Patent Publication Number: US-2002000745-A1

Title: Patient chair with quaternary spring motion

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims the benefit of U.S. Provisional Application No. 60/212,326 filed Jun. 16, 2000 and entitled PATIENT CHAIR WITH QUATERNARY SPRING MOTION 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to chairs and more particularly, patient chairs as used, for example, in health care facilities.  
       [0004] 2. Description of the Related Art  
       [0005] Patient or health care chairs are commonly used in hospital rooms, assisted living homes, waiting rooms, hospices, extended care facilities, and at home. Health care chairs are used primarily, but not exclusively, by persons who have difficulty rocking or reclining in commonly available rockers and/or recliners. An additional complication with the latter chairs is, a health care requiring person may have difficulty in entering, sitting, or egressing that chair.  
       [0006] There are many recliners and rocker type chairs on the current market and used in health care applications. Most of these recliners, and rockers, require some type of physical effort to make the chair rock or recline, that is by pulling on levers, pushing buttons, or using the force of legs onto a leg panel, or the human back pressing onto a chair&#39;s back-rest, to make it recline. All or any one of these physical efforts, i.e. motion, may not be possible for a sitting person who is recovering from surgery, age enfeebled or obese. The latter persons usually cannot lean down to grab a handle, or a post surgery person is unable or restricted from use of arm, chest, or back muscles. There are also powered chairs which are motor driven between a seated or reclining position and a forward upright position which aids ingress and egress. These powered chairs are relatively large, heavy and expensive, and not well suited to use in health care facilities.  
       [0007] Health care patient chairs typically have only two primary legs integral with and extending upward at the front of the chair from a sled type base. This type of structure possesses a significant degree of instability. The seat of this type of chair is supported by, and on, or cantilevered directly off of the front legs. This type of construction is inherently unstable for a person who may need to sit by impacting the seat, or otherwise falls into the seat due to disability. This type of impact could cause the entire chair to “skitter” backwards, away from the entering person, causing them to lose balance and fall. This type of action could impose a force upon the chair that would have force vector components that are substantially perpendicular to the support, the front legs, and be of a sufficient magnitude to result in upsetting the chair from its normal upright position. The seat of the typical patient chair has no structural connection to or support directly from the rear legs, if any, of the chair, thus adding to the instability of the chair.  
       [0008] The arm supports of typical patient chairs are supported only by the vertical extension of the front legs of the chair. The arm supports lack any structural connection to or support directly from the rear legs, if any, of the chair. Thus, even further instability is added to the typical patient chair. A weakened patient attempting to sit down in the typical patient chair will naturally use the arm supports to assist in maintaining balance and to enable a gradual entry into the chair. In so doing, a patient will impose a force which is, at any one moment in time, composed of vertical and horizontal vector components. In an unsteady patient, the magnitudes of those horizontal and vertical vector components will vary significantly over a very brief period of time. The typical patient chair, with arm supports lacking, connection to or support from the rear legs, if any, will become unstable when the sum of those horizontal and vertical vector components of the force applied by the patient is of a direction and magnitude which is not substantially and directly aligned with the support structure of the chair.  
       [0009] The front edge of the seat of the typical patient chair is positioned in line with the front legs, thereby making it difficult for an unsteady patient to place his feet and legs in a position and orientation that will enable sitting or standing. Furthermore, the arm supports of the typical patient chair do not extend substantially in front of the front edge of the seat, thereby increasing the difficulty encountered by an unsteady patient attempting to position their body in preparation for ingress or egress.  
       [0010] Some patient chairs provide a rocking motion. However, the rocking motion provided often forces the feet of the patient seated in the chair to lose contact with the floor, thus placing a degree of pressure on the back of the thigh of the patient&#39;s legs. Such pressure can severely restrict or cut off the circulation in a patient&#39;s lower legs. Furthermore, the rocking motion provided by some patient chairs is relatively undamped. An undamped rocking motion can cause an excited state in patients, particularly patients recovering from heart surgery and Alzheimer&#39;s.  
       [0011] Patient chairs typically have either all wood frames, or frames composed of wood and metal, which are mechanically fastened together. With continued use of a patient chair such mechanical fasteners are prone to loosen.  
       [0012] What is needed in the art is a patient chair which remains stable during a patient&#39;s ingress and egress, reduces the difficulty of ingress and egress, and provides a self-damped rocking, motion.  
       SUMMARY OF THE INVENTION  
       [0013] This invention provides a health care patient chair having a pair of arm supports extending forward of the seat, a seat positioned substantially rearward of the front legs. The present invention further provides a stable, self-damping, rocking motion, and a limited recline sitting position. Chair use is, of course, not limited to the infirmed.  
       [0014] The invention comprises, in one form thereof, a chair having a seat, a backrest, a support pedestal adapted to rest on a floor or other horizontal support surface, and a pair of U-shaped compound springs coupling the seat and backrest to the pedestal. Each spring has an upper longer portion, a lower shorter portion extending generally horizontally and parallel to the longer portion, and a bight or U-shaped end coupling the shorter and longer portions together. The shorter portion is fastened to the support pedestal between the shorter portion free end and the bight. The seat is fastened to the longer portion between the bight and longer portion free end, and the backrest is fastened to the longer portion free end. A pair of resilient pads are fixed to each spring shorter portion, engage the longer portion when the spring is compressed by a chair occupant and contribute to the overall spring action.  
       [0015] An advantage of the present invention is that the structure and configurations of the chair inhibit continued, volunteer oscillation, yet provide a stable rocking motion.  
       [0016] Another advantage is that the structure and configuration of the chair prevent movement as a result of the forces applied by a person during the process of sitting in or standing up (egressing) from the chair.  
       [0017] A further advantage of the present invention is that the suspension senses the size and weight of the sitting, person and reacts to these attributes, and/or limitations.  
       [0018] An additional advantage is that the suspension of this inventions does not require external actuating levers, buttons, or manually activated mechanisms to achieve rocking or reclining motion. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0019] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
     [0020]FIG. 1 is a perspective view of the basic chair components of leg frame, mesh seat, backrest and removable arms;  
     [0021]FIG. 2 is a more detailed perspective view of the chair suspension components;  
     [0022]FIGS. 3 a - 3   e  are side elevation views of progressive development of the spring system;  
     [0023]FIG. 4 is an exploded perspective view showing all the components of the basic chair of FIG. 1; and  
     [0024]FIG. 5 is a graph of load vs. deflection for an illustrative spring system. 
    
    
     [0025] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.  
     DETAILED DESCRIPTION OF THE INVENTION  
     [0026] Referring now to the drawings and particularly to FIGS. 1 and 4, there is shown a patient chair  12  having support pedestal  22  comprising two front legs  14  and  16 , two rear legs  18  and  20 , and a pair of side members  24  and  26 . A rear frame member  28  connects the two rear legs  18  and  20 . A cross member  30  connects the side members  24  and  26  intermediate the front and rear legs at a position substantially rearward of the front legs  14  and  16 . Two configured leaf springs  32  and  34  are attached to the bottom of the cross member  30 , for example, by screws such as  36 , and thereafter extend rearwardly in a substantially horizontal manner.  
     [0027] Comparing FIGS. 2 and 3, the front of the leaf spring extends forward of the cross member  30 , but terminates rearward of the front legs  14  and  16 , curves substantially downward and loops rearwardly passing under the cross member. The leaf spring attaches to the cross member as it passes thereunder, then the leaf spring continues rearwardly for a short distance or extension  38  (FIG. 3 b ), past the cross member, under and parallel to the leaf spring upper, longer top layer  60 .  
     [0028] The seat  40  is connected to and supported by the leaf springs  32  and  34 . The seat may be formed of a flexible, porous fabric sewn into a hammock shape and disposed between the two primary seat springs. This hammock shape and flexible, porous fabric allow the springs to act in harmony with each other, creating a continuously flexible seat. The front edge of the seat bottom is positioned rearwardly of the front of the front legs  14  and  16 . A compression spring medium such as and elastomeric spring mass  42  is attached to the topside of the cross member  30  under each leaf spring top layer, at the point where each leaf spring, passes over the cross member  30 . A second compression spring such as  44  is attached to the bottom rearward facing projection such as  38  of each leaf spring, and touches the underside of the leaf spring top layer.  
     [0029] Two arm supports  46  and  48  are positioned above the seat and extend substantially forward of the front edge of the seat  40 . The armrests or supports have reduced diameter sections such as  52  which are telescopically inserted into and supported by the open tops of the rear legs  18  and  20 . A rigid molded wood backrest  50  is connected to and supported by the leaf springs and terminates the ends of the two primary springs  32  and  34  by attachment to these springs in a substantially vertical position. The backrest is attached by screws such as  68 . This backrest has flexibility limited by its cantilever position at the terminus of the primary spring. Each of the rear legs  18  and  20  is angled forward upwardly toward the seat. Decorative and/or protective caps such as  70 ,  76  and  78  may be inserted into or over the upper open arm and leg ends, and floor engaging feet such as  72  may be inserted into or over the open lower leg ends.  
     [0030] In FIG. 3 a , primary leaf spring  32  is attached to cross bar  30  by bolt  36 . This is the primary spring system, a cantilevered leaf spring. In FIG. 3 b , secondary spring  42  is fixed to the cross bar  30 , also by the bolt  36 . In FIG. 3 c , trinary spring  44  is fastened to the lower extension  38  of leaf spring  32  by screw  54 . FIG. 3 e  illustrates a reverse (counterclockwise) deflection of one of the primary leaf springs, the fourth or quatenary spring mode of the support system.  
     [0031] For a simple horizontally cantilevered beam, the deflection or deformation x, is directly proportional to the product of the applied (concentrated) load, W, and the cube of the distance, L, from the load to the beam support, and inversely proportional to three times the flexural rigidity (EI, the product of the moment of inertia of the beam cross-section and the modulus of elasticity), that is 
       x=WL   3 /3 EI.   
     [0032] For a fixed distance between support and load, and assuming modest deflections, all terms except for the load are constants and this relationship may be written as 
       W=k   1   x   1 . 
     [0033] For large deflections, the effective lever arm length is not a constant, but continuously decreases with increased deflection. This relationship is also a good approximation of the deflection of other beam configurations, such as the doubly cantilevered beam of FIG. 3 a.    
     [0034] Assume that, in an unoccupied state, the chair upper spring portion  60  is spaced away from both compression springs  40  and  42 . For relatively small displacements, the spring assembly behaves as though these resilient members were absent as depicted in FIG. 3 a , the above linear relationship holds and is illustrated by the linear segment between the origin and the abscissa value at  56  in FIG. 5. Further assume that at this abscissa value, the upper spring portion engages the only the compression spring  42  as depicted in FIG. 3 b . Now the upper spring portion begins to behave like an overhanging beam and the load vs. displacement curve slope increases due to the additional resistance of the member  42  and due to an effectively shorter lever arm length. Depending on the respective stiffnesses, the beam may actually experience an upward deflection between the bight  62  and resilient member  42 . The relationship continues along the second linear path until the second resilient member  44  is engaged at abscissa value  58 . Between the values at  56  and  58 , the force required to depress the spring a distance x 2  is the force required to move it from its rest position into engagement with the compression spring plus the additional force required to compress the spring  42  and further flex the beam an additional incremental distance x i   
       W=k   1   x   1   +k   2   x   i . 
     [0035] If the upper spring portion is initially in contact with the compression spring  42 , the two distances are the same and the overall load may be approximated by 
       W=k   1   x   2   +k   2   x   2 . 
     [0036] When the deformation reaches point  58 , further downward seat motion additionally compresses the resilient member  44  as illustrated in FIG. 3 c  and, depending on the relative stiffness of the upper spring portion and resilient member, may deflect the lower spring portion  64  downwardly as in FIG. 3 d . In either case, there is even more resistance to loading and the slope of the relationship increases beyond point  58 . k 3  x i  expresses the additional force required to incrementally compress the member  44  beyond point  58  and k 4  x i  expresses the additional force to depress the free lower spring portion  64 . The natural resonant frequencies of the different spring elements corresponding to the differently sloping regions of the graph of FIG. 5 are, of course, different.  
     [0037] If both resilient members are initially engaged by the upper spring portion  60 , the three line segments of FIG. 5 blend together into a single generally linear relationship between the net deflection x and force required to achieve the deflection may be approximated as 
       W= ( k   1   +k   2   +k   3   +k   4 ) x.   
     [0038] When an occupant of the chair moves forward to exit the chair, the load may be shifted to the front seat edge as indicated by the egress load arrow  66  of FIG. 3 e . Upper spring portion  60  separates from the two resilient members and behaves much as discussed in conjunction with FIG. 3 a , but the deformation or deflection is counterclockwise with the bight  62  opening as deflection increases. Thus, the first and second resilient members  42  and  44  contribute forces opposing spring compression to close the U-shape from its unstressed position, while the forces opposing opening the U-shape are contributed solely by the leaf primary spring  32 . This relationship between load and deflection is illustrated by line  74  in FIG. 5. The effective lever arm is much shorter than earlier, the slope of line  74  is greater and the deflection in FIG. 3 e  is somewhat exaggerated. Note the force is still inboard of the front legs such as  14  and the probability of pivoting of the chair forwardly with potential injury to the occupant is minimized.  
     [0039] While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.