Patent Description:
Gears may show various kinds of fatigue and spontaneous damages depending upon time of use of the gears and other reasons. Generally, even non-damaged gear pairs induce vibration, due to time-variant mesh stiffness, amongst other reasons. This vibration excitation is changed by the presence of damage.

If the machine is a gearbox, the vibrations are transferred to the case of the gearbox across a gear bulk, shafts and bearings. One example of devices for detecting failure in gears mounted in a gearbox is disclosed in Japanese Patent Application Laid-Open Publication <CIT>.

The device described in Japanese Patent Application Laid-Open Publication <CIT> includes an acceleration sensor for detecting vibrations, which are caused as two gears mesh each other. The acceleration sensor is fixed to a case of a transmission.

Furthermore, <CIT> discloses a measuring device comprising a cover, an acceleration sensor provided on the inner side of the cover, an angle sensor provided on the inner side of the cover, and a data collecting unit provided on the inner side of the cover. Still further, <CIT> shows an abnormality diagnosing system for mechanical equipment, wherein sounds or vibrations generated in the mechanical system detected and processes. Moreover, <CIT> refers to a method for monitoring the kinematics of an epicyclic planetary gearbox, wherein, in a training phase, a model of the kinematics is determined by pattern recognition based on data measured at the epicyclic planetary gearbox by means of a vibration sensor device.

Part of vibration energy generated upon meshing of the gears is emitted to the outside, in the form of audible noise, from the case that houses the gears. Across the whole transfer path of the vibration energy (audible noise), the original mesh-excited vibration changes behavior as it is exposed to the transfer path properties from point of excitation towards point of picking up (location of the acceleration sensor). Thus, the vibration characteristics measured at the pick-up point are different from the vibration characteristics at the excitation point. This is due to damping and stiffness and mass properties of objects along the path of transfer, and changes the vibration time series with regard to modified amplitudes and phases across the whole frequency band.

Because the device disclosed in Japanese Patent Application Laid-Open Publication <CIT> has the acceleration sensor that is fixedly secured to the case of the speed-increasing mechanism, the vibrations generated upon meshing of the two gears are transferred to the acceleration sensor via the case of the speed-increasing mechanism. Because the vibrations transferred to the acceleration sensor are affected by the path of the vibration transfer through the case of the speed-increasing mechanism, the vibrations measured by the acceleration sensor may be different from the vibrations at the excitation point (point of gear-meshing) in terms of vibration characteristics. In addition, the device disclosed in Japanese Patent Application Laid-Open Publication <CIT> cannot detect failure of each gear in the speed-increasing mechanism.

An object of the present invention is to provide a technology that can accurately detect failure of gears.

According to one aspect of the present invention, as defined in claim <NUM>, there is provided a measuring device attached to one side face of a bearing part. The bearing part supports a shaft having a gear thereon such that the shaft can rotate. The measuring device includes a cover attached to an outer ring of the bearing part to cover the side face of the bearing part, an acceleration sensor provided on an inner face of the cover to measure vibrations of the bearing part, an angle sensor provided on the inner face of the cover to measure the angle between the outer ring and an inner ring of the bearing part, and a data collecting unit provided on the inner face of the cover to obtain the acceleration measured by the acceleration sensor and the angle measured by the angle sensor in a linked manner, sharing one common time base, in the form of time-synchronous angle-acceleration pairs.

According to another aspect of the present invention, there is provided a gear failure detecting system comprising a measuring device and a gear failure determining device.

Because the acceleration sensor is attached to the bearing part, the vibration transfer path from the gear to the acceleration sensor is very short. Therefore, it is possible to accurately detect gear failure, as compared to a case where an acceleration sensor is attached to a case of a machine.

A system for detecting gear failure according to an embodiment of the present invention is configured to monitor conditions of one of gears mounted in a gearbox and detect failure of the gear. The gear failure detecting system utilizes a bearing device, which has a self-power-generation function and includes a plurality of sensors, to monitor one of a plurality of gears and evaluate vibration signals from respective teeth of the gear. The bearing device has a function of rotatably supporting a shaft, which is an inherent function as a bearing, and three additional functions, i.e., self power generation, sensing, and wireless communication. The bearing device serves as a device for supporting the shaft, and also serves as a sensing device (measuring device). Because the sensing device can serve as a measuring device, the bearing device equipped with sensors may be referred to a bearing device equipped with a measuring device.

For the sake of easier description, the gearbox in the embodiment of the invention includes a single-stage gear set.

It should be noted that the scope of the present invention is not limited to the embodiment described below. The embodiment may be altered and/or modified within a scope of the present invention as defined in the claims.

The embodiment of the present invention will now be described with reference to the accompanying drawings.

<FIG> illustrates a gear failure determining device <NUM> and a gearbox <NUM> according to an embodiment of the present invention. The gearbox <NUM> has a housing <NUM>, a first gear <NUM> and a second gear <NUM>. The first gear <NUM> and the second gear <NUM> are provided in the housing <NUM> and mesh each other. The housing <NUM> has a first wall 21a and a second wall 21b. The first wall 21a faces the second wall 21b at a predetermined distance. The gearbox <NUM> also has a first shaft 24a, on which the first gear <NUM> is mounted. The first shaft 24a is supported by a first bearing <NUM> at its one end, and by a second bearing <NUM> at its opposite end. The first bearing <NUM> is provided in the first wall 21a of the housing <NUM>, and the second bearing <NUM> is provided in the second wall 21b of the housing <NUM>.

The gearbox <NUM> also has a second shaft 24b, on which the second gear <NUM> is mounted. The second shaft 24b is supported by a third bearing <NUM> at its one end, and by a fourth bearing <NUM> at its opposite end. The third bearing <NUM> is provided in the first wall 21a of the housing <NUM> at a position below the first bearing <NUM>, and the fourth bearing <NUM> is provided in the second wall 21b of the housing <NUM> at a position below the second bearing <NUM>. In this embodiment, each of the bearing <NUM>, <NUM>, <NUM> and <NUM> is a rolling bearing (e.g., a conical or taper roller bearing or a deep groove ball bearing).

In this embodiment, only one of the four bearings <NUM>-<NUM>, namely the first bearing <NUM>, is a bearing equipped with a measuring device <NUM> (see <FIG>). Thus, the first bearing <NUM> is a bearing device that has the measuring device <NUM>. The measuring device <NUM> detects and measured vibrations generated as the first gear <NUM> meshes with the second gear <NUM>. The measuring device <NUM> also detects an angular position of the first bearing <NUM> (i.e., angular position of the first shaft 24a). The measuring device <NUM> has a wireless communication unit such that the measuring device <NUM> communicates with the gear failure determining device <NUM> by wireless. The measuring device <NUM> also has a power generator <NUM> (see <FIG>). The gear failure determining device <NUM> detects (determines) whether there is any failure in the first gear <NUM> based on signals received from the measuring device <NUM> of the first bearing <NUM>. In this embodiment, the gear failure determining device <NUM> and the measuring device <NUM> constitute, in combination, a gear failure detecting system <NUM>. Because the first bearing <NUM> is equipped with the measuring device <NUM>, the first bearing <NUM> may be referred to as a bearing device.

<FIG> is a block diagram that shows a configuration of the gear failure determining device <NUM>. As shown in <FIG>, the gear failure determining device <NUM> includes an input unit <NUM>, a control unit <NUM>, a memory unit <NUM>, a display unit <NUM> and a communication unit <NUM>. The gear failure determining device <NUM> is, for example, a personal computer.

The input unit <NUM> has buttons, switches, a mouse, a touch panel and other elements. A user or operator can enter various instructions, data and information into the gear failure determining device <NUM> with the input unit <NUM>. For example, the user may enter the number of the teeth of the first gear <NUM> into the gear failure determining device <NUM>. When the user operates the gear failure determining device <NUM>, the user operates the input unit <NUM>. The input unit <NUM> may be referred to as an operation unit.

The control unit <NUM> may include one or more CPUs (Central processing units) or MPUs (Microprocessor units). The control unit <NUM> controls the units <NUM> and <NUM>-<NUM> of the gear failure determining device <NUM>. The control unit <NUM> processes signals received from the measuring device <NUM> to carry out the gear failure determination (perform the failure determination process). The control unit <NUM> controls the gear failure determining device <NUM> and carries out the gear failure determination by executing a control program, which is stored in the memory unit <NUM>.

The memory unit <NUM> may include HDD (Hard disk drive), ROM (Read only memory), RAM (Random access memory), IC (Integrated circuit) memory card and other elements. The memory unit <NUM> stores the control program that is executed by the control unit <NUM>. The memory unit <NUM> also stores other information such as algorithms, which are used to generate a map to define relationship between an angle (angular position) of the first gear <NUM> and teeth of the first gear <NUM>. The map is generated as the control unit <NUM> executes the control program stored in the memory unit <NUM>. The memory unit <NUM> stores data received from the measuring device <NUM>.

The display unit <NUM> may include a liquid crystal display. The display unit <NUM> displays various data, numbers, characters and images. For example, the display unit <NUM> displays data received from the measuring device <NUM>.

The communication unit <NUM> performs wireless communication with the measuring device <NUM>.

<FIG> is an exploded perspective view of the first bearing <NUM> to show a configuration of the first bearing <NUM>. <FIG> shows the first bearing <NUM> when viewed from the left. <FIG> is another exploded perspective view of the first bearing <NUM> when viewed from the right. As shown in <FIG>, the first bearing <NUM> includes the measuring device <NUM> and a bearing part <NUM>. The measuring device <NUM> is attached to a left side face of the bearing part <NUM>. The measuring device <NUM> includes a cover <NUM>, a coil substrate <NUM> (see <FIG>), a rotating module <NUM>, a circuit substrate group <NUM> (see <FIG>), an accumulator battery <NUM>, a retainer (not shown), and a Z-phase magnet unit <NUM>. The retainer is a thin annular member, and located between the cover <NUM> and the Z-phase magnet unit <NUM>. The circuit substrate group <NUM> includes a plurality of substrates (will be described later). The cover <NUM> may be a metallic cover.

The rotating module <NUM> is mounted on the first shaft 24a such that the rotating module <NUM> rotates with the first shaft 24a. When the cover <NUM> is attached to the bearing part <NUM>, the cover <NUM> is fixed to the left side face of an outer ring (outer race) of the bearing part <NUM>. Thus, the cover <NUM> does not rotate. The retainer is attached to an inner ring of the bearing part <NUM>. The Z-phase magnet unit <NUM> is fixed to the inner right of the bearing part <NUM> by the retainer. Thus, the Z-phase magnet unit <NUM> rotates with the inner ring of the bearing part <NUM>, i.e., the Z-phase magnet unit <NUM> rotates with the first shaft 24a.

The cover <NUM> is a flat annular member, and may be made from a magnetic material such as silicon steel, carbon steel (JIS, SS400 or S45C), martensitic stainless steel (JIS, SUS420) or ferrite-based stainless steel (JIS SUS430). Because a plurality of sensors are attached to an inner face of the cover <NUM> (will be described), the cover <NUM> may be referred to as a casing for the sensors or a sensor case.

As shown in <FIG>, the coil substrate <NUM>, the circuit substrate group <NUM> and the accumulator battery <NUM> are attached onto the inner face of the cover <NUM> (i.e., the face that is directed toward the bearing part <NUM>). The circuit substrate group <NUM> includes a power source control substrate <NUM>, an angle sensor substrate <NUM>, and a control substrate <NUM>. The power source control substrate <NUM>, the angle sensor substrate <NUM>, and the control substrate <NUM> are fixed to the cover <NUM> as bolts, which are made from a nonmagnetic material such as brass, are screwed into female bores formed in the cover <NUM>. The lengths of the bolts are decided such that the bolts do not protrude from the cover <NUM>.

The power source control substrate <NUM> includes a rectifier circuit <NUM> (<FIG>), a smoothing circuit <NUM> (<FIG>), a power management IC <NUM> (<FIG>) and an FET (Field effect transistor) <NUM> (<FIG>). The circuits <NUM>-<NUM> and the FET <NUM> of the power source control substrate <NUM> will be describe with <FIG>.

The cover <NUM> has a through hole <NUM>. The through hole <NUM> is closed by a lid <NUM>, which is made from a nonmagnetic material such as resin. An antenna <NUM> (see <FIG>) is disposed on the control substrate <NUM> (will be described). The cover <NUM> is magnetized, and shields the electromagnetic wave emitted from the antenna <NUM>. However, the antenna <NUM> is provided at a position that faces the lid <NUM>. Thus, the electromagnetic wave emitted from the antenna <NUM> can reach the gear failure determining device <NUM> through the nonmagnetic lid <NUM>.

The coil substrate <NUM> is attached to the cover <NUM> by, for example, an adhesive.

<FIG> is a plan view to show an exemplary configuration of the cover <NUM>, the coil substrate <NUM>, the circuit substrate group <NUM>, and the accumulator battery <NUM>. <FIG> only shows the outer boundary (outer contour) of the cover <NUM> and the coil substrate <NUM>. As shown in <FIG>, the coil substrate <NUM> includes a flexible substrate <NUM>, a coil pattern <NUM> disposed on the flexible substrate <NUM>, and a plurality of yokes <NUM> disposed on the flexible substrate <NUM>. It should be noted that the yokes <NUM> may be dispensed with. When viewed from the top, the flexible substrate <NUM> has a generally annular shape, with a rotation center Ax of the first shaft 24a being the center of the annular shape. The coil pattern <NUM> has a plurality of flat coils, which are piled up in the thickness direction of the flexible substrate <NUM>. The flat coil is a pattern of electric conductor formed on a predetermined surface (or surfaces) of an insulator by a patterning process. In this embodiment, a plurality of conductor patterns are formed on a plurality of surfaces of the insulator. It should be noted that the conductor pattern may be formed on a single surface of the insulator. The number of turns of the coil pattern <NUM> is proportional to the number of piling up of the flat coils. An amount of power generation may be adjusted by changing the number of piling up of the flat coils.

When viewed from the top, the coil pattern <NUM> alternately has protrusions and recesses in a circumferential direction around the rotation center Ax. Each yoke <NUM> is situated in each recess. The coil pattern <NUM> may have a cutout portion in order to place the angle sensor at a position that can detect a change in magnetism of an encoder magnet (will be described).

As illustrated in <FIG>, the power source control substrate <NUM>, the angle sensor substrate <NUM>, the control substrate <NUM> and the accumulator battery <NUM> are situated outside the coil substrate <NUM>, when viewed from the top. The power source control substrate <NUM> (i.e., a power management IC <NUM>, which will be described later in detail) has two DC-DC converters (i.e., a step-up DC-DC converter and a step-down DC-DC converter). The power source control substrate <NUM> can decrease a DC voltage, supplied from the accumulator battery (capacitor) <NUM>, and feed the DC voltage to the angle sensor substrate <NUM> and the control substrate <NUM>.

An angle sensor <NUM> and a Z-phase detector <NUM> are mounted on the sensor substrate <NUM>. The Z-phase detector <NUM> is, for example, a hall IC. The Z-phase detector <NUM> generates one pulse as a Z-phase magnet <NUM> (will be described) passes by the Z-phase detector <NUM>. In other words, the Z-phase detector <NUM> generates a single pulse every time the first bearing <NUM> rotates <NUM> degrees.

The control circuit <NUM>, the antenna <NUM>, the acceleration sensor <NUM> and the temperature sensor <NUM> are provided on the control substrate <NUM>. It should be noted that the acceleration sensor <NUM>, the temperature sensor <NUM>, the angle sensor <NUM>, the control circuit <NUM> and the antenna <NUM> may be provided in the form of separate IC chips, respectively. Alternatively, part or all of the sensors <NUM>-<NUM>, the control circuit <NUM> and the antenna <NUM> may be provided in the form of a single IC chip. The temperature sensor <NUM> is used to indicate (know) the temperature when (or before) the acceleration and the angle are detected. The acceleration sensor <NUM> in this embodiment is, for example, an MEMS acceleration sensor.

Two opposite ends of the coil pattern <NUM> are electrically connected to the power source control substrate <NUM> via an extending portion <NUM>, which extends from a predetermined position of the outer circumference of the coil substrate <NUM>. It should be noted that lead wires may be used instead of the extending portion <NUM> to connect the coil substrate <NUM> to the power source control substrate <NUM>. Alternatively, an FPC (Flexible printed circuit) connector may be used instead of the extending portion <NUM> to connect the coil substrate <NUM> to the power source control substrate <NUM>. If the FPC connector is used, soldering becomes unnecessary, and therefore the productivity of the measuring device <NUM> increases.

Referring back to <FIG>, the rotating module <NUM> includes an annular magnetic track <NUM>, an annular base member <NUM>, and an annular attaching jig <NUM>. Preferably, the base member <NUM> and the attaching jig <NUM> are metallic and magnetized. The magnetic track <NUM> is provided on the left side face of the base member <NUM>. The base member <NUM> has an opening. The attaching jig <NUM> is fixed to the right side face of the base member <NUM>. The attaching jig <NUM> extends through the opening of the base member <NUM> from the right side face of the base member <NUM>, and protrudes from the left side face of the base member <NUM>. The left side face of the base member <NUM> faces the cover <NUM>. It should be noted that the magnetic track <NUM> may be detachable from the base member <NUM>.

In this embodiment, the magnetic track <NUM> and the base member <NUM> are, in combination, referred to as the encoder magnet. For example, the encoder magnet is prepared by forming a plastic magnet on one surface of the metallic base member <NUM>, with N and S poles being alternately made (magnetized) on the surface of the plastic magnet. The attaching jig <NUM> is a jig to mount the encoder magnet (rotating module <NUM>) on the first shaft 24a.

The magnetic track <NUM> has a plurality of magnetic pole pairs <NUM>. Each magnetic pole pair <NUM> has an N pole 131N and an S pole <NUM>. The magnetic pole pairs <NUM> are arranged in the circumferential direction of the magnetic track <NUM>. The N poles 131N and the S poles <NUM> are alternately arranged.

The distance between the center of the N pole 131N and the center of the neighboring S pole <NUM> of the magnetic track <NUM> is the same as the distance between the center of one yoke <NUM> and the center of the neighboring yoke <NUM> on the coil substrate <NUM>.

In this embodiment, when the magnetic track <NUM> rotates relative to the coil substrate <NUM> about the center Ax (<FIG>), one of the two adjacent yokes <NUM> faces the N pole while the other yoke <NUM> faces the S pole. When one of the two adjacent yokes <NUM> faces the S pole, the other yoke <NUM> faces the N pole. In this manner, the two adjacent yokes <NUM> of the coil substrate <NUM> do not face the same pole of the magnetic track <NUM>. Thus, the phase of the changing magnetic flux density that passes through one yoke <NUM> is shifted <NUM> degrees from the phase of the changing magnetic flux density that passes through the other yoke <NUM>.

As described above, when the magnetic track <NUM> rotates relative to the coil substrate <NUM>, the magnetic poles that face the yokes <NUM> alternately change. As a result, the densities of the magnetic fluxes that penetrate the yokes <NUM> change periodically. As the magnetic flux density changes periodically, the voltage change (e.g., sine-wave AC voltage) occurs in the coil pattern <NUM> provided around the yokes <NUM>. In this embodiment, therefore, as the inner ring of the first bearing <NUM> rotates with the first shaft 24a, the power generation takes place in the first bearing <NUM> by means of electromagnetic induction. This power generation is self-power generation, i.e., the measuring device <NUM> of the first bearing <NUM> is self powered. In the following description, a combination of the encoder magnet (magnetic track <NUM>) and the coil substrate <NUM> may be referred to as a power generator unit <NUM>. The power generator unit <NUM> generates electric power based on the relative rotation between the outer ring of the first bearing <NUM> and the inner ring of the first bearing <NUM>. The DC voltage generated by the first bearing <NUM> is accumulated in the accumulator battery <NUM>.

The Z-phase magnetic unit <NUM> has a Z-phase magnet holder <NUM> and the Z-phase magnet (not shown). The Z-phase magnet holder <NUM> has a hole. The Z-phase magnet holder <NUM> is an annular member, and the Z-phase magnet is embedded in the hole of the Z-phase magnet holder <NUM>. The Z-phase magnet holder <NUM> is metallic (e.g. made from aluminum). As the Z-phase magnet unit <NUM> rotates <NUM> degrees together with the first shaft 24a, the Z-phase magnet passes by the Z-phase detector <NUM> once. Then, the Z-phase detector <NUM> generates one pulse.

<FIG> schematically depicts a mechanism of the above-described self-power generation. In <FIG>, the coil C corresponds to the coil pattern <NUM> provided on the cover (metallic case) <NUM>, and the magnet M corresponds to the encoder magnet provided on the inner ring of the first bearing <NUM>.

As shown in <FIG>, the electromagnetic induction occurs and the electric power is generated as the coil C and the magnet M rotate relative to each other. Because the generated electricity is the AC current, the AC current is converted to the DC current by the rectifier circuit <NUM>. The rectifier circuit <NUM> is, for example, a diode bridge. Because the DC current obtained from the rectifier circuit <NUM> may contain a pulsating current, the output of the rectifier circuit <NUM> is connected to the input of the smoothing circuit <NUM> in order to smooth the DC current in this embodiment.

The DC current, which has passed through the smoothing circuit <NUM>, is introduced to the power management IC <NUM>, and accumulated in the accumulator battery (capacitor) <NUM>. Because the power management IC <NUM> has the two DC-DC converters (the step-up DC-DC converter and the step-down DC-DC converter), the power management IC <NUM> can convert (increase) a very weak electricity, which is generated by the power generator ("C" and "M" in <FIG>), to a higher voltage, and this higher voltage is accumulated in the accumulator battery <NUM>. The charging to the accumulator battery <NUM>, the discharging in the case of overcharging, and feeding of a predetermined voltage Vcc to the load L (sensors and circuit boards) are controlled by the power management IC <NUM>.

To avoid an infinite voltage from entering the load L, which would otherwise make the control circuit <NUM> uncontrollable, the FET <NUM> is provided between the power management IC <NUM> and the load L. The FET <NUM> can completely stop the power feeding to the load L.

The electric power generated by the rotation of the first shaft 24a (i.e., by the relative rotations between the coil substrate <NUM> and the magnetic track <NUM>) is very small. Thus, the power management IC <NUM> used in this embodiment is, for example, a circuit that has an energy harvesting capability. Such circuit can accumulate the electric power even when the generated electric power is very small. One example of such circuit is "Ultra low power harvester power management IC, BQ25570" manufactured by Texas Instruments Incorporated.

The accumulator battery <NUM> has a condenser capacity that is, at least, enough for the measuring device <NUM> to perform a single operation. The single operation of the measuring device <NUM> is an operation from measuring the angular position of the gear tooth and the acceleration of the gear tooth for a predetermined period of time (e.g., one second) to sending the measurement results to the gear failure determining device <NUM>.

When the charging to the accumulator battery <NUM> is complete, the power management IC <NUM> sends a "charging complete" signal to the FET <NUM>, which informs a fact that the charging to the accumulator battery <NUM> is complete.

When the ESR (Equivalent Series Resistance) of the accumulator battery <NUM> decreases, an amount of electric current that can be instantaneously extracted increases. Thus, preferably, the accumulator battery <NUM> has a low ESR. If the accumulator battery <NUM> does not have a low ESR, a capacitor may be provided in parallel to the accumulator battery <NUM>, or an all solid state battery may be provided in parallel to the accumulator battery <NUM>.

It should be noted that the rectifier circuit <NUM>, the smoothing circuit <NUM>, the power management IC <NUM> and the FET <NUM> may collectively be referred to as a circuit group <NUM> (see <FIG>).

<FIG> shows two graphs, which are useful to describe the behavior of the power management IC <NUM>. In the upper graph of <FIG>, the vertical axis represents the voltage of the accumulator battery <NUM>, and the horizontal axis represents the time. The lower graph of <FIG> shows the charging complete signal. The vertical axis of the lower graph represents the intensity of the signal (High or Low), and the horizontal axis represents the time. When the charging complete signal is low, the charging to the accumulator battery <NUM> is not complete (charging state). When the charging complete signal is high, the accumulator battery <NUM> feeds the electricity (power supply state). When the charging complete signal moves to Low from High, it indicates that the accumulator battery <NUM> stops (finishes) the power supply and enters the charging state. The charging complete signal is a signal generated by the power management IC <NUM>. When the two graphs in <FIG> are looked at simultaneously, one can understand what control the power management IC <NUM> performs with regard to the voltage of the accumulator battery <NUM>.

As shown in <FIG>, when the charging complete signal is Low, an amount of charge accumulated in the accumulator battery <NUM> increases with time. Eventually, when the time t1 is reached, the charging complete signal becomes High. The voltage of the accumulator battery <NUM> is V2 at the time t1. The voltage V2 is a voltage that starts (triggers) the power supply to the load L.

After the time t1 (after the power supply to the load L starts), the voltage drops from V2 if an amount of electricity consumed by the load L is greater than an amount of power generation, as indicated by the line J1. When the voltage drops to V1, the power management IC <NUM> stops the power supply to the load L. V1 may be equal to Vcc or slightly higher than Vcc. If V1 is lower than Vcc, the power management IC <NUM> would not function as a converter.

After the time t1, the voltage maintains V2 if an amount of electricity consumed by the load L is equal to an amount of power generation, as indicated by the line J2.

After the time t1, the voltage rises from V2 if an amount of electricity consumed by the load L is smaller than an amount of power generation, as indicated by the line J3. When the voltage reaches V3, the power management IC <NUM> stops the charging to the accumulator battery <NUM> in order to prevent the overcharging.

In this embodiment, the accumulator battery <NUM> has a capacity that is sufficient for the measuring device <NUM> to perform a single operation. Specifically, the accumulator battery <NUM> ensures that the measuring device <NUM> can finish the single operation between the time t1 and the time t2, even if the voltage drops to V1 from V2 between the time t1 and the time t2 in <FIG>. The accumulator battery <NUM> can feed electricity to the measuring device <NUM> between the time t1 and the time t2, and the measuring device <NUM> can measure and send the acceleration data and the angle data to the device <NUM> between the time t1 and the time t2.

<FIG> is a block diagram that shows the configuration of the measuring device <NUM>. As described above, the measuring device <NUM> includes the power source control substrate <NUM>, the angle sensor substrate <NUM>, and the control substrate <NUM>. The angle sensor substrate <NUM> includes the sensor substrate <NUM> and the Z-phase detector substrate <NUM>.

The power source control substrate <NUM> has the circuit group <NUM>. The circuit group <NUM> includes the he rectifier circuit <NUM>, the smoothing circuit <NUM>, the power management IC <NUM> and the FET <NUM>, as shown in <FIG>. The circuit group <NUM> is connected to the accumulator battery <NUM> and the power generator <NUM>.

The power generator <NUM> includes the magnetic track <NUM> (<FIG>) and the coil substrate <NUM> (<FIG>). The power generator <NUM> generates electric power based on the relative rotation between the outer ring of the bearing part <NUM> and the inner ring of the bearing part <NUM>, and feeds electricity to the sensor substrate <NUM> and other elements.

The power generator <NUM> generates a single-phase AC voltage and supplies it to the circuit group <NUM>. The rectifier circuit <NUM> of the circuit group <NUM> is a full wave rectifier to rectify the single-phase AC voltage, which is received from the power generator <NUM>, and converts it to the DC voltage. The DC voltage prepared by the rectifier circuit <NUM> is smoothed by the smoothing circuit <NUM>, and becomes a stable DC voltage. Then, the DC voltage is stored in the accumulator battery <NUM> via the power management IC <NUM> (i.e., after the DC voltage is increased by the step-up DC-DC converter of the power management IC <NUM>). The DC voltage stored in the accumulator battery <NUM> is decreased by the step-down DC-DC converter of the power management IC <NUM> and supplied to the angle sensor substrate <NUM> and the control substrate <NUM> when the measuring device <NUM> carries out the measurement.

The angle sensor <NUM> is mounted on the sensor substrate <NUM>. The Z-phase detector <NUM> is mounted on the Z-phase detector substrate <NUM>. The acceleration sensor <NUM>, the temperature sensor <NUM>, the microcomputer <NUM>, the external memory <NUM>, and the wireless communication module (transmitter) <NUM> are mounted on the control substrate <NUM>. The microcomputer <NUM>, the external memory <NUM> and the wireless communication module <NUM> are included in the control circuit <NUM> (see <FIG>).

The acceleration sensor <NUM>, the temperature sensor <NUM>, and the angle sensor <NUM> use the DC voltage, which is supplied from the power source control substrate <NUM>, to detect the acceleration, the temperature and the angular position, respectively.

For example, the angle sensor <NUM> is mounted on the sensor substrate <NUM> such that the angle sensor <NUM> is situated in the vicinity of the side face of the magnetic track <NUM>. The rotating module <NUM>, which has the magnetic track <NUM>, is fixed to the inner ring of the bearing part <NUM>. The angle sensor <NUM> detects the changing magnetic flux density, which is caused when the magnetic track <NUM> rotates with the inner ring of the bearing part <NUM>, and obtains the angular position of the inner ring of the bearing part <NUM> relative to the outer ring of the bearing part <NUM> (angle between the inner ring and the outer ring of the bearing part <NUM>) based on the detected magnetic flux. The angle sensor <NUM> is a magnetic angle sensor.

The angle sensor <NUM> may be an incremental type that indicates the increment of the angle, or an absolute type that indicates an absolute angle.

The microcomputer <NUM> includes a CPU <NUM>, a DMA (Direct memory access) controller <NUM>, and an internal memory <NUM>. The microcomputer <NUM> writes the measurement values, which are obtained from the acceleration sensor <NUM> and the angle sensor <NUM>, into the external memory <NUM>. The DMA controller <NUM> may be referred to as a DMAC in the following description. Also, the internal memory <NUM> and the external memory <NUM> may collectively be referred to as a memory unit <NUM>.

The CPU <NUM> initializes the memory unit <NUM>, the acceleration sensor <NUM>, the temperature sensor <NUM> and the angle sensor <NUM>. The CPU <NUM> also performs an initial setting to the DMA controller <NUM>. Upon receiving a DMA trigger (INT signal from the acceleration sensor <NUM>), the DMA controller <NUM> starts the DMA data transfer. Specifically, as the DMA controller <NUM> receives the DMA trigger, the DMA controller <NUM> transfers the most recent measurement data (measured values) of the acceleration sensor <NUM> and the angle sensor <NUM> to the memory unit <NUM> (the external memory <NUM>), without using the CPU <NUM> and without processing the measurement data (i.e., in the form or raw data).

The acceleration sensor <NUM> and the angle sensor <NUM> update the measurement data at predetermined periods, respectively, and hold the measurement data. When the acceleration sensor <NUM> is the MEMS acceleration sensor, the updating period for the measurement data is an ODR (Output Data Rate) of the MEMS acceleration sensor. The acceleration sensor <NUM> generates an INT signal (interruption signal) every time the acceleration sensor <NUM> is ready to output the measurement data, and the INT signal is introduced to the DAM controller <NUM> as the trigger signal. The updating period (sampling period) will be described with reference to <FIG>.

The wireless communication module <NUM> sends the data, which are stored in the external memory <NUM>, to the gear failure determining device <NUM> under the control of the CPU <NUM>. The wireless communication module <NUM> has the antenna <NUM>. For example, the wireless communication module <NUM> sends the data to the gear failure determining device <NUM> by using a wireless communication technology such as BLE (Bluetooth® Low Energy). The data is received by the communication unit <NUM> of the gear failure determining device <NUM> and processed by the control unit <NUM> of the gear failure determining device <NUM>.

If the BLE is used, the data is sent one packet by one packet, for example. If the throughput should be increased, the communication technology such as More Data or Data Length Extension may be used. Alternatively, PHY 2Mbps defined in the BLE <NUM>. x may be used to increase the throughput.

When the first bearing <NUM> communicates with the gear failure determining device <NUM> by wireless communication, a wireless communication technology or standard other than BLE may be used. For example, Zigbee® or Thread may be used. Alternatively, a frequency band different from BLE may be used (e.g., a specific small electric power radio with a <NUM> band may be used).

Although the measurement data of the acceleration sensor <NUM> and the angle sensor <NUM> are written into the external memory <NUM> in the above-described embodiment, the measurement data of the acceleration sensor <NUM> and the angle sensor <NUM> may be written into the internal memory <NUM>. Alternatively, both of the internal memory <NUM> and the external memory <NUM> may be used together. Alternatively, the external memory <NUM> and the internal memory <NUM> may be combined to a single memory.

<FIG> is a set of timing charts useful to describe the operations and processing of the measuring device <NUM>. <FIG> shows the timing of starting the power supply (Power-ON) to the load L (the acceleration sensor <NUM>, the angle sensor <NUM>, and the circuit substrate group <NUM>). "Power-ON" in <FIG> indicates the timing when the power management IC <NUM> starts feeding the electricity to the load L, and this corresponds to the "Start Power Supply" at the time t1 in <FIG>.

<FIG> shows the timing for the measuring device <NUM> to connect to the gear failure determining device <NUM> by wireless communication (BLE). "Pairing Time" in <FIG> is time that is necessary for the measuring device <NUM> to establish the communication with the gear failure determining device <NUM>. The pairing time is, for example, <NUM>-<NUM> seconds. "Pairing completed" in <FIG> indicates the timing when the BLE connection is established.

<FIG> shows a pulse generated by the Z-phase detector <NUM>. In this embodiment, the output of the Z-phase detector <NUM> is so-called "Active Low. " The Z-phase detector <NUM> generates the Low signal when it detects the Z-phase magnet. "Interval Wait" is set to be equal to or larger than time necessary for the CPU <NUM> to finish a predetermined monitoring process. "Interval Wait" is, for example, thirty seconds. When the "Interval Wait" elapses, the angle sensor <NUM> is activated (Angle Sensor (Turn-On)). After the activation, the angle sensor <NUM> is initialized (Angle Initialization Wait). In the initialization, electricity is supplied to the angle sensor <NUM>, and the angle sensor <NUM> becomes ready to operate. The "Angle Initialization Wait" or the initialization time of the angle sensor <NUM> is, for example, <NUM>. After the initialization of the angle sensor <NUM>, the CPU <NUM> starts the preparation for measurement (Start Measurement).

<FIG> shows the pulse (acceleration measurement value) generated by the acceleration sensor <NUM>. The acceleration measurement value (pulse) is sent to the external memory <NUM> from the acceleration sensor <NUM>, and stored in the external memory <NUM>. The acceleration sensor <NUM> detects (measures) the acceleration of the first gear <NUM> during a predetermined measurement period, and holds the acceleration data. The predetermined measurement period is equal to or longer than time necessary for the first shaft 24a to rotate <NUM> degrees. The pulse generated by the acceleration sensor <NUM> (output of the acceleration sensor <NUM>) represents vibrations generated by the first gear <NUM> as the first gear <NUM> meshes with the second gear <NUM>. During the "Measurement Start Delay," the CPU <NUM> performs three processing (<NUM>)-(<NUM>). In the processing (<NUM>), the CPU <NUM> obtains the temperature data from the temperature sensor <NUM> before the measuring device <NUM> starts the measurement of the acceleration and the angle. The CPU <NUM> uses the temperature measured by the temperature sensor <NUM> to determine whether abnormal heat is generated in the first bearing <NUM>. When the temperature measured by the temperature sensor <NUM> is equal to or higher than a predetermined value, the CPU <NUM> determines that an abnormal situation has occurred, and sends a signal, which indicates the abnormal heat generation or the abnormal situation, to the gear failure determining device <NUM>. Upon receiving such signal, the gear failure determining device <NUM> displays a message, which indicates the abnormal heat generation, on the display <NUM> of the device <NUM>. The CPU <NUM> also uses the temperature measured by the temperature sensor <NUM> to amend or correct the angle measured by the angle sensor <NUM>. Because the angle sensor <NUM> is a magnetic sensor, the temperature may influence the magnetism, and such influence may cause the malfunctioning of the angle sensor <NUM> such that the angle data indicated by the angle sensor <NUM> may include a certain error. The possible measurement errors of the angle sensor <NUM> may be obtained by experiments in advance at various temperatures, and an amendment table may be prepared in advance to compensate for the measurement errors. Then, the CPU <NUM> uses the amendment table to amend the measured temperature. In the processing (<NUM>), the CPU <NUM> performs the programming to the DMA controller <NUM>. Specifically, the CPU <NUM> performs the programming by allowing the DMA controller <NUM> to obtain the measurement data from the acceleration sensor <NUM> and the angle sensor <NUM> upon receiving the INT signal (i.e., the trigger signal) from the acceleration sensor <NUM>, and store the measurement data into the external memory <NUM>. In the processing (<NUM>), the CPU <NUM> activates (sets) the wake-up timer to count the time up to the predetermined measurement time. The "Measurement Start Delay" is approximately <NUM>, for example. After the three processing of the "Measurement Start Delay" time, the CPU <NUM> enters a sleep state. The measurement of the acceleration and the angle is carried out by necessary minimum functional elements/blocks, including the DMA controller <NUM>, the acceleration sensor <NUM>, and the angle sensor <NUM>, while the CPU <NUM> is in the sleep state. The measurement of the acceleration and the angle ends when the number of the measured data (acceleration data and the angle data) reaches a predetermined value or the time set to the wake-up timer (time-out time) is reached. When the measurement of the acceleration and the angle ends, the CPU <NUM> exits from the sleep state and wakes up. In this manner, the necessary minimum elements are only activated during the measurement of the acceleration and the angle. Thus, the measuring device <NUM> can operate with small electricity.

"Data Transfer Time" is time necessary for the measuring device <NUM> to transfer the data (pairs of measurement values of the acceleration sensor and the angle sensor) to the gear failure determining device <NUM> from the measuring device <NUM>. "Data Transfer Time" is, for example, between two seconds and three seconds. The time from "Power-On" to the end of "Data Transfer Time" in <FIG> is the time for one operation of the measuring device <NUM>.

<FIG> shows the pulse (angle measurement value) generated by the angle sensor <NUM>. The angle measurement value (pulse) is sent to the external memory <NUM> from the angle sensor <NUM>, and stored in the external memory <NUM>. The angle sensor <NUM> detects (measures) the angular position of the first gear <NUM> during the predetermined measurement time. The pulse (waveform) of the angle sensor <NUM> delays from the pulse of the acceleration sensor <NUM> by "DMA Delay" and stored in the external memory <NUM>. Theoretically, the measurement value of the acceleration sensor <NUM> and the measurement value of the angle sensor <NUM> are simultaneously sent to the external memory <NUM> by DMA (this is referred to as "sampling") by using the INT signal as a mutual trigger. In reality, however, there is a nanosecond-order difference between the sending of the measurement value of the acceleration sensor <NUM> and the sending of the measurement value of the angle sensor <NUM>, and this difference is represented by "DMA Delay" in <FIG>.

<FIG> shows the updating period (sampling period) of the measurement value of the acceleration sensor <NUM> and the measurement value of the angle sensor <NUM>. In this embodiment, as shown in <FIG>, the update timing (sampling timing) for the measurement value of the acceleration sensor <NUM> is synchronous with the update timing (sampling timing) for the measurement value of the angle sensor <NUM>. In other words, the update timing of the acceleration sensor <NUM> coincides with the update timing of the angle sensor <NUM>. The measurement value of the acceleration sensor <NUM> and the measurement value of the angle sensor <NUM> are stored in the external memory <NUM> in a synchronized manner (i.e., sharing the same time base or sharing at least one time base). For example, a first pair of the acceleration sensor's output and the angle sensor's output is sent to the external memory <NUM> from the acceleration sensor <NUM> and the angle sensor <NUM> by DMA. Thus, it is possible to obtain the measurement data (the acceleration data and the angle data) in the paired form (in the one-to-one relationship sharing the same time base). The time-synchronous angle and acceleration measurements are performed in this manner. It should be noted that the sampling frequency of the acceleration sensor <NUM> (ODR) is selected, for example, between <NUM> and <NUM> in advance.

Upon finishing one operation, the measuring device <NUM> starts a next operation (second operation). Specifically, the measuring device <NUM> waits for the elapse of the "Interval Wait," initializes the angle sensor <NUM> and starts the measurement. During the "Interval Wait," the power management IC <NUM> feeds the electricity to the sensors. Upon sending the measurement data to the gear failure determining device <NUM>, the second operation of the measuring device <NUM> is complete.

<FIG> shows a flowchart to describe the behavior of the measuring device <NUM> and the processing carried out by the measuring device <NUM>. It should be assumed that the electricity is already fed to the measuring device <NUM> (i.e., "Power-On" in <FIG> is carried out), and the BLE communication is already established between the measuring device <NUM> and the gear failure determining device <NUM> (i.e., "Pairing Completed" in <FIG>). In <FIG>, "S" stands for step.

In S1, the measuring device <NUM> determines whether the "Interval Wait" (<FIG>) has passed or not. The "Interval Wait" is, for example, thirty seconds. If the determination result of S1 is Yes, the processing goes to S2. If the determination result of S1 is No, S1 is repeated.

In S2, the measuring device <NUM> determines whether the Z-phase detector <NUM> has detected the Z-phase magnet <NUM> (<FIG>). If the determination result of S2 is Yes, the processing goes to S3. If the determination result of S2 is No, S2 is repeated.

In S3, the measuring device <NUM> activates the angle sensor <NUM> (performs the initialization). This is performed in the "Angle Initialization Wait" in <FIG>. The "Angle Initialization Wait" is, for example, <NUM>. When the "Angle Initialization Wait" has passed, the processing proceeds to S4.

In S4, the measuring device <NUM> determines whether the Z-phase detector <NUM> has detected the Z-phase magnet <NUM> again after S3. If the determination result of S4 is Yes, the processing proceeds to S5. Specifically, if the Z-phase detector <NUM> detected the Z-phase magnet <NUM> after the initialization of the angle sensor <NUM>, the processing goes to S5. If the determination result of S4 is No, S4 is repeated.

In S5, the acceleration sensor <NUM> and the angle sensor <NUM> start the measurement, and the measurement data of the acceleration sensor <NUM> (<FIG>) and the measurement data of the angle sensor <NUM> (<FIG>) are synchronously stored in the external memory <NUM> by DMA.

In S6, the measuring device <NUM> transfers the measurement data of the acceleration sensor <NUM> and the angle sensor <NUM> to the gear failure determining device <NUM> through the BLE communication. After the data transfer, the processing returns to S1.

As described above, the single operation of the measuring device <NUM> is performed by the processing from S1 to S6.

Now, a general principle of the gear failure detection of this embodiment will be described. Specifically, the processing of the gear failure determining device <NUM> that receives the measurement data of the acceleration sensor <NUM> and the angle sensor <NUM> from the measuring device <NUM> will be described. Referring first to <FIG>, described is how to obtain an acceleration curve for each of the teeth of the first gear. For the sake of description, the first gear <NUM> is assumed to have three teeth X, Y and Z, as shown in <FIG>. The second gear <NUM> that meshes with the first gear <NUM> is assumed to have four or more teeth.

<FIG> shows an acceleration curve when the first gear <NUM> has the three teeth X, Y and Z. The vertical axis indicates the measurement value of the acceleration sensor <NUM> (<FIG>), and the horizontal axis indicates the measurement value of the angle sensor <NUM> (<FIG>). As the first gear <NUM> meshes with the second gear <NUM> and the first gear <NUM> rotates <NUM> degrees, the tooth X of the first gear <NUM> contacts a corresponding tooth of the second gear, the tooth Y of the first gear <NUM> contacts a next tooth of the second gear, and then the tooth Z of the first gear <NUM> contacts a subsequent tooth of the second gear. Thus, as shown in <FIG>, the measurement data of the acceleration sensor <NUM> is obtained in series for the vibration of the tooth X, the vibration of the tooth Y and the vibration of the tooth Z. As the first gear <NUM> rotates another <NUM> degrees, the tooth X contacts a fourth teeth of the second gear.

After obtaining the acceleration curve shown in <FIG>, i.e., the waveform generated by the acceleration sensor <NUM>, the gear failure determining device <NUM> collects (extracts and combines) the curve segments for the tooth X to make a per-tooth curve R1 for the tooth X, collects the curve segments for the tooth Y to make a per-tooth curve R2 for the tooth Y, and collects the curve segments for the tooth Z to make a per-tooth curve R3 for the tooth Z, as shown in <FIG>. The per-tooth curve R1 of <FIG> is formed by connecting in series the curve segments of the angular sections P1, P4, P7 (not shown) and P10 (not shown) of <FIG>. How many curve segments are connected in series to make the per-tooth curve R1 depends upon an amount of the measurement data received from the measuring device <NUM>.

Similarly, the per-tooth curve R2 is formed by connecting in series the curve segments of the angular sections P2, P5 (not shown), P8 (not shown) and P11 (not shown) of <FIG>.

Similarly, the per-tooth curve R3 is formed by connecting in series the curve segments of the angular sections P3, P6 (not shown), P9 (not shown) and P12 (not shown) of <FIG>.

In this manner, it is possible to obtain the three acceleration-angle curves R1, R2 and R3 for the three teeth X, Y and Z, respectively, in this embodiment.

Now, the defect detection (failure detection) carried out by the gear failure determining device <NUM> will be described with reference to <FIG>. It is assumed here that the first gear <NUM> has twenty-two teeth in order to consider a gear in a real world. The gear failure detection uses a Per-Tooth method to find gear failure on a tooth-by-tooth basis in this embodiment. The Per-Tooth method uses tooth-specific vibration energy derived from the acceleration data (will be described).

The gear failure determining device <NUM> receives the measurement values a(t) of the acceleration sensor <NUM> and the measurement values ϕ(t) of the angle sensor <NUM> in the form of time-synchronous angle-acceleration pairs from the measuring device <NUM>, and stores the measurement values a(t) and ϕ(t) in the storage unit <NUM> together with the time t (<NUM> in <FIG>).

A user of the gear failure determining device <NUM> enters a number of the teeth of the first gear <NUM> by using the input unit <NUM> (<NUM> in <FIG>). It should be noted that the user may also enter an angle offset value of the first gear <NUM> although this is not mandatory. The angle offset value of the first gear <NUM> indicates at which absolute angular position a particular tooth of the first gear <NUM> is present, and can be used as a calibration value to know which tooth is exactly damaged. The angle offset value will be described with reference to <FIG>.

The gear failure determining device <NUM> prepares an angle-tooth map (<NUM> in <FIG>). <FIG> shows an example of the angle-tooth map, and <FIG> shows another example of the angle-tooth map. In <FIG>, the vertical axis of the map indicates the twenty-two teeth of the first gear <NUM>, and the horizontal axis indicates the angle of the first shaft 24a. The horizontal axis indicates a relative value of the shaft angle. <FIG> shows a map prepared without an angle offset value. When the angle offset value is not used, any tooth that is present at the top position of the first shaft 24a in the map preparation process is considered as the #<NUM> tooth. Thus, an unknown tooth is referred to as the #<NUM> tooth in the example of <FIG>.

In <FIG>, the vertical axis of the map indicates the twenty-two teeth of the first gear <NUM>, and the horizontal axis indicates the absolute angle of the first shaft 24a. <FIG> shows the map prepared with the angle offset value. In the map preparation process, all the teeth of the first gear <NUM> is numbered as #<NUM> to #<NUM> beforehand by, for example, indicia. In the example of <FIG>, the tooth present at the <NUM>-degree position of the first shaft 24a in the map preparation process is #<NUM> tooth. Thus, the #<NUM> tooth starts meshing with teeth of the second gear <NUM> at the angle of <NUM> degrees (absolute angle). In the case of <FIG>, therefore, the user enters the angle offset value of <NUM> degrees into the gear failure determining device <NUM> (<NUM> in <FIG>).

The map in each of <FIG> has twenty-two line segments S. Because one rotation of the gear (or the shaft) is <NUM> degrees and the first gear <NUM> has twenty-two teeth, each line segment S represents approximately <NUM> degrees (<NUM> divided by <NUM> is approximately <NUM>). In each of <FIG>, one tooth is specified as the shaft angle is specified. Thus, each of <FIG> shows the mapping function. Therefore, the processing <NUM> generates the mapping function. The gear failure determining device <NUM> may use the map shown in <FIG> or the map shown in <FIG>. If the gear failure detennining device <NUM> uses the map shown in <FIG>, the gear failure determining device <NUM> does not know which tooth of the first gear <NUM> is the #<NUM> tooth of the map shown in <FIG>. However, the gear failure determining device <NUM> can determine whether the gear has a damaged tooth (e.g., the #<NUM> tooth). If the gear failure determining device <NUM> uses the map shown in <FIG>, the gear failure determining device <NUM> can know which tooth of the first gear <NUM> is the #<NUM> tooth of the map shown in <FIG>, and can also determine whether the #<NUM> tooth is damaged or not. In the following description, the gear failure determining device <NUM> uses the map shown in <FIG>.

After generating the angle-tooth map of <FIG> (angle-tooth mapping function), the gear failure determining device <NUM> calculates a per-tooth mean acceleration signal power (<NUM> in <FIG>). The mean acceleration signal power will simply be referred to as acceleration signal power. The information to be used in the calculation of the acceleration signal power includes the measurement data received from the measuring device <NUM> and the map shown in <FIG>. As indicated by <NUM>, the measurement data received from the measuring device <NUM> is the time-synchronous angle and acceleration measurements, i.e., the measured acceleration a(t), the angle position information ϕ(t) and the time t. The acceleration signal power of the #k tooth of the first gear <NUM> is calculated with the equation (<NUM>) below. <MAT> <MAT> <MAT>.

In the equation (<NUM>), P represents the acceleration signal power, and s(i) represents the measured acceleration. Tooth (ϕ(i)) indicates the tooth number in the mapping function at the angle position corresponding to the sampling number i. If the tooth number is not k, tooth (ϕ(i)) is not equal to k, and therefore s(ϕ(i)) becomes zero. If the tooth number is k, tooth (ϕ(i)) is equal to k, and therefore s(ϕ(i)) becomes the measured acceleration a(i). k indicates the number of sampled teeth that meet the condition (*).

The equation (<NUM>) calculates the sum of acceleration (sampled value) squared, and divided by the sampling number for each tooth (the #k tooth). Thus, the equation (<NUM>) provides the acceleration signal power for the #k tooth. This calculation is performed for all the teeth of the first gear <NUM>. Therefore, the equation (<NUM>) provides a list of twenty-two acceleration signal powers P. In other words, the processing <NUM> gives the twenty-two acceleration signal powers for the twenty-two teeth, respectively.

Reference numeral <NUM> in <FIG> shows the values used in the equation (<NUM>) for the respective teeth.

Upon finishing the calculation of the equation (<NUM>), the gear failure determining device <NUM> carries out the processing <NUM> in <FIG> to obtain relative power coefficients (relative signal power values). The relative signal power values can be used as damage indicators that indicate a degree of damage to the respective teeth. When two gears mesh each other, vibrations occur even if the teeth of the gears have no damages. In order to easily distinguish the vibrations transmitted from damaged teeth from the vibrations transmitted from undamaged teeth, the processing <NUM> is performed in this embodiment. Specifically, the processing <NUM> utilizes the equation (<NUM>) and the equation (<NUM>).

Firstly, the equation (<NUM>) is used to calculate the mean value of all per-tooth signal power values.

Subsequently, the equation (<NUM>) is used to calculate a relative power coefficient for each tooth.

Characteristic values of the relative signal power coefficients Prel(k) are:.

By normalizing the average vibration baseline to a value of zero, the value of Prcl(k) allows for simple normality (damaged or nondamaged) assessment of each tooth. The assessment may be made by manual and/or automated evaluation. In the automated evaluation, a threshold value may be set, and the gear failure determining device <NUM> may provide the "damaged" assessment when the value of Prel(k) is equal to or greater than the threshold value.

<FIG> shows the result of experiment, which was carried out by the inventors, to confirm the feasibility of the above-described embodiment, as a proof of concept. The first gear <NUM> was a helical gear, and the number of teeth is twenty-two. Prior to the experiment, it was confirmed that the second gear <NUM> that meshed with the first gear <NUM> had no damaged teeth. The vertical axis of the graph shown in <FIG> indicates the relative signal power coefficient Prel(k), and the horizontal axis indicates the tooth #. The title of <FIG> contains the following information: The data was evaluated according to the algorithm described in the paragraphs [<NUM>] to [<NUM>] of this specification ("Bearing std eval"). It was evaluated from the 3D sum vector (components made zero-mean before calculation of vector sum) of the triaxial acceleration data acquired by the measuring device <NUM> ("sum vec, comps <NUM>-mean"). A maximum Prel of <NUM> was reached, at an angular window shift position of <NUM>/<NUM> the angular span of one tooth. This position was identified by doing the per-tooth evaluation for all <NUM> shift positions and then picking the one that yields the maximum Prel value. The sampling frequency of both acceleration and angular data was set to <NUM>, with an acceleration range of +/- <NUM>. The speed of the shaft during this test was <NUM> /min, with a nominal pinion torque of <NUM>. If the threshold Prel(k) is set to two, the gear failure determining device <NUM> determines that the #<NUM> tooth (k=<NUM>) is damaged. In this manner, this embodiment allows for per-tooth evaluation of acceleration signal power as indicator for individual teeth's condition. This evaluation is done by sampling both acceleration and angle data periodically and simultaneously.

As described above, the measuring device <NUM> of this embodiment (the acceleration sensor <NUM>, the angle sensor <NUM>, the circuit substrate group <NUM> and other components) is housed in the first gear <NUM>. In addition, the electricity consumed by the measuring device <NUM> is generated as the first bearing <NUM> rotates, i.e., the measuring device <NUM> generates the electricity and feeds it to the measuring device <NUM>). Accordingly, the measuring device <NUM> can have a small size, and in turn the gear failure detecting system <NUM> can have a small size as a whole. Further, the power saving of the gear failure detecting system <NUM> is achieved.

As described above, the gear failure detecting system <NUM> includes the measuring device <NUM> that has a self-power generation mechanism and a wireless communication function, and utilizes a very small amount of electricity generated by the self-power generation mechanism to obtain and send the acceleration data and the associated angle data of the teeth of the first gear <NUM> to the gear failure determining device <NUM> by wireless communication.

The measuring device <NUM> obtains the measurement data (the acceleration data of the first gear <NUM> that is time-synchronous with the angle data of the first gear <NUM>). Then, the external memory <NUM> stores the measurement data (the acceleration data and the angle data on the one-to-one basis). Because the acceleration data is associated with the angle data on the one-to-one basis, it is possible to appropriately determine what vibrations are occurring on which teeth (or at which angle) while the first gear <NUM> is rotating, and accurately specify the location of the failure (the damaged tooth).

In this embodiment, the acceleration data and the angle data are obtained in the paired form (one by one), and the absolute angle data is available at the same sampling rate as the acceleration data. Thus, it is possible to ignore irregularities in the rotating speed of the first gear <NUM>.

The acceleration sensor <NUM>, the temperature sensor <NUM> and the angle sensor <NUM> are electrically coupled to the microcomputer <NUM> so that the measuring device <NUM> can have a small size. Thus, it is possible to house the measuring device <NUM> in the cover <NUM> even if the cover <NUM> is small.

The measurement data obtained from the acceleration sensor <NUM> and the angle sensor <NUM> are stored in the external memory <NUM> without any processing, i.e., the raw data of the measurements are stored in the external memory <NUM>. Thus, the measuring device <NUM> does not have perform data processing (e.g., converting a hexadecimal number to a decimal number) at the time of data storage. Accordingly, high-speed data storage is possible. Because such data processing is unnecessary, any load associated with such data processing would not be exerted on the measuring device <NUM>. Therefore, it is possible to keep the electricity consumption of the measuring device <NUM> to a low level.

Because the measuring device <NUM> stores the measurement data in the external memory <NUM> by DMA or the DMA controller <NUM>, loads exerted on the CPU <NUM> will be reduced as compared to a case where the data storage into the external memory <NUM> should be performed by the CPU <NUM>.

Therefore, the measuring device <NUM> of this embodiment can use an inexpensive MEMS sensor as the acceleration sensor. Also, the microcomputer <NUM> can be a low power consumption device.

The gear failure detecting system <NUM> of this embodiment uses the rolling bearing <NUM> (i.e., self-powered, sensor-equipped bearing device) to monitor the conditions of the gearbox <NUM> and evaluate the signals for the respective teeth of the first gear <NUM>.

The measuring device <NUM> has the acceleration sensor <NUM> located in the vicinity of the point of vibration excitation (point of the gear mesh). In other words, the physical proximity of the point of vibration picking-up to the point of vibration excitation is realized by the measuring device <NUM>. Thus, it is possible to obtain a signal having a high S/N ratio, as compared to the arrangement in which the vibration sensor is attached to the outer surface of the housing <NUM> of the gearbox <NUM>. Accordingly, it is possible to make a reliable gear evaluation even if an inexpensive acceleration sensor, such as MEMS acceleration sensor, is used.

The Per-Tooth method used in the algorithms for the gear failure determination (evaluation) in this embodiment has the following advantages.

It is possible to specify a damaged tooth among a plurality of teeth. The gear defect evaluation can be carried out with low computing cost. It is possible to prepare an evaluation result from the measurement data, and determine the gear defect or abnormality from the evaluation result, without comparing the measurement data to vibration data (acceleration data) of a normal gear. Before this invention has been made, the established theory requires the comparison of the measurement data to the vibration data of a normal gear when the gear failure diagnosis is carried out.

The gear defect evaluation can be carried out with low computing cost because the determining device <NUM> provides the evaluation result (or the failure diagnosis) with four arithmetic operations. The determining device <NUM> does not require high computing cost, such as FFT (Fast Fourier Transform). The processing shown in <FIG> also requires low computing power as compared to conventional time-frequency-domain methods, because the processing of <FIG> requires only few mathematical operations.

Because the acceleration sensor <NUM> is not attached to the outer surface of the housing <NUM> of gearbox <NUM>, the gear failure detecting system <NUM> can be employed regardless of the shape of the housing <NUM>, and the shape of the housing <NUM> does not influence the accuracy of the gear defect diagnosis.

It is possible to specify a damaged tooth among a plurality of teeth without knowing a behavior of the gear in a normal condition.

If the acceleration sensor is attached to the outer surface of the housing <NUM> of the gearbox <NUM>, the housing <NUM> exists between the point of the gear mesh and the acceleration sensor, and therefore an expensive and high-performance sensor is required to eliminate (compensate for) the adverse influence of the vibration transfer path. In this embodiment, on the other hand, the acceleration sensor <NUM> is included in the first bearing <NUM>, the acceleration sensor <NUM> can measure the vibrations of the first gear <NUM> in the vicinity of the first gear <NUM>. Thus, the acceleration sensor <NUM> is not influenced by the vibration transfer path very much, and does not have to be an expensive and high-performance sensor. In other words, the acceleration sensor <NUM> can be an inexpensive sensor. Even if the inexpensive acceleration sensor is used, the acceleration senor can accurately detect the vibration of the first gear <NUM> and the gear failure determining device <NUM> can provide an accurate diagnosis result.

When the acceleration sensor <NUM> included in the first bearing <NUM> is the MEMS acceleration sensor, the measuring device <NUM> (or the gear failure system <NUM>) has advantages in terms of cost and sensor position.

The acceleration sensor <NUM> is attached to the cover <NUM>, and the cover <NUM> is attached to the outer ring of the first bearing <NUM>. The outer ring of the first bearing <NUM> is the nearest non-rotating machine element to the point of gear mesh. Thus, the vibration detected by the acceleration sensor <NUM> is, in effect, the vibration generated by the gear mesh. Because the acceleration sensor <NUM> is located near the point of vibration excitation, the measurement data of the acceleration sensor <NUM> is not influenced by the vibration transfer path such as the housing <NUM>.

As shown in <FIG>, the angle-tooth map with the angle offset value is used in this embodiment. When the angle offset value is used, the per-tooth signal power split points are less arbitrary. Thus, the vibration power induced by the damaged tooth can be resolved more precisely to one tooth sub signal, as compared to the case where the map of <FIG> is used. In other words, when the three per-tooth curves R1, R2 and R3 of <FIG> are created from the single curve of <FIG>, the divisions P1, P2, P3, P4,. are made precisely.

It should be noted that although the gear failure determining device <NUM> is a personal computer in the above-described embodiment, the gear failure determining device <NUM> may be a tablet computer, a smartphone (cellular phone) or a wearable watch.

In the above-described embodiment, the measuring device <NUM> sends the measurement values to the gear failure determining device <NUM> without any processing. It should be noted, however, that part of the processing executed by the gear failure determining device <NUM> may be executed by the measuring device <NUM>. In other words, the measuring device <NUM> may have part of the functions of the gear failure determining device <NUM>. For example, the processing shown in <FIG> may be executed by the microcomputer <NUM>. The processing shown in <FIG> only involves a small amount of calculation, and therefore an amount of electric power to be consumed by such processing is small. Therefore, an electric power generated by the first bearing <NUM> is enough for the microcomputer <NUM> to operate. This modification may be referred to as "on-bearing data processing. " This massively reduces the amount of data to be transferred from the measuring device <NUM> to the gear failure determining device <NUM>, as thousands of angle and accelerations samples per measurement are condensed into one scalar value per tooth this way.

The measurement time may be changed depending upon a capacity of the memory unit <NUM> and an amount of electric power to be consumed. The temperature sensor <NUM> may be dispensed with.

In <FIG>, a protection circuit may be provided between the smoothing circuit <NUM> and the power management IC <NUM>. In <FIG>, the power generation, which is based on the electromagnetic induction, takes place as the magnet M rotates relative to the coil C. Thus, an electromotive force increases in proportion to the increasing rotation speed of the magnet M. If any mechanical element or device, which is connected to the first shaft 24a, breaks down, and the first shaft 24a rotates at an extremely high speed, the electromotive force of the magnet M and the coil C increases correspondingly. As a result, a voltage that is high beyond expectations is introduced to the power management IC <NUM> and may damage the measuring device <NUM>. In order to avoid such damage of the measuring device <NUM>, the protection circuit may be provided between the smoothing circuit <NUM> and the power management IC <NUM>. This protection circuit is an input-protection circuit, and may be selected from various kinds of circuits. For example, a Zener diode may be used as the protection circuit, and disposed between the smoothing circuit <NUM> and the power management IC <NUM>. The Zener diode converts the input voltage to heat when the input voltage is higher than a predetermined value. By converting the voltage to heat, the Zener diode consumes the excessive voltage and protects the measuring device <NUM>.

Claim 1:
A measuring device (<NUM>) attachable to one side face of a bearing part, the bearing part being adapted to support a shaft (24a) having a gear (<NUM>) thereon such that the shaft can rotate, the measuring device comprising:
a cover (<NUM>) attached to an outer ring of the bearing part to cover the side face of the bearing part;
an acceleration sensor (<NUM>) provided on an inner face of the cover to measure vibrations of the bearing part;
an angle sensor (<NUM>) provided on the inner face of the cover to measure an angle between the outer ring of the bearing part and an inner ring of the bearing part; and
a data collecting unit (<NUM>) provided on the inner face of the cover,
characterized in that
the data collecting unit (<NUM>) is configured to obtain the acceleration measured by the acceleration sensor and the angle measured by the angle sensor in a linked manner, sharing one common time base, in the form of time-synchronous angle-acceleration pairs.