Patent Publication Number: US-2021186217-A1

Title: Spring Actuated Rocking Mechanism for Collapsible Chair

Description:
REFERENCE TO RELATED CASES 
     This application is a continuation of application Ser. No. 15/706,359, filed on Sep. 15, 2017, which in turn is a continuation-in-part of application Ser. No. 15/424,163, filed on Feb. 3, 2017, still pending, which in turn claims priority under 35 U.S.C. § 119 (e) to provisional application No. 62/290,746 filed on Feb. 3, 2016, and is also a continuation-in-part application of application Ser. No. 14/640,659, filed on Mar. 6, 2015, abandoned, which in turn claims priority under 35 U.S.C. § 119 (e) to provisional application No. 61/948,780 filed on Mar. 6, 2014, the contents of these applications are also hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a spring actuated mechanism as part of a collapsible chair, which enables the user to enjoy a rocking chair type motion during leisure or outdoor activities. Prior practices typically consisted of curved rocking members joined to the front and rear chair legs. These members must be folded as a secondary action by the user upon deploying the chair for use, or compacting the chair for storage. This takes extra time and effort in setting up or putting the chair away. 
     The invention is intended to be incorporated as an integral part of a collapsible chair frame where a portion of the rear legs of the chair may be replaced by the device. This configuration allows the chair to be folded to its closed configuration without the user disconnecting any other embodiments. This type of rocker also achieves the rocking motion by means of a compressive spring attached to the rear frame members of the chair rather than traditional curved rocking members joined to the front and rear legs of the chair frame. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a rocking mechanism to attach to a single leg of a collapsible chair includes a tubular housing having an interior portion extending between an upper end and a lower end, an upper cap fixedly attached to the tubular housing at the upper end, the cap configured to engage the single leg of the collapsible chair, a lower cap fixedly attached to the tubular housing at the lower end and having an opening therethrough to receive a second leg portion that extends into the interior portion of the tubular housing, a plunger disposed within the interior portion of the tubular housing, the plunger connectable to the second leg portion and having a plurality of rollers disposed about a periphery of the plunger to engage an inside surface of the tubular housing, and a spring disposed in the interior portion of the tubular housing between the upper cap and the lower cap. 
     In yet another aspect, there is a plunger for a rocking mechanism that includes a base, a flat upper surface on one side of the base, a lower surface on a second side of the base, a cylindrical extension extending downward from the second side, a plurality of tabs extending from the cylindrical extension creating a plurality of spaces, and a plurality of rollers, each of the plurality of rollers disposed in between two of the plurality of tabs. 
     Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description of the present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operations of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of one embodiment of a rocking mechanism according to the present invention; 
         FIG. 2  is a perspective, exploded view of the rocking mechanism of  FIG. 1 ; 
         FIG. 3  is a cross section of the rocking mechanism of  FIG. 1 ; 
         FIG. 4  is a plan view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 5  is a perspective, exploded view of the rocking mechanism of  FIG. 4 ; 
         FIG. 6  is a cross section of the rocking mechanism of  FIG. 4 ; 
         FIG. 7  is a plan view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 8  is a perspective, exploded view of the rocking mechanism of  FIG. 7 ; 
         FIG. 9  is a cross section of the rocking mechanism of  FIG. 7 ; 
         FIG. 10  is an enlarged perspective cross-sectional view of a portion of the top and bottom portions of the rocking mechanism of  FIG. 1  showing the alignment member and alignment groove: 
         FIG. 11  is a plan view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 12  is a perspective, exploded view of the rocking mechanism of  FIG. 11 ; 
         FIG. 13  is a cross section of the rocking mechanism of  FIG. 11 ; 
         FIG. 14  is a plan view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 15  is a perspective, exploded view of the rocking mechanism of  FIG. 14 ; 
         FIG. 16  is a cross section of the rocking mechanism of  FIG. 14 ; 
         FIG. 17  is a plan view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 18  is a cross section of the rocking mechanism of  FIG. 17 ; 
         FIG. 19  is a perspective, exploded view of the rocking mechanism of  FIG. 17 ; 
         FIG. 20  is a cross section of one embodiment of a plunger according to the present invention in the rocking mechanism of  FIG. 17 ; 
         FIG. 21  is a perspective view of the plunger in  FIG. 20 ; 
         FIG. 22  is an enlarged view of the roller and pin in the plunger in  FIG. 21 ; 
         FIG. 23  is a side view of another embodiment of a plunger for a rocking mechanism according to the present invention; 
         FIG. 24  is an exploded view of the plunger in  FIG. 23 ; 
         FIG. 25  is an enlarged view of the roller and pin in the plunger in  FIG. 23 ; 
         FIG. 26  is a cross section view of another embodiment of a rocking mechanism according to the present invention that includes another embodiment of a plunger according to the present invention; 
         FIG. 27  is a side view of the plunger in  FIG. 26 ; 
         FIG. 28  is cross section view of the plunger in  FIG. 26 ; 
         FIG. 29  is a bottom view of the plunger in  FIG. 26 ; 
         FIG. 30  is a perspective view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 31  is a top view of the rocking mechanism of  FIG. 30 ; 
         FIG. 32  is a side view of the rocking mechanism of  FIG. 30 ; 
         FIG. 33  is a rear side view of the rocking mechanism of  FIG. 30 ; 
         FIG. 34  is a cross-section view of the rocking mechanism of  FIG. 30  along the lines illustrated in  FIG. 33 ; 
         FIG. 35  is a cross-section view of the rocking mechanism of  FIG. 30  along the lines illustrated in  FIG. 32 ; 
         FIG. 36  is an exploded view of the rocking mechanism of  FIG. 30 ; 
         FIG. 37  is a perspective view of another embodiment of a rocking mechanism according to the present invention; 
         FIG. 38  is a top view of the rocking mechanism of  FIG. 37 ; 
         FIG. 39  is a side view of the rocking mechanism of  FIG. 37 ; 
         FIG. 40  is a rear side view of the rocking mechanism of  FIG. 37 ; 
         FIG. 41  is a cross-section view of the rocking mechanism of  FIG. 37  along the lines illustrated in  FIG. 40 ; 
         FIG. 42  is a cross-section view of the rocking mechanism of  FIG. 37  along the lines illustrated in  FIG. 39 ; and 
         FIG. 43  is an exploded view of the rocking mechanism of  FIG. 37 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiment(s) of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
     Referring to  FIGS. 1-3 , a first embodiment of a rocking mechanism  20  is illustrated. The rocking mechanism  20  is preferably attached to a rear leg of a collapsible chair (not shown). Therefore, in order to make a collapsible chair (such as that produced by the current assignee of this patent application and illustrated in U.S. Pat. No. D593,759, the contents of which are hereby incorporated by reference herein), two of the rocking mechanisms  20  can be attached to the rear legs. As one of ordinary skill in the art would recognize, the cross members of the illustrated chair may need to be adjusted to accommodate the rocking mechanisms  20 . Clearly, the rocking mechanisms  20  could also be added to other such collapsible chairs. It should also be noted that the rocking mechanisms  20  can be added upon manufacture of the chair or added thereafter. As illustrated in the figures, a portion of a chair leg  22  is illustrated. 
     The rocking mechanism  20  has an upper portion  24 , the upper portion  24  having a first opening  26  in a top end  28 , the first opening  26  configured to receive at least a portion of the chair leg  22  of the collapsible chair. The upper portion  24  also has a second opening  30  on a side portion  32 , the second opening  30  being configured to receive a securing member  34  to engage and maintain the chair leg  22  in the upper portion  24 . As such, the second opening  30  is in communication with the first opening  26 . The upper portion  24  may also have a corresponding second second opening  36  to receive another securing member  38 . The second second opening  36  is therefore also in communication with the first opening  26 . See  FIG. 3 . 
     The upper portion  24  may have any number of external configurations and fall within the scope of the present invention. As illustrated, the upper portion  24  includes a generally cylindrical portion  40  adjacent the top end  28 , and then a frustoconical portion  42  immediately adjacent the cylindrical portion  40 . The frustoconical portion  42  becomes larger in diameter the farther away from the cylindrical portion  40 . The upper portion  24  then includes a shoulder  44  that faces away from the top end  28  and the frustoconical portion  42 . In fact, the shoulder  44  is formed by the frustoconical portion  42  and a second frustoconical portion  46  that extends distally from the shoulder  44 . The second frustoconical portion  46  then decreases in diameter the farther away from the first frustoconical portion  42 . 
     The rocking mechanism also includes a spring  50 , the spring  50  having a first end  52  that is disposed against the shoulder  44  of the upper portion  24 . The first end  52  of the spring  50  engages the shoulder  44  and surrounds at least a portion of the second frustoconical portion  46 . The spring  50  is preferably a coil spring, but other configurations are possible as well. The spring  50  has a second end  54  that engages a lower portion  70 . The lower portion  70  is configured to engage the second end (distal end)  54  of the spring  50 . Specifically, the lower portion  70  has a shoulder  72  facing upwards and toward the upper portion  24 . The lower portion  70  preferably has a rounded surface  74  on an opposite side of the lower portion  70  from the shoulder  72 . The lower portion  70  also includes a projection  76  radially inward from the shoulder  72  to assist in centering the spring  50  on the lower portion  70  and the shoulder  72 . The lower portion  70  may also have a center opening  78  that holds a guide member, as discussed in detail below. 
     The rocking mechanism  20  also includes a guide member  90  that extends between the upper portion  24  and the lower portion  70 . The guide member  90  has a first end  92  and a second end  94 . The first end  92  of guide member  90  includes a circular groove  96  extending around the periphery of guide member  90 . The groove  96  is configured to receive therein a circular retaining clip  98 . The second end  94  guide member  90  has a longitudinal opening  100  therein to receive a fastening member  102 . The fastening member  102  extends through the center opening  78  of the lower portion  70  to engage the guide member  90  and maintain it in a fixed relation thereto. The fastening member  102  is preferably a threaded screw to engage corresponding threads inside the longitudinal opening  100  of the guide member  90 . A cap  104  is also provided to be press-fit into the center opening  78  from the rounded surface  74 . 
     The first end  92  of the guide member  90  is movable within the first opening  26 , which as best illustrated in  FIG. 3  extends throughout the length of the upper portion  24 . Extending into the first opening  26  toward the distal end thereof and adjacent to the second frustoconical portion  46  is an inward extending ring  106 . The guide member  90 , having the retaining clip  98  inserted into the groove  96 , is inserted into the first opening  26 . The retaining clip  98  in gauges the inward extending ring  106  to prevent the guide member  90  from falling out the bottom end  110  of the upper portion  24 . The spring  50  is then disposed over and around the guide member  90  and the second frustoconical portion  46  to engage the shoulder  44 . The lower portion  70  is then attached to the guide member  90  as discussed above. The second end  54  of spring  50  engages the upward facing shoulder  72  of the lower portion  70 . 
     A bushing  112  is preferably disposed in the bottom end  110  of the upper portion  24 . As best seen in  FIG. 3 , the bushing  112  aligns and provides a wearable surface during linear movement of the guide member  90  in and out of the first opening  26  during use. As can be imagined, applying force to the rocking mechanism  20  through the chair leg  22  causes compression of the spring  50 , lowering of the upper portion  24  relative to the lower portion  70  thereby causing the guide member  92  move upward in the first opening  26 . Thus, the bushing  112  helps to keep the upper portion  24 , the spring  50 , and the lower portion  70 , in alignment during use. 
     The upper portion  24  and the lower portion  70  are preferably made from a high density polyethylene. The bushing  112  is preferably made of acetyl resin, while the guide member  90  is preferably made from stainless steel. The other parts of the rocking mechanism  20  are all preferably made from steel. It should be noted however that other appropriate materials may be used in the manufacture of the rocking mechanism  20  and still fall within the scope of the present invention. 
     It should be noted that the first opening  26  has a larger diameter adjacent the top end  28  of the upper portion  24 . The change in diameter of the first opening  26  below the second openings  30 ,  36  provides for a shoulder  120  that supports the end of chair leg  22 . 
     A second embodiment of a rocking mechanism  200  is illustrated in  FIGS. 4-6 . While many of the components in rocking mechanism  200  are similar to rocking mechanism  20 , the chair leg  22  has been omitted. It is understood, however, that a chair leg such as leg  22  would be fixed to the rocking mechanism  200  in the same manner as described above. 
     The rocking mechanism  200  has an upper portion  224 , the upper portion  224  having a first opening  226  in a top end  228  configured to receive at least a portion of a chair leg of a collapsible chair. The upper portion  224  also has a second opening  230  on a side portion  232 , the second opening  230  being configured to receive a securing member (not shown, but may be the same as or similar to the one for rocking mechanism  20 ) to engage and maintain the chair leg in the upper portion  224 . As such, the second opening  230  is in communication with the first opening  226 . The upper portion  224  may also have a corresponding second second opening  236  to receive another securing member. The second second opening  236  is therefore also in communication with the first opening  226 . See  FIG. 6 . 
     The upper portion  224  may, like the other embodiment, have any number of external configurations and still fall within the scope of the present invention. As illustrated, the upper portion  224  includes a generally cylindrical portion  240  adjacent the top end  228 , and then a frustoconical portion  242  immediately adjacent the cylindrical portion  240 . The frustoconical portion  242  becomes larger in diameter the farther away from the cylindrical portion  240 . The upper portion  224  then includes a shoulder  244  that faces away from the top end  228  and the frustoconical portion  242 . In fact, the shoulder  244  is formed by the frustoconical portion  242  and a second frustoconical portion  246  that extends distally from the shoulder  244 . The second frustoconical portion  246 , which is substantially shorter than the first frustoconical portion  242 , then decreases in diameter the farther away from the first frustoconical portion  242 . 
     The rocking mechanism  200  also includes a spring  250 , the spring  250  having a first end  252  that is disposed against the shoulder  240  of the upper portion  224 . The first end  252  of the spring  250  engages the shoulder  244  and surrounds at least a portion of the second frustoconical portion  246 . The spring  250  is preferably a coil spring, but other configurations are possible as well. The spring  250  has a second end  254  that engages a lower portion  270 . The lower portion  270  is configured to engage the second end (distal end)  254  of the spring  250 . The lower portion  270  has a shoulder  272  facing upwards and toward the upper portion  224 . The lower portion  270  is thicker than the lower portion  70  of the first embodiment, but also preferably has a rounded surface  274  on an opposite side of the lower portion  270  from the shoulder  272 . The lower portion  272  also includes a projection  276  disposed radially inward from the shoulder  272  to assist in centering the spring  250  on the lower portion  270 . The lower portion may also have a center opening  278  that holds a guide member, as discussed in detail below. 
     The rocking mechanism  200  also includes a guide member  290  that extends between the upper portion  224  and the lower portion  270 . The guide member  290  has a first end  292  and a second end  294 . The second end  294  of guide member  290  has a longitudinal opening  300  therein to receive a fastening member  302 . The fastening member  302  extends through the center opening  278  of the lower portion  270  to engage the guide member  290  and maintain it in a fixed relation thereto. The fastening member  302  is preferably a threaded screw to engage corresponding threads inside the longitudinal opening  300  of the guide member  290 . 
     The first end  292  of the guide member  290  is movable with in the first opening  226 , which as best illustrated in  FIG. 6 , extends throughout the length of the upper portion  224 . A bushing  312  is preferably disposed in the bottom end  310  of the upper portion  224 . As illustrated in  FIG. 6 , the bushing  312 , which is preferably made from a self-lubricating metal such as brass, aligns and provides a wearable surface during linear movement of the guide member  290  in and out of the first opening  226  during use. The bushing  312  is preferably injection-molded into the upper portion  224 . As can be imagined, applying force to the rocking mechanism  200  through the chair leg causes compression of the spring  250 , lowering the upper portion  224  relative to the lower portion  270  thereby causing the guide member  292  to move upward in the first opening  226 . Thus, the bushing  312  helps to keep the upper portion  224 , the spring  250 , and the lower portion  270  in alignment during use. 
     The guide member  290  is combined with a retaining member  298  inserted into the first end  292  of the guide member  290 . The retaining member  298  is preferably a screw that engages with threads in a longitudinal opening at the first end  292  of the guide member  290 . The retaining member  298  which has a larger head diameter than that of the guide member  290 , engages the bushing  312  to prevent the guide member  290  from falling out the bottom end  310  of the upper portion  224 . The spring  250  is then disposed over and around the guide member  290  end the second frustoconical portion  246  to engage the shoulder  244 . The lower portion  270  is then attached to the guide member  290  as discussed above. The second end  254  of spring  250  engages the upward facing shoulder  272  of the lower portion  270 . 
     Another embodiment of a rocking mechanism  400  is illustrated in  FIGS. 7-10 . The rocking mechanism  400  has an upper portion  424 , the upper portion  424  having a first opening  426  in a top end  428 , the first opening  426  configured to receive at least a portion of the chair leg  22  of the collapsible chair. While not illustrated, the upper portion  424  may also have a second opening configured to receive a securing member to engage and maintain the chair leg  22  in the upper portion  424  as with other embodiments. 
     The upper portion  424  may, like the other embodiments, have any number of external configurations and still fall within the scope of the present invention. As illustrated, the upper portion  424  includes a generally rounded (or domed) portion  440  adjacent the top end  428 , and then a cylindrical portion  442  immediately adjacent the rounded portion  440 . The cylindrical portion  442  terminates with a circumferential ring  444  (for reasons discussed below) and a flat bottom end  410  that faces away from the top end  428 . 
     The rocking mechanism  400  also includes a spring  450 , the spring  450  having a first end  452  that is disposed against the bottom end  410  of the upper portion  424 . The spring  450  is preferably a coil spring, but other configurations for the spring  450  are possible as well. The spring  450  has a second end  454  that engages a lower portion  470 . The lower portion  470  is generally cylindrical and is configured to receive the second end (distal end)  454  of the spring  450  and at least a portion of the upper portion  424 . In particular, the lower portion  470  has a flat bottom  472  to engage the second end (distal end)  454  of the spring  450 . Around the inside of lower portion  470  at a top end  446  thereof is an annular ring  474  to engage the circumferential ring  444  of the upper portion  424  to keep the spring  450  from separating the lower portion  470  from the upper portion  424 . The two rings  444 ,  474  engage one another, preventing the lower portion  470  from exiting the upper portion  424 . The two portions  424 ,  470  can be snap fit together. As a result of this configuration, it should be noted that the top end  478  of the lower portion  470  is always positioned between the top end  428  and the bottom end  410  of the upper portion  424 . 
     The lower portion  470  also has a vertically oriented groove  476  that cooperates with a projection  478  on the upper portion  424 . See  FIG. 9 .  FIG. 10 , a perspective view of the rocking mechanism  400  in cross section, shows the projection  478  on the upper portion  424  engaging the vertically oriented groove  476 . The combination of the groove  476  and the projection  478  prevents the lower portion  470  and the upper portion  424  of the rocking mechanism  400  from rotating relative to one another. This is important as rocking mechanism  400  has a foot portion  480  into which the lower portion  470  is placed. The foot portion  480  has a curved bottom portion  482  to assist with the rocking motion. The curved bottom portion  482  has two generally flat surfaces  482   a ,  482   b  that lie in two different planes that form an angle ∞, which is about 28°. The surface  482   b  forms an angle β with a center line of the rocking mechanism—see  FIG. 7 . Preferably, this angle is about 76°. Since the curved bottom portion  482  has surfaces that are direction oriented, unlike the embodiments disclosed above, the foot portion  480  needs to be maintained in the correct orientation. The combination of the groove  476  and the projection  478  maintain this orientation. 
     Another embodiment of a rocking mechanism  600  is illustrated in  FIGS. 11-13 . The rocking mechanism  600  has an upper portion  624 , the upper portion  624  having a first opening  626  in a top end  628 , the first opening  626  configured to receive at least a portion of the chair leg  22  of the collapsible chair. While not illustrated, the upper portion  624  may also have a second opening configured to receive a securing member to engage and maintain the chair leg  22  in the upper portion  624  as with the other embodiments. 
     The upper portion  624  may, like the other embodiments, have any number of external configurations and still fall within the scope of the present invention. As illustrated, the upper portion  624  includes a generally rounded (or domed) portion  640  adjacent the top end  628 , and then a cylindrical portion  642  immediately adjacent the rounded portion  640 . The cylindrical portion  642  is generally hollow and extends downward sufficiently far enough so as to contain the spring  650 . The cylindrical portion  642  has a projection  660  that extends downward from the domed portion  640  to engage the spring  650  and maintain it centrally in the rocking mechanism  600 . The upper portion  624  has an inner surface  662  that has a circumferential ring  644  extending into the cylindrical portion  642  to engage the lower portion  670  as discussed below. 
     The rocking mechanism  600  also includes a spring  650 , the spring  650  having a first end  652  that is disposed against projection  660  of the upper portion  624 . The spring  650  is preferably a coil spring, but other configurations of the spring  650  are possible as well. The spring  650  has a second end  654  that engages the lower portion  670 . The lower portion  670  is generally cylindrical and has a flat top surface  672  to engage the second end (distal end)  654  of the spring  650 . Around the outside of lower portion  670  is an annular ring  674  to engage the circumferential ring  644  of the upper portion  624  to keep the spring  650  from separating the lower portion  670  from the upper portion  624 . The two rings  644 ,  674  engage one another, preventing the lower portion  670  from exiting the upper portion  624 . The two portions  624 ,  660  can be snap fit together. The bottom of the lower portion  670  is rounded as with the first two embodiments to assist in the rocking motion of the chair. 
     Rocking mechanism  800  is illustrated in  FIGS. 14-16 . Rocking mechanism  800  is configured to be inserted into the leg of a collapsible chair, rather than be on the end portion of a leg as with the prior embodiments. As such, rocking mechanism  800  has leg portions  22  connected to both ends thereof, with a foot  24  attached to the bottom leg  22 . Rocking mechanism  800  has an upper portion  802  that includes a cap  804  and a cylinder  806 . The cap  804  and the cylinder  806  are illustrated as two pieces but they could be made as one integral unit. The cap  804  and the cylinder  806  can be secured to one another by a press-fit, since the cap  804  has a lip  808  that engages the cylinder  806  to prevent the cap  804  from being inserted too far. Additionally, the cap  804  and the cylinder  806  can be attached to one another by any other method, such as with an adhesive, welded, ultrasonically welded, with screws or rivets, etc. The cap  804  has an opening  810  on the top side  812  thereof that is configured to receive the upper portion of the chair leg  22 . The top side  812  includes a cylindrical portion  814  that could have an opening therein to accept a securing member to secure the leg  22  in the opening  810 . Alternatively, the chair leg  22  can be secured into the opening  810  by a press-fit, adhesives, welding, etc. The underside of the cap  804  has a centrally located projection  816  that extends into the cylinder  806 . The projection  816  centers a spring  850  within an interior space  818  in the cylinder  806 . 
     The rocking mechanism  800  also has a lower portion  870  that is at least partially disposed within the interior space  818  of the cylinder  806  of the upper portion  802 . The lower portion  870  has a cup-shaped main portion  872  and a projection  874  extending from the bottom side  876  thereof. The projection  874  is configured to engage the lower leg  22 . As illustrated in  FIG. 16 , the projection  874  is inserted into the lumen of the leg  22 . However, the lower portion  870  may also be configured such that the leg  22  is inserted into an opening in the lower portion  870 . The main portion  872  is configured to receive an end  854  of the spring therein. The lower portion  870  is movable relative the upper portion  802  and in particular, the lower portion  870  slides up and down in the interior space  818  of the cylinder  806 . 
     To maintain the lower portion  870  in the upper portion  802 , a sealing member  830  is used. The sealing member  830 , similar to the cap  804 , is partially inserted into the interior space  818  of the cylinder  806 . The projection  874  protrudes through an opening  832  in the sealing member  830 . The opening  832  may also be large enough to allow the leg  22  to be inserted therein as well. The sealing member  830  may be secured to the cylinder  806  in any appropriate manner, as discussed above. 
     While it is noted that the upper leg  22  is inserted into the opening  810 , the rocking mechanism  800  can be inverted relative to the chair so that the lower leg  22  is inserted into the opening  810 . 
     Another embodiment of a rocking mechanism  900  is illustrated in  FIGS. 17-22 . The rocking mechanism  900  has a tubular housing  902  that defines an interior portion  904  extending between an upper end  906  and a lower end  908 . There is an upper cap  910  fixedly attached to the tubular housing  902  at the upper end  906 , the upper cap  910  is configured to engage the single chair leg (not shown). In one embodiment, the upper cap  910  has a first opening  912  in a top end  914 , the first opening  912  configured to receive at least a portion of the chair leg of the collapsible chair. The upper cap  910  may also have a second opening  916  configured to receive a securing member to engage and maintain the chair leg in the upper cap  910  as with other embodiments. Alternatively, the chair leg can be secured into the opening  912  by a press-fit, adhesives, welding, threaded-engagement, etc. The underside of the upper cap  910  has a centrally located projection  918  that extends into the interior portion  904 . The projection  918  centers a spring  920  within the interior portion  904  in the tubular housing  902 . 
     The rocking mechanism  900  also includes a lower cap  930  fixedly attached to the tubular housing  902  at the lower end  908 —in the same manner as noted above for the upper cap  910 . The lower cap  930  has an opening  932  therethrough to receive a second leg portion  934  that extends into the interior portion  904  of the tubular housing  902 . The lower cap  930  has an upwardly-directed flat surface  936 , the purpose of which is described in more detail below. Both the upper cap  910  and the lower cap  930  preferably have a lip to engage the upper end  906  and the lower end  908 , respectively. Referring to  FIG. 18 , the upper cap  910  has a lip  938  and the lower cap  930  has a lip  940 , which assist in maintaining the relationship of the upper cap  910  and the lower cap  930  with the tubular housing  902 . 
     The rocking mechanism  900  also includes a plunger  950  disposed within the interior portion  904  of the tubular housing  902 . The plunger  950  includes a base  952  that has a first or upper flat surface  954 . The first or upper flat surface  954  engages the spring  920 . See  FIG. 18 . On the opposite or second side of the base  952  is a lower surface  956 . Projecting outward from the lower surface  956  (and away from the upper flat surface  954 ) is a cylindrical extension  958 . The cylindrical extension  958  has an opening  960  therein to receive the second leg portion  934 . The second leg portion  934  may be secured in the opening  960  in any appropriate manner. 
     Extending radially outward from the cylindrical extension  958  is a plurality of tabs  962 . The plurality of tabs  962  are spaced around the cylindrical extension  958  such that a plurality of spaces  964  are created with one space  964  being disposed between each of the plurality of tabs  962 . Alternating spaces  964  are configured to receive a roller  966  therein. As illustrated, the plunger  950  has 5 rollers  966 , but there could be more or fewer rollers  966  and still come within the scope of the present invention. A roller pin  968  is inserted through a hole  970  in the roller  966  and secured in holes  972  in each of the plurality of tabs  962 . The rollers  966  extend beyond the edge of the base  952  so that the rollers can engage the inside surface of the tubular housing  902 . See  FIG. 20 . 
     Each of the plurality of tabs  962  has a top surface  974 . Preferably each of the top surfaces  974  is the same distance from the lower surface  956 , providing a flat surface  974 . As also visible in  FIG. 20 , the height of the top surface of the tabs  962  is higher than the diameters of the rollers  966 . Thus, the top surface  974  provides an surface to engage the upwardly-directed flat surface  936  of the lower cap  930 . See  FIG. 18 . It is also preferable that each of the plurality of tabs  962  also engages the lower surface  956  of the opposite or second side of the base  952 . 
     In operation, the rocking mechanism  900  allows for a collapsible chair to become a rocking chair. Preferably, the rocking mechanism  900  is used on two of the back legs of the collapsible chair. The rocking mechanism  900  uses a portion of the legs of the collapsible chair and then the second leg portion  934 , with a foot  980 . When the chair user sits in the chair and begins to rock the second leg portion  934  and the plunger  950  are moved relative to the tubular housing  902 . The spring  920  may only compress so far when the plunger  950  is moved toward the upper cap  910 . On the return, the lower cap  930  prevents the plunger  950  from exiting the tubular housing  902  as the top surface  974  provides an surface to engage the upwardly-directed flat surface  936  of the lower cap  930 . As can be seen in  FIG. 18 , the spring  920  is under a slight compression even with no weight applied—the spring is touching both the plunger  950  and the upper cap  910 , thus requiring there to be some compression of the spring  920 . 
     An alternative version of a plunger  1050  according to the present invention is illustrated in  FIGS. 23-25 . The plunger plunger  1050  includes a base  1052  that has a first or upper flat surface  1054 . The first or upper flat surface  1054  engages the spring  920  as in the previous embodiment. On the opposite or second side of the base  1052  is a lower surface  1056 . Projecting outward from the lower surface  1056  is a cylindrical extension  1058 . The cylindrical extension  1058  has an opening  1060  therein to receive the second leg portion (not shown). The second leg portion may be secured in the opening  1060  in any appropriate manner. 
     Extending radially outward from the cylindrical extension  1058  is a plurality of tabs  1062 . The plurality of tabs  1062  are spaced around the cylindrical extension  1058  such that a plurality of spaces  1064  are created, one space  1064  is disposed between each of the plurality of tabs  1062 . Alternating spaces  1064  are configured to receive a roller  1066  therein. As illustrated, the plunger  1050  also has 5 rollers  1066 , but there could be more or fewer rollers  1066  and still come within the scope of the present invention. Rather than each of the rollers  1066  each having its own roller pin, all of the rollers  1066  are disposed on single wire  1068  using the holes  1070  in the rollers  1066 . See  FIG. 24 . Additionally, each of the plurality of tabs  1062  have a slot  1072 . The wire  1068  with the rollers  1066  is then inserted into the slots  1072  with the rollers  1066  disposed in the appropriate space  1064 . Preferably the wire  1068  is formed in a generally round configuration (more of a pentagon than a true circle), but having a diameter that is smaller when not installed in the plunger  1050  than when it is. Thus, the wire  1068  is biased inwardly toward the cylindrical extension  1058  to retain the rollers in the plunger  1050 . Additionally, the rollers  1066  extend beyond the edge of the base  1052  so that the rollers can engage the inside surface of the tubular housing. 
     Another embodiment of a rocking mechanism  1100  is illustrated in  FIGS. 26-29 . The rocking mechanism  1100  has a tubular housing  1102  that defines an interior portion  1104  extending between an upper end  1106  and a lower end  1108 . There is an upper cap  1110  fixedly attached to the tubular housing  1102  at the upper end  1106 , the upper cap  1110  is configured to engage the single chair leg (not shown). In one embodiment, the upper cap  1110  has a first opening  1112  in a top end  1114 , the first opening  1112  configured to receive at least a portion of the chair leg of the collapsible chair. The upper cap  1110  may also have at least one second opening  1116  (two are illustrated in  FIG. 26 ) configured to receive a securing member to engage and maintain the chair leg in the upper cap  1110  as with other embodiments. Alternatively, the chair leg can be secured into the opening  1112  by a press-fit, adhesives, welding, threaded-engagement, etc. The underside of the upper cap  1110  has a centrally located projection  1118  that extends into the interior portion  1104 . The projection  1118  centers a spring  1120  within the interior portion  1104  in the tubular housing  1102 . 
     The rocking mechanism  1100  also includes a lower cap  1130  fixedly attached to the tubular housing  1102  at the lower end  1108 —in the same manner as noted above for the upper cap  1110 . The lower cap  1130  has an opening  1132  therethrough to receive a second leg portion  1134  that extends into the interior portion  1104  of the tubular housing  1102 . The lower cap  1130  has an upwardly-directed flat surface  1136 , to engage the plunger. Both the upper cap  1110  and the lower cap  1130  preferably have a lip to engage the upper end  1106  and the lower end  1108 . Referring to  FIG. 26 , the upper cap  1110  has a lip  1138  and the lower cap  1130  has a larger lip  1140 , which assist in maintaining the relationship of the upper cap  1110  and the lower cap  1130  with the tubular housing  1102 . The lower cap  1130  may also have a set screw  1142  that allows the rocking mechanism  1100  to be locked—if the set screw  1142  engages the second leg portion  1134 , then the rocking mechanism  1100  can not rock. 
     The rocking mechanism  1100  also includes a plunger  1150  disposed within the interior portion  1104  of the tubular housing  1102 . The plunger  1150  includes a base  1152  that has a first or upper flat surface  1154 . The first or upper flat surface  1154  engages the spring  1120 . The upper flat surface  1154  may also have an opening  1162  extending downward into the base  1152 . See  FIG. 28 . On the opposite or second side of the base  1152  is a lower surface  1156 . Projecting outward from the lower surface  1156  is a cylindrical extension  1158 . The cylindrical extension  1158  has an opening  1160  therein to receive the second leg portion  1134 . The second leg portion  1134  may be secured in the opening  1160  in any appropriate manner. 
     The rocking mechanism  1100  has at least one or more grooves  1164  that encircle or circumscribe the plunger  1150 . The grooves  1164  may be broken into a number of smaller grooves, each of which do not completely encircle the base member  1152 . Inserted into each of the grooves  1164  are a plurality of ball bearings  1168 . The number of ball bearings in the grooves  1164  can differ, depending on the size of the ball bearings  1168 . Preferably each of the ball bearings  1168  extend beyond the edge of the base  1152  so that the ball bearings  1168  can engage the inside surface of the tubular housing  1102 . The ball bearings  1168  are also retained in the grooves  1164  by the inside surface of the tubular housing  1102 . However, it is conceivable that the grooves  1164  could be configured to assist in retaining the ball bearings through a lip in the grooves  1164 . 
     Another embodiment of a rocking mechanism  1200  is illustrated in  FIGS. 30-36 . The rocking mechanism  1200  includes a foot portion  1202  that forms the base of the rocking mechanism  1200 . The foot portion  1202  has a bottom  1204  that is preferably closed and an outside surface  1206  makes contact with the ground or other floor-type surface (not shown) on which the collapsible chair is placed. The outside surface  1206  may therefore have any number of surface treatments to assist in keeping the chair from any slippage on the surface if so desired. The foot portion  1202  also has side walls  1208  extending from the bottom  1204  to an open top  1210 . As can be seen in the figures, and particularly in  FIG. 34 , the side walls  1208  and the bottom  1204  appear to be seamless in the figures—that is all one piece that is formed all at the same time without any subsequent connection of any individual parts. However, the foot portion  1202  may also be made from a plurality of individual side walls and a bottom portion that are connected and joined together to form the foot portion  1202 . As best illustrated in  FIG. 32 , the rocking mechanism  1200  and, in particular, the foot portion  1202  are curved to allow for the rocking motion of a collapsible chair (not shown). The collapsible chair would have regular front legs, that would be pivot point for the rocking motion. 
     The foot portion  1202  also has an open top  1210  to allow for access into an internal cavity  1212  that is formed by the bottom  1204  and the side walls  1208  extending between the bottom  1204  and the open top  1210 . The internal cavity  1212  has a curvature that corresponds to the curvature of the foot portion  1202  and is illustrated in  FIG. 34  as having a radius R, which may be about 50 cm. Naturally, this radius could be different (either larger or smaller) depending on the size of the chair, length of the chair legs, etc. On the inside surface  1214  of the bottom  1204  of the foot portion  1202  is an elastic member extension  1216  that extends from the bottom  1204  upward into the internal cavity  1212 , whose use is explained below. 
     The open top  1210  and internal cavity  1212  receive a leg receiving member  1220  therein. The leg receiving member  1220  has an upper side  1222  and a lower side  1224 . Between the upper side  1222  and the lower side  1224 , the leg receiving member  1220  has a middle portion  1226  with a circumference that is generally configured to be the same shape and size as the internal cavity  1212 , allowing the leg receiving member  1220  to move within the internal cavity  1212 . The thickness of the middle portion  1226  maybe thicker or thinner than that illustrated in the figures. The thickness (relative or absolute) may depend on the curvature of the foot portion  1202  (a smaller radius may require a thinner middle portion), the size of the chair legs, the material from which it is made, etc. The upper side  1222  of the leg receiving member  1220  slopes upward from the middle portion  1226  to a central conical area that forms an opening  1230  to receive a portion of a leg of a chair therein. The leg of the chair may be secured within the opening  1230  in any known manner. However, holes  1232  in the upper side  1222  of the leg receiving member  1220  adjacent to the opening  1230  provide a way to connect the leg receiving member  1220  to the portion of the leg by way of rivets, a pin, or any other acceptable method. Alternatively, the two pieces could be connected by ultrasonic welding, adhesives, or other mechanical means of connecting the two pieces to one another. 
     The other side of the leg receiving member  1220  is the lower side  1224  and has a depression  1234  therein to receive and center a portion of an elastic member  1240  that is placed in the internal cavity  1212  between the inside surface  1214  of the bottom  1204  and the lower side  1224  of the leg receiving member  1220 . The elastic member  1240  is illustrated as a coil spring  1240  that biases the leg receiving member  1220  toward the open top  1210  of the rocking mechanism  1200 . Other types of resilient elements could be used in place of the coil spring, e.g., a urethane spring.  FIG. 35  illustrates that the elastic member extension  1216  is disposed inside the coil spring  1240  to keep the end of the coil spring  1240  from moving around within the internal cavity  1212  during operation of the rocking mechanism  1200 . It should be noted that the elastic member  1240  it&#39;s preferably under at least some compression (i.e., preloaded) when the leg receiving number  1220  is as high (towards the open top  1210 ) in the foot portion  1202  and when there is no force in a downward direction (toward the bottom  1204 ). The amount of compression can vary by the size, length, and/or compression coefficient of the elastic member  1240 . 
     The leg receiving member  1220  also has at least one guiding member  1250  extending from opposing sides of the middle portion  1226  of the leg receiving member  1220 . As illustrated, there are preferably two of the guiding members  1250  extending from opposing sides of the middle portion  1226  of the leg receiving member  1220  for a total of four guiding members  1250 . These guiding members  1250  preferably have a head portion  1252  and a threaded portion  1254  to allow for them to be securely inserted into corresponding threaded openings  1256  in the leg receiving member  1220 . The head portion  1252  extends outwardly away from and beyond the leg receiving member  1220  and into an elongated opening  1260  in the side walls  1208 . Preferably, there is an elongated opening  1260  on each side of the foot portion  1202 , but there may also be only one opening on one side. Additionally, the two guiding members  1250  could also be side-by-side and there be two of the elongated openings on each side of the foot portion  1202 . The elongated opening  1260  extends from adjacent the bottom  1204  upwards toward the open top  1210 . As seen in  FIG. 32 , the elongated opening  1260  has curvature that corresponds to the curvature of the internal opening  1210  and has the same curvature—radius R. The guiding members  1250  keep the leg receiving member  1220  moving along the curvature and prevents the leg receiving member  1220  from being pushed out of the open top  1210 . While the guiding members  1250  do not rotate relative to the foot portion  1202  or the leg receiving member  1220 , they could have a bushing or other configuration that allows a portion of the guiding members  1250  to rotate relative to the foot portion  1202  or the leg receiving member  1220 . 
     In order to assemble the rocking mechanism  1200 , the foot portion  1202  has an elastic member  1240  that is placed into the internal cavity  1212  and around the elastic member extension  1216 . The leg receiving member  1220  is inserted into the open top  1210  and pushed downward so that the threaded openings  1256  in the leg receiving member  1220  are aligned with the elongated openings  1260 , where the guiding members  1250  can be inserted into the leg receiving member  1220 . The leg of the collapsible chair is attached to the rocking mechanism  1200 . 
     Another embodiment of a rocking mechanism  1400  is illustrated in  FIGS. 37-43 . The rocking mechanism  1400  includes a foot portion  1402  that forms the base of the rocking mechanism  1400 . See  FIG. 43 . The foot portion  1402  has a bottom  1404  that is preferably closed and an outside surface  1406  makes contact with the ground or other floor-type surface (not shown) on which the collapsible chair is placed. The outside surface  1406  may therefore have any number of surface treatments to assist in keeping the chair from any slippage on the surface if so desired. The foot portion  1402  also has side walls  1408  extending from the bottom  1404  to an open top  1410 . As can be seen in the figures, and particularly in  FIGS. 41-42 , the side walls  1408  and the bottom  1404  appear to be seamless in the figures—that is all one piece that is formed all at the same time without any subsequent connection of any individual parts. However, the foot portion  1402  may also be made from a plurality of individual side walls and a bottom portion that are connected and joined together to form the foot portion  1402 . As best illustrated in  FIG. 39 , the rocking mechanism  1400  and, in particular, the foot portion  1402  are curved to allow for the rocking motion of a collapsible chair (not shown). The collapsible chair would have regular front legs, that would act as the pivot point for the rocking motion. 
     The foot portion  1402  also has an open top  1410  to allow for access into an internal cavity  1412  that is formed by the bottom  1404  and the side walls  1408  extending between the bottom  1404  and the open top  1410 . The internal cavity  1412  has a curvature that corresponds to the curvature of the foot portion  1402  and is illustrated in  FIG. 41  as having a radius R, which may be about 50 cm. Naturally, this radius could be different (either larger or smaller) depending on the size of the chair, length of the chair legs, etc. On the inside surface  1414  of the bottom  1404  of the foot portion  1402  is an elastic member extension  1416  that extends from the bottom  1404  upward into the internal cavity  1412  and whose use is explained below. 
     The open top  1410  and internal cavity  1412  receive a leg receiving member  1420  therein. The leg receiving member  1420  has an upper side  1422  and a lower side  1424 . Between the upper side  1422  and the lower side  1424 , the leg receiving member  1420  has a middle portion  1426  with a circumference that is generally configured to be the same shape and size as the internal cavity  1412 , allowing the leg receiving member  1420  to move within the internal cavity  1412 . The thickness of the middle portion  1426  maybe thicker or thinner than that illustrated in the figures. The thickness (relative or absolute) may depend on the curvature of the foot portion  1402  (a smaller radius may require a thinner middle portion), the size of the chair legs, the material from which it is made, etc. The upper side  1422  of the leg receiving member  1420  slopes upward from the middle portion  1426  to a central conical area that forms an opening  1430  to receive a portion of a leg of a chair therein. The leg of the chair may be secured within the opening  1430  in any known manner. However, holes  1432  in the upper side  1422  of the leg receiving member  1420  adjacent to the opening  1430  provide a way to connect the leg receiving member  1420  to the portion of the leg by way of rivets, a pin, or any other acceptable method. Alternatively, the two pieces could be connected by ultrasonic welding, adhesives, or other mechanical means of connecting the two pieces to one another. 
     The other side of the leg receiving member  1420  is the lower side  1424  and has a depression  1434  therein to receive and center a portion of an elastic member  1440  that is placed in the internal cavity  1412  between the inside surface  1414  of the bottom  1404  and the lower side  1424  of the leg receiving member  1420 . The elastic member  1440  is illustrated as a coil spring  1440  that biases the leg receiving member  1420  toward the open top  1410  of the rocking mechanism  1400 . Other types of resilient elements could be used in place of the coil spring, e.g., a urethane spring.  FIG. 42  illustrates that the elastic member extension  1416  is disposed inside the coil spring  1440  to keep the end of the coil spring  1440  from moving around within the internal cavity  1412  during operation of the rocking mechanism  1400 . It should be noted that the elastic member  1440  is preferably under at least some compression (i.e., preloaded) when the leg receiving number  1420  is as high (towards the open top  1410 ) in the foot portion  1402  and when there is no force in a downward direction (toward the bottom  1404 ). The amount of compression can vary by the size, length, and/or compression coefficient of the elastic member  1440 . 
     Referring to  FIGS. 42 and 43 , the leg receiving member  1420  also has at least one guiding member  1450  extending from opposing sides of the middle portion  1426  of the leg receiving member  1420 . As illustrated, there are preferably two of the guiding members  1450  extending from opposing sides of the middle portion  1426  of the leg receiving member  1420  for a total of four guiding members  1450 . These guiding members  1450  preferably have a roller portion  1452  and a threaded portion  1454  to allow the guiding members  1450  to be securely inserted into corresponding threaded openings  1456  in the leg receiving member  1420 . The threaded portion may also come from a brass insert that is either press-fit into the opening in the leg receiving member  1420  or insert molded in the leg receiving member  1420 . The guiding members  1450  extend outwardly away from and beyond the leg receiving member  1420  and into an elongated opening  1460  in the side walls  1408 . As noted in  FIG. 42 , the outside edge of the threaded portion  1454  does not extend beyond the edge of the elongated opening  1460 . The roller portion  1452  may loosely fit around the threaded portion  1542  or be a two piece roller that has ball bearings between the two pieces as illustrated in  FIG. 42 . 
     Preferably, there is an elongated opening  1460  on each side of the foot portion  1402 , but there may also be only one opening on one side. The elongated openings  1460  preferably have covers  1460   a  and  1460   b , but they may also remain open. The covers  1460   a / 1460   b  are added to keep debris and other unwanted material out of the internal cavity  1412 . The covers  1460   a / 1460   b  are preferably shaped to be streamlined with the rest of the foot portion  1402 . The covers  1460   a / 1460   b  are removably attached. As illustrated in  FIG. 43 , the covers  1460   a / 1460   b  have tabs  1462  and the foot portion  1402  has openings  1466 , the tabs frictionally engaging the foot portion  1402  around the openings  1466 . Other methods of securing the covers  1460   a / 1460   b  are also within the scope of the present invention. 
     Additionally, the two guiding members  1450  could also be side-by-side and there be two of the elongated openings on each side of the foot portion  1402 . The elongated opening  1460  extends from adjacent the bottom  1404  upwards toward the open top  1410 . As seen in  FIG. 41 , the elongated opening  1460  has curvature that corresponds to the curvature of the internal opening  1410  and has the same curvature—radius R. The guiding members  1450  keep the leg receiving member  1420  moving along the curvature and prevents the leg receiving member  1420  from being pushed out of the open top  1410 . 
     In order to assemble the rocking mechanism  1400 , the foot portion  1402  has an elastic member  1440  that is placed into the internal cavity  1412  and around the elastic member extension  1416 . The leg receiving member  1420  is inserted into the open top  1410  and pushed downward so that the threaded openings  1456  in the leg receiving member  1420  are aligned with the elongated openings  1460 , where the guiding members  1450  can be inserted into the leg receiving member  1420 . The leg of the collapsible chair is attached to the rocking mechanism  1400 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.