Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
1998-12-15
2001-01-30
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C356S389000, C356S370000, C356S370000
Reexamination Certificate
active
06181424
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-dimensional measurement apparatus, and more particularly to an apparatus for use in a solder paste printing machine and the like for an electronic component surface mounting system.
2. Description of the Related Art
On a printed circuit board to which electronic components are mounted, a solder paste pattern is generally printed for forming a conductor between the components and a wired pattern on the board. For measuring the shapes of the printed paste, three-dimensional measurement using the “light-section method” is widely applied. In the light-section method, an object (for example, solder paste) is irradiated by a stripe of light so as to section the surface thereof, and measure the shape or unevenness of the surface thereof from intersected lines on the surface. One example is shown in FIG.
8
.
Referring to
FIG. 8
, laser light emitted from a laser diode
21
is focused through an aspheric focusing lens
22
on the vicinity of an object
28
as a beam spot of 0.2 mm in diameter. The laser light passing through the focusing lens
22
is reflected by a galvano mirror
23
disposed in the midst of light path, passes through a semi-transparent mirror
24
, and is projected on the object
28
. As a galvano mirror
23
, driven by a driver (not shown) oscillates as indicated by an arrow in
FIG. 8
, the beam spot is scanned substantially in a line on the surface of object
28
, thereby forming a stripe of light necessary for the light-section method.
The scanned light is also reflected off the semi-transparent mirror
24
and directed to a position sensitive device (PSD)
25
, which detects a position in the scanning direction (X-axis) based on the rotating angle of the mirror
23
. Simultaneously, the reflected light from the object surface is focused on a PSD
27
provided for detecting a position in the vertical direction (Z-axis) through a receiving lens
26
disposed at an angle of between
18
and
30
degrees with the projected light axis. The spot position focused on the PSD
27
changes depending on the height of the object and can be taken out as a voltage change, thereby providing a measurement of the unevenness (position in the Z-axis) of the surface of the object
28
. With the repetition of abovementioned measuring method according to the movement of the whole measurement apparatus in a direction (Y-axis) perpendicular to the optical scanning direction, three-dimensional positions of the object
28
are measured.
In the foregoing three-dimensional measurement method, PSDs are used for detecting scanned positions. However, since PSDs do not have good voltage linearity characteristics, the detected positions must be corrected based on the calculation of characteristics of each PSD to be used. Another problem with the conventional PSDs is that because a change of the center of gravity of the focused spot on PSD is taken out when measuring height by PSDs, spot luminance related data is not obtainable. Also, PSD characteristics change depending on temperature, so it is difficult to measure accurate height.
Another problem arises in the conventional three-dimensional measurement method. Since the optical path length between the aspheric focusing lens and the object is long, which means a small numerical aperture (N.A.), and the laser light can not be focused to a small diameter, it is difficult to obtain a highly accurate measurement result.
Still another problem arises in the conventional three-dimensional measurement method. Since the whole measurement apparatus must be moved in a direction perpendicular to the longitudinal direction of the stripe of light every time the stripe of light is cast for the measurement of the whole surface of the object, a driving device for movement of the apparatus would be on a large scale, and thereby vibration would occur during movement. Consequently, accurate measurement is difficult.
Thus, as demonstrated by the foregoing problems, there exists a need for a three-dimensional measurement apparatus for measuring three-dimensional positions of an object with high accuracy and high speed.
SUMMARY OF THE INVENTION
In order to solve the problems mentioned above, the invention provides a three-dimensional measurement apparatus for measuring three-dimensional information of an object based on a light-section method, which utilizes irradiation of a stripe of light on the object. In an apparatus aspect of the invention, the invention includes a laser light source, means for collimating the laser light emitted from the laser light source, a projection unit for projecting the stripe of light on the object from the collimated laser light, means for moving the projection unit along the collimated light, and parallel therewith (so that the stripe of light moves on the object perpendicular to a longitudinal direction thereof), and an imaging means for capturing images of the object, which are scanned with the movement of the stripe of light, at given angles with the axis of the projected light, whereby three-dimensional information of the object is obtained from the captured images of the object.
With this arrangement, the collimated laser light is converted to a stripe of light to irradiate the object, and the projection unit projecting the stripe of light moves back and forth along the collimated light in the direction perpendicular to the longitudinal direction of the stripe of light. Because the projection unit radiates a stripe having a constant width of stripe of light on the object with constant reception of the collimated light, a plurality of stripes of light can be formed on the object by means of simple movement of the projection unit. As a result, three-dimensional measurement based on the light-section method can be attained with high speed and high accuracy.
REFERENCES:
patent: 5028799 (1991-07-01), Chen et al.
patent: 62-299706 (1987-12-01), None
patent: 7-26825 (1995-03-01), None
Goto Sumio
Okabayashi Mitsumasa
Saito Masaru
Font Frank G.
Punnoose Roy M.
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