Method and array for detecting the position of a plane...

Details Method and array for detecting the position of a plane... Method and array for detecting the position of a plane...

2001-03-16

2003-07-15

Tarcza, Thomas H. (Department: 3662)

Optics: measuring and testing

Angle measuring or angular axial alignment

Relative attitude indication along 3 axes with photodetection

C356S139100, C356S152100

Reexamination Certificate

active

06594006

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority of International Application No. PCT/EP00/04493, filed May 18, 2000 and German Application No. 199 23 821.9, filed May 19, 1999, the complete disclosures of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a method and an arrangement for detecting the position of the scanned plane XY of an object and for its positioning in the focal plane X′Y′ of a laser scanner, preferably in a laser scanning microscope.
b) Description of the Related Art
In the last two decades, scanners have achieved an advanced state of the art. Particularly in medical engineering, metrology and, above all, in microscopy, it is becoming more and more common for objects to be scanned by a laser beam. In the biological-medical field, for example, laser scanning microscopes have clear advantages over conventional microscopes which stem essentially from the higher resolution that can be achieved and the possibility of differentiating between determined depth layers.
Accordingly, in fluorescence microscopy, due to the high point intensity of the focused laser beam, it is possible to utilize the sensitivity of photomultipliers for image building when the fluorescence itself is weak. However, XY scanners require very high positioning accuracy in orientating the object to be scanned relative to the focusing plane of the microscope.
The precision with which the plane of the specimen to be analyzed must be brought into the focus of the laser beam in order to prevent intensity losses and avoid deficient image quality increases as depth resolution increases.
To this extent, in connection with the continuing development in this technical field, it is necessary to provide methods and arrangements by which the objects and planes to be scanned can be exactly and, if possible, automatically oriented relative to the focal plane. In general, requirements can no longer be met by the technique, still often applied, of positioning by means of sensitively adjustable manual drives with repeated position correction.
OBJECT AND SUMMARY OF THE INVENTION
On this basis, it is the primary object of the invention to provide a method enabling an automatic and precise positioning of a scan plane XY in the focal plane X′Y′ of a laser scanner.
According to the invention, it is provided in a method of the type described above that, after a rough orientation of the object carried out by fixing on an object holder, a laser beam is directed successively in time to at least three different points P
1
, P
2
. . . P
n
located in the scan plane XY of the object and, in doing so, each of the reflections proceeding from the points P
1
, P
2
. . . P
n
is imaged on a position-sensitive detector, an actual position value is determined at the detector for each reflection and is compared with a stored reference position value, actuating or adjustment commands for changing the inclination of the object holder are obtained from the deviations of the actual position values from the reference position values, and the inclination of the object holder is changed on the basis of these adjustment commands until points P
1
, P
2
. . . P
n
are located in the focal plane X′Y′ of the laser scanner.
The essential advantages of this method consist in that, to a great extent, components which already exist in a laser scanner can be used for determining position, e.g., the position transmitter for the laser beam and the optical elements for transmitting the laser radiation reflected by the specimen to an optoelectronic reception device, followed by an evaluating unit. Further, positioning is not only more exact in this way, but is also substantially faster than in any of the previously known methods.
In a preferred embodiment of the method according to the invention, three points P
1
(x
1
;y
1
), P
2
(x
2
;y
2
) and P
3
(x
3
;y
3
), where y
1
=y
2
=x
3
=0 and x
1
=−x
2
≠0; y
3
≠0, are sampled, wherein one point P
0
, where x
0
=y
0
=0, lies approximately in the center of the object and/or of the plane XY to be scanned, P
1
, P
2
, P
3
are preferably points near the edges of the object, and the deviations between the actual position values and reference position values are determined according to the principle of laser triangulation.
Accordingly, three points P
1
, P
2
, P
3
are defined which are advantageously suited to position detection because, first, they are located far apart from each other due to their position at the edges of the object or at the edges of the plane XY to be scanned, which creates favorable preconditions for laser triangulation, and, second, they can be controlled in an uncomplicated manner assuming that point P
0
approximately defines the starting position of the laser beam in the coordinate origin of the focal plane X′Y′.
In triangulation, a light point is projected by means of a laser beam onto the plane of the measurement object to be scanned and the reflected light is imaged on a position-sensitive detector. The position of the reflection on the detector varies depending on the distance between the plane XY to be scanned and the objective, as measured in coordinate Z. The signal emitted by the detector is accordingly a measure for the distance between the reflecting surface and the objective or a measure of whether or not the reflecting point lies in the focus of the objective.
According to the invention, the object is initially oriented in such a way that the laser beam is directed, e.g., on position P
0
, the scanning device is then controlled in such a way that the laser beam is directed to point P
1
, a parallel displacement of the object holder in Z-direction is effected, if need be, until the reflection of P
1
supplies a definite signal to the detector, the actual position value for point P
1
is acquired, the scanning device is then controlled in such a way that the laser beam is directed to point P
2
, the actual position value for point P
2
is now acquired, adjustment commands for tilting the object holder about the Y-axis are now determined from the deviations between the actual position values and reference position values, and the orientation of the X-axis of plane XY parallel to the focal plane X′Y′ is brought about, the scanning device is then controlled in such a way that the laser beam is directed to point P
3
, the actual position value for point P
3
is detected and, finally, an adjustment command for tilting the object holder about the X-axis is determined from the deviation of the actual position value from the reference position value of point P
3
and, accordingly, the parallel orientation of the Y-axis of plane XY relative to the focal plane X′Y′ is brought about.
In a particularly preferred construction of the invention, the steps indicated above are repeated in order to determine any existing deviations and to readjust in the described manner until no deviations are measurable and the planes XY are adjusted parallel with the focal plane X′Y′.
Further, it lies within the framework of the invention that after this orientation of plane XY a parallel displacement in Z-direction is carried out, namely, until the reflections of P
1
, P
2
, P
3
are imaged on the detector with maximum intensity. In this way, it is ensured with great dependability that the plane XY to be scanned is not only oriented parallel to the focal plane X′Y′, but coincides with it.
It is a further object of the invention to provide an arrangement for carrying out the method steps mentioned above and for determining the position of the scan plane XY of an object and for its positioning in the focal plane X′Y′ of a laser scanner, preferably a laser scanning microscope.
This object is met, according to the invention, by an arrangement which is outfitted with an object holder for receiving the object, with a photo-sensitive detector for

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