ES1278679U - DEVICE FOR MEASURING THREE-DIMENSIONAL FORCE APPLIED ON PEDALS (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Device for measuring three-dimensional force applied to pedals, in which the pedal comprises a connecting rod (9) and a support for the foot joined through a connection shaft (10), and the device comprising: - at least one first strain gauge (3) intended to be attached to the connecting rod (9), - at least a second and a third strain gages (1, 2), intended to be fixed to the shaft (10), offset from one another by an angle with respect to the shaft (10), - a data processing module (4) connected to the strain gauges (1, 2, 3), - a data storage module (5), connected to the processing module (4), and - a power module (6) connected to the processing module (4). (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

DEVICE FOR THE MEASUREMENT OF THREE-DIMENSIONAL FORCE APPLIED IN

PEDALS

OBJECT OF THE INVENTION

The object of the invention is a three-dimensional force sensor for bicycle pedals, which in the area of biomechanics, specifically in sports and clinical areas, is capable of providing data of vital importance for users who practice cycling professionally or as amateurs, in order to improve their pedaling performance through a more efficient application of forces. Likewise, in the clinical field, it allows monitoring the force that a user is exerting throughout the sessions in rehabilitation processes with cycling.

BACKGROUND OF THE INVENTION

The force that a cyclist is able to exert on a pedal has a direct impact on performance and the appearance of injuries, both professionally and recreationally. Several authors have carried out studies to determine pedaling force in order to maximize the cyclist's performance without involving a greater risk of injury, establish relationships between different parameters with pedaling characteristics, or demonstrate its benefits as a practice in training sessions. rehabilitation if you look at the clinical level.

In the same way, the recreational user increasingly needs more information to improve their technique. Due to all of the above, a multitude of devices have emerged for measuring the three-dimensional force applied to the pedal. Two types of devices can be fundamentally distinguished: commercial and scientific.

The commercial devices are mostly potentiometers, mainly intended to measure the power exerted by the cyclist during pedaling activity. You can find countless brands that market this type of device. Depending on the manufacturer, the potentiometer can be installed in different parts of the bicycle, such as the crank, the bottom bracket or the pedals. Depending on the solution adopted, data can be obtained from one or two legs, and a greater or lesser amount of additional information (such as cadence), but in no case data on the force applied to the pedal is provided.

Some more advanced models can measure applied force, but with limitations to take into account. For example, some models are capable of measuring effective force, that is, the tangential component to the connecting rod (the only component that produces useful work), in both legs. Others have a potentiometer that allows forces to be measured in the sagittal plane for the left leg only, but sampling is done every 30 °.

In short, the most advanced potentiometers on the market do not allow measuring three-dimensional force, staying at most in the sagittal plane, without taking into account the forces exerted in the lateral-medial direction. These forces may play a relevant role in the development of joint injuries, as several studies have shown. For this reason, these forces should be kept under control.

In addition, this type of device does not provide sufficient data for the precise calculation of the performance, since for its correct determination the three components of the force monitored with a sufficient sampling frequency are needed. Therefore, commercial potentiometers cannot provide adequate data for a complete biomechanical study of the cyclist, distancing them from professional or clinical applications as far as force measurement is concerned.

Regarding scientific devices, there are several studies and works that address their design and implementation for measuring three-dimensional force during pedaling. The most veteran captured two-dimensional measurements. These studies usually use instrumented pedals based on transducers or strain gauges manufactured specifically for experimentation. These are devices of a certain complexity, which restrict measurements to the laboratory environment and use configurations that involve a high number of gauges. Other works allow to determine the three-dimensional reactions in the pedal, however, they use remote assemblies of commercial cycling components, in addition to using a complex configuration of gauges to obtain the results. Similarly, measurements are necessarily made in the laboratory.

Other studies have managed to materialize devices or assemblies that make it possible to measure the three components of the force quite accurately, in addition to offering sufficient sampling. These employ strain gauges and force plates respectively. The downside is that they require a specific complex system that requires cabling, which is why measurements are focused on the laboratory. In the case of using force platforms, there is the same limitation.

The most recent studies have assumed an approximation to natural pedaling conditions, in which devices of specific manufacture capable of using commercial cleats and cranks are shown. These studies still have the laboratory as the main measurement environment, and continue to use complex gauge configurations, in addition to requiring a calibration process for these that is not always easy.

Therefore, there is currently no literature in the literature a device for measuring three-dimensional force on the pedal capable of adapting to the factory components of the bicycle without the need to manufacture specific components, which uses a reduced number of gauges and a calibration process. simple and that allows data collection in road tests.

Between commercial and scientific devices are bicycle adjustment systems that allow monitoring of different pedaling parameters to achieve an optimal adjustment of the rider to the bicycle interfaces, including the pedals, in order to achieve the maximum effective force with minimal effort.

Various devices can be found in relation to patent documents on pedal force measurement. If you look at the document on measuring pedaling force ES2279773 (2007), a device is exposed to determine force in the pedal and force in the chain, among others, but not to calculate the three-dimensional components of the force applied to the pedal, something similar to what was found in document EP2739950A2 (2012).

Regarding the patent document on the detection of pedaling effort EP2028098A2 (2008), the same case is had as in the previous one, the disclosed device does not allow obtaining the three components of the force applied to the pedal. For its part, The device shown in document ES2530352 (2011) consists of a pedal body instrumented with 8 gauges to measure each component of the applied force. Therefore, it is necessary to manufacture some component for the bicycle to which 24 extensometers must be attached.

Considering the potentiometer exposed in document ES2535582 (2015), this device is capable of measuring the component of the tangential force to the connecting rod, but not the other two. Something similar to the device disclosed in US9459167B2 (2016), aimed at measuring two-dimensional torque and force.

Based on the commercial devices, those shown in the scientific literature and those exposed in different patent documents, it can be established that, despite the fact that each type has interesting characteristics, none of them makes up for the deficiencies of the others. In other words, a device for measuring the three-dimensional force applied to the pedal has not been found that can adapt to factory components of the bicycle, does not require the manufacture of specific components, uses a reduced number of gauges and simple electronics, can be used in road tests and, suppose a reduced cost for the user interested in its use and / or commercialization.

DESCRIPTION OF THE INVENTION

The knowledge of the three-dimensional components of the force applied to a pedal supposes a series of advantages for a user, both at a sports level (amateur or professional) and at a clinical level. At the sports level, you can find settings to adjust to the bicycle that maximize performance and minimize the risk of injury. For its part, at the clinical level, knowledge of the forces that the user is capable of exerting is key to determining possible injuries or monitoring the rehabilitation process.

Next, a device for the measurement of three-dimensional force applied to a pedal, of little complexity and with a minimum cost, is described. The pedal comprises, like any usual pedal, a connecting rod and a footrest, connected to the connecting rod through a connecting shaft.

Specifically, the device object of the invention comprises three preferred strain gauges, although the number could be higher. A first strain gauge is intended to be attached to the connecting rod, and a second and a third strain gauge, which is intended to be attached to the axle. The second and third strain gauges are offset by an angle with respect to the axis, preferably equal to 90 °, so that each of the strain gauges has the ability to measure the force applied by the user in one of the three axes. X and Z. In this way it is possible to measure the three-dimensional force applied by the user.

Each gauge primarily measures a component of force. However, due to the geometry and the point of application of the load, all the gauges present response for each component of the force applied.

The three strain gauges are connected to a data processing module, in which the measurements taken are received and processed. Furthermore, connected to the processing module, the device comprises a data storage module. Finally, and connected to the processing module, the device comprises a power supply module.

In a second aspect of the invention, the device can additionally comprise an inertial measurement unit connected to the processing module, intended to be associated with the crank preferably and configured to measure the angle of rotation of the pedal with respect to the bicycle.

In a third aspect of the invention, the device may further comprise a communication module, connected to the processing module and configured to send the data collected in the device to an external system.

Compared to commercial devices, the device that is the object of the invention represents a step forward in terms of information provided, and is also much cheaper. Regarding the devices that can be found in the scientific literature, the device is capable of providing the same data, but using a much simpler and adaptable assembly to the components of commercial bicycles, also allowing its use in outdoor tests.

As described, the number of strain gauges that the device comprises is a minimum, three preferably, and there is no wiring that interferes with pedaling. The calibration of the device to obtain the applied forces through the information provided is simple and fast. Finally, validation performed with professional acquisition devices ensures that forces are accurately measured.

DESCRIPTION OF THE DRAWINGS

To complement the description that is being made and in order to help a better understanding of the characteristics of the invention, according to a preferred example of a practical embodiment thereof, a set of drawings is attached as an integral part of said description. where, with an illustrative and non-limiting nature, the following has been represented:

Figure 1.- Shows a view of the strain gauges and the inertial measurement unit positioned on the connecting rod and shaft.

Figure 2.- Shows a schematic view of the processing module connected to the strain gauges, the inertial measurement unit and the other modules of the device.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the device for measuring three-dimensional force applied to pedals is described below with the aid of Figures 1 and 2.

The device is intended to be associated with a pedal of a bicycle, in which the pedal, as usual, comprises a connecting rod (9), and a connecting rod (10) between the connecting rod (9) and a support element for the foot as shown in figure 1.

In order to be able to mediate the three-dimensional force applied by a user on the pedal, the device comprises a first strain gauge (3) destined to be fixed to the crank (9),

and a second and a third strain gauge (1, 2), intended to be fixed to the shaft (10), offset from each other by an angle 90 ° with respect to the shaft (10), as shown in detail in figure 1.

Likewise, and as schematically indicated in figure 2, the device comprises a data processing module (4) connected to the strain gauges (1, 2, 3), a data storage module (5), connected to the processing module (4), and a power module (6) connected to the processing module (4), a communication module (7), connected to the processing module (4) and configured to send the data collected in the device to an external system.

Next, it is detailed how the strain gauges (1, 2, 3) are connected so that the measurements from which the forces will be determined can be obtained. Each strain gauge (1, 2, 3) must be connected in a Wheatstone quarter bridge, completed with two resistors of the same value as said strain gauge (1,2, 3) and a potentiometer that allows adjustments higher or lower than the nominal value of the strain gauge (1, 2, 3) accurately.

Since the device comprises several Wheatstone bridges, the operation for one of them will be explained, being identical for the rest. The Wheatstone bridge receives an input voltage from the power module (6). When no force is being applied to the pedal, the output of the bridge is kept at 0 V. When applying load, the strain gauge (1, 2, 3) of the bridge modifies its resistance and causes the bridge to decompensate, causing the appearance of an output voltage of the order of millivolts. This voltage is proportional to the applied load. The output of the bridge must be sent to the processing module (4), specifically to an analog input of an Arduino microcontroller, which in one embodiment of the invention will be the processing module (4), for digitization using an analog-digital converter ( ADC). When working with millivolts, the signals coming from the jumpers are imperceptible to the inputs of the Arduino. It is necessary to properly amplify the signals.

The signals must be amplified by adjusting the value of the gain in such a way that the applied forces do not exceed the limits of the ADC of the Arduino input (4). One limitation of the Arduino ADC (4) is that it does not recognize negative signals. However, the voltages coming from the amplifier (which in turn are generated in the Wheatstone bridge) can be less than 0V. Therefore, to properly capture Positive and negative measures, the bridge must be unbalanced beforehand until the input of the Arduino (4) has an intermediate voltage between the limits set by the ADC.

Taking into account the increases and decreases on this unbalance value, positive measures are used at all times, recognizable by the input of the Arduino (4). Subsequently, this value is taken as a force equal to 0 N to carry out the calculations. The unbalance is done through the potentiometer corresponding to each Wheatstone bridge.

The amplified signals, once digitized, are stored in the storage module (5) which will preferably be an SD card connected to the Arduino (4).

On the other hand, the device comprises an inertial measurement unit (8) connected to the processing module (4), destined to be associated with the crank (9) and configured to measure the angle of rotation of the pedal with respect to the structure of the bicycle , digitizing this data in another of the Arduino's inputs (4). In this way, you have the force data as a function of the pedaling angle.

To get the angle measured in the inertial unit (8) to reset to 0 ° after each turn of the pedal, a Hall effect sensor activated by a magnet positioned on the bicycle frame by means of an adapter is used. The angle measured by the inertial unit (8) is also stored in the storage module (5).

Furthermore, the inertial unit (8) can comprise a stopwatch (12), so that it has the capacity, not only to measure the rotated angle, but also the moment in which each angle is reached.

Both the processing module (4), the storage module (5), the feeding module (6) and the inertial unit (8) are placed on a base plate with compact dimensions that will be positioned in areas of the support assembly to the foot (11) - crank (9) that do not interfere with the natural pedaling of the user.

At this point, the raw data from the strain gauges is available (1,2,3). Mathematical processing is necessary to determine the forces that have been applied during pedaling. To do this, you need to find a expression that relates the values produced by the strain gauges (1,2, 3) with the applied force. The appropriate calibration tests must be carried out to find this expression. In addition, the offset introduced by the initial unbalance of the Wheatstone bridge must be taken into account.

Calibration tests consist of applying various loads, of controlled value, so that they act like each of the components of the force that is intended to be known. In each test, the data from each strain gauge (1, 2, 3) are collected. Knowing the forces applied in the calibration and the response of the strain gauges (1, 2, 3) to each one of them, it is possible to mathematically determine a series of conversion factors that relate the response of the strain gauges (1,2, 3 ) with applied force.

In this way, an expression can be established that allows, from the data provided by the strain gauges (1, 2, 3) during the pedaling test, to calculate the forces applied during said test. Said calculation is carried out in the processing module (4). Therefore, there is a relationship of the type:

Applied Force = Conversion Factors x Strain Gauge Data

The device must undergo a validation process. For this, a second set of strain gauges can be used that is connected to a professional data acquisition equipment. As before, you need to perform calibration for this set of strain gauges in order to find their corresponding conversion factors.

Taking the data from both devices and their conversion factors, the forces can be calculated from each of them. Then a series of static and dynamic validation tests are carried out in order to guarantee the similarity between both devices. If the data is sufficiently even between the two devices, it can be guaranteed that the device measures correctly.

At this point, it is possible to disconnect the second set of strain gauges and proceed to measurements with test subjects to obtain data to compare with those of previous literature studies.

The device object of the invention can be adapted for its production as a consumer product focused on amateur or professional cyclists who need to know the force developed during the activity.

Claims (5)

1. - Device for measuring three-dimensional force applied to pedals, in which the pedal comprises a connecting rod (9) and a support for the foot joined through a connection shaft (10), and the device comprises: - at least one first strain gauge (3) intended to be attached to the connecting rod (9), - at least a second and a third strain gages (1,2), intended to be fixed to the axis (10), offset from one another by an angle with respect to the axis (10), - a data processing module (4) connected to the strain gauges (1,2,3), - a data storage module (5), connected to the processing module (4), and - a power module (6) connected to the processing module (4). 2. - The device of claim 1, in which the angle a is 90o. 3. - The device of claim 1, further comprising an inertial measurement unit (8) connected to the processing module (4), intended to be attached to the connecting rod (9) and configured to measure the angle of rotation of the pedal. 4. - The device of claim 3, wherein the inertial measurement unit (8) additionally comprises a stopwatch (12). 5. - The device of claim 1, further comprising a communication module (7), connected to the processing module (4) and configured to send data to an external system.