Patent Publication Number: US-9837805-B2

Title: System and apparatus for electrically coupling to a cable on a rotatable reel using optical communication devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application 61/991,445 entitled “SYSTEM AND APPARATUS FOR ELECTRICALLY COUPLING TO A CABLE ON A ROTATABLE REEL”, filed on May 9, 2014 and hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a rotatable reel apparatus and, more particularly, to system and apparatus for electrically coupling to a cable on a rotatable reel using optical communication devices. 
     BACKGROUND 
     Factories and other industrial environments are increasingly using remote devices (ex. video cameras, sensors, control devices, etc.) for control, monitoring, or other functions in their manufacturing equipment. Among other operations, these devices may be used to monitor activities for real-time or recorded operations or to control specific processes or equipment. They may be located in a wide range of static or mobile locations in the industrial facility and may require DC (Direct Current) or AC (Alternate Current) power to function and/or an ability to receive data (ex. instructions) from a distant location and/or an ability to transmit data (ex. video content) to a distant location. 
     Due to the remote locations and/or movement of these devices, it is not typically convenient to plug in the devices to local power outlets. Further, due to electromagnetic interference that is typical within industrial environments, wireless communication technologies may not provide a reliable communication channel. Further, in the case that there are a large number of these remote devices, the cost for adding wireless receivers/transmitters within each device can be high. 
     Most industrial environments employ the use of wired solutions to power and communicate to/from the remote devices. In many cases, cables spooled on rotatable reels are used to connect to the remote devices and control the extracting and retracting of the cable, thus reducing the risk of cables getting tangled or caught within equipment. One significant issue with using cables spooled on rotatable reels is how to transfer electrical current onto the cable when the cable is connected to an element on the reel that is rotating relative to a static power source. Another significant issue is how to transfer data to/from remote devices through the cable when the cable is connected to an element on the reel that is rotating relative to a static data receiver and/or transmitter. 
     In one implementation, to enable transfer of electrical power, the rotatable element within the reel that is connected to one end of the cable comprises one or more copper brushes. These brushes may come into contact with a static frame of the reel as the rotatable element rotates and can provide a continuous or semi-continuous electrical connection between the static frame of the reel and the rotatable element that the cable is connected to. Electrical power can be transferred through these copper brushes from the static frame to the rotatable element and can allow for electrical power to be transferred to remote devices connected to the rotatable element via the cable. A problem with this implementation is that the copper brushes have been shown to wear down and the continuous surface-on-surface friction is a significant source of failures for a wide variety of reasons including carbon buildup causing false contact, broken brushes and generation of heat. To overcome these problems with using copper brushes to transfer electrical power to the rotatable element, in some implementations thicker copper is used or gold alloy brushes replace the copper brushes. These solutions come at a significantly increased cost and have many of the same problems since they still rely on surface-to-surface friction to transfer the electrical power. An additional problem is that brushes, although suited to transfer DC power, cause significant electromagnetic noise and interference to any data being transferred either on themselves or on nearby lines. 
     Another implementation of a reel is disclosed within U.S. Pat. No. 3,430,179 issued Feb. 25, 1969 and entitled “Cable Reel” by Shoji, herein incorporated by reference. In this implementation, an electrical connector for connecting a multiconductor cable on a reel with an exterior multiconductor cable comprises a rotatable inner sleeve and a stationary outer sleeve, and a one-piece, flat flexible multiconductor element (commonly known as ribbon-cable or ribbon-wire or flat flex cable) wound around the inner sleeve. The inner end of the multiconductor element terminates at a multiple terminal electrical connector secured to the inner sleeve, and the outer end of the cable terminates at a multiple terminal electrical connector secured to the outer sleeve. The inner sleeve is rotatable with the reel, and the multiconductor element unwinds from the inner sleeve as the reel revolves and the multiconductor cable on the reel is payed out. In this implementation, data can be transferred along the multiconductor element. One problem with this solution is that the multiconductor element when wound around the inner sleeve can generate self-inductance and high distributed capacitance that can limit the bandwidth of data that can be communicated through the multiconductor element. 
     Against this background, there is a need for solutions that will mitigate at least one of the above problems. In particular, there is a need for a cable reel that has an improved apparatus for power and/or data communication transfer to/from a cable on the reel. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to cable reel apparatus which allow for improved transfer of power and/or data between a static frame and a cable wound around a rotatable element. The cable reel may comprise one or more torsional springs that are used to store mechanical energy that can be used to retract the cable onto the rotatable element and can also be used to electrically couple the cable wound on the rotatable element to a static node within the static frame. The cable reel may also comprise a data transfer apparatus that enables the transfer of data between a static node within the frame of the cable reel and the cable. In one implementation, the data transfer apparatus comprises two capacitive plates that together form a capacitor, one connected to the static frame and one connected to the rotatable element. In another implementation, the data transfer apparatus comprises an optically isolated zone in which an optical transmitter may communicate data to an optical receiver over free-space optical communications. The data in these implementations can be transferred through the data transfer apparatus without physical contact between the static frame and the rotatable element, even while the rotatable element may rotate relative to the static frame. 
     According to a first broad aspect, the present invention is an apparatus comprising: a frame having an axle; a rotatable element operable to rotate on the axle and having an outer surface surrounding the axle adapted to have a cable wrapped; and a torsional spring having windings surrounding the axle with a first end coupled to the axle and a second end coupled to the rotatable element. The torsional spring is conductive and operable to electrically connect a first node in the frame to a second node in the rotatable element. In embodiments of the present invention, the axle can comprise a cylindrical tube and a non-cylindrical shaft integrated within the cylindrical tube. The rotatable element may be adapted to rotate around the cylindrical tube of the axle and the first end of the torsional spring may be connected to the non-cylindrical shaft. In this case. the first end of the torsional spring is connected to the frame and is not operable to rotate with the rotatable element. The first node can be connected to a wire element that is routed through the non-cylindrical shaft to the first end of the torsional spring. The second node can be adapted to be connected to a cable wrapped around the outer surface of the rotatable element. The frame may comprise an interface connector that is adapted to connect to a cable external to the apparatus and to electrically connect the cable external to the cable to the first node and the rotatable element may comprise an interface connector that is adapted to connect to a cable wrapped around the outer surface of the rotatable element and to electrically connect the cable wrapped around the outer surface of the rotatable element to the second node. The torsional spring can be adapted to contract in response to rotation of the rotatable element in a first direction and to cause rotation of the rotatable element in a second direction opposite the first direction if the torsional spring is enabled to expand. Effectively, the torsional spring can be adapted to store mechanical energy in response to rotation of the rotatable element in a first direction and to cause rotation of the rotatable element in a second direction opposite the first direction when releasing the stored mechanical energy. 
     In some embodiments, the apparatus may comprise a plurality of electrically isolated torsional springs, each of the torsional springs having windings surrounding the axle with first ends coupled to the axle and second ends coupled to the rotatable element. In this case, each of the torsional springs can be conductive and operable to electrically connect respective first nodes in the frame to respective second nodes in the rotatable element. The plurality of torsional springs can each be electrically isolated by insulation elements, the first ends of the torsional springs can be electrically isolated at the axle, and the second ends of the torsional springs can be electrically isolated at the rotatable element. The second nodes in the rotatable elements can be adapted to be electrically connected to a cable wrapped around the outer surface of the rotatable element, each of the second nodes being electrically connected to a different conductive element within the cable. 
     In a specific implementation, the plurality of torsional springs may comprise first and second torsional springs and the cable wrapped around the outer surface of the rotatable element may comprise a coaxial cable. The second end of the first torsional spring can be adapted to be electrically connected to a central core of the coaxial cable and the second end of the second torsional spring can be adapted to be electrically connected to a metallic shielding of the coaxial cable. At least one of the torsional springs can be adapted to electrically connect a positive DC voltage from the frame to a first conductive element within the cable wrapped around the outer surface of the rotatable element and at least one other of the torsional springs can be adapted to electrically connect a negative DC voltage from the frame to a second conductive element within the cable wrapped around the outer surface of the rotatable element. The cable wrapped around the outer surface of the rotatable element may comprise a coaxial cable and the apparatus may further comprise a DC coupling circuit that is adapted to connect one of the positive and negative DC voltages to a central core of the coaxial cable and the other of the positive and negative DC voltages to a metallic shielding of the coaxial cable. In one implementation, at least one of the torsional springs can be adapted to electrically connect a grounded voltage from the frame to a conductive element within the cable wrapped around the outer surface of the rotatable element. 
     In some particular implementations, the apparatus may comprise an internal cable having windings surrounding the axle with a first end coupled to the axle and a second end coupled to the rotatable element. The cable can be operable to electrically connect respective one or more nodes in the frame to one or more nodes in the rotatable element. The internal cable may comprise at least one of a flat cable, a ribbon cable and a flat flex cable. The torsional spring may be adapted to electrically connect a DC voltage from the frame to a first conductive element within the cable wrapped around the outer surface of the rotatable element and the internal cable may be adapted to electrically connect a negative DC voltage from the frame to a second conductive element within the cable wrapped around the outer surface of the rotatable element. 
     In some embodiments, the apparatus of the first broad aspect may further comprise a first capacitive plate integrated with the frame and a second capacitive plate integrated with the rotatable element. The first and second capacitive plates can form a capacitor operable to pass data signals between the frame and the rotatable element. The first node can be electrically coupled to the first capacitive plate and the second node can be electrically coupled to the second capacitive plate. The frame may comprise a first isolation circuit adapted to prevent data at the first node from being transmitted to the first end of the torsional spring and the rotatable element may comprise a second isolation circuit adapted to prevent data at the second node from being transmitted to the second end of the torsional spring. The first isolation circuit can be adapted to prevent a DC voltage at the first node from being electrically connected to the first capacitive plate and the second isolation circuit can be adapted to prevent a DC voltage at the second node from being electrically connected to the second capacitive plate. 
     In some embodiments, the frame may comprise a first optical communication element and the rotatable element may comprise a second optical communication element, the first and second optical communication elements being adapted to optically communicate with each other during rotation of the rotatable element relative to the frame. The first optical communication element may comprise an optical receiver and the second optical communication element may comprise an optical transmitter operable to communicate data signals from the rotatable element to the frame using free-space optical communications. The second optical communication element may comprise an optical receiver and the first optical communication element may comprise an optical transmitter operable to communicate data signals from the frame to the rotatable element using free-space optical communications. The first node can be electrically coupled to the first optical communication element and the second node can be electrically coupled to the second optical communication element. The frame may comprise a first isolation circuit adapted to prevent data at the first node from being transmitted to the first end of the torsional spring and the rotatable element may comprise a second isolation circuit adapted to prevent data at the second node from being transmitted to the second end of the torsional spring. 
     According to a second broad aspect, the present invention is a system comprising the apparatus of the first broad aspect including the first and second capacitive plates and a first conversion element electrically connected to the first capacitive plate and operable to convert data between first and second formats. The first conversion element is operable to communicate data with a component external to the apparatus in the first format and to communicate data over the capacitor formed by the first and second capacitive plates in the second format. The system may further comprise a second conversion element electrically connected to the second capacitive plate and operable to convert data between the first and second formats. The second conversion element can be operable to communicate data with a component external to the apparatus in the second format and communicate data with the first conversion element in the second format via the capacitor formed by the first and second capacitive plates. The first format may be Ethernet and the second format may be a high frequency analog format, though other formats could be utilized. The first conversion element may be integrated within the frame of the apparatus and the second conversion element may be integrated within the rotatable element of the apparatus. The first conversion element may be operable to receive power from a component external to the apparatus and to couple a DC voltage to the first node in the frame and the second conversion element may be operable to receive power at least in part from the second node in the rotatable element. The second conversion element may be operable to transmit power to a component external to the apparatus. 
     According to a third broad aspect, the present invention is an apparatus comprising: a frame having an axle; a rotatable element operable to rotate on the axle and having an outer surface surrounding the axle adapted to have a cable wrapped; means for electrically connecting a first node in the frame to a second node in the rotatable element; and means for communicating data between the frame and the rotatable element independent of the means for electrically connecting the first and second nodes. The means for electrically connecting the first and second nodes may comprise at least one torsional spring connected between the frame and the rotatable element. The means for communicating data may comprise a first capacitive plate integrated with the frame and a second capacitive plate integrated with the rotatable element. The first and second capacitive plates can form a capacitor operable to pass data signals between the frame and the rotatable element. Alternatively, the means for communicating data may comprise a first optical communication device integrated with the frame and a second optical communication device integrated with the rotatable element, the first and second optical communication devices being adapted to optically communicate with each other during rotation of the rotatable element relative to the frame. 
     According to a fourth broad aspect, the present invention is an apparatus comprising: a frame comprising an axle; a rotatable element operable to rotate on the axle; and first and second capacitive plates. The first capacitive plate is integrated with the frame and the second capacitive plate is integrated with the rotatable element. The first and second capacitive plates form a capacitor operable to pass data signals between the frame and the rotatable element. The rotatable element may have an outer surface surrounding the axle adapted to have a cable wrapped, the second capacitive plate being adapted to be coupled to the cable. The first and second capacitive plates may each be centered on the axle such that the first and second capacitive plates are aligned to form the capacitor during rotation of the rotatable element on the axle. Each of the capacitive plates can be circular such that the capacitance of the capacitor formed by the first and second capacitive plates remains substantially consistent during rotation of the rotatable element on the axle relative to the frame. Further, the capacitive plates may each comprise a central capacitive surface and an annular capacitive surface that surrounds the central capacitive surface, the central capacitive surface and the annular capacitive surface being electrically isolated. In this case, the central capacitive surfaces of the first and second capacitive plates can form a first capacitor and the annular capacitive surfaces of the first and second capacitive plates can form a second capacitor. In one implementation, the central capacitive surface and the annular capacitive surface of the first capacitive plate can be electrically connected to a central core and a metallic shielding respectively of a first coaxial cable; and the central capacitive surface and the annular capacitive surface of the second capacitive plate can be electrically connected to a central core and a metallic shielding respectively of a second coaxial cable. In this case, data transmitted between a component electrically connected to the first coaxial cable and a component electrically connected to the second coaxial cable can be communicated via the central cores of the first and second coaxial cable and across the first capacitor formed from the central capacitive surfaces of the first and second capacitive plates. In some cases, other cables with alternative physical interfaces may be utilized. 
     In some embodiments, the apparatus of the fourth broad aspect may comprise an electrical connection element adapted to electrically connect a first node in the frame to a second node in the rotatable element independent of the capacitor formed by the first and second capacitive plates. The electrical connection element may comprise a torsional spring having windings surrounding the axle with a first end coupled to the axle and a second end coupled to the rotatable element. The torsional spring can be conductive and operable to electrically connect the first node in the frame to the second node in the rotatable element. The first node can be electrically coupled to the first capacitive plate and the second node can be electrically coupled to the second capacitive plate. In this case, the frame may comprise a first isolation circuit adapted to prevent data at the first node from being transmitted to the first end of the torsional spring and the rotatable element may comprise a second isolation circuit adapted to prevent data at the second node from being transmitted to the second end of the torsional spring. The first isolation circuit can be adapted to prevent a DC voltage at the first node from being electrically connected to the first capacitive plate and the second isolation circuit can be adapted to prevent a DC voltage at the second node from being electrically connected to the second capacitive plate. 
     According to a fifth broad aspect, the present invention is a system comprising the apparatus of the fourth broad aspect and a first conversion element electrically connected to the first capacitive plate and operable to convert data between first and second formats. The first conversion element can be operable to communicate data with a component external to the apparatus in the first format and to communicate data over the capacitor formed by the first and second capacitive plates in the second format. The system may further comprise a second conversion element electrically connected to the second capacitive plate and operable to convert data between the first and second formats. The second conversion element can be operable to communicate data with a component external to the apparatus in the second format and communicate data with the first conversion element in the second format via the capacitor formed by the first and second capacitive plates. The first format may be Ethernet and the second format may be a high frequency analog format, though other formats could be utilized. The first conversion element may be integrated within the frame of the apparatus and the second conversion element may be integrated within the rotatable element of the apparatus. The first conversion element may be operable to receive power from a component external to the apparatus and to couple a DC voltage to a first node in the frame and the second conversion element may be operable to receive power at least in part from a second node in the rotatable element. The apparatus may further comprise an electrical connection element for electrically connecting the first and second nodes independent of the capacitor formed by the first and second capacitive plates. In some implementations, the electrical connection element may comprise a torsional spring having windings surrounding the axle with a first end coupled to the axle and a second end coupled to the rotatable element. The torsional spring can be conductive and operable to electrically connect the first node in the frame to the second node in the rotatable element. The second conversion element may be operable to transmit power to a component external to the apparatus. 
     According to a sixth broad aspect, the present invention is a data transfer apparatus adapted to be integrated within a cable reel comprising a frame comprising an axle and a rotatable element operable to rotate on the axle and having an outer surface surrounding the axle adapted to have a cable wrapped. The data transfer apparatus comprises: a first capacitive plate integrated with the frame; and a second capacitive plate integrated with the rotatable element. The first and second capacitive plates form a capacitor operable to pass data signals between the frame and the rotatable element. Each of the first and second capacitive plates may be circular such that the capacitance of the capacitor formed by the first and second capacitive plates remains substantially consistent during rotation of the first and second capacitive plates relative to each other. The capacitive plates may each comprise a central capacitive surface and an annular capacitive surface that surrounds the central capacitive surface, the central capacitive surface and the annular capacitive surface being electrically isolated. The central capacitive surfaces of the capacitive plates can form a first capacitor and the annular capacitive surfaces of the capacitive plates can form a second capacitor. The central capacitive surface and the annular capacitive surface of the first capacitive plate can be adapted to be electrically connected to a central core and a metallic shielding respectively of a first coaxial cable; and the central capacitive surface and the annular capacitive surface of the second capacitive plate can be adapted to be electrically connected to a central core and a metallic shielding respectively of a second coaxial cable. In some cases, other cables with alternative physical interfaces may be utilized. 
     According to a seventh broad aspect, the present invention is an apparatus comprising: a frame comprising an axle and a first optical communication device; and a rotatable element operable to rotate on the axle and comprising a second optical communication device. The first and second optical communication devices are adapted to optically communicate with each other during rotation of the rotatable element relative to the frame. The rotatable element may have an outer surface surrounding the axle adapted to have a cable wrapped, the second optical communication device being adapted to be coupled to the cable. The first and second optical communication devices can be located within an optically isolated zone formed by the frame and the rotatable element and the optically isolated zone can be maintained by the frame and the rotatable element during rotation of the rotatable element relative to the frame. In some implementations, the optically isolated zone can be formed by a wall surrounding the first and second optical communication devices, the wall being coupled to one of the frame and the rotatable element. The wall surrounding the first and second optical communication devices may be cylindrical and centered on the axle. In one case, the frame may comprise a first cylindrical wall surrounding the first optical communication device and the rotatable element may comprise a second cylindrical wall surrounding the second optical communication device, the first and second cylindrical walls together forming the optically isolated zone. 
     In some embodiments, the first optical communication device can comprise an optical receiver and the second optical communication device can comprise an optical transmitter operable to communicate data from the rotatable element to the optical receiver of the frame using free-space optical communications within the optically isolated zone. In other embodiments, the second optical communication device can comprise an optical receiver and the first optical communication device can comprise an optical transmitter operable to communicate data from the frame to the optical receiver of the rotatable element using free-space optical communications within the optically isolated zone. In yet other implementations, both the first and second optical communication devices comprise an optical receiver and an optical transmitter. In this case, the optical transmitter of the first optical communication device is operable to communicate data from the frame to the optical receiver of the second optical communication device of the rotatable element using free-space optical communications within the optically isolated zone and the optical transmitter of the second optical communication device is operable to communicate data from the rotatable element to the optical receiver of the first optical communication device of the frame using free-space optical communications within the optically isolated zone. 
     In some implementations, the frame may comprise a plurality of first optical communication devices, each of the first optical communication devices comprising an optical receiver. In this case, the second optical communication device may comprise an optical transmitter operable to communicate data from the rotatable element to the optical receivers of the frame using free-space optical communications within the optically isolated zone. Similarly, in some implementations, the rotatable element may comprise a plurality of second optical communication devices, each of the second optical communication devices comprising an optical receiver, and the first optical communication device may comprise an optical transmitter operable to communicate data from the rotatable element to the optical receivers of the rotatable element using free-space optical communications within the optically isolated zone. In these cases, the plurality of optical receivers can provide a plurality of locations for reception of optical communications from the optical transmitter. In some implementations, the second optical communication device may comprises an optical receiver and the frame may comprise a plurality of first optical communication devices, each of the first optical communication devices comprising an optical transmitter operable to communicate data from the frame to the optical receiver of the rotatable element using free-space optical communications within the optically isolated zone. Similarly, the first optical communication device may comprise an optical receiver and the rotatable element may comprise a plurality of second optical communication devices, each of the second optical communication devices comprising an optical transmitter operable to communicate data from the rotatable element to the optical receiver of the frame using free-space optical communications within the optically isolated zone. In these cases, the plurality of optical transmitters can provide a plurality of locations for transmission of optical communications to the optical receiver. 
     In some embodiments, the frame may comprise a plurality of first optical communication devices and the rotatable element may comprise a plurality of second optical communication devices, at least one first optical communication device being paired with at least one second optical communication device for optically communicating with each other. In this case, each pair of first and second optical communication devices can be located within a separate optically isolated zone of a plurality of optically isolated zones formed by the frame and the rotatable element. Each of the optically isolated zones can be maintained by the frame and the rotatable element during rotation of the rotatable element relative to the frame. In some cases, the plurality of optically isolated zones may be formed by a plurality of cylindrical walls of different diameters centered on the axle and coupled to one of the frame and the rotatable element. The plurality of cylindrical walls can form a central circular optically isolated zone and one or more annular optically isolated zones surrounding the central optically isolated zone. Each of the pairs of first and second optical communication devices can be operable to communicate data to each other independently. 
     In some implementations, at least one of the optical communication devices may comprise an optical transmitter comprising an amplifier operable to amplify an input signal and a plurality of light emitting diode circuits operable to adjust intensity in response to the amplified input signal. In some implementations, at least one of the optical communication devices may comprise an optical receiver a phototransistor circuit operable to output a voltage and a plurality of amplifiers operable to output an amplified version of the voltage. 
     In some embodiments, the apparatus of the seventh broad aspect may comprise an electrical connection element adapted to electrically connect a first node in the frame to a second node in the rotatable element independent of the optical communication between the first and second optical communication devices. The electrical connection element may comprise a torsional spring having windings surrounding the axle with a first end coupled to the axle and a second end coupled to the rotatable element. The torsional spring can be conductive and operable to electrically connect the first node in the frame to the second node in the rotatable element. The first node can be electrically coupled to the first optical communication device and the second node can be electrically coupled to the second optical communication device. In this case, the frame may comprise a first isolation circuit adapted to prevent data at the first node from being transmitted to the first end of the torsional spring and the rotatable element may comprise a second isolation circuit adapted to prevent data at the second node from being transmitted to the second end of the torsional spring. 
     According to an eighth aspect, the present invention is a data transfer apparatus adapted to be integrated within a cable reel comprising a frame comprising an axle and a rotatable element operable to rotate on the axle and having an outer surface surrounding the axle adapted to have a cable wrapped. The data transfer apparatus comprises: a first optical communication device adapted to be integrated with the frame; and a second optical communication device adapted to be integrated with the rotatable element. The first and second optical communication devices are adapted to optically communicate with each other during relative rotation to each other. The first and second optical communication devices can be located within an optically isolated zone and the optically isolated zone can be maintained during rotation of the rotatable element relative to the frame. In some embodiments, the optically isolated zone may be formed by a wall surrounding the first and second optical communication devices. The wall surrounding the first and second optical communication devices may be cylindrical and adapted to be centered on the axle. In some implementations, the apparatus comprises a plurality of first optical communication devices adapted to be integrated with the frame and a plurality of second optical communication devices adapted to be integrated with the rotatable element. In this case, at least one first optical communication device is paired with at least one second optical communication device for optically communicating with each other. Each pair of first and second optical communication devices can be located within a separate optically isolated zone of a plurality of optically isolated zones. The plurality of optically isolated zones may be formed by a plurality of cylindrical walls of different diameters adapted to be centered on the axle. The plurality of cylindrical walls can form a central circular optically isolated zone and one or more annular optically isolated zones surrounding the central optically isolated zone. 
     These and other aspects of the invention will become apparent to those of ordinary skill in the art upon review of the following description of certain embodiments of the invention in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of embodiments of the invention is provided herein below, by way of example only, with reference to the accompanying drawings, in which: 
         FIGS. 1A and 1B  are a perspective view and a breakout view respectively of a cable reel according to one embodiment of the present invention; 
         FIG. 2A  is a perspective view of a frame of the cable reel of  FIGS. 1A and 1B ; 
         FIGS. 2B and 2C  are top and bottom perspective views respectively of a rotatable element of the cable reel of  FIGS. 1A and 1B ; 
         FIG. 3A  is a cross-sectional view of the cable reel of  FIGS. 1A and 1B  illustrating elements used to electrically connect nodes according to one implementation; 
         FIG. 3B  is a rear view of the cable reel of  FIGS. 1A and 1B ; 
         FIGS. 4A and 4B  are views of one implementation of a cable reel incorporating a data transfer apparatus according to an embodiment of the present invention; 
         FIG. 5  is a logical system diagram using the cable reel of  FIGS. 1A and 1B  according to one embodiment of the present invention; 
         FIG. 6  is a circuit diagram for coupling or decoupling DC power to/from a coaxial cable according to one implementation; 
         FIGS. 7A and 7B  are breakout views of an implementation of the data transfer apparatus of  FIGS. 4A and 4B  using a capacitance coupling apparatus; 
         FIG. 7C  is a breakout view of an implementation of two capacitive plates within the capacitance coupling apparatus of  FIGS. 7A and 7B ; 
         FIGS. 8A and 8B  are breakout views of first and second embodiments of alternative embodiments of the data transfer apparatus of  FIGS. 4A and 4B  using free-space optical communication apparatus; 
         FIGS. 9A and 9B  are sample circuit diagrams of an optical transmitter and an optical receiver that may be incorporated within the free-space optical communication apparatus of  FIGS. 8A and 8B ; 
         FIG. 10  is a logical system diagram according to an alternative embodiment of the present invention; and 
         FIGS. 11A and 11B  are breakout views of implementations of the data transfer apparatus of  FIGS. 4A and 4B  according to alternative embodiments of the present invention. 
     
    
    
     It is to be expressly understood that the description and drawings are only for the purpose of illustration of certain embodiments of the invention and are an aid for understanding. They are not intended to be a definition of the limits of the invention. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The present invention is directed to cable reel designs which allow for improved transfer of power and/or data between a static frame of the reel and a cable wound around a rotatable element of the reel. In embodiments of the present invention, data can be transferred to/from the cable without physical contact between the static frame and the rotatable element around which the cable is wound and power can be transferred to the cable using mechanical components such as one or more torsional springs. This lack of physical contact in the data transfer and the use of mechanical components such as torsional springs in the power transfer can improve reliability of the cable reel, reduce the generation of heat within the reel due to friction, increase the lifespan of the cable reel and/or reduce electromagnetic noise that is generated by brushes. 
     In some embodiments of the present invention, the cable reel comprises a torsional spring that is used to store mechanical energy that can be used to retract the cable onto the rotatable element. The torsional spring can be conductive and also be used to electrically couple the cable wound on the rotatable element to a static node within the static frame. In some cases, there may be a plurality of electrically isolated torsional springs that are used to electrically couple the cable to a plurality of static nodes. For example, two electrically isolated torsional springs may be incorporated within the cable reel to electrically couple a positive DC voltage and a negative DC voltage to the cable. In another example, three electrically isolated torsional springs may be incorporated within the cable reel to electrically couple a positive DC voltage, a negative DC voltage (possibly a reference ground) and an earth ground to the cable. It should be understood that other embodiments may also be implemented that use one or a plurality of electrically isolated torsional springs. 
     In some embodiments of the present invention, the cable reel comprises a data transfer apparatus that enables the transfer of data between a static node within the frame of the cable reel and a cable wrapped around the rotatable element of the cable reel. In one implementation, the data transfer apparatus comprises a capacitance coupling apparatus that contains two capacitive plates that together form a capacitor, one connected to the static frame and one connected to the rotatable element. The data can be transferred through the capacitance coupling apparatus without physical contact between the two capacitive plates, hence without physical contact between the static frame and the rotatable element, even when the capacitive plates rotate relative to each other. 
     In another implementation, the data transfer apparatus comprises a free-space optical communication apparatus that contains an optically isolated zone in which an optical transmitter may communicate data to an optical receiver. The optical transmitter/receiver system may be used to communicate data from the rotatable element to the static frame and/or may be used to communicate data from the static frame to the rotatable element without physical contact between the static frame and the rotatable element. In some implementations, the free-space optical communication apparatus may comprise a plurality of optically isolated zones that maintain alignment between optical transmitters/receivers when the rotatable element rotates relative to the static frame. In this case, each optically isolated zone can be used to communicate a separate data channel, thus enabling independent two way communications without time multiplexing and/or increased bandwidth of data to be communicated by using a plurality of parallel data channels. 
       FIGS. 1A and 1B  are a perspective view and a breakout view respectively of a cable reel  100  according to one embodiment of the present invention. The cable reel  100  comprises a frame  102  forming a cylindrical encasement and a rotatable element  104  integrated within the frame  102 . The frame  102  is a static element that may be mounted to equipment, walls or other fixed elements. The rotatable element  104 , as will be described in more detail, is operable to rotate within the frame  102  and may have a cable wrapped around it. As shown in  FIG. 1A , the cable reel  100  further comprises a circular cover  106  that may be a portion of the frame  102  or may be a removable component that allows for access to the elements within the frame  102 . In  FIG. 1B , the cover  106  has been removed for simplicity and the elements within the cable reel  100  in one implementation are illustrated in a breakout view. As shown in  FIG. 1B , the rotatable element  104  may further have a corresponding rotatable element cover  131  which when integrated with the rotatable element  104  is adapted to provide a circular area on the exterior capable of having a cable wrapped. Although shown as cylindrical, the frame  102  may be another shape that allows for the rotatable element  104  to rotate within it. 
     As shown in  FIG. 1B , the cable reel  100  may further comprise first and second torsional springs  108   a ,  108   b  within the rotatable element  104  with a separator  110   a  between the torsional springs  108   a ,  108   b  and a separator  110   b  on top of the second torsional spring  108   b . In these embodiments, the torsional springs  108   a ,  108   b  comprise a plurality of circular windings and are composed of a conductive material such as metal that may conduct a voltage from one end of the spring to the other end. In one specific implementation, the torsional springs  108   a ,  108   b  are composed of aluminum, though other conductive materials could be used. As shown in  FIG. 1B , the torsional springs  108   a ,  108   b  each have a respective inner end  125   a ,  125   b  adapted to enable insertion of a square element. Further, in the specific implementation of  FIG. 1B , the torsional springs  108   a ,  108   b  comprise respective perpendicular jutting element  141   a ,  141   b  on or local to the outer end of the torsional springs. The jutting element  141   a ,  141   b  may be used to insert within slots  142   a ,  142   b  within the rotatable element as will be described. In other embodiments, alternative techniques may be used to adapt the outer ends of the torsional springs to couple to the rotatable element  104 . 
     The separators  110   a ,  110   b  are used to electrically isolate the torsional springs  108   a ,  108   b  and are composed of a non-conductive material. In one specific implementation, the separators  110   a ,  110   b  may be composed of plastic, though other materials could be used. In some embodiments, there may be a further separator between the first torsional spring  108   a  and the rotatable element  104 . This would be the case if the rotatable element  104  is composed of a conductive material such as metal but a further separator may be used even if the rotatable element  104  is composed of a non-conductive material. Along with providing electrical isolation, the separators  110   a ,  110   b  also provide mechanical separation. 
     It should be understood that the cable reel  100  of  FIG. 1B  is only one implementation of the present invention. In other embodiments, the cable reel  100  may only comprise a single torsional spring. In other embodiments, the cable reel  100  may comprise more than two torsional springs. In each case, a separator would be implemented to electrically isolate the torsional springs if independent voltages are desired to be conducted on the torsional springs. 
       FIG. 2A  is a perspective view of the frame  102  of the cable reel  100  according to one embodiment of the present invention. The frame  102  comprises an open ended cylindrical element  112  having walls perpendicular to a circular end plate  113 . The cylindrical element has a slot  114  within its walls to allow a cable to go through from the interior of the frame  102  to the exterior. The frame  102  further comprises an axle  116  perpendicularly connected to the circular end plate  113  of the cylindrical element  112 . As shown in  FIG. 2A , the axle  116  is centered within the cylindrical element  112 . If the cylindrical element  112  was significantly larger than the rotatable element  104  that is operable to rotate within the frame  102 , then the axle  116  may not be centered in some embodiments. 
     The axle  116  comprises a slotted shaft  118  that is surrounded by a circular tube  120 . The slotted shaft  118  comprises a square hollow tube with a slot that extends the length of one side of the tube. The slotted shaft  118  extends beyond the circular tube  120 . The circular tube  120  comprises at least one slot  122  that is aligned with the slot of the slotted shaft  118 . The circular tube  120  provides a surface for the rotatable element  104  to rotate around. In some implementations, a ball bearing may also be added to ease rotation. The slotted shaft  118  allows wires to traverse the axle  116  between the slot  122  in the circular tube  120  and the portion of the slotted shaft  118  that extends past the circular tube  120 . The slotted shaft  118  also provides a fixed point around which elements cannot rotate. As shown in  FIG. 1B , the inner ends  125   a , 125   b  of the torsional springs  108   a ,  108   b  are shaped to fit around the portion of the slotted shaft  118  that extends beyond the circular tube  120 . This ensures that the inner ends  125   a ,  125   b  of the torsional springs  108   a ,  108   b  are physically connected to the frame  102  and will not rotate with the rotatable element  104 . When coupling to the slotted shaft  118 , it should be understood that the torsional springs  108   a ,  108   b  (if there are a plurality of electrically isolated torsional springs) should be kept electrically isolated at the slotted shaft  118  and the slotted shaft  118  may comprise a non-conductive material or be coated with a non-conductive coating. The separators  110   a ,  110   b  may sufficiently electrically isolate the torsional springs  108   a ,  108   b  at the slotted shaft  118  or further isolation elements may be used. 
     In alternative embodiments, the slotted shaft  118  may be other shapes than square, such as triangular, pentagonal, etc. The shape of the slotted shaft  118  in this implementation allows elements such as ends of the torsional springs to connect and not rotate with the rotatable element  104  while it rotates around the circular tube  120 . In an alternative embodiment, a plurality of slotted shafts may be implemented that are of different dimensions, each one decreasing in size inside the previous. In this case, if kept electrically isolated, the slotted shafts themselves could each be electrically conductive and be electrically coupled to a respective torsional spring. Thus the voltages transferred between the frame  102  and the rotatable element  104  could be transferred via a nested set of slotted shafts to a plurality of torsional springs. 
     In some embodiments of the present invention, the frame  102  further comprises a connector  124  integrated within a hole  128 . This connector  124  can be used as the electrical connection to the interface to the cable reel  100 . As will be described, power and/or data may be transferred via the connector  124 . A local cable may be connected to the connector  124  and extend inside the frame  102  to connect to other elements as will be described herein. In one case, the cable or one or more cables output from another element within the frame  102  could be routed through the slot  122  within the circular tube  120  and through the slotted shaft  118 . The cable connected to the connector  124  would be connected to the frame  102  and therefore would be static and not rotate with the rotatable element  104 . In alternative embodiments, the connector  124  may be removed and a local cable may extend through the hole  128  with no connector. The advantage of including the connector  124  is that it may keep the interior of the frame  102  environmentally isolated from the exterior of the frame  102 , hence reducing dust, dirt, water and other environmental elements from entering the cable reel  100  through the hole  128 . In some embodiments, the connector  124  may be implemented but the frame  102  may not be environmentally isolated from the exterior of the frame  102 . 
       FIGS. 2B and 2C  are top and bottom perspective views respectively of the rotatable element  104  of the cable reel  100  according to one embodiment of the present invention. As shown, the rotatable element  104  comprises an open ended cylindrical element  130  connected perpendicularly to a circular ring plate  132  that has an inner diameter equal to the diameter of the cylindrical element  130  and an outer diameter larger than the diameter of the cylindrical element  130 . In operation, a cable may be wrapped around the exterior of the cylindrical element  130  and the circular ring plate  132  along with the rotatable element cover  131  can be used as guide elements and prevent the cable from sliding off the circular element  130 . As shown, the rotatable element  104  further comprises a circular plate  134  perpendicularly connected to the inner surface of the cylindrical element  130 , the circular plate  134  dividing the interior of the cylindrical element  130  into an upper and lower cavity area within the cylindrical element  130 . The circular plate  134  has a circular hole  140  in the center that is of sufficient size to allow for the circular tube  120  of the axle  116  to traverse and allow for the rotatable element  104  to rotate around the axle  116 . 
     In the implementation of  FIG. 2C , the rotatable element  104  further comprises an inner cylindrical element  136  with a diameter less than the diameter of the cylindrical element  130  (herein also referred to as the outer cylindrical element). The inner cylindrical element  136  is perpendicularly connected to the lower side of the circular plate  134  and is connected to the outer cylindrical element  130  with use of a plurality of struts  138 , in this case three struts equally distant around the circumference of the inner cylindrical element  136 . The inner cylindrical element  136  and the struts  138  provide mechanical support to the outer cylindrical element  130 , making the component stronger and more resistant to external forces that may be applied during operation. Further, the inner cylindrical element  136  and struts  138  create a plurality of compartments on the lower cavity area of the outer cylindrical element  130  that may be used for electrical components or cables/wires if necessary. It should be understood that in some embodiments, there may be holes through the inner cylindrical element  136  and/or the struts  138  to pass wires or cables needed for operation of the cable reel  100 . Further, it should be understood that other mechanical structures could be used to provide support to the outer cylindrical element  130  and, in some cases, the inner cylindrical element  136  and the struts  138  are removed altogether. 
     As shown, in some embodiments of the present invention, the cylindrical element  130  further comprises one or more grooves  142   a ,  142   b  that run the length of the interior of the element. Each of the grooves  142   a ,  142   b  is adapted to connect to a respective one of the jutted elements  141   a ,  141   b  at the outer end of a respective one of the torsional springs  108   a ,  108   b . By connecting to the respective groove  142   a ,  142   b , the outer ends of the torsional springs  108   a ,  108   b  are connected to the rotatable element  104  while the inner ends  124   a ,  124   b  of the torsional springs  108   a ,  108   b  are connected to the frame  102  by the slotted shaft  118 . In  FIG. 2B , the cylindrical element  130  has two grooves  142   a ,  142   b  which is consistent with the two torsional springs  108   a ,  108   b  of  FIG. 1B , though it should be understood that there may be other numbers of grooves in other embodiments or alternative techniques for coupling the outer ends of the torsional springs to the rotatable element  104 . 
     In the architecture of  FIG. 1B , the torsional springs  108   a ,  108   b  will contract when the rotatable element  104  rotates in the same direction as the windings on the torsional springs  108   a ,  108   b , thus storing mechanical energy. This mechanical energy can be stored using a locking mechanism (not shown) on the rotatable element  104 . Once the force that is causing the rotation in the rotatable element  104  is no longer present and any locking function that may have been applied is released, the torsional springs  108   a ,  108   b  will attempt to rebound and expand, causing the rotatable element  104  to rotate in the opposite direction to the windings of the torsional springs  108   a ,  108   b.    
     In some embodiments of the present invention, the cylindrical element  130  further comprises a cable interface element  144  which protrudes on the exterior of the element. The cable interface element  144  comprises a connector  146  that can allow a cable that is to be wrapped around the cylindrical element  130  to be connected. The cable can then be connected to electrical components and/or cable/wiring within the interior of the cylindrical element  130 . In some embodiments of the present invention, other mechanical designs could be applied to allow a cable wrapped around the cylindrical element  130  to be connected to electrical components within the rotatable element  104  or to the outer ends of one or more of the torsional springs  108   a , 108   b . For instance, the connector  146  may not be implemented in some embodiments and a cable wrapped around the cylindrical element  130  could be directly electrically connected to a component within the rotatable element  104  or to the outer ends of one or more of the torsional springs  108   a , 108   b.    
     In the implementation of  FIGS. 2B and 2C , the circular ring plate  132  further comprises a plurality of holes  148  around the ring surrounding the cylindrical element  130 . These holes  148  allow for the cable reel  100  to be reduced in weight in the case that the rotatable element  104  is composed of a material that is relatively heavy. It should be understand that these holes  148  may be removed in some implementations. Further, there may be other holes in the circular plate  134  and/or the outer cylindrical element  130  and/or the rotatable element cover  131 . The holes in the circular plate  134  and/or the cylindrical element  130  and/or rotatable element cover  131  could be used to route required internal wiring (ex. an internal cable to connect components within the cable reel  100 ) or could be used to simply reduce weight similar to the holes  148 . 
       FIG. 3A  is a cross-sectional view of the cable reel  100  illustrating elements used to electrically connect nodes according to one implementation and  FIG. 3B  is a rear view of the cable reel  100 .  FIG. 3A  is shown with only a single torsional spring  108   a  for simplicity. It should be understood that the cable reel  100  may comprise one, two or more torsional springs. In one embodiment of the present invention, the cable reel  100  is designed to electrically connect a voltage node on the connector  124  with a voltage node on the connector  146 . In one case, the voltage node in the connector  124  may electrically connect to the connector  146  via a cable that traverses the slot  122 , the slotted shaft  118  and then coupled to the inner end  125   a  of the torsional spring  108   a . With the torsional spring  108   a  being composed of conductive material, the inner and the outer ends of the torsional spring  108   a  are electrically connected. The outer end of the torsional spring  108   a  that comprises the jutted element  141   a  that is mechanically coupled within the groove  142   a  of the cylindrical element  130  may be electrically connected to the connector  146  via a cable or wiring. Therefore, using the conductive torsional spring, a voltage node on the frame  102  that is static can be electrically connected to a voltage node on the rotatable element  104  that may be rotating in operation. 
     The use of one torsional spring may allow for a single pair of voltage nodes to be electrically connected between the frame  102  and the rotatable element  104 . With the use of a second torsional spring that is electrically isolated from the first torsional spring, two pairs of voltage nodes may be electrically connected between the frame  102  and the rotatable element  104 . With the use of a third torsional spring that is electrically isolated from the first and second torsional springs, three pairs of voltage nodes may be electrically connected between the frame  102  and the rotatable element  104 . One skilled in the art would understand that the use of a plurality of electrically isolated torsional springs could allow for the electrically connection between a plurality of pairs of voltage nodes between the frame  102  and the rotatable element  104  with a one to one ratio. Each of the plurality of voltage nodes in the frame  102  may be coupled to an inner end of one of the torsional springs via a wire or cable through the slot  122  and the slotted shaft  118 . These wires or cables could be combined within a single multi-stranded cable element or may be separate. Similarly, each of the plurality of voltage nodes in the rotatable element  104  may be coupled to an outer end of one of the torsional springs via a wire or cable through the cable interface element  144  and the grooves within the rotatable element  104 . These wires or cables could also be combined within a single multi-stranded cable element or may be separate. It should be understood that other mechanical designs are possible for connecting one or more voltage nodes in the frame  102  to corresponding voltage nodes in the rotatable element  104  via the torsional springs. 
     The electrically connection of pairs of voltage nodes between the frame  102  and the rotatable element  104  may be used to transfer one or more DC voltages and/or an earth ground from outside of the cable reel  100  to a cable wrapped around the rotatable element  104  that is connected to the connector  146 . For example, if a device (ex. video camera, sensor, etc.) coupled to the cable requires a particular DC voltage (ex. 24V) to operate, positive and negative voltage inputs for the particular required DC voltage could be applied to the connector  124  (on the back of the cable reel  100  of  FIG. 3B ) and the positive and negative voltages (ex. 24V, 0V) could be transferred to the cable via two torsional springs connecting to the connector  146 . In a further example in which a device coupled to the cable requires a DC voltage and earth ground, the cable reel could be adapted to have three torsional springs to allow for electrically connecting three pairs of voltage nodes from the frame  102  to the rotatable element  104 . 
     In some embodiments, there may be an AC to DC power supply external to the cable reel  100  that provides the desired voltage levels to the connector  124  or to another connector or to a plurality of connectors (not shown) in the frame  104 . In other embodiments, there may be an AC to DC power supply integrated within the cable reel  100 . In this case, an AC power source may be coupled to the connector  124  or another connector within the frame  102 . The AC to DC power supply may be integrated within the frame  102  and have voltage nodes that provide a DC voltage level. These voltage nodes may be electrically connected to voltage nodes in the rotatable element  104  through the torsional springs as previously described. Alternatively, an AC voltage may be input to the frame  102  and transferred to the rotatable element  104  via the torsional springs. The AC voltage may then be converted to positive and negative DC voltages (ex. 24V, 0V) using an AC to DC power supply integrated within the rotatable element  104  or may simply transfer the AC voltage to a cable wrapped around the rotatable element  104 . This implementation would be particularly useful in the case that one or more devices coupled to the cable require AC power to operate. 
     The above embodiments are focused on transferring DC or AC voltages from the frame  102  to the rotatable element  104  so that they can be transferred to a cable wrapped around the rotatable element and provided to one or more devices coupled to the cable. It should be understood that this implementation should not limit the scope of the present invention. In particular, a cable reel according to the present invention could be used to simply connect two voltage nodes together, one coupled to the frame  102  and one coupled to the rotatable element  104 . This may be used to ensure devices use a common ground level or are electrically connected for protection purposes. Further, the cable reel according to the present invention may be used to transfer a voltage level from the rotatable element  104  to the frame  102 . This could be useful in the case that a device coupled to a cable wrapped around the rotatable element  104  transmits one or more voltages that need to be measured/detected at a device coupled to the frame  102 . In one specific example, the device may be a sensor (ex. a light sensor circuit) that generates a voltage and/or changes its impedance when light is detected. This voltage may need to be detected and/or measured at a device coupled to the frame  102 . In this case, the voltage output from the device may be electrically connected via the cable to the connector  146  and via the torsional spring(s) to the connector  124 . In another example, the device may be a device that changes impedance (ex. a dry contact system that goes from an open impedance to a shunt impedance depending on the position of the contacts). In this case, the impedance of the device may be detected by a circuit coupled to the frame  102  through the electrically coupling of the device through the torsional spring. 
     In some embodiments in which a plurality of pairs of voltage nodes are to be electrically connected between the frame  102  and the rotatable element  104 , less than all of the pairs of voltage nodes may be electrically connected using a torsional spring. The use of a torsional spring to electrically connect voltage nodes allows for the mechanical devices reuse within the cable reel as a mechanical element and an electrical connection element. In some embodiments, one or more pairs of voltage nodes between the frame  102  and the rotatable element  104  may be electrically connected using other means than a torsional spring. In one implementation a flat cable or ribbon cable or flat flex cable is used to electrically connect one or more pairs of voltage nodes between the frame  102  and the rotatable element  104 . In this case, the flat cable may be wrapped around the axle  116  within the cylindrical element  130 , one end of the flat cable being coupled to the connector  124  via the slotted shaft  118  and the other end of the flat cable being coupled to the connector  146  via the cable interface element  144 . In this case, the flat cable operates to electrically connect pairs of voltage nodes but is not used for mechanical purposes similar to a torsional spring. In one embodiment, a single torsional spring is implemented within the cable reel and is used to electrically connect a voltage node in the frame  102  to a voltage node in the rotatable element  104  and a flat cable is used to electrically connect one or more other voltage nodes in the frame  102  to one or more corresponding voltage nodes in the rotatable element  104 . In other embodiments, no torsional spring may be used to electrically connect a voltage node in the frame  102  to a voltage node in the rotatable element  104 . Instead, aspects of the present invention relate only to the transfer of data between the frame  102  and the rotatable element  104  as will be described. In this case, a torsional spring may be included for only mechanical purposes or may be replaced with another element such as a motor. 
     Along with electrically connecting voltage nodes between the frame  102  and the rotatable element  104 , the cable reel  100  according to embodiments of the present invention may also transfer data between the frame  102  and the rotatable element  104 . Transferring data between a static element and a rotating element using the torsional springs or flat cables are possible but there are significant limits on the bandwidth of data that could be transmitted. If data is transmitted on the torsional spring or the flat cable as described, radio interference can occur as the element can start acting as an antenna. One skilled in the art can use significant error correction algorithms or a very slow bit rate to manage the radio interference but this would limit the overall bandwidth of data that can be transferred. In other implementations, shielding could be added to the torsional spring or flat cable to reduce the interference created from their windings on the data being transmitted. The shielding adds cost and would still have limits on the bandwidth of data that could be transferred. 
     In embodiments of the present invention, the cable reel  100  uses torsional springs to electrically connect pairs of voltage nodes between the frame  102  and the rotatable element  104  to transfer voltages that may be used for powering one or more devices connected to a cable wrapped around the rotatable element  104 . In addition, the cable reel  100  further comprises a data transfer apparatus  150  that can be used to independently transfer data between the frame  102  that may be static and the rotatable element  104  that may rotate in operation. By separating out the transfer of data, systems can be used to enable high bandwidth data transfer with minimal data error loss. Specifically, in two embodiments of the present invention that will be described in detail herein, capacitance coupling and free-space optical communications can be used to transfer data between the frame  102  and the rotatable element  104  independent of electrical connection of voltage nodes between the components. In both of these embodiments, transfer of data may occur without requiring physical contact between the frame  102  and the rotatable element  104  that may be in relative motion to each other in operation. 
       FIGS. 4A and 4B  are views of one implementation of a cable reel  100  incorporating a data transfer apparatus  150  according to an embodiment of the present invention. In this embodiment, the data transfer apparatus  150  comprises a cylindrical element that has first and second ends, one connected to the frame  102  and one connected to the rotatable element  104 . As will be described, the data transfer apparatus  150  is designed to allow data transfer between the frame  102  and the rotatable element  104  while the rotatable element  104  is rotating in operation relative to the frame  102 . In  FIGS. 4A and 4B , the data transfer apparatus  150  is integrated within the upper cavity of the cylindrical element  130  above the cylindrical plate  134  and the torsional springs  108   a ,  108   b . In this case, it has a diameter less than the cylindrical element  130 , though in some cases, the data transfer apparatus  150  may fit tightly into the interior walls of the cylindrical element  130  or may be another size or shape. In one embodiment, the bottom end of the data transfer apparatus  150  is coupled to the axle  116  and does not rotate with the rotatable element  104  while the top end of the data transfer apparatus  150  is coupled to the rotatable element  104  and rotates with it. In this embodiment, the circular walls may be connected to either the top or bottom ends and may rotate or not with the rotatable element  104 . In some embodiments, as will be described, the data transfer apparatus  150  comprises connectors integrated into the top and the bottom ends that are adapted to be coupled to the connector  146  and connector  124  respectively. 
     In alternative embodiments, the data transfer apparatus  150  may be implemented in other manners in which one end of the apparatus is coupled to the frame  102  and is electrically coupled to the connector  124  and one end is coupled to the rotatable element  104  and electrically coupled to the connector  146 . For instance, the ends of the data transfer apparatus  150  may be coupled to other elements within the upper or lower cavity of the cylindrical element  130 . As will be described in more detail, elements within the data transfer apparatus  150  can maintain alignment such that data can be transferred while the rotatable element  104  rotates relative to the frame  102 . 
     In some embodiments of the present invention, the cable wrapped around the rotatable element  104  is a coaxial cable and the connectors  124 ,  146  are connectors for coaxial cables. A coaxial cable has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. As is well known, the inner conductor of the coaxial cable may carry a data signal. Further, the inner conductor of the coaxial and the tubular conducting shield may carry positive and negative DC voltages respectively that can be used to power devices. In the case that a coaxial cable is used, data channels on the coaxial cable can be transferred between the frame  102  and the rotatable element  104  via the data transfer apparatus  150 . DC voltages transferred to voltage nodes on the rotatable element  104  via one or more of the torsional springs  108   a , 108   b  may be coupled to the coaxial cable wrapped around the rotatable element  104  so that the coaxial cable can be the source of DC power for one or more remotely located devices coupled to the coaxial cable. 
       FIG. 5  is a logical system diagram using the cable reel  100  according to one embodiment of the present invention. As shown, the cable reel  100  in this embodiment comprises connectors  124   a ,  124   b . The connector  124   a  is coupled to a DC power source  502  that can be used to couple DC voltages onto a coaxial cable  508  that may be wrapped around the rotatable element  104  and extracted and/or retracted as may be required in operation. The DC voltages may be coupled onto the coaxial cable  508  by transferring the voltages through the torsional springs  108   a ,  108   b  as previously described and using a DC voltage coupling element  510  integrated with the rotatable element  104  within the cable reel  100  to couple the DC voltages onto the coaxial cable. The connector  124   b  is coupled to a first Multimedia Over Coaxial Alliance (MOCA) component  504  that can convert data between a digital format such as Ethernet and an analog format that can be transmitted over a coaxial cable. As shown, the MOCA component  504  may be powered by a DC power source  506 . The DC power sources  502  and  506  may be the same component or may be separate components. Data transferred through the first MOCA component  504  may be transferred via the connector  124   b  to/from the cable  508  via the data transfer apparatus  150 . In essence, the coaxial cable  508  may receive DC power from the DC power source  502  via the connector  124   a , the torsional springs  108   a / 108   b  and the DC voltage coupling element  510  and may receive/transmit data to/from the first MOCA component  504  via the data transfer apparatus  150  and the connector  124   b.    
     Further, at a remote location, the cable  508  may be coupled to a DC voltage decoupling element  512  that may allow for decoupling of the DC voltages that were coupled onto the coaxial cable  508 . A coaxial output and a DC power output from the DC voltage decoupling element  512  are coupled to a second MOCA component  514  that may be powered by the DC power coupled on the coaxial cable  508 . The second MOCA component  514  may convert data between an analog format that can be transmitted over a coaxial cable and a digital format such as Ethernet. As shown, the second MOCA component  514  may be coupled to a plurality of devices  516   a ,  516   b ,  516   c  that input and/or output data in Ethernet format. The devices  516   a ,  516   b ,  516   c  may perform a variety of functions and, in some embodiments, may comprise a video camera, a sensor and/or a control device. Data generated by the devices  516   a ,  516   b ,  516   c  can be converted to an analog format capable to be transmitted via the coaxial cable  508  by the second MOCA component  514  and then transmitted via the cable  508  and the cable reel  100  (via the data transfer apparatus  150 ) to the first MOCA component  504  which then can convert the data to an Ethernet format that can be received by another component (not shown). Data input into the first MOCA component  504  may be converted from an Ethernet format to an analog format capable to be transmitted via the coaxial cable  508  by the first MOCA component  504  and then transmitted via the cable reel  100  (via the data transfer apparatus  150 ) and the cable  508  to the second MOCA component  514  which then can convert the data back to an Ethernet format that be received by the devices  516   a ,  516   b ,  516   c . In particular implementations of the present invention, the MOCA components  504 ,  514  operate at a frequency range of 1000 to 1500 MHz, though other frequencies may be used. This frequency range works well in data communication over coax and is not subject to intense broadcast frequencies or cellular spectrum interference. 
     It should be understood that, although described using MOCAs that translate between Ethernet and an analog format, other translation devices could be used and other data formats could be implemented depending on the particular requirements of the components on either end of the communications. In one alternative embodiment, Ethernet-over-Coax (EoC) technology may be utilized. In other alternative embodiments, non-Ethernet formats and/or non-coax physical layers may be used. In some embodiments, there may not be a need for the MOCA components  504 ,  514  or similar translation devices. For instance, in the case that the devices  516   a ,  516   b ,  516   c  are adapted to receive/transmit data in the same format that data is transmitted on the cable  508 , there would be no need for a translation function and potentially the cable  508  could be directly connected to one or more of the devices  516   a ,  516   b ,  516   c  or may be connected to the devices via a multiplexing component. In some embodiments, additional power amplifiers may be integrated to boost the signal on the transmitting end to ensure data is transferred sufficiently across the data transfer apparatus  150 . 
       FIG. 6  illustrates a circuit diagram for coupling or decoupling DC power to/from a coaxial cable according to one implementation. As shown, a DC voltage coupling/decoupling element  602  is connected between a first coaxial cable  604   a  comprising a center core  606   a  surrounded by an outer metallic shield  608   a  and a second coaxial cable  604   b  comprising a center core  606   b  surrounded by an outer metallic shield  608   b . As is well-known in the art, a coaxial cable typically includes insulation between the center core and the outer metallic shield and further includes a plastic jacket surrounding the outer metallic shield. The DC voltage coupling/decoupling element  602  comprises a pass through  610  that connects the outer metallic shields  608   a ,  608   b  of the first and second coaxial cables  604   a ,  604   b  and is further coupled to a negative DC voltage node (DC−). Further, the DC voltage coupling/decoupling element  602  comprises a capacitor  612  coupled between the center cores  606   a ,  606   b  of the first and second coaxial cables  604   a ,  604   b  and an inductor  614  coupled between a positive DC voltage node (DC+) and a node between the center core  606   a  of the first coaxial cable  604   a  and the capacitor  612 . In one implementation, the capacitor  612  may be 1000 pF and the inductor  614  may be 1000 nH though other values for these elements may be used in other embodiments. As will be described, the DC voltage coupling/decoupling element  602  may act as an isolation circuit with the capacitor  612  acting as an isolation element for DC and/or the inductor  614  acting as an isolation element for high frequency data signals. 
     The DC voltage coupling/decoupling element  602  can be used to couple DC voltages onto the first coaxial cable  604   a  if a DC voltage is applied to the positive and negative DC voltage nodes (DC+, DC−). In this case, the DC voltage coupling/decoupling element  602  may comprise the DC voltage coupling element  510 , the first coaxial cable  604   a  may be a first end of the cable  508  that is inside the cable reel  100  while the second coaxial cable  604   b  may be a cable that connects to the data transfer apparatus  150  within the cable reel  100 . The DC voltage nodes (DC+, DC−) may be nodes connected to the torsional springs  108   a ,  108   b  that are coupled to the DC power source  502 . In this case, the capacitor  612  is used to block the DC voltage from passing to the center core  606   b  of the second coaxial cable  604   b  and therefore be applied to the data transfer apparatus  150 . In essence, the capacitor  612  acts as an isolation element for the DC. The capacitor  612  only blocks DC and allows Ultra High Frequency (UHF) radio wave frequencies to pass freely between the first coaxial cable  604   a  and the second coaxial cable  604   b . In one example in which the capacitor  612  is 1000 pF and the data is transmitted at 1 GHz, the coaxial cable  604   b  may be 50Ω or 75Ω and the capacitor  612  may represent only an impedance of approximately 0.16Ω (effectively a closed circuit for the RF). The inductor  614  has the opposite effect and only allows DC to pass while blocking all radio frequencies from leaving the coaxial cables  604   a ,  604   b  and traveling to the torsional springs  108   a , 108   b  and potentially back to the DC power source  502 . In essence, the inductor  614  acts as an isolation element for high frequency data signals. Having the radio frequencies blocked reduces the potential of local interference within the cable reel  100 , thus preventing wires/cables or the torsional springs  108   a ,  108   b  (which may be unshielded) from acting as an antenna. In one example in which the inductor  614  is 1000 nH and the data is transmitted at 1 GHz, the inductor  614  may represent an impedance of approximately 6300Ω (effectively an open circuit for the RF). 
     Similarly, the DC voltage coupling/decoupling element  602  can be used to decouple DC voltages that are on the first coaxial cable  604   a  and apply the DC voltage to the positive and negative DC voltage nodes (DC+, DC−). In this case, the DC voltage coupling/decoupling element may comprise the DC voltage decoupling element  512 , the first coaxial cable  604   a  may be a second end of the cable  508  external to the cable reel  100 , and the second coaxial cable  604   b  may be a cable that connects into a data input/output of the second MOCA component  514 . The DC voltage nodes (DC+, DC−) may be nodes connected to a DC power input of the second MOCA component  514  via a cable  513 , which may be used to provide DC power to the second MOCA component  514 . In this case, the capacitor  612  is used to block the DC voltage from passing to the center core  606   b  of the second coaxial cable  604   b  and therefore be applied to the data input/output of the second MOCA component  514 . The capacitor  612  only blocks DC and allows Ultra High Frequency (UHF) radio wave frequencies to pass freely between the first coaxial cable  604   a  and the second coaxial cable  604   b . The inductor  614  has the opposite effect and only allows DC to pass while blocking all radio frequencies from leaving the coaxial cables  604   a ,  604   b  and traveling to the DC power input of the second MOCA component  514  via the cable  513 . Preventing the DC from being input to the data input/output of the second MOCA component  514  and preventing the radio frequencies from being input to the DC power input of the second MOCA component  514  can ensure proper operation of the second MOCA component  514 , though in some embodiments this prevention may not be necessary. 
     In some implementations of a DC voltage coupling or decoupling element, the capacitor  612  may not be necessary, the inductor  614  may not be necessary and/or other components may be added to the element. Further, in some embodiments, other values of capacitance or impedance or resistance is applied in the DC voltage coupling or decoupling element. In some embodiments, multiple stages of inductive and capacitive filtering may be implemented within an isolation circuit to isolate DC from the data signal. In its simplest form, a DC voltage coupling or decoupling element may connect the outer metallic shields  608   a ,  608   b  to each other and to a negative DC voltage node (DC−) and connect the center cores  606   a ,  606   b  to each other and to a positive DC voltage node (DC+), with no other isolation components. 
     Although the DC voltage coupling element  510  is depicted as being integrated within the rotatable element, it should be understood that in some embodiments coupling and decoupling of DC voltages onto a coaxial cable may occur in other locations. For instance, there may be a DC voltage coupling element external to the cable reel  100  that allows the DC power source  502  or the DC power source  506  or another DC power source to couple DC voltages onto the coaxial cable connecting between the first MOCA component  504  and the connector  124   b . In this case, an inductor may be implemented to protect the first MOCA component  504  from DC while a capacitor may be implemented to protect the DC power source from RF. In this case, a coaxial cable (not shown) internal to the cable reel  100  may connect to the connector  124   b  and then to a DC voltage decoupling element that separates the DC voltages that may be applied to the torsional springs  108   a ,  108   b  and a coaxial cable that may be connected to the data transfer apparatus  150 . In this implementation, the connector  124   a  may not be implemented. 
     In some embodiments of the present invention, the data transfer apparatus  150  comprises a capacitance coupling apparatus in which data is transferred using two capacitive plates that together form a capacitor. In these embodiments, one of the capacitive plates may rotate relative to the other capacitive plate but would still allow for data transfer during rotation.  FIGS. 7A and 7B  are breakout views of an implementation of the data transfer apparatus  150  using a capacitance coupling apparatus. As shown, the data transfer apparatus  150  comprises an encasement base  702  and cover  704  that together form a cylindrical encasement that holds first and second capacitive plates  706   a ,  706   b . In the embodiment illustrated, the encasement base  702  is an opened ended cylinder while the cover  704  is a circular disk, though it should be understood that other implementations may have different shapes and sizes of encasements for the data transfer apparatus  150 . 
     The cover  704  is integrated with the first capacitive plate  706   a  and the encasement base is integrated with the second capacitive plate  706   b . In one case, the encasement base  702  and the second capacitive plate  706   b  may be coupled to the frame  102  and may be static, while the cover  704  and the first capacitive plate  706   a  may be coupled to the rotatable element  104  and be rotatable in operation. In another case, the cover  704  and the first capacitive plate  706   a  may be coupled to the frame  102  and may be static, while the encasement base  702  and the second capacitive plate  706   b  may be coupled to the rotatable element  104  and be rotatable in operation. In either case, the two capacitive plates  706   a ,  706   b  may be separated slightly and rotatable in operation relative to each other. The encasement base  702  and the cover  704  are used to protect the capacitive plates  706   a ,  706   b  but are also rotatable in operation relative to each other. In some implementations, the edges of the encasement base  702  that are close to edges of the cover  704  are coated in a lubricant to reduce friction and heat in case of physical contact. 
     The first capacitive plate  706   a  may comprise a circular disk connected to a connector  708   a . The connector  708   a  in one implementation may be a coaxial connector that can allow a coaxial cable to connect to the first capacitive plate  706   a . The circular disk can comprise a circular copper track  710   a  that is centered on the circular disk and is of a first diameter and an annular copper track  712   a  that surrounds the circular copper track  710   a  and is of a second diameter. As shown, the annular copper track  712   a  is effectively an annulus with an outer diameter equal to the second diameter and an inner diameter slightly larger than the first diameter. In this design, the circular and annular copper tracks  710   a ,  712   a  are separated by a small etching so that each of the tracks is electrically isolated. In the case that the connector  708   a  is a coaxial connector, a center element of the connector  708   a  may be connected to a center core of a coaxial cable and an outer element of the connector  708   a  may be connected to an outer metallic shield of the coaxial cable. In embodiments of the present invention, the inner element of the connector  708   a  is connected to the circular copper track  710   a  and the outer element of the connector  708   a  is connected to the annular copper track  712   a.    
     Similarly, the second capacitive plate  706   b  may comprise a circular disk connected to a connector  708   b . The connector  708   b  in one implementation may be a coaxial connector that can allow a coaxial cable to connect to the first capacitive plate  706   b . The circular disk can comprise a circular copper track  710   b  that is centered on the circular disk and is of the first diameter and an annular copper track  712   b  that surrounds the circular copper track  710   b  and is of the second diameter. 
     The first diameter may be relatively small compared to the overall diameter of the circular disks of the first and second capacitive plates  706   a ,  706   b . In one implementation, the first diameter may be approximately equal to the inner diameter of a coaxial cable. In this case, the connectors  708   a ,  708   b  that may comprise a plurality of legs for connecting the connector to a PCB could be directly connected to the circular disk without additional track routing. In particular, a central leg of the connector  708   a ,  708   b  adapted to be connected to a central core of a coaxial cable connected to the connector could be connected to the corresponding circular copper tracks  710   a ,  710   b  and a set of outer legs of the connector  708   a ,  708   b  adapted to be connected to an outer metallic shield of a coaxial cable connected to the connector could be connected to the corresponding annular copper tracks  712   a ,  712   b . These connections, if the first diameter is sufficiently small, can be done directly through the capacitive plates  706   a ,  706   b.    
     The first and second capacitive plates  706   a ,  706   b  when separated slightly can form a capacitor. The circular copper tracks  710   a ,  710   b  can form a first capacitor and the annular copper tracks  712   a ,  712   b  can form a second capacitor. If data is being transmitted over a coaxial cable connected to one of the connectors  708   a ,  708   b , the data can be transferred across the capacitors formed with the first and second capacitive plates  706   a ,  706   b . The first capacitor formed with the circular copper tracks  710   a ,  710   b  effectively allows for data being communicated on a center core of a coaxial cable connected to the connector  708   a  to be transferred to a center core of a coaxial cable connected to the connector  708   b . Similarly, data being communicated on a center core of a coaxial cable connected to the connector  708   b  to be transferred to a center core of a coaxial cable connected to the connector  708   a . The second capacitor that is formed with the annular copper tracks  712   a ,  712   b  can be used to shield the data communication and ensure outside interference does not affect the transmission. This shield-coupling capacitance is further optimized as a relatively large capacitance using large effective capacitive plates that ensure the contiguous shielding of the center pin and represents an insignificant inconsistency in the distributed impedance of the coupled coaxial cable for all ultra high frequencies. If one of the capacitive plates  706   a  rotates relative to the other capacitive plate  706   b , the circular nature of the capacitive plates  706   a ,  706   b , allow for the continued alignment of the appropriate circular copper tracks  710   a ,  710   b  on the plates and therefore the continual transfer of data across the capacitor that is formed. 
     In some embodiments, it should be understood that additional sets of annular tracks of increasing diameter surrounding the circular tracks  710   a ,  710   b  may be used to transfer other data, for example for higher bandwidth applications or for data that may be in another format. In particular, additional annular copper tracks may be used to communicate a plurality of channels of data simultaneously. Further, in some embodiments, the use of a plurality of sets of annular copper tracks could replace the need to have the central circular copper tracks  710   a ,  710   b . Further, although the circular tracks  710   a ,  710   b  depicted in  FIGS. 7A and 7B  are of the same diameter, it should be understood in some implementations these could be different diameters. Similarly, the diameters of the annular copper tracks  712   a ,  712   b  could be different in some implementations. In some implementations, a lubricant may be applied between the capacitive plates  706   a ,  706   b , including, but not limited to, grease and/or Teflon. In other embodiments, no lubricant is applied as the two capacitive plates  706   a ,  706   b  may be sufficiently separated that contact between the elements would never occur. In various embodiments, air can be used as the dielectric, while in other embodiments, any material with good dielectric properties can be used as the separating dielectric. Further, although described using copper tracks, it should be understood that other conductive materials could be used when forming the tracks on the capacitive plates  706   a ,  706   b.    
       FIG. 7C  is a breakout view of an implementation of two capacitive plates within the capacitance coupling apparatus of  FIGS. 7A and 7B . As shown, the capacitive plate  706   a  comprises a printed circuit board comprising a plurality of layers. As shown in broken out view in  FIG. 7C , the capacitive plate  706   a  comprises a connector layer  720   a , a copper layer  722   a  and an insulation layer  724   a . The connector layer  720   a  may comprise an FR4 layer that is adapted with holes for attachment of the connector  708   a . The copper layer  722   a  is adapted to have the circular track  710   a  and annular track  712   a  etched into the layers. The connector  708   a  is adapted to be connected to the circular track  710   a  and annular track  712   a  through the connector layer  720   a . Similarly, the capacitive plate  706   b  comprises a connector layer  720   b , a copper layer  722   b  and an insulation layer  724   b . The insulation layers  724   a ,  724   b  are adapted to prevent the copper layers  722   a ,  722   b  from coming in contact. 
     In one sample implementation, the connector layers  720   a ,  720   b  combined with their corresponding copper layers  722   a ,  722   b  are 0.0625″ thick while the insulation layers  724   a ,  724   b  are 0.010″ thick. The two copper layers  722   a ,  722   b  may be separated with a total of 0.034″ of material in one implementation, a total of 0.020″ of insulation layers  724   a ,  724   b  (2×0.010″) with a dielectric constant of 4.3 and a total of 0.010″ of a material such as Teflon with a dielectric constant of 2.0. Between the Teflon layer and the two insulation layers  724   a ,  724   b , there may be grease with a thickness up to 0.002″. The Teflon layer and grease provide a reduced friction surface when the two capacitive plates  706   a ,  706   b  rotate relative to each other. It should be understood that this specific implementation should not limit the scope of the present invention and many other implementations for a capacitive plate may be used. A capacitive plate is an element that is half a capacitor and that when brought close to another capacitive plate can electrically form a capacitor element. By having the circular capacitive plates, the two plates can maintain a relatively consistent capacitance as one capacitive plate may rotate relative to the capacitive plate. 
     There may be limitations to the implementation as described with reference to  FIGS. 7A-7C  due to the standing wave ratio and impedance matching aspect of ultra high frequencies. Although there may not be any technical limits to the diameter of the outermost annulus that is associated with the shielding of the coaxial cable, there may be considerations of linearity of response with respect to the center pin that may carry a data signal. In the specific case of MOCA, the signal is typically broadband over a range of 500 MHz starting at 1000 MHz and ending at 1500 MHz. In this case, it is desirable to have a transfer characteristic at the capacitive plate that is relatively similar across the entire range of frequencies. For this condition to hold, the inner circular track of the capacitive plate should not be so large as to approach the resonant quarter wave antenna size of any of these frequencies. As the size of the inner circular track of the capacitive plate increases it will approach the quarter wave length of 1500 MHz which corresponds to 5 cm. It is desirable to avoid an inner circular copper track approaching this size or larger. Fortunately, there is sufficient capacitance created by a 2 cm diameter or less circular copper track to decrease the impedance to less than 30Ω over the range of used frequencies, thus rendering insignificant the impedance mismatch of the two coupled cables at the capacitive plates. It is noted that, if the impedance of the capacitor formed by the two circular copper tracks is too high, which may be caused by the capacitive plates being too distant or the circular tracks being too small, significant signal reflections at the plates may result, causing poor signal coupling. 
     In some embodiments of the present invention, the data transfer apparatus  150  comprises a free-optic communication apparatus in which data is transferred by light using one or more optical transmitters and one or more optical receivers. In these embodiments, at least one device capable of optical transmission may rotate relative to at least one device capable of optical reception but would still allow for data transfer during rotation using modulated light that may be implemented over a wide range of wavelengths which may or may not be visible to the human eye.  FIGS. 8A and 8B  are breakout views of first and second embodiments of alternative embodiments of the data transfer apparatus  150  using free-space optical communication apparatus. As shown, the data transfer apparatus  150  comprises an encasement base  802  and cover  804  that together form a cylindrical encasement that holds first and second communication modules  805 ,  812 , the first communication module  805  integrated with the encasement base  802  and the second communication module  812  integrated with the cover  804 . In the embodiment illustrated, the encasement base  802  is an open-ended cylinder while the cover  804  is a circular disk, though it should be understood that other implementations may have different shapes and sizes of encasements for the data transfer apparatus  150 . For instance, in some embodiments, both the encasement base  802  and the cover  804  may comprise open-ended cylinders that may connect together to form a closed cylinder. 
     In one case, the encasement base  802  and the first communication module  805  may be coupled to the frame  102  and may be static, while the cover  804  and the second communication module  812  may be coupled to the rotatable element  104  and be rotatable in operation. In another case, the cover  804  and the second communication module  812  may be coupled to the frame  102  and may be static, while the encasement base  802  and the first communication module  805  may be coupled to the rotatable element  104  and be rotatable in operation. Within  FIG. 8A , the encasement base  802  has a groove  816  that can allow for mechanical attachment of the encasement base  802  to the frame  102  or the rotatable element  104 . In other implementations, the groove may not be required or the groove  816  may instead be implemented within the cover  804 . In some cases, for mechanical attachment purposes, there may be two different grooves implemented within the encasement base  802  and the cover  804  to enable attachment. 
     The first and second communication modules  805 ,  812  may be parallel to each other and separated slightly and rotatable in operation relative to each other. The encasement base  802  and the cover  804  are used to protect the communication modules and limit exposure to external light but are also rotatable in operation relative to each other. In some implementations, the edges of the encasement base  802  that are close to edges of the cover  804  are coated in a lubricant to reduce friction and heat in case of physical contact. 
     As shown, the first communication module  805  comprises a circuit board integrated with first optical communication devices  808   a ,  808   b  located within cylindrical walls  806   a ,  806   b . In this implementation, the circuit board is circular. The cylindrical walls  806   a ,  806   b  comprise open-ended cylinders perpendicularly attached to the circuit board with first and second diameters, with one cylindrical wall  806   b  surrounding the other cylindrical wall  806   a . The cylindrical walls  806   a ,  806   b  create first and second optically isolated zones  810   a ,  810   b  within which the first optical communication devices  808   a ,  808   b  may operate independently without affecting each other. In the embodiment of  FIG. 8A , the first optically isolated zone  810   a  is a circular zone centered within the first communication module  805  and the second optically isolated zone  810   b  is an annular zone surrounding the first optically isolated zone  810   a . The second communication module  812  comprises a circuit board with second optical communication devices  814   a ,  814   b . In this implementation, the circuit board is circular. As shown in  FIG. 8A , the second optical communication device  814   a  is aligned to be within the first optically isolated zone  810   a  and the second optical communication device  814   b  is aligned to be within the second optically isolated zone  810   b . Each of the first optical communication devices  808   a ,  808   b  may be an optical transmitter, an optical receiver or a device capable of both optical transmission and reception. Similarly, each of the second optical communication devices  814   a ,  814   b  may be an optical transmitter, an optical receiver or a device capable of both optical transmission and reception. 
     Within the first optically isolated zone  810   a , the first and second optical communication devices  808   a ,  814   a  can optically communicate. For instance, the first optical communication device  808   a  may be capable of optical transmission and the second optical communication device  814   a  may be capable of optical reception and/or the second optical communication device  814   a  may be capable of optical transmission and the first optical communication device  808   a  may be capable of optical reception. In essence, communication can take place from the first device  808   a  to the second device  814   a  and/or from the second device  814   a  to the first device  808   a . In some implementations, the first device  808   a  and the second device  814   a  may be directly aligned in the centers of the optical communication elements  805 , 812 , though alignment is not necessary for communication as they are within the optically isolated zone  810   a  which allows for data to be transferred within the zone using modulated light. In operation, even as the first and second communication modules  805 ,  812  may rotate relative to each other, data communication between the first and second optical communication devices  808   a ,  814   a  can be maintained within the first optically isolated zone  810   a  since the integrity of the zone itself is maintained in rotation. 
     Within the second optically isolated zone  810   b , the first and second optical communication devices  808   b ,  814   b  can optically communicate. For instance, the first optical communication device  808   b  may be capable of optical transmission and the second optical communication device  814   b  may be capable of optical reception and/or the second optical communication device  814   b  may be capable of optical transmission and the first optical communication device  808   b  may be capable of optical reception. In essence, communication can take place from the first device  808   b  to the second device  814   b  and/or from the second device  814   b  to the first device  808   b . In operation, even as the first and second communication modules  805 ,  812  may rotate relative to each other, data communication between the first and second optical communication devices  808   b ,  814   b  can be maintained within the second optically isolated zone  810   b  since the integrity of the zone itself is maintained in rotation. Direct alignment of the first and second optical communication devices  808   b ,  814   b  is not necessary for communication as the elements  805 , 812  may rotate relative to each other as the devices are within the optically isolated zone  810   b , which allows for data to be transferred within the zone using modulated light. 
     In some alternative embodiments, there may be a plurality of optical communication devices integrated within the first communication module  805  and/or a plurality of optical communication devices integrated within the second communication module  812  within one or more of the optically isolated zones  810   a ,  810   b . The plurality of optical communication devices within a particular optically isolated zone can provide duplicate signal transmission and/or duplicate signal reception capabilities across a plurality of locations within the optically isolated zones. In particular, in the case that a plurality of devices capable of optical transmission is implemented, the plurality of devices could transmit identical data simultaneously and be physically spread out within the optically isolated zone to ensure even distribution of the modulated light signals. This ensures that a device capable of optical reception within the optically isolated zone will be capable of reception of the data signal irrespective of the rotational position of the first and second communication modules  805 , 812  relative to each other. Similarly, in the case that a plurality of devices capable of optical reception is implemented, the plurality of devices could be physically spread out within the optically isolated zone to ensure reception of modulated light signals irrespective of the location of the source of the modulated light within the optically isolated zone. This ensures that a device capable of optical reception within the optically isolated zone will be capable of reception of the data signal irrespective of the rotational position of the first and second communication modules  805 , 812  relative to each other. 
       FIG. 8B  illustrates an alternative embodiment of the free-optic communication apparatus of  FIG. 8A . Within  FIG. 8B , more than two optically isolated zones are implemented to allow for more than two channels of communications simultaneously. In this implementation, the first communication module  805  comprises four cylindrical walls  806   a ,  806   b ,  806   c ,  806   d  of increasing diameters instead of only two. It should be understood that other numbers of cylindrical walls may be implemented from one to a large number. Within  FIG. 8B , the cylindrical walls  806   a ,  806   b ,  806   c ,  806   d  form four distinct optically isolated zones  810   a ,  810   b ,  810   c ,  810   d . The optically isolated zone  810   a  is a circular zone centered on the first communication module  805 . The optically isolated zones  810   b ,  810   c ,  810   d  are annular zones surrounding the optically isolated zone  810   a  with ever increasing diameters. As shown in  FIG. 8B , the first communication module  805  comprises at least one first optical communication device  808   a ,  808   b ,  808   c ,  808   d  within each of the optically isolated zones  810   a ,  810   b ,  810   b ,  810   d . Although not shown, the second communication module  812  would comprise at least one second optical communication device within each of the optically isolated zones  810   a ,  810   b ,  810   c ,  810   d  as well. Similar to the embodiment of  FIG. 8A , the first and second optical communication devices within each optically isolated zone may communicate using modulated light and transmit data independent of data transferred in other optically isolated zones. These communication channels can be maintained during relative rotation of the first and second communication modules  805 , 812  as the integrity of the optically isolated zones  810   a ,  810   b ,  810   c ,  810   d  will be maintained during rotation. 
       FIGS. 9A and 9B  are sample circuit diagrams of an optical transmitter and an optical receiver that may be incorporated within the free-space optical communication apparatus of  FIGS. 8A and 8B . The optical communication devices that are capable of optical transmission may comprise an electrical circuit similar to the circuit of  FIG. 9A . The optical communication devices that are capable of optical reception may comprise an electrical circuit similar to the circuit of  FIG. 9B . It should be understood that these circuit diagrams are only sample designs and one skilled in the art would understand that other optical transmitter and optical receiver designs could be implemented within embodiments of the present invention. 
     The optical transmitter of  FIG. 9A  comprises an amplification circuit  900  that receives a data input and outputs an amplified signal on a node  912 , the node  912  being connected to a plurality of Light Emitting Diode (LED) circuits  920   a , 920   b , 920   c , 920   d . The LED circuits  920   a , 920   b , 920   c , 920   d  each comprise one or more LEDs which are linearly modulated by the amplified signal on the node  912 . The amplification circuit  900  ensures that the data input signal has sufficient current to linearly modulate the intensity of the LEDs within the LED circuits  920   a , 920   b , 920   c , 920   d . In some embodiments, there may only be a single LED circuit. When using a plurality of LED circuits, the circuits effectively provide duplicate outputs of modulated light. Each of the LED circuits  920   a , 920   b , 920   c , 920   d  may be considered a separate optical communication device in relation to the description of  FIGS. 8A and 8B , where a plurality of optical communication devices may be implemented on one of the communication modules  805 , 812  within one of the optically isolated zones. 
     In the particular implementation of  FIG. 9A , the amplification circuit  900  comprises: an operational amplifier  902  powered between a power rail Vcc and ground and having positive and negative inputs; two capacitors  904   a ,  904   b  that form a capacitive divider between the power rail Vcc and ground and are connected together at the positive input to the operational amplifier  902 ; two resistors  906   a ,  906   b  that form a resistive divider between the power rail Vcc and ground and are connected together at the positive input to the operational amplifier  902 ; an input resistor  908  coupled between the input signal and the negative input to the operational amplifier  902 ; and a feedback resistor  910  connected between the negative input and the output of the operational amplifier  902 . In one particular example, the operational amplifier  902  comprises a LM6181 component; the capacitors  904   a ,  904   b  are 470 μF; the resistors  906   a ,  906   b  are 1 kΩ; the input resistor  908  is 330Ω; and the feedback resistor is 900Ω. It should be understood that other components could be used within an amplification circuit and other values for the components could be used. In one sample implementation, the input signal is an NTSC video signal. Other input signals that may comprise video, audio or other data in various formats may also be used. 
     In the particular implementation of  FIG. 9A , the LED circuit  920   a  comprises: a resistor  922   a  and a capacitor  926   a  connected in parallel between the node  912  (output of the amplification circuit  900 ) and an LED voltage node  925   a ; a pull-up resistor  924   a  connected between the power rail Vcc and the LED voltage node  925   a ; and one or more LEDs  928   a  coupled in series between the LED voltage node  925   a  and ground. In one particular example, the resistor  922   a  is 330Ω; the capacitor  926   a  is 200 pF; the resistor  924   a  is 50Ω; and the LEDs are a mid-power LED that typically operates at 50 to 150 mA. In  FIG. 9A , the other LED circuits  920   b ,  920   c ,  920   d  comprise identical components to the LED circuit  920   a . In the example shown, there are four LEDs in series within each LED circuit  920   a ,  920   b ,  920   c ,  920   d  which would result in approximately a 12V forward voltage. It should be understood that other components could be used within the LED circuits, other numbers of LEDs could be implemented and other values for the components could be used. The output from the LED circuits would be light that is modulated based upon the input signal. 
     The optical receiver of  FIG. 9B  comprises an optical detection circuit  940  that outputs a signal at a node  955  in response to light detected, the node  955  being coupled to a set of three amplification circuits  960   a ,  960   b ,  960   c . In this particular example circuit, the optical detection circuit  940  comprises a phototransistor  942  with bandwidth up to 3 MHz before a 3 dB rolloff in response, which is corrected by high pass circuits in the form of a series capacitor network that sharpens the signal up to 10 MHz from 3 MHz where it otherwise falls off. Also, in this particular example circuit, the amplification circuits  960   a ,  960   b ,  960   c  are high bandwidth amplifiers that function up to 10 MHz with good linearity. In some embodiments, less than three amplification circuits may be used while, in other embodiments, more than three may be implemented. Three amplification circuits in series as shown in  FIG. 9B  is sufficient to reconstitute a common NTSC video signal that has been transmitted optically by light with satisfactory linear characteristics. 
     In the particular implementation of  FIG. 9B , the optical detection circuit  940  comprises the phototransistor  942  coupled in series with a resistor  946  between a node  949  and ground; a resistor  944  coupled between the supply rail Vcc and the node  949 ; a capacitor  948  coupled between the node  949  and ground; and a capacitor  950  coupled in series with a resistor/capacitor circuit comprising a resistor  952  and a capacitor  954  coupled in parallel, the capacitor  950  and the resistor/capacitor circuit being coupled in series between the node  949  and a pre-amplified output node  955 . In one particular example, the resistor  946  is 270Ω; the resistor  944  is 22Ω; the capacitor  948  comprises three capacitors in parallel, one at 1000 pF, one at 1 μF and one at 470 μF; the capacitor  950  comprises two capacitors in series, each at 470 μF; the resistor  952  is 5 KΩ; and the capacitor  954  is 300 pF. It should be understood that other components could be used within an optical detection circuit and other values for the components could be used. 
     In the particular implementation of  FIG. 9B , the amplification circuit  960   a  comprises: an operational amplifier  962  powered between a power node  963  and ground and having positive and negative inputs; two capacitors  964   1 ,  964   2  that form a capacitive divider between the power node  963  and ground and are connected together at the positive input to the operational amplifier  962 ; two resistors  966   1 ,  966   2  that form a resistive divider between the power node  963  and ground and are connected together at the positive input to the operational amplifier  962 ; an input resistor  968  coupled between the pre-amplified output node  955  and the negative input to the operational amplifier  962 ; a feedback resistor  970  connected between the negative input and the output of the operational amplifier  962 ; a resistor  972  coupled between the supply rail Vcc and the power node  963 ; and a capacitor  974  coupled between the power node  963  and ground. In one particular example, the operational amplifier  962  comprises a LM6181 component; the capacitors  964   a ,  964   b  are 470 μF; the resistors  966   a ,  966   b  are 1 kΩ; the input resistor  968  is 100Ω; the feedback resistor  970  is 2 KΩ; the resistor  972  is 1Ω; and the capacitor  974  is 470 μF. It should be understood that other components could be used within an amplification circuit and other values for the components could be used. In  FIG. 9B , each of the amplification circuits  960   a ,  960   b ,  960   c  are identical though they could be different in some implementations. Further, the circuit of  FIG. 9B  comprises a resistor  956  and a capacitor  958  that are coupled in series between the pre-amplified output node  955  and the positive input to the operational amplifier  962  within the first amplification circuit  960   a ; and an output resistor  980  coupled between the output of the operational amplifier  962  of the third amplification circuit  960   c  and an output signal to the circuit of  FIG. 9B . In one example implementation, the resistor  956  is 13 KΩ; the capacitor  958  is 1 μF; and the output resistor  980  is 100Ω. 
     In an alternative implementation, the optical communication devices capable of optical transmission could be implemented as an optical transmitter that generates a 12 MHz or higher carrier wave that is frequency or amplitude modulated at the transmitter input. The corresponding optical communication device capable of optical reception could be implemented to detect a higher frequency response and frequency or amplitude demodulate the incoming signal. The on/off nature of LEDs lends itself well to a physical layer of frequency modulation. 
     The specific sample circuits as described with reference to  FIGS. 9A and 9B  are reasonably linear over a range of between about 50 Hz and 6 MHz, which allows for signals with amplitude-like modulation and signal-to-noise ratio characteristics similar to NTSC to pass, such as PAL. There are other signaling techniques, however, such as frequency modulation, pulse width, and pulse position modulation that can also form the basis of communication of the physical channel over light. It should be understood that data may contain a wide variety of content with a wide variety of formats or modulation techniques. In particular implementations, the data could be data packets, audio, video, text, etc. 
     It should be understood that in the implementation of the data transfer apparatus  150 , the encasement bases  702 ,  802  may be coupled to the frame  102  while the covers  704 ,  804  may be coupled to the rotatable element  104 . In alternative embodiments, the encasement bases  702 ,  802  may be coupled to the rotatable element  104  while the covers  704 ,  804  may be coupled to the frame  102 . Other mechanical changes may also be implemented when integrating the data transfer apparatus  150  within the cable reel  100 . The data transfer apparatus  150  effectively provides a data transfer capability while one portion of the apparatus is static while another portion of the apparatus is operable to rotate relative to the static portion. This allows for transfer of high bandwidth data without requiring physical contact between elements to physically transfer the data. 
       FIG. 10  is a logical system diagram similar to  FIG. 5  according to an alternative embodiment of the present invention. In this alternative embodiment, the MOCA  504  is integrated with the frame  102  of the cable reel  100  and the MOCA  514  is integrated with the rotatable element  104  of the cable reel  100 . In this case, the cable reel  100  may be connected to a computing apparatus  1000  at the connector  124   b  via a cable that may communicate data in Ethernet format. Both data and DC power can be communicated via the cable to the MOCA  504 . The MOCA  504  can decouple the DC power and electrically couple the DC voltages via the torsional springs of the cable reel  100  in order to power the MOCA  514  which is integrated with the rotatable element  104  and may rotate relative to the MOCA  504 . The MOCAs  504 ,  514  can convert data between Ethernet format and a high frequency analog data format that can be transferred via the data transfer apparatus  150  to the MOCA  514 . The MOCA  514  can be powered by the DC voltages electrically coupled through the torsional springs. The MOCA  514  can output DC power over the cable  508  and further communicate data through the cable. In this case, the cable  508  may be an Ethernet cable. The cable  508  can be wrapped around the rotatable element  104  and unwrapped to connect to remote devices such as video device  516   a , sensor  516   b  and/or control device  516   c . The DC power over the cable  508  can be used to power the remote devices  516   a ,  516   b ,  516   c . The MOCA  514  can communicate with the remote devices  516   a ,  516   b ,  516   c  via the cable  508 . 
       FIGS. 11A and 11B  are breakout views of implementations of the data transfer apparatus of  FIGS. 4A and 4B  according to alternative embodiments of the present invention. In  FIG. 11A , the first and second capacitive plates  706   a ,  706   b  are implemented as previously described with reference to  FIGS. 7A, 7B and 7C . In particular, the capacitive plate  706   a  may comprise a circular disk with a circular copper track  710   a  that is centered on the circular disk and is of a first diameter and an annular copper track  712   a  that surrounds the circular copper track  710   a  and is of a second diameter. As shown, the annular copper track  712   a  is effectively an annulus with an outer diameter equal to the second diameter and an inner diameter slightly larger than the first diameter. In this design, the circular and annular copper tracks  710   a ,  712   a  are separated by a small etching so that each of the tracks is electrically isolated. Similarly, the second capacitive plate  706   b  may comprise a circular disk with a circular copper track  710   b  that is centered on the circular disk and is of the first diameter and an annular copper track  712   b  that surrounds the circular copper track  710   b  and is of the second diameter. In the embodiment of  FIG. 11A , the MOCA  504  and the MOCA  514  may communicate data over the capacitor that is formed between the circular copper tracks  710   a ,  710   b  and use the capacitor that is formed between the annular copper tracks  712   a ,  712   b  as shielding for the data communication. 
     In some embodiments, as shown in  FIG. 11B , there is only a single capacitor formed between the two capacitive plates. In this implementation, the MOCAs  504 ,  514  are coupled to first and second capacitive plates  1102   a ,  1102   b  respectively. In this case, each of the capacitive plates  1102   a ,  1102   b  may comprise a circular disk with only a single copper track  1104   a ,  1104   b  respectively. As shown, the single copper track  1104   a ,  1104   b  may comprise the entire surface area of the capacitive plates  1102   a ,  1102   b . In alternative embodiments, the copper tracks  1104   a ,  1104   b  may be smaller than the entire surface area of the capacitive plates  1102   a ,  1102   b  and the capacitive plates  1102   a ,  1102   b  may not be circular. 
     In some implementations in which the MOCAs  504 ,  514  are coupled to the data transfer apparatus  150 , the MOCAs  504 ,  514  may be used to simply bridge an Ethernet signal over a gap between a fixed element such as the frame  102  and a rotating element such as the rotatable element  104 . The MOCAs  504 ,  514  may be used to establish a robust ultra-high frequency (UHF) signal that can easily pass over a short divide such as that between the capacitive plates  706   a ,  706   b ; where the entire contents of the Ethernet signal is coded into the UHF signal under the MOCA standard and protocol and then decoded on the opposite side of the gap. 
     The capacitive plates  706   a ,  706   b  may comprise circuit board material which can also serve as a host to additional electronics on layers that are removed from the bottom, gap-facing layers which contain the copper tracks used to form one or more capacitors. In some embodiments, circuitry related to the MOCAs  504 ,  514  (ex. application specific chip or a MOCA chip-set) may be mounted on 2-or-more layer circuit boards whose input is Ethernet and whose output is an RF feed to the gap-facing capacitive plate portion of its respective circuit board. In some embodiments, the input may also be of the form power-over-Ethernet. In this case, the power may be decoupled from the data prior to the capacitive plate  706   a  and rerouted via a power coupling mechanism such as the torsional spring architecture previously described and coupled back to the data after the capacitive plate  706   b . In this manner, the data and the power can independently be transferred between the frame  102  and the rotatable element  104 . 
     Although various embodiments of the present invention have been described and illustrated, it will be apparent to those skilled in the art that numerous modifications and variations can be made without departing from the scope of the invention, which is defined in the appended claims.