Television – Camera – system and detail – Optics
Reexamination Certificate
1997-11-04
2001-05-01
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Optics
C348S345000
Reexamination Certificate
active
06226036
ABSTRACT:
BACKGROUND
The present invention relates to a device for three-dimensional investigation of an object according to the preamble of claim 1.
A device of this kind is known from DE 40 35 799. In that patent, an illuminating grid with a pixel size is imaged on a receiver array, which matches the pixel size of the photosensitive areas of the receiver array or is a whole-number multiple of said array. The diaphragm action of the receiver array is utilized. A system of this kind has the disadvantage that during the evaluation of images taken from various focal planes to determine the depth values, the absolute brightness values are always evaluated and their maximum must be determined.
A device is known from JP 1-55513(Feb. 3, 1989) which is suitable for rapidly focusing a microscope using incident light from the aid of a laser beam. For this purpose, a photodiode is utilized with four receiver segments and the object point illuminated by the laser is imaged through an optical system with cylindrical lenses on the four-quadrant receiver. This principle differs however basically in its effect from pupil division, since no focused image of the object point is produced. The device according to JP 1-55513 is unsuitable for rapid 3-D measurement.
DD 265 224 likewise describes a device with point-wise object illumination, but it only makes it possible to measure an object location simultaneously. It is likewise unsuited for rapid measurement of large sample areas.
DE 26 34 655 teaches a device for focusing a single-lens reflex camera. It is unsuited for measuring 3-D objects.
In the book “Technische Optik” [Technical Optics] by Gottfried Schroeder, Vogel-Verlag, 1977, page 145, a device from the field of photography is described that uses a double prism and serves to focus a camera. Since only one object position is detected, this system cannot be used for automatic measurement of larger object areas.
A device that makes it possible to determine the focus of an individual measurement point with a zero signal detection is known from the company publication “Microfokus, Beruehrungslos messen” [Microfocus, Measurement with Zero Contact] from UBM Messtechnik, D 76275 Ettlingen. In that publication, the light from a laser diode is imaged on the object to be illuminated and the light reflected from this object is split by a pair of prisms so that the two half pupils are imaged on two receiver pairs. The light from a laser diode is imaged on the object to be measured and the light reflected from the object is split by the pair of prisms in such fashion that two half pupils are imaged on two receiver pairs*. A system of this kind, apart from the focus, supplies a directional signal that indicates the direction in which the position of the measured object differs from the focus position. However, only a single point on the object is detected. Measurements with a system of this kind therefore require a great deal of time, especially when large areas of the object are to be measured.
*Evident repetition. Translator's note.
SUMMARY OF INVENTION
The present invention has the goal of providing a device that makes it possible to determine focus with zero signal detection and in this way to detect many measurement points at the same time. This goal is achieved according to the invention by the combination of features in claim 1.
Advantageous embodiments of the invention are shown in claims 2 to 6.
The system according to the invention has the advantage that the focus position of the individual measurement points is determined by zero signal detection and that very many measurement points are detected simultaneously. This is performed economically because receiver arrays, preferably CCD arrays, and prism arrays in the prism plane are used as the radiation receivers. The arrays can be produced economically by compression molding for example.
Zero signal detection is implemented by the arrangement of the receiver array relative to the prism array being so designed that in the focus case the image of the light reflected from the illuminated point on the sample and deflected by a prism falls symmetrically on the boundary line between two radiation receivers (pixels) of the receiver array.
The system according to the invention differs from the system described in Patent DE 40 35 799 in that the diaphragm function of the radiation receivers arranged in an array is utilized in the latter, with the photosensitive areas of said receivers being separated from one another by gaps. Focus detection is performed in this patent by evaluating the intensity maximum detected on each pixel of the radiation receiver array. For this purpose, a measurement series is performed that stores the values for several different z-positions of the object in the computer. For each pixel, this determines the z-position at which its intensity has its maximum. It supplies the depth value to be determined. In the present invention, on the other hand, the difference between the signals of two adjacent pixels and the receiver array is evaluated. When it is equal to zero, the focus position exists that supplies the depth of value to be determined. Receiver arrays are used for this purpose that have no zone that is insensitive to light, or only a small zone of this kind, between adjacent pixels. Instead, for detecting the difference signal in the present invention, it is necessary to use receiver arrays with photosensitive areas that are directly adjacent to one another. For this reason, the system according to the present invention differs basically from that described in the abovementioned DE.
The system according to the invention is especially suitable for three-dimensional measurement of mechanical parts in incident light and for recording 3-D images of fluorescent objects. For mechanical parts, a semi-transparent mirror is placed in known fashion in the beam path to separate the illuminating light from the light reflected from the object. For fluorescence applications, a dichroic mirror is used in a manner known of itself, and possibly light filters as well, to separate the illuminating light and the light emitted by fluorescence from the object.
REFERENCES:
patent: 4408853 (1983-10-01), Tokutomi et al.
patent: 4492449 (1985-01-01), Oinoue et al.
patent: 4500189 (1985-02-01), Aoki
patent: 4845352 (1989-07-01), Benschop
patent: 4849782 (1989-07-01), Koyama et al.
patent: 5239178 (1993-08-01), Derndinger et al.
Fish & Richardson P.C.
Garber Wendy R.
White Mitchell
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