Combined torque and velocity sensor

Abstract

Combined Torque and Velocity Sensor A combined torque and rotational velocity sensor (10) is provided for simultaneously measuring a torque applied thereto and a rotational velocity thereof. The sensor (10) comprises a first rotary encoder (12), a second rotary encoder (14), and a torsion bar (16) interconnecting the encoders (12, 14). The encoders (12, 14) are arranged such that a relative phase therebetween is detectable to determine a torque applied to sensor (10), and one of the encoders (12, 14) is configured as an absolute or pseudo-absolute encoder to in-use simultaneously measure a rotational velocity of the sensor (10).

Description

[0001] Combined Torque and Velocity Sensor

[0002] FIELD OF INVENTION

[0003] The present invention relates to a torque sensor, and more particularly to a combined torque and velocity sensor utilising two position encoders.

[0004] BACKGROUND

[0005] Torque sensors have many applications, such as precisely controlling motors in robotic arms and variable motor control in electric bikes.

[0006] It is common in such applications where torque is to be measured to also measure rotational or angular velocity. Existing torque sensors currently measure only torque, and a separate position or velocity sensor is required to obtain a measurement of angular velocity, leading to increased complexity and cost.

[0007] The present invention seeks to provide a solution which obviates or overcomes the above-mentioned deficiencies.

[0008] STATEMENTS OF INVENTION

[0009] According to a first aspect of the invention, there is provided a combined torque and rotational velocity sensor for simultaneously measuring a torque applied thereto and a rotational velocity thereof, the combined torque and rotational velocity sensor comprising: a first rotary encoder; a second rotary encoder; and a torsion bar interconnecting the first rotary encoder and second rotary encoder; the first and second rotary encoders being arranged such that a relative phase therebetween is detectable to determine a torque applied to the combined torque and rotational velocity sensor via a drive input connected thereto; and the first or second rotary encoder being configured as an absolute or pseudo-absolute encoder to in-use simultaneously measure a rotational velocity of the combined torque and rotational velocity sensor.

[0010] By utilizing one of the encoders of the torque sensor as a rotational velocity sensor, it becomes possible to provide a compact means of measuring both rotational velocity and torque simultaneously within the moving parts of an apparatus such as an e-bike or cobot.

[0011] The first or second rotary encoder may be provided as a unitary absolute encoder.

[0012] Absolute encoders allow for the position of the encoders and therefore the relative phase between them to be measured as soon as the combined torque and velocity system is powered, without first requiring position to be calibrated.

[0013] The combined torque and rotational velocity sensor may further comprise a static reference component forming a pseudo-absolute encoder.

[0014] The terms static reference component is intended to refer to static positioning with respect to a housing of the encoder or the sensor itself. A static reference component enables determination of angular position to allow an incremental encoder to act as an absolute encoder.

[0015] Optionally, the static reference component may be positioned between the first and second rotary encoders.

[0016] Utilising a static reference component between the encoders may provide relative phase or position calculation between the encoders at power on.

[0017] In an alternative arrangement, the static reference component may be positioned offset to the torsion bar.

[0018] A lateral offset of the static reference component may simplify assembly of the sensor, since the sensing components can be integrally formed or fixed to a housing of the sensor or an apparatus to which it is mounted.

[0019] Preferably, the first rotary encoder and / or the second rotary encoder may be a capacitive encoder.

[0020] Capacitive sensing has many advantages, since they are immune to external interference from, for instance, dust, debris, and magnetic fields. Capacitive sensors also have high tolerance for inaccuracy in the assembly of the combined torque and velocity sensor. As such, the capacitive arrangement has a very wide tolerance, whilst retaining excellent accuracy.

[0021] Optionally, there is a static reference component positioned between the first and second encoders, the static reference component comprising at least one transceiver thereon for determining the relative phase between the first and second encoders.

[0022] Alternatively, at least one of the first and second encoders may include a static reference component and a pair of rotary components respectively including a transmitter and a receiver for determining a rotational velocity of the combined torque and rotational velocity sensor.

[0023] In one embodiment, the first rotary encoder and / or the second rotary encoder may be a magnetic encoder.

[0024] Magnetic sensors can be manufactured to require low power input, and therefore in some circumstances may be preferable to capacitive sensors.

[0025] In an alternative embodiment, the first rotary encoder and / or the second rotary encoder may be an optical encoder.

[0026] Optical encoders have higher accuracy and resolution than magnetic encoders, though are more prone to interference from environmental conditions.

[0027] Preferably, the relative phase may be detectable via a moire pattern or beat frequency between the first rotary encoder and the second rotary encoder.

[0028] Optionally, the first and second rotary encoders have a different pitch to produce a vernier scale.

[0029] The use of moire patterns, beat frequencies, or a vernier scale significantly improves the accuracy of the relative phase measurement between the two encoders within the sensor.

[0030] Preferably, the torque may be measurable at standstill using the combined torque and velocity sensor . According to a second aspect of the invention, there is provided an electric bicycle comprising a combined torque and rotational velocity sensor in accordance with the first aspect of the invention.

[0031] According to a third aspect of the invention, there is provided a robot having a moveable joint comprising a combined torque and rotational velocity sensor in accordance with the first aspect of the invention.

[0032] The present sensor provides a very suitable and compact arrangement for sensing both rotational velocity and torque, which makes it highly suitable for e- bike and cobot use.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0035] Figure 1 shows an illustrative representation of a first embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention;

[0036] Figure 2 shows a diagrammatic representation of a circuit for measuring torque using the combined torque and rotational velocity sensor of Figure 1 ;

[0037] Figure 3 shows an illustrative representation of a second embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention;

[0038] Figure 4 shows a plan view of an encoder disc used as part of the combined torque and rotational velocity sensor of Figure 3;

[0039] Figure 5 shows an illustrative representation of a third embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention; Figure 6 shows an illustrative representation of a fourth embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention;

[0040] Figure 7 shows an illustrative representation of a fifth embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention; and

[0041] Figure 8 shows an illustrative representation of a sixth embodiment of a combined torque and rotational velocity sensor in accordance with the first aspect of the invention.

[0042] DETAILED DESCRIPTION OF THE DRAWINGS

[0043] Referring to Figure 1 , there is indicated a combined torque and rotational velocity sensor, referenced globally at 10, which is suitable for use in a wide variety of applications in which both torque and velocity sensing is required.

[0044] The combined torque and rotational velocity sensor 10 comprises a first rotary encoder 12 and second rotary encoder 14, each having a support member 15 associated therewith, and a torsion bar 16, which interconnects the support members 15 of the first and second rotary encoders 12, 14. The support members 15 and torsion bar 16 are interconnected or unitarily formed, with the first and second rotary encoders 12, 14 being mounted thereto.

[0045] The torsion bar 16 is deformable such that if a torque is applied on the combined torque and rotational velocity sensor 10 via a drive input Di, torsion in the torsion bar 16 causes a rotational displacement between the first rotary encoder 12 and the second rotary encoder 14. This rotational displacement is proportional to the torque applied to the torsion bar 16, allowing for torque to be measured, since torque is proportional to the torsion on the torsion bar 16, which is measurable in the angular displacement of the end faces 18, 20 of the support members 15, here formed as thicker metal cylinders, of the first and second rotary encoders 12, 14. The drive input Di may be provided by, for example, an external motor. In the depicted embodiment, the combined torque and rotational velocity sensor 10 comprises an input shaft 22, formed by a first support member 15, through which a drive input is provided, as well as an output shaft 24, formed by the other support member 15, through which a drive output Do is transmitted. The combined torque and rotational velocity sensor 10 is thus configured to be attached to measure the torque applied a shaft or crank.

[0046] The torsion bar 16 may be formed as, for example, an elastic member with known rotational stiffness. Torsion bars 16 with high angular stiffness provide a smaller deformation for a given torque than torsion bars 16 with lower angular stiffness, allowing for a larger range of torque to be measured at the cost of some precision. The torsion bar 16 may therefore be chosen based on the expected range of torque to be encountered.

[0047] The deformation of the across the torsion bar 16 is small so that the torsion bar 16 can transfer rotation effectively. The rotational velocity of the output shaft 24 is therefore the same as the rotational velocity of the input shaft 22, shifted only in phase according to the torque. This allows for the combined torque and velocity sensor 10 to be coaxial with a shaft or crank without reducing the transmitted torque and power from the drive input Di to the drive output Do.

[0048] Rotational velocity is simultaneously measured by one or both of the first and second rotary encoders 12, 14. It is preferred that velocity is measured with the first encoder 12, as it provides a more precise measurement of velocity due to being closer to the drive input Di and not affected by the phase shift. In the depicted embodiment, at least one of the first and second rotary encoders 12, 14 is provided as an absolute encoder. An absolute encoder is one which outputs digital information, typically a binary code, regarding the exact rotational position of the encoder, with each output being unique to the rotational position.

[0049] Rotational velocity can be calculated by either incremental or absolute encoders when combined with timing information, for example, from a processor clock, rotational velocity can be calculated. For instance, velocity can be determined from counting a number of pulses or modulation cycles in a given time interval.

[0050] At low velocities, this may be the time it takes to pass a single count.

[0051] Figure 2 shows an example pictorial circuit diagram 26 showing how torque applied on the combined torque and rotational velocity sensor 10 via the drive input Di may be determined by the combined torque and rotational velocity sensor 10.

[0052] The first and second rotary encoder output a respective first digital signal DSi and second digital signal DS2. The example digital signals shown here correspond to a 4-bit encoder. The respective first and second digital signals DS1 , DS2 are then converted into a first analogue signal AS1 and a second analogue signal AS2 by a respective first and second digital-to-analogue converters 28, 30. While the digital-to-analogue converters 28, 30 are here shown as separate components to the encoders, they may be included within the rotary encoders, such that the rotary encoders can be considered to directly output analogue signals AS1, AS2. Analogue signals can achieve a higher absolute resolution via interpolation, but for a sufficiently encoder with sufficiently high-resolution phase can be determined solely using the digital outputs. Each of the analogue signals AS1 , AS2 here have the form of a sawtooth wave with the same period. The period of the analogue signals AS1, AS2 depends on the configuration of the encoders and digital-to-analogue converters 28, 30. Preferably, the period is 360 degrees, equivalent to one full revolution, with a minimum intensity output at 0 degrees which linearly increases with rotation, reaching a maximum intensity immediately before a full revolution has occurred. More preferably, the period of each of the analogue signals AS1, AS2 is equal to the relative angular displacement of the two encoders encountered when the combined torque and velocity sensor is subject to the maximum rated torque, to increase the accuracy of torque measurement over the likely range of torque that will be measured.

[0053] The present invention allows for the measurement of torque not only under the application of torque, but also at standstill, that is, in a zero-external-applied torque scenario. When the combined torque and velocity sensor is at rest or substantially at rest, torque can be measured by comparing the intensity of the first and second analogue signals ASi, AS2, which is proportional to the phase between the two rotary encoders 12, 14 and thus the torque.

[0054] The phase between the first and second analogue signals AS1, AS2 is then measured and thus the torque applied on the combined torque and rotational velocity sensor 10 by the drive input Di can be determined. Alternatively, or additionally, the phase may be measured between each of the corresponding digital signals DS1, DS2 of the first and second rotary encoders 12, 14 and averaged to provide a measurement of the torque applied on the combined torque and rotational velocity sensor 10 during motion.

[0055] The phase is measured using a suitable phase comparator, such as for example by using a mixer-based phase comparator in the case of comparing analogue signals. The phase between corresponding digital signals can be measured by, for example, a digital phase detector comprising an XOR logic gate. It is appreciated that many other suitable methods of measuring phase in an electronic circuit could be utilised without deviating from the scope of the invention.

[0056] Since the first rotary encoder 12 is provided as an absolute encoder, time- stamped rotational position information can be used to determine velocity. Velocity may also be calculated from counting the number of different rotation states outputted by the encoder in a given time span. In a pseudo-absolute or incremental encoder, velocity can be determined simply by counting the pulses in a given time span. For more precise measurement of velocity at slow speeds, velocity can instead be determined by measuring the duration of a given pulse, or in the case of an absolute encoder the duration of a given rotation state. This may be achieved by an associated, or an onboard, processor or integrated circuit.

[0057] A further example of a suitable encoder arrangement for a combined torque and rotational velocity sensor 110 is illustrated in Figure 3. Identical or similar features to those of the first embodiment will be identified using identical or similar reference numerals, and further detailed description is omitted for brevity.

[0058] The first and second rotary encoders 112, 114 are configured to measure torque through the torsion bar 116. The first and second rotary encoders 112, 114 may be optical encoders, an arrangement of which is shown in Figure 3. For each of the first and second rotary encoders, there is provided a light transmitter 132 on one side of a respective first and second encoder disc 136 and a receiver 134 opposed to the light transmitter 132 on the other side of the respective encoder disc 136. The receiver 134 is here in the form of a photodiode. The light transmitter 132 and receiver 134 are stationary relative to one another and can be considered stationary relative to an external environment of the combined torque and velocity sensor, while the encoder disc 136 is attached to and rotate with the input shaft 122, torsion bar 116, and output shaft 124. Of course, the opposite arrangement is also possible, with the transmitter 132 and receiver 134 mounted to the shaft and the encoder disc 136 being connected to the external environment. However, electrical transmission would be more complex in this scenario, and conductive slip rings or similar would become necessary.

[0059] Whilst a transmitter-receiver optical arrangement may be shown, it will be apparent that a single optical encoder integrated chip could be provided which relies on reflective panels on the encoder discs instead of gaps in the disc which allow for light transmission.

[0060] Improved accuracy of the relative measurement may be achieved by use of a vernier scale present on the respective encoders 112, 114, where the first and second encoder are provided with patterns of different spatial frequency.

[0061] The first rotary encoder 112 comprises an encoder disc 136 including a pattern which varies in a circumferential direction of said disc 136 such that each radial portion of the disc 136 has a different arrangement. Such an arrangement is an absolute encoder, in that it provides a unique rotational coding, which provides certain information regarding the rotational position of the first rotary encoder 112. The first rotary encoder 112 provides angular position data when optical data is received at the receiver 134, and thus when combined with timing data, can yield the rotational velocity of the combined torque and rotational velocity sensor 110.

[0062] An exemplary encoder disc 136 is shown in Figure 4. Said encoder disc 136 has 4 tracks, which allows for the detection of 16 unique rotational positions per revolution. In practice, it is intended that the first rotary encoder 112 have much higher resolution, to accurately measure rotational velocity. Preferably, the first rotary encoder 112 may have a resolution of at least 12-bit, which allows for the identification of 4096 unique rotational positions per revolution. More preferably, the resolution of the first rotary encoder 112 is at least 14-bit, which allows for the identification of 16384 unique rotational positions per revolution. Other implementations for ‘n’ absolute encoders are known in the art, and will be similarly applicable within the present invention. No specific limitation is intended by the type of encoder described here.

[0063] The first encoder disc 136 may comprise a pattern according to a Gray code such that any two adjacent portions of the encoder disc 136 differ by only one bit position, which reduces the risk of an incorrect position reading. However, any appropriate code will be feasible, and no limitation is intended by this specific coding.

[0064] Whilst the rotational velocity can be calculated using only the first encoder 112, which is not necessarily the encoder closest to the drive input, it will be appreciated that the second encoder 114 could also be configured to measure rotational velocity, and this may improve the accuracy of the measurement. The rotational velocity measured by the encoder further from the drive input will be slightly out of phase with the measurement from the first encoder because of torsion in the torsion bar.

[0065] Torque is still measured by determination of the relative phase between the first and second rotary encoders 112, 114. A third embodiment of a combined torque and rotational velocity sensor 210 is shown in Figure 5. The first rotary encoder 212 and second rotary encoder 214 comprise a respective first and second encoder disc 236a, 236b and a respective first and second receiver 234a, 234b, here provided as a photodiode, either side of the torsion bar 216. A light transmitter 232 is provided on one side of the encoders 212, 214, opposed to both of the receivers 234a, 234b. It is, however, preferred that all active parts are stationary, in practice, to simplify the wiring of the combined torque and rotational velocity sensor 210.

[0066] The first encoder 212 provides angular position data when optical data is received at the first receiver 234a after interacting with the first encoder disc 236a, and thus the rotational velocity of the drive input can be determined in the same manner as is described in the previous embodiment.

[0067] In this embodiment, the first and second encoder discs 236a, 236b are superposed such that light from the light transmitter 232 interacts with both the first encoder disc 236a, received by the first receiver 234a, and the second encoder disc 236b and is then received at the second receiver 234b. The difference in angular position between the first and second encoder 212, 214 caused by torsion in the torsion bar causes a misalignment between the respective patterns of the first and second encoder discs 236a, 236b, resulting in moire fringes which are detectable by the second receiver 234b. These moire fringes are dependent on the relative rotational displacement between the first and second encoders 212, 214 allowing for the relative displacement and thus the torque to be determined from the moire fringes detected by the second receiver 234b. In some embodiments the beat frequencies of disks 236a and 236b may be slightly different to improve sensitivity.

[0068] Figure 6 shows a fourth embodiment of a combined torque and rotational velocity sensor 310 comprising first and second encoders 312, 314 interconnected by a torsion bar 316 and a static reference component 336 which is positioned between the first and second encoders 312, 314. The static reference component 336 is provided as a printed circuit board 338, comprising one or more transceivers 340. Each of the first and second encoders 312, 314 are capacitive encoders which may be formed on a printed circuit board 342, 344, for instance, having a rotationally encoded pattern thereon.

[0069] As the printed circuit boards 342, 344 of the first and second encoders 312, 314 rotate relative to the static reference component 336, the signals emitted by the transceivers 340 are modulated by respective patterns of the printed circuit boards 342, 344. The modulated signals can be used to determine the rotational positions of the first and second encoders 312, 314, from which rotational velocity and torque can be determined in the same manner as is described in previous embodiments.

[0070] The rotationally encoded pattern on each of the first and second encoders 312, 314 comprise conductive areas separated by gaps. The static reference component 336 is parallel to and disposed between the first and second encoders 312, 314, with the transceivers 340 aligned with the conductive areas of the first and second encoder discs 334a, 334b. The static reference component 336 reads an electrical signal from each of the encoder discs which encodes their position.

[0071] The static reference element 336 comprises a pattern formed as conductive strips on the printed circuit board, with the conductive strips of the static reference component 336 serving as one plate of a capacitor and the conductive areas of the first and second encoders 312, 314 serving as the other. As the printed circuit boards of the first and second encoders 312, 314 rotate relative to the static reference component 336, the conductive strips in the static reference component 336 overlap the conductive areas of the first and second encoders 312, 314 by an area that depends on the position of the static reference component 336 relative to the printed circuit boards of the first and second encoders 312, 314. The transceivers of the static reference element 336 here comprise transmitter elements which comprise a period set of rectangular conductive bars and receiving elements, formed as a single conductive pad.

[0072] In operation, the transmitter elements of the static reference element 336 transmit four excitation signals of equal amplitude which are separated in phase by 90°. The effective capacitance is a function of the area of overlap between the pattern of the static reference component 336 and the respective patterns of the first and second encoders 312, 314. During motion, the capacitance between the conductive strips of the static reference element and the respective conductive areas of the encoders 312, 314 changes. A charge amplifier circuit is used for position detection, with the electrical signal of a charge amplifier being proportional to the effective capacitance. The excitation signals are amplified by a charge amplifier and directed to two identical channels to generate sine and cosine outputs. Interpolation of the sine and cosine outputs yields accurate incremental rotational position information for each of the encoders 312, 314. To achieve absolute positioning, one or both of the encoders comprise one or more additional patterns which are periodic over a full revolution of the disc, which requires substantially less resolution than the patterns used to determine rotational position incrementally. Other patterns such as a Rosetta could be used to generate the incremental encoding.

[0073] Each of the encoders 312, 314 measure position relative to the same static reference component 336, which reduces the material cost and the size of the combined torque and rotational velocity sensor, making this embodiment particularly well suited to uses where space is limited.

[0074] Whilst two transceivers 340 are shown in Figure 6, it will be apparent that sensing could be achieved by a single transceiver.

[0075] The reverse arrangement is also feasible, where the encoded information or pattern is provided on the static reference component 336, and where a transceiver is provided on the rotating parts of the encoders 312, 314. It is preferred that the transceivers 340 are provided on the static reference component 336 for ease of readout connection.

[0076] In addition, capacitive encoders are robust to dust, temperature, and external magnetic fields, allowing for accurate measurement in harsh conditions.

[0077] A fifth embodiment of the combined torque and rotational velocity sensor 410 is shown in Figure 7. The first and second encoders 412, 414 each comprise a rotationally encoded pattern, which can be “read” by a static reference component 436a, 436b to determine the rotational position of the encoders 412, 414, either side of the torsion bar 416. The encoders 412, 414 here may be capacitive, wherein rotational position is determined from a measured capacitance, or magnetic, wherein a rotational position is determined from a measured magnetic field respectively.

[0078] Figure 8 shows a sixth embodiment of a combined torque and rotational velocity sensor 510, comprising first and second encoders 512, 514 interconnected by a torsion bar 516 and a static reference component 536 which is laterally offset from an axis of the torsion bar 516.

[0079] The static reference component 536 here comprises two sensors 554. Each of the first and second encoders 512, 514 are magnetic encoders, here shown as a printed circuit board 556 having circumferential magnetic encoding, by the provision of magnetic tape, embedded magnetic elements or having at least two magnetised portions thereof, that is, having north and south polarity.

[0080] In use, each of the first and second encoders 512, 514 rotate relative to the static reference component 536. The respective first and second sensors 554 detect the change in magnetic field as the printed circuit board 556 rotates and output an electrical signal corresponding to the rotational position of the first and second encoders 512, 514.

[0081] From the rotational position information measured by each of the first and second encoders 512, 514, the velocity and torque can be determined in the same manner as described in previous embodiments. The present combined torque and rotational velocity sensor is suitable for use in electric bicycles, also known as e-bikes, particularly for shifters and throttle control, as well as in robotic joints, particularly for collaborative robots, also known as cobots. For e-bikes, it is typically desirable that the combined torque and rotational velocity sensor be rated up to 85 Nm, with a maximum torque of 320 Nm, and a minimum measurable torque of 1 / 50 of the rated torque.

[0082] Other possible uses of the combined torque and rotational velocity sensor may be in portable devices, tablet foldable displays, flip mobile phones, smart door locks, low-power rotary human-machine interface and push buttons.

[0083] It is therefore possible to provide a combined torque and rotational velocity sensor, particularly suited for use in e-bikes or cobots, in which one of the encoders is specifically configured for the sensing of the rotational velocity simultaneously with the torque measurement. This composite sensor is therefore compact, and highly suited towards use in many settings.

[0084] The words ‘comprises / comprising’ and the words ‘having / including’ when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps, or components, but do not preclude the presence or addition of one or more other features, integers, steps, components, or groups thereof.

[0085] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

[0086] The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention as defined herein.

Claims

Claims1. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) for simultaneously measuring a torque applied thereto and a rotational velocity thereof, the combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) comprising: a first rotary encoder (12; 112; 212; 312; 412; 512); a second rotary encoder (14; 114; 214; 314; 414; 514); and a torsion bar (16; 116; 216; 316; 416; 516) interconnecting the first rotary encoder (12; 112; 212; 312; 412; 512) and second rotary encoder (14; 114; 214; 314; 414; 514); the first and second rotary encoders (12, 14; 112, 114; 212, 214; 312, 314; 412, 414; 512, 514) being arranged such that a relative phase therebetween is detectable to determine a torque applied to the combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) via a drive input (Di) connected thereto; and the first or second rotary encoder (12, 14; 112, 114; 212, 214; 312, 314; 412, 414; 512, 514) being configured as an absolute or pseudo-absolute encoder to in-use simultaneously measure a rotational velocity of the combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510).

2. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in claim 1 , wherein the first or second rotary encoder (12, 14; 112, 114; 212, 214; 312, 314; 412, 414; 512, 514) is a unitary absolute encoder.

3. A combined torque and rotational velocity sensor (310; 410; 510) as claimed in claim 1 , further comprising a static reference component (336; 436a, 436b; 536) forming a pseudo-absolute encoder.

4. A combined torque and rotational velocity sensor (310; 410; 510) as claimed in claim 3, wherein the static reference component (336; 436a,436b; 536) is positioned between the first and second rotary encoders (312, 314; 412, 414; 512, 514).

5. A combined torque and rotational velocity sensor (310; 410; 510) as claimed in claim 3, wherein the static reference component (336; 436a, 436b; 536) is positioned offset to the torsion bar (316; 416; 516).

6. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of the preceding claims, wherein the first rotary encoder (12; 112; 212; 312; 412) and / or the second rotary encoder (14; 114; 214; 314; 414) is a capacitive encoder.

7. A combined torque and rotational velocity sensor (310) as claimed in claim 6, wherein there is a static reference component (336) positioned between the first and second rotary encoders (312, 314), the static reference component comprising at least one transceiver (340) thereon for determining the relative phase between the first and second rotary encoders (312, 314).

8. A combined torque and rotational velocity sensor (410) as claimed in claim 6, wherein at least one of the first and second rotary encoders (412, 414) includes a static reference component (436) and a pair of rotary components (446) respectively including a receiver (452) and a transmitter (450) for determining a rotational velocity of the combined torque and rotational velocity sensor (410).

9. A combined torque and rotational velocity sensor (510) as claimed in claim 1 , wherein the first rotary encoder (512) and / or the second rotary encoder (514) is a magnetic encoder.

10. A combined torque and rotational velocity sensor (110) as claimed in claim 1 , wherein the first rotary encoder (112) and / or the second rotary encoder (114) is an optical encoder.

11. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of the preceding claims, wherein the relative phase is detectable via a moire pattern or beat frequencybetween the first rotary encoder (12; 112; 212; 312; 412; 512) and the second rotary encoder (14; 114; 214; 314; 414; 514).

12. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of the preceding claims, wherein the first and second rotary encoders (12, 14; 112, 114; 212, 214; 312, 314;412, 414; 512, 514) have a different pitch to produce a vernier scale.

13. A combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of the preceding claims, wherein the torque is measurable at standstill.

14. An electric bicycle comprising a combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of the preceding claims.

15. A robot having a moveable joint comprising a combined torque and rotational velocity sensor (10; 110; 210; 310; 410; 510) as claimed in any one of claims 1 to 13.

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