WO2016030859A1

WO2016030859A1 - A measuring device

Info

Publication number: WO2016030859A1
Application number: PCT/IB2015/056532
Authority: WO
Inventors: Gregory John ROBERTS-BAXTER
Original assignee: Roberts-Baxter Gregory John
Priority date: 2014-08-29
Filing date: 2015-08-28
Publication date: 2016-03-03

Abstract

A measuring device and method for measuring the power exerted on a pedal are described. The measuring device (1, 140) includes a sensor unit (3, 90, 120, 142) configured to be secured intermediate a pedal (52) and a crank (54, 124). The sensor unit (3, 90, 120, 142) includes at least one sensor (16, 80, 102) capable of measuring a force exerted between the pedal (52) and the crank (54, 124). The measuring device (1, 140) further includes a processor (24) for operating the or each sensor (16, 80, 102) to obtain measurements therefrom. The measuring device (1, 140) may include a transmitter (26) to transmit measurements to a remote processor (40). The measuring device (1, 140) may further include a cadence sensor (32) for measuring the rotational speed of the crank (54, 124). The processor (24) and transmitter (26) are included in a control unit (5) separate from the sensor unit (3, 90, 120).

Description

A MEASURING DEVICE

CROSS-REFERENCE(S) TO RELATED APPLICATIONS

This application claims priority to Australian provisional patent application number 2014903458, filed on 29 August 2014, which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to a device and method for measuring the power exerted on a pedal.

BACKGROUND TO THE INVENTION

A fast growing trend in cycling is that of measuring rider power output while riding a bicycle. Measured in watts, power is the rate at which work is done and indicates how much energy or work can be delivered in a time period. Power is important because it is a good indicator of strength and fitness. Also, the ability to understand and deliver high power for periods of time is critical in biking, while maintaining power output below determined levels is critical for endurance events. Measuring power can be one of the best training tools as it reflects current body output with no delays or side effects.

In simplistic terms, power is measured on a bicycle by determining the torque or force applied multiplied by the speed at which it is applied. It can, however, be fairly difficult to measure power on a bicycle. A number of devices exist for measuring power on bicycles. These either measure power at the crank spider, the chain, a wheel hub, a pedal crank, a pedal or shoe cleat. Most of these typically suffer one or more disadvantages in that they are expensive, are not interchangeable between bicycles, are not accurate and cannot be fitted by a home user or average cycle shop. Furthermore, most of these devices cannot measure power for the left and right leg independently.

Although reference will be made to bicycles and cyclists in this specification, such references must be interpreted to include any pedal driven vehicle or device or user of such vehicle or device. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a method of measuring the power exerted on a pedal secured to a crank which includes the steps of measuring a force exerted between the pedal and the crank, measuring rotational speed of the crank, and calculating power as a function of the measured force and the measured rotational speed.

Further features of the invention provide for the measured force and measured rotational speed to be transmitted to a remote processor; and for the remote processor to include one or more of a mobile phone, mobile global positioning system (GPS) unit and server.

A yet further feature provides for the step of measuring a force exerted between the pedal and the crank to measure the force exerted between a major portion of the pedal and the crank.

The invention further provides a measuring device which includes a sensor unit configured to be secured intermediate a pedal and a crank and which includes at least one sensor capable of measuring a force exerted between the pedal and the crank, and wherein the device further includes a processor for operating the or each sensor to obtain measurements therefrom.

Further features provide for the measuring device to include a transmitter to transmit measurements to a remote processor; for the device to include a cadence sensor for measuring the rotational speed of the crank; and for the processor and transmitter to be included in a control unit separate from the sensor unit.

Yet further features of the invention provide for the measuring device to further include one or more of an accelerometer, a position sensor, a temperature sensor, and a reed switch; and for the remote processor to be associated with a display device.

Still further features of the invention provide for the transmitter to be a wireless transmitter and to include a receiver; and for the control unit to be securable to the crank. The invention further provides a sensor unit for a measuring device as defined above, the sensor unit characterised in that it is configured to be securable intermediate a pedal and a crank and which includes at least one sensor capable of measuring a force exerted between the pedal and the crank.

Further features provide for the sensor unit to include a plurality of sensors; for the sensors to be carried on an annular base shaped to be securable over a pedal spindle; alternately for the sensors to be secured within a crank; or alternatively for the sensors to be secured to a pedal, the sensors being capable of measuring a force exerted between a major portion of the pedal and a crank.

The invention also provides a method of calibrating a power measuring device associated with either or both of a pedal and a crank, the method including measuring a force exerted between the pedal and the crank and using the measured force to provide a calibration measurement for the power measuring device.

Further features of the invention provide for force exerted between the pedal and the crank to be measured in a static or rest condition and with a force applied to the pedal and for such measured forces to be correlated to measurements from the power measuring device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:-

Figure 1 is an exploded three-dimensional view of a measuring device and a pedal and crank;

Figure 2 is an elevation of the measuring device secured between the pedal and crank in Figure 1 ;

Figure 3 is an exploded three-dimensional view of the sensor unit of the measuring device in Figure 1 ;

Figure 4 is a schematic diagram of system including the control unit of the measuring device in Figure 1 ; Figure 5 is an exploded plan view of a second embodiment of a sensor for a measuring device;

Figure 6 is a plan view of a cover plate and base plate of a third embodiment of a sensor unit for a measuring device;

Figure 7 is an exploded sectional elevation of the sensor unit in Figure 6;

Figure 8 is an exploded three-dimensional view of a fourth embodiment of a measuring device and pedal and crank; and

Figure 9 is a three-dimensional view of another embodiment of a measuring device.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

One embodiment of a measuring device (1 ) is shown in Figures 1 and 2 and includes a sensor unit (3) and control unit (5). Referring also to Figure 3, the sensor unit (3) has a disc-like, annular shape and is formed by an annular base plate (10) and an annular cover plate (12). The base plate (10) and cover plate (12) have the appearance of washers and are secured together spaced apart by circumferential flanges (14, 15) which extend from the outer circumference and annulus of the cover plate (12) respectively. In this embodiment, four piezoelectric sensors (16) are secured to the base plate (10) in a circumferentially evenly spaced relationship and within a pressure displacing body (18) which extends over the remaining surface of the plate (10) flush with the sensors (16). The body (18) is, in this embodiment, provided by a high density rubber and serves to absorb static pressure exerted on the sensor unit (3) as will become apparent from the further description below. The sensors (16) and body (18) abut the cover plate (12) such that the sensors (16) are capable of measuring force applied to either or both of the plates (10, 12), particularly axially directed force, or force which acts normally to the surfaces of the plates (10, 12).

A cable (20) connects the sensors (16) in the sensor unit (3) to the control unit (5) via a connector (34), which may allow for detachment of the cable (20) from the control unit (5). Referring also to Figure 4, the control unit (5) includes a weather-proof housing (22) made of a plastics material in which is secured a processor (24), wireless transceiver (26) and battery (28) which powers the device (1 ) and which can be recharged through a port (30). The processor (24) is configured to operate and obtain force measurements from each of the sensors (16) and to transmit or relay these through the transceiver (26) to a remote processor (40). The transceiver (26) provides communication with the remote processor (40) using one or more of Bluetooth, Bluetooth Low Energy (BLE), ANT, ZigBee, Wi-Fi and infrared. A cadence sensor (32) is also provided in the housing and connected to the processor (24) which transmits or relays measurements received from the cadence sensor (32) through the transceiver (26) to the remote processor (40)

In use, the sensor unit (3) is secured over a pedal spindle (50) between the pedal (52) and a crank (54). The annulus in the sensor unit (3) is shaped to provide a sliding fit over the spindle (50) and the unit is sufficiently thin to not interfere with the screw threaded spindle (50) securing in normal fashion in the complementarily threaded socket (56) at the end of the crank (54). The spindle (50) extends in conventional fashion from a head (58) or flange and is rotatably secured to the pedal (52). The opposite end of the crank is in turn secured through a spider to a cog assembly (not shown) on one side. On the other side it is secured to a bottom bracket (not shown).

The housing (22) of the control unit (5) is shaped to be securable to the crank (54) opposite the pedal (52). In this embodiment the housing is hook-shaped in side elevation and configured so that the hooked part (60) provides a friction fit over the end of the crank (54) with a lug (62) provided on the inner surface of the housing which locates in the threaded socket (56) opposite the pedal (52). To secure the housing (22) to the crank (54) the hooked part (60) is inserted over the end of the crank (54). In doing so the housing (22) is bent slightly away from the crank (54) until the lug (62) is able to locate in the socket (56) whereafter the housing (22) snaps back towards the crank (54).

When a cyclist (not shown) uses the pedal (52) a force is exerted on it which causes the spindle (50) to flex and results in a force being directed from the head (58) of the spindle (50) onto the crank (54). The power or force exerted on a pedal by the cyclist is proportional to the force on the spindle and can thus be calculated. With the sensor unit (3) located between the spindle head (58) and crank (54), the force is directed through the sensor unit (3) and can be measured by the sensors (16). These measurements are relayed though the processor (24) and wireless transceiver (26) to the remote processor (40) together with cadence measurements from the cadence sensor (32).

The remote processor (40) is in this embodiment a mobile phone, but it could be any suitable device, such as a mobile GPS unit or a server, and preferably includes a display. A software application is resident on the mobile phone (40) which includes computer-readable program code executable by a processing circuit of the mobile phone. The software application permits communication with the processor (24), via a communication link provided by the transceiver (26), and calculation of exerted power from the measurements received from the sensors (16) and cadence sensor (32) through the processor (24). Any suitable algorithm can be used in the calculations and may include the use of lookup tables.

The advantage of using a mobile phone, particularly a "smart phone", is that these typically have relatively sophisticated or powerful processing facilities which facilitate quick computation of relatively complex calculations. Also, they tend to have large, high quality displays or screens and often include GPS functions. Importantly, they can easily connect to public communications networks, for example Global System for Mobile Communications (GSM) or Universal Mobile Telecommunications System (UMTS) networks, to allow data to be downloaded or shared, or for calculations to be performed by a processor connected to the network.

As mentioned above, communication with the mobile phone can be by way of any of the standard wireless protocols including Bluetooth, BLE, ANT, ZigBee, Wi-Fi and infrared, or a combination of the systems. Of course, communication could also be through any other radio frequency (RF) system or even a wired link.

The mobile phone will typically be secured to the handlebars of the bicycle using a suitable cradle and be easily visible to the cyclist. The information displayed could be selectable and configurable by the cyclist and could include other measurements, including position, speed, time and the like.

It is also envisaged, however, that a mobile phone will be used to process measurement data to calculate power and that the calculated data will be sent back to the control unit which will relay the calculated data to a display unit such as a cycle computer or GPS unit. One of the advantages of processing data in this manner is that the cyclist can still use a standard cycle computer or GPS unit mounted to the bicycle while relatively processor intensive calculations are performed by the mobile phone which is kept on the person of the cyclist. In this embodiment, the control unit may typically communicate with the mobile phone through Bluetooth and with the cycle computer or GPS unit through ANT Protocol. Any suitable means of communication could, however, be used. It should also be appreciated that the mobile device (40) may be used to process measurement data to calculate power and that the calculated data will be sent from the mobile phone to a standard cycle computer or GPS unit mounted to the bicycle. After installation of the device (1 ), the sensor unit (3) can be calibrated by measuring the static force applied to the sensor unit (3) by the pedal once secured properly to the crank. Such static force is absorbed by the pressure displacing body (18). Changes in force resulting from a cyclist using the pedal can subsequently be measured and used in calculating the power exerted by the cyclist.

There exists great standardisation of many specifications relating to bicycle parts. Spindle diameter is almost universally standardised, particularly across high-end or performance bicycles. Thus, the sensor unit can be fitted to most bicycles by the user or an average cycle shop without any modification or special tooling.

A measuring device will preferably be fitted to each pedal, but, if desired, calculations can be performed using measurements from a single pedal only. The measuring device is advantageous in that it permits the cyclist to use his or her original crankset and original pedals. It can easily be transferred between bicycles and, as indicated, can be fitted by the user at home or in a rudimentary cycle shop. The measuring device is furthermore lightweight and does not interfere with the regular working of the bicycle. It can be fitted to all types of bicycles, including road bicycles, mountain bicycles and indoor training and commuting bicycles, as well as any other pedal driven vehicles. It can also be used with any bicycle or exercise equipment which has a crank arm and pedals, including indoor bicycles and stair or orbital climbers. Furthermore, the measuring device can be used with any type of pedal or crank systems, including those manufactured from alloy, steel or carbon, or any other material that may be used in bicycle or exercise equipment manufacture.

Importantly, the measuring device does not require a modified version of the pedal, the cranks, or the bicycle, although, as will become apparent from what follows, these could be modified if required. The measuring device also allows left and right measurement of power, which is important for commercial reasons, and may be used in a system to improve the pedalling technique of a cyclist. That it permits measurement on both legs through 360° of crank rotation makes the measuring device even more useful in comparing the performance and/or strength of a cyclist's legs with each other as well as the efficiency of the cyclist's pedal stroke throughout each rotation. The measuring device may self-calibrate to adjust for and interpret or offset external factors such as temperature, position, rider position, pedal tightening torque and drift while riding. It could also take into account sensor drift and static torque applied to a sensor due to tightening of the pedal to crank, and if this torque is inconsistently applied to each pedal, each sensor unit can self-calibrate to adjust as necessary to still provide an accurate power measurement. Such self-calibration can be determined by either mathematical algorithms, a laboratory testing results table, a field testing results table or a combination of these. The measuring device may also be calibrated in a cycle workshop at set-up and at intervals thereafter and equipment may be provided to assist in such calibration.

The measuring device may also be automatically calibrated through wireless transmission to and from the cyclist's mobile phone or other suitable device. The measuring device, through its wireless system, can communicate its operating parameters real-time to the user's cell phone, which can then interpret and process the data and then communicate calibration information back to it. The mobile phone could also communicate this information through a mobile telephone network or other public or private communications network to a further, possibly cloud based, software system which can interpret the information and send calibration information back to the measuring device.

The measuring device may also use information from third party providers, such as weather providers, or from other sensors, to calibrate and determine the force and power output of the rider at any point in time. It may also use the mobile phone to communicate real-time power and other rider information to third parties, including analysis providers such as Strava.

The measuring device may include any one or more of an accelerometer, gyro sensor, position sensor, cadence sensor and inclinometer to determine position, cadence, speed, velocity, rider position and other inputs as required, and may use this data in determining the rider force and power, or other analytics.

Any suitable software and a processor, either forming part of the measuring device, or being a separate module with which the device communicates, or the cyclist's mobile phone, or a combination can be used to process the information from the sensor unit, filter out any inaccuracies, interpolate or extrapolate data as necessary. It may also collect supplementary information from other sensors or external data providers, such as weather services.

It will be appreciated that many other embodiments of a measuring device exist. For example, the sensor unit can have any suitable shape and need not make use of piezoelectric sensors. Sensors may include a strain gauge, a singing strain gauge, piezoresistors, laser inferometers or other light measuring devices, a thin film sensor, a vibratory frequency sensor and a fluid displacement sensor, or combinations of these. Any suitable sensor could be used. The sensor unit may measure the force in a number of segments. For example, it may measure the force or compression at the top of the sensor unit and the force or displacement at the bottom of the sensor unit. The sensor unit may allow for measurement of the force vector at the pedal, either directly through the sensor itself, or through estimation by electronic and software means based on the sensor data, or through a combination of both. The sensor unit may include multiple planes to enable this measurement. Measurement of the force vector, however, allows for more detailed analysis of the output of the sensor.

The sensor unit may alter the electrical configuration of the components while in use. For example, if a Wheatstone bridge configuration with strain gauges is used, in order to determine the location of the force on the sensor unit, the sensors may be broken into a number of half Wheatstone bridges or planes and the force or changing pressure determined at the top of the sensor and at the bottom.

As shown in Figure 5, film sensors, in this embodiment a thin-film sensor (80), can also be used. These could be sandwiched or secured between thin, washer-like plates (82) or even carried on a substrate, or laminated between suitable substrates, for example discs made from a plastics material, and secured directly between the pedal and crank.

In a further embodiment, shown in Figures 6 and 7, the sensor unit (90) could include a base plate (92) and a cover plate (94) biased apart to have a floating configuration. In this embodiment the base plate (92) has an axially extending flange (96) about its central annulus (98) which terminates in a radial flange (100) on the outer surface of which are secured sensors (102). A biasing member (104), in this embodiment a coil spring, extends about the circumference of the radial flange (100). The cover plate (94) has a skirt (105) about its circumference and a radially extending lip (106) spaced apart therefrom which bears on the edge of the radial flange (100). In use, the coil spring (104) biases the cover plate (94) away from the base plate (92) and maintains the static force applied to the sensor unit (90). When the cyclist applies force to the pedal it exceeds the static force and results in the lip (106) bearing more forcefully on the radial flange (100) causing it to bend and the sensors (102) to register a change in force. The base plate and cover plate could be biased apart in any suitable manner, including through the use of a high density rubber or similar biasing member. The sensor unit could also be fitted to a crank or pedal in a more permanent manner, either during manufacture or thereafter. As shown in Figure 8, the sensor unit (120) could be secured in a socket (122) in the crank (124) which is coaxial with the threaded socket (126) for receiving the pedal spindle (128). In this embodiment the sensor unit (120) has a cylindrical body with a threaded passage (130) centrally therethrough complementary to the pedal spindle (128). In use the sensor unit (120) is secured in the socket (122). To this end it could be keyed or splined and provide a press fit in the socket (122). Alternatively it could be secured by a screw thread or by bonding it in place using a suitable adhesive, welding or the like. The pedal is then secured to the sensor unit and crank through its spindle and in conventional fashion. This embodiment permits a larger sensor unit to be used which may in turn have a more advanced sensor arrangement.

It will be apparent that the sensor unit could also be secured in a groove, recesses, or a similar arrangement about the threaded socket in the crank, or in the pedal about the spindle.

Figure 9 shows an example of another embodiment of a measuring device (140) in which the measuring device (140) is integrated into a pedal. In this embodiment, a sensor unit (142) as described in the various embodiments above is provided adjacent, and may be integrally formed with, the head (144) or flange of the pedal. In use, the sensor unit (142) is thus interposed between a crank and a major portion of the pedal (148). Force applied to the major portion of the pedal (148) is directed through the sensor unit (142) and can be measured by sensors included therein. A control unit (not shown) is provided in the pedal (140) and includes a battery, processor and transceiver for wirelessly relaying the measurements to a remote processor. Alternatively, it is anticipated that the sensor unit may include a transceiver for wirelessly relaying the measurements to a processor provided in a control unit or remote processor. In this case, the sensor unit may include a power harvesting component for powering the sensors and transceivers so that the measurements can be relayed to a processor provided in a control unit or remote processor. Measurements relating to the rotational speed of the crank may be provided by a separate cadence sensor or may be provided by an accelerometer included in the control unit in the pedal.

Many other embodiments of a sensor unit exist, as do other embodiments of a control unit. Any suitable housing could be used for the control unit and it could even be integrated into the sensor unit. The housing can be secured to the crank in any suitably secure manner. It may include a rubber or other suitable attachment means to ensure it stays on the crank arm, and may include a lug or nipple to latch it into the opposite side of the pedal threading to ensure it stays in place. The housing may be tailored to a specific crank and pedal configuration for a secure fit, or may be made in generic sizes or formats with universal securing clips to keep it in place. The housing may also be secured with cable ties or may have a threaded nipple to attach to the opposing side of the pedal spindle socket.

The control unit could include any suitable electronics and circuitry and could include one or more of an accelerometer, position sensor, temperature sensor, reed switch and the like. The control unit could also be configured to calculate the power exerted by the cyclist and could have a dedicated display associated with it. Also, any suitable display could be used, including one incorporated into a wristwatch, GPS unit, cycle computer, mobile phone and the like. The processor included in the control unit may be provided by an appropriate arrangement of circuitry. Furthermore, it is appreciated that in the various embodiments described herein, a power harvesting component may be provided in place of or in addition to a battery. The power harvesting component may be able to harvest kinetic or thermal energy to power the device and/or to recharge a battery.

Furthermore, there is also provided for the measuring device, in particular the sensor unit, to be used to calibrate a further power measuring device associated with either or both of a pedal and a crank, such as a pedal spindle. Such units are typically very difficult to calibrate without highly specialised equipment, particularly as they are sensitive to static torque between pedal and crank which can be inconsistent, especially in field use. Force exerted between the pedal and the crank in a static or rest condition, that is without any force being applied by a user, is measured and used to define zero calibration measurement for the further power measuring device. With the user then exerting force on the pedal further measurements are taken between the pedal and the crank and power calculated for each measurement. These are then correlated to readings from the further power measuring device and the device calibrated.

The sensor unit could communicate directly with the processor of the further power measuring device or it could communicate with a processor of a calibration device, or it could communicate with its own processor substantially as described above. Where the sensor unit communicates with the processor of the further power measuring device it permits continuous self-calibrating of the further power measuring device.

Throughout the specification and claims unless the contents requires otherwise the word 'comprise' or variations such as 'comprises' or 'comprising' will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS:

1 . A method of measuring the power exerted on a pedal (52) secured to a crank (54, 124) which includes the steps of measuring a force exerted between the pedal (52) and the crank (54, 124), measuring rotational speed of the crank (54, 124), and calculating power as a function of the measured force and the measured rotational speed.

2. The method as claimed in claim 1 , wherein the measured force and measured rotational speed are transmitted to a remote processor (40); and wherein the remote processor (40) includes one or more of a mobile phone, mobile global positioning system (GPS) unit and server.

3. A measuring device (1 , 140) which includes a sensor unit (3, 90, 120, 142) configured to be secured intermediate a pedal (52) and a crank (54, 124) and which includes at least one sensor (16, 80, 102) capable of measuring a force exerted between the pedal (52) and the crank (54, 124), and wherein the device (1 ) further includes a processor (24) for operating the or each sensor (16, 80, 102) to obtain measurements therefrom.

4. The measuring device (1 , 140) as claimed in claim 3, wherein the measuring device (1 140) includes a transmitter (26) to transmit measurements to a remote processor (40); wherein the device (1 , 140) includes a cadence sensor (32) for measuring the rotational speed of the crank (54, 124); and wherein the processor (24) and transmitter (26) are included in a control unit (5) separate from the sensor unit (3, 90, 120, 142).

5. The measuring device (1 , 140) as claimed in claim 4, wherein the measuring device (1 , 140) further includes one or more of an accelerometer, a position sensor, a temperature sensor, and a reed switch; and wherein the remote processor (40) is associated with a display device.

6. The measuring device (1 , 140) as claimed in either one of claims 4 or 5, wherein the transmitter (26) is a wireless transmitter and includes a receiver (26), and wherein the control unit (5) is securable to the crank (54, 124).

7. A sensor unit (3, 90, 120, 142) for a measuring device (1 , 140) as claimed in any one of claims 3 to 6, the sensor unit (3, 90, 120, 142) characterised in that it is configured to be securable intermediate a pedal (52) and a crank (54, 124) and which includes at least one sensor (16, 80, 102) capable of measuring a force exerted between the pedal (52) and the crank (54, 124).

8. The sensor unit (3, 90) as claimed in claim 7, wherein the sensor unit (3, 90) includes a plurality of sensors (16, 80, 102) and wherein the sensors (16, 80, 102) are carried on an annular base (10, 82, 92) shaped to be securable over a pedal spindle (50, 128).

9. The sensor unit (120) as claimed in claim 7, wherein the sensor unit (120) includes a plurality of sensors (16, 80, 102) and wherein the sensors (16, 80, 102) are secured within a crank (124).

10. The sensor unit (142) as claimed in claim 7, wherein the sensor unit (142) includes a plurality of sensors (16, 80, 102), wherein the sensors (16, 80, 102) are secured to a pedal, and wherein the sensors are capable of measuring a force exerted between a major portion of the pedal and a crank

1 1 . A method of calibrating a power measuring device associated with either or both of a pedal (52) and a crank (54, 124), the method including measuring a force exerted between the pedal (52) and the crank (54, 124) and using the measured force to provide a calibration measurement for the power measuring device.

12. The method as claimed in claim 1 1 , wherein the force exerted between the pedal (52) and the crank (54, 124) is measured in a static or rest condition and with a force applied to the pedal (52) and for such measured forces to be correlated to measurements from the power measuring device.