Abstract:
The present invention discloses an overload protection mechanism for a cable actuated feature on an office chair. The overload protection device allows a person seated in the chair to move a handle to actuate the particular feature of the chair, for example, a reclining backrest, even when the seated person&#39;s weight on the backrest prevents the backrest locking mechanism from engaging or disengaging. The movement of the handle causes the cable to move even when the locking mechanism connected to the opposite end of the cable is unable to engage or disengage. The mechanism stores the motion of the cable in a spring device connected to the movement actuators by a rack and pinion gear system. When the binding is released from the actuators, the mechanism moves as originally intended, motivated by the force of the decompressing springs.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of adjustable chairs and, in particular, to an office chair having an adjustable backrest. 
     BACKGROUND OF THE INVENTION 
     The typical office chair consists of a seat portion and a backrest portion and, optionally, armrest portions, all supported by a pedestal, usually having wheels thereon for movement of the chair about the work area. It is well known in the prior art for the backrest portion of the chair to be adjustable from an upright position to a position that is semi-reclined, usually as the result of pushing back of the backrest by a person seated in the chair. The seat portion of the chair may or may not move in accordance with the backrest portion when it is reclined. Typically, the backrest portion is coupled with a spring such that when pressure is released on the reclining backrest portion, the backrest portion returns to an upright position. 
     In many instances, it may be desirable to limit the motion of the backrest portion of the chair. The limiting of the motion of the backrest can be in one of two forms. First, the distance that the backrest can be reclined can be limited and, second, when the backrest is reclined, the backrest can be prevented from returning to the upright position when pressure is released, thereby leaving the chair in a reclined position. 
     One simple way to accomplish the locking of the backrest in various configurations is to have one or more locking members which can be inserted into recesses in the chair frame at the appropriate places to limit the movement of the backrest. However, one problem with this mechanism is that movement of the locking members into and out of the recesses tends to bind when pressure is being applied to the backrest, either by the backwards pushing of a person sitting in the chair or by the movement of the backrest to the upright position as a result of springs in the chair. As a result of the binding, the locking members will be unable to move into and out of the recesses. 
     In the type of movement limiting device described, the locking member is typically adjusted by the user through the use of a lever attached to the side of the chair, which is easily accessible to a person sitting in the chair. The lever may be attached to a cable which is in turn attached to the mechanism for moving the locking members into and out of the recesses in the frame of the chair. One problem with this mechanism is that it may be desirable to have one stop on each side of the chair frame, to ensure even operation. Therefore, a mechanism is needed to translate the motion of a single cable into a back and forth motion capable of moving one or more locking members. The second problem with such a mechanism is that when the locking members are bound by pressure applied by the backrest of the chair, the locking members will not move when the person seated in the chair actuates the cable. If the user exerts enough pressure on the bound mechanism, it can result in the breaking of any one of a number of parts in the linkage from the lever to the locking members. Therefore, it would be desirable to have a device which, first, translates the movement of a lever-actuated cable into a back and forth motion that can slide the locking members into and out of the recesses and, second, allows movement of the cable in response to the user actuating the lever connected to the cable without damaging the translation mechanism. 
     SUMMARY OF THE INVENTION 
     The present invention provides a mechanism using a rack and pinion gear configuration that is capable of translating the motion of a cable to the back and forth motion of one or more locking members with respect to one or more corresponding recesses in the chair frame. The mechanism also incorporates an overload protection device whereby movement of the cable, when the locking members are bound in the recesses, results in compression of springs which store the energy necessary to move the locking members with respect to the recesses once the binding is removed. 
     The mechanism is constructed generally of a housing and a member able to slide radially within the housing. A spring is disposed between the slide member and the housing which is compressed when the slide member slides within the housing, but when the housing is unable to move due to a binding condition. The slide member is attached to a cable which, when tensioned, causes motion of the slide member within the housing such as to compress the spring, thereby urging the housing in a first direction. An additional spring is disposed between the end of the cable and the housing to urge the housing in the opposite direction when the tension on the cable is released. Attached to the housing with a rack and pinion assembly are two actuators which, when rotated by the rack and pinion assembly, cause one or more locking members to be inserted into or withdrawn from recesses defined in the chair frame. The presence of the locking members in the recesses results in the locking of some aspect of the chair, such as the backrest. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the preferred embodiment of the invention. 
     FIG. 2 is a top plan view of the device of the invention wherein the locking mechanism is in a locked position and wherein movement of the cable and locking mechanism is unrestricted. 
     FIG. 3 is a top plan view of the device of the invention wherein the locking mechanism is in an unlocked position and wherein movement of the cable and locking mechanism is unrestricted. 
     FIG. 4 is a top plan view of the device of the invention wherein the locking mechanism is in a locked position and wherein movement of the cable and locking mechanism is restricted. 
     FIG. 5 is a top plan view of the device of the invention wherein the locking mechanism is in an unlocked position and wherein movement of the cable and locking mechanism is restricted. 
     FIG. 6 is a top plan view of the device of the invention in situ in a chair frame, where the locking mechanism is in an unlocked position. 
     FIG. 7 is a top plan view of the device of the invention in situ in a chair frame, where the locking mechanism is in a locked position. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, the construction of overload protection device  20  is clearly shown in a cross-sectional, exploded view. Slide member  22  includes cavity  23  which receives ball or barrel  12   a  disposed on the end of cable  12 . The housing of cable  12  is fitted on the end thereof with cable end coupling  25 , on which is defined slot  25   a.  Slot  25   a  serves to attach cable end coupling to chair frame  8  at any convenient spot (see FIGS.  6  and  7 ). Likewise, the opposite end of cable  12 , which is connected to cable actuator  10 , also is fitted near the end thereof with cable end piece  31 , which defines slot  31   a.  Slot  31   a  serves to attach this end of cable to any convenient spot on chair frame  8 . 
     Cable actuator  10  may be of any given shape, but, in the preferred embodiment, is in the shape of a cam having detents  7  defined therein. Detents  7  may engage protrusions defined in chair frame  8  (not shown) to define two or more positions as actuator  10  is rotated. 
     Spring  24  is situated around the outside circumference of slide member  22 , and slide member  22  and spring  24  are inserted within spring housing  26 . Spring housing  26  has shoulder  32  defined therein, which allows the travel of slide member  22  to be limited within spring housing  26 . Spring  24  rests against shoulder  32  of spring housing  26  and shoulder  22   a  defined on slide member  22 . Slide member  22  is held within spring housing  26  by E-ring  28 , which is disposed in slot  29  defined in slider  22 . Spring  30  at end  30   a  is situated around end portion  25   b  of cable end coupling  25  and is radially aligned with slide member  22 , spring housing  26 , cable  12  and spring  24 . The opposite end  30   b  of spring  30  is disposed around end portion  22   b  of slide member  22 . 
     Actuators  14  and  16  are coupled to spring housing  26  via a rack and pinion gear assembly comprised of teeth  21  defined on spring housing  26  and teeth  18  and  19 , defined on actuators  16  and  14  respectively. When spring housing moves in direction  43 , the interaction between teeth  21  on spring housing  26  and teeth  18  on actuator  16  causes actuator  16  to rotate in a clockwise direction about point  16   a.  The interaction between teeth  18  on actuator  16  and teeth  19  on actuator  14  causes actuator  14  to rotate in a counterclockwise direction about point  14   a.  Likewise, movement of spring housing  26  in direction  44  will cause actuators  14  and  16  to rotate in clockwise and counterclockwise directions respectively. 
     The rotational movement of actuators  14  and  16  causes a back-and-forth movement of locking members  52  via coupling rods  50 , which may be connected between actuators  14  and  16  and respective locking members  52  via ball and socket assemblies  15  and  17 . Thus, the linear motion of a single cable  12  is translated into a back-and-forth motion for multiple locking members  52 , fulfilling one object of the invention. 
     The device of the present invention is normally installed under the seat of an office type chair and is shown in situ in FIGS. 6 and 7. Chair frame  8  is a supporting structure of the chair which would typically be connected to a support post underneath and which would have the seat of the chair mounted thereon, covering the locking mechanism of the present invention from normal view. 
     The locking mechanism will typically lock and unlock some aspect of the movement of the chair, such as the reclining of the backrest  60 . Cable actuator  10  is preferably located at some convenient position on chair frame  8  in proximity to the hand of a person seated in the chair, such that cable actuator  10  can be comfortably manipulated. Typically, a lever type member (not shown) would be connected to cable actuator  10  to facilitate the manual rotational movement thereof by the user. 
     When in a locked position, locking members  52  are inserted into recesses  54 , best shown in FIGS. 6 (unlocked) and  7  (locked) via coupling rods  50  by movement of cable actuator  10  in direction  42  as shown in FIG.  2 . When unlocked, locking members  52  are withdrawn from recesses  54  by coupling rods  50  by movement of cable actuator  10  in direction  41  as shown in FIG.  3 . 
     FIGS. 2 and 3 show the locking mechanism in locked and unlocked positions respectively in a situation where no binding of locking members  52  within recesses  54  is occurring. In FIGS. 2 and 3, locking members  52  are unbound and free to move into and out of recesses  54 , therefore overload protection device  20  merely serves to transfer the motion of cable  12  to locking members  52 . 
     In normal operation the mechanism is moved from an unlocked position, as shown in FIG. 3, to a locked position, as shown in FIG. 2, when actuator  10  is rotated in direction  42 . FIGS. 2 and 3 show the mechanism absent a binding condition. In this situation, when actuator  10  is rotated in direction  42 , cable  12  moves in the direction of arrow  44  and allows the motion of spring housing  26  in direction  44  as the result of the decompression of spring  30 . Spring housing  26  has rack gears  21  defined thereon, which move pinion gears  19  and  18  on actuators  14  and  16  respectively. The rotation of actuators  14  and  16  causes connecting rods  50 , which may be connected to actuators  14  and  16  by ball and socket joints  15  and  17 , to move outwardly, thereby causing locking members  52 , connected to the opposite ends of connecting rods  50 , to be inserted into recesses  54  (see FIG.  7 ). This presence of locking member  52  within recesses  54  serves to lock backrest  60  of the chair, preventing it from moving. 
     The corresponding normal movement from a locked position in FIG. 2 to an unlocked position in FIG. 3 occurs when no binding condition exists and actuator  10  is rotated in direction  41 . Cable  12  moves in the direction of arrow  43 , causing slide member  22  to also move in direction  43  within spring housing  26 . The movement of slide member  22  causes spring  24  to contact shoulder  32  in spring housing  26 . Because spring housing  26  is free to move due to the absence of a binding condition, spring housing  26  also moves in direction  43 . Also, spring  30  compresses due to the pressure from E-ring  28  moving with slide member  22 . The resulting rotation of actuators  14  and  16  causes connecting rods  50 , to move inwardly, thereby causing locking members  52  to be withdrawn from recesses  54  (see FIG.  6 ). This unlocks backrest  60  of the chair, allowing it to move freely. 
     FIG. 4 shows the locking mechanism wherein cable actuator  10  has been rotated in direction  41  to the unlocked position, but wherein locking members  52  are unable to be withdrawn from recesses  54  because they are bound therein by pressure applied by the backrest of the chair. In this case, slide member  22  is moved in direction  43  within spring housing  26 , thereby compressing spring  24  between shoulder  32  defined within spring housing  26  and shoulder  22   a  defined on slide member  22 . Spring  30  is also compressed. When the binding condition has been removed, for example, by the release of pressure on the backrest of the chair, locking members  52  are able to move freely out of recesses  54 , spring  24  decompresses, urging spring member  26  to move in direction  43 , causing locking members  52  to be withdrawn from recesses  54 . 
     The corresponding locking motion is shown in FIG.  5 . In this case, cable actuator  10  has been moved into the lock position causing cable  12  to move in direction  44 . Note that ball or barrel  12   a,  disposed on the end of cable  12 , has moved in direction  44 , away from the end of slide member  22 . However, locking members  54  are prevented from being inserted into recesses  54  because the portion of recess  54  located on frame  8  and the portion of recess  54  located on backrest  60  of the chair are not aligned such as to allow locking members  54  to be inserted therein. When locking members  52  are again able to move freely into recesses  54 , both spring housing  26  and slide member  22  will move in direction  44  as the result of the decompression of spring  30 . 
     As mentioned previously, in the event that locking members  52  are bound in recesses  54  by a weight placed on backrest  60  of the chair, or prevented from being inserted into recesses  54  because of a blockage thereof by backrest  60 , motion  43  of cable  12 , spring housing  26  and the actual movement of overload protection device  20  and the associated locking mechanism is accomplished when the binding is removed. 
     Through the use of the overload protection device  20 , the user is able to feel the movement of cable  12  through the translation of the movement from the user lever to springs  24  and  30 , however, the locking mechanism, while prevented from moving, is not overloaded to the point where it may break. In this way, the user is prevented from forcing the locking mechanism to move when it is unable to do so because of the presence of a binding condition. 
     It should be noted that actuators  14  and  16  can be of any shape to accommodate different designs for different purposes and that the invention is not meant to be limited by the exact shape of actuators  14  or  16 , nor by the function of the mechanism as described, nor is its use to be limited to chairs or to the locking and unlocking of chair backrests. Likewise, connecting rods  50 , locking members  52 , recesses  54  and chair frame  8  may be of any configuration or shape. Overload protection device  20  is meant to be used with any configuration of chair members anytime binding is possible.