Absolute encoder

Abstract

An absolute encoder according to one embodiment of the present disclosure comprises: a first gear, a second gear, and a third gear, which are coaxially attached so as to rotate integrally with a rotating shaft, and each of which has a plurality of teeth on the outer periphery thereof; a magnet which is fixedly disposed so as to apply a magnetic flux in the radial direction to the first gear, the second gear, and the third gear; and a first detector, a second detector, and a third detector which are fixedly disposed between the magnet and the first gear, the second gear, and the third gear so as to face the first gear, the second gear, and the third gear, respectively, and which detect a change in magnetic flux density. The diameter of the third gear is smaller than the diameters of the first gear and the second gear, and the module of the third gear is larger than the modules of the first gear and the second gear.

Description

Absolute Encoder

[0001] The present invention relates to an absolute encoder.

[0002] A magnetic encoder is known that detects the rotational position of a gear by applying a radial magnetic flux to a gear attached to a rotating shaft and detecting a change in magnetic flux density at a position close to the outer periphery of the gear due to the magnetic flux being attracted to the gear teeth. An absolute encoder has also been proposed that detects the rotational positions of multiple gears with different numbers of teeth and more precisely calculates the rotational position of the rotating shaft from the phase difference between the teeth of the multiple gears. For example, Patent Document 1 discloses an absolute encoder with two gears, but it is being considered to detect the rotational position with even greater accuracy by providing three gears.

[0003] JP 2012-88276 A

[0004] In an absolute encoder with multiple gears, magnetic flux is attracted to the teeth of adjacent gears, which can cause crosstalk, making it impossible to accurately detect the phase of the teeth of the opposing gears. For this reason, the absolute encoder described in Patent Document 1 has multiple gears spaced apart. Increasing the number of gears can improve accuracy or resolution, but the axial width of the absolute encoder increases. For this reason, there is a demand for an absolute encoder that can suppress crosstalk between gears without increasing the size.

[0005] An absolute encoder according to one aspect of the present disclosure comprises a first gear, a second gear, and a third gear, each having a plurality of teeth on its outer periphery and attached coaxially to a rotating shaft so as to rotate integrally with the rotating shaft; magnets fixedly arranged to apply magnetic flux radially to the first gear, the second gear, and the third gear; and first detectors, second detectors, and third detectors fixedly arranged between the first gear, the second gear, and the third gear and the magnet so as to face the first gear, the second gear, and the third gear, respectively, and which detect changes in magnetic flux density, wherein the diameter of the third gear is smaller than the diameters of the first gear and the second gear, and the module of the third gear is larger than the modules of the first gear and the second gear.

[0006] Fig. 1 is a schematic diagram showing the configuration of an absolute encoder according to a first embodiment of the present disclosure. Fig. 2 is a schematic diagram showing the configuration of a detector of the absolute encoder of Fig. 1. Fig. 3 is a graph showing the waveform of a detected voltage in the detector of Fig. 2. Fig. 4 is a graph showing the waveform of a detected voltage when the spacing between sensor elements of the detector of Fig. 2 is halved. Fig. 5 is a graph showing the waveform of a detected voltage when the spacing between sensor elements of the detector of Fig. 2 is 3 / 2 times. Fig. 6 is a graph showing the waveform of a detected voltage when the spacing between sensor elements of the detector of Fig. 2 is doubled. Fig. 7 is a schematic diagram showing the configuration of an absolute encoder according to a second embodiment of the present disclosure.

[0007] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that in the embodiments described later, components similar to those in the embodiments described earlier will be designated by the same reference numerals, and redundant description will be omitted.

[0008] 1 is a schematic diagram showing the configuration of an absolute encoder 1 according to a first embodiment of the present disclosure. In the figure, the absolute encoder 1 detects the rotation speed of a rotation shaft S. The absolute encoder 1 includes a first gear 11, a second gear 12, a third gear 13, a magnet 21, a first detector 31, a second detector 32, a third detector 33, and a computing device 41.

[0009] The first gear 11, the second gear 12, and the third gear 13 are attached coaxially to the rotation axis S so as to rotate integrally with the rotation axis S. The gears 11, 12, and 13 are spur gears each having a plurality of teeth on their outer periphery. The gears 11, 12, and 13 are preferably made of a ferromagnetic material so that the teeth can attract the magnetic flux generated by the magnet 21.

[0010] If the diameters (diameters of the tip circles) of the first gear 11, the second gear 12, and the third gear 13 are D1, D2, and D3, the numbers of teeth of the first gear 11, the second gear 12, and the third gear 13 are N1, N2, and N3, and the modules of the first gear 11, the second gear 12, and the third gear 13 are M1, M2, and M3, then the relationships M1 = (D1 + 2) / N1, M2 = (D2 + 2) / N2, and M3 = (D3 + 2) / N3 hold. The number of teeth N2 of the second gear 12 is set smaller than the number of teeth N1 of the first gear 11, and the number of teeth N3 of the third gear 13 is set smaller than the number of teeth N2 of the second gear 12. In other words, the numbers of teeth N1, N2, and N3 of the first gear 11, the second gear 12, and the third gear 13 satisfy the relationship N1 > N2 > N3. As a result, the rotational position of the rotation axis S can be determined on a scale smaller than the tooth pitch using the vernier principle (nonius method) from the detection signals of the first detector 31, the second detector 32, and the third detector 33. Furthermore, the module M3 of the third gear 13 is set larger than the module M1 of the first gear 11 and the module M2 of the second gear 12. This reduces the error of the third detector 33, as will be explained in detail later.

[0011] The magnet 21 is fixedly disposed so as to apply magnetic flux in the radial direction to the first gear 11, the second gear 12, and the third gear 13. Therefore, the magnet 21 applies a higher density magnetic flux to the teeth of the gears 11, 12, and 13 that are located at opposing positions.

[0012] The first detector 31, the second detector 32, and the third detector 33 are fixedly disposed between the first gear 11, the second gear 12, and the third gear 13 and the magnet 21, radially facing the first gear 11, the second gear 12, and the third gear 13, respectively, and detect changes in magnetic flux density. The detectors 31, 32, and 33 are preferably disposed on the same plane perpendicular to the radial direction of the rotation axis S, to simplify mounting on the common board 34 and the internal structure of the common cover 35.

[0013] FIG. 2 shows the configuration of the first detector 31 as a representative example, but the second detector 32 and the third detector 33 may have similar configurations. The first detector 31 has a first pair of sensor elements 301 and 302 and a second pair of sensor elements 303 and 304. The circuit illustrated in FIG. 2 contemplates using magnetoresistive elements as the sensor elements 301, 302, 303, and 304. The first pair of sensor elements 301 and 302 are arranged side by side in the circumferential direction of the first gear 11 with a center-to-center distance equal to half the pitch of the teeth 101 of the gear 11. The second pair of sensor elements 303 and 304 are arranged side by side in the circumferential direction of the first gear 11 with a center-to-center distance equal to half the pitch of the teeth 101, similar to the first pair, but are offset in the circumferential direction by one-quarter of the pitch of the teeth 101. The first pair of sensor elements 301, 302 and the second pair of sensor elements 303, 304 are electrically connected in series, a constant voltage Vcc is applied, and the voltage at the intermediate connection point is output as a first detection signal V1 and a second detection signal V2. Because the positions of the first pair of sensor elements 301, 302 and the second pair of sensor elements 303, 304 are shifted by a quarter pitch, the first detection signal V1 and the second detection signal V2 become electrical signals having a phase difference of 90° in electrical angle.

[0014] The arithmetic unit 41 calculates the rotational position of the rotation shaft S from the detection signals of the first detector 31, the second detector 32, and the third detector 33. The arithmetic unit 41 is configured not only to count the number of teeth passed from the detection signals of the detectors 31, 32, and 33, but also to calculate the precise position within one tooth from the phase of the detection signals of the detectors 31, 32, and 33. As a specific example, by calculating the arc tangent (ATan(V1 / V2)) of the ratio of the two detection signals V1 and V2 of the detectors 31, 32, and 33, a detection value that changes in a two-peak sawtooth waveform within the angle range of one tooth can be obtained. The rotational position of the rotation shaft S can be determined with high accuracy by combining the phases of the sawtooth detection values ​​of the detectors 31, 32, and 33 that face the gears 11, 12, and 13 that have different numbers of teeth N1, N2, and N3. The arithmetic unit 41 can be configured to convert the detection signals V1 and V2 output from the detectors 31, 32, and 33 into digital values ​​and perform calculations. For example, the calculation device 41 may be configured as a calculation circuit having an integrated circuit that performs the above-mentioned calculations, or may be configured as a computer device that has memory, a processor, an input / output interface, etc. and executes a predetermined calculation program.

[0015] In the absolute encoder 1, the third gear 13, which has the largest module, is preferably disposed between the first gear 11 and the second gear 12, which have relatively small modules. It is generally known that when using gears with large modules and corresponding magnetic resistance elements, a wider gap can be provided between the gears and the element than when using gears with small modules.

[0016] Furthermore, in order to reduce the detection error of the first detector 31 and the second detector 32, the diameter D3 of the third gear 13 adjacent to the first gear 11 and the second gear 12 is smaller than the diameter D1 of the first gear 11 and the diameter D3 of the second gear 12. By reducing the diameter D3 of the third gear 13, the physical distance between the third gear 13 and the first detector 31 and the third detector 32 can be increased, thereby reducing magnetic crosstalk.

[0017] Furthermore, it is preferable that the module M1 of the first gear 11 and the module M2 of the second gear 12 are equal, and the module M3 of the third gear 13 is an even multiple of the module M1=M2 of the first gear 11 and the second gear 12. If the modules of the first gear 11 and the second gear 12 that generate magnetic flux changes that become noise components for the third detector 33 are an even multiple of the module M3 of the third gear 13 corresponding to the third detector 33, the phases of the teeth of the first gear 11 and the second gear 12 that are closest to the two paired sensor elements (301, 302) and (303, 304) of the third detector 33 will be equal. Therefore, the noise components due to the first gear 11 and the second gear 12 in the detection signals V1 and V2, which are the intermediate potentials of the two sensor elements 301 and 302, will be constant and will not distort the waveform of the detection signal from the third gear 13 of the third detector 33, and will not affect the calculation of the rotational position. 3 to 10 show changes in the waveform of the detection signal V1 when the center-to-center distance between the sensor elements 301 and 302 relative to the gear module is changed. When the center-to-center distance between the sensor elements 301 and 302 is set to a standard value of half the pitch of the teeth 101, the detection signal V1 is sinusoidal. However, changing the center-to-center distance between the sensor elements 301 and 302 distorts the waveform. When the center-to-center distance between the sensor elements 301 and 302 is set to an even multiple of the standard value, the detection signal V1 remains constant. Note that "even multiple" means within ±3% of the exact even multiple. If the error is within ±3%, the detection signal V1 can be considered substantially constant, providing sufficient crosstalk reduction.

[0018] As an example that satisfies the above requirements, the number of teeth N1 of the first gear 11 can be 512, the number of teeth N2 of the second gear 12 can be 511, the number of teeth N3 of the third gear 13 can be 126, the modules M1 and M2 of the first gear 11 and the second gear 12 can be 0.2, and the module M3 of the third gear 13 can be 0.8. In this case, the diameter D1 of the first gear 11 is 100.4 mm, the diameter D2 of the second gear 12 is 100.2 mm, and the diameter D3 of the third gear 13 is 98.8 mm.

[0019] Furthermore, if the number of teeth N1 of the first gear 11 is 512, the number of teeth N2 of the second gear 12 is 511, the number of teeth N3 of the third gear 13 is 128, the modules M1 and M2 of the first gear 11 and the second gear 12 are 0.2, and the module M3 of the third gear 13 is 0.78, then the diameter D1 of the first gear 11 is 100.4 mm, the diameter D2 of the second gear 12 is 100.2 mm, and the diameter D3 of the third gear 13 is 97.8 mm.

[0020] As described above, the absolute encoder 1 of this embodiment is provided with a third gear having a diameter D3 smaller than those of the first gear 11 and the second gear 12 and a module M3 larger than those of the first gear 11 and the second gear 12, thereby making it possible to suppress crosstalk between the gears 11, 12, and 13 without increasing the spacing between them, thereby making it possible to achieve both compactness and high resolution.

[0021] 12 is a schematic diagram showing the configuration of an absolute encoder 1A according to a second embodiment of the present disclosure. The absolute encoder 1A includes a first gear 11, a second gear 12, a third gear 13, a magnet 21, a first detector 31, a second detector 32, a third detector 33, and a computing device 41.

[0022] The absolute encoder 1A of this embodiment differs from the absolute encoder 1 of the first embodiment only in the arrangement of the first gear 11, the second gear 12, and the third gear 13. Specifically, in the absolute encoder 1A, the first gear 11, the second gear 12, and the third gear 13 are arranged in this order in the axial direction of the rotation shaft S, and the first gear 11 and the second gear 12 are arranged with a gap between them to prevent crosstalk, but the second gear 12 and the third gear 13 are arranged in close contact with each other with no gap between them.

[0023] In the absolute encoder 1A, conventional technology is used to suppress crosstalk between the first gear 11 and the second gear 12, and technology according to the present disclosure is used to suppress crosstalk between the second gear 12 and the third gear 13. In other words, the technology according to the present disclosure may be applied to suppress crosstalk only between some of the three or more gears.

[0024] The following supplementary notes are further disclosed regarding the above-described embodiment and modifications. (Supplementary Note 1) The absolute encoder (1, 1A) is attached coaxially with a rotating shaft (S) so as to rotate integrally with the rotating shaft (S), and includes a first gear (11), a second gear (12), and a third gear (13), each having a plurality of teeth on its outer periphery; a magnet (21) fixedly disposed so as to apply magnetic flux radially to the first gear (11), the second gear (12), and the third gear (13); and a first detector, a second detector, and a third detector fixedly disposed between the first gear (11), the second gear (12), and the third gear (13) and the magnet (21) so as to face the first gear (11), the second gear (12), and the third gear (13), respectively, and which detect changes in magnetic flux density, wherein the diameter of the third gear (13) is smaller than the diameters of the first gear (11) and the second gear (12), and the module of the third gear (13) is larger than the modules of the first gear (11) and the second gear (12).

[0025] (Supplementary Note 2) In the absolute encoder (1) of Supplementary Note 1, the third gear (13) may be disposed between the first gear (11) and the second gear (12).

[0026] (Supplementary Note 3) In the absolute encoder (1) of Supplementary Note 1 or 2, the first gear (11), the second gear (12), and the third gear (13) may be disposed in close contact with each other without any gaps.

[0027] (Supplementary Note 4) In the absolute encoder (1, 1A) of any one of Supplementary Notes 1 to 3, the module of the first gear (11) and the module of the second gear (12) may be equal, and the module of the third gear (13) may be an even multiple of the modules of the first gear (11) and the second gear (12).

[0028] (Supplementary Note 5) In the absolute encoder (1, 1A) of any one of Supplementary Notes 1 to 4, the first detector, the second detector, and the third detector may be arranged on the same plane.

[0029] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments described above. Various additions, substitutions, modifications, partial deletions, etc. are possible to these embodiments without departing from the gist of the present disclosure or the spirit of the present disclosure derived from the content of the claims and their equivalents. These embodiments can also be implemented in combination. For example, the same applies to the numerical values ​​and formulas used in the description of the above-described embodiments. For example, in the absolute encoder according to the present disclosure, the detector may be any detector capable of detecting magnetic flux density, and a detector using a Hall element or the like is also possible. The absolute encoder according to the present disclosure may also have four or more gears.

[0030] REFERENCE SIGNS LIST 1, 1A Absolute encoder 101 Teeth 11 First gear 12 Second gear 13 Third gear 21 Magnet 301, 302, 303, 304 Sensor element 31 First detector 32 Second detector 33 Third detector 34 Common substrate 35 Common cover 41 Calculation device S Rotation axis

Claims

1. An absolute encoder comprising: a first gear, a second gear, and a third gear, each having a plurality of teeth on its outer periphery, attached coaxially to a rotating shaft so as to rotate integrally with the rotating shaft; magnets fixedly disposed so as to apply magnetic flux radially to the first gear, the second gear, and the third gear; and first detectors, second detectors, and third detectors fixedly disposed between the first gear, the second gear, and the magnet and the magnet so as to face the first gear, the second gear, and the third gear, respectively, and which detect changes in magnetic flux density; wherein the diameter of the third gear is smaller than the diameters of the first gear and the second gear, and the module of the third gear is larger than the modules of the first gear and the second gear.

2. The absolute encoder according to claim 1, wherein the third gear is disposed between the first gear and the second gear.

3. An absolute encoder according to claim 1 or 2, wherein the first gear, the second gear, and the third gear are disposed in close contact with each other without any gaps.

4. An absolute encoder according to any one of claims 1 to 3, wherein the module of the first gear and the module of the second gear are equal, and the module of the third gear is an even multiple of the modules of the first gear and the second gear.

5. An absolute encoder according to any one of claims 1 to 4, wherein the first detector, the second detector and the third detector are arranged on the same plane.

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