Absolute encoder

Abstract: An absolute encoder wherein tracks (3-1, 3-2) are arranged side-by-side on a magnetic drum (1) in the axial direction thereof, and absolute patterns of circulatory random sequence codes are divided and recorded on the tracks (3-1, 3-2), respectively. An additional track (3-3) for generating sinewaves of two phases in synchronism with the reading of the absolute patterns is provided on the magnetic drum (1), so that an output can be obained by combining a coarse value of an absolute position obtained from the tracks (3-1, 3-2) and a fine value of an absolute position obtained from the additional track (3-3). The absolute patterns are detected from the two tracks (3-1, 3-2) recorded on the magnetic drum (1) by magnetic resistive elements (MR) connected with each other to form circuits each having a three-terminal. Terminals of the magnetic resistive elements (MR) are connected through a common line with an electric power source in order to prevent the lines from being crossed.

Description: The present invention relates to an encoder, and more particularly relates to an absolute encoder wherein an output of a rotary member is coded, so that an absolute position of the rotary member can be detected directly. A magnetic type absolute encoder is formed by combining a detector utilizing magneto-resistive elements (which will hereinafter be referred as MR elements) with a magnetic drum on which magnetic patterns of more than two rows are recorded magnetically as described in Japanese Patents Laid-Open Nos. 54-118259 and 62-83619. In general, magnetic patterns of n tracks are necessary in order to obtain a resolution of 2 n in such absolute encoder. Accordingly, as shown in Figs. 23 and 24, a plurality of tracks 30 (six in this case) are disposed on an outer peripheral surface of a magnetic drum 1, informations of three bits are recorded on said tracks 30, and a magnetic sensor 20 having MR elements (R 01 , R 01 , ---) of a number corresponding to said three bits are disposed facing the magnetic drum 1, so that an absolute value can be obtained by combining signals from the plural MR elements. Japanese Patent Laid-Open No. 2-24513 discloses an absolute encoder wherein absolute signals can be obtained from tracks having absolute patterns. However, it is necessary to arrange parallely a plurality of tracks on the magnetic drum 1 in the axial direction thereof, as shown in Fig. 23, in order to increase the resolution of the absolute encoder of the prior art, such as an absolute encoder shown in Japanese Patent Laid-Open No. 62-83619, thereby causing the absolute encoder large in size. Further, it is necessary to describe informations of 2 n on one track in order to obtain a resolution of 2 n , for example, in an absolute encoder using circulatory random sequence codes, so that the absolute encoder must be made precisely in dimension and becomes expensive. I.E.E.E. Transactions on Instrumentation and Measurement, 1987, No. 4, pages 950-955 entitled "Absolute-Type Position Transducers Using a Pseudorandom Encoding" describes the application of pseudorandom sequences to the encoding of absolute type position transducers. An absolute 360-position shaft encoder illustrates the features of the pseudorandom encoding technique. In the conventional absolute position detecting method described above, a plurality of absolute patterns are recorded on the peripheral surface of the magnetic drum in the circumferential direction thereof and MR elements corresponding thereto are arranged. In such case, it is better to increase the resolution by shortening the recording pitch in consideration of the size. However, the shortening of the recording pitch has a limitation in consideration of the arrangement of the MR elements, and if the recording pitch is increased, the magnetic drum becomes large in size. Further, as shown in Fig. 24, leakage magnetic fluxes of N, S shown by arrows on the magnetic drum are sensed by the MR elements to generate signals in the absolute encoder. Accordingly, if the recording pitch is increased, the width of the magnetic sensor 2 becomes large as shown in Fig. 25. Accordingly, as shown in Fig. 25, a distance α between an MR element at an end portion of the magnetic sensor 2 and the center of the magnetic drum 1 becomes larger than a distance d between an MR element at the center portion of the sensor 2 and the center of the magnetic drum 1. Experiments show that a good sensing property cannot be obtained, because the MR element at the end portion of the magnetic sensor 2 cannot sense enough, when the relation of the α and d is expressed by α > d+0.1d. It is an object of the present invention to solve the above-mentioned problems and to provide a compact and inexpensive absolute encoder having a high resolution. The above-described object is achieved by an absolute encoder comprising a magnetic drum having tracks and having absolute patterns of circulatory random sequence codes thereon, and a pattern detector for reading patterns on the tracks characterised in that absolute patterns of circulatory random sequence codes are divided and recorded on first and second tracks arranged side-by-side on the magnetic drum in the axial direction thereof, that an additional track is provided on the magnetic drum for generating sinewaves on two phases in synchronism with the reading of the absolute patterns on the first and second tracks and that an output is obtained by combining a value of an absolute position detected by the pattern detector from the first and second tracks having the absolute patterns with a value of an absolute position obtained by operating information of sinewaves from the additional track. The absolute encoder according to the present invention is further characterised in that a first signal and a second signal which are deviated in phase from each other by one half of pole pitch of magnetic recording are obtained from the plural tracks having the absolute patterns by the pattern detector, one of the first and second signals is selected according to said value of the absolute position obtained by operating the sinewave informations, and said output is obtained by interpolating the value of the absolute position obtained by operating the sinewave informations to the selected signal. The above-mentioned object can also be achieved by an absolute encoder further characterised in that the pattern detector has a plurality of sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track, each of said plurality of sets has two magneto-resistive elements facing said first and second tracks respectively and connected with each other to form a plurality of circuits, each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum and each of said plurality of circuits has a terminal at the first track side connected to one terminal of an electric power source, and a terminal at the second track side connected to another terminal of the electric power source, and an intermediate terminal between the two magneto-resistive elements of said circuit from which an output is obtained. The above-identified object can also be achieved by an absolute encoder further characterised in that the pattern detector has a plurality of sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track, each of said plurality of sets has two magneto-resistive elements facing said first and second tracks respectively and being connected with each other to form a plurality of circuits each having two magneto-resistive elements, and each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum, terminals at the first track side of odd number circuits and terminals at the second track side of even number circuits are connected to a first terminal of an electric power source, and terminals at the second track side of odd number circuits and terminals at the first track side of even number circuits are connected to a second terminal of the electric power source, and an output is obtained from an intermediate terminal between said two magneto-resistive elements in each of said circuits. The above-described object is also achieved by an absolute encoder further characterised in that the pattern detector has a first to (n+1)th sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track, each of said plurality of sets has two magneto-resistive elements facing said first and second tracks respectively and connected with each other to form a plurality of circuits each having two magneto-resistive elements, and each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum, terminals at the first track side of each of said plurality of circuits are connected to a first terminal of an electric power source, and terminals at the second track side of said first and (n+1)th circuits are connected to a second terminal of the electric power source, each terminal at the second track side of the second to nth circuits at the second track side is directly connected to only the neighbouring terminal at the second track side of a neighbouring circuit and then connected to said second terminal of the electric power source through a common line, and an output is obtained from an intermediate terminal between said two magneto-resistive elements in each of said circuits. Other objects as well as advantageous features of the present invention will become apparent from the following descriptions of the embodiments taken in conjunction with the accompanying drawings. Fig. 1 is a perspective view showing an embodiment of an absolute encoder according to the present invention; Fig. 2 is an extended view of an outer peripheral surface of a magnetic drum in the absolute encoder according to the present invention; Fig. 3 is an extended view showing MR elements of a magnetic sensor in the absolute encoder according to the present invention; Fig. 4 is a view showing wave forms of signals from the magnetic sensor and processing circuits in the absolute encoder according to the present invention; Fig. 5 shows a first processing circuit in the absolute encoder according to the present invention; Fig. 6 shows a second processing circuit in the absolute encoder according to the present invention; Fig. 7 is a view showing a pattern to be detected and a detector in the absolute encoder according to the present invention; Fig. 8 is a view explaining a detected pattern in the absolute encoder according to the present invention; Fig. 9 is a block diagram of an operating and processing device in the absolute encoder according to the present invention; Fig. 10 is a view explaining sinewaves divided into eight regions in the absolute encoder according to the present invention; Fig. 11 is a view explaining the sum of a coarse signal and a dense signal in the absolute encoder according to the present invention; Fig. 12 is an extended view showing magnetic tracks and MR elements of a magnetic sensor in another embodiment of the present invention; Fig. 13 is a third processing circuit in said embodiment of the absolute encoder according to the present invention; Fig. 14 is a view showing a magnetic track, a first signal, a second signal and sinewaves in said embodiment of the absolute encoder according to the present invention; Fig. 15 is a perspective view showing an absolute encoder in a further embodiment according to the present invention; Fig. 16 is an extended view of an outer peripheral surface of a magnetic drum in the absolute encoder of said embodiment according to the present invention; Fig. 17 is an extended view showing magnetic tracks and MR elements of a magnetic sensor in said embodiment according to the present invention; Fig. 18 is a view explaining the relation between the magnetic drum and a magnetic sensor in the said embodiment according to the present invention; Fig. 19 is a view showing a pattern to be detected and bits in said embodiment according to the present invention; Fig. 20 is a view showing detected patterns in said embodiment according to the present invention; Fig. 21 is an extended view showing magnetic tracks and MR elements of a magnetic sensor in a yet further embodiment of an absolute encoder according to the present invention; Fig. 22 is an extended view showing magnetic tracks and MR elements of a magnetic sensor in the other embodiment of an absolute encoder according to the present invention; Fig. 23 is an extended view showing magnetic tracks and MR elements of a magnetic sensor in the conventional absolute encoder; and Fig. 24 is a view explaining leakage magnetic fluxes of the magnetic drum in the conventional absolute encoder; and Fig. 25 is a view explaining the relation between the magnetic drum and the magnetic sensor in the conventional absolute encoder. An embodiment of the present invention will be explained with reference to Figs. 1 to 11. In Fig. 1 showing an absolute encoder according to the present invention, reference numeral 1 denotes a magnetic drum, 2 denotes a magnetic sensor having MR elements thereon, and 3 denotes a magnetic track formed on an outer peripheral surface of the magnetic drum 1 in a circumferential direction thereof. The magnetic track 3 in the present invention, as shown in Fig. 1, comprises three magnetic tracks 3-1, 3-2 and 3-3 arranged side-by-side on the magnetic drum 1 in the axial direction thereof, respectively. Two upper side tracks 3-1 and 3-2 are used as a track for outputting absolute positions. On the upper side magnetic tracks 3-1 and 3-2, absolute patterns using circulation random sequence codes are recorded, whereas on the lower side magnetic track 3-3, magnetic poles N and S are recorded one after the other regularly, so that sinewaves can be obtained from the magnetic track 3-3. As shown in Fig. 2, the magnetic track 3-1 has no signal recorded portions, whereas the magnetic track 3-2 has signal recorded portions corresponding in position to said no signal recorded portions on the magnetic track 3-1, and has no signal recorded portions corresponding in position to said signal recorded portions on the magnetic track 3-1. As shown in Fig. 3, MR elements R 11 and R 21 are arranged corresponding to the magnetic track 3-1 and separated from each other by one half of a minimum recording pitch λ on the recording track 3-1. Similarly, MR elements R 12 and R 22 are arranged corresponding to the magnetic track 3-2, and separated from each other by one half of the minimum recording pitch λ on the recording track 3-2. The MR elements R 11 and R 12 are connected to each other to form a circuit having three terminals. Similarly, the MR elements R 21 and R 22 are connected to each other to form a circuit having a three-terminal. In the arrangement of the magnetic tracks and the MR elements shown in Fig. 3, when the magnetic drum 1 is rotated outputs e 1 and e 2 as shown in Fig. 4 are generated from said two circuits, respectively. An output e 01 can be obtained by operating the outputs e 1 and e 2 in a first processing circuit shown in Fig. 5. In Fig. 5, reference numeral 4a denotes an operational amplifier and reference symbols Ri and Rf are fixed resistances, respectively. In Fig. 3, a set of "H bridge" comprising four MR elements R 11 , R 12 , R 21 and R 22 forms a detector of one bit. An output of absolute positions of n bits can be obtained, if n sets of the "H bridge" are arranged at an interval of the minimum recording pitch λ on the magnetic track. A minimum of recording pitch of the magnetic track 3-3 for generating sinewave signals of two phases is set to λ as like as that of the magnetic tracks 3-1 and 3-2. MR elements R 31 and R 32 are arranged corresponding to the magnetic track 3-3, and separated from each other by (n + 1/2)λ (where n = 0, 1, 2, ---) (in Fig. 3, n = 1) on the recording track 3-3. MR elements R 41 and R 42 are arranged corresponding to the magnetic track 3-3 and separated from each other by λ /2 on the magnetic track 3-3, as shown in Fig. 3. The MR elements R 31 and R 41 are separated from each other by nλ /3 (n = 1, 2,---) (in Fig. 3, n = 2) from each other. The MR elements R 31 and R 32 are connected to each other to form a circuit having a three-terminal generating an output e 3 and the MR elements R 41 and R 42 are connected to each other to form a circuit having a three-terminal generating an output e 4 , as shown in Figs. 3 and 6. An output e 02 having sinewaves of two phases, or of sin  and cos  which are separated from each other in phase by π/4, as shown in Fig. 4 can be obtained from a second processing circuit shown in Fig. 6 using the outputs e 3 and e 4 . In Fig. 6, reference numeral 4b denotes an operational amplifier. As stated above, the two circuits each having the three-terminal and forming "H bridge" are separated from each other by nλ /3, so that the output e 02 obtained by operating in the operational amplifier 4b shown in Fig. 6 becomes sinewaves having no third harmonic and having less distortion. A manner to detect absolute positions of eight portions of a rotary member will be explained with reference to Fig. 7 showing a pattern 5 to be detected and a detector 6. The absolute positions of eight portions can be detected as codes of 0 to 7 by detecting signals of three bits from the pattern 5 to be detected by the detector 6. Specifically, in Fig. 7, when the three bit signals are read by the detector 6 while shifting the detector 6 bit by bit in the rightward direction the bit signals can be coded to, as shown in Fig.8, 7 6 4 0 1 2 5 3. Accordingly, the eight positions of the rotary member can be detected as the codes of 0 to 7. If numerical values corresponding to the coded absolute positions of the 7, 6, 4, 0, 1, 2, 5, 3 are recorded preliminarily in memory elements, the codes can be read from 0 to 7, in order. In the above descriptions, such a case that eight portions of the outer periphery of the rotary member are read by the detector of three bits is explained. However, if a detector of n bits is used absolute positions of portions of 2 n on the outer periphery of the rotary member can be read. In Fig. 9 showing an operating and processing device of the absolute encoder according to the present invention, reference numeral 100 denotes a detector in the absolute encoder, 101 denotes a code converter, 102 denotes a latch circuit, 103 denotes a wave form processing circuit such as a sampling and holding circuit, 104 denotes a CPU, 105 denotes an A/D converter, 106 denotes a ROM and 107 denotes a buffer. In the operating and processing device shown in Fig. 9, an output indicating direct absolute positions obtained from the magnetic tracks 3-1 and 3-2 among the outputs of the detector 100 of the absolute encoder is applied as a coarse data to the CPU 104 through the code converter 101 and the latch circuit 102, as well as an output of sinewaves of two phases obtained from the magnetic track 3-3 is processed in the wave form processing circuit 103 and applied to the CPU 104 through the A/D converter 105. The output of sinewaves is referenced in the CPU 104 to a data stored in the ROM 106 and converted into a fine data which is combined with the output indicating the direct absolute positions and outputte from the buffer 107. Next, a manner to obtain the absolute positions in one cycle of the sinewave will be explained with reference to Fig. 10. As shown in Fig. 10, one cycle of the sinewave is divided into eight regions (1) to (8), so that if absolute values of sin  and cos  are considered the regions (1) and (2) are symmetric with each other centering about 45° . Similarly, the regions (3) and (4), (5) and (6), and (7) and (8) are symmetric, respectively. Accordingly, if the position of the region within 0 to 360 ° can be determined the absolute positions can be obtained by calculating only the data within 0 ° to 45 ° . According to the manner, the processing time of the software can be reduced. The absolute positions of the sinewave in one cycle obtained by the operation in the CPU 104 in the operating and processing device can be expressed by a formula  = arc tan (sin /cos ). This formula indicates that no detection error is generated if the sinewaves of sin and cos are varied synchronously with each other. As shown in Fig. 11, in the CPU 104 of Figure 9, signals from a coarse signal portion 7 and a fine signal portion 8 are combined. Specifically, a coarse value of absolute positions obtained from the tracks having the absolute pattern is added as a high rank value to a fine value of absolute positions obtained from one cycle of the sinewave as a low rank value, so that an absolute encoder small in size and high in resolution can be realized. In said embodiment, as shown in Fig. 3, magnetic patterns on the magnetic tracks 3-1 and 3-2 are detected by the MR elements R 11 , R 12 , R 21 , and R 22 . However, as shown in Fig. 2, the signal recording positions on the magnetic tracks 3-1 and 3-2 have a complemental relation with each other, that is, no signal recorded portions on one of the magnetic tracks 3-1 and 3-2 correspond to signal recorded portions on the other of the magnetic tracks 3-1 and 3-2. Accordingly, the output of the MR element generated at the borderline between the signal recorded portion and no signal recorded portion becomes instable. Especially, the output may have an error, when the coarse value of the absolute positions is obtained directly from the MR elements directly after the power switch is turned ON . In another or second embodiment of the present invention, in order to prevent the generation of error directly after the ON of the power switch, MR elements R 11 and R 12 , R 21 and R 22 , R 31 and R 32 , and R 41 and R 42 , --- R (n+1)1 and R (n+1)2 for detecting magnetic records on the magnetic tracks 3-1 and 3-2 are provided and connected to form circuits each having a three-terminal, and separated from the another by λ/2 to generate outputs e 1 , e 2 , e 3 --- and e 2n+1 , respectively, as shown in Fig. 12. The outputs e 1 and e 2 are applied to input terminals of an operational amplifier 4c of a third processing circuit, and the outputs e 2 and e 3 are applied to input terminals of an operational amplifier 4d of a fourth processing circuit, as shown in Fig. 13. Similarly, the outputs e 2n-1 , and e n , and e 2n and e 2n+1 are applied to input terminal of corresponding operational amplifiers, respectively. Fig. 14 shows magnetic tracks 3-1 and 3-2 having absolute patterns and a magnetic track 3-3 for forming outputs of sinewaves, as well as wave forms of first and second signals from an OR circuit 11a, and wave forms of cos and sin , respectively. The first signal is generated by processing the output e 1 of the circuit having the three-terminal formed by the MR elements R 11 and R 12 and the output e 2 of the circuit having the three-terminal formed by the MR element R 21 and R 22 by the operation amplifier 4c. The second signal is generated by processing the output e 2 of the circuit having the three-terminal formed by the MR elements R 21 and R 22 and the output e 3 of the circuit having the three-terminal formed by the MR elements R 31 and R 32 by the operation amplifier 4d. The amplitude of the first signal is zero at a position on the N pole of the magnetic track, increases gradually and becomes to a maximum at a position of π /2 thereon. The amplitude is constant during a range of  1 , decreased from a position of 3π /2 and becomes to zero at a position on the S pole of the magnetic track 3-1. The amplitude of the second signal is a maximum at the position on the N pole of the magnetic track, constant during a range of  2 , decreases from the position of π /2, becomes to zero at a position π , increases to a maximum at the position of 3π /2 and maintained to a position of 2π . As shown in Fig. 13, an output terminal of the operation amplifier 4c is connected to one of input terminals of an AND circuit 10a, as well as an output terminal of the operation amplifier 4d is connected to one of input terminals of an AND circuit 10b. An output of sin in the output of sinewaves is applied to the other of input terminals of the AND circuit 10a, and an output of cos is applied to the other of input terminals of the AND circuit 10b. Output terminals of the AND circuits 10a and 10b are applied two input terminals of an OR circuit 11a to obtain a signal of absolute positions from an output of the OR circuit 11a by using an output of the operational amplifier 4c during the range of  1 and an output of the operational amplifier 4d during the range of  2 . As stated above, the first signal is obtained during the range  1 of form π/2 to 3π/2, and the second signal is obtained during the range  2 of from 0 to π/2 with respect to the magnetic track 3-1, so that the signal of the absolute positions can be obtained at any positions on the magnetic track. The output signal of the OR circuit 11a shown in Fig. 13 is applied to the CPU 104 shown in Fig. 9 to combine with the sinewave signal, similar to the first embodiment. In this second embodiment, also, signals of absolute positions of n bits can be obtained by forming n sets of "H bridge" consisting of two sets of circuits each having a three-terminal, applying each output signal to each of the operational amplifiers in Figure 13, and selecting one of the first and second signals through the AND circuit and OR circuit, respectively. In a further or third embodiment according to the present invention, as shown in Figs. 15 and 16, absolute patterns of ½ of the information using circulatory random number sequence codes are recorded in two recording tracks 3-4 and 3-5 on the magnetic drum 1, separated from each other in the axial direction of the magnetic drum 1, as well as absolute patterns of remaining ½ of the information are recorded in two recording tracks 3-6 and 3-7. According to this embodiment, a high resolution can be obtained without being increased in size of the MR element and reduced in sensitivity of the MR element. As shown in Fig. 16, the absolute patterns of ½ of the information are recorded on first and second magnetic tracks 3-4 and 3-5. The first magnetic track 3-4 has no signal recorded portions and signa! recorded portions, whereas the second magnetic track 3-5 has signal recorded portions corresponding in position to said no signal recorded portions on the first magnetic track 3-4, and has no signal recorded portions corresponding in position to signal recorded portions on the first magnetic track 3-4. The absolute patterns of remaining ½ of the information are recorded on the third and fourth magnetic tracks 3-6 and 3-7. As shown in Fig. 17, MR elements R 01 , R 03 , R 05 ----R 15 , and R 02 , R 04 , R 06 ----R 16 , and R 17 , R 19 , R 21--- R 31 , and R 18 , R 20 , R 22 ----R 32 are arranged facing the magnetic tracks 3-4, 3-5, 3-6 and 3-7, respectively. The MR elements R 01 and R 02 , R 03 and R 04 , R 05 and R 06 , ----and R 31 and R 32 are each form a circuit having a three-terminal. Neighboring MR elements in the MR elements R 01 to R 32 are separated from each other by λ/2. The MR elements R 17 and R 18 on the third and fourth magnetic tracks 3-6 and 3-7 are continued with the MR elements R 15 and R 16 on the first and second magnetic track 3-4 and 3-5, respectively. The absolute patterns recorded on the third and fourth magnetic tracks 3-6 and 3-7 are the same with that on the first and second magnetic tracks 3-4 and 3-5 and deviated from each other by four bits. The outputs obtained from the circuits each having the three-terminals when the rotary member is rotated are applied to a processing circuit of a differential amplifier to obtain absolute outputs. As shown in Fig. 18, according to the present invention, the magnetic tracks are divided and arranged side-by-side on the magnetic drum, so that the distance L between the MR elements at the center portion and the end portion of the magnetic sensor 2 corresponding to the magnetic tracks becomes small, so that d ≒ α and leakage magnetic flux can be sensed fully to obtain a stable output. A method of detecting the absolute positions will be explained with reference to Figs. 19 and 20. Fig. 19 shows a relation in position between the first and third magnetic tracks 3-4 and 3-6 and the absolute patterns, and bit informations "1" and "0" corresponding to each magnetic track. In this case, four bit informations are obtained from the first track 3-4, as well as four bit informations are obtained from the third magnetic track 3-6. If the three bit informations are detected at a time, positions at eight portions can be detected using 0 to 7. Specifically, as shown in Fig. 20, the positions can be detected as 4 0 1 2 5 3 7 6 if the three bit informations are detected at a time by shifting bit by bit the detecting portion of the 1 to n/2 bits in the rightward direction. In a yet further or fourth embodiment shown in Fig. 21, MR elements R 11 , R 21 , R 31 , --- R 161 are arranged corresponding to the magnetic track 3-1, and MR elements R 12 , R 22 , R 32 , --- R 162 are arranged corresponding to the magnetic track 3-2. The MR elements R 11 and R 12 , R 21 and R 22 , R 31 and R 32 , --- R 161 and R 162 are connected to each other to form circuits each having a three-terminal, and first terminals of the circuits at the side of the magnetic track 3-1 are connected commonly to (V) line of the power source, second terminals of the circuits at the side of the magnetic track 3-2 are connected commonly to (G) line of the same to obtain outputs e 1 to e 16 from output terminals of the circuits. According to this embodiment, the magnetic sensor portion and the power source portion are formed in a first layer, and wirings of the output terminals of the circuits are formed in a second layer, so that no through holes between the magnetic sensor portion and the power source is required to thereby enhancing the reliability of the absolute encoder. In a still further or fifth embodiment according to the present invention shown in Fig. 22, MR elements R 11 , R 21 , R 31 , --- R (n+1)1 are arranged corresponding to the magnetic track 3-1, and MR elements R 12 , R 22 , R 32 , --- R (n+1)2 are arranged corresponding to the magnetic track 3-2. The MR elements R 11 and R 12 , R 21 and R 22 , R 31 and R 33 , --- R (n+1)1 and R (n+1)2 are connected to each other to form circuits each having a three-terminal, and terminals of the circuits at the side of the magnetic track 3-1 are connected commonly to (V) line of the power source. If all of terminals of the circuits at the side of the magnetic track 3-2 are connected to (G) line of the power source, output lines of the circuits must lead across the (G) line. Accordingly, adjacent terminals of neighboring "H bridge" at the side of the magnetic track 3-2 are connected directly to each other and a common (G) line is lead therefrom. In this embodiment, the MR elements can be formed in one layer so that the reliability of the absolute encoder can be increased, though the terminals are increased in number. With the construction thus far described, according to the present invention, an encoder small in size and high in resolution can be realized. It is possible to obtain finely the value of absolute positions in one cycle of sinewave, so that sinewave having less distortion can be obtained to form an absolute encoder of increased resolution. Further, the MR elements can be disposed without being cross the power line, and the MR elements can be formed in one layer, because the terminals of the circuits adjacent to each other to be connected to the (G) line are connected to the (G) line through a common line to form an absolute encoder having a high reliability. Obviously, many modifications and variations of the present invention are possible within the scope of the appended claims.

Claims: An absolute encoder comprising a magnetic drum (1) having tracks (3) and having absolute patterns of circulatory random sequence codes thereon, and a pattern detector (2) for reading patterns on the tracks (3), characterised in that absolute patterns of circulatory random sequence codes are divided and recorded on first and second tracks (3-1, 3-2) arranged side-by-side on the magnetic drum (1) in the axial direction thereof, that an additional track (3-3) is provided on the magnetic drum (1) for generating sinewaves of two phases in synchronism with the reading of the absolute patterns on the first and second tracks (3-1, 3-2) and that an output is obtained by combining a value of an absolute position detected by the pattern detector (2) from the first and second tracks (3-1, 3-2) having the absolute patterns with a value of an absolute position obtained by operating information of sinewaves from the additional track (3-3). The absolute encoder as set forth in Claim 1, wherein a first signal (e 1 ) and a second signal (e 2 ) which are deviated in phase from each other by one half of pole pitch of magnetic recording are obtained from the first and second tracks (3-1, 3-2) having the absolute patterns by the pattern detector (2), one of the first and second signals is selected according to said value of the absolute position obtained by operating the sinewave informations, and said output is obtained by interpolating the value of the absolute position obtained by operating the sinewave informations to the selected signal. An absolute encoder as set forth in Claim 1, characterised in that the pattern detector (2) has a plurality of sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track (3), each of said plurality of sets has two magneto-resistive elements facing said first and second tracks (3-1, 3-2) respectively and connected with each other to form a plurality of circuits each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum (1), and each of said plurality of circuits has a terminal at the first track side connected to one terminal of an electric power source, a terminal at the second track side connected to another terminal of the electric power source, and an intermediate terminal between the two magneto-resistive elements of said circuit from which an output is obtained. An absolute encoder as set forth in Claim 1, characterised in that said pattern detector (2) has a plurality of sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track (3), each of said plurality of sets has two magneto-resistive elements facing said first and second tracks (3-1, 3-2) respectively and being connected with each other to form a plurality of circuits each having two magneto-resistive elements, and each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum, terminals at the first track side of odd number circuits and terminals at the second track side of even number circuits are connected to a first terminal of an electric power source, and terminals at the second track side of odd number circuits and terminals at the first track side of even number circuits are connected to a second terminal of said electric power source, and an output is obtained from an intermediate terminal between said two magneto-resistive elements in each of said plurality of circuits. An absolute encoder as set forth in Claim 1 characterised in that the pattern detector (2) has a first to (n+1)th sets of magneto-resistive elements (MR) which are deviated in position from each other by one half of recording pitch of said track (3), each of said plurality of sets has two magneto-resistive elements facing said first and second tracks (3-1, 3-2) respectively and connected with each other to form a plurality of circuits each having two magneto-resistive elements, and each of said plurality of circuits has a first track side and a second track side corresponding to said first and second track sides of said magnetic drum, terminals at the first track side of each of said plurality of circuits are connected to a first terminal of an electric power source, and terminals at the second track side of said first and (n+1)th circuits are connected to a second terminal of the electric power source, each terminal at the second track side of the second to nth circuits is directly connected to only the neighbouring terminal at the second track side of a neighbouring circuit and then connected to said second terminal of the electric power source through a common line, and an output is obtained from an intermediate terminal between said two magneto-resistive elements in each of said circuits.

Inventors: ICHIKAWA MISAO, OHNISHI KAZUO, SEKIGUCHI TOKIO, ICHIKAWA, MISAO, OHNISHI, KAZUO, SEKIGUCHI, TOKIO
Applicants: JAPAN SERVO, JAPAN SERVO CO. LTD.
Application year: 1993
Main classification: G01D5
IPC codes: G01D5