MAGNETIC DETECTOR

Abstract: A magnetic detector (21) employs a magneto-resistive element (12, 13, 14) and is intended to detect in a non-contact manner the salients and slots of a member of magnetic ma­ terial which is the object to be detected. The magneto-resis­ tive element (12, 13, 14) has a non-linear magneto-resistive characteristic and is subjected to a constant DC magnetic field thereby avoiding the non-linear region of such DC mag­ netic field to permit the use of such elements in the region of good linearity. A DC magnetic field is obtained by means of a simple arrangement wherein the magneto-resistive ele­ ment (12, 13, 14) is arranged diagonally in the magnetic field between a permanent magnet (16) and the salients of the magnetic member. Furthermore, two magneto-resistive ele­ ments (12, 13, 14) exhibiting phases delayed by π/2 with respect to each other are used in the form of half-bridge so as to improve stability, waveform distorsion and the like of the detected signal with respect to temperature.

Description: The present invention relates to a detector which employs a ferro-magnetic thin film resistor element (hereinafter called "magneto-resistive element") having magnetic anisotropic effect of a linearly moving object or the rotating angle of a rotating object. (A) and (B) of Fig. 1 are a plan view and a front elevation showing an example of a magneto-resistive element. In Fig. 1, the magneto-resistive element 2 and the terminals 3, 4 for external connections are formed on the surface of the substrate 1. The resistance of the magneto-resistive element 2 changes according to the change of the intensity of the magnetic field in the direction of ±X shown in Fig. 1 whereas said resistance hardly changes in response to the change of the intensity of the magnetic field in other directions, and has what is called the magnetic anisotropic effect. Fig. 2 shows a characteristic curve of said magneto-resistive representing the change in the resistance of said magneto-resistive element with respect to the change of said intensity of the magnetic field in the direction of ±X. In Fig. 2, a, c, and e are the regions where the change of the resistance with respect to the intensity of the magnetic field is non-linear and b and d are the regions of relatively good linearity in connection with the change of the resistance with respect to the intensity of the magnetic field. The detector which utilizes the characteristic of the magneto-resistive element explained in Fig. 1 and Fig. 2 will hereinafter be described. Fig. 3 shows an example of a conventional detector which uses a magneto-resistive element, (A) in Fig. 3 a plan view, and (B) a sectional view of the line A-A of (A). In (A) and (B) in Fig. 3, the same parts shown in Fig. 1 are given the same numbers. Now, this conventional detector detects relative positions of both of a movable element 8 and a stator 9 as the movable element 8 moves linearly along the stator 9, and the movable element 8 is consisted of the substrate which forms the magneto-resistive element 2 and terminals 3, 4 on the surface thereof and a permanent magnet 7 which functions to supply the bias magnetic field. On the other hand, the stator 9 includes on the plane opposite to the movable element 8 a large number of teeth like salients and slots of magnetic material (hereinafter called the magnetic teeth). The opposing planes of the movable element 8 and the stator 9 are not illustrated, however, both planes are held by the travelling support system such as bearings so that a fixed clearance is being maintained for parallel movement. As shown in (A) in Fig. 3, it is generally known that when the magneto-resistive element 2 is connected through the terminals 3, 4 to an external constant-voltage regulated power supply 10, a fixed resistor 5, a grounding 11, and an output terminal 6 and the movable element 8 moves along the stator 9 at a constant speed, an output like sinewave of a half the pitch of the pitch of the magnetic teeth of the stator 9 is obtained from the output terminal 6. This is because that the magnetic field generated by the permanent magnet 7 is affected by the shapes of the magnetic teeth of the stator 9 to be bent cyclically thereby generating the component of the magneto-sensitive direction (±X direction) with respect to the magneto-resistive element 2 of the movable element 8 and that as explained of Fig. 2, the resistance of the magneto-resistive element 2 changes according to the affected intensity of the magnetic field there is a cyclic output like sinewave generated at the output terminal 6. This condition is further described in detail using Fig. 4, but the same parts shown in Fig. 3 are given the same numbers while the redundant descriptions are omitted. In Fig. 4, 101, 102, 103, 104, and 105 represent typical lines of magnetic force generated by the permanent magnet 7. In Fig. 4, the magneto-resistive element 2 is at a position where the line of magnetic force 103 passes through and since the line of magnetic force 103 passes through the magneto-resistive element 2 vertically there will be no component in the direction of ±X, and said line of magnetic force 103 is at the zero point of the magnetic field shown in the characteristic curve of Fig. 2 indicating that the resistance of the magneto-resistive element 2 is maximum. The maximum resistance is also indicated when the magneto-resistive element 2 is at positions of the lines of magnetic force 101 and 105 as the movable element 8 is moved. Now, if we consider that the movable element 8 has moved and the magneto-resistive element 2 come to the position of the line of magnetic force 102, the line of magnetic force 102 will have passed through the magneto-resistive element 2 diagonally. By dividing this line of magnetic force 102 into the orthogonal components, a component which vertically passes through the magneto-resistive element 2 and a component in the -X direction are obtained and the resistance of the magneto-sensitive part varies with the intensity of the magnetic field by the magnetic field of said component in the -X direction. Likewise, the magnetic field of the +X direction is generated of the line of magnetic force 104. As shown in Fig. 2, since the characteristic of the magneto-resistive element 2 shows a symmetrical shape centering upon the zero point of the magnetic field, when the movable element 8 moves at a constant speed and the magneto-resistive element 2 moves from the position of the line of magnetic force 101 to that of the line of magnetic force 105 (for one cycle of the magnetic teeth), the change of the resistance at that time will be symmetrical from 101 to 103 and from 103 to 105 with respect to the position of the line of magnetic force 103 as the center. In other words, an output of half the pitch of the magnetic teeth can be obtained. However, in a detector of such construction as above, since the characteristic of the magneto-resistive element shown in Fig. 2 is used in both the plus and minus directions with respect to the zero point of the magnetic field as a center, such detector had a defect in that the output signal was considerably distorted by the effect of the non-linear region c. Especially, in case a detector of highly accurate and fine resolution is necessary, making finer pitch of the magnetic teeth of the stator 9 can improve the condition to a certain extent on one hand but the signal detection becomes difficult on the other hand. Therefore, fine resolution of signals is also achieved in many cases by generally employing such method as an electrical interpolation. In such a case, it is desirable to have the output wave-form similar to the sinewave from the standpoint of the signal processing but it was difficult to materialize fine resolution by conventional detector because of poor linearity caused by said distortion of the output signal. Since the defect of the conventional detector as described above is caused by the use of the non-linear region c of the characteristic of the magneto-resistive element shown in Fig. 2, it is apparent that the region b or d of relatively good linearity of the characteristic shown in Fig. 2 should be used in order to remove this defect. To do so, it is necessary to always apply a constant DC magnetic field (the center of the region b or the center of the region d in Fig. 2) having a +X or -X direction to the magneto-resistive element 2 in Fig. 1 though it was difficult to supply such DC magnetic field (hereafter called as the offset magnetic field) stably. It is a primary object of the present invention to detect the magnetic teeth which is the object to be detected accurately by the non-contacting means using the magneto-resistive element, and more particularly, to provide a magnetic detector of less distorted detected signals by supplying an appropriate offset magnetic field to the magneto-resistive element and by using the magneto-resistive element in a region of good linearity with respect to the magneto-resistive characteristic. The present invention provides a magnetic detector for detecting relative movement in a predetermined direction (x) between a member having teeth-like salients and slots of magnetic material, and a detecting head which is arranged to be movable in said direction (x) at a constant distance from the surface of said member and which comprises a ferromagnetic thin film resistor element having magnetic anisotropy and a magneto-sensitive direction and a permanent magnet to supply a magnetic field thereto; said ferro-magnetic thin film resistor element being arranged so that its magneto-sensitive direction corresponds to the direction (x) of said relative motion, in order to respond to a change of the magnetic field in said direction occurring in the magnetic field between said permanent magnet and said teeth-like salientS and slots, characterized in that the thin film surface is arranged to be inclined at a constant angle to the surface of the member on which the teeth-like salients and slots are formed, so that an offset magnetic field Hx in the direction (x) of said relative motion is generated in the ferro-magnetic thin film resistor elements. Furthermore, the magneto-resistive element also uses the magnetic field and is not therefore arranged in parallel with the magnetic teeth but us inclined at a certain angle. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 (A) and (B) are a plan view and a front elevation showing an example of the magneto-resistive element used in the conventional embodiment and the embodiment according to the present invention; Fig. 2 is a characteristic curve of the magneto-resistive element shown in Fig. 1; Figs. 3 (A) and (B) are a partial plan view and a partial cross-sectional view showing an example of a conventional magnetic detector using the magneto-resistive element; Fig. 4 is an enlarged partial cross-sectional view of the conventional magnetic detector shown in Fig. 3; Fig. 5 is an external view showing an example of the mechanism of the magnetic detector according to the present invention; Figs. 6 (A) and (B) are a partial plan view and a partial cross-sectional view showing an embodiment of the magnetic detector according to the present invention; Figs. 7 and 8 are enlarged partial cross-sectional views showing an embodiment shown in Fig. 6; Figs. 9 (A) and (B) and Figs. 10 (A) and (B) are partial plan views and partial cross-sectional views showing other embodiment respectively according to the present invention; Figs. 11 (A) and (B) are a plan view and a front elevation showing an embodiment of other magneto-resistive element used for the magnetic detector according to the present invention; Figs. 12 (A) and (B) are a partial plan view and a partial cross-sectional view showing an embodiment of the magneto-resistive element of the present invention using the magneto-resistive element shown in Fig. 11; Fig. 13 is an equivalent circuit diagram showing electrical connections of the magneto-resistive element used in Fig. 12; Figs. 14 (A), (B), and (C) are diagrams showing fundamentals of the magnetic detector of the present invention; Fig. 15 is a diagram showing fundamentals of the magnetic detector of the present invention; and Figs. 16 through 22 are plan views showing embodiments of the magneto-resistive element used respectively in the magnetic detector of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will now be described with respect to drawings. Fig. 5 is an external view of the magnetic detector which uses the magneto-resistive element according to an embodiment of the present invention. In this Fig. 5, the movable element 215 moves linearly along the stator 20. The movable element 215 is comprised of a magneto-resistive element, a sensor housing 212 which incorporates therein a permanent magnet and the like, a fixture means 210 and 211 which hold therebetween said sensor housing 212, screws 213 which join the sensor housing and the fixture means, and bearings 216 which support the movable element 215 to permit it to move along the stator 20 including bearings 217 which hold a constant distance between the MR sensor and the stator while the stator 20 has a large number of magnetic teeth formed at constant pitches on the surface thereof. Fig. 6 shows a partial cross-sectional view of the magnetic detector which uses the magneto-resistive element according to an embodiment of the present invention, and (A) is a plan view and (B) a cross-sectional view of the line B-B of (A). This detector detects relative positions of the movable element 21 and the stator 20 while said movable element moves linearly along said stator, and the movable element 21 is comprised of a substrate 12 with the magneto-sensitive part 13 consisting of the magneto-resistive element and terminals 14, 15 formed on the surface thereof and a permanent magnet 16 to supply the bias magnetic field. On the other hand, the stator 20 has magnetic teeth of constant pitch formed on the plane opposing the movable element 21. Furthermore, the movable element 21 and the stator 20 are arranged as shown in Fig. 5, and more particularly, the substrate 12 and the stator 20 are inclined at an angle of α° while the permanent magnet 16 and the stator 20 are arranged in parallel. In Fig. 6, the travelling support system to movably hold the movable element 21 along the stator 20 is not shown for the convenience of description. Said magneto-sensitive part 13 shall have been connected, as shown in Fig. 6 (A), through the terminals 14, 15 to the constant voltage power source 18, the fixed resistor 17, the ground 22, and the output terminal 19. Operation of the detector according to embodiments of the present invention composed as above will hereinafter be described. In Fig. 6, when the movable element 21 travels along the stator 20 in the direction of ±X, the line of magnetic force moving from the permanent magnet 16 to the stator 20 (in -Z direction) changes its direction depending on the shapes of salients and slots of the magnetic teeth as in the case of the conventional embodiment shown in Fig. 4. Such condition is shown in Fig. 7, of which 106, 107, 108, 109, and 110 represent typical lines of magnetic force generated from the permanent magnet 16. Fig. 8 shows a partial cross-sectional view wherein the magneto-sensitive part 13 is at a position where the line of magnetic force 106 passes through. In this Figure, since the bias magnetic field ₀ passes the magneto-sensitive part 13 diagonally, offset magnetic field x is given in the magneto-sensitive direction (in +X direction) of the magneto-sensitive part 13, and the strength of such offset magnetic field x is expressed by the following equation. By this process, the characteristic of the magneto-resistive element shown in Fig. 2 which is used in both the plus and minus directions with respect to the zero point of the magnetic field as a center can now be used in one direction, i.e., either the plus direction or the minus direction centering on the operating point A. The same applies to the case when the magneto-sensitive part 13 is at a position where the lines of magnetic force 108 or 110 pass through. This offset magnetic field x permits to use the regions b or d of relatively good linearity by avoiding the region c of non-linearity among the characteristic of the magneto-resistive element shown in Fig. 2, thereby the distortion of the output wave-form which has been conventionally problematic is improved considerably and the detector of high accuracy is materialized. Other embodiment of the present invention will hereafter be described in reference to the drawings. Fig. 9 is a partial cross-sectional view of the detector using the magneto-resistive element according to other embodiments of the present invention, (A) a plan view, and (B) a cross-sectional view of the line C-C of (A). The same components of the first embodiment of this invention shown in Fig. 6 are used, the same numbers are provided with those components in Fig. 9 corresponding to those of the first embodiment, and therefore the description thereof is omitted. This detector detects relative positions of the movable element 22 and the stator 20 as said movable element travels linearly along said stator and is different from the first embodiment of this invention shown in Fig. 5 in that the substrate 12 and the permanent magnet 16 are securely jointed to make an integral piece and inclined to the stator 20 at α°. In the detector of this embodiment constructed as above, the magneto-sensitive part 13 is given the offset magnetic field by the permanent magnet 16 as in the case of the first embodiment shown in Fig. 6. It is therefore possible to use the magneto-resistive element in the regions b or d of relatively good linearity of the characteristic of the magneto-resistive element shown in Fig. 2, and it was confirmed that the signal like sinewave of less distortion can be obtained from the output terminal 19. Another embodiment of the present invention will hereafter be described in reference to the drawings. Fig. 10 shows a primary part of the magnetic detector using the magneto-resistive element according to other embodiment of this invention, Fig. (A) is a plan view, and (B) a front elevation. The same components as those of the embodiment of this invention shown in Fig. 6 are provided with the same numbers and the description thereof is omitted here. This magnetic detector is intended to detect the rotational position of the rotating gear 24 and comprised of the gear 24 made from magnetic material and the sensor block 23 consisting of the substrate 12 and the permanent magnet 16. The sensor block 23 is arranged, as shown in Fig. 10, at an angle of α° with respect to the side of the gear 24 so as to detect the rotating position of the gear 24 on the side of the teeth thereof. In such a case, the magneto-resistive element changes its resistance according to the intensity of the magnetic field in the direction of ±X shown by an arrow in the Figure. In the magnetic detector of this embodiment as constructed above, the operation and fundamentals are the same as those of the first embodiment of this invention shown in Fig. 6 and the only different is that the subject of detection is changed from the linear motion to rotational motion. The offset magnetic field is supplied to the magneto-sensitive part 13 by also inclining the sensor block at an angle of α° with respect to salients and slots of the teeth of the gear 24 as shown in Fig. 10. (A) so as to use the region of relatively good linearity among the characteristic of the magneto-resistive element shown in Fig. 2 thereby obtaining consequently an output like sinewave which has less distortion. Fig. 11 is illustrative of the appearance of other magneto-resistive element used for other magnetic detector of the present invention, Fig. 11 (A) is a plan view, and Fig. 11 (B) is a front elevation. In Fig. 11, the magneto-resistive elements 27, 28 and the terminals 29, 30, 31 are formed on the surface of the substrate 26. Assuming that the pitch of salients and slots of the object to be detected (magnetic teeth in this case) is P, the magneto-resistive elements 27, 28 are arranged in parallel at a distance of P/2. Fig. 12 shows an embodiment of the magnetic detector of the present invention, Fig. 12 (A) is a plan view, and (B) is a cross-sectional view of the line F-F of (A). The magneto-resistive element shown in Fig. 11 is used in this embodiment. The purpose of this detector is to detect the relative positions of the movable element 35 and the stator 20 as the former travels linearly along the latter. The movable element 35 is comprised of the magneto-resistive elements 27, 28 and the terminals 29, 30, 31 which form the substrate 26 described in Fig. 11 and the permanent magnet 16 for supplying the bias magnetic field to the magneto-resistive elements 27, 28. On the other hand, the stator 20 has the magnetic teeth with the pitch P for its salients and slots formed on the plane opposing the movable element 35 thereof. Furthermore, the movable element 35 and the stator 20 are arranged as shown in Fig. 12, and more particularly, the substrate 26 is inclined at an angle of α° with respect to the stator 20 while the permanent magnet 16 is arranged in parallel with the stator 20. As shown in Fig. 12 (A), said magneto-resistive elements 27, 28 shall have been connected through the terminals 29, 30, 31 to the constant current regulated power supplies 32, 33 and the output terminal 34 in terms of what is called the half-bridge and the constant-current regulated power supply in the case of this embodiment shall be +E volt and -E volt respectively. To avoid the complication of the drawings, the travelling support system to hold the movable element 35 movably along the stator 20 is not shown in the drawing. Operation of the detector of this embodiment as constructed above will hereafter be described. In Fig. 11 and Fig. 12, both of the magneto-resistive elements 27 and the magneto-resistive element 28 are given almost equal offset magnetic field x , as in the case of the embodiment of this invention shown in Fig. 6, by inclining them at an angle of α° with respect to the magnetic teeth, and have the same characteristic as said characteristic of the magneto-resistive element shown in Fig. 2 and the resistance varies centering upon the operating point A according to the external magnetic field. However, as shown in Fig. 12 (A), since the magneto-resistive element 27 and the magneto-resistive element 28 are arranged by deviating their phases by P/2 with respect to the pitch P of the magnetic teeth of the stator, each magneto-resistive element will be given the signal magnetic field which is deviated of its phase by 180°. Fig. 13 is an equivalent circuit diagram to clarify the electrical connections of the embodiment shown in Fig. 12 (A) and each component corresponding to that of Fig. 12 (A) is provided with the same number as that of Fig. 12 (A), and the description thereof is therefore omitted. In Fig. 13, assuming that the resistance of the magneto- resistive element 27 is Q and that of the magneto-resistive element 28 is R, the output signal Es generated at the output terminal 34 is expressed by the following equation. Es = E·(Q-R)/(R+Q) (2) Said resistance Q and R are decomposed into the resistance Q1 and R1 of the operating points determined by the magnitude of the offset magnetic field x and the varying resistance Q(Hs) and R(Hs) which change according to the signal magnetic field respectively. Since equal offset magnetic fields x are given to the magneto-resistive element 27 and the magneto-resistive element 28 respectively, Q1 and R1 are equal. Since signal magnetic fields respectively deviated by 180° are given to the magneto-resistive element 27 and the magneto-resistive element 28 as well, the relation between the varying resistance Q(Hs) and R(Hs) will almost satisfy the following equation. Q(Hs) = -R (Hs) (3) Substituting these contents into the equation (2) will give the following. Es = E·2Q(Hs)/2Q1 (4) Since E and Q1 are constant, said equation (4) means that the output signal Es is proportional to the varying resistance Q(Hs) of the resistance of the magneto-resistive element 27. Therefore, as shown in Fig. 12, if the magneto-resistive elements 27, 28 are used in regions of relatively good linearity by tilting them at an angle of α° with respect to the magnetic teeth of the stator 20, good output signal which has less distortion in proportion to the given signal magnetic field can be obtained. Since the magneto-resistive element 27 and the magneto-resistive element 28 are arranged on the same substrate at close distance, ambient environment are identical and coefficient of temperature of uniform resistance is available. For this reason, if the connection is made as shown in Fig. 13 and the ambient temperature rises causing the resistance of the magneto-resistive element 27 to change, the resistance of the magneto-resistive element 28 also changes to approximately the same extent, and consequently there is little temperature drift in the output signal of the output terminal 34. Figs. 14 (A), (B), (C) are conceptual drawings representing the relation of the magneto-resistive element 27 and the magneto-resistive element 28. The magneto-resistive element 27 and the magneto-resistive element 28 have uniform magneto-resistive character and their phases are deviated by 180° so that the signal magnetic fields of equal amplitude are given. Fig. 14 (A) illustrates such relation for easy and intuitive understanding though not accurate. As is apparent from said equation (4), since the output signal Es is proportional to the varying resistance, the characteristic of magnetic field-resistance of the magneto-resistive element will hereafter be considered about the operating point. In Fig. 14 (A), the resistance of the magneto-resistive element 27 and the magneto-resistive element 28 changing to the magnetic field are named as Q and R respectively in agreement with the description of Fig. 13. In this instance, the same signal magnetic fields are given to the magneto-resistive elements 27 and 28 for convenience, and the resistance R of the magneto-resistive element 28 is turned over to right and left symmetrically with respect to the vertical axis passing through the operating point A. The horizontal axis indicates the strength of the signal magnetic field and the vertical axis indicates the variation of the resistance of the magneto-resistive elements 27 and 28 with respect to the operating point A as the original point. The relation between these vertical axis and horizontal axis is regarded as the same regarding Figs. 14 (B) and (C). It is now understood from said equation (2) that the output signal Es is proportional to (Q-R), and Figs. (B) and (C) are diagrams showing such relation. Since (Q-R) of said equation (2) can be rewritten as {Q+(-R)}, the resistance R of the magneto-resistive element 28 in Fig. 14 (A) is made as -R by turning over the resistance vertically and symmetrically with respect to the horizontal axis passing through the operating point. Therefore, in Fig. 14 (B), addition of the resistance Q of the magneto-resistive element 27 and the resistance -R of the magneto-resistive element 28 gives said (Q-R). Fig. 14 (C) shows the result of the addition of Q and -R of Fig. 14 (B). If a signal magnetic field in the range of d of Fig. 14 (C) is given, the corresponding resistance changes into the one with good linearity as shown in the Figure. So far, appropriate offset magnetic field x is given to the magneto-resistive element and the case wherein the magneto-resistive element is used in a region of relatively good linearity among the magnetic field-resistance characteristic of the magneto-resistive element is described. However, we have noted some problems in actually giving the offset magnetic field of suitable magnitude to the magneto-resistive element. Firstly, not-uniform magnetization of the permanent magnet which gives the magnetic field to the magneto-resistive element is one of the problems. When the intensity of the magnetic field generated by the permanent magnet is changed, magnitude of said offset magnetic field x is changed accordingly. Secondly, though the offset magnetic field is obtained by tilting the magneto-resistive element at an angle of α° with respect to the magnetic teeth of the stator, it is extremely difficult to accurately establish the angle of α° and therefore the offset magnetic field x of suitable magnitude could not be obtained stably. As the result of this, the signal magnetic field which swings centering the offset magnetic field x will include the non-linear region among the magneto-resistive characteristic of the magneto-resistive element. Fig. 15 is illustrative of such condition. Fig. 15 is a conceptual drawing showing the relation of the magneto-resistive element 27 and the magneto-resistive element 28 when the offset magnetic field x is changed due to the reason of above and the operating point deviated from the point A in Fig. 14 (the center of the region of relatively good linearity) and moved to the point B. In Fig. 15, since the output signal Es is proportional to {Q+(-R)} as in the case of Fig. 14, the linearity of {Q+(-R)} is required. As compared, however, with the case wherein the magneto-resistive element 27 is used as 1 element, the non-linear region of the magneto-resistive element 3 is compensated in the region of good linearity of the magneto-resistive element 28 while the non-linear region of the magneto-resistive element 28 is compensated in the region of good linearity of the magneto-resistive element 27. Therefore, the region of relatively good linearity will expand as shown in the Figure. According to such conditions, it has become possible to hold the distortion of the output signal smaller than the case wherein the magneto-resistive element is used as 1 element should the magnitude of the offset magnetic field x to be given vary to some extent. Other embodiment of the present invention will hereafter be described in reference to the drawings. Fig. 16 through Fig. 22 are plan views showing embodiments of the magneto-resistive elements which can be used for the magnetic detector of the present invention. Since each magneto-resistive element can be considered to be replaced by the magneto-resistive elements 27 and 28 which are used in the embodiment of the magnetic detector shown in Fig. 12, components such as the permanent magnet and stator will hereafter be omitted from description but the description will be limited to the magneto-resistive element only. Fig. 16 shows an embodiment of the magneto-resistive element used in the magnetic detector of the present invention, on the surface of the substrate 36 are formed the magneto-resistive elements 37 and 38 and terminals 39, 40, 41 and more particularly, the terminals 39, 40 are connected to the constant-current regulated power supplies 32, 33 to thereby obtain the output signal from the output terminal 42. The magneto-resistive elements 37 and 38 are arranged at spaces of 3/2·P with respect to the pitch P of the magnetic teeth and one end of each element is connected electrically by means of the terminal 41. Furthermore, as shown in Fig. 16, each of the magneto-resistive elements 37, 38 are turned down within the same plane (on the surface of the substrate 36 in this case) at a constant space W whereas said constant space W is preferred to be sufficiently smaller with respect to the pitch P of the magnetic teeth. Since the operating principle of the magneto-resistive element composed as above is basically the same as that of the embodiment shown in Fig. 12, detailed description will be omitted. In the case of the embodiment of the present invention shown in Fig. 16, however, it is different in that the magneto-resistive element is used by turning it down at a constant space W. Since the constant space W is very small as described above, it is apparent that almost the same result as an example of Fig. 12 wherein the magneto-resistive element without the turn is arranged can be actually obtained at the center line of the turn. In addition, the embodiment of the present invention has an advantage wherein the detection sensitivity can be increased by doubling the resistance of the magneto-resistive element according to the shape of the turn. Fig. 17 shows an embodiment of the magneto-resistive element used in the detector of the present invention, on the surface of the substrate 43 are formed the magneto-resistive elements 44, 45, 46, 47, 48, 49, terminals 50, 51, 52, and the connectors 54, 55, 56 to connect each magneto-resistive elements electrically. All of these components are connected electrically as shown in the Figure, and more specifically, the terminals 50, 51 are connected to the constant-current regulated power supplies 32 and 33 while the terminal 52 is connected to the output terminal 53. The magneto-resistive elements 44, 45, 46 are arranged respectively at spaces P to compose the first group of elements and the magneto-resistive elements 47, 48, 49 are also arranged at spaces P to compose the second group of elements. Each element of the first group of elements and each element of the second group of elements are apart from each other by the space which satisfies (n+1/2)·P (n is an integer). In the magneto-resistive element composed as above, the first group of elements and the second group of elements respectively correspond to the magneto resistive element 27 and the magneto-resistive element 28 of the embodiment shown in Fig. 12. Because that the magneto-resistive elements are spaced at the pitch P means that they are delayed by 360° in terms of the phase angle, that is to say, there is no delay in the phase angle. For this reason, the same effect of Fig. 12 can also be obtained in this embodiment. In addition, since this embodiment has an advantage to triple the sensitivity by using three magneto-resistive elements of the same phase in series and each of the three magneto-resistive element connected in series detects different magnetic teeth simultaneously and averages the result of detection, it is advantageous to reduce the effect caused by breakage and the like of the magnetic teeth which is an object to be detected as compared with a case wherein the magnetic teeth are detected by the magneto-resistive element of one element. Fig. 18 shows an embodiment of the magneto-resistive element used in the detector of the present invention, on the surface of the substrate 58 are formed the magneto-resistive elements 59, 60, 61, 62 and the terminals 63, 64, 65, 66, 67, 68, 69, 70, and the magneto-resistive elements and the terminal 18 are electrically connected as shown in Fig. 18. More particularly, the terminals 63, 64, 65, 66 are connected to the constant-current regulated power supplies 32 and 33 and the pairs of magneto-resistive elements 59 and 61 (or 60 and 62) are arranged separately at 3/2·P spaces while the pairs of magneto-resistive elements 59 and 60 (or 61 and 62) are arranged separately at 1/4·P spaces respectively with respect to the pitch P of the magnetic teeth to be detected. Detailed description of the operating principle of the magneto-resistive element composed as above is omitted since it is basically the same as that of the embodiment shown in Fig. 12. However, the magneto-resistive element 59 (or 60) in Fig. 18 corresponds to the magneto-resistive element 27 in Fig. 12 and the magneto-resistive element 61 (or 62) in Fig. 18 corresponds to the magneto-resistive element 28 in Fig. 12. The magneto-resistive element of Fig. 12 and the magneto-resistive element of Fig. 18 are different in that the former can obtain only the output signal of one phase while the latter can obtain from the output terminals 71 and 72 the output signal of two phases delayed by 90°. According to these features, the embodiment of Fig. 18 has is advantageous in that it is possible to know the direction of the relative motion of the movable element and the stator. Fig. 19 shows an example of the embodiment of the magneto-resistive element used in the detector of the present invention, on the surface of the substrate 73 are formed the magneto-resistive elements 74, 75, 76, 77, 78, 79, 80, 81 and the terminals 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97. All of these components are electrically connected as shown, the terminals 82, 83 and 88, 89 are connected respectively with the constant-current regulated power supplies 32 and 33, and the terminals 84, 86 and 85, 87 are connected respectively with the output terminals 98, 99. In addition, the magneto-resistive elements 74 and 78 (or 75 and 79, 76 and 80, 77 and 81) are arranged with the same phase at paces P with respect to the pitch P of the magnetic teeth which is an object to be detected, and connected in series. Furthermore, the first group of elements consisting of the magneto-resistive elements 74 and 78 and the second group of elements consisting of the magneto-resistive elements of 76 and 80 are arranged separately at 1/2·P spaces respectively of each element thereof while the third group of elements consisting of the magneto-resistive elements 75 and 79 and the fourth group of elements consisting of the magneto-resistive elements 77 and 81 are likewise arranged separately at 1/2·P spaces respectively of each element thereof. In addition, each element of the first and third groups of elements is arranged by providing the phase difference of 1/4·P (=90°). The present embodiment of the present invention composed as above has two elements in each group of its elements as compared to the embodiment of Fig. 17 which has three elements in each group of its elements, however, the basic principle is the same. The embodiment of Fig. 17 can obtain an output signal of one phase only whereas the embodiment of Fig. 19 can obtain an output signal of two phases, thereby it becomes possible to know the direction of motion. Fig. 20 shows an example of the embodiment of the magneto-resistive element used in the detector of the present invention, on the surface of the substrate 120 are formed the magneto-resistive elements 121, 122, 123, 124, 125, 126 and the terminals 127, 128, 129 130, 131, 132, 133, 134, 135, 136, 137, 138. Each magneto-resistive element and each terminal are electrically connected as shown in Fig. 20. More particularly, the terminals 127, 129, 131 and 128, 130, 132 are connected with the constant-current regulated power supplies 32 and 33 and the pairs of magneto-resistive elements 121 and 124 (or 122 and 125 or 123 and 126) are arranged separately at 1/2·P spaces while the pairs of magneto-resistive elements 121 and 123, and 123 and 125 (or 124 and 126, and 122 and 124) are arranged separately at 1/3·P spaces respectively with respect to the pitch P of the magnetic teeth to be detected. Detailed description of the operating principle of the magneto-resistive element composed as above is also omitted since it is basically the same as that of the embodiment shown in Fig. 12. However, the embodiment of Fig. 20 has three pairs of the magneto-resistive elements (121 and 124, 123 and 126, 125 and 122) which have the same function as the one pair of the magneto-resistive elements 27 and 28 in Fig. 12 and each pair of the elements of Fig. 20 is arranged with the phase difference of P/3 (=120°). Therefore, output signals of three phases respectively different by 120° can be obtained from the output terminals 139, 140, 141. It is needless to say that the same effect as that of the embodiment of Fig. 12 can be obtained from each such pair as above. Fig. 21 shows an example of the embodiment of the magneto-resistive element used in the detector of the present invention, on the surface of the substrate 142 are formed the magneto-resistive elements 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154 and the terminals 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 178. All of these components are electrically connected as shown in Fig. 21, the terminals 155, 157, 159 and 156, 164, 166 are connected with the constant-current regulated power supplies 32 and 33, and the terminals 158 and 161, 160 and 163, 162 and 165 are connected respectively with the output terminals 179, 180, 181. More particularly, the magneto-resistive elements 143 and 149 (or 144 and 150, 145 and 151, 146 and 152, 147 and 153, 148 and 154) are arranged separately respectively at spaces P (with the same phase) with respect to the pitch P of the magnetic teeth to be detected, and connected in series. In addition, the magneto-resistive elements 143 and the magneto-resistive element 145 are arranged by delaying the phase by 1/3·P (=120°), the magneto-resistive elements 145 and the magneto-resistive element 147 are arranged by delaying the phase by 1/3·P (=120°), and the magneto-resistive elements 143 and 146, 145 and 148, 147 and 150 are arranged respectively by delaying the phase by 1/2·P (=180°). Whereas the embodiment of Fig. 19 outputs the output signal of two phases delayed by 90°, the embodiment of Fig. 21 composed as above is changed of the number of elements and the arrangement of elements so as to output the output signal of three phase delayed by 120°, and the basic operation is the same as the contents described of the embodiment in Fig. 17. With the embodiments of Fig. 19, Fig. 20 and Fig. 21 described above, output signals of small DC drift could be obtained from each output terminal with respect to the change in the ambient temperature, by using the half-bridge with the magneto-resistive elements which are arranged separately to make pairs at spaces (n+1/2)·P. However, each magneto-resistive element generates the heat by itself because of the current. Especially, when a large number of magneto-resistive elements are arranged on the same substrate as in the cases of embodiments shown in Fig. 19, Fig. 20 and Fig. 21, the temperature of the magneto- resistive element arranged at outer side of the substrate is often lower than that of the magneto-resistive element arranged close to the center of the substrate. DC drift of the output signal caused by such heat generated was as much as about 10% of the amplitude of the output signal in some cases. In addition, the line of magnetic force generated from the permanent magnet is changed under the effect of the magnetic teeth and is also subjected to the effect of the magneto-resistive element for the signal detection which is a magnetic material arranged in the magnetic field of the permanent magnet. For this reason, it is desirable to arrange each magneto-resistive element on the substrate in good balance and at equal spaces, however, as is apparent from the embodiments of Fig. 19, Fig. 20 and Fig. 21, the magneto-resistive elements at both ends of the substrate are poorly balanced respectively and the disturbance of the magnetic field is easily generated. Consequently, the output signal may be distorted in some cases. It is the object of the embodiment shown in Fig. 22 to remove problem occurring when a number of magneto- resistive elements are arranged on the same substrate. Fig. 22 shows an example of the embodiment of the magneto-resistive element used in the magnetic detector of the present invention, on the surface of the substrate 182 are formed the magneto-resistive elements for signal detection 184, 185, 186, 187, 188, 189, the magneto-resistive elements for compensation 183, 190, and the terminals 191, 192, 193, 194, 195, 196, 197, 198, 199, 200, 201, 202, 203, 204, 205, 206. All of the magneto-resistive elements for signal detection and compensation are electrically connected as shown in Fig. 22, and more particularly, the terminals 191, 192, 194, 196 are connected to the constant-current regulated power supply 32 and the terminals 193, 195, 197, 198 are connected to the constant-current regulated power supply 13. In addition, a pair of magneto-resistive elements for signal detection 184 and 187 (or 186 and 189 or 188 and 185) is arranged separately at spaces of 1/2·P with respect to the pitch P of the magnetic teeth to be detected while the magneto-resistive elements for signal detection 184 and 186, and 186 and 188 (or 185 and 187, and 187 and 189) are arranged separately at spaces of 1/3·P. Consequently, the composition is such that 3-phase output signal delayed respectively by 120° can be obtained from the output terminals 207, 208, 209, and said composition corresponds to the embodiment of Fig. 20. Furthermore, the magneto-resistive elements for compensation 183, 190 are arranged at both sides of the substrate with the magneto-resistive elements for signal detection disposed therebetween while the space between the magneto-resistive element for signal detection 184 and the magneto-resistive element for compensation 183 of this embodiment is arranged similarly to that of each magneto-resistive element for signal detection. Moreover, in this embodiment the magneto-resistive elements for compensation 183, 190 which are the same as the magneto-resistive elements for signal detection are used. With the magneto-resistive element used in the magnetic detector of the present invention, the magneto-resistive elements for compensation 183, 190 in the present invention are of the same materials and shapes as the magneto-resistive elements for signal detection 184, 185, 186, 187, 188, 189 and have the same magneto-resistive characteristics. In addition, by connecting to the constant-current regulated power supplies 32 and 33 which are common to the magneto-resistive elements for signal detection, the magneto- resistive elements for compensation 183 and 190 generate the heat by themselves almost like the magneto-resistive elements for signal detection. By this arrangement, it is possible to unify the temperature of the magneto-resistive elements for signal detection disposed between a pair of magnetio-resistive elements for compensation 183 and 190. More concretely, to solve the problem that the magneto-resistive elements 184 and 189 arranged at outer side on the substrate has lower temperature than the magneto-resistive elements for signal detection 186 and 187 arranged at the inner side on the substrate, the heat generated by said magneto-resistive elements for compensation 183 and 190 is utilized for heating the magneto-resistive elements for signal detection 184 and 189 to consequentially make the temperature of the magneto-resistive elements for signal detection uniform. But this arrangement, the temperature drift of the output signal obtained from the output terminals 207, 208, 209 is reduced and the magnetic detector of good accuracy can be materialized. In addition, the magneto-resistive elements for signal detection 184 and 189 as the magnetic materials which are arranged at the outermost locations on the substrate where the magnetic balance is the most poor are improved of its poor magnetic balance, as shown in Fig. 22, by the magneto-resistive elements for compensation 183 and 190 which are arranged at further outer locations than the magneto-resistive elements for signal detection thereby the disturbance of the magnetic field in such areas is decreased. By this arrangement, the distortion of the output signal obtained from the output terminals 207, 208, 209 is improved. Moreover, since the magneto-resistive elements for signal detection and compensation and the terminals are formed on the substrate 182 simultaneously by such for example as the metallization, the cost will not be increased by providing the magneto-resistive elements for compensation. In the present embodiment, the magneto-resistive elements for compensation and the magneto-resistive elements for signal detection of completely same material as well as the same constant-current regulated power supplies in terms of the power source are used, however, they are not limited thereto. The object is to make the temperature distribution of a plurality of magneto-resistive elements for signal detection uniform and to improve the magnetic balance, and it is also possible to appropriately adjust the heating value of the magneto-resistive elements by for example changing the shape of the magneto-resistive element for compensation to thereby vary its resistance. In addition, with the same object, the distance from the magneto-resistive element for compensation to the magneto-resistive element for signal detection is changed. It is also possible to control the voltage of the constant-current regulated power supply for the magneto-resistive element.

Claims: A magnetic detector for detecting relative movement in a predetermined direction (x) between a member (20) having teeth-like salients and slots of magnetic material, and a detecting head (21) which is arranged to be movable in said direction (x) at a constant distance from the surface of said member (20) and which comprises a ferromagnetic thin film resistor element (12,13,14) having magnetic anisotropy and a magneto-sensitive direction and a permanent magnet (16) to supply a magnetic field thereto; said ferro-magnetic thin film resistor element (12,13,14) being arranged so that its magneto-sensitive direction corresponds to the direction (x) of said relative motion, in order to respond to a change of the magnetic field in said direction occurring in the magnetic field between said permanent magnet and said teeth-like salients and slots, characterised in that the thin film surface (12) is arranged to be inclined at a constant angle to the surface of the member (20) on which the teeth-like salients and slots are formed, so that an offset magnetic field Hx in the direction (x) of said relative motion is generated in the ferro-magnetic thin film resistor element (12,13,14). A magnetic detector according to claim 1, wherein the detecting head (21) comprises two ferro-magnetic thin film resistor elements arranged spaced apart by a distance of (n+1/2).P (n : Integer, P : Pitch of said teeth-like salients and slots). A magnetic detector according to claim 1 or 2, wherein one end of the or each ferro-magnetic thin film resistor element (27,28) is connected electrically to a reference potential while the other end of the or each element is connected electrically to a constant-current regulated power supply, the output from the detector being taken from the junction between the or each element and the regulated power supply. A magnetic detector according to claim 1, 2 or 3 wherein the or each ferro-magnetic thin film resistor element (37,38) has a structure including at least one turn within the same thin film surface. A magnetic detector according to any one of the preceding claims, wherein the detecting head (21) comprises a group of ferromagnetic thin film resistor elements spaced apart by a distance of S.P (S : Integer, P : Pitch of said salients and slots) and the elements are electrically connected in series. A magnetic detector according to claim 1 or 2, wherein two ferromagnetic thin film resistor elements (27,28) are electrically connected in series between the constant voltage E1 and the constant voltage E2, and the electric signal is output from the junction between said ferromagnetic thin film resistor elements. A magnetic detector according to claim 1, wherein the detecting head comprises a first group of elements respectively separated by a distance of S.P (S : Integer, P : poll pitch of member), a second group of elements respectively separated by a distance of S.P, said ferromagnetic thin film resistor elements included in said first group of elements being electrically connected in series respectively; said ferro-magnetic thin film resistor elements included in said second group of elements being electrically connected in series respectively; and said first and second groups of elements being electrically connected in series between a constant voltage E1 and a constant voltage E2 so as to output an electric signal from the point of connection thereof. A magnetic detector according to any one of the preceding claims, wherein said detector head comprises at least two ferromagnetic thin film resistor elements arranged spaced apart by a distance of (λ + 1/4).P (λ : Integer, P : Pitch of said teeth-like salients slots) and further ferromagnetic thin film resistor elements arranged separately and respectively at spaces of (n+1/2).P (n : Integer) with respect to each of said at least two ferromagnetic thin film resistor elements. A magnetic detector according to claim 8, wherein the detector head comprises a plurality of ferromagnetic thin film resistor elements for signal detection and a plurality of ferromagnetic thin film resistor elements for compensation; said plurality of ferromagnetic thin film resistor elements for signal detection comprising said at least two ferromagnetic thin film resistor elements spaced apart by (λ + 1/4).P and said further ferromagnetic thin film resistor elements arranged separately and respectively at spaces of (n+1/2).P with respect to each of said at least two ferromagnetic thin film resistor elements; and said plurality of ferromagnetic thin film resistor elements for compensation being arranged at both sides of a substrate on which said elements are provided with said plurality of ferromagnetic thin film resistor elements for signal detection disposed therebetween while at both ends of respective elements are connected the constant voltage E1 and the constant voltage E2 electrically. A magnetic detector according to claim 9, wherein a plurality of ferromagnetic thin film resistor elements for signal detection and a plurality of ferromagnetic thin film resistor elements for compensation employ the same materials and have the same shapes. A magnetic detector according to any one of claims 1 to 7, wherein said detecting head includes at least m ferromagnetic thin film resistor elements arranged separately and respective at spaces of k / m.P (m : an integer denoting the number of phase and satisfying m = 3; P : Pitch of said teeth-like salients and slots: K : Integer) and further ferromagnetic thin film resistor elements arranged separately and respectively at spaces of (n+1/2).P (n : Integer) with respect to each of said at least m pieces of ferro-magnetic thin film resistor elements. A magnetic detector according to claim 11, wherein among m pieces of ferromagnetic thin film resistor elements arranged separately at space of k / m.P, a m th element comprising a m th group of elements comprising a plurality of ferromagnetic thin film resistor elements arranged separately and respectively at spaces of S.P (S : Integer); the m 'th group of elements comprising a plurality of ferromagnetic thin film resistor elements arranged separately and respectively at spaces of S.P, and being arranged at spaces of (n+1/2).P with respect to said m th group of elements; said ferromagnetic thin film resistor elements included in said m th group of elements being respectively electrically connected in series; said ferromagnetic thin film resistor elements included in said m 'th group of elements being respectively electrically connected in series; and said m th and m 'th groups of elements being electrically connected in series between a constant voltage E1 and a constant voltage E2 so as to output a m th electric signal from the point of connection thereof. A magnetic detector according to claim 11 wherein the detecting head comprises a plurality of ferromagnetic thin film resistor elements for signal detection and a plurality of ferromagnetic thin film resistor elements for compensation; said plurality of ferromagnetic thin film resistor elements for signal detection comprising said at least m pieces of ferromagnetic thin film resistor elements arranged separately at spaces of k / m.P and said ferro-magnetic thin film resistor elements arranged separately and respectively at spaces of (n+1/2).P with respect to each of said at least m pieces of ferro-magnetic thin film resistor elements; and said plurality of ferromagnetic thin film resistor elements for compensation being arranged at both sides of the substrate with said plurality of ferromagnetic thin film resistor elements for signal detection disposed therebetween while at both ends of respective elements are connected the constant voltage E1 and the constant voltage E2 electrically.

Inventors: ONODERA, HIROMI, SUGIZAKI, YASUSHI, WAKABAYASHI, NORIAKI
Applicants: MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1985
Main classification: G01P3
IPC codes: G01P3