Abstract:
A hospital bed has two mechanical drive mechanisms connected between each end of a bed support frame and a base, each of which has a respective actuator. Selective operation of each of the drive mechanisms with the actuators permits either end of the bed support frame to be inclined to the Trendelenburg and reverse Trendelenburg positions at any height of the hospital bed. The drive mechanisms transfer forces for raising and lowering the bed support frame but do not transfer force when the bed is lowered onto an obstacle. When an obstacle is encountered, a switch interrupts operation of its respective actuator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hospital bed and more particularly to dual drive mechanisms with respective actuators for selectively raising and lowering either end of a hospital bed. 
     2. Background of the Invention 
     Many activities and therapies require that a hospital bed be adjustable to different heights, and/or its ends be inclined relative to a horizontal plane so that either the foot of the bed is elevated above the head of the bed, i.e. the Trendelenburg position, or the head of the bed is elevated above the foot of the bed, i.e. the reverse Trendelenburg position. It is further desirable that the Trendelenburg or reverse Trendelenburg positions be achieved at any height of the bed. 
     U.S. Pat. No. 4,494,259 discloses one apparatus for controlling the height and inclination of either end of a hospital bed. In that disclosure an actuator drives one or two screw and nut drives which may be connected by a clutch. Engaging the clutch couples the screws causing both screws to rotate in unison. The bed is raised or lowered via a linkage mechanism connected between the bedframe and the nuts. Disengagement of the clutch decouples the screws, and one screw and nut drive is operative to raise or to lower a foot end of the bedframe. Consequently, the Trendelenburg position may be achieved by engaging the clutch, fully lowering the bed, disengaging the clutch and raising the foot end of the bed. The reverse Trendelenburg position is achieved by engaging the clutch, raising the bed, disengaging the clutch and lowering the foot end of the bed. Consequently, to move from the Trendelenburg position to the reverse Trendelenburg position or vice versa, it is often necessary to change the height of the bed before its inclination may be changed. 
     In view of the fact that hospital bed motion must be very slow to accommodate the sensitivities of a patient, this dual motion is inefficient and requires additional personnel time. 
     SUMMARY OF THE INVENTION 
     To overcome the disadvantages of existing mechanisms, a primary object of the invention is to provide a hospital bed in which the height of each end of the bed may be independently controlled regardless of the height of the bedframe. 
     According to the principles of the present invention, a hospital bed has a hospital bed support frame connected to a base by means of first and second mechanical drives connecting each end of the bed support to the base. The first and second mechanical drives are connected to first and second motors, respectively. The motors may be operated simultaneously to move both ends of the bed support together in the same direction thereby changing the height of the bed support frame relative to the base. Further, the motors may be selectively operated to move one end of the bed support vertically relative to the other end, thereby selectively moving the bed support to the Trendelenburg and reverse Trendelenburg positions. The mechanical drives are constructed to stop the operation of the motors upon either end of the bed support encountering an obstacle while being lowered. 
     One advantage of the present invention is that each end of the bed is under independent control at every height location. The independent control permits desired bed angles to be more efficiently and quickly attained. 
     Another advantage of the present invention is that upon the bed support engaging an obstacle or other interference while being lowered the operation of the mechanical drive is interrupted. 
    
    
     These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view illustrating a hospital bed in a raised position. 
     FIG. 2 is a partial side view of the hospital bed in a lowered position. 
     FIG. 3 is a partial side view of the hospital bed in the reverse Trendelenburg position. 
     FIG. 4 is a side elevation view of the hospital bed in the Trendelenburg position. 
     FIG. 5 is a larger side elevation view of the 6--6 of FIG. 5. 
     FIG. 6 is a cross-sectional view taken along lines 6--6 of FIG. 5. 
     FIG. 7 is a cross-sectional view taken along lines 7--7 of FIG. 6. 
     FIG. 8A is a cross-sectional view taken along lines 8A--8A of FIG. 7 illustrating a normal relationship between the lift nut and output block. 
     FIG. 8B is a cross-sectional view taken along lines 8A--8A illustrating separation between the lift nut and output block. 
     FIG. 9 is a cross-sectional view taken along lines 9--9 of FIG. 7. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-5 illustrate a hospital bed employing the present invention. The bed 10 includes a bed support frame 12 connected to a base 14 by means of first and second mechanical drives 16 and 18 which are connected to actuators 20 and 22, respectively. The mechanical drives 16 and 18 are pivotally connected to the bed support frame 12 at pivot points 23 and 25. One end of each of the mechanical drives 16 and 18 is connected to the base 14 and the other end of each of the mechanical drives 16 and 18 is connected to actuators 20 and 22, respectively. 
     The actuators 20 and 22 may be selectively operated to move the ends of the bed support frame 12 relative to the base 14 in the same vertical direction thereby changing the height of the bed support frame relative to the base. Consequently, the bed support frame typically in a horizontal position may be raised as shown in FIG. 1 or lowered as shown in FIG. 2. Further, if the bed support frame is at an inclined position, operating the actuators in unison will raise or lower the bed support frame without substantially changing its inclination. Alternatively, selectively operating the actuators to move one end of the bed support frame vertically relative to its other end will incline the bed support frame, thereby selectively moving the bed support frame to either the reverse Trendelenburg position shown in FIG. 3 or the Trendelenburg position shown in FIG. 4. 
     Referring to FIG. 5, the mechanical drives 16 and 18 are comprised of lift arm links 24 and 26 and drive mechanisms 28 and 30. The lift arm links 24 and 26 are substantially identical in construction. The lift arm links 24 and 26 are pivotally connected to the base 14 by support links 36 and 38, respectively. The support links are pivotally connected to first ends of the lift arm links 24 and 26 at pivot points 44 and 46, and support links 36 and 38 are pivotally connected to the base at pivot points 48 and 50. The lift arm links 24 and 26 are connected to the drive mechanisms 28 and 30 by drive links 40 and 42, respectively. Drive links 40 and 42 are pivotally connected to second ends of the lift arm links 24 and 26 at pivot points 52 and 54; and drive links 40 and 42 ar pivotally connected to the drive mechanisms 28 and 3 at pivot points 56 and 58. As shown in FIG. 6, each of the links and pivot points shown in FIG. 5 located on one side of the drive mechanism are replicated on an opposite side of the drive mechanism thereby providing a balanced application of forces. Each lift arm link 24, 26 is rigidly connected to a respective torque shaft 62 rotatably mounted through a pair of flanges 64a, 64a and 64b, 64b, respectively connected to the bed support frame 12 (FIG. 6). Each lift arm link 24, 26 comprises a pair of first arms 66, 66 rigidly connected to the ends of each shaft 62 at one end and pivotally connected to the pair of pivot links 36, 36 and 38, 38 at their other end. A pair of second arms 68, 68 are rigidly connected to each shaft 62 at one end and are pivotally connected to the pair of drive links 40, 40 and 42, 42 at their other end. The included angle between the first and second arms is approximately 90°. 
     The drive mechanisms 28 and 30 illustrated in detail in FIGS. 5-9 convert rotary motion of an actuator output shaft and drive screw into translation of a nut threadedly connected to the drive screw. The drive mechanisms 28 and 30 are comprised of drive screws 70 and 72 connected to output shafts 74 and 76 of actuators 20 and 22, respectively. Lift nuts 78 and 80 are rotatably mounted to their respective screws 70 and 72 and, in addition, are slidably mounted on rails 82 and 84, respectively. The rails 82 and 84 are effective to linearly guide the translating lift nuts and prevent deflection of the drive screws by providing a support transverse to the longitudinal axis of the drive screws. 
     Slidably mounted on the nuts 78 and 80 are output blocks 86 and 88 which are connected to the drive links 40, 40 and 42, 42, respectively. The lift nuts 78 and 80 contain splines 90 and 92, respectively, which, as shown in FIG. 9, mesh and engage with corresponding splines inside the output block such as shown at 94. The lift arm links are arranged such that a gravitational force exerted on the bed support frame 12 is effective to bias the output blocks 86 and 88 tightly against the lift nuts 78 and 80. When the bed support frame is being raised, the lift nuts 78 and 80 are moving in a direction so as to push the output blocks 87 and 88 along the drive screws 70 and 72, respectively. When the bed support frame is being lowered, the lift nuts are moving in the opposite direction along the drive screws. The gravitational force of the bed support frame and any patient support thereby, which is applied through the drive links 40, 40 and 42, 42, is effective to hold the output blocks 86 and 88 in contact with the lift nuts 78 and 80, as shown in FIG. 8A. As the bed support frame is moving downward, and if it encounters an obstacle which provides a reactive force in opposition to the gravitational force, the gravitational force is removed from the drive links 40, 40; and the continuing translation of the lift nut 78 results in the lift nut 78 separating from the output block 86 as shown in FIG. 8B. The relative motion of the lift nut to the output block is detected by a limit switch 100 connected to the drive link 40 or other element fixed with regard to the output block. The limit switch has a trigger arm 102 which is activated by shoulder 78a of the lift nut 78 in response to its separation from the output block 86. The electrical contacts within the switch 100 are connected in the power circuit to the actuator 20 in a manner well known to those who are skilled in the art. Actuation of the trigger arm 102 opens the electrical contacts within the switch 100 thereby interrupting power to the actuator 20 and terminating its operation, the rotation of the drive screw 70 and the translation of the lift nut 78. Therefore, the motion of the bed support frame in a downward direction is stopped in response to that end of the bed frame encountering the obstacle. 
     While the invention has been illustrated in some detail according to the preferred embodiments shown in the accompanying drawings, and while the preferred embodiments have been described in some detail, there is no intention to thus limit the invention to such detail. On the contrary, it is intended to cover all modifications, alterations and equivalents following within the spirit and scope of the appended claims.