Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
1999-11-12
2001-09-04
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S498000
Reexamination Certificate
active
06285456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an interferometer and a measurement method employing such an interferometer, and particularly to an interferometer for measuring length of end standards, such as a gauge block or a length bar.
2. Description of the Related Art
Conventional interferometers are employed for high precision measurement of length gauge blocks and length bars used for correcting various types of measurement machines. Such an interferometer operates by first calculating the integer of interference fringe N by preliminary measurement for measuring an end standard at a precision of half wavelength or less, obtaining the interference fringe fraction &egr; by main measurement using laser interference, and finally determining the dimension L of the end measure from the equation L=&lgr;/2 (N+&egr;)
When measuring an end standard at a precision of half wavelength or less, a so-called coincidence method is used where a plurality of wavelengths are used to perform preliminary measurements for each wavelength and use the value which coincides independent of a particular wavelength. As an interferometer, a Twyman-Green interferometer, for example, is used.
However, even when the coincidence method is employed, a comparator separate from the laser interferometer must be employed nd separate measurement must be made, and this in turn requires or temperature equalizations (removing any temperature non-uniformity within a work [end measure] due to human body heat and environment temperature, etc. by allowing the object to rest work for a few hours after placement, the work being the object to be measured) for both preliminary and main measurements (the main measurement being a measurement using laser interferometer), making the measurement steps complicated and thus causing a problem of efficiency being low.
Moreover, when a high precision measurement is made, temperature compensation is required to take into account elongation of the end measure according to the coefficient of linear expansion. However, if the preliminary measurement and the main measurement using laser interference are made separately, it is possible for the error in the thermometer used for preliminary measurement and the error in the thermometer used for main measurement to differ, increasing the difficulty of accurately determining the integer of interference fringe N.
SUMMARY OF THE INVENTION
The present invention is directed to solving the problems mentioned above and provides an interferometer that can successively perform the preliminary and main measurements within the same interferometer and that can measure work such as end measures quickly and with high precision, and a measurement method employing such an interferometer.
In order to achieve the above objective, the present invention provides an interferometer for measuring dimension of a work using laser light interference, comprising a laser light source, a white light source, a first optical assembly for introducing laser light from said laser light source onto a work and a first reference surface acting as reference for laser light interference, a second optical assembly for introducing white light from said white light source onto the work and a second reference surface acting as reference for white light interference, a work adjustment means for adjusting the slope of the work with respect to said first reference surface, an interference fringe detecting means for detecting laser light interference fringes generated by said first optical assembly and white light interference fringes generated by said second optical assembly, and a control means for controlling said first and second optical assemblies, work adjustment means, and interference fringe detecting means to successively perform positional adjustment of the work using laser light interference, preliminary measurement of the work using white light interference, and main measurement of the work using laser light.
By providing a first optical assembly for performing the position adjustment and main measurement of work and a second optical assembly for performing the preliminary measurement of work within the same interferometer, preliminary and main measurements can be performed under identical environment conditions, temperature differences between the preliminary and main measurements can be prevented, and quick and highly precise measurement of the work can be made.
In the present invention, it may be preferable for that said first optical assembly to include a first beam splitter for splitting the laser beam from said laser light source into laser light incident on said work and laser light incident on said first reference surface, and said second optical assembly includes a second beam splitter for splitting the white light from said white light source into white light incident on said work and white light incident on said second reference surface.
It may also be preferable for said first and second beam splitters to be a single splitter. By using a single beam splitter, the structure can be simplified while the precision of the preliminary measurement can be simultaneously improved because a common light path is employed.
In the present invention, it may also be preferred to have a means for introducing the laser light radiated from said beam splitter to said first reference surface and for introducing the white light radiated from said beam splitter to said second reference surface. By using such means, introduction of laser light or white light to respective reference surfaces when the first and second reference surface differ is ensured and interference can be generated.
In the present invention, it may also be preferable that a first shutter for turning the laser light on and off be provided on the light path between said laser light source and said first beam splitter in said first optical assembly, and a second shutter for turning the white light on and off be provided on the light path between said white light source and said second beam splitter in said second optical assembly, and said control means introduces laser light by controlling said first shutter to open and said second shutter to close during position adjustment and main measurement of said work, and introduces white light by controlling said first shutter to close and said second shutter to open during said preliminary measurement.
The present invention may further comprise a moving means for changing the optical distance from said second beam splitter to said second reference surface and means for detecting the moved distance of said moving means. By changing the optical distance, white light interference can be generated at a position corresponding to both ends of the work, and by detecting the change in distance, the distance between both ends, which is the dimension of the work, can be preliminary measured. The order of interference is calculated from this preliminary measurement.
It may also be preferable that said second reference surface be a plane mirror.
It may also be preferable that said second reference surface be a corner cube shaped reflection plane. By shaping the reference surface into a corner cube, the incident white light can be reflected to the direction of incidence and interference can be generated even when a small change occurs on the surface due to movement.
In the present invention, it may also be preferable that said first and second reference surfaces be common. By sharing the first and second reference surfaces, the structure can be simplified.
The present invention also provides a method of measuring a work employing the interferometer, this method comprising the steps of placing said work within the interferometer, introducing laser light into said interferometer and adjusting the position of said work with respect to a reference surface using interference of laser light, introducing white light into said interferometer and performing a preliminary measurement of said work using white light interference, and in
Mitutoyo Corporation
Oliff & Berridge PLC.
Turner Samuel A.
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