Optics: measuring and testing – Position or displacement
Reexamination Certificate
1999-05-21
2001-10-23
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Position or displacement
C356S624000
Reexamination Certificate
active
06307636
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for measuring the distance between an objective and an object, and to a distance measuring instrument which operates according to this method.
BACKGROUND OF THE INVENTION
In connection with microscopes, in particular, users need to know the distance from their object to the objective of the microscope.
The most varied methods have been proposed for this purpose. For example, there are transit-time measurements using pulse-coded laser beams. Various optical methods, such as the split-image method or triangulation method, are also known. Thus, for example, the so-called MKM microscope design from the Zeiss company applies a pulsing laser beam which is directed onto the focus. If the object plane is located in the Z-direction upstream or downstream of the focal plane, the laser luminous point blinks left or right of the optical axis of the microscope. Whereas the first method is electronically complicated and affected by functional errors, the second method requires a substantial optical outlay.
BRIEF SUMMARY OF THE INVENTION
It is therfore the object of the invention to find a new method for measuring distances which is easy to evaluate in optical terms and permits reliable measurement of distances.
The method is implemented according to the invention by means of the features described herein and the device is designed in accordance with the features described herein.
An important idea is for two essential parallel beams (as a rule, but not exclusively, these are laser beams) to be directed in the parallel beam path of a microscope onto the objective or through the objective. Even if the focal length of the objective is not known, it can be measured exactly by virtue of the fact that the two beams—brought to converge at the focus—appear as a single luminous point. The distance from the principal plane of the objective then corresponds to the focal length. If, however, the object plane is not located at the focal point, that is to say is located at a distance differing therefrom, two laser luminous points are seen on the object plane. The distance for the two laser luminous points from one another is a measure of the difference between the focal plane and the object plane. The distance can be determined by computation as a function of the focal length of the objective and the stereobase of the two luminous light sources by the objective. By means of a geometric coding of the laser luminous points, for example in a horizontal or vertical line, by corresponding upstream lenses or masks in the laser beam path, images of such markings are obtained, with the result that a negative or positive distance from the focal plane can be detected as well.
Variants of this and further specific designs are described in the dependent claims. Thus, for example, instead of the geometric coding it is possible to provide temporal coding in which, for example, one laser beam lights up on one occasion and then the other lights up with a time shift. It is not imperative according to the invention for the two laser beams actually to be present in parallel upstream of the parallel beam path of the objective. Any desired angular deviations from parallelism are conceivable, if the objective or the microscope is calibrated after installation of the elements producing laser light, and the calibration is taken into account in the calculation. In the case of such a design variant, a specific, defined distance between luminous points in the object plane indicates a focused state of the objective with reference to the object plane.
The accuracy of the measurement of distance according to the invention is influenced by the angle &khgr; which the two beams form with one another.
A good measurement result occurs at &khgr;=90°.
Also important is the position of the object plane relative to the optical axis. If these are mutually perpendicular, measurement is performed without any problem. There is no need for correction. The measuring points are then situated symmetrically relative to the optical axis. In the case of asymmetry, compensation can be performed computationally by measuring the respective distance of the respective measuring points from the optical axis and calculating back from there to the inclined position of the object plane. The position of the optical axis can be detected optically in this case in a simple way in as far as it is displayed by the point of intersection of the laser beams as soon as it becomes visible. The measuring system can thus be calibrated.
Of course, the optical frequency of the laser beams can be in the visible and also in the invisible region if appropriate detecting means are provided. Thus, for example, in the infrared region it is possible to use CCDs as detection means.
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Schwarz, et al. “Navigierte Neurochirurgie—High-Tech Für die Gesundheit”, Zeiss Information Mit Jenaer Rundschau, 4: pp 4-6, (1995) No. 5.
Foley & Lardner
Font Frank G.
Leica Microsystems AG
Punnoose Roy M.
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