GB2167191A - Hall-effect attitude sensors - Google Patents

Abstract

An attitude sensor comprises a frame 10 supporting a triangular (preferably isosceles or equilateral) plate pendulum 11 suspended on a shaft 13 adjacent the mid-point of one edge of the pendulum. A Hall- effect integrated switching circuit 19 is mounted adjacent the lowermost point of the pendulum, and a magnet 20 having a pair of equal but opposite poles is attached to the pendulum to act equally on the Hall- effect circuit 19 when in a position symmetrical thereto. A minor disturbance of the pendulum position, e.g. 0.001 DEG gives rise to a significant change in the magnetic flux acting on the circuit 19, so causing the circuit to yield an output indicative of that disturbance. Damping of the pendulum is provided by a helical spring 26 acting through a rigid spring-steel wire 21 wound on a groove 22 on shaft 13, the damping being adjustable by nut 25. it is stated that the magnet 20 and the Hall-effect circuit 19 can be reversed in position, but that this is disadvantageous since electrical connections then have to be made to the pendulum. <IMAGE>

Description

SPECIFICATION Attitude sensors This invention relates to an attitude sensor that is to say, a device adapted to provide an output indicative of the disposition of the sensor with respect to some pre-defined datum.

Not infrequently, it is necessary to provide apparatus with some means which automatically maintains the angular position (e.g. level) of that apparatus, or which gives an output indicative of the fact that the apparatus no longer is in a desired angular position. Though sophisticated apparatus may be provided with for example gyroscopic equipment for this purpose, most commonly a pendulum device is employed to sense deviations from the required angular position, the pendulum device having a pendulum suspended to hang vertically under the influence of gravity and there being means to sense the position of the pendulum with respect to some reference.Such means could comprise a linear optical encoder scale attached to the pendulum, there being an appropriate number of light transmitter and receiver pairs associated with the optical encoder to obtain a digital output of the pendulum position, the digital output then being processed as required.

Attitude sensors as described above, though satisfactory for many purposes, tend to have a relatively low resolution, especially in the region of the datum position. in other words, it may be difficult if at all possible to detect relatively minor perturbations of the sensor from its datum position. For example, if apparatus having the attitude sensor attached thereto is disturbed from its datum position by an angle of, say, one degree, the attitude sensor may be unable to provide an meaningful output of such a small movement.

It is a principal object of the present invention to provide an attitude sensor able to sense relatively small angular disturbances-- and typically of the order of 0.1 0of the sensor from a base or datum position.

According to this invention, there is provided an attitude sensor comprising position referencing means with at least one degree of freedom, a Hall-effect switching circuit disposed on a fixed part of the sensor so as to lie adjacent the position referencing means, and magnetic means mounted on the position referencing means for co-operation with the Hall-effect switching circuit, which magnetic means has two pole pieces of opposite polarity but of similar strength and arranged to act equally on the Hall-effect circuit when the sensor is in a datum position with the position referencing means in a base position.

It will be appreciated that in the attitude sensor of this invention, use is made of a Hall-effect switching circuit, to detect relatively small movements of the position referencing means with respect to the frame of the device. Conventionally, a Hall-effect circuit may be used to detect movement by detecting when a magnet is moved towards or away from the circuit, the circuit reacting correspondingly, but such an arrangement gives a relatively low resolution of the relative movement between the magnet and circuit. However, in the present invention magnetic amplification has been achieved, by providing two poles of equal but opposite polarity acting equally on the Hall-effect switching circuit when the sensor is in its datum position.The Hall-effect circuit thus behaves as though there are no magnetic lines of force in the region thereof so long as the sensor is in the datum position, but upon a very small movement of the position referencing means with respect to the circuit, the circuit is subjected to a relatively high magnetic flux density and so responds accordingly.

Most preferably, the position referencing means may comprise a pendulum suspended to hang vertically under the influence of gravity, the suspension arrangement giving the pendulum at least one degree of freedom. The Hall-effect switching circuit then conveniently lies adjacent the lower end of the pendulum, and when the sensor is in its datum position with the pendulum hanging vertically, the magnetic means acts equally on the Hall-effect circuit.

In the following description, reference will be made solely to a pendulum device serving as the position referencing means, though it will be appreciated that some other device may be employed, such as a gyroscopic device.

It is much preferred in a sensor of this invention to employ an integrated circuit form of Hall-effect device. By appropriate selection both of such a device and of the strength and positioning of the poles of the magnetic means, it is found that the attitude sensor may have high sensitivity, able to detect disturbances of as small as 0.001 .

The sensitivity of the sensor may be enhanced yet further by appropriate selection of the design of pendulum used in the device, when a pendulum is used as the position referencing means. Experimental tests have shown that optimum results may be obtained using a plate-like pendulum of generally isosceles or equilateral triangular form, suspended at or adjacent the mid-point of one of the sides and with the apex between two equal sides depending lowermost opposed to the pivot. Such a pendulum conveniently is manufactured from a relatively dense but non-magnetic material, such as copper or a copper alloy-for instance a bronze or brass.

A pendulum as hasjust been described above may be mounted on a shaft extending normally to the plane of the pendulum and carried in low-friction bearings in a frame of the sensor: For example, point contact conical bearings may be employed. However, with relatively low friction bearings and a pendulum of relatively high mass, it is advantageous to provide a certain amount of damping on the pendulum movement, to eliminate spurious outputs from the Hall-effect circuit. For the preferred form of bearing arrangement, it is convenient to add a mechanical damping device to the shaft of the pendulum, thereby to impart a braking effect on the pendulum movement. One possible form for such a damping device is to have an element passing at least partially around the shaft suspending the pendulum, a lateral force then being applied to that element.The lateral force may be adjustable in order to permit the degree of damping to be varied to suit a particular application.

It will be appreciated that the combination of the Hall-effect switching circuit and the magnetic means having two poles of opposite polarity acting equally on the circuit senses relative movement between the circuit and magnetic means. Accordingly, it would be possible to mount the circuit on the pendulum and the magnetic means on a fixed part of the frame, but the disadvantage of this is that wires must interconnect the circuit on the pendulum and a control arrangement which senses the circuit output. Nevertheless, this invention extends to such an arrangement as well as the preferred configuration of the magnetic means on the pendulum.

By way of example only, one specific embodiment of attitude sensor of this invention will now be described in detail, reference being made to the accompanying drawings, in which: Figure 1 is a front view of the sensor device constructed in accordance with this invention; Figure 2 is a side view of the sensor device of Figure 1; and Figure 3 is a sectional view of the apparatus of Figures 1 and 2, taken on line Ill-Ill marked on Figure 1.

The embodiment of attitude sensor of this invention illustrated in the drawings comprises a U-shaped frame 10 pressed from sheet material and serving as a support for the various parts of the sensor, and to permit the mount ing of the sensor on some apparatus. It will be appreciated however that the frame may take any convenient form and for certain appli cations may be formed by appropriate parts of the equipment with which the sensor is to be used.

The frame 10 supports a plate-like pendu lum 11 of generally triangular shape, the pen dulum being suspended by a pivot 12 dis posed adjacent one edge of the pendulum, mid-way therealong. The pendulum 11 is in the form of a flat sheet, for example of brass, and has an equi-lateral triangular form.

The pendulum itself is attached to a shaft 13 provided with conical bearing surfaces at its ends, which are received in correspondingly-formed bearing bolts 14 adjustably mounted in plates 15 secured to the frame 10 of the device, by means of bolts 16. In this way, the pendulum is able freely to pivot under the influence of gravity, in a vertical plane containing the pendulum itself.

Adjacent the lower end of the pendulum, a rectangular plate 17 is mounted by bolts 18 to lie parallel to the frame 10, but with the pendulum 11 disposed between the frame 10 and plate 17. The upper pair of bolts 18 are positioned so as to serve as movement limits for the pendulum 11. Mounted on the plate 17 is a Hall-effect integrated circuit 19, so as to face a magnet 20 bolted to the pendulum 11, adjacent the lower end thereof. The magnet 20 is of U-shaped form, as shown in Figure 3, but could be in the form of two similar bar magnets disposed with opposite poles facing the Hall-effect integrated circuit 19, with a magnetic yoke disposed therebetween.

Mechanical damping is applied to the pendulum 11, by means of a rigid spring-steel wire 21 having a part-circular form and received in a groove 22 provided in the shaft 13, the wire 21 depending from a helical coil spring 23 secured at its other end to a rod 24 passing through the top plate of the frame 10 and having a nut 25 threaded thereonto. A further spring 26 acts between the top plate of the frame and an abutment 27 provided on the rod 24, to urge that rod downwardly. Rotation of the nut 25 permits adjustment of the tension in the spring 23 and so of the degree of damping applied to the shaft 13.

In order to use the attitude sensor, it is appropriately affixed to equipment the angular disposition of which is to be sensed, and the Hall-effect sensor is connected to an appropriate electronic sensing circuit, arranged to detect when the output of the Hall-effect integrated circuit is switched from one of its states to another. The mounting of the sensor is carefully adjusted such that when the equipment is at a datum position (for example, level) the vertically-hanging pendulum is disposed with its lower apex immediately over the central bolt 18 of the three bolts supporting the plate 17. When so positioned, the two magnetic poles of opposite polarity act equally on the adjacent Hall-effect integrated circuit, but in the opposite sense, whereby the circuit responds as though no magnetic flux were present. However, on turning the sensor slightly such that the pendulum 11 is moved about its pivot under the influence of gravity, the effect of the two magnetic poles no longer is equal on the Halleffect integrated circuit, which thus is suddenly subjected to a significant magnetic flux. The output of the integrated circuit therefore switches to another state and the electronic circuit is able to give an indication of the movement of the sensor, and so of the equipment to which the sensor is attached.

The damping arrangement should appropriately be adjusted, to give a required degree of damping on the movement of the pendulum, so eliminating spurious outputs from the Halleffect integrated circuit.

Claims (10)

1. An attitude sensor comprising position referencing means with at least one degree of freedom, a Hall-effect switching circuit disposed on a fixed part of the sensor so as to lie adjacent the position referencing means, and magnetic means mounted on the position referencing means for co-operation with the Hall-effect switching circuit, which magnetic means has two pole pieces of opposite polarity but of similar strength and arranged to act equally on the Hall-effect circuit when the sensor is in a datum position with the position referencing means in a base position.

2. An attitude sensor according to claim 1, wherein the position referencing means comprises a pendulum suspended to hang vertically under the influence of gravity, the suspension arrangement giving the pendulum at least one degree of freedom.

3. An attitude sensor according to claim 2, wherein the Hall-effect switching circuit is mounted to be positioned adjacent the lower end of the pendulum, the magnetic means being mounted on the pendulum lower end such that when the sensor is in its datum position with the pendulum hanging vertically, the two poles of the magnetic means act equally on the Hall-effect circuit.

4. An attitude sensor according to any of claims 1 to 3, wherein the Hall-effect device is in the form of an integrated circuit.

5. An attitude sensor according to claim 2 or any claim dependent thereon, wherein the pendulum is generally of isosceles or equilateral triangular form, suspended at or adjacent the mid-point of one of the sides and with the apex between two equal sides depending lowermost from the pivot.

6. An attitude sensor according to claim 5, wherein the pendulum is of a metallic nonmagnetic material.

7. An attitude sensor according to claim 2, or any claim dependent thereon, wherein the pendulum has a shaft attached thereto which shaft is carried in lowfriction bearings provided in a frame of the sensor device.

8. An attitude sensor according to claim 2 or any claim dependent thereon, wherein damping means is provided for the pendulum.

9. An attitude sensor according to claim 8, wherein the damping device comprises a tension element wrapped at least partially around a shaft suspending the pendulum, means being provided to apply a variable tensile force to that element, thereby to permit adjustment of the degree of damping.

10. An attitude sensor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.