Abstract:
In order to shorten a time for preliminary original reading which is performed prior to reading of an original image, an image reading apparatus of the present invention scans an original mounted on a platen glass by a scan optical system that moves to the original and reads a scanned image of the original by using a CCD sensor, the apparatus having a function to perform a preliminary original read operation for automatically deciding a density of the original before the reading operation of the original image, wherein the preliminary original reading is performed while the scan optical system in an idling state is moving from a read standby position to an image read operation start position; a white background level correction operation of the CDD sensor is performed after collection of original density data by the preliminary original read operation; and a result of the correction is reflected on the original density data obtained by the preliminary original reading to control the decision of the original density.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an image reading apparatus for reading an image of an original mounted on a platen glass and an image forming apparatus, such as a copying machine, for forming an image of an original image using the image reading apparatus equipped. 
   2. Description of the Prior Arts 
   In an image reading apparatus for reading an image of the original mounted on a platen glass using a scan optical system adapted to move, if image data thus read are used to expose the image as they are onto a photosensitive body, it is difficult to obtain an image having an appropriate density. In order to correct a density of a read original image, preliminary original reading which is referred to as pre-scan is performed prior to an actual scan operation, and image information obtained by reading part of the original image is used to perform density correction on the image data which are read by actual scanning. 
   Japanese Patent Application KOKAI Publication No. 9-289590 (1997-289590) describes an approach by which, in an analog copying machine, in reading of an original, a density of the original is read when a scan optical system moves to a reading operation start position. It also describes an approach of providing means for altering a scanner stop position in a standby state, to reserve an original scan region for reading of the original density. 
   In a digital copying machine, an image of an original is read by a CCD sensor, so that data of the read image are converted by an A/D conversion circuit into a digital signal. In the digital copying machine, the read image data need to undergo correction of a relationship between a quantity of light reflected by an exposure lamp and a white background level of the original, wherein specifically shading correction is performed by reading the white background level, which is a quantity of light reflected from a white background portion illuminated by the exposure lamp, which quantity provides a reference before original reading. 
   In the digital copying machine, it is necessary to perform a shading operation, a preliminary original reading operation for automatic original density determination (EE), or an APS operation for automatic original size determination, before the original image is read. Conventionally, shading correction has been performed for correcting the white background level, prior to the preliminary original reading operation for original density decision, which provides the reference of the original density. Therefore, it takes a long time before a primary original scan operation starts, resulting in a drawback that there causes poor operability in copying to a user. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an image reading apparatus having improved copy operability and an image forming apparatus equipped with the reading apparatus that solve these problems to reduce a time elapsing from a moment when a copy button is depressed to a moment when a primary original scan operation starts. 
   To solve the problems and to achieve the object, the present invention proposed the following configuration. 
   According to a first aspect of the present invention, an image reading apparatus of the present invention scans an original mounted on a platen glass by a scan optical system that moves to the original and reads a scanned image of the original by using a CCD sensor, the apparatus having a function to perform a preliminary original reading operation for automatically determining a density of the original before the reading operation of the original image, wherein the preliminary original reading is performed while the scan optical system in an idling state is moving from a read standby position to an image read operation start position; a white background level correction operation of the CDD sensor is performed after collection of original density data by the preliminary original reading operation; and a result of the correction is reflected on the original density data obtained by the preliminary original reading to control the decision of the original density. 
   According to the first aspect, control is conducted so that shading may be performed after the preliminary original reading operation, thus making it possible to reduce a time spent until the start of primary original image reading. 
   In an image reading apparatus according to a second aspect of the present invention, if the preliminary original reading operation is performed in a condition where a platen cover is open, detection of an original size in a main scan direction and determination of an original density are performed simultaneously based on image data collected by the preliminary original reading operation, and if the preliminary original reading operation is performed in a condition where the platen cover is closed, the original size is detected in a process of the platen cover being closed. 
   According to the second aspect, in both cases of copying in a condition where the platen cover is closed and copying in a condition where it is closed, no time is spent in an APS operation for determination of the original size, thus making it possible to reduce a time spent until the start of primary original image reading. 
   An image reading apparatus according to a third aspect of the present invention has a preliminary original reading system for performing a preliminary original reading operation independently of a preliminary original reading system for performing the preliminary original reading operation when a scan optical system is moving from a read standby position to an image read operation start position, thus enabling changing the preliminary original reading systems by setting. 
   In the third aspect, the apparatus has also the system that enables altering a preliminary original reading operation time for automatic original density determination in accordance with a required degree of an image quality, so that it is possible to select either reducing the time spent until the start of primary original image reading or enabling sophisticated automatic original density determination at the cost of the time. 
   An image reading apparatus according to a fourth aspect of the present invention has a function for permitting a user to specify a kind of an original, so that the read standby position is altered in accordance with the specified kind of the original in a condition where the kind of the original is specified, thus changing an original scan region at the time of preliminary original reading. 
   In the fourth aspect, as the user selects the kind of the original such as a photograph image, a print image, or a color image, the original scan region changes, so that sophisticated automatic original density determination is performed while reducing the time spent until the start of primary original image reading. 
   An image forming apparatus according to a fifth aspect of the present aspect is equipped with an image reading apparatus according to any one of the first through fourth aspects, to form an image by using image data read by the image reading apparatus. 
   According to the fifth aspect, an image forming apparatus is provided which is equipped with an image reading apparatus having effects described in relation to the first through fourth aspects and which forms an image by using image data read by the image reading apparatus, thereby satisfying user&#39;s requirements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view for showing a construction of an image forming apparatus; 
       FIG. 2  is an explanatory illustration of a conventional original reading operation; 
       FIG. 3  is an explanatory illustration of an original reading operation according to the present invention; 
       FIG. 4  is a block diagram for showing control of original image reading; and 
       FIG. 5  is a flowchart for showing reading of an original image and processing of the read information. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (1) The following will describe a construction and operations of an image reading apparatus according to the present invention and an image forming apparatus equipped with the image reading apparatus. However, the image forming apparatus of the present invention is not limited to that of such a configuration as shown in  FIG. 1  but may include a color image forming apparatus for forming a color image by superimposing toner images one on another. 
   The apparatus comprises an original image reading section  10 , a laser writing section  20 , an image forming section  30 , and a sheet feeding section  40 . 
   The original image reading section  10  is configured as an independent image reading device  50  separate from a body of the apparatus and mounted and fixed to an upper face of the apparatus body. 
   The image reading device  50  comprises a platen glass  51  made of a transparent glass plate  51  as an upper part of the device and a platen cover  52  for covering an original D mounted on the platen glass  51  and is further equipped, below the platen glass  51 , with a scan optical system composed of a first mirror unit  12  and a second mirror unit  13  and the image reading section  10  composed of a main lens  14 , an image pickup device  15  such as CCD array, etc. The first mirror unit  12  is equipped with an illumination lamp  12 A and a first mirror  12 B and mounted in such a manner that it can straightly move in parallel with the platen glass  51  and horizontally in the figure, thus optically scanning an entire surface of the original D. The second mirror unit  13  integrally comprises a second mirror  13 A and a third mirror  13 B and straightly moves horizontally at half a speed of the first mirror unit  12  to always keep a predetermined optical path. Of course, similar to the first mirror unit  12 , the second mirror unit  13  also moves parallel to the platen glass. An image of the original D on the platen glass  51  which is illuminated by the illumination lamp  12 A passes through the main lens  14 , the first mirror  12 B, the second mirror  13 A, and the third mirror  13 B and is formed on the image pickup device  15 . When a start button is depressed, the first mirror  12  and the second mirror unit  13  are moved, to perform a preliminary original reading operation and an original reading operation in this order. When scanning is finished, the first mirror unit  12  and the second mirror unit  13  return to an original standby position and wait until a next image formation starts. 
   Data of the image obtained by the image pickup device  15  are converted into a digital signal, which undergoes at an image signal processing section (not shown) image data processing by use of a shading correction value and an original density correction value which are obtained by the preliminary original reading operation and is once stored as an image signal in a memory. Next, the image signal is input to the laser writing section  20 . 
   When the image signal from the memory is input under the control of a control section to the laser writing section  20  comprised of a drive motor  21 , a polygon mirror  22 , an fθ lens  23 , mirrors  24 ,  25 , and  26 , a semiconductor laser and a correction lens which are not shown, etc., the laser writing section  20  starts recording of the image. Next, at the image forming section  30 , a photosensitive drum  31 , which is an image carrier, is already rotated clockwise as shown by an arrow and discharged by a charge remover  36  for removing charge by means of pre-charge exposure and then charged by a charge  32  having a discharge wire  32 A and a charging grid  32 B, so that an electrostatic latent image that corresponds to the original D is formed on the photosensitive drum  31  with a laser beam L of the laser writing section  20 . Then, the electrostatic latent image on the photosensitive drum  31  undergoes inversion development by use of a developer carried by a developing sleeve  33 A supplied with a bias voltage obtained by superimposing an AC component on a DC component of a developing device  33 , thus providing a visible toner image. 
   On the other hand, a sheet feeding cassette  41 A or  41 B loaded in the sheet feeding section  40  delivers out sheets of transfer paper P having a specified size one by one through a delivering roller  42 A and supplies them through a delivering roller  43  and a guide member  42  toward an image transferring section. The transfer paper P thus supplied is sent onto the photosensitive drum  31  through a registration roller  44  operating in synchronization with the toner image present on the photosensitive drum  31 . The toner image on the photosensitive drum  31  is transferred onto this transfer paper P, separated from the photosensitive drum  31  by a discharging action of a separator  35 , sent via a conveyor belt  45  to a fixing device  37 , where the toner image is melted and fixed by a heating roller  37 A and a pressure roller  37 B respectively, and delivered out to a tray outside the apparatus by sheet delivering rollers  38  and  46 . 
   The photosensitive drum  31  continues rotating so that residual toner left un-transferred on the surface may be removed for cleanout by a cleaning blade  39 A butting against the surface in a cleaning device  39 . It is discharged again by the charge remover  36  and then charged uniformly by the charger  32 , thus entering a next process of image formation. 
   (2) The following will describe conventional operations for original reading with reference to an explanatory illustration of  FIG. 2  before describing those of the present invention. 
   The original D is mounted on the platen glass  51  and its image front end DA is set to a platen glass end face  51 A. The first mirror unit  12  for preliminarily reading an original image is halted at a position facing the original D separate by 30-50 mm from the image front end DA in the platen glass  51 , which position serves as a standby position  102 . 
   When the copy start button is depressed, the illumination lamp  12 A lights, so that {circle around (1)} automatic original size determination (APS) is performed while the first mirror unit  12  is in a halt condition and, after APS is performed, it moves toward a scan start position  101 . When the first mirror unit  12  thus moves and passes by a reference white background face  53  as facing it, {circle around (2)} a shading operation is performed and, therefore, {circle around (3)} the first mirror unit  12  arrives at the scan start position  101 . 
   The first mirror unit  12  turns back and {circle around (4)} goes through EE scan operation (forward route) to read original data preliminarily for automatic original density determination (EE) in a range facing the original D and turns back at the standby position  102  and {circle around (5)} goes through EE scan operation (backward route) to arrive at the scan start position  101 . 
   The first mirror unit  12  turns back again and {circle around (6)} goes through the actual scan operation (forward route) to read image density data over an entire screen of the original D determined by the automatic original size determination (APS) performed earlier and turns back at a position slightly separate from an image rear end DB of the original D and {circle around (7)} goes through the actual scan operation (backward route) to arrive at the scan start position  101 . Here, the first mirror unit  12  turns back again and {circle around (8)} moves to the standby position and stops at the standby position  102  to get ready for next reading of the original image. 
   (3) The following will describe an original image reading operation and read information processing according to the present invention. 
   In the present invention, the control section controls such that the shading operation may be performed after a preliminary original reading operation.  FIG. 3  is an explanatory illustration of the original reading operation,  FIG. 4  is a block diagram for showing control of original image reading, and  FIG. 5  is a flowchart for showing original image reading and read information processing. 
   Prior to a copy operation, the original D is mounted on the platen glass  51  and its image front end DA is set to the platen glass end face  51 A. The first mirror unit  12  for preliminarily reading an original image is halted at a position facing the original D separate by 30-50 mm from the image front end DA in the platen glass  51 , which position serves as the standby position. 
   In the vicinity of the rear end DB of the original D on the platen glass  51 , there is provided an original size sensor  54  which is constituted of a plurality of photo-couplers and which detects, for example, a sub-scan directional original size such as A4 size or B4 size, so that the sub-scan directional original size is detected on, for example, whether it is A4 size or B4 size, based on a state of a quantity of reflected light received in a condition where the platen cover  52  is open. When copying operation is performed in a condition where the platen cover  52  is closed over the original D, a process state of the platen cover  52  being closed is detected by a platen open/closed sensor not shown and indicated by short-period lighting of the illumination lamp  12 A, while the image pickup device  15  using a CCD sensor detects a main-scan directional original size (C 13 ). The detected original size is once recorded in the memory (C 17 ). When copying operation is performed in a condition where the platen cover  52  is open, on the other hand, main-scan directional original size detection and original density determination are performed simultaneously based on image data collected by the preliminary original reading operation. 
   It is to be noted that the shading operation need not always be performed at the time of returning but may be performed halfway through the actual scan operation or before the original data are read. 
   In  FIG. 3 , preliminary original reading covers a region ranging from the standby position  102  to the front end DA of the original D and original reading covers a region ranging from the front end DA of the original D to the rear end DB of the original D. 
   When the copy start button not shown is depressed (F 1 ), a control section (C 10 ) drives an image reading drive system (C 11 ) including the first mirror unit  12  positioned at the standby position  102 , to light the illumination lamp  12 A. Then, the first mirror unit  12 , while moving to a shading position (F 2 ), reads a preliminary original (F 3 ), thus performing preliminary original data reading for the purpose of {circle around (1)} automatic original size determination (APS) and {circle around (2)} automatic original density determination (EE). 
   The control section C 10  detects a main-scan directional image density distribution a plurality of number of times within an original size, which original size is determined on the basis of a difference in main-scan directional density of the original D detected by the CCD sensor  15  (F 11 ), so that an image density correction amount required by the EE processing is calculated from the detected main-scan directional image density distribution. 
   When the first mirror unit  12  moves and passes by the reference white background face  53  as facing it, {circle around (3)} a shading correction amount is read. That is, the density distribution is detected a plurality of number of times in a main-scan direction over the reference white background face  53  sandwiched between two points  53 A and  53 B (F 14 ), based on which data the control section (C 10 ) calculates the shading correction amount. 
   The first mirror unit  12  {circle around (4)} moves to the scan start position  101  and turns back {circle around (5)} to perform the actual scan operation (forward route), so that an original image density is read over the entire screen of the original D for which the automatic original size determination (APS) has been performed earlier (F 7 ). 
   The control section (C 10 ) uses a calculated shading correction amount (C 14 ) and calculated EE processing conditions and reflects the shading correction amount on the EE processing conditions (C 15 ), to performs shading/EE processing of an original image density (F 17 ), so that data of the processed original image density is recorded in a memory (C 17 ) and (F 18 ). 
   After having finished reading the image density over the entire surface of the original D, the first mirror unit  12  {circle around (6)} goes through the actual scan operation (backward route) and once returns to the scan start position  101  and then {circle around (7)} moves to the standby position to sops at the standby position  102  (F 8 ). 
   (4) Besides the preliminary original reading system of the present invention described in (3) above, the present invention has, for example, such a preliminary original reading system as described in (2) above, in which systems respective preliminary original reading programs are recorded as (C 12 ) in the memory. In the image forming apparatus, it is decided beforehand which one of these programs is to be used and set in the preliminary original reading, for reading of the original. By employing the preliminary original reading system described in (2) to make settings so that a sufficient preliminary original reading range (spacing between the image front end DA and the standby position  102 ) may be provided, the copy processing time is reduced; to improve processibility, the preliminary original reading system according to the present invention described in (3) above is employed; and to emphasize an image quality of a copy image while placing less emphasis on an improvement in a processing time, the preliminary original reading system described in (2) is employed. By thus selecting the systems, the original image is read corresponding to an application and a purpose. 
   (5) The following will describe another embodiment of the present invention. 
   In this embodiment, an operating section, not shown, of the image forming apparatus is provided with a function to select and specify a kind of an original such as a monochromatic image, a color image, a character image, or a picture image. Therefore, control is provided so that preliminary original reading may be performed by moving the standby position  102  corresponding to the specified kind of the original, according to the preliminary original reading system of the present invention described in (3) above. 
   For example, in the case of a monochromatic character image, the EE defined as being appropriate can be set easily, so that the preliminary original reading range (spacing between the image front end DA and the standby position  102 ) is set small to make EE settings defined as being appropriate, based on main-scan directional image density reading which has been performed a small number of times. In the case of a color picture image, on the other hand, EE set values defined as being appropriate cannot easily be set, so that the preliminary original reading range is set large to read the image density a large number of times for each of the B, G, and R colors in the main-scan direction, thus permitting the control section to obtain the EE set values defined as being appropriate through, for example, creation of a histogram of read data. 
   Therefore, in the present embodiment, the standby position  102  linked with a specified kind of the original is prepared as a table beforehand, so that when the specified kind of the original is detected, the control section sets the standby position  102  from the table, based on which standby position, preliminary original reading is performed. 
   According to the present embodiment, any originals, irrespective of the kinds thereof, are given the respective minimum required preliminary original reading time to set appropriate EE processing conditions. 
   According to the first aspect of the present invention, control is provided so that a shading operation may be performed after a preliminary original reading operation, thereby making it possible to reduce a time to be spent until the start of primary original image reading. 
   According to the second aspect of the present invention, in both cases of copying in a condition where the platen cover is open and copying in a condition where it is closed, no time is spent in the APS operation for determination of the original size, thus making it possible to reduce a time to be spent until the start of primary original image reading. 
   According to the third aspect of the present invention, the apparatus has also the system that enables altering a preliminary original reading operation time for automatic original density determination in accordance with a required degree of an image quality, so that it is possible to select either reducing the time to be spent until the start of primary original image reading or enabling sophisticated automatic original density determination at the cost of the time. 
   According to the fourth aspect, as the user selects the kind of originals such as a photograph image, a print image, or a color image, the original scan region changes, so that sophisticated automatic original density is determined while reducing the time to be spent until the start of primary original image reading. 
   According to the fifth aspect of the present invention, an image forming apparatus is provided which is equipped with an image reading apparatus having the effects described in relation to the first through fourth aspects and which forms an image by using image data read by the image reading apparatus, thereby satisfying user&#39;s requirements.