A machine vision inspection system consists of a camera, optics, illumination, and image acquisition system. The illumination system among these uses LED lighting source. Therefore, the driving method of LED lighting source is very important. The two main driving methods of LED lighting system for machine vision are Pulse Width Modulation (PWM) control driving and strobe control driving. PWM control driving method has problems such as a temperature rising of LED and a flickering in image measurement for inspection. On the other hand, strobe control driving method has a difficulty in the control of light intensity because of too short on-time. In this study, we propose a new hybrid-dimming control driving method for LED lighting source for machine vision. The proposed new hybrid-dimming control driving method can control current intensity and current on-time simultaneously so that it can extract clearer images with a high precision without the light saturation of image.

The machine vision technology has been widely used in the industrialized nations like the United States, Japan, and EU in the various industries from the late 1980s. Machine vision inspection system mainly consists of a camera, optics, illumination and an image acquisition system. Optimization of the illumination light source is very important. This paper shows a comparison between Pulse Width Modulation (PWM) control and strobe control in driving LED lighting system for machine vision. PWM control method has problems such as a temperature rising of LED and a flickering in image measurement for inspection. In contrast, the proposed strobe control method can suppress the temperature of LED light source below 40℃. Also, it can remove the flickering problem through a synchronization between a frame grabber and a camera shutter. Finally, the strobe control method was shown to extract clearer images with a high precision compared to PWM control method.

Currently, power conversion system which converts AC to DC Power is applied in domestic urban railway. The diode rectifier is used in most of them. However the diode rectifier can not control the output voltage and can not regenerate power as well. On the other hand, PWM (pulse width modulation) converter using IGBT (isolated gate bipolar transistor) can control output voltage, allowing it to reduce the output voltage drop. Moreover the Bi-directional conduction regenerates power which does not require additional device for power regeneration control. This paper compared the simulation results for the DC power supply system on both the diode rectifier and the PWM converter. Under the same load condition, simulation circuit for each power supply system was constructed with the PSIM (performance simulation and modeling tool) software. The load condition was set according to the resistance value of the currently operating impedance of light rail line, and the line impedance was set according to the distance of each substations. The train was set using a passive resistor. PI (proportional integral) controller was applied to regulate the output voltage. PSIM simulation was conducted to verify that the PWM Converter was more efficient than the diode rectifier in DC Traction power supply system.

This paper presents a comparative analysis of the parallel operation of different switches in a DC/DC converter. In high power applications, multi-switch PWM power conditioners may be preferred despite a higher component count, due to the absence of low frequency filters, reduced switching losses and fault tolerance. The paper demonstrates how current sharing (CSH) and time sharing (TSH) lead to the reduction of switching stress in the parallel operation of switches in any converter. The solutions proposed in this study can be applied on different scales to other power conditioners for DC/DC converter systems. Discussions of the concepts, hypotheses and computer simulations are verified by 1 kW experimental results.