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 in vitro 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 in vitro gastric simulation platforms.