Compliance Control of a Robotic Breast Ultrasound System Based on Variable Admittance Control

INTRODUCTION: In a robotic breast ultrasound (US) system (RBUS), ensuring patient safety, comfort, and high compliance is critical. METHOD: To improve low system compliance, this study proposes a Variable Admittance Control based on the Critical Damping Ratio (VAC-CDR). This algorithm enhances force control accuracy and compliance by adaptively adjusting damping and stiffness coefficients. Furthermore, a Breast Surface Adaptive Control Strategy (BrS-ACS) is introduced. This strategy adjusts the alignment of the probe with the normal of the breast surface. Meanwhile, the influence of admittance parameters on compliance is experimentally analysed, with an error band used for evaluation. RESULTS: The simulation and experimental validation demonstrate that the VAC-CDR algorithm achieves excellent compliance, robustness, and a force control precision of 0.4 N, while the BrS-ACS ensures accurate and reliable scanning of the US probe. CONCLUSION: This study contributes to the advancement of automated US image scanning.