Wear particle analysis is known. Wear particle analysis is a machine condition monitoring program for lubricated equipment. By examining the particles contained in the lubricant, wear related failures can be identified at an early stage. Wear particle analysis is conducted typically in two stages. The first stage involves monitoring and trending wear particles in the lubricant to detect abnormal wear. The second stage involves further analysis to identify, for example, the wear mechanisms causing particle formation, the sources of the particles, and hence the wearing components.
In order to monitor and trend wear particles in a lubricant, a sample of the particulate is typically taken from the lubricant. For example, Westcott U.S. Pat. No. 4,047,814 describes a method and apparatus for segregating particulate matter from a fluid. The particle-containing fluid such as the machine lubricant is flowed along a path over a collecting substrate in the presence of a magnetic or electric field having an intense gradient. The result is a stripe pattern of deposited material on the substrate, with particle size varying gradually from one end of the stripe pattern to the other. A collecting substrate having such a deposit is commonly referred to as a "ferrogram". The entire disclosure of U.S. Pat. No. 4,047,814 is incorporated herein by reference.
In the past, the deposit pattern formed on the substrate has been studied under a microscope by a laboratory technician. The laboratory technician visually compares the distribution and concentration of the particulate deposited on the substrate with previous samples to evaluate trending and the like. When abnormal wear is detected based on a changing distribution, concentration, etc., in the sample, the laboratory technician then studies the sample further in an attempt to diagnose the cause of the abnormal wear.
Unfortunately, there are several drawbacks associated with such prior art practices for analyzing wear particles. For example, visually studying a sample under a microscope is very time consuming for the technician and results in substantial labor costs. Moreover, the repeated study of samples under a microscope can lead to eye strain, fatigue, and other health related problems. Furthermore, the reliable detection and diagnosis of abnormal wear is highly dependent upon the knowledge and level of skill of the technician studying the sample. A relatively inexperienced technician, for example, may be more likely to misdiagnose abnormal wear based on the particulate than a technician having more experience.
The aforementioned U.S. Pat. No. 4,047,814 describes an automated apparatus for examining particle concentration/distribution on the substrate using a densitometer. However, the apparatus provides such particle concentration/distribution information only with respect to a few discrete locations along the deposit pattern on the substrate. The apparatus described in the '814 patent does not provide sufficient information to construct a substantially continuous profile of the particle concentration along the deposit pattern. As a result, information between the discrete locations is not considered when evaluating the particle concentration/distribution. This can lead to misdiagnoses and false negatives, for example.
According to another known automated apparatus, a pair of photodiodes are positioned adjacent the substrate at locations predetermined to hold particles of prescribed dimensions. For example, the first photodiode provides an output signal indicative of the concentration of particles which exceed a predetermined dimension, e.g., greater than 3.0 micrometers in diameter. The second photo diode provides an output signal indicative of the concentration of particles which are less than or equal to a predetermined dimension, e.g., less than or equal to 3.0 micrometers in diameter. While such an apparatus is capable of providing a rough indication of the particle concentration, the apparatus cannot provide a substantially continuous profile of the particle concentration along the deposit pattern.
Furthermore, the success rate of the above-discussed automated systems for identifying abnormal wear is still largely dependent on the level of skill of the technician. The technician must still be able to recognize and evaluate various trends, etc. in the resultant information. This can be particularly difficult in view of the limited information available to the technician from the automated apparatus. Thus, these systems are still likely to result in misdiagnoses, etc.
In view of the aforementioned shortcomings associated with conventional systems for analyzing wear particles deposited on a substrate, there is a strong need in the art for a method and apparatus for automatically analyzing the particle concentration and providing a substantially continuous profile of the concentration along the deposit pattern. Moreover, there is a strong need for a method and apparatus for automatically analyzing the deposit pattern and providing a diagnosis which is objective and less dependent on the particular level of skill of the technician.