Abstract:
Establishing a reading station for reading images on an document disposed in a transport path between paired transport rollers and paired discharge rollers to sequentially feed documents on a sheet supply tray enables a compact device and arranging a detection sensor that detects the trailing edge of an document to detect the discharge thereof to a discharge tray at a position on the discharge tray side from the pressing point of the paired discharge rollers, and the positioning of a detection sensor to detect the leading edge of an document to control the start of reading documents, at a position upstream of the transport roller prevents distortion of the document and enables the certain detection of documents.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
   This invention relates to an image reading apparatus for scanning and optically reading a document image and outputting electronic data. More particularly, this invention relates to a structure of an automatic document feeder for transporting documents to a determined reading station and for discharging documents. 
   Image reading apparatus optically read images on a document, convert the images to electronic data, and transmit that data to image forming apparatus, such as an external personal computer, a copier or a facsimile machine. Many image forming apparatus are equipped with such image reading apparatus. 
   Image reading apparatus are provided with a light source for irradiating light onto a document that is pulled out and transported by an automatic document feeder one at a time and image sensors that receive the light reflected from the surface of the document. 
   However, it has been demanded recently that the automatic document feeder apparatus disposed on image reading apparatus be compact, lightweight and comprise fewer parts. Such an improved apparatus disclosed in Japanese Patent Publication 62-179271 shows a structure that has discharge rollers immediately after the document reading station so that these discharge rollers discharge documents to a discharge tray. This apparatus shortens the path to transport documents, and due to a configuration using least minimum number of rollers required in the transport of the documents, the structure for the transport of documents can be compact, lightweight and has fewer parts. 
   This apparatus is provided with a detection means to detect documents between a reading position for reading documents and discharge rollers. In general, there are two types of detection means; a lever type sensor detection method (or a lever type sensor) detects a motion of a detection lever disposed in the transport path swung by a sheet of document; and a reflective type sensor detection method (or a reflective type sensor) detects an interruption of light caused by a sheet of document. The light is emitted from a light-emitting unit, and is configured to be reflected by a reflective plate and returned to a light reception unit. 
   However, when employing the former lever type detection method, having a detection means between the document reading station and the discharge roller causes a problem, where a shock of the document striking the lever distorts images while being read because the documents is in a free state when the edge of the document hits the lever. 
   In particular, when the image sensor is a contact image sensor (CIS) type using a SELFOC lens, not only distortion of the image but out-focus can occur since the focus depth of CIS type sensor is extremely shallow compared to a reduction type sensor. 
   Also, when the latter reflective type sensor is employed, the light generated by the light source for the reading means can be mistakenly detected. 
   Particularly, if the image sensor is a reduction type for reading images via a plurality of mirrors reflected from a document surface, there is a greater chance of such error due to higher intensity of light. 
   An object of the present invention is to provide a document reading apparatus that it will not create a shock to documents while being read even though a reading apparatus is compact and lightweight. Another object of the present invention is to provide a document image reading apparatus that prevents a detection error during document transportation and achieves reliable detection. 
   This invention comprises a transport path for sequentially feeding documents from a sheet supply tray, a reading station for reading images on the documents disposed in the transport path, a photoelectric conversion means for photo-electrically converting images on documents moving over the reading station, a discharge tray for storing documents coming from the reading station, a first transport roller disposed at a front position in the transport direction of the reading station, a second discharge roller disposed at a back position in the transport direction of the reading station, a first detection means arranged upstream of the transport roller and a second detection means arranged at a position on the discharge tray side from the point at which the second paired transport rollers contact each other. 
   Furthermore, the second detection means has a stick-shaped lever member hanging downward that is capable of being swung by an edge of document abutting thereon at a position on the side of the discharge tray from the point at which the second transport rollers contact each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an entire automated document feeder apparatus equipped with an image reading apparatus according to the present invention. 
       FIG. 2  is an expanded sectional view of the automatic document feeder apparatus shown in FIG.  1 . 
       FIG. 3  is a detailed sectional view of the discharge unit on the automatic document feeder apparatus shown in FIG.  1 . 
       FIG. 4  is an expanded sectional view of the essential portion of the reading transport path in the second reading station of the automatic document feeder apparatus shown in FIG.  2 . 
       FIG. 5  is a plan view of the reading transport unit shown in FIG.  3 . 
       FIG. 6  is a timing chart to explain the sensors on the automatic document feeder apparatus and the drive motor control. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   The following describes in detail embodiments of the present invention according to the accompanied drawings. As an example of the preferred embodiments,  FIG. 1  shows an automated document feeder according to the present invention, and  FIG. 2  shows the essential parts of the automated document feeder. 
   According to the present invention, an image reading apparatus operates as a so-called ADF, which continuously pulls out documents and feeds them to an image reading station. 
   The image reading apparatus  1  has the lower unit  2  and the upper unit  3  mounted to the lower unit  2  by a hinge so that it can be opened and closed. 
   The upper unit  3  is provided with a sheet supply tray  5  for storing documents in stacks, a main unit  6  that transports documents from the sheet supply tray  5  and reads images on the documents, a paper supply tray, and a discharge tray  7  to which processed documents are discharged. In addition, documents stacked in the sheet supply tray  5  are arranged along the width direction by the paper guide  5   a  that forms a wall of the document paper feed path. 
   As is described in further detail below, an image reading apparatus of the present invention has a frame  6   a  that holds the transport path for transporting documents, a pair of rollers for transporting documents, and an optical reading apparatus for reading images on the documents. To the frame  6   a  are formed the document inlet  6   b  corresponding to the sheet supply tray  5 , and the document outlet  6   c  corresponding to the discharge tray  7 . The document from the document inlet  6   b  is transported along the substantially U-shaped transport path  10  that is disposed inside the frame. After the images on the document are read, the document is discharged to the discharge tray  7  via the document outlet  6   c.    
   To the document inlet  6   b  on the frame  6   a  is provided a pick-up roller  11  that touches a document stacked in the sheet supply tray  5  and pulls the document out. At downstream of this pickup roller  11  is arranged a paper separation mechanism  12  that comprises a separation pad  12   b  that touches a separation roller  12   a  to achieve reliable separation of the pullout documents into a single sheet. At downstream of the transport path in the paper separation mechanism  12 , a pair of register rollers  14  is arranged. The edge of the document separated by the paper separation mechanism forms a bend thereby removing any skews thereof. 
   The reading station of the image reading apparatus according to the present invention is configured with two optical reading means to read images on both sides of a document. 
   Of these, the first photoelectric conversion means  20  is housed in the lower unit  2 , and reads the images on the documents that pass over the sheet-through platen  21  positioned between a pair of read rollers  16  arranged in continuation along the transport path  10  and intermediate rollers  17 . The first photoelectric conversion means  20  comprises a reduction sensor and is equipped with the first carriage  22  and the second carriage  24 . Each of the carriages  22  and  24  driven by a motor (not shown in the drawings) moves in the left and right directions of the drawing in unison while keeping a specific distance with each other. 
   On the carriage  22  are mounted the light source  25  for illuminating the document and the reflecting mirror  26  for receiving light reflected from the document illuminated by the light source  25  and changing the direction to a horizontal direction. On the carriage  24  are mounted a reflective mirror  28  to reflect the horizontally directed light from the reflective mirror  26  to a vertical direction, and a reflective mirror  29  that changes the direction of the vertically directed light by the reflective mirror  28  to a horizontal direction that is opposite to that of the light reflected from the reflective mirror  26 . 
   The first photoelectric conversion means  20  is disposed inside the lower unit  2 , and comprises a light collecting lens  30  for collecting light from the reflective mirror  29 , and the CCD image sensor  31  that receives collected light from the light collecting lens  30 . Light detected by this CCD image sensor  31  is converted to digital signal by a CCD circuit board  32 , and the signal is then transmitted to an interface printed circuit board in a copier via a control circuit board (not shown in the drawings) which operates various imaging processes. 
   According to this embodiment of the present invention, the first photoelectric conversion means  20  is configured so that a thick document such as a book can be placed and read. Specifically, a reading station (hereinafter referred to as a book platen)  35  for placing thick documents is disposed above the lower unit  2  adjacent to the sheet through platen  21 . The carriages  22  and  24  scan and read the contents of the documents placed on this book reading station. For this reason, to the lower surface of the discharge tray  7  is fastened with an elastic member  7   a  for pressing documents placed on the book platen  35 . 
   The second photoelectric conversion means  40  is disposed inside the upper unit  3  for reading images on the opposite side of the documents read by the first photoelectric conversion means  20 . The second photoelectric conversion means  40  is arranged at downstream of the pair of intermediate rollers  17  where the transport path on the upstream side of the discharge tray forms a straight line. A lifting guide  38  lifts documents passed through a reading position x1 on the sheet-through platen  21 , and then the second photoelectric conversion means  40  reads the images on the opposite sides of the document. 
   According to the present invention, the second photoelectric conversion means  40  comprises a CIS type image sensor. More specifically, it comprises a light source to irradiate light to an image on a document, a protective glass through which this irradiating light and the light reflected from the document pass, and a contact image sensor (CIS) unit holding the image sensor that detects the light reflected from the document that passes through the protective glass. Light detected by the line image sensor is converted into digital signals by a printed circuit board  41 , and the digital signal is transmitted to an interface printed circuit board in a copier via an image processing circuit board  33 . 
   The following section explains in detail the configuration of the reading guide means in the second photoelectric conversion means. 
     FIG. 4  is an expanded sectional view showing the essential portion of reading transport path relating to the second photoelectric conversion means  40 . A contact image sensor (CIS) is used in the second photoelectric conversion means  40 . As mentioned before, the CIS has a smaller focus depth compared to that of the image reduction optical system, so it is essential to ensure that documents travel in close proximity to the reading surface and in a stable manner. To that end, the space of the document transport path in this reading station is set to be narrow. Also, in order to feed documents smoothly in such a narrow transport path, it is preferred that the CIS is arranged such that the alignment of the transport path be formed in a straight line. According to the preferred embodiment of the present invention, the CIS as the second photoelectric conversion unit  40  is disposed at a position where the upstream transport path of the discharge tray  7  forms a straight line and at downstream of the pair of intermediate rollers  17 . 
   In this way, after reading one side of the document by the first photoelectric conversion means  20 , the document is guided to the transport guide  47  and transported to the reading position x2 on the second photoelectric conversion means  40 . Then, the other side of the document is read by the second photoelectric conversion means  40 . 
   The reading position x2 on the second photoelectric conversion means  40  is provided with the backup guide  46  which is equipped with the pressure means  49  such as a spring, etc., to press the document against the reading means side to hold the document within a narrow tolerance of the focus depth of the second reading device. 
   The backup guide  46  is supported in a floating state via the pressure means  49 , while the transport guide  47  is fixed on the apparatus chassis. Therefore, a step is created where the transport guide surface and the backup guide surface meet. 
   When the backup guide surface in the traveling surface of the document protrudes in the traveling surface more than the transport guide, the level will cause jams when a document is a thin sheet. Conversely, when the backup guide surface is lower with regard to the transport guide surface, the shock from the trailing edge of the document passing the step would cause distortion in the reading of the image. 
   To prevent this from happening, a reading guide  48  for guiding the document from the transport guide  47  to the backup plate  43  is provided. Therefore, the reading guide  48  is an adjustable part depending on the step generated between the transport guide  47  and the backup guide  46 . So, it is preferred to form the reading guide means  48  of a bendable filling member. One end of the reading guide  48  is mounted to the transport guide  47  and protrudes from the document transport surface on the transport guide  47  into the circumference of the intermediate rollers  17 . The backup guide means  46  is formed of a reference white plate for adjusting shade. 
   The other end of the reading guide  48  extends up to the image reading position, and eliminates the step between both guides by bending to the backup guide surface moving relative to the transport guide surface. Additionally, the backup plate  43  and the backup guide  46  are supported by a spring so that they can slide along the direction of document transport to enlarge the adjustable range. 
     FIG. 5  is a top plan view of the backup guide portion of the second photoelectric conversion means  40  shown in FIG.  4 . The reading guide means  48  is separated and disposed into four pieces sandwiching the intermediate rollers  17  in order to eliminate a step between the transport guide  47  and the backup guide means  46 . Also, the protrusion  51  is formed to maintain a gap between the document sheet and the second photoelectric conversion means  40 . This protrusion  51  controls the backup guide means  46 , which is pressed by the spring guide  49  on the reading guide means  48 , to be smaller than a specific gap. 
   At the downstream side of the second photoelectric conversion means  40  as shown in  FIG. 3 , a pair of discharge rollers  50  is arranged. The pair of discharge rollers discharges processed documents to the discharge tray  7  via the document discharge outlet  6   c . Furthermore, according to this embodiment, the discharge rollers  50  contact with each other and extend for a length same as the reading width of the image sensors or longer in their rotational axes direction as a fastened single body. They are configured to prevent the infusion of external light disturbance to the reading line x2 on the photoelectric conversion means  40  through the document discharge outlet  6   c . Thus, even if the optical reading device is composed of a CIS which is sensitive to light disturbances, such disturbance is suppressed so that no noise is generated in the analog signal detected by the CCD sensor, and accurate image processing is achieved. 
   Also, this embodiment of the present invention employs a lever type sensor as a discharge sensor  63  to detect the edge of document, as can be seen in FIG.  3 . This discharge sensor  63  is disposed downstream of the discharge rollers  50 , or the outlet  6   c , so that a shock created by the edge of the document abutting the detection lever  63   b , described below, does not affect the quality of processed images on the document. 
   This discharge sensor  63  comprises a sensor unit  63   a , which has a light emitting unit and a light reception unit, and the detection lever  63   b , which has one end dangled below the discharge outlet  6   c  and the other end interrupting the path of light from the light emitting unit to the light reception unit on the sensor unit  63   a . While nipped by the pair of read rollers  16 , the pair of intermediate rollers  17 , and the pair of discharged rollers  50 , the document hits one end of the detection lever  63   b  thereby swinging in the direction of the arrow in  FIG. 3  around the pivot point of the sensor pin  63   c . This, then, causes the other end of the detection lever  63   b  to interrupt light from the light emitting unit of the sensor unit  63   a  so that light can be received at the light reception unit, thus the edge of the sheet is detected. 
   If a reflective type sensor method is employed as the discharge sensor  63 , the pair of discharge rollers  50  would interrupt the light emitted from the light source of the reading means, so the sensors would not fail to detect. 
   However, according to the preferred embodiment of the present invention, the reflective type sensor can not detect the document if the light emitting unit, light reception unit, or the reflective plate has dirt sticking thereto, hence the lever type sensor method is applied otherwise periodic maintenance is required. 
   The transport means and the discharge means are driven by two drive motors (not shown in the drawings). The first motor M 1  drives the paper feed means, and the second motor M 2  drives the transport means and the discharge means. By separating these drive systems, even if a sudden load is applied to the first motor in the cases of separating documents, feeding paper or stopping, the document transportation is maintained stable as the second motor drives the document on the reading station of the second reading apparatus. 
   Note that, as is shown in  FIG. 2 , in addition to the discharge sensor  63 , a register sensor  61  and a read sensor  62  are disposed to the transport path  10  to detect documents. Based on detection signals from these sensors, the control means (not shown in the drawings) controls the motor that drives the register rollers  14 , the read rollers  16 , the intermediate rollers  17  and the discharge rollers  50 . 
   Also, the read sensor  62  detects the leading edge of the documents, and initiates adjustments of the movement of the carriages  22  and  24 , the reading start timing of each photoelectric conversion means  20  and  40 , and flashing of the light source. 
     FIG. 6  is an example of the timing chart of each sensor and each motor while reading a document. 
   In FIG.  1  and  FIG. 2 , when an empty sensor (not shown in the drawings) detects documents placed on the sheet supply tray and there is an instruction to read documents, the paper feed motor starts to feed a document one at a time by forward rotation. After the documents is fed and the register sensor  61  detects the edge of the first document, the paper feed motor continues to rotate for a determined amount of time (t 1 ) so that the edge of the document sheet abuts the register rollers  14  and bends. After stopping the forward rotation, the paper feed motor starts to rotate in reverse after a determined time (t 2 ), and drives the register rollers  14  to send the first document downstream. At the same time that the read sensor  62  detects the edge of the first document, the paper feed motor stops. The transport motor continues to rotate only for a specified time after the read sensor  62  detects the edge of the document and then stops. After adjusting the read timing, the document starts to be driven for reading the other side by the first photoelectric conversion means  20 . As described above, the first document is transported by the transport motor and the other side of the document is read by the second photoelectric conversion means  40 . 
   If the empty sensor continues to detect the second and more documents stacked on the sheet supply tray while the first document is transported and read, the second document is fed after a predetermined time (t 3 ) after the trailing edge of the first document has passed the register sensor. Thus, the time intervals between the first and second documents can be ensured. Then, the register sensor  61  detects the leading edge of the second document, and the leading edge thereof abuts against the register rollers  14 . The paper feed and transportation for the second and subsequent documents are operated in the same manner as the first document. While the second sheet is being fed and transported, the discharge rollers  50  discharge the first document. At that time, after the discharge sensor  63  detects the trailing edge of the first document, it is recognized that the document has been discharged to the discharge tray. 
   By passing a determined amount of time (t 4 ) after the trailing edge of the second document has been detected by the discharge sensor  63 , it is recognized that all documents have the discharge tray  7  and all motors are