Abstract:
A portable screen includes: a frame body having a rectangular shape; and a screen sheet provided with tension within the frame body and having an image projection surface, wherein one opposing side of two sets of opposing sides forming the frame body is configured to allow the frame body to be extendable along the side, and the other opposing side of two sets of opposing sides forming the frame body is configured to allow the frame body to be spreadable or foldable.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a portable screen. 
     2. Related Art 
     Recently, with downsizing of projectors, portable screens that can be conveniently carried have been in increasing demand. As a portable screen like this, a portable screen in which a frame body can be configured by coupling plural coupling members is disclosed (for example, see JP-A-2005-221609). 
     However, in a portable screen of a related art, there is a problem that spreading out and folding up the portable screen take a considerable amount of time and effort because, when the portable screen is spread out, it is necessary to form a frame body by coupling plural coupling members and then attach a screen sheet to the frame, and when the portable screen is folded up, it is necessary to detach the screen sheet from the frame body and then take the plural coupling members apart. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a portable screen, and the time and effort taken to spread out and fold up the portable screen can be greatly saved. 
     A portable screen according to an aspect of the invention includes a frame body having a rectangular shape; and a screen sheet provided with tension within the frame body and having an image projection surface, wherein one opposing side of two sets of opposing sides forming the frame body is configured to allow the frame body to be extendable along the side, and the other opposing side of the two sets of opposing sides forming the frame body is configured to allow the frame body to be spreadable or foldable. 
     In this case, the one opposing side in the frame body is configured to be extendable, and the other opposing side in the frame body is configured to allow the frame body to be spreadable or foldable. Accordingly, when the portable screen is spread out, the frame body is extended along the direction along the one opposing side (hereinafter, the direction may be referred to as “extending and retracting direction”), the frame body is spread along the direction along the other opposing side (hereinafter, the direction may be referred to as “spreading and folding direction”), and thereby, the portable screen can be spread out to the size on which an image of the projector can be projected with no problem. Further, when the portable screen is folded up, the frame body is folded up in the spreading and folding direction, the frame body is retracted in the extending and retracting direction, and thereby, the portable screen can be reduced to the size that can be carried. That is, the portable screen can be spread out and folded up only by two actions of extending or retracting it along the extending and retracting direction and spreading out or folding up along the spreading and folding direction, the time and effort taken to spread out and fold up the portable screen can be greatly saved. 
     Further, in this case, the portable screen can be spread out and folded up with the screen sheet remaining attached to the frame body as seen from  FIGS. 6A to 6E  and  7 A to  7 E, which will be described later, and thus, the time and effort taken to spread out and fold up the portable screen can be greatly saved in the viewpoint. 
     Furthermore, in this case, the one opposing side of the frame body is retracted and the other opposite part is folded up, and thus, the size when the portable screen is folded up is relatively small. As a result, the portable screen is very advantageous in portability. 
     It is preferable that a lock mechanism for maintaining an extended state of the frame body is provided at the one opposing side in the frame body. 
     When the portable screen is spread out, the extended state of the frame body can be maintained by locking it with the lock mechanism, and, when the portable screen is folded up, the frame body can easily be retracted by releasing the locking of the lock mechanism. 
     It is preferable that a lock mechanism for maintaining a spread state of the frame body is provided at the other opposing side in the frame body. 
     When the portable screen is spread out, the spread state of the frame body can be maintained by locking it with the lock mechanism, and, when the portable screen is folded up, the frame body can easily be folded up by releasing the locking of the lock mechanism. 
     It is preferable that the screen sheet is provided with tension within the frame body to make the image projection surface face inside when the frame body is folded up. 
     According to the configuration, dirt and scratches on the image projection surface can be suppressed when the portable screen is carried. 
     It is preferable that the screen sheet is provided with tension in the frame body only at the other opposing side in the frame body, and plural plate-like members are arranged in parallel along the one opposing side direction at two ends of the one opposing side in the frame body of the ends of the screen sheet. 
     According to the configuration, when the frame body is folded up, the screen sheet is folded up neatly with less distortion and irregular wrinkles generated on the screen sheet can be suppressed. 
     It is preferable that the number of the plate-like members respectively provided at the two ends in the screen sheet is an odd number. 
     When the number of the plate-like members provided at the ends of one side in the screen sheet is an odd number, the number of times at which the screen sheet is folded along the extending and retracting direction of the frame body is an even number. If the number is an odd number, for example, one, the screen sheet is folded in a V-shape, and in this case, the frame body and the screen sheet are connected at the other opposing side in the frame body, and the screen sheet is in the unnatural folded state (see  FIGS. 8B and 9B , which will be described later). 
     On the other hand, in this case, the number of times at which the screen sheet is folded along the extending and retracting direction of the frame body is an even number as described above, the screen sheet is neatly folded in the frame body as seen from  FIG. 2B , which will be described later. As a result, occurrence of wrinkles and damage on the screen sheet when the screen is carried can be suppressed. 
     It is preferable that fold-back processing for covering both surfaces of the arranged plate-like members by the screen sheet is performed on the respective two ends in the screen sheet. 
     According to the configuration, also the parts on which the plate-like members are provided can be widely used as the image projection surface. 
     Further, if the fold-back processing is not performed on the ends of the screen sheet, when the screen is folded up or when the folded-up screen is carried, the plate-like members may unintentionally be in contact with the screen sheet and damage the screen sheet, however, the occurrence of the damage can be prevented according to the above configuration. 
     It is preferable that the plate-like member is a plastic plate. 
     If relatively heavy members are used as the plate-like members, when the frame body is spread out, the ends of the screen sheet may bend or wrinkles may occur. However, in this case, relatively light plastic plates are used for the plate-like members, and thus, bending of the ends of the screen sheet and wrinkles thereon can be suppressed when the frame body is spread out. Further, the effect on the weight of the entire portable screen due to plural plate members provided thereon can be minimized. 
     It is preferable that the frame body forming the one opposing side includes extendable frames. 
     According to the configuration, the frame body can be extended and retracted relatively easily along the extending and retracting direction. 
     It is preferable that the frame body forming the other opposing side includes plural frame pieces, and hinge members that rotatably connect the plural frame pieces, respectively. 
     According to the configuration, the frame body can be spread out or folded up relatively easily along the spreading and folding direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIGS. 1A and 1B  are diagrams for explanation of a portable screen  1  according to embodiment 1. 
         FIGS. 2A and 2B  are diagrams for explanation of the portable screen  1  according to embodiment 1. 
         FIGS. 3A and 3B  are diagrams for explanation of an extendable frame of the portable screen  1 . 
         FIG. 4  is a diagram for explanation of hinge members of the portable screen  1 . 
         FIGS. 5A and 5B  are diagrams for explanation of a plate-like member. 
         FIGS. 6A to 6E  are diagrams for explanation of the operation when the portable screen  1  is spread out. 
         FIGS. 7A to 7E  are diagrams for explanation of the operation when the portable screen  1  is folded up. 
         FIGS. 8A and 8B  are diagrams for explanation of a portable screen  800  according to comparative example 1. 
         FIGS. 9A and 9B  are diagrams for explanation of a portable screen  900  according to comparative example 2. 
         FIGS. 10A and 10B  are diagrams for explanation of a portable screen  2  according to embodiment 2. 
         FIGS. 11A and 11B  are diagrams for explanation of a lock mechanism  130   a  for maintaining the extended state of the frame body in the portable screen  2  according to embodiment 2. 
         FIGS. 12A to 12C  are diagrams for explanation of a lock mechanism  130   c  for maintaining the spread state of the frame body in the portable screen  2  according to embodiment 2. 
         FIGS. 13A to 13C  are diagrams for explanation of the lock mechanism  130   c  for maintaining the spread state of the frame body in the portable screen  2  according to embodiment 2. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a portable screen of an embodiment of the invention will be described according to embodiments shown in the drawings. 
     Embodiment 1 
       FIGS. 1A ,  1 B,  2 A, and  2 B are diagrams for explanation of a portable screen  1  according to embodiment 1.  FIG. 1A  is a perspective view of the portable screen  1  seen from an image projection surface  52  side, and  FIG. 1B  is a perspective view of the portable screen  1  seen from an opposing side to the image projection surface  52 .  FIG. 2A  is a perspective view of the portable screen  1  when folded up, and  FIG. 2B  is a side view of the portable screen  1  for explanation of a folded state of a screen sheet  50 . 
       FIGS. 3A and 3B  are diagrams for explanation of an extendable frame of the portable screen  1  according to embodiment 1.  FIG. 3A  is a perspective view showing a state in which frame pieces  12   c  to  18   c  are extended, and  FIG. 3B  is a perspective view showing a state in which frame pieces  12   c  to  18   c  are retracted. 
       FIG. 4  is a diagram for explanation of hinge members of the portable screen  1  according to embodiment 1. In  FIG. 4 , only two hinge members  40   c ,  44   c  of plural hinge members are enlarged and shown. 
       FIGS. 5A and 5B  are diagrams for explanation of a plate-like member.  FIG. 5A  is a perspective view showing a plate-like member  62   a , and  FIG. 5B  is a sectional view of the screen sheet  50  for explanation of fold-back processing in the screen sheet  50 . 
     Note that, regarding the image projection surface  52  of the screen sheet  50  shown in the drawing, to facilitate understanding of the invention, of the two sides of the screen sheet  50 , the side on which the image projection surface  52  is formed is shown in white and the side on which the image projection surface  52  is not formed is shown in gray. 
     The portable screen  1  according to embodiment 1 is a portable screen including a frame body  10  having a rectangular shape in a plan view, the screen sheet  50  provided with tension within the frame body  10 , and six plate-like members  62   a  to  66   a ,  62   b  to  66   b  provided on ends of the screen sheet  50  as shown in  FIGS. 1A and 1B . 
     The frame body  10  has frame pieces  12   a  to  16   a ,  12   b  to  16   b  provided along the short sides of the frame body  10  by three pieces each, frame pieces  12   c  to  18   c ,  12   d  to  18   d  provided along the long sides of the frame body  10  by four piece each, respectively, joint members  20  to  26  provided on four corners of the frame body  10  for coupling the respective frame members, hinge members  40   c  to  44   c ,  40   d  to  44   d  for rotatably coupling the frame pieces  12   c  to  18   c ,  12   d  to  18   d , respectively, lock mechanisms  30   a ,  32   a ,  30   b ,  32   b  provided at the short sides of the frame body  10 , and lock mechanisms  30   c  to  34   c ,  30   d  to  34   d  provided at the long sides of the frame body  10 . 
     Two sides at the short sides of the frame body  10  correspond to “one opposing side” in the invention, and two sides at the long sides of the frame body  10  correspond to “the other opposing side” in the invention. 
     Further, the direction along the short sides of the frame body  10  correspond to “direction along one opposing sides” or “extending and retracting direction” in the invention, and direction along the long sides of the frame body  10  correspond to “direction along the other opposing sides” or “spreading out and folding up direction” in the invention. 
     The respective frame pieces  12   a  to  16   a ,  12   b  to  16   b  provided along the short sides of the frame body  10  are aluminum frames in nearly the same lengths and rectangular sections. These frame pieces  12   a  to  16   a ,  12   b  to  16   b  are extendable frames adapted to be extendable at two steps along the short sides. At one ends of the frame pieces  12   a ,  12   b , the frame pieces  14   a ,  14   b  thinner than the frame pieces  12   a ,  12   b  are slidably provided, and, at one ends of the frame pieces  14   a ,  14   b , the frame pieces  16   a ,  16   b  thinner than the frame pieces  14   a ,  14   b  are slidably provided. 
     Further, as shown in  FIGS. 1B and 3A , the lock mechanism  30   a  is provided between the frame piece  12   a  and the frame piece  14   a . Also, the lock mechanisms  32   a ,  30   b ,  32   b  are provided between the frame piece  14   a  and the frame piece  16   a , the frame piece  12   b  and the frame piece  14   b , and the frame piece  14   b  and the frame piece  16   b , respectively. These lock mechanisms  30   a ,  32   a ,  30   b ,  32   b , though the description with reference to the drawings is omitted, each includes a protrusion that can be pressed down and a fitting hole corresponding to the protrusion, and the protrusion is provided on an end of one frame piece and the fitting hole is provided on an end of the other frame piece. When the frame body  10  is extended along the short sides, locking of the lock mechanisms  30   a ,  32   a ,  30   b ,  32   b  works by pulling the respective frame pieces  12   a  to  16   a ,  12   b  to  16   b  until the protrusions reach the positions of the fitting holes. On the other hand, when the frame body  10  is retracted along the short sides, locking of the lock mechanisms  30   a ,  32   a ,  30   b ,  32   b  is released by pressing down the protrusions. Accordingly, the frame body  10  can be retracted in the directions along the short sides by pushing in the frame pieces  12   a  to  16   a ,  12   b  to  16   b.    
     The respective frame pieces  12   c  to  18   c ,  12   d  to  18   d  provided along the long sides of the frame body  10  are aluminum frames in rectangular sections. These lengths of the frame pieces  12   c ,  18   c ,  12   d ,  18   d  are nearly the same lengths and the lengths of the frame pieces  14   c ,  16   c ,  14   d ,  16   d  are shorter than those of the frame pieces  12   c ,  18   c ,  12   d ,  18   d  as seen from  FIGS. 1A ,  1 B, and  2 A. The hinge members  40   c  to  44   c ,  40   d  to  44   d  are provided between the respective frame pieces  12   c  to  18   c  and between the respective frame pieces  12   d  to  18   d  so that, when the frame body  10  is folded, it may be folded in a W-shape, and thereby, the frame body  10  is adapted to be spread out or folded up. 
     Further, on the respective hinge members  40   c  to  44   c ,  40   d  to  44   d , the lock mechanisms  30   c  to  34   c ,  30   d  to  34   d  are provided. The description of the lock mechanism  30   c  shown in  FIG. 4  is that the lock mechanism  30   c  includes a protruding part a 1  and a fitting part a 2  corresponding to the protruding part a 1 . When the frame body  10  is spread out, the hinge member  40   c  is rotated and the protruding part a 1  is fitted in the fitting part a 2 , and thereby, the locking of the lock mechanism  30   c  works. On the other hand, when the frame body  10  is folded up, the hinge member  40   c  is rotated and fitting of the protruding part a 1  in the fitting part a 2  is released, and thereby, the locking of the lock mechanism  30   c  is released. The other lock mechanisms  32   c ,  34   c ,  30   d  to  34   d  have the same configuration as that of the lock mechanism  30   c.    
     The screen sheet  50  has the image projection surface  52  on one side and provided with tension within the frame body  10  so that the image projection surface  52  may face inside when the frame body  10  is folded up (see  FIGS. 7B and 7C  described as below). Further, the screen sheet  50  is in contact with the frame pieces  12   c  to  18   c ,  12   d  to  18   d  but not in contact with the frame pieces  12   a  to  16   a ,  12   b  to  16   b  as shown in  FIGS. 1A and 1B . That is, the screen sheet  50  is provided with tension in the frame body  10  only at the long sides of the frame body  10 . 
     The plate-like member  62   a  includes a thin transparent plastic plate having a rectangular shape in a plan view as shown in  FIG. 5A . The other plate-like members  64   a ,  66   a ,  62   b  to  66   b  have the same configuration as that of the plate-like member  62   a.    
     The plate-like members  62   a  to  66   a ,  62   b  to  66   b  are provided at ends along the short sides of the screen sheet  50  by threes, respectively, as shown in  FIG. 1 . Further, the plate-like members  62   a  to  66   a ,  62   b  to  66   b  are provided in parallel seen along the long sides. In other words, the arrangements of the plate-like members  62   a  to  66   a ,  62   b  to  66   b  are symmetrical seen along the straight line passing through the hinge members  42   c ,  42   d.    
     At the ends along the short sides of the screen sheet  50 , fold-back processing for covering both surfaces of the arranged plate-like members  62   a  to  66   a ,  62   b  to  66   b  by the screen sheet  50  is performed (see  FIG. 5B ). Note that, the ends of the screen sheet  50  of the fold-back-processed parts may be bonded or stitched. 
     Here, an operation when the portable screen  1  according to embodiment 1 is spread out and an operation when it is folded up will be described using  FIGS. 6A to 6E  and  7 A to  7 E. 
       FIGS. 6A to 6E  are diagrams for explanation of the operation when the portable screen  1  according to embodiment 1 is spread out.  FIG. 6A  is a perspective view of the portable screen  1  that has been folded up,  FIG. 6B  is a perspective view showing a state when the frame body  10  is extended along the short side direction,  FIG. 6C  is a perspective view showing a state when the frame body  10  is spread along the long side direction,  FIG. 6D  is a perspective view seen from a different direction from that in  FIG. 6C , and  FIG. 6E  is a perspective view showing a state when the frame body  10  is finished to be spread. 
       FIGS. 7A to 7E  are diagrams for explanation of the operation when the portable screen  1  according to embodiment 1 is folded up.  FIG. 7A  is a perspective view of the portable screen  1  that has been spread out,  FIG. 7B  is a perspective view showing a state when the frame body  10  is folded along the long side direction,  FIG. 7C  is a perspective view seen from a different direction from that in  FIG. 7B ,  FIG. 7D  is a perspective view showing a state when the frame body  10  is retracted along the short side direction, and  FIG. 7E  is a perspective view showing a state when the frame body  10  is finished to be retracted. 
     When the portable screen  1  in the state shown in  FIG. 6A  is spread out, the frame body  10  is extended in the direction along the short sides by extending the extendable frames (see  FIG. 6B ), the frame body  10  is spread out in the direction along the long sides by rotating the hinge members  40   c  to  44   c ,  40   d  to  44   d  (see  FIGS. 6C and 6D ), and thereby, the portable screen  1  can be spread out to the size on which an image of the projector can be projected with no problem (e.g., about 40 inches) (see  FIG. 6E ). 
     On the other hand, when the portable screen  1  in the state shown in  FIG. 7A  is folded up, the frame body  10  is folded up by rotating the hinge members  40   c  to  44   c ,  40   d  to  44   d  (see  FIGS. 7B and 7C ), the frame body  10  is retracted in the direction along the short sides by retracting the extendable frames (see  FIG. 7D ), and thereby, the portable screen  1  can be reduced to the size that can be carried (e.g., about A4-size) (see  FIG. 7E ). 
     That is, according to the portable screen  1  according to embodiment 1, the portable screen  1  can be spread out and folded up only by two actions of extending or retracting it along the short side direction and spreading out or folding up along the long side direction, the time and effort taken to spread out and fold up the portable screen  1  can be greatly saved. 
     Further, according to the portable screen  1  according to embodiment 1, the portable screen  1  can be spread out and folded up with the screen sheet  50  remaining attached to the frame body  10  as seen from  FIGS. 6A to 6E  and  7 A to  7 E, and thus, the time and effort taken to spread out and fold up the portable screen can be greatly saved in the viewpoint. 
     Furthermore, according to the portable screen  1  according to embodiment 1, both sides (short sides and long sides) of the frame body  10  having rectangular shapes in the plan view are retracted or folded up, and thus, the size when the portable screen  1  is folded up is relatively small. As a result, the portable screen is very advantageous in portability. 
     In the portable screen  1  according to embodiment 1, the lock mechanisms  30   a ,  32   a ,  30   b ,  32   b  for maintaining the extended state of the frame body  10  are provided at the short sides of the frame body  10 . Thereby, when the portable screen  1  is spread out, the extended state of the frame body  10  can be maintained by locking it with the lock mechanisms  30   a ,  32   a ,  30   b ,  32   b , and, when the portable screen  1  is folded up, the frame body  10  can easily be retracted by releasing the locking of the lock mechanisms  30   a ,  32   a ,  30   b ,  32   b.    
     In the portable screen  1  according to embodiment 1, the lock mechanisms  30   c  to  34   c ,  30   d  to  34   d  for maintaining the spread state of the frame body  10  are provided at the long sides of the frame body  10 . Thereby, when the portable screen  1  is spread out, the spread state of the frame body  10  can be maintained by locking it with the lock mechanisms  30   c  to  34   c ,  30   d  to  34   d , and, when the portable screen  1  is folded up, the frame body  10  can easily be folded up by releasing the locking of the lock mechanisms  30   c  to  34   c ,  30   d  to  34   d.    
     In the portable screen  1  according to embodiment 1, the screen sheet  50  is provided with tension within the frame body  10  so that the image projection surface  52  may face inside when the frame body  10  is folded up, and thus, dirt and scratches on the image projection surface  52  can be suppressed when the portable screen  1  is carried. 
     In the portable screen  1  according to embodiment 1, the ends on which the plural plate-like members  62   a  to  66   a ,  62   b  to  66   b  are provided, out of the ends of the screen sheet are fold-back-processed as described above, and thus, also the parts on which the plate-like members  62   a  to  66   a ,  62   b  to  66   b  are provided can be widely used as the image projection surface. Further, when the screen is carried, the damage on the screen sheet, which may occur when the plate-like members are barely provided, can be prevented. 
     According to the portable screen  1  according to embodiment 1, relatively light plastic plates are used for the plate-like members  62   a  to  66   a ,  62   b  to  66   b , and thus, bending of the ends of the screen sheet  50  and wrinkles thereon can be suppressed. Further, the effect on the weight of the entire portable screen due to plural plate members provided thereon can be minimized. 
     In the portable screen  1  according to embodiment 1, the frame body  10  forming the short sides includes extendable frames, and thus, the frame body  10  can relatively easily be extended and retracted along the short side direction. 
     In the portable screen  1  according to embodiment 1, the frame body  10  forming the long sides has the frame pieces  12   c  to  18   c ,  12   d  to  18   d  and the hinge members  40   c  to  44   c ,  40   d  to  44   d  that rotatably couple the frame pieces  12   c  to  18   c ,  12   d  to  18   d , and thus, the frame body  10  can relatively easily be spread out or folded up along the long side direction. 
     In the portable screen  1  according to embodiment 1, the frame pieces include aluminum frames, and thus, the relatively high frame strength can be obtained. 
     In the portable screen  1  according to embodiment 1, the screen sheet  50  is provided with tension only at the long sides of the frame body  10 , i.e., the sides on which the hinge members  40   c  to  44   c ,  40   d  to  44   d  are provided, and the above described plural plate-like members  62   a  to  66   a ,  62   b  to  66   b  are provided at the ends of the short sides of the screen sheet. 
     Thereby, when the frame body  10  is folded up, the screen sheet  50  is folded up neatly with less distortion and irregular wrinkles generated on the screen sheet  50  can be suppressed. 
     Here, the portable screen  1  according to the embodiment will be described in further detail with a portable screen according to comparative examples of embodiment 1. 
       FIGS. 8A and 8B  are diagrams for explanation of a portable screen  800  according to comparative example 1.  FIG. 8A  is a perspective view of the portable screen  800 , and  FIG. 8B  is a side view of the portable screen  800  for explanation of a folded-up state of the screen sheet  50 . 
       FIGS. 9A and 9B  are diagrams for explanation of a portable screen  900  according to comparative example 2.  FIG. 9A  is a perspective view of the portable screen  900 , and FIG.  9 B is a side view of the portable screen  900  for explanation of a folded-up state of the screen sheet  50 . 
     In  FIGS. 8A ,  8 B,  9 A, and  9 B, the same signs are assigned to the same members as those in  FIGS. 1A and 1B , and the detailed description will be omitted. 
     The portable screen  800  according to comparative example 1 basically has the same configuration as that of the portable screen  1  according to the embodiment, but differs in the configuration of the extendable frames and the number of the plate-like members from the portable screen  1  according to the embodiment. 
     That is, in the portable screen  800  according to comparative example 1, as shown in  FIG. 8A , the number of frame pieces provided along the short side direction of a frame body  810  are two, respectively, and they are formed to be extendable only at one step. Further, plate-like members  862   a ,  864   a ,  862   b ,  864   b  are provided at ends at the short sides of the frame body  10  by two pieces each, according to the number of the frame pieces provided along the short side direction. Further, the lengths of the plate-like members  862   a ,  864   a ,  862   b ,  864   b  are nearly the same as lengths of the frame pieces  812   a ,  814   a ,  812   b ,  814   b , and the lengths of the plate-like members  862   a ,  864   a ,  862   b ,  864   b  correspond to the lengths of the frame pieces  812   a ,  814   a ,  812   b ,  814   b.    
     When the portable screen  800  according to comparative example 1 having the above configuration is folded up, because the number of the plate-like members provided at the ends of one side of the screen sheet  50  is two, the number of times at which the screen sheet  50  is folded is one, and the screen sheet  50  is folded in a V-shape as shown in  FIG. 8B . In this regard, since the frame body  810  and the screen sheet  50  are connected at the long sides of the frame body  810 , the screen sheet  50  is in the unnatural folded state (the screen sheet  50  protrudes from the frame body  810 ). Further, since the extendable frames are extended or retracted at one step only, the lengths in the short side direction (extending and retracting direction) when the portable screen  800  is folded up is relatively long, and the size of the portable screen  800  when folded up is larger than that of the portable screen  1  according to embodiment 1. 
     Further, the portable screen  900  according to comparative example 2 basically has the same configuration as that of the portable screen  1  according to the embodiment, but differs in the number of the plate-like members from the portable screen  1  according to the embodiment. 
     That is, in the portable screen  900  according to comparative example 2, as shown in  FIG. 9A , plate-like members  962   a ,  964   a ,  962   b ,  964   b  are provided at ends at the short sides of the screen sheet  50  by two pieces each. The lengths of the plate-like members  962   a ,  964   a ,  962   b ,  964   b  are longer than the lengths of the frame pieces  12   a  to  16   a ,  12   b  to  16   b.    
     When the portable screen  900  according to comparative example 2 having the above configuration is folded up, because the number of the plate-like members provided at the ends of one side of the screen sheet  50  is two, the number of times at which the screen sheet  50  is folded is one, and the screen sheet  50  is folded in a V-shape as shown in  FIG. 9B . In this regard, since the frame body  10  and the screen sheet  50  are connected at the long sides of the frame body  10 , the screen sheet  50  is in the unnatural folded state (the screen sheet  50  protrudes from the frame body  10 ). Further, since the lengths of the plate-like members  962   a ,  964   a ,  962   b ,  964   b  do not correspond to the lengths of the frame pieces  12   a  to  16   a ,  12   b  to  16   b , the screen sheet  50  more greatly protrudes from the frame body  10  than in the case of the portable screen  800  of comparative example 1. 
     On the other hand, according to the portable screen  1  according to embodiment 1, since the number of the plate-like members provided at the ends of one side of the screen sheet  50  is three, the number of times at which the screen sheet  50  is folded is two, and the screen sheet  50  is neatly folded nearly in an N-shape within the frame body  10  as shown in  FIG. 2B . Further, the lengths of the plate-like members  62   a  to  66   a ,  62   b  to  66   b  correspond to the lengths of the lengths of the frame pieces  12   a  to  16   a ,  12   b  to  16   b , and thereby, the screen sheet  50  is neatly folded within the frame body for that reason. As a result, occurrence of wrinkles and damage on the screen sheet  50  when the screen is carried can be suppressed. 
     Embodiment 2 
       FIGS. 10A and 10B  are diagrams for explanation of a portable screen  2  according to embodiment 2.  FIG. 10A  is a perspective view showing a state in which frame pieces  112   a  to  116   a ,  112   b  to  116   b  are extended, and  FIG. 10B  is a perspective view showing a state in which the frame pieces  112   a  to  116   a ,  112   b  to  116   b  are retracted. In  FIGS. 10A and 10B , the screen sheet is omitted to be shown. 
       FIGS. 11A and 11B  are diagrams for explanation of a lock mechanism  130   a  for maintaining the extended state of the frame body in the portable screen  2  according to embodiment 2.  FIG. 11A  shows a first lock mechanism  174   a  for locking the frame piece  112   a  and the frame piece  114   a , and  FIG. 11B  shows a second lock mechanism  180   a  for locking the frame piece  114   a  and the frame piece  116   a.    
       FIGS. 12A to 12C  are diagrams for explanation of a lock mechanism  130   c  for maintaining the spread state of the frame body in the portable screen  2  according to embodiment 2.  FIG. 12A  is a perspective view of a hinge member  140   c ,  FIG. 12B  is a perspective view of the hinge member  140   c  seen from a different angle from that in  FIG. 12A , and  FIG. 12C  schematically shows the lock mechanism  130   c . In  FIGS. 12A to 12C , only one hinge member  140   c  of the plural hinge members is enlarged and shown. 
       FIG. 13A to 13C  are diagrams for explanation of the lock mechanism  130   c  for maintaining the spread state of the frame body in the portable screen  2  according to embodiment 2.  FIG. 13A  shows the lock mechanism  130   c  when the portable screen  2  is folded up,  FIG. 13B  shows the lock mechanism  130   c  in the process of spreading out the portable screen  2 , and  FIG. 13C  shows the lock mechanism  130   c  when the portable screen  2  is spread out. 
     The portable screen  2  according to embodiment 2 basically has the same configuration as that of the portable screen  1  according to the embodiment, but differs in the configuration of the lock mechanism for maintaining the extended state of the frame body and the configuration of the lock mechanism for maintaining the spread state of the frame body from the portable screen  1  according to embodiment 1. 
     That is, in the portable screen  2  according to embodiment 2, the lock mechanism  130   a  for maintaining the extended state of the frame body includes the first lock mechanism  174   a  (a lock pin  170   a  and a fitting hole  172   a ) for locking the frame piece  112   a  and the frame piece  114   a , the second lock mechanism  180   a  (a lock pin  176   a  and a fitting hole  178   a ) for locking the frame piece  114   a  and the frame piece  116   a , a lock release button  182   a  provided in the upper part of an extendable frame  132   a , a first lock release member  184   a  connected to the lock release button  182   a  for releasing the locking of the first lock mechanism  174   a  and a second lock release member  190   a  for releasing the locking of the second lock mechanism  180   a  as shown in  FIGS. 10A ,  10 B,  11 A, and  11 B. 
     The first lock release member  184   a  has a guide part  186   a  for guiding the first lock release member  184   a  to move within the frame piece  112   a  and a lock release part  188   a  for fitting in a recessed portion  173   a  of the lock pin  170   a  and releasing the locking of the first lock mechanism  174   a . Further, the second lock release member  190   a  has a lock release part  191   a  attached to the frame piece  112   a  for fitting into a recessed portion of the  179   a  of the lock pin  176   a  and releasing the second lock mechanism  180   a . Springs  171   a ,  177   a  are connected to the lock pins  170   a ,  176   a , respectively, and the respective lock pins  170   a ,  176   a  are urged toward the inner surfaces of the frame pieces  114   a ,  116   a  by the elastic force of the springs  171   a ,  177   a . When the positions of the respective fitting holes  172   a ,  178   a  coincide with the positions of the lock pins  170   a ,  176   a , the respective lock pins  170   a ,  176   a  fit in the fitting holes  172   a ,  178   a , respectively. The lock mechanism  130   b  has the same configuration as that of the lock mechanism  130   a.    
     In the portable screen  2  according to embodiment 2, by pulling the respective frame pieces  112   a  to  116   a  until the lock pins  170   a ,  176   a  come to the position of the respective fitting holes  172   a ,  178   a  formed to the frames  114   a ,  116   a , locking of the lock mechanism  130   a  (the first lock mechanism  174   a  and the second lock mechanism  180   a ) works and the frame body  110  can be maintained in the state extended in the direction along the short sides (see  FIG. 10A ). 
     Further, by pressing the lock release button  182   a , the first lock release member  184   a  moves downwardly, the lock release part  188   a  fits into the recessed portion  173   a  of the lock pin  170   a , and the fitting of the lock pin  170   a  in the fitting hole  172   a  is released. As a result, the frame piece  114   a  becomes movable relative to the frame piece  112   a  and the frame body  110  can be retracted in the direction along the short sides. 
     Furthermore, by applying force to press the frame piece  112   a  into the frame piece  114   a , the second lock release member  190   a  connected to the frame piece  112   a  moves downwardly, the lock release part  191   a  fits into the recessed portion  179   a  of the lock pin  176   a , and the fitting of the lock pin  176   a  in the fitting hole  178   a  is released. As a result, the frame piece  116   a  becomes movable relative to the frame piece  114   a  and the frame body  110  can be further retracted in the direction along the short sides (see  FIG. 10B ). 
     The reliability and operability of the lock operation and lock release operation of the lock mechanism  130   a  (the first lock mechanism  174   a  and the second lock mechanism  180   a ) may be adjusted by the elasticity of the springs, the shapes of the lock pins  170   a ,  176   a , the shapes of the fitting holes  172   a ,  178   a , or the like. 
     In the portable screen  2  according to embodiment 2, the lock mechanism  130   c  for maintaining the spread state of the frame body has a lock pin  190   c  having a recessed portion at its leading end, and a cylindrical member  192   c  fixed to the frame piece  112   c  and having two grooves  194   c ,  196   c  formed diagonal positions as shown in  FIGS. 12A to 12C . A spring is connected to the lock pin  190   c  so that the lock pin  190   c  may fit in one of the two grooves  194   c ,  196   c  by the elastic force of the spring. The other lock mechanisms  132   c ,  134   c ,  130   d  to  134   d  have the same configuration as that of the lock mechanism  130   c.    
     In the portable screen  2  according to embodiment 2, as shown in  FIGS. 13A to 13C , from the locked state in which the frame pieces  112   c  and  114   c  are folded and the lock pin  190   c  fits into the groove  196   c , the hinge member  140   c  is rotated in a direction of arrow A, and thereby, the fitting state of the lock pin  190   c  and the groove  196   c  is released and the locking of the lock mechanism  130   c  is released. Further, in this state, by further rotating the hinge member  140   c  in a direction of arrow B, the lock pin  190   c  slidingly moves on the side surface of the cylindrical member  192   c . Then, when the frame body  110  is in the spread-out state, the lock pin  190   c  fits in the groove  194   c  and the locking of the lock mechanism  130   c  works again. As a result, the spread-out state of the frame body  110  is maintained. 
     Further, by rotating the hinge member  140   c  in an opposite direction to the arrow B, the fitting state of the lock pin  190   c  and the groove  194   c  is released and the locking of the lock mechanism  130   c  is released. Furthermore, in this state, by further rotating the hinge member  140   c  in the opposite direction to the arrow A to make the folded-up state of the frame body  110 , the lock pin  190   c  fits in the groove  194   c  and the locking of the lock mechanism  130   c  works again. As a result, the folded-up state of the frame body  110  is maintained. 
     The reliability and operability of the lock operation and lock release operation in the lock mechanism  130   c  may be adjusted by the magnitude of the elastic force of the spring, the shapes of the recessed portion in the lock pin  190   c , the shapes of the grooves  194   c ,  196   c , or the like. 
     As described above, in the portable screen  2  according to embodiment 2, the lock mechanism for maintaining the extended state of the frame body and the lock mechanism for maintaining the spread state of the frame body are different in configuration from the case of the portable screen  1  according to embodiment 1. However, as is the case of the portable screen  1  according to embodiment 1, the portable screen can be spread out and folded up only by two actions of extending or retracting it along the short side direction and spreading out or folding up along the long side direction, and thus, the time and effort taken to spread out and fold up the portable screen can be greatly saved. 
     Further, according to the portable screen  2  according to embodiment 2, since the first locking release member  184   a  is connected to the lock release button  182   a  and the second lock release member  190   a  is integrated with the frame piece  112   a , the release operation for the locking in the two lock mechanisms (the first lock mechanism  174   a  and the second lock mechanism  180   a ) can be performed by easy operations. 
     Furthermore, since the portable screen  2  according to embodiment 2 has the lock mechanism  130   c  having the lock pin  190   c  having the recessed portion at its leading end and the cylindrical member  192   c  having two grooves  194   c ,  196   c , the operations of making the spread-out state and the folded-up state of the frame body can be performed by reliable and easy operations. 
     The portable screen  2  according to embodiment 2 has the same configuration as that of the portable screen  1  according to embodiment 1 except that the configuration of the lock mechanism for maintaining the extended state of the frame body and the lock mechanism for maintaining the spread state of the frame body is different, and thus, has the corresponding advantages of the advantages that the portable screen  1  according to embodiment 1 has. 
     As above, the portable screen of the embodiment of the invention has been described based on the embodiments, but the invention is not limited to the above embodiments and can be implemented in various embodiments without departing the scope of the invention and the following modifications can be made, for example. 
     The case where the frame body has a rectangular shape in a plan view has been described as an example in the embodiments, however, the invention is not limited to that, but other shapes such as a circular shape may be adopted, for example. 
     The case where the short side part includes three frame pieces and the long side part includes four frame pieces has been described as an example in the embodiments, however, the invention is not limited to that, but the larger number of frame pieces than that described in the embodiments may be included. 
     The case where the short side part includes extendable frames as the configuration extendable in the frame body has been described as an example in the embodiments, however, the invention is not limited to that, but other means may be used as long as the frame body can be extended and retracted. Further, the case where the long side part includes the hinge members as the configuration that can be spread out or folded up in the frame body has been described as an example in the embodiments, however, the invention is not limited to that, but other means may be used as long as the frame body can be spread out and folded up. 
     The lock mechanism including the protruding portion and the fitting hole has been described as an example as the lock mechanism provided at the short sides of the frame body  10  in the embodiments, however, the invention is not limited to that, but other means may be used as long as the extended state of the frame body  10  can be maintained. Further, the lock mechanism including the protruding portion and the fitting hole has been described as an example as the lock mechanism provided at the long sides of the frame body  10  in the embodiments, however, the invention is not limited to that, but other means may be used as long as the spread state of the frame body  10  can be maintained. 
     The screen sheet on one side of which the image projection surface is formed has been used in the embodiments, however, the invention is not limited to that, but a screen sheet on both sides of which image projection surfaces are formed may be used. 
     The case where the respective frame pieces include aluminum frames has been used as an example in the embodiments, however, the invention is not limited to that, but frame pieces made of metal materials other than the aluminum may be used or frame pieces made of other materials such as a resin material may be used, for example. 
     The plastic plates have been used as the plate-like members in the embodiments, however, the invention is not limited to that, but plate-like members made of other materials may be used. Further, plate-like members having rectangular shapes in a plan view have been used as the plate-like members in the embodiments, however, the invention is not limited to that, but plate-like members having other shapes may be used. 
     The frame pieces at the short sides and the frame pieces at the long sides have been connected by joint members in the embodiments, however, the invention is not limited to that. For example, the frame piece at the short side (the frame piece  12   a  shown in  FIGS. 1A and 1B ) and the frame piece at the long side (the frame piece  12   c  shown in  FIGS. 1A and 1B ) may be integrated. 
     The entire disclosure of Japanese Patent Application No. 2008-028504, filed Feb. 8, 2008 and No. 2008-252651, filed Sep. 30, 2008 are expressly incorporated by reference herein.