Abstract:
A chair comprising a seat assembly and a support assembly is disclosed. The seat assembly has a deflectable body disposed about an axis that provides resilient convex seating surface. The support assembly retains the seat assembly and allows the seat assembly to rotate about its axis and additionally allows the seat assembly to rotate to cause limited tilt displacement of the axis from a neutral alignment. The support assembly includes biasing means that serve to urge the seat assembly towards the neutral alignment when the seat assembly is displaced from the neutral alignment.

Description:
BACKGROUND TO THE INVENTION 
       [0001]    1. Field of the invention 
         [0002]    This invention relates to chairs. In particular, it relates to a chair that promotes the health and fitness of a user. 
         [0003]    2. Summary of the Prior Art 
         [0004]    It is widely recognized that a sedentary lifestyle can give rise to health problems. Yet, an increasing number of people have an occupation that involves sitting for an extended period. Many alternatives to a conventional office chair have been proposed, with the general aim of encouraging a user to adopt a posture that imposes less strain on the lower back of the occupant. Some people have chosen to abandon the use of a chair altogether, and have chosen instead to sit on an exercise ball (also known as a “Swiss ball”). To sit upon such a ball requires some effort to maintain balance, which ensures that a sitting person&#39;s spine does not remain immobile and helps to strengthen the person&#39;s core muscles. However, use of a ball can be inconvenient since they tend not to remain in one place when unoccupied. They also do not allow a user to move freely across a floor, as does a conventional office chair supported on castor wheels. 
         [0005]    There is therefore a demand to provide a chair that enables a user to sit for an extended period with fewer detrimental effects as compared with a conventional chair. 
       SUMMARY OF THE INVENTION 
       [0006]    To this end, this invention provides a chair comprising a seat assembly and a support assembly, in which the seat assembly has a body disposed about an axis that provides resilient convex seating surface; wherein the support assembly retains the seat assembly and allows the seat assembly to rotate about its axis and additionally allows the seat assembly to rotate to cause limited tilt displacement of the axis from a neutral alignment and the support assembly includes biasing means that serve to urge the seat assembly towards the neutral alignment when the seat assembly is displaced from the neutral alignment. 
         [0007]    Such a chair allows the body much of the freedom of movement of an exercise ball placed on a floor, yet constrains it against bodily movement as with a ball rolling across a floor. 
         [0008]    Preferably, rotation about the axis is free—that is, it can be continuous and take place with little friction. 
         [0009]    The body may be formed of flexible material, which may for example be maintained in shape by being inflated pneumatically. Alternatively, the body may be formed of resilient material, such as in the form of a self-supporting shell, or it may be a solid body, for example being formed from a foamed plastic material. 
         [0010]    In a typical arrangement, when the support assembly is placed on flat, horizontal support such as a floor, in the neutral alignment, the axis is vertical. 
         [0011]    In preferred embodiments, the body is pneumatically inflatable. For example, it may be substantially spherical. This latter arrangement can conveniently be implemented by use of an exercise ball (such as that known as a “Swiss ball”). Alternatively, the deflectable body may be made of resiliently deformable material, such as a foam. The biasing means may include a plurality of elongate elastomeric members that are connected between the seat assembly and the support assembly to apply a balanced force to the seat assembly when the axis is in the neutral alignment. 
         [0012]    In preferred embodiments, the body is a generally spherical ball of elastomeric material. The ball may be retained by a shell that provides a bearing surface that interacts with the support assembly. The shell may be part-spherical to closely surround and support the ball. The support assembly may include a plurality of bearings, each of which has, for example, a spherical element that is in contact with the shell. 
         [0013]    The seat assembly typically carries a limiting element that makes contact with part of the support assembly once the axis has been displaced from the neutral alignment by a predetermined maximum limit. Preferably, the limiting element is formed of a resiliently deformable material such that movement of the seat assembly is stopped gradually when its displacement reaches the maximum limit. 
         [0014]    Advantageously, the support assembly is carried on a plurality of castor assemblies whereby it can be displaced across a surface on which it is supported, in much the same manner as a conventional office chair. 
     
    
     
       IN THE DRAWINGS 
         [0015]      FIGS. 1 ,  2  and  3  are side, top and bottom views of a chair being an embodiment of the invention; 
           [0016]      FIG. 4  shows a base assembly of the seat of  FIGS. 1 to 3 ; 
           [0017]      FIG. 5  shows a seat assembly of the seat of  FIGS. 1 to 3 ; 
           [0018]      FIG. 6  shows a lower part of the seat of  FIGS. 1 to 3  in more detail; and 
           [0019]      FIG. 7  is a cross-sectional view of a lower part of the seat of  FIGS. 1 to 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    With reference to the drawings, a chair being an embodiment of the invention comprises a support assembly ( FIG. 4 ) and a seat assembly ( FIG. 5 ). 
         [0021]    The support assembly comprises a base plate  10  that has five-fold rotational symmetry about an axis that is vertical during normal use of the chair. A circular aperture  12  is formed through the base plate  10 , centered on the vertical axis. 
         [0022]    The support assembly includes five castor and bearing regions spaced equally around the vertical axis. Each of such regions includes a sloping section  14  of the base plate  10  that extends upwardly from the base plate  10  at approximately 45° from the vertical axis. Each castor and bearing region further includes a support plate  16  that slopes downwardly away from the axis from a peripheral part of the sloping section  14 . A web  20  extends downwardly from an edge region of the plate  16  (including the sloping regions  14 ) to interconnect the support plates  16 . A mounting plate  22  extends horizontally and is secured to a lower portion of the support plate  16  and a peripherally outer part of the web  20 . An aperture  24  is formed through the mounting plate  22 , and a castor wheel  26  (one being omitted from  FIG. 3  for clarity) is secured through the aperture  24 . 
         [0023]    Each castor and bearing region further includes a bearing assembly  30 . Each bearing assembly has a ball  32  that is captive within the bearing assembly but is free to rotate in any direction with respect to it. A portion of the ball  32  projects from the bearing assembly  30  towards the vertical axis vertically angled from the axis by approximately 45°. 
         [0024]    A guard ring  36  formed as a very squat cylinder is centered on the vertical axis. The guard ring  36  is supported on five support members  38 , each of which extends upwardly from a respective castor and bearing region. The support members  38  are curved, such that close to the castor and bearing region, they extend at approximately 45° to the vertical axis, and where they join the guard ring  36 , they are approximately vertical. 
         [0025]    The support assembly, in this embodiment, is fabricated from steel. However, it could alternatively be formed from plastic material, for example by molding, or a combination of materials. 
         [0026]    The seat assembly comprises a generally hemispherical shell  40 , formed, in this embodiment, from a durable material such as acrylic. The shell  40  is supported on the five balls  32  of the bearing assemblies  30 , such that it presents an upwardly-directed circular opening. The bearing assemblies allow the shell  40  to rotate about its center in any direction. An externally-threaded stud  42  projects through an aperture in the shell  40 . The stud  42  has an axis that passes through the center of the opening of the shell  40  and a head  56  that is of diameter greater than that of the aperture. A load spreading plate  58  is disposed between the head  56  and the shell  40  to ensure that load from the stud  42  is not concentrated in the immediate vicinity of the aperture. In this embodiment, the load spreading plate  58  has a central region from which a plurality of fingers extend radially, the fingers being curved to confirm with the inner surface of the shell  40 . 
         [0027]    A connection member is carried on the stud  42 . The connection member comprises an annular flange  60  from which extends a tubular bush  62 , the bush  62  being carried as a close fit for rotation on the stud  42  and extending between the flange  60  and the head  56 . Five radially-extending tubes  66  are secured to the flange  60 , spaced equally around it. A nut  46  retains the connection member on the stud  42 . A boss  44  of elastomeric material is carried on the stud  42 . The boss  44  has an axial bush  68  that can rotate upon the bush  62  on the connection member, where it is retained by the flange  60 . Thus, both the boss  44  and the connection member can rotate with respect to one another and with respect to the shell  40 . 
         [0028]    Each tube  66  of the connection member is connected to a castor and bearing region by a respective connecting element  48 . Each connecting element  48  comprises an elongate element that is capable of elastic extension, for example, a length of latex rubber tube. 
         [0029]    Within the shell  40  there is a ball  50  of pneumatically inflated flexible material. This may be constituted by a ball of the type used in physical exercising, known as a “Swiss ball” of “fitness ball”. The relative sizes of the shell  40  and the ball  50  are chosen such that the ball is a close fit within the shell  40 . A portion of the shell  40  adjacent to the opening may be formed with a radially outward curve (not shown in the drawings) to reduce the risk of the ball  50  being damaged by the material of the shell  40 . In alternative embodiments, the ball may be formed of a resilient material which may be integral with the shell  40 . 
         [0030]    While unoccupied, the connecting elements  48  will pull upon the boss  44  to draw it towards the vertical axis of the seat—the neutral position of the seat assembly. Thus, the ball  50  will present an upwardly-directed hemispherical surface upon which a user can sit. In the neutral position, the boss  44  projects partially through the aperture  12  in the base plate  10 . Once a user sits upon the surface of the ball  50 , any component of the user&#39;s weight that is not coaxial with the vertical axis of the seat will tend to cause the seat assembly to rotate on the bearing assemblies  30  about the center of the ball  50 . Once such rotation takes place, the forces applied by the connecting elements  48  to the boss  44  will no longer be balanced, the imbalance giving rise to a restoring force that acts to tend to restore the seat assembly towards the neutral position. The ultimate limit to which the seat assembly can rotate is determined by the boss  44  coming into contact with the edge of the aperture  12  within the base plate  10 . 
         [0031]    It will be seen that the seat assembly is also free to rotate about an axis that is coaxial with the stud  42 . This axis is vertical when it is in the neutral position, and is tilted as the seat assembly is tilted away from the neutral position. Because the boss  44  is carries on the stud  42  by a bearing, such rotation is not inhibited when the boss  44  makes contact with the edge of the aperture  12 . 
         [0032]    The elastomeric stiffness of the connecting elements  48  determines the magnitude of the restoring force, and this can be adjusted to suit the needs of a particular user. In general, the lighter the restoring force (with respect to the user&#39;s body weight), the more effort a user will have to exert in order to stay upright on the ball. Therefore, a user may start using the chair with the connecting elements  48  configured to apply a relatively great restoring force. Then, over time, as the user becomes accustomed to the chair, and gains strength in his or her core muscles, the restoring force can be reduced such that the users strength continues to develop.