WO2010132926A1

WO2010132926A1 - Torque measuring device

Info

Publication number: WO2010132926A1
Application number: PCT/AU2010/000582
Authority: WO
Inventors: Robert Masterton Smith
Original assignee: Torque Wizz Pty Ltd
Priority date: 2009-05-20
Filing date: 2010-05-18
Publication date: 2010-11-25

Abstract

The present invention provides a device adapted for measuring a first torque (40 + 41) applied to a first body of revolution (21). The first body of revolution (21) comprising a hollow member (22). The device comprising: a first movable member (44) having a fixed portion adapted to be fixed directly or indirectly to the first body of revolution (21), and a movable portion adapted to extend at least partially into or within the hollow member (22); a first interferometer (1, 3, 6, 9, 10, 11, 14, & 16) adapted for location substantially within the hollow member (22), the first interferometer comprising: a first movable mirror (10) adapted to be fixed to the movable portion of the first movable member (44); and, first fixed components (1, 3, 6, 9, 11, 14, 16) comprising a first detector (14) adapted to detect displacement of the first movable mirror (44); and, electrical means (130, 131, 132, 133, 134) for calculating the first torque (40 + 41) from the displacement detected by the first interferometer.

Description

TORQUE MEASURING DEVICE

TECHNICAL FIELD

The present invention relates, in general terms, to apparatus for determining/measuring the torque exerted on a body of revolution, which is capable of being driven rotatably about an axis of rotation. More particularly, but not exclusively, the invention relates to apparatus and means for measuring/recording the torque applied by a cyclist during the pedalling of a bicycle, and more especially a bicycle fitted with a crankset of the type that has an integrated crank and chain ring spider incorporated with a hollow crank spindle.

BACKGROUND ART

Any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure herein.

What are referred to as power measurement devices, for use on or with a bicycle, typically fall into one of two basic categories, firstly devices that measure torque and/or angular velocity in driving components of a bicycle, such as, for example, pedals, cranks, chain ring spider and crank spindle, and secondly devices that measure torque and/or angular velocity in driven components of a bicycle, such as, for example, the chain rings, chain, rear wheel hub and rear wheel.

Measurement of what shall hereinafter be referred to as the pedalling power of a cyclist can be a useful tool, in terms of detection of inefficiencies in cycling techniques and in ultimately achieving better, if not peak, performance. However, what are referred to as bicycle power meters, of the type currently available, for measuring such pedalling power, measure the power being produced by only one leg of the cyclist or, the combined power produced by both legs or, the power produced independently by each leg. One known method of calculating power is by measuring the torque applied to a body of rotation and multiplying the obtained value with the angular velocity of the rotating body. Presently known and in use power meters use strain gauges to sense the torque applied to the driving and driven components of a bicycle. Angular velocity is obtained by measuring the time it takes the driving or driven component to undergo a specific arc of rotation.

Presently known and in use power meters that measure the power produced independently by each leg of a cyclist derive the magnitude of torque applied by the left and right leg in one of three ways. Firstly, by means of torque sensor(s) incorporated and/or associated with each of the left and right cranks or pedals respectively measuring the torque applied by the left and right legs. Secondly, by means of torque sensor(s) incorporated and/or associated with the chain ring spider, which measure the total torque applied in combination by both legs, and this value is subtracted from the value obtained by means of torque sensor(s) incorporated and/or associated with one crank that measure the torque applied by that leg. The difference between these two values is the torque being applied by the other leg. Thirdly, by means of torque sensor(s) incorporated and/or associated with the interface between the crank spindle and chain ring spider, which measure the torque applied by the left leg, and torque sensor(s) incorporated and/or associated with the interface between the chain ring spider and the right crank, which measure the torque applied by the right leg.

Power measurement devices that measure torque and angular velocity of the driven components of a bicycle are described in U.S. Patent No. 6,418,797, to Ambrosina and Pawelka, and European Patent No. 0909940A2, to Polar Electro.

Power measurement devices that measure torque and angular velocity in the driving components of a bicycle are described in the following citations.

Schroberer (EP 0 386 005 B1 ) specifies an arrangement wherein the force exerted on the crank is transferred to the chain ring spider via a deformation element. The deformation of the deformation element is converted to an electrical signal, which is electronically multiplied with angular velocity to give power. The deformation of the deformation element is measured by means of strain gauges, and the angular velocity is derived from the time it takes for the crank to complete one revolution. With Schroberer, only the combined power generated by both legs can be measured.

Gerlitzki (U.S. Patent No. 6,356,847) relates to a method and device for determining torque exerted on a body of revolution capable of being driven rotatably about an axis of rotation. The device therein possesses first and second measurement generators that are arranged on the body of revolution, each with a respective measurement transducer supplying a square-wave output signal in direct response to the measurement generator. With torque applied to the body of revolution, the body of revolution will twist, causing the square-waves to become out of phase. The torque is determined from the distance between the edges of the first and second measurement transducer square-wave signals. This method and device is incorporated within the bottom bracket and spindle unit that is mounted in the bicycle frame, where the body of revolution is the crank spindle. The angular velocity of the spindle is measured several times per crank revolution in this realisation. In a conventional bicycle the right hand crank and chain ring spider are immovably fixed to one another, consequently all the torque applied by the right leg is transferred directly to the chain ring spider and none is transferred to the spindle. Therefore, in Gerlitzki, it is only the power produced by the left leg that causes deformation of the body of revolution and hence this value has to be multiplied by a factor to estimate the total power from both legs, which is not an accurate representation of total power.

Contemporary cranksets have an integrated right crank and chain ring spider incorporated with a hollow crank spindle, which is assembled as an integrated unit that is rotatably mounted on bearings mounted on or within a bicycle frame. The Gerlitzki arrangement is not suited to this latest type of crankset because it is based on a previous generation crankset where the bottom bracket and crank spindle, to which the measurement transducers are attached, is a separate unit that is independent of the cranks.

Yet a further powermeter arrangement is found in Witte (US Patent No. 5,027,303), which describes three arrangements. The first arrangement includes strain gauges mounted on a selected element between the chain ring - A - and the right crank from which the total torque of both legs is determined. The second arrangement is identical to the first with the addition of strain gauges selectively mounted on the right crank. By subtracting the right leg torque from the total torque, the left leg torque is obtained. The third arrangement has strain gauges mounted on both the left and right cranks separately measuring the left and right leg torque.

Smith (US Patent Application Serial No. 12/447637) describes a method that directly and independently measures left and right leg power. The crankset comprises a hollow crank spindle, which at one end has a plurality of equally spaced dogs, a chain ring spider that has a centrally disposed aperture with equally spaced dogs and inner diameter that is complementary with the outer diameter of the crank spindle, and a crank that has an aperture with equally spaced dogs with inner diameter that is complementary with the crank spindle. The crank spindle, chain ring spider, and crank are assembled by interlocking the respective dogs as an integrated arrangement held together with a securing flange. Each dog of the hollow crank spindle, chain ring spider, and crank has a recess to which a strain gauge is attached thereby enabling torque generated by the left and right legs to be independently measured in the direction of pedalling and against that direction.

The solutions described hereinabove may limit customer/user choice of power measuring crankset to only those cranksets and/or bottom brackets that have been specifically manufactured for power measurement. Additionally, and in general, a bicycle is purchased complete with crankset-cum-bottom bracket and these components, or part thereof, become redundant on replacement with the purchase of a such existing power measuring type crankset/bottom bracket, increasing cost to the customer/user as well as increasing environmental waste.

A need exists for a power measurement apparatus that may overcome one or more of the problems associated with the known devices described hereinabove, one which preferably allows measurement, for display, of power generated by both legs of a cyclist, in either the direction of pedalling or against by being readily adaptable to an existing contemporary crankset with hollow crank spindle, without rendering any part thereof redundant. DISCLOSURE OF THE INVENTION

According to one aspect of the present invention there is provided a device adapted for measuring a first torque applied to a first body of revolution, the first body of revolution comprising a hollow member, the device comprising: a first movable member having a fixed portion adapted to be fixed directly or indirectly to the first body of revolution and a movable portion adapted to extend at least partially into or within the hollow member; a first interferometer adapted for location substantially within the hollow member, the first interferometer comprising: a first movable mirror adapted to be fixed to the movable portion of the first movable member; and, first fixed components comprising a first detector adapted to detect displacement of the first movable mirror; and, electrical means for calculating the first torque from the displacement detected by the first interferometer.

The hollow member may comprise one or more parts. It may have several separate cavities or a single cavity. Preferably the hollow member comprises a shaft. In a practical preferred embodiment, the shaft comprises a spindle.

Preferably the first interferometer is adapted to detect the amount of displacement of the first movable mirror. It is also preferred that the first interferometer is adapted to detect the direction of displacement of the first movable mirror.

Preferably the fixed components of the first interferometer comprise a light source, first and second beam splitters, first and second fixed mirrors, and a second detector. Preferably the first detector is adapted to detect the amount of displacement of the first movable mirror, and the second detector is adapted to detect the direction of displacement of the first movable mirror.

In a practical preferred embodiment, the first hollow member comprises a shaft, and the first movable member comprises a rod. Preferably the rod is adapted to extend substantially perpendicularly to the axis of the shaft.

In a practical preferred embodiment, the first body of revolution comprises a spindle or a hub.

Preferably the hub forms part of a crank-set of a bicycle having left and right pedals. Thus, the hub may form part of a chain ring spider of the bicycle. The first torque may substantially result from the combined force applied by the cyclist to both pedals.

Preferably the spindle may form part of a crank-set of a bicycle having left and right pedals. The first torque may substantially result from the force applied by the cyclist to only one of the pedals.

In a further practical preferred embodiment, the hub may form part of a gear wheel. Thus, there may be teeth projecting from the hub.

Preferably the device is adapted for measuring a second torque applied to a second body of revolution which comprises the hollow member. The electrical means is preferably adapted to calculate each of the first and second torques.

In a practical preferred embodiment, the second body of revolution comprises a spindle of the crank-set of the bicycle. The second torque may substantially result from the force applied by the cyclist to only one of the pedals. The electrical means may be adapted to calculate each of the first and second torques either in the direction of or against the direction of pedaling of the cyclist.

Preferably the device further comprises: a second movable member having a fixed portion adapted to be fixed directly or indirectly to the second body of revolution and a movable portion adapted to extend at least partially into or within the hollow member; a second interferometer adapted for location substantially within the hollow member, the second interferometer comprising: a second movable mirror adapted to be fixed to the movable portion of the second movable member; and, second fixed components comprising a third detector adapted to detect the amount of displacement of the second movable mirror, and a fourth detector which is adapted for detecting the direction of displacement of the second movable mirror. The electrical means being preferably adapted to calculate the second torque from the displacement detected by the second interferometer.

Preferably the device comprises an angular position sensor for calculating angular velocity of the hollow member. The electrical means preferably being adapted to calculate power from the torque and angular velocity measurements. Preferably the electrical means is adapted to determine the force applied by the cyclist to the other one of the pedals by subtracting the second torque from the first torque.

Preferably the device comprises a cartridge adapted for fixed insertion into the hollow member. Preferably the first movable member of the first interferometer is adapted to extend at least partially into or within the cartridge. It is also preferred that the first fixed components may be fixed to and substantially housed within the cartridge.

Preferably the second movable member of the second interferometer is also adapted to extend at least partially into or within the cartridge. It is also preferred that the second fixed components may be fixed to and substantially housed within the cartridge.

Preferably at least part of the electrical means is also housed within the cartridge. Preferably there is also a power source housed within the cartridge. It is also preferred that at least part of the angular position sensor is housed within the cartridge.

Thus, the first and second interferometers may be located substantially within different parts or different cavities of the hollow member.

According to a further aspect the present invention may also provide an apparatus for measuring and monitoring torque exerted on a hollow shaft and hub or gear assembly of a machine, the apparatus including a cartridge or the like which is adapted, in use, to be retained within a hollow shaft of the machine, the apparatus further including one or more sensor elements for progressively sensing and generating signals during rotation of a shaft of the machine, which signals are indicative of the torque applied to and angular position of the hollow shaft and hub or gear assembly of the machine.

Preferably the cartridge is of a substantially complementary shape to the hollow crank spindle and may be housed within the spindle. The cartridge may be constructed to arrange and securely mount the one or more sensor elements within the cartridge.

Preferably the sensor elements for progressively sensing and generating signals indicative of the torque applied to the hollow shaft and hub or gear assembly of the machine comprise an optical interferometer. The optical interferometer being preferably adapted, in use, to provide means to sense displacement between the hub or gear assembly and the hollow shaft, the displacement due to torque applied thereto.

Preferably the optical interferometer generate signals that enable by quadrature phase decoding, or other known means, the number of full and partial fringes to be counted, and the direction of the fringe pattern to be determined thereby indicating the direction of the applied torque. In a practical preferred embodiment, the optical interferometer is a Michelson Interferometer.

It is also preferred that the apparatus further comprises a cartridge, or the like, which is adapted, in use, to be retained within a hollow crank spindle of a machine. Preferably the apparatus includes one or more sensor elements for progressively sensing and generating signals, during rotation of a crankshaft of the machine, which signals are indicative of the angular position of the or each crank arm of the machine and/or the torque applied thereto.

Preferably the sensor element for progressively sensing and generating signals indicative of the torque of the drive-side crank arm may be an optical interferometer adapted, in use, to provide means to sense movement between the chain ring spider and the hollow crank spindle, the movement being due to torque applied thereto by each crank arm of the machine.

Preferably the sensor element for progressively sensing and generating signals indicative of the torque of the non-drive-side crank arm may be an optical interferometer adapted, in use, to provide means to sense torsion of the hollow crank spindle due to the torque applied thereto.

Preferably the torque applied to the or each crank arm may be measured in either the direction of, or against the direction of, pedaling of a cyclist.

Preferably the torque sensor(s) associated with the hollow crank spindle measure torque produced by one leg of the cyclist. It is also preferred that the torque sensor(s) associated with the chain ring spider and hollow crank spindle measure torque produced by both legs in combination of the cyclist. The difference between the two measurements may indicate torque applied by the other leg of the cyclist in or against the direction of pedaling.

Preferably the sensor element for progressively sensing and generating signals indicative of the angular position is an optical reflection sensor adapted, in use, to sense reflection from a reflective strip of varying reflectance mounted to the inside of a hollow crank spindle cover. Preferably the hollow crank spindle cover may be fixed in space relative to the hollow crank spindle and optical reflection sensor. Preferably rotation of the hollow crank spindle and optical reflection sensor results in the optical reflection sensor receiving varying levels of reflection from the reflective strip. Preferably the levels of received reflection may be indicative of angular position and direction of rotation of the hollow crank spindle.

Preferably the sensor element for progressively sensing and generating signals indicative of the angular position is a Sagnac Interferometer adapted, in use, to indicate the state of rotation of a frame of reference being the hollow crank spindle, by taking measurements within that frame. Preferably the indicated state of rotation enables angular position, angular velocity and cadence of the crank arm to be determined.

Preferably the rate of change of the angular position is measured to give angular velocity, and the duration may be measured of the angular position sensor returning to a predetermined angular position to give cadence of the crank arm.

Preferably the cartridge further comprises a power source, preferably rechargeable, an enclosure for accommodating electronic circuitry, and a wireless transceiver.

In a practical preferred embodiment, the electronic circuitry comprises: an amplifier and analogue to digital converter for the torque sensors; an amplifier and analogue to digital converter for the angular position sensors; and a microprocessor.

According to yet a further aspect the present invention may also provide an apparatus for measuring and monitoring the torque exerted by a cyclist during pedalling of a human-powered machine, the apparatus including a cartridge or the like adapted, in use, to be fixed within a hollow crank spindle of the machine, the apparatus further including one or more optical sensors and/or interferometers for progressively sensing and for generating signals, during rotation of a crank spindle of the machine, which signals are indicative of the angular position of the or each of the machine crank and/or the torque applied thereto.

Preferably torque is measured and monitored either in the direction of, or against the direction of, pedalling of the cyclist.

According to yet a further aspect the present invention may also provide an methods for measuring and monitoring, during the operation of a machine, the torque exerted by the machine, including providing the machine with an apparatus, to be associated with a hollow shaft and gear or hub arrangement of the machine, including sensing means for generating signals indicative of the torque applied to the shaft-cum-gear or hub.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more clearly understood and put into practical effect there shall now be described in detail preferred constructions of a power measuring apparatus for a bicycle in accordance with the invention. Also described is the application of the invention for measuring torque transferred by a hollow shaft and gear or hub arrangement. The ensuing descriptions are given by way of non-limitative example only and is with reference to the accompanying drawings, wherein:

FIG.1 is a diagram depicting a Michelson Interferometer, to be utilised in accordance with a preferred embodiment of the invention;

FIG.2 is a plan view of a crankset assembly to be located within the frame of a bicycle;

FIG.3 is a drive side elevation of a crankset assembly with mounted interferometer;

FIG.4 is an exploded view of the mounted interferometer depicted in FIG.3;

FIG.5 is an isometric view, along the axis of a crank spindle, of an interferometer adapted in accordance with a preferred embodiment of the invention, to measure total torque;

FIG.6 provides a plan view of a crankset assembly showing a hollow crank spindle subjected to torsion; FIG.7 is an isometric view along the axis of a crank spindle of an interferometer adapted in accordance with a preferred embodiment of the invention, to measure torque applied by the left leg;

FIG. 8 is an isometric view of a preferred embodiment for angular position and cadence measurement;

FIG. 9 is an isometric view of a further preferred embodiment for angular position and cadence measurement;

FIG. 10 is a sectional view of a preferred power meter cartridge, which accommodates the interferometers and electronics, adapted for mounting within a hollow crank spindle;

FIG. 11 is a schematic representation of preferred electrical/electronic circuitry for a power meter of the present invention; and,

FIG. 12 is a view of an interferometer adapted in accordance with a preferred embodiment of the invention, to measure torque of a hollow shaft and gear assembly.

MODES FOR CARRYING OUT THE INVENTION

With reference to FIG.1 to FIG. 11 , there are shown therein arrangements in accordance with preferred embodiments of the present invention, made up of a number of elements assembled together (as described in more detail later in this specification), as they would be located on and extend through a bicycle frame (not shown). As previously pointed out, the power measuring device/apparatus in accordance with the present invention is particularly, although not exclusively, suited for use with a bicycle fitted with a crankset of the type that has an integrated crank and chain ring spider incorporated with a hollow crank spindle.

An example of an alternative application for the present invention is given in FIG. 12, which shows a hollow shaft and gear arrangement where the torque or strain withstood by the gear teeth is being measured.

It should be understood, however, that under no circumstance is the apparatus in accordance with the present invention to be considered limited to use in such a context or apparatus.

It is well known that an optical interferometer is capable of obtaining measurements of movement of an object, and the direction of that movement, to extremely high precision. There are many configurations of interferometer designed specifically for this purpose and FIG.1 shows one such configuration, the Michelson Interferometer producing two interference beams in approximate phase quadrature.

With reference to FIG.1 , monochromatic light source 1 produces light beam 2 that is projected towards beamsplitter 3 inclined at an angle of 45° to the path of light beam 2. Beamsplitter 3, which is "lossless" and absorbs almost none of the incident light, splits light beam 2 into transmitted beam 4 and reflected beam 5, which are perpendicular to one another and of approximately equal intensity. Transmitted beam 4 is not required and therefore escapes the interferometer or, in an alternative, may be utilised for another purpose. Reflected beam 5 is projected towards beamsplitter 6, inclined at an angle of 45° to its path, and splits reflected beam 5 into reflected beam 7 and transmitted beam 8, which are perpendicular to one another and of approximately equal intensity. Beamsplitter 6 is "lossy" and absorbs some of the incident light from reflected beam 5. Reflected beam 7 is projected towards mirror 9, inclined at an angle 45° to its path, and continues to movable mirror 10, which is aligned in such a way that reflected beam 7 is reflected straight back along the incoming path towards beamsplitter 6. This beam is split at the beamsplitter into two perpendicular beams, one directed toward beamsplitter 3 and the other towards photodetector 14. Transmitted beam 8 is projected towards fixed mirror 11 , which is aligned in such a way that transmitted beam 8 is reflected straight back along the incoming path towards beamsplitter 6. This beam is split at the beamsplitter into two perpendicular beams, one directed toward photodetector 14 and the other towards beamsplitter 3. At beamsplitter 6, the two beams directed back towards beamsplitter 3 recombine and interfere with each other creating interference beam 12. At beamsplitter 6, the two beams directed towards photodetector 14 also recombine and interfere with each other creating interference beam 13. The relative phase of each pair of the recombining beams determines whether the interference of interference beams 12 and 13 is constructive or destructive. Relative phase of the recombining beams is a function of distances di and 6₂ of movable mirror 10 and fixed mirror 11 respectively from beamsplitter 6, and the optical properties of beamsplitter 6. The distances reflected and transmitted beams 7 and 8 travel from and back to beamsplitter 6 are 2di and 2d₂ respectively. The optical path difference between these two beams is:

OPD = 2di - 2d₂ = 2(di - d₂) = 2Δd (1 )

For maximum constructive interference, the two recombining beams are in exact phase with one another and the wave amplitudes of the recombining beams add to produce a maximum intensity beam.

The condition for maximum constructive interference is:

2Δd = mλ (2) where m is an integer and λ is the wavelength of light source 1. Whenever the optical path difference is an integer multiple of the wavelength, the recombining beams will be in phase since both beams originated from the same source.

For maximum destructive interference, the two recombining beams are in exact phase opposition with one another and the wave amplitudes of the recombining beams cancel out one another.

The condition for maximum destructive interference is:

2Δd = (m + ¹/₂)λ (3) where the optical path distance is an odd half integer multiple of the wavelength and the recombining beams will be exactly out of phase.

The interferometer is constructed so that beamsplitter 6 and fixed mirror 11 are fixed in space relative to one another, therefore setting distance d₂. To accurately measure the movement of an object, movable mirror 10 is mounted on the object (not shown) in such a way that reflected beam 7 is reflected straight back along the incoming path towards beamsplitter 6. Movement of the object will cause a change in di by an amount δύ, consequently changing the OPD and the phase relationship between the recombining beams. Presuming interference beam 13 is at maximum constructive interference and movable mirror 10 is slowly moved away from beamsplitter 6 to the next point of maximum constructive interference. The optical path difference will have increased by one wavelength, or otherwise commonly known as one "fringe". Referring to the condition for constructive interference in Eq. 2, the new OPD is: 2(di + &J) - 2 d₂ = (m + 1)λ (4) where δd is the distance movable mirror 10 has travelled. Subtracting Eq. 2 from Eq. 4 gives: δd = λ/2 (5)

Hence, if light source 1 has a wavelength of 650 nm, then δd is 325 nm. Presently known photodetectors are highly sensitive and linear over a range of luminance levels, therefore it is possible to use the electrical signal from photodetector 14 to interpolate movements of objects less than one wavelength of light to very high levels of accuracy.

However, by using the electrical signal from photodetector 14 alone, it is not possible to determine the direction of that movement. To do this, it is necessary that the interferometer provides the associated electronics with two signals. There are several known methods to generate the required two signals and considering the method described in the present invention, one is derived from interference beam 12 and the other from interference beam 13. These signals vary sinusoidally with change in optical path difference and ideally, they should be in phase quadrature (90° out of phase with each other).

By selecting lossy beamsplitter 6 with suitable optical properties, it is possible to obtain near phase quadrature between interference beams 12 and 13. Because reflected beam 5 and interference beam 12 overlap in space, it is impossible to insert a photodetector into this path to measure the intensity of the latter. However at beamsplitter 3, interference beam 12 splits into a reflected beam (not shown) and transmitted beam 15, which is directed towards photodetector 16, and it is this arrangement that provides the second signal that enables bidirectional fringe counting by what is generally known as a quadrature phase decoder. A quadrature phase decoder is a specialized up/down counter that counts the number of fringes and determines the count direction from the phase relationship of the two input signals.

FIG.2 is a plan view of a crankset and bottom bracket apparatus for what is commonly known in the industry as a two-piece crankset. Right crank 20 and chain ring spider 21 are fabricated either as a single component or alternatively as separate components immovably fastened to one another. Right crank 20 and chain ring spider 21 are immovably mounted to one end of hollow crank spindle 22 as per common practice with a two-piece crankset. At least one chain ring 23 (obscured) is mounted on the chain ring spider, which drives chain 24 and other driven components of the drive train (not shown). Left crank 25 is attached to the other end of hollow crank spindle 22. Hollow crank spindle 22 is rotatably mounted on bearing adapters 26 and 27, which are adapted to be securely mounted in a bicycle frame (not shown). Right and left pedals 28 and

29 are attached to the ends of right and left crank 20 and 25 respectively. Hole

30 is an aperture through chain ring spider 21 and crank spindle 22 to be utilised in accordance with the invention for measuring deformation of chain ring spider 21.

Consider now the drive side elevation of a crankset shown in FIG.3. When pedalling a bicycle, the application of torques 40 and 41 by the cyclist to right and left cranks 20 and 25 respectively is transferred by crank spindle 22, chain ring spider 21 and chain ring 23 to the chain 24 thereby creating tension 42 in the chain as it drives the rear wheel assembly (not shown) to propel the bicycle forwards. If one were to pedal the bicycle with the left leg only with no torque 40 whatsoever applied by the cyclist to right crank 20, then all torque 41 from left crank 25 is transferred via crank spindle 22 directly to chain ring spider 21. As the chain ring spider 21 drives chain ring 23 and chain 24, it is subjected to strain 43 and becomes deformed. This deformation causes chain ring spider 21 to undergo micrometric displacement relative to crank spindle 22. If one were to pedal the bicycle with the right leg only with no torque 41 at all applied by the cyclist to left crank 25, then crank spindle 22 will be free of torque and will rotate as one with the right crank 20. All torque 40 from right crank 20 will be transferred directly to chain ring spider 21 , subjecting it to strain 43 and causing it to become deformed as it drives chain ring 23 and chain 24. By virtue of this deformation and in like manner to the left leg example, the chain ring spider 21 undergoes micrometric displacement relative to crank spindle 22.

In accordance with a preferred aspect of the present invention, the relative displacement between crank spindle 22 and chain ring spider 21 is measured in terms of fringes by means of an interferometer that provides quadrature phase output signals from photodetectors 14 and 16.

Section 46 encircling the depicted small-scale elements, viz. rod 44, power meter cartridge 45 and the interferometer is elaborated in FIG.4. Now turning to FIG.4, power meter cartridge 45, which has outer an diameter which is complementary to the inner diameter of hollow crank spindle 22, is press-fitted into or immovably affixed by any known means and in any known manner to hollow crank spindle 22. Power meter cartridge 45 is moulded and/or machined to mount and align the fixed interferometer components 1 , 3, 6, 9, 11 , 14, and 16 (as shown in FIG.1 and FIG.5). Hole 30 is an aperture that is drilled or which is preformed through chain ring spider 21 , hollow crank spindle 22 and power meter cartridge 45. A rod 44, comprising a short section with a diameter which is complementary with the diameter of hole 30 and a long section with a diameter which is less than the short section, is press-fitted into hole 30. The long section of rod 44 projects into the cavity of power meter cartridge 45 and over its length, does not make contact with the wall of hole 30. Movable mirror 10 is affixed to the end of rod 44 that projects into the cavity of power meter cartridge 45 and is aligned with the plane defined by the axes of the rod 44 and hollow crank spindle 22, and in turn with beamsplitter 6 and the other fixed elements of the interferometer mounted in power meter cartridge 45.

As previously described, when chain ring spider 21 is subjected to deformation it undergoes displacement relative to hollow crank spindle 22. This displacement is translated by rod 44 to movable mirror 10, and is measured in terms of fringes by means of the interferometer that provides quadrature phase output signals from photodetectors 14 and 16

FIG.5 is an isometric illustration of the interferometer shown in FIG.1 and FIG.4 as it would be arranged in the power meter cartridge 45 and mounted in hollow crank spindle 22. The numbering and operation of the interferometer follows the description given with FIG.1. The power meter cartridge (not shown), which is immovably fixed within the hollow crank spindle (not shown), is fabricated to mount and align light source 1 , beamsplitter 3, beamsplitter 6, mirror 9, fixed mirror 11 , photodetector 14, and photodetector 16. Torque applied to the right and/or left cranks 20,25 will cause the chain ring spider 21 to deform, as previously described, and this is translated into movement of rod 44 and movable mirror 10. Movement of movable mirror 10 causes the intensity of interference beams 12 and 13 to vary sinusoidally, which is detected by photodetectors 16 and 14 respectively and converted into electrical signals. These signals are computed by the electronics (FIG. 11) in terms of the number of full and partial fringes counted and the direction thereof, and consequently translated into torque. The torque measured is that applied by the left and right legs in combination and therefore represents the total torque produced by the cyclist.

FIG.6 is a plan view of an apparatus for a two-piece crankset and bottom bracket where the numbering of components 20, 21 , 22, 23, 24, 25, 28 and 29 correlate with those depicted in FIG.2. Torque, which is applied to left crank 25 by the cyclist pushing on left pedal 29 when pedalling, is transferred by hollow crank spindle 22 to chain ring spider 21 , which in turn drives the driven parts of the bicycle drive train. As a consequence of transferring the torque from left crank 25 to the chain ring spider 21 , hollow crank spindle 22 is subjected to torsion 50 and experiences twisting along its length.

In accordance with this embodiment of the present invention, the magnitude of torsion 50 is measured by an interferometer and translated into torque applied by the cyclist's left leg.

Disc 51 has an outer diameter that is complementary with the inner diameter of hollow crank spindle 22 and is press-fitted or immovably fixed by known means and in any known manner to the hollow crank spindle 22. Disc 51 has a centrally disposed aperture through which a shaft 52 is immovably fixed. Shaft 52 projects into power meter cartridge 45, and at or near the end of shaft 52 is interferometer 53, which measures the amount of twist that occurs along a length of hollow crank spindle 22 when it is subjected to torsion 50.

Section 54 encircling the small-scale elements, viz. disc 51 , shaft 52 and interferometer 53 is described in FIG.7 as an isometric illustration.

Referring to FIG.7, the description of operation and elements of the interferometer numbered 61 to 76 correspond respectively to the description of operation and elements 1 to 16 depicted in and described with the embodiment of FIG.1 and FIG.5. The power meter cartridge (not shown), which is immovably fixed within the hollow crank spindle (not shown), is moulded and/or machined to mount and align light source 61 , beamsplitter 63, beamsplitter 66, mirror 69, fixed mirror 71 , photodetector 74, and photodetector 76. Disc 51 is immovably fixed in the radial plane to the hollow crank spindle, and has a centrally disposed aperture through which one end of shaft 52 is immovably fixed. Rod 77 is perpendicularly fixed at or near the other end of shaft 52, which projects into the power meter cartridge. Movable mirror 70 is attached to the opposite end of rod 77 and is aligned with the plane defined by the axes of shaft 52 and rod 77.

With the fixed elements of the interferometer mounted in the power meter cartridge immovably fixed to one end of the crank spindle, and disc 51 immovably fixed to the other end, torsion 50 along the crank spindle will cause disc 51 , shaft 52, rod 77 and movable mirror 70 to move relative to the fixed elements of the interferometer. Movement of movable mirror 70 causes the intensity of interference beams 72 and 73 to vary sinusoidally, which is detected by photodetectors 76 and 74 respectively and converted into electrical signals. These signals are computed by the electronics (FIG. 11) in terms of the number of full and partial fringes counted and the direction thereof, and consequently translated into torque. The torque measured is that applied to the left crank by the cyclist.

FIG. 8 is an isometric illustration that shows in accordance with the invention a means and method for measuring angular position, angular acceleration, and cadence of the crankset. Power meter cartridge 45, which is press-fitted or immovably affixed to crank spindle 22, is moulded and/or machined to mount and fix in position light source 90, beamsplitter 92 and photodetector 99. Light source 90 emits light beam 91 , which is projected towards beamsplitter 92 inclined at an angle of 45° to the path of the light beam. Reflected beam 93 is projected through aperture 94 in the power meter cartridge 45 and crank spindle 22, and onto reflective strip 95. Reflective strip 95 is fixed radially to the inside of the crank spindle cover 96 and is divided into alternating bands of white (100% on the greyscale) and non-white bands. Starting with the black band (0% on the greyscale) the next band is white. Thereafter each alternating non-white band reduces in intensity by a predetermined percentage compared with the intensity of the previous non-white band until the black band is re-encountered. Each band of reflective strip 95 reflects reflected beam 93 back along its path producing greyscale beam 97 of intensity proportional to the reflectance of the band. Greyscale beam 97 is transmitted through beamsplitter 92 becoming transmitted beam 98, which is projected onto photodetector 99. Photodetector 99 produces an electrical signal proportional to the intensity of transmitted beam 98.

Cylindrical crank spindle cover 96 is provided to afford water and dust- proofing for crank spindle 22, and is mounted on and between bearing adapters 26 and 27 depicted in FIG.2. Hence, crank spindle cover 96 is fixed in space relative to rotatable crank spindle 22 cum power meter cartridge 45. When crank spindle 22 rotates, reflected beam 93 rotates in unison and projects onto the alternating white and non-white bands of reflective strip 95, producing greyscale beam 97 of varying intensity. Correspondingly, photodetector 99 produces a varying electrical signal and the electronics (not shown), to which photodetector 99 is connected, interprets the electrical signal to determine angular position, angular acceleration and cadence of the crankset.

An alternative method to determine the angular position, angular acceleration, and cadence of the crankset is shown in FIG. 9. Power meter cartridge 45, which is press-fitted or immovably affixed to crank spindle 22, is moulded and/or machined to mount and fix in position light source 110, beamsplitter 112, mirrors 113, 114 and 115, and photodetector 117, which are arranged in a typical Sagnac Interferometer configuration in the radial plane of crank spindle 22. The Sagnac Interferometer is well known for its use as an extremely accurate gyroscope used in aircraft and therefore the theory of this interferometer will only be covered here very briefly.

Monochromatic light source 110 emits light beam 111 , which is projected towards beamsplitter 112 inclined at an angle of 45° to the path of light beam 111. Beamsplitter 112 splits light beam 111 into a reflected and transmitted beam, which are perpendicular to one another and of approximately equal intensity. Mirrors 113, 114 and 115 are arranged and aligned so that the reflected and transmitted beams simultaneously follow the same path along the four sides of a rectangle, but in opposite directions to one another, where they recombine at beamsplitter 112 producing interference beam 116.

When crank spindle 22 cum power meter cartridge 45 rotates, the Sagnac Interferometer rotates in unison, which in turn causes each of the counter- propagating beams to travel a different distance around the rectangular path. This difference in distance translates into a phase shift between the recombining beams producing a variation in the intensity of interference beam 116. Photodetector 117, onto which interference beam 116 projects, produces an electrical signal proportional to the intensity of the interference beam and the electronics (not shown), to which photodetector 117 is connected, interprets the electrical signal to determine angular position, angular acceleration and cadence of the crankset.

It is envisaged that means and methods other than those described in Figures 8 and 9 may be suitable for measuring angular position, angular acceleration, and cadence of the crankset. Thus the invention is not limited to the means and methods described in relation to Figures 8 and 9.

Turning now to FIG. 10, there is shown therein in cutaway section of a preferred power meter cartridge 45, to be located in accordance with the present invention within a hollow crank spindle (not shown), which cartridge 45 includes the following as principal components: a shaft 52 projecting therein for translating torsion in a crank spindle to an interferometer 53 for measurement of left leg power; a rod 77 perpendicularly connected to shaft 52 to which a movable mirror in interferometer 53 is affixed; an enclosure 120 for accommodating the electronics for:

(i) conversion of interferometer quadrature phase signals into torque;

(ii) receiving angular position signals from an angular position sensor and calculation of cadence, angular velocity and angular acceleration;

(iii) calculation of power from torque and angular velocity data;

(iv) voltage regulation;

(v) wireless transmission of torque, power, cadence, angular position, angular velocity, angular acceleration data to a remote computing and display unit; an enclosure for mounting an interferometer 53 for measuring torque applied by the left leg to the crankset; an enclosure for mounting an angular position sensor 121 ; an enclosure for mounting an interferometer 122 for measuring the torque applied in combination by both legs; a rechargeable battery or the like power source 123; a cap 124 for retaining the battery 123 in place.

In the preferred embodiment of power meter cartridge 45, there is a short section of an outer diameter which is complementary with the inner diameter of a crank spindle, and a long section of a diameter which is less than the short section, which over its length does not make contact with the crank spindle.

FIG. 11 is a block diagram of the electronics for a preferred embodiment of the invention.

Photodetectors 14 and 16, associated with the interferometer measuring total torque produced by the cyclist, provide electrical signals in phase quadrature to instrumentation amplifiers 130 and 131 respectively. The amplified signals are fed to respective analogue-to-digital converters 132 and 133 where the signals are digitised.

Photodetectors 74 and 76, associated with the interferometer measuring left leg torque produced by the cyclist, provide electrical signals in phase quadrature to instrumentation amplifiers 135 and 136 respectively. The amplified signals are fed to respective analogue-to-digital converters 137 and 138, where the signals are digitised.

Photodetector 99 (reflective strip embodiment) or 117 (Sagnac Interferometer embodiment) provides angular position of the crankset by means of an electrical signal to instrumentation amplifier 139. The amplified signal is fed to analogue-to-digital converter 140 where the signal is digitised.

Microprocessor 134 receives the digital signals from analogue-to-digital converters 132, 133, 137 and 138 and, by executing a program such as a quadrature phase decoder, counts the number of full and partial fringes detected by each interferometer, and the direction thereof. Digital signal processing functions, such as sampling, filtering, normalisation, and comparison with hysteresis may be applied to the received digital signals prior to passing them to the quadrature phase decoder.

Microprocessor 134 applies the outputs from the quadrature phase detector to an algorithm and computes the magnitude of total torque and left leg torque, as well as subtracts one from the other to determine the magnitude of right leg torque. Because the quadrature phase detector counts the number as well as the direction of the fringes from each interferometer, the aforementioned subtraction also indicates whether the torque from each leg is in the direction of pedalling, or against. For example, if the total torque measured is 45 Newton- metres and the left leg torque measured is +50 Newton-metres, then the right leg torque is calculated to be -5 Newton-metres. The right leg is experiencing what is known as a "dead zone" and is working against the torque applied by the left leg. Alternatively, if the total torque measured is 45 Newton-metres and the left leg torque measured is -5 Newton-metres, then the right leg torque is calculated to be +50 Newton-metres.

With reference to the angular position and cadence sensor described with FIG. 8, photodetector 99 produces an electrical signal proportional to the intensity of the greyscale beam 97. Microprocessor 134 receives the amplified and digitised signal from photodetector 99 and determines the direction of rotation of the crankset by comparing whether the intensity of the alternate non- white bands is increasing or decreasing. Angular position is determined by programming a reversible modulo-n counter in microprocessor 134 with the number of white bands on the reflective strip and stepping the counter each time a white band is detected. The number of each band is correlated with a predetermined position of the crankset. Angular velocity is determined by the microprocessor by measuring the time taken for the crankset to rotate from one non-white band to the next. Angular acceleration is determined by calculating the rate of change of angular velocity.

Cadence is derived by microprocessor 134 measuring the time it takes for angular position sensor 99 to complete a full revolution of rotation.

An alternative method of determining angular position and cadence of the crankset is by means of the Sagnac Interferometer described with FIG. 9. This interferometer is sensitive to any phase difference between the two counter- propagating beams caused by rotation of the crankset and is captured by variation of intensity of the fringe pattern of interference beam 116, which is detected by photodetector 117. Microprocessor 134 receives the amplified and digitised signal from photodetector 117 and determines the angular frequency of the interferometer and from this derives angular position, direction of rotation and angular velocity of the crankset based on the speed of light, wavelength of light source 110, area of the rectangle traversed by the counter-propagating beams of the interferometer, and time interval. Microprocessor 134 is able to determine the angular acceleration of the crankset by measuring the rate of change of angular velocity as well as cadence from the above-calculated parameters.

Having determined total, right and left leg torque together with angular velocity, microprocessor 134 calculates total, right and left leg power from the mathematical product thereof.

Transceiver/antenna 141 receives a signal from the microprocessor 134 with information of torque, power, angular position, angular velocity, angular acceleration and cadence, and transmits the information to a transceiver/antenna 142 that interfaces with bicycle computer 143. The transceiver 141 may also receive signals from the bicycle computer 143 to calibrate the torque sensor zero reference, adjust the sensitivity of any of the torque sensors, or perform diagnostics on the power meter electronics.

By measuring torque in the direction of pedalling, as well as against that direction of pedalling, for both legs of the cyclist, as well as angular position of the crank arm 20, 25, then a bicycle computer 143 either mounted on the handlebar of the bicycle or elsewhere on that bicycle may be employed to display, in real time, the exact position of a "dead zone."

In practical terms the power measuring apparatus in accordance with the present invention exhibits a number of advantages when compared with the prior art, as referred to hereinafter.

The power meter in accordance with the present invention is preferably designed as a cartridge to incorporate the torque sensor elements, angular position sensor, electronics, radio frequency transceiver, and battery. Because of its complementary shape with the hollow crank spindle, to mount it to the bicycle only requires it to be inserted in the hollow crank spindle and aligned with the movable mirrors of the torque sensor interferometers. The only modification required to a contemporary commercial hollow spindle crankset is drilling a small hole in the chain ring spider, crank spindle and power meter cartridge into which a rod is press-fitted, and to which a movable mirror is attached. Therefore a customer/user does not have to replace his/her current crankset, or even part thereof, not only saving cost but avoiding the customer/user affecting the environment negatively by having to dispose of what has been replaced.

The customer/user may also have more choice of crankset due to the adaptability of the power meter to the type of crankset that has a hollow crank spindle, and especially the type where the crank and chain ring spider are manufactured as a single unit that is incorporated with a hollow crank spindle. This latest trend of crankset is more rigid and lighter than previous generation cranksets offering the cyclist improved pedalling performance without losing robustness. In addition, a new standard has been introduced into the bicycle and crankset industry called the BB30 standard, which specifies a 30-millimetre diameter hollow crank spindle that is lighter, stiffer, narrower, and more durable than the current convention hollow crank spindle. The power meter according to this invention is not constrained by the diameter of the hollow crank spindle, and is therefore suited to this new standard further increasing customer/user choice.

The present invention is suitable to applications other than measuring the power generated by a cyclist pedalling a bicycle. By way of example, a further embodiment is shown in FIG. 12 where the torque of a hollow shaft and gear arrangement is measured by an optical interferometer of the type described above. Referring to FIG. 12, a gear 168 is shown mounted on hollow shaft 169, with said gear 168 meshed with to rotatably drive complementary gear 171 by way of mating/interacting teeth or lugs. Power meter cartridge 170, which has an outer diameter which is complementary to the inner diameter of hollow shaft 169, is press-fitted into or immovably affixed by known means and in any known manner to the hollow shaft 169. Power meter cartridge 170 is moulded and/or machined to mount and align the fixed interferometer components 151 , 153, 156, 159, 161 , 164, and 166. Hole 150 is an aperture that is drilled or preformed through gear 168, hollow shaft 169 and power meter cartridge 170. Hole 150 has been shown drilled or preformed through one of the teeth of gear 168, however, hole 150 could alternatively be drilled between the teeth of gear 168. A rod 167, comprising a short section with a diameter which is complementary with the diameter of hole 150 and a long section with a diameter which is less than the short section, is press-fitted into hole 150. The long section of rod 167 projects into the cavity of power meter cartridge 170 and over its length, does not make contact with the wall of hole 150. Movable mirror 160 is affixed to the end of rod 167 that projects into the cavity of power meter cartridge 170 and is aligned with the plane defined by the axes of the rod and hollow shaft 169, and in turn with beamsplitter 156 and the other fixed elements of the interferometer mounted in power meter cartridge 170. The description of operation and elements of the interferometer numbered 151 to 166 corresponds respectively to the description of operation and elements 1 to 16 depicted in and described with the embodiments of FIG.1 and FIG.5.

When hollow shaft 169 is driven in a clock-wise direction by a motor (not shown) it exerts torque 172 on gear 168, which in turn rotates in a clock-wise direction. Gear 168, being meshed with complementary gear 171 by means of teeth, transfers torque 172 to complementary gear 171. By virtue of friction and other forces 174 acting upon complementary gear 171 which oppose the torque exerted thereupon, the teeth and outer periphery of gear 168 are subjected to strain 173 and becomes deformed. This deformation causes gear 168 to undergo micrometric displacement relative to hollow shaft 169. This displacement is translated by rod 167 to movable mirror 160. and is measured in terms of fringes by means of the interferometer that provides quadrature phase output signals from photodetectors 164 and 166,

Alternative arrangements of the aforementioned embodiment include mounting a hub or flange on hollow shaft 169 to which torque 172 is transferred, said hub or flange and hollow shaft adapted to incorporate an interferometer to measure micrometric displacement therebetween and providing quadrature phase output signals.

In one aspect, the present invention therefore introduces a unique means of measuring the power produced independently by each leg of a cyclist and is suited, but not limited, to use with a crankset of the type that has an integrated crank and chain ring spider mounted on a hollow crank spindle. To measure the torque applied by the left leg an interferometer adapted in use, to be located within and immovably fixed to the hollow crank spindle, whereby to measure the amount of torsion the hollow crank spindle is subjected to in transferring the torque from the left crank to the chain ring spider mounted at the other end of the spindle. To measure the total torque of the combined left and right legs transferred by the chain ring spider to the driven components of a bicycle, a further interferometer may be adapted in use, to be immovably fixed and located within the hollow crank spindle for this purpose. The right leg torque may be derived by subtracting the magnitude of the left leg torque from the total torque measured.

In a further aspect, the present invention may also introduce a unique means of accurately measuring the angular position of the crankset assembly and proposes two embodiments, one using an interferometer and the other by detecting the reflectance of a strip of alternate bands of varying greyscale intensity. By measuring the time it takes the crankset to move from one predetermined angular position to the next, angular velocity may be determined. By measuring the right and left leg torque at each pre-determined angular position, an accurate profile per crank revolution may be obtained of the power generated by a cyclist.

Notwithstanding the application of the present invention to measuring torque and power in a crankset of a bicycle, use of the present invention may be applicable to the measurement of torque and power being transferred by a hollow shaft and gear or hub arrangement. Strain gauges are widely used in the field to sense strain in such arrangements, however, their fragility restricts their usage in extremely confined spaces, for example, measuring strain of a closely meshed spur gear of a pump. The present invention may overcome such restriction by measurement of the torque by an interferometer adapted in use, to be immovably fixed and located within the hollow shaft.

These and other advantages of the present invention will be apparent from the detailed description of the preferred embodiments provided hereinbefore.

While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifιcation(s). The present invention is intended to cover any variations, uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth. Finally, as the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and the appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced.

Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other features, integers, steps, components to be grouped therewith.

Claims

CLAIMS:

1. A device adapted for measuring a first torque applied to a first body of revolution, the first body of revolution comprising a hollow member, the device comprising: a first movable member having a fixed portion adapted to be fixed directly or indirectly to the first body of revolution and a movable portion adapted to extend at least partially into or within the hollow member; a first interferometer adapted for location substantially within the hollow member, the first interferometer comprising: a first movable mirror adapted to be fixed to the movable portion of the first movable member; and, first fixed components comprising a first detector adapted to detect displacement of the first movable mirror; and, electrical means for calculating the first torque from the displacement detected by the first interferometer.

2. The device according to claim 1 , wherein the first interferometer is adapted to detect the amount of displacement of the first movable mirror and the direction of displacement of the first movable mirror.

3. The device according to claim 1 or claim 2, wherein the fixed components of the first interferometer comprise: a light source; first and second beam splitters; first and second fixed mirrors; and, a second detector; wherein the first detector is adapted to detect the amount of displacement of the first movable mirror, and the second detector is adapted to detect the direction of displacement of the first movable mirror.

4. The device according to any one of the preceding claims, wherein the hollow member comprises a shaft, and the first movable member comprises a rod adapted to extend substantially perpendicularly to the axis of the shaft.

5. The device according to any one of the preceding claims, wherein the first body of revolution comprises a spindle or a hub.

6. The device according to any one of the preceding claims, wherein the first body of revolution comprises a hub of a crank-set of a bicycle having left and right pedals, and the first torque substantially results from the combined force applied by a cyclist to both pedals.

7. The device according to any one of claims 1 to 5, wherein the first body of revolution comprises a spindle of a crank-set of a bicycle having left and right pedals, and the first torque substantially results from force applied by a cyclist to only one of the pedals.

8. The device according to any one of claims 1 to 5, wherein the first body of revolution comprises a hub of a gear wheel.

9. The device according to any one of the preceding claims, wherein the device is adapted for measuring a second torque applied to a second body of revolution which comprises the hollow member, and the electrical means is adapted to calculate each of the first and second torques.

10. The device according to claim 6, wherein the device is adapted for measuring a second torque applied to a second body of revolution which comprises a spindle of the crank-set of the bicycle, wherein the second torque substantially results from the force applied by the cyclist to only one of the pedals, and the electrical means is adapted to calculate each of the first and second torques either in the direction of or against the direction of pedaling of the cyclist.

11. The device according to claim 9 or claim 10, wherein the device comprises: a second movable member having a fixed portion adapted to be fixed directly or indirectly to the second body of revolution and a movable portion adapted to extend at least partially into or within the hollow member; a second interferometer adapted for location substantially within the hollow member, the second interferometer comprising: a second movable mirror adapted to be fixed to the movable portion of the second movable member; and, second fixed components comprising a third detector adapted to detect the amount of displacement of the second movable mirror, and a fourth detector which is adapted for detecting the direction of displacement of the second movable mirror; wherein the electrical means is adapted to calculate the second torque from the displacement detected by the second interferometer.

12. The device according to any one of the preceding claims, comprising an angular position sensor for calculating angular velocity of the hollow member, wherein the electrical means is adapted to calculate power from torque and angular velocity measurements.

13. The device according to any one of the preceding claims, comprising a cartridge adapted for fixed insertion into the hollow member wherein, the first movable member of the first interferometer is adapted to extend at least partially into or within the cartridge, and, the first fixed components are fixed to and substantially housed within the cartridge.

14. The device according to claim 11 , comprising a cartridge adapted for fixed insertion into the hollow member wherein: the first movable member of the first interferometer is adapted to extend at least partially into or within the cartridge; and, the first fixed components are fixed to and substantially housed within the cartridge; the second movable member of the second interferometer is adapted to extend at least partially into or within the cartridge; and, the second fixed components are fixed to and substantially housed within the cartridge.

15. The device according to claim 12, comprising a cartridge adapted for fixed insertion into the hollow member wherein: the first movable member of the first interferometer is adapted to extend at least partially into or within the cartridge; and, the first fixed components are fixed to and substantially housed within the cartridge; at least part of the electrical means is housed within the cartridge; and, a power source is housed within the cartridge; and, at least part of the angular position sensor is housed within the cartridge.

16. The device according to claim 10, wherein the electrical means is adapted to determine the force applied by the cyclist to the other one of the pedals by subtracting the second torque from the first torque.