Robots in the real world experience wear and tear, leading to changing system dynamics. This challenge is particularly exacerbated for non-rigid systems such as soft robots or robotic systems made of metamaterials with hysteresis. This setting results in a challenging problem for most learning-based controllers that typically rely on the assumption that the system dynamics remain fixed over time. In the absence of explicit mechanisms to account for this change in dynamics, learning-based control algorithms show considerable degradation in performance over time. In this work, we consider a particular class of dynamics shift in under-actuated systems, that is localized to the dynamics of the fully actuated robot itself, while independently leaving the dynamics of the environment unchanged. This captures real-world phenomena such as fatigue or hysteresis in robotic systems. In this setting, we propose an efficient algorithm that can account for dynamics shift. Using a simple calibration procedure, we propose a technique for learning a non-linear “action-translation” model that can capture the localized shift in dynamics. This enables continual learning and transfer despite considerable dynamics shift during the learning process. We demonstrate the efficacy of this procedure on several tasks in simulation, as well as a real-world robotic system - a 4 DoF electrically driven handed shearing auxetic (HSA) platform.

Handed Shearing Auxetics (HSA) are a promising structure for making electrically driven robots with distributed compliance that convert a motors rotation and torque into extension and force. These structures expand and contract by changing an internal angle between links, the evolution of the structure as this angle changes is known as the auxetic trajectory. We overcome past limitations on the range of actuation, blocked force, and stiffness by focusing on two key design parameters: the point of an HSA's auxetic trajectory that is energetically preferred, and the number of cells along the HSAs length. Modeling the HSA as a programmable spring, we characterize the effect of both on blocked force, minimum energy length, spring constant, angle range and holding torque. We also examined the effect viscoelasticity has on actuation forces over time. By varying the preferred auxetic trajectory point, we were able to make actuators that can push, pull, or do both. We expanded the range of forces possible from 5 N to 150 N, and the range of stiffness from 2 N/mm to 89 N/mm. For a fixed point on the auxetic trajectory, we found decreasing length can improve force output, at the expense of needing higher torques, and having a shorter throw. We also found that the viscoelastic effects can limit the amount of force a 3D printed HSA can apply over time.

This work proposes a novel generative design tool for passive grippers---robot end effectors that have no additional actuation and instead leverage the existing degrees of freedom in a robotic arm to perform grasping tasks. Passive grippers are used because they offer interesting trade-offs between cost and capabilities. However, existing designs are limited in the types of shapes that can be grasped. This work proposes to use rapid-manufacturing and design optimization to expand the space of shapes that can be passively grasped. Our novel generative design algorithm takes in an object and its positioning with respect to a robotic arm and generates a 3D printable passive gripper that can stably pick the object up. To achieve this, we address the key challenge of jointly optimizing the shape and the insert trajectory to ensure a passively stable grasp. We evaluate our method on a testing suite of 22 objects (23 experiments), all of which were evaluated with physical experiments to bridge the virtual-to-real gap. Code and data are at https://homes.cs.washington.edu/~milink/passive-gripper/