1. Field of the Invention
The present invention relates to the technical field of sheet conveying preferably used in a printing apparatus.
2. Description of the Related Art
A printing apparatus has strict print quality-related requirements and now has a requirement for a further-improved accuracy. Thus, in order to detect the move of a sheet accurately to thereby realize a stable conveying by a feedback control, an attempt has been made to capture the surface of a sheet by an image sensor to detect the move of a conveyed sheet by an image processing.
U.S. Pat. No. 7,104,710 discloses a method for detecting this move of a sheet. This method captures the surface image of a moving sheet by an image sensor a plurality of times to compare a plurality of resultant images by a pattern matching processing to detect a sheet moving distance based on the displacement amount the images. A sensor of the type according to which the sheet image is captured to obtain the image data to subject the data to an image processing to directly detect the sheet moving will be hereinafter referred to as a direct sensor.
The direct sensor requires a huge amount of computation required for the image processing for the pattern matching. If the direct sensor tries to cope with a higher speed (printing speed), the direct sensor must detect the move within a shorter time, thus requiring a processor having a very high computational power. This consequently causes a higher cost, causing an increasing cost for the printing apparatus.
The present invention has been made in view of the above disadvantage. It is an objective of the invention to further improve the conventional apparatus. A specific objective of the present invention is to allow an apparatus using a direct sensor to directly detect an object to thereby cope with an object moving with a higher speed (higher printing operation) than in the conventional case. A further objective of the present invention to allow the direct sensor to detect the moving information within a short time even when the processing section has a smaller computational power than in the conventional case.
The present invention solving the above disadvantage is an apparatus comprising: a mechanism for causing an object to move; an information acquisition unit which acquires information regarding a driving amount of the mechanism; a sensor for capturing a surface of the object to acquire image data; a processing section for processing a first image data and a second image data acquired by using the sensor at different timings to thereby obtain moving information of the object; and a control unit for controlling the mechanism based on the moving information obtained by the processing section, wherein: the processing section performs processings of:(a) cutting out an image pattern of a region of a part of the first image data; (b) limiting a search range in the second image data within which a similar region similar to the image pattern is searched based on the information acquired by the information acquisition unit; (c) searching the similar region within the limited search range in the second image data; and (d) obtaining the moving information of the object based on a positional relation between the image pattern in the first image data and the similar region in the second image data.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. However, constituting elements shown in the illustrated embodiment are only illustrative and do not limit the scope of the present invention.
The present invention can be widely used in the field of moving detection for accurately detecting the moving of a sheet-like object as in a printing apparatus for example. The invention can be used, for example, for machines such as a printing apparatus and a scanner as well as industrial and distribution-related machines for conveying an object to subject the object to various processings in a processing section such as inspection, reading, treatment, and marking. Furthermore, when the present invention is applied to a printer, the present invention also can be used not only for a single-function printer but also for a so-called multifunction printer having a copying function and an image scanning function for example. The invention can be used for various printing methods such as an ink jet method, an electrophotographic method, and a thermal transfer method.
A print medium 8, which are sheet-like objects such as papers or thin plastic plates, are provided on an auto sheet feeder 32. When a printing operation is started, a paper-feeding motor 35 is driven and this driving force is transmitted to pickup rollers 31 via a gear for example. The rotation of the pickup rollers 31 causes the print medium 8 to be separated from the auto sheet feeder 32 one by one and are fed to the interior of the printing apparatus. During this feeding, a paper sensor 33 detects the existence or nonexistence of the print medium 8 to thereby determine whether the paper-feeding is performed correctly or not. By the rotation of the first conveying roller 9 as a rotating body, the fed print medium 8 is conveyed, while being abutted with the first conveying roller 9, at a predetermined speed in the direction Y.
With reference to
With reference to
The head cartridge 1 provided in the carriage 2 includes: the printing head 26 for ejecting ink based on the ink jet method; and an ink tank for storing ink to be supplied to the printing head 26. The printing head 26 is structured to eject, while moving together with the carriage 2 in the direction X, ink to the print medium 8 moving at the lower side at a predetermined timing and based on an image signal.
The printing apparatus of this embodiment is a serial-type ink jet printing apparatus. The direction along which the ejection openings 22 are arranged is in the direction intersecting with the moving direction of the carriage 2 (direction X). An image is formed on the print medium 8 by alternately repeating a printing scanning for ejecting ink through the ejection openings 22 while reciprocating the carriage 2 and a conveyance operation for rotating the first conveying roller 9 and the second conveying roller 10 to thereby convey, by a predetermined amount, the print medium in a stepwise manner in the direction Y. Alternatively, another printing method also may be used where the carriage 2 is reciprocated in the direction X simultaneously with conveyance of the print medium in an uninterrupted and continuous manner.
A side face of the carriage 2 has a direct sensor unit 16 for capturing the surface of the print medium 8 to directly sense the conveyed amount based on an image processing. The direct sensor unit 16 may be provided at any position so long as the sensing region thereof covers positions where the print medium passes. The direct sensor unit 16 may be provide at the side of the platen 17 in
The acquired image data herein means image information which characterizes a partial surface status of the print medium 8 and is based on an input values obtained from the capturing of the image capturing element 42. For example, the acquired image data may be information representing the shading appearing due to the surface shape of the print medium 8 (e.g., the fiber pattern of a paper) or a pattern printed on the surface in advance.
In
The direct sensor unit 16 also can be used for, in addition to the measurement of the moving information of the print medium, another purpose of determining the existence or nonexistence of the print medium based on the detection value of the direct sensor unit 16 (for example, a average value of the outputs about the pixels).
Image data, a command, and a status signal for example supplied from the host apparatus 110 can be transmitted to or received from the controller 100 via an interface (I/F) 112. An operation unit 120 is composed of a group of switches through which an instruction inputted by an operator is received. The operation unit 120 has a power source switch 122 and a recovery switch 126 for instructing the start of the recovery of absorption for example. A sensor unit 130 is composed of a group of sensors for detecting the status of the apparatus. In this embodiment, the sensor section 130 includes the above-described home position sensor 30, the paper sensor 33, the direct sensor unit 16 and the rotation angle sensor 18 for detecting the conveyed amount, and a temperature sensor 134 for detecting the environment temperature for example.
The reference numeral 140 denotes a head driver that drives the electrothermal transducing elements 25 of the printing head 26 depending on the printing data. The head driver 140 includes a shift register that arranges the printing data so as to correspond to the respective plurality of electrothermal transducing elements 25 and a latch circuit latched at an appropriate timing. The head driver 140 also includes a logic circuit element that causes, in synchronization with the driving timing signal, the electrothermal transducing element 25 to operate and a timing setting section for appropriately setting the discharge timing in order to adjust the positions of dots on the print medium for example.
In the vicinity of the printing head 26, a subheater 142 is provided that adjusts the temperature of the printing head 26 in order to stabilize the ink ejecting characteristic. The subheater 142 may be provided on a substrate of the printing head 26 as in the electrothermal transducing element 25 or also may be attached to the body of the printing head 26 or the head cartridge 1. The reference numeral 150 denotes a motor driver for driving the carriage motor 4. The reference numeral 160 denotes a motor driver for driving the paper-feeding motor 35. The reference numeral 170 denotes a motor driver for controlling the driving of the conveying motor 14.
In the above-described printing apparatus, the print medium is conveyed while being sandwiched at positions of the first conveying roller 9 and the second conveying roller 10, respectively. Another conveying mechanism for conveying a print medium also may be used in which the print medium is retained and transferred by a belt. This belt conveyance mechanism has rotation rollers provided at a plurality of positions and a belt extending among the plurality of rotation rollers. The rotation of the rotation rollers rotates the belt to thereby cause the print medium provided on the belt to move. The information acquisition means acquires the information regarding the rotation amount of a rotation roller or a rotation gear among the plurality of rotation rollers or gears. However, the information is not limited to the information regarding only one rotation roller or only one rotation gear. The information also may be information regarding of a plurality of rotation roller or a plurality of rotation gear.
The belt 19 has thereon the print medium 8 in a manner that the print medium 8 is closely provided on the belt 19 by electrostatic adsorption. The print medium 8 is conveyed, in accordance with the rotation of the belt 19, from the upstream to the downstream in the shown direction Y. The direct sensor unit 16 provided in the carriage 2 captures the surface of the print medium 8 or the surface of the belt 19 to thereby acquire the image data. The direct sensor may be provide at the back side of the belt to detect the inside surface of the belt. The print medium 8 on the belt 19 is strongly retained by electrostatic adsorption and thus is substantially prevented from being slipped or dislocated from the belt 19. Thus, capturing the belt 19 to calculate the moving of the belt is equivalent to calculating the moving of the print medium 8.
Next, the following section will describe a method of using the above-described printing apparatus to carry out a conveyance control at a higher speed than in the conventional case while using both of the conveyance information obtained from the rotation angle sensor 18 and the conveyance information obtained from the direct sensor unit 16 in accordance with some examples.
When the printing operation is started based on a printing start command from the host apparatus 110, the CPU 101 drives the paper-feeding motor 35 to feed one print medium 8 from the auto sheet feeder 32 (STEP 1). Next, STEP 2 causes the CPU 101 to determine whether the paper sensor 33 senses the tip end of the print medium 8 or not. When determining that the tip end of the print medium 8 is detected, then the processing proceeds to STEP 3. When determining that the tip end of the print medium 8 is not yet detected in STEP 2 on the other hand, the processing returns to STEP 1 and continues the paper-feeding operation. Thereafter, until the tip end of the print medium is sensed, STEP 1 and STEP 2 are repeated. In
In STEP 3, the CPU 101 starts the driving of the conveying motor 14 and simultaneously starts the detection by the rotation angle sensor 18 of the rotation amount of the code wheel 13. As a result, the print medium 8 is conveyed in the direction Y based on the information from the rotation angle sensor 18. This will be described specifically below. The CPU 101 determines the rotation amount and the rotation speed of the conveying roller 9 based on a timing at which the rotation angle sensor 18 senses a slit formed in the code wheel 13. Then, the control unit performs the conveyance control while feeding back this actual measurement value to the driving of the conveying motor 14.
Next, in STEP 4, the CPU 101 determines whether the direct sensor unit 16 senses the print medium 8 or not. When determining that the direct sensor unit 16 senses the print medium 8, the processing proceeds to STEP 5 and an actual conveyance amount detection sequence (which will be described later) is carried out. When determining that the direct sensor unit 16 has not sensed the print medium 8 yet on the other hand, the processing returns to STEP 3. Then, until the direct sensor unit 16 senses the print medium 8, the steps of STEP 3 and STEP 4 are repeated. In
Again, with reference to the flowchart of
In STEP 7, the CPU 101 uses the printing head 26 to perform a printing operation for one line based on the image data while causing the carriage 2 to move in the direction X. Next, in STEP 8, the CPU 101 determines whether the printing of the image data for one page is completed or not. When determining that not-yet-printed image data is still left, the processing returns to STEP 5 to subject the next line to the actual conveyance amount detection sequence. In STEP 8, until it is determined that the printing of the image data for one page is completed, the actual conveyance sequence and the printing operation as described above are repeated. In
Next, the following section will describe in detail the actual conveyance detection sequence performed in STEP 5.
When the actual conveyance detection sequence is started, the CPU 101 in Step A01 uses the direct sensor unit 16 to acquire the image of the print medium 8 as the first image data (1501). When the direct sensor unit 16 in the configuration of
The CPU 101 in Step A02 causes a matching region having a region of 5 pixels×5 pixels to be positioned at an appropriate position at the upstream-side of the first image data 1501.
In Step A03, based on the information from the rotation angle sensor 18 (i.e., while counting the actually-measured conveyed amount obtained from the rotation angle sensor 18), the print medium 8 is conveyed by the target amount (one stepwise travel) in the direction Y and this conveyed amount (moving distance) is stored. In this example, it is assumed that the actually-measured conveyed amount obtained from the rotation angle sensor 18 is 120 μm.
In Step A04, the CPU 101 uses the direct sensor unit 16 to acquire the image of the print medium 8 (or the belt 19) as the second image data (1503) at a timing different from the timing at which the first image data is acquired.
In Step A05, based on the conveyed amount (120 μm) stored in Step A03, a region (search range) that is for performing a correlation processing for searching the matching pattern in the second image data 1503 and that is a limited region in the entire image region.
The reason why the search range is provided with regard to the estimated region 1504 not only in the direction Y but also in the direction X is that, when the print medium is conveyed in the direction Y, the print medium may not be caused to accurately move in the direction Y and may be displaced also in the direction X (positional deviation phenomenon). In consideration of such an positional deviation phenomenon, the limited region is provided as a correlation computation search range around the estimated region 1504 so that the limited region includes margins corresponding to the predetermined number of pixels in the direction X and the direction Y. The range may be appropriately determined depending on the conveying accuracy or printing resolution of printing apparatus or the sizes of the image capturing element (photoelectric conversion element) for example and is not limited to the above value.
As described above, in the processing of A5, the range within which a similar region in the second image data that is similar to the image pattern cut out from the first image data is searched is limited based on the information acquired by the rotary encoder (information acquisition means). In particular, the neighboring range of the estimated position away from the image pattern of the first image data by the moving distance from the timing at which the first image data estimated based on the information acquired by the information acquisition means is acquired to the timing at which the second image is acquired is set as the search range for the second image data. The search range is set as a region obtained by adding, to the estimated position, a predetermined number of pixels to both of the upstream-side and the downstream-side of the moving direction of the print medium and adding a predetermined number of pixels to left and right sides in the width direction of the print medium orthogonal to the moving direction.
In Step A06, the search range set in Step A05 is subjected to the correlation computation processing in an order from an end pixel. In the processing of Step A06, with regard to the second image data, a similar region similar to the image pattern cut out from the first image data is searched in the limited search range (1603) as described above.
Here, the similarity degree is calculated by using SSD (Sum of Squared Difference) for example. SSD sets a discrepancy degree S which is obtained as a sum of absolute values of differences between each pixel f (I, j) in the matching pattern and each pixel g (I, j) in the matching region. Regarding SSD, as the discrepancy degree is smaller the similar degree is larger.
In Step A07, based on the relative positional relation between the matching region obtained in Step A06 and the matching region stored in Step A02 (a difference in the number of pixels), the actual moving amount of the print medium in the conveyance operation of Step A03 is calculated. Specifically, the processing of Step A07 calculates the moving information based on the positional relation (or an interval) between the image pattern cut out from the first image data and the most similar region in the second image data. In the case of this example, the positional relation corresponds to 13 pixels in the direction Y and thus the actual moving amount of the print medium is 130 μm. Then, the actual conveyance amount detection sequence in STEP 5 of
As described above, a target region of the correlation computation processing is reduced and the computation amount is significantly reduced by setting the search range that is limited based on the conveyed amount obtained from the information acquisition means (rotary encoder) for acquiring the information regarding the driving amount of the mechanism. In the case as in the conventional technique where the range for the correlation processing covers all regions of the second image data 1503, the correlation computation must be performed 16×7=112 times as shown in
In this example, the information acquisition means obtains the information regarding the driving amount of the conveying mechanism from an output value from the rotary encoder. This information functions as a key to estimate where the matching pattern cut out from the first image data is positioned in the second image data. However, the invention is not limited to this and another configuration also may be used. For example, if the conveying motor 14 is a stepping motor, the driving amount can be estimated based on the number of driving pulses. Based on the number of driving pulses, the moving distance between a timing at which the first image data is obtained and a timing at which the second image data is obtained is estimated. Based on this estimated moving distance, the search region is set. Specifically, the information acquisition means acquires the value obtained based on the number of driving pulses of the stepping motor of the driving mechanism as the information regarding the driving amount.
Another method also may be used to acquire the information regarding the driving amount of the conveying mechanism by acquiring this information based on a target control value in the conveyance control in one step in the conveyance control in the controller. Based on the target control value, the moving distance between a timing at which the first image data is obtained and a timing at which the second image data is obtained is estimated. Based on this estimated moving distance, the search region is set. Specifically, the information acquisition means acquires a value obtained based on the target control value in the control unit for controlling the driving of the driving mechanism as the information regarding the driving amount.
Still another method also may be used to acquire the information regarding the driving amount of the conveying mechanism based on a driving profile in the conveyance control by the controller. Based on the control profile, the moving distance between a timing at which the first image data is obtained and a timing at which the second image data is obtained is estimated. Based on this estimated moving distance, the search region is set. Specifically, the information acquisition means acquires the value obtained based on the driving profile of the driving mechanism in the control unit as the information regarding the driving amount.
The correlation processing for making comparison of feature points on image captured by the direct sensor unit is not limited to the configuration using a patterned image as described above. For example, another configuration also may be used where the information regarding reflected light obtained from the direct sensor unit is subjected to Fourier transformation and information obtained at different timings are checked for the matching with regards to each frequency. Alternatively, a moving distance between peak parts also may be acquired. Alternatively, speckle patterns caused by the interference with the reflected light from a coherent light source for example also may be compared. Any these methods must use the correlation processing means that can make comparison between the feature points of two types of image data.
Example 1 assumes a case where one target conveyed amount (one stepwise conveyance operation) is smaller than the detection region of the capturing element of the direct sensor unit 16 and one characteristic pattern (cross-shape pattern) is included in both of two pieces of image data acquired at different timings. In contrast with this, Example 2 is a control method for a case where one stepwisely-conveyed amount is larger than the length of arranged pixels of the direct sensor unit 16. The basic concept of this method is that a plurality of pieces of the image data are acquired in one stepwise moving to thereby perform the conveyance control.
The construction of the apparatus in Example 2 is the same as that in Example 1. The entire sequence is the same as that described in the flowchart of
When the actual conveyance amount detection sequence is started, the CPU 101 in Step B01 uses the direct sensor unit 16 to acquire the image of the print medium 8 as the first image data (2101). When the direct sensor unit 16 is used to capture the surface of the belt 19 in the configuration of
In Step B02, the CPU 101 causes the matching region having a region of 5 pixels×5 pixels to be positioned at an appropriate position at the downstream-side of the first image data 2101.
In Step B03, based on the information from the rotation angle sensor 18 (i.e., while counting the actually-measured conveyed amount obtained from the rotation angle sensor 18), the conveyance of the print medium 8 in the direction Y is started.
When the predetermined time or the predetermined count amount smaller than one stepwise moving has passed, the direct sensor unit 16 is used in Step B04 while the conveyance operation being performed to acquire the image of the print medium 8 (or the belt 19) as the second image data (2103).
In Step B05, based on the conveyed amount count value at the acquisition of the second image data, a limited search range in the second image data 2103 is set. The method of setting the search range is the same as that in Example 1 and thus will not be further described.
In Step B06, the search range set in Step B05 is subjected to the correlation computation processing in an order from an end pixel. A specific computation algorithm used in this example is the same as that in Example 1 described with reference to
In Step B07, based on the processing result of Step B06, the actually-measured moving distance of the print medium conveyed in a period from Step B03 to Step B07 is calculated and stored. In this example, the steps of Step B03 to Step B07 are repeated until the total conveyance amount of the print medium reaches the target conveyance amount corresponding to the one stepwise moving. In Step B07, the informations of actually-measured moving amount are stored every different region.
In Step B08, it is determined whether the count value of the conveyed amount by the rotation angle sensor 18 started from Step B03 has reached the target amount or not. When determining that the count value has not reached the target amount yet, the processing proceeds to Step B10. In Step B10, the second image data 2103 acquired in Step B04 is assumed as the first image data. Then, with regard to this image data, the matching region 2102 is placed at an appropriate position at the upstream-side as in Step B02.
Thereafter, the processing returns to Step B03 to perform the processing as described above based on the newly-stored matching pattern. Until the conveyance amount reaches the target conveyance amount corresponding to one stepwise is confirmed in Step B08, the print medium is conveyed and the steps from Step B03 to Step B08 are repeated. When the conveyance reached the target amount is confirmed in Step B08, then the processing proceeds to Step B09.
In Step B09, the sum of a plurality of actually-measured moving distances stored whenever Step B07 is performed is calculated and this sum is set as the total actual moving amount. Then, the processing proceeds to STEP 6 in the flowchart shown in
According to this example, even when one conveyed amount (target conveyed amount) of the print medium is larger than the detection region of the direct sensor unit 16, a plurality of parts of moving distance are detected during one conveyance operation to thereby detect the moving distance, thereby achieving the conveyance control. As a result, even when the direct sensor unit 16 has a small capturing element, the moving information can be accurately acquired. This example can be applicable to a printer which performs printing operation while continuous conveying of a print medium in the Y direction.
Example 1 and Example 2 assume a case where one target conveyed amount is smaller or larger than the detection region of the direct sensor unit 16. On the other hand, Example 3 is a control method for a case where, even in the middle of one printing job, a set search range is within the range of the second image data or not within this range.
The apparatus in this example has the same configuration as that of Example 1. The entire sequence is the same as that described in the flowchart in
When the actual conveyance amount detection sequence is started, the CPU 101 in Step D01 firstly uses the direct sensor unit 16 to acquire the image of the print medium 8 as the first image data. When the direct sensor unit 16 is used to capture the surface of the belt 19 in the configuration of
Next, the CPU 101 in Step D02 places the matching region having a region of 5 pixels×5 pixels at an appropriate position at the upstream-side of the first image data. Thereafter, the CPU 101 extracts the image data included in the matching region and stores this data as a matching pattern (image pattern of a part of the first image data). The processing so far is the same as that of Examples 1 and 2.
Next, in Step D03, the CPU 101 determines whether the image data included in the matching region stored in Step D02 will be beyond the detection region of the direct sensor unit 16 due to the next target amount conveyance operation or not. When determining that the image data will not be beyond the detection region, then the processing proceeds to Step D04 to perform the sequence A. The sequence A is the same as the steps of Step A03 to Step A07 in the flowchart of
On the other hand, when it is determined in Step D03 that the image data stored in Step D02 will be beyond the detection region due to the next conveyance operation, the processing proceeds to Step D05 to perform the sequence B. The sequence B is the same as the steps of Step B03 to Step B09 in the flowchart of
According to this example, even when a set search range is within the range of the second image data or is beyond the range, the moving information can be acquired accurately.
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 Nos. 2008-169046, filed Jun. 27, 2008, 2009-138277, filed Jun. 9, 2009 which are hereby incorporated by reference herein in their entirety.
Number | Date | Country | Kind |
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2008-169046 | Jun 2008 | JP | national |
2009-138277 | Jun 2009 | JP | national |