Bilateral Teleoperation of Wheeled Mobile Manipulator

Teleoperation offers humans the ability to extend their own reach and senses over various length and timescales in innumerable applications. These applications include remote control of semi autonomous robotic system in hazardous and remote environment from minimally invasive surgeries to deep-sea and planetary exploration. In a typical bilateral teleoperation setup, a user controls a master manipulator device that can range from a joystick to multi-degree of freedom force reflecting (haptic) device. The user's commands are transmitted through a communication medium to the slave device (a distant robotic manipulator), which attempts to execute received commands while interacting within the remote environment. The experienced forces and motions from the slave device-environmental interactions are communicated (and reflected in a scaled manner) back to the user. The reflected force allows the user to control the slave with kinesthetic cues, which along with auditory or visual feedback, allows a sense of immersion (telepresence) in the distant environment.

Telerobotic systems are faced with many complex issues stemming from: (i) master/slave devices themselves; (ii) environmental factors; (iii) communication delays; and (iv) control complexities. First and foremost the master and slave systems are typically complex electromechanical systems individually - requiring kinematically and dynamically dissimilar systems to interact and work together which can be challenging even in idealized environments with perfect/lossless communication. Second, slave systems are often placed in highly unstructured and diverse environments, typically not understood a priori, and failure to account for environmental interaction or varying conditions could lead to destabilization. Significant challenges also arise from the communication limitations and imperfections. The diversity of network architecture, protocols and loads can result in limited, lossy and variable delay communication between the master and slave machines. Last, but not least, is the contribution and role of the human user. The requirement for transparency of force feedback requires high sampling rates (1000 Hz or higher). This sampling rate puts a significant burden on the control algorithm to be computationally efficient while retaining performance and accuracy. Model-based nonlinear controllers with adaptivity can provide improved results, but depend significantly on accurate models and can increase computational burden of the slave robot.

The output synchronization framework for Lagrangian systems presented by Chopra, Spong and Lozano in was intended to overcome some of these limitations. Passivity based controllers take advantage of the inherent (passive) structure of rigid body systems to achieve the desired behavior. This framework was developed and theoretically proven to result in stable teleoperation between homogenous Lagrangian systems. This framework successfully incorporates adaptive nonlinear control, and drift-less stable teleoperation without the use of wave variables, and stability of this framework for use in teleoperation was analyzed by Lyapunov analysis.

We will adopt this framework and study its applicability to safely synchronize heterogeneous Lagrangian systems for teleoperation. The specific contribution of this work comes from adapting this teleoperation controller for use with an Omni haptic device as our master and a differentially driven nonholonomic WMM as the slave system. This was then systematically tested within a Hardware-In-the-loop (HIL) framework with a physical haptic master (Omni) and a simulated/virtual slave (WMM). We note that a non-adaptive bilateral teleoperation scheme for wheeled mobile robots was presented in. In contrast, we demonstrate that the adaptivity allows for increased robustness despite model uncertainties and disturbances.

 Students Involved:

- Patrick Miller, M.S., University at Buffalo [Graduated]

- Xiaobo Zhou, PhD Candidate, University at Buffalo

- Leng-Feng Lee, PhD Candidate, University at Buffalo


 Movies :

1. Hitting Box

- The slave device start with an initial offset with the coupling controller off. After a second, the controller is engaged and the slave and master positions converge. The end effector comes in contact with a real hard contact (the box) during the trajectory.

- File Size: MB [Download]

- Larger Screen: view it on YouTube:




 Related Publications - Conference Proceedings:

P. T. Miller, et al., "Output Synchronization for Teleoperation of a Wheeled Mobile Robot," in Proceedings of 2009 ASME Dynamic Systems and Control Conference, DSCC2009-2637, Hollywood, CA, 2009.

 Related Publications - Theses:
[01] P. T. Miller, "Output Synchronization for Teleoperation of Robot Manipulators," M.S. Thesis, Dept. of Mechanical & Aerospace Engineering, SUNY at Buffalo, Buffalo, Feb 2009. [PDF]

Sponsor: This project is supported in part by the NSF Awards IIS-0347653(CAREER) and CNS-0751132.

Last Updated: March 07, 2011