Lok Man Ho

Human machine interface concept for interactive motion control of a highly maneuverable robotic vehicle

A vehicle dynamics human machine interface (HMI) concept for the operation of a highly maneuverable vehicle is presented. This is motivated by the research vehicle ROMO, which is being developed by the German Aerospace Center (DLR) to facilitate research on a wide spectrum of scientific questions dealing with electric and autonomous mobility. With four wheel individual large range steering and electric wheel hub motors, the vehicle dynamics variables of yaw rate, side slip angle and vehicle velocity can be decoupled, thus opening new motion possibilities. The HMI approach includes distinction of various motion operating modes, suitable reference motion parameterization and adequate filtering of the operators inputs, both depending on the operating mode. For rotating on the spot the instantaneous center of rotation may be interactively set by the operator on a touch screen.

Application of Adaptive Thresholds in Robust Fault Detection of an Electro-Mechanical Single-Wheel Steering Actuator

Abstract A fault detection scheme has been developed for an electromechanical steering actuator under closed-loop control. The closed-loop system is modeled as a 2 nd order system with bounded parameter uncertainties given by the performance specifications. The residual is generated using an observer-based method. A dynamic adaptive threshold is generated based on the inputs and the measured system outputs to account for the residual deviating from zero under fault-free conditions due to parameter uncertainties. In addition to this, the error of the controlled system output due to a disturbance is handled by the residual evaluation function. This method is tested on a simple simulation as well as experimental data.

Fault detection and isolation of vehicle dynamics sensors and actuators for an overactuated X-by-wire vehicle

Model-based fault detection and isolation (FDI) for an overactuated mechatronic vehicle is presented. The linear single-track model is extend to reflect the layout of the overactuated vehicle as well as its longitudinal dynamics, and sensor and actuator faults are added into the model. The DLR Fault Detection Toolbox, which makes use of rational nullspace bases computation to design residual generators, is used for the systematic design of structured residuals. A minimum set of residuals is selected according to their robustness and ability to isolate faults. The fault detection and isolation system is validated in a simulation in connection with a double track model using the parameters of the ROboMObil prototype vehicle.

Fault-tolerant control of an electrohydraulic brake using virtual pressure sensor

An approach for fault tolerant control of an electrohydraulic brake (EHB) in case of a pressure sensor failure is presented. Automotive Brake-by-Wire actuators are safety critical components, and an EHB under closed-loop pressure control is critically affected by faults in the pressure sensor. Timely fault detection and reconfiguration to use a brake pressure estimate based on motor position enhances the reliability of the system. Since the relationship between position and pressure can vary over a systems lifetime due to wear and changes in brake system characteristics, it is necessary to adapt this relationship online using operating data. This paper presents the means to perform this update using a least squares estimation routine, adapted to account for persistence of excitation and data storage limitations. Model-based fault detection functions are also presented. The proposed fault-tolerant control approach is implemented and validated on an EHB test bench with promising results.

Sensor fault detection and isolation using a non-linear planar kinematic model of vehicle dynamics

An approach for fault detection and isolation (FDI) of sensors in chassis control systems is presented. This approach makes use of the analytical redundancy in the non-linear kinematic relationships between wheel speeds, steering angles, and the vehicle body motion, which is valid when negligible tyre slip can be assumed. Using a bounded-in-bounded-out approach, bounds for coherent sensor values are computed from a subset of the remaining sensor values and their tolerances. A sensor value lying outside these bounds indicates a fault candidate. The tolerance propagation is achieved by solving a linear programming problem. By estimating a variety of output signals using different combinations of input signals, each residual generator is sensitive to a different subset of sensor faults, thus permitting fault isolation through structured residuals. The effectiveness of this FDI approach is demonstrated using simulation results and experimental test drive measurements from the German Aerospace Centers highly manoeuvrable ROboMObil research platform with four wheel individual large-range steering. Because of the latter, state-of-the-art methods cannot be applied.

H ∞ structured residual generator synthesis using residual reference models with application to lateral vehicle dynamics

In the residual generation problem, one of the methods to achieve the fault sensitivity constraint is by optimising the residual to track a reference model for the fault-to-residual transfer function. A poorly selected, unrealistic reference model can have a detrimental impact on the robustness and decoupling performance of the residual. This can be particularly severe in the multiple fault case where the optimal ratio between the fault-to-residual gains are not known a priori. The proposed method is a measure to reduce this effect, by allowing the low frequency gain from each fault to the scalar residual to vary via an additional decision variable in the LMI formulation of the ffM estimator synthesis problem. The effectiveness of this method is demonstrated in a vehicle lateral dynamics application.