Patent Grant
9676182
Field of the Invention
The present invention relates to a printing apparatus and a calibration method thereof, and particularly to, for example, a printing apparatus capable of detecting the distance from a printhead to a print medium using a sensor, and a calibration method of the sensor.
Description of the Related Art
Conventionally, an inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) includes a number of sensors according to various purposes to, for example, raise the quality or resolution of a printed image or improve operability. For example, the printing apparatus includes a sensor that detects the width of a print medium such as print paper set on the printing apparatus, a sensor that detects the density of a print adjustment pattern printed on print paper, and a ranging sensor that detects the thickness of print paper.
By the way, minute ink particles, which do not land on a print medium and are called an ink mist, are dispersed from ink discharged from an inkjet printhead (to be referred to as a printhead hereinafter) used in the printing apparatus. The ink mist is dispersed together with an air flow created as the air in the apparatus is disturbed by, for example, the movement of a carriage with the printhead, adheres to various places, and contaminates the interior of the apparatus. The ink mist may adhere to the ranging sensor configured to detect the distance between print paper and the printhead, an encoder sensor and a linear scale configured to detect the position of the carriage, or an encoder sensor and a code wheel configured to detect the rotation amount of a print medium conveyance roller. When the ink mist adheres, detection errors may occur in the detection units, resulting in a failure in image printing or the operation of the apparatus.
Conventionally, an optical ranging sensor is used in the printing apparatus. Ranging detection using the sensor is generally performed in the following way. That is, the emitting element of the sensor irradiates a measurement target with light. A photoreception element receives the light reflected by the measurement target. The distance to the measurement target is obtained using triangulation.
In some conventional printing apparatuses, a ranging sensor is mounted on a carriage that includes a printhead and reciprocally moves. In the ranging sensor, a plurality of photoreception elements provided in the sensor irradiate a measurement target with light, receive the light reflected by the measurement target, and measure the ratio value of the intensity of the reflected light to that of the output light. The distance up to print paper is calculated based on a reference result of the measurement result and a distance information reference table that shows relationship between a light intensity and a distance detected by a calibration reference board mounted on the printing apparatus (see Japanese Patent Laid-Open No. 2008-265058).
In the prior art, however, if an ink mist adheres to the sensor over time, the degrees of adhesion to the plurality of emitting elements and photoreception elements are not always equal. In addition, if the degrees of adhesion to the plurality of photoreception elements are not equal, the ranging accuracy lowers. To solve this problem, a method of calibrating the ranging sensor as needed using a calibration reference board may be used. However, this arrangement greatly increases the cost of the apparatus.
Accordingly, the present invention is conceived as a response to the above-described disadvantages of the conventional art.
For example, a printing apparatus and a calibration method thereof according to this invention are capable of accurately and inexpensively measuring the distance between a printhead and a print medium.
According to one aspect of the present invention, there is provided a printing apparatus for, using a printhead mounted on a carriage that reciprocally moves in a predetermined direction, printing a print medium conveyed in a direction different from the predetermined direction, comprising: a detection unit provided on the carriage and configured to detect a distance between the printhead and the print medium at a print position by the printhead, a change unit configured to change a height from a print position to the carriage; a storage unit configured to store first distance information indicating a relationship between the height and a signal representing a result of detection of the distance by the detection unit for each of a plurality of heights while using a print medium for calibration of the detection unit and causing the change unit to change the height; an obtaining unit configured to obtain second distance information indicating a relationship between the height and the signal representing the result of detection of the distance by the detection unit for each of the plurality of heights while using a predetermined print medium and causing the change unit to change the height; and a correction unit configured to compare the first distance information and the second distance information and correct the first distance information stored in the storage unit, based on a result of the comparison.
According to another aspect of the present invention, there is provided a calibration method in a printing apparatus that, using a printhead mounted on a carriage that reciprocally moves in a predetermined direction, prints a print medium conveyed in a direction different from the predetermined direction and detects a distance between the printhead and the print medium at a print position by the printhead using a sensor provided on the carriage, the method comprising: detecting the distance between the printhead and the print medium while using a print medium for calibration of the sensor and changing a height from the print position to the carriage; storing, in a memory, first distance information indicating a relationship between the height and a signal representing a result of detecting the distance by the sensor for each of a plurality of heights; obtaining second distance information indicating a relationship between the height and the signal representing the result of detecting the distance by the sensor for each of the plurality of heights while using a predetermined print medium and changing the height; and comparing the first distance information and the second distance information and correcting the first distance information stored in the memory, based on a result of the comparison.
The invention is particularly advantageous since even if, for example, a foreign substance adheres to a unit that detects the distance between a print medium and the printhead, and lowers the sensitivity of the unit, it is possible to accurately measure the distance by recalibrating the unit and correcting the ranging detection result without using a member such as a calibration board. This makes it possible to inexpensively maintain the detection accuracy of a detection unit, for example, a sensor.
The invention also contributes to optimize the distance between the print medium and the printhead and more satisfactorily keep the position of the printhead at the time of printing.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Exemplary embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
In this specification, the terms “print” and “printing” not only include the formation of significant information such as characters and graphics, but also broadly include the formation of images, figures, patterns, and the like on a print medium, or the processing of the medium, regardless of whether they are significant or insignificant and whether they are so visualized as to be visually perceivable by humans.
Also, the term “print medium” not only includes a paper sheet used in common printing apparatuses, but also broadly includes materials, such as cloth, a plastic film, a metal plate, glass, ceramics, wood, and leather, capable of accepting ink.
Furthermore, the term “ink” (to be also referred to as a “liquid” hereinafter) should be extensively interpreted similar to the definition of “print” described above. That is, “ink” includes a liquid which, when applied onto a print medium, can form images, figures, patterns, and the like, can process the print medium, and can process ink. The process of ink includes, for example, solidifying or insolubilizing a coloring agent contained in ink applied to the print medium.
Further, a “print element” generically means an ink orifice or a liquid channel communicating with it, and an element for generating energy used to discharge ink, unless otherwise specified.
<Outline of Printing Apparatus (
An inkjet printing apparatus (to be referred to as a printing apparatus hereinafter) 100 shown in
Ink tank accommodation units 105 used to accommodate ink tanks of black, cyan, magenta, yellow, and the like and supply inks to a printhead are arranged on both sides of the printing apparatus 100.
As shown in
A carriage 202 with the printhead 201 is guided by a main rail 203 and a carriage belt 204 and reciprocally scanned in a direction perpendicular to the conveyance direction of print paper 209. At this time, the printhead 201 discharges ink droplets to print. The printhead 201 is provided with a plurality of nozzles. The nozzle arrays discharge inks of black, cyan, magenta, yellow, and the like to form an image on a print medium. At this time, the carriage 202 reads a scale provided on a linear scale 205, and an encoder sensor 206 outputs the result as a pulse signal. By counting the pulse signals, the relative moving distance and position of the carriage 202 are detected.
The carriage 202 also includes a ranging sensor 207 configured to detect the distance between the print paper 209 and the printhead 201. Since the carriage 202 reciprocally moves according to a print operation, the ranging sensor 207 can detect the distance between the print paper 209 and the printhead 201 at the print position of the printhead 201.
The carriage 202 is set to a plurality of heights by a lift elevating motor 208 in accordance with the type or thickness of print paper. The print paper 209 is supported by a platen 210 and conveyed by a conveyance roller (not shown). Power to drive the printhead 201 and the carriage 202 is supplied from a power supply unit 211 via a flat cable 212.
Note that ink is supplied from each ink tank (not shown) accommodated in the ink tank accommodation unit 105 to the printhead 201 via an ink tube (not shown).
The printing apparatus 100 includes a control unit 301 configured to control the entire apparatus, driving units 302 to 304, the carriage 202 including the printhead 201, the ranging sensor 207, the power supply unit 211, the display panel 103, and the operation panel 104. The carriage conveyance unit 302 is formed from a carriage motor used to drive the carriage 202 via the carriage belt 204, and the like. The conveyance unit 303 is formed from a conveyance roller that conveys the print paper 209, a discharge roller, a conveyance motor configured to drive these rollers, and the like. Note that the control unit 301 includes a CPU 306, and the remaining portions are made of ASICs.
The lift elevating unit 304 is connected to the lift elevating motor 208, coupled with a lift cam (not shown) and the main rail 203, and configured to adjust the height of the carriage 202. The lift elevating unit 304 can change the height in multiple stages based on the stop position of the lift cam, and can also grasp the height change amount at a predetermined accuracy.
The ranging sensor 207 is used to detect the distance between the printhead 201 and the print paper 209 and also reflect it on print control based on various kinds of reference information stored in a memory (to be described later) provided in the printing apparatus 100. The power supply unit 211 is used to supply power to the control unit 301 and cause the driving units 302 to 304 to operate.
As described with reference to
The control unit 301 includes an I/O control & driver unit 308, a sequence control unit 309, an image processing unit 310, a timing control unit 311, and a head control unit 312. The sequence control unit 309 executes general print control, that is, activation and stop of functional blocks, print paper conveyance control, carriage scan control, and the like. The I/O control & driver unit 308 generates a control signal based on an instruction from the sequence control unit 309 to control each driving unit, and also transmits an input signal from each driving unit to the sequence control unit 309. The image processing unit 310 performs image processing of, for example, decomposing input image data from the PC 300 into color components such as black, cyan, magenta, and yellow and converting the data into print data. The timing control unit 311 transfers the print data converted/generated by the image processing unit 310 to the head control unit 312 in association with the position of the carriage 202. The head control unit 312 converts the print data input from the timing control unit 311 into a head control signal and outputs it. In addition, the head control unit 312 controls the temperature of the printhead 201 based on an instruction from the sequence control unit 309.
The ranging sensor 207 includes an emitting unit 402 serving as a light source, a plurality of photoreception units 401, and a driving unit 404 that on/off-control the emitting unit 402 on the print paper 209. When the emitting unit 402 irradiates the print paper 209 with light, the light is reflected by the print paper 209, and the plurality of photoreception units 401 receive the reflected light. The plurality of photoreception units 401 each photoelectrically convert the received light and output an electrical signal according to the intensity of the reflected light. The ranging sensor 207 also includes an amplification circuit 403 that receives the electrical signal output from each photoreception unit 401 and amplifies the current value or voltage value. In this embodiment, an LED is used as the light source of the emitting unit 402.
The amplified electrical signal from each of the plurality of photoreception units 401 is input to an A/D conversion circuit 307a in an ASIC 307. The A/D conversion circuit 307a converts the amplified electrical signal into a digital value. The digital value (sensor data) is stored in a storage area 406 of a memory 405 via a memory control unit 307b in the ASIC 307.
The memory 405 also stores data used to perform predetermined correction processing from a calculation result of the CPU 306. For example, GAP data (distance reference information) indicating the relationship between the ratio value of the electrical signals output from the plurality of photoreception units 401 and the distance from the printhead 201 to the print paper 209 is stored in a storage area 407. Additionally, for example, GAP reference data (for example, peak output data of each photoreception unit) serving as the reference to a calibration result of the ranging sensor 207 upon shipping of the apparatus is stored in a storage area 408. As described above, the memory 405 is used to temporarily store the values.
As shown in
As shown in
With the ordinate representing the ratio (GAP ratio) of the outputs of the two photoreception units,
As shown in
When the distance to the irradiated surface of the print paper 209 is Mid, the received light amounts on the photoreception units 401-a and 401-b are about ½ those in the peak. For this reason, as for the light amount distributions on the ranging sensor 207, the outputs of SNS2 and SNS1 equal, as shown in
Finally, when the distance to the irradiated surface of the print paper 209 is High, the received light amount on the photoreception unit 401-b is minimized, and the received light amount on the photoreception unit 401-a is maximized. For this reason, as for the light amount distributions on the ranging sensor 207, SNS2 exhibits the minimum value, and SNS1 exhibits the maximum value, as shown in
Several embodiments of correcting the distance information reference table in a case where an ink mist adheres to the ranging sensor 207 to lower the sensitivity in the printing apparatus having the above-described arrangement will be described next. Note that the recalibration of the ranging sensor 207 may be executed, for example, in a case in which the number of ink droplets discharged from the printhead has exceeded a predetermined amount, or upon detecting that the output of the ranging sensor 207 has decreased by a predetermined amount when print paper has passed immediately under the ranging sensor 207.
An example will be described here with reference to
How to create the distance information reference table will be described here with reference to the flowchart of
Step S110 is skipped. In step S120, print paper 209 for calibration, whose thickness or distance from a printhead 201 is known, is fed, and a carriage 202 is moved to a reference position for ranging. In this embodiment, measurement is performed at three different carriage heights (the height from a platen 210 to the ink discharge surface of the printhead 201), as shown in
Next, in step S130, when the print paper 209 is conveyed to a point immediately under the ranging sensor 207, the LED is turned on, an emitting unit 402 irradiates the print paper 209 with light, and two photoreception units 401-a and 401-b measure the reflected light amounts.
After that, in step S140, output signals (GAP-SNS) of the two photoreception units 401-a (SNS1) and 401-b (SNS2) are detected, and the ratio (GAP ratio) of the output signals from the two photoreception units is calculated. It is checked whether calculation of the GAP ratio is completed. In this embodiment, measurement is performed at three different carriage heights, as suggested in
When the GAP ratios are calculated at the three different carriage heights (Low, Mid, and High), the process advances to step S160.
In step S160, the relationship between the GAP ratio and the carriage height (Height) is calculated from the GAP ratios at the three different carriage heights.
Note that steps S170 and S180 are processes for correcting the table, and a description thereof will be omitted here.
The number of times of light amount measurement performed on the two photoreception units while changing the carriage height is not limited to three and may be larger, as a matter of course.
Recalibration of the ranging sensor and correction of the distance information reference table which are executed in a case where the printing apparatus is used, and the sensitivity of the ranging sensor is expected to lower due to ink mist adhesion will be described here with reference to the flowchart of
First, in step S110, it is checked whether the count value (DCNT) of a dot counter that counts the number of ink droplets discharged from the printhead 201 is equal to or larger than a predetermined threshold (TH). If DCNT≧TH, the process advances to step S120. If DCNT<TH, the processing directly ends.
In step S120, the print paper 209 for calibration is fed, as described above, and the above-described processes of steps S120 to S150 are executed. Note that the print paper for calibration can be the same as that used initially. However, the print paper need not be the same, and any print paper may be used as long as it exhibits the same optical characteristic and has the same thickness as the print paper for calibration used initially.
Even in a case in which the outputs from the two photoreception units of the ranging sensor 207 lower due to the influence of ink mist adhesion, if the degrees of output lowering equal, the calculated GAP ratio does not change. In this case, since the distance reference information indicating the distance from the printhead 201 to the print paper 209 does not change, the ranging sensor 207 need not be recalibrated. However, if one of the two photoreception units suffers a decrease in the sensitivity due to ink mist adhesion, the GAP ratio changes. Hence, the distance reference information changes from that stored initially.
Such a decrease in the output signal of the photoreception unit causes an error in ranging detection from the printhead 201 to the print paper 209.
In the process of step S160, the relationship between the GAP ratio and the carriage height (Height) in a case in which the sensitivity of the photoreception unit 401-a (SNS1) has lowered is calculated as a distance information reference table. In step S170, the difference between the initial distance information reference table and the newly calculated distance information reference table is calculated as a correction coefficient. In step S180, the correction coefficient is stored in a storage area 407 of the memory 405.
Note that the initial distance information reference table stored in a storage area 406 of the memory 405 may be replaced with the distance information reference table calculated in step S160.
Hence, according to the above-described embodiment, if the number of ink droplets discharged from the printhead is equal to or larger than a predetermined number, recalibration of the ranging sensor can be performed. This recalibration is normally done by a serviceman. However, the user may execute the recalibration by himself/herself if, for example, he/she owns print paper for calibration.
An example will be described here with reference to
In this embodiment, pieces of thickness information of various kinds of print paper and the distance from the printhead 201 to the print paper 801 are stored in a storage area 406 of a memory 405 of a printing apparatus 100. Hence, in step S100, the printing apparatus 100 obtains distance information and thickness information of print paper from the storage area 406 in accordance with the information of print paper selected by the user.
Next, in step S105, it is checked whether the obtained thickness or distance falls within a predetermined range of the distance or the thickness of the print paper usable in recalibration. If the obtained thickness or distance falls outside the predetermined range, it is determined that the linearity of the GAP ratio calculated by the ranging sensor 207 cannot be maintained, and calibration is impossible, and the process advances to step S190. In step S190, the user is notified to change the print paper to be used for calibration. This notification is done by a message displayed on a PC 300 or a message display on a display panel 103. In step S200, a re-execution flag for calibration is set in the printing apparatus, and the processing ends.
On the other hand, if the obtained distance or thickness of the print paper falls within the predetermined range, it is determined that recalibration is executable, and the process advances to step S120′. Steps S120′ and S130′ are the same as steps S120 and S130 except that the print paper to be used is not the print paper for calibration but print paper selected by the user. Hence, as in the first embodiment, the processes of steps S120′, S130′, S140, and S150 are executed to calculate GAP ratios at three different carriage heights, as suggested in
In step S160, the relationship between the GAP ratio and the carriage height (Height) is calculated as a distance information reference table, as in the first embodiment. In step S165, the difference between the initial distance information reference table and the newly calculated distance information reference table is obtained. In step S170, the correction coefficient for the initial distance information reference table is calculated from the difference. Finally, in step S180, the correction coefficient is stored in a storage area 407 of the memory 405, as in the first embodiment.
Hence, according to the above-described embodiment, print paper used by the user can be used for recalibration without using print paper for calibration as long as a predetermined condition is met. Note that in this embodiment, recalibration is performed by referring to the information of the distance or thickness of print paper stored in the internal memory of the printing apparatus. However, for example, the user may be caused to directly input the thickness information of print paper to be used from an operation panel 104 of the printing apparatus.
An example will be described here with reference to
If the thickness of the print paper 209 used for recalibration is different from the thickness of the print paper 801 for calibration, the distance from the irradiated surface of the print paper 209 to the printhead 201 changes from that for the print paper for calibration. For this reason, as shown in
Hence, calculated distance reference information has a gradient equal to that of distance reference information initially stored in the memory but is translated in the abscissa direction. As described above, even if the thickness of the print paper 209 used for recalibration is different from the thickness of the print paper 801 for calibration, the calculated distance reference information exhibits a characteristic similar to the distance reference information initially stored in the memory. Hence, the calculated distance reference information can be used by correcting the moving amount in the abscissa direction.
The change in the GAP ratio caused by ink mist adhesion to a photoreception unit 401 will be described using equations.
Letting F be the output of the photoreception unit 401-a, N be the output of the photoreception unit 401-b, and R be the GAP ratio, the relationship between them is given by
R=F/N (1)
The data (distance information reference table) of the initial GAP ratio R with respect to the distance from the printhead 201 to the print paper 209 is stored in a storage area 408 of the memory 405. Letting GAP be the distance from the printhead 201 to the print paper 209, K be the gradient of the function of the distance information reference table shown in
GAP=K*R+C (2)
When the carriage heights are Low and Mid, distances (GAP1 and GAP2) from the printhead 201 to the print paper 209 obtained by moving a carriage 202 by a lift elevating operation are respectively given by
GAP1=K*R1+C (3)
GAP2=K*R2+C (4)
where R1 and R2 are GAP ratios obtained in a case where the carriage heights are Low and Mid. The difference between equations (3) and (4) is given by
(GAP1−GAP2)=K*(R1−R2) (5)
If the sensitivity of the photoreception unit 401-a is lowered by adhesion of the ink mist 500, as shown in
(GAP1−GAP2)=K′*(R1−R2) (6)
Letting M be the sensitivity deterioration coefficient by the adhesion of the ink mist 500, as shown in
K′=K*M(M≦1) (7)
In the above-described way, the sensitivity deterioration coefficient can be calculated from the change in the gradient of the function representing the distance information reference table and the result of comparison of the GAP ratios at a predetermined distance by the lift elevating operation of the carriage 202.
Processing in the above-described case will be described next with reference to the flowchart of
According to this embodiment, processing starts from step S110. If the count value of a dot counter is equal to or more than a predetermined amount, the processes of steps S120 to S150 are repeated. After that, in step S160, a distance information reference table as shown in
Here, assume that a decrease in the sensitivity takes place in the ranging sensor 207 due to adhesion of the ink mist 500, as shown in
After that, in step S163, to check whether the thickness of the print paper 209 to be used for recalibration falls within a predetermined range, it is checked whether the above-described change in the received light amounts on the two photoreception units or the change in the calculated GAP ratio exhibits linearity. Upon determining that the change does not indicate that the data has linearity, it is determined that the thickness of the print paper 209 to be used by the user exceeds a tolerable thickness, and the process advances to step S190 to prompt to change the print paper to be used for calibration. In step S200, a recalibration flag to execute recalibration is set, and processing is performed. On the other hand, upon determining that the change indicates that the data has linearity, it is determined that the thickness of the print paper used by the user for recalibration falls within the range of the tolerable thickness, and processes of steps S170 and S180 are executed.
Hence, according to the above-described embodiment, the ranging sensor can be calibrated using print paper even if its thickness information is not stored in the storage area of the memory in the printing apparatus.
An example will be described here with reference to
In this embodiment, as shown in
Assuming that the sensitivity of the ranging sensor 207 is lowered by ink mist adhesion, when the count value (DCNT) of a dot counter is equal to or larger than a predetermined threshold (DCNT≧TH), the distance information reference table of the ranging sensor is corrected by the user.
In this case as well, the lift elevating operation of the carriage 202 is executed using print paper used by the user for recalibration, and a carriage height at which the maximum received light amount is obtained from each of the two photoreception units and a peak output at that time are calculated, as in the early stage of the operation. Then, the carriage heights at which the maximum received light amounts are obtained from the photoreception units and the peak outputs at the above-described early stage of the operation are compared. The ratio of sensitivity decreases caused by ink mist adhesion is obtained for each of the two photoreception units from the comparison result. Based on the ratios of sensitivity decreases, deterioration coefficients by the ink mist are calculated.
Next, a function representing a distance information reference table indicating the relationship between the GAP ratio and the distance from a printhead 201 to print paper 209 at the early stage of the operation is multiplied by the deterioration coefficient of each photoreception unit, thereby newly calculating a function representing a new distance information reference table. Finally, the relationship between the carriage height (Height) in the lift elevating operation of the carriage 202 and the GAP ratio of the two photoreception units is redefined, thus completing correction of the distance information reference table.
Hence, according to the above-described embodiment, it is possible to determine the degree of deterioration of the photoreception units using print paper whose thickness information is not stored in the storage area of the memory in the printing apparatus and recalibrate the ranging sensor based on the determination.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2015-110798, filed May 29, 2015, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-110798 | May 2015 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20030169310 | Arquilevich | Sep 2003 | A1 |
| 20050024414 | Chong Hin | Feb 2005 | A1 |
| 20050100385 | Sato | May 2005 | A1 |
| 20150273823 | Kato | Oct 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 2008-265058 | Nov 2008 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20160347053 A1 | Dec 2016 | US |
