Patent Description:
Power-meter use has become very popular for training and racing since it objectively displays the power output by an athlete. This objective measure is more desirable than the subjective measures provided by heart rate monitors for example. The user's heart rate changes during a given exertion and this change typically lags strong efforts resulting in inaccurate indications of effort being exerted by the athlete. Thus, subjectively determined measurements have limitations, whereas power-meter measurements are more accurate and provide near instantaneous feedback without bias.

An adhesively coupled power-meter for measurement of force, torque, power and/or velocity of a mechanical arm, comprising three strain gauges, one of the strain gauges crossing the neutral axis of the mechanical arm, is known from <CIT>. <CIT> discloses a power measurement assembly comprising a pair of shear-sensing strain gauges crossing the neutral axis of an axle. <CIT> discloses a device for measuring a propulsion force and a loss force comprising two pairs of strain gauges, the strain gauges of one pair overlapping each other. <CIT> and <CIT> disclose similar measurement modules comprising one or more strain gauges detecting strain of a crank of a bicycle.

To measure power input to a bicycle for example, there are several locations where the forces, torques, and/or angular velocities may be measured, including shoe cleats, pedals, crank arms, the spider connecting the cranks to the chain ring, chain, wheel hub, and frame. Power measurement at each of these locations presents challenges, requiring specialized instrumentation by skilled technicians on specially engineered components that are specifically designed for attaching the instrumentation.

<FIG> depicts a prior art bicycle pedal-crank assembly <NUM> that includes a crank <NUM>, having a longitudinal axis X, a vertical axis Y, and a lateral axis Z. This assembly <NUM> is used for measuring torque being produced by the pedal force in the crank's rotation plane (the X-Y plane). The pedal-crank assembly <NUM> includes a crank <NUM>, having a top surface <NUM>, a bottom surface <NUM>, an inner surface <NUM>, and an outer surface <NUM>. Crank <NUM> is attached to a bottom bracket (not shown), that rotates about lateral axis Z, at axle fastener <NUM> located proximate a first end <NUM> of crank <NUM>. Proximate second end <NUM> of crank <NUM> is attached a pedal axle <NUM> for attaching a pedal (not shown). A rider applies force represented by arrow <NUM> to the pedal thereby causing crank <NUM> to rotate about lateral axis Z at the bottom bracket (not shown).

As the rider applies force <NUM>, the torque causes bending in the crank <NUM> which is measured by first and second strain gauges <NUM>, <NUM>. First strain gauge <NUM> is located on top surface <NUM>, and second strain gauge <NUM> is located on bottom surface <NUM> of crank <NUM> (and thus depicted in dashed lines). First and second strain gauges <NUM>, <NUM> are wired via circuitry (not shown) into a Wheatstone bridge. The configuration of first and second strain gauges <NUM>, <NUM> allows sensitivity to bending of crank <NUM> as force <NUM> is applied to the pedal, but insensitivity to axial forces applied along the longitudinal axis X. However, first and second strain gauges are very susceptible to physical damage because they are located on the top and bottom surfaces <NUM>, <NUM> and are frequently in physical contact with the rider and other elements. Moreover, having the first and second gauges <NUM>, <NUM> located on opposing surfaces of crank <NUM> makes manufacturing difficult and inefficient.

A crank power measurement system for measuring one or more of force, torque, power, and velocity of the crank is provided in claim <NUM>.

In another embodiment being part of the present disclosure, but not part of the claimed invention, a bicycle crank mounted power generator for generating power when the bicycle is being ridden by a user. The bicycle crank mounted power generator including a base ring fixedly attached to a frame of the bicycle, the base ring circling a bottom bracket attached to a crank, a plurality of magnets coupled with the base ring, a coil system attached to the crank located adjacent to the plurality of magnets such that when the crank rotates about the bottom bracket, the coil generates an output at leads of the coil, and electronics configured to manipulate the output to at least one of power an electronic device or store the output in a power supply.

Certain embodiments disclosed herein relate to a body instrumented with strain sensors to indirectly measure loads applied to the body. In a typical use case, it is desired to determine the applied forces or moments along a specified axis. To enable this measurement, one or more strain sensors are affixed to the body. Known loads are applied to the body and the strains are recorded to enable calibration of sensors to these loads. For regular geometries, homogeneous materials and well defined load cases, it is possible to apply only one primary strain sensor to enable accurate, repeatable measurements. In most situations however, several strain sensors must be applied to augment the primary strain sensor to correct for such things such as irregular geometries, variations in manufacturing, off-axis loading and non-ideal sensor placements, to name a few.

Calibration of various strain sensors may include attaching a single weight in one orientation and observing the strain output(s), or it may involve several weights applied to the body in various positions and orientations. This data can then be processed with sophisticated models that include regression.

The strain sensing is typically carried out with a strain gauge. A single gauge may be used to measure the strain in a particular orientation, but two, three, four or more gauges may be combined into a Wheatstone bridge to measure the strain response in a single direction. Any form of Wheatstone bridge, including quarter, half, three-quarter or full Wheatstone bridge may be utilized without departing from the scope hereof. Additional gauges have several benefits, such as to provide increased sensitivity - in some cases up to four times the sensitivity of a single gauge. Another benefit for additional gauges is that temperature changes in the metal cause the material to expand or contract, which is measured as a change in strain even though no loads have been applied. Where multiple gauges are configured in a Wheatstone bridge, they become less temperature sensitive.

Even when strain sensing gauges are wired into a Wheatstone bridge, temperature sensitivity may still be exhibited due to zero load offset changes and sensitivity slope changes in the output. Due to individual characteristics of the gauges, circuitry and enclosure, the zero offset changes may be individually tested. It may be possible to model these offset effects with a simple linear change over a small range in temperatures, thus only requiring a two-point temperature calibration. However, in the more general case, a multipoint temperature characterization may be conducted for a non-linear variation in zero load offset versus temperature. The same discussion can also be carried out for the change in slope sensitivity with respect to temperature. Each configuration may be tested over several different temperatures for a full non-linear mapping of the response option. In the simplest case, a simple two-point temperature test may be sufficient for example, when a global structural stiffness property is the dominant factor in the slope change.

<FIG> depicts an exemplary crank assembly <NUM> having inner surface strain gauges, in one embodiment part of the present disclosure, but not part of the present invention. Crank assembly <NUM> includes a crank <NUM>, having a longitudinal axis X, a vertical axis Y, and a lateral axis Z. Crank <NUM> has a top surface <NUM>, a bottom surface <NUM>, an inner surface <NUM>, and an outer surface <NUM>. Crank assembly <NUM> has first and second bend-sensing strain gauges <NUM>, <NUM> located on the inner surface <NUM>, with respect to crank assembly <NUM> positioned on a bicycle, of crank <NUM>. Crank <NUM> attaches to a bottom bracket (not shown), that corresponds to lateral axis Z, at axle fastener <NUM> located proximate a first end <NUM> of crank <NUM>. Proximate second end <NUM> of crank <NUM> is attached a pedal axle <NUM> for attaching a pedal (not shown). A rider applies force in the direction shown by arrow <NUM> to the pedal thereby applying force along vertical axis Y (and potentially longitudinal axis X) causing crank assembly <NUM> to rotate about lateral axis Z at the bottom bracket. It should be appreciated that the actual force on crank <NUM> is not limited to vertical force as shown by arrow <NUM>, but in reality includes forces in multiple dimensions including the X, Y, and Z axes. Arrow <NUM> is for illustrative purposes only.

As the rider applies force <NUM>, the torque causes bending in the crank assembly <NUM> which is measured by first and second bend-sensing strain gauges <NUM>, <NUM>. First strain gauge <NUM> is located on inner surface <NUM>, above the neutral axis <NUM> of the crank assembly <NUM>. Second strain gauge <NUM> is located on the inner surface <NUM> of crank assembly <NUM> located below the neutral axis of the crank assembly <NUM>. First and second bend-sensing strain gauges <NUM>, <NUM> are wired via circuitry (not shown) into a Wheatstone bridge such that they are insensitive to axial forces (e.g., around the X axis/neutral axis <NUM>) but remain sensitive to bending (along the X axis/neutral axis <NUM>). The circuitry and electronics associated with first and second bend-sensing strain gauges <NUM>, <NUM> are discussed in further detail below. Placing the bend-sensing strain gauges <NUM>, <NUM> on the inner surface <NUM> of crank assembly <NUM> provides significantly increased protection of the gauges because they are less susceptible to contact by the rider or other elements.

In <FIG>, neutral axis <NUM> is indicated the same as longitudinal axis X. For a completely symmetrical crank assembly <NUM>, the neutral axis <NUM> is along the geometric center (longitudinal axis X), whereas in other geometries, this must be experimentally or analytically determined. For maximum bend sensing, first and second bend-sensing gauges <NUM>, <NUM> are located farther away from neutral axis <NUM>.

Additional strain gauges may be added to increase the sensitivity of the system. For example, <FIG> depicts an additional strain gauge configuration <NUM> for use with crank assembly <NUM> of <FIG>, in one embodiment. Strain gauge configuration <NUM> attaches to crank assembly <NUM> in the same location <NUM> (referring to <FIG>) and orientation as first and second bend-sensing strain gauges <NUM>, <NUM> of <FIG>. Strain gauge configuration <NUM> includes first and second bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>, as well as third and fourth bend-sensing strain gauges <NUM>, <NUM>. Third bend-sensing strain gauge <NUM> is located between first bend-sensing strain gauge <NUM> and neutral axis <NUM>. Fourth bend-sensing strain gauge <NUM> is located between second bend-sensing strain gauge <NUM> and neutral axis <NUM>.

<FIG> depicts an additional strain gauge configuration <NUM> for use with crank assembly <NUM> of <FIG>, in one embodiment. Strain gauge configuration <NUM> attaches to crank assembly <NUM> in the same location <NUM> (referring to <FIG>) and orientation as first and second bend-sensing strain gauges <NUM>, <NUM> of <FIG>. Strain gauge configuration <NUM> includes first and second bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>, as well as third and fourth bend-sensing strain gauges <NUM>, <NUM>. Third bend-sensing strain gauge <NUM> is located adjacent to, and symmetrically opposed to, first bend-sensing strain gauge <NUM> at the same distance from neutral axis <NUM>. Fourth bend-sensing strain gauge <NUM> is located adjacent to, and symmetrically opposed to, second bend-sensing strain gauge <NUM> at the same distance from neutral axis <NUM>. Configurations <NUM> and <NUM> increase the sensitivity of the sensed strain detected by the strain gauges.

Using additional shear- and/or axial-sensing strain gauges allows compensation for asymmetries, non-design loads, and imperfections in manufacturing (e.g., of the crank assembly <NUM> and/or gauges <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) based upon additional data obtained by the shear- and axial-sensing strain gauges. Configurations <NUM> and <NUM> are set up such that first, second, third and fourth bend-sensing strain gauges are coupled in a full-Wheatstone bridge, or two half-Wheatstone bridges.

<FIG> depicts an additional strain gauge configuration <NUM> for use with crank assembly <NUM> of <FIG>, in one embodiment. Strain gauge configuration <NUM> attaches to crank assembly <NUM> in the same location <NUM> (referring to <FIG>) and orientation as first and second bend-sensing strain gauges <NUM>, <NUM> of <FIG>. Strain gauge configuration <NUM> includes first and second bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>. Strain gauge configuration <NUM> also includes third and fourth bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>. First, second, third, and fourth bend-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> may be coupled together in a first full-Wheatstone bridge, or first and second half-Wheatstone bridges.

Strain gauge configuration <NUM> also includes first, second, third, and fourth axial-sensing strain gauges <NUM>, <NUM>. <NUM>, <NUM>. Second axial-sensing strain gauge <NUM> is rotated <NUM> degrees with respect to first axial-sensing strain gauge <NUM>. Third axial-sensing strain gauge <NUM> is rotated <NUM> degrees with respect to second axial-sensing strain gauge <NUM>, and <NUM> degrees with respect to first axial-sensing strain gauge <NUM>. Fourth axial-sensing strain gauge <NUM> is rotated <NUM> degrees with respect to third axial-sensing strain gauge <NUM>, <NUM> degrees with respect to second axial-sensing strain gauge <NUM>, and <NUM> degrees with respect to first axial-sensing strain gauge <NUM>. In general, two of the axial-sensing strain gauges are horizontally oriented along the longitudinal axis Z, and two of the axial sensing strain gauges are vertically oriented. First, second, third, and fourth axial-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> are located along neutral axis <NUM> and may be coupled together in a second full-Wheatstone bridge, or third and fourth half-Wheatstone bridges.

Strain gauge configuration <NUM> also includes first, second, third, and fourth shear-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM>. Shear-sensing gauges are most sensitive to torsion of crank <NUM>, or in other words twisting of crank <NUM> about the X axis. First shear-sensing strain gauge <NUM> is located between first and third bend-sensing strain gauges <NUM>, <NUM> and second shear-sensing strain gauge <NUM>. Second shear-sensing strain gauge <NUM> is located between first shear-sensing strain gauge <NUM> and neutral axis <NUM>. Second shear-sensing strain gauge <NUM> may be oriented such that it is mirrored vertically with respect to first shear-sensing strain gauge <NUM>. Third shear-sensing strain gauge <NUM> is located between second and fourth bend-sensing strain gauges <NUM>, <NUM> and fourth shear-sensing strain gauge <NUM>. Fourth shear-sensing strain gauge <NUM> is located between third shear-sensing strain gauge <NUM> and neutral axis <NUM>. Fourth shear-sensing strain gauge <NUM> may be oriented such that it is mirrored vertically with respect to third shear-sensing strain gauge <NUM> and in the same orientation as second shear-sensing strain gauge <NUM>. First, second, third and fourth shear-sensing strain gauges <NUM>, <NUM>, <NUM>, and <NUM> may be coupled together in a third full-Wheatstone bridge, or fifth and sixth half-Wheatstone bridges.

<FIG> depict additional strain gauge configurations <NUM>, <NUM>, <NUM> for use with crank assembly <NUM> of <FIG>, in alternate embodiments. Strain gauge configurations <NUM>, <NUM>, <NUM> attach to crank assembly <NUM> in the same location <NUM> (referring to <FIG>) and orientation as first and second bend-sensing strain gauges <NUM>, <NUM> of <FIG>. Strain gauge configurations <NUM>, <NUM>, <NUM> include first and second bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>. Strain gauge configurations <NUM>, <NUM>, <NUM> include third and fourth bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>. First, second, third, and fourth bend-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> may be coupled together in a first full-Wheatstone bridge, or first and second half-Wheatstone bridges.

Strain gauge configurations <NUM>, <NUM>, <NUM> also include first, second, third, and fourth shear-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM>. First shear-sensing strain gauge <NUM> is located between third bend-sensing strain gauge <NUM> and second shear-sensing strain gauge <NUM>. Second shear-sensing strain gauge <NUM> is located between first shear-sensing strain gauge <NUM> and neutral axis <NUM>. Second shear-sensing strain gauge <NUM> may be oriented such that it is mirrored vertically with respect to first shear-sensing strain gauge <NUM>. Third shear-sensing strain gauge <NUM> is located between fourth bend-sensing strain gauges <NUM> and fourth shear-sensing strain gauge <NUM>. Fourth shear-sensing strain gauge <NUM> is located between third shear-sensing strain gauge <NUM> and neutral axis <NUM>. Fourth shear-sensing strain gauge <NUM> may be oriented such that it is mirrored vertically with respect to third shear-sensing strain gauge <NUM> and in the same orientation as second shear-sensing strain gauge <NUM>. First, second, third and fourth shear-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> may be coupled together in a second full-Wheatstone bridge, or third and fourth half-Wheatstone bridges.

Strain gauge configuration <NUM> also includes first, second, third, and fourth axial-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM>. First and second axial-sensing strain gauges <NUM>, <NUM> are located along neutral axis <NUM> offset, towards the bottom bracket, from the bend-sensing and shear sensing strain gauges. Third and fourth axial-sensing strain gauges <NUM>, <NUM> are located along neutral axis <NUM> offset, away from the bottom bracket, from the bend-sensing and shear sensing strain gauges. Second axial-sensing strain gauge <NUM> may be rotated <NUM> degrees with respect to first axial-sensing strain gauge <NUM>. Third axial-sensing strain gauge <NUM> may be rotated <NUM> degrees with respect to fourth axial-sensing strain gauge <NUM>. In general, two of the axial-sensing strain gauges are horizontally oriented along the longitudinal axis Z, and two of the axial sensing strain gauges are vertically oriented. First, second, third, and fourth axial-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> may be coupled together in a third full-Wheatstone bridge, or fifth and sixth half-Wheatstone bridges.

Strain gauge configuration <NUM> is similar to strain gauge <NUM>, however each of first, second, third, and fourth axial-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> are located along neutral axis <NUM> and offset towards the bottom bracket. Strain gauge configuration <NUM> is also similar to strain gauge <NUM>, however each of first, second, third and fourth axial-sensing strain gauges <NUM>, <NUM>, <NUM>, <NUM> are located offset from neutral axis <NUM> and offset towards the bottom bracket. It should be appreciated that strain gauge configuration <NUM> could be modified such that the axial-sensing strain gauges are offset from the natural axis and away from the bottom bracket as well.

<FIG> depicts an additional strain gauge configuration <NUM> for use with crank assembly <NUM> of <FIG>, in one embodiment. Strain gauge configuration <NUM> attaches to crank assembly <NUM> in the location <NUM> (referring to <FIG>) and orientation as first and second bend-sensing strain gauges <NUM>, <NUM> of <FIG>. Strain gauge configuration <NUM> includes first and second bend-sensing strain gauges <NUM>, <NUM>, as discussed above with respect to <FIG>, which may be coupled together in a first half-Wheatstone bridge.

Strain gauge configuration <NUM> includes first and second axial-sensing strain gauges <NUM>, <NUM>. Second axial-sensing strain gauge <NUM> is rotated <NUM> degrees with respect to first axial-sensing strain gauge <NUM>. First and second axial-sensing strain gauges <NUM>, <NUM> are located along neutral axis <NUM> and may be coupled together in a second half Wheatstone bridge.

Strain gauge configuration <NUM> also includes first and second shear-sensing strain gauges <NUM>, <NUM>. First shear-sensing strain gauge <NUM> is located between first bend-sensing strain gauge <NUM> and neutral axis <NUM>. Second shear-sensing strain gauge <NUM> may be oriented such that it is mirrored vertically with respect to first shear-sensing strain gauge <NUM>. Second shear-sensing strain gauge <NUM> is located between second bend-sensing strain gauge <NUM> and neutral axis <NUM>. First and second shear-sensing strain gauges <NUM>, <NUM> may be coupled together in a third half Wheatstone bridge.

A duplicate of configuration <NUM> may be placed adjacent to configuration <NUM> thereby resulting in four of each of the bend-, shear-, and axial-sensing strain gauges. In such an embodiment, the bend-, shear-, and axial-sensing strain gauges may be coupled together in respective first, second, and third full-Wheatstone bridges.

In each of configuration <NUM>-<NUM>, a calibration procedure may be carried out with variety of known loads to determine how each gauge set responds to these loads. Then, when real-life pedal forces are applied to the crank, it is possible to determine the loads of interest. These loads of interest are typically the moment causing corresponding to the bike's input power, as well the axial load and direction acting on the pedal as the crank rotates.

In a cycling application, the loads applied to the crank are due to loads being applied to the pedals. By the very nature of the pedal and crank design, these applied forces are offset from the crank and thus do not produce a pure bending moment about the longitudinal axis Z of the crank assembly <NUM>. Instead, this pedal offset causes several simultaneous applied loads that include, but are not limited to bending, torsion and axial loads. This is further compounded by the fact that individual cyclists have their own applied force profile as their legs move to produce a crank revolution. In general, the applied pedal forces aren't perpendicular to the crank and they may include axial and torsional components as well. The purpose of the multi-gauge sensors and the calibration is to separate these loads so that the bending moment of interest, axial forces and pedal offsets are accurately estimated.

In the above discussion of <FIG>, it should be appreciated that more or fewer strain gauges may be implemented, in additional configurations without departing from the scope hereof. Where the figures depict a given strain gauge, it should be understood that each individual depiction may represent a single strain gauge, or a pair of strain gauges joined together, or more than two strain gauges joined together without departing from the scope hereof. Moreover, where a given strain gauge is depicted on the neutral axis <NUM>, it should be appreciated that such strain gauge may also be offset from the neutral axis <NUM> without departing from the scope hereof. Further, where a given strain gauge is depicted offset from the neutral axis <NUM>, it should be appreciated that such strain gauge may also be located on the neutral axis <NUM> without departing from the scope hereof. Utilizing such configurations allows for one set of strain gauges to be a primary set of strain gauges. Secondary set(s) of strain gauges may then be utilized to augment the accuracy of the primary set. For example, the primary set may be any of the bend-sensing strain gauges discussed above, with the secondary set being any of the shear- or axial-sensing strain gauge sets. This combination allows for increased accuracy and efficiency while accommodating any variable, such as shape, size temperature, of crank assembly <NUM>.

Varying temperatures affect several aspects of strain gages differently based on gage materials and backings. These fall into the categories of zero offset shift, changes in the gage factor (the electrical response compared to the mechanical response) sensitivity, and change in material properties at temperature. For passively compensated sensing such as half bridges, full bridges, or other expansions that are passively compensated, the thermal error is a combination of changes in lead wire resistance and variance in the thermal response of the gage. As such by taking a minimum of two data points it is possible to linearly regress a zero offset shift versus temperature. For single gages which have a non-linear temperature response this method is expanded to include a non-linear regression to appropriately match. During operation, temperature measurements of the gage or the underlying material can be made and using the regression the zero offset may be compensated for.

If the crank is made from high thermally conductive materials, like aluminum, it is possible to take a temperature reading at a nearby site and assume that all gages are this temperature. For materials with low thermal conductivity, like carbon, measurements at the gage sites may be required and the same method of compensation can be used.

The strains measured may include one or all of bend, axial and shear, and may be multiplied by coefficients and then added together to determine the applied torque. These coefficients may be determined from calibration. A different calibration procedure is used to determine different coefficients that may be used to determine the applied axial forces or other load of interest. These coefficients are slightly sensitive to temperature. To determine their sensitivity to temperature, calibrations can be performed at different temperatures. For example, a calibration could be performed at room temperature and then in an oven and/or in a freezer.

A change in temperature can also affect the calibration values by modifying the gauge factor response or the modulus of a material. It is possible to compensate via linear or non-linear means by combining these two effects and measuring the response to calibration at various temperatures. This results in changes to the calibration factors that can be interpolated during operation in order to increase accuracy.

Accordingly, in addition to each of the above discussed strain gauges, crank assembly <NUM> may further include one or more temperature sensors. A single temperature sensor may be used in high thermally conductive materials. Alternatively, multiple temperature sensors may be used such that a temperature sensor is located next to each of, or a group of, the strain gauges discussed in <FIG>, above.

<FIG> depicts an exemplary strain gauge electronics module <NUM>, in one embodiment. Strain gauge electronics module <NUM> includes a housing <NUM> housing strain gauges <NUM>, additional sensors <NUM>, and electronics <NUM>.

Housing <NUM> may be permanently installed onto a crank (e.g. crank assembly <NUM> of <FIG>). Alternatively, housing <NUM> may be a part of an aftermarket device and be installed using the installation methods of, and include one or more features of, the housing discussed in PCT/IB2015/<NUM> with respect to housing <NUM> and installation features thereof.

The strain gauges <NUM> may include any of the strain gauge configurations discussed above with regards to <FIG>, or any other configuration of strain gauges. Strain gauges <NUM> are coupled to controller <NUM> of electronics <NUM>. Controller <NUM> may operate to control operation of strain gauges <NUM>, and also communicate power readings <NUM> to a rider. Power readings <NUM> may be based on the data obtained from strain gauges <NUM> and optionally sensors <NUM>, to a rider. In one example of operation, power readings <NUM> are transmitted via a wireless interface <NUM> to one or more of a smart phone <NUM>, bike computer <NUM>, or computer <NUM>. Power readings <NUM> may also be sent over hardwired communication lines as well. Strain gauges <NUM> may be incorporated with housing <NUM>, or may be located exterior thereto and attached to the crank at a different location. For example, the strain gauges <NUM> may be built into the crank, and housing <NUM> may be attached thereafter and electrically coupled to strain gauge leads once installed.

Strain gauges <NUM> may, in certain embodiments, include a thermal conductive pillow (see thermal conductive pillow <NUM> of <FIG>) mounted on top thereof (a) to improve measurement of gauge temperatures and corresponding electronic thermal compensation, (b) to improve dissipation of heat generated by strain gauges <NUM> during measurement, and (c) is used where the printed circuit board assembly has very uniform thermal dissipation characteristics. In an alternative embodiment, a thermally non-conductive pillow may be used to provide thermal isolation of strain gauges <NUM> to reduce localized thermal gradients from heat sources near the gauges. For example, the thermally non-conductive pillow may be used where a printed circuit board assembly has components that may create large thermal gradients that impact the strain gauges <NUM>. One or more thermal sensors may be positioned on strain gauges <NUM> to improve temperature measurement accuracy for electronic thermal compensation of measurements. A soft pillow layer may be included to prevent mechanical damage to strain gauges <NUM> by reducing localized forces on strain gauges <NUM>. For example, clamping forces used during installation may be spread over a larger area by a soft pillow to avoid damage to strain gauges <NUM>.

Additional sensors <NUM> may include the temperature sensors discussed above, as well as inertial sensors such as those discussed in PCT/IB2015/<NUM>. Other sensors than an inertial sensor may be used as well, such as magnetic reed switches or Hall effect sensors to measure angular velocity or cadence. Additional sensors <NUM> may further include sensor inputs from various sensors utilized by the rider. For example, sensors <NUM> may include data from aerodynamics, wind, inclination, heart rate, VO2max, etc. so that the efficiency of a cyclist may be determined by controller <NUM>. Such sensor data may be hardwired to housing <NUM>, or may be transmitted wirelessly using wireless interface <NUM>.

Electronics <NUM> may include the controller <NUM>, as well as a power supply <NUM> and any other circuitry required to implement the Wheatstone bridges used with strain gauges <NUM>. Power supply <NUM> may be a battery or other rechargeable power source.

Controller <NUM> may include power management logic for controlling operation of various devices housed in housing <NUM>. For example, the power management logic <NUM> may configure the strain gauges <NUM> according to various frequency sampling rates. During certain phases of the pedaling motion, the recorded strain levels are changing at a very slow rate, thus lower sampling rates may be utilized. During other parts of the pedal stroke however, the gauges may be experiencing rapidly changing loads and thus must be sampled more quickly. This variable sampling rate strategy could also be applied for different cadence rates, different riding styles and different road types.

Alternatively (or in addition to), power management logic <NUM> may switch on or off one or more of the strain gauges discussed above with respect to <FIG> such that only a portion of the strain gauges are operable at a given time. For example, if it is observed that the contribution of one or more sets of gauges (typically the secondary gauges such as the shear-sensing or axial-sensing strain gauges discussed above) are not contributing materially to the output power measurement, these sets of gauges could be turned off. However, in different load applications, these secondary gauges may have significant correctional effects and thus should be included. Another situation occurs whereby not including a certain set of strain gauges sets affects the accuracy by a known factor. This known factor may then be applied as a correction factor and thus the accuracy is preserved while the energy saving is achieved.

Additionally, power management logic <NUM> may include a learning algorithm whereby repeated patterns in the data produced by strain gauges <NUM> are recognized. For example, consistent pedal strokes by the rider may provide similar data outputs by the strain gauges <NUM>. Accordingly, the sampling rate of the strain gauges <NUM>, or particular strain gauges <NUM> which are turned on may be altered to reduce the power used by strain gauges <NUM> at these repetitive patterns.

Power management may be crucial to the life span of the device <NUM>. For example, where electronics module <NUM> is included on a stationary training bike in a training gym, it may be tedious to frequently change the battery of the power supply <NUM>. Therefore, power supply <NUM> may be rechargeable using various bicycle powered energy generators. Such bicycle powered energy generators include, but are not limited to: mechanically driven dynamos placed in wheel hubs, axles, bottom bracket of the bicycle frame, pedal spindles; solar panels placed on the rider, or the bicycle frame, or other part of the bicycle; wind generators that capture energy while the rider is moving; or piezo-electric energy supplies attached to the bicycle that creates energy based on bending/stretching of the frame during riding.

Such bicycle powered energy generator could be coupled to the power supply <NUM> to recharge a rechargeable battery, super capacitor, or other small flywheel capable of storing energy for use within electronics module <NUM>. Such power supply <NUM> could include a non-rechargeable back-up battery, as well as the rechargeable battery. Furthermore, such power supply <NUM> could be configured to supply power to other electronic devices on the bicycle, or in use by the user.

Energy generated by such bicycle powered energy generator could be transmitted to the power supply <NUM> using a variety of methods including, but not limited to, conducting wire, conducting foil, conducting thread, brush contracts to send the power from the bike frame to the crank assembly <NUM>, or wireless methods including non-radiative means such as magnetic inductive coupling, magnetic resonance coupling, capacitive coupling, and radiative far-field wireless using lasers or microwave.

One example of a bicycle powered energy generator will now be described in detail. <FIG> depicts a bottom perspective view of a bicycle mounted magnetic power generator system <NUM>, in one embodiment. <FIG> depicts a top front perspective view of the bicycle mounted magnetic power generator system <NUM>, of <FIG>. <FIG> depicts a front view of the base ring <NUM> having magnets <NUM> used in the bicycle mounted magnetic power generator system <NUM>, of <FIG>, in one embodiment. <FIG> depicts an exploded view of the bicycle mounted magnetic power generator system <NUM>, of <FIG>. <FIG> depicts the strain gauges <NUM>, electronics <NUM>, and coil <NUM> when mounted on the bicycle mounted magnetic power generator system <NUM>, without the base portion <NUM>, in one embodiment. <FIG> are best viewed in light of the following discussion.

Bicycle mounted magnetic power generator system <NUM> includes an electronics module <NUM> mounted to an inner surface of bicycle crank <NUM> coupled to a bicycle frame <NUM> on bottom bracket <NUM>. Crank <NUM> is operated via force exerted on a pedal (not shown) attached to crank <NUM> at pedal attachment point <NUM>. Electronics module <NUM> may include any feature of electronics module <NUM> discussed above, and be used to operate any one of strain gauge configurations discussed above with respect to <FIG>.

Generator system <NUM> is shown as a magneto system for generating power. Electronics module <NUM> includes at least one coil <NUM> coupled with a power storage element, such as a battery. Coil <NUM> is coupled with electronics <NUM> for controlling power generation by coil <NUM>. Coil <NUM> is mounted on crank <NUM> such that it is adjacent to a base ring <NUM> including a plurality of stationary magnets <NUM>(<NUM>), <NUM>(<NUM>),. Base ring <NUM> may be coupled such that is stationary as the crank <NUM> rotates about bottom bracket <NUM>. For example, base ring <NUM> may be mounted directly to frame <NUM>, or to an intermediary part around bottom bracket <NUM> such that it does not rotate or otherwise move. As coil <NUM> is rotated due to pedaling by the rider, a voltage is generated at the leads of the coil <NUM> based upon magnetic fields produced by magnets <NUM>.

As shown in <FIG>, base ring <NUM> is mounted to frame <NUM> and includes a plurality of magnets <NUM>(<NUM>)-<NUM>(N). Although shown with <NUM> magnets <NUM>, it should be appreciated that there may be more or fewer magnets without departing from the scope hereof. Magnets <NUM> are shown having alternating north (N) and south (S) polarities. Therefore, as coils <NUM> pass by magnets <NUM>, the coils generate alternating pulses of voltage depending on the polarity of the magnet <NUM>. Electronics module <NUM> then rectify and filter this single to generate a smooth DC signal for storage in a power storage module (such as a rechargeable battery in power supply <NUM> of <FIG>). The power supply then is capable of operating one or more electronic devices (such as controller <NUM> operating wireless interface <NUM> and strain gauges <NUM> having any of the configurations discussed above with regards to <FIG>). In alternate embodiments, magnets <NUM> all have the same polarity (e.g. N or S polarity).

Magnets <NUM> may further include various elements for focusing the magnetic field produced thereby to increase the power generated through coils <NUM>. For example, the magnets <NUM> could include ferrous cups that focus the magnetic field at the coil <NUM>. Additionally, magnets <NUM> may be formed from various materials to increase the magnetic field produced thereby. Magnets <NUM> may be formed of various rare earth metals, or alternatively may be electromagnets. Furthermore, the magnets <NUM> may be prism or cone shaped to focus their magnetic field at coil(s) <NUM>.

Electronics <NUM> may further include algorithms for determining various aspects of the rider's performance. Where magnets <NUM> are regularly spaced around ring <NUM>, the periodic nature of the output signal produced by coil <NUM> may be utilized by electronics to determine acceleration, rotation/minute, etc. In other words, coil <NUM> may be used as a rotary encoder based on the spacing between magnets <NUM>.

As shown in <FIG>, housing may include a base portion <NUM> including coil mounting location <NUM>. Base portion <NUM> may couple with electronics <NUM> and be mounted adjacent strain gauge <NUM> which is attached to crank <NUM>. In certain embodiments, base portion <NUM> may further include a shield (not shown) for providing a magnetic field shield such that magnetic field generated by magnets <NUM> and coil <NUM> do not interfere with operation of strain gauges <NUM>. As shown in <FIG>, when mounted onto crank <NUM>, the coils <NUM> are adjacent strain gauges <NUM> and only take up minimal physical area on the inner surface of crank <NUM>. As such, system <NUM> is easily installed on any crank <NUM>. Therefore, any crank may be modified to include power generation system <NUM>, and electronics module <NUM>.

It should be appreciated that in another embodiment, a magnet could be placed on the crank <NUM>, and one or more coils could be placed in ring <NUM> and connected to a power supply located on the frame. This power supply could be utilized to power or recharge a power supply located on the bicycle (such as on or in the frame <NUM>).

Coils <NUM> are located adjacent to magnets <NUM> and spaced apart from magnets <NUM> a given distance. As such, crank <NUM> may include a spacing element (not shown) to set the distance that coils <NUM> are located from magnets <NUM>. It should be appreciated that the closer the coil(s) <NUM> are located to magnets <NUM>, the more power that is output at the leads of the coils.

Although not shown, electronics <NUM> may further include an outer housing that may or may not cover coil <NUM>.

<FIG> depicts a coil system <NUM> for use in the bicycle mounted power generator <NUM>, of <FIG>, in one embodiment. Coil system <NUM> is an example of coil <NUM> and includes, stationary coil(s) <NUM> surrounding an internal magnet <NUM> that is rotatably mounted on axis <NUM>. Magnetic fields from magnets <NUM> within ring <NUM> (as discussed above) cause magnet <NUM> within coil system <NUM> to rotate about axis <NUM>. This rotation induces current in coils <NUM> to produce an output <NUM> at coil leads <NUM>. In operation, the magnetic field produced by magnets <NUM> located in base ring <NUM> is strong enough to rotate magnet <NUM> about axis <NUM>, but not strong enough to negatively affect the output <NUM> at coil leads <NUM>. In alternate embodiments, a magnetic shield may be placed between coils <NUM> and base ring <NUM> such that the magnetic field produced by magnets <NUM> only affect magnet <NUM> and do not induce electricity in coils <NUM>.

Claim 1:
A crank power measurement system for measuring one or more of force, torque, power, and velocity of the crank, comprising:
a crank (<NUM>),
two or more strain gauges located on one surface of the crank, and,
electronics for receiving strain data from the two or more strain gauges and determining at least one or more of bend-strain, shear-strain, and axial strain,
the two or more strain gauges including a first (<NUM>) and a second bend-sensing strain gauge (<NUM>) located away from opposing sides of a neutral axis (<NUM>) of the crank,
the two or more strain gauges further including a third (<NUM>, <NUM>) and a fourth bend-sensing strain gauge (<NUM>, <NUM>), and
a) the third bend-sensing strain gauge (<NUM>) being located between the neutral axis (<NUM>) and the first bend-sensing strain gauge (<NUM>), the fourth bend-sensing strain gauge (<NUM>) being located between the second bend-sensing strain gauge (<NUM>) and the neutral axis (<NUM>), or
b) the third bend-sensing strain gauge (<NUM>) being located adjacent and at substantially the same distance away from the neutral axis (<NUM>) as the first bend-sensing strain gauge (<NUM>), the fourth bend-sensing strain gauge (<NUM>) being located adjacent and at substantially the same distance away from the neutral axis (<NUM>) as the second bend-sensing strain gauge (<NUM>).