Variable shape frame and variable shape three-dimensional structure

1. A variable shape frame which has a polygonal shape and whose shape can be changed, comprising:

extendable arms forming each side of the polygonal frame; and

corner members located at at least two of all corners of the polygon, wherein

each of the extendable arms includes

a plurality of cross units each formed by two rigid members crossing each other in an X-shape and pivotally coupled by a middle coupling shaft, and

an end coupling portion pivotally coupling ends of adjacent ones of the cross units,

the end coupling portion includes inner end coupling shafts located on an inner side of the polygonal frame and outer end coupling shafts located on an outer side of the polygonal frame,

adjacent two of the extendable arms are pivotally coupled by a common one of the inner end coupling shafts at every corner of the polygon, and

the corner member located between the first extendable arm and the second extendable arm which are adjacent to each other includes a first guide portion and a second guide portion, the first guide portion linearly guiding two or more of the inner end coupling shafts, two or more of the middle coupling shafts, or two or more of the outer end coupling shafts of the first extendable arm in a longitudinal direction of the side formed by the first extendable arm, and the second guide portion linearly guiding two or more of the inner end coupling shafts, two or more of the middle coupling shafts, or two or more of the outer end coupling shafts of the second extendable arm in a longitudinal direction of the side formed by the second extendable arm.

2. The variable shape frame according to claim 1 , wherein

the corner member includes the common inner end coupling shaft that pivotally couples the first extendable arm and the second extendable arm, the first guide portion, and the second guide portion.

3. The variable shape frame according to claim 1 , wherein

the first guide portion linearly guides the two or more of the inner end coupling shafts of the first extendable arm in the longitudinal direction of the side formed by the first extendable arm, and the second guide portion linearly guides the two or more of the inner end coupling shafts of the second extendable arm in the longitudinal direction of the side formed by the second extendable arm.

4. The variable shape frame according to claim 1 , wherein

the corner member includes a first straight member extending in the longitudinal direction of the side formed by the first extendable arm and a second straight member extending in the longitudinal direction of the side formed by the second extendable arm,

the first guide portion is a slit extending from a distal end toward a proximal end of the first straight member, and

the second guide portion is a slit extending from a distal end toward a proximal end of the second straight member.

5. The variable shape frame according to claim 1 , wherein

the polygon is a quadrilateral, and

the corner members are located at two opposite ones of the corners.

6. The variable shape frame according to claim 1 , wherein

the corner members are located at every corner of the polygon.

7. A variable shape frame which has a polygonal shape and whose area can be changed, comprising:

extendable arms forming each side of the polygonal frame; and

a variable length coupling member whose length can be changed and which couples two of the extendable arms which form at least two opposite ones of the sides of the polygonal frame, wherein

each of the extendable arms includes

a plurality of cross units each formed by two rigid members crossing each other in an X-shape and pivotally coupled by a middle coupling shaft, and

an end coupling portion pivotally coupling ends of adjacent ones of the cross units,

the end coupling portion includes inner end coupling shafts located on an inner side of the polygonal frame and outer end coupling shafts located on an outer side of the polygonal frame,

adjacent two of the extendable arms are pivotally coupled by a common one of the inner end coupling shafts at every corner of the polygon,

the variable length coupling member that couples the first extendable arm and the second extendable arm which are located opposite to each other has its one end coupled to the outer end coupling shaft, the middle coupling shaft, or the inner end coupling shaft of the first extendable arm and has the other end coupled to the outer end coupling shaft, the middle coupling shaft, or the inner end coupling shaft of the second extendable arm,

the variable length coupling member includes a first adjustment member and a second adjustment member which can slide relative to each other,

the first adjustment member is a tube member,

the second adjustment member is a core member slidably fitted in the tube member,

the first adjustment member is coupled to the outer end coupling shaft of the first extendable arm,

the second adjustment member is coupled to the outer end coupling shaft of the second extendable arm,

the first adjustment member has a first guide slit that slidably receives the inner end coupling shaft of the first extendable arm, and

the second adjustment member has a second guide slit that slidably receives the inner end coupling shaft of the second extendable arm.

8. A variable shape three-dimensional structure, comprising:

a longitudinal coupling member that holds two of the variable shape frames according to claim 1 such that the two variable shape frames are separated from each other in a vertical direction and parallel to each other.

9. The variable shape three-dimensional structure according to claim 8 , wherein

the longitudinal coupling member is formed by the common inner end coupling shaft extending in the vertical direction so as to couple the upper and lower variable shape frames.

10. The variable shape three-dimensional structure according to claim 8 , wherein

the longitudinal coupling member has such a structure that a longitudinal height of the longitudinal coupling member can be adjusted.

11. The variable shape three-dimensional structure according to claim 8 , wherein

the longitudinal coupling member includes first and second variable shape frames having the same structure as the upper and lower variable shape frames and located opposite to each other,

the outer end coupling shafts of each of upper and lower ones of the extendable arms of the first variable shape frame forming the longitudinal coupling member are pivotally coupled to the outer end coupling shafts of one of the extendable arms of the upper or lower variable shape frame, and

the outer end coupling shafts of each of upper and lower ones of the extendable arms of the second variable shape frame forming the longitudinal coupling member are pivotally coupled to the outer end coupling shafts of another one of the extendable arms of the upper or lower variable shape frame.

12. The variable shape three-dimensional structure according to claim 11 , wherein

the first and second variable shape frames and the upper and lower variable shape frames form four sides of a quadrangular prism.