Patent Publication Number: US-11039969-B2

Title: Overhead lift units, systems, and methods for mounting and transporting an overhead lift unit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. Provisional Application Ser. No. 62/539,089, filed Jul. 31, 2017, and entitled “Overhead Lift Units, Systems, and Methods for Mounting and Transporting an Overhead Lift Unit,” the entirety of which is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present specification generally relates to overhead lift units and, more specifically, to overhead lift units, systems, and methods for transporting an overhead lift unit to and from an overhead rail. 
     BACKGROUND 
     Overhead lifting devices, or lift units, such as patient lifts used in the health care industry, may generally be coupled to an overhead rail system with a carriage which facilitates positioning the overhead lift unit along the length of the rail. Sometimes, it may be desirable or necessary to dismount the overhead lift unit from the overhead rail system, such as to transport the lift to a different overhead rail system not connected to the first overhead rail system or to service the overhead lift unit. Because such lift units are generally suspended well above the ground on the overhead rail system, ladders or other such structures may be required to allow an operator or service person to reach the overhead lift unit to manually remove it from the overhead rail. Manipulating the lift unit to extract the lift unit from the rail may be difficult due to the weight of the lift unit and may be further complicated by the overhead position of the lift unit. 
     Accordingly, a need exists for alternative overhead lift units, systems and methods for mounting and dismounting an overhead lift unit on an overhead rail system. 
     SUMMARY 
     In one embodiment, an overhead lift unit includes a carriage, a first wheel assembly, a second wheel assembly, and a guide assembly. The first wheel assembly includes a first wheel coupled to the carriage through a first support arm. The second wheel assembly includes a second wheel coupled to the carriage through a second support arm. The guide assembly includes a bearing member and a guide member along which the bearing member is slidable. The guide assembly is coupled to the second wheel assembly and is configured to shift the second wheel assembly in a lateral direction relative to the first wheel assembly between an expanded position and a retracted position. 
     In another embodiment, a lift system includes an overhead rail defining an opening and a carriage support channel and an overhead lift unit. The overhead lift unit includes a carriage, a first wheel assembly, a second wheel assembly, and an actuator. The first wheel assembly is configured to extend through the opening of the overhead rail and to ride along the carriage support channel and includes a first wheel coupled to the carriage through a first support arm. The second wheel assembly is configured to extend through the opening of the overhead rail and to ride along the carriage support channel and includes a second wheel coupled to the carriage through a second support arm. The actuator is coupled to the second wheel assembly and is configured to shift the second wheel assembly in a lateral direction relative to the first wheel assembly between an expanded position in which the first wheel assembly and the second wheel assembly are coupled with the overhead rail, and a retracted position in which the first wheel assembly and the second wheel assembly are configured to pass through the opening in the overhead rail. 
     In yet another embodiment, a method of transporting an overhead lift unit to and from an overhead rail includes: one of attaching the overhead lift unit to the overhead rail and detaching the overhead lift unit from the overhead rail. The overhead rail defines an opening and a carriage support channel. The overhead lift unit includes a first wheel assembly, a second wheel assembly, and an actuator. The first wheel assembly includes a first wheel coupled to the carriage through a first support arm. The second wheel assembly includes a second wheel coupled to the carriage through a second support arm. The actuator is coupled to the second wheel assembly. Attaching the overhead lift unit to the overhead rail includes extending the first wheel assembly and the second wheel assembly through the opening of the overhead rail, shifting the second wheel assembly from a retracted position to an expanded position with the actuator, wherein a lateral distance from an outer surface of the first wheel assembly to an outer surface of the second wheel assembly is increased; and supporting a weight of the overhead lift unit on the carriage support channel with the first wheel of the first wheel assembly and the second wheel of the second wheel assembly. Detaching the overhead lift unit from the overhead rail includes shifting the second wheel assembly from the expanded position to the retracted position, wherein the lateral distance from the outer surface of the first wheel assembly to the outer surface of the second wheel assembly is decreased, and lowering the overhead lift unit from the overhead rail through the opening. 
     These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  schematically depicts the an overhead lift system including an overhead lift unit, according to one or more embodiments shown and described herein; 
         FIG. 2  schematically depicts a carriage of the overhead lift unit of  FIG. 1  mounted in an overhead rail and in a locked configuration, according to one or more embodiments shown and described herein; 
         FIG. 3  schematically illustrates a front view of the carriage of  FIG. 2 , according to one or more embodiments shown and described herein; 
         FIG. 4  schematically illustrates a perspective view of the carriage of  FIG. 2  in isolation from the overhead rail, according to one or more embodiments shown and described herein; 
         FIG. 5  schematically illustrates a perspective view of an underside of the carriage of  FIG. 4 , according to one or more embodiments shown and described herein; 
         FIG. 6  schematically illustrates a front view of the carriage of  FIG. 2  in an unlocked configuration, according to one or more embodiments shown and described herein; 
         FIG. 7  schematically illustrates a front view of the carriage of  FIG. 6  in a retracted configuration, according to one or more embodiments shown and described herein; and 
         FIG. 8  schematically illustrates the carriage of  FIG. 7  being guided through an opening defined by the overhead rail, according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments disclosed herein include overhead lift systems and methods that allow for lift units, such as patient lift units used in hospital and/or rehabilitation settings, to be mounted and dismounted from rails of the overhead lift system. Specifically, embodiments described herein include an overhead lift unit that includes a carriage, a first wheel assembly, a second wheel assembly, and an actuator. The second wheel assembly can be actuated by the actuator to move laterally toward and away from the first wheel assembly to either reduce the distance between the first wheel assembly and the second wheel assembly (i.e., a retracted position) or increase the distance between the first wheel assembly and the second wheel assembly (i.e., an expanded position). In the retracted position, the carriage is able to slide through an opening in the overhead rail so as to be easily removed from or added to the overhead rail. This may allow operators and servicemen to more easily transport lift units to and away from overhead rails. While in the expanded position, the carriage may ride securely ride along the overhead rail. In some embodiments, the carriage may include a locking mechanism to lock the one of the second wheel assembly in the expanded position so as to prevent accidental movement of the carriage to the retracted position when the lift unit is carrying a load. Various embodiments of lift units, overhead lift systems comprising lift units, and methods of using the lift units will be described in more detail herein with specific reference to the corresponding drawings. 
       FIG. 1  schematically illustrates a perspective view of an overhead lift system  100 . The overhead lift system  100  generally comprises a lift unit  104  which is slidably coupled to an overhead rail  102  with a carriage  106 . The lift unit  104  may be used to support and/or lift a patient with a lifting strap  108  which is coupled to a motor (not shown) contained within the lift unit  104 . The motor facilitates paying-out or taking-up the lifting strap  108  from the lift unit  104  thereby raising and lowering a patient attached to the lifting strap  108 . In the embodiments described herein, the lift unit  104  further includes a battery which is housed in the lift unit  104  and electrically coupled to the motor thereby providing power to the motor. However, it should be understood that, in other embodiments, the lift unit  104  may be constructed without the battery, such as when the motor is directly coupled to a power source. 
     In the embodiment of the overhead lift system  100  shown in  FIG. 1 , a patient may be attached to the lifting strap  108  with a sling bar  110  or a similar accessory attached to the lifting strap  108 . More specifically, the sling bar  110  or a similar accessory may be attached to a harness or sling in which the patient is positioned thereby facilitating the lifting operation. The lift unit  104  may be actuated with a user input device  114  which is communicatively coupled to the motor. In the embodiment shown in  FIG. 1 , the user input device  114  is directly wired to the lift unit  104 . However, it should be understood that, in other embodiments, the user input device  114  may be wirelessly coupled to the lift unit  104  to facilitate remote actuation of the lift unit  104 . 
     In various embodiments, the lifting strap  108  is configured to be extended and retracted by the lift unit  104 . The sling bar  110  is coupled to an end of the lifting strap  108  through a connector. The lift unit  104  may further include a motor and a drum (not shown), each positioned within a housing of the lift unit  104 . The drum may be coupled to a shaft of the motor and the motor may be configured to extend and retract the lifting strap  108  as the motor rotates the drum in response to a user providing an input to the control system via the user input device  114 . Various lift units may be employed, including those described in U.S. Patent Application Publication No. 2015/0216753, entitled “Person Lift System,” which is hereby incorporated by reference in its entirety. Suitable commercially available lift units include, by way of example and not limitation, lift systems available under the trade names GOLVO®, LIKO®, SABINA®, VIKING®, UNO™, LIKOGUARD™, LIKORALL™, and MULTIRALL™, from Liko, HILL-ROM®, or Hill-Rom Services, Inc. (Batesville, Ind.). 
     In various embodiments, such as the embodiment depicted in  FIG. 1 , a subject support apparatus may be coupled to the lift unit  104  using the sling bar  110 . As shown in  FIG. 1 , the sling bar  110  includes an elongated bar and two hooks  111  coupled to the distal ends of the elongated bar. In other embodiments, the sling bar  110  may be an X-shaped sling bar that includes two curved frame members coupled by a middle frame member and including four support apparatus coupling mechanisms, or hooks. In still other embodiments, the sling bar may include a U-shaped frame including two support apparatus coupling mechanisms and a U-shaped handle extending from the frame to provide stability to a subject being lifted. Other sling bar configurations are contemplated. Various sling bar configurations are described in greater detail in U.S. Patent Application Publication No. 2015/0216753, entitled “Person Lift System,” which is hereby incorporated by reference in its entirety. 
     Suitable sling bars include, by way of example and not limitation, those commercially available under the trade names Universal SlingBar, SlingBar Mini, and Sling Cross-Bar, from Liko, HILL-ROM®, or Hill-Rom Services, Inc. (Batesville, Ind.). Additionally, it is contemplated that some embodiments may not include a sling bar. 
     Referring now to  FIGS. 2-5 , several views of the carriage  106  are provided. In the views, coordinate axes are depicted in which the Z axis is generally up and down while the X and Y axes lie in the same horizontal plane. The carriage  106  may be used to couple the lift unit  104  to the overhead rail  102 . Specifically,  FIG. 2  illustrates an isometric view of the carriage  106  positioned within an overhead rail  102  in an expanded position (described in further detail herein).  FIG. 3  illustrates a front view of the carriage  106  positioned within the overhead rail  102  in the expanded position (described in further detail herein).  FIG. 4  illustrates an isometric view of the carriage  106  in isolation from the overhead rail  102 .  FIG. 5  illustrates another isometric view of the carriage  106  in isolation from the overhead rail  102  to better schematically display a locking mechanism of the carriage  106 . 
     The carriage  106  generally comprises a carriage body  120  which includes a plurality of support wheels  122   a ,  122   b ,  122   c , and  122   d , which are rotatably attached for supporting the carriage  106  within the overhead rail  102 . The support wheels  122   a ,  122   b ,  122   c , and  122   d  facilitate positioning the carriage  106  and the lift unit  104  along the length of the rail. In the embodiments described herein, the carriage  106  is depicted with four support wheels. However, it is contemplated that the carriage  106  may be constructed with fewer than four support wheels. For example, the carriage  106  may be constructed with two support wheels (i.e., a pair of support wheels). In some embodiments, the carriage  106  may be constructed with more than four support wheels. 
     The support wheels  122   a ,  122   b ,  122   c , and  122   d  are each coupled to the carriage  106  through corresponding support arms  124   a ,  124   b ,  124   c , and  124   d . As used herein, a “wheel assembly” refers to at least one support wheel and corresponding support arm. Accordingly, in the embodiment depicted in  FIGS. 2-5 , the carriage  106  includes two wheel assemblies  123   a  and  123   b  each including two support wheels and corresponding support arms, although it is contemplated that embodiments may include three wheel assemblies, or more. In various embodiments, two or more wheel support wheels and the corresponding support arms may be coupled together to form the wheel assembly in order to enable simultaneous movement. For example, as shown in  FIGS. 4 and 5 , the support wheels  122   a  and  122   c  and corresponding support arms  124   a  and  124   c  on the left side of the carriage  106  may be coupled together into a wheel assembly  123   a  via a coupler  140  (shown in  FIG. 5 ) to enable the support wheels to be shifted into an expanded position simultaneously, as will be described in detail below. In various embodiments, the wheel assemblies  123   a  and  123   b  may be staggered in a longitudinal direction with respect to the overhead rail  102  (in the Z direction and along the length of the overhead rail  102 ). In such embodiments, when the wheel assemblies are in a retracted position relative to one another, at least a portion of the wheel assemblies are aligned in the lateral direction with respect to the overhead rail  102  (in the X direction and along the width of the overhead rail  102 ). 
     In the embodiment of the carriage  106  depicted in  FIGS. 3A and 3B , the support wheels  122   a ,  122   b ,  122   c , and  122   d  are passive (i.e., the support wheels are not actively driven with a motor or a similar drive mechanism) and the overhead lift unit  104  is manually traversed along the overhead rail  102 . However, in alternative embodiments (not shown), the support wheels  122   a ,  122   b ,  122   c , and  122   d  may be actively driven such as when the support wheels  122   a ,  122   b ,  122   c , and  122   d  are coupled to a motor or a similar mechanism. In such embodiments, the drive mechanism may be communicatively coupled to the user input device (such as user input device  114  shown in  FIG. 1 ) which actuates the drive mechanism and facilitates traversing the overhead lift unit  104  along the overhead rail  102  with the drive mechanism. 
     As will be described in greater detail below, in various embodiments, at least one of the wheel assemblies may be actuated to shift between an expanded position (shown in  FIGS. 2-6 ) and a retracted position (shown in  FIGS. 7 and 8 ). For example, the first wheel assembly may be fixed relative to the carriage  106  while the second wheel assembly is coupled to an actuator that is configured to move the wheel assembly in a lateral direction relative to the first wheel assembly. For example, in  FIGS. 3-5 , the support arms  124   b  and  124   d  are affixed to a carriage support plate  126  while the support arms  124   a  and  124   c  pass through the carriage support plate  126  and are moveable relative to the carriage support plate  126  and the wheel assembly  123   b  affixed thereto. In various embodiments, the expanded position enables the carriage  106  remain engaged with an overhead rail  102 , while the retracted position enables the carriage  106  to be inserted in or removed from the overhead rail  102 , as will be described in greater detail below. 
     Referring to  FIGS. 2, 3, and 6-8 , the overhead lift system  100  further comprises an overhead rail  102  in which the carriage  106  is slidably disposed for movement relative to the overhead rail  102 . Accordingly, it should be understood that, when the overhead lift unit  104  is mechanically coupled to the carriage  106 , the overhead lift unit  104  may be traversed along the overhead rail  102  with the carriage  106 . The overhead rail  102  may be formed from a metallic material, such as aluminum, an aluminum alloy, or a similar metallic material, and generally includes an upper portion  132 , a first sidewall  134   a  integrally formed with the upper portion  132 , and a second sidewall  134   b  integrally formed with the upper portion  132 . The upper portion  132 , the first sidewall  134   a , and the second sidewall  134   b  are oriented such that the upper portion  132 , the first sidewall  134   a , and the second sidewall  134   b  form a carriage support channel within which the carriage  106  is slidably disposed. To that end, the first sidewall  134   a  further comprises a first support flange  136   a  which extends from the first sidewall  134   a  into the support channel and the second sidewall  134   b  further comprises a second support flange  136   b  which extends from the second sidewall  134   b  into the support channel. In various embodiments, the first support flange  136   a  and the second support flange  136   b  form the carriage support channel. 
     In the embodiments described herein, the first support flange  136   a  and the second support flange  136   b  are generally opposed to one another and lie in a common horizontal plane. Accordingly, when the wheel assemblies are in the expanded position, the wheel assembly including the support wheel  122   a  rides along the first support flange  136   a  and the wheel assembly including the support wheel  122   b  rides along the second support flange  136   b . The first support flange  136   a  and the second support flange  136   b  define an opening in the overhead rail  102  through which the support arms  124   a ,  124   b  extend when the support wheels  122   a ,  122   b  are coupled with the overhead rail  102 . In various embodiments, when in the retracted position, an outer surface of the wheel assembly including the support wheel  122   a  and the outer surface of the wheel assembly including the support wheel  122   b  are separated by a distance less than the width of the opening between the first support flange  136   a  and the second support flange  136   b , thereby enabling the support wheels to pass through the opening in the retracted position. In various embodiments, the outer surface of each wheel assembly may be a surface of the support wheel separated from the support arm by the thickness of the wheel. 
     The first support flange  136   a  and the second support flange  136   b  may also be substantially parallel with the upper portion  132  of the overhead rail  102 . However, it should be understood that other configurations of the support flanges and the upper portion of the overhead rail  102  are also contemplated. For example, in an alternative embodiment, the support flanges may be upwardly angled with respect to the horizontal plane. Moreover, it should be understood that the structure of the overhead rail  102  depicted in the figures is exemplary and that other rail configurations are contemplated. 
       FIG. 3  depicts a front view of a carriage  106  slidably disposed within the carriage support channel of the overhead rail  102 . In particular, the wheel assembly that includes support wheel  122   a  and support arm  124   a  are shown in an expanded position relative to the wheel assembly that includes support wheel  122   b  and support arm  124   b . It can be seen in  FIG. 3  that the support arm  124   b  is affixed to the carriage support plate  126  while the support arm  124   a  passes through an aperture  150  (shown in  FIGS. 4 and 5 ) in the carriage support plate  126  such that the support wheel  122   a  and a first portion of the support arm  124   a  are proximate a top side of the carriage support plate  126  while a second portion of the support arm  124   a  is proximate a bottom side of the carriage support plate  126 . 
     In various embodiments, the support arm  124   a  passes through the aperture  150  in the carriage support plate  126  and is moveable laterally with respect to the support arm  124   b , or in the +/−X direction, as indicated by the X-Y axes shown in  FIG. 3  and by the arrow A in  FIG. 6 . To facilitate movement in the +/−X direction, the support arm  124   a  is coupled to a guide assembly that includes at least a bearing member  138   a  and a guide member  142   a . The bearing member  138   a  is slidable in the +/−X direction along the guide member  142   a  to enable expansion and retraction of the wheel assembly relative to the other wheel assembly. 
     In some embodiments, an actuator  139  (shown in  FIG. 3 ) is configured to drive the support arm  124   a  along the guide member  142   a , although it is also contemplated that the support arm  124   a  may be shifted between the expanded and retracted positions manually. In particular, the actuator  139  may be coupled to at least one support arm of the wheel assembly  123   a  (in  FIG. 3 , support arm  124   a ) and to the carriage support plate  126  such that actuating the actuator  139  exerts a force on the support arm  124   a  and slides the support arm  124   a  along the guide member  142   a  via the bearing member  138   a . In embodiments employing an actuator  139 , any suitable actuator may be used, including, but not limited to, pneumatic, hydraulic, piezoelectric, or electro-mechanical actuators. 
     In embodiments employing an actuator, the actuator  139  may be actuated by a user input, such as a button  152  (shown in  FIG. 1 ), lever, or similar input device. The button  152  may be located in any suitable position. For example, in the embodiment depicted in  FIG. 1 , the button  152  may be positioned on the lift unit  104  such that a user lifting the lift unit  104  into position within the overhead rail  102  can easily depress the button  152  with a thumb or finger while supporting the lift unit  104 . However, it is contemplated that the button  152  may be located elsewhere, such as on a side of the lift unit  104 . 
     In still other embodiments, a controller (not shown) is communicatively coupled to the actuator. The controller may be a microprocessor or other computing device that is operable to actuate the actuator and cause the wheel assemblies to move between the expanded and retracted positions. The controller may execute logic to cause the actuator  139  to shift the wheel assemblies between expanded and retracted positions. In various embodiments, the logic may be stored in a memory device and executed by a processor of the controller. A user input device, such as the user input device  114 , may be communicatively coupled to the controller. Accordingly, when the user input device  114  receives an input, the controller may cause the actuator  139  to shift the wheel assemblies between the expanded position and the retracted position. 
     In embodiments in which the actuator  139  is coupled to a controller, the controller may be further operable to provide feedback to the user regarding the expansion or retraction of the wheel assemblies. For example, when the wheel assemblies have been shifted to the expanded position by the actuator  139 , the controller may provide a notification to the user input device  114  indicating that the carriage  106  and the lift unit  104  are ready for use. Alternatively, when the wheel assemblies have been shifted to the retracted position by the actuator  139 , the controller may provide a notification to the user input device  114  indicating that the carriage  106  is ready for removal from the overhead rail  102 . It is contemplated that the controller may have additional functions and features that may be advantageous in various embodiments. 
     Still referring to  FIGS. 3-7 , a guide stop  148   a  is positioned along the guide member  142   a  to prevent the bearing member  138   a  from being shifted too far in the −X direction. Although depicted throughout the figures, it is contemplated that the guide stop  148   a  is optional. For example, in some embodiments in which the actuator is configured to stop at a predetermined position along the guide member  142   a , the guide stop  148   a  may not be included. However, in other embodiments, such as when the bearing member  138   a  is manually slid along the guide member  142   a , the guide stop  148   a  may be employed. 
     In various embodiments, the support arm  124   a  is moveable in both the +/−X direction and the +/−Y direction of the X-Y axes shown in  FIG. 3 . In such embodiments, the guide member  142   a  (and, therefore, the support arm  124   a ) is coupled to a vertical bearing member  144   a  which is slidable in the +/−Y direction through a vertical guide member  146   a . In various embodiments, a spring  145   a  may be positioned around the vertical bearing member  144   a  between a vertical stop member  147   a  and the vertical guide member  146   a  and biases the vertical bearing member  144   a  in a −Y direction relative to the carriage support plate  126 , as shown in  FIGS. 6 and 7 . Accordingly, the support arm  124   a  and the support wheel  122   a  may be moved vertically with respect to the support arm  124   b  and the support wheel  122   b.    
     In various embodiments, the vertical movement of the wheel assembly  123   a  including the support arm  124   a  and the support wheel  122   a  facilitates a locking mechanism  30  locking the wheel assembly in the expanded position thereby preventing the wheel assembly from being moved to a retracted position relative to the wheel assembly including the support arm  124   b  and the support wheel  122   b  when a load is supported by the carriage  106  and/or the overhead lift system  100 . In other words, the locking mechanism  30  may be actuated when the wheel assemblies are supporting at least the weight of the overhead lift unit within the overhead rail  102 . In the embodiments depicted in the figures, the locking mechanism  30  is in the form of a block, which prevents the wheel assembly including the support arm  124   a  and the support wheel  122   a  from moving in the +X direction when a load is supported by the carriage  106 . 
     In particular, the locking mechanism  30  may be affixed to an underside of the carriage support plate  126 . The carriage support plate  126  may be affixed to the housing of the lift unit  104  and may, for example, be affixed within the housing or form a top part of the housing. It should be understood that the carriage support plate  126  may be affixed to the lift unit in other ways, provided that there is sufficient space for movement of the components positioned below the carriage support plate  126  as depicted in  FIGS. 4 and 5 , including the locking mechanism  30 , the bearing member(s), the coupler  140 , the guide member(s), and the guide stop(s). When the lift unit  104  is coupled to the carriage support plate  126  and the lift unit is supported by the overhead rail  102 , as shown in  FIG. 3 , the weight of the load (i.e., the weight of the lift unit) pulls the carriage support plate  126  down relative to the support wheel  122   a , shifting the support arm  124   a  upward through the aperture in the carriage support plate  126 , and bringing the coupler  140  and/or the bearing member  138   a  at least partially into alignment with the locking mechanism  30 . Once the coupler  140  and/or the bearing member  138   a  is at least partially in alignment with the locking mechanism  30 , the locking mechanism  30  prevents the bearing member  138   a  from moving in the +X direction. Thus, the locking mechanism  30  prevents the support wheel  122   a  from shifting into the retracted position relative to the support wheel  122   b  when a load, such as the lift unit  104 , is supported by the carriage  106 . 
     In order to remove the lift unit  104  from the overhead rail  102 , a user applies an upward force F on the carriage support plate  126 , as shown in  FIG. 6 . The force F on the carriage support plate  126  may be, for example, a user pressing up on the lift unit  104  to which the carriage support plate  126  is affixed. As the force F is applied to the carriage support plate  126 , the carriage support plate  126 , the support arm  124   b , and the support wheel  122   b  are shifted upward relative to the support wheel  122   a , deactivating the locking mechanism by moving the locking mechanism  30  out of alignment with the bearing member  138   a  such that the bearing member  138   a  can be moved in the direction of the arrow A. The support wheel  122   a  and the support arm  124   a  may be shifted to the right along the guide member  142   a  in  FIG. 6  to move the wheel assembly from the expanded position, as shown in  FIG. 6 , to the retracted position, as shown in  FIG. 7 . For example, in embodiments where the carriage comprises an actuator, after applying the force F to the carriage support plate  126 , the user may press the button  152  to actuate the actuator to shift the wheel assembly along the guide member  142   a . In embodiments where the carriage does not include an actuator, after applying the force F to the carriage support plate  126 , the user may manually shift the when assembly along the guide member  142   a , such as by applying a force in the X direction to the support arm  124   a.    
     Once in the retracted position, as shown in  FIG. 7 , the carriage  106  may be moved in a vertical direction, as indicated by arrow B in  FIG. 7 , and removed from the overhead rail  102 , as shown in  FIG. 8 . 
     Conversely, to attach the lift unit  104  to the overhead rail  102 , the wheel assemblies of the carriage  106 , while in the retracted position, as shown in  FIG. 8 , are extended through the opening of the overhead rail  102  between the first support flange  136   a  and the second support flange  136   b . Next, the wheel assembly including the support wheel  122   a  and the support arm  124   a  are shifted from the retracted position to an expanded position relative to the wheel assembly including the support wheel  122   b  and the support arm  124   b , as shown in  FIG. 6 . In various embodiments, the wheel assembly may be shifted by the actuator in response to a user input. Alternatively, the wheel assembly may be shifted manually by a user. When the wheel assembly is shifted from the retracted position to the expanded position, a lateral distance from the outer surface of the wheel assembly including the support wheel  122   b  and the support arm  124   b  to an outer surface of the wheel assembly including the support wheel  122   a  and the support arm  124   a  is increased as compared to the lateral distance when the wheel assembly is in the retracted position. 
     When the wheel assembly has been shifted into the expanded position, the user may release the lift unit  104  and weight of the lift unit  104  may be supported by the first support flange  136   a  and the second support flange  136   b  of the overhead rail  102 , as shown in  FIG. 3 . In particular, when the user releases the lift unit  104 , the carriage support plate  126  may shift downward relative to the support wheel  122   a  and the support arm  124   a , allowing the support arm  124   a  to move vertically through the aperture in the carriage support plate  126  and bring the bearing member  138   a  into alignment with the locking mechanism  30 . 
     It should now be understood that various embodiments described herein enable a lift unit  104  to be removeably attached to an overhead rail  102 , such that the lift unit  104  may be used with various overhead rails  102 . In other words, the lift unit  104  may be transported and coupled to any one of a number of overhead rails, which may reduce the number of lift units that a facility needs to purchase. Various embodiments may further enable lift units  104  to be decoupled from the overhead rail for servicing or the like. In addition, various embodiments may enable the lift unit  104  to be locked into place when supporting a load, such as a subject, thereby preventing the lift unit  104  from being inadvertently removed from the overhead rails  102  while in use. 
     Embodiments can be described with reference to the following numbered clauses, with preferred features laid out in the dependent clauses: 
     1. A lift unit comprising a carriage; a first wheel assembly comprising a first wheel coupled to the carriage through a first support arm; a second wheel assembly comprising a second wheel coupled to the carriage through a second support arm; and a guide assembly comprising a bearing member and a guide member along which the bearing member is slidable, the guide assembly coupled to the second wheel assembly, wherein the guide assembly is configured to shift the second wheel assembly in a lateral direction relative to the first wheel assembly between an expanded position and a retracted position. 
     2. The overhead lift unit of clause 1, wherein the first wheel assembly is fixed relative to the carriage. 
     3. The overhead lift unit of either clause 1 or clause 2, wherein the first wheel assembly is staggered with the second wheel assembly along a longitudinal direction and the retracted position is characterized by at least a portion of the first wheel assembly and the second wheel assembly being aligned in the lateral direction. 
     4. The overhead lift unit of any preceding clause, further comprising a locking mechanism configured to lock the second wheel assembly in the expanded position. 
     5. The overhead lift unit of clause 4, wherein the first wheel assembly and the second wheel assembly are configured to support the overhead lift unit within an overhead rail, and the locking mechanism is actuated when the first wheel assembly and the second wheel assembly are supporting at least a weight of the overhead lift unit within the overhead rail. 
     6. The overhead lift unit of any preceding clause, further comprising a controller communicatively coupled to the actuator, wherein the controller executes logic to cause the actuator to shift the second wheel assembly between the expanded position and the retracted position. 
     7. The overhead lift unit of clause 6, further comprising a user input device communicatively coupled to the controller, wherein the controller causes the actuator to shift the second wheel assembly between the expanded position and the retracted position based on an input received from the user input device. 
     8. A lift system comprising an overhead rail defining a carriage support channel comprising a first support flange and a second support flange, the first support flange separated from the second support flange to define an opening in the overhead rail; and an overhead lift unit. The overhead lift unit comprises a carriage; a first wheel assembly configured to extend through the opening of the overhead rail and to ride along the carriage support channel, the first wheel assembly comprising a first wheel coupled to the carriage through a first support arm; a second wheel assembly configured to extend through the opening of the overhead rail and to ride along the carriage support channel, the second wheel assembly comprising a second wheel coupled to the carriage through a second support arm; and an actuator coupled to the second wheel assembly, wherein the actuator is configured to shift the second wheel assembly in a lateral direction relative to the first wheel assembly between an expanded position in which the first wheel assembly and the second wheel assembly are coupled with the overhead rail, and a retracted position in which the first wheel assembly and the second wheel assembly are configured to pass through the opening in the overhead rail. 
     9. The lift system of clause 8, wherein the first wheel assembly is configured to ride along the first support flange and the second wheel assembly is configured to ride along the second support flange when the one of the first wheel assembly and the second wheel assembly are within the overhead rail and in the expanded position. 
     10. The lift system of clause 8 or clause 9, wherein the first wheel assembly comprises a first outer surface and the second wheel assembly comprises a second outer surface, wherein the retracted position is characterized by the first outer surface of the first wheel assembly and the second outer surface of the second wheel assembly being separated by a distance less than a width of the opening between the first support flange and the second support flange. 
     11. The lift system of any of clauses 8-10, wherein the first wheel assembly is fixed relative to the carriage. 
     12. The lift system of any of clauses 8-11, wherein the first wheel assembly of the carriage is staggered with the second wheel assembly along a longitudinal direction and the retracted position is characterized by at least a portion of the first wheel assembly and the second wheel assembly being aligned in the lateral direction. 
     13. The lift system of any of clauses 8-12, wherein the overhead lift unit further comprises a locking mechanism configured to lock the second wheel assembly in the expanded position. 
     14. The lift system of clause 13, wherein the first wheel assembly is configured to ride along the first support flange and the second wheel assembly is configured to ride along the second support flange when the one of the first wheel assembly and the second wheel assembly are within the overhead rail and in the expanded position; and the locking mechanism locks the second wheel assembly in the expanded position when the first wheel assembly and the second wheel assembly are supporting a weight of at least the overhead lift unit on the first support flange and the second support flange of the overhead rail. 
     15. The lift system of any of clauses 8-14, further comprising a controller communicatively coupled to the actuator of the overhead lift unit, wherein the controller executes logic to cause the actuator to shift the second wheel assembly between the expanded position and the retracted position. 
     16. The lift system of clause 15, further comprising a user input device communicatively coupled to the controller, wherein the controller causes the actuator of the overhead lift unit to shift the second wheel assembly between the expanded position and the retracted position based on an input received from the user input device. 
     17. A method of transporting an overhead lift unit to and from an overhead rail, the method comprising one of attaching the overhead lift unit to the overhead rail and detaching the overhead lift unit from the overhead rail wherein the overhead rail defines a carriage support channel comprising a first support flange and a second support flange, the first support flange separated from the second support flange to define an opening in the overhead rail. The overhead lift unit comprises a carriage comprising: a first wheel assembly comprising a first wheel coupled to the carriage through a first support arm; a second wheel assembly comprising a second wheel coupled to the carriage through a second support arm; and an actuator coupled to the second wheel assembly. Attaching the overhead lift unit to the overhead rail comprises extending the first wheel assembly and the second wheel assembly through the opening of the overhead rail; shifting the second wheel assembly from a retracted position to an expanded position with the actuator, wherein a lateral distance from an outer surface of the first wheel assembly to an outer surface of the second wheel assembly is increased; and supporting a weight of the overhead lift unit on the carriage support channel with the first wheel of the first wheel assembly and the second wheel of the second wheel assembly. Detaching the overhead lift unit from the overhead rail comprises shifting the second wheel assembly from the expanded position to the retracted position, wherein the lateral distance from the outer surface of the first wheel assembly to the outer surface of the second wheel assembly is decreased; and lowering the overhead lift unit from the overhead rail through the opening. 
     18. The method of clause 17, wherein the overhead lift unit further comprises a locking mechanism configured to lock the second wheel assembly in the expanded position, and supporting the weight of the overhead lift unit within the carriage support channel activates the locking mechanism. 
     19. The method of clause 18, wherein detaching the overhead lift unit from the overhead rail comprises relieving the weight of the overhead lift unit from the first wheel of the first wheel assembly and the second wheel of the second wheel assembly, wherein relieving the weight of the overhead lift unit deactivates the locking mechanism. 
     20. The method of any of clauses 17-19, wherein the first wheel assembly is staggered with the second wheel assembly along a longitudinal direction and the retracted position is characterized by at least a portion of the first wheel assembly and the second wheel assembly being aligned in a lateral direction. 
     It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.