When the distance X between reflector and sensor is fixed, the received reflected light intensity is related to the reflector characteristics。 In intelligent vehicle systems, the infrared launched by infrared diode has some direction。 When the infrared light irradiates the white ground, a strong reflection is appeared。 If the distance X is appropriate, the intensity of reflected infrared light is larger。 If the infrared light irradiates the black mark line, the infrared intensity received is   weaker

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because the black mark line absorbs the majority of infrared light。 Thus the intelligent vehicle can trace automatically by detecting the black marks on the road。

Fig。  1。  Light intensity - distance curve。

The output of infrared photoelectric sensor is pided into digital and analog。 The digital infrared sensor has the interface with the microprocessor and simple hardware circuit。 But it has the disadvantage of acquiring rough path information and loss of path information。 The analog infrared sensor outputs the analog signal。 The accurate road information can be obtained by the photoelectric sensor array formed with appropriate combination of more analog sensors。 This has very high reliability and stability。 Figure 2 is the output of photoelectric sensor array distributed along the black mark lines。 In actual operation, the sensor output is pided into n- index by the sensor reflectivity of black and white line。 The location of vehicle relative path mask line can be achieved by combination of various sensor indexes。 Thus the vehicle location and direction can be controlled accurately。

Fig。 2。 The output of photoelectric sensor array distributed along the

black mark line。

III。THE INTELLIGENT VEHICLE HARDWARE DESIGN

The intelligent vehicle composed of the frame, power supply, sensors, drive motor, steer motor and single-chip microcomputer control system and so on。 Shown in figure 3。 The photoelectric sensor detects the path information。 The speed sensor detects the current speed。 The battery voltage detection circuit monitors the battery voltage。 The single-chip microcomputer control system sample all above information and send the control command to the intelligent vehicle。 The moving trace and speed can be real-time controlled by steer gear and drive motor。

A 16-bit microcontroller MC9S12DGl28 produced by Freescale Semiconductor, Inc's。 is employed as the main controller。 MC9S12DGl28 has the function of high integration, easy expand, low-voltage detection reset, watchdog counter, low-power, PWM output and so on[4]。。 The assignment of MC9S12DGl28 input/output ports is as follows: PA0 ~ PA7 and PB0 ~ PB2 are employed as the input ports for path identification。 PACNO is the speed detection input port。 PWM01    outputs    the    PWM    control    signal    for servo

steer。 PWM23 and PWM45 output PWM control signal for drive motor。

Fig。 3。 The intelligent vehicle system structure。

The power supply is the basis of the vehicle running stably and reliably。 The sensor, controller, drive motor, steer motor, and other external ancillary modules and so on are needed supply。 In design, the power conversion efficiency, noise and interference and so on are needed to optimize, besides some basic parameters such as voltage range and current capacity。 This vehicle uses 5 V and 7。2V voltage。 The drive motor and steer gear are supplied by Ni-cd pile with 7。2V/2000mAh。 The speed sensor, MCU and photoelectric sensor are supplied by 5V which is reached by the power management chip LM2575-

5。0。 The input voltage of LM2575-5。0 is 7V-40V typically。 See figure 4。 The main controller is supplied by a special power source on account of its central role。