Patent Publication Number: US-11646609-B2

Title: Power transfer system with patient transport apparatus and power transfer device to transfer power to the patient transport apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject patent application is a Continuation of U.S. patent application Ser. No. 17/125,337, filed on Dec. 17, 2020, which is a Continuation of U.S. patent application Ser. No. 16/168,205, filed on Oct. 23, 2018 and now granted as U.S. Pat. No. 10,910,888, which claims priority to and all the benefits of U.S. Provisional Patent Application No. 62/576,315 filed on Oct. 24, 2017, the disclosures of each of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Patient transport apparatuses, such as hospital beds, stretchers, cots, tables, wheelchairs, and chairs facilitate care of patients in a health care setting. Conventional patient transport apparatuses comprise several electrically powered devices to carry out desired functions in caring for the patient. When the patient transport apparatus is located in a patient room, for instance, the patient transport apparatus is connected to a fixed power source, such as conventional wall outlet power, to provide energy to these electrically powered devices. Usually, a power cord is required to connect the patient transport apparatus to the wall outlet power. The patient transport apparatus also typically carries one or more batteries to provide energy to the electrically powered devices when the patient transport apparatus is unable to connect to the wall outlet power, such as during transport or when located outside of the patient room. 
     Patient care increasingly demands more and more attention from caregivers and any activities that distract the caregiver from the patient are undesirable—one such activity is plugging the power cord from the patient transport apparatus into the wall outlet power. Wireless power transfer methods have been suggested to simplify connecting to a power source. However, owing to the large (and often unwieldy) nature of many patient transport apparatuses, caregivers will likely have trouble aligning a wireless power receiver on the patient transport apparatus with a wireless power transmitter located in the patient&#39;s room. For instance, the caregiver may not have good line-of-sight to both the wireless power transmitter and the wireless power receiver and may be unable to visualize when alignment is achieved. Good alignment may be desirable to ensure efficient power transfer. 
     A power transfer system with a patient transport apparatus and power transfer device designed to overcome one or more of the aforementioned disadvantages is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is perspective view of a patient transport apparatus with a power receiver assembly mounted to a base. 
         FIG.  2    is an illustration of the patient transport apparatus in relation to a power transfer device located in a floor. 
         FIG.  3    is a side elevational view of the power receiver assembly of the patient transport apparatus and a power transmitter assembly of the power transfer device. 
         FIG.  4    is a partial sectional view of the power transmitter assembly and the power receiver assembly. 
         FIG.  5    is a schematic view of a control system. 
         FIG.  6    is an illustration of a display screen showing that a power transmitter is not aligned with a power receiver. 
         FIG.  7    is an illustration of the display screen showing that the power transmitter is aligned with the power receiver. 
         FIG.  8    is a partial sectional view of an alternative power transmitter assembly and alternative power receiver assembly with locators. 
         FIG.  9 A  is a perspective view of an alternative power transfer device with an integrated alignment system. 
         FIG.  9 B  is a front side view of the power transfer device of  FIG.  9 A . 
         FIG.  9 C  is a left side view of the power transfer device of  FIG.  9 A . 
         FIG.  10    is a perspective view of an alternative power transfer device with an alignment system comprising markings and stops on a floor surface. 
         FIG.  11    is a perspective view of an alternative power transfer device with an alignment system comprising raised side walls of the power transmitter. 
         FIG.  12    is a perspective view of the power transfer device of  FIG.  11    being engaged by the patient transport apparatus. 
         FIG.  13    is a partial sectional view of the power transfer device of  FIG.  11    being engaged by the patient transport apparatus. 
         FIGS.  14 A- 14 C  are perspective views of an alternative alignment system to align a power transmitter with a power receiver. 
         FIG.  15    is a perspective view of multiple power transfer devices being employed to transfer power to multiple power receiver assemblies of the patient transport apparatus. 
         FIG.  16    is perspective view of an alternative patient transport apparatus with a power receiver assembly mounted to a support frame adjacent a headboard. 
         FIG.  17    is an illustration of the patient transport apparatus of  FIG.  16    in relation to a power transfer device located in a wall. 
         FIG.  18    is a partial sectional view of the power transmitter assembly and the power receiver assembly of  FIG.  17   . 
         FIG.  19    is an illustration of the patient transport apparatus of  FIG.  16    in relation to an alternative power transfer device located in the wall. 
         FIG.  20    is an illustration of the patient transport apparatus of  FIG.  19    engaging a power transmitter assembly of the power transfer device of  FIG.  19   . 
         FIG.  21    is a partial sectional view of the power transmitter assembly and a power receiver assembly of the patient transport apparatus of  FIG.  20   . 
         FIG.  22    is a perspective view of a power transmitter/power receiver having multiple modules of coils. 
         FIG.  23    is a perspective view of one of the modules. 
         FIG.  24    is a perspective view of an alternative power transfer device comprising a charging lane located on the floor surface. 
         FIG.  25    is a perspective view of a bank of power transfer devices for simultaneously transferring power to multiple patient transport apparatuses. 
         FIG.  26    is a perspective view of a power transfer device transferring power to multiple patient transport apparatuses via daisy-chained connections between the patient transport apparatuses. 
         FIG.  27    is a perspective view of an alternative power transfer device comprising a photovoltaic panel. 
         FIG.  28    is a partial sectional view of the photovoltaic panel transferring light energy to a power receiver of a patient transport apparatus. 
         FIG.  29    is a perspective view of an alternative power transfer system comprising an energy surface directing natural light to charge a photovoltaic panel on a patient transport apparatus. 
         FIG.  30    is an illustration of the natural light directed from the energy surface to the photovoltaic panel on the patient transport apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , a patient transport apparatus  30  is shown for supporting a patient in a health care setting. The patient transport apparatus  30  illustrated in  FIG.  1    comprises a hospital bed. In other embodiments, however, the patient transport apparatus  30  may comprise a stretcher, cot, table, wheelchair, chair, or similar apparatus utilized in the care of a patient. 
     A support structure  32  provides support for the patient. The support structure  32  illustrated in  FIG.  1    comprises a base  34  and a support frame  36 . The base  34  comprises a base frame  35 . The support frame  36  is spaced above the base frame  35  in  FIG.  1   . The support structure  32  also comprises a patient support deck  38  disposed on the support frame  36 . The patient support deck  38  comprises several sections, some of which are capable of articulating (e.g., pivoting) relative to the support frame  36 , such as a fowler section, a seat section, a thigh section, and a foot section. The patient support deck  38  provides a patient support surface  42  upon which the patient is supported. 
     A mattress (not shown) is disposed on the patient support deck  38  during use. The mattress comprises a secondary patient support surface upon which the patient is supported. The base  34 , support frame  36 , patient support deck  38 , and patient support surfaces  42  each have a head end and a foot end corresponding to designated placement of the patient&#39;s head and feet on the patient transport apparatus  30 . The base  34  comprises a longitudinal axis X along its length from the head end to the foot end. The base  34  also comprises a vertical axis V arranged crosswise (e.g., perpendicularly) to the longitudinal axis X along which the support frame  36  is lifted and lowered relative to the base  34 . The construction of the support structure  32  may take on any known or conventional design, and is not limited to that specifically set forth above. In addition, the mattress may be omitted in certain embodiments, such that the patient rests directly on the patient support surface  42 . 
     Side rails  44 ,  46 ,  48 ,  50  are coupled to the support frame  36  and thereby supported by the base  34 . A first side rail  44  is positioned at a right head end of the support frame  36 . A second side rail  46  is positioned at a right foot end of the support frame  36 . A third side rail  48  is positioned at a left head end of the support frame  36 . A fourth side rail  50  is positioned at a left foot end of the support frame  36 . If the patient transport apparatus  30  is a stretcher or a cot, there may be fewer side rails. The side rails  44 ,  46 ,  48 ,  50  are movable between a raised position in which they block ingress and egress into and out of the patient transport apparatus  30 , one or more intermediate positions, and a lowered position in which they are not an obstacle to such ingress and egress. In still other configurations, the patient transport apparatus  30  may not include any side rails. 
     A headboard  52  and a footboard  54  are coupled to the support frame  36 . In other embodiments, when the headboard  52  and footboard  54  are included, the headboard  52  and footboard  54  may be coupled to other locations on the patient transport apparatus  30 , such as the base  34 . In still other embodiments, the patient transport apparatus  30  does not include the headboard  52  and/or the footboard  54 . 
     Caregiver interfaces  56 , such as handles, are shown integrated into the footboard  54  and side rails  44 ,  46 ,  48 ,  50  to facilitate movement of the patient transport apparatus  30  over floor surfaces. Additional caregiver interfaces  56  may be integrated into the headboard  52  and/or other components of the patient transport apparatus  30 . The caregiver interfaces  56  are graspable by the caregiver to manipulate the patient transport apparatus  30  for movement. 
     Other forms of the caregiver interface  56  are also contemplated. The caregiver interface may comprise one or more handles coupled to the support frame  36 . The caregiver interface may simply be a surface on the patient transport apparatus  30  upon which the caregiver logically applies force to cause movement of the patient transport apparatus  30  in one or more directions, also referred to as a push location. This may comprise one or more surfaces on the support frame  36  or base  34 . This could also comprise one or more surfaces on or adjacent to the headboard  52 , footboard  54 , and/or side rails  44 ,  46 ,  48 ,  50 . In other embodiments, the caregiver interface may comprise separate handles for each hand of the caregiver. For example, the caregiver interface may comprise two handles. 
     Wheels  58  are coupled to the base  34  to facilitate transport over the floor surfaces. The wheels  58  are arranged in each of four quadrants of the base  34  adjacent to corners of the base  34 . In the embodiment shown, the wheels  58  are caster wheels able to rotate and swivel relative to the support structure  32  during transport. Each of the wheels  58  forms part of a caster assembly  60 . Each caster assembly  60  is mounted to the base  34 . It should be understood that various configurations of the caster assemblies  60  are contemplated. In addition, in some embodiments, the wheels  58  are not caster wheels and may be non-steerable, steerable, non-powered, powered, or combinations thereof. Additional wheels are also contemplated. For example, the patient transport apparatus  30  may comprise four non-powered, non-steerable wheels, along with one or more powered wheels. In some cases, the patient transport apparatus  30  may not include any wheels. 
     In other embodiments, one or more auxiliary wheels (powered or non-powered), which are movable between stowed positions and deployed positions, may be coupled to the support structure  32 . In some cases, when these auxiliary wheels are located between caster assemblies  60  and contact the floor surface in the deployed position, they cause two of the caster assemblies  60  to be lifted off the floor surface thereby shortening a wheel base of the patient transport apparatus  30 . A fifth wheel may also be arranged substantially in a center of the base  34 . 
     The patient transport apparatus  30  comprises one or more electrically powered devices PD (see  FIG.  5   ) that are employed to perform one or more functions of the patient transport apparatus  30  in caring for the patient. Such powered devices PD may comprise, for example, electric actuators, electric motors, electronic displays, electronic user interfaces, electronic therapy devices, communication devices, lighting systems, and the like. When the patient transport apparatus  30  is stationary for long periods of time, such as when the patient transport apparatus  30  is located in a patient room, a fixed power source FPS may be employed to provide energy to the powered devices PD. The fixed power source FPS may be conventional facility power routed throughout a facility, such as a hospital. An energy storage device B (see  FIG.  5   ) is located on the patient transport apparatus  30  to store energy utilized to power these powered devices PD, particularly when the patient transport apparatus  30  is being transported away from the patient room. The energy storage device B may comprise batteries, capacitors, and the like. The energy storage device B requires charging from time-to-time via the fixed power source FPS, as described further below. 
     As shown in  FIG.  2   , a power transfer system transfers energy from the fixed power source FPS to the patient transport apparatus  30 . The power transfer system comprises a power transfer device  70  provided to transfer power to a power receiver assembly  76  on the patient transport apparatus  30 . Referring to  FIG.  3   , the power transfer device  70  comprises a power transmitter assembly  72  with a power transmitter  74  configured to transfer power to the power receiver assembly  76 . The power receiver assembly  76  comprises a power receiver  78 . The power transmitter  74  is coupled to the fixed power source FPS and the power receiver  78  is coupled to the powered devices PD and the energy storage device B on the patient transport apparatus  30  (see  FIG.  5   ). In one embodiment, the power transmitter  74  is configured to transfer power wirelessly to the power receiver  78 , such as through inductive coupling. 
     The power transmitter  74  may comprise one or more coils and the power receiver  78  may comprise one or more coils. The coils of the power transmitter  74  create a magnetic field that, when the coils of the power receiver  78  are positioned nearby, creates electrical current within the coils of the power receiver  78  and within any electrical connections to the power receiver  78 . The patient transport apparatus  30  harnesses the electrical energy inductively generated within the coils of the power receiver  78  for providing electrical power to the electrically powered devices PD directly or indirectly, such as through the energy storage device B. Various sizes, shapes, and types of coils of the power transmitter  74  and/or the power receiver  78  are contemplated. 
     In the embodiment shown in  FIGS.  3  and  4   , the power receiver  78  is coupled to the base  34  of the support structure  32 . However, the power receiver  78  may be located at any suitable location on the patient transport apparatus  30 . In other embodiments, the power receiver  78  is mounted to the support frame  36 . The power transfer device  70  is located on the floor surface F in  FIG.  3    and may be in the form of a mat as shown, or may be integrated into the floor. The power transfer device  70  may be located at any suitable location to transfer power to the power receiver  78 . In other embodiments, the power transfer device  70  is located adjacent to a wall surface W and may be embodied in a pad attached to the wall surface W, or may be integrated into the wall. 
     Referring to  FIG.  5   , a control system is provided to control operation of the patient transport apparatus  30  and the power transfer device  70 . The control system comprises an apparatus controller  90  and a power transfer controller  92 . Each of the controllers  90 ,  92  have one or more microprocessors, microcontrollers, field programmable gate arrays, systems on a chip, discrete circuitry, and/or other suitable hardware, software, or firmware that is capable of carrying out the functions described herein. The controllers  90 ,  92  may communicate with a network via one or more communication devices C, which may be wireless transceivers that communicate via one or more known wireless communication protocols such as WiFi, Bluetooth, Zigbee, and the like. Wired communication is also contemplated. Additionally, the controllers  90 ,  92  may communicate with each other via the communication devices C such that the apparatus controller  90  could be configured to carry out all the functions of the power transfer controller  92  described herein, and vice versa. In some cases, only a single controller is needed to perform the functions recited herein. 
     The apparatus controller  90  may be carried on-board the patient transport apparatus  30 , or may be remotely located. In one embodiment, the apparatus controller  90  is mounted to the base  34 . In other embodiments, the apparatus controller  90  is mounted to the footboard  54 . The apparatus controller  90  is coupled to the powered devices PD in a manner that allows the apparatus controller  90  to control the powered devices PD (connections shown schematically in  FIG.  5   ). The apparatus controller  90  is also coupled to the power receiver assembly  76  to control operation of the power receiver  78 . The apparatus controller  90  may communicate with the powered devices PD, power receiver  78 , and/or other components via wired or wireless connections to perform one of more desired functions. The power transfer controller  92  is coupled to the power transmitter assembly  72  to control operation of the power transmitter  74 . The power transfer controller  92  may communicate with the power transmitter  74  and/or other components via wired or wireless connections to perform one or more desired functions. 
     The controllers  90 ,  92  are configured to process instructions or to process algorithms stored in memory to control operation of the power transmitter  74  and/or the power receiver  78 , or to control other electronic components described herein. 
     The user, such as a caregiver, may actuate a user input device UI (see  FIG.  5   ), which transmits a corresponding input signal to the apparatus controller  90  and/or the transfer controller  92  to initiate power transfer from the power transmitter  74  to the power receiver  78 . The user input devices UI may comprise any device capable of being actuated by the user. The user input devices UI may be configured to be actuated in a variety of different ways, including but not limited to, mechanical actuation (hand, foot, finger, etc.), hands-free actuation (voice, foot, etc.), and the like. The patient transport apparatus  30  may also comprise user input devices UI to actuate the powered devices PD. The user input devices UI may comprise buttons, such as separate buttons corresponding to lift, lower, Trendelenburg, reverse Trendelenburg, raise back section, lower back section, raise leg section, lower leg section, raise foot section, lower foot section, etc. 
     The user input devices UI may also comprise a gesture sensing device for monitoring motion of hands, feet, or other body parts of the user (such as through a camera), a microphone for receiving voice activation commands, a foot pedal, and a sensor (e.g., infrared sensor such as a light bar or light beam to sense a user&#39;s body part, ultrasonic sensor, etc.). Additionally, the buttons/pedals can be physical buttons/pedals or virtually implemented buttons/pedals such as through optical projection or on a touchscreen. The buttons/pedals may also be mechanically connected or drive-by-wire type buttons/pedals where a user applied force actuates a sensor, such as a switch or potentiometer. It should be appreciated that any combination of user input devices I may also be utilized. The user input devices UI may be located on one of the side rails  44 ,  46 ,  48 ,  50 , the headboard  52 , the footboard  54 , or other suitable locations. The user input devices UI may also be located on a portable electronic device (e.g., iWatch®, iPhone®, iPad®, or similar electronic devices). 
     Referring to  FIGS.  3  through  7   , an alignment system  100  is provided to align the power transmitter  74  with the power receiver  78  so that efficient energy transfer occurs from the power transmitter  74  to the power receiver  78 . Alignment may comprise any alignment between the power transmitter  74  and the power receiver  78 , such as vertical alignment, longitudinal alignment, lateral alignment, combinations thereof, and the like. Alignment may also comprise distance alignment, e.g., placing the power transmitter  74  within a desired distance of the power receiver  78  and/or may comprise orientation alignment so that the coils of the power receiver  78  are in a desired orientation to the coils of the power transmitter  74 . Other forms of alignment are also contemplated. In some cases, the distance between the coils of the power transmitter  74  and coils of the power receiver  78  is desired to be less than a wavelength of the frequency used for inductive coupling to ensure effective energy transfer. Orientations in which a large amount of magnetic field passes through the coils of the power receiver  78  may be desired for high energy transfer efficiency. 
     In the embodiments described herein, the power transmitter  74  is generally fixed with respect to the floor surface F and/or the wall surface W. Likewise, the power receiver  78  is generally fixed to the support structure  32 , or other component of the patient transport apparatus  30 . However, the power receiver  78  may be movable by virtue of a lift mechanism of the patient transport apparatus  30 , or other movable components of the patient transport apparatus  30 , such as when the power receiver  78  is located on the support frame  36 , which can be lifted or lowered relative to the base  34 . Nevertheless, alignment between the power transmitter  74  and the power receiver  78  is carried out by providing various forms of guidance to the user to guide the patient transport apparatus  30  into correct positioning relative to the power transfer device so that the power transmitter  74  and the power receiver  78  are aligned as needed. 
     Referring to  FIGS.  3  and  4   , the alignment system  100  comprises one or more locators L configured to locate one or more of the power receiver  78  and the power transmitter  74 . The locators L facilitate alignment of the power transmitter  74  and the power receiver  78  by providing feedback to the user so that the user is able to reposition the patient transport apparatus  30  as needed, usually by wheeling the patient transport apparatus  30  in a desired manner to accomplish desired alignment. The locators L may comprise sensors coupled (e.g. wired or wirelessly) to the apparatus controller  90  and/or power transfer controller  92 . The sensors are configured to sense the one or more of the power receiver  78  and the power transmitter  74  to facilitate alignment of the power transmitter  74  and the power receiver  78 . The locators L may also comprise one or more markers to be sensed by the sensors to determine relative alignment between the power transmitter  74  and the power receiver  78 . In many cases, the controllers  90 ,  92  utilize signals from the locators L to generate feedback to the user to achieve desired alignment of the power transmitter  74  and the power receiver  78 . 
     In this embodiment, the locators L comprise an optical sensor in the form of a camera CAM (e.g., video camera) and a corresponding marker MAR located in a center of the power transmitter  74 . Alignment is achieved once the camera CAM is able to view the corresponding marker MAR at a desired location. For example, referring to  FIGS.  6  and  7   , a display  102  of the patient transport apparatus  30  may be used to show a real-time image from the camera CAM so the user can align the marker MAR in a cross-hair on the display  102  to align the power transmitter  74  with the power receiver  78 . The display  102  may be mounted on the footboard  54  or other part of the patient transport apparatus  30  and/or may form part of a user interface UI. 
     Misalignment of the power transmitter  74  and power receiver  78  is indicated in  FIG.  6   . In this case, the current alignment of power transmitter  74  and the power receiver  78  (e.g, the marker MAR is at least visible in the image displayed albeit not centered) may be satisfactory for some power transfer to occur, but not at a desired transfer rate. After the user moves the patient transport apparatus  30  to move the cross-hair over the marker MAR so that the marker MAR is centered in the cross-hair, desired alignment is achieved, as shown in  FIG.  7   . When the desired alignment is reached, the power transfer controller  92  is configured to activate the power transmitter  74  either automatically, or in response to user input. The power transfer controller  92  may automatically activate the power transmitter  74  based on pattern recognition and the location of the marker MAR being at a center of the image taken by the camera CAM. A piezoelectric element, motor with eccentric weight, or other tactile indicator, for example, could be coupled to the apparatus controller  90  and/or the power transfer controller  92  to be activated once alignment is achieved to provide a tactile response to the user that the power transmitter  74  is aligned with the power receiver  78 . 
     Referring to  FIG.  8   , in another embodiment, the locators L may comprise hall-effect sensors S and corresponding magnets MAG wherein the hall-effect sensors S generate variable signals based on the relative alignment of the magnets MAG with the hall-effect sensors S. For instance, hall-effect sensors S may be connected to the power transmitter  74  while magnets MAG are connected to the power receiver  78 . When all the magnets MAG are in desired alignment with their corresponding hall-effect sensor S (e.g, around a periphery of the power transmitter  74 /power receiver  78 ), then corresponding alignment signals from all the hall-effect sensors S will be received by the power transfer controller  92  indicating that desired alignment has been achieved. Other ways of verifying alignment and providing corresponding alignment feedback to the controllers  90 ,  92  have been contemplated. 
     The display  102  can similarly be used to provide feedback to the user based on the signals from the hall-effect sensors S to help guide the user&#39;s movement of the patient transport apparatus  30 . For instance, the display  102  could show the locations of the magnets MAG relative to the hall-effect sensors S with instructions to the user as to how the patient transport apparatus  30  should be moved to achieve alignment. The instructions could be audible, visual, tactile, and the like. The instructions could comprise directional instructions (e.g., “move forward,” “move rearward,” “move left,” “move right,” etc.), distance instructions (e.g., “move 10 inches forward”), and/or other forms of instructions, such as graphical displays showing current positioning and desired positioning, and the like. A piezoelectric element, motor with eccentric weight, or other tactile indicator, for example, could be coupled to the apparatus controller  90  and/or the power transfer controller  92  to be activated once alignment is achieved to provide a tactile response to the user that the power transmitter  74  is aligned with the power receiver  78 . 
     Referring back to the schematic diagram of  FIG.  5   , sensors S are also configured to determine if power is being transferred from the power transmitter  74  to the power receiver  78 . In some cases, only one sensor is used. The sensor S may be coupled to the apparatus controller  90  and the power receiver  78  to generate a signal that varies in response to the power receiver  78  being energized during power transfer. A separate sensor S may also be connected to the power transfer controller  92  and used to verify that the coils of the power transmitter  74  are active—to avoid a false signal from the sensor S associated with the power receiver  78 . The sensors S may also be able to determine, through connection to the apparatus controller  90  and/or the power transfer controller  92 , a quality parameter of power transfer associated with alignment of the power transmitter  74  and the power receiver  78 , such as the efficiency of power transfer wherein higher efficiency means that more energy is being transferred per unit time because of better alignment. The quality parameter can be measured, for instance, by sensing current/voltage produced in the power receiver  78  resulting from the power transfer or by measuring some other power transfer related parameter. The controllers  90 ,  92  may be configured to provide audible, visual, and/or tactile feedback to the user based on feedback from the sensors S to increase the efficiency of power transfer. In other words, alignment can be improved by the user based on feedback to increase efficiency by better aligning the power receiver  78  with the magnetic field generated by the power transmitter  74 . The sensors S may comprise one or more of the coils of the power receiver  78  and/or the coils of the power transmitter  74 , separate coils connected to the apparatus controller  90  and/or power transfer controller  92 , sensors (e.g., circuits) to measure current and/or voltage, hall-effect sensors to sense changes in magnetic field, and the like. 
     One or more additional sensors S coupled to the apparatus controller  90  and the energy storage device B may be configured to sense charging of the energy storage device B as the energy storage device B is being charged by the power transmitter  74  through the power receiver  78  during inductive power transfer. The apparatus controller  90  may be configured to analyze signals from the sensor S and to modify operational parameters of the power transmitter  74  to account for sensed charging activity, e.g., by changing which coils are energized, modifying applied voltages, instructing the user to move the patient transport apparatus  30 , etc., to improve the charging speed/efficiency of the energy storage device B. 
     One or more indicators I are coupled to the apparatus controller  90  and/or the power transfer controller  92 . The indicators I are arranged to indicate that power is being transferred from the power transmitter  74  to the power receiver  78  based on the signals from the sensors S, to indicate whether desired alignment has been reached, and/or to indicate the quality parameter of the power transfer. The indicators I could be used in any of the embodiments described herein for this purpose. The indicators I comprise one or more of a visual indicator, an audible indicator, and a tactile indicator. The indicators I associated with the power transfer device  70  may be located on or adjacent to the power transmitter  74 , on the floor surface F, on the wall surface W, on a user interface UI coupled to the power transfer controller  92 , or any other suitable location. The indicators I associated with the patient transport apparatus  30  may be located on or adjacent to the power receiver assembly  76 , the base  34 , the headboard  52  and/or footboard  54 , the side rails  44 ,  46 ,  48 ,  50 , or any other suitable locations. The indicators I may comprise LEDs, displays, speakers, eccentric motors to generate tactile feedback, piezoelectric devices, and the like. 
     A state detector SD is coupled to the apparatus controller  90  to determine a state of the energy storage device B. The state of the energy storage device B may comprise an energy level of the energy storage device B, a current capacity of the energy storage device B, whether the energy storage device B is being actively charged, when the energy storage device B will be depleted, a time remaining for operation of the patient transport apparatus  30  based on the current state of the energy storage device B, and the like. The state detector SD may comprise any suitable electronic component or circuitry for measuring such states. For instance, the state detector SD may comprise one or more of a voltmeter, an amp-hour meter, and the like. Such states can also be indicated to the user via additional indicators I. 
     Referring to  FIGS.  4  and  8   , the patient transport apparatus  30  may comprise a unique identifier that is used by the power transfer controller  92  to confirm that the patient transport apparatus  30  (or power receiver  78  thereof) is an approved device authorized to receive power from the power transfer device  70 . This can be used as an obstacle detection method to avoid charging foreign objects sensed on the mat/pad or objects not approved or designed for charging. Once the power transfer controller  92  determines that the unique identifier matches one or more approved identifiers, then the power transfer controller  92  allows power transfer to commence by activating the power transmitter  74  appropriately. If the identifier is not recognized by the power transfer controller  92 , the power transfer device  70  may be inoperable for power transfer. A reader R (e.g., RFID reader) may be coupled to the power transfer controller  92  to read the identifier of the patient transport apparatus  30 . The identifier may be embodied in an identification device, such as a tag T. Such tags T could comprise a radiofrequency identification tag (RFID), NFC tag, or other suitable tag. For example, the identifier could also be embodied in a bar code to be read by the reader R. Other forms of identification of the patient transport apparatus  30  are also contemplated. Additionally, or alternatively, the identifier may be stored in memory (e.g., NvRAM) of the apparatus controller  90  to be transmitted to the power transfer controller  92  via the communication devices C. 
     Referring to  FIG.  9 A- 9 C , an alternative power transfer device  200  is shown in the form of a mat. This power transfer device  200  comprises a power transmitter assembly  202  with a power transmitter  204 . In this embodiment, the power transfer device  200  is similar to the power transfer device  70  except for size and arrangement. An alignment system  206  comprises a casing  208  supporting the power transmitter assembly  202 . The casing  208  comprises a geometric structure sized and shaped to guide the patient transport apparatus  30  so that a power receiver  78  of the patient transport apparatus  30  is aligned with the power transmitter  204  when the patient transport apparatus  30  is wheeled over the casing  208 . 
     Referring to  FIG.  9 B , in this embodiment, the mat has a first width W 1  and the patient transport apparatus  30  has a second width W 2  between two of the wheels  58  (e.g., between head end wheels or between foot end wheels). The second width W 2  may be measured between centers of the wheel stems or some other suitable location. The second width W 2  is substantially the same as the first width W 1  so that the two of the wheels  58  straddle the mat when the patient transport apparatus  30  is moved over the mat to align the power receiver  78  and the power transmitter  204 . In other embodiments, the first width W 1  is at least 50, 60, 70, 80, or 90% of the second width W 2 . Additionally, in some cases, to further ensure alignment, the mat has a first length L 1  (see  FIG.  9 C ) and the patient transport apparatus  30  has a second length L 2  between two of the wheels  58  (e.g., between left side wheels or between right side wheels), wherein the first length L 1  is greater than the second length L 2  so that the patient transport apparatus  30  can be fully seated over the mat with all wheels  58  straddling the mat. The second length L 2  may be measured between centers of the wheel stems or some other suitable location. Owing to the relative sizes of the power transmitter  204  and the power receiver  78 , alignment of the power transmitter  204  and the power receiver  78  is ensured if all the wheels  58  straddle the mat. 
     Referring to  FIG.  10   , another alignment system  300  is shown to align the power transmitter  74  and the power receiver  78 . In this embodiment, the alignment system  300  comprises markings  302  on the floor surface F to direct the user where to place the wheels  58  of the patient transport apparatus  30  when positioning the patient transport apparatus  30  over the power transmitter  74 . The markings  302  are sized and shaped to indicate recommended pathways for the wheels  58 . In the embodiment shown, the markings  302  comprise strips, such as stickers, paint, or the like, placed on the floor surface F. The markings  302  are also spaced from each other and parallel to each other so that if the user wheels the patient transport apparatus  30  over the power transmitter  74  while keeping the wheels  58  on the markings  302 , the power transmitter  74  will be sure to be at least laterally aligned with the power receiver  78 . Additionally, or alternatively, the alignment system  300  further comprises stops  304  located on the floor surface F at the ends of the markings  302  to be engaged by the wheels  58  to provide tactile indication to the user that the power transmitter  74  is longitudinally aligned with the power receiver  78 . The stops  304  act as a curb to prevent further motion of the patient transport apparatus  30  once engaged. The stops  304  may comprise blocks, metal brackets, or the like placed on the floor surface F and protruding above the floor surface F. The stops  304  may be fixed to the floor surface F. The stops  304  may also be fixed to the wall and may protrude from the wall surface W. The alignment system  300  shown in  FIG.  10    could likewise be used to align the patient transport apparatus  30  with a power transfer device located on the wall surface W. 
     Referring to  FIGS.  11 - 13   , an alternative power transfer device  400  is shown in the form of a mat. This power transfer device  400  comprises a power transmitter assembly  402  with a power transmitter  404 . In this embodiment, the power transfer device  400  is similar to the power transfer device  70  except for size and configuration. An alignment system  406  comprises a casing  408  supporting the power transmitter  404 . The casing  408  comprises a geometric structure sized and shaped to guide the patient transport apparatus  30  so that a power receiver  410  of the patient transport apparatus  30  is aligned with the power transmitter  404  when the patient transport apparatus  30  is wheeled over the casing  408 . 
     In this embodiment, the casing  408  has side portions on opposing sides of a floor engaging portion  413 . These side portions comprise raised wings  412  that define a channel  414  sized and shaped to receive one of the wheels  58  of the patient transport apparatus  30 . In this case, the power receiver  410  is part of a power receiver assembly  416  mounted to the base  34  adjacent to the wheel  58  so that if the wheel  58  is generally, centrally located on the floor engaging portion  413 , then the power receiver  410  is aligned with the power transmitter  404  in a way that enables power transfer to occur (see  FIG.  12   ). 
     Referring to  FIG.  13   , the mat has a first width W 1  and the patient transport apparatus  30  has a second width W 2  between two of the wheels  58  (e.g., between the head end wheels or between the foot end wheels). The second width W 2  is larger than the first width W 1  so that only one of the wheels  58  can engage the mat at one time. The wings  412  may be raised a distance off the floor surface F that is less than a distance from the floor surface F to the base  34  so that the base  34  is able to move over the wings  412  without contacting the wings  412 , e.g., so the only part of the patient transport apparatus  30  able to engage the mat is one of the wheels  58 . In other embodiments, two mats may be provided, one for each of the front wheels  58 , wherein both wheels  58  must engage their respective mat to enable power transfer to occur. Sensors S coupled to one or both of the controllers  90 ,  92  may be used to detect such contact and activate the power transmitters of the separate mats. 
     Referring to  FIGS.  14 A- 14 C , an alternative power transfer device  500  is shown in the form of rigid casing  508  mounted to the floor. The casing  508  may be mounted to the floor by fasteners, adhesive, and the like to fix the casing  508  to the floor surface F or within the floor, e.g., beneath the floor surface F. This power transfer device  500  comprises a power transmitter assembly  502  with a power transmitter  504 . In this embodiment, the power transfer device  500  is similar to the power transfer device  70 . An alignment system  506  comprises the casing  508  supporting the power transmitter assembly  502  above the floor surface F. The casing  508  comprises a geometric structure sized and shaped to guide the patient transport apparatus  30  so that a power receiver  510  of the patient transport apparatus  30  is aligned with the power transmitter  504  when the patient transport apparatus  30  is wheeled over the casing  508 . 
     In this embodiment, the alignment system  506  further comprises a guide  512  sized and shaped to receive and mate with the casing  508  when the casing  508  is fully seated within the guide  512 . The guide  512  is part of a power receiver assembly  516  mounted to the base  34 . The guide  512  comprises guide arms  520  that define a width therebetween that narrows toward the power receiver  510 . The guide  512  also has an opening  522  with a width sized to receive the casing  508  when the guide  512  is moved into position over the casing  508  by the user. Owing to the rigidly fixed nature of the casing  508  to the floor surface F, if during initial engagement of the guide  512  with the casing  508 , the two are not aligned, i.e., the casing  508  instead engages one of the guide arms  520 , then that engagement acts to steer the patient transport apparatus  30  into proper alignment. For instance, referring to  FIG.  14 B  (compare to  FIG.  14 A ), when the casing  508  engages the guide arm  520 , the force involved with such contact, along with continued pushing of the patient transport apparatus  30  by the user in a generally longitudinal direction, will cause the wheels  58  to swivel to the orientation shown, so that the patient transport apparatus  30  is directed laterally until the casing  508  is rightly aligned with the guide  512  and able to fit into the opening  522  to align the power transmitter  504  with the power receiver  510 .  FIG.  14 C  illustrates the casing  508  seated in the opening so that the power transmitter  504  is aligned with the power receiver  510 . 
     Referring to  FIG.  15   , multiple power transfer devices  70 ,  400  may be employed to transfer power to multiple power receiver assemblies  78 ,  416  either simultaneously or sequentially. The power transfer devices  70 ,  400  may have differently sized/shaped/type or numbers of coils to transfer power, and similarly the power receiver assemblies  78 ,  416  may have differently sized/shaped/type or numbers of coils to receive power. The power transfer devices  70 ,  400  may be matched to the respective power receiver assemblies  78 ,  416  in a way that quick, less efficient, power transfer occurs through one matched pair, while slower, more efficient, power transfer occurs through the other matched pair. 
     Referring to  FIGS.  16 - 18   , the patient transport apparatus  30  is shown with an alternative power receiver assembly  600  with power receiver  602  mounted to the support frame  36  adjacent to the headboard  52 . In this embodiment, a power transfer device  604  has a power transmitter assembly  606  with a power transmitter  608  that is oversized as compared to the headboard  52  (see  FIG.  17   ) and the power receiver (see  FIG.  18   ) so that as the user is moving the patient transport apparatus  30  into position for power transfer, the user is able to easily visually reference the edges of the power transmitter  608  so that alignment with the power receiver  602  is easily accomplished. More specifically, the headboard  52  has a first width W 1  and the power transmitter  608  has a second width W 2  larger than the first width W 1 . Likewise, visible markings  609  on the wall surface W having a width larger than the headboard  52  could similarly provide a suitable alignment system—in this case the power transmitter  608  could be smaller than the headboard  52 . In other embodiments, the visible markings  609  could comprise an outline of the headboard  52  with a similar size and/or shape of the headboard  52  so that the user only need to match up the headboard  52  with its outline on the wall surface W to ensure alignment. In this case, one or more locators L could be used to assist with alignment, but may be unnecessary as the user is able to visually align the power transmitter  608  and the power receiver  602 . 
     Referring to  FIGS.  19 - 21   , an alternative power transfer device  700  is shown that comprises two power transmitter assemblies  702 , each with its own power transmitter  704 . Similarly, the patient transport apparatus  30  comprises two power receiver assemblies  706 , each with its own power receiver  708  (only one shown). In this embodiment, each power transmitter  704  is sized and shaped to be contacted by one power receiver  708  to enable power transfer. One or more sensors S coupled to one or both of the controllers  90 ,  92  could be provided in the power transmitter assemblies  702  and/or the power receiver assemblies  706  to verify such contact or to verify that the power transmitters  704  are in a desired proximity to their associated power receivers  708 . Such sensors S may comprise contact switches, hall-effect sensors, other proximity sensors, or the like. 
     If one of the power receivers  708  is overlying both of the power transmitters  704  (referred to as a short condition), then the power transmitters  704  would be disabled. In some cases, the power transmitters  704  and/or power receivers  708  are sized and shaped, and spaced from one another at such a distance that one power receiver  708  is unable to contact both power transmitters  704  simultaneously. Still, the power transfer device  700  is configured so that the sensors S must first transmit signals to the power transfer controller  92  indicating that the corresponding pairs of power transmitters  704  and power receivers  708  are in contact before activating power transfer through the power transmitters  704 . As shown in  FIGS.  19  and  20   , a display  710  could be provided in a conspicuous location on the wall surface W, floor surface F, on the patient transport apparatus  30 , and/or on the power transfer device  700  that indicates when such contact has successfully been made and power transfer activated. 
     The arrangement of coils, windings, or other current carrying wires for the power transmitters and the power receivers described herein can comprise a number of different configurations. In the embodiment shown in  FIGS.  22  and  23   , an array  750  of coil modules  752  are located on a substrate  754  to form the power transmitter or the power receiver. The array  750  of coil modules  752  can be arranged in a grid pattern as shown or other suitable pattern. Each of the coil modules  752  may comprise a single coil or winding, multiple coils or windings, and/or combinations thereof. The coils/windings may have a circular, spiral, or rectangular shape when viewed in plan, or any other suitable shape for enabling wireless power transfer from the power transmitter to the power receiver. 
     In some cases, the array  750  of coil modules comprises coil modules of a first type arranged in a central portion  756  of the array and coil modules of a second type arranged along an outer periphery  758  of the array  750 , e.g., the outer rows/columns of coil modules. The array  750  may comprises spaced apart coil modules  752  as shown, or may comprise overlapping coil modules. The coil modules  752  at the edges of the array  750  may be one type of coil that allows for incomplete alignment, but provides some charging, while the coil modules  752  in the central portion are better aligned and at a smaller distance from the power receiver to do the majority of the charging. For example, the coils in the wings  412  in the embodiment of  FIGS.  11 - 13    could be different than the coils in the floor engaging portion  413 . 
     A combination of coils that charge according to different charging protocols may also be utilized, such as coils that charge according to the Qi wireless charging standard and coils that charge according to the A4WP wireless charging standard. In this case, if coil modules of different types are used, the coil modules are spaced at such a distance to avoid interference. 
     In some cases, the power transmitters described herein may be sized to be suitably aligned with more than one patient transport apparatus  30  at one time to charge more than one patient transport apparatus  30 . In this case, the power transmitter may have separately and selectively activatable coils or zones of coils to transfer power. The power transmitter may be configured to selectively transfer power to a first power receiver of a first patient transport apparatus  30  and a second power receiver of a second patient transport apparatus  30 . Operational parameters of one or more of the power transmitter and the power receivers may be controlled by one or more of the controllers  90 ,  92  to coordinate power transfer from the power transmitter to each of the power receivers, e.g., simultaneously, sequentially, etc. For instance, one or more of the coils may be selectively energized to transfer power to one power receiver, but not another. Sensors S may be coupled to the apparatus controller  90  and/or the power transfer controller  92  to determine if the power receivers of the patient transport apparatuses  30  are aligned with the power transmitter to receive power. The power transfer controller  92  may be configured to adjust a transmission frequency of the power transmitter to transfer power sequentially to the multiple power receivers and/or to control the transmission frequency of the power transmitter to be on resonance or off resonance with respect to one or more of the power receivers. 
     In some embodiments, data communication between the power transfer device and one or more of the patient transport apparatuses  30  may be provided through a harmonic of the transmission frequency. Communication may occur between one or more of the following: the power transmitter and the power receiver; different power transmitters; and different power receivers. Communication can be used to verify the presence of the power receiver and that it is compatible with the power transmitter. Modulation of the voltage in the power transmitter, for instance, can also be used to send data to the apparatus controller  90  coupled to the power receiver. The power receiver can likewise communicate data back to the power transfer controller  92 . The data may comprise signal strength, control errors, end power commands, and the like. Signal strength can help align the power transmitter and the power receiver by directing the user to move the power receiver as needed to improve the signal strength. Control error may indicate the amount of error between input voltage seen by the power receiver and the voltage required. The power transfer controller  92  may adjust the voltage based on this feedback in a control loop. Thus, power delivery can be tuned based on this feedback. 
     Referring to  FIG.  24   , an elongated power transfer device  800  (also referred to as a charging lane) may be provided on the floor surface F (or alternatively on the wall surface W, as shown in hidden lines). The elongated power transfer device  800  comprises either a single continuous power transmitter assembly  802  with a single power transmitter  804  or multiple power transmitter assemblies with multiple power transmitters  804  arranged serially along the floor surface F (or wall surface W). In either case, one or more lane markings  806  (stickers, paint, etc.) delineated on the floor surface F may indicate where the user is to push the patient transport apparatus  30  by indicating, for instance, pathways for the wheels  58  to follow or a centerline along which the patient transport apparatus  30  should be pushed. Separate indicators I could also be attached to the floor surface F adjacent to the lane markings  806  to indicate if power is being transferred, such as LEDs in the floor surface F placed along the lane markings  806 . Other locations for the indicators I are also contemplated (e.g., as part of the patient transport apparatus  30 , etc.). If the wheels  58  are kept on the wheel pathways or a center of the patient transport apparatus  30  is kept on the centerline, then the power transmitters  804  are able to transfer power to the power receiver  78  on the patient transport apparatus  30 . Thus, the markings  806  guide the user to move the patient transport apparatus  30  to the charging area to initiate the transfer of power from the power transmitter  804  to the power receiver  78 . 
     In some cases, sensors S coupled to the power transfer controller  92  are also continuously placed alongside the power transmitter  804  to detect where, along the path, the power receiver  78  is located. As the patient transport apparatus  30  is wheeled along the passageway, portions of the power transmitter  804  (or separate power transmitters  804 ) that are in a desired proximity of the power receiver  78  (e.g., those for which the power receiver  78  is directly overhead) are selectively activated so that power transfer remains localized to the area of the power transfer device  800  in alignment with the power receiver  78 . This helps to avoid energizing the power transmitter(s)  804  in locations where the user steps or where other objects may rest. Such locations are also too remote from the power receiver  78  to enable suitable power transfer. 
     As shown, in  FIG.  25   , multiple power transfer devices  900 , each having a power transmitter assembly  902  with a power transmitter  904 , are provided to transfer power to multiple patient transport apparatuses  30  simultaneously or sequentially. The power transmitters  904  may be placed along the floor surface F or the wall surface W to define a charging location with multiple charging areas. The multiple power transmitters  904  may be located throughout a facility to make connecting the patient transport apparatus  30  to a power source more convenient for users. As shown in  FIG.  25   , the exemplary power transfer device  900  (could be the same as power transfer device  70 ) is shown mounted to the floor surface F. Floor markings  906  provide an alignment system to align the patient transport apparatuses  30  with one of the power transmitters  904 . The power transmitters  904  may be unpowered until a connection with a power receiver  78  is detected, e.g., as detected by one or more sensors S such as hall-effect sensors, cameras, proximity sensors, or the like. Power may be transferred through inductive coupling as previously described. 
     Referring to  FIG.  26   , in one embodiment, a single power transfer device  70  can be used to transfer power to multiple patient transport apparatuses  30  in a daisy-chained manner. In particular, the power transmitter  74  transfers power to a power receiver  78  in the same manner previously described. A second patient transport apparatus  30  is then charged via a charging conduit  1000  interconnecting a second energy storage device B on the second patient transport apparatus  30  to the power receiver  78 . Current from the power receiver  78  could be automatically routed to the second energy storage device B once the first energy storage device B on the first patient transport apparatus  30  is full of charge, or a manual switch SW could be activated to transfer charging to the second energy storage device B. Additional patient transport apparatuses  30  could be charged in this manner as shown. Similarly, the coils/windings in the power receiver  78  could initially be configured to generate current in response to the magnetic field created by the power transmitter  74  to receive energy from the power transmitter  74 , but the coils/windings in the power receiver  78  could subsequently be configured to act as a power transmitter by the apparatus controller  90  in order to transfer power to the power receiver  78  on the second patient transport apparatus  30 . 
     Referring to  FIGS.  27  and  28   , an alternative type of power transfer device  1100  is shown comprising a power transmitter assembly  1102  having a power transmitter  1104 . The power transmitter  1104  in this embodiment comprises a light energy emitter panel mounted to the floor, wall, or ceiling. The light energy emitter panel may comprise LEDs or other light emitters mounted thereto that are connected to the fixed power source FPS (or other power source) and a controller (such as power transfer controller  92 ) to be controlled in a suitable manner to transmit light energy. A power receiving assembly  1106  has a power receiver  1108  mounted to the base  34 . The power receiver  1108  comprises a photovoltaic receiver panel connected to the powered devices PD and the energy storage device B of the patient transport apparatus  30  in the same manner as the power receivers previously described. The light energy emitter panel can be aligned with the photovoltaic receiver panel in any of the ways previously described herein for aligning power transmitters with power receivers. Moreover, any of the power transmitters and power receivers previously described could instead, or additionally, employ this light energy based arrangement for wirelessly transferring power from the fixed power source FPS to a patient transport apparatus  30 . 
     Photovoltaic cells are one way to transfer energy without using a wired connection to the facility. In this embodiment, the amplitude and frequency of the energy source (e.g., the LEDs) can be tuned with the photovoltaic receiver panel to ensure that energy transfer occurs at a desired rate, such as a maximum rate. Additionally, light from the light energy emitter panel could be in the non-visible spectrum. Additional energy harvesting methods could be used in addition to harvesting light energy. Vibration energy, motion energy, heat energy, and other forms of energy could be captured to complement the other forms described herein and could be similarly directed to the energy storage device B. For instance, motion of the patient transport apparatus  30  could operate a generator (not shown) coupled to one of the wheels  58  to generate energy as the wheel  58  rotates when the user moves the patient transport apparatus  30 . The generator feeds energy directly to the energy storage device B. 
     Referring to  FIG.  29   , another power transfer device  1200  is shown comprising a power transmitter assembly  1202  having a power transmitter  1204  in the form of an energy surface  1207  that is configured to deliver natural light to a power receiver assembly  1206  having a power receiver  1208  mounted to the support frame  36 . The power receiver  1208  comprises a photovoltaic receiver panel (e.g., solar panel) coupled to the energy storage device B. The energy surface  1207  is configured to deliver natural light, e.g., sunlight, to the photovoltaic receiver panel. Referring to  FIG.  30   , one or more light directing elements  1210  are arranged to redirect the natural light toward the energy surface  1207  so that the natural light is received by the photovoltaic receiver when the photovoltaic receiver is in a desired proximity to the energy surface  1207 . Any of the locators L or other alignment systems previously discussed could be used to provide alignment between the energy surface and the photovoltaic receiver. 
     As shown in  FIG.  30   , natural light NL could enter the facility through a skylight, opening in the roof, window, or the like, and be redirected toward the energy surface by one or more of the light directing elements  1210 . The light directing elements  1210  may comprise one or more mirrors, lenses, prisms, and the like. The light may be directed to pass generally perpendicularly through the energy surface  1207  to be routed directly to the photovoltaic receiver. The energy surface  1207  may be transparent or at least translucent (e.g., surface of transparent/translucent panel) to allow light to pass through. Alternatively, the energy surface  1207  may form part of a light emitter panel that has photovoltaic cells to convert the natural light NL into light energy, light emitting elements (e.g., LEDs) to emit artificial light from the energy surface  1207 , and a controller to control energy storage and transmission. In some embodiments, one or more openings may be present in the energy surface, wherein the natural light is directed through the one or more openings to reach the photovoltaic receiver. 
     It will be further appreciated that the terms “include,” “includes,” and “including” have the same meaning as the terms “comprise,” “comprises,” and “comprising.” 
     Several embodiments have been discussed in the foregoing description. However, the embodiments discussed herein are not intended to be exhaustive or limit the invention to any particular form. The terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teachings and the invention may be practiced otherwise than as specifically described.