JP2010111091A - Printer and sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve the followings in detecting a test pattern using a media sensor: to decrease an influence of a cockling generated on media on accuracy of detection more than before; to shorten a time required for detection; and to form an image with a high quality. <P>SOLUTION: The media sensor (102) has a light emitting diode (LED 210) for irradiating a light toward the media, a first light receiving diode (photo-diode 203) for receiving a reflected light from a site irradiated with the light for detecting a print density, and a second light receiving diode (PSD 202) for receiving the reflected light from the same site as the site for detecting a distance to the media from a direction different from the first light receiving part. The output of the first light receiving diode (photo-diode 203) is corrected by using the output of the second light receiving diode (PSD 202) and a converting table prepared in advance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technical field of a printer having an adjustment function using a media sensor.

  Calibration technology that improves printer color and gradation reproducibility, registration technology that accurately aligns the ink application to the media by overstrike, undischarge detection technology that detects the ink discharge status from the print head, etc. Various print adjustment techniques are known. In these methods, a test pattern is formed on a medium using a printer, and this is detected by reading it with an optical media sensor. Based on this detection, the print condition in actual printing is adjusted to improve the reproducibility of the printed image.

  The surface of the media is ideally flat, but in practice, cockling (partial waviness of the media may occur if the media absorbs a large amount of ink or by applying temperature, humidity, or physical external force. ) May occur. When the media surface in which cockling has occurred is relatively scanned by the media sensor, the detection distance between the detection surface of the media sensor and the media surface varies according to the undulation of the media surface. As a result, the output signal of the sensor may fluctuate accordingly, which hinders accurate detection.

Attempts have been made to correct the effect of cockling. In Patent Document 1, a reference region having a uniform surface state is provided adjacent to a region of a test pattern for determining a printing operation state (ink ejection state or the like). Signals are detected for both regions, and the detection signal of the test pattern is corrected based on the detection result in the reference region to reduce the influence of fluctuation due to cockling.
JP 2005-67093 A

  Patent Document 1 corrects the value of the read test pattern by referring to a region (white level) to which ink is not applied when the test pattern is read to detect the print state. For this reason, if the amount of cockling is different between the test pattern area and the reference area, the distance between the media sensor and the media surface is different between the two, and thus accurate correction cannot be performed. Further, it is necessary to scan another area together with the test pattern, and it takes time for the entire detection, and it is difficult to shorten it.

  The present invention has been made based on recognition of the above-described problems.

  It is an object of the present invention to reduce the influence of cockling generated on a medium on detection accuracy in detection of a test pattern using a media sensor, and to reduce the time required for detection and to form a high-quality image. The provision of a printer that enables this.

  Another object of the present invention is to provide a method for detecting an accurate surface state without being influenced by a sensor for detecting the surface state of an object even if the distance to the object varies.

  The present invention for solving the above-mentioned problems comprises a carriage mounted with a print head and reciprocatingly moved relative to a medium, and a media sensor mounted on the carriage and detecting a test pattern formed on the medium. The media sensor includes: a light emitting element that emits light toward the medium; and a reflected light from a portion irradiated with the light to detect a test pattern. A first light receiving element that receives light, a second light receiving element that receives reflected light from the same part as the part from a direction different from the first light receiving element in order to detect a distance to the medium, and the first light receiving element And a correction means for correcting the output of the first light receiving element using the output of the second light receiving element and a conversion table.

  According to the present invention, in the test pattern detection using the media sensor, the influence of cockling generated on the media on the detection accuracy is reduced more than before, and the time required for detection is shortened, and high-quality image formation is performed. It is possible to provide a printer that enables this.

  Exemplary embodiments of the present invention will be described below with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

  Hereinafter, an ink jet printer will be described as an example. However, the printer of the present invention can be applied to various color print printers such as an electrophotographic method and a thermal method in addition to the ink jet method. Further, the present invention can also be applied to a multifunction machine having a copying function and a scanning function, so-called a multi-function printer. The sensor of the present invention is not limited to media, but can be applied to a sensor that detects the surface state of an object such as the density and pattern position of the object surface.

<Embodiment 1>
FIG. 1 is a perspective view of a main part of an ink jet printer equipped with a media sensor.

  The carriage 101 has a media sensor 102 and a print head 103 mounted thereon, and reciprocates with the conveyance belt 104 guided by the shaft 105. The moving direction (main scanning direction) of the carriage 101 is defined as the X direction. A CR encoder (not shown) for detecting the position of the carriage 101 in the X direction is provided. Further, the medium 106 is conveyed on the platen 107 by a conveyance roller (not shown). A conveyance direction (sub-scanning direction) of the medium 106 is defined as a Y direction, and a direction perpendicular to a plane formed by the X direction and the Y direction is defined as a Z direction.

  Two-dimensional printing is performed on the medium 106 by repeating the operation of sub-scanning (step feeding) the medium 106 on the platen 107 with the transport roller and the operation of ejecting ink droplets while main-scanning the print head 103 with the carriage 101. Form an image.

  In the media sensor 102 mounted on the carriage 101, the detection area on the media 106 is positioned on the downstream side of the transport path of the media 106 with respect to the print position of the print head 103. Further, the media sensor 102 and the print head 103 are mounted on the carriage 101 so that the lower surface of the media sensor 102 is higher than the lower surface of the print head 103 or at the same height as viewed from the surface of the media 106. ing.

  2 shows a configuration diagram of the media sensor 102, FIG. 2 (a) is a plan view seen from above in the Z direction, FIG. 2 (b) is a side view seen from the X direction, and FIG. 2 (c) is Y direction. It is the side view seen from.

  In FIG. 2A, the media sensor 102 includes an LED 201 that is a light emitting element, a PSD (optical position sensor) 202 that is a light receiving element (corresponding to a second light receiving element), and a photodiode 203 (corresponding to a first light receiving element). It has. These are mounted on the same substrate 204.

  The LED 201 has light emitting elements of three colors, red, blue, and green, and can be selectively lit. Note that the light emitting element is not limited to an LED, and an OLED or a semiconductor laser may be used. The PSD 202 is a position sensor that detects the media height (distance from the media sensor to the media surface). The PSD 202 and the LED 201 are arranged in the same row in the Y direction. The photodiode 203 detects the density of a test pattern (density patch) for calibration or registration printed on the medium 106. The photodiode and the LED 201 are arranged in the same row in the X direction. That is, on the substrate 204, the photodiode 203 (first light receiving element) and the PSD 202 (second light receiving element) are arranged at a position orthogonal to the LED 201 (light source). The LED 201 lights up according to the color of the patch to be detected. Further, the PSD 202 can detect the height of the medium 106 regardless of the color of the LED 201.

  2B and 2C, the LED 201 has an irradiation angle in a substantially vertical direction (vertical or substantially vertical) with respect to the surface (measurement surface) of the medium 106, and irradiates the medium from above. The irradiation light from the LED 201 forms a circular irradiation spot having a diameter of 3 to 4 mm on the surface of the medium 106 at the reference distance. When the distance between the media 106 and the media sensor 102 is the reference distance, the PSD 202 converts the scattered reflected light from the portion of the media 106 irradiated by the LED 201 to 0 ° in the X direction with respect to the optical axis of the irradiated light and Y Light is received from a direction of 45 °. On the other hand, the photodiode 203 receives the scattered reflected light from the portion of the medium 106 irradiated by the LED 201 from the direction of 45 ° in the X direction and 0 ° in the Y direction with reference to the optical axis of the irradiated light. That is, the PSD 202 and the photodiode 203 receive reflected light from different directions.

FIG. 3 is a diagram for explaining the concept of distance detection using the PSD 202. The PSD 202 outputs _two current values I ₁ and I _2, which change depending on the light intensity distribution of the reflected light L 2 incident on the PSD 202. By looking at the two current values, it is possible to know where the maximum value (center of gravity position) of the light intensity distribution is located. The barycentric position moves on the PSD 202 in proportion to the distance between the PSD 202 and the medium 106. Therefore, by detecting the position of the center of gravity, the distance between the PSD 202 and the surface of the medium 106, that is, the height of the medium can be obtained. As described above, this value varies depending on the cockling of the media.

  FIG. 4 shows a circuit block diagram for processing input / output signals of the media sensor 102. The CPU 411 performs calculation of an output signal obtained in accordance with an ON / OFF control command for the LED 201 and an amount of light received by the photodiode 203. It also manages various controls of the entire printer related to media conveyance, printing operations, print adjustment (calibration, registration, non-ejection detection adjustment, etc.). The drive circuit 401 drives the LED 201 based on a command from the CPU 411. The amplifier circuit 402 converts output signals (current values) of the PSD 202 and the photodiode 203 into voltage values and amplifies the signals. The signal is converted to digital by the A / D converter 404 inside the ASIC 403 and stored in the data storage area 408 of the memory 407 via the memory control unit 405. The memory 407 stores two conversion tables, a height GAP table 409 and a density GAP table 410, in the form of a data table. Details will be described later. The CR encoder 406 is a sensor that detects the position of the carriage 101 in the X direction as described above, and this output signal is input to the memory control unit 405.

  Next, a processing procedure for detecting the distance to the medium 106 using the media sensor 102 will be described. A density patch is printed on the medium 106 in advance using the printer of this embodiment. When the medium 106 is conveyed onto the platen 107, the carriage 101 is moved so that the media sensor 102 is positioned on the density patch on the medium 106. Then, the LED 201 of the media sensor 102 is turned on. Since the LED 201 can selectively emit light of three colors of red, blue, and green, the color corresponding to the color of the density patch is turned on. Scattered light is generated from the portion of the medium 106 irradiated by the LED 201. The PSD 202 and the photodiode 203 receive part of the reflected light from different angular directions. The two outputs of the PSD 202 are values corresponding to the distance to the medium 106.

FIG. 5 is a diagram for explaining a processing procedure for correcting density data scanned at the time of density detection. When the density detection sequence is started, a density patch is printed on the medium in step S501. FIG. 6 shows an example of a density patch for a certain color component. The density patch 601 is formed of a multi-tone pattern whose density gradually changes along the X direction. In step S502, the medium is conveyed and the positions of the media sensor 102 and the density patch 601 in the Y direction are aligned. Next, the carriage 101 is moved in the X direction, and the media sensor 102 is moved to the scan start position. In step S503, the carriage 101 is moved in the X direction at a constant speed, and scanning of the media sensor 102 for the density patch is started. At this time, a predetermined color of the LED 201 of the media sensor 102 is caused to emit light, and the reflected light from the density patch 601 is received by the photodiode 203 to obtain an output signal reflecting the density. At the same time, reflected light from the same part of the density patch 601 is received by the PSD 202 from another direction, and an output signal (two current values I ₁ and I ₂₎ reflecting the distance from the media sensor 102 to the density patch. ) These output signals related to density and distance are converted into digital signals through an amplifier circuit 402 and an A / D converter 404, respectively.

  In step S <b> 504, the memory control unit 405 causes the data storage area 408 in the memory 407 to store digital data obtained by detection based on a preset scan start position, scan area, and sampling period. Specifically, the value of the CR encoder 406 is monitored, A / D conversion is performed at a sampling period set in the range of the scan area set from the scan start position, and the density and distance are reflected together with the CR encoder value. Are stored in the data storage area 408 of the memory.

  In step S505, it is determined whether the detection of the entire area of the density patch 601 has been completed. If the detection has been completed, the process proceeds to step S507. If not completed, the carriage 101 is moved to the scan start position of the next density in step S506, and the process returns to step S503 again to repeat the same detection process.

  Here, FIG. 7A is a table showing the results of acquiring density data and distance data for each sampling period when focusing on the density of a certain patch. The sampling period in the patch is 1 to N. In each cycle, “height sensor output (ratio)” indicates data reflecting the distance obtained from the ratio of the two output signals of the PSD 202, and “density sensor output” indicates the density obtained by the photodiode 203. Indicates the reflected data.

  In step S507, the actual distance from the media sensor 102 to the media 106 is obtained for each sampling period using the height GAP table 409 of the memory 407. For example, paying attention to the Nth sampling cycle, the height tip output (ratio) is a value E in the Nth sampling cycle in FIG. In step S507, the height GAP table 409 is referenced to calculate a distance value corresponding to the value E. FIG. 8A shows an example of the height GAP table 409. In this case, the relationship between the height sensor output (ratio) and the distance from the actual sensor to the medium 106 is acquired in advance and stored in the memory 407 in the form of a data table. According to FIG. 8A, when the value of the height sensor output (ratio) is E, the distance from the sensor to the medium is K (mm). Therefore, the actual distance in the Nth sampling period is calculated as K (mm).

  Next, in step S508, a normalization operation for aligning the “height sensor output (ratio)” to a predetermined height is performed to calculate a correction coefficient. For example, if the predetermined height is J (mm), the value of the height sensor ratio at this time is the value F from FIG. Here, the density GAP table 410 shown in FIG. 8B is used. The density GAP table 410 acquires in advance the relationship between the actual distance from the media sensor 102 to the medium 106 (between the sensor and the medium) and the output of the photodiode 203 which is the density sensor, and stores it in the memory 407 as a data table. I remembered it. The distance between the sensor and the media has a value of K (mm) in step S507, and the density sensor output (relative value) corresponding to this value K is the value Y when the density GAP table 410 is referred to. . The density sensor output (relative value) corresponding to the predetermined height J (mm) is a value X. Therefore, in order to align the height sensor output (ratio) to a predetermined height, a correction coefficient of X / Y can be obtained.

  In step S509, the density data is corrected using the correction coefficient acquired as described above. Assuming that the density sensor output at the Nth sampling period is O, the value calculated by correcting with the formula of O × X / Y becomes the data with the final density. The final density data P, Q, R,... T after correction are obtained for each of the sampling periods [1], [2], [3],. FIG. 7B shows these as a table.

  In step S510, it is determined whether the correction for each sampling period has been completed for all density data of the density patch 601, and if completed, the density detection sequence is terminated. If not completed, the process returns to step S507 and the same is repeated. In this way, the density data is acquired by correcting the outputs of all density sensors in accordance with the read density patch 601 height. The CPU 411 performs print adjustment such as printer calibration processing and registration processing based on the density data. Since these adjustment methods are well known, detailed description thereof is omitted here.

  According to the present embodiment, since the height is detected by detecting the reflected light from the same place at the same time as the density detection, it is possible to detect the accurate cockling amount and correct the density detection result. It becomes. In addition, since it is not necessary to provide another scan area, processing can be performed in a short time.

  9A and 9B are diagrams illustrating a configuration of a modified example of the media sensor 102. FIG. 9A is a plan view viewed from the Z direction, FIG. 9B is a side view viewed from the X direction, and FIG. ) Is a side view seen from the Y direction. The difference from the configuration of FIG. 2 is that the photodiode 203 (first light receiving element) and the PSD 202 (second light receiving element) are reciprocated by the carriage relative to the LED 201 (light emitting element) on the common substrate 204. It is arrange | positioning along the same direction as a direction (X direction). Thereby, the media sensor in the sub-scanning direction can be reduced in size.

  9B and 9C, the LED 201 has an irradiation angle substantially normal to the surface (measuring surface) of the medium 106, that is, substantially perpendicular (which means vertical or substantially vertical), and from above. Irradiate the media. The irradiation light from the LED 201 forms a circular irradiation spot having a diameter of 3 to 4 mm on the surface of the medium 106 at the reference distance. When the distance between the media 106 and the media sensor 102 is the reference distance, the PSD 202 converts the scattered reflected light from the portion of the media 106 irradiated by the LED 201 to 0 ° in the X direction with respect to the optical axis of the irradiated light and Y Light is received from a direction of 45 °. On the other hand, the photodiode 203 is configured such that the scattered reflected light from the portion of the medium 106 irradiated by the LED 201 is 0 ° in the X direction with respect to the optical axis of the irradiated light, and the Y direction is 45 ° opposite to the above. Light is received from the direction. That is, the PSD 202 and the photodiode 203 receive reflected light from different directions, and the angle formed by them is 90 °. Note that the circuit block for processing the input / output signals has the same operation procedure as that of the first embodiment, and thus detailed description thereof is omitted.

<How to create a conversion table>
Next, a procedure for creating two conversion tables, the height GAP table 409 and the density GAP table 410, using the printer of the above embodiment will be described.

  In FIG. 1, the carriage 101 includes an elevating mechanism that can move minutely in the Z direction as well as in the X direction. Further, as shown in FIG. 10, a cap 802 for covering the nozzles of the print head and performing a suction operation is provided at one moving end of the range in which the carriage moves in the X direction. This position becomes the home position of the carriage 101. In addition, a reference surface 801 facing the media sensor 102 is provided at the moving end opposite to the moving range in the X direction. The reference surface 801 is a flat plate having a white surface, and provides a reference for height and color detected by the media sensor 102.

  When creating the GAP table, first, the media sensor 102 is moved onto the reference plane 801. Then, height detection and density detection are performed according to the procedure described above to obtain a reference for height and density. Next, the carriage is slightly moved in the Z direction to change the distance to the medium 106 by a predetermined amount. Then, distance detection and density detection are performed again. The relationship shown in FIG. 8 can be obtained by acquiring the data by repeatedly performing this minute movement and detection in the Z direction a plurality of times. Based on this, a GAP table for height and a GAP table for density are created. The created data tables are stored in the memory 407 as a height GAP table 409 and a density GAP table 410, respectively. As described above, the distance and the density are detected while the height of the media sensor 102 is changed by the elevating mechanism, and the GAP table is automatically generated.

  As a modification, each GAP table can be created by the following procedure. A plurality of media having a plurality of thicknesses are prepared, and a media 106 having a certain thickness is set in the apparatus and conveyed onto the platen 107. Then, the carriage 101 is moved as shown in FIG. 11 so that the media sensor 102 faces a predetermined position on the media 106, and distance detection and density detection are performed. Next, the medium 106 having a different thickness is replaced, and the height detection and the density detection are performed in the same manner. Unlike the above example, the height of the carriage 101 in the Z direction is not changed, and the distance to the platen 107 is a constant value. This is repeated to acquire data for each thickness of media. Based on these data, a GAP table for height and a GAP table for density are respectively created.

  As described above, by obtaining the GAP table using the printer itself, even if there are individual differences in the printer, the error can be absorbed.

Perspective view of main parts of inkjet printer Media sensor configuration diagram The figure explaining the concept of the distance detection using PSD Circuit block diagram for processing media sensor input / output signals Flowchart diagram for correcting density data Explanatory drawing showing an example of density patch Concentration data and distance data table Diagram showing an example of a conversion table Configuration diagram of a modification of the media sensor Diagram for explaining the procedure to create a conversion table Diagram for explaining another procedure for creating a conversion table

Explanation of symbols

101 Carriage 102 Media sensor 103 Print head 106 Media 107 Platen

Claims (11)

A carriage mounted with a print head and reciprocally moved with respect to the medium, and a media sensor mounted on the carriage and detecting a test pattern formed on the medium, and performing print adjustment based on detection by the media sensor A printer,
The media sensor is
A light emitting element that emits light toward the media;
A first light receiving element for receiving reflected light from a portion irradiated with the light in order to detect a test pattern;
In order to detect the distance to the medium, a second light receiving element that receives reflected light from the same part as the part from a direction different from the first light receiving element;
A printer comprising correction means for correcting the output of the first light receiving element using the output of the second light receiving element and a conversion table.   The printer according to claim 1, wherein the light emitting element, the first light receiving element, and the second light receiving element are mounted on the same substrate.   The printer according to claim 1, wherein the light emitting element emits light from a substantially vertical direction toward the surface of the medium.   The printer according to claim 3, wherein the first light receiving element and the second light receiving element are arranged at orthogonal positions with respect to the light emitting element.   The printer according to claim 3, wherein the first light receiving element and the second light receiving element are arranged along the same direction as a reciprocating direction of the carriage with respect to the light emitting element.   6. The printer according to claim 1, wherein the first light receiving element is a photodiode, and the second light receiving element is an optical position sensor.   The printer according to claim 1, wherein the density of the test pattern is detected by the first light receiving element, and the adjustment is calibration or registration of the printer.   An elevating mechanism for elevating the carriage with respect to the medium is provided, and the conversion table is generated by performing detection with the first light receiving element and the second light receiving element while changing a distance from the media sensor to the medium. The printer according to claim 1, wherein:   8. The conversion table is generated by using a plurality of media having different thicknesses to detect each of the media with the first light receiving element and the second light receiving element. Or printer.   10. The printer according to claim 1, wherein printing is performed by an ink jet method. A sensor for detecting the surface state of an object,
A light emitting element that emits light toward an object;
A first light receiving element that receives reflected light from a portion of the object irradiated with the light;
In order to detect the distance to the object and correct the output of the first light receiving element, a second light receiving element that receives reflected light from the same part as the part from a different direction from the first light receiving element is provided. A sensor characterized by that.

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