Julien Beaudry

Discrete-Time State Feedback With Velocity Estimation Using a Dual Observer: Application to an Underwater Direct-Drive Grinding Robot

Hydro-Quebecs Research Institute has designed a robot to perform grinding tasks on underwater structures. This unique system is equipped with direct-drive linear motors, which have many useful dynamic characteristics. Since they lack intrinsic stiffness, however, their robustness to external disturbances must be achieved through the controller. Their lack of stiffness is a major disadvantage, because grinding generates very strong disturbance forces. Moreover, controller performance in such a system is limited by velocity feedback, which is usually derived from position encoder data. Though the state observer is recognized as an effective way to estimate velocity from position feedback without delay, it is not robust when applied to a system sensitive to external disturbances. The dual observer, which combines a state observer and a perturbation observer, aims to solve this problem. The simultaneous estimation of the state and disturbance not only improves state observer robustness, but also helps to compensate for disturbances in the controller. This paper presents the design of a discrete- time state-feedback controller with velocity estimation through a discrete- time dual observer. The design is validated by extensive comparative testing for a task that is as intensive as underwater grinding.

Laser scanning system for inspecting large underwater hydroelectric structures

A novel robotic laser scanning system for the inspection of large underwater hydroelectric structures is proposed. This system has been developed at the Hydro Quebec Research Institute and consists of a laser camera mounted on a 2-D Cartesian manipulator. Mechanical, electronic, and software design aspects; overall operational modalities; and proof of concept results are presented. We evaluated the performances of the system in the course of laboratory experiments and inspection trials carried out under normal operating conditions at the site of three of Hydro Quebecs hydroelectric dams.

Force Control Test Bench for Underwater Vehicle-Manipulator System Applications

This paper describes the first step to a global approach to the development of UVMS force control applications. A novel test bench has been developed to partly reproduce the behavior of such system while avoiding the needs and constraints implied for underwater experiments. This equipment shows most of the characteristics of a serial robot. Mechanical robustness, repeatability, reliability and friendly user interface are among the characteristics that have been inspired from industrial class of robots. However, the use of linear direct drive motors constitutes a very unique robot design. Preliminary force/position experiments demonstrate the functionality of the test bench and its great potential

Robotic systems applied to power substations - A state-of-the-art survey

This paper presents a state-of-the-art survey of robotic systems applied to power substations. Bibliographic research for this paper identified some 75 scientific publications and 39 patents dating from the late 1980s to 2013. Aside from recent work at Hydro-Québec (IREQ) in Canada on a field robot for power substations, almost all the R&D work identified comes from Asia, especially during the last decade, with the main research developments involving a mobile robot named SmartGuard from State Grid Corporation of China (SGCC). The first section of the paper presents robotic systems dedicated to inspection and security in power substations, while the second part of the paper looks at robots for operation and maintenance tasks in substations. A list of patents for robots for substations is also provided.

Hardware-in-the-loop simulation of an impedance controlled robot using a direct-drive test bench

This article presents the hardware-in-the-loop simulation of an impedance control applied to a virtual robot acting on a stiff environment. A test bench, which is composed of a direct-drive manipulator and a stiff environment, is used as the hardware part. A hardware-in-the-loop controller is used to command the manipulator so that it reproduces the virtual robot dynamics. Hence, the latter virtually acts on the real environment. Experimental results of the hardware-in-the-loop simulation are compared to pure simulation. It shows that both results are very similar and therefore the real robot can accurately reproduce the virtual robot dynamics.

Multiobjective optimization of an observer-based controller: theory and experiments on an underwater grinding robot

Hydro-Québec operates hundreds of dikes and dams built many decades ago, and is committed to the long-term sustainability of these facilities. The researchers and engineers at its research institute have designed and manufactured a submersible grinding robot prototype capable of performing the important task of grinding underwater metallic structures. This robot, with direct drive linear motors, has an excellent dynamic performance, but lacks intrinsic stiffness. The design of a control system for such a system is a major challenge for control engineers, as the algorithm must achieve sufficient dynamic stiffness to withstand the significant external perturbations generated by the grinding process and the underwater environment, while at the same time minimizing the sensitivity of the control effort to measurement noise. A discrete-time observer-based control structure has already been proposed in a previous work for this purpose, but the empirical design procedure for this structure did not consider the two contradictory objectives. Using the same controller structure, we propose a new design methodology in this brief, based on a multiobjective genetic algorithm, for these mechatronic systems, which are highly prone to the effects of disturbances. The results obtained through optimization are compared with those obtained using the empirical method. The effectiveness of the proposed design is demonstrated through underwater grinding experiments using the robot test bench we have developed.

Position tracking control of a direct-drive submersible grinding robot: A comparative study

This paper presents a comparative study of a sliding-mode controller (SMC) and a cascaded proportional/proportional integral (P/PI) controller with zero-phase error tracking controller (ZPETC) and disturbance observer (DOB). The tests are performed on a new underwater grinding robot. The comparison is based on trajectory tracking performance and robustness to external disturbances, such as those induced by the underwater environment and the grinding process. Experimental results show that for the same design criteria the P/PI controller produces better performance in terms of trajectory tracking error and disturbance rejection. The DOB was shown to be a simple and effective way to further reduce the positioning error.

Sliding-mode control of a direct-drive submersible grinding robot

The goal of this paper is to present the first controller that has been applied to an original system, which is a direct-drive submersible grinding robot. Since this application is quite recent, an analogy is made with machine tools equipped with linear motors, and the control methods that have been applied are reviewed. This review has led to the selection of the sliding-mode controller with the best potential because of its robustness to external perturbations and its ease of implementation. Experimental results show that the controller manages to maintain a good trajectory tracking error while being robust to disturbances, such as those generated by the grinding process.

COOPERATIVE ROBOTIC SYSTEM USING DISTRIBUTED DECISION MECHANISMS WITH DELIBERATIVE CENTRAL SUPERVISOR

Cooperative multi-robot systems with distributed decision mechanisms and distributed sensing may be the source of decisional conflicts which can lead to severe performance deterioration. A deliberative central supervisor is a simple approach to correct any incoherent decisions in the system. Given an application, the supervisor can be an autonomous software agent or a human-machine interface. Using Hierarchical Decision Machines (HDM) as distributed decision mechanisms, the decision supervision can use simple matrix representations of decisional data. The resulting architecture has been tested on a fully autonomous team of soccer-playing robots and results indicate that it is well adapted for, but not restricted to, the specific needs of autonomous multi-robot systems with real-time distributed sensing and decision taking.

Robotic rectification of underwater structural elements in power dams

Hydroelectric power dams are composed of intake and outtake structures made of concrete in which steel components are embedded. These components, for reasons briefly presented in this paper, tend to exhibit considerable wear and deformation with time. Rehabilitation of these embedded components, by rectification using machining techniques, can in some cases be the best approach. This work is traditionally done by human workers who, when possible, work in dry conditions. Drying out the structures can be very costly and sometimes impossible, in which case the work is done by divers. This paper presents a new and innovative approach to accomplishing these rehabilitation tasks. Two different submersible robotic systems are proposed. One system uses a milling process and is designed for vertical components. The second system uses a grinding machining process and is designed to rectify horizontal surfaces. The technical aspects of both systems are described.