Learning a State Transition Model of an Underactuated Adaptive Hand

Fully actuated multifingered robotic hands are often expensive and fragile. Low-cost underactuated hands are appealing but present challenges due to the lack of analytical models. This letter aims to learn a stochastic version of such models automatically from data with minimum user effort. The focus is on identifying the dominant, sensible features required to express hand state transitions given quasi-static motions, thereby enabling the learning of a probabilistic transition model from recorded trajectories. Experiments both with Gaussian processes (GP) and neural etwork models are included for analysis and evaluation. The metric for local GP regression is obtained with a manifold learning approach, known as Diffusion Maps, to uncover the lower-dimensional subspace in which the data lies and provide a geodesic metric. Results show that using Diffusion Maps with a feature space composed of the object position, actuator angles, and actuator loads, sufficiently expresses the hand-object system configuration and can provide accurate enough predictions for a relatively long horizon. To the best of the authors' knowledge, this is the first learned transition model for such underactuated hands that achieves this level of predictability. Notably, the same feature space implicitly embeds the size of the manipulated object and can generalize to new objects of varying sizes. Furthermore, the learned model can identify states that are on the verge of failure and which should be avoided during manipulation. The usefulness of the model is also demonstrated by integrating it with closed-loop control to successfully and safely complete manipulation tasks.