Ribin Balachandran

Cartesian task allocation for cooperative, multilateral teleoperation under time delay

Field robots used in unstructured and dynamic environments - and teleoperation have shifted into the focus of a variety of industrial branches in the past few years. The lack of space in the atomic industry, on oil platforms and in space applications demands additional adaptations to current robotic setups. In this paper a MMSS (Multi-Master-Single-Slave) haptic teleoperation system is proposed through which one operator using two master arms can manipulate objects in a cooperative way via one slave robot and a virtual gripping point. To ease the execution of a peg-in-hole task of big objects, a task allocation in the cartesian frame of the virtual gripping point is introduced additionally. The stability of this multilateral system with time delay is guaranteed by the Time Domain Passivity Approach. Therefore the system is divided into several modular subsystems which renders the system easily adaptable to other scenarios.

Weight and Weightlessness Effects on Sensorimotor Performance During Manual Tracking

The effects of extra arm weight and weightlessness on sensorimotor performance were investigated in three studies. In all studies, subjects performed two-dimensional tracking tasks with a joystick. Results indicated that extra arm weight did not decrease tracking performance, but decreased acceleration variance. In weightlessness, tracking performance decreased and the control of movement impulses was deteriorated. This result pattern was found during water immersion as well as during spaceflight. The sensorimotor performance losses in weightlessness could be compensated by providing additional haptic cues with the input device.

Teleoperation for on-orbit servicing missions through the ASTRA geostationary satellite

Force-feedback teleoperation for on-orbit servicing tasks demands real-time communication requirements, latencies below one second and the presence of a skilled human operator to perform the on-orbit servicing tasks in real-time from an on-ground station. On the other hand, teleoperation is a technology that enjoys high TRLs, has evidenced benefits in other domains as nuclear or medical and has little dependency on optical sensors and image processing algorithms that need to operate in extreme illumination conditions. While all of these factors could be of high value in future on-orbit servicing missions, the following questions remain still to be answered: 1) How is the free floating dynamics and time delay affecting the control structure of the system? 2) Can current space communication infrastructures support real time control requirements established by the bilateral controller (i.e. force-feedback teleoperation)? 3) Can a skilled human operator perform on-orbit servicing tasks through the teleoperation system, probably affected by high latencies and force-feedback distortions? This paper presents initial answers to these questions based on results from a force-feedback teleoperation system that has been implemented using the ASTRA geostationary satellite and the DLR on-orbit servicing facility (OOS-SIM).

Haptic intention augmentation for cooperative teleoperation

Multiple robotic agents, autonomous or teleoperated, can be employed to synergise and cooperate to achieve a common objective more effectively. Tasks using robotic manipulators can be eased and improved in terms of reliability, adaptability and ergonomics via robot cooperation. In spite of visual and haptic feedback, cooperative telemanipulation of multiple robots by distant operators can still be challenging due to practical limitations in synchronisation and supervision. This paper presents a new control approach for haptic intention augmentation between two human operators handling objects via teleoperation in a cooperative manner. The force feedback to each operator is enhanced by information on the motion intention of the other operator observed by a force sensor at the input devices. Besides on-ground experiments, an experiment is presented that involves the cooperative teleoperation of an on-ground robot by a cosmonaut on the International Space Station and another distant operator on ground.

Reproducing physical dynamics with hardware-in-the-loop simulators: A passive and explicit discrete integrator

In this paper we present a passive and reliable explicit discrete integrator, which allows to preserve the energy and dynamic properties of a physical body rendered on a hardware-in-the-loop simulator. Starting from the standard Euler integrator, we identify the energy generation that results from the integration process. This energy makes the time discrete dynamics deviate from the ideal one, resulting in position drifts or stability issues. By exploiting the time domain passivity approach, the simulated dynamics is reshaped in order to preserve its physical energy properties. The proposed integration method allows precise simulation of virtual bodies on industrial robot facilities. The method has been validated in simulation and experimentally tested on the DLR OOS-SIM facility.

Passivity-based stability in explicit force control of robots

Direct force control of robots is challenging, particularly since the interaction with the environment can render the robot unstable. This paper presents the results of novel approaches for passivity-based stability for a particular direct force control method, namely explicit force control. A step-by-step procedure to passivate and stabilise the control loop is presented and it explains how Time Domain Passivity Approach, a passivity-based tool widely used in teleoperation and haptics has been extended and applied in explicit force control. The electrical circuit and network-port representations derived in the process allows the analytical evaluation of the system and can be applied in other control architectures as well. The stability methods are presented both qualitatively and quantitatively with simulations and hardware experiments. A discussion about the results obtained and the energy behavior is also provided. Results are promising and suggest that these methods can be used for stable and high-bandwidth force control of robotic manipulators.

Performance comparison of Wave Variable Transformation and Time Domain Passivity Approaches for time-delayed teleoperation: Preliminary results

This paper presents initial results of a set of experiments to compare time-delayed teleoperation performance of selected architectures based on two popular passivity based methods, namely, Wave Variables Transformation (WVT) and Time Domain Passivity Approach (TDPA). Five different architectures widely used and available in literature are selected: 2-channel and 3-channel for both WV and TDPA, and 4-channel based on TDPA. An empirical approach for measuring transparency is proposed, which presents three main qualities: 1) Controller independency 2) Frequency dependency of performance and 3) Removal of the human operator out of the loop. In order to achieve this, the human operator is replaced by a linear actuator equipped with a force sensor. Deterministic interactions between the simulated operator and the rest of the system can thus be easily implemented and registered. Therefore, this approach allows to isolate pure effects of any control method and perform a proper analysis in terms of selected attributes for a desired metrics. In this article, these are chosen to be effective impedance and position tracking error, both in the frequency domain. In addition to the quantitative results, a qualitative analysis is presented which underlines practical implications of each architecture and control method. The comparison sample presented contains five different delays, varying from 0 to 200 milliseconds, five different environmental impedances and 5 bilateral control architectures along with an analysis of the results obtained.