The present invention relates to the field of orientation measurement, in particular the orientation of an object in a magnetic field and in a 3-dimensional space.
The measurement of the position, orientation and/or speed of objects in a 3-dimensional space can be performed by different devices, using e.g. light or electricity or magnetism or any other suitable medium. A magnetic field has the advantage to be not susceptible to electrostatic charged surfaces, which is not the case for electric fields. Light itself can be blocked by almost any material making flexible solutions for measuring the orientation and/or position difficult.
In the field of magnetism a magnetic field is normally generated by a coil due to electromagnetism and said magnetic field induces a voltage in another coil, also called receiver coil, under the premise that the magnetic field strength changes in the receiver coil. It is clear that a non-moving receiver coil is not capable to measure a non-altering magnetic field since no voltage is induced by said magnetic field.
There are already means, which can measure a position and/or orientation of a receiver means in relation to a specific magnetic field generating means. To measure the orientation in a 3-dimensional space normally three orthogonal arranged probes are used to calculate the Cartesian coordinates. These arrangements are most of the time very bulky and space taking.
Also the construction of the magnetic field generating means and of the magnetic field receiver means, specifically the arrangement of the coils has to be taken into account to evaluate the received information of the received magnetic field and associate the information to a specific orientation of one of the means.
The calculation of the orientation of a coil within a magnetic field is done normally by the use of coils that are arranged in an orthogonal way. The induced voltage in a coil is depending, among other factors, on the “angle of arrival” of the magnetic field lines.
Thales is holding a patent (WO 2004/065896 A1) on “Method and device for magnetic measurement of the position and orientation of a mobile object relative to a fixed structure”. This patent covers the usage of 3 orthogonal coils for distance and orientation measurement.
The object of the present invention is to provide a magnetic field measuring device which is small, can identify the distance, the orientation and the velocity of specific objects and which is mountable on mobile objects.
The present invention relates to a magnetic field generating apparatus operable to generate a magnetic field which comprises at least three coils operable to generate a magnetic field, respectively, said magnetic fields being modulated with different frequencies, respectively, wherein each of said coils has a symmetry axis and the symmetry axis of at least two of said coils are parallel.
Favourably at least two of said symmetry axes are non-identical.
Favourably each of said coils has a plane perpendicular to said symmetry axis, said plane is extending through the bottom of the respective coil and all planes of said coils are arranged to form a common plane, whereby all coils are located on the same side of the common plane.
Favourably the first and the second coil lie on a first straight line and the second and the third coil lie on a second straight line, whereby the first line is perpendicular to the second line.
Favourably the first, the second and the third coil lie on a first straight line and the fourth, the second and the fifth coil lie on a second straight line, whereby the first line is perpendicular to the second line.
Favourably said magnetic field generating apparatus comprises a pad, said pad being operable to carry said coils at a specific position.
Favourably said pad comprises a central pad operable to carry one coil, at least two outer pads operable to carry said coils, respectively, and at least two pad conjunctions operable to connect to said central pad and said respective outer pads.
Favourably said pad is flexible and/or stretchable and thus placeable on a non-planar surface before the point of a predetermined usage of the magnetic field generating apparatus.
Favourably at least one coil is operable to provide a uni- or bidirectional communication link by means of said magnetic field.
Additionally the present invention relates to a respective magnetic field receiver device which is operable to receive magnetic fields, said magnetic fields being modulated with different frequencies, respectively, said magnetic field receiver device comprising at least one coil operable to receive said magnetic fields and measure the strength of said magnetic fields.
Favourably said magnetic field receiver device comprises as many coils as said magnetic field generating apparatus, whereby said coils are located vis-à-vis to the coils of said magnetic field generating apparatus during the point of an initialisation of said magnetic field receiver device, said initialisation determines the magnetic field strength at a reference position.
Favourably said coils are operable to receive a respective frequency modulated magnetic field.
In the end the present invention relates to a respective magnetic field measuring system operable to measure a relative position, orientation and/or velocity, said magnetic field measuring system comprising said magnetic field generating apparatus and a magnetic field receiver device.
Further more the present invention relates to another magnetic field receiver apparatus which is operable to receive a magnetic field, said magnetic field being modulated with different frequencies, respectively, said magnetic field receiver apparatus comprising at least three coils operable to receive said magnetic field, wherein each of said coils has a symmetry axis and the symmetry axis of at least two of said coils are parallel.
Favourably at least two of said symmetry axes are non-identical.
Favourably each of said coils has a plane perpendicular to said symmetry axis, said plane is extending through the bottom of the respective coil and all planes of said coils are arranged to form a common plane, whereby all coils are located on the same side of the common plane.
Favourably the first and the second coil lie on a first straight line and the second and the third coil lie on a second straight line, whereby the first line is perpendicular to the second line.
Favourably the first, the second and the third coil lie on a first straight line and the fourth, the second and the fifth coil lie on a second straight line, whereby the first line is perpendicular to the second line.
Favourably said magnetic field receiver apparatus comprises a pad, said pad being operable to carry said coils at a specific position.
Favourably said pad comprises a central pad operable to carry one coil, at least two outer pads operable to carry said coils, respectively, and at least two pad conjunctions operable to connect to said central pad and said respective outer pads.
Favourably said pad is flexible and/or stretchable and thus placeable on a non-planar surface before the point of an initialisation of the magnetic field receiver apparatus, said initialisation determines the magnetic field strength at a reference position.
Favourably at least one coil is operable to provide a uni- or bidirectional communication link by means of said magnetic field.
The present invention also relates to a magnetic field generating device operable to generate a magnetic field, said magnetic field generating device comprising at least one coil operable to generate said magnetic field, said magnetic field being modulated with different frequencies, respectively.
Favourably said magnetic field generating device comprises as many coils as said magnetic field receiver apparatus, whereby said coils are located vis-à-vis to the coils of said magnetic field receiver apparatus during the point of an initialisation of said magnetic field receiver device, said initialisation determines the magnetic field strength at a reference position.
Favourably said coils are operable to generate a respective frequency modulated magnetic field.
In the end the present invention relates to a respective magnetic field measuring system which is operable to measure a relative position, orientation and/or velocity, said magnetic field measuring system comprising said magnetic field receiver apparatus and said magnetic field generating device.
The features, objects and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, wherein:
In the description of the present invention the wording “generating” corresponds to the wording “transmitting” to describe the principle operation of the coils operable to generate a magnetic field, whereby said coils are part of a transmitter device in a transmitter receiver setup. Moreover information can be modulated onto the magnetic field, thus turning the coil to a transmitter.
The magnetic field generating apparatus 12 comprises the coils 13, 14, 15, 16, 17 as well as the pad, whereby said coils are arranged in a cross form on said pad. Each coil 13, 14, 15, 16, 17 comprises a respective feeder 13a, 14a, 15a, 16a, 17a which provides the current for generating a magnetic field and/or receives the induced voltage from other altering magnetic fields. The feeders 13a, 14a, 15a, 16a, 17a are constructed in a way to interfere the least as possible with the magnetic field of the coils 13, 14, 15, 16, 17, by e.g. being twisted. The second coil 14 is located in the middle of the cross and has equal distance to the other coils 13, 16, 15, 17. The fifth, the second and the fourth coil 17, 14, 16 are located along the X-axis in a row or also called straight line. The first, the second and the third coil 13, 14, 15 are located along the Y-axis in a row. The X-axis and the Y-axis are perpendicular to each other and intersect in the middle of second coil 14. The first coil 13 comprises at least one winding of conductor wire which is/are formed in a circular way with a radius r. The more windings are formed for the coil 13, the less current is necessary to generate the equal amount of magnetic field strength at the same position. The coils might also be formed in e.g. a quadratic way/form. The coils 13 to 17 might also comprise at least one iron core or powdered iron core to increase the permeability and thus the magnetic flux density of the generated magnetic field. Also the implementation and the usage of additional coils is possible to help improve the accuracy of the movement and/or direction calculation.
In other embodiments the X- and Y-axis do not need to be perpendicular but inclined. Also the respective distance of the outer coils 13, 16, 15, 17 to the central coil 14 might differ to each other. Also the respective diameter of the coils 13 to 17 might vary.
The first coil 13 is located on an outer pad 18a, which is also formed in a circular way and has a radius R. The radius R is bigger than the radius r, but is not restricted to this embodiment. The coils 15, 16, 17 as well as the outer pads 18b, 18c, 18d, whereby said coils 15, 16, 17 are located on said outer pads 18b, 18c, 18d, correspond to the first coil 13 and its outer pad 18a. The second coil 14 is located on a central pad 20, which is circular formed. The central pad 20 is joined to the other outer pads 18a to 18d of the respective coils 13, 16, 15, 17 by means of a respective pad junction 19a, 19b, 19c, 19d. Each pad junction 19a to 19d has parallel sides of the length L and has a width B, said pad junction is operable to keep the coils in a cross form or any other desirable arrangement. The above-mentioned pads can be of any other form and/or material to interfere the least with the magnetic field generated by either the respective coil and/or all the coils 13 to 17. The pads 18a to 18d and 20 might comprise e.g. a hole to safe material and weight, respectively. The whole pad can be bendable and/or flexible and/or stretchable to better adjust said pad to a round or otherwise formed surface like e.g. a hand. If the pad is modified as said, the embodiment should still provide nearly parallel symmetry axis of the coils 13 to 17. If the symmetry axis differ from being parallel, the signal processing is adjusted by using different reference signal levels as described in
The present invention also proposes to use a magnetic field generating apparatus comprising three or more coils in a flat plane as generating and/or receiving means. The wording that coils are “in a flat plane” or “on the same plane” means that each coil is located with its bottom on the same side of a common plane, whereby the symmetry axis of the respective coil is perpendicular to said common plane. Eventually every coil has a plane at and extending through the bottom of the coil, said plane being perpendicular to the symmetry axis. In the case of three coils, the coils should be arranged in a rectangular angle to each other to better distinguish the relative location to each other. The rectangular angle means that at least a first and a second coil are on a first straight line, while at least the second and a third coil are on a second straight line, whereby the first straight line is perpendicular to the second straight line. It is emphasised that the two lines have to intersect with each other. But of course in other embodiments different angles and/or arrangements are possible. Favourable for 3 dimensional movement measurements, an embodiment comprises three coils whereby said first and second straight line is spanned by said coils. The second coil is part of both the first and the second straight line, thus both lines are intersecting.
Another embodiment comprising three coils is later shown in
In case when all coils are located on the same plane and along the same straight line, only 2 dimensional movements like e.g. along the z-axis and the x-axis, but not along the y-axis are possible to detect unambiguously.
In case when all coils have the same symmetry axis, also only specific measurable movements are possible.
Each coil can have a different resonance frequency (e.g. simple series resonance circuit RC) and/or can be fed by a different frequency signal to generate frequency-modulated magnetic fields. The delta of the carrier frequencies is constant. Furthermore the structure contains (not shown in
In another embodiment the structure of a magnetic field receiver apparatus corresponds to the structure shown in
Again, in another embodiment the apparatus is operable to both generate and receive magnetic fields, thus to work also as unidirectional communication link.
The circuit diagram of the magnetic field receiver device 23 comprises a receiving coil 47, a capacity 48, an amplifier 49, an AD converter 50, a μController 26b, an oscillator 24b as well as a battery 25b. The ground 51b connected to the battery 25b corresponds to every ground symbol shown in the circuit diagram of the magnetic field receiver device 23. The receiving coil 47 is connected to the ground 51b as well as to the amplifier 49 and to the capacity 48. The capacity 48 is also connected to the ground 51b. The capacity 48 and the receiving coil 47 form or are a part of a resonance circuit, which processes a preferable frequency f0 or a frequency range f1 to f2. Other frequency signals, which are induced by a modulated magnetic field, are not conducted through said resonance circuit.
The amplifier 49 is connected to the AD converter 50, whereby said converter is connected to the μController 26b. The oscillator 24b is connected to the ground 51b and to the μController 26b, whereby the battery 25b is connected to the ground 51b and the μController 26b. The battery 25b might be e.g. a low-voltage battery. The amplifier 49 is operable to amplify the received signal based on the received magnetic field. The AD converter 50 is operable to convert the signal received from the amplifier 49 from analogue to digital. The μController 26b is operable to analyse and process the digital signal received from the AD converter 50 and e.g. output a signal diagram as shown in
The magnetic field generating device 22 comprises a μController 26a, an oscillator 24a, a battery 25a, a ground 51a, whereby said μController 26a is connected to the respective coil 13b, 14b, 15b, 16b, 17b. The magnetic field generating device 22 as well as the coils 13b to 17b can correspond to the magnetic field generating apparatus 12 and to the coils 13 to 17 described in
A battery-powered μController with a reference oscillator is generating 5 output signals, either analogue or digital pulse-width modulated (PWM), with 5 different carrier frequencies. The signals are then amplified by an amplification stage, e.g. a digital switching amplifier and fed to a matching and resonance circuitry. The receiving coil is within the nearfield of the emitted magnetic field at the used frequencies, since the dependency between field strength and distance in the nearfield is stronger than in the farfield.
The Q (quality) factor of the magnetic field receiving resonance circuit is low in order to make the receiving means broadband enough to gather the induced voltages at the used frequencies. A low noise, broadband amplification stage amplifies the signal and feeds it to an A/D converter. The digitized signal can then be processed in the μController for extraction of the parameters and comparison to the reference values.
Instead of one receiving coil also multiple coils with different resonance frequencies can be used in the magnetic field receiver device 23 to better distinguish the movement of the magnetic field receiver and/or the magnetic field generating device 23, 22. Still several embodiments of the invention benefit from the flat coil arrangement of the magnetic field generating apparatus, meaning that said apparatus is located on a common plane.
The system is not limited to the use of pure continuous wave (CW) carriers. Also modulation and data transfer is possible, unidirectional as well as bi-directional.
Regarding the x-, y- and z-axis shown in
The induced voltages V1 to V5 can be described as
V1=2πf1SNB1Q cos α1 . . . V5=2πf5SNB5Q cos α5,
whereby
f1 to f5 stands for the different frequencies of the respective transmitter coil,
α1 to α5 stand for the different angles between the symmetry axis of the respective generating coils and the receiver device,
N stands for the number of windings of the receiver device,
S stands for the surface area of the receiver device,
B1 to B5 stands for the field strength in axial direction of the respective generating coil.
For further understanding, the coils 13 to 17 transmit the frequencies f1 to f5, respectively, said frequencies being different to each other.
Moreover in
When one of the outer coils 13, 16, 15, 17 is moved nearer to the magnetic field receiver device 23a by e.g. rotating as mentioned in one of the
The sequence of the diagrams of the
Eventually any of the above mentioned devices/apparatus can be place or attached on a fixed or a mobile object like on gloves. Also the magnetic field measuring system can comprises at least one of the receiver devices and at least one of the generating devices to provide better and more accurate measurements of the magnetic fields and/or to allow multiple users to be detected and use e.g. a gaming console.
Another embodiment comprises three coils, whereby two coils have the same symmetry axis.
Thus the herein proposed embodiments derive the position, the orientation and the relative velocity of two or more objects relative to each other in a 3-dimensional room by the use of multi-coil and multi-frequency arrangement at the generator side.
The technology background is based on the magnetic field. The magnetic field component H of an electromagnetic transmitter dominates the electric field component E in the nearfield of the transmitter. The limit distance between the nearfield and the so called farfield is depending on the frequency of the transmitter and is defined to be λ/2π, where λ is the wavelength. In the nearfield the magnetic field strength, measured in dBμA/m, drops along the x-axis of a conductor loop transmitter by 1/d3, where d is the axial distance from the centre of the conductor loop. This corresponds to a drop in strength of 60 dB per decade of distance. In the farfield after the separation of the field from the antenna only the free space attenuation of the electromagnetic waves is effective. The field strength is proportional to 1/d, this corresponds to a loss of 20 dB per decade of distance.
According to Ampere's law a magnetic field is produced by a current that is flowing through a conductor element, in the case of a circular loop with a radius r and N turns the magnetic field strength B in axial direction at a distance d can be calculated to be
A voltage V is induced into a second conductor loop if this is located in the vicinity of the first conducting loop within the time varying magnetic field B (Faradays law). Ψ is the magnetic flux, S the surface area
The level of induced voltage is depending on the frequency and strength of the generator current, the distance between the transmitting and the receiving conductor loop, the size and the number of turns of both conducting coils. The quality factor Q is a measure for the selectivity at the frequency of interest.
V=2πSNBQ cos α
Furthermore there is also an orientation dependency; this means that the induced voltage V is depending on the angle of arrival of the B field lines.
The frequency dependency is compared small when the frequencies are close to each other.
After detection of the level of the induced voltage(s) by a resonance circuit, RF processing with suitable means and further post processing (DAC, Derivation) of the received signal information the relative distance and the relative orientation of two or more objects can be derived. Also the change of the magnetic field strength versus time and distance can be derived and information about the velocity (distance vs. time) and acceleration (velocity vs. time) of the conducting loops can be gathered.
Number | Date | Country | Kind |
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07100545.8 | Jan 2007 | EP | regional |