In today's world, there are many places where human activities are required but humans are unable to reach there due to safety or logistics constraints. For example, nuclear site Maintenance, Underwater fibre-optic connections, space station repair and maintenance, Tele-surgery, etc. In these places, teleoperation is required and with recent developments, bilateral teleoperation is preferred as it enhances the feeling of telepresence with haptics (Sense of touch and awareness of movement and position). In (haptic) teleoperation, Information needs to travel back and forth constantly in the communication channels and if there is any time delay then it significantly affects the whole teleoperation.
Time delays present in discrete-time systems and in the communication channel can quickly destabilise the teleoperation. Currently, the feasibility of teleoperation is primarily restricted by the time delay in communication channels. To remove this bottleneck, It is required to develop a control architecture for telerobotic systems capable of handling variable time delays and mitigate uncertainties due to them.
Bilateral impedance reflection (BIR) architecture has shown good performance in stability and transparency under time delays (50 ms for specific cases). The concept is based on having a local model (modelled as virtual spring/Impedance controller) of the other end of the teleoperation system and exchanging its estimated impedance parameters between remote robot and operator interface to update the model. Although performance is good the stability is not guaranteed.
The destabilizing effect of time delays can be related to energy generation in the system. Hence monitoring the energy flows and registering them is essential. As the BIR controller architecture contains interfaces that do not directly exchange power, energy flows in the system are not trivial. Hence, It is required to study the energetic behaviour of the system which will aid in developing a mechanism to preserve stability. If the energetic consistency of the system is maintained then stability is guaranteed and this requires controlling the energy during operation which can be achieved by passivating the system. Hence, the goal of this assignment is to include the Passivity layer structure in the BIR architecture to ensure safety (stability under all conditions) and the modified architecture is studied. Generally adding passivity will affect transparency although it increases stability. To tackle this problem and to bring in positive effects of passivity a Time domain passivity control(TDPC) approach is chosen to implement the passivity layer due to its flexibility (independent optimization of passivity and transparency layers) and hardware independence.
The important aspects of energy flows and energy consistency in the system are studied in detail as they form the basis of passivating the system. The above understanding will help us in better designing the components of the passivity layer. The performance is validated by comparing the BIR and passivated BIR for defined tasks with and without time delays.