In many real applications, it is not sufficient for a robot to merely possess highly accurate repeatability, the highly accurate absolute positioning is also needed to meet the market demands to increase competitiveness and lower cost. In order to increase the absolute positioning ability, the two key issues, the accurate robot calibration and measurement, must be addressed. Although much research has been done on these two issues, the following two problems still persist and lack satisfactory solutions: 1. No generally applicable and satisfactory calibration methods are available due to the complicate nature of calibration process and difficulty of achieving precision parameter estimation; 2. The high precision measuring needs expensive instruments, which must be operated by highly trained professionals, and whose measuring process is tedious. This thesis aims to improve the robot’s absolute positioning accuracy. To this end, the above two problems are systematically studied. The main contributions include: 1. A Screw Axis Identification(SAI) method is proposed based on the Product of Exponentials (POE) model. Only n (n≥3) target points on the end-effector are required, and by measuring their position before and after each joint rotation, the twist and rotation angle of each robot joint are calibrated linearly. The method does not require the calibration of the robot exterior pose, the error propagation problem does not exist, and hence the calibration precision is substantially increased. In addition, with the Cayley representation of rotation matrix, the estimation of joint parameters is simplified and estimation accuracy is increased at the same time. Simulationand real experiments demonstrate the stability and efficiency of our proposed SAI method. Besides for the reference purpose, the relation between the measuring accuracy of the measuring instrument and the positioning accuracy of the calibrated robot is also given. 2. Due to the inconvenience and cost of using high precision measuring instruments in robot calibration, the feasibility of using high-resolution cameras to substitute the precision instruments is studied. To bridge the terminology difference between the computer vision community and that of photogrammetry, a comprehensive analysis on the relation and transformation of camera parameters is also carried out. Experiments show that the robot calibration using high resolution cameras as the measuring instrument can also achieve high ...
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