GB2174495A - Compass and method of producing same - Google Patents

Abstract

A compass is disclosed comprising a housing (1) defining a recess (3) and a magnetic compass card assembly (7) pivotally mounted in the recess (3). The recess (3) is filled with a transparent damping liquid and is closed by a transparent sheet or film (12) which is permanently sealingly secured to the housing (1) around the recess (3) as by welding or bonding. A method of producing the compass is also disclosed. <IMAGE>

Description

SPECIFICATION Compass and method of producing same This invention relates to compasses and to a method of producing same.

Compasses are known which comprise a housing defining a recess, a magnetic compass card assembly pivotally mounted in the recess, a transparent liquid filling said recess and a transparent cover which closes said recess. The housing is generally formed in two parts, one housing part defining said recess and the other housing part comprising optical means through which the compass card can be viewed. The transparent liquid, which is usually a transparent oil, serves to damp undesirable movement of the compass card assembly and to prevent leakage thereof from said recess suitable sealing means, such as an O-ring seal, is normally provided between the transparent cover and the housing.

Such conventional compasses are difficult to assemble because of the necessity to properly locate the O-ring seal and are liable to leakage if the 0ring seal should become displaced.

The present invention has as its object to provide a compass and a method of producing same which overcomes these disadvantages.

The present invention provides a compass comprising a housing defining a recess, a magnetic compass card assembly pivotally mounted in said recess, a transparent liquid filling said recess and a transparent sheet or film closing said recess and permanently sealingly secured to said housing around said recess.

The present invention also provides a method of producing a compass comprising the steps of providing a housing defining a recess, pivotally mounting a magnetic compass card assembly in said recess, closing said recess with a transparent sheet or film permanently sealingly secured to said housing around said recess, and filling said recess with transparent liquid either before or after the closing of the recess with the transparent sheet or film.

The transparent sheet or film closing said recess may be in the form of a diaphragm and preferably has at least one fold therein adjacent the periphery of the recess so that it can flex slightly to allow for expansion and contraction of the liquid in the re cess. The transparent sheet or film is preferably a suitable synthetic plastics sheet or film such as a polyester film of the kind sold under the registered trade marks MYLAR and ESTAR. A suitable thick ness for the transparent sheet or film is about 0.2mm.

The transparent sheet or film may be perma nently sealingly secured to the housing around said recess by welding, e.g., ultrasonic welding, by bonding, e.g. using a suitable adhesive, or in any other suitable manner.

The transparent liquid in said recess serves for damping the magnetic card assembly and may be a transparent oil or other suitable liquid. The said recess may be filled with the transparent liquid either before or after the recess is closed with said transparent sheet or film. Where the recess is filled with the transparent liquid after closing of the recess with the transparent sheet or film, a suitable filling hole may be provided in the housing and this filling hole closed after filling of the recess with the transparent liquid as by means of a suitable plug.

The magnetic card assembly may be of conventional design and may comprise a compass card having the points of the compass shown thereon in convention manner, a permanent magnet and a central hub portion providing a jewelled or other suitable bearing. This magnetic compass card assembly may be pivotally mounted on a pivot pin which extends upwardly from the bottom of said recess. A spider may be provided which is supported by said housing adjacent the periphery of said recess and which cooperates with the compass card assembly to prevent displacement of the compass card assembly from said pivot pin. Thus the spider may have a central boss which is normally out of contact with the hub of the compass card assembly but which is sufficiently close thereto as to prevent displacement of the compass card assembly from the pivot pin.The said spider is preferably transparent and may be formed from a suitable transparent plastics material.

At least one graticule or lubber line is provided which cooperates with the compass card to provide the required bearing indication. Such graticule may be provided on said transparent sheet or film and may be provided photographically or in any other suitable manner. The graticule may be in the form of a straight line which extends radially of the compass card and may be about .0015 inch (.038mm) in width. Alternatively, said graticule or graticules may be provided on a limb or limbs of said spider if the spider is transparent and said limb or limbs is/are suitably oriented The present invention will be more particularly described with reference to the accompanying drawings in which: Figure 1 is a side sectional elevation of a compass according to the present invention, and Figure 2 is a plan view of the compass of Figure 1 with an upper part of the housing removed.

Referring to the drawings it will be seen that the compass illustrated therein comprises a housing 1 having a lower part 2 which defines a recess 3 and an upper part 4, the two parts of the housing being secured together by screws 5 or the like. Extending upwardly from the bottom of the recess 3 is a pivot pin 6 on which is pivotally mounted a magnetic compass card assembly 7. The compass card as sembly comprises a compass card 8, a permanent magnet 9 and a central hub 10 which incorporates a jewelled bearing 11. The recess 3 is filled with a transparent damping liquid such as a suitable transparent oil. The recess 3 is closed by a trans parent sheet or film 12 which is in the form of a diaphragm and is formed from a suitable polyester or other suitable plastics sheet or film and which may be about 0.2mm in thickness.The transparent diaphragm 12 is ultrasonicaly welded or otherwise permanently sealingly secured to a surface 13 of the housing part 2 around the periphery of the recess 3. A shoulder 14 on the housing part 2 around the recess 3 accommodates a fold 15 in the transparent diaphragm 12 around the periphery of the recess 3 to allow some flexure of the diaphragm 12 to accomodate expansion and contraction of the transparent liquid in the recess 3. The shoulder 14 also serves to support a spider 16 which is preferably transparent and which is preferably formed from a suitable plastics material. The spider 16 has a central boss 17 which is normaly spaced from the hub 10 of the compass card assembly 7 but which is sufficiently close thereto as to prevent displacement of the compass card assembly 7 from the pivot pin 6.In the illustrated embodiment the spider 16 has three limbs 18 extending radially outward from the boss 17, although it will be understood that the spider could comprise more or less limbs if required.

The upper part 4 of the housing 1 comprises conventional optical means 19 through which the compass card 8 can be viewed. Interposed between the optical means 19 and the compass card 8 is a graticule 20. The graticule 20 may be photographically or otherwise provided on the transparent diaphragm 12 or on a suitably oriented limb 18 of the spider 16.

The compass illustrated is used for taking bearings on distant objects, e.g. on suitable landmarks, and so is normally used by holding it up to the eye and looking through the optical means 19. If it is also required that the compass be usable for taking bearings on a map then suitable lense or other means may be provided whereby the compass card can be viewed from above and in this case a second graticule 21 may be provided on either the diaphragm 12 or a suitably oriented limb 18 of the spider 16.

The recess 3 may be filled with the transparent liquid either before or after it is closed by the diaphragm 12. Where the recess 3 is to be filled with the transparent liquid after the recess 3 has been closed by the diaphragm 12 a suitable filler hole may be provided in the housing part 1 which is closable by means of a suitable sealing plug 22 as shown in Figure 2.

The housing parts 2 and 4 are preferably formed, e.g. moulded, from a suitable plastics material.

It will be understood by those skilled in the art that the present invention provides a compass which is both simple to manufacture and assemble and which is reliable in use.

Claims (22)

1. A compass comprising a housing defining a recess, a magnetic compass card assembly pivotally mounted in said recess, a transparent liquid filling said recess and a transparent sheet or film closing said recess and permanently sealingly secured to said housing around said recess.

2. A compass according to claim 1, wherein said transparent sheet or film is in the form of a diaphragm and has at least one fold therein adjacent the periphery of the recess so that it can flex slightly to allow for expansion and contraction of the liquid in the recess.

3. A compass according to claim 1 or 2, wherein said transparent sheet or film is formed from polyester or other synthetic plastics material.

4. A compass according to claim 1, 2 or 3, wherein said transparent sheet or film has a thickness of substantially 0.2mm.

5. A compass according to any one of the preceding claims, wherein said transparent sheet or film is permanently sealingly secured to said housing around said recess by welding or bonding.

6. A compass according to any one of the preceding claims, wherein said transparent liquid is a transparent oil.

7. A compass according to any one of the preceding claims, wherein said recess is filled with said transparent liquid prior to closing said recess with said transparent sheet or film.

8. A compass according to any one of claims 1 to 6, wherein said recess is closed with said transparent sheet or film prior to being filled with said transparent liquid, said housing having a filling hole therein through which the recess is filled with said liquid and which is closed after filling of the recess with the transparent liquid.

9. A compass according to claim 8, wherein said filling hole is closed by means of a plug.

10. A compass according to any one of the preceding claims, wherein said compass card assembly comprises a compass card having the points of the compass shown thereon, a permanent magnet and a central hub portion providing a bearing and wherein the compass card assembly is pivotally mounted on a pivot pin which extends upwardly from a bottom of said recess when the compass is in its position of use.

11. A compass according to claim 10, wherein a spider is provided which is supported by said housing adjacent the periphery of said recess, said spider cooperating with the compass card assembly to prevent displacement of the compass card assembly from said pivot pin.

12. A compass according to claim 11, wherein said spider has a central boss which is normally out of contact with the hub of the compass card assembly but which is sufficiently close thereto as to prevent displacement of the compass card assembly from the pivot pin.

13. A compass according to claim 11 or 12, wherein said spider is transparent.

14. A compass according to any one of the preceding claims, comprising a graticule or lubber line which cooperates with the compass card to provide a bearing indication.

15. A compass according to claim 14, wherein said graticule or lubber line is provided on said transparent sheet or film.

16. A compass according to claim 15, wherein said graticule or lubber line is provided photographically.

17. A compass according to claims 13 and 14, wherein said graticule or lubber line is provided on a limb of said spider.

18. A method of producing a compass comprising the steps of providing a housing defining a recess, pivotally mounting a magnetic compass card assembly in said recess, closing said recess with a transparent sheet or film permanently sealingly secured to said housing around said recess, and filling said recess with transparent liquid either before or after the closing of the recess with the transparent sheet or film.

19. A method according to claim 18, wherein the transparent sheet or film is welded or bonded to said housing around said recess.

20. A method according to claim 19, wherein the transparent sheet or film is ultrasonically welded to the housing around said recess.

21. A compass substantially as herein described with reference to the accompanying drawings.

22. A method of producing a compass substantially as herein described.