Laser alignment system with modulated field

• US 4,674,870 A
• Filed: 10/18/1985
• Issued: 06/23/1987
• 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:
  US06/788,764
• Time in Patent Office: 613 Days
• Field of Search: 356/1, 356/4, 356/141, 356/152, 356/400
• 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; and

indicator means coupled to the level detector means for providing an indication to a user when the magnitude of the level signal reaches a preset value; and

the transmitter further includes;

means for sensing the occurrence of an event at the transmitter and producing an event signal;

means for receiving the event signal and in response thereto turning the laser on and off at a pulsation rate which is lower in frequency than the modulation frequency; and

the receiver further includes;

event detector means coupled to the band pass filter to determine when the modulated frequency signal component changes in amplitude at the pulsation rate and producing in response thereto an event detected signal; and

second indicator means coupled to the event detector means for providing an indication to a user of the occurrence of the event when the event detected signal is produced.

2. 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;

indicator means coupled to the level detector means for providing an indication when the magnitude of the level signal reaches a preset value;

an event detector means coupled to receive an indication of the presence of a signal component in said filtered electrical signal which is at the modulation frequency, and which is operable to produce an event detected signal when said modulation frequency signal component is pulsed on and off at a preset rate; and

second indicator means coupled to the event detector means for providing an indication to a user of the occurrence of an event when the event detected signal is produced.

3. The receiver as recited in claim 2 in which the modulation frequency is approximately eight kiloHertz and the present pulsation rate is approximately 2.68 Hertz.