This paper is based on Freescale Intelligent Vehicle Competition.
It mainly introduces the hardware structure and the design of software control system of the Intelligent Vehicle. The Intelligent Vehicle takes MK60DN512VLQl0 microcontroller as the control core. Through detecting the alternating magnetic field generated by the conductor with 20KHz 100mA alternating current as the guiding signal, it is collected and processed by the Intelligent Vehicle. Runway signal, according to different runway conditions, automatically make different processing, so as to achieve the function of automatic tracking. The design is based on the B model of Freescale Intelligent Vehicle Competition, which is the main design platform of Intelligent Vehicle.
Through the electromagnetic detection module installed in front of the Intelligent Vehicle as the “eyes” of the Intelligent Vehicle, the information collected by the electromagnetic detection module is processed by the core control unit and returned to the steering control module to adjust the direction, and through the speed measurement module. Controlling the speed of the intelligent car and detecting the starting line of parking with the reed tube can achieve the goal of automatic tracking. Whether the electromagnetic detection module can correctly judge the information of the runway directly affects whether the K60 control unit can work correctly or not.
Moreover, the detection module must have a certain foresight, so that sufficient time can be set aside for the control unit to make correct judgement and processing. After many tests and adjustments, it is finally determined that the electromagnetic detection module will be placed in the front of the smart car 30 cm. In the position of 40 cm, six inductances are used to detect the alternating magnetic field on the runway. The inductance will produce a weak voltage signal. The voltage signal is amplified by TLV2462 operational amplifier.
After the circuit shaping and filtering, the collected signal is transmitted to the control unit for processing. The following is the schematic diagram. Because the whole system is composed of several modules, and the voltage requirements of different modules are different, we adopt four power management schemes: 3.3V, 5V, 7.2V and 6V. The whole system is powered by a 7.2V battery, and 7.2V is powered directly by the battery to the motor drive module.
The core control unit voltage is 3.3V electromagnetic detection and speed measurement module. The voltage of steering module is 6V and 5V.
In this module, we adopt the half-bridge integrated drive BTN7970, which is an integrated high-current half-bridge driver chip specially used for motor drive. It can occupy very little space of circuit board and satisfy the function of high-current drive motor.
It has strong anti-interference ability. Because the working voltage of the driver chip is different from that of the control unit, in order to prevent the damage of the control unit, 74LS244 is added between them to act as isolation protection. Speed measurement module, speed measurement module, we use Omron 200 line encoder, it has a high speed measurement accuracy, and can meet the needs of speed measurement. In this module, we use S-D5 digital steering gear.
By outputting 50Hz PWM wave with different duty cycle, we can control steering accurately and quickly. In this module, we use the reed to detect the steel magnet under the starting line. When the reed passes through the magnet, it will turn on and produce a jump signal to detect the starting line. The module is composed of 0.75 inch OLED screen, button and dial switch. Some parameters of the smart car can be debugged and set online by button, which not only saves the trouble of downloading and adjusting parameters many times, but also improves the efficiency of debugging. Before the intelligent vehicle works, the system should be initialized to prepare for the operation of the whole system, including clock initialization, IO port initialization FTM module initialization, interrupt initialization and other modules. After configuring the modules needed for each operation, the next work can be carried out.
We use six inductances as sensors to detect electromagnetic signals.
They are arranged symmetrically in the prospects of smart cars. By collecting six signals, thermostatic element we can find the middle line after processing the six signals and determine the offset from the real signal line.
According to this offset, we can control the steering of the steering gear in order to reduce the inductance. Due to the influence of uncontrollable factors such as value difference and current amplitude change, we apply normalization algorithm to the 6-way data collected, which makes the data more stable. In the aspect of steering control, in order to prevent the steering engine from shaking too much, we use the PD control algorithm to make the steering control of the steering engine more smoothly, while the PID control algorithm is used to control the speed. It can make the speed change of the intelligent vehicle more smoothly in the course of operation, and can control the set speed more quickly and steadily. When the starting line is detected, the smart car will stop automatically, and the starting line will be detected by interruption trigger. When jump is detected, it can be considered as passing through the starting line. In order to prevent misjudgement of interruption when starting, we can make the interruption 10 seconds after starting. In the process of production, we continuously optimize the hardware of the smart car. On the motherboard, we use plug-in devices, which greatly facilitates the maintenance of the vehicle and the upgrading of the circuit. In terms of software, we continue to optimize the algorithm, combining with the actual smart car to improve the algorithm, especially after adding human-computer interaction module to greatly improve the efficiency of debugging. In terms of debugging, we have not joined the host computer.
I believe that after our later research and development, there will be greater progress in the debugging of smart cars, efficiency. It will be even higher.