Perceptual coding of haptic data in time-delayed teleoperation

Abstract

In telepresence and teleaction systems the haptic communication channel plays a central role. As it closes a global control loop any introduced communication delay possibly destabilizes the system and impairs the performance. The scattering theory is known to solve these stability issues by transmitting wave variables instead of haptic signals, i.e. force and velocity, over the communication channel. For stability and performance additionally high packet rates are required stressing the underlying network resources. Perceptual coding techniques of haptic signals, such as the Weberinspired deadband approach, are known to successfully reduce the packet rate on the haptic channel. However, as wave variables do not directly represent haptic information but a linear transformation of both signals, perceptual coding is not directly applicable anymore. In this paper, we present a novel control scheme as well as a modification of the deadband approach to take advantage of the stabilization ability of the wave variables while allowing perceptual coding on the communication channel. Simulation results and comparison with the wave variables architecture indicate improved data compression for same degree of transparency for purely stiff as well as free environments.The prefix tele origins from the Greek word "odh¡" meaning on remote distance. Telepresence and teleaction (TPTA) systems allow humans to experience and to operate in a remote or inaccessible environment. Applications are not limited to remote and even dangerous environments but also range from scaled operation (e.g. micro assembly) over safety critical applications all the way to minimally invasive surgery. To enable the human operator to immerse into the remote environment, multimodal sensory and command data needs to be communicated over a communication channel, see Figure 1 for a schematic overview of a TPTA system.As in TPTA systems haptic signal are sent bidirectionally, a global control loop is closed over the communication system. Communication time delay between the human operator (OP) and the teleoperator (TO) is often unavoidable and can put the system's stability at risk [1] or at least deteriorates the transparency. Transparency refers to the performance of the TPTA system and is provided if the human user cannot distinguish between direct and teleoperated interaction with the environment. Two main sources of latency in haptic data communication are identified, namely haptic signal processing time due to encoding/compression/decompression/decoding and transmission time * sensor force haptic feedback (TO) array communication time delay packet loss e.g. Internet commanded velocity communication network human system interface (HSI) teleoperator microfon feedback auditory environment feedback visual stereo camera head environment force Figure 1: Multimodal telepresence and teleaction system delay. For the sake of stability and transparency, both time delay components are desired to be as small as possible.For the signal processing part this means that ins...

Point Cloud-Based Model-Mediated Teleoperation With Dynamic and Perception-Based Model Updating

“…Then, a perceptual deadband coding scheme with a JND of 10% is applied on the so-call locally computed wave-variables (LCWV) to reduce the packet rate. In our work, the environment is more complex and the communication delay is higher than in [42] (arbitrary 3-dimensional object surface vs. 1-dimensional planar surface and round-trip delay: 1000ms vs. 30ms). With such a complex case, our pcbMMT method can also significantly reduce the packet rate without degrading the system stability and transparency as the passivity-based haptic data reduction method described in [42] does.…”

“…We compare the result with a previous work for haptic data reduction in delayed teleoperation systems. In [42], the author uses the wave-variable approach [5] to enable a stable teleoperation system in the presence of communication delays. Then, a perceptual deadband coding scheme with a JND of 10% is applied on the so-call locally computed wave-variables (LCWV) to reduce the packet rate.…”

Energy Prediction for Teleoperation Systems That Combine the Time Domain Passivity Approach with Perceptual Deadband-Based Haptic Data Reduction

“…In [26], [27], the PD approach was combined with the WV control scheme (PD+WV). The authors of [26] applied the PD approach directly on the wave variables and found the subjectively best deadband parameter (DBP) for an interaction with a rigid wall in the presence of a 100 ms round-trip communication delay.…”

Haptic data reduction in multi-DoF teleoperation systems

“…Psychophysical studies indicate that the loss of information induced by the algorithm can be considered imperceivable. Teleoperation systems with timedelay are studied in [7], and perceptual-coding in time-delayed systems is presented in [8]. Stability of the global control loop is challenging as long as information is removed from it.…”