GB2189663A - Direction indicators - Google Patents

Abstract

A direction indicator, such as a compass or wind direction indicator, uses a coded disc (28) as a rotatable slave element. Sensors monitor a plurality of circular tracks (60,62,64) on the disc and enable one to determine from the two inner tracks (60,62) the direction of rotation of the disc and the angle through which the disc has rotated, and from the outer track (64) the initial angular setting of the disc. The outer track (64) is preferably readable as a serial bit code. Optical or magnetic sensors may be used. <IMAGE>

Description

SPECIFICATION Direction indicators This invention relates generally to direction indicators, and more particularly to rotational direction indicators such as wind vanes and compasses.

In modern navigational aids, particularly for water-borne craft, there is a need for indicator instruments which will provide a read-out which is easy to appreciate at a glance, for example in the form of a digital display. It is therefore necessary to be able to convert the movement of an element which is responsive to an external influence into an indication of a change in direction. This can apply for example to wind vane units where it is necessary to know the direction of the wind, and also to compasses where it is necessary to know the correct bearing.

Broadly in accordance with one aspect of the present invention there is provided a direction indicator comprising an element which is movable in response to a change either in an external influence or in the direction of travel of the element itself, a coded slave element rotatable in response to movement of said first element, and sensor means arranged to monitor the rotational movement of the coded element, wherein the coding is such as to enable an indication to be obtained both of the direction of rotation and of the angle of rotation of the coded element.

In a preferred embodiment of the invention the coded slave element is provided with areas of different opacity, whereby optical monitoring means can detect rotational movement thereof.

In an alternative arrangement, the coding on the slave element may comprise magnetic coding to which an appropriate sensor will respond.

In a preferred embodiment of the invention the slave element is a disc provided with three coded tracks, each in a circular array, wherein two of the tracks enable computation of the direction in which the disc is rotating and of the angle through which it has rotated, with the third track enabling the angular starting point to be determined.

Broadly in accordance with another aspect of the invention there is provided a coded disc, arranged to be rotatable in relation to associated sensing means, comprising a plurality of circular tracks, each having alternate zones to which the sensing means is responsive and non-responsive in turn, the tracks being such that the direction of rotation of the disc, the angle of rotation of the disc, and the initial angular setting of the disc can be determined therefrom.

Preferably three tracks are provided.

The zones are preferably alternate light and dark areas on the disc so that an optical sensing means can be used.

In order that the invention may be more fully understood, one embodiment of direction indicator in accordance with the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a side view, partly in section, of a wind vane unit incorporating a direction indicator in accordance with the present invention; and, Figure 2 is a plan view of the coded disc used in the indicator shown in Fig. 1.

Fig. 1 shows a wind vane unit comprising a housing 10, on the top of which is mounted a vane 12 comprising a deflector blade 14 and a counterweight 16. The vane 12 is mounted on the housing 10 for rotation relative thereto, with any appropriate form of bearing being used for that mounting. In the present embodiment the vane 12 is mounted on a pivot 18 and has a depending skirt portion 20 which incorporates one part 22 of a magnetic coupling. The other part 24 of the magnetic coupiing is mounted at the upper end of rotatable shaft 26. Towards the lower end of a the rotatable shaft 26 there is mounted a disc 28 which is rotatable with the shaft. The shaft 26 is rotatable within bearings carried by a sleeve 30, to which is secured a mounting plate 32 which is bolted to the housing 10.

The mounting plate 32 carries a support plate 34 for three light sources 36 which are arranged radially of the disc 28 and in alignment with respective tracks on the disc, as will be explained in more detail hereinafter with reference to Fig. 2. The support plate 34 for the light sources 36 is bolted to a second support plate 38 which is positioned below the disc 28 and which carries three optical detectors 40 which are aligned with the three light sources 36.

Below the housing 10 is fitted a set of three anemometer cups 42 which are connected to a rotatable shaft 44 which extends up into the lower half of the housing 10 and which carries, at its upper end, a rotatable disc 46. This disc 46 has associated with it a single light source 48 directed to beam its light towards a single optical detector 50 which is also carried by the support plate 38 which carries the other optical detectors 40.

The single light source 48 is carried by a support plate 52 fitted to a mounting plate 54 which is bolted to the housing 10.

The housing 10 is provided with a tubular metal stay 56, bolted to the housing, and by means of which the wind vane unit can be mounted in a suitable position for use, whether this is upon a movable object such as a boat, or in a fixed terrestrial position.

Referring now to Fig. 2, this shows the disc 28 of the wind vane unit. The disc 28 is a circle of clear plastics material provided with black zones which constitute three circular tracks. It will be appreciated that one could alternatively have a disc of black material provided with transparent holes or areas in order thereby to provide these tracks. It will further be appreciated that instead of using an optical sensing system for the disc, with light and dark areas, one could alternatively use some other sensing arrangement, for example based upon the use the of magnetic zones on the disc.

The two radially inner tracks, indicated at 60 and 62 respectively, each comprise 90 equally spaced dark zones alternating with 90 equally spaced clear zones. Thus, when the coded disc 28 rotates on its shaft 26 relative to the fixed-position optical sensor 36, 40, each track 60 and 62 will produce a pulse train output having a mark-space ratio of 1 1. The radially inner track 60 is so orientated in relation to track 62 that the pulse train outputs from the respective tracks are out of phase by 90". Thus, by counting an edge (leading edge or trailing edge) of each pulse from one of these pulse trains, the pulse count total will indicate the angle through which the disc has rotated. By additionally comparing the phase of the two pulse trains one can also determine the direction in which the disc has rotated.The use of these two coded tracks thus enabies one to determine both the direction of rotation of the disc and the angle through which it has rotated.

However, initially, when the instrument, i.e.

wind vane unit, is first switched on, the information obtained from the two inner tracks 60 and 62 is insufficient to enable one to determine the angular starting point. The two inner tracks only give information as to what is currently happening, and do not in themselves indicate the initial setting. In order to overcome this problem, the disc 28 is provided with a third track 64 which is positioned around the circumferential edge of-the disc.

This third track is again aligned with one of the sensor pairs 36, 40 and is provided as a serial nine-bit code. Thus, when the disc 28 rotates and nine bits of information from the outer track 64 have passed the respective sensor, the exact orientation of the wind vane, and therefore the exact wind direction is known. In order to be able to read this coded outer track 64, the direction of rotation and bit spacing must be known. This information is obtained from the information gained from the two inner tracks 60 and 62. Thus, the sensing of the three tracks on the coded disc 28 enables one to determine both the initial setting of the unit, as well as subsequent changes in direction and the magnitude and sense of such changes.

The rotatable disc 46 shown in Fig. 2 is also a coded disc which is provided in order to enable the unit to provide an output indicative of wind speed. This can be achieved by the use of just a single track on the disc 46, sensed by the optical sensor pair 48, 50.

The electrical outputs from the coded discs 28 and 46 are fed to external circuitry which can be linked up to any form of indicating and/or recording and/or display apparatus.

This can be adjacent to the unit itself or remote from it, and can be linked up to any number of repeater stations.

Although, as described above, the outer track 64 on disc 28 is used to determine the initial setting, it should be understood that this outer track can be used subsequently, as the instrument continues its function. For example, readings can be taken from the outer track every time that 9 bits pass the sensor unit and by applying this to an up/down counter one achieves an update of the movement of the disc.

More generally, the plurality of tracks on the disc are to be regarded as utilisable individually and/or in combination to provide the output information which is needed. Although three concentric tracks have been illustrated, two tracks or more than three tracks could alternatively be used, with appropriate coding.

Although the invention has been described in connection with a wind vane unit for determining wind direction, the invention is equally applicable to compasses where there is a need to determine directional settings and changes. A coded disc equivalent to the coded disc 28, if used in a magnetic compass, will then enable the user to determine both an initial compass setting and also subsequent changes in bearing both in terms of direction of movement and magnitude of movement.

Claims (24)

1. A coded disc which is arranged to be rotatable in relation to associated sensing means, the disc comprising a plurality of circular tracks, each having alternate zones which the sensing means is able to distinguish in turn, the tracks being such that the direction of rotation of the disc, the angle of rotation of the disc, and the initial angular setting of the disc can be determined from a reading of the tracks by the sensing means.

2. A coded disc as claimed in claim 1, in which three tracks are provided on the disc.

3. A coded disc as claimed in claim 2, in which two of the tracks enable computation of the direction in which the disc is rotating and of the angle through which it has rotated, with the third track enabling the angular starting point to be determined.

4. A coded disc as claimed in any preceding claim, in which at least one of the tracks is readable as a serial bit code.

5. A coded disc as claimed in claim 4, in which a circumferential track on the disc is readable as a serial bit code.

6. A coded disc as claimed in any preceding claim, in which the tracks have alternate light and dark zones suitable to be read by optical sensing means.

7. A coded disc as claimed in any of claims 1 to 5, in which the tracks have magnetically distinguishable zones suitable to be read by magnetically sensitive means.

8. A coded disc as claimed in any preceding claim, having a first track comprising first and second zones uniformly spaced to produce a pulse train output with a mark-space ratio of 1 : 1, and having a second track comprising first and second zones uniformly spaced to produced a pulse train output with a mark-space ratio of 1 : 1, with the pulse train outputs from the respective tracks being out of phase by 90 .

9. A direction indicator comprising an element which is movable in response to a change either in an external influence or in the direction of travel of the element itself, a coded slave element rotatable in response to movement of said first element, and sensor means arranged to monitor the rotational movement of the coded element, wherein the coding is such as to enable an indication to be obtained both of the direction of rotation and of the angle of rotation of the coded element.

10. A direction indicator as claimed in claim 9, in which the coding is such to enable an indication also to be obtained of the initial angular setting of the slave element.

11. A direction indicator as claimed in claim 9 or 10, in which the slave element comprises a rotatable disc having a plurality of circular tracks, each having alternate zones which the sensor means is able to distinguish in turn.

12. A direction indicator as claimed in claim 11, in which the disc has three tracks.

13. A direction indicator as claimed in claim 12, in which two of the tracks enable computation of the direction in which the disc is rotating and of the angle through which it has rotated, with the third track enabling the angular starting point to be determined.

14. A direction indicator as claimed in claim 11, 12 or 13, in which at least one of the tracks is readable by the sensor means as a serial bit code.

15. A direction indicator as claimed in any of claims 9 to 14, in which the sensor means is an optical sensor and the coded slave element has alternative zones of distinguishable opacity.

16. A direction indicator as claimed in any of claims 9 to 14, in which the sensor means is a magnetic sensor and the coded slave element has alternate magnetically distinguishable zones.

17. A direction indicator as claimed in any of claims 9 to 16, in which the slave element has a first track comprising first and second zones uniformly spaced to produce a pulse train output with a mark-space ratio of 1 . 1, and having a second track comprising first and second zones uniformly spaced to produce a pulse train output with a mark-space ratio of 1 : 1, with the pulse train outputs from the respective tracks being out of phase by 90 .

18. A direction indicator as claimed in claim 13, in which the output from the third track is connected to a counter to provide an updated read-out of the movement of the disc.

19. A direction indicator as claimed in any of claims 9 to 18, which is a magnetic compass.

20. A direction indicator as claimed in any of claims 9 to 18, which is a wind direction indicator.

21. A direction indicator as claimed in claim 20, in combination with means to provide an output indicative of wind speed.

22. The combination as claimed in claim 21, which includes a second coded slave element, in the form of a rotatable disc, having a circular coded track sensed by second sensor means which provides said output indicative of wind speed.

23. A coded disc substantially as hereinbefore described with reference to Fig. 2 of the accompanying drawing.

24. A direction indicator substantially as hereinbefore described with reference to Figs.

1 and 2 of the accompanying drawing.