METHOD FOR MEASURING POSITION AND ANGLE

Abstract: Method for position measurement, whereby a magnetic field is generated in a measuring volume comprising one or several elongated elements of amorphous material, the magnetic properties of which being influenced by the magnetic field, is arranged in the measuring volume. The measuring volume is composed of several sub-volumes, and the extension of the sub-volumes in the desired measuring direction is chosen in such a way that the extension corresponds to the desired measuring resolution in the measuring directions. The change in magnetic or mechanical properties of the element caused by the magnetic flux intensity in the respective sub-volume along the longitudinal direction of the element is detected, the change being a measure of the position of the element.

Description: METHOD FOR MEASURING POSITION AND ANGLE Method and device for measuring position and angle with variable accuracy. When measuring the position a measuring body or an angular alignment of the measuring body in relation to a reference axis it is of advantage if the measuring body can move freely in a measuring volume, i.e. without bearing on a measuring path or the like. It would also be of advantage if the sensing of the measuring body could take place with¬ out contact. One object of the present invention is to achieve a method and a device which makes such a measurement pos- sible. Furthermore, according to a further development of the invention a procedure has been achieved which makes a dynamically adjustable accuracy of measurement possible in a given measurement volume. The measurement procedure according to the present invention is based on certain magnetic and mechanical pro¬ perties of element in the shape of bands, threads or strips of a material which is amorphously changed when the ele¬ ments are exposed to a magnetic field, what is called a bias field. For example the position/direction of the element is related to the magnetic field in the longi¬ tudinal or axial direction of the amorphous element, thereby making the mechanical resonance frequency of the element a measure of the position/direction of the element. The same procedure is adaptable for a measuring component comprising an amorphous element which is magnetically connected to an inductive element which in turn is a part of an electric resonance cirquit. When the magnetic field is changed, the magnetic properties of the amorphous elements are changed so that the inductance of the in- ductive element is changed. Thereby the resonance frequency of the electric resonance cirquite is also changed. Other materials than amorphous materials are also applicable according to the invention. The crucial property of the material is its characteristics, e.g. magnetic or elastical properties, are influenced by magnetic fields. The influence should be of such an extent that the change in properties can be measurable by remote detection. Examples are materials which are magnetoresistive, the electric conductivity of which are changed in dependence of the magnetic field, and magnetooptical, the light conduct- ing property of which are changed in dependence of applied magnetic field. For materials of the latter type that phenomonen which is called the Faraday-effect can be used, i.e. the plane of oscillation for polarized light is rotated, the deflexion angle being proportional to the magnetized field strength, or the phenomonen which is called the Kerrer-effect, whereby a similar effect of cer¬ tain materials is achieved by the influence of an electric field. The resonance frequency of an amorphous element ex- hibiting a comparatively great magneto-mecanical coupling is varied with the intensity of the magnetic flow along the main direction of the element by what is called the delta- E-effect. Thus, if this intensity of magnetic flow is changed as a function of the position/direction of the amorphous element the resonance frequency of the amorphous element will be a function of its position/direction. It is very advantageous to give the measuring information in form of a frequency value since such a value is very immune to noice. Furthermore, mixed information from several measure- ment transmitters operating on different frequency bands can be transmitted together on one information channel. In order to achieve an enhanced position of measure¬ ment procedures can be used where several amorphous elements are placed in a measuring body. In these instances it is also suitable to register difference and sum fre- quencies. By utilizing such differential measurement pro¬ cedures sources of errors can be eliminated, such as for example distorsion of the system caused by temperature, properties of the material, changes in the field, etc. It should be noted that the effective magnetic field along the axial direction of the amorphous element is not necessarily equal to the projection of the total field vector along the amorphous element. By the flux conductive property and geometry of the amorphous element this rela- tionship can deviate from a pure projection. However, the relationship can always be mapped and thereby still permit a base for position/angular measurement. The invention will now be further described with reference to the embodiments shown in the accompanying drawings, wherein Fig 1 schematically shows field lines of a magnetic field while practicizing a measuring procedure according to the invention. Fig 2 schematically shows field lines of a magnetic field while practicizing an alternative measuring procedure according to the invention. Fig 3 schematically shows field lines of a magnetic field while practicizing another alternative measuring procedure according to the invention, ig 4 schematically shows a practical embodiment of a measuring device according to the invention for measuring the position of a measuring body. ig 5 schematically shows an alternative practical embodiment of a measuring device according to the invention for measuring the position of a measuring body. ig 6 schematically shows a practical embodiment of a measuring device according to the invention for measuring the angular alignment of a measuring body. Fig 7 schematically shows an alternative practical embodiment of a measuring device according to the invention for measuring the angular alignment of a measuring body, Fig 8 schematically shows a further development of a measuring device according to the invention for measuring the position of a measuring body and Fig 9 schematically shows an embodiment of the invention for determining the position and orientation of a measuring body in three dimensions. Fig 1 schematically shows the function when measuring the position according to one embodiment of the invention. An element 10 of amorphous material is placed with its longitudinal direction parallel to the field lines of a magnetic field Φ which is generated in a measuring volume. The increasing density of field lines in Fig 1 indicates that a field gradient is present within the magnetic field. The field gradient is aligned perperdicular to the field direction. By placing the element 10 within a measuring body which is movable in the direction of the the field gradient the element 10 will be subjected to a magnetizing field strength H of different magnitude in dependence of the position of the element. As already has been described in the beginning of the description a change in strength of the magnetic field working in the longitudinal direction of the element 10 results in a change in the magnetic proper¬ ties of the element. These are detectable, either by the change of the mechanical resonance frequency of the element and thus the change of the magnetic field around the element or by the element being coupled to an inductive element which is a part of an electric resonance cirquit, the resonance frequency of which is changed when the magnetic properties of the element 10 is changed. In the embodiment according to Fig 2 a magnetic field has been generated with a field gradient directed leftwards in the figure. This is evident from the longer lines of force in the left part of the figure. Here the element 10 is movable parallel to the field gradient in the direction of the arrow A. Another embodiment with a magnetic bias field is shown in Fig 3. In this embodiment the magnetic field has a constant intensity along the measuring distance but the field direction is changed, thus exposing the element 10 in its longitudinal direction for magnetic fields of different magnitudes in dependence of its position. In this embodi¬ ment, according to Fig 3, the element moves horizontally in the direction of the arrow A. Fig 4 shows in a simplified form how a magnetic field according to Fig 1 can be achieved. A magnet 11, which can be a permanent magnet or an electromagnet, generates a magnetic field which is indicated by the curved field lines from the north pole to the south pole of the magnet. If the magnetized field strength along the direction of a motion of the element 10 is completely known the magnetic proper¬ ties of the element 10 are in every point along the direc¬ tion of the motion directly related to the position of the element. It is also possible by a calibration procedure to obtain an indication of the magnetic properties in every point, whereby this indication later on can be used re¬ versely for the determination of the position of the element. Fig 5 shows a simplified embodiment for obtaining a measurement according to Fig 4. A coil 12 with varying pitch ratio is arranged with its extension length in the direction of motion of the element 10. The element 10 is movable, either inside the coil or outside in a direction which is parallel to the center axis of the coil. As to the rest, the measuring procedure according to Fig 5 corresonds with the procedure described in Fig 4. Fig 6 shows schematically an embodiment for angular measurement according to the invention. A magnetic field Φ is generated by a magnet 11 which can be a permanent magnet or an electromagnet. The field lines from the magnetic field is substantially parallel in one plane and the element is arranged rotatable in this plane. The vital and detectable magnetic properties of the element 10 is thereby directly related to the angular alignment of the element 10 in comparision with a reference direction (REF) . Measure¬ ments according to this embodiment results in angular alignments within the interval 0-90°. By arranging two elements 10 of different lengths fixed with a certain angular displacement in relation to each other measurements within the interval 0-180° are pos¬ sible. Nor is it necessary that the field lines are quite parallel. If the field picture is known in that plane which the element, or elements, are moving, or if the calibration procedure described above is used, angular measurements can nevertheless be performed. Alternatively, the magnetic field can be rotated/thrown over between different known directions, thereby eliminating ambiguities in detection. A further embodiment for angular measurement utilizes three orthogonal, known magnetic fields. Thereby it is pos¬ sible to determine the direction of an amorphous element in three dimensions (azimut and elevation) . It is also possible by a calibration procedure to de¬ termine the relationship between the orientation of the amorphous element and its resonance frequency. If this is accomplished with an arbitrary magnetic field which varies with the rotation angle/angles a complete angular deter- mination is possible. A further alternative embodiment is as follows. When passing the resonance frequency of the amorphous element with an exciting signal frequency a marked phase shift takes place between the excited and detected (amorphous) signal. An alternative procedure for measuring position/angle can thus be to excite with a fixed frequency and instead measuring the phase level between excitation and detection when the position of the amorphous element is varied around that position/orientation in a chosen bias which gives a resonance that is equal to the chosen, fixed exciting frequency. Again, a possibility can be seen for a high per¬ formance measurement around an arbitrary chosen (with the combination of biased and fixed frequency) point along the measuring interval. A further embodiment for angular measurement is evi¬ dent from Fig 7. A coil 11 generates a magnetic field which is directed through two flow conduits formed as shanks 13, between which a magnetic field in that way is directed. The shanks 13 are flat, substantially parallel plates which are bent in one plane. The shanks are also somewhat tapered to¬ wards their free ends. An element 10 is pivotally arranged in the area of the central point of the radius after which the shanks are curved. The element 10 extends inbetween the shanks. The measuring coil 14 is arranged around the element 10 in that area of the element which is positioned between the shanks 13. A second measuring coil 15, however anti-phase winded, is arranged in series with the coil 14, the measuring coil being positioned outside the magnetic field between the shanks 13 during the total rotating move¬ ment of the element 10. By this embodiment different types of disturbances from external sources generating a magnetic field which otherwise would influence the angular measure¬ ment negatively are eliminated. In Fig 8 an embodiment of measurement according to the invention is shown, according to which the measurement accuracy can be adjusted dynamically over a measuring area or a measuring volume. An amorphous element has a maximal working area, within which its magnetic properties are changed in a known way in relation to the magnetizing field strenght H. The applicable measuring area is thus limited by a maximum and a minimum value of the magnetizing field strength H (H max and H m -j n , resptectively) . In a first stage of the measurement the distance between H max and H m _ n is utilized over the total measuring area, which is marked by the line I in Fig 8. The magnetizing field strength H can be achieved by leading an electric current with con¬ tinuously increasing strength into the coil system 15 which is arranged at the measuring distance. In the embodiment shown in Fig 8 the current I_ is greater than the current Ig. When moving the element 10 in the direction of the arrow A the position of the element is detected as a function of the actual magnetic properties of the element, for example its resonance frequency. In order to increase the accuracy of measurement in a shorter interval of the measuring distance the current is increased through some of the coils present in the coil system 15 so as to attain a magnetizing field strength H according to the curve II. The total working area of the element 10 will then lie within a very narrow interval of length and a very accurate measurement of the position is thus possible. The magnetizing field strength H with its desired distribution can also be achieved in other ways. Several coils arranged together in different geometries can for example be made to generate the field strength by driving currents of dif¬ ferent magnitudes through the different coils. In most cases the embodiments described above refer to a one- or two-dimensional measurement, but it is also quite possible to achieve the measurement in three dimen- sions by combining several coil systems. If a measuring object is provided with two elements of different magnetic properties, e.g. of different length, the elements being so arranged that they are angularly displaced from each other or parallelly displaced in their transverse direction, the position of the object as well as its orientation can be determined. This is evident from Fig 9 which shows three orthogonally arranged coil systems. A measuring body 16 is arranged in that volume which on three sides is delimited by a coil system. Two elements 10 and 10' are arranged on the measuring body, the elements being rotated with a cer¬ tain angle in relation to each other. Each coil system com¬ prises a coil 17 for generating a magnetic bias field, a coil 18 for generating an exciting signal, and a coil 19 for detection of the signal from the elements 10, 10'. In an alternative embodiment, according to which the amorphous element is a part of an electric resonance circuit, the coil 19 is replaced by an antenna. One alternative procedure for increasing the resolu- tion within a small interval of length is based on the resonance frequency of an element 10 undergoing a drastic phase shift in relation to an exciting signal. In this pro¬ cedure the signal in form of a sweep frequency is generated to excite the element 10. When the sweep frequency passes the resonance frequency of the element the latter is brought into self-oscillation. This corresponds to the normal measuring procedure. Then the exciting signal is locked at the resonance frequency and the phase difference between exciting signal the respond signal generated from the element is detected instead. Since the phase difference varies very strongly around the point of resonance the re¬ solution of detection thus becomes very high. An amorphous band can be brought to self-oscillation by a magnetic field of a certain signal form and/or frequence being generated in an exciting coil. The signal form is suitably a short pulse but signals of more lasting nature can also be used. The exciting coil can be arranged at some distance from the band and have a working area which covers the total measuring volume. It is also pos- sible to arrange the exciting coil directly adjacent to the band and in such a way that the exciting coil accompanies the movement of the band in the measuring volume. In order to detect and register the changed proper¬ ties of an amorphous band in dependence of an external magnetic bias field, what is called a bias-field, e.g. the resonance frequency of the band, it is suitable to arrange a detection coil or a pickup-coil. As for the exciting coil the detection coil can be arranged at a distance from the band and have a working area which covers the total measuring volume. It is also possible to directly arrange the detection coil adjacent to the band and in such a way that the exciting coil accompanies the movement of the band in the measuring volume. Of course, combinations of the coil embodiments mentioned above are also possible. Since the measuring procedure according to the inven¬ tion is based on the position of an amorphous element in relation to an external magnetic field it is also possible to have the element fixedly arranged and the magnetic field being movable, rotatable or displaceable.

Claims: CLAIMS 1. Method for position measurement, whereby a magnetic field is generated in a measuring volume comprising one or several elongated elements of amorphous material, the magnetic properties of which is influenced by the magnetic field, which is arranged in the measuring volume, c h a r a c t e r i z e d in that the measuring volume is composed of several sub- volumes, in that the extension of the sub-volumes in the desired measuring directions is chosen in such a way that the extension correponds to the desired measuring resolution in the measuring directions, and in that the change in magnetic or mechanical properties of the element caused by the magnetic flux intensity in the respective sub-volume along longitudal direction of the element is detected, the change being a measure of the position of the element. 2. Method as in claim 1, c h a r a c t e r i z e d in that the magnetic field is given a known strength and direction in the longitudal direction of the band in each sub-volume. 3. Method as in claim 1, c h a r a c t e r i z e d in that the elements are brought to self-oscillation mechanically, and in that the resonance frequency av the elements are de¬ tected as a position-determined measuring signal. 4. Method as in claim 1, c h a r a c t e r i z e d in that the element is magnetically connected to an in¬ ductive element in an electric resonance cirquit. 5. Method as in claim 1, c h a r a c t e r i z e d in that the magnetic field is given a gradient in the measuring volume. 6. Method as in claim 5, c h a r a c t e r i z e d in that the gradient is brought to adopt a known value in the measuring directions. 7. Method as in claim 5, c h a r a c t e r i z e d in that the magnetic field is brought to adopt a greater steepness concerning gradient or regression co- efficient in chosen parts of the measuring volume. 8. Method as in claim 5, c h a r a c t e r i z e d in that the magnetic field is generated in a uniform field direction in the measuring volume and with the field gradient perperdicular to the field direction, and in that the amorphous element is arranged with its longi¬ tudinal direction parallel to the field direction of the magnetic field, the measuring direction being parallel to the field gradient. 9. Method as in claim 5, c h a r a c t e r i z e d in that the magnetic field is generated with a uniform field direction and with a field gradient paral¬ lel to the field direction, and in that the amorphous element is arranged with its longi¬ tudinal direction parallel to the field direction of the magnetic field, the measuring direction being parallel to the field gradient. 10. Method as in claim 5, c h a r a c t e r i z e d in that the position measurement is accomplished in two steps, the first step being accomplished with a gradient adapted to the total length of the total measuring area and the magnetic working area of the element, and the second step being ac- complished with a gradient adapted to a sub- distance of the length of the measuring area and the magnetic working area of the element. 11. Method as in claim 3, c h a r a c t e r i z e d in that the amorphous element is brought to self-oscilla- tion by an exciting signal of variable frequency, a certain phase shift arises between the exciting signal and a signal transmitted by the amorphous element, in that the exciting signal is locked at the resonance frequency, and in that the phase shift between the exciting signal and the signal transmitted by the amorphous element is detected as a signal dependent on the position of the amorphous element. 12. Method for position measurement, whereby a magnetic field is generated in a measuring volume and a measuring body comprising at least one elongated element of amorphous material which is arranged in the measuring volume, c h a r a c -t e r i z e d in that the magnetic field is given a known field picture in one plane, and in that the element is rotated in such a way that its longitudal direction is rotated in said plane. 13. Method as in claim 12, c h a r a c t e r i z e d in that two elements are arranged angular displaced in relation to each other, and in that the elements are rotated together in said plane.

Inventors: PERSSON LEIF ARNOLD, TYREN CARL, PERSSON, LEIF, ARNOLD, TYREN, CARL
Applicants: RSO CORP, RSO CORPORATION N.V.
Application year: 1993
Main classification: G01V3
IPC codes: G01B7, G01D5, G01V3, G06K7, G08B13