Patent Description:
To detect the rotation angle of a rotating part, semiconductor linear sensors including the one using a Hall element or magneto-resistive sensor, non-contact-type position sensor using an IC, or rotary encoder and resistive position sensor are known in the prior art. These sensors can detect rotation angles with high accuracy although they require the driving power supplies.

However, to detect opening or closing of a cover of an automatic warm water washing toilet seat, for example, it is unnecessary to ensure detection accuracy as high as that of a highly expensive rotation angle detection sensor. That is why rotation detection sensors and rotation angle detection sensors that use inexpensive reed switches are also known.

Patent Literature <NUM> discloses a gas meter where the longitudinal direction of a reed switch and the tangential direction of rotational trajectory of a magnet are placed almost in parallel, reeds are magnetized to the same pole when magnetic lines cross the reeds to open them by repulsive force, and the reeds are magnetized to the opposite pole when the magnetic lines pass almost in parallel to the reeds to close them by attraction force, thus outputting pulse signals according the opening and closing of the reed switch.

Patent Literature <NUM> discloses a pulse generator and a rotation angle detection apparatus where two bias magnets are placed apart from each other along the reeds of a reed switch with the counter magnetic pole set as an opposing pole, and when a sensor magnet that is placed so that magnetic lines cross the longitudinal direction of the reed switch moves, the output signals of the reed switch are switched at the central position between the bias magnets.

The document <CIT> discloses a rotation angle detection sensor according to the preamble of claim <NUM>.

The rotation angle sensors using a semiconductor device described above have the high functionality and the high detection accuracy. Meanwhile they have the high parts cost, require the driving power, and the running cost is also high. With rotation angle sensors that have a sliding contact such as a resistance-type position sensor and a rotary switch, the life of the sliding contact is short, the periodic maintenance is necessary, and the explosion-proof design is difficult, thus increasing the cost.

The gas meter in Patent Literature <NUM> detects rotation of a rotating member by using the reed switch placed outside the rotation trajectory of the magnet that rotates with the rotation of the rotating member. The reed switch itself is inexpensive and requires no driving power. However, since the increase and the decrease of magnetic lines that pass the reeds of the reed switch with the rotation of the magnet (change of magnetic flux density) are slow, the detection of rotation depends on the working value of the reed switch. Consequently, such meters are effective to measure the number of rotations, but the high-accuracy rotation angle detection cannot be expected.

With the pulse generator and the rotation angle detection apparatus disclosed in Patent Literature <NUM>, since magnets are placed so that the longitudinal direction of the magnets extend from the central axis of a part whose rotation is to be detected along its radius, the size of the apparatus itself increases. In addition, since bias magnets are necessary, the number of parts becomes large, thus increasing the cost.

The present invention intends to provide a compact and simple-structure rotation angle detection sensor capable of detecting the rotation angle of the rotating member.

To achieve the above-mentioned objective, the present invention provides a rotation angle detection sensor that is attached to a structure including a fixed part and a rotating part supported around a rotary shaft with respect to the fixed part to detect the rotation angle of the rotating part, the rotation angle detection sensor including a reed switch attached to the fixed part or the rotating part of the structure perpendicular to the rotary shaft with the reeds disposed near the rotary shaft, and a flat annular magnet arranged at a specified positions in the direction of the rotary shaft with its central axis disposed concentrically with the rotary shaft of the structure so that a magnetic circuit is formed in the reed switch, characterized in that the magnet is multi-pole magnetized in parallel to the central axis, and when the magnet rotates around the central axis with respect to the reed switch with the rotation of the rotating part of the structure, both reeds of the reed switch are respectively magnetized to the same pole if the same poles of the magnet are aligned in the longitudinal direction of the reed switch, thereby turning off the reed switch, and if different magnetic poles of the magnet are aligned in the longitudinal direction of the reed switch, the both reeds of the reed switch are respectively magnetized to a different pole, thereby turning on the reed switch.

According to the above structure, since the both reeds of the reed switch are respectively magnetized to the same pole when the same poles of the magnet are aligned in the longitudinal direction of the reed switch while the rotating part of the structures are rotating, the reeds move away from each other due to repulsive force, turning off the reed switch. Since the reeds of the reed switch are magnetized to an opposite pole when opposite poles of the magnet are aligned in the longitudinal direction of the reed switch, the reeds contact each other by the magnetic attraction force, turning on the reed switch. Thus, with the rotation of the rotating part of the structure with respect to the fixed part, the reed switch is turned on or off according to the multi-pole magnetization of the magnet, allowing the rotation of the rotating part of the structure to be detected.

When a back yoke is placed on the side of the reed switch, since the magnetic field lines of the magnet pass through the back yoke, thus preventing diffusion of the magnetic flux that acts on the reeds of the reed switch, higher accuracy in rotation angle detection is ensured.

If the magnet and the reed switch respectively have an engagement part, that of the magnet is engaged with that of the reed switch, and thus the rotation detection angle of the magnet with respect to the reed switch is regulated to an arbitrary angle without fail when the magnet rotates with respect to the reed switch.

If the magnet is structured to be magnetized in a direction opposite to other areas in a specified angle range only with respect to the central axis, the reeds of the reed switch are magnetized to the opposite pole when the specified angle range is positioned in the longitudinal direction of the reed switch, and thus the reed switch is turned on. In other words, the reed switch is turned on only within the specified angle range, ensuring detection of the specified angle range of the rotating part of the structure with respect to the fixed part. If the reed switch and the magnet are structured to be positioned along the central axis of the rotation angle detection sensor, the reed switch is turned on only within the specified angle range of the magnet, ensuring detection of the angle range of the rotating part of the structure with respect to the fixed part.

The present invention provides a compact, simple-structure, and highly functional rotation angle detection sensor capable of detecting the rotation angle of a rotating part.

A first embodiment shown in <FIG> will hereinafter be described in detail.

As shown in <FIG>, this rotation angle detection sensor <NUM> includes a base <NUM>, a cover <NUM>, a magnet <NUM>, a reed switch <NUM>, and a back yoke <NUM>. As shown in <FIG>, the rotation angle detection sensor <NUM> is mounted to a structure <NUM> whose rotation angle is to be detected. With the rotation angle detection sensor <NUM> as shown in <FIG>, the base <NUM> is fastened to a fixed part <NUM> of the structure <NUM>, and the cover <NUM> is fastened to a rotary shaft <NUM>, for example, of a rotating part <NUM>. The reed switch <NUM> is accepted by the base <NUM>, and the magnet <NUM> is housed in the cover <NUM>. Reverse mounting is also allowed: the base <NUM> may be fastened to the rotary shaft <NUM> and the cover may be fastened to the fixed part <NUM> respectively.

The base <NUM> of the rotation angle detection sensor <NUM> 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 <NUM> or the rotating part <NUM> of a structure <NUM> whose rotation is to be detected so that the central axis O of the rotation angle detection sensor <NUM> coincides with the rotary shaft <NUM> of the structure <NUM>. The base <NUM> 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 <NUM>, 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> are provided to regulate rotation.

The cover <NUM> is made of a non-magnetic material such a resin, formed in a flat disk shape as in the case of the base <NUM>, and fastened to the rotating part <NUM> or the fixed part <NUM> of the structure <NUM> whose rotation is to be detected. The cover <NUM> 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 <NUM> is placed on the base <NUM>, this engagement part 12b is engaged with the engagement part 11b of the base <NUM> and thus supported in relatively rotatable state around the central axis O on the base <NUM>. Furthermore, the cover <NUM> has a pair of protrusions 12c, 12d extending from the outer peripheral surface toward outside to regulate rotation.

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

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

The magnet <NUM> 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>, in a specified angle range, in area 13a of <NUM> degrees for example, as shown in 2A in detail. The area 13a of the magnet <NUM> is called a reversely magnetized area, whereas the remaining area 13b is called a forwardly magnetized area.

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

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

Depending on the arrangement of the above-mentioned magnet <NUM>, the reed switch <NUM>, and the back yoke <NUM>, and also depending on the type of the magnet <NUM> placed adjacent to the both ends of the reed switch <NUM>, the reed switch <NUM> is turned on or off as described below.

As shown in <FIG>, for example, when S pole of the magnet <NUM> comes close to the reeds 14d, 14e of the reed switch <NUM>, 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 <NUM>. In other words, when the area 13a of the magnet <NUM> is positioned perpendicular to the longitudinal direction of the reed switch <NUM> as shown in <FIG>, the same poles of the magnet <NUM> are lined up in the longitudinal direction of the reed switch <NUM>, turning off the reed switch <NUM>.

Meanwhile, as shown in <FIG>, when S and N poles of the magnet <NUM> respectively come close to the reeds 14d, 14e of the reed switch <NUM>, 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 <NUM>. In other words, when the area 13a of the magnet <NUM> is placed in the longitudinal direction of the reed switch <NUM>, the opposite poles of the magnet <NUM> are line up in the longitudinal direction of the reed switch <NUM>, turning on the reed switch <NUM>.

The rotation angle detection sensor <NUM> according to the embodiment of the present invention operates as follows.

Firstly, the base <NUM> of the rotation angle detection sensor <NUM> is mounted to the fixed part <NUM> or the rotating part <NUM> of the structure <NUM>, and the cover <NUM> is mounted to the rotating part <NUM> or the fixed part <NUM> of the structure <NUM>. When the rotating part <NUM> of the structure <NUM> rotates around the rotary shaft <NUM> with respect to the fixed part <NUM>, the cover <NUM> also rotates accordingly around the central axis O with respect to the base <NUM>. That means, as shown in <FIG>, that the reed switch <NUM> is turned on in the angle range of <NUM> degrees respectively with respect to the extending direction of the reed switch <NUM>, and it is turned off in the remaining angle range. When the area 13a of the magnet <NUM> is relatively positioned within this angle range with respect to the reed switch <NUM>, the reed switch <NUM> is turned on, and the rotating part <NUM> with respect to the fixed part <NUM> of the structure <NUM> is detected to be within the corresponding angle range.

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

It is therefore desirable, as shown in <FIG>, that the magnet <NUM> and the reed switch <NUM> 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 <NUM> under the reed switch <NUM>, keeping the magnetic flux 13af, 13bf extending from the magnet <NUM> approximately in parallel to each other, and decreasing the leakage of magnetic flux to outside. By placing the back yoke <NUM>, the area 13a of the magnet <NUM> and the angle range where the reed switch <NUM> is turned on become approximately the same, thus increasing the accuracy of rotation angle detection.

<FIG> show a typical modification of the magnet. This magnet 13A consists of <NUM>-degrees reversely magnetized area 13a, <NUM>-degrees forwardly magnetized area 13b, <NUM>-degrees reversely magnetized area 13c, and <NUM>-degrees forwardly magnetized area 13d, for example. Since the top and bottom faces of the magnet 13A are respectively magnetized to <NUM> poles, it is called as the double-sided <NUM>-pole magnetization.

<FIG> 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>, where <FIG> shows the case when the switch is on, and <FIG> shows the case when the switch is off. Since the rotation angle detection sensor 10A is the same as the rotation angle detection sensor <NUM> except for the magnet 13A, the explanation will be omitted. As shown in <FIG>, when area 13a, or area 13c, and area 13d, of the magnet 13A are positioned in the longitudinal direction of the reed switch <NUM>, opposite poles of the magnet are lined up in the longitudinal direction of the reed switch <NUM>, turning on the reed switch <NUM>. Meanwhile, as shown in <FIG>, when areas 13b and 13d of the magnet 13A are positioned perpendicular to the longitudinal direction of the reed switch <NUM>, the same poles (N) of the magnet 13A are lined up in the longitudinal direction of the reed switch <NUM>, turning off the reed switch <NUM>.

<FIG> is a schematic plan view showing ON and OFF angle ranges of the reed switch <NUM> with respect to the rotation angle of the magnet of the rotation angle detection sensor <NUM> using the modification of the magnet. Every time the both ends of the reeds 14d, 14e of the reed switch <NUM> 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 <NUM> is turned on. Meanwhile, every time the both ends of the reeds 14d, 14e of the reed switch <NUM> enter the area magnetized to the same pole of the magnet 13A, the reed switch <NUM> is turned off. In other words, while operating the rotation angle detection sensor 10A, rotating the magnet 13A by <NUM> degrees around the central axis O, the reed switch <NUM> is turned on <NUM> times in the range of approximately <NUM> degrees, and it is turned off in other angle ranges.

<FIG> show the rotation angle detection sensor <NUM> in embodiment <NUM>. Since the rotation angle detection sensor <NUM> has approximately the same structure as the rotation angle detection sensor <NUM> shown in <FIG>, the same symbols are assigned to the same parts, and description will be omitted. The rotation angle detection sensor <NUM> includes a base <NUM>, a cover <NUM>, a magnet <NUM>, a reed switch <NUM>, and a back yoke <NUM>.

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

The cover <NUM> 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 <NUM>, which is a part of the rotating part <NUM> of the structure <NUM>. The engagement hole 12f is formed in a shape corresponding to the rotary shaft, a part of which is cut off.

The cover <NUM> has a protrusion <NUM> that protrudes inwards in the radial direction within the concave part 12a that is open downwards, and has a stopper <NUM> 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 <NUM>.

The magnet <NUM> has a cut portion <NUM> for positioning on its outer periphery. When the magnet <NUM> is housed in the concave part 12a of the cover <NUM>, the cut portion <NUM> is engaged with the protrusion <NUM> to fix the rotational direction and rotation angle range of the magnet <NUM>. When placed on the base <NUM>, the engagement part 11b is engaged with the magnet <NUM> to the top edge from inside, and thus the magnet is prevented from coming off the base <NUM> and is support rotatably around the central axis O. The stopper <NUM>, which serves as the engagement part of the magnet <NUM>, and the engagement parts <NUM>, 11i of the reed switch are thus respectively provided, and the engagement part of the magnet <NUM> is engaged with the engagement part of the reed switch14, regulating the rotation detection angle of the magnet <NUM> with respect to the reed switch <NUM> to an arbitrary angle range.

The reed switch <NUM> 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, <NUM> as lead wires. In this case, since the reed switch <NUM> is placed so that the glass pipe that covers the reeds enters the inner periphery of the magnet <NUM>, the distance between the magnet <NUM> and the reeds 14b, 14c of the reed switch <NUM> is shortened, allowing downsizing of the entire device. The gap within the reed switch accepting part 11a of the base <NUM> is filled with a resin material, and when the material is hardened, the reed switch <NUM> is fastened.

The back yoke <NUM> 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.

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

The inventor et. al made a prototype of the rotation angle detection sensor <NUM> in embodiment <NUM>, and performed magnetic simulation of the rotation angle detecting operation. As the magnet <NUM>, a cylindrical isotropic ferrite magnet having outer diameter of <NUM>, inner diameter of <NUM>, and thickness of <NUM> was used, with double-sided <NUM>-pole magnetization performed over the <NUM>-dgree angle range. As the reed switch <NUM>, RD-18B by NIPPON ALEPH Co. was used, and as the back yoke <NUM>, a cold-rolled steel plate (SPCC) having outer diameter of <NUM>, inner diameter of <NUM>, and thickness of <NUM> was used. As shown in <FIG>, the magnet <NUM> was placed on the upper side <NUM> apart from the reed switch <NUM>, and the back yoke <NUM> was place on the lower side <NUM> apart from the reed switch <NUM>.

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

Claim 1:
A rotation angle detection sensor (<NUM>) mounted to a structure (<NUM>) that includes a fixed part (<NUM>) and a rotating part (<NUM>) rotatably supported around a rotary shaft (<NUM>) for detecting the rotation angle of the rotating part, comprising:
a reed switch (<NUM>) mounted to the fixed part or the rotating part of the structure perpendicular to the rotary shaft, with reeds (14d, 14e) arranged near the rotary shaft; and
a flat annular magnet (<NUM>) 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 characterised in that:
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.