Position measuring device

Abstract

To determine an absolute position with a simple structure.SOLUTION: A rotary encoder includes: a rotary scale having a scale pattern formed by arranging a plurality of patterns on a first virtual circle, the rotary scale rotating around the axial line of rotation that passes through a position dislocated from the central point of the first virtual circle; at least three reception units provided on a second virtual circle drawn virtually as opposed to the first virtual circle, the central point of which being located on the axial line of rotation; and a transmission unit for transmitting a signal to the reception units through the scale pattern.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present case relates to a rotary encoder and a position measuring device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, rotary encoders equipped with a rotary scale are known (see, for example, Patent Documents 1 to 4). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-178227 A [Patent Document 2] JP 2016-138759 A [Patent Document 3] JP 2018-059714 A [Patent Document 4] JP 2019-168410 A Summary of the Invention [Problem to be solved by the invention]

[0004] A rotary encoder is a position sensor that converts the amount of mechanical displacement in the rotational direction of an object to be measured into a digital amount, and is broadly divided into incremental and absolute types. The incremental type integrates pulses generated in response to the rotation angle from the measurement start point, while the absolute type measures the absolute angular position relative to the origin. The absolute type is convenient in that the current angle (absolute position) is immediately known. However, conventional absolute type rotary encoders have a more complex structure than incremental types, as they must be equipped with an absolute track with a complex scale pattern, etc.

[0005] According to one aspect, an object of the present invention is to provide a rotary encoder and a position measuring device that are capable of determining an absolute position with a simple structure. [Means for solving the problem]

[0006] In one aspect, a rotary encoder is characterized in that it comprises a rotary scale having a scale pattern formed by arranging a plurality of patterns on a first virtual circumference and rotating around a rotation axis passing through a position shifted from the center point of the first virtual circumference, three or more receiving units provided on a second virtual circumference drawn virtually opposite the first virtual circumference and having a center point at a point located on the rotation axis, and a transmitting unit that transmits a signal toward the receiving units via the scale pattern.

[0007] The rotary encoder may include three of the receiving units arranged on the second imaginary circumference at intervals of 120°.

[0008] In the above rotary encoder, the receiving portion may be a light receiving element, and the transmitting portion may be a light emitting element.

[0009] Furthermore, in the rotary encoder, the receiving section may be a receiving coil, and the transmitting section may be a transmitting coil.

[0010] In one aspect, a position measuring device includes a rotary encoder including: a rotary scale having a scale pattern formed by arranging a plurality of patterns on a first imaginary circumference, the rotary scale rotating about a rotation axis passing through a position shifted from a center point of the first imaginary circumference; three or more receiving units provided on a second imaginary circumference that is virtually drawn facing the first imaginary circumference and has a center point at a point located on the rotation axis; and a transmitting unit that transmits a signal toward the receiving units via the scale pattern; and a rotary encoder that transmits the signal toward the receiving units via the scale pattern when the first imaginary circumference is viewed from a direction in which an extension line that is parallel to the rotation axis and passes through the center point of the first imaginary circumference extends. the scale pattern includes an angle output calculation unit that calculates, for each receiving unit, a receiving unit arrangement angle that is an angle between a straight line connecting a position of the receiving unit projected on a virtual plane on which the first virtual circumference is drawn and the center point of the first virtual circumference, and a straight line connecting a scale origin set on the scale pattern and the center point of the first virtual circumference, a two-phase sine wave calculation unit that calculates a two-phase sine wave by a combination of the receiving unit arrangement angles calculated by the angle output calculation unit, and an absolute position calculation unit that calculates an absolute position based on the two-phase sine wave calculated by the two-phase sine wave calculation unit.

[0011] The position measuring device may include three of the receiving units arranged on the second imaginary circumference at intervals of 120°.

[0012] In the above position measuring device, the receiving section may be a light receiving element, and the transmitting section may be a light emitting element.

[0013] Furthermore, in the above position measuring device, the receiving unit may be a receiving coil, and the transmitting unit may be a transmitting coil. Effect of the Invention

[0014] The absolute position can be obtained with a simple structure. [Brief description of the drawings]

[0015] [Figure 1]FIG. 1 is a schematic diagram showing a schematic configuration of a rotary encoder according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing a schematic configuration of a rotary scale included in the rotary encoder according to the embodiment. [Diagram 3] Fig. 3(A) is an explanatory diagram of the first angle ANGLE1, the second angle ANGLE2, and the third angle ANGLE3. Fig. 3(B) is an explanatory diagram of the angle (absolute position θ) between the scale origin and the first light receiving element as viewed from the rotation axis. [Figure 4] FIG. 1 is an explanatory diagram illustrating a configuration of a position measuring device according to an embodiment; [Diagram 5] 4 is an explanatory diagram illustrating a two-phase sine wave calculated in the position measurement device according to the embodiment. FIG. [Figure 6] FIG. 13 is a schematic diagram showing a schematic configuration of a rotary encoder according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment will be described with reference to the drawings.

[0017] (Embodiment) First, the schematic configuration of a rotary encoder 1 according to an embodiment will be described with reference to Fig. 1 to Fig. 3(B). Fig. 1 is a schematic diagram showing the schematic configuration of a rotary encoder 1 according to an embodiment. Fig. 2 is a schematic diagram showing the schematic configuration of a rotary scale 2 included in the rotary encoder 1 according to an embodiment. Fig. 3(A) shows a first angle ANGLE, which is an angle output calculated when detecting an absolute position by the rotary encoder 1 according to an embodiment. 1 , second angle ANGLE 2 and the third angle ANGLE 3 3(B) is an explanatory diagram of the angle (absolute position θ) between the scale origin O as viewed from the rotation axis AX and the first light receiving element 4a corresponding to the first transmitting portion.

[0018] The rotary encoder 1 of the embodiment includes a rotary scale 2, and a first light receiving element 4a, a second light receiving element 4b, and a third light receiving element 4c, each of which corresponds to a receiving unit. The rotary encoder 1 also includes a first light emitting element 5a, a second light emitting element 5b, and a third light emitting element 5c, each of which corresponds to a transmitting unit and is provided in correspondence with the first light receiving element 4a to the third light receiving element 4c.

[0019] 1 and 2, the rotary scale 2 is a disk-shaped member, and includes a scale pattern 3 formed by arranging a plurality of patterns 3a on a first imaginary circumference R1. The radius of the first imaginary circumference R1 is r. The rotary scale 2 is attached to a rotating shaft of a measurement target. The rotary encoder 1 of this embodiment is a light-transmitting type. Therefore, the patterns 3a are formed as slits. Note that the patterns 3a shown in FIG. 1 are only an example, and the number of patterns can be increased or decreased as appropriate depending on the resolution required for the rotary encoder 1. A scale origin O is set on the scale pattern 3. The scale origin O can be set at any position.

[0020] The center point of the first imaginary circumference R1 drawn on the rotary scale 2 is Pc1 (hereinafter referred to as the "first center point Pc1"), but the rotary scale 2 rotates around a rotation axis AX that passes through a position shifted from the first center point Pc1. Here, the rotation axis AX is a line perpendicular to the rotary scale 2, which is a disk-shaped member, in other words, a line perpendicular to a plane including the first imaginary circumference R1. The rotary scale 2 is attached to the measurement object such that the rotation axis AX that passes through a position shifted from the first center point Pc1 coincides with the rotation axis of the measurement object. In this embodiment, the amount of deviation (eccentricity) between the first center point Pc1 and the rotation axis AX is S.

[0021] As shown in Fig. 1, the first light receiving element 4a, the second light receiving element 4b, and the third light receiving element 4c are arranged on a second imaginary circumference R2 that is imaginarily drawn on one side of the rotary scale 2 so as to face the first imaginary circumference R1. In other words, the first light receiving element 4a, the second light receiving element 4b, and the third light receiving element 4c are arranged on the second imaginary circumference R2 that is drawn in a plane parallel to the rotary scale 2. The center point of the second imaginary circumference R2 is Pc2 (hereinafter referred to as the "second center point Pc2"). The second center point Pc2 is located on the rotation axis AX.

[0022] Next, referring to FIG. 3A, the first angle ANGLE, which is an angle output calculated when detecting the absolute position, is 1 , second angle ANGLE 2 and the third angle ANGLE 3 The following will explain this. Since the first center point Pc1, which is the center of the scale pattern 3, is misaligned with the rotation axis AX of the rotary scale 2, an eccentricity error occurs in the angle output of each of the light-receiving elements 4a to 4c. This eccentricity error is a periodic error with a period of one revolution. The phase of this eccentricity error depends on the arrangement of each of the light-receiving elements 4a to 4c. Therefore, these angle outputs can be expressed as the sum of the incremental angle θinc and the eccentricity error (amplitude a, arrangement angle αn of the light-receiving element) based on the signal of each light-receiving element. Therefore, the angle output ANGLE of the nth light-receiving element n is represented by the general formula shown in Equation 1. (Formula 1) ANGLE n =θinc+a·sin(θ-αn)

[0023] In equation 1, a is the amplitude of the eccentricity error in the rotary encoder 1, and is approximately expressed by equation 2 below.

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[0024] Next, θ in Equation 1 will be described with reference to Fig. 3(B). θ is the rotation central angle, which is the angle between the scale origin O seen from the rotation axis AX that is the rotation center of the rotary scale 2, and the first light receiving element 4a set at the reference position, and corresponds to the absolute position. In other words, the rotation central angle θ is the angle that is ultimately desired to be detected. The value range of the rotation central angle θ is 0°≦θ<360°.

[0025] Here, since the rotary scale 2 in this embodiment is based on an incremental method in which the first virtual circumference R1 is divided into a predetermined number of parts and the patterns 3a are arranged (see FIG. 1), the incremental angle θinc can be expressed by the following equation 3 using the rotation central angle θ. (Equation 3) θinc=(θ,360° / div) Here, div is the number of patterns 3a in the scale pattern 3, that is, the number (division number) of scale patterns 3 per revolution. The range of the incremental angle θinc is 0°≦θinc<360° / div.

[0026] Next, αn in formula 1 will be described. The first light receiving element 4a, the second light receiving element 4b, and the third light receiving element 4c are arranged at intervals in the circumferential direction of the second virtual circumference R2. Here, as shown in FIG. 3B, the position where the first light receiving element 4a is provided is set as the reference position, and the positions of the second light receiving element 4b and the third light receiving element 4c are indicated by the angle (arrangement angle of the light receiving element) αn with respect to the line segment connecting the second center point Pc2 and the first light receiving element 4a. Therefore, in this embodiment, the arrangement angle α1 of the first light receiving element 4a is α1=0°. Moreover, the arrangement angle α2 of the second light receiving element 4b is α2=120°, and the arrangement angle α3 of the third light receiving element 4c is α3=240° (=-120°). In this embodiment, one circumference of 360° is divided into three equal parts, but the intervals may be unequal. The number of light receiving elements may be four or more, and in this case, the light receiving elements may be spaced equally or unevenly. By spaced equally as in this embodiment, the weighting of the angle output of each light receiving element is uniform when calculating the angle output described later, so that the light receiving elements are less susceptible to the influence of noise compared to the case where the light receiving elements are arranged at uneven intervals.

[0027] 1 again, the first light-emitting element 5a, the second light-emitting element 5b, and the third light-emitting element 5c are disposed on the opposite side of the rotary scale 2 from the first light-receiving element 4a, the second light-receiving element 4b, and the third light-receiving element 4c. The first light-emitting element 5a, the second light-emitting element 5b, and the third light-emitting element 5c are disposed on a third imaginary circumference R3 that is imaginarily drawn in a plane parallel to the rotary scale 2. The center point of the third imaginary circumference R3 is Pc3 (hereinafter referred to as the "third center point Pc3"). The third center point Pc3, like the second center point Pc2, is located on the rotation axis AX.

[0028] The diameters of the first imaginary circumference R1, the second imaginary circumference R2, and the third imaginary circumference R3 are not subject to any particular restrictions and can be set appropriately as long as they are within a range in which the encoder can function.

[0029] Next, a position measuring device 100 according to an embodiment will be described with reference to Fig. 4. The position measuring device 100 includes the above-mentioned rotary encoder 1, an angle output calculation unit 10, a two-phase sine wave calculation unit 20, an absolute position calculation unit 30, and the like.

[0030] The angle output calculation unit 10 includes an amplifier, an A / D converter, a calculator, etc. The angle output calculation unit 10 receives a signal for forming a first Lissajous from the first light receiving element 4a, receives a signal for forming a second Lissajous from the second light receiving element 4b, and receives a signal for forming a third Lissajous from the third light receiving element 4c.

[0031] The angle output calculation unit 10 digitizes the signals received from each light receiving element using an A / D converter, and outputs the angle using a calculator, i.e., the first angle ANGLE 1 , second angle ANGLE 2 and the third angle ANGLE 3 These angle outputs are calculated based on each equation that reflects the values ​​related to each light receiving element in the above-mentioned equation 1. In each of the following equations, the position of the scale origin O is set so that the eccentricity error in the first light receiving element 4a becomes "0".

[0032] A first angle ANGLE calculated based on a signal from the first light receiving element 4a 1 is calculated using the following formula 4-1. (Formula 4-1) ANGLE 1 =θinc+a·sin(θ) A second angle ANGLE calculated based on the signal from the second light receiving element 4b 2 is calculated using the following formula 4-2. (Formula 4-2) ANGLE 2 =θinc+a·sin(θ+120°) A third angle ANGLE calculated based on the signal from the third light receiving element 4c 3 is calculated using the following formula 4-3. (Formula 4-3) ANGLE 3 =θinc+a·sin(θ-120°)

[0033] The two-phase sine wave calculation unit 20 calculates the first angle ANGLE 1 , second angle ANGLE 2 and the third angle ANGLE 3 In order to calculate the two-phase sine wave X and the two-phase sine wave Y, the two-phase sine wave calculation unit 20 first calculates the difference between the angular velocities, that is, the first angle difference DIFANGLE, based on the following Equations 5-1 to 5-3. 1 , the second angle difference DIFANGLE 2 and the third angle difference DIFANGLE 3 Calculate. (Formula 5-1) DIFANGLE 1 =ANGLE 2 -ANGLE 1 =√3a sin(θ+150°) (Formula 5-2) DIFANGLE 1 =ANGLE 3 -ANGLE 2 =√3a·sin(θ+270°) (Formula 5-3) DIFANGLE 1 =ANGLE 1 -ANGLE 3 =√3a sin(θ+30°)

[0034] By performing these calculations, the term for the incremental angle θinc, which is the first term in Equation 1, is cancelled out, and only the term for the eccentricity error, which is the second term in Equation 1, remains, which become a three-phase sine wave with a phase difference of 120°. By performing a three-phase to two-phase conversion on the three-phase sine wave thus obtained, a Lissajous signal with a period of 360° (two-phase sine wave with a phase difference of 90°) can be obtained, as shown in FIG. 5. Here, the three-phase to two-phase conversion is performed by a matrix conversion shown in the following Equation 6. X and Y obtained by Equation 6 are the Lissajous signal.

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[0035] The absolute position calculation unit 30 calculates an absolute position, i.e., a rotation central angle θ, based on the two-phase sine wave X and the two-phase sine wave Y calculated by the two-phase sine wave calculation unit 20. The absolute position calculation unit 30 sets the two-phase sine wave X to cos θ and the two-phase sine wave Y to sin θ, and performs a calculation based on Equation 7.

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[0036] Then, the absolute position calculation section 30 can obtain the arctangent function of the obtained value Q to obtain the rotation central angle θ, that is, the absolute position.

[0037] As described above, the rotary encoder 1 and position measuring device 100 of this embodiment can obtain an absolute position with a simple structure. In other words, the rotary encoder 1 and position measuring device 100 of this embodiment can obtain an absolute position without providing an absolute track with a complex scale pattern or the like.

[0038] The rotary scale 2 in this embodiment has a scale pattern 3 formed by arranging a plurality of patterns 3a on a first imaginary circumference R1. The rotary scale 2 rotates around a rotation axis AX that passes through a position shifted from a first center point Pc1 of the first imaginary circumference R1. By processing a signal obtained by driving such a rotary scale 2, it is possible to obtain an absolute position with a simple structure.

[0039] The deviation S between the first center point Pc1 and the rotation axis AX does not affect the calculation of the absolute position, but its value must be set within an appropriate range when designing the rotary encoder 1. The deviation S depends on the arrangement of each light-receiving element, but can be set within a range in which the peak-to-peak error caused by eccentricity of the rotary scale 2 does not exceed the scale pitch. The peak-to-peak error caused by eccentricity of the rotary scale 2 is expressed as 2×atan(S / r).

[0040] The amplitude a of the eccentricity error is expressed as in the above formula 2 using the scale radius r, i.e., the radius r of the first imaginary circumference R1, and the deviation amount S. Furthermore, the scale pitch is expressed by the following formula 8 using the number div of patterns 3a in one revolution of the scale pattern 3. (Formula 8) scale pitch=2π / div

[0041] As a result, the allowable range of the deviation amount S can be set to the range shown in the following formula 9. (Formula 9) a <scale pitch ⇔S<2π / div

[0042] The rotary encoder 1 of this embodiment is a light transmission type, but it can also be a reflection type in which light irradiated by a light emitting element is reflected by a rotary scale and received by a light receiving element. Also, as shown in FIG. 6, an electromagnetic rotary encoder 50 may be provided with transmitting coils 15a to 15c as a transmitting section and receiving coils 14a to 14c as a receiving section. In the rotary encoder 50, the first light receiving element 4a, the second light receiving element 4b, and the third light receiving element 4c of the rotary encoder 1 are replaced with the first receiving coil 14a, the second receiving coil 14b, and the third receiving coil 14c. In the rotary encoder 50, the first transmitting coil 15a, the second transmitting coil 15b, and the third transmitting coil 15c of the rotary encoder 1 are replaced with them. Even with such a rotary encoder 50, the absolute position can be obtained in the same manner as the rotary encoder 1.

[0043] Furthermore, in this embodiment, three light receiving elements are provided as the receiving section, but the number of receiving sections is not limited to this, and four or more receiving sections may be provided.

[0044] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0045] 1,50 Rotary Encoder 2 Rotary Scale 3 Scale Patterns 3 Slit 4a First light receiving element 4b Second light receiving element 4c Third light receiving element 5a First light emitting element 5b Second light-emitting element 5c Third light-emitting element 10 Angle output calculation section 14a First receiving coil 14b Second receiving coil 14c Third receiving coil 15a First transmitting coil 15b Second transmitting coil 15c Third transmitting coil 20 2-phase sine wave calculation section 30 Absolute position calculation section 100 Position Measuring Device AX Rotation axis R1 First virtual circumference R2 Second virtual circumference Le extension line Pc1 1st center point

Claims

1. a rotary scale having a scale pattern formed by arranging a plurality of patterns on a first imaginary circumference, the rotary scale rotating about a rotation axis passing through a position shifted from a center point of the first imaginary circumference; three or more receiving units provided on a second imaginary circumference that is virtually drawn to face the first imaginary circumference and has a center point at a point located on the rotation axis line; a transmitter that transmits a signal toward the receiver via the scale pattern; an angle output calculation unit that calculates, when the first virtual circumference is viewed in a direction along which an extension line that is parallel to the rotation axis and passes through the center point of the first virtual circumference extends, for each of the receiving units, a receiving unit arrangement angle that is an angle between a straight line that connects a position of the receiving unit projected on a virtual plane on which the first virtual circumference is drawn and the center point of the first virtual circumference, and a straight line that connects a scale origin set on the scale pattern and the center point of the first virtual circumference; a two-phase sine wave calculation unit that calculates a two-phase sine wave by a combination of the receiver arrangement angles calculated by the angle output calculation unit; an absolute position calculation unit that calculates an absolute position based on the two-phase sine wave calculated by the two-phase sine wave calculation unit; With the angle output calculation unit calculates, for each of the receiving units, the receiving unit arrangement angle expressed as the sum of an incremental angle, which is a value obtained by dividing 360°, which is an angle of one revolution of the first virtual circumference, by the number of the plurality of patterns, and an eccentricity error of the target receiving unit; A position measuring device comprising:

2. 2. The position measuring device according to claim 1, further comprising three of the receiving units arranged on the second virtual circumference at intervals of 120 degrees.

3. 3. The position measuring device according to claim 1, wherein the receiving portion is a light receiving element, and the transmitting portion is a light emitting element.

4. 3. The position measuring device according to claim 1, wherein the receiving unit is a receiving coil, and the transmitting unit is a transmitting coil.

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