GB2344136A

GB2344136A - Fastening device

Info

Publication number: GB2344136A
Application number: GB9826128A
Authority: GB
Inventors: Robert Michael Biddle
Original assignee: Richco International Co Ltd
Current assignee: Richco International Co Ltd
Priority date: 1998-11-27
Filing date: 1998-11-27
Publication date: 2000-05-31
Also published as: GB9826128D0

Abstract

A fastening system for the screwing together of two bodies whose separation from each other may vary. The fastening system includes a female member (1) fixable to or integral with one of the bodies and a male member (2) being receivable and slidable within the female member (1). The male member (2) may rotate relative to the female member (1)when inserted therein and a screw (5) is screwed through the male (2) and female (1) members. The rotation locks the members against relative axial movement while the screw is inserted.

Description

FASTENING DEVICE This invention is concerned with a device for fastening together two elements whose separation is not consistently pre-determined.

Embodiments of this invention relate to the fixing of a cathode ray tube (CRT) to the plastic cabinet of a television or computer monitor. The CRT itself is supplied to the, for example, TV manufacturer with a metal band around the main glass body of the tube. In each of the four corners of the band, there is a fixing tab with a hole in the middle. Screws (which are typically selftapping) are used to secure the tabs on the CRT to fixing points or fixing bosses at the corners of the television cabinet.

An effective and secure fastening of a CRT tab to the appropriate fixing boss requires that the top of the boss or fixing point be flush with the underside of the tab so that there is a fixed bearing surface when the tab is fixed to the fixing boss by the insertion of a screw through the tab into the fixing boss. The possible wide variance in height of the location of these metal tabs and of the separation of the tabs relative to the fixing bosses therefore presents problems to the TV manufacturer.

Typically, combinations of metal and/or rubber washers are placed between the fixing boss and the CRT tab so as to extend the top of the boss up to the tab and thereby provide a bearing surface for the fixing screw.

However, the use of washers to compensate for different separations between CRT tabs and fixing bosses is both a time-consuming and an inaccurate task. The correct combination of washers must be selected so as to try and ensure that the top of the boss is extended by the correct amount, and washers of the necessary dimensions may not be available to give precisely the required extension.

The present invention provides a fastening system as defined in claims 1 or 14. Preferred features of such a system are defined in dependent claims 2 to 11. The present invention also provides a bush or fastening element as defined in claims 12 or 15, and a fixing boss as defined in claims 13 or 16.

Preferred embodiments of the invention will now be described with reference to the following figures, in which: Figures 1 and 2 are, respectively, upper perspective and top plan views of a first member embodying the invention; Figure 3 is a sectional view along section A-A of figure 2; Figure 4 is a top plan view of an alternative first member construction embodying the invention; Figures 5 to 7 are sectional views along sections A A, B-B and C-C respectively of figure 4; Figures 8 to 11 are, respectively, upper and lower perspective views, a side view and a top plan view, of a second member embodying the invention; Figure 12 is a perspective view of an alternative second member construction embodying the invention; Figures 13 to 16 are, respectively, top, bottom, first and second side views of the second member of figure 12; Figure 17 is a sectional view along section A-A of figure 13; Figures 18 to 20 illustrate the fastening of a tab to a boss using the system of figures 1 to 17; Figures 21 and 22 are cross-sectional views of tabs having different separations from their corresponding fixing bosses and fastened thereto using a fastening system embodying the invention (biasing means not ; Figures 23 and 24 are perspective views of an alternative embodiment of a first member embodying the invention; Figures 25 and 26 are perspective views of another second member embodying the invention; Figures 27 and 28 are perspective views of another second member embodying the invention; Figures 29 and 30 are perspective views of another second member embodying the invention; and Figures 31 and 32 are perspective views of another second member embodying the invention.

The locking or fastening devices or systems shown in Figures 1 to 32 include engaging first female 1 and second male 2 members.

The female 1 and male 2 members include surfaces 3, for engaging a screw 5 and are fastened together by a screw passing through the second male member 2 into the first female member 1 and engaging the respective surfaces 3,4 of each.

To, for example, fix a cathode ray tube (CRT) to a plastic cabinet, the female member or fixing boss 1 is rigidly fixed to the cabinet (either by being integrally formed therewith or affixed thereto by for example gluing), the male member or bush 2 is placed in the female fixing boss 1 and fixed to the bush 2 and a fixing tab 16 on the cathode ray tube by a screw 5 passing through the fixing tab 6 and the bush 2, and engaging the female cored boss 1.

The female member 1 of the locking device or system of figures 1 to 3 consists of an upstanding hollow cylinder 7 having an upstanding central boss 8 at its base 9. The boss 8 includes a screw receiving bore 10.

The inside of the cylinder 7 is divided by radial walls 11 into segments 12. The segments 12 could be solid but the use of hollow segments defined by radial walls 11 reduces section thickness (section thickness is the maximum wall thickness of the moulding) and the amount of material required for each female member. In the female member 1 of figures 1 to 3, the radial walls 11 define two segments 12 having surfaces 3 at their apexes which together define a passage 13 for receiving and engaging a screw 5.

The thread-engaging surfaces 3 of the two segments 12 are continuous with the inner surface 14 of the central boss 8 (see figures 1 and 3) such that as a screw 5 is threaded along and past the surfaces 3 it then engages the boss 8. (see figures 20 to 22).

The two segments 12 are evenly distributed around the axis 15 of the cylinder 7 and themselves define two segment-shaped spaces 16 within the hollow cylinder 7.

The distance between the inner surface 17 of the circumferential cylinder wall defining the outside of each segment-shaped space 16 and the central axis 15 of the screw-receiving passage 13 decreases as one moves clockwise (direction shown as X in figure 2) around the outer periphery of each space 16. Thus, the circumference of each space is eccentrically located relative to the central axis 15 of the female member or fixing boss 1; the radius of a space decreases as one moves clockwise (direction shown as X in figure 2) around the space circumference (i. e. in the direction in which a screw would be tightened into the first member).

In the female member of figures 1 to 3 the spaces 16 each subtend an angle of 105 about the centre axis 15 of the female member with the segments 12 each subtending an angle of 75 about the same axis. The angle subtended by the segments should be maximised within the design constraints of the subject invention (see discussion below) so as to maximise the area of the female member in contact with a screw 5 located in the first member's central core or passage 13.

It will be seen from the above and figures 1 to 3 that a passage or hole 13 runs concentric with, and the whole length of, the central axis 15 of the female member 1. At its lower end this passage or hole has a continuous wall defined by the inside surface 14 of the central bore in the upstanding cylindrical boss 10. However, for most of its length the arrangement of alternate segments 12 and spaces 16 mean that the passage or hole 13 does not have a continuous wall. Along most of its length the passage or hole is only bounded by the two 75 arcs of the threadengaging surfaces 3 of the segments 12.

The hole or passage 13 has a diameter corresponding to the core diameter of a screw 5 to be used with the fastening system of the subject invention.

The female member of figures 4 to 7 is similar to that of figures 1 to 3 except in that the eccentrically located cylinder inner walls 17 are defined by having a cylinder 18 made up of two halves which are displaced relative to each other along their common diameter rather than varying the wall thickness of the walls of a hollow cylinder 7 of constant outer radius.

The male members 2 of figures 8 to 11 and figures 12 to 16 each include two projections 19 attached to a head 20. The projections 19 fit within the spaces 16 of a corresponding female member 1.

In the embodiments of the invention shown in figures 8 to 16 the projections 19 each subtend an angle of 75 at the central axis 21 of the male member or bush 2. The projections 19 therefore subtend an angle 30 less than the spaces 16 within which they fit and the male member or bush 2 can therefore rotate a maximum of 30 within and relative to the female member 1 of figures 1 to 7 when inserted therein.

As shown in figures 8, 9 and 17 the projections 19 vary in cross-section along their length although they are all formed by segments or arcs of a solid cylinder. The projections 19 each have an outer circumference 22 which is smooth along the length of the projection 19. The cross-section of the projections 19 vary in their internal dimensions.

The outer circumference 22 of each projection has a similar shape to that of the spaces 16 of the female members of figures 1 to 7 with which it may cooperate. The distance between the outer surface 22 of a projection 19 and the male member's central axis 21 decreases as one moves around it in the direction shown as Y in figures 11, 13 and 14 (that is, clockwise when viewing the bush 2 from the top or in the direction in which a screw 5 inserted through the bush. 2 would be tightened).

The eccentric projections 19 and spaces 16 together define a wedging action. As a projection 19 is rotated clockwise within a space 16 its outer surface 22 bears or presses against the female member's 1 inner or wedging surface. As the projection 19 is rotated the larger radius portion of the projection 19 moves into the smaller radius portion of the space 16.

The projections each have four portions 23,24,25,26.

A first portion 23 at the distal end of the projection 19 has an internal radius which together with the first portion 23 of the other diametrically opposite projection defines a recess 27 concentric with the male member central axis 21. This recess 27 is sufficiently large to receive the upstanding boss 8 of the female member 1. The outer surface of the first portion 23 includes a chamfer 28 to allow for easy positioning of the projection 19 within a space 16 of a female member 1.

A second portion 24 has an internal radius equal to the radius of the hole 13 or passage of the female member and the core radius of a screw 5 for use in the fastening system of the subject invention. The internal surfaces 4 of the second portion 24 of the projections are threadengaging surfaces for engaging the thread of a screw 5.

A third portion 25 has a tapered or sloping inner surface 29. This sloping surface 29 has a minimum radius equal to that of the second portion 24 and a maximum radius equal to the clearance radius of the screw 5 for use in the fastening system. The third portion 25 slopes at an angle of about 15 and helps alignment of the screw 5 relative to the hole or passage 30 defined by the second portions 24 of the two projections 19.

The fourth portion 26 of each projection 19 has an inner radius equal to the clearance diameter of the screw 5. The fourth portions 26 of the two projections 19 together define a clearance counterbore 31 through which a screw 5 can pass without engaging the projections 19. The third portions 25 of the projections form a smooth transition from the fourth 26 to the second sections 24.

In addition to supporting the projections 19 described above, the head 20 of the male member 2 also supports two spring members 32.

The spring members 32 are arranged on the periphery of the head 20 diametrically opposite each other.

The spring members 32 of figures 8 to 11 may be made by removing material from a cylindrical head to form two curved resilient protuberances 33 on the underside of the head 20.

The spring members 32,33 of figures 8 to 11 operate on the principle of a built-in beam, since they are both attached at each end 34 to the head 20 of the male member or bush 2. They are profiled such that when the male member 2 is placed within a female member 1, the centre portion 35 of each beam 33 bears on the top of the cylindrical outer wall 7 of the female member.

As shown in figure 8, the male member 2 has two holes 36 in the head 20. These continue, with a slight draft angle, almost to the end of the device. These are core holes for reducing the section thickness, to eliminate sinking during moulding.

Figures 12 to 17 show an alternative male member construction. The projections 19 are the same as those of the bush or male member of figures 8 to 11. However, the spring members 32 are formed by a cantilevered beam spring. Such cantilevered spring members 37 of the bush of figures 12 to 17 experience lower values of stress than the in-built beams 33 of figures 8 to 11.

The depth of the spring members 33,32,37 is chosen to match the maximum possible height discrepancy between a cathode ray tube fixing tab 6 and its corresponding fixing boss 1. Consequently, when a male member 2 is placed within a female member 1 defining a fixing boss on a television cabinet the spring members 33,32 hold the head 20 of the male member 2 far enough above the fixing boss 1 so as to bear against the underside of any fixing tab 6 regardless of its position. If the actual discrepancy in height between the fixing tab 6 and the fixing boss 1 is less than the maximum discrepancy corresponding to the depth of the spring members 33,32, the spring members 33, 32 will deform to a depth matching the actual height discrepancy.

When viewed from the top, the spring members 33,32 blend in with the circular profile of the head 20.

Therefore, the profile of the spring members 33,32 can be described as a cosine wave on a circular development.

Appropriate radii have been included to reduce the stress at internal corners.

During the assembly of televisions/monitors (see figure 18 to 20), cabinet mouldings having integral fixing bosses 1 in each corner corresponding to the female members described above and shown in figures 1 to 7 lie face down on a conveyor. One of the male members 2 (a bush) is manually placed in each fixing boss 1. Each male bush drops into place with the spring members 32,33,37 resting on top of the fixing boss.

A cathode ray tube (CRT) is then lowered, manually or automatically depending on the size, until its profiled front face fits flush against a corresponding accurately profiled dust seal in the front of the cabinet. It is essential that the CRT fits flush all the way round to eliminate the ingress of dust.

With the CRT in this position most, if not all, of the bushes 2 positioned within the cabinet will have been forced downwards by fixing tabs 6 located on the CRL and through various distances until all the respective fixing tabs 6 on the CRT are in contact with the heads 20 of the bushes 2.

A self-tapping screw 5 is placed through each fixing tab 6 into the top of each corresponding bush 2. The screw 5 itself may specifically designed for use in thermoplastics and will ideally have a large diameter head or captive washer to allow for variations in the hole size in each CRT fixing tab. The screw 5 will be able to stand up on its own once inserted because of the clearance counterbore 31 of the bush 2.

The depth of the spring members 32,33,37 is smaller than the length of the fourth portions 26 of the projections 19 and the clearance counterbore 31 which they define. The screw 5 therefore rests on top of the apexes of the segments 12 of the fixing boss 1. This is important to prevent the bush member 2 from being irretrievably forced down into the fixing boss 1 when downward pressure is first applied to the screw 5.

Downward pressure is then applied to the screw 5 with an air driver or similar in order to start the tapping action of the screw.

As the screw moves downwards its thread cuts into the thread-engaging surfaces 3 of the female fixing boss 1.

When the screw 5 reaches the third portion 25 of the male bush 2, its thread rotates the bush 2 clockwise until the bush projections 19 are wedged in the boss spaces 16. The rotation of the bush 2 rotates the projections 19 such that the larger radius portions of the projections move into the smaller radius parts of the fixing boss spaces 16.

Once the bush projections 19 are wedged within the boss spaces 16, the bush 2 cannot rotate further. As well as the rotational wedging action, the screw 5 may also force the two projections 19 of the bush 2 slightly apart, which will also contribute to the locking action.

As the screw 5 continues to turr. and cut further into the central passage or hole 13 of the fixing boss 1, the screw thread also cuts into the thread-engaging surfaces 4 of the bush which are arranged between the threadengaging surfaces 3 of the fixing boss 1. The screw 5 continues its travel through the bush 2 and fixing boss 1 until it is biting on the central bore 10 in the upstanding boss 8 at the bottom of the fixing boss 1. The bush 2 is now rigidly fixed against vertical movement and the screw 5 can be tightened down onto the CRT fixing tab 16 to a predetermined torque setting.

The dimensions shown on figures 2,3,10 and 11 are in mm and the female 1 and male 2 members shown therein are designated for use together to accommodate a maximum height discrepancy of 3.50 mm and secure a cathode ray tube with a fixing tab thickness of 1.50 to 3.00 mm using a 05 x 25 thermoplastic screw with a captive washer.

Larger screws may be required for larger TV's.

Whilst the systems of figures 1 to 17 described above include two eccentric projections 19 on a bush 2 engaging two eccentric bearing surfaces 17 on a fixing boss 1, it will be readily appreciated that the system will also work with any number and shape of projections and matching bearing surfaces provided that rotation of the bush within the boss results in a wedging together of the bush and boss.

Figures 23 and 24 show a fixing boss 1 formed by a hollow cylinder 37 whose inner wall 39 forms three bearing or wedging surfaces 40. As with the wedging surfaces 17 of the fixing boss 1 of figures 1 to 7, the wedging surfaces 40 of the fixing boss 1 of figures 23 and 24 are eccentrically located relative to the boss central axis.

The distance between such wedging surface 40 defined by the inner wall of the cylinder 39 and the central axis decreases as one moves clockwise around each wedging surface 40. The wedging surfaces 40 are separated from each other by steps 41 rather than by the segments of figures 1 to 3.

The bushes or male members 2 of figures 25 to 32 are designed to work in the female member of figures 23 and 24. The bushes 2 of figures 25 to 32 all include three outer wedging surfaces for cooperating with the three wedging surfaces 40 of the boss of figures 23 and 24.

The bush 2 of figures 25 and 26 is a hollow cylinder 43 having a central screw receiving passage 44 whose inner surface forms a screw-thread-engaging surface.

The outer circumference of the cylinder 43 is divided into three surface portions 45 separated by a channel 46 in the cylinder surface. The different surface portions 45 are equivalent to the different projections of the bushes 1 of figures 8 to 17. As with the bushes 2 of figures 8 to 17, the distance between the surface of a particular surface portion 45 and the central longitudinal axis of the central screw receiving passage 44 decreases as one moves clockwise (looking down from the top of the bush-direction A shown by arrow in figure 25) around the surface portion.

A collapsible tube 47 is located in the upper part of each channel 46. The three collapsible tubes 47 provide an interference fit between the bush 2 and a fixing boss 1 as a fixing tab 6 is pushed down on the head of the bush, for example when a cathode ray rube is placed in a television cabinet. The interference fit of the collapsible tubes 47 within a fixing boss are to try and ensure that the bush projects out of a fixing boss 1 to contact the underside of a fixing tab 6.

A modification of the bushes of figures 8 to 17,25, 26 is shown in figures 27 and 28. The bush 2 includes three profiled sprung arms 48 which provide both an interference fit and the desired wedging action.

A possible problem with the bushes of figures 25 to 28 is the risk of the bush or male member 2 being pushed right to the bottom of the fixing boss or female member as soon as downward pressure is applied to a screw placed in the screw receiving passage 44, 49 at the top of the bush head. Such bottoming of the bush would mean that the top of the bush could be displaced away from the underside of a fixing tab as a screw is moved down through the fixing tab, bush and fixing boss.

The alternative bush configurations of figures 29 to 32 solve this problem by providing means for fixing the bush to a fixing tab.

Figures 29 and 30 show a bush 2 having three surfaces 50 for cooperating with the wedging surfaces 40 of a fixing boss 1 such as that shown in figures 23 and 24.

The top of the head 20 of the bush of figures 29 and 30 includes two projecting latching elements 51.

In use, these two latching elements 51 engage or snap over the edges of holes in a fixing tab (not shown) located around the screw receiving hole through the fixing tab. The holes through which the latching elements 51 pass and the hole edges which are engaged by the latching elements are shaped such that the a bush 2 latched onto the tab can rotate relative to the tab through the same angle as that through which the bush can rotate relative to the fixing boss.

Figures 31 and 32 show a bush 2 having a single latching element 51. In use, this engages or snaps over the edge of a fixing tab to hold the bush flush with the underside of the fixing tab.

During the assembly of televisions/monitors using the bushes of figures 29 to 32, a bush 2 is first latched onto each cathode ray tube fixing tab 6. The bushes are then located in the appropriate fixing bosses before a screw 5 is threaded through the fixing tab 6 and bush 2 and into the fixing boss 1.

Although this invention is typically used to secure cathode ray tubes inside television cabinets, it may be applied to anything that requires two bodies to be securely locked together where the distance between them may vary.

Claims

Claims 1. A fastening system for use in the screwing together of two bodies whose separation from each other may vary, the fastening system including a female and a male member, the female member being fixable to or integral with one of the bodies and including a surface for engaging the thread of a screw, the male member being receivable by and slidable within the female member and having a surface for engaging the thread of a screw, the fastening system also including means for ensuring that an end of the male member projects from the female member when first inserted therein, wherein the male member may rotate relative to the female member when inserted therein, and the male and female members being shaped such that the male member cannot rotate relative to the female member through more than a pre-determined angle.
2. A fastening system according to claim 1 wherein the fastening system includes biasing means for biasing the male member away from the female member when inserted therein.
3. A fastening system according to any preceding claim 1 wherein the male member is held relative to the female member when it reaches the limit of its possible rotation relative thereto.
4. A fastening system according to claim 3 wherein the male and female members are shaped such that an outer surface of the male member is wedged against an inner surface of the female member when the male member reaches the limit of its possible rotation relative to the female member.
5. A fastening system according to claim 4 wherein the male member is substantially cylindrical, its screw engaging surface is located around the male members longitudinal axis to define a central screw receiving passage and the distance of the outer surface of the male member from its longitudinal axis varies as one moves around the male member's circumference.
6. A fastening system according to claim 4 or claim 5 wherein the female member is substantially a hollow cylinder, its screw engaging surface is located around its longitudinal axis to define a central screw receiving passage and the distance of the inner surface of the female member from its longitudinal axis varies as one moves around the female member's circumference.
7. A fastening system according to any preceding claim wherein the male member includes a projection and the female member includes space for receiving the at least one projection, at projection having a cross-section corresponding to a segment of a circle with the apex of the segment removed to define a central surface for engaging the thread of a screw, and the space being shaped like the segment of a circle extending over a greater arc than that of the projection.
8. A fastening system according to claim 7 wherein the space of the female member is defined by radial walls within a hollow cylinder.
9. A fastening system according to claim 7 or claim 8 wherein the projection segment is eccentrically located relative to the male member's axis of rotation within the female member.
10. A fastening system according to any of claims 7 to 9 wherein the space segment is eccentrically located relative to the male member's axis of rotation within the female member.
11. A fastening system according to any preceding claim wherein the male member includes a head portion, on which the at least one projection is mounted, and the biasing means comprising a resilient beam having a first end fixed to the head portion and a second end for resting on top of the female member when the male member is received and slidable within the female member.
12. A bush for use in the screwing together of two bodies whose separation from each other may vary, the bush being substantially cylindrical and having a screw engaging surface located at its longitudinal axis to define a central screw receiving passage, the distance of the outer surface of the bush from its longitudinal axis varying as one moves around the bush's circumference.
13. A fixing boss for use in the screwing together of two bodies whose separation from each other may vary, the fixing boss being substantially a hollow cylinder and having a screw engaging surface located at its longitudinal axis to define a central screw receiving passage, the distance of the inner surface of the hollow cylinder from its longitudinal axis varying as one moves around the cylinder.
14. A fastening system substantially as hereinbefore described with preference to any of figures 1 to 32.
15. A bush substantially as hereinbefore described with reference to any of figures 8 to 22,25 to 32.
16. A fixing boss substantially as hereinbefore described with reference to any of figures 1 to 7,18 to 24.