Tapered whisker reservoir computing system for mobile robot environment perception
Creators: name: Yu, Zhenhua
Publisher: name: Imperial College London
Year: 2022

description: Mobile robots performing tasks in unknown environments need to traverse a variety of complex terrains, and they must be able to reliably and quickly identify and characterize these terrains to avoid getting into potentially challenging or catastrophic circumstances. However, currently, methods based on different sensors, such as vision, lidar, audio, inertial measurement units (IMU), and tactile sensors generally require huge computing resources for data processing, online training, and recognition, and the performance tends to degrade once there are outlier data that do not exist in the prior training dataset. To solve this problem, inspired by the animals, such as rats and seals, just relying on whiskers to perceive information about their surroundings and survive in dark and narrow environments, we explore the physical whisker-based reservoir computing for quick and cost-efficient mobile robots’ environment perception and navigation. This thesis has creatively solved a machine-learning terrain classification problem by using a tapered ‘electro-mechanical’ whisker-based reservoir computing system for the first time in the world. The first analysis comprises designing a straight whisker sensor with one Hall sensor in the base and evaluating its nonlinear interaction dynamics which will have one dominant frequency at the vertical perturbation frequency of the sensor base. This nonlinear dynamic feature is used in a deep multi-layer perceptron neural network to classify terrains. We achieved an 85.6% prediction success rate for seven flat terrain surfaces with different textures at 0.2m/s. Therefore, a tapered whisker-based reservoir computing (TWRC) system using a tapered whisker sensor with three Hall sensors along the axis is proposed. The results demonstrated that such compliant tapered mechanical whisker systems could achieve real-time perception using nonlinear vibration dynamics and providing morphological computation power to achieve frequency separation in the time domain simultaneously. Then, by running a numerical analysis and experiments, it was found that external terrain stimuli of different roughness and hardness will produce unique whisker reservoir features and different whisker axis locations and motion velocities provide variable dynamical response information. We achieved a prediction success rate of 94.3% for six terrain surface classification experiments and 88.7% for roughness estimation of the unknown terrain surface at a steady speed of 0.2m/s.Moreover, a tapered whisker-based semi-supervised reservoir computing (TWSSRC) system is proposed to reveal that the whiskered robot can learn from prior physical experiences through cost-efficient self-supervised reservoir computing to achieve auto-labelling of new terrain, terrain classification, and terrain roughness estimation. The experimental results show that this novel approach is capable of successfully adapting well to unknown terrains based on the tapered whisker reservoir outputs and detecting new terrains with high accuracy, achieving 84% accuracy over six terrains with carpet representing the new terrain class. Depending on the computational superiority of the TWSSRC system, an active improved-TWMC algorithm including an overlapping-window-based decision module is designed, which could achieve active rapid object classification, even for the extremely similar sandpaper including external disturbances. Finally, a real-time terrain identificationbased navigation method is proposed using an onboard tapered whisker-based reservoir computing (TWRC) system rather than an external computer. The results experimentally demonstrate that our proposed algorithm could cost-efficiently achieve highly accurate real-time terrain classification results, and analyzed and demonstrated experimentally how the mobile robot can be controlled by speed to elicit unique frequency domain responses in a whisker sensor to help surface identification. The research presented in this thesis demonstrates the exceptional performance of the reservoir computing system based on tapered-shaped whisker sensors in environmental perception, particularly in terrain recognition. This method provides a computationally efficient way to achieve high-precision terrain recognition and classification, as well as semi-supervised labelling of unknown terrain, texture information recognition, and roughness estimation. Additionally, this research sheds light on the importance of natural body dynamics, especially the tapered-shaped whiskers, in addressing challenging signal processing problems in robotics. It can also bridge the gap between high information processing performance and low energy dissipation of robots’ onboard hardware.