JP5371370B2 - Printer and object movement detection method - Google Patents

Description

  The present invention relates to a technique for detecting movement of an object by image processing, and a technical field of a printer that employs the technique.

  When printing is performed while transporting print media such as cut sheets (hereinafter referred to as media), if the transport accuracy is low, density unevenness of the halftone image or magnification error may occur, resulting in a printed image. The quality of the product deteriorates. For this reason, high-precision parts are used and a precise transport mechanism is installed, but the demand for print quality is severe and further improvement in accuracy is desired. On the other hand, the demand for cost is strict, and both high accuracy and low cost are required.

  In order to cope with this, an attempt is made to detect the movement of the media conveyed by image processing by imaging the surface of the media in order to detect the movement of the media with high accuracy and realize stable conveyance by feedback control. Has been made.

Patent Document 1 discloses a technique for detecting the movement of the media. In this method, the surface of a moving medium is imaged a plurality of times by an image sensor, and the obtained images are compared by image processing including pattern matching processing to detect the amount of movement of the media.
JP 2007-217176 A

  The apparatus disclosed in the above-mentioned patent document performs image processing in real time during conveyance of media. For this reason, when the number and frequency of media movement detection are large, such as when the media transport speed is high or when multi-pass printing is performed, the computation of image processing becomes a heavy load. Then, the time required for computation becomes a bottleneck, which may affect print throughput.

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

  An object of the present invention is to provide a printer that can reduce the influence on the throughput by changing the load required for the image processing for detecting the movement information of the media according to the situation. Another object of the present invention is to provide a method capable of detecting movement information of an object at high speed.

The present invention that solves the above-mentioned problems is a printer that conveys media and prints, and obtains image data by imaging fine irregularities on the surface of the media, and obtained at different timings using the sensor. A pattern cut out from a predetermined area of one image data among a plurality of image data is compared with other image data to detect movement information of the medium, and the conveyance of the medium is controlled based on the detected movement information. A control unit, wherein the control unit analyzes the image data acquired by the sensor to determine the contrast of the fine uneven shape on the surface of the media, and the higher the contrast is , the smaller the size of the predetermined area is It is characterized by setting to.

According to another aspect of the present invention, an image sensor is used to capture an image of a fine concavo-convex shape on the surface of the object to obtain image data, and a plurality of the images obtained as the object moves are obtained. a pattern cut from a given area of an image data of the image data as compared to other image data, movement detection of the object have a, a step of detecting the relative movement information of the object relative to the image sensor A method comprising: analyzing image data acquired by the image sensor to determine a contrast of a fine uneven shape on an object surface; and setting the size of the predetermined area to be smaller as the contrast is higher To do.

  According to the present invention, it is possible to provide a printer that can reduce the influence on the throughput by changing the load required for the image processing for detecting the movement information of the media according to the situation. In addition, it is possible to provide a method capable of detecting movement information of an object at high speed.

  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.

  An embodiment of an inkjet printer will be described as an example of an image forming apparatus to which the present invention is applied. The application range of the present invention is not limited to the ink jet system. For example, the present invention can be applied to various types of printers such as an electrophotographic system, a thermal system, and a dot impact system, or a device including a printer such as a copying machine, a facsimile machine, and a multifunction machine.

[First Embodiment]
FIG. 1 is a perspective view showing a configuration of a main part of an ink jet printer. The carriage 1 moves by mounting an ink jet print head. The print head can use various ink jet methods such as a method using a heating element, a method using a piezo element, a method using an electrostatic actuator, and a method using a MEMS element.

  The carriage motor 2 is a driving source for moving the carriage 1 in the main scanning direction, and the rotational driving force is transmitted to the carriage 1 by the belt 4. The carriage 1 reciprocates in the main scanning direction with respect to the chassis 9. The position of the carriage 1 in the main scanning direction is detected and monitored by a linear encoder. The linear encoder includes a linear encoder pattern 3 attached to the chassis 9 and a reading unit (not shown) mounted on the carriage 1 that optically, magnetically, or mechanically reads the pattern.

  A sheet-like medium M, which is a moving object, is conveyed on the platen 11 in the sub-scanning direction (arrow direction in the figure) orthogonal to the main scanning direction of the carriage 1. This conveyance is performed by a driving mechanism including a conveyance roller 5, a belt 8, and a conveyance motor 6. The driving state (rotation amount, rotation speed) of the transport roller 5 is detected and monitored by the rotary encoder 31. The rotary encoder 31 includes a circumferential encoder pattern 7 that rotates together with the transport roller 5 and a reading unit 10 that reads the pattern optically, magnetically, or mechanically.

  The media sensor 20 detects the media M conveyed on the platen 11 from the print surface side or the back surface side. The media sensor 20 detects the movement information (movement amount, movement speed, movement direction, etc.) of the medium M and the surface state of the medium. Details of the configuration and operation will be described later. Note that a plurality of media sensors 20 may be provided, and the arrangement positions are not limited to this.

  A controller 90, which is a controller, controls various operations of the entire printer. For example, the servo control of the media transport system forms a feedback loop based on the control target value and the detection value of the rotary encoder 31.

  Next, details of the media sensor 20 will be described. FIG. 2 shows a physical configuration, and FIG. 3 shows an electrical configuration. In FIG. 2, the media sensor 20 is an integrated reading unit including a light emitting element 71, a lens 72, and a photoelectric conversion element 73. As the light emitting element 71, an LED, an LD, an OLED, or the like is used. The photoelectric conversion element 73 is a two-dimensional image sensor composed of an image sensor with a CCD or CMOS structure. For example, a cell of 10 μm × 10 μm is arranged by 400 pixels in the transport direction × 200 pixels in the main scanning direction.

  In FIG. 3, the output of the photoelectric conversion element 73 is converted to digital by the A / D conversion circuit 74, and is output as a digital signal to the control unit 90 via the interface 75. Further, light emission of the light emitting element 71 is controlled via the interface 75. In this configuration, the surface of the medium M is spot illuminated with light emitted from the light emitting element 71. The scattered reflected light from the illuminated medium M is collected by the lens 72 and received by the photoelectric conversion element 73. The illuminated area of the medium M and the light receiving surface of the photoelectric conversion element 73 form an imaging relationship by the lens 72, and the photoelectric conversion element 73 acquires precise image information on the surface of the medium M.

  FIG. 4 is an electrical block diagram of the entire printer, centering on the control unit 90. The control unit 90 includes a CPU 91, a ROM 92, and a RAM 93. Signals from the reading units of the linear encoder 30 that detects the movement amount of the carriage 1 and the rotary encoder 31 that detects the rotation of the transport roller 5 are input to the control unit 90. Further, a signal from the media sensor 20 is input. In addition, a drive signal is output from the control unit 90 to a motor drive circuit 32 that drives the carriage motor 2 and a motor drive circuit 33 that drives the carry motor 6 times. Each motor is driven according to a command from the control unit 90. Further, an external computer 35 is connected to the control unit 90 via the printer interface 34, and an operation panel 36 is connected. The operation panel 36 has a display serving as a user interface and operation buttons.

  Next, an operation procedure including detection of the media conveyance amount using the media sensor 20 will be described with reference to a flowchart showing a printing operation in FIG. The detection of the media transport amount is roughly performed in the order of template pattern extraction (S100), media transport (S200), and media transport amount calculation by template matching (S300).

  When the printing operation is started, it is determined in step S1 whether the printing is the first line. If it is the first line (YES), in step S2, a target transport amount (control target value) is set as the transport amount for one pass to be commanded. If it is not the first line (NO), in step S3, for the feedback control, a one-pass conveyance amount for instructing to eliminate the difference between the target conveyance amount and the actual conveyance amount stored in the RAM 93 is set. The actual transport amount is obtained by pattern matching image processing in the following steps.

  In step S <b> 4, an image reading command is issued from the CPU 91 of the control unit 90 to the media sensor 20. In response to this, the media sensor 20 turns on the light emitting element 71 and the photoelectric conversion element 73 reads a two-dimensional image to acquire image data.

  FIG. 6 is a diagram showing a relationship between an image data reading area 701 by the media sensor and predetermined areas (area 702 and area 703) in which pattern matching is performed. The reading area 701 is composed of 4 mm (400 pixels) in the conveyance direction × 2 mm (200 pixels) in the main scanning direction. The media sensor captures the entire range of image data in the reading area 701 in FIG. 6A, and stores the acquired image data in the RAM 93 of the control unit 90.

  In step S5, data corresponding to the area 702 is cut out from the image data stored in the RAM 93 and stored in the RAM 93 as a template pattern. An area 702 is a square area of a predetermined size located upstream in the conveyance direction in the reading area 701. The area 703 is an area of the same size as the area 702, and is set downstream from the area 702 by the target value (distance Y) of the media conveyance amount of one line. The sizes of these areas 702 and 703 are variable according to the print mode, specifically, the number of print passes. In the example of FIG. 6A, the area is 1 mm × 1 mm (100 pixels × 100 pixels), and in the example of FIG. 6B, the area is 0.5 mm × 0.5 mm (50 pixels × 50 pixels). Cut out by setting any size according to the number of print passes. Details will be described later.

  In step S6 (step S200), the conveyance motor 6 is driven by a command from the CPU 91, and the conveyance roller 5 is rotated to convey the medium by the set step amount for one line.

  In step S <b> 7, the CPU 91 issues a second image reading command to the media sensor 20 to obtain an image. The image data of the reading area 701 acquired by the media sensor 20 is stored in the RAM 93 of the control unit 90.

  In step S8, a template matching process is performed by comparing the template pattern of the area 702 obtained before the media conveyance with the image pattern corresponding to the area 703 in the newly obtained image data of the reading area 701. This is obtained by performing an image search in the transport direction (sub-scanning direction) where the specific pattern included in the template pattern exists in the area 703.

  In step S9, the movement distance of the medium during this period is calculated from the difference in the number of pixels between the position of the template pattern before the medium conveyance and the position of the similar pattern after the medium conveyance. This value is stored in the RAM 93. If the image patterns in the area 702 and the area 703 coincide with each other without any deviation, it means that the image has been conveyed according to the target conveyance amount. If there is a deviation in the number of pixels in the conveyance direction, the actual conveyance is performed by the deviation. It means that an error has occurred in the quantity. That is, the actual transport amount of the medium can be obtained from the target value transport amount (distance Y) + the pattern matching shift amount.

  In step S10, printing for one line is performed. In step S11, it is determined whether printing for one page has been completed. If YES, the process ends. If NO, the process returns to step S1 to repeat the same operation.

  Next, the setting of the size of the cut-out area used for the pattern matching process will be described. During low-pass (one-pass) printing, since the transport distance Y per time is long as shown in FIG. 6A, the error between the target transport amount and the actual transport amount tends to increase. Even if this difference increases, the sizes of the areas 702 and 703 are increased so that the pattern matching process can be performed without any problem. In this example, an area of 1 mm × 1 mm (100 pixels × 100 pixels) is set. As the area becomes larger, the number of pixels included increases, so that the amount of image processing increases. However, since the transport distance per one-pass feed is long, the frequency of image processing is low and print throughput is not affected.

  On the other hand, during multi-pass printing (number of passes greater than 1), the transport distance Y per time is relatively short as shown in FIG. 6B, and the frequency of image processing increases accordingly. . At this time, if the sizes of the areas 702 and 703 are made large as in the case of low-pass printing, there is a possibility that the image processing for pattern matching cannot catch up with the conveyance speed of the media and the print throughput may be reduced. Therefore, when performing multi-pass printing, compared with low-pass printing, the size of the area for pattern matching is reduced, the amount of image processing is reduced, and the calculation time per time is shortened. In this example, an area of 0.5 mm × 0.5 mm (50 pixels × 50 pixels) is set to reduce the calculation amount to a quarter. In the case of multi-pass printing, since the distance per one-pass feed is short, the error between the target carry amount and the actual media carry amount tends to be small. Therefore, most of the patterns in the area 702 are included in the area 703, and the pattern matching process can be performed without any problem.

  In this embodiment, the images of the area 702 and the area 703 are extracted before and after the start of the one-pass feed. However, the images of the area 702 and the area 703 are extracted at different timings during the one-pass feed. You may make it do. Further, the area 702 and the area 703 are not limited to a rectangle, and may be, for example, a polygon or a circle (including an ellipse). The same applies to other embodiments described below.

[Second Embodiment]
A second embodiment will be described. Since the apparatus configuration is the same as that of the previous example and the operation flow has many common parts, description of overlapping parts is omitted.

  As shown in FIG. 7, there is a case where the medium conveyance direction is inclined with respect to the original conveyance direction (sub-scanning direction), and skewing occurs as shown by the locus S. When skew occurs, a deviation also occurs in the main scanning direction before and after the conveyance. Therefore, if the position of the area 703 is not set in consideration of the skew, there is a possibility that the pattern matching processing may be hindered. This is particularly noticeable when the size of the cut-out area used for template processing is small.

  Therefore, the area 703 is set so as to be shifted from the area 702 in the main scanning direction according to the skew amount so that the center 713 of the area 703 is positioned on the skew locus S. The skew amount is detected by using the media sensor 20 for each conveyance of one line.

  FIG. 8 shows a flowchart of the operation procedure. If the print is the first line in step S11, the process proceeds to step S12. If the print is not the first line (NO), the process proceeds to step S13. In step S13, for the feedback control, a one-pass conveyance amount for instructing that there is no difference between the target conveyance amount and the actual conveyance amount stored in the RAM 93 is set. Next, in step S14, a shift amount in the main scanning direction of the area 703 corresponding to the skew amount with respect to the center position of the area 702 is set. That is, the relative positions of the two areas are set so that the center 712 of the area 702 and the center 713 of the area 703 are both positioned on the oblique locus S. The skew amount is calculated based on the image data acquired by the media sensor.

  Steps S15 to S18 are the same as steps S4 to S7 in FIG.

  In step S19, template matching processing is performed on an image corresponding to the area 703 in the newly obtained image data of the reading area 701 using the template pattern of the area 702 obtained before the medium conveyance. This is obtained by searching the image in the transport direction (sub-scanning direction) and the direction orthogonal to it (main scanning direction) where the specific pattern included in the template pattern exists in the area 703.

  In step S20, the moving distance of the medium during this period is calculated from the difference in the number of pixels in the sub-scanning direction between the position of the template pattern before transporting the medium and the position of the similar pattern after transporting the medium. Further, the skew amount that has changed during this period is calculated from the difference in the number of pixels in the main scanning direction. These values are stored in the RAM 93. If the image patterns of the area 702 and the area 703 match in any direction without any deviation, it means that the image is conveyed according to the target conveyance amount and the skew amount does not change.

  In step S21, one line is printed. In step S21, it is determined whether printing for one page is completed. If YES, the process ends. If NO, the process returns to step S11 to repeat the same operation.

[Third Embodiment]
A third embodiment will be described. In multi-pass printing, since the distance per one-pass feed is short, the error between the target transport amount and the actual transport amount is generally small. However, especially in the initial stage of printing one page, the transport resistance of the media fluctuates. Since it is not stable, the error may increase.

  Therefore, at least one of the size and the relative position of the predetermined area is made variable according to the print area on the medium. Specifically, from the first line of the printing of one page to a predetermined number of lines, the sizes of the areas 702 and 703 are increased as shown in FIG. The area 703 can be reliably detected. After a predetermined number of lines, the size of the area 702 and the area 703 is reduced as shown in FIG. 9B to reduce the pattern matching calculation load. Furthermore, as in the second embodiment, the relative position in the main scanning direction may be varied according to the skew in FIGS. 9A and 9B.

  FIG. 10 shows a flowchart of the printing operation. In the first line, the area 702 and the area 703 are increased in size in step S33. For the first and subsequent lines, it is determined in step S34 whether or not a predetermined number of lines (for example, 100 lines) has passed. If YES, the sizes of the areas 702 and 703 are reset to be smaller in step S35. In the case of NO, step S35 is skipped and the process proceeds to step S36. The subsequent operations in steps S37 to S44 are the same as those in steps S4 to S11 in FIG.

  In multi-pass printing, if the pattern matching process is performed in a wide area as shown in FIG. 9A, the calculation process may not catch up with the original conveyance speed, and the conveyance speed may be reduced. On the other hand, in the present embodiment, the amount of calculation is large only in a partial area (initial stage of printing) in one page, so that the decrease in print throughput as viewed in total is negligible.

[Fourth Embodiment]
The sizes of the area 702 and the area 703 may be variable according to the surface state of the media. The surface condition varies depending on the type of media used. One method of determining the surface state is to analyze an image acquired by the media sensor 20. For example, when the surface of the medium is rough, the image acquired by the media sensor 20 has a fine contrast on the surface unevenness, so that the surface state can be determined from the contrast. When the contrast is high, the calculation amount can be reduced by setting the sizes of the area 702 and the area 703 small. In addition, the surface state can be determined from the type of media used. The type of media to be used is known because the user designates the printer body or printer driver.

The perspective view which shows the structure of the principal part of a printer Diagram showing the physical configuration of the media sensor Diagram showing the electrical configuration of the media sensor Diagram showing the electrical block of the entire printer The flowchart figure which shows the operation | movement procedure in 1st Embodiment. The figure which shows the area which performs pattern matching in image data The figure which shows the area which performs pattern matching in image data The flowchart figure which shows the operation | movement procedure in 2nd Embodiment. The figure which shows the area which performs pattern matching in image data The flowchart figure which shows the operation | movement procedure in 3rd Embodiment.

Explanation of symbols

1 Carriage 20 Media sensor 90 Control unit M Media

Claims (4)

A printer that transports media and prints,
A sensor that captures image data by capturing fine irregularities on the media surface ;
The movement information of the medium is detected by comparing the pattern cut out from a predetermined area of one of the plurality of image data acquired at different timings using the sensor with other image data, and detecting the movement information of the medium And a control unit for controlling the conveyance of the media based on
The control unit analyzes image data acquired by the sensor to determine a contrast of a fine uneven shape on a medium surface, and sets the predetermined area to be smaller as the contrast is higher. Printer.   The control unit sets at least one of the size and the relative position of the predetermined area according to at least one of a medium conveyance speed, a medium print pass number, a medium skew amount, and a print area on the medium. The printer according to claim 1.   3. The printer according to claim 1, wherein printing is performed by an ink jet method. Capturing image data by imaging fine irregularities on the surface of the object using an image sensor; and
A plurality of the images are taken along with the movement of the object, and a pattern cut out from a predetermined area of one image data among a plurality of obtained image data is compared with other image data, and the object with respect to the image sensor a object movement detection method for chromatic detecting the relative movement information, and
Analyzing image data acquired by the image sensor to determine the contrast of the fine irregularities on the surface of the object, and setting the size of the predetermined area to be smaller as the contrast is higher Method.

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