You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to Chinese Patent Application No. 2014-20157253.5 filed on Apr. 2, 2014, the entire contents of which is incorporated herein for all purposes by this reference. 
     FIELD OF THE INVENTION 
     The present utility model relates to a tent structure, and particularly to a tent frame top connecting structure. 
     BACKGROUND OF THE INVENTION 
     As an outdoor leisure product, the tent has been widely applied to various occasions. Generally, a tent frame is composed of several groups of support poles which are connected with top levers. The top levers form a top support. Each top lever is movably connected to a connecting piece at the top of the tent frame. In order to achieve unfolding and folding the tent, the connecting structure at the top of the tent is always complicated in structure, difficult to assemble, and high in cost. 
     Chinese Utility Model CN201220405537.2 discloses a tent top connecting piece. The tent top connecting piece is provided with pivoting open grooves which are radially arranged and have a number corresponding to that of the tent top levers. Pivoting holes are arranged to penetrate two sheet bodies of the pivoting open grooves. With this tent top connecting piece, it is required to mount a connector at the head of the top lever and cooperate with the tent top connecting piece. During assembly, it is further required to pivotally connect the connector and the top connecting piece with a pin. Thus, the assembly process is relatively complicated. 
     Chinese Utility Model CN201220367790.3 of the present applicant discloses a tent rest connecting structure, in which an open groove is formed in a connecting piece, and a longitudinal positioning groove is respectively formed on each inner side of two sheet bodies of the open groove in a concave mode. With this connecting structure, it is also required to mount a connector at the head of the top lever to cooperate with the connecting structure. Therefore, there remains room for further improvement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view showing parts in a tent frame top connecting structure; 
         FIG. 2  is a bottom view of the tent frame top connecting structure; 
         FIG. 3  is a cross-sectional view along the line A-A in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view along the line B-B in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view along the line C-C in  FIG. 3 ; and 
         FIG. 6  is a cross-sectional view illustrating a process for assembling the tent frame top connecting structure. 
     
    
    
     The figures depict a connecting piece and one top lever. For clarity, depictions of other top levers are omitted throughout these figures. 
     Reference numerals used in the figures are identified as follows: connecting piece  1 ; connecting groove  11 ; sidewall  111 ; positioning groove  112 ; front longitudinal edge  113 ; curved stop surface  114 ; back longitudinal edge  115 ; curved surface  116 ; convex point  117 ; bump stopper  118 ; lateral wall  119 ; top lever  2 ; pin hole  21 ; and pin  3 . 
     DETAILED DESCRIPTION 
     The present utility model will be described hereinafter by referring to the accompanying drawings and specific embodiments. 
       FIGS. 1-6  depict a tent frame top connecting structure comprising a connecting piece  1  and top levers  2 . An inner end of top lever  2  having an inner-end cross-section is movably connected to connecting piece  1 . The inner end of top lever  2  is provided with a pin hole  21  for receiving a pin  3  having a pin cross-section (e.g., a diameter) and a pin length. The pin length is such that both ends of pin  3  protrude from pin hole  21 . Connecting piece  1  comprises connecting grooves  11 , which are radially arranged and have a number corresponding to that of the top levers  2 . Connecting grooves  11  cooperate with top levers  2 . In one embodiment, connecting piece  1  comprises four connecting grooves  11  and four top levers  2 . For simplicity of illustration, the figures illustrate an assembling relationship between connecting piece  1  and one of top levers  2 ; a skilled artisan will readily ascertain pertinent details relating to other top levers  2  not shown in the figures. 
     Connecting groove  11  includes a top portion, a lateral wall  119 , and first and second sidewalls  111 . Each sidewall  111  further comprises a longitudinal positioning groove  112  for engaging pin  3 , and through which pin  3  can pass. The pin length is sufficient to engage both longitudinal positioning grooves  112 . A bump stopper  118  is arranged at the top portion (e.g., including a mouth) of connecting groove  11 . In the embodiments shown in  FIGS. 1-6 , the top portion and bump stopper  118  are co-extensive. In another embodiment, the bump stopper may be located adjacent to positioning grooves  112 . In another embodiment, a bump stopper not co-extensive with the top portion may be located on sidewall  111 . A curved stop surface  114  is formed on a front longitudinal edge  113  of positioning groove  112 , and a curved surface  116  is formed on a back longitudinal edge  115  of positioning groove  112  as a moving fulcrum for pin  3 . Curved stop surface  114  further comprises a convex point  117  located a first distance from curved surface  116 , thereby forming a positioning space between convex point  117  and curved surface  116  sufficient to accommodate the pin cross section of pin  3 . A second distance between convex point  117  and back longitudinal edge  115  of positioning groove  112  is smaller than the cross-section of pin  3 . 
     Top lever  2  also serves as an installation tool. During assembly, pin  3  is inserted into pin hole  21  in top lever  2 , preferably such that both ends of pin  3  protrude from pin hole  21 . More preferably, both ends of pin  3  protrude to the same extent as one another from pin hole  21 . Referring to  FIG. 6 , top lever  2 , into which pin  3  has been inserted, is inserted downward (e.g., by rotating top lever  2  clockwise as indicated by the arrow in  FIG. 6 ) into connecting groove  11  of connecting piece  1 . Pin  3  moves along positioning groove  112  toward curved surface  116 . When pin  3  passes convex point  117  on curved stop surface  114 , convex point  117  and the surrounding material are elastically deformed to a certain extent. As a result, pin  3  is embedded and engaged in the positioning space for pin  3  between convex point  117  on positioning groove  112  and curved surface  116 . In this way, top lever  2  and connecting piece  1  are assembled and movably connected. 
     In one embodiment, the connecting position between top lever  2  and connecting piece  1  indicates a connecting position for the tent frame in a folded state. To unfold the tent, top lever  2  is rotated downward, depicted as a clockwise rotation according to the arrow in  FIG. 6 , so that the inner end of top lever  2  rests against bump stopper  118  as depicted in  FIG. 3 . In this way, tent frame top levers  2  and connecting piece  1  can be unfolded as shown in  FIG. 3 , and the top frame connecting structure thereby enters the unfolded state. 
     Although the invention has been described in connection with specific embodiments, variations of these embodiments will be obvious to those of ordinary skill in the art. For example, more or fewer connecting grooves  11  and top levers  2  than described may be arranged on connecting piece  1 , bump stopper  118  may be moved to a position adjacent to positioning grooves  112 . In another embodiment, sidewall  111  may further comprise a bump stopper. Other modifications and variations likewise fall within the scope of the appended claims. Therefore, the spirit and scope of the claims should not be limited to the foregoing description. 
     Only those claims specifically reciting “means for” or “step for” should be construed in the manner required under the sixth paragraph of 35 U.S.C. §112.

Summary:
Disclosed is a tent frame top connecting structure comprising top levers movably connected to a connecting piece, connecting grooves, positioning grooves, sidewalls, lateral walls, a top portion, a bump stopper, and a moving fulcrum. Top levers serve as installation tools. The structure is simple and convenient to assemble.