Method and apparatus for positioning a scanning starting point of an image scanning apparatus

An apparatus for positioning a scanning starting point of an image scanning apparatus includes a platen, carriage, and a number of marks. The X-Y coordinate system defined by the platen has an X-axis defined by a first wide margin of the platen and a Y-axis defined by a first long margin of the platen. The carriage moves along the Y direction. The marks inside the image scanning apparatus indicate different Y coordinate values. The method for positioning a scanning starting point of an image scanning apparatus is as follows: the nearest mark to the document to be scanned is first chosen as a reference point. The vector from an image starting point of the document to be scanned to the reference point is then obtained. The carriage finally moves to the reference point chosen as a starting point and proceeds to scan.

This application incorporates by reference Taiwanese application Ser. No. 089109493, Filed May 17, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to the method and apparatus for positioning a scanning starting point of an image scanning apparatus, and more particularly to the method and apparatus for positioning a scanning starting point by utilizing multiple reference points to achieve high precision.

2. Description of the Related Art

In the multimedia age, image scanners are commonplace for users. The demand for high scanning quality and speed are increasing as well. The way to enhance the scanning speed is to make the image-capturing carriage move quickly and efficiently from its resting position to the scanning starting point to proceed the scanning. Conventionally, the methods for positioning a scanning starting point to initiate the image scanning are as follows:(a) Referring toFIG. 1, Taiwan Patent Publication No. 147499 discloses that the reference point P for positioning is a corner of a reflecting area12. The relative position between the reference point P and the scanning starting point Q is regulated before the product leaves the factory. After the position of the reference point P is determined, the carriage can then obtain the position of the scanning starting point Q. In this way, the carriage can move to the scanning starting point Q and proceed to scan.(b) Referring toFIG. 2, Taiwan Patent Publication No. 338868 discloses that a mark22is used for positioning. After getting any two reference points P1and P2of the mark22, the position of the scanning starting point Q can be obtained by the two reference points P1and P2according to the coordinates, functional relation, mark, and pre-determined length of the scanning starting point.

In the above cases, a scanning starting point is used as a starting position for the scanning carriage, however, the actual contents may not be exactly at the scanning starting point Q. Thus, in these cases, the carriage needs to traverse the distance between the scanning starting point Q and the actual contents of the document. Errors may occur during this due to the unsteady transmittal speed of the carriage, mechanical errors among transmission components, or transmittal errors of the carriage. Besides, the farther the actual contents are away from the scanning starting point, the larger the moving error is. Generally speaking, the moving error is around 2 mm when the carriage moves from the scanning starting point Q to the image starting point of the scanning area at a distance. This is not acceptable for high precision scanning and has become a topic that must be overcome.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an image scanning apparatus having a number of marks as reference points, disposed in the direction in which the carriage moves along. This will decrease errors due to wrongly selecting the scanning starting point as well as enhance both the precision and speed of image scanning by utilizing different reference points in different scanning areas.

The invention achieves the above-identified objects by providing an apparatus for positioning a scanning starting point of an image scanning apparatus. The apparatus includes a platen, carriage and a number of marks. The platen for a document to be placed thereon defines an orthogonal X-Y coordinate system. The X-Y coordinate system has an X-axis defined by a first wide margin of the platen and a Y-axis defined by a first long margin of the platen. The carriage is disposed in the image scanning apparatus and moves along the Y direction from a starting line for capturing an image of the document to be scanned. The marks inside the image scanning apparatus indicate different Y coordinate values as the reference points for the carriage to capture the images of the document to be scanned.

The invention achieves the above-identified objects by providing a method for positioning a scanning starting point of an image scanning apparatus. The image scanning apparatus includes a platen, carriage, and a number of marks. The platen for a document to be placed thereon defines an orthogonal X-Y coordinate system. The X-Y coordinate system has an X-axis defined by a first wide margin of the platen and a Y-axis defined by a first long margin of the platen. The carriage is disposed in the image scanning apparatus and moves along the Y direction from a starting line for capturing an image of the document to be scanned. The marks inside the image scanning apparatus indicate different Y coordinate values as the reference points for the carriage. The method for positioning a scanning starting point of an image scanning apparatus is as follows: the nearest mark to the document to be scanned is first chosen as a reference point. The vector from an image starting point of the document to be scanned to the reference point is then obtained. The carriage finally moves to the reference point chosen as a starting point and proceeds to scan.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 3, a top perspective view of an image scanning apparatus for positioning a scanning starting point by utilizing multiple reference points according to a preferred embodiment of the invention is shown. Taking a flatbed scanner for example, in general, a flatbed scanner includes a transparent platen302, which is made of glass disposed on the casing308. The document304to be scanned is placed upon the platen302. The carriage306inside the flatbed scanner provides illumination and captures the image of the document304to be scanned. The carriage306includes a light source, reflecting optical module, lenses, and light sensing unit. The light sensing unit can be a Charge Coupled Device (CCD). A number of marks310located on flatbed scanner are used as the reference points for carriage306to capture the images of the document304to be scanned.

The first wide margin of the platen302is defined as the X-axis and the first long margin of the platen302is defined as the Y-axis. As shown inFIG. 3, the first wide margin can be the leading edge312with the X direction while the first long margin can be the side edge314with the Y direction. Since the leading edge312and the side edge314are orthogonal, the X-Y coordinate plane of the orthogonal X-Y coordinate system can be defined by the platen302. The origin O (0,0) is the intersection of the X-axis and Y-axis. The X and Y coordinate values of all the points on the platen302are positive. The carriage306moves along the Y direction from the first starting line316, wherein the Y direction includes the positive-Y direction and negative-Y direction. The marking group area318contains all the marks. Each mark in the marking group area318is a fixed distance from the origin and set before the product leaves the factory. The basic unit of the X and Y coordinate is the pixel. Hence, the X coordinate value is controlled by counting the cells in the CCD while the Y coordinate value is controlled by the steps of the stepping motor.

All the marks disposed on the second side edge in the marking group area318preferably have the same X coordinate value. Taking the second side edge320for example, the marks in the marking group area318may have positive or negative Y coordinate values. As shown inFIG. 3, some marks disposed below the leading edge312of the platen302have positive Y coordinate value while the other marks disposed above the leading edge312of the platen302have negative Y coordinate value. There is no need to choose all the marks with positive Y coordinate value as reference points since the carriage306might move upwards or downwards.

Referring toFIG. 4along withFIG. 3, a flow chart of a method for positioning a scanning starting point of an image scanning apparatus according to a preferred embodiment of the invention is illustrated in FIG.4. In step402, the image scanning apparatus starts to pre-scan. The pre-scan is to scan the document304to be scanned at a low resolution in advance for obtaining the scanning area, namely, the image322to be scanned. The image322to be scanned includes an image starting point324and an image ending point326. The coordinates of the image starting point324and an image ending point326are obtained after determining the image322to be scanned. Besides, the image starting point324is the starting point for scanning the image322to be scanned.

Step404is then performed, users can choose a suitable mark in the marking group area as the reference point according to the image322to be scanned. This can be the nearest mark of the image starting point324as an example. In the next step406, a vector from an image starting point of the image322to be scanned to the reference point is obtained. For instance, the: vector (x, y) from the image starting point324to the mark328is shown in FIG.3. The “x” is the difference between the X coordinate value of the image starting point and that of the mark328while “y” is the difference between the Y coordinate value of the image starting point324and that of the marks328.

Step408is then performed whereby the carriage306moves to the second starting line329corresponding to the mark328being chosen as the reference point. The carriage306then moves y units towards the scanning starting line330, which is the Y coordinate of the image starting point324, and proceeds to scan the image322to be scanned. In this way, a scanning image of high precision is achieved.

As shown inFIG. 3, assuming that the determined scanning area is the rectangular image322defined by an image starting point324and an image ending point326. The mark328nearest the image starting point324can be chosen as the reference point, The coordinates of the image starting point324are (x1, y1), the coordinates of the image ending point326are (x2, y2), and the coordinates of the mark328are (x3, y3). The vector (x, y) from (x1, y1) to (x3, y3) can be obtained by means of calculation since the coordinates of the mark328are determined to be (x3, y3), wherein x=x1−x3and y=y1−y2. Hence, the carriage306directly moves to the second starting line329corresponding to mark328being chosen as the reference point. The carriage306then moves y units downward to the scanning starting fine330to arrive at the position (x1, y1) to commence scanning.

Conventionally, the carriage moves from O (0,0) to (x1, y1) and the number of step counted in the Y direction is y1−0=y1. According to the method of the invention, the carriage only has to move from (x3, y3) to (x1, y1) where the number of steps counted in the Y direction is y1−y3. Hence, the carriage306directly moves to the second starting line329corresponding to the reference point of the mark (x3, y3) and then starts to count the number of the steps from (x3, y3) to (x1, y1). This decreases the time for counting the number of steps and achieves speedy scanning.

The present invention can also attain a scanning image with high precision as illustrated in the following example. The moving error rate of the carriage is a constant equal to 0.001 units whenever the carriage moves a unit. Let the coordinates (x3, y3) of the mark328be (580,720) and the coordinates (x1, y1) of the image starting point324be (500,800). Conventionally, the carriage moves 800−0=800 (units) from the origin O (0,0) to the image starting line330with y=800. This results in a moving error of 800*0.001=0.8 (unit). According to the method of the invention, the carriage306only has to move 800−720=80 (units) from the second starting line329to image starting line330. The moving error of 80*0.001=0.08 (unit) is far less than the former moving error 0.8 (unit) with the origin O (0,0) as reference point. The moving error might result from the unsteady transmittal speed of the carriage, external interference, mechanical errors among transmission components, or the transmittal errors of the carriage.

This invention is suitable for the image scanning with high precision due to the high positioning precision of the image starting point, especially for the reduplicate scanning. The reduplicate scanning is performed in the following conditions:

(1) When the scanning comes to a standstill due to insufficient memory, a second scanning is required.

(2) When using a scanner provided with a high image scanning quality, merging two images is a way to promote image quality. After scanning the first chosen image of the document to be scanned once, the carriage moves half a pixel in the Y direction by mechanical adjustment to scan a second time. The two scanned images are then merged and a doubling of the scanning resolution is achieved. Take the scanner with a resolution of 600 dpi (dot per inch) for instance. A first image with a resolution of 600 dpi is obtained in the first scanning and a second image with a resolution of 600 dpi is then obtained in the second scanning after the carriage moves half a pixel. The second image has a displacement of half a pixel in respect to the first image. Hence, even a little moving error may greatly affect the scanning result. Furthermore, a moving error of up to 2 mm happens quite often resulting in double after superimposing the two scanned images. As such, only a tiny error is allowable for utilizing the merging of two images to enhance scanning resolution. The image scanning apparatus with a high precision according to this invention satisfies the requirement of reduplicate scanning. Besides, merging N (N is a positive integer) images deviated with a displacement of 1/N pixel can enhance the image scanning resolution.

There are several ways to set up marks on the image scanning apparatus. An example is stated as follows but not for limiting the invention. The marking group area318is a group of marks made of material, for example, plastic which is not easily deformed. The marking group area318is placed and plastered on the casing308near the platen302. Generally speaking, the platen302is made of glass and disposed on the casing308. The marking group area318can be placed between the glass and casing308for protection. While manufacturing, the coordinates of each mark relative to the origin has to be regulated and plastered on its exact position. Another way is to design a groove inside the casing308for placing the marking group area318. The groove having the same size with the marking group area318ensures the marking group area318is disposed on the exact position steadily.

Referring toFIGS. 5Ato5E, schematic diagrams of different marks for the marking group block ofFIG. 3are shown. As shown inFIG. 5A, the marks are lines perpendicular to the Y direction. The line color can be black while the bottom color is white, for example. One end of the line can be chosen as the reference point. After moving to the reference point directly, the carriage moves to the starting point and then proceeds to scan.

As shown inFIG. 5B, the marks are rectangles, and one corner of one rectangle is chosen as the reference point. After moving to the reference point directly, the carriage moves to the starting point and then proceeds to scan.

As shown inFIG. 5C, the marks are isosceles right triangles. One of two equal sides of the isosceles right triangle is parallel to X-axis while the other is parallel to Y-axis. One corner with the bigger Y coordinate value of one isosceles right triangle is chosen as the reference point. As long as the carriage moves to the isosceles right triangle, it is easy to obtain the distance between the carriage and the reference point so that the carriage can move to the starting point readily. As shown inFIG. 5C, point C is the reference point. When the carriage moves to the scanning line502, the positions of point A and point B can be detected and the line segment AB is determined. Since the length of the line segment AB is equal to the length of the line segment AC, the position of the reference point C is thus obtained. Hence, the carriage can quickly move to the starting point and proceed to scan.

As shown inFIG. 5D, the mark can be a specific function graph, a parabola for example. When the carriage moves to the scanning line504, the positions of the point D and point F can be detected and the position of the reference point E is obtained from the function of the parabola. Hence, the carriage can quickly move to the starting point and proceed to scan.

As shown inFIG. 5E, the mark can be a cross. The intersection of one cross is the reference point. After moving to the reference point directly, the carriage moves to the starting point and then proceeds to scan.

The image scanning apparatus according to the preferred embodiment provides precise scanning by positioning a scanning starting point of an image scanning apparatus with a simple marking design. The method for positioning a scanning starting point of an image scanning apparatus can be utilized in various applications, such as decreasing the error of obtaining the scanning starting point and increasing the resolution as well as the speed of image scanning.