An adjustable awning structure which can be assembled for use or disassembled for shipping and storage has two sides. The size of one or both sides of the canvas can be adjusted. The supporting angle of one or both sides of the canavas can also be adjusted. After being disassembled, the whole structure can be reduced to a small bundle for shipping and storage. The awning finds particular use for a user who travels quite often. Moreover, since the structure has a considerable supporting strength, the size of the canvas can be suitably varied, if necessary.

BACKGROUND OF THE INVENTION 
     Most of the conventional awnings are of the fixed type which may be classified into three categories, i.e. a one side type, a four-corner supporting type, and a two sloping side type. However, none of these types are adjustable. At most, the height of these may be adjusted. Since they are of the fixed structure, they are unable to meet the requirements of a travelling user, such as the ability to be set up, shipped and stored, etc. There is a sun umbrella recovered which can meet the aforesaid requirements, but its shading and covering area is limited as a result of its mechanical structure; in other words, it can not be used for covering a larger area because of its insufficient support structure. 
     SUMMARY OF THE INVENTION 
     This invention provides an adjustable awning structure, which comprises a main post assembly including main posts, supporting rods, and a fixing joint; a canvas setting-up structure including a canvas, a central shaft and canvas rods; a canvas driving mechanism including a housing, a worm, a crank, and a connecting pipe. The crank is used for driving the worm and the gear to rotate so as to cause the central shaft to roll up or unroll the canvas, and also to change the supporting angle of the supporting rod. Then, the slideable joint and extension rods are positioned. The aforesaid structure can also be used for adjusting the supporting angle of one side of the canvas awning, and for disassembling the whole structure for shipping and storing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the awning structure according to the present invention. 
     FIG. 2 is a disassembled view of the main post of the awning structure of the present invention. 
     FIG. 3 is a perspective view of the canvas set up on the awning structure according to the present invention. 
     FIG. 4 is a disassembled view of a driving mechanism to roll up the canvas of a recovered awning according to the present invention. 
     FIG. 5 is a perspective view of the awning of the present invention, being set up. 
     FIG. 6 illustrates the awning being recovered. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates an adjustable awning structure of the present invention which comprises three major assemblies, i.e. the main post, the canvas setting-up structure, and the canvas-driving mechanism. 
     The main post as shown in FIG. 2 includes: 
     two main posts 1, of which the lower ends are to be inserted into a hollow cylinder being either driven into the ground or mounted on a fixture, while the tops therof are each furnished with a fixing joint 11, and on the upper portion of the main posts 1, slideable joints 12 are mounted. Within the upper and lower sliding limits of the slideable joints, there are two stop rings 101 and one or several screw holes 102 spaced at regular intervals between the two stop rings. The screw hole may be a simple through hole or a groove extending around the main post. 
     The fixing joint 11 is directly fixed on the top end of each main post 1. The joint 11 may be replaced with a plate having two extended lugs with holes being welded on the top of the main post 1 so as to pivotally connect the supporting rods 13. 
     The slideable joint 12 with lugs is mounted between the upper and lower stop rings 101 and is to pivotally connected to the extension rods 14. The slideable joint 12 is also furnished with a screw hole 121 that is mated with a lock screw 122, which is to be screwed into the screw hole 102 or screwed against the main post 1 so as to fix the slideable joint 12 in position. 
     One end of the supporting rod 13 is pivotally connected to the fixing joint 11, while the other end thereof is furnished with a horizontal hollow cylinder 131 having a lock screw 132 for locking the canvas rod 23 in position. Under the middle portion of the supporting rod 13, there is a pair of joint lugs 133 for providing a pivotal connection for one end of the extension rod 14. The extension rod 14 includes outer and inner extension tubes, of which one end of the outer tube is furnished with an opened slot, some external threads and a coupling sheeve 141 so as to enable the outer and inner tubes connected together to adjust to a suitable length. The front end of the outer tube of the extension rod 14 is pivotally mounted to the lugs of the slideable joint 12. The upper end of the inner tube is pivotally mounted to the joint lugs 133 under the supporting rod 13. 
     After each main post 1, supporting rod 13 and the extension rod 14 are assembled together, the angle of between each supporting rod 13 and main post 1 can be determined by fixing the position of the slideable joint 12 and adjusting the length of the extension rod 14. The length of the two extension rods 14 may or may not be the same. 
     FIGS. 1 and 3 illustrate the canvas setting-up structure of the present invention, which includes a central shaft 2 having a round body portion and two ends shaped as square portions, an arc-shaped fastening strip 21 to be mounted with nails on the central shaft after the canvas 22 is mounted along the central shaft 2, and two canvas rods 23 being sleeved in the two canvas edges sewed into two sleeves respectively. Both ends of the two canvas rods 23 extend out of the canvas sleeves respectively so as to be inserted into the horizontal hollow cylinders 131 of the supporting rods 13 respectively. 
     FIG. 4 illustrates the canvas driving mechanism, which comprises a housing 3 made of two pieces in which the worm 31 and the gear 32 are mounted. The worm 31 engages with the gear 32 and has both ends thereof pivotally and fixedly monuted on the housing 3; the lower end thereof extends out of the housing 3 and comprises a hook ring 311 for engaging with a crank 33. The S-shaped crank 33 is used for driving the worm 31 to cause the gear 32 to rotate. 
     The connecting pipe 34 is substantially a T-shaped pipe of which the vertical portion is insertable into the fixing joint 11 on the top of the main post 1, while the horizontal portion thereof is optionally furnished with a fixing plate 341. As shown in FIG. 4, the horizontal portion is furnished with a fixing plate 341 so as to mount the housing 3 on the outer side thereof with the gear 32 and the horizontal portion of the connecting pipe 34 aligned coaxially. After the bearings 35 are mounted to the horizontal portion of the connecting pipe 34, the square end portion of the central shaft 2 can be mounted in the square hole of the gear 32 to complete a driving mechanism. Since the other end of the central shaft 2 has no driving mechanism, the other connecting pipe 34 is not mounted to a fixing plate 341 and a housing 3 but merely has a bearing 35 mounted to the horizontal portion of the connecting pipe 34 so as to accommodate the other end of the central shaft 2 therein. The connecting pipe offsets the central longitudinal axis of the shaft 2 from the pivotal connection between each supporting rod 13 and fixing joint 11. 
     Both of the ends of the central shaft 2 are mounted inside the horizontal portions of the two connecting pipes 34 on the top of the two main posts 1 respectively; one end of the central shaft 2 is further fitted into the gear 32 hole in the housing 3. Upon rotation of the crank 33, the worm 31 will drive the gear 32 to cause the central shaft 2 to rotate synchronously therewith. Since the canvas 22 is fixed on the central shaft 2, and the central longitudinal axis of the shaft 2 is offset from the pivotal connection between each supporting rod 13 and fixing joint 11 the rotation of the shaft 2 causes the canvas to roll up on or to unroll from the shaft so as to change the distance between the central shaft 2 and the two canvas rods 23 and to adjust the length of the extension rods 14. 
     FIG. 1 illustrates the awning structure being spread. The adjusting steps are that the coupling sleeves 141 of the extension rods 14 are first loosended, and the crank 33 is then rotated to adjust the spreading length of the canvas 22 so as to set the position of the supporting rod 13 (being pulled by the canvas), and then the position of the slideable joint 12 is fixed so as to fix the length of the extension rods 14 before they are locked in position. The length of the extension rods 14 may be adjusted so as to be different from each other if necessary. The supporting rod 13 may be comprised at one or more rods so as to allow the two canvas rods 23 to be set at different heights; in other words, the canvas 22 on either side of the central shaft 2 may be oriented at a different angle than that at the other side by merely adjusting the canvas rod 23 and the extension rod 14 without effecting the other canvas side. 
     FIG. 6 shows the awning structure of the present invention being recovered for storage. The canvas setting-up mechanism may be disassembled and rolled up and the canvas driving mechanism may also be removed from the main post 1. The slideable joint 12 may be slid down the lowest portion of the main post 1 so as to allow the extension rods 14 to become almost parallel with the main post 1 before pulling the main post out of the hollow cylinder 10. It is deemed that the present invention is an awning structure that is convenient and practical. Other modifications of the present invention will be apparent to those of ordinary skill in the art and are intended to be embraced by the true spirit and scope of the present invention as set forth in the appended claims.