Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1999-08-31
2002-06-25
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S005010, C356S005100
Reexamination Certificate
active
06411371
ABSTRACT:
The invention relates to a device for optical distance measurement in geodetic and industrial surveying, according to the features in the preamble of claim
1
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Optical distance measuring devices have wide-ranging applications in geodetic and industrial surveying. Together with an angle measurement, they help to determine the three-dimensional coordinates of target points or target objects in space. The target points to be surveyed are marked by means of reflection-supporting aids. Other target points or target objects are directly sighted as such. From the point of view of measurement, a distinction is made between cooperative and noncooperative target objects. Cooperative target objects are self-luminescent or reflecting target marks, such as spherical reflectors, reflecting foils or triple prisms. Noncooperative target objects are natural, rough surfaces, such as, for example, those of buildings or rocks.
The target objects are sighted by means of a theodolite, which contains a distance-measuring device mounted on the theodolite telescope, or by means of a tacheometer, i.e. a theodolite having an integrated distance-measuring device. The distance measurement is carried out by the phase or transit time measuring principle with intensity-modulated or pulsed radiation. The three-dimensional coordinates of the target objects are determined relative to a specified coordinate system by the angle and distance measurement. Consequently, the coordinates of individual target points can be determined in geodetics, in building surveying or in industrial surveying. Alternatively, surfaces, for example of aircraft, provided with cooperative target marks can be surveyed (W. Huep, O. Katowski: Theodolitsysteme fúr Industrielle und geodätische Messungen [Theodolite systems for industrial and geodetic measurements], in: Technische Rundschau No. 39, 1988, pages 14-18).
On the other hand, it is also possible to pinpoint the coordinates specified on a map or on a building plan by means of a tacheometer and a surveyor's staff equipped with reflectors. This is usual in the building industry or for locating in road construction. Tacheometers are also used for controlling advancing machines in road construction, tunnel construction and mining.
Conventional electronic theodolites measuring to target marks utilize distance-measuring devices which are integrated or mounted on the theodolite telescope. Virtually all integrated or mounted distance-measuring devices have a biaxial optical system for transmitted and received beams. Furthermore, EP 0 313 518 B1 discloses a distance-measuring device in a coaxial optical embodiment which has an He-Ne laser as a light source and can measure to reflection foils and to natural objects. However, this is a mounted distance-measuring device which as such has a parallax with respect to the theodolite sighting axis and in which the location of the measuring spot and the location sighted via the theodolite are not identical.
The biaxial integrated or mounted distance-measuring devices have a separate, in general laterally offset transmitted and received beam path. This takes into account the lateral offset of the light beam on reflection by retroreflecting target marks (e.g. triple prisms) which reflect an incident light beam parallel and with lateral displacement. In the case of the integrated distance-measuring device, one half of the theodolite telescope lens is used for the transmitted beam and the other half of the telescope lens for receiving the reflected beam. On the other hand, a mounted distance-measuring device has both a completely separate optical axis for the transmitting and receiving optical system and a parallax with respect to the sighting axis of the theodolite telescope. This means that the target point to which the sighting axis of the theodolite telescope is pointed and the location of the measuring spot of the mounted distance-measuring device on the target object are not identical. This is disadvantageous for point measurements. Because of this inter alia, mounted distance-measuring devices are gradually being replaced by integrated distance-measuring devices.
Biaxial distance-measuring devices capable of measuring the distance both to reflector targets and to noncooperative target objects having a naturally rough surface are furthermore known. For example, such devices are used for surveying poorly accessible surfaces, such as in plant construction (cooling towers of nuclear power stations), in bridges, dams, in quarries or in shipbuilding. Further applications are in the profile measurement of tunnels, shafts and roads and in the surveying of building facades. The range is a few hundred meters in the measurement to such noncooperative targets. The biaxiality of these distance-measuring devices gives rise to a parallax which results in an offset of the center of gravity of the image spot. This effect is so pronounced, particularly at close range, that a measurement is not possible without additional technical measures. For example, ancillary lenses are therefore mounted on the transmitting and receiving optical system in the measurement of short distances, as is the case with the distance-measuring device WILD DIOR 3002S from Leica. This implies a certain handling effort. In another technical solution, the parallax is compensated by rotating a rhomboid prism, mounted on ball bearings, as a function of the displacement of the focal lens of the theodolite telescope (biaxial tacheometer Rec Elta RL from Zeiss with two lenses for the transmitting and receiving optical system). With the precisely moved optical and mechanical components, such a compensation of the parallax means a high degree of technical complexity and moreover leads to a large and heavy surveying instrument.
The biaxial distance-measuring devices mentioned so far operate with radiation sources which emit infrared light with large beam spread angles. The light beam diameters are as much as 15-20 cm at a distance of 100 meters. In the case of distance measurements to reflectors, it is true on the one hand that large light beam diameters are advantageous for locating the reflectors. On the other hand, a large light beam diameter for measuring to noncooperative targets leads to greatly reduced local resolution since . the distance value intensity-weighted according to the local reflection properties is measured over the irradiated area. In the case of inclined or structured object surfaces, this does not result in a true distance to the target point of the distance-measuring device. Thus, for example, protuberances present on the object surface and having a small diameter, pipes and cables on facades or in inner rooms of buildings or the structures of window reveals are not measurable owing to the large cross-sectional area of the light beam. Even in the case of short distances of a few meters, the light beam diameter is already several centimeters. Consequently, even steps in surfaces are easily covered by the large measuring spot, resulting in an erroneous distance measurement.
In the case of inclined surfaces on which the measuring light beam is not perpendicularly incident, inhomogeneities of the object surface within the measuring spot can give rise to locally different degrees of reflection. Such inhomogeneities are formed, for example, by soiling, by different surface coatings, moisture or roughness of surfaces. The locally different reflections within the measuring spot result in an unequal weighting in the distance measurement, so that it is not the actual distance to the point of intersection of the sighting axis of the surface to be surveyed that is measured.
Finally, with the use of infrared radiation for the measurement, the actually measured object point on a surface is not detectable. The object point is sighted only indirectly either by means of the telescope optical system of the tacheometer or by the use of the visible radiation of a laser pointer aligned with the sighting axis of the distance-measuring device.
Hand-held distance-measuring devices wh
Benz Paul
Hinderling Jurg
Buczinski Stephen C.
Leica Geosystems AG
Oliff & Berridg,e PLC
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