GB2102209A - Clamp arrangements for cooling electrical circuits - Google Patents

Abstract

A clamp arrangement of the type disclosed in GB 2076228A for clamping a printed circuit board 1 extending between two opposed parallel walls 7a is mounted on a marginal portion 11a of the board 1 and includes a stack of slidable elements 19 within a channel member 23 extending along the marginal portion 11a.The elements 19 are maintained in a staggered configuration by a retaining member 25 extending along the channel member 23 through slots 21 in the elements 19. A lever arrangement 47 mounted on the upper portion of the board 1 causes a force to be exerted on the uppermost slidable element 19a, which is transmitted to all of the elements and gives rise to a lateral expansion of the mechanism, causing the board 1 to be driven into contact with one of the walls 7a, the web of the channel member 23 contacting the other of the walls 7a. <IMAGE>

Description

SPECIFICATION Clamp arrangements This invention relates to clamp arrangements and has especial relevance to clamp arrangements for securing parts in good thermal contact.

More particularly the invention relates to clamp arrangements for an elongate member extending between two opposed substantially flat parallel walls comprising a mechanism mounted on a surface of the elongate member which includes a stack of slidable elements within an enclosure extending along a region of the surface, the slidable elements being constrained in a staggered configuration in series relationship with one another; and manual actuating means connected to the elongate member operable to create forces acting on the endmostslidable elements of the stack to produce a resultant sliding motion between the slidable elements which, being limited in extent by the width of the enclosure, creates a distributed force along the said region of said surface, serving to drive an opposing surface of the elongate member into contact with one of said opposed walls, and a wall of the enclosure into contact with the other opposed wall. Such a clamp arrangement, which forms the subject of our co-pending UK Patent Application No.

81 14918, is hereafter referred to as a clamp arrangement of the kind specified.

It is an object of the invention to provide an improved form of clamp arrangement of the kind specified.

According to the present invention in a clamp arrangement of the kind specified the slidable elements are maintained in a staggered configuration by a retaining member extending along said enclosure through slots in the slidable elements.

Preferably said slidable elements are cylinders, and said slots extend into their curved surface.

In this case preferably said cylinders are substantially identical, and in each cylinder said slot extends substantially at right angles to the length of the cylinder towards the centre of the cylinder.

Preferably said retaining member comprises a wire.

Preferably said enclosure consists of a channel member loosely coupled to the rest of the mechanism.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of a box housing two printed circuit boards clamped therein by clamp arrangements according to the invention; Figure 2 is a view of one side of a printed circuit board furnished with a clamp arrangement; Figure 3 is an enlarged view of part of the other side of the printed circuit board of Figure 2; Figure 4 is a section on A-A of Figure 3; Figure 5 is a section on B-B of Figure 4; Figure 6 is a view along the arrow shown in Figure 3; Figure 7 is a section on C-C of Figure 4; Figure 8 is a section on D-D of Figure 3; Figure 9 is a section on E-E of Figure 3;; Figure 10 is an enlarged view of part of Figure 4 showing the clamp arrangement in a nonoperative state, and Figure 11 corresponds to the view of Figure 10 with the clamp arrangement in an operative state.

Referring firstly to Figure 1, the printed circuit boards 1 are disposed in the box 3 in parallel spaced relation. Opposite lateral marginal portions of each board are located in guide means in the form of slots 5 defined between adjacent pairs of ribs 7a formed on opposed side walls 7 of the box, the ribbed side walls constituting cold walls for dissipating heat generated by the electronic components 9 mounted on the major surface 11 of the board.

Referring now also to Figure 2, each board 1 has on the surface 11 a heat conductive ladder, the cross members 1 3b of which lie in close proximity to the components 9, and the side members 1 3a of which are strips extending along the lateral marginal portions 11 a of the surface 11.

Referring now particularly to Figures 3 and 4, in respect of each marginal surface portion 11 a carrying a side member 13a there is provided a mechanism 15 which is connected to the board 1 and extends along a corresponding marginal portion 17a of the reverse major surface 17 of the board 1. Each mechanism 15 includes a stack of identical slideable elements in the form of cylinders 1 9a, 1 9b within a channel member 23 extending along the surface 17a.The cylinders 1 9a, 1 9b are disposed with their axes parallel to the surface 17a in a staggered configuration in series contacting relationship with one another so that the curved surfaces of one set of alternate ones 1 9a of the cylinders contact the surface 17a and the curved surfaces of the other set of alternate ones 1 9b of the cylinders contact the internal surface of the web of the channel member 23. Each cylinder 19a, 19b has cut into it a slot 21 extending into its curved surface at right angles to the length of the cylinder, towards the centre of the cylinder as best shown in Figure 5, the cylinders 19a have their slot 21 directed away from the surface 17a and the cylinders 1 9b have their slot 21 directed towards the surface 17a.

The cylinders are maintained in the staggered series contacting configuration by having threaded through the channel formed by the slots 21 a wire 25 extending in the direction of the longitudinal axis of the mechanism 1 5.

At opposite ends of the mechanism 1 5 there are provided upper and lower posts 27, 29 respectively, which extend through the board 1 and the adjacent side member 13a of the heat conductive ladder, and are secured by being riveted over at their ends 27a, 29a in the surface 11 a. As best seen in Figure 6, extensions 23a, 23b of the flanges at either end of the channel member 23 fit round the posts 27, 29 respectively.

Referring now again particularly to Figure 4, the portions of the posts 27,29 on the surface 17 of the board 1 each have a bore 27b, 29b extending in the direction of the longitudinal axis of the mechanism 1 5. Through the bore 27b of the upper post 27 slidably fits a tubular plunger 31. The plunger 31 extends through the bore 27b into the channel member 23 to contact the uppermost cylinder 1 9a, the uppermost end 2 5a of the wire 25 being a sliding fit within the plunger 31. The movement of the plunger 31 through the bore 27b is limited by a head portion 33, having a slot 33a.

The bore 29b of the lower post 29 is tapped, and into this screws an externally threaded tubular sleeve 35, terminating at the lower end of the post 29 in a square section 35a as best seen in Figure 7. A shaft 37 fits slidably through the sleeve 35 and extends upwardly into the channel member 23, where it is attached to a buffer 39 in which is located the lower end 25b of the wire 25. An abutment 39a at the upper end of the buffer 39 contacts the lowermost cylinder 19a. Around the buffer 39, trapped between the abutment 39a, and a washer 43 round the shaft 37 adjacent the top of the post 29 is a compressed spring 45.

Upwards movement of the shaft 37 is limited by a circlip 41 fitted at the lower end of the shaft.

Referring particularly to Figures 2, 3 and 8 each mechanism 15 further includes a manual actuation means comprising a lever 47 which is pivoted at 49 to the top edge of the board 1 near the top of the mechanism 15. The lever 47 has a nose portion 51 positioned so that when the board 1 is fully inserted in its slot 5 in the box 3, it contacts the top surface of one of the ribs 7a.

Hence when the lever 47 is rotated anticlockwise as viewed in Figure 3, the nose portion 51 bears on the rib 7a to partially extract the board 1 from the box 3. A second lever 55 which is pivoted to the reverse surface 1 7 of the board 1 by a screw 57. As best seen in Figures 8 and 9, the lever 55 is spaced off from the surface 17, by means of a carrier 59. A nut 61 threaded on the screw 57 traps a washer 63 between the surface 17, and the carrier 59, passes through the carrier and the lever 55 to secure the lever by means of a lip portion 61 a which engages an appropriately shaped recess 55a in the lever 55. The carrier 59 and lever 55 are also connected to each other by a rivet 65.The lever 47 has further a projection 53 whose edge, when the lever 47 is rotated in a clockwise direction towards the position shown in Figure 3, engages the edge of the carrier 59 to cause rotation (anticlockwise in Figure 3) of the carrier 59 and the lever 55 about their pivotal connection to the board 1.

The lever 55 has a portion 55b which engages in the slot 33a in the head portion 33 of the plunger 31, and when operated on by the clockwise rotation of the lever 47 towards the position shown in Figure 3, urges the plunger 31 to act on the adjacent cylinder 19a and exert a thrust thereon, this thrust being reacted by the upper end of the buffer 39. As best shown in Figures 10 and 11 continued clockwise rotation of the lever 47 produces a sliding motion between the cylinders 19, the cylinders 19b being forced further away from the surface 1 7a, thus producing forces in the direction of the web of the channel member 23, and pushing the channel member 23 in the direction of the adjacent cold wall rib 7a providing a lateral expansion of the mechanism shown as the distance x in Figure 11.Hence by virtue of the constraint provided by the slot 5, the side member 1 3a of the heat conductive ladder 13 on the lateral marginal surface portion 11 a of the board 1 is pressed into intimate thermal contact with its adjacent cold wall rib 7a. The forces exerted by benefit of the mechanism are substantially evenly distributed along the length of the channel member 23. The function of the compressed spring 45 is to limit the force resulting from lateral expansion of the mechanism.

Coarse adjustment of the pressure exerted by the clamp mechanism 15 can readily be achieved by the addition, or removal of rollers 1 9a, the channel member 23 being removable to facilitate this. Fine adjustment of the pressure exerted is achieved by turning the sleeve section 35a when the clamp mechanism is in an expanded state in a standard width slot such that the position of the circlip 41 is a fixed distance from the sleeve section 35a. It will be appreciated that the mechanism is thus capable of tolerating a wide range of slot widths.

Release of the mechanism to allow the ready extraction and reinsertion of the board 1 from the slots 5 is achieved by manual rotation of the lever 47 in an anticlockwise direction as viewed in Figure 3, the movement being aided by the force exerted by the spring 45. As indicated earlier the extraction of the board from the slots 5 is assisted by the nose portion 51 of the lever 47 contacting the top surface of one of the ribs 7a.

It is a feature of the embodiment that the position of the lever 47 serves to indicate whether the clamp mechanism is engaged, that is to say whether good thermal contact exists between the side members 1 3a of the heat conductive ladder, and the associated cold walls 7.

Claims (8)

1. A clamp arrangement of the kind specified wherein the slidable elements are maintained in a staggered configuration by a retaining member extending along said enclosure through slots in the slidable elements.

2. A clamp arrangement according to Claim 1 in which said slidable elements are cylinders, and said slots extend into their curved surface.

3. A clamp arrangement according to Claim 2 in which said cylinders are substantially identical, and in each cylinder said slot extends substantially at right angles to the length of the cylinder towards the centre of the cylinder.

4. A clamp arrangement according to any one of the preceding claims in which said retaining member comprises a wire.

5. A clamp arrangement according to any one of the preceding claims in which said manual actuating means includes an abutment acting on one of said endmost slidable elements and into which one end of said retaining member slidably fits.

6. A clamp arrangement according to any one of the preceding claims in which said enclosure consists of a channel member loosely coupled onto the rest of the mechanism.

7. A clamp arrangement substantially as hereinbefore described with reference to the accompanying drawings.

8. A mechanism for use in a clamp arrangement according to any one of the preceding claims.