Face detection is a biometric identification technology based on human facial feature information. This study uses the logitech C310 camera to collect images with faces and automatically detect faces in the images, and then carry out a series of technical processing on the detected faces. The traditional face detection technology is mainly based on visible images, which is also familiar with the detection method. But this kind of method has insurmountable defect, especially when the light environment changes, the detection effect will fall sharply, cannot meet the need of the actual system. The purpose of this study is to solve the classic problem of face detection under different lights, and to develop an intelligent and efficient human face detection method on Visual Studio 2015 platform software and OpenCV technology.

Research on face detection under different lighting

This paper concerns about the implementation of dither signals to quench the undesirable limit cycle was produced by saturation and backlash in a dc servo motor system. Various shapes of dither signals are injected into the system. Simulation results show that three dither signals evidently work differently. In this system, sinusoidal and saw-tooth dither can quench the limit cycle better than square wave dither.

Quench limit cycle using different dither signal in a servo motor system

The studies and application of Brushless Motor Field Oriented Control (FOC) with dithering technique was built using real-time test platform in this work. Here, the dither signal was introduced to the system to eliminate the sustained oscillation called limit cycles which usually uncontrollable. To see the system performance, a Serial Communication Interface (SCI) was made to monitoring the digital signal output. The experimental results show the ability of dither injection signal to remove the limit cycles at speed and electromagnetic field.

Permanent magnet brushless motor field oriented control with dither signal injection

This paper described a method to design a limit-cycle suppressor. The dithering technique was used to eliminate self-sustained oscillations or limit cycles. Otherwise, the Dual Input Describing Function (DIDF) method was applied to design dither parameters and analyze the existence of limit cycles. This method was done in a nonlinear system with relay nonlinearity using three standard dither signals, namely sine, triangle, and square waves. The aim of choosing varying dithers was to investigate the effect of dither shapes and the minimum amplitude required for the quenching strategy. First, the possibility and amplitude of limit cycles were determined graphically on the DIDF curve. Then, the minimum amplitude of dither was calculated based on the DIDF analysis. Finally, a simulation was built to verify the analytical work using a digital computer. The simulation results were related to the analysis results. It was evident that the dithering technique is a simple way to suppress limit cycles in a nonlinear system. This paper also presented that dither is an amplitude function, and square-wave dither has the minimum amplitude to quench limit cycles.

Designing Limit-Cycle Suppressor Using Dithering and Dual-Input Describing Function Methods

This paper presents the used of dither signal injection technique to stabilize the effect of nonlinearities in feedback control system. Various form of dither has been proposed including square wave, sine wave, and triangle wave dither. The analytical study of modified nonlinear element concept and simulation results show that square wave dither required the minimum amplitude to eliminate the ‘hunt’ (self-oscillation) or limit cycles but the triangle wave dither signal has the best ability to eliminate the limit cycle because its actual of output signal is closest to the reference signal and smoothest than others.

Nonlinearities stabilization using dithering injection in permanent magnet DC motor system

Dither is a high frequency signal which is introduced into a nonlinear system with the object of augmenting stability, quenching undesirable limit cycle, and altering the apparent nonlinear element characteristics. In this paper, we investigate the performance of various high frequency dither signals with different wave forms in nonlinear feedback systems. Meanwhile, an analog experimental device is set up to simulate the nonlinear systems, which consists of dither and a nonlinear element such as a relay or a limiter. A describing function and an equivalent nonlinearity method are used to evaluate the dither performance. The performance of various dither signals having a certain wave form is examined through these studies, and the results could evaluate effectiveness of these dither-injection techniques into nonlinear feedback systems.

The performance of different dither signals in nonlinear systems

The nonlinear dynamics of a vibration-controlled magnetic system are studied via a three-mode discretization of the governing partial differential equations. The analysis focuses specifically on the effects of modal coupling through the nonlinear terms of the system equation. A bifurcation analysis of the system is performed using sophisticated nonlinear theories, including the center manifold theory and the normal form theorem. The results show that when the first mode and the higher modes are excited simultaneously by the control forces, the three-mode approximation method predicts the existence of a triple zero degeneracy accompanied by complicated bifurcation phenomena. Comparing the dynamics structure predicted by the three-mode approximation model with that obtained from a single-mode approach, it is found that if the higher modes are excited by the control forces, the effects of modal coupling should be taken into consideration since a complicated dynamics structure may exist as a result.

Hsun-Heng Tsai

Papers

The performance of different dither signals in nonlinear systems

Codimension-three bifurcations of nonlinear vibration-controlled systems