Patent Publication Number: US-8109564-B2

Title: Seat self-lifting device for portable chair

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a seat lifting device, and more particularly to a seat self-lifting device for a portable chair. 
     2. The Prior Arts 
     A conventional collapsible and portable chair usually uses two pivotal structures to pivotally connect the seat to an inner side of the front leg, such that the seat can flip upward. In particular, the seat can be managed from a horizontal deployed position to a vertical collapsed position by manually flipping the seat. Because such operation is cumbersome, certain portable chairs include a seat collapsing mechanism. The conventional seat collapsing mechanism usually includes a tension spring whose one end is connected with a bottom of a seat frame and another end of the spring is connected with the front leg. When the seat is in a horizontal deployed position, the spring is extended. When the pressing force to deploy the seat is released, the extended spring is released to flip the seat to the vertical collapsed position. However, using the tension spring has the following drawbacks. (1) Some of the portable chairs are provided with abutting elements to prevent the seat from over-flipping. The spring may flip the seat too fast, which causes the seat to impact against the abutting elements of the portable chair and therefore makes noise. (2) The seat collapsing mechanism is entirely exposed under the seat, which is likely to injure the user. (3) The tension spring is more likely to subject to elastic fatigue or being over-stretched, which results in malfunction of collapsing operation. 
     SUMMARY OF THE INVENTION 
     A primary objective of the present invention is to provide a seat self-lifting device for a portable chair that overcomes the aforementioned disadvantages of the conventional designs. The seat self-lifting device can automatically lift a seat after the user stands up without folding the portable chair. The seat is lifted in a gentler manner, without making annoying noise. Moreover, the seat self-lifting device includes a cap that covers the entire seat self-lifting device and prevents the user from injuries. In addition, the seat self-lifting device uses a spiral spring, which is more rigid and less subject to elastic fatigue, preventing the conventional drawbacks. 
     To accomplish the objectives mentioned above, a seat self-lifting device for a portable chair according to the present invention is disposed between the seat and the front leg. The seat self-lifting device comprises a rotary axle, a spiral spring and a fixing rod. The rotary axle passes through the front leg and connects with a connecting plate mounted on the seat frame. The fixing rod is perpendicularly mounted on the front leg. The spiral spring has a first end connected with the rotary axle, and a second end wrapped around the fixing rod. When the seat is deployed, the rotary axle is rotated along a direction and the second end of the rotary axle presses on a first point on the fixing rod, causing the spiral spring to deform and accumulate a resilient force. When the user leaves the seat, the resilient force is released and the rotary axle rotates along a reverse direction to flip the seat to a collapsed state. 
     Instead of using a tension spring as conventional design, the seat self-lifting device according to the present invention uses a spiral spring that can provide a gentler driving force and a longer service life. As a result, the seat self-lifting device is more reliable in operation. 
     Because the second end of the spiral spring is wrapped around the fixing rod, when the seat flips to cause the second end of the spiral spring to contact with a second point on the fixing rod for stopping rotation of the seat. Excessive rotation of the seat causing its collision against abutting portions on the portable chair can be thereby prevented, eliminating annoying noise. 
     Furthermore, the seat self-lifting device may further include a cap that is fixed on the fixing rod by a fastener assembly. The cap can cover the entire seat self-lifting device, preventing accidental injury by direct contact with the seat self-lifting device. 
     Compared to the conventional designs, the seat self-lifting device of the present invention operates in a gentler manner, does not produce annoying noise, is safer and has a longer service life. In addition to the collapsible and portable chair, the seat self-lifting device according to the present invention may also be used in other types of chairs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be apparent to those skilled in the art by reading the following detailed description of preferred embodiments thereof, with reference to the attached drawings, in which: 
         FIG. 1  is an exploded view illustrating a seat self-lifting device for a portable chair according to an embodiment of the present invention; 
         FIG. 1A  is an exploded view of the seat self-lifting device of  FIG. 1  in another viewing angle; 
         FIG. 2  is a perspective view showing the seat self-lifting device mounted on the portable chair according to the present invention; 
         FIG. 3  is a front view of the portable chair in a folded state of  FIG. 2 ; and 
         FIGS. 4-5  are schematic views illustrating operation of the seat self-lifting device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIGS. 1 ,  1 A and  2 , a seat self-lifting device for a portable chair according to an embodiment of the present invention include a pivotal structure  3  and a lifting device  4 . The pivotal structure  3  is connected between a seat frame  11  and a front leg  2  of the portable chair. The pivotal structure  3  includes a connecting plate  32  connected with the seat frame  11 , and a rotary axle  31 . The rotary axle  31  has two portions. A first portion of the rotary axle  31  is a semi-circular cylinder and a second portion of the rotary axle  31  is a circular cylinder. The connecting plate  32  has a fixing hole  321  having a semi-circular shape corresponding to the first portion of the rotary axle  31 . The first portion of the rotary axle  31  passes through the front leg  2  and the fixing hole  321  of the connecting plate  32 . The second portion of the rotary axle  31  is exposed from a surface of the front leg  2 . The connecting plate  32  can thereby rotate along with the rotary axle  31 , which prevents free rotation of the rotary axle  31  in the fixing hole  321  that may cause flipping of a seat  1 . The first portion of the rotary axle  31  may have a non-circular cross section other than the semi-circular one, as long as it can prevent the free rotation of the rotary axle  31 . The lifting device  4  is mounted on the surface of the front leg  2  by the rotary axle  31 . The lifting device  4  can lift the seat  1  to a collapsed state when the user leaves the seat  1 . 
     The lifting device  4  may be assembled on a reinforcing piece  46 . The reinforcing piece  46  have a width and a thickness corresponding to a width and a depth of a channel  21  of the front leg  2 , and the reinforcing piece  46  is soldered in the channel  21 , thereby reinforcing the strength of the lifting device  4 . The lifting device  4  includes a fixing rod  42  and a spiral spring  41 . The fixing rod  42  may be soldered perpendicular to the reinforcing piece  46 . The first portion of the rotary axle  31  laterally passes through the front leg  2  and the reinforcing piece  46 , and is assembled with the connecting plate  32 . The second portion of the rotary axle  31  is exposed on an outer side of the reinforcing piece  46 , and has a groove  311  that extends to a circumference surface thereof. A restoring force provided by the spiral spring  41  is gentler than that provided by a tension spring. Moreover, the spiral spring  41  allows a longer service life. The spiral spring  41  has two ends. A first end  411  of the spiral spring  41  is mounted on the rotary axle  31  and fixed in the groove  311 . The second end  412  of the spiral spring  41  is bent to an annular shape to wrap around the fixing rod  42 . The spiral spring  41  contacts with the surface of the reinforcing piece  46 , so that the spiral spring  41  is indirectly mounted on the front leg  2 . In order to prevent a user from being injured by the lifting device  4  exposed outside the front leg  2 , a cap  43  is assembled to cover the fixing rod  42 , the rotary axle  31  and the spiral spring  41 . The cap  43  can have any suitable shape for covering the aforementioned elements. A first fastener assembly  44  including a bolt  441  and a nut  442  is used to attach the cap  43 . The bolt  441  passes from the outside through the cap  43 , and the nut  442  is tightly locked with the bolt  441  from the inner side of the cap  43  for preventing the bolt  441  from separating away from the cap  43 . The bolt  441  further engages with a threaded hole  421  at an end of the fixing rod  42 , thereby fixing the cap  43  on the fixing rod  42 . The first fastener assembly may include any suitable elements other than bolt and nut, such as rivets, pins, and like detachable or non-detachable fastener elements. In order to prevent oscillation of a lower portion of the cap  43 , the second portion of the rotary axle  31  may include a blind hole  312  for mounting a second fastener assembly  45 . The second fastener assembly  45  includes a bolt  451  and a nut  452 . The bolt  451  passes from the outside through the cap  43 . The nut  452  is engaged with the bolt  451 . Then, an end of the bolt  451  is inserted into the blind hole  312 , which prevents the lower portion of the cap  43  from oscillation. However, a diameter of the bolt  451  is slightly smaller than that of the blind hole  312  and the bolt  451  is not in contact with the inner sidewall of the blind hole  312  so that the rotation of the rotary axle  31  is not affected. The second fastener assembly may include any suitable elements other than the bolt and the nut, such as rivets, pins, and like detachable or non-detachable fastener elements.  FIG. 3  is a front view of the portable chair in a folded state. As the whole lifting device  4  is positioned outside the front leg  2 , it does not interfere with the folding of the rear leg  5  to a stowed position at the inner side of the front leg  2  and the flipping of the seat  1 . 
       FIGS. 4 and 5  are schematic views illustrating the operation of the seat self-lifting device for the portable chair according to the present invention, wherein the cap  43  is omitted from drawings for clear illustration. Referring to  FIG. 4 , when a user sits on the seat  1 , a downward pressure is applied on the seat  1 , which causes the connecting plate  32  to rotate the rotary axle  31  counterclockwise. As a result, the first end  411  of the spiral spring  41  is pulled to tighten the spiral spring  41  by the rotation of the rotary axle  31 . During the seat  1  being pressed down, the second end  412  of the spiral spring  41  presses against the point A of the fixing rod  42 . As the downward pressure is continuously applied on the seat  1 , the rotation of the rotary axle  31  causes the first end  411  of the spiral spring  41  to deform by radial contraction, until the seat  1  is entirely deployed to a horizontal position and rested on the rear leg  5 . Referring to  FIG. 5 , when the user leaves the seat  1 , the downward pressure on the seat  1  is removed. As a result, the elastic force of the spiral spring  41  causes the rotary axle  31  to rotate clockwise. The connecting plate  32  co-rotates with and rotary axle  31  and then the seat  1  flips upward until the second end  412  of the spiral spring  41  leaves the point A of the fixing rod  42  and abuts against the point B of the fixing rod  42 . The spiral spring  41  thereby completes its restoring movement. The seat  1  is no longer subject to the force and does not continue to flip rearward. The position of the groove  311  and the torque applied by the spiral spring  41  is related to each other. In the illustrated embodiment, the position of the groove  311  can be set such that the spiral spring  41  can cause the seat  1  to flip to an angular position of about 70 degrees. In this manner, a space clearance can be created for allowing passage, while collision between the seat  1  and the seat abutting portion provided on the chair owing to excessive rotation or rotating speed of the seat  1  can be prevented. As a result, chair damages and annoying noise due to collision of the retracted seat  1  can be eliminated. 
     Although the present invention has been described with reference to the preferred embodiment thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims.