Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
2003-03-13
2004-08-24
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C396S106000, C356S005010, C356S005100
Reexamination Certificate
active
06781675
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electro-optical distance measuring system for large measurement ranges with parallel spaced arrangement of the optical transmitting and receiving axes, in para-axial arrangement, as an easy-to-use distance measuring device.
One such electro-optical distance measuring system, as described in U.S. Pat. No. 4,403,857, for example, features in addition to the computing and input/output unit, a phase and echo time measurement and a reference photo diode, particularly a beam source with transmitting optics and a separate beam receiver with receiving optics, whose optical axes are each oriented parallel to the measuring beam. The primary light beam leaving the beam source is, after collimating in a collimating lens, split into a measurement light beam and a reference light beam that impinges on the reference photo diode. Conventionally, the beam source has transmitting optics and a beam receiver with receiving optics each as a structural unit. The measurement range limited by the dynamics range and the effective aperture of the beam receiver is, in distance measuring systems of such simple design principle, too small.
According to DE19513823, in an electro-optical coaxial distance measuring system, the beam source designed as a laser diode and the beam receiver are each electrically conducting fastened directly to a common, rigid circuit board with other electronic components and oriented vertically to each other. Additionally, upstream of the transmitting optics, reference light beam output coupling of the primary light beam is at a reference photodiode. There is no para-axial arrangement of the optical transmitting and receiving axis, whereby additional beam deflection means such as deflection mirrors are required.
According to DE19855296, a large-area photodiode not requiring adjustment is used as the beam receiver. In use, large-area photodiodes enable only a small measurement range due to interference effects such as external light, homogeneity defects on the active detector surface, dark current and interference reflections from the local environment and on smaller limited measurement frequencies, e.g. 500 MHz. In addition, they have a comparatively high measurement error and require long measuring times.
According to DE 19860464, a manual laser distance measuring device for the large measuring ranges of from 0.30 m to 30 m common in the construction trade features in the focal point of the receiving optics a small-area photodiode for minimizing interference effects and modified receiving optics with an addition secondary focal point offset at an angle for the image, which is offset by the para-axial arrangement, of a measurement object situated in the near range. Essential to this solution is that the modified receiving optics features precisely two focal points on the image side, which arise in that the receiving lens consists of a primary lens region and a secondary lens region, wherein the secondary lens region runs, extended over the entire diameter of the receiving lens, vertical to the transmitting axis and has a trapezoidal shape, which becomes narrower towards the transmitting axis. The two lens regions are dimensioned so that over the entire desired distance range a reflex signal lying within its sensitivity range is received by the beam receiver.
The purpose of a highly sensitive distance measuring device is minimization of the interference effects limiting the measurement range, in particular those interference effects that are produced by detected foreign light. For reducing impingement of foreign light either small detector surfaces and/or large focal distances of the receiving optics can be used. When such an arrangement is used, the ratio of detector diameter to focal distance has a decisive role. The smaller the ratio, the less interfering foreign light is detected. In non-circular area active detector surfaces or in arrangements with a plurality of detector surfaces one refers to diameter in the following, whereby a circular area of equivalent detector diameter is meant. A small ratio of equivalent detector diameter to focal distance of the receiving optics makes the configuration and particularly the photodiode relative to the receiving optics and the measurement light beam, needful of adjustment. Such adjustment, which usually, for example, according to EP701702, is made possible by mechanically adjustable beam adjustment systems in the measurement path such as a light guide fiber, which represents potential sources of error in the rough construction industry.
During the adjustment procedure, the laser measurement device and conventional adjustment auxiliary means is adjusted, in the presence of an activated measurement light beam, to the optimal beam path. For the purpose of simplified description, reference will be made in the following to a small-area photodiode, wherein the small ratio of equivalent detector diameter to focal distance to the receiver optics is meant. Measures for signal extension for the lower distance measuring range are required since configurations with a small ratio of detector diameter to focal distance tend towards a strong lateral offset of the imaged light spot so that in short distances, under certain circumstances, no light reaches the photosensitive surface.
The measures are either the use of additional elements in the receiver beam path, which as in the device of DE 19860464, generate an additional secondary focal point or deflection elements, and as in the device of EP 701702, which guide the light from the near range to the active detector surface. Likewise, moveable active deflector surfaces, as in the device of EP 701702, can be used. Another measure is the use of at least one second active detector surface, which especially detects light from the near range. A slit-like active detector surface is also possible, wherein decreasing distance parts of the imaged measurement light beam run along the slit. All measures described are characterized in the description as measures for signal extension for the lower distance measurement range.
SUMMARY OF THE INVENTION
The object of the invention is to provide a robust adjustable, para-axial distance measuring device for large measurement ranges. A further object is that the adjustment procedure should require the shortest possible time and should be easy to automate. Additional beam deflection systems or beam adjustment systems such as deflecting mirrors and mechanical devices for tilting and offsetting should be eliminated. Such an arrangement results in a reduction of costs and in increased reliability of the distance measuring device because of the reduced component requirement.
This object is achieved, in accordance with the invention, by an electro-optical distance measuring system for large measuring ranges having a para-axial arrangement of a beam source with transmitting optics and a beam receiver, designed as at least one small-area photodiode, with receiving optics, which contains processing for signal extension for the lower distance measuring range. The beam source, the transmitting optics, the receiving optics and the beam receiver are each oriented parallel to the measurement light beam. The measurement light beam reaches directly; that is, without beam deflection devices or beam adjustment devices, through a protective window, through the transmitting optics to the measurement object and to the receiving optics. The beam source and the small-area photodiode are rigidly connected with each other by at least one intrinsically rigid connected circuit board. At least the small-area photodiode electrically conducts and temporarily adjusts to the position using its electrical contacts and, optionally, using its housing fixed directly to the adjusted position on the circuit board.
A robust para-axial distance measuring system is realized as result and, temporarily during the adjustment process, is adjustable in the position of the small-area photodiode with respect to the receiving optics, for example, by an enlarged
Gogolla Torsten
Penzold Martin
Schmidt Dieter
Schusser Gero
Seifert Helmut
Buczinski Stephen C.
Hilti Aktiengesellschaft
Sidley Austin Brown & Wood LLP
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