JP7664719B2 - Position Measuring Device - Google Patents

Description

This case relates to a rotary encoder and a position measuring device.

Conventionally, rotary encoders equipped with rotary scales are known (see, for example, Patent Documents 1 to 4).

JP 2014-178227 A JP 2016-138759 A JP 2018-059714 A JP 2019-168410 A

A rotary encoder is a position sensor that converts the amount of mechanical displacement in the rotational direction of the object being measured into a digital amount, and is broadly divided into incremental and absolute types. The incremental type integrates pulses generated in response to the angle of rotation from the measurement start point, while the absolute type measures the absolute angular position relative to the origin. The absolute type is convenient because it immediately determines the current angle (absolute position). 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.

In one aspect, the present invention aims to provide a rotary encoder and a position measuring device that can determine absolute position with a simple structure.

In one aspect, the rotary encoder is characterized by comprising: a rotary scale having a scale pattern formed by arranging a plurality of patterns on a first virtual circumference, 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 that is virtually drawn facing the first virtual circumference and has a center point located on a point on the rotation axis; and a transmitting unit that transmits a signal toward the receiving units via the scale pattern.

The rotary encoder may include three receivers arranged on the second virtual circumference at 120° intervals.

In addition, in the above rotary encoder, the receiving unit can be a light receiving element, and the transmitting unit can be a light emitting element.

Furthermore, in the above rotary encoder, the receiving unit can be a receiving coil, and the transmitting unit can be a transmitting coil.

In one aspect, the position measuring device includes a rotary encoder having a scale pattern formed by arranging a plurality of patterns on a first virtual circumference, a rotary scale that rotates around a rotation axis that passes through a position shifted from the center point of the first virtual circumference, three or more receiving units provided on a second virtual circumference that is virtually drawn facing the first virtual circumference with 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 is parallel to the rotation axis and views the first virtual circumference from a direction in which an extension line that passes through the center point of the first virtual circumference extends. The scale pattern includes an angle output calculation unit that calculates, for each receiving unit, a receiving unit arrangement angle that is the angle between a straight line connecting the 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 combining 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.

The position measuring device may include three receivers arranged on the second virtual circumference at 120° intervals.

In addition, in the above position measuring device, the receiving unit can be a light receiving element, and the transmitting unit can be a light emitting element.

Furthermore, in the above position measuring device, the receiving unit can be a receiving coil, and the transmitting unit can be a transmitting coil.

The absolute position can be determined using a simple structure.

FIG. 1 is a schematic diagram showing a schematic configuration of a rotary encoder according to an embodiment. FIG. 2 is a schematic diagram showing a schematic configuration of a rotary scale included in the rotary encoder according to the embodiment. Fig. 3A is an explanatory diagram of a first angle ANGLE ₁ , a second angle ANGLE ₂ , and a third angle ANGLE _3. Fig. 3B is an explanatory diagram of an angle (absolute position θ) between the scale origin and the first light receiving element as viewed from the rotation axis. FIG. 1 is an explanatory diagram illustrating a configuration of a position measuring device according to an embodiment; 4 is an explanatory diagram illustrating a two-phase sine wave calculated in the position measurement device according to the embodiment; FIG. FIG. 13 is a schematic diagram showing a schematic configuration of a rotary encoder according to a modified example.

The following describes the embodiment with reference to the drawings.

(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) is an explanatory diagram of a first angle ANGLE ₁ , a second angle ANGLE ₂ , and a third angle ANGLE _3, which are angle outputs calculated when detecting an absolute position by the rotary encoder 1 according to an embodiment. Fig. 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 a first light receiving element 4a corresponding to a first transmitter.

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, which correspond 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, which correspond to a transmitting unit and are provided in correspondence with the first light receiving element 4a to the third light receiving element 4c.

Referring to Figures 1 and 2, the rotary scale 2 is a disk-shaped member and has 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 object. 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 Figure 1 are one 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.

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 offset 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 that includes the first imaginary circumference R1. The rotary scale 2 is attached to the measurement object so that the rotation axis AX that passes through a position offset 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.

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 virtually drawn on one side of the rotary scale 2, facing 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.

Next, the first angle ANGLE ₁ , the second angle ANGLE ₂ , and the third angle ANGLE ₃ , which are angle outputs calculated when detecting the absolute position, will be described with reference to FIG. 3A. 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 circumference. 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 _n of the nth light receiving element is expressed by the general formula shown in Formula 1.
(Formula 1) ANGLE _n =θinc+a・sin(θ−αn)

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

Next, θ in Equation 1 will be explained with reference to FIG. 3(B). θ is the rotation center angle, which is the angle between the scale origin O as viewed from the rotation axis AX, which 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 center angle θ is the angle that is ultimately to be detected. The value range of the rotation center angle θ is 0°≦θ<360°.

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

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°. Also, 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 they may be unequal intervals. The number of light receiving elements may also 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 the light receiving elements are less susceptible to noise compared to when the light receiving elements are arranged at uneven intervals.

Referring again to FIG. 1, the first light-emitting element 5a, the second light-emitting element 5b, and the third light-emitting element 5c are arranged 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 arranged on a third imaginary circumference R3 that is virtually 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.

The diameters of the first virtual circumference R1, the second virtual circumference R2, and the third virtual circumference R3 are not subject to any particular restrictions and can be set as appropriate, provided they are within a range that allows the encoder to function.

Next, the position measuring device 100 according to the 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, and an absolute position calculation unit 30.

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, a signal for forming a second Lissajous from the second light receiving element 4b, and a signal for forming a third Lissajous from the third light receiving element 4c.

The angle output calculation unit 10 digitizes the signals received from each light receiving element with an A/D converter, and calculates the angle outputs, i.e., the first angle ANGLE ₁ , the second angle ANGLE _2, and the third angle ANGLE _3, with a calculator. These angle outputs are calculated based on each equation in which the values related to each light receiving element are reflected 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".

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

The two-phase sine wave calculation unit 20 calculates a two-phase sine wave X and a two-phase sine wave Y based on the first angle ANGLE ₁ , the second angle ANGLE ₂ , and the third angle ANGLE ₃ calculated by the angle output calculation unit 10. 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 differences between the angular velocities, that is, a first angle difference DIFANGLE ₁ , a second angle difference DIFANGLE ₂ , and a third angle difference DIFANGLE ₃ , based on the following equations 5-1 to 5-3.
(Formula 5-1)
DIFANGLE ₁ =ANGLE ₂ -ANGLE ₁
=√3a・sin(θ+150°)
(Equation 5-2)
DIFANGLE ₁ =ANGLE ₃ -ANGLE ₂
=√3a・sin(θ+270°)
(Equation 5-3)
DIFANGLE ₁ =ANGLE ₁ -ANGLE ₃
=√3a・sin(θ+30°)

By performing these calculations, the term of the incremental angle θinc, which is the first term in Equation 1, is cancelled out, and only the term of 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 (two-phase sine wave with a phase difference of 90°) with a period of 360° per revolution 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 Lissajous signals.

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.

Then, the absolute position calculation unit 30 can obtain the rotation central angle θ, i.e., the absolute position, by calculating the arctangent function of the obtained value Q.

As described above, the rotary encoder 1 and position measuring device 100 of this embodiment can determine the absolute position with a simple structure. In other words, the rotary encoder 1 and position measuring device 100 of this embodiment can determine the absolute position without equipping an absolute track with a complex scale pattern, etc.

The rotary scale 2 in this embodiment has a scale pattern 3 formed by arranging multiple 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.

The deviation S between the first center point Pc1 and the axis of rotation AX itself is not related to the calculation of the absolute position, but it is necessary to set this value 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 the eccentricity of the rotary scale 2 does not exceed the scale pitch. The peak-to-peak error caused by the eccentricity of the rotary scale 2 is expressed as 2 x atan (S/r).

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

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

The rotary encoder 1 of this embodiment is a light-transmitting type, but it can also be a reflective 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 used, which includes 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.

In addition, in this embodiment, the receiver is equipped with three light receiving elements, but the number of receivers is not limited to this, and four or more receivers can be equipped.

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

1, 50 rotary encoder 2 rotary scale 3 scale pattern 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 two-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 first center point

Claims (4)

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: The position measuring device according to claim 1, which is provided with three of the receiving units arranged on the second virtual circumference at 120° intervals. The position measuring device according to claim 1 or 2, wherein the receiving unit is a light receiving element and the transmitting unit is a light emitting element. The position measuring device according to claim 1 or 2, wherein the receiving unit is a receiving coil and the transmitting unit is a transmitting coil.

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