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Autonomous driving system for reversing an articulated vehicle

Written by Amro Elhassan

Paper category

Master Thesis

Subject

Electrical engineering

Year

2015

Abstract

Thesis: Qualisys motion capture system tractor-trailer attitude estimation is achieved by Qualisys motion capture system [27], which uses infrared cameras for tracking. Tracking the body is accomplished by attaching a special mark that reflects infrared rays on the body. By strategically installing twelve cameras around the working space of the test bench, good coverage can be obtained. The motion capture system can be integrated with MATLAB so that real-time data can be used with simple commands. Therefore, by attaching the markers to the tractor and trailer, two independent objects are formed for the motion capture system to track, and their postures can be obtained from MATLAB in real time. 4.1.2 Measurement reliability A small experiment was conducted to evaluate the reliability of the given measurement motion capture system. The tractor trailer remains stationary in the work space and the measurement is performed at a frequency of 10 Hz. This was done for a duration of ten minutes, resulting in 6000 measurements. Modeling the attitude measurement using Gaussian distribution gives the standard deviation shown in Table 4.1. These low values ​​indicate high measurement accuracy. 4.2 Tractor The remote control tractor is composed of a 1:32 scale Scania R620 tractor model and a Schmitz-Cargobull brand semi-tube dump trailer. The tractor-trailer wireless transmission is based on 2.4 GHz radio technology, which can control the steering and driving functions of the tractor, as well as the coupling and tipping of the trailer [28]. 4.2.1 The size of the vehicle is developing an automatic driving system. One reason is their use in collision prevention, and another reason is that many controllers require them in their calculations. However, they are particularly important in our case because they are used to avoid folding knives. The measured values ​​of the total length of tractors and trailers, Ltractor and Ltrailer and the dimensions shown in Figure 4.2 are given in Table 4.2. Please note that both the tractor and the trailer have the same width Lwan and the total length L of the tractor-trailer is less than the sum of the lengths of the individual bodies, this is due to the way they overlap. In addition, the tractor-trailer is not perfectly hung in front of the tractor axle, and the hitch point is slightly in front of the tractor axle. This deviation from the mathematical model may be a source of future errors, but it may be covered by others because it is too small. The shorter the sampling time, the better the theoretical result. However, in reality, the pose measurement will be affected by a certain degree of measurement noise, and then will be amplified with a smaller sampling time. Therefore, this trade-off must be kept in mind when setting the sampling time. 4.2.3 The relationship between the input and output of the actuator. The working area of ​​the tractor's speed actuator and steering actuator are both 0{3.2 V. For the speed actuator, the lower half of the working area corresponds to the tractor's reversing, 0 V gives the maximum reverse speed and 1.6 V to stop. The upper part corresponds to driving forward, and 3.2 V gives the maximum speed. For the steering actuator, the lower half corresponds to the wheel turning to the left, 0 V gives the maximum left turn and 1.6 V provides straight steering. The upper half corresponds to turning the wheel to the right, 3.2 V provides the maximum right turn. For speed, this is only the lower half of the entire working area (because we will only deal with reverse movement). The experiment was conducted with a duration of 120 seconds. Using such a long time is to reduce the influence of inertia. Figures 4.5 and 4.6 show the input-output relationship between speed and steering actuators. It can be seen that when the voltage is further reduced below 0.5, the reverse speed stops increasing by V. This is caused by the saturation of the actuator, and the same phenomenon can be seen in the steering actuator. In addition, the inertia effect is visible when the stopping speed is 1.6 V, and the increasing voltage curve has speed at higher voltages. Before the speed starts to become positive (which can be displayed as 1.98 V), there is obviously a dead zone/neutral zone after 1.6 V. The higher speeds seem quite noisy. However, our working area will be at a lower voltage, it is smooth, therefore, adding filtering is not necessary. Another phenomenon that can be achieved from the input-output relationship of the steering actuator is hysteresis, that is, the gap between the curves is unlikely to be caused by inertia, because the rate of change of voltage is so low. In addition, it can be seen from the figure that the minimum speed of the tractor is around -0.08 m/s. This is achieved with the minimum voltage that can overcome friction and inertia to move the tractor. On the other hand, the steering angle can reach a maximum of 30°. However, the steering angle measurement becomes quite noisy when it exceeds 20. For this reason, and the general rule of keeping the maximum value in order to avoid problems, the maximum steering angle will be set to 20 degrees. Read Less