Impedance Control on Uncertain Objects

Robots have been able to serve the original promise to replace human counterparts in laborious, hazardous, and repetitive tasks mainly in the area of position control that includes tasks such as pick and place of components, arc welding, grinding known objects, and even in bipedal walking on fairly smooth and known grounds. However, robots still find it hard to carry out stable force control tasks on uncertain objects or walk on natural soft terrains (grass, sand, mud). Just like the difference between the way we use the left hand and the right hand can not be explained using their biomechanical basis alone, the answer to robotic survival in uncertain environments does not come from an attempt to build robots that resemble human bodies alone. From early 1980s, scientists have begun to believe that the secrets of stable interactions with natural compliant environments will come from an ability of the robot itself to be compliant. The original work of Neville Hogan on impedance control was based on this concept. Since then, a considerable body of literature can be found on how impedance control is applied in various force control applications such as rehabilitation, massaging, bipedal walking, exoskeletal robotics, and several other direct interactions with humans. However, still there is no answer to how impedance control should be adaptively managed to sustain stability when the coupled dynamics between the robot and the environment evolves metastable dynamics. The theory of Metastability states that an uncertain dynamics system can exhibit intermittent instability though it may stay stable most of the time. A human using a screw driver is one example, where the dynamic contact with the screw may stay stable most of the time, but exhibit intermittent slipping due to uncertainty in the friction between the screw and the surrounding medium. Even a human walker can fall down in rare situations due to the same phenomenon. However, an uncertain dynamic system can enhance stability if it can predict where it is likely to fail. A number of recent advances in metastable systems use the concept of mean first passage time (MFPT) as an indicator to assess the current control policy in an uncertain environment. MFPT is the expected time to the next failure situation given the current knowledge of the uncertain dynamics of the coupled dynamics of the robot and the environment.Therefore, this project aims at developing a unifying theory of impedance control for robots that are in dynamic contact with uncertain environments. The generic method that can start to perform stable hybrid position/force control on an uncertain environment with partially known dynamics and recursively build a robust internal model to perform stable position/force control on an environment that changed its stiffness, viscosity, and inertia. Then an algorithm will be developed to use a locally linearised model of the above coupled dynamic system to estimate the MFPT of the robot and the environment. This MFPT will then be used in a novel real-time algorithm to adapt a bank of candidate impedance parameter sets and adaptively choose the best parameter set to suit the environment in order to maximise the MFPT. Rigorous theoretical proofs of stability and experimental validation of methods will be given. The project will use a custom built experimental platform to evaluate and refine the fundamental theories and algorithms that will be developed in this project. The PI will closely collaborate with Shadow Robotics Company, a UK based SME who develops biomimetic robotic hands, and the robotics group led by Professor Darwin Caldwell at the Italian Institute of Technology, where the researchers strive to enable the humanoid robot i-Cub to interact with natural uncertain environments. Therefore, this project will benefit from a wealth of experiences the collaborators have already gathered on real robots interacting with natural environments.

Industrial Impact: The proposed real-time adaptation of internal impedance to suit the external uncertain environment will have a broad impact on humanoid robotics in general, because stable interaction with uncertain environments is a major bottleneck in this area. The PI will closely collaborate with Shadow Robotics, a UK based SME specializing in Dextrous Hands that offer the possibility of constructing a robot with the same manipulation abilities as a human, which could be operated remotely to perform a task deftly and safely. Their customers include NASA, Carnegie Mellon Robotics Institute, Hughes Research, and a range of top university research groups across the Globe. This has led to work with ESA, CERN and CDE. As mentioned in the letter of support, Shadow Robotics group believes that a fundamental breakthrough in adaptive real-time impedance control on an uncertain object will significantly improve their competitiveness. Therefore, the proposed work will be carried out with regular communications with the team at Shadow Robotics in order to serve the most crucial technical and implementation needs in the industry. Academic impact on robotic manipulation and locomotion: The advancements in the area of adaptive impedance control to manage metastable dynamics arising out of dynamic interaction between a robot and an uncertain environment will open up new research opportunities in both manipulation and locomotion. Moreover, it will give useful insights to conduct research in the area of human motor learning. Professor Darwin Caldwell's robotics group at Italian Institute of Technology was chosen as the academic collaborator because his group is playing a pivotal role in a number of European humanoid robotics project like the C-Cub project in addition to several other EU funded research projects. The PI's close interaction with his group in the recent past has lead to a common agreement that a focused effort to develop a unified theory on adaptive tuning of internal impedance of robots will help to make a significant advance in direct robotic interaction with natural environments. Regular skype meetings with his group will be continued in order to exchange academic ideas. We will make a joint effort to maximise impact by organising seminars and workshops in international conferences. Social impact: Through periodic participation of workshops with mixed audiences such as the meetings of the Strategic Promotion of Ageing Research Capacity (SPARC), human adaptive mechatronics (HAM), and those organised by the Welcome Trust, we will establish a dialogue with potential broad beneficiaries of robots that will directly interact with humans. We will learn from them and try to extend our methods for stable robotic interaction with uncertain environments to suit their broad safety needs. Student population: We will develop a separate set of simple experiments for undergraduate students to internalize the fundamentals of robotic interaction with uncertain environments, impedance control, and adaptive learning. The PDRA will be given broad training to develop such experiments and to develop text to support students. This will be a strong addition to his/her CV when it comes to applying for academic positions at the end of the contract. Open access for UK students in general: At the end of the project, we will plan to open the experimental set up for registered UK students (free of charge) to remotely log in and conduct experiments on adaptive impedance control on the promise that the published results will be freely made available on the internet. This effort is to stimulate a wider interest in robotics and to provide a free platform to test initial ideas before applying for grants.