Patent Publication Number: US-10760591-B2

Title: Air blowing device

Description:
TECHNICAL FIELD 
     The present invention relates to an air circulator which is used in an air circulation-type mat, an air conditioned outer wear and the like which evaporate the sweat coming out from a human body by circulating the air and which is attached to a sheet member that is the material of the air circulation-type mat, air conditioned outer wear and the like. 
     BACKGROUND ART 
     Recently, air circulation-type mats, air conditioned outer wears and the like which evaporate the sweat coming out from human bodies by circulating the air are put into practical use (for example, see Patent Literatures 1 and 2). For example, an air circulation-type mat such as an air conditioned sitting mat includes a spacer, a sheet member and an air circulator. The spacer is for securing a space inside the air circulation-type mat. The sheet member is for covering the spacer and for example, a piece of cloth or the like is used as the sheet member. The air circulator is for generating an air flow inside the space which is secured by the spacer. Such air circulator is attached to the sheet member. By using a spacer having a configuration where its air resistance is very small, the air can flow inside the space secured by the spacer only consuming small amount of electricity. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: Japanese Patent No 4399765 
         Patent Document 2: Japanese Republication of PCT International Publication No. WO2006/009108 
       
    
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     With respect to the air circulators which are used in the air circulation-type mats, air conditioned outer wears and the like, in order to improve the air conditioning effect, the air circulators need to be firmly attached to the sheet members so that the air does not leak from the attaching parts of the air circulators when operating and so that the air circulators do not come off easily from the sheet members. On the other hand, in cases where the sheet members need to be washed and the like, users need to be able to easily take off the air circulators from the sheet members. 
     The conventional air circulators are configured so as to be attachable and detachable to and from the sheet members to a certain extent. However, when actually using them, the users cannot easily attach the air circulators to the sheet members and cannot easily detach the air circulators from the sheet members. Therefore, the conventional air circulators have a problem that they cannot be easily attached and detached. 
     The present invention was made in view of the above problem and an object is to provide an air circulator having a simple configuration which allows a user to easily attach and detach the air circulator to and from a sheet member. 
     Means for Solving the Problem 
     To solve the above problem, the present invention is an air circulator which is attached to a sheet member and which is for generating an air flow from one side of the sheet member to another side of the sheet member, including: 
     a fan main body; and 
     a ring member for attaching the fan main body to the sheet member, wherein 
     the fan main body includes:
         a hollow cylinder unit;   a flange which is formed on the cylinder unit so as to protrude from an outer surface of the cylinder unit in a direction approximately orthogonal to the outer surface;   a motor fixing unit for fixating a motor;   a motor which is fixated to the motor fixing unit;   a wing which is attached to a rotating shaft of the motor; and   first engaging units which are formed on outer surfaces of first parts of the cylinder unit, the first parts forming a pair and facing each other, the ring member includes:   second engaging units which are formed on inner surfaces of second parts that form a pair, the second parts facing each other, and which engage with the first engaging units; and   one or a plurality of protrusions formed, with respect to each of the second parts that form a pair, on an outer surface of the ring member at a part corresponding to the second part and nearby,       

     a width between two points on an inner surface of the ring member at the second parts that form a pair equals to a width between two points on the outer surface of the cylinder unit at the first parts that form a pair or smaller than the width between the two points on the outer surface of the cylinder unit at the first parts that form a pair, 
     a width between two points on the inner surface of the ring member at a pair of pressing parts, the pressing parts being two parts shifted from second parts that form a pair by approximately 90 degrees, is larger than a width between two points on the outer surface of the cylinder unit at two parts shifted from first parts that form a pair by approximately 90 degrees, 
     an inner circumference of the ring member is larger than an outer circumference of the cylinder unit, 
     the ring member is flexible, 
     by fitting the ring member around the outer surface of the cylinder unit utilizing the flexibility of the ring member so as to make an edge part of the sheet member around an opening formed in the sheet member be held between a back surface of the flange and one end surface of the ring member and to make the first engaging units and the second engaging units engage with each other, the fan main body is attached to the sheet member, and 
     by squeezing the pair of pressing parts of the ring member so as to make the ring member bend, engaging of the first engaging units and the second engaging unit is released and the fan main body can be detached from the sheet member. 
     To solve the above problem, the present invention is an air circulator which is attached to a sheet member and which is for generating an air flow from one side of the sheet member to another side of the sheet member, including: 
     a fan main body; and 
     a ring member for attaching the fan main body to the sheet member, wherein 
     the fan main body includes:
         a hollow cylinder unit;   a flange which is formed on the cylinder unit so as to protrude from an outer surface of the cylinder unit in a direction approximately orthogonal to the outer surface;   a motor fixing unit for fixating a motor;   a motor which is fixated to the motor fixing unit;   a wing which is attached to a rotating shaft of the motor; and   first engaging units which are formed on outer surfaces of first parts of the cylinder unit, the first parts forming a pair and the first parts facing each other,       

     the ring member includes:
         second engaging units which are formed on inner surfaces of second parts that form a pair, the second parts facing each other, and which engage with the first engaging units,       

     a width between two points on an inner surface of the ring member at the second parts that form a pair equals to a width between two points on the outer surface of the cylinder unit at the first parts that form a pair or smaller than the width between the two points on the outer surface of the cylinder unit at the first parts that form a pair, 
     a width between two points on the inner surface of the ring member at a pair of pressing parts, the pressing parts being two parts shifted from second parts that form a pair by approximately 90 degrees, is larger than a width between two points on the outer surface of the cylinder unit at two parts shifted from first parts that form a pair by approximately 90 degrees, 
     an inner circumference of the ring member is larger than an outer circumference of the cylinder unit, 
     the ring member is flexible, 
     parts of an outer corner at end parts of the ring member on the pressing part sides, the pressing parts forming a pair, and on a side that face the flange, are chamfered, 
     by fitting the ring member around the outer surface of the cylinder unit utilizing the flexibility of the ring member so as to make an edge part of the sheet member around an opening formed in the sheet member be held between a back surface of the flange and one end surface of the ring member and to make the first engaging units and the second engaging units engage with each other, the fan main body is attached to the sheet member, and 
     by squeezing the pair of pressing parts of the ring member so as to make the ring member bend, engaging of the first engaging units and the second engaging unit is released and the fan main body can be detached from the sheet member. 
     By having the above configuration, in the air circulator of the present invention, the fan main body is placed so that the back surface of the flange of the fan main body comes in contact with the edge part of the sheet member around the opening formed in the sheet member, the positions of the first engaging units of the fan main body and the positions of the second engaging units of the ring member are matched, the ring member is fit around the outside of the cylinder unit of the fan main body from below the fan main body by utilizing the flexibility of the ring member and the first engaging units of the fan main body and the second engaging units of the ring member are engaged with each other and in such way, the ring member can be easily attach and firmly fixated to the fan main body. When the ring member and the fan main body are fixated in such way, the edge part of the sheet member around the opening formed in the sheet member is held between the back surface of the flange of the fan main body and one end surface of the ring member and thereby, as a result, the air circulator can be firmly attached to the sheet member. Further, when detaching the air circulator from the sheet member, the ring member is held by the pair of pressing parts between a thumb and an index finger, for example, and the positions corresponding to the pressing parts that form a pair are squeezed toward each other so that the inner surfaces thereof come in contact with the outer surface of the cylinder unit of the fan main body by utilizing the flexibility of the ring member. In such way, the areas near the second parts of the ring member bulge and the engaging state of the first engaging units and the second engaging unit will be released and thus, the ring member can be easily detached from the fan main body. As described above, the air circulator of the present invention has a simple configuration and a user can easily attach and detach the air circulator to and from the sheet member. 
     Further, in the air circulator of the present invention, with respect to each of the second parts that form a pair, one or a plurality of protrusions are formed on the outer surface of the ring member at the second part and nearby thereof or parts of the outside corner at the end parts of the ring member on the pressing part sides, the pressing parts forming a pair, and on the side that faces the flange, is chamfered and thereby, the shape of the ring member which comes in contact with the sheet member substantially becomes close to a circle shape. Therefore, even if a force toward outside is applied to the air circulator of the present invention from inside of the sheet member for some reason, the same amount of force is equally applied to any parts of the ring member and the ring member can be prevented from falling off. 
     Effects of the Invention 
     The air circulator of the present invention has a simple configuration and a user can easily attach and detach the air circulator to and from a sheet member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1( a )  is a schematic perspective view where an air circulation-type mat for chair using an air circulator which is the first embodiment of the present invention is in use and  FIG. 1( b )  is a schematic cross-sectional view where the air circulation-type mat is in use. 
         FIG. 2( a )  is a schematic front view of the air circulator of the first embodiment and  FIG. 2( b )  is a schematic side view of the air circulator. 
         FIG. 3( a )  is a view for describing an opening formed in a sheet member and  FIG. 3( b )  is a schematic side view for describing a state where the air circulator is attached to the sheet member. 
         FIG. 4( a )  is a schematic side view of a main body case of the air circulator of the first embodiment,  FIG. 4( b )  is a schematic side view of a cylinder unit with flange of the main body case, the cylinder unit with flange being the main part of the present invention,  FIG. 4( c )  is a schematic side view of the cylinder unit with flange in a state where the cylinder unit with flange shown in  FIG. 4( b )  is rotated 90 degrees around the center axis of the cylinder unit with flange and  FIG. 4( d )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows A. 
         FIG. 5( a )  is a schematic front view of an attachment ring of the air circulator of the first embodiment,  FIG. 5( b )  is a schematic side view of the attachment ring,  FIG. 5( c )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows B and  FIG. 5( d )  is a schematic view of the attachment ring when cut along and seen in the directions indicated by the arrows C. 
         FIG. 6( a )  is a schematic perspective view of the cylinder unit with flange of the air circulator of the first embodiment and  FIG. 6( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows D. 
         FIG. 7( a )  is a schematic partial cross-sectional view for describing a state where the cylinder unit with flange and the attachment ring are engaged with each other and  FIG. 7( b )  is a schematic partial cross-sectional view for describing a state where the cylinder unit with flange and the attachment ring are engaged with each other where the attachment ring is being set up-side-down. 
         FIG. 8( a )  is a schematic side view for describing the condition where the fan main body is inserted in the opening of the sheet member and  FIG. 8( b )  is a schematic side view for describing the condition where the air circulator is attached to the opening of the sheet member. 
         FIG. 9( a )  is a schematic back side view of the fan main body to which the attachment ring is attached and  FIG. 9( b )  is a schematic back side view for describing a state where a pair of pressing parts of the attachment ring of the fan main body are pressed toward the center. 
         FIG. 10  is a view showing the force the attachment ring  50  receives from the sheet member  200  when it is bent. 
         FIG. 11( a )  is a schematic plan view of the attachment ring to which chamfering is carried out and  FIG. 11( b )  is a view for describing a state where the air circulator is attached to the sheet member by using the attachment ring to which chamfering is carried out. 
         FIG. 12( a )  is a schematic back side view of the fan main body of the air circulator of the second embodiment and  FIG. 12( b )  is a schematic front view of the attachment ring of the air circulator of the second embodiment. 
         FIG. 13( a )  is a schematic perspective view of the cylinder unit with flange of the air circulator of the third embodiment,  FIG. 13( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows E,  FIG. 13( c )  is a schematic front view of the attachment ring of the air circulator of the third embodiment and  FIG. 13( d )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows F. 
         FIG. 14( a )  is a schematic side view of the cylinder unit with flange of the air circulator of the fourth embodiment,  FIG. 14( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows G,  FIG. 14( c )  is a schematic perspective view of the attachment ring of the air circulator of the fourth embodiment and  FIG. 14( d )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows H. 
         FIG. 15( a )  is a schematic plan view of the attachment ring of the air circulator of the fifth embodiment,  FIG. 15( b )  is a schematic side view of the attachment ring and  FIG. 15( c )  is a schematic back side view of the air circulator of the fifth embodiment. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings. Here, in the following description, a case where the air circulator of the present invention is applied to an air circulation-type mat for chair will be described. 
     First Embodiment 
     First, the first embodiment of the present invention will be described with reference to the drawings.  FIG. 1( a )  is a schematic perspective view where an air circulation-type mat for chair using an air circulator which is the first embodiment of the present invention is in use and  FIG. 1( b )  is a schematic cross-sectional view where the air circulation-type mat is in use. 
     The air circulation-type mat  100  for chair is used by laying it on the sitting surface of a chair. As shown in  FIGS. 1( a ) and 1( b ) , the air circulation-type mat  100  includes a bag-like sheet member  200 , a spacer  102 , an air outlet  103 , an air circulator  1  of the present invention and a power supplying unit (not shown) such as a battery which supplies electricity to the air circulator  1 . 
     The bag-like sheet member  200  is for covering the spacer  102 . As for the sheet member  200 , for example, a piece of cloth is used. The spacer  102  is for securing a space inside the sheet member  200 . The space inside the sheet member  200  becomes the air flow path where the air flows through. The air circulation-type mat  100  is provided with the air outlet  103  at a predetermined end part thereof and the air which flows through the air flow path will be let out from the air outlet  103 . The air circulator  1  is attached at a predetermined part of the sheet member  200  located apart from the air outlet  103 . Although this will be described more in detail later, the air circulator  1  is placed at the opening which is formed in the sheet member  200  and is attached to the edge part of the sheet member  200  around the opening. The air circulator  1  is for generating an air flow from one side of the sheet member  200  to the other side. 
     The outside air which is taken inside the sheet member  200  by the air circulator  1  flows through the space which is secured by the spacer  102 . Thereby, the sweat that came out from a user&#39;s body who is sitting on the air circulation-type mat  100  is quickly evaporated and the humidity at the bottom area can be resolved. The detail description regarding the principal and the configuration of the air circulation-type mat  100  are described in patent literatures such as the pamphlet of International Publication No. 2004/012564 and the like. 
     Here, by using a spacer having a configuration where its air resistance is very small such as the one described in a patent literature, for example, in Japanese Patent No 4067034, a propeller type air circulator whose air circulating pressure is low can be used as the air circulator  1  of the first embodiment. Further, although a case where the propeller of the air circulator  1  is made to rotate so as to take in the outside air through the air circulator  1  in to the sheet member  200  and to let the air out from the air outlet  103  is considered in the first embodiment, the propeller of the air circulator  1  can be made to rotate so that the outside air can be taken in through the air outlet  103  and let out from the air circulator  1 . 
     Next, the air circulator  1  of the first embodiment will be described in detail.  FIG. 2( a )  is a schematic front view of the air circulator  1  of the first embodiment and  FIG. 2( b )  is a schematic side view of the air circulator  1 .  FIG. 3( a )  is a view for describing the opening formed in the sheet member  200  and  FIG. 3( b )  is a schematic side view for describing the state where the air circulator  1  is attached to the sheet member  200 .  FIG. 4( a )  is a schematic side view of the main body case of the air circulator  1  of the first embodiment,  FIG. 4( b )  is a schematic side view of the cylinder unit with flange of the main body case, the cylinder unit with flange being the main part of the present invention,  FIG. 4( c )  is a schematic side view of the cylinder unit with flange in a state where the cylinder unit with flange shown in  FIG. 4( b )  is rotated for 90 degrees around the center axis of the cylinder unit with flange and  FIG. 4( d )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows A.  FIG. 5( a )  is a schematic front view of the attachment ring of the air circulator  1  of the first embodiment,  FIG. 5( b )  is a schematic side view of the attachment ring,  FIG. 5( c )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows B and  FIG. 5( d )  is a schematic view of the attachment ring when cut along and seen in the directions indicated by the arrows C.  FIG. 6( a )  is a schematic perspective view of the cylinder unit with flange of the air circulator  1  of the first embodiment and  FIG. 6( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows D. 
     As shown in  FIGS. 2( a ) and 2( b ) , the air circulator  1  of the first embodiment includes a fan main body  10  and an attachment ring (a ring member)  50 . The fan main body  10  is for realizing the air circulation function which is the original function of the air circulator  1 . The attachment ring  50  takes a role as a tool exclusively used to attach the fan main body  10  to the sheet member  200 . 
     The fan main body  10  includes a main body case  14 , a motor (not shown) which is built in the main body case, a propeller (wing)  12  which is attached to the rotating shaft of the motor and a connector (not shown) for supplying power to the motor. Although the detail description is omitted, the main body case  14  shown in  FIG. 4( a )  includes two parts, the upper part and the lower part, and is formed by fitting these parts together. Here, since the present invention relates to a technique to attach the air circulator  1  to the sheet member  200 , detailed description on the motor and the propeller  12  will be omitted and the relationship between the main body case  14  and the attachment ring  50  will be mainly described. 
     Next, the main body case  14  will be described. Here, upon describing the main body case  14 , it is considered that the main body case  14  is divided in three parts which are the first flow unit  15 , the cylinder unit with flange  20  and the second flow unit  16 , in this order from the top, as shown in  FIG. 4( a )  for the sake of convenience. Among the drawings which are referred to in the present description,  FIGS. 4( b ), 4( c ) and 4( d ) ,  FIGS. 6( a ) and 6( b ) ,  FIGS. 7( a ) and 7( b ) ,  FIGS. 11( a ) and 11( b )  and  FIGS. 12( a ) and 12( b )  do not show the entire main body case  14  and only show the cylinder part with flange  20 , the first flow unit  15  and the second flow unit  16  being omitted. 
     As shown in  FIGS. 2( a ) and 2( b )  and  FIG. 4( a ) , the first flow unit  15  includes a round shaped center base unit  151 , a plurality of bar units  152  which extend radially from the center base unit  151  and a ring unit  153  whose center is the center base unit  151 . Since the first flow unit  15  has such configuration, the first flow unit  15  allows sufficient air to pass through easily and the outside air can be taken inside when the propeller  12  rotates. Further, the first flow unit  15  also takes up the role as a finger guard which protects fingers from being caught in the rotating propeller  12 . The lower part of the first flow unit  15  continues to the cylinder unit with flange  20 . 
     As shown in  FIGS. 2( a ), 2( b ) and 4( a )-4( d ) , the cylinder unit with flange  20  includes a flange  22  which is formed in continuation of the bar units  152  of the first flow unit  15  and a hollow cylinder unit  21 . The cross-section of the cylinder unit  21  when it is cut along the plan surface orthogonal to the center axis thereof is a round shape. Concaves (the first engaging units)  25  are formed at predetermined parts of the cylinder unit  21 . The lower part of the cylinder unit with flange  20  continues to the second flow unit  16 . 
     As shown in  FIG. 2( b )  and  FIG. 4( a ) , the second flow unit  16  includes a plurality of bar units  162 , a ring unit  163 , a motor fixing unit  164  for fixating the motor and a motor cover  165  which is attached under the motor fixing unit  164 . The part formed of the plurality of bar units  162  and the ring unit  163  allows sufficient air to pass through easily and this part can protect fingers from being caught in the rotating propeller  12 . 
     Since the main body case  14  has such configuration, when the motor fixated to the motor fixing unit  164  rotates and the propeller  12  is made to rotate by the motor, the outside air is taken in through the first flow unit  15  and is let out from the second flow unit  16 . 
     As described above, the present invention relates to a technique to attach the air circulator  1  to the opening formed in the sheet member  200  and the cylinder unit with flange  20  and the attachment ring  50  which are a part of the main body case  14  relate to this technique. Therefore, the cylinder unit with flange  20  will be described more in detail. 
     In the first embodiment, the outer diameter t (the width between two points on the outer surface) of the cylinder unit  21  of the cylinder unit with flange  20  is 90 mm as shown in  FIG. 4( b ) . In such case, the inner diameter c of the opening  201  formed in the sheet member  200  is 90 to 91 mm being the same size or slightly larger than the outer diameter t of the cylinder unit  21  as shown in  FIG. 3( a ) . Further, as shown in  FIG. 2( a )  and  FIGS. 4( b ) and 4( c ) , the flange  22  is formed in a round ring shape and protrudes in the direction approximately orthogonal to the outer surface of the cylinder unit  21  at the upper end of the cylinder unit  21 . The outer diameter f of the flange  22  is sufficiently larger comparing to the inner diameter c of the opening  201  formed in the sheet member  200  and is 97 mm, for example. Furthermore, the outer diameter of the second flow unit  16  is 90 mm at the part continuing from the cylinder unit  21  and becomes smaller as approaching the lower part thereof. 
     Since the relationship between the size of each part of the fan main body  10  and the size of the opening  201  formed in the sheet member  200  is as described above, the fan main body  10  can be easily inserted in to the opening  201  formed in the sheet member  200  from above. At this time, the back surface of the flange portion  22  comes in contact with the upper surface of the edge part  202  of the opening  201  (see  FIG. 8( a ) ). 
     Further, as shown in  FIGS. 4( c ), 4( d )  and  FIGS. 6( a ) and 6( b ) , the cylinder unit  21  is provided with concaves  25  which are the first engaging units at two predetermined parts of the cylinder unit  21  that are symmetrical with respect to the center axis, that is, at the outside of the two predetermined parts (a pair of the first engaging parts (the first parts)  23 ) of the cylinder unit  21  that face each other. The concaves  25  are for fixating the attachment ring  50  to the fan main body  10 . The concaves  25  are formed in an approximately square shape when seen from the front and are formed at approximately center of the cylinder unit  21  in the height direction thereof. Further, each of the concaves  25  includes an engaging wall  255  at the lower surface thereof. Here, the lower surfaces themselves of the concaves  25  correspond to the engaging walls  255 . Therefore, the engaging walls  255  are formed so as to be approximately orthogonal to the outer surface of the cylinder unit  21 . Furthermore, the guide inclination units  28  are formed on the outer surface of the cylinder unit  21  at the first engaging parts  23  below the concaves  25 . As shown in  FIG. 4( d )  and  FIG. 6( b ) , each of the guide inclination units  28  is formed so that the thickness of the cylinder unit  21  be thinner as approaching the lower side thereof. Moreover, as shown in  FIG. 4( c ) , the horizontal width of each of the guide inclination units  28  is about the same as the horizontal width of its corresponding concave  25  at the upper side thereof, but the horizontal width of the guide inclination unit  28  becomes wider as approaching the lower side thereof. 
     Next, the attachment ring  50  will be described. As shown in  FIG. 5( a ) , the attachment ring  50  is formed in an oval shape when seen from above (the cross-section shape when the attachment ring  50  is cut along the plan orthogonal to the center axis thereof). The attachment ring  50  is provided with protrusions  52  which are the second engaging units on the inner surface thereof at two predetermined parts facing each other in the minor axis direction thereof (a pair of the second engaging parts (the second parts)  53 ). Here, the attachment ring  50  provided with two protrusions  52  is formed as one by the plastic molding. Therefore, the attachment ring  50  has the plasticity characteristic. Here, the height of the attachment ring  50  is constant around the entire circumference thereof. 
     As shown in  FIGS. 5( c ) and 5( d ) , the protrusions  52  are formed slightly below the center in the height direction of the attachment ring  50 . Each of the two protrusions  52  is for engaging with its corresponding concave  25  of the fan main body  10  and for fixating the attachment ring  50  to the outside of the cylinder unit  21 . Therefore, the positional relationship of the two protrusions  52  is the same as the positional relationship of the two concaves  25 . As shown in  FIGS. 5( a ), 5( c ) and 5( d ) , each of the protrusions  52  are formed in an approximately quadratic prism shape and protrudes toward inside of the attachment ring  50 . In such way, although the shape of the protrusions  52  match the shape of the concaves  25 , the size of the protrusions  52  is slightly smaller than the size of the concaves  25  so that the protrusions  52  can engage with the concaves  25 . Further, each of the protrusions  52  includes an engaging wall  522  at the lower surface thereof. Here, the lower surfaces themselves of the protrusions  52  correspond to the engaging walls  522 . Therefore, the engaging walls  522  are approximately orthogonal to the inner surface of the attachment ring  50 . By the engaging wall  522  of each protrusion  52  and the engaging wall  255  of each concave  25  of the the cylinder unit  21  coming in contact with each other, the engaging state of the fan main body  10  and the attachment ring  50  is realized. Here, as will be described later, in a case where the attachment ring  50  is to be used in the up-side-down state, the upper surface of each protrusion  52  acts as the engaging wall  522 . That is, each protrusion  52  includes the engaging walls  522  at the upper surface and lower surface thereof. Therefore, the upper surface of each protrusion  52  is approximately orthogonal to the inner surface of the attachment ring  50 . 
     As shown in  FIGS. 5( a ) and 5( b ) , at the outside of the two parts that face each other in the long axis direction of the attachment ring  50 , that is, at the outside of the two parts (a pair of pressing parts)  54  shifted from the pair of second engaging parts  53  by approximately 90 degrees, letters “A” are respectively indicated at the upper ends thereof and letters “B” are respectively indicated at the lower ends thereof. In the first embodiment, as will be described later, the attachment ring  50  can be used by setting the A side facing up or by setting the B side facing up so that the air circulator  1  can be attached to different types of sheet members  200  having various thicknesses. The letters “A” and “B” are marks indicating the direction of the attachment ring  50 . Hereinafter, it is assumed that the attachment ring  50  is attached to the fan main body  10  by setting the “A” side facing up unless mentioned otherwise. 
     Further, the width k 1  between two points on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  is smaller than the outer diameter t of the cylinder unit  21  and the width k 2  between two points on the inner surface of the attachment ring  50  at the pair of pressing parts  54  is larger than the outer diameter t of the cylinder unit  21 . Here, since the cylinder unit  21  is formed in a cylinder shape, both the width between two points on the outer surface of the cylinder unit  21  at the pair of first engaging parts  23  and the width between two points on the outer surface of the cylinder unit at two parts shifted from the pair of first engaging parts by approximately 90 degrees equal to t. In particular, the width k 1  between two points on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  is 88 mm and the width k 2  between two points on the inner surface of the attachment ring  50  at the pair of pressing parts  54  is 95 mm. As a result, the length of the inner circumference of the attachment ring  50  is longer than the length of the outer circumference of the cylinder unit  21 . Although the length of the inner circumference of the attachment ring  50  varies according to the height or the like of the protrusions  52 , it is preferred that the length of the inner circumference of the attachment ring  50  is longer than the outer circumference of the cylinder unit  21  by 1.0% to 3.5% of the length of the outer circumference of the cylinder unit  21 . Actually, in the first embodiment, the length of the inner circumference of the attachment ring  50  is longer than the length of the outer circumference of the cylinder unit  21  by about 2% of the length of the outer circumference of the cylinder unit  21 . 
     Further, the thickness of the attachment ring  50  is 2 mm and its height is slightly lower than the height of the cylinder unit  21 . Since the attachment ring  50  is flexible, for example, when the two parts (the pair of pressing parts)  54  where the letters “A” and “B” are indicated are squeezed between a thumb and an index finger, the parts of the attachment ring  50  in the minor axis direction bulge outside and the attachment ring  50  can deform into an approximately circle shape when seen from above. Thereafter, when the squeezing force is released, the attachment ring  50  returns to its original oval shape. 
     As shown in  FIG. 2( b ) , the attachment ring  50  is attached so as to cover the outer surface of the cylinder unit  21  of the fan main body  10 . At this time, the upper end surface of the attachment ring  50  faces the back surface of the flange  22 . 
     Next, the attachment procedure of the air circulator  1  to the sheet member  200  will be described.  FIG. 7( a )  is a schematic partial cross-sectional view for describing a state where the cylinder unit with flange  20  and the attachment ring  50  are engaged with each other and  FIG. 7( b )  is a schematic partial cross-sectional view for describing a state where the cylinder unit with flange  20  and the attachment ring  50  are engaged with each other where the attachment ring  50  is being set up-side-down.  FIG. 8( a )  is a schematic side view for describing the condition where the fan main body  1  is inserted in the opening of the sheet member  200  and  FIG. 8( b )  is a schematic side view for describing the condition where the air circulator  1  is attached to the opening of the sheet member  200 . 
     As shown in  FIG. 3( a ) , the opening  201  for attaching the air circulator  1  is formed in the sheet member  200 . The opening  201  is formed in a circular shape and the inner diameter c of the opening  201  equals to or is slightly larger than the outer diameter t of the cylinder unit  21  which is formed in a cylinder shape. To attach the air circulator  1  to the sheet member  200 , first, the fan main body  10  is inserted in the opening  201  of the sheet member  200  as shown in  FIG. 8( a )  and make the back surface of the flange  22  be in contact with the ring-shaped edge part  202  of the sheet member  200  arranged around the opening  201 . 
     Next, the pair of pressing parts  54  of the attachment ring  50  is held between a thumb and an index finger, for example, and squeezed in the directions indicated by the arrows in  FIG. 8( a )  to deform the attachment ring  50  into an approximately circle shape. Then, while maintaining the deformed state of the attachment ring  50 , the positions of the protrusions  52  of the attachment ring  50  and the positions of the guide inclination units  28  formed at the lower part of the cylinder unit  21  are matched, the attachment ring  50  is fit around the outside of the cylinder unit  21  from below the fan main body  10  and the attachment ring  50  is moved so that the two protrusions  52  are guided along the guide inclination units  28 . In such way, the guide inclination units  28  guides the protrusions  52  when the attachment ring  50  is to be fit around the fan main body  10 . Thereafter, when the deformed state of the attachment ring  50  is released and the attachment ring  50  is further moved upward, the protrusions  52  of the attachment ring  50  respectively enter the concaves  25  of the fan main body  10  and the protrusions  52  and the concaves  25  engage with each other. At this time, due to the flexibility of the attachment ring  50 , the inner surface of the attachment ring  50  is firmly pressed against the outer surface of the cylinder unit  21  at the areas near the second engaging parts  53 . Therefore, since the engaging walls  255  of the concaves  25  and their corresponding engaging walls  522  of the protrusions  52  come in contact with each other, respectively, as shown in  FIG. 7( a ) , the engaging state of the protrusions  52  and the concaves  25  will not be released even if a large force is applied between the fan main body  10  and the sheet member  200 . Further, since the protrusions  52  of the attachment ring  50  are respectively engaged with the concaves  25  of the fan main body  10 , the attachment ring  50  will not rotate with respect to the fan main body  10 . 
     Here, in  FIG. 7( a ) , the engaging walls  255  and  522  can be formed so that the angles formed by the engaging walls  255  of the concaves  25  and the outer surface of the cylinder unit  21  and the angles formed by the engaging walls  522  of the protrusions  52  and the inner surface of the attachment ring  50  be sharp angles. In such case, the engaging state of the protrusions  52  and the concaves  25  can be made even firmer by the engaging walls  255  and the engaging walls  522  respectively biting into each other. 
     In such way, by the attachment ring  50  being firmly fixated to the fan main body  10  and the attachment ring  50  and the fan main body  10  being as one, as shown in  FIG. 8( b ) , the ring-shaped edge part  202  of the sheet member  200  around the opening  201  is held between the back surface of the flange  22  and the upper end surface of the attachment ring  50 . Therefore, the air circulator  1  can be attached to the sheet member  200  easily and unfailingly. Here, when the air circulator  1  is attached to the sheet member  200 , the upper surface of the ring-shaped edge part  202  of the sheet member  200  comes in contact with the back surface of the flange  22  and the back surface of the ring-shaped edge part  202  of the sheet member  200  comes in contact with the upper end surface of the attachment ring  50 . Therefore, the air does not leak from between the flange  22  and the attachment ring  50 . 
     With respect to the air circulation-type mats, air conditioned outer wears and the like, various types of sheet members  200  having different thicknesses are used according to their usage. The air circulator  1  of the first embodiment is designed so that it can be used with various types of sheet members  200  having different thicknesses. In particular, in such design, the protrusions  52  formed on the inner surface of the attachment ring  50  are arranged at positions slightly below the center with respect to the height direction of the attachment ring  50  as shown in  FIGS. 5( c ) and 5( d ) . Therefore, the width in the height direction between the upper end surface of the attachment ring  50  and the upper side engaging walls  522  of the protrusions  52  and the width in the height direction between the lower end surface of the attachment ring  50  and the lower side engaging walls  522  of the protrusions  52  are not the same width. As shown in  FIG. 5( b ) , the letters “A” and “B” are indicated at the pressing parts  54 . Since the height of the attachment ring  50  is constant around the entire circumference thereof, the attachment ring  50  can be used by setting either side, the “A” side or the “B” side, facing up.  FIG. 7( a )  shows the engaging state of the cylinder unit with flange  20  and the attachment ring  50  when the attachment ring  50  is used by setting the “A” side facing up and  FIG. 7( b )  shows the engaging state of the cylinder unit with flange  20  and the attachment ring  50  when the attachment ring  50  is used by setting the “B” side facing up. If the attachment ring  50  is used by setting the “A” side facing up, the space s 1  between the back surface of the flange  22  and the upper end surface of the attachment ring  50  which is formed when the protrusions  52  and the concaves  25  are engaged with each other is small as shown in  FIG. 7( a ) . Therefore, such method of using the attachment ring  50  is suited to the case where the sheet member  200  is a thin material. On the other hand, if the attachment ring  50  is used by setting the “B” side facing up, the space s 2  between the back surface of the flange  22  and the upper end surface of the attachment ring  50  which is formed when the protrusions  52  and the concaves  25  are engaged with each other is large as shown in  FIG. 7( b ) . Therefore, such method of using the attachment ring  50  is suited to the case where the sheet member  200  is a thick material. In such way, the air circulator  1  of the first embodiment can be used with various types of sheet members  200  having different thicknesses. 
     Here, in the first embodiment, by forming the concaves  25 , which are the first engaging units, at the center in the height direction of the cylinder unit  21  and by forming the protrusions  52 , which are the second engaging units, at the positions slightly below the center in the height direction of the attachment ring  50  as described above, the air circulator  1  of the first embodiment can be used with various types of sheet members  200  having different thicknesses. In general, in order to allow the air circulator  1  of the first embodiment be used with various types of sheet members  200  having different thicknesses, the space between the back surface of the flange  22  and the upper end surface of the attachment ring  50  should be different according to which side, the upper side or the lower side, of the attachment ring  50  is set to face up when the attachment ring  50  is attached to the fan main body  10 . Therefore, the positions of the first engaging units with respect to the height direction of the cylinder unit  21  and the positions of the second engaging units with respect to the height direction of the attachment ring  50  can be designed to be formed at different positions. 
     Next, the detaching procedure of the air circulator  1  from the sheet member  200  will be described.  FIG. 9( a )  is a schematic back side view of the fan main body  10  to which the attachment ring  50  is attached and  FIG. 9( b )  is a schematic back side view for describing a state where the pair of pressing parts  54  of the attachment ring  50  of the fan main body  10  are squeezed toward the center. 
     When seen from above (see  FIG. 5( a ) ), the attachment ring  50  is formed in an oval shape where the width k 1  between two points on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  is smaller than the outer diameter t of the cylinder unit  21  of the fan main body  10 , the width k 2  between two points on the inner surface of the attachment ring  50  at the pair of pressing parts  54  is larger than the outer diameter t of the cylinder unit  21  of the fan main body  10  and the length of the inner circumference of the attachment ring  50  is longer then the length of the outer circumference of the cylinder unit  21  by about 2% of the length of the outer circumference of the cylinder unit  21 . Therefore, in the state where the attachment ring  50  is attached to the fan main body  10 , the inner surface of the attachment ring  50  is in contact with the outer surface of the cylinder unit  21  at the areas near the pair of second engaging parts  53  as shown in  FIG. 9( a ) . On the other hand, the inner surface of the attachment ring  50  is not in contact with the outer surface of the cylinder unit  21  at the areas near the pair of pressing parts  54  and spaces  80  are formed between the inner surface of the attachment ring  50  and the outer surface of the cylinder unit  21 . 
     To detach the air circulator  1  from the sheet member  200 , first, the two pressing parts  54  are squeezed in the directions shown by the arrows in  FIG. 9( b ) . In particular, the pair of pressing parts  54  of the attachment ring  50  is held between a thumb and an index finger, for example, and squeezed so that the inner surfaces of the pressing parts come in contact with the outer surface of the cylinder unit  21  of the fan main body  10 . Then, due to the flexibility of the attachment ring  50 , the areas near the pair of second engaging parts  53  of the attachment ring  50  bulge and the engaging state of the protrusions  52  and the concaves  25  is released. Next, while the engaging state of the protrusions  52  and the concaves  25  being released, the attachment ring  50  is pulled downward from the fan main body  10 . In such way, the attachment ring  50  can be easily detached from the fan main body  10 . 
     Further, in the case where the air circulator  1  is to be detached from the sheet member  200 , the engaging state of the one side can be released first and then the engaging state of the other side can be released later instead of releasing the engaging state of both sides at the same time by squeezing the pair of pressing parts  54  of the attachment ring  50 . If the attachment ring  50  is to be detached by such method, there is no need to make the inner circumference of the attachment ring  50  be larger than the outer circumference of the cylinder unit  21  by a great extent. 
     In the air circulator of the first embodiment, the fan main body is placed so that the back surface of the flange of the fan main body comes in contact with the ring-shaped edge part of the sheet member, the positions of the concaves of the fan main body and the positions of the protrusions of the attachment ring are matched, the attachment ring is fit around the cylinder unit of the fan main body from below the fan main body by utilizing the flexibility of the attachment ring and the concaves of the fan main body and the protrusions of the attachment ring are engaged with each other and thereby, the attachment ring can be easily attached and firmly fixated to the fan main body. When the attachment ring and the fan main body are fixated in such way, the ring-shaped edge part of the sheet member is held between the back surface of the flange of the fan main body and the upper end surface of the attachment ring and thereby, as a result, the air circulator can be firmly attached to the sheet member. Further, the pair of pressing parts is squeezed so that the inner surfaces of the pressing parts come in contact with the outer surface of the cylinder unit of the fan main body by utilizing the flexibility of the attachment ring to deform the attachment ring and thereby, the areas near the pair of second engaging parts of the attachment ring bulge and the engaging state of the concaves of the fan main body and the protrusions of the attachment ring can be easily released. Therefore, the attachment ring can be easily detached from the fan main body and the fan main body can be easily detached from the sheet member. In such way, the air circulator of the first embodiment has a simple configuration and a user can easily attach and detach the air circulator to and from the sheet member. 
     Further, in the air circulator of the first embodiment, the length of the inner circumference of the attachment ring is longer than the length of the outer circumference of the cylinder unit by 1.0% to 3.5% of the length of the outer circumference of the cylinder unit. Therefore, the attachment ring can be smoothly attached to and detached from the fan main body. 
     Furthermore, in the first embodiment, the guide inclination units for guiding the protrusions of the attachment ring when fitting the attachment ring on the fan main body are formed at the pair of first engaging parts of the cylinder unit. Therefore, the protrusions of the attachment ring can be guided to the concaves of the fan main body and the attachment ring can be smoothly attached to the fan main body. 
     Moreover, in the first embodiment, the height of the attachment ring is constant around the entire circumference, each of the protrusions include the engaging walls at the upper surface and the lower surface thereof, the width in the height direction between the upper end surface of the attachment ring and the upper side engaging walls of the protrusions and the width in the height direction between the lower end surface of the attachment ring and the lower side engaging walls of the protrusions are not equal to each other, and the space between the back surface of the flange and the end surface of the attachment ring that faces the back surface of the flange formed when the attachment ring is fit around the fan main body in the normal direction and the concaves and the protrusions are engaged with each other and the space between the back surface of the flange and the end surface of the attachment ring that faces the back surface of the flange formed when the attachment ring is fit around the fan main body up-side-down and the concaves and protrusions are engaged with each other are not equal to each other. Therefore, by using the attachment ring by setting either sides thereof facing up, the air circulator can be firmly fixated to the sheet member regardless of whether the sheet member is a thick material or a thin material. 
     Here, in the embodiment, the case where each of the protrusions of the attachment ring is provided with the engaging walls at the upper surface and the lower surface thereof so that the attachment ring can be used either way, the upper side thereof facing up or the lower side thereof facing up, is described. However, if there is no need to use the attachment ring in two ways, the upper side thereof facing up and the lower side thereof facing up, it is sufficient that each of the protrusions of the attachment ring is provided with only the lower surface engaging wall. In such case, by forming the inclination units instead of the engaging walls at the upper parts of the protrusions of the attachment ring, the attachment ring can be attached more smoothly. 
     Further, in the embodiment, the case where the width k 1  between two points on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  is smaller than the outer diameter t of the cylinder unit  21  is described. However, the width k 1  between two points on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  may be equal to the outer diameter t of the cylinder unit  21 . This is because if the inner surface of the attachment ring  50  comes in contact with the outer surface of the cylinder unit  21  at the areas near the pair of second engaging parts  53 , the attachment ring  50  and the fan main body  10  will be firmly fixated to each other. 
     Furthermore, in the embodiment, it is preferred that the parts of the outside corner at the end parts of the attachment ring  50  on the pressing part  54  sides, the pressing parts  54  forming a pair, and on the side that faces the flange  22  is chamfered. In the state where the air circulator  1  is attached to the sheet member  200 , the air circulator  1  presses against the sheet member  200  and the sheet member  200  bends at the corner of the attachment ring  50  if a force toward outside is applied to the air circulator  1  from inside of the sheet member  200  for some reason and the attachment ring  50  receives a force toward the center thereof due to the sheet member  200  bending.  FIG. 10  shows the force which the attachment ring  50  receives due to the sheet member  200  bending. At this time, if the attachment ring is formed in a circle shape when seen from the above, any part of the attachment ring equally receives the same amount of force and thus, the attachment ring will not deform. In contrary, since the attachment ring  50  of the embodiment is formed in an oval shape when seen from above, the pair of pressing parts (the parts facing each other in the long axis direction)  54  of the attachment ring  50  receives a force that is greater comparing to the force which the pair of second engaging parts (the parts facing each other in the short axis direction)  53  receives. Therefore, the pair of pressing parts  54  may be pushed inside and the attachment ring  50  may deform into a circle shape causing the attachment ring  50  to fall off from the fan main body. By the parts of the outside corner at the end parts of the attachment ring  50  on the pressing part  54  sides, the pressing parts  54  forming a pair, and on the side that faces the flange  22  being chamfered, the shape of the attachment ring  50  which comes in contact with the sheet member  200  substantially becomes close to a circle shape and thus, even if a force toward outside is applied to the air circulator  1  from the inside of the sheet member  200  for some reason, the pair of pressing parts  54  acts so as to reduce the force from the sheet member  200  and the attachment ring  50  can be prevented from falling off.  FIG. 11( a )  is a schematic plan view of the attachment ring  50  to which chamfering is carried out and  FIG. 11( b )  is a view for describing a state where the air circulator  1  is attached to the sheet member  200  by using the attachment ring  50  to which chamfering is carried out. In  FIGS. 11( a ) and 11( b ) , the outer edge parts of the attachment ring  50  at the pair of pressing parts  54  and the surrounding areas thereof on the upper end side of the attachment ring  50  are the parts (chamfered parts)  541  where chamfering is carried out. Further, although the predetermined parts of the attachment ring  50  are chamfered by cutting off the parts so as to form plan surfaces in the example shown in  FIGS. 11( a ) and 11( b ) , in general, the predetermined parts of the attachment ring  50  may be chamfered by cutting off the parts so as to form curved surfaces. Here, it is preferred that the parts of the outside corner at the end parts of the attachment ring on the pressing part sides, the pressing parts forming a pair, and on the side that faces the flange be chamfered not only in the air circulator of the first embodiment but also in the air circulators of various embodiments which will be described later. 
     Modification Example 
     Next, a modification example of the first embodiment will be described. 
     In the above described first embodiment, the case where the first engaging units are the concaves  25  which are formed on the outer surface of the cylinder unit  21  at the pair of first engaging parts  23  and the second engaging units are the protrusions  52  which are formed on the inner surface of the attachment ring  50  at the pair of second engaging parts  53  is described. However, in this modification example, protrusions are used as the first engaging units instead of concaves and concaves are used as the second engaging units instead of protrusions. The rest of the configuration is the same as the configuration of the first embodiment described above. Therefore, the detail description will be omitted here. In the modification example, the upper surfaces of the protrusions which are the first engaging units are the engaging walls and the upper surfaces of the concaves which are the second engaging units are the engaging walls. Further, in the first embodiment, the guide inclination units are formed at the pair of first engaging parts  23 . However, in the modification example, the guide inclination units are formed at the pair of second engaging parts where protrusions are not formed. As described above, the only difference is that the protrusions and the concaves are replaced with each other and thus, the air circulator of the modification example operates in the same way as the air circulator of the first embodiment. That is, the attachment procedure and the detachment procedure of the air circulator are exactly the same as the procedures described in the first embodiment. Therefore, the air circulator of the modification example has the same advantages as those of the first embodiment. Here, in the above described case, the concaves as the second engaging units may be through holes. 
     Second Embodiment 
     Next, the second embodiment of the present invention will be described.  FIG. 12( a )  is a schematic back side view of the fan main body of the air circulator of the second embodiment and  FIG. 12( b )  is a schematic front view of the attachment ring of the air circulator of the second embodiment. 
     In the above first embodiment, the case where the cross-section of the cylinder unit of the fan main body when cut along the plan surface orthogonal to the center axis thereof is a circle shape is described. However, in the second embodiment, as shown in  FIG. 12( a ) , the cross-section of the cylinder unit  21   a  of the fan main body  10   a  when cut along the plan surface orthogonal to the center axis thereof is an approximately rectangular shape, for example. Concaves as the first engaging units are formed on the outer surface of the cylinder unit  21   a  at the pair of first engaging parts  23 , the first engaging parts  23  facing each other. In such case, as shown in  FIG. 12( b ) , the attachment ring  50   a  is also formed so that the cross-section of the attachment ring  50   a  when cut along a plan surface orthogonal to the center axis thereof be an approximately rectangular shape corresponding to the shape of the cylinder unit  21   a  of the fan main body  10   a . The protrusions  52   a  as the second engaging units which engage with the first engaging units are formed on the inner surface of the attachment ring  50   a  at the pair of second engaging parts  53 , the second engaging parts  53  facing each other. However, in the second embodiment, the areas near the protrusions  52   a  of the attachment ring  50   a  are curved inside and the width k 1  between two point on the inner surface of the attachment ring  50   a  at the pair of second engaging parts  53  is slightly smaller comparing to the width t 1  between two points on the outer surface of the cylinder unit  21   a  at the pair of first engaging parts  23 . Further, the two sides of the attachment ring  50   a  which face each other and which do not include the second engaging parts  53  are formed so as to slightly bulge toward outside. Therefore, similarly to the first embodiment, the areas near the pair of second engaging parts  53  will bulge outside when the two sides of the attachment ring  50   a  (a pair of pressing parts) that bulge toward outside are squeezed in the second embodiment. Therefore, the air circulator of the second embodiment has the function and advantages similar to those in the case of the above described first embodiment and a user can easily attach and detach the air circulator to and from the sheet member. Here, the rest of the configuration of the second embodiment is the same as that of the above described first embodiment. Therefore, the detail description thereof is omitted here. 
     Third Embodiment 
     Next, the third embodiment of the present invention will be described.  FIG. 13( a )  is a schematic perspective view of the cylinder unit with flange of the air circulator of the third embodiment,  FIG. 13( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows E,  FIG. 13( c )  is a schematic front view of the attachment ring of the air circulator of the third embodiment and  FIG. 13( d )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows F. 
     In the third embodiment, as shown in  FIGS. 13( a ) and 13( b ) , the cylinder unit  21  extends downward at the pair of first engaging parts  23 . Further, the protrusions  26  as the first engaging units are formed on the outer surfaces of the extended parts. Here, the upper surfaces of the protrusions  26  are the engaging walls  255   a . Furthermore, the inclination unit  61   a  for smoothly fitting the attachment ring is formed at the lower parts of the protrusions  26 . On the other hand, as shown in  FIGS. 13( c ) and 13( d ) , the second engaging units are not formed at the pair of second engaging parts  53  of the attachment ring  50  and the inclination units  61   b  for smoothly fitting the attachment ring  50  are formed at the upper end part of the attachment ring  50  at the pair of second engaging parts  53 . In the third embodiment, similarly to the first embodiment, the pair of pressing parts  54  are squeezed, the positions of the inclination units  61   a  formed on the cylinder unit  21  and the positions of the inclination units  61   b  formed on the attachment ring  50  are matched and the attachment ring  50  is fit around the cylinder unit  21  from below the fan main body and thereby, the attachment ring  50  is attached to the fan main body. At this time, the engaging walls  255   a  of the cylinder unit  21  and the lower end surface of the attachment ring  50  engage with each other. That is, in such case, the parts of the lower end surface of the attachment ring  50  at the pair of second engaging parts  53  act as the engaging walls  522   a  and they can be assumed as being the second engaging units. In such way, by the engaging walls  255   a  of the cylinder unit  21  and the lower end surface  522   a  of the attachment ring  50  engaging with each other, the attachment ring  50  will not falloff from the fan main body even if an outer force is applied to the air circulator. Further, in the third embodiment, small concaves (rotation stoppers)  62   a  are formed on the outer surface of the cylinder unit  21  at the pair of first engaging parts  23  and small protrusions (rotation stoppers)  62   b  are formed on the attachment ring  50  at the parts corresponding to the concaves  62   a  so that the two sets of the rotation stoppers  62   a  and  62   b  engage with each other when the attachment ring  50  is attached to the fan main body. In such way, the attachment ring  50  can be prevented from rotating with respect to the cylinder unit  21 . Since the air circulator of the third embodiment has such configuration, it has the function and the advantages similar to those of the first embodiment and a user can easily and unfailingly attach the air circulator to the sheet member and easily detach the air circulator from the sheet member. Here, the rest of the configuration of the third embodiment is the same as that of the above described first embodiment. Therefore, the detailed description thereof is omitted here. 
     Fourth Embodiment 
     Next, the fourth embodiment of the present invention will be described.  FIG. 14( a )  is a schematic side view of the cylinder unit with flange of the air circulator of the four embodiment,  FIG. 14( b )  is a schematic cross-sectional view of the cylinder unit with flange when cut along and seen in the directions indicated by the arrows G,  FIG. 14( c )  is a schematic perspective view of the attachment ring of the air circulator of the fourth embodiment and  FIG. 14( d )  is a schematic cross-sectional view of the attachment ring when cut along and seen in the directions indicated by the arrows H. 
     In the above third embodiment, the cylinder unit is extended downward at the pair of first engaging parts and the protrusions as the engaging units are formed on the outer surfaces of the extended parts. However, in the fourth embodiment, as shown in  FIGS. 14( a ) and 14( b ) , the cylinder unit  21  is not extended downward at the pair of first engaging parts  23  and the protrusions  26  as the first engaging units are formed on the outer surface of the cylinder unit  21  at the lower end part thereof. Here, the upper surfaces of the protrusions  26  are the engaging walls  255   b . Therefore, the engaging walls  255   b  are positioned slightly above the lower end surface of the cylinder unit  21 . On the other hand, as shown in  FIGS. 14( c ) and 14( d ) , the cutouts  57  are formed at the lower end part of the attachment ring  50  at the pair of second engaging parts  53  so as to correspond to the protrusions  26  formed on the cylinder unit  21 . Here, the cutouts  57  are the second engaging units and the upper surfaces of the cutout portions of the attachment ring  50  are the engaging walls  522   b . Further, the guide inclination units  58  for guiding the protrusions  26  are formed on the inner surface of the attachment ring  50  at the upper end part at the pair of second engaging parts  53 . Since the air circulator of the fourth embodiment has such configuration, it has the function and the advantages similar to those of the third embodiment and a user can easily and unfailingly attach the air circulator to the sheet member and easily detach the air circulator from the sheet member. Here, the rest of the configuration of the fourth embodiment is the same as that of the above described third embodiment. Therefore, the detailed description thereof is omitted here. 
     Fifth Embodiment 
     Next, the fifth embodiment of the present invention will be described.  FIG. 15( a )  is a schematic plan view of the attachment ring of the air circulator of the fifth embodiment,  FIG. 15( b )  is a schematic side view of the attachment ring and  FIG. 15( c )  is a schematic back side view of the air circulator of the fifth embodiment. 
     As described in the above first embodiment, as a method for preventing the attachment ring from falling off from the fan main body due to the force caused by the bending of the sheet member, the parts of the outside corner at the end parts of the attachment ring on the pressing part sides, the pressing parts forming a pair, and on the side that face the flange are chamfered. However, the method for preventing the attachment ring from falling off from the fan main body due to the force caused by the bending of the sheet member is not limited to the above described method of chamfering and for example, with respect each of the second engaging parts that form a pair, a plurality of protrusions can be formed at the part on the outer surface of the attachment ring corresponding to the second engaging part and the area nearby. The air circulator of the fifth embodiment is made by applying the method of forming, with respect to each of the second engaging parts that form a pair, a plurality of protrusions at the part on the outer surface of the attachment ring corresponding to the second engaging part and the area nearby. 
     In the air circulator of the fifth embodiment, as shown in  FIGS. 15( a )-15( c ) , with respect to the second engaging parts  53  that form a pair, three protrusions  531  are formed at the part on the outer surface of the attachment ring  50  corresponding to the second engaging part  53  and the area nearby. Further, the width k 3  between two points on the outer surfaces of the two protrusions  531  which are symmetrical with respect to the center of the attachment ring  50  approximately equals to the width k 4  between two points on the outer surface of the attachment ring  50  at the pair of pressing parts  54 . In such way, as indicated by the dashed-dotted line in  FIG. 15( c ) , the shape of the attachment ring  50  which come in contact with the sheet member substantially becomes close to a circle shape. Therefore, any part of the attachment ring equally receives the same amount of force even if a force toward outside is applied to the air circulator from inside of the sheet member for some reason and thus, the attachment ring  50  can be prevented from falling off. 
     Here, in order to make the shape of the attachment ring  50  which come in contact with the sheet member substantially be close to a circle shape, with respect to each of the second engaging parts  53  that form a pair, one protrusion may be formed on the outer surface of the attachment ring  50  at the position corresponding to the second engaging part  53  and nearby. However, if a wide protrusion is formed, the thickness of the attachment ring  50  be thick in the areas corresponding to the second engaging parts  53  and the attachment ring  50  cannot deform easily even when the attachment ring  50  is held by the pair of pressing parts  54  and squeezed. Therefore, it is preferred that a plurality of protrusions having small width, for example, three small protrusions be formed at each of the second engaging parts that form a pair as shown in  FIGS. 15( a )-15( c )  (total of 6 protrusions), so that the attachment ring  50  can easily deform. 
     The rest of the configuration of the fifth embodiment is the same as that of the above described first embodiment. Therefore, the detailed description thereof is omitted here. The air circulator of the fifth embodiment has the function and the advantages similar to those of the first embodiment. In particular, with respect to each of the second engaging parts that form a pair, three protrusions are formed on the outer surface of the attachment ring at the part corresponding to the second engaging part and nearby to make the shape of the attachment ring which come in contact with the sheet member substantially become close to a circle shape. Therefore, any part of the attachment ring equally receives the same amount of force even if a force toward outside is applied to the air circulator from inside of the sheet member for some reason and thus, the attachment ring  50  can be prevented from falling off. Here, the method of forming, with respect to each of the engaging parts that form a pair, one or a plurality of protrusions on the outer surface of the attachment ring at the part corresponding to the second engaging part and nearby applied in the air circulator of the fifth embodiment can be applied to the air circulators of various embodiments. 
     Other Embodiment 
     The present invention is not limited to the above described embodiments and various modification can be carried out within the scope of the invention. 
     In each of the above embodiments, the case where the flange is protruded from the upper end of the cylinder unit in the direction approximately orthogonal to the outer surface of the cylinder unit is described. However, in general, the flange can be formed on the cylinder unit so as to protrude from the outer surface of the cylinder unit in the direction approximately orthogonal to the outer surface of the cylinder unit. For example, the flange can be formed at approximately center of the cylinder unit instead of forming it at the upper end of the cylinder unit. 
     In each of the above embodiments, the case where one concave or one protrusion is formed at each of the first engaging parts and one protrusion or one concave is formed at each of the second engaging parts is described. However, a plurality of concaves or a plurality of protrusions can be formed at each of the first engaging parts and a plurality of protrusions or a plurality of concaves can be formed at each of the second engaging parts, for example. In such case, the plurality of concaves or the plurality of protrusions formed at each of the engaging parts correspond to the first engaging units or the second engaging units of the present invention. 
     Further, in each of the above embodiments, the case where the air circulator of the present invention is applied to an air circulation-type mat for chair is described. However, the air circulator of the present invention can be applied to various types of devices which make the air circulate inside thereof such as air conditioned outer wears, for example, and not limited to the air circulation-type mat. 
     INDUSTRIAL APPLICABILITY 
     As described above, in the air circulator of the present invention, the fan main body is placed so that the back surface of the flange of the fan main body come in contact with the edge part of the sheet member around the opening formed in the sheet member, the positions of the first engaging units of the fan main body and the positions of the second engaging units of the ring member are matched, the ring member is fit around the outside of the cylinder unit of the fan main body from below the fan main body by utilizing the flexibility of the ring member and the first engaging units of the fan main body and the second engaging units of the ring member are engaged with each other and thereby, the ring member can be easily attach and firmly fixate to the fan main body. When the ring member and the fan main body are fixated in such way, the edge part of the sheet member around the opening formed in the sheet member is held between the back surface of the flange of the fan main body and one end surface of the ring member and thereby, as a result, the air circulator can be firmly attached to the sheet member. Further, to detach the air circulator from the sheet member, the ring member is held by the pair of pressing parts between a thumb and an index finger, for example, and the pair of pressing parts are squeezed so that the inner surfaces of the pressing parts come in contact with the outer surface of the cylinder unit of the fan main body by utilizing the flexibility of the ring member. Thereby, the areas near the pair of second parts bulge and the engaging state of the first engaging units and the second engaging unit will be released and thereby, the ring member can be easily detached from the fan main body. In such way, the air circulator of the present invention has a simple configuration and a user can easily attach and detach the air circulator to and from the sheet member. Therefore, the air circulator of the present invention can be used in air circulation-type mats, air conditioned outer wears and the like which function by circulating the air inside thereof, for example.