Research Projects
Analysis and Control of Fixed and Mobile Base Cable Robots
Cable driven parallel manipulators, also called cable driven robots or cable robots, are formed by attaching multiple cables (instead of articulated links) to an end-effector/platform. They have significantly improved workspace as compared to conventional rigid-link architectures, while possessing many of the desirable features such as high payload-to-weight ratios, low inertial properties, low energy consumption, ease of assembly/disassembly and reconfiguration.
Cooperative payload manipulation using cables comes in two flavors: one class of approaches focuses on fixed bases and varying cable lengths (i.e. conventional cable robots); the other class is with fixed cable lengths and moving bases for manipulating of objects and payload manipulation and transportation on land, sea, and in the air (i.e. cable towing). We first explore the online redundancy resolution control of the former class of fixed bases cable robot (published in ICRA 2010 with K. Yu).
In another work, we explore merging the two, i.e. coupling mobile bases with articulated-cablearms together to create composite mobile-cable collectives for the combined payload transportation and reconfiguration tasks. We call this type of cable robots with moving bases cooperating mobile cable robots. While this combination potentially could greatly increase the capability of cable robots, it also introduces redundancy and complexity into the system. Hence, we focus on developing a systematic framework for design, analysis and control of such mobile cable robot collectives (published in ICRA 2012 with X. Zhou).
Related Papers:
X. Zhou, C. P. Tang and V. N. Krovi, "Analysis Framework for Cooperating Mobile Cable Robots," Proceedings of the IEEE Conference on Robotics and Automation, St. Paul, Minnesota, USA, May 14-18, 2012. [Preprint]
K. Yu, L.-F. Lee, C. P. Tang, and V. N. Krovi, "Enhanced Trajectory Tracking Control with Active Lower Bounded Stiffness Control for Cable Robot", Proceedings of the IEEE International Conference on Robotics and Automation, Anchorage, Alaska, USA, May 3-8, 2010. [Preprint]
Dynamic Sliding PID Control of a Quadrotor using Quaternion
Flying robots have been gaining popularity recently due to their ability to travel to places where ground robots cannot reach. In this work, we examine one of the popular yet important class of flying robot - a quadrotor system. It consists of four rotors attached with helicopter blades. The configuration allows easier and more agile positional control, and its dynamic model is much simpler than a conventional helicopter. In this work, we explore more advanced control method to achieve finite time (state) convergence for smoother trajectory control. We rely on the on-board sensor and the external positional (Vicon) tracking system to provide the full state information.
Our controller has a number of advantages. It was built from the prior work in Parra-Vega et. al., 2003. The most significant advantage is that the controller need minimal model information of the plant. The other controllers may require very precise aerodynamic model, but our control works well without such information. Furthermore, the control gains are very easy to tune. Here is the video of our successful hardware implementation:
Here is the earlier video of our calibration process and some simple results:
This work is collaborated with Prof. Anand Eleazar Sánchez Orta and Prof. Vicente Parra.
Related Paper:
A. Sanchez, V. Parra-Vega, C. P. Tang, F. Oliva-Palomo, C. Izaguirre-Espinosa, "Continuous Reactive-based Position-Attitude Control of Quadrotors," Proceedings of the American Control Conference, Montreal, Quebec, Canada, June 27-29, 2012.
Collision Avoidance of Mobile Robots
Collision avoidance is one of the fundamental issue in safety robotics. In this work, we examine the collision avoidance control for nonholonomic mobile robots using the novel avoidance function. The nonholonomic dynamic system is first linearized into a double integrator form. Then, previous result from Rodriguez-Seda et. al., 2011 is then applied to account for various measurement uncertainty caused by delay or noise. In this approach, the control goal such as setpoint or tracking is achieved while secondarily avoid collision. The control approach has been experimented extensively. Here are some of the videos of the results.
Teleoperation of Tightly Cooperative Mobile Robot Collectives
In this work, we require a robot collective to work closely together with a human operator over a communication network. The challenge comes from the requirement of the tight interaction between the robots and the human operator over the unreliable network. We created a software and electromechanical framework that integrates a host computer with multiple gumstix-operated iRobot Create's. The human operator can interact with the robot collective through a standard force-feedback joystick. Vicon motion tracking system is also integrated within the system to provide high fidelity robot tracking. The overall framework is created using the high performance QuaRC Real-Time Operating System.
Related Papers:
C. P. Tang, M. Goeckner and M. W. Spong, "Robotic Project-based Pre-training for In-coming Undergraduate Mechanical Engineering Students", Proceedings of the ASME International Design Engineering and Technical Conference, Montreal, Quebec, Canada, August 15-18, 2010. [PDF]
C. P. Tang, P. R. Maheshwari, and M. W. Spong, "Building verdex-based Framework for iRobot Create Using QuaRC", August 2009. [PDF]
Design and Analysis of Mechanism for Flapping Wing Micro Aerial Vehicles
This work is conducted at the Wright-Patterson Air Force Base in Ohio in the summer of 2010 as a visiting researcher. Our major goal was to design a mechanism driving system for hovering flapping wing micro-aerial vehicle (MAV). Much work has been done in the past to realize flapping wing "aviation". Despite these advances in mechatronics and material science, not much work has been focusing on hovering or agile operation, which is more critical in rescue and defense applications. Hence, our work is gearing towards the design and fabrication of such state-of-the-art hover-capable MAVs.
Related Papers:
D. B. Doman, C. P. Tang, and S. J. S. Regisford, "Modeling Interactions between Flexible Flapping Wing Spars, Mechanisms, and Drive Motors," Paper 2011-6389, Proceedings of the AIAA Guidance, Navigation, and Control Conference, Portland, Oregon, USA, August 8-11, 2011. [PDF]
D. B. Doman, C. P. Tang, and S. J. S. Regisford, “Modeling Interactions between Flexible Flapping Wing Spars, Mechanisms, and Drive Motors,” Proceedings of the AIAA Atmospheric Flight Mechanics Conference, Portland, Oregon, USA, August 8-11, 2011. [PDF]
Differential Flatness-based Control of Mobile Robots
Differential flatness-based integrated point-to-point trajectory planning and control method for a class of nonholonomic wheeled mobile manipulator is presented. We demonstrate that its kinematic model possesses a feedback-linearizable description due to the flatness property, which allows for full state controllability. Trajectory planning can then be simplified and achieved by polynomial fitting method in the flat output space to satisfy the terminal conditions, while control design reduces to a pole-placement problem for a linear system. The method is then deployed on our custom constructed WMM hardware to evaluate its effectiveness and to highlight various aspects of the hardware implementation.
Related Papers:
C. P. Tang, P. T. Miller, V. N. Krovi, J.-C. Ryu and S. K. Agrawal, "Differential Flatness-based Planning and Control of a Wheeled Mobile Manipulator – Theory and Experiment", IEEE/ASME Transactions on Mechatronics, 2010. [Preprint]
C. P. Tang, "Differential Flatness-based Kinematic and Dynamic Control of a Differentially Driven Wheeled Mobile Robot", Proceedings of the IEEE International Conference on Robotics and Biomimetics, Guilin, Guangxi, China, December 18-22, 2009. [Preprint]
C. P. Tang, P. T. Miller, V. N. Krovi, J.-C. Ryu and S. K. Agrawal, "Kinematic Control of Wheeled Mobile Manipulator - A Differential Flatness Approach", Proceedings of the ASME Dynamic Systems and Control Conference, Ann Arbor, Michigan, USA, Oct 20-22, 2008. [Best Session Paper] [PDF]
What is it like if the robot doesn't want to listen to you? Check [here]...
Dynamically Consistent Redundancy Resolution Scheme for Nonholonomic Mobile Manipulators
Mobile manipulators derive significant novel capabilities for enhanced interactions with the world by merging mobility with manipulation. However, a careful resolution of the redundancy and active control of the reconfigurability, created by the surplus articulated degrees-of-freedom and actuation, is the key to unlocking this potential. Nonholonomic wheeled mobile manipulators (NH-WMM), formed by mounting manipulator arms on disc-wheeled mobile bases, are a small but important subclass of mobile manipulators. The primary control challenges arise due to the dynamic-level coupling of the nonholonomy of the wheeled mobile bases with the inherent kinematic and actuation redundancy within the articulated-chain. The solution approach in this paper builds upon a dynamically-consistent and decoupled partitioning of the articulated system dynamics between the external (task) space and internal (null) space. The independent controllers, developed within each decoupled space, facilitate active internal reconfiguration in addition to resolving redundancy at the dynamic level. Specifically, two variants of null-space controllers are implemented to improve disturbance-rejection and active reconfiguration during performance of end-effector tasks by a primary end-effector impedance-mode controller. These algorithms are evaluated within an implementation framework that emphasizes both virtual prototyping (VP) and hardware-in-the-loop (HIL) testing with representative case studies.
Related Papers:
G. D. White, R. M. Bhatt, C. P. Tang and V. N. Krovi, "Experimental Evaluation of Dynamic Redundancy Resolution in a Nonholonomic Wheeled Mobile Manipulator", IEEE/ASME Transactions on Mechatronics, Vol. 14, No. 3, pp. 349-357, Jun 2009. [Preprint]
C. P. Tang, "Decoupled Dynamic Control of a Nonholonomic Wheeled Mobile Manipulators", Presented at the Third Annual New England Manipulation Symposium (NEMS), Jun 1, 2007. [PDF]
Geometric Approach to Formation Optimization of a Fleet of Wheeled Mobile Robots
Tight formation-based operations are critical in several emerging applications for robot collectives - ranging from cooperative payload transport to synchronized distributed data-collection. In this paper, we investigate the optimal relative layout for members of a team of Differentially-Driven Wheeled Mobile Robots (DD-WMRs) moving in formation for ultimate deployment in cooperative payload transport tasks. Our particular focus is on modeling such formations, developing the motion plans and determining the "best formation" in a differential-geometric setting. Specifically, the formation is comprised of a number of DD-WMRs forming the vertices of a virtual structure, with a preferred team-fixed frame to serve as a virtual leader. The induced motion plans for the individual DD-WMRs depend both on the specified team-frame motions as well as the relative layout within the formation. Emphasis is placed on developing suitable invariant yet quantitative measures of formation quality and a systematic optimization-based selection of formation-layout to enhance overall team-task performance. For an appropriate formation- parameterization, this team-level optimization can be accomplished by finding the optimal location of each DD-WMR with respect to the team-frame individually and the distributed nature of this approach scales well to large formations. Analytical and numerical results, from case studies of formation optimization of three DD-WMRs maneuvering along certain desired planar paths, are presented highlight the salient features and benefits.
Related Papers:
R. M. Bhatt, C. P. Tang and V. N. Krovi, "Formation Optimization for a Fleet of Wheeled Mobile Robots - A Geometrical Approach", Robotics & Autonomous Systems, Vol. 57, No. 1, pp. 102-120, Jan 2009. [PDF]
R. M. Bhatt, C. P. Tang and V. N. Krovi, "Geometric Motion Planning and Formation Optimization for a Fleet of Nonholonomic Wheeled Mobile Robots", Proceedings of IEEE International Conference on Robotics and Automation, New Orleans, Louisiana, USA, April 26-May 1, 2004. [PDF]
Screw Theoretic Feasibility Analysis of Cooperative Mobile Manipulators
The nature of individual modules and their interactions can effectively affect the overall cooperative system performance. We examine this aspect in the context of cooperative payload transport by robot collectives wherein the physical nature of the interactions between the various modules creates a tight coupling within the system. In this work, we leverage the rich theoretical background of analysis of constrained mechanical systems to provide a systematic framework for formulation and evaluation of system-level performance on the basis of the individual-module characteristics. The composite multi-degree-of-freedom wheeled vehicle, formed by supporting a common payload on the end-effectors of multiple individual mobile manipulator modules, is treated as an in-parallel mechanical system with articulated serial-chain arms. The system-level model, constructed from the twist- and wrench-based models of the attached serial chains, can be systematically analyzed for performance in terms of mobility and disturbance rejection with the effect of selections of different actuation schemes (active, passive or locked).
Related Papers:
M. Abou-Samah, C. P. Tang, R. M. Bhatt and V. N. Krovi, "A Kinematically Compatible Framework for Cooperative Payload Transport by Mobile Manipulator Collectives", Autonomous Robots, Vol. 21, No. 3, pp. 227-242, Nov 2006. [PDF]
C. P. Tang, R. M. Bhatt, M. Abou-Samah and V. N. Krovi, "Screw-Theoretic Analysis Framework for Payload Transport by Mobile Manipulator Collectives",IEEE/ASME Transactions on Mechatronics, Vol. 11, No. 2, pp. 169-178, Apr 2006. [PDF]
R. M. Bhatt, C. P. Tang, M. Abou-Samah and V. N. Krovi, "A Screw-Theoretic Analysis Framework for Payload Transport by Mobile Manipulator Collectives", IMECE2005-81525, Proceedings of the ASME International Mechanical Engineering Congress & Exposition, Orlando, Florida, USA, Nov 5-11, 2005. [PDF]
C. P. Tang, R. M. Bhatt and V. N. Krovi, "Decentralized Kinematic Control of Payload Transport by a System of Mobile Manipulators", Proceedings of the IEEE International Conference on Robotics and Automation, New Orleans, Louisiana, USA, April 26-May 1, 2004. [PDF]
Manipulability Analysis of Cooperative Mobile Manipulators
A suitable selection of the topology, dimensions, and configuration of the overall system can significantly influence the overall cooperative performance. In this research, we first develop the differential-level kinematics of the cooperative system, extending methods developed for treatment parallel-kinematic-chains to handle the presence of nonholonomic constraints and varied inclusion of active/passive joints, characteristic of our cooperative system. Then we examine the applicability of a manipulability measure (Isotropy Index), to quantitatively analyze the capability/performances of the cooperative system with different actuation schemes in representative case-studies.
Related Papers:
C. P. Tang, "Configuration Optimization for Multiple Nonholonomic Mobile Manipulators with Holonomic Interactions", Proceedings of the 42nd Southeastern Symposium on System Theory, Tyler, Texas, USA, March 7-9, 2010. [Preprint]
C. P. Tang and V. N. Krovi, "Manipulability-Based Configuration Evaluation of Cooperative Payload Transport by Mobile Manipulator Collectives", Robotica, Vol. 25, No. 1, pp. 29-42, Jan 2007. [PDF]
C. P. Tang and V. N. Krovi, "Manipulability-Based Configuration Evaluation of Cooperative Payload Transport by Mobile Robot Collectives", DETC2004-57476, Proceedings of the ASME Design Engineering Technical Conferences and Computer and Information in Engineering Conferences, Salt Lake City, Utah, USA, September 28-October 2, 2004. [PDF]
Distributed Dynamic Simulations: Compliance-Based and Feasible Motion Direction Projection Method
Traditionally, the numerical simulation problem of constrained mechanical systems has been treated as two separate stages: (a) the problem of algorithm development and (b) the subsequent numerical problem of advancing the discretized differential equations in time. However the potential numerical instabilities arising from the formulation stiffness of the algorithm development stage has the potential to hinder the subsequent numerical integration stage. In this work, we examine the modular development of two alternate methods, i.e. compliance-based and projection-based methods, for distributed computation of the forward dynamics simulations of constrained mechanical systems. We exploit the natural spatial parallelism of closed-chain linkages, initially, for the modular development of overall dynamics, and subsequently, for the distributed numerical simulation of the dynamics. These methods are evaluated in terms of the absolute time-history errors, the constraint errors, and the number of iterations with respect to the different stiffness values (in compliance-based method) and convergence factors (in projection-based method), in both undistributed and distributed manners.
Related Papers:
W. A. Khan, C. P. Tang and V. N. Krovi, "Modular and Distributed Forward Dynamic Simulation of Constrained Mechanical Systems - A Comparative Study", Mechanism and Machine Theory, Vol. 42, No. 5, pp. 558-579, May 2007. [PDF]
C. P. Tang, "Lagrangian Dynamic Formulation of a Four-Bar Mechanism with Minimal Coordinates", March 2006. [PDF]
