process cartridge 11, and further, a heating temperature corresponding to the type of the recording sheet P is set in the fixing device 19.
[0025]
4 and 5 are views in which the positional relationship between the recording sheet P set on the manual feed tray 30 and the surface detection sensor 35 is observed from the axial direction of the paper feed roll 31. FIG. When the recording sheet P is set on the manual feed tray 30, as shown in FIG. 4 , the bottom plate 34 is in a lowered state, whereby the leading edge of the recording sheet P is moved between the bottom plate 34 and the paper feed roll 31. It can be inserted in between. In this state, the positional relationship between the front end of the recording sheet P set on the manual feed tray 30 and the surface detection sensor 35 is not constant. For example, when the front end of the recording sheet P is curled, the curl Depending on the degree, the direction and distance of the recording sheet surface with respect to the surface detection sensor 35 are different. That is, as shown in FIG. 6, even if the illumination means 35a of the surface detection sensor 35 illuminates the surface of the recording sheet P, if the surface of the recording sheet P does not face the surface detection sensor 35, the correctness is detected. It becomes impossible for the light receiving element 35b to receive the reflected light.
[0026]
Therefore, in this embodiment, as shown in FIG. 5, after the bottom plate 34 is lifted and the leading edge of the recording sheet P set on the manual feed tray 30 is pressed against the paper feed roll 31, the surface detection sensor 35. Is used to detect the surface condition of the recording sheet P. When the bottom plate 34 is raised in this way, the leading edge of the recording sheet P set on the manual feed tray 30 is sandwiched between the bottom plate 34 and the paper feed roll 31, so that the curl is formed at the leading edge of the recording sheet P. Even in such a case, the leading edge of the recording sheet P is pressed down so as to be in close contact with the bottom plate 34. As a result, as shown in FIG. 7, the surface of the uppermost recording sheet P on the manual feed tray 30 can face the surface detection sensor 35 at a certain angle and distance, and the detection signal of the surface detection sensor 35 is It can be stable for each type of recording sheet. In particular, in the present embodiment, the surface detection sensor is disposed so as to overlap the paper feed roll in the axial direction of the paper feed roll, so that the surface detection sensor is located near the surface of the recording sheet in contact with the paper feed roll. The positional relationship between the surface of the recording sheet P and the surface detection sensor 35 is extremely stable.
[0027]
FIG. 8 is a flowchart showing a processing procedure in the sheet discriminating means 37. First, it is checked whether or not the recording sheet P is set on the manual feed tray 30 (ST1). This check can be performed by providing a sheet confirmation sensor 60 for confirming the set state of the recording sheet P on the manual feed tray 30 separately from the surface detection sensor 35 and checking the detection signal of the sheet confirmation sensor 60. . In this case, in order to detect that the leading edge of the recording sheet P is securely inserted to the back of the manual feed tray 30, the sheet check sensor 60 inserts the recording sheet P into the manual feed tray 30 as shown in FIG. 9. It is preferable that it is provided in the back | inner side rather than the said surface detection sensor 35.
[0028]
If it is determined that the recording sheet P has been set, the controller 38 raises the bottom plate 34 toward the paper feed roll 31 prior to the start of the print job, so that the sheet discrimination means 37 causes the bottom plate 34 to rise. Is checked (ST2). If it is determined that the bottom plate 34 has been lifted, the illumination means of the surface detection sensor 35 is turned on, and the detection of the surface state of the recording sheet P set on the manual feed tray 30 is started and the surface detection is performed. The detection signal of the sensor 35 is read (ST3, ST4). When the detection signal is read, the ratio between the regular reflection light quantity and the irregular reflection light quantity is obtained and compared with a table stored in advance to determine the type of the recording sheet P set on the manual feed tray 30. (ST5). Based on the type of the recording sheet P thus determined, the optimum image forming conditions for the recording sheet P, such as transfer voltage, heat fixing temperature, process speed, etc., are set for each device of the printing unit 10. Is done. The print job is started after the setting of such image forming conditions is completed, and the recording sheet P on the manual feed tray 30 is pulled into the printing unit 10 for the first time at this stage.
[0029]
As shown in this procedure, in this embodiment, after the recording sheet P is set on the manual feed tray 30, the leading edge of the recording sheet P is sandwiched between the bottom plate 34 and the paper feed roll 31, and the recording sheet P Since the surface state of the recording sheet P is detected and the type of the recording sheet P is discriminated before the conveyance is started, the detection signal of the surface detection sensor 35 is detected by the detection signal of the recording sheet P. It becomes stable for each type, and the type of the recording sheet P can be accurately determined.
[0030]
In the above embodiment, the example in which the present invention is applied to the manual feed tray of the printer has been described. However, the present invention can be similarly applied to a paper feed cassette provided at the lower part of the printer casing. It is.
[0031]
【The invention's effect】
As described above, according to the sheet feeding apparatus of the present invention, by detecting the surface state of the recording sheet while keeping the surface detection sensor and the recording sheet in a fixed positional relationship, In addition, since the detection signal of the surface detection sensor becomes stable, the type of the recording sheet can be determined more accurately, and the recording sheet is supplied to the printing unit of an image forming apparatus such as a copying machine or a printer. Before, the type of the recording sheet can be accurately determined, which can contribute to the convenience of the user.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a flow color laser beam printer to which the present invention is applied.
2 is a perspective view showing an outline of a paper feed mechanism in a manual paper feed tray of the printer shown in FIG. 1;
FIG. 3 is a block diagram showing a detection signal processing system of a surface detection sensor. FIG. 4 is a diagram showing a positional relationship between a recording sheet on a manual feed tray and a surface detection sensor when a bottom plate is lowered. .
FIG. 5 is a diagram illustrating a positional relationship between a recording sheet on a manual feed tray and a surface detection sensor in a state where a bottom plate is raised.
FIG. 6 is an enlarged view showing a positional relationship between the surface detection sensor and the leading end of the recording sheet when the leading end of the recording sheet is curled downward.
FIG. 7 is an enlarged view showing a case where the leading edge of the recording sheet maintains a predetermined positional relationship with the surface detection sensor.
FIG. 8 is a flowchart illustrating a processing procedure for recording sheet type determination in a sheet determination unit.
FIG. 9 is a diagram illustrating a positional relationship between a sheet check sensor and a surface detection sensor on a manual feed tray.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 30 ... Manual feed tray (paper feed tray), 31 ... Paper feed roll, 32 ... Retard roll (sheet separation member), 34 ... Bottom plate, 35 ... Surface detection sensor, 37 ... Sheet discrimination means, 60 ... Sheet confirmation sensor

Claims (4)

A paper feed tray on which recording sheets are stacked,
A paper feed roll that feeds a recording sheet on the paper feed tray toward a printing unit in the image recording apparatus;
A sheet separating member that is disposed opposite to the sheet feeding roll across the conveyance path of the recording sheet and prevents double feeding of the recording sheet;
The recording sheet pressed against the sheet feeding roll is illuminated on the surface of the sheet feeding tray, and regular reflection light and irregular reflection light generated on the sheet surface are received by separate light receiving elements , and the recording sheet is received. A surface detection sensor that outputs a detection signal related to the amount of received light of the regular reflection light and irregular reflection light received according to the surface state of
From the detection signal of the surface detection sensor, a ratio between the light quantity of the regular reflection light and the light quantity of the irregular reflection light is obtained, and sheet discrimination means for discriminating the type of the recording sheet by comparing with the data indicating the ratio prepared in advance. A sheet feeding apparatus comprising the sheet feeding device. A sheet check sensor for detecting that the recording sheet is set at a predetermined position of the paper feed tray, and the sheet determination means outputs a detection signal of the surface detection sensor after the sheet check sensor detects the presence of the recording sheet. The sheet feeding apparatus according to claim 1, wherein the sheet feeding apparatus reads the sheet. A bottom plate that lifts the leading end of the recording sheet set on the sheet feeding tray from below and abuts against the sheet feeding roll, and the sheet determination unit detects the surface after the lifting of the recording sheet by the bottom plate is completed. 2. A sheet feeding apparatus according to claim 1, wherein a detection signal of the sensor is read. The sheet feeding apparatus according to claim 1, wherein the surface detection sensor is disposed so as to overlap the sheet feeding roll in an axial direction of the sheet feeding roll.

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