Linear sensor

Abstract

A linear sensor capable of detecting a position of a shaft member in the axial direction and an angle of the shaft member in the circumferential direction is obtained. The linear sensor comprises: a shaft member that has a first part to be detected and a second part to be detected configured from a magnetic body, and that is movable in the axial direction; a first magnetic sensor; a second magnetic sensor; and a position angle calculation unit. A left-hand thread is formed on the outer circumferential surface of the first part to be detected, and a right-hand thread is formed on the outer circumferential surface of the second part to be detected. The first magnetic sensor outputs a first detection signal corresponding to the position of the left-hand thread with respect to the first magnetic sensor, the second magnetic sensor outputs a second detection signal corresponding to the position of the right-hand thread with respect to the second magnetic sensor, and the position angle calculation unit uses the first detection signal and the second detection signal to calculate the position of the shaft member in the axial direction and the angle of the shaft member in the circumferential direction.

Description

Linear sensor

[0001] This invention relates to a linear sensor.

[0002] Conventionally, a linear sensor including a shaft member made of a magnetic material and moving in the axial direction, and a magnetic sensor provided facing the outer peripheral surface of the shaft member is known. The shaft member has a plurality of convex portions arranged in the axial direction at preset intervals. The magnetic sensor detects the position of the shaft member in the axial direction by using the change in the magnetic flux density between the shaft member and the magnetic sensor (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2003-194583

[0004] However, in the configuration of the linear sensor described in Patent Document 1, although the position of the shaft member in the axial direction can be detected, there is a problem that the angle of the shaft member in the circumferential direction cannot be detected.

[0005] This invention has been made to solve the above-described problems, and an object thereof is to provide a linear sensor capable of detecting the position of a shaft member in the axial direction and the angle of the shaft member in the circumferential direction.

[0006] The linear sensor according to this invention comprises a shaft member that is movable in the axial direction and has a first detectable part and a second detectable part made of a magnetic material, a first magnetic sensor provided opposite the first detectable part, a second magnetic sensor provided opposite the second detectable part, and a position angle calculation unit. The first detectable part has a left-hand thread, and the second detectable part has a right-hand thread. The first magnetic sensor outputs a first detection signal, which is a signal corresponding to the position of the left-hand thread relative to the first magnetic sensor in the axial direction, and the second magnetic sensor outputs a second detection signal, which is a signal corresponding to the position of the right-hand thread relative to the second magnetic sensor in the axial direction. The position angle calculation unit uses the first and second detection signals to calculate the position of the shaft member in the axial direction and the angle of the shaft member in the circumferential direction. In the linear sensor according to this invention, the shaft member is made entirely of the same material. In the linear sensor according to this invention, the position angle calculation unit calculates the angle of the shaft member in the circumferential direction based on the difference between the first detection signal and the second detection signal, and calculates the position of the shaft member in the axial direction based on the sum of the first detection signal and the second detection signal.

[0007] According to the linear sensor of this invention, it is possible to detect the position of the shaft member in the axial direction and the angle of the shaft member in the circumferential direction.

[0008] This is a front view showing a linear sensor according to Embodiment 1. This is a block diagram of the linear sensor in Figure 1. This diagram illustrates the direction of movement of the left-hand thread and right-hand thread when the shaft member in Figure 1 moves in the axial direction. This diagram illustrates the direction of movement of the left-hand thread and right-hand thread when the shaft member in Figure 1 rotates in the circumferential direction. This is a graph showing the first detection signal and the second detection signal when the shaft member in Figure 1 moves in the axial direction. This is a graph showing the first detection signal and the second detection signal when the shaft member in Figure 1 rotates in the circumferential direction. This is a graph showing the first detection signal and the second detection signal when the shaft member in Figure 1 moves in the axial direction and rotates in the circumferential direction.

[0009] Embodiment 1. Figure 1 is a front view showing a linear sensor according to Embodiment 1. Figure 2 is a block diagram of the linear sensor in Figure 1. The linear sensor according to Embodiment 1 comprises a shaft member 1, a first magnetic sensor 2, a second magnetic sensor 3, and a position angle calculation unit 4.

[0010] The shaft member 1 is made of a magnetic material. The entire shaft member 1 is made of the same material. The shape of the shaft member 1 is formed as a long, elongated shape extending in one direction. Specifically, the shape of the shaft member 1 is formed as a cylinder.

[0011] The shaft member 1 is movable in the axial direction D1. Furthermore, the shaft member 1 is rotatable in the circumferential direction D2.

[0012] The shaft member 1 has a first detection portion 11 and a second detection portion 12. The first detection portion 11 and the second detection portion 12 are arranged offset from each other in the axial direction D1.

[0013] A left-hand thread groove is formed on the outer circumferential surface of the first detection part 11. As a result, the first detection part 11 has a left-hand thread 111, which is a left-hand thread. The left-hand thread 111 is formed by turning the shaft member 1 on a lathe.

[0014] A right-hand thread groove is formed on the outer circumferential surface of the second detection part 12. As a result, the second detection part 12 has a right-hand thread 121, which is a right-hand thread. The right-hand thread 121 is formed by turning the shaft member 1 on a lathe.

[0015] The pitch of the left-hand thread 111 and the pitch of the right-hand thread 121 are the same.

[0016] The first magnetic sensor 2 is provided facing the outer circumferential surface of the first detection unit 11. The first magnetic sensor 2 outputs a first detection signal S1, which is a signal corresponding to the position of the left-hand thread 111 in the axial direction D1 relative to the first magnetic sensor 2.

[0017] Examples of the first magnetic sensor 2 include a magnetoresistive element, a Hall sensor, and a wound-type sensor. The first magnetic sensor 2 outputs a first detection signal S1 using the change in magnetoresistance, change in magnetic induction, or change in magnetic flux density between the first magnetic sensor 2 and the first detected unit 11.

[0018] The second magnetic sensor 3 is provided facing the outer circumferential surface of the second detection unit 12. The second magnetic sensor 3 outputs a second detection signal S2, which is a signal corresponding to the position of the right-hand thread 121 in the axial direction D1 relative to the second magnetic sensor 3.

[0019] Examples of the second magnetic sensor 3 include a magnetoresistive element, a Hall sensor, and a wound-type sensor. The second magnetic sensor 3 outputs a second detection signal S2 using the change in magnetoresistance, change in magnetic induction, or change in magnetic flux density between the second magnetic sensor 3 and the second detected unit 12.

[0020] Figure 3 illustrates the direction of movement of the left-hand thread 111 and the right-hand thread 121 when the shaft member 1 in Figure 1 moves in the axial direction D1. In Figure 3, the shaft member 1 is not rotating in the circumferential direction D2. When the shaft member 1 moves in the axial direction D1, for example, to the right in Figure 3, the left-hand thread 111 moves to the right in Figure 3 relative to the first magnetic sensor 2, and the right-hand thread 121 moves to the right in Figure 3 relative to the second magnetic sensor 3.

[0021] On the other hand, if the shaft member 1 moves in the axial direction D1, for example, to the left in Figure 3, the left-hand thread 111 moves to the left in Figure 3 relative to the first magnetic sensor 2, and the right-hand thread 121 moves to the left in Figure 3 relative to the second magnetic sensor 3.

[0022] In other words, when the shaft member 1 moves in the axial direction D1, the direction of movement of the left-hand thread 111 relative to the first magnetic sensor 2 and the direction of movement of the right-hand thread 121 relative to the second magnetic sensor 3 coincide. Also, when the shaft member 1 moves in the axial direction D1, the distance traveled by the left-hand thread 111 relative to the first magnetic sensor 2 and the distance traveled by the right-hand thread 121 relative to the second magnetic sensor 3 coincide.

[0023] Figure 4 illustrates the direction of movement of the left-hand thread 111 and the right-hand thread 121 when the shaft member 1 in Figure 1 rotates in the circumferential direction D2. In Figure 4, the shaft member 1 is not moving in the axial direction D1. When the shaft member 1 rotates once clockwise in the circumferential direction D2, for example, when it is facing left along the axial direction D1 in Figure 4, the left-hand thread 111 moves to the left in Figure 4 relative to the first magnetic sensor 2, and the right-hand thread 121 moves to the right in Figure 4 relative to the second magnetic sensor 3.

[0024] On the other hand, when the shaft member 1 rotates counterclockwise once in the circumferential direction D2, for example, when it is oriented to the left along the axial direction D1 in Figure 4, the left-hand thread 111 moves to the right in Figure 4 relative to the first magnetic sensor 2, and the right-hand thread 121 moves to the left in Figure 4 relative to the second magnetic sensor 3.

[0025] In other words, when the shaft member 1 rotates in the circumferential direction D2, the direction of movement of the left-hand thread 111 relative to the first magnetic sensor 2 and the direction of movement of the right-hand thread 121 relative to the second magnetic sensor 3 are opposite to each other. Also, when the shaft member 1 rotates in the circumferential direction D2, the distance traveled by the left-hand thread 111 relative to the first magnetic sensor 2 and the distance traveled by the right-hand thread 121 relative to the second magnetic sensor 3 are equal to each other.

[0026] When the shaft member 1 moves in the axial direction D1 while rotating in the circumferential direction D2, the direction of movement of the left-hand thread 111 relative to the first magnetic sensor 2 and the direction of movement of the right-hand thread 121 relative to the second magnetic sensor 3 change in accordance with the speed of movement of the shaft member 1 in the axial direction D1 and the speed of rotation of the shaft member 1 in the circumferential direction D2.

[0027] The first magnetic sensor 2 and the second magnetic sensor 3 are each supported by a magnetic sensor support (not shown).

[0028] The position and angle calculation unit 4 receives the first detection signal S1 output from the first magnetic sensor 2 and the second detection signal S2 output from the second magnetic sensor 3. The position and angle calculation unit 4 uses the first detection signal S1 and the second detection signal S2 to calculate the position of the shaft member 1 in the axial direction D1 and the angle of the shaft member 1 in the circumferential direction D2.

[0029] Next, the method for calculating the position of the shaft member 1 in the axial direction D1 and the angle of the shaft member 1 in the circumferential direction D2 by the position angle calculation unit 4 will be explained.

[0030] As the left-hand thread 111 moves in the axial direction D1, the first magnetic sensor 2 generates a sinusoidal first detection signal S1 in response to a change in magnetoresistance, magnetic induction, or magnetic flux density between the first magnetic sensor 2 and the first detected part 11. The first magnetic sensor 2 converts the sinusoidal first detection signal S1 into an angle signal using an inverse trigonometric function. The angle signal is a signal indicating the angle of the left-hand thread 111 in the circumferential direction D2. The first magnetic sensor 2 outputs the first detection signal S1 converted into an angle signal.

[0031] As the right-hand thread 121 moves in the axial direction D1, the second magnetic sensor 3 generates a sinusoidal second detection signal S2 in response to the change in magnetoresistance, magnetic induction, or magnetic flux density between the second magnetic sensor 3 and the second detected part 12. The second magnetic sensor 3 converts the sinusoidal second detection signal S2 into an angle signal using an inverse trigonometric function. The angle signal is a signal indicating the angle of the right-hand thread 121 in the circumferential direction D2. The second magnetic sensor 3 outputs the second detection signal S2 converted into an angle signal.

[0032] Figure 5 is a graph showing the first detection signal S1 and the second detection signal S2 when the shaft member 1 in Figure 1 moves in the axial direction D1. In Figure 5, at time T1, the direction of movement of the shaft member 1 is reversed. When the shaft member 1 moves in the axial direction D1, before the direction of movement of the shaft member 1 is reversed, the first detection signal S1 and the second detection signal S2 each increase over time while the left screw thread 111 and the right screw thread 121 each move by one pitch. On the other hand, when the shaft member 1 moves in the axial direction D1, after the direction of movement of the shaft member 1 is reversed, the first detection signal S1 and the second detection signal S2 each decrease over time while the left screw thread 111 and the right screw thread 121 each move by one pitch.

[0033] Figure 6 is a graph showing the first detection signal S1 and the second detection signal S2 when the shaft member 1 in Figure 1 rotates in the circumferential direction D2. In Figure 6, at time T2, the direction of rotation of the shaft member 1 is reversed. When the shaft member 1 rotates in the circumferential direction D2, and before the direction of rotation of the shaft member 1 is reversed, the first detection signal S1 increases with time as the left screw thread 111 moves by one pitch, and the second detection signal S2 decreases with time as the right screw thread 121 moves by one pitch. On the other hand, when the shaft member 1 rotates in the circumferential direction D2, and after the direction of rotation of the shaft member 1 is reversed, the first detection signal S1 decreases with time as the left screw thread 111 moves by one pitch, and the second detection signal S2 increases with time as the right screw thread 121 moves by one pitch.

[0034] Figure 7 is a graph showing the first detection signal S1 and the second detection signal S2 when the shaft member 1 in Figure 1 moves in the axial direction D1 and rotates in the circumferential direction D2. In Figure 7, at time T3, the direction of movement of the shaft member 1 is reversed, and the direction of rotation of the shaft member 1 is also reversed. Also in Figure 7, the shaft member 1 moves in the axial direction D1 and rotates in the circumferential direction D2 so that the right-hand thread 121 does not move in the axial direction D1. When the shaft member 1 moves in the axial direction D1 and rotates in the circumferential direction D2, the first detection signal S1 and the second detection signal S2 change in accordance with the speed of movement of the shaft member 1 in the axial direction D1 and the speed of rotation of the shaft member 1 in the circumferential direction D2.

[0035] The first detection signal S1 includes a component CM1 due to the movement of the shaft member 1 in the axial direction D1 and a component CR1 due to the rotation of the shaft member 1 in the circumferential direction D2.

[0036] Therefore, the following equation (1) is satisfied: S1 = CM1 + CR1 (1)

[0037] The second detection signal S2 includes a component CM2 due to the movement of the shaft member 1 in the axial direction D1 and a component CR2 due to the rotation of the shaft member 1 in the circumferential direction D2.

[0038] Therefore, the following equation (2) is satisfied: S2 = CM2 + CR2 (2)

[0039] Since components CM1 and CM2 are each components resulting from the movement of the shaft member 1 in the axial direction D1, components CM1 and CM2 have the same value. On the other hand, since components CR1 and CR2 are each components resulting from the rotation of the shaft member 1 in the circumferential direction D2, components CR1 and CR2 have opposite signs and the same absolute value.

[0040] Therefore, the angle of the shaft member 1 in the circumferential direction D2 can be calculated based on the difference between the first detection signal S1 and the second detection signal S2. In addition, the position of the shaft member 1 in the axial direction D1 can be calculated based on the sum of the first detection signal S1 and the second detection signal S2.

[0041] As a result, the position angle calculation unit 4 calculates the angle of the shaft member 1 in the circumferential direction D2 based on the difference between the first detection signal S1 and the second detection signal S2, and calculates the position of the shaft member 1 in the axial direction D1 based on the sum of the first detection signal S1 and the second detection signal S2.

[0042] As described above, the linear sensor according to Embodiment 1 comprises a shaft member 1, a first magnetic sensor 2, a second magnetic sensor 3, and a position angle calculation unit 4. The shaft member 1 has a first detectable part 11 and a second detectable part 12 made of a magnetic material, and is movable in the axial direction D1. The first magnetic sensor 2 is provided opposite to the first detectable part 11. The second magnetic sensor 3 is provided opposite to the second detectable part 12. The first detectable part 11 has a left-hand thread 111, which is a left-hand screw thread, and the second detectable part 12 has a right-hand thread 121, which is a right-hand screw thread. The first magnetic sensor 2 outputs a first detection signal S1, which is a signal corresponding to the position of the left-hand thread 111 relative to the first magnetic sensor 2 in the axial direction D1. The second magnetic sensor 3 outputs a second detection signal S2, which is a signal corresponding to the position of the right-hand thread 121 relative to the second magnetic sensor 3 in the axial direction D1. The position angle calculation unit 4 uses the first detection signal S1 and the second detection signal S2 to calculate the position of the shaft member 1 in the axial direction D1 and the angle of the shaft member 1 in the circumferential direction D2. With this configuration, it is possible to detect the position of the shaft member 1 in the axial direction D1 and the angle of the shaft member 1 in the circumferential direction D2.

[0043] Furthermore, in the linear sensor according to Embodiment 1, the shaft member 1 is made entirely of the same material. This configuration allows the shaft member 1 to be easily manufactured.

[0044] Furthermore, in the linear sensor according to Embodiment 1, the position angle calculation unit 4 calculates the angle of the shaft member 1 in the circumferential direction D2 based on the difference between the first detection signal S1 and the second detection signal S2, and calculates the position of the shaft member 1 in the axial direction D1 based on the sum of the first detection signal S1 and the second detection signal S2. With this configuration, the position angle calculation unit 4 can calculate the position of the shaft member 1 in the axial direction D1 and the angle of the shaft member 1 in the circumferential direction D2 with a simple configuration.

[0045] In the linear sensor according to the first embodiment, the configuration in which the entire shaft member 1 is made of the same material has been described. However, the present invention is not limited to this configuration. For example, only the first detected portion 11 and the second detected portion 12 may be made of a magnetic material.

[0046] As described above, the linear sensor according to the preferred first embodiment has been described. However, the present invention is not limited to the linear sensor according to the first embodiment described above. Various modifications and conversions can be made to the linear sensor according to the first embodiment described above without departing from the scope described in the claims.

[0047] 1 Shaft member, 2 First magnetic sensor, 3 Second magnetic sensor, 4 Position angle calculation unit, 11 First detected portion, 12 Second detected portion, 111 Left thread, 121 Right thread.

Claims

1. The device comprises a shaft member (1) that is movable in the axial direction (D1) and has a first detectable part (11) and a second detectable part (12) made of a magnetic material, a first magnetic sensor (2) provided opposite to the first detectable part (11), a second magnetic sensor (3) provided opposite to the second detectable part (12), and a position angle calculation unit (4), wherein the first detectable part (11) has a left-hand thread (111) which is the thread of a left-hand screw, the second detectable part (12) has a right-hand thread (121) which is the thread of a right-hand screw, and the first magnetic sensor (2) outputs a first detection signal which is a signal corresponding to the position of the left-hand thread (111) relative to the first magnetic sensor (2) in the axial direction (D1). The second magnetic sensor (3) outputs a second detection signal which is a signal corresponding to the position of the right-hand thread (121) relative to the second magnetic sensor (3) in the axial direction (D1), and the position angle calculation unit (4) uses the first detection signal and the second detection signal to calculate the position of the shaft member (1) in the axial direction (D1) and the angle of the shaft member (1) in the circumferential direction (D2) of the shaft member (1).

2. The linear sensor according to claim 1, wherein the shaft member (1) is composed entirely of the same material.

3. The linear sensor according to claim 1 or 2, wherein the position angle calculation unit (4) calculates the angle of the shaft member (1) in the circumferential direction (D2) based on the difference between the first detection signal and the second detection signal, and calculates the position of the shaft member (1) in the axial direction (D1) based on the sum of the first detection signal and the second detection signal.

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