Image forming device

Abstract

To provide an image formation device which can suppress a conveyance failure even when a sheet is fed using a manual feed tray.SOLUTION: An image formation device 100 includes: a manual feed tray 244 that allows a sheet to be mounted thereon; a medium sensor 250 for detecting sheet characteristics of the sheet conveyed from the manual feed tray 244; a secondary transfer part 140 for transferring an image formed on an intermediate transfer belt 130 onto the sheet; a plurality of rollers for conveying the sheet conveyed from the manual feed tray 244 to a transfer nip part 141 of the secondary transfer part 140; and a control part for controlling driving of the plurality of rollers based on the sheet characteristics detected by the medium sensor 250. The plurality of rollers include a plurality of roller provided on the upstream in a conveyance direction of conveying the sheet of the transfer nip part 141. The medium sensor 250 is provided between the manual feed tray 244 and the predetermined roller.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus of an electrophotographic type, an electrostatic recording type, or the like. [Background technology]

[0002] Image forming apparatuses include electrophotographic copiers, electrophotographic printers such as LED printers and laser beam printers, electrophotographic facsimile machines, electrophotographic word processors, etc. In an image forming apparatus, a sheet on which an image is formed is fed from a paper feed cassette or a manual feed tray. The manual feed tray is generally provided on the front or side of the image forming apparatus. The manual feed tray is attached to the image forming apparatus so as to be openable and closable, and is opened by the user when the apparatus is to be used. The user places a sheet on the open manual feed tray.

[0003] Some image forming apparatuses have a skew correction function that corrects skew of a sheet fed from a paper feed cassette or a manual feed tray. Skew correction is performed, for example, by abutting the leading edge of the conveyed sheet against a nip portion of a registration roller that is in a stopped state, thereby forming a loop in the sheet.

[0004] In the image forming apparatus, sheet characteristics such as sheet thickness and surface properties are important in determining image forming conditions. By adjusting the image forming conditions according to the sheet properties, the optimal image fixing temperature and sheet conveying speed can be realized, and image quality is stabilized. The sheet properties are often set by the user using an operation unit or a driver screen. In recent years, image forming apparatuses equipped with sensors that detect sheet properties have been proposed. By using such sensors, user settings are no longer required, and convenience is improved. Patent documents 1 and 2 disclose image forming apparatuses that are provided with a sensor that detects the surface properties of a sheet in the image forming apparatus, determine the type of the sheet based on the detection result of the sensor, and determine image forming conditions according to the type of the sheet. This sensor detects the surface properties of the sheet based on the result of imaging the surface of the sheet. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-182518 A [Patent Document 2] JP 2004-38879 A Summary of the Invention [Problem to be solved by the invention]

[0006] The manual feed tray allows sheets of more flexible sizes to be placed on it than the paper feed cassette. The manual feed tray also allows a sheet that has already been printed to be used as the backing paper. In this way, the manual feed tray increases the variety of sheets that users can use. Therefore, when an image forming apparatus performs image formation on a sheet fed using the manual feed tray without user settings, the sheet transport conditions, which are image formation conditions, are not appropriately controlled, and transport problems such as paper jams may occur.

[0007] In view of the above problems, an object of the present invention is to suppress transport failure even when a manual feed tray is used to feed a sheet. [Means for solving the problem]

[0008] The image forming apparatus of the present invention includes a first stacking unit provided outside the image forming apparatus for stacking sheets, a second stacking unit provided inside the image forming apparatus for stacking sheets, and Placethe image forming apparatus includes a paper feeding means provided within the first stacking means for feeding a sheet loaded on the first stacking means, a pair of transport rollers provided within the image forming apparatus for transporting a sheet fed from the first stacking means by the paper feeding means, a detection means provided within the image forming apparatus for detecting sheet characteristics, and an image forming means for forming an image on the sheet, wherein the detection means is disposed downstream of the pair of transport rollers in the transport direction in which the sheet is transported and upstream of a junction of a first transport path for transporting a sheet from the first stacking means to the image forming means and a second transport path for transporting a sheet from the second stacking means to the image forming means. Effect of the Invention

[0009] According to the present invention, even when a manual feed tray is used to feed a sheet, transport failures can be suppressed. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Diagram 2] FIG. [Diagram 3] 1A and 1B are explanatory diagrams of a media sensor. [Figure 4] 5A to 5C are diagrams illustrating the relationship between the detection result of the media sensor and the sheet characteristics. [Diagram 5] 6 is an explanatory diagram of a method for determining the sheet type from the detection result of the media sensor. [Figure 6] FIG. 4 is an explanatory diagram of the arrangement of a media sensor. [Figure 7] 4A to 4C are diagrams illustrating sheet transport conditions. [Figure 8] 11 is a flowchart showing a method for determining a sheet transport condition. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings.

[0012] (Configuration of Image Forming Apparatus) 1 is a diagram showing the configuration of an image forming apparatus according to this embodiment. Image forming apparatus 100 includes a plurality of image forming units 120a-120d, laser scanners 122a-122d, primary transfer sections 123a-123d, an intermediate transfer belt 130, a secondary transfer section 140, and a fixing device 170. Image forming apparatus 100 can feed sheets, on which an image is to be formed, from a paper feed cassette 220 and a manual feed tray 244.

[0013] The image forming units 120a to 120d include charging rollers 124a to 124d, photosensitive drums 121a to 121d, and developing devices 125a to 125d. The image forming units 120a to 120d are configured to be removable from the main body of the image forming apparatus 100 by a user. The surfaces of the photosensitive drums 121a to 121d are charged by the charging rollers 124a to 124d, and are irradiated with laser light by the corresponding laser scanners 122a to 122d, so that electrostatic latent images are formed on the surfaces. The developing devices 125a to 125d develop the electrostatic latent images with toner of the corresponding color, so that toner images are formed on the photosensitive drums 121a to 121d. One of the image forming units 120a to 120d forms a black toner image, and the others form chromatic toner images. In this embodiment, a yellow toner image is formed on the photosensitive drum 121a of the image forming unit 120a. A magenta toner image is formed on the photosensitive drum 121b of the image forming unit 120b, a cyan toner image is formed on the photosensitive drum 121c of the image forming unit 120c, and a black toner image is formed on the photosensitive drum 121d of the image forming unit 120d.

[0014] When a primary transfer voltage is applied to the primary transfer sections 123a to 123d, the toner images formed on the photosensitive drums 121a to 121d of the corresponding image forming units 120a to 120d are transferred onto the intermediate transfer belt 130 in a superimposed manner. The intermediate transfer belt 130 rotates clockwise in the figure, and is an image carrier that carries the toner images to be transferred in the order of yellow, magenta, cyan, and black. The intermediate transfer belt 130 conveys the transferred toner images to the secondary transfer section 140 by rotating.

[0015] Paper feed cassette 220 accommodates sheets on which an image is to be formed. Usually, the same type of sheets are accommodated in paper feed cassette 220. Although one paper feed cassette 220 is provided in FIG. 1, image forming apparatus 100 may be provided with a plurality of paper feed cassettes. Manual feed tray 244 is used to place sheets on which an image is to be formed by a user. Various sheets of different materials and thicknesses can be placed on manual feed tray 244.

[0016] A sheet is fed from a paper feed cassette 220 or a manual feed tray 244, and is conveyed along a conveying path to a transfer nip portion 141 of a secondary transfer unit 140. The secondary transfer unit 140 transfers an image from the intermediate transfer belt 130 to the sheet at the transfer nip portion 141. On the conveying path from the paper feed cassette 220 to the secondary transfer unit 140, a pickup roller 151, a conveying roller 154, a conveying roller 155, and a registration roller 161 are provided in this order from the upstream side in the sheet conveying direction. A pickup sensor 152 is provided upstream of the conveying roller 154 in the sheet conveying direction. A registration sensor 160 is provided between the conveying roller 155 and the registration roller 161.

[0017] The sheets stored in the paper feed cassette 220 are fed from the paper feed cassette 220 to the conveying path by the pickup roller 151. The sheets fed to the conveying path are separated one by one by a known technique and conveyed to the registration roller 161 by the conveying roller 154 and the conveying roller 155. The registration roller 161 stops rotating at the timing when the sheet is conveyed. Therefore, the leading edge of the sheet is abutted against the nip portion of the registration roller 161. The sheet whose leading edge has been abutted forms a loop on the leading edge side by continuing to be conveyed by the conveying roller 155. The formation of the loop corrects the skew of the sheet. The registration roller 161 conveys the sheet to the transfer nip portion 141 of the secondary transfer portion 140 in accordance with the timing when the toner image carried on the intermediate transfer belt 130 is conveyed to the secondary transfer portion 140.

[0018] The pickup sensor 152 and the registration sensor 160 detect the sheet being conveyed along the conveying path. The position of the sheet on the conveying path is detected based on the detection results of the pickup sensor 152 and the registration sensor 160. Depending on the timing at which the registration sensor 160 detects the leading edge of the sheet, the timing of conveying the sheet is controlled so that the sheet and the leading edge of the toner image on the intermediate transfer belt 130 coincide with each other at the transfer nip portion 141 of the secondary transfer unit 140. For example, if the skew correction of the sheet with respect to the toner image is completed early, the sheet is stopped by the registration rollers 161 for a predetermined time, and then conveyance is resumed and the sheet is conveyed to the transfer nip portion 141 of the secondary transfer unit 140.

[0019] A sheet placed on the manual feed tray 244 is fed to conveyance rollers 155 by manual feed section 240. Manual feed section 240 includes a pickup roller 241, a separation roller 242, and a media sensor 250. Manual feed section 240 is disposed upstream in the sheet conveyance direction from a junction with the conveyance path of the sheet fed from paper feed cassette 220. A sheet placed on manual feed tray 244 is drawn into manual feed section 240 by pickup roller 241. The sheets drawn into manual feed section 240 are separated one by one by separation roller 242 using a known separation technique and conveyed to conveyance rollers 155.

[0020] Before the leading edge of the sheet reaches the conveying roller 155, the media sensor 250 detects the sheet characteristics such as the material (thickness, surface properties) of the sheet. Image formation conditions such as sheet conveying conditions are determined according to the sheet characteristics. For example, the sheet conveying speed is changed to a conveying speed according to the sheet characteristics. Specifically, if the detection result of the media sensor 250 determines that the sheet is thick paper, the conveying speed is changed to 1 / 3 the conveying speed (1 / 3 speed) of the conveying speed when the sheet is plain paper or thin paper. In this embodiment, further adjustment of the sheet conveying conditions specific to the use of the manual feed tray 244 is performed. Here, plain paper is paper having a basis weight of 60 [g / m 2 ] or more 200[g / m 2 Thin paper is a sheet with a basis weight of less than 60 [g / m2 ]. Cardboard is a sheet with a basis weight of 200 [g / m 2 ] or more sheets.

[0021] Depending on the configuration of media sensor 250, in order to improve detection accuracy, it may be necessary to temporarily stop the sheet or reduce the conveying speed at the detection position of media sensor 250. In this embodiment, since media sensor 250 is built into manual paper feed unit 240, conveyance of the sheet is temporarily stopped when detection is performed by media sensor 250 so that the conveying conditions at the time of sheet detection are constant.

[0022] Manual feed unit 240 resumes conveying the sheet under image formation conditions determined according to the detection result of the sheet characteristics by media sensor 250, and conveys the sheet to conveying rollers 155. The conveyance of the sheet from conveying rollers 155 to transfer nip portion 141 of secondary transfer unit 140 is the same as when the sheet is fed from paper feed cassette 220. That is, the sheet is conveyed from conveying rollers 155 to registration rollers 161, where skew correction is performed. After skew correction, the sheet is conveyed to transfer nip portion 141 of secondary transfer unit 140 at a timing such that the sheet and the leading edge of the toner image on intermediate transfer belt 130 coincide with each other at secondary transfer unit 140.

[0023] The secondary transfer unit 140 transfers the toner image formed on the intermediate transfer belt 130 to a sheet by applying a secondary transfer voltage. The sheet to which the toner image has been transferred is transported to the fixing device 170. The fixing device 170 thermally fixes the toner image to the sheet. The temperature (fixing temperature) of the fixing device 170 for thermal fixing is controlled according to the detection result of the media sensor 250. That is, the fixing temperature, which is an image formation condition, is determined according to the sheet characteristics obtained from the detection result of the media sensor 250. The fixing device 170 is temperature-controlled to the determined fixing temperature during thermal fixing.

[0024] A transport sensor 171 is provided downstream of the fixing device 170 to detect a sheet that has passed through the fixing device 170. The sheet on which the toner image has been fixed by the fixing device 170 is transported to a double-sided transport path 230 in the case of double-sided printing, and is transported to a paper discharge transport path 231 when image formation is completed. A transport flapper 172 operates in response to detection of the sheet by the transport sensor 171, and distributes the sheet to either the double-sided transport path 230 or the paper discharge transport path 231.

[0025] The sheet conveyed to the double-sided conveying path 230 has the side on which the image has been formed inverted and is conveyed to the conveying rollers 155. Thereafter, the sheet is conveyed to the transfer nip portion 141 of the secondary transfer portion 140, where an image is formed on the inverted side. The discharge conveying path 231 branches into a conveying path 180 and a conveying path 181. A flapper 190 distributes the sheet conveyed to the discharge conveying path 231 to either the conveying path 180 or the conveying path 181. The sheet conveyed to the conveying path 180 is discharged to the discharge tray 200. The sheet conveyed to the conveying path 181 is discharged to the discharge tray 196.

[0026] (Control unit) 2 is a configuration diagram of a control unit that controls the operation of image forming apparatus 100. Control unit 20 is built into image forming apparatus 100. Control unit 20 is an information processing device including a central processing unit (CPU) 10, a read only memory (ROM) 11, a random access memory (RAM) 12, and a storage unit 15. Image forming unit 17, operation unit 13, media sensor 250, feed motor 150, fixing unit 170, and registration sensor 160 are connected to control unit 20.

[0027] The operation unit 13 is an input / output device equipped with a touch panel consisting of a display and a touch pad, key buttons, etc. Using the operation unit 13, a user can input various information related to the image forming process (number of sheets, image quality, double-sided / single-sided printing, black and white printing, color printing, etc.), an instruction to start the image forming process, etc.

[0028] The CPU 10 reads a computer program from the ROM 11 and executes it using the RAM 12 as a working area to control the operation of the image forming apparatus 100. In this embodiment, the CPU 10 detects the sheet characteristics of the sheet from the detection result of the media sensor 250, and controls the image forming operation under image formation conditions according to the sheet characteristics. For example, the CPU 10 controls the operations of the image forming unit 17, the feed motor 150, and the fixing unit 170 in response to the detection results of various sensors including the media sensor 250, and various information and instructions input by the user from the operation unit 13, to perform the image forming process.

[0029] The image forming section 17 controls the operations of the image forming units 120a to 120d, the laser scanners 122a to 122d, the intermediate transfer belt 130, the primary transfer sections 123a to 123d, and the secondary transfer section 140 under the control of the control section 20. The image forming section 17 controls the driving of the image forming units 120a to 120d, the laser scanners 122a to 122d, and the intermediate transfer belt 130. The image forming section 17 supplies high voltages (primary transfer voltage, secondary transfer voltage) to the primary transfer sections 123a to 123d and the secondary transfer section 140. The feed motor 150 is a drive source for various rollers for conveying a sheet provided on a conveying path. The feed motor 150 operates under the control of the control section 20. The control section 20 controls the operation of the fixing device 170 and the fixing temperature.

[0030] When the control unit 20 configured as above receives an instruction to start the image forming operation from the operation unit 13 or an external device (not shown), it controls the operation of each unit to form an image. In response to the instruction to start the image forming operation, the control unit 20 first rotates the pickup roller 151 or the pickup roller 241 by the feed motor 150. The pickup roller 151 feeds sheets one by one from the paper feed cassette 220. The pickup roller 241 feeds sheets one by one from the manual feed tray 244. The sheet conveyed by the pickup roller 241 is detected by the media sensor 250. The control unit 20 detects the sheet characteristics of the sheet being conveyed based on the detection result of the media sensor 250. The control unit 20 determines the image forming conditions such as the image forming speed and the fixing temperature of the fixing unit 170 according to the sheet characteristics. For example, the control unit 20 determines the rotation speed of the photosensitive drum 121, the scanning speed of the laser scanners 122a to 122d, the rotation speed of the intermediate transfer belt 130, the sheet conveying speed, the fixing temperature, etc. according to the sheet characteristics. The control unit 20 controls the operations of the driving units such as the feed motor 150, the image forming unit 17, and the fixing unit 170 based on the determined image formation conditions.

[0031] (Media Sensor) Fig. 3 is an explanatory diagram of the media sensor 250. As shown in Fig. 3(a), the media sensor 250 includes an optical sensor unit 251 that detects the surface property of a sheet, and a thickness detection unit 252 that detects the thickness of the sheet.

[0032] The optical sensor unit 251 includes a light source 255 and a line sensor 256. The light source 255 is formed of, for example, an LED (Light Emitting Diode). The line sensor 256 is formed of a plurality of light receiving elements arranged in a straight line. The light receiving elements are arranged in the main scanning direction. As shown in FIG. 3(b), the line sensor 256 includes n light receiving elements P1 to Pn. One light receiving element corresponds to one pixel. The line sensor 256 outputs an output voltage based on the amount of received light for each pixel of the light receiving elements P1 to Pn.

[0033] The optical sensor unit 251 irradiates light from the light source 255 onto the surface of the sheet 253 drawn in from the manual feed tray 244 on the transport path 254 in the manual feed unit 240. The irradiated light is reflected by the sheet 253 and received by each of the light receiving elements P1 to Pn of the line sensor 256. Each of the light receiving elements P1 to Pn outputs an output signal (output voltage) according to the amount of reflected light received. The CPU 10 acquires the output signal (output voltage) from each of the light receiving elements P1 to Pn of the line sensor 256. If the surface of the sheet 253 is smooth, the difference in output voltage of each of the light receiving elements P1 to Pn is small. The CPU 10 can detect the unevenness of the surface of the sheet 253 based on the difference in output voltage output from adjacent light receiving elements (pixels). Also, the greater the amount of reflected light from the sheet 253, the greater the output voltage. Therefore, the CPU 10 can detect the glossiness of the sheet 253 based on the sum of the acquired output voltages.

[0034] The thickness detection unit 252 includes a roller 257 that contacts the surface of the sheet 253, and an encoder sensor 258. The thickness detection unit 252 detects the amount of depression of the roller 257 when the sheet 253 passes through the detection area of ​​the media sensor 250 using the encoder sensor 258. The encoder sensor 258 outputs a pulse signal with a number of pulses corresponding to the detection result of the amount of depression of the roller 257. The thickness detection unit 252 outputs an output voltage based on the pulse signal. The CPU 10 obtains an output signal (output voltage) indicating the amount of depression of the roller 257 from the thickness detection unit 252. The CPU 10 can detect the thickness of the sheet 253 based on the amount of depression.

[0035] FIG. 4 is an explanatory diagram of the relationship between the detection result of the media sensor 250 and the sheet characteristics. FIG. 4(a) shows the relationship between the roughness (irregularity) of the surface of the sheet 253 and the sum of the differences in the output voltage between adjacent pixels (difference sum A). FIG. 4(b) shows the relationship between the thickness (paper thickness) of the sheet 253 and the output signal (thickness detection value B) indicating the amount of pressing. FIG. 4(c) shows the relationship between the glossiness of the sheet 253 and the sum of the output voltage (brightness value) (brightness sum C). As the value of the detection result of the media sensor 250 increases, all of the sheet characteristics (irregularity, paper thickness, glossiness) increase linearly.

[0036] The difference sum A will now be described (FIG. 4(a)). If the output voltage (brightness value) of each pixel by each light receiving element P1 to Pn of line sensor 256 is P1, P2, ... Pn, the difference sum A is expressed by the following formula 1. The larger the unevenness and roughness of the surface of sheet 253, the larger the difference sum A will be, so the unevenness of the surface can be detected as the difference sum A of the output voltage (brightness value). The smoother the surface of sheet 253, the smaller the difference sum A will be. A=(P2-P1)+(P3-P2)+…(Pn-P(n-1))…(Formula 1)

[0037] The thickness detection value B will be explained (FIG. 4(b)). The thicker the sheet 253 is, the more the roller 257 is pressed in. Therefore, the thicker the sheet 253 is, the greater the amount of pressing of the roller 257 becomes. Since the thickness detection value B represents the amount of pressing of the roller 257, the thickness of the sheet detected by the CPU 10 tends to be as shown in FIG. 4(b).

[0038] The luminance sum C will now be described (FIG. 4(c)). If the output voltage (luminance value) of each pixel by each light receiving element P1 to Pn of line sensor 256 is P1, P2, ... Pn, then the luminance sum C is expressed by the following formula 2. The higher the glossiness of the surface of sheet 253, the larger the luminance sum C will be, and the lower the glossiness, such as in recycled paper, the lower the value. In this way, the luminance sum C represents the glossiness of sheet 253. C=P1+P2+P3+…+Pn…(Formula 2)

[0039] 5 is an explanatory diagram of a method for determining the sheet type from the detection result of media sensor 250. The sheet type of the sheet fed from manual feed tray 244 can be determined from difference sum A obtained from the detection result of media sensor 250 and thickness detection value B.

[0040] In the case of thick glossy paper, the sheet is a material with a smooth surface and a large thickness. Such sheets are plotted in group G1 in Fig. 5 because the difference sum A is small and the thickness detection value B is large. Sheets of a type that are thick and have an uneven surface, such as embossed paper, are plotted in group G2 in Fig. 5 because the difference sum A is large and the thickness detection value B is large. In this way, the sheet type is determined based on the difference sum A and the thickness detection value B.

[0041] The sheet type is determined by setting thresholds Ath, Bth, and Bth2 for the difference sum value A and the thick detection value B, respectively. If the difference sum value A < threshold Ath and thickness detection value B > threshold Bth, the sheet is determined to be thick glossy paper classified as G1 group. If the difference sum value A > threshold Ath and thickness detection value B > threshold Bth, the sheet is determined to be embossed paper classified as G2 group. If the thickness detection value B < threshold Bth2, the sheet is determined to be thin paper in G3 group regardless of the difference sum value A. Note that threshold Bth2 is a smaller value than threshold Bth.

[0042] The media sensor 250 of the present embodiment as described above is not limited to a configuration including an optical sensor unit 251 and a thickness detection unit 252. For example, the media sensor 250 may be configured to include an ultrasonic sensor such as a piezoelectric element and an optical sensor. When the ultrasonic sensor is included, the basis weight can be detected as a sheet characteristic from the detection result of the ultrasonic sensor. Since there is a correlation between the thickness and basis weight of a sheet, the CPU 10 determines that the sheet is thin paper when the basis weight is smaller than the thin paper threshold, and determines that the sheet is thick paper when the basis weight is larger than the thick paper threshold. Furthermore, in order to determine the type of sheet with higher accuracy, the media sensor 250 may be configured to include all of the optical sensor unit 251, the thickness detection unit 252, and the ultrasonic sensor.

[0043] 6 is an explanatory diagram of the arrangement of media sensor 250. As described above, media sensor 250 in this embodiment is arranged inside manual paper feed unit 240. Media sensor 250 is adjacent to the downstream side of separation roller 242 in the sheet transport direction. Media sensor 250 is also arranged upstream of the junction with the transport path of the sheet fed from paper feed cassette 220.

[0044] The sheet is taken in from the manual feed tray 244, and the conveyance is stopped once before the leading edge in the conveyance direction reaches the conveyance roller 155. The media sensor 250 detects the sheet characteristics in this state. By determining the type of the sheet at this timing, the detection result of the sheet characteristics can be reflected in the sheet conveyance conditions and image formation conditions such as the fixing temperature during the subsequent sheet feeding. When feeding a sheet from the manual feed tray 244, the type of sheet (size, surface property, thickness) is more diverse than when feeding a sheet from the paper feed cassette 220. Therefore, when feeding a sheet from the manual feed tray 244, the image formation conditions change more frequently than when feeding a sheet from the paper feed cassette 220.

[0045] For example, if the sheet is thick glossy paper, it is difficult to feed the thick glossy paper because the conveyance path from the paper feed cassette 220 is curved, and the sheet is fed from the manual feed tray 244. However, the surface friction of thick glossy paper is low, and sheet conveyance may be delayed due to slippage of the pickup roller 241 and the separation roller 242. In this case, if feeding of the second sheet is started at the same inter-sheet distance (the interval between consecutively conveyed sheets) as for plain paper, the leading edge of the second sheet may collide with the trailing edge of the first sheet, causing a conveyance failure such as a paper jam.

[0046] When the sheet is thin paper, the conveying path from the paper feed cassette 220 is curved, so that the thin paper wrinkles and is difficult to convey. However, when the thin paper is fed from the manual feed tray 244, the conveying path is straight, so that the thin paper is easy to convey. When feeding thin paper, it may be difficult to correct the skew of the conveyed sheet. As described above, the skew correction is performed by making the sheet collide with the nip part of the registration roller 161 while the registration roller 161 is stopped, and by conveying the sheet by a predetermined conveying amount with the conveying roller 155, forming a loop in the sheet. When the sheet is thin paper, this loop amount becomes large and wrinkles occur in the sheet. When wrinkles occur in the thin paper, it is damaged, and the quality of the finished product decreases, and the usability also decreases. In the case of thick paper, the conveying amount is adjusted to take slip into consideration, and the skew correction is performed by adjusting the loop amount, so the optimal sheet conveying conditions are different from those for thin paper.

[0047] The amount of loop of the sheet during skew correction is optimally set according to the type of sheet. For this purpose, the media sensor 250 needs to be disposed upstream of the registration sensor 160 in the sheet transport direction. The transport path between the transport roller 155 and the registration sensor 160 is located downstream of the junction of the transport path for feeding the sheet from the paper feed cassette 220 and the transport path for feeding the sheet from the manual feed tray 244. This position is an area where the sheet forms a loop during skew correction. For this reason, the media sensor 250 cannot accurately detect the sheet characteristics at this position. Therefore, the media sensor 250 that detects the sheet characteristics of the sheet fed from the manual feed tray 244 is disposed upstream of the registration sensor 160 and the transport roller 155 in the sheet transport direction.

[0048] (Sheet transport conditions) A case where the sheet transport conditions are adjusted as the image forming conditions will be described. Fig. 7 is an explanatory diagram of the sheet transport conditions based on the type of sheet identified from the detection result of the media sensor 250. Here, the sheet-to-sheet distance, the loop amount during skew correction, and the criteria for determining whether a jam has occurred will be described as the sheet transport conditions. Fig. 7(a) is an explanatory diagram of the sheet-to-sheet distance setting. Fig. 7(b) is an explanatory diagram of the loop control during skew correction. Fig. 7(c) is an explanatory diagram of the setting change of the time (jam margin) for determining a paper jam.

[0049] In FIG. 7(a), the distance between the leading edges of the sheets that are continuously conveyed is the inter-paper distance. The inter-paper distance in the standard mode in which plain paper or the like is fed is D0, and the inter-paper distance in the thick paper glossy paper mode in which thick glossy paper is fed is D1. In the case of thick glossy paper, D1 is a value larger than D0 to provide a margin for the inter-paper distance in consideration of slippage. As described above, the conveyance of thick glossy paper is delayed more than that of plain paper due to the small friction of the surface. When the sheet fed from the manual feed tray 244 is thick glossy paper, the CPU 10 sets the inter-paper distance to a value (D1) corresponding to the thick glossy paper and controls the feeding of the sheet. The CPU 10 determines the sheet characteristics of the sheet fed from the manual feed tray 244 from the detection result of the media sensor 250 and identifies the type of the sheet. The CPU 10 sets the inter-paper distance based on the identified type of sheet. CPU 10 starts feeding the next sheet when pickup roller 241 has conveyed the sheet for a time period corresponding to the inter-sheet distance since the start of feeding by CPU 10. In this manner, the inter-sheet distance is optimally set.

[0050] In loop control during skew correction, the leading edge of the sheet 253 abuts against the nip of the registration rollers 161 and the sheet 253 is stopped, and the conveying rollers 155 convey the sheet 253 by a predetermined conveying amount, thereby forming a loop of the sheet 253. The loop amount is determined by the time that the conveying rollers 155 continue to convey the sheet 253 after the registration sensor 160 detects the leading edge of the sheet 253. For all types of sheets, a certain amount of loop is generated by stopping the registration rollers 161 for a predetermined time, and skew is corrected, but for thick glossy paper and thin paper, problems may occur in image formation and the state of the sheet.

[0051] In the case of thick glossy paper, the transport amount is less than expected due to slippage between the sheet 253 and the transport roller 155, so there is a possibility that sufficient skew correction cannot be performed unless more time is secured for skew correction than for plain paper. In the case of thin paper, the sheet will wrinkle if the loop amount is the same as for plain paper, so the skew correction time must be shorter than for plain paper.

[0052] The CPU 10 determines the type of the sheet based on the detection result of the media sensor 250. As shown in FIG. 7B, when the sheet is plain paper or the like, the CPU 10 sets the transport time of the transport roller 155 from when the registration sensor 160 detects the leading edge of the sheet to R0 as the standard mode. When the sheet is thick glossy paper, the CPU 10 sets the transport time of the transport roller 155 from when the registration sensor 160 detects the leading edge of the sheet to R1 as the thick glossy paper mode. R1 is a longer time than R0. When the sheet is thin paper, the CPU 10 sets the transport time of the transport roller 155 from when the registration sensor 160 detects the leading edge of the sheet to R2 as the thin paper mode. R2 is a shorter time than R0. In this way, the optimal transport conditions for skew correction are set. After the transport time has elapsed, the registration roller 161 resumes transport of the sheet.

[0053] When changing the setting of the jam margin, the detection result of the registration sensor 160 is used to set the time for determining whether a paper jam occurs during sheet transport. In Fig. 7(c), the registration sensor 160 outputs a low-level signal when it detects a sheet. If it does not detect a sheet, the registration sensor 160 outputs a high-level signal. The CPU 10 detects that a sheet has been transported when the signal acquired from the registration sensor 160 transitions from high to low.

[0054] 7C illustrates an output of the registration sensor 160 when sheets are continuously fed, with the timing when the sheet feeding from the manual feed tray 244 starts being set as "0." Here, the sheets are continuously fed in the thick glossy paper mode, and the inter-sheet distance is D1. In the standard mode, when time S0 has elapsed since the start of sheet feeding, the sheet is conveyed to the detection position of the registration sensor 160. Taking into account the tolerance α1, the CPU 10 determines that a feeding problem such as a paper jam has occurred if the sheet is not detected by the registration sensor 160 within the time S1, which is the time S0 plus α1, has elapsed. In the thick glossy paper mode, since there is a possibility that the sheet may slip, the CPU 10 sets a larger tolerance than in the standard mode. The CPU 10 determines that a feeding problem such as a paper jam has occurred if the sheet is not detected by the registration sensor 160 within the time S2 obtained by adding a tolerance α2 larger than the tolerance α1 to the time S0.

[0055] That is, the CPU 10 identifies the type of sheet from the detection result of the media sensor 250. If the sheet is plain paper or the like, the CPU 10 sets, as the standard mode, a time S1 from the start of sheet feeding until the registration sensor 160 detects the leading edge of the sheet. If the registration sensor 160 does not detect the sheet within the time S1, the CPU 10 determines that a feeding problem has occurred. If the sheet is thick glossy paper, the CPU 10 sets, as the thick glossy paper mode, a time S2 from the start of sheet feeding until the registration sensor 160 detects the leading edge of the sheet. If the registration sensor 160 does not detect the sheet within the time S2, the CPU 10 determines that a feeding problem has occurred. Time S2 is longer than time S1.

[0056] Jam detection is also performed based on the detection results of other sensors provided on the conveying path. Similarly, for the other sensors, the time until the leading edge of the sheet is detected is set according to the type of sheet, and the occurrence of a feeding problem is determined.

[0057] (Method of determining sheet transport conditions) 8 is a flowchart showing a method for determining sheet conveying conditions, which are image forming conditions. This process is started when the user places a sheet on manual feed tray 244 and inputs an instruction to start image forming process through operation unit 13. Other image forming conditions, such as fixing temperature, are also determined by the same process.

[0058] When CPU 10 receives an instruction to start image forming processing, it causes pickup roller 241 and separation roller 242 to pull a sheet placed on manual tray 244 into manual paper feed section 240 (S1000). As illustrated in FIG. 3(a), CPU 10 pulls the sheet up to the detection position by media sensor 250. When the sheet reaches the detection position of media sensor 250, CPU 10 temporarily stops conveying the sheet (S1001). CPU 10 determines whether the sheet has reached the detection position of media sensor 250 based on, for example, a change in the output signal of optical sensor section 251 of media sensor 250.

[0059] The CPU 10 detects the sheet characteristics based on the detection result of the media sensor 250 (S1002). The CPU 10 detects the sheet unevenness (difference sum value A), paper thickness (thickness detection value B), and glossiness (brightness sum C) as the sheet characteristics. The CPU 10 stores the detected sheet characteristics (difference sum value A, thickness detection value B, brightness sum C) in the RAM 12. The CPU 10 determines whether the sheet to be fed is thick glossy paper or not based on the sheet characteristics stored in the RAM 12 (S1003). The CPU 10 determines that the sheet is thick glossy paper when the detection result of the media sensor 250 is such that the difference sum value A<threshold value Ath and the thickness detection value B>threshold value Bth, as exemplified in FIG. 5.

[0060] If the sheet is thick glossy paper (S1003: Y), the CPU 10 sets the sheet transport conditions for thick glossy paper. That is, the CPU 10 sets D1 (see FIG. 7(a)) as the distance between sheets when continuously fed (S1004). The CPU 10 sets R1 (see FIG. 7(b)) as the transport time of the transport roller 155 from the timing of sheet detection by the registration sensor 160 during skew correction (S1005). The CPU 10 sets S2 (see FIG. 7(c)) as the paper jam determination time from the start of sheet feeding to the timing of sheet detection by the registration sensor 160 (S1006). The CPU 10 sets 1 / 3 (1 / 3 speed) of the transport speed of plain paper as the sheet transport speed (S1007).

[0061] The CPU 10 resumes the sheet transport based on the sheet transport conditions thus set (S1017) The CPU 10 performs the image forming process instructed by the user and ends the process (S1018).

[0062] If the sheet is not thick glossy paper (S1003: N), the CPU 10 judges whether the sheet to be fed is thin paper or not (S1008) based on the sheet characteristics stored in the RAM 12. As shown in FIG. 5, the CPU 10 judges the sheet to be thin paper when the detection result of the media sensor 250 is that the thickness detection value B is less than the threshold value Bth2.

[0063] If the sheet is thin paper (S1008: Y), the CPU 10 sets the sheet transport conditions for thin paper. That is, the CPU 10 sets D0 (see FIG. 7(a)) as the distance between sheets when continuously fed (S1009). The CPU 10 sets R2 (see FIG. 7(b)) as the transport time of the transport roller 155 from the timing of sheet detection by the registration sensor 160 during skew correction (S1010). The CPU 10 sets S1 (see FIG. 7(c)) as the paper jam determination time from the start of sheet feeding to the timing of sheet detection by the registration sensor 160 (S1011). The CPU 10 sets the transport speed for plain paper (first speed) as the sheet transport speed (S1012).

[0064] The CPU 10 resumes the sheet transport based on the sheet transport conditions thus set (S1017) The CPU 10 performs the image forming process instructed by the user and ends the process (S1018).

[0065] If the sheet is not thin paper (S1008: N), the CPU 10 sets the sheet transport conditions (standard conditions) for plain paper. That is, the CPU 10 sets D0 (see FIG. 7(a)) as the distance between sheets when continuously fed (S1013). The CPU 10 sets R0 (see FIG. 7(b)) as the transport time of the transport roller 155 from the timing of sheet detection by the registration sensor 160 during skew correction (S1014). The CPU 10 sets S1 (see FIG. 7(c)) as the paper jam determination time from the start of sheet feeding to the timing of sheet detection by the registration sensor 160 (S1015). The CPU 10 sets the plain paper transport speed (first speed) as the sheet transport speed (S1016).

[0066] The CPU 10 resumes the sheet transport based on the sheet transport conditions thus set (S1017) The CPU 10 performs the image forming process instructed by the user and ends the process (S1018).

[0067] As described above, when feeding a sheet from the manual feed tray 244, the image forming apparatus 100 of the present embodiment detects the sheet characteristics of the sheet using the internal media sensor 250, and feeds the sheet under sheet transport conditions according to the detected sheet characteristics. Since the sheet transport conditions are appropriately adjusted, more types of sheets can be stably fed than before. As a result, more types of sheets can be used for image formation, improving usability. In addition, image formation conditions other than the sheet transport conditions are also adjusted according to the sheet characteristics. As a result, image formation suitable for the type of sheet used for image formation is performed, and a product with stable image quality can be provided.

Claims

1. a first stacking unit provided outside the image forming apparatus and configured to stack sheets; a second stacking unit provided in the image forming apparatus for stacking sheets; a sheet feeding means provided in the image forming apparatus for feeding the sheets stacked on the first stacking means; a pair of conveying rollers provided in the image forming apparatus for conveying a sheet fed from the first stacking means by the sheet feeding means; A detection unit provided in the image forming apparatus for detecting a sheet characteristic; and an image forming means for forming an image on the sheet, the detection means is disposed downstream of the pair of conveying rollers in a conveying direction in which the sheet is conveyed and upstream of a junction of a first conveying path that conveys the sheet from the first stacking means to the image forming means and a second conveying path that conveys the sheet from the second stacking means to the image forming means. Image forming device.

2. The second conveying path is not provided with a means for detecting characteristics of the sheet conveyed from the second stacking means. The image forming apparatus according to claim 1 .

3. the sheet feeding means includes a pickup roller that draws in a sheet from the first stacking means; The detection unit is disposed downstream of the pickup roller in the transport direction. The image forming apparatus according to claim 1 .

4. The present invention is characterized in that the sheet conveying device further comprises a control unit that determines a conveying speed of the sheet based on the sheet characteristics detected by the detection unit.

4. The image forming apparatus according to claim 1.

5. The control means determines an interval between successively conveyed sheets based on the sheet characteristics. The image forming apparatus according to claim 4 .

6. a first roller provided upstream of the image forming means in the transport direction; a sensor provided upstream of the first roller in the conveying direction and configured to detect the sheet being conveyed to the first roller; a second roller provided upstream of the sensor in the conveying direction, the second roller conveys the sheet while the first roller is stopped from rotating, causing the sheet to strike a nip portion of the first roller and generate a loop in the sheet; the control means sets a time for conveying the sheet by the second roller after the sensor detects the sheet based on the sheet characteristics, and causes the first roller to start conveying the sheet when the conveying time has elapsed after the sensor detects the sheet.

6. The image forming apparatus according to claim 4.

7. The detection means includes an optical sensor for detecting the surface property of the sheet and a thickness detection unit for detecting the thickness, and detects the sheet characteristics based on the surface property detected by the optical sensor and the thickness of the sheet detected by the thickness detection unit. The image forming apparatus according to claim 1 .

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