PROCEDURE AND DEVICE FOR ANALYZING OF PARTICLES IN A MEDIUM AND FOR CONTINUOUS DETERMINING OF WEAR CONDITION OF MECHANICAL CONTACTS IN CONTACT WITH THE MEDIUM

Abstract: A procedure and apparatus for analyzing wear particles present in a flowing fluid and for continuously determining the wear situation of mechanical contacts. The fluid is conducted to a point of examination in a measuring passage (2), stopped, and imaged there with a photoelectric detector (8). With a data processing device (13), the image in analog form is digitized, and from the image are, by methods of digital image processing, automatically determined the central index values in view of degree of purity and/or wear situation, which describe the size, size distribution, shape, surface structure, light transmittance and/or colour of the particles in the fluid. The information thus obtained is classified with the aid of the index values found and of a predetermined set of deduction rules, such as an expert system, and the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid is determined.

Description: PROCEDURE AND DEVICE FOR ANALYZING OF PARTICLES IN A MEDIUM AND FOR CONTINUOUS DETERMINING OF WEAR CONDITION OF MECHANICAL CONTACTS IN CONTACT WITH THE MEDIUM. The present invention concerns a procedure as defined in the preamble to Claim 1. The invention fur¬ ther concerns apparatus as defined in the preamble to Claim 18. The significance, and occurrence, of wear particles and other impurities in lubricating and hy¬ draulic systems has received increasing attention in recent years /Dowson D. Wear Particles: From the Cradle to the Grave, Proc. of the 18th Leeds-Lyon Symposium on Tribology, Elsevier 1992/. In order to increase the service life of apparatus and to improve the reliabili¬ ty of systems, apparatus and procedures have been deve¬ loped by which one could better recognize the prevai¬ ling conditions with regard to oil as well as compo- nents and which would enable action to be taken with regard to deviations efficiently and at an early enough stage /Radzikowski P., On-line monitoring of Contamina¬ tion Level in Hydraulic Oils p. 199-221, Operational Reliability ans Systematic Maintenance, Elsevier 1991./. Non-continuous procedures based on particle counting are known in prior art in which the size dis¬ tribution of the particles is determined, the purity class of the oil being determined on the basis thereof. Also procedures based on filtration of samples are known, in which the quantity and type of particulate impurities are assayed. Furthermore, spectrometric procedures are known by which elements and compounds present in the sample can be identified. The problem embarrassing said procedures of prior art is that they are only applicable in non-con¬ tinuous analyzing in laboratory conditions. However, in the course of development of con¬ dition monitoring procedures towards automation the need has arisen to work out continuously operating wear particle analysing methods and apparatus appropriate to be connected to the object which is being monitored. A typical continuous procedure is for instance known through the publication: "Proceedings, Condition Monitoring -91; "On-line monitoring of ferromagnetic debris concentration", p. 324". The procedure is based on collecting the particles with a magnet onto a sen¬ sor, and on inductive determination of the particle concentration. The limitation of this procedure, as well as of most other on-line, on-site or in-line met¬ hods of simple design is that none but ferromagnetic particles can be assessed. This implies that no infor¬ mation is gained concerning other, non-magnetic mate¬ rials. The parameters observed with the sensors are usually the particle concentration and/or count and/or size distribution. These indicators reflect the degree of purity and any aggravation of wear conditions (chan¬ ges of size distribution) . However, these procedures have significant deficiencies as regards minimum parti¬ cle size and/or maximum concentration of particles and/or air bubbles and/or free water. A significant drawback of existing on-line, on-site or in-line procedures is that only one or two parameters are monitored, which is significantly con¬ ducive to increased possibility of erroneous diagnosis. This is in practice due to the fact that wear particles and other impurities may accumulate at certain points in a hydraulic and lubricating system, whence they may be unexpectedly entrained with the flow, for instance as a consequence of some change in an operating parame¬ ter of the machine. A need has therefore arisen to develop procedures and apparatus by which one could also gain information on particle morphology, in order that potential changes of wear conditions could be verified on the basis of the particles' appearance prior to undertaking inspection or repair action, which is often very costly. The object of the invention is to eliminate the drawbacks mentioned. Specifically, the object of the invention is to disclose an automatic procedure and apparatus based on examining the features of wear particles by means of which the wear information which the particles carry could be analysed in numerical form during running. It is further an object of the invention to disclose a procedure and apparatus by which the sig¬ nificant deficencies of existing, previously known procedures hampering their commercial exploitability can be eliminated. The procedure of the invention is character¬ ized by that which is stated in Claim 1. The apparatus of the invention is characterized by that which is stated in Claim 18. As taught by the invention, the fluid is con¬ veyed to an observation point, the fluid is rendered stationary at the observation point, a still image is made of the fluid, the image in analog form is digi¬ tized, methods of digital image processing are applied to determine automatically from the image certain index values which are central in regard of degree of purity and/or wear situation, these values reflecting the size, size distribution, shape, surface structure, light transmittance and colour of the particles present in the fluid, and the information thus obtained is classified with the aid of the index values found and of a predetermined set of deduction rules, such as an expert system, and the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid is determined. A specific application of the invention is condition monitoring of a lubricating system or hy- draulic system. The invention affords the advantage that by stopping the fluid flow the particles in the flow can be recorded for analysis. Hereby, in additon to ferro- magnetic particles also other particle types can be included in the observation which are informationally significant, such as aluminium, copper, oxide, soot, polymer, molybdenum sulphide, silica (dust, sand) etc. particles, and fibres. It is a further advantage of the invention that the wear situation can be followed in real time adjacent to the object that is being monitored. Furthermore, owing to the invention, the pro¬ cedure can be substituted for present cumbersome labo- ratory analyses, and more accurate and more versatile information than before can be gained concerning the wear and the level of purity of the system. In addition, it is an advantage of the inven¬ tion that monitoring a plurality of parameters and the changes occurring in them enables the purity class of the fluid to be determined. Furthermore, it enables the wear situation of sliding and/or rolling contacts in contact with the fluid to be determined. The procedure also yields information on particle morphology, so that any change in wear situations that may occur can be verified on the basis of the particles' appearance before undertaking inspection or repair action invol¬ ving high expenditures. The procedure can be applied to monitor all or any types of wear mechanism including abrasive, shearing, adhesive, fatigue and tribochemical wear mechanisms. The wear mechanisms prevailing in the system can be identified by specific features in the external shape and appearance of the particle, indica¬ ting a certain wear mechanism, such features being converted by means belonging to image processing and shape identification into mathematical form for classi¬ fication. With the aid of the procedure, it is possible to get in time a suggestion to undertake preventive repair action before any expensive damage is incurred. The expert system may also be arranged to actuate an alarm and to make suggestions for repair action. The larger the entity into which the machine under moni¬ toring has been integrated, the greater the importance of its operation being predictable. In an embodiment of the procedure, the still image is produced by physically stopping the fluid flow at the point of observation. Alternatively, the still image is made by illuminating the moving fluid flow with a flash light source, such as a stroboscopic lamp. In an embodiment of the procedure, the still image is produced by using an exceedingly. short time of exposure, such as an exposure on the order of 1/100,000 second. In an embodiment of the procedure, the fluid is made to assume the shape of a thin film at the point of observation in order to enable light transmittance. In an embodiment of the procedure, the image in digital form is segmented into a monochromatic image and a coloured image, which are further processed by methods of digital image processing. In an embodiment of the procedure, immediately after stopping the fluid flow and before the particles settle on the surface of the lower window, an image is produced of the central part of the fluid made into a thin film, where the particles have random orienta- tions, for particle counting. In an embodiment of the procedure, the image is made of the particles present in the fluid, such as metallic and/or non-metallic particles, using illumi¬ nation from below. In an embodiment of the procedure, after the particles have settled on the lower window, an image is made of the fluid with its particles on the surface of the window, for wear situation analysis. In an embodiment of the procedure, a plurality of images is made using various magnifications. In an embodiment of the procedure, In the imaging is used continuous illumination and/or illumi¬ nation of photoflash type. In an embodiment of the procedure, in the imaging illumination from above and/or from below is used. In an embodiment of the procedure, in the imaging white light, polarised white light and/or com¬ binations of coloured light obtained with filters, such as red light from above and green light from below, are used. In an embodiment of the procedure, prior to determining sizes, shapes and surface structures, from the image are eliminated, by digital image processing methods, any particles which are outside the depth of focus field of the image-forming optics. In an embodiment of the procedure, images are made in statistically significant number with a view to collecting a time series material which is adequate for achieving purity classification determination compara¬ ble with international standards. In an embodiment of the procedure, a so-called dim classifier is employed in the set of deduction rules. In an embodiment of the procedure, as an in¬ termediate result and before the final wear situation diagnosis, are reported the classification results from the dim classifier and the development of the inter- distribution of wear mechanisms, as a function of time. In an embodiment of the procedure, as an in¬ termediate result and before the final wear situation diagnosis, is reported as a function of time, the de¬ velopment of individual particle features computed by the image processing software. As taught by the invention, the apparatus comprises a body, comprising a measuring passage pas¬ sing theretrough, for conducting the fluid flow to and away from the imaging point; an aperture extending at the imaging point through said body transversally to the measuring path; and two imaging windows, supported by the body in register with said aperture, the gap between said windows being in flow communication with the measuring passage. The apparatus further compises valves for stopping the fluid to be stationary in the measuring passage, a photoelectric detector and optical means supported by the body, for producing through the imaging windows, images of the fluid and of the parti ¬ cles therein; a light source for illuminating the ob- ject which is being imaged; and a data processing devi¬ ce. The data processing device comprises programme means for digitizing the analog-form image into a dig¬ ital image, for automatically determining by methods of digital image processing from the image the index va- lues which are central in view of the degree of purity of the fluid and/or the wear situation in the system, said characteristic values reflecting the size, size distribution, shape, surface structure, light transmit¬ tance and colour of the particles present in the fluid. The data processing device further comprises a set of deduction rules, such as an expert system, for classi¬ fying the information that has been obtained with the aid of the index values determined and for determining the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid. In an embodiment of the apparatus, the appa¬ ratus comprises valves, such as magnetic valves, for stopping the fluid flow in the measuring passage for making a still image. In an embodiment of the apparatus, the light source is a flash light source, such as a stroboscopic lamp, for making a still image. In an embodiment of the apparatus, the imaging windows have been disposed horizontally, with substan¬ tially small spacing, for rendering the fluid into a thin film at the imaging point. In an embodiment of the apparatus, the soft¬ ware means are disposed to segment the image in digital form into a monochromatic image and a coloured image. In an embodiment of the apparatus, the appa¬ ratus comprises a light source beneath for producing illumination from below. In an embodiment of the apparatus, the appa¬ ratus comprises a light source above for producing illumination from above. In an embodiment of the apparatus, the appa- ratus comprises filters for polarizing the light from the light source and/or filtering it into different colours or combinations thereof. In an embodiment of the apparatus, the photo¬ electric detector is a row-configurated, location-sen- sitive detector, such as a line camera. In an embodiment of the apparatus, the photo¬ electric detector is a matrix-configurated, location- sensitive detector, such as a CCD camera. In an embodiment of . the apparatus, the appa- ratus comprises a light conductor composed of optical fibres for carrying the light from the light source to the point of observation. In the following the invention is described in detail, referring to the attached drawing, wherein: Fig. 1 presents schematically an embodiment of the apparatus of the invention for implementing the procedure of the invention, Fig. 2 presents the body of an embodiment of the apparatus of the invention, Fig. 3 presents the body of Fig. 2, as viewed in the direction III-III, Fig. 4 presents in partial longitudinal sec- tion, the imaging point of the body of Figs 2 and 3, and Fig. 5 presents the schematic principle dia¬ gram of an embodiment of the procedure and apparatus of the invention. In Fig. 1 is depicted an apparatus by which it is possible to analyse wear particles and other solid impurities present in a flowing fluid and to determine the wear situation of mechanical contacts in contact with the fluid, continuously and in real time according to the on-line principle. The apparatus comprises a plate-like body 1 as shown in Figs 2-4 and comprising a horizontal measuring passage 2 passing theretrough, by which the fluid flow is conducted to and away from the imaging point 3. The apparatus is inserted e.g. in a hydraulic or lubrica¬ ting system, in which case hydraulic oil or lubricating oil is conducted into the measuring passage. The body 1 comprises at the imaging point 3 an aperture 4, passing through the body 1 at right angles and transversally to the measuring passage 2. Two transparent imaging win¬ dows 5, or glass plates, are connected to the body 1 in register with the aperture 4, parallel with and spaced from each other, so that the fluid can flow through the narrow gap, about 1 mm, between the windows 5. The gap shapes the fluid into a thin film between the windows 5, in order that light might pass through the fluid. The measuring passage 2 has inside threads on either end, in which magnetic valves 6,7 can be inserted. By closing the magnetic valves 6,7, the fluid can be stop¬ ped to be stationary in the measuring passage 2. In the fluid feeding direction, before the imaging point 3, is also provided a temperature pick-up 16 and a pressure transducer 17 for measuring the temperature and pressu- re of the fluid. The apparatus further comprises, connected to the body 1, a photoelectric detector 8 and optical means 9 and 10. The photoelectric detector 8 is, for instance, a CCD camera, for producing images of the fluid and the particles through the imaging windows 5. The optical means include in the present case an ob- jective lens 9 and a distance ring 10. The apparatus further comprises, connected to the body 1, a light source 11 beneath it for illuminating from below the object to be imaged, and a light source 12 above it for illuminating from above the object to be imaged. The light source 12 above, the objective lens 9, the dis¬ tance ring and the CCD camera 8 are combined in one entity which can be moved with the aid of a transport mechanism 18 perpendicularly relative to the body 1. It is thus understood that the apparatus resembles a mic- roscope fitted with a camera. The apparatus further comprises a number of filters 14, 15 and 19 for polar¬ izing the light from the light source and/or filtering it to different colours or combinations thereof. In the exemplary apparatus, the filters 14 and 15 are disposed between the light source 11 on the underside and the body 1. The top-side light source 12 is supported by a tubular component in a horizontal plane, and the filter 19 can be mounted on this component after the top-side light source 12. The apparatus further comprises a data pro¬ cessing device 13, e.g. a microcomputer. It is fur¬ nished with the requisite software means. The data processing device 13 is further fur¬ nished with a set of deduction rules, provided e.g. in the form of an expert system. An embodiment of the procedure is implemented in that the fluid is conducted from the system into the measuring passage, to the imaging point. The magnetic valves are closed, whereby the fluid stops in the mea- suring passage and the fluid with particles resides as a thin film between the windows. Immediately after stopping the fluid flow, before the particles have settled on the lower window, the CCD camera is operated to make an image of the central part of the fluid brought into the form of a thin film between the win¬ dows, in which image the metallic and non-metallic particles have random orientations, using illumination from below, for particle counting. Later, after the particles have settled on the lower window, an image is made of the fluid with particles on window surface level for wear situation analysis. Several such imaging processes are carried out, using different magnifica¬ tions, continuous illumination and/or photoflash-type illumination, employing illumination from above or from below or both simultaneously. As may be required, white light, polarized white light and/or combinations of coloured light achieved with filters, such as red light from above and green light from below, are used. Images are taken in statistically significant number in order to assemble a material which is adequate for achieving a purity classification determination comparable with international standards. Analysis of the images is performed automati¬ cally with the data processing device. The analog image from the CCD camera is digitized to become a digital image. The image in digital .form is segmented into a monochromatic image and a coloured image, which are further processed by means of digital image processing. From the images, index values which are central in view of degree of purity and of wear situation are deter¬ mined, these values describing the size, size distribu- tion, shape, surface structure, light transmittance and colour of the particles present in the fluid. However, prior to determining sizes, shapes and surface structu¬ res digital image processing methods are employed to eliminate from the image such particles which are out- side the depth of focus range of the image-forming optics. Subsequently, the data obtained from the images with the aid of the set of deduction rules is classified on the basis of the index values that were found. When from the images the feature combinations of particles present in the fluid have been determined, and when it is known from before that to a given wear mechanism correspond given feature combinations of the particle, one can conclude that the feature combination determined from the particle is consistent with a cer¬ tain wear mechanism. It is possible in this way to determine the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid. Now follows a closer description of running- time particle analysis, based on machine vision, ac¬ cording to the invention. The particle analysis can be coarsely divided into three steps: image acquisition, image processing and classification and diagnostics. In the deduction performed by the expert system the featu¬ re information from the particles is coupled with user and construction information and the user is given an estimate of the purity and wear situation. The structu¬ re of the procedure is illustrated by Fig. 5. Oil used in a hydraulic or lubricating system is made to flow through a perfusion cuvette (e.g. that shown in Figs 1-4). The oil is observed with the aid of a CCD camera attached to a microscope. The flow is stopped before imaging and the wear particles are al¬ lowed to settle on the bottom of the imaging chamber, upon a glass plate. Two images are made of each sample: a photo- graph rich in contrast from below in opposite light for particle shape analysis, and a photograph from above in normal light, which brings out the surface structure. The image produced by the camera is digitized from the video signal into memory on the image processing board, for analysis. The particles have been divided into four classes according to the wear mechanism which they indicate : 1. Shearing wear 2. Fatigue wear 3. Adhesive wear 4. Other abrasive or adhesive and abrasive wear. Classification is based on features describing the shape of the body, computed from its outline. " For classification algorithm one may select a so-called dim classifier of k nearest neighbours, which is programmed in a microcomputer. Use of a dim classifier is justi¬ fied because it is frequently difficult even for an expert to determine with assurance which wear mechanism the particle under examination represents. However, one or several wear mechanisms can always be rejected as being impossible. The classifier is taught by showing it images of particles belonging to different classes, together with the classification information supplied by the expert. In the teaching stage the memberships in each class of the particle being taught are given in the form of a vector. For instance, a fatigue wear particle belonging to Class 2 (fatigue wear) is taught by means of the vector [0 10 0]. If the expert was uncertain as to the exact classification of the particle, it is possible to teach the classifier with uncertain infor¬ mation: for instance, a particle representing fatigue wear in the first place but possibly also abrasive wear can be taught with the vector [0 0.7 0 0.3]. The classifier yields as result the member¬ ships in each class of the particle which is being classified. If, for instance, the result is the vector [1.0 0 0 0], the features of the object being classi¬ fied are fully consistent with the features of shearing wear particles and the result of classification can be considered reliable. On the other hand, if the mem¬ berships in several classes are different from zero and nearly equal, the result of classification is uncertain (e.g. [0.2 0.3 0,3 0.2] ) . On the basis of the results, shearing wear particles (Class 1) and particles representing adhesive wear (Class 3) can be rather well identified on the basis of their shape. Particles belonging to classes 2 (fatigue wear) and 4 (other abrasive or adhesive and abrasive wear) frequently resemble each other in shape to the extent that examination of the particle's surfa- ce structure is necessary in order to guarantee a re¬ liable result of classification. The surface structure of the wear particle is linked with the wear mechanism, and it is therefore justified to associate with the wear diagnostic system of lubricating and hydraulic systems such features detached from the surface structure which classify surface defects in accordance with the wear process. Since image acquisition is based on use of a CCD camera, one has to look for the surface structure in the internal grey level information of the wear particles, which algorithmically implies application of so-called 2 1/2 D methods, when an attempt is made to estimate the nature of the damage caused by the wear event. As an example may be mentioned, for instance, a ridge or dale (a scratch). The basis of the first step in the analysis is binarizing and segmentation of the image illuminated from below, these consisting methodologically of auto¬ matic thresholding and segmenting of the image. In this connection the oblongness of small particles is also estimated, which cannot be accomplished with any other index values describing shape. Among other features in the software may be mentioned a procedure for eli¬ minating optically non-focussed formations. Employing the particle outlines determined on the basis of seg¬ menting, the particles are detached from the image illuminated from above so that the surface structure might be estimated at the proper point. Feature of surface structure have not heretofore been evaluated in any statistically significant testing. The feature vector computed by the procedure developed for 2 1/2 D surface examination indicates, in proportional contributions, the characteristic features discernible on the surface of the object. In addition, the average evenness/unevenness of the surface is esti¬ mated. The former feature correlates strongly with the strength of unevenness. A modification of the features is based on using the estimated surface normals occur¬ ring within the particle in order to create an " une¬ venness map". Glossy reflections from a wear particle have also been considered to indicate unevenness of surface structure. On the strength of this an internal segmen¬ ting procedure has been developed in which the reflec¬ ting sites are separated from the background. A more detailed description of the procedure is forgone here because the operation consists of a great number of steps. With the aid of the procedure the oblongness of the reflecting points, their average orientation and the deviation of the orientation are computed and they are classified as oblong and round entities. Furthermo- re, the internal central moments of the particles are established, which furnish indications of the surface structures. This portion can be expanded in that the the location data of the image elements is fixed in the particle under examination, whereby the resolution of the procedure is improved. Since in certain situations the colour of the wear particle directly indicates the object of wear, the colour of the particle supplies unambiguous infor¬ mation to the diagnostics block. Colour analysis is based on computing the differences in colour between segmented particles in a certain colour space, the original RGB (red, green and blue) signal is by a multi-step transformation converted into a colour space presentation appropriate to this purpose. The procedure includes a certain teaching step in which the probable location in the three-dimensional colour space of cop- per, aluminium and iron metals is estimated. The loca¬ tion in the colour space of the plot condensations produced by the particles is determined by the colour of the particle. It has been found in tests carried out using the procedure just described that copper metals can be distinguised from iron and aluminium metals. The re¬ sults from the tests were manually analysed by compar¬ ing the locations in the above-mentioned colour space of the plot condensations of particles representing the three metal types. Advanced image processing methods present useful tools in developing automatic particle analysis. An absolute advantage is versatility and high degree of information. In addition to conventional particle con- centration or size distribution, the analysis can be extended to cover also outline or surface structure features, or material features such as transparency and colour, giving closer indication of the wear mechan¬ isms. When applied in run time, the procedure yields information which is more covering in time, and the conventional sources of error of bottle sampling are also eliminated. On the basis of the invention an expert system for wear particle analysis has been elaborated, which is more closely described in the following. The expert system has easy-to-use user ports. It can be used to facilitate determination of a machine's condition. The particles carried along by a fluid yield information on purity and wear situation. The system which has been developed can perform a manual test based on ferro- graphy and bichromatic microscopy, auto-test analysis on an existing data file, image data test based on distinguishing on-line particle features by a visual system, and a lubricant test. The results gained by the expert system are in good agreement with the results obtained from human experts. The system also affords possibilities for on-line queries and help functions. The system is a ferrography-based system com¬ piled with Microsoft Visual Basic in Windows environ¬ ment. The system comprises the following parts and functions: easy-to-use user ports, a knowledge base containing more than 400 rules of wear particle analy¬ sis, a data base containing data tables for recording general test information, a particle information table, results of analysis, and results of lubricant tests. The main steps in the analysis are: (1) manual test for off-line ferrographic testing with a bichromatic microscope, (2) auto-test for existing particle analysis, (3) image test for analysis of on-line particle image processing, (4) lubricant test for lubricant analysis. The system furthermore features on-line query procedures for data base processing functions. Some on¬ line auxiliary functions have been included in the system. An important part of the system is trend anal- ysis, providing a graphic presentation of the changes in wear situation in a given machine during a given period of time, the period being selectable by the user. The system also comprises procedures printing test information and test reports. The system has 14 ports for performing all predetermined operations, each such port having an independent functional role and containing functions. All the user has to do is to input at the port the requisite information and to press requisite keys. The particle input parameters include the particle characteristics which may be utilized in diagnosis of wear situation. The following features are collected: ferrometallic or non-ferrometallic, colours, fundamental shapes, surface structure, size, and num¬ ber. After this information has been input, the system can directly analyse these parameters, using the know- ledge base, and give the respective results. When these parameters and the lubricant information have been input, the system performs the analysis. The user may check the remarks in order to be advised of the lubri¬ cant's condition, which is determined on the basis of selected, recorded data. The first recorded data in the lubricant data table is always used to record the data of new oils. Type of filtering and pore size are also given to complement the lubricant analysis. Through the trend analysis port are input the customer's name, name of the machine, starting time and termination time, to define certain test records for trend analysis. A trend graph is given for the above- mentioned four different wear types. Through the image analysis port the system is supplied with the name of the image file and the number of time points. Two categories "Images" or "Particles" can be selected. The graphs which are produced repre¬ sent the changes of image or particle parameters within the selected period of time. Each plot in the graphs represents the average value of each image parameter during the period selected. In addition to the main ports just described, the system comprises additional ports for accomplishing on-line query functions or printing functions. The nucleus of the system is a knowledge base, which is used in replacement of human experts to derive various results from the different input parameters. It comprises more than 400 rules of wear particle analys¬ is. The rules are divided into four categories: identi- fication of the wear particles' material from the cha¬ racteristics and colours of the particles, analysis of the wear particles' shape and surface structure, ana- lysis of the wear particles' size and number, and fi¬ nally analysis of the wear situation. These rules cover the main aspects of ferrography and they are formulated using the "if...then" syntax, whereby they are easy to understand and to modify. It is also easy to add more rules to the knowledge base. The data base of the expert system is used to store and to process original or deduced data of the system. It comprises four tables, each table having its own data structure. The first table is used to record general test information, such as name of the test, customers' name, test date, etc. The second table is used to record particle information and to deliver it into the knowledge base. The third table is used to record the results of analysis which have been deduced in the knowledge base. The fourth table is used to record and to analyse lubricant. The procedures of the system employ these data structures to acquire, store, print, examine and compute data, and also to communica- te with the knowledge base. A procedure has been planed for accomplishing analysis of oil samples: manual test, automatic test, image test, and lubricant test. The system also offers tools for managing the data base so that the user can directly view and exam- ine, add, delete, transform and print such data as he requires. It is possible on the basis of the profound understanding of wear to give an accurate indication of the condition of a machine's parts and to predict the service life. At present, the most efficient way to determine the condition of a machine appears to be the use, in combination, of several lubricant analysis methods, such as SOAP, particle count, image analysis, etc. The information thus obtained is fed into an in- telligent, human-like diagnostic system, which produces a report of the system's condition and, possibly, also suggestions regarding remedial actions. The invention is not exclusively confined to concern the embodiment examples presented in the fore¬ going: numerous modifications are feasible within the scope of the inventive idea defined by the claims.

Claims: CLAIMS 1. A procedure for analysing wear particles and other solid impurities present in a flowing fluid and for continuously determining the wear situation of mechanical contacts in contact with the flowing fluid, characterized in that - the fluid is conducted to a point of examination, - a still image is made of the fluid, - the image in analog form is digitized, - methods of digital image processing are employed to determine from the image, automatically, the index values central in view of degree of purity and/or wear situation, which describe the size, size distribution, shape, surface structure, light transmittance and/or colour of the particles in the fluid, and - the information thus obtained is classified with the aid of the index values found and of a predetermined set of deduction rules, such as an expert system, and the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid is determined. 2. Procedure according to claim 1, charac¬ terized in that the still image is produced by physi¬ cally stopping the fluid flow at the point of examina- tion and/or by illuminating the fluid flow with a flash light source. 3. Procedure according to claim 1 or 2, characterized in that the still image is produced by using an exceedingly short exposure, such as an expo- sure on the order of 1/100,000 seconds. 4. Procedure according to any one of claims 1-3, characterized in that the fluid is at the point of examination made to become a thin film in order to enable light transmittance. 5. Procedure according to any one of claims 1-4, characterized in that the image in digital form is segmented into a monochromatic image and a coloured image, which are further processed by methods of digi¬ tal image processing. 6. Procedure according to any one of claims 1-5, characterized in that immediately upon stopping the fluid flow, prior to settling of the particles on the surface of the lower window, an image is made of the central part of the fluid formed into a thin film, where the particles have random orientation, for par¬ ticle counting. 7. Procedure according to claim 6, charac¬ terized in that the particles present in the fluid, such as metallic and/or non-metallic particles, are imaged employing illumination from below. 8. Procedure according to any one of claims 1-7, characterized in that after the particles have settled on the lower window, the fluid with particles is imaged on window surface level for wear situation analysis. 9. Procedure according to any one of claims 1-8, characterized in that a plurality of images is made, using various magnifications. 10. Procedure according to any one of claims 1-9, characterized in that in the imaging continuous illumination and/or illumination of photoflash type is employed. 11. Procedure according to any one of claims 1-10, characterized in that in the imaging illumination from above and/or from below is employed. 12. Procedure according to any one of claims 1-11, characterized in that in the imaging white light, polarized white light and/or combinations of coloured light accomplished by means of filters, such as red light from above and green light from below, are emplo¬ yed. 13. Procedure according to any one of claims 1-12, characterized in that prior to determination of sizes, shapes and surface structures from the image are by digital image processing methods eliminated any particles which are outside the depth of focus range of the imaging optics. 14. Procedure according to any one of claims 1-13, characterized in that images are produced in a statistically significant number for collecting a ma¬ terial which is adequate for accomplishing purity classification determination comparable with inter¬ national standards. 15. Procedure according to any one of claims 1-14, characterized in that in the set of deduction rules a so-called dim classifier is used. 16. Procedure according to any one of claims 1-15, characterized in that as an intermediate result prior to final wear situation diagnosis are reported the results of classification from the dim classifier and the development as a function of time of the in- terdistribution of the wear mechanisms. 17. Procedure according to any one of claims 1-16, characterized in that as an intermediate result prior to final wear situation diagnosis is reported the development as a function of time of individual parti¬ cle features computed by the image processing software. 18. Apparatus for analysing wear particles and other solid impurities present in a flowing fluid and for continuous determination of the wear situation of mechanical contacts in contact with the flowing fluid, characterized in that the apparatus comprises - a body (1), comprising a through-going measuring passage (2) for conducting the fluid flow to and away from an imaging point (3), an aperture (4) extending at the imaging point transversally to the measuring passa¬ ge through said body, and two imaging windows (5), supported by the body in register with said aperture, the gap between said windows being in flow communicati¬ on with said measuring passage; - a photoelectric detector (8) and optical means (9,10), supported by said body, for imaging the fluid and the particles present therein through said imaging windows; - a light source (11,12) for illuminating the object which is being imaged; and - a data processing device (13) comprising -- software means for digitizing the image in analog form to become digital and for automatically determin¬ ing by methods of digital image processing the index values central in view of degree of purity and/or wear situation of the system, describing the size, size distribution, shape, surface structure, light trans¬ mittance and/or colour of the particles present in the fluid, and -- a set of deduction rules, such as an expert system, for classifying the information thus obtained with the aid of the index values found and for determining the wear situation of sliding and/or rolling mechanical contacts in contact with the fluid. 19. Apparatus according to claim 18, charac¬ terized in that the apparatus comprises valves (6,7) for stopping the fluid in the measuring passage to the purpose of making a still image of the fluid. 20. Apparatus according to claim 18 or 19, characterized in that the light source (11,12) is a flash light source, such as a stroboscopic lamp, for making a still image of the fluid. 21. Apparatus according to any one of claims 18-20, characterized in that the imaging windows (5) are disposed horizontally, spaced at a substantially small distance, for making the fluid asume the form of a thin film at the imaging point. 22. Apparatus according to any one of claims 18-21, characterized in that the software means have been arranged to segment the image in digital form into a monochromatic and a coloured image. 23. Apparatus according to any one of claims 18-22, characterized in that the apparatus comprises an underside light source (11) for accomplishing illumina¬ tion from below. 24. Apparatus according to any one of claims 18-23, characterized in that the apparatus comprises a topside light source (12) for accomplishing illumina¬ tion from above. 25. Apparatus according to any one of claims 18-24, characterized in that the apparatus comprises filters (14,15,19) for polarizing the light from the light source and/or filtering it into different colours or combinations thereof. 26. Apparatus according to any one of claims 18-25, characterized in that the photoelectric detector (8) is a row-shaped, location-sensitive detector, such as a line camera, or a matrix-shaped location-sensitive detector, such as a CCD camera. 27. Apparatus according to any one of claims 18-26, characterized in that the apparatus comprises a light conductor composed of optic fibres for conducting light from the light source (11,12) to the point of examination (3).

Inventors: ENWALD PETRI, ENWALD, PETRI
Applicants: ENWALD PETRI, VALTION TEKNILLINEN, ENWALD, PETRI, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 1993
Main classification: G01N15
IPC codes: G01N3, G01N15