Sensor for detecting magnetic powders in a lubricant

One object is to increase the amount of abrasion powder accumulated in a sensing region to improve the sensitivity in sensing the abrasion powder. Provided is a sensor for sensing reduction of electric resistance between electrodes, a magnetic field being applied between the electrodes to accumulate magnetic powder floating in a lubricant between the electrodes, wherein at least one sensing region in which the magnetic powder is to be accumulated is provided in at least a part of a region between the electrodes, and the magnetic powder is inhibited from being accumulated in a non-sensing region constituted by a space around the electrodes other than the at least one sensing region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims the benefit of priority from Japanese Patent Application Serial Nos. 2017-061877 (filed on Mar. 27, 2017) and 2017-116250 (filed on Jun. 13, 2017), the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a sensor.

BACKGROUND

In a mechanical device such as a speed reducer, a housing that houses mechanical parts such as a gear and a bearing contains a lubricant to prevent damage to the mechanical parts. The lubricant includes an abrasion powder (mainly iron powder) mixed therein as the mechanical parts wear during operation of the mechanical device.

In general, when wear of mechanical parts advances into the wear-out failure period in the failure rate curve (the bathtub curve), a larger amount of abrasion powder (produced from the mechanical parts) is mixed into the lubricant. For preventive maintenance, it is necessary to timely sense the increase of the amount of produced abrasion powder.

For example, Japanese Patent Application Publication No. 2005-331324 (“the '324 Publication”) discloses a sensor that senses the amount of metal powder in an oil. The sensor of the '324 Publication includes: a sensor head having a permanent magnet; a cup-shaped electrode provided on a distal end surface of the sensor head; and a plurality of rod-shaped conductive members arranged on an outer peripheral surface of the sensor head. The output of the sensor is varied when a short circuit occurs between the rod-shaped conductive members due to the abrasion powder accumulated between opposed end surfaces of the conductive members and the cup-shaped electrode subjected to a magnetic field by the permanent magnet (a sensing region). In the '324 Publication, the uncleanness of the oil can be sensed by variation of the output of the sensor.

In the '324 Publication, the magnetic flux leaks into spaces around the sensing region to cause the abrasion powder to be accumulated in regions other than the sensing region. Therefore, a small amount of abrasion powder accumulates in the sensing region, resulting in lower sensitivity of the sensor.

SUMMARY

The present invention addresses the above drawback, and one object thereof is to allow efficient accumulation of a magnetic powder such as an abrasion powder in the sensing region thereby to improve the sensitivity of the sensor sensing the magnetic powder.

An embodiment of the present invention provides a sensor for sensing reduction of electric resistance between electrodes, a magnetic field being applied between the electrodes to accumulate magnetic powder floating in a lubricant between the electrodes, wherein at least one sensing region in which the magnetic powder is to be accumulated is provided in at least a part of a region between the electrodes, and the magnetic powder is inhibited from being accumulated in a non-sensing region constituted by a space around the electrodes other than the at least one sensing region.

The above sensor may be configured such that the electrodes include a first electrode and at least one second electrode, at least one gap is provided between the first electrode and the at least one second electrode, and the at least one gap includes the at least one sensing region to which the magnetic field is applied.

The above sensor may be configured such that the first electrode comprises a magnet producing the magnetic field.

The above sensor may further comprise a magnet producing the magnetic field.

The above sensor may further comprise a covering member that covers the electrodes to inhibit the magnetic powder from being accumulated in the non-sensing region.

The above sensor may be configured such that an entire periphery of the magnet is covered with a magnet covering member.

The above sensor may be configured such that the magnetic field is selectively applied to the at least one sensing region.

The above sensor may be configured such that the at least one sensing region comprises a plurality of sensing regions.

The above sensor may be configured such that the plurality of sensing regions comprise a first sensing region and a second sensing region, the first sensing region is provided adjacent to an N-pole of the magnet, and the second sensing region is provided adjacent to an S-pole of the magnet.

The above sensor may be configured such that the at least one second electrode comprises a plurality of second electrodes, the at least one gap comprises a plurality of gaps provided between the first electrode and each of the plurality of second electrodes, and each of the plurality of gaps includes one of the plurality of sensing regions.

The above sensor may be configured such that the plurality of sensing regions have different gap lengths.

The above sensor may comprise a plurality of pairs of the first and second electrodes, wherein the plurality of pairs of the first and second electrodes have different gap lengths.

The above sensor may be configured such that a narrow recess is provided in an outer periphery of the sensor, and the at least one sensing region is provided deep in the recess.

The above sensor may further comprise a filter member disposed between the at least one sensing region and an outer space, the filter member blocking foreign matter having a large particle diameter.

The above sensor may be configured such that magnetic flux is prevented from leaking out of the at least one sensing region.

The above sensor may be configured such that the at least one sensing region is interposed between a first plane formed on the first electrode and a second plane formed on the at least one second electrode and opposed in parallel to the first plane, and magnetic flux intersects the first plane and the second plane perpendicularly in the at least one sensing region.

Advantages

According to an embodiment of the present invention, the magnetic power is inhibited from accumulating in non-sensing regions, and thus it is possible to accumulate the magnetic powder efficiently in the sensing region. As a result, the sensitivity of the sensor is improved, making it possible to sense an increase of the amount of produced abrasion powder reliably (with a high reliability).

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described with reference to the appended drawings. The following description will be focused on an industrial robot as an example according to an embodiment of the present invention.

FIG. 1is a side view of an industrial robot1according to an embodiment of the present invention. The industrial robot1is a vertical articulated robot having six axes.

As shown inFIG. 1, the industrial robot1includes a mounting portion11, arms A1to A5, and joints J1to J6. The mounting portion11serves to mount the industrial robot1on a floor, a wall, a ceiling, or the like. The joint J1operatively connects between the mounting portion11and the arm A1. The joint J2operatively connects between the arm A1and the arm A2. The joint J3operatively connects between the arm A2and the arm A3. The joint J4operatively connects between the arm A3and the arm A4. The joint J5operatively connects between the arm A4and the arm A5. On the distal end of the industrial robot1(the distal end of the joint J6), there is mounted a hand piece (not shown).

Each of the joints J1to J6includes a servo motor for driving and a speed reducer. The joints J1to J6have the same basic configuration. Representing the joints J1to J6, the joint J2will now be described in detail. As for the joints J1, J3to J6, the detailed description will be omitted.

FIG. 2is a partially sectional view showing the joint J2and the vicinity thereof. As shown inFIG. 2, the joint J2includes a flange10, a speed reducer20, and a servo motor30.

The flange10is a frame of the joint J2. The casings of the speed reducer20and the servo motor30are mounted to the flange10. The flange10is fixed to the arm A1. The flange10is a substantially cylindrical member having a hollow portion (a space S). The openings of the flange10at both axial ends thereof are blocked by the speed reducer20and the servo motor30, and thus the space S is closed tightly. The space S is filled with a lubricant, and the flange10also serves as an oil bath.

The speed reducer20includes a casing206mounted to the flange10, an input shaft202connected to an output shaft31of the servo motor30, and an output shaft204fixed to the arm A2. The input shaft202and the output shaft204are supported so as to be rotatable around the rotational axis AX relative to the casing206. An output of the servo motor30is input to the speed reducer20via the input shaft202, reduced by the speed reducer20, and then transmitted to the arm A2via the output shaft204. With this arrangement, rotation of the servo motor30causes the arm A2to be rotated around the rotational axis AX relative to the arm A1.

A space in the casing206that houses a gear mechanism of the speed reducer20communicates with the space S in the flange10. During operation of the speed reducer20, rotation of the gear mechanism in the casing206causes the lubricant to be circulated between the space in the casing206and the space S in the flange10. As the lubricant is circulated, the abrasion powder produced in the speed reducer20is discharged into the space S in the flange10.

In the space S, a sensor40for sensing the increase of the amount of the abrasion powder floating in the lubricant is mounted on a support member214. The sensor40allows the abrasion powder to be accumulated in a gap between electrodes by a magnet and senses the amount of the abrasion powder in the lubricant by a change of electric resistance between the electrodes. There may be a plurality of variations of the sensor40.FIGS. 3ato 10dshow a part of examples of the variations of the sensor40. It is also possible that the sensor40is disposed in the casing206.

FIGS. 3ato 3eshow a sensor40A according to Embodiment 1 of the present invention.FIGS. 3a, 3b, 3care a plan view, a right side view, and a front view of the sensor40A, respectively.FIG. 3dis a sectional view along the line AA-AAinFIG. 3a.FIG. 3eis a sectional view along the line BA-BAinFIG. 3c. In the following description, the X-axis direction refers to the left-right direction inFIG. 3e, the Y-axis direction refers to the top-bottom direction inFIG. 3e, and the Z-axis direction (the height direction, or the axial direction) refers to the top-bottom direction inFIG. 3d. The top refers to the top inFIG. 3d(the positive direction in the Z-axis), and the bottom refers to the bottom inFIG. 3d(the negative direction in the Z-axis). In operation, any direction of the sensor40A may be oriented vertically.

As shown inFIGS. 3ato 3e, the sensor40A includes a permanent magnet402A, a box-shaped electrode (an electrode)406A, a retaining member408A, and a jacket member410A. As shown inFIG. 3d, a signal line41is connected to the box-shaped electrode406A, and a signal line42is connected to the permanent magnet402A. Thus, the permanent magnet402A serves as both a magnet and an electrode.

The box-shaped electrode406A is a magnetic member formed of a magnetic material having electric conductivity such as iron, ferrite core, or silicon steel. The box-shaped electrode406A has a substantially cylindrical shape with an opening on one axial end side thereof (the bottom side inFIG. 3d) blocked in the bottom portion406Aa. Thus, the box-shaped electrode406A has a cylindrical box-like shape with an opening in the top surface. The box-shaped electrode406A is not limited to a box-like shape but may be a rectangular parallelepiped opened in only one surface thereof or a polygonal tube with a blocked bottom surface. Further, it is also possible that the electrode406A is formed of a non-magnetic material such as copper.

In the hollow portion of the box-shaped electrode406A, there is disposed a retaining member408A (a covering member) formed of a resin, which is a non-magnetic material (an insulator). The permanent magnet402A is embedded in the middle of the top portion of the retaining member408A.

The box-shaped electrode406A surrounds the retaining member408A having the permanent magnet402A embedded therein. The shape of the permanent magnet402A is not limited to a rectangular parallelepiped but may be a cylinder, a polygonal column, or the like.

As shown inFIG. 3e, the outer shape of the permanent magnet402A is smaller than the inner periphery of the box-shaped electrode406A. Therefore, a gap GAis formed between the permanent magnet402A and the box-shaped electrode406A over the entire periphery of the permanent magnet402A (so as to surround the permanent magnet402A). In other words, the permanent magnet402A and the box-shaped electrode406A face each other with the gap GAinterposed therebetween.

The permanent magnet402A also serves as an electrode. Each of the permanent magnet402A and the box-shaped electrode406A is connected to an output line (the signal lines41,42shown inFIGS. 2 and 3d). In addition, another electrode formed of a magnetic material may be mounted on, for example, the top surface of the permanent magnet402A. Further, it is also possible that the permanent magnet402A is a magnet or an electromagnet covered with a non-magnetic material such as copper and the signal line42is connected to the non-magnetic material.

The output lines are connected, at the output ends thereof, to a sensor driving circuit (not shown) that monitors the resistance value of the sensor40A and determines the deterioration of the lubricant from the variation of the resistance value. When the amount of the abrasion powder accumulated in the gap GAexceeds a predetermined value (the gap GAis generally filled with the abrasion powder), the electric resistance between the permanent magnet402A and the box-shaped electrode406A is lowered (a short circuit occurs), resulting in variation of the output levels of the output lines. The sensor driving circuit senses the deterioration of the lubricant from the lowered electric resistance. It is also possible that the output levels include On signal (with electricity passing) and Off signal (with no electricity passing) for sensing the deterioration of the lubricant between these two states (hereinafter referred to as “the digital sensing”).

The sensor driving circuit is connected to a superior control device such as a manipulator in a wired or wireless manner. A circuit board43transmits the outputs of the output lines (the outputs of the sensor40A) to a superior control device either constantly or intermittently (at regular time intervals) for saving electricity.

When sensing the variation of the output level of the output lines received from the circuit board43, the superior control device gives an alert for demanding maintenance of, for example, the speed reducer20by a predetermined notification means (a display or a voice output device).

The permanent magnet402A is magnetized in the direction of the arrow MA inFIG. 3d. Therefore, the magnetic flux path φA shown inFIG. 3dis formed. In the gap GAextending over the entire periphery of the permanent magnet402A, intensive magnetic flux passes through regions positioned in the magnetic flux path. The intensive magnetic flux also passes through regions close to the S and N magnetic poles of the permanent magnet402A. For convenience in description, these regions are referred to as “the sensing region,” and the sensing region of Embodiment 1 is denoted by a sign “GA.”

The abrasion powder from the mechanical parts mixed into the lubricant is attracted onto the gap GAby the magnetism of the permanent magnet402A.

In particular, the abrasion powder is attracted onto a sensing region DAthat is passed through the intensive magnetic flux. A stable amount of abrasion powder (for example, an amount generally in proportion to the amount of the abrasion powder mixed into the lubricant) is attracted onto the sensing region DA.

There is a large distance from the permanent magnet402A to the region other than the sensing region DA(hereinafter referred to as “the non-sensing region”) in the gap GA. Therefore, almost no magnetic flux passes through the non-sensing region distant from the permanent magnet402A, and almost no abrasion powder is attracted onto the non-sensing region.

Thus, in Embodiment 1, the permanent magnet402A and the gap GAare disposed in an appropriate positional relationship, so as to set a limited region in the gap GAas the sensing region DA. Since a stable amount of abrasion powder is attracted concentratedly onto the sensing region DA, the outputs from the sensor40A are stable. Therefore, the superior control device can sense the increase of the produced abrasion powder reliably (with a high reliability). In case of the digital sensing, the increase of produced abrasion powder is sensed by passing of the electricity, and a sensing signal can be transmitted.

In addition, the magnetic flux is more weak in regions within the gap GAmore distant from the sensing region DA, and the amount of abrasion powder attracted onto such regions is not stable. In other words, the amount of abrasion powder attracted onto such regions is typically not proportional to the amount of the abrasion powder mixed into the lubricant. Since the amount of abrasion powder attracted onto the non-sensing region is instable, such abrasion powder can be a noise to the sensor40A.

In Embodiment 1, the jacket member410A (the covering member) made of a resin is mounted on the top of the gap GAby bonding or other means. The jacket member410A allows only the sensing region DAin the gap GAto be exposed outside. In other words, the jacket member410A covers the non-sensing region in the gap GA.

Since the jacket member410A is mounted on the top surface of the gap GA, the distance from the permanent magnet402A is large in the non-sensing region (or more accurately, the surface of the jacket member410A positioned above the non-sensing region). Therefore, almost no abrasion powder is attracted onto the outer surface of the jacket member410A that is distant from the permanent magnet402A. Accordingly, in Embodiment 1, the region onto which the abrasion power is attracted is substantially limited to the sensing region DA.

In this embodiment, the top surface of the permanent magnet402A is flush with the top end surface of the box-shaped electrode406A. Further, the sensor40A is configured such that the magnetic flux φApasses in parallel with the top surface of the permanent magnet402A in the gap GA, by adjusting the shapes, sizes, and arrangements of the permanent magnet402A and the box-shaped electrode406A. Therefore, the magnetic flux φAhardly deviates from the magnetic flux path φAand leaks out of the sensor40A. The abrasion powder is restrained by the magnetic flux φAand accumulated only in the sensing region DA, not on the non-sensing region (the region other than the sensing region DA) in the outer surface of the sensor40A.

FIGS. 4ato 4dshow a sensor40B according to Embodiment 2 of the present invention.FIGS. 4a, 4bare a plan view and a front view of the sensor40B, respectively.FIG. 4cis a sectional view along the line AB-ABinFIG. 4a.FIG. 4dis a sectional view along the line BB-BBinFIG. 4b. The same description as for previous embodiments will be hereinafter simplified or omitted.

As shown inFIGS. 4ato 4d, the sensor40B includes a permanent magnet402B, a box-shaped electrode404B (a first electrode), a box-shaped electrode406B (a second electrode), and a retaining member408B (a magnet covering member). As shown inFIG. 4c, a signal line41is connected to the box-shaped electrode404B, and a signal line42is connected to the box-shaped electrode406B. The magnet covering member may inhibit accumulation of the magnetic powder.

The box-shaped electrodes404B and406B are cylindrical members having a blocked opening on one axial end side thereof (in other words, these box-shaped electrodes are opened only on the other end side thereof). The box-shaped electrode404B is arranged with the opening thereof opposed to the box-shaped electrode406B. The box-shaped electrode406B is arranged with the opening thereof opposed to the box-shaped electrode404B such that the opening of the box-shaped electrode406B is opposed to the opening of the box-shaped electrode404B.

The retaining member408B has a columnar shape with an outer diameter slightly smaller than the inner diameter of the box-shaped electrodes404B and406B and is housed in the hollow portions of the box-shaped electrodes404B and406B. The retaining member408B is disposed in a space defined by the inner wall surface.

The box-shaped electrode404B and the box-shaped electrode406B are disposed such that the annular opposing surfaces thereof (denoted by signs404Bc and406Bc inFIG. 4c) are spaced apart from each other by a predetermined distance. Since the opposing surfaces are spaced apart from each other, there is an annular gap GBbetween the opposing surfaces, and the gap GBsurrounds the axially middle portion of the retaining member408B.

The permanent magnet402B is disposed such that the S-pole and the N-pole thereof are arranged in the direction of the arrow MB shown inFIG. 4c. The permanent magnet402B is embedded in the retaining member408B such that the line connecting between the magnetic poles is perpendicular to the central axis of the retaining member408B and intersects the gap GB. Therefore, the magnetic field is selectively applied to the region shaded deeply inFIGS. 4cand 4dwithin the gap GBextending over the entire periphery of the side surface of the retaining member408B, and this region is the sensing region in Embodiment 2. This sensing region will be hereinafter referred to as “the sensing region DB.”

The non-sensing region outside the sensing region DBis not positioned in the magnetic flux path and is spaced apart from the magnetic poles of the permanent magnet402B. Therefore, almost no magnetic flux passes in the non-sensing region, while intensive magnetic flux passes in the sensing region DB. Accordingly, almost no abrasion powder is attracted onto the region other than the sensing region DB.

Thus, in Embodiment 2, the permanent magnet402B and the gap GBare disposed in an appropriate positional relationship, so as to selectively set a limited region in the gap GBas the sensing region DB. Since a stable amount of abrasion powder is attracted concentratedly onto the sensing region DB, the outputs from the sensor40B are stable. Therefore, the superior control device can sense the increase of the produced abrasion powder reliably (with a high reliability).

Further, in Embodiment 2, not only the sensing region DBbut the entire gap GBis exposed outside. Since there are fewer structures surrounding the sensing region DBthan in Embodiment 1, the abrasion powder attracted toward the sensing region DBis less apt to be blocked by these structures and tends to be attracted onto the sensing region DB.

The shapes of the permanent magnet402B and the box-shaped electrodes404B and406B and the positional relationship between them are not limited to those shown inFIGS. 4ato 4d. Any other shapes or positional relationships may be substituted such that the abrasion powder is concentratedly attracted onto only a part of the region within the gap GB.

In this embodiment, the sensor40B is thus configured such that the abrasion powder is restrained by the magnetic flux and accumulated only in the sensing region DB, not attracted onto the outer surface of the sensor40B, by adjusting the shapes, sizes, and arrangements of the permanent magnet402B and the box-shaped electrodes404B and406B. Further, it is also possible that the permanent magnet402B is a magnet or an electromagnet. The box-shaped electrodes404B and406B are not limited to a box-like shape but may be a disk or a circular arc formed only in the sensing region DB.

FIGS. 5ato 5dshow a sensor40C according to Embodiment 3 of the present invention.FIGS. 5a, 5bare a plan view and a front view of the sensor40C, respectively.FIG. 5cis a sectional view along the line Ac-AcinFIG. 5a.FIG. 5dis a sectional view along the line Bc-BcinFIG. 5b.

As shown inFIGS. 5ato 5d, the sensor40C according to Embodiment 3 is formed by mounting protection members410C and412C made of a resin to the sensor40B according to Embodiment 2, so as to increase the ease of handling of the sensor40C as a part (the insulation quality). This arrangement inhibits an operator from touching the electrodes and receiving an electric shock.

The protection members410C,412C cover the entire outer surfaces of the box-shaped electrodes404C,406C, respectively. The distance between the opposed end surfaces of the protection member410C and the protection member412C is equal to or greater than the width of the gap GB, such that the abrasion powder attracted toward the sensing region DBis not blocked. In other words, the protection member410C and the protection member412C form an opening in a region including at least the entirety of the gap GB.

In Embodiment 3, since a stable amount of abrasion powder is attracted concentratedly onto the sensing region DB, the outputs from the sensor40C are stable. Therefore, the superior control device can sense the increase of the produced abrasion powder reliably (with a high reliability).

FIGS. 6ato 6dshow a sensor40D according to Embodiment 4 of the present invention.FIGS. 6a, 6bare a plan view and a front view of the sensor40D, respectively.FIG. 6cis a sectional view along the line AD-ADinFIG. 6a.FIG. 6dis a sectional view along the line BD-BDinFIG. 6b.

As shown inFIGS. 6ato 6d, the sensor40D includes a permanent magnet402B, a box-shaped electrode404Ba (a first electrode), a box-shaped electrode404Bb (a first electrode), a box-shaped electrode406Ba (a second electrode), a box-shaped electrode406Bb (a second electrode), and a retaining member408B. In this embodiment, two pairs of output lines (signal lines41a,41band signal lines42a,42b) are connected to the sensor40D. As shown inFIG. 6c, the signal lines41a,41b,42a,42bare connected to the box-shaped electrodes404Ba,404Bb,406Ba,406Bb, respectively.

The sensor40D according to Embodiment 4 is formed by configuring the sensor40B according to Embodiment 2 such that the box-shaped electrode404B is divided into two electrodes (the box-shaped electrodes404Ba,404Bb) and the box-shaped electrode406B is divided into two electrodes (the box-shaped electrodes406Ba,406Bb). A gap G′ is formed between the box-shaped electrode404Ba and the box-shaped electrode404Bb. A gap G″ is formed between the box-shaped electrode406Ba and the box-shaped electrode406Bb.

When a mechanical device such as the speed reducer20is worked, a foreign matter (for example, a cutting chip) having a large particle diameter may be produced and enter an oil bath10. When this kind of foreign matter is attracted onto the gap GBa, a short circuit may occur between the electrodes and vary the output levels of the output lines. As a result, an increase of the amount of produced abrasion powder may be erroneously sensed even when almost no abrasion powder has been produced.

To overcome this drawback, the sensor40D according to Embodiment 4 has a gap GBbin addition to a gap GBa. The sensor40D according to Embodiment 4 may be configured such that, when short circuits between electrodes occur at all the gaps (the gaps GBa, GBb), a sensing signal is transmitted or the superior control device determines that the amount of abrasion powder has increased. This configuration inhibits erroneous sensing caused by disturbance (for example, a cutting chip having a large particle diameter), and the superior control device can sense the increase of the produced abrasion powder reliably (with a high reliability). In case of the digital sensing, the increase of produced abrasion powder may be determined when short circuit signals (On signals) are sensed for both the sensing region DBaand the sensing region DBb.

FIGS. 7ato 7eshow a sensor40E according to Embodiment 5 of the present invention.FIGS. 7a, 7b, 7care a plan view, a right side view, and a front view of the sensor40E, respectively.FIG. 7dis a sectional view along the line AE-AEinFIG. 7a.FIG. 7eis a sectional view along the line BE-BE inFIG. 7c.

The sensor40E is formed by mounting a mesh cover412E (a filter member) to the sensor40A according to Embodiment 1.

The mesh cover412E covers the entirety of the gap GA(and the jacket member410A). This prevents a cutting chip or abrasion powder having a particle size larger than the mesh size from being undesirably attracted onto the sensing region DA. As a result, the robustness of the sensor40E is increased.

In Embodiment 5, since a stable amount of fine abrasion powder is attracted concentratedly onto the sensing region DA, the outputs from the sensor40E are more stable. Therefore, the superior control device can sense the increase of the produced abrasion powder reliably (with a high reliability).

FIGS. 8ato 8dshow a sensor40F according to Embodiment 6 of the present invention.FIG. 8ais a plan view of the sensor40F, andFIG. 8bis a front view of the same.FIG. 8cis a sectional view along the line AF-AFinFIG. 8a, andFIG. 8dis a sectional view along the line BF-BFinFIG. 8c.

The sensor40F includes a permanent magnet402F, a box-shaped electrode406F (a second electrode), a cap-shaped electrode404F (a first electrode), a retaining member408B, an insulating sheet407F, an external screw414F, and a nut415F. As shown inFIG. 8c, a signal line41is connected to the cap-shaped electrode404F, and a signal line42is connected to the box-shaped electrode406F.

The box-shaped electrode406F and the cap-shaped electrode404F are magnetic members formed of a magnetic material having electric conductivity.

The box-shaped electrode406F has a cylindrical box-like shape (a bottomed cylindrical shape) including a side wall portion406Fa having a cylindrical shape and a bottom portion406Fb having a disk-like shape and blocking an opening of the side wall portion406Fa on one axial end side thereof (the lower side). In the middle of the bottom portion406Fb, there is concentrically formed a through-hole416Fh through which the shaft of the external screw414F is inserted.

The cap-shaped electrode404F has a substantially disk-like shape, and in the middle of the cap-shaped electrode404F, there is concentrically formed a through-hole414Fh through which the shaft of the external screw414F is inserted. The outer diameter of the cap-shaped electrode404F is smaller than the inner diameter of the side wall portion406Fa of the box-shaped electrode406F. Between the outer peripheral surface of the cap-shaped electrode404F and the inner peripheral surface of the box-shaped electrode406F, there is formed a hollow portion (a gap GF) having an annular shape and communicating with the outer space (the oil bath20B) outside the sensor40F.

The permanent magnet402F has a substantially disk-like shape, and in the middle of the permanent magnet402F, there is concentrically formed a through-hole402Fh through which the shaft of the external screw414F is inserted.

The retaining member408F has a cylindrical shape and is formed of the same resin (non-magnetic material) as the retaining member408A in Embodiment 1. In the retaining member408F, there is concentrically embedded the box-shaped electrode406F. The outer diameter of the retaining member408F is slightly smaller than the inner diameter of the side wall portion406Fa of the box-shaped electrode406F, and the retaining member408F is concentrically disposed on the bottom of the hollow portion of the box-shaped electrode406F. Thus, the permanent magnet402F is positioned concentrically in the hollow portion of the box-shaped electrode406F and retained by the retaining member408F. The height (the length in the axial direction) of the retaining member408F is equal to the height of the permanent magnet402F, and the top surface of the retaining member408F is substantially flush with the top surface of the permanent magnet402F.

The insulating sheet407F is a tabular member formed of paper, resin, or the like and having an electrical insulating quality. The insulating sheet407F has a circular shape with an outer diameter larger than that of the permanent magnet402F, and in the middle of the insulating sheet407F, there is concentrically formed a through-hole407Fh through which the shaft of the external screw414F is inserted. The insulating sheet407F is placed on the bottom portion406Fb of the box-shaped electrode406F and electrically insulates the box-shaped electrode406F from the permanent magnet402F.

The external screw414F and the nut415F are non-magnetic members formed of a resin and having an electrical insulating quality.

The sensor40F is fabricated by placing the insulating sheet407F on the bottom portion406Fb of the box-shaped electrode406F, placing thereon the retaining member408F and the permanent magnet402F, placing thereon the cap-shaped electrode404F, inserting the shaft of the external screw414F through the through-holes404Fh,406Fh,407Fh,408Fh into the nut415F, and fastening integrally the box-shaped electrode406F, the insulating sheet407F, the permanent magnet402F, the retaining member408F, and the cap-shaped electrode404F with the external screw414F and the nut415F.

The permanent magnet402F is magnetized in the direction of the arrow MFinFIG. 8c, so as to form a magnetic flux path in the sensor40F that is shown by the arrow φFinFIG. 8cand passing the gap GF. In this embodiment, the magnetic flux φFis radiated from the entire periphery of the outer peripheral surface of the cap-shaped electrode404F, and the entire circumference of the annular gap GFis set as the sensing region DF.

The sum of the heights of the insulating sheet407F, the permanent magnet402F, and the cap-shaped electrode404F stacked together in the axial direction in the hollow portion of the box-shaped electrode406F is equal to the depth of the hollow portion of the box-shaped electrode406F. Therefore, after fabrication, the top surface of the cap-shaped electrode404F is flush with the top end surface of the box-shaped electrode406F. Further, the sensor40F is configured, by adjusting the shape, size, and arrangement of the cap-shaped electrode404F and the box-shaped electrode406F, such that the magnetic flux φFperpendicularly passes the outer peripheral surface of the cap-shaped electrode404F, runs straight in the gap GF, and perpendicularly enters the inner peripheral surface of the box-shaped electrode406F. Therefore, the magnetic flux φFhardly leaks out of the magnetic flux path φF. The abrasion powder is restrained by the magnetic flux φFand accumulated only in the sensing region DF, not attracted onto the outer surface of the sensor40F. That is, the abrasion powder is inhibited from being accumulated in regions other than the sensing region DFand is allowed to be accumulated concentratedly in the sensing region DF, resulting in a high sensitivity in sensing. Further, since the sensing region DFhas a circumferential shape, a large amount of abrasion powder can be accumulated in the sensing region DF, and the damage to devices such as the speed reducer caused by the abrasion powder can be reduced.

FIGS. 9ato 9dshow a sensor40G according to Embodiment 7 of the present invention.FIG. 9ais a plan view of the sensor40G, andFIG. 9bis a front view of the same.FIG. 9cis a sectional view along the line AG-AGinFIG. 9a, andFIG. 9dis a sectional view along the line BG-BGinFIG. 9b.

The sensor40G is a modification of the sensor40D of Embodiment 4 (specifically, the box-shaped electrodes404Bb and406Bb are modified). In the sensor40D of Embodiment 4, the box-shaped electrodes404Ba and404Bb have the same length in the Z-axis direction, and the box-shaped electrodes406Ba and406Bb have the same length in the Z-axis direction. Therefore, the gap GBabetween the box-shaped electrode404Ba and the box-shaped electrode406Ba has the same gap length (the distance between electrodes on the gap) as the gap GBbbetween the box-shaped electrode404Bb and the box-shaped electrode406Bb. By contrast, in this embodiment, the box-shaped electrode404Bb′ has a larger length in the Z-axis direction than the box-shaped electrode404Ba, and the box-shaped electrode406Bb′ has a larger length in the Z-axis direction than the box-shaped electrode406Ba. Therefore, the gap GBb′between the box-shaped electrode404Bb′ and the box-shaped electrode406Bb′ has a smaller gap length than the gap GBabetween the box-shaped electrode404Ba and the box-shaped electrode406Ba.

In this embodiment, as described above, the gap GBb′has a smaller gap length than the gap GBa, and therefore, the sensing region DBb′conducts electricity earlier than the sensing region DBabecause the sensing region DBb′requires a smaller amount of abrasion powder for conducting electricity between the electrodes. That is, in this embodiment, each of the positive electrode and the negative electrode (the box-shaped electrode404B and the box-shaped electrode406B) is divided into two pieces to provide two pairs of electrodes, and the gaps between the electrodes have different gap lengths, so as to provide two different threshold values of the amount of the abrasion powder enough to conduct electricity between the electrodes (in other words, two different timings at which electricity begins to be conducted). Use of such a sensor makes it possible to sense the increase of the abrasion powder stepwise, and therefore, the progress of wear of the parts of the speed reducer can be grasped in more detail, and the failure of the speed reducer can be predicted more accurately.

FIGS. 10ato 10dshow a sensor40H according to Embodiment 8 of the present invention.FIG. 10ais a plan view of the sensor40H, andFIG. 10bis a front view of the same.FIG. 10cis a sectional view along the line AH-AHinFIG. 10a, andFIG. 10dis a sectional view along the line BH-BHinFIG. 10b.

The sensor40H is a modification of the sensor40F of Embodiment 6 (specifically, the cap-shaped electrode404F is modified) such that the increase of the abrasion powder can be sensed stepwise as in the sensor40G of Embodiment 7.

The cap-shaped electrode404H of this embodiment includes four electrodes404Ha,404Hb,404Hc,404Hd and four spacers404Hs. The electrodes404Ha to404Hd are magnetic members provided by dividing the cap-shaped electrode404F of Embodiment 6 having a disk-like shape into four sectors. The radii of the electrodes404Ha,404Hb,404Hc,404Hd increase in this order stepwise (for example, in arithmetical proportion). In this embodiment, the output lines include one signal line42(a grounding wire) and four signal lines41a,41b,41c,41d. As shown inFIG. 10d, the signal line42is connected to the electrode406F, and the signal lines41a,41b,41c,41dare connected to the electrodes404Ha,404Hb,404Hc,404Hd, respectively.

The spacers404Hs are tabular members formed of a non-magnetic material having an electrical insulating quality such as a resin or ceramic. The four electrodes404Ha to404Hd are adhered to each other with an adhesive in the circumferential direction with the spacers404Hs interposed therebetween.

Thus, the radii of the cap-shaped electrodes404H vary stepwise in the circumferential direction, and therefore, the gap length of the gap GFbetween the outer peripheral surfaces of the cap-shaped electrodes404H and the inner peripheral surface of the box-shaped electrode406F also varies stepwise in the circumferential direction. The gap GFis divided into gaps GHa, GHb, GHc, GHdadjacent to the electrodes404Ha,404Hb,404Hc,404Hd, respectively and four gaps GHsadjacent to the spacers404Hs. Since the magnetic flux pi passes the entireties of the gaps GHa, GHb, GHc, GHd, these gaps constitute the sensing regions DHa, DHb, DHc, DHd, respectively. The magnetic flux φHfor accumulating the abrasion powder does not pass the gaps GHs, and therefore, these gaps constitute non-sensing regions.

The gap lengths of the gaps GHa, GHb, GHc, GHd(the sensing regions DHa, DHb, DHc, DHd) decrease in this order in arithmetical proportion. Also, the amounts of accumulated abrasion powder required for conducting electricity between electrodes decrease in this order. Accordingly, electricity begins to be conducted between the electrodes in the reverse order, that is, in the order of the sensing regions DHa, DHc, DHb, DHa. The sensor40H of this embodiment can sense the increase of the abrasion powder stepwise at four levels, which is a greater number than in the sensor40G of Embodiment 7, and therefore, the progress of wear of the parts of the speed reducer can be grasped in further detail, and the failure of the speed reducer can be predicted further accurately.

In this embodiment, the cap-shaped electrode404F is divided into four electrodes404Ha to404Hd. It is also possible to divide the cap-shaped electrode404F into two electrodes, three electrodes, or five or more electrodes.

The examples of the embodiments of the present invention have been described above. The embodiments of the present invention are not limited to the above examples but can be modified variously within the scope of the technical idea of the present invention. For example, the embodiments of the present invention include combinations of the above examples described herein and obvious embodiments.

For example, the sensor40in the above embodiments is installed in a speed reducer included in a turning portion of a turning barrel or an arm joint of an industrial robot1. In other embodiments, the sensor40may be installed in a speed reducer included in a turning portion of other machine tools.

The sensor40may be installed in other types of speed reducers such as a planetary gear speed reducer, in addition to the oscillating speed reducer shown inFIG. 2.

The sensor40may be used for mechanical devices other than speed reducers. By way of an example, the sensor40may be used as a check sensor for checking the uncleanness of an engine oil.

In Embodiment 1 described above, a part of the gap GAis covered with the jacket member410A (a covering member) to provide a non-sensing region. It is also possible to cover a part of the gap with a magnetism shield member (for example, a net made of a ferromagnetic material such as iron and coated with a resin) to magnetically shield the part from the outer space, thereby providing a non-sensing region.