Light source device for an image processor

A light source device for an image processor has a plurality of LEDs which are disposed below a television camera. A shelter plate is disposed above the light source so as to prevent light emitted from the light source from directly entering the television camera. A cylindrical light transmitting barrel is provided, extending from the television camera to a position sufficiently close to an object to be detected.

BACKGROUND OF THE INVENTION 
The present invention relates to a light source device for an image 
processor which converts a picture image detected by an industrial 
television (ITV) into a binary numeral for further processing, and more 
particularly to a light source device of an image processor adapted to 
detect a solder leveler formed on a print circuit board. 
The image processor which converts a picture image signal picked up by the 
ITV into a two-value data comprising a high level signal and a low level 
signal (1 and 0) is now used in various technical fields. In an automatic 
mounting system of electronic devices, the image processor is used for 
detecting the mounting positions of the devices and positions of standard 
marks on a print circuit board. 
Referring to FIG. 1, showing an example of a conventional image processor, 
an ITV camera 2 is mounted on a robot 1 at an appropriate vertical 
position dependent on a focal length of the camera. A light source device 
11 is mounted on the ITV camera 2 around a lens barrel 4 thereof. The 
light source device 11 has a light source such as a cold-cathode tube 
and/or LEDs which emits light, and a diffusing plate for transmitting and 
diffusing the light. In order that diffused light transmitted through the 
diffusing plate may have a sufficient quantity of light, a light source 
capable of emitting a relatively large quantity of light is selected. 
The diffused light from the light source device 11 is projected onto a 
standard mark 10 formed on a print circuit board 3. However, only the 
light within a range indicated by dot-dash lines 11a between the light 
source device 11 and the standard mark. 10 in FIG. 1 is applied to the 
standard mark 10. The direction of light beam to be projected on the mark 
10 is the direction included in the range between the lines 11a. 
Since the standard mark 10 is made of a conductive material such as a piece 
of copper foil, the surface thereof is flat. Therefore, in the case where 
the position of the mark 10 is detected, a comparatively sufficient 
quantity of light is reflected on the flat surface, although the light in 
the only small range defined by the lines 11a is projected on the mark. 
Consequently, an appropriate picture image can be obtained by the ITV 
camera. Hence no serious trouble occurs. 
The image processor is also used for detecting the position of a conductive 
member coated with solder, that is, a solder leveler. The thickness of the 
solder coated on the conductive member is often irregular and hence the 
surface of the solder leveler is uneven. Namely, as shown in FIG. 4, the 
surface of a solder leveler 12 formed on the standard mark 10 is uneven in 
most cases. Moreover, due to the surface tension of the molten solder, the 
surface of the leveler is smooth. Therefore, diffused reflection on the 
surface occurs very little. Consequently, the directions of the reflected 
light is determined by the incident angle of each light beam. Hence, 
depending on the inclination of the surface of the solder leveler, or the 
existence of pinholes, the light reflected on the surface, for example, at 
a point B shown in FIG. 4 is hardly detected by the ITV camera 2. As a 
result, the detected image data for the solder leveler 12 recognized by 
the image processor fails to show the portion corresponding to the point 
B. 
More particularly, as described above, the light applied to the solder 
leveler 12 from the conventional light source device 11 is in the range 
between the lines 11a in FIG. 1. Showing light as being applied to a point 
A in FIG. 4, the light within a hatched area defined by lines 11b is 
projected on the point A. An incident light Ai reflected on the point A 
becomes a reflected light Ao which is directed toward the ITV camera 2. If 
the inclination of the solder surface becomes larger than that of the 
point A, the light Ai does not reflect to the ITV camera. In order to 
reflect to the ITV camera on such a large inclination surface, the light 
Ai must be applied at a larger incident angle. In other words, a more 
inclined direction than the illustrated angle of the light Ai can be 
picked up by the camera. However, since the light having a maximum 
incident angle is the incident light Ai in the conventional light source 
device 11, none of the beams reflected on such a steep surface are fed to 
the ITV camera 2, so that the image processor forms an incomplete image 
data having gaps. 
As described above, if the inclination of the surface of the solder leveler 
is large or pinholes are formed on the surface, the quantity of light fed 
to the ITV camera decreases. Hence the images are darkened, thereby 
further causing the gaps to be formed when converted into a two-value 
data. 
When the image processor recognizes such an incomplete image, the detected 
contour or the center of the image inevitably differs from the actual 
contour or the correct center of the object, thereby causing error in the 
measurements. In order to solve such a problem, there has been proposed an 
image processor provided with a system where the gaps in the image are 
compensated through an exclusive operation so as to obtain a full image. 
However, not only is such an image processor expensive, but in many cases, 
it is difficult to detect the gap included in the image. Hence the 
conventional image processor system is insufficient to eliminate the 
defect. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a light source device 
where light projected on an object such as a solder leveler is reflected 
to an ITV camera without regard to inclinations of the surface of the 
object or existence of pinholes, thereby enabling to accurately detect the 
object. 
Another object is to provide a light source device wherein the components 
of the emitted light substantially parallel to the surface of the object 
may be increased, thereby to prevent the picture image from darkening. 
According to the present invention, there is provided a light source device 
for an image processor having a television camera comprising a light 
source disposed below the television camera, a shelter member disposed 
above the light source so as to prevent light emitted from the light 
source from directly entering the television camera, a cylindrical light 
transmitting barrel extending from the television camera to a position 
adjacent an object to be detected, and a diffusing plate having an opening 
at a central portion thereof and secured to an inside wall of the light 
transmitting barrel at a portion below the light source for diffusing the 
light emitted from the light source. 
The inside wall of the light transmitting barrel has an opaque pear-skin 
surface for causing diffused reflection of the light emitted from the 
light source. 
An auxiliary light source such as an electroluminescent element may be 
provided at a lower portion in the light transmitting barrel. 
A light transmitting member such as an optical fiber may be provided in the 
light transmitting barrel for transmitting the light of the light source 
to a lower end portion of the light transmitting barrel. 
In accordance with the light source device of the present invention, the 
light transmitting barrel from which light is emitted is sufficiently 
extended to face the object, thereby widely diffusing the light from the 
entire caliber of the light transmitting barrel. Hence most of the 
reflected light enters the ITV camera despite the large inclination of the 
surface of the object or the existence of the pinholes. Moreover, the 
quantity of light falling on the object is increased, thereby enabling one 
to use a light source emitting a relatively small quantity of light. 
In addition, when a surface light source or an additional light source is 
added, the components of light which are substantially parallel to the 
surface of the object can be increased. Hence the quantity of light 
reflected on the object is increased, thereby preventing the picture image 
from becoming dark even if the inclination of the surface is large, or 
when there is a pinhole, thus enabling the image processor to recognize a 
complete image. 
These and other objects and features of the present invention will become 
more apparent from the following detailed description with reference to 
the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 2 shows a light source device according to the present invention. The 
same references as those in FIG. 1 designate the same parts in FIG. 2. 
The robot 1 is adapted to move the ITV camera 2 of the image processor in 
the X and Y directions of the print circuit board 3. A screw thread 4a is 
formed on an inside wall of a lower portion of the lens barrel 4, and a 
light source device 5 of the present invention is attached to the lens 
barrel 4 by means of the screw thread 4a. 
The light source device 5 comprises a light transmitting opaque barrel 6 
screwed in the screw thread 4a of the lens barrel 4, a plurality of LEDs 7 
as a light source annually arranged in the light transmitting barrel 6 at 
a portion adjacent the upper edge of the light transmitting barrel 6. A 
shelter plate 8 having a light transmitting opening 8a is secured to the 
inside wall of the light transmitting barrel 6 at a portion above the LEDs 
7. A diffusing plate 9 having a light transmitting opening 9a is provided 
under the LEDs 7. An inner wall 6a of the light transmitting barrel 6 has 
a pear-skin (rough surface) reflector surface for causing diffused 
reflection. 
The radially disposed LEDs 7 are connected with one another as shown in 
FIG. 3 and are controlled by a controller (not shown) so as to be lighted. 
The shelter plate 8 prevents the light of the LEDs from directly entering 
the ITV camera 2, thereby preventing causing noises in the image 
processor. As long as the upper portions of LEDs are covered, the shelter 
plate 8 may be formed into various shapes other than the planar shape 
shown in the figure. For example, the shelter plate 8 may be a reflector 
plate enclosing an upper side of each LED except for a lower portion 
thereof. 
The light transmitting openings 8a and 9a are formed in the center portions 
of the shelter plate 8 and the diffusing plate 9, respectively, so that 
light reflected on the standard mark 10 formed on the print circuit board 
3 may reach the ITV camera 2. A transparent glass or a lens may be 
provided in the light transmitting openings. 
The lower end of the light transmitting barrel 6 is located at a position 
which is very close to the standard mark as an object. For example, the 
distance between the end of the barrel 6 and the standard mark 10 is 2 mm 
to 5 mm. 
In operation, the light emitted from the LEDs 7 is diffused by the 
diffusing plate 9. The diffused light is further reflected at random on 
the inner surface of the light transmitting barrel 6 which is formed into 
the pear-skin reflector surface. The diffused light is thus directly 
projected on the standard mark 10 on the print circuit board 3. Hence the 
light applied on the standard mark 10 is diffused light projected from the 
entire caliber of the opening of the light transmitting barrel 6 which is 
considerably closely situated to the object to be detected. 
Since the lower end of the light transmitting barrel 6 is close to the 
object, the range between the incident angles becomes wide as shown by a 
reference 11c in FIG. 4. The range corresponds to a hatched area which is 
shown as the range of light applied to the point B in FIG. 4. As the 
illustration shows, even at the point B of the solder leveler 12 where the 
inclination is large, a reflected light Bo falls in a range directed 
toward the ITV camera 2 including the incident light Bi. As a result, the 
solder leveler 12 is depicted as a complete image by a binary numeral, so 
that the position of the standard mark 10 is accurately detected. 
Even in the light device 5 as the first embodiment of the present 
invention, there may remain a small undetected portion along the periphery 
of the solder leveler 12 of FIG. 4. Namely, the light reflected on the 
periphery is not directed to the ITV camera 2. Such a portion is very 
small and only formed evenly along the periphery of the solder leveler, so 
that the undetected portion can generally be neglected as a position 
detecting error. If it is undesirable to neglect the error, the upper 
surface of the solder leveler is ground with abrasive such as sand paper 
to form a coarse surface, thereby causing a diffused reflection of the 
light. Thus, areas of the surface, the reflection therefrom is not 
directed to the ITV camera 2, are diminished. 
In a conventional system, polishing of the surface has already been carried 
out to form a smoother surface, hence decreasing the portion which does 
not reflect light aimed toward the ITV camera 2. However, in the present 
invention, there is no need to further smooth the surface so that only a 
rough grinding is sufficient. 
The light emitted from the light source, is lead through the light 
transmitting barrel 6, the lower opening of which is positioned adjacent 
the object, so that the quantity of light diffused outside decreases. 
Therefore, a light source emitting a relatively small quantity of light 
suffices. Thus, instead of the expensive cold-cathode tube, which emits a 
large quantity of light, inexpensive LEDs can be used. 
In order to increase the incident angle of the light falling on the object, 
it is preferable to increase the caliber of the lower opening of the light 
transmitting barrel 6 as much as possible. On the other hand, in order to 
decrease the quantity of light diffusing outside, the opening is made as 
small as possible. It is hence necessary to determine the caliber of the 
barrel 6 in consideration of these inconsistent problems. 
In the light source device 5 of the first embodiment, the quantity of 
components of light substantially parallel to the surface of the object is 
smaller than the components of light substantially perpendicular to the 
surface. In other words, when the inclination of the surface of the solder 
leveler is large, or pinholes are formed in the solder leveler, the 
picture image becomes dark, so that gaps may be formed in the two-value 
data for the detected image. The second to fifth embodiments shown in 
FIGS. 5 to 8, respectively, are intended to increase the components which 
are substantially parallel to the surface of the object. In each of the 
figures, the same references as those in FIG. 2 designate the same parts 
so that the descriptions thereof are omitted. 
Referring FIG. 5, the light source device 5 of the second embodiment of the 
present invention is provided with a cylindrical surface light source 13 
in addition to the light source of LEDs 7. The surface light source 13 
comprises an electroluminescent element, fixed to the inner wall 6a of the 
light transmitting barrel 6 at a lower portion thereof. The inner wall of 
the surface light source 13 has a pear-skin surface to cause the diffused 
reflection of light. The surface light source 13 is applied with electric 
current and has a capacity for emitting a predetermined quantity of light. 
The surface light source 13 emits light from the entire surface thereof. 
The emitted light is substantially parallel to the surface of the standard 
mark 10. Thus the horizontal components of light are increased so that 
sufficient quantity of light is transmitted to the ITV camera even if the 
surface of the solder leveler 12 is largely inclined, or pinholes are 
formed. Hence, no gaps are formed in the binary numerals for the detected 
image. 
In the third embodiment shown in FIG. 6, a light transmitting member 15 
comprising a cylindrical acrylic resin plate is attached to the inner 
surface of a lower portion of the light transmitting barrel 6. The inner 
surface of the light transmitting member 15 has a pear-skin surface so as 
to cause diffused reflection. The light transmitting member 15 has a light 
emitting portion 15a which flares out downwardly. The light emitted from 
the LEDs 7 passes through the light transmitting member 15 and is radiated 
from the light emitting portion 15a toward the standard mark 10. 
Referring to FIG. 7, showing the fourth embodiment of the present 
invention, a plurality of optical fibers 16 are annually disposed between 
the LEDs 7 and a lower end of the light transmitting barrel 6. The upper 
end of each optical fiber 16 is disposed adjacent the LEDs 7. An 
intermediate portion of the optical fiber is extended outside the barrel 
6. The lower end re-enters the barrel 6 so as to face the lower end to the 
inner space of the barrel, thereby emitting a light in the horizontal 
direction. The inner wall 6a of the light transmitting barrel 6 has a 
pear-skin surface. Thus, the third and fourth embodiments provide the same 
effect as that of the second embodiment shown in FIG. 5. 
Referring to FIG. 8, the fifth embodiment of the present invention has a 
cylindrical surface light source member 17 comprising an 
electroluminescent element which covers the entire inner surface of the 
light transmitting barrel 6. The surface light source member 17 has an 
annular plate 17a having a central opening 17c at the upper inner portion 
thereof. A cylindrical body 17b of the light source member 17 is fixed to 
the barrel 6 and the annular plate 17a is fixed to a mounting plate 9b 
attached to the inner wall of the light transmitting barrel 6. LEDs are 
not provided in this embodiment. 
Since an electroluminescent element having a large capacity is used as the 
light source 17, the same effect as those of the previous embodiments is 
obtained although the LEDs are omitted in the present embodiment. 
Although the present invention has been described in accordance with the 
image processor converting the picture image into two-value data, the 
invention may be arranged to produce an image data represented by multiple 
values. 
From the foregoing, it will be understood that the present invention 
provides a light source device for an image processor wherein the light 
projected to the object to be detected is diffused from lower opening of 
the light transmitting barrel which is sufficiently close to the object. 
Accordingly, the light reflected on the object is substantially completely 
transmitted to the ITV camera despite the large inclinations and pinholes 
formed on the surface of the object. 
The light emitted from the light source is lead through the light 
transmitting barrel without diffusing outside of the barrel, so that it is 
possible to use an inexpensive light source capable of emitting a small 
quantity of light. Moreover, the components of light which are 
substantially parallel to the surface of the object are increased, so that 
gaps in the detected image data are diminished. 
While the invention has been described in conjunction with preferred 
specific embodiment thereof, it will be understood that this description 
is intended to illustrate and not limit the scope of the invention, which 
is defined by the following claims.