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.