ELECTROMAGNETIC INDUCTION TYPE CODING DEVICE

Abstract

An electromagnetic induction type coding device (100) comprising: a detection head (10) which has a rectangular shape, and a scale (20) which has a rectangular shape, wherein the detection head (10) is directed towards the scale (20) and is configured to move relative to the scale (20) in a measuring axis direction, wherein the detection head (10) has a drive coil (11) configured to generate a magnetic flux, wherein the scale (20) has a plurality of connecting coils (21) arranged in a fundamental period λ in the measuring axis direction, configured to be electromagnetically coupled to the magnetic flux generated by the drive coil (11), and generate a magnetic flux fluctuating in a predetermined spatial period in the measuring axis direction, wherein the detection head (10) comprises a plurality of receiver coils (12) arranged in the fundamental period λ in the measuring axis direction and configured to be electromagnetically coupled to the magnetic flux generated by the plurality of connecting coils (21) and detect a phase of the magnetic flux, wherein λ / 2 - 2d < L < λ / 2 is satisfied when a distance between one line width center and another line width center of each of the plurality of connecting coils (21) in the measuring axis direction is "L" and a line width of the plurality of connecting coils (21) is "d".

Description

[0001] A certain aspect of embodiments described herein relates to an electromagnetic induction type encoder.

[0002] Electromagnetic induction type encoders are known that utilize an electromagnetic connection between a detection head and a scale (see, for example, JP H10-318781 A, JP 2001-255106 A, and JP 2016-206086 A). When a current flows in a drive coil of the detection head, a magnetic flux is generated. Thus, connecting coils of the scale generate an electromotive current. Next, receiving coils of the detection head generate an electromotive current due to the magnetic flux generated by the electromotive current of the connecting coils. Each electromagnetic connection between coils fluctuates in accordance with an amount of relative displacement between the detection head and the scale.This results in a sine wave signal with the same spacing as the connecting coils. By electrically interpolating the sine wave signal, it is possible to use the sine wave signal as a digital quantity with minimal resolution. Furthermore, it is possible to measure the relative displacement of the detection head.

[0003] JP 2016-206086 A describes an electromagnetic induction encoder having a detection head and a scale that are arranged opposite each other across a predetermined gap and move relative to each other in the direction of a measuring axis. The scale is provided with a scale pattern for generating a magnetic pattern that changes in the direction of a measuring axis in a predetermined spatial cycle. The scale pattern has a first track with a first pitch, the pitch of which is relatively short, and a second track with a second pitch, the pitch of which is longer than the first track. The first track is a coil pattern consisting of coils arranged at the first pitch. The second track is a fixed pattern consisting of fixed films arranged at the second pitch, each of the fixed films being island-shaped.

[0004] r is a coil pattern consisting of coils arranged at the first pitch. The second track is a fixed pattern consisting of fixed films arranged at the second pitch, with each of the fixed films being island-shaped.

[0005] It is thought that the line width of the connecting coils should be increased to ensure signal intensity in the electromagnetic induction type encoders. However, if the line width of the connecting coils is widened, the interpolation accuracy may deteriorate and the measurement accuracy may be reduced.

[0006] In one aspect of the present invention, it is an object to provide an electromagnetic induction type encoder capable of achieving both high measurement accuracy and assurance of a signal intensity.

[0007] The problem underlying the invention is solved by an electromagnetic induction type encoder having the features of independent claim 1. Further embodiments are defined in the dependent claims.

[0008] It is possible to provide a scale capable of achieving both high measurement accuracy and certainty of signal intensity. Fig. 1A illustrates a structure of an electromagnetic induction type encoder; Fig. 1B illustrates receiver coils; Fig. 2A illustrates a magnetic field between connecting coils adjacent to each other; Fig. Figure 2B illustrates a fundamental period of receiver coils; Fig. 2C illustrates an output signal of a received signal; Fig. 3 illustrates a size of a connecting coil; Fig. 4 illustrates a case where a line width of a connecting coil is widened; Fig. 5 illustrates a simulation result of a current density of a connecting coil; Fig. 6 illustrates a magnetic field generated by a current flowing in an outer circumference; Fig. 7A and Fig. 7B illustrates a relationship between a line width of a connecting coil and λ / 2; Fig. 8A to Fig. 8C illustrates a relationship between a line width of a connecting coil and λ / 2; Fig. 9A and Fig. 9B illustrate another shape of a connecting coil; Fig. 10A and Fig. 10B illustrates a relationship between a width of a connection coil and a width of a drive coil; Fig. 11A and Fig. 11B illustrates a relationship between a width of a connection coil and a width of a drive coil; Fig. 12 illustrates a modified embodiment; and Fig. 13A and Fig. 13B illustrates a relationship between a line width of a connecting coil and λ / 2.

[0009] The Fig. 1A to 7B show examples for a better understanding of the present invention. Fig. 8A to 8C show an embodiment according to the present invention.

[0010] The following is a description of embodiments with reference to the accompanying drawings.

[0011] Fig. 1A illustrates a structure of an electromagnetic induction type encoder 100 using an electromagnetic connection between a detection head and a scale. Fig. Figure 1B illustrates receiver coils, which will be described later.

[0012] The electromagnetic induction type encoder 100 includes a detection head 10 and a scale 20. The detection head 10 moves relatively in a measuring axis direction relative to the scale 20. The detection head 10 and the scale 20 have a flat plate shape and are aligned with each other by a predetermined gap. The electromagnetic induction type encoder 100 includes a drive signal generator 30 and a displacement amount measuring device 40, etc. Fig. 1A and Fig. 1B, an X-axis denotes a displacement direction of the detection head 10 (measuring axis). A Y-axis is perpendicular to the X-axis in a plane formed by the scale 20.

[0013] The detection head 10 comprises a drive coil 11, receiver coils 12, etc. The drive coil 11 is a rectangular coil, of which a longitudinal direction is the X-axis. As shown in Fig. As illustrated in FIG. 1B, the receiver coils 12 form a detection loop repeated in a fundamental period λ of the detection head 10 in the X-axis direction by positive sine wave patterns and negative sine wave patterns of the fundamental period λ formed by two patterns 13a and 13b formed on both surfaces of the detection head 10, and by wirings 14 connecting the pattern 13a and the pattern 13b inside the drive coil 11. In the embodiment, for example, the receiver coils 12 include three-phase receiver coils 12a to 12c whose spatial phase is shifted relative to each other in the X-axis direction. The receiver coils 12a to 12c are connected by a star connection.

[0014] In the scale 20, a plurality of connecting coils 21, each having a rectangular shape, are arranged in the fundamental period λ along the X-axis. Each of the connecting coils 21 is a closed-loop coil. The connecting coils 21 are electromagnetically coupled to the drive coil 11 and are also coupled to the receiver coil 12.

[0015] The drive signal generator 30 generates a drive signal of a single-phase alternating current and supplies the generated drive signal to the drive coil 11. In this case, a magnetic flux is generated in the drive coil 11. Thus, an electromotive current is generated in the plurality of connecting coils 21. The plurality of connecting coils 21 are electromagnetically coupled to the magnetic flux generated by the drive coil 11 and generate a magnetic flux that fluctuates in the X-axis direction at a predetermined spatial period. The magnetic flux generated by the connecting coils 21 generates an electromotive current in the receiver coils 12a to 12c. The electromagnetic coupling among each coil fluctuates in accordance with the displacement amount of the detection head 10. Thereby, a sine wave signal of the same period as the fundamental period λ is obtained.Therefore, the receiver coil 12 detects a phase of the magnetic flux generated by the plurality of connecting coils 21. The displacement amount measuring device 40 can use the sine wave signal as a digital quantity with minimum resolution by electrically interpolating the sine wave signal. The displacement amount measuring device 40 thereby measures the displacement amount of the detection head 10.

[0016] One track is structured by the drive coils 11, the receiver coils 12, and the connecting coils 21, which are electromagnetically coupled to each other. In the embodiment, the electromagnetic induction-type encoder 100 has a plurality of tracks Tr1 to Tr3. The plurality of tracks Tr1 to Tr3 are arranged at a predetermined interval in the Y-axis direction. Fundamental periods λ are different from each other in the tracks Tr1 to Tr3. Thus, the electromagnetic induction-type encoder 100 functions as an absolute-type encoder.

[0017] Fig. Figure 2A illustrates a magnetic field between the connecting coils 21 adjacent to each other. As shown in Fig. 2A, a magnetic field is generated between the connecting coils 21 adjacent to each other. A direction of the magnetic field between the connecting coils 21 is opposite to a direction of a magnetic field inside the connecting coils 21. The connecting coils 21 are arranged in the fundamental period λ, as mentioned above. As shown in Fig. 2B, the receiver coils 12a to 12c are also arranged in the fundamental period λ. As shown in Fig. As illustrated in Figure 2C, each of the output signals of the receiver coils 12a to 12c is a sine wave signal whose period is the fundamental period λ. The fundamental period λ is a distance between centers of the connecting coils 21 adjacent to each other in the X-axis direction. In other words, the fundamental period λ is a distance between an edge on the plus side in the X-axis of one of the connecting coils 21 and an edge on the plus side in the X-axis of another connecting coil 21 adjacent to the first one. The fundamental period λ of the receiver coils 12 is a period of sine wave patterns that structure the receiver coils 12.

[0018] For example, as shown in Fig. 3, the connecting coils 21 have a size in which an interval between centers of line widths of the two adjacent connecting coils 21 is λ / 2. A signal period determined by a structure of the electromagnetic induction type encoder is coarser than that of a photoelectric type encoder. Therefore, a requirement of the electromagnetic induction type encoder toward interpolation accuracy is not high. However, recently, a requirement for high accuracy has been increased. With respect to the electromagnetic induction type encoder, the interpolation accuracy comparable to that of the photoelectric type encoder is required.Whether a signal generated by moving the detection head exhibits a sine waveform without distortion, whether the signal intensity is appropriate, and whether fluctuations in the signal intensity are suppressed are important to meet this requirement. However, this point is not strictly observed.

[0019] And such is or will be, for example, as in Fig. 4, the line width of the connecting coil 21 is widened. This reduces a resistance component of the coil. And it is possible to increase the signal intensity. Furthermore, it is possible to suppress the fluctuation in the signal intensity caused by a defect in the coil that may occur during manufacturing. However, it is confirmed that when the line width is widened, an error of 1 / 3 period of the fundamental period λ (λ / 3 error), which is difficult to correct, increases, and the interpolation accuracy deteriorates. Therefore, it is difficult to achieve both high measurement accuracy and ensure the signal intensity. Ensuring the signal intensity involves a large magnitude of an absolute value of the signal and suppressing the signal fluctuation.

[0020] The present inventors have found that the current density in the connecting coil 21 is lower on an inner circumference side of the coil and higher on an outer circumference side of the coil. Fig. 5 illustrates a simulation result of the current density of the connecting coil 21. In Fig. 5, the deeper the pattern, the higher the current density. The unit of values ​​is A / m 2 . From the result of Fig. 5, it is understood that the current density is low on the inner peripheral side of the connecting coil 21, and the current density is high on the outer peripheral side of the connecting coil 21. Thus, there is a variation or change in the current density in the line width direction of the connecting coil 21.

[0021] When the line width of the connecting coil 21 is widened to ensure the signal intensity, a region of a plus side and a region of a minus side become unbalanced with respect to the magnetic field generated by the current flowing in the outer circumference of the coil, as shown in Fig. 6. And the sine wave differs from a theoretical sine wave. This may degrade or reduce the interpolation accuracy. The current density distribution is negligible when the line width is small or narrow. However, it is confirmed that the current density distribution is significant or remarkable when the line width is increased. For example, the current distribution is remarkable in the connecting coil 21 whose line width is 200 µm or more.

[0022] As this is Fig. As illustrated in Figure 7A, when an interval L between the line width centers of the two connecting coils 21 adjacent to each other is λ / 2, high interpolation accuracy cannot necessarily be achieved. And so, as shown in Fig. 7B, it is preferable that a distance (> L) between coil edge portions where current density is high is λ / 2 to suppress the influence of current density distribution. For example, it is preferable that edge portions of the receiver coils 12 located in the fundamental period λ are located near the edge portions of the connecting coils 21 where the current density is high. Thus, in the embodiment shown in FIG. Fig. 8A to Fig. As illustrated in Figure 8C, λ / 2 - 2d < L < λ / 2 satisfies the signal period (the fundamental period λ) with reference to the period of the receiver coils—the pitch of the connecting coils—when a distance between one line width center and another line width center of a single connecting coil 21 is "L" and a line width of the connecting coils is "d." With this structure, the distance between the coil edge portions where the current density is high is λ / 2 or close to λ / 2. In this case, the deterioration of the interpolation accuracy is suppressed, and high measurement accuracy is achieved. Furthermore, it is possible to widen the line width of the connecting coils 21. Therefore, it is possible to increase the signal intensity. Accordingly, it is possible to achieve both high measurement accuracy and safety of the signal intensity.It is preferable that λ / 2 - 3d / 2 < L < λ / 2 - d / 2 is satisfied to achieve higher interpolation accuracy.

[0023] In the embodiment, the connecting coils 21 have a rectangular shape. However, the connecting coils 21 may have other shapes. For example, as shown in Fig. 9A, the connecting coils 21 may be closed coils or loops, which have a form of a Fig. 8. Alternatively, as described in Fig. 9B, the connecting coils 21 may be closed coils having a circular shape. In the closed-loop coils, the current density on the outer peripheral side of the coils is higher than that on the inner peripheral side of the coils. And also in a portion of the connecting coil 21 that is electromagnetically coupled to the receiving coil 12, λ / 2 - 2d < L < λ / 2 is satisfied when a maximum distance between the line width centers in the X-axis direction is "L" and the line width of the connecting coil 21 is "d". With the structure, the interval between the coil edge portions where the current density is high is λ / 2 or nearly λ / 2. Thus, the deterioration of the interpolation accuracy is suppressed, and high measurement accuracy is achieved. It is preferable that λ / 2 - 3d / 2 < L < λ / 2 - d / 2 is satisfied to achieve higher interpolation accuracy.It is preferable that the connecting coils 21 have a shape that is linearly symmetrical relative to the Y-axis.

[0024] Next, a description will be given of a relationship between the position of the drive coil 11 of the detection head 10 and the position of the connecting coil 21 of the scale 20. It is advantageous that the width of the connecting coil 21 in the Y-axis direction is widened as much as possible, as shown in Fig. 10B, when the positional fluctuation of the receiver coil 12 is taken into account to increase an allowable amount of relative lateral fluctuation between the position of the detection head 10 and the position of the scale 20, as shown in Fig. 10A. However, as shown in Fig. As illustrated in Figure 11A, when the connecting coil 21 extends outside the drive coil 11, the extension portions absorb the magnetic field of the drive coil 11. Therefore, the signal intensity is reduced. And so, as shown in Fig. 11B, it is preferable that the width of the connecting coil 21 in the Y-axis direction is equal to or less than the width of the driving coil 11 in the Y-axis direction in order to ensure the signal intensity.

[0025] (Modified Embodiment) In the example of Fig. 1, the receiver coils 12 are located inside the drive coil 11. However, this structure is not limited. Fig. Figure 12 illustrates another example where the receiver coils 12 are not located inside the drive coil 11. For example, as shown in Fig. As illustrated in Figure 12, the drive coil 11 comprises a pair of drive coils 11a and 11b. The receiver coil 12 is arranged between the drive coils 11a and 11b.

[0026] The drive coils 11a and 11b are rectangular patterns extending in the X-axis direction. For example, the drive coils 11a and 11b are connected so that the current flowing in the drive coil 11a is opposite to that flowing in the drive coil 11b. For example, the current flows counterclockwise in the drive coil 11a, and the current flows clockwise in the drive coil 11b.

[0027] In the scale 20, a connecting coil 21a and a connecting coil 21b are alternately arranged. The connecting coils 21a are closed-loop coils arranged in the fundamental period λ. The connecting coils 21a include a first loop portion 22a electromagnetically coupled to the drive coil 11a and a second loop portion 23a electromagnetically coupled to the receiver coil 12. The connecting coils 21b are closed-loop coils whose phase difference from that of the connecting coil 21a is 180 degrees. The connecting coils 21b include a first loop portion 22b electromagnetically coupled to the drive coil 11b and a second loop portion 23b electromagnetically coupled to the receiver coil 12.In the modified embodiment, the connecting coils 21a and the connecting coils 21b are arranged in the fundamental period λ / 2.

[0028] In the structure, an edge of the connecting coil 21a and an edge of the connecting coil 21b contact each other when L = λ / 2 is satisfied. In this case, a maximum distance between the line width centers in the X-axis direction is "L", and it is the line width of the connecting coils 21a and 21b "d" in portions of the connecting coils 21a and 21b that are electromagnetically coupled to the receiver coil 12. And thus, in the modified embodiment, as shown in Fig. 13A, an interval or distance t between the connecting coil 21a and the connecting coil 21b is considered. And L < λ / 2 is satisfied. Specifically, L + d + t = λ / 2 is satisfied. And when "L" is widened as much as possible, t is 0. "L" becomes minimal when t=d is satisfied, as shown in Fig. 13B. Therefore, λ / 2 - 2d < L < λ / 2 - d is satisfied. In the structure, the distance between the coil edge portions where the current density is high is λ / 2 or close to λ / 2. Thus, the deterioration of the interpolation accuracy is suppressed, and high measurement accuracy is achieved. Furthermore, it is preferable that λ / 2 - 3d / 2 < L < λ / 2 - d is satisfied to achieve higher interpolation accuracy.

Claims

[1] An electromagnetic induction type encoder (100) comprising: a detection head (10) which has a rectangular shape, and a scale (20) which has a rectangular shape, wherein the detection head (10) is directed towards the scale (20) and is configured to move relative to the scale (20) in a measuring axis direction, wherein the detection head (10) has a drive coil (11) configured to generate a magnetic flux, wherein the scale (20) has a plurality of connecting coils (21) arranged in a fundamental period λ in the measuring axis direction, configured to be electromagnetically coupled to the magnetic flux generated by the drive coil (11), and generate a magnetic flux fluctuating in a predetermined spatial period in the measuring axis direction, wherein the detection head (10) comprises a plurality of receiver coils (12) arranged in the fundamental period λ in the measuring axis direction and configured to be electromagnetically coupled to the magnetic flux generated by the plurality of connecting coils (21) and detect a phase of the magnetic flux, wherein λ / 2 - 2d < L < λ / 2 is satisfied when a distance between one line width center and another line width center of each of the plurality of connecting coils (21) in the measuring axis direction is "L" and a line width of the plurality of connecting coils (21) is "d". [2] The electromagnetic induction type encoder according to claim 1, wherein a width of the plurality of connecting coils (21) in a direction normal to the measuring axis direction in a plane formed by the scale (20) is equal to or less than a width of the drive coil (11) in the direction normal to the measuring axis direction. [3] An electromagnetic induction type encoder according to claim 1 or 2, wherein said plurality of connecting coils (21) has a shape which is linearly symmetrical with an axis normal to the measuring axis direction in a plane formed by said scale (20). [4] An electromagnetic induction type encoder according to claim 3, wherein said plurality of connecting coils (21) have a rectangular shape. [5] An electromagnetic induction type encoder according to any one of claims 1 to 4, wherein the line width "d" of said plurality of connecting coils (21) is 200 µm or more.

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