Patent Publication Number: US-11033645-B1

Title: Apparatus for rapid disinfection of personal items

Description:
BACKGROUND 
     Technological Field 
     Embodiments of the invention relate ultraviolet disinfection. More specifically embodiments of the invention relate to rapid ultraviolet disinfection of personal items. 
     Background 
     The novel corona virus that causes COVID-19 has been highly disruptive to the global economy. It has also highlighted the degree to which contagion can be spread through contact with everyday items. Personal electronic devices such as cell phones have been found to be significant vectors for viral and bacterial transmission. Taking the smart phones as an example, the normal use of the touch screen result in repeated hand contact with the screen. That contact can result in pathogens transferred from the user&#39;s hands to the screen. The pathogens may originate on any surface that the user touches, such as a grocery cart, handrail in public transportation, doorknob are just some examples. When a call comes in, the user then often puts the phone to their ear and risks transfer of the pathogens to their face including potential exposure to the mucous membranes in the mouth and nose which are often the pathway to infection. 
     In an effort to combat the spread of the novel corona virus, particular attention in being given to hand washing. Unfortunately, immediately after handwashing the hands are often again contaminated through contact with a pathogenic rich smart phone or other such item. While some devices exist to disinfect smartphones, the typical model is a clam shell enclosure that requires the phone reside therein for thirty minutes or more to complete the disinfecting process. Such time requirement significantly reduces the utility of the device. Moreover, a user is required to manipulate the clam shell to open and close it, providing additional opportunities for transfer of pathogens. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that different references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
         FIG. 1  is a perspective view of a disinfecting unit and target object according to one embodiment of the invention. 
         FIG. 1A  show a sink with two possible footprints for embodiments of the invention. 
         FIG. 2  is a section view of the embodiment of  FIG. 1  taken through section A-A. 
         FIG. 3  is a perspective view of one embodiment of the invention with the end of the housing removed. 
         FIGS. 4A-4C  illustrate edge disinfection schematically according to one embodiment of the invention. 
         FIG. 5  is a perspective view of one embodiment of the invention with the end of the housing removed. 
         FIG. 6  is a block diagram of active components of a system of one embodiment of the invention. 
         FIGS. 7A and 7B  are a flow diagram of operation according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the invention provide a high-speed hands-free apparatus to destroy pathogens on personal items. By bringing the time to complete the disinfection process into a range consistent with the time required for proper handwashing, wider community adoption and reduced community infection is expected. Furthermore, event without the reduced time benefit a touchless design reduces the risk of disease transmission. 
       FIG. 1  is a perspective view of a disinfecting unit and target object according to one embodiment of the invention. Disinfector  100  has a housing  102  with an internal volume and particularly a disinfection zone sized to accept an object of interest  120  for disinfection. For example, in some embodiments the objects of interest  120  are smart phones and the disinfection zone is sized to accommodate the desired range of smart phone sizes. Other embodiment may be sized to accept a range of personal items such as personal electronic devices (PEDs), credit cards, wallets and the like. PEDs include smart phones, but may also include tablets, phablets, pagers, personal digital assistants, e-readers and the like. Ultraviolet (UV) light of an effective wavelength and intensity is applied within the disinfection zone to destroy pathogens on the object of interest  120 . In one embodiment, the selected wavelength of light is 200 nm to 280 nm. In some embodiments, the wavelength is in the range of 240 nm and 280 nm. As used herein, “disinfection zone” refers to the volume within the housing  102  in which disinfection occurs. 
     Housing  102  defines an object access port  104 . Object access port  104  is in communication with the interior volume and size to accept and object of interest  120 . One embodiment is sized to accept most smart phones. Currently, the larger end of the smart phone size range is at about 8.5 cm×16 cm×1.2 cm. If the embodiment is designed to accept the phone in landscape orientation, the port  104  may be in the range or 16.2-16.5 cm×1.3-1.5 cm to accommodate such a phone in a case. If the embodiment is designed to accept the phone in portrait orientation, the port  104  may be in the range or 8.7-9.00 cm×1.3-1.5 cm to accommodate such a phone in a case. These are merely examples and other dimension may be selected in different embodiments of the invention. It should be understood that the housing ratio of height to length is driven, at least in part, by which orientation the object of interest is to be accepted. By accepting the phone in a landscape orientation, the range of movement (as described below) is reduced. In one embodiment, the housing, in use, has a generally vertical orientation and the object access port is in an upper surface of the housing. This configuration allows gravity to help the object of interest remain in a desired orientation as discussed in more detail below. Other embodiments may have the object access port  104  in another surface of the housing  102 . 
     The access port  104  is occluded by resilient fingers  106 . Resilient fingers  106  occlude the access port to prevent the escape of UV light from within the housing  102  and support the object of interest  120  as it enters the housing. In some embodiments, an underside of the resilient fingers  106  is reflective. Generally, resilient fingers  106  could be formed of silicone or another generally nonreactive elastomer. The undersurface can be treated with a reflective coating. In some embodiments, monolithic resilient wipers may be used instead of the resilient fingers  106 , but this may not be as effective for blocking the light when different sized objects  120  are used with the same device. 
     In some embodiments, housing  102  has a gross geometry that does not change during use. As used herein, “gross geometry” refers to the bounding volume required to contain the housing. In the shown embodiment, a rectangular box with a length, width, and height can bound housing  102 . None of these bounding dimensions change during use. In contra distinction devices, such as clam shell devices that hinge open necessarily require a different bounding volume when open versus when closed and have different gross geometries in the different orientations. 
     Some embodiments have a small footprint. As use herein footprint is defined as the area given by length times width of the minimum bounding box that can enclose the disinfector at its widest point in the plane normal to the height dimension. That is, overhanging parts and extending arms for example are deemed to impact the “footprint.” The shown embodiment, disinfector  100  has a substantially uniform cross section for its full height. The footprint  112  has an area of L×W as shown in  FIG. 1 . In one embodiment, the disinfector  100  has length, width and height of 180 mm, 50 mm and 135 mm respectively. This yields a footprint of 9000 mm 2  and a gross geometry that fits in a bounding box that is 180 mm×50 mm×135 mm. 
       FIG. 1A  show a sink with two possible footprints for embodiments of the invention. This illustrates the limited real estate typical available around a sink and the importance of keeping footprints  112  small. 
     In some embodiments, the footprint is less than 15,000 mm 2 . In other embodiments, the footprint is less than 10,000 mm 2 . Generally, the width will be less than half of either the length or height dimension. This is particularly desirable for embodiments intended to be used in bathrooms in conjunction with hand washing. As a general matter the available space around a sink is relatively small and tend to be narrow. By keeping the footprint small, the disinfector can be deployed where it will be most useful, without interfering with normal sink operation. 
     Instead of standing on horizontal surface, some embodiments may include brackets  110  to facilitate mounting on a wall or other substantially vertical surface. Brackets  110  may be incorporated into the housing  102  or may be separately coupled thereto. Even in wall mounted embodiments, it is desirable to keep the width dimension small, so the disinfector remains relatively unobtrusive. 
       FIG. 2  is a section view of the embodiment of  FIG. 1  taken through section A-A. Within the housing  102  is a carriage  212  attached to a drive  216 . In use the carriage  212  receives the object  120 . The drive  216  is driven by an actuator  218  to move the carriage (and therefor the object  120 ) though a UV-C light stripe  222  (shown schematically in this figure). Preferably, UV-C light having a wavelength in the range of 200-280 nm is used. More preferably, UV-C light falling in the range of 240-280 nm is used. As used herein “light” refers to UV-C light. Also as used herein, “light stripe” refers to an area of UV-C light having a length dimension greater than a width dimension. 
     Carriage  212  has a plurality of object retention features  214  adapted to receive the object of interest. In some embodiments, object retention features  214  may rely solely on gravity and/or friction to maintain objects thereon. In other embodiments the features may have a mechanical grip or clamp that holds the object of interest. In some embodiments, the features  214  are formed of quartz or fused silica glass as these materials do not attenuate UV-C light as does regular glass or polycarbonate. In one embodiment, ends of retention features terminate in a resilient clip with a jaw sized to accommodate a range of objects of interest. Generally, object retention features  214  will be formed from a substantially transparent synthetic material to permit UV light to pass through the material to reach the object of interest where the features  214  contact that object. In some embodiments, carriage  212  may be injection molded or extruded. As described further below, an upper surface of the carriage  212  may be made reflective to facilitate disinfection of the object of interest. Similarly, the underside  206  of fingers  106  are treated or coated to be reflective. 
     In various embodiments, actuator  218  could be a gyro, a servo, a stepper motor, a dc motor, a piezo electric motor, a solenoid or the like. The actuator  218  should be selected to provide sufficient torque to drive the drive  216  when loaded with an object  120 . Drive  216  can be a screw drive, track drive, belt drive or any other transport that can cause relative movement between the carriage  212  and the light stripe  222 . In some embodiment, the drive merely carries the object  120  into and out of the housing  102 . In other embodiments, enable the selective exposure of the object  120  to the light stripes  222 . A controller  220  selectively activates one or more emitters and the motor responsive to one or more sensors as described in more detail below. Controller  220  could be a microcontroller, microprocessor, application specific integrated circuit (APIC), field programmable gate array (FPGA) or the like. 
     In one embodiment, light stripe  222  is generated by an emitter configured to emit a stripe of sufficient length to be greater than the maximum side dimension of the object (e.g. object  120 ) to be exposed to the emitter. In one embodiment, the light stripe  222  emitted is greater than the length of the object access port  104 . In one embodiment, the emitter is formed from a plurality of UV-C light emitting diodes LED&#39;s sufficient to create the light stripe  222  of the desired length by spacing the LED so that the cones of light produced overlap at a range of interest. For example, in one embodiment, six commercially available UV-C LEDs could be used spaced approximately 28.33 mm apart to yield a light stripe  222  approximately 194 mm long at a range of 16 mm (the stripe is longer than the internal cross dimension and is reflected by the side wall as described below). In another embodiment, a laser could be used to form the light stripe  222  by either spreading the laser beam or rastering the laser to form a stripe  222  of the desired length. Rastering can be performed by either moving the laser or moving a reflective element at which the laser is directed. In some embodiments, rastering the laser is under the control or controller  220 . 
     In some embodiments, a second emitter creates a second light stripe that mirrors light stripe  222  and is emitted on an opposite side the object of interest. In this way, the full cross dimension of both sides of the object of interest will be covered by a light stripe. In some embodiment, more than one emitter may reside on a side of the object so that a single side of the object tis expose to more than one light stripe at the same time. At the limit, sufficient light stripes could be generated to cover an entire side of the object at one time. 
     In some embodiments, a transparent partition  204  may be interposed between the emitter(s) and the carriage  212 . In principle, if the entire perimeter of the object is exposed to a light stripe, moving the object relative to the light stripe can expose the entire exposed surface area to the light stripe. The transparent partition  204  may be formed of quartz or fused silica glass to avoid blocking light from the emitters. The partitions reduce the risk of particulates entering the area of the housing  102  occupied by electronic components and prevent the possibility that the object of interest dislodges from the carriage  212  and interferes with the emitters or the transport mechanisms. 
     In some embodiments, interior surfaces such as end surfaces  202  of housing  102  are treated or coated to be reflective. In other embodiments, mirrored surfaces can be introduced beyond the limit of the internal volume expected to be occupied by the object of interest but still within the light stripe  222 . In this way, light from the light stripe(s)  222  is reflected on to the ends of the object of interest. In other embodiments, additional emitters can be added to the ends to specifically direct light on the ends of the object  120 . 
       FIG. 3  is a perspective view of one embodiment of the invention with the end of the housing removed. In this view the object  120  has been inserted in the object access portal  104 . The insertion causes the resilient fingers  106  to bend into the interior volume. In this position the underside  206  of the fingers  106  are exposed to the light strips  222 - 1  and  222 - 2  respectively (generically  222 ) for the right and left side fingers. Light stripes  222 - 1  and  222 - 2  are generated by emitters  322 - 1  and  322 - 2  respectively (generically  322 ). 
     In one embodiment, the emitters  322  include a plurality of UVC LEDs disposed along the inner walls of the long dimension of the housing  102 . In one embodiment, the LEDs are positions so that the light stripes  222  at least slightly impinge upon the undersides  206  of the resilient fingers  106  and reflective end surfaces  202 . In this way, substantially the entire extent of the underside  206  of the resilient fingers is disinfected as the object  120  enters the housing  102 . Furthermore, the reflective undersides  206  reflect the light onto the upper edged of the object  120  once the object  120  is fully within the housing  102 . 
     Object  120  can be inserted to rest upon object retention features  214  of carriage  212 . One or more sensors  302  detect the insertion and signal the controller (not shown in this view) of the insertion. Responsive to the sensors, the controller activates the emitters  322  and manages the downward transport of the object by drive  216  that is driven by actuator  218  under controller&#39;s control. In addition to signaling the insertion of the object  120 , the sensor(s)  302  signal when the trailing edge  320  of the object  120  passes the sensors such that the entire object  120  is within the housing  102 . This lets the controller  220  know how far it must lower the object  120  to achieve intended disinfection. Sensor  302  may be any type of sensor that can detect the presence of the object  120 . In one embodiment, an infrared (IR) break beam sensor may be used. In some embodiments, more than one IR break beam sensor may be used along the long dimension of the device. Using plural sensors can allow an embodiment to identify smaller object inserted and/or determine that the object  120  is fully/properly inserted before initiating the disinfection cycle. In some embodiments, a sensor may be located on the short sides (ends) of housing  102  the instead of or in addition to sensor  302  on the long side. 
     In one embodiment, the LED&#39;s of emitter  322 - 1 ,  3242 - 2  are rated for an energy emission of 12-15 mW. By appropriately driving the motor, the controller ensures that all parts of an exposed surface area of the object are exposed to sufficient UV-C energy to kill a desired pathogen or pathogens to an intended degree. In one embodiment, the “long” dimension of the of the object  120  is directly exposed to a light stripe  222  as the object  120  is moved into and subsequently out of the housing  102 . The thin edge is exposed to reflected light. Light reflected off the reflective underside  206  of resilient fingers  106  exposes the top edge once the object  120  is fully within the housing  102 . Light reflected off the carriage  212  exposes the bottom edge. Light reflected of the reflective interior end wall of housing  102  exposes the end edges. 
       FIGS. 4A-4C  illustrate edge disinfection schematically according to one embodiment of the invention. In one embodiment, when the object  120  is first inserted, sensor  302  signals the insertion causing the controller to activate the emitters  322 . Emitters  322  generate light stripes  222  that project onto object  120 . Carriage  212  receives the object  120  on its object retention features  214  such that the object  120  resides at or above the centerline of the light stripe  222 - 1 ,  222 - 2  and the reflective surface  512  of the carriage  212  resides below the center of the light stripes  222 - 1 ,  222 - 2 . In this way, light is reflected from the reflective surface  512  (shown schematically as rays  524 ) to disinfect lower edge  420 . After sufficient time has elapsed to complete the desired disinfection, the carriage  212  is lowered to transport the object through the light stripes  222 . 
     Once the top edge  320  of the object  120  passes the sensor  302 , the sensor signals the controller to allow the controller to know the range required to move the object  120  to complete the disinfecting process. As shown in  FIG. 4B , to complete the process, the upper edge  320  is transported to be below the center of the stripes  222 . Once the object is entirely within the housing  102 , the resilient finger  106  resiliently recoil to occlude the object access port  104 . This leaves reflective underside  206  to reflect the stripes  222  onto top side  320  (shown schematically as rays  432 ). The portion of the light stripes  222  that would extend through the object access portal  104  in the absence of fingers  106  is shown schematically as elements  422 - 1 ,  422 - 2 , that corresponding light is instead reflected by reflective undersides  206 . As noted above, underside  206  is exposed to disinfecting light while the object  120  is entering the housing  102 . It also continues to be exposed to sterilizing light while the object  120  is fully within the housing  102 . As a result, pathogens do not remain on the underside  206 . 
       FIG. 4C  schematically represent a top view of the emitters  224  that create the light stripes  222  that are reflected by end walls  202 . In the shown embodiment, each emitter  224  is formed from a plurality of LEDs  424 - 1 ,  424 - 2 ,  424 - 3   424 -N (generically  424 ). The number of LEDs  424  selected for a particular embodiment is driven by the desired length of stripe  222  and the desired overlap between light emitted by adjacent LEDs  424 . In one embodiment, six LEDs  424  are used for each emitter. Other embodiments may use more or fewer LEDs  424 . The ends  426 - 1 ,  426 - 2  (generically  426 ) of the stripes  222  shown schematically would extend as shown in the absence of end walls  202 . End walls  202  are reflective and cause the ends  426  of the light stripes  222  to instead be reflected on the side edges of the object. 
     Studies reveal the virus that causes influenza is destroyed to a 90% effectiveness by exposure the of 3.4 mJ/cm 2  and 99% effectiveness with 10.2 mJ/cm 2  other pathogens are more or less susceptible to destruction by UV-C light. In some embodiments, it is desirable to have the process from insertion to removal be consistent with the time required for a user to e.g. wash their hands. Accordingly, some embodiments transport the object  120  at a rate where the process is completed in 90 seconds. In some embodiments, the expected light exposure is greater than 3 mJ/cm 2  in 90 seconds. In another embodiment, the exposure may be greater than 11 mJ/cm 2  in 90 seconds. In another embodiment, exposure may be greater than 30 mJ/cm 2  in 90 seconds. A smart phone sized 8.5 cm×16 cm×1.2 cm has a surface area of about 340.2 cm 2 . Presuming twelve LEDs as describe above with a 12 mW rating, a surface area of 340.2 cm 2  can be exposed to greater than 11 mJ/cm 2  in under 30 seconds allowing a significant safety margin in a 90 second interval or even a 60 second interval. Some embodiments may use weaker emitters, fewer LEDs or for example have greater spacing between the emitters and the object, these variables can be addressed by driving the motor more slowly to insure longer exposure to the light stripe during the cycle. While maintaining cycle time under 90 seconds is believed to provide the greatest usability some embodiment may have a slower cycle time to but still provide touchless disinfection. 
       FIG. 5  is a perspective view of one embodiment of the invention with the end of the housing removed.  FIG. 5  is identical to  FIG. 3  above except it shows the object  120  leaving the housing  102  after the disinfecting process is complete. As drive  216  transports the object  120  up it passes through fingers  106  and is exposed for a user to remove it. Notably, on the underside of the fingers, which as described above, have been disinfected during the process come in contact with the disinfected object. As a result, pathogen between any surface in contact with the object  120  is avoided. Furthermore, since a user can insert and remove the phone without contact with the disinfecting apparatus, a touchless disinfection process is achieved. Sensor  302  detects when the object  120  is removed and can signal the controller to turn off the emitters  224 . 
     Some embodiments, descend and return at a substantially constant rate with disinfection occurring both while the object is transitioning downward and while it is transition upwards. Other embodiment may perform the entire disinfection while the object moves in one direction and move the object in the other direction at a greater rate of speed. 
       FIG. 6  is a block diagram of active components of a system of one embodiment of the invention. Controller  620  is coupled to a power source  610  that supplies power to the system. In one embodiment, power source  610  is portable such as a lithium ion battery or the like. In other embodiments, the power source could be a wall outlet or other fixed source of electrical power. Sensors  602  signal the processor responsive to an event to indicate that a disinfection process should begin. Sensors  602  could be an IR beam break sensor, a pressure sensor, or any other sensor that can adequately detect the presence of an object to be disinfected. In some embodiments, the controller  620  may poll the sensors  602 . In other embodiments, the sensors  602  may sent asynchronous events such as interrupts to the controller  620 . Controller  620  is coupled to one or more emitters  624 . Responsive to an event indicating the beginning of a disinfection session, the controller  620  turns on the emitters  624  to project one or more light stripes into a disinfection zone. The controller  620  is couple to the actuator  618  which is couple to a drive  616 . Under the control of the controller  620 , the actuator  618  causes the drive  616  to cause relative motion between the emitters and the object. That is, in some embodiment, the emitters may be moved while the object is held still and in other embodiments, the emitters may remain still while the object is moved. In still other embodiments, both the emitters and the object may be moved. 
       FIG. 7  is a flow diagram of operation according to one embodiment of the invention. At block  702 , the controller checks the sensors. At decision block  704 , the controller interprets the sensor readings to determine if an object is present to be disinfected. In not the sensors are periodically checked until an object is identified. If an object is identified, the controller sets a session flag at block  706 . The presence of the session flag prevents misinterpretation of subsequent sensor readings. At block  708 , the controller turns on the emitters to generate one or more UV-C light stripes. 
     At block  710 , the controller waits a predetermined time. This wait state is timed to ensure adequate exposure of the bottom edge of the object from the light reflected off the carriage. In some embodiments, the 5-6 seconds has been found to be an adequate wait. Other embodiments may have a longer or shorter wait state. At block  712 , the controller causes the actuator to lower the object into the housing. The sensors are checked at block  714 . Then a determination is made at decision block  716  whether the object has cleared the sensors. If the session flag is set and the sensors no longer detect the object, the object is deemed to have cleared the sensors and be fully within the housing. If that is not the case a determination is made if the bottom of the drive has been reached at decision block  718 . If not, the controller continues cause the object to be lowered and the loop repeats. In some embodiment, the lowering may be substantially continuous, in other embodiments, the lowering is step wise at some faction such as ½ or ¾ of the stripe width. 
     If the object has cleared the sensor, at block  716 , the object is lowered further at block  720 . In some embodiments, the object is lowered until its upper edge is below the midway point of the light stripe. The additional lowering required can be determined by the controller based on the point the sensors no longer detected the object. Of course, the amount of lowering possible is constrained by the bottom of the drive. Once the bottom is reached or the object has been lowered to a desired lowest position, the controller again waits at block  722  to allow adequate light to disinfect the top edge. In some embodiments, the 5-6 seconds has been found again to be an adequate wait. Other embodiments may have a longer or shorter wait state. 
     Thereafter at block  724 , the controller causes the actuator to raise the object. At decision block  726 , a determination made if the carriage has reached the top. If is has not the raising continues until the top is reached. If the top is reached, a timer is started at block  728 . The timer is used to force a shut off of the emitters if the object is not removed. Accordingly, at block  730  the sensors are checked. At decision block  732 , a determination is made if the object has been removed based on the sensor reading. If it has not, a determination is made at decision block  734  whether the timer is on. If the timer is on, the timer is checked at block  736 . A determination is then made at decision block  738  whether the timer has timed out. If it has the emitters are turned off at block  740  and the timer is cleared at block  742 . If the timer is not on at block  734 , the time is not up at block  738 , or after clearing the timer, the controller again checks the sensors and cycles until the object is removed. 
     If at decision block  732  the device is determined to have been removed, a determination is made at decision block  744  whether the timer is still on. If the timer is still on it is cleared at block  746  and the emitters are turned off at block  748 . After turning off the emitters, or if the timer was no longer on at block  744 , the session flag is cleared at block  750 . Thereafter the system progresses to block  702  and cycles until a new object is introduced. 
     Embodiments described above hold the emitters still and the object is moved by a linear drive past the emitter. It is contemplated that that some embodiments may for example have a cylindrical housing with a rotational drive such as a turn table. The turntable could be raised and lowered to accept and eject the object of interest. An emitter on the cylinder wall could cast a light stripe on the object that is rotated by the turn table. Rotation could be controlled to adjust exposure time based on the distance of the emitter from the object as it rotates. The object may be elevated off the turntable by object UV transmissive object retention features and the surface of the turntable may be reflective. In another embodiment, the emitter could be driven to circumnavigate a cylindrical space containing the object and a platform could be provided to lower the object into position for disinfection and raise the object for removal. 
     It should be understood that directional references in this application are intended for convenience of description only. For example, instead of a vertical orientation, embodiment of the invention may accept an object through an access port in a side wall and transport the object horizontally past a vertically oriented emitter. Embodiments in arbitrary orientations are contemplated. Emitters collectively should cover the perimeter of the object at some time during the transport cycle. 
     Some aspects of various aspect of embodiments of the invention are described with reference to a flow diagram, it should be understood that in some embodiments elements of the flow diagrams may be performed in a different order or in parallel to rather than the order shown. Applicant expressly does not intend to imply a particular temporal relationship unless expressly stated in the claims that follow. Furthermore, to the extent that a decision element is included in the flow diagram, in some cases, that decision may be implicit or default. That is asynchronous selection of an execution path, e.g., interrupt driven, is within the scope and contemplation off embodiments of the invention. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.