Patent Publication Number: US-11642264-B2

Title: Load sensor configurations for caster assemblies of a patient support apparatus

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 16/046,150, filed on Jul. 26, 2018 and issued as U.S. Pat. No. 11,123,247 on Sep. 21, 2021, which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/537,659, filed on Jul. 27, 2017, the entire contents and disclosures of each of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Patient support apparatuses such as hospital beds, stretchers, cots, wheelchairs, and chairs are routinely used by operators to move patients from one location to another. Conventional patient support apparatuses comprise a base and a support surface upon which the patient rests. Wheels are coupled to the base to enable transport over floor surfaces. 
     Often, sensors are placed by the support surface for sensing a load applied to the support surface by the patient. Through the force of gravity, a path of the load is transmitted from the support surface, through the base, and ultimately through the wheels to the floor upon which the patient support apparatus rests. 
     Having the sensors placed by the support surface has many shortcomings. For example, to achieve accurate load readings, the support surface must be as horizontal as possible (e.g., not tilted in litter/fowler/gatch/trend positions) at the time of load measurement. Mainly, tilting of the support surface may cause some of the load to be applied along load paths that circumvent the sensors. However, keeping the support surface horizontal is not always practical because the patient often requires movement or tilting of the support surface for convenience or health related purposes. Physical movement of the patient on the support surface may also cause inaccurate readings when the sensors are placed by the patient support surface. Leaning or posture adjustment of the patient may similarly cause some of the load to be applied along load paths that evade the sensors. As such, when the sensors are placed by the support surface, the sensors are placed in a position that has potential to be bypassed, in part, by the load path. In turn, this may also inhibit the ability for accurate load readings. A patient support apparatus with features designed to overcome one or more of the aforementioned challenges is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is perspective view of a patient support apparatus. 
         FIG.  2 A  is an elevational view, partially in phantom, of a caster assembly of the patient support apparatus according to one embodiment. 
         FIG.  2 B  is perspective view of the caster assembly of  FIG.  2 A . 
         FIG.  3    is a block diagram of one embodiment of a system of the patient support apparatus comprising a load sensor, a controller, and motors for controlling the caster assembly. 
         FIG.  4 A  is a perspective view, partially in phantom, of the caster assembly comprising the load sensor integrated around a stem of the caster assembly, according to one example. 
         FIG.  4 B  is a cross-sectional view of the stem and load sensor of the caster assembly of  FIG.  4 A  wherein the stem and load sensor are at rest. 
         FIG.  4 C  is the cross-sectional view of the stem and load sensor of  FIG.  4 B  wherein the stem is undergoing an applied load detectable by the load sensor. 
         FIG.  5    is a perspective view, partially in phantom, of another example of the load sensor integrated around the stem of the caster assembly. 
         FIG.  6 A  is a perspective view of the caster assembly comprising the load sensor integrated on a distal end of the stem, according to one example. 
         FIG.  6 B  is a cross-sectional view of the stem and load sensor of the caster assembly of  FIG.  6 A  wherein a load is applied to the distal end of the stem. 
         FIG.  7 A  is a perspective view of the caster assembly comprising the load sensor integrated on the distal end of the stem, according to another example. 
         FIG.  7 B  is a cross-sectional view of the stem and load sensor of the caster assembly of  FIG.  7 A  wherein the stem and the load sensor are at rest. 
         FIG.  7 C  is the cross-sectional view of the stem and load sensor of  FIG.  7 B  wherein the stem is undergoing an applied load detectable by the load sensor. 
         FIG.  8 A  is an elevational view, partially in phantom, of the caster assembly comprising the load sensor integrated on a wheel axle of the caster assembly, according to one example. 
         FIG.  8 B  is an elevational view of the wheel axle and the load sensor of the caster assembly of  FIG.  8 A  wherein the wheel axle and the load sensor are at rest. 
         FIG.  8 C  is the elevational view of the wheel axle and the load sensor of  FIG.  8 B  wherein the wheel axle is undergoing an applied load detectable by the load sensor. 
         FIG.  9 A  is a perspective view, partially in phantom, of the caster assembly comprising load sensor integrated with a wheel of the caster assembly wherein the wheel is at rest. 
         FIG.  9 B  is the perspective view of the caster assembly of  FIG.  9 A  wherein the wheel is undergoing an applied load detectable by the load sensor. 
         FIG.  10 A  is a diagram illustrating vertical and non-vertical components of a load detected by the load sensor of the caster assembly, according to one example. 
         FIG.  10 B  is a diagram illustrating a combined vertical component of the load from  FIG.  10 A  wherein non-vertical components of the load are negated by the controller. 
         FIG.  11    is a top view of the caster assembly in a trailing position after being rotated from a non-trailing position by a steering motor based on the load detected by the load sensor. 
     
    
    
     DETAILED DESCRIPTION 
     I. Patient Support Apparatus Overview 
     Referring to  FIG.  1   , a patient support apparatus  30  is shown for moving a patient from one location to another. The patient support apparatus  30  illustrated in  FIG.  1    is a hospital bed. In other embodiments, however, the patient support apparatus  30  may be a stretcher, cot, wheelchair, chair, or similar apparatus. 
     A support structure  32  provides support for the patient during movement of the patient support apparatus  30 . The support structure  32  illustrated in  FIG.  1    comprises a base  34  and an intermediate frame  36 . The intermediate frame  36  is spaced above the base  34 . The support structure  32  also comprises a patient support deck  38  disposed on the intermediate frame  36 . The patient support deck  38  may comprise several sections, some of which are pivotable relative to the intermediate frame  36 , such as a head section, a seat section, a thigh section, and a foot section. The patient support deck  38  provides a patient support surface  42  upon which the patient is supported. The patient support surface  42  is supported by the base  34 . 
     A mattress  40  is disposed on the patient support deck  38 . The mattress  40  comprises a direct patient support surface  43  upon which the patient is supported. The base  34 , intermediate frame  36 , patient support deck  38 , and patient support surfaces  42 ,  43  each have a head end and a foot end corresponding to the designated placement of the patient&#39;s head and feet on the patient support apparatus  30 . The construction of the support structure  32  may take on any suitable design, and is not limited to that specifically set forth above or shown in  FIG.  1   . 
     Side rails  44 ,  46 ,  48 ,  50  are coupled to the intermediate frame  36 . A first side rail  44  is positioned at a right head end of the intermediate frame  36 . A second side rail  46  is positioned at a right foot end of the intermediate frame  36 . A third side rail  48  is positioned at a left head end of the intermediate frame  36 . A fourth side rail  50  is positioned at a left foot end of the intermediate frame  36 . If the patient support apparatus  30  is a stretcher or a cot, there may be fewer side rails. The side rails  44 ,  46 ,  48 ,  50  are movable between a raised position in which they block ingress and egress into and out of the patient support apparatus  30 , one or more intermediate positions, and a lowered position in which they are not an obstacle to enable such ingress and egress. In still other configurations, the patient support apparatus  30  may not include any side rails. 
     A headboard  52  and a footboard  54  are coupled to the intermediate frame  36 . In other embodiments, when the headboard  52  and footboard  54  are included, the headboard  52  and footboard  54  may be coupled to other locations on the patient support apparatus  30 , such as the base  34 . In still other embodiments, the patient support apparatus  30  does not include the headboard  52  or the footboard  54 . 
     Operator (human control) interfaces  56 , such as handles, are shown integrated into the footboard  54  and side rails  44 ,  46 ,  48 ,  50  to facilitate movement of the patient support apparatus  30  over the floor surfaces. Additional operator interfaces  56  may be integrated into the headboard  52  and/or other components of the patient support apparatus  30 . The operator interfaces  56  are graspable by the operator to manipulate the patient support apparatus  30  for movement. The operator interface  56  may comprise one or more handles coupled to the intermediate frame  36 . The operator interface  56  may simply be a surface on the patient support apparatus  30  upon which the operator locally applies force to cause movement of the patient support apparatus  30  in one or more directions, also referred to as a push location. This may comprise one or more surfaces on the intermediate frame  36  or base  34 . This could also comprise one or more surfaces on or adjacent to the headboard  52 , footboard  54 , and/or side rails  44 ,  46 ,  48 ,  50 . In other embodiments, the operator interface  56  may comprise separate handles for each hand of the operator. For example, the operator interface  56  may comprise two handles. Other forms of the operator interface  56  are also contemplated. 
     One or more caster assemblies  58  are coupled to the base  34  to facilitate transport over floor surfaces. In one example, as shown in  FIG.  1   , four caster assemblies  58   a - 58   d  are arranged in each of four quadrants of the base  34  adjacent to corners of the base  34 . In the embodiment shown, the caster assemblies  58   a - 58   d  are able to rotate and swivel relative to the support structure  32  during transport. 
     The caster assemblies  58  may be non-steerable, steerable, non-powered, powered (driven), or any combinations thereof. The caster assemblies  58  may have any suitable shape or configuration other than those shown in the Figures. 
     The patient support apparatus  30  may comprise any suitable number of caster assemblies  58 , such as two or six, etc. The caster assemblies  58  may have any suitable configuration and arrangement depending on the specific type of patient support apparatus  30 . For example, when the patient support apparatus  30  is a wheelchair, the patient support apparatus  30  may comprise two front non-driven caster assemblies  58  and two rear driven caster assemblies  58 . 
     As shown in  FIGS.  2 A and  2 B , each caster assembly  58  comprises a stem  60 , a caster wheel  62 , and a caster wheel axle  64 . The caster wheel  62  rotates about a rotational axis R of the wheel axle  64  to effect motion of the patient support apparatus  30 , such as along a floor surface. The caster wheel  62  has a radial center  63 . The caster wheel  62  may be an airless (non-pneumatic) wheel or may be an inflatable, pneumatic or semi-pneumatic wheel. The stem  60  extends from the caster assembly  58  to provide an interface connection to the base  34 , as shown in one example of  FIG.  2 B . The stem  60  may be any suitable shape, such as cylindrical, box shaped, or the like. The caster assembly  58 , and more specifically, the stem  60  may be coupled to the base  34  according to any suitable manner and using any suitable fastening mechanism. 
     The caster wheel  62  rotates vertically about a swivel axis S defined through the stem  60 . The stem  60  and swivel axis S may be offset with respect to the radial center  63  of the caster wheel  62 , as shown in  FIG.  2 B . In other words, the swivel axis S and the rotational axis R do not directly intersect. In such instances, the caster wheel  62  exhibits a trailing orientation, meaning a bulk, offset portion, of the caster wheel  62  trails behind the swivel axis S when the caster wheel  62  is in motion. In another example, the swivel axis S is aligned with the radial center  63  and intersects the rotational axis R of the caster wheel  62 . In such instances, the caster wheel  62  has no specific trailing orientation and either side of the caster wheel  62  may trail behind the swivel axis when the caster wheel  62  is in motion. 
     Caster assemblies  58  and structures, functions and applications thereof may be like those described in U.S. Patent Application Publication No. 2016/0089283, entitled “Patient Support Apparatus,” the disclosure of which is hereby incorporated by reference in its entirety. 
     Additionally, one or more auxiliary wheels  66  (powered or non-powered), which may be movable between stowed positions and deployed positions, may be coupled to the support structure  32 . In some cases, when these auxiliary wheels  66  are located between the caster assemblies  58  and contact the floor surface in the deployed position, they cause two of the caster assemblies  58  to be lifted off the floor surface thereby shortening a wheel base of the patient support apparatus  30 . Such auxiliary wheels  66  may also be arranged substantially in a center of the base  34 . 
     The patient support apparatus  30  comprises a controller  68  in communication with and for controlling any suitable components of the patient support apparatus  30 , such as the electrical or electromechanical components described herein. The controller  68  may comprise any suitable signal processing means, computer executable instructions or software modules stored in non-transitory memory wherein the executable instructions or modules may be executed by a processor, or the like. Additionally, or alternatively, the controller  68  may comprise a microcontroller, a processor, one or more integrated circuits, logic parts, and the like for enabling the same. The controller  68  may have any suitable configuration for enabling performance of various tasks related to operation of the patient support apparatus  30 , such as those described below. The controller  68  may be located at any suitable location of the patient support apparatus  30 . 
     As shown in  FIG.  1   , the patient support apparatus  30  may comprise one or more steering motors  70   a - 70   d  for changing an orientation of the caster assemblies  58  about the swivel axis S. The steering motor  70  may be coupled to the stem  60  of the caster assembly  58 . Each steering motor  70  may change the orientation of the caster assemblies  58  to facilitate steering of the patient support apparatus  30 . For example, the steering motors  70  may change orientation of the caster assemblies  58  help to move patient support apparatus  30  in the direction desired by the caregiver. One steering motor  70  may be associated with each caster assembly  58 , and more specifically, the stem  60  of the caster assembly  58 . Alternatively, the steering motors  70  may be associated with only certain caster assemblies  58 , e.g., the front-leading caster assemblies  58   a ,  58   b . The steering motors  70  may be located inside or outside the respective caster assembly  58 . 
     Referring to  FIG.  3   , the steering motors  70  are coupled to the controller  68 . The steering motors  70  may be directly wired to the controller  68  or in wireless communication with the controller  68 . The steering motors  70  may receive control signals from the controller  68  commanding reorientation of the respective caster assemblies  58 . For example, the control signals may be derived from the controller  68  receiving readings indicative of user applied force and direction of force when pushing patient support apparatus  30 . Additional examples of control signals provided by the controller  68  to effect reorientation by the steering motors  70  are described below. Steering motors  70  and techniques for generating signals for controlling the same may be like those described in U.S. Patent Application Publication No. 2016/0089283, entitled “Patient Support Apparatus,” the disclosure of which is hereby incorporated by reference in its entirety. 
     In embodiments where one or more caster assemblies  58  are driven, a drive motor  72   a - 72   d  may be associated with the respective caster assembly  58 , as shown in  FIG.  1   . The drive motor  72  is configured to cause the caster assembly  58  to rotate about the rotational axis R of the caster assembly  58 . The drive motor  72  may be coupled to the caster wheel axle  64 . Referring to  FIG.  3   , the drive motors  72  are coupled to the controller  68 . The drive motors  72  may be directly wired to the controller  68  or in wireless communication with the controller  68 . The drive motor  72  is configured to cause the caster assembly  58  to rotate in response to receiving control signals provided by the controller  68 . For example, the controller  68  may command the drive motor  72  to rotate the respective caster assembly  58  to effect a desired velocity for the patient support apparatus  30  based on user input and/or sensed readings relating to the environment of the patient support apparatus  30 . The drive motor  72  may be located inside of the respective caster assembly  58 . Drive motors  72  and techniques for generating signals for controlling the same may be like those described in U.S. Patent Application Publication No. 2016/0089283, entitled “Patient Support Apparatus,” the disclosure of which is hereby incorporated by reference in its entirety. 
     II. Load Sensor Configurations For Caster Assemblies 
     Referring to  FIGS.  3 - 9   , the patient support apparatus  30  comprises one or more load sensors  80  that are utilized for measuring a load applied to the patient support apparatus  30 . For instance, the load is applied to one or more of the patient support surfaces  42 ,  43 . The load may be applied from any object, such as a patient, placed on one or more of the patient support surfaces  42 ,  43 . The load is not applied when the object is removed or otherwise not placed on one or more of the patient support surfaces  42 ,  43 . Specific structural embodiments and locations of load sensors  80  in relation to the patient support apparatus  30  are described below. 
     More specifically, the load sensor  80  is integrated into and/or with the caster assembly  58 , or components thereof. That is, the load sensor  80  is integrated with the caster assembly  58  during manufacturing/assembly of the caster assembly  58 . In other words, by being integrated with the caster assembly  58 , the load sensor  80  is not disposed on a component that is separate from the caster assembly  58  or a component that is otherwise not involved with functionality of the caster assembly  58 . Instead, the load sensor  80  is “in-line” with the caster assembly  58  thereby eliminating a need for secondary support structures, such as cantilevers, separately attached to the caster assembly  58  for experiencing the load and holding the load sensor  80 . Installation of the caster assembly  58  having the integrated load sensor  80  is made seamlessly to the base  34  without including additional features coupled to the base  34  and/or caster wheel  58  for accommodating such secondary support structures for the load sensor  80 . 
     As will be shown in the various examples below, the load sensor  80  is cooperative with at least one of the stem  60 , the caster wheel  62 , and the caster wheel axle  64  of the caster assembly  58  to measure the load. One or more load sensors  80  are affixed, attached, or otherwise directly coupled to the stem  60 , the caster wheel  62 , and/or the caster wheel axle  64 , individually, or in combination. In other examples, the load sensor  80  is coupled to the steering motor  70  and/or the drive motor  72 , when such motors  70 ,  72  are integrated with the caster assembly  58 . 
     Furthermore, by having the load sensor  80  integrated with the caster assembly  58 , there is an opportunity to avoid placing load sensors  80  by the patient support surfaces  42 ,  43 . Mainly, the path of the load transmitted from the patient support surfaces  42 ,  43  will ultimately bottle-neck and pass through the caster assemblies  58  to the floor upon which the patient support apparatus  30  rests. Therefore, having the load sensors  80  integrated with the caster assemblies  58  provides a unique opportunity to accurately and completely capture the applied load. Because the caster assemblies  58  are usually placed on a horizontal and stable floor surface, load sensors  80  will also be in a horizontal state thereby providing accurate readings. Thus, the described configuration avoids the shortcomings of having the support surfaces  42 ,  43  be as horizontal as possible (e.g., not tilted) at the time of load measurement to provide accurate readings. Even if the support surfaces  42 ,  43  are tilted in litter/fowler/gatch/trend positions, the load path must find its way through the caster assembly  58  such that circumvention of the load sensors  80  by the load path is unlikely. Thus, integrating the load sensor  80  with the caster assembly  58  will provide free tilting of the support surfaces  42 ,  43  for convenience or health related purposes of the patient, even during load measurement. 
     The described configuration further provides accurate readings even with physical movement of the patient on the support surfaces  42 ,  43  during load measurement. Leaning or posture adjustment of the patient is unlikely to cause some of the load to be applied along load paths that evade the load sensor  80  because the load sensor  80  is provided at the caster assembly  58  near the floor, and at a low and bottle-necked point in the load path. Additional advantages of the load sensor  80  configurations will be appreciated from the examples described below and those shown in the figures. 
     Of course, there may be other load sensors disposed in locations of the patient support apparatus  30  other than being integrated on or within the caster assembly  58 . These other load sensors may be utilized in conjunction with or separately from any load sensor  80  integrated with the caster assembly  58 . 
     As used herein, the term “load sensor” is not limited to a sensor only configured to measure the load directly. Since the load may be difficult to characterize based on sensor readings alone, and because various types of load sensors  80  are provided herein, it should be understood that load sensor  80  may produce readings that are indicative of, or corresponding to, the load such that the load can be inferred based on such readings. Examples of such readings are understood from the various examples of the load sensor  80 , as described below. 
     The load sensor  80  integrated with the caster assembly  58  may have any suitable configuration for sensing the load. For example, the load sensor  80  may be any type of load cell, such as a strain gauge load cell, a piezoelectric load cell, a hydraulic load cell, a pneumatic load cell, or the like. The load cell may be bending beam, compression, push-pull rod type or the like. The load cell may measure forces/torques applied by the load in any number of degrees of freedom, such as six degrees of freedom, as shown in  FIG.  5   , including forces along axes X, Y, Z and torques (pitch, roll, yaw) about these axes, respectively. The load cell may have configurations other than those described herein. 
     The load sensor  80  integrated with the caster assembly  58  may also comprise one or more strain gauges for converting strain caused by the applied load into signals. The strain gauges may be any suitable type, such as foil type, piezoresistive type, semiconductor based, microelectromechanical system (MEMS) type, or the like. The strain gauges may have configurations other than those described herein. 
     In other examples, the load sensor  80  integrated with the caster assembly  58  is a pressure sensor for converting pressure caused from the applied load into signals. The pressure sensor may use any suitable technology, such as piezoresistive, capacitive, electromagnetic, piezoelectric, and the like. The sensed pressure may be applied to any suitable medium, such as pressure applied to liquid, solid or gases. The pressure sensor may have configurations other than those described herein. 
     The load sensor  80  integrated with the caster assembly  58  may be a displacement sensor for converting physical displacement of an object into signals. The displacement sensor may have various configurations, such as a linear, rotational, inductive, capacitive, electrical, encoder based, potentiometric, optical sensors, or the like. The displacement sensor may have configurations other than those described herein. 
     Any of the examples for the load sensor  80  may be utilized individually, or in combination for any one or more load sensors  80 . Any other type of load sensor  80  other than those described herein may be utilized. 
     As shown in  FIG.  3   , the load sensors  80  are coupled to the controller  68  and provide readings or measurements to the controller  68 . The load sensors  80  may be directly wired to the controller  68  or in wireless communication with the controller  68 . When wired, electrical circuits may be passed from the caster assembly  58 , through the base  34 , and to the controller  68 . In wireless configurations, the load sensor  80  may be outfitted with an integrated antenna (e.g., printed circuit board (PCB) antenna) and may communicate using any suitable communication protocol or standard, such as Bluetooth, Zigbee, ISA100.11a, WirelessHART, MiWi, WiFi, near field communication (NFC), or the like. The load sensor  80  and the controller  68  may be coupled according to any suitable network scheme, such as local area network (LAN), body area network (BAN), personal area network (PAN), wireless PAN (WPAN), low-rate WPAN (LR-WPAN), wide area network (WAN), or the like. Communication may occur at any suitable frequency band. The load sensor  80  may also be integrated on a PCB within a larger component, such as a module, which includes additional functionality, such as communication capabilities as described in any of the examples described herein. 
     The readings of the load sensor  80  may be of different types (e.g., analog, digital, etc.) depending on the configuration of the load sensors  80 . The controller  68  may comprise a load analyzer  82  embodied as hardware and/or software for analyzing the readings from the load sensors  80 . The load analyzer  82  may also reference a transformation or calibration matrix that is storable in memory of the controller  68 . The matrix transforms the raw measurement values from the load sensor  80  into the resulting forces and torques. 
     The load analyzer  82  may analyze the load readings for making one or more determinations. For instance, the controller  68  may be coupled to a user interface  84 , which is configured to receive user input commands and to display information to the user. The load sensors  80  may be utilized as part of a scale system. The load analyzer  82  may determine a weight of the patient based on the readings from the load sensors  80 . The determined patient weight may be displayed on the user interface  84 . Thus, the load sensors  80  may be understood as weight sensors in certain examples. In other examples, the controller  68  may make determinations for commanding the steering motor  70  and/or drive motor  72  based on an outcome of analyzing the load sensor  80  readings. Examples of motor control based on load sensor  80  readings are provided below. 
     As shown in the examples of  FIGS.  4 - 7   , the load sensor  80  is coupled to the stem  60 . Here, the load sensor  80  is configured to measure load applied to the stem  60 . 
     In one example, as shown in  FIGS.  4  and  5   , the load sensor  80  is disposed about or around the stem  60 . Because the stem  60  has a cylindrical configuration in  FIG.  4 A , the load sensor  80  is disposed annularly or circumferentially about the stem  60 . Of course, where the stem  60  has other cross-sectional configurations (e.g., rectangular, etc.), the load sensor  80  may be disposed around any number of edges or faces of the stem  60 . The load sensor  80  may entirely surround a portion of the stem  60  (as shown in  FIG.  4 A ). Alternatively, the load sensor  80  may partially surround a portion of the stem  60 . 
     In the embodiment shown in  FIGS.  4 A- 4 C , the load sensor  80  is embodied as a load cell. Of course, the load sensor  80  may have other configurations besides or in addition to a load cell in this example.  FIG.  4 B  shows a cross-sectional view of the load sensor  80  and stem  60  of  FIG.  4 A  at rest.  FIG.  4 C  shows a cross-sectional view of the load sensor  80  and stem  60  of  FIG.  4 A  under load. In this example, the load sensor  80  has a disc-shape, but the load sensor  80  may have other shapes. The load sensor  80  is, or has, a deformable member coupled between a first side  82  that is fixed and an opposing second side  84  that moves. The first side  82  is fixed to a rigid structure of the caster assembly  58 , such as a housing component (not shown). The second side  84  is coupled to at an inner side to the stem  60  and moves according to movement of the stem  60 . The load sensor  80  may comprise any suitable number of strain gauges integrated therewith for sensing strain from the deformation. 
     The load sensor  80  is configured to undergo compression in response to the load applied to the stem  60  or tension in response to removal of the load. The stem  60  may shift according to any one of six degree of freedoms. In one example, as shown in  FIG.  4 C , the stem  60  slightly shifts downward due to vertical downward force and shifts at an angle due to non-vertical forces. The resulting circumferential deformation of the surrounding load sensor  80  caused by shifting of the stem  60  is sensed for measuring these vertical and non-vertical forces, if present. The shifting of the stem  60  and deformation of the load sensor  80  in  FIG.  4 C  are exaggerated for illustrative purposes and may not be representative of actual conditions, which may not be directly noticeable to the naked eye. Furthermore, the load sensor  80  may have any suitable thickness other than the thickness shown in  FIG.  4 C . 
     In this example, the load sensor  80  configuration can take into account the rotational moment force caused by the offset in caster assembly  58 . That is, in situations where the caster assembly  58  is offset, the load applied will tend to pass to the floor through a path that is not directly through the swivel axis S. Instead, load path will pass through the radial center  63  of the caster wheel  62 , which is offset from the swivel axis S, as described. Therefore, the load path may take an abrupt deviation from the swivel axis S, thereby causing non-vertical forces that tilt the stem  60 , as shown in  FIG.  4 C . Described below are techniques for compensating for these non-vertical forces. 
       FIG.  5    shows another example of the load sensor  80  disposed about or around the stem  60 . Again, the first side  82  is fixed to a rigid structure of the caster assembly  58  and the second side  84  is coupled to at an inner side to the stem  60 . Here, a plurality of spokes  86  connect the fixed and moveable sides  82 ,  84 . The spokes  86  bend in response to application of the load to stem  60 . The load sensor  80  in  FIG.  5    has four spokes  86 , however, any number of spokes  86  may be utilized. A plurality of strain gauges  88  attach to each spoke  86  for measuring the strain on the spoke  86 . Each spoke  86  and the strain gauges  88  associated with each spoke  86  collectively form a single-axis load cell in load sensor  80 . The spokes  86  bend in response to load applied to the stem  60 . As shown in  FIG.  5   , the strain gauges  88  attach to the top, bottom, and sides of each spoke  86  for measuring strain on the spokes  86  resulting axial loads along the X, Y, and/or Z-axes, and/or rotational loads about the X, Y, and/or Z-axes. As such, the load sensor  80  in  FIG.  5    is configured to measure the applied load in six-degree of freedom. The load sensor  80  may be disposed about or around the stem  60  according to configurations other than those shown in  FIGS.  4  and  5   . 
     Referring now to  FIGS.  6  and  7   , another example is shown wherein the load sensor  80  is disposed on a distal end  90  of the stem  60 . In this example, the load sensor  80  has the first side  82  fixed to a rigid structure (not shown) of the caster assembly  58  or base  34  and the second side  84  coupled to the distal end  90  of the stem  60 . In this example, either the first side  82  or the second side  84  of the load sensor  80  may be coupled to a non-moving member. That is, the stem  60  in this example may be stationary or non-moving, and the rigid structure of the caster assembly  58  or base  34  may move based on the applied load, or vice-versa. 
     In the example of  FIGS.  6 A and  6 B , the load sensor  80  is a load cell configured to measure compressional force applied to the distal end  90  of the stem  60 , or absence thereof. Because the stem  60  has a cylindrical configuration in  FIG.  6   , the load sensor  80  also has a cylindrical configuration. Of course, where the stem  60  has other cross-sectional configurations (e.g., rectangular, etc.), the load sensor  80  may have similar cross-sectional configurations. Alternatively, the load sensor  80  may have a cross-sectional configuration that differs from the cross-sectional configuration of the stem  60 . The load sensor  80  may entirely occupy a surface area of the distal end  90  of the stem  60  (as shown in  FIG.  6   ). Alternatively, the load sensor  80  may occupy a portion of the surface area of the distal end  90 . The load sensor  80  may be coupled to the distal end  90  according to any means that preserves accurate load measurement, such as mechanical mounting, adhesive, welding, or the like. 
       FIG.  6 B  shows a cross-sectional view of the load sensor  80  and stem  60  of  FIG.  6 A  under load. The load sensor  80  is, or has, a compressive medium coupled between the first and second sides  82 ,  84 . The compressive medium may be a solid, liquid or gas. The load sensor  80  may be hermetically sealed to be airtight from the environment. The load sensor  80  may have a low-profile to not interfere with installation or connection of the caster assembly  58  to the base  34 . The load sensor  80  may have any suitable thickness other than the thickness shown in  FIG.  6 B . The load sensor  80  is configured to undergo compression in response to the load applied to the distal end  90 . In one example, as shown in  FIG.  6 B , the load sensor  80  compresses (not shown) due to vertical downward force. The resulting compression of the load sensor  80  is sensed for measuring these vertical downward forces, if present. Compression of the load sensor  80  in  FIG.  6 B  may not be directly noticeable to the naked eye. In this example, the compression load sensor  80  may similarly take into account the rotational moment force caused by the offset in caster assembly  58 , as described above. 
       FIGS.  7 A- 7 C  illustrate another example of the load sensor  80  being disposed on the distal end  90  of the stem  60 . In this example, the load sensor  80  is a displacement sensor configured to undergo displacement in response to the load applied to the distal end  90  of the stem  60 . The load sensor  80  measures the resulting displacement, which is indicative of the applied load. The controller  68  can convert displacement readings into force readings using the load analyzer  82  and any suitable transformation matrix. In  FIG.  7 A- 7 C , the displacement sensor is embodied with a biasing member  92 , such a coil spring. Other biasing members  92  other than a coil spring may be utilized, such as tension (torsion) spring, leaf (flat) spring, conical springs, wire ring springs, or the like. The biasing member  92  may have any appropriate spring constant, which can be calibrated for expected loads applied to the patient support apparatus  30 . In this example, the load sensor  80  has a cylindrical shape, but the load sensor  80  may have other shapes, as described. 
     In this example, the load sensor  80  has the first side  82  fixed to a rigid structure of the caster assembly  58  or base  34  and the second side  84  coupled to the distal end  90  of the stem  60 . In this example, either the first side  82  or the second side  84  of the load sensor  80  may be coupled to a non-moving member. That is, the stem  60  in this example may be stationary or non-moving, and the rigid structure of the caster assembly  58  or base  34  may move based on the applied load, or vice-versa. Specifically, in  FIG.  7   , the first side  82  of the biasing member  92  is coupled to a plate  94  that is in-line with the distal end  90 . A plunger  96  is coupled between the plate  94  and the distal end  90  of the stem  60 . The load sensor  80  may comprise any suitable sensor, such as those described above, for measuring displacement of the biasing member  92 , plate  94  and/or plunger  95 . 
       FIG.  7 B  shows a cross-sectional view of the load sensor  80  and stem  60  of  FIG.  7 A  at rest.  FIG.  7 C  shows a cross-sectional view of the load sensor  80  and stem  60  of  FIG.  7 A  under load. At rest, the biasing member  92  has a length L, as shown in  FIG.  7 B . Under load, the biasing member  92  has a different length, L′, which will vary depending on the magnitude of the load. The biasing member  92  compresses when a vertical downward force is applied to the distal end  90 . Such compression may be due to force applied downward from movement of the plate  94  and/or from upward force applied from movement of the stem  60 . The length L′ of the biasing member  92  decreases as compared with the length L in the at-rest state as a result of this compression. The resulting displacement is shown by Δ in  FIG.  7 C , which is a difference between L and L′. In  FIG.  7   , the displacement is measured in the Z-direction. However, it should be appreciated that the displacement may be according to any other direction or directions depending on the configuration of the biasing member  92 . For example, displacement may be measured in a rotational fashion, e.g., by measuring how much the biasing member  92  has twisted based on the load, or the like. 
     In some examples, more than one load sensor  80  may be stacked on top of one another over the distal end  90  of the stem  60 . These stacked load sensors  80  may be of a similar or a different configuration from one another. Furthermore, load sensors  80  coupled directly to the distal end  90  of the stem  60  may have configurations other than those shown in  FIGS.  6  and  7    and may measure load according to techniques other than those shown. 
     Referring now to  FIG.  8   , another example is illustrated wherein the load sensor  80  is coupled to the caster wheel axle  64  and is configured to measure load applied to the caster wheel axle  64 . The caster wheel axle  64  comprises a first end  100  and a second end  102 , which are coupled to the caster wheel  62 . These ends  100 ,  102  may be fastened to the caster wheel  62  using any suitable means, such as bolts as shown in  FIG.  8   , or the like. 
     The load sensor  80  may be disposed according to any suitable fashion in cooperation with the caster wheel axle  64 , or any part thereof. For example, as shown in  FIG.  8   , the load sensor  80  is disposed on a surface of the caster wheel axle  64  and along the rotational axis R of the caster wheel axle  64 . The load sensor  80  may have any suitable length along the caster wheel axle  64 . For example, the load sensor  80  may extend along an entirety or a portion of the length of the caster wheel axle  64 . More than one load sensor  80  may extend along the rotational axis R of the caster wheel axle  64  and such load sensors  80  may be disposed circumferentially on opposing faces of the caster wheel axle  64 , e.g., four load sensors  80  being 90 degrees apart from one another. 
     Additionally or alternatively, one or more load sensors  80  may be disposed annularly or circumferentially about the caster wheel axle  64  and the rotational axis R. One or more load sensors  80  may entirely surround a portion of the caster wheel axle  64  or may partially surround a portion of the caster wheel axle  64 . Such load sensors  80  may be disposed laterally on opposing sides of the caster wheel axle  64 , e.g., every 1 mm along the length of the caster wheel axle  64 . 
     Additionally or alternatively, one or more load sensors  80  may be coupled to each of the ends  100 ,  102  of the caster wheel axle  64  for sensing the load. In such scenarios, the load sensors  80  may measure a sheer force applied between the caster wheel axle  64  and the ends  100 ,  102  of the caster wheel axle  64 . 
     In the embodiment shown in  FIGS.  8 A- 8 C , the load sensor  80  is embodied as a load cell. The load sensor  80  may comprise any suitable number of strain gauges integrated with the caster wheel axle  64  for sensing strain from the application of the load to the caster wheel axle  64 . Of course, the load sensor  80  integrated with the caster wheel axle  64  may have any other configuration besides or in addition to a load cell, such as those described above. 
       FIG.  8 B  shows an isolated view of the load sensor  80  and caster wheel axle  64  of  FIG.  8 A  at rest.  FIG.  8 C  shows the load sensor  80  and caster wheel axle  64  of  FIG.  8 A  under load. The load sensor  80  is configured to undergo compression or tension, depending on its positioning, in response to the load applied to the caster wheel axle  64  or in response to removal of the load. The caster wheel axle  64  may bend or deform along according to any one of six degree of freedoms. In one example, as shown in  FIG.  8 C , the caster wheel axle  64  slightly bends downward due to vertical downward force from the load. The resulting deformation of the caster wheel axle  64  is sensed by the load sensor  80  for measuring this vertical force, if present. The bending of the caster wheel axle  64  and the load sensor  80  in  FIG.  8 C  are exaggerated for illustrative purposes and may not be representative of actual conditions, which may not be directly noticeable to the naked eye. 
     As with the above examples, the load sensor  80  configuration in  FIG.  8    is also equipped to take into account the rotational moment force caused by the offset in caster assembly  58 . As described, the load path with the offset caster assembly  58  will pass through the radial center  63  and/or rotational axis R of the caster wheel  62 . Therefore, sensing the load on the caster wheel axle  64  is particularly suitable for accounting for rotational moment force caused by the offset because the caster wheel axle  64  is directly in the offset load path. The load sensors  80  may be cooperative with the caster wheel axle  64  for sensing the load according to configurations other than those described herein. 
     In another embodiment, the load sensor  80  may be integrated with the caster wheel  62 . In such examples, the load sensor  80  is configured to measure load applied to caster wheel  62 . The load sensor  80  may be integrated with the caster wheel  62  according to various manners. For instance, the load sensor  80  may be integrated with any one or more of an interior surface of the caster wheel  62 , an exterior surface of the caster wheel  62 , an interior volume  110  of the caster wheel  62 , and/or any other component of the caster wheel  62 , such as a wheel rim, wheel tread, wheel disc, wheel bearing, wheel fastener, wheel valve stem, wheel belt, wheel braking or steering member, or the like. Any number of load sensors  80  may be integrated with the caster wheel  62 . 
     In one example, as shown in  FIG.  9   , the caster wheel  62  is an inflatable type and comprises pressurized air within the interior volume  110  of the caster wheel  62 . In  FIG.  9   , the pressurized air is shown only for a portion of the interior volume  110  for simplicity. In this example, the load sensor  80  is embodied as a pressure sensor configured to measure air pressure of the caster wheel  62 . The load sensor  80  may be disposed at any suitable location for measuring air pressure. As shown in  FIG.  9   , the load sensor  80  is disposed in the interior volume  110  of the caster wheel  62 . For example, the load sensor  80  is coupled to a surface of the caster wheel  62  that defines the interior volume  110 , such as the wheel rim. The load sensor  80  may be integrated directly at the wheel valve stem of the caster wheel  62  or integrated on a flexible band coupled to the wheel rim. However, as described, other locations for the load sensor  80  are contemplated. In this example, the load sensor  80  wirelessly transmits readings to the controller  68  using any of the techniques described herein, or the like. 
       FIG.  9 A  shows the load sensor  80  measuring air pressure of the caster wheel  62  when the caster wheel  62  is at rest, e.g., without load being applied.  FIG.  9 B  shows the load sensor  80  measuring air pressure of the caster wheel  62  when load is applied to the caster wheel  62 . The applied load causes compression of the interior volume  110  of the inflatable caster wheel  62  relative to the floor surface, as shown in  FIG.  9 B . As a result, the pressure of the air within the interior volume  110  increases. This increase in air pressure is indicative of the applied load and is detected by the load sensor  80 . The controller  68  can convert pressure readings into force readings using the load analyzer  82  and any suitable transformation matrix. The load sensor  80  may measure air pressure according to other techniques not described herein. 
     In other examples for measuring air pressure, the load sensor  80  may measure physical characteristics of the caster wheel  62  such that the controller  68  and load analyzer  82  can implement algorithms (such as spectrum analysis) to predict the air pressure. Such physical characteristics may comprise angular velocity of the caster wheel  62 , frequencies emitted by the caster wheel  62  during rotation, and the like. 
     The caster wheel  62  may be an airless (non-inflatable) wheel, wherein the interior volume  110  is occupied by solid material, such as compressible rubber, polymer, etc. In such examples, air pressure is non-existent, and the load sensor  80  instead may be embodied as a load cell or strain gauge integrated on and/or within the solid material. As the solid material of the caster wheel  62  compresses under the applied load, the load sensor  80  is able to the detect strain indicative of the load. The load sensor  80  may be integrated with the caster wheel  62  according to techniques other than those described herein. 
     As with the above examples, the load sensor  80  configuration in  FIG.  9    is also equipped to take into account the rotational moment caused by the offset in caster assembly  58 . As described, the load path with the offset caster assembly  58  will pass through the radial center  63  and/or rotational axis R of the caster wheel  62 . Therefore, sensing the load on the caster wheel  62  is particular suitable for accounting for rotational moment caused by the offset because the caster wheel  62  is directly in the offset load path. 
     Referring now to  FIGS.  10  and  11   , techniques are described for analyzing readings of the load sensor  80  with the controller  68  and executing control schemes based on analysis of the load sensor  80  readings. 
     As described, the load sensor  80 , in many embodiments, is configured to measure the load according to many degrees of freedom. In other words, the applied load may have various components of force and/or torque. For instance, as described throughout, the load on the caster wheel  62  may comprise rotational moment caused by the offset nature of the caster wheel  62 . Thus, the components of force and/or torque may have magnitude and direction. The direction of the load components may depend on many factors, such as the load path, the configuration and/or location of the load sensor  80  on the caster assembly  58 , the nature of the applied load, and the like. 
     Because the load sensor  80  is particularly configured for the patient support apparatus  30 , accurately measuring the weight of the patient based on the sensed load is important. In order to accurately measure the patient weight, the primary focus of the applied load is a vertical component of the load, e.g., load in the downward Z-axis direction. For example, the vertical component of the load may be understood as the load component directed from the patient support surfaces  42 ,  43  to the floor surface. However, the load sensor  80  may produce measurements indicative of vertical load and non-vertical load applied to the caster assembly  58 , as described above. These non-vertical components may be rotational moments and/or forces in non-vertical directions, such as in the X or Y-axis directions. 
     Upon receiving the load measurements from the load sensor  80 , the controller  68 , and load analyzer  82 , may be configured to analyze the measurements to decompose these vertical and non-vertical components of the load. The controller  68  is configured to utilize computer-implemented techniques for negating the non-vertical components of the load. As a result, the controller  68  can output load determinations based on the vertical component of the load. The controller  68  may use software for implementing these techniques and may include known geometric data, such as calibration data, about the caster assembly  58  or any component thereof, and about the load sensor  80  for analyzing the load. 
     To illustrate according to one simplified example,  FIG.  10 A  is a diagram illustrating vertical and non-vertical components of the load applied to a rigid body as detected by the load sensor  80 . As illustrated, the controller  68  decomposes the load into four separate vectors, i.e., a, b, c, d. In this example, the vectors each have a vertical component a z , b z , c z , d z , which is a Z-axis downward force, and a non-vertical component, a x , b x , c x , d x , which in this example is an X-axis horizontal force. Here, vector a is purely horizontal and therefore has a vertical component a z  equal to zero. Vector c is purely vertical and therefore has a non-vertical component c x  equal to zero. Vectors b and d have non-zero vertical and non-vertical components. Of course, illustration of these load components in  FIG.  10    is for illustrative purposes and the controller  68  may decompose the load with or without any such visualization. 
       FIG.  10 B  is a diagram illustrating a combined vertical component of the load from  FIG.  10 A  wherein non-vertical components of the load are negated by the controller  68 . Here, the controller  68  negates, or otherwise factors out the non-vertical components a x , b x , c x , d x  decomposed from the applied load and preserves the vertical components a z , b z , c z , d z . Specifically, the controller  68  generates a vector n having a vertical component n z  having a magnitude based on the combination of the magnitudes of the vertical components a z , b z , c z , d z . In turn, the controller  68  can use computer-implemented techniques to extract the vertical component from the applied load quickly and accurately. 
     The phrases “vertical” and “non-vertical” with respect to the load, or components thereof, are orientation specific, i.e., Z-axis direction and non-Z-axis direction, respectively. However, it is fully contemplated that the controller  68  can negate any component of the load depending on the component of the load desired for extraction. For instance, the controller  68  may alternatively negate the vertical load where extraction of the horizontal load is desired. Furthermore, the example in  FIG.  10    shows vector components only for forces along the Z and X-axes. As described, the load may comprise rotational moments about any of the axes and therefore, the controller  68  may extract and/or negate any rotational moments. The controller  68  may do so using advanced vector analysis or any other mathematical technique. 
     Referring to  FIG.  11   , one example of control executed by the controller  68  in response to analysis of the load sensor  80  readings is described. In this example, the caster assembly  58  is an offset-type and therefore has a trailing orientation. The load sensor  80  is integrated with the caster assembly  58  according to any technique described herein. The controller  68  analyzes the load sensor  80  readings to determine a state of the caster assembly  58 . Specifically, the controller  68  can determine a location and/or orientation of the caster assembly  58  based on the load readings. For example, using techniques wherein the load sensor  80  is disposed around the stem  60  such as shown in  FIGS.  4  and  5   , the load sensor  80  detects circumferential strain relative to the stem  60 . Using this detection alone, or in conjunction with stored calibration data, the controller  68  can determine that the caster wheel  62  is in a specific orientation. 
     For instance, as shown in  FIG.  11   , the offset caster assembly  58  is shown in a top view in a first state (shown in phantom). Because of the offset configuration, the load sensor  80  detects a rotational moment. The rotational moment is detected about an axis that is parallel to position of the rotational axis R of the caster wheel  62 . In the first state as shown in  FIG.  11   , the rotational axis R of the caster wheel  62  extends vertically (from the top view), and hence, the rotational moment would be about an axis that extends vertically across the swivel axis S. From this, the controller  68  can determine the orientation of the rotational axis R, and ultimately, the orientation of the caster wheel  62 , which in this example is trailing to the left. Using this technique, the controller  68  can determine the orientation of the caster wheel  62  in full range of motion, e.g., 360 degrees about the swivel axis S. 
     The weight and bulk of the patient support apparatus  30 , including the weight of the patient supported thereon, can make it difficult for a caregiver to manually wheel the patient support apparatus  30  from one location to another. Free rotational movement of the caster assemblies  58  can increase this difficulty. Mainly, much of the effort in initiating movement of the patient support apparatus  30 , such as by pushing or pulling on the headboard  52 , is directed to first causing caster assemblies  58  to align with the direction of desired movement (shown by the arrow in  FIG.  11   ) so that the caster assemblies  58  have a trailing orientation with respect to the direction of desired movement. In other words, a start-up force needed to move the patient support apparatus  30  with the caster assemblies  58  in a non-trailing orientation is much greater than the start-up force needed to move the patient support apparatus  30  with the caster assemblies  58  aligned in the trailing orientation. Often, the orientation that the caster wheels  62  assumed when the patient support apparatus  30  was placed in a room is the opposite orientation that the caster wheels  62  need to assume in order to move the patient support apparatus  30  out of the room. 
     To minimize such effort, the controller  68  is configured to control the steering motor  70  of the caster assembly  58  in response to the orientation of the caster assembly  58  as determined based on the load sensor  80  readings, as described above. Specifically, the controller  68  is configured to control the steering motor  70  to move the caster assembly  58  to the trailing orientation with respect to the direction of desired movement. In  FIG.  11   , a second state of the caster assembly  58  (shown in solid lines) is shown in the trailing position relative to the desired direction of movement (arrow). The caster assembly  58  is moved to the trailing positon by the steering motor  70  after being rotated from the non-trailing position of the first state. 
     As such, the techniques described herein provide automatic re-alignment of the caster assembly  58 . Such re-alignment may occur before the patient support apparatus  30  is manually moved the operator. For instance, the operator need not be present near the patient support apparatus  30  in order for the re-alignment to occur. This is because re-alignment is based on readings from the load sensor  80  integrated with the caster assembly  58 . Therefore, even while the patient support apparatus  30  is stationary, the controller  68  can nevertheless make such determinations because the offset caster wheel  62  load is continuously detectable by the load sensor  80 . 
     In other examples, the controller  68  may command the steering motor  70  to re-align the caster assembly  58  upon detection of movement of the patient support apparatus  30  in the desired direction of movement. Techniques for determining the desired direction of movement of the patient support apparatus  30  may be like those described in U.S. Patent Application Publication No. 2016/0089283, entitled “Patient Support Apparatus,” the disclosure of which is hereby incorporated by reference in its entirety. 
     Although re-alignment to the trailing position has been described, it should be appreciated that the controller  68  can command various other types of re-alignment of the caster assembly  58  based on readings from the load sensor  80 . For instance, the controller  68  may command the steering motor  70  to move the caster wheels  62  to non-trailing orientations for purposes, such as steering of the patient support apparatus  30  based on prediction of a change in desired direction, or the like. 
     It will be further appreciated that the terms “include,” “includes,” and “including” have the same meaning as the terms “comprise,” “comprises,” and “comprising.” 
     Several embodiments have been discussed in the foregoing description. However, the embodiments discussed herein are not intended to be exhaustive or limit the invention to any particular form. The terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teachings and the invention may be practiced otherwise than as specifically described.