Abstract:
A tilt mechanism for a chair includes rotary stop means defining a plurality of selectable tilted positions of the chair seat/back. In another aspect, an anti kick-back feature is provided based. The mechanism includes upper and lower housing parts and a cushioning spring that normally maintains the parts in a rest position with respect to one another while allowing the mechanism to tilt. A further aspect of the invention provides an improved spring tension control that allows the spring to be installed and removed in a fully relaxed condition so that no special tools are required.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to tilt mechanisms for chairs such as office chairs. 
   BACKGROUND OF THE INVENTION 
   A typical office chair includes a seat/back assembly which is coupled to a chair base by a mechanism that allows controlled tilting of the seat/back assembly with respect to the base. The base usually has an upright post which carries a lower, stationary housing part of the tilt mechanism. Pivoted to the stationary housing part is an upper housing part that carries the seat/back assembly. The back may or may not be movable with respect to the seat. A spring extends between the two housing parts of the tilt mechanism and normally maintains the parts in a rest position with respect to one another. When a person sitting on the chair leans back, the upper housing part tilts with respect to the lower housing part and the spring is compressed, cushioning the tilting movement. The spring tension is adjustable to vary the degree of cushioning. 
   CA 2,446,654 discloses a chair spring tension control having a side operated actuator that is accessible to a person seated on a chair fitted with the control. CA 2,301,933 discloses a chair seat tilt lock mechanism. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a number of improvements in tilt mechanisms for chairs. 
   A mechanism in accordance with the present invention includes upper and lower housing parts adapted to be coupled respectively to a chair seat/back assembly and to a chair base, the parts being pivoted together for movement with respect to one another to permit tilting of the seat/back assembly with respect to the base in use. A compression spring is coupled between the upper and lower housing parts so as to normally maintain the parts in a rest position and to be compressed when the upper housing part tilts with respect to the lower housing part in use. The tilt mechanism includes a tension control for the compression spring between the housing parts, comprising co-operating wedges having confronting sliding surfaces so that movement of the wedges in one direction with respect to one another increasing spring tension while movement in the opposite direction reduces spring tension. In a minimum position, the spring is fully relaxed so that it can be removed and installed by hand, without the need for any special tools. 
   Stop means may be provided between the upper and lower housing parts and defines the rest position of those parts. The stop means includes a plurality of stop surfaces and is moveable to bring different ones of those surfaces selectively into an operative position between the housing parts, defining respectively different angular positions of the housing parts with respect to one another. The mechanism also includes an operator controlled actuator for moving the stop means. 
   The stop means may be a slide profiled to define the plurality of stop surfaces at positions spaced along the slide or a rotary stop with stop surfaces at different radial positions with respect to an axis about which the stop can be turned. 
   In the case of a rotary stop, the actuator may be a simple rotary shaft that extends transversely of the mechanism so as to project outwardly to one side of the seat of the chair when the mechanism is installed. A handle is provided on the outer end of the shaft, so that the shaft can conveniently be turned by a person seated on the chair, turning the rotary stop means to different positions. Conveniently, the stop means comprise a pair of rotary cam-like structures, one at each side of the tilt mechanism. The shaft is carried by the upper housing part and the cam-like structures, one at each side, rest on respective stop surfaces on the lower housing part. 
   The stop means provides a convenient way of defining different rest positions of the tilt mechanism. For example, in a typical mechanism, the cam-like structures are profiled to define three stop surfaces at different radial positions with respect to the shaft, one defining a 1.5 degree forward tilt, another defining a 6.5 degree forward tilt and the third defining a 3.5 degree backward tilt. 
   Of course, the number of stop surfaces and the degree of tilt can vary. 
   An anti kick-back feature may be provided; that is, a feature that prevents release of the mechanism in such a way as to allow uncontrolled return of the housing parts to their rest position under the effect of the compression spring. For example, if a chair has been set at a particular tilt using a locking device and the device is released, if there is no anti kick-back control, the seat back will be propelled rapidly forward and possibly even hit the user of the chair. If the chair is unoccupied, this can cause the chair to “kick” in an uncontrolled fashion, and possibly even fall over. 
   The tilt mechanism include anti kick-back control means comprising a tongue carried by one of the housing parts and a rack carried by the other housing part and having teeth for receiving the tongue. The rack is curved about a pivot axis between the upper and lower housing parts of the chair and the tongue is moveable between extended and retracted positions by a tension member in one direction and a tension spring that is extended for biasing the tongue to its extended position in engagement with the rack. 
   The compression spring between the housing parts provides a biasing force that causes the tongue to bind in the tooth of the rack in which it is received and prevents retraction of the tongue until a force counter to the biasing force is applied to the housing parts. 
   In a practical situation in which the tilt mechanism is installed in a chair, this counter force will be provided by a person who leans back in the chair against the force of the compression spring to so to speak “unbind” the tongue. In other words, by leaning back in the chair, the user moves the housing parts to a position in which the tongue is free to retract. Since the user is seated in the chair at the time and pushing back on the chair back, the user&#39;s body effectively controls return movement of the housing parts under the effect of the compression spring and there is no “kick” or uncontrolled movement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate preferred embodiments of the aspects of the invention. In the drawings: 
       FIG. 1  is a side elevational view of a typical office chair fitted with a chair control in accordance with the invention, with the control shown partly in cross-section; 
       FIG. 1   a  is an enlargement of the chair control of  FIG. 1 ; 
       FIGS. 2 to 5  are general assembly drawings showing respectively a side elevational view; a perspective view; a plan view; and an end elevational view of a chair tilt mechanism in accordance with the present invention; 
       FIG. 6  is a view similar to  FIG. 3  but with parts removed so as to illustrate only the forward tilt stop mechanism; 
       FIG. 6A  is a detail perspective view of part of  FIG. 6 ; 
       FIGS. 7 ,  8  and  9  are side elevational views corresponding to  FIG. 6  illustrating three different stop positions of the mechanism; 
       FIG. 10  is a view similar to  FIG. 4  illustrating a slightly modified embodiment of the invention in which a pair of parallel tension control springs are used instead of a single spring; 
       FIG. 11  is a partial view similar to  FIG. 10 , in which the springs are shown separate from the chair control, prior to installation; 
       FIG. 12  is a sectional view on line A-A in  FIG. 11 ; 
       FIG. 13  is a perspective view of the control mechanism illustrating the anti kick-back feature; and, 
       FIG. 14  is a fragmentary cross-sectional view of the tongue and rack arrangement. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring first to  FIG. 1 , a tilt mechanism in accordance with the invention is shown generally at  20  installed between a typical chair base  22  and a chair seat and back assembly including a seat  24  and a back  26 . The seat  24  and back  26  may be in fixed angular relationship with respect to one another. However, reference numeral  27  denotes a known clutch mechanism which allows the back to be tilted and locked with respect to the seat. Since the mechanism is known it will not be described. 
   The tilt mechanism  20  includes an upper housing part  28  and a lower housing part  30  coupled together for pivotal movement about a transverse pivot axis indicated at  32  in  FIG. 1 . The upper housing part  28  carries the seat/back assembly  24 ,  26 . Assuming the tilt mechanism is not locked, when a person sitting on the seat  24  pushes against the back  26 , the upper housing part moves in the clockwise direction about pivot axis  32  considering the mechanism as seen in  FIG. 1 . 
     FIG. 2  shows the tilt mechanism  20  of  FIG. 1  separate from the chair components. As indicated previously,  FIGS. 2 to 5  are general assembly drawings and as such include components not directly relevant to the present invention. Accordingly, only the principal components of the mechanism will be described. 
   It is important to note that the mechanism includes one or more compression springs  34  coupled between the upper and lower housing parts so as to normally maintain those parts in a rest position and which is compressed when the upper housing part  28  tilts with respect to the lower housing part  30  in use. In  FIG. 2 , for example, the spring is mostly hidden but from  FIGS. 1 and 1   a  it can be seen that the spring effectively acts between one end  36  of the lower housing part  30  and a transverse pin  38  that extends between the side walls of the upper housing part  28  and is received in elongate openings in side walls of the lower housing part  30 . Accordingly, if the upper housing part  28  is rotated clockwise from the position shown about pivot pin  32 , pin  38  moves to the left and compresses the spring. 
   A tension adjustment mechanism is provided for the spring and comprises a wedge arrangement somewhat similar to that disclosed in Canadian Patent Application No. 2,446,654 referred to previously, but incorporating improvements to be described. The mechanism is actuated by a shaft indicated at  40  in  FIGS. 3 and 4  which projects laterally below the seat of the chair and which has a handle  40   a  that can conveniently be turned by a person seated on the chair, to adjust spring tension. 
     FIGS. 1 ,  1   a  and  2  also show a rotary stop  42  that is carried by the upper housing part and that bears against a surface  44  on the lower housing part to define the rest position of the two housing parts with respect to one another. This stop is a component of the three-position tilt stop mechanism of the invention and is illustrated in more detail in  FIGS. 6 to 9 . Stop  42  is shown in each of  FIGS. 7 ,  8  and  9  but in respectively different angular positions corresponding to different stop positions of the housing parts. For example, in  FIG. 7  the stop position is designated at 1.5 degrees forward tilt, in  FIG. 8  as 6.5 degrees forward tilt and in  FIG. 9  as 3.5 degrees backward tilt. In this embodiment, the stop  42  has three stop surfaces  46 ,  48  and  50  shown respectively in  FIGS. 7 ,  8  and  9  in their “operative” rest position-defining orientations. Of course, there is no limitation to three surfaces only. The surfaces  46 ,  48  and  50  are at respectively different radial distances from an axis  52  about which the stop is turnable. 
     FIG. 6A  shows a plunger  53 , in the form of a spring loaded steel ball, that is provided on each stop  42  for engagement in one of three detents  53   a  in the adjacent sidewall of the lower housing part  30  for defining the three angular positions of the stops. 
   Axis  52  is defined by a transverse shaft  54  shown in  FIG. 6 . Shaft  54  carries a second rotary stop similar to stop  42  at the far side of the lower housing part in  FIG. 6 . The second stop is identical with stop  42  and is in the same angular position about the shaft. The second stop co-operates with a surface portion of the lower housing part corresponding to surface  44 , so that the upper housing part is supported equally at both sides. Shaft  54  also projects laterally from the mechanism so as to extend below the seat of a chair in which the mechanism is installed and be conveniently accessible to a person seated in the chair. Again, a handle or knob  54   a  is provided so that shaft  54  can be turned easily. 
   The tilt mechanism of the invention may have only a single compression spring  34 . However, the drawings in fact show an embodiment in which a pair of compression springs denoted  34 ′ and  34 ″ are used side-by-side. The upper ends of the springs  34 ′,  34 ″ as seen in  FIG. 10  bear against a pair of cylindrical blocks  56  that form spring seats. The blocks are carried by a tube  57  through which pin  38  extends (see  FIG. 13 ). The lower ends of the springs as seen in  FIG. 10  bear against a top surface of a wedge element  58  that is moveable towards and away from pin  38  to control the tension in the springs  34 ′,  34 ″ and hence the degree of cushioning that is encountered when a person seated on the chair leans back. Element  58  provides respective spring seats for the lower ends of springs  34 ′,  34 ″. 
   Tension adjustment is accomplished by a sliding wedge arrangement that is perhaps best seen in  FIGS. 11 and 12 . The mechanism essentially comprises wedge element  58  and a pair of co-operating wedge elements  60 ,  62  that are adjustable laterally of the mechanism towards and away from one another by turning the shaft  40  that projects laterally from the mechanism below the seat of the chair. Shaft  40  extends through bushings in the side walls  30   a  and  30   b  of the lower housing part  30 . Between those side walls, the shaft extends through aligned plain bores in the respective wedge elements  60 ,  62 . The external surface of the shaft is screw-threaded and carries a nut  63  received in a slot in the bottom of wedge element  62 . A corresponding slot  64  in wedge element  60  is empty. A shoulder  40   b  on shaft  40  bears against the outer face of wedge element  60 . Turning shaft  40  in one rotational direction moves the wedge elements  60 ,  62  towards one another by virtue of shoulder  40   b  moving wedge element  60  to the right in  FIGS. 11 and 12  and nut  63  drawing element  62  to the left. 
   Wedge element  58  is located between the two wedge elements  60 ,  62  and the springs  34 ′,  34 ″ of the tension control mechanism bear against element  58 . Wedge element  58  is symmetrical about a longitudinal centerline of the chair control mechanism and has a pair of inclined faces  58   a,    58   b  that bear against corresponding parallel faces of wedge element  60 ,  62 . Those faces are in fact formed by channel-shaped grooves in the respective wedge elements and the wedge element  58  is received between opposite faces of those grooves so that the wedge elements are positively located with respect to one another in the vertical direction. 
   It will of course be appreciated that, if the shaft  40  is turned in the appropriate rotational direction to move the wedge elements  60 ,  62  towards one another, wedge element  64  will be forced upwardly in  FIG. 11 , compressing the springs  34 ′,  34 ″. Turning of shaft  40  in the opposite rotational direction will allow the wedge elements  60 ,  62  to move apart under the influence of in the springs  34 ′,  34 ″, as those springs relax. 
   The mechanism is designed so that, when the wedge elements  60 ,  62  are at the maximum spacing as shown in  FIG. 11 , there is no tension in the springs  34 ′,  34 ″. In fact, the mechanism is designed so that there is a slight clearance c ( FIG. 11 ) between the springs (shown in exploded positions at S in  FIG. 11 ) and the spring seats at opposite ends of the springs, when the wedge elements  60 ,  62  are fully spaced apart and the springs are fully relaxed. This greatly facilitates assembly of the mechanism in that the springs can be simply dropped into place without any need for pre-compression or forcing the springs into place. 
   The mechanism can easily be hand assembled by positioning the wedge elements  60 ,  62  at their full outward spacing against respective sidewalls  30   b,    30   c  of the lower house part and without the shaft  40  in place. The shaft is then inserted through the aligned openings in the sidewalls of the housing part and bores in the wedge elements and is fitted at its distal end with a retaining collar  66 , after the springs have been placed into the mechanism. The shaft can then be turned to move the wedge elements towards one another and apply some compression to the springs  34 ′,  34 ″. 
   Collar  66  is screw threaded onto shaft  40  and has a hexagonal outer surface so that it can be adjusted on the shaft to apply any desired pre-load to springs  34 ′,  34 ″. The collar is then secured to the shaft by adhesive (e.g. LOCTITE™). 
   In summary, the particular tension adjustment mechanism provided in accordance with the invention is both easy to assemble without the need for any special tools or spring tensioning, and also provides for convenient tension adjustment by a person seated on the chair, who merely has to reach down and turn the shaft  40  until a comfortable tension level is achieved. 
   Reference will finally be made to  FIGS. 13 and 14  in describing the anti kick-back feature of the chair control. As best seen in  FIG. 14 , a curved rack element  68  extends downwardly from a top wall  28   a  of the upper housing part  28 . As the upper housing part tilts with respect to the lower housing part  30  when a person leans back in the chair, the rack  68  moves in an arcuate path with respect to the lower housing part. In fact, the rack  68  is curved to follow a radius centered on the pivot pin  32  between the two housing parts. A slide  70  carried by the lower housing part includes a tongue  72  that can be retracted to allow free movement of the rack  68  with respect to the slide, or projected into a selected one of the teeth of the rack to lock the two housing parts in respective angular positions. In  FIG. 13 , the tongue  72  is shown in a projected position in engagement with one of the teeth of the rack. 
   Tongue  72  is slideably mounted between upper and lower plates  74 ,  76  of slide  70  so that the tongue moves generally on a radial line centered on pivot shaft  72 . A tension spring  78  extends between the tongue  72  and the top plate  74  so that the spring is in tension (i.e. stretched) for urging the tongue  72  to the locking position in which it is shown in  FIG. 13 . As best seen in  FIG. 14 , spring  78  is a simple coil spring having hooked portions at its respective ends that are engaged in openings in the top plate  74  and in a projecting end portion of the tongue  72 . The tongue can be retracted against the biasing effect of spring  78  by a further spring  80  ( FIG. 13 ). A hooked portion at one end of spring  80  is engaged in an opening in tongue  72  while an “eye” formation at the opposite end of the tension element extends around a vertical limb  84  of an L-shaped actuating member. The member has a horizontal limb that extends laterally of the chair control and projects outwardly to one side thereof as shown at  88  in  FIG. 4 . A paddle  90  on limb  88  allows limb  88  to be turned angularly, moving the vertical limb  84  of the member back and forth generally on the longitudinal centerline of the chair control. As best seen in  FIG. 11 , limb  86  extends between a pair of resilient jaws  92  having detent positions  94 ,  96  at opposite ends, in either of which the limb is retained in an extreme end position. In other words, by depressing or lifting the paddle  90  at the outer end of the horizontal limb  88 , the vertical limb  86  can be caused to “snap” between extreme end positions to project or retract the tongue  72 . 
   As mentioned previously, the tongue and rack arrangement just described provides a so-called anti kick-back feature that prevents release of the chair control in such a way as to allow uncontrolled return of the housing parts to their rest position under the effect of the compression springs  34 ′,  34 ″. Thus, if the chair control has been set at a particular tilt by engaging the tongue  72  in an appropriate one of the teeth of the rack  68 , the compression springs  34 ′,  34 ″, acting between the upper and lower housing parts  28 ,  30  respectively cause the tongue  72  to bind in the rack so that the tongue and rack will remain engaged even if the paddle  90  is moved in a direction to retract the tongue. Retraction can take place only when the user of the chair leans back against the force of the compression springs so that the tongue  72  no longer binds in the rack and is free to retract. Since the user is seated in the chair at this time and is pushing back on the chair back, the user&#39;s body effectively controls return movement of the housing parts under the effect of the compression springs and there is no “kick” or uncontrolled movement. 
   It will of course be understood that the preceding description applies to particular preferred embodiments of the invention and that many modifications are possible within the broad scope of the invention. For example, the aspects of the invention described previously may be embodied in a single tilt mechanism, but are not necessary used together. Referring in particular to the anti kick-back feature, it is of course to be understood that other or different linkages or mechanisms can be used to retract the tongue  72  and that the particular mechanism shown is not essential.