JP2011186046A - Document carrying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a document carrying device which surely suppresses flap of a document and carrying speed fluctuation regardless of the document size, and can stably carry the document. <P>SOLUTION: The document carrying device is provided with: a pair of first carrying rollers arranged on an upstream side of a platen for reading a document and supplying the document onto the platen; a pair of second carrying rollers arranged on a downstream side of the platen and carrying the document carried out from the top of the platen; and a size detection means detecting the length of the document carried onto the platen. The document carrying device is provided with a roller separation means making one roller of the pair of first carrying rollers be away from the other roller and a drive means actuating the roller separation means, and controls operation timing of the roller separation means based on the length of the document detected by the size detection means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a document feeding apparatus that transports a document to a predetermined reading position, and more particularly to a mechanism for preventing image defects such as image misalignment in a read image of a document whose reading position has been read. is there.

  2. Description of the Related Art Conventionally, in a document reading apparatus equipped with a document feeding device, a reading mechanism having an image sensor for reading a document is stopped below a contact glass reading position, and this reading mechanism causes the document feeding device to place it on the contact glass. One that reads an image of a supplied document is known.

  Although there are various types of image sensors, a linear image sensor in which photoelectric conversion elements such as a CCD device and a MOS device are linearly arranged in a one-dimensional array is typical for monochrome, and a color filter is photoelectrically used for color. Each one-dimensional array of the three primary colors formed on the conversion element is arranged in parallel at a predetermined interval, and color image data is corrected by correcting the primary color data from the three lines read synchronously by a delay corresponding to the predetermined interval. The ones that have acquired are representative. In the photoelectric conversion elements formed in such a one-dimensional array, a document conveyed at a constant speed is read at regular intervals. Therefore, in order to acquire good image data, there is a demand for a function for suppressing document flapping and fluctuations in the conveyance speed and conveying the document stably.

  The above-described document flapping and speed fluctuation occur instantaneously when the document is released from the nip of the roller pair arranged upstream of the reading position, that is, when the trailing edge of the document passes the nip position of the roller pair. . Such fluttering of the document and fluctuations in speed cause distortion in the printed image, leading to deterioration in the quality of the printed image. In particular, in an image reading apparatus in which the reading sensor is composed of three RGB lines and reads the primary colors at the same time, the position at which the document is simultaneously read differs, so even if time difference correction is performed, the positions do not match between the primary colors, and color misalignment or color blurring occurs. It will be reproduced as.

  In order to solve such a problem, a pair of upstream rollers arranged on the upstream side of the document reading position is configured to be detachable, and the roller pair is moved before the trailing edge of the document passes the nip position of the roller pair. The thing which spaces apart is proposed (for example, patent document 1, patent document 2). According to this, since the roller pair is switched from the contact state to the separated state before the trailing edge of the document passes between the roller pairs, an instantaneous speed change occurs when the trailing edge of the document passes the roller. There is no. Therefore, the distortion and color shift of the image are improved, and a high quality printed image can be obtained.

JP 2003-34450 A JP 2005-289544 A

  However, in the conventional configuration in which the upstream roller pair is configured to be detachable, the sensor disposed on the upstream side of the upstream roller pair is controlled so that the roller pair is separated after a predetermined time after the trailing edge of the document is detected. Therefore, in the case of a small-size document, there arises a problem that the upstream roller pair is separated without being securely nipped by the roller pair on the downstream side of the reading position. This has caused speed fluctuations and document skew.

  The present invention has been made in view of the above-described problems, and provides a document transport device that can reliably control document fluttering and transport speed fluctuations and stably transport a document regardless of the document size. The purpose is to do.

  In order to achieve the above object, the present invention is arranged on the upstream side of a platen for reading a document, arranged on the downstream side of the platen, and a first conveying roller pair for supplying the document on the platen, and from above the platen In a document conveying apparatus including a second conveying roller pair that conveys a document to be carried out, and a size detection unit that detects the length of the document conveyed on the platen, one of the first conveying roller pair Roller separation means for separating the roller from the other roller, drive means for operating the roller separation means, control means for controlling the operation timing of the roller separation means based on the length of the document detected by the size detection means, Was provided.

  With the above configuration, the original can be controlled so as to separate the first conveying roller pair on the upstream side of the platen in a state where the original document is securely nipped to the second conveying roller pair on the downstream side of the platen regardless of the original size. It is transported without hindrance, and it is possible to suppress fluttering of the document and fluctuations in the transport speed.

1 is a cross-sectional view illustrating an entire document conveying device to which a sheet feeding device of the present invention is applied and an image reading apparatus on which the document conveying device is mounted. FIG. FIG. 3 is a cross-sectional view showing a main part of the document conveying device according to the present invention. It is sectional drawing which shows the roller separation mechanism of the document conveying apparatus which concerns on this invention. It is a top view showing a roller separation mechanism of the document conveying device according to the present invention. FIG. 4 is a perspective view showing a part of a roller separation mechanism of the document conveying device according to the present invention. It is a state figure which shows the press-contact / separation state of the carrying-in roller pair which concerns on this invention, (a) is a state figure which shows the separation state of a roller pair, (b) is a state figure which shows the press-contact state of a roller pair. FIG. 3 is a control block diagram showing a control system of the document feeder according to the present invention. It is an operation | movement flowchart figure which shows the press-contact operation | movement of the roller pair which concerns on this invention. It is an operation | movement flowchart figure which shows the separation operation | movement of the roller pair which concerns on this invention. It is an operation | movement flowchart figure which shows the initial operation | movement of the roller separation mechanism which concerns on this invention. It is a trial figure for demonstrating the setting of the separation timing of the roller pair which concerns on this invention. It is an operation flowchart figure showing roller separation operation in a 2nd embodiment concerning the present invention.

  FIG. 1 is a cross-sectional view showing an entire document feeding device to which the sheet feeding device of the present invention is applied and an image reading device on which the document feeding device is mounted. FIG. It is sectional drawing which shows a part. The configuration of the document feeder and the image reading apparatus on which the document feeder is mounted will be described below with reference to FIGS.

  Reference numeral 10 denotes a document feeder mounted on the image reading apparatus 1, and the document feeder 10 is attached to the upper surface of the image reading apparatus main body 1 so as to be freely opened and closed. In addition, a transport mechanism that transports the document so as to pass through the upper surface of the contact glass 2 of the apparatus main body 1 is provided.

  The image reading apparatus main body 1 is provided with a first platen glass 2 for reading and processing a document conveyed by the automatic document feeder 10, and a book document or the like provided adjacent to the first platen glass 2. A second platen glass 7 for reading and processing a large-size document is provided. Under the first and second platen glasses 2 and 7, reading means for reading an image of the document is provided.

  Then, the image reading apparatus main body 1 has a book document reading mode and an automatic document which read a document manually placed on the second platen glass 7 by moving first and second optical carriages of reading means described later. There is a document reading mode in which the first and second optical carriages are read with respect to a document moving on the first platen glass 2 by the feeding device 10.

  The reading unit includes a first carriage 8 including a light source 3 such as a xenon lamp that irradiates a document, and a first mirror 4a for guiding reflected light from the document, and a second mirror that guides reflected light from the first mirror 4a. 4b and the third mirror 4c for guiding the reflected light from the second mirror 4b, the reflected light of the original guided through the first mirror 4a, the second mirror 4b and the third mirror 4c is collected. A condensing lens 5 that emits light, a three-line sensor 6 that receives reflected light and performs photoelectric conversion, an A / D change process that converts an analog signal from the three-line sensor 6 into a digital signal, and three signals R, G, and B Is provided with a processing substrate for performing a delay process for aligning the information as information on the same line.

  Next, the reading operation of the reading means will be described. In the book document reading mode for reading a document manually placed on the second platen glass 7, the first carriage 8 and the second carriage 9 are moved to a sub-scanning motor (not shown). 2), the original on the second platen glass 7 is irradiated with the irradiation light from the light source 3, and the reflected light of the original is reflected by the first mirror 4a, the second mirror 4b, The light is incident on a three-line sensor 6 provided in a line shape via the third mirror 4 c and the lens 5. The incident light is photoelectrically converted to read document information (image information).

  In the original reading mode for reading an original moving on the first platen glass 2, the first carriage 8 and the second carriage 9 are stopped below the first platen glass 2 and conveyed by the automatic original feeder 10. Irradiation light from the light source 3 is irradiated on the document to be printed. Then, the reflected light of the original is made incident on the three-line sensor 6 by the first mirror 4a, the second mirror 4b, the third mirror 4c and the lens 5, and the incident light is made by the three-line sensor 6 as in the book original reading mode. Document information (image information) is read by photoelectric conversion.

  Then, an analog signal as document information photoelectrically converted by the three-line sensor 6 is converted into a digital signal by an A / D changer or the like, subjected to predetermined image processing, and then transmitted to an image forming apparatus (not shown).

  Here, in the three line sensor 6, three line sensors of RGB sensors are arranged in parallel on a monolithic substrate. The size of these pixels is about 7 μm × 7 μm (or 10 μm × 10 μm, 14 μm × 14 μm), and the sensor line interval is 10 to 20 times the pixel size (that is, about 0.1 to 10 μm). About 0.2 mm). Since there is a line interval between the three sensors in this way, the same position on the document surface cannot be read at the same time. For example, if at a certain time, the R sensor of the three-line sensor 6 reads the information of the scanning line N, the G sensor reads the information of the scanning line N-1, and the B sensor reads the information of the scanning line N-2, In order to obtain the three color information of G and B, the reading means further scans, the G sensor and the B sensor respectively read the information on the scanning line N, and delay processing is performed to combine the delayed information. ing.

  The document feeder 10 includes a paper feed tray 15 on which a plurality of documents can be placed, a feeding unit 11 that separates the documents on the paper feed tray 15 one by one and feeds them toward the contact glass 2; A transport unit 12 that allows a document to pass along the upper surface of the contact glass 2, a discharge unit 13 that receives and discharges the document that has passed through the upper surface of the contact glass 2, and stores a document that has been read from an image discharged from the discharge unit 13 And a paper discharge tray 16 to be used. Further, the document feeder 10 includes a switchback unit 14 that causes the document ejected from the upper surface of the contact glass 2 to be switched back by the ejecting unit 13 and sent again to the feeding unit 11 and fed to the upper surface of the contact glass 2. is doing. Here, the paper feed tray 15 is inclined at a certain angle and is disposed with a space above the paper discharge tray 16.

  The document placed on the sheet feeding tray 15 is regulated by a side guide 17 that regulates the side portion thereof, and the leading end is regulated by the stopper member 60. Further, an empty sensor S4 for detecting the presence or absence of a document on the paper feed tray 15 is provided upstream of the stopper member 60 in the paper feed direction.

  The paper feed unit 11 descends and comes into contact with the uppermost surface of the original on the paper feed tray 15, and a feed roller 18 that can be raised and lowered to feed the original, and a paper feed roller 19 that feeds the original fed by the feed roller 18. Separation means composed of a separating member 20 comprising a friction pad that passes through only one uppermost document and blocks the feeding of the second and subsequent documents, and of the document separated into one sheet by this separation means A pair of registration rollers 21 that are sent to the downstream side after aligning by abutting the leading end, and feeds the original along the paper feed path 25.

  The conveyance unit 12 includes a pair of carry-in rollers 22 (first conveyance roller pair) that supplies a document to the contact glass 2 on the upstream side of the contact glass 2, and a pair of carry-out rollers 23 that discharge the document from the contact glass 2 on the downstream side. (Second conveyance roller pair) is provided, and the document is conveyed along the conveyance path 26.

  The paper discharge unit 13 and the switchback unit 14 share a part on the paper discharge tray 16 side, and are provided with a paper discharge roller pair 24 that discharges the original to the paper discharge tray 16. The paper discharge roller pair 24 rotates in the forward direction when the original is discharged to the paper discharge tray 16. Further, when reading both sides of the document, in order to reverse the document and supply it to the contact glass 2 again, the paper discharge roller pair 24 rotates in the reverse direction with the rear end side of the document nipped to switch the document. Control is performed so that the paper is fed back to the paper feeding unit 11.

  That is, in the single-side mode for reading one side of the original, the original is discharged from the paper discharge path 27 onto the paper discharge tray 16, and in the double-side mode for reading both sides of the original, the original is switched back by the paper discharge path 27 and then the switchback path 28. Through the sheet feeding path 25.

  Here, the carry-in roller pair 22 is arranged corresponding to each of the three carry-in drive rollers 22a arranged along the width direction of the document and the three carry-in drive rollers 22a, and each of the carry-in drive rollers 22a. It is comprised by three carrying-in driven rollers 22b which press-contact to. Each driven roller 22b is in pressure contact with the corresponding carry-in drive roller 22a and cooperates with the drive roller 22a to nip and convey the document.

  The carry-in roller pair 22 is configured such that the carry-in driven roller 22b is pressed against and separated from the carry-in drive roller 22a. 3 is a cross-sectional view showing a roller separation mechanism for bringing the carry-in driven roller 22b into and out of contact with the carry-in drive roller 22a, FIG. 4 is a top view of the roller separation mechanism, and FIG. 5 is a part of the roller separation mechanism. FIG. This roller separation mechanism will be described with reference to FIGS. 3, 4, and 5. FIG.

  The roller separating mechanism is fixedly attached to a support arm 41 that supports a rotating shaft 40 that pivotally supports three driven rollers 22b, a working shaft 42 that supports the supporting arm 41, and a working shaft 42. A holding member 44, a torsion coil spring 43 spanned between the holding member 44 and the support arm 41, an operating piece 45 attached to one end of an operating shaft 42 extending in the width direction of the document, and an operating piece A cam member 46 for actuating 45, a tension spring 47 for urging the actuating piece 45 in a direction to contact the cam member, and a separation drive motor MT3 for actuating the cam member 46.

  Next, the pressure contact and separation operation of the carry-in driven roller 22b having the above-described configuration will be described. First, the cam member 46 is a circular rotary cam formed so as to increase or decrease its radius with respect to the shaft, and the operating piece 45 that contacts the cam surface of the cam member 46 by rotating by the separation drive motor MT3 is provided. Rock. When the operating piece 45 is swung by the cam member 46, the operating shaft 42 and the holding member 44 are rotated. This rotation is transmitted to the support arm 41 via the coil spring 43, the support arm 41 rotates in the same direction as the operating shaft 42, and the carry-in driven roller 22b is pressed against and separated from the carry-in drive roller 22a. As shown in FIG. 5, both ends of the coil spring 43 are attached to a holding member 44 fixed to the operating shaft 42 and a support arm 41 rotatably supported on the operating shaft 42, so that the holding member 44 is rotated counterclockwise. The rotation is attached so as to apply a force in the opening direction of the coil spring 43.

  Specifically, the operation and operation will be described with reference to FIG. 6A showing a state in which the carry-in driven roller 22b is separated from the carry-in driving roller 22a and FIG. As shown in a), the carry-in driven roller 22b is separated from the carry-in drive roller 22a in a state in which the surface of the cam member 46 having the minimum radius is in contact with the operating piece 45. When the separation drive motor MT3 is rotated 180 degrees from this state, the cam member 46 is also rotated 180 degrees. As a result, the radius of the cam member 46 at the contact position of the operating piece 45 is displaced, and the operating piece 45 swings leftward in FIG. As the operating piece 45 swings, the operating shaft 42 and the holding member 44 rotate counterclockwise, and the rotation of the holding member 44 counterclockwise is supported by the operating shaft 42 so as to be rotatable. Is transmitted through the coil spring 43. Then, the support arm 41 rotates upward, and the carry-in driven roller 22b supported by the support arm 41 moves upward to contact the carry-in drive roller 22a. The swing of the operating piece 45, that is, the rotation of the holding member 44 is set so that the carry-in driven roller 22b rotates by a certain amount after coming into contact with the carry-in drive roller 22a. As a result, a torsional force is generated in the coil spring 43 so that the carry-in driven roller 22b comes into pressure contact with the carry-in drive roller 22a with a constant pressure as shown in FIG. 6B.

  Next, the operation of changing the state in which the carry-in driven roller 22b is separated from the state in which the carry-in driven roller 22b is in pressure contact with the carry-in drive roller 22a will be described in FIG. 6A. In other words, the working piece 45 is in contact with the surface. When the separation drive motor MT3 is rotated 180 degrees from this state, the cam member 46 rotates and the radius of the cam member 46 at the contact position of the operating piece 45 becomes small. At this time, the operating piece 45 is always pulled toward the cam member 46 by the action of the tension spring 47, and swings rightward in FIG. 6 (b) as the radius of the cam member 46 is displaced. When the operating piece 45 swings, the operating shaft 42 and the holding member 44 rotate in the clockwise direction, and this rotational force is transmitted to the support arm 41 via the coil spring 43. At this time, the coil spring 43 gradually decreases the torsional force until the holding member 44 rotates by a certain amount, and transmits the rotational force of the holding member 44 to the support arm 41 when the torsional force is lost. When the rotational force of the holding member 44 is transmitted to the support arm 41, the support arm 41 rotates downward, and the carry-in driven roller 22b moves downward. As a result, the carry-in driven roller 22b is separated from the carry-in drive roller 22a as shown in FIG.

  According to this roller separation mechanism, the rotation of the holding member 42 is transmitted to the support arm via the coil spring 43, and the holding member 44 is brought into contact with the carry-in driving roller 22a during the pressure contact. Since a predetermined torsional force is generated in the coil spring 43 by rotating a certain amount, a constant pressure contact force with respect to the carry-in drive roller 22a can be easily applied to the carry-in driven roller 22b. Further, at the time of separation, the torsional force gradually decreases until the holding member 44 rotates by a certain amount, and when the torsional force is lost, the rotational force of the holding member 44 is transmitted to the support arm 41. Accordingly, since the carry-in driven roller 22b is separated from the carry-in drive roller 22a after the pressure contact force of the carry-in driven roller 22b with respect to the carry-in drive roller 22a is gradually reduced, the influence on the conveyed document at the time of separation is minimized and stable. Transport is possible.

  In the present embodiment, after the separation drive motor starts rotating, the cam member 46 does not act on the operating piece 45 until the cam member 46 rotates 30 degrees, and after 30 degrees, the operating piece 45 gradually increases. The cam member 45 is shaped so that the carry-in driven roller 22b is separated from or brought into pressure contact with the carry-in drive roller 22a when reaching 120 degrees.

  FIG. 7 is a control glock diagram. Each detection sensor will be described with reference to the block diagrams of FIGS. 1, 2, and 7. The paper feed tray 15 is provided with a plurality of sensors S1 and S2 for detecting the length size of the document. When a sheet document of the same size is placed on the sheet feed tray 15, the width direction of the sheet document is detected by a volume VR whose output changes depending on the amount of movement of the side guide 17, and the sheet document width is detected. The size is determined based on the result and the length of the sheet original detected by the plurality of sensors S1 and S2. On the other hand, when the sheet originals of different sizes are mixedly loaded on the paper feed tray 15, the trailing edge of the sheet original is described later when the paper feed motor MT1 starts to rotate in reverse, that is, when the registration roller pair 21 rotates. The time until the sensor S5 detects is measured, and the length size of the sheet document is obtained from the measurement result. Then, the width size is detected based on whether or not the sheet document is detected by a plurality of width sensors S8 arranged at a distance from the registration sensor S5 in the sheet document width direction. The sheet document size is determined for each sheet based on the obtained sheet document length size and the sheet document width size obtained by the width sensor.

  Further, in the route for guiding the document, an empty sensor S4 as a detecting means for detecting that the document is placed on the sheet feeding tray 15 described above, and an end portion of the document fed through the sheet feeding path 25 Are provided in front of the contact glass 2, a lead sensor S6 for detecting the edge of the document, and a discharge sensor S7 for detecting the edge of the document discharged from the contact glass 2, respectively. Each of the sensors S1 to S7 is connected to a control unit 100 including a CPU that controls driving of the entire apparatus. Based on detection signals from the sensors, the sheet feeding motor MT1, the transport motor MT2, and The separation drive motor MT3 described above is driven and controlled.

  Next, the document conveyance control operation of the document feeder configured as described above will be described. First, a description will be given of a single-side mode for reading one side of a document. First, a document is placed (set) on a paper feed tray in contact with a stopper 60 serving as a front end regulating unit. When it is detected that the empty sensor S4 is in an ON state, that is, when a document is placed on the sheet feed tray 15, and a sheet feed command is received, the restriction of the document on the stopper 60 is released, and the sheet feed motor MT1 is set correctly. Roll drive. As a result, the feeding roller 18 and the paper feeding roller 19 are rotated in the document feeding direction, and the document is fed. At this time, the registration roller pair 21 does not rotate by the action of the one-way clutch.

  Subsequently, after a predetermined time has elapsed since the registration sensor S5 detected the leading edge of the fed document, the paper feed motor MT1 temporarily stops. As a result, the leading edge of the document is applied to the nip portion of the registration roller pair 21 to form a bend, and the leading edge of the document is aligned.

  When the predetermined time t1 has elapsed after the leading edges of the originals are aligned, the paper feed motor MT1 is driven in reverse.

  At this time, the pressure contact operation of the carry-in roller pair 22 is executed simultaneously with the reverse rotation of the paper feed motor MT1. This pressure contact operation will be described based on the pressure contact operation flowchart of FIG.

  Simultaneously with the reverse rotation of the paper feed motor MT1, the number of rotation pulses is set in the counter B, and the separation drive motor MT3 is driven (ST1 to ST3). Here, the number of rotation pulses described above is the number of drive pulses for rotating the separation drive motor MT3 by 180 degrees, and the counter B in this apparatus subtracts one count every time one drive pulse is generated. The output value is transmitted when the counter value is “0”, that is, when the counter value is counted up. That is, here, the counter B is incremented when the motor rotates 180 degrees.

  When the counter B started simultaneously with the driving of the separation drive motor MT3 is counted up, the separation drive motor MT3 is stopped (ST4 to ST6). As a result, the carry-in driven roller 22b comes into pressure contact with the carry-in drive roller 22b as shown in FIG.

  Thereafter, the conveyance motor MT2 is driven, and the registration roller pair 21, the carry-in roller pair 22, the carry-out roller pair 23, and the paper discharge roller pair 24 are rotationally driven by the rotation driving of the paper feed motor MT1 and the conveyance motor MT2, and the document is fed. The paper is conveyed from the paper path 25 to the conveyance path 26, and passes over the contact glass 2 by the pair of carry-in rollers 22, the carry-out roller pair 23, and the paper discharge roller pair 24 before and after the contact glass 2. At this time, the surface (one side) of the document is sub-scanned and read by the reading means at the reading position on the contact glass 2.

  Here, in the process in which the document is read at the reading position on the contact glass 2, the carry-in driven roller 22b is separated from the carry-in drive roller 22a before the trailing end of the document passes through the carry-in roller pair 22. . If the separation of the pair of carry-in rollers 22 is performed at a position close to the rear end of the document, the vibration of the document increases and affects the read image of the document. For this reason, it is desirable to perform the separating operation of the carry-in roller pair 22 immediately after the trailing edge of the document passes through the registration roller pair 21. However, in the case of a small-size document, when the separation operation is started immediately after the trailing edge of the document passes through the registration roller pair 21, the carry-in roller pair 22 is depressurized or separated in a state where the leading edge of the document is not sufficiently nipped by the carry-out roller pair 23. Therefore, stable conveyance is not possible. Therefore, in the present embodiment, the timing of separating the carry-in roller pair 22 is varied according to the size of the document.

  The roller separation operation will be described with reference to the separation operation flowchart of FIG. 9. When the registration sensor S5 detects the trailing edge of the document, it is determined whether the document size is larger than A5 (ST10 to ST11). When the document size is larger than A5, the first transport pulse number is set in the counter A, and when the document size is A5 or less, the second transport pulse number is set in the counter A (ST11, ST12, ST13). ). When the number of carrier pulses is set in the counter A, the counter A is started (ST14). The value of the counter A is decreased every time a drive pulse of the transport motor M2 is generated, and when the value of the counter A is "0", that is, when the count is counted up, the rotation pulse number is set in the counter B, and the separation drive motor MT3 Is rotated (ST15 to ST17). Thereafter, when the counter B started simultaneously with the driving of the separation drive motor MT3 is counted up, the separation drive motor MT3 is stopped (ST18 to ST20). As a result, the carry-in driven roller 22b is separated from the carry-in drive roller 22b as shown in FIG.

  The number of first conveyance pulses set according to the sheet size is from the detection position of the registration sensor S5 to the first position P1 set upstream of the nip point of the carry-in roller pair 22 as shown in FIG. The number of drive pulses of the transport motor MT2 corresponding to the distance of the second transport pulse is equal to the nip point of the pair of carry-in rollers 22 from the detection position of the registration sensor S5 as shown in FIG. This is the number of drive pulses of the transport motor MT2 corresponding to the distance to the near second position P2.

  That is, here, in the case of the large size, the separating operation of the carry-in roller pair 22 is started when the trailing edge of the document reaches the first position P1, while in the case of the small size, the trailing edge of the document is the second position. Control is performed so that the separation operation of the carry-in roller pair 22 is started when the position is reached.

  In this embodiment, as shown in FIG. 11, the first position P1 is set to the first position P1 at a substantially central position between the registration roller pair 21 and the carry-in roller pair 22, and the registration sensor S5 detects the first position P1. The number of drive pulses of the transport motor MT2 corresponding to the distance L1 from the position to the first position P1 is calculated in advance and stored in the RAM. On the other hand, as shown in FIG. 7, the second position is calculated in advance from the size of the document when the leading edge of the document passes the nip point of the carry-out roller pair 23 by ΔX. Set. The number of drive pulses of the transport motor MT2 corresponding to the distance L2 from the detection position of the registration sensor S5 to the second position P2 is calculated in advance and stored in the RAM. That is, the second position is set based on the arrival position of the leading edge of the document, and the setting method of the first position P1 and the second position P2 is different. In the present embodiment, the above ΔX is set to 5 mm.

  The document read at the reading position pushes up the front end of a flapper 29 arranged so as to block the paper discharge path 27 at the front end, and is conveyed onto the paper discharge tray 16 by the paper discharge roller pair 24. Note that, after a predetermined time has elapsed after the trailing edge of the original is detected by the registration sensor S5, the paper feeding motor MT1 is driven to rotate forward again to start feeding the next original.

  Next, the duplex mode for reading both sides of a document will be briefly described.

  When the empty sensor S4 detects that an original is placed on the paper feed tray 15, the original is fed onto the contact glass 2 by the feeding roller 18, paper feed roller 19, and registration roller pair 21 as in the single-sided mode. Then, the surface is read by the reading means and guided to the paper discharge path 27.

  Thereafter, in this double-sided mode, a switchback reversing operation is performed in order to reverse the front and back of the document and re-supply the document on the contact glass 2 again. In this switchback reversal operation, first, when the trailing edge of the document reaches a predetermined position after passing through the flapper 29, the driving of the transport motor MT2 is stopped. At this time, the document is stopped with its rear end side being nipped by the discharge roller pair 24.

  Thereafter, the transport motor MT2 is driven in reverse. As a result, the paper discharge roller pair 24 rotates in the reverse direction, the original is switched back, and the switchback path 28 is guided along the original guide surface of the flapper 29 that has moved to a position that closes the paper discharge path 27 as the original passes. Is done. When the leading edge of the document guided to the switchback path 28 reaches the nip portion of the registration roller pair 21, the sheet feeding motor MT2 is driven in reverse to refeed the document. As a result, the registration roller pair 21 is rotated. When the leading edge of the document securely nips the registration roller pair 21, the transport motor MT2 is driven to rotate forward. As a result, the carry-in roller pair 22 and the carry-out roller pair 23 are rotated, and at the same time, the paper discharge roller pair 24 is also rotated in the paper discharge direction.

  By this series of operations of the registration roller pair 21, the carry-in roller pair 22, the carry-out roller pair 23, and the paper discharge roller pair 24, the original is reversed along the paper feed path 25 and the transport path 26 to be fed and transported. Then, it passes over the contact glass 2. At this time, the back side of the document is sub-scanned and read by the reading unit.

  After that, the document guided through the paper discharge path 27 is again subjected to the switchback inversion operation in order to discharge the original in the page order to the paper discharge tray 16. Then, the switchback reversal operation is executed, and the originals with the same page order are discharged from the discharge path 27 to the discharge tray 16. Even in the switchback reversing operation for page alignment, the document is transported onto the contact glass 2, but here the document is not scanned.

  In this embodiment, the number of drive pulses of the paper feed motor MT1 is used to measure the time, and the time is measured by counting the number of drive pulses of the paper feed motor MT1. Accordingly, the time used for the above-described control for feeding the document is equal to the driving amount of the sheet feeding motor MT1, that is, the rotation amounts of the feeding roller 18 and the sheet feeding roller 19.

  The initial operation of the cam member 46 will be described based on the flowchart of FIG. This initial operation is executed when the apparatus is turned on, when a document is fed, and when the original jam is removed and the original jam is released. In the initial operation, first, the separation drive motor MT3 is rotated (ST30). When the position sensor PS detects the edge of the detection flag 48 attached to the rotary shaft of the separation drive motor MT3, the number of initial pulses is set in the counter B, and the counter is counted every time one drive pulse of the separation drive motor MT3 is generated. B is subtracted by “1” (ST31 to ST34). When the counter B reaches “0” and counts up, the separation drive motor MT3 is stopped (ST34 to ST35). Accordingly, when the device is operated and when the abnormality of the device is released, the cam member 46 is always in the initial position where the surface with the smallest radius comes into contact with the operating piece 45 as shown in FIG. Therefore, even when the supply of power to the separation drive motor MT3 is cut off while the cam member 46 is rotating, the operation of the apparatus can be resumed without any trouble.

  The edge of the detection flag 48 can be easily determined by detecting the timing at which the position sensor PS switches from ON to OFF. In the present embodiment, the angle between the initial position of the cam member 46 and the edge of the detection flag 48 is 90 degrees. Therefore, the number of drive pulses for rotating the separation drive motor MT3 by 90 degrees is set as the number of initial pulses described above.

(Modification)
In the embodiment described above, the separation of the pair of carry-in rollers 22 based on the fact that the sensor (registration sensor S5) arranged on the upstream side of the pair of carry-in rollers 22 detects the trailing edge of the large-size and small-size documents. In the case of a small-size document, a sensor disposed on the upstream side controls the timing of separating the carry-in roller pair 22 based on the detection of the leading edge of the document. In the case of a large-size document, the sensor is disposed on the upstream side. The sensor may control the separation timing of the carry-in roller pair 22 based on the detection of the trailing edge of the document.

  In other words, in the case of a small-size document, control is performed so that the separation operation is started when the sensor disposed on the upstream side detects the leading edge of the document and the leading edge of the document is ΔX-niped by the carry-out roller pair 23. In the case of a size document, as described above, the separation operation is started when the sensor detects the trailing edge of the document and is conveyed by the distance L1.

(Second Embodiment)
In the above-described embodiment, the timing of separating the carry-in roller pair 22 after the trailing edge of the document is detected by the registration sensor S5 is set to be delayed with respect to the separation of the large document in the case of a small document. Although controlled, in the case of a small size, the carry-in roller may be controlled so as not to be separated. The second embodiment will be described with reference to the flowchart of FIG. 12. When the registration sensor S5 detects the trailing edge of the document, it is determined whether or not the document size is a large size document larger than a predetermined size (for example, A5). (ST40 to ST41). If the document size is a large size document, the first transport pulse number is set in the counter A (ST42). When the number of carrier pulses is set in the counter A, the counter A is started (ST43). Then, every time a drive pulse of the transport motor M2 is generated, the value of the counter A is decreased, and when the value of the counter A is “0”, that is, when the count is counted up, the number of rotation pulses is set in the counter B in the first counter, The separation drive motor MT3 is rotated (ST44 to ST46). Thereafter, when the counter B started simultaneously with the driving of the separation drive motor MT3 is counted up, the separation drive motor MT3 is stopped, and the carry-in driven roller 22b is separated from the carry-in drive roller 22b. (ST47 to ST49). On the other hand, when the document is not a large document, that is, when the document is small, the roller separation operation is not performed and the document is conveyed while the carry-in roller pair 22 is in pressure contact.

DESCRIPTION OF SYMBOLS 1 Image reading apparatus 10 Document feeder 2 Contact glass 21 Registration roller pair 22 Carry-in roller pair 22a Carry-in drive roller 22b Carry-in driven roller 23 Carry-out roller pair 40 Rotating shaft 41 Support arm 42 Actuating shaft 43 Torsion coil spring 44 Holding member 45 Actuating piece 46 Cam member 47 Tension spring 100 Control unit MT2 Transport motor MT3 Separation drive motor MT3
S1, S2 Size sensor S5 Registration sensor S8 Width sensor

Claims (3)

A first conveying roller pair that is arranged on the upstream side of the platen for reading the original and supplies the original on the platen, and a second that is arranged on the downstream side of the platen and conveys the original carried out from the platen. A document conveying device comprising: a pair of conveying rollers; and size detecting means for detecting the length of the document conveyed on the platen.
Based on the length of the original detected by the size detecting means, roller separating means for separating one roller of the first conveying roller pair from the other roller, driving means for operating the roller separating means, And a control means for controlling the operation timing of the roller separating means. When the length of the document detected by the size detection unit is equal to or greater than a predetermined length, the control unit moves the roller separation unit when the first position of the document reaches the nip position of the first conveying roller pair. When the length of the original detected by the size detecting means is shorter than a predetermined length, the second position on the rear end side of the original with respect to the first position in the original is the nip of the first conveying roller pair. 2. The document conveying apparatus according to claim 1, wherein the driving timing of the driving unit is controlled so that the roller separating unit is operated when the position is reached. When the length of the document detected by the size detection unit is equal to or greater than a predetermined length, the control unit is configured to detect the roller when the trailing edge of the document reaches a first position upstream of the first transport roller. When the separation means is activated and the length of the original detected by the size detection means is shorter than a predetermined length, the time when the leading edge of the original reaches the second position on the downstream side of the second conveying roller pair 2. The document conveying apparatus according to claim 1, wherein the driving timing of the driving means is controlled so as to operate the roller separating means.