GB2123232A - Compass - Google Patents

Abstract

A compass has a patterned reference member, typically a disc 2, which is concentrically supported for rotation normal to the axis of a spindle 3 which has bearings 8,10 at each end and a magnet 7 or other direction finding means associated. Clear and opaque regions in the pattern are arranged to form unique patterns for each 1 DEG of subtended angle and the pattern in each such sector is read and converted to an electrical signal. The pattern is preferably arranged in binary code in annular tracks and is preferably read using a light source 6 projected through the pattern to optical fibres 9 which actuate phototransistors 10 whose binary coded output is converted directly to seven segment display code for LED display. Transistor amplifiers 27 and 29 associated with additional coded tracks blank the display at transitional points where a plurality of bits change simultaneously. <IMAGE>

Description

SPECIFICATION Compass This invention relates to a compass adapted to provide an electronic read-out of the direction in which it is oriented.

In the past, navigation has relied upon magnetic compasses, which have been difficult and time consuming to read, or gyroscopic compasses, which require continual re-adjustment because of their precession.

It is an object of the present invention to provide a compass which can provide an electronic read-out of the compass direction suitable for display or for feeding into a nagivational computer.

Accordingly, in a first aspect, the present invention consists in a compass comprising a spindle rotatably supported at at least one end in a body, direction finding means mounted on the spindle to detect the horizontal component of the earth's magnetic field and to rotate the spindle in the body to be in alignment with the field component irrespective of the orientation of the body, a reference member substantially coaxial with the spindle so that as the spindle rotates the reference member rotates, said reference member having a pattern thereon dividing the reference member into differentiated portions such that there is a unique sequence of differentiated portions intersected by a chosen plurality of planes coaxial with the spindle corresponding to the angle of the body to the direction finding means, a detecting means fixed to said body to detect the pattern in a single said plane and interpreting means for converting the pattern as detected by the detecting means into an electrical signal and means triggered from the pattern detected by the detecting means to eliminate spurious signals.

In a second aspect the present invention consists in a method of determining a compass heading, the method comprising the steps of detecting a pattern on a reference member associated with a compass needle, converting the detected signal into an electronic code and then converting the code into a readable form and supressing spurious readings.

A preferred form of the invention will now be described by way of example with reference to the accompanying drawings in which Figure lisa diagrammatic representation of a compass according to the present invention and its associated circuitry; and Figure 2 is a plan view o'the disc of the compass in Figure 1.

The preferred compass 1 of the present invention comprises a reference member which is preferably in the form of a clear disc 2 coaxially supported on a vertical spindle 3 to rotate within its own plane i.e.

normal to the spindle. Ten annular tracks of markings 4 which provide binary code representing numbers from 0-359 are arranged concentric to the spindle. There is a separate binary code within each one-degree sector about the circle. Given a large enough disc and more tracks fractions of a degree could be read.

The binary code is preferably represented in the form of opaque and transparent or translucent regions formed in a photographic emulsion on top of the disc, as illustrated in Figure 2. However, light reflective or non reflective regions or ultrasonic reflective or absorbent regions could be used.

In the illustrated embodiment the ten tracks 4 of directional information are arranged so that the innermost two tracks define the first digit, the next four tracks define the second digit and the outermost four tracks define the third digit for numbers 000359. Thus, for example, the sector representing a heading of 259 degrees would be, from the innermost to the outermost tracks: opaque, transparent, transparent, opaque, transparent, opaque, opaque, transparent, transparent, opaque, to give the binary code 10,0101,1001 (2, 5, 9). Other binary codes may be used, of course.

Positioned underneath the edge of the disc are three or four light emitting devices (LEDs) 6, the number depending on light output needed, for transmitting light through the disc markings onto a reading head 5 above the edge of the disc. Within the reading head there is a row of optical or light fibres 9 for reading off the binary code. The light fibres conduct the light to a series of remote phototransistors 10 which are connected to an electronic circuit for converting the binary code into seven segment display code. Typically, the phototransistors comprise Darlington Pair Light Sensitive Transistors, to provide sufficient sensitivity to detect the light transmitted from the LEDs.

An eleventh track 11 on the disc, typically just inside the other ten, can be used for providing a signal for about one sixth of a degree every ten degrees (at the change over between the ninth and tenth degree). The change of bit information must be simultaneous on all sensors (optical fibres) to avoid momentarily erroneous readings on the digital display. A critical area has been found to be the changing of the third digit from 9 to 0, e.g. 239" to 240 when a large number of bits of the code are changing at a time. The additional track of coding is used on the disc to remove this error possibility caused by mechanical maladjustment or disc distortion. This track is in the form of a clear slot subtending an angle of about one sixth of a degree, spanning each transition point from 9's to 10's.The transistor amplifier 27 which is thus triggered one twelfth of a degree before the transition, blanks out the entire digital display on the 100's 10's and units LEDs 20,21 and 22 until the disc has moved to one twelfth of a degree past the transition, when all sensors have correct coded information again and the display is re-illuminated. This extra blanking sensor can also be used to drive a "one-shot" monostable circuit to sound an audible alarm to indicate either that the vehicle being guided has gone off course or has passed a 10 point of the compass. E.g. in an aircraft 9 bleeps from the alarm would indicate to the pilot that he had turned through 900-without his having to refer directly to the compass display.

Similarly, a twelfth track 12 on the disc, typically just outside the ten binary code tracks 4, is used to provide a blanking signal via transistor amplifier 29 at the changeover after every two degrees, where there are two or more bits of B.C.D. information changing at once, to blank out the units digit 22 of the readout for a fraction of a degree. This arrangement can, of course, be varied to suit the particular binary code being used. A diode gate 28 also ensures that when the hundreds and tens digits are blanked off via the transistor amplifier 27 then the units digit is synchronously blanked off, but not vice versa.

The disc 2 is mounted horizontally in the compass, the spindle 3 being preferably supported at both ends in jewel bearings 8,10.

The housing or body 13 is non-magnetic and has a slot 14 in the bottom covered with a sheet 15 of glass or other transparent material. The housing itself is typically of aluminium and is oil filled and is equipped with gimbal mountings 18,19. Light from the LEDs 6 is directed upwardly through the slot 14 and the glass 15 through the annular portion of the disc where the patterns 4, 11, 12 are located, through a mask 16 in the upper housing immediately adjacent and above the disc, to the ends of the light fibres 9.

The ends of the light fibres are arranged in a straight line, behind the mask 16. The mask has a single transparent slot which ensures that the light fibres receive a signal from only one sector (or radial row) of markings 4,11,12 at a time. This means that a light source comprising a few LEDs is adequate, eliminating the need for a collimated light beam which needs to be accurately focused. The mask 16 is a clear line on a black photographic emulsion, the line having a width of 0.03 mm. The optical fibres have a diameter of 0.3 - 0.4 mm and so even if the 12 fibres preferably used are not aligned in a perfectly straight row the mask ensures that all are signalled simultaneously. The effective sensor width is substantially less than 19 to achieve this in the case of a compact reference disc e.g. of 40 mm diameter.

The photo-transistor 10 and electronic circuitry may be located immediately on top of the housing, or the light fibres can transmit the light signals to a box 30 remote from the housing, which may be preferable to avoid stray fields. Also the B.C.D.

output can be converted to serial output, fed via coaxial cable elsewhere and reconverted to parallel form to operate the display using cheap known devices.

The use of light fibres means that standard phototransistors can be used to detect the light signals. However, the light fibres can be dispensed with, and light sensitive diodes or transistors placed directly within the reading head adjacent the edge of the disc. In this arrangement, however, these circuit elements must be very small, or else the disc must be quite large.

The compass can be perfectly balanced. As the spindle is preferably supported at both ends the compass is reasonably robust and able to be used on light aircraft and small boats. It is also less subject to turning errors caused by dip angle moments.

The photo transistors 10 are part of an electronic circuit which convert the light signals to binary coded electrical signals. The binary code is then converted to seven segment display code by standard cheap B.C.D. (binary coded decimal) to seven segment decoders 24,25,26 linked via resistors 23 to operate one or more 3 figure LED displays 20,21,22 which can then be directly read by a person using the compass. If desired, a microprocessor can be used to do an automatic adjustment for magnetic deviation. Alternatively, the binary code can be fed directly to a navigational computer as it is in standard parallel B.C.D. form.

Many modifications to the above may be made without departing from the scope of the present invention as defined. For example, other means can be used instead of light or ultrasonic beams for reading off the pattern of the reference marker. The pattern may take any of a wide variety of forms. The reference member need not necessarily be a round disc but could, for example, be hemispherical.

The reference member and spindle may not necessarily be provided with a magnet 7 as direction finding means to detect the horizontal component of the earth's magnetic field and to rotate the spindle in the housing, but may instead incorporate a gyroscopic compass. In this case, the electronic code from the readout would be adjusted by a microprocessor or other circuit for precession rather than for magnetic deviation. The magnetic version is preferred, however.

Claims (19)

1. A compass comprising a spindle rotatably supported at at least one end in a body, direction finding means mounted on the spindle to detect the horizontal component of the earth's magnetic field and to rotate the spindle in the body to be in alignment with the field component irrespective of the orientation of the body, a reference member substantially coaxial with the spindle so that as the spindle rotates the reference member rotates, said reference member having a pattern thereon dividing the reference member into differential portions such that there is a unique sequence of differentiated portions intersected by a chosen plurality of planes coaxial with the spindle corresponding to the angle of the body to the direction finding means, a detecting means fixed to said body to detect the pattern in a single said plane and interpreting means for converting the pattern as detected by the detecting means into an electrical signal and means triggered from the pattern detected by the detecting means to eliminate spurious signals.

2. A compass as claimed in claim 1 wherein the spindle is rotatably supported at both ends.

3. A compass as claimed in claim 1 or 2 wherein the direction finding means comprises one or more magnets.

4. A compass as described in any one of claims 1 to 3 wherein the pattern also lies in a plane normal to the spindle.

5. A compass as claimed in any one of the previous claims wherein the pattern is located in 360 planes each of 1" included angle each individually patterned in binary code to provide an indication of the compass direction in degrees.

6. A compass as claimed in any one of the previous claims wherein the detecting means com prise ends of optical light fibres positioned in a said plane close to said patterned region of the reference member and an associated light source and mask adapted to provide a beam of light in said plane capable of detection by the optical fibres only when not modified, or only when modified, by part of the pattern.

7. A compass as claimed in claim 6 wherein the interpreting means comprises an electronic circuit including photodiodes or transistors for detecting light from the optical fibres to convert them into electrical signals.

8. A compass as claimed in any one of the preceding claims wherein the pattern further comprises markings which result in blanking out or suppressing part of the readout signal at 2 intervals.

9. A compass as claimed in any one of the preceding claims wherein the pattern further comprises markings which result in blanking out or suppressing at least part of the read-out signal at 10 intervals.

10. A compass as claimed in claim 5 or any other preceding claim when dependent on claim 5 wherein the interpreting means comprises an electronic circuit for converting the binary code into seven segment display code.

11. A compass as claimed in claim 5 wherein the interpreting means comprises an electronic interface with a computer.

12. A compass as claimed in any one of the preceding claims which includes means to provide an audible signal as the compass turns through predetermined points.

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

14. A method of determining a compass heading, the method comprising the steps of detecting a pattern on a reference member associated with a compass needle, converting the detected signal into an electronic code and then converting the code into a readable form and suppressing spurious readings.

15. A method as claimed in claim 14 wherein the step of detecting the pattern comprises passing a beam of light through the pattern and detecting the beam.

16. A method as claimed in claim 14 or 15 further comprising the step of modifying the detected signal to allow for magnetic deviation or precession.

17. A method as claimed in any one of claims 14 to 15 further comprising the step of providing an audible signal from the detected signal as the compass turns through predetermined points.

18. A method as described in any one of claims 16 to 17 comprising the further step of providing means to prevent the creation of erroneous readings every 2" and every 10 .

19. A method of determining a compass heading, substantially as herein described with reference to the accompanying drawings.