Method and apparatus for measuring power output and for measuring tension and vibrational frequency of a elongate flexible member

Field of the Invention

0001This invention relates generally to a method and apparatus for measurement of power output of one powering a system driven by an elongate flexible member such as chain. The system preferably is a bicycle. More specifically, it relates to an apparatus and method for the measurement of power output of a bicyclist.

Background of the Invention

0002It is often desirable to measure power output of a bicyclist or a rider of other human powered vehicle. Such information is useful both for the casual rider as well as the high performance trainer. A bicyclist can use this information, among other things, to monitor increases in cardiovascular fitness, quantify maximum output and power, optimize pedaling cadence, and determine maximum efficiency. Such measurements are also useful to those seeking to reduce body fat though exercise or to replenish food during extended rides. While power measuring devices are available on stationary exercise equipment commonly found in health clubs and the like, the size of currently available power measuring devices makes it impractical to install them on actual human powered vehicles. A solution for measuring instantaneous power in such circumstances in disclosed in European Patent Application <patcit id="pcit0001" dnum="EP0422325A1"><text>0 422 325 A1</text></patcit>. Some force and power measurement equipments use strain gage sensors installed on the crank or the pedal of a bicycle. This attaching typically by gluing must be done carefully with special instructions. The sensor also needs calibration after attaching. One presented way to measure power is also done by sensoring the shoe of a bicyclist. This is not, however, practical in every day use.

0003In addition to human powered vehicles, power measurements would also be useful for motor driven devices. For example, in motor assisted bicycles, chain tension and/or human power output can be used to determine the relative instantaneous output of the motor. For motor-driven devices such as motorcycles, chain tension and power output can be used to monitor the load on the engine, which relates information on fuel consumption, mechanical wear, and efficiencies. A solution for measuring power transmitted by a belt is disclosed in patent publication <patcit id="pcit0002" dnum="DE4338819"><text>DE 43 38819</text></patcit>.

0004What is needed then, is a method and device which is compact in size and operatively arranged to measure power output of a bicyclist. Other quite necessary needs are that sensor unit can be easily attached and signal to be measured is easy to find with a good signal to noise ratio. On the other hand a measurement device could be taken to use without a difficult calibration procedure.

Summary of the Invention

0005The invention broadly provides a method and apparatus for measuring the power output of one powering a bicycle according to claims 1 and 12.

0006The advantages of this invention are simple easy to install sensor units avoiding complex calibration process and however accurate and reliable force and power measurement. Another object of the invention is to display power output of a bicyclist in real time as the cyclist is riding.

0007These and other objects, advantages and features of the invention will become obvious to those having ordinary skill in the art upon a reading of the following detailed description, read in conjunction with the drawings.

Brief Description of the Drawings

0008<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a side view of a typical multi-speed bicycle with which the present invention is used;</li><li><figref idref="f0002">Figure 2</figref> is a fragmentary side view of the rear derailleur of the bicycle shown in Figure I and a speed sensor mounted to the derailleur;</li><li><figref idref="f0002">Figure 3</figref> is a cross-sectional view of the derailleur/sensor combination of <figref idref="f0002">Figure 2</figref>, taken generally along line 3-3 of <figref idref="f0002">Figure 2</figref>;</li><li><figref idref="f0002">Figure 4</figref> is a fragmentary top view of the vibration sensor of the invention;</li><li><figref idref="f0002">Figure 5</figref> is a side view of the sensor shown in <figref idref="f0002">Figure 4</figref>;</li><li><figref idref="f0002">Figure 6</figref> is a cross-sectional view taken generally along line 6-6 in <figref idref="f0002">Figure 4</figref>;</li><li><figref idref="f0003">Figure 7</figref> is a schematic block diagram of the electrical and electronic circuit of the apparatus of the invention;</li><li><figref idref="f0004">Figure 8</figref> is an electrical schematic diagram of the connectors used to connect the peripheral interface circuit to the computer processing unit;</li><li><figref idref="f0005">Figure 9</figref> is an electrical schematic diagram of part of the peripheral interface circuit of the invention;</li><li><figref idref="f0006">Figure 10</figref> is an electrical schematic diagram of part of the peripheral interface circuit of the invention;</li><li><figref idref="f0007">Figure 11</figref> is an electrical schematic diagram of part of the peripheral interface circuit of the invention; and,</li><li><figref idref="f0008">Figure 12</figref> is a flow chart of the computer program operatively arranged to run the digital signal processor of the invention.</li></ul>

Detailed Description of the Preferred Embodiment

0009At the outset, it should be understood that the description which follows is directed to a preferred embodiment of the invention, but that the appended claims are not so limited. It should be also appreciated that like reference numerals on different drawing figures refer to identical structural elements.

0010<figref idref="f0001">Figure 1</figref> illustrates a typical multi-speed bicycle 10 which is well known in the art. The bicycle, which, in this embodiment is a 10-speed bicycle, comprises a frame 11, which frame comprises top tube 34, seat tube 32, seat stay 31, chain stay 23 and down tube 33. The bicycle further comprises front fork 17, front wheel 12, rear wheel 13, seat 14, handlebars 15, drive sprocket 16, pedal 25, chain 18, front derailleur 21, sprocket cluster 20, rear derailleur 19, front derailleur shift lever 28 and rear derailleur shift lever 26.

0011As is well known in the art, to propel the bicycle, the rider drives the pedal, turning the front sprocket and causing the chain to engage and drive one of the rear sprockets. The rear sprockets, in turn, are fixedly secured to the rear axle of the rear wheel, and thereby drive the wheel to cause the bicycle to move. The front derailleur is used to move the chain from one of a plurality of front drive sprockets. In a 10-speed bicycle as shown, there are typically two front sprockets, each with a different number of teeth (e.g., 22 teeth on the small sprocket and 54 teeth of the large sprocket). Similarly, the rear derailleur is used to move the chain from one rear sprocket to another. Typically, in a 10 speed bicycle as shown, there are five rear sprockets, each containing a different number of teeth (e.g., 12 teeth on the smallest diameter sprocket and 28 teeth on the largest diameter sprocket).

0012The power output of the cyclist is equal to the amount of work done by the cyclist per unit time. One measurement of this power is given by the equation: <maths id="math0001"><math display="block"><mi mathvariant="normal">P</mi><mfenced><mi>watts</mi></mfenced><mo mathvariant="normal">=</mo><mi>chain speed</mi><mspace width="1em" /><mfenced><mi>meters</mi><mo mathvariant="normal">/</mo><mi>sec</mi></mfenced><mo mathvariant="normal">*</mo><mi>chain tension</mi><mspace width="1em" /><mfenced><mi>Newtons</mi></mfenced></math><img file="EP0909940B1_D0001.tif" /></maths>

0013Thus, it is seen that power output is calculated from measurements of chain speed and chain tension.

0014It is noticed here that power output is not typically constant during a cadence cycle of rotating cranks. Power fluctuates due to different force and moment achieved against pedals and cranks. The minimum power or force is typically detected when one pedal is at highest position and another pedal is at lowest position. The maximum power or force is typically achieved when the pedals are at the same horizontal level. Because power and force is transmitted directly to the chain through the front sprocket, the power variation also causes chain speed and chain tension to fluctuate during a cadence cycle respectively.

0015It will be appreciated by those skilled in the art that the present invention can be used to measure the power transmitted by any elongate flexible member, for example, a bicycle chain. The elongate flexible member may be a belt made of materials including, rubber, plastic, and leather. The elongate flexible member may have a plurality of metal elements spaced throughout the belt.

0016Adverting to all of the drawings, the apparatus of the invention broadly comprises vibration sensor 24, speed sensor 22 and computer module 35. The vibration sensor measures the vibration of chain 18; the speed sensor measures the speed of the chain and the computer module calculates power output, which power output is calculated from the tension and speed values. The power output value is displayed on a LCD display which is integral with the computer module.

0017Chain speed is measured as the chain passes through the rear derailleur. As shown in <figref idref="f0002">Figure 2</figref>, derailleur 19 comprises cage 50, pulley wheel 30 and jockey wheel 29. Both the pulley wheel and the jockey wheel are arranged for rotation within the cage. Pulley wheel 30 rotates about mounting bolt 51, whereas jockey wheel 29 rotates about mounting bolt 36. Chain 18 engages both pulley wheels and is operatively arranged to rotate pulley wheel 30 in a counterclockwise direction and jockey wheel 29 in a clockwise direction when the chain is driven in a clockwise rotation by front sprocket 16. Jockey wheel 29 comprises a plurality of embedded magnets 29a, 29b, 29c, 29d, and 29e. The magnets are A1NiCo in composition and are equally spaced radially and angularly. Although five magnets are shown in the drawing, any number of magnets can be used. In fact, the attached software code for the invention is written for four equally spaced magnets.

0018Speed sensor 22 comprises approximately 4000 turns of 40 gauge enamel coated wire, wound about a 0.125 inch diameter mild carbon steel dowel, which is then bent to form a U-shape. The winding has a resistance of approximately 200 ohms. Once the winding is made, it is potted in place with epoxy. As shown in <figref idref="f0002">Figures 2 and 3</figref>, sensor 22 is mounted to bracket 50 by bolt 36. The body of the sensor may have an integral mounting bracket 38 or may be mounted using any standard mounting means known in the art. The sensor may be a proximity sensor such as a simple reed switch or some other type of sensor including, but not limited to, magnetic, inductive, or capacitive sensors.

0019In operation, speed sensor 22 detects the movement of the magnets as pulley wheel 29 rotates. For a known pulley diameter, the linear speed of the chain can be derived from the measured rotational speed of the pulley wheel from the following equation: <maths id="math0002"><math display="block"><mi mathvariant="normal">v</mi><mo mathvariant="normal">=</mo><mi mathvariant="normal">ωr</mi></math><img file="EP0909940B1_D0002.tif" /></maths> where <ul id="ul0002" list-style="none" compact="compact"><li>v = linear chain speed;</li><li>ω = rotational chain speed; and</li><li>r = radius of the pulley wheel</li></ul>

0020Although one means of measuring chain speed has been described in detail, it should be readily appreciated by those having ordinary skill in the art that other means of measuring chain speed are possible. For example, a magnet (or magnet ring containing multiple magnetic poles) can be mounted to one of the bicycle cranks. A speed sensor can be mounted to the bicycle's wheel. Crank speed, wheel speed, and a table of the bicycle's gear ratios then allows the calculation of chain speed. Alteratively, a magnet can be mounted to one of the cranks and the sensor can be a gear position indicator. This indicator would sense which of the bicycle's front sprockets is engaged with the chain. These sensors, along with a table of the bicycle's gear ratios then allows the calculation of chain speed. Finally, chain speed can be detected directly using a magnetic sensor, such as a variable reluctance (VR) sensor, a Hall Effect sensor or a magneto resistive sensor. This method measures the linear movement of chain pins past the sensor to produce a signal that is representative of chain speed.

0021The next step in determining power is to measure the vibration or tension of the drive chain. Examples of sensors that can be used to measure the vibration include but are not limited to variable reluctance sensors, Hall effect sensors, magneto resistive sensors, inductive, capacitive, optical and acoustic sensors. These sensors measure the frequency of vibration of the drive chain. In the case of a ferrous object, such as a bicycle chain moving past a magnetic-type sensor such as a variable sensor, an electric current is generated that is characteristic of the body's vibration. Such vibration results from excitation, or "plucking", which is a by-product of the normal operation of most devices, due to the inevitable friction and slight roughness of the tensioned body engaging with its drive or guide interfaces, such as rollers, sprockets, etc. In the case of a bicycle, this vibration is caused by the constant lateral and longitudinal accelerations of the bicycle, the motion induced by the individual rollers of the chain engaging and disengaging with the teeth of the drive sprockets, and the roughness of the surface on which the bicycle is being pedaled.

0022In a multi-speed bicycle the chain is capable of being shifted to a number of different sprockets at both the front and the rear. This causes the chain's position (relative to the bike) to change, but the overall length of the vibrating section remains essentially constant. This is because the chain engages drive sprockets at both ends of the tensioned section, and the position of the axis of rotation of these sprockets does not change. The constant length likewise means the mass of the vibrating section remains essentially constant.

0023In a preferred embodiment, vibration sensor 24 is a variable reluctance sensor (VR sensor). As shown in <figref idref="f0002">Figures 4 and 5</figref>, the VR sensor comprises a 1.0" x 0.5" x 0.25" rectangular A1NiCO magnet 40 wrapped with approximately 3000 turns of 40 gauge copper enamel coated wire having a resistance of 1.049 ohms/foot. The total resistance of the coil is approximately 1000 ohms. The faces of the magnet are laminated with rectangular carbonite plastic sheets. The winding is potted into place with epoxy. The sensor is housed in a plastic casing 42 and is mounted to chain stay 23, such that its face 44 is in close proximity to the upper run of chain 18. In a preferred embodiment, as shown more clearly in <figref idref="f0002">Figures 5 and 6</figref>, the sensor is mounted to the chain stay by means commonly known to those skilled in the art. so that face 44 of the sensor is directly below the upper run of the chain. During the operation of the bicycle, as the chain is moved from sprocket to sprocket in the front and rear, thereby changing the gear ratio, the position of the chain changes depending upon the front and rear sprockets it is on. As shown in <figref idref="f0002">Figure 6</figref>, the sensor is mounted at an angle so that face 44 of the sensor is at a constant distance from the chain irrespective of the sprockets being used by the rider. In a preferred embodiment, this angle is approximately 30 degrees. Nevertheless, a change in the distance between the sensor and the chain (due to shifting gears, for example) will affect the amplitude of the signal, but not the frequency. Since the tension in the chain is related to the frequency of vibration of the chain, and not the amplitude of vibration, the magnitude of excitation is not relevant to the tension measurement.

0024The natural frequency of vibration of a body such as a string or chain is related to the tension carried by the body. This relationship is defined by the equation: <maths id="math0003"><math display="block"><mi mathvariant="normal">F</mi><mo mathvariant="normal">=</mo><mn mathvariant="normal">4</mn><mo>⁢</mo><msup><mi>mlv</mi><mn mathvariant="normal">2</mn></msup></math><img file="EP0909940B1_D0003.tif" /></maths> where: <ul id="ul0003" list-style="none" compact="compact"><li>F = force carried by body in Newtons</li><li>m = mass of tensioned section of body in kilograms</li><li>I = length of tensioned section of body in meters</li><li>v = frequency of vibration in hertz.</li></ul>

0025In addition to the primary vibration that characterizes the tension in a body, other structures within the bicycle chain may cause extraneous signals. One such extraneous signal is caused by the pins of the bicycle drive chain moving past the sensor. Another extraneous signal is characteristic of the chain disengaging from the sprocket teeth. A yet another extraneous signal is caused by the uneven distribution of the mass of the chain between the links and pins. In addition, other extraneous signals may be generated due to the relationship of the sensor to the chain. These extraneous signals can be filtered out during signal processing so as to leave only the primary vibration signal. These signals can be eliminated by various means. One method is to construct the sensor so that it combines the signals from two or more physical locations in such a way that the extraneous signal components cancel, or to use a sensor that has a relatively low response in the frequency band where the extraneous signal components occur. A second method is to use analog circuitry in the computer to filter out the frequency range of the extraneous components, which can be a fixed range, or a variable range controlled by the chain speed sensor. In the preferred embodiment, a third method is employed, in which the extraneous signal components are filtered out by means of digital signal processing, as described in the attached computer code for the DSP

0026As previously described, the overall length of the vibrating section of the chain remains essentially constant because the axes of rotation of the sprockets at both ends of the chain section do not change. However, the length of the section of the chain that vibrates does not remain exactly constant as various front and rear sprockets are selected. If the sprockets being used are differing sizes, the length of the vibrating length will be reduced. Depending on the level of accuracy desired in the power measuring system, this variation can be ignored, as in many circumstances, the error introduced will be insignificant. In those cases, it is sufficient to perform calculations using a constant value for the length of the vibrating section of the chain. This value can be either the distance between the centers of the sprockets, or that value reduced by a small amount.

0027If greater accuracy is desired, or if there will be large variation in the sizes of the sprockets used, the exact vibrating length can be calculated. The vibrating length is, in mathematical terms, the length of a line segment that is externally tangent to the circles formed by the two sprockets. In mathematical terms, the length of such a segment is: <maths id="math0004"><math display="block"><mi mathvariant="normal">L</mi><mo mathvariant="normal">=</mo><mi mathvariant="normal">D</mi><mo mathvariant="normal">*</mo><mi>sqrt</mi><mo>⁢</mo><mfenced><mn mathvariant="normal">1</mn><mo mathvariant="normal">-</mo><mfenced><mfenced><mi mathvariant="normal">R</mi><mo>⁢</mo><mn mathvariant="normal">1</mn><mo mathvariant="normal">-</mo><mi mathvariant="normal">R</mi><mo>⁢</mo><mn mathvariant="normal">2</mn></mfenced><mo mathvariant="normal">/</mo><mi mathvariant="normal">D</mi></mfenced><mo mathvariant="normal">*</mo><mo mathvariant="normal">*</mo><mn mathvariant="normal">2</mn></mfenced></math><img file="EP0909940B1_D0004.tif" /></maths> where: <ul id="ul0004" list-style="none" compact="compact"><li>L = the desired length of the vibrating section</li><li>D = the distance between the centers of the two sprockets (this value does not change as the gears are shifted)</li><li>R1 = the radius of one of the sprockets</li><li>R2 = the radius of the other sprocket</li></ul>

0028The radius of a sprocket can be calculated from the number of teeth on the sprocket by means of the formula: <maths id="math0005"><math display="block"><mi mathvariant="normal">R</mi><mo mathvariant="normal">=</mo><mi mathvariant="normal">T</mi><mo mathvariant="normal">*</mo><mi mathvariant="normal">P</mi><mo mathvariant="normal">/</mo><mfenced><mn mathvariant="normal">2</mn><mo mathvariant="normal">*</mo><mi>PI</mi></mfenced></math><img file="EP0909940B1_D0005.tif" /></maths> where: <ul id="ul0005" list-style="none" compact="compact"><li>R is the desired radius</li><li>T is the number of teeth</li><li>P is the pitch (distance between adjacent teeth)</li></ul>

0029The sizes of the sprockets can be determined in various ways. If the shifting mechanism provides information as to what sprocket from a set has been selected, or if sensors are fitted to determine which sprockets the chain is actually on, then the sprocket sizes can be determined from a list of available sprockets.

0030Alternatively, if the chain linear speed, and the rotational speed of the two sprockets are known, sprocket sizes can be determined without prior information about what sprockets are available. The rotational speeds of the sprockets are commonly measured on bicycles, with the speed of the front sprocket used to calculate cadence, and the speed of the rear sprocket (which is equivalent to the speed of the bicycle wheel) used to calculate bicycle speed. This determination of the sprocket is by means of integrating the chain speed over one rotation of the desired sprocket. In a preferred embodiment, the chain speed sensor will detect links of the chain directly, and the links can be counted over the period of one revolution of the sprocket in question. To reduce the errors due to rounding the links can be counted over two or more revolutions and divided by the number of revolutions. Alternatively, if the size of one sprocket has been determined, the size of the other sprocket may be obtained by multiplying the size of the first sprocket by the ratio in speeds between the two sprockets.

0031The vibration sensor and the speed sensor are electrically connected to the computer module, which contains a signal processing unit. The module contains a liquid crystal display (LCD) and keyboard. The module is typically mounted on the handlebars for easy viewing during cycling, although it can be mounted in any convenient location. In a preferred embodiment, the computer module comprises a Texas Instruments TMS32OC3X Starter Kit, and an additional circuit board which comprises the peripheral interface circuit. The basic components of the TMS32OC3X DSP Starter Kit are the TMS32OC31 DSP, a TLC32040 analog interface circuit (AIC), expansion connectors, system clock, parallel printer port interface, and tri-color LED.

0032The operation of the electronic circuitry of the invention is best understood with reference to <figref idref="f0003">Figure 7</figref>, which illustrates a general schematic and block diagram of the invention. In this drawing, block 100 represents vibration sensor 24. As the chain vibrates in the vicinity of this sensor, a signal with a voltage in the range of approximately 2 mV to 200 mV is produced. The relevant signal due to the frequency characteristic of the tension in the chain will be one component of this signal, but it may be accompanied by other signal components. The output signal from this sensor is fed to block 103, which represents the chain vibration amplifier.

0033Amplifier 103 amplifies the chain vibration signal to a level that is appropriate for circuit components 104 and 105. The gain level can be adjusted two different ways, for four different gain settings. One adjustment is via jumper JP8, and the other is by means of the low gain signal, which is under control of the microprocessor. Although the amplitude of the signal from sensor 100 can vary, the dynamic range of circuit components 104 and 105 is high enough that the gain level should not need to be adjusted during operation; these two adjustments can be made once and left alone. The output of this section is an amplified version of its input, and is fed to circuit components 104 and 105. Alternatively, the output signal from this sensor is fed to block 104, which represents the low-pass filter.

0034Circuit component 104 is a low-pass filter and component 105 is a 14 bit A/D converter. These two circuits are both contained in the Texas Instruments TLC32040 AIC part on the Starter Kit board. This part can be configured to convert its analog input to a 14-bit digital stream, sampled at 450 Hz, and it includes a Nyquist frequency low-pass filter to eliminate aliasing. The digital output of this section is read by the DSP (circuit component 110) for frequency calculations.

0035Component 101 contains chain speed sensor 22 as described previously. The sensor comprises a wire coil mounted on rear derailleur cage 50. Jockey wheel 29 of the derailleur contains embedded magnets 29a, 29b, 29c, 29d and 29e that induce a voltage in the coil as they pass by. This results in an oscillating signal whose frequency is directly proportional to the rotational speed of the jockey wheel, and consequently, to the linear speed of the chain that is driving the jockey pulley. The amplitude of this signal is typically in the range of 20 mV to 2V. This signal is fed to hysteresis circuit 102. It should be noted that, although five magnets are embedded in the jockey wheel in the preferred embodiment, any number of magnets can be embedded. Also, other means of measuring chain speed may be employed.

0036Hysteresis circuit 102 converts the output signal of chain speed sensor 101 from its low voltage level to a TTL level that can be read by digital signal processor (DSP) 110. Intermediate level information is not of interest-only the fundamental frequency due to the passing of each jockey wheel magnet is relevant. For this reason, the circuit consists of a Schmitt Trigger, which has very high gain to "clip" the signal, and which has hysteresis to suppress any low-level noise that may be present in the signal. The result is a pulse train with each pulse corresponding to one of the jockey wheel magnets. This signal is input to digital signal processor 110.

0037Digital signal processor (DSP) 110 and random access memory (RAM) 106 operate together to perform the power calculations. In a preferred embodiment, the DSP is a Texas Instruments Model No. TMS32OC31. The RAM contains the program code for this device (although such code could also be stored in a ROM chip connected to the DSP in an analogous manner). The DSP calculates power based on two inputs. The first is the signal from circuit component 102, which can be used to determine the linear speed of the chain (given the fixed values of how many magnets are on the jockey wheel, and how many teeth are on the jockey wheel). The second is the signal from circuit components 104 and 105, which can be used to determine the vibrational frequency of the chain, and in turn the tension of the chain (the speed of the chain, determined from the jockey wheel signal, is also used to assist in selecting the proper component from the output signal of circuit components 104 and 105). The tension of the chain is multiplied by the speed of the chain to give a result of the power transmitted through the chain at any instant. The method used to do this calculation is described fully in the attached computer code for the DSP.

0038The signal is processed using a standard technique known to those skilled in the art including, but not limited to, Fast Fourier Transform, Discrete Fourier Transform, Fourier Transform, Zero-Crossing, 1-bit FFT with cosine/sine table look-up, wavelets, filter banks, FIR filters, IIR filters, adaptive filter techniques (including Least Mean Square Algorithm), adaptive interference cancelling, adaptive self-tuning filters, adaptive line enhancers, and gabor expansion. In one embodiment, particularly if there are no significant interference signals present, the frequency of the vibration can be determined by using "zero-crossing" algorithm, which measures the period of a sinusoid wave by realizing when the signal passes through the median voltage and measuring the time period between median voltage crossings. In another embodiment, a Fast Fourier Transform (FFT) is performed on the signal. Linear prediction algorithm (LPA) and auto regression method (AR) can be used to find more practical and more implementable solution in a microprocessor based technique.

0039To decrease the amount of calculation capacity for the vibration frequency determination the chain speed variation signal can also be used. Because the chain speed reflects the power and force variation against the pedals and cranks this chain speed variation signal can be used as a reference signal form for the power variation signal form. And because these signals are closely correlating it is enough to calculate absolute power only sometimes so that the absolute power level of varying signal can be fixed. So it is necessary calculate and define the absolute power of force and tension only some (for example 1-2) times per one cadence cycle. That is because the power signal form is now known from the chain speed signal and some points are used to fix that signal to the absolute scale values.

0040In a preferred embodiment of the invention the speed of the elongate flexible member can be measured directly by using a speed sensor. In another preferred embodiment of the invention the speed is determined indirectly, for example by using cadence measurement. In said another embodiment the speed of the elongate flexible member is determined by using cadence signal, wheel speed and sprocket sizes or the ratio of sprocket sizes.

0041Chain speed is calculated by counting the time between the rising edges of the jockey wheel signal.

0042Memory 107 is a non-volatile memory chip, such as a serial EEROM. The DSP is operatively arranged to write and read data to and from memory 107. Memory 107 is used to store installation- specific information such as chain-line length and chain linear density.

0043Circuit components 108 (liquid crystal display (LCD)), 109 (keyboard/CPU), and 111 (keyboard) comprise a simple "terminal" operating at TTL voltage levels and typically arranged to be mounted on the handlebars of the bicycle. The DSP can send the calculated power value (or any other relevant information) to this CPU, which will display the information on the LCD. Key presses on the keyboard will result in information being sent to the DSP, which can respond with some appropriate action (e.g., changing the displayed power value from watts to horsepower.) Any suitable user interface can be implemented. These three components comprise a standard off-the-shelf unit manufactured and available by Bolton Engineering of Melrose, MA. In a preferred embodiment, a Bolton unit which uses a Microchip PIC16C63 processor was used. Of course, other processor units would also function satisfactorily. In a preferred embodiment of the invention the computer generates a signal representing the power output of the elongate flexible member to a external unit coupled to said computer, said external unit having a display for displaying the power output. Said external unit is the terminal referred above. In a preferred embodiment of the invention the external unit coupled to said computer is a heart rate monitor having a display. Heart rate sensor measures the ECG of the bicycle user.

0044Circuit component 112 is an optional RS232 interface, well known to those having ordinary skill in the art. This interface converts the TTL signal levels of the UART connected to the DSP into RS232 levels for communication with an external device such as a personal computer (PC). The DSP can use this interface to upload a series of saved power values to a host PC for analysis.

0045Component 113 is a host PC. This PC is an external device which is not used in normal operation of the invention. It can be any sort of computer that can retrieve information from the power meter device for further processing. It would typically be connected to the power meter at the completion of a bicycle fide.

0046<figref idref="f0004 f0005 f0006 f0007">Figures 8-11</figref> show electrical schematic diagrams of the peripheral interface circuit of the invention. The peripheral interface circuit connects the several peripheral devices (e.g., RAM, keyboard, display, etc.) of the invention to the microprocessor unit 110. The signal connections in the physical connectors of the electronic unit are shown in <figref idref="f0004">Fig. 8</figref> and the connections of a keyboard and display in <figref idref="f0005">Fig. 9</figref> and the connection of a memory unit in <figref idref="f0006">Fig. 10</figref>. The connection of the sensors such as wheel speed sensor (WHEEL), cadence sensor (CADENCE), chain speed from the jockey wheel (JOCKEY) and vibration sensor (AUX) are shown in <figref idref="f0007">Fig. 11</figref> to the Texas Instruments TMS32OC3X DSP Starter Kit board.

0047<figref idref="f0008">Figure 12</figref> is a flowchart of the computer code used to run the DSP in a preferred embodiment of the invention.