Condition monitoring method and system

Abstract

A condition monitoring system for determining the presence of a change in moisture content in a fat. The system includes a sensor electrode disposed within a space in which the grease is located. Suitably, the electrode is a plate having a surface area that generates capacitance C. The resistor R is combined with the resistor R to generate an RC circuit. The system senses the RC circuit. The dielectric constant of the monitored grease varies according to the moisture content of the grease. The change in dielectric constant will change RC, which is then sensed by the system. Analysis of RC changes will determine whether there is a change in the water content level in the monitored fat.

Description

TECHNICAL FIELD

[0001] The present invention relates to condition monitoring, more in particular to detecting the presence of water in (lubricating) grease, especially in grease lubricated machine parts, such as rolling bearings. BACKGROUND

[0002] The reliable operation of rotating machine systems highly depends on proper lubrication. The condition of the lubricant is of great importance, especially for systems designed for long time operation with little or no need for maintenance. The presence of contaminants, such as water or particles, can cause wear and damage of the moving parts of the system, and even cause a catastrophic failure of the entire machine system prematurely. The lubricant of a machine system can be mainly oil or grease based. Monitoring the condition of the oil in an oil lubricated system can be achieved by circulating the oil past a sensor and can also be provided with a filter for removing contaminants. However, closed systems, such as bearings, are generally filled with a suitable (lubricating) grease. The grease is retained within the bearing or bearing housing by means of a seal. The seal also protects against the ingress of contaminants, such as water and particles. The seal can break or leak, allowing water to enter the bearing or bearing housing. The ingress of water reduces the lubricating ability of the grease and also increases the chance of corrosion damage of the bearing elements. It is therefore desirable to monitor the grease of a closed machine system, especially to monitor the water content of the grease. It is not possible to circulate the grease past a sensor without facing extreme difficulties and expenses. There still seems to be room for improvement in this respect. SUMMARY

[0003] It is an object of the present invention to define a method and apparatus for detecting changes in the water content of grease, thereby enabling monitoring of the grease within a machine system.

[0004] According to the present invention, the above objective is achieved by: a condition monitoring system that determines a change in the water content level of a (lubricating) grease. The system includes a sensor unit and an analysis unit. The sensor unit generates an output signal related to the water content level of the monitored grease. The analysis unit determines (or judges) that a change in the water content level of the monitored grease exists based on the output signal. According to the present invention, the sensor unit includes: a control unit, conductive electrodes (such as plates), an output port controllable by the control unit, and an input port readable by the control unit. The conductive sensor electrodes are intended to be mounted within a space containing the (lubricating) grease to be monitored, for example, within a bearing housing. The sensor electrodes may be, for example, plates with suitable shapes and geometries, such as circular, square, rectangular, irregular shapes, or any other shape having surface areas that can be flat or curved along one or more axes. The electrodes may be circles with a diameter of one centimeter or partially or completely surrounding a band, for example, a bearing. The controllable output port is coupled to the electrodes via a resistor. The readable input port is directly coupled to the sensor electrodes. The control unit switches the output port between two different voltage levels (high voltage level and low voltage level). This is done in such a way that the output port is switched to the level opposite to the level determined by the control unit to be present at the input port. That is, if the control unit determines that the input port is at a low voltage level, the control unit sets the output port to a high voltage level, and vice versa. The control unit also generates an output signal obtained by switching the output port, which is the state of the output port, a pulse signal that varies in frequency and cycle period according to the water content of the lipid. The output signal can be a direct pulse signal, a buffered control signal from the control unit switching the output port, a physical signal or simply a software instruction to the output port, or a representation of a pulse signal or control signal, all depending on how further processing is performed. The analysis unit includes a frequency and / or cycle period determination unit and a comparison unit. The frequency and / or cycle period determination unit (for) determining the frequency and / or cycle period of the output signal. The cycle period is the reciprocal of the frequency. The comparison unit compares the currently determined frequency and / or cycle period of the output signal with the previously determined frequency and / or cycle period of the output signal, thereby indicating whether there is a change in the level of water in the monitored lipid.

[0005] Appropriately, the comparison unit determines (or judges) that the water content is increasing when the frequency of the output signal decreases and / or the cycle period of the output signal increases.

[0006] Appropriately, the comparison unit determines that the water content is decreasing when the frequency of the output signal increases and / or the cycle period of the output signal decreases.

[0007] Appropriately, the comparison unit needs to consider the predetermined frequency or cycle difference between the currently determined frequency or cycle and the previously determined frequency or cycle within a predetermined time period before considering the difference (to determine whether there is a change in the level of water in the monitored lipid).

[0008] Appropriately, peaks in frequency and / or cycle difference occurring during periods shorter than the predetermined time period are not considered for determining whether there is a change in the level of water in the monitored lipid.

[0009] Advantageously, the frequency determination unit determines the initial frequency and / or cycle period of the output signal as the calibration frequency and / or cycle period.

[0010] Different additional enhancements to the condition monitoring system according to the first embodiment of the present invention can be combined in any desired manner, as long as no conflicting features are combined.

[0011] The first implementation is advantageous for implementing improvements as an extension of an existing condition monitoring system or for installing a new device with a standard condition monitoring system that includes digital input / output ports. Besides a resistor and sensor electrodes, what is required is: a free input port, a free output port, and some reprogramming of the system.

[0012] According to the present invention, the above objective is further achieved by: a condition monitoring system for determining a change in the water content level of (lubricating) grease, the condition monitoring system comprising a sensor unit and an analysis unit. The sensor unit generates an output signal related to the water content level of the monitored grease. The analysis unit determines, based on the output signal, that a change in the water content level of the monitored grease exists. According to the present invention, the sensor unit comprises conductive sensor electrodes, a first port and a second port, and an RC oscillator unit. The sensor electrode may, for example, be a plate having a suitable shape and geometry, such as circular, square, rectangular, irregular shape, or any other shape having a surface area that can be flat or curved along one or more axes. The electrode may be a circle with a diameter of one centimeter or a band that partially or completely surrounds, for example, a bearing. The conductive sensor electrode is intended to be mounted within a space including the grease to be monitored. The first port is coupled to the sensor electrode via a resistor. The second port is directly coupled to the sensor electrode. The sensor electrode and the resistor constitute the RC portion of the RC oscillator unit, the remainder of which is coupled to the first and second ports. The oscillator unit generates an output signal. The analysis unit includes a frequency and / or cycle period determination unit and a comparison unit. The frequency and / or cycle period determination unit determines the frequency and / or cycle period of the output signal. The comparison unit compares the currently determined frequency and / or cycle period of the output signal with the previously determined frequency and / or cycle period of the output signal, thereby indicating whether there is a change in the level of water in the monitored lipid.

[0013] Appropriately, the comparison unit determines that the water content is increasing when the frequency of the output signal decreases and / or the cycle period of the output signal increases.

[0014] Appropriately, the comparison unit determines that the water content is decreasing when the frequency of the output signal increases and / or the cycle period of the output signal decreases.

[0015] Appropriately, the comparison unit needs to consider the difference between the currently determined frequency or cycle period and the previously determined frequency or cycle period within a predetermined time period before considering the difference to determine whether there is a change in the level of water in the monitored lipid.

[0016] Appropriately, peaks in frequency and / or cycle difference occurring during periods shorter than the predetermined time period are not considered for determining whether there is a change in the level of water in the monitored lipid.

[0017] Advantageously, the frequency determination unit determines the initial frequency and / or cycle period of the output signal as the calibration frequency and / or cycle period.

[0018] Different additional improvements to the condition monitoring system according to the second embodiment of the present invention can be combined in any desired manner, as long as no conflicting features are combined.

[0019] According to the present invention, the above objective is further achieved by: a condition monitoring system that determines whether a change in the water content of a (lubricating) grease exists. The system includes a sensor electrode placed within the space where the (lubricating) grease is located. Suitably, the electrode is a plate having a surface area that generates a capacitance C. This, combined with a resistor R, creates an RC circuit. The system senses the RC circuit. The dielectric constant of the monitored grease varies according to its water content. The change in dielectric constant alters the RC circuit, which is then sensed by the system. Analysis of the change in the RC circuit determines whether a change in the water content level of the monitored (lubricating) grease exists.

[0020] Solutions utilizing sensors that measure the electrical properties of lubricants (e.g., capacitance and / or inductance) can also be considered. However, these solutions are best suited for oil-lubricated systems where the lubricant can be pumped to the sensor. However, installing these sensors would be very expensive, and more importantly, they are generally unusable for grease-lubricated components.

[0021] The key to the proposed method and apparatus lies in its simplicity, which leads to low cost and ease of installation. The proposed measurement technique utilizing digital measurement ports is also robust and insensitive to interference during measurement.

[0022] For large-scale industrial installations, sensors need to be inexpensive, reliable, robust, easy to install, and replaceable if necessary. These characteristics are often far more important than the maximum possible resolution of the measurement. In the case of water detection, for example in grease-lubricated bearings, the most critical industrial requirement is the ease of detecting high water content (e.g., in many cases, compared to accurately measuring low water content (which is only harmful to bearings during long-term operation), which can lead to rapid bearing failure due to seal rupture / leakage). The proposed sensor technology meets all of the above requirements and is also easy to use, communicating with existing SKF IMx (RTM) hardware / software or other condition monitoring equipment. This makes it easy to install at low cost within existing SKF or other brand systems while still addressing the most critical issues: detecting when water content is dangerously high and grease needs to be replaced, and when seals may need to be inspected and / or replaced.

[0023] Other advantages of the invention will become apparent from the detailed description. Attached Figure Description

[0024] The invention will now be described in more detail with reference to the accompanying drawings for illustrative purposes and not in any way limiting, in which:

[0025] Figure 1 A condition monitoring system according to the present invention is shown;

[0026] Figure 2 A flowchart of the frequency determination unit according to the present invention is shown;

[0027] Figure 3 A flowchart of the analysis unit according to the present invention is shown;

[0028] Figure 4 An example of cyclic measurement / generation related to lipid water content is shown.

[0029] Explanation of reference numerals in the attached figures

[0030] 100 Rolling Seat

[0031] 110 rolling bearing

[0032] 120 sensor electrodes, such as plates

[0033] 125 charging and discharging resistor

[0034] 130 control unit

[0035] 132 Sensor Electrode Input

[0036] 134 sensor electrode output

[0037] 140 analysis units

[0038] 142 Signal output from control unit to analysis unit

[0039] 144 Analysis Output

[0040] 146 Condition monitoring system as part of an existing condition monitoring system or a dedicated condition monitoring system for water in liposomes.

[0041] 200 sets the output to a high output level.

[0042] Test 210 to see if the input is considered high (level); if not, continue testing.

[0043] 220 sets the output to a low output level.

[0044] Test 230 to see if the input is considered low (level); if not, continue testing.

[0045] 240 sets the output to a high output level.

[0046] 250 determines the frequency and / or cycle period for switching the output high / low, then returns to 210.

[0047] 300 Initialize the system, such as resetting variables, etc.

[0048] 310 obtains the initial frequency from the frequency output of the control unit.

[0049] 320 obtains the current frequency from the frequency output of the control unit.

[0050] 330. Check if there is a frequency change between the current frequency and the initial frequency. If not, return to 320.

[0051] 340. Analyze the changes, differences, and trends in frequency.

[0052] 350 Determines whether frequency changes need to be communicated; if not, returns to 320.

[0053] 360 communicates the change and other necessary actions, then returns to 320.

[0054] 400 shows a graph illustrating the relationship between the measured / generated cycle number and the water content in the lipid.

[0055] 410 Y-axis, representing the period being measured. The period shown is merely an example and will depend on the application and parameters, such as the measuring device; (lubricating) grease type; the geometry, dimensions, and location of the sensor plate; and the geometry and dimensions of the mount ( / housing).

[0056] 420X axis, representing the percentage of water content in the (lubricating) grease.

[0057] 452 Initial measurement / generation cycle, and reaching approximately 1% moisture content.

[0058] 454 Circulation cycle at 5% water content

[0059] 456 Cycle at 10% moisture content

[0060] The 460° curve fitting shows the linear relationship between water content and the measured / generated cycle period. Detailed Implementation

[0061] In order to clarify the method and apparatus according to the present invention, it will now be combined with Figures 1 to 4 Here are some examples of its use.

[0062] Figure 1A condition monitoring system 146 according to the invention is shown (as part of an existing condition monitoring system or a dedicated condition monitoring system for water in grease). The system includes: electrically conductive sensor electrodes 120 (such as plates having suitable shapes and geometries); charge / discharge resistors 125; an analysis unit 140; a control unit 130 having a signal output 142 to the analysis unit 140; an input port 132 coupled to the sensor electrodes; an output port 134 coupled to the sensor electrodes 120 via the charge / discharge resistor 125; and suitably including an analysis output 144. The sensor electrodes 120 are intended to be mounted close to a lubricant (grease), for example, within a rolling bearing housing 100 of a rolling bearing 110, such that the lubricant serves as the dielectric of the sensor electrodes 120.

[0063] The present invention is based on the following basic inventive idea: the dielectric constant and conductivity of the (lubricating) grease vary with its water content. If the (lubricating) grease creates a bridge between the sensor electrode 120 and a grounded object, the impedance of the (lubricating) grease with respect to its water content also comes into play.

[0064] According to a first embodiment of the present invention, the control unit 130 toggles the output voltage of the output port 134 based on a determined voltage at the input port 132. The output voltage toggles between a high output voltage (e.g., 5 volts) and a low output voltage (e.g., 0 volts). If the voltage present at the input port 132 is equal to or higher than a first predetermined voltage (e.g., 3.6 volts), the control unit 130 determines that a high voltage (e.g., 5 volts) is present at the input port 132. Conversely, if the voltage present at the input port 132 is equal to or lower than a second predetermined voltage (e.g., 0.8 volts), the control unit 130 determines that a low voltage (e.g., 0 volts) is present at the input port 132. The control unit 130 maintains the output voltage of the output port 134 opposite to the determined voltage at the input port 132. Therefore, the output port 134 charges and discharges the sensor electrode 120 through the charge / discharge resistor 125. Sensor electrode 120 represents a capacitance C related to the dielectric constant of the grease, creating an RC circuit that will change according to the dielectric constant (relative permittivity) around sensor electrode 120. Resistor 125 must be selected with regard to the size and arrangement of sensor electrode 120 and the desired RC value to give a satisfactory dry grease value and wet grease value for output 142. A suitable starting value for charge / discharge resistor 125 could be, for example, 1 MΩ. If output port 134 is set to a high output voltage, the voltage level at input port 132 will rise from a second predetermined voltage until it reaches a first predetermined voltage. This will cause control unit 130 to set output port 134 to a low voltage output, and then the voltage level at input port 132 will drop from the first predetermined voltage to the second predetermined voltage. The rise and fall times depend on the values ​​of R (resistor 125) and C (sensor electrode 120, which is affected by the dielectric constant of the grease). The combined time required for the voltage level at the input port to rise and fall will define the cycle period (the reciprocal of the frequency), which will indicate the moisture content of the (lubricating) grease. If a calibrated measurement is performed on dry grease (and possibly one or more greases) to define how the cycle period / frequency changes relative to the water content, then the absolute value of the water content / percentage in the grease can be determined.

[0065] In a second embodiment of the present invention, the control unit 130 is an RC oscillator, wherein the resistor 125 and the sensor electrode 120 form the RC circuit of the oscillator.

[0066] In the second embodiment, the output signal 142 is suitably the output of an oscillator having a frequency with a corresponding cycle period (which represents the water content of the fat and varies with the water content of the fat). In the first embodiment, the output signal 142 may be a voltage present at the output port 134, or be converted into a software variable representing the frequency and / or cycle period, or a scaled version of one or both of these (this is achieved, for example, by a control signal used by a control unit to control the output port, which may be a physical signal or instruction). This depends on whether the processing and comparison are implemented directly in hardware or in computer software. The output signal 142 will enter the analysis unit 140, which suitably includes a determination unit and a comparison unit. The determination unit will determine the frequency and / or cycle period of the output signal. This is saved as the currently determined frequency and / or cycle period. The comparison unit will then compare the currently determined frequency and / or cycle period with one or more previously determined frequencies and / or cycle periods. Through this comparison and possible further analysis, it is determined whether there has been a change in the water content of the monitored fat. The comparison unit will then output analysis output 144, which can be used by other parts of the condition monitoring system, for example, to generate an alarm.

[0067] Figure 2 A flowchart of a control unit according to a first embodiment of the present invention is shown. In a first step 200, the output port is set to a high voltage level. In a second step 210, a test is performed to check whether the input port is determined to have a high voltage level; if not, the process ( / method) continues to perform the test in the second step 210. When it is determined that the voltage level at the input port is a high voltage level, the process continues to a third step 220, in which the output port is set to a low voltage output level. Then, in a fourth step 230, a test is performed to check whether the input port is determined to be a low voltage level; if not, the process continues to perform the test in the fourth step 230. When it is determined that the voltage level at the input port is a low voltage level, the process continues to a fifth step 240, in which the output port is set to a high voltage level. Afterwards, in a sixth step 250, the frequency or cycle period for switching the output port between high and low voltage levels is determined, and then the process returns to the second step 210.

[0068] Figure 3A flowchart of the analysis unit according to the present invention is shown. In a suitable optional step 300, system initialization (such as resetting variables) occurs. Optional steps may include a calibration part, in which one or more frequency / cycle measurements are performed on a (lubricating) grease having a known water content. Calibration enables the determination of the absolute value of the water content in the grease. Then, in a first step 310, an initial frequency / cycle is obtained from the control unit. The initial frequency / cycle is stored as historical data. Then, in a second step 320, the current frequency / cycle is obtained from the control unit. In a third step 330, it is determined whether there is a change in frequency / cycle between the current frequency / cycle and the historical data; if not, the process returns to 320. If a change is determined to exist, the process continues to a fourth step 340, which analyzes the changes, differences, and trends in frequency / cycle using the current (data) and historical data. The current frequency / cycle is added to the historical data. In step 5, 350, it is determined whether the change in frequency / cycle period needs to be communicated as a change in the water content of the (lubricating) grease; if not, return to 320. In step 6, 360, this change and other necessary actions are communicated, and then return to 320.

[0069] Figure 4 Examples of cycle measurements / generation related to grease moisture content are illustrated. Figure 400 shows the relationship between the measured / generated cycle and the moisture content in the grease, where the Y-axis 410 represents the measured cycle. The cycle shown is merely a scaled example and will depend on the application and parameters such as the measuring device; grease type; geometry, size, and location of the sensor electrodes; and the geometry and size of the housing. The X-axis 420 represents the percentage of moisture content in the grease. Several points are shown in Figure 400. The initial measured / generated cycle 452 reaches approximately 1% moisture content, cycle 454 shows 5% moisture content, and cycle 456 shows 10% moisture content. Curve fitting 460 has also been performed, showing a relatively linear relationship between moisture content and the measured / generated cycle.

[0070] The present invention is not limited to the embodiments described above, but can be varied within the scope of the claims.

Claims

1. Condition monitoring system for determining a change in the water content level in grease in a sealed space in a grease-lubricated component, the condition monitoring system comprising: - a sensor unit generating an output signal related to the water content level of the monitored grease; - an analysis unit determining a change in the water content level in the monitored grease from the output signal; characterized in that, - the sensor unit comprises: - a conductive sensor electrode intended to be mounted in the sealed space in the grease-lubricated component comprising the grease to be monitored, wherein the grease to be monitored forms a bridge between the sensor electrode and a grounded component in the sealed space; - an output port coupled to the sensor electrode via a resistor; - an input port directly coupled to the sensor electrode; - a control unit switching the output port between two different voltage levels being a high voltage level and a low voltage level in such a way that the output port switches to the opposite level of these two voltage levels from the level the control unit determines the input port to have, wherein the control unit further generates the output signal resulting from switching the output port; - the analysis unit comprises: - a determination unit determining the frequency and / or the cycle period of the output signal; - a comparison unit comparing the currently determined frequency and / or cycle period of the output signal with a previously determined frequency and / or cycle period of the output signal and thereby indicating whether there is a change in the level of water in the monitored grease. When the frequency of the output signal decreases and / or the cycle period of the output signal increases, the comparison unit determines that the water content is increasing. When the frequency of the output signal increases and / or the cycle period of the output signal decreases, the comparison unit determines that the water content is decreasing. The comparison unit requires a predetermined frequency and / or cycle period difference over a predetermined time period before considering the frequency and / or cycle period difference. Peaks in the frequency and / or cycle period difference occurring during less than the predetermined time period are not considered. The determination unit determines an initial frequency and / or cycle period of the output signal as a calibration frequency and / or calibration cycle period.

7. Condition monitoring system for determining a change in the water content level in grease in a sealed space in a grease-lubricated component, the condition monitoring system comprising: - a sensor unit generating an output signal related to the water content level of the monitored grease; - an analysis unit determining a change in the water content level in the monitored grease from the output signal; characterized in that, - the sensor unit comprises: - a conductive sensor plate intended to be mounted in the sealed space in the grease-lubricated component comprising the grease to be monitored, wherein the grease to be monitored forms a bridge between the sensor plate and a grounded component in the sealed space; - a first port coupled to the sensor plate via a resistor; - a second port directly coupled to the sensor plate; ​ ​ ​ ​ ​ 2. The condition monitoring system of claim 1, wherein, ​ 3. The condition monitoring system of claim 1, wherein, ​ 4. The condition monitoring system of any of the preceding claims, characterized in that ​ 5. The condition monitoring system of any one of claims 1 to 3, wherein, ​ 6. The condition monitoring system of any one of claims 1 to 3, wherein, ​ ​ ​ ​ ​ ​ ​ ​ ​ - an RC oscillator unit, wherein the sensor plate and the resistor constitute an RC part, the rest of the oscillator being coupled to the first port and the second port, wherein the oscillator unit generates the output signal; the analysis unit comprises: - a determination unit which determines the frequency and / or the cycle period of the output signal; - a comparison unit which compares the currently determined frequency and / or cycle period of the output signal with the previously determined frequency and / or cycle period of the output signal and thereby indicates whether a change in the level of water in the fat being monitored is present.

8. The condition monitoring system of claim 7, wherein, The comparison unit determines that the water content is increasing when the frequency of the output signal decreases and / or the cycle period of the output signal increases.

9. The condition monitoring system of claim 7, wherein, The comparison unit determines that the water content is decreasing when the frequency of the output signal increases and / or the cycle period of the output signal decreases.

10. The condition monitoring system of any one of claims 7 to 9, wherein, The comparison unit requires a predetermined frequency and / or cycle period difference over a predetermined time period before considering the frequency and / or cycle period difference.

11. The condition monitoring system of any one of claims 7 to 9, wherein, Peaks in the frequency and / or cycle period difference occurring during less than the predetermined time period are not considered.

12. The condition monitoring system of any one of claims 7 to 9, wherein, The determination unit determines an initial frequency and / or cycle period of the output signal as a calibration frequency and / or calibration cycle period.

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