For the hunt-walking of robots , in addition to the accuracy requirements, the hunt speed requirements of robots are also significantly improved, and speed is often the key to winning in certain races. In the recent National College Student Smart Car Competition launched by the Ministry of Education, the hunt speed was set as the theme of the competition. In this paper, a summary of such events is presented, and a design method of robot high-speed line-hunting walking mechanism using a single-chip microcomputer as a core controller and a low-resolution camera instead of a general-purpose photoelectric sensor is proposed.
Core controller design
In order to realize video acquisition, considering the factors such as comprehensive cost performance and equipment installation, the core controller selects Freescale's 16-bit high-performance single-chip microcomputer - MC9S12DG128 (hereinafter referred to as S12). Its instruction processing clock can reach 38MHz, and its A/D converter can work up to 16MHz for video capture. At the same time, it has 8 PWM channels, control steering and DC motors to complete steering and speed control; 8 capture/compare channels to acquire encoder pulse signals as speed sensors; serial communication interface for wireless debugging; up to 64 IOs (through IO multiplexing) is sufficient for status display and parameter setting. In addition, it has 128k of flash memory space, no need for memory expansion, video data storage and call can be realized on-chip. As shown in Figure 2, the whole system uses a single-chip microcomputer, without adding other controllers and memories, becoming a true "single-chip" system.
Video capture module
Due to the A/D speed limit of the microcontroller, a low resolution black and white camera is required. Because low resolution means an increase in video single-line scanning time, black and white cameras mean that only a single A/D is required to complete the video capture. The ov5116 chip produced by Omvision was selected as the core CMOS black-and-white camera with a resolution of 320×240 and an image refresh rate of 50 Hz. At the same time, the LM1881 video sync signal separation chip is used to extract the line sync and field sync signals in the video signal, and is connected to the pulse capture channel of s12. The AD module is triggered by the capture signal to capture and store the video data.
Video acquisition circuit schematic
Motor control and power supply
The RS-380SH DC motor is used as the main drive motor and is controlled by the PWM signal. Freescale's MC33886 full-bridge driver chip is used to realize motor reversal through two half-bridges. The motor reversal here is not for reversing, but mainly for vehicle body deceleration. When the motor is switched forward and reverse, the motor drive current will be amplified instantaneously as the load increases. Therefore, it is necessary to increase the voltage regulation capability to ensure the normal operating voltage of the system and avoid the automatic restart of the microcontroller. In the whole system, there are various voltage requirements, the single-chip microcomputer and the steering gear are powered by 5V; the CMOS camera is 6-9V. Therefore, for the convenience of development, the most commonly used 7.2V rechargeable battery pack is used here. Simply add a 5V regulator chip to the system to provide 5V.
This paper designs a vision-based walking robot system for high-speed line hunting. The system uses a high-performance single-chip microcomputer to complete a set of line-hunting functions from video capture to video processing to achieve speed and steering control. The system is light and sleek, requires no memory expansion and other programmable devices, and is inexpensive to build. In the first National College Student Smart Car Competition, the program operated smoothly and achieved excellent results.
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