Synthesis and Analysis of Novel Compliant Remote Center Motion Mechanisms

Systems with compliant manipulation of motion offer inherent advantages over their rigid counterparts, for example, more accuracy, no friction, no wear and tear, flexibility, enhanced life, light weight, low energy consumption. Hence compliant mechanisms are being increasingly preferred over rigid mechanisms, especially in high-precision, high-speed applications. This thesis presents synthesis, parametric analysis with semi-empirical modeling, and experimental validation of novel compliant remote center motion mechanisms (CRCMMs) with high cross-axes stiffnesses. Literature backs up ample use of rigid links in the synthesis of RCM mechanisms in various applications. However, the mechanisms proposed in this thesis are spatial, compliant-link remote center motion (RCM) mechanisms (Patent pending). Synthesis of the proposed compliant mechanisms poses the main challenge of achieving precise RCM with prominent cross axes stiffnesses. The proposed design is conceived with angularly assembled compliant links (with fixed -fixed boundary) which upon application of force undergo simultaneous twisting and bending resulting in the proposed RCM. Higher width as compared to the thickness along with angular arrangements gives the desired cross-axis stiffness. Extensive, non-linear FE analysis establishes the accuracy of the RCM, high cross-axis stiffnesses, and the accuracy of the proposed semi-empirical model based on parametric analysis. Further, one of the proposed mechanisms is fabricated and preliminary experiments validate accuracy in an example case. The proposed mechanisms have several potential applications including high-precision minimally invasive surgical instrument, hard disc arm motion, clutch system in an automobile and so on. Towards development of one of the applications in the domain of high-precision minimally invasive surgery, the thesis further proposes tremor suppressing control schemes along with their experimental validation using another mathematically equivalent (up to first order) compliant mechanism. Tremors in hands of surgeon could be detrimental to high-precision surgical procedures (ex. Retinal surgery). Moreover, human hand stability, a skill to be acquired by extensive training, decays with age and limits the number of surgeons qualified to perform microsurgery. Suppression of tremors is, therefore, a major challenge. Study in this thesis presents a possible use of compliant system for addressing the challenge of tremor. Three different control schemes, including feedback from low pass filtering and an adaptive filtering are proposed, implemented and compared. The adaptive control scheme shows promising results in reducing tremors at the surgeon’s tool tip by ~96%, when holding at a point and by ~68% while carrying out a voluntary motion. The results show a positive scope for complaint robotic systems based on CRCMMs presented before, towards microsurgeries with suppression of tremors.