Method of rotation angle measurement in machine vision based on calibration pattern with spot array.
We propose a method of rotation angle measurement with high precision in machine vision. An area scan CCD camera, imaging lens, and calibration pattern with a spot array make up the measurement device for measuring the rotation angle. The calibration pattern with a spot array is installed at the rotation part, and the CCD camera is set at a certain distance from the rotation components. The coordinates of the spots on the calibration pattern is acquired through the vision image of the calibration pattern captured by the CCD camera. At the initial position of the calibration pattern, the camera is calibrated with the spot array; the mathematical model of distortion error of the CCD camera is built. With the equation of coordinate rotation measurement, the rotation angle of the spot array is detected. In the theoretic simulation, noise of different levels is added to the coordinates of the spot array. The experiment results show that the measurement device can measure the rotation angle precisely with a noncontact method. The standard deviation of rotation angle measurement is smaller than 3 arc sec. The measurement device can measure both microangles and large angles.
Vision-Based Measurement System for Instantaneous Rotational Speed Monitoring Using Linearly Varying-Density Fringe Pattern
The instantaneous rotational speed (IRS) of a rotating machine is key information to understand the machine operation and diagnose the potential faults. A novel nonprojection fringe vision-based system was proposed to realize the measurement of IRS, which was simply composed of an artificial linearly varying-density fringe pattern (LVD-FP) as a sensor and a high-speed camera as a detector. The designed LVD-FP, printed by a normal printer, was pasted around the surface of the rotary shaft completely along the fringe density change direction. Part of the LVD-FP was captured by the high-speed camera. The fringe period density of each imaged LVD-FP intensity changed due to the rotation of the shaft, from which the rotational angle could be obtained. Subsequently, both the instantaneous angular speed (IAS) between two adjacent frames and the IRS could be accurately and efficiently obtained. The influences of the key parameters of the proposed system on the measurement accuracy were investigated by simulations and experiments. Both the simulation and experimental results demonstrated that the proposed system can accurately measure the IAS and correctly track the wide range IRS with the advantage of noncontact and cost effective. In addition, the rotation direction of the shaft could be directly obtained from the sign of the IRS curves. Therefore, the proposed system could provide a novel vision-based approach for IRS measurement, especially when the conventional speed sensor cannot be installed on the rotary shaft. The good performance of the system in IRS measurement makes it attractive for fault diagnosis of rotating machinery.
L1 Adaptive Controller for Attitude Control of Multirotors
In this work we show an application of L1 Adaptive control theory for attitude control of UAVs. We implement the flight control system on a multirotor to show robustness and precise attitude tracking in the presence of modeling uncertainties and environmental disturbances. We choose backstepping control architecture, since the kinematics and dynamics of multirotors in most cases can be written in strict feedback form. We further exploit the fact that the kinematics of the plant, while free of uncertainties, is nonlinear, which makes it highly suitable for dynamic inversion control at each level of backstepping. On the other hand, plant dynamics is uncertain and is affected by environmental disturbances such as wind gusts, unmodeled dynamics etc. Therefore, we consider 3 variants of the control architecture. The first method uses backstepping to determine the moment demand and augments it with the L1 adaptive controller to account for uncertainties and provide robustness with guaranteed transient performance. The second architecture apply the concept of L1 adaptive backstepping to the same problem; and the third architecture uses L1 backstepping for quaternion representation of the system dynamics, which helps to avoid the singularities associated with Euler angles.