Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C17/00—Sliding-contact bearings for exclusively rotary movement
  • F16C17/12—Sliding-contact bearings for exclusively rotary movement characterised by features not related to the direction of the load
  • F16C17/24—Sliding-contact bearings for exclusively rotary movement characterised by features not related to the direction of the load with devices affected by abnormal or undesired positions, e.g. for preventing overheating, for safety
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
  • F16C17/00—Sliding-contact bearings for exclusively rotary movement
  • F16C17/12—Sliding-contact bearings for exclusively rotary movement characterised by features not related to the direction of the load
  • F16C17/24—Sliding-contact bearings for exclusively rotary movement characterised by features not related to the direction of the load with devices affected by abnormal or undesired positions, e.g. for preventing overheating, for safety
  • F16C17/246—Sliding-contact bearings for exclusively rotary movement characterised by features not related to the direction of the load with devices affected by abnormal or undesired positions, e.g. for preventing overheating, for safety related to wear, e.g. sensors for measuring wear
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
  • G01K11/12—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
  • G01K11/12—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance
  • G01K11/125—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in colour, translucency or reflectance using changes in reflectance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
  • G01L5/0004—Force transducers adapted for mounting in a bore of the force receiving structure
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
  • G01L5/0009—Force sensors associated with a bearing
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M13/00—Testing of machine parts
  • G01M13/04—Bearings

Definitions

• the present invention relates to a method, according to the preamble of Claim 1, for monitoring a contact between two surfaces, particularly two surfaces that move relative to each other. Contacts of this kind between two surfaces typically appear in sliding and rolling bearings, in gear trains, and in other sliding and rolling contacts of a machine construction.
• the invention also relates to an arrangement intended to apply the method.
• Sliding bearings are a particularly interesting subject.
• Sliding bearings are components that are widely used in machine construction. They support and guide rotating machine components and are typically used in, for instance, motors and engines, turbines, and generators.
• a liquid film for example an oil film
• the moving machine component for example a shaft
• a fixed machine component for example the bearing shell
• the loadbearing capacity of the bearing is good and its wear is small.
• the lubricant film is the central factor, through which the forces are transmitted from the shaft to the bearing.
• One way to investigate the operation of the oil film of a sliding bearing is to drill a hole in the bearing metal and to place a small pressure sensor in the hole.
• the hole must be large enough for the sensor to fit into it and for the oil to be able to act directly on the sensor, so that the hole does not create a detrimental throttle effect.
• the hole must therefore be relatively large compared to the thickness of the liquid film.
• a hole extending to the liquid film will alter the flow of the liquid and thus the pressure at the measurement point.
• the sensor will thus not measure the real pressure in the film and so that a reliable picture will not be obtained of the real situation at the measurement point.
• the movement of the liquid film and the flow at the hole may also cause rapid wear in the very soft bearing metal at the location of the hole.
• the invention is intended to create a reliable and economical manner of measurement, by means of which it will be possible to measure the conditions in a contact between two surfaces moving relative to each other, in such a way that the object being measured is affected as little as possible.
• the invention is based on making a recess, which extends towards the surface in contact, behind the surface in contact in the immobile piece of two pieces moving relative to each other or in a piece at rest. At a distance from the bottom of the recess a detector is fitted, which is used to monitor the space between the detector and the bottom of the recess, in order to detect a desired variable.
• the position of the bottom of the recess is measured.
• the position of the bottom of the recess is measured with the aid of optical measurement.
• the method according to the invention is characterized by what is stated in the characterizing portion of Claim 1.
• the arrangement according to the invention is in turn characterized by what is stated in the characterising portion of Claim 17.
• the most important advantage of the invention is that the surface in the contact remains completely intact, so that the properties of the object being measured do not substantially change, nor does the measurement affect the phenomena taking place in the object, hi objects operating on a liquid film the liquid film remains intact and the flows in it remain unaltered, hi a rolling contact or dry sliding contact fracturing of the surface can be avoided, because flaws that will start a fracture are not formed in the surface. If an optical fibre is used in the measurement and the measurement is performed with the aid of light, the noise appearing in the measurement can be easily minimized by rapid sampling and, for example, sliding averaging. In addition, the powerful electrical interference that appears in an industrial environment cannot affect an optical measurement, thus facilitating the processing of the measurement data and avoiding the need for complicated and expensive interference protection.
• Optical detection is extremely reliable and stable. Thus, a manner of measuring that is reliable and cheap in price is achieved.
• the construction according to the invention is reasonable easy to implement with the aid of known techniques used in machine construction and optical fibres, hi some cases, it is possible to use other forms of detection too to measured the distance between the bottom of the recess formed behind the surface and the detector.
• Possible forms of detection include capacitive and inductive measurement. However, these forms of detection have the weakness of being sensitive to interference and unstable, compared to optical measurement.
• Optical measurement is preferably implemented as a simple measurement of the intensity of reflected light, hi this way a quite high degree of accuracy will be achieved.
• Figure 1 shows a schematic diagram of one embodiment of the mechanical construction of the invention.
• FIG. 2 shows an alternative embodiment of the invention.
• Figures 3 - 5 show schematic diagrams of the principle of the intensity measurement.
• Figure 6 shows a schematic diagram of the measurement arrangement of the intensity measurement.
• Figure 7 shows one shape of the recess required in the invention.
• tribologic contact refers to a contact between two surfaces, in which the surfaces act on each other either directly or by means of a liquid film.
• Such contacts are, among others, a sliding movement dry, a sliding movement on a liquid film, and a rolling movement, a contact between two surfaces that are immobile relative to each other, such as compression between the surfaces, and combinations of these.
• Figure 1 shows one construction according to the invention, in a highly simplified view. Ih it, a recess 5 is made in the bearing metal 1, which extends to close to the surface 8 in tribologic contact. Li this example, the surface is the surface of a bearing strip.
• the bottom 3 of the recess 5 is preferably a polished or an otherwise sufficiently reflectively finished surface. The need for polishing or surface treatment depends on the method of manufacturing the hole and addition treatment of the bottom of the hole will not necessarily always be required.
• the bottom is referred as the mirror surface 3.
• An optical fibre 4, which is formed of a core 6 and a casing layer 7, is fitted inside the recess. The end of the fibre is at a distance from the mirror surface 3, so that the an observation space, i.e. an etalon 2 is created between the end of the fibre and the mirror surface.
• the distance between the bottom of the recess and the surface in the contact is s.
• the etalon 2 is filled with a thermochromatic material 9, for example, with a thermochromatic polymer, the colour of which changes when the temperature changes.
• a thermochromatic material for example, with a thermochromatic polymer, the colour of which changes when the temperature changes.
• a thermochromatic polymer is acryl mixed with a thermochromatic pigment.
• the temperature of the sliding bearing or other surface is measured by measuring the radiation reflected from the mirror surface 3. Because the colour of the thermochromatic material changes when the temperature changes, the colour of the light reflected back to the optical fibre changes at the same time, and the temperature can be detected by detecting the colour of the light. The detection can be performed with the aid of a colour filter, by measuring the amount of light of each separate colour passing through the filter.
• An optically active substance the polarization of which changes according to the temperature, can also be used to detect temperature, in which case the temperature can detected with the aid of the rotation of the polarization.
• the advantage of this solution is that the temperature measurement can be brought close to the object being measured.
• An optical fibre will also require a much smaller hole or recess than a thermo-element, for example.
• Figures 3 - 5 show the principle for the measurement of the distance of the mirror surface. Because the mirror surface 3 moves due to the effect of the pressure acting on the surface 8 in the contact, the movement of the mirror surface can be used to measure, for example, the pressure acting on the bearing from the oil film in the sliding bearing.
• the measurement of the movement of the mirror is implemented as a measurement of the distance between the end of the optical fibre 4 and the mirror surface 3.
• the end of the fibre 4 is placed at a precisely defined distance / from the mirror surface 3.
• the fibre lens 10 focuses the beam 13 of light coming from the fibre to the focal length 11 of the focussing point.
• the focal length 11 is between the end of the fibre and the mirror surface 3.
• Figures 4 and 5 show the effect of altering the distance between the mirror surface 3 and the fibre lens 10.
• the mirror surface can also be between the optical fibre and the focal length. In that case, when the distance of the mirror surface changes, a change corresponding to that in the example described above will take place. The intensity of the change will, however, be lower, so that it is preferable for the mirror surface to be farther than the focal length.
• Figure 4 shows by way of illustration a surface 8 in the bearing contact, the rotating shaft 15 in the bearing, and the oil layer 16 separating them.
• Figure 6 shows a schematic view of one way of implementing the distance measurement described above.
• a light source 17 directs light to a fibre 18, by means of which the light is directed on over the fibre 19 to a sensor 20.
• a fibre 21 leading to an intensity detector 22 branches from the joint between the light source fibre 18 and the sensor fibre 19.
• the light source used can be a superbright led, or some other sufficiently strong light source.
• Conventional light detectors are suitable as the detector 22. Because in the invention the intensity change is great, high sensitivity is not required in the detector.
• monochromatic or wide-band light and the Fabry-Perot principle can be used to measure the distance between the mirror surface and the optical fibre.
• This form of measurement is based on the interference between the sent light and the reflected light in an etalon.
• the phase of the reflected light always coincides with the opposite phase between the wavelength and the distance form the light source, and with the same phase as the wave of the incoming light, so that the reflected light alternately extinguishes and amplifies the incoming light.
• This can be detected in the fibre as dark and light spots and with their aid the distance of the mirror surface from the source of incoming light can be calculated.
• Figure 7 shows one mechanical solution for implementing the sensor.
• a shoulder 23 is formed in the recess 5 in the bearing metal, against which the jacket 7 of the fibre can be pushed.
• An annular groove 24 is machined in the edges of the mirror surface 3.
• narrow necks 25 are formed in the bearing metal 1 at the sides of the mirror surface 3. Deflection will now take place at the necks 25 and the mirror surface will remain straight.
• the shapes of the recess, shoulder, and groove are shown here as rectangular and sharp for reasons of simplicity. In reality, the corners are, however, preferably rounded or otherwise shaped in such way that their fracturing effect is as small as possible. This will then minimize the possibility that the structure will form a start for a possible fracture. This shaping comes within the scope of conventional mechanical engineering.
• the dimensioning of the actual sensor construction depends partly on the dimensions of the optical fibre and partly on the actual object being measured.
• the diameter of the core of the optical fibre is about 10 - 50 ⁇ m and of the jacket about 125 ⁇ m.
• the fibre is surrounded by a protective collar, the diameter of which is about 0.5 - 2 mm.
• the diameter of the collar of course determines the diameter of the hole made in the bearing metal.
• the thickness s of the membrane between the mirror surface 3 and the surface 8 in the contact depends on the thickness of the oil layer in the bearing, the bearing material, and, when the question is of a bearing other than a sliding bearing, also on the type of contact.
• the thickness of the bearing-metal membrane is a few hundred ⁇ m, when the greatest distance of movement of the mirror will be a few ⁇ m.
• the accuracy achieved with the intensity measurement will be about one-hundredth of the distance of movement of the mirror.
• the mirror surface should be preferably farther than the focal length of the fibre lens from the end of the fibre.
• a suitable focal length is a few hundred ⁇ m while slightly inaccurate focussing can be used, nor is focussing to a precise point necessary.
• optical fibre includes the dispersion of light in a fan shape from the end of the fibre, unless the fibre ends in a lens. This phenomenon can be exploited in the measuring method described above. If the distance between the end of the fibre and the mirror is small, the amount of light reflected from the mirror and leaving the end of the fibre will change according to how close the mirror is to the end of the fibre. The closer the mirror is to the end of the optical fibre the narrower will be the light beam striking the mirror and the greater the proportion of light reflected back to the fibre. In this case the distance between the end of the fibre and the mirror must be in the order of the thickness of the fibre. The distance is defined more precisely according to the properties of the end of the fibre, i.e.
• the angle is of the light beam leaving the end of the fibre. With a narrower exit angle the mirror can naturally be farther away than with a larger angle.
• the construction and manufacture of the actual sensor are simpler than those described above, because a lens need not be created. This sensor too must be calibrated for its application, just like the constructions described above.
• the distance of the mirror surface and changes in the distance can also be measured using capacitive and inductive sensors or other detection devices.
• the pressure acting on this surface can also be measured in principle with the aid of a piezoelectric material.
• these measuring procedures have the weakness of the signal being difficult to process in interfering factory conditions and the expense of the necessary equipment.
• the space required in these measurement applications may also limit the use of these methods.
• One way to measure the pressure in the etalon is to use a capillary fibre and an etalon filled with liquid. The pressure can then be measured at the end of the capillary fibre, for example, using a silicon micro-mechanical sensor. Because in a silicon micro-mechanical sensor a change in pressure can be detected with the aid of a very small movement of the sensor, with the aid of it it is possible to detect pressure changes due to even the smallest movement of the mirror membrane of the etalon.
• the recess required by the sensor according to the invention need not necessary be made as a blind hole like that described above.
• the hole required by the sensor can also be made through the bearing material and then covered with a membrane made from a suitable material.
• the recess can also be made in a separate piece, which is set into the bearing material. What is important is that the shape of the bearing's or other measuring surface and preferably also its elasticity are as precisely as possible the same as those of the actual bearing material. Of course, the most preferable case is for the possible surface membrane or separate piece to be made from the same material as the surface of the bearing. In other applications, the material must of course be adapted according to the construction material in question.
• the shape of the mirror surface By changing the shape of the mirror surface it is possible to affect its reflective properties.
• the surface can be made either convex or concave according to whether it is wished for the light beam striking it to be focussed or refracted when it is reflected from the surface. If the edges of the bottom of the recess are shaped according to Figure 7, the shape of the mirror surface will remain essentially unchanged, because the deflection at the edges will be considerably greater than the deflection at the relatively thick centre. On the other hand, it may be preferable to made the bottom of the recess flat. Such a shape will be simpler in terms of manufacturing technique. Now the distance of the end of the optical fibre and the mirror can be set to be correct by shaping a collar from the protective casing of the fibre, which extends beyond the end of the fibre.
• the end of the fibre, the hole of the collar, and the mirror surface will form the measuring space, i.e. the etalon.
• Single or multimode fibre can be used for the measurement, or even two fibres, one of which transmits light to the etalon while the other receives it.
• the light used can be wideband, polarized, monochromatic, or otherwise processed, nor need its wavelength coincide with the wavelength of visible light.
• the sensor is placed in the sliding bearing at the point of the greatest pressure in the oil film, unless for some reason it is necessary to investigate the pressure of the film elsewhere on the circumference of the bearing. For example, in a ball or roller bearing the sensor would be situated on the rolling groove.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Length Measuring Devices By Optical Means (AREA)

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Citations (6)

• 2004
  • 2004-12-16 FI FI20041622A patent/FI119707B/sv not_active IP Right Cessation
• 2005
  • 2005-12-15 WO PCT/FI2005/000534 patent/WO2006064086A1/en not_active Ceased

Patent Citations (6)

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