Optics: measuring and testing – By polarized light examination – With light attenuation
Reexamination Certificate
2000-01-24
2001-02-20
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By polarized light examination
With light attenuation
C356S370000
Reexamination Certificate
active
06191857
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method and an apparatus for measuring selected characteristic magnitudes of specimens which have at least one edge, particularly a cutting edge.
Particularly cutting tools, such as milling, drilling or other chip-forming tools, have cutting edges adjoined by a rake face and a relief face. The properties of the cutting edge as well as the position and properties of the rake face and the relief face, and particularly the rake angle and the relief angle form characteristic values which are often of particular significance in chip-forming cutting tools. Further, it may be required to determine the relief angle of the tool to be able to reproduce the same, for example by re-grinding, and also to measure the relief angle of ground or otherwise machined tools to monitor the machining result or to verify the machine settings.
Measuring methods which operate by contacting require a mechanical scanning of the cutting and/or relief faces and are limited in their resolution.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved measuring method and apparatus of the above-outlined type which reliably detects the selected parameters of specimens (test pieces).
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the method of measuring selected values of a specimen having at least one edge is performed with an apparatus which positions the specimen in the path of a light beam such that the specimen at least partially interrupts the light beam and the edge borders a shadow cast by the specimen. Further, the apparatus rotates the specimen about a rotary axis through at least one predetermined angle; monitors, by an observing apparatus, a boundary of the shadow cast by the edge; generates, by the observing apparatus, signals representing positions of the boundary; and evaluates the signals for determining the selected values.
The measuring method and apparatus according to the invention provide for a contact-less measuring of edges and selected faces of specimens. The specimen is scanned by a light beam which, as a result, is partially blocked; that is, the illuminated specimen casts a shadow. For measuring or determining the desired parameter the specimen is moved and its shadow observed. For this purpose an observing apparatus, for example, a line camera or similar device is provided which detects the position of a light-to-dark transition. The light-to-dark transition is, as a rule, produced by the specimen edge to be examined. In case an angle or a position of a specimen face is to be determined as a characteristic value, the light-to-dark transition is generated in sequence for two edges which border the surface. For determining the characteristic value, the specimen is rotated in such a manner that the light-to-dark transition travels on the observing apparatus which, from the manner the light-to-dark transition travels as the specimen is rotated, draws conclusions concerning the values of interest.
It is an advantage of the method and the apparatus according to the invention that it determines characteristic values without contacting the specimen; measuring may be performed rapidly and, if required, in an automated manner. No particular equipment for measuring or testing the various specimens is required. It is not necessary to either replace the scanning components or to provide measuring edges or similar mechanical scanning devices which would have to be replaced.
By means of the optical measuring method and the optical apparatus according to the invention high-precision measurements may be performed even if the resolution of the observing apparatus is limited by the number of the individual light sensitive elements. This is in particular feasible if not only the number of the illuminated or, as the case may be, not illuminated elements is determined, but in the light-to-dark transition intermediate values are determined as well. This results in a resolution which is greater than the number of the light sensitive elements. The measuring accuracy of the detecting device which follows the rotation of the specimen is preferably so high that, for example, 0.1° or even smaller angular steps may be detected. Therefore, a very high number of measuring values may be worked with which, in turn, results in an accurate measurement of the specimen, at least as concerns the selected parameters.
If, for example, a relief angle is to be measured at a relief face of the specimen, the shadow of two specimen edges bordering the relief face and turned in sequence in the light beam is observed. It is an advantage of the invention that the angle of the relief face may be measured relatively independently from the actual configuration of the relief face. For example, a slightly concave relief face is considered as the imaginary connection between the cutting edge and a parallel edge spaced therefrom and bordering the relief face. As compared to mechanical scanning processes which rely on a contacting of the surface, the measuring reliability is appreciably increased.
The shifting of the shadow of the edge to be tested or, more precisely, the shifting of the light-to-dark boundary as a function of the rotation of the specimen yields further information which is detectable by the evaluating device. If, for example, an accurately formed edge of the specimen is rotated through the light beam, the length of the shadow detected by the observing apparatus represents a cosine curve as a function of the angle of rotation. The cosine function may contain a phase shift angle and an offset. Based on the deviation of the detected function from an ideal cosine function, conclusions may be drawn as concerns the quality of the edge, its rounding or chamfer size.
It is a further advantage of the process according to the invention that,. for example, the circumferential relief angle which is to be measured in a plane that is perpendicular to the rotary axis, may be determined independently from the inclination of the cutting edge. This permits the measurement of cutting edges and relief faces of chip-forming tools whose cutting edges extend parallel to the rotary axis or at an inclination thereto, as it is the case in helically grooved tools, conical milling tools or the like.
It has been found to be advantageous to approximate the measuring values obtained during rotation of the specimen through a light beam, as a cosine function and to read off the characteristic values of the tested edge or adjoining surface regions from such a cosine function or to obtain such values from cosine functions of different edges. The cosine curve of the shadow length as a function of the rotary angle is obtained while observing the projection of a mathematically exact edge and is thus an ideal function. By approximating the ideal function with actually obtained measuring values, the actual (real) edge is associated with an ideal edge. The relief face may then be considered, for example, as a planar face which connects two adjoining ideal edges with one another.
To obtain the parameters of the cosine function, a section-wise regression has been found to be an advantageous approximation step. To perform such a regression, the angular values detected in small steps and the associated positional values of the light-to-dark transition of the shadow projection of the edge are gathered into value pairs, wherein several value pairs form a value pair group. For each value pair group then the searched-for cosine function is determined. In graphic terms, a regression section is shifted stepwise over the entire measuring curve. The regression sections in which the determinations of the cosine functions are effected may be selected as being either overlapping or non-overlapping. In the former case, a measuring value pair is simultaneously associated with a plurality of value pair groups, while in the latter case, each value pair belongs only to a single value pair group. An overla
Font Frank G.
Kelemen Gabor J.
Merlino Amanda
Venable
Walter AG
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