Finite-Time Admittance Control for Adaptive Compliance of a Soft Actuator of Robotic Gastric Simulator

To test food, drug formulations, and medical devices, extensive research has focused on developing <i>in vitro</i> gastric simulators. Existing simulators range from rigid mechanical systems to flexible polymer-based designs, each with distinct limitations in replicating the stomach's complex biomechanical properties. While soft pneumatic actuators provide a foundation for soft robotics-based systems, achieving biomimetic functionality requires control strategies that address both contraction motility precision and compliant interaction dynamics. In this study, we integrate admittance control with finite-time state-dependent Riccati equation (FT-SDRE) and propose a compliant and robust combined force and displacement control for a soft actuator used in robotic gastric simulator. This approach enables a more biomimetic simulation of smooth muscle in gastrointestinal (GI) system when the actuators contact the contents and can help reduce excessive stress on the soft actuator. A three-phase contact model is proposed to describe the force-deformation behavior of the actuator while interacting with the contents, followed by experimental validation. The novel admittance-controlled FT-SDRE enhances both safety and physiological realism in soft tissue interaction. Experimental validation was conducted using three objects: an irregular-shaped gelatin sample, a regular-shaped gelatin sample (same material, different geometry), and an air-filled latex balloon. Compared with nonadmittance FT-SDRE control, the admittance-controlled FT-SDRE reduced 11.19% to 38.46% average contact force according to different objects. Across all tests, the time spent above a force threshold was reduced by 35-39%, which highlights the potential of the proposed method to improve safety, adaptability, and biomimicry in next-generation <i>in vitro</i> gastric simulation platforms.