Light beam heating apparatus and method utilizing a fiber optic cable with random fiber array

A light beam irradiation apparatus includes a light source, a reflector for condensing light emitted from the light source, and a fiber cable for transmitting light reflected by the reflector. The fiber cable accommodates at least one bundle of optical fibers arrayed at random so that a fiber array at its first end differs from that at its second end. The apparatus further includes a lens, mounted on the second end of the fiber cable, for focusing the light on an object to be treated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a light beam irradiation (or heating) 
apparatus and a method for use in local heat-processing wherein light from 
a light source is condensed by a reflector. The apparatus and method 
according to the present invention are particularly useful in heating for 
local soldering, local removal of a film coated on a thin wire of 
polyurethane, local heat-processing for resins, or the like. 
2. Description of the Prior Art 
An apparatus for performing local heating is conventionally known wherein 
light from a light emitting lamp as a light source is condensed by a 
reflector and is directly applied to a local area of an object. 
The light condensed by the reflector spreads to some extent because the 
light source itself is not an ideal point light source or for to other 
reasons. For example, when a xenon lamp is used as a light emitting lamp, 
it has a spread of about 5 mm in diameter even at a location (beam waist) 
where light therefrom is throttled to the utmost. The distribution of 
light energy at the beam waist is not uniform. If heating, for example 
soldering, is performed using light having a non-uniform energy 
distribution, solder in the area receiving the light beam is not uniformly 
fused, thereby producing unevenness in its finish. 
FIG. 1 depicts a conventionally known fiber cable accommodating a bundle of 
optical fibers. As shown in FIG. 1, all the optical fibers are arrayed in 
parallel with one another. This fiber cable is in wide practical use today 
but is disadvantageous in that the distribution of light energy is not 
uniform, as discussed later. 
In the meantime, light energy required for heat-processing large quantities 
or resin or the like is less than that required in soldering. Accordingly, 
the level of light energy to be irradiated must be lowered, thus reducing 
the utilization of the light beam irradiation apparatus. 
When light beam irradiation is utilized in soldering at high temperatures 
or in removing a film coated on a wire of polyurethane, not only the 
amount of whole energy to be irradiated but also the energy density at the 
center is required to be enlarged. However, it has been impossible to 
accomplish this so far without enlarging the capacity of the light 
emitting lamp. 
SUMMARY OF THE INVENTION 
The present invention has been developed to overcome the above-described 
disadvantages. 
It is accordingly an object of the present invention to provide a light 
beam irradiation apparatus and a method capable of applying uniform light 
to an arbitrary local area of an object to be treated. 
Another object of the present invention is to provide a light beam 
irradiation apparatus and method capable of simultaneously applying 
uniform light to a plurality of objects to be treated. 
In accomplishing these and other objects, a light beam irradiation 
apparatus according to the present invention comprises a light source, a 
reflector for condensing light emitted from the light source, and cable 
means for transmitting light reflected by the reflector. The cable means 
has at least one first end for receiving the light reflected by the 
reflector and at least one second end for emitting the light therefrom, 
and includes at least one bundle of optical fibers arrayed therein at 
random so that the fiber array at the first end may differ from that at 
the second end. The apparatus further comprises a lens, mounted on the 
second end of the cable means, for focusing the light on an object to be 
treated. 
The random array of the optical fibers in the cable means averages the 
distribution of light energy at the second end even when the distribution 
of light energy is not uniform at the first end. 
A plurality of branch fiber cables may be branched from an intermediate 
portion of the cable means to provide simultaneous applications of light 
to a plurality of locations. The branching of the cable means is 
particularly useful in enhancing the utility of the apparatus in 
applications where not much light energy is required. 
The cable means may be enlarged in diameter and be so constituted as to 
accommodate a first bundle of optical fibers and a second bundle of 
optical fibers coaxially covering the first bundle. Preferably, both the 
first and second bundles of optical fibers are arrayed at random so that 
each of them has first and second ends which differ in fiber array from 
each other. This cable means can transmit an increased amount of light 
energy and provides a stepped energy distribution wherein the central 
portion thereof is high in energy density and the portion peripherally 
thereof is low in energy density. The apparatus provided with this cable 
means is particularly useful in soldering at high temperatures or in 
removing a film coated on a wire of polyurethane. 
Conveniently, the apparatus further includes a conical mirror, mounted on 
the second end of the cable means, for reducing the angle of spread of the 
light emitted from the second end and a reduction optical system for 
throttling the beam diameter of light reflected by the conical mirror. 
The apparatus having this construction can reduce a spread of light energy, 
thereby enlarging the energy density.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, there is schematically shown in FIG. 2 a 
light beam irradiation apparatus according to a first embodiment of the 
present invention. 
The light beam irradiation apparatus comprises a light emitting lamp 1, a 
reflector 3 for reflecting light from the light emitting lamp 1 to 
condense the light, a fiber cable 4 accommodating a bundle of optical 
fibers, a lens holder 5 secured to one end of the fiber cable 4, and a 
lens 6 accommodated in the lens holder 5. The light emitting lamp 1 emits 
light from a light emitting point 2 thereof. An object 7 to be treated is 
placed so as to be opposed to the lens 6. 
FIG. 3 depicts a fiber cable 4 according to the present invention. Light 
entering a generally circular inlet end 8 of the fiber cable 4 passes 
through the fiber cable 4 and is emitted from a generally circular outlet 
end 9 thereof. As shown in FIG. 3, a bundle of optical fibers are arrayed 
at random in the fiber cable 4, unlike the optical fibers shown in FIG. 1. 
Accordingly, the fiber array at the inlet end completely differs from that 
at the outlet end 9. 
FIG. 4 is a graph representative of a distribution of light energy at the 
inlet end 8 and that at the outlet end 9. In FIG. 4, the former is 
represented by a solid line whereas the latter is represented by a dotted 
line. Symbol (r) represents a radius of the fiber cable 4. As shown in the 
graph of FIG. 4, the distribution of light energy at the outlet end 9 does 
not become non-uniform, unlike the conventional fiber cable shown in FIG. 
1. The random array of the optical fibers in the fiber cable 4 can average 
the distribution of light energy and provides uniformity of light energy 
substantially within the limits of the radius (r) of the fiber cable 4. 
The fiber cable 4 has flexibility because a number of optical fibers are 
bundled up therein. Since the lens holder 5 and the lens 6 mounted on one 
end of the fiber cable 4 are both light, the lens holder 5 along with the 
lens 6 can be readily incorporated into a small robot so that an object 7 
may be heat-processed from an arbitrary direction at an arbitrary 
location. 
FIG. 5 schematically depicts a light beam irradiation apparatus according 
to a second embodiment of the present invention, which includes one fiber 
cable 4a and two branch fiber cables 4a1 and 4a2 branched therefrom at a 
branch point 10. The branch fiber cables 4a1 and 4a2 have respective 
outlet ends 9a1 and 9a2, from which light entering an inlet end 8a of the 
fiber cable 4a is emitted. 
It is to be noted here that although the apparatus shown in FIG. 5 has two 
branch fiber cables 4a1 and 4a2, three or more fiber cables can be 
branched from one fiber cable. Since branching one cable uniformly or at a 
given ratio can provide plural simultaneous applications of light energy 
from a single light source, the light beam irradiation apparatus is 
enhanced in utility. 
The fiber cable 4 shown in FIG. 2 can be replaced by a two-layer fiber 
cable 4b as shown in FIG. 6. This fiber cable 4b accommodates two bundles 
4b1 and 4b2 of optical fibers of which the first bundle 4b1 is coaxially 
covered with the second bundle 4b2. In each of the two bundles 4b1 and 
4b2, the optical fibers are arrayed at random so that the fiber array at 
an inlet end 8b or 8c may completely differ from that at an outlet end 9b 
or 9c. 
FIG. 7 is a graph representative of a distribution of light energy at the 
inlet ends 8b and 8c and that at the outlet ends 9b and 9c in the 
two-layer fiber cable 4b shown in FIG. 6. In FIG. 7, the former is 
represented by a solid line whereas the latter is represented by a dotted 
line. Symbols (r.sub.a) and (r.sub.b) represent a radius of the first 
bundle 4b1 and that of the second bundle 4b2, respectively. FIG. 7 shows a 
stepped energy distribution wherein the central portion of the fiber cable 
4b is high in energy density and the portion peripherally thereof is low 
in energy density. Accordingly, the fiber cable of FIG. 6 is preferably 
employed in applications where a large concentrated energy is required, 
for example, in soldering at high temperatures or in removing a film 
coated on a wire of polyurethane. 
FIG. 8 schematically depicts a light beam irradiation apparatus according 
to a third embodiment of the present invention, which includes a conical 
mirror 11, secured to an outlet end 9 of a fiber cable 4 for reducing an 
angle of spread of light emitted from the outlet end 9, a lens holder 5 
secured to the outlet end 9 and covering the conical mirror 11, and a lens 
6 securely mounted in the lens holder 5 so as to be opposed to the conical 
mirror 11. Light emitted from the outlet end 9 radially spreads at an 
angle (about 20.degree. in this embodiment) determined by a numerical 
aperture (0.35 in this embodiment) inherent in the fiber cable 4. The 
light is then reflected by a reflective surface 12 of the conical mirror 
11 and enters the lens 6. An angle .alpha. of the reflective surface 12 is 
set to be about half (about 10.degree. in this embodiment) the angle 
determined by the aforementioned numerical aperture. When light emitted 
from the outlet end 9 at a maximum angle is reflected by the reflective 
surface 12 of the conical mirror 11, the light turns to generally parallel 
rays. Accordingly, even in an optical reduction system wherein the 
distance between the outlet end 9 and the lens 6 is extended, it is 
possible to condense almost all light on the lens 6, thereby increasing 
the energy density of light emitted from the lens 6. 
As described above, according to the present invention, the random array of 
optical fibers in a fiber cable can average the distribution of light 
energy and can condense the light energy to within predetermined limits, 
thus making it possible to easily apply uniform light energy to only that 
area of an object which requires heating. As a result, the surface finish 
after local soldering becomes good and there is no fear of damage of parts 
close to the object due to unintended heating of such parts. 
Furthermore, the present invention provides the selective use of branched 
fiber cables, which enables light energy from a single light source to be 
simultaneously applied to a plurality of locations, thereby enhancing the 
utility of the light beam irradiation apparatus. 
In addition, the use of the two-layer fiber cable having random fiber 
arrays and the conical mirror enables the application of light energy with 
a high energy density. As a result, local film removal of a polyurethane 
wire and soldering at a high temperature can be easily reliably carried 
out. 
Also, since the fiber cable has a flexibility and both the lens and the 
lens holder are small and light, these members can be easily mounted on a 
small robot. This fact facilitates the automation of a local 
heat-processing such as, for example, a local soldering. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless such changes and modifications otherwise depart 
from the spirit and scope of the present invention, they should be 
construed as being included therein.