Device and method for measuring the dynamic interaction between bodies

© Patent holder (s):

Xsens Technologies BV in Enschede.

© Granted:

03.03.2009 © Inventor (s):

Petrus Hermanus Veltink in Haaksbergen.

© Published:

06.05.2009 © Authorized representative:

Ir. H.Th. van den Heuvel cs in 5200 BN 's-Hertogenbosch.

© Apparatus and method for measuring the dynamic interaction between bodies.

The invention relates to a device for measuring the dynamic interaction, in particular power transfer and work performed, between a first and a second body, in particular during relatively random movements. The device comprises a housing in which at least one kinematic sensor and at least one kinetic sensor are included, as well as processing means for processing the signals originating from the sensors, and communication means for data exchange with the outside world. The invention also relates to a method for measuring the dynamic interaction between a first and a second body, and a carrier, provided with a number of devices according to the invention.

NL C 2000835

This patent has been granted regardless of the enclosed result of the prior art research and written opinion. The patent corresponds to the documents originally filed.

The Netherlands Patent Center is an agency of the Ministry of Economic Affairs.

Apparatus and method for measuring the dynamic interaction between bodies

The invention relates to a device and method for measuring the dynamic interaction between a first and a second body. The invention particularly relates to a device and method for measuring the dynamic interaction between a first and a second body during relatively random movements. The invention further relates to a miniature device for measuring the dynamic interaction between a first and a second body.

Devices for analyzing human walking motion are known in the art. Kinematic sensors such as inertial sensors (accelerometers, angular velocity sensors) and magnetometers are used for this. Devices are also known which can determine the transfer of forces between two bodies. Kinetic sensors, such as pressure sensors, force sensors and torque sensors, are used for this. A known method uses so-called force plates. Such plates, which are provided with several force sensors, are applied to the substrate. The force plate is then entered by a test subject, whereby the force plate is dynamically loaded. From the measured forces, information is obtained about the interaction between the substrate (force plate) and the test subject. When walking on a relatively hard surface, the reaction forces of the surface and the acceleration of the foot are generally not equal to zero. When the foot is on the hard surface, the speed of the foot will be practically zero, while the reaction force will differ from zero. When the foot is not on the ground, the opposite phenomenon occurs: the speed of the foot will be unevenly zero while the measured reaction force is zero. This means that when walking on a relatively hard surface, no power is transferred from the foot to the surface, except possible during the impact phase if the foot touches the ground during the transition from swing to standing phase.

However, there are also conceivable circumstances in which power is transferred by means of a movement of a body, in particular of a human body. For example, power is supplied during all kinds of physical work, in which objects are manipulated, or during sports. There is currently no adequate apparatus and method available that can measure the dynamic interaction between a first and a second body, and in particular the power transfer from a first body to a second body during relatively random movements. Being able to measure the interaction between two or more bodies during relatively random movements, for example between the body of an athlete and a ball, or between the body of the athlete and a preferably non-hard surface, provides useful information about the movement, about the forces, and about the power transferred by the athlete to the ball or to the ground. Such information can be used to improve the athlete's performance. Such information can also be very useful in ergonomics (evaluating physical load during work tasks) and for disabled people who use a prosthesis.

The object of the present invention is to provide an apparatus and method for measuring the dynamic interaction between a first and a second body, in particular during relatively random movements.

To this end, the invention provides a device comprising a housing in which at least one kinematic sensor and at least one kinetic sensor are included, as well as processing means for processing the signals originating from the sensors, and communication means for data exchange with the outside world. By placing the device between the contact surface of the first and the second body, and because the device is provided with at least one kinematic sensor and at least one kinetic sensor, it is possible to determine the power transmitted via the contact surface directly.

It is noted that devices are known from the prior art that are capable of determining the power transfer between two bodies. A well-known example is a bicycle that is equipped with a force transducer on the crankshaft, and a revolution speed sensor on the crankshaft, for example. However, such a device is only able to estimate the power transfer between two bodies (a person and the bicycle) for a limited series of movements, in this case a pedaling movement. Such a movement is imposed by the first and / or second body and is therefore not arbitrary, but is already predetermined substantially. The device according to the invention, on the other hand, makes it possible to obtain an estimate of the power transfer between two bodies which perform relatively arbitrary movements, such as is the case, for example, between a ball and a gripping hand. In the context of the present application, relatively arbitrary movement means any movement that is controlled by the first and / or second body (for example by the athlete's muscle strength), but which is in principle not predetermined.

The device according to the invention comprises kinematic and kinetic sensors for measuring speed and force, respectively. The processing means of the device according to the invention receive, for example when the first and second bodies come into contact, the force signals generated by the kinetic sensors and the velocity and / or angular velocity signals generated by the kinematic sensors. By estimating the speed from the motion signals - at any time, if desired, and then calculating the internal vector product from the force and speed signal (represented in the moving coordinate system of the sensor), a direct, if desired continuous measurement of the transmitted power is obtained. After all, when a first body comes into contact with a second body, the power delivered by the first body at any time t is given by the internal vector product of the measured force vector F and the measured velocity vector v in the same coordinate system:

P (t) = F (t) - v (t) (1)

When the force vectors F (Xj) and the velocity vectors v (x;) are measured at different positions Xj of a contact surface, the power is calculated at a given time by summing the internal vector products at all positions:

<img file="NL2000835C2_D0001.tif" />

(2)

Each pair of force and speed vectors must be shown in a random, potentially moving coordinate system. This coordinate system may differ for different pairs of force and speed vectors. Thus, the vectors can be expressed in the moving local coordinate system of the device. If, in addition to linear forces and speeds, torques M (Xj, t) and angular speeds ω (χι, t) are also measured, the above formulas (1) and (2) can be further supplemented by adding the (sum of the) internal vector products £ M (xi, t). to include (Xj, t).

In order to determine the transmitted power, an accurate estimate of the speed is preferably performed. According to the invention, the velocity vector can be estimated by integrating the acceleration acceleration a derived over time. An acceleration sensor measures the sum s_a of the acceleration of motion a and the gravitational acceleration g:

Sa = ag (3)

Because the gravitational acceleration g is always oriented vertically, the acceleration of motion a can be derived from the measured signal s_a are derived by adding the gravitational acceleration g. Preferably, the inclination of the acceleration sensor (the angle of the sensor relative to the vertical) should also be estimated for this purpose. For relatively small accelerations of motion, the inclination can be estimated from the signals from the acceleration sensor, which is then used as an inclinometer. This procedure is known per se and is described in detail in HJ Luinge, PH Veltink, Inclination Measurement of human movement using a 3-D accelerometer with autocalibaration, IEEE Transactions on Neural Systems and Rehabilitation Engineering, vol. 12, 2004, pp. 112-121. The signals can be low-pass filtered at a desired cutoff frequency. It is also possible to use a Kalman filter. At greater accelerations of motion, the inclination can be estimated by fusion of the information derived from a triaxial accelerometer and a triaxial angular velocity sensor. This procedure, which is also known per se, is described, for example, in HJ Luinge, PH Veltink, Measuring orientation of human body segments using miniature gyroscopes and accelerometers, Medical and Biological Engineering and Computing, vol. 43, 2005, pp. 273-282. Both references are expressly included in the present application. The device according to the invention is distinguished, inter alia, from the prior art by coupling movement information with the force information in the same sensor to estimate power transfer and characterize the dynamics of the body.

In order to make the measurement more accurate and easier, the device according to the invention is further characterized in that the at least one kinematic sensor and the at least one kinetic sensor are located in mutually predetermined fixed positions and preferably at a relatively small mutual distance in the housing . This ensures that the measured and / or estimated forces and speeds, and possibly torques and angular speeds, are measured in the same coordinate system. After all, in this preferred variant, the sensors have a fixed position and orientation relative to a coordinate system connected to the device. The measured quantities can then, with knowledge of the movement of the device, be converted by transformations known per se into a global coordinate system that is connected to the environment in which the device is located. What is to be understood by a relatively small distance is determined by the movement: the mutual distance of the sensors in the present preferred variant must be so small that this need not be taken into account in the calculations. The sensors should therefore effectively be in the same position in this preferred variant. This also requires relatively small sensor systems.

In another preferred embodiment of the device according to the invention, it is characterized in that the at least one kinematic sensor and / or the at least one kinetic sensor are triaxial sensors. In certain cases it is possible to measure a considerable part of the power transfer with uniaxial and / or possibly with biaxial sensors, but the use of triaxial sensors has the advantage that almost the entire power transfer between the bodies can be measured.

Since the contact of the invented device with the first and / or second body can take a relatively short period, a relatively high sample frequency of the measured signals is preferably applied during the contact. This promotes a more accurate measurement of the interaction between the first and second bodies. In a preferred embodiment of the device according to the invention, it comprises sensors whose sampling frequency can be temporarily increased during contact between the two bodies (when the interaction force is not zero), as well as a buffer unit for the measured signals.

According to the invention, the device is preferably a miniature device. In such a miniature device, for example in the form of a chip, the sensors are preferably incorporated in or between two plates that contact the two bodies. The kinetic sensors are preferably arranged in this miniature device such that they form the connection between top and bottom plate. Force and / or torque signals are derived from the deformation of this connection, measured with strain gauges and / or capacitive displacement sensors, for example. The kinematic sensors are preferably positioned in such a way that they are hardly affected, if at all, by mechanical deformations. For this purpose they are preferably coupled to the top or bottom plate.

In a preferred variant, the device according to the invention also comprises at least one triaxial angular velocity sensor. With such a triaxial angular velocity sensor (or gyroscope), an accurate estimate of the three-dimensional orientation of the device can be determined, so that the acceleration of motion a can always be derived from the acceleration sensor signals_a.

If desired, the device according to the invention can be used as a separate measuring unit. However, it is advantageous if a number of devices according to the invention are combined by accommodating them in a suitable carrier . Suitable carriers include, for example, a body suit, which preferably includes shoes or other parts for the body parts that make physical contact with the environment such as hands, feet, back, pelvis, etc. A particularly suitable carrier is in the form of a glove. Such a glove is easy to apply and can map a large number of interactions between the human body and objects of all kinds. Devices with kinetic and kinematic sensors as described above are preferably included in this embodiment variant at all contact points between body part (hand) and object, so that the full interaction force is measured. This full interaction force can be determined by adding the forces measured with all devices in one common sensor system, possibly the global coordinate system of the environment. For this purpose, the relative orientations of the sensor devices should preferably be determined. This determination can be made from the motion information measured with the kinematic sensors of the sensor devices, as already described above.

Alternatively, or in addition to this, information about the relative orientation of the sensors can be obtained if the angular velocities and differences in acceleration of the sensor devices are sufficiently small. This is the case with a hand, for example. Under these conditions, it can be assumed that the relative accelerations of the sensor devices relative to each other are small relative to the common accelerations. Under this assumption, it can be assumed that the triaxial acceleration sensors at all times measure the same acceleration in all sensor devices, only in a different coordinate system. The direction of the vectorial acceleration sensor signal at any time for each device provides partial information about the relative orientations of the devices. Moreover, if the direction of this acceleration varies sufficiently during a movement, the full relative orientations of the sensor devices can be determined. This is only possible if the relative orientations of the sensor devices and the hand / body segments to which they are attached do not significantly change before the acceleration is measured in a number of directions.

The invention also relates to a method for measuring the power transfer from a first body to a second body, and in particular for measuring the power transfer during relatively arbitrary movements. In the invented method, at least one device as described above is applied to the first and / or second body, and the power is obtained by the internal vector product of the force signals generated by the kinetic sensors and the speed signals generated by the kinematic sensors calculated by the processing means of at least one device. The advantages of the method have already been described above in the context of the description of the device, and will therefore not be repeated here.

It is advantageous to characterize the method in that the devices according to the invention are arranged at virtually every contact position between the first and second body. This can for instance be done excellently by accommodating the devices in a carrier, such as preferably a glove.

In the method according to the invention, the surface properties of the contact surface between the first and second body can be important. For some configurations where shear forces are undesired or limited, a low friction surface is preferably provided, while for other configurations where shear forces must be transferable, a high friction surface is preferably used. The method according to the invention preferably comprises a step in which the surface properties of the first and / or second body are adjusted or chosen in order to realize the desired interaction between both bodies.

According to the invention, the work performed by the first body over a period of time is obtained by integrating the internal vector products of the force signals generated by the kinetic sensors and the velocity signals generated by the kinematic sensors over this time. As is well known, small errors in the estimation of sensor offset, especially during long-term integration, can lead to significant integration errors, also referred to as integration drift. In order to minimize these integration errors, and thereby improve the estimate of the work performed, it is desirable to have knowledge about start and end conditions regarding speed, position, orientation and power and / or knowledge about average speeds, positions, orientations and / or capabilities, and / or it may be approximate, use the cyclical nature of a movement to minimize estimation error in sensor offset and / or use information about the duration of the interaction to minimize the duration of the integration.

The method and device according to the invention are excellently applicable for determining the power transfer between at least two bodies. However, it is also possible to obtain information about the dynamic properties of the bodies from the obtained sensor signals. In the context of the present application, dynamic properties is understood to mean the relationship between movement of and force on the body during a dynamic load. Properties such as mass, stiffness and damping, but also other properties, play an important role in this. In a preferred embodiment of the method according to the invention, information about the dynamic properties of the second, but also possibly the first, body is determined from the force signals generated between the two bodies, and the speed signals generated by the kinematic sensors, by means of recursive identification. In such a method, a mathematical model is made of the dynamic properties of the body or is based on such a model. In the model, however, the model parameters (the actual values ​​of stiffness, damping, mass, etc.) are not given a fixed value. Then, for a given set of parameter values, the force at the measured motion or relevant motion variables at the measured force is calculated, and it is compared with the measured magnitudes. The parameter values ​​are then adjusted so that the difference between calculated and measured quantities is minimized. Thus, the dynamic properties of the first and / or of the second body can be determined. It is noted that such recursive identification is known per se, however not in the present combination with a direct power measurement. In addition, it should be noted that in the interaction between two dynamic bodies in general, only partial characterization of the dynamic properties of each of the bodies can be obtained, since the interaction force and joint movement of the contact face must satisfy the dynamic characteristics of both bodies , and therefore both bodies, and due to the limited joint movements performed, may not be sufficiently excited throughout the work area of ​​each of the bodies. However, in many cases the relationship between measured force and movement information can lead to a useful characterization of the dynamics of one or both bodies.

The device and method according to the invention can be used for many purposes. It is thus possible to use these in motion tracking systems in general, and in particular in sports, for example in the analysis of power, strength and movement and the relationships between these quantities when throwing a ball, a disc, arrows. , when hitting with a tennis racket or golf club, when skating, where the device is placed in the skate, for example, when rowing, football (contact foot / ball), and the like. The measurement can be used to improve the athlete's performance. Another possible application is the measurement of power in ergonomics, which determines the interaction between the human body and a tool, chair, etc. The device is also suitable for all kinds of medical applications and in rehabilitation, for example when testing and optimizing prostheses, and to check and / or improve the interaction between a robot and its environment.

The invention will now be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures. Herein: figure 1 schematically shows the interaction between a first and a second body; figure 2 schematically shows a first exemplary embodiment of the device according to the invention;

figure 3 schematically a first exemplary embodiment of the method according to the invention; and figure 4 finally shows schematically a carrier provided with a number of devices according to the invention.

With reference to Figure 1, a first body 1 and a second body 2 are schematically shown. The first body 1 can for instance be a (part of a) human body, or a robot. The second body 2 can be, for example, a tool, or the surface, or a projectile such as, for example, a ball. The interaction between both bodies (1, 2) can take place by transfer of forces F and / or moments M from the first body 1 to the second body 2 (and of course also the other way around). In addition, if the two bodies have a velocity v or angular velocity ω not equal to zero at the location where interaction force and motion are measured, a power P is also transferred, which is given by the internal vector product of the force vector and the velocity vector (according to formula (1) ), and in case of moment / angular velocity added to this the internal vector product of moment vector and angular velocity vector.

Figure 2 shows an exemplary embodiment of a device 10 for measuring the dynamic interaction, and in particular of the power transfer, between the first body 1 and the second body 2. The device 10 comprises a housing 11, in which at least one kinematic sensor 12 and at least one kinetic sensor 13 is included, preferably of the triaxial type. The kinetic sensor (s) 13 are connected to both parts of the housing 11 via mechanical connections 130. The kinematic sensor (s) are attached to either part of the housing, in particular to a movable portion 110 of housing 11. Upper and parts of the housing form the contact plates for the two bodies. The housing 11 is also provided with processing means 14 known per se (electronics, processors, etc.) for processing the signals originating from the sensors (12, 13). The housing 11 also comprises, if desired, communication means 15 for data exchange with the outside world. In the embodiment shown, the communication means 15 are wireless, for example by means of radio waves. The sensors (12, 13) are located at mutually predetermined fixed positions in the housing 11, preferably at a relatively short distance from each other. They form a relatively rigid whole with the housing 11. The force and acceleration signals of the sensors (12, 13) are thus measured in a coordinate system connected to the device 10 (x_s, y_s, z_s). According to the invention, the power transfer from the first body 1 to the second body 2 is estimated in relatively arbitrary movements by arranging at least one device 10 on the first body 1, and / or on the second body 2, and / or between both bodies. in. As a result, the devices 10 are loaded by forces F, and possibly by torques M. Since at least one of the bodies (1, 2) is also in motion, the devices 10 will also be subjected to a speed v, and possibly a rotational speed ω.

The power is obtained by calculating the internal vector product of the force and / or torque signals generated by the kinetic sensors 13, and calculating the speed and / or rotation speed signals generated by the kinematic sensors 12 by the processing means 14 of the devices 10 or with processing means of a remote system receiving the signals via the communication facility of the device 10.

When measuring with several devices 10 at the same time, it is advantageous to include them in a carrier. Referring to Figure 4, a wearer is shown in the form of a glove 100. The glove 100 is provided on the palm side with a number of devices 10 according to the invention. As shown, the devices can be mounted on the palm itself, but also on the phalanges, for example. The glove 100 is applied to the hand of a person, the hand thus acting as the first body 1. With the glove 100 provided with the devices 10, the power transfer from the first body 1 to a second body can be carried out in a very simple and accurate manner, such as, for example, a ball 2. As shown in Figure 4, when positioning the devices 10 on the glove, it is important to position them preferably so that they are positioned at almost every possible contact position between the hand and the ball 2. If this is not the case, part of the power transfer can be “missed”. In the method according to the invention, the work performed by the hand 1 for a certain period of time is obtained by summing and integrating the internal vector products of the force and speed signals measured by all the devices 10 coming into contact with the ball 2 over these time.

It is also possible according to the invention to determine partial or complete information about the dynamic properties of the ball or other body 2 from the force signals generated per device 10 by the kinetic sensors 13 and the speed signals generated by the kinematic sensors 12. Such a determination is shown schematically in figure 3. A first body 1 is shown which is in contact with a second body 2. Between the two bodies (1,2) is a device 10 according to figure 2. The dynamic properties of the second body 2 are schematically represented by a number of parameters, such as the mass m, the stiffness K, and the damping D. It may be clear These parameters can be supplemented, if desired, by other parameters relevant to the dynamic behavior of the second body. The dynamic properties of the second body can be determined from the force and velocity signals generated by the device 10, by recursive identification or other suitable algorithms. A mathematical model is made of the dynamic properties of the second body 2. In the model, the model parameters m, Ken D are not given a fixed value. Then, for a given set of parameter values, the motion is calculated at the measured force (or vice versa), and this is compared to the measured force or motion. The parameter values ​​are then adjusted so that the difference between calculated and measured motion / force is minimized. Thus, the dynamic properties of the second, but possibly also the first body, can be determined at least in part. Once the dynamic properties of the second body have been determined, they can be used to separate the energy delivered to the second body 2 into delivered potential energy and kinetic energy on the basis of a measurement of the transmitted power. This, and the information obtained about the dynamic characteristics of body 2, makes it possible to determine the trajectory of the second body 2 (for example, if this body is a ball 2) after it has become detached from the first body 1.

It will be clear that the invention is not limited to the exemplary embodiments shown and described here, but that variants are possible within the scope of the appended claims, which will be obvious to the skilled person in this field.