TRACKING METHOD AND MEASURING SYSTEM COMPRISING A LASER TRACKER

• US 20110181872A1
• Filed: 01/04/2007
• Published: 07/28/2011
• Est. Priority Date: 01/13/2006
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Dold, Jürgen, Zumbrunn, Roland, Moser, Daniel
• Granted Patent: US 8,125,629 B2
• Time in Patent Office: Days
• US Class Current: 356/139.04
• CPC Class Codes: G01C 15/002 Active optical surveying means optical plumbing G01C15/105
• CPC Class Codes: G01S 17/66 Tracking systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders

Abstract

A measuring system includes a laser tracker (10), a target point marked by a reflector (12), a surveying apparatus (13), and an arithmetic and control unit (14). The laser tracker emits a measuring beam (M) which is reflected by the reflector, a process that is used for determining the distance between the laser tracker (10) and the reflector (12). The surveying apparatus has a known position and orientation relative to the measuring beam (M) while preferably being embodied as a survey camera. The inventive measuring system is designed so as to track the reflector (12) via the measuring beam (M). In a normal tracking mode (A), a measured value for controlling the orientation of the measuring beam (M) is derived from the detection of the measuring beam reflected by the reflector (12). If the measuring beam is not directed onto the reflector, the system switches to a special tracking mode in which the measured value for controlling the orientation of the measuring beam (M) is derived from an image (20) of the survey camera (13).

Claims

1. A tracking method, in which a target point provided with a reflector (12) is tracked by a measurement beam (M) of a laser tracker (10), comprising the steps of:

in an ordinary tracking mode (A), data for controlling the direction of the measurement beam (M) is derived from the detection of the measurement beam being reflected by the reflector (12), and

in an extraordinary tracking mode (B), the data for controlling the direction of the measurement beam (M) is derived from data being registered by an overview apparatus (13),

wherein the overview apparatus (13) has a known position and orientation relative to the measurement beam (M), and

wherein the extraordinary tracking mode (B) is active when no measurement beam reflected by the reflector (12) is detected.

2. The method according to claim 1, wherein the extraordinary tracking mode (B) is automatically activated as soon as no reflected measurement beam is detected by the tracker (10).

3. The method according to claim 1, wherein when the extraordinary tracking mode (B) is activated, the tracker (10) monitors detection of the reflected measurement beam, and that the ordinary tracking mode (A) is automatically activated, as soon as the reflected measurement beam is detected.

4. The method according to claim 1, wherein in the extraordinary tracking mode (B), the data for controlling the direction of the measurement beam (M) is computed from a direction to the target point being determined from data registered by the overview apparatus (13), and from the known position and orientation of the overview apparatus (13).

5. The method according to claim 4, wherein the overview apparatus (13) is an overview camera, that the data registered by the overview camera are image coordinates, and that the target point is in addition identified by the overview camera.

6. The method according to claim 5, wherein the target point is identified on images (20) registered by the overview camera with the aid of a plurality of light points (16) or reflected marking elements, which are arranged around the reflector (12) and imaged by the overview camera.

7. The method according to claim 6, wherein the image coordinates are determined by way of determining the optical center of gravity of an image of the light points (16) or the marking elements, which are arranged around the reflector (12).

8. The method according to claim 1, wherein the direction of an optical axis (O) of the overview apparatus (13) is coupled to the direction of the measurement beam (M) in a fixed manner.

9. A measurement system comprising:

a laser tracker (10),

a target point with a reflector (12) and

a computation and control unit (14),

in which measurement system a measurement beam (M) emitted by the laser tracker (10) tracks the reflector (12) in an ordinary tracking mode (A),

wherein the computation and control unit (14) is designed for controlling the direction of the measurement beam (M) with the aid of detecting the measurement beam being reflected by the reflector (12),

wherein the measurement system additionally comprises an overview apparatus (13) which is arranged in a known position and orientation relative the measurement beam (M), and that the computation and control unit (14) is in addition designed for controlling the direction of the measurement beam (M), in an extraordinary tracking mode (B), with the aid of data being generated by the overview apparatus (13), and with the aid of the known position and orientation of the overview apparatus (13).

10. The measurement system according to claim 9, wherein the overview apparatus (13) comprises an overview camera or a PSD.

11. The measurement system according to claim 9, wherein the overview apparatus (13) is arranged on the laser tracker (10) in a manner such that a direction of an optic axis (O) of the overview apparatus is coupled to the direction of the measurement beam (M).

12. The measurement system according to claim 11, wherein the overview apparatus (13) is arranged on the laser tracker (10) in a manner such that its optical axis (O) always runs coaxially or parallel to the measurement beam (M).

13. The measurement system according to claim 9, wherein the target point is arranged on a hand-held touch tool or scanner.

14. The measurement system according to claim 9, wherein a plurality of light points (16) or reflecting marking elements is arranged around the reflector (12) arranged in the target point, and that the computation and control unit (14) or the overview apparatus (13) is designed to evaluate the direction to the reflector (12) from an arrangement of light points (16) or marking elements.

15. The measurement system according to claim 9, wherein the overview apparatus (13) is designed for identifying the target point.