Optimization of the Dexter surgical robot
SIMULATION OF THE GRAVITY COMPENSATION MECHANISM ON THE DEXTER SURGICAL ROBOT WITH ANSYS WORKBENCH
Distalmotion is a medical device company based in Switzerland that establishes new standards to deliver best-in-class minimally invasive care for patients in general surgery, gynecology and urology. As such, it has developed the Dexter surgical robot, which combines the benefits of laparoscopy and robotics. At the prototyping stage of the development process simulation helped identify the failure mode of the transmission system for design optimization.
The surgeon console is responsible for precisely capturing the surgeon’s hand movements in order to transmit them to the robotic arms that operate the surgical instruments. These movements are received by passive master arms that support the various sensors. In order for the surgeon to maintain the greatest precision of movement and for the system to transfer these movements with finesse, it is imperative that these master arms have as little resistance as possible. This means that the force required to move these arms must be small and constant over the entire workspace. To achieve this, the force of gravity due to the masses of the moving elements must be compensated as accurately as possible according to the position of the master arm. The balancing system for the two degrees of freedom that are significantly affected by gravity is passive, with the compensating force being provided solely by linear compression springs.
The structural analysis of the initial design allowed for the quick identification of the failure mode of the transmission in the prototype, i.e., an excessive deformation of the parallelogram due to a suboptimal design and an underestimated torsional load. The simulations were performed in Ansys Workbench through the static analysis module. The simulation allowed for a significant simplification of the final design by removing the intermediate arm, which had led to torsional brittleness, and by adjusting the choice of material in order to reduce the total deformation by 50% and to achieve homogeneous behavior, regardless of the position.
Structural simulation eliminated costly testing steps and enabled a quick solution while simplifying the design. The analysis also improved understanding of the various forces involved in transmission and helped find a solution that met the specifications expected by users. Additionally, access to the Ansys Startup Program offered by CADFEM enabled Distalmotion to integrate simulation into its R&D processes in order to accelerate product development from the start, while limiting the financial impact.