Document feeder and image reading device

Abstract

To provide a document feeder and an image reading device that can reduce wrong detection made by a skew detection unit.SOLUTION: A printer 100 as an image forming apparatus comprises: a loading unit 21 on which a document D is loaded; a feeding unit 22 that feeds the document loaded on the loading unit in a feeding direction; a first sensor S1 and a second sensor S2 that detect the document fed by the feeding unit at a detection position; a driving unit that drives the feeding unit 22; and a control unit 81 that controls the driving unit. Before a rear end of a preceding document passes through the detection position, the control unit continues feeding of a subsequent document subsequent to the preceding document without stopping the drive of the driving unit irrespective of results of detection made by the first sensor S1 and second sensor S2, and after the rear end of the preceding document passes through the detection position, when a time difference between a signal output by the first sensor S1 and a signal output by the second sensor S2 exceeds a threshold during the feeding of the subsequent document, stops the drive of the driving unit to interrupt the feeding of the subsequent document.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a document feeder that feeds documents and an image reading device that includes the document feeder. [Background technology]

[0002] Image reading devices that are typically installed on top of a printer body and that read images from documents are known. These image reading devices have an ADF (Auto Document Feeder) that separates and feeds documents placed on a document tray, one by one. The ADF cannot separate and feed so-called "bound documents," such as stapled or glued documents. The ADF's internal mechanism for separating documents can cause the documents to become wrinkled or torn. Furthermore, if bound documents are fed without being separated by the ADF, they may jam in the transport path.

[0003] Conventionally, a sheet feeding device has been proposed that has multiple skew detection sensors arranged in a straight line in the width direction perpendicular to the paper feed direction (see Patent Document 1). If this sheet feeding device accidentally feeds a bound document with a corner bound, for example, the topmost document of the bound documents will rotate as it is fed. Then, the sheet feeding device detects with the multiple skew detection sensors that the bound document being fed is rotating while being transported, and stops feeding of the document. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-193287 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the sheet feeding device described in Patent Document 1, for example, when feeding a document with punched holes, the skew detection sensor switches from ON to OFF and then OFF to ON as the punched holes pass over the skew detection sensor. This can lead to the sheet feeding device mistaking the detection result of the skew detection sensor for the leading edge of the next document to be fed. This can lead to the document being erroneously detected as being skewed, which can cause the document feeding to stop unintentionally.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an original feeding device and an image reading device that can reduce erroneous detection by a skew detection unit. [Means for solving the problem]

[0007] The present invention is a document feeding device comprising: a loading section on which documents are loaded; a feeding section that feeds the documents loaded on the loading section in a feeding direction; a separation section that separates the documents fed by the feeding section into individual sheets; a first sensor that is arranged downstream of the separation section in the feeding direction and detects the documents fed by the feeding section; a second sensor that is arranged in a position overlapping with the first sensor when viewed in a width direction of the documents perpendicular to the feeding direction and detects the documents fed by the feeding section; and a control section that executes a stop process to stop the feeding of the documents by the feeding section if the second sensor does not detect the document within a predetermined time after the first sensor detects the document, and is characterized in that the control section ignores signals from the first sensor and the second sensor after the leading edge of the document fed by the feeding section has passed the detection positions of the first sensor and the second sensor until the trailing edge of the document has passed the first sensor and the second sensor. The present invention also provides a document feeding device comprising: a loading section on which documents are loaded; a feeding section that feeds the documents loaded on the loading section in a feeding direction; a separation section that separates the documents fed by the feeding section into individual sheets; a first sensor that is arranged downstream of the separation section in the feeding direction and detects the documents fed by the feeding section; a second sensor that is arranged in a position overlapping with the first sensor when viewed in a width direction of the documents perpendicular to the feeding direction and detects the documents fed by the feeding section; and a control section that executes a stop process to stop the feeding of the documents by the feeding section if the second sensor does not detect the document within a predetermined time after the first sensor detects the document, and is characterized in that the control section controls the first sensor and the second sensor so that signals are not output after the leading edge of the document fed by the feeding section has passed the detection positions of the first sensor and the second sensor, until the trailing edge of the document has passed the detection positions. The present invention also provides a document feeding device comprising: a loading section on which documents are loaded; a feeding section that feeds the documents loaded on the loading section in a feeding direction; a separation section that separates the documents fed by the feeding section into individual sheets; a first sensor that is arranged downstream of the separation section in the feeding direction and detects the documents fed by the feeding section; a second sensor that is arranged downstream of the separation section in the feeding direction and at a position different from the first sensor in a width direction of the documents perpendicular to the feeding direction and detects the documents fed by the feeding section; and a control section that determines whether the documents are stapled based on the detection results of the first sensor and the second sensor detecting the leading edges of the documents, wherein the control section does not perform staple detection for the documents based on the detection results of the first sensor and the second sensor after the leading edge of the document fed by the feeding section has passed the detection positions of the first sensor and the second sensor. [Effects of the Invention]

[0008] According to the present invention, it is possible to reduce erroneous detection by the skew detection unit. [Brief explanation of the drawings]

[0009] [Figure 1] (a) is a schematic diagram showing the overall printer, and (b) is a schematic diagram showing the image forming engine. [Figure 2] FIG. 4 is a plan view showing the arrangement of a skew detection sensor. [Figure 3] FIG. [Figure 4] 10 is a flowchart showing a copy operation. [Figure 5] 10 is a flowchart showing a document length calculation process. [Figure 6] 1A is a plan view showing a document positioned at the feeding start position, FIG. 1B is a plan view showing a document positioned at the timing start position, and FIG. 1C is a plan view showing a document positioned at the timing end position. [Figure 7] 10 is a flowchart showing a skew detection process. [Figure 8] (a) is a plan view showing the position of the document when it is determined whether or not it is skewed, (b) is a plan view showing the position of the document when the punch holes reach the skew detection sensor, and (c) is a plan view showing the position of the document when the trailing edge passes the sensor after separation. [Figure 9] FIG. 1A is a plan view showing bound documents, and FIG. 1B is a plan view showing the bound documents being fed. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Overall configuration] The printer 100 serving as the image forming apparatus according to this embodiment is an electrophotographic laser beam printer. As shown in Fig. 1(a), the printer 100 includes a printer main body 70 and an image reading device 10 attached to the top of the printer main body 70. In the following, the term "sheet" refers to plain paper as well as special paper such as coated paper, recording materials in special shapes such as envelopes and index paper, and plastic film or cloth for overhead projectors, and a manuscript is also an example of a sheet.

[0011] The printer main body 70 has an image forming engine 60 therein. As shown in FIG. 1(b), the image forming engine 60 includes an image forming unit PU as an electrophotographic image forming section, and a fixing device 7. When a command to start an image forming operation is issued, the photosensitive drum 1, which is a photosensitive member, rotates, and the drum surface is uniformly charged by the charging device 2. Then, the exposure device 3 modulates and outputs laser light based on image data transmitted from the image reading device 10 or an external computer, and scans the surface of the photosensitive drum 1 to form an electrostatic latent image. This electrostatic latent image is visualized (developed) into a toner image by toner supplied from the developing device 4.

[0012] In parallel with this image forming operation, a feeding operation is performed to feed sheets loaded on a cassette or manual feed tray (not shown) toward the image forming engine 60. The fed sheets are transported in accordance with the progress of the image forming operation by the image forming unit PU. The toner image carried on the photosensitive drum 1 is then transferred onto the sheet by the transfer roller 5. Any toner remaining on the photosensitive drum 1 after the toner image has been transferred is collected by a cleaning device 6. The sheet onto which the unfixed toner image has been transferred is passed to a fixing device 7, where it is sandwiched between a pair of rollers and heated and pressurized. The sheet, on which the toner has melted and adhered to the sheet and the image has been fixed, is discharged by a discharge section such as a pair of discharge rollers.

[0013] [Image reader] Next, the image reading device 10 will be described in detail. As shown in Fig. 1(a), the image reading device 10 includes an ADF 20 as a document feeder that feeds documents D loaded on a document tray 21 and discharges them onto a discharge tray 32, and a reading unit 40 that reads the documents transported by the ADF 20. The ADF 20 (Auto Document Feeder) is rotatably supported by a hinge relative to the reading unit 40 so that a document table glass 41 can be opened. The documents D may be blank paper or may have images formed on one or both sides.

[0014] The ADF 20 has a pickup roller 22 as a feeding section, a separation drive roller 23, a separation driven roller 24, a registration roller pair 25, conveyance roller pairs 26 and 30, a platen guide roller 27, and a discharge roller pair 31. The ADF 20 also has a document presence sensor S31 that detects the document D on the document tray 21, a post-separation sensor S32 that is disposed downstream of the separation drive roller 23 in the feeding direction and detects the document D, and skew detection sensors S1 and S2 that detect skew of the document D.

[0015] The reading unit 40 serving as an image reading section has a platen glass 28, a jump table 29, a reference white board 42, a document glass table 41, a first mirror table 43, a second mirror table 44, a lens 45, and a CCD line sensor 46. A lamp 47 and a mirror 48 are disposed inside the first mirror table 43, and mirrors 49 and 50 are disposed inside the second mirror table 44. The first mirror table 43 and the second mirror table 44 are configured to be movable in the sub-scanning direction, which is the left-right direction in the drawing, by wires and drive motors (not shown).

[0016] The image reading device 10 reads image information from the original D in a flow reading mode in which the original image is scanned while the original D loaded on the original tray 21 is fed by the ADF 20, and in a fixed reading mode in which the original placed on the original platen glass 41 is scanned. The flow reading mode is selected when the original presence / absence sensor S31 detects the original D loaded on the original tray 21 as a loading section, or when the user explicitly instructs it via the operation panel of the printer main body 70 or the like.

[0017] When the skimming mode is executed, pickup roller 22 supported by an arm (not shown) descends and contacts the uppermost document D on document tray 21. Document D is set on document tray 21 with the positions of its widthwise ends regulated by side regulation plates 21a and 21b (see FIG. 2).

[0018] The documents D are then fed by the pickup roller 22 and separated one by one at a separation nip N, which serves as a separation section and is formed by a separation drive roller 23 and a separation driven roller 24. The separation drive roller 23 is made of a material such as rubber that has slightly less friction than the separation driven roller 24. A torque limiter is disposed in the drive transmission path to the separation driven roller 24, so that the separation driven roller 24 rotates together with the separation drive roller 23 when one document is fed, and does not rotate when two or more documents are fed. This allows the documents to be separated one by one. Note that a drive force may be input to the separation driven roller 24 in the direction opposite to the feeding direction.

[0019] The leading and trailing edges of the document that has passed through the separation nip N are detected by the post-separation sensor S32, and serve as the basis for the timing of raising and lowering the pickup roller 22, the timing of starting and stopping its drive, and the timing of starting and stopping the drive of the registration roller pair 25.

[0020] The leading edge of the transported document D hits the stationary registration roller pair 25, which corrects the skew of the document D. The document D, whose skew has been corrected, is transported by the registration roller pair 25, and is transported toward the platen glass 28 by the transport roller pair 26. The platen guide roller 27 is disposed opposite the platen glass 28, and guides the document D so that it does not lift off the platen glass 28 as it passes through.

[0021] The image on the surface of the original D is then read by the reading unit 40 through the platen glass 28. Specifically, light from a lamp 47 is irradiated onto the original D being transported, and the reflected light from the original D is guided to a lens 45 via mirrors 48, 49, and 50. The light that passes through the lens 45 forms an image on the light receiving section of a CCD line sensor 46, undergoes photoelectric conversion, and image information is sent to the CPU 81. The reference white board 42 serves as a reference for the reading brightness of the original D. The original D that has passed through the platen glass 28 is guided by a jump platform 29 to a pair of transport rollers 30, and is discharged to a discharge tray 32 by a pair of discharge rollers 31.

[0022] On the other hand, the fixed reading mode is selected when the device detects an original D placed on the platen glass 41 or when the user explicitly instructs this via the operation panel of the printer main body 70. In this case, the original D on the platen glass 41 does not move, and the first mirror stand 43 and the second mirror stand 44 move along the platen glass 41. The original D is then scanned with light emitted by the lamp 47. Image information photoelectrically converted by the light receiving elements of the CCD line sensor 46 is transferred to the CPU 81.

[0023] [Skew detection sensor] 2, skew detection sensors S1 and S2 constitute a skew detection unit 90 that detects skew of the document D at a detection position DP located downstream of the pickup roller 22 and separation nip N in the feeding direction FD. The skew detection sensors S1 and S2 have the same configuration, and are each composed of a photointerrupter having a light-emitting unit that irradiates light onto the document D and a light-receiving unit that receives light irradiated from the light-emitting unit and reflected by the document D. The skew detection sensors S1 and S2, which are multiple sensors, are arranged at different positions in the width direction W perpendicular to the feeding direction FD, and output signals based on the presence or absence of a document at each position in the width direction W.

[0024] More specifically, the skew detection sensor S1 as the first sensor is disposed on one side in the width direction W with respect to a center line CL, which is the center in the width direction W of the conveying path CP through which the document passes. The skew detection sensor S2 as the second sensor is disposed on the other side in the width direction W with respect to the center line CL. Note that in this embodiment, two skew detection sensors S1 and S2 are provided, but any number greater than two may be provided. The post-separation sensor S32 is disposed downstream of the pickup roller 22 and upstream of the detection position DP in the feeding direction FD.

[0025] [Control Block] Fig. 3 is a control block diagram of CPU 81 as a control unit. As shown in Fig. 3, skew detection sensors S1 and S2, document presence / absence sensor S31, and post-separation sensor S32 are connected to the input side of CPU 81. A pickup motor 84 and a separation drive motor 85 are connected to the output side of CPU 81 via motor control unit 83. Pickup motor 84 as a drive unit drives pickup roller 22, and separation drive motor 85 drives separation drive roller 23.

[0026] The CPU 81 is also connected to an operation unit 506, a storage unit 507, and a document length calculation unit 508. The operation unit 506 has, for example, an operation panel, and can be used to start a copy job and perform various settings. The storage unit 507 stores a threshold value Tth [ms] for detecting skew of the document D by the skew detection sensors S1 and S2. The document length calculation unit 508 calculates the length of the document D in the sub-scanning direction (feed direction FD) from the detection result of the post-separation sensor S32 serving as a length detection unit, and inputs the calculated length of the document D to the CPU 81.

[0027] [Copy Action] Next, the copying operation by the image reading device 10 will be described with reference to the flowchart shown in Fig. 4. In this embodiment, a "bound document" refers to a document stack in which multiple documents are connected in the thickness direction of the documents by stapling, gluing, or the like, or to one document in the document stack. Furthermore, a "bound document" is not limited to a stapled or glued document, but may also be a stapleless bound or bookbound document.

[0028] 4, the CPU 81 determines whether or not a document is loaded on the document tray 21 using the document presence / absence sensor S31 (step S101). If no document is loaded on the document tray 21 (step S101: NO), the CPU 81 does not proceed to the next process and waits until a document is loaded on the document tray 21.

[0029] If it is determined that documents are loaded on document tray 21 (step S101: YES), CPU 81 determines whether or not an instruction to start a copy job has been issued (step S102). If an instruction to start a copy job has not been issued from operation unit 506 (step S102: NO), CPU 81 does not proceed to the next process and waits until an instruction to start a copy job is issued.

[0030] If it is determined that the start of a copy job has been instructed (step S102: YES), the CPU 81 causes the pickup roller 22 to feed the document D (step S103). After the document D has been fed, the CPU 81 determines whether the fed document is the first document of the job (step S104). If the fed document is the first document of the job (step S104: YES), the CPU 81 performs a document length calculation process (step S105) and a skew detection process (step S106), which will be described later, in parallel. If the fed document is the second or subsequent document of the job (step S104: NO), the CPU 81 performs only the skew detection process (step S106) without performing the document length calculation process (step S105).

[0031] Next, the CPU 81 determines whether skew of the document D has been detected in the skew detection process (step S106) (step S107). In this embodiment, if it is determined that skew has been detected in step S107, it is determined that, for example, a bound document has been fed. When a bound document is fed, the bound document rotates around the binding portion of the bound document. This causes the leading edge of the fed bound document to skew. Therefore, if skew of the document D is detected (step S107: YES), the CPU 81 stops the pickup motor 84 and the separation drive motor 85 to stop the feeding of the document D (step S108), and ends the process.

[0032] If skew of the document D is not detected (step S107: NO), the CPU 81 determines whether the fed document D is the last document of the copy job or the document tray 21 (step S109). If it is determined that it is the last document (step S109: YES), the process proceeds to step S108. If it is determined that it is not the last document (step S109: NO), the process returns to step S103, and the next document is fed.

[0033] Steps S106, S107, and S108 in this embodiment constitute a stop process for stopping the feeding of the document by the pickup roller 22 based on the detection result by the skew detection unit 90.

[0034] [Manuscript length calculation process] Next, the document length calculation process (step S105 in FIG. 4) will be described with reference to the flowchart shown in FIG. 5. As shown in FIG. 5, when the document length calculation process starts, the CPU 81 determines whether the post-separation sensor S32 has turned ON (step S201). The post-separation sensor S32 is configured, for example, with a photointerrupter similar to the skew detection sensors S1 and S2, and turns ON when the document D is present at the detection position of the post-separation sensor S32, and turns OFF when the document D is not present.

[0035] In the following description, the first document of the job is referred to as document D1, the second document of the job as document D2, the third document of the job as document D3, and the fourth document of the job as document D4.

[0036] If the post-separation sensor S32 is OFF (step S201: NO), the CPU 81 does not proceed to the next process but waits until the post-separation sensor S32 is turned ON. If the post-separation sensor S32 is turned ON (step S201: YES), the CPU 81 starts timing using a timer (not shown) (step S202). At this time, the original D1 has advanced from the feeding start position shown in FIG. 6(a) to the timing start position shown in FIG. 6(b), and its leading edge has just reached the detection position of the post-separation sensor S32. The timer may be built into the CPU 81 or provided externally to the CPU 81.

[0037] Next, the CPU 81 determines whether the post-separation sensor S32 has turned OFF (step S203). If the post-separation sensor S32 remains ON (step S203: NO), the CPU 81 does not proceed to the next process, but waits until the post-separation sensor S32 turns OFF. If the post-separation sensor S32 has turned OFF (step S203: YES), the CPU 81 ends the timer (step S204). At this time, the document D1 has advanced to the time-counting end position shown in FIG. 6(c), and its trailing edge has just passed the detection position of the post-separation sensor S32.

[0038] Then, CPU 81 calculates document length Lv [mm] based on the time measured by the timer between steps S202 and S204 and the transport speed of document D (step S205). For example, if the time measured by the timer is 142 [ms] and the transport speed of document D1 is 260 [mm / s], document length Lv is calculated as 260 × 1.142 = 296.92 [mm]. The calculated document length Lv is stored in memory unit 507 (see FIG. 3).

[0039] [Skew detection process] Next, the skew detection process (step S106 in FIG. 4) will be described with reference to the flowchart shown in FIG. 7. In the following description, it is assumed that the document length calculation process for the first document D1 of the job has already been completed, and the document length Lv [mm] has already been stored in the memory unit 507. The skew detection process when documents D2 and D3 are fed will be described below. Document D3 is, for example, the topmost document of a bound document.

[0040] 7, when the skew detection process is started, the CPU 81 determines whether the skew detection sensor S1 has turned ON (step S301). If it is determined that the skew detection sensor S1 has turned ON (step S301: YES), the CPU 81 determines whether the skew detection sensor S2 has turned ON (step S302). If it is determined that the skew detection sensor S2 has turned ON (step S302: YES), the CPU 81 determines that skew of the document D2 has not been detected (step S303).

[0041] Here, the behavior of the topmost document of the bound documents when the bound documents are fed will be described with reference to Figures 9(a) and 9(b). As shown in Figure 9(a), documents D3 and D4 constitute part of the bound documents bound with staples ST, and document D3 is the topmost document of the bound documents. Document D4 is the document adjacent to document D3.

[0042] When pickup roller 22 comes into contact with the upper surface of document D3 and starts feeding document D3, document D3 is fed while rotating around staple ST, as shown in Fig. 9(b) . This is because document D3 and document D4 are separated by separation drive roller 23 and separation driven roller 24, while only document D3 is transported by pickup roller 22 and separation drive roller 23.

[0043] When document D3 is fed in this manner, the staple ST side of document D3 is not transported in the width direction W, and only the side of document D3 opposite to staple ST advances downstream in the feeding direction. Therefore, skew detection sensor S1 remains OFF, but only skew detection sensor S2 turns ON, and it is detected that document D3 is skewed.

[0044] 7, if it is determined in step S301 that the skew detection sensor S1 is not ON (step S301: NO), the CPU 81 determines whether the skew detection sensor S2 is ON (step S304). If it is determined that the skew detection sensor S2 is not ON (step S304: NO), the process returns to step S301.

[0045] If it is determined that the skew detection sensor S2 has turned ON (step S304: YES), the CPU 81 again determines whether the skew detection sensor S1 has turned ON (step S305).If it is determined that the skew detection sensor S1 has turned ON (step S305: YES), the CPU 81 proceeds to step S303.

[0046] If it is determined that the skew detection sensor S1 is not ON (step S305: NO), the CPU 81 determines whether or not the threshold value Tth [ms] has elapsed since the skew detection sensor S2 turned ON (step S306). If it is determined that the threshold value Tth [ms] has not elapsed (step S306: NO), the process returns to step S305. Then, if it is determined that the threshold value Tth [ms] has elapsed (step S306: YES), the CPU 81 determines that skew of the document D2 has been detected (step S308).

[0047] Similarly, if it is determined in step S302 that the skew detection sensor S2 is not ON (step S302: NO), the CPU 81 determines whether the threshold value Tth [ms] has elapsed since the skew detection sensor S1 turned ON (step S307). If it is determined that the threshold value Tth [ms] has elapsed (step S307: YES), the CPU 81 determines that skew of the document D2 has been detected (step S308).

[0048] The threshold value Tth [ms] is a value stored in the storage unit 507 and is determined by the document conveyance speed. In this embodiment, the threshold value Tth [ms] is set to 30 [ms], for example. The threshold values ​​in steps S306 and S307 do not have to be the same value, and different threshold values ​​may be set for each. In either case, in steps S306 and S307, it is determined whether the time difference between the signal output by the skew detection sensor S1 and the signal output by the skew detection sensor S1 exceeds a predetermined threshold value. If this time difference exceeds the predetermined threshold value, skew of the document is detected.

[0049] After the processing of step S303 or step S308, the CPU 81 determines whether the currently fed document is the first sheet of the job (step S309). If the currently fed document is the first sheet of the job (step S309: YES), the processing ends. If the currently fed document is not the first sheet of the job (step S309: NO), the CPU 81 ignores the outputs of the skew detection sensors S1 and S2 until the trailing edge of the currently fed document passes the skew detection sensors S1 and S2 (step S310). As a result, even if the outputs of the skew detection sensors S1 and S2 are values ​​that would indicate the document is skewed, it is determined that the document is not skewed.

[0050] Step S310 will now be described in more detail with reference to Figures 8(a) to 8(c). In the following, an example will be described in which the original D2 is a perforated original. A plurality of punch holes Pd are punched in the width direction W at the rear end of the original D2. Figure 8(a) shows the position of the original D2 at the time when the CPU 81 determines whether the original D2 is skewed. Figure 8(b) shows the position of the original D2 at the time when the punch holes Pd of the original D2 pass the skew detection sensors S1 and S2. Figure 8(c) shows the position of the original D2 at the time when the rear end 91 of the original D2 passes the skew detection sensors S1 and S2.

[0051] 8(b), if the signals from the skew detection sensors S1 and S2 are used to determine whether the document is skewed when a punch hole Pd in ​​the document D2 passes through the skew detection sensors S1 and S2, the document may be erroneously detected as skewed, which may result in the document feeding being stopped unintentionally. For example, if the punch hole Pd turns only the skew detection sensor S1 OFF / ON while the skew detection sensor S2 remains ON, the time difference between the signal output by the skew detection sensor S1 and the signal output by the skew detection sensor S2 may exceed the threshold value.

[0052] Therefore, in step S310, the CPU 81 ignores the signals output from the skew detection sensors S1 and S2 from the time point in Fig. 8(a) to the time point in Fig. 8(c). Specifically, the CPU 81 ignores the signals from the skew detection sensors S1 and S2 from the time point when skew detection of the fed document D2 is completed until the rear end 91 of the document D2 passes through the skew detection sensors S1 and S2.

[0053] At this time, the transport distance of the original D2 required for the trailing edge 91 of the original D2 to pass the skew detection sensors S1 and S2 is predicted from the value calculated in the original length calculation process (step S105) and the positions of the skew detection sensors S1 and S2. Here, the distance in the feeding direction FD between the post-separation sensor S32 and the skew detection sensors S1 and S2 is defined as ds [mm]. Then, it can be predicted that the trailing edge 91 of the original D2 will pass the skew detection sensors S1 and S2 if the original D2 is transported a distance ds + Lv [mm] from the time when the leading edge 92 of the original D2 reaches the post-separation sensor S32. In this embodiment, the distance ds [mm] is set to, for example, 20 [mm].

[0054] Therefore, the distance ds+Lv=20+296.92=316.92 [mm], and if document D2 is transported 316.92 [mm] or more from the time when the leading edge of document D2 reaches post-separation sensor S32, the trailing edge of document D2 will pass through skew detection sensors S1 and S2. This reduces the chance of erroneous detection of skew in document D3 as the following document due to punch holes Pd in ​​document D2 as the preceding document, and prevents document feeding from being unintentionally stopped.

[0055] In particular, in recent image forming apparatuses, productivity has been improved by shortening the distance between the preceding document and the succeeding document (so-called paper gap), and feeding of the succeeding document may start while the preceding document is passing through the skew detection sensors S1 and S2. In this case, punch holes in the preceding document may cause erroneous detection by the skew detection sensors S1 and S2, leading to a determination that the succeeding document is skewed, and feeding of the succeeding document may be unintentionally stopped.

[0056] In this embodiment, the signals of the skew detection sensors S1 and S2 are ignored until the trailing edge of the preceding document passes the skew detection sensors S1 and S2. This reduces false detections by the skew detection sensors S1 and S2 and prevents unintended document stoppage. That is, after the leading edge of the preceding document passes the detection position DP of the skew detection sensors S1 and S2 but before the trailing edge of the preceding document passes the detection position DP, the stop process for the succeeding document is not executed regardless of the detection results of the skew detection sensors S1 and S2. That is, feeding of the succeeding document continues. Then, after the trailing edge of the preceding document passes the detection position DP, if the time difference between the signal output by the skew detection sensor S1 and the signal output by the skew detection sensor S2 exceeds the threshold value Tth during feeding of the succeeding document, the pickup motor 84 is stopped. This causes the stop process for the succeeding document to be executed, and feeding of the succeeding document is interrupted.

[0057] In the present embodiment, an example has been described in which the signals from the skew detection sensors S1 and S2 are ignored until the trailing edge of the second document D2 in the job passes the skew detection sensors S1 and S2, but the present invention is not limited to this. For example, while the document length calculation process is performed on the first document D1 in the job, the signals from the skew detection sensors S1 and S2 may be ignored until the trailing edge of the document D1 passes the skew detection sensors S1 and S2. Of course, the signals from the skew detection sensors S1 and S2 may also be ignored until the trailing edges of the third and subsequent documents in the job pass.

[0058] Furthermore, in this embodiment, the document D2 having punched holes Pd has been described, but the present invention is not limited to documents having punched holes Pd, and can also be applied to documents with bent corners or partially damaged documents.

[0059] In addition, in the present embodiment, the signals of the skew detection sensors S1 and S2 are controlled to be ignored in step S310, but this is not limiting. For example, the signals of the skew detection sensors S1 and S2 may be controlled not to be output, or the power supply to the skew detection sensors S1 and S2 may be stopped.

[0060] In the present embodiment, the length of the first document D1 of the job is detected by executing the document length calculation process using the post-separation sensor S32, but this is not limiting. For example, document length information may be input from the operation unit 506 provided in the printer 100 or an external computer. Furthermore, document length information from the previous job may continue to be used until the side regulating plates 21a and 21b are operated, and the document length calculation process may be omitted.

[0061] In addition, in this embodiment, the timing when the trailing edge of the document passes the skew detection sensors S1 and S2 is predicted using the detection result of the post-separation sensor S32, but this is not limiting. For example, it may be determined that the trailing edge of the document will pass the skew detection sensors S1 and S2 from the leading edge position of the document set in the document tray 21, the positions of the skew detection sensors S1 and S2, and the document length Lv.

[0062] In addition, in this embodiment, the post-separation sensor S32 and the skew detection sensors S1 and S2 are configured as photointerrupters, but other sensors such as a flag type or a pressure-sensitive type may also be applied. Also, although the document length calculation process, skew detection process, etc. are controlled by the CPU 81 provided in the printer main body 70, the present invention is not limited to this, and the above control may also be performed by a CPU provided in the image reading device 10, for example.

[0063] Although the above-described embodiments have been described using an electrophotographic printer, the present invention is not limited to this. For example, the present invention can also be applied to an inkjet image forming apparatus that forms an image on a sheet by ejecting ink liquid from nozzles. [Explanation of symbols]

[0064] 10: image reading device / 20: document feeder (ADF) / 21: loading section (document tray) / 22: feeding section (pickup roller) / 40: image reading section (reading unit) / 81: control section (CPU) / 84: drive section (pickup motor) / 91: trailing end / CL: center (center line) / CP: transport path / D2: preceding document (document) / D3: succeeding document (document) / DP: detection position / FD: feeding direction / N: separation nip / Pd: hole (punch hole) / S1: first sensor (skew detection sensor) / S2: second sensor (skew detection sensor) / S32: length detection section (post-separation sensor) / Tth: threshold / W: width direction

Claims

1. a loading section on which documents are loaded; a feeding section that feeds the originals loaded in the loading section in a feeding direction; a separation unit that separates the documents fed by the feeding unit into individual sheets; a first sensor disposed downstream of the separation unit in the feeding direction and configured to detect the document fed by the feeding unit; a second sensor that is arranged at a position overlapping with the first sensor when viewed in a width direction of the document perpendicular to the feeding direction, and that detects the document fed by the feeding unit; a control unit that executes a stop process to stop the feeding of the document by the feeding unit when the second sensor does not detect the document until a predetermined time has elapsed since the first sensor detected the document, the control unit ignores signals from the first sensor and the second sensor after a leading edge of the document fed by the feeding unit passes through detection positions of the first sensor and the second sensor until a trailing edge of the document passes through the first sensor and the second sensor. A document feeder characterized by:

2. a loading section on which documents are loaded; a feeding section that feeds the originals loaded in the loading section in a feeding direction; a separation unit that separates the documents fed by the feeding unit into individual sheets; a first sensor disposed downstream of the separation unit in the feeding direction and configured to detect the document fed by the feeding unit; a second sensor that is arranged at a position overlapping with the first sensor when viewed in a width direction of the document perpendicular to the feeding direction, and that detects the document fed by the feeding unit; a control unit that executes a stop process to stop the feeding of the document by the feeding unit when the second sensor does not detect the document until a predetermined time has elapsed since the first sensor detected the document, the control unit controls the first sensor and the second sensor so that signals are not output after a leading edge of the document fed by the feeding unit passes through detection positions of the first sensor and the second sensor until a trailing edge of the document passes through the detection positions. A document feeder characterized by:

3. a loading section on which documents are loaded; a feeding section that feeds the originals loaded in the loading section in a feeding direction; a separation unit that separates the documents fed by the feeding unit into individual sheets; a first sensor disposed downstream of the separation unit in the feeding direction and configured to detect the document fed by the feeding unit; a second sensor that detects the document fed by the feeding unit, the second sensor being disposed downstream of the separation unit in the feeding direction and at a position different from the first sensor in a document width direction perpendicular to the feeding direction; a control unit that determines whether the document is stapled or not based on the detection results of the first sensor and the second sensor detecting the leading edge of the document, the control unit does not perform staple detection for the document based on the detection results of the first sensor and the second sensor after the leading edge of the document fed by the feeding unit has passed the detection positions of the first sensor and the second sensor. A document feeder characterized by:

4. the control unit ignores signals from the first sensor and the second sensor after a leading edge of the document has passed the detection positions of the first sensor and the second sensor until a trailing edge of the document has passed the detection positions.

4. The document feeder according to claim 3.

5. the control unit controls the first sensor and the second sensor so that signals are not output after a leading edge of the document fed by the feeding unit passes through detection positions of the first sensor and the second sensor until a trailing edge of the document passes through the detection positions.

4. The document feeder according to claim 3.

6. the first sensor is disposed on one side in the width direction with respect to a center in the width direction of a transport path through which the document fed by the feeding unit passes, the second sensor is disposed on the other side in the width direction with respect to the center; 6. The document feeder according to claim 1, wherein the document feeder is a document feeder.

7. a length acquisition unit that acquires the length of the document in the feeding direction; the control unit determines that the trailing edge of the document has passed the detection position based on the length of the document acquired by the length acquisition unit.

7. The document feeder according to claim 1, wherein the document feeder is a document feeder.

8. the length acquisition unit is disposed downstream of the feeding unit and upstream of the detection position in the feeding direction; 8. The document feeder according to claim 7, wherein the document feeder is a document feeder.

9. a document feeder according to any one of claims 1 to 8; an image reading unit that reads an image of the document fed by the document feeding device; Equipped with An image reading device characterized by:

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