Intermittent control (IC) uses a sequence of parameterised open-loop control trajectories whose parameters are adjusted sporadically using feedback. The EU-funded ROBOTICS project proposed a specific robotics implementation of the IC model, and argued that this is a valuable element missing from current robotic schemes. Project partners implemented an IC module to run simulations. They validated the architecture on a physical system that runs the module in real time on a humanoid robot. It had two legs with six actuated degrees of freedom: three in the hip, one in the knee and two in the ankle. Findings show that IC can be a natural and effective control paradigm in a robot context. In the presence of actuators, sensors, systems and constraints, central refractoriness is an appropriate control mechanism especially when the plant model or sensor readings are unreliable and/or delayed, which is usually the case for ‘soft’ robots. The IC paradigm was further explored and supported by human participant data analysis. Scientists elaborated on the role of different sensory organs such as joint position, muscle length and spatial orientation, in order to construct the required control weightings. They collected data of a human subject controlling a balance task. To measure the participant’s state and differentiate between the sensory modalities, the ROBOTICS team recorded data in a human-in-the-loop set-up. Data analyses reveal that IC provides a deterministic explanation of linear and remnant components of human stance control without injection of random noise. By implementing the humanoid’s controller with an intermittent open-loop interval, project members replicated the modal frequency exhibited in human motor control. They demonstrated that this robot is more robust to system perturbations when the controller gains are either too low or too high. Results show that intermittent open-loop control is both relevant and beneficial. Thanks to ROBOTICS, autonomous robot design will beneﬁt from the proposed IC model. It may well put Europe on the cusp of developing marketable bionic robots.
Robots, humanoids, human motor control, intermittent control, ROBOTICS