Probability-Based Force Control for Flexible Ureteroscopy Robots

In robotic flexible ureteroscopy, great care should be taken to prevent excessive collision force at the ureteroscope tip to avoid urinary tissue damage. However, the passive flexure of a flexible ureteroscope from reaction forces with the surrounding tissue introduces great uncertainties in force control. To address this, a probability-based force control method is proposed in this paper. A morphological wavelet-based statistic test is proposed to detect collision by identifying the change point of the probability distribution of force signal, which is measured by a fiber optical sensor at the ureteroscope tip. The force signal and its change points are applied as an admittance model inputs to generate position command. It is augmented to the robot controller for minimizing the collision force. Meanwhile, a probabilistic model approximates the real interactive system, and combines Bayesian inference for safely online learning the admittance parameters. Experimental results on a flexible ureteroscopy robot show that collision can be detected instantly, and the force is reduced remarkably during the advancement of the robotic ureteroscope. Note to Practitioners -This paper is motivated by the rapidly increasing applications for robotic flexible ureteroscopy. As ureteroscope enters into urethra, urinary bladder, ureter, and reaches renal pelvis, it sometimes penetrates soft tissue, especially in the case of no ureteral access sheath placement. It is important to control the ureteroscope tip force for surgery safety. Therefore, a force control method is proposed in this paper. Experiments conducted on a flexible ureteroscopy robot demonstrate that the proposed method is a protective measure to mitigate the risk of inner surface perforation.