Abstract:
A permanent-contact mechanism for an office chair or the like is formed as a comparatively flat permanent-contact mechanism with a seat frame, which can be positioned on a chair upright, with a backrest support, which is arranged on the seat frame such that it can be pivoted about a transverse axis, and with at least one spring-activated or inherently resilient lever element, which interacts with the backrest support such that the backrest support is always pivoted counter to a spring force. The position of the point of rotation of the lever element differs from the position of the transverse axis.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a permanent contact mechanism for an office chair or the like. 
     Permanent contact mechanisms, also known as asynchronous mechanisms, are characterised in that a chair back is connected movably to a fixed seat. The chair back follows the movements of the seated person from a front (upright) to a rear (“lying”) position and vice versa. Permanent contact mechanisms thus facilitate and support frequently changing seating positions which are preferred for orthopaedic reasons, i.e. due to the associated reciprocal weight bearing of invertebral discs. 
     To ensure secure and pleasant motion sequence the chair back pivots mostly against the force of a spring component. An adjustment option for changing the resilient force is often also provided. But the drawback to solutions known from the prior art is that the construction elements, such as for example worm gears, threaded rods etc. required for resilient force adjustment, considerably increase the necessary overall height of the permanent contact mechanism. 
     An aim of the present invention is to provide a comparatively low permanent contact mechanism. 
     This task is solved by a permanent contact mechanism according to the present invention. According to this a permanent contact mechanism is provided with a seat frame placeable on a chair column, with a chair back frame arranged pivotably about a transverse axis on the seat frame, with at least one spring-loaded or intrinsically resilient lever element which cooperates with the chair back frame such that pivoting of the chair back frame occurs constantly against a resilient force, whereby the position of the lever fulcrum of the lever element is different from the position of the transverse axis. 
     BRIEF SUMMARY OF THE INVENTION 
     A fundamental idea of the invention is the spaced positioning of the lever fulcrum of the lever element impacting the chair back frame on the one hand and on the other hand the position of the transverse axis, about which the chair back frame can be pivoted. 
     The result of this constructive arrangement is that the lever element moving with the chair back frame travels another travel distance than does the chair back frame. This forms the basis for a structurally very simple and thus economic resilient force adjustment which can also be made in the smallest space, in particular realizing a particularly small overall height of the permanent contact mechanism. 
     A further fundamental idea of the invention is to provide a resilient force adjustment without a resilient element having to be (pre)stressed. It has proven advantageous in particular if the length of the effective lever arm can be changed without effort having to be directed against the resilient force via a change in the position of the articulation point of a lever arm of the lever element on the chair back frame. Otherwise expressed, a particularly easy, “feeble” resilient force adjustment is made. 
     An exemplary embodiment of the invention with further advantageous configurations will now be explained hereinbelow in greater detail by means of the drawings, shown here partly simplified and schematically, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows a permanent contact mechanism in a side view, 
         FIG. 2  shows a permanent contact mechanism in a first exploded illustration, 
         FIG. 3  shows a permanent contact mechanism in a second exploded illustration, 
         FIG. 4  shows a permanent contact mechanism without seat plate in a perspective view, 
         FIG. 5  shows a permanent contact mechanism without seat frame in a perspective view, 
         FIG. 6  shows a permanent contact mechanism in a sectional view along line VI-VI in  FIG. 4 , 
         FIG. 7  shows a schematic illustration of the position of the contact slide in a rear position, 
         FIG. 8  shows a schematic illustration of the position of the contact slide in a front position, 
         FIG. 9  shows a permanent contact mechanism in a sectional view along line IX-IX in  FIG. 6 , 
         FIG. 10  shows a permanent contact mechanism in a sectional view along line X-X in  FIG. 6 , 
         FIG. 11  shows a permanent contact mechanism in a sectional view along line XI-XI in  FIG. 6  in a front position in an “easy” setting, 
         FIG. 12  shows a permanent contact mechanism in a sectional view along line XI-XI in  FIG. 6  in a rear position in an “easy” setting, 
         FIG. 13  shows a permanent contact mechanism in a sectional view along line XI-XI in  FIG. 6  in a front position in a “harder” setting, und 
         FIG. 14  shows a permanent contact mechanism in a sectional view along line XI-XI in  FIG. 6  in a rear position in a “harder” setting. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The exemplary embodiment shows a permanent contact mechanism  1  for an office chair or the like, with a fixed, i.e. immovable seat frame  3  placeable by means of a conical flange  2  onto the upper end of a chair column  100 , and with a seat plate  4  attached to the seat frame  3 , which together with the seat frame  3  forms a housing for the actual pivoting mechanism, cf.  FIG. 1 . In the process the seat plate  4  extends well out over the leading edge  5  of the seat frame  3 . The seat frame is preferably made of a fibreglass-reinforced plastic material (Pa6Gf30), while the seat plate comprises polypropylene. 
     In addition, the permanent contact mechanism  1  includes a chair back frame  7  arranged pivotably about a transverse pivot axis  6  on the seat frame  3 , fork-shaped in plan view, the bearers  8  of which are arranged on both sides of the seat frame  3 . The seat fitted with an upholstered seat area is mounted on the seat plate  4 ; alternatively, a seat bearer or the like can also complete the seat frame  3  in an upward direction, instead of the seat plate  4  (neither shown). 
     As is evident in particular in  FIGS. 2 to 6 , the whole permanent contact mechanism  1  is built mirror-symmetrically with respect to a medium-length plane M(cf.  FIG. 4 ), which relates to the actual kinematics. The following description is always based on paired construction elements of the actual pivoting mechanism. 
     Attached to the chair back frame  7  is a chair back  9 , cf.  FIGS. 4 and 5 . For this, the upper free ends of the chair back frame  7  have a cradle  11  which is designed for pivotable bearing of the chair back  9  about a pivot axis  12 , cf.  FIG. 2 . Otherwise expressed, the chair back  9  can perform a pendulum motion, serving to effectively prevent lordosis separation. In other words, the result is permanent contact of the lordosis region of the seated person with the chair back  9 . This pivoting mechanism for the chair back  9  preferably also comprises a resilient element (not shown) for resetting the chair back  9  into its normal position, as soon as the seated person stands up. In order to perform the pendulum motion the seated person must therefore overcome a specific resilient force. The chair back is preferably made of plastic (Pa6). 
     The chair back frame  7  is articulated with the seat frame  3  to the front end  13  of its bearer  8 , which runs obliquely upwards starting from a horizontal main bearer element  14 , beginning approximately in the region of the conical flange  2 . For this purpose, a hollow crossmember  15  connecting both bearers  8  lies in U-shaped recesses  16  provided on both sides of the seat frame  3  and is held there by corresponding parts  17  with likewise U-shaped recesses  18 , arranged inside the seat frame  3  and mountable from above, cf.  FIG. 4 , whereby a pivot bearing is designed for the chair back frame  7 . 
     The position of the pivot axis  6 , about which the chair back frame  7  can be pivoted, and corresponding to the constructive edge parameter is in a position which effectively minimizes the so-called “shirt-pull effect”. The pivot axis  6  is arranged not directly under the actual H point of the seated person, but is offset relative to the actual H point in the direction of the leading edge  5  of the seat frame  3 . The pivot axis  6  is located in particular in a longitudinal direction  19 , as viewed from the conical flange  2 , therefore offset from the conical flange  2  in the direction of the seat leading edge  21 . In addition, the pivot axis  6  is in the immediate vicinity of the seat plate  4  terminating the seat frame  3 . 
     The crossmember  15  as integral part of the chair back frame  7  is connected integrally to a latch plate  22  which extends in the direction of the trailing edge  23  of the seat frame  3  and whereby at least its underside  24  runs parallel to the bearer main elements  14 . This latch plate  22  performs every movement of the chair back frame  7  in the direction of pivoting  25  and at the same time moves inside the seat frame  3 . The chair back frame  7  with all its components (latch plate  22 , . . . ) is preferably made of Pa6Gf30. 
     Inside the seat frame  3  a spring arrangement is provided with two torsion springs  27  aligning with one another in a transverse direction  26 . These are torsion springs with two legs in each case. The shorter fixed legs  28  point in the direction of the leading edge  5  of the seat frame  3  and are supported in specially provided openings  29  in the underside  31  of the seat frame  3 , through which they protrude outwards. The longer free leg  32  points in the direction of the trailing edge  23  of the seat frame  3  and is supported on a contact slide  33 , described in greater detail hereinbelow, acting mechanically reciprocally to the latch plate  22 . The torsion springs  27  themselves lie in specially provided prisms  34 , designed as part of the seat frame  3 . 
     The torsion springs  27  thus form lever elements, cooperating with the chair back frame  7  such that moving the chair back frame  7  in the direction of pivoting  25  occurs constantly against the resilient force of the torsion springs  27 . At the same time, both legs (fixed leg  28  and free leg  32 ) act as lever arms. The middle points  35  of the torsion springs  27  form the lever fulcrums of the lever elements and are spaced at a distance from the position of the pivot axis  6 . 
     A particular advantage is a structural form realized with this exemplary embodiment, wherein the middle points  35  of the torsion springs  27  are at any time on a horizontal plane  36  (illustrated in  FIG. 10 ) with the centre of the pivot axis  6 , cf.  FIGS. 10 to 15 . This arrangement enables a minimal overall height of the permanent contact mechanism  8  and at the same time enables an adequate regulating range of the chair back frame, thus constituting an optimal centre path between overall height and regulating range. 
     A particular advantage also is a further structural form realized with this exemplary embodiment, wherein the middle points  35  of the torsion springs  27  are located directly over the conical flange  2  and thus directly over the chair column. The advantage is that all areas subject to a high force influence, specifically the conical flange  2  made of steel, the bearing (shaft  46 , . . . ) of the chair back frame  7  as well as the bearing (prism  34 ) of the torsion spring  27 , lie close together. A particularly stable construction can be achieved accordingly with particularly low material use. 
     The contact slide  33  arranged centrally in the seat frame  3  is designed substantially T-shaped and preferably comprises plastic (Pa6). On the undersides  37  of both its T-legs  38  running in a transverse direction  26  it has in each case a U-shaped groove  39  running in a longitudinal direction  19 . In these grooves  39  lie the free legs  32  of the torsion springs  27 . In other words, the free legs  32  of the torsion springs  27  are supported on the T-legs  38  of the contact slide  33 . 
     Fixed to the underside  41  of the T base  42  of the contact slide  33  is a gear rack  43  which cooperates with a cog  44  to form a rack gear. The cog  44  is arranged in a specially provided recess  45  of the crossmember  15  and mounted on a shaft  46  running inside the crossmember  15  and at the same time acting as pivot axis  6  for the chair back frame  7 . An actuating element (not shown), for example a hand wheel, is attached to an end of the shaft  46  for actuating the cog  44 . 
     The top side  47  of the contact slide  33  cooperates with the underside  24  of the latch plate  22  as follows: at the point where both T-legs  38  of the contact slide  33  collide, therefore in a central position, is a cuboid block  48 , projecting upwards from the top side  47  in the direction of the latch plate  22  or respectively seat plate  4 , which is connected preferably in one piece to the contact slide  33  for reasons of improved mechanical strength and load-bearing capacity. 
     To the right and left of this block  48  on the top side  47  of the contact slide  33  a number of latch elements  49  is provided. At the same time, these are evenly spaced, cogged locking steps, arranged in the transverse direction  26 . These extend in the direction of the free ends  51  of the T-legs  38  as far as approximately the middle of the T-legs  38 , so that the top sides  52  of the T-legs  38  are free of the latch elements  49  in the region of their free ends  51  and exhibit smooth surfaces corresponding to the material selected. 
     Down the middle the underside  24  of the latch plate  22  has a rectangular opening  53  running in the longitudinal direction  19 . A number of latch elements  54  again extends on both sides of the opening  53  in the longitudinal direction  19 . These are designed as counter-elements to the latch elements  49  on the top side  47  of the contact slide  33 . Again corresponding to the selected material the surface is smooth on both sides of the latch element  54 , therefore on the lateral edge regions  55  of the underside  24  of the latch plate  22 . 
     Contact slide  33  and latch plate  22  are arranged relative to one another such that the block  48  arranged on the top side  47  of the contact slide  33  never contacts the latch plate  22 , but is arranged constantly in the region of the rectangular opening  53 . 
     When the chair back frame  7  swivels into a rear position the free “active” legs  32  of the torsion springs  27  cover a longer distance than the chair back frame  7 . The swivel movement of the free legs  32  occurs in other words over a greater range of angle than the swivel movement of the chair back frame  7 . At the same time, shearing forces occur in the construction elements concerned. 
     If the chair back frame  7  is in a pivoted, rear position (cf.  FIGS. 12 and 14 ), the force constituents of the torsion springs  27  acting on the contact slide  33  in the direction of the trailing edge  23  of the seat frame  3  are greater than the frictional forces between the smooth surfaces on the top side  47  of the contact slide  33  and the underside  24  of the latch plate  22 . According to the invention therefore the latch elements  49 ,  54  of contact slide  33  and latch plate  22  in this position are meshed in one another and form a self-arresting latch pawl, cf.  FIGS. 7 and 10 . The shearing forces can be absorbed, whereby the mechanical stability of the construction in a pivoted chair back frame  7  is guaranteed. At the same time, the smooth outer regions  56  of the T-legs  38  of the contact slide  33  rest on the smooth edge regions  55  of the latch plate underside  24 . 
     As a result this means that the contact slide  33  can no longer be moved in a longitudinal direction  19 . Therefore neither can any adjustment of the resilient force of the torsion springs  27  be made in this rear position. At the same time, the abovementioned construction elements are aligned to one another such that when the chair back frame  7  is in the rear position the block  48  lies freely in the rectangular opening  53  and does not contact the underside  57  of the seat plate  4 . 
     If the chair back frame  7  swivels back into its front position (cf.  FIG. 11 and 13 ), the distance  58  between the block  48  and the underside  57  of the seat plate  4  continues to lessen until the block  48  rests on the seat plate  4 . The underside  57  of the seat plate  4  is designed correspondingly. 
     If the chair back frame  7  then swivels further into its front position (see direction of pivoting  25  in  FIG. 7 ) the block  48  collides with the immovable seat plate  4 . Since the contact slide  33  is supported by the free ends  51  of its T-legs  38  on the free legs  32  of the torsion springs  27 , this causes sagging of the contact slide  33  in its top region, therefore in the region of the T-legs  38 . At the same time, the more the contact slide  33  sags, the further the chair back frame  7  is pivoted back with its contact plate  22 . 
     If the chair back frame  7  is swung back into its starting position the smooth outer regions  56  of the T-legs  38  of the contact slide  33  are still resting on the smooth edge regions  55  of the latch plate underside  24 . The latch elements  49 ,  54  of contact slide  33  and latch plate  22  are however no longer meshed in one another, but lie free, cf.  FIG. 8 . Since there are no shearing forces in this position, meshing is also no longer necessary. No force constituents of the torsion springs  27  are acting on the contact slide  33  in the direction of the trailing edge  23  of the seat frame  3 , since chair back frame  7  and torsion springs  27  are lying parallel to one another and the angle of rotation is zero. 
     As a result, this means that the contact slide  33  can now be moved in the longitudinal direction  19 . Adjustment of the resilient force of the torsion springs  27  can now occur. 
     Blocking wedges  59  act to fix the front position, and are arranged inside the seat frame  3  on a blocking device  60  and can be pivoted in the direction of pivoting  61  from a rest position to a blocking position, in which they engage with their free ends  62  on the underside  24  of the latch plate  22  and prevent pivoting of the latch plate  22  and thus pivoting of the chair back frame  7 . The blocking wedges  59  can be actuated by means of an actuating element, not illustrated in greater detail, from outside the seat frame  3 . For this, a fastening for a Bowden cable is provided on the blocking device  60 , by means of which the blocking device can be pivoted altogether. 
     With further pivoting of the chair back frame  7  rearwards separation of the block  48  from the underside  57  of the seat plate  4  occurs. This results in the contact slide  33  again being released and approaching the underside  24  of the latch plate  22 . The latch elements  49 ,  54  engage again so that adjusting the resilient force of the torsion springs  27  is no longer possible. 
     The cog  44  is actuated to adjust the resilient force in the front position, whereby a position change of the contact slide  33  occurs in a longitudinal direction  19 . At the same time, the positions of the U-shaped grooves  39  on the free legs  32  of the torsion springs  27  change, and thus the articulation points  63  of the torsion springs  27  on the chair back frame  7  which rests on the contact slide  33 . 
     The resilient force adjustment now takes place “feebly” according to the invention, specifically such that the length of the effective lever arm—therefore of the smallest, i.e. vertical distance between the line of influence of the resilient force and the fulcrum  35 —can be changed by a change in position of the articulation points  63  of the free leg  32  of the torsion springs  27  on the latch plate  33  of the chair back frame  7 , without effort having to be directed against the resilient force of the torsion springs  27 . This enables particularly easy resilient force adjustment. 
     The permanent contact mechanism can be set to “easy” or “hard”. With an “easy” setting (as shown in  FIGS. 4 ,  5 ,  9 ,  10 ,  11  and  12 ) the articulation points  63  are pushed in the grooves  39  on the T-legs  38  by means of the rack gear in the direction of the free ends  64  of the free legs  32  of the torsion springs  27 , resulting in comparatively long lever arms. The force constituents of the torsion springs  27  acting on the contact slide  33  in the direction of the trailing edge  23  of the seat frame  3  in the pivoted state (cf.  FIG. 12 ) are comparatively minimal. 
     In the case of “hard” setting (as shown in  FIGS. 13 and 14 ) the articulation points  63  are shifted by means of the rack gear in the direction of the fulcrums  35  of the torsion springs  27 , resulting in comparatively short lever arms. The force constituents of the torsion springs  27  acting on the contact slide  33  in the direction of the trailing edge  23  of the seat frame  3  in the pivoted state (cf.  FIG. 12 ) are comparatively big. 
     The construction described in the present invention provides a permanent contact mechanism  1  which has an extremely flat structural form. This is accomplished substantially by the inventive separation of the position of the fulcrum  35  of the torsion springs  27  from the position of the pivot axis  6  of the chair back frame  7 . 
     Instead of an intrinsically resilient lever element, such as the torsion spring  27  used here, other constructive arrangements can understandably also be employed to achieve the inventive function. Non-resilient construction parts can also be used in particular as lever elements which are impacted by a spring, for example a draw or compression spring. 
     Legend 
     
         
         
           
               1  permanent contact mechanism 
               2  conical flange 
               3  seat frame 
               4  seat plate 
               5  leading edge of the seat frame 
               6  pivot axis of the chair back frame 
               7  chair back frame 
               8  bearer 
               9  chair back 
               10  (free) 
               11  cradle 
               12  pivot axis of chair back 
               13  front end of the chair back frame 
               14  bearer main element 
               15  crossmember 
               16  recess 
               17  corresponding part 
               18  recess 
               19  longitudinal direction 
               20  (free) 
               21  seat leading edge 
               22  latch plate 
               23  trailing edge of the seat frame 
               24  underside of the latch plate 
               25  direction of pivoting 
               26  transverse direction 
               27  torsion spring 
               28  fixed leg 
               29  opening 
               30  (free) 
               31  underside of the seat frame 
               32  free leg 
               33  contact slide 
               34  prism 
               35  middle point of the torsion spring 
               36  horizontal plane 
               37  underside of the T-leg 
               38  T-legs 
               39  groove 
               40  (free) 
               41  underside of the T base 
               42  T base 
               43  gear rack 
               44  cog 
               45  recess 
               46  shaft 
               47  top side of the contact slide 
               48  block 
               49  latch element 
               50  (free) 
               51  free end of the T-leg 
               52  top side of the T-leg 
               53  opening 
               54  latch element 
               55  edge region 
               56  outer region 
               57  underside of the seat plate 
               58  distance 
               59  blocking wedge 
               60  blocking device 
               61  direction of pivoting 
               62  free end of the blocking wedge 
               63  articulation point 
               64  free end of the free leg