Multi-degree-of-freedom displacement measurement device and multi-degree-of-freedom displacement measurement method

Abstract

This multiple-degree-of-freedom displacement measurement device is provided with: a rotary scale disposed around a first rotation axis, the rotary scale having a scale pattern formed by arranging a plurality of patterns around the circumferential direction; a detection head group including a plurality of detection heads disposed in an installation plane that extends around the first rotation axis and that faces the rotary scale, each of the detection heads reading a pattern from the scale pattern; and a computation unit. On the basis of detection values acquired by the plurality of detection heads, the computation unit calculates a relative rotation angle about the first rotation axis, and calculates, in addition to the relative rotation angle about the first rotation axis, an amount of relative movement in a direction along the first rotation axis, and / or an amount of relative movement in a direction along a second rotation axis orthogonal to the first rotation axis.

Description

Technical Field

[0001] This invention relates to a multi-degree-of-freedom displacement measurement device and a multi-degree-of-freedom displacement measurement method.

Background Art

[0002] Conventionally, a rotary encoder is known as an angle detector for detecting the rotation angle around a specific axis (see, for example, Patent Document 1). A rotary encoder is mounted, for example, on a joint portion of an industrial robot such as an assembly robot (see, for example, Patent Document 2). Further, a rotary encoder may be incorporated into a machine tool and used for detecting the rotation angle of a swivel axis provided in the machine tool (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, since rotary encoders can detect the rotation angle around a specific axis, they can be attached to the joints of a robot, for example, to detect the angle between links (arm members) connected through that joint. If a robot has multiple joints, attaching a rotary encoder to each joint and knowing the detected value of each rotary encoder allows us to know the posture of the robot. However, when a robot grasps an object with an end effector at its tip, for example, its posture may change due to the weight of the object. Also, wear and shifting may occur in the components that make up the rotation axis. Such changes in the robot's posture are caused by a combination of rotational movements around multiple axes and movements along multiple axes, that is, complex movements due to multi-degree-of-freedom displacement in the robot. For this reason, in order to grasp such changes in posture and obtain accurate positional information for each part, a separate measuring device may be prepared in addition to the rotary encoder. When such measuring devices are installed, the robot becomes larger or the factory equipment becomes more complex.

[0005] Similar problems can occur in machine tools equipped with rotary encoders on the rotating parts. In machine tools, the tool attached to the slewing axis may be misaligned, or rotational vibrations may occur in the slewing axis. These phenomena may involve multi-degree-of-freedom displacement in the slewing axis. Therefore, conventional rotary encoders that only measure the rotation angle and rotational speed of the slewing axis cannot accurately capture these phenomena, and a separate monitoring device may be installed to monitor these phenomena. The installation of such monitoring devices increases the size of the machine tool or complicates the factory equipment, similar to the case with robots. Such problems can also occur in various types of machinery other than robots and machine tools.

[0006] In one aspect, the present invention aims to provide a multi-degree-of-freedom displacement measuring device that can measure the rotational movement of an object being measured around multiple axes, as well as the movement along multiple axial directions. [Means for solving the problem]

[0007] In one embodiment, the multi-degree-of-freedom displacement measuring device includes a rotary scale having a scale pattern formed by arranging a plurality of patterns along the circumferential direction and arranged around a first rotation axis, and a group of detection heads including a plurality of detection heads that spread around the first rotation axis and are arranged within an installation surface facing the rotary scale, each reading the pattern from the scale pattern, and a calculation unit that calculates the relative rotation angle around the first rotation axis based on the detection values ​​acquired by the plurality of detection heads, and also calculates at least one of the following in addition to the relative rotation angle around the first rotation axis: the relative amount of movement in the direction along the first rotation axis and the relative amount of movement in the direction along a second rotation axis perpendicular to the first rotation axis.

[0008] In another embodiment, the rotary scale includes a rotary scale having a scale pattern formed by arranging a plurality of patterns along the circumferential direction, arranged around a first rotation axis, and a group of detection heads including a plurality of detection heads that spread around the first rotation axis and are arranged in an installation surface facing the rotary scale, each reading the pattern from the scale pattern, and includes a calculation unit that calculates the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads, and also calculates at least one of the following in addition to the relative rotation angle around the first rotation axis: the relative displacement in the direction along the first rotation axis and the relative rotation angle around a second rotation axis perpendicular to the first rotation axis.

[0009] In yet another embodiment, the multi-degree-of-freedom displacement measuring device includes a rotary scale having a scale pattern formed by arranging a plurality of patterns along the circumferential direction and arranged around a first rotation axis, and a group of detection heads including a plurality of detection heads that spread around the first rotation axis and are arranged within an installation surface facing the rotary scale, each reading the pattern from the scale pattern, and a calculation unit that calculates the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads, and simultaneously calculates the relative displacement amount in the direction along a second rotation axis perpendicular to the first rotation axis and the relative rotation angle around the second rotation axis, in addition to the relative rotation angle around the first rotation axis.

[0010] In the multi-degree-of-freedom displacement measuring device described above, the plurality of detection heads are three or more, and the calculation unit calculates the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads, and in addition to the relative rotation angle around the first rotation axis, it can also calculate at least one of the following: the relative amount of movement in the direction along the first rotation axis, the relative amount of movement in the direction along the second rotation axis, and the relative amount of movement in the direction along the third rotation axis perpendicular to the first and second rotation axes.

[0011] Furthermore, in the multi-degree-of-freedom variation measuring device described above, the plurality of detection heads may be three or more, and the calculation unit may calculate the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads, and in addition to the relative rotation angle around the first rotation axis, it may also calculate at least one of the following: the relative displacement in the direction along the first rotation axis, the relative rotation angle around a second rotation axis perpendicular to the first rotation axis, and the relative rotation angle around a third rotation axis perpendicular to both the first and second rotation axes.

[0012] Furthermore, in the multi-degree-of-freedom variation measuring device described above, the plurality of detection heads may be three or more, and the calculation unit may calculate the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads, and may also simultaneously calculate at least two of the following in addition to the relative rotation angle around the first rotation axis: the relative amount of movement in the direction along the first rotation axis direction, the relative amount of movement in the direction along the second rotation axis direction, the relative amount of movement in the direction along the third rotation axis direction perpendicular to the first and second rotation axes, the relative rotation angle around the second rotation axis perpendicular to the first rotation axis, and the relative rotation angle around the third rotation axis perpendicular to the first and second rotation axes.

[0013] In the above-described multi-degree-of-freedom displacement measuring device, the installation surface is set parallel to the rotary scale, and the calculation unit calculates the distance between the rotary scale and each detection head based on the intensity of the detection signals detected by the plurality of detection heads. When these distances are equal, the calculation unit determines that the rotary scale and the group of detection heads have moved relative to each other along the first rotation axis direction, and the distance can be set to be the distance that the rotary scale and the group of detection heads have moved relative to each other.

[0014] In the multi-degree-of-freedom displacement measuring device described above, the plurality of detection heads can be arranged at equal intervals along the circumferential direction of the scale pattern.

[0015] Furthermore, in the multi-degree-of-freedom displacement measuring device described above, the detection head may be equipped with a receiving coil, and the receiving coil may be formed within a predetermined range perpendicular to the installation surface, including the installation surface.

[0016] Furthermore, in the multi-degree-of-freedom displacement measuring device described above, the receiving coil has a predetermined thickness, and the receiving coil is installed within an installation area that extends in both directions perpendicular to the installation surface, with the installation area being an area where the vertical distance from the installation surface corresponds to the predetermined thickness of the receiving coil in both directions of the installation surface.

[0017] Furthermore, in the above-described multi-degree-of-freedom displacement measuring device, the intermediate line in the thickness direction of the receiving coil may coincide with the installation surface.

[0018] In one embodiment, a multi-degree-of-freedom displacement measurement method is a method for measuring multi-degree-of-freedom displacement using a detection device comprising: a rotary scale having a scale pattern formed by arranging a plurality of patterns along the circumferential direction and arranged around a first rotation axis; and a group of detection heads including a plurality of detection heads that spread around the first rotation axis and are arranged in an installation surface facing the rotary scale, each reading the pattern from the scale pattern, the method comprising: a step of calculating the relative rotation angle around the first rotation axis based on the detection values ​​obtained by the plurality of detection heads; and a step of calculating, in addition to the relative rotation angle around the first rotation axis, at least one of the relative displacement in the direction along the first rotation axis and the relative displacement in the direction along a second rotation axis perpendicular to the first rotation axis.

[0019] In another aspect, the multi-degree-of-freedom displacement measurement method is a method for measuring displacements in multiple degrees of freedom using a detection device including a rotary scale having a scale pattern arranged around a first rotation axis and formed by arranging a plurality of patterns along the circumferential direction, and a detection head group including a plurality of detection heads that extend around the first rotation axis and are arranged in an installation plane facing the rotary scale, each reading the pattern from the scale pattern, the method including: a step of calculating a relative rotation angle around the first rotation axis based on detection values acquired by the plurality of detection heads; and a step of calculating at least one of a relative movement amount in a direction along the first rotation axis and a relative rotation angle around a second rotation axis orthogonal to the first rotation axis, in addition to the relative rotation angle around the first rotation axis.

[0020] In yet another aspect, the multi-degree-of-freedom displacement measurement method is a method for measuring displacements in multiple degrees of freedom using a detection device including a rotary scale having a scale pattern arranged around a first rotation axis and formed by arranging a plurality of patterns along the circumferential direction, and a detection head group including a plurality of detection heads that extend around the first rotation axis and are arranged in an installation plane facing the rotary scale, each reading the pattern from the scale pattern, the method including: a step of calculating a relative rotation angle around the first rotation axis based on detection values acquired by the plurality of detection heads; and a step of simultaneously calculating a relative movement amount in a direction along a second rotation axis orthogonal to the first rotation axis and a relative rotation angle around the second rotation axis, in addition to the relative rotation angle around the first rotation axis.

Advantages of the Invention

[0021] It is possible to measure rotational movements around a plurality of axes of a measurement object and movements along a plurality of axial directions.

Brief Description of the Drawings

[0022] [Figure 1] FIG. 1 is a block diagram illustrating the configuration of a multi-degree-of-freedom displacement measurement device according to an embodiment. [Figure 2]FIG. 2 is a plan view showing a schematic configuration of a rotary encoder included in the multi-degree-of-freedom displacement measuring device of the embodiment. [Figure 3] FIG. 3(A) is an explanatory view showing three degrees of freedom (X, Y, Z), and FIG. 3(B) is an explanatory view showing the remaining three degrees of freedom (θx, θy, θz). [Figure 4] FIG. 4(A) is an explanatory view schematically showing a state in which a rotary scale is relatively eccentric along the Y-axis direction in a multi-degree-of-freedom displacement measuring device having two detection heads, and FIG. 4(B) is an explanatory view schematically showing a state in which a rotary scale is relatively eccentric along the X-axis direction in a multi-degree-of-freedom displacement measuring device having two detection heads. [Figure 5] FIG. 5(A) is an explanatory view schematically showing a state in which a rotary scale is relatively rotated around the Y-axis in a multi-degree-of-freedom displacement measuring device having two detection heads, and FIG. 5(B) is an explanatory view schematically showing a state in which a rotary scale is relatively rotated around the X-axis in a multi-degree-of-freedom displacement measuring device having two detection heads. [Figure 6] FIG. 6 is an explanatory view schematically showing a state in which a rotary scale is relatively eccentric along the Y-axis direction and a state in which it is relatively eccentric along the X-axis direction in a multi-degree-of-freedom displacement measuring device having four detection heads. [Figure 7] FIG. 7 is an explanatory view schematically showing a state in which a rotary scale is relatively rotated around the Y-axis and a state in which it is relatively rotated around the X-axis in a multi-degree-of-freedom displacement measuring device having four detection heads. [Figure 8] FIG. 8(A) is an explanatory view schematically showing n detection heads and a rotary scale, FIG. 8(B) is an example of a sine wave drawn when detecting eccentricity in the X-axis direction and the Y-axis direction, and FIG. 8(C) is an example of a sine wave drawn when detecting θx and θy. [Figure 9]Figure 9(A) is an explanatory diagram showing the relationship between the eccentricity in the X-axis direction and the coefficient in the sine wave; Figure 9(B) is an explanatory diagram showing the relationship between the eccentricity in the Y-axis direction and the coefficient in the sine wave; Figure 9(C) is an explanatory diagram showing the relationship between the rotation angle around the X-axis and the coefficient in the sine wave; and Figure 9(D) is an explanatory diagram showing the relationship between the rotation angle around the Y-axis and the coefficient in the sine wave. [Figure 10] Figure 10 is a perspective view of a robot to which the multi-degree-of-freedom displacement measurement device of the embodiment is applied. [Figure 11] Figure 11 is an explanatory diagram showing the degrees of freedom at the first joint of the robot shown in Figure 10. [Figure 12] Figure 12 is a schematic diagram illustrating how the robot shown in Figure 10 tilts at its first joint. [Figure 13] Figure 13 is an explanatory diagram showing a part of a machine tool to which the multi-degree-of-freedom displacement measuring device of the embodiment is applied. [Figure 14] Figure 14 is a plan view showing the details of the rotary encoder configuration shown in Figure 2. [Figure 15] Figure 15 is an explanatory diagram showing how the detection head is positioned on the mounting surface opposite the rotary scale. [Figure 16] Figure 16 is an explanatory diagram showing the arrangement of the first to fourth detection heads in the rotary encoder. [Figure 17] Figure 17 is a plan view of the rotary scale. [Figure 18] Figure 18 is an explanatory diagram showing the configuration of the receiving coil. [Figure 19] Figure 19 is an explanatory diagram showing an example of a receiving coil formed on a printed circuit board. [Figure 20] Figure 20 illustrates the correlation between the distance between the detection head and the rotary scale and the intensity of the detection signal. [Figure 21] Figures 21(A) and 21(B) are explanatory diagrams showing the movable range of the pattern on the scale pattern relative to the rotary scale. [Figure 22]Figures 22(A) and 22(B) are explanatory diagrams showing the movable range of the pattern on the scale pattern relative to the rotary scale. [Modes for carrying out the invention]

[0023] The embodiments will be described below with reference to the drawings.

[0024] (Embodiment) First, the schematic configuration of the multi-degree-of-freedom displacement measuring device (hereinafter simply referred to as "measuring device") 50 of the embodiment will be described with reference to Figures 1 to 3(B) and Figures 14 to 22. Figure 1 is a block diagram illustrating the configuration of the measuring device 50 of the embodiment. Figure 2 is a plan view showing the schematic configuration of the rotary encoder 1 provided in the measuring device 50. Figure 3(A) is an explanatory diagram showing three degrees of freedom (X, Y, Z), and Figure 3(B) is an explanatory diagram showing the remaining three degrees of freedom (θx, θy, θz). Figure 14 is a plan view showing the details of the configuration of the rotary encoder 1, and shows a rotary encoder 1 that is closer to the actual device compared to Figure 2. Figure 15 is an explanatory diagram showing how the detection heads 5-0 to 5-(n-1) are arranged on the mounting surface facing the rotary scale 2. Figure 16 is an explanatory diagram showing the arrangement of the first detection head 5-0 to the fourth detection head 5-3 in the rotary encoder 1. Figure 17 is a plan view of the rotary scale 2. Figure 18 is an explanatory diagram showing the configuration of the receiving coil 5b. Figure 19 is an explanatory diagram showing an example in which the receiving coil 5b is formed on a printed circuit board.

[0025] Referring to Figure 1, the measuring device 50 comprises a rotary encoder 1 and a calculation unit 10. The rotary encoder 1 includes a rotary scale 2 and n detection heads 5-0 to 5-(n-1) (where n is an integer greater than or equal to 2).

[0026] The rotary encoder 1 is illustrated in Figures 3(A), 3(B), and 15. To define the detection axes for multi-degree-of-freedom displacement, Figure 3(A) shows the eccentricity detection axis, and Figure 3(B) shows the tilt detection axis. Figure 15 shows the rotary encoder 1 as viewed from the -Y direction to the +Y direction in Figure 3(A). As shown in Figure 15, the detection heads 5-0 to 5-(n-1) are positioned on the mounting surface F facing the rotary scale 2. The rotary encoder 1 shown in Figures 2, 3(A), 3(B), and 15 is equipped with four detection heads, from the first detection head 5-0 to the fourth detection head 5-3.

[0027] The detection heads 5-0 to 5-(n-1) are arranged around the Z-axis, which is the rotation center of the rotary scale 2. Each detection head 5-0 to 5-(n-1) is equipped with a transmitting coil 5a and a receiving coil 5b. Figure 16 shows the first detection head 5-0 to the fourth detection head 5-3, which are arranged on the rotary encoder 1.

[0028] The transmitting coil 5a is a sector-shaped coil with a length in the circumferential direction. As illustrated in Figure 16, the receiving coil 5b is located inside the transmitting coil 5a and forms a detection loop that repeats circumferentially with a fundamental period λ by a positive and negative sinusoidal waveform pattern of fundamental period λ.

[0029] As shown in Figure 17, the rotary scale 2 is a disc-shaped member and is mounted on a rotating body to be measured for multi-degree-of-freedom displacement (not shown) by aligning its axis of rotation with its center of rotation (Z-axis). The rotary scale 2 has a scale pattern 3 that includes multiple patterns 3a arranged along the circumferential direction of the rotary scale 2 with a fundamental period λ. Each pattern 3a is a closed-loop coil. Each pattern 3a is electromagnetically coupled to both the transmitting coil 5a and the receiving coil 5b.

[0030] The transmitting circuit 6 shown in Figure 16 generates a single-phase AC drive signal and supplies it to the transmitting coil 5a. In this case, magnetic flux is generated in the transmitting coil 5a. This generates electromotive forces in multiple patterns 3a. These multiple patterns 3a electromagnetically couple with the magnetic flux generated by the transmitting coil 5a, generating magnetic flux that changes in the circumferential direction with a predetermined spatial period. The magnetic flux generated by the transmitting coil 5a generates an electromotive force in the receiving coil 5b. The electromagnetic coupling between each coil changes according to the displacement of the rotary encoder 1, and a sinusoidal signal with the same period as the fundamental period λ is obtained.

[0031] The mounting surface F is, for example, a surface including the receiving coil 5b formed on the surface of a flat plate-shaped member. The flat plate-shaped member is, for example, a circuit board. Each receiving coil 5b has a positive / negative sine wave pattern switching section 5b1. Therefore, as shown in Figure 18, the receiving coil 5b has a thickness of the receiving coil thickness T, not just on the surface of the mounting surface F. Also, as shown in Figure 19, the receiving coil 5b can be formed on a printed circuit board. In this case, the sine wave pattern is arranged with an insulator in between, and a through-hole th is provided in the switching section 5b1 to electrically connect the two. Furthermore, since the sine wave pattern is arranged at a distance of the receiving coil thickness T, by setting the mounting surface F to the midpoint of the receiving coil thickness T, it is possible to detect with high accuracy while maintaining a good signal balance. In addition, each receiving coil 5b is connected to a signal processing circuit 10a provided in the calculation unit 10, and the signal acquired by each receiving coil 5b is used for calculations in the calculation unit 10. Each receiving coil 5b and the signal processing circuit 10a are connected by wire, but they may also be connected wirelessly.

[0032] In the rotary encoder 1 shown in Figures 2, 3(A), and 3(B), the first detection head 5-0 to the fourth detection head 5-3 are arranged circumferentially at equal intervals. However, the intervals between the detection heads do not have to be equal; they may be arranged at any interval. However, arranging the detection heads 5-0 to 5-(n-1) at equal intervals makes the calculations performed by the calculation unit 10, which will be explained later, easier. To put it another way, the detection heads 5-0 to 5-(n-1) are arranged circumferentially at equal intervals, meaning that the detection heads are arranged at equal angles around the Z-axis, which is the rotation center of the rotary scale 2 (on a circle with the Z-axis as the central axis).

[0033] In this embodiment, each detection head is equipped with a transmitting coil 5a, but for example, a single transmitting coil may be provided, and the signal transmitted from this transmitting coil toward the rotary scale 2 may be received by each receiving coil 5b.

[0034] In this embodiment, the rotary encoder 1 is mounted on the rotating body side of the object to be measured. However, the mounting surface F on which the detection heads 5-0 to 5-(n-1) are provided may also be set on the rotating body side. In short, the rotary encoder 1 only needs to be installed on the object to be measured such that the relative positional relationship between the rotary scale 2 and the mounting surface F changes.

[0035] The rotary encoder 1 in this embodiment is of the electromagnetic induction type, but it may also be of the capacitive or photoelectric type, or other detection principle. When using other types of rotary encoders, the transmitting coil and receiving coil will be of the type appropriate to the rotary encoder, respectively.

[0036] [Measurement principle] Next, the principle of measuring multi-degree-of-freedom displacement using the measuring device 50 will be explained with reference to Figures 4(A) to 9(D). Each figure depicts a rotary encoder with a different number and arrangement of detection heads. Strictly speaking, the detection heads and rotary encoders may differ between figures, but for the sake of explanation, a common reference number is used for different detection heads and rotary encoders. Also, elements shown in Figure 2, etc., are simplified or omitted in each figure.

[0037] First, referring to Figures 4(A) and 4(B), we will describe the case where the rotary scale 2 is eccentric in a rotary encoder 1 equipped with two detection heads. Referring to Figure 4(A), the rotary encoder 1 is equipped with two detection heads, namely a first detection head 5-0 and a second detection head 5-1. In the rotary encoder 1 shown in Figure 4(A), the first detection head 5-0 and the second detection head 5-1 are positioned 180° apart on the X-axis. In other words, the first detection head 5-0 and the second detection head 5-1 are positioned on opposite sides of the X-axis, separated by the Z-axis.

[0038] In such a rotary encoder 1, let's assume that the rotary scale 2 is eccentric to the +Y side, as shown in the rotary encoder 1 on the right side of Figure 4(A). Then, the first detection head 5-0 will show a detection value as if the rotary scale 2 has rotated to the positive side (+θz) around the Z axis. On the other hand, the second detection head 5-1 will show a detection value as if the rotary scale 2 has rotated to the negative side (-θz) around the Z axis. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 has moved (eccentrically) relatively to the +Y side. The amount of movement at this time is the absolute value of the detection value of the first detection head 5-0 and the detection value of the second detection head 5-1, respectively. Note that if the ± of the detection values ​​of the first detection head 5-0 and the second detection head 5-1 are swapped, it means that the rotary scale 2 has moved (eccentrically) relatively to the -Y side.

[0039] In the rotary encoder 1 shown in Figure 4(B), the first detection head 5-0 and the second detection head 5-1 are positioned 180° apart on the Y-axis. In other words, the first detection head 5-0 and the second detection head 5-1 are located on opposite sides of the Y-axis, separated by the Z-axis.

[0040] In such a rotary encoder 1, let's assume that the rotary scale 2 is eccentric to the -X side, as shown in the lower part of Figure 4(B). Then, the first detection head 5-0 will show a detection value as if the rotary scale 2 had rotated to the positive side (+θz) around the Z axis. On the other hand, the second detection head 5-1 will show a detection value as if the rotary scale 2 had rotated to the negative side (-θz) around the Z axis. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 has moved (eccentrically) to the -X side relatively. The amount of movement at this time is the absolute value of the detection value of the first detection head 5-0 and the detection value of the second detection head 5-1, respectively. Note that if the ± of the detection values ​​of the first detection head 5-0 and the second detection head 5-1 are swapped, it means that the rotary scale 2 has moved (eccentrically) to the +X side relatively.

[0041] Next, referring to Figures 5(A) and 5(B), we will describe the case where the rotary scale 2 is tilted in a rotary encoder 1 equipped with two detection heads. Referring to Figure 5(A), the rotary encoder 1 is equipped with a first detection head 5-0 and a second detection head 5-1, similar to the rotary encoder 1 shown in Figure 4(A). Here, the distance between the detection head and the rotary scale 2 is correlated with the intensity of the detection signal. Specifically, when the distance between the detection head and the rotary scale 2 is small (small gap fluctuation), the intensity of the detection signal becomes large (strong), and when the distance is large (far apart and gap fluctuation is large), the intensity of the detection signal becomes small (weak). Figure 20 is a diagram illustrating the correlation between the distance between the detection head and the rotary scale 2 and the intensity of the detection signal obtained from the receiving coil. In Figure 2, the horizontal axis shows the distance between the two [mm], and the vertical axis shows the signal intensity. The detection method of the rotary encoder 1 in this embodiment uses electromagnetic induction between a transmitting coil and a receiving coil. As illustrated in Figure 20, the signal strength decreases as the distance increases and increases as the distance decreases. A map showing the relationship between the distance between the detection head and the rotary scale 2 and the strength of the detection signal is stored in the calculation unit 10, as shown in Figure 20. By applying the strength of the detection signal obtained from each detection head to the Y axis of the map shown in Figure 20, the distance between each detection head and the rotary scale 2 can be calculated.

[0042] In such a rotary encoder 1, let's assume that the rotary scale 2 rotates in the +θy direction (clockwise in Figure 5(A)), as shown in the rotary encoder 1 on the right side of Figure 5(A). Then, the distance between the first detection head 5-0 and the rotary scale 2, as detected by the first detection head 5-0, is greater than the distance between the second detection head 5-1 and the rotary scale 2, as detected by the second detection head 5-1. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 is rotating relatively in the +θy direction. The amount of rotation at this time can be calculated from the difference between the detection value of the first detection head 5-0 and the detection value of the second detection head 5-1. Note that if the distance between the second detection head 5-1 and the rotary scale 2 is greater than the distance between the first detection head 5-0 and the rotary scale 2, then the rotary scale 2 is rotating relatively towards the -θy side.

[0043] Referring to Figure 5(B), the rotary encoder 1 is equipped with a first detection head 5-0 and a second detection head 5-1, similar to the rotary encoder 1 shown in Figure 4(B). In this case as well, the distance between each detection head and the rotary scale 2 is calculated based on the intensity of the detection signal.

[0044] In such a rotary encoder 1, let's assume that the rotary scale 2 rotates in the +θx direction (clockwise in Figure 5(B)) as shown in the lower part of Figure 5(B). Then, the distance between the second detection head 5-1 and the rotary scale 2 detected by the second detection head 5-1 is greater than the distance between the first detection head 5-0 and the rotary scale 2 detected by the first detection head 5-0. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 is rotating relatively in the +θx direction. The amount of rotation at this time can be calculated from the difference between the detection value of the first detection head 5-0 and the detection value of the second detection head 5-1. Note that if the distance between the first detection head 5-0 and the rotary scale 2 is greater than the distance between the second detection head 5-1 and the rotary scale 2, then the rotary scale 2 is rotating relatively towards the -θx side.

[0045] Next, referring to Figure 6, we will describe the case where the rotary scale 2 is eccentric in a rotary encoder 1 equipped with four detection heads. Referring to Figure 6, the rotary encoder 1 is equipped with four detection heads, namely the first detection head 5-0, the second detection head 5-1, the third detection head 5-2, and the fourth detection head 5-3. In this rotary encoder 1, the first detection head 5-0 and the third detection head 5-2 are positioned 180° apart on the X axis, and the second detection head 5-1 and the fourth detection head 5-3 are positioned 180° apart on the Y axis. In other words, the first detection head 5-0 and the third detection head 5-2 are positioned on opposite sides of the X axis separated by the Z axis, and the second detection head 5-1 and the fourth detection head 5-3 are positioned on opposite sides of the Y axis separated by the Z axis. The first detection head 5-0 to the fourth detection head 5-3 are positioned at equal intervals of 90° apart.

[0046] In such a rotary encoder 1, let's assume that the rotary scale 2 is eccentric to the +Y side, as shown in the rotary encoder 1 on the right side of Figure 6. Then, the first detection head 5-0 shows a detection value as if the rotary scale 2 had rotated to the positive side (+θz) around the Z axis. On the other hand, the third detection head 5-2 shows a detection value as if the rotary scale 2 had rotated to the negative side (-θz) around the Z axis. Furthermore, the detection values ​​of the second detection head 5-1 and the fourth detection head 5-3 both show the values ​​as if there had been no rotation around the Z axis. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 has moved relatively to the +Y side. The amount of movement at this time is the absolute value of the detection value of the first detection head 5-0 and the detection value of the third detection head 5-2, respectively. Note that if the ± signs of the detection values ​​of the first detection head 5-0 and the third detection head 5-2 are swapped, it means that the rotary scale 2 has moved relatively to the -Y side.

[0047] In the rotary encoder 1 shown in Figure 6, assume that the rotary scale 2 is eccentric to the -X side, as shown in the lower part of Figure 6. Then, the second detection head 5-1 shows a detection value as if the rotary scale 2 had rotated to the positive side (+θz) around the Z axis. On the other hand, the fourth detection head 5-3 shows a detection value as if the rotary scale 2 had rotated to the negative side (-θz) around the Z axis. The detection values ​​of the first detection head 5-0 and the third detection head 5-2 both represent the values ​​as if there had been no rotation around the Z axis. When such a combination of detection values ​​is obtained, it can be seen that the rotary scale 2 has moved relatively to the -X side. The amount of movement at this time is the absolute value of the detection value of the second detection head 5-1 and the detection value of the fourth detection head 5-3, respectively. Note that if the ± signs of the detection values ​​of the second detection head 5-1 and the fourth detection head 5-3 are swapped, it means that the rotary scale 2 has moved relatively to the +X side.

[0048] Next, referring to Figure 7, we will describe the case where the rotary scale 2 is tilted in a rotary encoder 1 equipped with four detection heads. Referring to Figure 7, the rotary encoder 1 is equipped with first detection heads 5-0 to 4th detection heads 5-3, similar to the rotary encoder 1 shown in Figure 6. The distance between each detection head and the rotary scale 2 is calculated based on the intensity of the detection signal from each detection head.

[0049] In such a rotary encoder 1, let's assume that the rotary scale 2 is rotating in the +θy direction (clockwise in Figure 7), as shown in the rotary encoder 1 on the right side of Figure 7. Then, the distance between the first detection head 5-0 and the rotary scale 2, as detected by the first detection head 5-0, is greater than the distance between the third detection head 5-2 and the rotary scale 2, as detected by the third detection head 5-2. Furthermore, the detected values ​​of the second detection head 5-1 and the fourth detection head 5-3 are the same. When such a combination of detected values ​​is obtained, it can be seen that the rotary scale 2 is rotating relatively in the +θy direction. The amount of rotation at this time can be calculated from the difference between the detected value of the first detection head 5-0 and the detected value of the third detection head 5-2. Note that if the distance between the third detection head 5-2 and the rotary scale 2 is greater than the distance between the first detection head 5-0 and the rotary scale 2, then the rotary scale 2 is rotating relatively towards the -θy side.

[0050] In such a rotary encoder 1, let's assume that the rotary scale 2 is rotating in the +θx direction (clockwise in Figure 7), as shown in the rotary encoder 1 at the bottom of Figure 7. Then, the distance between the fourth detection head 5-3 and the rotary scale 2, as detected by the fourth detection head 5-3, is greater than the distance between the second detection head 5-1 and the rotary scale 2, as detected by the second detection head 5-1. Furthermore, the detected values ​​of the first detection head 5-0 and the third detection head 5-2 are the same. When such a combination of detected values ​​is obtained, it can be seen that the rotary scale 2 is rotating relatively in the +θx direction. The amount of rotation at this time can be calculated from the difference between the detected value of the second detection head 5-1 and the detected value of the fourth detection head 5-3. Note that if the distance between the second detection head 5-1 and the rotary scale 2 is greater than the distance between the fourth detection head 5-3 and the rotary scale 2, then the rotary scale 2 is rotating relatively towards the -θx side.

[0051] Figures 4(A) to 7 illustrate the cases with two and four detection heads, but if there are two or more detection heads, displacements with multiple degrees of freedom can be measured in a similar manner. Rotation around the Z axis can be detected from the detection values ​​of each detection head, similar to conventional rotary encoders. The rotation angle (amount of rotation) around the Z axis can be, for example, the average value of the detection values ​​(angle output) of each detection head. In addition, the average value of the distance between each detection head and the rotary scale 2, calculated based on the detection of each detection head, can be used as the relative displacement along the Z axis.

[0052] Next, with reference to Figures 8(A) to 9(D), the calculation of the displacement of degrees of freedom included in a multi-degree-of-freedom system will be explained. The calculation of the degree of freedom displacement is performed by the calculation unit shown in Figure 1.

[0053] The following explanation refers to the rotary encoder 1 shown in Figure 8(A). The rotary encoder 1 shown in Figure 8(A) has n detection heads, from the first detection head 5-0 to the nth detection head 5-(n-1). In the figure, φ indicates the installation position of each detection head. Specifically, it indicates the clockwise angle with the installation position φ0 of the first detection head 5-0 as the reference position.

[0054] <When the rotary scale is relatively eccentric> First, referring to Figure 8(B), we will explain the case where the rotary scale 2 is eccentric relative to the detection head group. The relative displacement X (eccentricity) along the X-axis and the relative displacement Y (eccentricity) along the Y-axis can be determined by the amplitude and phase of the eccentricity error. The angular output outk of the k-th (k=0 to n-1) detection head out of n detection heads is expressed as the sum of the ideal angular output, i.e., the angular output obtained when there is no eccentricity, and the eccentricity error (see equation (1)).

number

[0055] Here, we consider the difference in angular output between the two detection heads i and j (see equation (2)).

number

[0056] Since the difference between the ideal angle (i) and the ideal angle (j) is equal to the difference between the placement of the two detection heads, φi-φj, the eccentricity error can be extracted by defining Δout using the following equation (3).

number

[0057] Here, if we let α be the amplitude and β be the phase of the eccentricity error with respect to φ=0, then these can be expressed as shown in equation (4) below.

number

[0058] Therefore, Δout(i,j) can be expressed as shown in equation (5) below.

number

[0059] Then, by rearranging equation (5), Δout(i,j) can be expressed as shown in equation (6) below.

number

[0060] Here, Δα(i,j) and Δφ(i,j) are constants that depend on the arrangement of the two detection heads. That is, Δout(i,j) is a sine wave whose amplitude is multiplied by Δα(i,j) and whose phase is shifted by φi,j compared to the eccentricity error with φ=0 as the reference. Therefore, if we plot Out(i,j) divided by Δα(i,j) on the vertical axis and Δφ(i,j) on the horizontal axis, we obtain a plot as shown in Figure 8(b), and by fitting this to a sine wave, we can determine the amplitude and phase of the eccentricity error.

[0061] Here, we will explain an example of fitting the equation y = a + b·sin(θ) + c·cos(θ), which represents a sine wave as shown in Figure 8(B), to calculate the coefficients a, b, and c. For the sake of simplicity, we will assume that the first detection head 5-0 to the nth detection head 5-(n-1) are arranged at equal intervals.

[0062] The coefficients a, b, and c can be calculated by applying the least squares method using the following equation (7). In equation (7), parts A and B are determined by the arrangement of the detection heads, and part C is Δout(i,j) / Δα(i,j) obtained from the difference in the angular output of each detection head and the arrangement of the detection heads.

number

[0063] Equation (7) is the general formula for the case of n detection heads, but when there are 4 detection heads, the coefficients a, b, and c can be determined by the following equation (8). Also, when there are 8 detection heads, the coefficients a, b, and c can be determined by the following equation (9).

number

number

[0064] By performing the above calculations, we can determine the coefficients a, b, and c, and identify the equation representing a sine wave: y = a + b·sin(θ) + c·cos(θ). Then, using the coefficient b in this equation, we can determine the relative displacement X (eccentricity) along the X-axis, and using the coefficient c, we can determine the relative displacement Y (eccentricity) along the Y-axis.

[0065] The relative displacement X [mm] has the relationship between the coefficient b [rad] and R [mm] as shown in Figure 9(A). Here, R [mm] is the radius of scale pattern 3.

[0066] Therefore, the relative displacement X [mm] is calculated by the following equation 10.

number

[0067] Similarly, the relative displacement Y [mm] has the relationship between the coefficient c [rad] and R [mm] as shown in Figure 9(B). Here, R [mm] is the radius of scale pattern 3.

[0068] Therefore, the relative displacement Y [mm] is calculated by the following equation 11.

number

[0069] In this way, the relative displacement X [mm] and relative displacement Y [mm] can be calculated.

[0070] <When the rotary scale is rotating relative to the scale> Next, referring to Figure 8(C), we will explain the case where the rotary scale 2 rotates relative to the detection head group. Specifically, we will explain the case where the rotary scale 2 rotates around the X-axis and also around the Y-axis relative to the detection head group. The relative rotation amount θx (tilt) around the X-axis and the relative rotation amount θy (tilt) around the Y-axis can be determined by the amplitude and phase of the gap fluctuation (distance between each detection head and the rotary scale 2).

[0071] When detecting relative rotation θx and relative rotation θy around the Y axis, the vertical axis represents the gap in the sine wave shown in Figure 8(C). By plotting the gaps at each detection head from the first detection head 5-0 to the nth detection head 5-(n-1) arranged circumferentially, and fitting them, the coefficients a, b, and c of the sine wave (a+b·sin(θ)+c·cos(θ)) can be obtained. The amplitude of this fitted sine wave becomes the amplitude of the gap fluctuation. That is, √(b 2 +c 2 ) represents the amplitude of the gap fluctuation.

[0072] The coefficients a, b, and c can be calculated by applying the least squares method using the following equation (12). In equation (12), parts A and B are determined by the arrangement of the detection heads, and part C is a matrix of gap values ​​for each detection head.

number

[0073] Equation (12) is the general formula for the case of n detection heads, but when there are 4 detection heads, the coefficients a, b, and c can be found using the following equation (13). Also, when there are 8 detection heads, the coefficients a, b, and c can be found using the following equation (14).

number

number

[0074] By performing the above calculations, we can determine the coefficients a, b, and c, and identify the equation representing a sine wave: y = a + b·sin(θ) + c·cos(θ). Then, using the coefficient b in this equation, we can find the relative rotation amount θx (slope) around the X axis, and using the coefficient c, we can find the relative rotation amount θy (slope) around the Y axis.

[0075] The relative rotation amount θx [rad] has the relationship between the coefficient b [mm] and R [mm] as shown in Figure 9(C). Here, R [mm] is the radius of scale pattern 3.

[0076] Therefore, the relative rotation amount θx [rad] is calculated by the following equation 15.

number

[0077] Similarly, the relative rotation amount θy [rad] has the relationship between the coefficient c [mm] and R [mm] as shown in Figure 9(D). Here, R [mm] is the radius of scale pattern 3.

[0078] Therefore, the relative rotation amount θy [rad] is calculated by the following equation 16.

number

[0079] In this way, the relative rotation amounts θx [rad] and θy [rad] can be calculated.

[0080] The rotary encoder 1 can detect the amount of eccentricity when the rotary scale 2 is in an eccentric position, and can also detect the amount of tilt when the rotary scale 2 is in a tilted position. In the above description, these are explained separately. Specifically, the detection of the amount of eccentricity when the rotary scale 2 is in an eccentric position is explained with reference to Figures 4(A), 4(B), and 6, and the detection of the amount of tilt when the rotary scale 2 is in a tilted position is explained with reference to Figures 5(A), 5(B), and 7. However, the rotary encoder 1 can simultaneously detect the amount of eccentricity and the amount of tilt even when the rotary scale 2 is both eccentric and tilted.

[0081] Here, with reference to Figures 21(A) to 22(B), the movable range of pattern 3a on the scale pattern 3 relative to the rotary scale 2 will be explained. Figures 21(A) to 22(B) both show a part of the rotary encoder 1 as viewed from the Z-axis direction. In Figures 21(A) to 22(B), reference numeral CP1 is the center of the scale pattern 3 and is indicated by a cross shape drawn with a dashed line. Reference numeral CP2 is the rotation center of the rotary scale 2 and is indicated by a cross shape drawn with a solid line. The transmitting coil 5a and the receiving coil 5b are arranged circumferentially around the rotation center CP2. Figures 21(A) to 22(B) show how the center CP1 of the scale pattern 3 and the rotation center CP2 of the rotary scale 2 are slightly offset relative to each other. The scale pattern 3 and the rotary scale 2 are provided so that when the eccentricity and tilt amount of the rotary scale 2 are detected simultaneously, pattern 3a can maintain the state described below. In other words, the scale pattern 3 and rotary scale 2 are arranged such that pattern 3a does not extend beyond the magnetic flux generation region generated by the transmitting coil 5a of each detection head, as shown in Figures 21(A) to 22(B).

[0082] The measuring device 50 of this embodiment is equipped with n detection heads 5-0 to 5-(n-1), and can output the position coordinates of a particular detection head included in the detection heads 5-0 to 5-(n-1) in a cylindrical coordinate system P(r,θ,Z). In other words, by using the detection values ​​of detection heads other than the detection head for which the position coordinates are to be output, the position coordinates of the target detection head can be determined. By outputting the position coordinates of the detection heads included in the detection heads 5-0 to 5-(n-1) to each other, it becomes possible to measure multi-degree-of-freedom displacement.

[0083] As described above, the rotation center of the rotary scale 2 in the rotary encoder 1 and the central axis of the circumferentially arranged detection heads 5-0 to 5-(n-1) are both the Z-axis. When the rotary encoder 1 is installed on the object to be measured, this positional relationship between the rotary encoder 1 and the detection heads 5-0 to 5-(n-1) is guaranteed. Here, the object to be measured by the rotary encoder 1 is assumed to be, for example, a joint in a robot or a rotating member on which a tool is attached in a machine tool. Robots and machine tools may experience displacement in various parts due to aging and loads applied to each part during use. The measuring device 50 of this embodiment makes it possible to measure this displacement. In other words, by using the state when the rotary encoder 1 is installed as the initial state and measuring the multi-degree-of-freedom displacement based on that state, the state of the object to be measured can be understood.

[0084] Note that the distances between each detection head, the dimensions of each detection head, and the dimensions of Rotary Scale 2 in each figure do not accurately represent the actual dimensions. Also, the dimensions of Pattern 3a and the distances between Pattern 3a in each figure do not accurately represent the actual dimensions.

[0085] Here, referring again to Figures 3(A) and 3(B), we will explain the multi-degree-of-freedom displacement that can be measured by the measuring device 50 of the embodiment. As shown in Figures 3(A) and 3(B), the rotary encoder 1 is installed with its rotation center coinciding with the Z-axis. At this time, the rotary scale 2 is installed so that the X-axis, which is orthogonal to the Z-axis, and the Y-axis, which is orthogonal to both the Z-axis and the X-axis, pass through it radially. Here, the Z-axis corresponds to the first rotation axis, the X-axis to the second rotation axis, and the Y-axis to the third rotation axis.

[0086] As shown in Figure 3(A) by +X and -X, the measuring device 50 can detect the relative movement of the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2 along the X-axis direction. Furthermore, as shown in Figure 3(A) by +Y and -Y, the measuring device 50 can detect the relative movement of the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2 along the Y-axis direction. In addition, as shown in Figure 3(A) by +Z and -Z, the measuring device 50 can detect the relative movement of the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2 along the Z-axis direction.

[0087] The measuring device can detect the relative rotation angle around the X axis between the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2, as shown by +θx and -θx in Figure 3(B). The measuring device 50 can also detect the relative rotation angle around the Y axis between the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2, as shown by +θy and -θy in Figure 3(B). Furthermore, the measuring device 50 can detect the relative rotation angle around the Z axis between the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2, as shown by +θz and -θz in Figure 3(B).

[0088] Of the six degrees of freedom described above, the relative rotation angle around the Z-axis between the detection head group, including detection heads 5-0 to 5-(n-1), and the rotary scale 2 is one of the degree of freedom displacements measured by a conventional rotary encoder. In the measuring device 50 of this embodiment, the relative rotation angle around the Z-axis can be measured in the same way as with a conventional rotary encoder. In addition to this relative rotation angle around the Z-axis, the measuring device 50 of this embodiment can also measure displacements of other degrees of freedom.

[0089] (First embodiment) Next, with reference to Figures 10 to 12, a robot 100 as a first embodiment to which the measuring device 50 of the embodiment can be applied will be described. The robot 100 is a so-called industrial robot used for assembly work in factories and the like.

[0090] The robot 100 includes a base section 101, which serves as the foundation and has a reference point P1 for the coordinates of each part of the robot 100, and first link members 102a to sixth link members 102f. The sixth link member 102f is an end effector, which is a hand section that grips the workpiece. Joints J1 to J6 are provided at the connection points of each link member. A motor (not shown) and a rotary encoder 1 as shown in Figure 1 are incorporated into each joint section J1 to J6. Note that the configuration in which a motor and a rotary encoder are incorporated into each joint section J1 to J6 is a conventionally known configuration, and the motors and rotary encoders incorporated into each joint section J1 to J6 are omitted in Figures 10 and 12.

[0091] The first joint J1 is provided between the base portion 101 and the first link member 102a. The second joint J2 is provided between the first link member 102a and the second link member 102b. The third joint J3 is provided between the second link member 102b and the third link member 102c. The fourth joint J4 is provided between the third link member 102c and the fourth link member 102d. The fifth joint J5 is provided between the fourth link member 102d and the fifth link member 102e. The sixth joint J6 is provided between the fifth link member 102e and the sixth link member (end effector) 102f. The center points of the rotary encoder 1 provided at each joint are P1, P2, P3, P4, P5, and P6, respectively. The position of the sixth link member 102f is represented by the gripping point HC. In controlling the robot 100, the coordinates of the gripping point HC relative to the coordinates of the reference point P1 (0,0,0) are specified. Specifically, the motors provided at each joint J1 to J6 operate so that the coordinates of the gripping point HC become the target coordinates. The center points P1 to P6 and the gripping point HC can be calculated by sequentially calculating, starting from the reference point P1, taking into account the rotation angle (amount of rotation) of the motors at each joint J1 to J6 and the dimensions of each link member.

[0092] Here, referring to Figures 11 and 12, the changes in the six degrees of freedom (X, Y, Z, θx, θy, θz) at the first joint J1 will be explained. The rotary encoder 1 provided at the first joint J1 is installed with the Z axis passing through a reference point P1 whose coordinates are (0,0,0). The motor incorporated in the first joint J1 rotates the first link member 102a around the Z axis, so the θz is the one that changes actively when the motor is operated. However, due to various reasons, for example, when the sixth link member 102f grips an object to be gripped, the link members from the first link member 102a onward may tilt relative to the base 101 due to the weight of the object to be gripped, as shown in Figure 12. Also, eccentricity in the X-axis direction or Y-axis direction may occur due to wear of the members forming the shaft portion.

[0093] When such a phenomenon occurs, it is thought that, in addition to the rotation angle θz around the Z axis, one of the remaining 5 degrees of freedom (X, Y, Z, θx, θy, θz) is also changing. If movement occurs in the X, Y, and Z directions, the reference point P1 becomes reference point P1', and its coordinates (0,0,0) are updated to (x,y,z). Furthermore, if rotations θx around the X axis and θy around the Y axis are measured, a Z' axis tilted to account for these rotations is set. The Z' axis passes through the new reference point P1'. In addition, new X' and Y' axes are set that take into account the original rotation θz around the Z axis. In this way, the X, Y, and Z axes are updated to the X', Y', and Z' axes. Thus, when displacement occurs across multiple degrees of freedom, the X, Y, and Z axes are updated.

[0094] This updating of the X, Y, and Z axes is also performed at each joint from J2 to J6. As a result, the position of the gripping point HC, for which the target coordinates are set, actually becomes gripping point HC', and its coordinates are different from the target coordinates.

[0095] The actual coordinates of the gripping point HC' are calculated sequentially by considering the multi-degree-of-freedom displacement detected by the rotary encoder 1 at each joint J1 to J6 and the dimensions of each link member.

[0096] If the coordinates of the actual gripping point HC' calculated in this way differ from the coordinates of the target gripping point HC as shown in Figure 12, the robot 100 performs position correction control by moving joints J1 to J6 to cancel out this coordinate difference. Note that the position correction control itself can be performed using conventionally known methods, so a detailed explanation thereof is omitted here.

[0097] As a result, the robot 100 can determine its posture and the deviation of its gripping point HC without needing to prepare any other measuring devices besides the rotary encoder 1. Furthermore, it can correct for this deviation.

[0098] (Second example) Next, with reference to Figure 13, a machine tool 150 as a second embodiment to which the measuring device 50 of the embodiment can be applied will be described. The machine tool 150 performs cutting, polishing, and other operations on a workpiece (not shown).

[0099] The machine tool 150 comprises a cylindrical body 151, a drive motor 152 housed within the body 151, and a rotating member 153 rotatably mounted by the drive motor 152. The drive motor 152 rotates the rotating member 153 around the main spindle AX. A chuck portion 153a is provided at the tip of the rotating member 153. Various tools can be attached to the chuck portion 153a, but in this embodiment, a cutting tool 154 is attached to the chuck portion 153a. A rotary encoder 1 is provided inside the body 151. The rotary scale 2 included in the rotary encoder 1 is fixed to the rotating member 153 and rotates together with the rotating member 153. The detection head 5 included in the rotary encoder 1 is fixed to the inner circumferential wall surface of the body 151. Multiple detection heads 5 are provided, and these detection heads 5 are arranged circumferentially on a virtual mounting surface F facing the rotary scale 2. The rotary encoder 1 is positioned so that the rotation axis AX coincides with the axial (Z-axis) direction.

[0100] In the machine tool 150, the rotary encoder 1 measures the rotation angle θz around the Z axis, and the remaining five degrees of freedom are measured as appropriate.

[0101] The machine tool 150 can calculate the precise coordinates of the tip 154a of the cutting tool 154 by measuring the displacement of multiple degrees of freedom. When the displacement of multiple degrees of freedom is measured by the rotary encoder 1, the coordinates of the tip 154a will be deviated from the target coordinates. Therefore, the machine tool 150 performs a correction operation to correct the deviation in the coordinates of the tip 154a. As a result, the machine tool 150 can perform machining with higher precision.

[0102] Furthermore, the machine tool 150 of the second embodiment can monitor the operating state of the rotating member 153. Specifically, by measuring the displacement of multiple degrees of freedom, it is possible to detect modulation of the drive motor 152 and the rotating member 153 and predict their failures. In other words, the rotary encoder 1 makes it possible to monitor the state of the rotating shaft (eccentricity, tilt, and their vibrations) in a simple configuration without adding any other sensors, which can be used to predict machine failures.

[0103] The measuring device 50 of this embodiment can measure the rotational movement of an object to be measured around multiple axes, as well as the movement along multiple axial directions. In other words, it can measure the rotation angle θz around the Z axis, and also measure the remaining five degrees of freedom as appropriate.

[0104] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0105] 1 Rotary encoder 2 Rotary Scales 3 scale patterns 3a Pattern 5 detection heads 5-0 First detection head 5-1 Second detection head 5-n-1 nth detection head 5a Transmitter coil 5b Receiving coil 50. Multi-degree-of-freedom displacement measurement device 100 robots 101 Base section 102a First link member 102b Second link member 102c Third link member 102d Fourth link member 102e Fifth link member 102f Sixth link member J1 First joint J2 Second joint J3 Third joint J4 Fourth joint J5 Fifth joint J6 Sixth joint

Claims

1. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, The system comprises a group of detection heads that extend around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each including a plurality of detection heads that read the pattern from the scale pattern, Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the first rotation axis, The relative amount of movement in the direction along the second rotation axis which is perpendicular to the first rotation axis, A calculation unit that simultaneously calculates and A multi-degree-of-freedom displacement measuring device equipped with the following features.

2. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, The system comprises a group of detection heads that extend around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each including a plurality of detection heads that read the pattern from the scale pattern, Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the first rotation axis, The relative rotation angle around the second rotation axis which is perpendicular to the first rotation axis, A calculation unit that simultaneously calculates and A multi-degree-of-freedom displacement measuring device equipped with the following features.

3. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, The system comprises a group of detection heads that extend around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each including a plurality of detection heads that read the pattern from the scale pattern, Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the second rotation axis which is perpendicular to the first rotation axis, The relative rotation angle around the second rotation axis and A calculation unit that simultaneously calculates and A multi-degree-of-freedom displacement measuring device equipped with the following features.

4. The aforementioned plurality of detection heads are three or more. The calculation unit, based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, Further calculations are made regarding the relative displacement in the direction along the third rotation axis direction, which is perpendicular to the first rotation axis and the second rotation axis. The multi-degree-of-freedom displacement measuring device according to claim 1.

5. The aforementioned plurality of detection heads are three or more. The calculation unit, based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, Further calculations are made regarding the relative rotation angle around a third rotation axis that is perpendicular to the first rotation axis and the second rotation axis. The multi-degree-of-freedom displacement measuring device according to claim 2.

6. The aforementioned plurality of detection heads are three or more. The calculation unit, based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative amount of movement in the direction along the first rotation axis, The relative amount of movement in the direction along the third rotation axis direction which is perpendicular to the first rotation axis and the second rotation axis, Of the relative rotation angles around the third rotation axis, Calculate at least one more thing. The multi-degree-of-freedom displacement measuring device according to claim 3.

7. The aforementioned mounting surface is set parallel to the rotary scale, The calculation unit calculates the distance between the rotary scale and each detection head based on the intensity of the detection signals detected by the plurality of detection heads, determines that the rotary scale and the group of detection heads have moved relative to each other along the first rotation axis direction when the distances are equal, and sets the distance to be the distance that the rotary scale and the group of detection heads have moved relative to each other, according to any one of claims 1, 2, or 6.

8. The plurality of detection heads are arranged at equal intervals along the circumferential direction of the scale pattern, A multi-degree-of-freedom displacement measuring device according to any one of claims 1 to 6.

9. The detection head comprises a receiving coil, which is formed within a predetermined range perpendicular to the mounting surface, including the mounting surface. A multi-degree-of-freedom displacement measuring device according to any one of claims 1 to 6.

10. The receiving coil has a predetermined thickness, and is installed within an installation area that extends in both directions perpendicular to the installation surface, with the installation surface as the center, and the installation area is an area where the vertical distance from the installation surface corresponds to the predetermined thickness of the receiving coil in both directions of the installation surface. The multi-degree-of-freedom displacement measuring device according to claim 9.

11. The midpoint of the receiving coil in the thickness direction coincides with the mounting surface. The multi-degree-of-freedom displacement measuring device according to claim 10.

12. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, A method for measuring multi-degree-of-freedom displacement using a detection device comprising: a detection head group including a plurality of detection heads that spread around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each of which reads the pattern from the scale pattern; Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the first rotation axis, The relative amount of movement in the direction along the second rotation axis which is perpendicular to the first rotation axis, A process of simultaneously calculating, A multi-degree-of-freedom displacement measurement method, including the following.

13. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, A method for measuring multi-degree-of-freedom displacement using a detection device comprising: a detection head group including a plurality of detection heads that spread around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each of which reads the pattern from the scale pattern; Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the first rotation axis, The relative rotation angle around the second rotation axis which is perpendicular to the first rotation axis, A process of simultaneously calculating, A multi-degree-of-freedom displacement measurement method, including the following.

14. A rotary scale having a scale pattern formed by arranging multiple patterns along the circumferential direction, arranged around a first axis of rotation, A method for measuring multi-degree-of-freedom displacement using a detection device comprising: a detection head group including a plurality of detection heads that spread around the first rotation axis and are arranged within a mounting surface facing the rotary scale, each of which reads the pattern from the scale pattern; Based on the detection values ​​obtained by the plurality of detection heads, For the rotary scale and the group of detection heads, The relative rotation angle around the first rotation axis and The relative amount of movement in the direction along the second rotation axis which is perpendicular to the first rotation axis, The relative rotation angle around the second rotation axis, A process of simultaneously calculating, A multi-degree-of-freedom displacement measurement method, including the following.

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