J. Ernesto Solanes

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.

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.

PWM and PFM for visual servoing in fully decoupled approaches

In this paper, novel visual servoing techniques based on Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM) are presented. In order to apply previous pulse modulations, a fully decoupled position based visual servoing approach (i.e. with block-diagonal interaction matrix) is considered, controlling independently translational and rotational camera motions. These techniques, working at high frequency, could be considered to address the sensor latency problem inherent in visual servoing systems. The expected appearance of ripple due to the concentration of the control action in pulses is quantified and analyzed under simulated scenario. This high frequency ripple does not affect the system performance since it is filtered by the manipulator dynamics. On the contrary it can be seen as a dither signal to minimize the impact of friction and overcome back-lashing. We develop novel visual servoing techniques based on pulse modulation (PWM and PFM).We use a fully decoupled position based visual servoing approach.The expected appearance of ripple is analyzed by simulation.The high frequency ripple would be filtered by the manipulator dynamics.

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.

Human-robot cooperation for robust surface treatment using non-conventional sliding mode control

This work presents a human-robot closely collaborative solution to cooperatively perform surface treatment tasks such as polishing, grinding, deburring, etc. The method considers two force sensors attached to the manipulator end-effector and tool: one sensor is used to properly accomplish the surface treatment task, while the second one is used by the operator to guide the robot tool. The proposed scheme is based on task priority and adaptive non-conventional sliding mode control. The applicability of the proposed approach is substantiated by experimental results using a redundant 7R manipulator: the Sawyer cobot.