Systems and methods for measurement of geometrical parameters of threaded joints
Thread parameters for a threaded object are determined. Spatial reference systems (X, Y, Z) and (X′, Y′, Z′) are respectively identified for a position sensor and the threaded object. A transformation matrix describing a quadratic form representing the threaded object in (X, Y, Z) may be determined to relate the reference systems. For example, a sensor trajectory on the threaded object may be determined, along with measurement points on the threaded object. The measurement points may be selected so the matrix, evaluated on these values, has maximum rank. Position data at measurement points in the second reference system may be transformed into the first reference system, yielding first results. After coating the threaded object, position data at the measurement points may be acquired again and transformed into the first reference system, yielding second results. Comparisons between the first and second results may provide thickness of the coating and quality verification.
1. A method of measuring thread parameters of a threaded object coated by at least one layer of coating material, comprising:
obtaining a shape of the threaded object including a nose;
identifying a first spatial reference system for the threaded object comprising first co-ordinate axes X′, Y′, Z′;
identifying a second spatial reference system comprising second co-ordinate axes X, Y, Z;
determining at least one trajectory on the threaded object in the second spatial reference system, the trajectory including selected measurement points;
obtaining first position data for the threaded object at the predefined measurement points of the at least one trajectory in the second spatial reference system;
converting the first position data for the threaded object from the second spatial reference system to the first spatial reference system to yield first measurement results;
coating at least a portion of the threaded object with a selected coating;
obtaining second position data for the coated, threaded object at the predefined measurement points of the at least one trajectory in the second spatial reference system;
converting the second position data for the coated, threaded object from the second spatial reference system to the first spatial reference system to yield second measurement results; and
determining the thickness of the coating from a comparison of the first and second measurement results.
2. The method of claim 1 , wherein the obtained position data is converted from the second spatial reference system to the first spatial reference system by applying a transformation matrix to the obtained position data, wherein the transformation matrix that relates the first spatial reference system to the second spatial reference system to the obtained position data.
3. The method of claim 2 , wherein the predefined measurement points are selected such that the transformation matrix evaluated on these values has maximum rank.
4. The method of claim 2 , wherein the transformation matrix describes the quadratic form representing the threaded object in the second spatial reference system.
5. The method of claim 1 , wherein one or more of the at least one trajectory is parallel to the Z axis of the second spatial reference system.
6. The method of claim 1 , wherein one or more of the at least one trajectories comprises a helicoidal trajectory.
7. The method of claim 1 , wherein at least one of the first and second position data comprises the position of at least one thread flank.
8. The method of claim 7 , further comprising determining a helicoidal thread lead trajectory passing along a middle point of one or more of a crests and roots of the threaded object from the position of the at least one thread flank.
9. The method of claim 8 , wherein one or more of the at least one trajectory comprises the helicoidal thread lead trajectory.
10. The method of claim 9 , further comprising:
fitting the first position data to a linear functional form to determine a linear dependence of the first position data;
determining a difference between the first position data and the linear fitting to the first position data;
conducting a Fourier analysis on said difference.
11. The method of claim 10 , wherein the difference between the first position data and the linear dependence of the first position data is evaluated at about a start position and a final position of the threaded object.
12. The method of claim 10 , wherein the difference between the first position data and the linear dependence of the first position data is evaluated at position intermediate to a start position and a final position of the threaded object.
13. The method of claim 1 , further comprising:
determining a circular trajectory along a metal-to-metal seal diameter in the first spatial reference system; and
transforming the circular trajectory into the second spatial reference system using the transformation matrix;
wherein at least one trajectory includes the transformed circular trajectory.
14. The method of claim 1 , further comprising:
determining a helicoidal trajectory is along a metal-to-metal seal diameter in the first spatial reference system; and
transforming the helicoidal trajectory into the second spatial reference system using the transformation matrix;
wherein the at least one trajectory includes the transformed helicoidal trajectory.
15. The method of claim 1 , further comprising:
determining a longitudinal trajectory along a run-in measuring point in the first spatial reference system; and
transforming the longitudinal trajectory into the second spatial reference system;
wherein the at least one trajectory includes the transformed longitudinal trajectory.
16. The method of claim 1 , further comprising:
determining a longitudinal trajectory is along a run-out measuring point in the first spatial reference system; and
transforming the longitudinal trajectory into the second spatial reference system;
wherein the at least one trajectory includes the transformed longitudinal trajectory.
17. The method of claim 1 , further comprising:
determining a longitudinal trajectory intersecting one or more flanks of the threads of the threaded object; and
fitting the positions of respective flanks as a function of their angular position to a linear functional form.
18. The method of claim 1 , further comprising:
determining at least one trajectory that intersects a thread lead;
identifying the respective positions of intersecting points;
determining respective positions of crests and roots of the threaded object;
calculating a first linear fit to the positions of two consecutive crests;
calculating a second fit to the positions of the root between said two consecutive crests;
determining the distance between a first line and a second line given by the first and second linear fit coefficients at a selected location of the threaded object.
19. A measurement device, comprising:
one or more optical sensors configured to:
measure positions of a surface of a threaded object;
obtain a shape of a threaded object including a nose;
identify a first spatial reference system for the threaded object comprising first co-ordinate axes X′, Y′, Z′;
identify a second spatial reference system comprising second co-ordinate axes X, Y, Z; and
obtain position data for the threaded object at predefined measurement points of at least one trajectory in the second spatial reference system;
a moveable mount configured to hold the one or more optical sensors; and
a computing device, the computing device configured to:
determine the at least one trajectory on the threaded object in the second spatial reference system, the trajectory including the selected measurement points; and
convert the position data for the threaded object from the second spatial reference system to the first spatial reference system to yield measurement results;
wherein the one or more optical sensors are configured to obtain position data on a coated and uncoated threaded object, and wherein the computing device is configured to determine a thickness of a coating on a threaded object from a comparison between position data obtained on the uncoated threaded object and position data on the coated threaded object.
20. The device of claim 19 , wherein the one or more sensors comprises a non-contact laser based sensor.
21. The device of claim 19 , further comprising an analysis component configured to receive images of threads of the threaded object and to determine one or more thread characteristics from the received images.
22. The device of claim 21 , wherein the thread characteristics comprise one or more of thread taper, seal diameter and ovality, run-in, run-out, thread diameter, pitch along multiple generatrices of the threaded object, and step height.
23. The device of claim 19 , wherein the computing device is further configured to convert the obtained position data from the second spatial reference system to the first spatial reference system by applying a transformation matrix to the obtained position data, wherein the transformation matrix that relates the first spatial reference system to the second spatial reference system to the obtained position data.