Vicent Girbés

On generating continuous-curvature paths for line following problem with curvature and sharpness constraints

The main contribution of the paper is to provide a method to generate continuous curvature paths in order to converge to a line, based on combinations of clothoids with line segments and circular arcs. Different kinds of continuous curvature paths have been defined in order to solve problems with different complexity. The type of paths that we have generated get the benefits of higher comfort and safety. Generated paths take into account lower and upper bounds of sharpness and curvature simultaneously, while it is not the case of other continuous curvature paths such as Elementary and BiElementary paths. Wheeled mobile robots following a path with continuous curvature may also get benefit on wheels slippage reduction and low odometry errors, since transitions are softer with constant curvature rates.

Continuous-Curvature Control of Mobile Robots with Constrained Kinematics

Abstract The main contribution of the paper is to provide a method to generate continuous-curvature paths in order to perform the kinematic control of a wheeled mobile robot, based on combinations of clothoids, line segments and circular arcs. Higher benefits on comfort and safety can be obtained when generating continuous-curvature paths, which is very important in transporting people or dangerous goods. Generated paths take also into account lower and upper bounds of sharpness and curvature simultaneously, while it is not the case of many kinematic controllers like pure-pursuit control. The proposed kinematic controller determines a continuous-curvature path to reach a target configuration by recomputing the whole path every step, applying next curvature planned in the curvature profile. The new method can be easily combined with global planners and vision systems that give some way-points to be followed. For that purpose, some simulations show that proposed method can solve problems with different complexity such as line following problem, path tracking, lane changing and overtaking. Finally, an analysis to evaluate the performance of the new method against pure-pursuit is done.

Mobile Robot Obstacle Avoidance Based on Quasi-Holonomic Smooth Paths

The paper explores the benefits of using continuous curvature 2D paths in obstacle avoidance methods in terms of safety and comfort. To this end the paper proposes a novel contribution by introducing clothoid-based smooth paths for non-holonomic robots defined from Cartesian (x,y) and angular velocities, as if they were intended to be applied to holonomic robots. To remark, these paths, coined as quasi-holonomic continuous curvature paths (QHCC), generate purely non-holonomic motions (combinations of linear and angular velocities) that mimic a holonomic motion. In fact, QHCC paths converge to the same asymptotic direction pointed by the holonomic motion while taking into account kinematic and dynamic constraints. In the paper, we show how these paths can be used and integrated in well-known obstacle avoidance algorithms such as Nearness Diagram (ND) and Dynamic Window Approach (DWA), among others. In addition to this, an ANN has been trained to considerably speed-up the path generation process and to learn the intrinsics of the path. Additionally, the paper shows the advantages of the proposed method over standard obstacle avoidance algorithms.

Continuous-curvature kinematic control for path following problems

The main contribution of the paper is to demonstrate the benefits of a new kinematic control method within the Pure-Pursuit framework, based on continuous-curvature paths, against a classic approach to Pure-Pursuit methods commonly used in mobile robotics. The new method can be applied in a generic path following problem and it is based on combinations of clothoids with line segments and circular arcs, providing a general curvature profile. The main advantage is that generated paths take into account lower and upper bounds of curvature and sharpness which implies smoother and safer trajectories, not considered in other methods. It is shown that the proposed method has better performance with respect to settling time, overshoot and little influence on design parameters. As application, a vision-based path following continuous-curvature control problem has been implemented on an industrial forklift vehicle in order to show the advantage of the method.

An Active Safety System for Low-Speed Bus Braking Assistance

Accidents in which buses or coaches are involved cause thousands of injuries and fatalities every year. To reduce their number and severity, this paper describes an advanced driver assistance system (ADAS) based on a haptic throttle pedal and emergency braking. It also proposes a computationally efficient algorithm with a methodology based on three main concepts: a simplified but accurate vehicle model, an efficient collision detection system considering the drivers intention and pedestrians wandering around the vehicle, and a risk evaluation system to generate warnings and emergency braking signals. Finally, the performance of the proposed ADAS is validated using a driving simulation cabin with a very realistic urban scenario and original elements from real buses. The results show a statistically significant improvement in safety, as the number of collisions and high-risk situations are clearly minimized, the reaction time to press the brake pedal is improved, and the time to collision increased in emergency situations. Implementation of the proposed ADAS into city buses would potentially improve safety, reducing the frequency and severity of accidents in pedestrians.

Dual-Rate Non-Linear High Order Holds for Visual Servoing Applications

This paper introduces a novel concept of dual-rate non-linear high order holds, based on artificial neuronal networks, in order to improve control, robustness and stability margin of non-linear processes. The main idea is that artificial networks provide accurate inter-sampling data estimation in dual-rate systems, allowing controlling the process at the fastest possible rate. In addition to this, the paper compares the performance with other approaches taking into account the ideal but non-feasible closed loop at high frequency. For that purpose, the paper considers metrics such as mean square error and settling time to measure the overall performance. The proposed dual-rate non-linear holds have been tested in both, simulation and real processes, and particularly, in an industrial robot within an image-based visual servoing application. The new approach improves with respect to the conventional single-rate behavior and showing higher stability margin than conventional dual-rate holds.

Multi-rate visual servoing based on dual-rate high order holds

This paper describes a multi-rate approach based on the extensive use of Dual-rate High Order Holds for visual servoing systems. Moreover a complete description of a general multi-rate approach, comparing Dual-rate Image-Based Visual Servoing algorithm with Dual-rate PID controller, where the PID is separated into its two different dynamics, using two different sampling periods is presented. In addition, a multi-rate Kalman filter is compared with Dual-rate High Order Holds, as an attempt to extend the use of this kind of interfaces to the estimation process. Results are obtained by simulation and also using a 6-DOF industrial robot (KUKA KR5 sixx R650) for the case of tracking objects with fast movement. This paper has validated the use of Dual-rate High Order Holds in non-linear systems, in general, and in robot visual servoing, in particular.

Smooth kinematic controller vs. pure-pursuit for non-holonomic vehicles

The paper introduces a method for generating trajectories with curve sharpness and curvature constraints. Trajectories are based on continuous-curvature paths using Single & Double Continuous-Curvature paths. The paper also proposes a multi-rate control scheme by considering different dynamics with different sampling frequencies: global path planner at low frequency; target update based on Look-Ahead distance and path computation at medium frequency; curvature control at high frequency. An exhaustive analysis to evaluate the performance of the new method with respect to Pure-Pursuit method has been carried out, showing that the proposed method has better performance in terms of settling time, overshoot and robustness against design parameters. As a conclusion, we can say that our method introduces improvements in comfort and safety because the sharpness, normal jerk and mean abruptness are lower than with the Pure-Pursuit control.

On improving robot image-based visual servoing based on dual-rate reference filtering control strategy

It is well known that the use of multi-rate control techniques have improved the performance of many systems in general, and robotic systems, in particular. The main contribution of this paper is the generalization of the Reference Filtering control strategy from a dual-rate point of view, improving its inherent properties by overcoming the problem of sensor latency. In the paper, we discuss and analyze the improvements introduced by the novel dual-rate reference filtering control strategy in terms of convergence time, reachability and robustness. More specifically, we discuss the capability to solve positioning tasks, when hardware limitations are present with large sampling rates. In addition, a comparison is made between the single-rate and the proposed dual-rate control strategies to prove the advantages of the latter approach. A complete set-up has been prepared for validation, including a six degree of freedom (DOF) industrial manipulator, a smart camera and embedded hardware used as a high level controller.

Improving image-based visual servoing with reference features filtering

In this paper, Image-Based Visual Servoing (IBVS) is addressed via a new control structure where reference features are previously filtered based on an estimation of these reference features using standard filters such as Kalman Filter (KF) or a combination of a Kalman Filter and a Smoother (KFS). In this sense, one of the key aspects of the paper is to predict feasible reference features for the low-level IBVS controller. Along the paper, we discuss and analyze the improvements introduced with the new control structure in terms of convergence time and reachability, that is, the ability to converge in complex scenarios such as rotations around the camera axis and large displacements. Validations are also provided through real experimentation with an industrial robot of 6 DOF in eye-in-hand configuration.