Patent Description:
A mechanical device such as a speed reducer is housed in a housing filled with a lubricating oil in order to prevent the mechanical parts such as gears from being damaged. If the mechanical parts are worn out during operation of the mechanical device, abrasion powder (for example, a conductive substance such as iron powder) is mixed into the lubricating oil. The abrasion powder is, for example, of a conductive substance such as iron powder. As the mechanical parts are increasingly worn out and enter a wear-out failure period, which is defined in a failure rate curve (a bathtub curve), an increased amount of abrasion powder is mixed into the lubricating oil. For this reason, a sensor for sensing the amount of the abrasion powder in the lubricating oil allows for accurate preventive maintenance of the mechanical parts.

For example, <CIT> discloses an oil check sensor, which can be used for the above purposes. The disclosed oil check sensor is mounted to, for example, a transmission of an automobile and configured to check, for example, deterioration of an oil in an oil container and the degree of wear of mechanical parts lubricated with the oil. This sensor includes a pair of electrodes and a magnet for attracting iron powder or the like (a conductive substance) contained in the oil. Based on the resistance between the electrodes, which depends on the conductive substance attracted, the sensor senses the amount of the conductive substance in the oil.

The abrasion powder to be detected in the speed reducer or the like first increases due to initial wear, then remains substantially constant during normal operation and finally suddenly increases before occurrence of failures. The sensor may be configured to sense the increase in the amount of the abrasion powder before the occurrence of failures, but may malfunction when a large amount of abrasion powder is produced due to initial wear, for example, when the speed reducer has a large size. If such is the case, the sensor may not be capable of sensing the increase in the amount of the abrasion powder before the occurrence of failures, which is originally intended to be sensed. There is also a demand for prevention of sensor malfunction and thereby detection of failures in advance in order to reliably suspend and replace the speed reducer and the like.

Furthermore, while the mechanical device such as a speed reducer is manufactured, foreign matter having a large particle size (for example, a cutting chip or the like) generated by cutting or other methods of processing may adhere to the constituent components of the mechanical device and get mixed in with the lubricating oil. If such foreign matter having a large particle size adheres to the sensor, a short circuit occurs between the paired electrodes even with little abrasion powder produced. For the reasons stated above, the sensor for sensing the amount of abrasion powder may operate unexpectedly even when a small amount of abrasion powder is produced. Further prior art is known from document <CIT>.

The present invention is made in light of the above, and aims to achieve an object of providing a sensor that can be prevented from operating unexpectedly due to foreign matter mixed in and a difference found between the amount of abrasion powder produced and the designated amount to trigger the operation.

A first aspect of the present invention provides a sensor including the features of claim <NUM>. In this way, the above-described problem is solved.

The sensor includes a short circuit preventing portion for preventing a large-diameter conductive piece (i.e., foreign matter) from causing a short circuit between the first electrode and the second electrode, and the large-diameter conductive piece has a larger dimension than the gap between the first electrode and the second electrode. This can prevent a short circuit from being caused by a large-diameter conductive piece between the first electrode and the second electrode. As a result, the sensor can be prevented from operating unexpectedly.

The sensor relating to the first aspect of the present invention can include a sensing unit for sensing the change in electrical resistance between the first electrode and the second electrode.

A sensor relating to a second aspect of the present invention includes the features of claim <NUM>.

A third aspect of the present invention provides a sensor including the features of claim <NUM>.

The above-described aspects of the present invention can produce an effect of providing a sensor that can be prevented from operating unexpectedly and thus achieve improved reliability.

The following describes a sensor relating to a first embodiment of the present invention with reference to the drawings. The constituents common to more than one drawing are denoted by the same reference signs throughout the drawings. It should be noted that the drawings do not necessarily appear to an accurate scale for the sake of convenience of explanation.

<FIG> is a sectional view showing one example of a mechanism <NUM> including a sensor <NUM> relating to one embodiment of the present invention. The mechanism <NUM> is, for example, a movable part such as a robot arm. The mechanism <NUM> includes a speed reducer <NUM>, a flange <NUM> provided on the input side, a servomotor <NUM>, and a device A1 provided on the output side.

The speed reducer <NUM> includes a casing <NUM> mounted to the flange <NUM>, an input shaft <NUM> connected to an output shaft <NUM> of the servomotor <NUM>, and an output shaft <NUM> connected to the output-side device A1. The input shaft <NUM> and the output shaft <NUM> are supported to be capable of rotating about an axis AX relative to the casing <NUM>. The output from the servomotor <NUM> is input to the speed reducer <NUM> via the input shaft <NUM>, reduced by the speed reducer <NUM>, and then transmitted to the output-side device A1 via the output shaft <NUM>. Thus, the output-side device A1 and the flange <NUM> are capable of rotating relative to each other.

The flange <NUM> is a tubular member and houses therein at least a portion of the speed reducer <NUM>. The servomotor <NUM> is mounted to the flange <NUM>. An opening at one end of the flange <NUM> in the direction along the axis AX is closed by the speed reducer <NUM>, and an opening at the other end of the flange <NUM> is closed by the servomotor <NUM>. Thus, the flange <NUM> has a tightly closed hollow portion (a space S) formed therein. The space S contains therein a lubricating oil, so that the flange <NUM> also serves as an oil bath.

The casing <NUM> of the speed reducer <NUM> houses therein a gear mechanism, for example. The space within the casing <NUM> communicates with the space S within the flange <NUM>. As the speed reducer <NUM> operates, the gear mechanism in the casing <NUM> rotates, which subsequently causes the lubricating oil to circulate between the space in the casing <NUM> and the space S in the flange <NUM>. As the lubricating oil circulates, a conductive substance such as abrasion powder (conductive abrasion powder) produced in the speed reducer <NUM> moves into the space S in the flange <NUM>.

In the space S, a sensor <NUM> is installed for sensing the amount of the conductive substance contained in the lubricating oil. The sensor <NUM> is fixed onto the flange <NUM> via, for example, a support member <NUM>. The sensor <NUM> uses a magnet to gather the conductive substance contained in the lubricating oil between paired electrodes and uses a change in electrical resistance between the paired electrodes to sense the amount of the conductive substance in the lubricating oil. The sensor <NUM> may be alternatively positioned, for example, inside the casing <NUM> but can be at any position within the mechanism <NUM> as long as the position is within the space containing therein the lubricating oil.

Next, with reference to <FIG>, a detailed description is given of the structure of the sensor <NUM>. <FIG> schematically shows the structure of the sensor relating to the first embodiment of the present invention. <FIG> includes a top view of the sensor <NUM> and a sectional view showing a cross-section along the A-A line in the top view.

As shown in <FIG>, the sensor <NUM> has a substantially columnar outer shape and includes a first electrode <NUM>, a magnet <NUM>, a second electrode <NUM>, a fastening member <NUM>, and an attracting portion <NUM>. As shown in <FIG>, the first electrode <NUM> has a circular shape when seen from the top surface of the sensor <NUM> and is positioned at the center of the sensor <NUM>. The second electrode <NUM> is a bottomed tubular member and includes a bottom portion 8a extending substantially parallel to the first electrode <NUM> and a wall portion (tubular portion) 8b continuous with the bottom portion 8a and extending substantially perpendicularly to the bottom portion 8a.

The magnet <NUM> has a substantially columnar shape and is positioned between the first electrode <NUM> and the bottom portion 8a of the second electrode <NUM>. The first electrode <NUM>, the magnet <NUM>, and the bottom portion 8a of the second electrode <NUM> each have therein a through hole, through which the fastening member <NUM> (a bolt in the illustrated embodiment) is inserted. The fastening member <NUM> is inserted through the through holes, so that the first electrode <NUM>, the magnet <NUM>, and the second electrode <NUM> are fixed to each other. The first electrode <NUM> and the second electrode <NUM> are fixed while being spaced away from each other. The first electrode <NUM> and the second electrode <NUM> are made of an electrically conductive magnetic material such as iron, ferrite core and silicon steel. The magnet <NUM> is, for example, a permanent magnet. Instead of using such a permanent magnet, however, the first electrode <NUM> may serve both as the magnet and as the electrode.

The attracting portion <NUM> is provided to fill the space between the first electrode <NUM> and the second electrode <NUM> and interposed between the first electrode <NUM> and the second electrode <NUM>. A distance X1 between the first electrode <NUM> and the wall portion 8b of the second electrode <NUM> is larger than the dimension of the conductive substance contained in the lubricating oil. For example, the conductive substance has a dimension of approximately <NUM> to <NUM>, and the distance X1 is preferably just large enough to prevent a short circuit from occurring due to iron powder produced by initial wear. In the illustrated embodiment, the magnet <NUM> is in contact with the first electrode <NUM> and surrounded by the attracting portion <NUM>. The attracting portion <NUM> is made of an insulating non-magnetic material, for example, a resin. The magnet <NUM> forms a magnetic flux line between the first electrode <NUM> and the second electrode <NUM>. Thus, the conductive substance contained in the lubricating oil is gathered to the vicinity of the attracting portion <NUM>.

The sensor <NUM> includes a short circuit preventing portion 10a for preventing a short circuit from being caused by a large-diameter conductive piece between the first electrode <NUM> and the second electrode <NUM>. Here, the large-diameter conductive piece is, for example, foreign matter such as a cutting chip produced by cutting or other methods of processing performed during the manufacturing process of the mechanism <NUM> (see <FIG>) and refers to a conductive particle having a dimension larger than the distance X1 between the first electrode <NUM> and the second electrode <NUM>. By way of an example, the large-diameter conductive piece has a size of approximately <NUM> to <NUM>.

In the embodiment shown in <FIG>, the short circuit preventing potion 10a is a protrusion on the attracting portion <NUM> and formed integrally with the attracting portion <NUM>. In other words, the short circuit preventing portion 10a and the attracting portion <NUM> form a one-piece structure. Therefore, similarly to the attracting portion <NUM>, the short circuit preventing portion 10a is made of an insulating non-magnetic material, for example, a resin. Alternatively, the attracting portion <NUM> and the short circuit preventing portion 10a may be separate members from each other. In the sectional view of <FIG>, the short circuit preventing portion 10a has a width substantially equal to the distance X1 between the first electrode <NUM> and the wall portion 8b of the second electrode <NUM>. When seen from the top surface of the sensor <NUM>, the short circuit preventing portion 10a has an annular shape and entirely surrounds the first electrode <NUM>.

The first electrode <NUM> and the second electrode <NUM> are respectively connected to output lines (not shown) and electrically connected to a sensing unit <NUM> (see <FIG>) via the output lines.

The sensing unit <NUM> is configured to sense a change in electrical resistance between the first electrode <NUM> and the second electrode <NUM>. The sensing unit <NUM> includes a sensor drive circuit for predicting a failure of the parts constituting the mechanism <NUM> based on, for example, a change in electrical resistance caused by the gathering of the conductive substance in the vicinity of the attracting portion <NUM>. If the conductive substance contained in the lubricating oil is gathered in the vicinity of the attracting portion <NUM>, this causes a drop in electrical resistance (or a short circuit) between the first electrode <NUM> and the second electrode <NUM> to which voltage is being applied, resulting in a change in output level of the output lines. The sensing unit <NUM> senses such a change in electrical resistance, thereby predicting a failure of the parts constituting the mechanism <NUM>.

The drop in electrical resistance may be indicated by an ON signal and an OFF signal corresponding to electrical disconnection and connection. The sensing unit <NUM> may sense two states of electrical disconnection and connection (hereinafter, may be referred to as "perform digital sensing"). The sensing unit <NUM> may be connected to a higher-level control device (not shown) such as a manipulator in a wired or wireless manner. The higher-level control device may be configured to, upon reception of a signal from the sensing unit <NUM>, issue an alert for demanding maintenance of, for example, the speed reducer <NUM> with a predetermined notifying unit (for example, a display or voice output device).

As described above, the sensor <NUM> includes the short circuit preventing portion 10a for preventing a short circuit between the first electrode <NUM> and the second electrode <NUM> caused by a large-diameter conductive piece having a dimension larger than the distance X1 between the first electrode <NUM> and the second electrode <NUM>. The short circuit preventing portion 10a is a protrusion on the attracting portion <NUM>. With the protrusion being provided between the first electrode <NUM> and the second electrode <NUM> in this manner, even when a large-diameter conductive piece is attracted to the vicinity of the attracting portion <NUM>, the large-diameter conductive piece is prevented from electrically contacting at least one of the first electrode <NUM> and the second electrode <NUM>. Accordingly, a short circuit can be prevented from being caused by the large-diameter conductive piece between the first electrode <NUM> and the second electrode <NUM>, resulting in preventing the sensor <NUM> from operating unexpectedly.

In the sensor <NUM>, the short circuit preventing portion 10a and the attracting portion <NUM> form a one-piece structure. This reduces the number of parts constituting the sensor <NUM>, so that the sensor <NUM> can be manufactured easily.

Next, with reference to <FIG>, a description is given of a modification example of the short circuit preventing portion of the sensor <NUM>. As shown in <FIG>, similarly to the short circuit preventing portion 10a, a short circuit preventing potion <NUM> relating to a modification example is a protrusion provided on the attracting portion <NUM> and formed integrally with the attracting portion <NUM>. Similarly to the short circuit preventing portion 10a, the short circuit preventing portion <NUM> is made of, for example, an insulating non-magnetic material such as a resin. When seen from the top surface of the sensor <NUM>, the short circuit preventing portion <NUM> has an annular shape and entirely surrounds the first electrode <NUM>. The short circuit preventing portion <NUM> is different from the short circuit preventing portion 10a in that the short circuit preventing portion <NUM> has a width smaller than the distance X1 between the first electrode <NUM> and the wall portion 8b of the second electrode <NUM>.

As described above, in the sensor <NUM> including the short circuit preventing portion <NUM> having a width smaller than the distance X1, electrical contact can be also prevented between a large-diameter conductive piece and at least one of the first electrode <NUM> and the second electrode <NUM>. Accordingly, a short circuit is prevented from being caused by the large-diameter conductive piece between the first electrode <NUM> and the second electrode <NUM>, resulting in preventing the sensor <NUM> from operating unexpectedly.

Next, with reference to <FIG>, a description is given of another modification example of a short circuit preventing portion of the sensor <NUM>. As shown in <FIG>, the short circuit preventing portion of the sensor <NUM> may be divided into a plurality of portions. In the embodiment shown in <FIG>, the sensor <NUM> includes three short circuit preventing portions 12a, 12b and 12c. The short circuit preventing portions 12a, 12b, and 12c are each a protrusion provided on the attracting portion <NUM> and formed integrally with the attracting portion <NUM>. Similarly to the attracting portion <NUM>, the short circuit preventing portions 12a, 12b and 12c are made of, for example, an insulating non-magnetic material such as a resin. When seen from the top surface of the sensor <NUM>, the short circuit preventing portions 12a, 12b and 12c are spaced at equal intervals from each other around the first electrode <NUM>.

Even if the short circuit preventing portion is divided into a plurality of portions as described above, electrical contact can be prevented between a large-diameter conductive piece and at least one of the first electrode <NUM> and the second electrode <NUM> at the positions of the short circuit preventing portions 12a, 12b and 12c. Accordingly, a short circuit can be prevented between the first electrode <NUM> and the second electrode <NUM>, resulting in preventing the sensor <NUM> from operating unexpectedly.

Next, with reference to <FIG>, a description is given of still another modification example of the short circuit preventing portion of the sensor <NUM>. As shown in <FIG>, the short circuit preventing portion of the sensor <NUM> may be a wire <NUM> extending in the direction intersecting the direction in which the first electrode <NUM> and the wall portion 8b of the second electrode <NUM> face each other. The wire <NUM> is supported by a plurality of support portions <NUM> and provided on the attracting portion <NUM> while being spaced away from the attracting portion <NUM>.

In the embodiment shown in <FIG>, the support portions <NUM> are each a stake-shaped member. One of the ends of each support portion <NUM> is fixedly embedded in the attracting portion <NUM>. The other end of each support portion <NUM> has therein a through hole, through which the wire <NUM> is inserted. The wire <NUM> is inserted through the through hole, thus being fixed while being spaced away from the attracting portion <NUM>. When seen from the top surface of the sensor <NUM>, the support portions <NUM> are spaced at equal intervals from each other in the circumferential direction of the first electrode <NUM>, and the wire <NUM> entirely surrounds the first electrode <NUM>. There are no particular limitations on the material used to form the wire <NUM>. The wire <NUM> may be made of a conductive material such as a metal or an insulating material such as a resin.

Even when the short circuit preventing portion is the wire <NUM> as described above, the wire <NUM> can also prevent electrical contact between a large diameter conductive piece and at least one of the first electrode <NUM> and the second electrode <NUM>. Accordingly, a short circuit is prevented from occurring between the first electrode <NUM> and the second electrode <NUM>, resulting in preventing the sensor <NUM> from operating unexpectedly.

Next, with reference to <FIG>, a description is given of yet another modification example of the short circuit preventing portion of the sensor <NUM>. As shown in <FIG>, a short circuit preventing portion <NUM> relating to the modification example may be an insulating protrusion provided on at least one of the first electrode <NUM> and the second electrode <NUM>. In the illustrated embodiment, the short circuit preventing portion <NUM> is provided on the wall portion 8b of the second electrode <NUM> to extend along the inner edge of the wall portion 8b, where the wall portion 8b is in contact with the attracting portion <NUM>. The short circuit preventing portion <NUM> may be provided on the first electrode <NUM> or on both of the first electrode <NUM> and the second electrode <NUM>.

Even when the short circuit preventing portion <NUM> is provided on at least one of the first and second electrodes <NUM> and <NUM> as described above, the short circuit preventing portion <NUM> prevents electrical contact between a large diameter conductive piece and at least one of the first electrode <NUM> and the second electrode <NUM>, similarly to the short circuit preventing portion 10a. Accordingly, a short circuit is prevented from occurring between the first electrode <NUM> and the second electrode <NUM>, resulting in preventing the sensor <NUM> from operating unexpectedly.

The following describes a sensor relating to an example, not the present invention with reference to the drawings. <FIG> is used to illustrate a sensor not relating to an embodiment. The sensor <NUM> relating to <FIG> is configured to sense the amount of a conductive substance contained in a lubricating oil, similarly to the sensor <NUM> relating to the above-described first embodiment.

The sensor <NUM> has a substantially columnar outer shape and includes a plurality of detecting units and a sensing unit <NUM> configured to output a signal when the detecting units experience a change in electrical resistance. More specifically, the sensor <NUM> includes a center electrode <NUM>, a plurality of outer electrodes <NUM>, an attracting portion <NUM> disposed between the center electrode <NUM> and the outer electrodes <NUM>, and a magnet <NUM>. The outer electrodes <NUM> are insulated from each other. Each of the detecting units is constituted by a pair of electrodes and the attracting portion <NUM> disposed between the electrodes. The pair of electrodes includes the center electrode <NUM> and one of the outer electrodes <NUM>.

In the illustrated example, the sensor <NUM> includes four outer electrodes 32A, 32B, 32C and 32D, and four detecting units are thus formed. There are no particular limitations on the number of the outer electrodes <NUM> and the number of the detecting units. The magnet <NUM> of the sensor <NUM> forms a magnetic flux line between the paired electrodes, so that a conductive substance contained in a lubricating oil is attracted to the attracting portion <NUM>. When the conductive substance is gathered in the vicinity of the attracting portion <NUM> in this manner, the detecting units experience a change in electrical resistance. While no conductive particles are attracted, the detecting units exhibit the same electrical resistance.

The center electrode <NUM> and the outer electrodes <NUM> are respectively connected to output lines, and each detecting unit is electrically connected to the sensing unit <NUM> via a corresponding one of the output lines. In this example, the detecting units are connected in parallel to each other, and voltage is applied by the same voltage source between the center electrode <NUM> and each of the outer electrodes <NUM>. The sensing unit <NUM> outputs a signal if a designated number of detecting units experience a change in electrical resistance. For example, the sensing unit <NUM> may be configured to output a signal to a higher-level control device such as a manipulator when two or more of the detecting units experience a drop in electrical resistance or when all of the detecting units experience a drop in electrical resistance.

As described above, the sensor <NUM> includes the plurality of detecting units, and the sensing unit <NUM> outputs a signal when a designated number of detecting units experience a drop in electrical resistance. In this way, the sensing unit <NUM> can be configured to output no signal when just one of the detecting units experiences a change in electrical resistance caused by a large-diameter conductive piece. This can prevent the sensor from operating unexpectedly due to a large-diameter conductive piece. Furthermore, in the sensor <NUM>, the sensing unit <NUM> can be configured to output a signal under a designated condition. Therefore, the single sensor <NUM> can be configured to output a signal in a timely and optimal manner for individual users, who have different requests for failure prediction timing.

While no conductive particles are attracted, the detecting units are equal in electrical resistance. This can lower the voltage to be applied to the sensor <NUM>.

The detecting units are connected in parallel to each other. This can lower the voltage applied between the paired electrodes in each detecting unit.

The following describes a sensor relating to a third embodiment of the present invention with reference to the drawings. <FIG> is a sectional view showing the sensor relating to the present embodiment. The present embodiment is different from the above-described embodiments in terms of the attracting portion. Note that <FIG> does not show all of the constituents.

As shown in <FIG>, a sensor <NUM> relating to the present embodiment has a substantially columnar outer shape and includes a first electrode (inner electrode) <NUM>, a magnet <NUM>, a second electrode (outer electrode) <NUM>, a fastening member (fastening portion) <NUM>, an attracting portion (insulator) <NUM> and a casing <NUM>. When seen from the top surface of the sensor <NUM>, the first electrode (inner electrode) <NUM> has a circular shape and is positioned at the center of the sensor <NUM>. The second electrode (outer electrode) <NUM> is a bottomed tubular member and has a bottom portion 62a extending substantially parallel to the first electrode (inner electrode) <NUM> and a wall portion (tubular portion) 62b continuous with the bottom portion 62a and extending substantially perpendicularly to the bottom portion 62a. The first electrode (inner electrode) <NUM> is positioned at the opening of the second electrode (outer electrode) <NUM>.

The magnet <NUM> has a substantially columnar (substantially disk-shaped) shape and is positioned between the first electrode (inner electrode) <NUM> and the bottom portion 62a of the second electrode (outer electrode) <NUM>. The first electrode (inner electrode) <NUM>, the magnet <NUM>, and the bottom portion 62a of the second electrode (outer electrode) <NUM> each have therein a through hole, through which the fastening member (fastening portion) <NUM> (a bolt in the illustrated embodiment) is inserted. The fastening member (fastening portion) <NUM> is inserted through the through hole, so that the first electrode (inner electrode) <NUM>, the magnet <NUM>, and the second electrode (outer electrode) <NUM> are fixed to each other. The magnet <NUM> is smaller in outer diameter than the second electrode (outer electrode) <NUM>.

The first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> are fixed while being spaced away from each other. The first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> are, for example, made of an electrically conductive magnetic material such as iron, ferrite core, or silicon steel. The magnet <NUM> is, for example, a permanent magnet. Instead of using such a permanent magnet, however, the first electrode (inner electrode) <NUM> may serve both as the magnet and as the electrode.

The attracting portion (insulator) <NUM> fills the space between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> and is interposed between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. The attracting portion (insulator) <NUM> has a bottom portion 63a extending along the bottom portion 62a of the second electrode (outer electrode) <NUM> and a tubular portion 63b extending along the wall portion (tubular portion) 62b of the second electrode (outer electrode) <NUM>. The bottom portion 63a and the tubular portion 63b are separate members. The bottom portion 63a is shaped like a sheet.

The bottom portion 63a of the attracting portion (insulator) <NUM> can be, for example, insulating paper having a thickness of <NUM> to <NUM>. The bottom portion 63a of the attracting portion (insulator) <NUM> can be circular paper having an outer diameter substantially the same as the inner diameter of the tubular portion 63b. Alternatively, the bottom portion 63a can be circular paper having an outer diameter larger than the inner diameter of the tubular portion 63b. In this case, the bottom portion 63a can be circular paper having an outer diameter smaller than the outer diameter of the tubular portion 63b. Alternatively, the bottom portion 63a can be circular paper having an outer diameter same as the outer diameter of the tubular portion 63b.

On the inner surface of the tubular portion 63b of the attracting portion (insulator) <NUM>, a step 63c is formed. In the tubular portion 63b of the attracting portion (insulator) <NUM>, the portion on the first electrode (inner electrode) <NUM> side with respect to the step 63c has an inner diameter equal to the outer diameter of the first electrode (inner electrode) <NUM>. In the tubular portion 63b of the attracting portion (insulator) <NUM>, the portion on the magnet <NUM> side with respect to the step 63c has an inner diameter equal to the outer diameter of the magnet <NUM>.

The thickness of the end of the tubular portion 63b of the attracting portion (insulator) <NUM>, in other words, the distance X1 between the first electrode (inner electrode) <NUM> and the wall portion 62b of the second electrode (outer electrode) <NUM> is larger than the dimension of the conductive substance contained in the lubricating oil. For example, the conductive substance has a dimension of approximately <NUM> to <NUM>, and the distance X1 is preferably just large enough to prevent a short circuit from occurring due to iron powder produced by initial wear. In the illustrated embodiment, the magnet <NUM> is in contact with the first electrode (inner electrode) <NUM> and surrounded by the attracting portion (insulator) <NUM>.

The attracting portion (insulator) <NUM> is made of, for example, an insulating non-magnetic material such as a resin. The magnet <NUM> forms a magnetic flux line between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. Thus, the conductive substance contained in the lubricating oil is gathered to the vicinity of the attracting portion (insulator) <NUM>. Note that the term "detection region" denotes the region within which the lubricating oil circulates.

In the sensor <NUM> relating to the present embodiment, a sensing plane 60a denotes the plane connecting the end of the second electrode (outer electrode) <NUM> and the surface of the first electrode (inner electrode) <NUM>, which are substantially flush with each other. In other words, on the sensing plane 60a, conductive abrasion powder is attracted between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> by the magnetic flux line, so that the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> are electrically connected. This causes a change in resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is to be detected. Note that the first electrode (inner electrode) <NUM> may not need to be flush with the opening of the second electrode (outer electrode) <NUM>.

As the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> increases, the amount of conductive abrasion powder required to be attracted to lower the resistance to a threshold value or to cause a short circuit between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> increases. As the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> decreases, the amount of conductive abrasion powder required to be attracted to lower the resistance to a threshold value or to cause a short circuit between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> decreases.

The sensor <NUM> relating to the present embodiment has a sensitivity adjusting unit for adjusting the attraction of the conductive abrasion powder to change the sensitivity. In the present embodiment, the sensitivity adjusting unit is the attracting portion (insulator) <NUM>. More specifically, in the present embodiment, the sensitivity adjusting unit is the tubular portion 63b of the attracting portion (insulator) <NUM>.

The attracting portion (insulator) <NUM> of the present embodiment is capable of adjusting the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> to adjust the amount of conductive abrasion powder to be attracted by the attracting portion (insulator) <NUM>. Specifically, a group of attracting portions (insulators) <NUM> are provided that have tubular portions 63b with different protruding heights with respect to the sensing plane 60a, as shown in <FIG>. In the sensor 60A shown in <FIG>, the sensing plane 60a is at the same level as the end of the tubular portion 63b of an attracting portion (insulator) 63A or at a height HA. In other words, the sensing plane 60a is flush with the tubular portion 63b of the attracting portion (insulator) 63A.

In the sensor 60B shown in <FIG>, the end of the tubular portion 63b of an attracting portion (insulator) 63B is higher than the sensing plane 60a by a height HB, in other words, the tubular portion 63b of the attracting portion (insulator) 63B protrudes with respect to the sensing plane 60a by the height HB. In the sensor 60C shown in <FIG>, the end of the tubular portion 63b of an attracting portion (insulator) 63C is higher than the sensing plane 60a by a height HC, in other words, the tubular portion 63b of the attracting portion (insulator) 63C protrudes with respect to the sensing plane 60a by the height HC. In the sensor 60D shown in <FIG>, the end of the tubular portion 63b of an attracting portion (insulator) 63D is higher than the sensing plane 60a by a height HD, in other words, the tubular portion 63b of the attracting portion (insulator) 63D protrudes with respect to the sensing plane 60a by the height HD.

Here, the heights HA, HB, HC and HD are related to each other as follows:<MAT>.

The sensor <NUM> relating to the present embodiment has a group of attracting portions (insulators) <NUM> that are different in the value of the tubular portion 63b as described above. The sensor <NUM> relating to the present embodiment can be assembled with a selected one of the attracting portions. This means that the group of attracting portions (insulators) <NUM> that are different in the height (axial dimension) of the tubular portion 63b serves as the sensitivity adjusting unit. In this way, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> can be selected from among a plurality of values by making a selection in the sensitivity adjusting unit.

A reference creepage distance denotes the creepage distance in the sensor 60A shown in <FIG> between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63A.

In the sensor 60B shown in <FIG>, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63B, is longer than the reference creepage distance. Accordingly, a larger amount of conductive abrasion powder can be attracted before the resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> drops to a threshold value or before a short circuit occurs. In this way, for example, even when the speed reducer <NUM> has a large size and thus produces an increased amount of initial abrasion powder, the sensor 60B can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder.

In the sensor 60C shown in <FIG>, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63C, is longer than in the sensor 60B. Accordingly, a further larger amount of conductive abrasion powder can be attracted before the resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> drops to a threshold value or before a short circuit occurs. In this way, even when the speed reducer <NUM> has a further larger size and thus produces an increased amount of initial abrasion powder, the sensor 60C can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder.

In the sensor 60D shown in <FIG>, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63D, is longer than in the sensor 60C. Accordingly, a further larger amount of conductive abrasion powder can be attracted before the resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> drops to a threshold value or before a short circuit occurs. In this way, even when the speed reducer <NUM> has a further larger size and thus produces an increased amount of initial abrasion powder, the sensor 60D can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder.

As described above, the sensor <NUM> can reliably sense the failure of the speed reducer <NUM> by selecting an appropriate one of the attracting portions (insulators) <NUM> without the need of increasing the size of the sensor <NUM> and also without affecting the other constituents. In other words, the sensor <NUM> can achieve different levels of sensitivity by replacing only the attracting portion (insulator) <NUM> while using the center electrode (inner electrode) <NUM>, the external electrode (outer electrode) <NUM>, the magnet <NUM>, the casing <NUM> and the fastening member (fastening portion) <NUM> in common.

In the present embodiment described above, four different attracting portions (insulators) <NUM> are employed as the sensitivity adjusting unit, but the present invention is not limited to such and the number can be determined appropriately.

The sensor <NUM> relating to the present embodiment can be assembled in the following manner.

To start with, the external electrode (outer electrode) <NUM> is placed within the casing <NUM>. Subsequently, the bottom portion 63a of the attracting portion (insulator) <NUM> is positioned on the bottom portion 62a of the external electrode (outer electrode) <NUM>. Following this, the tubular portion 63b of the attracting portion (insulator) <NUM> having a selected height is inserted into the external electrode (outer electrode) <NUM>. Subsequently, the magnet <NUM> is inserted into the tubular portion 63b, and the center electrode (inner electrode) <NUM> is further inserted. At this stage, the fastening member (fastening portion) <NUM> is inserted and fixedly fastened. In this way, the sensor <NUM> is assembled.

Having the sensitivity adjusting unit, the sensor <NUM> relating to the present embodiment is capable of setting the sensitivity at a predetermined level. Specifically, when a large amount of conductive abrasion powder is expected to be produced, the sensitivity adjusting unit can be selected such that a larger creepage distance to attract the abrasion powder can be obtained between the electrode <NUM> and the electrode <NUM> to set the sensitivity of the sensor <NUM> at a predetermined level. In addition, when a small amount of conductive abrasion powder is expected to be produced, the sensitivity adjusting unit can be selected such that a smaller creepage distance to attract the abrasion powder can be obtained between the electrode <NUM> and the electrode <NUM> to set the sensitivity of the sensor <NUM> at a predetermined level. In this way, the sensor <NUM> can reliably sense a failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder produced by the speed reducer <NUM>.

Speed reducers of different models (sizes) may produce different amounts of iron powder (abrasion powder) during the initial wear period. In the case of large speed reducers, a large amount of initial abrasion iron powder is produced, and the initial abrasion iron powder may fill the electrical gap in the sensor between the electrodes <NUM> and <NUM>. If such is the case, the sensor may react and erroneously operate. Therefore, the electrical gap in the sensor needs to be determined considering the model of the speed reducer, but this requirement may disadvantageously result in a larger sensor size in the diameter direction. To address this issue, the sensor <NUM> relating to the present embodiment has a sensitivity adjusting unit, which includes attracting portions (insulators) <NUM> with different heights. This configuration produces the same effects as the enlargement of the sensor in the diameter direction and thus allows the sensor <NUM> to maintain the size.

The following describes a sensor relating to a fourth embodiment of the present invention with reference to the drawings. <FIG> is a top view showing the sensor relating to the present embodiment. The present embodiment is different from the above-described third embodiment in terms of the attracting portion and outer electrode. <FIG> does not show all of the constituents.

As shown in <FIG>, the sensor <NUM> relating to the present embodiment has a substantially columnar outer shape and includes a first electrode (inner electrode) <NUM>, a magnet <NUM>, a second electrode (outer electrode) <NUM>, a fastening member (fastening portion) <NUM>, an attracting portion (insulator) <NUM> and a casing <NUM>. When seen from the top surface of the sensor <NUM>, the first electrode (inner electrode) <NUM> has a circular shape and is positioned at the center of the sensor <NUM>. The second electrode (outer electrode) <NUM> is a bottomed tubular member and has a bottom portion 62a extending substantially parallel to the first electrode (inner electrode) <NUM> and a wall portion (tubular portion) 62b continuous with the bottom portion 62a and extending substantially perpendicularly to the bottom portion 62a.

The attracting portion (insulator) <NUM> is, for example, made of an insulating non-magnetic material such as a resin. The magnet <NUM> forms a magnetic flux line between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. In this way, the conductive substance contained in the lubricating oil is gathered to the vicinity of the attracting portion (insulator) <NUM>.

In the sensor <NUM> relating to the present embodiment, a sensing plane 60a denotes the plane connecting the end of the second electrode (outer electrode) <NUM> and the surface of the first electrode (inner electrode) <NUM>, which are substantially flush with each other. In other words, on the sensing plane 60a, conductive abrasion powder is attracted between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> by the magnetic flux line, so that the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> are electrically connected. This causes a change in resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is to be detected.

The sensor <NUM> relating to the present embodiment has a sensitivity adjusting unit for adjusting the attraction of the conductive abrasion powder to change the sensitivity. In the present embodiment, the sensitivity adjusting unit is the attracting portion (insulator) <NUM>. More specifically, in the present embodiment, the sensitivity adjusting unit is the tubular portion 63b of the attracting portion (insulator) <NUM>, the external electrode (outer electrode) <NUM> and the casing <NUM>.

The attracting portion (insulator) <NUM> of the present embodiment is capable of adjusting the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> considering the large-diameter conductive chip to adjust the amount of the conductive abrasion powder to be attracted by the attracting portion (insulator) <NUM>. Specifically, as shown in <FIG>, a group of attracting portions (insulators) <NUM> are provided that are different in the radial thickness of the tubular portion 63b. A sensor 60E shown in <FIG> has an attracting portion (insulator) 63E, whose tubular portion 63b has an end with a thickness X1 on the sensing plane 60a, in other words, which provides a distance X1 on the sensing plane 60a between the first electrode (inner electrode) <NUM> and the wall portion 62b of the second electrode (outer electrode) <NUM>. The sensor 60E includes an external electrode (outer electrode) 62E and a casing 65E having a radial dimension corresponding to the attracting portion (insulator) 63E.

A sensor 60F shown in <FIG> has an attracting portion (insulator) 63F, whose tubular portion 63b has an end with a thickness X2 on the sensing plane 60a, in other words, which provides a distance X2 on the sensing plane 60a between the first electrode (inner electrode) <NUM> and the wall portion 62b of the second electrode (outer electrode) <NUM>. The sensor 60F includes an external electrode (outer electrode) 62F and a casing 65F having a radial dimension corresponding to the attracting portion (insulator) 63F. A sensor <NUM> shown in <FIG> has an attracting portion (insulator) <NUM>, whose tubular portion 63b has an end with a thickness X3 on the sensing plane 60a, in other words, which provides a distance X3 on the sensing plane 60a between the first electrode (inner electrode) <NUM> and the wall portion 62b of the second electrode (outer electrode) <NUM>. The sensor <NUM> includes an external electrode (outer electrode) <NUM> and a casing <NUM> having a radial dimension corresponding to the attracting portion (insulator) <NUM>.

Here, the thicknesses X1, X2 and X3 are related to each other as follows:<MAT>.

The sensor <NUM> relating to the present embodiment has a group of attracting portions (insulators) <NUM> that are different in the value of the tubular portion 63b as described above. The sensor <NUM> relating to the present embodiment can be assembled with a selected one of the attracting portions. This means that the group of attracting portions (insulators) <NUM> that are different in the thickness (radial dimension) of the tubular portion 63b serves as the sensitivity adjusting unit. In this way, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> can be selected from among a plurality of values by making a selection in the sensitivity adjusting unit.

A reference creepage distance denotes the creepage distance in the sensor 60E shown in <FIG> between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) 62E, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63E.

In the sensor 60F shown in <FIG>, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) 62F, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) 63F, is longer than the reference creepage distance. Accordingly, a larger amount of conductive abrasion powder can be attracted before the resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) 62F drops to a threshold value or to cause a short circuit. In this way, for example, even when the speed reducer <NUM> has a large size and thus produces an increased amount of initial abrasion powder, the sensor 60F can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder.

In the sensor <NUM> shown in <FIG>, the creepage distance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>, which is defined by the end of the tubular portion 63b of the attracting portion (insulator) <NUM>, is longer than in the sensor 60F. Accordingly, a further larger amount of conductive abrasion powder can be attracted before the resistance between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM> drops to a threshold value or to cause a short circuit. In this way, even when the speed reducer <NUM> has a further larger size and thus produces an increased amount of initial abrasion powder, the sensor <NUM> can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder.

As described above, the sensor <NUM> can reliably sense the failure of the speed reducer <NUM> by selecting an appropriate one of the attracting portions (insulators) <NUM> without the need of increasing the axial size of the sensor <NUM> and also without affecting the center electrode (inner electrode) <NUM>, the magnet <NUM> and the fastening member (fastening portion) <NUM>. In other words, the sensor <NUM> can achieve different levels of sensitivity by replacing the attracting portion (insulator) <NUM>, the external electrode (outer electrode) <NUM> and the casing <NUM> while using the center electrode (inner electrode) <NUM>, the magnet <NUM> and the fastening member (fastening portion) <NUM> in common.

In the present embodiment described above, three different attracting portions (insulators) <NUM> are employed as the sensitivity adjusting unit, but the present invention is not limited to such and the number can be determined appropriately.

To start with, the external electrode (outer electrode) <NUM> is placed within the casing <NUM> having a selected radial dimension. Subsequently, the bottom portion 63a of the attracting portion (insulator) <NUM> having a corresponding radial dimension is placed on the bottom portion 62a of the external electrode (outer electrode) <NUM>. Following this, the tubular portion 63b of the attracting portion (insulator) <NUM> having a selected radial dimension is inserted into the external electrode (outer electrode) <NUM>. Subsequently, the magnet <NUM> is inserted into the tubular portion 63b, and the center electrode (inner electrode) <NUM> is further inserted. At this stage, the fastening member (fastening portion) <NUM> is inserted and fixedly fastened, so that the sensor <NUM> is assembled. Here, the set of the casing <NUM>, external electrode (outer electrode) <NUM>, attracting portion (insulator) <NUM> having the selected radial dimension can be alternatively assembled together in advance.

Having the sensitivity adjusting unit, the sensor <NUM> relating to the present embodiment is capable of setting the sensitivity at a predetermined level. Specifically, when a large amount of conductive abrasion powder is expected to be produced, the sensitivity adjusting unit can be selected such that a larger creepage distance to attract the abrasion powder can be obtained between the electrode <NUM> and the electrode <NUM> to set the sensitivity of the sensor <NUM> at a predetermined level. In addition, when a small amount of conductive abrasion powder is expected to be produced, the sensitivity adjusting unit can be selected such that a smaller creepage distance to attract the abrasion powder can be obtained between the electrode <NUM> and the electrode <NUM> to set the sensitivity of the sensor <NUM> at a predetermined level. In this way, the sensor <NUM> can reliably sense the failure of the speed reducer <NUM> without being affected by the increased amount of initial abrasion powder produced by the speed reducer <NUM>.

The following describes a sensor relating to a fifth embodiment of the present invention with reference to the drawings. <FIG> is a sectional view showing the sensor relating to the present embodiment. The present embodiment is different from the above-described third and fourth embodiments in terms of the electrodes. <FIG> does not show all of the constituents.

The sensor <NUM> relating to the present embodiment is configured in substantially the same manner as the sensors <NUM> relating to the third and fourth embodiments, as shown in <FIG>. The sensor <NUM> relating to the present embodiment has a sensitivity adjusting unit for adjusting attraction of conductive abrasion powder to change the sensitivity.

In the present embodiment, the sensitivity adjusting unit is the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. The first electrode (inner electrode) <NUM> of the present embodiment has a surface treatment layer <NUM> formed thereon. The second electrode (outer electrode) <NUM> of the present embodiment has a surface treatment layer <NUM> formed thereon.

The surface treatment layers <NUM> and <NUM> both exhibit excellent slippery and non-adhesive properties and additionally have electrical conductivity, smoothness, lubricity and low adhesiveness. The surface treatment layers <NUM> and <NUM> can be formed of, for example, fluororesin electroless nickel composite plating or the like. Here, the fluororesin can be polytetrafluoroethylene particles or the like.

Here, sludge may possibly reduce the amount of abrasion powder to be attracted by the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. The surface treatment layers <NUM> and <NUM> can prevent the sludge from adhering to the first electrode (inner electrode) <NUM>, the second electrode (outer electrode) <NUM>, and the sensing plane 60a and resultantly from reducing the amount of abrasion powder to be attracted between the first electrode (inner electrode) <NUM> and the second electrode (outer electrode) <NUM>. In this way, the sensitivity of the sensor <NUM> can be set at a predetermined level. In <FIG>, the dotted lines indicate the adhering sludge.

Without the surface treatment layers <NUM> and <NUM>, the sludge produced by the lubricant accumulates on the electrodes of the sensor to form an insulating coating, which may possibly cause the sensor <NUM> to malfunction. To address this issue, the present embodiment includes the surface treatment layers <NUM> and <NUM>. The surface treatment layers <NUM> and <NUM> can improve the slipperiness, thereby achieving excellent flow of the lubricant. As a result, the sludge can be prevented from accumulating and the sensor <NUM> can be thus expected to predict a failure in a stable manner.

The following describes a sensor relating to a sixth embodiment of the present invention with reference to the drawings. <FIG> is used to illustrate the sensor relating to the sixth embodiment. The sensor <NUM> relating to the sixth embodiment is configured to sense the amount of conductive substance contained in a lubricating oil, similarly to the sensor <NUM> relating to the above-described second embodiment.

The sensor <NUM> has a substantially columnar outer shape and includes a plurality of detecting units and a sensing unit <NUM> configured to output a signal when the detecting units experience a change in electrical resistance and to prevent electrical leakage. More specifically, the sensor <NUM> includes a center electrode <NUM>, a plurality of outer electrodes <NUM>, an attracting portion <NUM> disposed between the center electrode <NUM> and the outer electrode <NUM>, and a magnet <NUM>. The outer electrodes <NUM> are insulated from each other. Each of the detecting units is constituted by a pair of electrodes and the attracting portion <NUM> disposed between the paired electrodes. The pair of electrodes includes the center electrode <NUM> and one of the outer electrodes <NUM>.

In the illustrated embodiment, the sensor <NUM> includes four outer electrodes 62A, 62B, 62C and 62D, and four detecting units are formed. There are no particular limitations on the number of the outer electrodes <NUM> and the number of the detecting units. Since the magnet <NUM> of the sensor <NUM> forms a magnetic flux line between the paired electrodes, the conductive substance contained in the lubricating oil is attracted by the attracting portion <NUM>. When the conductive substance is gathered in the vicinity of the attracting portion <NUM> in this manner, the detecting units experience a change in electrical resistance. While no conductive abrasion particles are attracted, the detecting units are equal in electrical resistance.

The center electrode <NUM> and the outer electrodes <NUM> are respectively connected to output lines, and each detecting unit is electrically connected to the sensing unit <NUM> via a corresponding one of the output lines.

In this embodiment, the detecting units are connected in parallel to each other, and voltage is applied between the center electrode <NUM> and each of the outer electrodes <NUM> by the same voltage source. The sensing unit <NUM> outputs a signal when a designated number of the detecting units experience a change in electrical resistance. For example, the sensing unit <NUM> may be configured to output a signal to a higher-level control device such as a manipulator when two or more of the detecting units experience a drop in electrical resistance, or configured to output a signal when all of the detecting units experience a drop in electrical resistance.

Alternatively, the sensing unit <NUM> selects a designated one of the detection units in a particular order and outputs a signal when the selected detecting unit experiences a change in electrical resistance. In addition, the sensing unit <NUM> is configured to output a signal when the detecting units experience a drop in electrical resistance as described above and to, subsequently, turn off the sensing power fed to the sensor <NUM>.

Specifically, the sensing unit <NUM> is configured to output a signal to put on a failure display when the detecting units experience a drop in electrical resistance as described above and to, subsequently, disconnect a switch <NUM> in order to turn off the sensing power fed to the sensor <NUM>. In other words, the power is no longer fed once the sensor <NUM> senses an increase in the amount of iron powder (a drop in resistance of the gap) and thus determines that the speed reducer <NUM> is malfunctioning.

This can prevent electrical leakage and shock even if the abrasion powder keeps accumulating to cause the sensor <NUM> to come into contact with the speed reducer <NUM> or mechanism <NUM>. If the speed reducer <NUM> is continuously used even after the sensor <NUM> reports the failure of the speed reducer <NUM>, the iron powder is continuously produced in the speed reducer <NUM> as the speed reducer <NUM> operates and the conductive abrasion powder resultantly keeps accumulating on the sensor <NUM>. As the iron powder accumulates, the dimensions of the sensor <NUM> increase. The abrasion powder resultantly causes the sensor <NUM> to come into contact with and establish electrical connection with the parts of the mechanism <NUM>, which may disadvantageously result in electrical leakage and shock. The present embodiment can prevent this case.

The following describes a sensor relating to a seventh embodiment of the present invention with reference to the drawings. <FIG> is used to illustrate the sensor relating to the seventh embodiment. The sensor <NUM> relating to the seventh embodiment is configured to sense the amount of a conductive substance contained in a lubricating oil, similarly to the sensors <NUM>, <NUM> and <NUM> relating to the above-described embodiments. According to the present embodiment, as shown in <FIG>, a cover <NUM> is provided to cover the sensor <NUM> in the space S. The cover <NUM> houses the sensor <NUM> therein and has a large number of through holes <NUM> positioned to face the sensing plane 60a of the sensor <NUM>.

The through holes <NUM> have a larger diameter at an external opening 67a thereof, which faces the space S external to the cover <NUM>, than at an internal opening 67b thereof, which faces the sensor <NUM> arranged within the cover <NUM>. When entering the inside of the cover <NUM> from the space S through the through holes <NUM>, the conductive abrasion powder passes through the through holes <NUM> having the decreasing diameter and then reaches the sensor <NUM>. The cover <NUM> is arranged such that the internal opening 67b of the through holes <NUM> is spaced away from the sensing plane 60a of the sensor <NUM>. The inside of the cover <NUM> is tightly sealed, except for the through holes <NUM>.

With such configurations, the sensor <NUM> can be protected by the cover <NUM> even if the mechanism <NUM> and the speed reducer <NUM> violently operate and the lubricant flows violently. This can prevent the conductive abrasion powder from moving back into the external space S after entering the inside of the cover <NUM>. As a result, the sensor <NUM> can keep the accurate amount of the attracted conductive abrasion powder and reliably predict a failure. In addition, since the conductive abrasion powder is prevented from leaving the space inside the cover <NUM> after entering the inside of the cover <NUM>, the influence on the mechanism <NUM> and the speed reducer <NUM> can be reduced. The cover <NUM> can have an inner diameter substantially equal to the outer diameter of the sensor <NUM>, when seen in the axial direction of the sensor <NUM>.

Furthermore, according to the present embodiment, the cover <NUM> can prevent a large amount of abrasion powder from being attracted by the sensor <NUM> at once during the initial stage of the operation of the speed reducer <NUM>, in which a small amount of abrasion powder is produced. As a result, the sensor <NUM> can be prevented from malfunctioning. In contrast to the initial stage of the operation of the speed reducer <NUM>, in which a small amount of abrasion powder is produced, a large amount of abrasion powder may be produced immediately before a failure of the speed reducer <NUM>. In this case, the sensor <NUM> can attract and sense a sufficient amount of abrasion powder that has passed through the through holes <NUM>.

The individual characteristics of the above-described embodiments of the present invention can be combined as appropriate.

In the sensor relating to the present invention, the sensitivity adjusting unit can include a group of insulators having different axial heights with respect to the opening of the outer electrode. In this way, by selecting an appropriate one of the insulators having different axial heights, the sensitivity of the sensor can be set at a predetermined level in accordance with an expected amount of conductive abrasion powder to be generated. Specifically, an insulator having a large axial height is selected when a large amount of conductive abrasion powder is expected to be produced. In this way, a longer distance can be obtained to attract the abrasion powder between the electrodes to set the sensitivity of the sensor at a predetermined level. Alternatively, an insulator having a small axial height or being flush with the electrode is selected when a small amount of conductive abrasion powder is expected to be produced. In this way, a shorter distance can be obtained to attract the abrasion powder between the electrodes to set the sensitivity of the sensor at a predetermined level.

In the sensor relating to the present invention, the sensitivity adjusting unit can include a group of insulators having different radial thicknesses, which are adjacent to the opening of the outer electrode, with respect to the outer diameter of the inner electrode and a corresponding group of outer electrodes corresponding to the outer diameters of the individual insulators. In this way, by selecting an appropriate one of the insulators having different radial thicknesses, the sensitivity of the sensor can be set at a predetermined level in accordance with an expected amount of conductive abrasion powder to be produced. Specifically, an insulator having a large radial thickness is selected when a large amount of conductive abrasion powder is expected to be produced. In this way, a longer distance can be obtained to attract the abrasion powder between the electrodes to set the sensitivity of the sensor at a predetermined level. Alternatively, an insulator having a small radial thickness is selected when a small amount of conductive abrasion powder is expected to be produced. In this way, a shorter distance can be obtained to attract the abrasion powder between the electrodes to set the sensitivity of the sensor at a predetermined level.

In the sensor relating to the present invention, the outer electrode can have an open end that is flush with the inner electrode.

In the sensor relating to the present invention, the sensitivity adjusting unit can include another magnet provided in addition to the above-mentioned magnet. In this case, the other magnet can be selected from a group of magnets capable of attracting different amounts of abrasion powder, or the other magnet can be omitted. In this way, depending on the expected amount of conductive abrasion powder to be produced, another magnet is employed to attract the abrasion powder, which can reduce the amount of the abrasion powder to be attracted between the electrodes. Thus, the sensitivity of the sensor can be set at a predetermined level. Specifically, when a large amount of conductive abrasion powder is expected to be produced, another magnet having strong magnetic force or a large size is selected, which reduces the amount of the abrasion powder to be attracted between the electrodes. Thus, the sensitivity of the sensor can be set at a predetermined level. Alternatively, when a small amount of conductive abrasion powder is expected to be produced, another magnet having weak magnetic force or a small size is selected, or another magnet is not provided, which allows a predetermined amount of abrasion powder to be attracted between the electrodes. Thus, the sensitivity of the sensor can be set at a predetermined level.

In the sensor relating to the present invention, the sensitivity adjusting unit can include a surface treatment layer of the outer electrode and a surface treatment layer of the inner electrode. Here, sludge may possibly reduce the amount of abrasion powder to be attracted. The sludge may adhere to the attraction surface of the electrodes and reduce the amount of abrasion powder to be attracted between the electrodes, which does not allow the sensor to provide required sensitivity. The above configuration of the present invention can prevent this problem. Specifically, the surface treatment layers may be only required to have electrical conductivity, smoothness, slipperiness, and low adhesiveness.

Claim 1:
A sensor (<NUM>) comprising:
a first electrode (<NUM>);
a second electrode (<NUM>) comprising a bottom portion (8a) and a wall portion (8b);
the first and second electrodes (<NUM>, <NUM>) defining a sensing plane that denotes the plane connecting the end of the wall portion (8b) of the second electrode (<NUM>) and the surface of the first electrode (<NUM>), which are flush with each other;
a magnet (<NUM>) positioned between the first electrode (<NUM>) and the bottom portion (8a) of the second electrode (<NUM>);
an attracting portion (<NUM>) arranged in a gap between the first electrode (<NUM>) and the second electrode (<NUM>),
the attracting portion (<NUM>) having an insulation property and the attracting portion (<NUM>) being configured to attract conductive particles smaller than the gap between the first electrode (<NUM>) and the second electrode (<NUM>) to cause a change in electrical resistance between the first electrode (<NUM>) and the second electrode (<NUM>);
the sensor (<NUM>) further comprises:
a short circuit preventing portion (<NUM>) configured for preventing a large-diameter conductive piece from causing a short circuit between the first electrode (<NUM>) and the second electrode (<NUM>), the large-diameter conductive piece having a larger dimension than the gap between the first electrode (<NUM>) and the second electrode (<NUM>),
characterized in that
the short circuit preventing portion (<NUM>) is provided on at least one of the first electrode (<NUM>) and the second electrode (<NUM>) and extends along the inner edge of the wall portion (8b), where the wall portion (8b) is in contact with the attracting portion (<NUM>) and/or extends along the outer edge of the first electrode (<NUM>), where the first electrode (<NUM>) is in contact with the attracting portion (<NUM>).