Method and apparatus for non-contact measurement of object surfaces

• US 5,251,156 A
• Filed: 07/11/1991
• Issued: 10/05/1993
• Est. Priority Date: 08/25/1990
• Status: Expired due to Term

• Current Assignee: Carl Zeiss Industrielle Messtechnik GmbH (Carl-Zeiss-Stiftung)
• Original Assignee: Carl-Zeiss-Stiftung
• Inventors: Koch, Klaus-Peter, Breyer, Karl-Hermann, Heier, Helmut
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): DAY, JULIE
• Application Number:
  US07/728,557
• Time in Patent Office: 817 Days
• Field of Search: 364/559, 364/525, 364/560, 364/713, 364/474.37, 364/478, 364/507, 364/474.05, 358/107, 358/108, 358/106, 358/109, 358/88, 33/503-504, 356/1, 356/375, 356/376, 356/426, 367/907, 340/712
• US Class Current: 702/167
• CPC Class Codes: G01B 11/005 coordinate measuring machines

Abstract

Pictures of an object to be measured are taken from several different positions or aspects by a video camera which is mounted via a two-axis articulating head to the measurement arm of a coordinate-measuring machine. The pictures taken from the different positions or aspects are stored and are evaluated with respect to the coordinates of characteristic points of interest on the surface of the object by the method of space intersection, known from photogrammetry. And, in this connection, the position-measurement values supplied by the scales of the coordinate-measuring machine and the angle-measurement values supplied by the articulating head are used for a calculated determination of the coordinates for each of the points of interest on the surface of the object.

Claims

1. A method of using a camera and a coordinate-measuring machine for non-contact measurement of coordinates on object surfaces, wherein the coordinate-measuring machine has a movable measurement arm (3) and associated measurement scales (4, 5, 6) for measuring measurement-arm movement in three directions in space, and wherein articulating-head means (8) mounts a camera and is carried by said measurement arm (3), said articulating-head means (8) having (i) two orthogonally related axes of independent action for controlled roatary and pivotal angular orientation of the mounted camera, and (ii) associated angle-measurement means providing angle-measurement values (a, b) of the articulating-head means (8), said method comprising:

moving the measurement arm (3) into two different positions that are spaced apart;

using the articulating-head means (8) to target the object to be measured, by rotating or pivoting the camera, and using the camera to take object-targeted pictures at each of the two positions;

storing and evaluating pictures taken by the camera in the two positions, the evaluating being with respect to the coordinates of characteristic points on the surface of the object, by known photogrammetric methods of evaluation; and

calculating object coordinates (xi, yi, zi) from picture coordinates (Uij, Vij) of the camera, using position and angle measurement values (xoj, yoj, zoj;

aoj, boj) obtained from the scales of the coordinating-measuring machine and angle-measurement values obtained from the articulating-head means (8).

2. A method according to claim 1, wherein for each of the positions of the measurement arm (3), several pictures are taken and digitally stored for different angles of rotation or pivoting (a, b) of the articulating-head means (8).

3. A method according to claim 1, wherein the camera is a video camera and the calculated object coordinates are corrected with calibration data which describe (a) the position of attachment of the articulating-head means (8) on the measurement arm (3) of the coordinate-measuring machine, and (b) the position of attachment of the video camera with respect to the articulating-head means.

4. A method according to claim 3, in which the calculated object coordinates are additionally corrected for deviation in geometry (distortion) of the video camera (9).

5. A method according to claim 1, wherein the object is targeted and measured from all sides by moving the measurement arm (3) into different positions.

6. A method of using a camera and a coordinate-measuring machine for non-contact measurement of coordinates on object surfaces, wherein the coordinate-measuring machine has a movable measurement arm (3) and associated measurement scales (4, 5, 6) for measuring measurement-arm movement in three directions in space, and wherein articulating-head means (8) mounts a camera and is carried by said measurement arm (3), said articulating-head means (8) having (i) two orthogonally related axes of independent action for controlled rotary and pivotal angular orientation of the mounted camera, and (ii) associated angle-measurement means providing angle-measurement values (a, b) of the articulating-head means (8), said method comprising:

mounting an object to be measured for rotation at offset from the camera, for camera viewing of the object from each of a plurality of different viewing aspects;

for at least two different aspects of object viewing, pictures taken by the camrea are stored and evaluated with respect to coordinate points on the surface of the object, by known photogrammetric methods of evaluation; and

calculating object coordinates (xi, yi, zi) from picture coordinates (Uij, Vij) of the camera, using position and angle measurement values (xoj, yoj, zoj;

aoj, boj) obtained from the scales of the coordinate-measuring machine and angle-measurment values obtained from the articulating-head means (8) and measurement of the rotated angular position of the object.

7. A coordinate-measuring machine for non-contact measurement of surfaces of objects, said machine having

a camera (9) which is mounted via an articulating head (8) having two orthogonally related axes of independent motor-driven angular displacement with built-in angle transmitters (a, b) for the rotary and pivoting movement of the camera on a measurement arm (3) of a coordinate-measuring machine, which arm is movable in three directions in space;

means (19,

     20) for calculating object coordinates from the position coordinates (xoj, yoj, zoj) of the measurement arm and from the angular position (aoj, boj) of the camera, as well as from the video signal of the camera (9), said means comprising;

a picture-storage device (31) into which several pictures of the same region of the object can be read;

picture-processing means (19) which, from the stored picture data of concordant object points, calculates their picture coordinates (Uij, Vij),

an evaluation computer (20) which, from the picture coordinates (Uij, Vij) of the object points and from the position-measurement values (xoj, yoj, zoj) of the scales (6) of the coordinate-measuring machine, as well as from the angle-measurement values (aoj, boj) of the articulating head (8), calculates the object coordinates (xi, yi, zi) of the picture points by the method of spaced intersection; and

a storage device for storage of calibration data of the articulating head (8) and of the camera (9).

8. A coordinate-measuring machine according to claim 7, characterized by the fact that the camera (9) is mounted, together with an optical projection unit (39), on the articulating head means (8) of the coordinate-measuring machine.

9. A coordinate-measuring machine according to claim 7, characterized by the fact that the camera (9) and the projection unit (39) form a common structural unit which can be automatically placed on a reproducible mounting on the articulating head (8).

10. A coordinate-measuring machine according to claim 9, characterized by the fact that the machine includes a magazine (10) for storage of one or more structural units (9'"'"') and one or more tactile probe sensors (40) having selective and interchangeably retrievable chuckable connection to the articulating head (8) of the coordinate-measuring machine.

11. A coordinate-measuring machine according to claim 7, characterized by the fact that the camera (9) is externally synchronized with the control system (22) of the coordinate-measuring machine.

12. The method of using a tactile coordinate-measuring machine for non-contact measurement of the coordinates of an object to be measured, wherein the machine is computer controlled and has a measuring arm which mounts a probe head having two orthogonally related axes of independent pivotal action, and wherein the probe head is rectilinearly displaceable over a workpiece table in each of three orthogonal axes (x, y, z), said method comprising the steps of:

(a) mounting a workpiece to the table;

(b) attaching a video camera to the probe head;

(c) using the camera to take and digitally store separate pictures of a point of object interest from each of two spaced positions wherein the camera is oriented to view different aspects of the point of object interest;

(d) measuring and digitally storing the x, y, and z coordinate data for the pictures taken and stored for said different aspects;

(e) measuring and digitally storing the angular-position data (a, b) about each of said pivotal axes for the pictures taken and stored for said different aspects;

(f) using photogrammetric methods to evaluate the stored pictures for picture coordinates of the point of object interest; and

(g) using the digitally stored data of steps (d) and (e), together with the picture coordinates evaluated in step (f), in a computer calculation of the positional coordinates of the point of object interest.

13. In a computer-operated coordinate-measuring machine having a base with means of workpiece support, and having a measurement arm measurably movable in the respective directions of three orthogonally related axes, said arm having an articulation probe head with provision for motor-driven rotary displacement and orientation-angle measurement of a tool-mounting means about each of two orthogonally related axes of rotation;

the improvement in which;

(a) a video camera is mounted to the tool-mounting means of said head,

(b) a picture-storage device connected to said camera has the capacity to store a plurality of pictures of a machine-supported object to be measured, said computer being programmed to take a plurality of said pictures for each of a plurality of different aspects of viewing a single region of the object;

(c) picture-processing means connected to process stored picture data of one or more concordant picture points of said region and to calculate picture coordinates of said points; and

(d) an evaluation computer connected to the machine computer and responsive to the calculated picture coordinates of said points, as well as to the measured coordinate data of said arm and to the measured orientation-angle data of said head, for calculating object-point coordinates of the picture points by the method of space intersection.

14. A coordinate-measuring machine according to claim 13, wherein the means of object support is a turntable rotatable with respect to said base and having means for measuring instantaneous angular position of the turntable, said evaluation computer being additionally responsive to measured angular position of the turntable.