Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1998-12-22
2001-06-26
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
Reexamination Certificate
active
06250142
ABSTRACT:
This application corresponds to and claims priority under 35 U.S.C. § 119 with respect to Swedish Application No. 9704864-9 filed on Dec. 22, 1997, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention generally relates to an apparatus for measuring waviness of surfaces. More particularly, the present invention pertains to an apparatus for measuring the waviness of surfaces of bearing parts, such as the rolling elements of bearing parts (i.e., balls, rollers and bearing rings) using a control element that is rotatably applied against a surface to be checked.
BACKGROUND OF THE INVENTION
The poor correlation between waviness and actual vibration measurements of assembled bearings at least for higher frequencies is a significant problem, as the vibrations cannot always be predicted after a waviness measurement using known technology. Also, known technology for effecting such a waviness measurement makes the measurement process rather time consuming.
Before now, it has only been possible to determine amplitude variations on the order of one hundred to ten nanometers in the production environment. However, a need exists for a method and apparatus that are able to measure amplitudes of a much smaller size. Such amplitudes might be on the order of or a part of the diameter of an atom or smaller.
The measurement is in particular needed for high precision bearings used in high precision instruments, bearings used in high speed applications such as household equipment and computer hard disc motors, and other applications to reduce noise caused by vibrations at a high frequency. Thus, the need for measuring apparatus and methods along the lines mentioned above is particularly acute in bearings where the bearing noise can be particularly disturbing because it occurs as a high frequency noise and in noise and vibration sensitive applications.
In the past, a lightly loaded pick-up has been used for measuring the waviness of different parts of bearings, such as balls, rollers, and rings. The pick-up is run in one or more narrow pathways on the surface to be tested. Variations in the bearing material, such as inhomogenities and surface roughness, influence the efficient waviness of the bearing, but is typically not correctly registered by the pick-up. The pick-up method thus does not measure all relevant effects which occur in real applications. The surface structure affects the pick-up in quite another way than a higher loaded rolling or rotating body working on a surface.
The difference might be due to the fact that only a fraction of the raceway area is measured, that local variations of the e-module in the subsurface material appear and affect the measurement; and/or that the EHD-film (ElastoHydroDynamic-film) thickness varies due to surface effects.
The rolling of a ball on a ring in a bearing affects the material down to, for example, a depth of thirty to forty microns on a small bearing, while a pick-up does not have such an impact on the material. This changes the requisites for a correct measurement of the functional behavior of the bearing. Additionally, a ball on a bearing ring is affected by the whole contact area and so by measuring just a fraction of the area it is thus not normally representative for the integrated value of the whole area.
It is of importance to measure the surface waviness of a bearing and its parts to obtain a tool or mechanism useful in quality determination after assembling such parts, i.e., so that the vibrations of the bearing can be predicted. It is of further importance to be able to control the process quality and thereby control the process equipment with regard to wear and other process parameters.
SE-C-314 214 discloses a method for testing the rotary movement of balls using a testing roller to check for the quality of the surface layer, the surface, or the shape. The roller is brought to act upon a ball with its surface being changeably active due to its shape. This document is not disclosed in the context of measuring waviness, but larger irregularities or unevenesses on the surface. The disclosed method is particularly adapted for use in connection with large balls.
In light of the foregoing, a need exists for a way of measuring the waviness of surfaces with higher accuracy than previously possible.
A need also exists for measuring the waviness on a larger surface (e.g., an adequate surface when considering a bearing surface) than with previously known apparatus to provide a functionality related integration, thereby making it possible to measure and integrate the influence of surface structure and surface roughness.
A need also exists to be able to produce bearings of higher quality, where the vibrations of a complete bearing can be predicted in an accurate manner.
A further need exists for controlling the process conditions under which the bearing parts are manufactured, as condition variations in the process will be monitored and considered.
SUMMARY OF THE INVENTION
In light of the foregoing, the present invention provides a method and apparatus for testing the waviness of surfaces, in particular the surfaces of balls, rollers and rings to be used in assembling bearings. A loaded element having a geometry similar to the geometry of the object of the final bearing is placed in a hydrostatic pocket and is loaded with a constant force. The element is adapted to be moved across the surface to be tested while a transducer monitors the movement of the element via the hydrostatic pocket, thus producing a signal corresponding to the surface waviness.
It is important to measure the surface waviness of a bearing to provide a tool or mechanism for separating bearings into different categories of quality (i.e., so that the vibrations of a bearing can be predicted). By virtue of the present invention, the waviness can be very accurately monitored, and by using a subsequent processing of the signal obtained, the signal related to the testing element can be separated from the signal related to the object tested. In this way, the waviness of the object tested can be registered or determined under conditions and geometries very similar to the actual existing conditions in the bearings.
According to another aspect of the invention, an apparatus for measuring the waviness of a surface in a bearing part that is adapted to cooperate with a bearing component to form an assembled bearing includes a movable control element that is to be applied against the surface of the bearing part to be measured, with the control element having a geometry similar to a geometry of the bearing component. The control element is carried in such a way as to allow free rotation of the control element. A device is provided for applying a load force to the control element to press the control element against the surface of the bearing part to be measured, and a device is provided for carrying and rotating the bearing part to be tested. At least one sensor measures the movement of the control element, and a device is provided to produce, based on the output from the sensor, a signal corresponding to the waviness of the surface of the bearing part.
REFERENCES:
patent: 5565623 (1996-10-01), Philpott et al.
patent: 2742326 (1979-03-01), None
patent: 314 214 (1969-09-01), None
patent: 526771 (1976-10-01), None
patent: 1193475 (1985-11-01), None
Burns Doane Swecker & Mathis L.L.P.
Larkin Daniel S.
SKF Nova AB
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