A novel method is proposed for star identification via uncalibrated cameras with wide fields of view (FOVs). In this approach some of the triangles created by the stars in the FOV are selected for pattern recognition. The triangles are selected considering the sensitivity of their interior angles to the calibration error. The algorithm is based on the intersection between sets of triangles that are found in the database for each selected triangle of the image. By this method, most of the image stars contribute to pattern recognition and thereby it is very robust against the noise and the calibration error. The algorithm is performed on 150 night sky images, which are taken by an uncalibrated camera in FOV of 114°± 12°with a success rate of 94% and no false positives. Based on the identification approach, an adaptive method is also developed for calibrating and obtaining the projection function of an uncalibrated camera.
Direct drive motors have the excellent ability for precision position control due to their direct connection to load and elimination of the gearbox and pulley backlash. Among the direct drive motors, permanent NdFeB magnet synchronous motors (PMSMs) are the best choice for control systems due to their high efficiency, high power density, good dynamic behaviour, and excellent controllability. This study deals with the design, analysis, and fabrication of a direct drive PMSM for precision position control. To reach this aim, the designed motor should have very low cogging torque and torque ripple to avoid the motor deviation at the target point. To achieve these purposes, at first, a suitable combination of slot and pole has been selected for the motor and then the optimum shape of the magnets has been obtained by using the 2D finite element method. For the magnet shape, two important parameters of the magnet are optimised simultaneously. The designed motor has been fabricated and tested. Both simulation and experimental results show that the designed motor has a very good performance as the point of cogging torque and torque ripple views. Also, the experimental results validate the theoretical calculations.
In synchros and resolvers, brushes, and slip-rings produce a lot of noise in the output signal. Compared to encoders, the application of such position sensors in precision control systems is restricted because of their low accuracy. In this paper, a novel scheme of a brushless synchro is introduced. In this scheme, the primary and secondary windings are mounted on the stator, and the stator magnetic flux passes a certain path in the rotor with inducing voltage in the secondary winding. In this paper, a software method based on simple look-up table is used to enhance accuracy and reliability of the output signal of the proposed synchro. The operation principle of the brushless synchro is clearly described in the paper using a finite element method (FEM). The number of turns for the stator coils is calculated by a method based on desired harmonic elimination to have a sinusoidal magneto motive force. Some prototypes have been fabricated, and two experiments have been implemented in order to verify the theoretical concepts and to evaluate the accuracy of the fabricated synchros. Results show the proposed brushless synchro has high accuracy. Figure 13. (a )Input line to line voltage and output signal at zero reference angle θ ref = 0. (b) Input line to line voltage and output signal at 90°difference will respect to zero reference angle θ ref = 0. (c) Input line to line voltage and output signal at 180°difference with respect to zero reference angle θ ref = 0. 586 M. GHAFARZADEH ET AL.
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