DESCRIPTION

The present patent application for industrial invention relates to an improved inspection trapdoor. As it is well known, a trapdoor is usually installed in correspondence of openings obtained in walls in such a way as to permit the inspection of a compartment disposed behind the wall.

It should be noted that in the present description the term “wall” refers indifferently to vertical walls and to ceilings or floors.

In order to better understand the problems and the drawbacks of the prior art, the description of the trapdoors of the prior art is continued with reference to the following figures defined as “PRIOR ART”, wherein: la Fig. 1 is a front view of the trapdoor according to the prior art;

Fig. 2 is a diagrammatic view of a section of the fixed frame of the trapdoor of Fig. 1 and of a section of the movable frame of the trapdoor of Fig. 2, which show the portions of sections that are discarded for the 45° cut;

Fig. 2A is a diagrammatic side view of two sections disposed one on top of the other;

Fig. 2B is a top view of the two sections of Fig. 2A; Fig. 2B shows a 45° cut, starting from a corner of the section;

Fig. 2C shows the two sections of Fig. 2B disposed side by side, and not one on top of the other; Fig. 2C shows the portion of the upper section and the portion of the lower section that are removed after the 45° cut with the sections disposed one on top of the other;

Figs. 3 and 3A are a view of two trapdoors according to the prior art, wherein the sections are connected by means of two different connection modes.

With reference to the aforementioned figures a conventional inspection trapdoor comprises: a fixed frame (91 ) suitable for being fixed to a wall in correspondence of an opening of the wall; a movable frame (92) disposed inside the fixed frame (91 ), in a movable way between an opening position and a closing position; a panel (not shown in the appended figures) internally connected to the movable frame (92); and connection means (not shown in Figs. 3 and 3A) for movably connecting and supporting the movable frame (92) with respect to the fixed frame (91 ).

Each frame (91 , 92) is composed of four sections (910, 920).

The ends of each section (910, 920) are cut at 45° in such a way that the ending edge of a section (910, 920) coincides and abuts with the ending edge of the section (910, 920) in adjacent position.

According to a first connection mode of the sections, which is shown in Fig. 3, the connection between two sections (910, 920) is obtained by means of metal corner pieces (931 ), each one of them comprising two wings, each wing being fixed to a section by means of screws (93v).

According to a second connection mode of the sections, which is shown in Fig. 3A, the connection between two sections (910, 920) is obtained by means of metal corner pieces (932), each one of them comprising two wings inserted in longitudinal notches of the two sections in adjacent position. In such a case, the connection of each wing to the corresponding section is obtained by means of punching.

Although similar inspection trapdoors have been very well received by the market up to now, it is evident that they are impaired by some drawbacks.

A first drawback occurs when cutting the sections to size. In fact, cutting the sections at 45° is an extremely complicated and delicate operation and is therefore extremely susceptible to errors.

Furthermore, dimensional tolerances are extremely complicated to manage when the ends of the sections are cut at 45°. More precisely, said trapdoors are not versatile, that is to say that each external fixed frame (91 ) coincides with a single internal movable frame (92) and therefore they are not interchangeable with each other. Otherwise said, between inspection trapdoors of the same size, the movable frames (92) cannot be interchanged because of the presence of minor imperfections that prevent the interchangeability between the movable frames (92) of the same size.

Another drawback that impairs the inspection trapdoors according to the prior art refers to the waste of material during the fabrication of the sections (910, 920).

In fact, according to the fabrication process of the sections (910, 920), a section is firstly provided and then the ends of the section are cut at 45° according to previously calculated measurements.

The cutting of the sections at 45° necessarily involves a waste of material that can usually vary from a minimum of 5% to a maximum of 20% depending on the size of the inspection trapdoor to be made and on the thickness of the section. In Fig. 2 the portion of the section (910, 920) that is wasted is indicated with a dotted line.

Moreover, because of the 45° cut, the operator cannot simultaneously cut multiple sections of the same size disposed one on top of the other.

Such a drawback will become clearer by referring to Figs. 2A, 2B and 2C.

Generally speaking, each section (910, 920) has a vertical wing that does not allow the sections to be perfectly stacked vertically, but rather generates a staggered effect, as shown in Fig. 2A. Two sections (910', 910") of the fixed frame (91 ) are shown in Fig. 2A, but the same would apply to the sections of the movable frame (92).

Such a staggered arrangement of the sections (910', 910") does not allow the user to simultaneously cut the sections (910', 910") in the same manner with a single cutting operation.

By way of example, with reference to Figs. 2B and 2C, when making a 45° cut starting from the edge (S10') of the lower section (910'), the lower section (910') will be cut properly, whereas the upper section (910') will be cut at 45°, losing a portion (t10') of section which is in direct proportion to the thickness of the vertical wing. The greater the thickness of the wing, the greater the portion (t10") lost by the upper section with respect to the lower section during the 45° cutting operation will be. Therefore the upper section (910") will be shorter than the lower section (910").

Therefore, because of such an inconvenience, it will be necessary to cut one section at a time, requiring a long time for the production of such an inspection trapdoor.

Such a long production time is very inconvenient in large-scale production processes of such inspection trapdoors.

A further drawback of the inspection trapdoor according to the prior art concerns the fact that, despite the precision and expertise of an operator during the assembly of the frames (91 , 92), said frames are frequently provided with steps (due to the imperfect alignment of the sections) that strongly affect the aesthetics of the final trapdoor.

In addition, the corners of the inspection trapdoor are provided with sharp corners that are extremely dangerous for an operator during the installation of the inspection trapdoor on the wall.

W02020120939A1 discloses a hatch, in particular for use in openings on the floor of buildings under construction. The hatch comprises an inner frame which is provided with lower dimensions than the opening and is inserted in the opening, and an outer frame which is provided with larger dimensions that the opening and is rested on the floor. The hatch also comprises two door panels that are hinged to the outer frame and can be moved between a closed position and an open position.

Each frame comprises frame members that define a rectangular frame. Each frame member has a square or rectangular section and each lateral side is provided with a longitudinal channel that extends for the entire length of the frame member. The frame member is cut at the ends at 90° in such a way that its end faces are disposed orthogonally to the lateral faces.

The frame members of a frame are connected by means of a first runner element inserted in a channel of a frame member, and a second runner element inserted in the channel of the other frame member, said runner elements being coupled to each other by means of threaded elements. In particular, one of the two runner elements is provided with a threaded hole, whereas the other runner element is provided with a screw suitable for being coupled with the threaded hole of the other runner element. In view of the above, in order to join the two frame members, it is necessary to dispose each runner element in the proximity of the end of the frame member, aligning the screw and the threaded hole. Then, with the help of a suitable tool (for instance, a screwdriver), the screw is screwed in the threaded hole, in such a way that the two runner elements are joined, connecting the two frame members.

Said runner elements that are coupled by means of threaded elements are also used to connect the inner frame to the outer frame.

Such a hatch is impaired by some drawbacks.

The assembly of the hatch, which provides for connecting the runner elements by means of threaded couplings, is complicated and time-consuming for an operator.

Moreover, the hatch is dangerous because the outer frame may have edges or protrusions that may injure the operators.

The presence of such edges or protrusions is due to the structural configuration of the frame, according to which at least four of the end faces of the four frame members are exposed outwards. In fact, the end faces of the frame members that are exposed outwards may have burrs or sharp parts that can injure a user.

Moreover, if the end face is not perfectly flush with the lateral face of the adjacent frame member, an edge or a step will be formed between the lateral face and the end face, with the risk of injuring the operator.

DE202006004357U1 discloses a cover for light and/or ventilation shaft. Such a cover comprises a frame with four rods and four connectors. Each connector connects two adjacent rods at 90°.

Each connector comprises: a square-based body having two channels disposed at right angle; two screws, each of them being inserted in one of said channels and being engaged in a threaded seat obtained at the end of the rod. Therefore, in order to connect two adjacent rods, it is necessary to dispose the two rods in perpendicular position, dispose the square-based body between the two rods with the channels aligned to the threaded seats, introduce the screws in the channels and finally screw the screws in the threaded seats. Evidently, such an operation is rather complicated and slow to be performed.

It is the purpose of the present invention to devise an inspection trapdoor that is efficient, simple and inexpensive to make.

A further purpose of the present invention is to devise a trapdoor wherein it is no longer necessary to cut the sections at 45°.

Another purpose is to provide a trapdoor that is reliable and suitable for preventing the operator from being injured.

These purposes are achieved in accordance with the invention with the features listed in the appended independent claim 1 .

Advantageous embodiments appear from the dependent claims.

The inspection trapdoor according to the invention is defined by claim 1 .

For the sake of clarity, the description of the inspection trapdoor according to the invention is continued with reference to the appended drawings, which exclusively have an illustrative and non-limiting value, wherein:

Fig. 1 is a front view of the trapdoor according to the prior art;

Fig. 2 is a diagrammatic view of a section of the fixed frame and of a section of the movable frame, which shows the portions of the sections that are discarded after the 45° cut;

Fig. 2A is a diagrammatic side view of two sections disposed one on top of the other;

Fig. 2B is a top view of the two sections of Fig. 2A; Fig. 2B shows a 45° cut starting from an edge of the section;

Fig. 2C is a view of the two sections of Fig. 2B disposed side by side instead of one on top of the other; Fig. 2C shows the portion of the upper section and the portion of the lower section that are removed after the 45° cut with the sections disposed one on top of the other; Figs. 3 and 3A are views of two trapdoors according to the prior art, wherein the sections are connected by means of two different connection modes;

Fig. 4 is a front view of the trapdoor according to the invention;

Fig. 4A is an axonometric front view of the trapdoor according to the invention;

Fig. 5 is a rear view of the trapdoor according to the invention;

Fig. 5A is an axonometric rear view of the trapdoor according to the invention;

Fig. 6 is an axonometric diagrammatic view of a corner piece of the movable frame of the trapdoor according to the invention, seen from the front;

Fig. 6A is a view of the corner piece shown in Fig. 6;

Fig. 7 is an axonometric diagrammatic view of a corner piece of the fixed frame of the trapdoor according to the invention, seen from the front;

Fig. 7A is a top view of the corner piece shown in Fig. 7;

Fig. 8 is an axonometric diagrammatic view of a section of the movable frame;

Fig. 9 is a schematic axonometric view of a section of the fixed frame;

Fig. 10 is an enlarged diagrammatic view of the way in which a corner piece is coupled with a section;

Fig. 10A is a sectional view of the corner piece and of the section of Fig. 10, sectioned along the X-X plane;

Figs. 1 1 and 1 1 A are two rear axonometric views of the corner piece of the fixed frame and of the mobile frame, wherein the end stop means and the locking means are provided;

Fig. 1 1 B is identical to Fig. 1 1 A, except for the provision of a snap-fit locking device connected to the corner piece of the fixed frame;

Fig. 1 1 C and 1 1 D are rear axonometric views of the corner piece of the fixed frame and of the corner piece of the mobile frame, respectively, wherein the end stop means and the locking means are provided;

Fig. 12 shows an alternative version of the trapdoor according to the invention. With reference to Figs. 4 to 1 1 D, an inspection trapdoor according to the invention is described.

With reference to Figs. 4, 4A, 5 and 5A, the inspection trapdoor according to the invention comprises: a fixed frame (TF) suitable for being fixed to a wall in correspondence of an opening of the wall; a movable frame (TM) disposed inside the fixed frame (TF), a panel (not shown in the appended figures) internally connected to the movable frame (TM) in such a way to close the opening; connection means (5, 6) for connecting the movable frame (TM) to the fixed frame (TF) in such a way that the movable frame (TM) can be moved between an opening position, wherein the movable frame (TM) is inclined with respect to the fixed frame (TF), and a closing position, wherein the movable frame (TM) lies on the same plane as the fixed frame (TF).

The trapdoor has a quadrangular shape with four corners (Q1 , Q2, Q3 and Q4).

In particular, the fixed frame (TF) comprises four sections (2) with ends (21 ) cut at 90°, and four corner pieces (4), each one of them connecting two sections (2) in adjacent position. Likewise, the movable frame (TM) comprises four sections (1 ) with ends (1 1 ) cut at 90°, and four corner pieces (3), each one of them connecting two sections (1 ) in adjacent position.

With reference to Figs. 6, 6A, 7 and 7A, each corner piece (3, 4) comprises a central portion (30, 40) suitable for abutting against said ends (11 , 21 ) of two adjacent sections and two lateral inserts (31 , 41 ) that protrude from the central portion (30, 40) in such a way to be coupled with said sections (1 , 2). Since the trapdoor has a square or rectangular shape, the two lateral inserts are orthogonal to each other and two adjacent sections are orthogonal and disposed at right angle.

The central portion (30, 40) and the lateral inserts (31 , 41 ) of each corner piece (3, 4) are machined in one piece. Preferably, said corner pieces (3, 4) are made of plastic material or diecast aluminum or composite material, such as, for example, polyamide PA6 loaded with glass and/or carbon fiber, or polyarylamide (Kitan X).

Each corner piece (3, 4) and each section (1 , 2) comprises a front face suitable for being visible and a rear face which is disposed in opposite position to said front face and is suitable for facing the compartment to be inspected.

The connection means (5, 6) are configured in such a way to let the movable frame (TM) oscillate relative to the fixed frame (TF), without uncoupling the movable frame (TM) from the fixed frame (TF).

With reference to Figs. 5 and 5A, the connection means (5, 6) are disposed on corner pieces (3, 4) positioned at two adjacent corners (Q3, Q4) of the inspection trapdoor. Said connection means (5, 6) are disposed on the rear face of the corner pieces (3, 4).

Each connection means (5, 6) comprises two elements, namely:

- a first element (6) having a first portion (61 ) obtained in one piece with the corner piece (4) of the fixed frame (TF), and a second portion (62) surmounting the corner piece (3) of the movable frame (TM) and interfering with the corner piece (3) of the movable frame (TM);

- a second element (5) having a first portion (51 ) obtained in one piece with the corner piece (3) of the movable frame (TM), and a second portion (52) surmounting the corner piece (4) of the fixed frame (TF) and interfering with the corner piece (4) of the fixed frame (TF).

Preferably, the second element (5) has a substantially L-shape and therefore the two portions (51 and 52) of the second element (5) are perpendicular.

The two elements (5 and 6) operate in such a way that the two frames (TM, TF) are never uncoupled, not even when the movable frame is moved relative to the fixed frame.

With reference to Figs. 6, 6A, 7 and 7A, the central portion (30, 40) of each corner piece (3, 4) has a quadrangular shape and comprises two external sides (302, 402) orthogonal to each other and two internal sides (301 , 401 ) orthogonal to each other, from which said lateral inserts (31 , 41 ) protrude, the latter being shaped as a rectangular plate. Each insert (31 , 41 ) has recessed seats (32, 42) wherein a portion of the section (1 , 2) is coupled by deformation.

Referring to Figs. 7 and 7A, the external sides (402) of the central portion (40) of the corner piece (4) of the fixed frame (TF) are connected by a curvilinear portion (40t) in such a way that the inspection trapdoor has no sharp edges on the outside. In this way, the inspection trapdoor is not dangerous for a user during the installation of the inspection trapdoor on the wall.

Referring to Figs. 8 and 9, each section (1 , 2) has a C-shaped crosssection defining a longitudinal channel (10, 20) that extends for the entire length of the section (1 , 2) and is open at the two ends (1 1 , 21 ) of the section.

The insert (31 , 41 ) is inserted from the ends (1 1 , 21 ) of the section into the longitudinal channel (10, 20), whereas the central portion (30, 40) remains outside the section (1 , 2), thus forming the corner of the frame (TM, TF). The lateral insert (31 , 21 ) is completely inserted in the longitudinal channel (10, 20) so that the end (1 1 , 21 ) of the section (1 , 2) abuts against the internal side (301 , 401 ) of the central portion (30, 40) of the corner piece (3, 4).

Still with reference to Figs. 8 and 9, each section (1 , 2) comprises two opposite longitudinal tabs (18, 28) that define the longitudinal channel (10, 20).

With reference to Figs. 10 and 10A, in order to connect an insert (31 , 41 ) to the section (1 , 2) in adjacent position, it is firstly necessary to introduce the insert (31 , 41 ) in the longitudinal channel (10, 20) of the section (1 , 2) (see Fig. 10) and then punch the longitudinal tabs (18, 28) in such a way that said longitudinal tabs (18, 28) are deformed in at least one point to form a protrusion (d) that protrudes inside the longitudinal channel (10, 20) and is coupled with the recessed seats (32, 42) of the lateral insert (31 , 41 ) (see Fig. 10A).

With reference to Figs. 6 and 6A, the central portion (30) of the corner piece (3) of the movable frame (TM) comprises two retention edges (35) disposed on the two external sides (302) of the central portion (30).

With reference to Figs. 7 and 7A, the central portion (40) of the corner piece (4) of the fixed frame (TF) comprises two columns (45) perpendicular to each other and disposed in correspondence of the angle defined by the two internal sides (401 ) of the central portion (40). Going back to Figs. 8 and 9, each section (1 , 2) preferably comprises two wings orthogonal to each other, namely:

- a first wing (14, 24) with C-shaped section having said longitudinal channel (10 ,20); and

- a second wing (15, 25) projecting from one side of said first wing (14, 24) in opposite direction with respect to the longitudinal channel (10, 20).

The second wing (15) of the section (1 ) of the movable frame (TM) is arranged side-by-side and abuts against the retention edge (35) of the central portion (30) of the corner piece (3) of the movable frame (TM) in such a way that all of the retention edges (35) and the second wings (15) of the sections (1 ) of the movable frame (TM) define a single external annular edge of the movable frame (TM).

Preferably, the height of the second wing (15) of the section (1 ) of the movable frame (TM) is identical to the height of the retention edge (35), in such a way that the top edges of the second wing (15) and of the retention edge (35) in adjacent position are flush with each other.

The second wing (25) of the section (2) of the fixed frame (TF) is arranged side-by-side and abuts the adjacent column (45) of the central portion (40) of the corner piece (4) of the fixed frame (TF) in such a way that the columns (45) and the second wings (25) of the sections (2) of the fixed frame (TF) define a single internal annular edge of the fixed frame (TF).

Preferably, the height of the second wing (25) of the section (2) of the fixed frame (TF) is identical to the height of the column (45), in such a way that the top edges of the second wing (25) and of the adjacent column (45) are flush with each other.

Going back to Figs. 5 and 6, end stop means (70, 71 , 72) are provided in correspondence of the corners (Q1 , Q2), opposite to the corners (Q3, Q4) wherein the connection means (5, 6) are provided, said end stop means (70, 71 , 72) being suitable for stopping the travel of the movable frame (TM) when the movable frame (TM) is moved from the closing position to the opening position. Said end stop means (70, 71 , 72) are provided between two adjacent corner pieces (3, 4) of the movable frame and of the fixed frame in correspondence with the rear faces of said corner pieces (3, 4).

With reference to Fig. 1 1 , the end stop means (70, 71 , 72) comprise:

- a first eyelet (71 ) connected to the corner piece (4) of the fixed frame (TF);

- a second eyelet (72) connected to the corner piece (3) of the movable frame (TM); and

- a chain (70) connected to the first eyelet (72) on one side and to the second eyelet (72) on the other side.

The chain (70) comprises two hooks (specifically, two spring catches), of which one hook is fastened to the first eyelet (71 ) and the other hook is fastened to the second eyelet (72).

Moreover, the chain (70) comprises a wire connected to the two hooks.

Advantageously, said first eyelet (71 ) is obtained in one piece with the corner piece (4) of the fixed frame (TF) and said second eyelet (72) is obtained in one piece with the corner piece (3) of the movable frame (TM).

With reference to Figs. 5, 1 1 , 1 1 A, 1 1 B, 1 1 C and 11 D, in correspondence with the corner (Q1 , Q2) wherein the end stop means (70, 71 , 72) are provided, locking means (81 , 83) are provided in such a way to stop the movable frame (TM) with respect to the fixed frame (TF) in the closing position. Also the locking means (81 , 83) are provided in correspondence with the rear face of the corner pieces (3 ,4).

Said locking means (81 , 83) comprise:

- a retention element (81 ) that is integral with the corner piece (3) of the movable frame (TM) and is configured in such a way to define a niche (82) in undercut;

- a snap-fit retention device (83), which is shown exclusively in Fig. 1 1 B, which is integral with the fixed corner piece (4); said retention device (83) comprises a fixed portion (831 ) and a movable portion (832) which is hinged to the fixed portion (831 ) and is provided with a striker (830) suitable for being engaged in the niche (82) in undercut. Preferably, the retention element (81 ) is obtained in one piece with the corner piece (3) of the movable frame (TM).

The snap-fit locking device (83) comprises retention means (not shown in the appended figures) connected to the fixed portion (831 ) on one side and to the movable portion (832) on the other side, which operate on the movable portion (832) in such a way that the striker (830) is engaged in the niche (82) in undercut when said movable frame (TM) is in closing position, allowing the movable frame (TM) to be removed from the closing position when said movable frame (TM) is pushed by a user to the opening position with a sufficient force to overcome the resistance offered by the retention means. By means of example, said retention means may consist in a torsional spring with one end connected to the movable portion (832) of the locking device (83) and one end connected to the fixed portion (831 ) of the locking device (83).

Therefore, it goes without saying that in order to move the movable frame (TM) from the closing position to the opening position, it will be necessary to push the movable frame (TM) (or the central panel) with a sufficient force to overcome the resistance provided by the retention means in order to disengage the striker (830) from the niche (82) in undercut.

With reference to Figs. 1 1 , 1 1 A, 1 1 B and 1 1 D, said snap-fit locking device (83) is mounted on a support element (85) obtained in one piece with the corner piece (4) of the fixed frame (TF).

Said support element (85) consists of a wall that protrudes orthogonally from the rear face of the corner piece (4) of the fixed frame (TF) and comprises an internal face (851 ) facing the interior of the trapdoor, an external face (852) facing the opposite side, and two lateral faces (853). The internal face (851 ) is provided with a recessed seat that is suitably configured to accommodate the snap-fit locking device (83). The fixed portion (831 ) of the locking device (83) is secured to the support member (85) by means of fixing screws (FF) inserted into holes of the fixed portion (831 ) and engaged in holes (sw) drilled in the support member (85).

A groove (86) is provided at the base of the support element (85), wherein the tab (28) of one of the sections (2) of the fixed frame (TF) is inserted. Preferably, the first eyelet (71 ) is obtained on the lateral face (853) of the support wall (85), whereas the second eyelet (72) is obtained on one of the inserts (31 ) of the corner piece (3) of the movable frame (TM).

Again with reference to Figs. 1 1 to 1 1 D, stiffening partitions (uf, urn) are preferably provided on the rear face of each corner piece (3, 4) and are disposed astride between the central portion (30, 40) and the inserts (31 , 41 ).

As a result of the foregoing description, the advantages of the present invention appear evident. Said advantages are the following:

- the waste or scrap is reduced compared to the prior art; in particular, in the inspection trapdoor according to the invention, no waste or scrap is practically generated during the cutting of the sections because it is no longer necessary to cut the ends of the sections at 45°;

- the dimensional tolerances are easy to manage; more precisely, because of the 90° cut of the ends (1 1 , 21 ) of the sections (1 , 2), trapdoors of the same size are perfectly identical; therefore, if more than one inspection trapdoor of the same size is installed, the movable frames (TM) are interchangeable;

- higher safety compared to the inspection trapdoor of the prior art, such an advantage being due to the absence of sharp edges on the outside of the fixed frame (TF);

- a highly flexible design, meaning that the corner pieces (3, 4) can be made of plastic material or die-cast aluminum; in both cases a simple modification of the mold used for production makes it possible to adjust them to any variation of the trapdoor;

- better aesthetics compared to the trapdoor of the prior art; in fact, the sections (1 , 2) and the corner pieces (3, 4) are perfectly aligned and therefore, unlike in the prior art, the frames (TM, TF) are not provided with steps that can be extremely dangerous for the operators, in addition to being aesthetically unpleasant;

- moreover, the 90° cut allows for simultaneously cutting several sections disposed one on top of the other one, in the same way and with the same dimensions; the possibility of simultaneously cutting several sections disposed one on top of the other one makes the trapdoor according to the invention considerably faster to make compared to the one of the prior art.

Furthermore, when comparing the inspection trapdoor according to the invention with the trapdoors disclosed in W02020120939A1 and DE202006004357U1 , the inspection trapdoor of the invention is:

- simpler to assemble than the other two trapdoors because it does not require the use of screws or multiple elements to be connected, and it only requires to couple the corner piece (3, 4) obtained in one piece with the two adjacent sections (1 , 2);

- more versatile than the other two trapdoors because the corner piece (3, 4) obtained in one piece can be provided with functional elements, such as, for example, the connection means (5, 6), the hooking means (81 , 83) and the eyelets (71 , 72) of the end stop means;

- safer than the trapdoor disclosed in W02020120939A1 because the ends of the sections (1 1 , 21 ) (portion of the section that may have burrs or imperfections due to cutting) abut against the internal sides (301 , 401 ) of the central portion (30, 40) of the corner pieces (3, 4) and therefore are not visible or exposed and there is no risk that a user could touch them or come in contact with them, causing injuries or lacerations.

Numerous variations and detailed modifications can be made to the present embodiment of the invention, within the reach of a person skilled in the art, but within the scope of the invention as expressed by the appended claims.

By way of example, although the trapdoor has been shown with a quadrangular shape, the trapdoor can have any other shape, such as triangular, pentagonal, hexagonal and the like.

In case of a triangular shape, each frame (TM, TF) will have three sections (1 , 2) with ends (1 1 , 21 ) cut at 90° and three corner pieces (3, 4). In such a case, each corner piece will connect two adjacent sections (1 , 2) in an arrangement wherein the two sections (1 , 2) are transverse to each other, but not orthogonal.

Finally, although Figs. 4 to 1 1 D show a trapdoor with a fixed frame (TF) and a movable frame (TM) composed of the sections and of the corner pieces, nothing would change for the purpose of achieving the objectives pursued by the invention if, instead of being composed of the sections and the corner pieces, the movable frame was made in one piece with the central panel, thus defining a single monolithic cover door (E) that oscillates with respect to the fixed frame (TF). Such an alternative version is shown in Fig. 12.