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PhD thesis: Control of nonlinear systems with algebraic constraints - application to cable robots taking into account the deformations of the cables

Description en Français

  • Contexte et objectifs

Following previous works within the Control-Vision-and-Robotics group of ICube lab, this Phd subject is at the interface between control and robotics (refer to the projets IDRAC and ManiLPV). Indeed, we wish to contribute to the development of methods for system analysis and controller synthesis that suits for cable-driven parallel robots (CDPR). The developed methods should be as generic as possible while taking into account the specificities of the cable robots.

CDPR are composed of a platform connected to attachment points through cables whose length and tension are adjusted by winding. Their low invasiveness, large workspace and high load-mass-per-robot-mass ratio make them interesting solutions for original applications. ICube is already involved in the Dexterwide project that aims at developing a solution combining a serial arm embedded on a CDPR for performing drilling or welding tasks in construction halls. A demonstrator of INCA-6D, developed by the company Haption, is available in the laboratory for research.

The control of these systems has to face many complexities. On the one hand, as for all parallel robots, models exhibit algebraic equations in addition to dynamic equations - we speak of a differential algebraic equation (DAE), which represents a complexity to be managed for modeling and simulation. On the other hand, it must be ensured that the cable tensions remain positive. Moreover, they introduce flexible modes to the nonlinear dynamics of these systems which are also multivariable.

In previous works, we developed methods for model identification [NLC12, CCL16] and for the synthesis of correctors to control the platform in translation and rotation [CCL16]. In these works, the cables were supposed to be rectilinear, which made it possible to solve the algebraic equations.

  • Expected contributions

In this research work, the simplifying hypothesis of straight cables will be relaxed and the models will be processed directly in DAE form. A first contribution was produced by the team on the possibility of directly addressing the problem in DAE form for a simplistic example of plane robot with three straight cables [CL14]. In addition, a publication has just been accepted [ALP17] on taking into account the non-rectilinear character of cables in dynamics based on the "assumed mode" method commonly used for series manipulators with deformations [GPK97, HLB14]. This work can serve as a starting point for dealing with more complex robots. The approach will consist in approaching the nonlinear DAE model by a linear (also called "descriptor") or linear DAE model with variant parameters in order to use the methods available for these classes of systems [MKO97, Yag10]. The team had used this type of approach in the past for controlling arm manipulators series [HLB14]; It will be a question of transposing these approaches to parallel manipulators.

  • References
    • [ALP17] J.I. Ayala Cuevas, E. Laroche, O. Piccin, Assumed-mode-based dynamic model for cable robots with non-straight cables, Third International Conference on Cable-Driven Parallel Robots (CableCon2017), August 2-4, 2017, Quebec City, Canada
    • [CCL16] R. Chellal, L. Cuvillon, E. Laroche. Model identification and vision-based H∞ position control of 6-DoF cable-driven parallel robots, International Journal of Control, pp. 1-18, 2016
    • [CL14] C. Cvetanovic, E. Laroche. Towards DAE methodology for the control of cable-driven parallel robots, dans IEEE Multi-Conference on Systems and Control, Antibes, France, October 2014.
    • [HLB14] H. Halalchi, E. Laroche, G. Bara. Flexible-link robot control using a linear parameter varying systems methodology, International Journal of Advanced Robotic Systems, Vol. 11(46):1-12, March 2014
    • [GPK97] H. Geniele, R.V. Patel K. Khorasani, End-point control of a flexible-link manipulator: theory and experiments, IEEE Transactions on Control Systems Technology, vol. 5, p. 556-570, 1997
    • [MKO97] I. Masubuchi, Y. Kamitane, A. Ohara, N. Suda, H∞ control for descriptor systems: a matrix inequalities approach, Automatica, vol. 33, no 4, p. 669-673, 1997
    • [NLC12] T. Nguyen, E. Laroche, L. Cuvillon, J. Gangloff, O. Piccin. Identification d’un modèle phénoménologique de robot à câbles, Journal Européen des Systèmes Automatisés, Hermès – Lavoisier, Vol. 56(6-7):673-689, November 2012.
    • [Yag10] M. Yagoubi, On multiobjective synthesis for parameter-dependent descriptor systems, IET Control Theory & Applications, vol. 4, No 5, p. 817-826, 2010
  • key-words

Model based on algebra-differential equations, constrained system, linear parameter-varying system, cable-driven parallel robot

  • Applicant profile

Student in second year of Master or in Engineer School in the last year with a strong specialization in automation, you are comfortable with the concepts of multivariable systems control and you use Matlab-Simulink without difficulty to implant models and To simulate them. You have a solid scientific base and you are comfortable with the mathematical tool. Your communication skills, especially in English, allow you to read scientific articles without difficulty understanding the language. You know how to be open-minded, you have the sense of initiative, while listening to the advice that is given to you. You know how to argue. You are able to demonstrate your ability to engage through your experiences.

Starting in October 2017

Location: ICube lab (Strasbourg south, Illkirch campus)

Funding: 3 year contract provided by the French Ministry of Higher Education

  • How to apply

Send a resume, a cover letter that explains your skills with respect to the project and your motivations and your Master grades (use a unique pdf document) to laroche@unistra.fr and homran@unistra.fr

Apply before: May, 15 2017

End of the session: June, 15 2017.

Internship for Master students (2nd year) in medical images processing (OCT)

  • Dates: From 4 to 6 months between januaray and december 2017 (more convenient between february and august)
  • Keywords: Optical Coherence Tomography (OCT), Images processing, Real-time processing, medical robotics
  • Detailed offer in pdf format can be obtained HERE
  • For applying, send an email with CV, cover letter, Master syllabus and grades to Florent Nageotte : Nageotte@unistra.fr

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The operating room is a high-tech environment in which the equipment generates a lot of data about the underlying surgical activities. Our research group aims at making use of this large amount of multi-modal data coming from both cameras and surgical devices to develop an artificial intelligence system that can assist the clinicians and staff in the surgical workflow. In this scope, we currently have two open PhD positions that will focus on developing new machine learning and computer vision methods to detect, recognize and analyze human activities. The successful candidates will have the rare opportunity to apply their work on large RGB-D and endoscopic video datasets captured during real procedures using the state-of-the-art facilities of our clinical partners. If interested, they will also have the exceptional possibility to collaborate with engineers and clinicians to implement real-time clinical demonstrators of their research, thereby contributing to the development of real-world AI-based solutions for the OR.
More information is available here.

Open Research Engineer Position in Computer Vision within Project CAMMA

We are looking for an engineer in Computer Vision to join the development of our clinical prototypes aiming at monitoring safety during image-guided interventions. The project involves the perception of the Operating Room through a set of RGB-D cameras mounted on the ceiling as well as the recognition of surgical activities using both RGB-D and endoscopic videos. More information is available here.

Open Internship Positions within Project CAMMA

We are looking for motivated and talented students with knowledge in computer vision, machine learning and/or augmented reality who can contribute to the development of our computer vision system for the operating room.

Please feel free to contact Nicolas Padoy if you are interested to do your master's thesis or an internship with us (funding of ~500Euros/month will be provided during 3 to 6 months). The successful candidates will be part of a dynamic research group hosted within the IRCAD institute at the University Hospital of Strasbourg. They will thereby have direct contact with clinicians, industrial partners and also have access to an exceptional research environment. The CAMMA project is supported by the laboratory of excellence CAMI, the IdEx Unistra and the MixSurg Institute.

Topics:

  • Multi-view Human Body Tracking for the Operating Room
  • Deep Learning for the Analysis of Large Surgical Video Databases
  • RGBD Camera Tracking in a Cluttered Operating Room
  • 3D Simulation and Visualization of X-ray Radiations for Radiation Safety Analysis

More information about CAMMA

Links: