Characterisation, modelling and analysis of a haptically enabled system for robotic assisted minimally invasive surgery

Abstract

In this research, the effects of realistic sensory feature of the lateral forces arisen from sideways interaction of the tool tip with soft tissue in palpation operations in robotic assisted minimally invasive surgery (RAMIS) operations with the scale factor of 100% were studied. A RAMIS system with ten degrees of freedom (DOF) consisting of a 6-DOF 6-RRCRR parallel micropositioning robot incorporated with a novel 2-DOF automated modular force feedback enabled laparoscopic instrument through a closed chain RPRR mechanism and an actuated linear guide (monocarrier) was also proposed. The special family of parallel manipulators with RRCRR architecture was studied and numerical solutions to the inverse and forward kinematics of 6-RRCRR parallel micromanipulators were proposed. Numerical and graphical simulations were also carried out to validate the proposed theoretical results. High accuracy in micron range and good performance were obtained by the proposed solutions to the inverse and forward kinematics problems of this special family of parallel robots. In order to accurately measure the tool/tissue interaction forces directly from surgery site in real-time during surgical operations, an actuated laparoscopic instrument with the capability to measure the tool/tissue sideways and normal interaction forces was proposed. A force sensing stainless-steel sleeve, with strain gauges incorporated into it, was designed and developed to measure lateral interaction forces. The instrument features actuation of the tip and also the measurement of interaction forces without using any actuator or sensor at the tip jaws. The grasping direction of the proposed instrument can also be adjusted during the surgical procedure. It is also able to convert between various tool tips of various functionalities (e.g. cutter, grasper, and dissector) without loss of control and force measurement capability. Thin wires of the strain gauges measuring sideways forces were placed and covered in four tiny grooves made on the outer surface of the force-sensing sleeve. The linear relationships between applied forces and the induced strains for the appropriate ranges of applied loads in laparoscopic surgery were confirmed by finite element analysis results. Three strain gauge configurations were also calibrated, and the experimental data verified the monotonic response of the bridge configurations. Experiments were conducted and the results verified the ability of the instrument in accurately measuring both magnitude and direction of the applied sideways forces and in distinguishing between tissue samples even with slight differences in stiffness. To manipulate the proposed 10-DOF parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS), a unique control algorithm was proposed making the PRAMiSS capable of performing the manipulations under the constraint of moving through the fixed penetration or so-called remote centre-of-motion (RCM) point. The control algorithm is also capable of minimising the displacements of the parallel micropositioning robotic system while it is preventing the tool tip to orient around the instrument axis due to the robot movements. Computational analysis integrated with graphical simulations, as well as experiments, were carried out to demonstrate the correlation between the numerical results and the PRAMiSS physical response and to validate the obtained theoretical results. Numerical and experimental results verified the accuracy, flexibility, and effectiveness of the proposed control algorithm in applying the RCM, the tip orientation, and the minimum displacement constraints in various situations of both manipulations with millimetre and micrmeter resolutions particularly MIS and minimally invasive microsurgery (MIMS) operations. Finally, the proposed control algorithm was employed to manipulate the proposed robotic assisted surgery system (PRAMiSS), and obtain feedback from the proposed force feedback enabled laparoscopic instrument. The proposed methodology was implemented in order to evaluate the effects of force feedback in characterising tissues of varying stiffness using realistic palpation. Four different experiments of characterising tissues using only vision feedback, only force feedback, simultaneous force and vision feedbacks and direct palpations were conducted to evaluate the effects of realistic force feedback in palpation of different tissues of varying stiffness with the scale factor of 100% . Experimental results were analysed using statistical analysis based on a single factor analysis of variance (ANOVA) and Tukey HSD methods to test whether a significant statistical difference exists between the data sets, and to examine pairwise mean comparisons, respectively. Experimental results and statistical analysis proved that providing visual and force feedbacks simultaneously, not only improves the accuracy of characterizing tissues, but also significantly increases the certainty of the results compared with those of vision feedback alone or force feedback alone. The statistical analysis also demonstrated that there is no significant difference between the average percent correct results of the direct palpation compared with that of the simultaneous vision and force feedback experiments. It was also concluded that providing both vision and force feedbacks together in robotic assisted surgery system increases the certainty of responses for tissue characterisation task compared even with direct palpation.