Patent Publication Number: US-2020292159-A1

Title: Follow Spot Control System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 15/944,487 filed Apr. 3, 2018 by Martin Farnik, et al. entitled, “Follow Spot Control System”, which claims priority to U.S. Provisional Application No. 62/480,967 filed Apr. 3, 2017 by Pavel Jurik, et al. entitled, “An Improved Follow Spot System”, both of which are incorporated by reference herein as if reproduced in their entirety. 
    
    
     TECHNICAL FIELD 
     The disclosure generally relates to a method for providing a follow spot system, specifically to methods for integrating control of a follow spot with control of a lighting rig and to adding automation to such a system. 
     BACKGROUND 
     Follow spots are a well-known part of many entertainment productions and are commonly used in theatres, television studios, concerts, theme parks, night clubs and other venues. Some follow spots are manually controlled luminaires where the operator has control over the direction the luminaire is pointing, typically to illuminate a performer, and to the color, size and other optical parameters of the luminaire. A production may include many follow spots, each with its own operator, as shown in  FIG. 1 . In this depiction, four follow spots  60 , each with attendant operator  62 , are directed towards a target point  242  on a performance area  240 . A performer may be situated at the target point  242  and, as that performer moves around the performance area  240 , the operators  62  will move their respective follow spots  60  to keep the performer illuminated. 
     In such systems, the skill of the operators  62  may not be similar, e.g., some operators may be slow to follow the performer or inaccurate in their use of the follow spot. Attempting to synchronize color or intensity changes between the multiple operators may be difficult and/or inaccurate. Additionally, a lighting designer may wish to situate the follow spots in locations where it would be difficult or unsafe to place an operator. For example, above the stage or in areas where there is insufficient height or space for an operator. Even if it is possible to safely situate the operator, he may be uncomfortable and forced to remain in a cramped position for the duration of the event. 
     SUMMARY 
     In one embodiment, a method of controlling a plurality of follow spots includes creating a three-dimensional model that includes one or more surfaces of a performance area; locations and mounting orientations for automated luminaires, relative to the performance area; and location and mounting orientation for a camera, relative to the performance area. The method also includes calculating a vector that represents the center of a light beam that is projected by a first automated luminaire, based on its location and mounting orientation, and calculating a target point on a surface of the performance area based on the vector. The method further includes calculating individual pan and tilt parameters for each of the other automated luminaires based on the luminaire target point, and sending the individual pan and tilt parameters to the other automated luminaires. 
     In another embodiment, a method of remotely controlling an automated luminaire includes receiving control parameters sent to an automated luminaire from a lighting control desk. The method also includes sensing a physical orientation of a mounting mechanism configured to mount a follow spot controller for motion in at least pan and tilt axes of movement, the physical orientation of the mounting mechanism sensed in the at least pan and tilt axes of movement. The method further includes creating modified control parameters by replacing received pan and tilt parameters in the received control parameters with replacement pan and tilt parameters that are based on the sensed physical orientation of the mounting mechanism in the at least pan and tilt axes of movement. The method still further includes sending the modified control parameters to the automated luminaire via a unidirectional communication link, the received pan and tilt parameters and the replacement pan and tilt parameters indicating physical orientations of the automated luminaire. 
     In yet another embodiment, a method of controlling a plurality of follow spots includes sensing a physical orientation of a mounting mechanism configured to mount a follow spot controller for motion in at least pan and tilt axes of movement, the physical orientation of the mounting mechanism sensed in at least pan and tilt axes of movement. The method also includes sending operator pan and tilt parameters to a first automated luminaire of a plurality of automated luminaires, the operator pan and tilt parameters based on the sensed physical orientation of the mounting mechanism. The method further includes sending individual calculated pan and tilt parameters to each of a remainder of the plurality of automated luminaires, the individual calculated pan and tilt parameters based on (i) the pan and tilt parameters of the first automated luminaire and (ii) a three-dimensional model of a surface of a performance area and individual locations and mounting orientations of each of the plurality of automated luminaires relative to the performance area, the operator pan and tilt parameters indicating a physical orientation of the first automated luminaire and the individual calculated pan and tilt parameters indicating physical orientations of the associated ones of the remainder of the plurality of automated luminaires. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in conjunction with the accompanying drawings in which like reference numerals indicate like features. 
         FIG. 1  illustrates a prior art follow spot system; 
         FIG. 2  illustrates the main components of an embodiment of a remotely controlled follow spot system; 
         FIG. 3  illustrates an embodiment of the follow spot controller illustrated in  FIG. 2 ; 
         FIG. 4  illustrates the main components of a further embodiment of a remotely controlled follow spot system; 
         FIG. 5  presents a block diagram of a control system for a follow spot controller according to the disclosure; 
         FIG. 6  illustrates a schematic of an embodiment of a complete remotely controlled follow spot system as it might be installed for a production; 
         FIG. 7  illustrates an embodiment of an automated luminaire modified to be used as a follow spot or a follow spot controller; 
         FIG. 8  illustrates a further embodiment of an automated luminaire modified to be used as a follow spot or a follow spot controller; and 
         FIG. 9  illustrates a schematic of a further embodiment of a complete remotely controlled follow spot system as it might be installed for a production. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments of the disclosure are illustrated in the figures, like numerals being used to refer to like and corresponding parts of the various drawings. 
     The disclosure generally relates to a method for providing remote control of a follow spot system. A physical orientation of a follow spot controller is sensed and used to control one or more automated luminaires. A three-dimensional model may be used to translate operator control of a first automated luminaire into pan and tilt control of other automated luminaires. 
     In recent years, it has become common to use automated luminaires on entertainment productions. These are luminaires where the pan and tilt position of the luminaire light beam can be remotely controlled from a lighting desk by an operator. Many products also provide control over other parameters such as the focus, beam size, beam shape and beam pattern. Attempts have been made in the past to combine these two technologies such that the effect of a follow spot can be achieved by using a remotely controlled automated light. However, such attempts have often failed or been less than satisfactory because of the slow response time of the system or the difficulty an operator had in accurately aiming a luminaire at a small spot on a stage and moving the light around in a manner which appears natural and organic, rather than mechanical and robotic. Jerky robotic movement is annoying to the audience, distracts them from the performer, and reduces their enjoyment of the performance. 
       FIG. 2  illustrates a first embodiment of a remotely controlled follow spot system according to the disclosure. Automated luminaires  120  and  122  are connected via a first lighting control communication link  232  to a follow spot controller  200 . In turn, follow spot controller  200  is connected via a second lighting control communication link  236  to main lighting control desk  126 . Each automated luminaire  120  may have its light output, pan and tilt position, color, beam size and other parameters controlled. First lighting control communication link  232  preferably uses DMX512 (Digital Multiplex) protocol, which is an industry standard, unidirectional communication protocol. However, the disclosure is not so limited and other communication protocols may be used, including Art-Net, ACN (Architecture for Control Networks), and Streaming ACN. Similarly, second lighting control communication link  236  is here shown as utilizing Art-Net, however the disclosure is not so limited and other communication interfaces or networks may be used. Both first and second lighting control communication links  232  and  236  may be wired, wireless, or optical communication links. 
     Follow spot controller  200  provides a bridge between first and second lighting control links  232  and  236  and may override or replace a limited set of parameters sent from lighting control desk  126  to automated luminaires  120 . For example, follow spot controller  200  may override just the pan and tilt parameters for one or more of the automated luminaires  120  and  122 , thereby controlling which directions the automated luminaires are pointing, while lighting control desk  126  retains control of the other parameters of the automated luminaires such as light intensity, size, color, and so on. In this way, an operator of follow spot controller  200  may concentrate solely on directing the pan and tilt parameters of one or more of the automated luminaires  120  and  122  and not be concerned about other parameters. In other embodiments, the override may include other light characteristics, such as an iris or focusing of the light beam and/or its intensity. In such embodiments, the overridden characteristics may be selectable by an operator of the follow spot controller  200  or an operator of the control desk  126 . In such embodiments, the overridden characteristics may be selected based upon cue data stored in the follow spot controller  200  or in the control desk  126 . 
     Follow spot controller  200  may control a single automated luminaire or may simultaneously control multiple automated luminaires. In the case where multiple automated luminaires  122  and/or  120  are being controlled, follow spot controller  200  may substantially continuously compensate for the different locations of each of the luminaires relative to the performance area  240  and adjust the pan and tilt parameters sent to each luminaire such that each luminaire is directed to the same spot on the performance area  240  based on the pan and tilt parameters of the manually controlled follow spot. Such substantially continuous compensation is described in more detail with reference to  FIGS. 6 and 9 . 
     Follow spot controller  200  may incorporate a display screen that displays a live video signal received via communication link  234  from a camera  124  mounted on an automated luminaire  122  (or several cameras on several luminaires (not shown)). The communication link  234  may be a wired, wireless, or optical communication link. Such a live video display may allow the operator controlling follow spot controller  200  to see the performance area  240  and the lighting and more accurately control the pan and tilt position of the automated luminaires  122  and/or  120 . Such a system allows the follow spot controller  200  to be situated in a convenient and safe location for the operator. Follow spot controller  200  may be mounted on a tripod or stand  238  to locate the follow spot controller  200  at a comfortable height for the operator. 
     In some embodiments, the communication link  234  is an analog video signal. In other embodiments, the communication link  234  is a digital communication link that carries a digital video signal. In still other embodiments, the communication link  234  may be bidirectional, allowing an operator of the follow spot controller  200  to control set up and other parameters of the camera  124 . 
     In further embodiments, multiple follow spot controllers  200  may be used in a single production. Each follow spot controller  200  would have its own attendant operator and would control one or more automated luminaires  122 . 
       FIG. 3  presents a schematic view of the follow spot controller  200  of  FIG. 2 . The follow spot controller  200  includes an operating handle  216 , which an operator uses to move the follow spot controller  200  to control the movement of an automated luminaire  120 . The handle  216  is fitted with encoders (not shown) to provide the follow spot controller  200  with information relating to a direction the operator has moved the handle  216  in at least pan and tilt axes of movement. In a simple system, the follow spot controller  200  may include only the handle  216 . 
     In some embodiments, the follow spot controller  200  includes additional user-operated controls such as faders or knobs  214  mounted on the handle  216 , the position or other state of which controls a parameter of the automated luminaire  120  and/or  122 . In other embodiments, grips of the handle  216  are user-operated controls that rotate relative to the handle  216 , their rotational state providing control of other parameters, such as focus, intensity, or beam angle. Such additional controls may be assignable to any desired function (or parameter) of the automated luminaire  120 . For example, one fader may control a brightness of the luminaire, while another controls a beam size. Additionally, yet further user-operated controls  212  may be provided on the console  204  and their rotational state used to control still other parameters. 
     In some embodiments, the console  204  provides the ability to store and recall cues containing information such as pan and tilt, color, size, or any other parameters of the luminaires under its control. The console  204  may also contain a display  206  that provides information and feedback relating to the control and working of the system, as well as function buttons  210  and indicators  208 . 
     Follow spot controller  200  may also include a display screen  202  showing a live video signal from a camera, as described earlier. In some embodiments, the operator may select between different video feeds using the control functionality of console  204 . 
     In some embodiments, the follow spot controller  200  is fixed in position, while in other embodiments it is gimballed so that it can be panned and tilted to point at different locations on the performance area  240  or around the house (performance facility). In installations where the controller is located to provide the operator a direct view of the performance area  240 , the operator can point the follow spots by dead reckoning while directly observing the performance area  240  by eye. In installations where the operator cannot directly view the performance area  240 , the operator may rely on the display screen  202  and a camera mounted on the follow spot controller  200 , where the camera is positioned to allow a view of the performance area  240 . In still other embodiments, the operator may rely on the display screen  202  and the camera  124  mounted on the automated luminaire  122 . 
     In some embodiments, the controller does not physically move. Instead, the operator controls the follow spots&#39; motion via a joystick or other interface device. In such embodiments, the follow spot controller  200  and the display screen  202  are stationary, but the displayed view changes with the direction of the follow spots based on the user&#39;s manipulation of the joystick. 
     In other embodiments the control is combined. The follow spots&#39; motion matches the pointing of the follow spot controller  200  when the performer or target point  242  is viewable from the location of the controller or by the camera relied on by the controller. When the target point  242  is outside that range, the display screen  202  presents a three-dimensional (3-D) rendered view (or virtual view), allowing the follow spots to follow a performer or target point  242  that is not in view of the operator or the camera. 
     In some embodiments, the follow spot controller  200  automatically or manually switches control of the luminaires  120  and/or  122  back to the main control desk  126  and then, at a later time, allows the operator of the follow spot controller  200  to take back control of the luminaires  120  and  122 . 
       FIG. 4  illustrates a second embodiment of a remotely controlled follow spot system according to the disclosure. In this embodiment, a camera  134  is provided that is separately mounted from any automated luminaire controlled by the follow spot controller  200 . The camera  134  is mounted on a PTZ (Pan-Tilt-Zoom) system  132  such that the operator may control an orientation of the camera  134 , thereby controlling a view obtained by the camera  134 . In various embodiments, such control of the orientation of the camera  134  is provided by the follow spot controller  200  or by a separate camera controller. When provided by the follow spot controller  200 , such control of the camera  134  may be provided in a separate mode of operation of the follow spot controller  200  from a mode where the follow spot controller  200  controls the luminaire  122 . 
     In other embodiments, such a separately mounted camera may be mounted in a fixed orientation, providing a static view of the performance area  240 . 
       FIG. 5  presents a block diagram of a control system (or controller)  500  for a follow spot controller according to the disclosure. The control system  500  is suitable for use in follow spot controllers  200 ,  300 , or  400 , as described with reference to  FIGS. 3, 7, and 8 , respectively. The control system  500  includes a processor  502  electrically coupled to a memory  504 . The processor  502  is implemented by hardware and software. The processor  502  may be implemented as one or more Central Processing Unit (CPU) chips, cores (e.g., as a multi-core processor), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). 
     The processor  502  is further electrically coupled to and in communication with a communication interface  506  and one or more sensors, actuators, and/or controls  508 . The communication interface  506  is coupled to, and configured to communicate with, automated luminaires  120  and  122  via first lighting control communication link  232 . The communication interface  506  also is coupled to, and configured to communicate with, lighting control desk  126  via second lighting control communication link  236 . 
     The processor  502  is further electrically coupled to and in communication with a video interface  510 , which is in turn electrically coupled to a video camera via communication link  234 . The video interface  510  is further electrically coupled to the display screen  202 . 
     The control system  500  is suitable for implementing processes, follow spot control, continuous compensation, and other functionality as disclosed herein, which may be implemented as instructions stored in the memory  504  and executed by the processor  502 . 
     The memory  504  comprises one or more disks, tape drives, and/or solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory  504  may be volatile and/or non-volatile and may be read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and/or static random-access memory (SRAM). 
       FIG. 6  illustrates a schematic of a first embodiment of a remotely controlled follow spot system according to the disclosure, as it might be installed for a production. Automated luminaires  120  are rigged (or mounted) above and/or around a performance area  240 . At least one luminaire  122  is fitted with a video camera  124 . In other embodiments, a camera may be mounted in a PTZ system, as described with reference to  FIG. 4 . Control data for the luminaires  120  and  122  is routed from a lighting control desk  126  through a second lighting control communication link  236  to a follow spot controller  200  and then via a first lighting control communication link  232  to luminaires  120  and  122 . A video signal is routed back from camera  124  via communication link  234  to a display screen  202  on the follow spot controller  200 . The image from the camera  124  may be displayed directly on the display screen  202  or may be processed in the follow spot controller  200  before being displayed. 
     As described previously, an operator of the follow spot controller  200  may take over control of some, or all, of the control parameters of one or more of the luminaires  120  and  122 . In particular, the follow spot controller  200  may control the pan and tilt parameters of one or more of luminaires  120  and  122  and direct them to illuminate a target point  242  on performance area  240 . In other embodiments, controls of the follow spot controller  200  may control other parameters of one or more of the luminaires  120  and  122 , e.g. brightness, focus, beam size, and/or color. Target point  242  may indicate a performer, and the operator may then move the handles on follow spot controller  200  such that the connected luminaire or luminaires continues to illuminate the performer as he/she moves around the performance area  240 . 
     The performance area  240  may include a stage or dais, a surrounding area, and/or some or all of the facility in which a performance takes place. 
     In some embodiments, a modified automated luminaire may be used as a follow spot controller according to the disclosure.  FIG. 7  illustrates a first embodiment of an automated luminaire  300  according to the disclosure, which has been modified to be used as a follow spot or as a follow spot controller. The automated luminaire  300  is a hybrid automated/manually controlled fixture. The automated luminaire  300  is modified to be used as a follow spot or a follow spot controller by a hands-on human user as he would a traditional manual follow spot. A conventional automated luminaire may be modified by adding handles  316  and  317 . By overriding or disabling the internal motor drives that control “pan” motion of yoke  302 , relative to base  303 , and “tilt” movement of head  301 , relative to yoke  302 , an operator can control the pan and tilt position of automated luminaire  300  using handles  316  and  317 . In some embodiments, controls  314  and console  304  provide control over further parameters of the luminaire. Such an automated luminaire may be manually controlled by the operator in the manner of a prior art follow spot. 
     Additionally, the automated luminaire  300  functions as a follow spot controller  200  as described with reference to  FIG. 2 . In such an embodiment, sensors in the pan and tilt mechanisms of automated luminaire  300  sense the operator&#39;s movement of the automated luminaire  300 . In embodiments that include controls  314  and console  304 , the automated luminaire  300  both tracks its movement by monitoring its pan and tilt position, as well as monitoring the operator&#39;s manipulations of other light modulating controls. 
       FIG. 8  illustrates a second embodiment of an automated luminaire  400  that has been modified to be used as a follow spot or as a follow spot controller. A conventional luminaire  400  is modified by adding handles  416  and  417  and overriding the internal motor drives that control pan motion of yoke  402  relative to base  403  and tilt movement of head  401  relative to yoke  402 . An operator can direct automated luminaire  400  by grasping the handles  416  and  417  and moving the head  401 . In some embodiments, controls  414  and console  404  provide control over further parameters of the luminaire. The operator can thus control the automated luminaire  400  in the same manner as a conventional follow spot. In some embodiments, the automated luminaire  400  may function as a follow spot controller  200  as described with reference to  FIG. 2 . In such embodiments, sensors in the pan and tilt mechanisms of the automated luminaire  400  sense the operator&#39;s movement of the luminaire. 
       FIG. 9  illustrates a schematic of a second embodiment of a remotely controlled follow spot system according to the disclosure, as it might be installed for a production. Multiple automated luminaires  120  are rigged to illuminate a performance area  240 . The control data for the luminaires  120  is routed from a lighting control desk  126  through network  236  to a combined luminaire and follow spot controller  400  and then via network  232  to luminaires  120 . In other embodiments, the automated luminaire  300 , described with reference to  FIG. 7 , may be used in the system shown in  FIG. 9 . 
     As described previously, an operator of the combined luminaire and follow spot controller  400  may take over control of some or all of the control parameters of one or more of the luminaires  120 . In such a circumstance, the automated luminaire becomes a follow spot controller. In particular, combined luminaire and follow spot controller  400  may control the pan and tilt positions of one or more of luminaires  120  such that they are collectively and individually directed to illuminate a target point,  242 , on performance area  240 . Thus the control of automated follow spots can be controlled by the manual control of a single follow spot. Target point  242  may indicate a performer, and the operator may then move the handles on combined luminaire and follow spot controller  400  to illuminate the performer with luminaires  120  as she moves around the performance area  240 . 
     As described briefly with reference to  FIG. 2 , in some embodiments, a processor, controller, or other control system in a follow spot controller according to the disclosure provides continuous compensation of pan and tilt positions of one or more automated luminaires  120 , based on an operator&#39;s manipulation of the follow spot controller  200  to control the automated luminaire  122 . The control system creates a 3-D model of the performance area  240  (represented by one or more surfaces), and locations and mounting orientations of the automated luminaires  120  and  122  relative to the performance area  240 . The 3-D model may also include locations and mounting orientations relative to the performance area  240  of the camera  124  and (where used) the camera  134 . 
     Such a 3-D model may be determined from manual measurements of the surface and locations and mounting orientations. In other embodiments, the extent and locations and mounting orientations may be determined using sensors placed in or on the performance area  240 , the automated luminaires  120  and  122 , and/or the camera  124 . In still other embodiments, the extent and locations of mounting orientations may be determined by the operator moving the center of the light beam projected by the luminaire  122  to each of a plurality of predetermined calibration points in the performance area  240 , and indicating to the system the illuminated calibration point. 
     As the operator moves the luminaire  122  associated with the camera  124 , the control system calculates a 3-D vector representing the center of a light beam projected by the luminaire  122 . Based on the calculated 3-D vector and, in some embodiments, the location and mounting orientation relative to the performance area  240  of the camera  124 , the control system calculates a location of the target point  242  on the performance area  240 . 
     Based on the calculated location of the target point  242  and the locations and mounting orientations relative to the performance area  240  of the automated luminaires  120 , the control system calculates individual pan and tilt parameters for each automated luminaire  120  that will result in light beams that also intersect the performance area  240  at the target point  242 . These calculations are performed substantially continuously in real time to provide continuous compensation of orientations of the automated luminaires  120 , based on the operator&#39;s manipulation of the follow spot controller  200 . 
     For the purposes of this disclosure, substantially continuously means sufficiently frequently to prevent perceivably jerky movement of the automated luminaires  120  and/or  122 . In some embodiments, such calculated pan and tilt parameters are sent to each automated luminaire  120  at least once every 100 milliseconds. In a preferred embodiment, such calculated pan and tilt parameters are sent to each automated luminaire  120  at least once every 23 milliseconds. 
     In embodiments where independent camera  134  is used, pan and tilt parameters may also be calculated for the camera  134  that will result in the camera  134  automatically tracking to provide a view of the performance area  240  at the target point  242 . Such camera pan and tilt parameters may be recalculated substantially continuously as described above, or with a period comparable to the recalculation of pan and tilt parameters for the automated luminaires  120 . 
     Based on the calculated location of the target point  242  and the location and mounting orientation of the camera relative to the performance area  240  of the automated luminaires  120 , the follow spot controller  200  calculates individual pan and tilt parameters for each automated luminaire  120  that will result in light beams that also intersect the performance area  240  at the target point  242 . 
     In some embodiments the follow spot controller  200  (or modified automated luminaire  400 ) may also control one or more of beam zoom, iris, and light intensity for each controlled automated luminaire  120  or  122 . Such control of beam zoom and/or iris would enable the follow spot controller  200  to maintain a constant beam size from each controlled luminaire on a performer as the performer moves within the performance area  240 . Further, such control of intensity would enable the follow spot controller  200  to maintain a consistent light intensity on performers as they move within the performance area  240 . In applications where the performance is being captured by a video or film camera it is of benefit to maintain a consistent light level on the performer, so that the camera does not have to be adjusted as the performer moves. 
     In such embodiments, the performer&#39;s position establishes a target point  242  in the 3-D model, as calculated from an operator&#39;s use of the follow spot controller  200  to point a controlled luminaire at the performer. The follow spot controller  200  may use an initial beam zoom, iris, and/or light intensity for each controlled luminaire, along with a varying throw distance from each controlled luminaire to the calculated moving target point in the 3-D model, to determine changes to make to the beam zoom, iris, and/or light intensity for each controlled luminaire. In such embodiments, an operator of the lighting control desk  126  (or the follow spot controller  200  or modified automated luminaire  400 ) may choose to allow any one, or any combination, of beam zoom, iris, and light intensity of controlled luminaires to be automatically adjusted by the follow spot controller  200  in order to maintain one or both of beam size and target light intensity, in addition to pan and tilt, for controlled luminaires. 
     In some embodiments, such a 3-D model is used to provide an operator with a virtual view of the performance area, for example where neither the operator nor any camera has a view of the performance area  240 . In various embodiments, such continuous compensation may be provided by a control system in any of follow spot controller  200 , modified automated luminaire  300 , or modified automated luminaire  400 . In other embodiments such continuous compensation is provided by a control system of the lighting control desk  126 . In various embodiments, such continuous compensation is enabled and disabled from one of the follow spot controller  200  or lighting control desk  126 , and may be enabled for selected ones of the automated luminaires  120 . 
     While the disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure herein. The disclosure has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the disclosure.