Abstract:
A body support for providing a beneficial effect has a frame and a first and a second plurality of flexible parallel bands, which are interdigitated. A primary shaft rotatably mounted in a frame can tighten and slacken the first plurality of bands. This can be done by having the shaft wind and unwind the first plurality of bands or by appropriately positioning a camshaft or the like at one edge of the body support surface to adjustably hold each of the first plurality of bands there. In the latter case the shaft provides a plurality of support locations at the first edge of the support surface that are moved, in order to alternately tighten and slacken the first plurality of bands. Other disclosed apparatus and methods can tighten and slacken the second plurality of bands as well.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to beneficial body supports, and in particular, to supports having alternating elements. 
   2. Description of Related Art 
   Bedridden patients being treated in the hospital or at home can develop bedsores (decubiti) under certain conditions. The Braden Scale evaluates the risk of sores by scoring six categories: (1) The ability of the patient to respond meaningfully to pressure-related discomfort, which may decline as a result of sedation, a diminished level of consciousness, or a limited ability to feel pain. (2) The degree of exposure of the skin to moisture from perspiration, body fluids, etc. (3) The amount of physical activity performed by the patient. (4) The patient&#39;s ability to change and control body position. (5) The adequacy and quality of the patient&#39;s nutritional status. (6) How often the patient moves or must be moved in a way that causes friction and shear forces. 
   One of the prime contributors to skin breakdown that causes decubiti, is the build-up of moisture between the patient&#39;s skin and the bedding on which the patient is resting (Braden Scale). 
   Insensible water loss from a body is approximately 50 ml/hour (“ Textbook of Medical Physiology ” Guyton &amp; Hall, 2000). When a patient is febrile, the amount of moisture exuded through the skin can increase dramatically. If the patient is also incontinent of bowel and/or bladder, more fluids are exuded and act to increase the damage of shear on skin, which promotes decubiti formation. 
   Existing hospital beds do not allow for free flow of air under the patient. One typically expensive model by Hill-Rom incorporates a mechanical flow of air but is predicated on existence of continual electrical power. 
   Keeping skin temperature down will also reduce the risk of decubiti. Unfortunately, known bedding systems do not incorporate effective features for reducing or moderating skin temperature. 
   The prediction of porosity or permeability of fabrics via theoretical models has proven somewhat frustrating ( The Relationship Between Porosity and Air Permeability of Woven Textile Fabrics , Epps &amp; Leonas,  Journal of testing and Evaluation , Vol. 25, 1997, pp 108-113). Fortunately the measurement of air and moisture is not, and is available for the common fabrics (sheeting, print cloth, flannel, sateen, plain weave, batiste, poplin, and the synthetics: taffeta, challis, and plain weave triacetate). 
   Rather complicated beds are available for providing a body support that reduces the tendency for bedsores. These beds provide continually changing pressure points that prevent stasis. However, these beds are not widely available because their complexity and cost make them impractical for widespread use in most hospitals, as well as being beyond the financial reach of most home users. Moreover, these beds have many drawbacks in that they do not promote adequate air circulation around the patient, are not easily dismantled for set up or cleaning, cannot be easily operated manually during a power failure, etc. 
   In U.S. Pat. No. 5,083,551 three endless bands are looped around the seat of a wheelchair and are tightened and slackened by a single camshaft with three cam faces phased 120° apart. 
   In U.S. Pat. No. 4,155,592 straps 28 secured to the right edge of a seatback stretch across a frame from left to right and are routed past a camshaft 36. Rotation of camshaft 36 will selectively tighten some of the straps to adjust the lumbar support. 
   In U.S. Pat. No. 4,837,878 a bed is provided with stretchable straps alternating with non-stretchable straps. Strap tension can be adjusted mechanically, including by winding the strap around a rotatable shaft. 
   In U.S. Pat. No. 2,112,367 levers 35 on the right side of a bed frame attach to the right end of odd straps 29 while levers 35 on the left side attach to the left end of even straps. Levers on opposite sides are either moving toward or away from the middle to move the consecutive straps in opposite longitudinal directions. 
   In FIG. 32 of U.S. Pat. No. 5,862,550 a panel is slotted to provide a plurality of flexible bands, flexibility being enhanced by providing the U-shaped bands at 108 of FIG. 3. Cams on an underlying camshaft raise and lower alternate bands to avoid bedsores. 
   In U.S. Pat. No. 5,443,439 plates 11 can be tilted in different phases by a camshaft. 
   In U.S. Pat. No. 5,103,511 a sling-like cradle is automatically rocked back and forth to avoid bedsores. 
   In U.S. Pat. No. 4,459,712 a mesh can circulate on rollers 14,16, and 18. The height of roller 18 can be changed to adjust the sag in the top span of the mesh. See also U.S. Pat. No. 4,109,329. 
   In FIG. 5 of U.S. Pat. No. 5,109,558 a crank rocks levers 273 to vertically reciprocate the bed elements 205 to avoid bedsores. See also U.S. Pat. No. 5,626,555. 
   In U.S. Pat. Nos. 6,557,937 and 6,676,215 six slats form the seat of a wheelchair. A motor associated with each slat drives a crankshaft to vertically reciprocate its slat. 
   In U.S. Pat. No. 5,776,048 a burn patient lies on a row of fixed bars 38 interleaved with reciprocating bars 43. The reciprocating bars rise above and descend below the fixed bars to prevent bedsores. The bars have a removable core that can be removed for washing. 
   In U.S. Pat. No. 5,161,267 a patient is lifted by a number of parallel straps in order to change bed linens. 
   In U.S. Pat. No. 4,625,487 a number of transverse cushions are held in cradles to form a bed. Alternate cradles can be rocked in opposite directions to produce alternating lift points that can massage a person and prevent bedsores. See also U.S. Pat. No. 4,494,260 where cradled cushions are all rocked in the same direction. 
   In U.S. Pat. No. 3,464,406 a bed surface is supported by a number of parallel rods 100, each mounted between an opposite pair of planetary gears 90. The rods 100 are mounted eccentrically and at different phases so that when gears 9 are rotated, the rods produce a wave-like motion. 
   In FIG. 5 of U.S. Pat. No. 4,999,861 a bed surface is formed from a number of parallel slats 18 with rollers that ride on cams 64, which are phased to produce a wave-like motion. See also U.S. Pat. No. 4,202,326. 
   In U.S. Pat. No. 4,958,627 a bed is formed of a number of parallel wires 13. A motor-driven cam swings a lever 32 (FIG. 3) to periodically hit and lift the wires 13 as shown in the upper left portion of FIG. 2. 
   In U.S. Pat. No. 6,009,873 a pair of inflatable wedges are placed on opposite sides of a patient and held in place with encircling straps to maintain the patient&#39;s position. 
   In U.S. Pat. No. 4,769,864 a single, stationary bed frame is strung with a wire that crosses the bed multiple times in a serpentine path. 
   See also, U.S. Pat. Nos. 2,112,367; 5,233,712; 4,999,861; 5,659,910; and 5,626,555. 
   Accordingly, there is a need for an improved body support and method for supporting a body that can provide a beneficial effect, such as preventing bedsores. 
   SUMMARY OF THE INVENTION 
   In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided a body support for providing a beneficial effect. The body support has a frame and a first and a second plurality of flexible parallel bands. The first plurality of bands is interdigitated with the second plurality of parallel bands. Also included is a primary shaft rotatably mounted in the frame for winding and unwinding the first plurality of bands in order to alternately tighten and slacken the first plurality of bands. 
   In accordance with another aspect of the present invention, there is provided a body support for providing a support surface with a first and a second edge for supporting a living body and providing a beneficial effect. The body support has a frame and a first plurality of flexible parallel bands, each reaching from a first to a second edge of the support surface. Also included is a second plurality of parallel bands. The first plurality of bands is interdigitated with the second plurality of parallel bands. The body support also includes a primary shaft rotatably mounted in the frame for alternately tightening and slackening the first plurality of bands. The shaft is positioned at the first edge of the support surface to hold each of the first plurality of bands at the first edge of the support surface. 
   In accordance with yet another aspect of the present invention, a method is provided that employs a first and second plurality of interdigitated parallel bands for supporting a body along a support surface and providing a beneficial effect. The method includes the step of winding and unwinding the first plurality of bands in order to alternately tighten and slacken the first plurality of bands. 
   In accordance with still yet another aspect of the present invention, a method is provided that employs a first and second plurality of interdigitated parallel bands for beneficially supporting a body at a support surface having a first and second edge. The method includes the step of supporting the first plurality of bands at a plurality of support locations at the first edge of the support surface. Another step is moving the plurality of support locations in order to alternately tighten and slacken the first plurality of bands. 
   By employing apparatus and methods of the foregoing type, a body can be supported in an improved fashion. In one embodiment a first plurality of flexible bands are attached to a right rail, and routed across a support surface and over a left rail before being wound onto a left shaft located below the left rail. A second plurality of flexible bands that interdigitate with the first plurality are attached to the left rail, and routed across the support surface and over the right rail before being wound onto a right shaft located below the right rail. Thus the left (right) shaft can wind and unwind the first (second) plurality of flexible bands to tighten and slacken them. Consequently, a person lying upon the flexible bands will be supported alternately by the first plurality and then by the second plurality of bands so that pressure is not continuously applied to discrete locations on the body in a way that promotes bedsores. In some embodiments the positions of the shafts and the rails can be reversed, so that the rails are below the winding shafts. 
   In other embodiments a right and a left shaft are mounted along the edges of the support surface with a right and left rail mounted below the two shafts. A first and a second plurality of flexible bands are attached to the right rail and routed over the two shafts before attaching to the left rail. In one case, one of the shafts is a camshaft with a number of cam tracks. The cam tracks are arranged into two groups having different phases. Accordingly, the cam can rotate to tighten the first plurality of bands while allowing the second plurality to slacken, and vice versa. In a second case, both shafts are camshafts, with one of the camshafts having cam tracks devoted to the first plurality of bands, and the cam tracks of the other camshaft devoted to the second plurality. The two camshafts are phased differently so that again the first plurality of bands are tightened while the second plurality is slackened, and vice versa. In the foregoing embodiments the rails can be eliminated and the ends of each of the bands connected together to form a number of endless loops. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above brief description as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is perspective view of the body support capable of performing a support method in accordance with principles of the present invention; 
       FIG. 2  is a perspective, exploded view of a portion of the structure of  FIG. 1 ; 
       FIG. 3A  is a free body diagram of components from  FIG. 2  showing the winding and unwinding of bands in one phase; 
       FIG. 3B  is a free body diagram similar to that of  FIG. 3A  but showing the arrangement shifted into a different phase; 
       FIGS. 4A and 4B  is a free body diagram showing an arrangement that is an alternate to that of  FIGS. 3A and 3B , respectively; 
       FIG. 5A  is a schematic diagram of a portion of a body support that is an alternate to that of  FIG. 1 ; 
       FIG. 5B  is a schematic diagram similar to that of  FIG. 5A  but showing the arrangement shifted into a different phase; 
       FIG. 6  is a perspective view of the camshaft of  FIG. 5A ; 
       FIG. 7A  is a schematic diagram of a portion of a body support that is an alternate to those mentioned above; 
       FIG. 7B  is a schematic diagram similar to that of  FIG. 7A  but showing the arrangement shifted into a different phase; 
       FIG. 8  is a perspective view of one of the camshafts of  FIG. 7A ; 
       FIG. 9A  is a schematic diagram of a portion of a body support that is an alternate to those mentioned above; 
       FIG. 9B  is the schematic diagram of  FIG. 9A  showing the arrangement shifted into a different phase; 
       FIG. 10A  is a schematic diagram of a portion of a body support that is an alternate to those mentioned above; and 
       FIG. 10B  is the schematic diagram of  FIG. 10A  showing the arrangement shifted into a different phase. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 and 2 , a body support is shown as a frame having a four-sided, open rectangular chassis  10  with four corner legs  12  attached to chassis  10  by welding, bolts, or other fastening means. An opposing pair of longitudinal rails  14 A and  14 B are likewise attached to legs  12  and constitute a right and left edge of a body support surface. A primary shaft  16  has on both ends a trunnion  16 A that is journalled in a hole, for example  12 A in leg  12 . A similar shaft  18  (a secondary shaft) has trunnions, such as trunnion  18 A, again designed to mount in holes, such as  12 A in legs  12 . Shaft  16  and  18  are mounted directly below shafts  14 A and  14 B, respectively. 
   A first plurality of parallel flexible bands  20  are routed over rails  14 A and  14 B with one end attached to the underside of rail  14 B by snaps, clamps, screws or the like. The opposite ends of bands  20  are routed over rail  14 A and are attached to the periphery of shaft  16  by screws, clamps, snaps, or the like. A second plurality of parallel flexible bands  22  are routed over rails  14 A and  14 B with one end attached to the underside of rail  14 A by snaps, clamps, screws or the like. The opposite ends of bands  22  are routed over rail  14 B and are attached to the periphery of shaft  16  by screws, snaps, clamps, or the like. It is advantageous to keep bands  20  and  22  easily removable for cleaning. In some cases the ends of the bands can have reinforced grommets that slip over hooks on rails and shafts. Alternatively, the ends of the bands can have stated into holes or loops on the rails and shafts. 
   The bands  20  and  22  may be cloth strips made of linen, canvas, or other fabrics made of natural or synthetic fibers. Alternatively, bands  20  and  22  may be continuous plastic strips or composite materials with a certain amount of elasticity. In still other embodiments, each of the bands  14  may be formed of a separate number of smaller strips or cords. In some embodiments, the bands may be formed of multiple layers that have different purposes; for example, an absorbent upper layer on top of a lower layer having a desired amount of strength and elasticity. 
   In most embodiments, the width of the bands will be between 0.5 to 12 inches (1.3 to 30.5 cm); but preferably the range will be 1 to 2 inches (2.5 to 5.1 cm). In any event, it is desirable to have bands that allow the passage of air, vapor and liquids to reduce the amount of moisture that can be trapped between a person&#39;s body and one of the bands. 
   To promote hygiene, bands  20  and  22  can be optionally covered with a strip of tape (such as Scotch 3M Safe-Release Painter&#39;s Masking Tape #2090, or Scotch 3M™ Tan Polyethylene Single Coated Medical Tape #1 523). In some embodiments the tape can be impregnated with an optional anti-bacterial, antiseptic or sanitizing agent to extend the life of the tape. 
   When such tape is used the bands  20  and  22  can be freshened by removing the tape should it become soiled and replacing it with clean tape, thereby reducing the need to wash the bands  20  and  22  every time there is a spill or a new patient. The staff in charge of maintaining the cleanliness of the bands  20  and  22  can make a judgment as to how many times and how frequently the strips will be replaced before washing the bands. For major spills or for environments where contamination or the spread of disease is the primary concern, the strips can be replaced more frequently. In some instances the optional strips will not be replaced except at the time of washing and thus will be discarded whenever the bands  20  and  22  are to be removed and washed. 
   Reducing the moisture at a patient&#39;s skin is highly desirable. Even in the absence of fluid excretion from incontinence or other such causes, perspiration can predispose the skin to decubiti development. This moisture is directly affected by the air permeability of the bands. Keeping air permeability greater than 9 cm 3 /cm 2 /sec is desirable and, preferably, the air permeability will be greater than 50 cm 3 /cm 2 /sec. In one highly preferred embodiment, the bands are made of a plain weave of triacetate fibers or other synthetic fibers having an air permeability exceeding 130 cm 3 /cm 2 /sec, although the use of other types of fabrics is anticipated. Air permeability will be measured as described in  The Relationship Between Porosity and Air Permeability of Woven Textile Fabrics , Epps &amp; Leonas,  Journal of testing and Evaluation , Vol. 25, 1997, pp 108-113. 
   The bands in the present arrangement can be of various strengths as needed without compromising moisture evaporation, or the effects of wicking or osmotic movement. 
   Also, since the bands are relatively permeable, thin, have small gaps between them, and alternate position, the overall air permeability is relatively high. Moreover, the same factors work to keep skin temperature down and therefore help to reduce the risk of decubiti. 
   Referring still to  FIGS. 1 and 2 , the trunnion  16 A of shaft  16  connects through right angle gear box  26  to a driver  28  in the form of an electrical motor. Instead of an electric motor, some embodiments may employ a solenoid, stepper motor, hydraulic piston, etc. Trunnion  18 A of shaft  18  connects in a similar fashion through right angle gear box  32  to another driver  34 , which is the same as driver  28 . 
   Drivers  28  and  34  can be operated sequentially by a controller  35  in the form of electronic timer. Alternatively, the controller  35  may employ a clock motor that slowly rotates a number of cams that operate switches to cause drivers  28  in  34  to operate in an appropriate sequence. Instead of operating electrical switches, an alternate controller can employ motor-driven cams that operate levers attached to shaft  16  and  18  to rotate them with an appropriate timing. In still other embodiments, shafts  16  and  18  can be operated manually by, for example, a hand crank. 
   An optional gear  30  can be mounted on trunnion  16 A and linked by an optional endless chain  31  to a similar gear (not shown) on trunnion  18 A. When employed, such gears and endless chain are referred to as a link mechanism. Accordingly, a single driver can rotate one of the gears  30  (or a separate driving gear (not shown) and engage chain  31 ) to cause the shafts  16  and  18  to reciprocate synchronously. Shaft  16  can then slacken bands  20  while shaft  18  tightens bands  22 , and vice versa. As explained further hereinafter, linking the shafts  16  and  18  in this way may create an undesirable transition interval when all bands  20  and  22  are slackened somewhat. 
   Referring to  FIGS. 3A and 3B , previously mentioned band  22  is shown attached to shaft  18  by snap fastener  24 . When shaft  18  is rotated clockwise as indicated in  FIG. 3A , band  22  is pulled tight over rail  14 B so its central section is approximately horizontal. When shaft  18  is rotated counterclockwise as indicated in  FIG. 3B , band  22  slackens and effectively descends (the magnitude of descent is exaggerated in  FIG. 3B ). As explained further hereinafter, band  20  (shown in phantom) likewise tightens and slackens under the influence of shaft  16  ( FIG. 2 ), but with a different phasing relative to band  22 . 
   It is desirable to tighten and slacken bands  20  and  22  in the following sequence: (a) bands  20  tightened and bands  22  slackened; (b) bands  20  and  22  both tightened; and (c) bands  20  slackened and bands  22  tightened. With this sequencing a person supported by the bands  20  and  22  does not experience a sinking feeling that might otherwise occur if all bands slackened. 
   In the alternate embodiment of  FIGS. 4A and 4B , the rails at the edge of the support surface are eliminated and replaced with winding shafts, such as winding shafts  36  shown winding the bands  20 ′. While only one edge is illustrated in these figures, it will be appreciated that a complementary winding shaft (not shown) exists at the opposite edge. In fact, bands  22 ′, which are wound around this other complementary shaft, also slide over the illustrated shaft  36  and attach to rail  38 . Rail  38  is similar to the previously illustrated rails (rails  14 A and  14 B in  FIG. 2 ). It will be appreciated that a complementary rail (not shown) on the opposite side of the body support will be mounted below the other complementary winding shaft there. Bands  20 ′ will slide over this other complementary winding shaft and terminate on this other complementary rail. 
   The foregoing shaft  36 , rail  38 , and the complementary shaft and rail will be mounted in a frame similar to that shown in  FIGS. 1 and 2 . As before, shaft  36  and the complementary shaft will be driven by a motor or other means. 
   Accordingly, winding shaft  36  can unwind bands  20 ′ so they sag as shown in  FIG. 4A . Shaft  36  can also wind bands  20 ′ as shown in  FIG. 4B  so they tighten and become effectively horizontal. The other complementary shaft can wind can unwind bands  22 ′ with a different phase to produce the same effect previously mentioned in connection with the embodiment of  FIG. 1 . 
   To facilitate an understanding of the principles associated with the foregoing apparatus, its operation will be briefly described in connection with the embodiment of  FIGS. 1 and 2  (the operation for the embodiment of  FIGS. 4A and 4B  will be similar). A bed sheet may be placed on the body support of  FIG. 1  over the bands  20  and  22 . Thereafter, a patient may be placed on the bed sheet and will be supported by bands  20  and  22 . Preferably, bands  20  and  22  will have a certain amount of elasticity so that the patient will be supported comfortably. 
   Initially, shaft  18  will be in the wound condition as shown in  FIGS. 2 and 3A . Shaft  16  will be in an unwound condition as shown in  FIG. 2 . This unwound condition will be similar to the unwound condition shown in  FIG. 3B  for shaft  18 . Therefore, as shown in  FIG. 2 , bands  20  will sag relative to bands  22 . Therefore, support will be provided primarily by bands  22 . Next, driver  28  ( FIG. 2 ) will be operated through gear box  26  to rotate shaft  16  in order to wind bands  20 . As a result, bands  20  and  22  will be at the same height and will simultaneously provide support. Therefore, a person lying on the bands will not experience a sinking feeling that might occur if all bands were slackened somewhat at the same time. 
   Once bands  20  are tightened, motor  28  will be stopped. Almost immediately thereafter, motor  34  will be operated through gear box  32  to rotate shaft  18  and slacken bands  22 . Once bands  22  are sufficiently slackened, motor  34  will stop. Both motors  28  and  34  then remain off for a period of time. In fact, for the most part the motors remain off except for the transition when the bands  20  and  22  reverse their roles. At the next role reversal, shaft  18  will tighten bands  22  and stop before shafts  16  slackens bands  20  and then stops too. 
   Preferably, the repetition periods of the shafts  16  and  18  can be adjusted to accommodate the specific needs of the patient using the body support. The period can be adjusted to give bands  20  and  22  a period of five seconds to two hours. 
   Preferably, the space between adjacent ones of the bands  20  and  22  will be kept very small so that a person lying on the bands will not feel gaps. However, a small gap will be desirable to avoid having locations on the patient&#39;s body that always experience support pressure. Also, allowing a small gap will avoid pinching, but sheets or other covers can be placed over the bands to reduce or eliminate the risk of pinching as well. 
   When the bands  20  and  22  are tightened and slackened their central portion will effectively move up and down under the weight of the body on them. The vertical amplitude produced in the center of the bands  20  and  22  will be at least 0.5 inch (1.3 cm), and preferably in the range of 0.5 to 2.5 inches (1.3 to 6.4 cm). For example, with an amplitude of 0.5 inch one set of bands may rise 0.5 inch up to the patient resting level while the other set of bands descends to a position 0.5 inch below that resting level. The amplitude will be selected depending on the condition of the patient and the thickness and resiliency of any covers between the patient and the bands  20  and  22 . In any event, the bands  20  and  22  will reciprocate in such a way as to the provide support from one set of bands while the other set of bands retracts just enough to take pressure off the patient. 
   Referring to  FIGS. 5A ,  5 B, and  6 , shafts  40  and  42  are rotatably mounted in a frame in a manner similar to that shown in  FIGS. 1 and 2 . Rails  44 A and  44 B are similar to the rails previously illustrated in  FIG. 2  (rails  14 A and  14 B) and are mounted in a frame in a similar manner. In this embodiment a first plurality of bands  20 ″ and a second plurality of bands  22 ″ are suspended in an interdigitated manner, similar to the previously illustrated bands (bands  20  and  22  in  FIG. 1 ). In particular, bands  20 ″ and  22 ″ are attached to rail  44 A, are routed over shafts  40  and  42 , and are attached to the opposite rail  44 B. The bands  20 ″ and  22 ″ are not attached to shafts  40  and  42  and simply slide over them. 
   Primary shaft  40  is located at a first edge of a support surface, while shaft  42  is located at a second edge of the support surface. Shaft  42  is a simple cylindrical shaft, but shaft  40  is a camshaft having a first group  40 A and second group  40 B of cam tracks all rotating around center of rotation  46 . Cam tracks  40 A and  40 B provide a plurality of support locations along the first edge of the body support. Bands  20 ″ are arranged to ride over cam tracks  40 A, while bands  22 ″ ride over cam tracks  40 B. Cam tracks  40 A are the same as cam tracks  40 B, except for having a first phase that is 180° out of phase with cam tracks  40 B (which are deemed to offer a second phase). 
   With the angular orientation shown in  FIG. 5A , the inwardly facing portion of cam tracks  40 A are retracted but do not engage bands  20 ″. Therefore, bands  20 ″ ride over the unretracted portion of cam tracks  40 A and remain tight. The outwardly facing portion of cam tracks  40 B are retracted along an interval interfacing with bands  22 ″, so these bands are slackened. 
   With the angular orientation shown in  FIG. 5B , the inwardly facing portions of cam tracks  40 B are retracted but do not engage bands  22 ″. Therefore, bands  22 ″ ride over the unretracted portion of cam tracks  40 B and remain tight. The outwardly facing portions of cam track  40 A are retracted along an interval interfacing with bands  20 ″, so these bands are slackened. 
   The bands  20 ″ and  22 ″ can be alternately tightened and slackened by rotating camshaft  40  continuously for intermittently in either the clockwise or counterclockwise direction. Alternatively, the camshaft  40  can be reciprocated ±180° either with continuous oscillatory motion or by a rapid shifting between discrete positions between relatively quiescent intervals. Shaft  42  can be either non-rotative, arranged for freewheeling rotation, or driven to rotate with the same cycle or anticyclically. 
   Referring to  FIGS. 7A ,  7 B, and  8 , components identical to those described in previous illustrations bear the same reference numerals. Shafts  48  and  50  are rotatably mounted in a frame in a manner similar to that shown in  FIGS. 1 and 2 . Rails  44 A and  44 B are similar to the rails previously illustrated in  FIG. 2  (rails  14 A and  14 B) and are mounted in a frame in a similar manner. In this embodiment a first plurality of bands  20 ″ and a second plurality of bands  22 ″ are suspended in an interdigitated manner, similar to the previously illustrated bands (bands  20  and  22  in  FIG. 1 ). In particular, bands  20 ″ and  22 ″ are attached to rail  44 A, are routed over shafts  48  and  50 , and are attached to the opposite rail  44 B. The bands  20 ″ and  22 ″ are not attached to shafts  48  and  50  and simply slide over them. 
   Primary shaft  48  with a center of rotation  49  is located at a first edge of a support surface, while secondary shaft  50  with a center of rotation  52  is located at a second edge of the support surface. Shafts  48  and  50  are camshafts having cam tracks  48 A and  50 A, respectively. Cam tracks  48 A provide a plurality of support locations along the first edge of the body support, while cam tracks  50 A provide a plurality of support positions along the second edge of the body support. Located between cam tracks  48 A and  50 A are concentric cylindrical portions  48 B and  50 B. Bands  20 ″ are arranged to ride over cam tracks  48 A and concentric portions  50 B, while bands  22 ″ ride over cam tracks  50 A and concentric portions  48 B. Camshaft  48  is the same as camshaft  50 , except for having been installed with its cam tracks  48 A in a first phase that is 180° out of phase with cam tracks  50 A (which are deemed to offer a second phase). 
   With the angular orientation shown in  FIG. 7A , the inwardly facing portions of cam tracks  50 A are retracted but do not engage bands  22 ″. Therefore, bands  22 ″ ride over the unretracted portions of cam tracks  50 A and remain tight. Note that the cylindrical, concentric portions  48 B engaging bands  22 ″ are radially invariant and do not affect the tension in bands  22 ″. The outwardly facing portions of cam tracks  48 A are retracted along an interval interfacing with bands  20 ″, so these bands are slackened. Again, the cylindrical, concentric portions  50 B of shaft  50  engaging bands  20 ″ are radially invariant and do not affect the tension in bands  22 ″. 
   With the angular orientation shown in  FIG. 7B , the inwardly facing portions of cam tracks  48 A are retracted but do not engage bands  20 ″. Therefore, bands  20 ″ ride over the unretracted portion of cam tracks  48 A and remain tight. Note that the cylindrical, concentric portions  50 B engaging bands  20 ″ are radially invariant and do not affect the tension in bands  20 ″. The outwardly facing portions of cam tracks  50 A are retracted along an interval interfacing with bands  22 ″, so these bands are slackened. Again, the cylindrical, concentric portions  48 B engaging bands  22 ″ are radially invariant and do not affect the tension in bands  20 ″. 
   The bands  20 ″ and  22 ″ can be alternately tightened and slackened by rotating camshafts  48  and  50  continuously or intermittently in either the same or opposite direction. Alternatively, the camshafts  48  and  50  can be reciprocated ±180° either with continuous oscillatory motion or by a rapid shifting between discrete positions between relatively quiescent intervals. 
   In one embodiment camshafts  48  and  50  may be oriented as shown in  FIG. 7A  with bands  20 ″ slack and bands  22 ″ tight. Thereafter, camshaft  48  can rotate 180° (either clockwise or counterclockwise) while camshaft  50  remains stationary. Consequently, camshaft  48  will have the orientation shown in  FIG. 7B  and camshaft  50  will have the orientation shown in  FIG. 7A  so both bands  20 ″ and  22 ″ will be tight. Next, camshaft  50  can rotate 180° (either clockwise or counterclockwise) while camshaft  48  remains stationary. Consequently, camshafts  48  and  50  will have the orientation shown in  FIG. 7B  so that bands  20 ″ will be tight and bands  22 ″ slack. The foregoing cycle avoids an interval where both bands  20 ″ and  22 ″ are slackened somewhat to give the undesirable feeling of descent. 
   Referring to  FIGS. 9A and 9B , components identical to those described in previous illustrations bear the same reference numerals. In particular, shafts  40  and  42  are identical to that shown in  FIGS. 5A ,  5 B, and  6 , and shaft  40  again provides a plurality of support locations. Shafts  40  and  42  are again rotatably mounted in a frame in a manner similar to that shown in  FIGS. 1 and 2 . In this embodiment a first plurality of bands  120  and a second plurality of bands  122  are all endless. Bands  120  and bands  122  are suspended in an interdigitated manner, similar to the previously illustrated bands (bands  20  and  22  in  FIG. 1 ). In particular, bands  120  and  122  are not attached to shafts  40  and  42  and simply ride over them. 
   Primary shaft  40  is located at a first edge of a support surface, while shaft  42  is located at a second edge of the support surface. Shaft  42  is a simple cylindrical shaft, but shaft  40  is a camshaft as shown in  FIG. 6 . Bands  120  are arranged to ride over cam tracks  40 A, while bands  122  ride over cam tracks  40 B. Cam tracks  40 A are the same as cam tracks  40 B, except for exhibiting a first phase that is 180° out of phase with cam tracks  40 B (which are deemed to offer a second phase). 
   With the angular orientation shown in  FIG. 9A , the inwardly facing portion of cam tracks  40 A are retracted but do not engage bands  120 . Therefore, bands  120  ride over the unretracted portion of cam tracks  40 A and remain tight. The outwardly facing portion of cam tracks  40 B are retracted along an interval interfacing with bands  122 , so these bands are slackened. 
   With the angular orientation shown in  FIG. 9B , the inwardly facing portions of cam tracks  40 B are retracted but do not engage bands  122 . Therefore, bands  122  ride over the unretracted portion of cam tracks  40 B and remain tight. The outwardly facing portions of cam track  40 A are retracted along an interval interfacing with bands  120 , so these bands are slackened. 
   The bands  120  and  122  can be alternately tightened and slackened by rotating camshaft  40  continuously or intermittently in either the clockwise or counterclockwise direction. Alternatively, the camshaft  40  can be reciprocated ±180° either with continuous oscillatory motion or by a rapid shifting between discrete positions between relatively quiescent intervals. Shaft  42  can be arranged for freewheeling rotation, or driven to rotate synchronously with shaft  40 . 
   Referring to  FIGS. 10A and 10B , components identical to those described in previous illustrations bear the same reference numerals. In particular, shafts  48  and  50  are identical to that shown in  FIGS. 7A ,  7 B, and  8  (in particular, shafts  48  and  50  provide a plurality of support locations and a plurality of support positions). Shafts  48  and  50  are rotatably mounted in a frame in a manner similar to that shown in  FIGS. 1 and 2 . In this embodiment a first plurality of bands  120 ′ and a second plurality of bands  122 ′ are all endless. Bands  120 ′ and bands  122 ′ are suspended in an interdigitated manner, similar to the previously illustrated bands (bands  20  and  22  in  FIG. 1 ). The bands  120 ′ and  122 ′ are not attached to shafts  48  and  50  and simply ride over them. 
   Primary shaft  48  with a center of rotation  49  is located at a first edge of a support surface, while secondary shaft  50  with a center of rotation  52  is located at a second edge of the support surface. Shafts  48  and  50  are camshafts having cam tracks  48 A and  50 A, respectively, as shown in  FIG. 8 . Bands  120 ′ are arranged to ride over cam tracks  48 A and concentric portions  50 B, while bands  122 ′ ride over cam tracks  50 A and concentric portions  48 B. Camshaft  48  is the same as camshaft  50 , except for having been installed with its cam tracks  48 A in a first phase that is 180° out of phase with cam tracks  50 A (which are deemed to offer a second phase). 
   With the angular orientation shown in  FIG. 10A , the inwardly facing portions of cam tracks  50 A are retracted but do not engage bands  122 ′. Therefore, bands  122 ′ ride over the unretracted portions of cam tracks  50 A and remain tight. Note that the cylindrical, concentric portions  48 B ( FIG. 8 ) engaging bands  122 ′ are radially invariant and do not affect the tension in bands  122 ′. The outwardly facing portions of cam tracks  48 A are retracted along an interval interfacing with bands  120 ′, so these bands are slackened. Again, the cylindrical, concentric portions  50 B of shaft  50  engaging bands  120 ′ are radially invariant and do not affect the tension in bands  120 ′. 
   With the angular orientation shown in  FIG. 10B , the inwardly facing portions of cam tracks  48 A are retracted but do not engage bands  120 ′. Therefore, bands  120 ′ ride over the unretracted portion of cam tracks  48 A and remain tight. Note that the cylindrical, concentric portions  50 B engaging bands  120 ′ are radially invariant and do not affect the tension in bands  120 ′. The outwardly facing portions of cam tracks  50 A are retracted along an interval interfacing with bands  122 ′, so these bands are slackened. Again, the cylindrical, concentric portions  48 B engaging bands  122 ′ are radially invariant and do not affect the tension in bands  120 ′. 
   The bands  120 ′ and  122 ′ can be alternately tightened and slackened by rotating camshafts  48  and  50  continuously or intermittently in either the clockwise or counterclockwise direction. Alternatively, the camshafts  48  and  50  can be reciprocated ±180° either with continuous oscillatory motion or by a rapid shifting between discrete positions between relatively quiescent intervals. 
   The four embodiments of  FIGS. 5A ,  5 B,  7 A,  7 B,  9 A,  9 B,  10 A, and  10 B can produce the same effect as described in connection with the embodiment ins of FIGS.  1 , 2 ,  3 A,  3 B,  4 A and  4 B. Therefore, it will be appreciated that the operation described in connection with all of these embodiments will be essentially the same, or can be designed to operate essentially the same. 
   It is appreciated that various modifications may be implemented with respect to the above described, preferred embodiments. The foregoing structure may be used to construct a bed on which an individual can recline or sleep. Alternatively the foregoing structure can be adapted to produce a seat for a wheelchair, a bench (for one or more persons), or other chair. In still other embodiments, a pair of supports of the foregoing type can be arranged end to end with one of them having an adjustable angle of orientation to simulate a bed with an adjustable head. Also the various components described herein can be made of metal, wood, ceramics, composite materials, or other materials having an appropriate strength, flexibility, stability, etc. Furthermore, the dimensions and shapes of the various components can be altered depending upon the desired size, capacity, strength, degree of motion, etc. In addition, the foregoing structure can be supported in various ways including open or closed frames, free columns that are supported from below, one or more continuous panels, etc. Moreover, the support structure can be relatively short and be designed for placement inside a larger frame in much the way a mattress and box spring may be placed inside a bed frame. Also, in some embodiments the power for reciprocating the bands can be from utility power, emergency power, battery power (either normal or backup), and the like. While the foregoing embodiments showed two alternately phased groups of parallel bands, other embodiments may employ three or more groups, in which case then the individual groups will have individual phases (i.e., three or more alternating phases) produced by appropriately configured cams, controllers, etc. 
   Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.