Lately, active disturbance rejection control (ADRC), a model-independent controller, has become popular for combating various forms of uncertain disturbances incurred in industrial applications. ADRC was validated for external disturbances, internal disturbances, and nonlinearities incurred under realistic scenarios. Time delay challenges all controllers, especially when it coexists with nonlinearities. This paper investigates the impacts of time delay and backlash-like hysteresis nonlinearity in ADRC-controlled systems. These impacts are analyzed, as in the case study, in two ADRC-based methods, namely the ADRC with delayed input method and the predictive extended state observer (PESO)-based ADRC (PESO-ADRC) method. To improve the system response and to attain a decent attenuation of uncertainties, the time-delay estimation (TDE) mechanism is introduced to the concerned ADRC-based methods. Experimental studies are conducted to verify the effectiveness and stability of the proposed TDE-ADRC methods. The results demonstrate the robustness and decent recovery of the transient response after the adverse impact of the backlash-like hysteresis on both concerned ADRC-controlled systems.

Vibrotactile displays can substitute for sensory channels of individuals experiencing temporary or permanent impairments in balance, vision, or hearing, and can enhance the user experience in professional or entertainment situations. This massive range of potential uses necessitates primary research on human vibrotactile perception. One leading aspect to consider when developing such displays is how to develop haptic patterns or symbols to represent a concept. In most settings, individual patterns are sorted as alphabets of haptic symbols which formulate tactons. Tactons are structured and perceivable tactile patterns (i.e., messages) that transfer information to users by employing the sense of touch. Hence, haptic patterns are critical when designing vibrotactile displays, as they not only affect the rate of information transfer but also determine the design of the displays (e.g., the number and the placement of tactors engaged) and how the information is encoded to achieve separability. Due to this significance, this paper presents an overview study on the cutaneous perception parameters (i.e., intensity, loci, frequency, duration, illusions, and combinations of these) for designing haptic symbols to identify mutual best-practices and knowledge gaps for future work. The study also provides developers from different scientific backgrounds with access to complex notions when engaging this specialized topic (i.e., the use of cutaneous perception parameters towards information transfer). Finally, it offers recommendations on defining which parameters to engage for a specific task or pattern.

In real-world applications, time delays and uncertain nonlinearities are inevitable and impose significant challenges in modern control systems. The uncertainties commonly include nonlinear backlash-like hysteresis, external disturbances, parameter perturbation (internal disturbance), measurement noise (white noise), and varying time-delay components. Recently, time-delay estimation (TDE) techniques have gained widespread traction for compensating for nonlinearities in various time-delay control systems. This study evaluates the performance of weighted TDE-based proportional-integral-derivative (PID) control on a complex, high-order system comprising a third-order system with a repeated pole structure. The concerned system can be regarded as analogous to a conveyor belt or a real-world thermal system. Experimental analyses are conducted to validate the effectiveness of integrating the TDE mechanism and the PID controller, with their respective weighting coefficients, during controller operation for a high-order time-delay nonlinear system under the effects of hysteresis, white noise, system parameter perturbation, external output disturbance, and varying time-delay scenarios. The simulation results, compared with the traditional PID controller, demonstrate that the proposed weighted TDE-PID control method outperforms in terms of improved transient performance characteristics, resilience, and robustness, with negligible steady-state errors. Moreover, stability and sensitivity analyses for the selection of the weighted coefficients are performed for the weighted TDE-PID-controlled high-order time-delay system, thereby further substantiating the validity of the proposed weighted control law. Hence, the results corroborate the applicability of this improved TDE-PID control method for high-order time-delay nonlinear processes encountered in realistic industrial settings.

The haptic communication of languages by engaging wearable displays has recently attracted much attention because of the continuous technological improvements (e.g., miniaturized hardware, and software). Currently, one of the primary research goals towards the haptic communication of language is to develop training protocols that reduce the time of learning by making the learning experience less cumbersome. This study provides a novel training protocol by separating learning into two sections, that is, offline, and online training. During offline training, the technique is based on visual learning, i.e., the spatial-temporal information of the haptic patterns is obtained by sight without stimulating the skin. During online training, the technique is based on kinesthetic learning, i.e., the knowledge of the patterns is obtained by hands-on experience. The learning of English letters is used to illustrate the proposed technique. The results show that the proposed two-section protocol lowers the time of online learning in the state-of-the-art methods.

Tactile language systems transmit language through temporally sequenced vibrotactile patterns on the skin. However, the Inter-Stimulus Interval (ISI) separating successive patterns is usually chosen a priori and applied uniformly, without grounding in individual perceptual performance or learning dynamics. This work introduces a user-centered approach for deriving ISI values from longitudinal behavioral data, using each participant's voice onset time (VOT) as a functional measure for decoding readiness. Over 28 consecutive days of practice in tactile letter recognition, the participants' VOTs systematically decreased and stabilized in accordance with the power law of practice. These stabilized VOT values were then used to derive performance-based ISIs. In a following word recognition task engaging untrained 2-3 letter words, ISIs derived from stabilized performance yielded higher recognition accuracy (67.4%) than a fixed baseline ISI of 75 ms (28.3%). Instead of identifying an optimal ISI value, these results illustrate the viability of a reproducible, performance-driven methodology for ISI allocation, supporting the development of wearable haptic displays that adapt timing parameters to users' learned decoding behavior.