Patent Publication Number: US-2021186783-A1

Title: Power Management Techniques For Actuators Of Patient Support Apparatuses

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/041,014, filed on Jul. 20, 2018 which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/535,278, filed on Jul. 21, 2017, the disclosures of each of which are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Actuators are commonly used on a patient support apparatus for various purposes. For example, the patient support apparatus may be equipped with a lift assembly that uses actuators to lift a patient resting on a patient support surface to a desired height. Another example of is an actuator used to manipulate angular positioning of portions of the patient support surface, such as the fowler, etc. 
     Control of such actuators according to conventional techniques falls short in many ways. For example, the actuator is typically preconfigured and controlled to provide the same output regardless of the load applied to the actuator. For instance, the actuator responds with the same speed of movement regardless of weight of the patient. 
     Moreover, actuators typically draw in more electrical current with increases in torque applied to the actuator, and consequently with increases in load applied to the actuator. Accordingly, conventional control systems for actuators do not take into account such increases in drawn electrical current when patients of greater weight are on the patient support apparatus. Patient support apparatuses often receive power from the AC electrical outlets of a healthcare facility when they are docked. Consequently, when one or more actuators are under heavy load, there is a possibility to overload the electrical system of the facility based on overload in drawn electrical current. Such overload may result in triggering circuit protection means (e.g., circuit breakers) for the facility electrical system. In turn, critical power to the patient support apparatus may be interrupted. Furthermore, resetting such circuit protection means is inconvenient and time consuming. As such, there are opportunities to address at least the aforementioned problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present disclosure will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of a patient support apparatus. 
         FIG. 2  is a perspective view, partially in phantom, of the patient support apparatus comprising actuators shown undergoing an applied load. 
         FIG. 2A  is a magnified view, partially in phantom, of the actuator of the patient support apparatus. 
         FIG. 3A  is a side view of a base and support structure of the patient support apparatus wherein the support structure is at a lowered position relative to the base. 
         FIG. 3B  is a side view of the base and the support structure of the patient support apparatus wherein the support structure is elevated from the base by the actuators. 
         FIG. 4  is a block diagram of one example of a controller of the patient support apparatus for controlling the actuators based on the applied load. 
         FIGS. 5, 6, and 7  are various examples of graphs showing output power of the actuator of the patient support apparatus controlled relative to desired output power. 
         FIGS. 8 and 9  are examples of graphs showing output power of two actuators of the patient support apparatus controlled relative to common desired output power. 
         FIG. 10  is a block diagram showing further aspects of the controller for monitoring an applied electrical current. 
         FIG. 11  is a block diagram showing further aspects of the controller for determining an applied voltage. 
         FIG. 12  is a block diagram of the controller interacting with a resettable fuse of the patient support apparatus. 
         FIG. 13  is a block diagram of the controller implementing a feedback loop based on the applied electrical current to the actuator for controlling the applied voltage to the actuator. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, power management techniques for one or more actuators  140  of a patient support apparatus  100  are provided. 
     I. Patient Support Apparatus Overview 
     Referring to  FIG. 1 , a patient support apparatus  100  is shown for supporting a patient in a health care setting. The patient support apparatus  100  illustrated in  FIG. 1  comprises a hospital bed. In other embodiments, however, the patient support apparatus  100  may comprise a stretcher, cot, table, wheelchair, or similar apparatus utilized in the care of a patient. 
     A support structure  110  provides support for the patient. The support structure  110  illustrated in  FIG. 1  comprises a base  120  and a support frame  36 . The base  120  comprises a base frame  35 . The support frame  36  is spaced above the base frame  35  in  FIG. 1 . The support structure  110  also comprises a patient support deck  38  disposed on the support frame  36 . The patient support deck  38  comprises several sections, some of which are capable of articulating relative to the support frame  36 , such as a back section, a seat section, a thigh section, and a foot section. The patient support deck  38  provides a patient support surface  130  upon which the patient is supported. 
     A mattress (not shown) is disposed on the patient support deck  38  during use. The mattress comprises a secondary patient support surface upon which the patient is supported. The base  120 , support frame  36 , patient support deck  38 , and patient support surfaces  130  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  100 . The construction of the support structure  110  may take on any suitable design, and is not limited to that specifically set forth above. In addition, the mattress may be omitted in certain embodiments, such that the patient rests directly on the patient support surface  130 . 
     Side rails  44 ,  46 ,  48 ,  50  are coupled to the support frame  36  and are thereby supported by the base  120 . A first side rail  44  is positioned at a right head end of the support frame  36 . A second side rail  46  is positioned at a right foot end of the support frame  36 . A third side rail  48  is positioned at a left head end of the support frame  36 . A fourth side rail  50  is positioned at a left foot end of the support frame  36 . If the patient support apparatus  100  is a stretcher or a cot, there may be fewer side rails. The side rails  44 ,  46 ,  48 ,  50  are movable to a raised position in which they block ingress and egress into and out of the patient support apparatus  100 , one or more intermediate positions, and a lowered position in which they are not an obstacle to such ingress and egress. In still other configurations, the patient support apparatus  100  may not include any side rails. 
     A headboard  52  and a footboard  54  are coupled to the support frame  36 . In other embodiments, when the headboard  52  and footboard  54  are included, the headboard  52  and footboard  54  may be coupled to other locations on the patient support apparatus  100 , such as the base  120 . In still other embodiments, the patient support apparatus  100  does not include the headboard  52  and/or the footboard  54 . 
     Caregiver interfaces  56 , such as handles, are shown integrated into the footboard  54  and side rails  44 ,  46 ,  48 ,  50  to facilitate movement of the patient support apparatus  100  over floor surfaces. Additional caregiver interfaces  56  may be integrated into the headboard  52  and/or other components of the patient support apparatus  100 . The caregiver interfaces  56  are graspable by the caregiver to manipulate the patient support apparatus  100  for movement. 
     Wheels  58  are coupled to the base  120  to facilitate transport over the floor surfaces. The wheels  58  are arranged in each of four quadrants of the base  120  adjacent to corners of the base  120 . In the embodiment shown, the wheels  58  are caster wheels able to rotate and swivel relative to the support structure  110  during transport. Each of the wheels  58  forms part of a caster assembly  60 . Each caster assembly  60  is mounted to the base  120 . It should be understood that various configurations of the caster assemblies  60  are contemplated. In addition, in some embodiments, the wheels  58  are not caster wheels and may be non-steerable, steerable, non-powered, powered, or combinations thereof. Additional wheels are also contemplated. For example, the patient support apparatus  100  may comprise four non-powered, non-steerable wheels, along with one or more powered wheels. In some cases, the patient support apparatus  100  may not include any wheels. 
     In other embodiments, one or more auxiliary wheels (powered or non-powered), which are movable between stowed positions and deployed positions, may be coupled to the support structure  110 . In some cases, when these auxiliary wheels are located between caster assemblies  60  and contact the floor surface in the deployed position, they cause two of the caster assemblies  60  to be lifted off the floor surface thereby shortening a wheel base of the patient support apparatus  100 . A fifth wheel may also be arranged substantially in a center of the base  120 . 
     An actuator  140 , shown in  FIG. 2 , is coupled to the support structure  110  and is operable to move the patient support surface  130 , and/or one or more components thereof. In the embodiment of the patient support apparatus  100  shown in  FIG. 2 , the patient support apparatus  100  includes two actuators  140 . However, the patient support apparatus  100  and any of the techniques described herein may utilize any number of actuators  140  individually or in combination. 
     The actuator  140  may have any configuration suitable for moving the patient support surface  130 . For example, the actuator  140  may be a mechanical, hydraulic, pneumatic, electric, thermal, or magnetic actuator. The actuator  140  may include a motor and may be a rotational actuator or a linear actuator. In a further example, the actuator  140  may be an inflatable actuator that inflates to move the patient support surface  130 . The actuator  140  may create any suitable type of motion for the patient support surface  130 , such as linear motion, rotational motion, angular motion, and the like. 
     Additionally, the actuator  140  may be configured to move the patient support surface  130  in a variety of directions. In  FIGS. 3A and 3B , the actuator  140  moves the patient support surface  130  along a vertical Y-axis. However, the actuator  140  may move the patient support apparatus  100  along any combination of Y, X, and Z-axes, which are shown in  FIG. 2 . 
     The patient support apparatus  100 , as shown in  FIG. 2 , also includes a controller  170  coupled to and controlling the actuator  140 . For example, in  FIGS. 3A and 3B , the controller  170  controls the actuator  140  to move the patient support surface  130  along the vertical Y-axis. 
     The actuator  140  may be configured to move the patient support surface  130  based on a state of the patient support apparatus  100 . For example, as shown in  FIG. 2 , a load  160  is applied to the actuator  140 . In  FIG. 2 , the load  160  is applied because of a placement of the patient on the patient support surface  130 . The load  60  may relate, for example, to a weight of the patient  150 . As shown in  FIGS. 2, 2A, 3A, 3B , the patient support apparatus  100  may also include a sensor  178 , which is coupled to the controller  170  and configured to produce readings indicative of the load  60 . As follows, the actuator  140  may move the patient support surface  130  based on the load  160 , an existence of the load  160 , a current demanded by the load  160 , and a voltage to be applied by the actuator  140  as a result of the load  160 . 
     II. Operation of the Controller and Actuator 
     As shown in  FIG. 4 , a power supply  190  provides the actuator  140  with electrical energy, which the actuator  140  uses to produce an output power  186  to move the patient support surface  130 . The output power  186  is the actual power produced by the actuator  140  during movement of the patient support surface  130 . The power supply  190  may provide electrical energy to the actuator  140  through an input of the controller  170  in the form of an applied electrical current  184  and an applied voltage  182 . For instance, the applied electrical current  184  provided by the power supply  190  may be drawn in by the actuator  140  after the actuator  140  receives the load  160 . In such an instance, the applied electrical current  184  may be a function of the load  160 , such as a torque, applied to the actuator  140 . Additionally, the applied voltage  182  may be provided to the actuator  140  via the controller  170 , allowing the controller  170  to modify the applied voltage  182 . In such an instance, the controller  170  may control a rate of motion, such as a rotational speed, of the actuator  140  by modifying the applied voltage  182 . In this way, the controller  170  may control the actuator  140 . The actual output power  186  may be monitored by the controller  170  periodically (e.g., every 1 millisecond) or continuously. 
     The controller  170  is configured to control the actuator  140  relative to a desired output power  176 . The desired output power  176 , represented by block  176  in the controller  170  of  FIG. 4 , is a desired amount of power to be used or consumed by the actuator  140  during operation, such as to move the patient support surface  130 . For example, the controller  170  may control the actuator  140  such that a difference (e.g., error) between the (actual) output power  186  and the desired output power  176  is minimized. However, there may be other ways to control the actuator  140  relating to the actual and desired output power  186 ,  176 . The desired output power  176  may be stored in a memory device integrated with or coupled to the controller  170 . The desired output power  176  may be known to the system prior to starting production of the output power  186  or known and updated “on the fly” prior to subsequent production of output power  186 . In some embodiments, the desired output power  176  relates to a predetermined maximum power value of the power supply  190  or other power parameters of the power supply  190  coupled to the actuator  140 . The desired output power  176  may be a limit that should not be exceeded over a period of time. As such, the system and techniques for operating the patient support apparatus  100  allow for control of the actuator  140  using a maximum power available from the power supply  190  without overloading the power supply  190 . The desired output power  176  may also relate to performance parameters of the actuator  140  itself. 
     Furthermore, the controller  170  is configured to control the actuator  140  in response to the load  160  being applied to the actuator  140 . Referring back to the embodiment of the patient support apparatus  100  shown in  FIGS. 3A and 3B , the controller  170  is shown receiving a reading of the load  160  from the sensor  178 . In this embodiment, the load  160  corresponds to the force of gravity on the mass of the patient and is therefore applied in a direction along the Y-axis. Of course, the load  160  may be applied in a variety of other ways. After receiving a reading of the load  160 , the controller  170  controls the actuator  140  to move the patient support surface  130  in response to the load  160 . In some embodiments, the controller  170  may control a rate of motion (e.g., a rotational speed) of the actuator  140  in response to the load. 
       FIG. 4  illustrates an embodiment of the controller  170 . The controller  170  of  FIG. 4  may be configured to control the actuator  140  relative to the desired output power  176  and in response to the load  160 . For example, the controller  170  may be configured to control the actuator  140  by determining the desired output power  176  of the actuator  140  and controlling the actuator  140  such that a difference between the (actual) output power  186  produced by the actuator  140  and the desired output power  176  is minimized. The output power  186 , shown in  FIG. 4 , represents the amount of power the actuator  140  produces to move the patient support surface  130 . For simplicity, the output power  186  is shown at an output side of the actuator  140 . To minimize the difference between the output power  186  and the desired output power  176 , the controller  170  controls the electrical energy provided to the actuator  140  from the power supply  190 . In the embodiment of  FIG. 4 , the actuator  140  draws in the applied electrical current  184  in response to the load  160 . In response, the controller  170  controls the electrical energy provided to the actuator  140  by modifying the applied voltage  182  based on the desired output power  176  and a reading of the applied electrical current  184 . Therefore, once the actuator  140  draws in the applied electrical current  184  from the power supply  190  and receives the applied voltage  182  from the power supply  190  via the controller  170 , the actuator  140  produces the corresponding output power  186  to move the patient support apparatus  100 . 
     The controller  170  of  FIG. 4  may modify the applied voltage  182  based on the desired output power  176  and the applied electrical current  184 . Depending on the load  160  being applied to the actuator  140 , the applied electrical current  184  drawn from the power supply  190  will vary. Accordingly, when the applied electrical current  184  varies, the applied voltage  182  may be modified to minimize a difference between the output power  186  and the desired output power  176 . As shown in  FIG. 4 , the controller  170  senses the applied electrical current  184  drawn from the power supply  190  with the sensor  178 . An applied voltage determination block  174  of the controller  170  then determines the applied voltage  182  based on the desired output power  176  and the applied electrical current  184  reading from the sensor  178 . For example, the voltage determination block  174  may determine the applied voltage  182  by dividing the desired output power  176  by the applied electrical current  184  reading. As such, when variations in the load  160  affect the applied electrical current  184 , the controller  170  modifies the applied voltage  182  to modify the output power  186  relative to the desired output power  176 . Furthermore, the controller  170  is able to modify the applied voltage  182  prior to, after, or concurrent to the applied electrical current  184  being drawn by the actuator  140 . In this way, the controller  170  controls the actuator  140  relative to the desired output power  176  by modifying the applied voltage  182  to compensate for the load  160  being applied to the actuator  140 . 
     In some embodiments, the controller  170  modifies a rate of motion by which the actuator  140  moves the patient support surface  130  by modifying the applied voltage  182 . For example, referring the  FIG. 2 , the actuator  140  is a rotational actuator, which includes a rotational motor  142 , and the applied voltage  182  relates to a rotational speed  188  (referring to  FIG. 2A ) by which the rotational actuator  140  moves, producing motion (e.g., linear motion or otherwise) of the patient support surface  130 . As such, the controller  170  may control the rotational speed  188  of the rotational actuator  140  by modifying the applied voltage  182 . The power management techniques described herein may be utilized with any type of actuator  140  and any type of actuator  140  motion (e.g., rotational, linear, etc.) 
     The controller  170  of  FIGS. 2 and 2A  modifies the rotational speed  188  of the rotational actuator  140  relative to the desired output power  176  and in response to the load  160 . In  FIG. 2 , the load  160  relates to a weight of the patient  150 . In one scenario, a heavier patient  150  will cause the rotational actuator  140  to draw more electrical current from the power supply  190  when moving the patient support surface  130 , increasing the applied electrical current  184  value. The controller  170  may then minimize a difference between the output power  186  and the desired output power  176  by preventing an increase in the output power  186  from the increased applied electrical current  184 , the controller  170  decreases the applied voltage  182 . As such, the controller  170  decreases the rotational speed  188  of the rotational actuator  140  to compensate for the heavier weight of the patient  150 , and ultimately, causes the rotational actuator  140  to produce the output power  186  relative to the desired output power  176 . In an alternative scenario, a lighter patient  150  will cause the rotational actuator  140  to draw relatively less electrical current from the power supply  190  when moving the patient support surface  130 . The controller  170  may then minimize a difference between the output power  186  and the desired output power  176  by preventing a decrease in the output power  186  from the decreased applied electrical current  184 , the controller  170  increases the applied voltage  182 . As such, the controller  170  increases the rotational speed  188  of the rotational actuator  140  to compensate for the lighter weight of the patient  150 , and ultimately, causes the rotational actuator  140  to produce the output power  186  relative to the desired output power  176 . Through these techniques, the controller  170  is able to effect movement of the patient support apparatus  100  with the rotational actuator  140 , or any suitable actuator  140 , at the fastest possible rate of motion and without overloading the power supply  190 . 
     There are various methods the controller  170  may use to manage the output power  186  relative to the desired output power  176 , or vice-versa. For example,  FIGS. 5-9  demonstrate a variety of methods where the difference between the output power  186  and the desired output power  176  is minimized, as well as a variety of other methods of controlling the actuator  140  relative to the desired output power  176 . 
     In  FIG. 5 , a first example is shown where the controller  170  is configured to control the actuator  140  such that the output power  186  (dotted line) produced by the actuator  140  is adjusted to be equivalent to the desired output power  176 . In this example, the output power  186  is near instantaneously adjusted to be the same as the desired output power  176  at t=0. Such adjustment may occur prior to the output power  186  being produced, after the output power  186  is produced, or concurrent to the output power  186  being produced. 
     In another example in  FIG. 5 , the controller  170  controls the actuator  140  such that the output power  186 ′ is adjusted progressively towards the desired output power  176 . Here, the controller  170  is able to monitor the output power  186  of the actuator  140  to reduce the error between the output power  186  and the desired output power  176 . Closed loop control schemes, such as, but not limited to those described herein, may be utilized to accomplish this control. For example, in some instances, the output power  186 ′ may overshoot the desired output power  176  before stabilizing at the desired output power  176 . 
     In  FIG. 6 , the desired output power  176  is a range. In embodiments of the patient support apparatus  100  that require a greater level of flexibility for operation of the actuator  140 , providing the range for the desired output power  176  may be desirable. In such embodiments, the controller  170  may control the actuator  140  such that the output power  186  (dotted line) is equivalent to any value within the range or such that the output power  186 ′ (solid line) progressively approaches the range. 
     In  FIG. 7 , the desired output power  176  is variable. In embodiments of the patient support apparatus  100  that require a variable amount of power with respect to time, such a configuration of the controller  170  may be desirable. For instance, the desired output power  176  may be varied depending upon a monitored load on the power supply  190 , a monitored power consumption by the patient support apparatus  100 , a monitored number of actuators  140  being utilized, or the like. In such embodiments, the controller  170  may control the actuator  140  such that the output power  186  (dotted line) is equivalent to the variable desired output power  176  or such that the output power  186 ′ (solid line) progressively approaches the variable desired output power  176 . 
     The desired output power  176  may be varied according to any mathematical function. For example, the desired output power  176  may be controlled according to any order and type of function, such as a linear function, a quadratic function, an exponential function, a polynomial function, a sinusoidal function, a logarithmic function, or irregularly/intermittently based on factors that may dynamically cause modification to the desired output power  176 . 
     As described, the controller  170  may control more than one actuator  140 , and may do so relative to the desired output power  176 . For example, as shown in  FIG. 8 , the controller  170  controls the actuators  140  such that the output power  186  produced by each of the actuators  140  individually is controlled relative to the desired output power  176 . In the example of  FIG. 8 , the controller  170  accomplishes this task by controlling the more than one actuators  140  relative to an Output Power 1 and an Output Power 2, where a sum of Output Power 1 and Output Power 2 is equivalent to the desired output power  176 . In other words, the controller  170  controls each actuator  140  such that an output power  186  of a first actuator  140  is equivalent to Output Power 1 and an output power  186  of a second actuator  140  is equivalent to Output Power 2, where a sum of Output Power 1 and Output Power 2 is equivalent to the desired output power  176 . Therefore, the controller  170  is able to control more than one actuator  140 , while controlling the sum of the output powers  186  relative to the desired output power  176 . Additionally, while the control technique shown in  FIG. 8  illustrates that the controller  170  controls the first and second actuators  140  simultaneously at a time “t=0”, in other instances of the control technique, the controller  170  may control the first and second actuators  140  at a different time. For example, in one embodiment, the controller  170  may control one actuator  140  after controlling another actuator  140 . 
     Alternatively, as shown in  FIG. 9 , the controller  170  employs a different technique for controlling more than one actuator  140 , while maintaining the desired output power  176 . As shown, after the first actuator  140  produces the output power  186  (Output Power 1) at time “t=0”, the controller  170  controls the second actuator  140  at time “t=1” such that the output power  186  (Output Power 2) produced by the second actuator  140  is equivalent to the difference between the desired output power  176  and Output Power 1. In this way, the controller is also able to control more than one actuator  140 , while controlling the sum of the output powers  186  relative to the desired output power  176 . 
     In  FIGS. 8 and 9 , Output Power 1 and Output Power 2 are shown to be different values for simplicity in illustration. Output Power 1 and Output Power 2 may of course be the same values or different values depending on the function and position of the actuators  140  and the load applied to each respective actuator  140 . Furthermore, the controller  170  may use any combination of the above-described methods (e.g., the methods shown in  FIGS. 5-7 ) to control the actuators  140  as described in  FIGS. 8 and 9 . For example, while the desired output power  176  is a value in  FIGS. 8 and 9 , the desired output power  176  may also be a range and may be variable. In another example, while the controller  170  in  FIGS. 8 and 9  controls each actuator  140  such that the sum of output powers  186  produced by each actuator  140  is maintained to be equivalent to the desired output power  176 , the controller  170  may also control each actuator  140  such that the sum of output power  186  produced by each actuator  140  progressively approaches the desired output power  176 . 
     Additionally, while  FIGS. 8 and 9  demonstrate two different techniques for controlling two actuators  140  while controlling the sum of the output powers  186  of the two actuators  140 , the controller  170  is able to control more than two actuators  140  using the techniques shown in  FIGS. 8 and 9 , or a combination of those techniques. For example, consider an embodiment where the patient support apparatus  100  comprises a total of “n” actuators  140 , where “n” is greater than two. In such an embodiment, the controller  170  may use any permutation or combination of the above techniques to control the desired output power  176  for the sum of the “n” actuators  140 , the desired output power  176  for any one actuator  140  of the “n” actuators, and the desired output power  176  for any finite number (from one to “n”) of the “n” actuators. In other words, the controller  170  may control the desired output power  176  for any permutation or combination of the “n” actuators using the above-described techniques. 
     Furthermore, using the above-described techniques, the actuators  140  may also be controlled based on a position of said actuators  140 , a priority of said actuators, and a usage count of said actuators. For example, in some embodiments, the controller  170  may control the actuators  140  positioned on a side of the patient support apparatus, or distribute electrical energy such that the actuators  140  positioned on the side of the patient support apparatus  100  receive more electrical energy. Similarly, the controller  170  may control the actuators  140  based on a priority of the actuators  140 , a usage count of the actuators  140 , or any other relevant characteristic of the actuators  140 . 
     III. Sensor Configurations 
     Referring back to the examples shown in  FIGS. 2, 2A, 3A, 3B , the patient support apparatus  100  includes the sensor  178 . In  FIGS. 2, 2A, 3A, 3B , the sensor  178  is located on the actuator  140  and senses the load  160  being applied to the actuator  140 . As shown in  FIGS. 3A and 3B , the sensor  178  is coupled to the controller  170 . The controller  170  is configured to control the actuator  140  in response to analyzing readings from the sensor  178 . 
     The sensor  178  may be configured to sense the load  160  using a variety of methods. Accordingly, the controller  170  may be configured to analyze readings from the sensor  178  using a variety of methods.  FIG. 4  and  FIG. 10  demonstrate various embodiments of the sensor  178  and a variety of methods of analyzing readings from the sensor  178 . 
     For example, referring to  FIG. 4 , the sensor  178  is coupled to the power supply  190  and is configured to sense the applied electrical current  184  drawn in by the actuator  140 . In such an embodiment, the sensor  178  may be coupled to the power supply  190  while also being located on the actuator  140 . After the sensor  178  of  FIG. 4  senses the applied electrical current  184 , the controller  170  receives readings of the applied electrical current  184  from the sensor  178  to determine the applied voltage  182 . 
     Referring to  FIG. 10 , the sensor  178  senses the load  160  and sends a reading  161  indicative of the load  160  to a load analyzer block  172  in the controller  170 , where the load  160  is analyzed and the applied electrical current  184  determined. The controller  170  then modifies the applied voltage  182  relative to the applied electrical current  184  and the desired output power  176  using the applied voltage determination block  174 . Once this determination is complete, the controller  170  provides the applied electrical current  184  and the applied voltage  182  to the actuator  140 . The controller  170  may modify and provide the applied voltage  182  prior to, after, or concurrent to providing the applied electrical current  184  to the actuator  140 . 
       FIGS. 4 and 10  demonstrate two examples of the sensor  178 , which may be embodied as different sensor types. In  FIG. 4 , the sensor  178  is configured to sense the amount of electrical current drawn by the actuator  140  because of the load  160  instead of directly sensing the load  160 . In this example, the sensor  178  may be embodied as an electrical current sensor. In  FIG. 10 , the sensor  178  directly senses the load  160  and, in such scenarios, the sensor  178  may be embodied as a load cell, force transducer, torque sensor, or the like. Additionally, in some instances, both embodiments of the sensor  178 , as shown in  FIGS. 4 and 10 , may be present in a single embodiment of the patient support apparatus  100 . 
     The sensor  178  may also include any one or more of a motion sensor, a pressure sensor, a camera, a switch, an optical sensor, an infrared sensor, an electromagnetic sensor, an accelerometer, a potentiometer, and an ultrasonic sensor. As such, the sensor  178  may be configured to sense various types of readings derived from electrical, mechanical, or electromechanical physics for providing an indication of the load  160  to the controller  170 . 
     For example, in  FIGS. 2, 2A, 3A, and 3B , the sensor  178  may be configured to sense the load  160  by sensing the torque being applied to the actuator  140 . The controller  170  then controls the actuator  140  in response to the torque sensed. In another embodiment where the sensor  178  includes a motion sensor, the sensor  178  may sense a motion of the patient  150  thereby providing some indication of the load  160 . In another embodiment, where the sensor  178  includes an infrared sensor, the sensor  178  may sense a heartbeat of the patient  150  via an infrared signal, indicating a presence of the patient  150 , and hence, presence of the load  160 . Thus, the load  160  may be directly measured by the sensor  178  or presence of the load  160  may be inferred by measurements from the sensor  178 . The sensor  178  functions, readings, and configurations may be other than those described herein for detecting the load  160  or presence of the load  160 . 
     IV. Power Supply Configurations 
     As described, the actuator  140  is configured to receive electrical energy, and more specifically, the applied electrical current  184  and the applied electrical voltage  182  from the power supply  190 . The power supply  190  may have various configurations. For example, in one embodiment, the power supply  190  may be a mains electricity of a hospital. In another embodiment, the power supply  190  may be a battery, such as a battery located on the patient support apparatus  100  itself. Furthermore, the power supply  190  may be a DC or AC power supply. 
     In the embodiment shown in  FIG. 11 , the controller  170  includes a modulator  192 , which is configured to modulate the electrical energy provided by the power supply  190 , either directly from the power supply  190  or transformed from the power supply  190 , to produce a pulse-width modulated applied voltage  182 ′ to control the actuator  140 . However, the inclusion of the modulator  192  does not limit the power supply  190  to a type of power supply. The power supply  190  may be DC or AC based. 
     V. Overcurrent Protection 
     As previously stated, in some embodiments, the desired output power  176  may be specified in relation to power parameters related to the power supply  190  coupled to the actuator  140 . For example, the desired output power  176  may be based on a power rating of the power supply  190 . 
     In some embodiments, the patient support apparatus  100  may protect the power supply  190  from overcurrent situations. Usually, the power supply  190  is coupled to an overcurrent protection mechanism (such as a circuit breaker) that is configured to trip as an electrical current from the power supply  190  exceeds a predetermined threshold. However, the patient support apparatus  100  may also include its own overcurrent protection mechanism, which will trip in overcurrent situations to avoid tripping of the overcurrent protection mechanism of the power supply  190 . 
     One example of an overcurrent protection mechanism of the patient support apparatus  100  is shown in in  FIG. 12 , where the patient support apparatus  100  further includes a resettable fuse  194  coupled to the actuator  140  to provide overcurrent protection. Here, the resettable fuse  194  is configured to trip as the applied electrical current  184  exceeds a predetermined threshold for electrical current, known as a trip current. In an embodiment where the actuator  140  is coupled to the power supply  190  with an overcurrent protection mechanism, the resettable fuse  194  may be sized or configured such that the trip current of the resettable fuse  194  is equal to or less than the predetermined threshold of the overcurrent protection mechanism of the power supply  190 . As such, the resettable fuse  194  may be configured to trip, avoiding tripping of the overcurrent protection mechanism of the power supply  190 . 
     In other embodiments, the resettable fuse  194  may be configured to protect the power supply  190  by holding the applied electrical current  184  at an electrical current hold value, known as a hold current. In such embodiments, the resettable fuse  194  would not instantly trip, but instead would hold the applied electrical current  184  at the hold current or allow the applied electrical current  184  to step over the hold current for a certain amount of time. Of course, the resettable fuse  194  may be sized such that the hold current of the resettable fuse  194  is less than the predetermined threshold of the overcurrent protection mechanism of the power supply  190 . Such an embodiments not only avoids tripping of the resettable fuse  194 , but also avoids tripping of the overcurrent protection mechanism of the power supply  190 . The resettable fuse  194  may be an active or passive device. The resettable fuse  194  may be a polymeric temperature coefficient (PTC) device, a polymeric positive temperature coefficient (PPTC) device, a polyfuse, a polyswitch or the like. The resettable fuse  194  may be disposed at any suitable location relative to the actuator  140  other than the location shown in  FIG. 12 . 
     Furthermore, the trip current and the hold current of the resettable fuse  194  may be adjustable. As such, for power-intensive embodiments of the patient support apparatus  100 , the trip current and the hold current may be increased, allowing the actuator  140  to receive more electrical energy from the power supply  190 . For example, in one such embodiment, the controller  170  may control the actuators  140  to move the patient support surface  130  and the patient  150 , into a CPR mode, which is a position conducive for performing CPR. It is advantageous, in such embodiments, for the controller  170  to control the actuators  140  as quickly as possible, allowing the patient  150  to be promptly transitioned to the CPR mode. Therefore, by increasing the trip current and the hold current, the actuators  140  are able to receive more electrical energy, allowing the actuators  140  to more quickly move the patient support surface  130  into the CPR mode. Alternatively, for embodiments of the patient support apparatus  100  where the actuator  140  is sensitive to higher levels of electrical energy, the trip current and hold current may be decreased accordingly. 
     Another example of an overcurrent protection mechanism of the patient support apparatus  100  is shown in  FIG. 13 , where the controller  170  is coupled to the actuator  140  to implement a feedback loop to limit the applied electrical current  182 . As shown in  FIG. 13 , the applied electrical current  184  is monitored and a feedback loop sends the applied electrical current  184  to an overcurrent determination block  196 , where the controller  170  determines whether an overcurrent situation has occurred. Once an overcurrent situation is detected, the controller  170  may use a variety of methods to limit the applied electrical current  182 . For example, during an overcurrent situation, the controller  170  may override the applied electrical current  184  by providing the actuator  140  a maximum allowable electrical current instead of the applied electrical current  184 . In another embodiment, the controller  170  may simulate a tripping of a circuit by preventing the power supply  190  from providing the applied electrical current  184 . In various embodiments, the overcurrent determination block  196  may be a hardware-based system or a software-controlled system for sensing overcurrent. In one embodiment of the hardware-based system, the overcurrent determination block  196  may include a current sensor, such as a current sense FET, or the resettable fuse  194 . Furthermore, while the overcurrent determination block  196  is coupled to the applied voltage determination block  174  via the load analyzer block  172  in  FIG. 13 , the overcurrent determination block  196  may be directly coupled to the applied voltage determination block  174  in other embodiments. 
     Several embodiments have been discussed in the foregoing description. However, the embodiments discussed herein are not intended to be exhaustive or limit the disclosure 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 disclosure may be practiced otherwise than as specifically described.