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Joint Calibration of Dual LiDARs and Camera using a Circular Chessboard

Tongji University-Zhenwen Deng, Lu Xiong, Dong Yin, Fengwu Shan
  • Technical Paper
  • 2020-01-0098
To be published on 2020-04-14 by SAE International in United States
Environment perception is a crucial subsystem in autonomous vehicles. In order to build safety and efficient traffic transportation, several researches have been proposed to build accurate, robust and real-time perception systems. Camera and LiDAR are widely mounted on self-driving cars and developed with many algorithms in recent years. The fusion system of camera and LiDAR provides state-of the-art methods for environmental perception due to the defects of single vehicular sensor. Extrinsic parameter calibration is able to align the coordinate systems of sensors and has been drawing enormous attention. However, differ from spatial alignment of two sensors’ data, joint calibration of multi-sensors (more than three devices) should balance the degree of alignment between each one. In this paper, we assemble a test platform which is made up of dual LiDARs and monocular camera and is the same as the sensing hardware architecture of intelligent sweeper designed by our laboratory. Meanwhile, we propose the related joint calibration method using a circular chessboard. The center of circular chessboard is respectively detected in camera image to get pixel coordinates…
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IMM-KF Algorithm for Multitarget Tracking of on-Road Vehicle

Tongji University-Puhang Xu, Lu Xiong, Dequan Zeng, Zhenwen Deng, Zhuoren Li
  • Technical Paper
  • 2020-01-0117
To be published on 2020-04-14 by SAE International in United States
Tracking vehicle motion trajectories is essential for autonomous vehicles and advanced driver-assistance systems to understand traffic environment and evaluate collision risk. In order to reduce the position deviation and fluctuation of tracking on-road vehicle by millimeter-wave radar (MMWR), an adaptive interactive multi-model Kalman filter (IMM-KF) tracking algorithm including data association and track management is proposed. In general, it is difficult to model the target vehicle accurately due to lack of vehicle kinematics parameters, like wheel base, uncertainty of driving behavior and limitation of sensor’s field of view. To handle the uncertainty problem, an interacting multiple model (IMM) approach using Kalman filters is employed to estimate multitarget’s states. Then the compensation of radar ego motion is achieved, since the original measurement is under the radar coordinate system. In addition, an adaptive Kalman filter is engaged to handle the uncertainty of radar measurement noise and process noise. Taking into account the real-time performance of the algorithm and the distinguishability of vehicles involved in traffic, the nearest neighbor data association (NNDA) is used to associate observation with trajectory,…
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Vehicle validation for pressure estimation algorithms of decoupled EHB based on actuator characteristics and vehicle dynamics

DIAS Automotive Electronics Co.,.Ltd.-Songyun Xu
Tongji University-Wei Han, Lu Xiong, Zhuoping Yu
  • Technical Paper
  • 2020-01-0210
To be published on 2020-04-14 by SAE International in United States
In the automotive field, electro-hydraulic brake systems (EHB) has been developed to take place of the vacuum booster, having the advantage of faster pressure built-up and continuously pressure regulation. Most of the pressure control solutions are based on standard pressure-based feedback control, requiring a pressure signal. Although the pressure sensor can produce the pressure feedback signal, it will increase cost and enlarge installation space. The rotation angle of electric motor is available by the built-in sensor, so the pressure can be estimated by using the rotation angle. The pressure control is influenced intensely by the typical nonlinearities (i.e. friction, pressure-position relationship) and uncertainties (i.e. brake pads wear, temperature effect). To address these issues, this work improves an interconnected pressure estimation algorithm based on actuator characteristics [W. Han, L. Xiong, and Z. Yu, “Pressure estimation algorithms in decoupled electro-hydraulic brake system considering the friction and pressure-position relationship,” SAE Technical Paper 2019-01-0438, 2019] by introducing the vehicle dynamics and validates it via vehicle tests. The mathematical model of the motor-type EHB is built. The Gauss exponential model…
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Distributed Drive Electric Vehicle Longitudinal Velocity Estimation with Adaptive Kalman Filter: Theory and Experiment

China Automotive Engineering Research Institute Co., Ltd.-Yaming Zhang
Tongji University-Bo Leng, Lu Xiong, Zhuoping Yu, Dequan Zeng
Published 2019-04-02 by SAE International in United States
Velocity is one of the most important inputs of active safety systems such as ABS, TCS, ESC, ACC, AEB et al. In a distributed drive electric vehicle equipped with four in-wheel motors, velocity is hard to obtain due to all-wheel drive, especially in wheel slipping conditions. This paper focus on longitudinal velocity estimation of the distributed drive electric vehicle. Firstly, a basic longitudinal velocity estimation method is built based on a typical Kalman filter, where four wheel speeds obtained by wheel speed sensors constitute an observation variable and the longitudinal acceleration measured by an inertia moment unit is chosen as input variable. In simulations, the typical Kalman filter show good results when no wheel slips; when one or more wheels slip, the typical Kalman filter with constant covariance matrices does not work well. Therefore, a gain matrix adjusting Kalman filter which can detect the wheel slip and cope with that is proposed. Simulations are carried out in different conditions, including no wheel slips, one wheel slips, all wheel slip, passing a bump, and variable acceleration…
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Model-Based Pitch Control for Distributed Drive Electric Vehicle

Tongji University-Yize Yu, Lu Xiong, Zhuoping Yu, Xing Yang, Yuye Hou, Bo Leng
Published 2019-04-02 by SAE International in United States
On the dual-motor electric vehicle, which is driven by two electric motors mounted on the front and rear axles respectively, longitudinal dynamic control and electro-dynamic braking can be achieved by controlling the torque of front and rear axle motors respectively. Suspension displacement is related to the wheel torque, thus the pitch of vehicle body can be influenced by changing the torque distribution ratio. The pitch of the body has a great influence on the vehicle comfort, which occurs mainly during acceleration and braking progress. Traditionally active suspension is adopted to control the pitch of body. Instead, in this paper an ideal torque distribution strategy is developed to limit the pitch during acceleration and braking progress. This paper first explores the relationship between the torque distribution and the body pitch through the real vehicle test, which reveals the feasibility of the vehicle comfort promotion by optimizing the torque distribution coefficient. A two-degree-of-freedom semi-vehicle model is established according to the actual vehicle parameters. Based on the vehicle model, the control system is established to minimize the pitch…
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A Steerable Curvature Approach for Efficient Executable Path Planning for on-Road Autonomous Vehicle

Tongji University-Dequan Zeng, Zhuoping Yu, Lu Xiong, Junqiao Zhao, Peizhi Zhang, Zhiqiang Fu
Published 2019-04-02 by SAE International in United States
A rapid path-planning algorithm that generates drivable paths for an autonomous vehicle operating in structural road is proposed in this paper. Cubic B-spline curve is adopted to generating smooth path for continuous curvature and, more, parametric basic points of the spline is adjusted to controlling the curvature extremum for kinematic constraints on vehicle. Other than previous approaches such as inverse kinematics, model-based prediction postprocess approach or closed-loop forward simulation, using the kinematics model in each iteration of path for smoothing and controlling curvature leading to time consumption increasing, our method characterized the vehicle curvature constraint by the minimum length of segment line, which synchronously realized constraint and smooth for generating path. And Differ from the path of robot escaping from a maze, the intelligent vehicle traveling on road in structured environments needs to meet the traffic rules. Therefore, the path could be simplified and segmented to four basic parts: go straight, lane change/merge, turn and U-turn. By given reasonable start and terminal, all the basic segments could be generated via parameterized cubic B-spline curve and…
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Pressure Estimation Algorithms in Decoupled Electro-Hydraulic Brake System Considering the Friction and Pressure-Position Relationship

Lu Xiong
Tongji University-Wei Han, Zhuoping Yu
Published 2019-04-02 by SAE International in United States
This paper presents several pressure estimation algorithms (PEAs) for a decoupled electro-hydraulic brake system (EHB), which is driven by an electric motor + reduction gear. Most of the pressure control solutions are based on standard pressure-based feedback control, requiring a pressure signal. Although the pressure sensor can produce the pressure feedback signal, it will increase cost and enlarge installation space. The rotation angle of electric motor is available by the built-in sensor, so the pressure can be estimated by using the rotation angle. Considering the typical nonlinearities (i.e. friction, pressure-position relationship) and uncertainties (i.e. disturbance caused by friction model), the estimation-oriented model is established. The LuGre model is selected to describe the friction, and the pressure-position relationship is fitted by a quadratic polynomial. Based on the estimation-oriented model, the force-based PEA (FPEA) and the interconnected PEA (IPEA) are designed, respectively. What makes these two PEAs different is that the IPEA considers the pressure-position relationship. The comparison and analysis of the proposed PEAs have been conducted via some typical ordinary braking scenarios. The sensitivity analysis has…
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Coordinated Control under Transitional Conditions in Hybrid Braking of Electric Vehicle

Tongji Univ.-Zhuoping Yu, Biaofei Shi, Lu Xiong, Wei Han
Published 2018-10-05 by SAE International in United States
In the hybrid brake system of electric vehicle, due to the limitation of the motor braking force when the motor is at high speed and the failure of the regenerative braking force when the motor is at low speed, there are three transitional conditions in hybrid braking: the hydraulic brake system intervenes the braking, the hydraulic brake system withdraws the braking and the regenerative braking force withdraws the braking. Due to the response speed of the hydraulic system is slower than that of the motor, there is a large braking impact (the derivative of braking deceleration) in the transitional conditions of hybrid braking, which deteriorates the smoothness and comfort in braking. Aiming at the impact caused by the poor cooperation between the hydraulic braking force and the motor braking force, a coordinated strategy of double closed-loop feedback and motor force correction is proposed in this paper. The double closed-loop feedback strategy relies on the motor force to compensate the tracking error of hydraulic pressure of the hydraulic brake system. The purpose of the motor force…
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Braking Pressure Tracking Control of a Pressure Sensor Unequipped Electro-Hydraulic Booster Based on a Nonlinear Observer

Tongji University-Wei HAN, Lu Xiong, Zhuoping Yu
Published 2018-04-03 by SAE International in United States
BBW (Brake-by-wire) can increase the vehicle safety performance due to high control accuracy and fast response speed. As one solution of BBW, the novel Integrated-electro-hydraulic brake system (I-EHB) is proposed, which consists of electro-hydraulic booster and hydraulic pressure control unit. The electro-hydraulic booster is activated by an electric motor that driving linear motion mechanism to directly produce the master cylinder pressure. With electro-hydraulic booster as an actuator, the hydraulic pressure control problem is a key issue. Most literatures deal with the pressure control issue based on the feedback pressure signal measured by pressure sensor. As far as the authors are aware, none of the proposed techniques takes into account the pressure sensor unequipped BBW. In this paper, there is no pressure feedback signal, but there is only position feedback signal measured by position sensor for control law design. This paper presents a cascade controller based on a nonlinear observer to track desired master cylinder pressure for a pressure sensor unequipped electro-hydraulic booster in the presence of both external disturbances and parameter uncertainties. The outer pressure…
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Optimal Torque Allocation for Distributed Drive Electric Skid-Steered Vehicles Based on Energy Efficiency

Tongji University-Letian GAO, Lu Xiong, Xiang Gao, Zhuoping Yu
Published 2018-04-03 by SAE International in United States
Steering of skid-steered vehicles without steering mechanism is realized by differential drive/brake torque generated from in-wheel motors at left and right sides. Compared to traditional Ackerman-steered vehicles, skid-steered vehicles consume much more energy while steering due to greater steering resistance. Torque allocation is critical to the distributed drive skid-steered vehicles, since it influences not only steering performance, but also energy efficiency. In this paper, the dynamic characteristics of six-wheeled skid-steered vehicles were analyzed, and a 2-DOF vehicle model was established, which is important for both motion tracking control and torque allocation. Furthermore, a hierarchical controller was proposed. Considering tire force characteristics and tire slip, the upper layer calculates the generalized force and desired yaw moment based on anti-windup PI (proportion-integral) control method. On the fundamental of dynamic characteristics of skid-steered vehicles and electric motor efficiency characteristics, the lower layer utilizes different optimal torque allocation strategies based on energy efficiency at different driving conditions, namely, straight line driving condition and steering condition. The control results show that the motion controller can track the reference yaw rate…
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