Colorimetric device

Abstract

To reduce the time required for correction processing of a colorimetric device and prevent a reduction in colorimetric accuracy.SOLUTION: A colorimetric unit 202 has a colorimetric sensor 2001a that can read an image formed on a sheet and a white reference plate and performs colorimetry by measuring reflected light of light from a light source with which a test image formed on the sheet is irradiated, and performs calibration of the colorimetric sensor 2001a by using a result of the reading of the white reference plate with the colorimetric sensor 2001a. The colorimetric sensor 2001a selectively executes any one of first correction processing including light quantity adjustment as correction processing and second correction processing not including the light quantity adjustment, and the time required for the second correction processing is shorter than the time required for the first correction processing. The colorimetric sensor performs the first correction processing and subsequently performs the second correction processing not including performing the light quantity adjustment so as to reduce the time required for the calibration.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a technique for measuring the color of a test image formed on paper using a color measuring device and correcting the color measuring device. [Background technology]

[0002] In recent years, electrophotographic image forming devices have penetrated the office market as laser printers and multifunction devices, and are also accelerating their entry into the commercial printing market. This is because, in a market where printed matter is a commodity, electrophotographic image forming devices can meet the printing demands for small runs and a wide variety of items, such as local newspapers and direct mail, in a short period of time and at low cost, compared to conventional offset printing machines.

[0003] Items for evaluating image quality include graininess, in-plane uniformity, character quality, and color reproducibility, with color reproducibility being the most important. Color reproducibility is the ability to output colors identical to those of the printed document. Conventionally, in order to output an image with high color reproducibility, a test chart on which a number of specified color patch images are formed is output, and the output test chart is measured with a color measuring device to perform color correction. However, the color measurement of the test chart is performed offline, which increases the work time required for color correction.

[0004] Therefore, it is desired to shorten the color measurement time in the color measurement device, and an image forming apparatus equipped with an in-line color measurement device near the paper discharge section of a printer is also on the market. Patent Document 1 discloses an image forming apparatus equipped with an in-line color measurement device that detects patch images formed on a recording medium using a spectrophotometer. However, in the image forming apparatus described in Patent Document 1, if the number of spectrophotometers is not increased, the patches arranged on the test chart are only in one line in the paper transport direction. Therefore, in this case, the number of patches that can be arranged on one test chart is reduced, and the time required for color measurement is increased. In addition, increasing the number of spectrophotometers is not desirable because it increases costs.

[0005] Patent Document 2 discloses a configuration in which a spectrophotometer as a color measuring device performs color measurement while scanning a test chart in the main scanning direction. This configuration is adopted in an inkjet type image forming apparatus, and since patches can be arranged in the main scanning direction without increasing the number of color measuring devices, it is possible to dramatically reduce the number of test charts required for color correction. Here, the measurement of patch images by the spectrophotometer is performed after a calibration operation using a white reference plate is performed. However, when performing control to measure a large number of patch images, such as color profile creation, the time required for adjustment by the spectrophotometer becomes longer. If the adjustment time becomes longer, there is a high possibility that the state of the spectrophotometer, such as the temperature, will differ from the state when the calibration operation is performed. To prevent this, for example, calibration can be performed at predetermined intervals during adjustment by the spectrophotometer. In addition, if it is desired to shorten the adjustment time, the temperature of the spectrophotometer can be monitored, and a calibration operation can be performed when there is a temperature change of a predetermined value or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-147562 A [Patent Document 2] Patent No. 5751812 Summary of the Invention [Problem to be solved by the invention]

[0007] The adjustment time by the in-line spectrophotometer may take a long time depending on the control performed during the adjustment, so that it is necessary to increase the number or frequency of performing the calibration of the white reference plate. However, the calibration of the white reference plate involves multiple steps such as dark current adjustment, light amount adjustment, distortion correction, and updating of the white reference plate data, and performing all of these steps requires a lot of time for the calibration operation. As a result, the overall adjustment time by the spectrophotometer may be extended due to the time required for the calibration of the white reference plate, which may result in a decrease in productivity. In addition, it is desirable to prevent a decrease in productivity of the image forming apparatus by shortening the time required for the calibration of the white reference plate in processes such as color measurement, not limited to the adjustment by the spectrophotometer.

[0008] An object of the present invention is to reduce the time required for correction processing of a color measuring device and to prevent a decrease in color measuring accuracy. [Means for solving the problem]

[0009] In order to solve the above problems, the color measuring device of the present invention has a light emitting unit and a light receiving unit, and is configured to measure reflected light irradiated from the light emitting unit and reflected from a test image including a plurality of patch rows each composed of a plurality of patch images formed on a sheet of paper, or to measure reflected light irradiated from the light emitting unit and reflected from a reference member, a moving unit that moves the color measuring unit in a direction in which the patch images are arranged perpendicular to a conveying direction of the sheet of paper, and a control unit that performs a correction process of the color measuring unit using a reading result of the reference member by the color measuring unit, and the control unit performs the correction process by Either a first correction process or a second correction process is selectively performed, and the first correction process is a first measurement for measuring reflected light reflected by the reference member, and a correction process is performed based on the measurement result. The light amount of the light emitting unit is adjusted. A second measurement is performed to measure the reflected light reflected by the reference member. The output value of the light received by the light receiving unit is corrected based on the The second correction process performs a third measurement to measure the reflected light reflected by the reference member, and performs a third correction process based on the measurement result. The light amount of the light emitting unit is not adjusted. Light received by the light receiving section Correct the output value. stomach,The time required for the second correction process is shorter than the time required for the first correction process, and the control means performs the first correction process before measuring the multiple patch images formed on paper, measures a predetermined number of patch rows among the multiple patch rows after performing the first correction process, and performs the second correction process after measuring the predetermined number of patch rows. Effect of the Invention

[0010] According to the present invention, it is possible to reduce the time required for the correction process of the color measuring device and prevent a decrease in color measurement accuracy. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming system. [Diagram 2] FIG. 2 is a control block diagram of the image forming system. [Diagram 3] FIG. 2 is a schematic configuration diagram of a color measurement unit. [Figure 4] FIG. 4 is a control block diagram of the color measuring device. [Diagram 5] FIG. 2 is a schematic diagram of a color measurement sensor. [Figure 6] Graphs (a) to (e) show dark voltage outputs for pixels, etc. [Figure 7] 13 is a flowchart of a first correction process. [Figure 8] 13 is a flowchart of a second correction process. [Figure 9] 13A and 13B are flowcharts showing measurement control of a patch row. [Figure 10] 4 is a flowchart of color measurement control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following embodiment, an image forming apparatus has a color measurement device, and a colorimeter provided in the color measurement device moves a stationary test chart while maintaining a certain distance to measure the color and density of a patch image on the test chart. The definition of a test chart will be described later.

[0013] 1 shows a schematic configuration diagram of an image forming system 10 including an image forming apparatus 100 that generates printed matter, a color measurement device 200 that measures the printed image with a colorimeter and executes various adjustment controls, and a finisher 300 that performs post-processing such as sorting and stapling. The image forming apparatus 100 includes an operation unit 172, a paper feed unit 110, an intermediate transfer belt 111, a fixing device 119, and a fixing cooling fan 120. An image is formed on a printing medium such as paper fed from the paper feed unit 110 based on data read from a document or data received from a PC or the like, and a printed matter is generated.

[0014] The printing process is, for example, an electrophotographic method or an inkjet recording method. FIG. 1 shows an example of an electrophotographic method, which has image forming units and exposure devices corresponding to the respective toners of yellow (y), magenta (m), cyan (c), and black (k). Since all of these have the same configuration, in order to simplify the explanation, in FIG. 1, the image forming unit and exposure device corresponding to the black toner are given reference numerals, and the reference numerals are omitted for the image forming units corresponding to the other color toners. The image forming units form a toner image on an intermediate transfer belt 111 according to data read from an original or data received from a PC or the like. The details are described below.

[0015] In the figure, the image forming unit 113k includes a photosensitive drum, a charger, and a developing unit, and an exposure unit 114k is provided near the image forming unit 113k. The photosensitive drum is a drum-shaped photoconductor with a photosensitive layer on its surface, and rotates at a predetermined process speed in a counterclockwise direction in the figure by a driving motor (not shown). The charger charges the photosensitive layer of the rotating photosensitive drum to a uniform potential. The exposure unit 114k irradiates the photosensitive layer of the charged photosensitive drum with a laser beam modulated by scanning line image data that is a black separation color image. The exposure unit 114k has a built-in rotating mirror. The laser beam is reflected by the rotating mirror and irradiates the photosensitive drum, thereby scanning the photosensitive drum according to the rotation of the rotating mirror. An electrostatic latent image is formed on the photosensitive layer of the photosensitive drum by scanning with the laser beam.

[0016] The developing unit develops the electrostatic latent image by attaching toner of the corresponding color to the electrostatic latent image. This forms a toner image of the corresponding color on the surface of the photosensitive drum. The surface of the photosensitive drum comes into contact with the intermediate transfer belt 111, and the toner image carried on the photosensitive drum is transferred to the intermediate transfer belt 111 (primary transfer). The toner images are transferred from the photosensitive drums of each color in a superimposed manner, forming a full-color toner image on the intermediate transfer belt 111.

[0017] The intermediate transfer belt 111 is an endless belt member with no elasticity. The intermediate transfer belt 111 is supported by being stretched across a tension roller 117, a belt drive roller 116, and a secondary transfer inner roller 115, which are support mechanisms. The belt drive roller 116 is driven to rotate by a drive mechanism (not shown), thereby rotating the intermediate transfer belt 111 in a clockwise direction in the figure. A secondary transfer outer roller 118 is provided at a position facing the secondary transfer inner roller 115 across the intermediate transfer belt 111. The secondary transfer inner roller 115 and the secondary transfer outer roller 118 form a secondary transfer region. The intermediate transfer belt 111 is driven by the belt drive roller 116 to transport a toner image transferred from an image forming unit to the secondary transfer region. The toner image carried by the intermediate transfer belt 111 is transferred to a print medium by a transfer electric field in the secondary transfer region, forming a toner image (secondary transfer). The print medium P on which the toner image is formed is transported to a fixing device 119, where the toner image is fixed, and a printed matter is generated. The printed matter discharged from the fixing device 119 is cooled by a fixing cooling fan 120, and then transported to the color measurement device 200.

[0018] The colorimetric device 200 is a device for adjusting the color and density of an output image of the image forming device 100. In order to adjust the color and density, it is necessary to print and output an image for adjustment on paper by the image forming device 100 in addition to a normal printed matter output by a user. The printed matter on which the image for adjustment is printed is hereinafter referred to as a test chart, and the image on the test chart is referred to as a chart image. The chart image is an image in which a large number of patch images printed in a predetermined size are arranged. The patch image is a test image for adjusting the image quality of an image formed by the image forming device 100, and is composed of various densities and colors. The colorimetric device 200 measures patch images such as color patches or density patches output by the image forming device 100. The measurement results are used for correction of the colorimetric device, such as calibration, and various adjustments of the image forming device 100. The colorimetric device 200 can also operate in a plurality of adjustment modes according to the parameters to be corrected, such as an adjustment mode by color profile generation, a density gradation adjustment mode, and the like. In addition, a temperature sensor S that detects the temperature of the color measuring device 200 is provided inside the color measuring device 200.

[0019] When the test chart is output from the image forming apparatus 100, the color measurement device 200 switches the transport path of the flag 210 from the path of normal printed matter to the transport path leading to the color measurement unit 202 so as to transport the test chart to the color measurement unit 202. When the measurement of the test chart by the color measurement unit is completed, the color measurement device 200 switches the flag 211 from the path along which normal printed matter is transported to the transport path leading to the paper output tray 201 so as to discharge the test chart to the paper output tray 201. This executes the transport of the test chart. The finisher 300 performs a predetermined post-processing designated by the user, such as sorting and stapling, on the normal printed matter discharged from the color measurement device 200, and transports it to the paper output tray 310.

[0020] <Electrical hardware configuration> 2 shows a control block of the image forming system. In the figure, printer control unit 150 of image forming apparatus 100 has CPU 151, ROM 152, RAM 153, and ASIC 154. CPU 151 loads a control program stored in ROM 152 into RAM 153 and executes instructions. ASIC 154 is connected to various loads such as an image forming unit and a paper feed conveying unit, and executes various controls according to instructions from CPU 151. CPU 151 communicates with CPU 171 of controller control unit 170 that controls operation unit 172, and controls the printer based on input information input through operation unit 172 of controller control unit 170.

[0021] The CPU 151 is also provided with a communication IF 161 for communicating with the color measurement device 200 and finisher 300 connected downstream. The communication lines connected to the downstream devices via the communication IF 161 include a serial signal line and a parallel signal line including a power remote signal. The serial signal line transmits and receives information between the devices as serial data. Also, the downstream devices can be powered on by transmitting a power remote signal. The CPU 151 controls the CPUs 251 and 351 (described later) via the communication IF 161 as necessary.

[0022] The colorimetry control unit 250 of the colorimetry device 200 has a CPU 251, a ROM 252, a RAM 253, and an ASIC 254, similar to the image forming apparatus 100. The CPU 251 loads a control program stored in the ROM 252 into the RAM 253 and executes instructions. The ASIC 254 is connected to each load such as a paper conveying unit, and executes various controls according to instructions from the CPU 251. The CPU 251 also communicates with the image forming apparatus 100 and the finisher 300 through a communication IF 261.

[0023] The finisher control unit 350 of the finisher 300 has a CPU 351, a ROM 352, a RAM 353, and an ASIC 354, similar to the image forming apparatus 100. The CPU 351 loads a control program stored in the ROM 352 into the RAM 353 and executes instructions. The ASIC 354 is connected to each load such as a paper conveying unit, a punching unit, and a staple unit, and executes control according to instructions from the CPU 351. The CPU 351 also communicates with the image forming apparatus 100 and the color measurement device 200 through a communication IF 361.

[0024] <Color measurement unit configuration> FIG. 3 is a schematic diagram of the color measurement unit 202. The color measurement sensor 2001a is held by a color measurement sensor holder 2001b, and the color measurement sensor holder 2001b is connected to a rail 2006 for moving in a direction described as the scanning direction. The color measurement sensor 2001a and the color measurement sensor holder 2001b are collectively called a color measurement carriage 2001. When the test chart is transported into the color measurement unit 202, the color measurement carriage 2001 is retracted outside the test chart transport path, and is specifically disposed on a white reference plate 2002. In order to correct reading unevenness due to characteristic variations of the optical system, light emitting element, and image sensor included in the color measurement unit 202, shading correction and the like are performed using the reading result of a white reference member. In this embodiment, the white reference plate 2002 is used as the reference member, but it is also possible to use, for example, a white reference original as the reference member.

[0025] Since the color measurement carriage 2001 is moved above the white reference plate 2002, a position sensor 2005a for detecting the position of the color measurement sensor 2001a is disposed in the color measurement unit 202. The color measurement carriage 2001 is configured to move above the white reference plate 2002 by the position sensor 2005a moving a predetermined distance from the timing at which it detects the color measurement sensor 2001a and stopping. This position at which the color measurement sensor 2001a can read the white reference plate 2002 is set as a reference position, and the color measurement sensor 2001a reads a test image. The color measurement carriage 2001 can move on a rail 2006 by a motor 204 shown in FIG. 4, which will be described later.

[0026] The test chart is indicated by reference symbol C in Fig. 3, and is composed of a plurality of rectangular patch images of a predetermined size arranged in a two-dimensional array. The back surface of the test chart is supported by a backing member 2003. The operation of the colorimetry carriage 2001 and test chart transport control during colorimetry will be described below. The test chart is stopped at a predetermined position in the colorimetry unit 202 by transport rollers 2004a and 2004b. Specifically, the center position of the first patch row in the paper transport direction coincides with the reading center position of the colorimetry sensor 2001a.

[0027] The patch that the colorimetric carriage 2001 detects first is a solid black patch image called a trigger patch, and the timing of detecting the second and subsequent patches (represented by reference characters P1, P2, ... in FIG. 3) is controlled from the timing of detecting the trigger patch. The colorimetric sensor 2001a has a window surface on the chart image side, and is disposed in a direction that allows it to detect patch images on the test chart. The colorimetric carriage 2001 moves the colorimetric sensor 2001a to a position on the test chart where it can be read. After the colorimetric sensor 2001a has finished measuring the first row of patches, the colorimetric carriage 2001 moves in the scanning direction indicated by D1 in FIG. 3 until it detects the position sensor 2005b. After detecting the position sensor 2005b, the colorimetric carriage 2001 moves a predetermined distance and stops.

[0028] Thereafter, the test chart is conveyed by conveyance rollers 2004a and 2004b a distance equivalent to the length of one patch in the paper conveyance direction indicated by D2 in the figure. The color measurement carriage 2001 moves in the opposite direction to the scanning direction D1 shown in Figure 3 and starts measuring the second patch row. For the third and subsequent patch rows, the measurement is basically performed by repeating the same measurement operations as for the first and second rows.

[0029] <Hardware configuration of color measurement device> FIG. 4 shows a control block diagram of the colorimetric device 200. As described in FIG. 2, the CPU 251 executes the program stored in the ROM 252 to execute the process. The RAM 253 is a memory for temporarily storing the calculation results during the program processing. The ASIC 254 is connected to the motor 204, the motor 205, and the PIs 206 and 207, and is configured to control each load. Note that FIG. 4 shows only the load related to the colorimetric unit 202, but in reality, it is also connected to other loads not shown. For example, the ASIC 254 is connected to a motor, SL, reflective photosensor, etc. not shown for controlling each conveying roller in the colorimetric device 200.

[0030] The CPU 251 communicates with the image forming apparatus 100 and the like through a communication IF 261. The CPU 251 also communicates with the microcomputer of the colorimetric sensor 2001a through a communication IF 262 by a communication method such as SPI communication to perform control. Here, a motor 204 is a driving means for moving the colorimetric carriage 2001 along a rail 2006. A motor 205 is a driving means for driving the conveying rollers 2004a and 2004b. PI 206 indicates a position sensor 2005a, and PI 207 indicates a position sensor 2005b.

[0031] <Colorimeter sensor configuration> FIG. 5 is an explanatory diagram of a schematic configuration of the colorimetric sensor 2001a controlled by the CPU 251. In this example, a spectral sensor is used as the colorimetric sensor 2001a. The colorimetric sensor 2001a includes a CPU 24, a light source 20 for irradiating light onto a patch on a test chart, and a light guide 21 for guiding the light from the light source 20 to the patch. The reflected light from the patch is incident on a diffraction grating 22 by the light guide 21. The diffraction grating 22 separates the light incident from the light guide 21, and the separated light is incident on line sensors 23-1 to 23-n. The light source 20 is, for example, a white LED, and the line sensor 23 is suitably a CCD sensor or a CMOS sensor. The CPU 24 loads a program stored in the ROM 25 into the RAM 26 and executes it to control the light source 20 and the line sensor 23. The CPU 24 also performs various arithmetic processing on the signal received by the line sensor to calculate the spectral reflectance.

[0032] Figures 6(a) to (d) are graphs showing the dark voltage output for a pixel, the dark voltage output for a wavelength, and the reflectance for a wavelength, which are obtained in conjunction with the calculation of the spectral reflectance. In Figures 6(a) to (c), the horizontal axis of the graph shows the pixel number (1 to N), and the vertical axis shows the output voltage. In Figure 6(d), the horizontal axis of the graph shows the wavelength (400 to 700 nm), and the vertical axis shows the output voltage. Figure 6(e) is a graph showing the reflectance for a wavelength, with the horizontal axis showing the wavelength (400 to 700 nm) and the vertical axis showing the reflectance.

[0033] The CPU 24 measures the dark voltage of the line sensor 23 before emitting light from the light source 20. The result is shown in FIG. 6(a). As shown in the figure, the value of the dark voltage and its change are both small. Note that in FIG. 6(a), the maximum value of the dark voltage is shown as Vdark. Next, the CPU 24 executes a calibration operation using the reading result of the white reference plate 2002. As the calibration operation, first, a light amount adjustment is executed. The light amount adjustment is an adjustment to make the maximum value (Vpeak) of the peak output value of the line sensor coincide with a target value (Vtar). The output value of the line sensor during the calibration is shown in FIG. 6(b). This adjustment is performed to correct the fluctuation of the output of the line sensor 23 caused by the life of the light source 20, dirt on the window surface of the colorimetric sensor 2001, and temperature change of the sensor 2001. As shown in FIG. 6(b), two peaks appear in the line sensor output value, and the peak with the higher output value is shown in the figure as Vpeak.

[0034] Next, the spectral data of the white reference plate 2002 is measured using the adjusted light amount. The results are shown in FIG. 6(c). The CPU 24 calculates the amount of positional deviation α of the light incident on the line sensor 23 from the measurement data shown by the solid line in FIG. 6(c). The amount of positional deviation α is calculated by comparing with the spectral data of the white reference plate measured at the time of shipment of the colorimetric sensor 2001 from the factory (FIG. 6(c): dashed line). The spectral data of the white reference plate measured at the time of shipment from the factory is referred to as initial white reference plate data. The initial white reference plate data is stored in the ROM 25.

[0035] The CPU 24 corrects this positional deviation amount α and converts the output value for each pixel into an output value for each wavelength. This correction is referred to as distortion correction. The result is shown in FIG. 6(d). Since the conversion is performed in this manner, unlike FIGS. 6(a) to (c), the horizontal axis in FIG. 6(d) is wavelength instead of pixel. Hereinafter, the conversion of the output value for each pixel into an output value for each wavelength will be referred to as pixel wavelength conversion. After that, the CPU 24 actually measures the patch image, performs dark voltage correction and pixel wavelength conversion processes on the measured data, and calculates the spectral reflectance by comparing it with the spectral data of the white reference plate. The result is shown in FIG. 6(e). The formula for patch spectral reflectance (Rp) is shown below. Rp = (Patch spectral data / White reference plate spectral data) x Reference plate reflectance...Equation 1 The reference plate reflectance is data obtained by measuring the reflectance of a white reference plate using a general measuring device such as a commercially available measuring device. In this embodiment, the reference plate reflectance is stored in the ROM 25.

[0036] FIG. 7 is a flowchart of a white reference plate calibration operation executed by the CPU 24, which is an example of the correction process of the color measurement device 200. Hereinafter, the process of adjusting the amount of light and the like shown in this figure will be referred to as a first correction process. The CPU 24 performs a color measurement operation when a user inputs an instruction to perform color measurement through the operation unit 172, or when the color measurement device 200 is started up. In the color measurement operation, a transport control and an initial position setting control of a test chart, which will be described later, are performed, and the first correction process is executed. In the first correction process, the processes are executed in the following order: dark voltage correction (S100), light amount adjustment (S101), standby (S102), white reference plate measurement (S103), and white reference plate correction (S104). This order is the same as the order described in FIGS. 6(a) to (e).

[0037] The CPU 24 performs dark voltage correction (S100), performs light intensity adjustment (S101), and then waits (S102). This wait time indicates the time until the light intensity of the light source stabilizes after the light intensity adjustment. The time until the light intensity stabilizes is correlated with the time until the temperature of the light source 20 stabilizes, so it takes a very long time. After waiting, the CPU 24 performs white reference plate measurement (S103), and then performs white reference plate correction (S104). The white reference plate correction here refers to distortion correction.

[0038] FIG. 8 shows a flowchart showing the second correction process of the white reference plate calibration operation. In this case, the CPU 24 performs the white reference plate measurement (S200) without performing the dark current correction, the light amount adjustment, and the standby shown in S100 to S102 of FIG. 7, and performs the white reference plate correction (S201). In the second correction process, the remaining processes except for some processes (in this example, the dark current correction, the light amount adjustment, and the standby process) are performed among the processes performed in the first correction process, and the time required for the second correction process is shorter than the time required for the first correction process. In the second correction process, a process not included in the first correction process may be performed as long as the time required for the second correction process is shorter than that for the first correction process. For example, a simple light amount adjustment process that is less accurate than the light amount adjustment in S101 of FIG. 7 but has a shorter processing time may be performed. Alternatively, another process that is different from the light amount adjustment process in the first correction process and has a shorter processing time may be performed.

[0039] In the second correction process, the light amount adjustment and the waiting time for the light amount stabilization thereafter are eliminated, so the measurement time is shortened and the calibration operation can be performed very quickly. In addition, in the color measurement control by the color measurement device 200, a large number of patch images may be formed on a test chart and measurements may be performed on multiple sheets. In such a case, the time required for measurement may be, for example, 5 minutes or more. As a result, in order to prevent a decrease in the accuracy of the measurement value due to the influence of the change in the ambient temperature of the color measurement sensor 2001a, it is necessary to perform white reference plate calibration during the measurement.

[0040] In this embodiment, the second correction process is performed every time a predetermined process is performed after the start of colorimetry. The details will be described later. The second correction process may be performed after a first predetermined time has elapsed (for example, after 5 minutes or more have elapsed) after the start of colorimetry. Alternatively, the temperature of the colorimetry device 200 may be detected by the temperature sensor S, and the second correction process may be performed when the difference between the temperature at the time of the first correction process (or the temperature at the previous second correction process) exceeds a predetermined temperature difference. By performing the second correction process in this manner, the influence of temperature changes can be suppressed, and the colorimetry device 200 can be corrected without time-consuming light amount adjustment. Therefore, it is possible to prevent a decrease in the colorimetry accuracy of the colorimetry device 200 while keeping the influence on the time required for measurement to an extremely small value.

[0041] The main purpose of the light amount adjustment is to adjust the output reduction of the line sensor 23 caused by stains on the window surface of the colorimetric sensor 2001a. Therefore, by performing the first correction process and adjusting the light amount at the start of colorimetric measurement, it is possible to suppress the decrease in measurement accuracy caused by the decrease in the output of the line sensor 23. On the other hand, if the measurement time from the start of colorimetric measurement is 5 minutes or more, the output of the line sensor 23 may change due to fluctuations in the ambient temperature of the colorimetric sensor 2001a. In this case, by performing the second correction process, it is possible to suppress the decrease in accuracy of the measured value caused by the influence of such fluctuations in the ambient temperature. This is because the measurement device is corrected so as to suppress the decrease in accuracy of the measured value caused by the influence of changes in the ambient temperature of the colorimetric sensor 2001a by performing the white reference plate calibration. Note that, in the above-mentioned short time of about 5 minutes, the influence of stains on the window surface, etc. is small, so there is little need to adjust the light amount. Therefore, even in the second correction process that does not perform light amount adjustment, it is possible to prevent the decrease in measurement accuracy of the colorimetric device 200.

[0042] As described above, the CPU 24 selectively determines whether to execute the first correction process, which adjusts the amount of light, or the second correction process, which does not adjust the amount of light, for the color measurement device 200. In this embodiment, the CPU 24 executes the first correction process when the color measurement device 200 is started up, or when a user inputs an instruction to perform calibration. The second correction process is executed when the time elapsed since the first correction process has been executed exceeds the above-mentioned first predetermined time. Furthermore, in this embodiment, the CPU 24 executes the second correction process again when the time elapsed since the second correction process has been executed exceeds the second predetermined time. This is because a temperature change may occur even after the second correction process has been executed. The second predetermined time may be the same as the first predetermined time, but is preferably longer than the first predetermined time. This is because the temperature usually converges to the saturation temperature as time passes, and the temperature fluctuation over that time becomes small.

[0043] On the other hand, if a long time has passed since the first correction process including the light amount adjustment was performed, dirt on the white reference plate 2002 or dirt on the window surface of the colorimetric sensor 2001a may become unignorable. Therefore, the CPU 24 may perform the first correction process again after a third predetermined time, which is longer than the above-mentioned first and second predetermined times, has elapsed since the first correction process was performed. From the above, even if a simple calibration is performed by the second correction process in which a white reference plate measurement and distortion correction (white reference plate correction) are performed without performing light amount adjustment, sufficient measurement accuracy can be obtained.

[0044] The color measurement operation of the color measurement device 200 in this embodiment will be described below. In the color measurement operation, the color measurement carriage 2001 shown in FIG. 3 scans the test chart and always returns to the position of the white reference plate during this scan. Therefore, the color measurement carriage 2001 is configured to easily perform calibration at the timing when it returns to the position of the white reference plate. The test chart includes multiple patch rows. When color measurement control is executed at the start of the color measurement device 200, the first patch row of the test chart is measured by the color measurement carriage 2001. A flowchart showing the measurement control in this case is shown in FIG. 9(a). Moreover, the measurement control of the first patch row is referred to as the first scan control.

[0045] In the first scan control, the CPU 251 of the color measurement control unit 250 sets the rotation direction of the motor 204 to a direction D1 for scanning the first patch row (S300). This direction D1 is the direction shown as D1 in FIG. 3 described above. Next, the CPU 251 actually drives the motor 204 to start scanning (S301). The CPU 251 determines whether or not a trigger patch is detected (S302), and if the trigger patch is not detected (S302: No), executes S302 again. If the trigger patch is detected (S302: Yes), the CPU 251 determines whether a predetermined time Ta has elapsed after the trigger patch detection (S303). If Ta has not elapsed (S303: No), the CPU 251 executes S303 again. If Ta has elapsed (S303: Yes), the CPU 251 executes patch measurement a (S304).

[0046] CPU 251 determines whether a preset predetermined time Tb has elapsed from the timing of starting patch measurement in S304 (S305), and executes S305 again if the predetermined time Tb has not elapsed (S305: No). If the predetermined time Tb has elapsed (S305: Yes), CPU 251 executes patch measurement b (S306). Note that patch measurement a indicates measurement of the first patch image after the trigger patch, and patch measurement b indicates measurement of subsequent patch images.

[0047] Next, the CPU 251 determines whether or not the measurement of N patches has been completed, where N is the total number of patches in the first row (S307). If the measurement of N patches has not been completed (S307: No), the CPU 251 executes S307 again. If the measurement of N patches has been completed (S307: Yes), the CPU 251 determines whether or not the position sensor 2005b has been detected (S308). If the position sensor 2005b has not been detected (S308: No), the CPU 251 executes S308 again. If the position sensor 2005b has been detected (S308: Yes), the CPU 251 moves the color measurement carriage 2001 by a predetermined amount and then stops it (S309). This completes the first scan control.

[0048] Next, FIG. 9B shows a flow chart showing the measurement control of the second patch row of the test chart by the color measurement carriage 2001 when the color measurement control is executed. Hereinafter, this measurement control will be referred to as the second scan control. The CPU 251 sets the rotation direction of the motor 204 to D2, which is the opposite direction to D1 (S400). The operations from S401 to S407 are the same as S301 to S307 in the operation flow of the first scan control described in FIG. 9A, so the description will be omitted. After executing S407, the CPU 251 determines whether the position sensor 2005a is detected (S408), and if the position sensor 2005a is not detected (S408: No), executes S408 again. If the position sensor 2005a is detected (S408: Yes), the CPU 251 stops the color measurement carriage 2001 after moving it a predetermined amount (S409). The above is the operation flow of the second scan control.

[0049] 10 shows a flowchart showing the process executed by the CPU 251 during color measurement control. When a user inputs a color measurement control command via the operation unit 172 of the image forming apparatus 100 or a PC (not shown), the image forming apparatus 100 outputs a test chart on which a plurality of predetermined color patch images are formed. In the color measurement device 200, under the control of the CPU 251, the test chart is transported to a predetermined position of the color measurement unit 202 (S500). Next, the CPU 251 executes an initial positioning control of the color measurement carriage 2001 (S501).

[0050] The initial positioning control is executed by grasping the current position of the colorimetric carriage 2001 based on the signal outputs of the position sensors 2005a and 2005b. When the position sensor 2005a is detected, the colorimetric carriage 2001 is moved toward the position sensor 2005b until the position sensor 2005a is no longer detected. Thereafter, the rotation direction of the motor 204 is reversed, so that the position sensor 2005a is detected again. After the position sensor 2005a is detected again, the colorimetric carriage 2001 is moved a predetermined distance and stopped. This makes it possible to move the colorimetric carriage 2001 a predetermined distance above the white reference plate 2002.

[0051] Next, the CPU 251 executes a first correction process (S502). This completes the calibration of the colorimetric sensor 2001a, including the light amount adjustment. The CPU 251 executes a first scan control (S503). Next, the CPU 251 controls the driving of the motor 205 to move the test chart a predetermined distance (S504). This predetermined distance corresponds to the length of the patch in the transport direction. This makes it possible to align the position of the second row with the detection position of the colorimetric sensor 2001a. The CPU 251 executes a second scan control (S505). Here, the colorimetric carriage 2001 has moved directly above the white reference plate 2002. The CPU 251 executes a second correction process after executing the first scan control and the second scan control (S506).

[0052] In this manner, in this embodiment, the second correction process is performed after the execution of a predetermined process, that is, the first scanning control and the second scanning control. The first scanning control and the second scanning control are performed in a short time, not exceeding 5 minutes, so that the temperature change that occurs during that time is small. Even if a temperature change occurs, the effect of the temperature change can be corrected by performing the second correction process, so that the effect of the temperature change of the colorimetric device 200 can be suppressed and the colorimetric accuracy can be prevented from decreasing. After that, the CPU 251 determines whether the measurement of all the patch rows on the test chart has been completed (S507).

[0053] If the measurement is not complete (S507: No), the CPU 251 moves the test chart a predetermined distance (S508) and executes S503 again. The movement distance here is the same as the movement distance in S504. If the CPU 251 determines that the measurement is complete (S507: Yes), it discharges the test chart to the discharge tray 201 (S509). This completes the color measurement control. In this way, by separating the processing contents into the white reference plate correction processing before patch measurement and the white reference plate correction after patch measurement, it is possible to execute a color measurement operation that can achieve stable measurement accuracy while suppressing an increase in the time required for color measurement control.

[0054] In the example shown in FIG. 10, since the time required for the second correction process is short, the second correction process is executed every time two patch rows of the test chart are measured by performing the reciprocating motion of the color measurement carriage 2001 (i.e., the first scan control and the second scan control). However, the present invention is not limited to this. In other words, the second correction process may be executed every time any predetermined number of patch rows are measured. This makes it possible to further shorten the time required for color measurement control.

[0055] The present invention is not limited to the example shown in FIG. 10. As described above, in another embodiment, the second correction process may be performed when the time elapsed since the start of color measurement exceeds a first predetermined time. Alternatively, the second correction process may be performed when the temperature detected by the temperature sensor S exceeds a predetermined temperature difference from the temperature at the time of the first correction process. Furthermore, the second correction process may be performed again after the second correction process is performed. In this case, the second correction process from the second time onwards may be performed when a second predetermined time longer than the first predetermined time is exceeded.

[0056] In addition, if a long time has passed since the first correction process was performed, the influence of stains on the window surface, etc., may become impossible to ignore. Therefore, the first correction process may be performed again after a third predetermined time, which is longer than the first and second predetermined times, has elapsed after the first correction process was performed.

[0057] As described above, according to the present embodiment, it is possible to perform measurement of patch images with high accuracy without increasing the time required for adjustment of the color measurement device. In particular, even when performing adjustment control that requires a long time such as measuring a large number of patch images, it is possible to reduce the time required for adjustment and prevent a decrease in color measurement accuracy due to temperature changes.

Claims

1. a color measurement means having a light emitting unit and a light receiving unit, and measuring light irradiated from the light emitting unit and reflected from a test image including a plurality of patch rows each including a plurality of patch images formed on a sheet, or measuring light irradiated from the light emitting unit and reflected from a reference member; a moving means for moving the color measurement means in a direction in which the patch images are arranged, the direction being perpendicular to a paper transport direction; and a control unit that performs a correction process on the color measurement unit using a result of reading the reference member by the color measurement unit, the control means selectively executes either a first correction process or a second correction process as the correction process; The first correction process includes performing a first measurement to measure the reflected light reflected by the reference member, adjusting the amount of light of the light emitting unit based on a measurement result, performing a second measurement to measure the reflected light reflected by the reference member, and correcting an output value of the light received by the light receiving unit based on the measurement result, The second correction process includes performing a third measurement to measure the reflected light reflected by the reference member, correcting an output value of the light received by the light receiving unit without adjusting the amount of light of the light emitting unit based on a measurement result, a time required for the second correction process is shorter than a time required for the first correction process, the control means performs the first correction process before measuring the plurality of patch images formed on a sheet, performs the first correction process, measures a predetermined number of patch rows among the plurality of patch rows, and performs the second correction process after measuring the predetermined number of patch rows. Colorimetric device.

2. The control unit executes the first correction process when the color measuring device is started up. The color measurement device according to claim 1 .

3. The control unit executes the first correction process when receiving an input from a user instructing to correct the color measuring device. The color measuring device according to claim 1 or 2.

4. The control means executes the second correction process after a first predetermined time has elapsed since the first correction process was executed. The color measuring device according to any one of claims 1 to 3.

5. The control means executes the second correction process after a second predetermined time, which is longer than the first predetermined time, has elapsed since the second correction process was executed. The color measurement device according to claim 4 .

6. The control means executes the first correction process again after a third predetermined time, which is longer than the first predetermined time and the second predetermined time, has elapsed since the first correction process was executed. The color measurement device according to claim 5 .

7. The control means executes the second correction process when a difference between a temperature detected by a temperature sensor in the color measuring device and a temperature detected by the temperature sensor when the first correction process is executed exceeds a predetermined temperature difference. The color measuring device according to any one of claims 1 to 6.

Images