The present invention relates to a rotary encoder, in particular a rotary encode comprising at least one length of shape-memory alloy (SMA) wire.

Such a rotary encoder may be used in a wide range of applications. Such a rc encoder may be used, for example, to determine the position of a dial (e.g. in a dishwasher) or in robotics. Other areas of application include photographic lenses, computer input devices such as optomechanical mice and trackballs, controlled stress rheometers, and rotating radar platforms.

Rotary encoders come in different types. One type is a mechanical rotary enc in which a row of sliding contacts is fixed to a stationary object so that each contact å a conductive disc that rotates (e.g. by being fixed to a shaft). As the disc rotates with shaft, some of the contacts touch metal, while others fall in the gaps where the metal been cut out. Electrical connection between the contacts and the disc is determined s to determine the rotation of the disc and therefore the shaft.

Another type of rotary encoder is an optical rotary encoder. The optical rotar encoder comprises a disc with transparent and opaque areas. A light source and photodetector array reads the optical pattern that results from the position of the disc optical pattern can be read to determine the angle of the disc and therefore the shaft.

Another type of rotary encoder is a magnetic rotary encoder. The magnetic n encoder uses a series of magnetic poles to represent the encoder position to a magnet sensor. The magnetic sensor reads the magnetic pole positions, from which angle of shaft can be determined.

The present invention is concerned with providing an improved rotary encode

According to an aspect of the invention, there is provided a rotary encoder comprising: a rotatable part configured to rotate about a rotation axis; at least one she memory alloy, SMA, wire arranged to convert an angular position of the rotatable pa a strain of the SMA wire; and means for generating an output signal dependent on th< strain of the SMA wire, such that the output signal is dependent on the angular positi the rotatable part. The present invention makes use of the property of the SMA wire that strain i closely correlated with its electrical characteristics. The present invention provides a rotary encoder that has a simple construction and is capable of performing accurate measurements of the angular position of the rotatable part. The strain of the SMA wi may vary continuously depending on the angular position of the rotatable part. This for a precise measurement of the angular position of the rotatable part.

In some embodiments the rotatable part comprises a cam, or the rotatable pari cam. The at least one SMA wire is arranged in a manner allowing continuous rotatio the cam and/or rotatable part. So, the rotatable part may be able to rotate indefinitely there may not be a limit to the rotation of the rotatable part. However, this is not ess( and in some other embodiment the at least one SMA wire may be connected directly rotatable part so as to allow measurements of the angular position of the rotatable par rotatable part may be configured to rotate within a limited range of rotation angles.

In some embodiments multiple SMA wires are provided. The SMA wires are arranged to have different relationships between the angular position of the cam and strain of the SMA wire. In some embodiments the output signal is dependent on a combination of the strains of the SMA wires. This may allow more accurate determi of the angular position of the cam.

In some embodiments the rotary encoder comprises a mechanism configured intermediate between the cam and the SMA wire. However, this is not essential to al continuous rotation of the cam, and the SMA wire may in some embodiments be in d contact with the cam. For example, the SMA wire may be connected at both ends to support structure or reference structure relative to which the cam is arranged to rotate the SMA wire may bend around the cam so as to be in direct contact with the cam at middle portion of the SMA wires. So, the SMA wire itself may, in essence, act as a follower to the cam.

In some embodiments the mechanism comprises a follower arranged to abut t cam. In some embodiments the follower comprises a body, such as a plate, comprisi hole through which the cam extends. In some embodiments one of the cam and the body or plate comprises a flang against which a major surface of the other of the cam and the plate abuts.

In some embodiments the rotary encoder comprises an anti-rotation arrangem configured to constrain rotation of the body or plate about an (or any) axis parallel to rotation axis of the cam. The anti-rotation arrangement may thus constrain rotation c by friction with the cam. In some embodiments the anti-rotation arrangement compr two bearing portions connected in mechanical series, each bearing portion allowing movement in a respective one of two non-colinear directions in a movement plane of body. The movement plane of the body may correspond to a plane of the plate. The movement plane may be perpendicular to the rotation axis.

In some embodiments the mechanism comprises two followers arranged to at cam at angular positions about the rotation axis that are offset from each other by an of between 0 and 180 degrees, preferably of 45 to 135 degrees, further preferably of ; 90 degrees. In some embodiments, more than two followers may be provided.

In some embodiments the mechanism is configured to convert a change in dis from the rotation axis to an edge of the cam abutting the follower into a change in ler of the SMA wire, the change in length being smaller than the change in distance. Pui another way, the cam may have an eccentric cam profile about the rotation axis. The follower is configured to abut the cam and to remain in contact with an edge of the c: during rotation of the cam, such that the distance of the follower from the rotation ax changes as the cam rotates. The SMA wire elongates or contracts as the follower mo relative to the rotation axis. The elongation or contraction of the SMA wire may be 1 than the movement of corresponding the follower.

In some embodiments the mechanism is configured to convert a change in dis from the rotation axis to an edge of the cam abutting the follower into a change in ler of the SMA wire, the change in length being larger than the change in distance. The mechanisms may thus be configured to amplify the movement of the edge of the folh abutting the cam.

In some embodiments the mechanism is configured to convert a change in dis from the rotation axis to an edee of the cam abiittine the follower into a chanee in ler of the SMA wire, the change in length being smaller than the change in distance. Th mechanisms may thus be configured to de-amplify or reduce the movement of the ed the follower abutting the cam, such that the change in length of the SMA wire is less the movement of the edge of the follower abutting the cam. This may be advantageo because the maximum elongation or stroke of the SMA wire is preferably kept relath small to reduce the risk of damage to the SMA wire. The absolute dimensions of the profile, and so movement of the edge abutting the follower, are preferably relatively ! to account for manufacturing tolerances of the cam profile.

In some embodiments the mechanism comprises a lever to which the SMA w fixed, wherein the lever is arranged relative to the cam such that the cam converts the angular position of the cam into a rotational position of the lever and the lever strains SMA wire dependent on its position. In some embodiments the rotary encoder comp a resilient component configured to bias the lever against the cam. The lever may correspond to a follower of the cam. So, the lever may remain in continuous contact the cam upon rotation of the cam.

In some embodiments the lever is arranged such that a force imposed on the 1 by the cam comprises a force component that opposes a force imposed on the lever b SMA wire. In some embodiments the lever comprises a flexure configured to act as pivot for the lever. In some embodiments the flexure extends in a direction that is ali with a point where a force vector of force imposed on the lever by the cam crosses a vector of force imposed on the lever by the SMA wire.

In some embodiments the rotary encoder comprises an elastic component in s with the SMA wire such that strain caused by the cam is divided between the elastic component and the SMA wire. This elastic component may, for example, form part mechanisms configured to de-amplify or reduce the movement of the edge of the foil abutting the cam, such that the change in length of the SMA wire is less than the movement of the edge of the follower abutting the cam.

In some embodiments the means for generating an output signal is configurec measure an electrical characteristic of the SMA wire, the electrical characteristic heir dependent on the strain of the SMA wire. The electrical characteristic may, for exam be a measure of the resistance of the SMA wire.

In some embodiments the rotary encoder comprises a temperature sensor configured to measure the ambient temperature of the SMA wire, wherein the means generating an output signal take into account the ambient temperature, such that the c signal is dependent on the temperature signal. This is because the ambient temperatu may affect the electrical characteristic of the SMA wire. Taking into account the temperature signal thus may allow a more accurate measure of the angular position o cam.

In some embodiments the rotary encoder comprises at least one pair of SMA arranged such that when the strain of one SMA wire of the pair increases the strain o: other SMA wire of the pair decreases. Put another way, the pair of SMA wires may comprise opposing SMA wires. The output signal may be dependent on a difference between the strains of the pair. In some embodiments the rotary encoder comprises å plurality of said pair, wherein the pairs have different relationships between the angu position of the cam and the difference between the strains of the pair. In some embodiments the means for generating an output signal is configured to measure a difference between the electrical characteristics of the SMA wires of the pair, the difference between the electrical characteristics being dependent on the difference be the strains of the pair.

In some embodiments the SMA wire is arranged to be taut (i.e. in tension) foi angular positions of the cam. In some embodiments the SMA wire is a super-elastic wire.

In some embodiments the rotary encoder comprises a temperature conditionei configured to control a temperature of the SMA wire to a target range. The temperat conditioner may, for example, comprise an electrical power supply configured to pro supply electrical power (e.g. in the form of voltage or power pulses) to the SMA win

In some embodiments the cam has a profile that is mirror symmetric in the pi perpendicular to the rotation axis. The profile may be eccentric or irregular about the rotation axis. The profile may have an edge, wherein the distance between the edge i the rotation axis changes with angular position about the rotation axis.

The various features of the aspects of the present invention set out above may applied equally to other aspects of the present invention.

To allow better understanding, embodiments of the present invention will no\ described by way of non-limitative example with reference to the accompanying dra\ in which:

Figure 1 is a schematic diagram of a rotary encoder;

Figure 2 schematically illustrates the rotary encoder shown in Figure 1 at a different angular position;

Figure 3 is a schematic view of a rotary encoder;

Figure 4 is a graph showing the relationship between angular position of the c and the distance from the rotation axis to the edge of the cam that abuts the lever of tl rotary encoder shown in Figure 3;

Figure 5 is a schematic diagram of a rotary encoder;

Figure 6 is a schematic diagram of a rotary encoder;

Figure 7 is a schematic diagram of a pivoted lever of a rotary encoder;

Figure 8 is a schematic diagram of a rotary encoder;

Figure 9 is a schematic diagram of a modified version of the rotary encoder si in Figure 8;

Figure 10 is a schematic diagram of a modified version of the rotary encoder shown in Figure 8;

Figure 11 is a schematic diagram of an anti-rotation arrangement;

Figure 12 is a schematic diagram of an anti-rotation arrangement;

Figure 13 is a schematic view of part of a rotary encoder; and

Figure 14 is a schematic view of part of a rotary encoder.

Figure 1 is a schematic diagram of a rotary encoder 1. As shown in Figure 1, rotary encoder 1 comprises a cam 2. The cam 2 is configured to rotate about a rotatic axis 3. For example, the cam 2 may be attached to a shaft 4. The shaft 4 is configun rotate about the rotation axis 3 The cam 2 mav be fixed relative to the shaft 4 such t the cam 2 rotates together with the shaft 4. The shaft 4 may not be part of the rotary encoder 1. The rotary encoder 1 may be configured to output a signal that is indicatr the angular position of the cam 2, which may correspond to the angular position of tb shaft 4. For example, the rotary encoder 1 may be configured to convert the angular position of the cam 2 (or the shaft 4) into an output signal.

As shown in Figure 1, the rotary encoder 1 comprises at least one SMA wire : The SMA wire 5 is arranged to convert the angular position of the cam 2 into a strain the SMA wire 5. The SMA wire 5 is arranged such that its length depends on the am position of the cam 2. This will be described in more detail below.

As shown in Figure 1, the rotary encoder 1 may comprise means 6 for genera an output signal dependent on the strain of the SMA wire 5. By providing that the or signal is dependent on the strain of the SMA wire 5, the output signal is dependent oi angular position of the cam 2. For example, the means 6 for generating the output si _j may be configured to measure an electrical characteristic of the SMA wire 5. The m may generate the output signal as a function of the electrical characteristic, or may oi the measured electrical characteristic as the output signal. The electrical characteristi dependent on the strain of the SMA wire 5. As one example, the electrical characteri may be a measure of the electrical resistance of the SMA wire 5. The means 6 for generating an output signal may measure the electrical resistance of the SMA wire 5. However, alternative electrical characteristics of the SMA wire 5 may be measured example, the means 6 for generating an output signal may be configured to measure 1 conductance of the SMA wire 5. The conductance of the SMA wire is dependent on strain of the SMA wire 5. As shown in Figure 1, the means 6 for generating an outpi signal is electrically connected to the SMA wire 5. The electrical connection allows means 6 for generating an output signal to measure the electrical characteristic of the wire 5.

There are different possible ways of measuring the electrical characteristic of SMA wire 5. As one example, the means 6 for generating an output signal is configi apply a current pulse through the SMA wire so as to measure the resistance. An alternative is that the means 6 for eeneratine an oiitnut sienal mav be confieured to a voltage across the SMA wire 5 and a sense resistor (of known resistance) in electrica series with the SMA wire, and measure the voltage across the SMA wire 5 or sense resistor. Other methods for measuring the resistance or conductance or other electric characteristic dependent on the strain of the SMA wire 5 may be known to the persor skilled in the art.

The means 6 may, for example, comprise an integrated circuit (IC) or other controller. The controller is configured to generate the output signal. For example, t controller may be configured to measure the electrical characteristic of the SMA win and generate the output signal as a function of the electrical characteristic. The mean for generating an output signal may be embodied in the controller. The controller or may be a dedicated controller or IC for measurement of electrical resistance of the SI wire 5, or may be embodied (at least in part) on a processor of a device incorporating rotary encoder 1.

The present invention provides a rotary encoder that has a simple constructioi is capable of performing accurate measurements of the angular position of the cam 2. strain of the SMA wire 5 may vary continuously depending on the angular position o cam 2. This allows for a precise measurement of the angular position of the cam 2. present invention makes use of the property of the SMA wire 5 that strain is closely correlated with its electrical characteristics.

Figure 2 is a schematic view of the rotary encoder shown in Figure 1 at a diff angular position of the cam 2. In the view shown in Figure 1, the longest distance fire rotation axis 3 to the edge of the cam is in the up-down direction in the figure. Figur shows the same rotary encoder 1 in which the cam 2 is rotated by 90°. As a result, tb longest distance from the rotation axis 3 to the edge of the cam 2 is in the left-right direction in the figure. As can be seen from a comparison between Figure 1 and Figi the SMA wire 5 is longer in the situation shown in Figure 2 than in the situation shov Figure 1. As a result, the resistance of the SMA wire 5 is different in the two situatic because the resistance (together with other electrical characteristics) is correlated wit strain of the SMA wire 5. Therefore, a measurement of the electrical characteristic o SMA wire 5 allows for an output signal to be generated as indicative of the strain, an therefore indicative of the angular position of the cam 2.

As shown in Figure 1, optionally the SMA wire 5 is arranged in a manner alk continuous rotation of the cam 2. The rotation of the cam 2 is not limited by the SM, wire 5. The cam 2 is arranged to freely rotate. The SMA wire 5 is arranged relative cam 2 such that the SMA wire 5 does not constrain the cam 2 from rotating. Optiona the cam 2 is arranged to continuously rotate by at least 90°, optionally by at least 18C and optionally by at least 360°. This allows a greater range of angular positions of th 2 to be measured. This may also improves the accuracy of the rotary encoder 1 becai the measurement is unaffected by any mechanical limitation that the wire 5 may othe place on the rotation of the cam 2.

However, it is not essential that the cam 2 may freely rotate. In an alternative arrangement, the SMA wire 5 may be arranged to constrain, to an extent, the rotation the cam 2. For example, the SMA wire 5 may be fixedly connected to the cam 2.

As shown in Figure 1, optionally the rotary encoder 1 comprises a mechanisn configured to intermediate between the cam 2 and the SMA wire 5. The SMA wire f the mechanism 7 are arranged such that the angular position of the cam 2 is convert» the strain of the SMA wire 5. The mechanism 7 is configured to allow the cam 2 to f rotate without being hindered by the SMA wire 5. The mechanism 7 may comprise e contact region configured to abut the cam and to slide along the egde of the cam as tl cam rotates.

As shown in Figure 1, optionally the mechanism 7 comprises a lever 8. The ί wire 5 is fixed to the lever 8. The lever 8 is arranged such that its movement affects 1 length of the SMA wire 5. The lever 8 is arranged relative to the cam 2 such that the 2 converts the angular position of the cam 2 into a rotational position of the lever 8. lever 8 strains the SMA wire 5 dependent on the rotational position of the lever 8.

As shown in Figure 1, the lever 8 may be provided with connection element S as a crimp 9. The connection element or crimp 9 may be integrally formed with the 1 8. The crimp 9 may be provided at one end of the lever 8. Alternatively, the lever 8 extend bevond the nosition at which the crimn 9 is nrovided The crirrm 9 is confiem hold the SMA wire 5 such that the SMA wire 5 is fixed to the lever 8. Optionally, or of the SMA wire 5 is attached to the crimp 9 at the lever 8. Alternatively, the SMA \ may continue beyond its position where it is attached to the lever 8. It will be apprec that instead of the crimp 9, any other connection element that can fixedly connect to 1 SMA wire 5 may be used.

As shown in Figure 1, optionally the lever 8 comprises a fixed base 10. The l 10 is stationary. For example, the base 10 may be fixed to a support structure 14 (no shown in Figure 1). The position of the base 10 (and the position of the support strut 14) is stationary with respect to the rotation axis 3.

As also shown in Figure 1, in an embodiment the lever 8 comprises a pivot 11 The pivot 11 may be provided by a flexure. The flexure may be a particularly thin p _< the lever 8. The flexure is configured to allow the rotational position of the main hoc the lever 8 to rotate when a force is exerted on it. This can be seen from a compariso between Figure 1 and Figure 2. In the situation shown in Figure 2 the cam 2 exerts a approximately in the left-to-right direction on the main body of the lever 8. As a resi flexure at the pivot 11 bends such that the main body of the lever 8 becomes angled compared to its position in Figure 1. This causes the end of the lever 8 to which the ! wire 5 is fixed to move away from the fixed wire terminal 12. The fixed wire termin has its position fixed relative to the rotation axis 3 and the base 10 of the lever 8. Th terminal may be fixed relative to the support structure 14. The movement of the leve away from the wire terminal 12 causes the SMA wire 5 to lengthen. This increases tl strain of the SMA wire 5.

The lever 8 provides a mechanically simple way for the rotational position of cam 2 to be converted into the strain of the SMA wire 5, without constraining rotatio the cam. The rotational position of the lever 8 can vary continuously over a range of values such that a continuous range of measurements of the angular position of the ci is possible. This is an improvement over known rotary encoders that can determine å angular position only among a given set of discrete values.

Figure 3 is a schematic diagram of the rotary encoder 1 arranged differently f the rotarv encoder shown in Fieures 1 and 2 Tn the arraneement shown in Fieure 3 cam 2 is eccentric or irregularly shaped about the rotation axis 3. However, for purel illustrative purposes, the eccentricity of the cam 2 is not as exaggerated as in Figures 2. The features that are the same as described above in relation to Figures 1 and 2 an described again below in order to avoid redundancy of description.

As shown in Figure 3, optionally the rotary encoder 1 comprises a plurality oi SMA wires 5. As will be described in conjunction with Figure 4, the SMA wires 5a, are arranged to have different relationships between the angular position of the cam 2 the strain of the SMA wire 5. This allows the angular position of the cam 2 to be determined uniquely over a wider range of possible angular positions of the cam 2.

As shown in Figure 3, the rotary encoder 1 may be provided with two levers i The levers 8a, 8b have neutral positions that are at different angles. In the example s in Figure 3, the neutral positions of the levers 8a, 8b are approximately perpendiculai each other. The levers 8a, 8b are arranged relative to the cam 2 such that they abut tl cam 2 at positions that are approximately 90° separated from each other. In general, positions at which the levers 8a, 8b abut the cam 2 may be spaced apart by an angle between 0° and 180°, preferably between 45° and 135°. As shown in Figure 3, the le 8a, 8b are associated with respective SMA wires 5a, 5b. The SMA wires 5a, 5b may arranged at different angles relative to each other. For example, the SMA wires 5a, 5 may be arranged perpendicularly to each other.

As shown in Figure 3, optionally the levers 8a, 8b share a common base 10. Alternatively, the levers 8a, 8b may have separate bases 10.

As the cam 2 rotates, the levers 8a, 8b change their rotational position accordi the angular position of the cam 2. The rotational position of the first lever 8a depend the first distance X between the rotation axis 3 and the edge of the cam 2 that abuts tl first lever 8a. The second lever 8b has a rotational position that depends on the secoi distance Y between the rotation axis 3 and the edge of the cam 2 that abuts the secon lever 8b.

Figure 4 is a graph showing the relationship between the angular position of t cam 2 (along the x axis) and the distances X, Y (along the y axis). The angular positi the cam 2 is measured relative to an arbitrarv fixed annular nosition Tn Fieure 4 the arbitrary fixed angular position used as the reference point is the position at which th distance from the rotation axis 3 to the edge of the cam is at its greatest in the left-to- direction in Figure 3. Accordingly, at 0°, the first distance X is at its maximum valui shown by the upper-line in Figure 4. This causes the first lever 8a to take its most ex position that causes the greatest strain to the first SMA wire 5a. When the cam 2 is r by 180°, the first distance X takes its minimum value, indicated by the lower-line in ] 4. The first distance X gradually decreases from 0° to 180° degrees. From 180° to 3 the first distance X gradually increases. Optionally, as indicated in Figure 4, the cam may have a profile that is mirror symmetric in the plane perpendicular to the rotation 3.

The relationship between the angular position of the cam 2 and the strain of tl SMA wire 5 is different for the second SMA wire 5b. At the angular position of 0°, 1 second distance Y is at a mid-point between its maximum and minimum possible val As the cam 2 is rotated to 90°, the distance Y gradually increases to its maximum val From 90° to 270°, the second distance Y gradually decreases from its maximum valu its minimum value. From 270° to 360° (which is equivalent to 0°), the second distan gradually increases from its minimum value to its mid-point value.

If only the first SMA wire 5a the first lever 8a were provided (i.e. if the secon SMA wire 5b and the second lever 8b were omitted), then a measurement of the strai the first SMA wire 5a could correspond to multiple possible angular positions of the 2. For example, if the strain of the first SMA wire 5a were measured indicating that first distance X took its mid-point value between its maximum and minimum possibl values, then this could mean that the angular position of the cam 2 is either 90° or 27 least for a mirror-symmetric cam profile). By providing a plurality of SMA wires 5a ambiguity can be avoided. As can be seen from Figure 4, at the angular positions of and 270°, the second distance Y is different, leading to different strain measurements the second SMA wire 5b. Optionally, the output signal is dependent on a combinatic the strains of the SMA wires 5 a, 5b.

The number of SMA wires 5 may be two, three or four, for example (as will 1 described below! Optionally, each SMA wire 5 is attached to a crimp 9 mounted on the lever 8. Optionally, the rotary encoder 1 comprises a resilient component (not shown) configi to bias the lever 8 against the cam 2. For example, the resilient component may be a spring. The lever 8 may be sprung against the eccentric cam 2 which is mounted to t shaft 4. As the cam 2 rotates the lever arms move in and out stretching the SMA wir The bias force helps to ensure that when the cam 2 rotates, the lever 8 moves in and ( This can help to reduce slop, thereby improving the accuracy of the rotary encoder 1.

Optionally, the SMA wire 5 is a super-elastic SMA wire 5. By providing tha1 SMA wire 5 is super-elastic, the SMA wire may remain taut at all times for larger movement of the follower compared to standard SMA wire. Providing that the SMA 5 remains in tension, the correlation between the angular position of the cam 2 and tb electrical characteristic of the SMA wire 5 is strengthened. It is desirable for the SM wire 5 to be arranged to be taut, (i.e. in tension) for all angular positions of the cam 2

It is not essential for the cam to have a profile that is mirror symmetric in the perpendicular to the rotation axis 3. In an alternative arrangement, the edge of the ca may have, for example, a spiral shape. Optionally, for each angular position of the c; there is a unique distance from the rotation axis 3 to the edge of the cam 2. This can angular position of the cam 2 to be uniquely identified by using only one lever 8 and SMA wire 5, for example.

Alternatively, by providing a mirror symmetric cam, the distance from the ro1 axis 3 to the edge of the cam 2 may vary continuously (i.e. without discontinuities) f( angular positions of the cam 2. This helps the cam 2 to rotate through more than 360 without requiring a mechanism that overcomes a step change in the distance from the rotation axis to the edge of the cam 2. This also ensures that bi-directional rotation o cam 2 is not constrained by the rotary encoder 1.

Figure 5 is a schematic diagram of a rotary encoder 1 arranged differently fro those shown in Figures 1-3. The rotary encoder 1 comprises an eccentric cam 2 confi to rotate about the rotation axis 3. Functions of components of the rotary encoder 1 1 are the same as in those described above are not repeated here to avoid redundancy o description. As shown in Figure 5, optionally the rotary encoder 1 comprises four Si wires 5a-5d.

As shown in Figure 5, optionally the mechanism configured to intermediate between the cam 2 and the SMA wire 5 comprises a follower. The follower is arrang abut the cam 2. As the cam 2 rotates about the rotation axis 3, the cam 2 abuts a diff< portion of the follower. Optionally, the follower comprises a body, such as a plate V. The body or plate 13 comprises a hole 17 through which the cam 2 extends. Figure f shows the moment when the cam 2 abuts the inner wall of the hole 17 towards the rig hand side of the diagram. This causes the plate 13 to move towards the right hand si< As the cam 2 rotates, the plate 13 moves in a complementary manner.

In the position shown in Figure 5, the plate 13 is in its rightward most extrem position. This causes the second SMA wire 5b to shorten and the fourth SMA wire 5 lengthen. At a later point in time the cam 2 will have rotated by 180°, causing the ph to take its leftward most extreme position. This causes the second SMA wire 5b to lengthen and the fourth SMA wire 5d to shorten. At another point in time, the cam 2 would abut the inner wall defining the hole 17 at the upper side of the diagram in Fig This causes the plate 13 to take its upward most extreme position, with the first SMA 5a lengthening and the third SMA wire 5c shortening. At another point in time, the c moves the plate 13 downwards (according to the view of Figure 5). This causes the 1 SMA wire 5a to shorten and the third SMA wire 5c to lengthen.

As shown in Figure 5, optionally each SMA wire 5 is connected to the plate 1 plate connection point 15. For example, a crimp fixed to the plate 13 may be provide the plate connection point 15 to hold the SMA wire 5. As shown in Figure 5, optio the rotary encoder 1 comprises a support structure 14. The support structure 14 may a fixed position with respect to the rotation axis 3. The plate 13 moves relative to the support structure 14 when it is moved by the force applied from the cam 2.

As shown in Figure 5, optionally the rotary encoder 1 comprises at least one { SMA wires 5a-5d. Figure 5 shows two pairs of SMA wires. One pair of SMA wires comprises the first SMA wire 5a and the third SMA wire 5c. The other pair of SMA comnrises the second SMA wire 5b and the fourth SMA wire 5d As shown in Fieur optionally the two wires of the pair of SMA wires are provided on opposite sides of t rotation axis 3. The wires may be provided at opposite sides of the follower, for exai the plate 13.

Each pair of SMA wires may comprise two opposing SMA wires. For examf the pair of SMA wires 5a, 5c may be arranged such that when the strain of one SMA 5a of the pair increases the strain of the other SMA wire 5c of the pair decreases. Th described above context of the SMA wires 5a, 5c lengthening or shortening dependir the angular position of the cam 2. Optionally, the output signal of the means for generating an output signal is dependent on a difference between the strains of the pa SMA wires 5a, 5c. As described above, the strains of the SMA wires 5 may be inferi from the electrical characteristics, such as the resistance, of the SMA wires 5. In the arrangement shown in Figure 5, the x-position of the plate 13 can be inferred from th difference in strains between the second SMA wire 5b and the fourth SMA wire 5d. y-position of the plate 13 can be inferred from the difference in strains between the fi SMA wire 5a and the third SMA wire 5c. Hence, the x-position can be inferred from difference in resistance of the second SMA wire 5b and the fourth SMA wire 5d. Th position can be inferred from the difference in resistance of the first SMA wire 5a an third SMA wire 5c.

The x- and y-positions of the plate 13 uniquely identify the angular position c cam 2. In particular, as shown in Figure 5 the rotary encoder 1 may comprise a plura pairs of SMA wires 5a-5d. The pairs may have different relationships between the ai position of the cam 2 and the difference between the strains of the pair. For example shown in Figure 5, the different pairs may be provided in different directions. The directions may be orthogonal to each other as shown in Figure 5. Alternatively, a dif angle may be provided between the directions between 0 and 180°, preferably 45-13i By providing different relationships, the angular position of the cam 2 can be unique! identified from the two pairs of SMA wires.

By providing pairs of SMA wires and measuring the difference in strains betv the wires of the pair, the accuracy of the rotary encoder 1 may be improved. In parth the electric characteristics such as resistance of the SMA wires 5 mav be influenced 1 factors such as the ambient temperature. Different ambient temperatures can undesir affect the accuracy of the rotary encoder 1. Within a pair of SMA wires, the electric; characteristics of both wires within the pair are expected to be influenced in the same by the ambient temperature. As a result, the impact of the ambient temperature on th difference in electrical characteristics is less than the impact of the ambient temperah the electrical characteristics of a single SMA wire. Accordingly, the effect of ambiei temperature or other environmental factors on the accuracy of the rotary encoder 1 is reduced.

Optionally, the means 6 for generating output signal comprises means for measuring a difference in electrical resistance between two SMA wires 5a, 5c. For example, the difference in resistance could be measured by a Wheatstone bridge type arrangement. The skilled person knows of other ways of measuring a difference in electrical resistance between two SMA wires.

Optionally, the rotary encoder 1 comprises a temperature conditioner (not she the figures). Such a temperature conditioner may be provided to any of the types of i encoder 1 described in this document. For example, the temperature conditioner ma; configured to supply electrical power to the SMA wires (e.g. in the form of voltage o current pulses) so as to heat the SMA wires. The SMA wires may cool by convectioi conduction or radiation when the supply of electrical power is ceased. The temperah conditioner is configured to control a temperature of the SMA wire 5 to a target rang _' The temperature conditioner may help to reduce the effect of ambient temperature on electrical characteristics of the SMA wire 5, which could otherwise reduce the accur; the rotary encoder 1. The temperature conditioner may keep the temperature of the S wire 5 steady, for example maintaining the temperature within a target range or at a t temperature. This helps to keep the relationship between the angular position of the and the strain of the SMA wire 5 more predictable and reliable.

Optionally the temperature conditioner is configured to maintain the SMA wi within a temperature range of 60°C-80°C, preferably a temperature of about 70°C. A such temperatures, the SMA wire may 5 may undergo less hysteresis. This can help imnrove the acciiracv of the rotarv encoder 1 Optionally, the rotary encoder 1 comprises a temperature sensor (not shown ii figures). The temperature sensor is configured to measure the ambient temperature c SMA wire 5. The electrical characteristics of the SMA wire 5 may be affected by th< ambient temperature. By measuring the ambient temperature, the ambient temperatu be taken into account. Optionally, the means 6 for generating an output signal take ii account the ambient temperature, such that the output signal is dependent on the temperature signal. The temperature sensor can improve the accuracy of the rotary encoder 1. Such a temperature sensor can be provided to any of the types of rotary encoder 1 described in this document. Optionally the temperature sensor comprises : thermistor.

As shown in Figure 5, the SMA wire 5 may be connected to the support struc 14. For example, an end of the SMA wire 5 may be attached to the support structure a support connection point 16. A crimp may be provided at the support connection p 16. The crimp may be fixed to the support structure 14. The crimp may be configun hold the SMA wire 5.

Figure 13 is a schematic side view of part of a rotary encoder 1. The rotary encoder 1 shown in Figure 13 is of a similar type to that shown in Figure 5 in that it comprises a follower plate 13 that is moved by the rotation of the cam 2.

As shown in Figure 13, optionally one of the cam 2 and the plate 13 comprise flange 18. A major surface of the other of the cam 2 and the plate 13 abuts against tli flange 18. In the example shown in Figure 13, the cam 2 comprises the flange 18. T flange 18 may be formed integrally with the shaft 4. The flange 18 may be formed integrally with the cam 2. The cam 2 may be formed integrally with the shaft 4. The lower major surface of the plate 13 abuts against the flange 18.

The flange 18 helps to align the plane of the cam 2 with the plane of the plate Planes of the cam 2 and the plate 13 align at least partially so that the cam 2 applies a lateral force so as to move the plate 13 depending on the angular position of the cam Misalignment between the cam 2 and the plate 13 could break the link between the ai position of the cam 2 and the movement of the plate 13, thereby making the rotary er 1 less reliable Rv nrovidine that the maior surface of the nlate 13 abuts aeainst the f 18, the axial position of the plate 13 relative to the cam 2 is kept more stable. The m surfaces of the cam 2 and of the plate 13 extend perpendicular to an axis parallel to tl rotation axis 3. Optionally, an elastic component may be provided configured to bias plate 13 against the flange 18.

By providing the flange 18, the thickness of the cam 2 and the plate 13 can be reduced without unduly increasing the risk of misalignment between the cam 2 and tl plate 13. For example, the cam 2 may have a thickness of at most 1mm, optionally a 500pm, optionally at most 200pm, and optionally at most 100pm.

Figure 14 shows an alternative arrangement of the flange 18. In the example shown in Figure 14, the plate 13 comprises a flange 18. A major surface of the cam ' abuts against the flange 18. Optionally, the flange 18 may be formed integrally with plate 13. Optionally, an elastic component may be provided configured to bias the fl 18 against the cam 2.

As will be described with reference to Figure 11 and Figure 12, optionally the rotary encoder 1 comprises an anti-rotation arrangement 20. The anti-rotation arrang 20 is configured to constrain rotation of the plate 13 about an axis parallel to the rotai axis 3 of the cam 2 caused by friction with the cam 2. The anti-rotation arrangement configured to reduce any undesirable rotation of the plate 13. Undesirable rotation o: plate 13 can be caused by friction from the cam 2 as the cam 2 rotates and abuts agaii follower plate 13. The anti-rotation arrangement 20 is expected to improve the accur the rotary encoder 1.

Figure 11 is a schematic diagram of one type of anti-rotation arrangement 20 the rotary encoder 1. In the example shown in Figure 11, the anti -rotation arrangeme comprises a bearing arrangement 21. The bearing arrangement 21 is configured to constrain rotation of the moveable part 19 relative to the support structure 14. The moveable part 19 may comprise or be fixed to the plate 13. The rotation that is constrained is rotation about an axis parallel to the rotation axis 3 of the cam 2. The bearing arrangement 21 comprises a first pair of flexure arms 22. The first pair of fie arms 22 are configured to allow movement in one of two orthogonal directions in the nemendiciilar to the rotation axis 3 The first nair of flexure arms 22 is confieured to restrain movement in any other direction. The bearing arrangement 21 comprises a s pair of flexure arms 23. The second pair of flexure arms is configured to allow move in the other of the two orthogonal directions in the plane perpendicular to the rotatior 3. The second pair of flexure arms 23 is configured to constrain movement in any ot direction. In combination, the two pairs of flexure arms 22, 23 are configured to alio movement in the two orthogonal directions (x and y) in the plane perpendicular to th< rotation axis 3 and to constrain rotation about the rotation axis 3 or an axis parallel to rotation axis 3. Optionally, the bearing arrangement 21 is formed as a single piece, i. integrally. The bearing arrangement 21 may be rigidly connected to the moveable pa and the support structure 14, or may be integrally formed with the moveable part 19 _< the support structure 14.

Another type of anti-rotation arrangement 20 for the rotary encoder 1 is depic Figure 12. The anti-rotation arrangement 20 comprises a bearing arrangement 21. T bearing arrangement 21 is an arrangement of rolling bearings connected between the support structure 14 and the moveable part 19. The rolling bearings may be ball bear roller bearings or rocker bearings, for example. The rolling bearings may comprise a rolling element that bears upon two bearing surfaces. Optionally, the bearing arrangi 21 comprises two rolling bearings 24, 25 that are arranged in mechanical series betw the moveable part 19 and the support structure 14. Optionally, the bearing arrangerm comprises a first rolling bearing 24. The first rolling bearing is configured to allow movement in one of the two orthogonal directions in the plane perpendicular to the rotation axis 3, for example in the x-direction. The first rolling bearing 24 is configu constrain movement in any other direction. The first rolling bearing 24 may compris rolling elements that bear upon a surface of the moveable part 19 and a surface of an intermediary plate 26. The moveable part 19 may move in the x-direction with respe the intermediary plate 26. The bearing arrangement 21 may comprise a second rollin bearing 25. The second rolling bearing 25 is configured to allow movement in the ot the two orthogonal directions in the plane perpendicular to the rotation axis 3, for exå in the y-direction. The second rolling bearing 25 is configured to constrain movemei anv other direction The second rolline bearine 25 mav comnrise rolline elements th bear upon a surface of the support structure 14 and a surface of the intermediary plah The intermediary plate 26 may move in the y-direction with respect to the support structure 14. In combination, the two rolling bearings 24, 25 thus allow movement ii plane perpendicular to the rotation axis 3 and constrain rotation about an axis parallel the rotation axis 3.

The anti-rotation arrangement 20 may comprise any mechanism that constraii rotation of the moveable part 19 relative to the support structure 14. Further exampk such anti-rotation arrangements 20 are disclosed in British patent application GB 2005570.3, which examples are incorporated by reference herein. In general, the ant rotation arrangement comprises two bearing portions connected in mechanical series. Each bearing portion is configured to allow movement in a respective one of two nor colinear directions in a plane of the plate 13.

As described above with reference to Figure 3, optionally the mechanism 7 th intermediates between the cam 2 and the SMA wire 5 comprises at least two followei the example shown in Figure 3, the followers comprise levers 8. The followers may arranged to abut the cam 2 at angular positions about the rotation axis 3 that are offse from each other by an angle of between 0 and 180°, preferably of 45-135°, further preferably of about 90°. In the example shown in Figure 3, the angle between the an; positions at which the levers 8 abut the cam 2 is about 90°. A further example of sue mechanism 7 comprising at least two followers is provided below.

Figure 6 is a schematic diagram of a rotary encoder 1. In the example shown Figure 6, the rotary encoder 1 comprises four levers 8a-8d associated with four respe SMA wires 5a-5d. Rotation of the eccentric cam 2 causes the levers 8a-8d to rotate depending on the angular position of the cam 2. The rotational positions of the lever: 8d affect the strain of the respective SMA wires 5a-5d. The levers 8a-8d are configu rotate about pivots 11. The pivots 11 may be formed by flexures.

As depicted in Figure 6, optionally the mechanism 7 that is configured to intermediate between the cam 2 and the SMA wire 5 is configured to convert a cha distance from the rotation axis 3 to the edge of the cam 2 abutting the follower (e.g. t lever 81 into a chanee in leneth of the SMA wire 5 As shown in the examnle of Fiei optionally the mechanism 7 is configured such that the change in length of the SMA is smaller than the change in distance. For example, as shown in Figure 6, optionally distance between the point at which the cam 2 abuts the lever 8 and the pivot 11 is gr than the distance between the pivot 11 and the crimp 9 (i.e. where the SMA wire 5 connects to the lever 8). Hence, the eccentricity of the cam 2 is geared down as it is converted into a change in strain of the SMA wire 5. This can help to improve the accuracy of the rotary encoder 1. In particular, it can be difficult to manufacture the to have exactly the targeted eccentricity. By gearing down the changes in eccentricit they are converted into changes in strain of the SMA wire 5, any accuracies in the sh the cam 2 are less likely to undesirably affect the accuracy of the rotary encoder 1.

Alternatively, as shown in Figure 3, the mechanism 7 may be configured suet the change in length of the SMA wire 5 is larger than the change in distance from the rotation axis 3 to the edge of the cam 2 abutting the follower (e.g. the lever 8). As sh in Figure 3, optionally the distance from the pivot 11 to the point at which the cam 2 the follower (e.g. the lever 8) is less than the distance from the pivot 11 to the point a which the SMA wire 5 connects to the follower. This can help to improve the resolu of the rotary encoder 1. In particular, this may help to measure particularly small differences in angular position of the cam 2.

Figure 7 is a schematic diagram of part of a rotary encoder 1. Figure 7 shows lever 8 as the follower for the eccentric cam 2. The lever 8 is configured to rotate ah pivot 11. The pivot 11 may be formed by a flexure. In the example shown in Figure intermediary mechanism 7 is configured such that the change in distance from the ro1 axis 3 to the edge of the cam 2 abutting the follower is converted into a smaller chanj length of the SMA wire 5.

As shown in Figure 7, optionally the lever 8 is arranged such that a force imp on the lever 8 by the cam 2 comprises a force component that opposes a force imposi the lever 8 by the SMA wire 5. As mentioned above, the SMA wire 5 is in tension. SMA wire 5 imposes a force on the lever 8 via the crimp 9. In the view provided in 1 7, the SMA wire 5 imposes a force on the lever 8 in the left to right direction. The fc imnosed bv the cam 2 on the lever 8 is shown as an arrow in Fieure 7 As shown in 1 7, the main component of the force is perpendicular to the SMA wire 5. The force al includes a component parallel to the SMA wire 5. The component that is parallel to 1 SMA wire 5 opposes the force imposed on the lever 8 by the SMA wire 5.

As shown in Figure 7, optionally the lever 8 comprises a flexure configured t< as the pivot 11 for the lever 8. The flexure may extend in a direction that is aligned \ point 27 where a force vector of force imposed on the lever 8 by the cam 2 crosses a vector of force imposed on the lever 8 by the SMA wire 5. The point 27 where the fc vectors is shown in Figure 7. An imaginary line is shown as a dashed line in Figure ' The imaginary line corresponds to the direction in which the flexure extends 11. The flexure that acts as a pivot 11 is oriented so that the force through the pivot 11 places pivot 11 in tension so as to reduce distortion of the pivot 11 by the varying forces. T can help to improve the reliability and/or stability of the rotary encoder 1.

Figure 8 is a schematic diagram of a rotary encoder 1. As shown in Figure 8, rotary encoder 1 comprises a follower plate 13 moved by rotation of the cam 2 about rotation axis 3. As the follower plate 13 is moved, the lengths of the SMA wires 5 ar changed. The strain of the SMA wires 5 indicates the angular position of the cam 2. Optionally, the SMA wires 5 are connected at one end to the follower. For example, end of each SMA wire 5 may be fixed to the follower plate 13. The other end of the wires 5 may be provided at a fixed wire terminal 12. The fixed wire terminals 12 ma fixed relative to the support structure 14.

In an alternative arrangement, the SMA wires 5 may be fixedly connected to 1 cam 2. However, by providing the intermediary mechanism 7, the rotation of the car less limited.

Another method of controlling the extent to which motion of the cam 2 transl into a change in strain of the SMA wire 5 is described below in Figure 9 and Figure 1 Figure 9 is a schematic diagram of a rotary encoder 1. The rotary encoder 1 may be < similar type to as shown in Figure 8. Alternatively, the features described below ma; applied to the rotary encoder of any of the other arrangements described herein.

As shown in Figure 9, optionally the rotary encoder 1 comprises an elastic comnonent 28 The elastic comnonent 28 is in series with the SMA wire 5 such that caused by the cam 2 is divided between the elastic component 28 and the SMA wire The elastic component 28 may comprise a spring. The elastic component 28 allows 1 greater deflections of the cam 2, while keeping the deflection of the SMA wire 5 the and still proportional to the movement of the cam 2. Preferably, the stiffness of the e component 28 is linear. This helps the elastic component 28 to gear down motions o cam 2 into strains of the SMA wire 5 in a predictable manner. As shown in Figure 9, optionally the elastic component 28 is connected between the SMA wire 5 and the follower (e.g. plate 13, or lever 8 in other arrangements).

Figure 10 is a schematic diagram of an alternative arrangement in which the e component 28 is provided at the other end of the SMA wires 5. As shown in Figure optionally the SMA wire 5 is connected between the elastic component 28 and the follower.

The term SMA wire may refer to any element comprising SMA. The SMA v may have any shape that is suitable for the purposes described herein. The SMA wir be elongate and may have a round cross-section or any other shape cross-section. Th cross-section may vary along the length of the SMA wire. It is also possible that the length of SMA wire may be similar to one or more of its other dimensions. The SM/ may be flexible. Optionally, when connected in a straight line between two elements SMA wire can apply only a tensile force which urges the two elements together.

The above-described embodiments show a cam and a follower remaining in continuous contact with the cam, where the SMA wire is arranged to the contract and elongate on movement of the follower. However, provision of the follower is not ess and the SMA wire itself may, in alternative embodiments, act as a follower to the car For example, the SMA wire may be connected at both ends to the support structure 1 (either directly or via resilient elements) and may bend around the cam. So, the SM/ ⁵ may comprise two straight end portions that are angled relative to each other. A mid portion of the SMA wire may remain in direct contact with the cam and be arranged 1 slide along the cam on rotation of the cam. Due to the eccentric cam profile, cam rot may thus be directly converted into a change in length of the SMA wire, thus allowin annular nosition of the cam to be determined Although the embodiments described above comprise a cam and a follower tc allow for continuous rotation, this is not essential and the cam may in general be repl by any generic rotatable part. The SMA wire may, for example, be directly connecte the rotatable part. The rotatable part may be arranged to rotate within a limited range angular positions (e.g. at least within a range of 360 degrees, or at least within a rang 270 degrees, or at least within a range of 180 degrees), but need not be arranged to rc continuously.

Those skilled in the art will appreciate that the present disclosure should not 1 limited to the specific configurations disclosed in this description of the preferred embodiment. Those skilled in the art will recognise that, unless evidently incompatil features from different arrangement may be combined together. Those skilled in the will recognise that the present invention has a broad range of applications, and that tl embodiments may take a wide range of modifications without departing from the sco the claims.