Movement detection apparatus and recording apparatus

A conveyance mechanism includes a conveyance belt having a detection pattern containing a plurality of isolated patterns. The shape of the plurality of isolated patterns contained in the detection pattern, the size of a template area from which a template pattern is to be extracted, and the size of a seek area are associated with each other so that a part of the detection pattern contained in the template pattern extracted from first image data invariably serves as a unique pattern in the seek area of second image data.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for detecting the movement of an object through image processing, and to a technical field of a recording apparatus.

2. Description of the Related Art

When performing printing on a medium such as a print sheet while it is being conveyed, a low conveyance precision causes an uneven density of a halftone image or a magnification error, resulting in degraded quality of a printed image. Therefore, although recording apparatuses employ high-precision components and carry an accurate conveyance mechanism, there is a strong demand for higher print quality and higher conveyance precision. At the same time, there is also a strong demand for cost reduction. The achievement of both higher precision and lower cost is demanded.

To meet this demand, an attempt is made to detect the movement of a medium with high precision to achieve stable conveyance through feedback control. A method used in this attempt, also referred to as direct sensing, images the surface of the medium to detect through image processing the movement of the medium being conveyed.

Japanese Patent Application Laid-Open No. 2007-217176 discusses a method for detecting the movement of the medium. The method in Japanese Patent Application Laid-Open No. 2007-217176 images the surface of a moving medium a plurality of times in a time sequential manner by using an image sensor, and compares acquired images through pattern matching to detect an amount of movement of the medium. Hereinafter, a method for directly detecting the surface of an object to detect its moving state is referred to as direct sensing, and a detector employing this method is referred to as a direct sensor.

With direct sensing, a template pattern is extracted from first image data, and an area having a large correlation with the template pattern is sought among areas in second image data through image processing. In this process, a pattern which is identical or very similar to a certain template pattern may exist at a plurality of positions within a seek range. In this case, if a wrong position among the plurality of positions is determined in pattern matching, a detection error results. Therefore, for high-precision direct sensing, a template pattern becomes a unique pattern within the seek range.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an apparatus includes a conveyance mechanism including a conveyance belt having detection patterns containing a plurality of isolated patterns and configured to convey a medium in a predetermined direction, a sensor configured to capture an image of an area on the conveyance belt containing at least a part of the detection patterns to acquire first and second data, and a processing unit configured to extract a template pattern containing a part of the detection patterns from the first data, and seek an area having a correlation with the template pattern within a seek area of the second data to obtain a moving state of the conveyance belt, wherein form of the plurality of isolated patterns contained in the detection patterns, size of the template pattern, and size of the seek area are associated with each other so that the part of the detection patterns contained in the template pattern serves as a unique pattern in the seek area.

According to the present invention, direct sensing reliably enables detecting a moving state of an object with high precision.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. However, the components described in the following exemplary embodiments are illustrative and are not meant to limit the scope of the present invention.

The scope of the present invention widely ranges from a printer to a field of movement detection requiring high-precision detection of the movement of an object. For example, the present invention is applicable to printers, scanners, and other devices used in technical, industrial, and physical distribution fields for conveying an object and performing inspection, reading, processing, marking, and other various pieces of processing to the object. Further, the present invention is applicable to diverse types of printers including ink jet printers, electrophotographic printers, thermal printers, and dot impact printers. In the present specification, a medium means a sheet-like or plate-shaped medium such as paper, a plastic sheet, a film, glass, ceramics, resin, and so on. Further, in the present specification, the upstream and downstream sides mean the upstream and downstream sides of the sheet movement direction at the time of image recording on a sheet.

An embodiment of an ink jet printer which is an exemplary recording apparatus will be described below. The printer according to the present exemplary embodiment is termed a serial printer which alternately performs main scanning and sub scanning to form a two-dimensional image. With main scanning, the printer reciprocally moves a print head. With sub scanning, the printer conveys a medium in a stepwise feeding by a predetermined amount. The present invention is applicable not only to a serial printer but also to a line printer having a full line print head covering the print width which moves a medium with respect to the fixed print head to form a two-dimensional image.

FIG. 1is a sectional view illustrating a configuration of a part of a printer. The printer includes a conveyance mechanism for moving the medium in the sub scanning direction (first direction or a predetermined direction) by a belt conveyance system, and a recording unit configured to perform recording on the moving medium by using a print head. The printer further includes a rotary encoder133configured to indirectly detect a moving state of an object, and a direct sensor134configured to directly detect the moving state of the object.

The conveyance mechanism includes a first roller202and a second roller203which are rotating members, and a wide conveyance belt205applied between the first and second rollers by a predetermined tension. A medium206adhering to the surface of the conveyance belt205by electrostatic attraction or adhesion is conveyed by the movement of the conveyance belt205. The rotational force of the conveyance motor171, a driving source for sub scanning, is transmitted to the first roller202, i.e., a drive roller, via the drive belt172to rotate the first roller202. The first roller202and the second roller203rotate in synchronization with each other via the conveyance belt205. The conveyance mechanism further includes a feed roller pair209for separating one medium from media207loaded on a tray208and feeding it onto the conveyance belt205, and a feed motor161(not illustrated inFIG. 1) for driving the feed roller pair209. A paper end sensor132disposed on the downstream side of the feed motor161detects a leading edge or trailing edge of a medium to acquire a timing of medium conveyance.

The rotary encoder (rotational angle sensor)133is used to detect a rotating state of the first roller202to indirectly acquire the moving state of the conveyance belt205. The rotary encoder133including a photograph interrupter optically reads slits circumferentially arranged at equal intervals on a code wheel204coaxially attached to the first roller202to generate a pulse signal.

The direct sensor134is disposed below the conveyance belt205(on the rear surface side of the medium206, i.e., the side opposite to the side on which the medium206is loaded). The direct sensor134includes an image sensor (imaging device) for capturing an image of an area containing markers on the surface of the conveyance belt205. The direct sensor134directly detects a moving state of the conveyance belt205through image processing to be described below. Since the medium206firmly sticks to the surface of the conveyance belt205, a variation in the relative position by the slip between the surface of the conveyance belt205and the medium206is vanishingly small. Therefore, it is assumed that the direct sensor134can directly detect a moving state of the medium206. The function of direct sensor134is not limited to capturing an image of the rear surface of the conveyance belt205, but may be configured to capture an image of an area on the front surface of the conveyance belt205not covered by the medium206. Further, the direct sensor134may capture an image of the surface of medium206instead of the surface of the conveyance belt205.

The recording unit includes a carriage212reciprocally moving in the main scanning direction, a print head213, and an ink tank211, the latter two being mounted on the carriage212. The carriage212reciprocally moves in the main scanning direction (second direction) by the driving force of a main scanning motor151(not illustrated inFIG. 1). Nozzles of the print head213discharge ink in synchronization with the movement of the carriage212to perform printing on the medium206. The print head213and the ink tank211may be detachably attached to the carriage212either integrally as one unit or individually as separate components. The print head213discharges ink through the ink jet method. The ink discharge method may be based on a heater element, a piezo-electric element, an electrostatic element, an MEMS element, and so on.

FIG. 2is a system block diagram of the printer. A controller100includes a central processing unit (CPU)101, a read-only memory (ROM)102, and a random access memory (RAM)103. The controller100serves also as a control unit and a processing unit to perform various control of the entire printer as well as image processing. An information processing apparatus110is an apparatus which supplies image data to be recorded on a medium, such as a computer, a digital camera, a TV, and a mobile phone. The information processing apparatus110is connected with the controller100via an interface111. An operation unit120, which is a user interface for an operator, includes various input switches121including a power switch and a display unit122. A sensor unit130includes various sensors for detecting various states of the printer. A home position sensor131detects the home position of the carriage212reciprocally moving. The sensor unit130includes the above-mentioned paper end sensor132, the rotary encoder133, and the direct sensor134. Each of these sensors is connected to the controller100. Based on commands of the controller100, the print head and various motors for the printer are driven via respective drivers. A head driver140drives the print head213according to record data. A motor driver150drives the main scanning motor151. A motor driver160drives the feed motor161. A motor driver170drives the conveyance motor171for sub scanning.

FIG. 3illustrates a configuration of the direct sensor134for performing direct sensing. The direct sensor134is a single sensor unit which includes a light-emitting unit including a light source301such as a light-emitting diode (LED), an organic light-emitting diode (OLED), and a semiconductor laser; a light receiving unit including an image sensor302and an imaging optical system303such as a refractive-index distribution lens array; and a circuit unit304such as a drive circuit and an A/D converter circuit. The light source301illuminates a part of the rear surface of the conveyance belt205which is an image capture target. The image sensor302images via the imaging optical system303a predetermined imaging area illuminated by the light source301. The image sensor302is a two-dimensional area sensor such as a CCD image sensor and a CMOS image sensor, or a line sensor. An analog signal from the image sensor302is converted to digital form and captured as digital image data. The image sensor302is used to image the surface of an object (conveyance belt205) and acquire a plurality of pieces of image data at different timings (these pieces of image data acquired in succession are referred to as first and second image data). As described below, by extracting a template pattern from the first image data, and seeking an area in the second image data having a large correlation with the extracted template pattern through image processing, the moving state of the object can be acquired. The image processing may be performed by the controller100or a processing unit included in the unit of the direct sensor134.

FIG. 4is a flow chart illustrating processing of medium feeding, recording, and discharging. This processing is performed based on commands of the controller100. In step S501, the processing drives the feed motor161to rotate the feed roller pair209to separate one medium from the medium207on the tray208and feed it along the conveyance path. When the paper end sensor132detects the leading edge of the medium206being fed, the processing performs the medium positioning operation based on the detection timing to convey the medium to a predetermined recording start position.

In step S502, the processing conveys the medium in a stepwise feeding by a predetermined amount by using the conveyance belt205. The predetermined amount equals the length in the sub scanning direction in recording of one band (one main scanning of the print head). For example, when performing multipass recording in a two-pass manner while causing each stepwise feeding by the length of a half of the nozzle array width in the sub scanning direction of the print head213, the predetermined amount equals the length of a half of the nozzle array width.

In step S503, the processing performs recording for one band while moving the print head213in the main scanning direction by the carriage212. In step S504, the processing determines whether recording of all record data is completed. When the processing determines that recording is not completed (NO in step S504), the processing returns to step S502to repeat recording in a stepwise feeding (sub scanning) and one band (one main scanning). When the processing determines that recording is completed (YES in step S504), the processing proceeds to step S505. In step S505, the processing discharges the medium206from the recording unit, thus forming a two-dimensional image on the medium206.

Processing of the stepwise feeding in step S502will be described in detail below with reference to the flow chart illustrated inFIG. 5. In step S601, an image of an area containing markers of the conveyance belt205is captured by using the image sensor of the direct sensor134. The acquired image data denotes the position of the conveyance belt205before starting movement and is stored in the RAM103. In step S602, while monitoring the rotating state of the roller202by the rotary encoder133, the processing drives the conveyance motor171to move the conveyance belt205, in other words, starts conveyance control for the medium206. The controller100performs servo control so that the medium206is conveyed by a target conveyance amount. The processing executes step S603and subsequent steps in parallel with the medium conveyance control using the rotary encoder133.

In step S603, an image of the conveyance belt205is captured by using the direct sensor134. Specifically, the processing starts imaging the conveyance belt205when the medium is assumed to have been conveyed by a predetermined amount based on the target amount of medium conveyance (hereinafter referred to as target conveyance amount) to perform recording for one band, the image sensor width in the first direction, and the medium movement speed. In this example, a specific slit on the code wheel204to be detected by the rotary encoder133when the medium has been conveyed by a predetermined conveyance amount is specified, and the processing starts imaging the conveyance belt205when the rotary encoder133detects the slit. Step S603will be described in detail below.

In step S604, through image processing, the processing detects the distance over which the conveyance belt205has moved between imaging timing of the second image data in step S603and that of the first image data in the previous step. Processing for detecting an amount of movement will be described below. An image of the conveyance belt205is captured the number of times predetermined for the target conveyance amount at predetermined intervals. In step S605, the processing determines whether the image of the conveyance belt205has been captured the predetermined number of times. When the image of the conveyance belt205has not been captured the predetermined number of times (NO in step S605), the processing returns to step S603to repeat processing until imaging is completed. The processing repeats the processing the predetermined number of times while accumulating a conveyance amount each time a conveyance amount is detected, thus obtaining a conveyance amount for one band from the timing of first imaging in step S601. In step S606, the processing calculates a difference between a conveyance amount acquired by the direct sensor134and a conveyance amount acquired by the rotary encoder133for one band. Since the rotary encoder133indirectly detects a conveyance amount while the direct sensor134directly detects a conveyance amount, the detection precision of the former is lower than that of the latter. Therefore, the above-mentioned difference can be recognized as a detection error of the rotary encoder133.

In step S607, the processing corrects medium conveyance control by the detection error amount of the rotary encoder obtained in step S606. There are two different correction methods: a method for increasing or decreasing the current position information for medium conveyance control by the detection error, and a method for increasing or decreasing the target conveyance amount by the detection error. Either method can be employed. When the processing has accurately conveyed the medium206by the target conveyance amount through feedback control, the conveyance operation for one band is completed.

FIG. 6illustrates in detail direct sensing in step S604.FIG. 7schematically illustrates first image data700and second image data701of the conveyance belt205acquired in imaging by the direct sensor134. A black dot pattern702(a portion having a luminance gradient) in the first image data700and the second image data701is an image of one of many markers applied to the conveyance belt205on a random basis or based on a predetermined rule. When the subject is a medium as is the case with the apparatus illustrated inFIG. 2, a microscopic pattern on the surface of the medium (for example, a paper fiber pattern) plays a similar role to the markers. The processing sets a template area at an upstream position in the first image data700, and extracts an image of this portion as a template pattern703. When the second image data701is acquired, the processing searches for a position (within the second image data701) of a pattern similar to the extracted template pattern703. Search is made by using a technique of pattern matching. Any one of known similarity determination algorithms including sum of squared difference (SSD), sum of absolute difference (SAD), and normalized cross-correlation (NCC) can be employed. In this example, a most similar pattern is located in an area704. The processing obtains a difference in the number of pixels of the image sensor (imaging device) in the sub scanning direction between the template pattern703in the first image data700and the area704in the second image data701. By multiplying the difference in the number of pixels by the distance corresponding to one pixel, the amount of movement (conveyance amount m) can be obtained.

FIG. 7is a schematic view of the inside of the conveyance belt205, i.e., a part of an endless belt. An optically recognizable detection pattern290is marked in an area on the inner surface of the belt facing the image sensor. The detection pattern290is formed over the entire circumferential surface of the conveyance belt205along the moving direction (y direction). The detection pattern290is marked with at least any one of the following methods (1) to (6).(1) Directly paint a coating material onto the conveyance belt.(2) Stick a patterned seal on the conveyance belt.(3) Form concave and convex portions on the surface of the conveyance belt.(4) Scrape the film surface of the conveyance belt.(5) Apply laser marking to the material of the conveyance belt.(6) Form a non-transparent pattern on the inner surface of a transparent conveyance belt.

FIG. 8is an enlarged view of a detection pattern290marked on the conveyance belt205. The detection pattern290is oblong along the moving direction (y direction). In one embodiment, the lateral size of the detection pattern290is equal to or larger than the imaging area of the image sensor, and is 2.000 mm in this example. The detection pattern290is formed by repetitively arranging a unit pattern over the entire circumferential surface of the conveyance belt205. The unit pattern has a predetermined unit length (one period) not less than the moving directional length of the imaging area to be imaged by the image sensor. In this example, the circumferential length of the conveyance belt205is 256 mm, and one unit is 12.800 mm which is 1/20 of the circumferential length of the conveyance belt205.

Each unit pattern (one unit) forming the detection pattern290includes a plurality of isolated patterns arranged so that all of the five rules (first to fifth rules) described below are satisfied.

The first rule is that one or more isolated patterns exist in the template area from which a template pattern is extracted. The size of the template area is associated with isolated patterns so that one or more isolated patterns are invariably contained in the template pattern extracted from the first image data700. To satisfy this condition, a moving directional interval between isolated patterns contained in a unit pattern is made smaller than the moving directional size of the template area.

If the pitch of isolated patterns is much larger than the size of the template area, there may be a situation that the template area contains no isolated pattern and a blank template pattern is invariably acquired. There may be another situation that a template pattern containing only apart of one isolated pattern is acquired and a blank template pattern is acquired in other cases. Such a template pattern does not serve as a unique pattern in a seek area in which the second image data701is sought, and therefore may cause a detection error in pattern matching.

The second rule is that each individual isolated pattern is given uniqueness with which each pattern is distinguishable from other ones. A method for giving uniqueness to each isolated pattern is to differentiate isolated patterns in at least any one of size, shape, contrast, density, color, and arrangement. If the seek area in the second image data contains a plurality of patterns identical or very similar to the template pattern, the template pattern does not serve as a unique pattern and therefore may cause a detection error in pattern matching.

FIG. 9illustrates an exemplary unit pattern satisfying the above-mentioned first and second rules. Referring toFIG. 9, dashed lines3109illustrate a template area to be extracted as a template pattern in the first image data. The size of this template area is such that the template area can contain at least a part of any one isolated pattern. As the second rule, a plurality of isolated patterns contained in one unit is different in size. In one embodiment, to give uniqueness in size to each isolated pattern, the minimum size difference is equal to or larger than the pixel pitch of the image sensor. In this example, isolated patterns3101,3102,3103, and3104are 1.600 mm, 1.400 mm, 1.200 mm, and 1.000 mm in diameter, respectively. Differentiating isolated patterns in size in this way enables distinguishing each individual isolated pattern from other ones in terms of the size regardless of whether all or part of these isolated patterns are contained in the template pattern.

The third rule is a condition related to the interval between adjacent isolated patterns based on the moving speed. The moving directional interval between adjacent isolated patterns is made larger than the moving distance of the conveyance belt205during an exposure time for one image capturing. In this example, the maximum moving speed of a speed range detectable with direct sensing is 400 mm/s, and the exposure time for one image capturing by the image sensor, i.e., exposure time for acquisition of one image, is 1 ms. Therefore, the maximum moving distance during the exposure time for one image capturing is 400 mm/s×1 ms=400 μm. Therefore, the interval between any two adjacent isolated patterns is made larger than 400 μm. Referring toFIG. 9, intervals3105,3106,3107, and3108between isolated patterns are 1.600 mm, 1.800 mm, 2.000 mm, and 2.200 mm, respectively, which are sufficiently larger than 400 μm.

A reason for the above will be described below. When imaging an object moving at high speed, acquired image data involves image extension in the moving direction as seen in defocusing by camera shake. A difference in moving speed at the time of imaging of the first and second image data may degrade the accuracy of pattern matching since the two pieces of image data are different in amount of image extension. Although with an exposure time sufficiently shorter than the moving speed, image extension can be restrained, an integrated amount of incident light decreases, which results in degradation of image contrast and an increase in image noise.

Referring toFIG. 10, image data3601is obtained by imaging an isolated pattern (having a diameter of 160 μm) in a motionless state during a 1 ms exposure time by using an image sensor having a pixel pitch of 12 μm. On the other hand, image data3602is obtained by imaging the same isolated pattern while it is moving at a speed of 150 mm/s.FIG. 11illustrates states of first image data4100and second image data4101.

Although an identical isolated pattern has been imaged, the image data3602has an oblong isolated pattern shape in the moving direction in comparison with the image data3601. Further, the image data3602has slightly defocused edge portions (having a moderate density transition) in comparison with the image data3601. The amount of extension is determined by the product of the moving speed and the exposure time. Therefore, a difference in moving speed at the time of first and second image data acquisitions results in different image shapes of the isolated pattern because of a difference in amount of image extension.

FIG. 12is a graph illustrating a relation between the amount of image extension (μm) and the pattern detection accuracy (μm).FIG. 12demonstrates that the pattern detection accuracy decreases (the value of ±3σ increases) with increasing amount of image extension. Therefore, when image extension occurs, an isolated pattern changes in shape, and the pattern detection accuracy in pattern matching decreases.

Further, this phenomenon of image extension causes image interference between adjacent isolated patterns possibly resulting in degradation of pattern detection accuracy. A mechanism of image extension and a method for restraining image extension will be described below. Referring toFIG. 13, image data3801and3802denote two different isolated patterns having an interval between adjacent isolated patterns of 34 μm and 70 μm, respectively.FIG. 14is a graph illustrating change in pattern detection accuracy with respect to change in the amount of image extension.FIG. 14demonstrates that a difference in interval between adjacent isolated patterns causes a difference in amount of image extension with which the pattern detection accuracy rapidly decreases. This difference arises because image interference between adjacent isolated patterns by image extension is more likely to occur as an interval between adjacent isolated patterns becomes smaller. Image data3803inFIG. 13illustrates a state of image interference caused by image extension. When image interference occurs, the shape of the isolated pattern is largely deformed causing remarkable degradation in pattern detection accuracy. When an interval between adjacent isolated patterns is 34 μm, image interference occurs with less amount of image extension than when an interval therebetween is 70 μm. For this reason, a difference in tendency of accuracy degradation arises.

To restrain effects of image extension and image interference, the interval, in a moving direction between adjacent isolated patterns, is made larger than the moving distance of the conveyance belt during the exposure time for one image capturing by the image sensor.

The fourth rule is a condition related to the interval between adjacent isolated patterns based on the characteristics of the imaging optical system303included in the direct sensor.

The above-mentioned third rule pays attention to image interference between isolated patterns. One of causes of image interference between isolated patterns is the aberration performance of the imaging optical system303. More specifically, inferior aberration performance of the imaging optical system303included in the direct sensor causes image defocusing and deformation of an image captured by the image sensor, which possibly results in the above-mentioned image interference.

FIG. 15illustrates a defocusing state of a captured image of isolated patterns illustrated inFIG. 9. Each of defocused isolated patterns has a larger size and a lower contrast than a focused isolated pattern (white dashed lines). Therefore, since the interval between adjacent isolated patterns decreases, image interference is more likely to occur. To restrain this phenomenon, patterning with wider intervals is performed while predicting image extension and image deformation in consideration of the aberration performance of the imaging optical system303. In other words, the interval in the moving direction between adjacent isolated patterns is maintained so that image interference between isolated patterns does not occur by the effect of aberration of the imaging optical system303when an image is captured by the image sensor.

In one embodiment, the fifth rule is a condition related to the isolated pattern size. When a phenomenon of image extension occurs, the contrast (gray scale) of the image of the isolated pattern decreases. Each graph illustrated inFIG. 10denotes a density transition of isolated pattern for each of the image data3601and3602. The image data3602has a more moderate density transition at edge portions and a narrower range of the peak density value than the image data3601. This means that the peak density value further decreases when the amount of image extension exceeds the isolated pattern size. This phenomenon becomes noticeable when the isolated pattern size is small with respect to image extension. In image correlation processing for pattern matching, a decrease in contrast (decrease in the amount of pixel gradation information) causes a quantization error, which possibly results in degradation of pattern detection accuracy. To acquire sufficient gradation information even in the case of image extension, the isolated pattern size in the moving direction is larger than the amount of image extension. More specifically, the size of each of the isolated patterns in the moving direction is larger than the moving distance of the conveyance belt during the exposure time at the time of one image capturing. Further, the size is at least four times the size of one pixel of the image sensor.

FIG. 16illustrates a modification of the second rule. In the modification, each isolated pattern is given uniqueness by being differentiated in shape. Referring toFIG. 16, dashed lines denote a template area to be extracted as a template pattern in the first image data. The size of this template area is such that it can contain at least a part of any one isolated pattern. A size (diameter) of each of four isolated patterns3201,3202,3203, and3204in the moving direction is identical and 1.600 mm, but is different in size (diameter) in a direction perpendicular to the moving direction (also referred to as other direction). In this example, isolated patterns3201,3202,3203, and3204are 1.600 mm, 1.400 mm, 1.200 mm, and 1,000 mm in size in the other direction, respectively. The isolated pattern3201is a true circle. The isolated patterns3202,3203, and3204are ellipses differentiated in shape, i.e., gradually collapsing in the moving direction. As a result, the shape of each isolated pattern contained in the template pattern is given uniqueness.

FIG. 17illustrates another modification of the second rule. In the modification, each isolated pattern is given uniqueness by being differentiated in at least any one of contrast, density, and color. Each of four isolated patterns3301,3302,3303, and3304is identical in shape and size (a true circle having a diameter of 1.600 mm), but is different in contrast (gray scale), density, or color. As a result, each isolated pattern contained in the template pattern is given uniqueness by being differentiated in contrast, density, or color.

FIG. 18illustrates still another modification of the second rule. In the modification, each isolated pattern is differentiated in interval in a moving direction. Each isolated pattern is identical in shape and size (a true circle having a diameter of 0.500 mm), but is different in interval to an adjacent isolated pattern (intervals3401,3402,3403,3404,3405, and3406). In this example, the intervals3401,3402,3403,3404,3405, and3406are 2.000 mm, 1.800 mm, 1.600 mm, 1.400 mm, and 1.000 mm, respectively. As a result, each isolated pattern contained in the template pattern is given uniqueness by being differentiated in interval to an adjacent isolated pattern.

FIG. 19illustrates still another modification of the second rule. In the modification, each isolated pattern is differentiated both in interval in a moving direction and in interval in a direction perpendicular to the moving direction. Each isolated pattern is identical in shape and size (a true circle having a diameter of 1.000 mm) and in interval in the moving direction to an adjacent isolated pattern, but is different in interval to an adjacent isolated pattern in a direction perpendicular to the moving direction (intervals3501,3502,3503,3504,3505,3506,3506, and3507). In this example, the intervals3501,3502,3503,3504,3505,3506,3506, and3507are 0.200 mm, −0.200 mm, 0.400 mm, −0.400 mm, 0.600 mm, −0.600 mm, and 0.800 mm, respectively. As a result, each isolated pattern contained in the template pattern is given uniqueness by being differentiated in interval to an adjacent isolated pattern in a direction perpendicular to the moving direction. Isolated patterns may be arranged based on the modifications ofFIGS. 19 and 18, i.e., each isolated pattern may be differentiated both in interval in a moving direction and in interval in a direction perpendicular to the moving direction.

Any combination of the above-mentioned modifications may be used. More specifically, each isolated pattern is given uniqueness with which each pattern is distinguishable from other ones, by being differentiated in at least anyone of size, shape, contrast, density, and color. Although the above descriptions have been made based on cases where each isolated pattern has a circular form, the isolated pattern shape is not limited thereto but may be any other shape, for example, a polygon (a rectangle or triangle) and any combination of polygons and circles.

As mentioned above, the form of each isolated pattern in a detection pattern, the size of a template area from which the template pattern is to be extracted, and the size of the seek area are associated with each other so that a part of the detection pattern contained in the template pattern serves as a unique pattern in the seek area. If accuracy degradation is permissible to a certain extent, it is not necessary to satisfy all of the above-mentioned five rules. For example, only the first and second rules may be applied. Alternatively, at least any one of the third to fifth rules may be added to the first and second rules.

According to the above-mentioned exemplary embodiments, pattern matching can be accurately determined and high-precision direct sensing can be achieved. Accordingly, media can be conveyed with high precision, thus a recording apparatus capable of high-quality image recording is achieved.

This application claims priority from Japanese Patent Application No. 2009-250830 filed Oct. 30, 2009, which is hereby incorporated by reference herein in its entirety.