WO2009072042A2

WO2009072042A2 - Angular sensor, angle measurement system, base station, garment and band aid or plaster comprising an angular sensor

Info

Publication number: WO2009072042A2
Application number: PCT/IB2008/054990
Authority: WO
Inventors: Robert Pinter; Anke Schmeink
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2007-12-06
Filing date: 2008-11-27
Publication date: 2009-06-11
Also published as: WO2009072042A3

Abstract

An angular sensor (100) comprising at least one loop (140,150) of electrical conductive material being attached to a preferably flexible substrate is provided. The substrate is foldable and an inductance of the loop (140,150) is dependent on a folding angle (160). The angular sensor (100) may be included in a garment (400) to facilitate the determination of a body posture, or in a plaster (500) to apply to the skin of a patient. Preferably the angular sensor transfers data indicative of the measured angle wireless to a base station (300). The base station is configured to receive the data of a plurality of angular sensors. The angular sensor (100) and the base station (300) are included in an angle measurement system (350) that may be used by a physiotherapist to supervise rehabilitation exercises.

Description

Angular sensor, angle measurement system, base station, garment and band aid or plaster comprising an angular sensor

FIELD OF THE INVENTION

The invention relates to an angular sensor as defined in claim 1. The invention further relates to an angle measurement system comprising an angular sensor. The invention further relates to a base station comprised in the angle measurement system and to a garment, band aid or plaster comprising an angular sensor.

BACKGROUND OF THE INVENTION

Measuring angles is a basic task in determining the status of a physical entity. The physical entity may be an industrial apparatus, for example a robot of which the motions have to be supervised, but may also be a human being that is performing exercises.

An angular sensor is known from IEEE Transactions on Instrumentation and measurement, Vol. 47, No. 4, August 1998 by Romain Roduit et. al. This publication discloses an angular sensor wherein the angle to be measured is obtained by measuring the longitudinal displacement of two parallel wires that are bent in the plane of rotation. A flexible girdle is used that maintains a constant space between the wires. The profile of the girdle must be chosen correctly to be sure that the wires stay in a plane during flexion. The girdle is bound to two reference plates, and two wires are passing through this girdle. At one side, the wires are bound to the first plate, and at the other side the differential position of the wires is measured. The operation of said angular sensor is based on the mechanical displacement of wires in the girdle, and thus on a mechanical principle. It is a trend to simplify devices having mechanical moving parts to increase their reliability.

SUMMARY OF THE INVENTION It is an object of the invention to provide an angular sensor having a minimal amount of moving parts.

The object of the invention is achieved with an angular sensor that comprises at least one loop of electrical conductive material that is attached to a substrate. The substrate comprises a first substrate part that is foldable with respect to a second substrate part. A first part of the loop is located at the first substrate part and a second part of the loop is located at the second substrate part. By folding the substrate the angle between the first and second substrate part will change. When the loop is conducting a current, an electromagnetic field or EM field is generated by said loop. By folding the substrate the EM field generated by the first part of the loop may partly or completely compensate the EM field generated by the second part of the loop and consequently the inductance of the loop is dependent on the angle between the first and second substrate part. With the angular sensor according to the invention mechanical movement is limited to the first substrate part being foldable with respect to the second substrate part, the angle between the first and second substrate part being the angle to be measured. This provides an angular sensor having a minimal amount of moving parts, thereby achieving the object of the invention.

In a further embodiment the angular sensor further comprises inductance measurement means. This has the advantage that the angular sensor provides data that is indicative of the measured inductance, and thus changes in the angle are reflected in changes in the data that is provided by the measurement means. The data may comprise an analogue signal. The data may however also be a digital signal comprising a plurality of bits, the measured angle being represented by the value of a plurality of bits.

In a further embodiment the measurement means comprises an oscillator, an oscillation frequency of the oscillator being dependent on the inductance value of the looped wire. The data indicative of the measured inductance may be an analogue voltage or current signal of the oscillator, the frequency of the signal being indicative of the inductance that is coupled to the oscillator.

In a further embodiment the angular sensor further comprises wireless communication means providing the advantage that a person having the angular sensor attached to his limbs, for example at the back of his knees, is not hindered by wiring attached to the sensor as the data indicative of the measured inductance, and thus indicative of the angle between his upper leg and lower leg, is sent wireless.

In a further embodiment of the angular sensor the looped wire may be used as a transmitting antenna to send the data indicative of the measured inductance. In this embodiment the magnetic field produced by the looped wire is used to transmit information of the measured angle, providing a low cost wireless link.

According to an aspect of the invention there is provided an angle measurement system that comprises at least one angular sensor and a base station. Each one of the angular sensors provides to the base station data indicative of the measured inductance. The base station comprises receiving means for receiving the transmitted data. A physiotherapist may use the angle measurement system to supervise rehabilitation exercises. According to a further aspect of the invention there is provided a base station. The base station is configured to receive the data indicative of the measured inductance from the angular sensor.

In an embodiment the base station comprises filter means to separate the data of a plurality of angular sensors, each one of the sensors sending data indicative of the measured inductance to the base station. According to a further aspect of the invention there is provided a garment comprising the angular sensor. The substrate of the angular sensor may be flexible, for example a patch of cloth. The patch may be knitted in a garment, for example a jacket. As example each sleeve of the garment may comprise a patch. In the example this provides the advantage that the angular sensor does not need to be attached to the body of a person to be able to measure the bending of his arms.

According to a further aspect of the invention there is provided a band-aid or plaster comprising the angular sensor. The plaster is conveniently applied to the skin of a person to measure the angle between limbs coupled by a joint.

BRIEF DESCRIPION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. Ia shows an embodiment of an angular sensor,

Fig. Ib shows the embodiment of the angular sensor of fig. Ia, the substrate being folded,

Fig. Ic shows the embodiment of the angular sensor of fig. Ia, the substrate being folded,

Fig. 2a shows the embodiment of the angular sensor of fig. Ia, the substrate being folded, Fig. 2b shows a schematic diagram of the superposition of magnetic field vectors,

Fig. 2c shows a schematic diagram of the superposition of magnetic field vectors,

Fig. 3a shows a further embodiment of an angular sensor, Fig. 3b shows the embodiment of the angular sensor of fig. 3a, the substrate being folded,

Fig. 4a shows a further embodiment of an angular sensor, Fig. 4b shows the embodiment of the angular sensor of fig. 4a, the substrate being folded,

Fig. 5a shows a further embodiment of an angular sensor, Fig. 5b shows the embodiment of the angular sensor of fig. 5a, the substrate being folded,

Fig. 6 shows a schematic diagram of an angular sensor comprising inductance measurement means and communication means,

Fig. 7 shows a schematic diagram of an angle measurement system Fig. 8 shows a garment comprising an angular sensor

Fig. 9 shows a person having a plaster comprising an angular sensor attached to his elbows and knees.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. Ia shows an embodiment of an angular sensor 100 comprising a loop 140, 150 of electrical conducting material that is attached to a substrate 110, 130. For example the substrate may be a flexible printed circuit board having a loop comprising a copper trace. In an other example the substrate may be fabric and the loop comprising conductive fibres that are woven in the fabric. The loop may have a plurality of shapes such as circular or rectangular. The loop of electrical conductive material has an inductance L that equals the ratio of the magnetic flux and a current I that flows in the loop. As example the inductance Lo of a circular loop of a wire of conductive material is given by

I₀ = r - μ₀ - μ_r Equation 1

In equation 1 μ₀ is the permeability of the vacuum, μ_r is the relative permeability of the material in the loop, r is the radius of the loop, and a is the radius of the wire forming the loop. Y is a constant which is equal to 0.25, if the current I is distributed equally across the wire's cross-section.

The substrate comprises a first substrate part 130 and a second substrate part 110. For example the first and second substrate part may be relatively rigid material coupled with a folding axis 120, the folding axis having the function of a joint. The folding axis 120 separates the loop in a first part 140 and a second part 150.

Fig. Ib shows a situation wherein the substrate of the angular sensor 100 is folded causing an angle 160 between the first substrate part 130 and the second substrate part 110 to change from 0 degrees to φ degrees. Due to the change an electromagnetic field being caused by a current I through the loop will also change, as the electromagnetic field Bl generated by the first part 140 of the loop will partly compensate the electromagnetic field B2 generated by the second part 150.

Fig. Ic shows a situation where the angle has further increased to a value larger than 90 degrees. When the angle increases even further to 180 degrees the electromagnetic field lines of the first part 140 of the loop and the second part 150 of the loop have opposite directions. Assuming that the folding axis 120 splits the area enclosed by the loop in two equal parts 140a and 140b (see Fig. 2a) the resulting magnetic field will be zero resulting in an inductance of 0 H. Figs. 2a-2c show how using vector algebra and applying super position the magnetic field vectors of the electromagnetic field generated by the first part 140 and second part are added. A magnetic field comprises a plurality of magnetic field lines B. A vector may be used to represent a magnetic field line. To add two magnetic fields Bl and B2 their corresponding vectors are added. As shown in Fig. 2b and 2c, each vector is decomposed in a component that is parallel to the resulting field vector for B 1,2 and a component that is perpendicular to the resulting field vector for B 1,2. As shown in Fig. 2c the perpendicular components Blpp and B2pp compensate each other. The components of Bl and B2 parallel to the resulting field vector B 1,2 are calculated as:

\B\p\ = \B\\ • cos(0.5 ^■ φ) Equation 2

|52p| = |52| - cos(0.5 - φ)

wherein |B1|=|B2| =|B| as the two vectors Bl and B2 result from the same current I through the loop and consequently have the same absolute value. The angle between each one of Bl, B2 and the resulting field B 1,2 is φ/2 degrees.

The magnitude of the resulting field vector B 1,2 is therefore given by:

51,2 = 2B ^■ cos(0.5 • φ) Equation 3 The inductance L of the loop is proportional to the absolute value of magnitude of the resulting field vector, |B1,2|, and is derived as being given by

L = L₀ - cos(0.5 • φ) Equation 4

In equation 4 Lo refers to the inductance as calculated by equation 1 representing the inductance of an unfolded substrate wherein B 1,2 has its maximal value of 2|B|. L is the inductance of the loop that has been folded φ degrees 160. Thus the inductance L of the loop 140,150 is dependent on an angle 160 between the first and second substrate part 130, 110.

Fig. 3a shows a further embodiment of an angular sensor 100 wherein the loop comprises a further loop 140 attached to the first substrate part 130 and an other loop 150 attached to the second substrate part 110. The further loop and the other loop conduct a same current I, and the electromagnetic fields B caused by the current I have the same direction for the further loop and the other loop.

Fig. 3b shows the situation wherein the substrate of the further embodiment of the angular sensor 100 has been folded causing an angle 160 between the first substrate part 130 and the second substrate part 110 to change from 0 degrees to φ degrees. Due to the change an electromagnetic field Bl being caused by a current I through the further loop 140 will partly compensate an electromagnetic field B2 being resulting from the current I through the other loop 150. As a result the inductance L of the loop will change, and thus is the inductance L of the angular sensor indicative of the angle 160 between the first and second substrate part 130, 110. The inductance L will be maximal when the angle φ 160 equals 0 degrees. When the first and second substrate parts have been folded maximal, that is 180 degrees, the inductance will decrease to its minimal value. When the areas enclosed by the further loop 140 and the other loop 150 are equal and fully overlap the inductance has reduced to 0 H (Henry).

Fig. 4a and Fig. 4b show a further embodiment of an angular sensor 100 wherein with respect to the embodiment shown in Figs. 3a and 3b only the current direction of the further loop 140 and the other loop 150 has reversed resulting from a 'x' coupling between the further and other loops 140, 150 in stead of the '=' coupling used in Figs. 3a and b. The maximal inductance L is obtained when the angle φ 160 equals 180 degrees as for this angle the magnetic fields Bl and B2 have a same direction. With the angle φ 160 equalling 0 degrees a minimal inductance is obtained. As the magnetic field caused by the further loop 140 and the other loop 150 only partly compensate each other the minimal inductance will not be equal to 0 H. The loop of the angular sensor 100 shown in the embodiments of Figs la-4b may comprise a plurality of loops. For example the loop shown in Fig. Ia may comprise a plurality of wires that are preferably stacked, each wire being positioned preferably on top of an other wire, conducting a same current and enclosing preferably a same area. Also the folding axis 120 may not split said same area in equal parts. Referring to Fig. 2a, the area 140a enclosed by the first part 140 of the loop may not be equal to the area 150a enclosed by the second part 150 of the loop.

Fig. 5a and Fig. 5b show a further embodiment of an angular sensor 100. The angular sensor 100 comprises at least one loop 140 of electrical conductive material attached to a first substrate part 130 and at least one further loop 150 of electrical conductive material attached to a second substrate part 110. The second substrate part 110 is foldable with respect to the first substrate part. A mutual inductance of the at least one loop and the at least one further loop is dependent on an angle 160 between the first and second substrate part. In Figs. 5 a and 5b for example the loop 140 is arranged to be coupled to an electric source causing a current Il in said loop, resulting in the generation of a magnetic field B. Said field will cause a flux in the other loop 150, and consequently there is a mutual inductance between the loop and the further loop, the voltage measured across the further loop being indicative for the folding angle 160. An advantage of the embodiment of the angular sensor of Figs. 5a and 5b is that the current conductive material is not being repeatedly folded, as there is no need for an electrical coupling by conductive material between the further and the other loop. This enhances the reliability of the angular sensor 100.

Fig. 6 shows an angular sensor 100 that further comprises inductance measurement means 200 arranged for providing data 230 indicative of the measured inductance. The inductance measurement means is coupled to the looped wire 140, 150 and to a power source 220 such as for example a battery. Said angular sensor may further comprise wireless communication means 210 coupled to the inductance measurement means 200. The communication means are arranged to provide transmitted data 360, said transmitted data 360 being dependent on said data 230 indicative of the measured inductance. The communication means 210 may for example comprise modulation means such as for example an AM or FM modulator. Said angular sensor 100 has the advantage of being configured to operate wireless. For example it will cause less obstruction to the movements of an object or person to which said angular sensor is attached.

The inductance measurement means 200 may comprise a current source providing an alternating current at a predefined frequency. The ratio of a voltage across the loop of electrical conductive material and said alternating current provides a value for the inductance L of said loop of electrical conductive material. With a predetermined value of the current the voltage across said loop provides the data 230 indicative of the measured inductance. In an other embodiment the inductance measurement means 200 comprises an electrical oscillator whose value of the oscillation frequency f₀ is dependent on the inductance value of the loop of electrical inductive material. Consequently the value of the oscillation frequency provides the data 230 indicative of the measured inductance. As an example for illustration purpose only an angular sensor 100 according to Fig. Ia may comprise a loop of electrical conductive material having a diameter of 6cm realized by one turn of copper wire with a diameter of 0.22mm glued on a substrate made of paper. With this loop an electrical oscillator coupled to said loop provided a frequency of 106OkHz when the angle φ 160 equalled 0 degrees and a frequency of HOOkHz when the angle φ 160 equalled 180 degrees.

The substrate to which the loop of electrical conductive material is attached is preferably of flexible material providing an advantage that the first substrate part 130 may be folded in a plurality of ways with respect to the second substrate part 110. An other advantage is that the angular sensor 100 may be more easily attached to a non-flat or bended surfaces that are coupled by a joint. For example for monitoring the movement of a patient's arm an angular sensor may be attached to his elbow. The substrate of the angular sensor may be for example a patch of cloth, the loop being woven in the cloth using electrical conductive fibres.

Fig. 7 shows an angle measurement system 350 comprising at least one angular sensor 100. Preferably said angle measurement system further comprises a base station 300 that is configured to receive the transmitted data 360, said transmitted data being dependent on the data 230 indicative of the measured inductance. Said base station comprises receiving means 310, 340 arranged for receiving the transmitted data 360 of at least one angular sensor 100. The receiving means may for example comprise an antenna 340 and a demodulator 310. The data 230 is transmitted with the help of a wireless link from the angular sensor 100 to the base station 300. The base station 300 is preferably arranged to receive data from multiple angular sensors. Therefore in a further embodiment of the base station 300 said base station further comprises filter means 320. The filter means are arranged for retrieving further data 330 indicative of the measured inductance from the received transmitted data 360 of a plurality of angular sensors 100. As an example each angular sensor 100 may comprise an electrical oscillator such as previously discussed, each oscillator being arranged to operate in its own frequency range not overlapping with the frequency ranges of the other oscillators, the value of the frequency in said range being indicative of the folding angle 160 measured by said angular sensor. The filter means 320 in said base station 300 may comprise at least one bandpass filter to obtain said further data 330 indicative of the measured inductance from all received transmitted data 360.

In a further embodiment of the angular sensor 100 the electromagnetic field generated by the loop of the angular sensor may be used to provide the transmitted data 360. In general the generated magnetic field of the loop does not cover a large range, and the field strength varies with the folding angle of the loop. However when the base station 300 is in a range of 1 meter from the angular sensor 100 the transmitted data 360 may be received and processed by the base station, and the measured angle may be retrieved. In this embodiment of the angular sensor 100 the wireless communication means 210 is further coupled to the looped wire 140, 150 and is arranged to transmit the data 230 indicative of the measured inductance using an electro-magnetic field generated by the loop 140, 150. In an embodiment of the base station 300 that is configured to operate with said angular sensor 100 the receiving means 310 may comprise a broadband receiver configured to receive a plurality of frequency ranges.

Alternatively, in a further embodiment the angular sensor 100 is coupled to the base station 300 by means of wires. This provides the advantage that the inductance measurement means 200 are inside the base station, such that the angular sensors 100 are simplified and comprise no active components. In this setup, for connecting the angular sensors to the base station, one has to use wires with very low inductivity, so that only the loop contributes to the measurement result. Fig. 8 shows a garment 400 comprising at least one angular sensor 100. With the angular sensor a joint angle may be measured. A patient that is performing rehabilitation exercises may wear such a garment. To allow free movement of the patient an angle measurement system 350 with a wireless coupling between the angular sensor 100 and the base station 300 is preferred. With the further data 330 obtained from the base station the body posture of the patient is determined. The further data may be transferred to a physiotherapist for an assessment.

The garment 400 with at least one angular sensor 100 may also be worn in daily life. A fall detector may monitor the inductance of each angular sensor. The fall detector is arranged to give an alarm when, after interpretation of the measured inductance of a plurality of angular sensors 100, an unnatural body posture is detected, or when an adverse body posture is kept for a long time.

Fig. 9 shows a band-aid or plaster 500 comprising an angular sensor 100. An advantage is that the plaster is easy to attach to for example a joint of a machine such as for example an industrial robot. Also the plaster can be applied to the skin of a person to be supervised when doing exercises.

Summarizing, the invention relates to an angular sensor 100 that comprises at least one loop 140,150 of electrical conductive material and is attached to a preferably flexible substrate. The substrate is foldable and an inductance of the loop 140,150 is dependent on a folding angle 160. The angular sensor 100 may be included in a garment 400 to facilitate the determination of a body posture, or in a plaster 500 to apply to the skin of a patient. Preferably the angular sensor transfers data indicative of the measured angle wireless to a base station 300. The base station is configured to receive the data of a plurality of angular sensors. The angular sensor 100 and the base station 300 are included in an angle measurement system 350 that may be used by a physiotherapist to supervise rehabilitation exercises.

Claims

CLAIMS:

1. An angular sensor (100) comprising at least one loop (140,150) of electrical conductive material being attached to a substrate, the substrate having a first substrate part (130) being foldable with respect to a second substrate part (110), a first part (140) of the loop being located at the first substrate part (130) and a second part (150) of the loop being located at the second substrate part (110), an inductance of the loop (140,150) being dependent on an angle (160) between the first and second substrate part.

2. An angular sensor (100) according to claim 1, the first part (140) of the loop comprising at least one further loop of electrical conductive material and the second part (150) of the loop comprising at least one other loop of electrical conductive material.

3. An angular sensor (100) comprising at least one loop (140) of electrical conductive material attached to a first substrate part (130) and at least one further loop (150) of electrical conductive material attached to a second substrate part (110), the second substrate part (110) being foldable with respect to the first substrate part, a mutual inductance of the at least one loop and the further loop being dependent on an angle (160) between the first and second substrate part.

4. An angular sensor (100) according to any one of claims 1-3 further comprising inductance measurement means (200) arranged for providing data (230) indicative of the measured inductance, the inductance measurement means being coupled to the loop (140, 150).

5. An angular sensor (100) according to claim 4 further comprising wireless communication means (210) arranged for transmitting data (230) indicative of the measured inductance, the communication means being coupled to the inductance measurement means (200).

6. An angular sensor (100) according to claim 4 or 5 wherein the inductance measurement means (200) comprises an oscillator having a frequency dependent on the inductance.

7. An angular sensor (100) according to claim 5 or claim 6 wherein the wireless communication means (210) is coupled to the looped wire (140, 150) and is arranged to transmit the data (230) indicative of the measured inductance using an electro-magnetic field generated by the looped wire (140, 150).

8. An angle measurement system (350) comprising an angular sensor (100) as defined in any one of claims 5-7.

9. An angle measurement system (350) according to claim 8 further comprising a base station (300), the base station (300) comprising receiving means (310, 340) arranged for receiving the transmitted data (360) of at least one angular sensor (100).

10. A garment (400) comprising at least one angular sensor (100) as defined in any one of claims 1-7.

11. A band-aid or plaster (500) comprising an angular sensor (100) as defined in any one of claims 1-7.