Optics: measuring and testing – Range or remote distance finding – With photodetection
Reexamination Certificate
1999-07-29
2001-09-18
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
With photodetection
C356S139100, C356S148000
Reexamination Certificate
active
06292258
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to laser beam receivers and, more particularly, to laser beam receiver units arranged to detect the presence and elevation of a rotating reference laser beam.
Rotating laser beams are commonly used in the fields of civil engineering, construction, agriculture, and surveying to establish a reference plane of light. U.S. Pat. No. 5,033,847, issued Jul. 23, 1991, illustrates a laser transmitter which provides such a rotating reference beam. Photosensitive laser beam receivers are frequently used to monitor the elevation of the reference plane of light. A conventional photosensitive laser beam receiver circuit is described in U.S. Pat. No. 4,693,598, issued Sep. 15, 1987. Many conventional laser receiver circuits employ a plurality of photodetectors disposed in a vertical row. The signals produced by the photodetectors in response to the incidence of a laser beam upon the detector array are utilized to provide an indication of the elevation of the laser beam. The indication may be displayed graphically in an array of LED's or as a numerical value on a visual display.
The above-described laser receivers are designed to provide an accurate indication of laser beam elevation. However, the accuracy of the elevation measurement is limited significantly if the laser receiver is not arranged in a vertical orientation. Indeed, it is often difficult for operators to position a laser receiver close to vertical because the associated terrain may skew their frame of reference. Further, it is often difficult for operators to maintain the receiver at vertical because adverse working conditions and physical constraints of the work environment may make it difficult to stabilize the receiver. Accordingly, there is a need for a laser receiver that is characterized by reduced vulnerability to environmental factors that lead to inadvertent, undetected, or undue laser receiver tilt.
BRIEF SUMMARY OF THE INVENTION
This need is met by the present invention wherein a laser receiver is provided that is capable of providing an accurate indication of laser receiver tilt. Further, the laser receiver of the present invention is capable of correcting a generated elevation signal based upon the indicated laser receiver tilt.
In accordance with one embodiment of the present invention, a laser receiver is provided comprising a laser beam detection unit, an inclination detection unit, and suitable laser receiver control circuitry. The laser beam detection unit is arranged to enable production of an elevation signal indicative of an elevation of a laser beam relative to the laser receiver. The inclination detection unit comprises a reference light source, an optical fiber, and an optical detector. The optical fiber defines a light input end and a light output end and is coupled to the reference light source such that light from the reference light source enters at the light input end and exits from the light output end as an output beam of light. The optical detector is arranged to receive the output beam of light. The inclination detection unit is arranged to permit the output end of the optical fiber to move relative to the optical detector as the primary receiver axis tilts relative to a vertical reference axis. The optical detector is arranged to produce an optical detection signal indicative of a position of the output beam on the optical detector. The laser receiver control circuitry is arranged to generate a receiver tilt signal from the optical detection signal. The receiver tilt signal is indicative of a degree to which the primary receiver axis is tilted relative to the vertical reference axis. The laser receiver control circuitry is also arranged to correct the elevation signal as a function of the receiver tilt signal.
The inclination detection unit may further comprise an index matching compound positioned in an optical path defined between the reference light source and the light input end of the optical fiber. The index matching compound may be arranged to bond the reference light source to the light input end of the optical fiber. The inclination detection unit may further comprise an input lens positioned in an optical path defined between the reference light source and the light input end of the optical fiber. The input lens is preferably arranged to direct light from the reference light source into the input end of the optical fiber.
The inclination detection unit preferably further comprises an optical frame and a ferrule arranged about the optical fiber proximate the light input end. The ferrule is mechanically coupled to the optical frame and is arranged to mechanically isolate the light input end from fiber movement proximate the light output end of the optical fiber. The output end of the optical fiber may be provided with an output lens arranged to focus the output beam of light on the optical detector. The optical detector may comprise any one of a number of commercially available detectors; however, preferably, the detector should comprise a quadrant cell optical detector.
The optical detector defines a vertical reference point at the center of an X-axis and an orthogonal Y-axis. The laser receiver control circuitry may be operative to generate the receiver tilt signal from a first signal x indicative of a position of a centroid of the output beam of light relative to the X-axis and a second signal y indicative of a position of a centroid of the output beam of light relative to the Y-axis. The receiver control circuitry is preferably arranged to correct the elevation signal by reducing an elevation value corresponding to the elevation signal. The reduction is a function of a degree of receiver tilt.
The inclination detection unit may further comprise a pendulum mass coupled to the optical fiber proximate the light output end of the optical fiber and a magnetic damping mechanism arranged to damp motion of the pendulum mass relative to the primary receiver axis. The magnetic damping mechanism may include a magnet assembly defining a magnetic damping field and the pendulum mass may be arranged to define an eddy current disk configured to move through the magnetic damping field as the primary receiver axis tilts relative to the vertical reference axis.
The receiver may further comprise an audible signal generator responsive to the receiver tilt signal. The audible signal generator may be arranged to generate an audible tilt warning when the receiver tilt signal exceeds a predetermined value. The receiver may further comprise a visual signal generator responsive to the receiver tilt signal and the visual signal generator may be arranged to generate a visual representation of the receiver tilt signal.
In accordance with another embodiment of the present invention, a laser receiver is provided comprising a laser beam detection unit, an inclination detection unit, and laser receiver control circuitry. The laser beam detection unit is arranged to enable production of an elevation signal indicative of the elevation of a laser beam relative to the laser receiver. The inclination detection unit comprises a reference light source, an optical fiber, an optical detector, pendulum mass, and a magnetic damping mechanism. The optical fiber defines a light input end and a light output end and is coupled to the reference light source such that light from the reference light source enters at the light input end and exits from the light output end as an output beam of light. The optical detector is arranged to receive the output beam of light. The inclination detection unit is arranged to permit the output end of the optical fiber to move relative to the optical detector as the primary receiver axis tilts relative to a vertical reference axis. The optical detector is arranged to produce an optical detection signal indicative of a position of the output beam on the optical detector. The laser receiver control circuitry is arranged to generate a receiver tilt signal from the optical detection signal. The receiver tilt signal is indicative of a degre
D'Alessandro Richard
Hart Edward E.
Jackson Jonathan Appleget
Perchak Robert Matthew
Buczinski Stephen C.
Killworth, Gottman Hagan & Schaeff LLP
Spectra Precision, Inc.
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