Laser alignment system with modulated field

• US 4,756,617 A
• Filed: 01/27/1987
• Issued: 07/12/1988
• Est. Priority Date: 10/18/1985
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Spectra-Physics Incorporated (MKS Instruments Incorporated)
• Inventors: Cain, Gary L., Goren, Sidney B.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US07/006,862
• Time in Patent Office: 532 Days
• Field of Search: 356/400, 356/4, 356/141, 356/152
• US Class Current: 356/4.08
• CPC Class Codes: G01C 15/004 Reference lines, planes or sectors

Abstract

A laser alignment system includes a transmitter and one or more receivers. The transmitter produces an alignment field by projecting laser energy in a non-planar reference cone, and the receivers locate this reference cone with photodetectors. The laser energy in the alignment field is modulated at 8 kHz and the signals produced by the photodetectors are filtered and amplified to increase the range of the system. Each receiver operates a display which indicates when it is aligned in the reference cone, and it produces an out-of-level indication when the transmitter is not properly aligned.

Claims

1. In a laser alignment system having a transmitter for producing an alignment field in the form of energy directed from a laser and a remotely located receiver for detecting the presence of the alignment field and producing an electrical signal proportional to the magnitude of the laser energy, the improvement therein comprising:

modulation means at the transmitter for turning the laser on and off at a modulation frequency;

a band pass filter at the receiver for suppressing components in said electrical signal at frequencies other than said modulation frequency;

level detector means for receiving the filtered electrical signal and producing a level signal indicative of the magnitude of the modulation frequency signal component therein;

indicator means coupled to the level detector means for providing an indication to a user when the filtered electrical signal is present; and

locking means coupled to the band pass filter for sensing the presence of a signal component at the modulation frequency and producing in response thereto a lock signal which indicates that the receiver is positioned in the alignment field, and

in which the locking means include a phase-locked loop which operates at a frequency in the range of the modulation frequency.

2. In a laser alignment system having a transmitter for producing an alignment field in the form of energy directed from a laser and a remotely located receiver for detecting the presence of the alignment field and producing an electrical signal proportional to the magnitude of the laser energy, the improvement therein comprising:

modulation means at the transmitter for turning the laser on and off at a modulation frequency;

a band pass filter at the receiver for suppressing components in said electrical signal at frequencies other than said modulation frequency;

level detector means for receiving the filtered electrical signal and producing a level signal indicative of the magnitude of the modulation frequency signal component therein, and

in which the level detector means is an auto correlator that includes means for producing a synchronous signal which is employed by the detector means to sample the filtered electrical signal periodically in synchronism with the modulation frequency; and

indicator means coupled to the level detector means for providing an indication to a user when the filtered electrical signal is present.

3. The improvement as recited in claim 2 in which the detector means further includes circuit means for receiving the periodic samples and producing said level signal by generating a voltage which substantially corresponds to the magnitude of said samples.

4. The improvement as recited in claim 3 in which modulation frequency is greater than four kiloHertz.

5. A receiver for locating the position of a laser alignment field in which the radiant energy in the field is amplitude modulated at a selected modulation frequency, which comprises:

a photodetector which is sensitive to radiant energy in the laser alignment field and which produces an electrical signal that is proportional in magnitude to the radiant energy impinging on its surface;

a band pass filter circuit which couples to receive the electrical signal from the photodetector and which produces a filtered electrical signal in which the magnitude of the signal component at the modulation frequency is increased relative to the magnitude of signal components at other frequencies;

level detector means for receiving the filtered electrical signal and producing a level signal indicative of the magnitude of the modulation frequency signal component therein, and

in which the level detector means is an auto correlator which samples the magnitude of the filtered electrical signal periodically at a rate which corresponds to the modulation frequency; and

indicator means coupled to the level detector means for providing an indication when the filtered electrical signal is present.

6. A receiver for locating the position of a laser alignment field in which the radiant energy in the field is amplitude modulated at a selected modulation frequency, which comprises:

a photodetector which is sensitive to radiant energy in the laser alignment field and which produces an electrical signal that is proportional in magnitude to the radiant energy impinging on its surface;

a band pass filter circuit which couples to receive the electrical signal from the photodetector and which produces a filtered electrical signal in which the magnitude of the signal component at the modulation frequency is increased relative to the magnitude of signal components at other frequencies;

level detector means for receiving the filtered electrical signal and producing a level signal indicative of the magnitude of the modulation frequency signal component therein;

a second photodetector positioned adjacent the first photodetector;

a second band pass filter circuit for receiving the electrical signal from the second photodetector;

a second level detector for receiving the filtered electrical signal from the second band pass filter circuit; and

indicator means which includes;

a ratio comparator for receiving the level signals from both of said level detector means and comparing their relative magnitudes to produce an ON signal when their magnitudes are substantially the same, a LO signal when one of said level signals is substantially greater than the other of said level signals, and a HI signal when the other of said level signals is substantially greater than said one level signal; and

display means having three elements which are separately energized in response to the respective ON, LO and HI signals.

7. The receiver as recited in claim 6 in which the surface of each of said photodetectors is tapered.