This paper presents a novel 3D coordinate measurement method based on the rotary-laser scanning technique for large-scale metrology. The method is implemented by a rotary-laser transmitter and a probe integrated with several photoelectric receivers. Measurement is accomplished with the tip of the probe contacting the measured point. The receivers capture the scanning angles of the laser planes emitted by the transmitter to calculate their corresponding equations. Then, we can establish the multi-plane constraint that the receiver points are in the corresponding planes. Subsequently, the coordinates of the measured point can be obtained through an optimization calculation method. In a 480 mm × 480 mm × 480 mm measurement volume that is 6 m away from the transmitter, the distance measurement accuracy of the proposed method is better than 0.40 mm and repeatability remains within 0.17 mm. For coordinate measurement, the accuracy and repeatability exceed 0.46 mm and 0.12 mm respectively. Experimental results show that the method is feasible and valid with good accuracy.
This article aims to improve the absolute accuracy of an individual industrial robot by means of integrating itself with the workspace Measuring and Positioning System, which is currently under development at Tianjin University, China. We found that the absolute positioning error persists in the robot base frame, whereas the errors, both in position and orientation, can be reduced by changing the reference frame from the robot to the integrated metrology system, that is, the workspace Measuring and Positioning System. What it needs more is several additional corrective movements. And this correction work just needs roughly calibrated parameters between the robot frame and the workspace Measuring and Positioning System frame. To validate it, we present the experiment which demonstrates that the absolute error of the industrial robot can be less than 0.2 mm by virtue of the workspace Measuring and Positioning System and the convergent corrective movements. Aiming to explain the results, this study deduces the mathematical model in detail about the integration of the robot with the workspace Measuring and Positioning System. The model explains why the integration of the robot with the workspace Measuring and Positioning System applies. First, the model tells that there exists a low requirement, that is, the tolerable rough level of the parameters between the robot frame and the workspace Measuring and Positioning System frame, for assuring the convergence of the corrective movements. Second, the relationship among the relevant factors in the corrective process is given. Finally, besides the workspace Measuring and Positioning System, this model is of general significance for any available metrology systems with which the industrial robot can integrate, and it may also provide theoretical instructions for the improvement of the robot off-line programming, that is, the robot can work at a higher accuracy provided by the integrated metrology system.
Abstract. Occlusion is a major problem for real-time position and orientation measurement with distributed optical large-scale metrology systems. This paper presents two novel methods with occlusion handling to address this issue, which should be used in combination for practical applications. These two approaches are based on the constraints established by three control points and six control points, respectively, and then the position and orientation can be calculated through iterative optimization algorithms. In this paper, all the work is carried out by using the workspace measuring and positioning system as a verification platform. Subject terms: position and orientation measurement; occlusion handling; distributed metrology system; optical large-scale metrology system; workspace measuring and positioning system.
Indoor GPS is one of the most popular positioning systems own to its high accuracy, real-time characteristics and multi-task management. In order to simplify the calibration process and extend its application, a single station model was presented recently. This paper proposes a novel ultrasonic ranging method used for the single station model. The traditional high-accuracy ultrasonic ranging method mainly uses a phase detection method by transmitting a multiple-frequency continuous wave. However, this method requires high accuracy of the phase detector and is still limited to small-scale application as a result of applying a continuous wave. Based on the constant time difference between the corresponding zero-cross points, this paper proposes a novel two-frequency pulse wave method, which can estimate the time of flight using the time differences between two received waves. Then a least squares estimation is used to eliminate random errors. Finally, an ultrasonic ranging experiment was conducted to validate its feasibility and stability.
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