Abstract:
A method of assembling a spring inside of a tube includes providing a coil spring and a tube having a first retaining structure at a first end of the tube. The method includes positioning a rod in the tube. The spring is positioned in the tube, and a second retaining structure is attached to the rod with the spring positioned between the first and second retaining structures. A force is applied to the spring, and the second retaining structure is fixed at a position wherein the spring provides a desired preload.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Nos. 61/703,677 filed on Sep. 20, 2012, entitled “CHAIR ASSEMBLY,” 61/703,515 filed on Sep. 20, 2012, entitled “SPRING ASSEMBLY AND METHOD,” 61/703,663 filed on Sep. 20, 2012, entitled “CHAIR BACK MECHANISM AND CONTROL ASSEMBLY,” 61/703,659 filed on Sep. 20, 2012, entitled “CONTROL ASSEMBLY FOR CHAIR,” and 61/703,661 filed on Sep. 20, 2012, entitled “CHAIR ASSEMBLY,” 61/703,666, filed on Sep. 20, 2012, entitled “CHAIR ASSEMBLY WITH UPHOLSTERY COVERING,” 61/703,667, filed on Sep. 20, 2012 entitled “CHAIR ARM ASSEMBLY,” and 61/754,803 filed on Jan. 21, 2013, entitled “CHAIR ASSEMBLY WITH UPHOLSTERY COVERING,” the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Various springs and spring assemblies have been developed for providing a resistance or assistance force for devices such as chair tilt mechanisms, height adjustment mechanisms for chairs and tables, door opening/closing mechanisms and other applications requiring an assistance or resistance force. Due to production tolerances and other such variables, the amount of force generated by a spring may vary from one spring to another. This can lead to inconsistent resistance forces assemblies such as office chairs, height adjustable tables, or other devices or products that utilize springs. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the present invention is a method of assembling a spring inside of a tube or enclosure. The method includes providing a coil spring having first and second opposite spring ends. The method also includes providing an enclosure such as a tube having an interior space and a first retaining structure at a first end of the tube, such that the spring transmits force to the tube upon insertion of the spring into the second end of the tube. The method also includes providing an elongated rod having first and second ends, and providing first and second retainers that are configured to engage the first and second opposite ends of the coil spring and transmit axial loads to the first and second opposite spring ends and compress the coil spring. The method further includes positioning the rod in the tube with the first rod end towards the first tube end and the second end towards the second tube end. The spring is positioned in the tube with the first end of the spring engaging the first retaining structure. The method further includes providing a second retaining structure, which is positioned inside the tube. The second retaining structure is attached to the second end of the rod with the spring positioned at least partially inside the tube between the first and second retaining structures. This spring is compressed utilizing a force acting on the spring. A target preload force is determined, and the magnitude of the force acting on the spring is varied or adjusted. The second retaining structure is fixed at a position wherein the spring provides a preload force meeting predefined acceptance criteria. The predefined acceptance criteria may comprise a condition wherein the magnitude of the force acting on the spring is within a predefined tolerance range of the target preload force. 
     Another aspect of the present invention is a method of fabricating a force-generating assembly of the type that includes a resilient member providing a predefined preload acting on an enclosure and an actuator. A dimension of the enclosure and actuator does not change unless a force acting on the enclosure and actuator exceeds a predefined preload force. The method includes providing an enclosure and an actuator. At least a portion of the actuator is positioned in the enclosure with a portion of the actuator extending outside the enclosure. A resilient member is provided, and the enclosure and the actuator are operably interconnected utilizing the resilient member. The resilient member is capable of generating a resistance force tending to return the actuator and the enclosure to the assembled positions relative to one another. The resilient member is deformed such that the resilient member generates a force falling within a predefined range. The enclosure or other component is fixed relative to the actuator such that the resilient member provides a predefined preload force. 
     Yet another aspect of the present invention is an energy mechanism including a coil spring and an enclosure housing the spring. The mechanism also includes an actuator that is movable between an initial position and at least one displaced position. The actuator extends out of the enclosure, and it is connected to the coil spring to transmit a spring force outside of the enclosure. The spring is supported in a preselected preloaded state within the enclosure after being preloaded to a predetermined spring force. An initial spring force required to move the actuator from the initial position correlates to the predetermined force amount. 
     These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a chair including one or more spring assemblies according to the present invention; 
         FIG. 2  is a side elevational view of the chair of  FIG. 1 ; 
         FIG. 3  is a schematic view of the linkage and springs of the chair of  FIG. 1 ; 
         FIG. 4  is a partially fragmentary isometric view of a spring assembly according to the present invention; 
         FIG. 5  is a side elevational view of a spring assembly according to the present invention; 
         FIG. 5A  is an exploded cross sectional view of the pin and retainer of  FIG. 5 ; 
         FIG. 6  is an exploded isometric view of a spring assembly according to the present invention; 
         FIG. 7  is a cross-sectional view of a machine utilized to assemble the spring assembly according to the present invention; 
         FIG. 8  is a partially fragmentary view of a spring subassembly according to the present invention; 
         FIG. 9  is a partially fragmentary view of a spring assembly according to the present invention; and 
         FIG. 10  is a cross-sectional view of a spring assembly according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in  FIG. 1 . However, it is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise. 
     A chair  1  includes a back  2 , a seat  3 , armrests  4  and a base  5  with castors  6 . With further reference to  FIGS. 2 and 4 , chair  1  includes a four bar linkage comprising a base link  12  that is fixed to the chair base  5 , a seat link  14 , a control link  16 , and a lower link  18 . The links  12 - 16  are interconnected by first, second, third, and fourth pivots  21 ,  22 ,  23 , and  24 , respectively. A spring assembly  30  generates tension forces F 1  and F 2  acting on points  31  and  32  to thereby bias the four bar linkage  10  into an upright position as shown in  FIGS. 2 and 3 . It will be understood that the spring and method of the present invention is not limited to coil springs, and also is not limited to spring assemblies generating a tension force. 
     With further reference to  FIGS. 4-6  and  FIGS. 9-10  spring assembly  30  includes a coil spring  34 , an actuator or rod  36  having an opening  52  at end  54 , a housing or enclosure  38 , and an end plug or fitting  40 . The spring assembly  30  also includes washers,  42 A,  42 B and bushings  44 A,  44 B. A pin  46  extends through an opening  50  in end plug or fitting  40 , and a retainer  48  retains the pin  46  in the opening  50 . Retainer  48  may comprise a C clip that is received in an annular grove, or it may comprise other suitable retaining devices to retain pin  46  in opening  50  of end plug  40 . With reference to  FIG. 5A , in a preferred embodiment, pin  46  includes a cylindrical portion  46 A having a raised ring-like protrusion or ridge  46 B and a slot  46 C. Retainer  48  includes an annular ridge  48 A that snaps over ridge  46 B such that retainer  48  is retained on pin  46 . Pin  46  and/or retainer  48  may comprise steel or other suitable material. 
     When assembled, pin  46  and opening  52  at end  54  of rod  36  are utilized to transmit forces through the spring assembly  30 . When spring assembly  30  is assembled, end flanges  56  and  58  of housing  38  retain the spring  34  in a prestressed, compressed condition. As discussed in more detail below, the flange  58  is formed during assembly while measuring a force applied to rod  36  and end plug or fitting  40 , such that the spring  34  has a predefined preload. Thus, the magnitude of tension forces F 1  and F 2  applied to rod  36  and end plug  40 , respectively, must exceed a specified preload force amount before the rod  36  and end fitting  40  will move relative to one another from the initial position shown in  FIG. 5 . If tension forces F 1  and F 2  exceed the predefined preload force, coil spring  34  will compress further, resulting in movement of rod  36  in the direction of the arrow “A” ( 5 ) relative to end plug or fitting  40 . The spring assembly  30  of the present invention can be assembled in a way that ensures that the actual tension forces F 1  and F 2  required to cause movement of rod  36  relative to fitting  40  fall within a predefined acceptable range. 
     With reference to  FIG. 8 , housing  38  is initially formed to include an inwardly-extending flange  56 A at first end  62 A of housing  38 . Circular edge  66  at second end  62 B of housing  38  is not initially formed to include a flange. During assembly, a first washer  42 A is initially positioned in the inner space  60  of housing  38  in position against flange  56 A at a first end  62 A of housing  38 , and a first bushing  44 A and rod  36  are positioned as shown in  FIG. 8 . Rod  36  initially includes a reduced diameter end portion  64  that receives second washer  42 B. A coil spring  34  is then positioned in housing  38 , and a second bushing  44 B and second washer  42 B are then positioned in the interior space  60  with second washer  42 B disposed on reduced diameter end portion  64  of rod  36 . The edge  66  of housing  38  is initially not formed to include a flange, such that washers  42 A and  42 B, and bushings  44 A and  44 B can be inserted into interior space  60  of housing  38 . 
     End  64  of rod  36  is then deformed utilizing a known radial riveting process or other suitable process to create an enlarged end portion  65  which securely retains the washer  42 B on end  68  of rod  36 . Enlarged end portion  65  is shown in dashed lines in  FIG. 8 , and in solid lines in  FIG. 9 . This forms a subassembly  30 A as shown in  FIG. 8 . 
     Subassembly  30 A is then positioned in a fixture  70  ( FIG. 7 ). Fixture  70  includes first and second pins  72  and  74 , respectively, that are received in openings  50  and  52 , respectively of spring subassembly  30 A. An end plug or fitting  40  is positioned in second end  62 B of housing  38 . Pins  72  and  74  may be inserted utilizing pneumatic or hydraulic cylinders (not shown). Upper pin  72  fixes the plug  40  relative to upper plate  90  of fixture  70 , and lower pin  74  fixes the rod  36  relative to a vertically adjustable cylinder  84 . Cylinder  84  can be driven upwardly by threaded force adjustment device  86  by rotating a hand wheel  88 . A load cell  82  is utilized to measure the force generated by coil spring  34  on pin  74  due to upward movement of cylinder  84 . Although a threaded adjustment device  86  and hand wheel  88  are shown in the fixture  70 , the force adjustment device utilized to compress coil spring  34  may comprise a hydraulic cylinder, an electrically-powered actuator, or other suitable powered device. 
     Once a predetermined or predefined force is generated as measured by load cell  82 , a forming tool  92  is shifted downwardly into position adjacent second end  62 B of housing  38  utilizing a hydraulic cylinder  80  or other suitable powered actuator. The forming tool  92  then forms edge  66  ( FIG. 8 ) into flanges  56 B ( FIG. 9 ) to retain plug  40  at a position wherein the coil spring  32  is preloaded at the desired level. This process thereby sets the preload force at a desired, predefined level or to a predefined range that includes acceptable tolerance variations. The final spring assembly  30  ( FIGS. 9 and 10 ) is then removed from fixture  70 . 
     Referring again to  FIG. 1 , chair assembly  1  includes two spring assemblies  30 . Because the spring assemblies  30  are consistent with respect to the preload or initial force required to initially extend the spring assemblies  30 , a plurality of chairs  1  can be manufactured and the springs  30  do not need to be adjusted at the time of assembly of the chair  1 . Furthermore, each chair  1  assembled will have substantially the same tilt characteristics with respect to the amount of force required to tilt the chair back.