SHEET WITH 90° CORNERS

Technical field

This disclosure relates to an apparatus for making a mattress cover sheet with 90° corners.

More specifically, this mattress cover sheet is of the type comprising a main portion which covers the top face of the respective mattress and from which respective perimeter portions extend peripherally to cover the lateral faces of the mattress, the perimeter portions being perpendicular, in particular in use, to the main portion and being joined to each other by stitches which join together the opposite lateral edges of respectively adjacent perimeter portions.

Background art

At present, mattress cover sheets with 90° corners are made by hand by cutting quadrangular portions at the corners of the piece of material used to make the mattress cover sheet and then joining together the respective opposite lateral edges of the adjacent potions of the piece of material defining the perimeter portions of the mattress cover sheet.

This, however, results in products of poor workmanship and excessively high production costs owing to labour intensiveness.

Disclosure of the invention

This invention therefore proposes a new solution as an alternative to the solutions known up to now and, more specifically, proposes to overcome one or more of the above mentioned drawbacks or problems and/or to meet one or more of the needs felt by the trade and which, in particular, may be inferred from the above. Brief description of the drawings

An apparatus is therefore provided for making a mattress cover sheet with 90° corners, that is, of the type comprising a main portion which covers the top face of the respective mattress and from which respective perimeter portions extend peripherally to cover the lateral faces of the mattress, the perimeter portions being perpendicular, in particular in use, to the main portion and being joined to each other by stitches which join together the opposite lateral edges of respectively adjacent perimeter portions, characterized in that it comprises supporting means, in particular in the form of a respective framework for means which are adapted to make the mattress cover sheet from a corresponding piece of suitable material.

Thus, mattress cover sheets can be made quickly, at a low cost and, above all, with repeatable good quality.

These and other innovative aspects, or specific advantageous embodiments are set out in the appended claims and the technical features are apparent from the detailed description which follows of preferred embodiments, to be considered, however, purely as non-limiting examples of the disclosure; the description being made with reference to the accompanying drawings, in which:

- Figure 1 is a schematic perspective view of a preferred embodiment of a mattress cover sheet according to this disclosure in a condition for use;

- Figure 2A is a perspective view of a first preferred embodiment of the apparatus according to this disclosure;

- Figure 2B shows a top plan view of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 2C shows a side elevation view of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 2D shows a front elevation view of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3A is a perspective view of a first step in the operation of the first preferred embodiment of the apparatus according to this disclosure; - Figure 3B is a perspective view of a second step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3C is a perspective view of a third step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3D is a perspective view of a fourth step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3E is a perspective view of a fifth step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3F is a perspective view of a sixth step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3G is a perspective view of a seventh step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3H is a perspective view of an eighth step in the operation of the first preferred embodiment of the apparatus according to this disclosure; - Figure 31 is a perspective view of a ninth step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 3L is a perspective view of a tenth step in the operation of the first preferred embodiment of the apparatus according to this disclosure;

- Figure 4A is a perspective view of a first step in the operation of a second preferred embodiment of the apparatus according to this disclosure;

- Figure 4B is a perspective view of a second step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4C is a perspective view of a third step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4D is a perspective view of a fourth step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4E is a perspective view of a fifth step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4F is a perspective view of a sixth step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4G is a perspective view of a seventh step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4H is a perspective view of an eighth step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 41 is a perspective view of a ninth step in the operation of the second preferred embodiment of the apparatus according to this disclosure;

- Figure 4L is a perspective view of a tenth step in the operation of the second preferred embodiment of the apparatus according to this disclosure.

Detailed description of preferred embodiments of the invention

Figures 2A to 3L illustrate a first preferred embodiment 10 of an apparatus for making a mattress cover sheet 1 1 with 90° corners.

As shown in Figure 1 , a mattress cover sheet 1 1 with 90° corners comprises a main portion 1 1 1 which covers the top face of the respective mattress and from which respective perimeter portions 1 12 extend peripherally to cover the lateral faces of the mattress, the perimeter portions being perpendicular, in particular in use, to the main portion 1 1 1 and being joined to each other, at 1 13, by stitches which join together the opposite lateral edges of respectively adjacent perimeter portions 1 12. As may be inferred from Figures 2A to 3L, the first embodiment of the apparatus comprises supporting means, in particular in the form of a respective framework 12 for means which are adapted to make the mattress cover sheet 1 1 from a corresponding piece 13 of suitable material.

Thus, mattress cover sheets can be made quickly, at a low cost and, above all, with repeatable good quality.

Advantageously, as may be inferred from the corresponding drawings, the means for making the mattress cover sheet 1 1 comprise means 14 which define a template 141 for supporting the piece 13 of material, the template preferably having a shape which is generally quadrangular, preferably generally rectangular, and a size, in particular along the direction longitudinal of, and/or the direction transverse to, the piece of material, which is smaller than that of the main portion 1 1 1 of the mattress cover sheet.

Advantageously, the means defining the template comprise a respective board 141 for supporting the piece of material 13, the board being preferably adjustable in length and/or width.

More specifically, the board 141 constitutes means for supporting the piece of material and which, as may be inferred from Figure 3A, have a top supporting face 142 and a respective perimeter edge 143.

Advantageously, retaining means 16 are provided for keeping a main part 13a of the piece of material 13, in particular the central part thereof, on the means 14 defining the template for supporting the piece 13 in such a way that a part 13b of the piece 13 which is perimetrically peripheral to the main part 13a protrudes beyond the peripheral edge 142 of the means 14 defining the template, and, in particular, protrudes by a corresponding longitudinal and/or transverse stretch having one dimension, or length, perpendicular to the corresponding edge of the main part of the piece of material, which is such as to be greater than the height, especially in use, of the respective peripheral portion 1 12 of the mattress cover sheet.

Advantageously, as may be inferred in particular from Figure 3G, folding means 16 are provided for folding the peripheral protruding part 13b of the piece 13, especially in a direction perpendicular to the main part 13a, with the main part 13a of the piece resting on the means 14 defining the template for supporting the piece. That way, in particular, the peripheral part 13b of the piece has defined on it respective lateral portions 13c which extend beyond the corresponding edge or side 143 of the template 141 and, at the corners 144 of the template 141 , respective corner portions 13d which are defined by corresponding opposing panels 13cd, 13cd extending from the adjacent lateral portions 13c of the piece 13.

Advantageously, as may be inferred in particular from Figure 3H, means 16 are provided for positioning the corresponding corner portion 13d of the peripheral protruding part 13b of the piece 13 longitudinally on the extension of a respective lateral portion 13c of the piece and transversely to the adjacent lateral portion 13c of the piece 13.

Advantageously, as may be inferred in particular from Figure 3F means 16 are provided, in particular gripper means for engaging and retaining a corresponding elongate, oblique strip of the peripheral protruding part 13b of the piece 13 situated on the extension of the corner portion 144 of the supporting template 141 .

Advantageously, as may be inferred in particular from Figure 3F, the means, in particular the gripper means 16 for engaging and retaining a corresponding elongate, oblique strip of the peripheral protruding part 13b comprise first and second opposing jaws 161 , 162 which are adapted to engage the respective top and underside face of the piece 13, in particular starting from the corner 134 of the piece and extending on the latter, preferably until reaching a respective predetermined distance from the corresponding edge of the supporting template 141 .

Advantageously, as may be inferred in particular from Figures 3E to 3G, the first and second opposing jaws 161 , 162 of the gripper means 16 are movable between an open position and a closed position, where the jaws 161 , 162 engage and retain the respective top and underside faces of the piece 13, and vice versa.

Advantageously, the first and second opposing jaws 161 , 162 of the gripper means 16 are movable into a position where they grip the piece 13 through a movement of the gripper means 16 from a withdrawn position, illustrated in Figure 3E, to an advanced position, illustrated in Figure 3F, especially in a linear direction of motion oblique to the piece and/or template means 14.

Advantageously, as may be inferred in particular from Figure 3F, the gripper means 16 for engaging and retaining the elongate, oblique strip of the protruding peripheral part 13b of the piece 13 are adapted to lower the elongate, oblique strip of the piece 13 until it makes an angle, in particular usually equal to 45°, relative to the template 141 or to the main part 13a of the piece 13 resting thereon, especially through a downward rotational movement of the upstream or mutually connecting end of the first and second jaws 161 , 162 in a condition where they engage and retain the elongate, oblique strip of the piece 13.

Advantageously, as may be inferred in particular from Figure 3G, the gripper means 16 for engaging and retaining the elongate, oblique strip of the protruding peripheral part 13b of the piece are adapted to position the corner portion 13d of the piece longitudinally on the extension of a respective lateral portion 13c and transversely to the adjacent lateral portion 13c of the protruding peripheral part 13b of the piece, in particular through a rotational movement about a respective perpendicular or vertical axis of the first and second jaws 161 , 162 which are engaging and retaining the elongate, oblique strip of the piece 13 at an angle, especially at an angle usually equal to 45°, relative to the template 141 or main part 13a of the piece 13.

Advantageously, as may be inferred in particular from Figure 3F, the gripper means 16 adapted to engage and retain an elongate, oblique strip of the peripheral protruding part 13b of the piece define means which, together with the means defining the supporting template 141 of the main, central part of the piece, are adapted to fashion the respective piece 13 into the general shape of an open bag, which, especially, is open along the perpendicular edge opposite to that defined by the main, central part or panel 13a of the piece, and in particular having respective corner portions 13d, with juxtaposed or closed panels, protruding longitudinally from the corresponding peripheral parts 13c, specifically transverse parts, of the piece.

More specifically, as illustrated, there are four grippers 16, each normally inclined at an angle to the vertical and disposed at the corners of the template means 141 , the grippers 16 being mounted on a curved slider 164 and being rotatable on corresponding guides to allow the gripper to rotate about a respective horizontal axis. Further, each gripper 16 is supported by a respective base 165 which can be translated obliquely and which is rotatable about a respective vertical or perpendicular axis.

Advantageously, means 18 are provided, in particular second means for engaging and retaining the corresponding corner portion 13d at the corner of the template 141 which supports the piece 13, in particular at the zone between the selfsame corner 144 of the template 14 and of the corresponding, in particular of the first means 16 for engaging and retaining the piece, that is, of the means 16 which are adapted to fashion the piece 13 into the general shape of an open bag.

Advantageously, the means for retaining the corresponding corner portion 13d at the corner of the means defining the piece supporting template 141 are in the form of gripper means 18 having first and second jaws 181 , 182 which are adapted to engage opposite faces of the corresponding corner portion 13d.

Advantageously, as may be inferred from Figure 3I, the first and second jaws 181 , 182 of the means for retaining the corresponding corner portion 13d have corresponding faces or elements, respectively orthogonal, which are adapted to engage, in particular for the full height, corresponding lateral, longitudinal and transverse portions 13c of the protruding peripheral part 13b of the piece.

Advantageously, as may be inferred from Figures 3H and 3I, the means 18 for retaining the corresponding corner portion 13d at the corner of the means defining the piece supporting template 141 are movable, in particular vertically, between a rest position, in particular a raised position, and a position, in particular a lowered position, for engaging and retaining the respective corner portion 13d of the piece 13.

Advantageously, as may be inferred from Figure 3A, the means 18 for retaining the corresponding corner portion 13d of the piece are movable, in particular vertically, between a rest position, in particular a raised position, and a position, in particular a lowered position, for engaging and retaining the respective corner portion 13d of the piece 13.

Advantageously, as may be inferred from Figure 3H, the means 18 for retaining the corresponding corner portion 13d of the piece delimit, upstream, a linear cutting zone of a respective free end portion 13e for removing the piece and for stitching together the edges of the remaining corner portion 13d.

Advantageously, as may be inferred from Figures 3L and 3A, the means 18 for retaining the corresponding corner portion 13d are movable between a lowered position, for engaging and retaining the respective corner portion 13d of the piece 13 and a raised position for transporting the piece, in particular to the final station for cutting and stitching the piece.

Advantageously, as may be inferred from Figures 3L and 3A, the means 18 for retaining the corresponding corner portion 13d, in particular in the raised position, are movable rotationally about a horizontal axis, in particular longitudinal, in order to position the respective corner portion 13d of the piece so it is parallel to the main central part 13a of the piece 13, that is to say, to position it horizontally, in particular under it.

More specifically, as illustrated, there are four grippers 18 which are disposed at the corners of the template means 141 and which are adapted to grip the four corner portions 13d of the piece.

Advantageously, means 20 are provided for cutting the end portion 13e of the corner portion 13d of the piece, in particular at a position spaced from the corresponding edge or side of the main part 13a of the piece.

Advantageously, the means 20 for cutting the corner end portion 13e of the piece move horizontally, in particular moving horizontally to cut the corner end portion 13e off the piece.

Advantageously, the means 20 for cutting the corner end portion 13e of the piece move from one side to the other relative to the piece, in particular to cut the corner end portion 13e off the piece.

Figures 4A to 4L illustrate a second preferred embodiment of the apparatus, comprising components which are similar or equivalent to those of the first embodiment described above; these components are labelled with the same reference numerals and, to avoid an excessively long description, are not described in detail again.

Advantageously, in the second embodiment, the means 20 for cutting the corner end portion 13e of the piece move vertically, in particular moving vertically to cut the corner end portion 13e off the piece.

More specifically, the means 20 for cutting the corner end portion 13e of the piece advantageously move from a position under the piece to a position above the piece, in particular to cut the corner end portion 13e off the piece.

Advantageously, in both the first and the second preferred embodiment, the means 20 for cutting the corner end portion 13e move upstream and/or downstream of the corresponding edge of the main part of the piece and at the longitudinally extended corner portion.

Advantageously, means 22 are provided for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion 13d of the piece, left over after removing the free end portion 13e thereof, that is, specifically, after the corner end portion 13e has been removed, that is, cut off, from the piece.

Advantageously, the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion move horizontally, in particular moving horizontally to stitch the opposite edges of the panels forming the remaining portion 13f of the corner portion.

Advantageously, the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion move from one side of the piece to the other, in particular to stitch the opposite edges of the panels forming the remaining portion 13f of the corner portion.

Advantageously, in the second embodiment shown in Figures 4A to 4L, the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion move vertically, in particular moving vertically to stitch the opposite edges of the panels forming the remaining portion 13f of the corner portion.

Advantageously, in the second embodiment shown in Figures 4A to 4L, the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion move, in particular to stitch the opposite edges of the panels forming the remaining portion 13f of the corner portion, between a lower position and an upper position relative to the piece.

Advantageously, in both the first and the second preferred embodiment, the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion move upstream and/or downstream of the corresponding edge of the main part 13a of the piece and at the longitudinally extended corner portion 13d of the piece.

Advantageously, the means 22, in particular at least one of these, for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion apply, or stitch, a corresponding label, in particular defining corresponding means which are adapted to apply or stitch a corresponding label.

Advantageously, the means 20 for cutting the end portion 13e of the corner portion 13d and the means 22 for stitching the opposite edges of the panels forming the remaining portion 13f of the corner portion, and possibly also the means for applying the label are mounted on the same mobile carrier.

Advantageously, means 24 are provided for feeding a continuous or elongate web 15 of respective mattress cover material.

Advantageously, the means 24 for feeding a web 15 of material for making the mattress cover comprise means 241 for pulling the continuous or elongate web 15 preferably from a respective roll 151 , and which comprise means for engaging and retaining an end of the web or bolt of material, in particular in the form of gripper means which are movable longitudinally downstream of the working zone of the piece.

Advantageously, according to the first embodiment illustrated in Figures 3A to 3L, the means 241 for pulling the continuous or elongate web 15 are movable for a longitudinal stretch which is slightly greater in length than the working zone of the piece.

Advantageously, according to the second embodiment illustrated in Figures 4A to 4L, the means 241 for pulling the continuous or elongate web 15 are movable for a longitudinal stretch which is slightly greater in length than the cutting zone of the piece.

Advantageously, means 26 are provided for cutting a piece 13 used to make a corresponding mattress cover sheet from the continuous or elongate web 15 of respective mattress cover material.

Advantageously, the means 26 for cutting a piece 13 used to make a corresponding mattress cover sheet from the continuous or elongate web 15 of respective mattress cover material move horizontally upstream of the working zone of the piece.

Advantageously, means 28 are provided for temporarily retaining the piece 13 in the working position, in particular while the means 241 for pulling the piece return to the starting position, especially to grip the end of the web or bolt of mattress cover material.

Advantageously, the means 28 for temporarily retaining the piece 13 are in the form of corresponding gripper means which comprise means for engaging the top face and the underside face of the piece 13. Advantageously, the means 28 for temporarily retaining the piece 13 are in the form of corresponding gripper means having respective means for engaging the piece and which are movable vertically between a position for releasing and a position for retaining the piece.

Advantageously, according to the second embodiment illustrated in Figures 4A to 4L, the means 28 for temporarily retaining the piece 13 are in the form of corresponding gripper means which are movable longitudinally between a position for cutting the piece and a position for actually working on the piece.

Advantageously, in the first preferred embodiment of the apparatus, there is a zone or station 101 for fashioning the piece into a bag-like shape and which is located preferably downstream, specifically immediately downstream, of the zone 102 for cutting the piece from a corresponding web or bolt.

Advantageously, there is a zone or station 103 for cutting and/or stitching the corner end portion 13d of the piece 13 which is situated above, in particular vertically aligned with, the zone or station for fashioning the piece into a bag-like shape.

Advantageously, in the second preferred embodiment of the apparatus, there is a zone or station for fashioning the piece into a bag-like shape and which is located preferably downstream of the zone for cutting the piece from a corresponding web or bolt.

Advantageously, in the second embodiment illustrated in Figures 4A to 4L, there a zone or station for cutting and/or stitching the corner end portion 13d of the piece 13 which is situated in the selfsame zone or station for fashioning the piece into a bag-like shape.

These preferred embodiments of the apparatus allow implementing a method for making a mattress cover sheet 1 1 with 90° corners, illustrated in Figure 1 , that is to say, of the type comprising a main portion 1 1 1 which covers the top face of the respective mattress and from which respective perimeter portions 1 12 extend peripherally to cover the lateral faces of the mattress, the perimeter portions being perpendicular, in particular in use, to the main portion 1 1 1 and being joined to each other, at 1 13, by stitches which join together the opposite lateral edges of respectively adjacent perimeter portions 1 12, wherein the mattress cover sheet is made from a corresponding piece of suitable material.

Advantageously, in the method for making the mattress cover sheet means 14 are used which define a template 141 for supporting the piece 13 of material, the template preferably having a shape which is generally quadrangular, preferably generally rectangular, and a size, in particular along the direction longitudinal of, and/or the direction transverse to, the piece of material, which is smaller than that of the main portion 1 1 1 of the mattress cover sheet, covering the top face of the mattress.

Advantageously, according to the method, the means defining the template comprise a respective board 141 for supporting the piece of material 13, the board being preferably adjustable in length and/or width. Advantageously, according to the method, each piece 13 is fashioned into the general shape of an open bag, which, especially, is open on the face opposite to the main, central part or panel of the piece and which has respective corner portions 13d extending from the edge or side of a main part of the piece 13a resting on the template means 14.

Advantageously, according to the method, the end portion 13e of the corner portion 13d of the piece is cut, in particular at a position spaced from the corresponding edge or side of the main part 13a of the piece, spaced from the corner of the means defining the supporting template 141 , and opposite edges of the panels forming the remaining portion 13f of the corner portion 13d are stitched, in particular applying or stitching a corresponding label to the piece which defines the mattress cover sheet. Advantageously, according to the method, the end portion 13e of the corner portion 13d of the piece is cut, in particular at a position spaced from the corresponding edge or side of the main part 13a of the piece, spaced from the corner of the means defining the supporting template 141 , and/or opposite edges of the panels forming the remaining portion 13f of the corner portion 13d are stitched, with a horizontal cutting and/or stitching movement.

Advantageously, according to the method, the end portion 13e of the corner portion 13d of the piece is cut, in particular at a position spaced from the corresponding edge or side of the main part 13a of the piece, spaced from the corner of the means defining the supporting template 141 , and/or opposite edges of the panels forming the remaining portion 13f of the corner portion 13d are stitched, with a vertical cutting and/or stitching movement.

The operation of the apparatus of Figures 2A to 3L is briefly as follows: in a first step, as illustrated in Figure 3A, the means 241 for pulling the web 15 of mattress cover material are gripping the end of the web and, as may be inferred from Figure 3B, they pull a panel thereof downstream of the zone where the corresponding piece is fashioned into a bag-like shape, the piece being cut off and separated from the web by the cutting means 26, as illustrated in Figure 3C.

As may be inferred also from Figure 3D, the piece 13 is then retained by the retaining means 28 at the station where it is fashioned into a bag-like shape. At this point, the folding grippers 16 are placed round the piece and fold it into a bag-like shape in a direction perpendicular to the board 14 and also form the corner portions 13d of the piece, as may be inferred from Figures 3E to 3I.

Next, as may be inferred from Figure 3L, once the piece has been fashioned into a bag-like shape, it is picked up by the grippers 18 and lifted into the upper station where the same grippers 18 fold the corner portions 13d of the piece until they are parallel to the main part 13a, as may be well inferred from Figure 3A.

Then, as may be inferred from Figure 3D, the means for cutting and stitching 20 and 22 cut and stitch the protruding free end 13e of the corner portion 13d, simultaneously applying a corresponding label thereto. After that, the mattress cover sheet 1 1 is unloaded from the apparatus 10 with an upward vertical movement, as may be inferred from Figure 3F.

The operation of the apparatus of Figures 4A to 4L is in turn briefly as follows: in a first step, as illustrated in Figure 4A, the means 241 for pulling the web 15 of mattress cover material are gripping the end of the web and they pull a panel thereof downstream of the zone where the corresponding piece is fashioned into a bag-like shape, the piece being cut off and separated from the web by the cutting means 26, as may be inferred from Figure 4B.

Next, as illustrated in Figure 4C, the grippers 28 carry the piece 13 longitudinally to the zone where the piece itself is fashioned into a bag-like shape.

As may be inferred also from Figure 4D, the piece 13 is then retained by the retaining means 28 at the station where it is fashioned into a bag-like shape. At this point, the folding grippers 16 are placed round the piece and fold it into a bag-like shape in a direction perpendicular to the board 14 and, at the same time, form the corner portions 13d of the piece, as may be inferred from Figures 4E to 4I.

Next, as may be inferred from Figure 4L, the piece, while still in the station where it has been fashioned into a bag-like shape, is picked up by the grippers 18 which fold the corner portions 13d of the piece until they are parallel to the main part 13a, as may be well inferred from Figure 4A.

Then, as may be inferred from Figure 4D, the means for cutting and stitching 20 and 22 cut and stitch, with a vertical movement, the protruding free end 13e of the corner portion 13d, simultaneously applying a corresponding label thereto. After that, the mattress cover sheet 1 1 is unloaded from the apparatus.

The invention described above is susceptible of industrial application. It would be obvious to one skilled in the art that several changes and modifications can be made to the invention without departing from the spirit and scope of the invention, described in depth above. Also, further preferred embodiments of the invention comprising one or more of the features described herein can easily be imagined. It will also be understood that all the details of the invention may be replaced by technically equivalent elements.