APPARATUS FOR DETECTING THE POSITION OF MOVING MEMBER

Abstract: An apparatus for detecting the position of a moving member comprising a moving member (M) having a mag­ netic substance with magnetical signals recorded thereon, and a stationary magnetic sensor (N) confronting the moving member and having a plurality of magnetoresistive elements (R a to R d ; R a ′ to R d ′), wherein the magnetoresistive elements are disposed in the magnetic sensor such that the elements have a phase difference of π/m in electrical angle, where m is an even number larger than or equal to four, for obtaining the positional signal of the moving member.

Description: The present invention relates to an apparatus for detecting the position of a moving member, and particularly, to a position detecting apparatus using magnetoresistive elements. It is known that when a magnetoresistive element made of a magnetoresistive material such as permalloy is placed in the magnetic field with a current conducted therethrough, the resistance R of the element varies depending on the intensity of the magnetic field H, as shown in Fig. 6. By using a magnetoresistive element in place of the usual magnetic head, it is possible to detect information recorded magnetically on a magnetic recording medium at its zero speed with respect to the magnetoresistive element, i.e., in a stationary state of the medium. It is also known that this principle of the magnetoresistive element is applicable to the detection of the moving speed, moving direction and position of a moving member which rotates or travels along a straight line. For example, U.S. Patent No. 4,319,188 discloses a rotation detecting system with a plurality of magnetoresistive elements for detecting the angular position, rotational speed and rotational direction of a rotating member which carries information in a magnetic form. The inventors of the present invention have developed, in advance of this invention, a position detecting system, which will first be described with reference to Figs. 1 through 5. A motor 1 has a drive shaft 2 with a magnetic drum 5 coupled thereto, and signals are recorded magnetically on the circumferential surface of the drum 5. Confronting the drum surface, a magnetic sensor 4 consisting of magnetoresistive elements is fixed to the motor 1 by a magnetic sensor fixture 3. Fig. 2 shows by expansion the positional relationship between the magnetic drum 5 and the magnetic sensor 4. For the wavelength λ (electrical angle of 2π) of the recording signal, magnetoresistive elements R₁₁-R₁₄ and R₂₁-R₂₄ are arranged at an interval of λ/4 in the magnetic sensor 4 as shown in Fig. 2. These magnetoresistive elements are connected as shown in Fig. 3 to form two sets of bridge circuit. The output e₁ across terminals a₁ and b₁ of one bridge circuit and the output e₂ across terminals a₂ and b₂ of another bridge circuit are conducted to amplifiers OP a and OP b , as shown in Fig. 4, which provide the output OA and OB, respectively. Fig. 5 shows the waveforms of the bridge outputs e₁ and e₂ by (A) and (B), and the amplifier outputs OA and OB by (C) and (D), respectively. When the magnetic drum 5 shown in Fig. 1 rotates, the magnetic field strength to the magnetoresistive elements R₁₁-R₁₄ and R₂₁-R₂₄ varies, causing the resistance of each element to vary with a phase difference of λ/4 (electrical angle of π/2) from each other. The output voltages e₁ and e₂ of the bridge circuits vary as shown in Fig. 5 (A) and (B), and the signals are amplified and shaped to rectangular waves as shown by (C) and (D) in Fig. 5. Then, the outputs with a phase difference of λ/4 from each other are obtained. When the motor 1 rotates in the opposite direction, the phase relationship of the outputs OA and OB shown in Fig. 5 (C) and (D) is reversed, that makes possible the discrimination of rotational direction. In the foregoing conventional magnetic encoder, it is requested to increase the number of pulses per revolution so that the accuracy of the control system which employs the encoder is improved. In this case, however, if the wavelength λ of the recording signal, i.e., the recording pitch shown in Fig. 2, is made shorter, the magnetic field strength to the magnetic sensor 4 decreases and thus the outputs e₁ and e₂ fall unless the clearance CL between the magnetic sensor 1 and the magnetic drum 5 shown in Fig. 1 is made smaller. A narrower clearance CL will pose problems of assembling accuracy and eccentricity of the motor 1. The magnetic drum 5 may have a larger diameter, but it invites disadvantageously the larger inertia and bulkiness. Alternatively, the magnetic rotation sensor may be arranged to provide three or more final outputs, but, at a cost of increased number of magnetoresistive elements and a complex control system and wiring for converting multi-phase signals into dual-output signals, since it is a common practice in servo motor control systems to use dual-output signals from rotation sensors. US-A-4,039,936 discloses a rotation detecting system with a plurality of magnetoresistive elements and permanent magnets for detecting the angular position of a rotating member having a plurality of teeth, wherein three outputs in separate phases produced by the magnetoresistive elements are processed so that the output with a frequency three times that of each output is obtained. The output frequency of this prior art system may be increased by increasing the number of teeth of the rotating member, but, at a risk of machining accuracy. EP-A-0 048 983 discloses an apparatus as set forth in the first part of claim 1. Two pairs of magnetoresistive elements are disposed on the stationary sensor such that the interval between the two elements of each pair corresponds to the mutual spacing of magnetized portions on the moving member, i.e. 2π, and the interval between the two pairs of magnetoresistive elements corresponds to an angle of π/2. The output signals produced by differential amplifier circuits, to which the magnetoresistive elements are connected, are the same as those shown in Fig. 5 referred to above. It is an object of the present invention to provide an apparatus for detecting the position of a moving member in rotation or linear motion which provides the improved accuracy of detection at the minimum number of magnetoresistive elements by increasing the number of pulses per revolution or unit traveling length, without reducing the wavelength λ (2π) of the magnetic recording signal nor increasing the diameter of the magnetic drum or disk. Preferred embodiments of the invention will now be described with reference to the drawings, in which: Fig. 1 is an illustration showing the prior art system including a magnetic rotation sensor and a rotating member; Fig. 2 is an illustration showing by expansion the positional relationship between the magnetic rotation sensor and the rotating member shown in Fig. 1; Fig. 3 is a schematic diagram showing the connection of the magnetoresistive elements in the rotation sensor shown in Fig. 1; Fig. 4 is a schematic diagram of the waveform shaping circuit which performs waveform shaping for the signals produced by the circuit shown in Fig. 3; Fig. 5 is a set of waveform diagrams showing the timing relationship between the output waveforms provided by the circuit of Fig. 3 and the waveforms shaped by the circuit of Fig. 4; Fig. 6 is a graph explaining the relation between the magnetic field strength and the resistance of a magnetoresistance element; Fig. 7 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the present invention; Figs. 8, 9, 10 and 11 are schematic diagrams showing the connection of the magnetoresistive elements shown in Fig. 7; Fig. 12 is a vectorial diagram explaining the phase relationship of the circuits shown in Figs. 8, 9, 10 and 11; Fig. 13 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the first embodiment of the invention; Fig. 14 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 13; Fig. 15 is a set of waveform diagrams showing the resistance variations of the magnetoresistive elements shown in Fig. 13 and the waveforms of output voltages produced by the circuit of Fig. 14; Fig. 16 is a diagram explaining the output vol. tage shown in Fig. 15, Fig. 17 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit of Fig. 14; Fig. 18 is a set of waveform diagrams showing th phase relationship between the voltage signals at various portions of the circuit shown in Fig. 17; Fig. 19 is a waveform diagram for the supplemental explanation on the positional relationship between the output signals OA and OB; Fig. 20 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the second embodiment of the invention; Fig. 21 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 20; Fig. 22 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the third embodiment of the invention; Fig. 23 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 22; Fig. 24 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit of Fig. 23; Fig. 25 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the fourth embodiment of the invention; Fig. 26 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 25; Fig. 27 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit of Fig. 26; Fig. 28 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the fifth embodiment of the invention; Fig. 29 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 28; Fig. 30 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit of Fig. 29; Fig. 31 is a schematic diagram showing the connection of the magnetoresistive elements according to the sixth embodiment of the invention; Fig. 32 is an illustration showing by expansion the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the position detecting apparatus according to the seventh embodiment of the invention; Fig. 33 is a set of waveform diagrams showing the resistance variations of the magnetoresistive elements shown in Fig. 32; Fig. 34 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 32; Fig. 35 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit shown in Fig. 35; Fig. 36 is a set of waveform diagrams showing the phase relationship between the voltage signals at various portions of the circuit of Fig. 35; Fig. 37 is an illustration showing the positional relationship between the magnetoresistive elements and the wavelength λ of the magnetic recording signal on the moving member constituting the eighth embodiment of the invention; Fig. 38 is a schematic diagram showing the connection of the magnetoresistive elements shown in Fig. 37; Fig. 39 is a schematic diagram of the waveform shaping circuit for shaping the output voltages produced by the circuit of Fig. 38; and Fig. 40 is a set of waveform diagrams showing the phase relationship between the voltage signals at various portions of the circuit shown in Fig.39. Before entering into the embodiments of the present invention, the fundamental idea of the invention will first be described in connection with Figs. 7 through 12. In Fig. 7, the arrangement includes a magnetic moving member M such as a magnetic drum, magnetic disk or a linear-motion member, and a magnetic sensor N incorporating magnetoresistive elements (MR elements) R a -R d and R a '-R d '. Throughout Figs. 7 to 12, the MR elements are disposed with a spacing of λ/8 (electrical angle of π/4) for the wavelength λ of the recording signal so that quad voltage outputs (4-phase outputs) are obtained (defined to be m = 4). The basic arrangement of the magnetic sensor is the use of m+1 sets, i.e., 5 sets, of MR elements (R a , R a '; R b , R b '; R c , R c '; R d , R d '; R a , R a ') disposed such that the resistance variation of each MR element has a phase shift of ±π/m in electrical angle from each other. Making reference to the output e a produced by the MR elements R a and R a ' forming a 3-terminal connection element in the circuit of Fig. 8, the output e b produced by the elements R b and R b ' has a phase lag of π/4, and the outputs e c , e d and e a ' lag by π/4 from each preceding output. In the following description, the connection termed "3-terminal connection element" implies the arrangement as shown, for example, in Fig. 8 wherein both terminals of a serial connection of R a and R a ' are connected across a voltage source V, and the node of the R a and R a ' provides the output terminal. Adding the output e a to e b provides the output e a +e b as shown in Fig. 12. By adding adjacent outputs sequentially, the 4-phase outputs of e a +e b , e b +e c , e c +e d , and e d +e a ' with a phase difference of π/4 from each other are obtained. Thereafter, two signals with the doubled frequency are extracted from signals e a +e b and e c +e d and signals e b +e c and e d +e a ', each pair having a phase difference of π/2, through the process described later. The doubled number of pulses causes the phase relationship of the two signals with π/2, providing the 2-phase outputs representing the position of the moving member. With respect to the output e a from the MR elements R a and R a ' in the circuit of Fig. 9, the output e d ' has a phase lead by π/4, and each of the output e c ', e b ' and e a ' leads the successive output by π/4 in this order. Adding these outputs sequentially provides 4-phase outputs of e a +e d ', e d '+e c ', e c '+e b ' and e b '+e d ' with a phase difference of π/4 from each other as shown in Fig. 12. Pairs of signals e a +e d ' and e c '+e b ', and e d '+e c ' and e b '+e a ' are processed as will be described later, and 2-phase outputs with doubled number of pulses are obtained. The circuit of Fig. 10 provides a phase difference of (π+π/4) between the outputs, so that the signal e b ' has a phase lag of (π+π/4) with respect to the output e a and the signals e c , e d ' and e a ' follow in this order with a phase lag of (π+π/4) from the preceding one. Performing subtraction for output voltages, e a -e b ', e c -e b ', e c -e d ', and e a '-e d ' sequentially provides 4-phase outputs, which are equal to the signals obtained by the circuit shown in Fig. 8, with a phase difference of π/4 from each other as shown in Fig. 12. The connection of Fig. 11 provides a phase difference of π-π/4 between the outputs. The output e d follows the output e a with a phase lag of π-π/4, and then the outputs e c ', e b and e a ' follow in this order with a phase difference of π-π/4 from the preceding one. Substraction is performed for these outputs sequentially, and signals e a -e d , e c -e d , e c '-e b , and e a '-e b are obtained. As shown in Fig. 12, these signals are equal to the signals e a +e d ', e d '+e c ', e c '+e b , and e b '+e a ' obtained by the circuit shown in Fig. 9, forming 4-phase outputs with a phase difference of π/4 from each other. Thus, the fundamentals of the present invention are to combine five sets of signals among the outputs e a through e d ' as described in connection with Figs. 7 to 12 so as to obtain 4-phase (m-phase) signals with an amplitude approximately twice that of the signals e a through e d ' and a phase difference of π/4 (π/m) from each other, and to obtain 2-phase output signals with doubled number of pulses by the successive processing. The embodiments of the present invention will now be described with reference to Figs. 13 through 40, where signals and components identical to those shown in Figs. 7 through 11 are referred to by the common symbols. Fig. 13 shows the first embodiment of the invention, in which the number of phases m is selected to be four. In the figure, five MR elements are disposed in a 4-phase magnetic sensor N in such a way that an element R b ' is spaced by 5/8 λ from R a , an element Rc is spaced by 5/8 λ from the R b ', and then R d ' and R a ' follow with the same phase difference from the preceding one. In addition, MR elements R a ', R b , R c ', R d , and R a are disposed correspondingly to the MR elements R a , R b ', R c , R d ', and R a ' with a spacing of λ/2 (π) from each corresponding element located on the right-hand side in the figure so that the resistance variations of each pair have a phase difference of π. This arrangement provides 3-terminal connection for the MR elements R a -R d and R a '-R d '. Although the arrangement includes two sets of R a and R a ', an arbitrary combination may be taken for these elements. Namely, for the number of phases m=4 with n=1, in order to obtain the phase difference of 5/8 λ = 5/8 x 2π = 5/4π = (n+1/m)π = (1+1/4)π , MR elements of m+1 = 4+1 = 5 sets are disposed to form a multi-phase magnetic sensor N. The following describes the multi-phase to 2-phase conversion of this embodiment. The MR elements are connected to respective three terminals as shown in Fig. 14 and a voltage V is applied to the ends of the 3-terminal connections so that voltage outputs e a , e b ', e c , e d ', and e a ' are obtained at respective output terminals in response to the movement of a magnetic moving member M. As mentioned previously, the MR element has a variable resistance responsive to the magnetic field, and when the moving member M shown in Fig. 13 travels to the right the MR elements provide varying resistances as shown by (A) through (H) in Fig. 15. In Fig. 15, one set of MR elements R a and R a ' has the same resistance variation as that of another set, and the waveform of the former is omitted. In response to the resistance variations, the voltage outputs vary as shown by (I) through (M) in Fig. 15. Fig. 16 shows the mean voltage level (V/2) of the output voltage e a . As stated previously, the outputs of the MR elements have a phase difference of 5/8 λ, i.e., 5/4 π which is larger than π/2 and the outputs are combined as follows to obtain m-phase, i.e., 4-phase, outputs as shown by (A)-(D) in Fig. 18. Namely, differential voltages between outputs e a and e b ', outputs e c and e b ', outputs e c and e d ', and outputs e a ' and e d ' are evaluated sequentially. The signals e a , e b ', and so on are conducted to the inputs of the amplifiers OP₁ through OP₄, which may be voltage comparators or differential amplifiers, so that signals Ea through Ed are obtained at their outputs, as shown in Fig. 17. The amplifiers are designed to have a sufficiently high gain, so that they provide m-phase, i.e., 4-phase rectangular output signals Ea through Ed as shown by (E)-(H) in Fig. 18. Thereafter, the first output signal Ea and the third output signal Ec, and the second output signal Eb and the fourth output signal Ed are combined respectively, i.e., odd numbered phase outputs and even numbered phase outputs are paired on exclusive OR gates EOR₁ and EOR₂ or other waveform combine circuits, respectively, as shown in Fig. 17, so that the 2-phase outputs OA and OB carrying positional information of the moving member are obtained as shown by (I) and (J) in Fig. 18. The 2-phase outputs OA and OB have a frequency (output pulses) twice that of the intermediate signals Ea through Ed, with a phase difference of π/2 in an electrical angle between the two outputs. When the moving member M moves reversely, i.e., from right to left, the phase relationship of the waveforms shown in Fig. 15 reverses, causing the 2-phase outputs OA and OB shown by (I) and (J) in Fig. 18 to have the opposite phase relationship, and the output OB leads the output OA by π/2 as shown in Fig. 19. According to this embodiment, as described above, the number of output pulses is doubled without changing the wavelength λ of the signal recorded on the magnetic moving member M. The number of MR elements is ten as shown in Fig. 13, the only increase of two from the conventional arrangement with eight elements shown in Fig. 2. The 2-phase outputs have a phase difference of π/2, with its polarity depending on the moving direction, allowing discrimination of moving direction in the same way as the conventional system. In the foregoing embodiment, it should be noted that the MR elements in 3-terminal connections as described with Fig. 13 may be simple resistors, and also the MR elements wired may separately be mounted on another member instead of being disposed within the sensor. Output conversion takes place automatically due to the connection of each section in response to the movement of the moving member, and this is common to all embodiments of the invention. The second embodiment of the present invention will be described with reference to Figs. 20 and 21. Five MR elements R a , R b ', R c , R d ', and R a ' are disposed with a spacing of 5/8 λ from each other within a magnetic sensor N, as in the case of the first embodiment. Resistors R o in 3-terminal connections are disposed in the magnetic sensor N to form a multi-phase magnetic sensor. The MR elements and resistors R o are connected in 3-terminal connections as shown in Fig. 21, with a voltage V applied to the ends of each connection, so that voltage outputs e a , e b ', e c , e d ', and e a ' are obtained at the output terminals of the connections. These outputs have the same waveform as that shown previously in Fig. 15, and processing of the output signals by the circuit shown in Fig. 17 provides the 2-phase outputs OA and OB with doubled number of pulses as shown in Fig. 18, whereby the same effect as of the first embodiment is achieved. The resistors in 3-terminal connections in this embodiment may be of simple resistors or MR elements insusceptible to the magnetic field of the magnetic moving member and also they may separately be mounted on another member, as in the case of the first embodiment. The third embodiment will be described with reference to Figs. 22 through 24. In Fig. 22, five MR elements R a , R b , R c , R d , and R a ' are disposed with a spacing of λ/8, where λ is the wavelength of the recording signal, within a magnetic sensor N. Namely, for the number of phases m=4 with n=0, MR elements of m+1 = 4+1 = 5 in number (R a , R b , R c , R d , and R a ') are disposed such that the phase difference of λ/8 = 1/8 x2π= π/4 = (n+1/m)π = (0+1/4)π (0+1/4)π is obtained. In addition, resistors R o (not shown) are disposed in the magnetic sensor N to form a multi-phase magnetic sensor. The MR elements and resistors are connected in 3-terminal connections as shown in Fig. 23, with a voltage V applied to the ends of each connection, so that the voltage outputs e a , e b , e c , e d , and e a ' are obtained at the output terminals of the connections. The outputs e a , e c and e a ' have waveforms identical to those shown by (I), (K) and (M) in Fig. 15, and the outputs e b and e d have waveforms with a phase difference of π from the previous outputs e b ' and e d ' shown by (J) and (L), respectively, in Fig. 15. Accordingly, each pair of the outputs e a and e b , outputs e b and e c , outputs e c and e d , and outputs e d and e a ' has a phase difference of λ/8. These MR elements provide the outputs with a phase difference of λ/8, i.e., π/4 and it does not exceed π/2, and these outputs are combined as follows to obtain m-phase, i.e., 4-phase, outputs. The outputs e a , e b , e c , e d , and e a ' are connected as shown in Fig. 24 and the output signals Ea through Ed are obtained at the outputs of amplifiers OP₁ through OP₄ which perform amplification and wave shaping. The amplifier outputs have a phase relationship as shown previously in Fig. 18, and the same 2-phase outputs OA and OB carrying positional information as those of the first embodiment are obtained. The resistors in 3-terminal connections may be dealt with identically to the case of the second embodiment. The fourth embodiment will be described with reference to Figs. 25 through 27 in Fig. 25, MR elements of m+1 = 5 in number are disposed with a spacing of 7/8 λ, i.e., for n=2 and m=4, (n-1 /m)π = 7/4π, where λ is the wavelength of the recording signal, within a magnetic sensor N. In addition, resistors R o (not shown) in 3-terminal connections are disposed in the magnetic sensor N so that they are insusceptible to the magnetic field of the magnetic moving member M, and a multi-phase magnetic sensor is completed. The MR elements and resistors are connected in 3-terminal connections as shown in Fig. 26, with a voltage V applied to the ends of each connection, so that voltage signals e a , e d ', e c ', e b ', and e a ' are obtained at the output terminals of the connections. The outputs e a , e d ', e b ', and e a ' have the same waveforms as those shown in Fig. 15 and the output e c ' is out of phase with e c shown by (K) in Fig. 15 by the amount of π. The outputs are amplified and shaped by the circuit shown in Fig. 27, and signals Ea, Eb, Ec and Ed are obtained. These signals Ea, Eb, Ec, and Ed are processed to obtain 2-phase outputs OA and OB as in the case of the previous embodiments. Also in this embodiment, the resistors R o may be dealt with identically to the case of the second embodiment. The fifth embodiment will be described with reference to Figs. 28 through 30. In Fig. 28, MR elements R a , R d , R c ', R b , and R a ' of m+1 = 5 in number are disposed with a spacing of 3/8λ, i.e., (n-1/m)π = 3/4π for n=1 and m=4 within a magnetic sensor N. Resistors R o are disposed so that they are insusceptible to the magnetic field of the magnetic moving member M, and a multi-phase magnetic sensor is formed. The MR elements and resistors are connected as shown in Fig. 29, and outputs e a , e d , e c ', e b , and e a ' are obtained. The outputs are processed by the circuit shown in Fig. 30, and signals Ea, Eb, Ec, and Ed are obtained. Also in this embodiment, the resistors R o may be dealt with identically to the case of the second embodiment. Fig. 31 shows the connection of MR elements and resistors in the multi-phase magnetic sensor according to the sixth embodiment of the invention. The arrangement employs the disposition of MR elements of the third embodiment shown in Fig. 22, but with different connections for the resistors R o in 3-terminal connections to the power source as shown in Fig. 31, and outputs e a , e b ', e c , e d ' are obtained. These outputs are the same shown in Fig. 14, and the 2-phase outputs OA and OB are obtained as has been described in connection with Figs. 15 through 19. Although various combinations of disposition for MR elements are possible in the foregoing embodiments for 4-phase sensors (m=4), the basic arrangement is the provision of a phase difference of λ/2m, i.e., π/m, for the number of phases of m, and this value is added by π or the value of π is subtracted by π/m to form individual dispositions. In the connection diagrams referred to in the foregoing embodiments, the output terminals for output e a , e b , and so on are led out to the right or left, but both are functionally identical. Next, the 6-phase magnetic sensor (m=6) according to the present invention will be described with reference to Figs. 32 through 36. In Fig. 32, seven MR elements R a , R b ', R c , R d ', R e , R f ', and R a ' are disposed with a spacing of 7/12 λ, i.e., (n+ 1/m) π = 7/6 π for n=1 and m=6, and connected to a terminal section T₁. Also disposed with a phase difference of π (opposite phase) from the former element group are MR elements R a ', R b , R c ', R d , R e ', R f , and R a , which are connected to a terminal section T₂ to complete a multi-phase magnetic sensor N. The MR element R a on the terminal section T₁ is out of phase with the MR element R a ' on the terminal section T₂ by (7/12) λ x 6 + λ = (54/12)λ = (9/2)λ = 9π, i.e., a phase difference of π in electrical angle. In Fig. 34, serial connections are made for pairs of MR elements R a and R a ', R b ' and R b , R c and R c ', R d ' and R d , R e and R e ', R f ' and R f , and R a ' and R a , with the terminal section T₁ connected to the positive side of the power source V and the terminal section T₂ to the negative side. When the magnetic moving member M is moved to the right, the resistance of the MR elements R a through R f will vary as shown in Fig. 33. On the other hand, the MR elements R a ' through R f ' provide the waveforms which are out of phase by π, i.e., opposite phase, with the waveforms shown in Fig. 33. Accordingly, the outputs e a , e b ', e c , e d ', e e , e f ', and e a ' shown in Fig. 34 provide voltage waveforms corresponding to the MR elements R a , R b ', R c , R d ', R e , R f ', and R a '. These outputs are combined on amplifiers OP₁ through OP₆ as shown in Fig. 35 to take the difference of each pair, and the amplifiers provide the rectangular outputs Ea through Ef as shown in Fig. 36. These signals are grouped into one block including Ea, Ec and Ee and another block including Eb, Ed and Ef, so that both groups are processed through exclusive-OR gates EOR₁ and EOR₃ shown in Fig. 35 or other waveform combine circuits to obtain intermediate outputs OA' and OB' as shown by (G) and (I) of Fig. 36, respectively, and further processed by exclusive-OR gates EOR₂ and EOR₄ shown in Fig. 35 or other waveform combine circuits to obtain 2-phase outputs OA and OB. The 2-phase output signals OA and OB have a phase difference of π/2 and a period 1/3 that of the wavelength λ of the recording signal, thus increasing the number of pulses by three times. When the magnetic moving member M shown in Fig. 32 is moved to the left, the waveforms of Figs. 33 and 36 will have the opposite phase relationship, i.e., output OA lags behind output OB by π/2, allowing the discrimination of rotational direction as in the conventional 2-phase rotation sensor. These are the arrangements using m+1 sets of magnetoresistive elements. The following describes an example using m sets of magnetoresistive elements with reference to Figs. 37 through 40. With the disposition of MR elements as shown in Fig. 37, the movement of the magnetic moving member M causes the resistance of the MR elements R a through R d , and R a ' through R d ' to vary in the same waveforms as those shown in Fig. 15. The MR elements are connected as shown in Fig. 38, and the outputs e a through e d of the 3-terminal connections are as shown in Fig. 40. These outputs are processed by the waveform shaping/output converting circuit shown in Fig. 39. Waveform shaping amplifiers OP₁ through OP₄ receives at their one inputs the respective signals e a through e d , with their remaining inputs receiving commonly a voltage e o produced by dividing the voltage V of the power source by a fixed resistor R o . In this arrangement, the amplifiers, OP₁ through OP₄ provide the outputs Ea through Ed as shown in Fig. 40. These waveforms are the same shown by (E), (F), (G) and (H) in Fig. 18, and output OA is produced from Ea and Ec and output OB is produced from Eb and Ed as described previously. Thus, this is a rotation sensor with 2-phase outputs, which needs only m sets of MR elements, less than the arrangement of Fig. 13 by one element. Although the foregoing embodiments are of 4-phase or 6-phase, the present invention is applicable to realize multi-phase magnetic sensors of even number of phases, such as 8-phase, 10-phase, 12-phase, etc., by using MR elements larger in number by one set than the number of phases m, or MR elements equal in number to m. The advantages of the present invention are summarized in the following. (1) The number of output pulses of an m-phase magnetic sensor can be increased by m/2 times by using m+1 or m MR elements, but without decreasing the wavelength λ of the signal recorded on the magnetic moving member. (2) Use of m+1 sets of MR elements for a m-phase magnetic sensor provides output pulses m/2 times in number, allowing reduction in the number of MR elements. (3) Owing to the above properties (1) and (2), a compact, light weight, and precise multi-phase magnetic sensor can be designed without increasing the outer diameter of the rotational magnetic member. (4) The number of output pulses can be increased without decreasing the wavelength λ of the signal recorded on the magnetic moving member, allowing a larger gap between the magnetic moving member and the magnetic sensor, whereby multi-phase magnetic sensors suited to mass production can be designed. (5) The inventive m-phase magnetic sensor provides 2-phase outputs OA and OB with a frequency (output pulses) m/2 times as much as the 1-phase output, e.g., two times for a 4-phase arrangement, or three times for a 6-phase arrangement, with a phase difference of π/2 in electrical angle between the outputs OA and OB. (6) The output phase difference of π/2 in electrical angle, with its polarity depending on the moving direction of the magnetic moving member, allows discrimination of the moving direction in the same way as of the conventional sensor.

Claims: An apparatus for detecting the position of a moving member (M) relative to a stationary magnetic sensor (N), said moving member (M) having magnetized portions aligned in a row in the direction of movement and mutually spaced by equal intervals, said stationary magnetic sensor (N) having a plurality of magnetoresistive elements (Ra, Rb, ...) disposed so as to confront said row of magnetized portions, each of said magneto resistive elements (Ra, Rb, ...) being connected in series with a resistance element (Ra', Rb', ...; R0) to form a three-terminal circuit having an output terminal for producing an output (ea, eb, ...) having a phase related to the position of the respective one of said magnetoresistive elements(Ra, Rb, ...) relative to said magnetized portions, selected pairs of the outputs (ea, eb, ...) of said three-terminal circuits being applied to amplifier circuits (OP1, OP2, ...) to produce a plurality of m first periodic waveforms (Ea, Eb, ...) having equal periods related to the interval between said magnetized portions and having phases which are shifted relative to each other by a phase difference corresponding to the interval between said magnetoresistive elements (Ra, Rb, ...), characterised in that said magneto resistive elements (Ra, Rb, ...) are spaced from each other by such an interval and the circuit arrangement is such that said first periodic waveforms (Ea, Eb, ...) have a phase difference of π/m from each other, where m is an even number larger than or equal to 4, and that said first periodic waveforms (Ea, Eb, ...) are applied to logic circuits (EOR1, EOR2, ...) to produce a pair of second periodic waveforms (OA, OB) having each a period equal to 2/m of the period of said first periodic waveforms (Ea, Eb, ...) and being phase-shifted relative to each other by π/2. The apparatus of claim 1, wherein m + 1 of said magneto resistive elements (Ra, Rb, ...) are provided. The apparatus of claim 1, wherein m of said magneto resistive elements (Ra, Rb, ...) are provided. The apparatus of any one of claims 1 to 3, wherein said resistance elements are further magnetoresistive elements (Ra', Rb', ...). The apparatus of any one of claims 1 to 3, wherein said resistance elements are resistors (R0) of fixed resistance. The apparatus of any one of claims 1 to 5, wherein said logic circuits include exclusive-OR circuits (EOR1, EOR2, ...) each having two inputs receiving selected two of said first periodic waveforms.

Inventors: KAWAMATA, SYOOICHI, MIYASHITA, KUNIO, MORINAGA, SHIGEKI, TAKAHASHI, TADASHI
Applicants: HITACHI, LTD.
Application year: 1983
Main classification: G01D5
IPC codes: G01P3, G01D5