Patent Description:
Hitherto, an image reading apparatus configured to read an image of a sheet through a transparent member through use of an image sensor while conveying the sheet is known (see <CIT>). In addition, in general, shading correction is performed by reading a white reference plate through use of an image sensor in order to correct light amount unevenness of a light source of the image sensor in a main scanning direction and sensitivity unevenness of a light-receiving portion in the main scanning direction.

In order to perform the shading correction with a high degree of accuracy, the distance between the white reference plate and the image sensor exhibited when the image sensor reads the white reference plate is required to be set to the distance between the image sensor and a sheet, which is exhibited when the image sensor reads an image on the sheet being conveyed. In view of this, it is conceivable to provide a white reference plate on a side of a transparent member opposite to the image sensor, that is, on the conveyance path. When the white reference plate is provided on the conveyance path, the sheet may be rubbed by the white reference plate, and a part of the image formed on the sheet may be peeled off. A part of the peeled image may adhere to the white reference plate or may be suspended to stain the image reading apparatus. The resulting stain will cause a streak in the image. This inhibits the image of the sheet from being read correctly, and thereby lowers reading accuracy. In addition, when the white reference plate is provided on the conveyance path, there is a possibility that a leading end of the sheet may be brought into contact with the white reference plate, causing buckling of the sheet which in turn may cause a paper jam.

Japanese patent application publication no. <CIT> describes a measurement device that measure an image pattern on a sheet conveyed from an image forming apparatus. The measurement device comprises: a first sheet conveyance path through which a sheet conveyed from an image formation device is conveyed; a second sheet conveyance path branched from the first sheet conveyance path at the midway of the first sheet conveyance path and merged with the first sheet conveyance path at a further downstream in a sheet conveyance direction than the position at which the path is branched; a measurement part that measures an image pattern formed on the sheet conveyed along the second sheet conveyance path; and a switching part that switches the conveyance paths so that a sheet of a print job that is not measured by the measurement part is conveyed along the first sheet conveyance path and a sheet of a measurement job which is measured by the measurement part is conveyed to the second sheet conveyance path. The system can execute two types of jobs, a print job and a measurement job. A measurement path is provided with a colorimetric unit and reading unit. The colorimetric unit is a measurement unit that reads an image pattern on a sheet and performs color measurement. The reading unit reads an image pattern formed on the front surface and the back surface of the sheet, and calculates an adjustment amount for performing print position alignment on the front and back.

According to the present invention there is provided an image forming system as claimed in claim <NUM>.

Each of the embodiments of the present invention described below can be implemented solely or as a combination of a plurality of the embodiments. Also, features from different embodiments can be combined where necessary or where the combination of elements or features from individual embodiments in a single embodiment is beneficial.

<FIG> is a partial cross-sectional view of an image forming system <NUM>. The image forming system <NUM> includes an image forming apparatus (image forming portion) <NUM>, an operation portion (user interface) <NUM>, an adjustment unit (automatic adjustment apparatus) <NUM>, and a post-processing apparatus (finisher) <NUM>. The image forming apparatus <NUM> is configured to form an image on a recording medium (hereinafter referred to as "sheet") P. The operation portion <NUM> is operated by a user in order to set a condition for image formation to be performed by the image forming apparatus <NUM>, and is configured to display a state of the image forming apparatus <NUM>. The adjustment unit <NUM> is configured to perform front/back registration for measuring position misregistration between an image formed on a front side of the sheet P by the image forming apparatus <NUM> and an image formed on a back side of the sheet P by the image forming apparatus <NUM>. The post-processing apparatus <NUM> is configured to discharge the sheet P having the image formed thereon to a discharge tray <NUM>, and to perform post-processing including staple processing, punching processing, and sorting processing.

The image forming apparatus <NUM> is an electrophotographic laser beam printer. The image forming apparatus <NUM> uses an electrophotographic image forming process to form an image on a sheet. Examples of the image forming apparatus <NUM> include not only a laser beam printer but also an electrophotographic copying machine (for example, digital copying machine), a color LED printer, a multifunction peripheral (MFP), a facsimile apparatus, and a printing machine. The image forming apparatus <NUM> is not limited to a color image forming apparatus configured to form a color image, and may be a monochrome image forming apparatus configured to form a monochrome image. The image forming apparatus <NUM> is not limited to an electrophotographic image forming apparatus, and may be an ink-jet printer, a sublimation type printer, or a heat-drying type thermal printer.

The image forming apparatus <NUM> is described with reference to <FIG> and <FIG> is a block diagram of the image forming apparatus <NUM> and the adjustment unit <NUM>. The image forming apparatus <NUM> includes a printer controller <NUM>, an engine control portion <NUM>, and an engine portion <NUM>. The printer controller <NUM> includes a sheet library <NUM> and an image shape correction portion <NUM>. The printer controller <NUM> is electrically connected to the operation portion <NUM>, the engine control portion <NUM>, and a communication portion <NUM> of the adjustment unit <NUM>.

The engine control portion <NUM> is electrically connected to a conveyance roller drive motor <NUM> and a flapper drive portion <NUM>. The flapper drive portion <NUM> is configured to drive flappers <NUM>, <NUM>, <NUM>, and <NUM>. The engine control portion <NUM> is further electrically connected to a first post-fixing sensor <NUM>, a second post-fixing sensor <NUM>, a surface reverse sensor <NUM>, and the engine portion <NUM>. The engine control portion <NUM> is configured to control the engine portion <NUM> to execute the image forming process (including sheet feeding processing). The engine portion <NUM> includes a yellow image forming portion <NUM>, a magenta image forming portion <NUM>, a cyan image forming portion <NUM>, and a black image forming portion <NUM>. The engine portion <NUM> further includes a feed cassette <NUM>, an intermediate transfer member <NUM>, a secondary transfer roller <NUM>, a first fixing device <NUM>, and a second fixing device <NUM>.

The yellow image forming portion <NUM> is configured to form a yellow (Y) toner image. The magenta image forming portion <NUM> is configured to form a magenta (M) toner image. The cyan image forming portion <NUM> is configured to form a cyan (C) toner image. The black image forming portion <NUM> is configured to form a black (K) toner image. The yellow image forming portion <NUM>, the magenta image forming portion <NUM>, the cyan image forming portion <NUM>, and the black image forming portion <NUM> have substantially the same structure except for their toner colors, and hence the following description is directed to the yellow image forming portion <NUM>.

The yellow image forming portion <NUM> includes a photosensitive drum <NUM> configured to rotate. A charging device <NUM>, a laser scanner <NUM>, a developing device <NUM>, and a primary transfer roller <NUM> are arranged around the photosensitive drum <NUM>. The charging device <NUM> is configured to uniformly charge a surface of the photosensitive drum <NUM>. The laser scanner <NUM> includes a laser driver (not shown) configured to turn on and off laser light emitted from a semiconductor laser <NUM> based on image data supplied from the printer controller <NUM>. The laser light emitted from the semiconductor laser <NUM> is deflected in a main scanning direction by a rotary polygon mirror (not shown). The laser light deflected in the main scanning direction is guided to the surface of the photosensitive drum <NUM> by a reflecting mirror <NUM> to expose the uniformly charged surface of the photosensitive drum <NUM> in the main scanning direction. Thus, an electrostatic latent image is formed on the surface of the photosensitive drum <NUM> based on the image data.

The developing device <NUM> is configured to develop the electrostatic latent image on the surface of the photosensitive drum <NUM> with the yellow (Y) toner to form the yellow (Y) toner image. A voltage having a polarity reverse to that of the toner image is applied to the primary transfer roller <NUM> to transfer the yellow (Y) toner image on the surface of the photosensitive drum <NUM> onto the intermediate transfer member <NUM>. In the same manner, the magenta (M) toner image, the cyan (C) toner image, and the black (K) toner image that are formed by the magenta image forming portion <NUM>, the cyan image forming portion <NUM>, and the black image forming portion <NUM>, respectively, are sequentially transferred onto the intermediate transfer member <NUM>. The yellow (Y) toner image, the magenta (M) toner image, the cyan (C) toner image, and the black (K) toner image are transferred onto the intermediate transfer member <NUM> so as to be superimposed on each other, to thereby form a full-color toner image.

Meanwhile, the sheets P stored in the feed cassette <NUM> are conveyed to the secondary transfer roller <NUM> one by one. The secondary transfer roller <NUM> brings the sheet P into press contact against the intermediate transfer member <NUM>, and at the same time, a bias having a polarity reverse to that of the toner is applied to the secondary transfer roller <NUM>. The secondary transfer roller <NUM> transfers the toner image on the intermediate transfer member <NUM> to the sheet P. The photosensitive drum <NUM> and the developing device <NUM> are attachable and removable. A feed timing sensor <NUM> for adjusting a timing to feed the sheet P is arranged on a conveyance path for the sheet before the secondary transfer roller <NUM>. An image formation start position detection sensor <NUM> for determining a print start position when the image formation is to be performed and a density sensor <NUM> for measuring the density of a patch image during density control are arranged around the intermediate transfer member <NUM>. When the density control is to be performed, the density of each patch image is measured by the density sensor <NUM>.

The image forming apparatus <NUM> includes the first fixing device <NUM> and the second fixing device <NUM> each configured to heat and pressurize the toner image transferred to the sheet P to fix the toner image to the sheet P. The first fixing device <NUM> includes a fixing roller <NUM> including an internal heater, a pressure belt <NUM> configured to bring the sheet P into press contact against the fixing roller <NUM>, and the first post-fixing sensor <NUM> configured to detect the completion of the fixing. The fixing roller <NUM> and the pressure belt <NUM> fix the toner image to the sheet P by heating and pressurizing the sheet P while nipping the sheet P, and simultaneously convey the sheet P. The second fixing device <NUM> is arranged on downstream of the first fixing device <NUM> in a conveyance direction of the sheet P. The second fixing device <NUM> is provided to increase the gloss of the image fixed to the sheet P by the first fixing device <NUM> and to ensure the fixability. The second fixing device <NUM> includes a fixing roller <NUM>, a pressure roller <NUM>, and the second post-fixing sensor <NUM>.

The second fixing device <NUM> is not required to be used depending on the type of the sheet P. In this case, for the purpose of reducing an energy consumption amount, the sheet P is conveyed to a conveyance path <NUM> without passing through the second fixing device <NUM>. The flapper <NUM> switches a conveyance destination of the sheet P between the second fixing device <NUM> and the conveyance path <NUM>. The flapper <NUM> switches the conveyance destination of the sheet P between a conveyance path <NUM> and a discharge path <NUM>. For example, in a face-up discharge mode, the flapper <NUM> switches the conveyance destination of the sheet P to the discharge path <NUM> in order to convey the sheet P having an image formed on its first surface to the discharge path <NUM>. For example, in a face-down discharge mode, the flapper <NUM> switches the conveyance destination of the sheet P to the conveyance path <NUM> in order to convey the sheet P having the image formed on the first surface to the conveyance path <NUM>. When a trailing end of the sheet P passes through the flapper <NUM>, the conveyance direction of the sheet P is reversed, and the conveyance destination of the sheet P is switched to the discharge path <NUM> by the flapper <NUM>.

For example, in a double-sided printing mode, in order to print a chart for adjustment on a second surface of the sheet P after a chart for adjustment (test pattern for measurement) has been printed on the first surface of the sheet P, the flapper <NUM> switches the conveyance destination of the sheet P to the conveyance path <NUM>. The sheet P conveyed to the conveyance path <NUM> is conveyed to a reversing portion <NUM>. The sheet P conveyed to the reversing portion <NUM> has the trailing end of the sheet P detected by the surface reverse sensor <NUM>, and then has the conveyance direction of the sheet P reversed. The flapper <NUM> switches the conveyance destination of the sheet P to a conveyance path <NUM>. Thus, the front side and the back side of the sheet P are reversed. The sheet P is conveyed from the conveyance path <NUM> to a secondary transfer nip formed between the intermediate transfer member <NUM> and the secondary transfer roller <NUM>. The chart for adjustment is transferred to the second surface of the sheet at the secondary transfer nip. The sheet P having the charts for adjustment printed on both sides is conveyed from the discharge path <NUM> to the adjustment unit <NUM>.

The adjustment unit <NUM> is arranged on downstream of the image forming apparatus <NUM> in the conveyance direction of the sheet P. <FIG> is a cross-sectional view of the adjustment unit <NUM>. The adjustment unit <NUM> includes a through pass <NUM>, a measurement path (conveyance path) <NUM> diverted downward, and a discharge path <NUM> for discharging the sheet from the through pass <NUM> or the measurement path <NUM> to the post-processing apparatus <NUM> arranged on downstream of the adjustment unit <NUM>. The measurement path <NUM> is provided with a front/back registration portion (image reading apparatus) <NUM> serving as a measurement portion configured to perform front/back registration for reading the charts for adjustment formed on both sides of the sheet P. The adjustment unit <NUM> includes a flapper <NUM> configured to switch the conveyance destination of the sheet P between the through pass <NUM> and the measurement path <NUM>.

When the front/back registration is not to be performed by the front/back registration portion <NUM>, the flapper <NUM> waits in a downward state for switching the conveyance destination of the sheet P to the through pass <NUM>. The adjustment unit <NUM> receives the sheet P from the image forming apparatus <NUM>, and conveys the sheet P to the through pass <NUM> by first conveyance rollers <NUM>. The sheet P is conveyed from the through pass <NUM> to the discharge path <NUM> by second conveyance rollers <NUM> and third conveyance rollers <NUM>. The sheet P is discharged to the post-processing apparatus <NUM> by fourth conveyance rollers <NUM>.

Meanwhile, when the front/back registration is to be performed by the front/back registration portion <NUM>, the flapper <NUM> waits in an upward state for switching the conveyance destination of the sheet P to the measurement path <NUM>. The adjustment unit <NUM> receives the sheet P from the image forming apparatus <NUM>, and conveys the sheet P to the measurement path <NUM> by the first conveyance rollers <NUM>. The sheet P is conveyed to the front/back registration portion <NUM> by conveyance roller pairs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. The front/back registration portion <NUM> reads the charts for adjustment formed on both sides of the sheet P while conveying the sheet P by conveyance roller pairs <NUM>, <NUM>, and <NUM>. The sheet P is conveyed to the discharge path <NUM> by the conveyance roller pair <NUM>, and is discharged to the post-processing apparatus <NUM> by the fourth conveyance rollers <NUM>.

As illustrated in <FIG>, the adjustment unit <NUM> includes the communication portion <NUM>, an image processing portion <NUM>, and a control portion (controller) <NUM>. The communication portion <NUM> is electrically connected to the image processing portion <NUM> and the control portion <NUM>. The communication portion <NUM> is electrically connected to the printer controller <NUM> of the image forming apparatus <NUM>. The adjustment unit <NUM> further includes a conveyance motor <NUM>, a conveyance path sensor <NUM>, a flapper switching motor <NUM>, a backing motor <NUM>, a shading motor <NUM>, a photosensor <NUM>, an image sensor <NUM>, and an image sensor <NUM>. The conveyance motor <NUM>, the conveyance path sensor <NUM>, the flapper switching motor <NUM>, the backing motor <NUM>, the shading motor <NUM>, the photosensor <NUM>, the image sensor <NUM>, and the image sensor <NUM> are electrically connected to the control portion <NUM>. The image processing portion <NUM> is electrically connected to the image sensor <NUM> and the image sensor <NUM>. The engine control portion (controller) <NUM> controls a geometric characteristic of the image formed on the recording medium by the image forming apparatus <NUM> based on images read by the image sensor <NUM> and the image sensor <NUM>.

A structure of the front/back registration portion <NUM> is described with reference to <FIG> is a view for illustrating the front/back registration portion <NUM>. The front/back registration portion <NUM> is configured to measure a shape of the sheet P, shapes of image patterns formed on the sheet P, and a positional relationship between the image patterns. In order to obtain a highly accurate measurement result, it is required to average shape variations and print position variations for each sheet P, and hence a plurality of sheets P are measured. In order to shorten an adjustment time for measuring the plurality of sheets P, the front/back registration portion <NUM> performs the measurement while conveying the sheets P. In addition, a size of the front/back registration portion <NUM> is preferred to be small, and hence the front/back registration portion <NUM> uses the image sensors (reading sensors) <NUM> and <NUM> that are contact image sensors (CISs).

The front/back registration portion <NUM> includes a front-side reading portion (reading unit) <NUM> configured to read the front side of the sheet P and a back-side reading portion (reading unit) <NUM> configured to read the back side of the sheet P. The front-side reading portion <NUM> includes a reading box <NUM> for the front side, a reading glass (glass plate) <NUM> serving as a transparent member (light transmitting member), and backing rollers <NUM> and <NUM>. The back-side reading portion <NUM> includes a reading box <NUM> for the back side, the reading glass <NUM>, and the backing rollers <NUM> and <NUM>. The reading glass <NUM> forms a part of the measurement path <NUM>. The reading box <NUM> for the front side is arranged on one side of the measurement path <NUM>. The reading box <NUM> for the back side is arranged on another side of the measurement path <NUM>. The reading box <NUM> for the front side and the reading box <NUM> for the back side continuously read the front side and the back side of the sheet P being conveyed in the conveyance direction CD. Each of the reading box <NUM> for the front side and the reading box <NUM> for the back side is provided with a plurality of image sensors (hereinafter referred to as "CISs") <NUM> and <NUM> as reading units. Each of the reading box <NUM> for the front side and the reading box <NUM> for the back side is arranged so as to be opposed to the measurement path <NUM> with respect to the reading glass <NUM>. The backing rollers <NUM> and <NUM> are arranged on the opposite side of the measurement path <NUM> so as to be opposed to the reading glass <NUM>.

The conveyance roller pairs (conveyance units) <NUM>, <NUM>, and <NUM> are configured to convey the sheet P in the conveyance direction CD at a stable conveyance speed. The conveyance roller pairs <NUM>, <NUM>, and <NUM> are driven by the conveyance motor (drive unit) <NUM>. The reading glass <NUM> functions as a guide member configured to guide movement of the sheet P in order to stabilize the position of the sheet P in a depth-of-focus direction of the CISs <NUM> and <NUM> of the reading box <NUM> for the front side and the CISs <NUM> and <NUM> of the reading box <NUM> for the back side. The backing rollers <NUM> and <NUM> each have a black surface in order to clarify a contrast with an end portion of the sheet P. The backing rollers <NUM> and <NUM> are driven by the backing motor <NUM>.

The front-side reading portion <NUM> has the same configuration as that of the back-side reading portion <NUM>, and hence the front-side reading portion <NUM> is described below by omitting description of the back-side reading portion <NUM>. <FIG> and <FIG> are cross-sectional views of the front-side reading portion <NUM>. A state in which the sheet P is conveyed to the front-side reading portion <NUM> is described with reference to <FIG> and <FIG>. The CIS <NUM> is arranged so as to be opposed to the backing roller <NUM> with respect to the reading glass <NUM>. The CIS <NUM> is arranged so as to be opposed to the backing roller <NUM> with respect to the reading glass <NUM>. The CISs <NUM> and <NUM> are carried by a carriage (carrying member) <NUM>. The CISs <NUM> and <NUM> can be moved by the carriage <NUM> in a sub-scanning direction Y along the conveyance direction CD.

The sheet P is conveyed to an upper surface of the transparent reading glass <NUM> by the conveyance roller pair <NUM> in the conveyance direction CD. A plurality of white reference plates (plurality of reference members) <NUM> and <NUM> are arranged on a surface (first surface) of the reading glass <NUM> on the measurement path (conveyance path) <NUM> side. The white reference plates <NUM> and <NUM> are provided on the opposite side of the reading glass <NUM> from the CISs <NUM> and <NUM>. A sheet guide member <NUM> is arranged on the white reference plates <NUM> and <NUM>. The sheet P is conveyed on the sheet guide member <NUM>, passes through a reading position between the CIS <NUM> and the backing roller <NUM> and a reading position between the CIS <NUM> and the backing roller <NUM>, and is conveyed by the conveyance roller pair <NUM> on the downstream side as illustrated in <FIG>.

The CISs <NUM> and <NUM> irradiate the sheet P with light from light-emitting portions <NUM> each having a light source, and collect reflected light from the sheet P on a line-shaped light-receiving portion (light-receiving sensor surface) <NUM> by, for example, a rod lens array. The reflected light received by each of the CISs <NUM> and <NUM> is photoelectrically converted and output to the image processing portion <NUM> as an output signal. The image processing portion <NUM> generates image data based on the output signals from CISs <NUM> and <NUM>. The CISs <NUM> and <NUM> located at a reading position RP read the image of the sheet P being conveyed on the reading glass <NUM> at a constant speed by a sheet flow reading method. The image processing portion <NUM> generates a front-side measurement pattern image <NUM> of the sheet P, which is described later, based on the output signals from CISs <NUM> and <NUM>.

The backing rollers <NUM> and <NUM> are driven by the backing motor <NUM> so as to rotate in the direction indicated by the arrows in <FIG> and <FIG> at a circumferential speed substantially equal to the conveyance speed (reading speed) of the sheet P. The backing rollers <NUM> and <NUM> have a gap set between the backing rollers <NUM> and <NUM> and the reading glass <NUM> so as to reduce the unexpected movement (wobbling) of the sheet P being conveyed to the reading position RP of the CISs <NUM> and <NUM>. Abutment rollers (gap securing members) <NUM> and <NUM> for securing a gap between the backing rollers <NUM> and <NUM> and the reading glass <NUM> by being brought into abutment with the reading glass <NUM> are arranged at both end portions of the backing rollers <NUM> and <NUM> in their axial direction, respectively. The gap between the backing rollers <NUM> and <NUM> and the reading glass <NUM> is obtained by adding a margin (margin gap) to a thickness of the sheet P to be conveyed. The gap is set so that the surface (surface to be read) of the sheet P falls within a readable range of each of the CISs <NUM> and <NUM> even when the sheet P unexpectedly moves.

Shading correction is described with reference to <FIG> and <FIG>. <FIG> is a cross-sectional view of the front-side reading portion <NUM> with the CISs <NUM> and <NUM> having been moved to a shading correction position SH. <FIG> is a perspective view of the CISs <NUM> and <NUM> viewed from the reading glass <NUM> side. In order to execute the shading correction, the CISs <NUM> and <NUM> are moved by the carriage <NUM> in the sub-scanning direction Y from the reading position RP of <FIG> on the downstream side to the shading correction position SH of <FIG> on the upstream side in the conveyance direction CD of the sheet P.

The CISs <NUM> and <NUM> cannot perform uniform image reading due to light amount unevenness of the light-emitting portions <NUM> and sensitivity unevenness of the light-receiving portion <NUM>. In view of this, the shading correction is executed in order to enable uniform image reading. In the shading correction, the CISs <NUM> and <NUM> read the white reference plates <NUM> and <NUM> through the reading glass <NUM>. The color of the surfaces of the white reference plates <NUM> and <NUM> to be read has the tint managed entirely. The CISs <NUM> and <NUM> output, as reading results, output signals (image data) to the image processing portion <NUM>. The image processing portion (correction unit) <NUM> generates a correction value for correcting the image data when the sheet P is read, based on the output signals from the CISs <NUM> and <NUM> to be obtained when the white reference plates <NUM> and <NUM> are read. The control portion <NUM> corrects, based on the correction value, an amount of light emitted from each light-emitting portion <NUM> irradiating the sheet P, and corrects, based on the correction value, an amplification factor (gain) for amplifying the output signal from each light-receiving portion <NUM> to be obtained when the sheet P is read. In this manner, the CISs <NUM> and <NUM> can uniformly read the sheet P by adjusting the amount of light emitted from the light-emitting portions <NUM> and/or the amplification factor (gain) of the light-receiving portion <NUM> based on results of reading the white reference plates <NUM> and <NUM>.

In this embodiment, the shading correction position SH of <FIG> is arranged on the upstream side of the reading position RP of <FIG> in the conveyance direction CD of the sheet P. Therefore, the white reference plates <NUM> and <NUM> are arranged on the upstream side of the reading position RP in the conveyance direction CD of the sheet P. When the white reference plates <NUM> and <NUM> are at the same height as the sheet P being conveyed on the measurement path <NUM> in the depth-of-focus direction of the CISs <NUM> and <NUM> as much as possible, accuracy of the shading correction is improved. In view of this, in this embodiment, the white reference plates <NUM> and <NUM> are arranged on the surface (upper surface) of the reading glass <NUM> on the measurement path <NUM> side.

It is assumed that the white reference plates <NUM> and <NUM> are arranged on the upper surface of the reading glass <NUM> on the downstream side of the reading position RP of <FIG> in the conveyance direction CD of the sheet P. In that case, the leading end of the sheet P that has passed through the reading position RP while being regulated by the backing rollers <NUM> and <NUM> in the depth-of-focus direction may get caught by the white reference plates <NUM> and <NUM> to cause a jam. When the white reference plates <NUM> and <NUM> are arranged on the lower surface (back side) of the reading glass <NUM> in order to prevent an occurrence of a jam, the accuracy of shading correction deteriorates. In view of this, in this embodiment, as described above, the white reference plates <NUM> and <NUM> are arranged on the surface (upper surface) of the reading glass <NUM> on the measurement path <NUM> side on the upstream side of the reading position RP of <FIG> in the conveyance direction CD of the sheet P.

The white reference plates <NUM> and <NUM> may be formed on the surface (upper surface) of the reading glass <NUM> on the measurement path <NUM> side through printing or painting. In another case, the white reference plates <NUM> and <NUM> may be affixed to the surface (upper surface) of the reading glass <NUM> on the measurement path <NUM> side with an adhesive or a double-coated tape. The white reference plates <NUM> and <NUM> are provided so that white reference surfaces having the tint managed entirely are on the surface side of the reading glass <NUM>. The white reference plates <NUM> and <NUM> are expensive, and are handled so as not to be scratched or dusted.

As illustrated in <FIG>, the CIS <NUM> and the CIS <NUM> are arranged so as to be offset in a main scanning direction X (width direction) and the sub-scanning direction Y (conveyance direction CD) (staggered arrangement). The two CISs <NUM> and <NUM> are arranged so as to partially overlap each other in the main scanning direction X, to thereby be able to read a reading area wider than a reading area that can be read by one CIS <NUM>. In this embodiment, the two CISs <NUM> and <NUM> are arranged so as to partially overlap each other in the main scanning direction X, to thereby be able to read a reading area wider than the width of the sheet P in the main scanning direction X. The CISs <NUM> and <NUM> read black areas of the backing rollers <NUM> and <NUM> being backgrounds together with the image of the sheet P, to thereby be able to detect an end portion of the sheet P in the main scanning direction with an increased contrast between the end portion of the sheet P and the black area of the sheet P. This improves accuracy of the front/back registration.

In the same manner as the CISs <NUM> and <NUM>, the white reference plates <NUM> and <NUM> are also arranged so as to be offset in the main scanning direction X and the sub-scanning direction Y (staggered arrangement) as illustrated in <FIG>. This can reduce the areas of the white reference plates <NUM> and <NUM>, and can lower the cost. In addition, the sheet guide member (guide sheet) <NUM> is arranged so as to cover the white reference plates <NUM> and <NUM>. The sheet guide member <NUM> is bonded to the white reference plates <NUM> and <NUM> so as to cover the entire surfaces of the white reference plates <NUM> and <NUM> in order to prevent the leading end of the sheet P being conveyed from getting caught in the white reference plates <NUM> and <NUM>. As a result, it is possible to suppress the occurrence of a jam. The white reference plates <NUM> and <NUM> arranged in a staggered manner are arranged on the upper surface of the reading glass <NUM> on the upstream side in the conveyance direction CD and covered with the sheet guide member <NUM>, to thereby be able to prevent the leading end of the sheet P from being brought into contact with the white reference plates <NUM> and <NUM>. That is, it is possible to suppress the occurrence of a jam ascribable to the white reference plates <NUM> and <NUM> provided on the measurement path (conveyance path) <NUM>. In addition, the white reference plates <NUM> and <NUM> are prevented from being stained, and deterioration in reading accuracy is suppressed.

The sheet guide member <NUM> may be affixed to the reading glass <NUM> so as to be smoothly connected to a conveyance guide member <NUM> forming a part of the measurement path <NUM> between the conveying roller pair <NUM> arranged on upstream of the reading glass <NUM> and the reading glass <NUM>. In addition, an upstream edge portion of the sheet guide member <NUM> in the conveyance direction CD may be provided on an upper surface of the conveyance guide member <NUM>. <FIG> is an enlarged view of a sheet guide member <NUM> according to a modification example. The sheet guide member <NUM> is provided so as to cover the white reference plates <NUM> and <NUM> provided on the surface of the reading glass <NUM> on the measurement path <NUM> side. This can prevent the leading end of the sheet P from being brought into contact with the white reference plates <NUM> and <NUM>, and can suppress the occurrence of a jam. In addition, an upstream edge portion 836a of the sheet guide member <NUM> in the conveyance direction CD is provided so as to cover the upper surface of the conveyance guide member <NUM>. The upstream edge portion 836a of the sheet guide member <NUM> may be provided below a nip line (common tangent of two rollers) NL of the conveyance roller pair <NUM>. Thus, a leading edge of the sheet P is appropriately guided to the measurement path <NUM> by the upper surface of the upstream edge portion 836a of the sheet guide member <NUM>. An upstream edge 836b of the upstream edge portion 836a of the sheet guide member <NUM> may also be located on upstream of an upstream edge 833a of the conveyance guide member <NUM> in the conveyance direction CD. This can prevent the sheet P from being brought into contact with the upstream edge 836b of the upstream edge portion 836a of the sheet guide member <NUM> or the upstream edge 833a of the conveyance guide member <NUM>, and can suppress the occurrence of a jam.

A shading drive portion <NUM> is described with reference to <FIG> and <FIG>. <FIG> is a perspective view of the shading drive portion <NUM>. <FIG> is a side view of the shading drive portion <NUM>. The shading drive portion <NUM> includes the shading motor <NUM>, a motor gear <NUM>, a gear pulley <NUM>, a timing belt <NUM>, idler pulleys <NUM>, and a slide guide shaft <NUM>. The shading drive portion <NUM> further includes the photosensor <NUM>, a sensor flag <NUM>, a belt holding portion <NUM>, and the carriage <NUM>.

The carriage <NUM> is configured to hold the CISs <NUM> and <NUM>. The slide guide shaft <NUM> extends in the sub-scanning direction Y parallel to the conveyance direction CD of the sheet P. The slide guide shaft <NUM> is configured to support the carriage <NUM> so that the carriage <NUM> is slidable in the sub-scanning direction Y. The carriage <NUM> is provided with the belt holding portion <NUM>. The belt holding portion <NUM> is configured to hold a part of the timing belt <NUM>, and is fixed to the timing belt <NUM>. The timing belt <NUM> is wound around a pulley of the gear pulley <NUM> and the idler pulleys <NUM>. The idler pulleys <NUM> are provided so as to stretch the timing belt <NUM>. A gear of the gear pulley <NUM> is configured to mesh with the motor gear <NUM> of the shading motor <NUM> serving as a drive source. A drive force of the shading motor <NUM> is transmitted to the timing belt <NUM> through intermediation of the motor gear <NUM> and the gear pulley <NUM>.

When the shading motor <NUM> is rotated, the carriage <NUM> is moved in the sub-scanning direction Y through intermediation of the timing belt <NUM>. The carriage <NUM> is provided with the sensor flag <NUM>. The photosensor <NUM> uses the sensor flag <NUM> to detect transmission and blocking of light involved in movement of the carriage <NUM>. A home position and a stop position of the carriage <NUM> are controlled based on a timing at which the photosensor <NUM> detects the sensor flag <NUM>. The shading motor <NUM> is controlled based on a result of detecting the photosensor <NUM>, to thereby be able to cause the CISs <NUM> and <NUM> to reciprocate between the reading position RP and the shading correction position SH.

The front-side reading portion <NUM> can continuously read the sheet P discharged from the image forming apparatus <NUM>. In the electrophotographic image forming apparatus <NUM>, the sheet P is conveyed from the feed cassette <NUM> to the discharge path <NUM> by a large number of rollers, and may therefore be charged with static electricity.

The sheet guide member <NUM> in this embodiment is formed of a conductive member, for example, a stainless steel sheet, and is grounded in order to suppress frictional static electricity generated due to rubbing against the sheet P being conveyed. The sheet guide member <NUM> is held in the reading box <NUM> for the front side together with the reading glass <NUM> by a holding portion <NUM> described below, and is grounded.

The holding portion <NUM> and holding portions <NUM>, <NUM>, and <NUM> that are configured to hold the transparent reading glass <NUM> are described with reference to <FIG>, <FIG> and <FIG>. <FIG> is a side view of the front-side reading portion <NUM>. <FIG> is a perspective view of the front-side reading portion <NUM>. <FIG> is a cross-sectional view of the holding portions <NUM> and <NUM>. The reading box <NUM> for the front side, which is a casing having conductivity, is a box-shaped structure formed of a metal plate (conductive member) capable of electrical conduction, and includes the CISs <NUM> and <NUM> in its inside. The holding portions <NUM>, <NUM>, <NUM>, and <NUM> are formed of glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> and pressing members <NUM>, <NUM>, <NUM>, and <NUM>, respectively.

The glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> are arranged at four corners on the reading surface (upper surface) side of the reading box <NUM> for the front side. The glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> are portions protruding toward the inside of the reading box <NUM> for the front side. The reading glass <NUM> is supported by the glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM>. The glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> are accurately arranged on substantially the same plane, and hence the reading glass <NUM> mounted on the glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> is also maintained in a flat state.

The pressing members <NUM>, <NUM>, <NUM>, and <NUM> are each formed of a metal plate having a spring property, for example, a leaf spring. The reading glass <NUM> is held against the reading box <NUM> for the front side with urging forces of the pressing members <NUM>, <NUM>, <NUM>, and <NUM>. As can be understood from <FIG>, <FIG>, and <FIG>, the pressing members <NUM>, <NUM>, <NUM>, and <NUM> each have a substantially L-shaped cross-sectional shape. As illustrated in <FIG>, one end portion of the pressing member <NUM> sandwiches the conductive sheet guide member <NUM> with the reading glass <NUM>, and applies the urging force in the direction indicated by an arrow <NUM> by being brought into abutment with the sheet guide member <NUM>. Another end portion of the pressing member <NUM> is fixed to the reading box <NUM> for the front side. The pressing member (holding unit) <NUM> not only has a holding function of holding the reading glass <NUM>, but also forms a part of an electricity supply path (static electricity elimination path) <NUM> illustrated in <FIG> for providing passage of static electricity due to being made of metal and having conductivity. As indicated as the electricity supply path <NUM> in <FIG>, the static electricity of the sheet P is transmitted from the conductive sheet guide member <NUM> to the reading box <NUM> for the front side, which is the casing made of metal, through the metallic pressing member <NUM>. The static electricity is further transmitted to a main body 200a of the adjustment unit <NUM> illustrated in <FIG> through a positioning pin <NUM> made of metal and protruding from the reading box <NUM> for the front side.

The pressing member <NUM> applies an urging force equal to or greater than a predetermined force to the sheet guide member <NUM> so as to reliably bring the pressing member <NUM> into contact with the sheet guide member <NUM>. The pressing members <NUM>, <NUM>, and <NUM> each apply an urging force equal to or greater than a predetermined force to the reading glass <NUM> to hold the reading glass <NUM> against the reading box <NUM> for the front side. The pressing members <NUM>, <NUM>, <NUM>, and <NUM> are fixed to the reading box <NUM> for the front side by screws <NUM>. The pressing member <NUM> is reliably electrically connected to the reading box <NUM> for the front side by the screw <NUM> made of metal. The positioning pin <NUM> made of metal and protruding from the reading box <NUM> for the front side is inserted into a hole (not shown) of the main body 200a of the adjustment unit <NUM>, and is fixed thereto. The holes (not shown) provided to the main body 200a are formed in a frame made of metal, and hence the reading box <NUM> for the front side is reliably electrically connected to the main body 200a of the adjustment unit <NUM> through intermediation of the positioning pin <NUM>. The electricity supply path <NUM> for the static electricity is formed in this manner, and hence the static electricity of the sheet P is transmitted to the main body 200a of the adjustment unit <NUM> through the electricity supply path <NUM> so as to prevent the static electricity of the sheet P from being accumulated in the front-side reading portion <NUM>.

The sheet P being conveyed is subjected to the conveyance while being in contact with the sheet guide member <NUM>, to thereby efficiently transfer the static electricity charged on the sheet P to the sheet guide member <NUM>. The sheet guide member <NUM> extends to the upstream portion of the reading position RP, and hence the static electricity of the sheet P can be transferred to the sheet guide member <NUM> until immediately before the image reading. In addition, the static electricity can be eliminated from the entire width of the sheet P. The static electricity transferred to the sheet guide member <NUM> flows to the main body 200a through the pressing member <NUM>.

The sheet P is conveyed toward a gap δ between the reading glass <NUM> and the backing roller <NUM>, which is illustrated in <FIG>. The front-side reading portion <NUM> reads the image on the sheet P being conveyed through the gap δ. The sheet P is conveyed within a sheet conveyance area having a sheet-passing width WO, which is provided between the abutment rollers <NUM> provided at the both end portions of the backing roller <NUM>. A width W1 of the sheet guide member <NUM> is wider than the sheet-passing width WO (W1>WO). The sheet guide member <NUM> extends to the outside of the sheet conveyance area having the sheet-passing width WO. The pressing member <NUM> is arranged outside the sheet conveyance area having the sheet-passing width WO, and holds the sheet guide member <NUM>.

The abutment rollers <NUM> and the pressing member <NUM> that apply loads to the reading glass <NUM> are arranged in close proximity to each other on the outside of the sheet conveyance area having the sheet-passing width WO, to thereby suppress deformation of the reading glass <NUM> and ensure flatness. The pressing member <NUM> may be in abutment with the sheet guide member <NUM> on the outside of the abutment rollers <NUM>. The abutment rollers <NUM> are in abutment with the reading glass <NUM> with a predetermined pressurizing force. The pressing member <NUM> urges the reading glass <NUM> with the urging force equal to or greater than the predetermined force. The glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> on which the reading glass <NUM> is placed are arranged at or near positions opposed to one end portion of the pressing members <NUM>, <NUM>, <NUM>, and <NUM> that apply the urging forces, respectively. The glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> receive the pressurizing force of the abutment rollers <NUM> and the urging forces of the pressing members <NUM>, <NUM>, <NUM>, and <NUM>, to thereby ensure the flatness of the reading glass <NUM>.

Assuming that the pressing member <NUM> is arranged in the sheet conveyance area having the sheet-passing width WO, the reading glass <NUM> is deformed by the urging force of the pressing member <NUM>, and the gap δ between the reading glass <NUM> and the backing roller <NUM> is partially widened. When the gap δ is widened, a distance between the sheet P and the CISs <NUM> and <NUM> may increase to cause the sheet P to deviate from focus positions of the CISs <NUM> and <NUM>. When the sheet P deviates from the focus positions of the CISs <NUM> and <NUM>, the quality of the image read by the CISs <NUM> and <NUM> deteriorates. In view of this, in this embodiment, the pressing member <NUM> is arranged outside the sheet conveyance area having the sheet-passing width WO.

In order to ensure the flatness of the reading glass <NUM>, the glass seat surfaces <NUM>, <NUM>, <NUM>, and <NUM> are formed on the same plane with high accuracy. In order to ensure the flatness of the reading glass <NUM>, the pressing members <NUM>, <NUM>, <NUM>, and <NUM> and the abutment rollers <NUM> and <NUM> are arranged in close proximity to each other on the outside of the sheet conveyance area. The pressing member <NUM> forms an electricity supply path for the static electricity, and hence the static electricity is reliably eliminated from the sheet P. Therefore, the sheet P charged with the static electricity is attracted to the front-side reading portion <NUM>. As a result, conveyance resistance is generated due to the charged sheet, and it is possible to prevent the occurrences of a jam and conveyance unevenness due to the conveyance resistance.

The conductive sheet guide member <NUM> having the width W1 wider than the sheet-passing width WO of the sheet conveyance area is arranged on an upstream side portion of the front-side reading portion <NUM> in the conveyance direction CD of the sheet P. The conductive pressing member <NUM> is arranged outside the sheet conveyance area. The pressing member <NUM> holds the reading glass <NUM> through use of the sheet guide member <NUM>. According to this embodiment, the sheet guide member <NUM> can be reliably grounded with a simple structure without deterioration of the flatness of the reading glass <NUM>.

Measurement to be performed by the front/back registration portion <NUM> and a feedback destination of a result of the measurement are described. <FIG> is a table for showing the sheet library <NUM>. As shown in <FIG>, a first geometric adjustment value <NUM> for the front side and a second geometric adjustment value <NUM> for the back side are set in association with a sheet type <NUM>. <FIG> is a view for illustrating a sheet library editing screen <NUM> displayed on the operation portion <NUM>. The user can select and set the sheet type <NUM> from the sheet library editing screen <NUM>. When the image forming apparatus <NUM> receives a request from a "PRINT POSITION ADJUSTMENT" button <NUM> on the sheet library editing screen <NUM> illustrated in <FIG> through an operation performed on the operation portion <NUM> by the user, patch images <NUM> illustrated in <FIG> serving as the chart for adjustment are formed on the sheet P.

<FIG> are views for illustrating the patch images <NUM> formed on the sheet P. The front/back registration portion <NUM> reads the front side of the sheet P on which the patch images <NUM> serving as the chart for adjustment have been formed by the CISs <NUM> and <NUM> of the reading box <NUM> for the front side while conveying the sheet P by the conveyance roller pairs <NUM>, <NUM>, and <NUM>. The front side of the sheet P is continuously read by the CISs <NUM> and <NUM>, and read line images are connected to combine image data. The measurement is performed based on the combined image. In the same manner, the CISs <NUM> and <NUM> of the reading box <NUM> for the back side read the back side of the sheet P being conveyed by the conveyance roller pairs <NUM>, <NUM>, and <NUM>.

<FIG> is a view for illustrating the front-side measurement pattern image <NUM> obtained by reading the front side of the sheet P on which the patch images <NUM> have been formed by the CISs <NUM> and <NUM> of the reading box <NUM> for the front side. The four patch images <NUM> are formed in the four corner areas of the front-side measurement pattern image <NUM>. The front-side measurement pattern image <NUM> includes a leading edge 822a and a trailing edge 822b in the conveyance direction CD of the sheet P and a left-side edge 822c and a right-side edge 822d along the conveyance direction CD. The conveyance direction CD of the sheet P is set as the sub-scanning direction Y, and a direction perpendicular to the sub-scanning direction Y is set as the main scanning direction X.

The image processing portion <NUM> calculates detection coordinates (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), and (X<NUM>, Y<NUM>) of the sheet P from the front-side measurement pattern image <NUM>. The image processing portion <NUM> calculates detection coordinates (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), and (X<NUM>, Y<NUM>) of the patch images <NUM> from the front-side measurement pattern image <NUM>. The image processing portion <NUM> measures a distortion amount of the image on the front side and a position misregistration amount between the sheet P and the image based on the detection coordinates (X<NUM>, Y<NUM>) to (X<NUM>, Y<NUM>). The image processing portion <NUM> calculates the first geometric adjustment value <NUM> shown in <FIG>, which enables shape correction instruction for the image shape correction portion <NUM>, based on the distortion amount and the position misregistration amount of the image on the front side. The first geometric adjustment value <NUM> includes a lead position, a side position, a main scanning magnification, a sub-scanning magnification, a right angle property, and a rotation amount.

<FIG> is a view for illustrating the back-side measurement pattern image <NUM> obtained by reading the back side of the sheet P on which the patch images <NUM> have been formed by the CISs <NUM> and <NUM> of the reading box <NUM> for the back side. The four patch images <NUM> are formed in the four corner areas of the back-side measurement pattern image <NUM>. The back-side measurement pattern image <NUM> includes a leading edge 823a and a trailing edge 823b in the conveyance direction CD of the sheet P and a left-side edge 823c and a right-side edge 823d along the conveyance direction CD.

The image processing portion <NUM> calculates detection coordinates (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), and (X<NUM>, Y<NUM>) of the sheet P from the back-side measurement pattern image <NUM>. The image processing portion <NUM> calculates detection coordinates (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), (X<NUM>, Y<NUM>), and (X<NUM>, Y<NUM>) of the patch images <NUM> from the back-side measurement pattern image <NUM>. The image processing portion <NUM> measures a distortion amount of the image on the back side and a position misregistration amount between the sheet P and the image based on the detection coordinates (X<NUM>, Y<NUM>) to (X<NUM>, Y<NUM>). The image processing portion <NUM> calculates the second geometric adjustment value <NUM> shown in <FIG>, which enables shape correction instruction for the image shape correction portion <NUM>, based on the distortion amount and the position misregistration amount of the image on the back side. The second geometric adjustment value <NUM> includes a lead position, a side position, a main scanning magnification, a sub-scanning magnification, a right angle property, and a rotation amount.

The first geometric adjustment value <NUM> and the second geometric adjustment value <NUM> calculated by the image processing portion <NUM> are transmitted to the sheet library <NUM> in the image forming apparatus <NUM> through the communication portion <NUM>. The first geometric adjustment value <NUM> and the second geometric adjustment value <NUM> are stored in the sheet library <NUM> as a parameter for the front side and a parameter for the back side. In this manner, setting values are stored in the sheet library <NUM> for each sheet type <NUM>. A print image with the front and back print positions corrected with high accuracy can be output by reading the setting values from the sheet library <NUM> based on the sheet type <NUM> of a sheet on which a print job is to be executed and correcting the image position and image distortion. In this case, the front-side measurement pattern image <NUM> and the back-side measurement pattern image <NUM> which have been exemplified in this description may be measured before the execution of the print job, or may be automatically measured at a predetermined timing as calibration during the execution of the print job.

Now, a control operation for conveying the sheet P in the image forming apparatus <NUM> and the adjustment unit <NUM> is described with reference to <FIG> is a flow chart for illustrating the control operation for conveying the sheet P. The control portion <NUM> executes the control operation according to a program stored in an internal memory (not shown). When a job is input from the operation portion <NUM> by the user, the control portion <NUM> starts the control operation. The control portion <NUM> determines whether or not the job is a normal print job (Step S1101). When the job is a normal print job (YES in Step S1101), the control portion <NUM> makes each member of the image forming apparatus <NUM> and the adjustment unit <NUM> wait at the home position (HP) (Step S1102). At this time, in order to guide the sheet P to the through pass <NUM> in the adjustment unit <NUM>, the control portion <NUM> makes the flapper <NUM> wait in a downward state (at a position for the through pass) (Step S1102).

The image forming apparatus <NUM> forms an image on the sheet P (Step S1103). The adjustment unit <NUM> receives the sheet P having the image formed thereon by the image forming apparatus <NUM> (Step S1104). The control portion <NUM> controls the conveyance motor <NUM> to cause the sheet P to be passed through the through pass <NUM> and discharged to the post-processing apparatus <NUM> by the first conveyance rollers <NUM>, the second conveyance rollers <NUM>, the third conveyance rollers <NUM>, and the fourth conveyance rollers <NUM> (Step S1105). The control portion <NUM> determines whether or not the sheet P is the last sheet (Step S1106). When the sheet P is not the last sheet (NO in Step S1106), the control portion <NUM> returns the processing to Step S1101. When the sheet P is the last sheet (YES in Step S1106), the control portion <NUM> ends the control operation.

Meanwhile, when the user selects the "PRINT POSITION ADJUSTMENT" button <NUM> by selecting the sheet type <NUM> from the sheet library <NUM> through the operation portion <NUM>, a front/back registration job is input. When the job is a front/back registration job (NO in Step S1101), the control portion <NUM> makes each member of the image forming apparatus <NUM> and the adjustment unit <NUM> wait at the home position (HP) (Step S1107). At this time, in order to guide the sheet P to the measurement path <NUM> in the adjustment unit <NUM>, the control portion <NUM> makes the flapper <NUM> wait in an upward state (at a position for the measurement path) (Step S1107).

The image forming apparatus <NUM> forms the patch images <NUM> serving as the chart for adjustment on both sides of the sheet P (Step S1108). The control portion <NUM> moves the CISs <NUM> and <NUM> to the shading correction position SH before reading both sides of the sheet P, and executes the shading correction (Step S1109). The control portion <NUM> moves the CISs <NUM> and <NUM> to the reading position RP (Step S1110). The adjustment unit <NUM> receives the sheet P having the patch images <NUM> formed thereon (Step S1111). The sheet P conveyed to the adjustment unit <NUM> is conveyed to the measurement path <NUM> by the flapper <NUM> (Step S1112). The sheet P is conveyed to the front/back registration portion <NUM> by the conveyance roller pairs <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

The control portion <NUM> reads the sheet P and the patch images <NUM> formed on both sides of the sheet P by the CISs <NUM> and <NUM> of the reading box <NUM> for the front side and the reading box <NUM> for the back side, respectively (Step S1113). The image processing portion <NUM> obtains the front-side measurement pattern image <NUM> and the back-side measurement pattern image <NUM> from the reading results obtained by CISs <NUM> and <NUM>. The front/back registration portion <NUM> performs line image composition with high definition, and measures print misregistration of the patch images <NUM> on the sheet P and the shape of the sheet P. The image processing portion <NUM> calculates the first geometric adjustment value <NUM> and the second geometric adjustment value <NUM> from the front-side measurement pattern image <NUM> and the back-side measurement pattern image <NUM>. The image processing portion <NUM> stores the first geometric adjustment value <NUM> and the second geometric adjustment value <NUM> in the sheet library <NUM> of the image forming apparatus <NUM> through the communication portion <NUM> (Step S1114). Thus, the print position adjustment for front/back registration adjustment is brought to an end.

The sheet P that has passed through the front/back registration portion <NUM> is conveyed to the through pass <NUM> by the conveyance roller pair <NUM> (Step S1115). After that, the sheet P is conveyed to the discharge path <NUM> by the third conveyance rollers <NUM>, and is discharged to the post-processing apparatus <NUM> by the fourth conveyance rollers <NUM> (Step S1105). The control portion <NUM> determines whether or not the sheet P is the last sheet (Step S1106), and when the sheet P is the last sheet (YES in Step S1106), the control portion <NUM> ends the control operation.

According to this embodiment, it is possible to suppress the occurrence of a jam due to the white reference plates <NUM> and <NUM> provided to the surface of the reading glass <NUM> on the measurement path (conveyance path) <NUM> side.

Claim 1:
An image forming system, comprising:
an image forming portion (<NUM>, <NUM>, <NUM>, <NUM>) configured to form an image on a first sheet (P);
a conveyance unit (<NUM>) configured to convey the first sheet (P) on which the image has been formed by the image forming portion (<NUM>, <NUM>, <NUM>, <NUM>);
a transparent member (<NUM>) provided downstream of the conveyance unit (<NUM>) in a conveyance direction in which the first sheet (P) is conveyed;
a reading unit (<NUM>, <NUM>) including a reading sensor configured to read the image on the first sheet (P) through the transparent member (<NUM>) at a reading position in the conveyance direction;
a reference member (<NUM>, <NUM>) provided on the transparent member (<NUM>) on a side opposite to the reading unit (<NUM>, <NUM>) with respect to the transparent member (<NUM>);
a guide member (<NUM>) configured to guide, to the reading position, the first sheet (P) conveyed in the conveyance direction, the reference member (<NUM>, <NUM>) being covered with the guide member (<NUM>); and
a controller (<NUM>) configured to perform shading correction on image data obtained by the reading unit (<NUM>, <NUM>) reading the image on the first sheet (P) based on image data obtained by the reading unit (<NUM>, <NUM>) reading the reference member (<NUM>, <NUM>) through the transparent member (<NUM>), and to set, based on image data obtained by the reading unit and subjected to the shading correction, an image forming condition for forming an image on a second sheet by the image forming portion (<NUM>, <NUM>, <NUM>, <NUM>),
wherein the image forming portion (<NUM>, <NUM>, <NUM>, <NUM>) is configured to form the image on the second sheet based on the image forming condition set by the controller (<NUM>).