DDBot: Differentiable Physics-Based Digging Robot for Unknown Granular Materials
IEEE Transactions on Robotics, 2025 (vol. 42, pp. 152-169)
Yang X., Wei M., Ji Z., Lai Y.-K.
DDBot combines a GPU-accelerated differentiable granular simulator with gradient-based optimisation. It identifies unknown material properties and optimises digging strategy without prior material knowledge, then transfers zero-shot to real robots.
Key contributions
First-order gradient optimisation for differentiable granular simulation
Efficient convergence (5-20 min) for both system identification and skill optimisation
High-precision zero-shot deployment on sand and soil
Parallel simulation with automatic differentiation
Differentiable Physics-Based System Identification for Robotic Manipulation of Elastoplastic Materials
International Journal of Robotics Research (IJRR), 2025
Yang X., Ji Z., Lai Y.-K.
DPSI estimates physically interpretable material parameters from one real robot interaction and incomplete point clouds, enabling accurate long-horizon simulation and manipulation planning for elastoplastic materials.
Key contributions
Material parameter estimation from a single real-world interaction
Works with incomplete and occluded 3D point cloud observations
AutomaChef: A Physics-Informed Demonstration-Guided Learning Framework for Granular Material Manipulation
IEEE Transactions on Neural Networks and Learning Systems (TNNLS), 2025
Wei M., Yang X., Lai Y.-K., Tafrishi S.A., Ji Z.
AutomaChef uses differentiable simulation to generate expert demonstrations through optimisation, then uses those demonstrations to train manipulation policies for granular transport with real-world transfer.
Key contributions
Differentiable granular simulator implemented with Taichi
Demonstrations generated automatically via gradient optimisation
Outperforms standard RL, imitation learning, and prior task-specific methods
Successful real-world granular transport deployment
Affordance and Reinforcement Learning for Rigid Object Manipulation
GAM: General Affordance-Based Manipulation for Contact-Rich Object Disentangling Tasks
Neurocomputing, 2024 (vol. 578, 127386)
Yang X., Wu J., Lai Y.-K., Ji Z.
GAM learns where and how to act in contact-rich disentangling tasks, combining affordance prediction with goal-conditioned reinforcement learning to handle diverse object configurations.
Key contributions
General affordance prediction without task-specific engineering
Generalises to diverse and unseen disentangling configurations
Combines affordance learning and goal-conditioned RL
Validated in real and simulated contact-rich scenarios
Abstract Demonstrations and Adaptive Exploration for Efficient and Stable Multi-Step Sparse Reward Reinforcement Learning
International Conference on Automation and Computing (ICAC), 2022
Yang X., Ji Z., Wu J., Lai Y.-K.
A2E improves sparse-reward long-horizon robotic learning by combining abstract sub-task demonstrations with adaptive exploration that changes as each sub-task is mastered.
Key contributions
Task decomposition into ordered sub-task sequences with abstract demonstrations
Adaptive exploration strategy across mastered and weak sub-tasks
Validated on grid-world and real robotic manipulation benchmarks
Improves both sample efficiency and training stability
Efficient Hierarchical Reinforcement Learning for Mapless Navigation with Predictive Neighbouring Space Scoring
IEEE Transactions on Automation Science and Engineering (TASE), 2023
Gao Y., Wu J., Yang X., Ji Z.
This work introduces Predictive Neighbouring Space Scoring to generate compact sub-goals in hierarchical RL for mapless navigation, reducing complexity compared with end-to-end learning from raw observations.
Key contributions
Predictive Neighbouring Space Scoring (PNSS) for compact sub-goal generation
Hierarchical RL with high-level goal selection and low-level control
Lower learning complexity than end-to-end raw-sensor approaches
Recent Advances of Deep Robotic Affordance Learning: A Reinforcement Learning Perspective
IEEE Transactions on Cognitive and Developmental Systems (TCDS), 2023
Yang X., Ji Z., Wu J., Lai Y.-K.
A survey of deep robotic affordance learning from an RL perspective, including taxonomy, limitations, and future directions focused on action-consequence prediction.
Key contributions
Taxonomy of deep robotic affordance learning from RL perspective
Connects affordance theory and modern deep RL
Identifies open challenges in representation and deployment
Proposes action-consequence prediction as a future direction
Hierarchical Reinforcement Learning with Universal Policies for Multi-Step Robotic Manipulation
IEEE Transactions on Neural Networks and Learning Systems (TNNLS), 2021
Yang X., Ji Z., Wu J., Lai Y.-K., Wei C., Liu G., Setchi R.
The Universal Option Framework (UOF) decomposes long-horizon tasks into reusable sub-goals with universal low-level policies for efficient sparse-reward manipulation learning.
Key contributions
Hierarchical decomposition of long-horizon tasks into reusable sub-goals
Universal low-level policies generalise across sub-task instances
Efficient learning under sparse rewards
Demonstrated on challenging multi-step manipulation tasks
An Open-Source Multi-Goal Reinforcement Learning Environment for Robotic Manipulation with PyBullet
Towards Autonomous Robotic Systems (TAROS), 2021
Yang X., Ji Z., Wu J., Lai Y.-K.
An open-source PyBullet re-implementation of robotic multi-goal benchmarks with extra APIs and long-horizon tasks, removing dependency on commercial simulators.
Key contributions
Open-source alternative to MuJoCo-based benchmark environments
Added APIs for joint control, image observations, and cameras