Micaël Michelin

Towards vision-based control of cable-driven parallel robots

This paper deals with the vision-based control of cable-driven parallel robots. First, a 3D pose visual servoing is proposed, where the end-effector pose is indirectly measured and used for regulation. This method is illustrated and validated on a cable-driven parallel robot prototype. Second, to take into account the dynamics of the platform and using a Cartesian pose and velocity estimator, a vision-based computed torque control is developed and validated in simulation.

A Reconfigurable Robot for Cable-Driven Parallel Robotic Research and Industrial Scenario Proofing

Picturing the interest of research institutions and industrial actors, the list of research and demonstration parallel cable-driven robot prototypes is growing by the day. LIRMM and Tecnalia have decided to put knowledge in common in order to develop novel concepts for cable-driven parallel robotics and demonstrate its capabilities in industrial tasks. We have developed together a reconfigurable cable robot for this purpose. The robot main characteristics, e.g. footprint, mobile platform geometry and drawing point layout can be modified at will, making it particularly suitable for studying in good conditions new configurations or novel control laws, as well as any scenario suggested by our partners. The present paper first provides an overview of the robot. Afterwards, a more specific view on the different components and the capabilities of reconfiguration are presented, as well as examples of layouts meant for various research and industrial projects.

Dynamic task/posture decoupling for minimally invasive surgery motions: simulation results

This paper deals with the use of an original dynamic task/posture decoupling control algorithm that allows a robot to achieve motions under the constraint of moving through a fixed point. This work takes place in the context of minimally invasive surgery where the tool is telemanipulated by the surgeon through a penetration point: the trocar fixed on the patient. The algorithm is based on the dynamic control in the operational space of a redundant robot: the total control torque is decoupled into a task behavior torque and a posture behavior torque. By minimizing the contact force applied to the trocar (or equivalently, by forcing to zero the distance between the instrument passing through the trocar and the current location of the trocar), we compute the posture behavior torque guaranteeing that the trocar constraint is satisfied. Simulation results highlight the performance of this algorithm for various trajectories such as straight lines and circles.

MARGE Project: Design, Modeling, and Control of Assistive Devices for Minimally Invasive Surgery

MARGE is a joint project in the framework of the interdisciplinary national program in Robotics, called ROBEA, launched by the French National Research Center (CNRS) in 2001. The focus is on the development of design methodologies and on the control of high mobility and dexterity assistive devices for complex gesture assistance in minimally invasive surgery, especially for coronary artery bypass grafting. This paper presents the main results of this two-year project.

Design and Control of a Redundant Suspended Cable-Driven Parallel Robots

This paper introduces a six degree-of-freedom suspended parallel robot driven by eight cables. The determination of an optimal geometry of such a parallel cable robot together with the design of a prototype are briefly outlined. Then, based on usual kinematic modeling, a basic control strategy is presented. Since the parallel cable-driven robot presented here is redundantly actuated, this control strategy has to deal with the problem of cable tension distribution. This latter turns out to be challenging because of the under-constrained nature of the considered cable-driven robot. The extension to these robots of existing tension distribution methods is finally discussed.

Identification and Vibration Attenuation for the Parallel Robot Par2

Par2 is a parallel robot with two degrees of freedom designed for high-speed and high-accuracy industrial pick-and-place operation tasks. As a result of the high acceleration trajectories, the end-effector undergoes some undesirable vibrations after reaching the stop positions, compromising its precision and leading to an increase in the operation cycle time. Accelerometer sensors placed on the end-effector and piezoelectric patch actuators wrapped around the robot arms are employed in order to actively reduce these vibrations in a noncollocated closed-loop setting. After submitting the robot to an identification procedure, the obtained nominal model is used to synthesize a reduced order controller with the H∞ loop-shaping technique. Performance analysis as well as simulation and experimental results show that vibration reduction is achieved around the nominal operating point, but fails for some extreme operating points, due to high control efforts. An anti-windup strategy is then employed to deal with the saturation of the actuator, which allows achieving vibration attenuation on the whole operation domain, for a given configuration of the robot at the stop point.

Simulation and Control with XDE and Matlab/Simulink of a Cable-Driven Parallel Robot (CoGiRo)

We present in this paper the process allowing to create a cable-driven parallel robot (CDPR) simulation within the XDE software environment in C\({+}{+}\) language. The elementary classes constituting a CDPR are shown with their constructor specificities. The winches, the pulleys, the cable fastenings and the platform are presented. The parameterization of elements such as the cable material characteristics, structure and size are detailed. An interface between the XDE cable-driven parallel robot simulator and a Matlab/Simulink controller have been developed. Inputs and outputs are exchanged between the controller and the simulated cable-driven robot, exactly as it is done with a physical robot.

Flexible model identification of the parallel robot Par2

The open-loop flexible modes identification of a high-speed and high-accuracy pick-and-place parallel robot is carried out based on two approaches: an ARMAX model and a subspace identification technique. Models of piezoelectric dynamics and disturbances can be obtained for many distinct operation conditions, allowing, in a future work, the conception of robust control laws.

Piezo-actuated Vibration Attenuation of the Parallel Robot Par2

Abstract Par2 is a two degrees of freedom high-speed and high-accuracy pick-and-place parallel robot. Considering trajectory accelerations at the order of 10g in its 3.5 kg charged end-effector, significant vibrations show up immediately after reaching a stop position, consequently jeopardizing operation cycle times. These vibrations, measured by three orthogonally oriented accelerometers, are particularly less damped in the direction normal to the trajectory plane. In order to actively minimize these vibrations, piezoelectric patches are wrapped around the robot arms. For this system, an identified model interconnected with an ℋ ∞ controller are calculated. Laboratory experiments attest the adequacy of the controller.

H ∞ control applied to the vibration minimization of the parallel robot Par2

Conceived for high-speed and high-accuracy pick-and-place tasks, the parallel robot Par2 aims at reducing industrial operation cycle times. As a consequence of its high acceleration levels, the end-effector precision at the stop positions is subjected to undesirable vibrations of the manipulators arms, leading consequently to an increase in the cycle time. Piezoelectric patches are wrapped around the robot arms in order to actively minimize these vibrations, which are by their turn measured by three accelerometers orthogonally oriented and placed on the end-effector. After submitting the robot to an identification procedure, the obtained model is used to synthesize a reduced order H∞ control law that succeeds in minimizing the residual vibrations.