Patent Publication Number: US-2023149233-A1

Title: Patient Support Apparatus With Ramp Transition Detection

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The subject patent application claims priority to, and all the benefits of, U.S. Provisional Patent Application No. 63/278,722, filed on Nov. 12, 2021, the entire contents of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     Patient support systems facilitate care of patients in a health care setting. Patient support systems may comprise patient support apparatuses such as, for example, hospital beds, stretchers, cots, wheelchairs, and transport chairs, to move patients between locations. A conventional patient support apparatus comprises a base, a patient support surface, and several support wheels, such as four swiveling caster wheels. Often, the patient support apparatus has one or more non-swiveling auxiliary wheels, in addition to the four caster wheels. The auxiliary wheel, by virtue of its non-swiveling nature, is employed to help control movement of the patient support apparatus over a floor surface in certain situations. 
     Those having ordinary skill in the art will appreciate that patient support apparatuses which employ powered auxiliary wheels can advantageously help caregivers propel, position, and manipulate the patient support apparatus. For example, powered auxiliary wheels can help caregivers move the patient support apparatus up or down ramps, around corners, and the like, and also may facilitate fine positioning of the patient support apparatus in rooms, elevators, and the like. 
     While patient support apparatuses have generally performed well for their intended use, there remains a need in the art for improved usability and adaptability to enable utilization of patient support apparatus in and between different environments and use case scenarios. 
     SUMMARY 
     The present disclosure is directed towards a patient support apparatus with a support structure. The support structure comprises a base and a frame, and the frame includes a velocity sensor configured to sense a velocity of the patient support apparatus over a floor surface. A support wheel is coupled to the support structure. The patient support apparatus further comprises an auxiliary wheel assembly, which includes an auxiliary wheel coupled to the support structure to influence motion of the patient support apparatus over the floor surface. The auxiliary wheel assembly is positionable to a deployed position with the auxiliary wheel engaging the floor surface and to a retracted position with the auxiliary wheel spaced a distance from the floor surface. The auxiliary wheel assembly also includes an auxiliary wheel actuator operatively coupled to the auxiliary wheel by a wheel support structure. The auxiliary wheel assembly further includes an auxiliary wheel drive system having a motor coupled to the auxiliary wheel to rotate the auxiliary wheel relative to the support structure at a rotational speed, and a control system coupled to the auxiliary wheel drive system for operating the auxiliary wheel drive system. The control system includes an auxiliary wheel position sensor coupled to the wheel support structure and configured to sense a plurality of positions of the auxiliary wheel actuator relative to the frame of the support structure. The control system further includes a memory device configured to store a plurality of transition profiles, wherein at least one of the plurality of transition profiles represents a transition over an inclined floor surface. The control system additionally includes a processor coupled to the memory device and programmed to calculate, based on the velocity of the patient support apparatus over the floor surface, a distance traveled by the patient support apparatus over the floor surface. The processor is further configured to compare the plurality of positions of the auxiliary wheel actuator and the distance traveled by the patient support apparatus with the inclined floor surface profile, and determine that the patient support apparatus is traveling on an inclined floor surface. 
     The present disclosure is also directed towards a patient support apparatus with a support structure, a support wheel coupled to the support structure, and a drive system. The drive system includes a drive member coupled to the support structure to influence motion of the patient support apparatus over a floor surface, a motor coupled to the drive member to operate the drive member at a speed, and a motor control circuit for transmitting power signals from a power source to the motor. The patient support apparatus also includes a user interface for receiving user commands from a user to operate the drive system. The patient support apparatus further includes a control system coupled to the user interface and the drive system for operating the drive system, the control system including: a memory device configured to store a plurality of transition profiles, wherein at least one of the plurality of transition profiles represents a transition over an inclined floor surface, and a processor coupled to the memory device and configured to: sense a plurality of positions of the drive member relative to the support structure, calculate a distance traveled by the patient support apparatus over the floor surface, compare the plurality of positions of the auxiliary wheel actuator and the distance traveled by the patient support apparatus with the inclined floor surface profile, and determine that the patient support apparatus is traveling on an inclined floor surface. 
     The present disclosure is also directed towards a patient support apparatus with a support structure, a support wheel coupled to the support structure, and a drive system. The drive system includes a drive member coupled to the support structure to influence motion of the patient support apparatus over a floor surface, a motor coupled to the drive member to operate the drive member at a speed, and a motor control circuit for transmitting power signals from a power source to the motor. The patient support apparatus also includes a user interface for receiving user commands from a user to operate the drive system. The patient support apparatus also includes a floor sensor operatively attached to the support structure to determine a distance to the floor surface. The patient support apparatus further includes a control system coupled to the user interface and the drive system for operating the drive system, the control system including: a memory device configured to store a plurality of transition profiles, wherein at least one of the plurality of transition profiles represents a transition over an inclined floor surface, and a processor coupled to the memory device and configured to: sense changes in the distance to the floor surface based on signals received from the floor sensor, calculate a distance traveled by the patient support apparatus over the floor surface, compare the changes in the distance to the floor surface and the distance traveled by the patient support apparatus with the plurality of transition profiles, and determine that the patient support apparatus is traveling on an inclined floor surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view of a patient support apparatus, according to the present disclosure. 
         FIG.  2    is a perspective view of an auxiliary wheel assembly of the patient support apparatus coupled to a base of the patient support apparatus shown in  FIG.  1   . 
         FIG.  3    is a perspective view of the auxiliary wheel assembly shown in  FIG.  2    comprising an auxiliary wheel, a lift actuator, and a spring cartridge assembly. 
         FIG.  4    is an elevational view of the auxiliary wheel assembly shown in  FIG.  2    in a retracted position. 
         FIG.  5    is an elevational view of the auxiliary wheel assembly shown in  FIG.  2    in a deployed position. 
         FIG.  6    is a perspective view of a handle and a throttle assembly that may be used with the patient support apparatus shown in  FIG.  1   . 
         FIG.  7 A  is an elevational view of a first position of a throttle of the throttle assembly relative to the handle. 
         FIG.  7 B  is an elevational view of a second position of the throttle relative to the handle. 
         FIG.  7 C  is an elevational view of a third position of the throttle relative to the handle. 
         FIG.  7 D  is another elevational view of the first position of the throttle relative to the handle. 
         FIG.  7 E  is an elevational view of a fourth position of the throttle relative to the handle. 
         FIG.  7 F  is an elevational view of a fifth position of the throttle relative to the handle. 
         FIG.  8    is a schematic view of a control system of the patient support apparatus shown in  FIG.  1   . 
         FIG.  9    is a schematic wire diagram of a control circuit that may be used with the auxiliary wheel assembly shown in  FIG.  1   . 
         FIG.  10    is a schematic wire diagram of a motor control circuit that may be used with the auxiliary wheel assembly shown in  FIG.  1   . 
         FIG.  11    is an elevation view of the auxiliary wheel assembly shown in  FIG.  2   , according to an alternative version. 
         FIG.  12    is a perspective view of a portion of the auxiliary wheel assembly shown in  FIG.  11   . 
         FIG.  13    is another perspective view of a portion the auxiliary wheel assembly shown in  FIG.  11   . 
         FIG.  14    is a perspective view of the lift actuator assembly that may be used with the auxiliary wheel assembly shown in  FIG.  11   . 
         FIGS.  15 A and  15 B  are elevation views of the spring cartridge assembly of the auxiliary wheel assembly shown in  FIG.  11   . 
         FIG.  16 A  is an elevation view of the auxiliary wheel assembly shown in  FIG.  11    in a deployed position. 
         FIG.  16 B  is an elevation view of the auxiliary wheel assembly shown in  FIG.  11    in a stowed position. 
         FIGS.  17 A- 17 C  are elevation views illustrating a movement of the auxiliary wheel with the auxiliary wheel assembly shown in  FIG.  11    in the deployed position. 
         FIG.  18    is a flow chart of a method illustrating an algorithm to recognize a plurality of transition profiles during operation of the auxiliary wheel assembly of the patient support apparatus shown in  FIG.  1   . 
         FIG.  19    is a flow chart of a method illustrating an algorithm to recognize a plurality of transition profiles during operation of the drive member of the patient support apparatus shown in  FIG.  1   . 
         FIG.  20 A  is an elevation views illustrating operation along a flat surface. 
         FIGS.  20 B- 20 C  are elevation views illustrating operation during ramp transitions. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG.  1   , a patient transport system comprising a patient support apparatus  10  is shown for supporting a patient in a health care setting. The patient support apparatus  10  illustrated in  FIG.  1    comprises a hospital bed. In some versions, however, the patient support apparatus  10  may comprise a stretcher, a cot, a wheelchair, and a transport chair, or similar apparatus, utilized in the care of a patient to transport the patient between locations. 
     A support structure  12  provides support for the patient. The support structure  12  illustrated in  FIG.  1    comprises a base  14  and an intermediate frame  16 . The base  14  defines a longitudinal axis  18  from a head end to a foot end. The intermediate frame  16  is spaced above the base  14 . The support structure  12  also comprises a patient support deck  20  disposed on the intermediate frame  16 . The patient support deck  20  comprises several sections, some of which articulate (e.g., pivot) relative to the intermediate frame  16 , such as a fowler section, a seat section, a thigh section, and a foot section. The patient support deck  20  provides a patient support surface  22  upon which the patient is supported. 
     In certain versions, such as is depicted in  FIG.  1   , the patient support apparatus  10  further comprises a lift assembly, generally indicated at  24 , which operates to lift and lower the intermediate frame  16  relative to the base  14 . The lift assembly  24  is configured to move the intermediate frame  16  between a plurality of vertical configurations relative to the base  14  (e.g., between a minimum height and a maximum height, or to any desired position in between). To this end, the lift assembly  24  comprises one or more bed lift actuators  26  which are arranged to facilitate movement of the intermediate frame  16  with respect to the base  14 . The bed lift actuators  26  may be realized as linear actuators, rotary actuators, or other types of actuators, and may be electrically operated, hydraulic, electro-hydraulic, or the like. It is contemplated that, in some versions, separate lift actuators could be disposed to facilitate independently lifting the head and foot ends of the intermediate frame  16  and, in some versions, only one lift actuator may be employed, (e.g., to raise only one end of the intermediate frame  16 ). The construction of the lift assembly  24  and/or the bed lift actuators  26  may take on any known or conventional design, and is not limited to that specifically illustrated. One exemplary lift assembly that can be utilized on the patient support apparatus  10  is described in U.S. Patent Application Publication No. 2016/0302985, entitled “Patient Support Lift Assembly”, which is hereby incorporated herein by reference in its entirety. 
     A mattress, although not shown, may be disposed on the patient support deck  20 . The mattress comprises a secondary patient support surface upon which the patient is supported. The base  14 , intermediate frame  16 , patient support deck  20 , and patient support surface  22  each have a head end and a foot end corresponding to designated placement of the patient&#39;s head and feet on the patient support apparatus  10 . The construction of the support structure  12  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 versions, such that the patient rests directly on the patient support surface  22 . 
     Side rails  28 ,  30 ,  32 ,  34  are supported by the base  14 . A first side rail  28  is positioned at a right head end of the intermediate frame  16 . A second side rail  30  is positioned at a right foot end of the intermediate frame  16 . A third side rail  32  is positioned at a left head end of the intermediate frame  16 . A fourth side rail  34  is positioned at a left foot end of the intermediate frame  16 . If the patient support apparatus  10  is a stretcher, there may be fewer side rails. The side rails  28 ,  30 ,  32 ,  34  are movable between a raised position in which they block ingress and egress into and out of the patient support apparatus  10  and a lowered position in which they are not an obstacle to such ingress and egress. The side rails  28 ,  30 ,  32 ,  34  may also be movable to one or more intermediate positions between the raised position and the lowered position. In still other configurations, the patient support apparatus  10  may not comprise any side rails. 
     A headboard  36  and a footboard  38  are coupled to the intermediate frame  16 . In some versions, when the headboard  36  and footboard  38  are provided, the headboard  36  and footboard  38  may be coupled to other locations on the patient support apparatus  10 , such as the base  14 . In still other versions, the patient support apparatus  10  does not comprise the headboard  36  and/or the footboard  38 . 
     User interfaces  40 , such as handles, are shown integrated into the footboard  38  and side rails  28 ,  30 ,  32 ,  34  to facilitate movement of the patient support apparatus  10  over floor surfaces. The user interfaces  40  are graspable by the user to manipulate the patient support apparatus  10  for movement. 
     Other forms of the user interface  40  are also contemplated. The user interface may simply be a surface on the patient support apparatus  10  upon which the user logically applies force to cause movement of the patient support apparatus  10  in one or more directions, also referred to as a push location. This may comprise one or more surfaces on the intermediate frame  16  or base  14 . This could also comprise one or more surfaces on or adjacent to the headboard  36 , footboard  38 , and/or side rails  28 ,  30 ,  32 ,  34 . 
     Additional user interfaces  40  may be integrated into the headboard  36 , footboard  38 , and/or other components of the patient support apparatus  10 . Such additional user interfaces  40  may include, for example, a graphical user interface  41 . The user interface  41  may be configured to receive user commands from a user to operate an auxiliary wheel assembly  60  of a drive system  78  configured to influence motion of the patient support apparatus  10 . 
     In the version shown in  FIG.  1   , one set of user interfaces  40  comprises a first handle  42  and a second handle  44 . The first and second handles  42 ,  44  are coupled to the intermediate frame  16  proximal to the head end of the intermediate frame  16  and on opposite sides of the intermediate frame  16  so that the user may grasp the first handle  42  with one hand and the second handle  44  with the other. As is described in greater detail below in connection with  FIGS.  1  and  6   , in some versions the first handle  42  comprises an inner support  46  defining a central axis C, and handle body  48  configured to be gripped by the user. In some versions, the first and second handles  42 ,  44  are coupled to the headboard  36 . In still other versions the first and second handles  42 ,  44  are coupled to another location permitting the user to grasp the first and second handle  42 ,  44 . As shown in  FIG.  1   , one or more of the user interfaces (e.g., the first and second handles  42 ,  44 ) may be arranged for movement relative to the intermediate frame  16 , or another part of the patient support apparatus  10 , between a use position PU arranged for engagement by the user, and a stow position PS (depicted in phantom), with movement between the use position PU and the stow position PS being facilitated such as by a hinged or pivoting connection to the intermediate frame  16  (not shown in detail). Other configurations are contemplated. 
     Support wheels  50  are coupled to the base  14  to support the base  14  on a floor surface such as a hospital floor. The support wheels  50  allow the patient support apparatus  10  to move in any direction along the floor surface by swiveling to assume a trailing orientation relative to a desired direction of movement. In the version shown, the support wheels  50  comprise four support wheels each arranged in corners of the base  14 . The support wheels  50  shown are caster wheels able to rotate and swivel about swivel axes  52  during transport. Each of the support wheels  50  forms part of a caster assembly  54 . Each caster assembly  54  is mounted to the base  14 . It should be understood that various configurations of the caster assemblies  54  are contemplated. In addition, in some versions, the support wheels  50  are not caster wheels and may be non-steerable, steerable, non-powered, powered, or combinations thereof. Additional support wheels  50  are also contemplated. 
     In some versions, the patient support apparatus  10  comprises a support wheel brake actuator  56  (shown schematically in  FIG.  8   ) operably coupled to one or more of the support wheels  50  for braking one or more support wheels  50 . In some versions, the support wheel brake actuator  56  may comprise a brake member  58  coupled to the base  14  and movable between a braked position engaging one or more of the support wheels  50  to brake the support wheel  50  and a released position permitting one or more of the support wheels  50  to rotate freely. 
     Referring to  FIGS.  1 - 3   , the auxiliary wheel assembly  60  is coupled to the base  14 . The auxiliary wheel assembly  60  forms part of the drive system  78  in the illustrated versions. As noted above, the drive system  78  is configured to influence motion of the patient support apparatus  10  during transportation over the floor surface. To this end, the drive system  78  generally includes a drive member  62  and a motor  80  coupled to the drive member  62  to operate the drive member  62  at various speeds. In the illustrated versions, the drive member  62  is realized as an auxiliary wheel  62  forming part of the auxiliary wheel assembly  60  of an auxiliary wheel drive system  78  as described in greater detail below. However, those having ordinary skill in the art will appreciate that the drive system  78  could be configured in other ways, with various types of drive members  62  other than those configured as auxiliary wheels  62  of auxiliary wheel assemblies  60 . By way of non-limiting example, the drive member  62  could be realized by various types and/or arrangements of one or more belts, treads, wheels, tires, and the like, which may be arranged in various ways about the patient support apparatus  10  and may be deployable, retractable, or similarly movable, or may be generally engaged with the floor surface (e.g., realized as powered wheels at one or more corners of the base  14 ). Accordingly, it will be appreciated that the auxiliary wheel drive system  78  described and illustrated herein represents one type of drive system  78  contemplated by the present disclosure, and the auxiliary wheel  62  described and illustrated herein represents one type of drive member  62  contemplated by the present disclosure. 
     With continued reference to  FIGS.  1 - 3   , the illustrated auxiliary wheel assembly  60  employs an auxiliary wheel actuator  64  operatively coupled to the auxiliary wheel  62  and operable to move the auxiliary wheel  62  between a deployed position  66  (see  FIG.  5   ) engaging the floor surface, and a retracted position  68  (see  FIG.  4   ) spaced away from and out of contact with the floor surface. The retracted position  68  may alternatively be referred to as the “fully retracted position.” The auxiliary wheel  62  may also be positioned in one or more intermediate positions between the deployed position  66  (see  FIG.  5   ) and the retracted position  68  ( FIG.  4   ). The intermediate positions may alternatively be referred to as a “partially retracted position,” or may also refer to another “retracted position” (e.g., compared to the “fully” retracted position  68  depicted in  FIG.  4   ). The auxiliary wheel  62  influences motion of the patient support apparatus  10  during transportation over the floor surface when the auxiliary wheel  62  is in the deployed position  66 . In some versions, the auxiliary wheel assembly  60  comprises an additional auxiliary wheel movable with the auxiliary wheel  62  between the deployed position  66  and the retracted position  68  via the auxiliary wheel actuator  64 . 
     By deploying the auxiliary wheel  62  on the floor surface, the patient support apparatus  10  can be easily moved down long, straight hallways or around corners, owing to a non-swiveling nature of the auxiliary wheel  62 . When the auxiliary wheel  62  is in the retracted position  68  (see  FIG.  4   ) or in one of the intermediate positions (e.g. spaced from the floor surface), the patient support apparatus  10  may be subject to moving in an undesired direction due to uncontrollable swiveling of the support wheels  50 . For instance, during movement down long, straight hallways, the patient support apparatus  10  may be susceptible to “dog tracking,” which refers to undesirable sideways movement of the patient support apparatus  10 . Additionally, when cornering, without the auxiliary wheel  62  deployed, and with all of the support wheels  50  able to swivel, there is no wheel assisting with steering through the corner, unless one or more of the support wheels  50  are provided with steer lock capability and the steer lock is activated. 
     The auxiliary wheel  62  may be arranged parallel to the longitudinal axis  18  of the base  14 . The differently, the auxiliary wheel  62  rotates about a rotational axis R (see  FIG.  2   ) oriented perpendicularly to the longitudinal axis  18  of the base  14  (albeit offset in some cases from the longitudinal axis  18 ). In the version shown, the auxiliary wheel  62  is incapable of swiveling about a swivel axis. In some versions, the auxiliary wheel  62  may be capable of swiveling, but can be locked in a steer lock position in which the auxiliary wheel  62  is locked to solely rotate about the rotational axis R oriented perpendicularly to the longitudinal axis  18 . In still other versions, the auxiliary wheel  62  may be able to freely swivel without any steer lock functionality or may be steered. 
     The auxiliary wheel  62  may be located to be deployed inside a perimeter of the base  14  and/or within a support wheel perimeter defined by the swivel axes  52  of the support wheels  50 . In some versions, such as those employing a single auxiliary wheel  62 , the auxiliary wheel  62  may be located near a center of the support wheel perimeter, or offset from the center. In this case, the auxiliary wheel  62  may also be referred to as a fifth wheel. In some versions, the auxiliary wheel  62  may be disposed along the support wheel perimeter or outside of the support wheel perimeter. In the version shown, the auxiliary wheel  62  has a diameter larger than a diameter of the support wheels  50 . In some versions, the auxiliary wheel  62  may have the same or a smaller diameter than the support wheels  50 . 
     In the version shown in  FIG.  3   , the base  14  comprises a first cross-member  70  and a second cross-member  72 . The auxiliary wheel assembly  60  is disposed between and coupled to the cross-members  70 ,  72 . The auxiliary wheel assembly  60  comprises a first auxiliary wheel frame  74  coupled to and arranged to articulate (e.g. pivot) relative to the first cross-member  70 . The auxiliary wheel assembly  60  further comprises a second auxiliary wheel frame  76  pivotably coupled to the first auxiliary wheel frame  74  and the second cross-member  72 . The second auxiliary wheel frame  76  is arranged to articulate and translate relative to the second cross-member  72 . 
     In the version shown in  FIGS.  2 - 3   , the auxiliary wheel assembly  60  comprises an auxiliary wheel drive system  78  (described in more detail below) operatively coupled to the auxiliary wheel  62 . The auxiliary wheel drive system  78  is configured to drive (e.g. rotate) the auxiliary wheel  62 . In the version shown, the auxiliary wheel drive system  78  comprises the motor  80  coupled to the auxiliary wheel  62  for rotating the auxiliary wheel  62  relative to the support structure and a motor control circuit  82  (shown in  FIGS.  9  and  10   ) that is configured to transmit control and power signals to the motor  80 . The motor control circuit  82  is also coupled to a power source  84  (shown schematically in  FIG.  9   ) for use in generating the control and power signals that are used to operate the motor  80 . In the version shown, the motor control circuit  82  includes a motor bridge circuit  86  that includes a plurality of field-effect transistor (FET) switches  88  (e.g. Q 1 , Q 2 , Q 3 , Q 4  shown in  FIG.  10   ) that are coupled to motor leads  92  of the motor  80 . In some versions, the motor  80  includes a 3-phase BLDC motor. In some versions, any suitable motor may be used with auxiliary wheel drive system  78 . 
     The auxiliary wheel drive system  78  also includes a gear train  94  that is coupled to the motor  80  and an axle of the auxiliary wheel  62 . In the version shown, the auxiliary wheel  62 , the gear train  94 , and the motor  80  are arranged and supported by the second auxiliary wheel frame  76  to articulate and translate with the second auxiliary wheel frame  76  relative to the second cross-member  72 . In some versions, the axle of the auxiliary wheel  62  is coupled directly to the second auxiliary wheel frame  76  and the auxiliary wheel drive system  78  drives the auxiliary wheel  62  in another manner. Electrical power is provided from the power source  84  to energize the motor  80 . The motor  80  converts electrical power from the power source  84  to torque supplied to the gear train  94 . The gear train  94  transfers torque to the auxiliary wheel  62  to rotate the auxiliary wheel  62 . 
     In the version shown, the auxiliary wheel actuator  64  is a linear actuator comprising a housing  96  and a drive rod  98  extending from the housing  96 . The drive rod  98  has a proximal end received in the housing  96  and a distal end spaced from the housing  96 . The distal end of the drive rod  98  is configured to be movable relative to the housing  96  to extend and retract an overall length of the auxiliary wheel actuator  64 . In the version shown, the auxiliary wheel assembly  60  also comprises a biasing device such as a spring cartridge  100  to apply a biasing force. Operation of the auxiliary wheel actuator  64  and the spring cartridge  100  to retract/deploy the auxiliary wheel  62  is described in U.S. patent application Ser. No. 16/690,217, filed on Nov. 21, 2019, entitled, “Patient Transport Apparatus With Controlled Auxiliary Wheel Deployment,” which is hereby incorporated herein by reference. 
     Referring to  FIGS.  4  and  5   , when moving to the retracted position  68 , auxiliary wheel actuator  64  retracts the drive rod  98  into the housing  96  to move the auxiliary wheel  62  from the deployed position  66  to the retracted position  68 . When moving to the deployed position  66 , auxiliary wheel actuator  64  extends the drive rod  98  from the housing  96  to move the auxiliary wheel  62  from the retracted position  68  to the deployed position  66 . Various linkages are contemplated for such movement, including those disclosed in U.S. patent application Ser. No. 16/690,217, filed on Nov. 21, 2019, entitled, “Patient Transport Apparatus With Controlled Auxiliary Wheel Deployment,” which is incorporated herein by reference. In some versions, the housing  96  of the auxiliary wheel actuator  64  may be fixed to the cross member  70  and directly connected to the auxiliary wheel  62  to directly retract/deploy the auxiliary wheel  62 . Other configurations are also contemplated. 
     In some versions, the auxiliary wheel assembly  60  comprises an auxiliary wheel brake actuator  102  (shown schematically in  FIG.  8   ) operably coupled to the auxiliary wheel  62  for braking the auxiliary wheel  62 . The auxiliary wheel brake actuator  102  may comprise a brake member  104  coupled to the base  14  and movable between a braked position engaging the auxiliary wheel  62  to brake the auxiliary wheel  62  and a released position permitting the auxiliary wheel  62  to rotate. 
     In the version shown, the auxiliary wheel assembly  60  includes an auxiliary wheel assembly control circuit  106  (see  FIGS.  9  and  10   ) that is coupled to the auxiliary wheel actuator  64 , the auxiliary wheel drive system  78 , the auxiliary wheel brake actuator  102 , and a power supply  84  for controlling operation of the auxiliary wheel assembly  60 . In some versions, the power supply  84  may include a pair of rechargeable  12 -volt batteries for providing electrical power to the auxiliary wheel assembly  60 . In some versions, the power supply  84  may include one or more batteries that may be rechargeable and/or non-rechargeable and may be rated for use at voltages other than  12 -volts. In some versions, as shown in  FIG.  9   , the auxiliary wheel assembly control circuit  106  includes a printed circuit board  108  mounted to the base  14  and having a user interface control unit  110 , a brake control unit  112 , an auxiliary wheel actuator control unit  114 , and an auxiliary wheel control unit  116  mounted thereon. The auxiliary wheel assembly control circuit  106  may also include one or more auxiliary wheel position sensors  118 , one or more auxiliary wheel speed sensors  120  (shown in  FIG.  8   ), an override switch  122  operable to disconnect power to the motor  80 , and a circuit breaker  124  coupled to the power supply  84 . 
     In some versions, the auxiliary wheel assembly control circuit  106  includes an electrical current sense circuit  126  that is configured to sense the electrical current drawn by the motor  80  from the power supply  84 . The electrical current sense circuit  126  may also be configured to sense an electrical current through motor phase windings of the motor  80 . In addition, the electrical current sense circuit  126  may be configured to sense the electrical current drawn by the auxiliary wheel brake actuator  102 . 
     The user interface control unit  110  is configured to transmit and receive instructions from the user interface  40  to enable a user to operate the auxiliary wheel assembly  60  with the user interface  40 . The auxiliary wheel control unit  116  is configured to control the operation of the auxiliary wheel drive system  78  based on signals received from the user interface  40  via the user interface control unit  110 . The brake control unit  112  is configured to operate the auxiliary wheel brake actuator  102  for braking the auxiliary wheel  62 , or may control another electronic braking system on the patient support apparatus  10 , such as one for the support wheels  50 . The auxiliary wheel actuator control unit  114  is configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  between the deployed and retracted positions. The auxiliary wheel position sensor  118  is configured to sense a position of the auxiliary wheel actuator  64  relative to the intermediate frame  16  or to the base  14  of the support structure  12 . In some versions, the auxiliary wheel position sensor  118  may include a mid-switch that is configured to detect a position of the auxiliary wheel  62  in the deployed position  66 , the retracted position  68 , and any intermediate position between the deployed position  66  and the retracted position  68 . In s 
     In some versions, the auxiliary wheel position sensor  118  may be configured to read off a cam surface (not shown) and indicates when the auxiliary wheel  62  is in a specific position between fully deployed and fully retracted. In some versions, two or more limit switches, optical sensors, hall-effect sensors, or other types of sensors may be used to detect the current position of the auxiliary wheel  62 . 
     The auxiliary wheel speed sensor  120  is configured to sense a rotational speed of the auxiliary wheel. In some versions, the auxiliary wheel speed sensor  120  may include one or more hall effect devices that are configured to sense rotation of the motor  80  (e.g., the motor shaft). The auxiliary wheel speed sensor  120  may also be used to detect a rotation of the auxiliary wheel  62  for use in determining whether the auxiliary wheel  62  is in a stop position and is not rotating. The auxiliary wheel speed sensor  120  may also be any other suitable sensor for measuring wheel speed, such as an optical encoder. 
     The override switch  122  is configured to disconnect power to the drive motor  80  to enable the auxiliary wheel  62  to rotate more freely. It should be appreciated that in some versions, such as that shown in  FIG.  9   , when power to the drive motor  80  is disconnected, frictional forces may still be present between the drive motor  80  and auxiliary wheel  62  by virtue of the gear train  94  such that rotation of the auxiliary wheel  62  is at least partially inhibited by the gear train  94 . Depending on the nature of the gear train  94 , the torque required to overcome such frictional forces vary. In some versions, the gear train  94  may be selected to minimize the torque required to manually drive the auxiliary wheel  62 . In some versions, a clutch may be employed between the auxiliary wheel  62  and the gear train  94  that is operated to disconnect the gear train  94  from the auxiliary wheel  62  when the override switch  122  is activated. In some versions, the drive motor  80  may directly drive the auxiliary wheel  62  (e.g., without a gear train), in which case, the auxiliary wheel  62  may rotate freely when power to the drive motor  80  is disconnected. If the auxiliary wheel  62  remains stuck in the deployed position or an intermediate position, the auxiliary wheel assembly control circuit  106  may operate the override switch  122  to disconnect power to the drive motor  80  and allow the auxiliary wheel  62  to rotate more freely. The circuit breaker  124  is configured to trip if an accidental electrical current spike is detected. In addition, the circuit breaker  124  may be switched to an “off” position to disconnect the power supply  84  to save battery life for storage and shipping. 
     Although exemplary versions of an auxiliary wheel assembly  60  is described above and shown in the drawings, it should be appreciated that other configurations employing an auxiliary wheel actuator  64  to move the auxiliary wheel  62  between the retracted position  68  and deployed position  66  are contemplated. 
     In the version shown in  FIG.  6   , the auxiliary wheel drive system  78  is configured to drive (e.g. rotate) the auxiliary wheel  62  in response to a throttle  128  operable by the user. As is described in greater detail below in connection with  FIGS.  6 - 7 F , the throttle  128  is operatively attached to the first handle  42  in the illustrated version to define a throttle assembly  130 . 
     In some versions, such as those shown in  FIGS.  6 - 7 F , one or more user interface sensors  132  (e.g., capacitive sensors or the like) are coupled to the first handle  42  to determine engagement by the user and generate a signal responsive to touch (e.g. hand placement/contact) of the user. The one or more user interface sensors  132  are operatively coupled to the auxiliary wheel actuator  64  to control movement of the auxiliary wheel  62  between the deployed position  66  and the retracted position  68 . Operation of the auxiliary wheel actuator  64  in response to the user interface sensor  132  is described in more detail below. In some versions, the user interface sensor  132  is coupled to another portion of the patient support apparatus  10 , such as another user interface  40 . 
     In some versions, such as is depicted in  FIG.  6   , engagement features or indicia  134  are located on the first handle  42  to indicate to the user where the user&#39;s hands may be placed on a particular portion of the first handle  42  for the user interface sensor  132  to generate the signal indicating engagement by the user. For instance, the first handle  42  may comprise embossed or indented features to indicate where the user&#39;s hand should be placed. In some versions, the indicia  134  comprises a film, cover, or ink disposed at least partially over the first handle  42  and shaped like a handprint to suggest the user&#39;s hand should match up with the handprint for the user interface sensor  132  to generate the signal. In still other versions, the shape of the user interface sensor  132  acts as the indicia  134  to indicate where the user&#39;s hand should be placed for the user interface sensor  132  to generate the signal. In some versions (not shown), the patient support apparatus  10  does not comprise a user interface sensor  132  operatively coupled to the auxiliary wheel actuator  64  for moving the auxiliary wheel  62  between the deployed position  66  and the retracted position  68 . Instead, a user input device is operatively coupled to the auxiliary wheel actuator  64  for the user to selectively move the auxiliary wheel  62  between the deployed position  66  and the retracted position  68 . In some versions, both the user interface sensor  132  and the user input device are employed. 
     Referring now to  FIGS.  7 A- 7 F , the throttle  128  is illustrated in various positions. In  FIGS.  7 A and  7 D , the throttle is in a neutral throttle position N. The throttle  128  is movable in a first direction  136  (also referred to as a “forward direction”) relative to the neutral throttle position N and a second direction  138  (also referred to as a “backward direction”) relative to the neutral throttle position N opposite the first direction  136 . As will be appreciated from the subsequent description below, the auxiliary wheel drive system  78  drives the auxiliary wheel  62  in a forward direction when the throttle  128  is moved in the first direction  136 , and in a rearward direction opposite the forward direction when the throttle  128  is moved in the second direction  138 . When the throttle  128  is disposed in the neutral throttle position N, as shown in  FIG.  7 A  (see also  FIG.  7 D ), the auxiliary wheel drive system  78  does not drive the auxiliary wheel  62  in either direction. In many versions, the throttle  128  is spring-biased to the neutral throttle position N. 
     As is described in greater detail below, when the throttle  128  is in the neutral throttle position N, the auxiliary wheel drive system  78  may permit the auxiliary wheel  62  to be manually rotated as a result of a user pushing on the first handle  42  or another user interface  40  to push the patient support apparatus  10  in a desired direction. In other words, the motor  80  may be unbraked and capable of being driven manually. 
     It should be appreciated that the terms forward and backward are used to describe opposite directions that the auxiliary wheel  62  rotates to move the base  14  along the floor surface. For instance, forward refers to movement of the patient support apparatus  10  with the foot end leading and backward refers to the head end leading. In some versions, backward rotation moves the patient support apparatus  10  in the direction with the foot end leading and forward rotation moves the patient support apparatus  10  in the direction with the head end leading. In such versions, the handles  42 ,  44  may be located at the foot end. 
     Referring to  FIG.  6   , the location of the throttle  128  relative to the first handle  42  permits the user to simultaneously grasp the handle body  48  of the first handle  42  and rotate the throttle  128  about the central axis C defined by the inner support  46 . This allows the user interface sensor  132 , which is operatively attached to the handle body  48  in the illustrated version, to generate the signal responsive to touch by the user while the user moves the throttle  128 . In some versions, the throttle  128  comprises one or more throttle interfaces (e.g., ridges, raised surfaces, grip portions, etc.) for assisting the user with rotating the throttle  128 . 
     In some versions, the throttle assembly  130  may comprise one or more auxiliary user interface sensors  140  (shown in phantom), in addition to the user interface sensor  132 , to determine engagement by the user. In the version illustrated in  FIG.  6   , the auxiliary user interface sensors  140  are realized as throttle interface sensors respectively coupled to each of the throttle interfaces and operatively coupled to the auxiliary wheel drive system  78  (e.g., via electrical communication). The throttle interface sensors are likewise configured to determine engagement by the user and generate a signal responsive to touch of the user&#39;s thumb and/or fingers. When the user is touching one or more of the throttle interfaces, the throttle interface sensors generate a signal indicating the user is currently touching one or more of the throttle interfaces and movement of the throttle  128  is permitted to cause rotation of the auxiliary wheel  62 . When the user is not touching any of the throttle interfaces, the throttle interface sensors generate a signal indicating an absence of the user&#39;s thumb and/or fingers on the throttle interfaces and movement of the throttle  128  is restricted from causing rotation of the auxiliary wheel  62 . The throttle interface sensors mitigate the chances for inadvertent contact with the throttle  128  to unintentionally cause rotation of the auxiliary wheel  62 . The throttle interface sensors may be absent in some versions. As is described in greater detail below in connection with  FIG.  6   , other types of auxiliary user interface sensors  140  are contemplated by the present disclosure besides the throttle interface sensors described above. Furthermore, it will be appreciated that certain versions may comprise both the user interface sensor  132  and the auxiliary user interface sensor  140  (e.g., one or more throttle interface sensors), whereas some versions may comprise only one of either the user interface sensor  132  and the auxiliary user interface sensor  140 . Various visual indicators  142  (e.g., LEDs, displays, illuminated surfaces, etc.) may also be present on the throttle  128  or the handle body  48  to indicate a current operational mode, speed, state (deployed/retracted), condition, etc. of the auxiliary wheel assembly  60 . Other configurations are contemplated. 
     Referring again to  FIGS.  7 A- 7 F , various positions of the throttle  128  are shown. The throttle  128  is movable relative to the first handle  42  to a first throttle position, a second throttle position, and intermediate throttle positions therebetween. The throttle  128  is operable between the first throttle position and the second throttle position to adjust the rotational speed of the auxiliary wheel. 
     In some versions, the first throttle position corresponds with the neutral throttle position N (shown in  FIG.  7 A and  7 D ) and the auxiliary wheel  62  is at rest. The second throttle position corresponds with a maximum forward throttle position  148  (shown in  FIG.  7 C ) of the throttle  128  moved in the first direction  136 . One intermediate throttle position corresponds with an intermediate forward throttle position  150  (shown  FIG.  7 B ) of the throttle  128  between the neutral throttle position N and the maximum forward throttle position  148 . Here, both the maximum forward throttle position  148  and the intermediate forward throttle position  150  may also be referred to as forward throttle positions. 
     In other cases, the second throttle position corresponds with a maximum backward throttle position  152  (shown in  FIG.  7 F ) of the throttle  128  moved in the second direction  138 . Here, one intermediate throttle position corresponds with an intermediate backward throttle position  154  (shown in  FIG.  7 E ) of the throttle  128  between the neutral throttle position N and the maximum backward throttle position  152 . Here, both the maximum backward throttle position  152  and the intermediate backward throttle position  154  may also be referred to as backward throttle positions. 
     In the versions shown, the throttle  128  is movable from the neutral throttle position N to one or more operating throttle positions  146  between, and including, the maximum backward throttle position  152  and the maximum forward throttle position  148 , including a plurality of forward throttle positions between the neutral throttle position N and the maximum forward throttle position  148  as well as a plurality of backward throttle positions between the neutral throttle position N and the maximum backward throttle position  152 . The configuration of the throttle  128  and the throttle assembly  130  will be described in greater detail below. 
       FIG.  8    illustrates a control system  160  of the patient support apparatus  10 . The control system  160  comprises a controller  162  coupled to, among other components, the user interface sensors  132 , the throttle assembly  130 , the auxiliary interface sensors  140 , the auxiliary wheel assembly control circuit  106 , the auxiliary wheel actuator  64 , the auxiliary wheel drive system  78 , the support wheel brake actuator  56 , the auxiliary wheel brake actuator  102 , and the lift assembly  24 . 
     The controller  162  is configured to operate the auxiliary wheel actuator  64  and the auxiliary wheel drive system  78 . The controller  162  may also be configured to operate the support wheel brake actuator  56 , the bed lift actuator  26  to operate the lift assembly  24 , and the auxiliary wheel brake actuator  102 . The controller  162  is generally configured to detect the signals from the sensors and may be further configured to operate the auxiliary wheel actuator  64  responsive to the user interface sensor  132  generating signals responsive to touch. 
     The controller  162  comprises one or more microprocessors  164  that are coupled to a memory device  166 . The memory device  166  may be any memory device suitable for storage of data and computer-readable instructions. For example, the memory device  166  may be a local memory, an external memory, or a cloud-based memory embodied as random access memory (RAM), non-volatile RAM (NVRAM), flash memory, or any other suitable form of memory. 
     The one or more microprocessors  164  are programmed for processing instructions or for processing algorithms stored in memory  166  to control operation of patient support apparatus  10 . For example, the one or more microprocessors  164  may be programmed to control the operation of the auxiliary wheel assembly  60 , the support wheel brake actuator  56 , and the lift assembly  24  based on user input received via the user interfaces  40 . Additionally or alternatively, the controller  162  may comprise one or more 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. For example, in some versions, the instructions and/or algorithms executed by the controller  162  may be performed in a state machine configured to execute the instructions and/or algorithms. The controller  162  may be carried on-board the patient support apparatus  10 , or may be remotely located. In some versions, the controller  162  may be mounted to the base  14 . 
     The controller  162  comprises an internal clock to keep track of time. In some versions, the internal clock may be realized as a microcontroller clock. The microcontroller clock may comprise a crystal resonator; a ceramic resonator; a resistor, capacitor (RC) oscillator; or a silicon oscillator. Examples of other internal clocks other than those disclosed herein are fully contemplated. The internal clock may be implemented in hardware, software, or both. 
     In some versions, the memory  166 , microprocessors  164 , and microcontroller clock cooperate to send signals to and operate the lift assembly  24  and the auxiliary wheel assembly  60  to meet predetermined timing parameters. These predetermined timing parameters are discussed in more detail below and are referred to as predetermined durations. 
     The controller  162  may comprise one or more subcontrollers configured to control the lift assembly  24  and the auxiliary wheel assembly  60 , or one or more subcontrollers for each of the actuators  26 ,  56 ,  64 ,  102 , or the auxiliary wheel drive system  78 . In some cases, one of the subcontrollers may be attached to the intermediate frame  16  with another attached to the base  14 . Power to the actuators  26 ,  56 ,  64 ,  102 , the auxiliary wheel drive system  78 , and/or the controller  162  may be provided by a battery power supply. 
     The controller  162  may communicate with auxiliary wheel assembly control circuit  106 , the actuators  26 ,  56 ,  64 ,  102 , and the auxiliary wheel drive system  78  via wired or wireless connections. The controller  162  generates and transmits control signals to the auxiliary wheel assembly control circuit  106 , the actuators  26 ,  56 ,  64 ,  102 , and the auxiliary wheel drive system  78 , or components thereof, to operate the auxiliary wheel assembly  60  and lift assembly  24  to perform one or more desired functions. 
     In some versions, and as is shown in  FIG.  8   , the control system  160  comprises an auxiliary wheel position indicator  168  to display a current position of the auxiliary wheel  62  between or at the deployed position  66  and the retracted position  68 , and the one or more intermediate positions. In some versions, the auxiliary wheel position indicator  168  comprises a light bar that lights up completely when the auxiliary wheel  62  is in the deployed position  66  to indicate to the user that the auxiliary wheel  62  is ready to be driven. Likewise, the light bar may be partially lit up when the auxiliary wheel  62  is in a partially retracted position and the light bar may be devoid of light when the auxiliary wheel  62  is in the fully retracted position  68 . Other visualization schemes are possible to indicate the current position of the auxiliary wheel  62  to the user, such as other graphical displays, text displays, and the like. Such light indicators or displays are coupled to the controller  162  to be controlled by the controller  162  based on the detected position of the auxiliary wheel  62  as described below. Such indicators may be located on the handle  42  or any other suitable location. 
     In the illustrated version, the control system  160  comprises a user feedback device  170  coupled to the controller  162  to indicate to the user one of a current speed, a current range of speeds, a current throttle position, and a current range of throttle positions. The user feedback device  170  may be similar to the visual indicators  142  described above, and also provide feedback regarding a current operational mode, current state, condition, etc. of the auxiliary wheel assembly  60 . The user feedback device  170  may be placed at any suitable location on the patient support apparatus  10 . In some versions, the user feedback device  170  comprises one of a visual indicator, an audible indicator, and a tactile indicator. 
     The actuators  26 ,  56 ,  64 ,  102  and the auxiliary wheel drive system  78  described above may comprise one or more of an electric actuator, a hydraulic actuator, a pneumatic actuator, combinations thereof, or any other suitable types of actuators, and each actuator may comprise more than one actuation mechanism. The actuators  26 ,  56 ,  64 ,  102  and the auxiliary wheel drive system  78  may comprise one or more of a rotary actuator, a linear actuator, or any other suitable actuators. The actuators  26 ,  56 ,  64 ,  102  and the auxiliary wheel drive system  78  may comprise reversible DC motors, or other types of motors. A suitable actuator for the auxiliary wheel actuator  64  comprises a linear actuator supplied by LINAK A/S located at Smedevenget 8, Guderup, DK-6430, Nordborg, Denmark. It is contemplated that any suitable actuator capable of deploying the auxiliary wheel  62  may be utilized. 
     The controller  162  is generally configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the deployed position  66  responsive to detection of the signal from the user interface sensor  132 . When the user touches the first handle  42 , the user interface sensor  132  generates a signal indicating the user is touching the first handle  42  and the controller operates the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the deployed position  66 . In some versions, the controller  162  is further configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the retracted position  68  responsive to the user interface sensor  132  generating a signal indicating the absence of the user touching the first handle  42 . 
     In some versions, the controller  162  is configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the deployed position  66  responsive to detection of the signal from the user interface sensor  132  indicating the user is touching the first handle  42  for a first predetermined duration greater than zero seconds. Delaying operation of auxiliary wheel actuator  64  for the first predetermined duration after the controller  162  detects the signal from the sensor  132  indicating the user is touching the first handle  42  mitigates chances for inadvertent contact to result in operation of the auxiliary wheel actuator  64 . In some versions, the controller  162  is configured to initiate operation of the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the deployed position  66  immediately after (e.g., less than  1  second after) the user interface sensor  132  generates the signal indicating the user is touching the first handle  42 . 
     In some versions, the controller  162  is further configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the retracted position  68 , or to the one or more intermediate positions, responsive to the user interface sensor  132  generating a signal indicating the absence of the user touching the first handle  42 . In some versions, the controller  162  is configured to operate the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the retracted position  68 , or to the one or more intermediate positions, responsive to the user interface sensor  132  generating the signal indicating the absence of the user touching the first handle  42  for a predetermined duration greater than zero seconds. In some versions, the controller  162  is configured to initiate operation of the auxiliary wheel actuator  64  to move the auxiliary wheel  62  to the retracted position  68 , or to the one or more intermediate positions, immediately after (e.g., less than  1  second after) the user interface sensor  132  generates the signal indicating the absence of the user touching the first handle  42 . 
     In versions including the support wheel brake actuator  56  and/or the auxiliary wheel brake actuator  102 , the controller  162  may also be configured to operate one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  between the braked position and the released position. In some versions, the controller  162  is configured to operate one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the braked position responsive to the user interface sensor  132  generating the signal indicating the absence of the user touching the first handle  42  for a predetermined duration. In some versions, the predetermined duration for moving brake members  58 ,  104  to the braked position is greater than zero seconds. In some versions, the controller  162  is configured to initiate operation of one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the braked position immediately after (e.g., less than  1  second after) the user interface sensor  132  generates the signal indicating the absence of the user touching the first handle  42 . 
     The controller  162  is configured to operate one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the released position responsive to the user interface sensor  132  generating the signal indicating the user is touching the first handle  42  for a predetermined duration. In some versions, the predetermined duration for moving brake members  58 ,  104  to the released position is greater than zero seconds. In some versions, the controller  162  is configured to initiate operation of one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the released position immediately after (e.g., less than  1  second after) the user interface sensor  132  generates the signal indicating the user is touching the first handle  42 . 
     In some versions, the auxiliary wheel position sensor  118  (also referred to as a “position sensor”) is coupled to the controller  162  and generates signals detected by the controller  162 . The auxiliary wheel position sensor  118  is coupled to the controller  162  and the controller  162  is configured to detect the signals from the auxiliary wheel position sensor  118  to detect positions of the auxiliary wheel  62  as the auxiliary wheel  62  moves between the deployed position  66 , the one or more intermediate positions, and the retracted position  68 . 
     In some versions, the controller  162  is configured to operate one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the released position responsive to detection of the auxiliary wheel  62  being in the deployed position  66 . In some versions, the controller  162  is configured to operate one or both brake actuators  56 ,  102  to move their respective brake members  58 ,  104  to the released position responsive to detection of the auxiliary wheel  62  being in a position between the deployed position  66  and the retracted position  68  (e.g., the one or more intermediate positions). 
     In some versions, an auxiliary wheel load sensor  172  is coupled to the auxiliary wheel  62  and the controller  162 , with the auxiliary wheel load sensor  172  configured to generate a signal responsive to a force of the auxiliary wheel  62  being applied to the floor surface. In some versions, the auxiliary wheel load sensor  172  is coupled to the axle of the auxiliary wheel  62 . The controller  162  is configured to detect the signal from the auxiliary wheel load sensor  172  and, in some versions, is configured to operate the auxiliary wheel drive system  78  to drive the auxiliary wheel  62  and move the base  14  relative to the floor surface responsive to the controller  162  detecting signals from the auxiliary wheel load sensor  172  indicating the auxiliary wheel  62  is in the partially deployed position engaging the floor surface when a force of the auxiliary wheel  62  on the floor surface exceeds an auxiliary wheel load threshold. This allows the user to drive the auxiliary wheel  62  before the auxiliary wheel  62  reaches the fully deployed position without the auxiliary wheel  62  slipping against the floor surface. 
     In some versions, a patient load sensor  174  is coupled to the controller  162  and to one of the base  14  and the intermediate frame  16 . The patient load sensor  174  generates a signal responsive to weight, such as a patient being disposed on the base  14  and/or the intermediate frame  16 . The controller  162  is configured to detect the signal from the patient load sensor  174 . Here, the auxiliary wheel load threshold may change based on detection of the signal generated by the patient load sensor  174  to compensate for changes in weight disposed on the intermediate frame  16  and/or the base  14  to mitigate probability of the auxiliary wheel  62  slipping when the controller  162  operates the auxiliary wheel drive system  78 . 
     In some versions, a patient support apparatus leveling sensor  176  is coupled to the controller  162  and to one of the base  14  and the intermediate frame  16 . The leveling sensor  176  generates a signal responsive to the horizontal orientation of the base  14 . The controller  162  is configured to detect the horizontal orientation of the patient support apparatus  10  based on signals received from the leveling sensor  176  and determine whether the patient support apparatus  10  is positioned on a ramp, an inclined floor surface, a declined floor surface, and/or a substantially flat floor surface. 
     In some versions, a velocity sensor  177  is coupled to the controller  162  and to one of the base  14  and the intermediate frame  16 . In some configurations, the velocity sensor  177  may be wheel speed sensor  120  or a separate sensor. The velocity sensor  177  generates a signal indicative of the rate and amplitude of travel of the patient support apparatus  10  relative to the floor surface. In various configurations, the velocity sensor  177  may sense actual speed of the patient support apparatus  10 , changes in commanded speed of the patient support apparatus  10 , and/or ground speed. 
     In some versions, a floor sensor  179  is coupled to the controller  162  and is operatively attached to the support structure  12  to determine a distance to the floor surface  220 . In some versions, the floor sensor  179  is configured as a discrete component that is coupled to the base  14  to determine the distance to the floor surface  220  from a position adjacent to the drive member  62  (e.g., an ultrasonic distance sensor). In some versions, the floor sensor  179  may be realized as a “feeler” wheel/roller arranged at a leading edge ahead of support wheels  50  and/or at a trailing edge behind support wheels  50  which engages against and moves relative to the base  14  in response to changes in the floor surface  220  (e.g., when approaching an incline or a flat surface). In some versions, the floor sensor  179  could be defined by the wheel position sensor  118 . Other configurations are contemplated. 
     Each of the sensors described above may comprise one or more of a force sensor, a load cell, a speed radar, an optical sensor, an electromagnetic sensor, an accelerometer, a potentiometer, an infrared sensor, a capacitive sensor, an ultrasonic sensor, a limit switch, a level sensor, a 3-Axis orientation sensor, or any other suitable sensor for performing the functions recited herein. Other configurations are contemplated. 
     In the illustrated versions, where the auxiliary wheel drive system  78  comprises the motor  80  and the gear train  94 , the controller  162  is configured to operate the motor  80  to drive the auxiliary wheel  62  and move the base  14  relative to the floor surface responsive to detection of the auxiliary wheel  62  being in the at least partially deployed position as detected by virtue of the controller  162  detecting the motor  80  drawing electrical power from the power source  84  above an auxiliary wheel power threshold, such as by detecting a change in current draw of the motor  80  associated with the auxiliary wheel  62  being in contact with the floor surface. In this case, detection of the current drawn by the motor  80  being above a threshold operates as a form of auxiliary wheel load sensor  172 . 
     In some versions, when power is not supplied to the motor  80  from the power source  84 , the motor  80  acts as a brake to decelerate the auxiliary wheel  62  through the gear train  94 . In some versions, the auxiliary wheel  62  is permitted to rotate relatively freely when power is not supplied to the motor  80 . 
     The controller  162  may be programmed to execute the algorithms operating the auxiliary wheel assembly  60  in a plurality of operating modes, as described in U.S. patent application Ser. No. 17/131,947, filed on Dec. 23, 2020, entitled, “Patient Transport Apparatus With Controlled Auxiliary Wheel Speed,” which is hereby incorporated herein by reference. For example, the controller  162  may be programmed to operate the auxiliary wheel assembly  60  in a drive mode, a free wheel mode, a coast mode, a free wheel speed limiting mode, and a drag mode. The controller  162  may also be programmed to quickly turn the modes on/off and quickly toggle between modes in certain scenarios. 
     The controller  162  may additionally be programmed to detect a position of the throttle assembly  130  determine a desired rotational speed value associated with a current operating throttle position, determine a current rotational speed of the auxiliary wheel  62 , select an acceleration rate based on the current rotational speed of the auxiliary wheel  62 , generate an output signal based on the selected acceleration rate, and transmit the generated output signal to the motor control circuit  82  to operate the motor  80  to rotate the auxiliary wheel  62  at the selected acceleration rate, as described in U.S. patent application Ser. No. 17/132,009, filed on Dec. 23, 2020, entitled, “Patient Transport Apparatus With Auxiliary Wheel Control Systems,” which is hereby incorporated herein by reference. 
     Referring to  FIG.  11   , an elevation view of the auxiliary wheel assembly shown in  FIG.  2    is shown, according to an alternative version. In the versions shown, the base  14  includes a support assembly  200  that includes a forward support member  202 , a rear support member  204 , and a pair of opposing side support members  206 ,  208 . The side support members  206 ,  208  extend between the forward support member  202  and the rear support member  204  and are orientated parallel to the longitudinal axis  18 . 
     Referring to  FIGS.  11 - 17 C , an auxiliary wheel system  210  is coupled to the base  14 . The auxiliary wheel system  210  influences motion of the patient support apparatus  10  during transportation over the floor surface. 
     Referring to  FIGS.  2  and  11   , the auxiliary wheel system  210  includes a support frame  212  that is coupled to the base  14 , an auxiliary wheel assembly  214  that is coupled to the support frame  212  and arranged to articulate (e.g. pivot) with respect to the support frame  212 , and an actuator assembly  216  that is coupled the support frame  212  and the auxiliary wheel assembly  214 . The auxiliary wheel assembly  214  includes an auxiliary wheel  218  that is configured to influence motion of the patient support apparatus  10  over a floor surface  220 . The auxiliary wheel assembly  214  is positionable to a deployed position  222  (shown in  FIG.  16 A ) with the auxiliary wheel  218  engaging the floor surface  220 , and a stowed position  224  (shown in  FIG.  16 B ) with the auxiliary wheel  218  spaced a vertical distance  226  from the floor surface  220 . The actuator assembly  216  is coupled to the support frame  212  and to the auxiliary wheel assembly  214 . 
     Referring to  FIGS.  11 ,  12 ,  13 , and  14   , the actuator assembly  216  includes a lift actuator  228  and a spring cartridge assembly  230 . The lift actuator  228  is operable to move the auxiliary wheel  218  to the deployed position  222  engaging the floor surface and to the stowed position  224  spaced away from and out of contact with the floor surface. The spring cartridge assembly  230  is coupled between the lift actuator  228  and the auxiliary wheel  218 , and is configured to transfer a force from the lift actuator  228  to the auxiliary wheel  218  to facilitate moving the auxiliary wheel  218  to the deployed position  222  and to the stowed position  224 . In addition, the spring cartridge assembly  230  is configured to bias the auxiliary wheel  218  outwardly from the support frame  212  and towards the deployed position  222 , and to allow a vertical movement of auxiliary wheel  218  with respect to the support frame  212  with the auxiliary wheel assembly  214  in the deployed position  222 . 
     In the versions shown, the lift actuator  228  is positionable between an extended position  232  (shown in Figurel 6 A) and a retracted position  234  (shown in  FIG.  16 B ). For example, a movement of the lift actuator  228  towards the extended position  232  causes the spring cartridge assembly  230  to move the auxiliary wheel  218  towards the deployed position  222 . A movement of the lift actuator  228  towards the retracted position  234  causes the spring cartridge assembly  230  to move the auxiliary wheel  218  towards the stowed position  224 . In addition, the spring cartridge assembly  230  is configured to allow vertical movement of the auxiliary wheel  218  with the lift actuator  228  in the extended position  232 . 
     The auxiliary wheel  218  influences motion of the patient support apparatus  10  during transportation over the floor surface when the auxiliary wheel  218  is in the deployed position  222 . In some versions, the auxiliary wheel assembly  214  comprises an additional auxiliary wheel movable with the auxiliary wheel  218  between the deployed position  222  and stowed position  224  via the actuator assembly  216 . 
     By deploying the auxiliary wheel  218  on the floor surface, the patient support apparatus  10  can be easily moved down long, straight hallways or around corners, owing to a non-swiveling nature of the auxiliary wheel  218 . When the auxiliary wheel  218  is stowed (see  FIG.  16 B ), the patient support apparatus  10  is subject to moving in an undesired direction due to uncontrollable swiveling of the support wheels  50 . For instance, during movement down long, straight hallways, the patient support apparatus  10  may be susceptible to “dog tracking,” which refers to undesirable sideways movement of the patient support apparatus  10 . Additionally, when cornering, without the auxiliary wheel  218  deployed, and with all of the support wheels  50  able to swivel, there is no wheel assisting with steering through the corner, unless one or more of the support wheels  50  are provided with steer lock capability and the steer lock is activated. 
     The auxiliary wheel  218  may be arranged parallel to the longitudinal axis  18  of the base  14 . Said differently, the auxiliary wheel  218  rotates about a rotational axis R (see  FIG.  11   ) oriented perpendicularly to the longitudinal axis  18  of the base  14  (albeit offset in some cases from the longitudinal axis  18 ). In the versions shown, the auxiliary wheel  218  is incapable of swiveling about a swivel axis. In other versions, the auxiliary wheel  218  may be capable of swiveling, but can be locked in a steer lock position in which the auxiliary wheel  218  is locked to solely rotate about the rotational axis R oriented perpendicularly to the longitudinal axis  18 . In still other versions, the auxiliary wheel  218  may be able to freely swivel without any steer lock functionality. 
     The auxiliary wheel  218  may be located to be deployed inside a perimeter of the base  14  and/or within a support wheel perimeter defined by the swivel axes  52  of the support wheels  50 . In some versions, such as those employing a single auxiliary wheel  218 , the auxiliary wheel  218  may be located near a center of the support wheel perimeter, or offset from the center. In this case, the auxiliary wheel  218  may also be referred to as a fifth wheel. In other versions, the auxiliary wheel  218  may be disposed along the support wheel perimeter or outside of the support wheel perimeter. In the versions shown, the auxiliary wheel  218  has a diameter larger than a diameter of the support wheels  50 . In other versions, the auxiliary wheel  218  may have the same or a smaller diameter than the support wheels  50 . 
     As the patient support apparatus  10  travels over an uneven floor surface, the spring cartridge assembly  230  allows the auxiliary wheel  218  to move vertically with respect to base  14 , and biases the auxiliary wheel  218  towards the floor surface with sufficient force to maintain traction between the floor surface and the auxiliary wheel  218 . In addition, the spring cartridge assembly  230  permits the auxiliary wheel  218  to move upward when encountering a high spot in the floor surface and to dip lower when encountering a low spot in the floor surface. 
     For example,  FIGS.  17 A- 17 C  illustrate a vertical movement of the auxiliary wheel  218  with the auxiliary wheel assembly  214  in the deployed position  222 . With the auxiliary wheel assembly  214  in the deployed position  222 , the spring cartridge assembly  230  biases the auxiliary wheel  218  towards the floor surface  220  such that the auxiliary wheel  218  is spaced a first vertical distance, V 1 , from the support frame  212 . In addition, the spring cartridge assembly  230  imparts sufficient downward force to the auxiliary wheel  218  to maintain sufficient traction between the auxiliary wheel  218  and the floor surface  220 . During operation, as the patient support apparatus  10  travels over an inclined floor surface  220  such as, for example, over a peak (e.g., during the transition onto a ramp to travel down the ramp, or during the transition off of a ramp when traveling up the ramp; see  FIG.  20 B ), the spring cartridge assembly  230  allows the auxiliary wheel  218  to move towards the support frame  212  and to a second vertical distance, V 2 , from the support frame  212  that is less than the first vertical distance, V 1 . In addition, as the patient support apparatus  10  travels over a declining floor surface  220  such as, for example, through a trough (e.g., during the transition onto a ramp to travel up the ramp, or during the transition off of a ramp when traveling down the ramp; see  FIG.  20 C ), the spring cartridge assembly  230  biases the auxiliary wheel  218  away from the support frame  212  and towards a third vertical distance, V 3 , from the support frame  212  that is greater than the first vertical distance, V 1 . By enabling the auxiliary wheel  218  to travel vertically with respect to the support frame  212  with the auxiliary wheel assembly  214  in the deployed position  222 , the spring cartridge assembly  230  facilitates maintaining sufficient traction between an uneven floor surface  220  and the auxiliary wheel  218  to enable the auxiliary wheel  218  to influence motion of the patient support apparatus  10  during operation. 
     Referring to  FIGS.  12 ,  13 , and  14   , in the versions shown, the support frame  212  includes a first cross-member  236  and a second cross-member  238 . The second cross-member  238  is spaced a distance from the first cross-member  236  along the longitudinal axis  18 . The first cross-member  236  and the second cross-member  238  are each coupled between the pair of opposing side support members  206 ,  208 . 
     In the versions shown, the auxiliary wheel assembly  214  also includes a crank shaft  240  and a wheel support frame  242 . The crank shaft  240  is coupled to the first cross-member  236  with a crank shaft bracket  246  that extends outwardly from an outer surface of the first cross-member  236 . The crank shaft  240  extends along a centerline axis  248  and is rotatably coupled to the first cross-member  236  such that the crank shaft  240  is rotatable about the centerline axis  248 . The wheel support frame  242  extends radially outwardly from the crank shaft  240  such that a rotation of the crank shaft  240  cause a rotation of the wheel support frame  242  about the centerline axis  248  of the crank shaft  240 . The wheel support frame  242  is coupled to the auxiliary wheel  218  such that a rotation of the crank shaft  240  causes a vertical movement of the auxiliary wheel  218 . The auxiliary wheel assembly  214  also includes a crank  250  that extends radially outwardly from the crank shaft  240  such that a rotation of the crank  250  causes a rotation of the crank shaft  240  about the centerline axis  248  of the crank shaft  240 . The crank  250  is coupled to the spring cartridge assembly  230  such that a movement of spring cartridge assembly  230  via the lift actuator  228  causes a rotation of the crank shaft  240 . 
     The spring cartridge assembly  230  includes a piston rod  252 , a cartridge housing  254 , and a compression spring  256 . The piston rod  252  is pivotably coupled to the crank  250  and the cartridge housing  254  is coupled to the lift actuator  228 . The cartridge housing  254  is movable with respect to the piston rod  252 . The compression spring  256  acts between the cartridge housing  254  and to the piston rod  252  such that a movement of the cartridge housing  254  causes a movement of the piston rod  252 . In addition, a movement of the piston rod  252  causes a movement of the crank  250  which in turn causing a rotation of the crank shaft  240  and wheel support frame  242 . 
     The piston rod  252  extends between a first rod end  258  and a second rod end  260 , and is at least partially positioned within the cartridge housing  254 . The cartridge housing  254  includes a plurality of sidewalls  262  extending between a first end  264  and a second end  266 . A guide plate  268  is coupled to the plurality of sidewalls  262  and is positioned at the first end  264  of the cartridge housing  254 . The guide plate  268  includes a rod opening  270  that is defined through the guide plate  268 . The rod opening  270  is sized and shaped to receive the piston rod  252  therethrough. The second rod end  260  extends through the rod opening  270 . The first rod end  258  is located at an enlarged head of the piston rod  252  that is sized larger than the rod opening  270  so that the guide plate  268  is able to abut the enlarged head when stowing the auxiliary wheel  218 . The enlarged head is pivotably coupled to the crank  250  via a fastening pin extending through the enlarged head and the crank  250 . The second rod end  260  is positioned with the cartridge housing  254  and extends toward the second end  266  of the cartridge housing  254 . The second rod end  260  is considered a free end, unconnected to any other structure. 
     The compression spring  256  extends between a first end  272  and a second end  274  and is positioned with the cartridge housing  254  such that the compression spring  256  surrounds a portion of the piston rod  252 . The compression spring  256  is configured to bias the cartridge housing  254  towards the first rod end  258 . The first end  272  of the compression spring  256  engages the guide plate  268  of the cartridge housing  254  and the second end  274  of the compression spring  256  acts against the piston rod  252  via a guide assembly  276  described below. 
     In the versions shown, the spring cartridge assembly  230  includes the guide assembly  276  that is coupled to the piston rod  252  and engages the compression spring  256 . The guide assembly  276  includes a guide ring  278  that is coupled to the piston rod  252  and engages the compression spring  256 . The guide ring  278  includes a pair of opposing positioning flanges  280  that extend outwardly from an outer surface of the guide ring  278 . Each sidewall  262  of the cartridge housing  254  includes a guide slot  282  that extends through the sidewall  262 . Each positioning flange  280  is inserted through a corresponding guide slot  282  to support the piston rod  252  from the cartridge housing  254 . Each positioning flange  280  is slideably engaged within the guide slot  282  to enable the cartridge housing  254  to move with respect to the piston rod  252 . In addition, the guide slots  282  are sized and shaped to allow a movement of the piston rod  252  with respect to the cartridge housing  254  with the lift actuator  228  in the extended position  232 . For example, the guide slot  282  includes a length that enables the guide ring  278  to slide along a length of the guide slot  282  to enable the piston rod  252  to translate relative to the cartridge housing  254 . 
     In some versions, the guide assembly  276  includes a biasing load adjustment assembly  284  for adjusting a load imparted by the compression spring  256 . In the illustrated version, the biasing load adjustment assembly  284  includes an adjustment member  285  (see  FIGS.  15 A and  15 B ) that is coupled to the piston rod  252  and engages the guide ring  278  for adjusting an operating length of the compression spring  256  to adjust a load imparted by the compression spring  256  onto the piston rod  252  and cartridge housing  254 . In addition, the biasing load adjustment assembly  284  enables a service technician to release the tension of the compression spring  256  thereby removing the biasing force on the auxiliary wheel  218  to enable the service technician to safely service the actuator assembly  216 . 
     For example, the piston rod  252  may include an outer surface having a threaded portion  283 . The adjustment member  285  may comprise a tensioning nut, threadably coupled to piston rod  252  along the threaded portion  283  such that a rotation of the tensioning nut with respect to the piston rod  252  adjusts the length of the compression spring  256 . For example, a rotation of the tensioning nut in a first rotational direction  287  moves the tensioning nut  285  and the guide ring  278  along the piston rod  252  in a first linear direction  289  that decreases the length of the compression spring  256  to preload a compressive force onto the compression spring  256 . A rotation of the tensioning nut  285  in a second opposite rotational direction  291  moves the tensioning nut  285  and the guide ring  278  along the piston rod  252  in a second linear direction  293  that increases the length of the compression spring  256  to reduce the compressive force of the compression spring  256 . In addition, during normal operation, the compression spring  256  is in compression in all positions. In order to service the actuator assembly  216 , the service technician may remove the compression on the compression spring  256  by loosening the tensioning nut  285 , thereby allowing the service technician to safely remove the crank  240  pin and service the actuator assembly  216 . 
     Referring to  FIGS.  16 A and  16 B , the actuator assembly  216  includes an actuator support bracket  286  that is hingedly coupled to the second cross-member  238 . The cartridge housing  254  is pivotably coupled to the actuator support bracket  286  via a fastening pin  288  inserted through the second end  266  of the cartridge housing  254  and the actuator support bracket  286 . The lift actuator  228  is coupled to the actuator support bracket  286  such that a movement of the lift actuator  228  causes a movement of the actuator support bracket  286  and the cartridge housing  254 . 
     In the versions shown, the lift actuator  228  is a linear actuator that includes an actuator housing  290  and an actuator rod  292 . The actuator rod  292  has a proximal end received in the actuator housing  290  and a distal end spaced from the actuator housing  290 . The distal end of the actuator rod  292  is configured to be movable relative to the actuator housing  290  to extend and retract an overall length of the lift actuator  228 . The actuator rod  292  is movable between the extended position  232  (shown in  FIG.  16 A ) with the actuator rod  292  extending outwardly from the actuator housing a first distance, and the retracted position  234  (shown in  FIG.  16 B ) with the actuator rod  292  extending outwardly from the actuator housing a second distance that is longer than the first distance. The actuator housing  290  is coupled to the first cross-member  236 . The actuator rod  292  is pivotably coupled to the actuator support bracket  286  with a fastening pin  294 . The support frame  212  includes an actuator support arm  296  that extends outwardly from the first cross-member  236 . The actuator support arm  296  is coupled to the actuator housing  290  to support the actuator housing  290  from the first cross-member  236 . 
     In the versions shown, the auxiliary wheel assembly  214  also includes an auxiliary wheel drive system  298  (see  FIGS.  12 - 13   ) operatively coupled to the auxiliary wheel  218 . The auxiliary wheel drive system  298  is configured to drive (e.g. rotate) the auxiliary wheel  218 . In the version shown, the auxiliary wheel drive system  298  includes a motor assembly  300  coupled to a power source  302  such as, for example, a battery for providing electrical power to energize the motor assembly  300 . The motor assembly  300  that is coupled to the auxiliary wheel  218  for rotating the auxiliary wheel  218  about the rotational axis R. The motor assembly  300  includes a motor assembly housing  304  and a motor  306  positioned within the motor assembly housing  304 . The motor  306  is coupled to the auxiliary wheel  218  for providing motive power to the auxiliary wheel  218 . The motor assembly housing  304  includes a body (also referred to as a link) that extends between a first housing end  308  and a second housing end  310  (see  FIG.  13   ). The first housing end  308  is pivotably coupled to the wheel support frame  242  via a fastener such that a rotation of the crank shaft  240  causes a vertical movement of the motor assembly housing  304  and the auxiliary wheel  218 . The second housing end  310  is pivotably coupled to the second cross-member  238 . 
     Referring to  FIG.  13   , the support frame  212  includes a motor assembly support bracket  312  that extends outwardly from the second cross-member  238 . The motor assembly support bracket  312  is coupled to the motor assembly housing  304  to support the motor assembly housing  304  from the second cross-member  238 . The motor assembly support bracket  312  includes a translation slot  314  that extends through an outer surface of the motor assembly support bracket  312 . The motor assembly housing  304  is pivotably and moveably coupled to the motor assembly support bracket  312  with a fastening pin  316  that extends outwardly from the motor assembly housing  304  and through the translation slot  314 . The motor assembly housing  304  is configured to articulate and translate relative to the second cross-member  238 . The translation slot  314  is sized and shaped to enable the fastening pin  316  to slide along a length of the translation slot  314  to enable the motor assembly housing  304  to translate relative to the motor assembly support bracket  312 . 
     In some versions, the motor assembly  300  includes a gear train assembly  318  that is coupled to the motor  306  and the auxiliary wheel  218  for transferring torque from the motor  306  to the auxiliary wheel  218 . The gear train assembly  318  may also be positioned within motor assembly housing  304 . 
     In the versions shown, referring back to  FIG.  16 A , during operation, as the lift actuator  228  moves to the extended position, the actuator rod  292  causes the actuator support bracket  286  to pivot toward the second cross-member  238  which causes the cartridge housing  254  to move towards the second cross-member  238  and away from the crank shaft  240 . As the cartridge housing  254  moves toward the second cross-member  238 , the guide plate  268  engages and compresses the compression spring  256  which, in turn, pushes the piston rod  252 toward the second cross-member  238 . As the piston rod  252  moves toward the second cross-member  238 , the piston rod  252  causes the crank  250  to rotate the crank shaft  240  and the wheel support frame  242  in a first rotational direction. The rotation of the wheel support frame  242  causes the motor assembly housing  304  and the auxiliary wheel  218  to move away from the support frame  212  to the deployed position  222 . In the deployed position  222 , the lift actuator  228  is in the extended position  232  and an outer surface of the actuator support bracket  286  contacts the second cross-member  238  to prevent further extension of the actuator rod  292 . In addition, referring back to  FIG.  13   , as the motor assembly housing  304  moves away from the support frame  212 , the fastening pin  316  slides along the translation slot  314  to enable the motor assembly housing  304  to pivot and translate relative to the motor assembly support bracket  312 . 
     As the lift actuator  228  moves to the retracted position  234 , as shown in  FIG.  16 B , the actuator rod  292  causes the actuator support bracket  286  to pivot away from the second cross-member  238  which causes the cartridge housing  254  to move towards the first cross-member  236  and towards the crank shaft  240 . As the cartridge housing  254  moves toward the crank shaft  240 , the guide plate  268  engages the enlarged head of the piston rod  252  pivotally connected to the crank  250  which, in turn, causes the crank  250  to rotate the crank shaft  240  and the wheel support frame  242  in a second opposite rotational direction, which causes the motor assembly housing  304  and the auxiliary wheel  218  to move to the stowed position  224 . 
     The guide ring  278  moves within the guide slot  282  to enable the piston rod  252  and compression spring  256  to move with respect to the cartridge housing  254  which, in turn, allows for a rotation of the crank shaft  240  to enable movement of the auxiliary wheel  218  in the vertical direction. By enabling the auxiliary wheel  218  to travel vertically with respect to the support frame  212  with the auxiliary wheel assembly  214  in the deployed position  222 , the spring cartridge assembly  230  facilitates maintaining sufficient traction between an uneven floor surface  220  and the auxiliary wheel  218  to enable the auxiliary wheel  218  to influence motion of the patient support apparatus  10  during operation. 
     Referring to  FIGS.  17 A- 17 C , with the with the auxiliary wheel assembly  214  in the deployed position  222 , as the patient support apparatus  10  travels over uneven floor surfaces, the compression spring  256  provides suspension functions for the auxiliary wheel assembly  214  by acting between the cartridge housing  254  and the piston rod  252 . 
     For example, as shown in  FIGS.  17 A and  17 B , as the patient support apparatus  10  transitions from a flat surface to an inclined floor surface, the spring cartridge assembly  230  allows the auxiliary wheel  218  to move towards the support frame  212 . As the downward force imparted on the auxiliary wheel  218  by the patient support apparatus  10  increases, the crank shaft  240  rotates to move the enlarged head of the piston rod  252  away from the cartridge housing  254 . The guide ring  278  then moves towards the guide plate  268  compressing the compression spring  256  against the guide plate  268 , allowing the compression spring  256  to absorb the downward force of the weight of the patient support apparatus  10 . 
     Referring to  FIGS.  17 A and  17 C , as the patient support apparatus  10  transitions from a flat surface to a declined floor surface, the spring cartridge assembly  230  biases the auxiliary wheel  218  away from the support frame  212 . As the downward force of the patient support apparatus  10  decreases, the compression spring  256  expands to move the guide ring  278  away from the guide plate  268  which causes the crank shaft  240  to rotate in the opposite direction to move the auxiliary wheel  218  away from the support frame  212  to remain in contact with the declining floor surface. 
     Although an exemplary version of an auxiliary wheel assembly  214  is described above and shown in the figures, it should be appreciated that other configurations employing a lift actuator  228  to move the auxiliary wheel  218  between the retracted position  234  and deployed position  222  are contemplated. A control system and associated controller, one or more user input devices, and one or more sensors, may be employed to control operation of the lift actuator  228  and the auxiliary wheel drive system  298 , in the manner described in U.S. patent application Ser. No. 16/222,506, hereby incorporated herein by reference. 
       FIG.  18    is a flow chart of method  400  illustrating an algorithm that is executed by the controller  162  to recognize a plurality of transition profiles during operation of the auxiliary wheel assembly  60 . The method includes a plurality of steps. Each method step may be performed independently of, or in combination with, other method steps. Portions of the methods may be performed by any one of, or any combination of, the components of the controller  162  and/or the auxiliary wheel assembly control circuit  106 . In some versions, the controller  162  may include an auxiliary wheel control module  178  that is configured to execute one more of the algorithms illustrated in method  400 . In addition, the auxiliary wheel control module  178  may be configured to operate the auxiliary wheel assembly control circuit  106  to perform one or more of the algorithm steps illustrated in method  400 . In some versions, the auxiliary wheel control module  178  may include a state machine configured to execute the steps illustrated in method  400 . In some versions, the auxiliary wheel control module  178  may include computer-executable instructions that are stored in the memory device  166  and cause one or more processors  164  of the controller  162  to execute the algorithm steps illustrated in method  400 . 
     Referring to  FIG.  18   , in some versions, the controller  162  is programmed to execute the algorithm illustrated in method  400  for recognizing a plurality of transition profiles and for operating the patient support apparatus  10 , at least one of which represents a transition over an inclined floor surface. In some configurations, the transition profile that represents a transition over an inclined floor surface includes a threshold value based on the wheel position sensor  118  indicating that the auxiliary wheel  218  is above a plane PLN associated with the support wheel  50  (see  FIG.  20 B ). Here, the plane PLN may be defined based on engagement of the support wheels  50  with a flat and non-inclined floor surface  20 , and the threshold value of the wheel position sensor may correspond to “upward” movement of the auxiliary wheel  218  away from the plane PLN which places the auxiliary wheel  218  “above” the plane PLN (see  FIG.  20 B ). When this threshold is reached, it may indicate that the patient support apparatus  10  is traveling onto a downward incline (from level ground down a ramp, for example). It will be appreciated that the forgoing description of the plane PLN and the threshold value is illustrative and non-limiting, and the plane PLN may be defined in a number of different ways. Similarly, it will be appreciated that the threshold value could be determined in other ways, and that the controller  162  could determine changes in the floor surface  220  which represent transitions onto (or off of) inclined surfaces in other ways (e.g., via the floor sensor  179 ). Other configurations are contemplated. 
     In yet other configurations, the transition profile that represents a transition over an inclined floor surface includes a threshold value based on the wheel position sensor  118  indicating that the auxiliary wheel  218  is below a plane PLN associated with the support wheel  50  (see  FIG.  20 C ). Here too, the plane PLN may be defined based on engagement of the support wheels  50  with a flat and non-inclined floor surface  20 , and the threshold value of the wheel position sensor may correspond to “downward” movement of the auxiliary wheel  218  away from the plane PLN which places at least a portion of the auxiliary wheel  218  “below” the plane PLN (see  FIG.  20 C ). When this threshold is reached, it may indicate that the patient support apparatus  10  is traveling onto an upward incline (from level ground up a ramp, for example). Here too, it will be appreciated that the forgoing description of the plane PLN and the threshold value is illustrative and non-limiting, and the plane PLN may be defined in a number of different ways. Similarly, it will be appreciated that the threshold value could be determined in other ways, and that the controller  162  could determine changes in the floor surface  220  which represent transitions onto (or off of) inclined surfaces in other ways (e.g., via the floor sensor  179 ). Other configurations are contemplated. 
     In method step  402 , the controller  162  calculates or otherwise determines, based on a velocity of the patient support apparatus  10  over the floor surface, a distance traveled by the patient support apparatus  10  over the floor surface. As will be appreciated from the subsequent description below, the controller may calculate distance traveled based on sensor data associated with actual movement (e.g., monitoring movement of wheels, monitoring the floor, receiving tracking information from an external source, and the like), and/or may calculate distance traveled in other ways, such as based on an expected amount of movement based on changes in commanded inputs, previous motion, weight or load, friction or wheel slippage, motor current, and the like. In some configurations, a processor  164  calculates or otherwise determines a distance traveled by the patient support apparatus  10  over the floor surface based on one or more signals received from the velocity sensor  177 . In yet other configurations, a processor  164  calculates or otherwise determines a distance traveled by the patient support apparatus  10  over the floor surface based on one or more signals received from a user interface (e.g., user interface  40  or graphical user interface  41 ). Here, for example, the controller  162  could calculate the distance traveled based on known output speeds of the auxiliary wheel  218  expected from inputs made to the throttle assembly  130 . 
     In method step  404 , the controller  162  compares a plurality of positions of the auxiliary wheel actuator  64  (in some configurations, a log of these positions may be stored in the memory device  166 ) and the distance traveled by the patient support apparatus  10  with the known transition profiles. In some versions, instead of using the positions of the auxiliary wheel actuator  64  in this comparison, the controller  162  could instead use signals received from the floor sensor  179  to sense changes in the distance to the floor surface. In method step  406 , the controller  162  determines that the patient support apparatus  10  is traveling on an inclined floor surface. Here, for example, the controller  162  could monitor changes in signals generated by the wheel position sensor  118  (and/or the floor sensor  179 ) with respect to the calculated distance traveled over time to determine that the patient support apparatus  10  has transitioned onto a ramp. In this example, a known transition profile representing movement onto a ramp could be defined based on a predetermined amount of change in the signal generated by the wheel position sensor  118  over time correlated with an expected predetermined amount distance traveled by the patient support apparatus  10  over that period of time. If, for example, the signal generated by the wheel position sensor  118  (and/or the floor sensor  179 ) changes to indicate movement from the first vertical distance V 1  (see  FIG.  17 A ) to the second vertical distance V 2  (see  FIG.  17 B ) and then back to the first vertical distance V 1  at a rate which, in view of the calculated distance traveled, indicates a transition onto a declined surface (e.g., down a ramp) has occurred (e.g., fully onto the declined ramp from the position shown in  FIG.  20 B ). It will be appreciated that changes in the signals generated by the wheel position sensor  118  over time can be used to ignore “bumps” on the floor surface that would otherwise cause the auxiliary wheel  218  to move towards the second vertical distance V 2  but which do not correspond to movement onto an inclined surface. 
     In an optional method step  408 , the controller  162  (or a processor  164 ) associates a transition profile with a specific location. In method step  410 , the memory device  166  stores the transition profile. By way of example and not limitation, a location may be a medical/healthcare facility. The transition profile may include or otherwise be defined based on information about an architectural layout associated with the location, which may include a plurality of features such as: length, width, and shape of hallways; ramps or other features that effect changes in elevation of floor surface; number and width of hallway corners; bridges between buildings of a facility; changes in floor surface; elevators; floors of a building; ingress/egress points of a building; paths, sidewalks, roads, and the like adjacent to one or more buildings; and/or any other feature of the location layout that might affect maneuverability of the patient support apparatus  10  (e.g., locations defined relative to specific units such as med-surge, intensive care, radiology, and the like). In some versions, the process of generating or otherwise calibrating transition profiles may be carried out by a technician or another user (e.g., by selecting an option using the user interface  40  or graphical user interface  41 ) to place the patient support apparatus  10  into a “learn” mode where the distance traveled is measured or otherwise determined and is monitored, logged, recorded, or otherwise evaluated relative to the distance to the floor measured such as via signals generated by the position sensor  118  (and/or the floor sensor  179 ). Here, in such a “learn” mode, data associated with particular ramps, inclines, and the like may be stored as transition profiles (e.g., such as waveforms, data logs, and the like) for later use by the controller  162  to recognize during operation, such as by observing current movement of the position sensor  118  (and/or the floor sensor  179 ) over calculated distances and recognizing corresponding transition profiles stored in memory. 
     In some versions, the controller  162  can identify its location within a particular healthcare facility based on uniquely recognized inclines that are associated with stored transition profiles, such as where a healthcare facility has only one “long” ramp and the controller  162  recognizes the transition onto and subsequently off of the ramp based on sensor data and calculated or sensed distance traveled). However, it will be appreciated that stored In some versions, stored transition profiles may represent the sensor data associated with movement onto of one end of a ramp, while in other versions data may represent movement onto one end of a ramp along with movement along the ramp and/or subsequent movement off of the ramp. In some versions, stored transition profiles may represent irregular profiles that can be “ignored” for certain purposes, such as with one or more “short” ramps or other incline changes that may otherwise appear to be a “long” ramp but for the distance traveled relative to one or more transitions. Other configurations are contemplated. It will be appreciated that stored transition profiles may be standardized for general purpose use in various facilities, such as with “default” transition profiles stored in memory for predetermined incline angles, ramp lengths, ramp transition profiles, and the like. These types of standardized transition profiles may be calibrated to correspond to sensor data associated with a specific patient support apparatus  10  (e.g., to calibrate or recalibrate gain, offset, and the like when replacing wheel position sensors  118 ). Put differently, calibration may be used to modify or differently interpret “standard” transition profiles stored in memory. In addition or alternatively, non-standardized transition profiles may be generated, selected, or created to suit particular facility layout. These may involve adjustments made by technicians (e.g., selecting an option with a service tool used for facilities with particularly long ramps). Similarly, non-standardized transition profiles may be calibrated and/or generated using the “learn” mode described above. Accordingly, it will be appreciated that transition profiles may be associated with particular locations within a facility, may be associated with particular facilities and not with respect to discrete ramps or locations within a facility, or may be associated with certain types of ramps based on the specific sensor output ranges of a particular patient support apparatus  10 . Other configurations are contemplated. 
       FIG.  19    is a flow chart of an alternative method  500  illustrating an algorithm that is executed by the controller  162  to recognize a plurality of transition profiles during operation of the drive member  62 . The method includes a plurality of steps. Each method step may be performed independently of, or in combination with, other method steps. Portions of the methods may be performed by any one of, or any combination of, the components of the controller  162  and/or the control circuit  106 . In some versions, the controller  162  may include a control module  178  that is configured to execute one more of the algorithms illustrated in method  500 . In addition, the control module  178  may be configured to operate the control circuit  106  to perform one or more of the algorithm steps illustrated in method  500 . In some versions, the control module  178  may include a state machine configured to execute the steps illustrated in method  500 . In some versions, the control module  178  may include computer-executable instructions that are stored in the memory device  166  and cause one or more processors  164  of the controller  162  to execute the algorithm steps illustrated in method  500 . 
     Referring to  FIG.  19   , in some versions, the controller  162  is programmed to execute the algorithm illustrated in method  500  for recognizing a plurality of transition profiles and for operating the patient support apparatus  10 , at least one of which represents a transition over an inclined floor surface. 
     In method step  502 , the controller  162  senses a plurality of positions of the drive member  62  relative to the support structure  12 . In some configurations, a log of these positions may be stored in the memory device  166 . In method step  504 , the controller  162  calculates or otherwise determines a distance traveled by the patient support apparatus  10  over the floor surface. In some configurations, a processor  164  calculates or otherwise determines a distance traveled by the patient support apparatus  10  over the floor surface based on one or more signals received from a sensor coupled to the support structure  12  (e.g., velocity sensor  177  or another sensor described herein). In yet other configurations, a processor  164  calculates or otherwise determines a distance traveled by the patient support apparatus  10  over the floor surface based on one or more signals received from a user interface (e.g., user interface  40  or graphical user interface  41 ). 
     In method step  506 , the controller  162  compares a plurality of positions of the drive member  62  and the distance traveled by the patient support apparatus  10  with the plurality of known transition profiles. In some versions, the controller  162  instead compares changes in the distance to the floor surface  220  (based on signals received from the floor sensor  179 ) and the distance traveled by the patient support apparatus  10  with the plurality of known transition profiles. In method step  508 , the controller  162  determines that the patient support apparatus  10  is traveling on an inclined floor surface. 
     In an optional method step  510 , the controller  162  (or a processor  164 ) associates a transition profile with a specific location. By way of example and not limitation, a location may be a medical/healthcare facility. The transition profile may include information about an architectural layout associated with the location, which may include a plurality of features such as: length, width, and shape of hallways; ramps or other features that effect changes in elevation of floor surface; number and width of hallway corners; bridges between buildings of a facility; changes in floor surface; elevators; floors of a building; ingress/egress points of a building; paths, sidewalks, roads, and the like adjacent to one or more buildings; and/or any other feature of the location layout that might affect maneuverability of the patient support apparatus  10  (e.g., locations defined relative to specific units such as med-surge, intensive care, radiology, and the like). In method step  512 , the memory device  166  stores the transition profile. In some configurations, the transition profile may be updated periodically or continuously. 
     Several configurations have been discussed in the foregoing description. However, the configurations 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.