Thibaut Raharijaona

Sliding Mode Control Applied to Active Suspension Using Nonlinear Full Vehicle and Actuator Dynamics

For the purpose of fault diagnosis and tolerance, a sliding mode controller (SMC) is designed for a nonlinear full vehicle active suspension system. Since actuators are used to generate forces in active suspension, the dynamics of the four electro-hydraulic actuators are taken into consideration. Simulation is made to illustrate the proposed controller where the active suspension system performances are compared to those of passive suspension

Control of linear full vehicle active suspension system using Sliding Mode techniques

For the purpose of fault diagnosis and accommodation, a Sliding Mode Controller (SMC) is designed for a linear full vehicle active suspension system. An investigation about the available sensors for the controller implementation is also presented. Two levels are studied: the level of vehicle prototypes and the level of industrial vehicles. Difficulties of vehicle instrumentation and possible solutions are discussed. Simulation is made to illustrate the proposed controller where the active suspension system performances are compared with those of passive suspension.

Event-based LQR with integral action

In this paper, a state-feedback linear-quadratic regulator (LQR) is proposed for event-based control of a linear system. An interesting property of LQRs is that an optimal response of the system can be obtained in accordance to some specifications, like the actuator limits. An integral action is also added in order to not only restrict the study to null stabilization but also to tracking. The idea is to consider an external control loop and stabilize the integral of the error between the measurement and a desired setpoint to track. However, an event-triggered integral can lead to important overshoots when the interval between two successive events becomes large. Therefore, an exponential forgetting factor of the sampling interval is proposed as a solution to avoid such problems. The whole proposal is tested on a real-time system (a gyroscope) in order to highlight its ability, the reduction of control updates and the respect to the actuator limits.

Optimal Sensor Network Design for Observability of Complex Systems

Plants instrumentation is a crucial issue due to the importance of sensors in allowing the observability and in increasing the redundancy and the reliability. However, the task of designing a sensor network becomes complicated when the complexity of the system increases. In this paper, a strategy is proposed to design a minimal sensor network ensuring the observability of complex systems. The strategy is based on the decomposition of complex systems into subsystems. This decomposition helps in treating each subsystem separately and in allowing the use of reduced order observers rather than a large scale observer for the whole system. An example is given to illustrate the proposed strategy.

Local Positioning System Using Flickering Infrared LEDs

A minimalistic optical sensing device for the indoor localization is proposed to estimate the relative position between the sensor and active markers using amplitude modulated infrared light. The innovative insect-based sensor can measure azimuth and elevation angles with respect to two small and cheap active infrared light emitting diodes (LEDs) flickering at two different frequencies. In comparison to a previous lensless visual sensor that we proposed for proximal localization (less than 30 cm), we implemented: (i) a minimalistic sensor in terms of small size (10 cm3), light weight (6 g) and low power consumption (0.4 W); (ii) an Arduino-compatible demodulator for fast analog signal processing requiring low computational resources; and (iii) an indoor positioning system for a mobile robotic application. Our results confirmed that the proposed sensor was able to estimate the position at a distance of 2 m with an accuracy as small as 2-cm at a sampling frequency of 100 Hz. Our sensor can be also suitable to be implemented in a position feedback loop for indoor robotic applications in GPS-denied environment.

HyperCube: A Small Lensless Position Sensing Device for the Tracking of Flickering Infrared LEDs.

An innovative insect-based visual sensor is designed to perform active marker tracking. Without any optics and a field-of-view of about 60°, a novel miniature visual sensor is able to locate flickering markers (LEDs) with an accuracy much greater than the one dictated by the pixel pitch. With a size of only 1 cm3 and a mass of only 0.33 g, the lensless sensor, called HyperCube, is dedicated to 3D motion tracking and fits perfectly with the drastic constraints imposed by micro-aerial vehicles. Only three photosensors are placed on each side of the cubic configuration of the sensing device, making this sensor very inexpensive and light. HyperCube provides the azimuth and elevation of infrared LEDs flickering at a high frequency (>1 kHz) with a precision of 0.5°. The minimalistic design in terms of small size, low mass and low power consumption of this visual sensor makes it suitable for many applications in the field of the cooperative flight of unmanned aerial vehicles and, more generally, robotic applications requiring active beacons. Experimental results show that HyperCube provides useful angular measurements that can be used to estimate the relative position between the sensor and the flickering infrared markers.

Toward an Autonomous Lunar Landing Based on Low-Speed Optic Flow Sensors

For the last few decades, growing interest has returned to the quite challenging task of the autonomous lunar landing. Soft landing of payloads on the lunar surface requires the development of new means of ensuring safe descent with strong final conditions and aerospace-related constraints in terms of mass, cost and computational resources. In this paper, a two-phase approach is presented: first a biomimetic method inspired from the neuronal and sensory system of flying insects is presented as a solution to perform safe lunar landing. In order to design an autopilot relying only on optic flow (OF) and inertial measurements, an estimation method based on a two-sensor setup is introduced: these sensors allow us to accurately estimate the orientation of the velocity vector which is mandatory to control the lander’s pitch in a quasi-optimal way with respect to the fuel consumption. Secondly a new low-speed Visual Motion Sensor (VMS) inspired by insects’ visual systems performing local angular 1-D speed measurements ranging from 1.5°/s to 25°/s and weighing only 2.8 g is presented. It was tested under free-flying outdoor conditions over various fields onboard an 80 kg unmanned helicopter. These preliminary results show that the optic flow measured despite the complex disturbances encountered closely matched the ground-truth optic flow.

Robust control for an off-centered quadrotor

The development of quadrotor unmanned aerial vehicles -UAVs- in potential civil applications is conditioned by the embedded elements such as removable payload, miniature actuators, sensors and power storage. As simple as the structure of the quarotor is, the dynamic behavior is complex. The paper details a model of a quadrotor which considers the effects of the location of the center of gravity and the gyroscopic torques due to the derivative of the speed propellers. A simple control law in order to regulate the angular velocities and to track angular references is designed. Time domain constraints and parameters which belong to a polytope define the basis of the regulator synthesis. The relevance of the study is fulfilled thanks to math simulations and experimental plateform is presented.

Generalized Disturbance Estimation via ESLKF for the Motion Control of Rotorcraft Having a Rod-suspended Load

The aim of the paper is to propose a navigation strategy applied to a class of rotorcraft having a free rod-suspended load. The presented approach relies on the Linear Kalman Filter to estimate the not only the state vector but also a generalized disturbance term containing parametric, couplings and external uncertainties. A simple hierarchical control is used to drive the motion of the rotorcraft, which is thus updated with the estimation of the disturbance evolving during the a navigation task. Despite the time-scale separation due to the underactuated nature of the flying robot, the estimation approach has shown its effectiveness considering the same sampling time. A detailed simulation model is used to evaluate the performance of the proposal under different disturbed scenarios

A Shape-Adjusted Tridimensional Reconstruction of Cultural Heritage Artifacts Using a Miniature Quadrotor

The innovative automated 3D modeling procedure presented here was used to reconstruct a Cultural Heritage (CH) object by means of an unmanned aerial vehicle. Using a motion capture system, a small low-cost quadrotor equipped with a miniature low-resolution Raspberry Pi camera module was accurately controlled in the closed loop mode and made to follow a trajectory around the artifact. A two-stage process ensured the accuracy of the 3D reconstruction process. The images taken during the first circular trajectory were used to draw the artifact’s shape. The second trajectory was smartly and autonomously adjusted to match the artifact’s shape, then it provides new pictures taken close to the artifact and, thus, greatly improves the final 3D reconstruction in terms of the completeness, accuracy and quickness, in particular where the artifact’s shape is complex. The results obtained here using close-range photogrammetric methods show that the process of automated 3D model reconstruction based on a robotized quadrotor using a motion capture system is a realistic approach, which could provide a suitable new digital conservation tool in the cultural heritage field.