Patent Description:
In the related art, some technologies have been proposed that obtain the spectral characteristics of the image of an object such as a recording medium to enhance the color reproduction of an image in a spectral-characteristic acquisition apparatus such as a printer or a copier. Such a spectral-characteristic acquisition apparatus includes a sheet conveyor that conveys an object such as a recording medium, and measures the colors of an image in a measurable area at a destination of conveyance of the object to obtain the spectral characteristics of the object.

Moreover, some technologies have been proposed that measure the color of an image with a high degree of precision. For example, a configuration or structure has been proposed that reverses the direction of rotation of a first sheet conveyance roller while stopping the rotation of a second sheet conveyance roller arranged downstream from the first sheet conveyance roller (see <CIT>). Due to such a configuration or structure, the sheet can be in full contact with a reference plane for measurement.

However, the tension that is applied to the recording medium or the like varies depending on the sheet type or the thickness of the recording medium. For this reason, when a conventional method in the related art is employed and conditions such as the sheet type and thickness of the recording medium vary, the stop position of the measurable area tends to be shifted. <CIT> discloses a spectral property acquisition apparatus and image forming apparatus. <CIT> discloses an image reading apparatus and image forming system.

Embodiments of the present disclosure described herein provide a spectral-characteristic acquisition apparatus and a method of obtaining spectral characteristics.

According to one aspect of the present disclosure, an object can stably be stopped at a stop position of a measurable area.

A more complete appreciation of embodiments and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

It will be further understood that the terms "includes" and/or "including", when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In describing example embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same structure, operate in a similar manner, and achieve a similar result.

A spectral-characteristic acquisition apparatus and a method of acquiring a spectral characteristic according to an embodiment of the present disclosure are described below in detail with reference to the accompanying drawings.

In the description of embodiments of the present disclosure given below, an object from which its spectral characteristics are obtained is an image-carrying medium such as a sheet of paper, and the object from which the spectral characteristics are obtained is referred to simply as the sheet. In the following description, unless otherwise specified, an X-axis direction indicates the width direction of a sheet, a Y-axis direction indicates the direction in which the sheet is conveyed, and a Z-axis direction indicates a direction orthogonal to an X-Y plane. In the present embodiment, the X-axis direction indicates a direction intersecting with the conveyance direction, and the Y-axis direction indicates the conveyance direction. The terms such as image formation," "recording," "printing," "image printing," and "fabricating" used herein may be used synonymously with each other.

Firstly, a first embodiment of the present disclosure is described below with reference to accompanying drawings.

<FIG> is a perspective view of a configuration of a spectral-characteristic acquisition apparatus <NUM> according to the first embodiment of the present disclosure.

As illustrated in <FIG> and <FIG>, the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment includes a color data obtainer <NUM>, a plurality of sheet conveyors <NUM>, <NUM>, and <NUM>, a pair of sheet sensors <NUM> and <NUM>, a color data obtainer conveyor <NUM>, color charts for correction <NUM>, and a controller <NUM>. The color data obtainer <NUM> according to the present embodiment includes a linear light source <NUM>, a reduction imaging lens <NUM>, and a spectroscopic unit <NUM>. The sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> according to the present embodiment serve as a conveyance unit, and the color data obtainer conveyor <NUM> according to the present embodiment serves as a second conveyance unit. The controller <NUM> according to the present embodiment serves as a controller.

The sheet <NUM> is conveyed in the Y-axis direction at a constant speed by the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM>. The use of terms "upstream" and "downstream" are described and defined as follows. The direction in which the sheet <NUM> is conveyed is defined as a direction from an upstream portion of a color-data acquisition area <NUM> to a downstream portion of the color-data acquisition area <NUM>. In <FIG>, the sheet <NUM> is conveyed in the -Y-axis direction. Accordingly, an upstream portion of the color-data acquisition area <NUM> in the conveyance direction is located in the +Y-axis direction, and a downstream portion of the color-data acquisition area <NUM> in the conveyance direction is located in the -Y-axis direction. For example, in view of the sheet conveyor <NUM> and the sheet conveyor <NUM>, the sheet conveyor <NUM> is arranged at an upstream portion of the color-data acquisition area <NUM> in the conveyance direction, and the sheet conveyor <NUM> is arranged at a downstream portion of the color-data acquisition area <NUM> in the conveyance direction. In view of the sheet sensor <NUM> and the sheet conveyor <NUM>, the sheet sensor <NUM> is arranged at an upstream portion of the color-data acquisition area <NUM>. In the following description, the terms "upstream" and "downstream" are used in view of the definition as described above.

The sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> are described below in detail. A printed sheet from which its color data is to be obtained has a significant impact on the performance of conveyance due to the differences in the thickness of the sheet or the differences in surface properties depending on, for example, the coating or image on the sheet. For example, the frictional resistance of the surface of a coated sheet is small. In such cases, for example, a conveyance roller may skid, and the amount of conveyance of the sheet may become smaller than a desired amount of conveyance. It is effective to stably feed the sheet <NUM> to the color-data acquisition area <NUM> by preventing the sheet <NUM> from going further than intended from a desired position or by preventing the sheet <NUM> from failing to reach the desired position due to the insufficient amount of conveyance.

<FIG> is a diagram illustrating the configuration or structure around the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM>, according to the present embodiment.

Each one of the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> is composed of, for example, a drive roller and a driven roller, and each one of the rollers is made of a nip roll having grip or adhesion. Each of the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> conveys the sheet <NUM> at a constant speed while nipping the sheet <NUM> between the drive roller and the driven roller. Among these conveyors, the sheet conveyor <NUM> according to the present embodiment is controlled in the color-data acquisition area <NUM> together with the sheet conveyor <NUM>, and has a function to smooth out the wrinkles of the sheet <NUM>. The drive roller and the driven roller of the sheet conveyor <NUM> according to the present embodiment serve as a first conveyance roller pair. The drive roller and the driven roller of the sheet conveyor <NUM> according to the present embodiment serve as a second conveyance roller pair.

The sheet conveyor <NUM> according to the present embodiment has an arm <NUM> used to move a roller <NUM> that is a driven roller. The arm <NUM> according to the present embodiment serves as a pressurizer that presses the roller <NUM> against the roller <NUM> that serves as a drive roller to apply pressure to the sheet <NUM>. The sheet conveyor <NUM> moves the arm <NUM> to press the roller <NUM> against the roller <NUM>. By so doing, each one of the roller <NUM> and the roller <NUM> can rotate while nipping the sheet <NUM> with a certain level of force. The controller <NUM> according to the present embodiment drives the roller <NUM> of the sheet conveyor <NUM> by a predetermined amount with a driving force greater than the driving force of the drive roller of the sheet conveyor <NUM>, and then stops driving the roller <NUM> of the sheet conveyor <NUM>. By so doing, the slack and wrinkles of the sheet <NUM> can be smoothed out.

The sheet conveyor <NUM> and the sheet conveyor <NUM> are coupled to a drive motor <NUM> and a drive motor <NUM>, respectively. The sheet conveyor <NUM> may be coupled to the drive motor <NUM> of the sheet conveyor <NUM>. When the function to smooth out the slack or wrinkles of the sheet <NUM> is performed, the conveyance is performed upon making the driving force of the drive motor <NUM> for driving the roller <NUM> higher than the driving force of the drive motor <NUM> for driving the drive roller of the sheet conveyor <NUM>.

In other words, the sheet conveyor <NUM> that is located at the downstream portion of the color-data acquisition area <NUM> in the conveyance direction feeds the sheet <NUM> to the downstream portion of the color-data acquisition area <NUM> while firmly pressing and sandwiching the sheet <NUM> with the arm <NUM>, and the sheet conveyor <NUM> that is located at the upstream portion of the color-data acquisition area <NUM> in the conveyance direction rotates to apply load to the sheet <NUM> in the conveyance direction due to the driving force smaller than that of the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM>. Due to such control as described above, the force to feed the sheet <NUM> in the conveyance direction by the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM> and the force that applies a load to the sheet <NUM> by the sheet conveyor <NUM> on the upstream portion of the color-data acquisition area <NUM> act to such an extent that the slack and wrinkles of the sheet <NUM> can be smoothed out.

The sheet conveyor <NUM> that is arranged at an upstream portion of the color-data acquisition area <NUM> in the conveyance direction can perform contrarotation in addition to the normal rotation.

The spectral-characteristic acquisition apparatus <NUM> includes a sheet sensor <NUM> and a sheet sensor <NUM>. The sheet sensor <NUM> detects that the leading end of the sheet <NUM> has been conveyed to the sheet conveyor <NUM> arranged at an upstream portion of the color-data acquisition area <NUM> in the conveyance direction. The sheet sensor <NUM> serves as a sensor and detects that the leading end of the sheet <NUM> has been conveyed to and has reached the sheet conveyor <NUM> arranged at a downstream portion of the color-data acquisition area <NUM> in the conveyance direction.

For example, the sheet sensor <NUM> and the sheet sensor <NUM> irradiate the sheet <NUM> with light and detect the reflected light with, for example, a photodiode. Based on the output from the sheet sensor <NUM> and the sheet sensor <NUM>, it is detected that the sheet <NUM> is at the position of the color-data acquisition area <NUM> implemented by the color data obtainer <NUM>.

As illustrated in <FIG>, a reference plane for measurement <NUM> is arranged under the bottom face of the color-data acquisition area <NUM>. The reference plane for measurement <NUM> covers the area in which the color-data acquisition area <NUM> is moved in the X-direction by the color data obtainer conveyor <NUM>, and is arranged so as to be in full contact with the sheet <NUM>.

The reference plane for measurement <NUM> is made of, for example, a wide guide plate formed by painting a sheet metal in white or black. The color of such a painting has varying conditions for different purposes, and the reference plane for measurement <NUM> is replaceable. For example, the color of such painting is to be black in the case of use in conformity with the International Organization for Standardization (ISO) or when the reference plane for measurement <NUM> is used to calibrate the printing machine, and the color of such painting is to be white when a color profile for printing is to be generated.

Return to <FIG>. As illustrated in <FIG>, the color data obtainer conveyor <NUM> conveys the color data obtainer <NUM> in the width direction of the sheet <NUM>. The color data obtainer conveyor <NUM> is, for example, a conveyance stage composed of, for example, a ball screw and a guide.

The color charts for correction <NUM> according to the present embodiment are used to correct the transformation matrix that is used to compute the spectral characteristics. The color charts for correction <NUM> will be described below in detail.

The spectral-characteristic acquisition apparatus <NUM> can simultaneously acquire spectral characteristics at a plurality of positions in the Y-axis direction in the color-data acquisition area <NUM> of the sheet <NUM>.

The linear light source <NUM> irradiates the color-data acquisition area <NUM> with the linear light in a direction inclined by about <NUM> degrees with respect to a normal to the sheet <NUM>. Further, the linear light source <NUM> illuminates an appropriate area with respect to the color-data acquisition area <NUM> such that reflected light from an area other than the color-data acquisition area <NUM> in the sheet <NUM> does not enter the spectroscopic unit <NUM>.

As the linear light source <NUM>, for example, an array of white light-emitting diodes (LEDs) that have radiation intensity for about the entire range of visible light may be used. However, no limitation is intended thereby, and a fluorescent lamp or a lamp light source such as a cold-cathode tube may be used as the linear light source <NUM>.

It is desired that the linear light source <NUM> emit light in a wavelength range used for the spectral operation. Moreover, it is desired that the linear light source <NUM> can evenly irradiate all over the color-data acquisition area <NUM> with light. A collimator lens that concentrates the light emitted from the linear light source <NUM> and irradiates the sheet <NUM> with parallel light or converging light may additionally be arranged around such a linear light source.

The reduction imaging lens <NUM> according to the present embodiment is disposed such that the optical axis thereof will be parallel to a normal to the sheet <NUM>, and has a function to form an image of the light beam reflected by the sheet <NUM> on the incident plane of the spectroscopic unit <NUM> with a prescribed magnifying power. In the present embodiment, the image-side telecentric characteristics are added to the reduction imaging lens <NUM>. By so doing, the main light beam of the light flux incident on the imaging plane becomes approximately parallel to the optical axis. The reduction imaging lens <NUM> may be composed of a plurality of lenses.

By adding the image-side telecentric characteristics to the reduction imaging lens <NUM>, the main light beam of the light flux incident on the imaging plane can easily be made approximately parallel to the optical axis. However, it is not always necessary to add the image-side telecentric characteristics to the reduction imaging lens <NUM>. In such cases, similar advantageous effects can be achieved by adjusting, for example, the relative positions of each pinhole of a pinhole array <NUM> and each lens of a lens array <NUM>, which will be described later in detail, according to the inclination of the main light beam at varying positions of the imaging plane.

The spectroscopic unit <NUM> has a function to distribute the diffuse reflection light of the light emitted to the sheet <NUM> and a function to output a signal in response to the reception of the distributed light. The spectroscopic unit <NUM> according to the present embodiment will be described later in detail with reference to <FIG>.

The optical system as illustrated in <FIG> is a so-called <NUM>/<NUM> optical system in which the illumination light emitted from the linear light source <NUM> is incident on the sheet <NUM> at approximately <NUM> degrees and the spectroscopic unit <NUM> receives the light diffusely reflected by the sheet <NUM> in the vertical direction. However, the configuration or structure of the optical system according to the present embodiment is not limited to the one as illustrated in <FIG>. For example, the optical system according to the present embodiment may be a so-called <NUM>/<NUM> optical system in which the illumination light emitted from the linear light source <NUM> is incident on the sheet <NUM> at <NUM> degrees and the spectroscopic unit <NUM> receives the light diffusely reflected by the sheet <NUM> at <NUM> degrees.

The configuration or structure of the spectroscopic unit <NUM> is described below with reference to <FIG>.

<FIG> is a cross-sectional view of the spectroscopic unit <NUM> provided for the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment, and illustrates a part of a cross section parallel to the YZ plane of the spectroscopic unit <NUM>.

As illustrated in <FIG>, the spectroscopic unit <NUM> according to the present embodiment includes the pinhole array <NUM>, the lens array <NUM>, a diffraction element <NUM>, and an imaging device <NUM>. Further, the spectroscopic unit <NUM> includes a package <NUM>, a spacer <NUM>, a cover glass <NUM>, and a plurality of glass bases 88a, 88b, and 88c.

The pinhole array <NUM> has a plurality of pinholes that serve as openings through which the light reflected from the sheet <NUM> passes. The multiple pinholes according to the present embodiment are arranged in the Z-axis direction on the imaging plane where the image of the light incident from the reduction imaging lens <NUM> is formed, and are arrayed at equal distances in the Y-axis direction.

<FIG> illustrates an embodiment in which three pinholes are arranged in the Y-axis direction.

The pinhole array <NUM> is integrally arranged on the glass base 88a that is transparent and flat and serves as a frame with optical transparency. A thin metal film such as a film made of nickel is evaporatively deposited on a transparent glass base, and a plurality of openings that serve as a plurality of pinholes are arrayed. As a result, the pinhole array <NUM> is formed. The light flux of the light reflected by varying points of the color-data acquisition area <NUM> of the sheet <NUM> is extracted by the multiple pinholes provided for the pinhole array <NUM>.

However, no limitation is intended thereby, and a slit array with a plurality of rectangular openings or an oblique slit array in which a plurality of rectangular slits are inclined with respect to the Y-axis direction may be adopted in place of the pinhole array <NUM>.

On the other side of the face of the glass base 88a on which the light reflected by the sheet <NUM> is incident, a glass base 88b that is transparent and is shaped like a flat plate and serves as a light-transmitting frame is bonded face-to-face. On the other side of the glass base 88b that is not bonded to the glass base 88a, a plurality of lenses are arrayed at equal distances in the Y-axis direction. In the present embodiment described with reference to <FIG>, three lenses are arranged in the Y-axis direction to form the lens array <NUM>. Each one of the multiple lenses of the lens array <NUM> concentrates the light flux of multiple laser beams that have passed through the multiple pinholes of the pinhole array <NUM>, and forms an image on the imaging device <NUM>.

In the lens array <NUM>, a plurality of lenses 82a are arranged in a line in the Y-axis direction, and the multiple lenses 82a of the lens array <NUM> have a function to transform the diffused light flux that has passed through the multiple openings of the pinhole array <NUM> into weakly diffused light flux.

The weakly diffused light flux is a diffused light flux closer to a parallel luminous flux than an incident diffused light flux. In other words, the diffused light flux is diffused to a smaller extent, that is, weakened as compared with the incident diffused light flux.

The lenses 82a constituting the lens array <NUM> are arranged at positions corresponding to the openings constituting the pinhole array <NUM>, and the diameters of the multiple lenses 82a are set such that all the light transmitted through the openings enters the lenses SL. However, no limitation is indicated thereby, and the planar shape of the multiple lenses 82a is not necessarily circular.

In the present embodiment, the pinhole array <NUM> and the lens array <NUM> are disposed so as to have the glass base 88a and the glass base 88b therebetween. However, no limitation is intended thereby. The thicknesses of the glass base 88a and the glass base 88b are determined such that the optical-path length of the pinhole array <NUM> and the lens array <NUM> will be shorter than the object-side focal length of each one of the multiple lenses 82a of the lens array <NUM>. In the lens array <NUM>, it is desired that the portions other than the openings of the multiple lenses 82a are shielded from light in order to eliminate the stray light.

In the Z-axis direction, a glass base 88c that is transparent and flat and serves as a frame with optical transparency is arranged so as to face the lens array <NUM>. The glass base 88b and the glass base 88c are bonded through a spacer <NUM>.

The spacer <NUM> is a member that gives a certain gap or space between the glass base 88b and the glass base 88c, and is, for example, a member in which a plurality through holes are arranged as desired on the planar portion of a flat metallic plate. On the face of the spacer <NUM> that faces the lens array <NUM>, a portion of the spacer <NUM> that does not serve as a through-hole and a portion of the glass base 88b that does not have a lens are brought into contact with each other and bonded together.

On the surface of the spacer <NUM> facing the diffraction element <NUM>, a portion of the spacer <NUM> that does not correspond to the through-hole and any desired portion of the 88c of the glass base are brought into contact with each other and bonded. Due to such a configuration, a certain gap or space is given between the glass base 88b and the glass base 88c. The through hole may be a small hole in which the multiple lenses of the lens array <NUM> can be accommodated, or may be a large hole in which a plurality of lenses are accommodated.

On the surface of the glass base 88c on which the light reflected by the sheet <NUM> is incident and that faces the lens array <NUM>, a diffraction element <NUM> is arranged. The diffraction element <NUM> has a sawtooth shape formed at predetermined intervals on the glass base 88c, and serves as a diffraction grating that diffracts and spectrally distributes the incident light. The multiple bundles of light flux that have passed through the multiple lenses of the lens array <NUM> are spectrally separated by the diffraction element <NUM>. On the imaging device <NUM>, a plurality of diffraction patterns that correspond to the above multiple bundles of light flux are formed.

As the diffraction element <NUM> according to the present embodiment, it is desired that blazed grating whose diffraction efficiency of the primary diffracted light is enhanced be used. Using a blazed grating as the diffraction element <NUM> enables enhancement in the diffraction efficiency of only the primary diffracted light. As a result, the utilization efficiency of light in the optical system can be increased. Due to such a configuration, a signal of sufficient quality can be successfully obtained in a relatively short time, and the length of time required to obtain the spectral characteristics can be shortened.

The imaging device <NUM> is a line sensor in which a plurality of pixels are arranged in the Y-axis direction. The imaging device <NUM> uses a plurality of light-receiving elements arranged at different positions to receive the light of the multiple diffraction patterns formed by the lens array <NUM> and the diffraction element <NUM>. By so doing, the radiation intensity of the incident light at a certain band of wavelength can be obtained. For example, a metal oxide semiconductor (MOS), a complementary metal-oxide-semiconductor (CMOS), and a charge-coupled device (CCD) may be used as the imaging device <NUM>.

<FIG> is a diagram illustrating a plurality of diffraction patterns A, B, and C and how the light is received by the imaging device <NUM> in the spectral-characteristic acquisition apparatus <NUM>, according to the present embodiment.

The diffraction axis of the diffraction element <NUM> is inclined by an angle α with respect to the Y-axis direction. As illustrated in <FIG>, a plurality of diffraction patterns A, B, and C are incident on the imaging device <NUM> with an angle α inclined with reference to the X-axis direction. In <FIG>, three zero-order diffraction patterns A, thee +first-order diffraction patterns B, and three +second-order diffraction patterns C are arranged in line with each other in the Y-axis direction. Among those diffraction patterns, the first-order diffraction patterns B are to be received by the imaging device <NUM> in the arrangement. In <FIG>, the three first-order diffraction patterns B that are formed by three lenses are received by the pixel area 84a, the pixel area 84b, and the pixel area 84c of the imaging device <NUM> and are converted into electrical signals. The electrical signal is output as the color data obtained by the spectroscopic unit <NUM>.

As described above, in the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment, the crosstalk of the multiple diffraction patterns is removed, and the spectral characteristic of the sheet <NUM> can be obtained based on the +primary diffraction pattern B. In the following description, the +primary diffraction pattern B may be referred to simply as a diffraction pattern.

The imaging device <NUM> according to the present embodiment is fixed inside the package <NUM>, and the opening of the package <NUM> is covered with a transparent cover glass <NUM> that serves as a frame with optical transparency. The cover glass <NUM> is bonded to the side of the glass base 88c where the diffraction element <NUM> is not formed.

One of the multiple pinholes of the pinhole array <NUM>, one of the multiple lenses of the lens array <NUM> that corresponds to the above one pinhole, a portion of the diffraction element <NUM> through which the light flux from the above lens passes, and a portion of the rows of pixels of the imaging device <NUM> together serve as one optical spectroscope. Accordingly, a portion that has the function of one spectroscope may be referred to as a spectral sensor in the following description.

In <FIG> and <FIG>, only three spectral sensors are illustrated for the sake of simplification. However, no limitation is intended thereby, and a configuration having a large number of spectroscopic sensors may be employed. For example, when the imaging device <NUM> that has one-thousand and twenty-four pixels are adopted and the number of pixels in the portion of the rows of pixels is set to ten, one-hundred two spectral sensors can be configured. Such spectral sensors are arranged in the Y-axis direction parallel to the conveyance direction of the sheet <NUM>, and serve as a plurality of spectral sensors arranged in the conveyance direction of the object.

In the optical system for spectrometry that makes up the spectroscopic unit <NUM>, the relative positional displacement between the imaging device <NUM> and the multiple diffraction patterns formed by the pinhole array <NUM>, the lens array <NUM>, and the diffraction element <NUM> has a great influence on the accuracy of the acquisition of the spectral characteristics. In the present embodiment, in order to control such positional displacements, the pinhole array <NUM>, the lens array <NUM>, the diffraction element <NUM>, and the imaging device <NUM> are overlaid on top of each other in layers in the optical-axis direction of the reduction imaging lens <NUM> and bonded together in an integrated manner.

An outline of the controller <NUM> of the spectral-characteristic acquisition apparatus <NUM> is described below with reference to <FIG>.

<FIG> is a block diagram of a hardware configuration of the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment.

The controller <NUM> according to the present embodiment includes a main controller 300A, an input and output (I/O) <NUM>, a light source driving circuit <NUM>, an imaging-device controller <NUM>, a motor driver <NUM>, and a hard disk drive (HDD) <NUM>.

The main controller 300A according to the present embodiment includes a central processing unit (CPU) <NUM>, a read-only memory (ROM) <NUM>, and a random access memory (RAM) <NUM>.

These elements of the main controller 300A are electrically coupled to each other through a system bus <NUM>.

The CPU <NUM> controls the operation of the spectral characteristic acquisition apparatus <NUM> in a centralized manner. The CPU <NUM> uses the RAM <NUM> as a work area, and executes a program stored in the ROM <NUM> or the like to control all operations of the spectral-characteristic acquisition apparatus <NUM> and implement various kinds of functions as will be described later in detail. The HDD <NUM> stores, for example, the obtained color information.

The input and output (I/O) <NUM> receives, for example, the detection signal (ON signal) obtained by the sheet sensor <NUM> or the sheet sensor <NUM>.

The light source driving circuit <NUM> is an electric circuit that outputs, based on the received control signal, a driving signal such as a driving voltage used to turn on the linear light source <NUM> to emit light.

The imaging-device controller <NUM> controls imaging by the imaging device <NUM> included in the spectroscopic unit <NUM> according to the input control signal. The image data that is captured by the imaging device <NUM> is sent to the HDD <NUM> as color data through the imaging-device controller <NUM> and stored therein.

The motor driver <NUM> is an electric circuit that outputs a driving signal such as a driving voltage to a plurality of motors that drive or operate a plurality of sheet conveyors <NUM>, <NUM>, and <NUM>, and a color data obtainer conveyor <NUM> according to the input control signal. The multiple motors that drive the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> to rotate include, for example, a motor that drives the arm <NUM> to move in addition to the drive motor <NUM> and the drive motor <NUM> that drive a plurality of drive rollers.

A method of controlling the sheet conveyor for conveying the sheet <NUM> in the Y-axis direction is described below.

The control in which the sheet <NUM> is detected by the sheet sensor <NUM> at an upstream portion of the color-data acquisition area <NUM> is similar to conventional control in the related art, and thus the description of such a control is omitted. A control method to be used when the sheet <NUM> is detected by the sheet sensor <NUM> at a downstream portion of the color-data acquisition area <NUM> is described below.

<FIG> are schematic views of the operation of the sheet conveyor <NUM> and the sheet conveyor <NUM>, according to the present embodiment.

Firstly, the controller <NUM> drives the drive rollers of the sheet conveyor <NUM> and the sheet conveyor <NUM> to convey the sheet <NUM> in the conveyance direction (see <FIG>).

Subsequently, when the sheet sensor <NUM> detects the leading end of the sheet <NUM>, the controller <NUM> stops the conveyance of the sheet <NUM>, and drives the arm <NUM> to press the roller <NUM> against the sheet <NUM> (see <FIG>). The timing at which the controller <NUM> stops the conveyance of the sheet <NUM> may be determined as desired. In the present embodiment, the conveyance of the sheet <NUM> is stopped as soon as the leading end of the sheet <NUM> is detected by the sheet sensor <NUM>. However, no limitation is indicated thereby, and the sheet <NUM> may be stopped at a prescribed timing after the leading end of the sheet <NUM> is detected by the sheet sensor <NUM>, depending on, for example, the relative positions of the sheet sensor <NUM> and the color-data acquisition area <NUM>. As described above, due to the use of the sheet sensor <NUM>, the sheet <NUM> can be stopped at the color-data acquisition area <NUM> with a high degree of precision, and the area of the sheet <NUM> at a downstream portion of the color-data acquisition area <NUM> can be firmly held by the arm <NUM>.

Subsequently, the controller <NUM> operates the drive motor <NUM> by a predetermined amount in order to smooth out the slack or wrinkles of the sheet <NUM> (see <FIG>). When the drive motor <NUM> is operated by a predetermined amount, the driving force of the drive motor <NUM> is made smaller than that of the drive motor <NUM>. For example, the driving force of the drive motor <NUM> is set to <NUM>. Alternatively, the driving force to the drive roller of the sheet conveyor <NUM> may be disengaged by a clutch. As the roller <NUM> of the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM> rotates by a predetermined amount, the sheet <NUM> is fed by a predetermined amount in the conveyance direction with the rotation of the driven roller <NUM>. The driving force of the sheet conveyor <NUM> at an upstream portion of the color-data acquisition area <NUM> is <NUM>. Accordingly, when the sheet conveyor <NUM> at a downstream portion of the color-data acquisition area <NUM> sends out the sheet <NUM> in the conveyance direction, the slack, sag, or wrinkles of the sheet <NUM> are smoothed out. After that, even if the sheet <NUM> is under tension due to the load and the degree of tension reaches a predetermined value, the sheet conveyor <NUM> on the upstream portion of the color-data acquisition area <NUM> rotates as pulled by the sheet <NUM>, or the sheet <NUM> is pulled by the sheet conveyor <NUM> on the upstream portion of the color-data acquisition area <NUM> in the conveyance direction. Accordingly, the damage to the sheet <NUM> can be reduced.

The amount of rotation of the roller <NUM> of the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM> is controlled to such an extent that the slack and wrinkles of the sheet <NUM> can sufficiently be smoothed out, and is typically set to a few percent or less of the distance between the sheet conveyor <NUM> and the sheet conveyor <NUM>.

With such control, the sheet <NUM> can be conveyed to a stable position of the color-data acquisition area <NUM>, and color measurement can stably be performed as there is no slack, sag, or wrinkle. Further, the damage to the sheet <NUM> can be further reduced.

<FIG> are timing charts illustrating the timings at which the sheet conveyor <NUM> and the sheet conveyor <NUM> are driven, according to the present embodiment.

<FIG> is a timing chart illustrating the timing at which the sheet conveyor <NUM> and the sheet conveyor <NUM> are driven, according to the present embodiment.

As illustrated in <FIG>, the controller <NUM> turns on the operation of the sheet conveyor <NUM> and the sheet conveyor <NUM> at a timing t1 when the leading end of the sheet <NUM> is detected by the sheet sensor <NUM>, and conveys the sheet <NUM> in the conveyance direction.

Subsequently, the controller <NUM> turns off the operation of both the sheet conveyor <NUM> and the sheet conveyor <NUM> at a timing t2 when the leading end of the sheet <NUM> is detected by the sheet sensor <NUM>, and turns on the operation of the arm <NUM> that serves as a pressurizer.

After that, at a timing t3 when the arm <NUM> reaches a position where the sheet <NUM> is to be nipped, the controller <NUM> turns on the sheet conveyor <NUM>.

Further, at the timing t3 when the arm <NUM> moves and reaches the position where the sheet <NUM> is to be nipped, the controller <NUM> turns on and drives the sheet conveyor <NUM> by a predetermined amount at a timing t4. It is assumed that the arm <NUM> is at a position to hold or nip the sheet <NUM> even after the timing t3.

After the timing t4, the controller <NUM> turns off the sheet conveyor <NUM> and reads the color data from the color-data acquisition area.

When a stepping motor is adopted as a motor for driving the sheet conveyor <NUM> and the sheet conveyor <NUM> and such a stepping motor is abruptly stopped at the stop position of the sheet <NUM>, a large load may be placed and a step-out error may occur. In order to handle such a situation, the conveyance speed of the sheet <NUM> is reduced in advance from the first conveyance speed to the second conveyance speed at an upstream portion of the color-data acquisition area <NUM> before reaching the sheet sensor <NUM>, and the stepping motor that is controlled to drive at the second conveyance speed is stopped as soon as the sheet sensor <NUM> is turned on. By so doing, the stepping motor can instantaneously be stopped at the stop position of the sheet <NUM>. In order to decelerate the conveyance speed of the sheet <NUM> ahead of the sheet sensor <NUM>, the conveyance speed of the sheet <NUM> may be reduced based on the estimated timing at which the sheet <NUM> is fed, or an additional sheet sensor may be arranged at a position where the speed of the sheet <NUM> is decelerated. Other desired methods may be adopted to decelerate the conveyance speed of the sheet <NUM> ahead of the sheet sensor <NUM>.

<FIG> is a timing chart when the conveyance speed of the sheet <NUM> is reduced immediately before the sheet <NUM> reaches the sheet sensor <NUM>, according to the present embodiment.

As illustrated in <FIG>, the controller <NUM> reduces the driving force of the sheet conveyor <NUM> and the sheet conveyor <NUM> from <NUM>% immediately before the timing at which the sheet sensor <NUM> is turned on. By so doing, the conveyance speed is decreased from the first conveyance speed to the second conveyance speed. Then, the controller <NUM> turns off the sheet conveyor <NUM> and the sheet conveyor <NUM> to stop the stepping motor at the timing t2 where the conveyance speed is reduced to the second conveyance speed. The second conveyance speed is relatively slow but is not so slow as to cause a step-out failure. In the other respects, <FIG> is equivalent to <FIG>. The conveyance speed of the sheet <NUM> may be reduced immediately before the sheet sensor <NUM> step by step instead of being reduced at a time.

As described above, in the present embodiment, each one of the sheet conveyor <NUM> and the sheet conveyor <NUM> is coupled to a different drive motor. However, no limitation is intended thereby, and a clutch including an electromagnetic clutch or a gear including a reverse gear may be used, and the above operation may be performed by one drive motor.

The evaluation result that is obtained when the apparatus according to the above embodiments of the present disclosure is implemented is given below by way of example. As a first example of the apparatus according to the above embodiments of the present disclosure, the performance of conveyance of the sheet <NUM> was evaluated under the conditions given below.

In a first example of the present disclosure, the distance between the sheet conveyor <NUM> at an upstream portion of the color-data acquisition area <NUM> and the sheet conveyor <NUM> at a downstream portion of the color-data acquisition area <NUM> is <NUM> millimeters (mm). In the first example of the present disclosure, the linear velocity of the conveyors is <NUM> per second (sec).

In a first control sample of the above example of the present disclosure, a control that is triggered by a feeding operation is performed as follows. When the sheet <NUM> is conveyed at a conveyance speed of <NUM> / sec and the distance of conveyance and the linear velocity per second of the sheet conveyor are <NUM> and <NUM>, respectively, the sheet <NUM> is stopped in <NUM> seconds (sec), which is obtained by dividing <NUM> by <NUM>.

For each one of the first example of the present disclosure and the first control sample of the above example of the present disclosure, the stop position of the sheet <NUM> at the sheet conveyor <NUM> at a downstream portion of the color-data acquisition area <NUM> was measured, and the amount of misalignment from the desired stop position of the sheet was measured. By way of example, the measurement was performed five times, and the average values of the amounts of misalignment were compared with each other. When the sheet <NUM> is at an upstream portion of the color-data acquisition area <NUM> than the desired position, the value is indicated with a minus sign.

In view of the results in the first table, it is understood from the first control sample of the above example of the present disclosure that the performance of conveyance of the sheet <NUM> is worse in the coated paper than in the plain paper and gets worse as the thickness of the sheet or paper is thicker. In order to handle such a situation, in the first example of the present disclosure, the conveyance of the sheet <NUM> is stopped as soon as the leading end of the sheet <NUM> is detected by the sheet sensor <NUM>. Due to such a configuration, even when the conditions in, for example, the type of sheet change, the sheet <NUM> can be stopped at a stop position in the measurable area in a stable manner.

Return to <FIG>. As illustrated in <FIG>, the controller <NUM> can estimate and calculate the spectral characteristics of the sheet <NUM> using a transformation matrix based on the obtained color data. Some of or the entirety of these controlling functions of the CPU <NUM> may be implemented by an electronic circuit such as an application-specific integrated circuit (ASIC) and a field-programmable gate array (FPGA).

<FIG> is a block diagram illustrating a functional configuration used to estimate and calculate the spectral characteristics of the spectral-characteristic acquisition apparatus <NUM>, according to the present embodiment.

The controller <NUM> according to the present embodiment includes a computing unit <NUM> and a storage unit <NUM>. The computing unit <NUM> includes a color-data input unit <NUM>, a transformation-matrix calculation unit <NUM>, and a spectral-characteristic computing unit <NUM>. The storage unit <NUM> includes a reference-data storage unit <NUM>, a color-data storage unit <NUM>, and a transformation-matrix storage unit <NUM>. The multiple functions of the computing unit <NUM> and a method of estimating and calculating the distribution of spectral reflectance as the spectral characteristics of the sheet <NUM> are described below.

Once the sheet <NUM> is irradiated with the light emitted from the linear light source <NUM> in the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment, an electrical signal is output from the imaging device <NUM> of the spectroscopic unit <NUM> that has received the light of the diffraction patterns, and the output electrical signal is input to the color-data input unit <NUM> of the controller <NUM> as color data.

Once the color data is received, the spectral-characteristic computing unit <NUM> computes the spectral characteristic of the sheet <NUM> from the color data using the transformation matrix stored in advance in the transformation-matrix storage unit <NUM>.

In the present embodiment, a method is described in which the spectral-characteristic computing unit <NUM> estimates and calculates, based on the color data obtained by one of the multiple spectral sensors provided for the spectroscopic unit <NUM>, the distribution of spectral reflectance as the spectral characteristics of a sheet. The spectral characteristics may be determined by a method different from the method as will be described later in detail.

The color data vi, where i denotes one of the natural numbers <NUM> to N, is obtained from the N pixels that make up one of the multiple spectral sensors of the spectroscopic unit <NUM>, and is stored in a matrix V. A matrix r that uses the matrix V and the transformation matrix G to store the spectral reflectance of varying wavelength bands such as thirty-one wavelength bands with a <NUM>-nanometer (nm) pitch between <NUM> to <NUM> is expressed in a first equation given below. The transformation matrix G according to the present embodiment serves as a transformation matrix specified in advance.

As indicated by the second equation, the third equation, and the fourth equation given below, a method of least squares is used based on a matrix R that stores the distribution of the spectral reflectance of a plurality of reference samples such as n reference samples known in the art and a matrix V that stores the color data v of a reference sample obtained by the multiple optical sensors, and the transformation matrix G is obtained by minimizing the square norm // // <NUM> of errors. <MAT> <MAT> <MAT>.

The transformation matrix G that serves as a regression equation and obtains R using V, where V and R denote an explanatory variable and a target variable, respectively, can be obtained based on a fifth equation given below and, for example, the Moore-Penrose generalized inverse matrix with which the square of the minimum norm solution of matrix V can be obtained. In the fifth equation, the superscript T denotes the transpose of a matrix, and superscript -<NUM> denotes the inverse matrix.

In the spectral-characteristic acquisition apparatus <NUM>, the acquisition result of the spectral reflectance of the reference sample is stored in advance in the reference-data storage unit <NUM> of the controller <NUM>.

The transformation-matrix calculation unit <NUM> generates the matrix Vref based on the color data obtained from the reference sample in the spectral-characteristic acquisition apparatus <NUM>. Moreover, the transformation-matrix calculation unit <NUM> generates the matrix Rref from the spectral reflectance distribution of the reference sample stored in the reference-data storage unit <NUM>. The transformation-matrix calculation unit <NUM> calculates the transformation matrix G from the matrices Vref and Rref generated as above based on the fifth equation.

The transformation matrix G that is calculated by the transformation-matrix calculation unit <NUM> as above is stored in the transformation-matrix storage unit <NUM>. In the spectral-characteristic acquisition apparatus <NUM>, the matrix Vref of the color data that is obtained from the reference sample is stored in the color-data storage unit <NUM> of the controller <NUM>.

When the spectral characteristic of the sheet <NUM> is estimated, the spectral-characteristic computing unit <NUM> first generates the matrix Vexp from the color data of the sheet <NUM> and obtains the transformation matrix G stored in the transformation-matrix storage unit <NUM>. The spectral-characteristic computing unit <NUM> can obtain the spectral characteristic Rexp of the sheet <NUM> by estimation based on the second equation using the matrix Vexp and the transformation matrix G.

In the above-described estimation and calculation, it is desired that a plurality of reference samples that are used for the calculation of the transformation matrix G be evenly selected from the color range or the color gamut that can be reproduced on a print image in the color space of, for example, an XYZ color system and a L*a*b* color system. By using the transformation matrix G that is calculated based on such reference samples as above, for example, the spectral characteristics of the image on the sheet <NUM> can be estimated with a high degree of precision.

However, the preparation, maintenance, and measurement of such reference samples require a large amount of time and cost. Accordingly, it is desired that the transformation matrix G be obtained based on a small number of reference samples within a range in which the estimation accuracy of the spectral characteristics can be maintained to a sufficient degree.

As an example of the multiple reference samples, a toner image can be used with the twenty-seven colors that are evenly selected from a color reproducible range of an electrophotographic image forming apparatus.

<FIG> illustrates the xy chromaticity of a plurality of reference samples of twenty-seven colors, according to the present embodiment.

Each point in <FIG> indicates the xy chromaticity of the multiple reference samples, and the solid lines in <FIG> indicate the range of color reproduction of a toner image. <FIG> illustrates that the reference samples are evenly selected from the color reproduction range of the toner image.

In the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment, based on the reference samples as selected above the transformation matrix G that is calculated by the transformation-matrix calculation unit <NUM> as above is stored in advance in the transformation-matrix storage unit <NUM>.

The operations of the color data obtainer <NUM> and the sheet <NUM> when the spectral-characteristic acquisition apparatus <NUM> obtains the color data are described below with reference to <FIG>.

<FIG> are plan views of the sheet <NUM> as viewed in the +Z-axis direction when the color data is being obtained, according to the present embodiment.

<FIG> are diagrams each illustrating the sheet <NUM> being conveyed in the -Y-axis direction indicated by an arrow of the reference plane for measurement <NUM>.

In <FIG>, the color data obtainer <NUM> is positioned at an end of the sheet <NUM> in the -X-axis direction and the -Y-axis direction. From the position illustrated in <FIG>, the color data obtainer <NUM> is continuously conveyed in a direction 20a indicated by a hollow arrow. Such continuous conveyance of the color data obtainer <NUM> may be referred to as a scan drive in the following description. While the color data obtainer <NUM> is continuously conveyed, the spectroscopic unit <NUM> obtains the color data of the color-data acquisition area <NUM> of the sheet <NUM> at predetermined time intervals. The predetermined time intervals are, for example, the frame periods of the imaging device <NUM>. At that moment in time, the conveyance of the sheet <NUM> is stopped.

Once the spectroscopic unit <NUM> is conveyed to the end of the sheet <NUM> in the +X-axis direction, the conveyance of the color data obtainer <NUM> is stopped.

In the arrangement of the sheet <NUM> and the sheet sensor <NUM> as illustrated in <FIG>, it is detected that the sheet <NUM> is at the position where the color data is to be obtained, based on the output from the sheet sensor <NUM>.

<FIG> illustrates the sheet <NUM> that is conveyed by a specified length in the +Y-axis direction from the position as illustrated in <FIG>.

The specified length is equivalent to, for example, the length in the Y-axis direction corresponding to the area from which the color data is to be obtained by the spectroscopic unit <NUM>. In <FIG>, the color data obtainer <NUM> is positioned at an end of the sheet <NUM> in the +X-axis direction.

From the position illustrated in <FIG>, the color data obtainer <NUM> is continuously conveyed in a direction 20b indicated by a hollow arrow. While the color data obtainer <NUM> is continuously conveyed, the spectroscopic unit <NUM> obtains the color data of the color-data acquisition area <NUM> of the sheet <NUM> at predetermined time intervals. In a similar manner to the above, the conveyance of the sheet <NUM> is stopped at this time. Once the color data obtainer <NUM> is conveyed to the end of the sheet <NUM> in the -X-axis direction, the conveyance of the color data obtainer <NUM> is stopped.

Also in <FIG>, in a similar manner to the above, the color data obtainer <NUM> obtains the color data from the color-data acquisition area <NUM> of the sheet <NUM>.

In the arrangement of the sheet <NUM> and the sheet sensor <NUM> as illustrated in <FIG>, it is detected that the sheet <NUM> has moved away from the position where the color data is to be obtained, based on the output from the sheet sensor <NUM>.

Through the operations as illustrated in <FIG>, the color data in the entirety of the sheet <NUM> can be obtained. In the above description, the color data obtainer <NUM> is conveyed four times in the X-axis direction to acquire the color data in the entirety of the sheet <NUM>. However, no limitation is indicated thereby, and the number of times the sheet is to be conveyed may be any desired number determined based on the size of the sheet <NUM>.

<FIG> is a flowchart of the acquisition processes of the spectral characteristics in the spectral-characteristic acquisition apparatus <NUM>, according to the present embodiment.

Firstly, in a step S801, the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> convey the sheet <NUM> in the Y-axis direction.

Subsequently, in a step S803, the sheet sensor <NUM> obtains a detection signal that indicates whether the sheet <NUM> is at the position where the color data is to be obtained, and outputs the obtained detection signal to the controller <NUM>.

Subsequently, in a step S805, the controller <NUM> determines whether the sheet <NUM> is at the position where the color data is to be obtained, based on the detection signal obtained by the sheet sensor <NUM>.

Once it is determined in the step S805 that the sheet <NUM> is at the position where the color data is to be obtained, in a step S807, the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> stop conveying the sheet <NUM> in the Y-axis direction. On the other hand, when it is determined that the sheet <NUM> is not at the position where the color data is to be obtained, the process returns to the step S803.

Subsequently, in a step S809, the color data obtainer conveyor <NUM> continuously conveys the color data obtainer <NUM> in the X-axis direction.

Subsequently, in a step S811, the color data obtainer <NUM> obtains the color data at predetermined time intervals. In other words, the imaging device <NUM> of the color data obtainer <NUM> captures a plurality of diffraction patterns A, B, and C formed by the light reflected from the color-data acquisition area <NUM>, and outputs the captured diffraction patterns as color data.

Subsequently, in a step S813, the controller <NUM> determines whether the color data obtainer <NUM> has been conveyed to an end in the X-axis direction. In other words, it is determined whether the color data has been obtained in the entire range in the X-axis direction.

When it is determined in the step S813 that the color data obtainer <NUM> has been conveyed to the end in the X-axis direction, in a step S815, the color data obtainer conveyor <NUM> stops conveying the color data obtainer <NUM>. When it is determined in the step S813 that the sheet has not been conveyed, the process returns to the step S811.

Subsequently, in a step S817, the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> convey the sheet <NUM> by a predetermined length in the Y-axis direction.

Subsequently, in a step S819, the sheet sensor <NUM> obtains a detection signal that indicates whether the sheet <NUM> is at the position where the color data is to be obtained, and outputs the obtained detection signal to the controller <NUM>.

Subsequently, in a step S821, the controller <NUM> determines whether the sheet <NUM> is at the position where the color data is to be obtained, based on the detection signal obtained by the sheet sensor <NUM>.

When it is determined in the step S821 that the sheet <NUM> is at the position where the color data is to be obtained, the process returns to the step S809, and the color-data acquisition is continued. On the other hand, when it is determined in the step S821 that the sheet <NUM> is not at the position where the color data is to be obtained, in a step S823, the spectral-characteristic computing unit <NUM> uses the transformation matrix G stored in the transformation-matrix storage unit <NUM> to compute the spectral characteristics of the sheet <NUM> based on the obtained color data.

As a result, the acquisition processes of the spectral characteristics by the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment are completed.

As described above, the spectral-characteristic acquisition apparatus <NUM> according to the present embodiment conveys the sheet <NUM>, and can obtain the color data of the entirety of the sheet <NUM> while conveying the color data obtainer <NUM> having a plurality of spectral sensors in the width direction of the sheet <NUM>.

The spectral-characteristic acquisition apparatus <NUM> according to the present embodiment has a function to correct the transformation matrix G, and such a function of the spectral-characteristic acquisition apparatus <NUM> is described below. In such correction, the color charts for correction <NUM> are used. The transformation matrix that is stored in the transformation-matrix storage unit <NUM> is corrected using the color data obtained from the color charts for correction <NUM> by the color data obtainer <NUM>. The color charts for correction <NUM> according to the present embodiment serves as a plurality of color charts for correction that have a plurality of color chart whose spectral characteristics are known.

It is desired that the multiple color areas whose colors differ from one another in the color charts for correction <NUM> be evenly selected from, for example, the color range or the color gamut that can be reproduced on an image in the color space of, for example, an XYZ color system and a L*a*b* color system.

In a similar manner to the reference sample as described above, the preparation, maintenance, and measurement of such a color area in the color charts for correction <NUM> require a large amount of time and cost. For this reason, a small number of color areas tend to be used within a range in which the estimation accuracy of the spectral characteristics can be maintained to a sufficient degree. Typically, several colors to several tens of colors, which are selected from a color-reproducible range of image formation, are used. However, in order to enhance the estimation accuracy of the spectral characteristics and perform measurements with a high degree of precision, areas of several hundred to several thousand colors are used. This is typical when multicolor coloring materials of four or more colors are used in, for example, electrophotography and ink-jet printing for high resolution. The term multicolor as used herein refers to, for example, orange, green, white, clear, and fluorescent colors in addition to yellow, magenta (M), cyan (C), and black (K).

In the present embodiment, reference samples of several colors to several thousand colors selected from a color reproducible range of image formation by the image forming apparatus are used.

<FIG> illustrates color charts for correction <NUM> that include such reference samples, according to the present embodiment.

In <FIG>, the color charts for correction <NUM> include a plate-like component <NUM> formed by cutting a metal material such as aluminum, and a plurality of color charts <NUM> disposed on an upper surface of the plate-like component <NUM>. The multiple color charts <NUM> is a band-like member colored with toned paint. The width D1 and the length D2 of each band are satisfactory as long as it is wider than a range in which the spectroscopic unit <NUM> can obtain color data at a time. For example, when the color-data obtaining ranges in the width direction and the conveyance direction are <NUM> and <NUM>, respectively, the width D1 of the band may be <NUM> or more, and the length D2 may be <NUM> or more. In the color chart for correction <NUM>, the multiple color charts <NUM> as above are arranged in the width direction on the plate-like component <NUM> such that the length direction will approximately be parallel to the conveyance direction.

The multiple color charts <NUM> according to the present embodiment may be directly applied to and formed on the plate-like component <NUM>. Alternatively, a band-like sheet on which a color image is formed may be adopted as the multiple color charts <NUM>, and maybe pasted onto the plate-like component <NUM>. The plate-like component <NUM> is made large enough not to touch the multiple color charts <NUM> when held or conveyed, and a plurality of plate-like components <NUM> are prepared when the number of colors of the multiple color charts <NUM> is large.

<FIG> is a perspective view of the spectral-characteristic acquisition apparatus <NUM>, illustrating its arrangement when performing the correction, according to the present embodiment.

As illustrated in <FIG>, the sheet <NUM> is placed within a range in which the color data obtainer <NUM> is conveyed, and the color charts for correction <NUM> are placed adjacent to the sheet <NUM> in the width direction. In other words, the color charts for correction <NUM> are arranged in an area other than the area in which the sheet <NUM> is to be placed within the range in which the color data obtainer <NUM> is conveyed by the color data obtainer conveyor <NUM>. By conveying the color data obtainer <NUM> to the position of the color charts for correction <NUM>, correction using the color charts for correction <NUM> can be performed.

The spectral characteristics of each one of the color charts that are included in the color charts for correction <NUM> are measured in advance using a high-accuracy spectrometer, and a matrix R1 that indicates the spectral characteristics of the object area is stored in advance in the reference-data storage unit <NUM>.

A method of correcting the transformation matrix G using the transformation-matrix calculation unit <NUM> is described below. Each one of the spectral sensors provided for the color data obtainer <NUM> includes a transformation matrix G. The transformation matrix G of each one of the multiple spectral sensors is corrected by the transformation-matrix calculation unit <NUM>. The transformation-matrix calculation unit <NUM> according to the present embodiment serves as a transformation matrix correction unit.

When the transformation matrix G is corrected, the color data obtainer <NUM> moves to the position of the color charts for correction <NUM>. The color charts for correction <NUM> are irradiated with the light emitted from the linear light source <NUM>, and each one of the multiple spectral sensors of the color data obtainer <NUM> captures diffraction patterns and outputs the color data.

Firstly, the transformation-matrix calculation unit <NUM> obtains a matrix Rref indicating the spectral characteristics of the reference sample measured in advance and the matrix R1 indicating the spectral characteristics of the multiple color charts <NUM> of the color charts for correction <NUM> from the reference-data storage unit <NUM>, and obtains a matrix Rrev by adding the matrix R1 to the matrix Rref. The transformation-matrix calculation unit <NUM> obtains a matrix Vrev by adding the matrix V1 obtained from the multiple color charts <NUM> to the matrix Vref obtained from the reference sample stored in the color-data storage unit <NUM>.

The transformation-matrix calculation unit <NUM> obtains the transformation matrix G1 based on the fifth equation using the matrix Rrev and the matrix Vrev obtained as above, and stores the corrected transformation matrix G1 in the transformation-matrix storage unit <NUM>.

<FIG> is a flowchart of the correction processes of a transformation matrix by the spectral-characteristic acquisition apparatus as described above, according to the present embodiment.

Firstly, in a step S1101, the color data obtainer conveyor <NUM> conveys the color data obtainer <NUM> in the width direction of the sheet <NUM>, and moves the color data obtainer <NUM> to the position of the color chart closest to the end in the color charts for corrections <NUM>. The color chart closest to the end is, for example, as illustrated in <FIG>, the color chart closest to the end of the color chart in the -X-axis direction.

Subsequently, in a step S1103, the color data obtainer <NUM> obtains the color data of the color chart.

Subsequently, in a step S1105, the color data obtainer conveyor <NUM> conveys the color data obtainer <NUM> in the width direction in order to change the color chart from which the color data is to be obtained.

Subsequently, in a step S1107, the controller <NUM> determines whether the color data of all the color charts have been obtained.

When it is determined in the step S1107 that the color data of all the color charts have been obtained, in a step S1109, the transformation-matrix calculation unit <NUM> obtains the transformation matrix G1 based on the fifth equation, and stores the corrected transformation matrix G1 in the transformation-matrix storage unit <NUM>.

<FIG> is a table of the spectral characteristics obtained for each one of the color charts by each one of a plurality of spectral sensors <NUM> in the color data obtainer <NUM>, according to the present embodiment.

On the other hand, when it is determined in the step S1107 that not the color data of all the color charts have been obtained, the process returns to the step S1103, and the color data of the next color chart is obtained.

The transformation matrix G1 is corrected as described above. The spectral-characteristic computing unit <NUM> according to the present embodiment can use the corrected transformation matrix G1 to estimate the spectral characteristic of the sheet <NUM> with a high degree of precision.

As described above, according to the present embodiment, the color data obtainer <NUM> is conveyed in the width direction. Due to such a configuration, even when the width of the image formed on the sheet <NUM> is wide, the color data over the entire width of the image can be obtained without using an expensive light source that can irradiate the entire width of the image at once. Due to such a configuration, the spectral-characteristic acquisition apparatus <NUM> that can obtain the spectral characteristics with a high degree of precision can be implemented at a low cost with no need for an expensive light source.

As a plurality of spectral sensors are arrayed in the conveyance direction of the sheet <NUM>, for example, the spectral characteristics of the sheet <NUM> in a wider range in the conveyance direction can be obtained at once. The conveyance of the color data obtainer <NUM> and the conveyance of the sheet <NUM> may be performed in a cooperative manner to obtain the spectral characteristics of a wide range of the sheet <NUM> at high speed.

On the other hand, by correcting the transformation matrix using the color charts for correction <NUM>, the changes over time in the accuracy of the acquisition of the spectral characteristics due to, for example, the changes in outside air temperature or the characteristics of the wavelength of the light source can be controlled.

According to the present embodiment, the color charts for correction <NUM> may be arranged in an area other than the area in which the sheet <NUM> is disposed within the range in which the color data obtainer <NUM> is conveyed. Moving the color data obtainer <NUM> enables switching between a spectral-characteristic acquisition mode and a correction mode. Accordingly, correction can be easily performed without arranging a complicated configuration or mechanism used for mode switching. The color data obtainer conveyor <NUM> according to the present embodiment that moves the color data obtainer <NUM> to the position where the color charts for correction <NUM> are arranged serves as a mode switching unit.

The multiple color charts <NUM> are arranged such that the longer-side direction of the multiple color charts <NUM> having a band-like shape will be parallel to the conveyance direction of the sheet <NUM>. According to such a configuration, the multiple spectral sensors of the color data obtainer <NUM> can be corrected at once, and correction can be efficiently performed.

As described above, according to the present embodiment, the sheet <NUM> can be stopped at a stop position in the measurable area in a stable manner. Moreover, according to the present embodiment, the load on the motor can be reduced by reducing the conveyance speed of the sheet in stages, and the motor can be instantaneously stopped in response to a turning-on signal of the sheet sensor <NUM>. As a result, the sheet <NUM> can be stopped at a desired position.

A second embodiment of the present disclosure is described below.

The second embodiment of the present disclosure is different from the first embodiment of the present disclosure in that the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> are coupled to the same drive motor <NUM>. Note that like reference signs are given to elements similar to those described in the first embodiment, and their detailed description is omitted in the description of the second embodiment of the present disclosure.

<FIG> is a diagram illustrating a configuration or structure around the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> of the spectral-characteristic acquisition apparatus <NUM>, according to the second embodiment of the present disclosure.

As illustrated in <FIG>, the sheet conveyor <NUM>, the sheet conveyor <NUM>, and the sheet conveyor <NUM> are coupled to the same drive motor <NUM>. The sheet conveyor <NUM> is coupled to a clutch 30C that can turn on or turn off the transmission of the driving force of the sheet conveyor <NUM>.

The conveyance of the sheet <NUM> in the Y-axis direction is described below.

<FIG> are schematic views of the operation of the sheet conveyor <NUM> and the sheet conveyor <NUM> according to the second embodiment of the present disclosure.

Firstly, the controller <NUM> turns on the drive motor <NUM> to convey the sheet <NUM> in the conveyance direction (see <FIG>). During such conveyance, the clutch 30C is turned on. In other words, the clutch 30C engages power transmission during such conveyance.

Subsequently, when the sheet sensor <NUM> detects the leading end of the sheet <NUM>, the controller <NUM> turns off the drive motor <NUM> to stop the conveyance of the sheet <NUM>, and drives the arm <NUM> to press the roller <NUM> against the sheet <NUM> (see <FIG>).

Subsequently, the controller <NUM> turns off the clutch 30C and disengages power transmission to operate the drive motor <NUM> by a predetermined amount in order to smooth out the slack or wrinkles of the sheet <NUM> (see <FIG>). As the roller <NUM> of the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM> rotates by a predetermined amount, the sheet <NUM> is fed by a predetermined amount in the conveyance direction with the rotation of the driven roller <NUM>. The driving force of the sheet conveyor <NUM> at an upstream portion of the color-data acquisition area <NUM> is <NUM>. Accordingly, when the sheet conveyor <NUM> at a downstream portion of the color-data acquisition area <NUM> sends out the sheet <NUM> in the conveyance direction, the slack, sag, or wrinkles of the sheet <NUM> are smoothed out. After that, even if the sheet <NUM> is under tension due to the load and the degree of tension reaches a predetermined value, the sheet conveyor <NUM> on the upstream portion of the color-data acquisition area <NUM> rotates as pulled by the sheet <NUM>, or the sheet <NUM> is pulled by the sheet conveyor <NUM> on the upstream portion of the color-data acquisition area <NUM> in the conveyance direction. Accordingly, the damage to the sheet <NUM> can be reduced.

In the present embodiment, the clutch 30C is turned on or turned off to engage or disengage the driving force of the drive motor <NUM>. However, no limitation is intended to the configuration or structure in which the clutch 30C is turned off to disengage the driving force of the drive motor <NUM>. An alternative configuration may be adopted in which the clutch 30C is turned off to switch the gear to a lighter gear. Even in such cases, the driving force of the sheet conveyor <NUM> on the downstream portion of the color-data acquisition area <NUM> is greater than that of the sheet conveyor <NUM> on an upstream portion of the color-data acquisition area <NUM>. Accordingly, the slack and wrinkles of the sheet <NUM> can be smoothed out with minimized damage.

As described above, according to the present embodiment, a spectral-characteristic acquisition apparatus provided with a plurality of arrayed spectral sensors can be implemented at a low cost. Moreover, according to the present embodiment, a spectral-characteristic acquisition apparatus that uses a plurality of spectral sensors to two-dimensionally scan a recording medium and that does not cause wrinkles or floatation of a recording medium even if the interval between a couple of pairs of rollers that hold a recording medium is long can be implemented at low cost.

In the above description, some preferred embodiments of the present disclosure and the modifications of those embodiments of the present disclosure are described. However, the description of the above embodiments and the modifications of those embodiments is given by way of example, and no limitation is intended thereby.

Note that numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the embodiments of the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.

Claim 1:
A spectral-characteristic acquisition apparatus (<NUM>) comprising:
a conveyor (<NUM>, <NUM>, <NUM>) including
a first conveyance roller pair disposed in a conveyance direction in which an object (<NUM>) is conveyed and
a second conveyance roller pair disposed downstream from the first conveyance roller pair in the conveyance direction;
a sensor (<NUM>) configured to detect that the object (<NUM>) has reached the second conveyance roller pair;
a controller (<NUM>) configured to control the second conveyance roller pair;
a color data obtainer (<NUM>) configured to obtain color data from the object (<NUM>) at a position where the object (<NUM>) stops moving;
a spectral-characteristic computing unit (<NUM>) configured to estimate a spectral characteristic of the object (<NUM>) based on the color data obtained by the color data obtainer (<NUM>); and
characterised by
an arm (<NUM>) configured to press a driven roller (<NUM>) of the second conveyance roller pair against a driving roller (<NUM>) of the second conveyance roller pair to apply pressure to the object (<NUM>) upon detecting that the object (<NUM>) has reached the second conveyance roller pair by the sensor (<NUM>),
wherein the controller (<NUM>) is configured to control the second conveyance roller pair to drive by a predetermined amount with a driving force greater than a driving force of the first conveyance roller pair and then to stop the second conveyance roller pair, while the second conveyance roller pair is pressing the object (<NUM>) with the arm (<NUM>).