FIELD OF THE INVENTION 
     The present invention relates to an easel, and more particularly, to an easel allowing for adjustment of a tilt angle as desired and enabling to reliably maintain an adjusted tilt angle. 
     BACKGROUND OF THE INVENTION 
     Easels are generally used to hold drawing boards, photographs, pictures, menu blackboards, signboards, or the like to allow many people to view them. 
     Such easels usually include three support frames provided on both sides and at the center, a drawing board prop coupled to the front of the support frames, and a rear support frame coupled to the rear of the central support frame, among the three support frames, by means of a folding member. 
     Further, in the drawing board prop, after coupling bolts are led into the two support frames on both sides and the drawing board prop, coupling nuts are fastened to the coupling bolts. 
     Thus, the drawing board prop is used after the central support frame is lifted or lowered to fit the height of a user and fastened. 
     However, these general easels have a structure that the rear support frame supports the entirety of a load of painting materials including a canvas, or the like held on the drawing board prop with respect to the two support frames on both sides. 
     Thus, the rear support frame may fail to tolerate the load of the painting materials, opened with respect to the two support frames on both sides, to cause the easel to collapse. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an easel allowing for adjustment of a tilt angle as desired and enabling to reliably maintain an adjusted tilt angle. 
     In accordance with the invention, there is provided˜ 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which: 
         FIGS. 1 and 2  are perspective views illustrating an overall structure and an operational state of an easel according to an embodiment of the present invention; 
         FIG. 3  is a conceptual view viewed from a point ‘A’ in  FIG. 1 ; 
         FIGS. 4 to 7  are conceptual views sequentially illustrating a procedure of fixing a prop as a major part of the easel to a front support, as viewed from a point ‘D’ in  FIG. 2 , according to an embodiment of the present invention; and 
         FIGS. 8 to 15  are conceptual views illustrating a structure and an operational state of a tilting unit as a major part of the easel according to various embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with the accompanying drawings. 
       FIGS. 1 and 2  are perspective views illustrating an overall structure and an operational state of an easel according to an embodiment of the present invention. 
     As illustrated, it can be recognized that the present invention has a structure that front supports  200  and a rear support  300  are rotatably coupled to a main bracket  100 , a prop  400  is coupled to the front supports  200 , a lift  500  ascends and descends between the front supports  200  through the main bracket  100 , and a tilting unit  600  is coupled between the rear support  300  and the prop  400  to adjust a tilt angle. 
     For reference, unexplained reference numeral  700  in  FIGS. 1 and 2  denote a support clamp for stretching and fixing the front and rear supports  200  and  300 , and reference numeral  710  denotes a fixture. 
     Further, unexplained reference numeral  800  indicated by the dotted line in the main bracket  100  in  FIGS. 1 and 2  denotes an upper clamp for fixing a lift position of the lift  500  after adjusting the lift position. 
     The main bracket  100  is disposed in an upper portion of the easel according to an embodiment of the present invention to provide a rotation space of the front and rear supports  200  and  300  and a reciprocating space of the lift  500 . 
     The front supports  200  are rotatably installed on both sides of the front of the main bracket  100  and stretchable, and support a load of painting materials such as a canvas at the front. 
     The rear support  300  is rotatably installed in the rear of the main bracket  100  and stretchable, and distributedly supports a load of the painting materials such as a canvas together with the front supports  200  at the rear. 
     The prop  400  is detachably coupled to the front supports  200  on both sides thereof and allows a lower edge portion of the canvas to be mounted thereon for painting materials such as a canvas to be mounted with a cross-section having a shape of “           ”, “         ”, or “         ”, providing convenience such that an operator may work.
     The lift  500  is installed at the center of the front side of the main bracket  100  such that it ascends and descends, and a lower end thereof is supported by the prop  400 . Although not shown particularly, a fixture may be disposed at an upper end of the lift  500  to face the prop  400 , and the lift  500  may be appropriately lifted depending on the size of painting materials such as a canvas to fix the painting materials between the fixture and the prop  400 . 
     The tilting unit  600  is rotatably and stretchably coupled between the rear support  300  and the prop  400  to adjust a tilt angle of the rear support  300  with respect to the front supports  200 . When adjustment of a tilt angle is completed, the tilting unit  600  serves to fixedly maintain a tilt angle maintenance state of the rear support  300 . 
     In the present invention, it will be understood that the foregoing embodiment may be applied and various embodiments as follows may also be applied. 
     As described above, it can be recognized that the tilting unit  600  adjusts a tilt angle of the rear support  300  with respect to the front supports  200  and has a structure that includes first and second auxiliary brackets  611  and  612 , first and second rotational pieces  621  and  622 , and a pivot assembly. 
     The first auxiliary brackets  611  is coupled to the rear support  300  and connected to the first rotational piece  621 , and the second auxiliary bracket  612  is coupled to the prop  400  and connected to the second rotational piece  622 . 
     Here, the first auxiliary bracket  611  further includes a bracket fixing screw  611 ′ as shown in the enlarged part of  FIG. 2 , and an end portion of the bracket fixing screw  611 ′ is screw-coupled through the first auxiliary bracket  611  so as to be fixedly in contact with the rear support  300 , thus preventing the first auxiliary bracket  611  from running idle or moving with respect to the rear support  300 . 
     In this case, one end portion of the first rotational piece  621  is rotatably coupled to the first auxiliary bracket  611 , and one end portion of the second rotational piece  622  is rotatably coupled to the second auxiliary bracket  612 . 
     Further, the pivot assembly connects the other end portions of the first and second rotational pieces  621  and  622  to rotate the other end portions of the first and second rotational pieces  621  and  622  such that an angle can be adjusted, various embodiments of which will be described below in more detail. 
     Also, as illustrated in the enlarged part of  FIG. 2  and  FIG. 3 , the second auxiliary bracket  612  further has a release preventing bracket  613  having a wedge shape of “           ” or “         ” fixing edges of the upper end portion of the prop  400 .
     Further, the release preventing bracket  613  is fixed to an upper portion of the prop  400  by a fixing bolt  615  through a fixing hole  614  as illustrated in  FIGS. 4 to 7 . 
     The prop  400  will be described in detail. A plurality of adjustment holes  401  are formed at equal intervals on both sides of the prop  400  in a length direction such that the prop  400  is fixed by a bolt  701  in respective appropriate positions with the pair of front supports  200 , and a pair of fixing holes  614  are provided in a central portion of the prop  400  to fix the fixing bolt  615 . 
     Here, a lower portion of each of the adjustment holes  401  has a width greater than that of the upper portion of each of the adjustment holes  401 , and thus, a screw portion of the bolt  701  passes from the narrow upper portion and a head of the bolt  701  is fixedly in contact with the relatively wide lower edge. 
     In contrast, an upper portion of each of the fixing holes  614  has a width greater than a lower portion of each of the fixing holes  614 , and thus, a screw portion of the fixing bolt  615  passes from the narrow lower portion and a head of the fixing bolt  614  is fixedly in contact with the relatively wide upper edge. 
     It will be understood that structural shapes of the adjustment holes  401  and the fixing holes  614  may be variously applied and designed; that is, conversely, the adjustment holes  401  are formed such that an upper portion thereof is wider than a lower portion thereof and the fixing holes  614  are formed such that a lower portion is wider than an upper portion thereof. 
     When the adjustment holes  401  and the fixing holes  614  are formed to be reversed in their structural shapes as described above, the bolt  701  is pushed down so as to be fixed and the fixing bolt  614  is pushed up so as to be fixed, thus maintaining the upper and lower edges of the prop  400  in a firmly fixed state by the fixing bolt  615  and the bolt  701  together with the release preventing bracket  613  as illustrated in  FIG. 7 . 
     Then, the process of fastening the prop  400  will be described briefly as follows. 
     First, when a user inserts the fixing bolt  615  from the wide side of the fixing hole  614  and pushes down the release preventing bracket  613  in the arrow direction as shown in  FIG. 4 , the release preventing bracket  613  pushed down together with the fixing bolt  615  comes into contact with an upper edge of the prop  400  as shown in  FIG. 5 , the fixing bolt  615  is installed, and the release preventing bracket  613  is then tightly fixed to the prop  400 . 
     Next, the user appropriately adjusts an angle of the front supports  200 , inserts a bolt  701  into the adjustment hole  401  in an appropriate position, and then pushes up the bolt  701  to install it (in this case, the clamps  700  for supporting the rear of the support  400  (see  FIG. 7 ) are also adjusted in position) as shown in  FIG. 6 . Then, the prop  400  is firmly tightly fixed by the upper release preventing bracket  613 , the lower bolt  701 , and the rear supporting clamps  700  as shown in  FIG. 7 . 
     Meanwhile, as shown in  FIGS. 1, 2, and 8 , it can be recognized that the pivot assembly  630  includes a first rotary member  631  extending from the other end portion of the first rotational piece  621 , a second rotary member  632  rotating in contact with the first rotary member  631  and extending from the other end portion of the second rotational piece  622 , and a fixed piece  633  screw-coupled through the first and second rotary members  631  and  632  and having a handle formed in an end portion thereof. 
     Specifically, the user may grasp the fixed piece  633  and rotate the same in a direction opposite the screw-coupled direction to release a coupled state to allow the first and second rotary members  631  and  632  to freely rotate from each other, and then, the user may form a tilt angle of the rear support  300  with respect to the front supports  200  as desired, such as the states of  FIGS. 1 and 2 , and subsequently rotate the fixed piece  633  to lock it, maintaining the tilt angle. 
     Further, as illustrated in  FIGS. 9 and 10 , in the pivot assembly  640 , a tilt angle may be adjusted by a mutual contact coupling structure of contact recesses  643  and contact protrusions  644  between first and second rotary members  641  and  642 . 
     Specifically, the pivot assembly  640  includes the first rotary member  641  extending from the other end portion of the first rotational piece  621  and the second rotary member  642  rotating in contact with the first rotary member  641  and extending from the other end portion of the second rotational piece  622 . Here, the hemispherical contact recesses  643  are formed at equal intervals on a contact surface of the first rotary member  641  in contact with the second rotary member  642 , and the hemispherical contact protrusions  644  are formed at equal intervals on a contact surface of the second rotary member  642  in contact with the first rotary member  641 . 
     Here, the pivot assembly  640  includes a cylinder  645  protruding from the first rotary member  641  and the second rotary member  642  and allowing rotation, separately from rotation of the first and second rotary members  631  and  632 , wherein the cylinder  645  is stretchable. 
     This is because a spring  648  to be described later may be twisted to be damaged or deformed if the cylinder  645  rotates in conjunction with the first and second rotary members  641  and  642 . 
     As illustrated, the cylinder  645  includes a cylinder body  646  protruding from a central portion of the first rotary member  641  and a rod  647  protruding from a central portion of the second rotary member  642 , and the rod  647  contracts or stretches in an overall length as it insertedly enters or exits the cylinder body  646 . 
     Thus, as illustrated, the cylinder  645  includes the rod  647  protruding from the second rotary member  642  with respect to the cylinder body  646  protruding from the first rotary member  641  so as to insertedly enter or exit the cylinder body  646 , and here, preferably, the cylinder body  646  and the rod  647  have flanges  646 ′ and  647 ′ to rotate with respect to the first and second rotary members  641  and  642 , respectively. 
     Here, an edge of the flange  646 ′ of the cylinder body  646  is caught by a step  641 ′ provided at an inner side of the first rotary member  641  so as to be prevented from being released, and an edge of the flange  647 ′ of the rod  647  is caught by a step  642 ′ provided at an inner side of the second rotary member  642  so as to be prevented from being released. 
     Further, it will be understood that the cylinder body  646  and the rod  647  may be modified and designed to have a reverse structure of the illustrated structure, that is, the cylinder body  646  may be provided in the second rotary member  642  and the rod  647  may be provided in the first rotary member  641 . 
     In this case, the pivot assembly  640  includes a spring  648  having both end portions fixed to an outer circumferential surface of the cylinder  645 , i.e., to an end portion of the cylinder body  646  and an end portion of the rod  647 , respectively, to elastically support the cylinder  645  in a contracted direction. 
     Thus, when the user wants to adjust the tilt angle of the rear support  300  with respect to the front supports  200  little by little, as illustrated in  FIG. 9 , the user may adjust the tilt angle little by little in stages by mutually rotating the first and second rotary members  641  and  642  in a mutually contacted state. 
     Further, when the user wants to significantly adjust the tilt angle of the rear support  300  with respect to the front supports  200  or wants to completely fold to be received, as illustrated in  FIG. 5 , the user may separate the second rotary member  642  from the first rotary member  641  and significantly rotate the second rotary member  642  to adjust the tilt angle. 
     Meanwhile, as illustrated in  FIGS. 11 and 12 , a pivot assembly  650  may also have a ratchet structure in which sawteeth  653  and  653 ′ between first and second rotary members  651  and  652  are engaged, allowing rotation only in one direction but preventing rotation in another direction, to adjust the tilt angle and temporarily maintain a firmly fastened state. 
     That is, the sawteeth  653  and  653 ′ are formed at equal intervals on the surface in which the first and second rotary members  651  and  652  are in contact, and sloped in one direction. 
     Further, a cylinder  654  protrudes from the first rotary member  651  and the second rotary member  652 , allows rotation separately from rotation of the first and second rotary members  651  and  652 , and is stretchable. 
     This is because a spring  657  to be described later may be twisted to be damaged or deformed if the cylinder  654  rotates in conjunction with the first and second rotary members  651  and  652 . 
     As illustrated, the cylinder  654  includes a cylinder body  655  protruding from a central portion of the first rotary member  651 , and a rod  656  protruding from a central portion of the second rotary member  652 , and the rod  656  contracts or stretches in an overall length as it insertedly enters or exits the cylinder body  655 . 
     Thus, as illustrated, the cylinder  654  includes the rod  656  protruding from the second rotary member  652  with respect to the cylinder body  655  protruding from the first rotary member  651  so as to insertedly enter or exit the cylinder body  655 , and here, preferably, the cylinder body  655  and the rod  656  have flanges  655 ′ and  656 ′ to rotate with respect to the first and second rotary members  651  and  652 , respectively. 
     Here, an edge of the flange  655 ′ of the cylinder body  655  is caught by a step  651 ′ provided at an inner side of the first rotary member  651  so as to be prevented from being released, and an edge of the flange  656 ′ of the rod  656  is caught by a step  652 ′ provided at an inner side of the second rotary member  652  so as to be prevented from being released. 
     Further, it will be understood that the cylinder body  655  and the rod  656  may be modified and designed to have a reverse structure of the illustrated structure, that is, the cylinder body  655  may be provided in the second rotary member  652  and the rod  656  may be provided in the first rotary member  651 . 
     In this case, the pivot assembly  650  includes a spring  657  having both end portions fixed to an outer circumferential surface of the cylinder  654 , i.e., to an end portion of the cylinder body  655  and an end portion of the rod  656 , respectively, to elastically support the cylinder  654  in a contracted direction. 
     Thus, when the user wants to adjust the tilt angle of the rear support  300  with respect to the front supports  200  little by little, as illustrated in  FIG. 11 , the user may rotate the first and second rotary members  651  and  652  in a mutually contacted state in mutually opposite directions to allow the sawteeth  653  and  653 ′ in mesh to slide on the sloped surfaces sloped to be lopsided in one direction, respectively, thus adjusting the tilt angle little by little in stages. 
     Further, when the user wants to significantly adjust the tilt angle of the rear support  300  with respect to the front supports  200  or wants to completely fold to be received, as illustrated in  FIG. 5 , the user may separate the second rotary member  652  form the first rotary member  651  and significantly rotate the second rotary member  652  to adjust the tilt angle. 
     Meanwhile, as illustrated in  FIGS. 13 and 14 , it will be understood that a pivot assembly  670  may have a structure allowing a mutual rotational contact of first and second rotary members  671  and  672  each having contact holes  673  and contact protrusions  674  between a central shaft  675  and a bearing casing  676 . 
     For reference, unexplained reference numeral  679  denotes a washer. 
     The first rotary member  671  extends from the other end portion of the first rotational piece  621  and the second rotary member  672  rotates in contact with the first rotary member  671  and extends from the other end portion of the second rotational piece  622 . 
     The contact holes  673  penetrate through a contact surface of the first rotary member  671  in contact with the second rotary member  672  at equal intervals, and the contact protrusions  674  are formed on a contact surface of the second rotary member  672  in contact with the first rotary member  671  at equal intervals and disposed in a position corresponding to the contact holes  673 , wherein the contact protrusions  674  have a hemispherical shape. 
     The central shaft  675  penetrates through central portions of the first and second rotary members  671  and  672  with the contact protrusions  674  in contact with the contact holes  673 , so as to be screw-coupled, and a handle  675 ′ provided in one end portion thereof is in contact with an outer side of any one of the first and second rotary members  671  and  672 . 
     The bearing casing  676  is a container-shaped member allowing the central shaft  675  to penetrate therethrough so as to be screw-coupled, and in contact with an outer side of the remaining of the first and second rotary members  671  and  672 . 
     A screw release preventing nut  677  is screw-coupled to the other end portion of the central shaft  675  penetrating to be exposed from the central portion of the bearing casing  676 . 
     A spring  678  is installed in the bearing casing  676 , allows the central shaft  675  to penetrate a central portion thereof, and elastically supports the bearing casing  676  in a direction away from the first and second rotary members  671  and  672 . 
     Here, it can be recognized that the bearing casing  676  includes a container-shaped casing body  676 ′ opened toward the first and second rotary members  671  and  672  and a both-side penetrative bearing  676 ″ protruding toward the first and second rotary members  671  and  672  from the center of the casing body  676 ′ and having a thread formed on an inner circumferential surface thereof to allow the central shaft  675  to penetrate and be screw-coupled therein. 
     In this case, the spring  678  is disposed between an outer circumferential surface of the bearing  676 ″ and an inner circumferential surface of the casing body  676 ′. 
     Thus, when the user wants to adjust a tilt angle of the rear support  300  with respect to the front supports  200  little by little, the user may rotate the handle  675 ′ in a direction in which the central shaft  675  is released with respect to the screw release preventing nut  677  in a state in which the first and second rotary members  671  and  672  are in contact, to release the tightly attached state of the first and second rotary members  671  and  672  to form a small gap therebetween. 
     In this case, even though the first and second rotary members  671  and  672  are allowed to have a gap therebetween, the first and second rotary members  671  and  672  are maintained in a mutually tightly attached state due to elastic repulsive power of the spring  678 . 
     Thereafter, when the user rotates the first and second rotary members  671  and  672  in mutually opposite directions, the contact protrusions  674  insertedly positioned in the contact holes  673  are inserted into other contact holes  673  spaced apart by a predetermined interval in stages, thereby adjusting the tilt angle little by little. 
     Meanwhile, even in a state in which the tilt angle is adjusted by the pivot assemblies  630 ,  640 , and  650  of the tilting unit  600  according to various embodiments described above, the tilt angle of the rear support  300  needs to be more finely adjusted with respect to the front supports  200 . 
     Thus, the tilting unit  600  may have a structure allowing third and fourth rotational pieces  603  and  604  to enter and exit first and second container bodies  661  and  662  extending to both sides based on the pivot assembly  630 ,  640 , or  650  as illustrated in  FIG. 15  (In  FIG. 5 , it will be understood that the pivot assembly  630  of  FIG. 8  is applied, and the pivot assemblies  640  and  650  according to the other embodiments may also be applied). 
     That is, the tilting unit  600  includes the third rotational piece  603  rotatably coupled to the rear support  300  and the fourth rotational piece  604  rotatably coupled to the prop  400 . 
     Further, the tilting unit  600  includes the first container body  661  forming an internal space in which the third rotational piece  603  is accommodated and coupled such that it enters and exits, and the second container body  662  forming an internal space in which the fourth rotational piece  604  is accommodated and coupled such that it enters and exits. 
     Thus, the pivot assembly  630  connects the end portions of the first and second container bodies  661  and  662  and rotates the end portions of the first and second container bodies  661  and  662  to adjust an angle. 
     In addition, the tilting unit  660  further includes positioning pins  663  and  664  penetratingly coupled to the first and second container bodies  661  and  662 , respectively, and positioning recesses  605  and  606  formed at equal intervals on one edges of the third and fourth rotational pieces  603  and  604  and having a shape corresponding to an outer circumferential surface of the positioning pins  663  and  664 . 
     Thus, the tilting unit  600  allows the third and fourth rotational pieces  603  and  604  to enter and exit in a length direction of the first and second container bodies  661  and  662 , respectively, thus finely adjusting the tilt angle of the rear support  300  with respect to the front supports  200 . 
     As described above, according to the present invention, the easel enabling a tilt angle to be adjusted as desired and reliably maintain an adjusted tilt angle can be provided. 
     According to the present invention having the configuration as described above, a stable structure can be obtained by the tilting unit which is rotatably and stretchably coupled between the rear support and the prop, adjusts a tilt angle of the rear support with respect to the front supports according to various embodiments such as the contact recesses and the contact protrusions or the sawteeth structure, and maintains an adjusted tilt state. 
     While the invention has been shown and described with respect to the embodiments, the present invention is not limited thereto. It will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.
The present invention relates to an easel allowing the angle of inclination thereof to be adjusted and reliably maintaining the adjusted angle of inclination, the easel comprising: a main bracket; expandable front supports rotatably attached on both sides of the front of the main bracket; an expandable rear support rotatably attached to the back of the main bracket; a supporting platform, both sides of which are detachably coupled to the front supports; a raising-and-lowering bar attached on the front center of the main bracket so as to allow raising and lowering of same, and the lower end of which is vertically slidably supported by the supporting platform; and a tilting unit, rotatably and expandably coupled in between the rear support and the front support platform, for controlling the angle of inclination of the rear support with respect to the front supports.