Air curtain former for creating an air curtain to compensate for impurity buildup

This invention presents a method of clearing a sensor field of debris, including liquids, through the use of an air curtain. An embodiment of this invention addresses the problem of impurity buildup in the sensing field of an optical sorter. An air curtain is created which prevents film buildup between the light sensor and the light source by blowing material and impurities, which form the film as they fall off articles being sorted, out of the sensing field.

Be it known that I, Arthur G. Doak, a citizen of United States, residing at 
Nashville, Tenn.; have invented "An Air Curtain Former for Creating an Air 
Curtain to Compensate for Impurity Buildup." 
BACKGROUND OF THE INVENTION 
This invention relates to clearing sensors of debris to provide more 
accurate sensing data. A particular embodiment specifically relates to 
reducing film buildup over optical sensors in an optical sorting machine 
due to impurities carried along with the articles to be sorted. 
Optical sorting machines, of the type to which an embodiment of this 
invention relates, work on the principle of light attenuation. Generally, 
sorters of this type are used to sort articles, such as glass cullet or 
other material, for post consumer recycling and processing. The glass 
cutlet are intermixed with dirt, sand, and other impurities; it is not 
economically viable to preclean the cullet. Although optical sorting of 
glass is offered as an example, the problems of impurity build-up applies 
to any sorting machine. For example, metallic build-up on an eddy current 
sensor can affect its operation. Liquid or particulate build-up on a 
plastic sorting machine can affect its operation. 
Optical sorters of this type generally work as follows. The cullet pass 
through a sensing field where light of different wavelengths is emitted by 
light sources and sensed by sensors. The sensors generate signals 
corresponding to the magnitude of light sensed. Cullet of different color 
attenuate different wavelengths of light different amounts. This 
attenuated light signal is compared against a baseline value for the 
signal to determine the color of the cullet. 
Impurities carried along with the cullet buildup over the sensors. This 
shifts the attenuation value and leads to missorts. These missorts may 
lead to less pure sorted lots. Lower quality lots are, thus, passed on for 
subsequent processing. Alternatively, cullet having potential value are 
erroneously discarded due to shifted attenuation readings. 
Prior art has attempted to compensate for impurity, or film, buildup by 
increasing, or lowering, the baseline value over time. This has proved 
less than satisfactory. One reason for the short fall is that the impurity 
layer is not uniform. As the film layer builds, cutlet tend to create 
furrows in the film layer. This results in nonuniformities in the film 
layer, and tends to lead to missorts. 
The prior art has also attempted to solve the problem by cleaning the 
screen. However, the cleanser can affect the sort. 
The prior art has also attempted to solve the problem by repeatedly 
replacing the wearcover; this increases expense and down time. 
What is needed is a device to reduce light attenuation shifts due to film 
build up in an optical sorting device. This needed system must be 
efficient and economical. This needed system must decrease down time. This 
needed system must efficiently clean the sensor area to reduce the effects 
of particulate and fluid build-up. This needed system is lacking in the 
prior art. 
SUMMARY OF THE INVENTION 
This invention presents apparatus and methods to clear sensors of debris 
through use of an air curtain. Reliability of the sensor data is, thus, 
improved. Generally, most sensors susceptible to distortion by debris, or 
impurities, including liquids, in the sensing field, may benefit from this 
invention. One embodiment of this invention, in particular, addresses the 
problem of impurity buildup in the sensing field of any sorter including 
an optical sorter. Buildup of film and other impurities affect the 
attenuation values because light is attenuated by the film as well as the 
article to be sorted. These articles are generally glass cullet. Glass 
cullet, generally, are broken pieces of glass bottles and the like. The 
shifted attenuation readings lead to article missorts. This invention 
overcomes attenuation problems due to nonuniformities associated with 
cullet furrowing. 
The nonuniformities in the film layer are overcome by providing a layer of 
air between the sensors (or sensor) and the cullet. Impurities often fall 
off often the cutlet as the cullet pass through the sensing field. An air 
curtain is created which protects the sensors from film buildup by blowing 
impurities out of the sensing field. 
The device which creates the air curtain has an airflow plane below a slide 
on which cutlet slide. The slide in a cullet sorting machine is frequently 
called a `wearcover`. The slide portion of the device ends at the sensing 
field. In the sensing field emitted light is sensed by sensors and 
attenuated by cullet. 
Between the slide and airflow plane is an air passage. Air is forced 
through the passage with sufficient force to provide an air curtain. The 
air curtain blows impurities which fall toward the sensors out of the 
sensing field, typically downstream, thus, providing an air curtain over 
the sensors. 
Beyond the sensing field, the airflow plane is curved away from the 
wearcover. The air layer will follow the curved plane. This phenomena of 
the air layer adhering to the airflow plane is generally referred to as 
"pneumatic wall attachment." This phenomena is employed to divert the air 
stream below the path of the cullet. Diverting the air stream below the 
cutlet path limits the chance that the air curtain may interfere with the 
ejector. The ejector used with the sorter is generally an air jet, or air 
valve. After through the sensor field, cullet are then ejected from the 
cullet stream by an ejector, or allowed to pass. 
In one embodiment, the sensors are covered with a transparent cover which 
is in plane with the airflow plane and below the layer of air. To reduce 
optical distortion, the transparent cover is adapted to be bonded to the 
sensors with transparent silicone grease, or similar substance. The 
silicone grease provides an optical connection medium with properties 
similar to the transparent cover. 
An object of the invention is to provide a device to reduce light 
attenuation shifts due to film build up in an optical sorting device. 
Another object of the present invention is to provide a system for cleaning 
the sensor area of any sensing system. 
Another object of the present invention is to provide a system which is 
economical to manufacture and use; and may be adapted to use with existing 
sensing systems.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Applicant's invention will be best understood when considered in light of 
the following description of the preferred embodiment of the invention as 
illustrated in the attached drawings wherein like referenced numerals and 
characters refer to like parts. 
FIG. 1 shows an air curtain former 5. It includes an airflow plane 10 and a 
transparent cover 20. The transparent cover 20 sits in plane with the 
airflow plane 10 and below the path an air layer will flow. Beyond the 
sensing field 82, the airflow plane 10 includes a curve 12 and a terminus 
15. 
The curve 12 curves away from the path of the cullet to limit possible 
interference with the ejector jets by the air curtain. The curve 12 and 
the terminus 15 may be separated by a fall away (14), as in FIG. 1, or 
merged into a single curve, as in FIG. 3. The curve 12, if used, should be 
sufficiently gradual so as to maintain a pneumatic wall attachment 
phenomena. 
FIG. 1 also includes a slide (or wearcover) 30 parallel to the airflow 
plane 10. Together the wearcover 30 and the airflow plane 10 form an air 
passage 40. The slide 30 includes a terminating end 35 which terminates at 
the onset of the sensing field 82. FIG. 2 show the slide terminating end 
35 ending prior to a plane in which the light source 90 and the light 
sensor lie 92. 
In one embodiment, the airflow plane curve 12 is downstream of the plane in 
which the light 90 and the sensor 92 lie. Downstream is defined in the 
direction of the cullet path. A fluid conduit 50 for conducting air 
supplied to the air passage is also shown in FIG. 1. 
FIG. 2 shows an air curtain former 5 substantially similar to the air 
curtain former shown in FIG. 1, however, it is shown with the light source 
90 the light sensor 92, and the cullet 84. The forced air layer 80 which 
flows through the air passage 40 is also shown in FIG. 2. The air layer 
80, as shown, adheres to the airflow plane 10 around the curve 12 of the 
airflow plane 10. An upstream slide 96 delivers cullet 84 to the air 
curtain former 5; the cullet then pass through the sensing field 82. 
FIG. 3 shows an air curtain former 5 substantially similar to the air 
curtain former shown in FIGS. 1 and 2. FIG. 3 further shows an ejector 
system 70 including a splitter 72, an ejector nozzle 74 and a solenoid 
valve 76. The solenoid valve 76 allows air from an air supply 94 to eject 
ejected material 83 and allow non-ejected material 85 to pass downstream. 
The preferred embodiment is an air curtain former 5 for forming an air 
curtain to compensate for false signal readings which are due to dirt, 
film, and other impurities building up between the light sensor 92 and the 
light source 90. The light sensor 92 senses the emitted light and 
generates signals. The signals have amplitudes corresponding to the 
magnitude of the light sensed. 
It will be apparent to those skilled in the art of sensors, that the 
invention may be used to clear foreign material, including debris, film, 
liquid, and the like, from a multitude of sensor types. Some sensor types 
that may benefit from an air curtain to clear the sensing field include 
those that use magnetic fields, electromagnetic fields (including thermal 
and nuclear radiation), acoustic fields, and optical sensing. Generally, 
any sensor field which may be distorted by impurities, and not effected by 
air flow, may benefit from the invention. In those systems which may be 
interfered with by air flow, the air curtain may be adapted to limit, or 
avoid, interference by the air flow. The curve 12 shown in FIGS. 1 through 
3 is an example of one such adaptation; it diverts air away from the 
cullet stream using pneumatic wall phenomena. 
Referring to an optical sorting machine of the type in which a preferred 
embodiment of this invention is used, when cullet 84 pass through the 
sensing field 82, the cullet 84 attenuate the light sensed. Different 
color cullet 84 attenuate different wavelengths of light different 
amounts. For instance a red cullet would attenuate a green light 
wavelength more than a red light wavelength. The attenuated signal is 
compared to a baseline amplitude value for the given wavelength of light; 
color of the cullet can be determined from an attenuation analysis. 
Cullet are, however, intermixed with film, dirt, sand and the like. Cullet 
carry this film with them through the sensing field 82. The film rubs off 
and is deposited on the sensor 92. The film layer further attenuates the 
light source 90; this leads to false optical signal readings. Missorted 
cullet 84 result from this attenuation shift. 
An airflow plane 10 is oriented parallel to the path of the cullet 84. The 
airflow plane 10 is adapted to receive the light sensor 92. A transparent 
cover 20 fits in plane with the airflow plane 10 and beneath the path an 
air layer 80 will take. The transparent cover 20 covers and protects the 
sensor 92. The transparent cover 20 is adapted to be bonded to the sensor 
92 with transparent silicone grease. The silicone grease should be packed 
in and around the sensor 92 and up against the transparent cover 20. This 
reduces bending and light defraction as the emitted light passes through 
different mediums. The silicone grease has properties more similar to the 
transparent cover than air, so the light rays are bent less than if they 
were to pass through an air medium after passing through the transparent 
cover 20 before being sensed by the sensors 92. 
One of the preferred embodiments also includes a slide (or wearcover) 30 
which is oriented parallel to the airflow plane 20. The wearcover 30 is 
offset from the airflow plane 10 to form an airflow passage 40. The 
wearcover 30 has a terminating end 35 which abuts the sensing field 82. 
The other end of the wearcover 30 mates with an upstream slide 96. The 
upstream slide 96 provides a means for the cullet 84 to ultimately reach 
the sensing field 82. 
A fluid conduit 50 conducts air supplied from an air supply 94 to the 
airflow passage 40 such that an air layer 80 flows along the airflow plane 
10. Film and impurities are thereby blown off of, and away from, the 
sensor 92 as the cullet pass through the sensing field 82. 
The airflow plane 10 has a terminus 15 and a curve 12. The curve 12 is 
curved away from the cutlet path. It is sufficiently curved to divert the 
air layer 80 away from the cullet path. If the curve 12 is curved or bent 
too sharply, the air layer 80 will not adhere to the wall. If the air 
layer 80 is not diverted, it may interfere with passage of material 
through the ejector. 
Cullet are then ejected from the cullet stream by the ejector system 70, or 
allowed to pass. One such ejector system 70 employs a splitter 72 and air 
forced through an ejector nozzle 74. The ejector nozzle 74 is attached to 
an air supply. A solenoid valve 76 operates to allow air through the 
ejector nozzle 74 and blow ejected material 83 out of the path of 
non-ejected material 85. The non-ejected material, or accepted cullet, 
continue downstream. 
Because there is no film buildup to attenuate the light, the light is only 
attenuated by the passing cullet, and the attenuated light more accurately 
represents the colors of the cullet. The more accurate color distinction 
results in fewer missorts which improves purity of the sorted lot and 
increases the material to be processed on down the line. Because the 
sensor was cleared of attenuating debris in an economical manner, greater 
profit is derived from the purer sorted lot. 
Thus, although there have been described particular embodiments of the 
present invention of "Air Curtain Former for Creating an Air Current to 
Compensate for Impurities," it is not intended that such references be 
construed as limitations upon the scope of this invention except as set 
forth in the following claims.