GB2194836A - Door handle assembly - Google Patents

Abstract

A door designed to exclude electromagnetic radiation has two handles 3, 4 joined by an electrically insulating door spindle 6. The insulating nature of the spindle prevents electromagnetic interference being transmitted along it from the outside to the inside of the door. <IMAGE>

Description

SPECIFICATION A door designed to exclude electromagnetic radiation This invention relates to a door designed to exclude electromagnetic radiation.

The invention arose in the design of a shelter for electronic equipment formed from a metal framework carrying wall, roof and floor panels. The panels are formed from a laminar structure having an insulating inner layer of rigid foam plastics material and carrying outer sheets of conductive material to form continuous inner and outer conductive layers over the whole of the shelter to exclude electromagnetic interference.

The need for a door in such radar shelters presents particular problems with regard to the need for an effective seal against electromagnetic interference. One particular problem encountered was that the handle on the outside of the door acted as an aerial which received interfering signals and transmitted them through the door spindle to the internal handle which re-transmitted them into the interior of the shelter. The invention arose with a view to overcoming the problem.

The invention provides a door designed to exclude electromagnetic radiation including: two handles as herein defined, one on each side of the door; an electrically insulating shaft linking the two handles; and a door securing mechanism operated by the shaft.

The term door handle when used in this specification is defined as meaning any manually manipulable member. It need not be a simple handle. It could for example be a wheel-like device.

The use of the electrically insulating shaft has been found to reduce or eliminate the aforementioned problem. The insulating shaft could however present a break in the continuity of the continuous inner and outer conductive surfaces. For this reason the shaft preferably passes through a conductive member held in electrical contact with one of the handles by spring action to form an electromagnetic radiation proof seal around the end of the electrically insulating shaft. A similar arrangement can be provided at each end of the shaft i.e. at the inner and outer surfaces of the shelter.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a schematic perspective view of a shelter for electronic equipment, constructed in accordance with the invention; Fig. 2 is a side elevation of a door and door frame forming part of the shelter of Fig. 1 as viewed from the inside of the door; Fig. 3 is a horizontal cross-section through the line Il-Il of fig. 2 showing detailed construction of the door handles and bolt operating mechanisms; Fig. 4 an elevational view of the bolt operating mechanisms seen from the inside of the door with the handle 4 and plate 13 removed to reveal rack and pinion mechanisms; and Fig. 5 is a vertical cross-section through the line IV-IV of fig. 2.

The illustrated shelter 1 is formed from a framework 1A carrying panels 1B forming the walls, roof and floor. One wall of the shelter has a door frame 2 (fig. 1) formed from extruded aluminium tubing. The door frame 2 receives a door which is hinged on the lefthand side as viewed in fig. 1 and is formed by a panel 2A and a rim 2B. The panel 2A is formed from a material similar to the panels 1B and has a central layer L1 of insulating rigid foam plastics material bonded to sheets L2 and L3 of conductive metal, in this case aluminium. The outer rim 2B of the door is made of extruded aluminium tubing.

The door frame 2 and door 2A have seals which will be described in detail later and which are compressed when the door is closed. This compression of the seals requires a large closing force to be applied to the door and this force is applied by the mechanism which will now be described.

The door has electrically conductive external and internal handles 3 and 4 (fig. 3). The handle 3 fits into a recess where the outer sheet L2 and part of the thickness of the inner layer L1 are cut away. The handles are secured by screws 5 to a spindle or shaft 6 made of synthetic plastics material and extending through a hole bored through the door panel 1A. The use of synthetic plastics material in making the door spindle is siqnificant because of its electrically insulating properties.

It ensures that there is no continuous conductive path between the external handle 3 and the internal handle 4 which could transmit electromagnetic interference from the outside to the inside of the shelter. Thus the handle 3 is unable to act as a receiving aerial which transmits electromagnetic interference through the door spindle to the internal handle, as could occur if the spindle 6 were made of electrically conductive material as in conventional systems.

The shaft 6 is mounted for rotation in a bore formed in a bearing block 7 which has a flange 7' shaped to form a lining to the handle recess and to make electrical contact with the edge of the cut-away portion of the layer 2D.

The shaft 6 has teeth 6A which engage toothed portions 8A,9A,10A on three door bolts 8,9,10 serving to secure the unhinged sides of the door.

The bolts 8,9 and 10 are guided for longitudinal movement in respective channels 11A,11B,11C machined in a guide block 11.

The block 11 also has threaded bores 11A which receive threaded PTFE plugs 11B. The latter bear against the bolts 8,9 and 10 to hold them in accurate engagement with the shaft 6. The block 11 is secured by screws 12 to the bearing block 7 and the bolts are retained in their respective channels by a cover plate 13 secured to the guide block 11 by screws 14. Mating surfaces 3A and 7A of components 3 and 7 are held together by the action of a conical spring washer 15 acting between the handle 4 and a plain PTFE washer 16 which rests against the cover plate 13. This ensures an effective continuity of a conductive outer surface of the door, the components L2, 7 and 3 all making electrical contact with each other. It should be noted that the continuity of these conductive surfaces is obtained despite the need to use an insulating door spindle 6.A circular groove is machined in surface 7A and receives an O-ring 7B to provide an effective weatherproof seal without the use of oil or grease which would impair the electrical contact between surfaces 7A and 3A.

A lower end of the bolt 10 is shown on figures 3 and 4. The three ends of the other bolts are similar and therefore will not be described in detail though they are shown on figure 2.

Referring now to figure 4, the lower end of the bolt 10 is guided by a guide 16 having a PTFE bearing 16A. The bolt 10 also has, at its end, a block 10B of PTFE formed with a bearing surface arranged at an angle to the direction of motion of the bolt. This bearing surface bears against a similarly angled surface 17A at the bottom of a groove 17B in a stop member 17-secured to the door frame 1.

When the bolt is shot by the rack and pi nion action of the teeth on members 6 and 10, the co-operating surfaces of block 10B and stop 17 cause a wedging or camming action serving to press the door into a recess defined by the door frame 2 until mating surfaces 18 and 19 of the frame 2 and door rim 2B meet in the position illustrated in figure 5.

From figure 5 it will be noted that the door -rim 2B and the frame 1 are specially shaped with interleaving ridges and depressions.

These form a seal against electromagnetic interference. Some of the depressions contain compressible seals 20 formed from rubber tubing covered with a metal braid. When the door is closed to the position illustrated in figure 5 the seals are compressed, this requiring a considerable force which is adequately provided for by the camming action of the three bolts.

Claims (5)

1. A door designed to exclude electromagnetic radiation including: two handles as herein defined, one on each side of the door; an electrically insulating shaft linking the two handles; and a door securing mechanism operated by the shaft.

2. A door as claimed in claim 1 where the insulating shaft passes through a conductive member held in electrical contact with one handle by spring means to form an electromagnetic radiation proof structure.

3. A door as claimed in claim 2 where the spring means is a conductive compression spring between the conductive member and the door so as to form an electromagnetic radiation proof seal.

4. A door as claimed in claim 3 where said conductive compression spring is a metallic cone washer.

5. An electromagnetic radiation proof enclosure including a door as claimed in any preceding claim.