In this work, we describe an energy-based control method for under-actuated soft manipulators. The continuous dynamics of the soft robot are modeled by the differential geometry of Cosserat beams. Through a finite-dimensional truncation, a reduced port-Hamiltonian model is obtained that preserves desirable passivity conditions. Exploiting the passivity, we propose a stabilizing energy-shaping controller that ensures the potential energy is minimal at the desired end-effector configuration. Finally, the effectiveness of the energy-based controller is demonstrated through simulations of a soft manipulator inspired by the tentacle of an octopus.

Currently, the driver plays a crucial role in the safety of autonomous vehicles, functioning as the fall back for vehicle control systems. Fast and accurate detection of driver intervention is therefore of importance. In this article a novel driver intervention detection method for automated vehicles is presented and tested. Non-critical transitions are considered, excluding safety related applications. The transfer function between the electric power steering torque and steering column angle is estimated by perturbing the steering system with a known disturbance. This estimated value is used to detect whether a driver is intervening. The detection algorithm has been tested in simulations using a four degree-of-freedom vehicle model. The parameters of this vehicle model have been obtained via frequency response measurements performed on a test vehicle. Secondly, the performance of the algorithm has been tested with on-road measurements. The results show that driver intervention can be successfully detected within 0.4 seconds. The performance in terms of true and false detections has been analyzed, and the presented solution is shown to be robust to measurement noise and road disturbances.

Recently, increasing interest has been shown in cooperative driving and platooning, as they show great potential for increasing the road throughput, by both increasing road capacity and preventing so called `ghost' traffic jams. These cooperative vehicles make use of controllers or trajectory planners that achieve a certain spacing policy. However, these systems may result in large accelerations when the host vehicle is trying to close a gap to a preceding vehicle, leading to uncomfortable responses. In this work, a trajectory planning method is presented that is able to smoothly close a large gap, by means of a time-varying spacing policy. The resulting trajectory planner is capable of both maintaining a desired spacing as well as closing a gap comfortably to a preceding vehicle.

This paper presents a novel extended look-ahead concept of an integrated lateral and longitudinal vehicle following controller with an orientation-error observer. The control law is based on input-output feedback to address a local tracking problem. It is known that due to the position control in the look-ahead approach, the follower vehicle may cut corners. To address this problem, a reference-induced extended look-ahead tracking point is introduced such that the cutting-corner is compensated. Moreover, the stability of the internal dynamics is analyzed. To address the situation where the orientation tracking error is not measurable or corrupted by noise, an orientation-error observer, constructed from the position tracking error, is designed. The performance of the extended look-ahead controller and the orientation-error observer is investigated by means of a simulation study, and validated with experiments on a mobile robot platform.

High-speed visual servo systems are used in an increasing number of applications. Yet modeling and optimizing these systems remains a research challenge, largely because these systems consist of tightly-coupled design parameters across multiple domains, including image sensors, vision algorithms, processing systems, mechanical systems, control systems, among others. To overcome such a challenge, this work applies an axiomatic design method to the design of high-speed visual servo systems, such that cross-domain couplings are explicitly modeled and subsequently eliminated when possible. More importantly, methods are proposed to model the sample rate, measurement error, and delay of visual feedback based on design parameters across multiple domains. Lastly, methods to construct a holistic model and to perform cross-domain optimization are proposed. The proposed methods are applied to a representative case study that demonstrates the necessity of cross-domain modeling and optimization, as well as the effectiveness of the proposed methods.

This paper proposes a cooperative intersection control strategy, which aims to decrease the number of accidents and to increase the traffic flow at intersections. Existing high-level automation methodologies mainly focus on the determination of a safe crossing sequence of the involved vehicles, typically ignoring realistic vehicle dynamics aspects. The solution proposed in this paper, referred to as cooperative intersection control (CIC), takes into account the dynamics of the vehicles and is based on the novel concept of virtual platooning. Virtual platooning allows to form platoons of vehicles that are in different lanes of the intersection and have different directional intentions. Herewith, both safe passage of the vehicles through the intersection and a high intersection throughput (due to close “virtual” vehicle following) can be achieved. The performance of the proposed strategy is assessed, and a comparison between the CIC and an intersection controlled with traffic lights is presented.

Cooperative driving is based on wireless communications between vehicles and between vehicles and roadside infrastructure, aiming for increased traffic flow and traffic safety, while decreasing fuel consumption and emissions. To support and accelerate the introduction of cooperative vehicles in everyday traffic, in 2011, nine international teams joined the Grand Cooperative Driving Challenge (GCDC). The challenge was to perform platooning, in which vehicles drive in road trains with short intervehicle distances. The results were reported in a Special Issue of IEEE Transactions on Intelligent Transportation Systems, published in September 2012 [item 1 in the Appendix].

We propose a two-layer control architecture for bilateral teleoperation with communication delays. The controller is structured with an (inner) performance layer and an (outer) passivity layer. In the performance layer, any traditional controller for bilateral teleoperation can be implemented. The passivity layer guarantees that, from the operator and environment perspective, the overall teleoperator is passive: The amount of energy that can be extracted from the teleoperator is bounded from below and the rate of increase of the stored energy in the teleoperator is bounded by (twice) the environment and operator supplied power. Passivity is ensured by modulating the performance layer outputs and by injecting a variable amount of damping via an energy-based logic that follows the innovative principle of energy duplication and takes into account the detrimental effects of time delays. In contrast to the traditional teleoperation approach, in which the master and slave controllers implement an as-stiff-as-possible coupling between the master and slave devices, our scheme is specifically designed for direct force-reflecting bilateral teleoperation: The slave controller mimics the operator action, whereas the master controller reflects the slave-environment interaction. We illustrate the performance of the two-layer approach in a challenging experiment with a round-trip communication delay of 300 ms while making and breaking contact with a stiff aluminum environment. Finally, we also compare our controller with the state of the art.

This work explores the stabilization of desired dynamic motion tasks involving hard impacts at non-negligible speed for humanoid robots. To this end, a so-called reference spreading hybrid control law is designed showing promising results in simulation. The simulations are performed employing a dynamical model of an existing humanoid robot and impacts are assumed to be inelastic. The desired motion task consists of having the robot balancing on one foot while repeatedly making and breaking contact with a wall by means of one hand. The simulation results illustrate that the considered controller is suited to control humanoid robot motions with impacts.

This paper presents the controller design for combined lateral and longitudinal Cooperative Adaptive Cruise Control (CACC) for a unicycle-type platoon with emphasis on the cornering maneuvers. A decentralized controller for lateral and longitudinal behavior is designed using input-output linearization by static feedback. A preceding vehicle look-ahead approach is adapted in the controller to maintain desired inter-vehicle distance. However, due to the position control of the look-ahead point, the follower vehicle may cut corners on turns. In this paper, the extension of a look-ahead point that is able to compensate the cutting-corner behavior is then proposed. To validate the theoretical analysis, the full nonlinear system together with the developed controller is simulated for two scenarios, a circular path and a particular path scenario, and a comparison is made between the system with the preceding vehicle look-ahead and the extended look-ahead. The simulation shows that the proposed lateral and longitudinal controller using the extended look-ahead eliminates the cutting corner behavior.

Platooning has shown to be technically feasible, but safety aspects are still challenging. Wireless communication between vehicles allows to maintain reduced inter-vehicle distances, thereby improving traffic throughput and decreasing fuel consumption. As the driver can no longer be a backup at short inter-vehicle distances, the system needs to be fail-safe for both hazardous traffic situations as well as failures. In this paper, a scenario is defined which combines a hazardous traffic situation with a communication failure. First, the methodology for developing safety related functionality in automated driving is presented. This methodology combines aspects of the ISO26262 standard with the Harmony profile. Second, the safety mechanism to avoid a collision by braking is described. This ensures that a safe state can be reached for a set of use cases which are derived from the defined scenario. Finally, the proposed solution is tested in a simulation environment and is also implemented on test vehicles. The result of the simulations and experiments demonstrate the practical validity and show increased safety related functionality.

This work presents a merging strategy for cooperative vehicles. In the proposed strategy, each vehicle possesses a tracking controller that considerers both tracking and coupling error signals, where all vehicles in the group know their positions. The trajectories of the cooperative vehicles are developed, to guarantee that each vehicle keeps a certain distance from the rest of the vehicles in the group, and are designed by using the virtual structure approach. The merging strategy is successfully validated in an experimental setup consisting of a group of nonholonomic mobile vehicles that represents the simplest bicycle model for cars with a zero vehicle length. It is shown using Lyapunov theory that this strategy is global asymptotically stable for the group.

In controlling teleoperation systems subject to communication delays, unstable behavior is often prevented by injecting damping. A proper perception of hardness is required to efficiently interact with an object, but it is unknown if and how this injected damping influences the perceived hardness of objects. To investigate the effect of damping on the perceived hardness of an object, 12 participants compared the hardnesses of lightly and heavily damped objects in a two-alternative forced choice experiment. Two tasks were investigated: an in-contact and a contact-transition task. For each task, 3 reference stiffnesses were used. Both force and position data were recorded. The results show that adding damping increases the perceived hardness of an object for an in-contact task, while it decreases perceived hardness for a contact-transition task. Movement and force data show that object indentation, mean and maximum velocity and adjusted rate-hardness, a new parameter defined in this paper, correlate with perceived object hardness. From a fundamental perspective, the results show that perceived hardness is influenced by damping in a task-specific way. Moreover, for designers of teleoperation systems the results provide insights for tuning and designing control architectures that properly reflect the desired hardness.

Cooperative adaptive cruise control (CACC) employs wireless intervehicle communication, in addition to onboard sensors, to obtain string-stable vehicle-following behavior at small intervehicle distances. As a consequence, however, CACC is vulnerable to communication impairments such as latency and packet loss. In the latter case, it would effectively degrade to conventional adaptive cruise control (ACC), thereby increasing the minimal intervehicle distance needed for string-stable behavior. To partially maintain the favorable string stability properties of CACC, a control strategy for graceful degradation of one-vehicle look-ahead CACC is proposed, based on estimating the preceding vehicle's acceleration using onboard sensors, such that the CACC can switch to this strategy in case of persistent packet loss. In addition, a switching criterion is proposed in the case that the wireless link exhibits increased latency but does not (yet) suffer from persistent packet loss. It is shown through simulations and experiments that the proposed strategy results in a noticeable improvement of string stability characteristics, when compared with the ACC fallback scenario.

In research there is a considerable interest in developing interactive educational systems. However, the typical classroom remains a rather lowtech environment. Allowing teachers to create, adapt and share interactive learning applications might increase the uptake of technology in the classroom. In this paper a study is presented that explores the deployment of a robotstorytelling application for preschoolers, while simultaneously investigating the teacher's requirements for a toolkit to create stories for the robot. The results suggest that a robotstorytelling application can be a valuable addition to the classroom and that indeed a toolkit for creating stories would increase its usefulness in the curriculum.

The use of redundant sensors brings a rich diversity of information, nevertheless fusing different sensors that run at vastly different frequencies into a proper estimate is still a challenging sensor fusion problem. Instead of using the size-varying measurements and thereby the size-varying filters during each sampling period, we propose to find a substitute of the unavailable low frequency measurements such that we can avoid using different sampling frequencies in one filter. In the gap between the sampling of two low frequency measurements, the use of these substitutes produces smoother estimates. In both the proof of concept simulation and the localization experiment performed on an indoor soccer robot, our proposed approach exhibits an improved performance compared to the size-varying Kalman filter methods.

This paper presents direct methods for vision-based control for the application of industrial inkjet printing. In this, visual control is designed with a direct coupling between camera measurements and joint motion. Traditional visual servoing commonly has a slow visual update rate and needs an additional local joint controller to guarantee stability. By only using the product as reference and sampling with a high update rate, direct visual measurements are sufficient for controlled positioning. The proposed method is simpler and more reliable than standard motor encoders, despite the tight real-time constraints. This direct visual control method is experimentally verified with a 2D planar motion stage for micrometer positioning. To achieve accurate and fast motion, a balance is found between frame rate and image size. With a frame rate of 1600 fps and an image size of 160 × 100 pixels we show the effectiveness of the approach.

In this paper, we consider a Cooperative Adaptive Cruise Control (CACC) system, which regulates intervehicle distances in a vehicle string, for achieving improved traffic flow stability and throughput. Improved performance can be achieved by utilizing information exchange between vehicles through wireless communication in addition to local sensor measurements. However, wireless communication introduces network-induced imperfections, such as transmission delays, due to the limited bandwidth of the network and the fact that multiple nodes are sharing the same medium. Therefore, we approach the design of a CACC system from a Networked Control System (NCS) perspective and present an NCS modeling framework that incorporates the effect of sampling, hold, and network delays that occur due to wireless communication and sampled-data implementation of the CACC controller over this wireless link. Based on this network-aware modeling approach, we develop a technique to study the so-called string stability property of the string, in which vehicles are interconnected by a vehicle following control law and a constant time headway spacing policy. This analysis technique can be used to investigate tradeoffs between CACC performance (string stability) and network specifications (such as delays), which are essential in the multidisciplinary design of CACC controllers. Finally, we demonstrate the validity of the presented framework in practice by experiments performed with CACC-equipped prototype vehicles.

Cooperative adaptive cruise control (CACC) allows for short-distance automatic vehicle following using intervehicle wireless communication in addition to onboard sensors, thereby potentially improving road throughput. In order to fulfill performance, safety, and comfort requirements, a CACC-equipped vehicle platoon should be string stable, attenuating the effect of disturbances along the vehicle string. Therefore, a controller design method is developed that allows for explicit inclusion of the string stability requirement in the controller synthesis specifications. To this end, the notion of string stability is introduced first, and conditions for L2string stability of linear systems are presented that motivate the development of an H∞controller synthesis approach for string stability. The potential of this approach is illustrated by its application to the design of controllers for CACC for one- and two-vehicle look-ahead communication topologies. As a result, L2string-stable platooning strategies are obtained in both cases, also revealing that the two-vehicle look-ahead topology is particularly effective at a larger communication delay. Finally, the results are experimentally validated using a platoon of three passenger vehicles, illustrating the practical feasibility of this approach.

Different models are used in literature to approximate the complex dynamics of a humanoid robot. Many models use strongly varying model assumptions that neglect the influence of feet, discontinuous ground impact, internal dynamics and coupling between the 3D coronal and sagittal plane dynamics. Often motivation is lacking why a certain model should be chosen or why certain dynamical aspects may or may not be neglected. A simple model like a linear inverted pendulum with low computational cost is frequently used on-line in foot placement algorithms, where model inaccuracy may lead to low control performance. A full 3D multi-body model with higher computational cost is typically used off-line in a simulator, where model inaccuracy may lead to unreliable results. This paper contributes experimental validation of both types of models by comparing them to the real dynamics of the humanoid robot TUlip during balance recovery side-stepping. Hereto, we evaluate the aforementioned most common model assumptions. The validated multi-body model that we implemented in the ROS Gazebo simulator is released on-line.

In this paper, we consider the problem of distributed formation control for a group of unicycle robots. We propose a control algorithm that solves the formation control problem in that it ensures that robots create a desired time-varying formation shape while the formation as a whole follows a prescribed trajectory. Moreover, we show that it is also possible to obtain coordination of robots in the formation, regardless of the trajectory tracking of the formation. We illustrate the behavior of a group of robots controlled by the formation control algorithm proposed in this paper in a simulation study.

When humanoid robots are going to be used in society, they should be capable to maintain the balance. Knowing where to step appears to be crucially important to remain balanced. This paper contributes the foot placement indicator (FPI), an extension to the foot placement estimator (FPE) for planar bipeds with point feet and an arbitrary number of non-massless links. The method uses conservation of energy to determine where the planar biped needs to step to remain in balance. Simulations of the FPI show improved foot placement for balance with respect to the FPE.

A new visual servoing method is proposed which uses position based visual servoing (PBVS) in combination with an additional image based control layer on the target pose to maintain fixation on an object. The proposed method (denoted feed forward PBVS) does not require trajectory generation but instead uses via-points to explore the object. It exploits the advantages of PBVS without the disadvantages of image based visual servoing (IBVS) as occurs in hybrid approaches. The proposed method is experimentally validated with a redundant 7-DOF manipulator. Comparison with existing visual servoing methods (PBVS and one partitioned approach) shows the effectiveness of the method.

This paper describes the implementation and testing of a Cooperative Adaptive Cruise Control (CACC) strategy on a heavy-duty truck. The adopted control strategy utilizes additional information exchange through wireless communication to improve the vehicle-following behavior achieved by the underlying adaptive cruise controller (ACC). The control method is evaluated in a mixed traffic condition. It is shown that the truck can perform smooth predecessor following in most of the test scenarios, even for small intervehicle distances. Furthermore, the results demonstrate how string stability is affected by wireless communication imperfections and acceleration (deceleration) limitations of the heavy-duty truck in an inhomogeneous platoon.

We discuss synchronization in networks of Hindmarsh-Rose neurons that are interconnected via gap junctions, also known as electrical synapses. We present theoretical results for interactions without time-delay. These results are supported by experiments with a setup consisting of sixteen electronic equivalents of the Hindmarsh-Rose neuron. We show experimental results of networks where time-delay on the interaction is taken into account. We discuss in particular the influence of the network topology on the synchronization.

We consider the problem of how to recover the state and parameter values of typical model neurons, such as Hindmarsh-Rose, FitzHugh-Nagumo, Morris-Lecar, from in-vitro measurements of membrane potentials. In control theory, in terms of observer design, model neurons qualify as locally observable. However, unlike most models traditionally addressed in control theory, no parameter-independent diffeomorphism exists, such that the original model equations can be transformed into adaptive canonic observer form. For a large class of model neurons, however, state and parameter reconstruction is possible nevertheless. We propose a method which, subject to mild conditions on the richness of the measured signal, allows model parameters and state variables to be reconstructed up to an equivalence class.

Advanced driver assistance systems are increasingly available on road vehicles. These systems require a thorough development procedure, an important part of which consists of hardware-in-the-loop experiments in a controlled environment. To this end, a facility called vehicle hardware-in-the-loop (VeHIL) is operated, aiming at testing the entire road vehicle in an artificial environment. In VeHIL, the test vehicle is placed on a roller bench, whereas other traffic participants, i.e., vehicles in the direct neighborhood of the test vehicle, are simulated using wheeled mobile robots (WMRs). To achieve a high degree of experiment reproducibility, focus is put on the design of an accurate position control system for the robots. Due to the required types of maneuvers, these robots have independently driven and steered wheels. Consequently, the robot is overactuated. Furthermore, since the robot is capable of high-dynamic maneuvers, slip effects caused by the tires can play an important role. A position controller based on feedback linearization is presented, using the so-called multicycle approach, which regards the robot as a set of identical unicycles. As a result, the WMR is position controlled, whereas each unicycle is controlled, taking weight transfer and longitudinal and lateral tire slip into account.

In this paper the problem of global trajectory tracking for the kinematic model of a unicycle-type mobile robot is considered. It is assumed that some of the tracking error coordinates are not measurable. Using a cascaded systems approach we develop full order and reduced order observers, and introduce an observer based controller resulting in K-exponential convergence of the tracking error. Simulations are provided to illustrate the results.

The synchronization problem for complex discrete-time systems is revisited from a control perspective and it is argued that the problem may be viewed as an observer problem. It is shown that for several classes of systems a solution for the synchronization (observer) problem exists. Also, by allowing past measurements a dynamic mechanism for state reconstruction is provided.

In this paper we present two approaches to estimate the Hausdorff dimension of an invariant compact set of a dynamical system: the method of characteristic exponents (estimates of the Kaplan-Yorke type) and the method of Lyapunov functions. In the first approach, using Lyapunov's first method we exploit characteristic exponents for obtaining such estimates. A close relationship with uniform asymptotic stability is established. A second bound for the Hausdorff dimension is obtained by exploiting Lyapunov's direct method and thus relies on the use of certain Lyapunov functions.

One of the results of a research project on mechatronics is a mobile robot, which was used as a carrier for research on the design of mechatronical systems. This mobile robot, the Mobile Autonomous Robot Twente (MART), is intended to be used as major part of a future assembly factory. In this paper the implementation on the MART-robot of a hybrid controller for stabilization of non-holonomic systems is described. Limitations of the physical model of the mechanical structure of the MART-robot lead to a number of practical problems. An interesting result given in the paper is the insight obtained into the geometrical meaning of different parameters of the controller, which allowed considerable improvements in the performance of the controller on the actual mobile robot.>

Passivity-based control methods for robots, which achieve the control objective by reshaping the robot system's natural energy via state feedback, have, from a practical point of view, some very attractive properties. However, the poor quality of velocity measurements may significantly deteriorate the control performance of these methods. In this paper the authors propose a design strategy that utilizes the passivity concept in order to develop combined controller-observer systems for robot motion control using position measurements only. To this end, first a desired energy function for the closed-loop system is introduced, and next the controller-observer combination is constructed such that the closed-loop system matches this energy function, whereas damping is included in the controller- observer system to assure asymptotic stability of the closed-loop system. A key point in this design strategy is a fine tuning of the controller and observer structure to each other, which provides solutions to the output-feedback robot control problem that are conceptually simple and easily implementable in industrial robot applications. Experimental tests on a two-DOF manipulator system illustrate that the proposed controller-observer systems enable the achievement of higher performance levels compared to the frequently used practice of numerical position differentiation for obtaining a velocity estimate.>

A globally convergent adaptive control scheme for robot motion control with the following features is proposed. First, the adaptation law possesses enhanced robustness with respect to noisy velocity measurements. Second, the controller does not require the inclusion of high gain loops that may excite the unmodeled dynamics and amplify the noise level. Third, we derive for the unknown parameter design a relationship between compensator gains and closed-loop convergence rates that is independent of the robot task. A simulation example of a two-DOF manipulator featuring some aspects of the control scheme is given.>

The authors propose a globally convergent adaptive control scheme for robot motion control with the following features: first, the adaptation law processes enhanced robustness with respect to noisy velocity measurements; secondly, the controller does not require the inclusion of high-gain loops that may excite the unmodeled dynamics and amplify the noise level; thirdly the authors derive for the known parameter design a relationship between compensator gains and closed-loop convergence rates which is independent of the robot task. This helps the designer to carry out the gain tuning with an analysis of the robustness-performance tradeoff.>