JP2016075494A - Stroke sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the detection of an absolute amount of stroke of a direct-acting component.SOLUTION: A stroke sensor 100 comprises: a cylinder tube 20; a piston rod 30 provided so as to be able to freely advance and retreat to and from the cylinder tube 20; magnetic scales 60, 70 formed by locally fusing the piston rod 30; and an MR sensor 50 provided in the cylinder tube 20 and whose output changes in accordance with the shapes of the magnetic scales 60, 70 close thereto, the magnetic scales 60, 70 being provided with depth change parts 67a-67e, 71 whose depths gradually change along the advance/retreat direction of the piston rod 30.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a stroke sensor.

  Conventionally, a stroke sensor has been used to detect the stroke amount of a linear component such as a cylinder. The stroke sensor detects the stroke amount of the linear motion component by detecting a magnetic scale provided on a second member that is movable forward and backward with respect to the first member by a detection element provided on the first member. Patent Document 1 discloses a stroke sensor that can detect the absolute stroke amount of a linear motion component by changing the shape of a magnetic scale according to the stroke amount.

JP 2010-256122 A

  The magnetic scale of the stroke sensor disclosed in Patent Document 1 is formed by cutting. For this reason, for example, high processing accuracy is required to form a fine portion whose width gradually decreases, such as the vicinity of the apex portion of a triangular shape.

  The present invention has been made in view of such a technical problem, and an object thereof is to realize detection of an absolute stroke amount of a linear motion component by easy processing.

  In the first invention, the depth is gradually changed along the advancing / retreating direction of the second member to a scale formed by locally melting the second member provided so as to be movable back and forth with respect to the first member. A depth changing unit is provided.

  In 1st invention, the magnetism which acts on the 2nd member changes according to the stroke amount of the 2nd member by the depth change part of a scale. For this reason, the output of the detection element that detects the magnetism acting on the second member changes according to the stroke amount of the second member.

  The second invention is characterized in that the scale is constituted by a plurality of scales having a depth changing portion.

  In the second invention, the stroke amount of the second member is detected by a plurality of scales having a depth changing portion. For this reason, compared with the case where the whole stroke amount of the 2nd member is detected by one scale which has a depth change part, processing of each scale becomes easy.

  The third invention is characterized in that the depth changing portions are arranged so as to be continuously located in the advancing and retreating direction of the second member.

  In the third invention, since the depth changing portion is continuously located, the magnetism acting on the second member changes proportionally according to the stroke amount of the second member. Therefore, the absolute stroke amount of the second member can be easily detected based on the output of the detection element that detects magnetism.

  The fourth invention is characterized in that the longest central scale faces the center of the detection element.

  In the fourth invention, the central scale formed from the most contracted end portion to the most extended end portion always faces the central portion where the sensitivity of the detection element is high. For this reason, the detection accuracy of the detection element can be improved.

  The fifth invention is characterized in that the length of the scale is shorter as the scale is separated from the central scale in a direction perpendicular to the advancing / retreating direction of the second member.

  In the fifth invention, a relatively long scale is opposed to the vicinity of the central portion where the sensitivity of the detection element is high. For this reason, the detection accuracy of the detection element can be improved.

  The sixth invention is characterized in that the scale has a width changing portion whose width in a direction perpendicular to the advancing and retreating direction of the second member changes toward the depth changing portion and whose depth is constant.

  In 6th invention, the magnetism which acts on the 2nd member according to one scale which has a depth change part and a width change part changes proportionally according to the amount of strokes of the 2nd member. Therefore, the absolute stroke amount of the second member can be easily detected based on the output of the detection element that detects magnetism.

  The seventh invention is characterized in that a scale having a depth changing portion is formed by melting the second member by a local heating device and magnetizing or demagnetizing the locally heated portion.

  In 7th invention, the scale which has a depth change part is formed by local heating apparatuses, such as a laser. Therefore, it is possible to form a scale whose depth easily changes as compared with the cutting process.

  According to the present invention, detection of an absolute stroke amount of a linear motion component can be realized by easy processing.

It is a block diagram of the stroke sensor which concerns on embodiment of this invention. It is an enlarged view of the magnetic scale of FIG. It is sectional drawing of the magnetic scale of FIG. It is a graph of the output signal of a stroke sensor. It is an enlarged view of the modification of the magnetic scale of FIG. It is sectional drawing of the magnetic scale of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  A stroke sensor 100 according to an embodiment of the present invention will be described with reference to FIG. A cylinder 10 shown in FIG. 1 is a hydraulic cylinder that is operated by hydraulic oil discharged from a hydraulic pump (not shown). The stroke sensor 100 is provided in the cylinder 10.

  The cylinder 10 includes a cylinder tube 20 as a first member that is a main body of the cylinder 10, and a piston rod 30 as a second member that is provided so as to be movable forward and backward with respect to the cylinder tube 20.

  The cylinder tube 20 has a cylindrical shape, and a piston 31 that is slidable in the axial direction is provided inside the cylinder tube 20. The piston 31 defines two oil chambers 11 and 12 inside the cylinder tube 20.

  The two oil chambers 11 and 12 are respectively connected to a switching valve (not shown), and the hydraulic oil discharged from the hydraulic pump can enter and exit the two oil chambers 11 and 12. The cylinder 10 is a double-acting cylinder, but may be a single-acting cylinder. The cylinder 10 is not limited to a hydraulic type, and may be a pneumatic type, a hydraulic type, an electric mechanical type, or the like.

  The piston rod 30 is a columnar magnetic member having a base end portion 30 a fixed to the piston 31 and a tip end portion 30 b exposed from the cylinder tube 20. The piston rod 30 is operated by a hydraulic force acting on the piston 31.

  Next, the stroke sensor 100 provided in the cylinder 10 will be described.

  The stroke sensor 100 includes an MR sensor 50 as a detection element disposed in the cylinder tube 20 and a magnetic scale 60 as a scale formed on the piston rod 30. The stroke sensor 100 is provided to detect the stroke amount of the piston rod 30 with respect to the cylinder tube 20.

  The MR (Magneto-Resistive) sensor 50 has an MR element whose electrical resistance changes depending on the strength of magnetism. The MR sensor 50 is disposed on the inner peripheral side of the end of the cylinder tube 20 so as to face the outer periphery of the piston rod 30 exposed from the cylinder tube 20. A permanent magnet (not shown) that is a magnetic source is disposed on the outer peripheral side of the MR sensor 50.

  The MR sensor 50 detects magnetism emitted from the permanent magnet, and outputs a voltage corresponding to the detected magnetism to a controller (not shown). The magnetism emitted from the permanent magnet acts on the magnetic material, but does not act on the non-magnetic material. That is, the MR sensor 50 detects how the magnetism generated from the permanent magnet is changed by the magnetism of the member facing the MR sensor 50.

  Instead of the MR sensor 50, a more sensitive GMR (Giant Magneto-Resistive: Giant Magnetoresistance) sensor, an MI sensor using an MI (Magneto-Impedance) effect, or the like may be used.

  The magnetic scale 60 is a nonmagnetic material formed on the outer periphery of the piston rod 30 that is a magnetic material. The magnetic scale 60 is formed by melting the outer peripheral surface of the piston rod 30 with a laser irradiated by a laser device as a local heating device and adding Ni or Mn to austenite. The depth of the magnetic scale 60 can be changed by adjusting the energy supplied from the laser device and the operating time of the laser device.

  The piston rod 30 may be made of a non-magnetic material. In this case, the magnetic scale 60 is formed as a magnetic material by melting the piston rod 30 with a laser device and adding Sn or the like. . The means for locally heating is not limited to a laser, and any means may be used as long as it is a locally heatable means such as an electron beam, high-frequency induction heating, or arc discharge.

  The magnetic scale 60 is formed over the entire stroke from the most contracted end facing the MR sensor 50 when the piston rod 30 is most contracted to the most extended end facing the MR sensor 50 when most extended. The Although only one magnetic scale 60 shown in FIG. 1 is provided on the outer periphery of the piston rod 30, a plurality of magnetic scales 60 may be provided at intervals in the circumferential direction. In addition, the thermal strain which arises when forming the magnetic scale 60 by fusion | melting can be removed by arrange | positioning the several magnetic scale 60 equally in the circumferential direction.

  In the stroke sensor 100 having such a configuration, the magnetism emitted from the permanent magnet and acting on the piston rod 30 varies depending on the size of the magnetic scale 60 that is a non-magnetic material. The size of the magnetic scale 60 changes according to the stroke amount of the piston rod 30 as will be described later. For this reason, the stroke sensor 100 detects the absolute stroke amount of the piston rod 30, that is, the absolute position of the piston rod 30 by detecting the magnetism that changes according to the stroke amount of the piston rod 30 with the MR sensor 50. can do.

  Next, the magnetic scale 60 will be described in detail with reference to FIGS. FIG. 2 is an enlarged view of the magnetic scale 60 shown in FIG. FIG. 3 is a cross-sectional view of the magnetic scale 60 shown in FIG. For the sake of explanation, the magnetic scale 60 shown in FIG. 2 shows the enlarged length in the circumferential direction B of the piston rod 30 relative to the length in the forward / backward direction A of the piston rod 30 with respect to FIG. . Further, the hatched portion in FIG. 3 shows a magnetic scale 60 that has been made non-magnetic.

  The magnetic scale 60 formed on the side surface 30 c of the piston rod 30 has a plurality of magnetic scales 61 to 65 formed in parallel along the forward / backward direction A of the piston rod 30. As shown in FIG. 2, these magnetic scales 61 to 65 are disposed within a detection width 50 a that can be detected by the MR sensor 50 when the piston rod 30 reciprocates.

  When the piston rod 30 reciprocates, a first magnetic scale 61 as a central scale is disposed at a portion where the central portion 50b of the MR sensor 50 faces. 2, the second magnetic scale 62, the third magnetic scale 63, the fourth magnetic scale 64, and the fifth magnetic scale 65 are spaced apart from each other in the circumferential direction B of the piston rod 30 with the first magnetic scale 61 as the center. Arranged as shown. 3A is a cross-sectional view of the first magnetic scale 61 in the forward / backward direction A of the piston rod 30, FIG. 3B is a cross-sectional view of the second magnetic scale 62, and FIG. FIG. 6 is a cross-sectional view of the third magnetic scale 63, (d) is a cross-sectional view of the fourth magnetic scale 64, and (e) is a cross-sectional view of the fifth magnetic scale 65.

  The first magnetic scale 61 is formed from the most contracted end portion to the most extended end portion, and is formed to be the longest as compared with the other magnetic scales 62 to 65. The lengths of the other magnetic scales 62 to 65 become shorter as they are arranged away from the first magnetic scale 61 in the circumferential direction B. The detection accuracy of the MR sensor 50 can be improved by arranging the magnetic scales 61 to 63 having a relatively long length in the vicinity of the central portion 50b where the sensitivity of the MR sensor 50 is high. The arrangement of the magnetic scales 61 to 65 is not limited to the above arrangement, and the shortest fifth magnetic scale 65 may be arranged in the vicinity of the central portion 50 b of the MR sensor 50.

  As shown in FIGS. 2 and 3, each of the magnetic scales 61 to 65 has depth changing portions 67 a to 67 e in which the depth of the non-magnetized region gradually changes along the forward / backward direction A of the piston rod 30. In addition, each of the magnetic scales 61 to 64 other than the shortest fifth magnetic scale 65 further includes flat portions 68a to 68d that are formed continuously with the depth changing portions 67a to 67e and have a constant depth.

  As shown in FIG. 3, the lengths of the depth changing portions 67a to 67e in the forward / backward direction A of the piston rod 30 are set equal. Further, the depth of the depth changing portions 67a to 67e is increased at a constant rate from the surface of the side surface 30c of the piston rod 30 until it becomes the same as the depth of the flat portions 68a to 68d. The depth changing units 67a to 67e may have a configuration in which the depth changes in a convex curve or a concave curve instead of the configuration in which the depth changes linearly.

  Moreover, each depth change part 67a-67e is arrange | positioned so that it may shift to the advancing / retreating direction A of the piston rod 30, and may be located continuously, as FIG. 3 shows. In other words, the depth changing portions 67a to 67e are arranged so as not to overlap each other when viewed from a direction perpendicular to the forward / backward direction A.

  The magnetic scales 61 to 65 shown in FIGS. 2 and 3 are provided with depth changing portions 67a to 67e on the distal end portion 30b side of the piston rod 30, and flat portions 68a to 68d on the proximal end portion 30a side. And each magnetic scale 61-65 is arrange | positioned so that the end surface at the side of the base end part 30a of the piston rod 30 may align in the same position in the advancing / retreating direction A of the piston rod 30. Instead, the depth changing portions 67 a to 67 e may be provided on the base end portion 30 a side, and the end surface on the tip end portion 30 b side may be aligned at the same position in the forward / backward direction A of the piston rod 30. Also in this case, the depth changing portions 67 a to 67 e are arranged so as to be continuously located while being shifted in the forward / backward direction A of the piston rod 30.

  The number of scales constituting the magnetic scale 60 is not limited to five, and may be one or a plurality other than five. When the magnetic scale 60 is composed of a single scale, a depth changing portion is provided at a portion facing the MR sensor 50 from the most contracted position to the most extended position.

  Hereinafter, the operation of the stroke sensor 100 will be described.

  Here, the case where the piston rod 30 extends from the state in the most contracted position will be described. When the piston rod 30 in the extended state contracts, the operation is the reverse of the following description.

  When the switching valve is switched and the hydraulic oil discharged from the hydraulic pump is supplied to the oil chamber 12, the hydraulic oil accumulated in the oil chamber 11 is discharged to the outside. As a result, the internal pressure of the oil chamber 12 increases, and the internal pressure of the oil chamber 11 relatively decreases. For this reason, the piston 31 located between the oil chambers 11 and 12 is moved to the oil chamber 11 side. As the piston 31 moves, the piston rod 30 that is integral with the piston 31 starts to extend from the cylinder tube 20.

  When the piston rod 30 starts to expand, the MR sensor 50 detects a change in magnetism due to the depth changing portion 67a of the first magnetic scale 61 facing each other. The depth of the depth changing portion 67a of the first magnetic scale 61 facing the MR sensor 50 increases as the piston rod 30 extends. That is, as the piston rod 30 extends, the proportion of the nonmagnetic material that occupies the portion facing the MR sensor 50 increases. Thus, the change in magnetism increases as the proportion of non-magnetic material increases. As a result, when the piston rod 30 starts to expand, the output of the MR sensor 50 gradually increases.

  When the piston rod 30 further expands, the MR sensor 50 faces the flat portion 68a of the first magnetic scale 61 and simultaneously faces the depth changing portion 67b of the second magnetic scale 62. Here, since the flat portion 68a has a constant depth, a constant magnetic change occurs, but no further magnetic change occurs even if the piston rod 30 further expands. On the other hand, the depth changing portion 67b of the second magnetic scale 62 increases the magnetic change as the piston rod 30 extends, similarly to the depth changing portion 67a of the first magnetic scale 61. As a result, the MR sensor 50 detects a magnetic change gradually increased by the depth changing unit 67b in addition to the constant magnetic change by the flat portion 68a, and thus the output is further increased.

  Similarly, the MR sensor 50 sequentially confronts the other depth changing portions 67c to 67e and the flat portions 68a to 68d as the piston rod 30 extends. As a result, the output of the MR sensor 50 increases according to the stroke amount of the piston rod 30, and changes linearly as shown in FIG. In FIG. 4, the horizontal axis represents the stroke amount of the piston rod 30, and the vertical axis represents the voltage output from the MR sensor 50.

  As described above, in the stroke sensor 100 according to the present embodiment, the magnitude of the voltage output from the MR sensor 50 changes according to the stroke amount of the piston rod 30. Therefore, the absolute stroke amount of the piston rod 30 can be detected based on the magnitude of the voltage output from the MR sensor 50.

  In addition, although each depth change part 67a-67e is shifted and arrange | positioned in the advancing / retreating direction A, it may be arrange | positioned so that one part may overlap, seeing from a perpendicular | vertical direction with respect to the advancing / retreating direction A. In this case, the amount of change in the voltage output from the MR sensor 50 becomes large at the portion where the depth change portions 67a to 67e overlap. For this reason, the output change of the MR sensor 50 is a non-linear change. However, since there is a one-to-one relationship between the magnitude of the voltage and the stroke amount, it is based on the magnitude of the voltage output from the MR sensor 50 by grasping the relationship between the magnitude of the voltage and the stroke amount. The absolute stroke amount of the piston rod 30 can be detected.

  According to the above embodiment, there exist the following effects.

  In the present embodiment, depth changing portions 67a to 67e in which the depth gradually changes along the advancing / retreating direction A of the piston rod 30 on the magnetic scales 60 and 70 formed by locally melting the piston rod 30. 71 is provided. For this reason, the magnetism acting on the piston rod 30 changes according to the stroke amount of the piston rod 30 by the depth changing portions 67a to 67e, 71. As a result, the output of the MR sensor 50 that detects magnetism changes according to the stroke amount of the piston rod 30. Thus, detection of the absolute stroke amount of the linear motion component can be realized by easy processing.

  Next, with reference to FIG.5 and FIG.6, the modification of the stroke sensor 100 which concerns on embodiment of this invention is demonstrated. FIG. 5 corresponds to FIG. 2 and shows an enlarged magnetic scale 70 of a modified example. FIG. 6 is a cross-sectional view of the magnetic scale 70 shown in FIG.

  In the above embodiment, a plurality of magnetic scales 60 are formed in parallel along the forward / backward direction A of the piston rod 30. Instead, the magnetic scale 70 of the modified example is composed of one scale formed along the forward / backward direction A of the piston rod 30, and includes a depth changing unit 71 in which the depth gradually changes and a depth changing unit 71. A width changing portion 72 formed continuously and having a constant depth. This magnetic scale 70 is formed by melting the outer peripheral surface of the piston rod 30 by a local heating device such as a laser device, as in the above embodiment.

  The depth changing portion 71 is deeper at a constant rate from the surface of the side surface 30c of the piston rod 30 to the depth of the width changing portion 72 in the same manner as the depth changing portions 67a to 67e of the above embodiment. Become. On the other hand, the width changing portion 72 has a constant depth, but the width in the direction perpendicular to the forward / backward direction A of the piston rod 30 increases as the distance from the depth changing portion 71 increases. As shown in FIG. 5, the width changing portion 72 is formed such that the portion with the largest width is within a detection width 50 a that can be detected by the MR sensor 50 when the piston rod 30 reciprocates.

  Also in this modified example, the stroke sensor 100 operates in the same manner as in the above embodiment. When the piston rod 30 starts to expand, the MR sensor 50 detects a change in magnetism due to the opposing depth change unit 71. The depth of the depth changing portion 71 facing the MR sensor 50 increases as the piston rod 30 extends. That is, as the piston rod 30 extends, the proportion of the nonmagnetic material that occupies the portion facing the MR sensor 50 increases. Thus, the change in magnetism increases as the proportion of non-magnetic material increases. As a result, when the piston rod 30 starts to expand, the output of the MR sensor 50 gradually increases.

  When the piston rod 30 further expands, the MR sensor 50 faces the width changing portion 72. Here, the width changing portion 72 has a constant depth, but the width in the direction perpendicular to the forward / backward direction A of the piston rod 30 increases as the distance from the depth changing portion 71 increases. Therefore, the magnetism around the MR sensor 50 is changed proportionally by the width changing portion 72 as the piston rod 30 extends. As a result, the output of the MR sensor 50 increases proportionally.

  As described above, even when the magnetic scale 70 is a single scale having the depth changing portion 71 and the width changing portion 72, the output characteristics shown in FIG. 4 can be obtained.

  According to the above modification, the following effects are obtained.

  In the modification, the magnetism acting on the piston rod 30 is changed according to the stroke amount of the piston rod 30 by the depth changing portion 71 and the width changing portion 72. For this reason, the output of the MR sensor 50 that detects magnetism changes according to the stroke amount of the piston rod 30. As a result, as in the above-described embodiment, detection of the absolute stroke amount of the linear motion component can be realized by easy processing.

  Hereinafter, the configuration, operation, and effect of the embodiment of the present invention will be described together.

  In the present embodiment, the stroke sensor 100 is formed on the cylinder tube 20, the piston rod 30 provided so as to be movable back and forth with respect to the cylinder tube 20, and the side surface 30 c of the piston rod 30. The magnetic scales 60 and 70 that have been changed and the MR sensor 50 that is provided in the cylinder tube 20 and whose output changes according to the shape of the adjacent magnetic scales 60 and 70 are provided. It is characterized by having depth changing portions 67a to 67e, 71 whose depth gradually changes along the forward / backward direction A.

  In this configuration, depth changing portions 67 a to 67 e, 71 in which the depth gradually changes along the advance / retreat direction A of the piston rod 30 on the magnetic scales 60, 70 formed by locally melting the piston rod 30. Is provided. For this reason, the magnetism acting on the piston rod 30 changes according to the stroke amount of the piston rod 30 by the depth changing portions 67a to 67e, 71. As a result, the output of the MR sensor 50 that detects magnetism changes according to the stroke amount of the piston rod 30. Thus, according to the said structure, the detection of the absolute stroke amount of a linear motion component is realizable by easy process.

  In the present embodiment, a plurality of magnetic scales 60 are formed in parallel along the forward / backward direction A of the piston rod 30, and the plurality of magnetic scales 61 to 65 have depth changing portions 67 a to 67 e, respectively. To do.

  In this configuration, the magnetic scale 60 includes a plurality of magnetic scales 61 to 65 having depth changing portions 67a to 67e. If detection of the stroke amount of the piston rod 30 is performed by one magnetic scale having the depth changing portion, the deepest portion of the depth changing portion is deepened according to the maximum stroke amount, or the depth of the depth changing portion is increased. The degree of change in length must be moderated. However, in order to increase the depth of the non-magnetic material formed by melting, it is necessary to increase the supplied melting energy, and in order to reduce the degree of change in depth, the supplied melting energy It becomes difficult to process the magnetic scale, such as the need for fine adjustment. On the other hand, according to the said structure, the stroke amount which each depth change part 67a-67e bears becomes a part of maximum stroke amount. For this reason, compared with the case where the stroke amount is detected by the depth changing portion of one magnetic scale, the degree of freedom in processing each depth changing portion 67a to 67e is high. Therefore, each depth change part 67a-67e can be processed easily.

  In the present embodiment, the depth change portions 67a to 67e of the plurality of magnetic scales 61 to 65 are arranged so as to be continuously located in the forward / backward direction A of the piston rod 30.

  In this configuration, the depth changing portions 67 a to 67 e are continuously located in the forward / backward direction A of the piston rod 30. For this reason, the magnetism acting on the piston rod 30 changes in proportion to the stroke amount of the piston rod 30. Therefore, the absolute stroke amount of the piston rod 30 can be easily detected based on the magnitude of the voltage output from the MR sensor 50 that detects magnetism.

  Moreover, in this embodiment, the 1st magnetic scale 61 which passes the center part of MR sensor 50 among several magnetic scales 61-65 is compared with the other magnetic scales 62-65. A is the longest formed in A.

  In this configuration, the longest first magnetic scale 61 is formed so as to face the central portion of the MR sensor 50. For this reason, the sensitivity of the MR sensor 50 of the first magnetic scale 61 formed from the most contracted end portion to the most extended end portion always faces the center portion. As a result, the detection accuracy of the MR sensor 50 can be improved.

  In the present embodiment, the lengths of the plurality of magnetic scales 61 to 65 are shorter as the scales are separated from the first magnetic scale 61 in the direction perpendicular to the forward / backward direction A of the piston rod 30. And

  In this configuration, the relatively long magnetic scales 61 to 63 are opposed to the vicinity of the central portion where the sensitivity of the MR sensor 50 is high. For this reason, the detection accuracy of the MR sensor 50 can be improved.

  In the present embodiment, the magnetic scale 70 includes the width changing portion 72 whose width in the direction perpendicular to the forward / backward direction A of the piston rod 30 gradually changes toward the depth changing portion 71 and whose depth is constant. It is characterized by having.

  In this configuration, the magnetic scale 70 having the depth changing portion 71 and the width changing portion 72 is formed by locally melting the piston rod 30. The magnetism acting on the piston rod 30 changes according to the stroke amount of the piston rod 30 by the depth changing portion 71 and the width changing portion 72. For this reason, the output of the MR sensor 50 that detects magnetism changes according to the stroke amount of the piston rod 30. As a result, detection of the absolute stroke amount of the linear motion component can be realized by easy processing.

  Further, in the present embodiment, the magnetic scales 60 and 70 are portions where the piston rod 30 is melted and made magnetized or non-magnetic by a laser.

  In this configuration, the magnetic scales 60 and 70 are formed by melting the piston rod 30 with a local heating device such as a laser device and magnetizing or demagnetizing the locally heated portion. For this reason, compared with cutting, the magnetic scales 60 and 70 can be formed easily.

  The embodiment of the present invention has been described above. However, the above embodiment only shows a part of application examples of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above embodiment. Absent.

  In the present embodiment, the change in the magnetic field is detected by the MR sensor 50. Instead, it is provided facing the coil surrounding the outer periphery of the piston rod 30 or the magnetic scales 60, 70 on the surface of the piston rod 30. It may be detected by a coil. In this case, the impedance of the coil changes according to the displacement of the piston rod 30.

100 ... stroke sensor, 10 ... cylinder, 20 ... cylinder tube (first member), 30 ... piston rod (second member), 50 ... MR sensor (detection element), 60, 70 ... magnetic scale (scale), 61 ... first magnetic scale (center scale), 62 ... second magnetic scale (scale), 63 ... third magnetic scale (scale), 64 ··· -4th magnetic scale (scale), 65 ... 5th magnetic scale (scale), 67a-67e, 71 ... Depth change part, 68a-68d ... Flat part, 72 ... Width change part, A ... Advancing / retreating direction of piston rod, B ... Peripheral direction of piston rod

Claims (7)

A first member;
A second member provided to be movable forward and backward with respect to the first member;
A scale formed on the surface of the second member, the second member is melted and the magnetism is changed;
A detection element provided on the first member, the output of which varies depending on the shape of the scale close to the first member;
The scale has a depth changing portion in which the depth gradually changes along the advancing / retreating direction of the second member. A plurality of the scales are formed in parallel along the advance / retreat direction,
The stroke sensor according to claim 1, wherein each of the plurality of scales includes the depth changing unit.   3. The stroke sensor according to claim 2, wherein the depth changing portions of each of the plurality of scales are arranged so as to be continuously located in the forward / backward direction.   4. The stroke according to claim 2, wherein a central scale that passes through a central portion of the detection element among the plurality of scales is formed to be the longest in the forward / backward direction compared to other scales. Sensor.   5. The stroke sensor according to claim 4, wherein the lengths of the plurality of scales are shorter as the scale is arranged away from the central scale in a direction perpendicular to the advance / retreat direction.   2. The scale according to claim 1, further comprising: a width changing portion having a constant depth while a width in a direction perpendicular to the advancing / retreating direction gradually changes toward the depth changing portion. Stroke sensor.   The stroke sensor according to any one of claims 1 to 6, wherein the scale is a portion in which the second member is melted and magnetized or made nonmagnetic by a local heating device.

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