Self-calibrating electronic distance measurement instrument

• US 6,774,839 B2
• Filed: 07/07/2003
• Issued: 08/10/2004
• Est. Priority Date: 07/24/1998
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: McCusker, Michael V., Talbot, Nicholas C.
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US10/615,266
• Publication Number:
  US 20040012520A1
• Time in Patent Office: 400 Days
• Field of Search: 342/127, 342/357.06, 342/357.15, 342/357.17
• US Class Current: 342/357.31
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 19/14 specially adapted for specific applications
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 7/4021 of receivers
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A combined satellite positioning and electro-optical total station system includes a reference oscillator that provides local oscillator signals for a satellite navigation receiver and a precision frequency source for use by an electronic distance meter. When the satellite navigation receiver is locked onto and tracking orbiting navigation satellites, the highly precise cesium-rubidium clocks in the navigation satellite system can be used as standards to control the reference oscillator in the combined satellite positioning and electro-optical total station system. Baseline measurements made by the electronic distance meter are therefore not subject to mis-calibrations and drift as long as the satellite navigation receiver is locked onto and tracking the orbiting navigation satellites.

Claims

1. A method of operating an electronic distance meter (EDM) subsystem of a total station, comprising the steps of:

substantially continuously receiving from at least one orbiting GPS satellite radio signals with timing information controlled by an atomic clock on board said satellite;

constantly providing a global positioning system (GPS) receiver with a navigation computer for maintaining tracking of said radio signals and for deriving precise timing information from said radio signals;

persistently providing a local reference oscillator with a timing signal based on said derived precise time information;

permanently providing the EDM subsystem with a signal from said oscillator wherein said EDM subsystem sends an outbound laser signal to a distant target and receives an inbound signal reflected by said target;

measuring a difference between said out-bound signal and said resulting in-bound signal reflected from said distant surveyor target to determine the line-of-sight distance to said target;

wherein, the step of measuring provides a signal time-of-flight measurement with an accuracy derived from said precise timing information in said timing signal and from which a similarly accurate distance-to-target is computed.

2. The method of claim 1 wherein;

the step of measuring is based on a reference time base signal obtained from said local reference oscillator.

3. The method of claim 2 wherein:

said EDM subsystem includes a transmitter for sending said out-bound signal through a telescope to said distant target and a receiver for receiving said in-bound signal through said telescope.

4. The method of claim 3 wherein:

the step of measuring includes use of a phase measurement device connected to said reference oscillator, said transmitter and said receiver, wherein said phase measurement device provides said time measurement using said reference time base signal.

5. The method of claim 1 wherein:

said global positioning system receiver is remotely located to said EDM subsystem, and including the step of, communicating via a radio link between said receiver and said EDM subsystem to drive said EDM system with a signal from said oscillator.

6. The method of claim 4 wherein:

said phase measurement device conducts pulse time-of-flight to determine the line-of-sight distance to said target.

7. The method of claim 4 wherein:

said phase measurement device conducts carrier phase measurements to determine the line-of-sight distance to said target.

8. The method of claim 4 wherein:

the step of measuring the time difference includes observations of a plurality of phase differences observed by said EDM subsystem at a plurality of out-bound and in-bound signals.

9. The method of claim 4 further including:

mounting said telescope to an angle measurement instrument connected to a servo actuator;

computing in said computer a space vector to target signal;

commanding said servo actuator to direct said telescope towards said target; and

locking in said telescope onto said target.

10. The method of claim 9 further including:

computing a target location seed representing a current position estimate of said telescope;

outputting said target location seed as a position estimate to determine an altitude and azimuth vector to said target;

creating a space vector to target signal from said position estimate;

commanding said servo actuator by said vector to target signal.

11. The method of claim 1 further including:

providing a 1.00 Hz signal from said GPS receiver with timing characteristics derived from said atomic clock; and

stabilizing said local reference oscillator by comparing zero crossings of signals of said local reference oscillator with zero crossings of said 1.00 Hz signal.

12. The method of claim 1 further including:

providing a first 1.00 Hz signal from said GPS receiver with timing characteristics derived from said atomic clock;

reducing the signal frequency of said local reference oscillator to a second 1.00 Hz signal;

phase comparing said first and second 1.00 Hz signals to provide an error signal;

providing the error signal to a phase control port in said local reference oscillator; and

synchronizing said reference oscillator to said 1.00 Hz signal from said GPS receiver.

18. The method of claim 1 further including the step of:

computing in said navigation computer a current three-dimensional position of the EDM subsystem.

13. A method of operating an electronic distance meter (EDM) subsystem of a total station, comprising the steps of:

substantially continuously receiving from a time-standard broadcast transmitter source a timing reference signal from which a first comparison signal is derived;

operating a local reference oscillator at a particular frequency of operation;

continuously receiving a first signal from said local reference oscillator and reducing said first signal to a second comparison signal;

constantly phase comparing said first comparison signal with said second comparison signal to provide an error signal;

persistently processing said error signal to create a control signal to provide to said local reference oscillator to obtain phase synchronization of said local reference oscillator with said time-standard broadcast transmitter timing reference signal; and

continuously providing the EDM system with a synchronized reference signal from said local reference oscillator.

14. The method of claim 13 wherein:

said EDM subsystem further provides an out-bound signal directed towards a distance target, and receives an in-bound signal reflected by said target;

measuring a difference between said out-bound signal and said resulting in-bound signal reflected from said distant target to determine the line-of-sight distance to said target; and

wherein the step of measuring provides a signal time-of-flight measurement with an accuracy derived from said time standard broadcast transmitter and from which a similarly accurate distance-to-target estimate is computed.

15. The method of claim 13 wherein:

said time-standard broadcast transmitter source includes a receiver tuned to receive and synchronized to time data broadcast from NIST via short-wave radio.

16. The method of claim 13 wherein:

said time-standard broadcast transmitter source includes a receiver to receive alternate timing signals and to synchronize said time-standard broadcast transmitter to said alternate timing signals, wherein said alternate timing signals are provided from a second time reference station drawn from the group of WWV in Fort Collins, Colo. or WWVH in Hawaii.

17. The method of claim 13 wherein:

said time-standard broadcast transmitter includes an orbiting GPS satellite.