ABSTRACT
In any precision manufacturing process, positioning systems play a very important role in achieving a quality product. As a new approach to current systems, camera-LCD positioning systems are a new technology that can provide substantial improvements enabling better accuracy and repeatability. However, in order to provide stability to the system a global positioning system is required. This paper presents an improvement of a positioning system based on the treatment of images on an LCD in which a new algorithm with absolute reference has been implemented. The method is based on basic geometry and linear algebra applied to computer vision. The algorithm determines the spiral center using an image taken at any point. Consequently, the system constantly knows its position and does not lose its reference. Several modifications of the algorithm are proposed and compared. The simulation and test of the algorithm provide an important improvement in the reliability and stability of the positioning system providing errors of microns for the calculation of the global position used by the algorithm.
ABSTRACT
This article presents a method to obtain the overall positioning of the focus of a camera from an image that includes a rectangle in a fixed reference with known position and dimension. This technique uses basic principles of descriptive geometry introduced in engineering courses. The document will first show how to obtain the dihedral projections of a rectangle after three turns and one translation. Secondly, we will proceed to obtain the image of the rectangle rotated in a conical perspective, taking the elevation plane as the drawing plane and a specific point in space as the view point, and represented in the dihedral system. Thirdly, we proceed with the inverse perspective transformation; we will expose a method to obtain the coordinates in the space of a rectangle obtained from an image. Finally, we check the method experimentally by taking an image of the rectangle with a camera in which the coordinates in the drawing plane (center of the image) are the only available position information. Then, the positioning and orientation of the camera in 3D will be obtained.
ABSTRACT
In this article, we present a method to position the tool in a micromachine system based on a camera-LCD screen positioning system that also provides information about angular deviations of the tool axis during its running. Both position and angular deviations are obtained by reducing a matrix of LEDs in the image to a single rectangle in the conical perspective that is treated by a photogrammetry method. This method computes the coordinates and orientation of the camera with respect to the fixed screen coordinate system. The used image consists of 5 × 5 lit LEDs, which are analyzed by the algorithm to determine a rectangle with known dimensions. The coordinates of the vertices of the rectangle in space are obtained by an inverse perspective computation from the image. The method presents a good approximation of the central point of the rectangle and provides the inclination of the workpiece with respect to the LCD screen reference system of coordinates. A test of the method is designed with the assistance of a Coordinate Measurement Machine (CMM) to check the accuracy of the positioning method. The performed test delivers a good accuracy in the position measurement of the designed method. A high dispersion in the angular deviation is detected, although the orientation of the inclination is appropriate in almost every case. This is due to the small values of the angles that makes the trigonometric function approximations very erratic. This method is a good starting point for the compensation of angular deviation in vision based micromachine tools, which is the principal source of errors in these operations and represents the main volume in the cost of machine elements' parts.
