Abstract:
Disclosed is an image reading apparatus for moving a document reading unit to a point below a document feeder that feeds documents, and emitting light from a light source of the document reading unit toward a feed roller of the document feeder, whereby light reflected from a document that travels between the feed roller and the light source is sensed by the document feeding unit to thereby read an image on the document. The apparatus includes a photoelectronic converter for outputting an electric signal that conforms to amount of incident light, and a reading position setting unit for moving the document reading unit, irradiating the feed roller with light from the light source at each position to which the document reading unit is moved, causing the photoelectronic converter to output an electric signal that conforms to amount of light reflected from the feed roller at each position, detecting a range in a sub-scan direction over which this electric signal exceeds a predetermined threshold value, and setting a position at the center of this range as a reading position.

Description:
FIELD OF THE INVENTION 
   This invention relates to an image reading apparatus having an automatic document feeder and to a method of setting reading position in this image reading apparatus. More particularly, the invention relates a method of setting reading position in an image reading apparatus in a case where a reading operation is performed while feeding a document using an automatic document feeder. 
   BACKGROUND OF THE INVENTION 
   Conventional digital copiers include those equipped with a document feeder such as an automatic document feeder (referred to as an ADF below) capable of dealing with double-sided copying. 
   When a document that has been supplied to the ADF is copied in a digital copier having an ADF of this kind, a reading unit provided below the ADF is moved by a motor and stopped at a set position, namely a point substantially directly beneath a platen roller within the ADF, after which light is emitted from a lamp unit and the document transported between the platen roller and a glass plate to thereby scan the document with the light so that light reflected from the document may be detected by the reading unit. A plurality of images are obtained by executing processing in a printer section based upon data obtained by such detection. 
   When the reading unit provided below the ADF is moved to the set position by the motor in the conventional arrangement described above, the motor is stopped at such time that a predetermined number of pulses have been counted starting from the moment at which a position sensor senses the reading unit, and the stopping position is adopted as being the reading position. A problem which arises is that the precision of the reading apparatus declines (on the order of about ±2 mm), causing a decline in image quality at reading of the document, owing to differences in the mounting position of the ADF or a variance in the reading position of the ADF relative to the position of the reading unit. 
   The specification of Japanese Patent No. 2993810 proposes means for solving this problem, namely means for moving a reader in a sub-scan direction and, while the reader is being moved, adopting as the reading position a position that maximizes a value obtained by reading light entrant upon being reflected from the platen roller. 
   However, it has been found that as a result of reading reflected light from the platen roller using the reader, there are instances where a plurality of positions that give maximum values exist owing to the diameter and surface conditions of the platen. 
   Further, the actual path traversed by a document varies depending upon document thickness. In addition, with regard to documents having a glossy surface, there are instances where the value obtained by reading reflected light from the platen roller while the reader is being moved in the sub-scan direction is not necessarily the optimum reading position. 
   SUMMARY OF THE INVENTION 
   The present invention has been made in consideration of the circumstances set forth above and its object is to suppress a decline in image quality at reading of a document by improving the reading position precision of the reading apparatus. 
   According to the present invention, the foregoing object is attained by providing an image reading apparatus for moving a document reading unit to a point below a document feeder that feeds documents, and emitting light from a light source of the document reading unit toward a feed roller of the document feeder, whereby light reflected from a document that travels between the feed roller and the light source is sensed by the document reading unit to thereby read an image on the document, the apparatus comprising: a photoelectronic converter for outputting an electric signal that conforms to amount of incident light; and a reading position setting unit adapted to move the document reading unit, irradiate the feed roller with light from the light source at each position to which the document reading unit is moved, cause the photoelectronic converter to output an electric signal that conforms to amount of light reflected from the feed roller at each position, detect a range in a sub-scan direction over which this electric signal exceeds a predetermined threshold value, and set a position at the center of this range as a reading position. 
   According to the present invention, the foregoing object is also attained by providing a reading position setting method in an image reading apparatus for moving a document reading unit to a point below a document feeder that feeds documents, and emitting light from a light source of the document reading unit toward a feed roller of the document feeder, whereby light reflected from a document that travels between the feed roller and the light source is converted to an electric signal by a photoelectronic converter to thereby read an image on the document, the method comprising: a read-out step of moving the document reading unit, irradiating the feed roller with light from the light source at each position to which the document reading unit is moved and causing the photoelectronic converter to output an electric signal that conforms to amount of light reflected from the feed roller at each position; a detection step of detecting a range in a sub-scan direction over which the electric signal exceeds a predetermined threshold value; and a setting step of setting a position at the center of the range, which has been detected at the detection step, as a reading position. 
   Further, the foregoing object is also attained by providing an image reading apparatus for moving a document reading unit to a point below a document feeder that feeds documents, and emitting light from a light source of the document reading unit toward a feed roller of the document feeder, whereby light reflected from a document that travels between the feed roller and the light source is sensed by the document reading unit to thereby read an image on the document, the apparatus comprising: a photoelectronic converter for outputting an electric signal that conforms to amount of incident light; and a reading position setting unit adapted to move the document reading unit, irradiating the feed roller with light from the light source at each position to which the document reading unit is moved, cause the photoelectronic converter to output an electric signal that conforms to amount of light reflected from the feed roller at each position, detect a range in a sub-scan direction over which this electric signal exceeds a predetermined threshold value, detect a flat portion of the read signal within this range, and set the center of the detected flat portion as a reading position. 
   Further, the foregoing object is also attained by providing a reading position setting method in an image reading apparatus for moving a document reading unit to a point below a document feeder that feeds documents, and emitting light from a light source of the document reading unit toward a feed roller of the document feeder, whereby light reflected from a document that travels between the feed roller and the light source is converted to an electric signal by a photoelectronic converter to thereby read an image on the document, the method comprising: a read-out step of moving the document reading unit, irradiating the feed roller with light from the light source at each position to which the document reading unit is moved and causing the photoelectronic converter to output an electric signal that conforms to amount of light reflected from the feed roller at each position; a first detection step of detecting a range in a sub-scan direction over which the electric signal exceeds a predetermined threshold value; a second detection step of detecting a flat portion of the read signal within the range detected at the first detection step; and a setting step of setting the center of the flat portion, which has been detected at the second detection step, as a reading position. 
   Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a sectional view illustrating the general structure of an image reading apparatus according to a first embodiment of the present invention; 
       FIG. 2A  is a diagram for explaining a reading position according to the first embodiment of the present invention; 
       FIG. 2B  is a diagram for explaining a reading position according to the first embodiment of the present invention; 
       FIG. 3  is a block diagram illustrating the general structure of the control system of the image reading apparatus according to the first embodiment of the present invention; 
       FIG. 4  is a flowchart illustrating processing for setting a reading position according to the first embodiment of the present invention; 
       FIG. 5  is a diagram for explaining a reading position according to a second embodiment of the present invention; and 
       FIG. 6  is a flowchart illustrating processing for setting a reading position according to the second embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described in detail in accordance with the accompanying drawings. 
   (First Embodiment) 
     FIG. 1  is a sectional view illustrating the general structure of an image reading apparatus according to a first embodiment of the present invention. The image reading apparatus includes a scanner  105  proper and an ADF  101  adapted so as to be removably mounted on the scanner  105 . 
   The ADF  101  transports placed documents  102  to, and recovers them from, a platen glass  106  of the scanner  105  by a feed roller  103 . At this time the documents  102  pass between the feed roller  103 , which is mounted on the ADF  101 , and the platen glass  106  of the scanner  105 . During this passage of the documents, they are scanned optically by the scanner  105  so that the information on the documents is read. 
   More specifically, the scanner  105  has a lamp  107  for illuminating the document surface with light, and mirrors  108 ,  110 ,  111  for introducing reflected light from the document, which light corresponds to that emitted by the lamp  107 , to a lens  116  and CCD  117 . The lamp  107  and the mirror  108  are mounted on a first optical bench  109 , and the mirrors  110 ,  111  are mounted on a second optical bench  112 . 
   The first and second benches  109 ,  112  are coupled to a motor  114  (see  FIG. 3 ) by a wire (not shown) and are controlled so as to travel parallel to a platen glass  118  by driving the motor  114  into rotation. 
   A position sensor  115  senses the home position of the first optical bench  109 . By rotating the motor  114  in forward and reverse directions using the position of the position sensor  115  as a reference, the optical benches  109 ,  112  can be moved to optically scan the document on the platen glass  118 . 
   The motor  114  is constituted by a stepping motor. An encoder  302  (see  FIG. 3 ) is connected to the motor  114  and outputs a signal by which it is possible to recognize how many pulses the first and second benches  109 ,  112  have been moved. That is, it is possible to ascertain the positions of the optical benches  109 ,  112  by the pulses output from the encoder  302 . 
   Light reflected from the document is introduced to the lens  116  via the mirrors  108 ,  110 ,  111  and is condensed on the CCD  117  by the lens  116 . The CCD  117  photoelectronically converts the reflected light, in which the document information is contained, and outputs an electrical image signal. 
   The image reading apparatus of the first embodiment constructed as set forth above is capable of reading document information in two modes, namely “an ADF document reading mode” and “a platen glass document reading mode”. In the ADF document reading mode, document information is read while the document is fed by the ADF  101  in a state in which the first optical bench  109  is stopped at the document reading position. In the platen glass document reading mode, a document is fixedly placed on the platen glass  118  and the document information is read while the optical benches  109 ,  112  are moved in the sub-scan direction. 
     FIG. 3  is a block diagram illustrating the general structure of the control system of this image reading apparatus, in which components identical with those shown in  FIG. 1  are designated by like reference characters. The image reading apparatus shown in  FIG. 1  includes the feed roller  103  mounted on the ADF  101  for feeding documents  102 ; the lamp  107  for illuminating the surface of a document with light; the motor  114  for scanning the document by moving the first and second optical benches  109 ,  112  in the sub-scan direction; the CCD  117  for photoelectronically converting light reflected from the document surface; an A/D converting circuit  301  for converting the analog output signal of the CCD  117  to a digital signal; the encoder  302  connected to the motor  114 ; the position sensor  115  for positioning the first optical bench  109  at the home position; a back-up RAM  303  for setting a normal document reading position in the ADF document reading mode; and a scanner controller  304 . 
   The scanner controller  304  includes a ROM  304   a  in which have been stored various programs such as a program corresponding to the flowchart shown in  FIG. 4 , described later. 
   The scanner controller  304  ascertains the position of the first and second optical benches  109 ,  112  based upon the output of the encoder  302  and the output signal from the position sensor  115 , adjusts the reading position by a method, described below, based upon the output of the CCD  117  digitized by the A/D converting circuit  301 , and saves the set position in the back-up RAM  303 . 
   This operation for sensing and setting the document reading position may be performed when the ADF  101  is mounted on the scanner  105 , whenever the reading operation in the ADF document reading mode is designated by the operator, or when power is introduced to the image reading apparatus. 
   In any case, documents can be read at high speed because the sensing and setting of document reading position is not carried out prior to the reading of each document whenever documents are read one after another. It is preferred that the timing for sensing and setting the document reading position be selectable by the operator at will. 
   It is also possible to sense and set the document reading position at any timing by operating a prescribed key, for example. This configuration is particularly effective in a case where the mechanism connecting the ADF  101  and scanner  105  is such that the ADF  101  and scanner  105  may readily experience a deviation in position when the ADF  101  is touched by one&#39;s hand. 
   Processing for sensing and setting the image reading position will now be described with reference to the flowchart of  FIG. 4 . 
   In accordance with the program that has been stored in the ROM  304   a , the scanner controller  304  first drives and controls the motor  114  at step S 1  to thereby move the first and second optical benches  109 ,  112  by a pre-set number of pulses from the home position along the platen glass  106 . The amount of movement at this time is set in such a manner that the first optical bench  109  will be situated substantially directly below the center position of the feed roller  103 . 
   Next, the scanner controller  304  lights the lamp  107  at step S 2  and drives the motor  114  at step S 3 . As a result, while the first and second optical benches  109 ,  112  are moved over a prescribed range in the sub-scan direction about this point, electric charge is read out of the CCD  117  and is converted to a digital signal by the A/D converting circuit  301 . Next, at step S 4 , a position Pmax, which indicates the maximum value of the digital signal obtained over this prescribed range, and the maximum value Lmax are detected and stored.  FIG. 2A  illustrates an example of the read signal in the sub-scan direction read at this time. 
   It is determined at step S 5  whether the detected maximum value Lmax is greater than a predetermined value k. If Lmax is equal to or less than k (“NO” at step S 5 ), then an error message is displayed on the display unit of a control panel (not shown) at step S 6  and operation is halted. The reason for this is to take into account a situation where the feed roller  103  does not reside within the prescribed range with respect to the scanner  105  or floats above the platen glass  106  owing to an improper positional relationship between the ADF  101  and scanner  105 . 
   If the maximum value Lmax is greater than the predetermined value k (“YES” at step S 5 ), then a value obtained by multiplying the detected maximum value Lmax by a predetermined coefficient is set as a threshold value  201  ( FIG. 2A ) at step S 7 . 
   Next, at step S 8 , the scanner controller  304  drives the motor  114 , whereby the first and second optical benches  109 ,  112  are moved to the position Pmax stored at step S 4  and indicating the maximum value of the digital signal. 
   Next, at step S 9 , the scanner controller  304  lights the lamp  107  and drives the motor  114  to thereby move the first and second optical benches  109 ,  112  back-and-forth in the sub-scan direction over a prescribed range ( 2   d ) about the position Pmax as center.  FIG. 2B  illustrates the read value output from the CCD  117  and converted to the digital signal by the A/D converting circuit  301  at this time. The read value and the threshold value  201  are compared and sub-scan positions (two locations)  202 ,  203  ( FIG. 2B ) at which the read value falls below the threshold value  201  are stored in the back-up RAM  303  at step S 10 . It has been determined in investigations concerning this case that similar image quality is obtained at positions where a read-signal level above a predetermined threshold value can be detected. 
   As shown in  FIG. 2B , the point midway between the two sub-scan positions  202 ,  203  at which the read value falls below the threshold value is stored in the back-up RAM  303  as the reading position. However, if the distance between the two sub-scan positions  202 ,  203  is found to be equal to or less than a predetermined value (“NO” at step S 12 ), then an error message is displayed on the display unit of the control panel (not shown) and operation is halted at step S 11 . 
   If the distance between the two sub-scan positions  202 ,  203  is found to be greater than the predetermined value (“YES” at step S 12 ), then the point  204  midway between the two locations  202 ,  203  is set as the reading position at step S 13 . 
   In accordance with the first embodiment, as described above, a decline in image quality when a document is read can be suppressed by improving the precision of the reading position of the reading apparatus. 
   In the description rendered above, the amount of movement is set in such a manner that the first optical bench  109  will arrive substantially directly below the center position of the feed roller  103  at step S 1 , and the first and second optical benches  109 ,  112  are moved over a prescribed range in the sub-scan direction centered on this position at step S 3 . However, the present invention is not limited to this arrangement. It may be so arranged that the amount of movement is set in such a manner that the first optical bench  109  will arrive at one end of the prescribed range at step S 1 , after which the first optical bench  109  is moved from this point to the other end of the prescribed range. Similarly, the first optical bench  109  is moved to the position Pmax, which indicates the maximum value, at step S 8 . However, control may be exercised so as to move the first optical bench  109  to one end (Pmax+d or Pmax−d) of a prescribed range (2d) centered on the position Pmax, and then move the first optical bench  109  over the prescribed range. 
   Further, with regard to the center position of the feed roller  103  or either end of the prescribed range in step S 1 , a fixed amount of movement may be stored in the ROM  304   a  or back-up RAM  303  as a default value, and the amount of movement may be found based upon a center position obtained by processing for detecting the document reading position the preceding time. 
   Furthermore, in the first embodiment, a case is described in which the reading of the feed roller  103  is performed twice. However, the present invention is not limited to this arrangement. It is obvious that setting of the reading position based upon a signal value obtained by a single reading operation also can readily be executed based upon the first embodiment. 
   (Second Embodiment) 
   In the first embodiment, the CCD  117 , which detects the amount of light reflected when light is emitted from the light source toward the feed roller  103 , and the document reader are moved back and forth, the amount of light reflected from the feed roller  103  is detected by the CCD  117  at each travelling position, the range in the sub-scan direction at which the detected value from the light-quantity detection means exceeds a predetermined threshold value is sensed and the center position of this range is set as the reading position. However, there are instances where a read signal of the kind shown in  FIG. 5  is detected owing to difference in the diameter of the feed roller. 
     FIG. 6  is a flowchart of processing in such case. If a signal of the kind shown in  FIG. 5  is obtained at step S 9 , second and third threshold values  502 ,  503  are calculated at step S 21  after execution of processing similar to that from step S 1  to step S 12  described in the first embodiment. A region (delimited by  504  and  505  in  FIG. 5 ) in which the read signal is flat is detected (step S 22 ) in a region in which the read signal is greater than a first threshold value  501  (which corresponds to the threshold value  201  in  FIGS. 2A ,  2 B), and the center  506  of this region is set as the reading position (step S 23 ). This makes it possible to obtain effects similar to those of the foregoing embodiment. 
   &lt;Other Embodiment&gt; 
   The present invention can be applied to a system constituted by a plurality of devices (e.g., host computer, interface, reader, printer) or to an apparatus comprising a single device (e.g., copying machine, facsimile machine). 
   Further, the object of the present invention can also be achieved by providing a storage medium storing program codes for performing the aforesaid processes to a computer system or apparatus (e.g., a personal computer), reading the program codes, by a CPU or MPU of the computer system or apparatus, from the storage medium, then executing the program. 
   In this case, the program codes read from the storage medium realize the functions according to the embodiments, and the storage medium storing the program codes constitutes the invention. 
   Further, the storage medium, such as a floppy disk, a hard disk, an optical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, a non-volatile type memory card, and ROM can be used for providing the program codes. 
   Furthermore, besides aforesaid functions according to the above embodiments are realized by executing the program codes which are read by a computer, the present invention includes a case where an OS (operating system) or the like working on the computer performs a part or entire processes in accordance with designations of the program codes and realizes functions according to the above embodiments. 
   Furthermore, the present invention also includes a case where, after the program codes read from the storage medium are written in a function expansion card which is inserted into the computer or in a memory provided in a function expansion unit which is connected to the computer, CPU or the like contained in the function expansion card or unit performs a part or entire process in accordance with designations of the program codes and realizes functions of the above embodiments. 
   In a case where the present invention is applied to the aforesaid storage medium, the storage medium stores program codes corresponding to the flowcharts shown in  FIG. 4  or  6  described in the embodiments. 
   The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore to apprise the public of the scope of the present invention, the following claims are made.