The present invention relates to a board recognizing apparatus and method for recognizing a position of a hole located at a specified location on a circuit board for use in an electronic component mounting process in which a lead of an electronic component is fitted into such a hole.
A conventional arrangement of a board recognizing apparatus for recognition of hole positions in a circuit board is explained with reference to FIGS. 3 to 5.
In FIG. 3, the conventional board recognizing apparatus includes a belt 23 and rails 24 in combination for moving a circuit board 20. The apparatus also includes a light source 21 fixed above the circuit board 20. The light source 21 has substantially the same width as the circuit board 20. The apparatus also includes a compact line sensor 22 fixed beneath the circuit board 20. The sensor 22 has a condenser lens. In an alternative, the light source 21 may be fixed beneath the circuit board 20, and the compact type line sensor 22 may be fixed above the circuit board 20.
Next, operation of the conventional arrangement is explained with reference to FIGS. 3 to 5.
In FIGS. 3 to 5, when light is projected from the light source 21 toward the circuit board 20 as the circuit board 20 is moved by means of the belt 23 and rails 24 as shown in FIG. 3, light rays passing through holes 20a, 20b, 20c of the circuit board 20 are allowed to pass through the condenser lens for incidence on the compact type line sensor 22. Thus, positions of the holes 20a, 20b, 20c can be recognized by the compact type line sensor 22.
However, the foregoing conventional arrangement involves the following issues.
(1). As FIG. 4 shows, the angle of incidence .theta. of the light rays falling on the compact type line sensor 22 is such that, when the hole 20a is located at the middle of the board 20, the angle is zero. The angle becomes proportionally larger as the hole position gets nearer to the position of either of the holes 20b, 20c located at edge portions of the board 20. Therefore, while the hole 20a located at the middle of the board 20 can be recognized to be of a circular shape in the case where the holes 20a, 20b, 20c are circular in shape, the holes 20b, 20c at edge portions of the board 20 will be recognized to be of a distorted circular shape. As such, positions of the centers of the holes 20b and 20c may not be accurately recognized.
(2). As FIG. 5 illustrates, where the board 20 has electronic components 25, 25 mounted thereon, the hole 20b goes out of sight because of the component 25. Therefore, the hole cannot be recognized.
(3). Since the number of pixels of the compact type line sensor 22 is limited, the reading range of the sensor must be reduced if higher image resolution is to be obtained for enabling image recognition. Correspondingly, if the reading range is to be increased, the resolution aspect must be sacrificed.
(4). The speed of movement in a direction perpendicular to the compact type line sensor 22, that is, the speed of movement in the direction of transport of the board 20 must be uniform, or otherwise a read image is subject to expansion and contraction and cannot be relied upon for recognition of accurate position. Therefore, a high precision control is required to maintain the speed of transport of the board 20 at a uniform level.
(5). Since the board 20 moves relative to the recognizing section, it is required that at the recognizing section the belt 23 and rails 24 be twice as long as the board 20. This poses a limitation upon the ability to reduce the size of the board recognizing apparatus.