Coupling structure and cloth stretching frame using said coupling structure

Abstract: Members to be coupled (1a-1d) have hollow coupling parts (4) at opposite side surfaces, a coupling member (2) has, at opposite ends, press-fitting parts (11) which are press-fitted in the hollow coupling parts, and angle shape concavities and convexities (22) having crests which are corrupted upon press-fitting are formed on at least either one of an inner peripheral surface of the hollow coupling part and an outer peripheral surface of the press-fitting part. When the opposite end parts of the coupling members are press-fitted in the hollow coupling parts of the members to be coupled, the crests of concave parts of the angle shape concavities and convexities are corrupted by the opposed surface so as to be made into close contact with and firmly coupled to the associated surface. Thereby it is possible to securely couple a pair of members to be coupled by means of a simple press-fitting operation.

Description: The present invention relates to a coupling structure according to the preamble of claim 1 and to a cloth stretching frame according to claim 9. In particular, the present invention relates to a coupling structure for coupling at a corner of a cloth stretching frame for stretching a cloth such as a painting canvas or the like, or at a corner of an architrave, or adapted to used for building materials, and further relates to a cloth stretching frame using the coupling structure. Conventionally, a pair of coupling members having hollow coupling parts have been coupled together by a coupling member interposed therebetween, and then, the hollow coupling parts have been pressed by a press or the like so as to fix the coupling member, or the members are coupled together by tightening screws into holes formed in the members to be coupled and the coupling member. However, there has been a disadvantage such that a complicated work has been required for coupling the members to be coupled by means of the coupling members. Further, in a coupling structure in which protrusions of a coupling member are fitted in hollow coupling parts of members to be coupled, if the internal dimensions of the hollow coupling parts are set to be substantially equal to the external dimensions of the protrusions, the protrusion and the hollow coupling parts fitted therein with the protrusions can be frictionally locked together. However, such a coupling structure has required a large force for the coupling. Further, dimensional errors would cause come-off due to loose fitting, or difficulty in fitting. Further, there has been a such a coupling structure in which a coupling member is hidden by a pair of members to be coupled when a coupling member is fitted in hollow coupling parts of the members to be coupled so as to couple the latter together. However, in this coupling structure in which end faces of the members to be coupled are made into surface contact with each other with no gap, the shape of the end faces has to be limited so that their corners should been cut by an angle of, for example, 45 deg. Moreover, it the fitting of the members to be coupled is hard, a gap can be found between the end faces of the member to be coupled, resulting in unsatisfactory appearance. On the contrary, if the fitting is slightly loosened, the coupling parts become unstable. From the document EP-A-0 655 521 a generic coupling structure is known which forms the basis for the preamble of claims 1 and 9. This coupling structure comprises a plurality of elongated members which can be coupled via coupling members. Each of these coupling members are formed from an extrusion-molded body which is cut into such dimensions that the coupling members can be press-fitted into recesses at the opposite ends of said members of the coupling structure. From the further document EP-A-0 382 127 another coupling structure is known. In this coupling structure the coupling members are hollow-shaped. An object of the present invention is to provide a coupling structure which can simplify the coupling work. Furthermore, an aim of the present invention is to provide a coupling structure and a cloth stretching frame which exhibit easy fitting and hard come-off, and which can absorb dimensional errors, and a cloth stretching frame. Another aim of the present invention is to provide a coupling structure and a cloth stretching frame. A further aim of the present invention is to provided a coupling structure and a cloth stretching frame with which the end face shape of the members to be coupled is not subject to limitations, and further, the coupling parts can be closely fitted together. The above-stated object is achieved by means of the features defined in claims 1 and 8, respectively. Preferred embodiments of the coupling structure according to claim 1 are set forth in the dependent claims 2 to 7 respectively, whereas preferred embodiments of the cloth stretching frame according to claim 8 are set forth in the dependent claims 9 to 13, respectively. According to an aspect of the present invention, there is provided a coupling structure comprising a plurality of elongated members to be coupled, having recesses at its opposite end faces, and coupling members having press-fit parts adapted to be press-fitted into said recesses, wherein angle-like convexities and concavities having crests adapted to be collapsed upon fitting, are formed on at least either one of the inner peripheral surfaces of the above-mentioned coupling members and the outer peripheral surfaces of the above-mentioned press-fit parts. With this coupling structure, when the opposite end parts of the coupling members are fitted into the recesses of the members to be coupled, the crests of the angle-like convexities and concavities are collapsed by the associated opposed surfaces so that the coupling member is made into close contact with and are firmly coupled to the members to be coupled. Accordingly, a pair of members to be coupled are surely coupled to each other by a simple work. In another form of the coupling structure, the recesses have a rectangular cross-sectional shape, and concavities and convexities are formed on the inner peripheral surface, being arranged circumferentially, and the coupling member is formed of a V-like plan shape flat plate, having its outer surface formed thereon with concavities and convexities which are arranged in a direction orthogonal to the projecting direction of the bent part thereof. With this coupling structure according to the present invention, since the extending directions of the concavities and convexities cross together at an angle of about 45 deg., the crests of the convexities are collapsed by one another, and further, the members to be coupled and the coupling member can be extrusion-molded, resulting in easy manufacturing thereof. Further, in another form of the coupling structure, the above-mentioned recesses have a rectangular cross-sectional shape, and concavities and convexities are formed on the inner peripheral surfaces thereof, being arranged circumferentially, and the coupling member is formed of a bent plate which is formed on the outer surface thereof with concavities and convexities arranged from the bent part to the opposite end thereof. With this coupling structure, since the extending directions of the concavities and convexities cross together, the crests of the convexities are collapsed by one another so as to effect locking, and the members to be coupled and the coupling member can be extrusion-molded, thereby the manufacturing thereof can be facilitated. Further, in another form of the coupling structure, the hollow coupling parts have a rectangular cross-sectional shape, concavities and convexities which are circumferentially arranged on the inner peripheral surface are formed on at least either one of a pair of opposed surfaces of the rectangular cross-sectional shape, and at least one of a convexity is formed on the other one of the pair of opposed surfaces. With this coupling structure, the number of concavities and convexities can be reduced while the coupling strength is ensured, and further, the molding surfaces of molding dies can be simplified. Further, in another form of the coupling structure, a plurality of hollow coupling parts are provided. With this coupling structure, the coupling strength can be enhanced. Further, in another form of the coupling structure, the above-mentioned plurality of hollow coupling parts each have a rectangular cross-sectional shape, and at least one of the hollow coupling parts has a widthwise direction which is orthogonal to that of the other hollow coupling parts. In an inventive form of the coupling structure, there are provided a plurality of members to be coupled, having at their opposed surface hollow coupling parts, and a coupling member formed of an extrusion-molded hollow body that is cut so as to have dimensions with which the coupling member can be press-fitted into the above-mentioned hollow coupling parts, the end parts of the coupling members being adapted to be inserted into the above-mentioned hollow coupling parts. Further, in another form of the coupling structure, one end part of the hollow coupling member is press-fitted in a hollow coupling part of one of the members to be coupled, and the other end part of the coupling member is press-fitted in a hollow coupling part of another member to be coupled, whereby a plurality of members to be coupled can be coupled together by the coupling members. In this arrangement in which the coupling member can be formed of an extrusion-molded hollow body that is cut so as to have dimensions with which the coupling member can be press-fitted into the hollow coupling part, since the hollow part of the coupling member can exhibit a resiliency more or less when an end part of the coupling member is press-fitted in the hollow coupling part, the press-fitting can be facilitated in comparison with a coupling member having no hollow part, and further, the coupling part can be closely fitted in the hollow coupling part without looseness but with a high binding force so that the dimensional errors of the hollow coupling part and the coupling member can be absorbed, resulting in easy fitting, thereby it is possible to facilitate the coupling between the members to be coupled. Further, since the coupling member is formed by cutting a molded article, the manufacturing thereof can be facilitated. Further, in another form of the coupling structure, the opposed surfaces of above-mentioned coupling member are inclined, having an L-like shape so that the above-mentioned members to be coupled are coupled at a right angle, the corner part thereof having a reinforcing member and the opposite end faces thereof being flush with the above-mentioned opposed surfaces in a direction substantially orthogonal to the latter. With this coupling structure, the coupling member and the members to be couple can be extrusion-molded, and further, the strength of the coupling member can be enhanced by the reinforcing member, thereby it is possible to decrease the thickness of the wall of the coupling member. Since the surfaces of the hollow body corresponding to the opposite ends of the coupling member are flush, the hollow body can be stably, safely and easily cut by supporting these surfaces on a support surface, and further, the opposite end parts of the coupling member can be easily press-fitted in the hollow coupling parts. Further, in another form of the coupling structure, concavities and convexities are formed on a contact surface of at least either one of the above-mentioned coupling member and the above-mentioned members to be coupled. With this coupling structure in which the concavities and convexities are formed only one of the contact surfaces, the coupling member can be easily press-fitted, and tip ends of the convexities are made into press-contact with the associated contact surface so as to exhibit a strong binding force. Further, it the concavities and convexities are formed on both contact surfaces, tip ends of the convexities are meshed with one another so as to exhibit a strong binding force. Further, in another form of the coupling member, there are provided a plurality of a plate members having a half-lap surface formed at least either one of the rear surface of one side part and the front surface of the other side pat, and recesses formed on each of the half-lap surfaces so that the recesses face to each other when the half-lap surfaces are superposed with each other, and adapted to be joined by half-lap joint therebetween, and a coupling member adapted to be fitted in the recesses in the half-lap surfaces of the above-mentioned plurality of plate members. With this coupling structure, several plate members can be coupled one after another. laterally or longitudinally, with a predetermined positional relationship, and further, the coupling member can be extrusion-molded so that the manufacturing thereof can be facilitated. Further, in another form of the coupling structure, the above-mentioned coupling member is hollow, and one side part thereof is convexly curved outward. With this coupling structure, when the coupling member is press-fitted in the recess, the curved part is resiliently deformed, and accordingly, the coupling member can be easily press-fitted in the recess, and the binding force can be enhanced. Further, in another form of the coupling structure, the recess has angle-shape concavities and convexities having large pitches, the above-mentioned coupling member has angle-shape concavities and convexities having pitches smaller than that of the former. With this coupling structure, the convexities can be easily press-fitted in the concavities. Further, in another form of the coupling structure, when the convexities of the coupling member are fitted in the concavities of the members to be coupled, since the crests of convexities are press-contacts with the associated opposed surfaces, the crests of the convexities wedge into the associated opposed surfaces, or are collapsed thereby in such a case that the convexities are formed on only one side, crests of the convexities are collapsed by one another, or either of the convexities are collapsed by other in such a case that the convexities are formed on both sides, thereby it is possible to closely couple them with each other. Accordingly, the coupling member can be easily fitted in the members to be coupled so that they can hardly come off from each other, and further, dimensional error can be absorbed. Further, in another form of the coupling structure, the above-mentioned coupling member is formed of a material having a flexibility equal to or higher than that of the above-mentioned members to be coupled. Further, in another form of the coupling structure, the coupling member is made of a plastic material which is softer than that of the members to be coupled. With this coupling structure, the coupling member can be easily manufactured Further, in another form of the coupling structure, each of the above-mentioned members to be coupled has, at one side surface, a pin insertion hole communicating to the above-mentioned recess, and the above-mentioned coupling member has a cave formed one of the opposed surfaces of the above-mentioned protrusion, and a pin fitting barrel part located in the cave at a position aligned with the pin insertion hole, a pin being fitted in the barrel part through the pin insertion hole. With this coupling structure in which the pin is fitted in the barrel part, the fitting between the coupling member and the members to be coupled can be enhanced so that they can hardly come off from each other. Further, the coupling structure, each of the above-mentioned members to be coupled has, at one side surface, a pin insertion hole communicating to the above-mentioned recess, and the above-mentioned coupling member has a hollow part communicating to a side part of the above-mentioned protrusion, and a pair of clamping pieces projected from the inner surface of the hollow part at a position aligned with the pin insertion hole, a pin being clamped between the clamping pieces through the pin insertion hole. Further, in another form of the coupling structure, there are provided members to be coupled, having, at its end face, a recess, and a coupling member which has at its end face an abutting part adapted to abut against the former end face, and from which a protrusion adapted to be fitted in the recess is projected, and a protrusion having a crest made into press-contact with the associated surface is formed at least either the inner surface of the recess or the outer surface of the protrusion. With this coupling structure, when the protrusion of the coupling member is fitted in the recess of the members to be coupled, they are fitted together while the crest of the protrusion is made into press-contact with the inner surface of the recess so that the abutting part of the coupling member can surely abut against the end face of the member to be coupled, and accordingly, the close coupling can be effected. Further, since the end faces of the members to be coupled are not made into surface-contact with each other, no limitation is applied to the shape of the end faces. Further, since the intermediate part of the coupling member is exposed from the members to be coupled, if the material of the coupling member is different from that of the other and so forth, a gap which is even defined more or less between the abutting part and the end face of the coupling part, can be made to be unnoticeable by means of the different material. Further, in another form of the coupling structure, the above-mentioned members to be coupled have a pin insertion hole communicating to the above-mentioned recess on a side surface thereof, and the above-mentioned coupling member has a pin attaching part formed on the above-mentioned protrusion at a position which is aligned with the pin insertion hole, a pin being inserted into the pin insertion hole, and is then fitted in the pin attaching part. With this coupling structure, the effect of checking the coupling member from coming off, can be enhanced. Further, in another form of the coupling structure, the above-mentioned protrusion is composed of a pair of projecting parts which are juxtaposed, being spaced from each other, and which are adapted to be fitted in the recess. With the coupling structure, when the pair of the projecting parts are fitted in the recess, it is likely to easily cause resilient deformation in directions in which they approach together, the fitting into the recess can be facilitated, and further, the movement in the come-off direction can hardly occur due to the press-contact by the crest of the protrusion. According to another aspect, a cloth stretching frame is composed of frame pieces each defining one side of the cloth stretching frame, and each having hollow coupling parts formed therein, a cloth fixing bead part formed on the front surface thereof, a groove extending between the outer surface to the rear surface thereof, and frictionally locking concavities and convexities formed on the inner surface of the groove, and coupling members each formed from an, according to the invention, extrusion-molded, L-like cross-sectional shape hollow member that is cut so as to have dimensions with which opposite end part of the coupling member can be fitted in the hollow coupling parts. With this cloth stretching frame, the coupling between the above-mentioned frame pieces can be facilitated, a cloth can be retained and fixed to the rear surfaces thereof by fitting fixtures into the grooves. In another form of the cloth stretching frame, a folding-back and hooking piece for folding back one edge part of the cloth and also hooking the same onto a hook is extended on the rear surface of at least one of the frame pieces which defines the upper side of the frame, at a level below the above-mentioned groove. With the cloth stretching frame, the edge part of the cloth which is stretched and fixed in the groove by the fixtures, is folded back by the folding-back and hooking piece, and is fixed to the same by retainers such as clips as other members so as to enhance its appearance. Further, the folding-back and hooking piece is hooked to a hook provided on a wall surface, so that the cloth stretching frame can be conveniently hung on a wall surface. In another form of the cloth stretching frame, a projecting part is formed on the rear surface of the frame piece so as to form a slope surface continuous to the above-mentioned outer surface of the frame piece, and the above-mentioned groove is formed in this slip surface, a bead part cooperating with a canvas stretching pliers is formed in the groove on the side remote from the above-mentioned outer surface. With the cloth stretching frame, the groove is formed in the slope surface so that the fixtures becomes hardly visible, thereby it is possible to enhance the appearance thereof. Further, by supporting the projecting project part of the pliers to the pliers cooperating bead part, a cloth can be stretched easily and fully on the slope surface under leverage, and further, the bead part on which the supporting project part of the pliers is supported, is projected linearly so that the position thereof can be easily located, thereby it is possible to facilitate the cloth stretching work, and further it is possible to fix a fixture in the groove in a cloth stretching condition. Further, in another form of the cloth stretching frame, the bead part has suspender attaching holes. With this cloth stretching frame, by attaching a suspender to the suspender attaching holes, the cloth stretching frame can be simply suspended on a wall surface or the like. Further, in another form of the cloth stretching frame, a cloth hooking bead part is formed on the slope surface on the outer surface side of the groove. With this cloth stretching frame, by retaining the cloth with the use of the head part of the fixture in the vicinity of the bead part, the cloth can be caught on the bead part, and accordingly, the cloth can hardly slack, and due to the provision of the bead part, the head part is more hardly visible from the front surface side of the frame piece. Further, in another form of the cloth stretching frame, the above-mentioned frame piece has a bar receiver which is projected in a direction inward of the cloth stretching frame, coupling holes formed in the bar receiver, reinforcing bar fixing grooves formed in the inner surface of the frame piece of the cloth stretching frame, a reinforcing bar having end parts formed at their side surfaces with screw holes aligned with the above-mentioned coupling holes being provided, and side grooves aligned with the above-mentioned reinforcing bar fixing grooves formed on opposite sides, and a coupling member adapted to be press-fitted in the side grooves and the reinforcing bar fixing groove is provided. With this cloth stretching frame, the reinforcing bar can easily and surely be attached. Further, in another form of the cloth stretching frame, there are provided frame pieces each defining each side of the cloth stretching frame, having, at end faces, recesses, a cloth stretching bead part formed on the front surface thereof, a groove extending from the outer surface to the rear surface, and frictionally locking concavities and convexities formed in the inner surface of the groove; and a coupling member having a continuous groove continuous to the end part of the former groove, extending from the outer surface to the rear surface, a protrusion being formed at least either one of the inner surface of the groove and the outer surface of the projecting part, and having a crest adapted to be made into press-contact with the other one. In the following the invention is further illustrated by embodiments with reference to the attached figures. Fig. 1 is a partial exploded perspective view illustrating a cloth stretching frame; Fig. 2 is a perspective illustrating a coupling member according to a first comparative example; Fig. 3 is a front view illustrating the cloth stretching frame; Fig. 4 is a partial plan view illustrating a strip plate from which a coupling member according to the first comparative example is punched out; Fig. 5 is a partial cross-sectional view showing a condition in which the coupling member shown in fig. 4 is connected to members to be coupled; Fig. 6 is a perspective view illustrating a second comparative example; Fig. 7 is an end view illustrating a frame piece of a cloth stretching frame; Fig. 8 is an end view illustrating a frame piece of a cloth stretching frame; Fig. 9 is an end view illustrating a frame piece of cloth stretching frame; Fig. 10 is an end view illustrating a frame piece of a cloth stretching frame; Fig. 11 is a partial exploded perspective view illustrating a cloth stretching frame in which a coupling member according to a first embodiment of the present invention, is applied; Fig. 12 is a side view illustrating the coupling member shown in fig. 11; Fig. 13 is a sectional view illustrating a frame piece in a condition in which a cloth is stretched; Fig. 14 is a perspective view illustrating a coupling member in a second embodiment of the present invention; Fig. 15 is a partial exploded perspective view illustrating a coupling member and a member to be coupled, in a third embodiment of the present invention; Fig. 16 is an enlarged view illustrating a condition in which a pin is clamped between clamping pieces: Fig. 17 is a partial cross-sectional view illustrating a cloth stretching frame; Fig. 18 is an enlarged view illustrating a detail of the frame shown in Fig. 17; Fig. 19 is a perspective view illustrating a coupling member according to a third comparative example; Fig. 20 is a partial perspective view illustrating a frame piece of a cloth stretching frame; Fig. 21 is an end view illustrating the coupling member shown in fig. 19; Fig. 22 is a partial view illustrating an inner surface of a corner part of a recess as viewed in front thereof; Fig. 23 is a sectional view illustrating a variant form of a protrusion; Fig. 24 is an explanatory view for a condition in which concavities and convexities are meshed with one another; Fig. 25 is a perspective view illustrating a member to be coupled and a coupling member in a fourth embodiment, the coupling member is in a condition before separation from a hollow body: Fig. 26 is a sectional view illustrating a frame piece of a cloth stretching frame; Fig. 27 is a sectional view illustrating a reinforcing bar; Fig. 28 is a side view illustrating a coupling member according to a fourth comparative example; Fig. 29 is a partial enlarged view illustrating a part thereof: Fig. 30 is an explanatory view illustrating a procedure of attaching a coupling member according to a fifth comparative example. Explanation will be made of a cloth stretching frame in which a first comparative example is applied, with reference to Fig. 1 to 5. That is, this coupling structure has a plurality of frame pieces la to ld as members to be coupled, and a coupling member 2. The plurality of frame pieces 1a to 1d are made of aluminum, and have been extrusion-molded. Referring to Fig. 3, the frame is composed of a frame piece la serving as an upper frame, a frame piece 1c serving as a lower frame, and frame 1b, 1d serving as side frames, having their opposite end faces which are inclined surfaces at an angle of about 45 deg. The frame pieces 1a to 1d which has been extrusion-molded, have following structures. That is, as shown in Fig. 1, each of the frame pieces 1a to 1d, has a recess 7 formed in the outer surface which defines an outer peripheral surface of a frame, a cloth stretching bead part 5 on the front end side nearer to the front side of the frame, than the groove 7, and a hollow coupling part 4 in which one end part of a coupling member 2 is fitted, and which is formed in each end part. The inner wall surface of the groove 7 is formed thereon with concavities and convexities 8 for frictionally locking a leg part 19 of a fixture 3, and the inner peripheral surface of the hollow coupling part 4 is formed thereon with concavities and convexities 15. The coupling member 2 has a press-fitting part 11 adapted to be press-fitted in the hollow coupling part 4, at each end thereof. The press-fitting part 11 is formed on the outer peripheral surface thereof with angle-shape concavities and convexities 22. In this comparative example, as shown in Fig. 4, a band plate 21 is prepared. The band plate 21 having a width of, for example, 60 mm, is formed in the center part on each of opposite surfaces thereof with the angle shape concavities and convexities 22 having a width of about 30 mm, which extend widthwise. The height of the crests of the concavities and convexities 22 is about 0.5 mm. A plurality of coupling members 2 are successively cut into a V-like shape from the band plate 21 in the longitudinal direction, and accordingly, planar coupling members 2 having a V-like shape in a plan view and arranged in a direction orthogonal to the projecting direction of the bent part are formed. In this case, as shown in Fig. 4, each coupling member 2 is tapered so that the width of the opposite end parts thereof is smaller than that of the V-like bent part in order to be easily inserted into the hollow coupling parts 4. It is noted that plate 21 may have a thickness which is slightly larger in the center part thereof having a front and rear surface which are flat, and may be longitudinally cut into a V-like shape as shown in Fig. 4, so as to form coupling members 2 without concavities and convexities. Referring to Fig. 5 which shows a condition in which adjacent frame pieces 1a, 1d are coupled with the coupling member 2, the concavities and convexities 15, 22 are meshed with each other for coupling, having their longitudinal directions crossing together at an angle of about 45 deg. In this case, convex parts of the concavities and convexities 15, 22 are collapsed by one another so as to provide a coupling condition. Accordingly, the frame pieces 1a, 1d are surely and firmly coupled together without using a screw or the like. Further, in order to assemble the cloth stretching frame 1, four coupling members 2 are interposed between the frame pieces 1a to 1d, and then, the frame pieces 1a to 1d are knocked so that they are all assembled together, simultaneously. Referring to Fig. 1, the fixture 3 is adapted to fix a cloth 18 such as a canvas adapted to be stretched at the front of the cloth stretching frame. The fixture 3 in this embodiment, has a leg part 19 which is adapted to break through the cloth 18, and is driven into the groove 7, and a head part 20 for pressing the cloth 18 against the outer surface 16. The cloth 18 is set on the front surface 13 of the cloth stretching frame 1 composed of the frame pieces 1a to 1d which are coupled together by means of four coupling members 2, and the peripheral edge part of the cloth 18 is wound around onto the outer surfaces 6 of the frame pieces 1a to 1d while it is supported to the cloth stretching bead parts 5. Then, the peripheral edge part is pulled toward the rear side of the frame by pliers or the like, and then, the leg part 19 of the fixture 3 is driven into the groove 7 so that it breaks through the cloth 18, while the cloth 18 is pressed against the outer surfaces 16 of the frame pieces 1a to 1d of the head part 20. Thus, the cloth 18 is stretched in such a condition that the center side of the cloth 18 is drawn toward the peripheral edge. Further, since the concavities and convexities 8 are formed on the inner surface of the groove 7, they are easily frictionally locked to the leg part 19 of the fixture 3 only by press-fitting the fixture 3. The material of the fixture 3 is preferably softer than that of the cloth stretching frame 1. However, it may be made of a hard material such as steel which is harder than that of the frame pieces la to ld, so that the convex parts of the concavities and convexities 15 are collapsed for locking. Referring to Fig. 3, there is shown a reinforcing bar 21. In Fig. 3, when both end parts of the coupling members 2 are fitted in the hollow coupling parts 2 of the frame pieces la to ld, the crests of the convex parts of the concavities and convexities 15 having an angle shape, are collapsed by the associated opposed surface so that coupling members 2 are coupled to the frame pieces la to ld, being in close-contact with one another. Accordingly, the frame pieces la to ld can be surely and firmly coupled together with a simple work. Further, the hollow coupling part 4 has a rectangular cross-sectional shape, having concavities and convexities 15 which are arranged in the circumferential direction of the inner peripheral surface, and the coupling member 2 is a planar V-like flat plate, having its outer surface formed thereon with concavities and convexities 22 which are arranged in a direction orthogonal to the projecting direction of the bent part. Accordingly, the extending directions of the concavities and convexities 15, 22 cross together at an angle of about 45 deg. so that the crests of the convex parts thereof are locked together, being collapsed by one another, and the frame pieces la to ld as the members to be coupled, and the coupling members may be extrusion-molded, thereby it is possible to easily manufacture thereof. It may be sufficient that the angle shape concavities and convexities 15, 22 may be formed on at least either one of the members to be coupled and the coupling members 2. Fig. 6 shows a second comparative example invention, that is, the coupling structure is applied in such a case that a pair of planar members to be coupled are connected in the thicknesswise direction thereof. The structure of the members to be coupled has a cross-sectional shape which is substantially the same as that shown in Fig. 1, a coupling member 2 is bent into a V-like shape in the thicknesswise direction, that is, it has a bent V-like shape, and the concavities and convexities 22 on the outer surface thereof, are arranged in a direction from the bent part to the end parts of the coupling member 2', and are extended in parallel with each other in the widthwise direction. It is noted that the corner part on the projecting surface side of the bent part is formed so as to be lower than that of the convex parts of the concavities and convexities 22. The coupling member to which the coupling member 2 is applied is a panel or the like, the joint surfaces are inclined at an angle of about 45 deg in the thicknesswise direction, so as to form hollow coupling parts in which the coupling members 2 can be fitted, on the joint surfaces of the member to be coupled. Further, concavities and convexities similar to those in the first comparative example are formed on the inner surfaces of the hollow coupling parts. It is noted that the coupling member 2 in this comparative example can be extrusion-molded. However, if the concavities and convexities 22 are inclined widthwise of the coupling member 2, it can be manufactured by casting. Further, similar to that first embodiment, it is sufficient that the concavities and convexities 15, 22 may be formed on at least either one of the members 1 to be coupled or the coupling member 2. Fig. 7 shows a cloth stretching frame. That is, in this coupling structure, in comparison with the first comparative example, the hollow coupling parts 4 of the members 1a to 1d to be coupled have an angular shape cross-sectional shape, in particular, a substantially rectangular shape cross-sectional shape, and further, the concavities and convexities 15 arranged in the circumferential direction of the inner peripheral surface are formed on one of opposed surface in the angular cross-sectional shape, and a groove is formed in the center part of the other of the opposed surfaces while corner parts 25' for setting the width of the rectangular shape are left on opposite sides of the groove. Further, a protrusion 30 is formed on each of the other opposed side surfaces. Further, in order to increase the height of the cloth stretching bead parts 5 of the frame pieces 1a to 1d, slope surfaces are formed on the front surfaces thereof, in its entirety, and when the frame pieces 1a to 1d are assembled so as to stretch the cloth, the cloth is supported only on the cloth stretching bead parts 5. In Fig. 7, the frame pieces 1a to 1d are formed also by extrusion-molding aluminum. Reference numeral 31 denotes a recess having an opening at its front surface. The remainder of this embodiment are similar to the first embodiment, identical reference numerals are attached to the common parts. According to Fig. 7, the hollow coupling part 4 has an angular cross-sectional shape, and the concavities and convexities 15 arranged circumferentially of the inner peripheral surface, are formed on at least either one of opposed surfaces of the angular cross-sectional shape, and at least one protrusion 30 is formed on each of the other opposed surfaces thereof. Thus, the number of the concavities and convexities can be reduced while the coupling strength is ensured, thereby it is possible to simplify the molding surfaces of molding dies. Further, a plurality of protrusions 30 may be formed. Fig. 8 shows another cloth stretching frame. That is, the frame pieces 1a to 1d in this cloth stretching frame have a plurality of hollow coupling parts 4, 4a in the third embodiment. In Fig. 8, a pair of hollow coupling parts 4, 4a are arranged being overlapped with each other, in the longitudinal direction of a rectangular cross-sectional shape, and concavities and convexities 15a similar to the concavities and convexities 15 are formed even in the hollow coupling part 4a. Reference numeral 32 is a recess formed in the front surface side, bridging between the hollow coupling parts 4, 4a, being juxtaposed with a recess 31. The remainder in Fig. 8 are similar to the cloth stretching frame shown in Fig. 7. In Fig. 9, still another cloth stretching frame is shown. The frame pieces 1a to 1d of this cloth stretching frame have a plurality of hollow coupling parts 4, 4a which are shifted in a short side direction and a long side direction of a rectangular cross-sectional shape in Fig. 8. Accordingly, the width of the frame is less than that in Fig. 8, but the thickness thereof is more or less increased. The reason why the width of the frame is small is such that the hollow coupling part 4 is formed in the position corresponding to the recess 31 in Fig. 8. Reference numeral 33 denotes a recess, 33 denotes a recess into which a fixture (which is not shown) is driven when the cloth stretching frame is loaded on a support bed (which is not shown), and concavities and convexities having pitches which are small than that of the concavities and convexities 8 are formed in the inner surface thereof. 34, 35 denote projecting pieces between which one end part of the reinforcing bar is fitted if the reinforcing bars (refer to 21 in Fig. 3) are interposed between the frame pieces 1a to 1d. Further, with the frame pieces 1a to 1d, the cloth stretching frame becomes larger than that shown in Fig. 8, that is, the space between the pair of hollow coupling parts 4, 4a becomes larger than that shown in Fig. 8, and a hollow part 39 is formed therebetween. The remainder are similar to the cloth stretching frame shown in Fig. 8. Another cloth stretching frame is shown in Fig. 10. That is, in the cloth stretching frame, the pair of hollow coupling parts 4, 4a which are disclosed in Fig. 9, are formed on the frame pieces 1a to 1d, being orthogonal to each other, and a rod-like resilient member 52 such as a circular rod made of rubber, formed urethane or the like is press-fitted in the groove 7 therealong, thereby the cloth 18 is pushed into the groove 7 so as to stretch the cloth 18. In this case, in Fig. 10 fine concavities and convexities may be formed around the resilient member 52. Alternatively, concavities and convexities may be formed circumferentially, or may be formed circumferentially and axially. Instead of fixing the cloth to the groove 7, an edge part of the cloth 8 is located above the recess 34 into which then the resilient member 52 is then pushed so that the cloth 8 is stretched and secured. Further, fine angle shape concavities and convexities are formed on the outer surfaces 6 of the frame pieces 1a to 1d in order to check the cloth from slipping. Explanation will be hereinbelow made of a cloth stretching frame in which a first embodiment of the present invention is applied with reference to Figs. 11 to 13. That is, this coupling structure comprises a plurality of frame pieces 1a to 1d, as members to be coupled, of the cloth stretching frame, and coupling members 2. The frame pieces 1a to 1d each have hollow coupling parts 8 at opposite faces 6, that is, as shown in Fig. 3, the frame pieces 1a and 1c made of aluminum define respectively upper and lower frames, and the frame pieces 1b, 1d define side frames, opposite surfaces 24 at opposite ends of each frame piece are formed into inclined surfaces at an angle of about 45 deg. so that each adjacent frame pieces la to ld are coupled together at a right angle. The frame pieces 1a to 1d are extrusion-molded so as to have the following structure. That is, each of them has a cloth stretching bead part 5 on its front surface 13 at an outside position, a groove 7 extending from the outer surface 6 to the rear surface 40, collapsible concavities and convexities 8 formed on the inner surface of the groove 7 and adapted to be frictionally locked to a leg part 19 of a fixture 3. Further, the rear surface 40 has a projecting part 42 which is projected in a V-like cross-sectional shape so as to form a slope surface 41 continuous to the outer surface 6 of each of the frame pieces la to ld. That is, the slope surface 41 is inclined at angle of about 45 deg. to the outer surface 6, and is formed therein with the groove 7. A bead part 45 for cooperating with canvas stretching pliers 44 is formed on the rear surface 40 on the side remote from the outer surface 6, that is, on the inner surface 4 side, and is formed therein with suspender attaching holes (which is not shown). Further, a cloth catching bead part 46 is formed on the slope surface 41 of the groove 7 on the outer surface 6 side. The widthwise size of the angular cross-sectional shape hollow coupling part 4 is set to be equal to a value which is obtain by subtracting a wall thickness from the entire width of the frame piece la at a position on the outer surface 6 side of the groove 7. Further, angle shape concavities and convexities 15 circumferentially arranged and having collapsible crests are formed on two surfaces facing toward the outer surface 6 and the inner surface 43 and defined on the inner peripheral surface of the hollow coupling part 4. Reference numeral 47 is a channel. The coupling member 2 is formed from extrusion-molded hollow body which is cut into dimensions with which the coupling member 2 can be press-fitted in the hollow coupling part 4, and opposite ends, in cutting directions, of the coupling member 2 is insertable into the hollow coupling parts 4. The coupling member 2 in this embodiment is made of metal such as aluminum, and has an L-like shape, having a widths with which the coupling member 2 can be press-fitted in the entire width of the hollow coupling part 4, and concavities and convexities 22 arranged on the outer surface of the coupling member 2 in a direction from the bent part to the distal end, having collapsible crests. This coupling member 2 can be formed simply by cutting an extrusion-molded hollow body 48 having an L-like cross-sectional shape so as to have a predetermined longitudinal length. Further, in this embodiment, a reinforcing member 50 is provided in a bent part in a hollow part 49 of the coupling member 2, having opposite ends 2a, 2b are extended in a direction substantially orthogonal to opposite surfaces 55 serving as end faces of each of the frame pieces 1a to 1d, and are flush with each other. When the cloth stretching frame is assembled, the four coupling member 2 are interposed between the frame pieces 1a to 1d, and then the frame pieces 1a to 1d are knocked so that they are simultaneously assembled. At this time, due to the provision of the concavities and convexities 15, 22, the contact area becomes less, and accordingly, the coupling member 2 can be easily press-fitted into the hollow coupling part 4, and further, after the coupling member 2 is press-fitted in the hollow coupling part 4, the crests of the concavities and convexities 15, 22 are collapsed so as to ensure a large binding force. The fixture 3 is adapted to be pressed into the groove 7 so as to fix the cloth 18 such as a canvas stretched over the front surface of the cloth stretching frame, and has a leg part 9 which driven into the groove 7 breaking through the cloth 18 set on the frame piece 1a and the like, and is then press-fitted and secured in the groove 7, and a head part 20 for pressing the cloth on the outer surfaces of the frame pieces 1a to 1d. Before the fixture 3 is press-fitted in the groove 7, the cloth 8 as shown in Fig. 15 is at first set on the front surface 13 of the cloth stretching frame which are assembled by coupling the frame pieces la to ld with the use of the coupling members 2, and then the peripheral edge part of the cloth 18 is supported on the cloth stretching bead part 5, and is turned around onto the outer surfaces of the frame pieces la to ld while a projecting support part 56 of canvas stretching pliers 44 is made to abut against the bead part 45, and then, a grip 44a is moved in the direction of the arrow so that the cloth 18 nipped between cloth nipping parts 44b is pulled along the slope surface 41 with the use of leverage action. In this condition, the leg part 19 of the fixture 3 is driven into the groove 7, breaking through the cloth 18 while the cloth 18 is pressed against rear surfaces 40 of the frame pieces la to ld and against the rear surfaces 40 of the frame pieces la to ld by the head part 20. Accordingly, the center side of the cloth 18 is stretched toward the peripheral edge thereof, and accordingly, the cloth 18 is flatly stretched, being supported on the cloth stretching bead 5. Further, since the concavities and convexities 8 are formed on the inner surface of the groove 7, the leg part 9 of the fixture 3 is easily frictionally locked only by press-fitting the fixture 3. The material of the fixture 3 is preferably softer than that of the cloth stretching frame 1. However, for example, if it is made of a material which is harder than that of the frame pieces 1a to 1d, such as steel, it is locked while the crests of the concavities and convexities 8 are collapsed. Referring to Fig. 3, reference numeral 57 denotes a suspender screwed in the suspender attaching holes formed in the bead part 45, and accordingly, the cloth stretching frame can be suspended on a wall surface by means of the suspender through the intermediary of a rope which is threaded through the suspender. 58 denotes a bar receiver to which one end part of the reinforcing bar (reference numeral 21 in Fig. 3) is attached. In this embodiment, one end part 2a of the coupling member 2 in a cutting direction of a hollow body 48 is press-fitted in the hollow coupling part 4 of the frame piece 1a as a member to be coupled while the other end part 2b of the coupling member 2 is press-fitted in the hollow coupling part 4 of the frame piece 1b, and accordingly, the frame pieces 1a and 1b are coupled by the coupling member 2. In this case, since the coupling member 2 is formed by cutting the exclusion-molded hollow body 48 so as to have dimensions with which the coupling member 2 can be press-fitted in the hollow coupling part 4, when the end part 2a of the coupling member 2 is press-fitted in the hollow coupling part 4, a resiliency can be more or less obtained from the hollow part 49 of the coupling member 2, and accordingly, it is possible to closely fit the coupling member 2 into the hollow coupling part 4 without no looseness, thereby it is possible to obtain a strong binding force. Further, the angle shape concavities and convexities 15, 22 are collapsed and meshed with each other so as to obtain also a strong binding force. Accordingly, it is possible to facilitate the coupling of the frame pieces 1a to 1d. Further, the hollow coupling part 4 has an angular cross-sectional shape, having the concavities and convexities 15 arranged circumferentially of the inner surface, and further, the coupling member 2 has an L-like shape, having the concavities and convexities 22 arranged on the outer surface thereof in a direction from the bent parts to ends. Accordingly, in addition to the coupling member 2, the frame pieces la and the like can be easily manufactured by extrusion-molding. Further, since the coupling member 2 includes the reinforcing member 50 in the hollow part 49 thereof, the strength of the coupling member can be increased, and accordingly, the wall-thickness of the coupling member 2 can be reduced. Further, since the members to be coupled are frame pieces la to ld which define respectively sides to the cloth stretching frame, having opposite end faces 55 which are inclined at an angle of substantially 45 deg so that the frame pieces are coupled together at a right angle, and since the opposite ends 2a, 2a of the coupling member 2 are inclined so that they are flush with each other in a direction substantially orthogonal to the opposite face 55, surfaces of the hollow body 48 corresponding to the opposite end parts 2a, 2b of the coupling member 2 are flush with each other, and accordingly, the cutting of the hollow body 48 can be stably, safely and easily made. Further, the opposite end parts 2a, 2b of the coupling member 2 are easily press-fitted in the hollow coupling parts 4. Further, the leg part 19 of the fixture 3 is frictionally locked to the concavities and convexities 8 in the groove 7 so as to be checked from coming off, the cloth 18 is retained and fixed to the rear surface 40 by the head part 20. Further, since the projecting part 42 is formed on the rear surface 40 of each of the frame pieces 1a to 1d so as to obtain the slope surface 41 continuous to the outer surface 6 of each of the frame piece 1a to 1d, and the groove 7 is formed in the slope surface 41 while the bead part 40 cooperated with the canvas stretching pliers is formed on the rear surface 40 on the side remote from the outer surface, the fixture 3 is hardly visible from the front side by forming the groove 7 in the slope surface 41, and accordingly, the appearance can be improved. Further, when the projecting support part 56 of the pliers 44 is supported to the pliers cooperating bead part 45, the cloth 18 can be easily and fully fixed on the slope surface 41 by leverage action, and further, the bead part 45 to which the projecting support part 56 of the pliers 44 is supported is linearly projected. Accordingly, the position thereof is easily found so that the stretching of the cloth can be facilitated, and further, the fixture 3 can be easily fixed in the groove 7 in a condition in which the cloth 18 is stretched. Further, since the suspender holes are formed in the bead part 45, the cloth stretching frame can be easily suspended on wall surface by means of a suspender 57 attached to the suspender holes. Further, the cloth catching bead part 46 is formed on the slope surface 41 of the groove 7 on the outer surface 6 side, the cloth 18 can be caught on the cloth catching bead 46 by retaining the cloth 18 with the use of the head part 20 of the fixture 3 in the vicinity of the cloth catching bead part 46, and accordingly, the cloth can hardly slack while the head part 20 is hardly visible from the front side of the frame pieces 1a to 1d due to the provision of the bead part 46. Further, the coupling member 2 is formed so as to have a widthwise size with which the coupling member can be press-fitted in the entire width of the hollow coupling part 4 which is formed in a range obtained by subtracting the wall thickness from the entire width of the frame pieces 1a to 1d, and accordingly, the looseness of the frame pieces 1a to 1d can be easily suppressed. It is sufficient that, according to the present invention, the angle shape concavities and convexities 15, 22 may be formed on at least either the frame pieces 1a to 1d or the coupling member 2. Further, the concavities and convexities 15 may be formed on the inner peripheral surface of the frame piece 1a or the like, in its entirety or in part, and also the concavities and convexities 22 may be formed on the outer surface of the coupling member 2 in its entirety or in part. Further, in any of the above-mentioned comparative examples and embodiments, the coupling structure is used in each of the corner parts of the frame. However, if the frame pieces are coupled together in a straight line manner, a straight coupling can be used. Further, it can be used as building materials for frames of windows, doors or the like. Explanation will be made of a painting cloth stretching frame in which a second embodiment of the present invention is applied with reference to Fig. 14. This embodiment is similar to the first embodiment, except that a member 1 to be coupled as a frame piece has a recess or a hollow coupling part 4 at an end face, and a pin insertion hole 60 communicating the hollow coupling part 4 is formed at a side surface. Different from the first embodiment, the coupling member 27 has a recess 61 having a bottom without the hollow part 49, and the recess 61 has a barrel part 62. That is, the coupling part 2 is made of a material softer than that of the member 1 to be coupled, and has opposite end parts 2a, 2b serving as projecting parts adapted to be fitted in the hollow coupling parts 4. Concavities and convexities 33 as a one kind of protrusions having crests which resiliently makes contact with the associated opposite surface are formed on one opposed surfaces of the opposite end parts 2a, 2b, and further, caves 61 are formed at another opposite surfaces of end parts 2a, 2b in each of which the pin fitting barrel part 62 is provided at a position aligned with the pin insertion hole 60. In this embodiment, the coupling member 2 is extrusion-molded of plastic materials such as thermoplastic resin (nylon 6, nylon 66 or the like) in which about 30 % of glass fibers is mingled so as to obtain an L-like shape in order to couple the frame pieces 1a to 1b at the corner parts of the frame. Further, it is obliquely formed so that both end parts 2a, 2b are tapered, and the concavities and convexities 22 have each a convex arcuate cross-sectional shape, and are extended in a direction orthogonal to the extending direction of the concavities and convexities 15 which are one kind of the protrusions, that is, in the widthwise direction of the coupling member, and are arranged toward the distal ends of the end parts 2a, 2b. Further, the barrel part 62 has an oval shape longitudinally extending toward the distal end of each of the end parts 2a, 2b, and a plurality of beads 64 for inhibiting axial movement of the pin 63 are formed at an inner surface of the barrel part 62. The pin 63 is fitted in the barrel part 62 through the pin insertion hole 60. At this time, the pin 63 is clamped between the beads 64 so as to inhibit movement of the member to be coupled, absorbing dimensional errors and unevenness in degree of fitting of the end parts 2a, 2b into the hollow coupling part 4. In this cloth stretching frame, the members 1 to be coupled are arranged in a frame-like pattern, and the coupling members 2 are interposed therebetween. They are pressed against one another in order to the coupling members 2 are pushed into and press-fitted in the members 1 to be coupled, and finally, the pins 63 are driven thereinto so as to assemble the cloth stretching frame. In this embodiment, when the opposite end parts 2a, 2b of the coupling member 2, serving as the projecting parts, are fitted in the recesses in the members 1 to be coupled, that is, the hollow coupling parts 8, the crests of the concavities and convexities 12, 14 constituting protrusions are made into resilient contact with the associated opposite surfaces. In this arrangement, since the coupling member 2 is made of a material softer than that of the members 1 to be coupled, the concavities and convexities 15 collapse the crests of the concavities and convexities 22 so as to effect close-contact coupling. Accordingly, the coupling member can easily be fitted in the members 1 to be coupled, and can hardly come off. Further, dimensional errors can be absorbed. Further, the degree of difficulty in come-off, can be determined a degree of fitting of the opposite end parts 2a, 2b into the hollow coupling part 4. Further, since the pin 63 is fitted in the barrel part 62, the coupling member 2 can more hardly come off from the members 1 to be coupled. In this arrangement, the beads 64 are formed in the oval barrel part 62, the pin 63 can be clamped between the beads 64, dimensional unevenness can be absorbed, and further, unevenness in the degree of fitting of the coupling member 2 cal also be absorbed. Further, the coupling member 2 is made of a plastic material which is softer than that of the members 1 to be coupled, thereby the manufacture of the coupling member 2 can be facilitated. It is noted that the concavities and convexities 15, 22 may be formed of a single protrusion or a bead. A third embodiment of the present invention will be explained with reference to Figs. 15 and 16. In this arrangement, the coupling structure is applied a frames such as a window frame, and the members 1 to be coupled and the coupling member 2 are made of aluminum, having an equal hardness, and the members 1 to be coupled are formed of a rectangular pipe. The hollow end parts the members 1 to be coupled are formed therein with a recess 8, and several concavities and convexities 15 as one kind of protrusions having an angle-like cross-sectional shape with angle shape crests are formed on the inner surface of the recess 8 in the one opposed direction by a large number in the widthwise direction so that their beads are extended longitudinally of the members 1 to be coupled, and further, a pin insertion hole 60 communicated to the hollow coupling part 4 which is a recess is formed in one side surface of the hollow coupling part 4 in the other opposite direction. Further, the end faces of the members 1 to be coupled are obliquely inclined at an angle of about 45 deg. so that four members 1 to be coupled are coupled together so as to form a rectangular frame. The members 1 to be coupled are longitudinally extrusion-molded. The coupling member 2 is made of a plastic material, having a L-like shape, and has hollow parts 49 communicated to the side surfaces of the opposite end parts 2a, 2b serving as the projecting parts. Further, a plurality of pairs of clamping pieces 67a, 67b for clamping a pin are projected from the inner surface of each of the hollow parts 49 at positions aligned with pin insertion holes 60, in directions orthogonal to each other. Further, concavities and convexities 22 serving as angular cross-sectional shape protrusions having angular crests are formed on the outer surface of the coupling member 2, longitudinally of the opposite end parts 2a, 2b, by a large number, being extended widthwise so that they are opposed to the concavities and convexities 15, orthogonal to the latter. Concavities and convexities 22' having a shape similar to that of the concavities and convexities 22 are formed on the opposed surfaces of the clamping pieces 67a, 67b. Such a hollow parallelepiped coupling member 2 having an L-like shape can be cut so as to have a predetermined width after extrusion-molding, as indicated by the phantom lines shown in Fig. 15. Aluminum pegs, rivets or the like are used as pins 63 which are driven into gaps between the clamping pieces 67a, 67b through the pin insertion holes 60 with the use of a hammer in order to ensure the fixing of the coupling member 2 fitted in the members 1 to be coupled. In this embodiment, when the opposite end parts 2a, 2b are fitted in the hollow coupling part 4, the angle shape concavities and convexities 15, 22 are collapsed by one another since both coupling member 2 and the members 1 to be coupled have an equal hardness so as to effect close-contact coupling. Further, the pins 63 are clamped between the pairs of the clamping pieces 67a extending in the extending directions of the opposite end parts 2a, 2b, and between the pairs of the clamping pieces 67b extending in a direction perpendicular to the extending directions of the concavities and convexities 22. The pins 63 clamped between the clamping pieces 67a are completely checked from coming off. However, the pins 63 clamped between the clamping pieces 67b are effectively checked from coming off but can be pulled off due to the frictional locking. Thus, effects equal to or higher than that of the eighth embodiment can be obtained. In particular, in the case of the clamping pieces 67b, estimating that the bore diameter of the pin insertion hole 60 is, for example, 6 mm while the outer diameter of the pin 63 is 4 mm, the concavities and convexities 15 extended in the longitudinal direction of the members 1 to be coupled are displaced by about 2 mm, and accordingly, a gap would be produced in the corner part of the members 1 to be coupled assembled in a rectangular frame shape. In this case, after the four corners of the members 1 to be coupled are mated together, the pin 63 are driven into the pin insertion holes 60 so that each of the pins 63 approaches the corner side or the inward side of the clamping pieces 67 (indicated by the solid lines shown in Fig. 6), thereby it is possible to regulate the displacement by 2 mm. Thus, the diameter of the pin insertion hole 63 can be increased so that the pin 63 can be easily inserted. Further, if the concavities and convexities 22' are formed on the opposed surfaces of the clamping pieces 67a, 67b, when the pins 63 are clamped, the clamping pieces 67a, 67b can be surely inhibited from longitudinally moving. Further, the pins 63 are aluminum pegs or rivets having a hardness equal to or less than that of the coupling member 2, and accordingly, it can be fixed by being collapsed by the concavities and convexities 22'. If the pins 63 have been pulled off, another new pin 63 can be used for reusing the coupling structure. It is noted that the concavities and convexities can be formed of a single protrusion or bead. Another cloth stretching frame is shown in Figs. 17, 18. In this cloth stretching frame another groove 7a in addition to a groove 6, is additionally formed in the outer surface 6 on the front end side, a folding-back and hooking piece 70 is provided, the cloth stretching bead part 5 is formed in such a shape that the end part of the frame piece 1a is folded back, and further, a bar receiver 58a for receiving an end part of a reinforcing bar 21 in its entirety, is extended. A groove-like cave 6a is formed in the outer surface of the frame piece la on the front end side, and a groove 7a is formed in the bottom surface of the cave 6a. Concavities and convexities 8 are formed on the inner surface of the groove 7a, similar to the groove 7, A side part 6b of the cave 6b is not perpendicular, has an inclined angles that it can be opened outward by an angle of about 160 deg. Further, an edge part of the cloth (which is not shown) is folded back below the groove 7 at the rear surface of each of the frame pieces 1a to 1d, and a folding-back and hooking piece 70 for folding back the cloth and as well for hooking onto a hook is extended. The edge part of the cloth (which is not shown) is folded back by the folding-back and the hooking piece 95, and a retainer (which is not shown) such as U-like shape clip is fitted onto the folding-back and hooking piece 95 so as to fix the edge part of the cloth. If a hooking unit such a hook is attached on a wall surface, the folding-back and hooking piece 70 is hooked onto the hook or the like so as to suspend the cloth stretching frame. Due to the provision of the groove 7a, the cloth has not to have a size with which the cloth can extend the groove 7, thereby it is possible to save the cloth, and it is convenient for folding a canvas cloth into the four corners of the frame pieces la to ld. In this case, if the outer periphery of the cloth stretching frame is preferably covered with an architrave in order to enhance the appearance. Further, since the cave 6a is formed, no protrusions are produced on the outer surface 6 when the cloth is retained by the groove 7. Further the edge part of the cloth stretched and fixed by the fixtures 3 is folded at the folding-back and hooking piece 70, and is then fixed to the folding-back and hooking piece 70 a retainer such as a clip. Thus, the appearance can be enhanced. Further, by hooking the folding-back and hooking piece 70 is hooked onto a hook provided wall surface, the cloth stretching frame can be conveniently hooked to the wall surface. The remainder is similar to the first embodiment. It is noted that the folding-back and hooking piece 70 may be provided on only the frame piece la serving as the upper frame. A painting cloth stretching frame in which a third comparative example is applied will be explained with reference to Figs. 19 to 21. That is, members 1 to be coupled in this coupling structure each has a hollow coupling part 4 as a recess at an end face 85, and concavities and convexities 15 serving as protrusions are formed on the inner surface of the hollow coupling part 4 while a pin insertion hole 74 communicated to the hollow coupling part 4, concavities and convexities 15 serving as protrusions are formed on the inner surface of the hollow coupling part 4, and an pin insertion hole 74 communicating to the hollow coupling part 4 is formed in a side surface. In this comparative example, grooves 7, 7a are formed at two positions on the outer surface and the rear surface of the frame piece la as shown in Fig. 20, and several concavities and convexities 15 having beads longitudinally extended are formed on opposite side surfaces of the grooves 7, 7a. Further, the hollow coupling part 4 is formed so as to have a large width which is about three-times as large as the thickness, and several concavities and convexities 15 serving as protrusions having an angle-like cross-sectional shape, having angular crests and longitudinally extended,are formed all over the inner peripheral surface thereof. Further, a folding-back and hooking piece 70 is suspended in rear of the groove 7 on the rear surface side, an edge part of a cloth stretched and fixed in the groove 7 or 7a by the fixture 3 (refer to Fig. 3) is folded back at the folding-back and hooking piece 70, similar to the third comparative example. Further, suspending pieces 77 for attaching a bar 21 (refer to Fig. 2) is formed. The frame pieces 1b to 1d is also similar to the frame piece 1a. However, the folding-back and hooking piece 70 may be formed only on the frame piece 1a, and the suspender 77 is formed on each of only the frame pieces 1a, 1c.These frame pieces 1a to 1d are extrusion-molded of metal such as aluminum. The coupling member 2 has abutting parts 86 adapted to abut against end faces 85, at one end part, projecting parts 23, 24 adapted to be fitted in the hollow coupling parts 4 being projected from the abutting parts 86, and pin attaching parts 73 are formed in the projecting parts 23, 24 at position aligned with pin insertion holes 74. In Fig. 19, the coupling member 2 is extrusion-molded of a plastic material such as a thermoplastic resin in which about 30% of the glass fibers are mingled (nylon 6, nylon 66 and the like). The coupling member has an L-like shape as view in a plan view, having grooves 7', 7a' continuous to one end parts of the continuous grooves 7, 7a, and several concavities and convexities 8' having beads extending depthwise are formed on opposite side surfaces of grooves 7', 7a' as shown in Fig. 22. Further, a cloth stretching bead part 5' continuous to the cloth stretching bead 5 is formed. Further, the projecting parts 23, 24 corresponding to the opposite end parts 2a, 2b of the coupling member 2, and adapted to be fitted in the hollow coupling parts of the frame pieces 1a to 1d are arranged being spaced from each other, concavities and convexities 22, 22a having beads extending widthwise are formed on the side surfaces of the projecting parts 23, 24, other than the opposed surfaces. The vertical length a and a lateral length b of a pair of projecting parts 23, 24 as viewed form the front surface 86 side, have relationship with the vertical length a' and the lateral length b' (refer to Fig. 20), that is, a > a', b > b'. When the crests of the concavities and convexities 22, 22a crosses the concavities and convexities 15, they are collapsed so as to effect close contact coupling. The concavities and convexities 22, 22a are harder than the synthetic resin coupling 2 since the frame pieces la to ld are made of aluminum, and accordingly, they have a moderate angle shape having wide pitches in comparison with the concavities and convexities 15. Further, the projecting part 23 is formed therein with a pin attaching part 73 into which a screw-like pin inserted in the pin insertion hole 74 of the frame piece 74 is tightened. The pin attaching part 73 can be tapped by the pin. Further, a continuous suspending piece 77' continuous to the suspending piece 77 is formed, a continuous folding-back and hooking piece 70' continuous to the folding-back and hooking piece 70, and is formed therein a hooking hole 78. The coupling member 2 is made of synthetic resin. Reference numeral 79 denotes a recess for lightning in view of the formation. Further, identical reference numerals are attached to components common to these in Figs. 17 and 18. Further, in this cloth stretching frame, the frame pieces 1a to 1d are arranged in a frame-like pattern, the coupling members 2 are interposed between the frame pieces 1a to 1d which are then pushed together so as to press the coupling members 2 into the end parts of the frame pieces 1a to 1d so as to be fitted therein. At this time, although the hollow coupling parts 4 of the frame pieces 1a to 1d and the projecting parts 23, 24 of the coupling members 2 are coupled together with the crests of the concavities and convexities 15 and the crests of the concavities and convexities 22 are made into press-contact with each other, only the crests of the concavities and convexities 22 are collapsed since the coupling members 2 are made of plastic material. Further, the crests of the concavities and convexities 22a are also collapsed, being made into press-contact with the inner surfaces of the hollow coupling parts 4. Next, the pins 73 are driven into the pin attaching parts 73 through the pin insertion holes 74, and accordingly, the coupling members 2 are checked from coming off from the frame pieces 1a to 1d. With the coupling member shown in Fig. 19, when the projecting parts 23, 24 are fitted into the hollow coupling parts 4 of the members 1 to be coupled, since the crests of the concavities and convexities 22 are made into press-contact while the coupling members 2 are fitted. the fitting is easily made, and the abutting parts of the coupling members 2 can surely abut against the end faces 85 of the members 1 to be coupled, thereby it is possible to tight coupling. Further, since the end faces of the members 1 to be coupled are not made into contact with each other, no limitation is imparted to the shapes of the end faces. Accordingly, it is possible to cut the end face 85 at an angle of 45 deg. Further, since the intermediate parts of the coupling members 2 are exposed from the members 1 to be coupled, if the material of the coupling parts 2 is different, a gap which would be defined more or less between the abutting part 86 and the end face 85 of the members 1 to be coupled can be made to be unnoticeable. It is noted that the degree of difficulty in come-off of the coupling members 2 without the pins being driven into, can be determined, depending upon a degree of fitting of the projecting parts 22, 23 into the hollow coupling parts 4. Further, the coupling members 2 can be surely checked from coming off by attaching the pins to the pin attaching parts 73 through the pin insertion holes 74. Further, when a pair of projecting parts 23, 24 are fitted in the coupling parts 4, since they are likely to be resiliently deformed toward one another, the fitting thereof into the hollow coupling parts 4 can be easily made, and further, they can hardly be moved in a pull-out direction due to the press-contact of the crests of the concavities and convexities 22, 22a. It is noted that the grooves 7, 7a, 7', 7a' may be formed, being extended from the outer surfaces to the rear surfaces of the members 1 to be coupled and coupling members 2. Although it has been explained that the pins are screws, and the pin attaching parts 73 are threaded holes. Pins with no threads, may be press-fitted and fixed in holes or the like having protrusions formed on the inner surfaces of the pin attaching parts 73. Further, although it has been explained that the concavities and convexities 15, 22, 22a are formed on both members 1 to be coupled and the coupling members 2, they may be formed on only either one of them. Further, the coupling members 2 may be made of metal, together with the members 1 to be coupled. Further, if the hardness of the concavities and convexities 15, 22, 22 are identical or less, the crests of these concavities and convexities are collapsed, alternately, if these protrusions are harder, they wedge into the softer surface or protrusions. Fig. 23 shows a variant form of protrusions which are one of the concavities and convexities 15, 22, 22a, Fig. 23(a) illustrating an angle-like cross-sectional shape having a curved crest, and Fig. 23(b) illustrating a angle-like cross-sectional shape having an angle crest, and having moderate inclined surfaces. Reference numeral 81 shows an example of the crest 80 which has been collapsed. The concavities and convexities 22 or the like may be formed in a conical or pyramid-like shape, other than the bead-like shape, and can be spotted. In this case, the concavities and convexities 15, 22, 22a are arranged so as to exhibit a letter, a number, a symbol or the like. Fig. 24 is a partial enlarged view illustrating such a condition that the concavities and convexities 22 are press-fitted into concavities and convexities 15, the concavities and convexities 15 having crests which have a bottom side length (a) of 1 mm and a height (h) of 1 mm, the concavities and convexities 22 having crests which have a bottom side length (e) is 0.5 mm, and the height (b) is 0.3 mm, the respective crests 15b (height d 2 = 0.2 mm), 22b (height d 1 is 0.1 mm) are collapsed so as effect coupling. In this example, the pitches, the shape and dimensions of the concavities and convexities 15 are larger than those of the concavities and convexities 22. However, the former may be equal to or larger than the latter. On the contrary, the pitches of the concavities and convexities 15 may be small, or the pitches of the concavities and convexities 22 may be large. It is noted that the embodiment shown in Figs. 23, 24 may be applied to the case in which the coupling member 2 and the members 1 to be coupled to be fitted therein with the coupling member 2 are made of aluminum. Further, it can be applied to the afore-mentioned all other embodiments, and embodiments mentioned below. A fourth embodiment of the present invention is shown in Fig. 25. That is, this coupling structure comprises a plurality of plate members 93, 93' having half-lap surfaces 90, 9a formed on at least either the rear surface side of one side part or the front surface of the other side part, and recesses 92 opposed with half-lap surfaces 90, 91 being superposed with the former half-lap surfaces 90, 91, and adapted to be half-lap joined, and coupling members 94 adapted to be fitted in the recess 92 between the half-lap surfaces 90, 91 of the plurality of plate members 93, 93'. With this embodiment, rise-up pieces 95 are provided inward of the recesses 92 between the half-lap surfaces 91, and the plate members 93, 93' are extrusion-molded. When the plate member 93, 93' are superposed with each other, a water-tight packing 97 is interposed between the rise-up piece 95 and the inward end part 91a. Further, attaching holes 96 into which attaching screws 95 are inserted are formed, and accordingly, the plate members 93, 93' are attached to a base (which is not shown) by the attaching screws 95. Further, the concavities and convexities 15 are formed on the inner surface of the recesses 92. The coupling members 94 are formed of a substantially rectangular cross-sectional shape hollow body 98, having side parts outward convexly curved. Convexly curved surfaces 97 are formed on opposite side surfaces, and further, concavities and convexities 22 are formed on the outer surface, and the coupling members 94 are extrusion-molded and are cut at a predetermined length position 94a. It is noted that the crests of the concavities and convexities 15 on the recess side may be made to be large while the crests of the concavities and convexities 22 of the coupling members 94 may be made to be small, and accordingly, the coupling members 94 can be easily press-fitted. With this arrangement, several plate members 93, 93' can be successively, and longitudinally and crosswise coupled together in a simple manner with a predetermined positional relationship, and further, the coupling members 94 and the plate members 93, 93' can be simply manufactured by extrusion-molding. When the coupling members 94 are press-fitted in the recesses 92, the convex curved surfaces 97 are resiliently deformed, and accordingly, the coupling members 95 can be easily press-fitted in the recesses 92. Further, the binding force can be enhanced. It is noted that the concavities and convexities 15. 22 are may be formed on either the recesses 92 or the coupling members 94. That is, it is not necessary to form then on both components. Further, in the recesses 92, the crests of the concavities and convexities 22 may become higher and higher inward from the coupling side, and accordingly, the coupling members 94 can be more easily fitted in the recesses 92. Further, a more strong binding force can be held. Further, in this arrangement, the crests of the concavities and convexities 15 may become higher and higher toward the fitting side. Another cloth stretching frame is shown in Figs. 26 to 30. Fig. 26 shows a section of a frame piece 1a, and a bar receiver 58 is projected in a direction inward of the cloth stretching frame, and a coupling hole 100 is formed in the bar receiver 58 while a reinforcing bar fixing groove 101 is formed in the inner surface 43 of the frame piece la as the cloth stretching frame. Further, the reinforcing bar fixing groove 101 are formed on its inner surface with concavities and convexities 15. The same arrangement is taken for other frame pieces 1b to 1d. These frame pieces 1a to 1d are extrusion-molded. Further, hollow coupling parts 4, grooves 7, concavities and convexities 15, recesses 34, cloth catching bead parts 46 and the like similar to those in Figs. 9 and 11. Thus, like reference numerals are attached to common parts. Fig. 27 shows a section of a reinforcing bar 21 formed on one side surface of an end part thereof with a thread hole 103 adapted to be aligned with the coupling hole 100, and formed on opposite sides, with side grooves 12 aligned with the reinforcing bar fixing groove 101. Further, the side grooves 12 are formed therein with the concavities and convexities 15. The reinforcing bar 21 is also extrusion-molded. Figs. 28 and 29 show a reinforcing bar coupling member 104 which are formed on the outer surface thereof with longitudinally arranged concavities and convexities 22. This reinforcing bar coupling member 104 is also formed by cutting an extrusion-molded strip-like body so as to have a predetermined length. Fig. 30 is an explanatory view for attachment of the reinforcing bar 21. One end part of the reinforcing bars 21 are made into contact with the bar receiver 58 and with inner surface 43,and the reinforcing bar coupling member 104 are pushed widthwise so as to be press-fitted in the side groove 102 as shown by the arrow L 1 . Further, the reinforcing bar coupling member 104 is pushed longitudinally so as to be fitted in the reinforcing bar fixing groove 101. The a screw is inserted in the aligned holes and is then tightened into the thread hole so as to fix the reinforcing bar. Accordingly, it is possible to simply and surely attach the reinforcing bar. Members to be coupled have hollow coupling parts at opposite side surfaces, a coupling member has, at opposite ends, press-fitting parts which are press-fitted in the hollow coupling parts, and angle shape concavities and convexities having crests which are corrupted upon press-fitting are formed on at least either one of an inner peripheral surface of the hollow coupling part and an outer peripheral surface of the press-fitting part. When the opposite end parts of the coupling members are press-fitted in the hollow coupling parts of the members to be coupled, the crests of concave parts of the angle shape concavities and convexities are corrupted by the opposed surface so as to be made into close contact with and firmly coupled to the associated surface, thereby it is possible to surely couple a pair of members to be coupled with a simple work.

Claims: A coupling structure comprising: a)- a plurality of elongated members (1a-1d; 93, 93') to be coupled together at an angle in order to form a frame, said members having recesses (4) at their opposite ends, and b)- coupling members (2; 94) having end parts which are insertable in said recesses (4; 92), said coupling members (2; 94) being formed from an extrusion-molded body (48; 98) which is cut into dimensions with which said coupling members (2; 94) can be press-fitted into said recesses (4; 92), characterized in that said extrusion-molded body (18; 98) comprises hollow sectors (49) which extends in the extrusion-direction of said extrusion-molded body. A coupling structure as set forth in claim 1, wherein the end surfaces (55) of said elongated members (1a-1d) are inclined so that said members (1a-1d) are coupled together at a right angle, and said coupling members (2) have an L-like shape wherein a corner part is provided with a reinforcing member (50), and wherein the legs of the L-like shape terminate with inclined faces (2a, 2b) so as to be directed substantially orthogonal to said end surfaces (55), and so as to be flush with each other. A coupling structure as set forth in claim 1, wherein concavities and convexities (15, 22) are formed on at least one of contact surfaces of said coupling members (2) and said elongated members (1a-1d) to be coupled. A coupling structure as set forth in claim 1, wherein each of said recesses (4) has a rectangular cross-sectional shape, and the widthwise direction of at least one of said recesses (4) is orthogonal to the widthwise direction of the other recess (4). A coupling structure as set forth in claim 1, wherein said elongated members are formed by a plurality of plate members (93, 93') each having a half-lap surface (90, 90a) at least either one of a rear surface of one side part, and a front surface of the other side part, having opposed recesses (92) in a position such as to be aligned when said half-lap rear surfaces (90) are superposed respectively with said half-lap front surfaces (90a), and adapted to be half-lap-joined together by means of a coupling member (94) adapted to be fitted between said opposed recesses (92) of said half-lap surfaces of said plurality of plate members (93, 93'). A coupling structure as set forth in claim 5, wherein said coupling member (94) is formed of a hollow body (98) having a side part (97) which are curved outward convexly. A coupling structure as set forth in claim 5, wherein said recesses (92) have concavities and convexities (15) having large pitches, and said coupling members (94) has concavities and convexities (22) having pitches smaller than that of the recesses (92). A cloth stretching frame characterised in that it comprises a coupling structure according to anyone of the preceding claims, and a cloth stretching bead part (5) on a front surface (13) of the elongated members, a groove (7) being located between an outer surface (6) to a rear surface (40) of the bead part. A cloth stretching frame as set forth in claim 8, wherein a folding-back and hooking part (70) for folding back an edge part of said cloth (18) and hooking the same onto a hook, is extended on the rear surface (40) of the elongated members (1a-1d) defining the upper side of said cloth stretching frame at a level lower than that of said groove (7). A cloth stretching frame as set forth in claim 8 or 10, wherein a projecting part (42) is formed on said rear surface (40) so as to form a slope surface (41) continuous to said outer surface, at a level lower than said groove (7). A cloth stretching frame as set forth in claim 10, wherein said bead part (45) has suspender attaching holes. A cloth stretching frame as set forth in claim 10, wherein a cloth catching bead part (46) is formed on said slope surface of said groove (7) on said outer surface side. A cloth stretching frame as set forth in claim 8, wherein a bar receiver (58) is projected from said elongated members (1a-1d) in a direction inward of said cloth stretching frame, a coupling hole is formed in said bar receiver (58a), a reinforcing bar fixing groove is formed in the inner surface of said elongated members (1a-1d), the reinforcing bar having a side surface is provided with a thread hole aligned with said coupling hole, in the side surface of said opposite ends and further, side grooves aligned with said reinforcing bar fixing groove, are formed on opposite sides, and the coupling member (2) is provided so as to be press-fitted in said side grooves and said fixing groove.

Inventors: YAMAWAKI SHIGEHIRO, YAMAWAKI, SHIGEHIRO
Applicants: EBARIS CO LTD, EBARIS CO., LTD.
Application year: 1996
Main classification: B44D3
IPC codes: B44D3