We present a novel method for the 3D optical measurement of tube eccentricity. The prototype is based on two pairs of laser slits that illuminate the external and internal walls of the tube respectively. Each laser slit captures a 3D semi-profile in the zone close to the cut section of the tube. The laser slits are assembled following a suitably designed layout, which allows us to obtain the circumferential profiles of the internal and external tube surfaces. These profiles are fitted to two circles, and the eccentricity is measured as the distance between their respective centres. The system is suitable for monitoring the wall thickness in correspondence of tube cross sections characterized by scratches and chippings left by the cutting tool in a static way. In this paper, the method and the procedures developed to implement the measurement are described. The characterization of the laser slits, as well as the measurement performance of the system, is detailed. A number of experimental results highlighting the system performance in comparison with a 2D vision approach are discussed.
We describe Roboscan, a Robot cell that combines-2D and 3D vision in a simple device, to aid a Robot manipulator in pick-and-place operations in a fast and accurate way. The optical head of Roboscan combines the two vision systems: the camera is used “stand-alone” in the 2D system, and combined to a laser slit projector in the 3D system, which operates in the triangulation mode. The 2D system, using suitable libraries, provides the preliminary 2D information to the 3D system to perform in a very fast, flexible and robust way the point cloud segmentation and fitting. Roboscan is mounted onto an anthropomorphic, 6-DOF Robot manipulator.\ud
The most innovative part of the system is represented by the use of robust 2D geometric template matching as a mean to classify 3D objects. In this way we avoid time-consuming 3D point cloud segmentation and 3D object classification, using 3D data only for estimating pose and orientation of the robot gripper. \ud
In addition, a novel approach to the template definition in the 2D geometric template matching is proposed, where the influence of surface reflectance and colour of the objects over the definition of the template geometry is minimized.\ud
We describe the procedures for 2D and 3D vision of Roboscan, together with the calibration procedures that have been implemented. We also present a set of tests that show the performance of the system and its effectiveness in a number of pick-and-place operations
A rugged 3D optical system, easy to use and to calibrate, for the measurement of tube eccentricity has been developed in response to industrial demands for improved compactness and lower cost with respect to a previous layout developed in our laboratory. The system makes use of two optical laser projector–detector heads, and of suitably updated calibration and measurement procedures. This new layout shows a type A standard uncertainty of 0.03 mm over a tube diameter range from 10 to 60 mm and for tube thicknesses in the order of 3 mm. The new system can be easily built into a compact engineered version for applications in the industrial harsh environments of tube production. This system solves in a remarkable way the problem of measuring the eccentricity of a tube directly along the production line, without the need for machining it at the cut ends, and therefore reducing the amount of waste by means of the reduction in the time required to correct the process as a consequence of an eccentricity error.
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