Our Ref: 5018Inno P/00/009 Regulation 3.2 AUSTRALIA Patents Act 1990 INNOVATION SPECIFICATION FOR AN INVENTION ENTITLED Invention title: Chair with pre-pressing structure Name of Applicant: Wen-Shan Ko Address for Service A.P.T. Patent and Trade Mark Attorneys PO Box 222 Mitcham, S.A. 5062 The invention is described in the following statement: CHAIR WITH PRE-PRESSING STRUCTURE BACKGROUND OF THE INVENTION 1. Field of the Invention 5 The present invention relates generally to a chair, and more particularly to an innovative chair with a pre-pressing structure for extending service life thereof. 2. Description of the Related Art There are currently available a variety of chairs, which are designed functionally to meet the requirements of ergonomics and to improve convenience. 10 Generally, the seat back is permanently assembled with a seat cushion, so the users have to maintain a fixed posture, leading to a lack of flexibility in practice. For this problem, a chair with an elastic mechanism has been developed recently; namely, an elastic mechanism is arranged between the seat cushion and seat back, so that the seat back enables comfortable and flexible seating via the torsional force of the elastic 15 mechanism. Thus, to overcome the aforementioned problems of the prior art, it would be an advancement in the art to provide an improved structure that can significantly improve efficacy. Therefore, the inventor has provided the present invention of practicability 20 after deliberate design and evaluation based on years of experience in the production, development and design of related products. SUMMARY OF THE INVENTION There is enhanced efficacy of the present invention. Based on the unique present invention, a chair is mainly composed of the 25 main body and pre-pressing structure. The pre-pressing member's permanent seat is 2 arranged onto the backingplate's assembly surface of the main body, and the pre-pressing member is assembled onto the pre-pressing member's permanent seat, so that the main body presents elastic restoring force. Moreover, the multi-segment directional bulge of the pre-pressing member is correspondingly mated with the 5 multi-segment directional groove of the pivoted seat, so the circular elastic member of the pre-pressing member can obtain a torsional restoring force, thereby enhancing the structural strength, improving the durability and extending the service life of the chair. Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and 10 variations can be made without departing from the spirit and scope of the invention as hereinafter claimed. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an assembled perspective view of the present invention that the pre-pressing structure is applied to the chair. 15 FIG. 2 shows an exploded perspective view of the pre-pressing structure of the present invention. FIG. 3 shows a top plan view of the present invention, showing the pre-pressing structure assembled. FIG. 4 shows a sectional view of the present invention, showing the 20 pre-pressing structure unassembled. FIG. 5 shows a top plane view of the present invention, showing the pre-pressing structure assembled. FIG. 6 shows a sectional view of the present invention, showing the pre-pressing structure assembled in two segments. 25 FIG. 7 shows a schematic view of the application of the pre-pressing 3 structure of the present invention. DETAILED DESCRIPTION OF THE INVENTION FIGS. 1-4 depict preferred embodiments of a chair of the present invention with pre-pressing structure. The embodiments are provided for only explanatory 5 purposes with respect to the patent claims. The chair comprises a main body 10, including at least a backing plate 11 with an assembly surface 111 as well as supports 12. The main body 10 is fitted with a pre-pressing structure 20, so that the main body 10 presents elastic restoring force. The pre-pressing structure 20 comprises at least a pre-pressing member's 10 permanent seat 21 ,arranged onto the assembly surface 111 of the backing plate 11. The pre-pressing member's permanent seat 21 is provided with a chamber 210. The pre-pressing member 20 also comprises at least a pre-pressing member 22, assembled into the chamber 210 of the pre-pressing member's permanent seat 21. The pre-pressing member 22 contains a limiting seat 221, a circular elastic member 222 and 15 a multi-segment directional bulge 223. The chair includes at least a pivoted seat 23, which is provided with a multi-segment directional groove 233 that is interlocked with the multi-segment directional bulge 223, so the circular elastic member 222 can obtain a torsional restoring force. Moreover, a pre-pressing locator 30 is used to realize a pre-pressing 20 locating. The pivoted seat 23 is fitted with an inserting portion 234 for inserting into the support 12 of the main body 10. The pre-pressing locator 30 is arranged onto the locating bulge 31 of the limiting seat 221 and also into an embedding groove 32 of the pivoted seat 23. The width of the embedding groove 32 is bigger than that of the locating bulge 31, along 25 with an angle difference, so the locating bulge 31 can be forcibly turned to an angle 4 and embedded into the embedding groove 32 of the pivoted seat 23, thus forming a tilting space (shown in FIG. 7), and enabling the users to swing flexibly within it ergonomically and comfortably. The backing plate 11 is applied to either of the seat back or seat cushion of 5 the chair 10. The present invention is applied to the seat back of the chair 10 for providing elastic restoring force. The multi-segment directional bulge 223 and multi-segment directional groove 233 are of a criss-crossed or polygonal shape. Based upon above-specified structures, the present invention is operated as 10 follows: Referring to FIGS. 3, and 4, the limiting seat 221 of the pre-pressing member 22 is embedded into the chamber 210 of the pre-pressing member's permanent seat 21. In such a case, the multi-segment directional bulge 223 is protruded from one side of the limiting seat 221, next the multi-segment directional groove 233 of the pivoted seat 15 23 is inserted partially into the multi-segment directional bulge 223, such that the other part of the multi-segment directional bulge 223 is protruded out of the pivoted seat 23(shown in FIG. 6(a)). In such a state, the locating bulge 31 has an angle difference with the embedding groove 32. Then, the pivoted seat 23 is turned anticlockwise to an angle, and the multi-segment directional groove 233 will drive the multi-segment 20 directional bulge 223 to rotate anticlockwise, enabling the anticlockwise rotation of the circular elastic member 222 in a pre-pressing state. In such a case, the locating bulge 31 is positioned correspondingly to the embedding groove 32, so that the locating bulge 31 can be embedded into the embedding groove 32, and the locating bulge 31 of the limiting seat 221 is driven to be abutted onto one side of the embedding groove 32 25 via the circular elastic member 222 (the locating bulge 31 is abutted onto left side of 5 the embedding groove 32 as shown in FIG. 7). Meanwhile the multi-segment directional groove 233 is fully inserted into the multi-segment directional bulge 223 (shown in FIG.6(b)) for a pre-pressing state (referring also to FIG. 5). Finally, the inserting portion 234 is inserted into the support 12 of the main body 10 for elastic 5 assembly. The pre-pressing structure 20 of the present invention is assembled onto the seat back of the chair. In the practice, the user sits on the seat cushion, when the seat back is tilted backwards, the locating bulge 31 of the pre-pressing locator 30 is rotated clockwise in line with the tilting angle, and the circular elastic member 222 is driven to 10 rotate for accumulating elastic restoring force, allowing the seat back to swing within the tilting space. When the user leaves from the seat back, the locating bulge 31 could drive the seat back for resetting via the elastic restoring force of the circular elastic member 222. In such a way, the user could sit on chair comfortably with tilting or swinging functions. 15 As the width of the embedding groove 32 is bigger than that of the locating bulge 31, the tilting angle of the seat back could be adapted to the size of me embedding groove 32 with angle limitation (referring also to FIG. 7). 6