Laser shielding device

A laser shielding device is disclosed, having two spaced-apart layers of shielding material defining a sealed chamber between the two. At least one layer will degrade in the presence of an impinging laser beam, creating a hole through the layer. A pressure change in the chamber is sensed and signaled to a machine controller to stop the lasing operation.

BACKGROUND OF THE INVENTION 
This invention relates generally to the field of work zone enclosures for 
laser beam and for shielding of the environmental areas surrounding laser 
work zones. 
The invention relates in particular to work zones where a wieldable laser 
gun or focusing apparatus is moved through multispatial orientations when 
performing operations on a workpiece. 
It has been known to use low power laser beams for performing a variety of 
functions such as aligning machines, wherein a red visible laser beam 
might be employed to effect the alignment. Such low power laser beams 
generally present no problem to surrounding areas and personnel. Recently, 
however, it has become useful to employ what are known as "power lasers" 
to effect material cutting and welding operations. What is meant by power 
lasers are those typically, in the neighborhood of lkw, more or less, 
which have a light beam capable of burning through material if left on the 
target spot and, similarly, which are capable of inflicting injury on 
personnel because of the level of energy employed. 
Many types of laser generating media may be employed to effect power 
lasing, for example, solid lasers (e.g. ruby crystal), and gas lasers 
(e.g., carbon dioxide) to name several. 
Conventional laser cutting and welding apparatus generally employ a fixed 
laser focus unit with a means for moving a workpiece around with respect 
to the laser beam. From the advent of robots in the industrial workplace, 
robots have advanced from being utilized as merely loaders, or part 
manipulators, to the present state-of-the-art where the robot actually 
becomes a full process machine having as many as six axes of movement due 
to advanced wrist designs. These full process robots, are capable of 
performing many operations, such as precision measurement of a workpiece. 
Recently, it has been suggested that the end effector of a robot wrist 
might be utilized to carry a laser focus unit so that complex operations 
could be performed on a workpiece through use of a "wieldable" laser, that 
is, capable of movement through a high degree of multispatial 
orientations. Many power lasers operate in the infrared or invisible light 
spectrum, so that personnel may not be able to visually detect the 
presence or absence of a laser beam such as that emitted by a carbon 
dioxide laser. Several formidable problems arise when using a wieldable 
laser, particularly that which emits radiation in the infrared spectrum: 
(1) The laser beam may be directed at surfaces other than in the work zone 
by improper focusing on the target; or (2) the laser beam, which is 
reflectable radiation, may strike a reflective surface and be redirected 
to a point outside the work zone. As a result of these problems, injury to 
personnel and damage to environmental points outside the work zone may 
occur. It has been known in the robot industry, at least on an 
experimental basis, that a single layer of shielding material might be 
employed around a laser work zone, to protect the environment from a stray 
laser beam. Ideal shielding materials should be capable of absorbing at 
least a portion of the laser beam energy. 
The carbon dioxide laser is probably the most widely used and versatile 
type of power laser in use. It can emit infrared radiation at many 
discrete wave lengths between nine and eleven micrometers. While carbon 
dioxide gas is the light emitter, CO.sub.2 lasers usually contain a 
mixture of other gases together with carbon dioxide to accomplish the 
lasing of light. The internal workings of CO.sub.2 (and other types) power 
lasers is generally of no concern to the shielding designer, provided that 
the wave length of the emitted light is known for shielding purposes. It 
is known that ordinary glass will totally absorb 10.6 micrometer energy 
and, in fact, can be cut with CO.sub.2 lasers. Conversely, many optical 
materials are transparent at 10 micrometers but do not transmit visible 
light very well. It is preferable in many cases to have shield which is 
transparent to the human eye so that the work zone may be viewed while the 
operation is being performed. 
Single shielding layers of a thermoplastic material such as transparent 
acrylic, commonly available under the trademarks LEXAN and PLEXIGLAS have 
been successfully employed for shielding a power laser beam, because the 
material will absorb at least a portion of the laser beam and will degrade 
accordingly. For example, a power laser beam in the range of lkw will take 
approximately 15 seconds to burn through a 1/4 inch thickness acrylic 
plastic. Personnel in laboratory situations can readily detect the 
discoloration occurring on a portion of a plastic shield, and generally 
have sufficient time to shut down the system and find the fault in 
misdirection of the laser beam. Obviously such a scheme depends totally on 
manual intervention. 
Applicant has obviated many difficulties inherent in the laboratory 
attempts to shield a laser beam work zone and visibly detect a stray laser 
beam, by designing an automatic device which will, upon continued presence 
of a stray laser beam, provide a signal which is indicative of the fault 
condition, and which is capable of automatically initiating a machine shut 
down condition. 
It is therefore an object of the present invention to provide an automatic 
sensing system for shielding a laser work zone. 
Another object of the present invention is to provide a signaling device to 
indicate a laser direction fault condition. 
Still another object of the present invention is to provide a shielding 
device for a laser work zone which is capable of sensing and signaling a 
laser fault condition, wherein the signal may be utilized for a variety of 
purposes, including actuating an alarm such as an annunciator or visual 
device for machine personnel, and for initiating a shut down of the lasing 
apparatus. 
SUMMARY OF THE INVENTION 
The invention is shown embodied in a laser shielding device wherein first 
and second shielding layers are held in structure with a means for spacing 
the layers from one another and creating a chamber between the two. At 
least one layer is comprised of material capable of absorbing at least a 
portion of a laser light beam and degrading in the presence of the beam. A 
pressure source is connected to the chamber created between the two 
shielding layers, and means is provided for sensing and signaling a 
pressure change in the chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawing FIG., there is shown an industrial robot 10 of the 
kind depicted in U.S. Design Pat. No. 269,681 and having a wrist device 11 
such as that shown and described in U.S. Pat. No. 4,068,536. The forearm 
12 of the industrial robot 10 has a bracket 13 adapted thereto for 
carrying a laser generator 14, such as the CO.sub.2 laser depicted. The 
power unit 15 for the laser generator 14 is carried on a special bracket 
16 fixed to the rotatable shoulder joint 17 carried on the robot base 18. 
The laser generator 14 utilizes a light pipe system 19, mounted to its 
forward end 20, to direct a laser beam 21 through serially-related light 
pipes 22 joined at articulations 23, or reflective joints, which might 
employ totally reflecting mirrors. The terminal part 24 of the light pipe 
system 19 utilizes a focusing unit 25 to converge the light beam 21 on a 
target or work zone. The focusing unit 25 is carried by the robot wrist 
end effector 26 so that the laser beam 21 will be "wieldable", i.e., 
manipulatable through movements comprising multispatial orientations. 
An exemplary workpiece has not been shown, but rather a work support base 
27 is depicted having a reflective top surface 28. An improperly focused 
or misdirected light beam 21 may be reflected off the top surface 28 and 
continue on to an environmental area outside the work zone. 
To interrupt the travel of the misdirected light beam 21, a laser shielding 
device 29 is shown in conjunction with the laser work zone in broken-away 
cross-sectional. The laser shielding device 29, in its simplest 
constructed form, comprises a fabricated structure having first and second 
spaced apart layers 30,31 of laser shielding material. The layers 30,31 
are separated by a continuous spacer 32 which maintains a constant space 
between the layers 30,31 and which serves to create an enclosed chamber 33 
between the two layers 30,31. The layers 30,31 are fastened to the spacer 
32 by a plurality of screws 34. The laser shielding device 29 further 
employs a channel-shaped member 35 at its bottom edge for supporting the 
device 29 in a vertical orientation. 
A fluid port 36 is provided in the second layer 31 of material, and a pipe 
37 and tee 38 are shown connected from the port 36 to an air pressure 
source 39. The air pressure source 39 serves to pressurize the enclosed 
chamber 33 to a point just above atmospheric pressure, so as not to 
distort the shielding layers 30,31. The tee 38 has a side outlet 40 
connected by a suitable pipe nipple 41 to a pressure switch 42 which may 
be any of a number of commercial switches well-known in pneumatic art. The 
pressure switch has pair of internal contacts (not shown) which are used 
for creating a signal on an output line 43 when a pressure change occurs 
within the enclosed chamber 33. The output line 43 is shown connected to 
the laser generator power unit 15 so that, upon sensing a pressure drop in 
the enclosed chamber, the laser beam will be turned off. 
It may be appreciated by those skilled in the art, that the signal line 43 
may be similarly provided to a robot control (not shown) to cease 
movements of the robot 10, and/or the line 43 may be connected to a 
personnel alarm, such as an annunciator or flashing red light, to indicate 
a pressure drop in the enclosed chamber 33. 
The pressure drop signaling a fault condition occurs by virtue of the laser 
beam 21 striking the first shielding layer 30. Continuous absorption of at 
least a portion of the laser beam 21 will cause a degradation to take 
place and subsequently a hole will be generated through the first laser 
shielding layer 30 and escape of air pressure will occur. The first 
shielding layer 30 is selected to be compatibly matched with absorption of 
the laser light employed in the operation. In the preferred embodiment, a 
CO.sub.2 laser source is utilized which emits light in the infrared 
spectrum in the range of 9 to 11 micrometers. Common glass might have been 
employed as the first shielding layer 30, wherein total of any CO.sub.2 
light beam of 10.6 micrometer wave length would occur, but the shielding 
layer may tend to crack and possibly shatter. A more suitable material for 
the purpose is acrylic plastic, in the thickness of 1/4 inch, where the 
laser beam impingement will cause discoloration and burning through after 
approximately 15 seconds. The second shielding layer 31 may be any of a 
variety of materials, which may be opaque or transparent. However, for 
additional safety in controlling the stray laser beam, acrylic plastic 
becomes a very suitable material for the second shielding layer 31, as 
well. 
Several advantages are had when using the desirable acrylic plastic layers: 
(1) a lightweight structure is formed which may be easily supported and 
moved about with respect to the laser work zone; (2) transparent acrylic 
plastic may be employed so that personnel may be easily able to view the 
laser work zone. 
While the invention has been shown in connection with a preferred 
embodiment, it must be additionally noted that variations on the 
embodiment may be employed without departing from the scope and nature of 
the present invention. For instance, negative pressure might be employed 
within the enclosed work chamber 33 and yet still be active to operate a 
sensing and signaling means such as the pressure switch or a substitute 
therefor. Another variation is to fill the chambers 33 with a colorless 
gas under low pressure which, when released, could be detected with an 
electronic monitor, i.e. "sniffer", capable of detecting low 
concentrations (ppm). 
Additionally, while planar sheet members have been shown to depict the 
laser shielding layers 30,31, it may be appreciated that curved or 
specially molded shaped might be employed around the laser work zone, so 
long as a substantially enclosed chamber 33 is formed between the two 
shielding layers 30,31. It may be further appreciated that additional 
layers of laser shielding material may be employed for increased 
reliability and safety. 
The invention as shown and described in the foregoing preferred embodiment 
is not intended to be limited to said embodiment, but rather the invention 
extends to all such designs and modifications as come within the scope of 
the appended claims.