Patent Description:
For example, in machine tools such as machining centers, there is a need to detect an initial position of the tool in order to achieve precise machining. As a position detection device that detects a position of a movable body that is moved by an object to be detected, such as a tool, a device wherein an electric contact point is mechanically switched on or off according to the movement of the movable body is known (for example, see Patent Document <NUM>).

However, in such a conventional position detection device, there is a problem that the contact point deteriorates with repeated mechanical on/off switching, and thus has a short lifespan. There is also a problem that the intrusion of foreign objects or the formation of oxide films cause poor conductivity between contact points, and that detection precision is reduced due to wear and denting of the contact points due to repeated contact.

<CIT> discloses a position detection apparatus. A magnetic flux detection unit and a rectangular solid magnet are provided. The magnetic flux detection unit includes one or more pairs of Hall sensors, each pair having two Hall sensors arranged on a substrate. The solid magnet is arranged movably in a direction in a plane parallel to the substrate. Each pair of two Hall sensors is arranged on the substrate so that a line connecting the centers of magnetism sensing sections of each pair of two Hall sensors is orthogonal to a movement direction of the magnet. A tetragon has a long side and a short side and the long side has an inclination angle to the line connecting the centers of magnetism sensing sections of the each pair of two Hall sensors. The magnet has one N-pole and one S-pole separately magnetized in orthogonal to the substrate on which the Hall sensors are arranged.

<CIT> discloses a magnetic sensor unit. Voltage/current (V/I) conversion sections for performing V/I conversion of sensor outputs are provided upstream of a subtraction section for calculating a difference signal of the sensor outputs. An addition section for calculating a sum signal of the sensor outputs is provided. The V/I conversion sections are switched with a predetermined period, and as a result, an average value of divided values of the difference signal and sum signal obtained by treating the sensor outputs with the V/I conversion sections is outputted as a position detecting signal.

<CIT> discloses a position detector. The position detector comprises at least one pair of magnetic sensors disposed and spaced from each other, a magnet disposed so as to be movable and inclinable to the magnetic sensor pair, a V/I conversion circuit for converting output voltages of the magnetic sensors into currents, a subtraction circuit for generating a differential current based on the currents converted by the V/I conversion circuit, an addition circuit for generating an addition current based on the currents converted by the V/I conversion circuit, a current division circuit for dividing the differential current by the addition current, and an output circuit for outputting a value obtained by a division in the current division circuit as a position signal.

The present invention was made in view of these problems of the conventional art, and has an object of providing a position detection device that can stably detect a position with high detection precision over a long lifespan.

According to an aspect of the present invention, a position detection device that can stably detect a position with high detection precision over a long lifespan is provided. This position detection device is provided with a magnet configured to move, together with a movable body, on a movement path extending along a first direction. The magnet has different magnetic poles in a second direction that is perpendicular to the first direction. The position detection device is also provided with a pair of magnetic sensors that are separated by equal distances, in the second direction, from the movement path, and that are disposed at equal distances from a reference line extending in the second direction. The pair of magnetic sensors have identical sensor characteristics. The position detection device is also provided with a detection unit configured to detect that the magnet is positioned on the reference line in a state where absolute values of output change rates of both of the pair of magnetic sensors are maximum.

An embodiment of a position detection device according to the present invention is described below with reference to <FIG>. In <FIG>, the same or corresponding structural elements are given the same reference numerals, and redundant description thereof is omitted. Further, in <FIG>, the scales and dimensions of structural elements may be illustrated in an exaggerated manner, and some structural elements may be omitted.

<FIG> is a schematic view of the structure of a position detection device <NUM> according to a first embodiment of the present invention. As illustrated in <FIG>, the position detection device <NUM> according to the present embodiment includes a fixed part <NUM>, a pair of magnetic sensors <NUM>, <NUM> fixed on the fixed part <NUM>, a detection unit <NUM> connected to the magnetic sensors <NUM>, <NUM> via a signal line <NUM>, and a magnet <NUM> mounted to a movable body <NUM> that is moved by an object to be detected, for example, a tool of a machining center. The movable body <NUM> is movable in an X direction (first direction) as indicated by an arrow, and the magnet <NUM> mounted to the movable body <NUM> is configured so as to move on a movement path M extending along the X direction. The position detection device <NUM> detects whether or not the movable body <NUM> (and, by extension, an object to be detected, such as a tool of a machining center) that is movable along the X direction in this way is in a predetermined position (reference line S in <FIG>).

The magnet <NUM> has different magnetic poles in a Z direction (second direction). For example, as illustrated in <FIG>, a magnetic pole <NUM> of the magnet <NUM> on the positive side of the Z direction may be the N-pole, and a magnetic pole <NUM> on the negative side of the Z direction may be the S-pole, or vice versa. Possible shapes of the magnet <NUM> include a rectangular parallelepiped shape, a cube shape, a cylindrical shape, and a disc shape, etc..

The magnetic sensors <NUM>, <NUM> detect magnetic fields in the surroundings and have the same sensor characteristics (electric, magnetic, and temperature characteristics). These magnetic sensors <NUM>, <NUM> are lined up on the fixed part <NUM> extending in the X direction, and are disposed at positions separated by equal distances, in the Z-direction, from the movement path M on which the magnet <NUM> moves. The magnetic sensors <NUM>, <NUM> have sensor surfaces 21A, 22A, each of which is perpendicular to the Z direction. The magnetic sensor <NUM>, <NUM> are disposed at equal distances from a reference line S extending in the Z direction. In other words, the reference line S is positioned over a midpoint of a line segment connecting the two magnetic sensors <NUM>, <NUM>. As illustrated in <FIG>, the distance between the two magnetic sensors <NUM> and <NUM> is the same as the length L of the magnet <NUM> in the X direction. Especially when the shape of the magnet <NUM> is a rectangular parallelepiped shape or a cube shape, the distance between the two magnetic sensors <NUM> and <NUM> is the same as the length of the side of the magnet <NUM> in the X direction. When the shape of the magnet <NUM> is a cylindrical shape or a disc shape, the distance between the magnetic sensors <NUM> and <NUM> is the same as the length of the diameter of the magnet <NUM>. As these magnetic sensors <NUM>, <NUM>, a Hall element, a magnetic modulation sensor, a magnetoresistive element, a SQUID magnetic sensor, etc. may be used.

The detection unit <NUM> is input with the outputs of the magnetic sensors <NUM>, <NUM>, and includes a comparison circuit that compares the outputs from the magnetic sensors <NUM>, <NUM>. <FIG> is a graph illustrating the relationship between the position of the magnet <NUM> and the outputs of the magnetic sensors <NUM>, <NUM>. In <FIG>, the output of the magnetic sensor <NUM> is illustrated by a solid line, and the output of the magnetic sensor <NUM> is illustrated by a dotted line. The horizontal axis in <FIG> represents the distance from the reference line S to the center of the magnet <NUM>, and the vertical axis represents the outputs of the magnetic sensors <NUM>, <NUM>. In this example, the distance between the center of the magnetic sensor <NUM> in the X direction and the center of the magnetic sensor <NUM> in the X direction is about <NUM>, and the width of the magnet <NUM> in the X direction is about <NUM>.

As illustrated in <FIG>, the sensor outputs of the magnetic sensors <NUM>, <NUM> become convex according to the position of the magnet <NUM> in the X direction. The magnetic sensor <NUM> and the magnetic sensor <NUM> have the same sensor characteristics, and therefore, when the magnet <NUM> is positioned at the midpoint of the line segment connecting the magnetic sensor <NUM> and the magnetic sensor <NUM>, that is to say when the movement distance equals <NUM> (when the magnet <NUM> is positioned on the reference line S), the outputs of both sensors match each other. In other words, as illustrated in <FIG>, the point P where the output characteristics of the magnetic sensor <NUM> and the output characteristics of the magnetic sensor <NUM> intersect is positioned on the reference line S. Therefore, when the outputs of the magnetic sensor <NUM> and the magnetic sensor <NUM> match each other, it can be determined that the magnet <NUM> is positioned on the reference line S. The detection unit <NUM> uses this principle and compares the output from the magnetic sensor <NUM> and the output from the magnetic sensor <NUM>, and determines that the magnet <NUM> is positioned on the reference line S when both outputs match each other.

Due to this configuration, it can be detected that the magnet <NUM> is positioned on the reference line S without using mechanical contact points. Thus, the position detection device <NUM> according to the present embodiment is capable of detecting the position of the movable body <NUM> without using mechanical contact points. Because no mechanical contact points are used, there are no problems such as the lifespan being shortened and poor conductivity between contact points due to deterioration of the contact points, and the detection precision being reduced due to wear and denting of the contact points.

By disposing the magnetic sensors <NUM>, <NUM> such that the output change rates of the magnetic sensors <NUM>, <NUM> are maximum when the magnet <NUM> is positioned on the reference line S, the outputs of the magnetic sensors <NUM>, <NUM> easily change when the magnet <NUM> is in the vicinity of the reference line S, and therefore, the point at which the outputs of the magnetic sensors <NUM>, <NUM> match each other is more precisely identified. Therefore, the detection precision of the position of the magnet <NUM> is increased.

The output characteristics of the magnetic sensors <NUM>, <NUM> change according to temperature, but because the sensor characteristics of the magnetic sensors <NUM>, <NUM> are the same, the change in output characteristics of the magnetic sensor <NUM> and the change in output characteristics of the magnetic sensor <NUM> cancel each other out even if the output characteristics of the magnetic sensors <NUM>, <NUM> change according to temperature. Therefore, as illustrated in <FIG>, a point PL, where the output characteristics of the magnetic sensor <NUM> at a low temperature and the output characteristics of the magnetic sensor <NUM> at a low temperature intersect, is on the reference line S, and a point PH, where the output characteristics of the magnetic sensor <NUM> at a high temperature and the output characteristics of the magnetic sensor <NUM> at a high temperature intersect, is also on the reference line S. Accordingly, as described above, by determining whether or not the output of the magnetic sensor <NUM> and the output of the magnetic sensor <NUM> match each other, it can be stably detected that the magnet <NUM> is positioned on the reference line S even when the temperature changes. In <FIG>, the output characteristics of the magnetic sensors <NUM>, <NUM> illustrated in <FIG> are indicated by thin, dotted lines.

Similarly, changes in output characteristics of the magnetic sensor <NUM> and the changes in output characteristics of the magnetic sensor <NUM> cancel each other out even if the electric characteristics or magnetic characteristics of the magnetic sensors <NUM>, <NUM> change, and therefore the position of the magnet <NUM> can be stably detected. External magnetic fields in the Z direction or a Y direction perpendicular to the paper surface also act on both the magnetic sensor <NUM> and the magnetic sensor <NUM> in a similar manner, but because the changes in output characteristics of the magnetic sensor <NUM> and the changes in output characteristics of the magnetic sensor <NUM> cancel each other out, the position of the magnet <NUM> can be stably detected while suppressing the influence of such external magnetic fields. In addition, because changes in output characteristics of the magnetic sensors <NUM>, <NUM> due to a displacement of the magnet <NUM> in the Z direction or the Y direction are canceled out, the position of the magnet <NUM> can be stably detected while suppressing the influence of the displacement of the magnet <NUM> in the Z direction and the Y direction.

In addition, the outputs of the magnetic sensors <NUM>, <NUM> may be A-D converted and filtered for noise reduction. Alternatively, noise in the analog outputs of the magnetic sensors <NUM>, <NUM> may be removed by a low-pass filter.

The magnet <NUM> and the sensor substrate need to be as small as possible so that they can be fitted in precision instruments. Therefore, the magnet <NUM> preferably has a size that is equal to or smaller than a square having sides of approximately <NUM> in length, or has a diameter of <NUM> or less. Meanwhile, considering ease of assembly of the position detection device <NUM>, the magnet <NUM> needs to have a suitable size, and thus the magnet <NUM> preferably has a size that is equal to or larger than a square having sides of approximately <NUM> in length.

The stronger the magnetic field of the magnet <NUM>, the better the S/N ratio, and the better the repeat precision. As such, a big and thick magnet <NUM> is desired. It is also desirable that the distance between the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is short. <FIG> is a graph illustrating the relationship between the shape of the magnet and the maximum magnetic flux when the gap between the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is <NUM> and the thickness (length in the Z direction) of the magnet <NUM> is <NUM>. The lines in <FIG> indicate the length of the magnet <NUM> in the Y direction. That is to say, <FIG> illustrates changes in a magnetic flux density when the length of the magnet <NUM> in the X direction is changed, in each of the cases wherein the length of the magnet <NUM> in the Y direction is respectively <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. As can be seen from the graph in <FIG>, the magnetic flux density becomes too low when the length of the magnet <NUM> in the X direction is less than <NUM>, but the magnetic flux density does not change greatly even when said length exceeds <NUM>. In other words, the length of the magnet <NUM> in the X direction is preferably <NUM> to <NUM>. Meanwhile, the length of the magnet <NUM> in the Y direction is preferably <NUM> to <NUM>.

The magnetic field in the magnetization direction of the magnet <NUM> is substantially proportional to the thickness (length in the Z direction) of the magnet <NUM>, but in order to prevent the shape of an exceedingly thick magnet <NUM> from becoming too big and to prevent cutting chips from adhering to the magnet, the magnetic shielding must be made strong, and it is therefore desirable to set the thickness of the magnet <NUM> to a suitable range. <FIG> is a graph illustrating the relationship between the length of the magnet <NUM> in the Z direction (thickness) and magnetic flux density, when the lengths of the magnet <NUM> in the X direction and the Y direction are respectively <NUM> by <NUM>, and <NUM> by <NUM>. As indicated by the graph in <FIG>, the magnetic flux density becomes too low when the thickness of the magnet <NUM> is less than <NUM>, but the magnetic flux density value does not change greatly even when said thickness exceeds <NUM>. In other words, the thickness of the magnet <NUM> is preferably <NUM> to <NUM>.

Based on the principle of the position detection device <NUM> including the magnetic sensor <NUM> and the magnetic sensor <NUM> used in the present embodiment, positioning precision in the X direction does not depend on track displacement of the magnetic sensor <NUM> and the magnetic sensor <NUM>, but when a mounting error of the magnetic sensor <NUM> and the magnetic sensor <NUM> occurs, the track displacement causes a position error to occur. At this time, when a small and round or rectangular magnet is used as the magnet <NUM>, attenuation of the magnetic field from the track, or the X-axis, toward the Y-axis becomes greater, whereby the S/N ratio easily drops and origin position displacement easily occurs. Therefore, the magnet <NUM> is preferably of a rectangular shape where the longitudinal direction is in the Y direction. <FIG> illustrates the positional relationship between a track displacement of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM>, when the magnet <NUM> has a rectangular shape. As illustrated in <FIG>, the magnetic field of the magnet <NUM> has an elliptical shape with the Y direction as the longitudinal direction, and therefore the influence of track displacement is small. <FIG> is a graph illustrating the relationship between the displacement of the magnetic sensor <NUM> and the magnetic sensor <NUM> in the track direction and the output distribution, when the gap between the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is <NUM>, and the lengths of the magnet <NUM> in the X direction, the Y direction, and the Z direction are respectively <NUM>, <NUM>, and <NUM>. The magnet <NUM> has a rectangular shape where the longitudinal direction is the Y direction, and in this case, even when the displacement in the track direction is <NUM>, the attenuation rate of the output is within a range of <NUM>%. In view of this, it can be seen that the magnet <NUM> preferably has a rectangular shape where the longitudinal direction is the Y direction.

The magnet <NUM> is preferably made of a material that is strong, is not susceptible to rusting, and has a favorable temperature coefficient. More specifically, a samarium-cobalt magnet having a temperature coefficient of -<NUM>%/°C, or a rust-proofed neodymium magnet having a temperature coefficient of -<NUM>%/°C, is preferable.

When the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> are surface-mounted, the magnetic sensor <NUM> and the magnetic sensor <NUM> are preferably spaced apart by approximately <NUM> or more.

The length of the magnet <NUM> in the X direction that allows for a maximum change rate of the outputs of the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> to be obtained is equal to the mounting distance between the magnetic sensor <NUM> and the magnetic sensor <NUM>, and therefore, as described above, when the magnetic sensor <NUM> and the magnetic sensor <NUM> are spaced apart by approximately <NUM> or more, the length of the magnet <NUM> in the X direction is preferably also approximately <NUM> or more. <FIG> is a graph illustrating a relationship between the position of the magnet <NUM> and the output change rates of the magnetic sensor <NUM> and the magnetic sensor <NUM>, when the gap between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is <NUM>, and the lengths of the magnet in the X direction, the Y direction, and the Z direction are respectively <NUM>, <NUM>, and <NUM>, and the length of the magnet <NUM> in the X direction is substantially equal to the mounting distance between the magnetic sensor <NUM> and the magnetic sensor <NUM>. As illustrated in <FIG>, when the position of the magnet <NUM> is <NUM>, that is to say when the magnet <NUM> is positioned on the reference line, both of the absolute values of the output change rates of the magnetic sensor <NUM> and the magnetic sensor <NUM> are substantially maximum.

The distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is determined by repeat precision, component precision, assembly precision, ease of assembly checking, etc. Specifically, it is determined with consideration to the required values of, for example, ±<NUM> as the component precision, <NUM> as the mounting precision, and <NUM> or less as mechanical variation, that is to say, variations due to play in the shaft, etc. As a result, the distance (gap) between the pair of the magnetic sensors <NUM> and the magnet <NUM> is preferably <NUM> to <NUM>.

<FIG> is a graph illustrating the relationship between the distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM>, and the magnetic flux density. When the distance (gap) is <NUM> to <NUM>, the magnetic flux density becomes generally <NUM> mT to <NUM> mT.

<FIG> is a graph illustrating the relationship between a distance in the X direction centered on a detection point and the outputs, in cases where the distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is respectively <NUM>, <NUM>, <NUM>, and <NUM>. In the graph of <FIG>, "Ch1" indicates the output of the magnetic sensor <NUM>, and "Ch2" indicates the output of the magnetic sensor <NUM>. As can be seen from <FIG>, it is indicated that in the graph wherein the distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is <NUM>, the output is smaller compared to the other graphs.

<FIG> is a graph illustrating the relationship between a distance in the X direction centered on a detection point and an actual value of the output change rate, in cases where the distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is respectively <NUM>, <NUM>, <NUM>, and <NUM>. In the graph of <FIG>, "Ch1" indicates the output change rate of the magnetic sensor <NUM>, and "Ch2" indicates the output change rate of the magnetic sensor <NUM>. As can be seen from <FIG>, it is indicated that in the graph wherein the distance (gap) between the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> and the magnet <NUM> is <NUM>, the absolute value of the output change rate is smaller compared to the other graphs.

By monitoring the magnetic force data (sensor data) that is the internal data of the position detection device <NUM>, the state of the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM> can be comprehended, allowing for a fault diagnosis of the position detection device <NUM>. More specifically, by monitoring the internal data, it is possible to diagnose a maintenance time for the position detection device <NUM>, diagnose faults in the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM>, and diagnose the operating environment of the position detection device <NUM>.

In order to diagnose the maintenance time, it is effective to use the internal data to get a grasp on return failures due to adhesion and accumulation of cutting chips or cutting fluid on the sliding parts of the position detection device <NUM>, and to get a grasp on the number of operations. In order to diagnose faults in the pair of the magnetic sensor <NUM> and the magnetic sensor <NUM>, it is effective to get a grasp on return failures due to adhesion of cutting chips or cutting fluid, internal negative pressure, and deterioration of bearings, and to get a grasp on detent damage caused by impacts. In order to diagnose the operating environment, it is effective to get a grasp on return failure caused by a negative pressure in the interior of the position detection device <NUM> due to, for example, a change in the surrounding temperature, and to get a grasp on deterioration of bearings caused by machining vibrations, impacts due to pallet changes, mounting or removal of workpieces, impacts due to clamping/unclamping, and impacts due to removal of the device from storage.

A method for detecting return failure and deterioration of bearings is described below with reference to <FIG>.

<FIG> illustrates an internal output using conventional contact points, wherein a contact <NUM> returns after being pushed in.

In <FIG>, as indicated by numeral (a), the contact <NUM> is at a normal standby height during standby. Next, as indicated by numeral (b), the contact <NUM> is pushed in. Thereafter, when the load on the contact <NUM> is released, the contact <NUM> returns to the original position as indicated by numeral (c). At this time, the standby height of the contact <NUM> at (a) and the standby height of the contact <NUM> at (c) are equal, and thus the push-in amount of the contact <NUM> when going from (a) to (b) and the return amount of the contact <NUM> when going from (b) to (c) are equal. Further, regarding the value of the internal sensor, the value before pushing in the contact <NUM> and the value after the contact <NUM> has returned after being pushed in are equal.

<FIG> illustrates a change in an internal sensor value as internal data when the position detection device <NUM> is in an abnormal state due to a return failure. In the example illustrated in <FIG>, as indicated by numeral (c), cutting fluid and cutting chips have adhered to a region where the contact <NUM> of the position detection device <NUM> slides. Therefore, when going from (b) to (c), the contact <NUM> cannot return to the normal position. Accordingly, the return amount of the contact <NUM> when going from (b) to (c) is smaller than the push-in amount of the contact <NUM> when going from (a) to (b). Further, regarding the value of the internal sensor, the value after the contact <NUM> has returned after being pushed in is smaller than the value before pushing in the contact <NUM>.

<FIG> illustrates an internal sensor value as internal data when the position detection device <NUM> is in an abnormal state due to a deteriorated bearing. As indicated by numeral (a), during normal standby, the value of the internal sensor does not fluctuate. On the other hand, when the bearing has deteriorated, when a machining vibration and a vibration due to mounting or removal of a workpiece, a vibration when moving the sensor into or out of storage, or an impact due to a pallet change has occurred, the contact <NUM> vibrates accordingly, and, as indicated by numeral (b), the value of the internal sensor fluctuates.

Therefore, the position detection device <NUM> may further include a comparison unit (not illustrated) that compares the outputs of the magnetic sensor <NUM> and the magnetic sensor <NUM> during standby of the position detection device <NUM> with the outputs of the magnetic sensor <NUM> and the magnetic sensor <NUM> when the magnet <NUM> has been moved in the X direction and then returned in the direction opposite to the X direction, and a first diagnosis unit (not illustrated) that diagnoses an abnormality of the position detection device <NUM> on the basis of the comparison results from the comparison unit.

In addition, the position detection device <NUM> may further include a second diagnosis unit (not illustrated) that diagnoses an abnormality of the position detection device <NUM> on the basis of the waveforms of the outputs of the magnetic sensor <NUM> and the magnetic sensor <NUM> during standby of the position detection device <NUM>.

As described above, an aspect of the present invention provides a position detection device that can stably detect a position with high detection precision over a long lifespan. This position detection device is provided with a magnet configured to move, together with a movable body, on a movement path extending along a first direction. The magnet has different magnetic poles in a second direction that is perpendicular to the first direction. The position detection device is provided with a pair of magnetic sensors that are separated by equal distances, in the second direction, from the movement path, and that are disposed at equal distances from a reference line extending in the second direction. The pair of magnetic sensors have the same sensor characteristics. The position detection device is provided with a detection unit configured to detect that the magnet is positioned on the reference line in a state where the absolute values of the output change rates of both of the pair of magnetic sensors are substantially maximum.

This allows for detecting that the magnet is positioned on the reference line without using mechanical contact points. Thus, the position detection device according to the present invention is capable of detecting the position of the movable body without using mechanical contact points. The position detection device according to the present invention thus does not use any mechanical contact points, and therefore, there are no problems such as the lifespan being shortened or poor conductivity between contact points due to deterioration of the contact points, or the detection precision being reduced due to wear and denting of the contact points. In addition, changes in output characteristics of the pair of magnetic sensors due to temperature changes cancel each other out, and therefore, the position of the magnet can be stably detected.

The outputs of the pair of magnetic sensors preferably exhibit the maximum change rates when the magnet is positioned on the reference line. According to this configuration, the outputs of the magnetic sensors easily change when the magnet is in the vicinity of the reference line, and therefore, the point at which the outputs of the magnetic sensors match each other is more precisely identified, and detection precision of the position of the magnet is increased.

The present invention provides a position detection device that can stably detect a position with high detection precision over a long lifespan.

In addition, the present invention provides a position detection device capable of fault diagnosis and predictive maintenance.

Claim 1:
A position detection device (<NUM>) comprising:
a magnet (<NUM>) configured to move, together with a movable body (<NUM>), on a movement path (M) extending along a first direction (X), the magnet (<NUM>) having different magnetic poles (<NUM>, <NUM>) in a second direction (Z) that is perpendicular to the first direction (X);
a pair of magnetic sensors (<NUM>, <NUM>) that are separated by equal distances, in the second direction (Z), from the movement path (M), and that are disposed at equal distances from a reference line (S) extending in the second direction (Z), the pair of magnetic sensors (<NUM>, <NUM>) having identical sensor characteristics; and
a detection unit (<NUM>) configured to detect that the magnet (<NUM>) is positioned on the reference line (S) in a state where absolute values of output change rates of both of the pair of magnetic sensors (<NUM>, <NUM>) are maximum, wherein a distance between the pair of magnetic sensors(<NUM>, <NUM>) and the length (L) of the magnet (<NUM>) in the first direction (X) are equal.