Abstract:
An image scanning apparatus with scan-starting point positioning function comprising a casing, a carriage and a calibration sheet is provided. Of which, the casing comprises a scan-platform used to place documents to be scanned, while the calibration sheet, which is fixed to the inner surface of the carriage and lies between the home line of the carriage and the upper wider margin of the scan-platform, comprises a hollowed-out mark completed through a punch-cutting manufacturing process. The mark can be defined using a predefined function set and has a reference point. After the carriage has moved to a scan line, the reference point can be located according to the intersection points between the mark scanned and the scan line accompanied by the predefined function set of the mark. Of which, the calibration sheet and the inner surface of the casing are of different levels of brightness.

Description:
This application incorporates by reference Taiwanese application Serial No. 090110227, Filed Apr. 27, 2001. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates in general to an image scanning apparatus, and more particularly to an apparatus, which precisely and effectively positions and determines the scan-reference point. 
   2. Description of the Related Art 
   The use of image scanners has become more and more popular along with the coming of multimedia age. Meanwhile, the users&#39; expectations of the quality and speed of image scanners are getting higher and higher. The carriage of an image scanner is normally driven using a step motor. After having finished scanning, it is not guaranteed that the carriage will return to exactly the same home position. If the carriage of an image scanner used to fetch images can be effectively and precisely shifted from home position to a document scan-starting point before scanning, no parts of the to-be-scanned documents will be missed out, nor will there be any non-document images scanned. Thus, the quality of document scanning can be improved. Conventionally, before image scanning is started, a ‘scan-reference point’ which has been predefined before the scanner leaves factory must be located first. Given the coordinates of the scan-reference point already known, the position of the scan-starting point will be located according to the ‘vector relationship’ between the scan-reference point and the scan-starting point, wherein the vector relationship has been defined before the scanner leaves factory. Conventional methods for positioning a starting point for image scanning are as follows: 
   (a) Referring to  FIG. 1 , a method using a corner of a reflection area  12  on a calibration sheet  10  as a reference point Q to define the position of the scan-starting point is disclosed in Taiwanese publication patent no. 147499. The relative position between the reference point Q and scan-starting point P has already been defined before the scanner leaves factory. To locate the position of the reference point Q, the carriage  11  only needs to move in the direction of Y-axis differentiating color changes between the reflection area  12  and the calibration sheet  10 . The position of the scan-starting point P will thus be located accordingly; and the carriage  11  will start scanning after having returned to the scan-starting point P. 
   (b) Referring to  FIG. 2 , a method using an existing mark  22  on a calibration sheet  20  to define the position of the scan-starting point is disclosed in Taiwanese publication patent no. 338868. When the carriage  21  stops on any scan lines of the mark  22 , two reference points Q 1  and Q 2  are chosen from the mark  22 ; the position of the scan-starting point P will be located according to the coordinates of the two reference points, the predefined function relation of mark  22 , and a predefined length between a predefined reference point Q on the mark  22  and the scan-starting point P. After that, scanning proceeds. 
   However, the conventional method will result in at least the following three types of errors when printing a reflection area and a mark and installing a calibration sheet: 
   First, the error would occur when printing a reflection area or mark onto a calibration sheet. 
   Second, the error of cutting calibration sheet would occur. That is, when cutting a large calibration sheet into smaller ones after having finished the printing of reflection areas or marks onto a large calibration sheet, the cutting process could not produce patterns whose specifications of sizes and distances would match their original designs completely. 
   Third, the error of pasting would occur. That is, when pasting a calibration sheet onto a scanning apparatus, the position onto which the calibration sheet is pasted could not match with the position and vector relation of its original design completely. 
   When scanning images, a carriage&#39;s movements on the X-axis and Y-axis are measured by picture elements. Taking an ordinary scanner whose resolution is 600 dpi for instance, there are 600 picture elements per inch. For a scanner requiring a high standard of precision, the above-mentioned errors are not only unbearable but also unavoidable. 
   SUMMARY OF THE INVENTION 
   It is therefore an objective of this invention to provide an image scanning apparatus capable of positioning a scan-starting point, excluding the errors that would occur during the process of cutting and printing the calibration sheet, and thus improving the precision and quality of image scanning. 
   It is another objective of the invention to provide another image scanning apparatus capable of positioning the scan-starting point, comprising a casing, a carriage and a calibration sheet. The casing comprises a scan-platform on which documents to be scanned are placed. The calibration sheet, which is fixed to the inner surface of the carriage lying between the home line of the carriage and the upper wider margin of the scan-platform, comprises a hollowed-out mark completed through a punch-cutting manufacturing process. The mark can be defined using a predefined function set and has a reference point. After the carriage has moved to a scan line, the reference point can be located according to the intersection points between the mark scanned and the scan line accompanied by the predefined function set of the mark. The calibration sheet and the inner surface of the casing are of different levels of brightness. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiments. The description is made with reference to the accompanying drawings in which: 
       FIG. 1  shows a diagram of the positioning of a scan-starting point for a conventional image scanning apparatus; 
       FIG. 2  shows another diagram of the positioning of a scan-starting point for a conventional image scanning apparatus; 
       FIGS. 3A and 3B  show two top views of a scanning apparatus according to a preferred embodiment of the invention; 
       FIG. 4  is a pictorial view showing a scanning apparatus according to the invention; 
       FIGS. 5A to 5C  show three flow diagrams of manufacturing processes of a calibration sheet used in the invention using a punch-cutting method; 
       FIG. 6  illustrates another diagram of the mark in  FIG. 3 ; 
       FIG. 7  shows a diagram when the hypotenuse of the mark in  FIG. 3  is of any function figures; 
       FIG. 8  shows a diagram of a mark defined by two function curves; and 
       FIG. 9  shows a diagram of two marks. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Please refer first to  FIGS. 3A and 3B  showing two top views of a scanning apparatus according to a preferred embodiment of the invention.  FIG. 3A  shows a diagram of a calibration sheet according to the invention while  FIG. 3B  shows the diagram of a calibration sheet  310  fixed to a scanning apparatus to define a reference point Q.  FIG. 4  shows a pictorial view of a scanning apparatus according to the invention, wherein label  402  refers to an upper cover of a scanner. 
   Please refer to  FIGS. 3A ,  3 B and  FIG. 4  at the same time. The image scanning apparatus of this invention includes a casing  308 , a carriage  302 , a scan-starting point P, a calibration sheet  310 , and a hollowed-out mark  312 . The casing  308  includes a scan-platform  306  for a to-be-scanned document to be placed on. The carriage  302  is movably installed within the casing  308  and below the scan-platform  306  for scanning a plurality of scanning lines  314  (only one is shown) on the casing  308  and the to-be-placed document. The scan-starting point P is defined on the scan-platform  306  and is a point for the carriage  302  to start scanning the to-be-scanned document. The calibration sheet  310  is attached to the casing  308 . The hollowed-out mark  312  is formed in the calibration sheet  310 . 
   The carriage  302  stations on a home line  304  before it is started or is in the READY status. The scan-platform  306  for a document (not shown in the diagram) to be placed on has four margins including an upper wider margin  306   a . The scan-platform  306  is situated on the inner side of a casing  308 , and the directions of X-axis and Y-axis are defined as shown in  FIG. 3A . The carriage  302  moves alongside Y-axis to acquire the image of the to-be-scanned document. The calibration sheet  310  is fixed to the inner surface of casing  308  and lies between the home line  304  of the carriage and the upper wider margin  306   a  of the scan-platform. The home line and the upper wider margin are actually parallel to each other. A hollowed-out mark  312  is situated at the approximate center of the calibration sheet  310 . The ideal figure for the mark is an isosceles right-angled triangle. One leg of the isosceles right-angled triangle  313  is parallel to Y-axis and is perpendicular to another leg of the isosceles right-angled triangle  317  with a hypotenuse  319  intersecting the leg  313  at point Q. 
   The method to position the reference point Q to proceed image scanning is as follows. First, after the to-be-scanned document is placed on the scan-platform  306 , the carriage  302  moves to a scan line  314  which is roughly determined providing it falls within the area of the mark  312  such that the carriage  302  can sense the mark  312  and fetch the two intersection points A and B at which the scan line  314  intersects the leg  313  and the hypotenuse  319  of the isosceles right-angled triangle. Next, the coordinates of the reference point Q is determined using the characteristics of an isosceles right-angled triangle that the distance between the intersection points A and B is equal to that between intersection point A and reference point Q. Last, scanning is ready to be started. 
   For example, let the coordinates of intersection point B be (x1, y1) and that of an angular point C be (x2, y2). the X-axis coordinates for intersection point A, reference point Q and angular point C are all the same, i.e., x2. Since both intersection points A and B fall at the same scan line, their Y-axis coordinates are the same, i.e., y1. In other words, the coordinates for intersection point A are (x2, y1). Therefore, the length for line segment AB equals x1−x2. Since the function curve is a straight line whose slope is 1, the length of line segment AQ equals to that of line segment AB. Therefore, the Y-axis coordinate for reference point Q is y1+x1−x2. Accordingly, the coordinates for reference point Q are (x2, y1+x1−x2). The carriage  302  can thus fast and precisely locate the position of reference point Q to proceed scanning. Therefore, it can be concluded that the distance between the scan-starting point P and one of the scanning lines  314  intersecting the mark  312  at intersection points is determined according to the intersection points and a pattern of the mark  312 . 
   One characteristic of this invention is to produce a hollowed-out mark using a punch-cutting manufacturing process, which largely reduces printing and cutting errors when compared to conventional methods. Conventionally, marks are printed onto a large calibration sheet which has not yet been hollowed out. Then, plural marks are cut out sequentially. Printing and cutting involve two different processes. As a consequence, errors are large. The punch-cutting method according to the invention is free of printing and cutting errors, because this method involves neither printing nor cutting. The only error remains is a precision problem during the process of mold manufacturing. But generally speaking, this method causes much less errors than that caused by the printing method. 
   Please refer to  FIGS. 5A to 5C , which shows three flow diagrams of the manufacturing process of a calibration sheet used in the invention using punch-cutting method.  FIG. 5A  shows a front view of the mold used in punch-cutting manufacturing process;  FIG. 5B  shows a diagram before punch-cutting is processed; and  FIG. 5C  shows a diagram after punch-cutting has been processed. The calibration plate pattern  502  to be punch-cut is inscribed onto a mold  504 . After using the mold  504  to punch-cut the material for calibration sheet  506 , a calibration sheet  310  can be obtained. It is worthy noting that for illustrating purpose, each time the punch-cutting method according to the invention as shown in  FIGS. 5A to 5C  produces one calibration sheet only. However, in real application, a mold with a plurality of calibration plate patterns can produce plural pieces of calibration sheet in a single punch-cutting process. 
   Another characteristic of the invention is to define the reference point Q using the properties that the calibration sheet  310  and the inner surface of the casing  308  have different performances in reflecting the light. The calibration sheet  310  can be pasted onto the inner surface of the casing  308 , so the color of the hollowed-out mark  312  sensed by the carriage  302  is exactly the color of the inner surface of the casing  308 . Therefore, the larger luminance difference between the color of calibration sheet  310  selected and that of the inner surface of the casing  308 , black and white for instance, the better effect will be achieved. Most scanning apparatus are able to recognize the mark  312  provided color difference exists. In the above explanation, a mark  312  in the shape of an isosceles right-angled triangle is used as an example. Of course, the mark  312  can be a pattern of any functions provided the function relations have been set in the scanner before it leaves factory, and becomes an already known function when the user starts to operate. 
   Please refer to the calibration sheet as shown in  FIG. 6 , wherein the mark  602  is an isosceles obtuse triangle with the vertex of one of its two non-obtuse angles being used as a reference point Q. The opposite side of reference point Q is parallel to X-axis; and vertex S is the vertex of the obtuse angle, whereas vertex R is the vertex of another non-obtuse angle. So, line segment SR and line segment SQ are of equal length; line segment QR is the longest side of the isosceles obtuse triangle; and the included angle θ has already been known. When the carriage  302  moves to the scan line  314 , the two intersection points S′ and R′ at which the scan line  314  intersects line segments QS and QR will be sensed. Since the triangle S′R′Q is still an isosceles triangle and the included angle θ has already been known, the coordinates for reference point Q can thus be accurately obtained using these geometric relations. 
   Please refer to  FIG. 7 , which shows a diagram when the hypotenuse of the mark in  FIG. 3  is of any function figures. In real application, a simple function is easier to be implemented. Let the function figure in  FIG. 7  be a parabola  704 ; and further let the intersection point Q at which the parabola  704  intersects a line  706  be used as a reference point, wherein the line  706  is perpendicular to Y-axis. When the carriage  302  moves to the scan line  314 , the coordinates for the intersection point T at which the scan line  314  intersects the parabola  704  will be obtained. After having obtained the coordinates for the image scanning reference point Q through parabola function relations, the carriage  302  can thus be positioned immediately and start to scan the to-be-scanned document. 
   Please refer to  FIG. 8 , which shows a diagram of a mark  802  defined by two function curves. The two function curves can be function curve  804  and function curve  806  which intersect each other at point S and point Q. Point Q is a reference point while function curve  804  can be a straight line for instance. The scan line  314  intersects function curve  804  and function curve  806  at point U and point V respectively. The coordinates for the reference point Q can be obtained using function relations between intersection point U and intersection point V. 
   The above examples are illustrated when the marks are situated at the approximate center of the calibration sheet. It has been found through experiments that the luminance distribution of a tube gives the best luminance around the central area on an ordinary scan-platform. Nevertheless, the location of marks is not necessarily to be limited to be at the central area. In real application, the marks can be located at the left-hand side, the right-hand side or any other parts of the calibration sheet provided the luminance of the tube is sufficient to differentiate color difference between the calibration sheet and the inner surface of the casing. As shown in  FIG. 9 , two marks  902  are located at the two sides of the calibration sheet  910  respectively. 
   It is noteworthy that marks are enlarged in the above examples for illustrating purpose. In real application, only small-sized marks are needed to position a scan-starting point. 
   Although the foregoing preferred embodiments only illustrate how to locate a scan-reference point, anyone who is familiar with this technology should be able to obtain the position of a scan-starting point given a reference point having been positioned because the distance between the scan-starting point and the scan-reference point is determined during manufacturing. So, the method to position a scan-starting point will not be repeated here. 
   The calibration sheet used in the image scanning apparatus disclosed in the foregoing preferred embodiments according to the invention is easy to be manufactured and is small in errors, which greatly improves the quality of image scanning. 
   While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.