18-02-2013, 09:55 AM
Study on Adaptive Front-lighting System of Automobile Based on Microcontroller
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Abstract
When the automobile turns in curve at night, it can
always appear “the blind spot” in the turn, for the lights are
unable to adjust the illumination angle. In order to enhance
safety driving at night, an adaptive front-lighting system (AFS)
of automobile controlled by STC12C5A60AD which is the core
of electric control unit is designed in this paper. The AFS is
based on the steering wheel angle and speed changes to adjust
light axis angle to light up the road in the front, so the drivers'
security vision are improved. The work principles of the AFS
and control model and hardware circuits are particularly
described. Application and design of sensors circuit, signal
conditioning circuit, stepper motor circuit and power supply and
power protection circuit, and then a software method was
brought up.
INTRODUCTION
The headlamp is an important active safety component
on the automobile, it will provide appropriate lighting
function when we driving at night. Especially when we
turning at night, if we cannot see each other very well in
time, it will lead to a serious traffic accident. The
associated survey shows that the number of traffic at night
is less than one-fifth during in the day, the traffic accidents
occurred at night is more than a quarter of the total
accidents. And the majority accidents happened in the
turn[1].
THE CONTROL MODEL OF ADAPTIVE FRONTLIGHTING
SYSTEM
The vehicle model of linear two degree of freedom
We assumed that in the normal speed range, ignoring
the suspension effect and left and right wheels tires which
due to the changes of load caused the changes in the tire
and the Aligning torque. It means that the car only have a
plane motion which parallel to the ground, in this case, the
two degrees of freedom vehicle model accuracy is enough.
The model is shown in Figure 2.
THE HARDWARE DESIGN OF THIS SYSTEM
The adaptive front-lighting system(AFS) of automobile
uses the STC12C5A60AD for the control of the core. The
peripheral circuits contains the speed signal acquisition
circuit, steering wheel angle signal acquisition circuit,
stepping motor drive circuit, and power supply, the power
supply and power protection circuit and other components.
The microcontroller of STC12C5A60AD
The STC12C5A60AD belongs to STC12 Series MCU,
use a RISC-type CPU core, and it compatible with the
ordinary 8051instruction set. And it contains the program
memory with 60KB Flash, RAM data memory with
1028B, EPROM function, at the same time, there is an
watchdog (WDT); a special reset circuit which used the
Integrated MAX8, a 8-channel-10 bit ADC and 2-channel
PWM; with in-System Programming (ISP) and in-
Application Programming (IAP), particularly fit for the
motor control and the stronger interference place. This
chip is rich resource, high integration and easy to use.
The drive circuit of the stepper motor
The stepper motor is a actuator which converted the
electrical pulse signal to the corresponding angular
displacement or linear displacement, it can be controlled
by the direct digital. Its mechanical angular displacement
and the input digital pulse signal has a strict
correspondence relationship: a pulse signal could make the
stepper motor forward further, it is an ideal actuator. The
motor speed and the stop position only depend on the pulse
frequency and the pulse number. Control the motor
actually control the input pulse sequence, make the stepper
motor in accordance with the needed pre-rotation angle.
CONCLUSION
In this paper, we study on the control principle of the
adaptive front-lighting system(AFS) of automobile at the
bend, established the mathematical model about this
system, and gave the system's overall design. The entire
system consists of 5 modules: the sensor module, signal
conditioning circuit module, the central controller module,
stepper motor drive module, power supply and power
protection modules. In this article, we describe the various
hardware performance and the algorithms of the software.
The pilot test showed that this system reached the
performance requirements of vehicle’s adaptive curve
lighting system at night and had important reference value
for improving the adaptive curve lighting effects and
traffic safety at night.