The present invention relates to an angula displacement sensor comprising an electrical device fo providing a signal relating to angular displacement, e.g For use as a shaft angle transducer. It particularl relates to sensors responsive over a full 360° of rotatio and/or continuous rotation. Such a sensor, i gravitationally biased, can be used as an inclinometer. Summary of the Invention

The present invention provides an angular displacemen sensor comprising an electrical device for providing signal relating to angular displacement, said electrica device comprising first and second angular displacemen transducers each having a first component that is rotatabl relative to a second component; means coupling rsaid firs components of the first and second transducers together s that their angular displacements are synchronised; eac said transducer having a respective electrical paramete that varies with said angular displacement; each of sai transducers having electrical output means for deriving fo each transducer an electrical signal indicative of said parameter; the arrangement being such that for the first component of the first transducer the path of relative angular displacement has a plurality of successive like portions in each of which the parameter varies

substantially uniformly over the same range; and for the first component of the second transducer the path of relative angular displaement has a like plurality of successive portions in each of which the associated electrical parameter has a characteristic value or range, the synchronisation of displacements being such that as the first component of the first transducer traverses any path portion, the first component of the second transducer traverses a respective path portion whereof the associated electrical parameter serves to distinguish between the like portions of the path of the first component of the first transducer.

For example, the second transducer may also have successive like path portions in each of which its parameter varies substantially uniformly over the same range, the two first components being mutually out of phas such that when one is at the start of a portion, the othe is in the middle of a portion.

Typically each path has two portions. Thus for th first transducer there may be two portions in each of whic the parameter varies from a maximum positive value to maximum negative value. (This may be relative to a arbitrary baseline.) The second transducer's parameter ma show the same variation overall but, since it is out o phase, for one portion (corresponding to one portion of th first transducer's path) it is always negative, while fo the other portion it is always positive. Thus it serves t

provide a logic signal for telling whether a given value of the output of the first transducer represents a position on the first path portion or on the second path portion.

Alternatively, the second transducer can have a respective characteristic constant value of its parameter for each path portion.

The displacement path is preferably a complete revolution, and the path portions may be of 180° or other integral fraction of 360°. The parameters may be voltage, capacitance, or inductance (and may be different for the two transducers). The variation over each path portion (of the first transducer and also of the second when this has variation within path portions) is preferably substantially linear with displacement. The transducers may share a single path-defining element as their second components, the element being acted on by both of the first components. For example the second component may be an annular resistor, and the two first components may be coaxial rotors having wipers that each run on the same track. Alternatively there may be different paths for the two transducers, e.g. provided by two resistors which may be axially spaced along a shaft whose displacement is to be monitored. A capacitance-based sensor may employ a pair of differential capacitors whose moving parts are mechanically linked.

An inductance-based sensor may use a transducer having a coil portion and a relatively rotatable core portion

whose permeability to magnetic flux from the coil portion varies over its angular extent. The coil portion may extend over 180°. The core portion may extend over 360°, with two 180° portions of different permeabilities. The variation of the parameter associated with one transducer can be used to provide an analogue displacement signal, while the variation of the parameter of the second transducer can serve to provide a logic signal indicative of the path portion occupied by the first component of the first transducer. There may be signal processing means for deriving an output related to displacement.

The provision of the second transducer enables a device to be constructed that can provide data about the complete range of displacement, i.e. in general a complete revolution.

Brief Description of the Drawings

Some embodiments of the invention will now be described with reference to the accompanying drawings i which: Fig. 1 is a schematic view of a first embodiment o the invention which is an angular displacement sensor usin resistance variation;

Fig. 2 is a graph for use in explaining the operatio thereof; . Fig. 3 is a schematic view of a second embodiment o the invention which is an angular displacement sensor usin resistance variation;

Fig. 4 is a schematic view of part of a third embodiment of the invention which is an angular displacement sensor using capacitance variation;

Fig. 5 and 6 are plan and end elevational views of a third type of transducer which employs variable inductance; and

Fig. 7 is a graph showing variation of inductance of the third transducer.

Description of the Preferred Embodiments Fig. 1 shows a resistive transducer which comprises a 360° resistive toroid 1 which may be wirewound or of carbon film or other appropriate construction, the toroid being fed with a suitable voltage at diametrically opposed tapping points A and B. A contact wiper 2 is rotatable continuously around the toroid, and connected (via a slipring if for more than 360" rotation) to a terminal C. A second identical contact wiper 3 is mechanically coupled to the first with a displacement of 90°, and connected to terminal D, the two wipers being electrically insulated from each other.

If the voltages at terminals C and D are measured relative to either terminal A or B, as the rotor constituted by the two wiper assemblies is turned, the voltages will rise and fall in accordance with the Fig. 2 curves. That is, as a wiper moves from A to B, the voltage falls linearly with angular displacement to a minimum value. Continued rotation reverses the process. The two

wipers 2,3 give identical characteristics, but 90° out of phase. It will be apparent that, if voltage output C-B is used to give an analogue level corresponding with 180° rotation either side of a datum position, the level of output D-B will be high for 180° in one direction, and low for the other. By converting the high/low comparison into a logic signal, a plus/minus sign can be assigned to the analogue output to give full 360° data. This may be carried out by a signal processing and display unit P. While the illustration shows a single resistive element with two wipers displaced 90°, it would obviously be possible to use two identical such resistive elements with single wipers, coupled mechanically to give the required 90° displacement. Fig.3 shows a second resistive embodiment which again has a 360° resistive toroid 1 with diametrical taps A,B and a contact wiper 2 connected to a terminal C. There is a second contact wiper 3 which is rotationally coupled to the first wiper 2 and electrically connected to a terminal D. However, it does not run on the toroid 1. Instead it runs on a ring 10 of contact material split to form two semicircular fixed contacts 14,15 separated by minimal gaps 16, positioned so that the gaps occupy the 0° and 180° degree transition points of the analogue output channel. One contact 14 may be connected via a suitable resistor 6 to supply high voltage, the other similarly to supply low voltage. The output from the second contact wiper 3 will

then be a square wave logic output 16 with continuous rotation. The phase relationship of the outputs from the two wipers 3,4 is such that this square wave signal 16 provides a plus/minus logic signal directly, for assigning the output of the first wiper 3 to the correct 180° sector. Fig. 4 shows in principle how a transducer of the differential capacitor type may be adapted to produce similar characteristics to the first embodiment. The transducer incorporates two stator surfaces 24 and 25, swept by a rotor 26 at a constant separation. The surface areas are configured so that capacitance differential between the rotor and the two stators can be used to derive a signal which rises and falls in a substantially linear manner with 180° rotation either side of a datum position. By coupling two such transducers together displaced by 90° from each other, two signals following the general form of Fig. 2 may be derived, and from them an analogue plus logic signal for plus and minus 180° rotation. The surface configurations shown are schematic only, and not necessarily accurate representations of those required to produce the linear analogue characteristics of Fig. 2.

Figs. 5 - 8 show an example of another form of transducer in which the variable parameter is inductance. A cylindrical half-stator 31 of suitable ferromagnetic material for a.c. magnetisation has a number of similar poles 41 which extend radially inwardly over 180°, each of which is wound with the same number of turns of wire 36 of

alternate direction so that adjacent poles are of opposite polarity. All the poles are connected in series to terminals A and B, and energised with a.c. Concentric with this is a cylindrical rotor 32 on a shaft 35. The surface annulus of the rotor is divided into two sections of differing effective permeability to the magnetic flux from the stator, which loops into and out of the rotor as indicated by the broken lines. Section 33 is of high permeability, and section 34 of low permeability. This low effective permeability may be produced either by omitting ferromagnetic material, or by using a surface screen of high conductivity metal such as copper or aluminium, in which the magnetic flux produced by induced eddy currents opposes the stator flux. The interface between sections 33 and 34 is skewed by one pole as can be seen from Fig. 6. This is so as to produce a stepless increase in inductanc as the rotor is turned to present a high permeabilit path, rising from L _Q to L^ through 180° as shown in Fig. 7, returning to Lg as the full 360° is traversed. A simila stator-rotor assembly displaced 90° from this will produc a characteristic change of inductance displaced 90° as shown by the broken line in Fig. 7. The inductance can b measured by any suitable method familiar to the skilled, e variation of volt-drop with constant current passing, o variation in frequency if the winding forms part of a oscillator circuit.

With any embodiment, signal processing means of

generally known type can be employed to process the dat from the two sets of terminals to provide data relating t angular displacement, as will be apparent to the ma skilled in the art. Of course, much variation is possibl within the scope of the invention. For example, a singl capacitive transducer as shown in Fig. 4 could be used i conjunction with the contact-type resistive device 3,4,5 shown in Fig. 3 for providing a logic signal.