speed of shift rod can be upgraded。 The intelligent vehicle steering sensitivity is enhanced effectively。 Because the steer gear current change greatly and is an interference source, a separate power supplies for the steer motor。

Fig。6。 The schedule circuit of motor drive。

In addition, in order to adjust the control parameters online, some man-machine interface such as keyboard, display and so on is set in the intelligent vehicle。 The control parameter is set by key to call different procedures to meet the requirements of different road。

IV。THE SOFTWARE DESIGN

Based on the current path and speed information, the steer gear and drive motor are controlled to adjust the vehicle moving direction and speed。 C language is employed to program control system software based on the Metrowerks CodeWarrior 4。5 program environment。 Figure 7 is the control system software flow chart。

Fig。  7。 The control system software flow chart

V。AFFECT OF SENSOR LAYOUT ON TRACE

When photoelectric sensor is employed to identify the path, the wavelength characteristics of transmission and receive sensor should be same。 The various performances should be close as possible when sensors group。 The sensor installation layout has an effect on trace significantly, such as the space between the sensors, sensor height and angle and so on。 These factors affect the light reflection and receive [5]。

To the road with black guide line in the middle, the sensor space must be larger than the black line width so that the same time induction phenomenon does not appear, that is every time only one sensor can detect the black line。 However, if the interval between the sensors is too large, a blank space appears。 If the interval is less than the black line width, a number of sensors will detect the black line each time。 This will help to determine the migration distance between the track and vehicle。

The sensor radial measurement distance is the longest straight distance detected by sensor。 In theory this distance is long better, because for unknown trace, if front path information can be obtained as soon as possible, the adjustment is made in time so that the vehicle can run over this path in optimal strategy。 If the sensor radial measurement distance is too large, the intelligent vehicle gravity center is likely to shift so as to cause the vehicle run unsteady or vibration。 Therefore, in order to increase the radial distance and cause no shift of gravity center, the sensor setting mode with pitch is employed。 See figure 8。

Fig。 8。 The sensor installation mode。

The sensor layout mainly has linear type and fan type。 The linear type is the most common mode。 All sensors are on one straight line so that the vertical consistency is ensured and the control strategies focus on the horizontal direction。 In fan type layout, some sensors in the middle are ahead。 Thus the vertical features are increased and front path information can be obtained as early as possible。 Claim attention is that the possibility of more sensors finding the mark at the same time is increased in fan type layout because the sensors vertical layout is inconsistent。 Therefore, this situation should be considered when the control strategy is determined。 Meanwhile, we can also take advantage of this situation to complete some specific adjustment, such as determining the angle of bend road and so on。

In order to reduce the interference from the external light source, the photoelectric sensor should be as close as possible to the ground。 Generally the sensor vertical height is about5- 10mm。 If the sensor is too far from the ground, the reflective light signal is weak。 However the sensor is too near to the ground, the reflective angle become too much and the light diffused interference increase。

VI。TEST

The intelligent vehicle was tested。 The test path and condition are shown in figure 9。 A black guideline was set on the white ground。 The line width is two centimeters and total length is about 36 meters。 The straight line, curve, S type line and cross path were included。 30 times test was completed in day and at night respectively。 Table 1 is test result。