APPARATUS FOR MAGNETICALLY DETECTING POSITIONS

Abstract: The present invention relates to an apparatus for magnetically detecting positions and intends to provide a position detecting apparatus of the kind with high accuracy in which when recording magnetic signals of a predeter­ mined length on magnetization tracks (M₀ to M₃ M 0b to M 3b ; M 0c to M 3c ), a plurality of recording units are continuously arranged in the direction of the magnetization track and are set as the predetermined recording length, thereby sharpen­ ing the output waveform of the signal corresponding to the edge portion of the magnetization recording length. The present invention is suitable for the absolute type having a plurality of magnetization tracks.

Description: The present invention relates to an apparatus for magnetically detecting positions as defined in detail in the preamble of claim 1. The present invention may be applied to apparatus of the absolute type having a plurality of magnetic tracks and to apparatus of the incremental type having only one magnetic track. Moreover, the invention may be employed in connection with rotating machines and with machines moving along a straight line. In US-A-3.192.521 there is disclosed an apparatus for magnetically detecting positions which comprises at least one magnetic track having a plurality of first portions therealong where magnetic information is recorded. Magnetic sensing means are disposed close to the magnetic track for detecting its magnetic information portions and to generate signals indicative thereof. Further, moving means are provided to move the magnetic track and the magnetic sensing means relative to each other. The magnetic sensing means consist of a magnetic coil head including a magnetic core provided with an interrogate winding and an output winding. That arrangement is for detecting the change of the magnetic field of the core due to applying an external magnetc field thereto. A pulsed output signal is induced in the output winding from the magnetic signal recorded on the track, and an oscillator is required to energize the interrogate winding. Another example for an apparatus for magnetically detecting positions is disclosed in US-A-4.274.053. To further illustrate the problems to be overcome a short explanation of that known apparatus herebelow. Fig. 1 is a constructional diagram showing the principle of the invention of Ito et al, in which it is illustrated as three tracks in place of five tracks. Fig. 2 shows developing diagrams of the rotary drum and magnetic sensor, and Fig. 3 shows resistance change waveform diagrams of the magneto-resistance effect devices. In the diagrams, reference numeral 1 denotes a rotary member, e.g. motor according to a rotary member to be detected; 2 a rotatable shaft thereof; 3 an attaching base; 4 a magnetic sensor having magnetic detecting devices; and 5 a rotary drum adapted to support a plurality of magnetizating tracks M a - M c ; R a - R c denote magnetic detecting devices, e.g., magneto-resistance effect devices each facing the above magnetization tracks M a - M c . This example shown here is constituted by the rotary drum 5 and the magnetic sensor 4. This rotary drum 5 is supported through the rotatable shaft 2 to the rotary member 1 according to the rotary member to be detected and has a plurality of magnetization tracks M a - M c . Magnetic signals for the magnetic recording medium have been recorded adjacently on each of the above-mentioned tracks using different recording wavelengths of N-S such as shown in Fig. 2. On the other hand, the magnetic sensor 4 is disposed closely to the above magnetization tracks M a - M c , respectively, and are attached to the rotary member 1 by the attaching base 3. The magnetic signals are fetched as the resistance changes as shown in Fig. 3 by the magneto-resistance effect devices R a - R c . The resistance change waveforms are then shaped, thereby to obtain the three-bit absolute signals. However, as is obvious from Fig. 2, according to such an apparatus shown, the magnetic signals indicated by the arrows in the diagrams recorded adjacently on each of the magnetization tracks M a - M c have various wavelengths and their polarities are not coincident at all; therefore, there is a fear of mutual magnetic interference and it is considered that there is a fear such that it is difficult to obtain the signals in accordance with the resistance change waveforms as shown in Fig. 3. In addition, since the wavelengths of the magnetic signals in response to the recording signals largely differ in dependence upon the respective magnetization tracks M a - M c , this causes the different magnetic field distributions on the surfaces of the magnetic recording mediums of the rotary drum 5. In other words, in the magnetization tracks M a where the magnetic signal has a short wavelength, the output such as shown in Fig. 3 is obtained on the surface of the magnetic recording medium, but the magnetic field becomes very weak in the location slightly apart therefrom. On the other hand, in the magnetization track M c where the magnetic signal has a long wavelength, the magnetic field distribution like a pulse is obtained on the surface of the magnetic recording medium, but the magnetic field becomes weak in the location apart from the surface, so that there is a fear such that the output such as shown in Fig. 3 cannot be derived. Furthermore, if a strong magnet is used for the portions where the magnetic signal has a long wavelength, such as for the magnetization track M c in order to obtain the outputs as shown in Fig. 3, in recording the magnetic signal, other magnetization tracks M a and M b will be contrarily largely affected due to the strong magnetic field caused by that magnet. As a result of this, there is a drawback peculiar to the absolute type such that it is difficult to increase the number of bits. In addition to the above drawback, in the portions where the magnetic signal has a long wavelength, e.g., in the magnetization track M c , the edge portion of the output waveform becomes dull and this makes it difficult to obtain the accurate edge when shaping the waveform into the square wave; therefore, there is a drawback such that it is impossible to realize a magnetic rotary sensor with high degree of accuracy. This drawback is similarly caused even in the incremental type having a single magnetization track. From "Control Engineering", Vol. 13, No. 3, March 1966, page 92, a digital angle sensor is known comprising a continuous loop of magnetic tape actuating Hall generators in a digital manner. The tape is alternately magnetized along its length of uniform distances. FR-A-1 394 483 discloses a magnetic de- and encoder comprising a magnetic cylinder or the like, which can be displaced relative to a magnetic decoding element comprising a certain number of tracks, each of said tracks comprising a certain number of separated areas being adjacent or in contact to each other. Each of these areas is magnetized so as either to be a magnetic North-pole or a magnetic South-pole. It is a main object of the present invention to provide an apparatus for highly accurately detecting positions which can sharpen the output waveform edge portion corresponding to the edge portion of the recording wavelength recorded in the magnetization track, thereby to improve the accuracy of the edge when shaping the waveform. Additionally the present invention is intended to provide an apparatus for detecting positions of the absolute (absolute position) type with high resolution which enables the signals to be detected with similar sensitivity even in each of magnetication tracks where the magnetic signals have different recording widths and at the same time which eliminates the magnetic interference between the respective magnetizatin tracks, thereby to sharpen the edge portions of the output waveforms. According to the present invention these objects are achieved by means of an apparatus as claimed in claim 1; advantageous developments of that apparatus are defined in the subclaims depending thereon. The basic feature of the present invention is to obtain magnetic signals by continuously magnetically arranging a plurality of magnetic recording units and to use magneto-resistance effect devices as the detecting device. The present invention does not detect changes of a magnetic field but basically uses magneto-resistance effect devices to detect the presence or the absence of a magnetic field or a magnetic field strength. Therefore, magnetism can be precisely detected by means of the present invention even if the external magnetic field does not change, i. e. even if the carrier provided with magnetic track is in a stop state. No oscillator and no digital signal are required, and the whole circuit becomes very simple. Further, with the present invention a magnetic signal of a predetermined length is obtained by continuously magnetically arranging a desired number of minimum recording units. That is, a magnetic signal of a predetermined length is generated by a plurality of magnetic recording units. Additionally, with the present invention magnetic interference between a plurality of magnetic tracks may be prevented and the edge of the magnetic signal may be sharpened through coincidence both of the N/S polarities and of the wavelength magnetically recorded between the respective magnetic tracks and through continuously arranging a number of minimum recording units as has been described above. Moreover, with the present invention, the magneto-resistance effect devices may be arranged with a distance of one half of the wavelength with regard to each other where the wavelength marks a recording pitch of the polarity, and they may be connected in a bridge circuit or in a three-terminal circuit so taht a large output signal can be obtained for precisely detecting the N/S polarities magnetically recorded on the respective tracks. The present invention will be still more apparent from the following detailed description when taken in connection with the accompanying drawings, in which: Fig. 1 is a constructional diagram showing the principle of a conventional detecting apparatus of the absolute type; Fig. 2 shows developing diagrams of the rotary drum and magnetic sensor of the apparatus of Fig. 1; Fig. 3 shows resistance change waveform diagrams of the magneto-resistance effect devices of Fig. 2; Fig. 4 is a principle constructional diagram showing one embodiment of the present invention; Fig. 5 shows developing diagrams of the rotary drum and magnetic sensor of the magnetic rotary sensor according to one embodiment of the present invention; Fig. 6 shows resistance change waveforms of the magneto-resistance effect devices; Fig. 7 is a bridge connection diagram of the magneto-resistance effect devices; Fig. 8 shows output voltage waveforms of the bridge; Fig. 9 shows waveform diagrams after the output voltage waveforms were shaped; Fig. 10 shows developing diagrams of the rotary drum and magnetic sensor of the magnetic rotary sensor according to another embodiment of the present invention; Fig. 11 is a bridge connection diagram of the magneto-resistance effect devices; Fig. 12 shows resistance change waveform diagrams of the magneto-resistance effect devices; Fig. 13 shows output voltage waveform diagrams of the bridge; Fig. 14 shows waveform diagrams after the out put voltage waveforms were shaped; Fig. 15 is a constructional diagram showing a magnetic rotary sensor according to another embodiment of the present invention; and Fig. 16 shows developing diagrams of the rotary disk and magnetic sensors. The constitution of the present invention will be described hereinbelow as an example whereby the absolute position of the rotation is detected. Shown here is one example and the present invention includes the incremental type by means of a single track, the straight moving type, and the type of which magnetization tracks and magneto-resistance effect devices relatively move. Fig. 4 is an external side elevational view showing the schematic consittution of the present invention. Fig. 5 shows developing diagrams of the rotary drum and magnetic sensor of the magnetic rotary sensor according to one embodiment of the present invention. Fig. 6 shows resistance change waveform diagrams of the magneto-resistance effect devices. Fig. 7 is a bridge connection diagram of the magneto-resistance effect devices. Fig. 8 shows output voltage waveform diagrams of the bridge. Fig. 9 shows waveform diagrams after the output voltage waveforms were shaped. In the figures, a reference numeral 4 denotes the magnetic sensor in which magneto-resistance effect devices (hereinbelow, referred to as MR devices) R₀₁ - R₃₂ according to the magnetic detecting devices are arranged, and 5 denotes the rotary drum having four magnetization tracks M₀ - M₃, on each track the magnetic signals with different recording widths according to the magnetic recording medium have been recorded. This embodiment relates to a magnetic rotary sensor of the absolute position type having four-bit gray code in accordance with the resolution 1/16 of the magnetic rotary sensor in which it is constituted by the magnetic sensor 4 and rotary drum 5 as shown in Fig. 4 in place of the magnetic sensor and rotary drum in the magnetic rotary sensor shown in Fig. 1 described previously. That is to say, the rotary drum 5 is divided into four magnetization tracks M₀ - M₃ on which the magnetic signals according to the magnetic recording medium having a wavelength λ with respect to the minimum recording unit of the N-S porality as indicated by the arraws in Fig. 5 have been recorded. This wavelength λ with respect to the minimum recording unit equivalently corresponds to the resolution of the relevant magnetic rotary sensor. On the magnetization track M₀ with regard to the least significant bit, two magnetic signals each having a wavelength λ are successively recorded and then the blank corresponding to such two signals follows, i.e., no signals are recorded in this blank, and thereafter the two magnetic signals are similarly recorded; in this way, this pattern is repeated as shown in Fig. 5. At this time, the magnetic recording length is 2λ. The above-mentioned blank portion is the perfect blank portion where no magnetic flux exist and other blanks are similar to that. On the next magnetization track M₁ with respect to the second bit, four magnetic signals each having a wavelength λ are continuously recorded and then the blank portion corresponding to such four signals follows, i.e., four signals are not recorded in this portion at all; in this way, this pattern is likewise repeated. The magnetic recording length at this time is 4λ. On the next magnetization track M₂ relating to the third bit, eight magnetic signals each having a wavelength λ are continuously recorded and then the blank portion corresponding to such eight signals follows in the same manner as above. The magnetic recording wavelength at this time is 8λ. On the other hand, the magnetization track M₃ with regard to the most significant bit has the same magnetic recording wavelength 8λ as that of the above-mentioned magnetization track M₂, but their phases are different. In other words, the magnetic recording lengths of the magnetization signals on the magnetization tracks M₀, M₁, M₂, and M₃ are 2λ, 4λ, 8λ, and 8λ, respectively, and the phases of the magnetization tracks M₀, M₁ and M₃ are out of phase by only λ, 2λ and 4λ from the phase of the magnetization track M₂. Furthermore, the magnetic signals are recorded in the manner such that the N-S polarities of the adjacent magnetic signals each having a wavelength λ on each magnetization track are identical in the lateral direction of the tracks, respectively, as shown in Fig. 5. The magnetic sensor 4 will now be described. The MR devices are disposed closely to each of the above-mentioned magnetization tracks. Namely, as shown in Fig. 5, a pair of MR devices R₀₁ and R₀₂ regarding the least significant bit are disposed to face the magnetization track M₀; similarly, the MR device pairs R₁₁, R₁₂, and R₂₁, R₂₂, and R₃₁, R₃₂ with respect to the second, third and most significant bits are arranged to face the magnetization tracks M₁ - M₃, respectively. In addition, the MR devices R₀₁ and R₀₂; R₁₁ and R₁₂; R₂₁ and R₂₂; and R₃₁ and R₃₂ are respectively disposed in the positions only λ/2 (i.e., the half of the wavelength λ) apart from each other. Moreover, the respective MR devices are arranged in a line as shown in Fig. 5. In this constitution, when the magnetic field perpendicular to the longitudinal direction of the MR devices R₀₁ - R₃₂ is applied, their resistance values decrease and this characteristic is utilized here. Namely, when the rotary drum 5 is moved in the direction indicated by an arrow in the arrangement as shown in Fig. 5, the resistances of the MR devices R₀₁ - R₃₂ change as shown in Fig. 6, respectively. It will be appreciated from Fig. 6 that in any cases, the waveform edge portions become sharp since each resistance value changes on the minimum recording unit basis with respect to a wavelength λ. By constructing resistance bridges for each magnetization track respectively, as shown in Fig. 7, which bridge circuits are constituted by the MR devices R₀₁ - R₃₂ in the magnetic rotary sensor as described above, and resistors R, namely, other MR devices or resistors R regarding resistive materials which are arranged so as not to be affected by hte magnetic field of the rotary drum 5 which was disposed for example to the magnetic sensor 4 or was separately attached and disposed, and by applying voltages to each of these bridges from a power supply V, the absolute position can be detected in the following modes. That is, assuming that the output voltage between output terminals a₀ and b₀ which are the detection terminals regarding the least significant bit of the magnetization track M₀ is e₀; that the output voltage between output terminals a₁ and b₁ with respect to the second bit is e₁ similarly; and that the output voltages between output terminals a₂ and b₃ relating to the third bit and between a₃ and b₃ regarding the most significant bit are e₂ and e₃, respectively, the waveform edge portions of these output voltages e₀ - e₃ of the magnetization tracks M₀ - M₃ become similarly sharp as shown in Fig. 8 even when the widths of the output signals are different. Fig. 8 shows waveform diagrams with respect to the amplitude of the voltage e₀₁ corresponding to the sum of voltage changes due to the resistance changes of Fig. 6. When the waveforms of these output voltages e₀ - e₃ are shaped by an amplifier or voltage comparator, their waveforms E₀ - E₃ become as shown in Fig. 9. These outputs E₀ - E₃ are four-bit gray code outputs and the signal change of each bit has a phase difference of λ, so that the absolute positions of 16 equal parts can be detected. As described above, in the present constitution, the magnetic signals as described with respect to Fig. 5 are recorded, and the polarities of the adjacent magnetization tracks in the lateral direction thereof are identical, i.e., they are the same N porality or the same S porality, so that this causes the mutual repulsion but does not cause the magnetic interference. In addition, since the magnetic signals can be recorded on the basis of the waveform with respect to the same minimum recording unit, the magnetic field distributions of the respective magnetization tracks are aligned and their output levels of the magnetization tracks are almost equal, thereby enabling the stable outputs to be obtained. This is particularly effective when the absolute positions are detected in response to the magnetic signals of a plurality of tracks. Furthermore, since the edge portions of the output waveforms change sharply, detection accuracy and resolution can be improved. In the above embodiment, the minimum recording unit is equivalent to the resolution of the relevant magnetic rotary sensor; however, if it is reduced to less than that resolution or to a factor of integer thereof, the output waveform edge portion can be further shaped. This effect can be also derived even in the incremental type position detecting apparatus having a single track. Moreover, in the above embodiment, although an example of four bits has been shown, similar effect will be obtained even if the number of bits increases to five bits of the resolution of 1/32 or eight bits of the resolution of 1/256. The gray code is frequently used as a magnetic rotary sensor since only one bit changes at any time to change a value by one step. However, a similar effect can be obtained even when using a binary code of which two or more bits together change. Although there is a positonal difference of only λ/2 (half of the wavelength λ) between the MR devices for each track in the above embodiment, this wavelength difference may be selected to (n-1/2)λ(where, n is an integer), and a similar effect can be also obtained even in this case. Another embodiment of the present invention will be then described with reference to Fig. 10 - 14. This embodiment uses two magnetization tracks for each bit and relates to the four-bit gray code in which the output voltages are increased. Fig. 10 shows developing diagrams of the rotary drum and magnetic sensor of the magnetic rotary sensor according to another embodiment of the present invention. Fig. 11 is a bridge connection diagram of the MR devices. Fig. 12 shows resistance change waveform diagrams of the MR devices. Fig. 13 shows output voltage waveform diagrams of the bridges. Fig. 14 shows waveform diagrams after the output voltage waveforms were shaped. In the diagrams, reference numeral 4 denotes the magnetic sensor to which the MR devices R₀₁ - R₃₄ as the magnetic detecting devices are disposed, and 5 indicates the rotary drum having magnetization tracks M 0b -M 3b , on each track the magnetic signals with different magnetic recording lengths according to the magnetic recording medium have been recorded, wherein two magnetization tracks with respect to the same bit are combined and are used as a pair, respectively. The present embodiment relates to an absolute position type magnetic rotary sensor having the four-bit gray code as described above and is constituted by the magnetic sensor 4 and rotary drum 5 as shown in Fig. 10 in the same manner as in the former embodiment in place of the magnetic sensor and rotary drum in the magnetic rotary sensor shown in Fig. 1. That is to say, the rotary drum 5 is divided into eight tracks (a) - (h). As shown by the arrows in Fig. 10, the magnetic signals with respect to the magentic recording medium of a wavelength λ of the N-S polarity which are similar to the former magnetic signals are recorded on these eight magnetization tracks (a) - (h). The magnetization tracks M 0b - M 3b corresponding to the least significant, second, third, and most significant bits with respect to the magnetization tracks of each one bit are constituted by each two magnetization tracks, i.e., (a) and (b); (c) and (d), (e) and (f); and (g) and (h). The wavelength λ equivalently corresponds to the resolution (1/16) of the relevant magnetic rotary sensor. The pattern of the magnetization track (a) in the magnetization track M 0b regarding the least significant bit is the same recording pattern of the magnetization track M₀ in the former embodiment. On the contrary, no magnetic signal is recorded in the portion of the magnetization track (b) corresponding to the portion of the magnetization track (a) in which the magnetic recording medium was recorded. On the other hand, the magnetic signal is recorded in the portion of the track (b) corresponding to the portion of the track (a) in which it is not recorded. Likewise, the magnetization tracks (c), (e) and (g) of the magnetization tracks M 1b , M 2b and M 3b with respect to the second, third and most significant bits have the same recording patterns of the magnetization tracks M₁, M₂ and M₃ in the former embodiment. On the contrary, the magnetic recording mediums are recorded on the magnetization tracks (d), (f) and (h) under the same recording conditions as those in the former embodiment. Each pair of these magnetization tracks constitutes the magnetization tracks M 1b , M 2b and M 3b with respect to the same bit. The magnetic signals each having a wavelength λ are recorded on each magnetization track in the same manner as in the former embodiment such that the polarities of N or S of the adjacent tracks are identical in the lateral direction of the tracks. The MR devices R₀₁ - R₀₄, R₁₁ - R₁₄, R₂₁ - R₂₄, and R₃₁ - R₃₄ with respect to the least significant, second, third, and most significant bits are disposed in the magnetic sensor 4 as shown in Fig. 10 so as to face the magnetization tracks M 0b - M 3b with respect to the least significant, second, third, and most significant bits, respectively. In addition, the MR devices R₀₁, R₀₃, R₁₁, R₁₃, R₂₁, R₂₃, R₃₁, and R₃₃ are arranged in a line. Similarly, the MR devices R₀₂, R₀₄, R₁₂, R₁₄, R₂₂, R₂₄, R₃₂, and R₃₄ are arranged in a line; however, there is a positional difference of only λ/2 between the former line and the latter line. With such an arrangement, when the rotary drum 5 is moved in the direction indicated by the arrow in Fig. 10, the resistances of the above-mentioned MR devices R₀₁ - R₃₄ change as shown in Fig. 12, respectively. The bridges are constituted for each bit using these MR devices as shown in Fig. 11. When the voltages are applied to these bridges from the power supply V, the voltage e₀ between the output terminals a₀ and b₀ of the least significant bit shown in Fig. 11, the voltage e₁ between the output terminals a₁ and b₁ of the second bit, the voltage e₂ between the output terminals a₂ and b₂ of the third bit, and the voltage e₃ between the out-put terminals a₃ and b₃ of the most significant bit become as shown in Fig. 13. It is therefore possible to obtain the voltage which is about twice the amplitude of the output voltage shown in Fig. 8 in the former embodiment. Even in this embodiment, the output waveform edge portions of each bit change sharply similarly. When the above-mentioned output voltages e₀ - e₃ are waveform-shaped by an amplifier or voltage comparator, their output waveforms E₀ - E₃ are as shown in Fig. 14, so that the four-bit gray code is obtained. From the above description, according to this embodiment, it is possible to expect an effect similar to the former embodiment and to enlarge the amplitude of the output voltage, thereby enabling the accuracy to be improved. In addition, the wavelength with respect to the minimum recording unit can be selected to various values and the number of bits may be increased similarly to the former embodiment. Each of the above-described embodiments has the rotary drum 5 attached to the rotary member 1 through the rotatable shaft 2. The magnetically recorded tracks are supported on the outer peripheral surfaces of the rotary drum 5. However, as such a rotary drum, it is possible to use the rotary disk type drum which has the magnetically recorded tracks on its edge surface. That is to say, Fig. 15 and 16 show one embodiment constituted by the rotary disk type. Fig. 15 is a constructional diagram of a magnetic rotary sensor according to another embodiment of the present invention. Fig. 16 shows developing diagrams of the rotary disk and magnetic sensor. In the diagrams, a reference numeral 3-1 denotes an attaching base; 4-1 indicates a magnetic sensor in which MR devices R₀ - 1, R₁ - 1, R₂ - 1, and R₃ - 1 with respect to the magnetic detecting devices are disposed; and 5-1 is a rotary disk having four magnetization tracks M 0c to M 3c , on each track the magnetic signals regarding the magnetic recording medium having different recording widths have been recorded. Numeral 1 denotes the same rotary member as that in the former embodiment and 2 is the rotatable shaft. Namely, the magnetization track M 0c with respect to the least significant bit, the magnetization tracks M 1c and M 2c regarding the 2nd and 3rd bits, and the magnetization track M 3c with respect to the most significant bit are arranged sequentially concentrically from the outer periphery on the rotary disk 5-1. The MR device pairs R₀ - 1, R₁ - 1, R₂ - 1, and R₃ - 1, each consisting of two MR devices of the magnetic sensor 4-1 are disposed in a line closely to those magnetization tracks M 0c - M 3c so as to face them, respectively. In this case, the minimum recording unit is an angle ϑ. Even in this embodiment, an effect similar to that of the former embodiment can be expected. In addition, the recording of the magnetic signals with respect to the magnetic recording medium in each embodiment also includes the arrangement of thin permanent magnets. Although the present invention is constituted as described above, it includes the following apparatuses - as previously mentioned. (a) Apparatus of the type in which the magnetically recorded tracks are moved in the direction of a straight line. (b) Apparatus of the incremental type having only a single magnetically recorded track. (c) Apparatus of the absolute type having a plurality of magnetically recorded tracks. (d) Apparatus in which the magnetically recorded tracks and magnetic sensor are relatively moved. (e) Apparatus in which the magnetically recorded tracks are stationary but the magnetic sensor is moved. (f) Apparatus in which the magnetic tracks are disposed on the outer periphery of the rotary drum or on the side surface of the rotary disk. (g) Other apparatuses each having a uniform constitution without departing from the present invention. According to the present invention, the following effects can be mainly obtained. (a) Even in case of the recording signals each having a wide or narrow recording width, their output edge portions are similarly sharp, thereby enabling high accuracy and high resolution to be obtained. (b) Even in case of the multimagnetization tracks having different recording widths, it is possible to detect the recording signals with the same sensitivity. (c) It is possible to detect the recording signals on the magnetization tracks without causing the magnetic interference between the magnetization tracks having different recording widths.

Claims: An apparatus for magnetically detecting positions, comprising at least one magnetic track (M₀ to M₃; M 0b to M 3b ; M 0c to M 3c ) having a plurality of first portions therealong where magnetic information is recorded, magnetic sensing means (4; R₀₁, R₀₂, R₁₁, R₁₂, R₂₁, R₂₂, R₃₁, R₃₂; R 01 to R₀₄, R₁₁to R₁₄, R₂₁to R₂₄, R₃₁ to R₃₄; R₀-1 to R₃-1) disposed closely to the magnetic track for detecting its magnetic information portions and providing signals indicative thereof and moving means (1) for moving the magnetic track and the magnetic sensing means relative to each other, characterised in that said magnetic track also includes an equal plurality of second portions therealong where magnetic information is not recorded, the first and second portions each extending over at least one predetermined length and the first portions each comprising a plurality of the same minimum length magnetic information units recorded continuously along the direction of the track and that the magnetic sensing means are composed of a plurality of related pairs of magneto-resistance effect devices. The apparatus of claim 1, characterised in that each magnetic track is supported by a rotary member (1) and that magneto-resistance effect devices are disposed closely to each of the magnetic tracks to provide signals indicative of the magnetic information recorded by the minimum recording units on the tracks as an indication of the absolute position of the rotary member. The apparatus of claim 1 or 2, characterised in that each minimum recording unit comprises an N pole portion and an S pole portion extending in the direction of the track and that all the minimum recording units are continuously recorded along the direction of the track so that the N pole portion of one minimum recording unit is adjacent to an N pole portion of an adjacent minimum recording unit and the S pole portion of one minimum recording unit is adjacent to an S pole portion of an adjacent minimum recording unit. The apparatus of claim 1, characterised in that the minimum recording units are recorded on the tracks so as to be arranged on the same line crossing the tracks. The apparatus of claim 1, characterised in that the magnetic recording mediums of the minimum recording units are recorded so as to be arranged on the same line crossing the tracks and that the polarities of the magnetic recording mediums recorded on the same line are identical. The apparatus of claim 1, characterised in that two tracks are constituted as a pair and are divided into portions where the minimum recording units are continuously recorded and portions where such recording is not performed, the portions of one of the two tracks corresponding to the recording portions of the other track are used as the nonrecording portions, whereas the portions of one of the two tracks corresponding to the nonrecording portions of the other track are made recording porttions. The apparatus of claim 1, characterised in that the minimum recording units are continuously recorded on the tracks such that the polarities of the minimum recording of adjacent tracks are identical to each other. The apparatus of claim 1, characterised in that the minimum recording units on the tracks are made equal to or lower than the resolution of the magnetic sensing means or said resolution divided through an integer. The apparatus of claim 1, characterised in that the magnetic sensing devices disposed closely to the magnetic tracks are arranged on the same line. The apparatus of claim 1, characterised in that two magnetic sensing devices are provided for one magnetic track and that the distance between the two magnetic sensing means is (n - 1/2)λ, λ being the width of the minimum recording unit of the magnetic recording medium and n being an integer. The apparatus of claim 6 or 10, characterised in that two magnetic sensing devices which are not affected by the magnetic fields from the magnetic tracks or two resistors (R) are disposed to constitute a bridge together with two magnetic sensing devices disposedfor one magnetic track or a pair of two magnetic tracks. The apparatus of claim 1, characterised in that the portions where magnetic information is not recorded are blank portions having substantially no magnetic flux and being arranged on both sides of a magnetically recorded information portion of predetermined length. The apparatus of claim 12, characterised in that each blank portion has the same length as the magnetically recorded information portion of predetermined length. The apparatus of claim 1, characterised in that the moving means moves the magnetic tracks and the magnetic sensing devices are statioary. The apparatus of claim 1, characterised in that a plurality of magnetic tracks are provided and the magnetically recorded information extends over a different predetermined length for at least two of the tracks, each different predetermined length magnetic information recorded portion for a respective track comprising a different number of the same minimum recording units recorded continuously along the direction of a respective track. The apparatus of claim 1, characterised in that the magnetic tracks are annular tracks. The apparatus of claim 1, characterised in that the magnetic tracks are tracks having two ends not connected with each other. The apparatus of claim 1, characterised in that the magnetic tracks are straight tracks.

Inventors: KAWAMATA, SYOOICHI, MIYASHITA, KUNIO, TAKAHASHI, TADASHI
Applicants: HITACHI, LTD.
Application year: 1983
Main classification: H03M1
IPC codes: G01B7, H03M1, G01P3, G01D5