Force measuring unit for use with sports equipment

Abstract

The invention relates to a force measuring unit (1) comprising a housing (10) with at least two force introduction elements (11) for connection to sports equipment, wherein a measuring module (20) is arranged in the housing (10) in order to detect a force acting on the at least two force introduction elements (11). The force measuring unit (1) is characterized in that the measuring module (20) has at least one strain measuring sensor (21) which is connected to the housing (10) in order to determine the force acting on the at least two force introduction points (11) via an expansion of the housing (10).

Description

The invention relates to a force measuring unit for use with sports equipment. The force measuring unit has a housing with at least two force introduction elements for connection to sports equipment, wherein a measuring module is arranged in the housing in order to detect a force acting on the at least two force introduction elements.A sports device with which such a force measuring unit can be used is, for example, a loop trainer ("suspension trainer"). Such a device comprises straps which are fastened to an anchor point. This allows for a variety of body weight exercise that is conducive to force, flexibility, and balance. Suspension trainers are frequently used in fitness studios, personal training studios and even home for fitness and rehabilitation purposes. The disadvantage of such a suspension trainer is that the user does not receive any information about the force used in the respective exercise, since this depends on his body weight and the exercise geometry.Monitoring load, force and repetitions during suspension training is decisive for effective training design, prevention of injury and checking of the progress of training. Advanced feedback technologies that connect to mobile terminals such as smart phones, computers, tablets, smart watches, or smart glasses may help optimize training and create personalized training plans. Moreover, the measurement of the training progress can contribute to increasing the end user's marketing. In addition, the integration of these technologies into suspension may allow trainer telehealth applications for physiology by supporting remote monitoring and guidance.Studies have analyzed training biomechanismally with suspension trainers and in laboratory environment conventional strain gauges or force sensors have been used to check the applied force during exercise execution. The scientific work provides insight into the importance of precise measurements and feedback for effective training. it is found that determining the force, velocity, angle and acceleration during exercise execution is a significant advantage in assessing the progress of training of suspension trainer.The publication US 2021 / 0283457 A1 describes a force measuring unit of the type mentioned at the beginning with a housing which is mounted on force application elements, e.g. rings or eyes, between two belts and has a force measuring sensor not described in more detail. Measurement results of the force measurement sensor are detected in the force measurement unit and forwarded via a radio connection to an external mobile device, e.g. a smartphone.US 2019 / 0126097 A1 shows a force measuring unit in which a strain gauge is applied as a force measuring sensor to a section of a belt.Strain gauges typically consist of an electrically conductive film material which is applied to a generally metallic carrier plate. The film is usually arranged in a specific pattern to measure strains in the structure to which it is applied. However, the use of a metallic backing plate may make integration of other sensing characteristics difficult because it limits the flexibility and flexibility of the sensor.Another approach to force measurement in a sports device is known from the publication DE 10 2016 003 697 A1. The document discloses an elastic training band incorporating a strain gauge sensor. The training band consists of an extensible plastic which is rendered conductive in a core region by an addition of, for example, carbon-based materials, wherein a resistance of the training band depends on its state of extension. The training belt is inserted with both ends into the electronic measuring unit, so that the resistance and thus the state of expansion of the training belt can be measured and evaluated.During a train on the training belt, its length changes significantly, which is also intended and useful for carrying out the exercises carried out with the belt. In static or dynamic applications with small changes in position, such as suspension trainers, this behavior is disadvantageous because the tension on an elastic band would change the positioning of the trainer, which impairs execution of the repetition.The object of the invention is to specify a force measuring unit which has a limited elongation, can be produced cost-effectively, is space-saving and has a long life taking into account the action of force.This object is achieved by a force measuring unit having the features of the independent claim. Advantageous embodiments and developments are specified in the dependent claims.A force measuring unit according to the invention is characterized in that the measuring module has at least one strain measurement sensor which is connected to the housing in order to determine the force acting on the at least two force introduction points via a strain of the housing.The housing itself is thus used as a strain element in order to convert a force acting on the force introduction elements into a strain which can be determined with the aid of the strain measurement sensor. The housing simultaneously protects the measurement module with the strain measurement sensor, so that the force measurement unit is also suitable for a rough training environment. In addition, a compact design is achieved by integrating the measuring module into the housing.The housing material preferably has a tough or hard base material, so that the housing absorbs the forces sufficiently without stretching too much. This further offers the advantage that the force absorption by the housing is damped. An elastic plastic can be used as material, for example. The housing can be produced cost-effectively by injection molding, 3D printing or casting methods, since it is fully integrated.In an advantageous embodiment of the force measuring unit, the housing has a cavity in which the strain measurement sensor is arranged and which is filled with an elastic material. The elastic material is also referred to below as potting material and can be silicone, for example. The elastic material protects the measurement module from moisture and from impacts and at the same time couples the strain measurement sensor mechanically to the housing, so that the measurement module absorbs the strain of the housing.Preferably, an elastic resistance wire is used as the strain measurement sensor, which runs e.g. in a meandering or loop-shaped manner. The resistance of an elastic resistance wire changes when the wire stretches. In the context of the application, the term "wire" is not restricted to a metallic conductor, but rather also encompasses, in particular, conductors which consist of an elastic conductive plastic. For example, silicone can be used as plastic in which conductive particles, for example made of carbon black, graphite or silver, are embedded.In one configuration, the resistance wire and the potting material of the cavity of the housing can consist of the same base material, so that they connect particularly well in a materially bonded manner.Preferably, the elastic resistance wire is guided through the cavity in a plurality of loops, wherein the loops can be electrically insulated from one another by the elastic material. By using a plurality of loops, a greater change in resistance results overall with only slight expansion of the housing. The measurement accuracy is increased accordingly.Due to the loops of the elastic resistance wire, the strain measurement sensor is configured two- or even three-dimensionally. Forces in a plurality of spatial directions can thus be detected. For this purpose, it can be provided not only to provide a pair of opposing force introduction elements on the housing, but to provide two or three pairs. In addition, torsional forces and torques acting on the housing can be measured.Particularly preferably, the loops run around a printed circuit board (printed circuit board) of the measurement module, for example in the form of ellipses. The circuit board is directly connected to the sensor material. The resistance can thus be measured, evaluated and passed on reliably and continuously.In a further advantageous embodiment of the force-measuring unit, the force-introduction elements are feedthroughs through the housing, which are formed on opposite sides of the housing. Into these passages, for example, hooks or bolts of shackles can be inserted for connection to straps or the like. This results in a large-area and uniform transmission of force to the housing.In a further advantageous embodiment, the measurement module has a radio interface for transmitting measurement results of the strain measurement sensor. The measured values can thus be transmitted simply and wirelessly to, for example, a mobile terminal (smartphone, tablet computer) and can be further evaluated and / or (graphically) presented there.Furthermore, the force measuring unit can have a position sensor and / or an acceleration sensor, the measurement results of which are likewise detected and transmitted for evaluation or display.The invention is explained in more detail below with reference to exemplary embodiments with the aid of figures. The figures show: FIG. 1 shows an example of application for a force measuring unit; FIG. 2 shows a force measuring unit in a first exemplary embodiment in a schematic sectional illustration; FIG. 3 shows a force measuring unit in a second exemplary embodiment in a three-dimensional exploded illustration; FIG. 4 shows a three-dimensional detailed illustration of a measurement module of the force measurement unit of FIG. 3 ; and FIG. 5 shows a three-dimensional sectional illustration of the force measuring unit of FIG. 3.In all the figures, the same reference numerals identify the same or identically acting elements.FIG. 1 first schematically shows an example of application for a force-measuring unit 1 according to the invention. The force-measuring unit 1 is connected on two opposite sides to a section of a belt 2, respectively. A free end of the strap 2 is fastened to an anchor point 3, for example to a wall. The other free end of the strap 2 is connected to a handle 4 which is gripped by a person 5. As a sports exercise, the person pulls repeatedly counter to the weight in the direction of the anchor point 3 and can be pulled back again.In this case, a force is exerted on the force measuring unit 1 via the handle 4 and the belt 2, said force being measured by the force measuring unit 1 and being transmitted via a radio interface contained in the force measuring unit 1, for example according to the Bluetooth standard, to a device, in particular a smartphone or a tablet computer, which is not shown here. The force is preferably measured continuously (quasi-), for example with a time resolution which is in the range of or below a measurement value per second. The measured values are further evaluated in the smartphone or tablet computer and, if appropriate, graphically represented in order to be able to record and analyze the training sequence.FIG. 2 shows a simplified schematic illustration of the basic structure of a force measuring unit 1 in a first exemplary embodiment. The force measuring unit 1 has a housing 10 which has approximately the shape of a cuboid. Force introduction elements 11 are arranged on two opposite sides of the housing. In the application example of FIG. 1, the belt 2 is fastened to this force introduction element 11.The housing 10 comprises a cavity 12, in which a measurement module 20 is arranged, which comprises a strain measurement sensor 21 and an evaluation device 22. The strain gauge sensor 21 in this example is an elastic resistance wire whose resistance value changes with strain. Preferably, the wire is made of a resilient conductive plastic. In particular, silicone can be used as plastic in which conductive particles, for example made of graphite, are embedded.The evaluation unit 22 has a power supply source and electronic components which make it possible to evaluate the resistance value of the resistance wire and to transmit the measured values by means of radio.The cavity 12 is filled with a likewise elastic material which is connected to the housing 10 and in which the measurement module 20 including the resistance wire is embedded. This potting material is preferably introduced in (viscous) liquid and then solidifies.If the housing 10 is stretched by the action of force on the force introduction elements 11, this stretching is also transmitted to the resistance wire, which is detected by the measuring module 20 as a change in resistance. A reference measurement curve can be stored in the evaluation unit 22, via which a measured resistance value is assigned to an applied force. A linearization of the measured values is also achieved via this reference measurement curve. The reference measurement curve can be defined in the form of a table or a functional relationship.In a further embodiment, the long-term behavior of the materials used for the housing and the resistance wire and the potting material can be determined in order to take account of measurement displacements in the event of prolonged or frequent expansion and, if appropriate, to digitally adapt them. Measurement inaccuracies can thus be avoided.In the illustrated example, the resistance wire is arranged in a plurality of loops similar to a winding in the housing 10. The loops surround the evaluation unit 22 in an approximately ellipsoidal shape. The fact that a plurality of loops is used results in a greater change in resistance overall with only slight expansion of the housing 10, which increases the measurement accuracy. The coupling between the resistance wire and the housing 10 by the elastic potting material with which the cavity 12 is filled also protects the measurement module 20 from moisture and shocks that may occur during a harsher treatment in a training environment.The maximum force which can be absorbed by the force-measuring unit 1 at the force-introduction elements 11 can be influenced by the selection of the material of the housing 10 and its wall thickness just as well as by the selection of the elastic material in the cavity 12.FIG. 3 shows a second exemplary embodiment of a force measuring unit 1 according to the invention. Specifically, an elastic resistance wire laid in a plurality of loops within the cavity 12 of the housing 10 is also used as the strain gauge sensor 21. The cavity 12 is in turn filled with an elastic material which transmits an extension of the housing 10 to the resistance wire. With regard to possible materials, reference is made to the explanations relating to FIG. 2.In the embodiment shown in FIG. 3, the housing 10 is formed from two half shells 13 which are placed one on top of the other and which enclose the measuring module 20. In FIG. 3, the force-measuring unit 1 is shown in the form of an exploded drawing before the assembly and before the filling of the cavity 12 with the elastic material.In the example shown, the force introduction elements 11 are apertures in the housing 10, through which bolts of shackles can be guided, for example, in order to connect the force measurement unit 1 to the belt 2 (compare FIG. 1 ) or to another sports device. In each half shell 13, channel-shaped depressions are formed, which together form the force introduction element 11 in each case. In the example, the parting plane between the two half shells 13 runs along a longitudinal axis of the apertures which form the force introduction elements 11. It is understood that the housing 10 can also be formed with two half-shells 13 which lie on top of one another in another, which runs, for example, perpendicular to the plane shown.In the exemplary embodiment of FIG. 3, the evaluation unit 22 has a printed circuit board (circuit board) which carries a battery 23, a terminal 24 and a plurality of electronic components 25. The resistance wire is directly connected to the circuit board of the evaluation unit 22. The battery 23 serves to supply power to the measuring module 20 and is in particular a rechargeable battery which can be charged via the connection 24. The connection 24 can be designed, for example, according to a USB (Universal Serial Bus) standard, in particular according to the USB-C standard. A recess, not shown here, is present in the housing in order to be able to insert a connecting cable into the connector 24. Instead of or in addition to the connection 24, inductive energy transfer for charging the battery 23 can also be provided.An enlarged illustration of the measuring module 20 from a somewhat different perspective is also reproduced again separately in FIG. 4.FIG. 5 shows a three-dimensional cross-sectional illustration through the force measuring unit 1 of FIG. 3 The section is embodied perpendicularly to the connecting line of the force introduction elements 11. In this illustration, it can be seen in particular how the channel-shaped depressions of the half shells 13 of the housing 10 complement one another to form the force-influencing elements 11. It can also be seen how the loops of the resistance wire of the strain measurement sensor 21 within the housing 10 surround the evaluation unit 22, which for the sake of simplicity of illustration is presented in FIG. 5 only in the form of a rectangular cross section.Reference numerals denote reference numerals1 Force measurement unit 2 Belt 3 Anchor 4 Handle 5 Person 10 Housing 11 Force introduction element 12 Cavity 13 Half shell 20 Measurement module 21 Strain measurement sensor 22 Evaluation unit 23 Battery 24 Connection 25 ComponentReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS 2021 / 0283457 A1

[0005] US 2019 / 0126097 A1

[0006] DE 10 2016 003 697 A1

[0008]

Claims

Force measuring unit (1) comprising a housing (10) with at least two force introduction elements (11) for connection to sports equipment, wherein a measuring module (20) is arranged in the housing (10) in order to detect a force acting on the at least two force introduction elements (11), characterized in that the measuring module (20) comprises at least one strain measurement sensor (21) which is connected to the housing (10) in order to determine the force acting on the at least two force introduction points (11) via an extension of the housing (10).Force measuring unit (1) according to Claim 1, in which the housing (10) has a cavity (12) in which the strain measurement sensor (21) is arranged and which is filled with an elastic material.Force measuring unit (1) according to Claim 2, in which the elastic material is silicone.The force measurement unit (1) according to claim 2 or 3, wherein the strain measurement sensor (21) is an elastic resistance wire.Force measuring unit (1) according to claim 4, wherein the elastic resistance wire runs in a meandering fashion.Force measuring unit (1) according to claim 4, wherein the elastic resistance wire runs in a loop shape.The force sensing unit (1) according to claim 6, wherein the elastic resistance wire is passed through the cavity (12) in a plurality of loops.The force sensing unit (1) according to claim 7, wherein the loops of the resistance elastic wire are electrically insulated from each other by the elastic material.Force measuring unit (1) according to Claim 7 or 8, in which the loops run around a printed circuit board (22) of the measuring module (20).Force measuring unit (1) according to one of Claims 4 to 9, in which the elastic resistance wire consists of a plastic, in particular silicone, which is admixed with conductive particles, in particular of carbon black, graphite and / or silver.Force-measuring unit (1) according to one of Claims 1 to 10, in which the force-introduction elements (11) are feedthroughs which are formed on opposite sides of the housing (10).Force measuring unit (1) according to one of Claims 1 to 11, having a position sensor and / or an acceleration sensor.Force measuring unit (1) according to one of Claims 1 to 12, in which the measurement module (20) has a radio interface for transmitting measurement results of the strain measurement sensor (21).Force measuring unit (1) according to Claims 12 and 13, in which the measuring module (20) is configured to transmit measurement results of the position sensor and / or of the acceleration sensor via the radio interface.

Images