1. Field of the Invention

The present invention relates to display devices of the cathode ray tube type (particularly computer or television monitors) and to a corresponding fixing screw.

2. State of the Art

According to the state of the art, a cathode ray tube (or CRT) comprises fixing lugs in its corners, these being intended for fixing it to a casing of a display device. Figure 1 illustrates a fixing screw 10 for fixing such a tube to the casing. The screw 10 comprises a head 100 and a threaded shank 101 and is associated with a non-deformable metal washer 11. The washer 11 comprises a flat part 110 and teeth 111 around the periphery of its lower part. Thus, the screw 10 is positioned in a metal fixing lug belonging to the tube and screwed onto a threaded part situated in one of the corners of the casing. The four fixing lugs have a hole for the passage of the screw; this hole has an inside diameter very much larger than the diameter of the threaded shank 101 so that the tube can be positioned with respect to a standard casing. As the washer 11 is clamped between the head 100 and a fixing lug, the teeth 111 hold the tube firmly in its fixed position and prevent it from slipping with respect to the casing, for example if the casing is dropped or in the event of an impact.

The washer 11 is suitable for tubes of a limited weight. Recently, the weight of the tubes has increased (in particular, larger sized tubes and flat tubes). The use of toothed metal washers therefore presents the disadvantage of no longer being ideally suited to modern tubes. Furthermore, in some instances, the bite of the toothed metal washers is uneven.

According to another state of the art, the document US4.651 ,219 discloses the use of elastomeric grommets. Indeed, these kind of grommets does not enables a good assembly of heavy tubes.

3. Summary of the Invention

The object of the invention is to alleviate these disadvantages of the prior art.

More specifically, the objective of the invention is to improve the fixing of a tube to a casing of a display device while at the same time allowing the fixing to hold firm, for example if the display device is knocked or dropped.

To this end, the invention proposes a display device comprising a cathode ray tube and a casing, the cathode ray tube being fixed to the casing using at least one at least partially threaded shank fitted with a washer interposed between tightening means and a fixing lug of the cathode ray tube, the fixing lug being positioned between the washer and the casing, the inside diameter of an opening in the fixing lug being greater than the outside diameter of the shank, and the opening accommodating the shank. According to the invention, the first part of the washer at least partially fills the gap around the shank in the opening, the first part being made of a deformable material, and a second part of the washer presses against the fixing lug.

The tightening means here are either the head of a screw (which comprises the threaded shank) which is itself screwed into the casing or a nut screwed onto the threaded shank which is then secured to the casing.

Thus, a washer made of a deformable material has been used, so that part of the washer positions itself in the gap around the screw shank in the opening, during the tightening of the tightening means that allow the tube to be fixed to the casing. In this way, lateral movements of the tube with respect to the casing are greatly limited or prevented, for example in the event of the display device being knocked or dropped.

Advantageously, the material has a Young's modulus of between 2000 and 3000 MPa.

As a preference, the material is a plastic.

According to one particular feature, the material is of the polystyrene type.

According to other features, the material belongs to the group comprising: polycarbonate; acrylonitrile-butadiene-styrene; styrene-butadiene-styrene; - expanded styrene-butadiene-styrene; alloys of polycarbonate and of acrylonitrile-butadiene-styrene; polyamide; noryl ®; and - polypropylene.

Advantageously, the washer comprises means for screwing the washer onto the shank.

According to an advantageous feature, the edge face of the washer comprises at least two opposed flats.

As a preference, the exterior shape of the washer is a regular polygon.

Advantageously, the thickness of the washer is greater than or equal to 2 mm and less than or equal to 4 mm.

According to a preferred feature, the shank comprises a non-threaded part around which the washer is positioned.

Advantageously, the mean diameter of the tightening means is smaller than the mean diameter of the opening in the fixing lug and, more specifically, the difference between the mean diameter of the tightening means and the mean diameter of the opening in the fixing lug is greater than or equal to 3 mm and less than or equal to 6 mm.

According to one particular feature, the device is of the television monitor type.

The invention also relates to a system for fixing a cathode ray tube to a casing of a display device, comprising an at least partially threaded shank, a washer placed around the shank and tightening means, the shank equipped with a washer being intended to fix the cathode ray tube to the casing, the washer being interposed between the tightening means and a fixing lug of the cathode ray tube, the fixing lug being positioned between

- A - the washer and the casing, the inside diameter of an opening in the fixing lug being greater than the outside diameter of the shank, and the opening accommodating the shank. According to the invention, the washer comprises a deformable material having a Young's modulus of between 2000 and 3000 MPa.

4. List of Figures

The invention will be better understood and other particular features and advantages will become apparent from reading the description which will follow, the description making reference to the attached figures, of which:

Figure 1 depicts a screw equipped with a washer for fixing a tube into a casing of a display device, according to a technique known per se;

Figures 2A and 2B illustrate a screw and an associated washer according to one particular embodiment of the invention;

Figure 3 shows a display device equipped with the screw and with the washer as illustrated with reference to Figures 2A and 2B;

Figures 4 and 5 describe a detail of the device of Figure 3; Figures 6 and 7 illustrate a screw and an associated washer according to a variant embodiment of the invention; and

Figure 8 shows another particular embodiment of the invention.

5. Detailed Description of the Invention

The general principle of the invention therefore relies on the use of a partly or entirely threaded shank equipped with a washer that can deform but not break when the screw head or a nut are tightened in order to fix a CRT to the casing of a display device. Specifically, when the screw is tightened in order to fix a fixing lug of the CRT to the casing, the washer deforms to completely or partially fill the empty space between the screw and the CRT fixing lug. Thus, having positioned and tightened the screws fixing the CRT, the latter is no longer able to move laterally or, at the least, its movement is very much limited in the event of the casing sustaining a knock or droppage. The invention thus goes against the preconceptions of the person skilled in the art who, according to the state of the art, uses non-deformable metal washers to fix a CRT to a casing, the washers using friction to limit or prevent the lateral movements of the CRT with respect to the screws.

According to state of art document US 4 651 218 A, elastomeric grommets is used to assemble a CRT on a cabinet. As elastomeric grommets can be deformed in a elastomeric manner and, thus, in no way these kind of grommets can be plastically deformed (a Young's modulus has no meaning for an elastomeric material). According to the invention, the washer can deform in a plastic manner and preferably its Young's modulus of between 2000 and 3000 MPa.

Figure 2A illustrates a screw 20 and a washer 21 according to one particular embodiment of the invention.

The screw 20 is preferably made of metal and comprises a head 200 with a mean diameter D1 of between 10 and 14 mm and threaded shank 201. The outside diameter Dmax of the threaded shank of the shank has, for example, a diameter of between 6 and 11 mm and is typically equal to 7 or 10 mm, which corresponds to a screw root diameter Dmin of the order of 5 or 8 mm.

A non-threaded part 202 preferably separates the head 200 from the threaded shank 201 and is able to accept the washer 21. The part 202 advantageously has a diameter equal to Dmin and a length greater than or equal to the thickness e of the washer 21.

The material of the washer 21 preferably has a Young's (or elastic) modulus of between 2000 and 3000 MPa (which allows the washer to deform enough according to the invention without breaking). Such a Young's modulus in particular allows the washer to deform during screwing and gives it the ability to withstand any deformations associated with any knocking and/or droppage of the CRT display device.

The washer 21 is made of a deformable material and does not break when the screw 20 is being tightened. The material is preferably made of a deformable plastic, for example of the polycarbonate (or PC), polystyrene (or PS), acrylonitrile-butadiene-styrene (or ABS), alloy of PC and of ABS (or PC-ABS), polyamide (or PA), Noryl ® (or NR200), polypropylene (or PP), styrene-butadiene-styrene (or SBS) type, or dense deformable rubber with good rigidity, particularly expanded SBS (or SEBS). Nonetheless, it may be of any type suited to deforming in order to at least partially fill a gap around the screw 20 in the opening of a fixing lug when the screw 20 is

being tightened. More preferably still, the material used is polystyrene which is a relatively common and inexpensive material.

The washer 21 has, at its centre, an opening 22 of a diameter d very slightly greater than the root diameter Dmin of the shank 201. The diameter d may, for example, exceed the diameter Dmin by a value less than or equal to 0.3 mm and preferably by a value equal to 0.1 mm.

The maximum outside diameter D of the washer 21 is preferably such that it does not extend beyond the external part of the lug of the tube against which lug the washer is pressed. The outside diameter needs to be large enough for the washer to be unable to pass through the tube lug against which it is pressed, upon screwing. As a preference, the outside diameter of the washer (in the example ranging between the maximum outside diameter D and minimum outside diameter D' of the washer 21 ) is such that the washer overlaps the opening in the corresponding tube lug by a width on average greater than or equal to 1.5 mm (for an opening having a mean diameter of 16 mm, the mean diameter of the washer is then at least 19 mm). This is an average overlap. As the screw 20 is not necessarily centred with respect to the opening in the tube lug, it is possible that a peripheral part of the washer 21 enters the opening in the tube lug while another peripheral part exceeds it by 3 mm. By way of illustration, the mean outside diameter of the washer 21 thus ranges for example between 18 and 20 mm. The thickness e of the washer 21 is advantageously between 2 and 4 mm and is preferably equal to 4 mm. It has an internal opening of circular shape and a hexagonal external shape allowing it to be positioned on the screw 20 as indicated with reference to Figure 2B.

The washer 21 is flat on both sides, which makes for ease of manufacture.

Thus, the washer 21 is first of all screwed onto the screw 20 using a suitable tool (for example a spanner applied across two opposed flats) or manually until it reaches the non-threaded part 202. As a preference, the inside diameter d of the washer is greater than the minimum diameter Dmin of the threaded shank 201 and less than the maximum diameter Dmax so that the washer 21 can be screwed onto the screw 20 but cannot become separated from the screw after positioning. Thus, fixing a CRT to a casing becomes easier because the washer is held captive on the screw. Furthermore, this facilitates at least partial filling of the gap around the

screw. As the washer is made of a material that is deformable but not breakable, there is no need to make a screw thread in the washer prior to screwing, this thread creating itself naturally during screwing. In some embodiments, the washer 21 may comprise an internal screw thread to make it easier to screw onto the screw 20.

According to another variant of the invention, the washer is solid or has an opening smaller than the root diameter of the screw and the screw punctures the washer as it is screwed in. The excess washer material obtained by perforation then contributes to the filling of a gap around the shank of the screw in the corresponding tube lug opening.

Figure 3 illustrates another display device 3, for example of the television of computer monitor type, with CRT.

The device 3 comprises: a casing front face 30; a CRT 31 ; and a casing lateral and rear part 32.

The CRT 31 is fixed to the front face 30 which is itself secured to the part 32.

Figure 4 schematically depicts an exploded perspective view of a detail identified by the letter A, of the display device 3 prior to final fixing of the CRT.

More specifically, the front face 30 comprises a non-threaded hollow part 300 able to accommodate the screw 20 for fixing the CRT.

The CRT 31 comprises a metal lug 310 3 mm thick with a cylindrical opening 311 having an inside diameter D2 of, on average, 16 mm. Of course, the invention is also suited to CRT fixing lug openings that are non-cylindrical and/or that have an inside diameter greater than or smaller than 16 mm (for example ranging between 14 and 15 mm). The mean diameter D1 of the screw head is preferably smaller than the mean diameter D2 of the opening 311. The difference 2Δd between the mean diameters D1 and D2 is advantageously greater than or equal to 3 mm and less than or equal to 6 mm and, for example, is equal to 5 mm (D1 then

having the value 11 mm with D2 equal to 16 mm). In general, the difference Δd (namely the difference between the mean diameters D1 and D2 divided by two) is preferably less than the thickness e of the washer. As a still greater preference, the mean difference between Δd and the thickness e is at least equal to 1 mm.

A bushing 40 separates the lug 310 from the threaded part 300. Such a bushing is described in the French patent application published under the number 2570769 and entitled "dispositif d'assemblage a entretoise reglable, notamment pour Ia fixation d'un tube de television a son coffret [assembly device with adjustable spacer piece particularly for fixing a television tube to its casing]". To sum up, this bushing positioned between the threaded part 300 and the lug 310 comprises two rigid parts 401 and 402 which can move by screwing one with respect to the other so as to be able to fill spaces of different sizes. Its height h can thus vary between about 10 and 15 mm depending on the casing and tube model. The bushing 40 comprises an opening 41 for the passage of the threaded part 201.

When the CRT 31 is being fixed to the front face 30 of the casing, the screw 20 fitted with the washer 21 is positioned to face, in succession, the opening 311 in the lug 310, the opening 41 in the bushing 40 and the threaded part 300 of the front face 30 of the casing. The screw 20 is then screwed into the threaded part 300 with a tightening or screwing torque of between 2 and

7 Nm, and more preferably still of between 5 and 6 Nm, the two opposed faces of the bushing 40 becoming pressed against the front face of the casing 30 and against the fixing lug 310. Since the washer 21 is made of a material that deforms but does not break when such a tightening torque is applied, it deforms as illustrated by way of example with reference to Figure 5 (Figure 5 showing the view in section on BB of the detail A after the CRT 31 has been fixed to the casing 3). A first part 210 of the washer 21 thus completely or partly fills the gap 50 around the shank 20 in the opening 311 and a second part 211 of the washer 21 comes to bear against the fixing lug 310. Thus, it is the washer 21 that essentially provides the mechanical secureness of the tube 31 , for example in the event of droppage. Depending on the shape of the washer, on its thickness, and on the volume of the gap 50, the filling of the gap 50 by part of the washer 20

may thus be complete or partial, for a given tightening torque applied to the screw 20.

As a preference, the tightening torque is between 2 and 7 Nm, and more preferably still is between 5 and 6 Nm. Such a torque allows the washer 21 according to the invention to deform sufficiently. The tightening torque may take account of the rigidity of the material of the washer (typically between 2 and 6 Nm in the case of materials with a Young's modulus of between 2000 and 3000 MPa) and between 5 and 7 for more rigid materials.

As a preference, the tightening torque takes account of the diameter of the threaded shank: the larger the diameter of the shank, the higher the tightening torque. Typically, for a shank with a diameter of 7 mm, a tightening torque of the order of 5.5 Nm may be chosen.

According to various variants of the invention, the washer may be of any shape (for example, may be perfectly round, may be hexagonal, may be square, etc); its shape and its thickness are preferably defined in such a way as to allow it to be positioned on the shank in a simple way.

Thus, the edge face of the washer preferably comprises tightening means, for example in the form of rough edges of two opposed flats so that it can be positioned on the screw 20 by simple screwing using a suitable tool (for example, pliers in the case of rough edges or a spanner in the case of flats). Thus, according to various variants of the invention, the washer has a polygonal external shape in order, for example, to form a regular polygon with four, six, eight, ten or twelve sides.

According to another variant of the screwing system according to the invention, which is illustrated with reference to Figure 6, a washer 61 has an internal opening 62 similar to the opening 22 already described and an external circular shape interrupted by two opposed flats 64 and 65 so that it can be turned using an appropriate tool.

Figure 7 illustrates a fixing system according to a variant of the invention, which comprises a screw 20 and a washer 71.

The washer 71 has any external shape, particularly is polygonal or circular, its thickness e' being relatively small. Specifically, this thickness ranges

between 2 and 4 mm and is preferably 2 mm. In order to allow firm attachment of the tube, the material 71 has great rigidity. It is, for example, Noryl ®. This embodiment is particularly well suited to manual positioning of the washer 71 on the screw 20.

Figure 8 diagrammatically illustrates a sectioned view of a fixing system according to another embodiment of the invention, employing a screw 83 secured to a casing 80 of a display device.

More specifically, the screw 83 is equipped with a fixed or movable base 831 attached to the casing 80 by the base 831.

A nut 82 is screwed onto the threaded shank 830 to fix a bushing 84, a tube lug 85 and a washer 81 in turn to the casing 80. The mean diameter D1 of the nut 82 is preferably smaller than the mean diameter D2 of the opening 86 in the tube lug 85. The difference 2Δd between the mean diameters D1 and D2 is advantageously between 3 and 6 mm and for example is equal to 5 mm. In general, the difference Δd is preferably smaller than the thickness e of the washer. As an even greater preference, the difference between Δd and the thickness e is at least equal to 1 mm. The bushing 84 and the tube lug 85 are similar to the elements 40 and 310 respectively and will therefore not be described further.

The washer 81 is also similar to the plastic washers already described (particularly the washer 21 and its variants). However, it will be noted that, according to the embodiment described in Figure 8, the screw 83 is first of all positioned on the casing, then the bushing 84 and the tube lug 85 are positioned around the threaded shank 830. The washer 82 is positioned next, screwing it onto the threaded shank 830, then the nut 82 is tightened with a screwing torque advantageously of between 2 and 7 Nm, and preferably of between 5 and 6 Nm.

In this way, a first part 810 of the washer 81 thus completely or partly fills the gap 87 around the shank 830 in the opening 86 and a second part 811 of the washer 81 comes to bear against the fixing lug 85.

Of course, the invention is not restricted to the embodiments described above.

The person skilled in the art will, in particular, be able to conceive of any type of display device comprising a CRT fixed or intended to be fixed to a casing. The display devices themselves may be of any kind : they may, in particular, be small (for example 14") or very large (measuring more than 90 cm across the diagonal) devices, devices with a screen of any format (4/3 or 9/16 for example), or devices suited to various applications (for example television screens, computer monitors).

Furthermore, any type of screw the material and dimensions of which are compatible with the fixing of a CRT to a casing may be used according to the invention.

Likewise, the invention is not restricted to CRT fixing systems that use a bushing as described hereinabove. In particular, the invention is compatible with a monolithic bushing made of rigid material, for example made of polystyrene, able to fill the space between the fixing lug and the casing. According to one particular embodiment, the other part of such a bushing comprises tabs extending axially the ends of which can be deformed when they come into contact with a fixing lug upon tightening, the non-deformed part partially entering the opening in the lug. Thus, such a bushing is able both simply to fill the space between a CRT fixing lug and the casing to cause the tube to bear stably against the casing, and to improve the securing of the tube.

According to a variant embodiment of the invention, the side of the washer that is in contact with the screw head or the nut is flat whereas the opposite side comprises a part near the opening that is domed, the latter part having, for example, an additional thickness of 1 mm by comparison with the periphery of the washer. Thus, the penetration of the washer into the opening in the corresponding tube lug occurs more readily.

According to another variant embodiment of the invention, the side of the washer in contact with the screw head or the nut is flat whereas the opposite side comprises a part near the opening that is recessed to make it easier to screw; thus, the thickness of the washer is, for example, between 3 and 4 mm, except for a part bordering the central opening, which is less than 3 mm thick and preferably 2 mm thick, over a width corresponding to the difference between the outside diameter of the threaded shank and its root diameter.

According to other variants, the washer comprises raised or recessed striations advantageously less than 1.5 mm and typically 1 mm or less tall or deep, on the corresponding tube lug side, these running in one or two directions or running radially.

A tube generally has four fixing lugs. As a preference, the four lugs are fixed using screws and washers as previously described. Nonetheless, the loadings on the casing and the tube in the event of droppage are often higher in the bottom part of the display device. Hence, according to one variant embodiment of the invention, just some of the tube lugs (for example the two lower tube lugs) are fixed using a screw and a washer made of deformable material, it being possible for the other lugs to be fitted with conventional metal washers.