Cubic Connector Structure for Connecting Frame Bars and Method of Producing Same

This invention relates to structures for connecting together a plurality of frame bars at their ends and a method of producing such structures.

For connecting together elongated construction materials such as frame bars at their ends, it has been known, as shown in FIG. 10, to attach an L-shaped metal bracket 31 on the surface of each frame bar 3, leaving an end surface 3a of one of them exposed to the exterior. Frame bars thus connected, however, are unsightly because the metal brackets used to connect them together protrude from their side surfaces. Such metal brackets, as well as screws which are used to attach them to the frame bars, can be a source of serious accidents because they can easily catch a part of the worker's clothes.

It is therefore an object of this invention to eliminate such problems of the prior art technology and to provide safe connector structures which do not have any externally protruding parts and can be attached to frame bars securely and easily.

It is another object of this invention to provide methods of producing such connector structures efficiently.

A connector structure according to this invention, with which the above and other objects can be accomplished, may be characterized as comprising a main part having side walls with three mutually perpendicular quadrangular outer surfaces and a cover piece which similarly has three side walls with mutually perpendicular quadrangular outer surfaces. Each of the side walls of the main part has a hole for allowing a screw to pass therethrough. A protruding member for engaging with the cover piece is formed on the inner surfaces of the side walls of the main part, and a protrusion is formed on the inner walls of the cover piece. When the main part and the cover piece are attached to each other by engaging the engagement member on the main part and the protrusion from the cover piece, the main part and the cover piece together assume a single cubic shape with smooth outer surfaces.

The main part of such a connector structure can be produced by a die-casting method by using only one lower mold piece and one upper mold piece. The lower mold piece has an indentation with three mutually perpendicular inner surfaces each making a same angle with the vertical direction for forming the three outer surfaces of the main part. The upper mold piece has a convex part for forming the inner surface. For forming the screw-passing holes through the side walls, while allowing the upper mold piece to be moved towards or away from the lower mold piece linearly along a single straight line, small protrusions are formed both downward from the convex part of the upper mold piece and upward from the inner surfaces of the lower mold piece, both having vertical surfaces such that, as the two mold pieces are moved toward each other, pairs of these protrusions from the upper and lower mold pieces slide against and come to contact with each other across their vertical surfaces. The cover piece can be produced by an ordinary injection molding method by using similarly designed mold pieces.

With connector structures according to this invention, frame bars can be connected together securely and the joint is left with smooth external surfaces with no protrusions, the connector structure becoming a cube after the cover piece is attached to the main part by engaging the protrusion from the cover piece with the engagement member on the main part. The invention also teaches how easily the main parts and the cover pieces of this invention can be produced by using only two mold pieces which can be moved toward and away from each other linearly.

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a diagonal view of components of a connector structure embodying this invention before being attached to frame bars;

FIGS. 2A, 2B, 2C and 2D (referred to together as FIG. 2) are views of the main part of the connector structure of FIG. 1 as seen respectively from the top (FIG. 2A), from the front (FIG. 2B), from the left-hand side (FIG. 2C) and from the right-hand side (FIG. 2D);

FIGS. 3A, 3B, 3C and 3D (referred to together as FIG. 3) are views of the cover piece of the connector structure of FIG. 1 as seen respectively from the top (FIG. 3A), from the front (FIG. 3B), from the left-hand side (FIG. 3C) and from the right-hand side (FIG. 3D);

FIG. 4 is a diagonal external view of the connector structure of FIG. 1 used for connecting three frame bars as an example;

FIG. 5A is a diagonal external view of the main part of FIG. 1 as taken in the direction of arrows 5 in FIG. 2D, and FIG. 5B is a sectional view of the same taken along line 5--5 of FIG. 2D;

FIG. 6 is a sectional view of portions of mold pieces for the production of the main part;

FIG. 7 is an enlarged view and part of FIG. 6;

FIGS. 8A and 8B are respectively a plan view and a sectional side view of the lower mold piece of FIG. 7;

FIGS. 9A, 9B and 9C are external views of connector structures of this invention used in different situations; and

FIG. 10 is a diagonal external view of two frame bars connected by means of a prior art connector structure.

As shown in FIG. 1 by way of an example, a connector structure according to this invention comprises a main part 1 and a cover piece 2. The main part 1 is made of a metallic material such as aluminum and has three side walls 1a, 1b and 1c, forming a half-open empty space on their internal side, as shown in FIGS. 1 and 2. The outer surfaces of these side walls 1a, 1b and 1c are mutually perpendicular and are each a square of the same size as the end surfaces of frame bars 3 to be connected thereto. The three side walls 1a, 1b, and 1c are each sufficiently thick so as to provide adequate strength required of a connector structure and are each provided with a screw-passing hole 1d at the center. The inner surfaces of the three side walls 1a, 1b and 1c are indented so as to together form a concave surface 15. The boundary of this concave surface 15 runs along the peripheries of the three side walls 1a, 1b and 1c, as can be seen in FIG. 1, and protrudes uniquely therefrom, as can be seen in FIGS. 1, 5A and 5B, in the direction of an imaginary line which makes the same angle with each of the three mutually perpendicular outer surfaces of the walls 1a, 1b and 1c. This unidirectionally protruding boundary of the concave surface 15 serves as an engagement member 1e, as will be explained below more in detail, for tightly attaching the main part 1 to the cover piece 2 when they are in a closed relationship.

The cover piece 2 is somewhat smaller than the main part 1 but is of a similar structure, as shown in FIG. 3, having three side walls 2a, 2b and 2c with mutually perpendicular outer surfaces to form a half-open empty space on the side of their inner surfaces. These inner surfaces are provided with a protrusion 2e entirely along their peripheries, as shown in FIGS. 3A, 3B and 3D, corresponding to the engagement member 1e on the main part 1 and protruding uniquely in the direction of an imaginary line which makes the same angle with each of the three mutually perpendicular outer surfaces of the side walls 2a, 2b and 2c. This makes it possible for the protrusion 2e of the cover piece 2 to slide inside and thereby engage with the engagement member 1e of the main part 1 as the main part 1 and the cover piece 2 are attached together when they are in the aforementioned closed relationship. The outer surface of each side wall 2a, 2b or 2c is substantially square-shaped such that when the main part 1 and the cover piece 2 are thus attached to each other and are in the closed relationship, they together assume a substantially cubic shape, as shown in FIG. 4.

Next will be described a manner in which this connector structure may be used for connecting ends of three frame bars such that they will be mutually perpendicular, as shown in FIG. 4. Each frame bar 3 is provided with a screw-receiving opening 3d (tapping hole) at the center of its end surface, as shown in FIG. 1. First, one of the side walls 1a, 1b or 1c of the main part 1 is attached to an end surface of one of the frame bars 3 with the screw-passing hole 1d at the center of that side wall aligned with the screw-receiving opening 3d and a screw 4 is passed through them both from the side of the concave surface 15 of the main part 1, thereby securely attaching the main part 1 to the end surface of the first frame bar 3. In identical manners, two other frame bars 3, each with an end surface similarly provided with a screw-receiving opening 3d, are securely attached to the other two side walls of the main part 1. The cover piece 2 is thereafter attached to the main part 1 by pushing it in the direction of the imaginary line which makes the same angle to all three outer surfaces of the side walls 1a, 1b and 1c and engaging the protrusion 2e of the cover piece 2 with the engagement member 1e on the inner surfaces of the main part 1. FIG. 4 shows the joint thus completed.

The main part 1 is made of a metallic material such as aluminum, and the cover piece 2 is made of a synthetic resin material such as polyacetal, but other materials may be selected as long as adequate strength can be obtained for the purpose of serving as a connector structure. According to a preferred method of producing connector structures of this invention as described above, the main part 1 is manufactured by a die-casting method and the cover piece by a general injection molding method, both methods requiring appropriate mold pieces. Although many mold pieces are normally required to form a structure with a concave inner surface such as the main part 1 according to this invention, the method of this invention not only requires only two mold pieces but they can be moved toward or away from each other to be engaged together or to be separated from each by moving one of them linearly along a single straight line with respect to the other.

According to this invention, use is made of a lower mold piece 10 for forming the outer surfaces of the side walls 1a, 1b and 1c and an upper mold piece 20 for forming the concave inner surface 15 and the engagement member 1e therearound, as shown in FIG. 6. The lower mold piece 10 has a horizontal top surface provided with an indentation in the form of a triangular pyramid with three mutually perpendicular inner surfaces 11 (as shown more clearly in FIG. 8A) for the purpose of forming the mutually perpendicular outer surfaces of the three side walls 1a, 1b and 1c of the main part 1. Each of these three mutually perpendicular inner surfaces 11 makes the same angle with the vertical direction (that is, the direction perpendicular to the horizontal top surface). FIG. 5A shows the main part 1 as oriented when formed inside the lower mold piece 10.

The upper mold piece 20 has a horizontal bottom surface provided with a convex part for forming the concave inner surface 15. Both the inner surfaces 11 of the indentation in the lower mold piece 10 and the convex part of the upper mold piece 20 are provided with small protrusions 10a and 20a for forming the screw-passing holes 1d through the side walls 1a, 1b and 1c. These small hole-forming protrusions 10a and 20a are shaped and positioned with respect to each other as shown in FIG. 7, having vertical walls which are tangent to an imaginary vertical plane from opposite sides such that, as the upper mold piece 20 is lowered vertically, the protrusions 10a and 20a slide against each other over their vertical walls, joining together and becoming positioned next to each other as shown by a broken line in FIG. 7 such that they can together serve to form the screw-passing hole 1d. It is to be noted that neither the convex part of the upper mold piece 20 nor any of the inner surfaces 11 of the lower mold piece 10 has any horizontally protruding part and hence that the upper mold piece 20 can be lifted vertically upward without any hindrance from the lower mold piece 10.

For practical applications, mold pieces are formed, as shown in FIGS. 8A and 8B, for example, for achieving mass production such that a plurality of main parts 1 can be produced simultaneously. Mold pieces for mass production of the cover pieces 2 by an injection molding method are similarly designed with a pair of upper and lower mold pieces which can be brought towards and moved away from each other by a linear motion along a single straight line (the vertical line) with respect to the other and provide three mutually perpendicular surfaces making a same angle to the direction of this straight line.

Although the manner of using the connector structure according to the present invention has been illustrated above with reference only to FIGS. 1 and 4, it goes without saying that it can be used in a variety of different ways. For example, it may be used for connecting only two frame bars 3 as shown in FIG. 9A. In such an application, a masking cap 5d is inserted into the remaining screw-passing hole 1d of the main part 1 such that it can be hidden. When two frame bars with a rectangular cross-sectional shape are connected, as shown in FIG. 9B, two of the connector structures of the invention are used, each at one of the longitudinal edge part of the end surfaces. A short bar 6 is inserted between the two connector structures to complete a joint without unevenness in the exterior. FIG. 9C shows a situation where three frame bars 3 with different cross-sectional shapes are connected. It should be clear to a person skilled in the art, from these illustrated examples, how connector structures of this invention can be used in many different situations without leaving any surface protrusions or indentations at the joint.

In summary, the connector structures according to the present invention are capable of connecting two or three frame bars securely at their ends and without leaving surface protrusions or indentations such that externally exposed surfaces are all smooth. This makes the joints not only sightly but also safe for the operators to work around. The method of producing such connector structures according to this invention is advantageous in that only two mold pieces are required. This not only simplifies the production process but also reduces the cost of producing the mold significantly.