HUP0900341A2 - Force measuring method for measuring tangential surface forces developped in the contact surface of foot and groung - Google Patents

Description

PUBLICATION·! ^::: : f:

···©··· _<e · · ·

COPY

Force measurement method for measuring tangential surface forces acting on the contact surface of the foot and the ground

The subject of the invention:

The invention is a force measurement method that can be used primarily for sports and studying foot movement, and is suitable for measuring the force exerted by the sole on the ground, distributed over the surface, and arising tangentially along the surface.

In the following, based on Figure 1, the direction of travel is called the x direction, the force perpendicular to this but falling in the tangent plane at the point of contact is called the y direction, and the direction perpendicular (vertical) to this plane is called z. Our invention is a method suitable for measuring the force effect in the x-y direction as described above.

The invention can be used in all areas where it is necessary to measure the force exerted by the foot on the ground during walking and running, measured in the tangential plane, especially in the field of improving the effectiveness of athletes, planning training, orthopedic measurements and examinations, movement improvement, rehabilitation of the disabled, and related research. A device suitable for measuring force in the x and y directions can be prepared based on the invention, which can be built into an insole, placed in a shoe, built into the sole of the shoe, built into a sock or stocking.

State of the art:

When running or walking, the legs exert forces in order to move forward, which forces arise on the contact surface of the ground and the foot. These forces are represented in a coordinate system in Figure 1 in the x, y, z directions, where the x axis points in the direction of movement, the y axis is perpendicular to the x axis, but also falls in the tangent plane of the contact surface, while the axis is perpendicular to these, pointing upwards. Of the forces exerted by the legs, the force pointing in the -z direction serves to support the body Figure 2. The force F _x acting in the -x direction serves to move forward a walking or running person. This force, pointing backwards, exerted by the leg accelerates the movement and counteracts the force exerted by the other leg (or swinging leg) in the air, which has a decelerating effect on the movement. If the force exerted by the leg points forward, the movement slows down. The lateral force 7^, perpendicular to the x and z planes, pointing in the ±y direction, helps maintain the body's lateral balance, but its excessive magnitude can also cause the body's center of mass to sway laterally, and may also indicate incorrect foot position or movement.

The forces F _x and F _y exerted by the foot on the ground, and the opposing forces F _x and F _y exerted by the ground on the foot, are pairwise shear forces.

When walking or running, the feet alternately touch the ground. When running, both feet never touch the ground at the same time, while when walking, both feet are on the ground for a short time. When running fast, the foot touches the ground for a maximum of 0.2-0.4 s during a period. The point of contact with the ground is not one, constant, well-defined point on the foot, but can be in different places on the foot, depending on the type of movement, its speed, and the individual characteristics of the runner. When walking, the contact usually occurs on the heel, and when running fast, it occurs on the cushioned part of the foot at the base of the toes. In general, the faster the movement, the more contact with the ground occurs towards the toes. After contact with the ground, the foot rolls from the heel towards the toes, a process called rollover. During the rollover, the point of application of the force moves along a curve from the back towards the toes, especially the big toe, as shown in Figure 3. The rollover occurs over the entire surface of the foot when walking, while during running it starts from the midfoot or the toes, but it sometimes happens that someone runs on the tips of their toes.

Doctors, sports doctors, athletes, coaches, and other researchers involved in walking and running are demanding the measurement of forces generated by the foot. The research results so far have brought many good solutions, with their help they have achieved improvements in the rehabilitation of people with disabilities, in the correction of minor movement and posture errors, and in the improvement of the effectiveness of athletes.

1.

The flat force measuring benches manufactured by the Swiss company Kistler Instrumente AG and designed for biomechanical measurements are suitable for measuring the forces acting on the foot. Piezo-electric force meters are placed in the bench. The bench is suitable for determining the force acting on the ground by the foot of a person stepping on, walking or running on its surface in all 3 coordinate directions. This measurement is possible under laboratory conditions or on a treadmill designed for this purpose. Its robust design and the method used for the measurement are not suitable for anyone, regardless of place and time, to use it as a simple to use tool in daily practice (e.g. for training).

2.

A similar device is presented in the invention entitled “Force sensing treadmill” No. US 6878100 B2, which solves the measurement problem by using a measuring device that can be connected to an ordinary treadmill. The measurement is also made in the direction of the 3 axes. The operation of the device is ensured by the sufficiently rigid design of the running surface, because the force exerted by the legs is transmitted along the surface as a rigid body, which is detected by sensors placed in the treadmill. The device also contains other accessories necessary for the measurement. Although the device does not need to be in laboratory conditions, it is stationary and cannot be used simply in daily practice.

3.

A device that can be used in everyday life is presented in the patent specification US 5471405, entitled “Apparatus for measurement of forces and pressure applied to a garment”, and in the patent specification US 4503705, entitled “Flexible Force Sensor”. The former uses a pressure measuring device as a stamp that can be glued to the shoe, the latter to the foot, which transmits the measurement result to a microprocessor. The problem with the method is that it only measures the force acting in the z-axis direction, it does not provide information about the forces in the x-y direction that we want to measure.

Currently, there is no known device that measures forces in the x and y directions using a device placed in or built into the shoe, stores this data for training or general use, and ensures data retrieval, all in a way that its small size, weight, and portable design make it suitable for everyday use in the gym, on the street, or in the field.

The task to be solved by the invention

The invention is based on the recognition that during running or walking, a shear force is generated between the foot and the ground on the contact surface of the ground and the foot, in the tangential plane. The shear force is two forces in opposite directions, the lines of action of which are parallel.

Shear force can also be interpreted if a shoe, insole, sock, stocking, or other device is placed between the foot and the ground, because the force is transmitted along the entire cross section. In the case of surfaces that are in close contact with each other, the force arising along one surface is transmitted to the other surface due to adhesion. Shear force can also be interpreted inside materials, the force pair is also transmitted along imaginary planes in the structure of the material. Overall, the shear force between the foot and the ground is transmitted along both homogeneous and inhomogeneous layers interpreted between the two surfaces, so it can be measured in any two parallel planes perpendicular to the z-axis.

When a shear force acts on an elastic body, it deforms it. The amount of deformation is proportional to the applied force, depends on the strength properties of the material, and its direction is the same as the direction of the applied force. Deformation, as a form change, is a measurable characteristic, as it causes two appropriately selected points to move relative to each other.

The solution to the problem is to apply a shear force pair in parallel xy planes to two selected points or surfaces of an elastic body placed between the foot and the ground during running or walking, in order to move forward, in such a way that it deforms the elastic body. The deformation is characterized by the displacement of two points or layers of the elastic body in parallel x-y planes by measuring the displacement. We can use numerous well-known solutions to measure the displacement. We can assign a clear force value to the value of the displacement measured by the displacement meter.

The solution according to the invention

Our invention is a force measurement method that is suitable for measuring the force exerted by the human foot on the ground, distributed over the surface, tangentially on the contact surface of the sole and the ground, but arising separately on the two surfaces, of the same magnitude, opposite direction, continuously varying magnitude and position, i.e. the force F _x exerted by the foot 7, and the counterforce F' _x arising on the ground 8, the two forces together as a shear force, by measuring the displacement 9 As of the surfaces 1 of the elastic lining 1 placed between the sole and the ground, parallel to the tangent plane, in a known position, and mechanically connected to the elastic lining 1 at appropriate intervals with a displacement measuring device 2 suitable for measuring displacement, which displacement is converted into an electrical signal 11 by the displacement meter 2, a force value is assigned to the electrical signal 11, and then the measured data are stored on a data recorder 6.

A device is suitable for measuring the displacement 9 As, which converts the displacement 9 As into an electrical signal 11. Any displacement meter 2 known today, suitable for the purpose in terms of size and sensitivity, is suitable for measuring the displacement 9 As. Such displacement meters 2 may include, without limitation, a strain gauge stamp, a displacement meter based on capacitance change measurement, a displacement meter based on inductive change measurement, a piezo crystal displacement meter and an optical displacement meter, which transmits the electrical signal 11 generated by the devices via a wire 26, or wirelessly, as an electromagnetic signal 19 to the appropriate point of the insole, where it is transmitted in a suitably designed manner to the signal processing unit.

An electrical signal is considered to be any characteristic of direct, variable or alternating electric current, or its change (including its time course), if it originates from the displacement sensor 2 of the force measuring device implementing the force measuring method according to the invention, but in particular the current strength, voltage, resistance, impedance, capacitance, inductance, frequency, phase, and amplitude as measured characteristics.

The electrical signal 11 is independent of whether it is generated by the displacement sensor 2 itself or converts a signal from an external source. For example, a strain gauge stamp changes electrical resistance, a piezo crystal generates electrical voltage.

To measure the displacement 9 As, a direction-sensitive 2-displacement meter is used. This means that the resultant displacement in the x-y plane is decomposed into two perpendicular components, but the method is insensitive to the displacement caused by the force in the z direction.

The displacement in the z direction can cause measurement inaccuracy, this can be reduced by using a measuring device in which the displacement of the measuring surface in the z direction does not affect the measured value. By using a spacer, the displacement in the z direction can also be eliminated. We can achieve a result if we measure the total resultant force acting on the base and separately measure the force in the z direction with a suitable device and subtract it from the resultant force.

In our invention, we have named the elastic body located between the sole and the ground as elastic lining 1, the deformation of which is 9 As suffered by the shear force 7-8 is measured.

The change in shear force 7-8 can be monitored in analog or digital form. In the case of analog signal form, the frequency of change, in the case of digital, the sampling frequency, determines the characteristics of each circuit. Analog and digital signal conversion and signal processing are performed in the generally known and widespread manner.

A person running or walking alternately touches the ground with his right and left feet. A person walking takes, for example, 120 steps per minute, which means that the cycle time of one foot is approx. 1 s. During one cycle, the foot on the ground lifts off the ground, moves forward in the direction of travel around the pivot point of the raised knee, and then, after the moment of contact with the ground, moves backward using the friction between the sole and the ground, as a result of the application of force. As a result, the body's center of mass moves forward. This cycle time, for example, when running at a speed of 20 km/h and a step length of lm, is reduced to approximately 0.2 s. The foot is both on the ground and in the air during the cycle time. Staying on the ground is 60% of the cycle time when walking at the above pace, and 40% when running. The duration is reduced to 0.6 s when walking and 0.072 s when running.

Rounded up, this means a sampling frequency of 15 Hz. In our invention, this means the lower limit at which 11 evaluable signals are always generated in the 2 displacement meters. The evaluability of all signals can be further improved by increasing the sampling frequency.

During the rolling process, the magnitude of the x-y force at the measurement location changes continuously. In order to obtain an accurate picture of the change, the instantaneous force values must be measured at certain times. 1-100 measurements per step and per measurement location are sufficient, a higher sampling frequency may be justified by the requirements for data transmission or other technical considerations.

The magnitude of the shear force is determined by the force value assigned to the 11 electrical signals.

The force of 7 F _x exerted by the foot acts on the inner surface of the shoe and is transmitted to the ground through the sole of the shoe 28. The ground exerts a counterforce of 8 F' _x through the sole of the shoe, these two forces acting as shear forces. The maximum shear force depends on the friction coefficient of the ground and the shoe. This can reach 300 Nt for a person weighing 80 kg and even more for sprinters.

The 7 F _x force exerted by the foot is therefore transmitted through the layers of material from the foot to the ground. These layers can be conventional, such as socks or stockings, insoles, shoe soles, or unconventional, such as measuring instruments, medical aids, etc. An elastic lining 1 is placed in these layers or between the layers, and we ensure that the force F _x exerted by the foot at the given point and the counterforce F' _x reflecting from the ground are transmitted to the elastic lining 1 at the given point. The elastic lining 1 deforms, which typically and in a known way occurs in such a way that the layers between its upper and lower surfaces move 9 As on each other due to the low-energy connection of the molecules that give the structure of the material. The displacement between the molecules of the material is small, but between two sufficiently distant layers, the small displacements add up to a measurable magnitude.

When designing the foot movement during walking and running, it must be taken into account that, in addition to the material of the shoe and the lining, the foot also naturally moves under force due to the skin and elastic tissues of the human sole. This movement can be up to 8-10 mm in the forward-backward direction without the sole slipping on the ground. The elastic movement of the shoe sole is added to the natural elastic movement of the foot, and the person wearing the shoe perceives these two movements together. If this movement is too large, it can impair the efficiency of the force application and cause a feeling of instability. Since the deformation of 1 elastic lining causes the movement of any two different layers located in a plane perpendicular to the z-axis, therefore - after appropriate calibration - by measuring the movement of a designated point of two planes/layers at a suitable distance from each other, we get an accurate picture of the amount of force acting.

The 11 electrical signals obtained are assigned a measurement number and a force unit. The assignment must be unambiguous. This can be determined by calculation, calibration, or a combined procedure, depending on the measurement parameters.

If 1 elastic liner is made of a material with a known modulus of elasticity, then the applied force is determined by the known Hooke's equation

F = —k · As can be calculated, where F is the force vector, k is the stiffness of the elastic material, As is the elongation, or in our case the displacement vector.

There are materials that follow the linearity of Hooke's law, or follow it with negligible error, but for example the elasticity of rubber depends on both load and temperature, and its elongation (creep) changes even under constant load. (We include here the well-known calculations based on Hooke's law, such as shear stress calculation, or the tensor form of Hooke's law, as well as the tabular assignment of displacement and force and the algorithms describing them, but we will not detail them separately.)

For authentic measurement, it must be calibrated. In this case, we do not examine the exact strength properties of the elastic lining, but rather perform a series of measurements under known conditions in which the elastic lining is exposed to known forces acting in the x-y plane, then the deformation caused and the change in the position of the two designated points are measured with a displacement meter, the resulting signal level and the force are assigned to each other. The results are registered, and then the unknown force occurring during running or walking is compared to this registered value.

Figure 4 shows a preferred embodiment of the force measurement method according to the invention. The force measuring device consists of 1 flexible liner, 2 displacement meter, 3 connections, 4 amplifiers, 5 analog-to-digital converters (A/D), 15 real-time real-time generator, and 6 data recorder. The system receives power from an external power source via 13 power supply connection points. The force exerted by the foot 7 creates a counterforce 8 on the ground. Under the influence of the force pair 7-8, the flexible liner 1 is distorted in a trapezoidal manner, and the edges of the lower and upper surfaces are displaced relative to each other by a magnitude 9. The displacement has a time-varying value 10 as a function of the force exerted 7-8. The displacement is converted into an electrical signal 11 by the displacement meter 2 as a signal converter. The electrical signal is fed to the input of the amplifier 4 via 3 connectors, amplified to the desired extent, and then converted into 12 digitized signals with 5 A/D converters. The sampling frequency of the force measurement is at least 15 Hz, however, due to the need for miniaturization and data transmission requirements, it can be selected higher. The 12 digitized signals are recorded with 6 data recorders. During data recording, the data must be synchronized with the course of the movement and with real time, and for this purpose, real time is also recorded. All units of the force meter are placed between the foot and the ground in a practical way. The data are extracted at 14 connection points for further processing. The force is determined from the data, knowing the stiffness k of the elastic liner 1, and after appropriate calibration, and - if necessary - taking into account other parameters (e.g. temperature).

Figure 5 shows another preferred embodiment of the method according to the invention. The force gauge consists of a flexible liner 1, a displacement meter 2, a connection 3, an amplifier 4 and a data recorder 6. The method differs from the previous one in that the analog electrical signal 11 is not digitized, but is stored with a data recorder 6. The electrical units receive power at a power supply connection point 13.

Figure 6 shows a third preferred embodiment of the method according to the invention, which consists of two separate units. The flexible liner 1, the displacement sensor 2, the connection 3, the amplifier 4, the analog-to-digital converter (A/D) 5, the RF module 17, and the transmitter antenna 18 are placed at the measuring site. The receiver antenna 20, the RF receiver module 21, the real-time generator 15 providing real time, and the data recorder 6 are placed as a separate unit, for example, attached to the upper body. The process operates according to the described process up to the A/D converter 5. The digital signal 12 originating from the A/D converter 5 is modulated in the RF module 17 and transmitted via the transmitter antenna 19 to the receiver antenna 20. The coded or uncoded radio signal is demodulated by the RF receiver module 21 and then recorded by the data recorder 6. The operation of the other modules in the process is logical based on the above. The power supply of the units is done separately at 13 power supply connection points.

Figure 7 implements the arrangement of the method according to the invention described in Figure 6 with the difference that the analog electrical signal 11 is not digitized, but is modulated in an RF module 17 and transmitted via a transmitter antenna 19 to the receiver antenna 20. The radio signal is demodulated by the RF receiver module 21, and then the signals are recorded by a data recorder 6.

During the determination of force, the electrical signal generated by the displacement is converted into a force value. The As/F conversion can be implemented at several points in the process, for example, directly after the displacement measurement, at the output of the amplifier, after digitization, or after the extraction of the stored data. The conversion can be implemented using calculation methods based on Hooke's law, calibration, or a combination of these, in accordance with what was described earlier.

Figure 8 shows a preferred embodiment of the method according to the invention, where the electrical signal 11 generated by the displacement sensor 2 is converted into a force value by the converter 22 placed immediately after it.

In the preferred embodiments of the method according to the invention, as shown in Figures 5-8, the displacement data is recorded and converted into force values only after being extracted from the data recorder. In the example shown in Figure 9, the data stored in the data recorder 6 is extracted via a standard cable 23 by a computing device 42 and evaluated by suitable software.

The implementation of the method according to the invention is illustrated, for example, by the force measuring device according to Figure 10. The displacement measuring assembly 24, the circuit assembly 25, and the wiring harness 26 connecting the two assemblies, which are connected to each other via the connector 3, are placed in the shoe 32. The displacement measuring assembly 24 is installed in the sole of the shoe 43, in a suitably formed cavity 27 from above. From above, the foot comes into contact with the sole part 28, which is firmly fixed to the displacement measuring assembly 24, but is not in mechanical connection with the other parts of the shoe. From below, the displacement measuring assembly 24 is firmly fixed to the bottom of the cavity 27 inside the shoe. The wiring harness 26 runs in a channel 29 formed in the sole of the shoe 43. The encapsulated circuit board 25 is placed in a cavity formed on the outside and side of the shoe sole 43. The circuit board 25 contains the power source, which is covered by the cover plate 30. The stored data can be retrieved via the USB connector 31.

The essential structural elements of the displacement measuring assembly 24 are the upper limiting plate 33, the elastic liner 1, the displacement measuring device 2 and the lower limiting plate 34.

One measuring point of the displacement meter 2 is fixedly fixed to the upper limiting plate 33, the other to the lower limiting plate 34. The relative displacement of the surfaces of the two limiting plates 33,34 is limited by a suitable and known elastic material, an elastic liner 1. The elastic liner 1 is always fixedly fixed to the limiting plates 33,34 in contact with it.

The circuit assembly 25 includes the amplifier 4, the A/D converter 5, the real-time generator 15, the data recorder 6, the power source 35, the USB connector 31 enabling data extraction, and these 25 circuit assemblies are encapsulated 36. The enclosure 36 has a cover plate 30 for the power source.

After the foot 16 touches the ground, the force F _x exerted by the sole 7 is transmitted through the sole part 28 to the upper limiting plate 33 of the displacement measuring assembly 24. The sole of the shoe 43 adheres to the ground, and the lower limiting plate 34 is momentarily at rest relative to the ground through the sole of the shoe. The displacement measuring assembly 24 generates an electrical signal 11 proportional to the amount of displacement 9, which is fed to the circuit assembly 25 via the connector 3. The circuit assembly 25 continuously measures the signal level appearing at the output of the displacement measuring assembly 2 by sampling. The measured value is stored by the data recorder 6. After data collection is completed (e.g. after training), the measurement data can be transferred to a computer using the USB connector 31.

The displacement measuring assembly 24 can be placed anywhere from the human foot to the ground, such as on the bottom of the shoe sole 43, built into the material of the shoe sole 43, built between the folds of the shoe sole 37, placed on the inner surface of the shoe sole 41, or built into the insole 38, stockings, socks, or applied directly to the human skin.

An example of the placement of the displacement measuring assembly 24 on the sole of a shoe 43 is shown in Figure 11. In this arrangement, the sole part containing the displacement measuring assembly 24 is placed on the sole of the shoe 43 with a releasable bond. The electrical signal generated by the displacement measuring 2 is transmitted to the circuit assembly 25 located on the heel of the shoe by the wire harness 26.

An example of the placement of the force measuring device between the folds of the shoe sole 37 is shown in Figure 12. The shoe sole contains islands, or cleats, sufficiently deep folds 37 between the cleats. Each cleat absorbs the force independently and deforms elastically relative to each other. The flexibility of the shoe sole 43 is ensured by the sole part between the cleats 37. The displacement measuring assembly 24 is fixed in the folds, between the cleats. The upper limiting plate 33 of the force measuring device is fixed to the deep parts of the folds of the sole, to the base of the cleat, and the lower limiting plate 34 to the layer close to the walking surface. The force measuring device measures the displacement due to the deformation of the cleat. The circuit assembly 25 can be placed, for example, on the heel of the shoe, to which the electrical signal is delivered via a bundle of wires 26 routed between the folds.

An example of the placement of the force measuring device in an insole 38 is shown in Figure 13. The insole 38 is made in a conventional, comfortable design according to its appearance and general properties, and at the same time, it enables the determination of the x-y forces exerted by the sole for walking/running due to its special sandwich structure. The displacement measuring assembly 24 is placed inside the layered insole 38. The insole 38 is placed inside the shoe without displacement. The insole 38 is essentially flexible, but sufficiently rigid along its surface to not crumple, and the dimensional change of the layers forming the upper 41 and lower 40 surfaces during the load occurring during running and walking is minimal to such an extent that it does not cause significant errors in the values measured by the displacement meter attached to the layers. The outer surfaces 40-41 of the insole 38 are suitable, due to their appropriate friction, to adhere to the sole on one side and to the upper surface of the sole part inside the shoe on the other side under load. The force sensor measures this displacement. The electrical signal is transmitted to the connector 35 via the wiring harness 26.

The number of measuring devices depends on how many points on the sole we want to measure.

A further practical solution is shown in Figure 14, where more than one displacement measuring assembly 24 is used in the insole 38. The displacement measuring assembly 24 separately and independently measure the force acting in the x-y plane between the foot and the ground. The resulting force is determined as the vector sum of the forces measured by the individual devices. The multiple measuring devices can eliminate the measurement error caused by the bending of the sole, which occurs because the two surfaces of the insole 38 are at a measurable distance from each other and when bent, the upper and lower curvatures will have different arc lengths. The electrical signal 11 reaches the connector 35 via the conductive foil 39.

The two outer surfaces 40-41 of the insole can be of any topology, even different from each other. The surfaces considered for the displacement measurement, lying opposite each other, can be at the same distance at all points (let us consider them simply as parallel surfaces), or at different distances (non-parallel surfaces). If the upper and lower surfaces 41 are parallel, the measurement is a simple displacement measurement, during which the change in the electrical signal 11 proportional to the displacement 9 is converted into a force 22 by a suitable calculation method. If the upper and lower surfaces 41 and 40 are not parallel, in this case, a clear assignment of the forces and the electrical signals 11 according to the above must be ensured by a suitable calculation algorithm, diagram, table, or other means.

Claims (24)

Patent claims 1. Our invention is a force measurement method that is suitable for measuring the shear forces exerted by the human foot (16) on the ground, distributed over the surface, arising tangentially on the contact surface of the sole and the ground, but separately on the two surfaces, i.e. the force F _x (7) exerted by the foot and the counterforce F' _x arising on the ground, as shear forces of the same magnitude, opposite direction, and continuously varying magnitude and position in time, characterized in that the displacement As of the surface/layer of one or more flexible linings (1) placed between the sole and the ground in two planes approximately parallel to the tangent _plane and in a known position, as a _shear force, the displacement (9) of which is the magnitude and direction, and then the displacement (9) is converted into an electrical signal (11), a force value calculated from the material properties of the elastic lining (1), or determined by calibration, or a combination thereof, is assigned to the electrical signal (11) (22), the force and direction data are stored in a data recorder (6) synchronously with the course of the movement, from which the data is extracted using connectors (3), (31) (23), (42). 2. The force measurement method according to claim 1, characterized in that the flexible lining (1) is designed to have a surface facing the foot and a surface facing the ground, of which surfaces the surface facing the foot is directly or indirectly acted upon by the force F _x (7) exerted by the foot, and the surface facing the ground is directly or indirectly acted upon by the counterforce F' _x (8) of the opposite direction and of the same magnitude, exerted from the ground to the sole or shoe sole, arising on the ground. 3. Force measurement method according to claims 1 and 2, characterized in that, as a result of the force according to point 2, the elastic lining (1) deforms proportionally to the acting force, and as a result of the deformation, the layers of its structure between the lower and upper surfaces, parallel to the tangent plane, elastically move (9) by an amount As relative to each other. 4. Force measurement method according to claims 1, 2 and 3, characterized in that measuring points are designated on two layers/surfaces of the elastic lining (1) that are sufficiently distant from each other, and the relative positions of these measuring points are measured during the displacement measurement. 5. Force measurement method according to claims 1, 2 and 3, characterized in that the elastic liner (1) is deformed as a result of the force effect in such a way that the deformation determines the direction of the acting force. 6. The force measurement method according to claim 1, 2, 3 and 5, characterized in that during the displacement measurement, the magnitude and direction of the displacement are also determined in the x-y direction interpreted in the tangent plane. 7. Force measurement method according to claim 1, 2, 3, 5 and 6, characterized in that the elastic liner (1) and the displacement meter (2) form an assembly unit (24) (Figure 10). 8. The force measurement method according to claim 1, characterized in that the displacement meter (2) outputs an electrical signal (11) related to the amount of displacement As (9). 9. Force measurement method according to claims 1 and 8, characterized in that the electrical signal (11) produced by the displacement sensor (2) is amplified (4) (Figures 4-8). 10. Force measurement method according to claims 1, 8 and 9, characterized in that the electrical signal (11) proportional to the displacement As (9) is converted into a digital signal (12) by an analog-to-digital converter (5) (Figure 4). 11. The force measurement method according to claim 1, characterized in that the displacement values As (9) are converted into a force value (22), which force value quantifies the forces acting on the foot of a running or walking person in the x-y plane by designating the direction relative to the foot. 12. Force measurement method according to claims 1 and 11, characterized in that the conversion (22) of the displacement As (9) into a force value is performed by calculation based on the material properties of the elastic lining (1). 13. Force measurement method according to claims 1 and 11, characterized in that the conversion of the displacement As (9) into a force value (22) is carried out by comparison with the displacement caused by a known force effect, as a reference value, by calibration. 14. Force measurement method according to claims 1 and 11, characterized in that the conversion of the displacement As (9) into a force value (22) is carried out by combining the methods used in points 12 and 13. 15. The force measurement method according to claims 1, 8, 9 and 10, characterized in that the displacement value As (9) is stored on a data recorder (6) (Figure 5). 16. The force measurement method according to claims 1, 8, 9 and 11, characterized in that the force values are stored on a data recorder (6) (Figure 8). 17. The force measurement method according to claim 1, characterized in that the signal proportional to the displacement is transmitted in the form of an electromagnetic signal (19) to the data recording unit (6) containing the radio frequency receiver (20), (21) (Figures 6 and 7). 18. The force measurement method according to claim 1, characterized in that the elastic lining (1) and the displacement sensor (2) forming a single assembly unit with it are installed in the sole part (28) of the shoe between the sole and the ground (Figure 10). 19. The force measurement method according to claim 1, characterized in that the elastic liner (1) and the displacement sensor (2) forming a single assembly unit with it are installed in the insole (38) between the sole and the ground (Figure 13). 20. The force measurement method according to claim 1, characterized in that the elastic lining (1) and the displacement sensor (2) forming an assembly unit with it are installed between the folds (37) of the shoe sole, specially designed islands, between the sole and the ground (Figure 12). 21. Force measurement method according to claim 1, characterized in that the elastic lining (1) and the displacement sensor (2) forming a single assembly unit with it are mounted on the sole (43) of the shoe from below between the sole and the ground (Figure 11). 22. The force measurement method according to claim 1, characterized in that the elastic liner (1) and the displacement sensor (2) forming an assembly unit with it are placed in a stocking or sock that can be pulled on the foot between the sole and the ground. 23. The force measurement method according to claim 1, 18, 19, 20, 21, 22, characterized in that more than one elastic liner (1) and a displacement meter (2) forming an assembly unit with it are used to determine the exact position of the forces arising in the x-y plane at different points of the sole (Figure 14). 24. The force measurement method according to claim 1, characterized in that the stored data (6) is extracted via the appropriate connector (31) and processed on a computer (24) or a suitable device (Figure 9).