Patent Abstract:
A bed with a leg assembly coupled to a support link assembly by a joint, the joint comprising a slot having at least two paths. A support link assembly defining a length that automatically varies as the support link assembly moves relative to the leg assembly.

Full Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/246,635 for BED LIFT MECHANISM filed Oct. 7, 2008, which claims the benefit of U.S. provisional patent application Ser. No. 60/998,287 for BED LIFT MECHANISM filed Oct. 10, 2007, the entire disclosures of which are fully incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Patients residing in long-term care facilities such as nursing homes and rehabilitation facilities usually require beds that include movable head end and foot end sections of the sleep surface. The sleep surface and related components are attached to a frame which provides a rigid supporting structure. Also attached to the frame are the components for elevating or tilting the bed frame relative to the support surface. These beds typically utilize multiple manual crank devices or electric actuators to provide separate elevating movement of the head end and foot end sections of the sleep surface and also to raise, lower or tilt the entire frame and sleep surface relative to the support surface. 
       SUMMARY 
       [0003]    The present invention relates to a bed incorporating a leg assembly coupled to a support link assembly by a joint, the joint comprised of a slot having at least two paths. Another aspect of the present invention relates to a length that automatically varies as the support link assembly moves relative to the leg assembly. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a perspective view of a long-term care bed according to one embodiment of the present invention with the head end sleep surface section elevated and the foot end sleep surface section partially elevated in the knee area; 
           [0005]      FIG. 2  is a perspective view of a long-term care bed according to one embodiment of the present invention with the sleep surface and related components removed; 
           [0006]      FIG. 3  is an exploded perspective view of one end of a long-term care bed according to one embodiment of the present invention; 
           [0007]      FIG. 4  is a cross-sectional view of one end of the bed lift mechanism taken along section line  4 - 4  in  FIG. 2 ; 
           [0008]      FIG. 5A  illustrates the components of  FIG. 4  with the bed frame at its lowest position relative to the support surface; 
           [0009]      FIG. 5B  illustrates the components of  FIG. 4  with the bed frame at approximately its midpoint position relative to the support surface; 
           [0010]      FIG. 5C  illustrates the components of  FIG. 4  with the bed frame at its highest position relative to the support surface; 
           [0011]      FIG. 6A  is a schematic representation of the bed lift mechanism pivot positions of  FIG. 5A ; 
           [0012]      FIG. 6B  is a schematic representation of the bed lift mechanism pivot positions of  FIG. 5B ; 
           [0013]      FIG. 6C  is a schematic representation of the bed lift mechanism pivot positions of  FIG. 5C ; 
           [0014]      FIG. 7A  is a cross-sectional view taken along section line  7 - 7  in  FIG. 2  illustrating link length versus frame height; and 
           [0015]      FIG. 7B  is a graphical representation depicting several possible relationships between link length and frame height. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    A long-term care bed  10  as illustrated in  FIG. 1  includes a frame  40  to which a sleep surface  12  is attached to provide a platform for a typical mattress. The sleep surface  12  is segmented into a head end frame section  14  and foot end frame sections  16  and  18 . The head end frame section  14  can be elevated as shown in  FIG. 1  by means of a lifting mechanism, such as an electric actuator or manual crank in conjunction with an appropriate structure. Likewise, the foot end frame sections  16  and  18  can be elevated as shown in  FIG. 1  by a similar type of lifting mechanism employed for the head end frame section  14 . The foot end frame sections  16  and  18  are pivotally coupled at or near the occupant&#39;s knee area to follow the natural contours of a person. As used herein, where two components are shown or described as being coupled, joined or connected, such coupling, joining or connecting can be accomplished directly between the two components or through one or more intermediary components. 
         [0017]    The elevation of the frame  40  above a support surface can be adjusted or readjusted by means of two leg assemblies  30 . Caster assemblies  20  are attached for pivotal movement to the lower outside ends of each leg assembly  30 . Alternatively, wheels or fixed ground engaging elements can be used in place of caster assemblies  20 . As will be described, the two leg assemblies  30  work in conjunction with other bed lift mechanism components to achieve zero or substantially zero horizontal or lateral movement of the caster assemblies  20  relative to the support surface when changing the elevation of the frame  40  above the support surface. It should be noted that the frame  40  can be tilted relative to the support surface to achieve a therapeutically desired Trendelenburg position. 
         [0018]    Referring to  FIG. 2 , sleep surface  12  and related components are removed from frame  40  for clarity. Frame  40  provides the central structure to which the sleep surface  12 , leg assemblies  30 , support links  60  and actuators  90  are mounted. The frame  40  is comprised of opposing side rails  42 , two end cross rails  44  and central cross rail  46 . The side rails  42  and cross rails  44  and  46  are made from metal tubing and can be of various cross-sectional shapes such as round, square, rectangular or the like. The side rails  42  are laterally spaced apart and substantially parallel to each other and provide mounting surfaces for other components. Cross rails  44  and  46  span laterally between and are joined to the side rails  42  and also provide mounting surfaces for other components. Attached to the inside vertical surfaces of side rails  42  are four tracks  48  which are made from “U-shaped” or similarly shaped metal channel and are located so as to provide a guide means for the upper portion of leg assemblies  30 . 
         [0019]    In the present embodiment as shown in  FIG. 2 , leg assemblies  30 , work in conjunction with support links  60  and actuators  90  to support and position frame  40  relative to the support surface. Leg assemblies  30  can be made to move in unison so as to position and maintain the frame  40  substantially horizontal with respect to the support surface or can be separately commanded such that the head or foot end is positioned higher than the other for the therapeutic Trendelenburg position. In this embodiment, leg assemblies  30  and support links  60  are substantially identical in appearance and function, but they can be configured differently as design requirements dictate. 
         [0020]    The main portion of leg assembly  30  is comprised of caster tube  32  and legs  34 . Legs  34  are positioned laterally apart and substantially parallel to each other and joined at their lower ends to cross tube  32  to form a substantially “U-shaped” structure. Caster assemblies  20  are pivotally attached to the outer ends of cross tube  32  and allow leg assembly  30  to rotate about the longitudinal axis of cross tube  32  designated as pivot axis D. Legs  34  are metal tubing with any of a variety of cross-sectional shapes such as round, square, rectangular or the like and can be straight as shown or incorporate curved regions. 
         [0021]    Referring to  FIGS. 2-4 , attached to each leg  34  is shield  36 , bracket  38  and pins  70  and  72 . Shield  36  is made from flat sheet metal and covers the mechanism to prohibit finger access and therefore eliminate any potential pinch point. Bracket  38  is attached near the upper end of leg  34  at approximately a 45° degree angle although the angle and placement can vary depending on design requirements. Pin  50  has a metal cylindrical shape and is attached to bracket  38  and projects substantially perpendicular in an outward direction. Low friction roller  52  is installed on pin  50  for engaging with and translating longitudinally in track  48 . Roller  52  can be a conventional bushing, bearing or similar device and constructed of various metal or plastic materials. Roller  52  is retained on pin  50  by only the limited clearance between the end of pin  50  and track  48 , although if needed, any conventional retaining means such as a screw, nut, clip or the like could be employed to retain the roller  52  on pin  50 . The longitudinal axes of pins  50  on opposing brackets  38  are aligned so as to be substantially coaxial and define a pivot axis about which the upper ends of leg assembly  30  rotate and laterally translate and is designated as pivot axis B. So constructed, pivot axis B forms or approximates a pivot axis spanning laterally across frame  40  since the upper ends of leg assembly  30  will move substantially in unison. 
         [0022]    Pins  70  and  72  are preferably metal and cylindrical in shape and are joined to leg  34  so that their longitudinal axes project substantially perpendicular to the inside surface of leg  34 . The longitudinal axes of pins  70  on opposing legs  34  are aligned so as to be substantially coaxial. So constructed, the axes of pins  70  forms or approximates a pivot axis spanning laterally across leg assembly  30  and is designated as pivot axis C. Likewise, the longitudinal axes of pins  72  on opposing legs  34  are aligned so as to be substantially coaxial. Although it is shown that pins  70  and  72  project inwardly toward the longitudinal center line of bed  10 , the mechanism can be rearranged so that pins  70  and  72  project perpendicularly outward from leg  34 . Low friction rollers  74  and  76  are installed on pins  70  and  72  respectively for engaging with and following the contour of a slot  66  described later in more detail. Rollers  74  and  76  can be a conventional bushing, bearing or similar device and be constructed of various metal and plastic materials. Rollers  74  and  76  are retained on pins  70  and  72  respectively by any conventional retaining means such as a screw, nut, clip or the like. 
         [0023]    Support link  60  is comprised of two links  62 , cross member  64  and bracket  68 . Links  62  are positioned laterally apart and substantially parallel to each other and are joined at their lower ends to cross member  64  to form a substantially “U-shaped” structure. The upper end of each link  62  contains a through hole for pivotal attachment to brackets  54  by means of a bolt, pin or the like. Brackets  54  are formed from metal as one piece or by combining two pieces and are mounted by any conventional means to rails  42  and/or cross rails  44 . The through holes in brackets  54  at each end of bed frame  40  are aligned so as to be coaxial and thus create pivot axis A. These pivoting joints may also employ conventional bushings or bearings in the link  62  holes and/or the bracket  54  holes to reduce friction and/or noise. 
         [0024]    Cross member  64  enables both links  62  to move in unison and also allow for one actuator  90  to be used for each end of bed  10 . Cross member  64  is made from metal and can have a cross-sectional shape such as circular, square, rectangular, etc. Bracket  68  is formed or cast from metal as a separate component or can be integrated with cross member  64  into one larger casting. Bracket  68  is centrally located on cross member  64  and projects towards the center of bed  10 . 
         [0025]    Links  62  are mirror images of each other about the bed  10  longitudinal centerline. Each link  62  can be one piece or a multi-piece assembly made from metal and formed by any conventional fabrication process such as machining, stamping, laser cutting, welding, etc. or cast and machined by any well-known conventional processes. At the lower end of link  62  is slot  66  depicted in  FIGS. 3-4  as substantially “T” shaped with an upper path being arcuate or semi-arcuate, and the lower path being mostly straight. Alternatively, slot  66  could be inverted such that the mostly straight path is oriented above the arcuate path or even segmented into two separate slots with paths of either orientation. The exact shape of slot  66 , including the number of paths, can be developed using CAD software or manually using prototype materials. 
         [0026]    The behavior of the bed lift mechanism is dependent on the shape of slot  66  and can be configured such that the caster assemblies  20  are motionless relative to support surface  5  during raising or lowering of the frame  40  above support surface  5 , or in specific situations where movement of the caster assemblies  20  is desired, the slot  66  shape can be tailored to achieve the desired movement. It is understood that alternate arrangements of the slot  66  shape may cause various desired forms of frame  40  movement. For example, alternate slot  66  shapes may include causing frame  40  to initially rise slowly away from the support surface  5  to minimize loading on the actuator  90  or to minimize any jolting movement to the occupant. Yet another alternate slot  66  shape may cause the frame  40  to translate horizontally a short distance away from an adjacent object such as a wall or furniture before rising vertically. Other movements are also possible including combinations of the preceding. 
         [0027]    Referring back to  FIGS. 2-3 , actuators  90  extend and contract in length in response to control signals to provide the motive force that elevates the frame  40  above the support surface  5 . Actuators of this type as well as the control elements used to generate the control signal are well known in the art. An example of such electric actuators is Linak® linear actuator model no. LA27. It is also possible that a manually-operated crank-type mechanism could be substituted for the electric actuators. One end of actuator  90  is pivotally attached to bracket  92  by means of a bolt, pin or the like while the opposite end of the actuator  90  is pivotally attached to bracket  68  also by means of a bolt, pin or the like. Bracket  92  is formed in the same manner as brackets  54  and mounted by any conventional means to central cross rail  46 . The actuator  90  pivoting attachment joints may also employ conventional bushings or bearings to reduce friction and/or noise. Alternately, it is possible that instead of actuator  90  applying the motive force to support link  60  via bracket  68 , it could apply the motive force to leg assembly  30  if a crossbar similar to crossbar  64  with actuator mounting bracket  68  were added to leg assembly  30 . 
         [0028]    Actuator  90  positions support link  60  which in turn determines the position and motion of leg assembly  30 . The extension in length of actuator  90  rotates support link  60  counterclockwise about pivot axis A as viewed in  FIG. 4  which in turn transmits the motive force to leg assembly  30  via the sliding pivotal interface at pivot axis C. The motive force rotates leg assembly  30  clockwise about pivot axis D without imparting any translational forces to caster assemblies  20  thereby prohibiting any horizontal movement of the caster assemblies  20 . While leg assembly  30  rotates about pivot axis D thereby raising frame  40 , it simultaneously translates and rotates the upper end of leg assembly  30  on roller  52  in track  48 , moving pivot axis B closer to pivot axis A. The contraction in length of actuator  90  reverses this motion and pivots support link  60  clockwise about pivot axis A and allows leg assembly  30  to rotate counterclockwise about pivot axis D and thereby lower frame  40 . 
         [0029]    Leg assembly  30  is pivotally and slideably coupled to support link  60  at pivot axis C by the arrangement of the roller  74  in the lower path of slot  66  and roller  76  in the upper path of slot  66 . Roller  74  contacts the left side surface of the lower path of slot  66  while roller  76  contacts the upper surface of the upper path of slot  66 . The upper path is configured in such a manner that the distance from any point along the upper surface to pivot axis C could vary from any other point. Dimension L defines the variable radial distance between pivot axis C and pivot axis A. While roller  74  at pivot axis C provides a sliding pivotal connection between leg assembly  30  and support link  60 , roller  76  bearing against the upper surface of the upper path of slot  66  controls the variable length L. The rotation of leg assembly  30  relative to support link  60  causes roller  76  to follow the upper path of slot  66 , which because of its shape, automatically changes the distance from pivot axis A to the contact point between roller  76  and the upper surface of the upper path. This varying distance causes roller  74  to translate longitudinally in the lower path of slot  66  and, in effect, constantly change the length L thereby providing a variable length connection between pivot axis A and pivot axis C. In one embodiment, length L changes by approximately one inch as frame  40  is elevated from its lowest position relative to the support surface to its fully elevated position. 
         [0030]    To illustrate how frame  40  is raised relative to support surface  5 , it will be assumed that frame  40  is being raised substantially horizontal and both leg assemblies  30  perform in the identical manner, therefore only the operation of one combination of leg assembly  30  and support link  60  will be described.  FIG. 5A  depicts the condition where actuator  90  is fully contracted in length and frame  40  is at its lowest position relative to support surface  5 . Roller  76  is located at one end of the semi-arcuate portion of slot  66 , while roller  74  is located at the upper end of the lower portion of slot  66 . Length L is at its shortest length, L 1 , and pivot axis B is at its farthest distance from pivot axis A. To effect raising of frame  40 , actuator  90  begins to extend in length and applies a motive force to support link  60  which rotates it counterclockwise about pivot axis A. In response to the rotation of support link  60 , leg assembly  30  begins to rotate clockwise about pivot axis D while simultaneously translating pivot axis B towards pivot axis A. 
         [0031]      FIG. 5B  depicts frame  40  after it has risen to approximately the midpoint of its vertical travel with respect to support surface  5 . Actuator  90  has extended in length so as to further rotate support link  60  counterclockwise about the pivot axis A. Leg assembly  30  has further rotated clockwise about pivot axis D and translated pivot axis B towards pivot axis A. Roller  76  has moved to a position approximately at the midpoint of the semi-arcuate portion of slot  66  thereby automatically increasing length L from L 1  to L 2  as evidenced by roller  74  moving to the lower end of the lower portion of slot  66 . 
         [0032]      FIG. 5C  depicts frame  40  at a fully elevated position with respect to support surface  5 . Actuator  90  has fully extended in length such that link  60  and leg assembly  30  are at their fully rotated positions and pivot axis B is at its closest distance to pivot axis A. Roller  76  has moved to a position at the other end of the upper portion of slot  66  and because of the shape of the upper portion of slot  66 , it has automatically decreased length L from L 2  to L 1  as evidenced by roller  74  returning back to approximately its starting position close to the upper end of the lower portion of slot  66 . 
         [0033]    Lowering of frame  40  is accomplished by commanding the actuator to contract in length. This reverses the motion of all related components such that they follow the same path in moving to a lower vertical position. It is understood that frame  40  can be vertically positioned at any level within the range from its lowest position relative to support surface  5  to its highest position and can be subsequently repositioned in either direction as desired. 
         [0034]      FIGS. 6A-6C  are schematic representations of the pivot point locations of  FIGS. 5A-5C , respectively. It can be seen that the length L from pivot axis A to pivot axis C, denoted by AC, varies from L 1  in  FIG. 6A  to L 2  in  FIG. 6B  and returns back to L 1  in  FIG. 6C . Also, it can be seen that the distance from pivot axis A to pivot axis B, denoted by AB, varies from  FIG. 6A  to  FIG. 6C . The distance from pivot axis B to pivot axis C, denoted BC, remains constant in this embodiment. The relationship between these three pivot axis can be furthered represented by the following inequalities: 
         [0000]      AB 1 &gt;AB 2 &gt;AB 3    
         [0000]      AC 1 &lt;AC 2 &gt;AC 3    
         [0035]      FIG. 7A  illustrates dimension H as the height of frame  40  above the support surface  5  and dimension L as the distance between pivot axis A and pivot axis C.  FIG. 7B  is a plot of length L as it varies between L 1  and L 2  as a function of frame  40  height above support surface  5 . When frame  40  is at its lowest position relative to support surface  5 , length L is at its shortest length, L 1 . As frame  40  elevates above support surface  5 , length L automatically grows in length until it reaches its longest length L 2  when frame  40  is at approximately its mid-height position. As frame  40  continues to rise past the mid-height position, length L automatically contracts in length back to approximately its shortest length, L 1 . This motion is represented by curve M 1 . The automatic length adjustment of length L can be configured such that it changes linearly, nonlinearly or a combination of both in relation to the frame  40  height change. Curve M 2  depicts a motion where the automatic length adjustment of length L is delayed for an initial period of frame  40  height change. Curve M 3  depicts a motion where the automatic length adjustment only extends length L as frame  40  changes height above support surface  5 . 
         [0036]    In an alternate embodiment, the bed lift mechanism can be configured such that support link  60  has only one link  62  to support the leg assembly  30 . A single link  62  with slot  66  is positioned approximately at the longitudinal center line of bed  10 . This single link  62  would be coupled to a single arrangement of rollers  74  and  76  located on a cross tube spanning between legs  34  of the leg assembly  30 . The actuator  90  is pivotally coupled to either the support link  60  or the cross tube on leg assembly  30 . The single link  62  would provide the identical lifting function as the two link  62  arrangement described previously, but may require other modifications or additional elements to keep the mechanism aligned and functioning properly. For instance, rollers  74  and  76  may need to be specified with a higher load rating to accommodate the increased loading that a single support link would carry. Also, rollers  74  and  76  may require some alignment features to mate consistently with slot  66  in link  62 . 
         [0037]    In another alternate embodiment, it may be desirable to raise and lower the frame  40  using only one actuator  90 . In such a case, actuator  90  is connected to both leg assemblies  30  or to both support links  60  by appropriate cables, levers, rack and pinion gearing, or any other well known linkage mechanism. Actuator  90  is then able to reposition both ends of the bed lift mechanism simultaneously. 
         [0038]    While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the specification to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, individual components can be combined, assemblies can be divided into separate components or components can be rearranged without affecting the operation. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.

Technology Classification (CPC): 0