EP2268999A1

EP2268999A1 - System and method for determining parameters representing orientation of a solid in movement subject to two vector fields

Info

Publication number: EP2268999A1
Application number: EP09732406A
Authority: EP
Inventors: Etienne De Foras
Original assignee: Movea SA
Current assignee: Movea SA
Priority date: 2008-04-18
Filing date: 2009-04-08
Publication date: 2011-01-05
Also published as: US9297660B2; US20110035172A1; FR2930335A1; FR2930335B1; WO2009127561A1

Abstract

The system for determining parameters representing the orientation of a solid in movement subject to a first vector field (A) and a second vector field (M) includes a first triaxial sensor (CAPT1) and a second triaxial sensor (CAPT2) secured to said solid to measure the components of said respective vector fields (A, M) according to the axes of said sensors, and a determining means (DETROT) for determining the rotation matrix (ROT) for the solid. Said determining means (DETROT) for determining said rotation matrix (ROT) includes: a correction means (CORR) for correcting the influence of an additional vector field of the same nature as said measured vector field; and a first calculation means (CALC1) for calculating a third vector (U) not coplanar to the plane formed by the two vectors (A_pp, M) delivered by said correction means (CORR), and realized such that the angles of the axis system formed by the third vector (U) and the two vectors (A_pp, M) delivered by said correction means (CORR) remain constant.

Description

System and method for determining parameters representative of the orientation of a moving solid subjected to two vector fields.

The invention relates to a system and a method for determining parameters representative of the orientation of a moving solid subjected to two vector fields.

In general, motion capture systems of a solid have applications in various fields such as health, multimedia, or geophysics.

For video applications or video games, a user's movements can be used to control virtual reality systems. For example, the movements of a player can be recorded to control the evolution of a virtual character in a synthesis scene.

In the field of portable electronics, motion capture devices allow devices to adapt to the context of use. They allow, for example, to optimize the reception of a mobile phone by the knowledge of its orientation, or to improve the interfaces of the personal assistants.

In the field of health, such systems can be used to position surgical tools, or to monitor the movement of elderly people or those with health problems resulting in reduced mobility.

Motion sensors, and more precisely angular position sensors, are highly miniaturized and researched to give them robustness and cost compatible with applications aimed at the general public. The position of a solid in space is entirely determined by the knowledge of six magnitudes. Among these are three sizes that can translate translations and three other sizes likely to translate rotations. The last three magnitudes correspond to angular positions, called attitude angles, that can be used to determine motions. In addition, a rotation can be defined by a quaternion. For example the document FR 2 838 185 (Commissariat à l'Energie

Atomic) discloses a device for capturing the orientation of a solid comprising at least one angular position sensor that can be made integral with the solid and to deliver at least one measurement data representative of the orientation of the solid, a means for generator of test data representative of an estimated orientation of the solid, and means for modifying the estimated orientation of the solid by confronting the measurement data and test data. After one or more modifications of the estimated orientation, it converges towards the effective orientation of the solid, or, more precisely, towards the measured orientation. This device does not require calculation means to establish the orientation or the inclination of the solid on the basis of a function of the measurement data of the sensors, and makes it possible to overcome the non-linear behaviors of these.

However, such a device requires many calculations and can not, or hardly, be embedded on a system of reduced size. Such a device is also sensitive to the proper acceleration of the solid.

Also, the present invention aims to solve the problems mentioned above.

According to one aspect of the invention, there is provided a system for determining parameters representative of the orientation of a moving solid, subjected to a first vector field and a second vector field, said fields being of known directions in a reference frame. fixed not bound to the solid. Said system comprises a first triaxial sensor and a second triaxial sensor integral with said solid to measure the components of said respective vector fields along the axes of said sensors, and means for determining the rotation matrix of the solid. Said means for determining said rotation matrix comprise: correction means, deactivatable on command, adapted to correct the influence exerted on the measurements of at least one of said sensors by an additional vector field of the same nature as said measured vector field and to deliver at least one vector corrected vector field ; and

first means for calculating a third vector adapted to calculate said third non-coplanar vector to the plane formed by the two vectors delivered by said correction means, and such that the angles of the trihedron formed by the third vector and the two vectors delivered by said correction means remain constant.

Such a system makes it possible, at reduced cost, to produce a system for calculating the attitude angles of a moving solid using a greatly reduced number of computations, facilitating its implementation in an onboard manner on board a portable set of small size. In one embodiment, said means for determining said rotation matrix further include means for orthogonalizing and centering the measurements transmitted by said triaxial sensors.

Thus, the simplicity of the algorithm allows an implementation consuming little energy, easily achievable with an embedded processor.

According to one embodiment, said means for determining said rotation matrix further comprise control means adapted to deactivate said correction means at a time taken for reference, while said first calculation means calculate a third vector of reference.

The user can thus choose his reference.

Advantageously, the system further comprises automatic activation means adapted to activate said correction means when a standard of one of said vector fields transmitted by said triaxial sensors is greater than a reference threshold and for deactivating said correction means when said standard is less than or equal to said reference threshold.

Thus, automatically, the system can disable the correction, for example, to initiate a gesture recognition mode. In one embodiment, said means for determining said rotation matrix further comprise second means for calculating an intermediate matrix whose successive columns are the components of said third vector, the components of said first vector field measured and possibly corrected by said correction means, and the components of said second vector field measured and possibly corrected by said correction means.

It is thus possible to indicate reference fields, for example in a magnetically disturbed environment, and to use them to make a rotation matrix correct. According to one embodiment, said means for determining said rotation matrix further comprise third matrix inversion calculating means adapted to be activated by said control means when calculating the third reference vector and for calculating the inverse matrix of said intermediate matrix corresponding to the third reference vector and named reference inverse matrix.

Matrix inversion calculations are performed only for the intermediate reference matrix, which greatly limits the computational complexity of carrying out the invention.

In one embodiment, said means for determining said rotation matrix further comprise storage means for storing said reference inverse matrix.

Thus the inversion of this matrix is performed only once.

According to one embodiment, said means for determining said rotation matrix further comprise a multiplier for multiplying said intermediate matrix and said stored reference inverse matrix and outputting said rotation matrix.

The matrix of rotation of the solid is obtained directly in a simple manner. In one embodiment, the system further comprises means for determining said parameters representative of the orientation of the solid from the coefficients of said rotation matrix.

The attitude angles of the solid or the quaternion representative of the orientation of the solid from the rotation matrix of the solid are then immediately deduced.

According to one embodiment, said third vector is the vector product of the first measured and possibly corrected vector field and the second vector field measured and possibly corrected.

The vector product is a third vector that fulfills the above conditions and is simple to compute.

In one embodiment, said first vector field is the terrestrial gravitational field and said second field is the terrestrial magnetic field.

The invention applies in a non-limiting manner to gravitational and magnetic terrestrial fields.

According to one embodiment, said correction means are adapted to correct the measured gravitational field in a corrected gravitational field by adding to the measured gravitational vector a vector proportional to the measured terrestrial magnetic vector so that the corrected gravitational vector forms with the terrestrial magnetic vector measured at an angle equal to a reference angle equal to the substantially constant angle between the terrestrial gravitational field and the terrestrial magnetic field in said fixed frame not bound to solid, and adapted to center the corrected gravitational vector. In one embodiment, said parameters representative of the orientation of the solid comprise attitude angles such as Cardan angles or Euler angles, or a quaternion.

According to another aspect of the invention, there is also provided a method for determining parameters representative of the orientation of a moving solid, subjected to a first vector field and a second vector field, of substantially constant directions in a reference frame. fixed non-solid bond, wherein the components of said respective vector fields are measured along the respective triaxial sensor axes, and the rotation matrix of the solid is determined. The influence exerted on the measurements of at least one of said sensors by an additional vector field of the same nature as said measured vector field is corrected and at least one vector corrected vector vector is corrected. A third non-coplanar vector is calculated from the plane formed by the two vectors delivered at the correction output, and such that the angles of the trihedron formed by the third vector and the two vectors delivered at the correction output remain substantially constant.

In one embodiment, the measurements of the first and second vector fields are orthogonalized and centered, and said correction is deactivated at an instant taken for reference during the calculation of a third reference vector.

The invention will be better understood from the study of some embodiments described by way of non-limiting examples and illustrated by the appended drawings in which: FIG. 1 schematically illustrates an embodiment of a system according to an aspect of FIG. the invention; and

FIG. 2 diagrammatically illustrates a mode of implementation of the method according to one aspect of the invention.

In the description which follows, reference is made to the attitude angles of a solid. However, the solid is not part of the attitude angle determination system, which corresponds more precisely to those sensors that can be attached to the solid. In addition, the terms orientation and angular position are used as synonyms.

In the remainder of the description, in a nonlimiting manner, the two vector fields are the terrestrial gravitational field and the terrestrial magnetic field. Of course, the invention also applies to any two arbitrary vector fields that are substantially constant in a non-solid fixed reference frame.

As illustrated in FIG. 1, the system comprises a triaxial accelerometer CAPT1 which measures, in a reference frame linked to the solid, the gravitational field A and a triaxial magnetometer CAPT2 which measures in the reference frame the magnetic field M.

The measurements transmitted by the triaxial accelerometer CAPT1 and the triaxial magnetometer CAPT2 are transmitted to a DETROT module for determining the rotation matrix ROT are orthogonalized and centered by an ORTHOC module. As a variant, the orthogonalization and the centering of the measurements transmitted by the triaxial sensors CAPT1 and CAPT2 can be directly carried out within the sensors themselves.

Orthogonalization means measurements delivered by a triaxial sensor, a posterior correction of the perpendicularity defects of the sensor, and by centering the measurements delivered by a sensor, a correction of the offset of the sensor so that it has a zero response. for a null stimulus.

A correction module CORR, which can be deactivated on command by a user of the system, via a command module CONTROL, makes it possible to correct the influence exerted on the measurements of at least one of the sensors by an additional vector field of the same nature as that measured. In this case, an acceleration proper to the solid is measured by the triaxial accelerometer CAPT1 in addition to the reference gravitational field A1. In such an exemplary embodiment, the correction module CORR adds to the measurement vector A a vector parallel to the measurement vector M: A + tM, which is called A _PP , t being a determined scalar of so that the angle formed by A _PP and M is equal to the angle between the gravitational and magnetic terrestrial fields of substantially constant directions in a fixed reference unrelated to the solid.

Optionally, an ACTAUTO automatic activation module tests whether a standard of one of said vector fields is greater than a reference threshold, and, if the standard of one of said vector fields is greater than this reference threshold, active automatically the correction module CORR, and to disable it otherwise.

A first calculation module CALC1 calculates a third vector U which is not coplanar with the plane formed by the two vectors delivered by the correction module CORR, and such that the angles of the trihedron formed by the third vector U and the two vectors A _PP and M delivered by the correction module remain constant. In this example with terrestrial gravitational and magnetic fields, the first calculation module CALC1 calculates the vector product U of the vectors A _PP and M delivered by the correction module CORR (U = A, _pp XM ₁ x being the symbol of the vector product) .

A second calculation module CALC2 forms an intermediate matrix (UA _PP M) whose successive columns are formed by the components of the third vector U, the corrected measurement vector A _PP , and the measurement vector M.

During the deactivation of the correction module CORR by the command module COMMAND, the second calculation module CALC2 elaborates an intermediate matrix (U- _I A- _I M- _I ) corresponding to the third reference vector Ui. A third calculation module CALC3 is activated by the command module CONTROL allowing a user to define the reference of the system. The third control module CALC3 performs the computation of the inverse of a matrix, in this case the computation of the inverse of the matrix (U- _I A- _I M- _I ) of the reference vectors (Ui = Ai x Mi) which is called reference inverse matrix inv ((UiA ₁ M ₁ )), and which is stored in a memory module MEM. This inversion reference matrix inv ((U-ιA-ιM-ι)) is calculated once. In system operation, the correction module CORR is activated, and the third calculation module CALC3 is deactivated.

A multiplication module MULT receives as input the intermediate matrix (UAp _P M) and the inverted reference inverse matrix inv ((U-ιA-ιM-ι)), respectively of the second calculation module CALC2 and of the memory module MEM, and outputs the matrix product of these two matrices, equal to the rotational matrix ROT representative of the rotation of the solid.

From the rotation matrix ROT, a determination module DET determines the parameters representative of the orientation of the solid. The parameters representative of the orientation of the solid may be, for example, the attitude angles of the solid, such as yaw, roll and pitch angles. Alternatively, the parameters representative of the orientation of the solid may be, for example, a quaternion. In the case of attitude angles, this determination by identification of attitude angles can be performed by multiplying the rotation matrix ROT by the vector V1 = [1 OO], which gives a second vector V2 = [xyz], as that the yaw angle YAW, which is the projection of V2 on the (x, y) plane, satisfies the following equation: tan (YAW) = y / x. For ROLL roll angles and PITCH pitch, similar identifications may be used.

In the case of quaternion, this determination makes it possible to find the quaternion (vector of the axis of rotation and rotation) associated with the rotation, by a simple calculation using the trace of the rotation matrix. FIG. 2 illustrates the operation of a system according to FIG.

1. The CAPT1 and CAPT2 triaxial sensors perform measurements (step

20), which are orthogonalized and centered (step 21) by the ORTHOC module.

The influence exerted on the measurements of at least one of the sensors by an additional field of the same nature as that measured, in this case an acceleration proper to the solid, is measured by the triaxial accelerometer CAPT1 in addition to the reference gravitational field A1 , is corrected (step 22) by the CORR correction module as previously described. This step may be deactivated, or in other words not carried out, on temporary command (step 23) of a user of the system, especially when he wants to define a reference of the system. An optional automatic test, (step 21 a) comparing whether the norm of one of the orthogonalized and centered vectors A or M, delivered by the ORTHOC orthogonalization and centering module, is greater than a reference threshold, and, if this condition is verified, the ACTAUTO automatic activation module activates the correction module CORR. A third vector U is then calculated (step 24) so that it is non-coplanar with the plane formed by the two vectors delivered by the correction module CORR, and such that the angles of the trihedron formed by the third vector U and the two vectors A _PP and M delivered by the correction module remain constant. For example, U may be the vector product of the vectors A _PP and M delivered by the correction module CORR, calculated by the first calculation module CALC1.

The second calculation module CALC2 then calculates (step 25) an intermediate matrix (UA _PP M) whose successive columns are formed by the components of the third vector U, the corrected measurement vector A _PP , and the measurement vector M.

During the control (step 23) of deactivation of the correction (step 22) made by the correction module CORR, the command module COMMAND also activates the third calculation module CALC3 (step 26) to calculate the inverse reference matrix inv ( (UiA ₁ M ₁ )) previously defined. This inverse reference matrix inv ((UiAiM-ι)) is stored (step 27) in the memory module MEM.

In operation established, out of command (step 23) for referencing for the system, the multiplication module MULT performs the matrix product or multiplication (step 28) of the intermediate matrix (UA _PP M) and the stored reference inverse matrix inv ((U-ιA-ιM-ι)) for outputting the rotation matrix ROT of the rotation of the solid. The determination module DET then determines (step 29) the attitude angles of the solid or the quaternion from the rotation matrix ROT, for example as previously described for the DET module.

The present invention thus makes it possible, with a reduced number of computations providing the attitude angles of a moving solid or a quaternion from the rotation matrix, to produce a small portable system allowing the motion capture of a solid.

Claims

1. System for determining parameters representative of the orientation of a moving solid, subjected to a first vector field (A) and a second vector field (M), said fields being of known directions in a fixed reference frame unrelated to solid, said system comprising a first triaxial sensor (CAPT1) and a second triaxial sensor (CAPT2), integral with said solid, for measuring the components of said respective vector fields (A, M) along the axes of said sensors, and determining means ( DETROT) of the rotation matrix (ROT) of the solid, characterized in that said means for determining (DETROT) said rotation matrix (ROT) comprise:

correction means (CORR), deactivatable on command, adapted to correct the influence exerted on the measurements of at least one of said sensors (CAPT1, CAPT2) by an additional vector field of the same nature as said measured vector field, and delivering at least one corrected vector (A _PP ); and

first calculation means (CALC1) of a third vector (U) adapted to calculate said third vector (U) which is non-coplanar with the plane formed by the two vectors (A _PP , M) delivered by said correction means (CORR); , and such that the angles of the trihedron formed by the third vector (U) and the two vectors (A _PP , M) delivered by said correction means (CORR) remain constant.

2. System according to claim 1, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprise orthogonalization and centering means (ORTHOC) measurements transmitted by said triaxial sensors (CAPT1). , CAPT2).

3. System according to claim 1 or 2, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprises control means (CONTROL). adapted to disable said correction means (CORR) at a time taken for reference, while said first calculating means (CALC1) calculates a reference third vector (U) (Ui).

4. System according to claim 3, further comprising automatic activation means (ACTAUTO) adapted to activate said correction means (CORR) when a standard of one of said vector fields (A, M) transmitted by said triaxial sensors (CAPT1, CAPT2) is greater than a reference threshold, and for deactivating said correction means (CORR) when said standard is less than or equal to said reference threshold.

5. System according to claim 4, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprises second calculation means (CALC2) of an intermediate matrix (UAp _P M) whose successive columns are the components of said third vector (U), the components of said first vector field measured and possibly corrected (A _PP ) by said correction means (CORR), and the components of said second vector field measured and possibly corrected (M) by said correction means (CORR).

6. System according to claim 5, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprises third matrix inversion calculating means (CALC3) adapted to be activated by said control means (CONTROL) during the calculation of the third reference vector (Ui) and for calculating the inverse matrix of said intermediate matrix (U-IA-I MI) corresponding to the third reference vector (Ui) and named reference inverse matrix (JnV (UiA ₁ M ₁ )).

7. System according to claim 6, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprises storage means (MEM) for storing said reference inverse matrix (JnV (U ₁ A ₁ M)).

The system of claim 7, wherein said means for determining (DETROT) said rotation matrix (ROT) further comprises a multiplier (MULT) for multiplying said intermediate matrix (UAp _P M) and said inverse matrix of reference (inv (U-ιA-ιM-ι)) stored and outputting said rotation matrix (ROT).

9. System according to one of claims 1 to 8, further comprising means for determining (DET) said parameters representative of the orientation of the solid from the coefficients of said rotation matrix (ROT).

10. System according to one of the preceding claims, wherein said third vector (U) is the vector product of the first measured and optionally corrected vector field (A _PP ) and the second measured vector field and possibly corrected (M).

11. System according to one of the preceding claims, wherein said first vector field (A) is the terrestrial gravitational field and said second vector field (M) is the terrestrial magnetic field.

The system of claims 10 and 11, wherein said correction means (CORR) is adapted to correct the measured gravitational field (A) to a corrected gravitational field (A _pp ) by adding to the measured gravitational vector ( A) a vector proportional to the measured terrestrial magnetic vector (M) so that the corrected gravitation vector (A _PP ) forms with the measured terrestrial magnetic vector (M) an angle equal to a reference angle equal to the substantially constant angle between the terrestrial gravitational field and the terrestrial magnetic field in said fixed reference frame not bound to solid, and adapted to center the corrected gravitation vector (A _PP ).

13. System according to one of the preceding claims, wherein said parameters representative of the orientation of the solid. include attitude angles such as Cardan angles or Euler angles, or a quaternion.

14. A method for determining parameters representative of the orientation of a moving solid, subjected to a first vector field (A) and a second vector field (M), of substantially constant directions in a fixed reference frame unrelated to the solid, in which the components of said respective fields are measured according to the respective triaxial sensor axes (CAPT1, CAPT2), and the rotation matrix (ROT) of the solid is determined, characterized in that: - the influence exerted on the measurements is corrected at least one of said sensors by an additional vector field of the same nature as said measured vector field and delivers at least one corrected vector (A _PP ); and

a third vector (U) which is not coplanar with the plane formed by the two vectors (A _PP , M) delivered at the correction output, and such that the angles of the trihedron formed by the third vector (U) and the two vectors ( A _PP , M) delivered at the correction output remain substantially constant.

15. The method according to claim 14, in which the measurements of the first and second vector fields are orthogonalized and centered, and said correction is deactivated at a time taken for reference, during the calculation of a third vector (U) of reference ( Ui).