Laser operation for survey instruments

• US 7,323,670 B2
• Filed: 03/16/2005
• Issued: 01/29/2008
• Est. Priority Date: 03/16/2004
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems Limited (Melker Schörling Tjänste AB)
• Inventors: Aindow, Alan, Walsh, Gregory C., Storz, Ralph
• Primary Examiner(s): Epps; Georgia
• Assistant Examiner(s): LeGasse, Jr.; Francis M
• Application Number:
  US11/081,354
• Publication Number:
  US 20050205755A1
• Time in Patent Office: 1,049 Days
• Field of Search: 250234-236, 250/205, 250/221, 356/3.01, 356/3.09, 356/5.01, 356 503- 508, 372/25, 372/30, 372/38.02, 372/38.07
• US Class Current: 250/205
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

The performance of a laser scanner is optimized in the field by automatically determining appropriate laser parameters for the scan location. A laser control system uses information such as the environmental temperature to select an appropriate range of start points for various laser parameters, such as pump temperature and laser currents. Test pulses over that range can be used to determine optimal operating parameters. In order to also meet safety regulations, the laser control system can use information such as range and pulse timing information to fire regularly spaced pulses that do not exceed acceptable exposure limits. Alternatively, the laser can be operated at a regular speed of about 24 Hz, or can be operated in burst mode where a burst of pulses creates what appears to be a brighter scan spot, but the time delay between bursts allows time for a blink reflex.

Claims

1. A method of safely operating a laser scanner, comprising the steps of:

determining range information for a first scan point;

determining an orientation of a beam steering portion of the laser scanner;

using the range information and orientation to predict a location of a subsequent scan point; and

waiting to fire the laser scanner for the next scan point until the separation between the first scan point and the subsequent scan point reaches a minimum safety threshold.

2. A method according to claim 1, further comprising:

selecting the minimum safety threshold using an acceptable exposure limit for the laser scanner.

3. A method according to claim 1, wherein:

the range information is determined by measuring the time between an emission and a detection of a laser pulse from the scanner, reflected from an object being scanned.

11. A method for safely operating a laser scanner according to claim 1, further comprising repeating the step of determining range information and constructing a point cloud from the range information and orientation, whereby the point cloud has a spatially even sampling of points despite waiting to fire the laser until reaching a minimum safety threshold.

4. A method of safely operating a laser scanner, comprising the steps of:

determining a first position of a first scan point on an object being scanned;

estimating a second position for a second scan point on the object; and

delaying firing of the laser scanner for the second scan point until an estimated separation between the first scan point and the second scan point reaches a minimum safety threshold.

5. A method of safely operating a laser scanner, comprising the steps of:

firing a first burst of pulses of visible light toward a first scan position on an object to be scanned, the first burst of pulses including a plurality of pulses having a first spacing of time between them;

collecting range data for the first burst of pulses;

determining a safe time when a firing of a subsequent burst of pulses will not exceed a safety threshold for the laser scanner, the safe time being different than the first spacing; and

firing a second burst of pulses of visible light toward a second scan position on the object after reaching the safe time,

whereby the burst of pulses enhances visibility of the visible light.

6. A method according to claim 5, wherein the first spacing is such that the laser is fired at a maximum average speed of 24 Hz.

7. A method according to claim 5, further comprising:

determining a number of pulses to be included in each of the first and second bursts, the number of pulses being determined using an acceptable exposure limit for the laser scanner.

8. A method according to claim 5, wherein:

each of the first and second bursts contains between about 4 and about 20 pulses.

9. A method according to claim 5, wherein:

each of the first and second bursts contains about 6 pulses.

12. A method for safely operating a laser scanner according to claim 5, further comprising repeating the step of collecting range data and constructing a point cloud from the range data, whereby the point cloud has a spatially even sampling of points despite not exceeding the safety threshold for the laser scanner.

13. A method for safely operating a laser scanner according to claim 5, wherein the step of firing a burst of pulses includes firing a pulse of sufficient power to collect range data from objects up to 100 meters from the laser scanner, and wherein collecting range data includes collecting range data returned from the object that us up to about 100 meters from the laser scanner, whereby firing a second burst of pulses after reaching the safe time makes the laser scanner eye-safe even if an eye is closer than 100 meters from the laser scanner.

10. A method of safely operating a laser scanner, comprising:

determining range information for a first scan point;

determining an orientation of a beam steering portion of the laser scanner;

determining additional information including at least one of a relative change in distance between scan points and intensity of light measured for the first scan point; and

using the range information, orientation and additional information to predict a location of a subsequent scan point; and

waiting to fire the laser scanner for the subsequent scan point until separation between the first scan point and the subsequent scan point reaches a minimum safety margin.