Patent Publication Number: US-2023152676-A1

Title: Focusing module and projection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of China application (202111365815.6), filed on Nov. 18, 2021. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     FIELD OF THE INVENTION 
     The invention relates to a focusing module, and more particularly to a focusing module adapted for a projection apparatus, and a projection apparatus including the focusing module. 
     BACKGROUND OF THE INVENTION 
     A conventional projection lens assembly for a projector typically includes a focusing ring and a projection lens. In general, the focusing ring is fixed on the projection lens and allows the user to conveniently rotate the focusing ring so that the projection lens is driven with the focusing ring to focus the projection lens. Further, the focusing ring is usually designed to be fixed on the projection lens with a locking structure. When the rotation of the projection lens reaches a threshold, the focusing ring will be locked on the projection lens, so that the focus ring and the projection lens cannot continue to rotate in the same direction. 
     However, many users often fail to notice that the rotation of the lens has reached a threshold and continue to forcefully rotate the focusing ring, which results in damage to the locking structure. 
     The information disclosed in this “BACKGROUND OF THE INVENTION” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “BACKGROUND OF THE INVENTION” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The invention provides a focusing module adapted for a projection lens, so as to prevent the structure of the focusing module and the projection lens from being damaged due to excessive rotation of the focusing ring. 
     The invention provides a projection device with the advantage of good durability. 
     Other advantages and objects of the invention may be further illustrated by the technical features broadly embodied and described as follows. 
     In order to achieve one or part or all of the above-mentioned purposes or other purposes, the focusing module provided by the invention is adapted for a projection lens with an optical axis. The focusing module includes a focusing ring and a projection lens mounting ring. The focusing ring has a first ring body and a first annular wall. The first ring body has a first opening and a second opening opposite to each other. The first annular wall is connected to the first ring body and surrounds the first opening. The first annular wall has a limiting hole, an inner annular surface and an outer annular surface. The inner annular surface is opposite to the outer annular surface. The limiting hole penetrates the inner annular surface and the outer annular surface of the first annular wall along a direction perpendicular to the optical axis. The projection lens mounting ring has a second annular wall adapted to be fixed to the projection lens along the optical axis. The second annular wall is disposed on an inner side of the first annular wall and is adapted to rotate relative to the first annular wall along a circumferential direction of the first annular wall. The second annular wall has a through hole and a rotation buffer structure. The rotation buffer structure is located in the through hole and has a limiting portion and a cantilever portion. The cantilever portion is connected between the limiting portion and a hole edge of the through hole. The limiting portion has a center surrounded by the hole edge. The center protrudes toward a direction facing the first annular wall of the focusing ring and has a first side and a second side opposite to each other in the circumferential direction. A thickness of the limiting portion gradually decreases from the center toward the first side and the second side in a radial direction of the second annular wall. The center of the limiting portion is located in the limiting hole and the first annular wall is pressed against the first side and the second side when the limiting portion of the rotation buffer structure contacts against the limiting hole of the focusing ring. 
     In an embodiment of the invention, the first side and the second side of the center of the limiting portion each have a guiding slope. 
     In an embodiment of the invention, the guiding slopes are connected to each other and surround the center of the limiting portion. 
     In an embodiment of the invention, the first annular wall of the focusing ring surrounds an outer side of the second annular wall with the optical axis as a center, and the inner annular surface of the first annular wall faces the second annular wall. When the focusing ring rotates around the optical axis, the limiting hole of the focusing ring presses against the limiting portion of the rotation buffer structure, so that the projection lens mounting ring and the focusing ring rotate synchronously. 
     In an embodiment of the invention, when the cantilever portion of the rotation buffer structure of the projection lens mounting ring is elastically deformed in a direction away from the inner annular surface and the center of the limiting portion leaves the limiting hole, the center of the limiting portion is pressed against the inner annular surface of the first annular wall of the focusing ring, so that the focusing ring rotates relative to the projection lens mounting ring. 
     In an embodiment of the invention, the inner annular surface of the first annular wall of the focusing ring has a plurality of stage difference structures. The stage difference structures are spaced apart from each other and arranged along the circumferential direction. The stage difference structures correspond to the center of the limiting portion. 
     In an embodiment of the invention, a number of the limiting holes is plural, and a number of the through holes corresponds to the number of the limiting holes. The limiting holes and the through holes are arranged equidistantly in the circumferential direction. 
     In an embodiment of the invention, the second annular wall of the projection lens mounting ring is adapted to be locked to the projection lens along the direction perpendicular to the optical axis via a plurality of locking members. Each of the locking members has a shaft portion and a head portion. The second annular wall further has an inner side surface, an outer side surface, an annular top edge and a plurality of installation openings. The annular top edge is connected between the inner side surface and the outer side surface. Each of the installation openings penetrates the inner side surface and the outer side surface along the direction perpendicular to the optical axis and extends to the annular top edge along a direction parallel to the optical axis. Each of the installation openings is provided with two hook portions opposite to each other. A clamping area and a channel area are formed between the two hook portions. The channel area is communicated with the clamping area along the direction parallel to the optical axis and extends to the annular top edge. When the projection lens mounting ring is assembled to the projection lens along the optical axis, the two hook portions in each of the installation openings are adapted to deform so that the shaft portion passes through the channel area and is fixed in the clamping area. 
     In an embodiment of the invention, the projection lens mounting ring further has a third opening and a fourth opening. The third opening and the fourth opening are respectively located on opposite sides of the second annular wall and the second annular wall surrounds the third opening and the fourth opening. The fourth opening is adapted for the projection lens to be installed. The second annular wall has a third side close to the third opening and a fourth side close to the fourth opening. An outer diameter of the second annular wall on the fourth side is smaller than an inner diameter of the first opening, and an outer diameter of the second annular wall on the third side is bigger than the inner diameter of the first opening. 
     In an embodiment of the invention, two opposite ends of the cantilever portion of the rotation buffer structure are respectively connected to the limiting portion and the hole edge of the through hole, and the cantilever portion and the limiting portion are arranged along a direction parallel to the optical axis. 
     In order to achieve one or part or all of the above-mentioned purposes or other purposes, the projection apparatus provided by the invention includes a housing, an illumination system, a light valve, and a projection lens assembly. The illumination system is disposed in the housing and adapted to provide an illumination beam. The light valve is disposed in the housing and located on a transmission path of the illumination beam from the illumination system to convert the illumination beam into an image beam. The housing has an opening. The projection lens assembly is disposed in the opening and located on a transmission path of the image beam from the light valve to project the image beam out of the projection apparatus. The projection lens assembly includes a projection lens and a focusing module. The lens has an optical axis. The focusing module is connected to the projection lens. 
     In the focusing module of the invention, the focusing ring has the limiting hole, the projection lens mounting ring has the rotation buffer structure corresponding to the limiting hole, and the limiting portion of the rotation buffer structure can be located in the limiting hole. Further, the thickness of the limiting portion gradually decreases from the center toward the opposite first side and second side, and the first annular wall can press against the first side and the second side. Therefore, when the rotational force on the focusing ring is too large, the first annular wall will gradually move toward the center from the second side (or the first side) and then press against the center to disengage the center from the limiting hole. In this case, because the center of the limiting portion is pressed against by the first annular wall, the second annular wall will move along the first annular wall when the focusing ring is continuously rotated. In this way, the focusing ring can rotate relative to the projection lens mounting ring instead of driving the projection lens mounting ring to rotate together, thereby preventing the structures of the focusing module and the projection lens from being damaged due to excessive rotation of the focusing ring. On the other hand, the projection apparatus of the invention has the advantage of good durability due to adopting the aforementioned focusing module. 
     Other objectives, features and advantages of the invention will be further understood from the further technological features disclosed by the embodiments of the invention wherein there are shown and described preferred embodiments of this invention, simply by way of illustration of modes best suited to carry out the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG.  1    is a schematic view of an assembly of a focusing module and a projection lens according to an embodiment of the invention; 
         FIG.  2    is a schematic exploded view of the focusing module and the locking member in  FIG.  1   ; 
         FIG.  3    is a schematic cross-sectional view of the focusing module in  FIG.  1   ; 
         FIG.  4    is a schematic enlarged view of the rotation buffer structure in  FIG.  2   ; 
         FIG.  5    is a schematic enlarged view of the area Z in  FIG.  1   ; 
         FIG.  6    is a schematic cross-sectional view of the center in  FIG.  5    located in the limiting hole; 
         FIG.  7    is a schematic view of the first annular wall in  FIG.  5    being pressed against the center; 
         FIG.  8    is a schematic cross-sectional view of the first annular wall in  FIG.  7    being pressed against the center; 
         FIG.  9    is a schematic view of the locking member being fixed in the installation opening; and 
         FIG.  10    is a schematic view of a projection apparatus according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top”, “bottom”, “front”, “back”, etc., is used with reference to the orientation of the Figure(s) being described. The components of the invention can be positioned in a number of different orientations. As such, the directional terminology is used for purposes of illustration and is in no way limiting. On the other hand, the drawings are only schematic and the sizes of components may be exaggerated for clarity. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including”, “comprising”, or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless limited otherwise, the terms “connected”, “coupled”, and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Similarly, the terms “facing”, “faces”, and variations thereof herein are used broadly and encompass direct and indirect facing, and “adjacent to” and variations thereof herein are used broadly and encompass directly and indirectly “adjacent to”. Therefore, the description of “A” component facing “B” component herein may contain the situations that “A” component facing “B” component directly or one or more additional components is between “A” component and “B” component. Also, the description of “A” component “adjacent to” “B” component herein may contain the situations that “A” component is directly “adjacent to” “B” component or one or more additional components is between “A” component and “B” component. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. 
       FIG.  1    is a schematic view of an assembly of a focusing module and a projection lens according to an embodiment of the invention. Please refer to  FIG.  1   . The focusing module  100  is suitable for the projection lens L and includes a focusing ring  110  and a projection lens mounting ring  120 . The projection lens mounting ring  120  is adapted to be fixed on the projection lens L, and the focusing ring  110  is connected to the projection lens mounting ring  120 . The projection lens L is, for example, a projection lens and has an optical axis A. The focusing module  100  can be used to adjust the focal length of the projection lens. Features of the focusing ring  110  and the projection lens mounting ring  120  will be described below. 
       FIG.  2    is a schematic exploded view of the focusing module and the locking member in  FIG.  1   .  FIG.  3    is a schematic cross-sectional view of the focusing module in  FIG.  1   . Please refer to  FIGS.  1 ,  2  and  3    together. The focusing ring  110  has a first ring body  111  and a first annular wall  112 . The first ring body  111  and the first annular wall  112  are, for example, annular members. The first ring body  111  has a first opening O 1  and a second opening O 2  opposite to each other, and the first opening O 1  and the second opening O 2  communicate with each other. The first annular wall  112  is connected to the first ring body  111  and surrounds the first opening O 1 . The first annular wall  112  has a limiting hole H 1  (shown in  FIG.  2   ), an inner annular surface IS 1  and an outer annular surface OS 1 . The inner annular surface IS 1  is opposite to the outer annular surface OS 1 . The limiting hole H 1  penetrates the inner annular surface IS 1  and the outer annular surface OS 1  of the first annular wall  112  along a direction perpendicular to the optical axis A of the projection lens L. Incidentally, the limiting hole H 1  of this embodiment extends, for example, to the top edge of the first annular wall  112 , but other embodiments are not limited thereto. 
     Please continue to refer to  FIGS.  1  and  2   . In this embodiment, the projection lens mounting ring  120  has a second annular wall  121 , and the second annular wall  121  is adapted to be fixed to the projection lens L along the optical axis A. The second annular wall  121  is disposed on the inner side of the first annular wall  112 , and the second annular wall  121  is adapted to rotate relative to the first annular wall  112  along the circumferential direction D 1  of the first annular wall  112 . The second annular wall  121  has a through hole H 2  and a rotation buffer structure  1211 . The through hole H 2  penetrates, for example, the second annular wall  121  along the direction perpendicular to the optical axis A of the projection lens L. When the projection lens mounting ring  120  and the focusing ring  110  are sleeved on the projection lens L along the optical axis A, the second annular wall  121  of the projection lens mounting ring  120  is disposed on the inner side of the first annular wall  112  of the focusing ring  110 , that is, the second annular wall  121  of the projection lens mounting ring  120  and the first annular wall  112  of the focusing ring  110  are both disposed around the optical axis A. 
       FIG.  4    is a schematic enlarged view of the rotation buffer structure in  FIG.  2   .  FIG.  5    is a schematic enlarged view of the area Z in  FIG.  1   . Please refer to  FIGS.  1 ,  2 ,  4  and  5    together. The rotation buffer structure  1211  of the projection lens mounting ring  120  is located in the through hole H 2  and has a limiting portion  1211   a  and a cantilever portion  1211   b.  The cantilever portion  1211   b  is connected between the limiting portion  1211   a  and the hole edge  1210  of the through hole H 2 . The limiting portion  1211   a  has a center C surrounded by the hole edge  1210 . In detail, one end of the cantilever portion  1211   b  is connected to the hole edge  1210  of the through hole H 2 , and the other end thereof is connected to the limiting portion  1211   a  along the direction parallel to the optical axis A (shown in  FIG.  1   ), for example. That is, the cantilever portion  1211   b  and the limiting portion  1211   a  are arranged, for example, along the direction parallel to the optical axis A, but the invention is not limited thereto. In this embodiment, when the projection lens mounting ring  120  and the focusing ring  110  are sleeved on the projection lens L along the optical axis A, the center C of the limiting portion  1211   a  protrudes toward the direction facing the first annular wall  112  (shown in  FIG.  5   ), and has a first side S 1  and a second side S 2  opposite to each other in the circumferential direction D 1  (labeled in  FIGS.  1  and  2   ). In addition, please also refer to  FIG.  6   . In the radial direction D 2  of the second annular wall  121 , the center C is located between the first side S 1  and the second side S 2 , and the thickness T of the limiting portion  1211   a  may gradually decrease from the center C toward the first side S 1  and toward the second side S 2 . 
     Please continue to refer to  FIGS.  5  and  6   . When the limiting portion  1211   a  of the rotation buffer structure  1211  contacts against the limiting hole H 1  of the first annular wall  112  of the focusing ring  110 , the center C of the limiting portion  1211   a  protruding toward the first annular wall  112  is aligned in the limiting hole H 1  and the first annular wall  112  (i.e., the hole edge of the limiting hole H 1 ) presses against the first side S 1  and the second side S 2  (labeled in  FIG.  4   ) of the limiting portion  1211   a.  Therefore, when the focusing ring  110  rotates relative to the projection lens mounting ring  120  along the circumferential direction D 1  (labeled in  FIG.  5   ) and the rotational force that the focusing ring  110  bears is bigger than a threshold, the position where the first annular wall  112  presses against the projection lens mounting ring  120  can be moved from the second side S 2  of the limiting portion  1211   a  to the center C of the limiting portion  1211   a,  so that the center C of the limiting portion  1211   a  is disengaged from the limiting hole H 1  of the first annular wall  112 , as shown in  FIGS.  5  and  7   . In this way, the first annular wall  112  can continue to rotate relative to the second annular wall  121  of the projection lens mounting ring  120  along the circumferential direction D 1  (labeled in  FIG.  5   ) to prevent the focusing module  100  and the projection lens L (shown in  FIG.  1   ) from being damaged by over-turning the focusing ring  110 . Further, please refer to  FIGS.  4 ,  5  and  6    together. The first side S 1  and the second side S 2  of the center C of the limiting portion  1211   a  may each have a guiding slope GS. Thus, the position where the first annular wall  112  presses against the projection lens mounting ring  120  can be moved from the second side S 2  (or the first side S 1 ) to the center C along the guiding slope GS, so that the focusing ring  110  can be easily rotated relative to the projection lens mounting ring  120 . Please continue to refer to  FIG.  4   . The guiding slope GS in this embodiment can be arranged to surround the center C, but the invention is not limited thereto. For example, the guiding slope GS can only be arranged on the first side S 1  or the second side S 2  in an embodiment. 
       FIG.  8    is a schematic cross-sectional view of the first annular wall in  FIG.  7    being pressed against the center. Please refer to  FIGS.  7  and  8    together. In this embodiment, the cantilever portion  1211   b  of the rotation buffer structure  1211  of the projection lens mounting ring  120  is elastically deformed when the center C is disengaged from the limiting hole H 1  of the first annular wall  112  and pressed by the first annular wall  112 . Further, the cantilever portion  1211   b  is elastically deformed in the direction away from the inner annular surface IS 1  (shown in  FIG.  8   ), that is, elastically deformed in the direction toward the optical axis A. When the cantilevered portion  1211   b  is elastically deformed in the direction away from the inner annular surface IS 1  and the center C of the limiting portion  1211   a  leaves the limiting hole H 1 , the center C presses against the inner annular surface IS 1  of the first annular wall  112  of the focusing ring  110 , so that the focusing ring  110  rotates relative to the projection lens mounting ring  120 . Incidentally, the cantilever portion  1211   b  in this embodiment is, for example, integrally formed with the limiting portion  1211   a.  However, in another embodiment, the cantilever portion  1211   b  may include a spring structure with an elastic deformation function. 
     Please refer to  FIGS.  1  and  5    again. On the other hand, when the rotational force that the focusing ring  110  bears is less than or equal to the threshold in this embodiment, the first annular wall  112  of the focusing ring  110  is pressed against the first side S 1  and the second side S 2  (shown in  FIG.  4   ) of the limiting portion  1211   a  and at least part of the center C is clamped in the limiting hole H 1  of the first annular wall  112 , so that the focusing ring  110  can drive the projection lens mounting ring  120  to rotate synchronously. Specifically, the first annular wall  112  of the focusing ring  110  can surround the outer side of the second annular wall  121  with the optical axis A as the center, and the inner annular surface IS 1  (shown in  FIGS.  2  and  3   ) of the first annular wall  112  may face the second annular wall  121 . When the focusing ring  110  rotates around the optical axis A, the hole edge of the limiting hole H 1  of the focusing ring  110  can press against the limiting portion  1211   a  of the rotation buffer structure  1211  and then push against the projection lens mounting ring  120 , so that the projection lens mounting ring  120  rotates synchronously with the focusing ring  110 . Further, the hole edge of the limiting hole H 1  and the part of the inner ring surface IS 1  close to the hole edge can press against the first side Si and the second side S 2 , so that the focusing ring  110  can drive the projection lens mounting ring  120  to rotate synchronously when the rotational force is less than or equal to the threshold. 
     Refer to  FIG.  2    again. In order to facilitate the user to determine the rotation state of the focusing ring  110  and the projection lens mounting ring  120 , the inner ring surface IS 1  of the first annular wall  112  of the focusing ring  110  may have a plurality of stage difference structures  1120 . The stage difference structures  1120  are spaced apart from each other, and each stage difference structure  1120  is arranged along the circumferential direction D 1 . The stage difference structures  1120  corresponds to the center C of the rotation buffer structure  1211 . In this way, when the focusing ring  110  rotates relative to the projection lens mounting ring  120 , the center C of the limiting portion  1211   a  will press against the stage difference structures  1120  in sequence while moving along the inner annular surface IS 1 . Thus, a feeling of segmented rotation is provided and a sound of the center C passing through the stage difference structures  1120  is generated, and therefore the user can know the current rotation state. It can be understood that the detailed features of the stage difference structure  1120  may vary according to the structure of the center C. For example, the center C of this embodiment may include a plane, and the shape of each stage difference structure  1120  is, for example, protruding from the inner ring surface IS 1 , that is, protruding toward the direction of the optical axis A. In other embodiments, the shape of the stage difference structure  1120  may be recessed on the inner annular surface IS 1 , and the invention is not limited thereto. 
     Incidentally, the number of the limiting holes H 1  in this embodiment may be plural, and three limiting holes H 1  are exemplarily shown in the figure. The number of the through holes H 2  corresponds to the number of the limiting holes H 1 , and the limiting holes H 1  and the through holes H 2  are arranged equidistantly in the circumferential direction D 1 . In this way, the focusing ring  110  can be easily rotated to a position where the limiting hole H 1  and the limiting portion  1211   a  are aligned with each other, thereby improving the convenience of operation. The specific number of the limiting holes H 1  can be determined according to the overall structural strength of the focusing ring  110 , and the invention does not limit the number of the limiting holes H 1 . 
     Please refer to  FIGS.  2  and  3    together to illustrate the assembling method and corresponding features of the focusing ring  110  and the projection lens mounting ring  120 . The projection lens mounting ring  120  further has a third opening O 3  and a fourth opening O 4 . The third opening O 3  and the fourth opening O 4  are located on opposite sides of the second annular wall  121 , respectively. The third opening O 3  and the fourth opening O 4  are communicated with each other, and the second annular wall  121  surrounds the third opening O 3  and the fourth opening O 4 . The projection lens L is adapted to be disposed from the fourth opening O 4  of the projection lens mounting ring  120 . As shown in  FIG.  3   , the second annular wall  121  has a third side  122  close to the third opening O 3  and a fourth side  123  close to the fourth opening O 4 . The outer diameter OR 1  of the second annular wall  121  of the projection lens mounting ring  120  on the fourth side  123  is smaller than the inner diameter IR of the first opening O 1  of the first ring body  111  of the focusing ring  110 , and the outer diameter OR 2  of the second annular wall  121  of the projection lens mounting ring  120  on the third side  122  is bigger than the inner diameter IR of the first opening O 1  of the first ring body  111  of the focusing ring  110 . Therefore, when assembling the focusing ring  110  and the projection lens mounting ring  120 , the fourth side  123  of the projection lens mounting ring  120  can be inserted into the focusing ring  110  from the second opening O 2  of the focusing ring  110  in the direction toward the first opening O 1  and is fixed in the first opening O 1 , and the third side  122  of the projection lens mounting ring  120  can be fixed in the second opening O 2  of the focusing ring  110 . In this embodiment, the third side  122  has, for example, an annular base B. The annular base B extends outward along the outer edge of the third side  122  in the direction perpendicular to the optical axis A, so as to increase the outer diameter OR 2  and therefore block the annular base B of the third sides  122  in the focusing ring  110 , but the specific structure of the third side  122  is not limited thereto. 
     Please refer to  FIGS.  1 ,  2 ,  3  and  9    together to illustrate the assembling method and corresponding features of the projection lens mounting ring  120  and the projection lens L. The second annular wall  121  of the projection lens mounting ring  120  is adapted to be locked to the projection lens L along the direction perpendicular to the optical axis A via a plurality of locking members SE. Each locking member SE has a shaft portion SE 1  and a head portion SE 2  connected to each other. The second annular wall  121  further has an inner side surface IS 2  (also shown in  FIG.  3   ), an outer side surface OS 2  (also shown in  FIG.  3   ), an annular top edge  1212  and a plurality of installation openings  1213 . The annular top edge  1212  is connected between the inner side surface IS 2  and the outer side surface OS 2  and is located on the fourth side  123  of the second annular wall  121 . The installation openings  1213  are, for example, spaced along the circumferential direction, and each installation opening  1213  penetrates the inner side surface IS 2  and the outer side surface OS 2  of the second annular wall  121  along the direction perpendicular to the optical axis A and extends to the annular top edge  1212  along the direction parallel to the optical axis A. As shown in  FIG.  9   , each installation opening  1213  is provided with two hook portions  1213   a  opposite to each other. A clamping area CA and a channel area TA are formed between the two hook portions  1213   a.  The channel area TA communicates with the clamping area CA along the direction parallel to the optical axis A and extends to the annular top edge  1212 . Please refer to  FIGS.  1  and  9    together. The locking members SE are locked to the outer side of the lens barrel (not labeled) of the projection lens L along the direction perpendicular to the optical axis A, so that a part of the shaft portion SE 1  of the locking member SE is locked to the projection lens L, and another part of the shaft portion SE 1  and the head portion SE 2  are exposed to the projection lens L. When the projection lens mounting ring  120  is assembled to the projection lens L along the optical axis A, the two hook portions  1213   a  located in each installation opening  1213  of the second annular wall  121  are adapted for deformation, so that the shaft portion SE 1  exposed to the projection lens L passes through the channel area TA and is fixed in the clamping area CA. Specifically, the shaft portion SE 1  is, for example, in transition fit with the channel area TA and the clamping area CA, and the head portion SE 2  can be in an interference fit with the clamping area CA. Please refer to  FIGS.  1 ,  2  and  9    together again. When assembling the projection lens mounting ring  120  and the projection lens L, the locking member SE is locked on the projection lens L, the channel area TA on the second annular wall  121  is aligned with the shaft portion SE 1 , and then the projection lens L is inserted into the projection lens mounting ring  120  through the third opening O 3  (shown in  FIG.  2   ). In this way, the shaft portion SE 1  of the locking member SE can extend from the channel area TA between the two hook portions  1213   a  along the optical axis A and be fixed in the clamping area CA, so that the two hook portions  1213   a  are pressed by the shaft portion SE 1  and deformed. The two hook portions  1213   a  are restored when the shaft portion SE 1  moves into the clamping area CA, and the restored hook portions  1213   a  and the head portion SE 2  can prevent the locking member SE from falling off from the clamping area CA. Thus, the projection lens mounting ring  120  of this embodiment can be quickly assembled on the projection lens L and can be axially limited through the hook portions  1213   a.  When the focusing ring  110  rotates around the optical axis A, the hole edge of the limiting hole H 1  of the focusing ring  110  can press against the limiting portion  1211   a  of the rotation buffer structure  1211  and then push against the projection lens mounting ring  120 , so that the projection lens mounting ring  120  rotates synchronously with the focusing ring  110 , and the projection lens L locked with the projection lens mounting ring  120  is also driven to adjust the focal length synchronously. 
     Incidentally, the locking member SE of this embodiment may include stepped screws, so the shaft portion SE 1  may have a wide section (not shown) and a narrow section (not shown) connected to each other. The narrow section has an external thread for screwing to the projection lens L, and the wide section may be connected between the narrow section and the head portion SE 2 . The clamping area CA is, for example, clamping the wide section. When the projection lens mounting ring  120  is detached from the projection lens L, the locking member SE on the projection lens L can be loosened from the head portion SE 2  to move the narrow section into the clamping area CA, so that the shaft portion SE 1  can pass through the channel area TA more easily and therefore the projection lens mounting ring  120  is easier to be detached. 
     Compared with the prior art, in the focusing module  100  of this embodiment, the focusing ring  110  has the limiting hole H 1 , the projection lens mounting ring  120  has the rotation buffer structure  1211  corresponding to the limiting hole H 1 , and the limiting portion  1211   a  of the rotation buffer structure  1211  can be located in the limiting hole H 1 . Further, the thickness T of the limiting portion  1211   a  gradually decreases from the center C toward the opposite first side S 1  and second side S 2 , and the first annular wall  112  can press against the first side S 1  and the second side S 2  of the limiting portion  1211   a.  Therefore, when the rotational force on the focusing ring  110  is too large, the first annular wall  112  will gradually move toward the center C from the second side S 2  (or the first side S 1 ) and then press against the center C to disengage the center C from the limiting hole H 1 . In this case, because the center C is pressed against by the first annular wall  112 , the second annular wall  121  will move relative to the first annular wall  112  when the focusing ring  110  is continuously rotated. In this way, the focusing ring  110  can rotate relative to the projection lens mounting ring  120  instead of driving the projection lens mounting ring  120  to rotate together, thereby preventing the focusing module  100  and the projection lens L from being damaged due to excessive rotation of the focusing ring  110 . 
       FIG.  10    is a schematic view of a projection apparatus according to an embodiment of the invention. Referring to  FIG.  10   , the projection apparatus  200  includes a housing  210 , an illumination system  220 , a light valve  230  and a projection lens assembly  240 . The illumination system  220  is disposed in the housing  210  and is adapted to provide an illumination beam L 1 . The light valve  230  is disposed in the housing  210  and located on a transmission path of the illumination beam L 1  to convert the illumination beam L 1  into an image beam L 2 . The housing  210  has an opening  211 . The projection lens assembly  240  is disposed in the opening  211  and located on a transmission path of the image beam L 2  to project the image beam L 2  out of the projection apparatus  200 . The projection lens assembly  240  includes the aforementioned projection lens L and the aforementioned focusing module  100 , and the focusing module  100  is connected to the projection lens L. For example, in this embodiment, the focusing ring  110  is disposed beside the opening  211 , and the projection lens mounting ring  120  may be connected between the focusing ring  110  and the projection lens L. The user can rotate the focusing ring  110  which synchronously drives the projection lens L to perform the focusing operation. Because the features of the focusing module  100  have been described in detail above, no redundant detail is to be given herein. 
     The illumination system  220  is configured to generate the illumination beam L 1 . In this embodiment, the illumination system  220  may include an excitation light source and a wavelength conversion element. The excitation light source includes, for example, a light emitting diode (LED) or a laser diode (LD), wherein the number of the light emitting diode or the laser diode can be one or plural. For example, the light emitting diodes (or laser diodes) may be arranged in a matrix when the number of light emitting diodes (or laser diodes) is plural. The excitation light source is configured to generate an excitation beam. A wavelength conversion material is disposed on the wavelength conversion element to convert the excitation beam into the illumination beam L 1 . Specifically, the wavelength of the excitation beam incident on the wavelength conversion material is converted by the wavelength conversion material, while the wavelength of the excitation beam not incident on the wavelength conversion material is not converted, wherein the illumination beam L 1  includes the unconverted excitation beam and the converted excitation beam. In another embodiment, the illumination system  220  may include a metal halide lamp or an ultra-high pressure mercury lamp, and the invention is not limited thereto. 
     The light valve  230  in this embodiment includes, for example, a digital micromirror device (DMD), but the invention is not limited thereto. For example, in one embodiment, the light valve  230  may include a liquid crystal on silicon (LCoS) display or a liquid crystal display (LCD). In addition, this embodiment does not limit the number of light valves. For example, in the embodiment in which the light valve  230  includes the aforementioned liquid crystal display panel, the projection apparatus  200  may adopt the structure of a single-chip liquid crystal display or a three-chip liquid crystal display, but the invention is not limited thereto. 
     In this embodiment, the projection lens L includes, for example, one or more optical lenses and is accommodated in a lens barrel (not labeled), and the dioptric powers of the optical lenses may be the same or different from each other. For example, the optical lens may include various non-planar lenses such as bi-concave lenses, bi-convex lenses, concave-convex lenses, convex-concave lenses, plano-convex lenses, and plano-concave lenses, or any combination of the above non-planar lenses. On the other hand, the projection lens L may include a flat optical lens. The invention does not limit the specific structure of the projection lens L. 
     Compared with the prior art, the projection apparatus  200  of this embodiment has the advantage of good durability due to adopting the focusing module  100 . 
     In summary, in the focusing module of the invention, the focusing ring has the limiting hole, the projection lens mounting ring has the rotation buffer structure corresponding to the limiting hole, and the limiting portion of the rotation buffer structure can be located in the limiting hole. Further, the thickness of the limiting portion gradually decreases from the center toward the opposite first side and second side, and the first annular wall can press against the first side and the second side. Therefore, when the rotational force on the focusing ring is too large, the first annular wall will gradually move toward the center from the second side (or the first side) and then press against the center to disengage the center from the limiting hole. In this case, because the center of the limiting portion is pressed against by the first annular wall, the second annular wall will move along the first annular wall when the focusing ring is continuously rotated. In this way, the focusing ring can rotate relative to the projection lens mounting ring instead of driving the projection lens mounting ring to rotate together, thereby preventing the structures of the focusing module and the projection lens from being damaged due to excessive rotation of the focusing ring. On the other hand, the projection apparatus of the invention has the advantage of good durability due to adopting the aforementioned focusing module. 
     The foregoing description of the preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiments disclosed. Accordingly, the foregoing description should be regarded as illustrative rather than restrictive. Obviously, many modifications and variations will be apparent to practitioners skilled in this art. The embodiments are chosen and described in order to best explain the principles of the invention and its best mode practical application, thereby to enable persons skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents in which all terms are meant in their broadest reasonable sense unless otherwise indicated. Therefore, the term “the invention”, “The invention” or the like is not necessary limited the claim scope to a specific embodiment, and the reference to particularly preferred exemplary embodiments of the invention does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is limited only by the spirit and scope of the appended claims. Moreover, these claims may refer to use “first”, “second”, etc. following with noun or element. Such terms should be understood as a nomenclature and should not be construed as giving the limitation on the number of the elements modified by such nomenclature unless specific number has been given. The abstract of the disclosure is provided to comply with the rules requiring an abstract, which will allow a searcher to quickly ascertain the subject matter of the technical disclosure of any patent issued from this disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. Any advantages and benefits described may not apply to all embodiments of the invention. It should be appreciated that variations may be made in the embodiments described by persons skilled in the art without departing from the scope of the invention as defined by the following claims. Moreover, no element and component in the disclosure is intended to be dedicated to the public regardless of whether the element or component is explicitly recited in the following claims.