Power Adaptation-Enabled Admittance Control for Stable and Safe Actuated Interaction in Unmodeled Environment

Pin-based shape display is a type of interactive interface researched in the field of human-robot interaction (HRI) for physical shape rendering through a grid of linear motion actuators. Some researchers have enabled it with the abilities of manipulating objects and interacting with humans. This important expansion of usages in pin-based shape display to dynamic shape rendering imposes a potential challenge in interacting with unmodeled environment dynamics consisting of humans or other objects in a safe and stable way. We have previously introduced admittance control to the pin-based shape rendering in an attempt to regulate the relation between the motions of pins and the external force applied by the unmodeled environment. Despite the functional realization, there is a need for a safe and stable interaction as the admittance controller may lead to excessive power output. To overcome this, one approach is to apply the energy-based control method to the admittance controller. Bounded energy is allocated to the admittance controller, and bounded power is introduced to limit the power output of the pin-based shape rendering. However, these boundaries are difficult to estimate. Especially for the power boundary, which needs to be dynamically adjusted to balance the safety and quick interaction response of the system. To address the above issues, we introduce a power adaptation method to the admittance controller in pin-based shape rendering. Experiments with previously developed pin-based shape rendering are used to validate the benefit of the power adaption method. The results support the fact that the proposed method has better performance in terms of safety and interaction response, demonstrating the potential to introduce higher-level planning frameworks.