2016 3rd International Conference on Vehicle, Mechanical and Electrical Engineering (ICVMEE 2016)
ISBN: 978-1-60595-370-0
Vehicle Driving Wandering Automatic System Based
on Laser Ranging
PENGJU SONG AND YAOHUA HE
ABSTRACT
Laser ranging has so many advantages, such as rapid response, high accuracy, and
excellent reliability and so on, it is widely used in numerous engineering test field. To
use laser range on the measurements of vehicle driving wandering can simplify the
structure of vehicle driving wandering test system and improve its usability. With
lucubrating the compose and theory, test procedure and data processing method of
vehicle driving wandering system which is based on laser ranging, it has developed a
new set of vehicle driving wandering system which is based on laser ranging. Making
use of the symmetric method of laser ranging can eliminate the effect of auto
vibration; Vehicle driving wandering test system based on the lab view platform will
achieve automatic control, signal transmission, data acquisition and processing, test
result’s sharing, inquiring and so on.
INTRODUCTION
The vehicle driving wandering belongs to the category of safety testing. To ensure
driving safety, they need a test on the vehicle driving wandering before ex-factory , and
in use of the process, many factors may impress vehicle driving wandering such as the
change of wheel alignment parameters, tire uneven wear, permanent deformation of
suspension components, so it needs to conduct periodic detection on vehicle driving
wandering. Therefore it is necessary to research the more simple structure, lower
maintenance cost, more convenient vehicle driving wandering automatic test system.
HARDWARE COMPOSITION AND FUNCTION OF TEST SYSTEM
The vehicle driving wandering test needs to proceed in the open air, test system
adopts the wireless communication network server test controller to implement the
communication with the client (handle terminal). Hardware of test system mainly
includes data acquisition system which is installed on both sides of the runway, wireless
communication system, laser range finder, acquisition card, support frame, test
controller and other auxiliary hardware devices，as shown in Table1.
_________________________________________
Pengju Song, Yaohua He, School of Automotive Engineering, Wuhan University of
Technology, Wuhan 430070, China
Table 1. Main Test System Hardware Composition and Function.
System hardware
Data acquisition
system
Laser ranging finder
Analog input card
Wireless
communication
system
Wireless AP
Wireless Switch
Handle terminal
Laser range finder stent
AP stent
Holder
Others
Fiber Optic Converter
Optical fiber terminal box
Photoelectric switch
Function
Measure distance between laser
range finder and vehicle lateral
Gather the sensor data
Launch RF signal
Unified manage wireless AP
Complete the data transmission
Fix laser range finder
Fix wireless AP
Convert optical signals into
electrical signals
Fixed cable terminal
Provide the trigger signal
THE WORKING PRINCIPLE OF THE TEST SYSTEM
In order to avoid the interference which comes from other vehicles, each vehicle
has a single VIN code (Vehicle Identification Number). When testing, the operator will
steer test vehicle along the guide line in figure 1, and the test road is divided into
preparation area, instruction emission area and test area. Firstly, when reaching
preparation area, the driver should discern the test vehicle’s VIN to login vehicle’s
information. Secondly, when reaching instruction emission area, the operator should
send the test instruction by handle terminal. Finally, the data is successfully acquired
with the operations of straightening the body and releasing the steering wheel, and then
it will obtain final result by corresponding software; All the test procedure adopts the
wireless communication network server ( test controller) to realize the communication
with the client (handle terminal).
As shown in figure 2 is layout of the main hardwares, in order to make wireless
communication to cover the whole test area, three wireless access points are arranged
in following areas, 80m before starting position, starting position, 20m after the end
position. Two pairs of laser ranging sensors and two pairs of photoelectric switches
( R1 、 T 1 、 R2 、 T 2 )are symmetrically installed on both sides of the runway, at the same
time, it should ensure the ray of laser range sensor is perpendicular to the test guide line.
On account of the further distance between test controller and testing site, it makes use
of fiber optic converter to realize the correspondence between sensor and test controller,
wireless access points and test controller.
Figure 1. Test area distribution.
Figure 2. Construction of main hardwares.
Figure 3. Part of acquisition program.
DATA ACQUISITON AND PROCESSING
This module is the central part of the whole test system. The hardwares of data
acquisition part consists of signal sampling card and test controller. The signal of laser
ranging sensor is captured by signal sampling card, and then being transferred to test
controller by the optical fiber. The program of data acquisition part is compiled as
shown in Figure 3.
The laser ranging sensor has two output modes: current (4mA-20mA) and
voltage (0V-10V). In both two ranges, it shows a linear relationship between analog
output data and test distance. The current mode is selected for the system and the
measurement distance range is setting between 1200mm and 3000mm in consideration
of the particular condition of test area. By calculating we find that the relational
expression between measuring distance (S) and analog current (I) is:
S = 112 . 5 * I + 750
(1)
As is shown in the Figure 4, Lr1 , Lr 2 , Lr3 , Lr 4 respectively represent laser ranging
sensors of four positions, and T1 , R1 , T 2 , R 2 are four correlation photoelectric switches.
S 1 , S 2 , S 3 , S 4 represent measurement distances which are tested by laser ranging
sensors, and L is the installation distance between two symmetric sensors.
Figure 4. Distance of measurement points.
Figure 5. Data distribution.
Supposing the eventual shift is represented by S final , then we can conclude that:
S final = L2 − L1 = [(S 3 + S 2) − (S 4 + S1)] 2
(2)
L2 = ( L − S 3 − S 4) 2 + S 3
(3)
L1 = ( L − S1 − S 2) 2 + S1
(4)
In (2) , (3) and (4), S final is the difference between Lr3 and Lr1 ; L2 is the distance
between Lr3 and vehicle longitude axis. L1 is the distance between Lr1 and vehicle
longitude axis. If the value of S final is greater than 0, then the shift direction is right, and
the condition of S final being less than 0 is just the opposite.
SENSOR WORKING MODE
Laser ranging sensor has two working modes: standby and normal open. If users
give priority to the service life of the sensor, we will select the standby mode. When
test vehicle triggers photoelectric switches, there will be a high level signal to make the
laser ranging sensor put into service, in order to collect more data, photoelectric
switches and laser ranging sensor must be reasonably arranged, but this working mode
will use more hardware.
If users give priority to the structure’s simplicity, we will select normal open mode.
To avoid acquiring vast invalid signals, we should set the threshold value to gain valid
electrical level signals. For the sensor, when the measuring distance is out of the range,
it will display a fixed value which is included in factory settings or it will not show
distance information. Assuming that the preset level of threshold value is a, initial
direction is descending; interdictory level is b, interdictory direction is rising. When
there are no test vehicles passing by, the threshold will not be triggered, and it will not
get valid signals. When test vehicles passing by, the threshold will be triggered, it will
collect data until the vehicle leaves. By comparing two working modes of laser ranging
sensor, we can find that standby mode is better than normal open mode in the vehicle
driving wandering automotive system.
METHOD OF REDUCING THE TEST ERROR
By the error theory we know that test error will decrease with the increase of
testing applications. In test, in order to obtain more testing applications, we set the laser
ranging sensor in S-Fast file whose test frequency is 3000Hz, in other words, acquiring
a single data just need 0.33ms. Taking an example of minicar, if the test vehicle passes
by the test area at a speed of 50Km/h, there can also acquire more than 800 times’
testing applications. In addition, in order to obtain the actual error of laser ranging
sensor, we carried out a simulation experiment, the number of analog data was 1000,
and measuring distance was 2620mm. As shown in figure 5 was data distribution.
Based on the formula (1), when S is 2620mm, then I will be 16.22mA. Through
the operation we can know that the maximum error of output current is 0.034mA, the
average error of output current is 0.0044mA; the maximum error of relevant distance is
3.825mm, the average error of relevant distance is 0.495mm which meets the test
requirements of system.
SUMMARY
Choosing the appropriate hardware equipment based on the test precision and
environment. We can decrease the affection of vehicle vibration by distributing the
laser ranging sensor symmetrically.
Choosing the standby working mode of laser ranging sensor and using
photoelectric switch to trigger it, this way is accordance with demand of the test system.
Utilizing the fast test function of laser ranging sensor, it will acquire vast datas so
that we can diminish the test error. In other words, it can improve the precision of the
vehicle driving wandering system.
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