ROTATION ANGLE DETECTION SENSOR

Abstract

A rotation angle detection sensor detects the rotation angle of a rotating part attached to a structure including a fixed part and a rotating part that rotates around a rotary shaft. The rotation angle detection sensor includes a reed switch attached to the fixed or rotating part with reeds placed near the rotary shaft. An annular magnet is attached to the rotating or fixed part. A magnetic circuit is formed with respect to the reed switch, with its central axis arranged concentrically with the rotary shaft. When the magnet rotates around the central axis with respect to the reed switch, if the same poles of the magnet are lined up in the longitudinal direction of the reed switch, the reed switch is turned off. If opposite poles of the magnet are lined up in the longitudinal direction of the reed switch, the reed switch is turned on.

Claims

1. A rotation angle detection sensor mounted to a structure that includes a fixed part and a rotating part rotatably supported around a rotary shaft for detecting the rotation angle of the rotating part, comprising: a reed switch mounted to the fixed part or the rotating part of the structure perpendicular to the rotary shaft, with reeds arranged near the rotary shaft; and a flat annular magnet mounted to the rotating part or the fixed part of the structure at a specified position in the direction of the rotary shaft so that a magnetic circuit is formed with respect to the reed switch, central axis of the magnet being arranged concentrically with the rotary shaft, wherein the magnet is multi-pole magnetized in parallel to the central axis, and during the rotation of the magnet around the central axis with respect to the reed switch accompanying the rotation of the rotating part of the structure, when the same poles of the magnet are lined up in the longitudinal direction of the reed switch, both reeds of the reed switch are magnetized to the same pole, turning off the reed switch, and when opposite poles are lined up in the longitudinal direction of the reed switch, the both reeds of the reed switch are respectively magnetized to the opposite pole, turning on the reed switch.

2. The rotation angle detection sensor as set forth in claim 1, wherein a back yoke made of a magnetic material is arranged on the side of the reed switch, facing the circumference of the magnet.

3. The rotation angle detection sensor as set forth in claim 1, wherein the magnet and the reed switch are respectively provided with an engagement part, and as a result of engagement between the engagement part of the magnet and the engagement part of the reed switch, the rotation detection angle of the magnet with respect to the reed switch is regulated to an arbitrary angle.

4. The rotation angle detection sensor as set forth in claim 1, wherein only a specified angle range of the magnet with respect to the central axis is magnetized in a direction reverse to that of the remaining area.

5. The rotation angle detection sensor as set forth in claim 1, wherein the reed switch and the magnet are placed along the central axis of the rotation angle detection sensor.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0018] FIG. 1A is a front view of a first embodiment of the rotation angle detection sensor of the present invention.

[0019] FIG. 1B is a cross-sectional view of FIG. 1A taken along line A-A.

[0020] FIG. 1C is an exploded perspective view of FIG. 1A.

[0021] FIG. 2A is a plan view of the major part of the rotation angle detection sensor.

[0022] FIG. 2B is a front view of FIG. 2A.

[0023] FIG. 3A is a schematic plan view showing the positional relation between a reed switch and a magnet when the reed switch is off.

[0024] FIG. 3B is a schematic plan view showing the positional relation between the reed switch and the magnet when the reed switch is on.

[0025] FIG. 4 is a schematic plan view showing the angle range of the reed switch when it is on and off with respect to the rotation angle of the magnet.

[0026] FIG. 5A is a schematic side view showing the distance of the magnet in the direction of central axis and the distribution of magnetic field lines generated when no back yoke is provided.

[0027] FIG. 5B is a schematic side view showing a case when the magnet in FIG. 5A is rotated.

[0028] FIG. 5C is a schematic side view showing the distance of the magnet in the direction of central axis and the distribution of magnetic field lines generated when a back yoke is provided.

[0029] FIG. 6A is a plan view of a modification of the magnet.

[0030] FIG. 6B is a perspective view of FIG. 6A.

[0031] FIG. 7A is a schematic plan view showing the positional relation between the reed switch and the magnet in the modification where the reed switch is on.

[0032] FIG. 7B is a schematic plan view showing the state where the reed switch in FIG. 7A is off.

[0033] FIG. 8 is a schematic plan view showing the angle range of the reed switch when it is on and off with respect to the rotation angle of the magnet.

[0034] FIG. 9A is a plan view of a second embodiment of the rotation angle detection sensor.

[0035] FIG. 9B is a cross-sectional view of FIG. 9A taken along line A-A.

[0036] FIG. 9C is an exploded perspective view of FIG. 9A.

[0037] FIG. 10 is a graph showing the movement in the simulation of the embodiment of the rotation angle detection sensor in FIG. 9A.

[0038] FIG. 11 is an external view showing a fixed part of a structure and a rotation angle detection sensor attached to a rotating part of the structure.

EMBODIMENTS OF THE INVENTION

[0039] A first embodiment shown in FIGS. 1A to 5C will hereinafter be described in detail.

[0040] As shown in FIGS. 1A to 1C, this rotation angle detection sensor 10 includes a base 11, a cover 12, a magnet 13, a reed switch 14, and a back yoke 15. As shown in FIG. 11, the rotation angle detection sensor 10 is mounted to a structure 20 whose rotation angle is to be detected. With the rotation angle detection sensor 10 as shown in FIG. 11, the base 11 is fastened to a fixed part 21 of the structure 20, and the cover 12 is fastened to a rotary shaft 23, for example, of a rotating part 22. The reed switch 14 is accepted by the base 11, and the magnet 13 is housed in the cover 12. Reverse mounting is also allowed: the base 11 may be fastened to the rotary shaft 23 and the cover may be fastened to the fixed part 21 respectively.

[0041] The base 11 of the rotation angle detection sensor 10 is made of a non-magnetic material such as a resin, for example, formed in an approximately flat disk shape, and fastened to the fixed part 21 or the rotating part 22 of a structure 20 whose rotation is to be detected so that the central axis O of the rotation angle detection sensor 10 coincides with the rotary shaft 23 of the structure 20. The base 11 has a reed switch accepting part 11a that is open upwards, and on its top face peripheral edge, an engagement part 11b is provided. On the bottom face peripheral edge of the base 11, a ring-shaped groove 11c is formed, and furthermore on the outside in the radial direction, a pair of protrusions 11d, 11e extending in the right direction as shown in FIG. 1C are provided to regulate rotation.

[0042] The cover 12 is made of a non-magnetic material such a resin, formed in a flat disk shape as in the case of the base 11, and fastened to the rotating part 22 or the fixed part 21 of the structure 20 whose rotation is to be detected. The cover 12 has a concave part 12a that is open downwards on the bottom face, and on the bottom face peripheral edge, an engagement part 12b is provided. When the cover 12 is placed on the base 11, this engagement part 12b is engaged with the engagement part 11b of the base 11 and thus supported in relatively rotatable state around the central axis O on the base 11. Furthermore, the cover 12 has a pair of protrusions 12c, 12d extending from the outer peripheral surface toward outside to regulate rotation.

[0043] As shown in FIG. 1C, the pair of protrusions 12c, 12d of the cover 12 is placed apart from the central axis O to one side, i.e. to the right side in the case shown in FIG. 1C, and extending downwards exceeding the bottom edge of the cover 12. When the cover 12 shown in FIG. 1C rotates counterclockwise, the protrusion 12c of the cover 12 abuts against the protrusion 11d of the base 11, thus regulating the counterclockwise rotation of the cover 12. Also, when the cover 12 rotates clockwise, the protrusion 12d abuts against the protrusion 11e of the base 11, regulating the clockwise rotation of the cover 12 and limiting the rotation angle range to 180 degrees.

[0044] The magnet 13 is made of a permanent magnet such as ferrite and neodymium, etc., and formed in a flat annular shape. The magnet 13 is housed in the concave part 12a of the cover 12 and fixed concentrically with the central axis O of the cover 12. The magnet 13 is fixed to the rotating part 22 or the fixed part 21 of the structure 20 at a specified distance away from the reed switch 14 in the direction of the rotary shaft of the rotating part 22 so that a magnetic circuit is formed for the reed switch 14.

[0045] The magnet 13 is multi-pole magnetized in parallel to the central axis O of the rotation angle detection sensor so that the upper part becomes S pole and the lower part becomes N pole, whereas in the remaining area the upper part becomes N pole and the lower part becomes S pole as shown in FIG. 2B, in a specified angle range, in area 13a of 30 degrees for example, as shown in 2A in detail. The area 13a of the magnet 13 is called a reversely magnetized area, whereas the remaining area 13b is called a forwardly magnetized area.

[0046] The reed switch 14 has a known structure and is placed with its longitudinal direction perpendicular to the central axis O of the base 11. The reed switch 14 is mounted to a printed circuit board 14a, and by engaging the printed circuit board 14a with the reed switch accepting part 11a of the base 11 for fastening, a pair of reeds 14d, 14e (FIG. 3A) are positioned with respect to the base 11 so that they come near the central axis O of the base 11, and lead wires 14b, 14c are drawn outside of the printed circuit board 14a. The reed switch 14 is thus mounted to the fixed part 21 or the rotating part 22 of the structure 20 perpendicular to the rotary shaft of the rotating part 22, with the lead wires 14b, 14c placed around the rotary shaft.

[0047] A back yoke 15 is made of a magnetic material, formed in an annular shape having almost the same external and internal diameters as those of the magnet 13, and inserted into and fastened to annular groove 11c on the bottom face of the base 11.

[0048] Depending on the arrangement of the above-mentioned magnet 13, the reed switch 14, and the back yoke 15, and also depending on the type of the magnet 13 placed adjacent to the both ends of the reed switch 14, the reed switch 14 is turned on or off as described below.

[0049] As shown in FIG. 3A, for example, when S pole of the magnet 13 comes close to the reeds 14d, 14e of the reed switch 14, the outer ends of each reed 14d, 14e become N pole, and the inner ends of each become S pole accordingly. The reeds 14d, 14e thus move away from each other by repulsive force, turning off the reed switch 14. In other words, when the area 13a of the magnet 13 is positioned perpendicular to the longitudinal direction of the reed switch 14 as shown in FIG. 3A, the same poles of the magnet 13 are lined up in the longitudinal direction of the reed switch 14, turning off the reed switch 14.

[0050] Meanwhile, as shown in FIG. 3B, when S and N poles of the magnet 13 respectively come close to the reeds 14d, 14e of the reed switch 14, the outer end of each reed 14d, 14e respectively become N and S poles, and the inner ends respectively become S and N poles accordingly. As a result, the reeds 14d, 14e contact each other by magnetic attraction force, turning on the reed switch 14. In other words, when the area 13a of the magnet 13 is placed in the longitudinal direction of the reed switch 14, the opposite poles of the magnet 13 are line up in the longitudinal direction of the reed switch 14, turning on the reed switch 14.

[0051] The rotation angle detection sensor 10 according to the embodiment of the present invention operates as follows.

[0052] Firstly, the base 11 of the rotation angle detection sensor 10 is mounted to the fixed part 21 or the rotating part 22 of the structure 20, and the cover 12 is mounted to the rotating part 22 or the fixed part 21 of the structure 20. When the rotating part 22 of the structure 20 rotates around the rotary shaft 23 with respect to the fixed part 21, the cover 12 also rotates accordingly around the central axis O with respect to the base 11. That means, as shown in FIG. 4, that the reed switch 14 is turned on in the angle range of 30 degrees respectively with respect to the extending direction of the reed switch 14, and it is turned off in the remaining angle range. When the area 13a of the magnet 13 is relatively positioned within this angle range with respect to the reed switch 14, the reed switch 14 is turned on, and the rotating part 22 with respect to the fixed part 21 of the structure 20 is detected to be within the corresponding angle range.

[0053] In this case, as shown in FIG. 5A, the farther the downward position of the reed switch 14 from the magnet 13, the more the magnetic flux 13af from the reversely magnetized area 13a of the magnet 13 diffuse, expanding the angle range where the reed switch 14 is turned on to exceed the angle range of the area 13a of the magnet 13. Consequently, as shown in 5B, even if the area 13a goes away from the reeds of the reed switch 14 with the rotation of the magnet 13, the magnetic flux 13af reaches the reeds, turning on the reed switch 14. The angle range where the reed switch 14 is turned on thus expands, decreasing the accuracy of rotation angle detection.

[0054] It is therefore desirable, as shown in FIG. 5C, that the magnet 13 and the reed switch 14 come as close to each other as possible, minimizing the distance d between them, and at the same time a magnetic circuit be formed by placing the back yoke 15 under the reed switch 14, keeping the magnetic flux 13af, 13bf extending from the magnet 13 approximately in parallel to each other, and decreasing the leakage of magnetic flux to outside. By placing the back yoke 15, the area 13a of the magnet 13 and the angle range where the reed switch 14 is turned on become approximately the same, thus increasing the accuracy of rotation angle detection.

[0055] (Modification of the Magnet)

[0056] FIGS. 6A and 6B show a typical modification of the magnet. This magnet 13A consists of 30-degrees reversely magnetized area 13a, 60-degrees forwardly magnetized area 13b, 30-degrees reversely magnetized area 13c, and 240-degrees forwardly magnetized area 13d, for example. Since the top and bottom faces of the magnet 13A are respectively magnetized to 4 poles, it is called as the double-sided 8-pole magnetization.

[0057] FIGS. 7A and 7B are schematic plan views showing an example of positional relation between the reed switch and the magnet 13A of the rotation angle detection sensor 10A that uses the magnet 13A as shown in FIG. 6B, where FIG. 7A shows the case when the switch is on, and FIG. 7B shows the case when the switch is off. Since the rotation angle detection sensor 10A is the same as the rotation angle detection sensor 10 except for the magnet 13A, the explanation will be omitted. As shown in FIG. 7A, when area 13a, or area 13c, and area 13d, of the magnet 13A are positioned in the longitudinal direction of the reed switch 14, opposite poles of the magnet are lined up in the longitudinal direction of the reed switch 14, turning on the reed switch 14. Meanwhile, as shown in FIG. 7B, when areas 13b and 13d of the magnet 13A are positioned perpendicular to the longitudinal direction of the reed switch 14, the same poles (N) of the magnet 13A are lined up in the longitudinal direction of the reed switch 14, turning off the reed switch 14.

[0058] FIG. 8 is a schematic plan view showing ON and OFF angle ranges of the reed switch 14 with respect to the rotation angle of the magnet of the rotation angle detection sensor 10 using the modification of the magnet. Every time the both ends of the reeds 14d, 14e of the reed switch 14 come close to N and S poles of the magnet 13A, namely every time the both ends enter the angle range magnetized to the opposite pole, the reed switch 14 is turned on. Meanwhile, every time the both ends of the reeds 14d, 14e of the reed switch 14 enter the area magnetized to the same pole of the magnet 13A, the reed switch 14 is turned off. In other words, while operating the rotation angle detection sensor 10A, rotating the magnet 13A by 360 degrees around the central axis O, the reed switch 14 is turned on 4 times in the range of approximately 30 degrees, and it is turned off in other angle ranges.

[0059] FIGS. 9A to 9C show the rotation angle detection sensor 30 in embodiment 2. Since the rotation angle detection sensor 3 has approximately the same structure as the rotation angle detection sensor 10 shown in FIG. 1, the same symbols are assigned to the same parts, and description will be omitted. The rotation angle detection sensor 30 includes a base 11, a cover 12, a magnet 13, a reed switch 14, and a back yoke 15.

[0060] As shown in FIG. 9C, the reed switch accepting part 11a of the base 11 penetrates down to the bottom face, and grooves 11f, 11g for accepting the reeds 14d, 14e of the reed switch 14 penetrate from the reed switch accepting part 11a in the longitudinal direction. Furthermore, the base 11 includes engagement parts 11h, 11i that extrude upward from the top face instead of the protrusions 11d, 11e (FIG. 1C) of the rotation angle detection sensor 10.

[0061] The cover 12 includes a rotary shaft mounting part 12e that extends from the top face concentrically with the central axis O, and this rotary shaft mounting part 12e has an engagement hole 12f that is open upwards. The engagement hole 12f is formed so that it can accept the rotary shaft 23, which is a part of the rotating part 22 of the structure 20. The engagement hole 12f is formed in a shape corresponding to the rotary shaft, a part of which is cut off.

[0062] The cover 12 has a protrusion 12g that protrudes inwards in the radial direction within the concave part 12a that is open downwards, and has a stopper 12h that protrudes from the top face inside the concave part 12a downwards instead of the engagement part 12c, 12d of the rotation angle detection sensor 10.

[0063] The magnet 13 has a cut portion 13h for positioning on its outer periphery. When the magnet 13 is housed in the concave part 12a of the cover 12, the cut portion 13h is engaged with the protrusion 12g to fix the rotational direction and rotation angle range of the magnet 13. When placed on the base 11, the engagement part 11b is engaged with the magnet 13 to the top edge from inside, and thus the magnet is prevented from coming off the base 11 and is support rotatably around the central axis O. The stopper 12h, which serves as the engagement part of the magnet 13, and the engagement parts 11h, 11i of the reed switch are thus respectively provided, and the engagement part of the magnet 13 is engaged with the engagement part of the reed switch 14, regulating the rotation detection angle of the magnet 13 with respect to the reed switch 14 to an arbitrary angle range.

[0064] The reed switch 14 is not mounted on a printed circuit board 14a but housed directly within the reed switch accepting part 11a, and its reeds 14d, 14e are drawn outside through the grooves 11f, 11g as lead wires. In this case, since the reed switch 14 is placed so that the glass pipe that covers the reeds enters the inner periphery of the magnet 13, the distance between the magnet 13 and the reeds 14b, 14c of the reed switch 14 is shortened, allowing downsizing of the entire device. The gap within the reed switch accepting part 11a of the base 11 is filled with a resin material, and when the material is hardened, the reed switch 14 is fastened.

[0065] The back yoke 15 has cut portions 15a, 15b respectively on both ends in the radial direction, and these cut portions 15a, 15b avoid contact with the reeds 14d, 14e drawn toward outside.

[0066] With the rotation angle detection sensor 30 in embodiment 2, when the area 13a of the magnet 13 is positioned perpendicular to the longitudinal direction of the reed switch 14 as shown in FIG. 3A, the same poles of the magnet 13 are lined up in the longitudinal direction of the reed switch 14, turning off the reed switch 14, which occurs twice during one turn. From this state, the rotating part 22 of the structure 20 rotates, allowing the cover 12 to be rotated around the rotary shaft 23 and the area 13a of the magnet 13 to be positioned in the longitudinal direction of the reed switch 14 as shown in FIG. 3B, and the opposite poles of the magnet 13 are line up in the longitudinal direction of the reed switch 14, turning on the reed switch 14. The rotation angle detection sensor 30 can thus detect that the rotation angle of the rotating part 22 is within a specified angle range with respect to the fixed part 21 of the structure 20.

[0067] The inventor et. al made a prototype of the rotation angle detection sensor 30 in embodiment 2, and performed magnetic simulation of the rotation angle detecting operation. As the magnet 13, a cylindrical isotropic ferrite magnet having outer diameter of 12 mm, inner diameter of 8 mm, and thickness of 1 mm was used, with double-sided 4-pole magnetization performed over the 30-degree angle range. As the reed switch 14, RD-18B by NIPPON ALEPH Co., Ltd. was used, and as the back yoke 15, a cold-rolled steel plate (SPCC) having outer diameter of 12 mm, inner diameter of 8 mm, and thickness of 0.5 mm was used. As shown in FIG. 5C, the magnet 13 was placed on the upper side 1 mm apart from the reed switch 14, and the back yoke 15 was place on the lower side 1 mm apart from the reed switch 14.

[0068] The angle of on/off operation of the reed switch 14 was calculated based on magnetic simulation performed by operating the above-mentioned rotation angle detection sensor 30 with the magnet 13 rotated by 360 degrees around the central axis O. The result is shown in FIG. 10, the horizontal axis representing the longitudinal direction of the reed switch 14. The reed switch 14 operated bisymmetrically, was turned on respectively in the 30-degree angle range with respect to the longitudinal direction (horizontal axis) of the reed switch, and was turned off in the 142-degree angle range with four hysteresis ranges appearing in between. It was found that depending on the position of the back yoke 15, the hysteresis range becomes narrow, thus improving the accuracy of angle measurement. The actual operation of the prototype rotation angle detection sensor 30 also exhibited similar results.

[0069] The present invention can be executed in various embodiments without departing from the scope of the invention. As the magnet, 13, not only ferrite magnets but also magnets of other types, a neodymium magnet for example, can be used. In the embodiment shown, the back yoke 15 is placed so as to face the magnet 13, vertically sandwiching the reed switch 14. However, the back yoke 15 may be omitted. The area 13a of the magnet 13 is not limited to the range shown in the above embodiment, but the magnet may be reversely magnetized in an angle range larger than or smaller than 30 degrees. It is also apparent that the double-sided 8-pole-magnetized magnet 13A is applicable not only to the rotation angle detection sensor 10A in embodiment 1 but also to the rotation angle detection sensor 30 in embodiment 2. Rotation angle detection sensors 10, 10A, 30 may also be provided with a plurality of reversely magnetized areas 13a, in addition to the double-sided 8-pole magnetization, to detect angles at a plurality of positions, of the rotation angle range.

REFERENCE SIGN LIST

[0070] 10, 10A, 30: Rotation angle detection sensor [0071] 11: Base [0072] 11a: Reed switch accepting part [0073] 11b: Engagement part [0074] 11c: Annular groove [0075] 11d, 11e: Protrusion [0076] 11f, 11g: Groove [0077] 11h, 11i: Engagement part [0078] 12: Cover [0079] 12a: Concave part [0080] 12b: Engagement part [0081] 12c, 12d: Protrusion [0082] 12e: Rotary shaft mounting part [0083] 12f: Engagement hole [0084] 12g: Protrusion [0085] 12h: Stopper [0086] 13, 13A: Magnet [0087] 13a, 13c: Reversely magnetized area [0088] 13b, 13d: Forwardly magnetized area [0089] 13af, 13bf: Magnetic flux [0090] 13h: Cut portion [0091] 14: Reed switch [0092] 14a: Printed circuit board [0093] 14b, 14c: Drawn lead wire [0094] 14d, 14e: Reed [0095] 15: Back yoke [0096] 15a, 15b: Cut portion [0097] 20: Structure [0098] 21: Fixed part [0099] 22: Rotating part [0100] 23: Rotary shaft