GB2149500A - Sensing systems - Google Patents

Abstract

A sensing system for measuring the tilt of a spinning rotor 1 device without the necessity for slip-rings or fly leads utilises a peripheral surface 1a on the rotor-the surface having regions of differing reflectivity 2,3, an emitter for projecting radiation onto the surface, and a receiver for receiving the radiation reflected back from the surface, radiation being obtained at the receiver which varies in response to the tilting of the spinning rotor. For sensing tilt about two axes, two receivers may be provided, each being arranged to view the rotor 1 in a direction perpendicular to a respective axis. <IMAGE>

Description

SPECIFICATION Sensing systems This invention relates to sensing systems and is concerned with sensing the position of a body.

Although it is particularly suitable for sensing the position of a spinning body, for example the spinning rotor of a gyroscope, and hence its rate of change of position, it is also suitable for sensing the position of non-spinning bodies.

As before stated the invention is particularly useful in gyroscopic applications as it provides information without the need for devices such as pick-offs and rate gyros. It also reduces the loading on any gimbals providing rotor mountings and removes the need for supply and output signals to be transferred via slip-rings or fly leads. The spinning rotor can be a momentum mass, acting as a gyroscope, for example, to stabilise a seeker eye unit, thereby providing data to control the spinning rotor.

According to one aspect of the invention, there is provided a system for measuring the position of a body which includes a surface upon the body, an emitter fixedly arranged to project radiation onto the surface, and a receiver fixedly arranged to receive any radiation reflected from the surface, the surface being provided with regions of differing reflectivity, such that as the body moves the radiation received by the receiver varies in response to such movement.

According to a further aspect of the present invention, there is provided a system for measuring tilt of a spinning rotor, including a rotorwhich in use spins about a given axis and tilts about an axis normal to the axis of spin, a peripheral surface on the rotor, an emitter fixedly arranged to project radiation onto the surface, and a receiver fixedly arranged to receive any radiation reflected from the surface, the surface being provided with regions of differing reflectivity, such that as the rotor tilts the radiation received by the receiver varies in response to such tilting.

From this variation in the reflected radiation, the instantaneous angle of tilt can be established. Naturally, rate of tilt can be established by a simple differentiation process.

Although the reflectivity may be arranged to vary in a graded fashion over the surface, preferably, it is arranged to vary in a pattern of well-defined distinct areas of relatively high and relatively low reflectivity.

In this case, conveniently the distinct areas can be in the fonn of complementary serrations, eg triangles. Irrespectively, the width of the serrations changes in a direction parallel to the axis of rotation of the rotor so that a pulsed variation in reflectivity is provided, the pulses varying in width and spacing according to the degree of tilt.

The system has particular application where the rotor tilts about two perpendicular axes, eg pitch and yaw, and measurement is required for both. In this case, a further emitter - receiver arrangement is provided. The emitters and receivers are positioned such that the impingment of their respective radiations are in register with the axes of tilt. Naturally, the distance between an emitter and its associated receiver and the impingement region are such as to take into account the physical attributes of the radiation and the pattern of reflectivity.

For a better understanding of the invention, refer ence will now be made, by way of example to the accompanying drawings in which: Figure lisa side elevation of a rotor spinning about axis X-X; Figure 2 is a front elevation of the rotor, showing the positions of the two detector elements; Figure 3 shows the rotor tilting about axis Z-Z; Figure 4 shows the rotor tilting about axis Y-Y; Figure 5 shows the rotor tilting about both the Y-Y and Z-Z axes; Figures 6, 7, 8, and 9 show the outputs obtained when the spinning rotor is in the positions given by Figures 2, 3, 4, and 5 respectively.

Figure 1 shows a rotor 1 which spins about an axis X-X. The peripheral surface la of the rotor is covered by a symmetrical pattern of triangles which are made of reflective and non-reflective material, 2 and 3 respectively. The strips of reflective material are arranged such that on the edge 1b of the surface la 99% of the edge is reflective and 1% is non-reflective.

Similarly, on the edge ic 1% of the edge is reflective and 99% non-reflective. The strips of material extend across the surface la as shown.

Figure 2 shows the axes about which the rotor 1 may tilt, Y-Y and Z-Z. In order to monitor tilt about axis Y-Y, an emitter-receiver arrangement is mounted such that a receiver 4 is placed in line with the axis Z-Z. Similarly, for tilt about axis Z-Z, a receiver 5 is placed in line with the axis Y-Y. If the rotor 1 spins such that there is no tilt about either axis, the output from the receivers 4 and 5 is of the form shown in Figure 6. In this case, the output is complementary due to the number of triangles present on the surface 1a, ie the output from 4 is a maximum when the output from 5 is a minimum and vice versa. However, by altering the number of triangles of material, it would be possible to obtain identical outputs from receivers 4 and 5.

When the rotor 1 tilts about the Z-Z axis only to its furthest position ie with receiver 5 over the edge 1c, as shown in Figure 3, the incident radiation is only reflected from 1% of the surface and the outputs obtained from the receivers 4 and 5 are given in Figure 7 - the output from receiver 5 showing that only a small part of the radiation incident on 1 C is reflected back, whereas the output from receiver 4 is unaltered. Similarly, if the rotor 1 tilts about the Y-Y axis only, to its furthest position, as shown in Figure 4, the receiver 4 is over edge 1 C and the outputs from both detectors are shown in Figure 8.It should be noted that if the rotor 1 tilts so that the edge 1 b of the surface la is under the receivers 4 and 5 in Figures 3 and 4 respectively, then the outputs obtained would be in the inverse of Figures 7 and 8 ie long maximum pulses with short minimum pulses.

When the rotor 1 tilts about both the Y-Y and Z-Z axes as shown in Figure 5, ie a combination of Figures 3 and 4, the outputs from the receivers 4 and 5 are given in Figure 9. From these pulses, the relationship between phase and amplitude related to the position of the spinning rotor 1 can be determined.

The emitter-receiver arrangements may be mounted adjacent to the spinning rotor 1, but if required, either the emitter, the receiver or both may be mounted away from the rotor 1, and using fibre-optic tubes, they can be coupled to scan the spinning rotor.

The emitter-receiver arrangements may use infrared radiation, visible light or low power laser light, but in systems which are not sealed, the use of infra-red radiation is preferred. Naturally, the materials used to manufacture the reflective strips 2 and the non-reflective strips 3, are chosen to give the greatest contrast for the type of radiation used in the system.

The pattern of high reflectivity-low reflectivity areas may be obtained by using gloss white and matt black paint respectively. Self-adhesive high reflectivity tape may also be used instead of the gloss white paint. Both these schemes can be used with visible light and infra-red radiation systems.

Further methods of producing the pattern or grading include exposing a photographically modified emulsion bonded to the peripheral surface; and plating the surface with rhodium or a similar material, interspacing the plating with a chemically produced matt black surface.

The outputs from the receivers 4 and 5 may be sampled at a suitable frequency to provide a function which is proportional to the rate of change of rotor position.

The output pulses may also be used to determine rotor speed and may be used to control the rotor speed and keep it to a predetermined value.

The angular position ofthe rotor during each revolution relative to the rotor spin axis may be determined by modifying the pattern of reflective and non-reflective strips.

If a clearly defined pulse output is not required, then the reflectivity of the pattern on the peripheral surface may vary in a gradual fashion ie the variation between the reflective and non-reflective area is graded. If such a graded surface is provided, then the position of the body may be determined even when it is not rotating.

Claims (8)

1. A system for measuring the position of a body which includes a surface upon the body, an emitter fixedly arranged to project radiation onto the surface, the surface being provided with regions of differing reflectivity, such that as the body moves the radiation received by the receiver varies in response to such movement.

2. A system for measuring the tilt of a spinning rotor, including a rotorwhich in use spins about a given axis and tilts about an axis normal to the axis of spin, a peripheral surface on that rotor, an emitter fixedly arranged to project radiation on the surface, and a receiver fixedly arranged to receive any radiation reflected from the surface, the surface being provided with regions of differing reflectivity, such that as the rotor tilts the radiation received by the receiver varies in response to such tilting.

3. A system according to claim 2, wherein said rotor tilts about two perpendicular axes of spin, and a further emitter and receiver are provided so that tilting about both axes can be measured.

4. A system according to claim 1, 2 or 3, wherein the reflectivity of said surface varies in a graded fashion over the surface.

5. A system according to claim 4, wherein said reflectivity varies in a pattern of well-defined distinct areas of relatively high and relatively low reflectivity.

6. A system according to claim 5, wherein said distinct areas are in the form of complementary serrations, the width of the serrations changing in a direction parallel to the axis of rotation of the rotor so that a pulsed variation in reflectivity is provided, the pulses varying in width and spacing according to the degree of tilt.

7. A system according to any one of claims 1 to 6, wherein said radiation is infra-red radiation,

8. A system substantially as hereinbefore described with reference to the accompanying drawings.