JP2024027726A - Absolute encoder, absolute encoder angular deviation correction device, and absolute encoder angular deviation correction method - Google Patents

Abstract

An object of the present invention is to suppress the maximum value of angular deviation regardless of the position of a rotating body at the time of startup. The absolute encoder includes an angle information generating section that generates first angle information indicating an absolute angle of a first rotating body, a second angle information generator that generates first angle information indicating an absolute angle of a first rotating body, and a second rotating body that has a rotation period different from that of the first rotating body. the second rotation generated by rotating the first rotating body until the second rotating body returns to the starting angle based on second angle information indicating an absolute angle of the rotating body and a predetermined coefficient; a second rotating body offset value determination unit that determines a second rotating body offset value to be corrected so that a second rotating body angular deviation indicating an angular deviation of the body is small; a correction unit that corrects the second rotating body angular deviation, and the coefficient is determined based on the second rotating body angular deviation. [Selection diagram] Figure 9

Description

The present invention relates to an absolute encoder, an absolute encoder angular deviation correction device, and an absolute encoder angular deviation correction method.

2. Description of the Related Art Conventionally, rotary encoders have been known that are used in various control devices to detect the position and angle of a rotating shaft of a motor or the like. As a technology related to such a rotary encoder, for example, the following control device is known (see, for example, Patent Document 1). This control device corrects an angle detection value by an encoder that detects a rotation angle of a rotating body using a correction amount corresponding to a detection error due to an axis deviation. This control device compares the corrected angle detection value with a position command to determine a positional deviation, and controls the motor so that the positional deviation approaches zero.

Japanese Patent Application Publication No. 2010-148248

By the way, rotary encoders include incremental encoders that detect relative angles and absolute encoders that detect absolute angles (hereinafter referred to as "absolute encoders"). The absolute encoder uses the angle of the rotating body at startup as a reference, and detects the angle of the rotating body based on the amount of rotation from that reference.

However, in the absolute encoder, an error (hereinafter referred to as "angular deviation") may be included between the detected angle of the rotating body and the actual angle of the rotating body due to manufacturing variations or the like. Further, in general, an absolute encoder uses the angle of the rotating body at startup (hereinafter referred to as "starting angle") as a reference, that is, a zero point, and detects the subsequent angle of the rotating body. At this time, the angular deviation at the zero point is regarded as 0 [deg] in terms of detection. For this reason, in conventional absolute encoders, the standard for the angular deviation of the rotating body differs depending on the starting angle of the rotating body. ) changes.

The present invention takes the above-mentioned problem as an example, and aims to provide an absolute encoder that suppresses the maximum value of the angular deviation regardless of the angle of the rotating body at the time of startup.

In order to achieve the above object, an absolute encoder according to the present invention includes: an angle information generation section that generates first angle information indicating an absolute angle of a first rotating body; is to rotate the first rotating body until the second rotating body returns to the starting angle based on second angle information indicating the absolute angle of the second rotating body having a different rotation period and a predetermined coefficient. a second rotating body offset value determining unit that determines a second rotating body offset value to be corrected so that a second rotating body angular deviation indicating an angular deviation of the second rotating body generated in the second rotating body; a correction unit that corrects the second rotating body angular deviation using a body offset value, and the coefficient is determined based on the second rotating body angular deviation.

According to the absolute encoder according to the present invention, the maximum value of the angular deviation can be suppressed regardless of the position of the rotating body at the time of startup.

1 is a perspective view schematically showing the configuration of an absolute encoder according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing the configuration of the absolute encoder shown in FIG. 1 with a shield plate removed. FIG. 3 is a perspective view schematically showing the configuration of the absolute encoder shown in FIG. 2 with the case removed. FIG. 4 is a plan view schematically showing the configuration of the absolute encoder shown in FIG. 3 with an angle sensor support substrate removed. FIG. 4 is a view of the angle sensor support substrate shown in FIG. 3 viewed from the bottom side. 5 is a sectional view taken along line AA of the absolute encoder shown in FIG. 4. FIG. 5 is a cross-sectional view taken along line BB of the absolute encoder shown in FIG. 4. FIG. 5 is a sectional view taken along the line CC of the absolute encoder shown in FIG. 4. FIG. 2 is a block diagram schematically showing the functional configuration of a microcomputer included in the absolute encoder shown in FIG. 1. FIG. 2 is a graph showing an example of angular deviation in one rotation of the main shaft in the absolute encoder 2 shown in FIG. 1. FIG. 2 is a graph showing an example of angular deviation when the main axis reference is 72 [deg] in the absolute encoder 2 shown in FIG. 1. FIG. 2 is a graph showing an example of a waveform of an angular deviation after correction when the reference of the main axis in the absolute encoder shown in FIG. 1 is 0 [deg]. 2 is a graph showing an example of a waveform of an angular deviation after correction when the main axis reference in the absolute encoder shown in FIG. 1 is 72 [deg]. 2 is a graph showing an example of a waveform of an angular deviation in the main shaft that rotates 10 times per revolution of the sub-shaft in the absolute encoder shown in FIG. 1. FIG. 2 is a flowchart showing an example of an offset value determination process for correcting angular deviation in the absolute encoder shown in FIG. 1. FIG. FIG. 7 is a diagram illustrating an example of Fourier coefficients obtained from a waveform showing a variation in the angular deviation component of sin1θ. FIG. 6 is a diagram illustrating an example of Fourier coefficients obtained from a waveform showing a variation in an angular deviation component of cos1θ. FIG. 7 is a diagram showing an example of a waveform representing a variation in amplitude change of an angular deviation component of sin1θ. FIG. 7 is a diagram showing an example of a waveform representing a variation in amplitude change of an angular deviation component of cos1θ. FIG. 3 is a diagram showing an example of a waveform representing a multi-rotation angular deviation of an angular deviation component of sin1θ. FIG. 3 is a diagram showing an example of a waveform representing a multi-rotation angular deviation of an angular deviation component of cos1θ.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An absolute encoder, an absolute encoder angular deviation correction device, and an absolute encoder angular deviation correction method according to embodiments of the present invention will be described below with reference to the drawings.

Embodiments of the present invention will be described below with reference to the drawings. In each of the embodiments and modified examples described below, the same or equivalent components and members are denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. Further, the dimensions of members in each drawing are shown enlarged or reduced as appropriate to facilitate understanding. Further, in each drawing, some members that are not important for explaining the embodiments are omitted. Further, in the drawings, the gears are shown with the shape of the tooth portion omitted. Also, although ordinal terms such as first, second, etc. are used to describe various components, these terms are used only to distinguish one component from another; The components are not limited by this. Note that the present invention is not limited to this embodiment.

FIG. 1 is a perspective view schematically showing the configuration of an absolute encoder 2 according to an embodiment of the present invention. FIG. 2 is a perspective view schematically showing the configuration of the absolute encoder 2 with the shield plate 7 removed. In FIG. 2, the case 4 of the absolute encoder 2 and the angle sensor support substrate 5 are shown transparently. FIG. 3 is a perspective view schematically showing the configuration of the absolute encoder 2 with the case 4 removed. In FIG. 3, the angle sensor support substrate 5 of the absolute encoder 2 is shown transparently. FIG. 4 is a plan view schematically showing the configuration of the absolute encoder 2 with the angle sensor support substrate 5 removed.

FIG. 5 is a plan view of the angle sensor support substrate 5 viewed from below. FIG. 6 is a cross-sectional view of the absolute encoder 2 taken along the line AA. FIG. 7 is a BB sectional view of the absolute encoder 2. FIG. 8 is a cross-sectional view of the absolute encoder 2 taken along the line CC. FIG. 9 is a block diagram schematically showing the functional configuration of the microcomputer 121 included in the absolute encoder 2. The structure of the absolute encoder 2 will be specifically explained below.

In this embodiment, for convenience of explanation, the absolute encoder 2 will be explained based on an XYZ orthogonal coordinate system. The X-axis direction corresponds to the horizontal left-right direction, the Y-axis direction corresponds to the horizontal front-back direction, and the Z-axis direction corresponds to the vertical up-down direction. The Y-axis direction and the Z-axis direction are each perpendicular to the X-axis direction. In this embodiment, the X-axis direction is also referred to as left side or right side, the Y-axis direction is also referred to as front side or rear side, and the Z-axis direction is also referred to as upper side or lower side. In the posture of the absolute encoder 2 shown in FIGS. 1 and 2, the front side in the X-axis direction is the left side, and the back side in the X-axis direction is the right side. In addition, in the posture of the absolute encoder 2 shown in FIGS. 1 and 2, the front side in the Y-axis direction is the front side, and the back side in the Y-axis direction is the rear side. In addition, in the posture of the absolute encoder 2 shown in FIGS. 1 and 2, the upper side in the Z-axis direction is the upper side, and the lower side in the Z-axis direction is the lower side. A state seen from above in the Z-axis direction is called a plan view, a state seen from the front in the Y-axis direction is called a front view, and a state seen from the left side in the X-axis direction is called a side view. The notation of such directions does not limit the usage posture of the absolute encoder 2, and the absolute encoder 2 can be used in any orientation.

The absolute encoder 2 is, for example, an absolute rotary encoder that specifies and outputs the rotation angle of the main shaft 1a of the motor 1 over multiple rotations. In this embodiment, the absolute encoder 2 is provided at the upper end of the motor 1 in the Z-axis direction. In this embodiment, the absolute encoder 2 has a substantially rectangular shape in plan view, and has a thin horizontally elongated rectangular shape in the vertical direction, which is the extending direction of the main shaft 1a, in front and side views. . That is, the absolute encoder 2 has a flat rectangular parallelepiped shape that is longer in the horizontal direction than in the vertical direction.

The absolute encoder 2 includes a hollow rectangular cylindrical case 4 that houses an internal structure. The case 4 includes a plurality of ( For example, four outer wall portions 4a are included, and the upper end portion is opened.

The shield plate 7 is a rectangular plate member. The shield plate 7 closes the case 4 by being fixed to the upper end of the outer wall 4a with screws. The shield plate 7 is a plate-shaped member provided between the angle sensors Sp, Sq, Sr and the outside of the absolute encoder 2 in the axial direction (Z-axis direction). The shield plate 7 is a magnetic flux shielding member for preventing the angle sensors Sp, Sq, and Sr provided inside the case 4 from receiving magnetic interference due to magnetic flux generated outside the absolute encoder 2. The shield plate 7 is made of, for example, a magnetic material.

The motor 1 may be, for example, a stepping motor or a DC brushless motor. As an example, the motor 1 may be a motor applied as a drive source for driving an industrial robot or the like via a speed reduction mechanism such as a wave gear device. Both sides of the main shaft 1a of the motor 1 in the vertical direction protrude from the motor case. The absolute encoder 2 outputs the rotation angle of the main shaft 1a of the motor 1 as a digital signal.

The motor 1 has a substantially rectangular shape in plan view, and also has a substantially rectangular shape in the vertical direction. That is, the motor 1 has a substantially cubic shape. The length of each of the four outer wall portions constituting the outer shape of the motor 1 in plan view is, for example, 25 mm, that is, the outer shape of the motor 1 is 25 mm square in plan view. Note that the outer shape of the motor 1 is not limited to 25 mm square in plan view. The outer shape of the motor 1 may have different sizes depending on the use of the motor 1. Further, the absolute encoder 2 provided in the motor 1 is, for example, 25 mm square in accordance with the external shape of the motor 1. Note that the absolute encoder 2 may have a size that matches the external shape of the motor 1, and is not limited to a size of 25 mm square.

In FIGS. 1 and 2, the angle sensor support substrate 5 is provided to cover the inside of the absolute encoder 2 together with the case 4 and the shield plate 7.

As shown in FIGS. 3 and 5, the angle sensor support substrate 5 is a printed wiring board that has a substantially rectangular shape in plan view and is thin in the vertical direction. As shown in FIGS. 2 to 4, the connector 6 is connected to the angle sensor support board 5, and is used to connect the absolute encoder 2 to an external device (not shown).

As shown in FIGS. 2 to 4, the absolute encoder 2 includes a main shaft gear 10 having a first worm gear portion 11 (first drive gear). The absolute encoder 2 also includes a first intermediate gear 20 having a first worm wheel section 21 (first driven gear), a second worm gear section 22 (second drive gear), and a third worm gear section 28 (third drive gear). Contains. Further, the absolute encoder 2 includes a second intermediate gear 30 having a third worm wheel portion 31 (third driven gear) and a first spur gear portion 32 (fourth driving gear). The absolute encoder 2 also includes a first countershaft gear 40 having a second worm wheel portion 41 (second driven gear), and a second countershaft gear 50 having a second spur gear portion 51 (third driven gear). Contains. The absolute encoder 2 also includes a magnet Mp, an angle sensor Sp corresponding to the magnet Mp, a magnet Mq, an angle sensor Sq corresponding to the magnet Mq, a magnet Mr, an angle sensor Sr corresponding to the magnet Mr, and a microcomputer. 121.

As shown in FIGS. 4 and 6, the main shaft 1a of the motor 1 is an output shaft of the motor 1, and is an input shaft that transmits rotational force to the absolute encoder 2. The main shaft gear 10 is fixed to the main shaft 1a of the motor 1, and is rotatably supported by a bearing member of the motor 1 integrally with the main shaft 1a. The first worm gear section 11 is provided on the outer periphery of the main shaft gear 10 so as to rotate according to the rotation of the main shaft 1a of the motor 1. In the main shaft gear 10, the first worm gear part 11 is provided so that its central axis coincides or substantially coincides with the central axis of the main shaft 1a. The main shaft gear 10 can be formed from various materials such as resin materials and metal materials. The main shaft gear 10 is made of polyacetal resin, for example.

As shown in FIGS. 3 and 4, the first intermediate gear 20 is a gear portion that transmits the rotation of the main shaft gear 10 to the first sub-shaft gear 40 and the second intermediate gear 30. The first intermediate gear 20 is supported by a shaft 23 around a rotation axis extending substantially parallel to the gear base portion 3 . The first intermediate gear 20 is a substantially cylindrical member extending in the direction of its rotational axis. The first intermediate gear 20 includes a first worm wheel section 21, a second worm gear section 22, and a third worm gear section 28, and has a through hole formed therein, into which the shaft 23 is inserted. . By inserting this shaft 23 into a first intermediate gear shaft support 27 provided in the gear base portion 3, the first intermediate gear 20 is pivotally supported. The first worm wheel section 21, the second worm gear section 22, and the third worm gear section 28 are arranged at positions separated from each other in this order. The first intermediate gear 20 can be formed from various materials such as resin materials and metal materials. The first intermediate gear 20 is made of polyacetal resin.

As shown in FIGS. 4 and 7, the first worm wheel portion 21 is provided on the outer periphery of the first intermediate gear 20. As shown in FIGS. The first worm wheel section 21 is provided so as to mesh with the first worm gear section 11 and rotate according to the rotation of the first worm gear section 11. The axial angle between the first worm wheel section 21 and the first worm gear section 11 is set to 90 degrees or approximately 90 degrees.

Although there is no particular restriction on the outer diameter of the first worm wheel section 21, in the illustrated example, the outer diameter of the first worm wheel section 21 is configured to be smaller than the outer diameter of the first worm gear section 11. As a result, the absolute encoder 2 is made smaller in size in the vertical direction.

The second worm gear section 22 is provided on the outer periphery of the first intermediate gear 20 together with the first worm wheel section 21 and rotates as the first worm wheel section 21 rotates. In the first intermediate gear 20 , the second worm gear section 22 is provided so that its central axis coincides or substantially coincides with the central axis of the first worm wheel section 21 .

As shown in FIGS. 4 and 8, the third worm gear section 28 is provided on the outer periphery of the first intermediate gear 20, and rotates as the first worm wheel section 21 rotates. In the first intermediate gear 20 , the third worm gear section 28 is provided so that its central axis coincides or substantially coincides with the central axis of the first worm wheel section 21 .

As shown in FIG. 4, the first subshaft gear 40 is decelerated and rotates integrally with the magnet Mq in accordance with the rotation of the main shaft 1a. The first countershaft gear 40 is supported by a shaft that projects substantially perpendicularly from the gear base portion 3, and has a substantially circular shape in a plan view, and includes a second worm wheel portion 41 and a holding portion that holds the magnet Mq. It is a member. The first subshaft gear 40 can be formed from various materials such as resin materials and metal materials. The first subshaft gear 40 is made of polyacetal resin.

The second worm wheel portion 41 is provided on the outer periphery of the first subshaft gear 40, meshes with the second worm gear portion 22, and is provided to rotate as the second worm gear portion 22 rotates. The axial angle between the second worm wheel section 41 and the second worm gear section 22 is set to 90 degrees or approximately 90 degrees. The rotational axis of the second worm wheel section 41 is parallel or substantially parallel to the rotational axis of the first worm gear section 11 .

4 and 8, the second intermediate gear 30 is a disc-shaped gear portion that rotates according to the rotation of the main shaft 1a, decelerates the rotation of the main shaft 1a, and transmits it to the second sub-shaft gear 50. The second intermediate gear 30 is provided between the second worm gear section 22 and the second spur gear section 51 provided on the second subshaft gear 50. The second spur gear portion 51 meshes with the first spur gear portion 32 . The second intermediate gear 30 includes a third worm wheel section 31 that meshes with the third worm gear section 28 of the first intermediate gear 20 and a first spur gear section 32 that drives the second spur gear section 51 . The second intermediate gear 30 is made of, for example, polyacetal resin. The second intermediate gear 30 is a substantially circular member in plan view. The second intermediate gear 30 is pivotally supported by the gear base portion 3.

By providing the second intermediate gear 30, the second subshaft gear 50, which will be described later, can be arranged at a position further away from the third worm gear section 28. Therefore, by increasing the distance between the magnets Mr and Mq, it is possible to reduce the influence of mutual leakage magnetic flux. Further, by providing the second intermediate gear 30, the range in which the reduction ratio can be set is expanded, and the degree of freedom in design is improved.

The third worm wheel portion 31 is provided on the outer periphery of the second intermediate gear 30, meshes with the third worm gear portion 28, and is provided to rotate as the third worm gear portion 28 rotates. The first spur gear portion 32 is provided on the outer periphery of the second intermediate gear 30 so that its center axis coincides or substantially coincides with the center axis of the third worm wheel portion 31 . The first spur gear part 32 is provided so as to mesh with the second spur gear part 51 and rotate according to the rotation of the third worm wheel part 31. The rotation axes of the third worm wheel section 31 and the first spur gear section 32 are provided parallel or substantially parallel to the rotation axis of the first worm gear section 11 .

In FIG. 8, the second subshaft gear 50 is a gear portion having a circular shape in plan view, which rotates according to the rotation of the main shaft 1a, decelerates the rotation of the main shaft 1a, and transmits the reduced rotation to the magnet Mr. The second subshaft gear 50 is pivotally supported around a rotation axis extending substantially perpendicularly from the gear base portion 3 . The second countershaft gear 50 includes a second spur gear portion 51 and a magnet holding portion that holds the magnet Mr.

The second spur gear portion 51 is provided on the outer periphery of the second subshaft gear 50 so that its center axis coincides or substantially coincides with the center axis of the first spur gear portion 32 . The second spur gear part 51 is provided so as to mesh with the first spur gear part 32 and rotate according to the rotation of the third worm wheel part 31. The rotational axis of the second spur gear portion 51 is parallel or substantially parallel to the rotational axis of the first spur gear portion 32 . The second subshaft gear 50 can be formed from various materials such as resin materials and metal materials. The second subshaft gear 50 is made of polyacetal resin.

Here, in order for the first worm wheel part 21 to mesh with the first worm gear part 11, the direction in which the first worm wheel part 21 faces the first worm gear part 11 is referred to as a first meshing direction P1 (direction of arrow P1 in FIG. 4). do. Similarly, since the second worm gear part 22 meshes with the second worm wheel part 41, the direction in which the second worm gear part 22 faces the second worm wheel part 41 is referred to as the second meshing direction P2 (direction of arrow P2 in FIG. 4). do. Furthermore, since the third worm gear part 28 meshes with the third worm wheel part 31, the direction in which the third worm gear part 28 moves toward the third worm wheel part 31 is defined as a third meshing direction P3 (direction of arrow P3 in FIG. 4). . In this embodiment, the first meshing direction P1, the second meshing direction P2, and the third meshing direction P3 are all along a horizontal plane (XY plane).

The magnet Mp is fixed to the upper surface of the main shaft gear 10 so that both center axes coincide or substantially coincide. The magnet Mp is supported via a holder portion 16 by a magnet support portion 17 provided on the central axis of the main shaft gear 10 . The holder portion 16 is made of a non-magnetic material such as an aluminum alloy. The inner circumferential surface of the holder portion 16 is formed into, for example, an annular shape corresponding to the outer diameter and the shape of the outer circumferential surface of the magnet Mp so as to contact and hold the outer circumferential surface of the magnet Mp in the radial direction. ing. Further, the inner circumferential surface of the magnet support portion 17 is formed, for example, in an annular shape, corresponding to the outer diameter and the shape of the outer circumferential surface of the holder portion 16, so as to be in contact with the outer circumferential surface of the holder portion 16. The magnet Mp has two magnetic poles arranged in a direction perpendicular to the rotational axis of the main shaft gear 10.

As shown in FIGS. 2, 3, and 5, in order to detect the rotation angle of the main shaft gear 10, the angle sensor Sp functioning as the first sensor unit has its lower surface vertically connected to the upper surface of the magnet Mp through a gap. It is provided on the lower surface 5a of the angle sensor support substrate 5 so as to face the angle sensor support substrate 5. As an example, the angle sensor Sp is fixed to an angle sensor support substrate 5 supported by a substrate support 110 disposed on a gear base portion 3 of the absolute encoder 2, which will be described later. The angle sensor Sp detects the magnetic pole of the magnet Mp, and outputs detected information (hereinafter referred to as “detection information”) as a first signal to the microcomputer 121. The microcomputer 121 specifies the rotation angle of the magnet Mp based on the input detection information regarding the magnetic poles, thereby specifying the rotation angle of the main shaft gear 10, that is, the rotation angle of the main shaft 1a. The resolution of the rotation angle of the main shaft 1a corresponds to the resolution of the angle sensor Sp. As described later, the microcomputer 121 specifies the rotation angle of the main shaft 1a based on the specified rotation angle of the first subshaft gear 40 and the specified rotation angle of the main shaft 1a, and outputs this. For example, the microcomputer 121 may output the rotation angle of the main shaft 1a of the motor 1 as a digital signal.

The angle sensor Sq functions as a second sensor section and detects the rotation angle of the second worm wheel section 41, that is, the rotation angle of the first subshaft gear 40. The magnet Mq is fixed to the upper surface of the first subshaft gear 40 such that both center axes coincide or substantially coincide. The magnet Mq has two magnetic poles arranged in a direction perpendicular to the rotational axis of the first subshaft gear 40. As shown in FIG. 3, the angle sensor Sq is provided so that its lower surface vertically faces the upper surface of the magnet Mq with a gap therebetween, in order to detect the rotation angle of the first subshaft gear 40.

As an example, the angle sensor Sq is fixed to the angle sensor support substrate 5 to which the angle sensor Sp is fixed, on the same surface as the surface to which the angle sensor Sp is fixed. Angle sensor Sq detects the magnetic pole of magnet Mq and outputs detection information as a second signal to microcomputer 121. The microcomputer 121 specifies the rotation angle of the magnet Mq, that is, the rotation angle of the first subshaft gear 40, based on the input detection information regarding the magnetic poles.

The angle sensor Sr functions as a second sensor section and detects the rotation angle of the second spur gear section 51, that is, the rotation angle of the second subshaft gear 50. The magnet Mr is fixed to the upper surface of the second subshaft gear 50 such that both center axes coincide or substantially coincide. The magnet Mr has two magnetic poles arranged in a direction perpendicular to the rotational axis of the second subshaft gear 50. As shown in FIG. 3, in order to detect the rotation angle of the second subshaft gear 50, the angle sensor Sr is provided such that its lower surface vertically faces the upper surface of the magnet Mr with a gap therebetween.

As an example, the angle sensor Sr is fixed to an angle sensor support substrate 5 supported by a substrate support 110 disposed on a gear base portion 3 of the absolute encoder 2, which will be described later. The angle sensor Sr detects the magnetic pole of the magnet Mr, and outputs detection information as a second signal to the microcomputer 121. The microcomputer 121 specifies the rotation angle of the magnet Mr, that is, the rotation angle of the second subshaft gear 50, based on the input detection information regarding the magnetic poles.

A magnetic angle sensor with relatively high resolution may be used for each angle sensor. The magnetic angle sensor is, for example, disposed to face an end face including a magnetic pole of each magnet with a certain gap in between, in the axial direction of each rotating body. The absolute encoder 2 is not limited to the configuration of a magnetic angle sensor used as an angle sensor. For example, the magnetic angle sensor may be arranged to face an end face including a magnetic pole of each magnet with a certain gap in between in the outer circumferential direction of each rotating body. The magnetic angle sensor specifies the rotation angle of the opposing rotating body by detecting as a physical quantity the strength of the magnetic field that varies based on the rotation of the magnetic poles of these magnets, and outputs a digital signal. A magnetic angle sensor includes, for example, a sensing element that detects a magnetic pole and an arithmetic circuit that outputs a digital signal based on the output of this sensing element. The sensing element may include a plurality (for example, four) of magnetic field sensing elements such as a Hall element or a GMR (Giant Magneto Resistive) element. Note that each angle sensor may be configured to detect the direction (vector) of the magnetic field as a physical quantity.

The arithmetic circuit may specify the rotation angle through table processing using a look-up table using, for example, a difference or ratio between the outputs of a plurality of sensing elements as a key. The sensing element and the arithmetic circuit may be integrated on one IC chip. This IC chip may be embedded in a resin having a thin rectangular parallelepiped outer shape. Each angle sensor outputs to the microcomputer 121 an angle signal that is a digital signal corresponding to the rotation angle of each rotating body detected via a wiring member (not shown). For example, each angle sensor outputs the rotation angle of each rotating body as a multi-bit (for example, 7-bit) digital signal.

As shown in FIG. 5, the microcomputer 121 is fixed to the angle sensor support substrate 5 by a method such as soldering or adhesion. The microcomputer 121 is composed of a CPU (Central Processing Unit), acquires digital signals representing rotation angles output from each of the angle sensors Sp, Sq, and Sr, and calculates the rotation angle of the main shaft gear 10.

Each block of the microcomputer 121 shown in FIG. 9 represents a function realized by the CPU as the microcomputer 121 executing a program. As shown in FIG. 9, the microcomputer 121 includes an angle information generation section 121p, a coefficient determination section 121s, a sub-axis offset value determination section 121q, a storage section 121b, and a correction section 121r in order to execute the angular deviation correction method. Be prepared. That is, the microcomputer 121 functions as an angular deviation correction device for executing the angular deviation correction method. Each block of the microcomputer 121 can be realized in terms of hardware by elements and mechanical devices such as a computer's CPU and RAM (Random Access Memory), and can be realized in terms of software by a computer program or the like. This section depicts the functional blocks that are realized through their cooperation. Therefore, those skilled in the art who have been exposed to this specification will understand that these functional blocks can be realized in various ways by combining hardware and software.

Next, an outline of the angular deviation of the rotating shaft and the offset value, which is a value for correcting the angular deviation, in the absolute encoder 2 of this embodiment will be explained.

FIG. 10 is a graph showing an example of the angular deviation in one rotation of the main shaft 1a in the absolute encoder 2. In the angular deviation waveform Ar1 shown in FIG. 10, the horizontal axis represents the rotation angle of the main shaft 1a, and the vertical axis represents the angle represented by the angle generated by rotating the main shaft 1a, and the actual angle of the main shaft 1a. shows the angular deviation of The main shaft 1a is an example of a first rotating body. In the absolute encoder 2, the angular deviation of the main shaft 1a spans one rotation (360°) of the main shaft 1a.

The absolute encoder 2 outputs the rotation angle of the main shaft 1a of the motor 1 generated by the angle information generation unit 121p to an external control device (hereinafter referred to as "controller C") that controls the motor 1. The controller C controls the operation of the motor 1 based on the rotation angle output from the absolute encoder 2.

However, the rotation angle specified by the absolute encoder 2 includes an inherent angular deviation depending on the position (angle) of the main shaft 1a. The specific angular deviation differs for each absolute encoder 2. The inherent angular deviation is caused by manufacturing variations in the absolute encoder 2. Manufacturing variations are, for example, variations included in the manufacturing process, such as assembly of parts such as gears, and positional relationships of magnets Mp, Mq, Mr and angle sensors Sp, Sq, Sr used to detect the position of the rotating shaft in the absolute encoder 2. be.

The absolute encoder 2 uses the starting position of the main shaft 1a at startup as a reference (zero point) and detects the subsequent position of the main shaft 1a. In the angular deviation waveform Ar1 shown in FIG. 10, the reference of the main axis 1a is 0 [deg]. In the angular deviation waveform Ar1 shown in FIG. 10, the maximum angular deviation in one rotation of the main shaft 1a is 0.224 [deg].

FIG. 11 is a graph showing an example of the waveform Ar2 of the angular deviation in the absolute encoder 2 when the reference of the main axis 1a is 72 [deg]. In FIG. 11, the horizontal axis indicates the rotation angle of the main shaft 1a. Moreover, in FIG. 11, the vertical axis indicates the value of the angular deviation corresponding to the rotation angle of the main shaft 1a. FIG. 11 shows a waveform Ar2 of angular deviation with a reference of 72 [deg] for the main axis 1a, as well as a waveform Ar1 of angular deviation with a reference of 0 [deg] shown in FIG. 10 for comparison. In the angular deviation waveform Ar2, the maximum angular deviation is 0.160 [deg]. The maximum angular deviation is the maximum value when comparing the absolute values of a plurality of angular deviations (0.224 for -0.224, 0.160 for +0.160). As shown in FIG. 11, in the absolute encoder 2, an angular deviation waveform Ar1 with a reference of 0 [deg] and an angular deviation Ar2 with a reference of 72 [deg] are compared. The difference in maximum angular deviation compared between starting positions 0[deg] and 72[deg] is |-0.224|-|0.160|=0.064[deg] due to the difference in starting positions. A difference will occur. That is, in the absolute encoder 2, the value of the angular deviation serving as a reference for the main shaft 1a differs depending on the starting position of the main shaft 1a. Therefore, in the absolute encoder 2, if the starting position of the main shaft 1a differs, the maximum angular deviation may vary.

The rotary absolute encoder has a periodicity in which the angular deviation caused by one rotation of the main shaft 1a returns to the original state by one rotation of the main shaft 1a. Therefore, by performing Fourier transformation on the angular deviation of the main axis 1a, the magnitude (amplitude) of the periodic component included in the angular deviation can be calculated. Note that the periodic component is a component in the form of an angular deviation waveform, which is shown in the form of a sine wave or a cosine wave. A unique waveform of the angular deviation waveform is formed by overlapping waveforms of a plurality of periodic components having different periods and amplitudes.

In a rotary absolute encoder, the sub-shaft rotates at a different cycle from the main shaft 1a. The magnetic flux of the magnets Mq and Mr used to detect the rotational speed of the subshaft leaks to the angle sensor Sp of the main shaft 1a, resulting in an angular deviation depending on the rotation period of the main shaft 1a and the subshaft. The occurrence of angular deviation means that the maximum angular deviation differs depending on the starting angle. Therefore, the purpose of the absolute encoder 2 is to correct and suppress the angular deviation due to the influence of the magnets Mq and Mr used for detecting the rotational speed of the sub-shaft by using an offset value.

Therefore, in the absolute encoder 2, the secondary shaft offset value determining unit 121q, which is a second rotary body offset value determining unit and implemented by the microcomputer 121, sets the second An offset value Ofs _sub as a rotating body offset value is determined. The information used to determine the offset value Ofs _sub is the angle information Ap of the main shaft 1a at startup, and the absolute value of the sub shaft as a second rotating body that rotates in accordance with the rotation of the main shaft 1a and has a rotation period different from that of the main shaft 1a. These are angle information Aq, Ar on the secondary axis as second angle information indicating the angle, and predetermined coefficients (for example, Fourier coefficients). The predetermined coefficient is calculated based on the angular deviation in the main shaft 1a that rotates multiple times per revolution of the sub shaft. The angular deviation caused by multiple rotations of the main shaft 1a is referred to as multi-rotation angular deviation. The multi-rotation angle deviation corresponds to the second rotating body angle deviation. By performing such processing, the absolute encoder 2 can suppress the maximum angular deviation of the angle information Aq and Ar, regardless of the position of the main shaft 1a at the time of startup.

FIG. 12 is a graph showing a waveform Ar3 of the angular deviation after correction when the reference of the main axis 1a is 0 [deg]. As shown in FIG. 12, the maximum angular deviation of the corrected angular deviation waveform Ar3 is 0.137 [deg]. The maximum angular deviation of the corrected angular deviation waveform Ar3 is suppressed compared to the maximum angular deviation (0.224 [deg]) of the angular deviation waveform Ar1 shown in FIG.

FIG. 13 is a graph showing a waveform Ar4 of the angular deviation after correction when the reference of the main axis 1a is 72[deg]. As shown in FIG. 13, the maximum angular deviation of the corrected angular deviation waveform Ar4 is 0.137 [deg]. The maximum angular deviation of the corrected angular deviation waveform Ar4 is suppressed compared to the maximum angular deviation (0.160 [deg]) of the angular deviation waveform Ar2 shown in FIG.

The angle information generation unit 121p generates information (hereinafter referred to as "angle information") Ap indicating the rotation angle of the main shaft gear 10, that is, the main shaft 1a, based on the detection information output from the angle sensor Sp. The angle information generation unit 121p generates angle information Aq of the first subshaft gear 40 based on the detection information output from the angle sensor Sq. The angle information generation unit 121p generates angle information Ar, which is angle information indicating the rotation angle of the second subshaft gear 50, based on the detection information detected by the angle sensor Sr. In the present embodiment, in the process of determining Ofs _sub1 , a value (hereinafter referred to as "offset value") for correcting the angular deviation so that the maximum angular deviation of the first subshaft gear 40 is minimized, the microcomputer 121 adjusts the angle In order to correct the deviation included in the information Aq, angle information Ap generated by the magnet Mp and the angle sensor Sp is used. That is, in this embodiment, the configuration may be such that the magnets Mq and Mr and the angle sensors Sq and Sr are not included.

The coefficient determining unit 121s determines Fourier coefficients (parameters) used to determine the sub-axis offset value in the sub-axis offset value determining unit 121q. The coefficient determination unit 121s stores the determined Fourier coefficients in the storage unit 121b. The Fourier coefficient is a coefficient obtained by Fourier transforming the angular deviation obtained by the number of rotations of the main shaft 1a per multiple rotations of the main shaft 1a, specifically, one rotation of the sub-shaft.

FIG. 14 is a graph showing an example of the waveform of the multi-rotation angle deviation in the absolute encoder 2. In the waveform of the multi-rotation angle deviation shown in FIG. 14, the horizontal axis shows the rotation angle of the main shaft 1a, and the vertical axis shows the angle generated by rotating the main shaft 1a, which is an example of a rotary body, and the main shaft. The actual angle of 1a and the angular deviation are shown. FIG. 14 shows an example in which one rotation of the subshaft of the absolute encoder 2 corresponds to 10 rotations (3600°) of the main shaft 1a. Note that the microcomputer 121 of the absolute encoder 2 may not include the coefficient determining section 121s. That is, the coefficient used to determine the offset value may not be calculated by the microcomputer 121, but may be stored in advance in the storage unit 121b.

The sub-axis offset value determining unit 121q determines an offset value Ofs _sub . The offset value Ofs _sub corresponds to the second rotating body offset value. The offset value Ofs _sub is the angle information Ap of the main shaft 1a at startup, and the sub shaft (first sub angle information Aq and angle information Ar of the shaft gear 40 and/or the second subshaft gear 50), and a predetermined coefficient (for example, a Fourier coefficient) calculated based on the angular deviation of the subshaft. Determined based on Specifically, the offset value Ofs _sub is based on the angle information Ap of the main axis 1a as the first angle information, the angle information Aq and the angle information Ar of the sub axis, and the Fourier coefficient determined by the coefficient determination unit 121s. It is obtained by summing the values calculated for each rotation period of the sub-shaft.

In determining the offset value, the sub-axis offset value determining unit 121q uses the angle information Ap of the main axis 1a detected when the absolute encoder 2 is activated, and the Fourier coefficient of the sine component at an arbitrary period n included in the angular deviation waveform. An offset value Ofs _sub in the angle information Ap of the main axis 1a is specified from Fs _n and the Fourier coefficient Fc _n of the cosine component at period n included in the angular deviation waveform. The specified offset value Ofs _sub is added to the angle information of the sub-axis. Specifically, the specified offset value Ofs _sub1 of the first subshaft gear 40 is added to the angle information Aq of the first subshaft gear 40. Further, the specified offset value Ofs _sub2 of the second subshaft gear 50 is added to the angle information Ar of the second subshaft gear 50. In the absolute encoder 2, the rotation period of the first subshaft gear 40 and the rotation period of the second subshaft gear 50 are different. Further, in the absolute encoder 2, the angle information Aq of the first subshaft gear 40 and the angle information Ar of the second subshaft gear 50 are different. That is, the offset value Ofs _sub1 of the first subshaft gear 40 and the offset value Ofs _sub2 of the second subshaft gear 50 are different values. By performing such processing, the absolute encoder 2 can obtain angle information Aq, Ar of the subshafts (first subshaft gear 40, second subshaft gear 50) regardless of the position of the main shaft 1a at the time of startup. Maximum angular deviation can be suppressed.

The storage unit 121b is a functional unit that stores information used in the process of determining the offset value Ofs _sub . The storage unit 121b is configured using a storage device such as a magnetic hard disk device or a semiconductor storage device, for example. The storage unit 121b may store information on the angular deviation of the main shaft 1a over the entire angular range, which is measured before shipping. In addition, the storage unit 121b stores the Fourier coefficients used in the process of determining the offset value Ofs _sub according to the number of cycles (n=1, 2, . . . , N, m= 1, 2, . . . , M). You may remember it accordingly.

The correction unit 121r corrects the angular deviation using the offset value Ofs _sub determined by the sub-axis offset value determination unit 121q.

Next, a specific example of the process of determining the offset value Ofs _sub executed in the absolute encoder 2 will be described.

FIG. 15 is a flowchart illustrating an example of the process of determining the offset value Ofs _sub for correcting the angular deviation in the absolute encoder 2.

Referring to FIG. 15, for details of the offset value Ofs _sub determination process performed by the subshaft offset value determination unit 121q, the offset value Ofs _sub1 as the offset value of the first subshaft gear 40, which is an example of the subshaft, is determined. The processing to do this will be explained as an example. In the following description, the first subshaft gear 40 will be simply referred to as a subshaft.

The sub-axis offset value determination unit 121q generates _sub -axis angle information (hereinafter referred to as "multi-rotation arc degree ω (0≦ω<2π)") that corresponds to the second angle information and is used to determine the offset value Ofs sub1. .) is obtained (step S101). In the absolute encoder 2, when the subshaft makes one revolution, the main shaft 1a, which has a rotation period different from that of the subshaft, rotates a plurality of times according to the difference in rotation period (reduction ratio). The rotation angle of the sub-shaft also corresponds to the difference in rotation period from the main shaft 1a. In step S101, the sub-axis offset value determining unit 121q obtains the Fourier coefficient determined by the coefficient determining unit 121s and stored in the storage unit 121b, the angle information Ap of the main shaft 1a, and the rotation speed t of the sub-shaft.

The value of the Fourier coefficient differs for each absolute encoder 2. The value of the Fourier coefficient can be obtained by Fourier transforming the angular deviation of the secondary axis obtained from the absolute encoder 2.

The Fourier coefficient is calculated by calculating the sine component and the cosine component of the arc degree ω of the secondary axis for each period n (n=1, 2, 3, ..., N) of the arc degree θ of the main axis 1a. A cosine component is calculated every period m (m=1, 2, 3, . . . , M). For example, the Fourier coefficients F _snsm , F _sncm , F _cnsm , and F _cncm are expressed as shown in Tables 1 and 2 below. Table 1 shows the Fourier coefficient F _snsm and the Fourier coefficient F _sncm , which are the component amounts of the arc degree ω on the sub-axis of the waveform indicating the fluctuation of the angular deviation component with respect to the sine component of the arc degree θ. Table 2 shows the Fourier coefficient F _{cnsm and} the Fourier coefficient F _cnsm , which are the component quantities of the arc degree ω on the secondary axis of the waveform indicating the fluctuation of the angular deviation component with respect to the cosine of the arc degree θ.

The sub-axis offset value determination unit 121q uses the information acquired in step S101 to calculate the multi-rotation arc degree ω used to determine the offset value Ofs _sub1 based on the following equation (1) (step S102 ).

In equation (1), θ: degree of arc of the main shaft 1a (0≦θ<2π), t: rotational speed of the sub-shaft (t=0, 1,...T-1), T: relative to one rotation of the main shaft 1a This is the maximum rotation speed of the subshaft, that is, the reduction ratio of the subshaft to the main shaft 1a.

FIG. 16 is a diagram illustrating an example of Fourier coefficients obtained from a waveform showing a variation in the angular deviation component of sin1θ. In FIG. 16, as an example of the Fourier coefficient obtained from the waveform showing the fluctuation of the angular deviation component of sin1θ, the amount of sin1ω component of the waveform showing the fluctuation of the angular deviation component of sin1θ shown in Table 1 is: F _s1s1 , the amount of cos1ω component: F _s1c1 , sin2ω component amount: F _s1s2 , and cos2ω component amount: F _s1c2 are shown. FIG. 17 is a diagram illustrating an example of Fourier coefficients obtained from a waveform showing fluctuations in the angular deviation component of cos1θ. In FIG. 17, as an example of the Fourier coefficient obtained from the waveform showing the fluctuation of the angular deviation component of cos1θ, the amount of sin1ω component of the waveform showing the fluctuation of the angular deviation component of sin1θ shown in Table 2: F _s1s1 , the amount of cos1ω component: F _s1c1 , sin2ω component amount: F _s1s2 , and cos2ω component amount: F _s1c2 are shown.

FIG. 18 is a diagram showing an example of a waveform representing a variation in amplitude change of the angular deviation component of sin1θ. In the waveform shown in FIG. 18 representing the fluctuation in the amplitude change of the angular deviation component of sin1θ, the horizontal axis represents the rotation angle of the main shaft 1a, and the vertical axis represents the angular deviation component of sin1θ when the main shaft 1a is rotated. FIG. 19 is a diagram showing an example of a waveform representing a variation in amplitude change of the angular deviation component of cos1θ. In the waveform shown in FIG. 19 representing the fluctuation in amplitude change of the angular deviation component of cos1θ, the horizontal axis indicates the rotation angle of the main shaft 1a, and the vertical axis shows the angular deviation component of cos1θ when the main shaft 1a is rotated.

The sub-axis offset value determination unit 121q decodes the waveform showing the amplitude fluctuation of the angular deviation of the sinnθ component shown in FIG. 18 from the Fourier coefficients showing the amplitude fluctuation of the angular deviation of the sinnθ component shown in FIG. Further, the sub-axis offset value determination unit 121q decodes a waveform showing the amplitude fluctuation of the angular deviation of the cosn θ component shown in FIG. 19 from the Fourier coefficients showing the amplitude fluctuation of the angular deviation of the cosn θ component shown in FIG. 17 (step S103 ). The process of decoding the waveform representing the amplitude change of the fluctuation of the angular deviation component from the Fourier coefficient representing the fluctuation of each angular deviation component is performed as follows.

The sub-axis offset value determining unit 121q performs inverse Fourier transform on the Fourier coefficients indicating the fluctuation of each angular deviation component for each angular deviation component. The sub-axis offset value determination unit 121q performs an inverse Fourier transform on the Fourier coefficient to determine the amount of rotation of the main shaft 1a corresponding to one revolution of the sub-shaft, for example, a sinnθ component corresponding to 10 revolutions (3600 degrees) of the main shaft 1a, Also, the value of the amplitude change of the angular deviation of the cosnθ component can be obtained.

Next, the sub-axis offset value determination unit 121q plots the amplitude change values of the angular deviations of the sinn θ component and the cosn θ component over 10 rotations (3600 degrees) of the main axis 1a, thereby obtaining the sinn θ shown in FIGS. 18 and 19. A waveform indicating the amplitude change of the angular deviation of the cosnθ component and the cosnθ component is generated.

FIG. 20 is a diagram showing an example of a waveform representing a multi-rotation angular deviation of the angular deviation of the sin1θ component. In the waveform shown in FIG. 20 representing the variation in amplitude change of the angular deviation component of sin1θ, the horizontal axis indicates the rotation angle of the main shaft 1a, and the vertical axis shows the angular deviation component of sin1θ when the main shaft 1a is rotated. The broken line in FIG. 20 is a waveform showing the amplitude fluctuation of the angular deviation of the sin1θ component shown in FIG. The solid line in FIG. 20 is a waveform showing the amplitude fluctuation of the multi-rotation angle deviation of the sin1θ component. FIG. 21 is a diagram showing an example of a waveform representing a multi-rotation angular deviation of the angular deviation of the cos1θ component. In the waveform shown in FIG. 21 showing the fluctuation in amplitude change of the angular deviation component of cos1θ, the horizontal axis indicates the rotation angle of the main shaft 1a, and the vertical axis shows the angular deviation component of cos1θ when the main shaft 1a is rotated. The broken line in FIG. 21 is a waveform showing the amplitude fluctuation of the angular deviation of the cos1θ component shown in FIG. The solid line in FIG. 21 is a waveform showing the amplitude fluctuation of the multi-rotation angle deviation of the cos1θ component.

The sub-axis offset value determination unit 121q further performs inverse Fourier transform on the values indicating the amplitude changes of the angular deviations of the sinnθ component and the cosnθ component shown in FIGS. 18 and 19, thereby obtaining the sinnθ shown in FIGS. 20 and 21. The multi-rotation angle deviation of the component and the cosnθ component is calculated (decoded) (step S104).

The sub-axis offset value determination unit 121q determines the period n included in the angular deviation obtained by one rotation of the sub-axis and the multi-rotation of the main axis 1a from the multi-rotation angular deviation of the decoded sinnθ component and cosnθ component. In other words, the offset value Ofs _nm of the deviation component of period m included in the multi-rotation angular deviation is determined (step S105). The offset value Ofs _nm can be determined using equation (2). Note that the values of the Fourier coefficients F _snsm , F _sncm , F _cnsm , and F _cncm shown in Tables 1 and 2 differ depending on each absolute encoder 2.

The sub-axis offset value determination unit 121q determines whether the determination of the offset value Ofs _nm has reached the number of cycles included in the one-rotation angular deviation and the multi-rotation angular deviation (for example, n=N, m=M). is determined (step S106). If the number of cycles for which the offset value Ofs _nm has been determined has not reached N and M (S106: NO), the sub-axis offset value determining unit 121q returns to step S103 and reaches the numbers N and M of cycles. The determination of the offset value Ofs nm is repeated until the offset value Ofs _nm is determined.

When the number of cycles for determining the offset value Ofs _nm reaches N or M (S106: YES), the sub-axis offset value determination unit 121q calculates each cycle (n=1, 2,...N, m=1,2,...M), that is, the offset value Ofs _sub1 used to correct the angular deviation included in one rotation of the main shaft 1a. Determine (step S107). After determining the offset value Ofs _sub1 , the sub-axis offset value determining unit 121q ends the process of determining the offset value Ofs _sub1 .

The correction unit 121r corrects the waveform of the angular deviation using the offset value Ofs _sub1 determined by the sub-axis offset value determination unit 121q.
Note that the process of determining the offset value Ofs _sub performed by the subshaft offset value determination unit 121q described above is not limited to the process of determining the offset value Ofs _sub1 of the first subshaft gear 40, and may be performed in other examples of the subshaft. It can be used in the process of determining the offset value Ofs _sub2 of a certain second subshaft gear 50.

[Operations and effects of the embodiment]
As explained above, according to the absolute encoder 2, the Fourier coefficient for determining the amplitude of each angular deviation component of the multi-rotation angular deviation can be expressed by a constant. Therefore, according to the angular deviation correction method executed by the absolute encoder 2 in this embodiment, by storing the Fourier coefficients in the storage unit 121b, the detected angle information Ap of the main shaft 1a and the rotation speed t of the sub-shaft can be adjusted. The offset value can be easily determined accordingly.

In other words, according to the method for correcting the angular deviation of the absolute encoder 2 configured as described above, it is possible to determine the offset value for correcting the angular deviation of the secondary shaft corresponding to the starting position of the main shaft 1a of the absolute encoder 2. . For this reason, the microcomputer 121 or the controller C determines the maximum angular deviation based on the angular deviation waveform and the offset value Ofs _sub1 for the multiple rotations (multi-rotations) of the main shaft 1a corresponding to one rotation of the sub-shaft shown in FIG. Value can be suppressed. More specifically, the microcomputer 121 or the controller C can suppress the maximum value of the angular deviation waveform by adding or subtracting an offset value to each value of the angular deviation waveform. According to such an absolute encoder 2, the maximum value of the angular deviation can be suppressed regardless of the position of the rotating body at the time of startup.

Furthermore, according to the absolute encoder 2, the coefficients (Fourier coefficients Fs _n , Fc _n ) necessary to determine the offset value Ofs _sub1 are divided into two coefficients for each number of cycles N and M included in the angular deviation. Just store it. Therefore, according to the absolute encoder 2, it is possible to suppress the maximum value of the angular deviation regardless of the position of the rotating body at the time of startup while suppressing the storage capacity of the storage unit 121b.

Furthermore, according to the absolute encoder 2, as shown in equations (2) and (3), the offset value Ofs _sub1 can be obtained by a simple linear formula without case division or approximation for the detected angle. , it is possible to suppress the maximum value of angular deviation with stable accuracy.

Therefore, according to the absolute encoder 2 in which the microcomputer 121 includes the sub-axis offset value determining section 121q, the maximum value of the angular deviation can be suppressed regardless of the position of the rotating body at the time of startup.

In addition, those skilled in the art can appropriately modify the absolute encoder 2 of the present invention based on conventionally known knowledge. As long as such modifications still have the structure of the present invention, they are, of course, included within the scope of the present invention.

For example, in the embodiment described above, the Fourier coefficients of the sin and cos components are stored as coefficients in the storage unit 121b, but the present invention is not limited to this. For example, the storage unit 121b may store a Fourier coefficient obtained by adding up the sinnθ component and the cosnθ component and the argument as predetermined coefficients.

In the embodiment described above, the Fourier coefficient of the multi-rotation angle deviation is stored in the storage unit 121b of the microcomputer 121 of the absolute encoder 2, but the present invention is not limited to this. The Fourier coefficient of the multi-rotation angle deviation may be stored in an external storage area (not shown), such as a storage area of the controller C, for example.

In the present embodiment described above, the process of determining the offset value Ofs _sub1 of the angular deviation of the sub-axis is executed by the sub-axis offset value determination unit 121q realized by the microcomputer 121 of the absolute encoder 2, but the present invention is not limited to this. The process of determining the offset value Ofs _sub1 may be performed by causing an external computer (not shown), such as a microcomputer of the controller C, to execute a program for executing the offset value determining method. In this case, the external computer functions as an angular deviation correction device.

For example, if the microcomputer 121 of the absolute encoder 2 is not equipped with a function to perform inverse Fourier transform from the angle information Ap, the multi-rotation arc degree ω, and a predetermined coefficient, or does not have the calculation processing capacity, the controller C It is preferable that a host device such as the above stores the Fourier coefficients of the multi-rotation angular deviation and determines the offset value Ofs _sub1 . An example of a criterion for determining whether offset value determination processing is possible in the absolute encoder 2 is, for example, whether floating point calculation is possible by the microcomputer 121.

In the present embodiment described above, the offset value is a value that corrects the angular deviation so that the maximum angular deviation becomes the minimum, but it may be any value that corrects the angular deviation so that it becomes small.

DESCRIPTION OF SYMBOLS 1...Motor, 1a...Main shaft, 2...Absolute encoder, 3...Gear base part, 4...Case, 4a...Outer wall part, 5...Angle sensor support board, 5a...Bottom surface, 6...Connector, 7...Shield plate, 10... Main shaft gear, 11... First worm gear part, 16... Holder part, 17... Magnet support part, 20... First intermediate gear, 21... First worm wheel part, 22... Second worm gear part, 23... Shaft, 27... Third 1 intermediate gear shaft support, 28... third worm gear section, 30... second intermediate gear, 31... third worm wheel section, 32... first spur gear section, 40... first subshaft gear, 41... second worm wheel Part, 50... Second subshaft gear, 51... Second spur gear part, 110... Board support, 121... Microcomputer, 121b... Storage unit, 121p... Angle information generation unit, 121q... Subshaft offset value determination unit, 121r... Correction unit, 121s...coefficient determination unit

Claims (8)

an angle information generation unit that generates first angle information indicating an absolute angle of the first rotating body;
Based on the first angle information, second angle information indicating an absolute angle of a second rotating body whose rotation period is different from that of the first rotating body, and a predetermined coefficient, the second rotating body is activated when the second rotating body is activated. determine a second rotating body offset value that is corrected so that a second rotating body angular deviation indicating an angular deviation of the second rotating body generated by rotating the first rotating body until it returns to an angle of . a second rotating body offset value determination unit;
a correction unit that corrects the second rotating body angular deviation using the second rotating body offset value;
Equipped with
The coefficient is determined based on the second rotating body angular deviation,
Absolute encoder. The coefficient is a Fourier coefficient determined based on the second rotating body angular deviation in a predetermined period.
The absolute encoder according to claim 1. The second rotating body offset value is
obtained by the sum of values calculated for each rotation period of the second rotating body based on the first angle information, the second angle information, and the coefficient,
The absolute encoder according to claim 1 or 2. comprising a first sensor unit that generates a first signal indicating a value of a predetermined physical quantity that changes in accordance with rotation of the first rotating body;
The angle information generation unit generates the first angle information based on the first signal.
The absolute encoder according to claim 3. The second rotating body offset value determining unit generates the second angle information based on the first signal, a difference in rotation period of the second rotating body, and a rotation speed of the second rotating body.
The absolute encoder according to claim 4. comprising a second sensor unit that generates a second signal indicating a value of a predetermined physical quantity that changes in accordance with the rotation of the second rotating body;
The angle information generation unit generates the second angle information based on the second signal.
The absolute encoder according to claim 3. Based on first angle information indicating the absolute angle of the first rotating body, second angle information indicating the absolute angle of the second rotating body whose rotation period is different from that of the first rotating body, and a predetermined coefficient, the second rotating body A second rotating body that corrects so that a second rotating body angular deviation indicating an angular deviation of the second rotating body generated by rotating the first rotating body until the rotating body returns to the starting angle is reduced. a second rotating body offset value determination unit that determines an offset value;
a correction unit that corrects the second rotating body angular deviation using the second rotating body offset value;
Equipped with
The coefficient is determined based on the second rotating body angular deviation,
Angle deviation correction device for absolute encoder. Based on first angle information indicating the absolute angle of the first rotating body, second angle information indicating the absolute angle of the second rotating body having a different rotation period from the first rotating body, and a predetermined coefficient, A second rotating body angular deviation representing an angular deviation of the second rotating body generated by rotating the first rotating body until the second rotating body returns to the starting angle is corrected so that it becomes smaller. 2 Determine the rotating body offset value,
correcting the second rotating body angular deviation using the second rotating body offset value;
The coefficient is determined based on the second rotating body angular deviation,
Angle deviation correction method for absolute encoders.

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