Power and electrical signal interface for a therapeutic bed

A direct electrical signal and power interface is provided to the patient support platform of a therapeutic bed that allows for a complete rotation of the patient support platform in either direction. In one embodiment, an electrical signal and/or power cable is housed within a chain-like cable carrier that is disposed within an annular channel attached to the patient support platform. In another embodiment, a flexible ribbon cable is disposed within the annular channel. The cable carrier or ribbon cable is long enough to allow a full 360 degrees of rotation of the patient support platform in either direction from 0 degrees supine flat while maintaining a direct electrical signal or power connection. To ensure that the electrical signal and power connection is not articulated beyond its physical limit as a result of manually rotating the bed in the emergency backup mode, a mechanical stop is provided to limit rotation of the patient support platform to about 730 degrees. Sensors are provided to detect activation of the mechanical stop.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to therapeutic beds, and more particularly to beds with a patient support platform operable to rotate about a longitudinal axis of the platform.

2. Description of the Related Art

One of the problems in the art of prone positioning therapeutic beds is to provide electrical signal and power connections to the bed for both the power and controller equipment that moves the bed and for the patient monitoring systems on the bed. To allow unrestricted rotation of the bed of WO 99/62454, for example, electrical power has been provided by wire brushes at the interface between the rotating part of the bed and the nonrotating part of the bed. However, due to vibration and other abrupt movements, such wire brushes cause problems of electrical intermittence, which can be detrimental to the therapy of the patient. A direct electrical signal or data carrier would be preferable to eliminate such intermittence, provided that the wired connection is capable of articulation during movement of the rotating part of the bed into the prone position, and provided that a mechanism is provided to prevent excessive rotation in any one direction.

SUMMARY OF THE INVENTION

In U.S. patent application Ser. No. 09/812,552 filed Mar. 29, 2001, and Ser. No. 09/884,749 filed Jun. 19, 2001, the first of which is herein incorporated by reference, a prone positioning bed is disclosed that encompasses several distinct innovations. This divisional application is directed to a mechanism to provide a direct, wired connection to the patient support platform.

A therapeutic bed in accordance with the present invention is provided comprising a base frame, a patient support platform rotatably mounted on the base frame for rotational movement about a longitudinal rotational axis of the patient support platform, and a drive system for rotating the patient support platform on the base frame. A direct, wired connection is provided to the patient support platform that allows for a complete rotation of the patient support platform in either direction. The necessary electrical wires are housed within a chain-like cable carrier that is disposed within an annular channel attached to the patient support platform. An annular cover is installed adjacent the annular channel to retain the cable carrier within the annular channel, but the annular cover is not attached to the annular channel. Rather, the annular cover is attached to the nonrotating part of the bed. One end of the cable carrier is attached to the annular channel, and the other end is attached to the annular cover. The length of the cable carrier is sufficient to allow a full 360 degree rotation of the patient support platform in either direction from 0 degrees supine flat while maintaining a direct electrical connection.

More preferably, the direct, wired electrical connection to the patient support platform may be provided with a flat ribbon cable or flexible printed circuit board (PCB) cable in lieu of a chain-like cable carrier. The cable resides within an annular channel attached to the patient support platform, and an annular cover is fastened to a flange of the annular channel such that a gap exists between the annular channel and the annular cover around the outer periphery. One end of the cable is attached to the annular channel, which provides power and electrical signals to the rotating part of the bed, and the other end of the cable passes through the gap between the annular channel and the annular cover and is connected to the electrical apparatus on the nonrotating part of the bed. Like the cable carrier mentioned above, the cable has a length sufficient to allow a full rotation of the patient support platform in either direction while maintaining a direct electrical connection between the nonrotating and rotating parts of the bed. To ensure that the wired electrical connection is not articulated beyond its physical limit as a result of manually rotating the bed in the emergency backup mode, a mechanical stop is provided to limit rotation of the patient support platform to about 365 degrees. Sensors are provided to detect activation of the mechanical stop.

It is an object of this invention to provide a prone positioning therapeutic bed having a direct, wired electrical connection between the rotating part of the bed and the nonrotating part of the bed.

It is another object of this invention to mechanically limit rotation of the bed in either direction to one full 360 degree turn plus about 5 degrees, and to electrically detect when one full turn has been reached.

Further objects and advantages of the present invention will be readily apparent to those skilled in the art from the following detailed description taken in conjunction with the annexed sheets of drawings, which illustrate a preferred embodiment of the invention.

DETAILED DESCRIPTION

Referring toFIGS. 1 and 2, a therapeutic bed10in accordance with the present invention preferably comprises a ground engaging chassis12mounted on wheels14. A base frame16is mounted on chassis12with pivot linkages18. Rams15,17housed within base frame16cooperate with pivot linkages18to form a lift system to raise and lower base frame16on chassis12. A patient support platform20having upright end rings22,24is rotatably mounted on base frame16with rollers26such that patient support platform20may rotate about a longitudinal axis between a supine position and a prone position. Side support bars28,30extend between end rings22,24. At the head of bed10, a guide body32having a plurality of slots34for routing patient care lines (not shown) is slidably mounted on rails36with support rod31. Similarly, at the foot of bed10, a central opening118is provided for receiving a removable patient care line holder (not shown) having a plurality of circumferential slots for routing patient care lines. Central opening118is preferably of sufficient size to allow passing of patient connected devices, such as foley bags (not shown), through the central opening118without disconnecting such devices from the patient. For such purposes, central opening118is preferably as large as possible, provided that strength and configuration requirements of the bed are maintained. The foregoing basic structure and function of bed10is disclosed in greater detail in international application number PCT/IE99/00049 filed Jun. 3, 1999, which is incorporated herein by reference.

Still referring toFIG. 1, bed10preferably comprises one or more folding side rails62pivotally mounted to patient support platform20to assist in securing a patient to support platform20before rotation into the prone position. As further described below in connection withFIG. 15, side rails62fold underneath platform20for easy access to a patient lying atop cushions21a,21b,21cin the supine position. Bed10also preferably has a head rest50and a pair of head restraints48, which are described in more detail below in connection with FIG.3.

As shown inFIG. 2, end ring22at the head of bed10is split into two sections for improved access to a patient lying on bed10. Upper section22ais removable from lower section22b. Upper section22ahas a pair of shafts40that are inserted into vertical stabilizer tubes38in the closed position. Likewise, tabs46on upper section22amate with tubular openings on lower section22b. Latches44secure upper section22ato lower section22bin the closed position. When latches44are unlatched, upper section22amay be raised, pivoted about the vertical axis of one of the shafts40, and left in an open position supported by one of the shafts40in corresponding stabilizer tube38. Alternatively, upper section22amay be removed entirely. In either case, upper section22amay be moved out of the way for unobstructed access to the patient and manipulation of patient care lines. As an alternative to a split end ring, patient support platform20could be cantilevered from the base frame at one end of the bed, but such a configuration would be extremely heavy.

Referring now toFIGS. 3 and 3A, head restraints48are slidably mounted to transverse support rails58,60on guides54with mounting arms52. For the sake of clarity, only one head restraint48is shown inFIGS. 2 and 3. Each guide54has a clamp56that is manually operable by a handle56aand serves to secure each guide54in a desired lateral position as further described below. Mounting arms52are slidably mounted in holes56hof bosses56bto provide vertical positioning of head restraints48. Handle56ais attached to a drum56fthat is rotationally mounted to flanges54aof guide54by shaft56gwhich is disposed within hole56dof drum56fDrum56fhas a ramp56cfor engaging one of the flanges54aand hole56dis offset from the central axis of drum56fto form a cam56e. Movement of handle56ain the appropriate direction causes ramp56cto engage one of the flanges54aand thereby spread flanges54aapart slightly, which causes one of the flanges54ato frictionally engage mounting arm52and thereby fix the vertical position of head restraint48. Simultaneously, such rotation of handle56acauses cam56eto frictionally engage one of the transverse support rails58,60and thereby fix the lateral position of head restraint48. Thus, clamps56simultaneously provide both lateral and vertical positioning of head restraints48, which have pads48afor comfortably engaging the front and sides of the head of a patient whose head is resting on head rest50. Head rest50may be mounted to transverse support rails58,60or to pad21a. Head restraints48thereby provide increased stability and comfort for a patient when bed10is rotated to the prone position.

If a particular patient requires only partial rotation for therapy such that patient support platform20need not be rotated beyond about, for example, 30 degrees in either direction, alternative head restraints248as shown inFIG. 2Amay be mounted in clamps56using mounting arms252in like manner as head restraints48. Alternative head restraint248is designed to provide lateral support for the patient's head in instances when the patient will not be rotated into the prone position such that vertical restraint of the head is not required.

FIGS. 4 and 15illustrate a preferred structure and operation of folding side rails62. Preferably, four independently operable side rails62are pivotally mounted on each side of bed10. For each side rail62, main rail66is slidably mounted on shaft80with mounting cylinders82. Shaft80has a slot80afor receiving guides such as set screws83installed in holes82aof mounting cylinders82. Preferably, set screws83are not tightened against slot80abut simply protrude into slot80ato prevent side rail62from rotating with respect to shaft80. In that regard, set screws83could be replaced with unthreaded pins. When set screws83are loosened, side rail62is free to slide longitudinally along shaft80for proper positioning with respect to the patient. When set screws83are tightened, side rail62is fixed with respect to shaft80. Shaft80is rotatably mounted to side support bar28,30with rail mounts78. Pivot link68is hinged to main rail66with hinge72, and cushion64is hinged to pivot link68with hinge70, which has a hinge plate70afor attaching cushion64. Side rails62are thus capable of folding under patient support platform20as shown inFIG. 15, which is a view looking up from beneath patient support platform20. A strap174with one end secured around shaft80may be provided to retain cushion64in the folded under position with mating portions of a snap respectively provided on cushion64and strap174. A pair of straps74and an adjustable buckle76are provided to fasten each opposing pair of side rails62securely over the patient. One end of strap74is secured to side support bar28with a strap connector88, which is15slidably mounted in slot28aof side support bar28. When strap74is properly secured with the appropriate tension using buckle76, tabs160on strap connector88are sandwiched between main rail66and side support bar28, which further helps to prevent longitudinal movement of side rail62. Side rails62thus serve to hold the patient securely in place as bed10is rotated into the prone position, and side rails62fold neatly out of the way for easy access to the patient in the supine position.

As best illustrated inFIG. 4A, an indexed disc86is preferably provided on one end of shaft80for cooperation with a pull knob84to form a detent that holds side rail62in one or more predetermined rotational positions. To that end, disc86preferably has one or more recesses228for receiving a pin84awhich is manually operated by pull knob84. Pull knob84is fixedly mounted to rail mount78with boss230. Preferably, pin84ais biased into engagement with disc86. By engaging one of the recesses228, pin84aprevents rotation of shaft80and thereby functions as a detent to hold side rail62in a predetermined rotational position. Side rail62may be moved to a different predetermined rotational position by pulling knob84sufficiently to disengage pin84afrom the given recess228so that shaft80is free to rotate. Preferably, one of the predetermined rotational positions of side rail62corresponds to the folded under position.

Referring now toFIGS. 5 and 6, each strap connector88comprises a tension-sensitive mechanism that provides both visual and electrical indications of whether strap74is properly secured over the patient. The following description describes the attachment of a strap connector88to side support bar28. It will be understood that strap connectors88may be similarly attached to side support bar30. Each strap connector88comprises a tension plate90that partially resides within a housing96. A cover plate176is attached to housing96by fasteners182inserted into holes96a. Tabs160extend from housing96, and studs178protrude from tabs160as shown. Discs180are mounted to studs178with screws183. Slots28bon the inner side of support bar28provide access for installation of screws183. Studs178are adapted to slide in slots28aof side support bar28, and discs180serve to retain strap connector88on side support bar28. Tension plate90has a slot92to which strap74is attached and a central cut-out93that forms a land100. Inverted U-shaped channels102protrude from the back of housing96into central cut-out93of tension plate90. Land100of tension plate90cooperates with channels102of housing96to capture springs98which tend to force tension plate90downward toward lower edge95of housing96such that switch104is disengaged when strap74is slack. Switch104is connected to an electrical monitoring and control system (not shown) in a customary manner. When strap74is buckled and tightened sufficiently, the tension in strap74overcomes the biasing force of springs98, and tension plate90moves upward to engage switch104, which sends a signal to the electrical monitoring and control system indicating that strap74is properly tensioned. Preferably, the electrical monitoring and control system is programmed such that bed10cannot rotate until each strap74is properly tensioned to ensure that the patient will be safely secured in bed10as it rotates to the prone position. Additionally, tension plate90preferably has a tension indicator line94that becomes visible outside housing96when strap74is properly tensioned.

More preferably, as illustrated inFIG. 16, instead of utilizing tension-sensitive strap connectors88, a pressure-sensitive tape switch234may be installed to side support bars28,30adjacent each side rail62. Tape switch234is preferably of the type commonly available from the Tape Switch company. Strap74is attached to a crossbar240that spans main rails66. When strap74is properly tensioned, main rails66depress tape switch234, which sends a signal through electrical leads238to the monitoring and control system indicating that side rail62is properly secured over the patient. Preferably, the monitoring and control system s programmed such that the patient support platform20is not allowed to rotate into the prone position unless all side rails62have been properly secured as indicated by tape switches234. To help calibrate each tape switch234, a pad236may be attached to side support bars28,30below the tape switch234adjacent each side rail62. Pads236are made of a compressible material, such as rubber, having a suitable hardness and thickness so that, as strap74is buckled, main rails66will first compress pads236and then depress tape switch234when strap74is buckled to the appropriate tension.

FIG. 17illustrates a preferred embodiment of tape switch234. A mounting bracket242, which is preferably made of extruded aluminum, houses two conductive strips250and246that are separated at their upper and lower edges by insulator strips248. Conductive strip250is a planar conductor oriented in a vertical plane as shown. Conductive strip246is installed under a preload such that it is bowed away from conductive strip250in its undisturbed position. Conductive strips250,246and insulator strips248are enclosed within a plastic shroud244. When main rails66engage tape switch234with sufficient pressure, conductive strip246is displaced to the position shown at246a, which completes the circuit with conductive strip250and sends a signal through leads238indicating that the strap74is properly secured.

As shown inFIG. 7, bed10preferably comprises a pair of lateral support pads116for holding a patient in place laterally. Lateral support pads116are connected to mounts108, which are slidably mounted on transverse support rails106that span the gap between side support bars28,30. Mounts108are also threadably engaged with a threaded rod112, the ends of which are mounted in side support bars28,30with bearings110. Mounts108are symmetrically spaced from the longitudinal centerline of bed10. Preferably, another bearing111supports the15middle portion of rod112, and a manually operable handle114is provided on at least one end of rod112. With respect to element114, the term “handle” as used herein is intended to mean any manually graspable item that may be used to impart rotation to rod112. Alternatively, rod112may be motor driven. One side112aof rod112has right-hand threads, and the other side112bhas left-hand threads. By rotating handle114in the appropriate direction, lateral support pads116are symmetrically moved toward or away from the patient, as desired. Due to the symmetrical spacing of mounts108and the mirror image threading112a,112bof rod112, lateral support pads116provide for automatic centering of the patient on bed10, which enhances rotational stability. Similarly, leg adductors/abductors184having straps186for securing a patient's legs may be mounted to mounts108in like manner as lateral support pads116. The term “patient support accessory” is used herein to mean any such auxiliary equipment, including but not limited to lateral support pads and leg adductors/abductors, that is attachable to mounts108for the purpose of providing symmetric lateral support to a patient on bed10.

FIGS. 8 through 13and22illustrate an apparatus at the foot of bed10for supplying a direct electrical connection between non-rotating base frame16and a patient monitoring device300connected to a rotating patient support platform20. As best shown inFIGS. 8 and 13, end ring24, which is fastened to rotating patient support platform20, is also connected to an annular channel126that serves as a housing for a cable carrier148. Cable carrier148carries an electrical cable253comprising power, ground, and signal wires as is customary in the art. Channel126, which preferably has a C-shaped cross-section, may be attached to end ring24by way of support bars192. Because channel126is attached to end ring24, channel126rotates with patient support platform20. As shown inFIGS. 12 and 13, an annular cover198is connected to upright foot frame144, which extends upward from base frame16. Cover198is preferably mounted on a ring196with fasteners200, and ring196is preferably mounted to support bars194that extend from stiffeners144aof foot frame144. Cover198, which is preferably made of metal to shield cable carrier148from radio frequency signals external of bed10, is positioned longitudinally adjacent channel126to retain cable carrier148within channel126, but cover198is not connected to channel126. Thus, channel126is free to rotate with end ring24, but cover198is stationary. One end150of cable carrier148is attached to channel126, and the other end152of cable carrier148is attached to cover198. The length of cable carrier148is preferably sufficient to allow patient support platform20to rotate a little more than 360 degrees in either direction. This arrangement provides a direct, wire-based electrical connection to the rotating part of bed10while still allowing a complete rotation of patient support platform20in either direction.

More preferably, as shown inFIG. 18, instead of cable carrier148, a flexible cable252may be used to supply a direct electrical connection between non-rotating base frame16and rotating patient support platform20.FIG. 18is a view of a preferred embodiment in the same direction asFIG. 13, butFIG. 18shows only flexible cable252and its channel260and cover264for the sake of clarity. Like channel126described above, channel260is basically C-shaped in cross-section as shown in FIG.19. However, channel260has an inner flange258to which cover264is attached, preferably with fasteners262. Flexible cable252resides generally within channel260. A gap266exists between channel260and cover264through which one end of flexible cable252may pass for attachment to non-rotating base frame16(not shown) at connection256. The other end254of flexible cable252is attached to channel260, which is attached to rotating patient support platform20. Like cover198above, cover264is preferably made of metal to shield flexible cable252from radio frequency signals external of bed10. As shown inFIG. 20, flexible cable252comprises a plurality of flexible conductive strips268surrounded by a flexible insulator270. Conductive strips268carry signals or ground connections, as desired, and multiple flexible cables252may be used if necessary, depending on the number of signals required. Like cable carrier148above, flexible cable252is preferably long enough to allow patient support platform20to rotate a little more than 360 degrees in either direction.

To prevent excessive rotation of patient support platform20and the attendant damage that excessive rotation would cause to cable carrier148or flexible cable252and its enclosed electrical wires, a rotation limiter128is provided on the inner surface of upright foot frame144as shown inFIGS. 8,10, and11. Rotation limiter128is pivotally mounted on frame144at point162and comprises contact nubs128aand128bfor engaging a boss134that protrudes from frame144. Thus, rotation limiter128may pivot about point162between the two extreme positions illustrated inFIGS. 10 and 11. Rotation limiter128preferably has a pair of tabs130,132that cooperate with sensors140and142, respectively, which are mounted in frame144. Sensors140,142are preferably micro switches but may be any type of sensor that is suitable for detecting the presence of tabs130,132. By respectively detecting the presence of tabs130and132, sensors140and142provide an indication of the direction in which patient support platform20has been rotated. A spring136is attached to rotation limiter128at over-center point164and to boss134at point166. Spring136keeps rotation limiter128in either of the two extreme positions until rotation limiter128is forced in the opposite direction by a stop pin146, as discussed below.

Still referring toFIGS. 8,10, and11, rotation limiter128has fillets128c,128dand flats128e,128ffor engaging stop pin146, which is rigidly attached to crossbar168. When patient support platform20is in its initial supine position (i.e., the position corresponding to zero degrees of rotation and referred to herein as the “neutral supine position”), stop pin146is located at the top of its circuit between flats128eand128fAs used herein to describe the rotation of end ring24and, necessarily, patient support platform20, “positive” rotation means rotation in the direction of arrow170as shown inFIG. 8, and “negative” rotation means rotation in the direction of arrow172. As end ring24is rotated in the positive direction, stop pin146engages flat128fand forces rotation limiter128into the extreme position shown inFIG. 11under the action of spring136. End ring24may be rotated slightly more than 360 degrees in the positive direction until stop pin146engages fillet128c, at which point rotation limiter128prevents further positive rotation. End ring24may then be rotated in the negative direction to return to the neutral supine position. As end ring24approaches the neutral supine position, stop pin146will engage flat128e. Further rotation in the negative direction beyond the neutral supine position will force rotation limiter128into the extreme position shown inFIG. 10under the action of spring136. End ring24may be rotated slightly more than 360 degrees in the negative direction until stop pin146engages fillet128d, at which point rotation limiter128prevents further negative rotation. In this manner, stop pin146and rotation limiter128cooperate to limit the rotation of platform20so that the electrical wires in cable carrier148will not be ripped out of their mountings and the direct electrical connection will be preserved.

Referring toFIGS. 8,9,12, and13, the foot of bed10preferably has a positioning ring122with a central opening118through which patient care lines may pass as discussed above. Positioning ring122, which is preferably fastened to support bars192, preferably has a plurality of circumferential holes124for cooperation with a longitudinal lock pin120to lock patient support platform20in one of several predetermined rotational positions. Lock pin120, which is mounted in upright frame144, is capable of limited longitudinal movement along its central axis to engage or disengage a hole124of positioning ring122, as desired. Preferably, lock pin120and positioning ring122include a twistable locking mechanism for preventing accidental disengagement of lock pin120from positioning ring122. For example, lock pin120may be provided with a protrusion such as nub120athat fits through slot124aof hole124. After pin120is pushed through hole124sufficiently for nub120ato clear positioning ring122, handle120bmay be used to twist lock pin120such that nub120aprevents retraction of pin120. Alternatively, lock pin120and positioning ring122may be respectively provided with cooperating parts of a conventional quarter-turn fastener or the like. Any such suitable device for preventing disengagement of lock pin120from positioning ring122by twisting lock pin120about its central axis is referred to herein as a twist lock.

More preferably, as illustrated inFIG. 21, a lock pin274with a spring-loaded detent278and proximity switches288,290may be mounted to frame144with a bracket272. Lock pin274has a central boss292with a peripheral groove280for cooperation with ball282of detent278in the neutral position shown in FIG.21. In the neutral position, pin274is disengaged from hole124of locking ring122, and proximity switches288,290preferably send “neutral” signals to the control system to electrically prevent rotation of patient support platform20. If handle276is used to push pin274into engagement with a hole124of locking ring122, ball282of detent278engages edge284of boss292, and proximity switch288senses edge286of boss292and sends a “locked” signal to the control system to electrically prevent rotation of patient support platform20in addition to the mechanical locking of pin274in locking ring122. If manual rotation of patient support platform20is desired, handle276may be used to pull pin274to its fully retracted position in which ball282of detent278engages edge286of boss292, and proximity switch290senses edge284of boss292and sends an “unlocked” signal to the control system to allow rotation of patient support platform20.

As discussed in international application number PCT/IE99/00049, bed10preferably has a drive system essentially comprising a belt drive between patient support platform20and an associated electric motor152at the foot end of base frame16. The drive system may be of the type described in Patent Specification No. WO97/22323, which is incorporated herein by reference. As illustrated inFIG. 14, bed10preferably includes a quick release mechanism156installed on foot frame144to provide a means to quickly disengage patient support platform20from the belt drive system. Quick release156may be conveniently made from a tool and jig lever available from WDS Standard Parts, Richardshaw Road, Grangefield Industry Estate, Pudsey, Leeds, England LS286LE. Quick release156comprises a mounting tube210secured to foot frame144. A lever222is pinned to tube210at point220. A tab218extends from lever222, and a linkage214is pinned to tab218at point216. Linkage214is also pinned at point212to a shaft208that is slidably disposed within tube210. Shaft208extends through foot frame144toward belt204which is engaged with pulley202of the drive system. A roller206is attached to shaft208for engaging belt204. By rotating lever222in the direction of arrow224, roller206is forced into engagement with belt204, which provides sufficient tension in belt204to engage patient support platform20with the drive system. By rotating lever222in the direction of arrow226, roller206is retracted from belt204, which disengages patient support platform20from the drive system thereby allowing manual rotation of patient support platform20. This capability of quick disengagement of the drive system to allow manual rotation of patient support platform20is very useful in emergency situations, such as when a patient occupying bed10suddenly needs CPR. In such a circumstance, if patient support platform20is not in a supine position, a caregiver may quickly and easily disengage the drive system using quick release156, manually rotate patient support platform20to a supine position, and begin administering CPR or other emergency medical care.

As disclosed in international application number PCT/IE99/00049, the rotational position of patient support platform20, which is governed by motor152of the aforementioned drive system, may be controlled through the use of a rotary opto encoder. Alternatively, the rotational position of patient support platform20may be controlled through the use of an angle sensor232(shown schematically inFIG. 13) of the type disclosed in U.S. Pat. No. 5,611,096, which is incorporated herein by reference. As disclosed in the '096 patent, angle sensor232comprises a first inclinometer (not shown) that is sensitive to its position with respect to the direction of gravity. By mounting angle sensor232to patient support platform20in the proper orientation, the output signal from angle sensor232may be calibrated to control the rotational position of patient support platform20in cooperation with motor152. Likewise, angle sensor232may include another properly oriented inclinometer (not shown) that may be used in association with rams15and17(seeFIG. 1) to control the Trendelenburg position of patient support platform20.

Although the foregoing specific details describe a preferred embodiment of this invention, persons reasonably skilled in the art will recognize that various changes may be made in the details of the method and apparatus of this invention without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, it should be understood that this invention is not to be limited to the specific details shown and described herein.